CYP2E1 is not involved in early alcohol-induced liver injury

The continuous intragastric enteral feeding protocol in the rat was a major development in alcohol-induced liver injury (ALI) research. Much of what has been learned to date involves inhibitors or nutritional manipulations that may not be specific. Knockout technology avoids these potential problems. Therefore, we used long-term intragastric cannulation in mice to study early ALI. Reactive oxygen species are involved in mechanisms of early ALI; however, their key source remains unclear. Cytochrome P-450 (CYP)2E1 is induced predominantly in hepatocytes by ethanol and could be one source of reactive oxygen species leading to liver injury. We aimed to determine if CYP2E1 was involved in ALI by adapting the enteral alcohol (EA) feeding model to CYP2E1 knockout (-/-) mice. Female CYP2E1 wild-type (+/+) or -/- mice were given a high-fat liquid diet with either ethanol or isocaloric maltose-dextrin as control continuously for 4 wk. All mice gained weight steadily over 4 wk, and there were no significant differences between groups. There were also no differences in ethanol elimination rates between CYP2E1 +/+ and -/- mice after acute ethanol administration to naive mice or mice receiving EA for 4 wk. However, EA stimulated rates 1.4-fold in both groups. EA elevated serum aspartate aminotransferase levels threefold to similar levels over control in both CYP2E1 +/+ and -/- mice. Liver histology was normal in control groups. In contrast, mice given ethanol developed mild steatosis, slight inflammation, and necrosis; however, there were no differences between the CYP2E1 +/+ and -/- groups. Chronic EA induced other CYP families (CYP3A, CYP2A12, CYP1A, and CYP2B) to the same extent in CYP2E1 +/+ and -/- mice. Furthermore, POBN radical adducts were also similar in both groups. Data presented here are consistent with the hypothesis that oxidants from CYP2E1 play only a small role in mechanisms of early ALI in mice. Moreover, this new mouse model illustrates the utility of knockout technology in ALI research.