Quantification and mechanisms of oleic acid-induced steatosis in HepG2 cells
Developing a quantifiable in vitro model of steatosis is critical in understanding the pathogenesis of nonalcoholic fatty liver disease (NAFLD) and searchingfor effective therapies. Using an ORO-based colorimetric measurement, we developed a convenient assay to qualify the degree of OA-induced steatosis in HepG2 cells. We demonstrated that in the absence of exogenous inflammatory mediators, OA-induced steatosis was associated with increased production and secretion of tumor necrosis factor alpha and decreased expression of peroxisome proliferators-activated receptor α in HepG2 cells. OA-induced steatosis was also associated with increased lipid peroxidation, apoptosis, but decreased proliferation in these cells. The increased lipid peroxidation was related to decreased SOD-1, a free radical scavenger enzyme; while increased apoptosis was related to increased active caspase-9. The decreased proliferation mediated by OA-induced steatosis was associated with increased production of p27 with unchanged alanine transaminase (ALT) level in the culture medium, indicating OA-induced steatosis alters cell cycle progression without direct toxicity to these cells. In conclusion, the present study developed a colorimetric assay that accurately quantifies OA-induced steatosis in HepG2 cells. In the absence of exogenous inflammatory mediators, OA-induced steatosis results in a series of pathophysilogical changes in HepG2 cells, indicating direct pathogenic roles of hepatocytes in NAFLD.