High cut-off hemodialysis membrane for use in liver dialysis

Abstract

A system for liver dialysis makes use of a high cut-off hemodialysis membrane for removing water-soluble and protein-bound toxins from the blood of a person in need. A high cut-off hollow fiber hemodialysis membrane has improved potential to remove albumin-bound toxins and inflammatory mediators.

Claims

1. A method for treatment of liver failure, the method comprising: passing blood of a patient with liver failure into a dialysis device comprising a dialysis membrane that allows the passage of molecules having a molecular weight of up to 45 kDa with a sieving coefficient of about 0.1 to about 1.0 in the presence of whole blood, wherein the dialysis membrane has a sieving coefficient in plasma for albumin of from about 0.1 to about 0.2, and wherein the dialysis membrane has a sieving coefficient in plasma for myoglobin of from about 0.85 to about 1.0, wherein the dialysis device comprises a dialysis side and a dialysate side, and wherein dialysate on the dialysis side of the dialysis device is an albumin solution comprising human serum albumin at a concentration of from about 5% to about 12% by weight; recycling the albumin solution by passing it through a low-flux dialyzer opposite of an aqueous buffered solution for the removal of water-soluble substances from the albumin solution; passing the recycled albumin solution into the dialysate side of the dialysis device; and returning the blood from the dialysis device to the patient.

2. The method for treatment of claim 1, wherein the method reduces concentration of protein-bound toxins and inflammatory cytokines in blood of the patient.

3. The method for treatment of claim 1, wherein the method reduces concentration of unconjugated bilirubin and bile acids in blood of the patient.

4. The method for treatment of claim 3, wherein the reduction in concentration of unconjugated bilirubin is a reduction of about 47% after 6 hours of treatment.

5. The method for treatment of claim 3, wherein the reduction in concentration of unconjugated bilirubin is about a 40% improvement in reduction of unconjugated bilirubin compared to a dialysis device comprising a high flux dialysis membrane.

6. The method for treatment of claim 1, wherein at least one hydrophilic polymer and at least one hydrophobic polymer are present as domains on the surface of the dialysis membrane.

7. The method for treatment of claim 1, wherein the dialysis membrane is a hollow fiber membrane and has at least a 3-layer asymmetric structure, wherein the at least 3-layer asymmetric structure comprises an innermost layer, and wherein the innermost layer comprises a separation.

8. The method for treatment of claim 7, wherein the dialysis membrane has pores in the separation layer, said pores having a diameter in the range of about 15 to about 60 nm.

9. The method for treatment of claim 7, wherein the dialysis membrane has pores in the separation layer, said pores having a diameter in the range of about 20 to about 40 nm.

10. The method for treatment of claim 1, wherein the step of recycling the albumin solution further comprises passing it through an activated carbon adsorber, a filter for removing carbon particles, and an anion exchanger.

11. The method for treatment of claim 1, wherein dialysate on the dialysis side of the dialysis device is an albumin solution comprising human serum albumin at a concentration of about 5% by weight.

12. The method for treatment of claim 1, wherein dialysate on the dialysis side of the dialysis device is an albumin solution comprising human serum albumin at a concentration of about 10% by weight.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the setup of a liver support system according to the invention. The patient's (1) blood is passed into a hollow fiber membrane dialyzer (3b). The dialysate side of the dialyzer (3a) provides for a dialysate solution comprising clean human albumin. Water-soluble and protein bound toxins in the blood are transported through the membrane and into the dialysate albumin solution on the other side (8). The cleansed blood returns to the patient. This part of the system (9) can be referred to as the “blood circuit”. The albumin solution carrying the toxins is recycled by passing first through a low-flux dialyzer (4) opposite of a buffered aqueous solution (the “dialysate circuit” (11)). The albumin then passes through an activated carbon adsorber (5) and, after passing a filter which removes carbon particles (6), passes through an anion exchanger (7) that removes toxins bound to albumin. This part of the system may be referred to as the “albumin circuit” (10). The recycled albumin can then again enter the dialyzer (3). The dialysis machine used within the system is displayed as (2). Circles (∘) denote where test samples for analysis are taken.

