Antioxidative activity and cytotoxicity of four different flavonoids for dermal applications

Four different flavonoids (phloretin, phlorizin, naringenin and naringin) were evaluated in terms of antioxidant activity. Their ability in permeating porcine skin and retention in skin was also tested. The permeated amount was evaluated for cytotoxic and hemolytic properties. In vitro percutaneous absorption through excised porcine skin was studied with Franz-type diffusion cells. Antioxidant activity was measured with a system employing rat liver microsomes, followed by thiobarbituric acid reacting substances (TBARS)-test. Hæmolytic activity was analyzed with rat blood and cytotoxicity was evaluated using MTT and the BrdU test using L-929 cells. The studies demonstrated distinct antioxidative properties for all flavonoids in a concentration of 1% (w/w), which correlated with the amount of the applied hydroxyethylcellulose (HEC) hydrogels. The aglyca phloretin and naringenin exerted a significantly higher antioxidative activity than the glycosides phlorizin and naringin. All tested flavonoids permeated porcine skin and could be retained. The tested amounts showed, on the one hand, no hemoglobin release and, on the other, no relevant cytotoxicity. Phloretin, phlorizin, naringenin and naringin featured a high antioxidative effect without cytotoxic side effects. Therefore, flavonoids per se as non-toxic plant components may be excellent candidates for skin formulations to prevent photo-aging and photo-damaging.