Inhibition of NF-κB Activation by 4-Hydroxynonenal Contributes to Liver Injury in a Mouse Model of Alcoholic Liver Disease

Long-term alcohol exposure sensitizes hepatocytes to tumor necrosis factor-alpha (TNF) cytotoxicity. 4-Hydroxynonenal (4-HNE) is one of the most abundant and reactive lipid peroxides. Increased hepatic 4-HNE contents present in both human alcoholics and alcohol-fed animals. In the present study, we investigated the effects of intracellular 4-HNE accumulation on TNF-induced hepatotoxicity and its potential implication in the pathogenesis of alcoholic liver disease. Male C578L/6 mice were fed an ethanol-containing or a control diet for 5 weeks. Long-term alcohol exposure increased hepatic 4-HNE and TNF levels. Cell culture studies revealed that 4-HNE, at nontoxic concentrations, sensitized hepatocytes to TNF killing, which was associated with suppressed NF-kappa B transactivity. Further investigation demonstrated that 4-HNE prevented TNF-induced inhibitor of KB alpha phosphorylation without affecting upstream I kappa B kinase activity. An immunoprecipitation assay revealed that increased 4-HNE content was associated with increased formation of 4-HNE inhibitor of KBa adduction in both 4-HNE treated hepatocytes and in the livers of alcohol-fed mice. Prevention of intracellular 4-HNE accumulation by bezafibrate, a peroxisome proliferator-activated receptor-alpha agonist, protected hepatocytes from TNF killing via NF-kappa B activation. Supplementation of N-acetylcysteine, a glutathione precursor, conferred a protective effect on alcohol-induced liver injury in mice, was associated with decreased hepatic 4-HNE formation, and improved hepatic NF-kappa B activity. In conclusion, increased 4-HNE accumulation represents a potent and clinically relevant sensitizer to TNF-induced hepatotoxicity. These data support the notion that removal of intracellular 4-HNE can serve as a potential therapeutic option for alcoholic liver disease. (Am J Pathol 2012, 181:1702-1710; http://dx.doi.org/10.1016/j.ajpath.2012.08.004)