Induction of cytochrome P-4502E1 by ethanol in rat Kupffer cells

Ethanol has been shown to affect several Kupffer cell functions, but the mechanisms underlying these changes are unknown. One possible mediator is cytochrome P-4502E1 (CYP2E1), an ethanol-inducible enzyme that has been associated with toxic effects in the liver, as well as in many extrahepatic organs. To assess whether CYP2E1 can be induced by ethanol in Kupffer cells, male rats pair-fed ethanol-containing or control Lieber-DeCarli diets for 3 weeks were studied. Immunoblotting experiments showed that ethanol-treatment caused a 7-fold increase in CYP2E1 content both in Kupffer cells and hepatocytes. When expressed per milligram of S9 protein, the content of CYP2E1 in Kupffer cells was, however, 10 times lower than in hepatocytes. Immunohistochemical studies revealed that CYP2E1 is located in the endoplasmic reticulum of Kupffer cells in vivo and that it is also present in isolated Kupffer cells. In both Kupffer cells and hepatocytes, ethanol feeding increased the hydroxylation of p-nitrophenol, a relatively specific substrate for CYP2E1, demonstrating that the induced CYP2E1 was catalytically active. This reaction was significantly inhibited by anti-CYP2E1 IgG in both types of cells. Although CYP2E1 may not be the predominant pathway for ethanol metabolism in hepatocytes, it is possibly the major one in Kupffer cells. Thus, the induction of CYP2E1 by ethanol in these cells could cause significant changes in intracellular acetaldehyde concentrations which, together with increased lipid peroxidation, may contribute to the development of alcoholic liver injury.