What progress with artificial livers?

Future of bioartificial liver support

Many different artificial liver support systems (biological and non-biological) have been developed, tested pre-clinically and some have been applied in clinical trials. Based on theoretical considerations a biological artificial liver (BAL) should be preferred above the non-biological ones. However, clinical application of the BAL is still experimental. Here we try to analyze which hurdles have to be taken before the BAL will become standard equipment in the intensive care unit for patients with acute liver failure or acute deterioration of chronic liver disease.

Cell-Free Artificial Liver Support: Design of Appropriate Clinical Studies

The clinical use of cell-free liver support devices is dependent upon proof of safety and efficacy in clinical trials. The current published data to support their use is limited in both quantity and quality. In most studies, the methodology is such that the effects of these devices are difficult to establish with certainty. Bias might be introduced by the use of uncontrolled studies, and in randomized controlled trials limited size, poorly matched control groups or medical therapy or the use of clinically inappropriate endpoints might be important. Guidelines are now available to provide a framework for the design and execution of such trials, specifically to minimize the systematic errors that are frequently present and that might result in biased estimates of treatment effects. In the present review, the limitations of current studies are discussed and suggestions made as to the design and conduct of future clinical trials.

Improvement of C3A cell metabolism for usage in bioartificial liver support systems

BACKGROUND/AIMS

The use of cell lines in bioartificial liver support systems (BALSS) to treat fulminant hepatic failure (FHF) is hindered by their reduced metabolic functions, which could be further decreased by the patient's serum/plasma. Hence, the aim of this study was to (i) test the effect of the FHF serum on C3A cell metabolism; (ii) precondition the cells to improve their metabolic capacity.

METHODS

C3A cells were preconditioned in a medium developed at the University of Edinburgh (UoE) or a 10% FHF serum medium. Metabolism capacity was assessed on days 3, 7 and 10 and compared with primary porcine hepatocytes. Preconditioned-cell metabolism was reassessed after (i) passage and (ii) incubation with 10% FHF serum.

RESULTS

UoE-preconditioned cells showed time-dependent increase in gluconeogenesis (500%), ureogenesis (200%), galactose elimination (240%) albumin synthesis (250%). These results were in the same order of magnitude as the ones obtained with primary porcine hepatocytes and were further enhanced by cell passage. UoE-preconditioning prevented the decrease of metabolism induced by acute incubation with FHF serum on control C3A cells. Preconditioning with FHF serum did not improve cell metabolism.

CONCLUSIONS

Cell preconditioning with UoE-medium increases metabolic capacity and would greatly improve BALSS efficacy.

Pharmacokinetic considerations in development of a bioartificial liver

We consider the pharmacokinetics of bioartificial livers (BALs) prepared using a hollow fibre module with respect to two key functions, detoxification and plasma protein supply, and present the results in a simple form. We then discuss the advantages and disadvantages of BAL therapy in comparison with the non-biological therapies of haemodialysis and plasma exchange. Nitrogenous and other potentially toxic compounds, such as ammonia, mercaptans, short-chain fatty acids and gamma-aminobutyric acid, are produced in the bowels and accumulate in the systemic blood because of impaired elimination by the ailing liver. Adrenal and gonadal steroids, including corticosteroids, estrogens, progestins and androgens, are biosynthesised, and high concentrations of these hormones become harmful. All these endogenously produced toxins require effective metabolism. In haemodialysis, toxins that permeate through the hollow fibre membrane are rapidly removed by the dialysate flow, and their concentrations decrease to almost zero. In a BAL bioreactor, the toxins are slowly metabolised by hepatocytes in the hollow fibres, and decreased to concentrations that are inversely proportional to the number of hepatocytes in the BAL, even after a long-term assist. It is difficult to rationalise the clinical usage of BAL systems containing small amounts of hepatocytes (70-100g) to remove the toxins. Concentrations of plasma proteins in a patient after long-term BAL treatment are proportional to the number of hepatocytes in the device. BAL reactors prepared using porcine hepatocytes supply porcine proteins, not human proteins, to the recipient. Plasma exchange increases protein concentrations much more effectively than BAL as long as a sufficient amount of plasma is available. The blood inflow rate to the liver is about 1500 mL/min in a normal adult. On the other hand, blood draw rates to a BAL system are restricted to the range of 100-300 mL/min. Toxins that are rapidly cleared by the liver (for example, the ammonia clearance of the normal human liver is several hundred mL/min) cannot be effectively eliminated from the systemic blood by BAL systems currently under clinical evaluation. Hepatocytes are the only elements in a BAL reactor that can metabolise toxins and synthesise proteins, and thus BAL performance increases with the increasing number of hepatocytes in the bioreactor. The human liver weighs about 1500 g and contains about 80% hepatocytes, i.e. about 1200 g of hepatocytes. The blood flow through the liver is about 1500 mL/min in a normal adult. To effectively replace liver functions would require a BAL reactor containing the functional equivalent of several hundreds of grams of human hepatocytes with an extracorporeal perfusion rate of more than 1000 mL/min. At this point, only orthotopic liver transplantation can meet these criteria.

