Francielli Weber Santos

Bis selenide alkene derivatives: A class of potential antioxidant and antinociceptive agents

Bis and tris-selenide alkene derivatives, a class of organoselenium compounds, were screened for antinociceptive and antioxidant activities. In vitro, bis-selenide alkene 1c (R=2,4,6-Me(3)C(6)H(2)), 1d (R=4-ClC(6)H(4)) and 1e (R=4-MeOC(6)H(4)) protected against lipid peroxidation about 50%, whereas 1b (R=C(6)H(5)) and 1a (R=C(4)H(9)) protected only 23%. Compound 1d presented lesser IC(50) against lipid peroxidation than other bis-selenide alkene compounds (1d>1e> or =1c>1a=1b). The maximal inhibitory effect of tris-selenide alkenes on lipid peroxidation was in the following order 2c>2a=2b. Compound 1e increased the rate of GSH, but not DTT, oxidation. Tris-selenide alkene 2c (R=4-MeOC(6)H(4)) demonstrated the higher rate of thiol oxidation, while 2a (R=C(6)H(5)) did not change DTT oxidation but oxidized GSH. Conversely, compound 2b (R=4-ClC(6)H(4)) did not change the rate of GSH oxidation, but oxidized DDT. Bis-selenide alkene derivatives 1c, 1d and 1e were the most promising compounds tested in vitro. In vivo, compounds 1c and 1d (5-50mg/kg, subcutaneously) produced significant inhibition of acetic acid- and capsaicin-induced pain. Compounds 1c and 1d increased the tail-flick response latency time. The antinociception effect of 1c and 1d was not abolished by naloxone (an antagonist of opioid receptor, 1mg/kg, subcutaneously), suggesting that the antinociceptive effect is not influenced by the opioidergic mechanism.

γ-Oryzanol protects against acute cadmium-induced oxidative damage in mice testes.

Cadmium is a non-essential heavy metal that is present at low levels mainly in food and water and also in cigar smoke. The present study evaluated the testicular damage caused by acute cadmium exposure and verified the protective role of γ-oryzanol (ORY). Mice were administrated with a single dose of 2.5mg/kg of CdCl2, and then treated with ORY (50mM in canola oil, 5mL/kg). Testes were removed after 24h and tested for lipid peroxidation (TBARS), protein carbonylation, DNA breakage, ascorbic acid, cadmium and non-proteic thiols contents, and for the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione S-transferase (GST) and δ-aminolevulic acid dehydratase (δ-ALA-D). Cadmium presented a significant alteration in all parameters, except GPx and CAT activities. Therapy reduced in a slight degree cadmium concentration in testes (around 23%). ORY restored SOD and GST activities as well as TBARS production to the control levels. Furthermore, ORY partially recovered δ-ALA-D activity inhibited by cadmium. This study provides the first evidence on the therapeutic properties of ORY in protecting against cadmium-induced testicular toxicity.

Interaction between metals and chelating agents affects glutamate binding on brain synaptic membranes.

The present study investigates the possible effects of Hg2+, Pb2+, and Cd2+ on [3H]-glutamate binding. To better understand the role of the thiol-disulfide status on the toxicity of such metals toward glutamatergic neurotransmission, we used three thiol chelating agents, 2,3-dimercaptopropanol (BAL), 2,3-dimercaptopropane 1-sulfonate (DMPS), and meso-2,3-dimercaptosuccinic acid (DMSA). Dithiotreitol (DTT) was tested for its ability to prevent metals-induced inhibition on [3H]-glutamate binding. Hg2+, Pb2+, and Cd2+ showed a concentration-dependent inhibition on [3H]-glutamate binding, and mercury was the most effective inhibitor. BAL did not prevent [3H]-glutamate binding inhibition by Hg2+, Cd2+, and Pb2+. However, DMPS and DMSA prevented the inhibition caused by Cd2+ and Pb2+, but not by Hg2+. DTT did not prevent the inhibition on [3H]-glutamate binding caused by 10 μM Hg2+. In contrast, it was able to partially prevent [3H]-glutamate binding inhibition caused by 40 μM Pb2+ and Cd2+. These results demonstrated that the heavy metals present an inhibitory effect on [3H]-glutamate binding. In addition, BAL was less effective to protect [3H]-glutamate binding inhibition caused by these metals than other chelating agents studied.

Apocynin prevents vascular effects caused by chronic exposure to low concentrations of mercury.

