Formation of γ-ketoaldehyde–protein adducts during ethanol-induced liver injury in mice

Ethanol metabolism promotes the formation of a variety of reactive aldehydes in the liver. These aldehydes can rapidly form covalent protein adducts. Accumulating evidence indicates that these protein adducts may contribute to ethanol-mediated liver injury. Overproduction of γ-ketoaldehydes, levuglandins (LGs) and isolevuglandins, is implicated in the pathogenesis of several chronic inflammatory diseases. γ-Ketoaldehydes can form protein adducts orders of magnitude more quickly than 4-hydroxynonenal (4-HNE) or malondialdehyde. We hypothesized that ethanol-induced oxidative stress in vivo results in overproduction of LGE2– and iso[4]LGE2–protein adducts in mouse liver. Female C57BL/6 mice were allowed free access to an ethanol-containing diet for up to 39 days or pair-fed control diets. Pathological markers of ethanol-induced hepatic injury including serum alanine aminotransferase, hepatic triglyceride, and CYP2E1 were elevated in response to ethanol feeding. Ethanol-induced formation of iso[4]LGE2–, LGE2–, and 4-HNE–protein adducts in mouse liver was dependent on both dose and duration of ethanol feeding. Deficiency of cyclooxygenase 1 or 2 did not prevent ethanol-induced iso[4]LGE2 or LGE2 adducts in the liver, but adduct formation was reduced in both TNFR1- and CYP2E1-deficient mice. In summary, ethanol feeding enhanced γ-ketoaldehyde–protein adduct production via a TNFR1/CYP2E1-dependent, but cyclooxygenase-independent, mechanism in mouse liver.