ANTIOXIDANT ACTIVITY OF 5-AMINOSALICYLIC ACID AGAINST LIPID-PEROXIDATION IN THE PRESENCE OF VITAMIN-C AND VITAMIN-E

It is now recognized that the antioxidant defences in the colonic muco sa from patients with inflammatory bowel disease (IBD) are particularl y low. On account of this we studied the antioxidant capacity of 5-ASA , the first choice therapy in this pathological situation, in combinat ion with the endogenous antioxidants vitamins C (ASC) and E (alpha-toc opherol (alpha-T)) against lipid peroxidation in phosphatidylcholine ( PC) liposomes as a model membrane. The oxidative process was initiated by peroxyl radicals generated at different sites in liposomes by ther mal decomposition of azocompounds. 5-ASA interacts additively with ASC in the protection of membranes against peroxyl radicals generated in the aqueous phase, as evaluated by the oxygen consumption or formation of conjugated dienes. HPLC analysis of 5-ASA indicates that this drug is consumed at a constant rate throughout the oxidation reaction, but in the presence of ASC there is a lag phase of its consumption, denot ing that ASC affords an efficient protection to 5-ASA. On the other ha nd, 5-ASA and ASC cooperate, in an additive way, in the protection of alpha-T. When the oxidation starts within the membrane, alpha-T is the preferential target of peroxyl radicals, but 5-ASA and ASC also inter act additively in sparing of alpha-T, increasing not only the inhibiti on period of oxidation reaction, but also decreasing significantly the rate of alpha-T consumption. (C) 1998 Elsevier Science B.V. All right s reserved.