IS A CLINICAL APPLICATION OF HYBRID LIVER SUPPORT SYSTEMS LIMITED BY AN INITIAL DISORDER IN CELLULAR AMINO ACID AND ??-KETO ACID METABOLISM, RATHER THAN BY LATER GRADUAL LOSS OF PRIMARY HEPATOCYTE FUNCTION?

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Abstract
The in-vitro amino acid (AA) and α-keto acid (KA) metabolism of bioreactors initially seeded with 2.5×109 pig hepatocytes was investigated with a perfusion technique. Considerable changes in the culture medium concentrations of AA and KA were measured during the first days in culture. This is indicative of dynamic cellular metabolism in the initial phase. While the concentration of pyruvate decreased starting on the first day, α-ketoglutarate, α-ketoisocaproate, α-ketoisovalerate, and α-keto-β-methyl-n-valerate were synthesized. The long term use of hepatocyte cultures in bioreactors and thus a desirable clinical hybrid liver support therapy appears to be possible since the hepatocytes switched, after 15 days in culture, to steady-state conditions with a stable amino acid turnover featuring general AA uptake accompanied by KA release. The release of branched chain KA, in particular that of α-ketoisocaproate, reflects an effective transamination activity in the bioreactor system. Primary pig hepatocytes cultivated in hybrid liver support systems for therapy of acute liver failure or as devices for bridging to liver transplantation can sustain amino acid metabolism for at least 30 days in vitro. However, an initial disorder following the cell isolation that is demonstrated may limit immediate utilization of the systems prior to the reorganisation of the cells to tissue-like structures in bioreactors.