Inhibitory Effects of Pentamethine Trinuclear Cyanine Dyes on ADP/Fe²⁺-Induced Lipid Peroxidation in Rat Liver Mitochondria : Changes in the Mode of Action with the Hydrophobic Nature of the Dyes

Abstract

The effects of various pentamethine trinuclear cyanine dyes, each of which has three alkyl chains, on ADP/Fe²⁺-induced lipid peroxidation in rat liver mitochondria were examined. Although the dye having the shortest -C₂H₅ chains (tri-S-C₂(5)) did not show any appreciable effect, the dyes having -C₄H₉ (tri-S-C₄(5)), -C₇H₁₅ (tri-S-C₇(5)), and -C₁₂H<25> (tri-S-C₁₂(5)) chains significantly inhibited lipid peroxidation, the most potent inhibitory effect being observed with tri-S-C₇(5). The mode of antiperoxidation effect of the dyes was dependent on the length of the alkyl chains. The relatively hydrophilic dye tri-S-C₄(5) was suggested to scavenge radicals more efficiently at or near the membrane surface rather than in the interior of the lipid membrane, whereas the more hydrophobic dye tri-S-C₇(5) was suggested to scavenge radicals efficiently in the membrane rather than at or near the membrane surface. The hydrophilic/hydrophobic balance of the dye was found to regulate the site of action of the dyes.