Search

Artificial cells contain biologically active materials. Artificial cells containing adsorbents have been a routine form of treatment in hemoperfusion for patients. This includes acute poisoning, high blood aluminum and iron, and supplement to dialysis in kidney failure. Artificial cells are being tested for use as red blood cell substitutes. Artificial cells encapsulated cell culture are being tested in animals for the treatment of diabetes and liver failure. A novel 2 step method has prevented xenograft rejection. Artificial cells containing enzymes are being studied for treatment in hereditary enzyme deficiency diseases and other diseases. Recent demonstration of extensive enterorecirculation of amino acids in the intestine has allowed its oral administration to deplete specific amino acids. Artificial cells containing complex enzyme system convert wastes like urea and ammonia into essential amino acids. Artificial cell is being used for the production of monoclonal antibodies, interferons and other biotechnological products. It is also being investigated for drug delivery, and for use in other applications in biotechnology, chemical engineering and medicine.

Artificial cells were first conceived as vehicles for adsorbents, organelles, microorganisms, enzymes, and other biological materials [1–5]. Artificial cells are being used in biotechnology and medicine [5], including artificial liver support [6]. For example, coated charcoal hemoperfusion was effective in removing sufficient toxic substances in grade IV hepatic coma to result in the temporary recovery of consciousness [7]. Other groups have supported this observation [6–8]. Randomized control studies in fulminant hepatic failure (FHF) rats showed a significant increase in survival rates if hemoperfusion was performed in the earlier grade of coma [9]. Clinical trials carried out by William’s group supported our finding [10]. We have also used biodegradable artificial cells for substained release of prostaglandin E2 in FHF rats to delay the development of cerebral edema [11–14]. Microencapsulation of hepatocyte organelles was also studied [15]. Artificial cells containing cell suspension have also been prepared [2, 3] and proposed for use for hepatocytes for artificial liver support [2, 3]. Implantation of artificial cells containing hepatocytes increased the survival time of FHF rats [16].

Repeated subcutaneous immunizing injections into rats of Freund's adjuvant containing rat hemoglobin or o-raffinose rat polyhemoglobin did not result in increase in IgG antibody liters. However, heterologous hemoglobin injected as above is antigenic (49.50 + 6.70 % CPM). Crosslinking heterologous hemoglobin into o-raffinose polyhemoglobin further increased its antigenicity (75.60 + 4.08). Thus, unlike homologous hemoglobin, cross-linking of heterologous hemoglobin increased its antigenicity. Liposome encapsulated homologous hemoglobin injected subcutaneously with or without Freund's adjuvant did not show antigenicity. Encapsulated heterologous hemoglobin resulted in a minimal increase in antibody tilers (10.73 + 4.64) only with Freund's adjuvant, but no increase when injected without Freund's adjuvant. Conjugated heterologous hemoglobin (PEG-Hb) injected intravenously by ilself at weekly inlervals did not result in significant increase in antibody tilers on the 5th week.

This study is based on an unanesthetized lethal hemorrhagic shock rat model (67% blood volume bled in 2 stages). The 8 groups studied were as follows. 1. Control--no resuscitation fluid. 2. Reinfusion of rat's own shed whole blood. 3. Ringer lactate solution--3 times shed blood volume. The following 4 fluids were each given as equal to the shed blood volume. 4. 7.5g% NaCl hypertonic saline/6% Dextran 70, followed by 3 volumes Ringer lactate dextran. 5. Ringer lactate solution. 6. Human albumin 7g% in Ringer lactate. 7. Stroma-free hemoglobin in Ringer lactate 8. o-raffinose polyhemoglobin in Ringer Lactate. Blood pressure and other vital signs were recorded continuously during the control period, bleeding periods, infusion period and 60 minutes after infusion. After this all surviving animals were followed for 14 days with no other special treatments. Group 4 had transient (10 minutes) returned of blood pressure to control levels. The 3 groups with sustained blood pressure at control level when followed for 1 hour were groups 2, 6 and 7. The 2 groups with 100% survival on days 14 were group 2 and group 7.

