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Concentrations of nucleophilic sulfur species in small Indian mongoose (Herpestes auropunctatus) in Okinawa, Japan. CHEMOSPHERE 2022; 295:133833. [PMID: 35120952 DOI: 10.1016/j.chemosphere.2022.133833] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 01/27/2022] [Accepted: 01/31/2022] [Indexed: 06/14/2023]
Abstract
Reactive sulfur species (RSS), such as hydrogen per (poly)sulfide, cysteine per (poly)sulfide, glutathione per (poly)sulfide, and protein-bound per (poly)sulfides, can easily react with environmental electrophiles such as methylmercury (MeHg), because of their high nucleophilicity. These RSS are produced by enzymes such as cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) and are found in mammalian organs. Organs of wildlife have not been analyzed for hydrogen sulfide, cysteine, glutathione, and RSS. In this study, low molecular weight nucleophilic sulfur substances, including RSS, were quantified by stable isotope dilution assay-based liquid chromatography-mass spectrometry using β-(4-hydroxyphenyl)ethyl iodoacetamide to capture the target chemicals in the small Indian mongoose which species possesses high mercury content as same as some marine mammals. Western blotting revealed that the mongoose organs (liver, kidney, cerebrum, and cerebellum) contained proteins that cross-reacted with anti-CBS and CSE antibodies. The expression patterns of these enzymes were similar to those in mice, indicating that mongoose organs contain CBS and CSE. Moreover, bis-methylmercury sulfide (MeHg)2S, which is a low toxic compound in comparison to MeHg, was found in the liver of this species. These results suggest that the small Indian mongoose produces RSS and monothiols associated with detoxification of electrophilic organomercury. The animals which have high mercury content in their bodies may have function of mercury detoxification involved not only Se but also RSS interactions.
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Cardiac robustness regulated by reactive sulfur species. J Clin Biochem Nutr 2022; 70:1-6. [PMID: 35068674 PMCID: PMC8764107 DOI: 10.3164/jcbn.21-84] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 08/17/2021] [Indexed: 11/22/2022] Open
Abstract
The human myocardium contains robust cells that constantly beat from birth to death without being replaced, even when exposed to various environmental stresses. Myocardial robustness is thought to depend primarily on the strength of the reducing power to protect the heart from oxidative stress. Myocardial antioxidant systems are controlled by redox reactions, primarily via the redox reaction of Cys sulfhydryl groups, such as found in thioredoxin and glutathione. However, the specific molecular entities that regulate myocardial reducing power have long been debated. Recently, reactive sulfide species, with excellent electron transfer ability, consisting of a series of multiple sulfur atoms, i.e., Cys persulfide and Cys polysulfides, have been found to play an essential role in maintaining mitochondrial quality and function, as well as myocardial robustness. This review presents the latest findings on the molecular mechanisms underlying mitochondrial energy metabolism and the maintenance of quality control by reactive sulfide species and provides a new insight for the prevention of chronic heart failure.
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Adverse effects of methylmercury on gut bacteria and accelerated accumulation of mercury in organs due to disruption of gut microbiota. J Toxicol Sci 2021; 46:91-97. [PMID: 33536393 DOI: 10.2131/jts.46.91] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Methylmercury (MeHg), an environmental electrophile, binds covalently to the cysteine residues of proteins in organs, altering protein function and causing cytotoxicity. MeHg has also been shown to alter the composition of gut microbes. The gut microbiota is a complex community, the disturbance of which has been linked to the development of certain diseases. However, the relationship between MeHg and gut bacteria remains poorly understood. In this study, we showed that MeHg binds covalently to gut bacterial proteins via cysteine residues. We examined the effects of MeHg on the growth of selected Lactobacillus species, namely, L. reuteri, L. gasseri, L. casei, and L. acidophilus, that are frequently either positively or negatively correlated with human diseases. The results revealed that MeHg inhibits the growth of Lactobacillus to varying degrees depending on the species. Furthermore, the growth of L. reuteri, which was inhibited by MeHg exposure, was restored by Na2S2 treatment. By comparing mice with and without gut microbiota colonization, we found that gut bacteria contribute to the production of reactive sulfur species such as hydrogen sulfide and hydrogen persulfide in the gut. We also discovered that the removal of gut bacteria accelerated accumulation of mercury in the cerebellum, liver, and lungs of mice subsequent to MeHg exposure. These results accordingly indicate that MeHg is captured and inactivated by the hydrogen sulfide and hydrogen persulfide produced by intestinal microbes, thereby providing evidence for the role played by gut microbiota in reducing MeHg toxicity.
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Abstract
Significance: Redox homeostasis is precisely modulated by intricate systems that regulate production, elimination, and metabolism of electrophilic substances (electrophiles) in the nervous system. Since the first report of the endogenous production of reactive persulfide species in cells, such as cysteine persulfides (CysSSH), these reactive species have been a topic of extreme interest in the field of redox biology; persulfides/polysulfides possess unique chemical properties and are involved in multiple cellular functions. Recent Advances: Electrophilic signaling is mainly regulated by endogenous electrophiles that are generated from reactive oxygen species, nitric oxide, and their derivatives during stress responses, as well as by exogenous electrophiles, including compounds in foods and environmental pollutants, such as methylmercury (MeHg). Among diverse electrophiles that are endogenously generated, 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) possesses unique redox properties, of which the biosynthetic pathway, signaling mechanism, and metabolism in cells have been elucidated. Critical Issues: Persulfides, such as CysSSH, that are endogenously produced are critically involved in 8-nitro-cGMP metabolism. Exposure of neurons to the exogenous neurotoxicant, MeHg, causes severe neurodegeneration via disruption of persulfide-dependent 8-nitro-cGMP metabolism. Future Directions: Accumulating evidence indicates that persulfides are involved in various cellular functions under physiological and pathological conditions. These new aspects of redox biology related to persulfides may be frontiers of cell research, medical and clinical investigations of neurodegenerative diseases, as well as other fields. 8-Nitro-cGMP-mediated signaling and its persulfide-dependent metabolism in cells could, therefore, be potential targets for drug development, which may lead to the discovery of new therapeutic agents for many diseases, including neurodegenerative diseases.
