Peroxide dependent and independent lipid peroxidation: site-specific mechanisms of initiation by chelated iron and inhibition by alpha-tocopherol

Abstract

Peroxidation of linoleic acid (LA) was catalyzed by Fenton reagent (H2O2 and Fe2+) in positively charged tetradecyltrimethylammonium bromide (TTAB) micelles, but not in negatively charged sodium dodecylsulfate (SDS) micelles. However, more hydroxyl radicals formed via the Fenton reaction were trapped by N-t-butyl-alpha-phenyl-nitrone (PBN) in SDS micelles than in TTAB micelles. Generation of linoleic acid alkoxy (LO) radicals by Fe2+ via reductive cleavage of linoleic acid hydroperoxide (LOOH) resulted in peroxidation of LA and formation of PBN-LO. adducts in SDS micelles, but not in TTAB micelles. This LOOH dependent lipid peroxidation could be catalyzed in TTAB micelles in the presence of a negatively charged iron chelator, nitrilotriacetic acid (NTA). LO radicals formed by the LOOH dependent Fenton reaction were also trapped by PBN at the surface of TTAB micelles in the presence of NTA, but not in its absence. The consumption of a spin probe, 16-(N-oxyl-4,4'-dimethyloxazolidin-2-yl)stearic acid (16-NS) during the LOOH dependent Fenton reaction in the presence of NTA was higher in TTAB micelles of LA than in those of lauric acid (LauA), although the rates and amounts of LO radicals formed in the two types of fatty acid micelles were similar. The rates of 5-NS consumption in LA and LauA micelles were almost the same, and were lower than the rate of 16-NS in LA micelles. NTA-Fe2+ initiated peroxidation of LA in TTAB micelles without a lag time in the presence of LOOH, but after a lag period, peroxidation occurred without LOOH.(ABSTRACT TRUNCATED AT 250 WORDS)