Advances in understanding the renal transport and toxicity of mercury

Imaging gastrointestinal damage due to acute mercury poisoning using a mitochondria-targeted dual near-infrared fluorescent probe

Mercury (Hg) is one of the most widespread pollutants that pose serious threats to public health and the environment. People are inevitably exposed to Hg via different routes, such as respiration, dermal contact, drinking or diet. Hg poisoning could cause gingivitis, inflammation, vomiting and diarrhea, respiratory distress or even death. Especially during the developmental stage, there is considerable harm to the brain development of young children, causing serious symptoms such as intellectual disability and motor impairments, and delayed neural development. Therefore, it's of great significance to develop a specific, quick, practical and labor-saving assay for monitoring Hg2+. Herein, a mitochondria-targeted dual (excitation 700 nm and emission 728 nm) near-infrared (NIR) fluorescent probe JZ-1 was synthesized to detect Hg2+, which is a turn-on fluorescent probe designed based on the rhodamine fluorophore thiolactone, with advantages of swift response, great selectivity, and robust anti-interference capability. Cell fluorescence imaging results showed that JZ-1 could selectively target mitochondria in HeLa cells and monitor exogenous Hg2+. More importantly, JZ-1 has been successfully used to monitor gastrointestinal damage of acute mercury poisoning in a drug-induced mouse model, which provided a great method for sensing Hg species in living subjects, as well as for prenatal diagnosis.

Interaction of mercury species with proteins: towards possible mechanism of mercurial toxicology

The nature of the binding of mercurials (organic and inorganic) and their subsequent transformations in biological systems is a matter of great debate as several different hypotheses have been proposed and none of them has been conclusively proven to explain the characteristics of Hg binding with the proteins. Thus, the chemical nature of Hg-protein binding through the possible transportation mechanism in living tissues is critically reviewed herein. Emphasis is given to the process of transportation, and binding of Hg species with selenol-containing biomolecules that are appealing for toxicological studies as well as the advancement of environmental and biological research.

Association of low cadmium and mercury exposure with chronic kidney disease among Chinese adults aged ≥80 years: A cross-sectional study

BACKGROUND

The heavy metals cadmium (Cd) and mercury (Hg) are known to be widespread environmental contaminants and high occupational exposure adversely affects the risk of chronic kidney disease (CKD). However, evidence from epidemiological studies linking low Cd and Hg exposure (or non-industrial) to the risk of progression to CKD are conflicting. This study aimed to explore the association of low Cd and Hg exposure with the risk of CKD in Chinese adults aged ≥80 years.

METHODS

The participants were recruited for the Healthy Aging and Biomarkers Cohort Study in 2017, an ongoing perspective survey conducted in longevity areas in China initially involving 3016 older adults. We used logistic regression models to estimate odds ratios (ORs) with 95% confidence intervals of CKD setting Cd and Hg as categorical variables. Logistic regression with restricted cubic spline was used to characterize a dose-response relationships between Cd or Hg concentrations and the risk of CKD in the study population.

RESULTS

The ORs for the risk of CKD comparing the fourth to the first quartile of blood Cd, blood Hg, urine Cd, and urine Hg were 1.77, 1.57, 2.03, and 1.50, respectively. Restricted cubic spline models showed that blood Cd and urine Hg were significantly linearly correlated with the risk of CKD, while blood Hg and urine Cd were non-linearly correlated with the risk of CKD with a steeper slope at concentrations <2.30 μg/L and 3.30 μg/g creatinine.

CONCLUSIONS

Our findings suggest that even low Cd and Hg exposure (or non-industrial) were associated with increased risk of CKD in Chinese oldest old, although we did not find a significant multiplicative and additive interaction between Cd and Hg levels in relation to the risk of CKD.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

Chronic Mercury Exposure in Prehypertensive SHRs Accelerates Hypertension Development and Activates Vasoprotective Mechanisms by Increasing NO and H2O2 Production

Mercury is a heavy metal associated with cardiovascular diseases. Studies have reported increased vascular reactivity without changes in systolic blood pressure (SBP) after chronic mercury chloride (HgCl₂) exposure, an inorganic form of the metal, in normotensive rats. However, we do not know whether individuals in the prehypertensive phase, such as young spontaneously hypertensive rats (SHRs), are susceptible to increased arterial blood pressure. We investigated whether chronic HgCl₂ exposure in young SHRs accelerates hypertension development by studying the vascular function of mesenteric resistance arteries (MRAs) and SBP in young SHRs during the prehypertensive phase. Four-week-old male SHRs were divided into two groups: the SHR control group (vehicle) and the SHR HgCl₂ group (4 weeks of exposure). The results showed that HgCl₂ treatment accelerated the development of hypertension; reduced vascular reactivity to phenylephrine in MRAs; increased nitric oxide (NO) generation; promoted vascular dysfunction by increasing the production of reactive oxygen species (ROS), such as hydrogen peroxide (H₂O₂); increased Gp91Phox protein levels and in situ levels of superoxide anion (O₂^·-); and reduced vasoconstrictor prostanoid production compared to vehicle treatment. Although HgCl₂ accelerated the development of hypertension, the HgCl₂-exposed animals also exhibited a vasoprotective mechanism to counterbalance the rapid increase in SBP by decreasing vascular reactivity through H₂O₂ and NO overproduction. Our results suggest that HgCl₂ exposure potentiates this vasoprotective mechanism against the early establishment of hypertension. Therefore, we are concluding that chronic exposure to HgCl₂ in prehypertensive animals could enhance the risk for cardiovascular diseases.

The relationship of mercury exposure with neurological problems in artisanal gold in Makassar city

Objectives This research aims to analyse the relationship between urine mercury levels and neurological problems. Methods This research is an observational study with a cross-sectional approach. There are 44 goldsmiths in the gold jewellery small scale industry involved in this study. Urine mercury levels were measured using an atomic absorption spectrophotometer. Neurological problems were assessed by a medician. Data collected includes age, time of exposure, work duration, smoking behaviour and nutrition status of the goldsmiths which were obtained by interview. Results The results showed that the concentration of mercury in the goldsmith's urine was around 0.93-64.59 μg/L. The analysis showed that there were 63% of goldsmiths experiencing neurological problems, such as tremors (9.1%) and knee pass reflex (6.8%). The bivariate analysis showed that there is no significant relationship between the concentration of mercury (p=0.133), age (p=0.155), time of exposure (p=0.702), time of working (p=0.354), smoking behaviour (p=0.169) and nutrition status (p=0.541) with neurological problems. Conclusions The goldsmiths who had high levels of mercury in urine samples were diagnosed with at least one of the neurological symptoms. It is recommended that the goldsmith use personal protective equipment during work such as mask, glasses and gloves.

Evaluation of Dietary Organic and Inorganic Mercury Threshold Levels on Induced Mercury Toxicity in a Marine Fish Model

Simple Summary

This investigation was executed to establish the threshold level of inorganic and organic mercury incorporated in the diet of juvenile olive flounder in relation to the broken-line regression model for the percentage of weight gain of fish. Organic mercury incorporated diet resulted in more toxic behavior than its counterpart inorganic mercury in olive flounder. Mercury was found to be more biomagnified in kidney tissue than liver and gill tissues of fish. The study has importance in terms of knowledge on mercury toxicity in marine fish.