Mercury increases the risk of cardiovascular disease and oxidative stress and alters vascular reactivity. This metal elicits endothelial dysfunction causing decreased NO bioavailability via increased oxidative stress and contractile prostanoid production. NADPH oxidase is the major source of reactive oxygen species (ROS) in the vasculature. Our aim was to investigate whether treatment with apocynin, an NADPH oxidase inhibitor, prevents the vascular effects caused by chronic intoxication with low concentrations of mercury. Three-month-old male Wistar rats were treated for 30 days with a) intramuscular injections (i.m.) of saline; b) HgCl2 (i.m. 1st dose: 4.6 µg/kg, subsequent doses: 0.07 µg/kg/day); c) Apocynin (1.5 mM in drinking water plus saline i.m.); and d) Apocynin plus HgCl2. The mercury treatment resulted in 1) an increased aortic vasoconstrictor response to phenylephrine and reduced endothelium-dependent responses to acetylcholine; 2) the increased involvement of ROS and vasoconstrictor prostanoids in response to phenylephrine, whereas the endothelial NO modulation of such responses was reduced; and 3) the reduced activity of aortic superoxide dismutase (SOD) and glutathione peroxidase (GPx) and increased plasma malondialdehyde (MDA) levels. Treatment with apocynin partially prevented the increased phenylephrine responses and reduced the endothelial dysfunction elicited by mercury treatment. In addition, apocynin treatment increased the NO modulation of vasoconstrictor responses and aortic SOD activity and reduced plasma MDA levels without affecting the increased participation of vasoconstrictor prostanoids observed in aortic segments from mercury-treated rats. Conclusions: Mercury increases the vasoconstrictor response to phenylephrine by reducing NO bioavailability and increasing the involvement of ROS and constrictor prostanoids. Apocynin protects the vessel from the deleterious effects caused by NADPH oxidase, but not from those caused by prostanoids, thus demonstrating a two-way action.

Chronic exposure to low doses of mercury impairs sperm quality and induces oxidative stress in rats.

Mercury (Hg) is a widespread environmental pollutant that adversely affects the male reproductive system. The precise mechanisms underlying mercuric chloride (HgCl2)-induced toxicity are not fully understood; however, evidence indicates that oxidative stress may be involved in this process. Although the adverse effects of high levels of inorganic Hg on the male reproductive system have been investigated, the effects of low levels of exposure are unknown. Therefore, the aim of this study was to investigate the effects of chronic exposure to low concentrations of HgCl2 on sperm parameters, lipid peroxidation, and antioxidant activity of male rats. Three-month-old male Wistar rats were treated for 30 d and divided into groups: control (saline, i.m.) and HgCl2 group (i.m., first dose 4.6 μg/kg, subsequent doses 0.07 μg/kg/d). Sperm parameters (count, motility and morphology) and biomarkers of oxidative stress in testis, epididymis, prostate, and vas deferens were analyzed. Mercury treatment produced a reduction in sperm quantity (testis and epididymis) and daily sperm production, following by decrease in sperm motility and increase on head and tail morphologic abnormalities. HgCl2 exposure was correlated with enhanced oxidative stress in reproductive organs, represented not only by augmented lipid peroxidation but also by changes in antioxidant enzymes activity superoxide dismutase (SOD) and catalase (CAT) and nonprotein thiol levels. In conclusion, chronic exposure to low doses of Hg impaired sperm quality and adversely affected male reproductive functions, which may be due, at least in part, to enhanced oxidative stress.

Memory deficits and oxidative stress in cerebral ischemia–reperfusion: Neuroprotective role of physical exercise and green tea supplementation

Ischemic stroke is a major cause of morbidity and mortality all over the world. Among impairments observed in survivors there is a significant cognitive learning and memory deficit. Neuroprotective strategies are being investigated to minimize such deficits after an ischemia event. Here we investigated the neuroprotective potential of physical exercise and green tea in an animal model of ischemia-reperfusion. Eighty male rats were divided in 8 groups and submitted to either transient brain ischemia-reperfusion or a sham surgery after 8 weeks of physical exercise and/or green tea supplementation. Ischemia-reperfusion was performed by bilateral occlusion of the common carotid arteries during 30 min. Later, their memory was evaluated in an aversive and in a non-aversive task, and hippocampus and prefrontal cortex were removed for biochemical analyses of possible oxidative stress effects. Ischemia-reperfusion impaired learning and memory. Reactive oxygen species were increased in the hippocampus and prefrontal cortex. Eight weeks of physical exercise and/or green tea supplementation before the ischemia-reperfusion event showed a neuroprotective effect; both treatments in separate or together reduced the cognitive deficits and were able to maintain the functional levels of antioxidant enzymes and glutathione.

Antioxidants and metallothionein levels in mercury-treated mice

Acute effects of mercury on mouse blood, kidneys, and liver were evaluated. Mice received a single dose of mercuric chloride (HgCl2, 4.6 mg/kg, subcutaneously) for three consecutive days. We investigated the possible beneficial effects of antioxidant therapy (N-acetylcysteine (NAC) and diphenyl diselenide (PhSe)2) compared with the sodium salt of 2,3-dimercapto-1-propanesulfonic acid (DMPS), an effective chelating agent in HgCl2 exposure in mice. We also verified whether metallothionein (MT) induction might be involved in a possible mechanism of protection against HgCl2 poisoning and whether different treatments would modify MT levels and other toxicological parameters. The results demonstrated that HgCl2 exposure significantly inhibited δ-aminolevulinate dehydratase (δ-ALA-D) activity in liver and only DMPS treatment prevented the inhibitory effect. Mercuric chloride caused an increase in renal non-protein thiol groups (NPSH) and none of the treatments modified renal NPSH levels. Urea concentration was increased after HgCl2 exposure. NAC plus (PhSe)2 was partially effective in protecting against the effects of mercury. DMPS and (PhSe)2 were effective in restoring the increment in urea concentration caused by mercury. Thiobarbituric acid-reactive substances (TBARS), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities and ascorbic acid levels were not modified after mercury exposure. Mercuric chloride poisoning caused an increase in hepatic and renal MT levels and antioxidant treatments did not modify this parameter. Our data indicated a lack of therapeutic effect of the antioxidants tested.

