Effect of phenobarbital and 3-methylcholanthrene on aldehyde dehydrogenase activity in cultures of HepG2 cells and normal human hepatocytes.

Aldehyde dehydrogenase (ALDH) activity was measured in primary cultures of normal human hepatocytes and of the human hepatoma cell line HepG2 after application of phenobarbital (PB) or 3-methylcholanthrene (MC) for 5 days. Treatment with PB alone resulted in a significant increase in both protein and DNA content at concentrations of 2 and 3 mM. Treatment with MC at a concentration as low as 5 microM led to a significant loss of cells when it lasted more than 5 days. Concentrations of 3-5 mM of PB in the media of HepG2 cell cultures caused a 2-fold enhancement of the activity of ALDH, as measured with NAD and propionaldehyde (P/NAD) or benzaldehyde (B/NAD). On the other hand, MC-treated cultures (5 microM) showed a 20-fold increase in enzyme activity measured with NADP and benzaldehyde (B/NADP), and a 2-fold increase in B/NAD activity. Combined treatment with both PB and MC led to an effect of dynamic synergism as far as B/NAD and B/NADP activities are concerned, suggesting a metabolite of MC as the mediator for the increase of ALDH activity. Normal human hepatocytes in primary cultures responded to PB (3 mM) in a similar way as HepG2 cells as far as DNA and protein content and ALDH activity are concerned. It is concluded, that HepG2 hepatoma cells behave similar to the normal hepatocytes in terms of ALDH regulation and can be used for studies on the activity of ALDH as modified by added xenobiotics.