Mercuric chloride toxicity in rat liver mitochondria and isolated hepatocytes

An Overview of Bacteria-Mediated Heavy Metal Bioremediation Strategies

Contamination-free groundwater is considered a good source of potable water. Even in the twenty-first century, over 90 percent of the population is reliant on groundwater resources for their lives. Groundwater influences the economical state, industrial development, ecological system, and agricultural and global health conditions worldwide. However, different natural and artificial processes are gradually polluting groundwater and drinking water systems throughout the world. Toxic metalloids are one of the major sources that pollute the water system. In this review work, we have collected and analyzed information on metal-resistant bacteria along with their genetic information and remediation mechanisms of twenty different metal ions [arsenic (As), mercury (Hg), lead (Pb), chromium (Cr), iron (Fe), copper (Cu), cadmium (Cd), palladium (Pd), zinc (Zn), cobalt (Co), antimony (Sb), gold (Au), silver (Ag), platinum (Pt), selenium (Se), manganese (Mn), molybdenum (Mo), nickel (Ni), tungsten (W), and uranium (U)]. We have surveyed the scientific information available on bacteria-mediated bioremediation of various metals and presented the data with responsible genes and proteins that contribute to bioremediation, bioaccumulation, and biosorption mechanisms. Knowledge of the genes responsible and self-defense mechanisms of diverse metal-resistance bacteria would help us to engineer processes involving multi-metal-resistant bacteria that may reduce metal toxicity in the environment.

Mercury chloride alters heterochromatin domain organization and nucleolar activity in mouse liver

Mercury is a highly toxic element that induces severe alterations and a broad range of adverse effects on health. Its exposure is a global concern because it is widespread in the environment due to its multiple industrial, domestic, agricultural and medical usages. Among its various chemical forms, both humans and animals are mainly exposed to mercury chloride (HgCl₂), methylmercury and elemental mercury. HgCl₂ is metabolized primarily in the liver. We analysed the effects on the nuclear architecture of an increasing dosage of HgCl₂ in mouse hepatocytes cell culture and in mouse liver, focusing specifically on the organization, on some epigenetic features of the heterochromatin domains and on the nucleolar morphology and activity. Through the combination of molecular and imaging approaches both at optical and electron microscopy, we show that mercury chloride induces modifications of the heterochromatin domains and a decrease of some histones post-translational modifications associated to heterochromatin. This is accompanied by an increase in nucleolar activity which is reflected by bigger nucleoli. We hypothesized that heterochromatin decondensation and nucleolar activation following mercury chloride exposure could be functional to express proteins necessary to counteract the harmful stimulus and reach a new equilibrium.

Amelioration of mercuric chloride-induced physiologic and histopathologic alterations in rats using vitamin E and zinc chloride supplement

The drastic effects of mercuric chloride and the protective efficiency of vitamin E and zinc chloride co-supplementation were clearly investigated in this study. Male rats were divided into four groups. The first was the control. The second received vitamin E (100 mg/kg) and zinc chloride (30 mg/kg) daily. In comparison, the third received mercuric chloride (1 mg/kg) daily, and the fourth received the same mercuric chloride dose supplemented with the same vitamin E and zinc chloride doses. Mercury promotes a significant decline in body weight. It causes a considerable reduction in total red blood cells (RBCs) count and hemoglobin concentration; however, white blood cells (WBCs) increased significantly. Significant mercury-induced elevations in hepatic and renal functions were observed. Mercury induced substantial reductions in catalase (CAT) and superoxide dismutase (SOD). Mercury caused apoptotic DNA fragmentation. It induced degeneration and necrosis in the liver and kidney. It induced necrosis, leukocyte infiltration and blood vessel congestion in the cerebral cortex. Shrinkage and deterioration of Purkinje cells of the cerebellum were observed in response to mercuric chloride toxicity. Mercuric chloride enhanced shrinking in seminiferous tubules and Leydig cells. It reduced sperm count, sperm motility, and testosterone concentration; however, it promoted abnormal sperm morphology. Administration of vitamin E and zinc chloride showed marked improvement in different parameters under investigation, however, further research is needed to determine fate of mercury.

