ヒト赤血球膜中のα-トコフェロールの酸化に対するケルセチンとアスコルビン酸の効果 : ケルセチンの抗酸化作用機構の解析

Abstract

The effects of quercetin, one of flavonoids, and ascorbate on the photooxidation of α-tocopherol (α-TH) and the lipid photoperoxidation in blood cell membranes in the presence of hematoporphyrin (HP) as a photosensitizer were investigated. Based on the results obtained, antioxidative function of quercetin was discussed. 1. α-TH in human blood cell membranes was oxidized during illumination. Quercetin inhibited the photooxidation and was oxidized itself by the inhibition. 2. Superoxide anion and hydrogen peroxide did not participate in the photooxidation of α-TH in human blood cell membranes, while singlet oxygen partially did. It was suggested that α-TH was oxidized by excited HP itself and lipidic radicals which were generated in the redox reactions between unsaturated fatty acids and excited HP. 3. Quercetin inhibited the photooxidation of α-TH by removing excited HP and by reducing α-tocopherol radical (α-T・), which was generated during inhibition of lipid peroxidation, to α-TH and by scavenging lipidic radicals generated during lipid peroxidation. 4. Quercetin cooperated with ascorbate in the inhibition of α-TH photooxidation and lipid photoperoxidation. The cooperation can be considered to be due to reducing oxidized intermediate of quercetin by ascorbate and chelating ions by quercetin to inhibit the prooxidative function of ascorbate. 5. That quercetin is effective on stopping bleeding in capillary bleeding disease can be considered to be due to scavenging active oxygen and lipidic radicals by the flavonoid, reducing α-T・ to reproduce α-TH, and cooperating with ascorbate to increase the antioxidative function of the flavonoid.