PLASMA DIALYSIS SYSTEMS AND METHODS OF USE THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to systems and methods for plasma dialysis and to methods for disease control and quality of life improvement for patients with renal disease and other patients undergoing kidney dialysis treatment.

BACKGROUND OF THE INVENTION

[0002] Hemodialysis is the most commonly administered treatment for patients with chronic kidney disease (CKD), stage 5, which is also referred to as end stage renal disease (ESRD). During hemodialysis, whole blood is passed through a dialyzer, while dialysis solution or dialysate also passes through the dialyzer. A semipermeable membrane in the dialyzer separates the blood from the dialysate and allows diffusion and osmosis to take place between the dialysate and the blood. This movement of substances across the membrane results in the removal of waste products, including solutes such as urea, creatinine, and other uremic toxins from the blood. It also regulates the levels of other substances, such as sodium and water, in the blood. In this way, a dialysis system acts as an artificial kidney.

[0003] The major components of a conventional, hemodialysis system (arteriovenous fistula, dialyzer with hollowfiber membrane, electronic dialysis device, dialysate, and tubing) and standard therapy protocols are well established. Although hemodialysis has been used for over half a century to treat ESRD patients, and aside from transplant is the most effective treatment, it is not without limitations.

[0004] Hemodialysis requires significant time commitment, as patients typically receive a 3-4 hour treatment, and need an additional 1-2 hours for preparation and logistics, up to three times a week. Missing a single treatment can be harmful, and missing multiple treatments can be fatal. In addition, hemodialysis does little to prevent progression of ESRD and only delays the onset of renal failure.

[0005] The Kt/V value is the standard measurement of toxin clearance in conventional hemodialysis dosage in the U.S. healthcare system. K is dialyzer clearance of urea in milliliter/minute, t is treatment time in minutes, and V is the volume of distribution of urea in milliliters (V = (0.6 liters/kilogram body weight * X kilograms body weight)* 1000, given that approximately 60% of a person’s body weight is water and uremic toxins are diffused in this water). The Kt/V value is a dimensionless number representing the amount of blood urea nitrogen (BUN) cleared during a given treatment period with respect to the volume of distribution of BUN (based on a patient’s water weight). BUN level is the gold standard of dialysis clearance because urea clearance indicates proportional removal of other small molecule toxins from the patient’s blood.

[0006] Urea reduction ratio (URR) (%) is the percentage of urea removed during dialysis and is considered to be a generally accurate and quick method to calculate dialysis adequacy based on the equation Kt/V = -ln(l-URR/l00). Dialysis dose is considered adequate at Kt/V > 1.2, which is roughly equivalent to 70% URR using the Kt/V = -ln(l-URR/l00) equation. However, a URR of 70% indicates that a patient still carries 30% of non-dialyzed residual BUN in the bloodstream after a treatment. Over time, as renal functions decline, accumulation of BUN between treatments, average pre dialysis concentration of BUN, and risk of uremia-related complications will increase, even though URR may be adequate (based on Kt/V = -ln(l-URR/l00), in accordance with Kt/V > 1.2).

[0007] Patients who receive dialysis three times a week at Kt/V > 1.2 display lower rates of mortality. However, it is difficult to achieve Kt/V > 1.2, particularly for overweight patients who have a large V denominator and for whom K typically peaks at 250 mL/minute urea at a 400 mL/minute blood flow rate. During hemodialysis, a dialyzer can filter only 60-70% of BUN from blood entering the system at any given time. Because V is a fixed value and K is limited, increasing t is often the only variable that can be used to achieve dose adequacy. Although shorter treatment times and reduced treatment frequency are preferable to patients, the limitations of K in conventional dialysis do not allow such reduced treatment schedules.

[0008] Greater clearance of middle molecule toxins during dialysis is associated with lower all-cause mortality rates. These toxins range from 500 daltons to 15 kilodaltons in size and are most commonly represented by the compound beta-2 microglobulin (which is approximately 11-12 kilodaltons). For conventional hemodialysis methods, clearance of beta-2 microglobulin may be improved through the use of high-flux dialysis membranes. These membranes have a pore size large enough to allow middle- sized molecules to diffuse across the membrane. The majority of hemodialysis treatments in the United States are administered with high-flux dialysis membranes. However, during a typical high-flux hemodialysis treatment, an unintended loss of 3- 12% of daily protein intake and up to 0.3% albumin from blood can occur. Evidence suggests that greater protein and essential amino acid loss during dialysis treatment elevates all-cause mortality and increases hospitalization due to malnutrition. While healthcare providers can recommend that patients increase their protein intake in order to curb protein loss, a higher protein diet is generally accompanied by increased sodium intake, which can lead to greater interdialytic fluid gain and in turn poor cardiovascular outcomes. Therefore, a dialysis method in which protein and amino acid retention is not sacrificed for increased clearance of middle molecule toxins is needed.

[0009] ln addition to toxin clearance, removal of excess fluid or ultrafiltration is a critical goal of hemodialysis. The Centers for Medicare & Medicaid Services guideline for safe fluid removal in dialysis calls for a maximum ultrafiltration rate (UFR) of 13 milliliters of fluid per kilogram of body weight per hour of treatment. A UFR greater than 13 mL/kg/hr in hemodialysis can increase hemodynamic instability and pose a risk for cardiovascular disease; in hemodialysis treatment, where blood flow rate can exceed 300 mL/minute and extracorporeal blood volume can be greater than 400 mL (e.g., 500 mL), hemodynamic stability is already compromised. However, a maximum 13 mL/kg/hr UFR could mean that hemodialysis patients with exceptional ultrafiltration needs will require longer treatment times, e.g., treatment times lasting more than 4 hours. With improved dialysis systems and methods that maintain hemodynamic stability, UFR can be safely increased, eliminating the need for longer treatment periods.

[0010] Thus, dialysis apparatuses and methods that improve dialyzer clearance efficacy, patient stability, and treatment time are necessary. New dialysis systems and methods that can elevate current dosage and UFR standards would deliver clinical benefit and improve quality of life in patients with renal disease, including CKD and ESRD.

SUMMARY OF THE INVENTION

[0011] The present invention provides apparatuses and methods for kidney dialysis in which at least a portion of plasma is separated from the cellular portion of blood, and the separated plasma (instead of whole blood) is dialyzed. The apparatuses and methods of the present invention can remove toxins more efficiently, and with greater hemodynamic stability and lower rates of hemolysis, compared to conventional dialysis of whole blood. In some embodiments, various optional features, including a centrifugal blood pump and/or hemoglobin detector, further increase the safety of plasma dialysis compared to hemodialysis.

[0012] In certain embodiments, the plasma that is dialyzed is plasma-ultrafiltrate as described herein. Once plasma ( e.g ., plasma-ultrafiltrate) is generated from whole blood, it can be dialyzed to achieve efficient removal of toxins.

[0013] In certain embodiments, the present invention provides kidney dialysis systems comprising a first filter configured to receive whole blood and separate the whole blood into a plasma portion and a cellular portion, and a second filter that is a dialyzer. The first filter can be a plasma exchange filter or an ultrafiltration filter, for example. In some embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are greater than about 200 nm, and in other embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are less than or equal to about 200 nm. In certain embodiments, the pores have diameters that are from about 100 nm to about 200 nm. In some embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are less than or equal to about 100 nm. The diameter of each pore can be, for example, less than or equal to about 100 nm, less than or equal to about 75 nm, or less than or equal to about 50 nm. In certain embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are from about 10 nm to about 50 nm. In other embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are from about 3 nm to about 10 nm. In further embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are from about 3 nm to about 5 nm. In other embodiments, the first filter comprises a

semipermeable membrane with pores having diameters that are from about 6 nm to about 11 nm. In some embodiments, the first filter is a hollowfiber dialysis filter.

[0014] In some embodiments, the first filter (which may be a hollowfiber filter) comprises a semipermeable membrane with a molecular weight cut-off (MWCO) of less than or equal to about 100 kDa. The membrane of the first filter may have a 25 kDa - 65 kDa MWCO, for example. In some embodiments, the membrane has a MWCO of about 65 kDa or less. In further embodiments, the membrane has a MWCO of about 30 kDa or less. In other embodiments, the membrane has a MWCO of about 50 kDa. In certain embodiments, such MWCO is determined by dextran sieving.

[0015] In certain embodiments, the first filter used to separate blood into a plasma ( e.g ., plasma-ultrafiltrate) portion and a cellular portion comprises a semi-permeable membrane having a membrane surface area that is about 1 to 2 times the membrane surface area of the filter used for dialysis (the dialyzer). In some embodiments, the ratio of the membrane surface area of the first filter used to generate plasma, to the membrane surface area of the second filter used for dialysis, is about 1 : 1 to about 2: 1.

In certain embodiments, the ratio is about 1.5: 1 to about 2: 1, and in some embodiments, the ratio is about 1 : 1.

[0016] The kidney dialysis systems of the present invention may include a pump for drawing whole blood from the subject and delivering the whole blood to the first filter. Such a pump may be a roller pump or a centrifugal pump, for example. In some embodiments, the first filter is configured to receive whole blood through an input port, and is configured to deliver the plasma portion through an output port, and the second filter is configured to receive the plasma portion through an input port; the output port of the first filter and the input port of the second filter may be connected by tubing. The dialysis system may further comprise a hemoglobin detector configured to detect free hemoglobin in the tubing connecting the output port of the first filter to the input port of the second filter. The second filter may comprise an output port configured to deliver the plasma portion after the plasma portion has passed through the second filter. The second filter may also comprise a dialysate input port and a dialysate output port.

[0017] In the kidney dialysis systems of the present invention, the first filter may comprise a second output port configured to deliver the cellular portion, and tubing that connects this second output port of the first filter to the output port of the second filter. In some embodiments, the tubing connecting the second output port of the first filter to the output port of the second filter is connected to a pump, such as a roller or centrifugal pump. In certain embodiments, the tubing connecting the second output port of the first filter to the output port of the second filter is configured to combine the plasma portion and the cellular portion; the tubing may be connected to a pump, such as a roller pump or a centrifugal pump. In certain other embodiments, the tubing connected to the first output port of the first filter is connected to a pump, such as a roller pump or a centrifugal pump.

[0018] In some embodiments, the kidney dialysis systems of the present invention further comprise a fillable waste container, tubing connecting the fillable waste container to the dialysate output port, and a weight scale configured to measure the weight of the contents of the fillable waste container.

[0019] In any of the embodiments described herein, the kidney dialysis system may also comprise a hemoglobin detector. Such a system may be configured to stop dialysis if the hemoglobin detector detects free hemoglobin.

[0020] In certain embodiments, the dialyzer is part of a conventional, hemodialysis machine. The present invention therefore also provides a device comprising a filter for separating plasma from blood, whereby the device is configured to be attached to a conventional dialysis machine such that the device’s filter is upstream of the dialysis machine’s dialyzer, thereby allowing the machine to dialyze plasma ( e.g ., plasma- ultrafiltrate) instead of blood. In certain embodiments, the device’s filter comprises a semipermeable membrane with pores having diameters that range from about 3 nm to about 50 nm. In certain embodiments, the pores of the semipermeable membrane in the device’s filter have diameters of from about 3 nm to about 15 nm, and in further embodiments the pores have diameters of from about 5 nm to about 10 nm. In certain embodiments, the pores have diameters that are no less than about 3 nm and that are no more than about 11 nm. For example, in certain embodiments, the pores of the semipermeable membrane in the device’s filter have diameters that are, on average, about 2.5 nm, about 3 nm, about 3.5 nm, about 4 nm, about 4.5 nm, about 5 nm, about 5.5 nm, about 6 nm, about 6.5 nm, about 7 nm, about 7.5 nm, about 8 nm, about 8.5 nm, about 9 nm, about 9.5 nm, about 10 nm, about 10.5 nm, about 11 nm, or about 11.5 nm. In specific embodiments, the pores have an average pore diameter that is within the range of about 6 nm to about 11 nm. In some embodiments, the pores of the

semipermeable membrane have a MWCO that is within the range of about 1 kDa to about 100 kDa; in some embodiments, the MWCO is about 30 kDa to about 60 kDa, or about 10 kDa to about 30 kDa— e.g., about 10 kDa, about 15 kDa, about 20 kDa, about 30 kDa, about 40 kDa, about 50 kDa or about 60 kDa. In certain embodiments, the device configured to be attached to a conventional dialysis machine includes a hemoglobin detector. In additional embodiments, the conventional dialysis machine can perform high-flux dialysis, or dialysis using a high-permeability membrane.

[0021] In some embodiments, the device configured for attachment to a conventional hemodialysis machine may also comprise, in addition to a filter, one or more of the following features: a pump (e.g., peristaltic roller pump), a hemoglobin detector, a filtrate drip chamber for collecting separated plasma, a pressure sensor, a flow sensor for sensing arterial flow from the dialysis machine to the device’s filter, and a pinch clamp for blocking plasma from flowing to the dialyzer.

[0022] The present invention also provides methods of performing kidney dialysis on a subject. Some embodiments provide a method of performing dialysis on a subject comprising: drawing blood from the subject, separating the blood into a plasma portion and a cellular portion, dialyzing the plasma portion to generate cleansed plasma, and returning the cleansed plasma and the cellular portion into the subject. In some embodiments, the plasma portion is dialyzed to cleanse and allow for fluid removal from the plasma portion and generate dialyzed plasma. Dialyzed plasma may be plasma that is cleansed, or plasma that is cleansed and has had fluid removed.