A multienzyme system consisting of leucine dehydrogenase (EC 1.4.1.9), L-lactic dehydrogenase (EC 1.1.1.27), urease (EC 3.5.1.5), and dextran-NAD+ was microencapsulated within artificial cells. This system could convert ammonia and urea into essential amino acids, L-leucine, L-valine, and L-isoleucine. L-lactate acted as a cosubstrate for the regeneration of dextran-NADH. Greater concentrations of L-lactate favored the higher conversion ratios. The effects of ammonium salts and urea on reaction rate were also studied. The relative reaction rates in ammonium salts solutions were 44.6-78.8% of those in urea solutions. More than 90% of the original activity was retained when artificial cells were kept at 4 degrees C for 6 wk.

We prepared artificial cells each containing leucine dehydrogenase (EC 1.4.1.9), urease (EC 3.5.1.5), soluble dextran-NAD(+), and one of the following coenzyme regenerating dehydrogenases: glucose dehydrogenase (EC 1.1.1.47); yeast alcohol dehydrogenase (EC 1.1.1.1); malate dehydrogenase (EC 1.1.1.37); or lactate dehydrogenase (EC 1.1.1.27). Artificial cells were packed in small columns. L-Leucine, L-valine, and L-isoleucine were continuously produced with simultaneous dextran-NADH regeneration. The maximum production ratios depended on the coenzyme regenerating systems used: 83-93% for D-glucose and glucose dehydrogenase system; 90% for ethanol and yeast alcohol dehydrogenase system; 45-55% for L-malate and malate dehydrogenase system; and 64-78% for L-lactate and lactate dehydrogenase system. Kinetic experiments were also carried out. The apparent K(m) values are as follows: 0.33 mM for alpha-ketoisocaproate (KIC); 0.51 mM for alpha-ketoisovalerate (KIV); 0.58 mM for DL-alpha-keto-beta-methyl-n-valerate (KMV); 3.52 mM for urea; 27.82 mM for D-glucose; 3.89 mM for ethanol; 3.02 mM for L-malate; and 16.67 mM for L-lactate. Kinetic analysis showed that KIC, KIV, and KMV were all competitive inhibitors in the reactions catalyzed by leucine dehydrogenase. Their inhibitor constants were the corresponding K(m) values.

A negative chronotropic effect of bovine stroma-free hemoglobin was identified in spontaneously contracting myocardiocytes derived from neonatal rats. This model allowed for the evaluation of direct effects of hemoglobin solutions without the influence of hemodynamic reflexes. Significant slowing of myocardiocyte beating rates were observed from 0.8 to 11.6 g.dl-1 stroma-free hemoglobin solution. Polymerization of hemoglobin into soluble crosslinked polyhemoglobin markedly reduced its negative chronotrophic effects by more than 50% at most concentrations assayed. Chronotropic potency (% change in beating rate from baseline per g.dl-1 was significantly higher for stroma-free hemoglobin when compared to polyhemoglobin and albumin solutions. Colloid osmotic potency (% change in beating rate from baseline per mmHg) however, was similar for stroma-free hemoglobin and polyhemoglobin but significantly lower for albumin solutions. This negative chronotropic effect may in part contribute to the transient bradycardia observed following hemoglobin infusion.

In 1965, the use of artificial cells for the microencapsulation of living cells was demonstrated. At that time, this technique was also proposed for use in immunoisolation of endocrine cells, islets, and hepatocytes as hybrid artificial organs. Progress in the biotechnology of cell culture in the last 10 years has allowed this approach to be extensively investigated by an increasing number of centers. The author's recent studies concentrated on microencapsulation of hepatocytes as a model system. Such cells were implanted to increase the survival of galactosamine induced fulminant hepatic failure rats, or to decrease the high bilirubin levels in Gunn rats and xenografts of microencapsulated rat hepatocytes into mice provided immunoisolation. Furthermore, hepatocyte secreted hepatic stimulating factors (mw 110,000 D) accumulating in the microcapsules helps to increase the viability of the hepatocytes. In addition to these studies, a novel, two step cell encapsulation method was developed to improve immunoisolation and biocompatibility. Microencapsulation of microorganisms was also carried out using a model microorganism to convert serum cholesterol to carbon dioxide.

