Antioxidant action of thiopalmitic acid on microsomal lipid peroxidation

The antioxidant action of thiopalmitic acid (SH-Pal) was studied in a lipid peroxidation system using microsomes from rat liver. The Fe(II)/ascorbic acid (AsA)-induced lipid peroxidation, as measured by the amount of thiobarbituric acid-reactive substances (TBA-RS), was progressively inhibited by the addition of increasing amounts of SH-Pal. The inhibitory effect of SH-Pal in this experimental system was greater than that of alpha-tocopherol, glutathione (GSH) and palmitic acid. The antioxidative effect was abolished gradually by the addition of increasing amounts of N-ethylmaleimide to the system. Similarly, microsomal lipid peroxidation induced by Fe(III)-ADP/NADPH or CCl4/NADPH was inhibited in a dose-dependent fashion by the addition of SH-Pal. Moreover, SH-Pal was able to reduce 1,1-diphenyl-2-picrylhydrazyl (DPPH). The alpha-tocopherol content of the microsomal lipid peroxidation system decreased rapidly when no SH-Pal was present. However, upon adding SH-Pal (90 microM), the decrease in the alpha-tocopherol content of the assay system was markedly reduced. These findings indicate that SH-Pal acts as an antioxidant and free radical scavenger in lipid peroxidation carried out by rat liver microsomes.