Xenobiotic-enhanced expression of cytochromes P450 2E1 and 2B in primary cultured rat hepatocytes.

Cytochrome P450 2E1 (CYP2E1) and 2B (CYP2B) mRNA and protein expression was examined in primary cultured rat hepatocytes under basal cell culture conditions and in response to three prototypic CYP2E1 inducers, i.e. ethanol, acetone, and pyrazine. Xenobiotic treatment for 24 hr, initiated after hepatocytes had been maintained in culture for 72 hr, resulted in 2-8-fold increases in CYP2E1 protein levels, relative to untreated cells. A >/=2-fold increase in CYP2E1 protein levels was detected at the lowest concentration (1 mM) of each of the xenobiotics examined. The increase in CYP2E1 protein expression was not accompanied by any significant increase in 2E1 mRNA expression. In contrast, CYP2B protein and mRNA levels were increased by acetone or pyrazine at concentrations greater than 1 mM. Ethanol (up to 100 mM) failed to significantly increase CYP2B protein or mRNA levels. The maximal increases measured for CYP2B protein and mRNA ( approximately 25-fold and approximately 90-fold, respectively) after treatment of hepatocytes with acetone were comparable to those measured in our laboratory, and reported by others, for phenobarbital treatment of primary cultured rat hepatocytes. The results of this study show that the pattern of expression of CYP2E1 and 2B in this primary cultured rat hepatocyte system and the magnitude of induction parallel those reported for rat liver in vivo in response to these xenobiotics. This primary hepatocyte culture system provides opportunities for studies of the role of CYP2E1 in the metabolism and bioactivation of drugs, chemicals, and putative carcinogens, as well as mechanistic studies on xenobiotic-mediated regulation of CYP2E1 expression.