The objective of this experiment was to determine the flow characteristics of a hemoperfusion device. The standard device consists of a cylindrical container which is tapered towards the outlet end. Flow enters the column through a small inlet tube into the wide frontal area of the column. Having passed through the column containing collodian coated activated charcoal spheres, it leaves by the tapered outlet. In order to achieve our aim, we designed and built a two-dimensional plexiglass model consisting of a vertical cross section of the actual hemoperfusion device. Glass beads were used to simulate the artifi-cal carbon cells and a colored solution was used to enable us to visualize the flow. In the normal configuration, it was determined that stagnation and channelling were present. The model was then analysed in the inverse configuration. This way, flow inlet is through the tapered end and flow outlet is towards the wider cylindrical end. This inverse flow configuration improved the flow characteristics and eliminated most of the channelling and stagnation.

Semipermeable aqueous collodion microcapsules were prepared containing both yeast alcohol dehydrogenase (EC 1.1.1.1) and malic dehydrogenase (EC 1.1.1.37). These microcapsules exhibited both enzymic activities in good amount in the ratio 3:1 with respect to malic dehydrogenase:alcohol dehydrogenase. Both NAD+ and NADH were successfully cycled within the microcapsules by employing the included enzyme activities acting sequentially. A soluble, immobilized NAD+ derivative was also recycled within the semipermeable microcapsules.

Galactosamine-induced fulminant hepatic failure rats were used for in vivo studies of the removal of tyrosine and total free phenol by means of hemoperfusion over immobilized tyrosinase within artificial cells. The elevated plasma tyrosine level was decreased to about half the value after one hour of hemoperfusion. The studies of tyrosine clearance suggest that it is efficient and remains constant throughout the one-hour hemoperfusion. In those galactosamine-induced fulminant hepatic failure rats with increased total free phenol levels hemoperfusion over tyrosinase artificial cells significantly lowered the level.

Lactic acid was polymerized using tetraphenyl tin as a catalyst. The molecular weight of the resultant poly(lactic acid) varied between 0.89 X 10(6) and 2.94 X 10(6) depending upon the concentration of the catalyst used. In-vivo degradation of the poly(lactic acid) samples having 4 different molecular weights were studies by implanting these in Wistar rats. It was found that at the end of a 48-week implantation period lower molecular weight poly(lactic acid) samples were degraded at a faster rate than the higher molecular weight samples.

Albumin-collodion coated activated charcoal was found to effectively remove mercaptan in aqueous solution or in «plasma» solution. An initial clearance of 150 ml/min at a flow rate of 200 ml/min could be obtained. The roles of middle molecules, loosely protein-bound molecules, phenols, mercaptan and other molecules were discussed.

Rat liver microsomes and cytosol have been co-immobilized by microencapsulation into artificial cells. The immobilized enzyme retained good enzyme activity. Enzyme kinetics, storage stability, pH profiles and temperature profiles have been analyzed.

Five hemodialysis patients were treated with combined hemodialysis-hemoperfusion with their conventional hemodialyzer plus a 70-gram ultrathin collodion coated activated charcoal device for a total of 63 months. Indications for this therapy included pericarditis, peripheral neuropathy, clotting of conventional hemodialyzers and reduction of dialysis time and frequency. The outcome was beneficial in all cases and stable biochemical and hematological parameters were maintained. No increase in heparin requirements was noted and the therapy was thought to be cost-effective.

A galactosamine-induced fulminant hepatic failure (FHF) rat model was used to study the effects of homologous cross-circulation and in situ liver perfusion. Cross-circulation with homologous donors did not significantly improve the survival time or recovery rate of grade II hepatic coma rats. Homologous in situ liver perfusion significantly improved the survival time and recovery in FHF only when started in grade II coma; it has no effect in the later stage of coma.

