Aging and the disposition and toxicity of mercury in rats

Integration of proteomics and network toxicology reveals the mechanism of mercury chloride induced hepatotoxicity, in mice and HepG2 cells

Mercury is one heavy metal toxin that could cause severe health impairments. Mercury exposure has become a global environmental issue. Mercury chloride (HgCl₂) is one of mercury's main chemical forms, but it lacks detailed hepatotoxicity data. The present study aimed to investigate the mechanism of hepatotoxicity induced by HgCl₂ through proteomics and network toxicology at the animal and cellular levels. HgCl₂ showed apparent hepatotoxicity after being administrated with C57BL/6 mice (16 mg/kg.bw, oral once a day, 28 days) and HepG2 cells (100 μmol/L, 12 h). Otherwise, oxidative stress, mitochondrial dysfunction and inflammatory infiltration play an important role in HgCl₂-induced hepatotoxicity. The differentially expressed proteins (DEPs) after HgCl₂ treatment and enriched pathways were obtained through proteomics and network toxicology. Western blot and RT-qPCR results showed Acyl-CoA thioesterase 1 (ACOT1), Acyl-CoA synthetase short chain family member 3 (ACSS3), Epidermal growth factor receptor (EGFR), Apolipoprotein B (APOB), Signal transducer and activator of transcription 3 (STAT3), Alanine--glyoxylate aminotransferase (AGXT), cytochrome P450 3A5(CYP3A5), CYP2E1 and CYP1A2 may be the major biomarkers for HgCl₂-induced hepatotoxicity, which involved chemical carcinogenesis, fatty acid metabolism, CYPs-mediated metabolism, GSH metabolism and others. Therefore, this study can provide scientific evidence for the biomarkers and mechanism of HgCl₂-induced hepatotoxicity.

Biochemical Parameters of Female Wistar Rats and Their Offspring Exposed to Inorganic Mercury in Drinking Water during the Gestational and Lactational Periods

The aim of this study was to investigate the effects of inorganic mercury (Hg²⁺) exposure on biochemical parameters of dams and their offspring exposed to metal in drinking water. Female Wistar rats were exposed to 0, 10, and 50 µg Hg²⁺/mL (as HgCl₂) for 42 days corresponding to gestational (21 days) and lactational (21 days) periods. The offspring were sacrificed on postnatal days 10, 20, 30, and 40. Dams exposed to Hg²⁺ presented a decrease in water intake in gestation [total: F(2,19) = 15.84; p ≤ 0.0001; daily: F(2,21) = 12.71; p = 0.0002] and lactation [total: F(2,19) = 4.619; p = 0.024; daily: F(2,21) = 5.309; p = 0.0136] without alteration in food intake. Dams exposed to 50 µg Hg²⁺/mL had an increase in kidney total [F(2,21) = 8.081; p = 0.0025] and relative [F(2,21) = 14.11; p = 0.0001] weight without changes in biochemical markers of nephrotoxicity. Moreover, dams had an increase in hepatic [F(2,10) = 3.847; p = 0.0577] and renal [F(2,11) = 6.267; p = 0.0152] metallothionein content concomitantly with an increase in renal Hg levels after Hg²⁺ exposure. Regarding offspring, the exposure to Hg²⁺in utero and breast milk increased the relative liver [F(2,18) = 5.33; p = 0.0152] and kidney [F(2,18) = 3.819; p = 0.0415] weight only on the postnatal day 40. In conclusion, dams were able to handle the Hg²⁺ avoiding the classic Hg²⁺ toxic effects as well as protecting the offspring. We suggest that this protection is related to the hepatic and renal metallothionein content increase.

The protective effect of nano calcium produced from freshwater clam shells on the histopathological overview of the liver and kidneys of mice exposed to mercury toxins

BACKGROUND AND AIM

Freshwater clam shells nanoparticles powder is one of the uses of freshwater clams that can manufacture instant granular mineral supplements. This product can be used as a supplement to detoxify heavy metal toxins, such as Mercury. Mercury is an element that is detectable in all environmental media. Adults and children receive the most Mercury from food, air, and water intake. The majority of Mercury in the environment comes from the waste from mining activities and the metal industry. Mercury was found widely in the biosphere and is known as a dangerous hepatotoxicant. This study aimed to describe the hepatoprotective role of nano minerals (Ca, Mg, and Zn) produced from freshwater clam shells against mercury acetate poisoning in mice.

