Interactions of methylmercury with rat primary astrocyte cultures: methylmercury efflux
Methylmercury (MeHg) efflux from rat astrocyte cultures was studied to complement our previous studies on uptake of MeHg in these cells. Exchange with extracellular MeHg was not obligatory for the efflux of [203Hg]MeHg into the extracellular media, because efflux occurred into MeHg-free extracellular media, but stimulation of [203Hg]MeHg net efflux was shown when astrocytes were equilibrated in the presence of ‘cold’ MeHg and graded concentrations ofl-cysteine. Net efflux of MeHg was most rapid for the first 5 min, and approximately 20% of preloaded [203Hg]MeHg was lost from the astrocytes by 60 min. Uptake of [203Hg]MeHgCl was maximal by 30 min and did not increase when the loading period was extended up to 4 h. However, the total amount of intracellular203Hg that was available for net efflux gradually decreased as the duration of the preloading period increased. MeHg net efflux from astrocytes was unchanged when [203Hg]MeHgCl preloaded astrocytes were equilibrated in hypotonic buffer, suggesting that unlike ions and amino acids swollen astrocytes remain impervious to MeHg efflux. Thus, the main MeHg efflux transport system is apparently specific for the MeHg-l-cysteine conjugate and represents transport by the same neutral amino acid System L that facilitates its uptake.
References (26)
- AschnerM. et al.
Methylmercury uptake in rat primary astrocyte cultures: the role of the neutral amino acid transport system
Brain Research
(1990) - CangianoC. et al.
Brain microvessels take up large neutral amino acids in exchange for glutamine: cooperative role of Na+-dependent and Na+-independent systems
J. Biol. Chem.
(1983) - ChoiD.W.
Glutamate neurotoxicity and diseases of the nervous system
Neuron
(1988) - ChristensenH.N.
Organic ion transport during seven decades: the amino acids
Biochim. Biophys. Acta.
(1984) - RansomB.R. et al.
Astrocytes convert the parkinsonism inducing neurotoxin, MPTP, to its active metabolite, MPP+
Neurosci. Lett.
(1987) - ToribaraT.Y.
Preparation of CH3203HgCl of high specific activity
Int. J. Appl. Radiat. Isot.
(1985) - BrookesN.
Specificity and reversibility of the inhibition by HgCl2 of glutamate transport in astrocyte cultures
J. Neurochem.
(1988) - SpecialeC. et al.
High affinity uptake of L-kynurenine by a Na+-independent transporter of neutral amino acids in astrocytes
J. Neurosci.
(1989) - CartyA.J. et al.
- FedoroffS. et al.
Dissociation of neonatal rat brain by dispase for preparation of primary astrocyte cultures
Neurochem. Res.
Alkylmercurial encephalopathy in the monkey; a histopathologic and autoradiograohic study
Acta Neuropathol.
Protein analysis of mammalian cells in monolayer culture using the bicinchoninic assay
Anal. Biochem.
Cited by (27)
Mercury
2021, Handbook on the Toxicology of Metals: Fifth EditionMercury occurs as elemental mercury and as inorganic and organic compounds (mercury vapor, mercury liquid, mercury salts, short-chain alkylmercury compounds, alkoxyalkylmercury compounds, and phenylmercury compounds), all with different toxicological properties. Total mercury can be analyzed in water, air, and biological material by cold vapor atomic absorption methods and by neutron activation analysis and can be detected down to concentrations of a 10th of a nanogram per gram in biological material. Methylmercury (MeHg) can be detected in biological material at levels of a few nanograms by extraction with benzene after strong acidification with hydrochloric acid, followed by gas chromatographic analysis of MeHg chloride. Other analytical methods for speciating inorganic mercury and several of the organomercurial forms have also been published. These methods include isotope dilution mass spectrometry, time-of-flight mass spectrometry, high-performance liquid chromatography inductively coupled plasma (ICP) mass spectrometry, capillary electrophoresis-ICP, gas chromatography-ICP, and X-ray absorption fine structure spectroscopy.
