Capsaicin Attenuates Oleic Acid-Induced Lipid Accumulation via the Regulation of Circadian Clock Genes in HepG2 Cells

As the major component in red chili peppers, capsaicin is useful in the prevention of lipid metabolism disorders. In this study, the attenuation effect of capsaicin on oleic acid (OA)-induced lipid accumulation in HepG2 cells was evaluated with respect to circadian clock gene expressions. Lipid profiles, including triacylglycerols, total cholesterols, high-density lipoproteins, low-density lipoproteins, and aspartate aminotransferase content, were measured using enzymatic assay kits. The mitochondrial membrane potential, cellular redox status, and lipid droplet morphology were also determined using different assay kits and staining methods. The mRNA and protein expressions of core circadian clock genes and major lipometabolism-related factors were assessed using RT-qPCR and western blotting. Results showed that 50 μM capsaicin alleviated the circadian desynchrony and inhibited OA-induced ROS overproduction (from 166.44 ± 12.63% to 119.90 ± 5.43%) and mitochondrial dysfunction (from 0.60 ± 0.08 to 0.83 ± 0.09, represented by the red/green fluorescence ratio) in HepG2 cells. The amelioration effect of capsaicin on OA-induced lipid accumulation was weakened after Bmal1-knockdown, demonstrating that the rhythmic expression of the circadian clock gene is involved in the regulation process of capsaicin in lipid metabolism.