(2) FIG. 2 shows the sieving coefficients of a high-flux dialysis membrane and a High Cut-off dialysis membrane. The sieving coefficients shown have been derived from clinical studies. Dialysis has been performed according to the method described in Morgera et al. (2003): Intermittent high permeability haemofiltration in septic patients with acute renal failure. Intensive Care Med. 29, 1989-1995. The HCO 1100® dialyzer (Gambro Lundia AB) serves as an example for a High Cut-Off dialysis membrane. The conventional high-flux dialyzer used is Polyflux® 170H (Gambro Lundia AB).

(3) FIG. 3 shows the development of the HSA concentration within the blood circuit as determined at B.sub.in during the testing. Tests 54 and 56 were run with a HSA concentration of 5% (50 g/l). Tests 53 and 55 were run with a HSA concentration of 10% (100 g/l).

(4) FIG. 4 shows the development of the HSA concentration in the albumin circuit. Tests 54 and 56 were run with a HSA concentration of 5% (50 g/l). Tests 53 and 55 were run with a HSA concentration of 10% (100 g/l).

(5) FIG. 5 A depicts the development of the bilirubin concentration in the blood circuit with a HSA concentration in the albumin circuit of 10% at 0 min. FIG. 5 B depicts the development of the bilirubin concentration in the blood circuit with a HSA concentration in the albumin circuit of 5% at 0 min.

(6) FIG. 6 A depicts the development of the bile acid concentration in the blood circuit with a HSA concentration in the albumin circuit of 10% at 0 min. FIG. 6 B depicts the development of the bile acid concentration in the blood circuit with a HSA concentration in the albumin circuit of 5% at 0 min.

(7) FIG. 7 depicts the development of the concentration of unconjugated bilirubin in the blood circuit in a liver dialysis system using a High Cut-off (HCO) membrane (P5SH) according to the invention and in a liver dialysis system using a conventional MARS®Flux high-flux filter. Samples were obtained from the blood circuit, B.sub.in.

(8) FIG. 8 shows the development of the concentration of bile acid in the blood circuit over 6 hours in a liver dialysis system using a High Cut-off membrane (P5SH) and in a liver dialysis system using a conventional MARS®Flux high-flux filter. Samples were taken at B.sub.in.

DETAILED DESCRIPTION

(9) Liver dialysis according to the invention is preferably carried out using a dialyzer comprising a High Cut-off dialysis membrane (3) which allows passage of molecules having a molecular weight of up to 45 kDa in the presence of whole blood and have a molecular weight exclusion limit in water of about 200 kDa. As can be seen from FIG. 2, the High Cut-off dialysis membrane allows the limited passage, in whole blood, of molecules up to 70 kD, including albumin with a molecular weight of 68 kD. The molecular weight cut-off (MWCO) of the High Cut-off dialysis membrane is higher than the MWCO of the conventional high-flux membrane (FIG. 2), which generally lies in the range of 15 to 20 kDa. FIG. 2 demonstrates that the high-flux membrane as used allows the passage of molecules up to 25 kD only.

(10) Liver dialysis according to the invention is carried out (FIG. 1) by passing the patient's (1) blood into the High Cut-off membrane dialyzer (3). The dialysate side of the dialyzer (3a) provides for clean human serum albumin (HSA) that acts as a dialysate. The concentration of the HSA may vary. In general, it may be in the range of 1% to 25% by weight. A range of 2% to 20% by weight of HSA is preferable. A range of 5% to 20% by weight of HSA is used with special preference. Liver dialysis systems like the MARS® system are preferably run with a HSA concentration of 10%-25%. HSA concentration may lie in the range of from 5% to 12%, however, if a system according to the invention is used. Systems like SPAD are preferably run with a HSA concentration of 2%-5%. The HSA solution may further contain a physiological amount of NaCl, e.g. 0.9% NaCl. Water-soluble and protein bound toxins in the blood (3b) are transported through the membrane and into the dialysate albumin solution on the other side (3a), which marks the passage into the albumin circuit (10). The cleansed blood returns to the patient.