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Fluoride-induced testicular degeneration and sperm quality deteriorations: Salutary role of Cyperus esculentus tubers (tiger nut) extract in animal model. Rev Int Androl 2020; 19:201-212. [PMID: 32703668 DOI: 10.1016/j.androl.2020.01.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Revised: 01/14/2020] [Accepted: 01/28/2020] [Indexed: 01/14/2023]
Abstract
OBJECTIVE Chronic exposure to fluoride causes tissue damage induced by oxidative imbalance, Cyperus esculentus (CE) possess anti-inflammatory and immunostimulatory properties. This study focused on Salutary role of Cyperus esculentus in sodium fluoride (NaF) induced testicular degeneration and sperm quality deteriorations. METHODS Sexually mature male Sprague-Dawley rats were randomly divided into four groups (n=6). Animals in control group received 2 mls of normal saline per day; CE group received 500mg/kg bw of CE; NaF group received 5mg/kg bw of NaF; NaF+CE group received 500mg/kg bw of CE (for 14 days pre-treatment) and NaF co-treatment till 56 days via gastric gavage. Parameters tested include: testicular histology, sperm parameters, sex hormone, fertility test, malondialdehyde (MDA), superoxide dismutase (SOD), reduced glutathione, glutathione peroxidase (GPX), catalase (CAT), testicular fluoride and testicular cholesterol. RESULTS Sodium fluoride significantly (p<.05) decrease testicular antioxidant (SOD, CAT, GSH and GPx), sperm quality, hormone profiles (TT, FSH, LH, estrogen levels), testicular cholesterol, morphometric parameters, Johnsen's Score and number of implantations in female rats with corresponding (p<.05) increase in oxidative stress makers and abnormal sperm morphology. Also depleted seminiferous epithelium and degenerate spermatogenic cells. Pretreatment with 500mg/kg bw of CE lowered NaF toxicity by significantly reducing the lipid peroxidation products, fluoride accumulation in the testis, histopathological changes of the testes and spermatozoa abnormalities and reverted observed NaF-induced inhibition in antioxidant parameters and weight of accessory sex organs. CONCLUSIONS Cyperus esculentus attenuated NaF-induced testicular injuries and protected the seminiferous epithelium, reduced oxidative stress and promoted spermatogenesis.
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Toxicity of mercury: Molecular evidence. CHEMOSPHERE 2020; 245:125586. [PMID: 31881386 DOI: 10.1016/j.chemosphere.2019.125586] [Citation(s) in RCA: 144] [Impact Index Per Article: 36.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2019] [Revised: 11/28/2019] [Accepted: 12/08/2019] [Indexed: 05/25/2023]
Abstract
Minamata disease in Japan and the large-scale poisoning by methylmercury (MeHg) in Iraq caused wide public concerns about the risk emanating from mercury for human health. Nowadays, it is widely known that all forms of mercury induce toxic effects in mammals, and increasing evidence supports the concern that environmentally relevant levels of MeHg could impact normal biological functions in wildlife. The information of mechanism involved in mercurial toxicity is growing but knowledge gaps still exist between the adverse effects and mechanisms of action, especially at the molecular level. A body of data obtained from experimental studies on mechanisms of mercurial toxicity in vivo and in vitro points to that disruption of the antioxidant system may play an important role in the mercurial toxic effects. Moreover, the accumulating evidence indicates that signaling transduction, protein or/and enzyme activity, and gene regulation are involving in mediating toxic and adaptive response to mercury exposure. We conducted here a comprehensive review of mercurial toxic effects on wildlife and human, in particular synthesized key findings of molecular pathways involved in mercurial toxicity from the cells to human. We discuss the molecular evidence related mercurial toxicity to the adverse effects, with particular emphasis on the gene regulation. The further studies relying on Omic analysis connected to adverse effects and modes of action of mercury will aid in the evaluation and validation of causative relationship between health outcomes and gene expression.
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Depolysulfidation of Drp1 induced by low-dose methylmercury exposure increases cardiac vulnerability to hemodynamic overload. Sci Signal 2019; 12:12/587/eaaw1920. [DOI: 10.1126/scisignal.aaw1920] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Exposure to Electrophiles Impairs Reactive Persulfide-Dependent Redox Signaling in Neuronal Cells. Chem Res Toxicol 2017; 30:1673-1684. [PMID: 28837763 DOI: 10.1021/acs.chemrestox.7b00120] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Electrophiles such as methylmercury (MeHg) affect cellular functions by covalent modification with endogenous thiols. Reactive persulfide species were recently reported to mediate antioxidant responses and redox signaling because of their strong nucleophilicity. In this study, we used MeHg as an environmental electrophile and found that exposure of cells to the exogenous electrophile elevated intracellular concentrations of the endogenous electrophilic molecule 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP), accompanied by depletion of reactive persulfide species and 8-SH-cGMP which is a metabolite of 8-nitro-cGMP. Exposure to MeHg also induced S-guanylation and activation of H-Ras followed by injury to cerebellar granule neurons. The electrophile-induced activation of redox signaling and the consequent cell damage were attenuated by pretreatment with a reactive persulfide species donor. In conclusion, exogenous electrophiles such as MeHg with strong electrophilicity impair the redox signaling regulatory mechanism, particularly of intracellular reactive persulfide species and therefore lead to cellular pathogenesis. Our results suggest that reactive persulfide species may be potential therapeutic targets for attenuating cell injury by electrophiles.
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Alkyl Mercury-Induced Toxicity: Multiple Mechanisms of Action. REVIEWS OF ENVIRONMENTAL CONTAMINATION AND TOXICOLOGY 2017; 240:105-149. [PMID: 27161558 PMCID: PMC10508330 DOI: 10.1007/398_2016_1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
There are a number of mechanisms by which alkylmercury compounds cause toxic action in the body. Collectively, published studies reveal that there are some similarities between the mechanisms of the toxic action of the mono-alkyl mercury compounds methylmercury (MeHg) and ethylmercury (EtHg). This paper represents a summary of some of the studies regarding these mechanisms of action in order to facilitate the understanding of the many varied effects of alkylmercurials in the human body. The similarities in mechanisms of toxicity for MeHg and EtHg are presented and compared. The difference in manifested toxicity of MeHg and EtHg are likely the result of the differences in exposure, metabolism, and elimination from the body, rather than differences in mechanisms of action between the two.
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S-Mercuration of ubiquitin carboxyl-terminal hydrolase L1 through Cys152 by methylmercury causes inhibition of its catalytic activity and reduction of monoubiquitin levels in SH-SY5Y cells. J Toxicol Sci 2016; 40:887-93. [PMID: 26558469 DOI: 10.2131/jts.40.887] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Methylmercury (MeHg) is an environmental electrophile that covalently modifies cellular proteins. In this study, we identified proteins that undergo S-mercuration by MeHg. By combining two-dimensional SDS-PAGE, atomic absorption spectrometry and ultra performance liquid chromatography mass spectrometry (UPLC/MS/MS), we revealed that ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) is a target for S-mercuration in human neuroblastoma SH-SY5Y cells exposed to MeHg (1 µM, 9 hr). The modification site of UCH-L1 by MeHg was Cys152, as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. MeHg was shown to inhibit the catalytic activity of recombinant human UCH-L1 in a concentration-dependent manner. Knockdown of UCH-L1 indicated that this enzyme plays a critical role in regulating mono-ubiquitin (monoUb) levels in SH-SY5Y cells and exposure of SH-SY5Y cells to MeHg caused a reduction in the level of monoUb in these cells. These observations suggest that UCH-L1 readily undergoes S-mercuration by MeHg through Cys152 and this covalent modification inhibits UCH-L1, leading to the potential disruption of the maintenance of cellular monoUb levels.
