Effects of flavonoid antioxidants on oxidative stress in vivo.

摘要

Flavonoids are non-nutrient plant antioxidants associated with the protective effect of fruits and vegetables on chronic diseases in which oxidative stress is present. It has been hypothesized that the antioxidant properties of flavonoids in vitro mediate the beneficial effects observed in vivo . In these studies, a model of oxidative stress, created by feeding rats a diet deficient in vitamin E and selenium (Se), was used to test whether the in vitro antioxidant properties of multiple flavonoids can be extrapolated to provide antioxidant protection in vivo by scavenging free radicals, interacting with antioxidant nutrients, or boosting the endogenous antioxidant defense system. In initial studies only epigallocatechin-3-gallate (EGCG) at 30 mg/kg of diet partially protected rats from oxidative stress. Consumption of naringenin and hesperetin resulted in lower total aldehydes and higher liver coenzyme Q (CoQ) concentrations. Because the concentrations used might have been a potential limiting factor in observing complete protection, in the second set of studies increasing concentrations of either naringenin or EGCG were tested for antioxidant activity under low (Lox) and high (Hox) oxidative conditions in vivo. The results confirmed that EGCG at 30 mg/kg of diet provided partial protection, but this effect was not replicated at higher EGCG concentrations.;In Lox rats, EGCG showed evidence of antioxidant activity by decreasing the amounts of F2-isoprostanes and shifting liver CoQ status towards the reduced state. Naringenin consumption was not associated with antioxidant protection in Hox, nor was a prooxidant effect observed in Lox rats. Finally, increasing concentrations of either tested flavonoid led to higher liver quinone reductase (NQO1) activities only in Hox animals. It is proposed that this effect resulted from the accumulation of flavonoid metabolites with stronger NQO1 gene induction abilities generated only under Hox conditions, but this hypothesis needs to be tested. In conclusion, under the present model of vitamin E and Se deficiency, only EGCG exhibited antioxidant protection in vivo, and further studies should be conducted to evaluate the metabolism of flavonoids under oxidative stress conditions as these critical changes could affect their potential properties as antioxidants in vivo.