The in vitro removal of tyrosine by means of perfusion over immobilized tyrosinase within artificial cells was studied. The assayed activity of the microencapsulated tyrosinase was about half the value of the same amount of enzyme in free solution. Further studies were conducted to determine the stability, kinetics, and clearance of this system. The results obtained suggest that immobilized tyrosinase within artificial cells is efficient in removing tyrosine in vitro and further study in an animal model is feasible.

The feasibility of containing microencapsulated urease within a fludized-bed reactor, eliminating problems of membrane rupture, was demonstrated. Hydrolysis of urea under conditions simulating that of an artificial kidney device was measured as a function of reactor residence time, microcapsule diameter, volume of microcapsules, urea concentration in the feed, and enzyme activity. Empirical correlations were developed based on dimensional analysis, which may be used to predict urea conversion within the range of experimental operating conditions. Results under transient state conditions better represent the operation of the reactor in treatment of uremic patients.

The author reviewed artificial cells and their applications in hemoperfusion for chronic renal failure, poisoning, fulminant hepatic failure, removal of aluminium and iron, and metabolic assists. Other areas reviewed included artificial cells containing enzymes, multienzymes, immunosorbents, cell cultures and other areas.Artificial cells can be formed as membrane coated adsorbent or microencapsulated adsorbent, enzymes and cells (1-3). The large surface to volume relationship and the ultrathin membrane of artificial cells allows the rapid equilibration of metabolites (1-3). Artificial cells containing enzymes, ion exchange resin and activated charcoal have been used for hemoperfusion (4). The microencapsulated or membrane coated absorbents, enzymes, cells, immunosorbents and other material are prevented from releasing unwanted material into the circulation and prevented from adverse effects on blood cells. Because of the problem of charcoal in releasing emboli and depleting platelets (5) we first developed coated activated charcoal hemoperfusion for clinical application (6, 7). This has been used extensively in clinical studies. The artificial cell approach has also been applied to a number of other hemoperfusion approaches. The lack of space only allows this paper to summarize some of the approaches originated from this research centre.

During treatment for asthma, a 3-year-old, 15-kg child was given 750 mg of theophylline in error. Within three hours she was treated with albumin-collodion activated charcoal (ACAC) hemoperfusion. Immediately before treatment her serum theophylline level was 74 µg/ml. At the end of three hours of hemoperfusion, her theophylline level had fallen to 14.4 µg/ml and four hours later it was 8.8 µg/ml. The ACAC hemoperfusion system completely removed all the theophylline passing through it without saturation, and the total amount of drug removed was 500.8 mg (more than two thirds of the dose administered). The technique described is an efficient and rapidly effective method for the treatment of potentially lethal theophylline intoxication. For maximum effectiveness, it must be instituted as soon after intoxication as possible.

Different thicknesses of a cellulose nitrate (CN) coating were applied to petroleum pitch bead activated charcoal. The effect of this on the adsorption of small and middle molecules in vitro was studied. This was done by measuring the rate of adsorption of Vitamin B12, creatinine and uric acid from aqueous solution by activated charcoal having CN coatings of varying thickness (0.1% to 4.0% by weight). A CN coating weight of up to 0.2% caused negligible or no decrease in the rate of adsorption of all three solutes as compared with uncoated charcoal. Coating weights greater than 0.2% caused a significant decrease in the rate of adsorption of Vitamin B12, and uric acid but had little effect on the rate of adsorption of creatinine. Coating weights greater than 1.8% caused a significant decrease in the rate of adsorption of creatinine.

Anhydrous ammonia gaseous plasma technique was used for the surface modification of polypropylene beads. Amino groups were added onto the surfaces of beads by exposing them to ammonia plasma. Through these amino groups covalent immobilization of glucose oxidase and peroxidase were carried out. The total amounts of immobilized glucose oxidase and immobilized peroxidase were found to be 52 and 43 micrograms/cm2, respectively. To assess the stability of enzyme-polypropylene linkage, beads with covalently immobilized glucose oxidase and peroxidase were washed with phosphate buffer. It was found that after the removal of the adsorbed enzymes, the concentration of covalently immobilized enzymes tended to reach a steady state. After additional washing with buffer for 5 to 6 h, 40-55% of the immobilized enzymes were found to be in the active form.