MATERIAL AND METHODS

The mice were divided randomly into a control group (aqua bidest and mercury acetate) and an experimental group for this purpose. The experimental mice group was given orally nano Ca supplementation in three dose groups (9 mg, 18 mg, and 27 mg/200 g animal body weight) once a day for 21 consecutive days. The mice are then given mercury acetate (1300 µg/200 g animal body weight intraperitoneally) on the 21st day. One hour after giving the nano Ca supplement, the mice's blood was taken. Liver and kidney were autopsied two days later to check quantitative and qualitative changes caused by mercury concentrations in liver and kidney histopathologies.

RESULTS

The results demonstrated the importance of nano Ca supplementation before mercury acetate induction, which has been shown to reduce necrotic depletion and hepatocyte degeneration.

CONCLUSION

Nano Ca supplementation has decreased the concentration of Hg in the blood of mice so that it can be used as a potential health supplement to detoxify mercury toxins.

Prophylactic supplementation with selenium alters disposition of mercury in aged rats

Mercury (Hg) is a prevalent environmental toxicant to which older individuals are particularly susceptible. Selenium (Se) has been used as an antidote following exposure to Hg. However, little is known about the effect of prophylactic supplementation with Se on the handling of Hg. The current study was designed to test the hypothesis that oral pre-treatment with Se alters the corporal disposition of Hg and reduces the risk of Hg-induced toxicity. Young and aged rats were gavaged for 10 days with sodium selenite or saline. On day 11, rats were injected intravenously with 0.5 μmol HgCl₂·kg^-1·2 mL^-1 normal saline. After 24 h, rats were euthanized and organs and tissues were harvested for determination of Hg content. Accumulation of Hg in the kidney was reduced significantly by pre-treatment with Se in both young and aged rats. In the renal cortex, the magnitude of the reduction was greater in aged rats than in young rats but in the outer stripe of the outer medulla, the magnitude of the reduction was similar between groups of rats. Urinary excretion of Hg was also reduced in rats pre-treated with Se. In contrast, the hepatic and hematologic burden of Hg increased in rats pre-treated with Se. Fecal excretion of Hg was decreased significantly by pre-treatment with Se in young rats but not in aged rats. These data suggest that prophylactic supplementation with Se alters the corporal disposition of Hg in a way that may reduce Hg-induced toxicity in target organs.

Sex differences in renal handling of inorganic mercury in aged rats

The sex of an individual/animal has been shown to play an important role in many biological processes. Furthermore, sex may also be a factor in the way environmental toxicants, such as heavy metals, are handled by organisms. However, the effect of sex on the handling and disposition of heavy metals, such as mercury (Hg), has not been shown. Aging has also been shown to be a factor in the accumulation of heavy metals in that older individuals tend to have higher burdens of these metals. Therefore, the purpose of the current study was to evaluate the effect of sex on the accumulation of mercury in aged animals. Aged male and female rats were injected intravenously with 0.5 μmol or 2.0 μmol·kg⁻¹ HgCl₂ (containing radioactive Hg) and organs were harvested after 24 h. In general, the renal accumulation of Hg was significantly greater in males than in females. Similarly, urinary excretion of Hg was greater in males than in females. There were no significant differences between males and females in the burden of Hg in other organs. Sex differences in the renal accumulation of Hg may be related to differences in the expression of membrane transporters involved in the uptake of mercuric species into tubular epithelial cells. The results of the current study illustrate the need to evaluate both sexes when assessing the renal effects of environmental toxicants.

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Renal accumulation of mercury is greater in aged male rats than aged female rats.

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Mercury accumulation differed among zones of the kidney.

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Sex did not appear to alter accumulation of mercury in other organs studied.

