RESUMO
Mercury chloride (HgCl2), a neurotoxicant that cannot penetrate the blood-brain barrier (BBB). Although when the BBB are got damaged by neurodegenerative disorders, the absorbed HgCl2, mainly in form of Hg (II)-serum albumin adduct (Hg-HSA) in human plasma, can penetrate BBB and affect central nervous system (CNS) cells. Current study planned to evaluate the effect of Hg-HSA on the physiological function of N9 microglial cells. At low dosage (15â¯ng/mL) of Hg-HAS, the observed outcomes was: promoted cell propagation, Nitric Oxide (NO) and intracellular Ca2+ levels enhancement, suppressed the release of TNF-α and IL-1ß and inhibited cell proliferation. At high dosage (15⯵g/mL) we observed decline in NO and intracellular Ca2+ levels, and increment in the release of TNF-α and IL-1ß. These biphasic effects are similar to hormesis, and the hormesis, in this case, was executed through ERK/MAPKs and JAK/STAT3 signaling pathways. Study of quantum chemistry revealed that Hg2+ could form stable coordination structures in both Asp249 and Cys34 sites of HSA. Although five-coordination structure in Asp249 site is more stable than four-coordination structure in Cys34 site but four-coordination structure is formed easily in-vivo in consideration of binding-site position in spatial structure of HSA.
Assuntos
MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Hormese , Janus Quinases/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/etiologia , Microglia/efeitos dos fármacos , Fator de Transcrição STAT3/metabolismo , Transdução de Sinais/efeitos dos fármacos , Animais , Sítios de Ligação , Cálcio/metabolismo , Linhagem Celular , Sobrevivência Celular/efeitos dos fármacos , Interleucina-1beta/genética , Interleucina-1beta/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Camundongos , Microglia/enzimologia , Microglia/patologia , Simulação de Dinâmica Molecular , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase Tipo II/genética , Óxido Nítrico Sintase Tipo II/metabolismo , Ligação Proteica , Conformação Proteica , Fator de Necrose Tumoral alfa/genética , Fator de Necrose Tumoral alfa/metabolismoRESUMO
Methylmercury (MeHg) induces site-specific neurotoxicity in the adult brain. In this study, we investigated the site-specific expression of the signaling cascade related to neural activity in a mouse model of MeHg intoxication showing neurodegeneration only in the deep layer of the cerebral cortex, especially layer IV. We performed time course studies of c-fos and brain-derived neurotrophic factor (BDNF) expression levels which are proper markers of neural activity. We showed that upregulation of both markers preceded the neuronal degeneration in the cerebral cortex. Immunohistochemical analysis revealed the site-specific upregulation of c-fos in the deep layer of the cerebral cortex. Western blot analysis showed that c-fos and BDNF expression was associated with CREB phosphorylation, which was triggered by the activation of the p44/42 MAPK, p38 MAPK and PKA pathways. However, we did not detect any changes in the expression levels of c-fos and BDNF proteins and no signs of neuronal degeneration in the hippocampus and cerebellum, despite the fact that we could detect accumulation of MeHg in these two brain regions. These results suggested an intriguing possibility that MeHg-induced neuronal degeneration was caused by site-specific neural hyperactivity triggered by the activation of MAPK and PKA/CREB pathways followed by c-fos and BDNF upregulation.
