抄録
Evidence that vitamin B_2 acts as an antioxidant has been provided by the following in vitro and in vivo experiments : When a fat-soluble riboflavin derivative, riboflavin tetrabutyrate, was added to the peroxidative reaction system comprising linoleic acid and soybean lipoxygenase, its visible absorption spectrum was converted gradually to become like that of its reduced form and the isoalloxazine nucleus trapped a portion of linoleic acid hydroperoxide at the C(4a) position to form a new flavin derivative, 4a-CH_3(CH_2)_4-4a, 5-dihydroflavin tetrabutyrate, indicating that B_2 acts as a radical trapper. When young male Wistar rats were fed a B_2-deficient diet, the levels of riboflavin, flavin mononucleotide, and flavin adenine dinucleotide (FAD) were decreased, and the activities of the FAD-containing enzyme glutathione reductase in the liver and erythrocytes were also decreased after 2 weeks' feeding. Then the serum lipid peroxide level was increased significantly one week later. If riboflavin was given sufficiently, such a decrease in glutathione reductase activity and increase in lipid peroxides were not observed, indicating that B_2 acts to degrade lipid peroxides in conjunction with the potent lipid peroxide-scavenging enzyme glutathione peroxidase. Platelets from rats fed a linoleic acid hydroperoxide-supplemented diet containing a minute amount of B_2 aggregated significantly, whereas those from rats fed the same diet containing an excess amount of B_2 turned to the normal level of aggregation. When oxidized corn oil was administered to rats, peripheral blood flow decreased in spite of treatment with α-tocopherol, and the flow increased by the administration of the fat-soluble riboflavin derivative in dose-dependent manner. At that time, plasma tocopherol level increased in proportion to the concentration of the administered riboflavin derivative.