[0023] A roller pump or a centrifugal pump may be used for drawing blood from the subject. In some embodiments, the dialyzed plasma and the cellular portion are combined before they are returned into the subject. A roller pump or a centrifugal pump may be used to return the combined dialyzed plasma and the cellular portion into the subject.

[0024] In some embodiments of the dialysis methods of the present invention, drawing the blood from the subject is performed at a blood draw flow rate that is less than or equal to about 200 milliliters per minute. The blood draw flow rate may be less than or equal to about 150 milliliters per minute, for example.

[0025] In certain embodiments, returning the combined dialyzed plasma and the cellular portion is performed at a blood return flow rate that is less than or equal to about 300 milliliters per minute. The blood return flow rate may be less than or equal to about 200 milliliters per minute, or less than or equal to about 150 milliliters per minute, for example.

[0026] In certain embodiments of the methods provided herein, dialyzing the plasma portion to generate dialyzed plasma (e.g., cleansed plasma) comprises pumping the plasma portion through a dialyzer comprising a semipermeable membrane and dialysate, wherein the dialysate is pumped through the dialyzer at a dialysate flow rate that is less than about 400 milliliters per minute. The dialysate flow rate may be less than or equal to about 300 milliliters per minute; for example, the dialysate flow rate may be about 200 milliliters per minute.

[0027] In embodiments comprising removing fluid from the plasma portion, the fluid removed from the plasma portion may be weighed. In addition, in some embodiments, removing fluid from the plasma portion is performed at an ultrafiltration rate that is lower than or equal to about 13 milliliters of fluid per kilogram of body weight of the subject per minute. In other embodiments, removing fluid from the plasma portion is performed at an ultrafiltration rate that is higher than about 13 milliliters of fluid per kilogram of body weight of the subject per minute. In certain embodiments, the ultrafiltration rate is from about 14 to about 20 milliliters of fluid per kilogram of body weight of the subject per minute. For example, the ultrafiltration rate can be about 14 milliliters of fluid per kilogram of body weight of the subject per minute, or about 15 milliliters of fluid per kilogram of body weight of the subject per minute. In further embodiments of the methods of the present invention, the ultrafiltration rate is increased or decreased during the removal of fluid from the plasma portion.

[0028] In any of the embodiments of the methods described above, the blood may be separated into a plasma portion and a cellular portion by pumping the blood through a plasma exchange filter. In other embodiments, the blood is separated into a plasma portion and a cellular portion by pumping the blood through a hollowfiber filter.

[0029] Separating the blood into a plasma portion and a cellular portion may be accomplished by pumping the blood through a semipermeable membrane comprising pores having diameters that are less than or equal to about 200 nm, for example. In some embodiments, the pores of the semipermeable membrane have diameters of from about 100 nm to about 200 nm. In other embodiments, the pores of the semipermeable membrane have diameters that are less than or equal to about 100 nm. For example, the pores of the semipermeable membrane may each have a diameter that is less than or equal to about 100 nm, less than or equal to about 75 nm, or less than or equal to about 50 nm. In further embodiments, the pores of the semipermeable membrane have diameters of from about 3 nm to about 50 nm. In certain embodiments, the pores of the semipermeable membrane have diameters of from about 3 nm to about 15 nm and in further embodiments the pores have diameters of from about 5 nm to about 10 nm. In certain embodiments, the pores have diameters that are no less than about 3 nm and that are no more than about 11 nm. For example, in certain embodiments, the pores of the semipermeable membrane have diameters that are, on average, about 2.5 nm, about 3 nm, about 3.5 nm, about 4 nm, about 4.5 nm, about 5 nm, about 5.5 nm, about 6 nm, about 6.5 nm, about 7 nm, about 7.5 nm, about 8 nm, about 8.5 nm, about 9 nm, about

9.5 nm, about 10 nm, about 10.5 nm, about 11 nm, or about 11.5 nm. In specific embodiments, the pores have an average pore diameter that is within the range of about 6 nm to about 11 nm. In some embodiments, the semipermeable membrane has a MWCO that is within the range of about 1 kDa to about 100 kDa, e.g., about 25 kDa to about 65 kDa, about 30 kDa to about 60 kDa, or about 10 kDa to about 30 kDa. In further embodiments, the MWCO is about 10 kDa, about 15 kDa, about 20 kDa, about 25 kDa, about 30 kDa, about 35 kDa, about 40 kDa, about 45 kDa, about 50 kDa, about 55 kDa, about 60 kDa, or about 65 kDa, for example. In certain embodiments, the MWCO is determined by dextran sieving.

[0030] In certain embodiments, separating the blood into a plasma portion and a cellular portion comprises pumping the blood through a hollowfiber filter comprising pores having diameters that are less than or equal to about 100 nm. The hollowfiber filter may comprise pores having diameters of from about 3 nm to about 50 nm, for example. In some embodiments, the hollowfiber filter comprises pores having diameters of from about 10 nm to about 50 nm. In other embodiments, the hollowfiber filter comprises pores having diameters of from about 3 nm to about 11 nm; and in still other embodiments, the hollowfiber filter comprises pores having diameters of from about 5 nm to about 10 nm. In some embodiments, the hollowfiber filter comprises pores having diameters of from about 3 nm to about 5 nm. In certain embodiments, the hollowfiber filter comprises pores having diameters of about 5 nm. In some

embodiments, the pores of the hollowfiber filter have diameters that are, on average, about 2.5 nm, about 3 nm, about 3.5 nm, about 4 nm, about 4.5 nm, about 5 nm, about

5.5 nm, about 6 nm, about 6.5 nm, about 7 nm, about 7.5 nm, about 8 nm, about 8.5 nm, about 9 nm, about 9.5 nm, about 10 nm, about 10.5 nm, about 11 nm, or about 11.5 nm. In specific embodiments, the pores have an average pore diameter that is within the range of about 6 nm to about 11 nm. In some embodiments, the hollowfiber filter has a MWCO that is within the range of about 1 kDa to about 100 kDa, e.g., about 25 kDa to about 65 kDa, about 30 kDa to about 60 kDa, or about 10 kDa to about 30 kDa. In further embodiments, the MWCO is about 10 kDa, about 15 kDa, about 20 kDa, about 25 kDa, about 30 kDa, about 35 kDa, about 40 kDa, about 45 kDa, about 50 kDa, about 55 kDa, about 60 kDa, or about 65 kDa, for example. In certain embodiments, the MWCO is determined by dextran sieving.

[0031] In certain embodiments, separating blood into a plasma (e.g., plasma- ultrafiltrate) portion and a cellular portion comprises pumping the blood through a filter that has a membrane surface area that is about 1 to 2 times the membrane surface area of the filter used for dialysis (the dialyzer). In some embodiments, the ratio of the membrane surface area of the first filter used to generate plasma, to the membrane surface area of the second filter used for dialysis, is about 1 : 1 to about 2: 1. In certain embodiments, the ratio is about 1.5: 1 to about 2: 1, and in some embodiments, the ratio is about 1 : 1.

[0032] In embodiments of the methods of the present invention, the plasma portion is less viscous than the subject’s blood. In some embodiments, the plasma portion has a concentration of a uremic toxin (e.g., urea and/or creatinine) that is greater than the concentration of the toxin in the subject’s blood. In some embodiments, the plasma portion is plasma-ultrafiltrate.

[0033] In some embodiments of the methods of the present invention, the plasma portion is passed through a hemoglobin detector before the plasma portion is dialyzed. In further embodiments, the method is stopped if the hemoglobin detector detects free hemoglobin. In some embodiments, the dialysis methods of the present invention do not result in hemolysis.

[0034] Any of the methods of the present invention may be performed on a subject that has renal disease. The renal disease may be chronic kidney disease or end stage renal disease, for example. In some embodiments, the subject has acute renal impairment, and in certain embodiments, the subject has hepatorenal syndrome. In further embodiments, the subject has renal disease and liver disease.

[0035] In certain embodiments, a dialysis method of the present invention is performed on a subject at least once a week, for at least one week. For example, the method may be performed on a subject once or twice or thrice a week, for two or more weeks. In certain embodiments, a dialysis method of the present invention is performed on a subject once or twice a week, for about 3 hours or less, and for at least one week ( e.g ., for two weeks). The method may be performed at least once a week, for about 2 hours or less, and for at least one week, for example. In some embodiments, the method is performed for at least one month— e.g., for about 3 months, about 4 months, about 6 months, or longer. In addition, in any of the embodiments described herein, the subject may also be administered a liver assist therapy.

[0036] In some embodiments, the plasma dialysis methods of the present invention, when performed for an amount of time, achieve a higher urea reduction ratio compared to the urea reduction ratio resulting from a reference method comprising dialyzing whole blood, when the reference method is performed for the same amount of time. For example, the methods of the present invention, when performed on a subject for a set time period, can achieve a urea reduction ratio that is greater than a conventional urea reduction ratio achieved when performing conventional dialysis on a subject for the same set time period. In addition, in some embodiments, the plasma dialysis methods of the present invention, when performed for an amount of time, achieve greater creatinine clearance from blood compared to the creatinine clearance resulting from a reference method comprising dialyzing whole blood, when the reference method is performed for the same amount of time. For example, the methods of the present invention, when performed on a subject for a set time period, can achieve a creatinine clearance level that is greater than a conventional creatinine clearance level achieved when performing conventional dialysis on a subject for the same set time period.

[0037] In some embodiments, the plasma dialysis methods of the present invention, when performed for an amount of time, result in a degree of hemolysis that is less than the degree of hemolysis resulting from a reference method comprising dialyzing whole blood, when the reference method is performed for the same amount of time. For example, the methods of the present invention, when performed on a subject for a set time period, can result in a hemolysis level that is less than a conventional hemolysis level resulting from performing conventional dialysis on a subject for the same set time period. The set time period may be about 1 hour or more. For example, the set time period may be about 90 minutes, about 120 minutes, or about 180 minutes.

[0038] Furthermore, in some embodiments, the present invention provides kidney dialysis methods that minimize the loss of total amino acids and/or the loss of protein ( e.g ., albumin) from the subject’s blood during treatment. In some embodiments, the percentage of total amino acids in the subject’s blood that is lost during treatment is less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less than about 1%. In certain embodiments, the present invention provides plasma dialysis methods wherein the percentage of albumin in the subject’s blood that is lost during treatment is less than about 1%, less than about 0.5%, less than about 0.3%, less than about 0.1%, or less than about 0.05%.

[0039] In certain embodiments, the present invention provides plasma dialysis methods wherein the loss of total amino acids and/or the loss of protein (e.g., albumin) following plasma dialysis is less than the loss of total amino acids and/or protein following hemodialysis, when the plasma dialysis and hemodialysis are performed for the same amount of time using the same or substantially equivalent blood source, the same dialyzer membrane, and the same blood draw flow rate, or are performed using the same dialyzer membrane on the same or substantially equivalent blood source until a target URR is achieved. For example, in certain embodiments of the methods described herein, the loss of total amino acids and/or the loss of protein (e.g., albumin) following plasma dialysis is at least about 25% less than, at least about 20% less than, at least about 15% less than, at least about 10% less than, at least about 5% less than, or at least about 1% less than, the loss of total amino acids and/or protein following hemodialysis, when the plasma dialysis and hemodialysis are performed under equivalent conditions (e.g., on the same or equivalent blood source, using the same membrane for dialysis, and/or performed until a target URR is achieved).

[0040] In some embodiments, the loss of amino acids and/or proteins (e.g., albumin) from blood following a treatment using the plasma dialysis systems and methods described herein may be up to about 25%, up to about 20%, up to about 10%, up to about 5%, or up to about 1% of the loss of amino acids and/or proteins that occurs following a typical hemodialysis treatment, when each treatment is administered to the same or substantially equivalent blood source for the same amount of time and using the same dialyzer membrane and flow rates, or is administered using the same dialyzer membrane to the same or substantially equivalent blood source to achieve the same URR. [0041] In any of the embodiments described herein, the plasma that is dialyzed can be plasma-ultrafiltrate. Thus, certain embodiments of the present invention provide apparatuses and methods for kidney dialysis using a plasma-ultrafiltrate separation filter in conjunction with a dialyzer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 is a schematic drawing of a hemodialysis system with the following components: a. hemodialysis hollowfiber filter, bl. peristaltic roller pump for blood drawing, b2. peristaltic roller pump for dialysate, cl-c3. pressure monitor, d. dialysate reservoir, e. waste bag.

[0043] FIG. 2 is a schematic drawing of exemplary plasma dialysis systems of the present invention: a. filter for separating plasma ( e.g ., hemodialysis hollowfiber filter for plasma-ultrafiltrate production), b. dialysis filter (e.g., hollowfiber filter for dialysis), cl. pump (e.g., roller or centrifugal pump) for blood drawing, c2. pump (e.g., roller or centrifugal pump) for blood returning, d. optional hemoglobin detector, el-e4. pressure monitor, fl. pump (e.g., roller pump) for control of ultrafiltrate, f2. pump (e.g., roller pump) for dialysate, g. dialysate reservoir, h. waste bag and weight scale.

