Inhibitory effects of thiol-containing drugs on erythrocyte oxidative damages investigated with an improved assay system.

The involvement of oxygen-derived free radicals and other oxidant species in numerous physiopathological processes makes it necessary to develop suitable analytical systems to study their effects and also to assess the antioxidant activity of endogenous and exogenous compounds. In this respect, the properties of three selected thiol-containing drugs (Captopril, N-acetylcysteine and its lysine salt Nacystelyn, a newly developed mucoactive agent) and of reference compounds were examined in a lipid peroxidation model using human red blood cells (RBC) as biological substrate. The thermolabile azo-compound 2,2'-azobis-2-amidinopropane dihydrochloride (AAPH) served for the generation of an oxidative stress and the determination of the extent of RBC haemolysis was recorded. Experimental conditions were developed and optimised to ensure the stability and reproducibility of the system and to establish complete dose-response relationships in order to determine relevant pharmacological parameters. Actually, the AAPH/haemolysis system shrewdly combined with a procedure to measure the extent of haemolysis in which all common haemoglobin derivatives released following haemolysis are converted to cyanomethaemoglobin, allowed the assessment of the antioxidant activity of most investigated drugs. Precision was also improved by considering readings at 50% haemolysis (T(50)). The following sequence was obtained for the antioxidant properties of investigated drugs: uric acid>Trolox>ascorbic acid>N-acetylcysteine approximately Nacystelyn>Captopril>>l-lysine.