Effect of interaction between phenolic compounds and copper ion on antioxidant and pro-oxidant activities

► We conducted ESR measurements for the increase in reactive oxygen species in relation to their structure and interaction with copper ion. ► ESR method could detect OH, which is not affected by copper ion. ► Ortho-dihydroxyl groups that can chelate with copper induce the greatest pro-oxidant activity. Phenolic compounds are widely used in food and cosmetics to prevent undesirable oxidation. On the other hand, phenolic compounds are also strong reducing agents and under in vitro conditions and in the presence of copper ion, they can act as pro-oxidants. In this study, we conducted electron spin resonance (ESR) measurements for the increase in reactive oxygen species (ROS) in relation to their structure and interaction with transition metals. Moreover, the antioxidant activity was assessed with the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, and the pro-oxidant effect of phenolic compounds on DNA damage was assessed by measuring 8-hydroxy-2′-deoxyguanosine (8-OHdG), which is effectively formed during oxidative damage. In conclusion, ortho-dihydroxyl groups that can chelate with Cu2+ induce the greatest pro-oxidant activity. Moreover, the interaction between phenolic compounds and copper induced to H2O2. The obtained results indicated that ROS participated in oxidative DNA damage induced by phenolic compounds in the presence of Cu2+.