Cytochrome P450 maintenance and diazepam metabolism in cultured rat hepatocytes.

Diazepam metabolism has been investigated in rat hepatocytes cultured for 3, 24, 48 and 72 hr under five different conditions. Although four of the treatments studied reduced markedly the spontaneous loss of cytochrome P450, they had different effects on the metabolism of diazepam (DZ) presumably by affecting the relative proportions of cytochrome P450 isozymes during the period of culture. Thus P450 medium or dimethyl sulphoxide-supplemented medium maintained the rate of disappearance of DZ from the culture medium and metabolite profile in 24 hr cultures at the initial levels found in 3 hr cultures, while culture at 30 degrees or in metyrapone-containing medium resulted in the production of oxazepam, a metabolite normally only produced by dog, monkey and human hepatocytes. These findings indicate that the well recognized phenotypic alteration of cytochrome P450-dependent mono-oxygenase activities that occurs when rat hepatocytes are cultured in different media can result in a range of metabolic options that are normally only available in other animal species.