Excess fructose enhances oleatic cytotoxicity via reactive oxygen species production and causes necroptosis in hepatocytes

Non-alcoholic fatty liver disease (NAFLD), the hepatic phenotype of metabolic syndrome, has been identified as a major health concern as the number of cirrhosis and deaths associated with NAFLD is expected to increase. Although fructose intake has been considered to be a progressive factor in the pathophysiology of NAFLD, it remains unclear how fructose contributes to hepatocellular damage during lipotoxicity. In the present study, we aimed to analyze the hepatotoxicity of fructose in steatosis. Fructose effects on lipotoxicity were evaluated in HepG2 cells, primary mouse hepatocytes, and in mice fed a high-fat diet with or without sucrose (HFDS/HFD). Oleate induced caspase 3-independent cell death in HepG2 cells and primary mouse hepatocytes cultured in fructose-supplemented medium, and induced cleavage of caspase-1 in primary mouse hepatocytes. In addition, the number of cells stained positive for reactive oxygen species (ROS) was significantly increased, and N-acetyl cysteine was found to inhibit ROS production and cell death. Cell death was confirmed to be through necrotic cell death, and phosphorylation of mixed lineage kinase domain-like (MLKL) protein was observed. Taken together, hepatocyte cytotoxicity was due to excess fructose with oleate-induced ROS-mediated necroptosis. HFDS mice showed progressive hepatic fibrosis and inflammation and a higher NAS score than HFD mice or mice fed a control diet. The expression of hemoxygenase-1, phosphorylation of MLKL, cleavage of caspase1, and apoptosis were significantly increased in the livers of mice fed a HFDS. Overall, excess fructose intake induces necroptosis through the production of ROS and enhances the toxicity of oleatic cytotoxicity.