Mercury is circulated naturally in the biosphere, with 5500 metric tons (t) being released into the atmosphere by degassing from the Earth's crust and the oceans. In addition, 2500 t of mercury are released into the environment each year through human activities such as the combustion of fossil fuels and other industrial releases. Approximately 2000 tons of mercury per year is produced for industrial use, a small part of which is used for synthesizing organic mercury compounds. The world production of mercury for commercial uses has been slowly declining over the past 20 years. There is now a ban on the export of mercury from the European Union and the United States.
In nature, MeHg is produced from inorganic mercury as a consequence of microbial activity. In mammals, oxidative demethylation occurs in vivo to produce inorganic mercury. In fish, most mercury is present as MeHg. Factors determining the MeHg concentration in fish are the mercury content in water and bottom sediments, the pH and redox potential of water, and the species, age, and size of the fish.
The toxic properties of mercury vapor are a consequence of mercury accumulation in the brain causing neurological signs involving an unspecific psychasthenic and vegetative syndrome (micromercurialism). At high exposure levels, mercurial tremor is seen, accompanied by severe behavioral and personality changes, increased excitability, loss of memory, and insomnia. Mercurials may also affect other organ systems, such as the kidney. On a group basis, exposure levels are likely to be reflected by mercury concentrations in the blood and urine. Occupational exposure to mercury concentrations in air of >0.1 mg/m3 may produce mercurialism. Micromercurialism has not been reported at concentrations <0.01 mg/m3. Exposure to mercury vapor inhibits brain development in primates and in humans with certain genotypes. The exact dose–response relationship in humans is not known. Inorganic mercury, but not MeHg, has been found to induce and bind to the low molecular weight metal-binding protein, metallothionein.
The acute and long-term actions of mercuric salts, phenylmercury compounds, and alkoxyalkylmercury compounds are likely to be gastrointestinal disturbance and renal damage appearing as tubular dysfunction, with tubular necrosis in severe cases. The lethal dose in humans is approximately 1 g mercuric salt. The mercury load on the kidney is best determined by analysis of renal biopsy. Mercury concentrations in the kidney of between 10 and 70 mg/kg have been reported in poison cases with renal injury. Levels <3 mg/kg may be found in normal cases. Occasionally, mercuric compounds may cause idiosyncratic skin symptoms, which may develop into severe exfoliative dermatitis or cause glomerular nephritis. Animal and clinical observations have shown that mercuric mercury stimulates and MeHg inhibits the immune system. A specific form of idiosyncrasy, called acrodynia or pink disease, is seen in children. Most cases are associated with mercury exposure in which increased levels of mercury in urine are detected.
Hazards involved in the long-term intake of food containing MeHg or ethylmercury (EthylHg) and in occupational exposure to MeHg are a result of the efficient absorption (90%) of alkylmercury in humans and the long retention time (half-life of 70 days for MeHg and shorter for EthylHg) leading to accumulation of alkylmercury in the brain. Chronic poisoning results in degeneration and atrophy of the sensory cerebral cortex, paresthesia, ataxia, hearing, and visual impairment, and an increased risk for cardiovascular diseases such as myocardial infarction and stroke. The latter effects are attenuated by the intake of polyunsaturated fatty acids (PUFAs) through fish consumption. Prenatal exposure causes cerebral palsy and, in less severe cases, psychomotor retardation. MeHg concentration in the blood and hair reflects the body burden and the brain concentration of MeHg. Intake resulting in body burdens of <0.5 mg/kg body weight is not likely to give rise to detectable neurological signs in adults. This intake corresponds to blood values of <200 μg/L and mercury levels in the hair of <50 mg/kg. However, this level of MeHg exposure in pregnant women may result in inhibited brain development of the fetus, with psychomotor retardation of the child. This effect also appears to be reduced by the intake of PUFAs through fish consumption. The highest level of MeHg load in pregnant women that is not associated with inhibition of fetal brain development is not known. Recent epidemiological studies have revealed that genetic polymorphisms can modify mercury metabolism and susceptibility to mercury exposure. Specific genotypes have been associated with increased susceptibility to mercury exposure in humans.