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Methylmercury, an environmental electrophile capable of activation and disruption of the Akt/CREB/Bcl-2 signal transduction pathway in SH-SY5Y cells. Sci Rep 2016; 6:28944. [PMID: 27357941 PMCID: PMC4928048 DOI: 10.1038/srep28944] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Accepted: 06/06/2016] [Indexed: 11/24/2022] Open
Abstract
Methylmercury (MeHg) modifies cellular proteins via their thiol groups in a process referred to as “S-mercuration”, potentially resulting in modulation of the cellular signal transduction pathway. We examined whether low-dose MeHg could affect Akt signaling involved in cell survival. Exposure of human neuroblastoma SH-SY5Y cells of up to 2 μM MeHg phosphorylated Akt and its downstream signal molecule CREB, presumably due to inactivation of PTEN through S-mercuration. As a result, the anti-apoptotic protein Bcl-2 was up-regulated by MeHg. The activation of Akt/CREB/Bcl-2 signaling mediated by MeHg was, at least in part, linked to cellular defence because either pretreatment with wortmannin to block PI3K/Akt signaling or knockdown of Bcl-2 enhanced MeHg-mediated cytotoxicity. In contrast, increasing concentrations of MeHg disrupted Akt/CREB/Bcl-2 signaling. This phenomenon was attributed to S-mercuration of CREB through Cys286 rather than Akt. These results suggest that although MeHg is an apoptosis-inducing toxicant, this environmental electrophile is able to activate the cell survival signal transduction pathway at lower concentrations prior to apoptotic cell death.
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NADPH-cytochrome P450 reductase-mediated denitration reaction of 2,4,6-trinitrotoluene to yield nitrite in mammals. Free Radic Biol Med 2016; 91:178-87. [PMID: 26454083 DOI: 10.1016/j.freeradbiomed.2015.09.011] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/03/2015] [Revised: 09/01/2015] [Accepted: 09/03/2015] [Indexed: 10/22/2022]
Abstract
While the biodegradation of 2,4,6-trinitrotoluene (TNT) via the release of nitrite is well established, mechanistic details of the reaction in mammals are unknown. To address this issue, we attempted to identify the enzyme from rat liver responsible for the production of nitrite from TNT. A NADPH-cytochrome P450 reductase (P450R) was isolated and identified from rat liver microsomes as the enzyme responsible for not only the release of nitrite from TNT but also formation of superoxide and 4-hydroxyamino-2,6-dinitrotoluene (4-HADNT) under aerobic conditions. In this context, reactive oxygen species generated during P450R-catalyzed TNT reduction were found to be, at least in part, a mediator for the production of 4-HADNT from TNT via formation of 4-nitroso-2,6-dinitrotoluene. P450R did not catalyze the formation of the hydride-Meisenheimer complex (H(-)-TNT) that is thought to be an intermediate for nitrite release from TNT. Furthermore, in a time-course experiment, 4-HADNT formation reached a plateau level and then declined during the reaction between TNT and P450R with NADPH, while the release of nitrite was subjected to a lag period. Notably, the produced 4-HADNT can react with the parent compound TNT to produce nitrite and dimerized products via formation of a Janovsky complex. Our results demonstrate for the first time that P450R-mediated release of nitrite from TNT results from the process of chemical interaction of TNT and its 4-electron reduction metabolite 4-HADNT.
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Abstract
Bismethylmercury sulfide (MeHg)2S has been found to be a detoxified metabolite of methylmercury (MeHg) that is produced by SH-SY5Y cells and in livers of rats exposed to MeHg. (MeHg)2S could be formed through the interactions between MeHg and sulfur species such as hydrogen sulfide (H2S or HS(-)), but the origin of its sulfur has not been fully identified. We herein examined the formation of (MeHg)2S through interactions between MeHg and persulfides, polysulfides, and protein preparations. Investigations using HPLC/atomic absorption spectrophotometry and EI-MS revealed that NaHS and Na2S4 react readily with MeHg to give (MeHg)2S, and similar results were found using GSH persulfide (GSSH) formed endogenously or generated enzymatically in vitro. (MeHg)2S was also formed by incubation of MeHg with liver and heart cytosolic fractions prepared from wild-type mice but not with those from mice lacking cystathionine γ-lyase (CSE) that catalyzes the formation of cysteine persulfide. Consistent with this, (MeHg)2S was detected in a variety of tissues taken from wild-type mice intraperitoneally injected with MeHg in vivo but not in those from MeHg-injected CSE knockout mice. By separating liver fractions by column chromatography, we found numerous proteins that contain persulfides: one of the proteins was identified as being glutathione S-transferase pi 1. These results indicate that the formation of (MeHg)2S can be attributed to interactions between MeHg and endogenous free persulfide species, as well as protein-bound cysteine persulfide.
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Correlation Between Attenuation of Protein Disulfide Isomerase Activity Through S-Mercuration and Neurotoxicity Induced by Methylmercury. Neurotox Res 2014; 27:99-105. [DOI: 10.1007/s12640-014-9494-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 09/22/2014] [Accepted: 09/29/2014] [Indexed: 10/24/2022]
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Cytotoxicity evaluation and antioxidant enzyme expression related to heavy metals found in tuna by-products meal: An in vitro study in human and rat liver cell lines. ACTA ACUST UNITED AC 2013; 65:1025-33. [DOI: 10.1016/j.etp.2013.03.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2012] [Revised: 02/18/2013] [Accepted: 03/07/2013] [Indexed: 11/19/2022]
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Effect of Bacopa monniera extract on methylmercury-induced behavioral and histopathological changes in rats. Biol Trace Elem Res 2013; 155:56-64. [PMID: 23872736 DOI: 10.1007/s12011-013-9756-y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Accepted: 07/04/2013] [Indexed: 11/28/2022]
Abstract
Methylmercury (MeHg) is a well-recognized environmental contaminant with established health risk to human beings by fish and marine mammal consumption. Bacopa monniera (BM) is a perennial herb and is used as a nerve tonic in Ayurveda, a traditional medicine system in India. This study was aimed to evaluate the effect of B. monniera extract (BME) on MeHg-induced toxicity in rat cerebellum. Male Wistar rats were administered with MeHg orally at a dose of 5 mg/kg b.w. for 21 days. Experimental rats were given MeHg and also administered with BME (40 mg/kg, orally) 1 h prior to the administration of MeHg for 21 days. After treatment period, MeHg exposure significantly decreases the body weight and also caused the following behavioral changes. Decrease tail flick response, longer immobility time, significant decrease in motor activity, and spatial short-term memory. BME pretreatment reverted the behavioral changes to normal. MeHg exposure decreases the DNA and RNA content in cerebellum and also caused some pathological changes in cerebellum. Pretreatment with BME restored all the changes to near normal. These findings suggest that BME has a potent efficacy to alleviate MeHg-induced toxicity in rat cerebellum.