Assuntos
Córtex Cerebral/efeitos dos fármacos , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/prevenção & controle , Compostos de Metilmercúrio , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Degeneração Neural , Neurônios/efeitos dos fármacos , Animais , Western Blotting , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Córtex Cerebral/enzimologia , Córtex Cerebral/patologia , Córtex Cerebral/fisiopatologia , Modelos Animais de Doenças , Ativação Enzimática , Imuno-Histoquímica , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Camundongos Endogâmicos ICR , Neurônios/enzimologia , Neurônios/patologia , Fosforilação , Proteínas Proto-Oncogênicas c-fos/metabolismo , Transdução de Sinais , Fatores de Tempo , Regulação para CimaRESUMO
Methylmercury (MeHg) is a neurotoxin that binds strongly to thiol residues on protein and low molecular weight molecules like reduced glutathione (GSH). The mechanism of its effects on GSH homeostasis particularly at environmentally relevant low doses is not fully known. We hypothesized that exposure to MeHg would lead to a depletion of reduced glutathione (GSH) and an accumulation of glutathione disulfide (GSSG) leading to alterations in S-glutathionylation of proteins. Our results showed exposure to low concentrations of MeHg (1µM) did not significantly alter GSH levels but increased GSSG levels by â¼12-fold. This effect was associated with a significant increase in total cellular glutathione content and a decrease in GSH/GSSG. Immunoblot analyses revealed that proteins involved in glutathione synthesis were upregulated accounting for the increase in cellular glutathione. This was associated an increase in cellular Nrf2 protein levels which is required to induce the expression of antioxidant genes in response to cellular stress. Intriguingly, we noted that a key enzyme involved in reversing protein S-glutathionylation and maintaining glutathione homeostasis, glutaredoxin-1 (Grx1), was inhibited by â¼50%. MeHg treatment also increased the S-glutathionylation of a high molecular weight protein. This observation is consistent with the inhibition of Grx1 and elevated H2O2 production however; contrary to our original hypothesis we found few S-glutathionylated proteins in the astrocytoma cells. Collectively, MeHg affects multiple arms of glutathione homeostasis ranging from pool management to protein S-glutathionylation and Grx1 activity.
Assuntos
Astrocitoma/enzimologia , Neoplasias do Sistema Nervoso Central/enzimologia , Glutarredoxinas/antagonistas & inibidores , Glutationa/biossíntese , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Compostos de Metilmercúrio/toxicidade , Neurônios/efeitos dos fármacos , Astrocitoma/patologia , Linhagem Celular Tumoral , Neoplasias do Sistema Nervoso Central/patologia , Relação Dose-Resposta a Droga , Glutarredoxinas/metabolismo , Dissulfeto de Glutationa , Homeostase , Humanos , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Neurônios/enzimologia , Neurônios/patologia , Oxirredução , Estresse Oxidativo/efeitos dos fármacos , Processamento de Proteína Pós-TraducionalRESUMO
Salts of heavy metals are excreted by the kidneys and, as pro-oxidants, stimulate the processes of free radical oxidation. Mercury ions are accumulated in the kidneys. So the study of the features of antioxidant enzymes adaptive response of different kidney layers in response to mercury dichloride is important. Catalase and glytathionperoxidase activity within rat kidneys 72 hours after mercury dichloride intoxication in the ratio of 5 ml per 1 kg of the animal weight was studied. It was important to reveal the influence of the mercury salts on rat kidney antioxidative system. Decreasing glytathionperoxidase activity in cortical and cerebral substances and renal papillae were accompanied by increased contents of oxidative modified proteins and lipids and morphological changes in renal tissue under salt and water loading after mercury dichloride poisoning. The results obtained evidence for the inhibition of antioxidative protection of enzymes in rat kidneys under the mercury dichloride effect.
Assuntos
Córtex Renal/enzimologia , Glomérulos Renais/enzimologia , Medula Renal/enzimologia , Cloreto de Mercúrio/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Animais , Antioxidantes/metabolismo , Peso Corporal/efeitos dos fármacos , Catalase/metabolismo , Glutationa Peroxidase/metabolismo , Histocitoquímica , Córtex Renal/efeitos dos fármacos , Córtex Renal/patologia , Glomérulos Renais/efeitos dos fármacos , Glomérulos Renais/patologia , Medula Renal/efeitos dos fármacos , Medula Renal/patologia , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Oxirredução , Ratos , Espécies Reativas de Oxigênio/metabolismo , Substâncias Reativas com Ácido Tiobarbitúrico/metabolismo , Equilíbrio HidroeletrolíticoRESUMO
The metabolic test with antipyrine was performed, the relationship between genotypes of GSTT1 and GSTM1 polymorphisms were studied, and cotinine level was measured in 116 men chronically exposed to mercury. The individuals were divided in 4 groups depending on the diagnosis of chronic mercury intoxication. The changes in the parameters of antipyrine test were studied in linked samples (N=62, 4 year interval); in patients with chronic mercury intoxication, the disease stage was taken into account. Inhibition of antipyrine metabolism, increased frequency of combination of GSTT1(0/0)/GSTM1(+) genotypes in patients with chronic mercury intoxication, and the specificity of cytochrome P450 inhibition with mercury suggest that disease progression is related to inhibition of cytochrome P450 isoforms in the brain that catalyze regulation of endogenous substrates.
