A question in cell culture and dietary studies on protection by flavonoids against conditions such as hepatocyte steatosis is whether effects might be due to phenolic breakdown/digestion products. In HepG2 hepatocytes, treatment with quercetin, cyanidin, or their phenolic breakdown/digestion products (protocatechuic acid, 2,4,6-trihydroxybenzaldehyde, and caffeic acid), starting 2 h prior to oleic acid for 24 h, protected similarly against increases in intracellular lipid and reactive oxygen species and decreased mitochondrial membrane potential. Cyanidin or the phenolic products also protected against decreased mitochondrial content. After preincubation for only 1 h (to limit spontaneous degradation) and removal prior to oleic acid, only the phenolic products protected against decreased mitochondrial content, and without adding oleic acid, only protocatechuic acid and caffeic acid, and less so cyanidin, induced mitochondrial content. The results suggest that phenolic breakdown/digestion products of cyanidin and quercetin contribute to the protective effects in vitro, and perhaps in vivo.
Keywords: flavonoids; mitochondrial biogenesis; mitochondrial membrane potential; phenolic degradation products; steatosis.