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The role of the Keap1/Nrf2 pathway in the cellular response to methylmercury. OXIDATIVE MEDICINE AND CELLULAR LONGEVITY 2013; 2013:848279. [PMID: 23878621 PMCID: PMC3710591 DOI: 10.1155/2013/848279] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/28/2013] [Revised: 05/26/2013] [Accepted: 06/03/2013] [Indexed: 12/26/2022]
Abstract
Methylmercury (MeHg) is an environmental electrophile that covalently modifies cellular proteins with reactive thiols, resulting in the formation of protein adducts. While such protein modifications, referred to as S-mercuration, are thought to be associated with the enzyme dysfunction and cellular damage caused by MeHg exposure, the current consensus is that (1) there is a cellular response to MeHg through the activation of NF-E2-related factor 2 (Nrf2) coupled to S-mercuration of its negative regulator, Kelch-like ECH-associated protein 1 (Keap1), and (2) the Keap1/Nrf2 pathway protects against MeHg toxicity. In this review, we introduce our findings and discuss the observations of other workers concerning the S-mercuration of cellular proteins by MeHg and the importance of the Keap1/Nrf2 pathway in protection against MeHg toxicity in cultured cells and mice.
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Ratiometric sensing of mercury(II) based on a FRET process on silica core-shell nanoparticles acting as vehicles. Mikrochim Acta 2013. [DOI: 10.1007/s00604-013-1002-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Improvement of mercuric chloride-induced testis injuries and sperm quality deteriorations by Spirulina platensis in rats. PLoS One 2013; 8:e59177. [PMID: 23555627 PMCID: PMC3610915 DOI: 10.1371/journal.pone.0059177] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2012] [Accepted: 02/12/2013] [Indexed: 01/24/2023] Open
Abstract
The present study was undertaken to investigate the protective effect of the filamentous cyanobacterium Spirulina platensis (S. platensis) on mercury (II) chloride (HgCl(2))-induced oxidative damages and histopathological alterations in the testis of Wistar albino rats. The animals were divided into four equal groups, i) control, ii) HgCl(2), iii) S. platensis and iv) combination of HgCl(2)+S. platensis. Oxidative stress, induced by a single dose of HgCl(2) (5 mg/kg, bw; subcutaneously, s.c.), substantially decreased (P<0.01) the activity level of testicular key enzymatic antioxidant biomarkers (superoxide dismutase, SOD; catalase, CAT and glutathione peroxidase, GPx), oxidative stress makers (blood hydroperoxide; testicular reduced glutathione, GSH and malondialdehyde, MDA), and testicular mercury levels. Moreover, HgCl(2) administration resulted in a significant (P<0.01) increase in the number of sperms with abnormal morphology and decrease in epididymal sperm count, motility, plasma testosterone level and testicular cholesterol. Furthermore, HgCl(2) exposure induced histopathological changes to the testis including morphological alterations of the seminiferous tubules, and degeneration and dissociation of spermatogenic cells. Notably, oral pretreatment of animals with Spirulina (300 mg/kg, bw) lowered the extent of the observed HgCl(2)-mediated toxicity, whereby significantly reducing the resulting lipid peroxidation products, mercury accumulation in the testis, histopathological changes of the testes and spermatozoal abnormalities. In parallel, the pretreatment with Spirulina also completely reverted the observed Hg-Cl(2)-induced inhibition in enzymatic activities of antioxidant biomarkers (SOD, CAT and GPx) back to control levels. The pretreatment of rats with S. platensis significantly recovered the observed HgCl(2)-mediated decrease in the weight of accessory sex organs. Taken together, our findings clearly highlight the role of S. platensis as a protective modulator of HgCl(2)-induced testicular injuries and suggest some therapeutic potential in mammals. Further investigation of therapeutic strategies employing Spirulina against heavy metals toxicity in humans is therefore warranted.
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Inhibitory effect of α-tocopherol on methylmercury-induced oxidative steress. Environ Health Prev Med 2012; 9:111-7. [PMID: 21432319 DOI: 10.1007/bf02898069] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2003] [Accepted: 02/16/2004] [Indexed: 10/21/2022] Open
Abstract
OBJECTIVES The present study investigated the involvement of oxidative stress in the degeneration of the cerebellum during methylmercury (MeHg) intoxication and the protective effect of α-tocopherol (Vit E) against MeHg toxicity. METHODS After 5 mg/kg of MeHg was administered to Wistar rats for 12 consecutive days, the cerebellum were examined histopathologically. In addition, the same amount of MeHg was administered to 3 different groups of Wistar rats: rats with a Vit E-deficient diet, rats fed 150 mg/kg of Vit E for 20 consecutive days after initial MeHg administration, and rats with an ordinary diet. RESULTS Positive immunoreactivity against anti-hydroxynonenal (HNE), a marker of lipid peroxidation, was observed in the cerebellum after MeHg administration. Levels of thiobarbituric acid reactive substance (TBARS), another marker of lipid peroxidation, and those of protein carbonyl, a biomarker for protein oxidation, increased after MeHg administration. In the rats with MeHg and a Vit E-deficient diet, mortality and prevalence of piloerection significantly increased, and in the rats with MeHg and Vit E, mortality, piloerection, retracted and crossed hind leg, and ataxic gait significantly decreased, compared with the rats with MeHg alone. The levels of NO(2) (-) and NO(3) (-) in the serum significantly increased in the rats with MeHg alone 14 days after the initial MeHg administration, but were significantly suppressed by Vit E administration. CONCLUSIONS Oxidative stress, especially lipid peroxidation, may play an important role in the cerebellar degeneration process during MeHg intoxication and Vit E may play a protective role against MeHg toxicity as an effective antioxidant.