Mercury
2015, Handbook on the Toxicology of Metals: Fourth EditionMercury occurs as elemental mercury and as inorganic and organic compounds (mercury vapor, mercury liquid, mercury salts, short-chain alkylmercury compounds, alkoxyalkylmercury compounds, and phenylmercury compounds), all with different toxicological properties. Total mercury can be analyzed in water, air, and biological material by cold vapor atomic absorption methods and by neutron activation analysis, and can be detected down to concentrations of a tenth of a nanogram per gram in biological material. Methylmercury (MeHg) can be detected in biological material at levels of a few nanograms by extraction with benzene after strong acidification with hydrochloric acid, followed by gas chromatographic analysis of MeHg chloride. Other analytical methods for speciating inorganic mercury and several of the organomercurial forms have also been published. These methods include isotope dilution mass spectrometry, time-of-flight mass spectrometry, high performance liquid chromatography inductively coupled (ICP) plasma mass spectrometry, capillary electrophoresis-ICP, gas chromatography-ICP, and X-ray absorption fine structure spectroscopy.
Mercury is circulated naturally in the biosphere, with 30,000-50,000 tons being released into the atmosphere by degassing from the Earth’s crust and the oceans. In addition, 20,000 tons of mercury is released into the environment each year through human activities such as combustion of fossil fuels and other industrial releases. Approximately 2000 tons of mercury per year is produced for industrial use, a small part of which is used for synthesizing organic mercury compounds. The world production of mercury for commercial uses has been slowly declining over the past 20 years. There is now a ban on the export of mercury from the European Union.
In nature, MeHg is produced from inorganic mercury as a consequence of microbial activity. In mammals, oxidative demethylation occurs in vivo to produce inorganic mercury. In fish, most mercury is present as MeHg. Factors determining the MeHg concentration in fish are the mercury content in water and bottom sediments, the pH and redox potential of water, and the species, age, and size of the fish.
The toxic properties of mercury vapor are a consequence of mercury accumulation in the brain causing neurological signs involving an unspecific psychoasthenic and vegetative syndrome (micromercurialism). At high exposure levels, mercurial tremor is seen, accompanied by severe behavioral and personality changes, increased excitability, loss of memory, and insomnia. Mercurials may also affect other organ systems, such as the kidney. On a group basis, exposure levels are likely to be reflected in mercury concentrations in the blood and urine. Occupational exposure to mercury concentrations in air of > 0.1 mg/m3 may produce mercurialism. Micromercurialism has not been reported at concentrations < 0.01 mg/m3. Exposure to mercury vapor inhibits brain development in primates and in humans with certain genotypes. The exact dose-response relationship in humans is not known. Inorganic mercury but not MeHg has been found to induce and bind to the low molecular weight metal-binding protein, metallothionein.
The acute and long-term actions of mercuric salts, phenylmercury compounds, and alkoxyalkylmercury compounds are likely to be gastrointestinal disturbance and renal damage appearing as tubular dysfunction, with tubular necrosis in severe cases. The lethal dose in humans is approximately 1 g mercuric salt. The mercury load on the kidney is best determined by analysis of renal biopsy. Mercury concentrations in the kidney of between 10 and 70 mg/kg have been reported in poison cases with renal injury. Levels < 3 mg/kg may be found in normal cases. Occasionally, mercuric compounds may cause idiosyncratic skin symptoms, which may develop into severe exfoliative dermatitis or cause glomerular nephritis. Animal and clinical observations have shown that mercuric mercury stimulates and MeHg inhibits the immune system. A specific form of idiosyncrasy, called acrodynia or pink disease, is seen in children. Most cases are associated with mercury exposure in which increased levels of mercury in urine are observed.
Hazards involved in the long-term intake of food containing MeHg or ethylmercury (EthylHg) and in occupational exposure to MeHg are a result of the efficient absorption (90%) of alkylmercury in humans and the long retention time (half-life of 70 days for MeHg and shorter for EthylHg) leading to accumulation of alkylmercury in the brain. Chronic poisoning results in degeneration and atrophy of the sensory cerebral cortex, paresthesia, ataxia, hearing, and visual impairment, and implies an increased risk for cardiovascular disease such as cardiac infarction and stroke. The latter effects are attenuated by the intake of polyunsaturated fatty acids (PUFAs) through fish consumption. Prenatal exposure causes cerebral palsy and, in less severe cases, psychomotor retardation. MeHg concentration in the blood and hair reflects the body burden and the brain concentration of MeHg. Intake resulting in body burdens of < 0.5 mg/kg body weight is not likely to give rise to detectable neurological signs in adults. This intake corresponds to blood values of < 200 μg/L and mercury levels in the hair of < 50 mg/kg. However, this level of MeHg exposure in pregnant women may result in inhibited brain development of the fetus, with psychomotor retardation of the child. This effect also appears to be reduced by intake of PUFAs through fish consumption. The highest level of MeHg load in pregnant women that is not associated with inhibition of fetal brain development is not known. Recent epidemiological studies have revealed that genetic polymorphisms can modify mercury metabolism and susceptibility to mercury exposure. Specific genotypes have been associated with increased susceptibility to mercury exposure in humans.