[0044] FIG. 3 is a schematic drawing of the plasma dialysis system used in Example 2. Components b, d, el-e4, fl, f2, g, and h are as described for FIG. 2. Component a' in FIG. 3 is a hemodialysis hollowfiber filter for plasma-ultrafiltrate production, and cl' and c2' in FIG. 3 are centrifugal pumps for blood drawing and blood returning, respectively.

[0045] FIG. 4A shows the concentration of urea in blood over time, and FIG. 4B shows URR over time, for high BUN blood as described in Example 2.

[0046] FIG. 5A shows the concentration of urea in blood over time, and FIG. 5B shows URR over time, for low BUN blood as described in Example 2.

[0047] FIG. 6A shows BUN clearance during dialysis for high BUN blood, and FIG.

6B shows BUN clearance during dialysis for low BUN blood, as described in Example 2

[0048] FIG. 7A shows the concentration of creatinine in blood over time, and FIG. 7B shows creatinine clearance during dialysis, as described in Example 2. [0049] FIG. 8 shows schematically conventional dialysis of whole blood and plasma dialysis according to embodiments of the present invention. In certain embodiments, a unit of dialysate exiting the dialyzer in plasma dialysis contains less albumin and more toxins ( e.g ., urea, creatinine, and medium-sized toxins such as b2 microglobulin) compared to a unit of dialysate exiting the dialyzer in hemodialysis.

[0050] FIG. 9A, 9B, and 9C provide schematic drawings of a hemodialysis system and of an embodiment of an interceptor device attached to a conventional dialysis machine: PA, pressure sensor (artery); PV, pressure sensor (venous); PF, pressure sensor

(filtrate); PP1 and PP2, peristaltic pump; DC, drip chamber (A-artery, V-venous, F- filtrate: DCA - drip chamber arterial blood; DCV - drip chamber venous blood; DCF - drip chamber filtrate (untreated plasma); DCV - drip chamber venous and treated plasma)); HIP, heparin infusion pump; HD, hemoglobin detector; CD, conventional dialyzer; UC, upstream concentrator; DD, downstream dialyzer (e.g., same dialyzer as used in a conventional system); Cl, pinch clamp after venous drip chamber; C2, pinch clamp after hemoglobin detector and filtrate drip chamber; FS, flow sensor; LD1, arterial blood level detector (e.g., ultrasonic fluid detector for drip chamber of arterial, untreated blood); LD2, dialysis machine level detector (e.g., ultrasonic fluid detector for drip chamber of treated blood in hemodialysis system, and for drip chamber of cellular portion (downstream of UC) and treated filtrate (downstream of DD) in a system with an interceptor device); LD3, interceptor level detector (e.g., ultrasonic fluid detector for drip chamber of filtrate, downstream of UC and upstream of DD, in a system with an interceptor device).

[0051] FIG. 10A and 10B depict the operation of safety features that may be included when using an interceptor device attached to a hemodialysis machine, such as in the embodiment shown in FIG. 9A-C, for example.

DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention provides apparatuses and methods for plasma dialysis. Whole blood is composed of a cellular portion (which includes cells, platelets, and a small amount of water) and plasma. Plasma is composed of water and non-cellular components such as electrolytes, lipids, proteins, and vitamins. Dialysis patients also typically have 1.5 liters or more of excess water in the bloodstream that they cannot excrete naturally. Toxins, including BUN and beta-2-microglobulin, primarily exist in water, and therefore in the plasma (and any excess water) of blood. While in conventional dialysis whole blood is dialyzed to remove toxins, the systems and methods of the present invention first separate plasma from the cellular portion. The separated plasma (which may also include excess water from the blood) is then dialyzed to remove toxins. Thus, as used herein, conventional dialysis or hemodialysis generally refers to dialysis of whole blood, while plasma dialysis refers to the dialysis systems and methods of the present invention as described herein. Unless otherwise noted, conventional dialysis or hemodialysis as used herein refers to dialysis of whole blood, regardless of the dialysis membrane used ( e.g ., low- flux, high-flux, protein-leaking or super- flux, etc.).

[0053] Plasma is the portion of blood where toxins are located. Dialyzing plasma increases toxin concentration in the fluid being dialyzed, increases the surface area contact of toxins to the dialyzer membrane and dialysate, and thereby increases toxin clearance ln certain embodiments, the present invention provides plasma dialysis systems and methods that allow a greater amount of water from blood to contact the dialysate (through a semi-permeable membrane, such as in a hollowfiber filter, for example), for each milliliter of fluid passing through the dialyzer, compared to conventional dialysis systems and methods. This increased contact of water, and therefore of the toxins within the water, with the dialysis membrane and the dialysate increases the toxin clearance ratio; with a higher toxin concentration in plasma versus whole blood, the probability that the toxins will contact the dialyzer membrane and diffuse across it into the dialysate increases ln addition, with a higher concentration of toxins in plasma versus whole blood, the concentration gradient driving toxins to and across the dialyzer membrane and into the dialysate is increased when dialyzing plasma compared to whole blood. Stated differently, in conventional dialysis of whole blood, each milliliter of blood coming into contact with the dialyzer membrane and dialysate contains a smaller amount of water (and therefore of toxins) compared to the plasma that is dialyzed in the systems and methods of the present invention; this decreased concentration of toxins in whole blood relative to plasma decreases the concentration gradient of toxins across the dialyzer membrane, and also decreases the surface area contact of toxins to dialyzer membrane and dialysate.

[0054] Furthermore, because the plasma dialyzed according to the methods and systems described herein contains a higher percentage of water (per volumetric unit (e.g., milliliter)) compared to whole blood, it is less viscous than whole blood. For example, the viscosity of healthy human blood is 5.50 ± 0.05 mPa s and the viscosity of healthy human plasma is 1.68 ± 0.04 mPa s. The reduced viscosity allows small- and medium sized molecule toxins to move more easily in the fluid being dialyzed, and to therefore move more easily to and across the dialyzer membrane and into the dialysate. For example, increased blood viscosity is negatively correlated with creatinine clearance. Sugimori et al, Hypertension Research 36: 247-251 (2013). In plasma (e.g., plasma- ultrafiltrate) dialysis, the dialyzed portion is less viscous than blood, and greater creatinine clearance can be achieved.

[0055] Thus, without being bound by theory: it is believed that plasma dialysis is more efficient at removing small molecule toxins (e.g, toxins such as urea and creatinine that have a molecular weight that is less than about 500 daltons) and medium-sized molecule toxins (e.g, toxins such as endotoxin fragments that have a molecular weight of from about 500 daltons to about 15 kilodaltons) compared to conventional dialysis, because of the greater contact surface area of toxins to dialysate in plasma versus whole blood, the higher concentration of toxins in plasma versus whole blood (which results in a greater concentration gradient to drive toxins into the dialysate), and because of the reduced viscosity of plasma compared to whole blood (which allows toxins to move more easily in plasma than in whole blood). To the extent that non-toxin molecules (e.g., vitamin B12, insulin) are also more efficiently removed from plasma, such molecules can be added to the dialysate to increase their concentration in the dialysate so that the concentration gradient of such molecules does not drive them out of the plasma and into the dialysate.

[0056] In addition, the systems and methods of the present invention permit kidney dialysis to be performed while minimizing the loss of essential amino acids and proteins (e.g., albumin) from blood. It has been reported that the plasma concentration of total amino acids decreases by 24% following a standard 4-hour hemodialysis session (Navarro et al, Am J Clin Nutr 71 : 765-773 (2000)); it has also been reported that during a 4-hour hemodialysis treatment, less than 0.5 grams of albumin can be lost with the use of certain dialyzer membranes (Ward, R.A., J Am Soc Nephrol 16: 2421-2430 (2005)); 0.5 grams of albumin corresponds to about 0.3% albumin loss for an average person having 4.7 liters of blood and 35 grams of albumin per liter of blood. [0057] However, as described herein, when a filter is used to separate blood into a cellular portion that is returned to the patient, and a plasma portion that is dialyzed, most of the amino acids and proteins in the blood will be retained in the cellular portion, and only a fraction of the amino acids and proteins in blood will be separated out into the plasma portion that is delivered to the dialyzer. Accordingly, the amount of amino acids and proteins that can be lost during dialysis of the plasma portion will be a fraction of the loss typically observed during conventional dialysis of whole blood. For example, if 0.3% loss of albumin is observed in a conventional dialysis treatment, in the plasma dialysis methods described herein, that 0.3% would roughly correspond to the amount of albumin in the plasma portion (after pre-filtering the blood to generate the plasma filtrate) that is then dialyzed; the other 99.7% of albumin from the blood would be retained in the cellular portion that is returned to the patient. If another 0.3% albumin is lost during dialysis of the plasma portion, then the total loss would be 0.3%

* 0.3%, or 0.0009%. This loss would be less than the loss observed during the hemodialysis treatment. Similarly, for amino acids, if 24% of the amino acids from blood can be lost during a typical hemodialysis treatment, the amino acid loss resulting from the plasma dialysis methods described herein would be a fraction of that 24%:

24% of the blood’s amino acids would be delivered to the dialyzer in the separated plasma portion while the remaining 76% amino acids would be retained in the cellular portion that is returned to the patient; if there is another 24% amino acid loss from the plasma being dialyzed, the total amino acid loss would be 24% * 24%, or 5.76%.

[0058] In addition, when separating blood into a plasma portion and a cellular portion and performing dialysis on the separated plasma, dialysis can be performed at a blood draw flow rate that is less than the blood flow rate typically employed during conventional hemodialysis methods; furthermore, dialysis treatment requires a shorter treatment time compared to the treatment times used for hemodialysis. The reduced flow rate, which may be accompanied by a reduced treatment time, compared to the flow rates and treatment times of conventional hemodialysis methods, reduces the volume of fluid that passes through the dialyzer, which in turn decreases the

opportunity for essential amino acids and proteins to travel out of the fluid during treatment. For example, during hemodialysis, it is common to dialyze 96 liters or more of fluid ( e.g ., 4 hours of treatment at a pump speed (which sets the blood draw flow rate) of 400 mL/minute); however, using the plasma dialysis systems and methods described herein, which achieve efficient toxin removal using a lower blood flow rate and/or shorter treatment time, less volume of fluid will pass through the dialyzer during treatment ( e.g ., 4 hours of treatment at a pump speed or blood draw flow rate of 200 mL/minute will dialyze 48 liters of fluid, compared to the 96 liters when using a blood flow rate of 400 mL/minute as is typical in hemodialysis). Accordingly, as the cellular portion is not dialyzed and the plasma portion being dialyzed will pass through the dialyzer fewer times (compared to the number of times blood passes through the dialyzer during hemodialysis), the cellular portion and the plasma portion retain higher amounts of amino acids and proteins (e.g., albumin) compared to blood that is dialyzed using conventional hemodialysis methods, resulting in less amino acid and protein loss during treatment.

[0059] Furthermore, by dialyzing plasma (instead of whole blood) and targeting dialysis on the portion of the blood containing the toxins, plasma dialysis can be performed at a lower dialysate flow rate compared to the dialysate flow rate typically employed in conventional dialysis. In some embodiments, the plasma that is dialyzed is plasma- ultrafiltrate as described herein.

[0060] Accordingly, in certain embodiments, the plasma dialysis systems and methods of the present invention allow dialysis to occur at a low dialysate flow rate (e.g., a dialysate flow rate lower than the dialysate flow rate typically used in hemodialysis). A low dialysate flow rate increases the contact time of the dialyzer membrane and dialysate with the plasma, and further increases toxin clearance. Such a low dialysate flow rate may be less than about 400 mL/minute, for example. In certain embodiments, the dialysate flow rate used in the methods of the present invention is less than or equal to about 350 mL/minute, is less than or equal to about 300 mL/minute, or is less than or equal to about 250 mL/minute. In certain embodiments, the dialysate flow rate is less than or equal to about 200 mL/minute. In further embodiments, the dialysate flow rate is about 200 mL/minute.

[0061] Dialyzing plasma also allows dialysis to be performed with a lower blood flow rate (e.g., drawing blood flow rate and/or returning blood flow rate) compared to the blood flow rate that is typical for hemodialysis. A low blood flow rate (e.g., less than 300 mL/minute, in comparison to 300 to 400 mL/minute for conventional dialysis) prevents mixing of treated venous and untreated arterial blood in the blood accesses of the subject. A lower blood flow rate is also more hemodynamically stable for the subject.

[0062] Thus, in some embodiments, the systems and methods of the present invention employ a lower blood flow rate compared to the blood flow rates used in conventional dialysis ln general, the higher the blood flow, the higher the hemolysis. Hemolysis indicates red blood cell damage caused by mechanical stress or shearing during dialysis ln certain embodiments, the blood flow rates employed in the plasma dialysis systems and methods of the present invention result in reduced damage to blood cells as compared to the degree of such damage resulting from conventional dialysis systems and methods ln some embodiments of the present invention, the rate of blood flow ( e.g ., blood flow out of the patient and/or blood flow into the patient) is less than about 300 mL/minute; in certain embodiments, the blood flow rate is less than or equal to about 200 mL/minute. ln further embodiments, the blood flow rate is less than or equal to about 150 mL/minute. ln still further embodiments, the blood flow rate is from about 75 mL/minute to about 100 mL/minute.

