Immunoisolation of Hybrid Liver Support Systems by Semipermeable Membranes

Immunoisolation of hybrid liver support systems (LSS) utilizing suitable semipermeable membranes as an immune barrier enables neither immunocompetent cytotoxic factors to cause damage to the hepatocytes in the bioreactor nor xenogenic hepatocyte products to cause immunological side effects in patients. To determine the capability of membranes as an immune barrier, 6 flat membranes were investigated: Cuprophan (C-100), cut-off MW 1000, Cuprophan (C-240), cut-off MW 10,000, Polypropylen hydrophilic and hydrophobic (PPhi, PPho), cut-off MW 500,000-1,000,000, Polysulfon (PS), cut-off MW 1,000,000, Polyamid (PA), cut-off beyond MW 1,000,000. The permeability of the membranes to plasma factors and liver protein fractions (LP) was studied by routine biochemical methods and gel electrophoresis. In a second study, pigs (n=7) were immunised by LP after membrane passage. The results showed PA, PS, and PPhi to be completely permeable for plasma factors and LP, C-100 and C-240 for urophanic substances, and C-240 again for LP under MW 14.000. All 7 pig sera studied by Western blot discovered pre-formed xenoreactive natural IgG-antibodies (NAB) against human liver antigen (AG) with MW 26.000. AB de-novo-synthesis was demonstrated for AG with MW 45.000. No AB-synthesis was induced for epitopes under MW 26,000. These results suggest that limiting the cut-off of bioreactor outflow membranes to MW < 26,000 could avoid immunological side effects to patients.

Contribution of bone marrow mesenchymal stem cells to porcine hepatocyte culture in vitro

One of the greatest challenges in the attempt to create functional bioartificial liver designs is the maintenance of porcine hepatocyte differentiated functions in vitro. Co-cultivation of hepatocytes with nonparenchymal cells may be beneficial for optimizing cell functions via mimicry of physiological microenvironment. However, the underlying mechanisms remain to be elucidated. An equal number of freshly isolated porcine hepatocytes and purified bone marrow mesenchymal stem cells (MSCS) was randomly co-cultured and the morphological and functional changes of heterotypic interactions were characterized. Furthermore, contributions of soluble factors involved in the separated co-culture system were evaluated. The purity of the third-passage MSCS and primary hepatocytes was more than 90% and 99%, respectively. Hepatocyte viability was greater than 95%. A rapid attachment and self-organization of three-dimensional hepatocyte spheroids were encouraged, which was due to the supporting MSCS of high motility. The elevated induction of both albumin production and urea synthesis was achieved in co-culture (P < 0.05). Data from semipermeable membrane cultures suggested that interleukin-6 is one of the key stimulators in hepatic functional enhancement. These results demonstrate for the first time that soluble factors have beneficial effects on the preservation of hepatic morphology and functionality in the co-culture of hepatocytes with MSCS in vitro, which could represent a promising tool for tissue engineering, cell biology, and bioartificial liver devices.

Bioreactors for extracorporeal liver support

Hybrid extracorporeal liver support is an option to assist liver transplantation therapy. An overview on liver cell bioreactors is given and our own development is described. Furthermore, the prospects of the utilization of human liver cells from discarded transplantation organs due to steatosis, cirrhosis, or traumatic injury, and liver progenitor cells are discussed. Our Modular Extracorporeal Liver Support (MELS) concept proposes an integrative approach for the treatment of hepatic failure with appropriate extracorporeal therapy units, tailored to suit the actual clinical needs of each patient. The CellModule is a specific bioreactor (charged actually with primary human liver cells, harvested from human donor livers found to be unsuitable for transplantation). The DetoxModule enables albumin dialysis for the removal of albumin-bound toxins, reducing the biochemical burden of the liver cells and replacing the bile excretion of hepatocytes in the bioreactor. A Dialysis Module for continuous veno-venous hemofiltration can be added to the system if required in hepato-renal syndrome.

