Lipid peroxidation of colonocyte membranes

Effects of various oxidants on the colonic membrane lipid peroxidation have been studied in rats. 2,2-Azobis (2-amidinopropane) dihydrochloride (ABAP), which generates free radicals by thermal decomposition, induced peroxidation as judged by the formation of conjugated diene, malondialdehyde (MDA), and depletion of arachidonic acid. Exposure to other oxidants which require free iron for peroxidation was ineffective. Alpha tocopherol level was not altered on exposure to various oxidants except with ABAP which depleted its level in these membranes. Exposure of the membranes to both ABAP and xanthine-xanthine oxidase (X-XO) decreased total protein thiols, whereas other oxidants had no significant effect. Isolated colonocyte membranes were found to contain considerable amount of nonesterified fatty acids as part of the total lipids and removal of free fatty acids from the membrane using fatty acid-free albumin made the membranes susceptible to iron-induced free radical generation and lipid peroxidation. These studies suggest that colonocytes are possibly protected from lipid peroxidation by the free fatty acids associated with the membrane.