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None of the established liver support systems currently in use are capable of replacing the complex functions of the liver to a sufficient degree. New therapies based on biological detoxification methods offer new ways of dealing with hepatic failure.Metabolic screening of cell lines mHepR1, HepG2, L929 and the novel immortalized human liver cell line HepZ was carried out. No capacity of glucose regulation in a monolayer culture was found with any of the established cell lines. Besides, lactate production was shown toincrease with higher glucose consumption. Likewise, ureogenesis was not detected with any of the cell lines.Investigations of the cytochrome P-450 activity showed increased levels exclusively with cell line mHepR1. After two hours of testing, its levels were significantly increased compared to the other cell lines. With primary rat hepatocytes, the P-450 concentration more than ninetyfold higher. Additional testing with the novel liver cell line HepZ proved this cell line to be able to degrade aromatic amino acids in a monolayer culture.Tested in in vitro bioreactor, cell line HepZ was shown to achieve contact inhibition when reaching a sufficiently high number. It was shown that, at a concentration of 100 million immortalized human hepatocyte cells seeded in the bioreactor, glucose consumption decreased.Moreover, the cells were even capable of consuming lactate as detected in tests with 50 and 100 million seeded cells.Used in in vivo bioreactor, on the basis of ~S (molecular adsorbents recirculating system), no negative effect of xenogeneic cell line HepZ on the physiological parameters of theanimals was found. Concerning biocompatability, it was found that no specific changes in blood pictures, levels of liver encymes and scrum proteins occurred. HepZ was shown to survive its use with the rabbits, without being damaged, at an average survival rate of more than ninety per cent. Thus the MARS-membrane seems to be able to protect both patient and cells from immunological interaction. Further investigations concerning biocompatability will, however, be necessary prior to the clinical application of this hybrid liver support system with humans.The use of the cells in the dialysate metabolism of rabbits was found to have a positive effect on blood parameters glucose and lactate. Their capacity, however, was not sufficient enough to keep the parameters within physiological reference range. Furthermore, a positive influence of the cells on the amino acid metabolism of the rabbits was detected. In contrast to the control group, a decrease in the concentration of aromatic amino acids in the blood of the rabbits, and thus a significantly lesser drop of the Fischerindex, was found.The use of cell line HepZ has been shown to produce some positive effect. Its achievement, however, is much too poor to allow for its use in such an extracorporeal liver support system. In the future, quantitatively as well as qualitatively more efficient liver cell lines will have to be developed such as to make even better use of the possibilities MARS can offer.