[0063] Low blood flow rates also minimize mixing of arterial and venous blood at the blood ports. The drawing and returning blood flow rates used in hemodialysis are typically very high (greater than 300-400 mL/minute). Under such high blood flow rates, and given the typical distance between the arterial blood drawing port and the venous blood return port, the arterial blood port can draw a portion of venous dialyzed blood, resulting in mixing of arterial (before dialysis) blood and venous (after dialysis) blood and low dialysis efficiency. Because the systems and methods of the present invention allow for low blood flow rates (e.g., less than or equal to about 200 mL/minute), they decrease or prevent mixing of blood from the arterial blood drawing and venous blood returning ports.

[0064] A low blood flow rate (e.g., less than about 300 mL/minute) also allows the use of smaller hollowfiber dialysis filters compared to the filters used in conventional dialysis. A reduced dialyzer size reduces priming volume and hemodynamic instability. A reduced dialyzer size also reduces dialysate volume. Thus, in certain embodiments, the present invention provides apparatuses and methods for dialysis using a plasma separation filter (which, in certain embodiments, is a dialyzer membrane that generates plasma-ultrafiltrate) in conjunction with a low- volume dialyzer. [0065] The present invention contemplates employing any combination of the dialysate and blood flow rates in the systems and methods described herein. For example, in some embodiments, the dialysate flow rate is less than about 400 mL/minute, and each of the blood draw and return flow rates is less than about 300 mL/minute. ln certain embodiments, the dialysate flow rate is less than or equal to about 300 mL/minute, and each of the blood draw and return flow rates is less than or equal to about 200 mL/minute. ln addition, in any of these embodiments, the dialysate flow rate may be about 200 mL/minute. Furthermore, in any of these embodiments, the blood draw flow rate may be about 150 mL/minute, and the blood return flow rate may be about 200 mL/minute. Thus, the blood return flow rate can be the same as the blood draw flow rate, or the blood return flow rate can be different from ( e.g ., higher than) the blood draw flow rate.

[0066] The present invention provides plasma dialysis systems and methods that increase toxin clearance efficiency and allow for shorter treatment times compared to conventional dialysis ln conventional dialysis, dialysis of whole blood is inefficient because whole blood contains cellular components and therefore contains less water (which contains the toxins) per unit volume passing through the dialyzer; in

conventional dialysis, a URR of 60-70% is typically achievable ln contrast, in certain embodiments where plasma-ultrafiltrate is dialyzed, a URR of up to 96-99.99% can be achieved ln such embodiments, post-treatment BUN level will be close to 0 mg/dl; this improvement of dialysis performance can decrease the dialysis needed— e.g., from 3-4 hours per treatment for three treatments per week (as is typically done for conventional dialysis) to 2 hours or less per treatment, one-to-two treatments a week. Accordingly, the plasma dialysis systems and methods described herein allow for fewer treatments per week (e.g., 1-2 treatments per week compared to 3 treatments per week), and/or allow for treatments that are shorter in duration (e.g., 2 hours or less compared to 3-4 hours per treatment), compared to dialysis of whole blood using conventional dialysis techniques.

[0067] ln some embodiments, the plasma that is dialyzed includes most to

approximately all (e.g., greater than about 50%, up to about 100%) of the water content of a subject’s blood ln certain embodiments, the plasma contains about 60% or more, about 70% or more, or about 80% or more of the water content of a subject’s blood ln further embodiments, the plasma contains about 90% or more of the water content of a subject’s blood, and in still further embodiments, the plasma contains about 95% or more of the water content of a subject’s blood. In certain embodiments, the plasma contains about 99% or more of the water content of a subject’s blood.

[0068] In some embodiments, a plasma separator is used to separate whole blood into a cellular portion and plasma. Such a plasma separator may be a plasma exchange filter, such as Plasmacure™PE, or a plasma component exchange filter, such as

Evacure™/Evaclio™, for example. Plasma can also be separated from whole blood using a plasma fractionator, such as Evaflux™, for example.

[0069] In certain embodiments, a filter is used to separate whole blood into a cellular portion and plasma. In certain embodiments, the filter comprises pores with diameters that are in the range of about 200 nm to about 600 nm. In other embodiments, the filter comprises pores with diameters that are less than about 200 nm. In certain

embodiments, the filter comprises pores with diameters that are in the range of about 100 nm to about 200 nm. In certain other embodiments, the filter comprises pores with diameters that are less than or equal to about 100 nm. Persons skilled in the art would recognize that the pores of a filter or membrane are irregular and variable, such that a stated pore size represents an approximation of the actual pore diameters of the membrane.

[0070] In some embodiments, the filter or membrane used to separate plasma from whole blood generates plasma-ultrafiltrate. In general, plasma-ultrafiltrate can be generated by separating plasma from whole blood using a filter or membrane ( e.g ., a hollowfiber filter) comprising pores that have diameters that are less than or equal to about 100 nm. Accordingly, as used herein,“plasma-ultrafiltrate” refers to plasma that has been separated from whole blood by passing the whole blood through a

semipermeable membrane having pores with diameters less than or equal to about 100 nm. In some embodiments, the pores have diameters that are less than or equal to about 90 nm, and in further embodiments, the pores have diameters that are less than or equal to about 80 nm. In certain embodiments, the diameters are less than or equal to about 75 nm, and in further embodiments the diameters are less than or equal to about 50 nm. In certain preferred embodiments, the pores of the filter or membrane used to separate plasma from whole blood have diameters that are in the range of about 3 nm to about 50 nm. In other preferred embodiments, the pores have diameters that are in the range of about 5 nm to about 50 nm, and in further embodiments the pores have diameters that are in the range of about 5 nm to about 11 nm. In certain embodiments, the pores have diameters that are in the range of about 3 nm to about 5 nm, or about 6 nm to about 11 nm. In other embodiments, the pores have diameters that are in the range of about 10 nm to about 100 nm.

[0071] In certain embodiments, the pores of the semipermeable membrane used to separate blood into a plasma portion and a cellular portion have diameters of from about 3 nm to about 11 nm. In further embodiments, the pores have diameters that are no less than about 3 nm and that are no more than about 5 nm. For example, in certain embodiments, the pores of the semipermeable membrane have diameters that are, on average, about 2.5 nm, about 3 nm, about 3.1 nm, about 3.2 nm, about 3.3 nm, about 3.4 nm, or about 3.5 nm. In other embodiments, the pores have diameters that are, on average, about 4 nm, about 4.5 nm, about 5 nm, or about 5.5 nm. In other embodiments, the pores of the semipermeable membrane have diameters that are no less than about 6 nm and that are no more than about 11 nm. For example, in certain embodiments, the pores of the semipermeable membrane have diameters that are, on average, about 5.5 nm, about 6 nm, about 6.5 nm, about 7 nm, about 7.5 nm, about 8 nm, about 8.5 nm, about 9 nm, about 9.5 nm, about 10 nm, about 10.5 nm, or about 11 nm. In some embodiments, the average pore diameter of the semipermeable membrane is within the range of about 6 nm to about 11 nm.

[0072] While nanometer pore size is described herein by reference to pore diameter (except when noted otherwise), such pore sizes also describe membranes with pores having radii within certain ranges, as the diameter of a spherical shape is twice its radius. For example, a semipermeable membrane with pores having an average pore diameter of about 6 nm to about 11 nm would correspond to a membrane having an average pore radius of about 3 nm to about 5.5 nm. Example dialysis filters having membranes with an average pore radius within such range include high-flux dialyzer membranes (e.g., Revaclear™, Revaclear™ 300, Revaclear™ Max, and Revaclear™ 400).

[0073] The average size and size distribution of the pores of a semipermeable membrane affect the membrane’s permeability to solutes. A membrane’s permeability to solutes can also be described by the membrane’s molecular weight cut-off (MWCO). Typically, a membrane’s MWCO refers to the smallest average molecular mass of a molecule that will not effectively diffuse across the membrane; for dialysis membranes, the smallest size molecule (in Daltons) for which at least about 90% of the molecules are retained by the membrane upon a single pass can be used to define the membrane’s nominal MWCO. For example, a membrane with a 10 kDa MWCO will retain at least about 90% of proteins with a molecular mass of 10 kDa or greater. In general, a larger MWCO corresponds to a larger pore size. Boschetti-de-Fierro et al, Int. J. Artificial Organs 7: 455-463 (2013); Boschetti-de-Fierro, A. et al., Science Reports 5: 18448 (2015).

[0074] The MWCO of a membrane can be determined by analyzing the sieving profile of dextran, polyethylene glycol, or proteins of various molecular weights suspended in an aqueous solution via a single pass through the dialyzer. The amount of solutes present in the filtrate will determine the MWCO of the filter’s membrane. Dialyzer MWCO is often rated in vitro using pristine hollowfibers in the absence of blood or biological components. Once the hollowfibers make contact with blood, the sieving profile of the membranes generally decreases (e.g., for a Revaclear high-flux membrane, MWCO was reported to be 32 ± 3 kDa before blood exposure and 14.2 ± 2 kDa after blood exposure). Boschetti-de-Fierro, A. et al. Sci. Rep. 5, 18448; doi:

10.1038/srep 18448 (2015). Therefore it is common practice for dialyzer manufacturers to produce dialyzers rated with a MWCO greater than the molecular weight of a target molecule.

[0075] In some embodiments, the semipermeable membrane used to separate blood into a plasma portion and a cellular portion has a MWCO that is within the range of about 1 kDa to about 100 kDa, about 30 kDa to about 60 kDa, or about 10 kDa to about 30 kDa. In further embodiments, the MWCO is about 10 kDa, about 15 kDa, about 20 kDa, about 30 kDa, about 40 kDa, about 50 kDa or about 60 kDa, etc. In such embodiments, the MWCO of the membrane is determined (before blood contacts the membrane) by analyzing the sieving profile of dextran molecules of various molecular weights combined with ultrapure water. US Patent Publication No. 2017/0165616 (Example 3) provides a method that can be used to obtain dextran sieving profiles.

[0076] In certain embodiments, the present invention provides a dialysis system that uses a filter or membrane to separate plasma from whole blood and generate plasma- ultrafiltrate. Such a filter used to generate plasma-ultrafiltrate can be a hemodialysis hollowfiber dialyzer, for example. In certain embodiments, a hollowfiber dialysis filter can generate plasma-ultrafiltrate that contains approximately all of the water content of blood, including excess water that a patient may have in his or her bloodstream. A hollowfiber dialysis filter can produce plasma-ultrafiltrate that contains more water, and is less viscous, compared to the plasma separated by traditional plasma separation techniques ( e.g ., a therapeutic plasma exchange filter). Without being bound to any theory: a hemodialysis filter can extract more water from whole blood compared to other plasma separation filters in part because the pore size of a hollowfiber filter is smaller than the pore size of a plasma separation filter (which has a pore size diameter of 200-600 nm, for example). A smaller pore size (e.g., about 10-100 nm in diameter) causes higher tangential pressure on the hollowfibers; this higher tangential pressure can be maintained at a low blood flow rate, such as 150 mL/minute, such that plasma- ultrafiltrate can be produced without stressing hemodynamic stability. A hollowfiber filter also typically contains more fibers than a plasma separation filter. For example, a filter used to generate plasma-ultrafiltrate may contain about 10,000 fibers, providing a membrane surface area of about 1 m ² to about 2.4 m ² . In some embodiments, the surface area of the membrane is about 1.5 m ² to about 2 m ² . In certain embodiments, the filter used for generating plasma-ultrafiltrate is a commercially available high-flux dialyzer (e.g., Baxter™ (Gambro) Revaclear™ 400 and Revaclear™ 300; Fresenius FX 60ciassix; Fresenius FX 80ciassix). In addition, in certain embodiments, when generating plasma-ultrafiltrate using an upstream filter (e.g., hollowfiber filter), toxins pass through the filter along with the plasma, such that they are concentrated in the separated plasma (which in this case is plasma-ultrafiltrate). When the separated plasma is then dialyzed, toxin removal is more efficient (compared to toxin removal when dialyzing whole blood), at least in part due to a greater concentration gradient of toxins across the dialyzer membrane (compared to the typical concentration gradient of toxins when dialyzing whole blood).