Studies on the preparation of chitosan microcarriers cross-linked by oxidized lactose and culture of primary hepatocytes

Chitosan microcarriers were prepared using oxidized lactose as a cross-linking agent which was oxidized by sodium periodate. The effect of amount of oxidized lactose on the preparation of chitosan microcarriers was studied and optimized. Rat hepatocytes cultivated on chitosan microcarriers cross-linked by oxidized lactose retained the spherical shape as they have in vivo. Liver-specific functions such as albumin secretion and glucose metabolism were stably maintained for seven days. The metabolic activities of hepatocytes cultured on the oxidized lactose cross-linked chitosan microcarriers were higher than those of hepatocytes on chitosan microcarriers cross-linked by glutaraldehyde and on cytodex 3. The results suggest that oxidized lactose could be an interesting cross-linking agent for chitosan thus reducing the toxic side effects caused by using glutaraldehyde.

Successful MARS treatment in severe cholestatic patients with acute on chronic liver failure

Extracorporeal liver devices have gained great attention as a complementary approach to liver transplantation in patients with acute on chronic liver failure. Among others, Molecular Adsorbent Recycling System (MARS) is a hemodiafiltration against albumin able to remove low molecular weight toxins. We aimed to validate the use of MARS in patients presenting with acute on chronic liver failure with severe cholestasis. We enrolled 7 patients with acute on chronic liver failure, presenting with bilirubin >25 mg/dl and hepatorenal syndrome and/or hepatic encephalopathy grade >II. Liver biochemistry, coagulation, blood cell count, electrolytes, ammonia, lactate, blood urea nitrogen, creatinine, bile acids, Fischer ratio, and encephalopathy grade were assessed before and after each MARS treatment. MARS can represent a safe therapeutic choice to achieve a quick improvement of neurological status, a hemodynamic stability, and a better clinical outcome. In particular, our encouraging results suggest that also, patients with severe cholestasis may represent in the future a good indication for MARS treatment.

Extracorporeal liver support: porcine or human cell based systems?

Initial results of the clinical use of primary porcine liver cells for extracorporeal liver support are being reviewed as the cell source is controversial. According to Eurotransplant data 20-25% of explanted donor livers are not transplanted, due to factors such as steatosis or cirrhosis. This number corresponds to the number of patients with acute liver failure who require bridging therapy to transplantation. Primary human liver cells from transplant discards can be isolated, purified and maintained in bioreactors and provide an alternative for cell-based extracorporeal liver support therapy. A four-compartment bioreactor enables recovery from preservation and isolation injury in a three-dimensional network of interwoven capillary membranes with integrated oxygenation, rendering the liver cells from these discarded donor organs viable for clinical utilization. Patient contact with additional animal-derived biomatrix and fetal calf serum can be avoided. The initiation of an in vitro cultivation phase allows cell stabilization, quality control, and immediate availability of a characterized system without cryopreservation. The hypothesis of this paper is that with appropriate logistics and four-compartment bioreactor technology, cells from human liver transplant discards can serve the demand for cell-based therapy, including extracorporeal liver support.

Extracorporeal support of the failing liver

Successes in machine-based extracorporeal support for different organ functions stimulated research in the field of liver support approximately 50 years ago. Initial failure to improve outcome using detoxification methods like dialysis, blood and plasma exchange, or plasmapheresis over sorbents fueled interest in biologic liver support concepts using bioreactors or combined methods. New device configurations, technical improvement of existing detoxification methods, and the refinement in cell culture techniques led to a boost in research on biologic and nonbiologic approaches. Currently, many systems are in the preclinical phase or have entered clinical studies. A number of completed clinical trials have reported a favorable therapeutic impact of the most advanced solutions on the course and outcome of liver failure. Often, findings must be reconfirmed. However, current knowledge suggests that extracorporeal liver support can successfully stabilize liver function, improve the clinical condition of patients, and considerably improve survival in certain subgroups of patients with fulminant hepatic failure and acute decompensation of chronic hepatic failure. Although the initial focus of liver support methods was bridging to liver transplantation, bridging to recovery of organ function and treatment of intractable pruritus are now valuable indications.