Engineered Whole-Cell-Based Biosensors: Sensing Environmental Heavy Metal Pollutants in Water-a Review

The frequent exposure and accumulation of heavy metals in organisms cause serious health issues affecting a range of organs such as the brain, liver, and reproductive organs in adults, infants, and children. Several parts of the world have high levels of heavy metals affecting millions of people, costing millions of dollars for improving the potability of water and medical treatment of the affected. Hence, water quality assessment is required to monitor the degree of heavy metal contamination in potable water. In nature, organisms respond to various environmental pollutants such as heavy metals, allowing their survival in a diverse environmental niche. With the advent of recombinant DNA technology, it is now possible to manipulate these natural bioreporters into controlled systems which either turn on or off gene expression or activity of enzymes in the presence of specific heavy metals (compound-specific biosensors) otherwise termed as whole-cell biosensors (WCBs). WCBs provide an upper hand compared to other immunosensors, enzyme-based sensors, and DNA-based sensors since microbes can be relatively easily manipulated, scaled up with relative ease, and can detect only the bioavailable heavy metals. In this review, we summarize the current knowledge of the various mechanisms of toxicity elicited by various heavy metals, thence emphasizing the need to develop heavy metal sensing platforms. Following this, the biosensor-based platforms including WCBs for detecting heavy metals developed thus far have been briefly elaborated upon, emphasizing the challenges and solutions associated with WCBs.

Regulation of Single-Channel Conductance of Voltage-Dependent Anion Channel by Mercuric Chloride in a Planar Lipid Bilayer

The existence of mercury in various forms, e.g., elemental, organic, and inorganic has been known for decades. In any of these forms, it is poisonous to metabolism. In this, an investigation about the effect of the inorganic form of mercury, i.e., mercuric chloride (HgCl₂) to the mitochondrial voltage-dependent anion channel (VDAC), has been done after isolation from the cardiac and brain tissues of Wistar rats. In vitro electrophysiology experiments were performed in Cardiolipin planar lipid bilayer membrane (BLM) to study the change in the conductance, selectivity, and gating charge of VDAC post HgCl₂ treatment. A reduction in mean conductance of VDAC from 4.3 ± 0.18 to 1.66 ± 0.11 nS was observed. Further, the Gating charge calculated before (± 3.5) and after HgCl₂ treatment (± 2.3) showed significant difference. Later, VDAC's behavior was studied at different concentrations of HgCl₂ ranging from 0.1 μM to 1 mM. The Inhibitory concentration (IC₅₀) was calculated from the linear regression plot. The IC₅₀ was found to be 488.1 μM. In the asymmetrical HgCl₂ (5:1), a permeability ratio of cation to anion was found to be 4.2. It is interpreted that VDAC functioning is affected due to the application of 4 mM HgCl₂ and a reduction in the conductance, gating charge, and permeability of VDAC was detected. The results provide clues to HgCl₂-induced toxicity mediated through VDAC in the Cardiolipin BLM.

Effects of mercuric chloride on spatial memory deficit-induced by beta-amyloid and evaluation of mitochondrial function markers in the hippocampus of rats

Mercury is a highly poisonous heavy metal abundantly found in the environment in its inorganic form. Although evidence have been provided about the possible role of inorganic mercury in the pathology of Alzheimer's disease (AD), its effect on cognitive and mitochondrial functions have not yet been completely understood. Thus, the purpose of the present study was to examine the effects of the chronic exposure to mercuric chloride (0.4, 0.8 and 1.6 mg kg-1 per day for 3 weeks) through drinking water (by gavage) on spatial learning and memory and hippocampal mitochondrial function in beta-amyloid treated rats (1 μg per μL per side, intrahippocampally). The acquisition and retention of spatial memory were evaluated by the Morris water maze (MWM) test. Several parameters of hippocampal mitochondrial function were also measured. The results indicated that mercury impaired spatial learning and memory as well as aggravated Aβ-induced memory impairments in a concentration-dependent manner. Furthermore, mercury exposure resulted in a significant increase in ROS generation, MMP collapse, mitochondrial swelling, glutathione oxidation, lipid peroxidation, and outer membrane damage. In addition, a reduced cytochrome c oxidase (complex IV) activity and elevated ADP/ATP ratio in the rats' hippocampus was also observed. The findings of the current study revealed that chronic mercury exposure led to mitochondrial dysfunction, which resulted in spatial memory impairments. The results also showed that mercury can exacerbate the toxic effects of Aβ on spatial memory and hippocampal mitochondrial function.