[0077] Thus, in certain embodiments, a hollowfiber dialysis filter is used to produce plasma-ultrafiltrate. In further embodiments, the hollowfiber dialysis filter has a pore size (average diameter) of about 3-100 nm. In certain embodiments, the hollowfiber dialysis filter has a pore size of about 3-50 nm. In other embodiments, the hollowfiber dialysis filter has a pore size of about 5-50 nm. In further embodiments, the hollowfiber dialysis filter has a pore size of about 3-10 nm, and in some embodiments, the filter has a pore size of about 6-11 nm. In some embodiments, the hollowfiber dialysis filter has a pore size of about 3-5 nm. In certain embodiments, the hollowfiber filter has a pore size minimum of about 3 nm or about 6 nm. [0078] The membrane surface area of the filter used to separate blood into a cellular portion and a plasma portion may be the same as, or different from, the membrane surface area of the filter used for dialysis (the dialyzer). In certain embodiments, the filter used to separate blood into a cellular portion and a plasma portion has a filter membrane surface area that is about 1 to 2 times the surface area of the filter used for dialysis. Thus, in some embodiments, the ratio of the surface area of the upstream filter used to generate plasma to the surface area of the downstream dialyzer is 1 : 1 to 2: 1. In certain embodiments, the surface area ratio is 1.5: 1 to 2: 1. For example, in some embodiments, both filters may have a surface area of 1.2 m ² , whereas in other embodiments, the surface area of the filter used to generate plasma ( e.g ., plasma- ultrafiltrate) is 1.8 m ² or 2.4 m ² , while the surface area of the dialyzer membrane is 1.2 m ² . In certain embodiments, increasing the surface area of the upstream plasma generating filter relative to the surface area of the dialyzer reduces the risk of clogging. Examples of upstream filter (used to separate the plasma from blood, e.g., to generate plasma-ultrafiltrate) and downstream filter (used for dialyzing the separated plasma) combinations include but are not limited to: upstream - Baxter (Gambro) Revaclear 400, downstream - Revaclear 300 (surface area ratio of 1.3: 1); upstream - Revaclear 300, downstream - Revaclear 300 (surface area ratio of 1 : 1); upstream - Fresenius FXci _assix 60, downstream - Fresenius FXci _assix 50 (surface area ratio of 1.4: 1); upstream - Fresenius FXci _assix 80, downstream - Fresenius FXci _assix 50 (surface area ratio of 1.3 : 1); upstream - Baxter (Gambro) Polyflux 21R, downstream - Polyflux 17R (surface area ratio of 1.2: 1).

Table A: Example parameters for selecting currently available filters for upstream concentrator and downstream dialyzer

[0079] In some embodiments, the ratio of whole blood to separated plasma is 2: 1 to 4:3 following passage of whole blood through the membrane ( e.g ., a hemodialysis filter) to generate plasma-ultrafiltrate. This range for the ratio of whole blood to separated plasma is different from the range for the ratio of whole blood to separated plasma following use of a plasma separation filter, the latter ratio range being typically 2: 1 to 3: 1 (e.g., 150 mL of whole blood and 50-75 mL of separated plasma), because ultrafiltrate is included in the separated plasma when generating plasma-ultrafiltrate (e.g., following use of a hemodialysis filter). In general, the more fluid in a subject’s blood, the more plasma-ultrafiltrate will be generated for a given blood flow rate. As explained herein, generating and dialyzing plasma-ultrafiltrate increases efficiency of toxin clearance at a lower overall blood flow rate. Generating and dialyzing plasma- ultrafiltrate also can reduce treatment time.

[0080] ln some embodiments of the plasma dialysis systems and methods of the present invention, a centrifugal blood pump, instead of a traditional peristaltic roller pump, is used for blood drawing and/or blood returning. A centrifugal blood pump causes less damage to platelets and red blood cells compared to the traditional peristaltic roller pump, and therefore provides a lower rate of hemolysis. A centrifugal blood pump also allows blood flow to be easily controlled. In certain embodiments, the dialysis systems and methods use a centrifugal blood pump for both blood drawing and returning.

Although using a centrifugal blood pump can further improve hemodynamic stability, it is not required, as the plasma dialysis systems and methods described herein improve hemodynamic stability compared to conventional dialysis even when a traditional pump ( e.g ., roller pump) is used for blood drawing and returning.

[0081] The dialysis systems and methods of the present invention also permit accurate monitoring and control of ultrafiltration (removal of excess fluid). By producing plasma (e.g., plasma-ultrafiltrate) that is then dialyzed, monitoring and controlling the ultrafiltration rate (the rate at which excess fluid is removed from the plasma that passes through the dialyzer) is more accurate in part because there is no cellular component to account for. Blood is a viscous mixture containing free-floating heterogeneous elements such as cells that cause fluctuations in pressure, whereas plasma is more homogeneous and less viscous, with fewer or no elements that cause fluctuations in pressure. Having less pressure fluctuation allows more accurate monitoring of ultrafiltration and more control of the ultrafiltration rate. As illustrated in the embodiments shown in FIG. 2, a pressure monitor (FIG. 2 (e)) can be used to monitor the ultrafiltration rate. Ultrafiltration can also be monitored during dialysis by attaching a weight scale to the waste bag (FIG. 2 (h)) so that the amount of waste (including fluid) is continuously being weighed as waste accumulates into the waste bag.

[0082] In addition, the systems and methods of the present invention provide several ways for controlling and adjusting the ultrafiltration rate, and each such control mechanism can be used alone or in combination with one or more of the others. In some embodiments, a pump (e.g., roller pump) is used to control the ultrafiltration rate, as shown, for example, in FIG. 2 (fl). For example, a peristaltic roller pump can control the rate at which plasma (e.g., plasma-ultrafiltrate) flows into the dialyzer. In certain embodiments, the plasma (e.g., plasma-ultrafiltrate) flow rate is less than or equal to about 75% of the blood draw flow rate; in further embodiments, such plasma (e.g., plasma-ultrafiltrate) flow rate that is less than or equal to about 75% of the blood draw flow rate is increased or decreased to accommodate a particular patient’s ultrafiltration needs. The pump optionally can be set so that ultrafiltration does not exceed a maximum ultrafiltration rate (e.g., 13 mL/kg/hour, 14 mL/kg/hr, 15 mL/kg/hr, etc.). The ultrafiltration rate can also be adjusted by altering the rate at which dialysate flows through the dialyzer; the dialysate flow rate can be controlled by another pump ( e.g ., roller pump), as shown, for example, in F1G. 2 (f2). ln general, the higher the flow rates set by fl and/or f2, the higher the ultrafiltration rate. Additionally or alternatively, the ultrafiltration rate can be altered by adjusting the negative pressure on the dialysate flowing through the dialyzer; this negative pressure can be changed by altering the diameter of the tube used to deliver dialysate from the dialyzer into the waste bag (see, e.g., F1G. 2 (h)); a pressure monitor (see, e.g., F1G. 2 (e)) can be used to monitor this negative pressure. Generally, incremental decreases in tube diameter can produce incremental decreases in dialysate flow rate, and therefore incremental decreases in the ultrafiltration rate.

[0083] Ultrafiltration can also be controlled by altering blood flow rates. For example, decreasing the blood draw flow rate decreases the rate at which plasma (e.g., plasma- ultrafiltrate) is generated, which in turn decreases the ultrafiltration rate ln addition, decreasing the blood return flow rate also decreases the rate at which plasma (e.g., plasma-ultrafiltrate) is generated, which in turn decreases the ultrafiltration rate.

Adjusting blood draw flow rate and/or blood return flow rate as a way to increase or decrease the ultrafiltration rate can be used alone or in combination with any of the other ways described herein for adjusting the ultrafiltration rate.

[0084] Thus, the systems and methods of the present invention allow continuous monitoring and control of the ultrafiltration rate by permitting adjustment of the plasma and/or dialysate flow rates (e.g., as set by pumps such as those indicated by fl and/or f2 in F1G. 2), and/or by having available a variety of tubes of different diameters and that can be used to adjust negative pressure on the dialysate incrementally, and/or by adjusting blood flow rate(s). ln this way, the systems and methods of the present invention permit continuous and accurate control of the ultrafiltration rate once dialysis begins ln contrast, ultrafiltration in conventional dialysis cannot be accurately controlled during dialysis and is monitored only by body weight change (pre- and post dialysis)— for example, prior to receiving dialysis treatment, a patient is weighed; post-treatment, the patient is weighed again, and the weight difference indicates how much fluid was removed during dialysis.

[0085] The plasma dialysis systems and methods of the present invention also improve hemodynamic stability of subjects undergoing dialysis treatment. Hemodynamic instability as a result of high blood flow rate, high extracorporeal volume, and/or high treatment time is common in conventional dialysis. This instability can lead to a variety of cardiovascular complications such as intradialytic hypotension (IDH), which affects 20-30% of the hemodialysis population. IDH can contribute to subclinical, transient myocardial ischemia (McGuire et al, BioMed Research International Article ID 8276912 (2018)), which is associated with increased incidence of cardiac events and ultimately reduced patient survival (Burton et al., Clin J Am Soc Nephrol 4(5): 914-920 (2009)). Other issues can include hypoxemia, which can lead to hypoxia, cerebral ischemia, stroke, or sudden cardiac arrest. Reduced flow rate(s) and reduced treatment time in plasma dialysis promote hemodynamic stability.

[0086] The present invention allows for reduced treatment dose and/or treatment times ( e.g ., lower blood flow rate(s) and/or shorter treatment times), which minimizes hemodynamic instability. Thus, in some embodiments, the systems and methods of the present invention maintain or promote hemodynamic stability in subjects undergoing dialysis by employing blood drawing rates that are less than or equal to about 200 mL/minute, by employing a dialysis treatment time that is less than or equal to about 2 hours, or both, for example. In certain embodiments, the blood drawing flow rate is less than or equal to about 150 mL/minute.

[0087] In some embodiments, the maximum flow rate for blood drawing is about 150 mL/minute. In certain embodiments, the maximum flow rate of dialysate is about 200 mL/minute. In further embodiments, the maximum ultrafiltration rate is set at 13 mL/kg/hr and ultrafiltration and the ultrafiltration rate are monitored and controlled continuously during dialysis, as described herein. In other embodiments, the maximum ultrafiltration rate is set to be higher than 13 mL/kg/hr (e.g., 14 mL/kg/hr, 15 mL/kg/hr, 16 mL/kg/hr, etc.) and ultrafiltration and the ultrafiltration rate are monitored and controlled continuously during dialysis, as described herein. In additional

embodiments, hemolysis is also continuously monitored during dialysis, as described herein.

[0088] In addition, because the plasma dialysis systems and methods of the present invention achieve efficient dialysis with hemodynamic stability, they allow dialysis to be performed at ultrafiltration rates that are higher than the current maximum UFR set by the Centers for Medicare & Medicaid Services, which is 13 mL/kg/hr. Thus, in some embodiments, plasma dialysis as described herein is performed with an ultrafiltration rate that is higher than about 13 mL/kg/hr. In certain embodiments, the UFR is greater than or equal to about 14 mL/kg/hr. In further embodiments, the UFR is greater than or equal to about 15 mL/kg/hr, greater than or equal to about 16 mL/kg/hr, greater than or equal to about 17 mL/kg/hr, greater than or equal to about 18 mL/kg/hr, or greater than or equal to about 19 mL/kg/hr. In further embodiments, hemodynamic stability is continuously monitored ( e.g ., by using a hemoglobin detector as described herein), and the UFR is continuously monitored and adjusted as described herein, so that the UFR can be incrementally increased up to a pre-selected maximum (e.g., 20 mL/kg/hr) while monitoring for hemolysis. In such embodiments, dialysis can be stopped upon detection of hemolysis.

[0089] In further embodiments of the present invention, the plasma dialysis systems and methods allow detection of hemolysis during dialysis. Blood cells can be damaged and bleeding may occur as a result of a system failure or from an improper protocol— e.g., high transmembrane pressure, insufficient heparinization (which can result in coagulation of blood and subsequent clogging of the filter’s lumen), or too much heparinization (e.g., the bolus dose and/or steady dose of heparin during the treatment are too high, such that bleeding may be induced). When hemolysis occurs in whole blood, it is not visible with the naked eye and cannot be otherwise detected, as existing hemolysis detectors can only detect free hemoglobin in plasma and not in whole blood. Thus, hemolysis that occurs during conventional dialysis of whole blood is not detected until post-treatment; typically in conventional dialysis, hemolysis is tested post treatment in centrifuged plasma from a patient’s blood samples if the patient exhibits symptoms of excessive hemolysis. Because dialysis should be stopped immediately if significant hemolysis occurs, detection of hemolysis post-treatment is not optimal. In contrast, hemolysis that may occur during plasma dialysis is easily detectable in the separated plasma (e.g., plasma-ultrafiltrate), even to the naked eye, due to the clarity of the plasma and the contrasting red resulting from lysed blood cells. Thus, the plasma dialysis systems and methods of the present invention allow for hemolysis to be easily and quickly detected by simply examining (e.g., visually examining) the fluid in the tubing following plasma separation.

[0090] In addition, in some embodiments of the present invention, the dialysis apparatuses include a hemoglobin detector. A hemoglobin detector detects free hemoglobin in plasma and allows early detection of hemolysis during plasma dialysis. Continuous monitoring of hemolysis reduces anemia incidence, and reduced hemolysis decreases or eliminates the need for synthetic erythropoietin ( e.g ., EPOGEN) and/or supplements or nutritional support. In some embodiments, the detection of hemolysis by a hemoglobin detector triggers the dialysis system to stop dialysis, to prevent or minimize injury to the patient. For example, a plasma dialysis system may include a hemoglobin detector to detect free hemoglobin in the plasma following plasma separation from whole blood, and the system can be configured to automatically shut off if free hemoglobin is detected.

