Abstract
We examined the inhibitory effects of “group A saponin” and “group B saponin” fractions, which were extracted and separated from soybean seed hypocotyls, on water-soluble 2, 2′-azobis(2-amidinopropane) (AAPH)- and lipid-soluble 2, 2′-azobis(2, 4-dimethylvaleronitrile)(AMVN)-initiated lipid peroxidation reactions that were conducted with mouse liver microsomes. The simultaneous addition of the group A saponin fraction dose-dependently inhibited AAPH- or AMVN-initiated lipid peroxidation in microsomes more strongly than that of the group B saponin fraction. The group A saponin fraction inhibited the AAPH-initiated lipid peroxidation with a lag phase, while it immediately blocked the AMVN-initiated lipid peroxidation. The group A saponin fraction inhibited microsomal AAPH-initiated lipid peroxidation even when added to the reaction mixture after the lag phase period. Microsomes pretreated with the group A saponin fraction showed inhibition of AAPH-initiated lipid peroxidation with a prolonged lag phase, and the saponin fraction-pretreated microsomes showed inhibition of the AMVN-initiated lipid peroxidation in which a lag phase was found. These results indicate that in mouse liver microsomes, the group A saponin fraction from soybean seed hypocotyls, which is present outside and/or near the microsomal membranes, inhibits AAPH-initiated lipid peroxidation by inhibiting the initiation and propagation of this reaction, while it prevents microsomal AMVN-initiated lipid peroxidation mainly by inhibiting the propagation of this reaction. In addition, the present results indicate that the group A saponin fraction can inhibit AAPH- or AMVN-initiated lipid peroxidation in mouse liver microsomes by its presence within the membranes and/or by binding to them.
