INFLUENCE OF HIGH MOLECULAR WEIGHT THIOLS ON THE REDOX CATALYTIC CHEMISTRY OF EBSELEN IN ACIDIC pH IN VITRO.

Abstract

Recent evidence suggests that the translation of the chemical model of glutathione peroxidase (GPx) mimicry of ebselen in simple biological model in vitro involves oxidation of available non-protein or protein thiols that are critical to the activities of some key sulfhydryl enzymes. However, this hypothesis is rather speculative and yet to be fully clarified and thus still very open. In the present study, the effect of ebselen on lipid peroxidation was tested in the presence or absence of various prooxidants (Fe2+, 10 μM; sodium nitroprusside, 3 μM; H2O2, 1mM; 3-nitropropionic acid, 2 mM; or quinolinic acid, 2 mM) with or without the alkylating agents, iodoacetamide (IA, 2 mM) and diamide (DA, 100 μM). In addition, the possible inhibitory effect or otherwise of ebselen on formation of cerebral and hepatic thiobarbituric acid reactive substances was also tested at different acidic pH range (4.4 – 7.4). Finally, the likely involvement of key thiols of cerebral sodium pump and hepatic delta aminolevulinic acid dehydratase in the GPx mimetic catalytic mechanism of ebselen was also evaluated. The results revealed that irrespective of the prooxidant employed to initiate lipid peroxidation or pH of the incubation system, ebselen exerted marked inhibitory effect on the lipid peroxidation process and this was characterized by decreased formation of aldehydic products of lipid peroxidation. However, the alkylating agents [IA and DA] profoundly counteracted the inhibitory effect of ebselen on the lipid peroxidation process regardless of the prooxidant employed or the pH of the reacting system. Furthermore, the results also showed that the inactivation of the sulfhydryl enzymes, cerebral sodium pump and hepatic δ-ALAD, by the alkylating agents was marked with concomitant decrease in the antioxidant potency of ebselen. From the foregoing, considering the fact that the chemical model of the GPx mimicry of ebselen is integrally linked with availability of thiols, consequently, it is rational to speculate that aside free thiols, the essential thiols of the cerebral sodium pump and hepatic δ-ALAD may be implicated in the GPx-like antioxidant catalytic mimicry of ebselen