(11) The albumin solution in the HSA circuit carrying the toxins is recycled by passing first through a standard low-flux dialyzer (4) opposite of a buffered aqueous solution in order to remove water-soluble substances from the albumin. An example for such low-flux dialyzer is the diaFLUX 1.8 dialyzer used in the MARS® system.

(12) Afterwards, the albumin passes through an activated carbon adsorber (5). For example, the MARS® system uses vapor-activated carbon, which is used to clean the HSA dialysate in the HSA circuit (diaMARS® AC250). The carbon is especially suited for removing low-molecular, non-polar compounds. After passing a filter for removing carbon particles (6), the HSA dialysate passes through an anion exchanger (7) that especially removes anionic molecules, such as bilirubin (diaMARS® IE250). Inflammatory molecules such as cytokines are also removed in the HSA circuit and will not re-enter the blood circuit. The recycled albumin then re-enters the dialyzer (3) and binds again to toxins which can thus be removed from the patient's blood.

(13) Flow rates used in the liver dialysis system may vary. It is advantageous to use flow rates with a Q.sub.B (blood flow) of 100-500 ml/min, preferably 150-250 ml/min, a Q.sub.Alb (flow in the albumin circuit) of 100-500 ml/min, preferably 150-250 ml/min and a Q.sub.D (dialysate circuit) of 10-1000 ml/min, preferably 50-500 ml/min.

(14) Typically, the High Cut-off membranes according to the invention have a water permeability of >40 ml/h per mmHg/m.sup.2 in vitro. They may have a β.sub.2-microglobulin clearance of at least 80 ml/min for conventional hemodialysis with a blood flow rate of 300 to 400 ml/min. Albumin loss is preferably 0.5 to 2 g, in particular 1.0 to 1.5 g per hour of dialysis. The sieving coefficient may be 0.9 to 1.0 for β.sub.2-microglobulin and 0.01 to 0.1, preferably 0.03 to 0.07, for albumin, when measured according to EN 1283. Measured in the presence of whole blood, the sieving coefficient is preferably smaller than 0.05, in particular smaller than 0.01 (see Table I).

(15) TABLE-US-00001 TABLE I Sieving Coefficients for a conventional high-flux dialysis membrane, Polyflux ® 170H (Gambro Lundia AB), and a High Cut-Off dialysis membrane, HCO 1100 ®(Gambro Lundia AB). The Sieving Coefficients in plasma have been determined according to DIN EN1283 (maximum blood flow, 20% of blood flow UF. HCO1100: QB = 400 mL/min; UF = 80 mL/min. P170H: QB = 500 mL/min; UF = 100 mL/min. For the Sieving Coefficients in aqueous solution the following flow rates were used: HCO1100: QB = 228 mL/min, UF = 46 mL/min. P170H: QB = 234 mL/min, UF = 67 mL/min. Sieving coefficients (%) Filter type Plasma Aqueous Validation Validation/Others P170H Vitamin B12 100 n.d. Inulin 100 n.d. beta2M 75 n.d. Myoglobin 25 70 Albumin <1  8 HCO 1100 Vitamin B12 100 n.d. Inulin 100 n.d. beta2M n.d. n.d. Myoglobin 95 97-98 Albumin 10 46-53

(16) More preferably, the membrane is a permselective membrane of the type disclosed in WO 2004/056460. Such membranes preferably allow passage of molecules having a molecular weight of up to 45 kDa in the presence of whole blood and have a molecular weight exclusion limit in water of about 200 kDa. In one embodiment of the invention, the membrane takes the form of a permselective asymmetric hollow fiber membrane. It preferably comprises at least one hydrophobic polymer and at least one hydrophilic polymer. Preferably the polymers are present as domains on the surface.

(17) In one embodiment, the membrane is free light chain (FLC) leaking. That is, the κ or λ free light chains pass through the membrane. High flux membranes, with smaller pore sizes, have been observed to remove some free light chains. However, this appears to be primarily due to binding of the FLC onto the dialysis membranes. FLC may be used as markers of middle molecular weight proteins. Although clearing of free light chains is not a primary target of the invention, their reduction can be used as an indicator of membrane functionality.