Cellular pathologies and genotoxic effects arising secondary to heavy metal exposure: A review

Environmental pollution is significant and oftentimes hazardous in the areas, where mining, foundries and smelters and other metallurgical operations are located. Systematic research on the chronic effects of metals started during the past century; nevertheless, it is evident that even today, there are large gaps in knowledge regarding the assessment of the health effects caused by environmental and occupational exposures to these metals. Heavy metals induce the production of reactive oxygen species (ROS) causing oxidative stress, make several repair-inhibiting cellular changes and alter the DNA repair processes. They favour the ‘false’ repairing of double-strand breaks (DSBs), propagate DNA mutations and induce carcinogenesis. A detailed literature search was performed using the MedLine/PubMed database. Depending on the mechanism of action, arsenicals can act as genotoxins, non-genotoxic agents and carcinogens. Cadmium can bind to proteins, reduce DNA repair, activate protein degradation, up-regulate cytokines and proto-oncogenes (c-fos, c-jun and c-myc), induce the expression of metallothionein, haeme-oxygenases, glutathione transferases, heat-shock proteins, acute-phase reactants and DNA polymerase β at lower concentrations. Inorganic mercury damages oxidative phosphorylation and electron transport pathways at the ubiquinone–cytochrome b5 locus and thus induces ROS production. Abandoned mining areas generate environmentally persistent waste. These specific sites urgently require maximally efficient and cheap remediation. This bears the need for methodologies employing green and sustainable remediation. Phytoremediation is important in that it is a prevalent in situ remediation technique. Its advantages include the use of solar energy, cost-effectiveness, easy operation, reduction in secondary contaminants, the use of biomass for biofuel production and low-cost adsorbents.

Shared gene-network signatures between the human heavy metal proteome and neurological disorders and cancer types

In this work, for the first time, the human heavy metal proteome was predicted.

Impairment of mitochondrial energy metabolism of two marine fish by in vitro mercuric chloride exposure

The goal of this work was to understand the extent of mercury toxic effects in liver metabolism under an episode of acute contamination. Hence, the effects of in vitro mercuric chloride in liver mitochondria were assessed in two commercial marine fish: Senegalese sole (Solea senegalensis) and gilthead seabream (Sparus aurata). Liver mitochondria were exposed to 0.2mgL(-1) of mercury, the average concentration found in fish inhabiting contaminated areas. Mercuric chloride depressed mitochondrial respiration state 3 and the maximal oxygen consumption in the presence of FCCP indicating inhibitory effects on the oxidative phosphorylation and on the electron transport chain, respectively. The inhibition of F1Fo-ATPase and succinate-dehydrogenase activities also corroborated the ability of mercury to inhibit ADP phosphorylation and the electron transport chain. This study brings new understanding on the mercury levels able to impair fish mitochondrial function, reinforcing the need for further assessing bioenergetics as a proxy for fish health status.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Genotoxicity in earthworm after combined treatment of ionising radiation and mercury

This study was performed to investigate the acute genotoxic effects of mercury and radiation on earthworms (Eisenia fetida). The levels of DNA damage and the repair kinetics in the coelomocytes of E. fetida treated with mercuric chloride (HgCl₂) and ionising radiation (gamma rays) were analysed by means of the comet assay. For detection of DNA damage and repair, E. fetida was exposed to HgCl₂ (0-160 mg kg(-1)) and irradiated with gamma rays (0-50 Gy) in vivo. The increase in DNA damage depended on the concentration of mercury or dose of radiation. The results showed that the more the oxidative stress induced by mercury and radiation the longer the repair time that was required. When a combination of HgCl₂ and gamma rays was applied, the cell damage was much higher than those treated with HgCl₂ or radiation alone, which indicated that the genotoxic effects were increased after the combined treatment of mercury and radiation.