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Hematotoxicity and genotoxicity of mercuric chloride following subchronic exposure through drinking water in male rats. Biol Trace Elem Res 2012; 148:76-82. [PMID: 22351102 DOI: 10.1007/s12011-012-9342-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Accepted: 01/23/2012] [Indexed: 10/14/2022]
Abstract
Erythrocytes are a convenient model to understand the subsequent oxidative deterioration of biological macromolecules in metal toxicities. The present study examined the variation of hematoxic and genotoxic parameters following subchronic exposure of mercuric chloride via drinking water and their possible association with oxidative stress. Male rats were exposed to 50 ppm (HG1) and 100 ppm (HG2) of mercuric chloride daily for 90 days. A significant dose-dependent decrease was observed in red blood cell count, hemoglobin, hematocrit, and mean cell hemoglobin concentration in treated groups (HG1 and HG2) compared with controls. A significant dose-dependent increase was observed in lipid peroxidation; therefore, a significant variation was found in the antioxidant enzyme activities, such as superoxide dismutase, catalase, and glutathione peroxidase. Interestingly, mercuric chloride treatment showed a significant dose-dependent increase in frequency of total chromosomal aberration and in percentage of aberrant bone marrow metaphase of treated groups (p < 0.01). The oxidative stress induced by mercury treatment may be the major cause for chromosomal aberration as free radicals lead to DNA damage. These data will be useful in screening the antioxidant activities of natural products, which may be specific to the bone marrow tissue.
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S-Mercuration of rat sorbitol dehydrogenase by methylmercury causes its aggregation and the release of the zinc ion from the active site. Arch Toxicol 2012; 86:1693-702. [PMID: 22752181 DOI: 10.1007/s00204-012-0893-4] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2012] [Accepted: 06/12/2012] [Indexed: 11/25/2022]
Abstract
We previously developed a screening method to identify proteins that undergo aggregation through S-mercuration by methylmercury (MeHg) and found that rat arginase I is a target protein for MeHg (Kanda et al. in Arch Toxicol 82:803-808, 2008). In the present study, we characterized another S-mercurated protein from a rat hepatic preparation that has a subunit mass of 42 kDa, thereby facilitating its aggregation. Two-dimensional SDS-polyacrylamide gel electrophoresis and subsequent peptide mass fingerprinting using matrix-assisted laser desorption and ionization time-of-flight mass spectrometry revealed that the 42 kDa protein was NAD-dependent sorbitol dehydrogenase (SDH). With recombinant rat SDH, we found that MeHg is covalently bound to SDH through Cys44, Cys119, Cys129 and Cys164, resulting in the inhibition of its catalytic activity, release of zinc ions and facilitates protein aggregation. Mutation analysis indicated that Cys44, which ligates the active site zinc atom, and Cys129 play a crucial role in the MeHg-mediated aggregation of SDH. Pretreatment with the cofactor NAD, but not NADP or FAD, markedly prevented aggregation of SDH. Such a protective effect of NAD on the aggregation of SDH caused by MeHg is discussed.
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Protective Effect of Bacopa monniera on Methyl Mercury-Induced Oxidative Stress in Cerebellum of Rats. Cell Mol Neurobiol 2012; 32:979-87. [DOI: 10.1007/s10571-012-9813-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2011] [Accepted: 02/04/2012] [Indexed: 01/21/2023]
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Impairment of spermatogenesis in rats by mercuric chloride: involvement of low 17β-estradiol level in induction of acute oxidative stress. Biol Trace Elem Res 2011; 142:598-610. [PMID: 20820944 DOI: 10.1007/s12011-010-8774-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Accepted: 07/09/2010] [Indexed: 11/24/2022]
Abstract
Mercuric chloride (HgCl(2)) has been shown to affect the male reproductive organs, and oxidative stress has been linked with hypospermatogenesis and with male infertility. However, the specific mode of impairment of spermatogenesis during HgCl(2) exposure has not yet been clarified fully. Because of the involvement of 17β-estradiol (E2) in the male reproductive tract and its putative role on spermatogenesis, the present study aimed to investigate the possibility that HgCl(2)-induced oxidative stress-mediated modulation of the E2 level exerts adverse effects on testicular steroidogenic and gametogenic activities. HgCl(2) treatment at 50 and 100 ppm for 90 days by continuous oral administration in the drink water resulted in significant dose-dependent fashion decrease in serum and testicular E(2) levels and an increase in testicular testosterone levels in dose-dependent manner, without statistical alteration in serum testosterone level among HgCl(2) exposed groups compared to the control. Cauda epididymal sperm count and motility were decreased significantly (p < 0.01), in a dose-dependent manner, in the HgCl(2)-treated groups, and qualitative examination revealed inhibition of spermatogenesis and the preferential loss of maturing and elongated spermatids. The seminiferous tubules were dilated in treated animals. When compared to the control, increase in lipid peroxidation due to toxic effects of HgCl2 was accompanied by significant reduction (p < 0.01) in antioxidant enzymes activities, superoxide dismutase, catalase, and glutathione peroxidase of testes, implicating the presence of oxidative tissue damage. Furthermore, these tissue injuries caused functional impairment as evidenced with testicular elevated activity of lactate dehydrogenase. Unless oxidative stress can lead to cancer development, testis' tumor markers as beta human chorionic gonadotropin and alpha-fetoprotein levels have shown no significant differences in the HgCl(2)-exposed group compared with respect to the control. Large quantities of metal accumulated in the testis tissue are in agreement with the testis-activity failure verified in this tissue. These findings suggest that a decrease in E2 level after mercury exposure may render testis more susceptible to oxidative damage leading to its functional inactivation, thus providing new dimension to mechanisms underlying heavy metal-induced male infertility.
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Reduction of arginase I activity and manganese levels in the liver during exposure of rats to methylmercury: a possible mechanism. Arch Toxicol 2008; 82:803-8. [PMID: 18488197 DOI: 10.1007/s00204-008-0307-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2008] [Accepted: 04/22/2008] [Indexed: 10/22/2022]
Abstract
The toxicity of methylmercury (MeHg) is, in part, thought to be due to its interaction with thiol groups in a variety of enzymes, but the molecular targets of MeHg are poorly understood. Arginase I, an abundant manganese (Mn)-binding protein in the liver, requires Mn as an essential element to exhibit maximal enzyme activity. In the present study, we examined the effect of MeHg on hepatic arginase I in vivo and in vitro. Subcutaneous administration of MeHg (10 mg/kg) for 8 days to rats resulted in marked suppression of arginase I activity. With purified arginase I, we found that interaction of MeHg with arginase I caused the aggregation of arginase I as evaluated by centrifugation and subsequent precipitation, and then the reduction of catalytic activity. Experiments with organomercury column confirmed that arginase I has reactive thiols that are covalently bound to organomercury. While MeHg inhibited arginase I activity, Mn ions were released from this enzyme. These results suggest that MeHg-mediated suppression of hepatic arginase I activity in vivo is, at least in part, attributable to covalent modification of MeHg or substantial leakage of Mn ions from the active site.
