Methionine augments endogenous antioxidant capacity of rice protein through stimulating MSR antioxidant system and activating Nrf2-ARE pathway in growing and adult rats.

To elucidate the influence of methionine on the endogenous antioxidant activity of rice protein (RP), growing and adult rats were fed with RP and methionine-supplemented RP (RM). After 2 weeks feeding, hepatic contents of ROS were significantly reduced by RP and RM. The endogenous antioxidant responses were induced by RP and increased by RM, in which methionine sulfoxide reductases (MsrA, MsrB2, MsrB3) expression and glutathione synthesis were uniformly stimulated and up-regulated with increasing consumption of methionine. With the intake of RP and RM, Nrf2 was activated through depressing Keap1 and Cul3, resulting in the up-regulation of antioxidant-responsive element (ARE)-driven antioxidant expressions (GCLC, GCLM, CAT, SOD, HO-1, NQO1) with increasing dietary level of methionine. The present study demonstrates that methionine can augment the endogenous antioxidant activity of rice protein, which is primarily attributed to stimulating methionine sulfoxide reductases expression and enhancing glutathione synthesis via Nrf2-ARE pathway. Results suggest that the methionine availability might play a key role in inducing and augmenting the endogenous antioxidant response exerted by rice protein, which is independent of age. [ABSTRACT FROM AUTHOR]