Abstract: BACKGROUND: Studies have shown NADPH oxidase (NOX) protein expression will up-regulate in the myocardium, skeletal muscle, kidney, and brain under stress conditions. However, its role in alcoholic liver damage is still unclear.
OBJECTIVE: To investigate the role of NOX-mediated oxidative stress in normal liver tissue and alcoholic liver damage.
METHODS: (1) Six male C57BL/6J mice were randomly divided into normal control group and normal drug group, with three mice in each group. Mice in the normal drug group were intraperitoneally injected with 10 mg/kg apocynin for 4 consecutive days, while those in the normal control group were injected with the same dose of solvent. Lipid metabolism-related indexes in serum and liver tissue of mice were detected, and the protein expressions of NOX2 and NOX4 in liver tissue were determined. (2) Another 18 male C57BL/6J mice were randomly divided into common control group, alcoholic control group, alcoholic drug group, with 6 mice in each group. Mice in the common control group were given TP4030C, while those in the other two groups were given Lieber-DeCarli liquid diet to construct animal models of alcohol-induced hepatocellular injury. During the modeling, mice in the alcoholic drug group were intraperitoneally injected with 10 mg/kg apocynin, 6 days a week, for 5 continuous weeks, while those in the other two groups were injected with the same dose of solvent. (3) Body mass, epididymal fat relative mass, liver index and relative mass of the skeletal muscle were recorded or calculated. Glucose tolerance test was used to detect insulin sensitivity, and serum liver function and lipid metabolism indexes were measured. Levels of malondialdehyde, superoxide dismutase, triglycerides, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol were determined. Pathological changes of the liver were observed using hematoxylin-eosin staining. Western blot assay was applied to detect NOX2 and NOX4 protein expression in liver tissue. 
RESULTS AND CONCLUSION: Compared with the normal control group, the content of triglycerides in liver tissue and the levels of serum alanine aminotransferase and aspartate aminotransferase in serum were significantly increased, while high-density lipoprotein cholesterol level and the expression of NOX2 and NOX4 in liver tissue decreased significantly in the normal drug group (P < 0.05 or P < 0.01). Compared with the common control group, the relative content of epididymal fat and the level of high-density lipoprotein cholesterol in both serum and liver tissue were significantly decreased in the alcoholic control group, while triglyceride and low-density lipoprotein cholesterol levels in liver tissue, serum alanine aminotransferase level and NOX4 protein expression were significantly increased in the alcoholic control group. Compared with the alcoholic control group, the alcoholic drug group had a significant increase in the high-density lipoprotein cholesterol levels in the serum and liver tissue but had a significant decrease in serum alanine aminotransferase level and low-density lipoprotein cholesterol level and NOX4 protein expression in liver tissue. In conclusion, inhibiting NOX alleviates alcohol-induced hepatocellular injury and lipid metabolism disorder; apocynin has different effects on liver physiological and pathological states of alcoholic liver damage.

Key words: alcoholic liver damage, oxidative stress, NADPH oxidase, NOX4, lipid metabolism, apocynin