Gender related differences in kidney injury induced by mercury

Renal organic anion transporter 1: clinical relevance and the underlying mechanisms in chronic kidney disease

Organic anion transporter 1 (OAT1), primarily found in the renal proximal tubule, is essential for the excretion of various uremic toxins that contribute to the onset and progression of chronic kidney disease (CKD). OAT1 also plays a vital role in the remote sensing and signaling network, facilitating the removal of metabolites through the kidneys. The function of OAT1 is impaired under conditions such as renal ischemia/reperfusion injury, oxidative stress, and fibrosis. Several transcription factors, post-translational modifications, and endocrine hormones control the activity and expression of OAT1. This review explores the unique contribution of OAT1 to the excretion of CKD-related UTs and the mechanisms involved.

Re-thinking the link between exposure to mercury and blood pressure

Hypertension or high blood pressure (BP) is a prevalent and manageable chronic condition which is a significant contributor to the total global disease burden. Environmental chemicals, including mercury (Hg), may contribute to hypertension onset and development. Hg is a global health concern, listed by the World Health Organization (WHO) as a top ten chemical of public health concern. Most people are exposed to some level of Hg, with vulnerable groups, including Indigenous peoples and small-scale gold miners, at a higher risk for exposure. We published a systematic review and meta-analysis in 2018 showing a dose-response relationship between Hg exposure and hypertension. This critical review summarizes the biological effects of Hg (both organic and inorganic form) on the underlying mechanisms that may facilitate the onset and development of hypertension and related health outcomes and updates the association between Hg exposure (total Hg concentrations in hair) and BP outcomes. We also evaluated the weight of evidence using the Bradford Hill criteria. There is a strong dose-response relationship between Hg (both organic and inorganic) exposure and BP in animal studies and convincing evidence that Hg contributes to hypertension by causing structural and functional changes, vascular reactivity, vasoconstriction, atherosclerosis, dyslipidemia, and thrombosis. The underlying mechanisms are vast and include impairments in antioxidant defense mechanisms, increased ROS production, endothelial dysfunction, and alteration of the renin-angiotensin system. We found additional 16 recent epidemiological studies that have reported the relationship between Hg exposure and hypertension in the last 5 years. Strong evidence from epidemiological studies shows a positive association between Hg exposure and the risk of hypertension and elevated BP. The association is mixed at lower exposure levels but suggests that Hg can affect BP even at low doses when co-exposed with other metals. Further research is needed to develop robust conversion factors among different biomarkers and standardized measures of Hg exposure. Regulatory agencies should consider adopting a 2 µg/g hair Hg level as a cut-off for public health regulation, especially for adults older than child-bearing age.

Algorayed R, Bakry N. The Protective Activity of Withania somnifera Against Mercuric Chloride (HgCl2)-Induced Renal Toxicity in Male Rats

The purpose of this study was to test the protective effect of Withania somnifera (WS) against the harmful effects of mercuric chloride (HgCl2)-induced kidney failure at the histological, biochemical, and immune levels in Wistar rats. The study assessed the biochemical and immunological changes in five groups (n = 6): Group 1 (G1) was the negative control, and the other rats received a single subcutaneous dose of HgCl2 (2.5 mg/kg in 0.5 mL of 0.9% saline solution) and randomly divided into 4 groups. Group 2 (G2) was the positive control and left without treatment. Groups 3, 4, and 5 (G3, G4, and G5) were treated with different doses of WS root powder for 30 days. The HgCl2-positive group showed significant signs of renal toxicity as reflected by increased levels of kidney function parameters (blood urea nitrogen, urea, and creatinine), inflammatory biomarkers, immunological indices (SDF-1, IL-6, NGAL, and KIM-1), and oxidative stress (SOD, TAC, CAT, GSH, and MDA). The positive group rats also showed drastic pathological changes in renal tissues. Different doses of WS treatment significantly reduced the levels of all biochemical markers and decreased pathological damage to the kidney tissues. The antioxidant, phenolic, and flavonoid constituents of WS root powder helped protect rats' kidneys against HgCl2-induced kidney toxicity in male rats.

Sex and the Kidney Drug-Metabolizing Enzymes and Transporters: Are Preclinical Drug Disposition Data Translatable to Humans?

Cross-species differences in drug transport and metabolism are linked to poor translation of preclinical pharmacokinetic and toxicology data to humans, often resulting in the failure of new chemical entities (NCEs) during clinical drug development. Specifically, inaccurate prediction of renal clearance and renal accumulation of NCEs due to differential abundance of enzymes and transporters in kidneys can lead to differences in pharmacokinetics and toxicity between experimental animals and humans. We carried out liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based protein quantification of 78 membrane drug-metabolizing enzymes and transporters (DMETs) in the kidney membrane fractions of humans, rats, and mice for characterization of cross-species and sex-dependent differences. In general, majority of DMET proteins were higher in rodents than in humans. Significant cross-species differences were observed in 30 out of 33 membrane DMET proteins quantified in all three species. Although no significant sex-dependent differences were observed in humans, the abundance of 28 and 46 membrane proteins showed significant sex dependence in rats and mice, respectively. These cross-species and sex-dependent quantitative abundance data are valuable for gaining a mechanistic understanding of drug renal disposition and accumulation. Further, these data can also be integrated into systems pharmacology tools, such as physiologically based pharmacokinetic models, to enhance the interpretation of preclinical pharmacokinetic and toxicological data.

