Complex I inhibitor decreases ROS level. HepG2 cells were pretreated with the inhibitor of mitochondrial complex I- rotenone (0.5 μM) for 30 minutes, and then exposed to 0.7 mM palmitate for 24 h. After the treatment, the cells were then washed with PBS, and exposed to 5 μM AM-DCFDA in DMEM for 30 min, following which the cells were washed again. The fluorescence was read by exciting the cells at 488 nm and reading the emission at 527 nm. Data presented as average +/- s.d. of n = 9 from three independent experiments. *, significantly higher than the control.