The circular dichroism (CD) active phospholipid bis (4′-n- octanoxyazobenzene-4-carboxyl)- l -α-phosphatidylcholine (CDPC) was used to study the effects of cholesterol and melittin on the spontaneous lipid transfer between liposomes. For this purpose, CD spectral changes with time were observed at 20°C and 50°C for a mixture of liposomes composed of CDPC and egg lecithin (EPC) (50%CDPC-EPC-liposomes) and pure EPC-liposomes, and for a mixture of liposomes composed of CDPC and cholesterol (50%CDPC-CHO-liposomes) and pure EPC-liposomes. In both cases, CDPC molecules were found to be diluted by the EPC matrix without significant changes in the liposome size. The spontaneous transfer of CDPC was dramatically accelerated with the rise of temperature in the 50% CDPC-EPC-liposomes/EPC-liposomes system, and it was less temperature dependent in the 50%CDPC-CHO-liposomes/EPC-liposomes system. In the presence of melittin, the acceleration of CDPC transfer accompanied by CD enhancement was observed only in the 50%CDPC-EPC-liposomes/EPC-liposomes system at 20°C.

Charcoal hemoperfusion has been effective in reversing grade IV hepatic encephalopathy in patients. In animal studies essential factors have to be added to result in significant increase in the survival rate of grade III coma rats treated by hemoperfusion. In the present study, a water soluble liver extract was prepared and injected intraperitoneally into fulminant hepatic failure rats in grade II hepatic coma. This significantly (p < 0.001) increased the survival time in these animals. However, no significant increase in survival rate was obtained. We were also able to significantly (p < 0.0005) control gastrointestinal bleeding in the treated rats. We postulate that this supplementation of essential factors in combination with detoxification using hemoperfusion could form the basis of a more complete artificial liver support system.

Case reports of the use hemoperfusion-hemodialysis to reduce the frequency of dialysis in patients with vascular access problems.

Phenylalanine ammonia-lyase immobilized within semipermeable microcapsules has an assayed enzyme activity which is 20% +/- 4% of the enzyme in free solution. The Km for the immobilized enzyme remained the same as that of the free enzyme. The pH optimum also remained unchanged at pH 8.5 +/- 1.0. At the lower pH range, enzyme activity is higher for the immobilized enzyme. Daily oral administration of microencapsulated phenylalanine ammonia-lyase to phenylketonuric rats decreased the systemic phenylalanine level by 35 +/- 8% in 2 days (P less than 0.05) and by 75 +/- 8% in 7 days (P less than 0.001).

A detialed preparative procedure is described for the preparation of nylon—polyethyleneimine microcapsules containing yeast alcohol dehydrogenase (EC 1.1.1.1), malic dehydrogenase (EC 1.1.1.37), and a soluble dextran bound NAD+ derivative. In the presence of substrate, the microencapsulated dextran—NAD+ can be recycled at a rate of 2 cycles per minute. A column of the microcapsules forms a continuous flow system. Efficient and stable recycling rates could be maintained continuously when used for 3 h. Each column of microcapsules when reused several times during a two-week period still retained 40% of its original activity.

A microencapsulated multi-enzyme system has been used for the conversion of urea and ammonia into an amino acid, glutamate. The microencapsulated multi-enzyme system contains urease (E.C.3.5.1.5), glutamate dehydrogenase (E.C.1.4.1.3), and glucose-6-phosphate dehydrogenase (E.C.1.1.1.49). The conversion of urea into glutamate is achieved by the sequential reaction of urease and glutamate dehydrogenase; while glutamate dehydrogenase and glucose-6-phosphate dehydrogenase allow for the cyclic regeneration of NADP + :NADPH required for the reaction. The rate of production of glutamate is 1.3 μmole per min per ml of microcapsules. The encapsulated multi-enzyme system thus allows for the sequential enzyme reaction for the conversion of urea and ammonia into an amino acid.