Abstract

Mercury as one of the most toxic elements can be present in organic or inorganic form in marine fishes, which may cause a potential threat to public health. In this study, we investigated to determine the dietary organic (O-Hg) and inorganic (I-Hg) mercury threshold levels on induced mercury toxicity in juvenile olive flounder, Paralichthys olivaceus as a marine fish model. Twenty-eight fish averaging 3.1 ± 0.05 g (mean ± SD) were arbitrarily assigned to each of 27 tanks. Each tank was arbitrarily restricted to triplicates of nine experimental diets for eight weeks. The experimental diets were manufactured to contain 0 (Control), 10 (I-Hg10, O-Hg10), 20 (I-Hg20, O-Hg20), 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) mg/kg diet in organic form as methylmercury (MeHg) or in inorganic form as mercuric chloride (HgCl₂). At the termination of the experimental trial, weight gains (WGs) of fish fed the control and 10 (I-Hg10, O-Hg10) diets were remarkably higher than those of fish fed the 20 (I-Hg20, O-Hg20), 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) (p < 0.05). Specific growth rate and feed efficiency of fish fed control and 10 (I-Hg10, O-Hg10) diets were significantly higher than those of fish fed 40 (I-Hg40, O-Hg40) and 160 (I-Hg160, O-Hg160) diets. In comparison to the dietary inorganic mercury, dietary MeHg bioaccumulation rates were significantly higher in the tissue levels according to the dietary inclusion levels. MeHg accumulated mostly in kidney, followed by liver and gill tissues. HgCl₂ accumulated in tissues, in decreasing order, liver > kidney > gills. A broken-line regression model for percentage of WG indicated that the threshold toxicity level for an Hg-incorporated diet of juvenile olive flounder could be 13.5 mg Hg/kg in the form of HgCl₂ and 8.7 mg Hg/kg in the form of MeHg.

Evaluation of the potential nephrotoxicity and mechanism in rats after long-term exposure to the traditional Tibetan medicine tsothel

CONTEXT

Tsothel, a traditional Tibetan medicine, is regarded as 'the king of essences'. Nevertheless, tsothel has aroused serious concern regarding its biosafety because its main component is HgS. Unfortunately, toxicological studies on tsothel are scarce.

OBJECTIVE

As inorganic mercury has high affinity for the kidney, the present investigation was designed to determine the potential nephrotoxicity and mechanism of tsothel.

MATERIALS AND METHODS

Sprague-Dawley rats were orally administered different doses of tsothel (0, 66.70, 33.35 and 16.68 mg/kg) daily for 180 days, followed by the withdrawal of tsothel for 120 days. Then, the related nephrotoxicity was examined by the ICP-MS, ELISA, colorimetric, RT-PCR, HE staining, immunohistochemical staining and flow cytometry methods.

RESULTS

Although tsothel administration led to a large accumulation of Hg (794.25 ± 464.30 ng/g in the 66.70 mg/kg group, 775.75 ± 307.89 ng/g in the 33.35 mg/kg group and 532.60 ± 356.77 ng/g in the 16.68 mg/kg group) in the kidney after 120 days of tsothel withdrawal, the blood CREA and BUN, urinary Kim-1, NAG, RBP and β2-MG, renal SOD, MDA, pathology, proliferation, apoptosis and cell cycle had no significant changes compared with the control group. Additionally, the high GSH content (318.87 ± 44.19 nmol/mL in the 33.35 mg/kg group) and the relative expression levels of Kim-1 (1.08 ± 0.11 in the 33.35 mg/kg group), MT-1 (1.46 ± 0.10 in the 66.70 mg/kg group, 1.61 ± 0.19 in the 33.35 mg/kg group and 1.57 ± 0.14 in the 16.68 mg/kg group) and GST-Pi (1.76 ± 0.89 in the 33.35 mg/kg group) mRNA recovered to normal after tsothel withdrawal. Interestingly, the change trend of GST-Pi gene expression was consistent with the change trend of GSH activity.

CONCLUSIONS

Overall, our study shows that tsothel administration did not induce overt nephrotoxicity but did have reversible stress-related effects. These results suggest that tsothel affects stress response mechanisms with the involvement of detoxifying enzyme systems. The formulation method and chemotype could play a role in the reduced toxicity potential of tsothel compared to common mercurials.

Interactive effect of dietary vitamin E and inorganic mercury on growth performance and bioaccumulation of mercury in juvenile olive flounder, Paralichthys olivaceus treated with mercuric chloride

A 6-week feeding trial was carried out to evaluate the effects of dietary vitamin E (dl-α-tocopheryl acetate, TA) on growth and mercury (Hg) accumulation in juvenile olive flounder (Paralichthys olivaceus) treated with mercuric chloride (HgCl₂). Vitamin E and HgCl₂ were added to the semi-purified basal diet. Six semi-purified diets in a 2 × 3 factorial design were formulated to contain 2 levels of Hg (0 or 20 mg HgCl₂/kg diet) and 3 levels of vitamin E (0, 100, or 200 mg TA/kg diet). Experimental fish (n = 360, 9.99 ± 0.15 g) were randomly allocated into 30-L tanks at a density of 20 fish per tank with 3 replicates in each treatment and were fed twice a day. At the end of the feeding trial, dietary Hg depressed the growth performances in terms of weight gain (WG), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) in fish, while fish fed the diets supplemented with vitamin E showed significant growth improvement in both presence and absence of HgCl₂ in the diets (P < 0.05). Survival rate was not affected in fish fed the experimental diets. Whole body compositions of fish such as lipid and moisture contents were influenced by dietary vitamin E supplementation. Total Hg contents of muscle, liver and kidney tissues were significantly reduced in fish fed diets supplemented with vitamin E (P < 0.05), while the two-way ANOVA showed that increasing Hg concentration has resulted in a reduction in vitamin E. Whole body fatty acids of fish like eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents were decreased by dietary Hg. However, supplementation of dietary vitamin E improved the α-linolenic acid (ALA) and EPA contents in fish. Our results suggest that dietary supplementation of vitamin E has potential effects on growth improvement and ameliorating inorganic Hg bioaccumulation in juvenile olive flounder.

Reduced egfr, elevated urine protein and low level of personal protective equipment compliance among artisanal small scale gold miners at Bibiani-Ghana: a cross-sectional study

BACKGROUND

Mercury is a toxic metal with its effects on human health ranging from acute to chronic in a very short time of exposure. Artisanal and small-scale gold mining (ASGM) is the main source of direct human exposure to mercury.

AIM

To access the effect of mercury exposure on the renal function and level of personal protective equipment (PPE) compliance among small-scale gold miners in Bibiani District of the Western Region of Ghana METHOD: 110 consenting male gold miners were purposively recruited for this study. A structured questionnaire was used to collect socio-demographic information from the participants. Work place assessment and interviews were conducted. Urine samples were analysed for protein; blood was analysed for mercury and creatinine. Estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation.

RESULTS

Of the 110 participants, 61(55.5%) exceeded the occupational exposure threshold (blood mercury <5μg/L). Urine protein (41.72±68.34, P<0.0001), serum creatinine (2.24±1.19, P<0.0001) and blood mercury (18.37±10.47, P<0.0001) were significantly elevated among the exposed group compared to the non-exposed group. However, the exposed group had a significantly reduced eGFR (P<0.0001). There was a significant correlation (r=0.7338, p<0.0001) between blood mercury concentration and urine protein concentration. An increase in blood mercury correlated negatively (r = -0.8233, P<0.0001) with eGFR among the exposed group. High urine protein (P< 0.0001) and high serum creatinine (P< 0.0001) were significantly associated with increased mercury exposure. Increased mercury exposure was significantly associated with burning of amalgam (P=0.0196), sucking of excess mercury (P=0.0336), longer work duration (P=0.0314) and low educational background (P=0.0473).

CONCLUSION

Small scale miners at the Bibiani work site are exposed to excess mercury. Proteinuria and reduced eGFR is common in mine workers exposed to excess mercury. We found poor PPE compliance among the study population.

Reduced egfr, elevated urine protein and low level of personal protective equipment compliance among artisanal small scale gold miners at Bibiani-Ghana: a cross-sectional study

Background

Mercury is a toxic metal with its effects on human health ranging from acute to chronic in a very short time of exposure. Artisanal and small-scale gold mining (ASGM) is the main source of direct human exposure to mercury.