Metalloproteomic Investigation of Hg-Binding Proteins in Renal Tissue of Rats Exposed to Mercury Chloride

Results obtained from rat studies indicate that, even at low concentrations, mercurial species cause harmful effects on the kidneys, by inducing the nephrotic oxidative stress response. In the present work, Hg-associated proteins were identified as possible mercury-exposure biomarkers in rat kidneys exposed to low mercury chloride concentrations for 30 days (Hg-30) and 60 days (Hg-60), using metalloproteomic strategies. The renal proteomic profile was fractioned by two-dimensional electrophoresis and the mercury determinations in kidney samples, protein pellets and protein spots were performed using graphite furnace atomic absorption spectrometry. The characterization of Hg-associated protein spots and the analysis of differentially expressed proteins were performed by liquid chromatography, coupled with tandem mass spectrometry. Eleven Hg-associated protein spots with a concentration range of 79 ± 1 to 750 ± 9 mg kg-1 in the Hg-60 group were identified. The characterization and expression analyses allowed the identification of 53 proteins that were expressed only in the Hg-60 group, 13 "upregulated" proteins (p > 0.95) and 47 "downregulated" proteins (p < 0.05). Actin isoforms and hemoglobin subunits were identified in protein spots of the Hg-60 group, with mercury concentrations in the range of 138 to 750 mg kg-1, which qualifies these proteins as potential mercury-exposure biomarkers.

Toxic nephropathy secondary to chronic mercury poisoning: clinical characteristics and outcomes

Introduction

Kidney disease secondary to mercury poisoning has not been well documented and is often misdiagnosed and mistreated.

Methods

We performed a retrospective analysis of patients diagnosed with having mercury poisoning over a 6-year period between July 2013 and June 2019. Demographics, clinical measures, renal pathologic examinations, treatments, and outcomes were compared between patients with kidney disease and those without kidney disease.

Results

Of the 172 patients with mercury poisoning, 46 (26.74%) had renal damage. Among the 46 patients, 41 (89.13%) presented nephrotic syndrome, and 5 (10.87%) showed proteinuria alone. The pathologic abnormality associated with kidney disease caused by mercury poisoning was mainly membranous nephropathy (18 of 35 patients, 51.43%). Among 41 patients with nephrotic syndrome, 25 were treated with chelation therapy alone and 12 with mercury chelation therapy and glucocorticoids. The remaining 4 patients were treated with chelation therapy, glucocorticoids, and immunosuppressive therapies. The overall effective rate was 97.5% (40 patients). There was no significant difference in complete remission rate among the 3 treatment methods (P < 0.05).

Conclusion

The main clinical manifestation of kidney disease secondary to chronic mercury poisoning was nephrotic syndrome, which was reflected in pathologic examinations as membranous nephropathy. Kidney disease to chronic mercury poisoning is prone to misdiagnosis and missed diagnosis. Chelation therapy is the main treatment, and the prognosis is good. Patients with severe condition can be supplemented with glucocorticoid.

Effect of Solanum vegetables on memory index, redox status, and expressions of critical neural genes in Drosophila melanogaster model of memory impairment

African eggplant (Solanum macrocarpon L) (AE) and Black Nightshade (Solanum nigrum L) (BN) leaves are green leafy vegetables with nutritional and ethnobotanical values. We have previously characterized the vegetables via HPLC/LC-MS to reveal notable phenolic acids, flavonoids and alkaloids. In this present study, we addressed the efficacy of the two vegetables in mitigating mercuric chloride (HgCl₂)-induced neurotoxicity and memory impairment in Drosophila melanogaster. Flies were exposed to HgCl₂ (0.30 mg/g) alone or in combination with the vegetables (0.1 and 1.0%) of both samples in their diets for seven days. The results showed that HgCl₂ (Hg)-exposed flies had significantly reduced survival rate and memory index, which were ameliorated in the Hg-exposed flies fed AE or BN. This was accompanied by increased reactive oxygen species (ROS) levels, reduced total thiol, as well as catalase, glutathione transferase (GST) and acetylcholine esterase (AChE) activities in Hg-exposed fly heads, but ameliorated in Hg-exposed flies fed dietary inclusions of the vegetables. In addition, the Hg-induced alterations in SOD, NF-ҝB/Relish, Dronc and Reaper mRNA levels were statistically indistinguishable from controls in Hg-treated flies fed diets containing AE or BN. Normalization of cnc/Nrf2 and FOXO were observed only in Hg-treated flies fed BN. These findings suggest that dietary AE or BN leaves offer protection against Hg-induced memory impairment and neurotoxicity in D. melanogaster, and further justify them as functional foods with neuroprotective properties.

Association of Blood Mercury Levels with the Risks of Overweight and High Waist-to-Height Ratio in Children and Adolescents: Data from the Korean National Health and Nutrition Examination Survey

A previous study in adults demonstrated the substantial role of mercury exposure in the development of overweight and obesity. Although children and adolescents are more susceptible to the toxic effects of mercury than adults, studies on the association of overweight and obesity with mercury exposure is limited. This study aimed to investigate the association of blood mercury levels with the body mass index (BMI) and waist-to-height ratio (WHtR) as obesity indices in Korean children and adolescents. The analyzed cross-sectional data were obtained from 1327 participants (age: 10–18 years; 672 male and 655 female) who completed the Korean National Health and Nutrition Examination Survey 2010–2013. The covariates included sociodemographic factors (age, sex, and household income), dietary factors (fish, shellfish, and seaweed consumption), lifestyle factors (alcohol consumption, smoking status, and exercise), and blood hematocrit levels. The adjusted geometric mean blood mercury level was 2.19 µg/L, and the level of mercury was significantly higher in the overweight (BMI ≥ 85th gender and age-specific percentiles) and high WHtR (cutoff: ≥0.5) groups than in the normal group. In all the participants, the blood mercury levels were significantly positively associated with the BMI and WHtR after adjusting for all covariates (p < 0.05). All the participants in the highest blood mercury level quartile were at a higher risk for overweight and a high WHtR than those in the lowest quartile after adjusting for all covariates (p < 0.05). Our study suggests a significant association between mercury exposure and the risks of overweight and high WHtR in Korean children and adolescents.

