Purification, structural identification and in vivo antioxidant activity of Douchi antioxidant peptides

Abstract In this study, antioxidant peptides were isolated and purified from Tongchuan Douchi through ultrafiltration and gel chromatography. To further assess the in vivo antioxidant activity of the fraction (F3) which had a high DPPH radical scavenging rate, 60 male mice were randomly divided into 6 groups (normal, positive control, model group, and low-, medium-, and high-dose group), and immunosuppression was induced via intraperitoneal cyclophosphamide injection. Hepatorenal function was evaluated by determining organ coefficients and oxidative stress markers including total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) levels. The results showed that 10 peptides (LLLPH, KDFPPR, DDFFL, ADFYNPK, IIGGI, DTPMIG, SVVDM, LVSPP, C(+57.02)ADLF, and VIVEL) which are rich in hydrophobic amino acids were identified in the fraction F3 by LC-MS/MS. The quantitative analysis of the animal experiments demonstrated that administration of medium and high doses of the F3 fraction significantly ( P < 0.05) improved the liver, kidney, and spleen coefficients in immunosuppressed mice compared to the model group. The high-dose F3 administration significantly increased the SOD and GSH-Px activities while reducing the MDA levels in both hepatic and renal tissues of mice. These results revealed that Douchi-derived peptides can mediate antioxidant effects in vivo by both scavenging free radicals and activating endogenous antioxidant enzymes.