A general overview of mercury from a historical perspective has been reviewed by Goldwater (1972). The pharmacology and toxicology of mercury was previously reviewed by Clarkson et al. (1972), the chemistry of mercury in biological systems by Carty and Malone (1979), the toxicology of MeHg by a Swedish Expert Group (1971), and the toxicology and epidemiology of mercury by Friberg and Vostal (1972), the Task Group on Metal Accumulation (1973), the Task Group on Metal Toxicity (1976), and the World Health Organization (WHO (World Health Organization), 1976, WHO, 1980, WHO., 1990, WHO., 1991). The toxicology of mercury has been reviewed in the U.S. Environmental Protection Agency Report to Congress (EPA, 1997), the Agency for Toxic Substances and Disease Registry (ATSDR, 1999), National Academy of Sciences National Research Council (NAS/NRC, 2000), and Institute of Medicine Report on Mercury in Vaccines (IOM, 2004).
Mercury
2014, Handbook on the Toxicology of MetalsMercury occurs as elemental mercury and as inorganic and organic compounds (mercury vapor, mercury liquid, mercury salts, short-chain alkylmercury compounds, alkoxyalkylmercury compounds, and phenylmercury compounds), all with different toxicological properties. Total mercury can be analyzed in water, air, and biological material by cold vapor atomic absorption methods and by neutron activation analysis, and can be detected down to concentrations of a tenth of a nanogram per gram in biological material. Methylmercury (MeHg) can be detected in biological material at levels of a few nanograms by extraction with benzene after strong acidification with hydrochloric acid, followed by gas chromatographic analysis of MeHg chloride. Other analytical methods for speciating inorganic mercury and several of the organomercurial forms have also been published. These methods include isotope dilution mass spectrometry, time-of-flight mass spectrometry, high performance liquid chromatography inductively coupled (ICP) plasma mass spectrometry, capillary electrophoresis-ICP, gas chromatography-ICP, and X-ray absorption fine structure spectroscopy.
Mercury is circulated naturally in the biosphere, with 30,000-50,000 tons being released into the atmosphere by degassing from the Earth’s crust and the oceans. In addition, 20,000 tons of mercury is released into the environment each year through human activities such as combustion of fossil fuels and other industrial releases. Approximately 2000 tons of mercury per year is produced for industrial use, a small part of which is used for synthesizing organic mercury compounds. The world production of mercury for commercial uses has been slowly declining over the past 20 years. There is now a ban on the export of mercury from the European Union.
In nature, MeHg is produced from inorganic mercury as a consequence of microbial activity. In mammals, oxidative demethylation occurs in vivo to produce inorganic mercury. In fish, most mercury is present as MeHg. Factors determining the MeHg concentration in fish are the mercury content in water and bottom sediments, the pH and redox potential of water, and the species, age, and size of the fish.
The toxic properties of mercury vapor are a consequence of mercury accumulation in the brain causing neurological signs involving an unspecific psychoasthenic and vegetative syndrome (micromercurialism). At high exposure levels, mercurial tremor is seen, accompanied by severe behavioral and personality changes, increased excitability, loss of memory, and insomnia. Mercurials may also affect other organ systems, such as the kidney. On a group basis, exposure levels are likely to be reflected in mercury concentrations in the blood and urine. Occupational exposure to mercury concentrations in air of > 0.1 mg/m3 may produce mercurialism. Micromercurialism has not been reported at concentrations < 0.01 mg/m3. Exposure to mercury vapor inhibits brain development in primates and in humans with certain genotypes. The exact dose-response relationship in humans is not known. Inorganic mercury but not MeHg has been found to induce and bind to the low molecular weight metal-binding protein, metallothionein.