Aim

To access the effect of mercury exposure on the renal function and level of personal protective equipment (PPE) compliance among small-scale gold miners in Bibiani District of the Western Region of Ghana

Method

110 consenting male gold miners were purposively recruited for this study. A structured questionnaire was used to collect socio-demographic information from the participants. Work place assessment and interviews were conducted. Urine samples were analysed for protein; blood was analysed for mercury and creatinine. Estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease-epidemiology collaboration (CKD-EPI) equation.

Results

Of the 110 participants, 61(55.5%) exceeded the occupational exposure threshold (blood mercury <5μg/L). Urine protein (41.72±68.34, P<0.0001), serum creatinine (2.24±1.19, P<0.0001) and blood mercury (18.37±10.47, P<0.0001) were significantly elevated among the exposed group compared to the non-exposed group. However, the exposed group had a significantly reduced eGFR (P<0.0001). There was a significant correlation (r=0.7338, p<0.0001) between blood mercury concentration and urine protein concentration. An increase in blood mercury correlated negatively (r = −0.8233, P<0.0001) with eGFR among the exposed group. High urine protein (P< 0.0001) and high serum creatinine (P< 0.0001) were significantly associated with increased mercury exposure. Increased mercury exposure was significantly associated with burning of amalgam (P=0.0196), sucking of excess mercury (P=0.0336), longer work duration (P=0.0314) and low educational background (P=0.0473).

Conclusion

Small scale miners at the Bibiani work site are exposed to excess mercury. Proteinuria and reduced eGFR is common in mine workers exposed to excess mercury. We found poor PPE compliance among the study population.

Effect of mercury vapour exposure on urinary excretion of calcium, zinc and copper: relationship to alterations in functional and structural integrity of the kidney

Background: The kidney has a remarkable capacity to concentrate mercury (Hg) and as such is a primary target organ when exposure to Hg occurs, and it is also an organ for Hg excretion. Objective: The present work aims to investigate the effect of occupational Hg vapour exposure on the urinary excretion of calcium (Ca), zinc (Zn) and copper (Cu), and the possible association of this excretion to work duration as well as renal alterations. Methods: 83 non-smoker participants (36 referents, age: 35.69/9.5 years; 27 Hg vapour-exposed workers with 5/10 years work duration, age: 33.09/5.1 years; and 20 Hg vapour-exposed workers with]/11 years work duration, age: 39.509/8.50 years) were included in the present study. Urinary levels of microalbumin (U-Malb) and retinol-binding protein (U-RBP) as well as cytosolic glutathione S-transferase activity (U-GST) were measured to assess the glomerular and proximal tubular reabsorption functions as well as structural integrity of proximal tubules; respectively. In addition, blood Hg (B-Hg), serum levels of Hg (S-Hg) and Ca (S-Ca), and urinary levels of Hg (U-Hg), Ca (U-Ca), Zn (U-Zn), Cu (U-Cu) and creatinine (U-cr) were estimated. Results: In comparison to referents, all investigated parameters showed significant increase (except S-Ca and U-Zn/U-Cu ratio that significantly decreased among the workers as one group, S-Ca and U-Zn/U-Cu ratio that significantly and nonsignificantly decreased; respectively among workers with 5/10 years work duration, S-Ca and U-Zn/U-Cu ratio that significantly decreased among workers with]/11 years work duration). In addition, B-Hg was nonsignificantly increased and S-Ca was significantly decreased; also, both U-Hg and U-Zn/U-Cu were nonsignificantly decreased among workers with]/11 years work duration in comparison to those with 5/10 years work duration. Also, each of U-Hg, U-Ca, U-Zn and U-Cu was related to one another, while each of U-Ca, U-Zn and U-Cu was related to each of U-Malb, U-RBP and U-GST (except U-Zn was not related to U-GST). Conclusion: Hg vapour exposure leads to renal alterations which may parallel the change in proteinuria and enzymuria as well as the increased loss in urine of each of Ca, Zn and Cu. The urinary assessment of these metals may be used as a good indicator for renal dysfunction.

Single excited state intramolecular proton transfer (ESIPT) chemodosimeter based on rhodol for both Hg2+ and OCl−: ratiometric detection with live-cell imaging

We have synthesised a ratiometric fluorescence chemodosimeter, STBR, for the detection of Hg²⁺ and OCl⁻ in one platform over other cations, anions and oxidants in aqueous solution.

Heavy Metals and Human Health: Mechanistic Insight into Toxicity and Counter Defense System of Antioxidants

Heavy metals, which have widespread environmental distribution and originate from natural and anthropogenic sources, are common environmental pollutants. In recent decades, their contamination has increased dramatically because of continuous discharge in sewage and untreated industrial effluents. Because they are non-degradable, they persist in the environment; accordingly, they have received a great deal of attention owing to their potential health and environmental risks. Although the toxic effects of metals depend on the forms and routes of exposure, interruptions of intracellular homeostasis include damage to lipids, proteins, enzymes and DNA via the production of free radicals. Following exposure to heavy metals, their metabolism and subsequent excretion from the body depends on the presence of antioxidants (glutathione, α-tocopherol, ascorbate, etc.) associated with the quenching of free radicals by suspending the activity of enzymes (catalase, peroxidase, and superoxide dismutase). Therefore, this review was written to provide a deep understanding of the mechanisms involved in eliciting their toxicity in order to highlight the necessity for development of strategies to decrease exposure to these metals, as well as to identify substances that contribute significantly to overcome their hazardous effects within the body of living organisms.

Cadmium and mercury accumulation in European hare (Lepus europaeus): age-dependent relationships in renal and hepatic tissue

A total of 63 European hares have been collected from five Serbian agricultural regions. The hares assayed were divided into four age groups (3-6 months, 12 months, 12-24 months, and 24-36 months) and investigated upon presence at cadmium (Cd) and mercury (Hg) in the kidney and liver. The positive significant correlation (Ps-Pearson's coefficient) between Cd concentrations in the kidney and liver within age group the 3-6 months was found (Ps = 0.81, p < 0.001). Differences between Cd content in the kidney in comparison to liver were significant within all presented age groups (p < 0.001). Differences between recorded Hg levels in the kidney were not significant between presented age groups (p > 0.05). Statistically significant differences were registered between Hg content in the liver of the hares aged 24-36 and 12 months (p < 0.05). There were no statistically significant correlations registered between Hg concentrations in the kidney and liver within any particular age group (p > 0.05). The strong statistically significant associations were registered between Cd and Hg content in the liver (Cd L/Hg L) in the age group 3-6 and 12-24 months (Cd L/Hg L, Ps = 0.94; p < 0.001 and Ps = 0.91; p < 0.001, respectively). The polynomial regression model used for graphing the observed data seems to be a method for modeling the relationship between measured Cd and Hg concentrations in the liver and kidney as first approximation for bioaccumulation in hares.