(18) According to one aspect of the invention, a High Cut-off dialysis membrane that allows the passage of molecules having a molecular weight of up to 45 kDa with a sieving coefficient of 0.1 to 1.0 in the presence of whole blood, and with a molecular weight exclusion limit in water of 200 kDa is provided for treating conditions of liver failure. The treatment preferably consists in the elimination of protein-bound toxins from the patient's blood wherein the dialysate contains human serum albumin (HSA).

(19) Preferably, the treatment is directed to removing albumin bound toxins and inflammatory mediators, especially cytokines, from the blood of patients suffering from liver failure.

(20) The treatment preferably results in a reduced blood level of protein-bound toxins and inflammatory mediators.

(21) According to another aspect of the invention, a liver dialysis device, especially to support the liver function during conditions of liver failure, is provided, which device comprises a dialysis membrane, in the blood circuit, that allows the passage of molecules having a molecular weight of up to 45 kDa with a sieving coefficient of 0.1 to 1.0 in the presence of whole blood, and with a molecular weight exclusion limit in water of about 200 kDa. It is provided, in a further aspect of the invention, a liver dialysis system wherein the dialysis membrane has a sieving coefficient for albumin, in plasma, of from 0.1 to 0.2 and a sieving coefficient for myoglobin, in plasma, of from 0.85 to 1.0.

(22) It is provided, in a further aspect of the invention, a liver dialysis system wherein the dialysis membrane has a clearance (ml/min) for κ-FLC of from 35 to 40, and for λ-FLC of from 30 to 35. Clearance is determined in vitro (±20%) with Q.sub.B=250 ml/min, Q.sub.D=500 ml/min, U.sub.F=0 ml/min in bovine plasma having a protein level of 60 g/l at 37° C. The plasma level is for human κ=500 mg/l and human λ=250 mg/l.

(23) According to yet another aspect of the invention, a liver device especially to support the liver function during conditions of liver failure, is provided, which device comprises a dialysis membrane, in the blood circuit, that allows the passage of molecules having a molecular weight of up to 45 kDa with a sieving coefficient of 0.1 to 1.0 in the presence of whole blood, and with a molecular weight exclusion limit in water of about 200 kDa, wherein the dialysate comprises HSA in the range of from 1% by weight to 25% by weight. Preferably, HSA concentration lies in the range of from 2% by weight to 20% by weight.

(24) Preferably, a dialysis membrane of the invention comprises at least one hydrophilic polymer and at least one hydrophobic polymer. In one embodiment, at least one hydrophilic polymer and at least one hydrophobic polymer are present in the dialysis membrane as domains on the surface of the dialysis membrane.

(25) The hydrophobic polymer may be chosen from the group consisting of polyarylethersulfone (PAES), polypropylene (PP), polysulfone (PSU), polymethylmethacrylate (PMMA), polycarbonate (PC), polyacrylonitrile (PAN), polyamide (PA), or polytetrafluorethylene (PTFE).

(26) The hydrophilic polymer may be chosen from the group consisting of polyvinylpyrrolidone (PVP), polyethyleneglycol (PEG), polyvinylalcohol (PVA), and copolymer of polypropyl-eneoxide and polyethyleneoxide (PPO-PEO).

(27) In one embodiment, the dialysis membrane is a hollow fiber having at least a 3-layer asymmetric structure with a separation layer present in the innermost layer of the hollow fiber. Preferably the separation layer has a thickness of lees than 0.5 μm. Preferably, the separation layer contains pore channels having a pore size of 15 to 60 nm, more preferably 20 to 40 nm.

(28) The next layer in the hollow fiber membrane is the second layer, having the form of a sponge structure and serving as a support for said first layer. In a preferred embodiment, the second layer has a thickness of about 1 to 15 μm.

(29) The third layer has the form of a finger structure. Like a framework, it provides mechanical stability on the one hand; on the other hand a very low resistance to the transport of molecules through the membrane, due to the high volume of voids. During the transport process, the voids are filled with water and the water gives a lower resistance against diffusion and convection than a matrix with a sponge-filled structure having a lower void volume. Accordingly, the third layer provides mechanical stability to the membrane and, in a preferred embodiment, has a thickness of 20 to 60 μm.