Assuntos
Sistema Enzimático do Citocromo P-450/metabolismo , Glutationa Transferase/genética , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Mercúrio/toxicidade , Doenças Profissionais/enzimologia , Antipirina/metabolismo , Encefalopatias/induzido quimicamente , Encefalopatias/enzimologia , Estudos de Associação Genética , Genótipo , Glutationa Transferase/metabolismo , Humanos , Masculino , Doenças Profissionais/induzido quimicamente , Exposição Ocupacional , Polimorfismo GenéticoRESUMO
Mercury (Hg) is neurotoxic, and children may be particularly susceptible to this effect. A current major challenge is the identification of children who may be uniquely susceptible to Hg toxicity because of genetic disposition. We examined the hypothesis that CPOX4, a genetic variant of the heme pathway enzyme coproporphyrinogen oxidase (CPOX) that affects susceptibility to mercury toxicity in adults, also modifies the neurotoxic effects of Hg in children. Five hundred seven children, 8-12 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral effects of Hg from dental amalgam tooth fillings in children. Subjects were evaluated at baseline and at 7 subsequent annual intervals for neurobehavioral performance and urinary mercury levels. Following the completion of the clinical trial, genotyping assays for CPOX4 allelic status were performed on biological samples provided by 330 of the trial participants. Regression modeling strategies were employed to evaluate associations between CPOX4 status, Hg exposure, and neurobehavioral test outcomes. Among girls, few significant CPOX4-Hg interactions or independent main effects for Hg or CPOX4 were observed. In contrast, among boys, numerous significant interaction effects between CPOX4 and Hg were observed spanning all 5 domains of neurobehavioral performance. All underlying dose-response associations between Hg exposure and test performance were restricted to boys with the CPOX4 variant, and all of these associations were in the expected direction where increased exposure to Hg decreased performance. These findings are the first to demonstrate genetic susceptibility to the adverse neurobehavioral effects of Hg exposure in children. The paucity of responses among same-age girls with comparable Hg exposure provides evidence of sexual dimorphism in genetic susceptibility to the adverse neurobehavioral effects of Hg in children and adolescents.
Assuntos
Comportamento Infantil/efeitos dos fármacos , Coproporfirinogênio Oxidase/genética , Amálgama Dentário/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio/genética , Polimorfismo de Nucleotídeo Único , Criança , Feminino , Humanos , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/etiologia , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Testes Neuropsicológicos , Portugal , Fatores SexuaisRESUMO
Industrial pollution due to heavy metals such as mercury is a major concern for the environment and public health. Mercury, in particular methylmercury (MeHg), primarily affects brain development and neuronal activity, resulting in neurotoxic effects. Because chemokines can modulate brain functions and are involved in neuroinflammatory and neurodegenerative diseases, we tested the possibility that the neurotoxic effect of MeHg may interfere with the chemokine CCL2. We have used an original protocol in young mice using a MeHg-contaminated fish-based diet for 3 months relevant to human MeHg contamination. We observed that MeHg induced in the mice cortex a decrease in CCL2 concentrations, neuronal cell death, and microglial activation. Knock-out (KO) CCL2 mice fed with a vegetal control food already presented a decrease in cortical neuronal cell density in comparison with wild-type animals under similar diet conditions, suggesting that the presence of CCL2 is required for normal neuronal survival. Moreover, KO CCL2 mice showed a pronounced neuronal cell death in response to MeHg. Using in vitro experiments on pure rat cortical neurons in culture, we observed by blockade of the CCL2/CCR2 neurotransmission an increased neuronal cell death in response to MeHg neurotoxicity. Furthermore, we showed that sod genes are upregulated in brain of wild-type mice fed with MeHg in contrast to KO CCL2 mice and that CCL2 can blunt in vitro the decrease in glutathione levels induced by MeHg. These original findings demonstrate that CCL2 may act as a neuroprotective alarm system in brain deficits due to MeHg intoxication.