Dibenzofuran-induced mitochondrial dysfunction: Interaction with ANT carrier

Exposure to environmental pollutants such as dibenzofurans and furans is linked to the pathophysiology of several diseases. Dibenzofuran (DBF) is listed as a pollutant of concern due to its persistence in the environment, bioaccumulation and toxicity to humans, being associated with the development of lung diseases and cancers, due to its extremely toxic properties such as carcinogenic and teratogenic. Mitochondria play a key role in cellular homeostasis and keeping a proper energy supply for eukaryotic cells is essential in the fulfillment of the tissues energy-demand. Therefore, interference with mitochondrial function leads to cell death and organ failure. In this work, the effects of DBF on isolated rat liver mitochondria were analyzed. DBF exposure caused a markedly increase in the lag phase that follows depolarization induced by ADP, indicating an effect in the phosphorylative system. This was associated with a dose-dependent decrease in ATPase activity. Moreover, DBF also increased the threshold to the induction of the mitochondrial permeability transition (MPT) by calcium. Pretreatment of mitochondria with DBF also increased the concentration of carboxyatractyloside (CAT) necessary to abolish ADP phosphorylation and to induce the MPT, suggesting that DBF may interfere with mitochondria through an effect on the adenine nucleotide translocase (ANT). By co-immunoprecipitating ANT and Cyclophilin D (CypD) following MPT induction, we observed that in the presence of DBF, the ratio CypD/ANT was decreased. This demonstrates that DBF interferes with the ANT and so prevents CypD binding to the ANT, causing decreased phosphorylative capacity and inhibiting the MPT, which is also reflected by an increase in calcium retention capacity. Clarifying the role of pollutants in some mechanisms of toxicity, such as unbalance of bioenergetics status and mitochondrial function, may help to explain the progressive and chronic evolution of diseases derived from exposure to environmental pollutants.

Heavy metal toxicity and the environment

Heavy metals are naturally occurring elements that have a high atomic weight and a density at least five times greater than that of water. Their multiple industrial, domestic, agricultural, medical, and technological applications have led to their wide distribution in the environment, raising concerns over their potential effects on human health and the environment. Their toxicity depends on several factors including the dose, route of exposure, and chemical species, as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the priority metals that are of public health significance. These metallic elements are considered systemic toxicants that are known to induce multiple organ damage, even at lower levels of exposure. They are also classified as human carcinogens (known or probable) according to the US Environmental Protection Agency and the International Agency for Research on Cancer. This review provides an analysis of their environmental occurrence, production and use, potential for human exposure, and molecular mechanisms of toxicity, genotoxicity, and carcinogenicity.

Non-invasive monitoring of cytotoxicity based on kinetic changes of cellular autofluorescence

A quantitative, non-destructive cellular autofluorescence based in vitro imaging assay has been developed and applied to study the cytotoxicity of Sodium Lauryl Sulfate (SLS) and HgCl2 on Balb/c 3T3 cells. A phenomenological double logistic model was proposed to quantify and relate the observed kinetic changes of fluorescence to the toxic potency of chemical compounds. This work forms the basis for cellular autofluorescence measurements in in vitro toxicity screening assays.

Testicular mitochondrial alterations in untreated streptozotocin-induced diabetic rats

Diabetes-induced complications are associated with mitochondrial dysfunction and increasing evidence suggests that diabetes has an adverse effect on male reproductive function. The STZ-induced diabetic rat was used as an animal model for the type 1 form of the disease with the aim of determining its effects in spermatogenesis and testicular mitochondrial function. Several aspects of mitochondrial function were measured, including respiratory and electric potential function, as well as mitochondrial calcium loading capacity. Additionally oxidative stress production, antioxidant levels and possible apoptotic alterations were also evaluated. We observed that diabetic animals present alterations in spermatogenesis in both the testis and epidydimus. However, and surprisingly, the overall results in mitochondrial parameters failed to reveal severe testicular mitochondrial dysfunction in diabetic animals, with the exception of a decrease in calcium load. Taken together, results suggest that in animal models that mimic untreated type 1 diabetes the severe effects of the condition on spermatogenesis are not directly mitochondrial-mediated.

Mitochondria as an important target in heavy metal toxicity in rat hepatoma AS-30D cells

The mechanisms of toxic effects of divalent cations of three heavy metals Hg, Cd and Cu in rat ascites hepatoma AS-30D cells cultivated in vitro were compared. It was found that the toxicity of these ions, applied in the micromolar range (10-500 microM), decreased from Hg(2+) (most toxic) to Cu(2+) (least toxic). Hg(2+) and Cd(2+) produced a high percentage of cell death by both necrosis and apoptosis, whereas Cu(2+) at concentrations up to 500 microM was weakly effective. Hg(2+) at concentration of 10 microM appeared slightly uncoupling (i.e., stimulated resting state respiration and decreased the mitochondrial transmembrane potential), whereas it exerted a strong inhibitory effect on the respiratory chain and rapid dissipation of the membrane potential at higher concentrations. Cu(2+) had inhibitory effect on cell respiration only at 500 microM concentration and after incubation of 48 h but produced a significant uncoupling effect at lower concentrations. Cu(2+) induced an early and sharp increase of intracellular production of reactive oxygen species (ROS). The action of Hg(2+) and Cd(2+) on ROS generation was biphasic. They stimulated ROS generation within the cells at low concentrations and at short incubation times but decreased ROS generation at higher concentrations and at longer incubation. It is concluded that mitochondria are an important target for toxic effects of Hg(2+), Cd(2+) and Cu(2+) in AS-30D rat hepatoma cells.

