Mercuric chloride-induced kidney damage in mice: time course and effect of dose

Assessing Kidney Injury Induced by Mercuric Chloride in Guinea Pigs with In Vivo and In Vitro Experiments

Acute kidney injury, which is associated with high levels of morbidity and mortality, affects a significant number of individuals, and can be triggered by multiple factors, such as medications, exposure to toxic chemicals or other substances, disease, and trauma. Because the kidney is a critical organ, understanding and identifying early cellular or gene-level changes can provide a foundation for designing medical interventions. In our earlier work, we identified gene modules anchored to histopathology phenotypes associated with toxicant-induced liver and kidney injuries. Here, using in vivo and in vitro experiments, we assessed and validated these kidney injury-associated modules by analyzing gene expression data from the kidneys of male Hartley guinea pigs exposed to mercuric chloride. Using plasma creatinine levels and cell-viability assays as measures of the extent of renal dysfunction under in vivo and in vitro conditions, we performed an initial range-finding study to identify the appropriate doses and exposure times associated with mild and severe kidney injuries. We then monitored changes in kidney gene expression at the selected doses and time points post-toxicant exposure to characterize the mechanisms of kidney injury. Our injury module-based analysis revealed a dose-dependent activation of several phenotypic cellular processes associated with dilatation, necrosis, and fibrogenesis that were common across the experimental platforms and indicative of processes that initiate kidney damage. Furthermore, a comparison of activated injury modules between guinea pigs and rats indicated a strong correlation between the modules, highlighting their potential for cross-species translational studies.

Assessment of Total Mercury in Hair, Urine and Fingernails of Small-Scale Gold Miners in the Amansie West District, Ghana

BACKGROUND

Mercury (Hg) is a heavy metal that can cause several adverse health effects based on its form (organic, inorganic or elemental), duration and pathway of exposure. Measurement of mercury present in human biological media is often used to assess human exposure to mercury at mining sites.

OBJECTIVES

The aim of the present study was to measure the concentrations of total mercury in urine, hair, and fingernails of miners and inhabitants of Amansie West District, Ghana.

METHODS

Concentrations of total mercury were measured in sixty-eight miners and twelve non-miners in the study area using cold vapor atomic absorption spectrophotometry with an automatic mercury analyzer (HG 5000).

RESULTS

Total mercury in nails and hair of smelter miners was 3.32 ± 0.36 and 6.59 ± 0.01 μg/g, respectively. Total mercury concentrations in hair samples obtained from smelter miners were above the 1 μg/g guideline set by the United States Environmental Protection Agency (USEPA). Moreover, the total mercury concentration in urine samples was 6.97 ± 0.06 μg/L, far below the >25 μg/L level considered to be a high level of mercury contamination. The total mercury accrued by the individuals was not dependent on age, but was positively associated with duration of stay.

CONCLUSIONS

Based on the total mercury (THg) levels analyzed in the biological media, artisanal gold mining activities in Amansie West District are on the increase with a potential risk of developing chronic effects. However, the majority of the population, particularly those engaged in artisanal small-scale gold mining, are unmindful of the hazards posed by the use of mercury in mining operations. The results showed that THg in urine, hair, and fingernails more efficiently distinguished mercury exposure in people close to mining and Hg pollution sources than in people living far from the mining sites. Further education on cleaner artisanal gold mining processes could help to minimize the impact of mercury use and exposure on human health and the environment.

PARTICIPANT CONSENT

Obtained.

ETHICS APPROVAL

This study was approved by the Ghana Environmental Protection Agency and the Ministry of Local Government and Rural Development in Manso Nkwanta.

COMPETING INTERESTS

The authors declare no competing financial interests.

