Scavenging Activities of α-, β- and γ-Thujaplicins against Active Oxygen Species

Abstract

α-, β- and γ-Thujaplicins are three-tropolone-related compounds purified from the woods of Chamaecyparis obtusa SIEB. et ZUCC. and Thuja plicata D. DON. Based on our recent finding that β-thujaplicin inhibits the formation of sunburn cells (SBC), which appear in the epidermis after UVB irradiation, we have speculated that β-thujaplicin is a potent scavenger against active oxygen species. ESR spin-trapping, chemiluminescence and fluorescence methods, and cyclic voltammetry were used to evaluate the abilities of β-thujaplicin and its isomers, α- and γ-thujaplicins, as scavengers of five kinds of active oxygen species such as superoxide anion radicals, hydroxyl radicals, singlet oxygens, tert-butyl peroxyl radicals and hydrogen peroxides. These compounds were found to have comparable inhibitory effects of hydroxyl radicals generated by the Fenton reaction and high scavenging activities against tert-butyl peroxyl radicals as compared with those of l-ascorbic acid and dl-α-tocopherol, and α-thujaplicin was found to have the highest activity against hydrogen peroxides among the thujaplicins.However, the effects of these compounds on superoxide anion radicals and singlet oxygens were less than those of l-ascorbic acid and dl-α-tocopherol. These facts suggest that thujaplicins have effective antioxidant ability. This ability is thought to be due in part to the chelating ability and redox potential of the compounds, which in turn are related to the prevention of UV-induced photo-damage in vivo.