succimer and arsenic-acid

Oxidative stress (OS) has been implicated in the pathophysiology of many neurodegenerative disorders. Several studies have shown that exposure to arsenic (As) and lead (Pb) produces oxidative stress, one of the most noted molecular mechanisms for the neurotoxicity of these metals. In the present study, we examined the effect of combined exposure to these metals (As and Pb) on the activity levels of antioxidant enzymes and apoptotic marker enzymes in brain regions (cerebral cortex, hippocampus and cerebellum) of rats at postnatal day (PND) 21, 28 and 3 months age and compared the toxicity levels with individual metals (As or Pb). Further, we also evaluated the therapeutic efficacy of a chelating agent, monoisoamyl dimercaptosuccinic acid (MiADMSA) against arsenic and lead induced developmental neurotoxicity. Pregnant rats were exposed to sodium meta-arsenite (50 ppm) and lead acetate (0.2%) individually, and in combination (As=25 ppm+Pb=0.1%) via drinking water throughout perinatal period (GD 6 to PND 21). MiADMSA (50 mg/kg, orally through gavage) was given for three consecutive days to the PND 18 pups (i.e., PND 18 to PND 20). Exposure to metal mixture resulted in a significant decrease in the activity levels of antioxidant enzymes such as manganese-superoxide dismutase (Mn-SOD), Cu/Zn superoxide dismutase (Cu/Zn-SOD), catalase (CAT) and glutathione peroxidase (GPx) while the malondialdehyde (MDA) levels and mRNA expression levels of caspase-3 and caspase-9 were significantly increased in all the three brain regions. The observed alterations were greater with exposure to metal mixture than individual metals (As or Pb) and the changes were more prominent at PND 28 and greater in cerebral cortex than hippocampus and cerebellum. Interestingly, chelation therapy with MiADMSA showed significant recovery in antioxidant enzymes, lipid peroxidation and gene expression levels of caspase-3 and caspase-9. From these findings, it can be concluded that combined exposure to As and Pb showed an additive effect on antioxidant enzymes than individual metal exposure and chelation therapy with MiADMSA significantly reversed the As and Pb induced apoptosis and oxidative stress, a major contributing factor to neurotoxicity.

Topics: Age Factors; Animals; Animals, Newborn; Antioxidants; Apoptosis; Arsenates; Brain; Catalase; Embryo, Mammalian; Female; Lead; Male; Malondialdehyde; Oxidative Stress; Pregnancy; Rats; Rats, Wistar; Succimer; Superoxide Dismutase

To support the key role of glutathione (GSH) in the mechanisms of tolerance and accumulation of arsenic in plants, this work examines the impact of several effectors of GSH synthesis or action in the response of maize (Zea mays L.) to arsenic. Maize was exposed in hydroponics to iso-toxic rates of 150 μM arsenate or 75 μM arsenite for 9 days and GSH effectors, flurazole (an herbicide safener), l-buthionine-sulfoximine (BSO, a known inhibitor of GSH biosynthesis), and dimercaptosuccinate (DMS) and dimercaptopropanesulfonate (DMPS) (two thiols able to displace GSH from arsenite-GSH complexes) were assayed. The main responses of plants to arsenic exposure consisted of a biomass reduction (fresh weight basis) of about 50%, an increase of non-protein thiol (NPTs) levels (especially in the GSH precursor γ-glutamylcysteine and the phytochelatins PC₂ and PC₃) in roots, with little effect in shoots, and an accumulation of between 600 and 1000 ppm of As (dry weight basis) in roots with very little translocation to shoots. Growth inhibition caused by arsenic was partially or completely reversed in plants co-treated with flurazole and arsenate or arsenite, respectively, highly exacerbated in plants co-treated with BSO, and not modified in plants co-treated with DMS or DMPS. These responses correlated well with an increase of both NPTs levels in roots and glutathione transferase activity in roots and shoots due to flurazole treatment, the decrease of NPTs levels in roots caused by BSO and the lack of effect on NPT levels caused by both DMS and DMPS. Regarding to arsenic accumulation in roots, it was not modified by flurazole, highly reduced by BSO, and increased between 2.5- and 4.0-fold by DMS and DMPS. Therefore, tolerance and accumulation of arsenic by maize could be manipulated pharmacologically by chemical effectors of GSH.