Effects of soft electrophiles on selenium physiology

This review examines the effects of neurotoxic electrophiles on selenium (Se) metabolism. Selenium-dependent enzymes depend on the unique and elite functions of selenocysteine (Sec), the 21st proteinogenic amino acid, to perform their biochemical roles. Humans possess 25 selenoprotein genes, ~ half of which are enzymes (selenoenzymes) required for preventing, controlling, or reversing oxidative damage, while others participate in regulating calcium metabolism, thyroid hormone status, protein folding, cytoskeletal structure, Sec synthesis and Se transport. While selenoproteins are expressed in tissue dependent distributions and levels in all cells of all vertebrates, they are particularly important in brain development, health, and functions. As the most potent intracellular nucleophile, Sec is subject to binding by mercury (Hg) and other electron poor soft neurotoxic electrophiles. Epidemiological and environmental studies of the effects of exposures to methyl-Hg (CH₃Hg⁺), elemental Hg (Hg°), and/or other metallic/organic neurotoxic soft electrophiles need to consider the concomitant effects of all members of this class of toxicants in relation to the Se status of their study populations. The contributions of individual electrophiles' discrete and cooperative rates of Se sequestration need to be evaluated in relation to tissue Se reserves of the exposed populations to identify sensitive subgroups which may be at accentuated risk due to poor Se status. Additional study is required to examine possibilities of inherited, acquired, or degenerative neurological disorders of Se homeostasis that may influence vulnerability to soft electrophile exposures. Investigations of soft electrophile toxicity will be enhanced by considering the concomitant effects of combined exposures on tissue Se-availability in relation to pathological consequences during fetal development or in relation to etiologies of neurological disorders and neurodegenerative diseases. Since selenoenzymes are molecular "targets" of soft electrophiles, concomitant evaluation of aggregate exposures to these toxicants in relation to dietary Se intakes will assist regulatory agencies in their goals of improving and protecting public health.

Evaluation of mercury exposure level, clinical diagnosis and treatment for mercury intoxication

Mercury occurs in various chemical forms, and it is different to health effects according to chemical forms. In consideration of the point, the evaluation of the mercury exposure to human distinguished from occupational and environmental exposure.

With strict to manage occupational exposure in factory, it is declined mercury intoxication cases by metallic and inorganic mercury inhalation to occupational exposure. It is increasing to importance in environmental exposure and public health.

The focus on the health impact of exposure to mercury is more on chronic, low or moderate grade exposure—albeit a topic of great controversy—, not high concentration exposure by methylmercury, which caused Minamata disease.

Recently, the issue of mercury toxicity according to the mercury exposure level, health effects as well as the determination of what mercury levels affect health are in the spotlight and under active discussion. Evaluating the health effects and Biomarker of mercury exposure and establishing diagnosis and treatment standards are very difficult.

It can implement that evaluating mercury exposure level for diagnosis by a provocation test uses chelating agent and conducting to appropriate therapy according to the result. but, indications for the therapy of chelating agents with mercury exposure have not yet been fully established.

The therapy to symptomatic patients with mercury poisoning is chelating agents, combination therapy with chelating agents, plasma exchange, hemodialysis, plasmapheresis. But the further evaluations are necessary for the effects and side effects with each therapy.

Effects of 1-methyl-3-octylimidazolium bromide on the anti-oxidant system of earthworm

The activity changes of anti-oxidant enzymes and the levels of glutathione and malondialdehyde were determined when Eisenia foetida were exposed to different concentrations of 1-methyl-3-octylimidazolium bromide for 14d. The results showed catalase activity in all treatment groups was elevated significantly after 1d of exposure, and superoxide dismutase activity in higher-dosage groups (120 and 160mgkg(-1)) was increased at 3d post-exposure. On the 7thd, the activity of glutathione-S-transferase in the 20 and 40mgkg(-1) dosage groups was inhibited while increased in the 80 and 160mgkg(-1) groups compared with the control groups. During exposure, the level of intracellular glutathione in all treatment groups was much higher than that of the control groups. Changes in malondialdehyde indicate that [C(8)mim]Br may lead to cellular lipid peroxidation in earthworm. Our results suggest that exposure to [C(8)mim]Br induce the formation of reactive oxygen species in earthworms.