Chronic kidney disease in pregnant mothers affects maternal and fetal disposition of mercury

Chronic kidney disease (CKD) affects over 15 % of the adults in the United States. Pregnant women with CKD present an additional challenge in that they are at increased risk for adverse events such as preterm birth. Exposure to environmental toxicants, such as methylmercury, may exacerbate maternal disease and increase the risk of adverse fetal outcomes. We hypothesized that fetuses of mothers with CKD are more susceptible to accumulation of methylmercury than fetuses of healthy mothers. The current data show that when mothers are in a state of renal insufficiency, uptake of mercury in fetal kidneys is enhanced significantly. Accumulation of Hg in fetal kidneys may be related to the flow of amniotic fluid, maternal handling of Hg, and/or underdeveloped mechanisms for cellular export and urinary excretion. The results of this study indicate that renal insufficiency in mothers leads to significant alterations in the way toxicants such as mercury are handled by maternal and fetal organs.

Potential mechanisms of cellular injury following exposure to a physiologically relevant species of inorganic mercury

Mercury is a toxic metal that is found ubiquitously in the environment. Humans are exposed to different forms of mercury via ingestion, inhalation, and/or dermal absorption. Following exposure, mercuric ions may gain access to target cells and subsequently lead to cellular intoxication. The mechanisms by which mercury accumulation leads to cellular injury and death are not understood fully. Therefore, purpose of this study was to identify the specific intracellular mechanisms that are altered by exposure to inorganic mercury (Hg²⁺). Normal rat kidney (NRK) cells were exposed to a physiologically relevant form of Hg²⁺, as a conjugate of cysteine (10 μM or 50 μM). Alterations in oxidative stress were estimated by measuring lipid peroxidation and mitochondrial oxidative stress. Alterations in actin and tubulin were measured using specific fluorescent dyes. Calcium levels were measured using Fluo-3 AM Calcium Indicator while autophagy was identified with Premo^™ Autophagy Sensor LC3B-GFP. The current findings show that exposure to Hg²⁺ leads to enhanced oxidative stress, alterations in cytoskeletal structure, increases in intracellular calcium, and enhanced autophagy. We have established a more complete understanding of intoxication and cellular injury induced by a relevant form of Hg²⁺ in proximal tubule cells.

Disposition of methylmercury over time in a 75% nephrectomized rat model

Chronic kidney disease (CKD) is a highly relevant clinical condition that is characterized by the permanent loss of functional nephrons. Individuals with CKD may exhibit impaired renal clearance, which may alter corporal handling of metabolites and xenobiotics. Methylmercury (MeHg) is an important environmental toxicant to which humans are exposed to on a regular basis. Given the prevalence of CKD and ubiquitous presence of MeHg in the environment, it is important to understand how mercuric ions are handled in patients with CKD. Therefore, the purpose of the current study was to characterize the disposition of MeHg over time in a rat model of CKD (i.e., 75% nephrectomized (NPX) rats). Control and NPX rats were exposed intravenously (iv) to a non-nephrotoxic dose of MeHg (5 mg/kg) once daily for1, 2, or 3 d and the amount of MeHg in organs, blood, urine, and feces determined. The accumulation of MeHg in kidneys and blood of controls was significantly greater than that of NPX animals. In contrast, MeHg levels in brain and liver of controls were not markedly different from corresponding NPX rats. In all organs examined, accumulation of MeHg increased over the course of exposure, suggesting that urinary and fecal elimination are not sufficient to fully eliminate all mercuric ions. The current findings are important in that the disposition of mercuric ions in rats with normal renal function versus renal insufficiency following exposure to MeHg for a prolonged period differ and need to be taken into account with respect to therapeutic management.

The chemical speciation, spatial distribution and toxicity of mercury from Tibetan medicine Zuotai，β-HgS and HgCl2 in mouse kidney

Zuotai, a famous Tibetan medicinal mixture containing β-HgS, has been used to combine with herbal remedies for treating diseases for more than 1 300 years. The target organ for inorganic mercury toxicity is generally considered to be the kidney. Therefore, it is crucial to reveal the chemical speciation, spatial distribution and potential nephrotoxicity of mercury from Zuotai in kidney. To date, this remains poorly understood. We used X-ray absorption spectroscopy (XAS) and micro X-ray fluorescence (μ-XRF) imaging based on synchrotron radiation to study mercury chemical forms and mercury special distribution in kidney after mice were treated orally with Zuotai, β-HgS or HgCl₂. Meanwhile, the histopathology of kidney was observed. Mice exposed with Zuotai showed kidney with significant proportion of mercury ions bound to sulfydryl biomolecules (e.g. Cys-S-Hg-S-Cys) plus some of unknown species, but without methylmercury cysteine, which is the same as β-HgS and HgCl₂. The mercury is mainly deposited in renal cortex in mouse treated with Zuotai, β-HgS or HgCl₂, but with a low level of mercury in medulla. The total mercury in kidney of mice treated with HgCl₂ was much higher than that of β-HgS, and the later was higher than that of Zuotai. And, HgCl₂ cause severe impairments in mouse kidney, but that was not observed in the Zuotai and β-HgS groups. Meanwhile, the bio-metals (Ca, Zn, Fe and Cu) micro-distributions in kidney were also revealed. These findings elucidated the chemical nature, spatial distribution and toxicity difference of mercury from Zuotai, β-HgS and HgCl₂ in mouse kidney, and provide new insights into the appropriate methods for biological monitoring.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats

Humans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

Zuotai and HgS differ from HgCl2 and methyl mercury in Hg accumulation and toxicity in weanling and aged rats

Mercury sulfides are used in Ayurvedic medicines, Tibetan medicines, and Chinese medicines for thousands of years and are still used today. Cinnabar (α-HgS) and metacinnabar (β-HgS) are different from mercury chloride (HgCl₂) and methylmercury (MeHg) in their disposition and toxicity. Whether such scenario applies to weanling and aged animals is not known. To address this question, weanling (21d) and aged (450d) rats were orally given Zuotai (54% β-HgS, 30mg/kg), HgS (α-HgS, 30mg/kg), HgCl₂ (34.6mg/kg), or MeHg (MeHgCl, 3.2mg/kg) for 7days. Accumulation of Hg in kidney and liver, and the toxicity-sensitive gene expressions were examined. Animal body weight gain was decreased by HgCl₂ and to a lesser extent by MeHg, but unaltered after Zuotai and HgS. HgCl₂ and MeHg produced dramatic tissue Hg accumulation, increased kidney (kim-1 and Ngal) and liver (Ho-1) injury-sensitive gene expressions, but such changes are absent or mild after Zuotai and HgS. Aged rats were more susceptible than weanling rats to Hg toxicity. To examine roles of transporters in Hg accumulation, transporter gene expressions were examined. The expression of renal uptake transporters Oat1, Oct2, and Oatp4c1 and hepatic Oatp2 was decreased, while the expression of renal efflux transporter Mrp2, Mrp4 and Mdr1b was increased following HgCl₂ and MeHg, but unaffected by Zuotai and HgS. Thus, Zuotai and HgS differ from HgCl₂ and MeHg in producing tissue Hg accumulation and toxicity, and aged rats are more susceptible than weanling rats. Transporter expression could be adaptive means to reduce tissue Hg burden.

Pathophysiological Mechanisms of Renal Fibrosis: A Review of Animal Models and Therapeutic Strategies

Chronic kidney disease (CKD) is a long-term condition in which the kidneys do not work correctly. It has a high prevalence and represents a serious hazard to human health and estimated to affects hundreds of millions of people. Diabetes and hypertension are the two principal causes of CKD. The progression of CKD is characterized by the loss of renal cells and their replacement by extracellular matrix (ECM), independently of the associated disease. Thus, one of the consequences of CKD is glomerulosclerosis and tubulointerstitial fibrosis caused by an imbalance between excessive synthesis and reduced breakdown of the ECM. There are many molecules and cells that are associated with progression of renal fibrosis e.g. angiotensin II (Ang II). Therefore, in order to understand the biopathology of renal fibrosis and for the evaluation of new treatments, the use of animal models is crucial such as: surgical, chemical and physical models, spontaneous models, genetic models and in vitro models. However, there are currently no effective treatments for preventing the progression of renal fibrosis. Therefore it is essential to improve our knowledge of the cellular and molecular mechanisms of the progress of renal fibrosis in order to achieve a reversion/elimination of renal fibrosis.

