Ethanol Increases NADPH Oxidase-derived Oxidative Stress and Induces Apoptosis in Human Liver Adenocarcinoma Cells (SK-HEP-1)

Alcohol-induced liver injury is linked to oxidative stress and increased production of reactive oxygen species (ROS). Oxidative stress is an early event in the process of apoptosis. However, it is not completely understood how ethanol-induced oxidative stress induces apoptosis. In contrast, nicotinamide adenine dinucleotide phosphate oxidase (NOX) is known to generate ROS in hepatocytes. The purpose of the present study was to determine whether or not ethanol-induced ROS generation stimulates the death receptor or mitochondrial pathways of apoptosis in alcohol dehydrogenase containing human liver adenocarcinoma (SK-HEP-1) cells. Treatment with ethanol increased the generation of ROS and expression of NOX4 mRNA, and also induced mitochondrial dysfunction in SK-HEP-1 cells. Moreover, ethanol induced the activation of caspase-8 and -3 in hepatocytes. These activities were suppressed by pretreatment with N-acetyl-cysteine, an antioxidant, or apocynin, an inhibitor of NOX activity. These results suggested that ethanol induces an increase in NOX-derived ROS generation upstream of caspase-8 activation and in the mitochondria in SK-HEP-1 cells. In conclusion, this study demonstrated that ethanol increases the generation of ROS and subsequently induces apoptosis using a mechanism involving mitochondrial dysfunction and caspase activation in SK-HEP-1 cells.