Associations between exposure to heavy metals and the risk of chronic kidney disease: a systematic review and meta-analysis

We performed a systematic review and meta-analysis to examine the relationship between heavy metals (HMs) exposure and the risk of chronic kidney disease (CKD). Databases of Web of Science, Embase, MEDLINE, and Scopus were searched through June 2020 to identify studies assessing the relationships between exposure to HMs (i.e. cadmium, lead, arsenic, mercury) and the risk of CKD, evaluated by decreased estimated glomerular filtration rate (eGFR) and/or increased proteinuria risks in adults (≥18 years). Data were pooled by random-effects models and expressed as weighted mean differences and 95% confidence intervals. The risk of bias was assessed by the Newcastle-Ottawa scale (NOS). Twenty-eight eligible articles (n = 107,539 participants) were included. Unlike eGFR risk (p = 0.10), Cadmium exposure was associated with an increased proteinuria risk (OR = 1.35; 95% CI: 1.13, 1.61; p < 0.001; I² = 79.7%). Lead exposure was associated with decreased eGFR (OR = 1.12; 95%CI: 1.03, 1.22; p = 0.008; I² = 87.8%) and increased proteinuria (OR = 1.25; 95% CI: 1.04, 1.49; p = 0.02; I² = 79.6) risks. Further, arsenic exposure was linked to a decreased eGFR risk (OR = 1.55; 95% CI: 1.05, 2.28; p = 0.03; I² = 89.1%) in contrast to mercury exposure (p = 0.89). Only two studies reported the link between arsenic exposure and proteinuria risk, while no study reported the link between mercury exposure and proteinuria risk. Exposure to cadmium, lead, and arsenic may increase CKD risk in adults, albeit studies were heterogeneous, warranting further investigations. Our observations support the consideration of these associations for preventative, diagnostic, monitoring, and management practices of CKD.

Trimetazidine Protects from Mercury-Induced Kidney Injury

INTRODUCTION

The presence of mercury in the environment is a worldwide concern. Inorganic mercury is present in industrial materials, is employed in medical devices, is widely used in batteries, is a component of fluorescent light bulbs, and it has been associated with human poisoning in gold mining areas. The nephrotoxicity induced by inorganic mercury is a relevant health problem mainly in developing countries. The primary mechanism of mercury toxicity is oxidative stress. Trimetazidine (TMZ) is an anti-ischemic drug, which inhibits cellular oxidative stress, eliminates oxygen-free radicals, and improves lipid metabolism. The aim of this study was to evaluate whether the administration of TMZ protects against mercuric chloride (HgCl2) kidney damage.

METHODS

Adult male Wistar rats received only HgCl2 (4 mg/kg bw, sc) (Hg group, n = 5) or TMZ (3 mg/kg bw, ip) 30 min before HgCl2 administration (4 mg/kg bw, sc) (TMZHg group, n = 7). Simultaneously, a control group of rats (n = 4) was studied. After 4 days of HgCl2 injection, urinary flow, urea and creatinine (Cr) plasma levels, Cr clearance, urinary glucose, and sodium-dicarboxylate cotransporter 1 (NaDC1) in urine were determined. Lipid peroxidation (MDA) and glutathione (GSH) levels were measured in kidney homogenates.

RESULTS

Rats only treated with HgCl2 showed an increase in urea and Cr plasma levels, urinary flow, fractional excretion of water, glucosuria, and NaDC1 urinary excretion as compared with the control group and a decrease in Cr clearance. TMZHg group showed a decrease in urea and Cr plasma levels, urinary flow, fractional excretion of water, glucosuria, NaDC1 urinary excretion, and an increase in Cr clearance when compared to the Hg group. Moreover, MDA and GSH levels observed in Hg groups were decreased and increased, respectively, by TMZ pretreatment.

CONCLUSION

TMZ exerted a renoprotective action against HgCl2-induced renal injury, which might be mediated by the reduction of oxidative stress. Considering the absence of toxicity of TMZ, its clinical application against oxidative damage due to HgCl2-induced renal injury should be considered. The fact that TMZ is commercially available should simplify and accelerate the translation of the present data "from bench to bedside." In this context, TMZ become an interesting new example of drug repurposing.

Erythropoietin alters the pharmacokinetics of organic anions mainly eliminated by the kidney in rats

Erythropoietin (EPO) is a cytokine originally used for its effects on the hematopoietic system, and is widely prescribed around the world. In the present study, the effects of EPO administration on p-aminohippurate (PAH, a prototype organic anion) pharmacokinetics and on the renal expression of PAH transporters were evaluated. Male Wistar rats were treated with EPO or saline (control group). After 42 h, PAH was administered, and plasma samples were obtained at different time points to determine PAH levels. PAH levels in renal tissue and urine were also assessed. The renal expression of PAH transporters was evaluated by Western blotting. EPO-treated rats showed an increase in PAH systemic clearance, in its elimination rate constant, and in urinary PAH levels, while PAH in renal tissue was decreased. Moreover, EPO administration increased the expression of the transporters of the organic anions evaluated. The EPO-induced increase in PAH clearance is accounted for by the increase in its renal secretion mediated by the organic anion transporters. The goal of this study is to add important information to the wide knowledge gap that exists regarding drug-drug interactions. Owing to the global use of EPO, these results are useful in terms of translation into clinical practice.