(30) In one embodiment, the membrane also includes a fourth layer, which is the outer surface of the hollow fiber membrane. In this preferred embodiment, the outer surface has openings of pores in the range of 0.5 to 3 μm and the number of said pores is in the range of from 10,000 to 150,000 pores/mm.sup.2, preferably 20000 to 100000 pores/mm.sup.2. This fourth layer preferably has a thickness of 1 to 10 μm.

(31) The manufacturing of the membrane of the present invention follows a phase inversion process, wherein a polymer or a mixture of polymers is dissolved in a solvent to form a polymer solution. The solution is degassed and filtered and is thereafter kept at an elevated temperature.

(32) Subsequently, the polymer solution is extruded through a spinning nozzle (for hollow fibers) or a slit nozzle (for a flat film) into a fluid bath containing a non-solvent for the polymer. The non-solvent replaces the solvent and thus the polymer is precipitated to an inverted solid phase.

(33) To prepare a hollow fiber membrane, the polymer solution preferably is extruded through an outer ring slit of a nozzle having two concentric openings. Simultaneously, a center fluid is extruded through an inner opening of the nozzle. At the outlet of the spinning nozzle, the center fluid comes in contact with the polymer solution and at this time the precipitation is initialized. The precipitation process is an exchange of the solvent from the polymer solution with the non-solvent of the center fluid.

(34) By means of this exchange the polymer solution inverses its phase from the fluid into a solid phase. In the solid phase the pore structure, i.e. asymmetry and the pore size distribution, is generated by the kinetics of the solvent/non-solvent exchange. The process works at a certain temperature which influences the viscosity of the polymer solution. The temperature at the spinning nozzle and the temperature of the polymer solution and center fluid is 30 to 80° C. The viscosity determines the kinetics of the pore-forming process through the exchange of solvent with non-solvent. Subsequently, the membrane is preferably washed and dried.

(35) By the selection of precipitation conditions, e.g. temperature and speed, the hydrophobic and hydrophilic polymers are “frozen” in such a way that a certain amount of hydrophilic end groups are located at the surface of the pores and create hydrophilic domains. The hydrophobic polymer builds other domains. A certain amount of hydrophilic domains at the pore surface area are needed to avoid adsorption of proteins. The size of the hydrophilic domains should preferably be within the range of 20 to 50 nm. In order to repel albumin from the membrane surface, the hydrophilic domains also need to be within a certain distance from each other. By the repulsion of albumin from the membrane surface, direct contact of albumin with the hydrophobic polymer, and consequently the adsorption of albumin, are avoided.

(36) The polymer solution used for preparing the membrane preferably comprises 10 to 20 wt.-% of hydrophobic polymer and 2 to 11 wt.-% of hydrophilic polymer. The center fluid generally comprises 45 to 60 wt.-% of precipitation medium, chosen from water, glycerol and other alcohols, and 40 to 55 wt.-% of solvent. In other words, the center fluid does not comprise any hydrophilic polymer.

(37) In a preferred embodiment, the polymer solution coming out through the outer slit openings is, on the outside of the precipitating fiber, exposed to a humid steam/air mixture. Preferably, the humid steam/air mixture has a temperature of at least 15° C., more preferably at least 30° C., and not more than 75° C., more preferably not more than 60° C.

(38) Preferably, the relative humidity in the humid steam/air mixture is between 60 and 100%. Furthermore, the humid steam in the outer atmosphere surrounding the polymer solution emerging through the outer slit openings preferably includes a solvent. The solvent content in the humid steam/air mixture is preferably between 0.5 and 5 wt.-%, related to the water content. The effect of the solvent in the temperature-controlled steam atmosphere is to control the speed of precipitation of the fibers. When less solvent is employed, the outer surface will obtain a denser surface, and when more solvent is used, the outer surface will have a more open structure. By controlling the amount of solvent within the temperature-controlled steam atmosphere surrounding the precipitating membrane, the amount and size of the pores on the outer surface of the membrane are controlled, i.e. the size of the openings of the pores is in the range of from 0.5 to 3 μm and the number of said pores is in the range of from 10,000 to 150,000 pores/mm.sup.2, preferably 20,000 to 100,000 pores/mm.sup.2. The fourth layer of the membrane is preferably prepared by this method.