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Attenuation by methyl mercury and mercuric sulfide of pentobarbital induced hypnotic tolerance in mice through inhibition of ATPase activities and nitric oxide production in cerebral cortex. Arch Toxicol 2007; 82:343-53. [DOI: 10.1007/s00204-007-0255-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2007] [Accepted: 10/16/2007] [Indexed: 12/15/2022]
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Abstract
Mechanistic studies on the effects of MeHg in the central nervous system (CNS) have been limited to morphology, substrate uptake and macromolecular synthesis, differentiation, and changes in gene expression during development and adulthood, but its primary site of action has yet to be identified. Proper functioning of the nitric oxide synthase (NOS)-cyclic GMP and the cyclooxygenase (COX)-prostaglandin (PG) signaling pathways in the CNS depend on post-translational modifications of key enzymes by chaperone proteins. The ability of MeHg to alter or inhibit chaperone-client protein interactions is hitherto unexplored, and potentially offers an upstream unifying mechanism for the plethora of MeHg effects, ranging from reactive species generation (ROS) generation, mitochondrial dysfunction, changes in redox potential, macromolecule synthesis, and cell swelling. In view of the prominent function of astrocytes in the maintenance of the extracellular milieu and their critical role in mediating MeHg neurotoxicity, they afford a relevant and well-established experimental model. The present review is predicated on (a) the remarkable affinity of mercurials for the anionic form of sulfhydryl (-SH) groups, (b) the essential role of thiols in protein biochemistry, and (c) the role of molecular chaperone proteins, such as heat shock protein 90 (Hsp90) in the regulation of protein redox status by facilitating the formation and breakage of disulfide bridges. We offer potential sites where MeHg may interfere with cellular homeostasis and advance a novel mechanistic model for MeHg-induced neurotoxicity.
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Roundtable Discussion Groups Summary Papers: New Bioindicators for Mercury Toxicological Assessment: Recommendations from the First International Bioindicators Roundtable. ACTA ACUST UNITED AC 2007. [DOI: 10.1080/15555270701626422] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Cytoprotective role of Nrf2/Keap1 system in methylmercury toxicity. Biochem Biophys Res Commun 2007; 363:645-50. [PMID: 17904103 DOI: 10.1016/j.bbrc.2007.09.017] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2007] [Accepted: 09/06/2007] [Indexed: 11/27/2022]
Abstract
Human exposure to methylmercury (MeHg) from contaminated fish is a potential health risk. Because of its chemical properties as a soft electrophile, we investigated the participation of Nrf2 in the cellular response to and protection against MeHg with SH-SY5Y cells and with primary mouse hepatocytes from Nrf2- and Keap1-deficient mice. Exposure of SH-SY5Y cells to MeHg activated Nrf2 through the binding of MeHg and Keap1. Nrf2 overexpression attenuated MeHg-induced cytotoxicity in SH-SY5Y cells. In addition, primary mouse hepatocytes extracted from Nrf2-deficient mouse was susceptible, and hepatocyte-specific conditional Keap1-deficient mouse was resistant to MeHg-induced cytotoxicity. Consistent with this data, MeHg was accumulated by Nrf2 deficiency and reduced by Keap1 deficiency. Our findings indicate that MeHg activates Nrf2 and the activation of Nrf2 is essential for reduction of MeHg toxicity by facilitating its excretion into extracellular space.
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MESH Headings
- Adaptor Proteins, Signal Transducing/genetics
- Adaptor Proteins, Signal Transducing/metabolism
- Adaptor Proteins, Signal Transducing/physiology
- Animals
- Blotting, Western
- Cell Line, Tumor
- Cell Survival/drug effects
- Cells, Cultured
- Cytoskeletal Proteins/genetics
- Cytoskeletal Proteins/metabolism
- Cytoskeletal Proteins/physiology
- Dose-Response Relationship, Drug
- Hepatocytes/cytology
- Hepatocytes/drug effects
- Hepatocytes/metabolism
- Humans
- Kelch-Like ECH-Associated Protein 1
- Luciferases/genetics
- Luciferases/metabolism
- Methylmercury Compounds/metabolism
- Methylmercury Compounds/toxicity
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- NF-E2-Related Factor 2/genetics
- NF-E2-Related Factor 2/metabolism
- NF-E2-Related Factor 2/physiology
- Protein Binding
- RNA, Small Interfering/genetics
- Recombinant Fusion Proteins/metabolism
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Downregulation of arginase II and renal apoptosis by inorganic mercury: overexpression of arginase II reduces its apoptosis. Arch Toxicol 2007; 82:67-73. [PMID: 17874066 DOI: 10.1007/s00204-007-0244-z] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2007] [Accepted: 08/22/2007] [Indexed: 11/27/2022]
Abstract
Inorganic mercury is a toxic metal that accumulates in the proximal tubules of the kidney, causing apoptosis. Arginase II is known to inhibit apoptosis, but its role in the renal apoptosis caused by inorganic mercury is poorly understood. In the present study, we examined the involvement of arginase II in inorganic mercury-dependent apoptosis. A single exposure to mercuric chloride (HgCl(2), 1 mg/kg) in rats resulted in a dramatic time-dependent reduction in the activity of arginase II in the kidney; for example, the activity at 48 h after exposure was 31% of the control level. The decrease in arginase II activity was due to a decrease in the protein level, not to a reduction in gene expression or to direct inhibition of the activity itself. More interestingly, diminished arginase II activity was well correlated with the induction of apoptosis as evaluated by renal DNA fragmentation (r = 0.99). Overexpression of arginase II in LLC-PK(1) cells blocked cell death during exposure to inorganic mercury. These results suggest that inorganic mercury causes a reduction in protein levels of arginase II, and that impaired arginase II activity is, at least in part, associated with the apoptotic cell damage caused by this heavy metal.
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Comparative effects of dietary methylmercury on gene expression in liver, skeletal muscle, and brain of the zebrafish (Danio rerio). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2005; 39:3972-80. [PMID: 15984772 DOI: 10.1021/es0483490] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Effects of dietary methylmercury (MeHg) on gene expression were examined in three organs (liver, skeletal muscle, and brain) of the zebrafish (Danio rerio). Adult male fish were fed over 7, 21, and 63 days on three different diets: one control diet (C0: 0.08 microg of Hg g(-1), dry wt) and two diets (C1 and C2) contaminated by MeHg at 5 and 13.5 microg of Hg g(-1), dry wt. Total Hg and MeHg concentrations were determined in the three organs after each exposure duration, and a demethylation process was evidenced only in the liver. Thirteen genes known to be involved in antioxidant defenses, metal chelation, active efflux of organic compounds, mitochondrial metabolism, DNA repair, and apoptosis were investigated by quantitative real-time RT-PCR and normalized according to actin gene expression. Surprisingly, no change in the expression levels of these genes was observed in contaminated brain samples, although this organ accumulated the highest mercury concentration (63.5 +/- 4.4 microg g(-1), dry wt after 63 days). This lack of genetic response could explain the high neurotoxicity of MeHg. coxI and cytoplasmic and mitochondrial sod gene expressions were induced early in skeletal muscle and later in liver, indicating an impact on the mitochondrial metabolism and production of reactive oxygen species. Results demonstrated that skeletal muscle was not only an important storage reservoir but was also affected by MeHg contamination. The expression of the metallothionein mt2 and the DNA repair rad51 genes was up-regulated in liver between 21 and 63 days, whereas in skeletal muscle, mt2 remained uninduced, and gadd and rad51 were found to be repressed.