Stem Cells for Next Level Toxicity Testing in the 21st Century

The call for a paradigm change in toxicology from the United States National Research Council in 2007 initiates awareness for the invention and use of human-relevant alternative methods for toxicological hazard assessment. Simple 2D in vitro systems may serve as first screening tools, however, recent developments infer the need for more complex, multicellular organotypic models, which are superior in mimicking the complexity of human organs. In this review article most critical organs for toxicity assessment, i.e., skin, brain, thyroid system, lung, heart, liver, kidney, and intestine are discussed with regards to their functions in health and disease. Embracing the manifold modes-of-action how xenobiotic compounds can interfere with physiological organ functions and cause toxicity, the need for translation of such multifaceted organ features into the dish seems obvious. Currently used in vitro methods for toxicological applications and ongoing developments not yet arrived in toxicity testing are discussed, especially highlighting the potential of models based on embryonic stem cells and induced pluripotent stem cells of human origin. Finally, the application of innovative technologies like organs-on-a-chip and genome editing point toward a toxicological paradigm change moves into action.

Effect of erythropoietin on mercury-induced nephrotoxicity: Role of membrane transporters

Mercury is a widespread pollutant. Mercuric ions uptake into tubular cells is supported by the Organic anion transporter 1 (Oat1) and 3 (Oat3) and its elimination into urine is through the Multidrug resistance-associated protein 2 (Mrp2). We investigated the effect of recombinant human erythropoietin (Epo) on renal function and on renal expression of Oat1, Oat3, and Mrp2 in a model of mercuric chloride (HgCl2)-induced renal damage. Four experimental groups of adult male Wistar rats were used: Control, Epo, HgCl2, and Epo + HgCl2. Epo (3000 IU/kg, b.w., i.p.) was administered 24 h before HgCl2 (4 mg/kg, b.w., i.p.). Experiments were performed 18 h after the HgCl2 dose. Parameters of renal function and structure were evaluated. The protein expression of Oat1, Oat3 and Mrp2 in renal tissue was assessed by immunoblotting techniques. Mercury levels were determined by cold vapor atomic absorption spectrometry. Pretreatment with Epo ameliorated the HgCl2-induced tubular injury as assessed by histopathology and urinary biomarkers. Immunoblotting showed that pretreatment with Epo regulated the renal expression of mercury transporters in a way to decrease mercury content in the kidney. Epo pretreatment ameliorates HgCl2-induced renal tubular injury by modulation of mercury transporters expression in the kidneys.

Physiochemical characterization and toxicity assessment of colloidal mercuric formulation-'Sivanar amirtham'

The study aims to characterize and understand the toxicological effects of colloidal mercuric formulation. The physiochemical characterization was carried out using Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray microanalysis system (EDS), Inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), Zeta potential, Brunauer-Emmett-Teller (BET) and electron microscopy. Based on the physiochemical characterizations, the pairwise relationship between the parameters such as size, surface area, surface charge, reactivity and band gap energy were described. The biological effects of the sample were studied by both in vitro and in vivo assays. The in vitro cytotoxicity assay confirmed that the colloidal mercuric formulation was effective against cancer cells (MCF-7) and less toxic to normal cells (Hek 293). The formulation was effective against MCF-7 with more than 85% of apoptotic and necrotic cells, positive for PI staining when treated with 100 μg/mL. The inflammatory response on the macrophage cell lines was studied. The colloidal mercuric formulation upregulated the expression of TGF-β, IL-6 and TNF-α, due to the presence of arsenic and other organic compounds such as piperine. The in vivo developmental toxicity was observed in Zebrafish hampered growth and survival in a dose and time dependent manner. The formulation was safe at lower concentration and exhibit a dose and time dependent toxicity. Based on the results obtained, it is confirmed that the selective toxicity towards MCF-7 cells is promising to develop an effective formulation for the treatment of cancer, provided more such proofs obtained from in vivo experiments.

A toxicogenomic approach to assess kidney injury induced by mercuric chloride in rats

Kidney injury caused by disease, trauma, environmental exposures, or drugs may result in decreased renal function, chronic kidney disease, or acute kidney failure. Diagnosis of kidney injury using serum creatinine levels, a common clinical test, only identifies renal dysfunction after the kidneys have undergone severe damage. Other indicators sensitive to kidney injury, such as the level of urine kidney injury molecule-1 (KIM-1), lack the ability to differentiate between injury phenotypes. To address early detection as well as detailed categorization of kidney-injury phenotypes in preclinical animal or cellular studies, we previously identified eight sets (modules) of co-expressed genes uniquely associated with kidney histopathology. Here, we used mercuric chloride (HgCl₂)-a model nephrotoxicant-to chemically induce kidney injuries as monitored by KIM-1 levels in Sprague Dawley rats at two doses (0.25 or 0.50 mg/kg) and two exposure lengths (10 or 34 h). We collected whole transcriptome RNA-seq data derived from five animals at each dose and time point to perform a toxicogenomics analysis. Consistent with documented injury phenotypes for HgCl₂ toxicity, our kidney-injury-module approach identified the onset of necrosis and dilation as early as 10 h after a dose of 0.50 mg/kg that produced only mild injury as judged by urinary KIM-1 excretion. The results of these animal studies highlight the potential of the kidney-injury-module approach to provide a sensitive and histopathology-specific readout of renal toxicity.

