Anti- and prooxidant effects of chronic quercetin administration in rats.

The present study was performed to investigate the effects of chronic administration of quercetin on lipid peroxidation and glutathione concentration in rat liver. Male Sprague-Dawley rats were divided into two groups, one of which was fed a normal diet and the other a vitamin E-free diet. Each of these groups was divided further into three subgroups and treated with quercetin administered orally at either 2 or 20 mg/day or with vehicle for 4 weeks. The concentrations of alpha-tocopherol in serum and liver increased following quercetin treatment, and these increases were significantly greater in rats maintained on a vitamin E-free diet. Quercetin significantly decreased the concentration of malondialdehyde (an indicator of lipid peroxidation) in the liver and this decrease was more pronounced in vitamin E-deprived rats than in those maintained on a normal diet (55-60% and 25-35% decrease in malondialdehyde concentrations, respectively). Quercetin treatment decreased the glutathione concentration and glutathione reductase activity (40 and 34%, respectively) in the liver significantly and to a similar extent in vitamin E-deprived and -undeprived rats. Collectively, these results suggest that quercetin may act not only as an antioxidant, but also as a prooxidant in rats.