[0091] As explained above, one advantage of the plasma dialysis systems and methods described herein is the reduced loss of amino acids and proteins during dialysis. When blood is separated into a plasma portion that is dialyzed and a cellular portion that is returned to the patient, amino acids and proteins will be retained in the cellular portion, and those amino acids and proteins retained in the cellular portion cannot be lost to the dialysate when the plasma portion passes through the dialyzer. Thus, in certain embodiments, the present invention provides plasma dialysis methods wherein the loss of total amino acids and/or the loss of protein (e.g., albumin) following plasma dialysis is less than— for example, at least about 25% less than, at least about 20% less than, at least about 15% less than, at least about 10% less than, at least about 5% less than, or at least about 1% less than— the loss of total amino acids and/or protein following hemodialysis, when the plasma dialysis and hemodialysis are performed for the same amount of time using the same or equivalent blood source, the same dialyzer membrane, and the same blood draw flow rate, or are performed on the same or equivalent blood source using the same dialyzer membrane until a target URR is achieved. In some embodiments, the present invention provides plasma dialysis methods wherein the percentage of total amino acids in the subject’s blood that is lost during treatment is less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less than about 1%. In certain embodiments, the present invention provides plasma dialysis methods wherein the percentage of albumin in the subject’s blood that is lost during treatment is less than about 1%, less than about 0.5%, less than about 0.3%, less than about 0.1%, or less than about 0.05%.

[0092] In some embodiments, the loss of amino acids and/or proteins (e.g., albumin) from blood following a treatment using the plasma dialysis systems and methods described herein may be up to about 25%, up to about 20%, up to about 10%, up to about 5%, or up to about 1% of the loss of amino acids and/or proteins that occurs following a typical hemodialysis treatment, when each treatment is administered to the same or substantially equivalent blood source for the same amount of time and using the same flow rates and membrane for dialysis, or is administered to the same or substantially equivalent blood source using the same dialyzer membrane to achieve the same URR.

[0093] The present invention further provides apparatuses that can be used in combination with conventional dialysis machines ( e.g ., hemodialysis machines that are used to perform dialysis of whole blood such as, for example, Fresenius 2008K, 2008T, and B. Braun Dialog+). Such apparatuses can separate blood into a cellular portion and a plasma portion, so that the plasma portion can then be dialyzed in the dialysis filter of a conventional hemodialysis machine. Thus, the benefits of plasma dialysis can be achieved with hemodialysis machines when such machines are used in conjunction with an upstream filter or concentrator that separates blood into a cellular portion and a plasma portion; as described above, such separation concentrates toxins in the fluid undergoing dialysis and allows for more efficient toxin removal while also minimizing loss of amino acids and albumin when compared to methods of dialyzing whole blood.

[0094] For example, as depicted in F1G. 8, in conventional dialysis, the fluid exiting the dialyzer (shown as dialysate out) contains toxins, including small-sized toxins such creatinine (113 daltons) and urea (60 daltons) that are less than about 500 daltons, and in high-flux dialysis, the fluid also contains medium-sized toxins such as b2- microglobulin (around 11,700 daltons) that range from about 500-15,000 daltons; this fluid often also contains amino acids (75-204 daltons) and in high-flux dialysis also contains large-sized proteins (e.g., proteins that are about 15 kilodaltons or larger in size) such as albumin (66.5 kilodaltons), erythropoietin/epoetin-alpha (30.4

kilodaltons), and myoglobin (17 kilodaltons) (all molecular weights are approximate). Thus, in conventional dialysis, and particularly high-flux dialysis, toxin removal (which is typically less than 65% URR) is accompanied by loss of amino acids and loss of albumin. While low-flux hemodialysis may be associated with relatively less protein and amino acid loss compared to high-flux hemodialysis, low-flux hemodialysis does not remove toxins, particularly medium-sized toxins such as P2-microglobulin, as well as high-flux hemodialysis. However, using an upstream filter (referred to in F1G. 8 as an upstream concentrator) in combination with a hemodialysis machine allows for more efficient toxin removal; using an upstream filter in combination with a conventional dialysis machine also reduces the loss of amino acids and albumin during dialysis compared to the loss of these blood components reported with conventional dialysis methods. The upstream filter separates plasma from whole blood, and the separated plasma (referred to in FIG. 8 as separated filtrate) undergoes dialysis in the

conventional dialyzer.

[0095] Accordingly, in certain embodiments, the present invention provides an apparatus that can be used with a conventional dialysis machine ( e.g ., a hemodialysis machine currently available and used in the clinic) to concentrate toxins that exist in the blood, so that dialysis by the machine is performed on fluid having a higher

concentration of toxins compared to the concentration of toxins in whole blood. In specific embodiments, such a device is referred to herein as the small and middle molecule interceptor (SAMMI) device or interceptor device.

[0096] The SAMMI device is an electronic device that can be attached to the dialyzer pole of a conventional dialysis machine to intercept blood before the blood is pumped through the dialyzer of the conventional dialysis machine. For conventional dialysis, the arterial line containing blood drawn by the conventional dialysis machine’s blood pump is normally connected to a dialyzer; with the SAMMI device, this blood in the arterial line is directed into the arterial input port of a filter attached to SAMMI. The filter, which may be referred to herein as a first filter, pre-filter, or upstream

concentrator, may contain, for example, hollowfibers with a semi-permeable membrane. A pump (e.g., peristaltic pump) on SAMMI applies pressure, causing less viscous plasma to separate from the blood through the semi-permeable membrane of the pre filter. The plasma or filtrate collects in the cavities surrounding the hollowfibers within the housing of the pre-filter and exits a side plasma port of the pre-filter; as shown in the embodiment in FIG. 9A-C, the plasma or filtrate (which contains toxins and excess fluid) enters a drip chamber on the SAMMI device. The plasma is then pumped, through tubing connected to the SAMMI pump, into the arterial input port of a dialyzer (e.g., high-flux dialyzer) that is part of the conventional dialysis machine. The machine can then perform dialysis and ultrafiltration as normal, but would be dialyzing the separated plasma generated by SAMMI instead of whole blood as in conventional dialysis methods. During dialysis, small and middle molecule toxins in the plasma are cleared by dialysate flowing the opposite direction through the dialyzer, while water is also removed for ultrafiltration.

[0097] As depicted in the embodiment of FIG. 9A-C, as the separated plasma exits the pre- filter through the side plasma port, the arterial pressure provided by the blood pump of the conventional dialysis machine pushes the cellular portion of blood remaining in the pre-filter hollowfibers out of the venous output port of the pre-filter. This cellular portion of blood enters a venous drip chamber of the conventional dialysis tubing set, where it is joined by the treated plasma exiting from the venous output port of the conventional dialyzer ( e.g ., high- flux dialyzer); the combined cellular portion and treated plasma is returned to the patient. The cellular portion of blood, which is about 30-50% of total blood volume, depending on a patient’s fluid retention volume, is free of uremic toxins and excess water and does not need to be dialyzed before being returned to the patient.

[0098] In some embodiments, the pre- filter that is used with a conventional dialysis machine is configured to receive whole blood through an arterial input port, and is configured to deliver the separated plasma portion through a plasma port into a chamber. The dialyzer of the conventional machine is configured to receive the plasma portion through an input port. The dialysis system may further comprise a hemoglobin detector configured to detect free hemoglobin in the tubing connecting the plasma port of the pre-filter to the chamber, or in the tubing connecting the chamber to the input port of the dialyzer.

[0099] When using an interceptor in combination with a conventional dialysis machine, the interceptor’s pump and the dialysis machine’s pump may be set at different speeds. In certain embodiments described herein, the pump speed of the interceptor pump is lower than the pump speed of the dialysis machine’s pump, because the volume of the plasma being separated is less than the volume of whole blood being drawn from the patient; adjusting pump speed to accommodate the lower volume of fluid being pumped has been found to reduce the risk of hemolysis. In general, for plasma-ultrafiltrate, the volume of plasma-ultrafiltrate will be about 40-50% of the volume of whole blood, although this percentage may vary on a patient-by-patient basis, depending on a patient’s fluid retention volume and duration of treatment. In certain embodiments, the dialysis machine’s pump may be set at a speed of 200 or 300 mL/minute, while the interceptor pump’s speed may be set at 80, 100, 120, 133, or 150 mL/minute. For example, the dialysis machine’s pump may be set at a speed of 200 mL/minute and the interceptor pump may be set at a speed of 100 mL/minute.

[0100] When using a pre- filter, such as the pre-filter that is part of an interceptor device as described herein, in combination with a conventional dialysis machine, pressure and/or flow may be monitored to ensure proper operation and safety. Pressure may be monitored at various points along the fluid line to detect pressure changes. For example, a tube used for monitoring arterial blood pressure may be split into two lines, one line that is connected to the conventional dialysis machine and another line that is connected to the interceptor lf there is any sudden or extreme change in pressure in the arterial line, then both the conventional machine and the interceptor device will detect this change in pressure. The system can be configured such that, if the dialysis machine detects such pressure change, it will turn off its pump and the machine optionally will trigger an alarm, and if the interceptor detects such pressure change, it also will stop its pump ln addition, if the dialysis machine’s pump stops or pauses for another reason, causing a sudden increase in arterial pressure, the interceptor will detect such pressure change and its pump will turn off. ln addition or alternatively, a flow sensor may be used to sense arterial flow from the dialysis machine to the pre-filter lf this flow sensor detects a decrease or stoppage of flow, for example, the system may be configured so that the interceptor’s device pump turns off.

[0101] Pressure in the pre-filter also may be monitored. For example, in the

embodiment depicted in F1G. 9A-C, if the pre-filter (or upstream concentrator) becomes clogged, a pressure sensor (PF, which measures pressure in the drip chamber DCF; such pressure in the chamber is an indication of the transmembrane pressure of the filter) will detect a high transmembrane pressure (TMP) for the upstream concentrator; this high pressure reading can trigger the interceptor pump to turn off. ln addition, pinch valves or clamps may be included to control the flow of fluid to the hemodialysis machine’s dialyzer and/or to the patient, for example. Pinch valves are shown as Cl and C2 in the embodiment depicted in F1G. 9A-C. lf the pre-filter or upstream concentrator becomes clogged and the pressure sensor (PF) detects a transmembrane pressure above a specified limit, the interceptor device can trigger the C2 pinch valve to clamp down and the interceptor pump (PP2) to stop ln such a circumstance of stopping the interceptor pump (PP2), plasma will not be separated from whole blood and the blood instead will pass through the pre-filter and be returned to the patient. The system can be configured so that an alarm/light signal is triggered to alert the operator that the interceptor pump has stopped; the operator can then manually stop the dialysis machine pump (PP1).

[0102] Controlling and monitoring elapsed treatment time is another way to ensure proper operation and safety when using a pre-filter, such as the pre- filter that is part of an interceptor device as described herein, in combination with a conventional dialysis machine. During conventional dialysis, a predetermined treatment time is set on the hemodialysis machine’s computer, and the machine’s pump runs for the predetermined treatment time; in turn, treatment time elapses when the machine’s pump is running, and when the pump is not running, treatment time does not elapse ( e.g ., if the pump pauses, treatment time does not elapse during the pause). When the treatment time has fully elapsed, the machine’s pump will stop. Similarly, for the interceptor device, the interceptor pump’s run time is controlled by a timer and the pump will run for a predetermined, set time; and the pump’s run time elapses only when the pump is running. By setting both the hemodialysis machine’s pump and the interceptor’s pump for the same treatment time, the two pumps will be synchronized and run for the same length of time, even if the interceptor’s computer and the hemodialysis machine’s computer are not communicating with each other.

[0103] A system in which a pre-filter is used with a conventional hemodialysis machine may include additional safety features to ensure that the interceptor pump does not run when the hemodialysis machine’s pump has stopped. For example, a flow sensor may be included to detect fluid movement within the arterial tubing entering the pre-filter. If the hemodialysis machine pump has stopped, then the flow of fluid in this arterial tubing will stop; the flow sensor will detect such a change in flow and send a signal to the interceptor device to turn off its pump. Turning off the interceptor pump in such a scenario is important because, if the interceptor pump runs when the dialysis machine’s pump is not running, the interceptor pump will pull blood from a closed arterial line forcefully, which may induce hemolysis. On the other hand, if the dialysis machine’s blood pump is running while the interceptor device or pump has stopped, blood drawn from the patient will pass through the pre-filter and directly back to the patient without affecting system stability. In such a circumstance when the interceptor device or its pump independently stops, the dialysis machine’s pump will continue to pump blood through the pre-filter, but because the interceptor pump is not running and its filter already contains separated plasma, the blood entering the filter will not be separated into a plasma portion and a cellular portion, and plasma will not enter the dialyzer (dialysis in the downstream filter will not occur). Instead, the blood being pumped by the dialysis machine’s pump will pass through the pre- filter without separation and will be returned untreated back to the patient. The system may be configured so that, in such a circumstance, an alarm sounds to alert the treating healthcare professional that the interceptor device or pump is not running. In addition, the system optionally may include a pinch valve on the tubing configured to deliver plasma to a drip chamber (if present) or to the downstream dialyzer, and the system may be configured such that this pinch valve clamps down on this tubing if the interceptor device or its pump stops running during a treatment. It will also be understood that any one or more of the above safety features may be included in other embodiments of the present invention, including the embodiments described in FIG. 2 and FIG. 3, for example.

[0104] A hemoglobin detector may also be used to detect hemolysis; for example, a hemoglobin detector may be included as part of the interceptor device, to detect free hemoglobin in the separated filtrate ( e.g ., plasma-ultrafiltrate) before it enters the dialysis machine’s dialyzer.

