Augmenter of Liver Regeneration Modulates Hepatic Metabolism by Reduction of Cytochrom P450 Activity in Human Hepatocytes in Vitro

Hypothesis: Pathological disorders of the liver were shown to be associated with an impairment of hepatic drug metabolism, particularly that mediated by cytochrome P450s (CYP). Cytokines and growth factors, regulators of liver regeneration, were identified to modulate CYP expression. Recently, a novel liver specific hepatotrophic growth factor ALR, augmenter of liver regeneration, were found to have beneficial effects on liver growth, whereas its action on CYP metabolism is fully unknown. Methods: Primary human hepatocytes in vitro were treated with recombinant human ALR followed by determination of proliferation rate (thymidine incorporation, polyamine metabolism), specific CYP isoenzyme activity, protein expression using western blotting and mRNA quantification using RT-PCR technique. Results: Application of ALR enhanced proliferation associated processes of human hepatocytes like thymidine incorporation and putrescine synthesis. Further, culture time-course analysis of effects on CYP 1A2 activity and dose response investigations of effects on CYP 1A2 and 2A6 activity revealed, that maximal inhibition was reached at 48–72h of exposure with 50 nM ALR. The impact of ALR on basal activities of CYP isoenzymes demonstrated an overall reduction for CYP 1A2 of 34.5±16.0% (n=19), CYP 2A6 of 55.5±21.1% (n=19), CYP 2B6 of 18.1±7.2% (n=4) and CYP 2E1 of 44.9±26.4% (n=9). Additional an inhibitory effect of ALR after induction of CYP isoenzymes with methylcholantherene (CYP 1A2, 40.6±10.1%, n=12) and phenobarbital (CYP 2B6, 34.7±7.1%, n=3) were observed. Investigations of protein and mRNA expression of basal and induced CYP 1A2 and 3A4 isoenzymes after ALR treatment suggest a regulation on pretranscriptional level. Influence of ALR on phase II reactions (GSH/GSSG ratio, UGT conjugation) was not detected. Conclusion: Here we demonstrate that ALR, as a member of hepatotrophic factors, not only function as augmenter of hepatocyte proliferation but also as an effective agent to down-regulate basal and induced CYP in human liver. This further implies a possible role of ALR in drug interactions of impaired hepatic function while tissue regeneration is triggered.

Key words

cytochrome P450 - liver regeneration - metabolism