The acute and long-term actions of mercuric salts, phenylmercury compounds, and alkoxyalkylmercury compounds are likely to be gastrointestinal disturbance and renal damage appearing as tubular dysfunction, with tubular necrosis in severe cases. The lethal dose in humans is approximately 1 g mercuric salt. The mercury load on the kidney is best determined by analysis of renal biopsy. Mercury concentrations in the kidney of between 10 and 70 mg/kg have been reported in poison cases with renal injury. Levels < 3 mg/kg may be found in normal cases. Occasionally, mercuric compounds may cause idiosyncratic skin symptoms, which may develop into severe exfoliative dermatitis or cause glomerular nephritis. Animal and clinical observations have shown that mercuric mercury stimulates and MeHg inhibits the immune system. A specific form of idiosyncrasy, called acrodynia or pink disease, is seen in children. Most cases are associated with mercury exposure in which increased levels of mercury in urine are observed.
Hazards involved in the long-term intake of food containing MeHg or ethylmercury (EthylHg) and in occupational exposure to MeHg are a result of the efficient absorption (90%) of alkylmercury in humans and the long retention time (half-life of 70 days for MeHg and shorter for EthylHg) leading to accumulation of alkylmercury in the brain. Chronic poisoning results in degeneration and atrophy of the sensory cerebral cortex, paresthesia, ataxia, hearing, and visual impairment, and implies an increased risk for cardiovascular disease such as cardiac infarction and stroke. The latter effects are attenuated by the intake of polyunsaturated fatty acids (PUFAs) through fish consumption. Prenatal exposure causes cerebral palsy and, in less severe cases, psychomotor retardation. MeHg concentration in the blood and hair reflects the body burden and the brain concentration of MeHg. Intake resulting in body burdens of < 0.5 mg/kg body weight is not likely to give rise to detectable neurological signs in adults. This intake corresponds to blood values of < 200 μg/L and mercury levels in the hair of < 50 mg/kg. However, this level of MeHg exposure in pregnant women may result in inhibited brain development of the fetus, with psychomotor retardation of the child. This effect also appears to be reduced by intake of PUFAs through fish consumption. The highest level of MeHg load in pregnant women that is not associated with inhibition of fetal brain development is not known. Recent epidemiological studies have revealed that genetic polymorphisms can modify mercury metabolism and susceptibility to mercury exposure. Specific genotypes have been associated with increased susceptibility to mercury exposure in humans.
A general overview of mercury from a historical perspective has been reviewed by Goldwater (1972). The pharmacology and toxicology of mercury was previously reviewed by Clarkson et al. (1972), the chemistry of mercury in biological systems by Carty and Malone (1979), the toxicology of MeHg by a Swedish Expert Group (1971), and the toxicology and epidemiology of mercury by Friberg and Vostal (1972), the Task Group on Metal Accumulation (1973), the Task Group on Metal Toxicity (1976), and the World Health Organization (WHO (World Health Organization), 1976, WHO, 1980, WHO., 1990, WHO., 1991). The toxicology of mercury has been reviewed in the U.S. Environmental Protection Agency Report to Congress (EPA, 1997), the Agency for Toxic Substances and Disease Registry (ATSDR, 1999), National Academy of Sciences National Research Council (NAS/NRC, 2000), and Institute of Medicine Report on Mercury in Vaccines (IOM, 2004).
Methylmercury-induced neurotoxicity and apoptosis
2010, Chemico-Biological InteractionsCitation Excerpt :In addition to the antioxidant role of GSH, its conjugation with methylmercury has been shown to be critical for methylmercury efflux in different neural cell types [88]. In primary cultures of astrocytes isolated from neonatal rat brains, the specific efflux of methylmercury-GSH conjugates seems to be mediated via the probenecid-sensitive organic acid transport system [89] and the neutral amino acid system-L [90]. Thus, cells with higher GSH levels may have an enhanced elimination of intracellular methylmercury with consequent higher resistance to its toxicity.