Assuntos
Encéfalo/efeitos dos fármacos , Quimiocina CCL2/fisiologia , Poluentes Ambientais/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio/etiologia , Compostos de Metilmercúrio/toxicidade , Neurônios/efeitos dos fármacos , Animais , Encéfalo/enzimologia , Encéfalo/metabolismo , Encéfalo/patologia , Técnicas de Cultura de Células , Morte Celular/efeitos dos fármacos , Células Cultivadas , Quimiocina CCL2/deficiência , Quimiocina CCL2/genética , Relação Dose-Resposta a Droga , Poluentes Ambientais/farmacocinética , Expressão Gênica/efeitos dos fármacos , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Compostos de Metilmercúrio/farmacocinética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/enzimologia , Neurônios/metabolismo , Neurônios/patologia , Superóxido Dismutase/genética , Fatores de Tempo , Distribuição TecidualRESUMO
Methylmercury (MeHg) is a well-known neurotoxicant inducing neuronal degeneration in the central nervous system. This in vivo study investigated the involvement of tau hyperphosphorylation in MeHg-induced neuropathological changes in the mouse brain, because abnormal tau hyperphosphorylation causes significant pathological changes associated with some neurodegenerative diseases. Mice that were administrated to 30 ppm MeHg in drinking water for 8 weeks exhibited neuropathological changes, e.g. a decrease in the number of neuron; an increase in the number of migratory astrocytes and microglia/macrophages; necrosis and apoptosis in the cerebral cortex, particularly the deep layer of primary motor cortex and prelimbic cortex. Western blotting revealed that MeHg exposure increased tau phosphorylation at Thr-205, Ser-396 and Ser-422 in the cerebral cortex, consistent with the phosphorylation patterns noted in Alzheimer's disease and frontotemporal dementia. Immunohistochemical analyses revealed that the distribution of tau-phosphorylated (Thr-205) neurons corresponded with the areas showing considerable neuropathological changes. Among the kinases and phosphatases related to tau hyperphosphorylation, the activation of mitogen-activated protein kinase kinase 4 (MKK4) and c-Jun N-terminal kinase (JNK) was recognized. Neither neuropathological changes nor tau hyperphosphorylation was detected in the hippocampus in this study although the mercury concentration here was twice that in the cerebral cortex. These findings suggest that MeHg exposure induces tau hyperphosphorylation at specific sites of tau mainly through the activation of JNK pathways, leading to neuropathological changes in the cerebral cortex selectively, but not in the hippocampus of mouse brain.
Assuntos
Córtex Cerebral/metabolismo , Hipocampo/metabolismo , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/etiologia , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Compostos de Metilmercúrio/toxicidade , Transdução de Sinais/efeitos dos fármacos , Proteínas tau/metabolismo , Animais , Córtex Cerebral/efeitos dos fármacos , Modelos Animais de Doenças , Hipocampo/efeitos dos fármacos , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Compostos de Metilmercúrio/sangue , Camundongos , Camundongos Endogâmicos C57BL , Fatores de TempoRESUMO
Methylmercury (MeHg) is a known neurotoxin, yet the mechanism for low dose chronic toxicity is still not clear. While N-methyl-D-aspartate receptors (NMDARs) were found to be induced after exposure to MeHg in a mink model, its role on neurotoxicity is not known. The aims of this study were to investigate the expression and the functional roles of NMDARs on the induction of cell death in the human SH-SY 5Y neuroblastoma cell line after exposure to MeHg. NMDARs were measured using a radiolabeled phencyclidine receptor ligand [(3)H] (MK801) and cell death was quantified using fluorogenic substrates specific for caspase-3 (DEVD-AFC) and lactate dehydrogenase (LDH) release. We found a significant increase in NMDARs followed by increased caspase-3 activity after 4 h of exposure to MeHg (0.25-1 microM). Necrotic cell death was found after 4 and 24 h of exposure to MeHg (0.25-5 microM). The NMDAR antagonists dizocilpine ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-iminemaleate [(+)-MK801]) and Memantine (1-amino-3,5-dimethyl-adamantane) (10 microM) completely attenuated MeHg-mediated cell death by blocking NMDARs, thus demonstrating the importance of NMDARs in mercury neurotoxicity. Intracellular calcium chelator BAPTA-AM (1 microM) partially attenuated the neurotoxicity effect of 1 microM MeHg. These results suggest that MeHg toxicity can be mediated through the binding and increase of NMDARs.
