Radical scavenging activities of Tyr-, Trp-, Cys- and Met-Gly and their protective effects against AAPH-induced oxidative damage in human erythrocytes

• Tyr- and Trp-Gly quenched ABTS+ and ROO most efficiently, followed by Cys-Gly.
• Met-Gly showed moderate scavenging activity towards ROO but was inert to ABTS+.
• These dipeptides could protect erythrocytes against AAPH-induced oxidative damage.
• The protective effects decreased in the order of Trp-, Tyr-, Met- and Cys-Gly.
• Dipeptides protected oxidized erythrocytes by acting as direct radical scavengers.

Radical scavenging activities of Tyr-, Trp-, Cys- and Met-Gly and their protective effects against AAPH-induced oxidative damage in erythrocytes were evaluated in this study. This damage includes hemolysis, oxidation of hemoglobin, formation of MDA and the depletion of glutathione (GSH) and catalase (CAT). Results showed that Tyr- and Trp-Gly could quench the radicals effectively in ABTS and ORAC assays with TE (Trolox equivalent) values of more than 1.0 μmol TE/μmol, followed by Cys- and Met-Gly. All these dipeptides could protect erythrocytes against AAPH-induced hemolysis in a dose-dependent manner. They could also significantly (p < 0.05) retard the oxidation of hemoglobin and depletion of GSH in erythrocytes. The protective effects of these dipeptides decreased in the following order: Trp-Gly > Tyr-Gly > Met-Gly > Cys-Gly, which were consistent with their peroxyl radical scavenging activities. It suggested that these dipeptides might protect erythrocytes against AAPH-induced oxidative damage, mainly by acting as the direct radical scavengers.