Modulation of mitochondrial glutathione status and cellular energetics in primary cultures of proximal tubular cells from remnant kidney of uninephrectomized rats

Compensatory renal hypertrophy following reduction in renal mass leads to a hypermetabolic state and increases in basal mitochondrial oxidative stress and susceptibility to several nephrotoxicants. Previous studies provide conflicting data on whether renal mitochondria after reduction in renal mass undergo proliferation or hypertrophy or both. In the present study, our goal was to determine whether mitochondria of hypertrophied kidney undergo hypertrophy or proliferation after uninephrectomy using the uninephrectomized (NPX) rat model. Renal proximal tubular (PT) cells from NPX rats exhibited increased mitochondrial density, membrane potential and protein but no significant difference in mitochondrial DNA, as compared to PT cells from control rats. Our previous studies showed that overexpression of two mitochondrial anion transporters, the dicarboxylate (DIC, Slc25a10) and oxoglutarate (OGC, Slc25a11) carriers, in NRK-52E cells resulted in increased mitochondrial uptake of glutathione (GSH) and protection from chemically induced apoptosis. In the present study, we overexpressed DIC- and OGC-cDNA plasmids to assess their function in renal PT cells after compensatory renal hypertrophy. PT cells from NPX rats that were first preincubated with GSH were protected from cytotoxicity due to the mitochondrial inhibitor antimycin A by overexpression of either of the two mitochondrial GSH transporters. Our present results provide further evidence that compensatory renal hypertrophy is associated primarily with mitochondrial hypertrophy and hyperpolarization and that manipulation of mitochondrial GSH transporters in PT cells of hypertrophied kidney can alter susceptibility to chemically induced injury under appropriate conditions and may be a suitable therapeutic approach.

Toxic effects of mercury on the cardiovascular and central nervous systems

Environmental contamination has exposed humans to various metal agents, including mercury. This exposure is more common than expected, and the health consequences of such exposure remain unclear. For many years, mercury was used in a wide variety of human activities, and now, exposure to this metal from both natural and artificial sources is significantly increasing. Many studies show that high exposure to mercury induces changes in the central nervous system, potentially resulting in irritability, fatigue, behavioral changes, tremors, headaches, hearing and cognitive loss, dysarthria, incoordination, hallucinations, and death. In the cardiovascular system, mercury induces hypertension in humans and animals that has wide-ranging consequences, including alterations in endothelial function. The results described in this paper indicate that mercury exposure, even at low doses, affects endothelial and cardiovascular function. As a result, the reference values defining the limits for the absence of danger should be reduced.

Relationships between the renal handling of DMPS and DMSA and the renal handling of mercury

Within the body of this review, we provide updates on the mechanisms involved in the renal handling mercury (Hg) and the vicinal dithiol complexing/chelating agents, 2,3-bis(sulfanyl)propane-1-sulfonate (known formerly as 2,3-dimercaptopropane-1-sulfonate, DMPS) and meso-2,3-bis(sulfanyl)succinate (known formerly as meso-2,3-dimercaptosuccinate, DMSA), with a focus on the therapeutic effects of these dithiols following exposure to different chemical forms of Hg. We begin by reviewing briefly some of the chemical properties of Hg, with an emphasis on the high bonding affinity between mercuric ions and reduced sulfur atoms, principally those contained in protein and nonprotein thiols. A discussion is provided on the current body of knowledge pertaining to the handling of various mercuric species within the kidneys, focusing on the primary cellular targets that take up and are affected adversely by these species of Hg, namely, proximal tubular epithelial cells. Subsequently, we provide a brief update on the current knowledge on the handling of DMPS and DMSA in the kidneys. In particular, parallels are drawn between the mechanisms participating in the uptake of various thiol S-conjugates of Hg in proximal tubular cells and mechanisms by which DMPS and DMSA gain entry into these target epithelial cells. Finally, we discuss factors that permit DMPS and DMSA to bind intracellular mercuric ions and mechanisms transporting DMPS and DMSA S-conjugates of Hg out of proximal tubular epithelial cells into the luminal compartment of the nephron, and promoting urinary excretion.

Effects of dietary methylmercury on growth performance and tissue burden in juvenile green (Acipenser medirostris) and white sturgeon (A. transmontanus)

Triplicate groups of juvenile green and white sturgeon (30 ± 2 g) were exposed to one of the four nominal concentrations of dietary methylmercury (MeHg, 0 (control), 25, 50, and 100mg MeHg/kg diet) for 8 weeks to determine and compare the effects on growth performance and mercury (Hg) tissue burden in the two sturgeon species. Mortality, growth performance as measured by percent body weight increase per day, hepatosomatic index, proximate composition of whole body, and Hg burden in the whole body, gill, heart, liver, kidney, and white muscle were determined to assess the adverse growth effects and bioaccumulation of dietary MeHg in sturgeon. Significantly higher mortality and lower growth rate (p<0.05) were noted in green and white sturgeon fed the MeHg diets compared to the controls. Green sturgeon fed the MeHg diets exhibited earlier and more severe adverse effects compared to white sturgeon. Mercury accumulated in all tissues in a dose-dependent manner regardless of species, and the highest Hg concentrations were found in the kidneys of both species. Dietary MeHg had no significant effect (p>0.05) on the whole body proximate compositions of either sturgeon species. In conclusion, green sturgeon was more susceptible to dietary MeHg toxicity than white sturgeon in our 8-week growth experiment based on the higher mortality and lower growth rate and body energy contents.

Transport of inorganic mercury and methylmercury in target tissues and organs

Owing to the prevalence of mercury in the environment, the risk of human exposure to this toxic metal continues to increase. Following exposure to mercury, this metal accumulates in numerous organs, including brain, intestine, kidneys, liver, and placenta. Although a number of mechanisms for the transport of mercuric ions into target organs were proposed in recent years, these mechanisms have not been characterized completely. This review summarizes the current literature related to the transport of inorganic and organic forms of mercury in various tissues and organs. This review identifies known mechanisms of mercury transport and provides information on additional mechanisms that may potentially play a role in the transport of mercuric ions into target cells.

The role of intracellular glutathione in inorganic mercury-induced toxicity in neuroblastoma cells

It is well known that antioxidants containing sulfhydryl (-SH) groups are protective against the toxic effects of mercury. The current study was designed to elucidate the mechanism(s) of the cytoprotective effects of glutathione (GSH) and N-acetylcysteine (NAC) against the toxicity of inorganic mercury (HgCl(2)) in neuroblastoma cells (N-2A). The obtained results demonstrated the protective effects of these compounds in a dose dependant manner up to 95 and 74% cell viability, respectively as compared to the control of HgCl(2) of 10%. The administration of buthionine sulfoximine (BSO), an inhibitor of GSH synthesis, increased the toxicity of HgCl(2) in a dose dependent manner. Moreover, BSO treatment attenuated the levels of the cellular free -SH concentrations at low concentrations (1-100 microM) of HgCl(2). The data also show that cellular thiol concentrations were augmented in the presence of GSH and NAC and these compounds were cytoprotective against HgCl(2) and this is due to up regulating of GSH synthesis. A reduction in intracellular levels of GSH was observed with treatment of HgCl(2). In addition, the ratio of GSH/GSSG increased from 16:1 to 50:1 from 1 to 10 microM concentration of HgCl(2.) The ratio of GSH/GSSG then decreased from 4:1 to 0.5:1 with the increase of concentration of HgCl(2) between 100 microM and 1 mM due to the collapse of the N-2A cells. It was of interest to note that the synthesis of GSH was stimulated in cells exposed to low concentration of HgCl(2) when extra GSH is available. These data support the idea that the loss of GSH plays a contributing role to the toxic effects of HgCl(2) and that inorganic mercury adversely affects viability, through altering intracellular -SH concentrations. The data further indicate that the availability of GSH to the cells may not be sufficient to provide protection against mercury toxicity and the de novo synthesis of intracellular GSH is required to prevent the damaging effects of mercury.

Survey of slaughtered pigs for occurrence of ochratoxin A and porcine nephropathy in Serbia

Samples of blood, kidney and liver were randomly selected from slaughtered pigs (n=90) and analyzed for ochratoxin A by HPLC. In addition, in order to obtain information on the occurrence of nephropathy, histological examinations were carried out. Of the 90 liver samples, 26.6% contained OTA in the range of 0.22-14.5 ng/g. The incidence of OTA in serum and kidney were very similar (31%, 33.3%), with a maximum concentration of 220.8 ng/mL, and 52.5 ng/g, respectively. Histopathological examination of kidneys confirmed tubulopathies with edema and cell vacuolization. In addition, hemorrhages and necrosis of proximal kidney tubules' cells were found.