Assuntos
Intoxicação do Sistema Nervoso por Mercúrio/patologia , Compostos de Metilmercúrio/toxicidade , Receptores de N-Metil-D-Aspartato/efeitos dos fármacos , Caspase 3/metabolismo , Caspases/metabolismo , Morte Celular/efeitos dos fármacos , Linhagem Celular Tumoral , Membrana Celular/efeitos dos fármacos , Membrana Celular/metabolismo , Quelantes/farmacologia , Maleato de Dizocilpina/farmacologia , Ácido Egtázico/análogos & derivados , Ácido Egtázico/farmacologia , Ativação Enzimática/efeitos dos fármacos , Antagonistas de Aminoácidos Excitatórios/farmacologia , Glutationa/metabolismo , Humanos , L-Lactato Desidrogenase/metabolismo , Memantina/farmacologia , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Compostos de Metilmercúrio/antagonistas & inibidores , Receptores de N-Metil-D-Aspartato/agonistas , Receptores de N-Metil-D-Aspartato/antagonistas & inibidoresRESUMO
Methylmercury (MeHg), a potent neurotoxicant, easily passes through the blood-brain barrier (BBB), accumulates in the brain regions and causes severe irreversible damage. However, the neurotoxic effects and action mechanisms of MeHg are still unclear, especially in low-dose and long-term exposure. In this study, we attempted to explore the toxic effects of low-dose MeHg (0.05 mg/kg/day), which was the possible exposed dose by ingestion in MeHg-contaminated areas, on the time course of changes in locomotor activities and auditory brainstem response (ABR) system after administration for 7 consecutive weeks in mice. The results showed that the retention time on the rotating rod (60 rpm) was preferentially decreased after 1-week oral administration with MeHg. The locomotor activities parameters of ambulatory distances and stereotype-1 episodes were significantly increased and vertical-plane entries were progressively decreased after MeHg exposure in 3 consecutive weeks. Gradually progressive abnormality of ABR (increase in hearing thresholds, prolonged absolute and interwave latencies) was found during 4-6 weeks administration of MeHg. These impairments correlated with significant Hg accumulation and biochemical alterations in brain regions and/or other tissues, including the increase of lipid peroxidation (LPO) production, influence of Na+/K(+)-ATPase activities and nitric oxide (NO) levels were found. These findings provide evidence that the signaling of oxidative stress/Na+/K(+)-ATPase/NO plays a role in the underlying mechanisms of the neurotoxic effects induced by low-dose and long-term exposure of MeHg.
Assuntos
Poluentes Ambientais/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio , Compostos de Metilmercúrio/toxicidade , Estresse Oxidativo/efeitos dos fármacos , ATPase Trocadora de Sódio-Potássio/metabolismo , Animais , Encéfalo/efeitos dos fármacos , Encéfalo/enzimologia , Encéfalo/metabolismo , Relação Dose-Resposta a Droga , Regulação para Baixo , Poluentes Ambientais/farmacocinética , Potenciais Evocados Auditivos do Tronco Encefálico/efeitos dos fármacos , Peroxidação de Lipídeos/efeitos dos fármacos , Masculino , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/etiologia , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Compostos de Metilmercúrio/farmacocinética , Camundongos , Camundongos Endogâmicos ICR , Atividade Motora/efeitos dos fármacos , Óxido Nítrico/metabolismo , Equilíbrio Postural/efeitos dos fármacos , Fatores de TempoRESUMO
Methylmercury (MeHg) is an environmental toxicant, while mercuric sulfide (HgS) is a main active component of cinnabar, a Chinese mineral medicine used as a sedative. Because the neurotoxicological effects of HgS were not clearly understood, in this study, we attempted to compare HgS with MeHg in various physiological responses in Sprague-Dawley rats. After oral administration (2 mg/(kg day)) for consecutive 5 and 14 days, MeHg reversibly decreased both of motor nerve conduction velocity (MNCV) and tail flick response, whereas irreversibly inhibited all of the motor equilibrium performance, recovery of compound muscle action potentials (CMAP) following exhaustic tetanic stimuli and Na+/K+-ATPase activity of the isolated sciatic nerve. These toxic effects of MeHg were found in well correlation of Hg contents of various tissues (blood, cerebral cortex, liver and kidney) in rats. For comparison, a dose of 1g/(kg day) of HgS was orally administered to the rats based on our previous findings on ototoxicity of HgS. The results revealed that HgS only reversibly delayed the recovery of suppressed CMAP and inhibited sciatic nerve Na+/K+-ATPase activity in accordance to the lower Hg contents of the tissues. These findings provide the important information on the differential susceptibility of various nervous tissues to MeHg and HgS. The neruotoxic effects produced by HgS was estimated to be about 1000 of those induced by MeHg found in this study and our previous reports.
