Upregulation of 4-Hydroxynonenal Contributes to the Negative Effect of n-6 Polyunsaturated Fatty Acid on Alcohol-Induced Liver Injury and Hepatic Steatosis

The present study aimed to investigate the effects of saturated fatty acids (SFA) and n-6 polyunsaturated fatty acids (PUFA) on alcoholic liver disease (ALD) and the underlying mechanisms. C57BL/6J male mice were randomly fed a corn oil or palm oil diet (rich in n-6 PUFA and SFA, respectively) with or without ethanol for four weeks (n = 10/group). A series of experiments in vitro with AML-12 hepatocyte were conducted to better elucidate the potential mechanisms underlying the phenomenon observed in animals. Compared with palm oil, corn oil aggravated alcohol-induced liver injury and hepatic steatosis, indicated by a histological analysis and significant elevations of plasma alanine aminotransferase and hepatic triacylglycerol (TG) level. Apoptosis-associated proteins in the ASK1-JNK pathway were significantly enhanced in the liver of mice from the corn oil + ethanol group than in the palm oil + ethanol group. The corn oil + ethanol diet also inhibited the activation of both AMPK and downstream protein acetyl-CoA carboxylase (ACC) and promoted the SREBP-1c expression, subsequently accelerating lipid synthesis. In addition, 4-hydroxynonenal (4-HNE) levels in plasma and liver were significantly upregulated in response to corn oil + ethanol feeding. Interestingly, the in vitro study showed that 4-HNE significantly attenuated cell viability, elevated the expression of cleaved-caspase 3 protein and TG level, and regulated key molecules in ASK1-JNK and AMPK pathways in a dose-dependent manner. In conclusion, the n-6 PUFA diet showed a negative effect on alcohol-induced liver injury and steatosis. It might be related to the upregulation of 4-HNE and subsequent changes of proteins, namely, ASK1, JNK, AMPK, ACC, and SREBP-1c.