The aim this study was to compare metabolic activity of a hollow fiber bioreactor with a perfused liver. A special construction of a hollow fiber bioreactor was used with freshly isolated rat hepatocytes. After isolation, hepatocytes were incubated in the bioreactor for the duration of 3 hrs in the following conditions: 100 ml medium Hanks Balances Salts Solution supplemented with 4% albumin, 2 mM ornithine, 10 mM ammonium chloride and 6 mM ethanol were used; the medium was perfused in a circulated system for 25 ml/min; samples of the medium were taken to estimate ammonia, urea, glucose, lactate, ethanol, AST and ALT activity before and after 5 min and every 15 min of perfusion time. The same experimental condition was used in the perfused rat liver system. Utilization of ammonia was different in both systems and amounted to: 8.89 and 5.23 µmol/h/g hepatocytes in the bioreactor and perfused liver, respectively. Urea production was: 2.35 and 8.22 µmol/h/g hepatocytes, respectively. The largest differences between the compared systems were observed in the glucose and lactate metabolism. The bioreactor did not release glucose and lactate during the entire time of perfusion. In contrast, perfused liver intensively released glucose (31.32 µmol/hr/g cells) and produced lactate (29.42 µmol/hr/g cells). On the other hand, there was no statistically significance difference in the rate of ethanol metabolism between both systems, which amounted to 2.55 and 2.04 umol/h/g hepatocytes in the bioreactor and perfused liver, respectively. The results indicate that a bioreactor with freshly isolated hepatocytes is not bioequivalent to a perfused liver if estimation is made on the basis of ureogenesis and/or glucose utilization. However, ethanol utilization gives evidence that the metabolic activity of the bioreactor is comparable with a perfused liver. On the basis of the obtained results it can be concluded that the difference in metabolic activity of the bioreactor and perfused liver is connected with catabolic state and disturbances of energy metabolism in freshly isolated hepatocytes. In such a condition HBSS is not the proper medium for the recovery of homeostasis. To estimate the metabolic activity of freshly isolated hepatocytes cultivated in various in vitro systems such as a marker of model usefulness it is suggested to use the activity of inducible enzymes, but not constituent enzymes.
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