Relationship between effects of phenolic compounds on the generation of free radicals from lactoperoxidase-catalyzed oxidation of NAD(P)H or GSH and their DPPH scavenging ability

Abstract

The influence of various phenolic compounds on the lactoperoxidase LPO/hydrogen peroxide (H2O2)-catalyzed oxidation of biochemical reductants such as reduced β-nicotinamide adenine dinucleotide (NADH), reduced β-nicotinamide adenine dinucleotide phosphate (NADPH) or reduced glutathione (GSH) was investigated by electron spin resonance (ESR) spectroscopy. Micromolar quantities of phenolic compounds such as 17 β-estradiol, phenol, and p-chlorophenol enhanced the LPO/H2O2-catalyzed oxidation of NAD(P)H or GSH to generate a large amount of superoxide radical (O2.-) or glutathione thiyl radical (GS.), while, phenolic compounds such as quercetin and Trolox C greatly suppressed the generation of O2.- and GS.. In order to elucidate the effects of phenolic compounds on the generation of O2.- and GS., their quenching activities for a stable radical, 1.1-diphenyl-2-picrylhxydrazyl (DPPH), were investigated by ESR spectroscopy. 17 β-Estradiol, phenol, and p-chlorophenol showed very weak scavenging activities for DPPH, but quercetin and Trolox C showed strong activities. This suggests that the ability of phenolic compounds to enhance LPO/H2O2-catalyzed oxidation of NAD(P)H of GSH relates inversely to their ability to quench DPPH. That is, phenolic compounds having weak quenching activity against DPPH may enhance the LPO/H2O2-catalyzed oxidation of NAD(P)H of GSH to generate a large amount of O2.- or GS..