INDUCTION OF CYTOCHROME P-4502E1 IN THE HUMAN LIVER BY ETHANOL IS CAUSED BY A CORRESPONDING INCREASE IN ENCODING MESSENGER-RNA

The propensity of centrilobular liver damage to develop in alcohol abusers after exposure to various hepatotoxins, including ethanol itself, has been linked to the induction by ethanol of P-4502E1, a microsomal P-450 enzyme that bioactivates these agents to reactive metabolites. Whereas long-term ethanol consumption elicits a marked increase in hepatic P-4502E1 content, the molecular mechanism by which ethanol produces this effect is the subject of controversy in animals, and it has not been elucidated in human beings. Possible mechanisms include increased enzyme synthesis stemming from elevated 2E1 messenger RNA levels, enhanced translation of preexisting messenger RNA or stabilization of P-4502E1 protein. To determine which, if any, of these mechanisms underlies P-4502E1 induction in human beings, we examined the effects of ethanol intake on the hepatic intralobular distribution of P-4502E1 messenger RNA and the corresponding protein. Liver sections derived from needle biopsy specimens were obtained from five recently drinking alcoholics (last drink no more than 36 hr before) and eight control subjects (five abstaining alcoholics [last drink 96 hr or more before] and three nondrinkers). In situ hybridization of these liver sections with a hu an P-4502E1 complementary DNA probe was used to localize P-4502E1 messenger RNA transcripts. Quantitative image analysis of hybridized sections from control subjects revealed that P-4502E1 transcript content in perivenular (zone 3) hepatocytes was significantly higher (p < 0.05) than in midzonal (zone 2) and periportal (zone 1) cells (18.3 +/- 1, 9.5 +/- 2 and 3.1 +/- 2 arbitrary density units, respectively, mean +/- S.E.M.). In recent drinkers, acinar regions containing P-4502E1 transcripts were elevated 2.9-fold compared with those in controls (32.8% +/- 7% vs. 11.2% +/- 2%; p < 0.01), with this messenger RNA increase occurring mainly in perivenular cells (29.6 +/- 3 vs. 18.3 +/- 1 units; p < 0.01). P-4502E1 protein distribution, assessed by the immunohistochemical staining of liver sections with P-4502E1 antibodies, was found to be analogous to that of the messenger RNA in control subjects (the level in perivenular cells was greater than that in midzonal cells, which was greater than that in periportal cells), whereas recent drinkers exhibited marked elevations in enzyme content in both perivenular and midzonal hepatocytes. Moreover, cellular levels of P-4502E1 protein and messenger RNA were significantly correlated (r(s) = 0.79; p < 0.001) in all patients. Our results indicate that the induction by ethanol of P-4502E1 protein in human liver tissue is associated with, and appears to stem from, a corresponding increase of P-4502E1 messenger RNA. This ethanol-mediated enhancement of P-4502E1 enzyme levels mediated through the encoding messenger RNA, a process occurring primarily in perivenular hepatocytes, may explain why these cells are preferentially damaged after exposure to P-4502E1-activated hepatotoxins.