(39) Before the extrusion, suitable additives may be added to the polymer solution. The additives are used to form a proper pore structure and optimize the membrane permeability, the hydraulic and diffusive permeability, and the sieving properties. In a preferred embodiment, the polymer solution contains 0.5 to 7.5 wt.-% of a suitable additive, preferably chosen from the group comprising water, glycerol and other alcohols.

(40) The solvent may be chosen from the group comprising n-methylpyrrolidone (NMP), dimethyl acetamide (DMAC), dimethyl sulfoxide (DMSO) dimethyl formamide (DMF), butyrolactone and mixtures of said solvents.

(41) In one embodiment of the invention, the sieving coefficient of the High Cut-off dialysis membrane for IL-6 in the presence of whole blood is 0.9 to 1.0 and the sieving coefficient for albumin in the presence of whole blood is less than 0.1. In yet another embodiment, said sieving coefficient for albumin is less than 0.05.

(42) As used herein, the term “sieving coefficient (S)” refers to the physical property of a membrane to exclude or pass molecules of a specific molecular weight. The sieving coefficient can be determined according to standard EN 1283, 1996.

(43) Put simply, the sieving coefficient of a membrane is determined by pumping a protein solution (bovine or human plasma) under defined conditions (QB, TMP and filtration rate) through a membrane bundle and determining the concentration of the protein in the feed, in the retentate and in the filtrate. If the concentration of the protein in the filtrate is zero, a sieving coefficient of 0% is obtained. If the concentration of the protein in the filtrate equals the concentration of the protein in the feed and the retentate, a sieving coefficient of 100% is obtained.

(44) The sieving coefficient, S, is calculated according to S=(2C.sub.F)/(C.sub.Bin+C.sub.Bout), where C.sub.F is the concentration of a solute in the filtrate; C.sub.Bin is the concentration of a solute at the blood inlet side of the device under test; and C.sub.Bout is the concentration of a solute at the blood outlet side of the device under test.

(45) Furthermore, the sieving coefficient allows determining the nominal cut-off of a membrane (corresponding to a sieving coefficient of 0.1). As used herein the term “cut-off” refers to the molecular weight of a substance having a sieving coefficient (S) of 0.1.

(46) The membrane of the present invention allows the passage of molecules having molecular weights up to 45 kDa in the presence of whole blood/blood proteins, which means that it has a sieving coefficient (S) of 0.1 to 1.0 in presence of whole blood for substances having a molecular weight of less than 45 kDa.

(47) Methods for producing suitable membranes are disclosed, for example, in WO 2004/056460, incorporated herein by reference. An example of a suitable membrane is available from Gambro under the trade name “HCO 1100®”. The HCO 1100® dialyzer comprises a steam sterilized membrane based on polyethersulfone and polyvinylpyrrolidone with a wall thickness of 50 μm and an inner diameter of 215 μm. The in vivo albumin loss (HD) of the HCO 1100® at Q.sub.D=500 ml/min is 1.5 g per hour of dialysis.

(48) If no other meaning for this expression is indicated, the term “High Cut-off membrane” or “High Cut-off dialysis membrane” as used herein is used to describe a membrane according to the invention, i.e. a membrane which allows passage of molecules having a molecular weight of up to 45 kDa with a sieving coefficient of 0.1 to 1.0 in the presence of whole blood. Specific embodiments of such High Cut-off dialysis membranes in addition may have a molecular weight exclusion limit in water of about 200 kDa with a sieving coefficient of 0.1 to 1.0 The sieving coefficient in water-can be determined according to Leypoldt et al., Trans Am Soc Artif Intern Organs. 1983; 29:678-83. The membrane is otherwise characterized by sieving coefficients as indicated in FIG. 2.