The distribution of light elements in biological cells measured by electron probe X-ray microanalysis of cryosections

The intracellular distribution of the elements carbon, nitrogen, and oxygen was measured in cultured rat hepatocytes by energy dispersive electron probe X-ray microanalysis of 100-nm-thick freeze-dried cryosections. Electron irradiation with a dose up to 106 e/nm2 caused no or merely negligible mass loss in mitochondria and in cytoplasm. Cell nuclei lost carbon, nitrogen, and-to a clearly higher extent-oxygen with increasing electron irradiation. Therefore, electron doses less than 3 x 105 e/nm2 were used to measure the subcellular compartmentation of carbon, nitrogen, and oxygen in cytoplasm, mitochondria, and nuclei of the cells. The subcellular distribution of carbon, nitrogen, and oxygen reflects the intracellular compartmentation of various biomolecules. Cells exposed to inorganic mercury before cryofixation showed an increase of oxygen in nuclei and cytoplasm. Concomitantly the phosphorus/nitrogen ratio decreased in mitochondria. The data suggest mercury-induced production of ribonucleic acid (RNA) and decrease of adenosine triphosphate (ATP). Although biomolecules cannot be identified by X-ray microanalysis, measurements of the whole element spectrum including the light elements carbon, nitrogen, and oxygen can be useful to study specific biomolecular activity in cellular compartments depending on the functional state of the cell.

Fluorescent imaging of acute mercuric chloride exposure on cultured human kidney tubular epithelial cells

BACKGROUND

Imaging of intracellular mercuric ion is necessary for mechanism of renal toxicity of exposure to HgCl2. The distribution of Hg2+ inside a living cell, however, is still invisible due to the lack of high selective and sensitive fluorescent molecular probe for Hg2+.

METHODS

A new fluorescent probe, EPNP, was applied to the cultured cells of human kidney proximal tubular epithelial cell line (HKC) in the presence of HgCl2 and some other bivalent ions. The relative fluorescence intensity of EPNP was measured and fluorescence images were taken by laser scanning confocal microscope.

RESULTS

Results showed it led to an Hg2+ concentration- and time-dependent increase in fluorescence intensity, and responded weakly for some other heavy and transition metal ions. It could be seen during acute exposure on HKC cells, Hg2+ locate perinuclear, and on nuclear membrane, which was beyond what one knew before.

CONCLUSION

EPNP is a real-time and on-line probe for imaging Hg2+ in a living cell due to its high selectivity and sensitivity for Hg2+ and slow bleaching/fading. Both the probe and the new results about the distribution of intracellular Hg2+ may be helpful for relevant biologic research.

Frozen mitochondria as rapid water quality bioassay

A rapid and relatively low cost bioassay, usable in routine screening water test has been developed modifying the beef heart mitochondria test. In our experiments, mitochondria (FM22) were frozen at -22 degrees C, instead of -80 degrees C (FM80), and their applicability and sensitivity was verified. The oxygen consumption was measured by a Clark electrode that was interfaced to a PC to collect test analysis data. Blank tests were carried out to verify the oxygen consumption linear fitting. Toxicity tests were performed using pure organic and inorganic compounds, such to verify the FM22 sensitivity. A piecewise regression, through an Excel Macro, identified the break-point in the oxygen consumption and calculated the toxicity. The IC50s of the tested compounds were calculated and ranged from 0.123 to 0.173 mg/l for heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) and from 0.572 to 10.545 mg/l for organics (benzene, DMSO, DDE, endrin, dichloromethane, chlorobenzene, 1,2-dichlorobenzene and 1,3-dichlorobenzene). Water effluent samples were then tested. The FM22 gave different toxic reactions to them. Water samples were characterised for heavy metals. The FM22 bioassay had a higher sensitivity than the FM80 and a high reproducibility in the toxicity test with pure compounds. The FM22 test was a good predictor of toxicity for water samples; the bioassay is easy, low cost and rapid, then usable for routine tests.