Exposure to heavy metals (lead, cadmium and mercury) and its effect on the outcome of in-vitro fertilization treatment

We investigated the effect of lead, cadmium and mercury exposure on pregnancy and fertilization rate outcome among 619 Saudi women (age 19-50 years) who sought in-vitro fertilization (IVF) treatment between 2002 and 2003. The concentrations of lead, cadmium and mercury were measured in both blood and follicular fluids. At levels well below the current US occupational exposure limit guidelines (40microg/dL) and even less than the current Centers for Disease Control and Prevention level of concern for preventing lead poisoning in children (10microg/dL), blood lead level was negatively associated with fertilization outcome in both adjusted and unadjusted logistic regression models. We found that among various demographic, socioeconomic and environmental factors, fish consumption was positively associated with blood lead levels. These results support the hypothesis that a raised blood lead level affects infertility and intervention to reduce the lead exposure might be needed for women of reproductive age. The present results also revealed unexpected finding - the positive relationship between follicular cadmium levels and fertilization outcome, which points to the necessity for further investigation. Though adverse effect of mercury on pregnancy outcome or fertilization rate was not evident in this study, mercury5.8microg/L (EPA safety limit) was found in the blood and follicular fluid of 18.7% and 8.3% of the women, respectively. Concerns about its possible adverse effects on the physiology of reproduction or fetal development cannot be ruled out. It should be noted that skin-lightening creams and dental amalgam were important contributors to mercury exposure. Such finding is alarming and priority for further studies are, urgently, needed.

Autometallographic tracing of Hg-S quantum dots in frogs exposed to inorganic mercury

The histochemical distribution of mercury in the kidneys and gut of frogs (Rana ridibunda) exposed to inorganic mercury was analyzed with autometallography (AMG). It was found that most mercury in the kidneys accumulated in the proximal convoluted tubules as Hg-S nanocrystal, while control animals were totally void of AMG grains. In the gut the highest concentration of mercury was observed in the large intestine. The AMG grains were primarily located in the apical part of the absorptive cells, although rather high concentrations of silver enhanced mercury quantum dots were also detected in a special cell type of gut epithelium and the glycocalyx. A certain amount of AMG grains were detected in the lumen of the gut. We hypothesize that this pool of quantum dots results from sloughed off epithelial cells and macrophages. Such still intact cells and red blood cells containing AMG grains were also found in the lumen of the gut.

Interactive toxicity of inorganic mercury and trichloroethylene in rat and human proximal tubules: effects on apoptosis, necrosis, and glutathione status

Simultaneous or prior exposure to one chemical may alter the concurrent or subsequent response to another chemical, often in unexpected ways. This is particularly true when the two chemicals share common mechanisms of action. The present study uses the paradigm of prior exposure to study the interactive toxicity between inorganic mercury (Hg(2+)) and trichloroethylene (TRI) or its metabolite S-(1,2-dichlorovinyl)-l-cysteine (DCVC) in rat and human proximal tubule. Pretreatment of rats with a subtoxic dose of Hg(2+) increased expression of glutathione S-transferase-alpha1 (GSTalpha1) but decreased expression of GSTalpha2, increased activities of several GSH-dependent enzymes, and increased GSH conjugation of TRI. Primary cultures of rat proximal tubular (rPT) cells exhibited both necrosis and apoptosis after incubation with Hg(2+). Pretreatment of human proximal tubular (hPT) cells with Hg(2+) caused little or no changes in GST expression or activities of GSH-dependent enzymes, decreased apoptosis induced by TRI or DCVC, but increased necrosis induced by DCVC. In contrast, pretreatment of hPT cells with TRI or DCVC protected from Hg(2+) by decreasing necrosis and increasing apoptosis. Thus, whereas pretreatment of hPT cells with Hg(2+) exacerbated cellular injury due to TRI or DCVC by shifting the response from apoptosis to necrosis, pretreatment of hPT cells with either TRI or DCVC protected from Hg(2+)-induced cytotoxicity by shifting the response from necrosis to apoptosis. These results demonstrate that by altering processes related to GSH status, susceptibilities of rPT and hPT cells to acute injury from Hg(2+), TRI, or DCVC are markedly altered by prior exposures.

Mercury exposure and public health

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.

Organic anion transporters of the SLC22 family: biopharmaceutical, physiological, and pathological roles

The human organic anion transporters OAT1, OAT2, OAT3, OAT4 and URAT1 belong to a family of poly-specific transporters mainly located in kidneys. Selected OATs occur also in liver, placenta, and brain. OATs interact with endogenous metabolic end products such as urate and acidic neutrotransmitter metabolites, as well as with a multitude of widely used drugs, including antibiotics, antihypertensives, antivirals, anti-inflammatory drugs, diuretics and uricosurics. Thereby, OATs play an important role in renal drug elimination and have an impact on pharmacokinetics. In this review we focus on the interaction of human OATs with drugs. We report the affinities of human OATs for drug classes and compare the putative importance of individual OATs for renal drug excretion. The role of OATs as sites of drug-drug interaction and mediators cell toxicity, their gender-dependent regulation in health and diseased states, and the possible impact of single nucleotide polymorphisms are also dealt with.

DMPS and N-acetylcysteine induced renal toxicity in mice exposed to mercury

Acute effects of mercuric chloride (HgCl2) were evaluated on mice. Mice received a single dose of HgCl2 (4.6 mg/kg, subcutaneously) for three consecutive days. Thirty minutes after the last injection with HgCl2, mice received one single injection of 2,3-dimercapto-1-propanesulfonic acid (DMPS) or N-acetylcysteine (NAC) or diphenyl diselenide (PhSe)2. DMPS, NAC and (PhSe)2 were utilized as therapy against mercury exposure. At 24 h after the last HgCl2 injection, blood, liver and kidney samples were collected. delta-Aminolevulinate dehydratase (delta-ALA-D) and Na+, K- (+) ATPase activities, thiobarbituric acid-reactive substances (TBARS), non-protein thiols (NPSH) and ascorbic acid concentrations were evaluated. Plasma aspartate (AST) and alanine (ALT) aminotransferase activities, as well as urea and creatinine levels were determined. The group of mice exposed to Hg + (PhSe)2 presented 100% of lethality. Exposure with HgCl2 caused a decrease on the body weight gain and treatments did not modify this parameter. delta-ALA-D, AST and ALT activities, TBARS, ascorbic acid levels and NPSH (hepatic and erythrocytic) levels were not changed after HgCl2 exposure. HgCl2 caused an increase in renal NPSH content and therapies did not modify these levels. Mice treated with (PhSe)2, Hg + NAC and Hg + DMPS presented a reduction in plasma NPSH levels. Creatinine and urea levels were increased in mice exposed to Hg + NAC, while Hg + DMPS group presented an increase only in urea level. Na+, K- (+) ATPase activity was inhibited in mice exposed to Hg + DMPS and Hg + NAC. In conclusion, therapies with (PhSe)2, DMPS and NAC following mercury exposure must be better studied because the formation of more toxic complexes with mercury, which can mainly damage renal tissue.

