POSSIBLE INVOLVEMENT OF HYDROPHILIC THIOLS OF LACTATE DEHYDROGENASE ON THE GLUTATHIONE PEROXIDASE-LIKE CATALYTIC MECHANISM OF DIPHENYL DISELENIDE.

Abstract

The antioxidant mechanism of action of diphenyl diselenide, an organoselenium, is largely linked with its glutathione peroxidase (GPx) activity. However, the precise relationship between the GPx-mimicry of diphenyl diselenide (DPDS) and its thiol utilization in eliciting their antioxidant activity is yet to be fully clarified and thus still open. The present study sought to investigate the influence of thiols on the antioxidant chemistry of DPDS in different in vitro models of oxidative stress involving phospholipids and tissue homogenates. The influence of thiols on the antioxidant action of DPDS against Fe2+-induced deoxyribose degradation was also investigated. Furthermore, studies on the interaction of diphenyl diselenide (DPDS) with thiols of lactate dehydrogenase (LDH), a sulphydryl enzyme, from renal tissue was also investigated under in vitro condition. In doing this, iodoacetamide, a thiol oxidant, was employed in the study to examine the contribution of thiols of lactate dehydrogenase in the glutathione peroxidase mimetic properties of diphenyl diselenide. The results show that DPDS markedly inhibited the formation of TBARS induced by Fe2+ in the absence of iodoacetamide and no inhibition was observed in its presence. Also, DPDS distinctly prevented deoxyribose degradation in the presence of exogenous thiols but not in the absence of thiols. Moreso, DPDS inhibited Fe2+-induced TBARS formation in phospholipid extract in the presence and absence of thiols. Furthermore, both iodoacetamide and DPDS significantly inhibited the activity of the thiol containing enzyme, LDH. The inhibition by DPDS was prevented but not reversed by a dithiol, DTT, while inhibition by iodoacetamide was neither prevented nor reversed by the dithiol. Summarily, the presence of thiol is evidently a critical requirement for DPDS to effect its antioxidant action against lipid peroxidation in tissue homogenate as well as deoxyribose degradation. However, additional experimental data are needed to clarify the possible involvement of thiols in the antioxidant activity of DPDS against oxidant-induced phospholipid assault. Furthermore, considering the fact that both DPDS and iodoacetamide inhibited the activity of the sulphydryl enzyme LDH, it is rational to speculate that thiols play a critical role in the antioxidant chemistry of diphenyl diselenide and that DPDS possibly utilizes important thiols on lactate dehydrogenase in carrying out its GPx mimicry antioxidant action against lipid peroxidation in rat kidney homogenate.