Palmitic acid induced lipotoxicity is associated with altered lipid metabolism, enhanced CYP450 2E1 and intracellular calcium mediated ER stress in human hepatoma cells

The aim of the present investigation was to study the events associated with palmitic acid induced metabolic and lipotoxic changes in human hepatoma cells (Hep3B, Huh7 and HepG2). The cells were lipid-overloaded with varied concentrations of saturated fatty acid (palmitic acid). It was observed that (a) SFA induced significant metabolic changes including CD36/FAT, SREBP1, PPAR gamma and SCD1 upregulation and decreased Mttp levels in HepG2 and Huh7 cells but not in Hep3B cells; (b) the toxic manifestations including changes in Ca2+ levels, mitochondrial dysfunction and activation of the PERK-eIF2 alpha-CHOP pathway due to SFA were more pronounced in Huh7 and Hep3B cells as compared to HepG2 cells; (c) induction of CYP2E1 and oxidative stress by SFA was observed in all three hepatoma cells. Interestingly, CYP2E1 overexpressing cells (E47 cells) were found to be significantly sensitized towards lipotoxicity; and (d) metabolic and toxic manifestations including altered blood biochemistry, ER stress and CYP2E1 induction were evident in C57BL/6J mice fed with a diet rich in cholesterol and saturated fatty acids (2% cholesterol/12% SFA-HC/HF) for 16 weeks (the model used to confirm the key events taking place in the in vitro system). Histopathological analysis of livers of HC/HF fed mice showed micro- and macro-vesicular steatosis, hepatocyte ballooning, infiltration of neutrophils and prominence of Kupffer cells. In conclusion our data suggest that palmitic acid alters lipid metabolism, causes oxidative stress and disturbs the intracellular Ca2+ balance that terminates in CYP2E1 induction, ER stress and lipoapoptosis.