Exploration of the direct metabolic effects of mercury II chloride on the kidney of Sprague–Dawley rats using high-resolution magic angle spinning 1H NMR spectroscopy of intact tissue and pattern recognition

Mercury II chloride (HgCl2) toxicity was investigated in Sprague-Dawley rats using high-resolution magic angle spinning (HRMAS) 1H NMR spectroscopy in conjunction with principal component analysis (PCA). Intact renal cortex and papilla samples from Sprague-Dawley rats treated with HgCl2 at two dose levels (0.5 and 2 mg/kg) and from matched controls (n=5 per group) were assessed at 48 h p.d. HgCl2) caused depletion of renal osmolytes such as glycerophosphocholine (GPC), betaine, trimethylamine N-oxide (TMAO), myo-inositol and taurine in both the renal cortex and the papilla. In addition, relatively higher concentrations of valine, isobutyrate, threonine and glutamate were observed in HgCl2-treated rats, particularly in the renal cortex, which may reflect a counterbalance response to the observed loss of other classes of renal osmolytes. Increased levels of glutamate were present in the cortex of treated rats, which may be associated with HgCl2-induced renal acidosis and disruption of the tricarboxylic acid cycle. A dose response was observed in both cortical and papillary tissue with increasing severity of metabolic disruption in the high dose group. 1H HRMAS NMR profiles of individual animals correlated well with conventional clinical chemistry and histology confirming the reproducibility of the technology and generating complementary molecular pathway information.

Handling of cysteine S-conjugates of methylmercury in MDCK cells expressing human OAT1

BACKGROUND

The activity of the organic anion transporter 1 (OAT1) has been implicated recently in the basolateral uptake of thiol conjugates of inorganic mercury in renal proximal tubular cells. However, very little is known about the role of OAT1 in the renal epithelial transport of organic forms of mercury, such as methylmercury (CH(3)Hg(+)), especially when it is in the form of the cysteine (Cys) S-conjugate of methylmercury (CH(3)Hg-Cys), which is believed to be a biologically relevant form of mercury.

METHODS

Accordingly, the present study, was designed to characterize the transport of CH(3)Hg-Cys in Madin-Darby canine kidney (MDCK) cells transfected stably with the human isoform of OAT1 (hOAT1) and in proximal tubular-derived NRK-52E cells.

RESULTS

Data on saturation kinetics, time dependency, substrate specificity, and temperature dependency demonstrate that CH(3)Hg-Cys is transported by hOAT1. Substrate-specificity data from the control cells also show that CH(3)Hg-Cys is a substrate of one or more transporter(s) that is/are not hOAT1. Additional findings indicate that at least one amino acid transport system is involved in the uptake of CH(3)Hg-Cys in MDCK cells. Furthermore, in the presence of cytotoxic concentrations of CH(3)Hg-Cys, rates of survival were lower in hOAT1-transfected cells than in wild-type control cells.

CONCLUSION

The present data demonstrate clearly that CH(3)Hg-Cys is indeed a transportable substrate of OAT1. Moreover, the collective findings from the MDCK cells and NRK-52E cells infer that CH(3)Hg-Cys is a likely transportable mercuric species in proximal tubular epithelial cells that is taken up in vivo by both OAT1 and amino acid transporters.

Role of organic anion and amino acid carriers in transport of inorganic mercury in rat renal basolateral membrane vesicles: influence of compensatory renal growth

Susceptibility to renal injury induced by inorganic mercury (Hg(2+)) increases significantly as a result of compensatory renal growth (following reductions of renal mass). We hypothesize that this phenomenon is related in part to increased basolateral uptake of Hg(2+) by proximal tubular cells. To determine the mechanistic roles of various transporters, we studied uptake of Hg(2+), in the form of biologically relevant Hg(2+)-thiol conjugates, using basolateral membrane (BLM) vesicles isolated from the kidney(s) of control and uninephrectomized (NPX) rats. Binding of Hg(2+) to membranes, accounted for 52-86% of total Hg(2+) associated with membrane vesicles exposed to HgCl(2), decreased with increasing concentrations of HgCl(2), and decreased slightly in the presence of sodium ions. Conjugation of Hg(2+) with thiols (glutathione, L-cysteine (Cys), N-acetyl-L-cysteine) reduced binding by more than 50%. Under all conditions, BLM vesicles from NPX rats exhibited a markedly lower proportion of binding. Of the Hg(2+)-thiol conjugates studied, transport of Hg-(Cys)(2) was fastest. Selective inhibition of BLM carriers implicated the involvement of organic anion transporter(s) (Oat1 and/or Oat3; Slc22a6 and Slc22a8), amino acid transporter system ASC (Slc7a10), the dibasic amino acid transporter (Slc3a1), and the sodium-dicarboxylate carrier (SDCT2 or NADC3; Slc13a3). Uptake of each mercuric conjugate, when factored by membrane protein content, was higher in BLM vesicles from uninephrectomized (NPX) rats, with specific increases in transport by the carriers noted above. These results support the hypothesis that compensatory renal growth is associated with increased uptake of Hg(2+) in proximal tubular cells and we have identified specific transporters involved in the process.

Morphologic and functional alterations induced by low doses of mercuric chloride in the kidney OK cell line: ultrastructural evidence for an apoptotic mechanism of damage

Mercury produces acute renal failure in experimental animal models, but the mechanism of tubular injury has not completely been clarified. There is an increased interest in the role of apoptosis in the pathogenesis of renal diseases that result primarily from injury to renal tubular epithelial cells. However, detailed studies of morpho-functional alterations induced by mercuric chloride in kidney cell lines are scarce. This work characterizes these alterations in OK cell cultures. Morphological alterations were profiled using light microscopy, transmission electron microscopy, and confocal microscopy, as well as mitochondrial functional assays in the cells exposed to low concentrations of HgCl2. At concentrations of 1 and 10 microM of HgCl2 there were no morphological or ultrastructural alterations, but the mitochondrial function (MTT assay) and intracellular ATP content was increased, especially at longer incubation times (6 and 9 h). At 15 microM HgCl2, both the mitochondrial activity and the endogenous ATP decreased significantly. At this concentration the OK cells rounded up, had increased number of cytoplasmic vacuoles, and detached from the cell monolayer. At 15 microM HgCl2 ultrastructural changes were characterized by dispersion of the ribosomes, dilatation of the cisterns of the rough endoplasmic reticulum, increase of number of cytoplasmic vacuoles, chromatin condensation, invaginations of the nuclear envelope, presence of cytoplasmic inclusion bodies, and alterations in the size and morphology of mitochondria. At 15 microM HgCl2 apoptotic signs included membrane blebbing, chromatin condensation, mitochondrial alterations, apoptotic bodies, and nuclear envelope rupture. Using confocal microscopy and the mitochondrial specific dye MitoTracker Red, it was possible to establish qualitative changes induced by mercury on the mitochondrial membrane potential after incubation of the cells for 6 and 9h with 15 microM HgCl2. This effect was not observed at short times (1 and 3h) with this same concentration, neither with 1 and 10 microM HgCl2 in all the studied times. Taken together, these findings indicate that low concentrations of HgCl2 induce apoptosis by inhibiting mitochondrial function, and the OK cell line may be considered a useful tool for the study of programmed cell death involving mercurial species and other heavy metals.

Transport ofN-AcetylcysteineS-Conjugates of Methylmercury in Madin-Darby Canine Kidney Cells Stably Transfected with Human Isoform of Organic Anion Transporter 1

Recent studies have implicated the activity of the organic anion transporter 1 (OAT1) protein in the basolateral uptake of inorganic mercuric species in renal proximal tubular epithelial cells. However, very little is known about the potential role of OAT1 (and other OATs) in the renal epithelial transport of organic forms of mercury such as methylmercury (CH(3)Hg(+)). The present investigation was designed to study the transport of N-acetyl cysteine (NAC) S-conjugates of both methylmercury (CH(3)Hg-NAC) and inorganic mercury (NAC-Hg-NAC) in renal epithelial cells [Madin-Darby canine kidney (MDCK) cells] stably transfected with the human isoform of OAT1 (hOAT1). These mercuric species were studied because numerous mercapturates have been shown to be substrates of OATs. Data on saturation kinetics, time dependence, substrate specificity, and temperature dependence for the transport of CH(3)Hg-NAC and NAC-Hg-NAC indicate that both of these two mercuric species are indeed transportable substrates of hOAT1. Substrate specificity data also show that CH(3)Hg-NAC is a substrate of a transporter in MDCK cells that is not hOAT1. These data indicate that an amino acid carrier system is a likely candidate responsible for this transport. Furthermore, the rates of survival of the hOAT1-transfected MDCK cells were significantly lower than those of corresponding control MDCK cells when they were exposed to cytotoxic concentrations of CH(3)Hg-NAC or NAC-Hg-NAC. Collectively, the present data support the hypothesis that CH(3)Hg-NAC and NAC-Hg-NAC are transportable substrates of OAT1 and thus potentially transportable mercuric species taken up in vivo at the basolateral membrane of proximal tubular epithelial cells.