Lymphocyte proliferative response and tissue distribution of methylmercury sulfide and chloride in exposed rats

The immunotoxic effects and tissue distribution of different forms of methylmercury compounds were studied in rats. Methylmercury sulfide or methylmercury chloride was fed to rats at concentrations of 5 or 500 microg/L in drinking water for 8 wk. T-cell lymphocyte proliferative response to phytohemagglutinin (PHA) and determination of tissue distribution of mercury by gas chromatography using electron capture were assayed. Four different forms of mercury compounds were employed: MeHgS-, (MeHg)2S, (MeHg)3S+, and MeHgCl. Results indicated that exposure to methylmercury significantly enhanced lymphocyte responsiveness in most of the exposed groups at the low concentration of 5 microg/L, with the highest proliferative response (fourfold increase) in the MeHgCl group. At 500 microg/L, a significant decrease in the lymphocyte proliferative response was observed in the (MeHg)3S+ and MeHgCl groups; conversely, the MeHgS(-)- and (MeHg)2S-exposed animals had a modest increase of the lymphocyte proliferative response. The largest concentrations of all four mercury forms were detected in the kidney and spleen. The levels of mercury found in kidney, spleen, liver, brain, and testis were lower in the MeHgCl group than in those exposed to (MeHg)2S and (MeHg)3S+. These data indicate that the organ distribution of mercury and immune alteration may vary according to the chemical structure of the compound. This observation may have important implications in humans potentially exposed to low levels of methylmercury present in the environment, since the immune system plays an important regulatory role in the host-defense mechanisms.

Lipid peroxidation in rats administrated with mercuric chloride

Parenteral administration of mercuric chloride (HgCl2) to rats enhanced lipid peroxidation in liver, kidney, lung, testis, and serum (but not in heart, spleen, or muscle), as measured by the thiobarbituric acid reaction for malondialdehyde (MDA) in fresh tissue homogenates and body fluids. After sc injection of HgCl2 (5 mg/kg body wt), MDA concentrations in liver and kidney became significantly increased by 9 h and reached peak values at 24 h. Dose-response studies were carried out with male albino rats of the Fisher-344 strain (body wt 170-280 g) injected with 1, 3, 5 mg Hg/kg as HgCl2 and sacrificed after 24 h. In time-response studies, animals were administered 5 mg Hg/kg as HgCl2 and sacrificed after 3, 9, 18, 24, and 48 h. Studies in the authors' laboratory have shown that (1) concentrations of MDA are increased in targets (liver, kidney, lung, and testis) of HgCl2-treated rats; (2) severity of hepatotoxicity and nephrotoxicity is generally consistent with the elevation of Hg and MDA concentrations, based upon the time-course and dose-effect relationships observed after administration of HgCl2 to rats; and (3) concentrations of MDA are reduced in target tissues after pre-treatment with antioxidants and chelators to HgCl2-treated rats. The results of this study implicate that the lipid peroxidation is one of the molecular mechanisms for cell injury in acute HgCl2 poisoning.

Cytotoxicity of mercury compounds in LLC-PK1, MDCK and human proximal tubular cells

Six mercury compounds [HgCl2 (MC), Hg(CH3COO)2 (MA), Hg(NO3)2 (MN), C2H5HgSC6H4COONa (EMT), C6H5HgOCOCH3 (PMA) and CH3CIHg (MMC)] were studied using two kidney cell lines (MDCK and LLC-PK1), primary cultures of human proximal tubular cells (hPTC) and nonrenal cell lines (SAOS and Hep G2). Cell damage was measured with four different tests: neutral red uptake, mitochondrial dehydrogenase activity (MTT conversion), thymidine incorporation and protein content. Relative toxicity was established by the determination of the concentration of test compound inducing a 50% reduction of the parameter considered (EC50 value). Two groups could be distinguished: PMA, EMT and MMC are one order of magnitude more toxic than MC, MN and MA. Cellular uptake was measured by the HPLC-hybrid generation AAS after 24 hours treatment with 1.5 microM MC, MMC, PMA or EMT in MDCK cells, revealing Hg concentrations of 42.8 +/- 2.5 ng/mg protein for MC, 596.9 +/- 87.8 ng/mg protein for MMC, 269.8 +/- 75.7 ng/mg protein for PMA and of 115.9 +/- 25.2 ng/mg protein for EMT. Cytotoxicity was positively correlated with cellular uptake. The effect of the cellular GSH content on the toxicity of mercury was studied using the GSH synthesis inhibitor L-buthionine sulfoximine (BSO). In all cases an enhanced cytotoxicity was observed after BSO treatment. 2-Oxo-4-thiazolidine carboxylic acid (OTC) was used as a substrate for the GSH synthesis. Although OTC did not enhance the GSH content, the cytotoxicity of MC, MN and MA decreased significantly, no changes were observed for the other mercurials.(ABSTRACT TRUNCATED AT 250 WORDS)