The aging kidney and the nephrotoxic effects of mercury

Owing to advances in modern medicine, life expectancies are lengthening and leading to an increase in the population of older individuals. The aging process leads to significant alterations in many organ systems, with the kidney being particularly susceptible to age-related changes. Within the kidney, aging leads to ultrastructural changes such as glomerular and tubular hypertrophy, glomerulosclerosis, and tubulointerstitial fibrosis, which may compromise renal plasma flow (RPF) and glomerular filtration rate (GFR). These alterations may reduce the functional reserve of the kidneys, making them more susceptible to pathological events when challenged or stressed, such as following exposure to nephrotoxicants. An important and prevalent environmental toxicant that induces nephrotoxic effects is mercury (Hg). Since exposure of normal kidneys to mercuric ions might induce glomerular and tubular injury, aged kidneys, which may not be functioning at full capacity, may be more sensitive to the effects of Hg than normal kidneys. Age-related renal changes and the effects of Hg in the kidney have been characterized separately. However, little is known regarding the influence of nephrotoxicants, such as Hg, on aged kidneys. The purpose of this review was to summarize known findings related to exposure of aged and diseased kidneys to the environmentally relevant nephrotoxicant Hg.

Mercury sulfides are much less nephrotoxic than mercury chloride and methylmercury in mice

Mercury sulfides (α-HgS, β-HgS) are frequently included in traditional medicines. Mercury is known for nephrotoxicity, their safety is of concern. To address this question, mice were orally administrated with Zuotai (54% β-HgS, 30mg/kg), α-HgS (HgS, 30mg/kg), HgCl₂ (33.6mg/kg), or MeHgCl (3.1mg/kg) for 7days, and nephrotoxicity was examined. Animal body weights were decreased by HgCl₂ and to a lesser extent by MeHg, but unaltered after Zuotai and HgS. HgCl₂ and MeHg produced renal tubular vacuolation, interstitial inflammation and cell degeneration with protein cysts in the tubular lumen, while these pathological lesions were mild in Zuotai and HgS-treated mice. Electron microscopy showed that HgCl₂ and MeHg produced spotted swelling endothelium reticulum, while these lesions were mild or absent in Zuotai and HgS-treated mice. Renal Hg contents reached 250-300ng/mg kidney in HgCl₂ and MeHg groups as compared to 2-3ng/mg in Zuotai and HgS groups. The expression of kidney injury biomarkers, kidney injury molecule-1 (Kim-1) and neutrophil gelatinase-associated lipocalin (Ngal), were increased after HgCl₂ and MeHg, but unaltered after Zuotai and HgS. The expression of renal influx transporters Oat3 and Oatp4c1 was decreased, while the expression of renal efflux transporter such as Mrp2, Mrp4, and Mate2 was increased following HgCl₂ and MeHg. These gene expressions were unchanged after Zuotai and HgS. In summary, both α-HgS and β-HgS are less nephrotoxic than HgCl₂ and MeHg, indicating that chemical forms of mercury are a major determinant of mercury disposition and toxicity.

Mechanisms involved in the transport of mercuric ions in target tissues

Mercury exists in the environment in various forms, all of which pose a risk to human health. Despite guidelines regulating the industrial release of mercury into the environment, humans continue to be exposed regularly to various forms of this metal via inhalation or ingestion. Following exposure, mercuric ions are taken up by and accumulate in numerous organs, including brain, intestine, kidney, liver, and placenta. In order to understand the toxicological effects of exposure to mercury, a thorough understanding of the mechanisms that facilitate entry of mercuric ions into target cells must first be obtained. A number of mechanisms for the transport of mercuric ions into target cells and organs have been proposed in recent years. However, the ability of these mechanisms to transport mercuric ions and the regulatory features of these carriers have not been characterized completely. The purpose of this review is to summarize the current findings related to the mechanisms that may be involved in the transport of inorganic and organic forms of mercury in target tissues and organs. This review will describe mechanisms known to be involved in the transport of mercury and will also propose additional mechanisms that may potentially be involved in the transport of mercuric ions into target cells.

Genome-Wide Association Study to Identify Genes Related to Renal Mercury Concentrations in Mice

BACKGROUND

Following human mercury (Hg) exposure, the metal accumulates in considerable concentrations in kidney, liver, and brain. Although the toxicokinetics of Hg have been studied extensively, factors responsible for interindividual variation in humans are largely unknown. Differences in accumulation of renal Hg between inbred mouse strains suggest a genetic interstrain variation regulating retention or/and excretion of Hg. A.SW, DBA/2 and BALB/C mouse strains accumulate higher amounts of Hg than B10.S.

OBJECTIVES

We aimed to find candidate genes associated with regulation of renal Hg concentrations.

