Modulation of liposomal lipid peroxidation in presence of nickel by incorporation of alpha-tocopherol in the bilayer.

alpha-Tocopherol is a well-known membrane associated chain-breaking phenolic antioxidant which functions as a trap for peroxyl and other free radicals and thus inhibits lipid peroxidation of membranes. Antioxidative effect of alpha-tocopherol when incorporated in liposomes was examined by the generation of Thiobarbituric acid (TBA) reacting species in the presence of nickel. The incorporation of alpha-tocopherol in the lipid bilayer resulted in the enhancement of lipid peroxidation at low concentration (1.0 mg) but at higher concentration (2.5 and 5.0 mg) considerably reduced the enhancement in lipid peroxidation of liposomes in the presence of nickel. When alpha-tocopherol was added (unincorporated) to liposomes in the presence of nickel, enhancement in lipid peroxidation was observed compared to nickel alone. Thus the antioxidative effect of alpha-tocopherol in the liposomes may depend on its mode of incorporation in the lipid bilayer.