[0105] Accordingly, a system in which a pre-filter or upstream concentrator is used with a conventional dialysis machine can be configured such that certain events— such as a pause/stop of the blood pump of the conventional machine, a sudden change in pressure in the pre-filter or arterial blood pressure, a sudden change in the flow to the pre-filter, detection of hemolysis, and/or the presence of air in the drip chamber containing the untreated filtrate or in the drip chamber containing the combined cellular portion and treated filtrate (e.g., through the use of ultrasonic fluid detector that detects whether the level of fluid falls below a pre-set fluid level)— will stop the interceptor pump, and optionally also trigger an alarm and/or activate pinch valves. For example, the system can be configured such that, if the dialysis machine’s pump pauses or stops, the interceptor device’s pump will stop.

[0106] Thus, in certain embodiments, the present invention provides kidney dialysis systems comprising a pre-filter configured to receive whole blood and separate the whole blood into a plasma portion and a cellular portion, and that is configured to be used in combination with a conventional dialysis machine (e.g., a low- volume, high- flux dialyzer). The first filter can be a plasma exchange filter or a hollowfiber dialysis filter, for example. In some embodiments, the pre-filter comprises a semipermeable membrane with pores having diameters that are less than or equal to about 200 nm. In certain embodiments, the pores have diameters that are from about 100 nm to about 200 nm. In some embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are less than or equal to about 100 nm. The diameter of each pore can be, for example, less than or equal to about 100 nm, less than or equal to about 75 nm, or less than or equal to about 50 nm. In certain embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are from about 3 nm to about 50 nm. In some embodiments, the pores have diameters that are about 12 nm or less. In certain embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are from about 3 nm to about 10 nm. In other embodiments, the first filter comprises a semipermeable membrane with pores having diameters that are no less than about 3 nm and that are no greater than about 11 nm. In further embodiments, the membrane has an average pore diameter within the range of about 3 to about 11 nm.

[0107] The permeability of the pre-filter’s membrane may also be described by MWCO. Accordingly, in certain embodiments, the membrane of the pre-filter in an interceptor device has a MWCO between about 1 kDa to about 100 kDa— e.g., about 25 kDa to about 65 kDa, about 30 kDa to about 60 kDa, or about 10 kDa to about 30 kDa.

[0108] Using a pre-filter in combination with a conventional dialysis machine provides the advantages of plasma dialysis discussed above. For example, using a pre-filter (e.g., as part of an interceptor device as described herein) to separate plasma from blood so that the separated plasma is dialyzed can reduce the loss of amino acids and proteins.

As discussed above, when fluid is removed from blood via a high-flux dialyzer hollowfiber membrane, subjects may lose 24% of total amino acids from blood during a 4-hour treatment at 300 mL/min blood flow rate and 500 mL/min dialysate flow rate (Navarro et al. 2000). When using a pre-filter, such as in the interceptor device described herein, to separate blood into a plasma portion (e.g., plasma-ultrafiltrate) and a cellular portion, dialysis can be performed at a blood draw flow rate (e.g., 200 mL/min or less) that is less than the blood draw flow rate typically employed during hemodialysis (which can exceed 400 mL/min); furthermore, dialysis can be performed during a treatment period that is less than 4 hours. The reduced flow rate and reduced treatment time, compared to the flow rates and treatment times of conventional hemodialysis methods, reduces the volume of fluid that is passed through the dialyzer; this reduced volume, in addition to the diluted concentration of amino acids and proteins in the plasma compared to whole blood, in turn reduces the amount of proteins and amino acids that can be lost into the dialysate.

[0109] In particular, when separating plasma from the cellular portion in the pre-filter (upstream concentrator), much of the blood’s amino acids and proteins are retained in the cellular portion that will be returned to the patient, and therefore the amount of amino acids and proteins that can be lost in the downstream dialyzer is reduced; the plasma being delivered to the dialyzer contains less amino acids and proteins compared to whole blood that is delivered to the dialyzer in conventional dialysis, and thus less amino acids and proteins can be lost during dialysis (the amino acids and proteins in the plasma are diluted, compared to the amino acids and proteins in blood). Accordingly, the amount of amino acids and proteins that can be lost from the plasma passing through the dialyzer is limited to, and will be a proportion of, the amount of amino acids and proteins lost into the filtrate from the first filter. For example, if there is a 20% loss of amino acids in the pre-filter such that the filtrate contains 20% amino acids from blood, and then a subsequent 20% loss of amino acids through the dialyzer and into the dialysate, then the total loss of amino acids from the blood drawn from the patient would be 4% (.20 * .20 *100). Thus, when using a pre-filter (e.g., an upstream concentrator that is part of an interceptor device) as described herein, the cellular portion and plasma portion being dialyzed retain higher amounts of amino acids and proteins compared to blood treated using conventional hemodialysis methods, and this cellular portion and plasma portion retaining higher amounts of amino acids and proteins will be returned to the patient, resulting in less amino acid and protein loss during treatment. For example, the loss of amino acids and/or proteins (e.g., albumin) from blood following a treatment using an interceptor device as described herein may be up to about 25%, up to about 20%, up to about 10%, up to about 5%, or up to about 1% of the loss of amino acids and/or proteins that occurs following a hemodialysis treatment performed without the interceptor device, when each treatment is

administered to the same or equivalent blood source (e.g., cow blood) for the same amount of time and using the same flow rates, or is administered to the same or equivalent blood source to achieve the same UR . [0110] Accordingly, using an interceptor device with a conventional dialysis machine to perform plasma dialysis can achieve numerous improvements compared to conventional dialysis methods, including: reduced treatment time due to more efficient toxin clearance; improved small and middle molecule toxin clearance rates; decreased volume of fluid passing through the dialyzer during treatment due to a lower blood draw flow rate ( e.g ., to a blood draw flow rate at or below 200 mL/minute, including, for example, 150 mL/minute); and reduced protein and amino acid loss. Such improvements can be realized by integrating a pre-filter into a conventional dialysis machine without modifying the machine or the clinic’s infrastructure.

[0111] For example, the attachment of a pre- filter to a conventional dialysis device allows the operator to set an ultrafiltration target and rate as normal on the original hemodialysis device. Although the attachment system (e.g., the interceptor device as described herein) may operate at or below 200 mL/min flow rate and the viscosity of the plasma (e.g., plasma-ultrafiltrate) undergoing dialysis and ultrafiltration is lower than the viscosity of blood, the ultrafiltration performance of the conventional dialysis machine remains unaffected. A pre-filter, as part of an interceptor system as described herein, for example, can be used without affecting the ultrafiltration rate control in the conventional dialysis machine.

[0112] The present invention further provides methods for calculating dialysis treatment times based on a patient’s ultrafiltration needs. As explained above, dialysis treatment aims to remove toxins as well as excess water from a patient’s blood. With respect to toxin clearance, given the improved toxin clearance efficiency of plasma dialysis compared to conventional dialysis, the plasma dialysis systems and methods described herein allow for dialysis treatment in which the Kt/V goal is achieved in about half the treatment time compared to conventional dialysis treatment times (e.g., 2 hours compared to 4 hours), regardless of a patient’s body weight (or volume of urea distribution). However, for many patients, if treatment is stopped once the target Kt/V is achieved, they may not receive an adequate ultrafiltration dose and still may have excess water in the blood, given the Centers for Medicare & Medicaid Services ultrafiltration rate limit of 13 mL/mg/hr. The present invention provides for safer dialysis systems and methods, and thus the ultrafiltration rate safely can be increased to a rate higher than 13 mL/kg/hr, as described above. Additionally or alternatively, the present invention provides dialysis methods wherein treatment time is determined based on a patient’s ultrafiltration need, taking into account a given ultrafiltration limit ( e.g .,

13 mL/kg/hr or other limit), so that sufficient treatment for ultrafiltration is

administered. For example, for a patient weighing 70 kg and having 2 kg (2000 mL) of fluid retention in the blood (e.g., based on the difference in the patient’s weight prior to and after dialysis treatments), if the UFR is set to 13 mL/kg/hr, then the maximum rate of fluid removal is 910 mL/hr (calculated by multiplying 70 kg by 13 mL/kg/hr), and it would take about 2.20 hours to remove the excess 2000 mL of fluid when removal is occurring at 910 mL/hr. Accordingly, while in certain embodiments the plasma dialysis systems and methods described herein can achieve Kt/V = 1.44 at URR = 76% in about 1 hour, and Kt/V = 3.22 at URR = 96% in about 2 hours, the determining factor for dialysis treatment time can be based on a given patient’s fluid retention and his or her ultrafiltration need.

[0113] The plasma dialysis systems and methods described herein can be used in a variety of clinical settings. For example, the plasma dialysis systems and methods described herein can be used in the treatment of acute renal impairment and in the treatment of hepatorenal syndrome. They can also be used to treat CKD and ESRD and other kidney diseases or conditions of renal dysfunction where dialysis may be useful. Furthermore, the plasma dialysis systems and methods described herein can be used to treat subjects with a liver disease that is associated with or leads to renal impairment. In some embodiments, the plasma dialysis systems and methods of the present invention are used to treat ascites. In any of these embodiments, the plasma that is dialyzed can be plasma-ultrafiltrate.

[0114] In some embodiments, the systems and methods described herein improve prognosis in patients with kidney disease, including patients with ESRD. Currently, patients with ESRD undergoing dialysis suffer a gradual loss in kidney function, and about 25% of patients do not live past 12 months after initiating hemodialysis treatment. Because the systems and methods of the present invention achieve a high level of toxin clearance, they can improve survival and prolong life. In addition, in view of the frequent treatment sessions and long duration of each treatment session typically required with conventional dialysis, the comparatively less frequent and shorter treatment sessions permitted by the methods and systems of the present invention can improve patients’ quality of life. [0115] The plasma dialysis systems and methods of the present invention can also be used in conjunction with liver assist therapy. Deterioration of kidney function is a frequent complication for patients with cirrhosis or liver disease. For example, 20-25% of liver disease patients have kidney disease. Gonwa and Wadei, Kidney Disease in the Setting of Liver Failure: Core Curriculum 2013, American Journal of Kidney Disease 62: 1198-1212 (2013). The plasma dialysis systems and methods of the present invention can be used in conjunction with an extracorporeal liver assist device to treat liver disease states, for example as a prophylactic treatment to help prevent or minimize kidney dysfunction. Liver disease states include, for example, non-alcoholic fatty liver disease, non-alcoholic steatohepatitis, acute intoxication, hepatorenal syndrome, acute liver failure, and acute on chronic liver failure. Liver assist devices include, for example, molecular adsorbent recirculating systems. In some embodiments, the liver assist device is a bio-artificial liver. Examples of liver assist devices are also described in U.S. Patent Nos. US 5976870 A, US 5773285 A, and US D552740 Sl, each of which is hereby incorporated in its entirety by reference herein.

[0116] In certain embodiments, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with non-alcoholic fatty liver disease (NAFLD). NAFLD is a risk factor for developing CKD, and NAFLD

accelerates CKD. Jang et al. , Nonalcoholic Fatty Liver Disease Accelerates Kidney Function Decline in Patients with Chronic Kidney Disease: a Cohort Study, Nature Scientific Reports 8:4718 (2018); Targher et al, Increased Risk of CKD among Type 2 Diabetics with Nonalcoholic Fatty Liver Disease, Journal of the American Society of Nephrology 19: 1564-1570 (2008). In addition, individuals with liver enzymes (alanine aminotransferase or ALT) greater than 40 units per liter are reported to have lower estimated glomerular filtration rates compared to individuals with ALT of less than 40 units per liter. Orlic et al, Chronic Kidney Disease and Nonalcoholic Fatty Liver Disease Is There a Link?, Gastroenterology Research and Practice, Article ID 847539 (2014). In some embodiments, a liver assist device is used in conjunction with plasma dialysis as a preventative measure to slow or prevent CKD progression in patients with NAFLD. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0117] In other embodiments, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with non-alcoholic steatohepatitis (NASH). CKD has a higher prevalence in patients with NASH, as twenty-one percent of NASH patients were reported to have CKD, compared to six percent of non-NASH patients. Yasui et al, Nonalcoholic Steatohepatitis and Increased Risk of Chronic Kidney Disease, Metabolism Clinical and Experimental 60: 735-739 (2011). In addition, thirty-five percent of patients with liver transplants for NASH-related cirrhosis are reported to develop stage 3 -4b CKD within two years. Musso et al, Chronic kidney disease (CKD) and NAFLD: Time for awareness and screening, Journal

of Hepatology 62: 983-984 (2015). In some embodiments, a liver assist device is used in conjunction with plasma dialysis as a preventative measure to slow or prevent CKD progression in patients with NASH. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0118] In certain embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein to treat severe liver disease in patients that have hyperammonia. Ammonia is one of the major toxins appearing in elevated amounts in hepatic encephalopathy patients. Gupta et al., The role ofRRT in hyperammonic patients, Clinical Journal American Society of Nephrology 11 : 1872- 1878 (2016). Plasma ( e.g ., plasma-ultrafiltrate) that is dialyzed as described herein can reduce the toxic burden of liver tissues in a bioreactor of a bio-artificial liver and can promote long-term viability and maintenance of full functionality of such a liver.