Food chain transfer and potential renal toxicity of mercury to small mammals at a contaminated terrestrial field site

Mercury concentrations were determined in surface soil and biota at a contaminated terrestrial field site and were used to calculate transfer coefficients of mercury through various compartments of the ecosystem based on trophic relationships. Mercury concentrations in all compartments (soil, vegetation, invertebrates, and small mammals) were higher than mercury concentrations in corresponding samples at local reference sites. Nonetheless, mercury concentrations in biota did not exceed concentrations in the contaminated surface soil, which averaged 269 μg g(-1). Plant tissue concentrations of mercury were low (0.01 to 2.0 μg g(-1)) and yielded soil to plant transfer coefficients ranging from 3.7×10(-5) for seeds to 7.0×10(-3) for grass blades. Mercury concentrations in invertebrates ranged from 0.79 for harvestmen (Phalangida) to 15.5 μg g(-1) for undepurated earthworms (Oligochaeta). Mean food chain transfer coefficients for invertebrates were 0.88 for herbivores/omnivores and 2.35 for carnivores. Mean mercury concentrations in target tissue (kidney) were 1.16±1.16 μg g(-1) for the white-footed mouse (Peromyscus leucopus), a granivore, and 38.8±24.6 μg g(-1) for the shorttail shrew (Blarina brevicauda), an insectivore. Transfer coefficients for diet to kidney were 0.75 and 4.40 for P. leucopus and B. brevicauda, respectively. A comparison of kidney mercury residues measured in this study with values from controlled laboratory feeding studies from the literature indicate that B. brevicauda but not P. leucopus may be ingesting mercury at levels that are nephrotoxic.

Toxicokinetics of mercuric chloride and methylmercuric chloride in mice

Future human exposure to inorganic mercury will probably lead to a few individuals occupationally exposed to high levels and much larger populations exposed to low or very low levels from dental fillings or from food items containing inorganic mercury; human exposure to methylmercury will be relatively low and depending on intake of marine food. Ideally, risk assessment is based on detailed knowledge of relations between external and internal dose, organ levels, and their relation to toxic symptoms. However, human data on these toxicokinetic parameters originate mainly from individuals or smaller populations accidentally exposed for shorter periods to relatively high mercury levels, but with unknown total body burden. Thus, assessment of risk associated with exposure to low levels of mercury will largely depend on data from animal experiments. Previous investigations of the toxicokinetics of mercuric compounds almost exclusively employed parenteral administration of relatively high doses of soluble mercuric salts. However, human exposure is primarily pulmonary or oral and at low doses. The present study validates an experimental model for investigating the toxicokinetics of orally administered mercuric chloride and methylmercuric chloride in mice. Major findings using this model are discussed in relation to previous knowledge. The toxicokinetics of inorganic mercury in mice depend on dose size, administration route, and sex, whereas the mouse strain used is less important. The "true absorption" of a single oral dose of HgCl2 was calculated to be about 20% at two different dose levels. Earlier studies that did not take into account the possible excretion of absorbed mercury and intestinal reabsorption during the experimental period report 7-10% intestinal uptake. The higher excretion rates observed after oral than after intraperitoneal administration of HgCl2 are most likely due to differences in disposition of systemically delivered and retained mercury. After methylmercury administration, mercury excretion followed first-order kinetics for 2 wk, independently of administration route, strain, or sex. However, during longer experimental periods, the increasing relative carcass retention (slower rate of excretion) caused the elimination to deviate from first-order kinetics. Extensive differences in the toxicokinetics of methylmercury with respect to excretion rates, organ deposition, and blood levels were observed between males and females.(ABSTRACT TRUNCATED AT 400 WORDS)