Possible involvement of membrane lipids peroxidation and oxidation of catalytically essential thiols of the cerebral transmembrane sodium pump as component mechanisms of iron-mediated oxidative stress-linked dysfunction of the pump's activity.

The precise molecular events defining the complex role of oxidative stress in the inactivation of the cerebral sodium pump in radical-induced neurodegenerative diseases is yet to be fully clarified and thus still open. Herein we investigated the modulation of the activity of the cerebral transmembrane electrogenic enzyme in Fe(2+)-mediated in vitro oxidative stress model. The results show that Fe(2+) inhibited the transmembrane enzyme in a concentration dependent manner and this effect was accompanied by a biphasic generation of aldehydic product of lipid peroxidation. While dithiothreitol prevented both Fe(2+) inhibitory effect on the pump and lipid peroxidation, vitamin E prevented only lipid peroxidation but not inhibition of the pump. Besides, malondialdehyde (MDA) inhibited the pump by a mechanism not related to oxidation of its critical thiols. Apparently, the low activity of the pump in degenerative diseases mediated by Fe(2+) may involve complex multi-component mechanisms which may partly involve an initial oxidation of the critical thiols of the enzyme directly mediated by Fe(2+) and during severe progression of such diseases; aldehydic products of lipid peroxidation such as MDA may further exacerbate this inhibitory effect by a mechanism that is likely not related to the oxidation of the catalytically essential thiols of the ouabain-sensitive cerebral electrogenic pump.

In vitro glutathione peroxidase mimicry of ebselen is linked to its oxidation of critical thiols on key cerebral suphydryl proteins - A novel component of its GPx-mimic antioxidant mechanism emerging from its thiol-modulated toxicology and pharmacology.

The antioxidant mechanism of ebselen in rats brain is largely linked with its glutathione peroxidase (GPx) rather than its peroxiredoxin mimicry ability. However, the precise molecular dynamics between the GPx-mimicry of ebselen and thiol utilization is yet to be fully clarified and thus still open. Herein, we investigated the influence of dithiothreitol (DTT) on the antioxidant action of ebselen against oxidant-induced cerebral lipid peroxidation and deoxyribose degradation. Furthermore, the critical inhibitory concentrations of ebselen on the activities of sulphydryl enzymes such as cerebral sodium pump, δ-aminolevulinic acid dehydratase (δ-ALAD) and lactate dehydrogenase (LDH) were also investigated. We observe that ebselen (at ≥42 µM) markedly inhibited lipid peroxidation in the presence and absence of DTT, whereas it inhibited deoxyribose degradation only in the presence of DTT. Furthermore, under in vitro conditions, ebselen inhibited the thiol containing enzymes; cerebral sodium pump (at ≥40 µM), δ-ALAD (≥10 µM) and LDH (≥1 µM) which were either prevented or reversed by DTT. However, the inhibition of the activities of these sulphydryl proteins in diabetic animals was prevented by ebselen. Summarily, it is apparent that the effective in vitro inhibitory doses of ebselen on the activity of the sulphydryl proteins are far less than its antioxidant doses. In addition, the presence of DTT is evidently a critical requirement for ebselen to effect its antioxidant action against deoxyribose degeradation and not lipid peroxidation. Consequently, we conclude that ebselen possibly utilizes available thiols on sulphydryl proteins to effect its GPx mimicry antioxidant action against lipid peroxidation in rat brain homogenate.

Gallic acid modulates cerebral oxidative stress conditions and activities of enzyme-dependent signaling systems in streptozotocin-treated rats.

Redox imbalances and altered signaling processes in the brain are characteristic features of diabetic complications. Hence, the present study therefore sought to evaluate the effect of gallic acid (GA) on disturbed redox systems and activity of neurotransmission signaling dependent enzymes such as sodium pump, purinergic enzymes and acetylcholinesterase in diabetic animal models. We observed that GA markedly improves the antioxidant status of diabetic animals. Furthermore, the diminution of the activity of Na(+)/K(+)-ATPase and increased activities of acetylcholinesterase and the purinergic enzymes associated with diabetes progression were reversed to normalcy with the administration of GA in diabetic animals. Hence, we conclude that GA is a potential candidate in the management of neuronal dysfunction that often accompanied complications associated with diabetic hyperglycemia.

Inorganic mercury interacts with thiols at the nucleotide and cationic binding sites of the ouabain-sensitive cerebral electrogenic sodium pump.