(49) The term “liver failure” in the context of the present invention refers to the inability of the liver to perform its normal synthetic and metabolic function as part of normal physiology. Liver failure thus leads to an insufficient detoxification of albumin, which is followed by an exhaustion of the binding capacity of the albumin and an enrichment of the otherwise albumin-bound toxins, e.g. of unconjugated bilirubin. Treatment is indicated, for example, at a bilirubin concentration of >10 mg/dL. However, there are liver disorders where a liver dialysis treatment is indicated, but which is not characterized by increased bilirubin levels. Disorders which are associated with the expression “liver failure” as used in the present invention include, but are not limited to, hepatorenal syndrome, decompensated chronic liver disease, acute liver failure, graft dysfunction after liver transplantation, liver failure after liver surgery, secondary liver failure, multi organ failure or intractable pruritus in cholestasis.

(50) It will be readily apparent to one skilled in the art that various substitutions and modifications may be made to the invention disclosed herein without departing from the scope and spirit of the invention.

(51) The present invention will now be illustrated by way of non-limiting examples of preferred embodiments in order to further facilitate the understanding of the invention.

EXAMPLES

Example 1

HSA Concentration in the System

(52) It was the goal of the present experiment to monitor the development of the HSA concentration within the liver support system. The development of the HSA concentration is of interest, as the High Cut-off dialysis membrane allows, to a certain extent, the passage of albumin (see also Table 1). For this test a standard MARS system with an AK95/MARS Monitor were used, in combination with a 2.1 m.sup.2 High Cut-off dialysis membrane, hereinafter referred to as P5SH (FIG. 1 (3)). The P5SH dialyzer is equivalent to the HCO 1100® dialyzer, with the exception of the membrane area which is smaller in the HCO 1100® version. The P5SH filter was used to have a membrane area which is equivalent to the conventional MARSFlux® filter membrane area. Further, a diaFlux 1.4 filter (FIG. 1 (4)) was used. The activated carbon adsorber was AC 250 AE, the anion exchanger was IE 250. Unconjugated bilirubin was from Sigma (EC 211-239-7). Bile acid (chenodeoxycholic acid) was from Sigma (Lot 094K075). 20% human serum albumin was from Baxter (Lot VNA1F007). The plasma (FIG. 1 (1)) used was Octaplas® SD virally inactivated human plasma from Octapharma (Lot 548 209 950). The blood circuit (re-circulating) of the test system contained 3 l plasma, unconjugated bilirubin (100 mg/l) and chenodesoxycholic acid (100 mg/l). The albumin concentration was set to be 35 g/l. The temperature was adjusted to 37° C. The albumin circuit contained 5% or 10% human serum albumin in 0.9% NaCl solution, respectively. The dialysate circuit comprised dialysis concentrate only (138 mmol Na.sup.+; 1.0 mmol K.sup.+; 0.25 mmol Mg.sup.++; 1.25 mmol Ca.sup.++; 107 mmol Cl.sup.−; 3.0 mmol acetat; 32.0 mmol HCO.sup.3−) and a BiCart® cartridge containing sodium bicarbonate. Test samples for albumin analysis were taken at B.sub.in and Alb.sub.1. Test samples for the analysis of unconjugated bilirubin and chenodesoxycholic acid were taken at B.sub.in, B.sub.out, Alb.sub.1, Alb.sub.1.1, Alb.sub.2 and Alb.sub.3 after 0, 10, 20, 30, 40, 60, 80, 100, 120, 180, 240, 300 and 360 minutes. Treatment parameters in the test were Q.sub.B: 175 ml/min; Q.sub.Alb: 175 ml/min; Q.sub.D: 500 ml/min; UF: 0 ml/min. Treatment time was 6 hours. Analysis of clearance rates for bile acids, diazepam, ammonium and creatinin is done according to the following formula:

(53) $K=\ln \frac{C_0}{C_t}*\frac{V_{\mathrm{Pool}}}{t}$

(54) For determining the clearance rates for bilirubin, the following formula is used:

(55) $K=\frac{\left(C_0-C_t\right)*V_{\mathrm{Pool}}}{t*C_0}$

(56) Additionally, the reduction rate is determined according to the following formula:
RR=cBin.sub.0 min[%]−cBin.sub.360 min[%].