In our previous paper (1), we discussed the in-vitro adsorption spectrum of plasma amino acids by coated charcoal hemoperfusion. We now describe the general amino acid disturbances in plasma, CSF and cerebrum in the galactosamine induced hepatic coma model in rats. All aromatic amino acids (AAA) increased significantly in the three compartments studied. Branched chain amino acids (BCAA) were either elevated to a much lesser extent or remained unchanged. The molar ratio of BCAA:AAA was consequently reduced. This is similar to findings in fulminant hepatic failure in human and other animal models. Most of the 20 amino acids analyzed were increased significantly in the plasma. Increases of amino acids were minimal in the brain tissue studied, i.e. the cerebrum.

Dextran 70 infusion into dogs prevents platelet adhesion to extracorporeal surfaces as effectively as direct coating of the surfaces with albumin. This is demonstrated by two experimental approaches. One of these involves a detailed analysis in 14 mongrel dogs of the effects of hemoperfusion on the systemic platelet levels, hematocrits, and dextran concentrations. The second approach is in the form of 23 platelet retention tests carried out in four mongrel dogs.

Galactosamine-induced fulminant hepatic failure rats have been used as a model for statistical assessment of liver support systems. The present study reports in detail the biochemical, hematological and histological changes in these animals. They have been used to study statistically the effects of ACAC charcoal hemoperfusion, cross-circulation and liver perfusion on long-term survival in fulminant hepatic failure.

Cross-linking hemoglobin (Hb) into Polyhemoglobin (PolyHb) for use as an artificial blood substitute may affect its antigenicity. To investigate this, male Sprague-Dawley rats are immunized with one of the following: rat stroma-free Hb (rSFHb), rat PolyHb (rPolyHb), human stroma-free Hb (hSFHb), and human PolyHb (hPolyHb). Antibody titers are quantified using a double antibody radioimmunoassay. These results show that more antibodies are produced to hPolyHb than to hSFHb, whereas rSFHB and rPolyHb are relatively non-antigenic. Thus, under homologous conditions, cross-linking hemoglobin does not significantly increase its antigenicity, whereas under heterologous conditions the molecule becomes more antigenic.

Cofactors cannot be retained within polyamide membrane microcapsules unless the cofactors have been covalently linked to macromolecules. In this paper, a new approach using lipid-polyamide membrane microcapsules has resulted in the retention of unmodified cofactors. Lipid-polyamide microcapsules can be made to contain urease (urea amidohydrolase, EC 3.5.1.5), glutamate dehydrogenase (NAD(P)+) [l-glutamate: NAD(P)+ oxidoreductase (deaminating), EC 1.4.1.3], alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1), NAD+, NADH and α-ketoglutarate. Lipophilic substrates like ammonia can equilibrate rapidly into the microcapsules. The rate of conversion of ammonia into glutamate was studied. NAD+ retained in the microcapsules was effectively recycled into NADH and 0.25 μmol NAD+ converted 10 μmol ammonia into glutamate. Without cofactor recycling, 10 μmol NADH had to be microencapsulated to convert the same amount of ammonia into glutamate. By adjusting the ratio of cholesterol and lecithin in the lipid component of the membrane, it was also possible to achieve a good urea-permeable membrane without any leakage of cofactor or α-ketoglutarate. This way urea permeated through the lipid-polyamide membrane microcapsules was sequentially converted into ammonia and then glutamate.

A soluble immobilized NAD + was prepared by creating a peptide binding between bovine serum albumin and N 6 -[(6-aminohexyl)]carbamoyl-methyl] nicotinamide adenine dinucleotide. When immobilized within semipermeable microcapsules with alcohol dehydrodgenase (EC 1.1.1.1) and malic dehydrogenase (EC 1.1.1.37) the albumin-NAD + exhibited high cofactor recycling rates. NAD + can also be similarly crosslinked to hemoglobin.