From the Cover: Identification of Natural Products as Inhibitors of Human Organic Anion Transporters (OAT1 and OAT3) and Their Protective Effect on Mercury-Induced Toxicity

Mercury accumulates in kidneys and produces acute kidney injury. Semen cassiae (SC), a widely consumed tea and herbal medicine in Eastern Asia, has been reported to have protective effects on kidneys. In this study, SC extract was shown to almost abolish the histological alterations induced by mercuric chloride in rat kidneys. A total of 22 compounds were isolated from SC, and 1,7,8-methoxyl-2-hydroxyl-3-methyl-anthraquinone was detected in SC for the first time. Among the eight compounds identified in the blood of rats after SC treatment, six were strong inhibitors of human organic anion transporter 1 and 3 (OAT1 and OAT3). Inhibitory studies revealed that OAT1 and OAT3 were inhibited by SC constituents, in both a competitive and noncompetitive manner. Both OAT1- and OAT3-overexpressing cells were susceptible to the cytotoxicity of the cysteine-mercury conjugate, but only OAT1-overexpressing cells could be protected by 200 μM probenecid or 10 μM of the eight inhibitors in SC, suggesting that OAT1 is the major determinant in the cellular uptake of mercury. To facilitate the identification of inhibitors of OAT1 and OAT3, models of OAT1 and OAT3 were constructed using recently determined protein templates. By combining in silico and in vitro methods, inhibitors of OAT1 and OAT3 were predicted and validated from SC constituents. Collectively, the present study suggests that additional inhibitors of OAT1 and OAT3 can be predicted and validated from natural products by combining docking and in vitro screening, and could be a source of pharmaceutical compounds for developing treatments for mercury-induced kidney injury.

Renal expression of organic anion transporters is modified after mercuric chloride exposure: Gender-related differences

Mercuric ions (Hg⁺²) gain access to proximal tubule cells primarily by the Organic Anion Transporter 1 (Oat1) and 3 (Oat3) in the basolateral plasma membrane. The removal process of Hg⁺² ions from cells into the lumen involves an efflux process mainly mediated by the Multidrug Resistance-Associated Protein 2 (Mrp2). The aim of this study was to compare the sex-related differences in the renal expression of Oat1, Oat3, and Mrp2 after mercuric chloride (HgCl₂) treatment and analyze their relevance in the mercury-induced nephrotoxicity. Control and Hg-treated male and female Wistar rats were used. Animals received a dose of HgCl₂ (4 mg/kg bw, ip) 18 h before the experiments. Tubular injury was assessed by histopathological studies. The renal expression of Oat1, Oat3, and Mrp2 was analyzed by Western Blotting. Mercury levels were determined in urine by cold vapour atomic absorption spectroscopy. HgCl₂ treatment increased the expression of renal Oat1 and Mrp2 in both sexes, being more evident in females than in males. The Oat3 renal expression only increased in female rats. The higher expressions of Oat1, Oat3, and Mrp2 could explain the higher renal excretion of mercury and consequently, the lesser renal tubular damage in female rats than in male rats.

Gender differences in mercury-induced hepatotoxicity: Potential mechanisms

The accumulation of mercury in the liver causes hepatotoxicity. The organic anion transporter 3 (Oat3) and the multidrug-resistance associated protein 2 (Mrp2) are involved in the hepatic excretion of toxins and drugs and in the hepatic handling of mercury. The aim of this work was to study if there are gender-related differences in mercuric chloride (HgCl₂)-induced hepatotoxicity in rats. Total mercury levels and protein expressions of Oat3 and Mrp2 in liver samples were also assessed to clarify the mechanisms underlying mercury-induced liver damage in male and female rats. Control and HgCl₂-treated male and female Wistar rats were used. Hepatotoxicity was evaluated by plasma activity of transaminases and alkaline phosphatase, as well as by histopathological analysis. Oat3 and Mrp2 expression was assessed by immunoblotting. Female rats displayed a higher HgCl₂-induced hepatotoxicity than male rats as demonstrated by the higher alterations in the plasma markers of liver damage and in the histopathology. The sex-related differences observed in the hepatic damage can be explained by the higher accumulation of mercury in liver from female rats. In this connection, after mercury treatment the expression of Mrp2 decreased in both sexes and the expression of Oat3 decreased only in males. The decreased in Oat3 abundance in the hepatocytes membranes in mercury-treated males would limit the uptake of mercuric ions into the liver protecting them from mercury hepatotoxicity.

Toxicodynamics of Lead, Cadmium, Mercury and Arsenic- induced kidney toxicity and treatment strategy: A mini review

Environmental pollution has become a concerning matter to human beings. Flint water crisis in the USA pointed out that pollution by heavy metal is getting worse day by day, predominantly by Lead, Cadmium, Mercury and Arsenic. Despite of not having any biological role in flora and fauna, they exhibit detrimental effect following exposure (acute or chronic). Even at low dose, they affect brain, kidney and heart. Oxidative stress has been termed as cause and effect in heavy metal-induced kidney toxicity. In treatment strategy, different chelating agent, vitamins and minerals are included, though chelating agents has been showed different fatal drawbacks. Interestingly, plants and plants derived compounds had shown possible effectiveness against heavy metals induced kidney toxicity. This review will provide detail information on toxicodynamics of Pb, Cd, Hg and As, treatment strategy along with the possible beneficiary role of plant derived compound to protect kidney.