METHODS

A.SW, B10.S and their F1 and F2 offspring were exposed for 6 weeks to 2.0 mg Hg/L drinking water. Genotyping with microsatellites was conducted on 84 F2 mice for genome-wide scanning with ion pair reverse-phase high-performance liquid chromatography (IP RP HPLC). Quantitative trait loci (QTL) were established. Denaturing HPLC was used to detect single nucleotide polymorphisms for haplotyping and fine mapping in 184 and 32 F2 mice, respectively. Candidate genes (Pprc1, Btrc and Nfkb2) verified by fine mapping and QTL were further investigated by real-time polymerase chain reaction. Genes enhanced by Pprc1 (Nrf1 and Nrf2) were included for gene expression analysis.

RESULTS

Renal Hg concentrations differed significantly between A.SW and B10.S mice and between males and females within each strain. QTL analysis showed a peak logarithm of odds ratio score 5.78 on chromosome 19 (p = 0.002). Haplotype and fine mapping associated the Hg accumulation with Pprc1, which encodes PGC-1-related coactivator (PRC), a coactivator for proteins involved in detoxification. Pprc1 and two genes coactivated by Pprc1 (Nrf1 and Nrf2) had significantly lower gene expression in the A.SW strain than in the B10.S strain.

CONCLUSIONS

This study supports Pprc1 as a key regulator for renal Hg excretion.

CITATION

Alkaissi H, Ekstrand J, Jawad A, Nielsen JB, Havarinasab S, Soderkvist P, Hultman P. 2016. Genome-wide association study to identify genes related to renal mercury concentrations in mice. Environ Health Perspect 124:920-926; http://dx.doi.org/10.1289/ehp.1409284.

Compensatory renal hypertrophy and the handling of an acute nephrotoxicant in a model of aging

Aging often results in progressive losses of functioning nephrons, which can lead to a significant reduction in overall renal function. Because of age-related pathological changes, the remaining functional nephrons within aged kidneys may be unable to fully counteract physiological and/or toxicological challenges. We hypothesized that when the total functional renal mass of aged rats is reduced by 50%, the nephrons within the remnant kidney do not fully undergo the functional and physiological changes that are necessary to maintain normal fluid and solute homeostasis. We also tested the hypothesis that the disposition and handling of a nephrotoxicant are altered significantly in aged kidneys following an acute, 50% reduction in functional renal mass. To test these hypotheses, we examined molecular indices of renal cellular hypertrophy and the disposition of inorganic mercury (Hg(2+)), a model nephrotoxicant, in young control, young uninephrectomized (NPX), aged control and aged NPX Wistar rats. We found that the process of aging reduces the ability of the remnant kidney to undergo compensatory renal growth. In addition, we found that an additional reduction in renal mass in aged animals alters the disposition of Hg(2+) and potentially alters the risk of renal intoxication by this nephrotoxicant. To our knowledge, this study represents the first report of the handling of a nephrotoxicant in an aged animal following a 50% reduction in functional renal mass.

Disposition of inorganic mercury in pregnant rats and their offspring

Environmental toxicants such as methylmercury have been shown to negatively impact fetal health. Despite the prevalence of inorganic mercury (Hg(2+)) in the environment and the ability of methylmercury to biotransform into Hg(2+), little is known about the ability of Hg(2+) to cross the placenta into fetal tissues. Therefore, it is important to understand the handing and disposition of Hg(2+) in the reproductive system. The purpose of the current study was to assess the disposition and transport of Hg(2+) in placental and fetal tissues, and to test the hypothesis that acute renal injury in dams can alter the accumulation of Hg(2+) in fetal tissues. Pregnant Wistar rats were injected intravenously with 0.5 or 2.5 μmol kg(-1) HgCl2 for 6 or 48 h and the disposition of Hg(2+) was measured. Accumulation of Hg(2+) in the placenta was rapid and dose-dependent. Very little Hg(2+) was eliminated during the initial 48 h after exposure. When dams were exposed to the low dose of HgCl2, fetal accumulation of Hg(2+) increased between 6h and 48 h, while at the higher dose, accumulation was similar at each time point. Within fetal organs, the greatest concentration of Hg(2+) (nmol/g) was localized in the kidneys, followed by the liver and brain. A dose-dependent increase in the accumulation of Hg(2+) in fetal organs was observed, suggesting that continued maternal exposure may lead to increased fetal exposure. Taken together, these data indicate that Hg(2+) is capable of crossing the placenta and gaining access to fetal organs in a dose-dependent manner.