Urease, (urea amidohydrolase, EC 3.5.1.5) co-encapsulated with haemoglobin in cellulose nitrate membranes was found to exhibit apparent Michaelis-Menten kinetics; however, a steadily increasing apparent Michaelis-Menten constant over the lifetime of the preparation was observed. The activity of the enzyme in a continuous feed stirred tank reactor (CSTR) was investigated and correlated with a mathematical model derived from basic Michaelis-Menten kinetics. Plots relating substrate conversion to feed substrate concentration and tank reactor capacity were constructed and found to be accurate to less than 15% error under the experimental conditions studied.

Microencapsulation of the enzyme phenylalanine ammonia-lyase was developed for in vivo depletion of systemic phenylalanine in phenylketonuric rats. Compared to normal rats, systemic phenylalanine blood levels in phenylketonuric rats was increased by 15-20-fold. Daily oral administration of 1 unit of phenylalanine ammonia-lyase-loaded artificial cells to phenylketonuric rats lowered the systemic phenylalanine level to 58% +/- 18% (mean + S.D.) in 7 days (P less than 0.010), while 5 units lowered the systemic phenylalanine level to 25% +/- 8%. 5 units of the immobilized enzyme lowered the systemic phenylalanine level to normal levels within 6 days. Phenylketonuric treated rats showed no signs of abnormal behavior and weight loss compared to phenylketonuric non-treated rats. The immobilized enzyme within artificial cells is therefore protected against low gastrointestinal pH and proteolytic enzymes.

Using the galactosamine induced hepatic coma rat model, we studied the effects of coated charcoal hemoperfusion on amino acids in plasma and CSF in grade III hepatic coma. We found that 1 hour of hemoperfusion significantly reduced AAAs and BCAAs in plasma and increased the molar ratio of BCAA:AAA. When rats in grade III coma were treated with 2 consecutive 1-hour hemoperfusions, the substantial reduction of plasma AAAs resulted in a significant decrease of AAA levels in CSF.

Microencapsulated activated charcoal was prepared by coating charcoal granules (2-5 μm diameter) with different concentrations of poly (vinylidene fluoride) and of poly (vinylidene chloride/vinyl chloride). These microcapsules were tested for the removal of large lipophilic molecules (e.g. vitamin B 12 ) and small hydrophilic molecules (e.g. creatinine). Activated charcoal with thicker polymer coatings rapidly removes large lipophilic molecules (30-60 minutes) and excluded 80-84% of small hydrophilic molecules over a period of 4 hours. Activated charcoal with less polymer coating was permeable to both lipophilic and hydrophilic molecules. However, large lipophilic substrate were removed faster than small hydrophilic molecules.

Dialysis is the conventional treatment for chronic renal failure. It is cumbersome, expensive and time-consuming and thus alternate treatments have long been sought. A compact system consisting of haemoperfusion in series with ultrafiltration can nearly replace dialysis. A urea removal system is the only step required to complete this approach. The potential of combining a microencapsulated enzyme, urease, with an ammonium ion adsorbent, zirconium phosphate, to remove urea was examined in vitro. Urease converts urea to ammonium ions which are then adsorbed on-to zirconium phosphate. This combination would be most effective in the intestinal tract. The capacity of zirconium phosphate is probably not enough to effect the removal of enough urea to completely replace dialysis in patients with no renal function. However, this system could potentially 1) delay the onset of dialysis therapy in patients who still have some renal function, either alone or in combination with haemoperfusion-ultrafiltration, or 2) reduce dialysis treatment times.

This paper reports the effects of initial urea concentrations and pH values on the performance of a capillary hemodialyzer for the removal of free ammonia (NH3) formed by enzymatic hydrolysis of urea. Air was chosen as the gas phase. NaOH was used for alkalinization of dialysate. It was shown that one of the most important parameters was free ammonia concentration. The degrees of alkalinization and the initial urea concentration, were also important. Although even without the addition of NaOH, about 42% of the initial urea can be removed in one hour.