Protective effect of Moringa oleifera oil against HgCl2-induced hepato- and nephro-toxicity in rats

BACKGROUND

Various parts of the Moringa oleifera (M. oleifera) tree are widely accepted to have ameliorative effects against metal toxicity. In the present study, M. oleifeira oil (MO) was tested against HgCl2-induced tissue pathologies and oxidative stress.

METHODS

Male Wistar rats were administered MO (1.798 mg/kg p.o.) or HgCl2 (5 mg/kg body wt) alone or in combination (5 mg/kg HgCl2+1.798 mg/kg MO p.o.) three times per week for 21 days. After exposure and treatment periods, rats were sacrificed; blood collected and the oxidative status of the liver and kidney homogenates were evaluated.

RESULTS

In the liver, malondialdehyde (MDA) level, glutathione (GSH), and superoxide dismutase (SOD) activities were higher whereas catalase (CAT) activity was lower in the HgCl2 group than in the control group. In the kidney, MDA level, SOD, and CAT activities were higher whereas GSH activity was unchanged in the HgCl2 group compared to the control group. In the liver, MDA level, SOD, and CAT activities were lower in the HgCl2+MO group than in the HgCl2 group. In the kidney, MDA level, SOD and CAT activities were lower in the HgCl2+MO than in the HgCl2 group. Furthermore, Hg-induced increases in creatinine and bilirubin levels as well as the increase in γ-glutamyl transferase, lactate dehydrogenase, and alkaline phosphatase activities were attenuated in the combine exposure group and the animals showed improvement in the histology of the liver and kidney.

CONCLUSIONS

MO decreased the negative effects of Hg-induced oxidative stress in rats.

Xenobiotic transporters and kidney injury

Renal proximal tubules are targets for toxicity due in part to the expression of transporters that mediate the secretion and reabsorption of xenobiotics. Alterations in transporter expression and/or function can enhance the accumulation of toxicants and sensitize the kidneys to injury. This can be observed when xenobiotic uptake by carrier proteins is increased or efflux of toxicants and their metabolites is reduced. Nephrotoxic chemicals include environmental contaminants (halogenated hydrocarbon solvents, the herbicide paraquat, the fungal toxin ochratoxin, and heavy metals) as well as pharmaceuticals (certain beta-lactam antibiotics, antiviral drugs, and chemotherapeutic drugs). This review explores the mechanisms by which transporters mediate the entry and exit of toxicants from renal tubule cells and influence the degree of kidney injury. Delineating how transport proteins regulate the renal accumulation of toxicants is critical for understanding the likelihood of nephrotoxicity resulting from competition for excretion or genetic polymorphisms that affect transporter function.

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.

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.

Exaggerated arsenic nephrotoxicity in female mice through estrogen-dependent impairments in the autophagic flux

Gender is one of the essential factors in the development of various diseases and poisoning. Therefore, we herein examined gender differences in sodium arsenite (NaAsO2)-induced acute renal dysfunction. When male and female BALB/c mice were subcutaneously injected with NaAsO2 (12.5mg/kg), serum and urinary markers for proximal tubular injury were significantly higher in female mice than in male ones. NaAsO2-induced histopathological alterations were consistently more evident in females than in males. Ovariectomy, but not orchiectomy significantly attenuated NaAsO2-induced renal injury. These results imply that the hypersusceptibility of female mice is attributed to estrogen signals. NaAsO2 suppressed the autophagic flux in tubular cells through the activation of ERK. Enhancements in the activation of ERK were significantly greater in females than in males, with the eventual accumulation of LC3-II and P62 in the kidneys, implying that the autophagic flux is impaired in females. The IL-6/STAT3 signaling pathway had protective roles in NaAsO2-induced nephrotoxicity through the suppression of ERK activation. Despite the absence of differences in intrarenal IL-6 expression between male and female mice, STAT3 was less activated with enhanced SOCS3 expression in females than in males. An in vitro study using mProx24 cells revealed that the estrogen treatment induced SOCS3 expression, and eventually suppressed the autophagic flux, as evidenced by greater increases in the accumulation of LC3-II and p62 with ERK activation, which was canceled by the knockdown of Socs3. Collectively, these results indicate that estrogen has a negative impact on the development of NaAsO2 nephrotoxicity through its suppression of the autophagic flux.

Expression of drug transporters in human kidney: impact of sex, age, and ethnicity

Background

Differences in expression of drug transporters in human kidney contribute to changes in pharmacokinetics and toxicokinetics of a variety of drug compounds. The basal expression levels of genes involved in drug transport processes in the kidney introduces differences in bioavailability, distribution, and clearance of drugs, possibly influencing drug efficacy and adverse reactions. Sex differences in gene expression of transporters are a key cause of differences in sex-dependent pharmacokinetics, which may characterize many drugs and contribute to individual differences in drug efficacy and toxicity. Therefore, evaluating the expression of drug transporters in normal human kidneys is important to better understand differences in drug bioavailability, distribution, and clearance of drugs in humans. Other factors such as age and ethnicity may also contribute to individual differences in gene expression of drug transporters in the human kidney.

Methods

Quantitative real-time PCR (QRT-PCR) was performed to determine the gene expression of 30 drug transporters in 95 age-matched normal human kidney tissues. Multiple Student’s t-tests (Sidak-Bonferroni correction) and two-way ANOVA (Bonferroni correction) analyses were used to determine statistically significant differences.