The molecular events leading to neuronal dysfunction often associated with mercury toxicity can be complex and is yet to be fully elucidated. Hence, the present study sought to evaluate the interaction of inorganic mercury (Hg(2+)) with the ouabain-sensitive electrogenic pump in partially purified mammalian brain membrane preparations. The results show that Hg(2+) significantly inhibited the transmembrane enzyme in a concentration dependent manner. In addition, Hg(2+) exerts its inhibitory effect on the activity of the enzyme by interacting with groups at the adenosine triphosphate (ATP), Na(+) and K(+) binding sites. However, preincubation of the enzyme with exogenous monothiols, cysteine, prevented the inhibition of Hg(2+) on the pump's activity suggesting that Hg(2+) may be interacting with the thiols at the nucleotide (ATP) and cationic (Na(+) and K(+)) binding sites. In fact, our data show that Hg(2+) oxidizes sulphydryl groups in cysteine in a time dependent fashion in vitro. Finally, we speculate that the small molecular volume of Hg(2+) in comparison with the substrates (ATP, Na(+) and K(+)) of sodium pump, its possibly high reactivity and strong affinity for thiols may account for its high toxicity towards the membrane bound ouabain-sensitive electrogenic pump.

Attachment of rhamnosyl glucoside on quercetin confers potent iron-chelating ability on its antioxidant properties.

The pharmacological essence of the natural addition of rhamnosyl glucoside on quercetin that is commonly found in nature in medicinal plants is rather obscure. The present study therefore sought to compare the antioxidant activities of both compounds by comparing their ability to decolourise DPPH radicals, reduce Fe(3+), chelate Fe(2+), prevent deoxyribose degradation and inhibit hepatic thiobarbituric acid reactive substances induced by both Fe(2+) and sodium nitroprusside. The results show that quercetin is generally a more potent antioxidant than its rhamnosyl glucoside derivative (rutin). However, rutin exerted a more potent iron-chelating ability than quercetin which diminishes in a time dependent fashion suggesting why it exhibited a reduced inhibitory effect on lipid peroxidation and deoxyribose degradation under harsh prooxidant assault than quercetin. Taken together, we speculate that rutin may have been produced initially in plants as a possible defense mechanism for protection and survival under oxidative assaults and where both flavonoids are found to co-exist in nature, there is a possible synergy in their antioxidant actions.

Comparative study on the influence of subcutaneous administration of diphenyl and dicholesteroyl diselenides on sulphydryl proteins and antioxidant parameters in mice.

Although in vitro data from our previous studies show that the antioxidant effect and reactions of both diphenyl diselenide (DPDS) and dicholesteroyl diselenide (DCDS) towards thiol-containing proteins differ considerably, the present study sought to evaluate the interaction of both organodiselenides with thiol-containing proteins in vivo. Mice were injected subcutaneously with DPDS or DCDS previously dissolved in soya bean oil at doses of 0.5 mmol kg⁻¹ body weight for four consecutive days. The activities of delta aminolevulinic acid dehydratase (ALA-D), Na+/K+-ATPase, and isoforms of lactate dehydrogenase (LDH) and catalase were investigated. In addition, the antioxidant status of the mice was determined by measuring the levels of glutathione (GSH), vitamin C (Vit C) and thiobarbituric acid reactive substances. The results show that both diselenides significantly increased the levels of GSH and Vit C but did not markedly alter other antioxidant indices. With respect to the thiol-containing enzymes that were evaluated, DPDS and not DCDS caused a marked reduction in the activities of hepatic ALA-D; however, both diselenides inhibited all isoforms of LDH evaluated. In addition, the activities of cerebral Na+/K+-ATPase were not markedly inhibited by both diselenides, suggesting that this cerebral enzyme may not be a molecular target of organodiselenides toxicity. Taken together, the pharmacological and toxicological chemistry of organoselenium compounds is complex and multifactorial and is dependent on delicate equations which include vehicle solution, animal species and mode of delivery.

Altered pH homeostasis modulates the glutathione peroxidase mimics and other antioxidant properties of diphenyl diselenide.