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Neuronal nitric oxide synthase (NNOS) catalyzes one-electron reduction of 2,4,6-trinitrotoluene, resulting in decreased nitric oxide production and increased nNOS gene expression: implication for oxidative stress. Free Radic Biol Med 2004; 37:350-7. [PMID: 15223068 DOI: 10.1016/j.freeradbiomed.2004.04.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/09/2003] [Revised: 03/22/2004] [Accepted: 04/22/2004] [Indexed: 11/23/2022]
Abstract
To determine the mechanism of 2,4,6-trinitrotoluene (TNT)-induced oxidative stress involving neuronal nitric oxide synthase (nNOS), we examined alterations in enzyme activity and gene expression of nNOS by TNT, with an enzyme preparation and rat cerebellum primary neuronal cells. TNT inhibited nitric oxide formation (IC(50) = 12.4 microM) as evaluated by citrulline formation in a 20,000 g cerebellar supernatant preparation. A kinetic study revealed that TNT was a competitive inhibitor with respect to NADPH and a noncompetitive inhibitor with respect to L-arginine. It was found that purified nNOS was capable of reducing TNT, with a specific activity of 3900 nmol of NADPH oxidized/mg/min, but this reaction required CaCl(2)/calmodulin (CaM). An electron spin resonance (ESR) study indicated that superoxide (O(2)(.-)) was generated during reduction of TNT by nNOS. Exposure of rat cerebellum primary neuronal cells to TNT (25 microM) caused an intracellular generation of H(2)O(2), accompanied by a significant increase in nNOS mRNA levels. These results indicate that CaM-dependent one-electron reduction of TNT is catalyzed by nNOS, leading to a reduction in NO formation and generation of H(2)O(2) derived from O(2)(.-). Thus, it is suggested that upregulation of nNOS may represent an acute adaptation to an increase in oxidative stress during exposure to TNT.
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Abstract
Mercury is a ubiquitous contaminant, and a range of chemical species is generated by human activity and natural environmental change. Elemental mercury and its inorganic and organic compounds have different toxic properties, but all them are considered hazardous in human exposure. In an equimolecular exposure basis, organomercurials with a short aliphatic chain are the most harmful compounds and they may cause irreversible damage to the nervous system. Methylmercury (CH(3)Hg(+)) is the most studied following the neurotoxic outbreaks identified as Minamata disease and the Iraq poisoning. The first description of the CNS pathology dates from 1954. Since then, the clinical neurology, the neuropathology and the mechanisms of neurotoxicity of organomercurials have been widely studied. The high thiol reactivity of CH(3)Hg(+), as well as all mercury compounds, has been suggested to be the basis of their harmful biological effects. However, there is clear selectivity of CH(3)Hg(+) for specific cell types and brain structures, which is not yet fully understood. The main mechanisms involved are inhibition of protein synthesis, microtubule disruption, increase of intracellular Ca(2+) with disturbance of neurotransmitter function, oxidative stress and triggering of excitotoxicity mechanisms. The effects are more damaging during CNS development, leading to alterations of the structure and functionality of the nervous system. The major source of CH(3)Hg(+) exposure is the consumption of fish and, therefore, its intake is practically unavoidable. The present concern is on the study of the effects of low level exposure to CH(3)Hg(+) on human neurodevelopment, with a view to establishing a safe daily intake. Recommendations are 0.4 micro g/kg body weight/day by the WHO and US FDA and, recently, 0.1 micro g/kg body weight/day by the US EPA. Unfortunately, these levels are easily attained with few meals of fish per week, depending on the source of the fish and its position in the food chain.
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Abstract
Nitric oxide (NO) is produced in the vascular endothelium and is a potent vasodilator substance that participates in the regulation of local vascular tone. Exercise causes peculiar changes in systemic and regional blood flow, i.e., an increase of systemic blood flow and a redistribution of local tissue blood flow, by which the blood flow is greatly increased in the working muscles, whereas it is decreased in some organs such as the kidney and intestine. Thus we hypothesized that exercise causes a tissue-specific change of NO production in some internal organs. We studied whether exercise affects expression of NO synthase (NOS) mRNA and protein, NOS activity, and tissue level of nitrite/nitrate (stable end products of NO) in the kidneys (in which blood flow during exercise is decreased) and lungs (in which blood flow during exercise is increased with the increase of cardiac output) of rat. Rats ran on a treadmill for 45 min at a speed of 25 m/min. Immediately after this exercise, kidneys and lungs were quickly removed. Control rats remained at rest during this 45-min period. Expression of endothelial NOS (eNOS) mRNA in the kidneys was markedly lower in exercise rats than in control rats, whereas that in the lungs was significantly higher in exercise rats than in control rats. Western blot analysis confirmed down- and upregulation of eNOS protein in the kidney and lung, respectively, after exercise. On the other hand, neither expression of neuronal NOS (nNOS) mRNA and nNOS protein nor inducible NOS (iNOS) mRNA and iNOS protein in the kidneys and lungs differed between exercise and control rats. NOS activity in the kidney was significantly lower in exercise rats than in control rats, whereas that in the lung was significantly higher in exercise rats than in control rats. On the other hand, the iNOS activity in the kidneys and lungs did not differ between exercise rats and control rats. Tissue nitrite/nitrate level in the kidneys was markedly lower in exercise rats, whereas that in the lungs was significantly higher in exercise rats. The present results show that production of NO is markedly and tissue-specifically changed in the kidney and lung by exercise.
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Impairment of spermatogenesis in rats by methylmercury: involvement of stage- and cell- specific germ cell apoptosis. Toxicology 2001; 169:25-35. [PMID: 11696407 DOI: 10.1016/s0300-483x(01)00487-5] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Methylmercury has been shown to affect the male reproductive organs. However, the specific mode of impairment of spermatogenesis during methylmercury exposure remains unknown. In this study, we characterized the induction of germ cell apoptosis and reproductive toxicity in Wistar male rats that had been exposed to methylmercuric chloride (MMC). Subcutaneous injection of MMC at a dose of 10 mg/kg per day for 8 days resulted in a 28% testicular weight loss at 14 days after the first injection. In addition, the ventral and dorso-lateral prostatic lobes showed a 65 and 52% decrease, respectively, at 14 days, although no effects were observed in the epididymis. Sperm production also was suppressed by the administration of MMC. After exposure to MMC, fragmentation of testicular DNA was found to be increased at 3 days after the first injection, with a 20-fold increase over control levels at 14 days. In situ detection of apoptosis by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end-labeling (TUNEL) staining revealed that spermatocytes and spermatids at stages VII-VIII and IX-XI, respectively, steps which are considered to be highly sensitive to testosterone, were the major cell types affected. Consequently, a marked cell loss in elongated spermatids at stages XII-XIV and I was observed at 14 days. In addition, plasma testosterone levels were reduced at 6 days after exposure to MMC, and remained at approximately 20% of control levels during the 14-day observation period. Our results suggest that methylmercury impairs spermatogenesis by germ cell deletion via cell- and stage- specific apoptosis.