Assuntos
Compostos de Mercúrio/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Compostos de Metilmercúrio/toxicidade , Condução Nervosa/efeitos dos fármacos , Potenciais de Ação/efeitos dos fármacos , Animais , Peso Corporal/efeitos dos fármacos , Córtex Cerebral/metabolismo , Técnicas In Vitro , Rim/metabolismo , Fígado/metabolismo , Masculino , Compostos de Mercúrio/sangue , Compostos de Mercúrio/farmacocinética , Intoxicação do Sistema Nervoso por Mercúrio/sangue , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Compostos de Metilmercúrio/sangue , Compostos de Metilmercúrio/farmacocinética , Neurônios Motores/efeitos dos fármacos , Músculos/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Nervo Isquiático/efeitos dos fármacos , Nervo Isquiático/enzimologia , ATPase Trocadora de Sódio-Potássio/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Cauda/efeitos dos fármacosRESUMO
Mercuric chloride (HgCl(2)) is a well-known nephrotoxic agent. Increasing number of evidences suggest the role of oxidative stress in HgCl(2) induced nephrotoxicity. Eruca sativa is widely used in folklore medicines and has a good reputation as a remedy of renal ailments. In the present study, the antioxidant potential of ethanolic extract of E. sativa seeds was determined and its protective effect on HgCl(2) induced renal toxicity was investigated. The extract was found to possess a potent antioxidant effect, with a large amount of polyphenols and a high reducing ability. HPLC analysis of the extract revealed glucoerucin and flavonoids to be the major antioxidants present in it. E. sativa extract significantly scavenged several reactive oxygen species (ROS) and reactive nitrogen species (RNS). Feeding of the extract to rats afforded a significant protection against HgCl(2) induced renal toxicity. Subcutaneous administration of 4 mg/kg body weight HgCl(2) induced renal injury evident as a marked elevation in serum creatinine and blood urea nitrogen levels, and histopathological changes such as necrosis, oedema and congestion of stroma and glomeruli. Oxidative modulation of renal tissues following HgCl(2) exposure was evident from a significant elevation in lipid peroxidation and attenuation in glutathione (GSH) contents and activities of antioxidant enzymes viz., catalase (CAT), glutathione peroxidase (GPX), superoxide dismutase (SOD) and glutathione reductase (GR). Oral administration of E. sativa extract to rats at a dose regimen: 50-200 mg/kg body weight for 7 days prior to HgCl(2) treatment significantly and dose dependently protected against alterations in all these diagnostic parameters. The data obtained in the present study suggests E. sativa seeds to possess a potent antioxidant and renal protective activity and preclude oxidative damage inflicted to the kidney.