A novel bioartificial liver with culture of porcine hepatocyte aggregates under simulated microgravity

An extracorporeal bioartificial liver device could provide vital support to patients suffering from acute liver failure. We designed a novel, customized bioreactor for use as a bioartificial liver (patent pending). The Innsbruck Bioartificial Liver (IBAL) contains aggregates of porcine hepatocytes grown under simulated microgravity. The culture vessel rotates around its longitudinal axis and is perfused by two independent circuits. The circuit responsible for exchange of plasma components with the patient consists of a dialysis tube winding spirally around the internal wall of the culture vessel. IBAL was evaluated in vitro. Viability tests showed sufficient viability of hepatocytes for up to 10 days. Cytologic examination of samples from the bioreactor showed liver cell aggregates. These were also examined by electron microscopy. A number of biochemical parameters were analyzed. In conclusion, cell culture is possible for at least 10 days in the IBAL system, organoid hepatocyte aggregates are formed and synthetic activity of the hepatocytes was demonstrated.

Treatment of acute liver failure in pigs reduces hepatocyte function in a bioartificial liver support system

Several different types of bioartificial liver (BAL) support systems have been developed to bridge patients suffering from acute liver failure (ALF) to transplantation or liver regeneration. In this study we assessed the effects of ALF plasma on hepatocyte function in the BAL system that has been developed in our center. Pigs (40-60 kg) were anaesthetised and a total hepatectomy was performed. Cells were isolated from the resected livers and were transferred to the bioreactor of the BAL system. Twenty hours after cell isolation, hepatocytes in the BAL were tested for cell viability and functional activity by using a recirculating test medium in which assessment of LDH leakage, ammonia clearance, urea synthesis, 7-ethoxycoumarin O-deethylase (ECOD) activity and pseudocholine esterase production was performed. Subsequently, two groups were studied. In one group (I, n=5), the cell-loaded bioreactor was used to treat the donor pig, rendered anhepatic, for 24 hours. In the second group (II, n=5) the bioreactor was cultured for 24 h and served as a control. After 24 hours treatment or culturing, the cell viability count and functional activity tests were repeated. The results show that hepatocytes in the BAL remained viable after 24 h treatment of anhepatic pigs, as shown by the LDH release and pseudocholine esterase production. However, metabolic functions such as ammonia clearance, ECOD and urea synthesis were reduced after 24 h exposure of hepatocytes to autologous ALF plasma, whereas these functions were unaltered after 24 h culturing of the cells in the bioreactor.

Long-term maintenance of cytochrome P450 activities by rat hepatocyte/3T3 cell co-cultures in heparinized human plasma

Little information on the effect of plasma on hepatocyte cytochrome P450 (CYP) activities is currently available. We characterized the effect of plasma on CYPs of hepatocyte-mesenchymal cell co-cultures, which exhibit stable liver specific functions and may be potentially useful for bioartificial liver design. Rat hepatocyte-mouse 3T3-J2 cell co-cultures were maintained for 6 days in medium, and then switched to heparinized human plasma containing 3-methylcholanthrene (3MC; 2 microM), phenobarbital (PB; 1 mM), or no inducer for up to 7 days. CYP activities were measured in situ based on the o-dealkylation of ethoxy- (EROD), methoxy- (MROD), pentoxy- (PROD), or benzyloxy- (BROD) resorufin. Plasma alone increased PROD/BROD but not EROD/MROD. The endogenous inducer was in the high molecular weight fraction (>5 kD) of plasma and inhibited by >5 nM okadaic acid and >10 microM dibutyryl cyclic AMP, two inhibitors of PB-inducible CYPs. Furthermore, plasma increased CYP1A1 and CYP2B1/2 mRNA levels. In plasma, 3MC induced EROD/MROD to about 60% of the level induced in culture medium while PB induced PROD/BROD that were three- to 10-fold above levels induced in medium. CYP activities decreased between days 2 and 7 of plasma exposure, but were enhanced by plasma supplementation with amino acids, insulin, glucagon, and hydrocortisone.

Advances in bioartificial liver assist devices

Rapid advances in development of bioartificial liver assist devices (BLADs) are exciting clinical interest in the application of BLAD technology for support of patients with acute liver failure. Four devices (Circe Biomedical HepatAssist, Vitagen ELAD, Gerlach BELS, and Excorp Medical BLSS) that rely on hepatocytes cultured in hollow-fiber membrane technology are currently in various stages of clinical evaluation. Several alternative approaches for culture and perfusion of hepatocytes have been evaluated in preclinical, large animal models of liver failure, or at a laboratory scale. Engineering design issues with respect to xenotransplantation, BLAD perfusion, hepatocyte functionality and culture maintenance, and ultimate distribution of a BLAD to a clinical site are delineated.