Topics: Arsenates; Arsenic; Arsenites; Biological Transport; Biomass; Buthionine Sulfoximine; Chelating Agents; Enzyme Inhibitors; Glutathione; Glutathione Transferase; Hydroponics; Phytochelatins; Plant Roots; Plant Shoots; Seedlings; Succimer; Sulfhydryl Compounds; Thiazoles; Unithiol; Zea mays

Members of the SLC20 family or type III Na(+) -coupled P(i) cotransporters (PiT-1, PiT-2) are ubiquitously expressed in mammalian tissue and are thought to perform a housekeeping function for intracellular P(i) homeostasis. Previous studies have shown that PiT-1 and PiT-2 mediate electrogenic P(i) cotransport when expressed in Xenopus oocytes, but only limited kinetic characterizations were made. To address this shortcoming, we performed a detailed analysis of SLC20 transport function. Three SLC20 clones (Xenopus PiT-1, human PiT-1, and human PiT-2) were expressed in Xenopus oocytes. Each clone gave robust Na(+)-dependent (32)P(i) uptake, but only Xenopus PiT-1 showed sufficient activity for complete kinetic characterization by using two-electrode voltage clamp and radionuclide uptake. Transport activity was also documented with Li(+) substituted for Na(+). The dependence of the P(i)-induced current on P(i) concentration was Michaelian, and the dependence on Na(+) concentration indicated weak cooperativity. The dependence on external pH was unique: the apparent P(i) affinity constant showed a minimum in the pH range 6.2-6.8 of approximately 0.05 mM and increased to approximately 0.2 mM at pH 5.0 and pH 8.0. Xenopus PiT-1 stoichiometry was determined by dual (22)Na-(32)P(i) uptake and suggested a 2:1 Na(+):P(i) stoichiometry. A correlation of (32)P(i) uptake and net charge movement indicated one charge translocation per P(i). Changes in oocyte surface pH were consistent with transport of monovalent P(i). On the basis of the kinetics of substrate interdependence, we propose an ordered binding scheme of Na(+):H(2)PO(4)(-):Na(+). Significantly, in contrast to type II Na(+)-P(i) cotransporters, the transport inhibitor phosphonoformic acid did not inhibit PiT-1 or PiT-2 activity.

Topics: Animals; Arsenates; Female; Foscarnet; Humans; Hydrogen-Ion Concentration; Kinetics; Lithium; Membrane Potentials; Microinjections; Models, Biological; Oocytes; Patch-Clamp Techniques; Phosphates; Phosphorus Radioisotopes; Sodium; Sodium Radioisotopes; Sodium-Phosphate Cotransporter Proteins, Type III; Succimer; Sulfates; Xenopus laevis; Xenopus Proteins

Gluconeogenesis is one of the metabolic pathways severely affected in acute arsenic poisoning. We have studied gluconeogenesis in isolated kidney tubules of male Sprague-Dawley rats to screen various sulfur compounds for antidotal properties against inorganic and organic arsenicals. Freshly prepared kidney cells from starved rats synthesized glucose from added pyruvate (10 mmol/liter) at a rate of 9.74 +/- 0.90 nmol/min/mg protein (mean +/- SD; n = 61). Gluconeogenesis was inhibited almost 90% in the presence of phenylarsonate (700 mumol/liter), arsenate (350 mumol/liter), arsenite (30 mumol/liter), or PhAsO (1 mumol/liter). mumol/liter). With effective antidotes the rate of gluconeogenesis was restored to almost control values within 10 min. Among 21 sulfur compounds tested, only BAL, DMPS, and DMSA were effective in PhAsO poisoning. With inorganic arsenic also DTE and DTT restored the rate of glucose formation. The observed in vitro efficacies were in good agreement with in vivo results obtained with male NMRI mice severely poisoned with arsenite (As2O3, 20 mg/kg approximately 0.2 mmol As/kg) or PhAsO (3.4 mg/kg approximately 0.02 mmol As/kg). We conclude that isolated kidney tubules are a useful in vitro screening system (a) to compare the metabolic toxicity of various arsenicals and (b) to evaluate potential antidotes.

Topics: Animals; Antidotes; Arsenates; Arsenic; Arsenic Poisoning; Arsenicals; Arsenites; Chelating Agents; Dimercaprol; Drug Evaluation, Preclinical; Gluconeogenesis; In Vitro Techniques; Kidney Tubules; Male; Mice; Mice, Inbred Strains; Rats; Rats, Sprague-Dawley; Succimer; Unithiol