Recent evidences have shown that the in vivo antioxidant chemistry of organoselenium compounds such as diphenyl diselenide (DPDS) is complex and it is not completely understood. The complexity is partly due to the fact that DPDS is generally thought to exert its antioxidant action by mimicking glutathione peroxidase (GPx) with concomitant utilization of glutathione (GSH) in vitro. In contrast to in vitro data, we recently observed that DPDS increases rather than diminish GSH levels in diabetic models. The present study therefore sought to investigate a possible change in the antioxidant mechanisms of DPDS in changing physiological pH that may be associated with hyperglycaemia. The results show that in all the pHs tested (acidic, neutral or basic), DPDS did not exhibit either free radical scavenging ability or Fe2+ chelating effect. However, DPDS exhibited increasing ability to reduce Fe3+ with increasing pH. On the other hand, the GPx mimic of DPDS was maximal at physiological pH and totally abolished in the acidic medium. Furthermore, we observed that irrespective of the pH of the medium, DPDS significantly inhibited both deoxyribose degradation under H2O2 and Fe2+ assault and lipid peroxidation induced by either Fe2+ or sodium nitroprusside; suggesting that the antioxidant mechanism of DPDS in the acidic medium may not be related to its generally accepted GPx mimic. Taken together, we speculate that the antioxidant mechanism of DPDS against macromolecular damage in biological system is complex and may not be strictly related to its GPx mimic, a mechanism generally regarded as the most important antioxidant mechanism of organoselenium compounds.

Diphenyl diselenide and streptozotocin did not alter cerebral glutamatergic and cholinergic systems but modulate antioxidant status and sodium pump in diabetic rats.

Neuronal malfunction is a characteristic feature of diabetic mellitus. Hence, the present study therefore sought to evaluate the effect of diphenyl diselenide (DPDS) on the antioxidant status, sodium pump, cholinergic and glutamatergic system in the rat brain of streptozotocin (STZ) induced diabetes. The results show that although STZ evoke a significant diminution on the antioxidant status and activity of Na(+)/K(+)-ATPase, the activity of acetylcholinesterase and glutamate uptake and release was not altered. However, DPDS was able to markedly restore the observed imbalance in cerebral antioxidant status and also relieve the inhibition of Na(+)/K(+)-ATPase caused by streptozotocin. Hence, we conclude that DPDS is a potential candidate in the management of neuronal dysfunction that often accompanied complications associated with diabetic hyperglycemia.

Studies on the antioxidant effect and interaction of diphenyl diselenide and dicholesteroyl diselenide with hepatic delta-aminolevulinic acid dehydratase and isoforms of lactate dehydrogenase.

Studies on the interaction of dicholesteroyl diselenide (DCDS) and diphenyl diselenide (DPDS) with hepatic delta-aminolevulinic acid dehydratase (ALA-D) and different isoforms of lactate dehydrogenase (LDH) from different tissues were investigated. In addition, their antioxidant effects were tested in vitro by measuring the ability of the compounds to inhibit the formation of hepatic thiobarbituric acid reactive species (TBARS) induced by both iron (II) and sodium nitroprusside (SNP). The results show that while DPDS markedly inhibited the formation of TBARS induced by both iron (II) and SNP, DCDS did not. Also, the activities of hepatic delta-aminolevulinic acid dehydratase (ALA-D) and different isoforms of lactate dehydrogenase (LDH) were significantly inhibited by both DPDS and DCDS. Moreover, we further observed that the in vitro inhibition of different isoforms of lactate dehydrogenase by DCDS and DPDS likely involves the modification of the groups at the NAD+ binding site of the enzyme. Since organoselenides interacts with thiol groups on proteins, we conclude that the inhibition of different isoforms of lactate dehydrogenase by DPDS and DCDS possibly involves the modification of the thiol groups at the NAD+ binding site of the enzyme.

Effect of oral administration of diphenyl diselenide on antioxidant status, and activity of delta aminolevulinic acid dehydratase and isoforms of lactate dehydrogenase, in streptozotocin-induced diabetic rats.

Male albino rats with diabetes induced by the administration of streptozotocin (STZ) (45 mg/kg, i.v.) were treated with oral administration of diphenyl diselenide (DPDS) pre-dissolved in soya bean oil. A significant reduction in blood glucose levels was observed in STZ-induced diabetic rats treated with DPDS compared with an untreated STZ diabetic group. The pharmacological effect of DPDS was accompanied by a marked reduction in the level of glycated proteins, and restoration of the observed decreased levels of vitamin C and reduced glutathione (GSH; in liver and kidney tissues) of STZ-treated rats. DPDS also caused a marked reduction in the high levels of thiobarbituric acid reactive substances (TBARS) observed in STZ-induced diabetic group. Finally, the inhibition of catalase, delta aminolevulinic acid dehydratase (eth-ALA-D) and isoforms of lactate dehydrogenase (LDH) accompanied by hyperglycemia were prevented by DPDS in all tissues examined. Hence, in comparison with our earlier report, the present findings suggests that, irrespective of the route of administration and the delivery vehicle, DPDS can be considered as an anti-diabetic agent due to its anti-hyperglycemic and antioxidant properties.