Molecular and ionic mimicry and the transport of toxic metals

Despite many scientific advances, human exposure to, and intoxication by, toxic metal species continues to occur. Surprisingly, little is understood about the mechanisms by which certain metals and metal-containing species gain entry into target cells. Since there do not appear to be transporters designed specifically for the entry of most toxic metal species into mammalian cells, it has been postulated that some of these metals gain entry into target cells, through the mechanisms of ionic and/or molecular mimicry, at the site of transporters of essential elements and/or molecules. The primary purpose of this review is to discuss the transport of selective toxic metals in target organs and provide evidence supporting a role of ionic and/or molecular mimicry. In the context of this review, molecular mimicry refers to the ability of a metal ion to bond to an endogenous organic molecule to form an organic metal species that acts as a functional or structural mimic of essential molecules at the sites of transporters of those molecules. Ionic mimicry refers to the ability of a cationic form of a toxic metal to mimic an essential element or cationic species of an element at the site of a transporter of that element. Molecular and ionic mimics can also be sub-classified as structural or functional mimics. This review will present the established and putative roles of molecular and ionic mimicry in the transport of mercury, cadmium, lead, arsenic, selenium, and selected oxyanions in target organs and tissues.

Mercuric conjugates of cysteine are transported by the amino acid transporter system b(0,+): implications of molecular mimicry

Humans and other mammals continue to be exposed to various forms of mercury in the environment. The kidneys, specifically the epithelial cells lining the proximal tubules, are the primary targets where mercuric ions accumulate and exert their toxic effects. Although the actual mechanisms involved in the transport of mercuric ions along the proximal tubule have not been defined, current evidence implicates mercuric conjugates of cysteine, primarily 2-amino-3-(2-amino-2-carboxyethylsulfanylmercuricsulfanyl)propionic acid (Cys-S-Hg-S-Cys), as the most likely transportable species of inorganic mercury (Hg(2+)). Because Cys-S-Hg-S-Cys and the amino acid cystine (Cys-S-S-Cys) are structurally similar, it was hypothesized that Cys-S-Hg-S-Cys might act as a molecular mimic of cystine at one or more of the amino acid transporters involved in the luminal absorption of this amino acid. One such candidate is the Na(+)-independent heterodimeric transporter system b(0,+). Therefore, the transport of Cys-S-Hg-S-Cys and cystine was studied in MDCK II cells that were or were not stably transfected with b(0,+)AT-rBAT. Transport of Cys-S-Hg-S-Cys and cystine across the luminal plasma membrane was similar in the transfected cells, indicating that Cys-S-Hg-S-Cys can behave as a molecular mimic of cystine at the site of system b(0,+). Moreover, only the b(0,+)AT-rBAT transfectants became selectively intoxicated during exposure to Cys-S-Hg-S-Cys. These findings indicate that system b(0,+) likely contributes to the nephropathy induced by Hg(2+) in vivo. These data represent the first direct molecular evidence for the participation of a specific transporter in the luminal uptake of a large divalent metal cation in proximal tubular cells.

Human organic anion transporter 1 mediates cellular uptake of cysteine-S conjugates of inorganic mercury

BACKGROUND

The epithelial cells lining the renal proximal tubule have been shown to be the primary cellular targets where mercuric ions gain entry, accumulate, and induce pathologic effects in vivo. Recent data have implicated at least one of the organic anion transport systems in the basolateral uptake of inorganic mercury (Hg(2+)).

METHODS

Using a line of Madin-Darby canine kidney (MDCK) II cells transfected stably with the human organic anion transporter 1 (hOAT1), and oocytes from Xenopus laevis microinjected with cRNA for hOAT1, we tested the hypothesis that hOAT1 can transport biologically relevant mercuric conjugates of cysteine (Cys).

RESULTS

Indeed, MDCK II cells expressing a functional form of hOAT1 gained the ability to transport the mercuric conjugate 2-Amino-3-(2-amino-2-carboxy-ethylsulfanyl-mercuricsulfanyl)-propionic acid (Cys-S-Hg-S-Cys), but not the corresponding di-glutathione S-conjugate of Hg(2+) (G-S-Hg-S-G). Moreover, p-aminohippurate (PAH), adipate, and glutarate (but not succinate or malonate) inhibited individually the uptake of Cys-S-Hg-S-Cys in a dose-dependent manner. Uptake of Cys-S-Hg-S-Cys, but not G-S-Hg-S-G, was also documented in Xenopus oocytes expressing hOAT1.

CONCLUSION

These data represent ostensibly the most direct line of evidence implicating a specific membrane protein (i.e., hOAT1) in the transport of a biologically relevant molecular species of Hg(2+) in a mammalian cell. Moreover, these data indicate that the organic anion transporter(s) likely play a prominent role in the basolateral transport of mercuric ions by proximal tubular cells and in the nephropathy induced by Hg(2+).

Toxic nephropathy: environmental chemicals

The kidney is the target of numerous xenobiotic toxicants, including environmental chemicals. Anatomical, physiological, and biochemical features of the kidney make it particularly sensitive to many environmental compounds. Factors contributing to the sensitivity of the kidney include: large blood flow, the presence of a variety of xenobiotic transporters and metabolizing enzymes, and concentration of solutes during urine production. In many cases, the conjugation of environmental chemicals to glutathione and/or cysteine targets these chemicals to the kidney where inhibition of renal function occurs through a variety of mechanisms. For example, heavy metals such as mercury and cadmium target the kidney after glutathione/cysteine conjugation. Trichloroethlene and bromobenzene are metabolized and conjugated to glutathione in the liver before renal uptake and toxicity. In contrast, renal injury produced by chloroform and aristolochic acids is dependent on renal cytochrome P450 metabolism to toxic metabolites. Other compounds, such as paraquat or diquat, damage the kidney via the production of reactive oxygen species. Finally, the low solubility of ethylene glycol metabolites causes crystal formation within the tubular lumen and nephrotoxicity. This chapter explores mechanisms of nephrotoxicity by environmental chemicals, using these example compounds. What remains to be accomplished and by far the most difficult process is the elucidation of the detailed mechanisms of tubular cell injury after toxicant uptake and metabolism. The large number of individuals experiencing a decline in renal function with age makes the search for these mechanisms very compelling.

Molecular handling of cadmium in transporting epithelia

Cadmium (Cd) is an industrial and environmental pollutant that affects adversely a number of organs in humans and other mammals, including the kidneys, liver, lungs, pancreas, testis, and placenta. The liver and kidneys, which are the primary organs involved in the elimination of systemic Cd, are especially sensitive to the toxic effects of Cd. Because Cd ions possess a high affinity for sulfhydryl groups and thiolate anions, the cellular and molecular mechanisms involved in the handling and toxicity of Cd in target organs can be defined largely by the molecular interactions that occur between Cd ions and various sulfhydryl-containing molecules that are present in both the intracellular and extracellular compartments. A great deal of scientific data have been collected over the years to better define the toxic effects of Cd in the primary target organs. Notwithstanding all of the new developments made and information gathered, it is surprising that very little is known about the cellular and molecular mechanisms involved in the uptake, retention, and elimination of Cd in target epithelial cells. Therefore, the primary purpose of this review is to summarize and put into perspective some of the more salient current findings, assertions, and hypotheses pertaining to the transport and handling of Cd in the epithelial cells of target organs. Particular attention has been placed on the molecular mechanisms involved in the absorption, retention, and secretion of Cd in small intestinal enterocytes, hepatocytes, and tubular epithelial cells lining both proximal and distal portions of the nephron. The purpose of this review is not only to provide a summary of published findings but also to provide speculations and testable hypotheses based on contemporary findings made in other areas of research, with the hope that they may promote and serve as the impetus for future investigations designed to define more precisely the cellular mechanisms involved in the transport and handling of Cd within the body.