Methylmercury is a widely distributed environmental toxicant with detrimental effects on the developing and adult nervous system. Due to its accumulation in the food chain, chronic exposure to methylmercury via consumption of fish and sea mammals is still a major concern for human health, especially developmental exposure that may lead to neurological alterations, including cognitive and motor dysfunctions. Mercury-induced neurotoxicity and the identification of the underlying mechanisms has been a main focus of research in the neurotoxicology field. Three major mechanisms have been identified as critical in methylmercury-induced cell damage including (i) disruption of calcium homeostasis, (ii) induction of oxidative stress via overproduction of reactive oxygen species or reduction of antioxidative defenses and (iii) interactions with sulfhydryl groups. In vivo and in vitro studies have provided solid evidence for the occurrence of neural cell death, as well as cytoarchitectural alterations in the nervous system after exposure to methylmercury. Signaling cascades leading to cell death induced by methylmercury involve the release of mitochondrial factors, such as cytochrome c and AIF with subsequent caspase-dependent or -independent apoptosis, respectively; induction of calcium-dependent proteases calpains; interaction with lysosomes leading to release of cathepsins. Interestingly, several pathways can be activated in parallel, depending on the cell type. In this paper, we provide an overview of recent findings on methylmercury-induced neurotoxicity and cell death pathways that have been described in neural and endocrine cell systems.
Uptake and efflux of methylmercury in vitro: Comparison of transport mechanisms in C6, B35 and RBE4 cells
2009, Toxicology in VitroMethylmercury (MeHg) is a neurotoxicant which enters the brain and may cause permanent change. Thus, the properties of MeHg transport across cell membranes are a key factor in designing an appropriate model for MeHg neurotoxicity. This study uses cell cultures to examine the uptake and efflux mechanisms of methylmercury in C6 glioma, B35 neuroblastoma and rat brain endothelial (RBE4) cells. The cellular uptake and efflux of MeHg was investigated using 14C-labeled MeHg. The uptake of MeHg-chloride was temperature-independent while the uptake of MeHg-l-cysteine was temperature-dependent in all the three cell types. This indicates that uptake of MeHg-chloride is due to passive diffusion and uptake of MeHg-l-cysteine is due to a protein carrier. Substrates of the amino acid transport system L inhibited uptake of MeHg-l-cysteine in C6 and RBE4 cells, but not B35 cells, indicating a role for system L in MeHg-uptake in the former two. Probenecid, Na+-free medium, MeHg and several l-amino acids did not alter the efflux of MeHg from C6 and RBE4 cells. The amino acids l-cysteine and cystine however, increased the efflux. Both cysteine and cystine are important in the generation of glutathione (GSH), suggesting the involvement of GSH in MeHg efflux. HgCl2 at low concentrations (0.5 and 1.0 μM) decreased the MeHg efflux and at high concentrations (5.0 and 10.0 μM) increased the efflux. This inhibiting effect of HgCl2 at low concentrations is possibly due to binding to GSH while the effect of high HgCl2 concentrations is attributed to disrupted membrane integrity, as measured by Trypan blue. This study demonstrates differing transport mechanisms of MeHg in the cell lines C6, B35 and RBE4.
Mercury Exposure and Public Health
2007, Pediatric Clinics of North AmericaCitation Excerpt :The primary targets of CH3Hg+ with resultant adverse clinical manifestations include the CNS and the placenta [94,W31]. From animal studies, it has been postulated that the thiol conjugate, CH3Hg-S-Cys, structurally mimics methionine, which then allows this conjugate to cross the blood-brain barrier [93,95–97,W83–W93]. The mercury level within the brain may be three to six times the levels in the blood [98].
Mercury is a metal that is a liquid at room temperature. Mercury has a long and interesting history deriving from its use in medicine and industry, with the resultant toxicity produced. In high enough doses, all forms of mercury can produce toxicity. The most devastating tragedies related to mercury toxicity in recent history include Minamata Bay and Niagata, Japan in the 1950s, and Iraq in the 1970s. More recent mercury toxicity issues include the extreme toxicity of the dimethylmercury compound noted in 1998, the possible toxicity related to dental amalgams, and the disproved relationship between vaccines and autism related to the presence of the mercury-containing preservative, thimerosal.