Results

In the 30 transporter genes examined, sex, ethnicity, and age differences in gene expression were exhibited in normal human kidney tissue. These changes in expression were not found to be differentially significant. However, sex-age and sex-ethnicity interactions were found to be statistically significant. For sex-age interactions, SCL22A12 was found to be significantly higher expressed in females <50 years compared to males <50 years. Expression levels of SLC22A2, SLC22A12, SLC6A16, and ABCB6 were significantly higher in females <50 years compared to females ≥50 years. In sex-ethnicity interactions, expression levels of ATP7B and KCNJ8 were found to be significantly higher in African American females compared to European American females. Also, the expression of SLC31A2 was significantly higher in European American males compared to European American females.

Conclusions

Sex, age, and ethnic differences impacted the expression of drug transporters in normal human kidneys, which suggests that the analysis of gene expression of drug transporters will aid in improving the usage/dosage of drug therapies influencing personalized medicine and susceptibility to adverse drug reactions.

Age and sex differences in kidney microRNA expression during the life span of F344 rats

Background

Growing evidence suggests that epigenetic mechanisms of gene regulation may play a role in susceptibilities to specific toxicities and adverse drug reactions. MiRNAs in particular have been shown to be important regulators in cancer and other diseases and show promise as predictive biomarkers for diagnosis and prognosis. In this study, we characterized the global kidney miRNA expression profile in untreated male and female F344 rats throughout the life span. These findings were correlated with sex-specific susceptibilities to adverse renal events, such as male-biased renal fibrosis and inflammation in old age.

Methods

Kidney miRNA expression was examined in F344 rats at 2, 5, 6, 8, 15, 21, 78, and 104 weeks of age in both sexes using Agilent miRNA microarrays. Differential expression was determined using filtering criteria of ≥1.5 fold change and ANOVA or pairwise t-test (FDR <5%) to determine significant age and sex effects, respectively. Pathway analysis software was used to investigate the possible roles of these target genes in age- and sex-specific differences.

Results

Three hundred eleven miRNAs were found to be expressed in at least one age and sex. Filtering criteria revealed 174 differentially expressed miRNAs in the kidney; 173 and 34 miRNAs exhibiting age and sex effects, respectively. Principal component analysis revealed age effects predominated over sex effects, with 2-week miRNA expression being much different from other ages. No significant sexually dimorphic miRNA expression was observed from 5 to 8 weeks, while the most differential expression (13 miRNAs) was observed at 21 weeks. Potential target genes of these differentially expressed miRNAs were identified.

Conclusions

The expression of 56% of detected renal miRNAs was found to vary significantly with age and/or sex during the life span of F344 rats. Pathway analysis suggested that 2-week-expressed miRNAs may be related to organ and cellular development and proliferation pathways. Male-biased miRNA expression at older ages correlated with male-biased renal fibrosis and mononuclear cell infiltration. These miRNAs showed high representation in renal inflammation and nephritis pathways, and included miR-214, miR-130b, miR-150, miR-223, miR-142-5p, miR-185, and miR-296*. Analysis of kidney miRNA expression throughout the rat life span will improve the use of current and future renal biomarkers and inform our assessments of kidney injury and disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13293-014-0019-1) contains supplementary material, which is available to authorized users.

Amelioration of mercury nephrotoxicity after pharmacological manipulation of organic anion transporter 1 (Oat1) and multidrug resistance-associated protein 2 (Mrp2) with furosemide

Furosemide improves HgCl₂-induced tubule injury up-regulating Oat1 and Mrp2, thus increasing renal elimination of mercuric ions.

Protein expression of kidney and liver bilitranslocase in rats exposed to mercuric chloride--a potential tissular biomarker of toxicity

Bilitranslocase (BTL) is a plasma membrane carrier that transports organic anions of physiological and pharmacological interest. It is expressed in basolateral plasma membrane of kidney and liver. BTL has been recently described as a marker of transition from normal tissue to its neoplastic transformation in human kidney. Inorganic mercury is a major environmental contaminant that produces many toxic effects. Previous reports have described an interaction between BTL and mercuric ions. This study was designed to evaluate the renal and hepatic expression of BTL in rats exposed to a nephrotoxic and hepatotoxic dose of HgCl2. Male rats were treated with a single injection of HgCl2 at a dose of 4mg/kg body wt, i.p. (HgCl2 group). Control rats received the vehicle alone (Control group). Studies were carried out 18h after injection. Afterwards, the kidneys and livers were excised and processed for histopathological studies or immunoblot (homogenates and crude membranes) techniques. In rats treated with HgCl2, immunoblotting showed a significant decrease in the abundance of BTL in homogenates and plasma membranes from kidney and liver. BTL decrease of expression might reflect the grade of damage in renal tubule cells and in hepatocytes. Thus, BTL might be postulated as a new biomarker of tissue toxicity induced by mercury.