[0119] In other embodiments, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with acute or chronic liver failure. Individuals with compensated or uncompensated liver failure often have or are diagnosed with CKD or ESRD. In addition, acute liver failure can progress to multi-organ failure, particularly kidney failure, as a result of hepatorenal syndrome. In certain embodiments, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with acute liver failure. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate. In other embodiments, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with chronic liver failure; in further embodiments, the plasma that is dialyzed is plasma- ultrafiltrate.

[0120] In certain embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with hepatorenal syndrome (HRS). Approximately 19% of hospitalized liver cirrhosis patients have acute renal impairment, which includes HRS. Low et al, Hepatorenal syndrome aetiology, diagnosis, and treatment, Gastroenterology Research and Practice, Article ID 207012 (2015). HRS occurs in about 4% of patients admitted with

decompensated cirrhosis, and the cumulative probability of developing HRS for these patients is 18% at 1 year and 39% at 5 years. Ng et al, Hepatorenal syndrome, Clinical Biochem Review 28: 11-17 (2007). In some embodiments, a liver assist device is used in conjunction with plasma dialysis to treat or prevent HRS (type I and/or type II). In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0121] In certain embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein for organ transplant recipients to reduce metabolic overload during recovery. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0122] In certain embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for patients with acute viral hepatitis. Acute viral hepatitis (particularly hepatitis A and B) can cause liver failure, which can lead to loss of kidney function. In some embodiments, a liver assist device is used in conjunction with plasma dialysis to treat a patient with acute viral hepatitis, in part to prevent or minimize kidney impairment. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0123] In some embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for ascites management. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

[0124] In certain embodiments of the present invention, a liver assist device is used in conjunction with plasma dialysis as described herein as a treatment for intoxicated subjects. In many intoxication cases, damage is observed in both the liver and kidney. Diverting toxins away from these organs is necessary in acute intoxication. A liver assist device (including, for example, a bio-artificial liver) in conjunction with plasma dialysis can reduce the metabolic burden on a subject as damaged organs recover. In further embodiments, the plasma that is dialyzed is plasma-ultrafiltrate.

EXAMPLES

[0125] The following examples serve only to illustrate the invention and practice thereof. The examples are not to be construed as limitations on the scope or spirit of the invention.

Example 1

[0126] FIG. 2 depicts exemplary plasma dialysis apparatuses of the present invention. Component a in FIG. 2 separates plasma from blood; in certain embodiments, component a is a plasma exchange filter, and in other embodiments, component a is a hemodialysis hollowfiber filter. In embodiments where a is a hemodialysis hollowfiber filter, blood enters a into hollowfibers with small pores (e.g., 10-100 nm) and the cellular portion exits through a port at the top and plasma-ultrafiltrate exits through a port on the side. In certain embodiments, a pump (e.g., roller pump) is used to control the ultrafiltration rate, as shown in FIG. 2 (fl). The suction pressure created by fl (pump for ultrafiltrate) and the small pores of the hollowfibers maximize the amount of water that can be pulled out of whole blood. The resulting plasma-ultrafiltrate then enters b

(dialyzer) to be dialyzed.

[0127] The plasma (e.g., plasma-ultrafiltrate) that has been separated from blood travels through hollowfibers within b (dialyzer) and comes into contact with dialysate from g.

A pump (12) moves the dialysate from g into b. As the plasma (e.g., plasma-ultrafiltrate) comes into contact with the dialysate, uremic toxins are removed from the hollowfiber filter and are washed away into h (dialysate waste bag).

[0128] The systems illustrated in FIG. 2 also provide effective ways for monitoring and controlling the rate at which fluid is removed from the plasma during dialysis in b. A pressure controller (e4) and weight scale (h) provide an estimate of the rate at which fluid is being pulled from the plasma (e.g., plasma-ultrafiltrate). This rate can be controlled, for example, by altering the dialysate flow rate with 12 (pump for dialysate).

[0129] A plasma dialysis apparatus may optionally include a hemoglobin detector (d), which can detect free hemoglobin. Such a system may be programmed so that, if the hemoglobin detector detects free hemoglobin and therefore detects hemolysis, an emergency stop of the dialysis system is triggered.

[0130] Cleansed plasma that exits b then joins the separated cellular portion from a and is returned to the subject.

[0131] Table 1 below sets forth a comparison of certain features of specific, exemplary embodiments of the present invention to the corresponding features in conventional dialysis.

Table 1

Example 2

[0132] Urea clearance and creatinine clearance were tested using a dialysis system containing a hollowfiber dialysis filter to produce plasma-ultrafiltrate for dialysis. The dialysate fluid used was a commercially available 2.25 Ca, 0.00 K solution (mEq/L), made from a mixture of Fresenius NaturaLyte ^® Liquid Acid Concentrate (Acetic Acid Based - 45X Proportioning) and NaturaLyte ^® Bicarbonate Concentrate (45X

Proportioning). Urea or creatinine was diffused into bovine blood to obtain three toxin pools (5 liters each): high BUN, low BUN, and high creatinine. The viscosity and osmolality of bovine blood and human blood are similar, and thus toxin clearance from bovine blood is an accepted method by which to measure dialyzer performance. Each toxin pool was processed in the system illustrated in FIG. 3. Flow rates were the same for all experiments: blood flow rate was 150 mL/minute, the plasma-ultrafiltrate flow rate was 75 mL/minute, and the dialysate flow rate was 200 mL/minute. Clearance of the toxin (here, urea or creatinine) was measured every 30 minutes over a 2-3 hour period. Samples were collected from two sampling ports: one port to sample plasma- ultrafiltrate pre-dialysis, or before it enters the dialyzer (component b); and another port to sample plasma-ultrafiltrate post-dialysis, or after it exits the dialyzer. Pre-dialysis samples represent total toxin pool in the blood, and the amount of toxins in pre-dialysis samples over time was compared to provide a measure of accumulated clearance rate ln addition, the amount of toxins in pre-dialysis samples was compared to the amount of toxins in post-dialysis samples as a measure of dialyzer efficiency.

[0133] The amount of urea or creatinine in each sample was measured using an enzyme- linked immunosorbent assay (EL1SA). Urea and creatinine reside in the plasma portion of whole blood, and detecting these toxins in whole blood using EL1SA requires diluting blood samples to 1 :250 due to the color of the blood— hemoglobin present in whole blood can interfere with colorimetric detection ln contrast, with the present invention, these toxins are detected in plasma directly, thereby avoiding the imprecision associated with whole blood analysis.

[0134] The toxin concentrations measured from the pre-dialysis samples at time = 0 were 276.4 mg/dl BUN (high BUN), 62.53 mg/dl (low BUN), and 12.385 mg/dl creatinine (high creatinine). The amounts or concentrations of urea in the blood over time were compared using the equation URR % = (Uo - pre-dialysis Ux)/Uo * 100, where Uo is the urea concentration at time 0 and Ux is the urea concentration in the blood at a given time x (as urea concentration in the plasma reflects the urea concentration in blood). Urea or BUN clearance during dialysis was calculated using the equation BUN clearance % = (pre-dialysis Ux - post-dialysis Ux)/pre-dialysis Ux * 100. Similarly, creatinine clearance during dialysis was calculated using the equation creatinine clearance % = (pre-dialysis Cx - post-dialysis Cx)/pre-dialysis Cx * 100, where Cx is the concentration of creatinine at time x.

[0135] Table 2 provides urea (BUN) concentration and URR over time, and % urea clearance during dialysis, for the high BUN pool. Kt/V was calculated for the 60-minute and 130-minute time points, using the equation Kt/V = -ln(l-URR/l00). Kt/V at 60 minutes = 1.44, and Kt/V at 130 minutes = 3.23. Table 2

[0136] Table 3 provides urea (BUN) concentration and URR over time, and % urea clearance during dialysis, for the low BUN pool. Kt/V was calculated for the 60-minute and 180-minute time points, using the equation Kt/V = -ln(l-URR/l00). Kt/V at 60 minutes = 1.33, and Kt/V at 180 minutes = 3.22.

Table 3

[0137] Table 4 provides creatinine concentration over time and % creatinine clearance during dialysis. Table 4

[0138] These experiments demonstrate that an apparatus and method for dialyzing plasma-ultrafiltrate achieves greater performance than hemodialysis. For example, URR (%) for the high BUN blood was 76.45% following 1 hour of dialysis using the system illustrated in FIG. 3, whereas conventional dialysis typically achieves 63-70% URR after a 4-hour treatment. See Table 2 and FIG. 4B. The URR (%) for the low BUN blood at the l-hour time point was 73.57% and therefore was also better than conventional dialysis. See Table 3 and FIG. 5B. Moreover, the system illustrated in FIG. 3 achieved 96% URR for both high and low BUN blood; for high BUN blood, 96% URR was achieved by 130 minutes of dialysis. See FIG. 4B and FIG. 5B. BUN clearance reached 100% at the 90-minute time point for high BUN blood, and reached 93% at the 3 -hour time point for low BUN blood. See FIG. 6 A and FIG. 6B. For high BUN blood, dialysis to remove urea was stopped after 2 hours 10 minutes because after this period, the amount of urea in the post-dialysis samples was too low to measure. The dialysis system illustrated in FIG. 3 also achieved 100% creatinine clearance at the 3-hour time point.

See Table 4 and FIG. 7B. Together, these results show that plasma-ultrafiltrate dialysis can achieve close to 100% spot clearance of urea and creatinine, such that all or nearly all of these toxins can be cleared before blood is returned to the subject. In addition, clearance of urea and creatinine can serve as a proxy for clearance of other small molecule toxins, such that demonstrating clearance of urea and creatinine indicates that other small-molecule toxins have also been removed.

[0139] These experiments also demonstrate that plasma dialysis can be performed with little or no hemolysis. The plasma dialysis system used in the studies included a hemoglobin detector (Introtek ^® BC1 - Miniature Blood Component Detector) (see FIG.

3 (d)) and was configured such that the hemoglobin detector would trigger an alarm and automatic shutdown of the system if hemolysis was detected. During the experiments described herein, no such alarm and shutdown were triggered, indicating that hemolysis was not detected.

[0140] In sum, plasma-ultrafiltrate dialysis is superior to conventional dialysis.

Conventional hemodialysis devices achieve Kt/V = 1.2 and URR = 60-70% at blood flow rates of 300-400 mL/min, a dialysate flow rate of > 400 mL/minute, and with 3-4 hours of treatment time ln contrast, a plasma dialysis system and method as provided by the present invention is able to achieve Kt/V = 3.23, URR = 96% at a blood flow rate of 150 mL/min and a dialysate flow rate of 200 mL/minute, with less treatment time.

Moreover, such plasma dialysis was performed without causing hemolysis.

[0141] High clearance of toxins is important because a subject will carry a smaller amount of toxins, and therefore not accumulate as much toxins, between treatments. Lower interdialytic toxin concentration levels have been linked to lower mortality rates in dialysis patients receiving treatments up to three times a week. In addition, higher clearance per dose of dialysis (Kt/V) over time is associated with lower mortality rates. The systems and methods of the present invention can achieve high toxin clearance in half the treatment time compared to conventional dialysis and present a significant clinical advantage over conventional dialysis methods and apparatuses.

Example 3

[0142] FIG. 10A depicts the operation of safety features that can be included when using an interceptor device attached to a conventional dialysis machine, such as in the embodiment shown in FIG. 9A-C, for example. With these features, when the dialysis machine stops, the interceptor will then stop, as the negative pulling pressure by PP2 without arterial blood supply by PP1 can result in hemolysis. For example, as shown in FIG. 10, if PP1 stops or if a flow sensor at the arterial blood line (FS) does not sense any flow, then the interceptor can trigger a stop of PP2. The system may also be configured such that, if PP1 stops, a pinch valve located downstream or at the outlet of the venous drip chamber containing the cellular portion and treated plasma (pinch valve Cl located downstream of DCV in FIG. 9A-C) automatically closes. In addition, the system may contain a pinch valve downstream or at the outlet of the filtrate drip chamber (pinch valve C2 located downstream of DCF in FIG. 9A-C); this pinch valve may be configured to receive signals from FS, PP2, PF, HD, and when the interceptor is turned on and off. C2 may be configured to close under circumstances such as: if the interceptor pump PP2 stops; the hemoglobin detector (HD) detects a blood leak; LD3 detects a low fluid level in the filtrate drip chamber; and FS detects no flow (due to, for example, a stop of PP1).

[0143] F1G. 10B shows events that trigger a stop of the interceptor device. For example, in the embodiment depicted in F1G. 9A-C, clogging of the UC filter may increase the pressure detected at PF and/or result in a low level of fluid in the DCF. ln such a circumstance, the increase in pressure detected at PF and/or the low fluid level detected by LD3 can trigger a stop of the interceptor device, e.g., by turning off PP2 or closing Cl .

[0144] Other than in the examples herein, or unless otherwise expressly specified, all of the numerical ranges, amounts, values, ratios, and percentages, may be read as if prefaced by the word“about” even though the term“about” may not expressly appear with the value, amount, range, ratio, etc. In addition, when numerical ranges are set forth herein (even when prefaced with the word“within”), these ranges are inclusive of the recited range end points ( i.e ., end points may be used). Furthermore, any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of“1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10. The terms“one,”“a,” or“an” as used herein are intended to include“at least one” or“one or more,” unless otherwise indicated.

[0145] While this invention has been particularly shown and described with references to preferred embodiments thereof, in light of the present disclosure it will be understood by persons skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.