Prooxidant and antioxidant properties of Trolox C, analogue of vitamin E, in oxidation of low-density lipoprotein

Abstract

Trolox C (Trolox), a water-soluble analogue of vitamin E lacking the phytyl chain, was investigated with respect to its effect on the oxidation of low-density lipoprotein (LDL). Trolox was added at different time points of LDL oxidation induced by Cu²⁺ and aqueous peroxyl radicals. In the case of Cu²⁺ -induced LDL oxidation, the effect of Trolox changed from antioxidant to prooxidant when added at later time points during oxidation; this transition occurred whenever α-tocopherol was just consumed in oxidizing LDL. Thus, in the case of Cu²⁺-dependent LDL oxidation, the presence of lipophilic antioxidants in the LDL particle is likely to be a prerequisite for the antioxidant activity of Trolox.

When oxidation was induced by peroxyl radicals, as a model of metal-independent oxidation, the effect of Trolox was always antioxidant, suggesting the importance of Cu²⁺/Cu⁺ redox-cycling in the prooxidant mechanism of Trolox. Our data suggest that, in the absence of significant amounts of lipophilic antioxidants, LDL becomes highly susceptible to oxidation induced by transition metals in the presence of aqueous reductants.

Keywords:

• Low-density lipoprotein
• lipid peroxidation
• antioxidants
• Trolox
• prooxidant effect