Assuntos
Antioxidantes/farmacologia , Nefropatias/induzido quimicamente , Nefropatias/prevenção & controle , Intoxicação do Sistema Nervoso por Mercúrio/prevenção & controle , Mostardeira/química , Extratos Vegetais/farmacologia , Animais , Antioxidantes/metabolismo , Nitrogênio da Ureia Sanguínea , Creatinina/sangue , Sequestradores de Radicais Livres/farmacologia , Glutationa/metabolismo , Histocitoquímica , Rim/efeitos dos fármacos , Rim/metabolismo , Nefropatias/enzimologia , Nefropatias/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Masculino , Cloreto de Mercúrio/toxicidade , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/metabolismo , Ratos , Ratos Wistar , Sementes/química , Substâncias Reativas com Ácido Tiobarbitúrico/metabolismoRESUMO
We previously described a polymorphism in exon 4 of the gene encoding the heme biosynthetic pathway enzyme, coproporphyrinogen oxidase (CPOX4), which significantly modifies the effect of mercury exposure on urinary porphyrin excretion in humans. Here, we examined potential consequences of this polymorphism ("CPOX4") on performance within neurobehavioral domains, symptoms, and mood that are known to be affected by elemental mercury (Hg degrees ) exposure in human subjects. A behavioral test battery was administered on the day of urine and buccal cell collections for 194 male dentists (DDs) and 233 female dental assistants (DAs) occupationally exposed to Hg degrees for an average of 19 and 10 years, respectively. Subjects had no history of health disorders and were employed for a minimum of 5 years in the dental profession. Respective mean urinary mercury (HgU) levels in DDs and DAs were 3.32 (4.87) microg/l and 1.98 (2.29) microg/l. Corresponding indices of chronic occupational Hg degrees exposure, weighted for historical exposure, were 27.1 (20.6) and 15.2 (12.3). The frequencies of the homogygous common (A/A), heterozygous (A/C), and homozygous polymorphic (C/C) genotypes were 75%, 23% and 2% for DDs and 73%, 25%, and 2% for DAs, respectively. DDs and DAs were evaluated separately. Regression analyses controlled for age, premorbid intelligence, alcohol consumption, and education. Statistically significant associations with HgU (p<0.05) were found for nine measures among DDs (BEES Digit SpanForward and Backward, WMS-R Visual ReproductionN Correct, BEES Symbol DigitRate, BEES Finger TappingDom/Non-dom, and Alternate Partialed, Hand SteadinessFactor1, and BEES Tracking), and eight measures among DAs (BEES Digit SpanForward, BEES Symbol DigitRate, BEES Pattern Discrimination Rate, BEES Trailmaking B, BEES Finger TappingDom/Non-dom, and Alternate Partialed, Hand SteadinessFactor1, and Vibration SensitivityHits). CPOX4 status was associated with four measures in DDs (BEES Spatial SpanForward, BEES Pattern MemoryN Correct, BEES Symbol DigitRate, and BEES VigilanceHit) and five measures in DAs (BEES Digit SpanForward, WMS-R Visual ReproductionsN Correct, BEES Symbol DigitRate, BEES Simple and Choice Reaction TimeMove. Both groups experienced an additive effect (no interaction term) for HgU and the CPOX4 polymorphisms on the DigitRate whereas DAs also had additive effects for BEES Digit SpanForward and for Beck's Depression factor 'Worthlessness'. These exploratory findings suggest that the CPOX4 polymorphism may affect susceptibility for specific neurobehavioral functions associated with mercury exposure in human subjects.
Assuntos
Transtornos Cognitivos/induzido quimicamente , Coproporfirinogênio Oxidase/genética , Odontologia/estatística & dados numéricos , Predisposição Genética para Doença/genética , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Intoxicação do Sistema Nervoso por Mercúrio/genética , Exposição Ocupacional/efeitos adversos , Adulto , Sintomas Comportamentais/induzido quimicamente , Sintomas Comportamentais/enzimologia , Sintomas Comportamentais/genética , Transtornos Cognitivos/enzimologia , Transtornos Cognitivos/genética , Análise Mutacional de DNA , Transtorno Depressivo/induzido quimicamente , Transtorno Depressivo/enzimologia , Transtorno Depressivo/genética , Feminino , Testes Genéticos , Genótipo , Humanos , Masculino , Mercúrio/efeitos adversos , Mercúrio/urina , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Pessoa de Meia-Idade , Testes Neuropsicológicos , Polimorfismo Genético/genética , Desempenho Psicomotor/efeitos dos fármacos , Desempenho Psicomotor/fisiologiaRESUMO