Development of a hybrid liver support system

Hybrid liver systems are being developed as temporary extracorporeal liver support therapy. The overview given here emphasizes the development of both hepatocyte culture models for bioreactors and of systems for clinical therapy. In vitro studies demonstrate long term external metabolic function in isolated primary hepatocytes within bioreactors. These systems are capable of supporting essential liver functions. Animal experiments verify the possibility of upscaling bioreactors for clinical treatment. However, since there is no reliable animal model for investigating the treatment of acute liver failure, the promising results obtained from these studies have limited relevance to human beings. The small number of clinical studies performed thus far are not sufficient to enable any conclusions concerning improvements in the therapy of acute liver failure. Although important progress has been made in the development of these systems, multiple hepatocyte culture models and bioreactor constructions are being discussed in the literature, indicating competition in this field of medical research. For the use of hepatocytes and sinusoidal endothelial cells in coculture, a bioreactor has been designed. The construction is based on capillaries for hepatocyte aggregate immobilization. Four separate capillary membrane systems, each permitting a different function, are woven in order to create a three-dimensional network. Cells are perfused via independent capillary membrane compartments. Decentralized oxygen supply and carbon dioxide removal with low gradients is possible. The parallel use of identical units enables easy upscaling. Initial studies on the use of discarded organs that are unsuitable for transplantation as a source for primary human liver cells seem to be promising.

Novel bioartificial liver support system: preclinical evaluation

Preclinical safety and efficacy evaluation of a novel bioartificial liver support system (BLSS) was conducted using a D-galactosamine canine liver failure model. The BLSS houses a suspension of porcine hepatocytes in a hollow fiber cartridge with the hepatocytes on one side of the membrane and whole blood flowing on the other. Porcine hepatocytes harvested by a collagenase digestion technique were infused into the hollow fiber cartridge and incubated for 16 to 24 hours prior to use. Fifteen purpose-bred male hounds, 1-3 years old, 25-30 kg, were administered a lethal dose, 1.5 g/kg, of D-galactosamine. The animals were divided into three treatment groups: (1b) no BLSS treatment (n = 6); (2b) BLSS treatment starting at 24-26 h post D-galactosamine (n = 5); and (2c) BLSS treatment starting at 16-18 h post D-galactosamine (n = 4). While maintained under isoflurane anesthesia, canine supportive care was guided by electrolyte and invasive physiologic monitoring consisting of arterial pressure, central venous pressure, extradural intracranial pressure (ICP), pulmonary artery pressure, urinary catheter, and end-tidal CO2. All animals were treated until death or death-equivalent (inability to sustain systolic blood pressure > 80 mmHg for 20 minutes despite massive fluid resuscitation and/or dopamine administration), or euthanized at 60 hours. All animals developed evidence of liver failure at 12-24 hours as evidenced by blood pressure lability, elevated ICP, marked hepatocellular enzyme elevation with microscopic massive hepatocyte necrosis and cerebral edema, elevated prothrombin time, and metabolic acidosis. Groups 2b and 2c marginally prolong survival compared with Group 1b (pairwise log rank censored survival time analysis, p = 0.096 and p = 0.064, respectively). Since survival times for Groups 2b and 2c are not significantly different (p = 0.694), the groups were combined for further statistical analysis. Survival times for the combined active treatment Groups 2b and 2c are significantly prolonged versus Group 1b (p = 0.047). These results suggest the novel BLSS reported here can have a significant impact on the course of liver failure in the D-galactosamine canine liver failure model. The BLSS is ready for Phase I safety evaluation in a clinical setting.

Hepatocyte liver-assist systems--a clinical update

Liver failure is a serious problem that affects thousands of people in the United States each year. Other than liver transplantation, a supportive therapy has been unavailable for patients with liver failure that is refractory to medical treatment. An apparent solution to this problem is a hepatocyte liver-assist system. Such a system is composed of mammalian hepatocytes loaded in a mechanical apparatus, such as a hollow fiber cartridge. During extracorporeal perfusion of the system, the hepatocytes provide metabolic function to the patient with liver failure. At least two extracorporeal hepatocyte systems have shown promise in human clinical trials of acute liver failure. In fact, one system has gained approval from the Food and Drug Administration for testing in a randomized multicenter clinical trial. In this article, key issues of clinical testing are reviewed, and major contributions and questions that remain unresolved are emphasized.