Antioxidant activity of 5-aminosalicylic acid against lipid peroxidation in the presence of vitamins C and E

Abstract

It is now recognized that the antioxidant defences in the colonic mucosa from patients with inflammatory bowel disease (IBD) are particularly low. On account of this we studied the antioxidant capacity of 5-ASA, the first choice therapy in this pathological situation, in combination with the endogenous antioxidants vitamins C (ASC) and E ([alpha]-tocopherol ([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 thermal 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, denoting that ASC affords an efficient protection to 5-ASA. On the other hand, 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 interact additively in sparing of [alpha]-T, increasing not only the inhibition period of oxidation reaction, but also decreasing significantly the rate of [alpha]-T consumption.