2,3-Dimercaptopropanol, 2,3-dimercaptopropane-1-sulfonic acid, and meso-2,3-dimercaptosuccinic acid inhibit δ-aminolevulinate dehydratase from human erythrocytes in vitro

The effects of dithiol chelating agents meso-2,3-dimercaptosuccinic acid (DMSA), 2,3-dimercaptopropane-1-sulfonic acid (DMPS), and 2,3-dimercaptopropanol (BAL) on delta-aminolevulinate dehydratase (delta-ALA-D) from human erythrocytes were evaluated. Furthermore, possible protective effects of zinc chloride (ZnCl(2)), dithiothreitol (DTT), and cysteine were studied. delta-ALA-D activity from human erythrocytes was inhibited by dithiol chelating agents in a concentration-dependent manner. Cysteine, at all concentrations tested, did not protect the inhibitory effect of 1 and 4 mM DMPS and DMSA, but protected 1 mM BAL inhibition. Dithiotreitol was able to protect the inhibition caused by 1 mM BAL (28%), DMPS (56%), and DMSA (40%) in a concentration-dependent manner. Zinc chloride protected and restored 1 mM BAL inhibitory effect on delta-ALA-D. Zinc chloride at 500 microM and 1 mM, respectively, protected inhibitory effects of DMPS and DMSA (1 and 4 mM), but did not reverse its effects. The preincubation of dithiol chelating agents with enzyme demonstrated that DMSA was the most potent delta-ALA-D inhibitor of human erythrocytes. These data are in agreement with delta-ALA-D activity from purified enzyme. ZnCl(2) (1 microM) added, in the reaction mixture, increased enzyme activity and DTT (100 microM) totally restored the enzyme activity for all chelating agents tested.

Involvement of non-enzymatic antioxidant defenses in the protective effect of diphenyl diselenide on testicular damage induced by cadmium in mice.

The involvement of non-enzymatic antioxidant defenses in the protective effect of diphenyl diselenide (PhSe)(2) on testicular damage caused by cadmium in mice was investigated. Mice received a single dose of CdCl(2) (5mg/kg, intraperitoneally). Thirty minutes after the CdCl(2) injection, they received a single oral dose of (PhSe)(2) (400micromol/kg). Twenty-four hours after CdCl(2) administration, blood samples were collected and mice were killed and had their testes dissected. Parameters in plasma (aspartate (AST) and alanine (ALT) aminotransferases and lactato dehydrogenase (LDH) activities as well as creatinine levels) were determined. The activity of delta-aminolevulinate dehydratase (delta-ALA-D), the levels of thiobarbituric acid-reactive substances (TBARS), ascorbic acid and nonprotein thiols (NPSH) and histological analysis were determined in collected samples. Results demonstrated that (PhSe)(2) protected against toxicity induced by CdCl(2) on delta-ALA-D activity, ascorbic acid and NPSH levels. (PhSe)(2) protected against the increase in plasma AST, ALT and LDH activities caused by CdCl(2). Testes of mice exposed to CdCl(2) showed marked histopathological alterations that were ameliorated by administration of (PhSe)(2). (PhSe)(2) protected against toxicity induced by CdCl(2) in testes of mice. Ascorbic acid and NPSH, non-enzymatic antioxidant defenses, are involved in the protective effect of (PhSe)(2) against testicular damage caused by CdCl(2) in mice.

Heavy Metals Modulate Glutamatergic System in Human Platelets

Research strategies have been developed to characterize parameters in peripheral tissues that might easily be measured in humans as surrogate markers of damage, dysfunction or interactions involving neural targets of toxicants. The similarities between platelet and neuron may even be clinically important, as a number of biochemical markers show parallel changes in the central nervous system (CNS) and platelets. The purpose of our research was to investigate the effect of Hg2+, Pb2+ and Cd2+ on the [3H]-glutamate binding and [3H]-glutamate uptake in human platelets. The involvement of oxidative stress in the modulation of glutamatergic system induced by heavy metals was also investigated. The present study clearly demonstrates that Hg2+, Cd2+, and Pb2+ inhibited [3H]-glutamate uptake in human platelets. Hg2+ inhibited [3H]-glutamate binding, while Cd2+ and Pb2+ stimulated [3H]-glutamate binding in human platelets. Hg2+, Cd2+ and Pb2+ increased lipid peroxidation levels and reactive oxygen species (ROS) measurement in platelets. The present limited results could suggest that glutamatergic system may be used as a potential biomarker for neurotoxic action of heavy metals in humans.