Nephrotoxic effects of mercury exposure and smoking among Egyptian workers in a fluorescent lamp factory

BACKGROUND

It is known that mercury (Hg) has a nephrotoxic effect in exposed workers. This effect is evident when there is advanced damage of kidney tissue.

METHODS

A random morning urine sample was collected from each participant for measuring urinary concentrations of total protein (UTP), retinol-binding protein (URBP), creatinine (UCr), Hg (UHg), and the activities of leucine-aminopeptidase (ULAP) and glutathione S-transferase (UGST) as well as N-acetyl-beta-D-glucosaminidase (UNAG).

RESULTS

Urinary excretion of the measured parameters was significantly increased among Hg-exposed workers who were smokers and among Hg-exposed workers with work duration >or=11 years than those with <or=10 years work duration.

CONCLUSIONS

Results of this investigation demonstrated that these urinary parameters of kidney integrity could be used as indicators of nephrotoxic effect of Hg exposure and that cigarette smoking has toxic and synergistic effects with Hg exposure on kidney. Present results additionally suggest reduction in recommended biological threshold limit (50 microg Hg/g Ucr) or biological exposure index (35 microg Hg/g Ucr) of urinary mercury levels because elevated levels of measured parameters were observed at urinary Hg levels of 17.3-28.2 microg Hg/g Ucr.

Simultaneous coexposure to inorganic mercury and cadmium: a study of the renal and hepatic disposition of mercury and cadmium

This study was designed to evaluate the effects of simultaneous coexposure to inorganic mercury and cadmium on the renal and hepatic disposition of each metal. Dispositional changes were assessed in rats 1 h and 24 h after the coexposure to relatively low doses of the metals (which individually are nonnephrotoxic in rats). The rational for studying mercury and cadmium is that both of these metals are encountered frequently in the same contaminated areas. Coadministration of a 0.5- micromol/kg dose of mercuric chloride with a 10- micromol/kg dose of cadmium chloride resulted in a decrease in the net renal accumulation of inorganic mercury at 1 and 24 h after exposure. Assessment of the disposition of both metals in renal zones indicates that the decreased renal accumulation of inorganic mercury was due specifically to changes in the accumulation of mercury in the renal cortex. Coexposure to inorganic mercury and cadmium also caused both the hepatic accumulation of mercury and the urinary excretion of mercury to increase during the initial 24 h after coexposure. During the initial 1 h after coexposure, the content of mercury in the blood was enhanced significantly. However, by the end of the first 24 h after exposure, the content of mercury in the blood was lower than that in animals treated with only inorganic mercury, likely due to the increased urinary excretion of mercury. Interestingly, with the exception of decreased fecal excretion of cadmium, no other changes in the disposition of cadmium were detected in the animals treated with both mercury and cadmium. These novel findings indicate that at the doses of inorganic mercury and cadmium used in the present study, cadmium has profound effects on the renal and hepatic handling of mercury. Based on the present findings, it appears that cadmium [by some currently unknown mechanism(s)] interferes with the luminal and/or basolateral uptake and/or net accumulation of mercury along S1 and S2 segments of the proximal tubules, which results in an overall decrease in the renal burden of mercury and an increased rate in the urinary excretion of mercury.

Antioxidant potential and gap junction-mediated intercellular communication as early biological markers of mercuric chloride toxicity in the MDCK cell line

In this study, the early nephrotoxic potential of mercuric chloride (HgCl(2)) has been evaluated in vitro, by exposing a renal-derived cell system, the tubular epithelial Madin-Darby canine kidney (MDCK) cell line, to the presence of increasing HgCl(2) concentrations (0.1-100 microM) for different periods of time (from 4 to 72 h). As possible biological markers of the tubular-specific toxicity of HgCl(2) in exposed-MDCK cultures we analysed: (i) critical biochemical parameters related to oxidative stress conditions and (ii) gap-junctional function (GJIC). HgCl(2) cytotoxicity was evaluated by cell-density assay. The biochemical analysis of the pro-oxidant properties of the mercuric ion (Hg(2+)) was performed by evaluating the effect of the metal salt on the antioxidant status of the MDCK cells. The cell glutathione (GSH) content and the activity of glutathione peroxidase (Gpx) and catalase (Cat), two enzymes engaged in the H(2)O(2) degradation, were quantified. HgCl(2) influence on MDCK GJIC was analysed by the microinjection/dye-transfer assay. HgCl(2)-induced morphological changes in MDCK cells were also taken into account. Our results, proving that subcytotoxic (0.1-10 microM) HgCl(2) concentrations affect either the antioxidant defences of MDCK cells or their GJIC, indicate these critical functions as suitable biological targets of early mercury-induced tubular cell injury.

Organic mercury compounds: human exposure and its relevance to public health

Humans may be exposed to organic forms of mercury by either inhalation, oral, or dermal routes, and the effects of such exposure depend upon both the type of mercury to which exposed and the magnitude of the exposure. In general, the effects of exposure to organic mercury are primarily neurologic, while a host of other organ systems may also be involved, including gastrointestinal, respiratory, hepatic, immune, dermal, and renal. While the primary source of exposure to organic mercury for most populations is the consumption of methylmercury-contaminated fish and shellfish, there are a number of other organomercurials to which humans might be exposed. The antibacterial and antifungal properties of organomercurials have resulted in their long use as topical disinfectants (thimerosal and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Phenylmercury has been used in the past in paints, and dialkyl mercurials are still used in some industrial processes and in the calibration of certain analytical laboratory equipment. The effects of exposure to different organic mercurials by different routes of exposure are summarized in this article.

Distribution of inorganic mercury in liver and kidney of beluga and bowhead whales through autometallographic development of light microscopic tissue sections

Inorganic mercury was localized through autometallography (AMG) in kidney and liver of free-ranging, subsistence-harvested beluga (Delphinapterus leucus: n = 20) and bowhead (Balaena mysticetrus: n = 5) whales. AMG granules were not evident in bowhead tissues, confirming nominal mercury (Hg) concentrations (range = 0.011 to 0.038 microg/g ww for total Hg). In belugas, total Hg ranged from 0.30 to 17.11 and from 0.33 to 82.47 microg/g ww in liver and kidney, respectively. AMG granules were restricted to cortical tubular epithelial cytoplasm in belugas with lower tissue burdens; whales with higher tissue burdens had granules throughout the uriniferous tubular epithelium. In liver, AMG granular densities differed between lobular zones, concentrating in stellate macrophages and bile cannalicular domains of hepatocytes. AMG granules aggregated in periportal regions in belugas with lower hepatic Hg concentrations, yet among whales with higher Hg, AMG granule deposition extended to pericentral and midzonal regions of liver lobules. Mean areas occupied by AMG granules correlated well with hepatic Hg concentrations and age. In beluga livers, AMG staining density was not associated with lipofuscin quantity (an index of oxidative damage). Occasionally, AMG granules and lipofuscin were colocalized, but more often were not, implying that Hg was not a prominent factor in hepatic lipofuscin deposition in belugas.