There are conflicting reports on the antioxidant activity of hispidulin. Antioxidant activity of hispidulin was evaluated using assays of ABTS• reduction, ferric ion reducing antioxidant power (FRAP) assay, DPPH reduction assay, and protection of erythrocyte membranes against lipid peroxidation and protein thiol oxidation. ABTS• reduction assay pointed to the involvement of all three phenol groups of hispidulin in ABTS• reduction. The reactivity of hispidulin in the FRAP assay and DPPH reduction assay was low (0.09 and 0.019 of the reactivity of Trolox). However, hispidulin was effective in protection against erythrocyte membrane lipid peroxidation and highly effective in protection against erythrocyte membrane protein thiol group oxidation (more effective than Trolox). These results point to the necessity of caution in extrapolating the antioxidant activity evaluated in simple cell-free systems on more complex systems.
Keywords: ABTS; DPPH; FRAP; Hispidulin; antioxidant; lipid peroxidation; thiol groups.