Neurotrophin signaling through Trk receptors is important for differentiation and survival in the developing nervous system. The present study examined the effects of CH(3)Hg on (125)I-nerve growth factor (NGF) binding to the TrkA receptor, NGF-induced activation of the TrkA receptor, and neurite outgrowth in an in vitro model of differentiation using PC12 cells. Whole-cell binding assays using (125)I-NGF revealed a single binding site with a K(d) of approximately 1 nM. Methylmercury (CH(3)Hg) at 30 nM (EC(50) for neurite outgrowth inhibition) did not affect NGF binding to TrkA. TrkA autophosphorylation was measured by immunoblotting with a phospho-specific antibody. TrkA autophosphorylation peaked between 2.5 and 5 min of exposure and then decreased but was still detectable at 60 min. Concurrent exposure to CH(3)Hg and NGF for 2.5 min resulted in a concentration-dependent decrease in TrkA autophosphorylation, which was significant at 100 nM CH(3)Hg. To determine whether the observed inhibition of TrkA was sufficient to alter cell differentiation, NGF-stimulated neurite outgrowth was examined in PC12 cells after exposure to 30 nM CH(3)Hg, a concentration that inhibited TrkA autophosphorylation by approximately 50%. For comparison, a separate group of PC12 cells were exposed to a concentration of the selective Trk inhibitor K252a (30 nM), which had been shown to produce significant inhibition of TrkA autophosphorylation. Twenty-four hour exposure to either CH(3)Hg or K252a reduced neurite outgrowth to a similar degree. Our results suggest that CH(3)Hg may inhibit differentiation of PC12 cells by interfering with NGF-stimulated TrkA autophosphorylation.
Assuntos
Proteínas de Transporte/efeitos dos fármacos , Diferenciação Celular/efeitos dos fármacos , Sistema Nervoso Central/efeitos dos fármacos , Proteínas de Membrana/efeitos dos fármacos , Intoxicação do Sistema Nervoso por Mercúrio/enzimologia , Compostos de Metilmercúrio/toxicidade , Fator de Crescimento Neural/antagonistas & inibidores , Neuritos/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal , Receptor trkA , Animais , Sítios de Ligação/efeitos dos fármacos , Sítios de Ligação/fisiologia , Ligação Competitiva/efeitos dos fármacos , Ligação Competitiva/fisiologia , Proteínas de Transporte/metabolismo , Diferenciação Celular/fisiologia , Sistema Nervoso Central/anormalidades , Sistema Nervoso Central/patologia , Relação Dose-Resposta a Droga , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/fisiologia , Inibidores Enzimáticos/farmacologia , Feminino , Proteínas de Membrana/metabolismo , Intoxicação do Sistema Nervoso por Mercúrio/patologia , Intoxicação do Sistema Nervoso por Mercúrio/fisiopatologia , Fator de Crescimento Neural/metabolismo , Neuritos/enzimologia , Neuritos/patologia , Células PC12 , Fosforilação/efeitos dos fármacos , Gravidez , RatosRESUMO
Methylmercury (MeHg) is highly neurotoxic with an apparent dose-related latency period between time of exposure and the appearance of symptoms. Astrocytes are known targets for MeHg toxicity and a site of mercury localization within the central nervous system (CNS). Glutamine synthetase (GS) is an enzyme localized predominately within astrocytes. GS converts two potentially toxic molecules, glutamate and ammonia, to the relatively non-toxic amino acid, glutamine. During prolonged exposure to MeHg, inorganic mercury (I-Hg) accumulates within the brain, suggesting in situ demethylation of MeHg to I-Hg. To determine if speciation of mercurials would differentially alter GS activity and expression, neonatal rat primary astrocyte cultures were exposed to MeHg or mercuric chloride (HgCl2) for 1 or 6 h. MeHg produced no changes in GS activity, protein, or mRNA at any time or dose tested. In contrast, HgCl2 produced a dose dependent decrease in astrocytic GS activity at both 1 and 6 h. There were no changes in GS protein or mRNA levels following HgCl2 exposure. Additional studies were carried out to determine GS activity in cell lysates incubated with HgCl2 or MeHg. In cell lysates, HgCl2 was three-times more potent than MeHg in inhibiting GS activity. The inhibition of GS activity in cell lysates by HgCl2 was reversed by the addition of dithiothreitol (DTT), while DTT did not restore GS activity following MeHg. These data suggest that astrocytic GS activity is not inhibited by physiologically relevant concentrations of MeHg, but is inhibited by I-Hg, which is present in CNS following chronic MeHg exposure.