Developmental study of mercury effects on the fruit fly (Drosophila melanogaster)

Environmental pollution caused by heavy metals such as mercury is one of the most important human problems. It might have severe teratogenic effects on embryonic development. Some pharmacological and physiological aspects of fruit flies (Drosophila melanogaster) are similar to humans. So the stages of egg to adult fruit fly, as a developmental model, were employed in the study. Wild adult insects were maintained in glass dishes containing standard medium at 25 °C in complete darkness. Five pairs of 3-day old flies were then transferred to standard culture dishes containing different concentrations of mercury ion. They were removed after 8 hours. We considered the following: The rate of larvae becoming pupae and pupae to adults; the time required for the development; the hatching rate in the second generation without mercury in the culture; the morphometric changes during development in both length and width of the eggs through two generations; larvae, pupae and adult thorax length and width. The results showed that mercury in culture (20–100 mg/l) increase the duration of larvae (p<0.01) and pupae (p<0.01) development, the rate of larvae becoming pupae (p<0.001); pupae maturation (p<0.05), the hatching rate (p<0.01), the length (p<0.05) and width of larvae (p<0.01) and pupae (p<0.001) and the length in the adult thorax (p<0.01) decreased significantly. There was no effect upon the size of eggs. There were also no larvae hatching in concentrations of 200 mg/l of mercury. Negative effects of mercury as a heavy metal are possibly due to the interference of this metal in cellular signaling pathways, such as: Notch signaling and protein synthesis during the period of development. Since it bonds chemically with the sulfur hydride groups of proteins, it causes damage to the cell membrane and decreases the amount of RNA. This is the cause of failure of many enzyme mechanisms.

Sex-dependent regulation of cytochrome P450 family members Cyp1a1, Cyp2e1, and Cyp7b1 by methylation of DNA

Sexual differences are only partially attributable to hormones. Cultured male or female cells, even from embryos before sexual differentiation, differ in gene expression and sensitivity to toxins, and these differences persist in isolated primary cells. Male and female cells from Swiss Webster CWF mice manifest sex-distinct patterns of DNA methylation for X-ist and for cytochrome P450 (CYP; family members 1a1, 2e1m, and 7b1. Dnmt3l is differentially expressed but not differentially methylated, and Gapdh is neither differentially methylated nor expressed. CYP family genes differ in expression in whole tissue homogenates and cell cultures, with female Cyp expression 2- to 355-fold higher and Dnmt3l 12- to 32-fold higher in males. DNA methylation in the promoters of these genes is sex dimorphic; reducing methylation differences reduces to 1- to 6-fold differences in the expression of these genes. Stress or estradiol alters both methylation and gene expression. We conclude that different methylation patterns partially explain the sex-based differences in expression of CYP family members and X-ist, which potentially leads to inborn differences between males and females and their different responses to chronic and acute changes. Sex-differential methylation may have medical effects.

Organic anion transporter 5 renal expression and urinary excretion in rats with vascular calcification

It has been described renal damage in rats with vascular calcification. The organic anion transporter 5 (Oat5) is only expressed in kidney, and its urinary excretion was proposed as potential early biomarker of renal injury. The aim of this study was to evaluate the Oat5 renal expression and its urinary excretion in an experimental model of vascular calcification in comparison with traditional markers of renal injury. Vascular calcification was obtained by the administration of an overdose of vitamin D₃ (300,000 IU/kg, b.w., i.m.) to male Wistar rats. Oat5 urinary abundance was evaluated by Western blotting. Traditional markers of renal injury, such as creatinine and urea plasma levels, urinary protein levels, and urinary alkaline phosphatase (AP) activity, were determined using commercial kits. Histology was assessed by hematoxylin/eosin staining. Oat5 renal expression was evaluated by Western blotting and by immunohistochemistry. An increased expression of Oat5 in renal homogenates, in apical membranes, and in its urinary excretion was observed in rats with vascular calcification. The traditional parameters used to evaluate renal function were not modified, with the exception of histology. It is possible to postulate the urinary excretion of Oat5 as a potential noninvasive biomarker of renal injury associated with vascular calcification.

Sex differences in kidney gene expression during the life cycle of F344 rats

Background

The kidney functions in key physiological processes to filter blood and regulate blood pressure via key molecular transporters and ion channels. Sex-specific differences have been observed in renal disease incidence and progression, as well as acute kidney injury in response to certain drugs. Although advances have been made in characterizing the molecular components involved in various kidney functions, the molecular mechanisms responsible for sex differences are not well understood. We hypothesized that the basal expression levels of genes involved in various kidney functions throughout the life cycle will influence sex-specific susceptibilities to adverse renal events.

Methods

Whole genome microarray gene expression analysis was performed on kidney samples collected from untreated male and female Fischer 344 (F344) rats at eight age groups between 2 and 104 weeks of age.

Results

A combined filtering approach using statistical (ANOVA or pairwise t test, FDR 0.05) and fold-change criteria (>1.5 relative fold change) was used to identify 7,447 unique differentially expressed genes (DEGs). Principal component analysis (PCA) of the 7,447 DEGs revealed sex-related differences in mRNA expression at early (2 weeks), middle (8, 15, and 21 weeks), and late (104 weeks) ages in the rat life cycle. Functional analysis (Ingenuity Pathway Analysis) of these sex-different genes indicated over-representation of specific pathways and networks including renal tubule injury, drug metabolism, and immune cell and inflammatory responses. The mRNAs that code for the qualified urinary protein kidney biomarkers KIM-1, Clu, Tff3, and Lcn2 were also observed to show sex differences.

Conclusions

These data represent one of the most comprehensive in-life time course studies to be published, assessing sex differences in global gene expression in the F344 rat kidney. PCA and Venn analyses reveal specific periods of sexually dimorphic gene expression which are associated with functional categories (xenobiotic metabolism and immune cell and inflammatory responses) of key relevance to acute kidney injury and chronic kidney disease, which may underlie sex-specific susceptibility. Analysis of the basal gene expression patterns of renal genes throughout the life cycle of the rat will improve the use of current and future renal biomarkers and inform our assessments of kidney injury and disease.