Rice Protein Exerts Endogenous Antioxidant Capacity via Methionine Sulfoxide Reductase and the Nrf2 Antioxidant System Independent of Age

The major aim of this study was to investigate the effect of rice protein (RP) on the activation of endogenous antioxidant defense in growing and adult rats. After 2 weeks, RP activated nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2) by suppressing Kelch-like ECH-associated protein 1 (Keap1) and Cullin 3 (Cul3) in growing and adult rats. Compared with casein, the upregulation of antioxidant responsive element (ARE)-driven antioxidant expression levels (glutamate cysteine ligase catalytic subunit, glutamate cysteine ligase modulatory subunit, glutathione synthase, glutathione reductase, glutathione S-transferase, glutathione peroxidase, catalase, superoxide dismutase, heme oxygenase 1, NAD(P)H:quinone oxidoreductase 1) were found in RP groups. Also, RP upregulated methionine sulfoxide reductase (MsrA, MsrB2, and MsrB3) expression levels in growing and adult rats. As a result, RP enhanced endogenous antioxidative capacities to reduce hepatic accumulations of malondialdehyde, protein carbonyl, and reactive oxygen species. This study demonstrates that RP exerts the endogenous antioxidant capacity in growing and adult rats, which is due to stimulating Msr antioxidant expression and activating Nrf2-ARE pathway. Results suggest that the antioxidant activity induced by RP is independent of age.