Cholestasis induced by chronic treatment with alpha-naphthyl-isothiocyanate (ANIT) affects rat renal mitochondrial bioenergetics

Chronic cholestasis is characteristic of many human liver diseases. Renal injury has been often associated with this type of disease. The aim of this study was to evaluate the effect of cholestasis on kidney mitochondrial bioenergetics following in vivo chronic administration of alpha-naphthyl-isothiocyanate (ANIT), a known cholestatic agent. Serum markers of renal injury, kidney morphology and endogenous adenine nucleotides were measured in ANIT-treated rats (80 mg/kg per week s.c. for 16 weeks). Changes in membrane potential and mitochondrial respiration as well as alterations in mitochondrial calcium homeostasis were monitored. Cholestatic animals shown no alterations in renal morphology when compared with control. Additionally, following chronic ANIT administration, no significant alterations in mitochondrial respiratory function have been shown. The phosphorylation capacity of cholestatic kidney mitochondria was enhanced. Associated with these parameters, mitochondria from treated animals exhibited a decreased susceptibility to disruption of mitochondrial calcium homeostasis, due to permeability transition induction. These data suggest that, despite being submitted to chronic treatment with ANIT, kidney mitochondria from cholestasis-induced rats present some defense mechanisms to circumvent this aggression. They show improved phosphorylative capacity and, moreover, a decreased susceptibility to mitochondrial permeability transition induction, probably due to adaptative mechanisms of calcium transport.

Uncoupling effect of mercuric chloride on mitochondria isolated from an hepatic cell line

A human fetal hepatic cell line (WRL-68) was used as a model to study the damage produced by mercury. The Hg(II) uptake by WRL-68 cells was found to be in a biphasic manner with a rapid initial uptake phase lasting about 5 min, followed by a sustained phase of slower accumulation. Distribution of mercury was studied and mitochondria were found to be the major target for mercury in this cell line (48%), followed by nuclei (38%), cytosol (8%) and microsomes (7%). Mitochondrial morphological damage after mercury treatment was observed by transmission electron microscopy. To determine if the toxic effect of mercury on mitochondrial bioenergetics was direct or indirect, mitochondria were isolated from WRL-68 cells after 1 h of pre-incubation with 0.5 microM HgCl(2). Oxygen consumption was quantified in two sets of experiments: in the presence of classical mitochondrial respiratory inhibitors; and in the presence of oligomycin. No significant difference was found in respiration with classical inhibitors, indicating that mercury does not affect directly the mitochondrial respiratory chain. However, mitochondria of Hg-treated cells were not inhibited when oligomycin was added, probably due to an uncoupling effect. This effect was prevented with dithiothreitol (DTT) treatment. A possible explanation for mercury's effect on mitochondria and its relation with oxidative stress is presented.

Heavy metal cytotoxicity studied by electron probe X-ray microanalysis of cultured rat hepatocytes

Cytotoxicity of the heavy metals gold, mercury, thallium and lead was studied by measuring the intracellular element distribution of cultured rat hepatocytes by energy dispersive electron probe X-ray microanalysis of freeze-dried cryosections in a scanning transmission electron microscope. Exposure of the cells to aqueous solutions containing heavy metal ions in concentrations reaching a critical concentration caused increase of intracellular sodium and chloride content accompanied or followed by decrease of intracellular potassium content. Thus, the intracellular potassium/sodium ratio drastically decreased from control values of approximately 10 to values below 1 before changes of cell morphology became visible. In experiments with gold or mercury the decrease of the potassium/sodium ratio was preceded by transient cytoplasmic increase of sulfur and phosphorus. Heavy metal concentrations exceeding the critical concentration also caused an increase of cytoplasmic calcium concentration and finally decay of the cell structure. Cytotoxicity of heavy metals was found to increase in the order Pb, Au, Tl, Hg. Cytotoxic effects by Au, Tl or Hg in moderate concentrations were reduced by simultaneous addition of Zn or Pb to the culture medium. The results obtained prove electron probe X-ray microanalysis of cryosections as a sensitive probe of cell viability.