(57) FIG. 3 shows the development of the HSA concentration as determined at B.sub.in during the testing, i.e. within the blood circuit. Tests 54 and 56 were run with a HSA concentration of 5% (50 g/l). Tests 53 and 55 were run with a HSA concentration of 10% (100 g/l).

(58) As can be seen, albumin can pass the membrane of the HCO 1100® dialyzer. Therefore, the concentration of albumin in the blood circuit, which was 35 g/l at the beginning, slowly increases over time as the albumin concentration in the albumin and blood circuit move in the direction of equilibrium. The HSA concentration of the blood circuit finally reaches 40 and 49 g/l, respectively.

(59) FIG. 4 shows the development of the HSA concentration in the albumin circuit in the same tests 53, 54, 55 and 56. As expected with regard to the blood circuit results, the albumin concentration in the albumin circuit which started from 50 g/l or 100 g/l, respectively, decreases as albumin passes the membrane of the dialyzer (3) into the blood circuit where the concentration is lower. After 360 minutes the albumin concentration reaches 41 g/l and 52 g/l, respectively. Tests 53 and 55 (100 g/l albumin in the albumin circuit) result in an albumin concentration of 49 g/l in the blood circuit and 54 g/l in the albumin circuit after 6 h. Tests 54 and 56 (50 g/l albumin in the albumin circuit) result in an albumin concentration of 40 g/l in the blood circuit and 42 g/l in the albumin circuit after 6 h.

Example 2

Bilirubin Reduction

(60) Tests were done as described in Example 1. The albumin concentration was again 5% and 10%. The concentration of unconjugated bilirubin was determined in samples taken at B.sub.in. FIG. 5 A depicts the development of the bilirubin concentration in the blood circuit when the HSA concentration in the albumin circuit is 10% at 0 min. FIG. 5 B depicts the development of the bilirubin concentration in the blood circuit when the HSA concentration in the albumin circuit is 5% at 0 min. As can be seen, the bilirubin concentration decreases in both system settings. The reduction rate is about 47% in both cases.

Example 3

Bile Acid Reduction

(61) Tests were done as described in Example 1. The albumin concentration was again 5% and 10%. The concentration of bile acid was determined in samples taken at B.sub.in. FIG. 6 A depicts the development of the bile acid concentration in the blood circuit when the HSA concentration in the albumin circuit is 10% at 0 min. FIG. 6 B depicts the development of the bile acid concentration in the blood circuit when the HSA concentration in the albumin circuit is 5% at 0 min. As can be seen, the bile acid concentration decreases in both system settings. The reduction rate is about 83% at a HSA concentration of 10% and 87% at a HSA concentration of 5%.

Example 4

Comparison Between Conventional High-Flux and High Cut-Off Dialysis Membrane: Removal of Unconjugated Bilirubin and of Bile Acids

(62) Tests were performed as described in Example 1 to 3. However, a conventional MarsFlux 2.1 filter was used instead of the P5SH dialyzer. The results were compared with the results obtained with the P5SH dialyzer according to the above Examples.

(63) FIG. 7 depicts the development of the concentration of unconjugated bilirubin over 360 minutes in a liver dialysis system using the P5SH dialyzer and in a liver dialysis system using a conventional MARSFlux filter. Samples were taken from the blood circuit, B.sub.in. Two tests which were run with the MARSFlux filter resulted in a reduction of unconjugated bilirubin of 6%. Two analogous tests with the P5SH dialyzer resulted in a seven-fold better reduction rate of 46%.

(64) FIG. 8 shows the development of the concentration of bile acid in the blood circuit over 6 hours in a liver dialysis system using the P5SH dialyzer and in a liver dialysis system using a conventional MARSFlux filter. Samples were taken at B.sub.in. Two tests were run with each of the filters. Results show that the MARSFlux filter achieves a reduction rate for bile acids of 87%. The P5SH dialyzer achieves a reduction rate of 83%, which means that there is no improvement with regard to the removal of bile acids. However, the reduction rate is not worse than what can be achieved with the conventional filter. During the first 80 minutes of the treatment the P5SH dialyzer shows a better efficiency regarding the removal of bile acids. However, after 80 minutes the MARSFlux filter shows a somewhat better removal rate.