Cinnabar induces renal inflammation and fibrogenesis in rats

The purpose of this study was to investigate whether cinnabar causes renal inflammation and fibrosis in rats. Rats were dosed orally with cinnabar (1 g/kg/day) for 8 weeks or 12 weeks. The control rats were treated with solvent (5% carboxymethylcellulose solution) over the same time periods, respectively. Renal mercury (RHg), urinary mercury (UHg), serum creatinine (SCr), urine kidney injury molecule 1 (KIM-1), renal pathology, and renal mediators were examined. At both 8 weeks and 12 weeks, RHg, UHg, and urine KIM-1 were significantly higher in the cinnabar group than in the control group, although SCr was unchanged. Kidney lesions in the cinnabar-treated rats occurred mainly in the tubules and interstitium, including vacuolization, protein casts, infiltration of inflammatory cells, and slight increase in interstitial collagen. In addition, mild mesangial proliferation was observed in glomeruli. Moreover, the expression of inflammatory and fibrogenic mediators was upregulated in the cinnabar group. In conclusion, cinnabar may cause kidney damage due to the accumulation of mercury, and renal inflammation and slight fibrogenesis may occur in rats. In the clinic, the potential risk of renal injury due to the prolonged consumption of cinnabar should be considered even though the agent is relatively nontoxic.

Mitochondrial functional impairment in response to environmental toxins in the cardiorenal metabolic syndrome

Environmental toxins can promote cardiovascular, metabolic, and renal abnormalities, which characterize the cardiorenal metabolic syndrome (CRS). Heavy metals, such as mercury and arsenic, represent two of the most toxic pollutants. Exposure to these toxins is increasing due to increased industrialization throughout much of the world. Studies conducted to understand the impact of environmental toxins have shown a major impact on mitochondrial structure and function. The maladaptive stress products caused by these toxins, including aggregated proteins, damaged organelles, and intracellular pathogens, can be removed through autophagy, which is also known as mitophagy in mitochondria. Although the underlying mechanisms involved in the regulation of mitophagy in response to pollution are not well understood, accumulating evidence supports a role for maladaptive mitochondrial responses to environmental pollution in the pathogenesis of the CRS. In this review, we discuss the ongoing research, which explores the mechanisms by which these toxins promote abnormalities in mitophagy and associated mitochondrial dysfunction and the CRS.

Novel Hg2+-induced nephropathy in rats and mice lacking Mrp2: evidence of axial heterogeneity in the handling of Hg2+ along the proximal tubule

The role of the multi-resistance protein 2 (Mrp2) in the nephropathy induced by inorganic mercuric mercury (Hg(2+)) was studied in rats (TR(-)) and mice (Mrp2(-/-)), which lack functional Mrp2, and control animals. Animals were exposed to nephrotoxic doses of HgCl2. Forty-eight or 24 hours after exposure, tissues were harvested and analyzed for Hg content and markers of injury. Histological analyses revealed that the proximal tubular segments affected pathologically by Hg(2+) were significantly different between Mrp2-deficient animals and controls. In the absence of Mrp2, cellular injury localized almost exclusively in proximal tubular segments in the subcapsular (S1) to midcortical regions (early S2) of the kidney. In control animals, cellular death occurred mainly in the proximal tubular segments in the inner cortex (late S2) and outer stripe of the outer medulla (S3). These differences in renal pathology indicate that axial heterogeneity exists along the proximal tubule with respect to how mercuric ions are handled. Total renal and hepatic accumulation of mercury was also greater in animals lacking Mrp2 than in controls, indicating that Mrp2 normally plays a significant role in eliminating mercuric ions from within proximal tubular cells and hepatocytes. Analyses of plasma creatinine, BUN, and renal expression of Kim-1 and Ngal tend to support the severity of the nephropathies detected histologically. Collectively, our findings indicate that a fraction of mercuric ions is normally secreted by Mrp2 in early portions of proximal tubules into the lumen and then is absorbed downstream in straight portions, where mercuric species typically induce toxic effects.