INFLUENCE OF THIOL ON REACTION MECHANISM SWITCHING OF ORGANOSELENIUM IN in vitro MODELS OF OXIDATIVE STRESS

Abstract

The antioxidant mechanism of action of organoseleniums in rat’s brain is largely linked with either their glutathione peroxidase (GPx) or peroxiredoxin mimetic activities. However, the precise molecular dynamics between the GPx-mimicry of organoseleniums and thiol utilization is yet to be fully clarified and thus still open. Herein, the influence of monothiols (glutathione (GSH) and cysteine (CYS)) and dithiothreitol (DTT) on the antioxidant action of’ both ebselen (EBS) and diphenyl diselenide (DPDS) against oxidant-induced cerebral lipid peroxidation and deoxyribose degradation were investigated in vitro. Furthermore, the critical inhibitory concentrations of DPDS and EBS on the activity of the sulphydryl enzyme, δ-aminolevulinic acid dehydratase (δ-ALAD) were also investigated. Antioxidant assay carried out were Free radical scavenging property, Ferric Reducing property, Deoxyribose degradation and production of thiobarbituric acid reactive substances (TBARS). Glutathione peroxidase mimetic assay (GPx) of both organoselenium (Ebselen and diphenyl diselenide) was also tested in the presence of mono and dithiols. The rate of thiol disappearance was measured at 412nm. Hepatic ð -ALA-D activity was assayed by measuring the rate of product [porphobilinogen (PBG)] formation. The results showed that both organoseleniums exhibited similar antioxidant and toxicological effects. They markedly inhibited lipid peroxidation (at ≥ 42 μM for both DPDS and EBS) either in the presence or absence of the thiols, whereas they inhibited deoxyribose degradation only in the presence of DTT. In addition, although both organoseleniums showed neither free radical scavenging nor reducing properties either in the presence or absence of the thiols, they exhibited strong classical GPx mimetic activities in the presence of either the mono- and di-thiols. Conversely, under in vitro conditions, both organoseleniums inhibited the thiol containing enzyme, δ-ALAD (≥ 10 μM) which were either prevented or reversed by DTT. In addition, the presence of the dithiol appears to be a critical requirement for the organoseleniums to effect their antioxidant action against deoxyribose degradation and not lipid peroxidation. Consequently, it is rational to partly conclude that both DPDS and EBS possibly utilize available thiols on sulphydryl proteins to effect their GPx mimicry antioxidant action against lipid peroxidation in rat brain homogenate