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Involvement of enhanced sensitivity of N-methyl-d-aspartate receptors in vulnerability of developing cortical neurons to methylmercury neurotoxicity. Brain Res 2001; 901:252-8. [PMID: 11368974 DOI: 10.1016/s0006-8993(01)02281-8] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The developing cortical neurons have been well documented to be extremely vulnerable to the toxic effect of methylmercury (MeHg). In the present study, a possible involvement of N-methyl-D-aspartate (NMDA) receptors in MeHg neurotoxicity was examined because the sensitivity of cortical neurons to NMDA neurotoxicity has a similar developmental profile. Rats on postnatal day 2 (P2), P16, and P60 were orally administered MeHg (10 mg/kg) for 7 consecutive days. The most severe neuronal damage was observed in the occipital cortex of P16 rats. When MK-801 (0.1 mg/kg), a non-competitive antagonist of NMDA, was administered intraperitoneally with MeHg, MeHg-induced neurodegeneration was markedly ameliorated. Furthermore, there was a marked accumulation of nitrotyrosine, a reaction product of peroxynitrite and L-tyrosine, after chronic treatment of MeHg in the occipital cortex of P16 rats. The accumulation of nitrotyrosine was also significantly suppressed by MK-801. In the present electrophysiological study, the amplitude of synaptic responses mediated by NMDA receptors recorded in cortical neurons of P16 rats was significantly larger than those from P2 and P60 rats. These observations strongly suggest that a generation of peroxynitrite through activation of NMDA receptors is a major causal factor for MeHg neurotoxicity in the developing cortical neurons. Furthermore, enhanced sensitivity of NMDA receptors may make the cortical neurons of P16 rats most susceptible to MeHg neurotoxicity.
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Role of nitric oxide in the ethylcholine aziridinium model of delayed apoptotic neurodegeneration in vivo and in vitro. Neuroscience 2000; 97:383-93. [PMID: 10799770 DOI: 10.1016/s0306-4522(99)00599-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The involvement of nitric oxide in neurodegenerative processes still remains incompletely characterized. Although nitric oxide has been reported to be an important mediator in neuronal degeneration in different models of cell death involving NMDA-receptor activation, increasing evidence for protective mechanisms has been obtained. In this study the role of nitric oxide was investigated in a model of NMDA-independent, delayed apoptotic cell death, induced by the neurotoxin ethylcholine aziridinium ethylcholine aziridinium both in vivo and in vitro. For the in vivo evaluation rats received bilateral intracerebroventricular injections of ethylcholine aziridinium (2nmol/ventricle) or vehicle. In the hippocampus a transient decrease in nitric oxide synthase activity occurred, reaching its lowest levels three days after ethylcholine aziridinium treatment (51.7+/-9.8% of controls). The decrease coincided with the maximal reduction in choline acetyltransferase activity as marker for the extent of cholinergic lesion. The effect of pharmacological inhibition of nitric oxide synthase was tested by application of various nitric oxide synthase inhibitors with different selectivity for the nitric oxide synthase-isoforms. Unspecific nitric oxide synthase inhibition resulted in a significant potentiation of the loss of choline acetyltransferase activity in the hippocampus measured seven days after ethylcholine aziridinium application, whereas the specific inhibition of neuronal or inducible nitric oxide synthase was ineffective. These pharmacological data are suggestive for a neuroprotective role of nitric oxide generated by endothelial nitric oxide synthase. In vitro experiments were performed using serum-free primary neuronal cell cultures from hippocampus, cortex and septum of E15-17 Wistar rat embryos. Ethylcholine aziridinium-application in a range of 5-80microM resulted in delayed apoptotic neurodegeneration with a maximum after three days as confirmed by morphological criteria, life-death assays and DNA laddering. Nitric oxide synthase activity in harvested cells decreased in a dose- and time-dependent manner. Nitric oxide production as determined by measurement of the accumulated metabolite nitrite in the medium was equally low in controls and in ethylcholine aziridinium treated cells (range 0.77-1.86microM nitrite). An expression of inducible nitric oxide synthase messenger RNA could not be detected by semiquantitative RT-PCR 13h after ethylcholine aziridinium application. The present data indicate that in a model of delayed apoptotic neurodegeneration as induced by ethylcholine aziridinium neuronal cell death in vitro and in vivo is independent of the cytotoxic potential of nitric oxide. This is confirmed by a decrease in nitric oxide synthase activity, absence of nitric oxide production and absence of inducible nitric oxide synthase expression. In contrast, evidence for a neuroprotective role of nitric oxide was obtained in vivo as indicated by the exaggeration of the cholinergic lesion after unspecific nitric oxide synthase inhibition by N-nitro-L-arginine methylester.
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Selective induction of apoptosis of renal proximal tubular cells caused by inorganic mercury in vivo. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 1999; 7:179-187. [PMID: 21781924 DOI: 10.1016/s1382-6689(99)00012-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/1998] [Revised: 02/24/1999] [Accepted: 03/01/1999] [Indexed: 05/31/2023]
Abstract
A recent notion, that a variety of toxicants causing necrosis can lead to apoptosis as well, has been demonstrated with cultured cells, but not with in an vivo system. In the present study, we examined the induction of both apoptosis and necrosis in the kidneys of Wistar rats exposed to mercuric chloride (HgCl(2)). A single injection of HgCl(2) to rats at a dose of 4 mg/kg resulted in an increase in the renal DNA fragmentation evaluated as an occurrence of apoptosis, prior to urinary excretion of alkaline phosphatase (ALP) and renal morphological changes assessed as necrotic phenomena. The mercury-promoted DNA fragmentation was induced in a dose-dependent manner. Terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) staining and morphological observation of the nuclei revealed that apoptotic cells caused by HgCl(2) were predominantly found in the proximal tubules, but not in the distal tubules, glomeruli or medullary tubules. When we confirmed the proximal tubular-selective apoptosis by inorganic mercury with a combined technique of TUNEL staining with synchrotron radiation X-ray fluorescence (SR-XRF) imaging, it was shown that the apoptotic cells localized in the proximal tubules did contain higher level of mercury. Thus these results indicate that the proximal tubular cells-dominant site-specific distribution of mercury appears to be associated with induction of renal apoptosis and necrosis.
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