Acute study of interaction among cadmium, calcium, and zinc transport along the rat nephron in vivo

Is Environmental Cadmium Exposure Causally Related to Diabetes and Obesity?

Cadmium (Cd) is a pervasive toxic metal, present in most food types, cigarette smoke, and air. Most cells in the body will assimilate Cd, as its charge and ionic radius are similar to the essential metals, iron, zinc, and calcium (Fe, Zn, and Ca). Cd preferentially accumulates in the proximal tubular epithelium of the kidney, and is excreted in urine when these cells die. Thus, excretion of Cd reflects renal accumulation (body burden) and the current toxicity of Cd. The kidney is the only organ other than liver that produces and releases glucose into the circulation. Also, the kidney is responsible for filtration and the re-absorption of glucose. Cd is the least recognized diabetogenic substance although research performed in the 1980s demonstrated the diabetogenic effects of chronic oral Cd administration in neonatal rats. Approximately 10% of the global population are now living with diabetes and over 80% of these are overweight or obese. This association has fueled an intense search for any exogenous chemicals and lifestyle factors that could induce excessive weight gain. However, whilst epidemiological studies have clearly linked diabetes to Cd exposure, this appears to be independent of adiposity. This review highlights Cd exposure sources and levels associated with diabetes type 2 and the mechanisms by which Cd disrupts glucose metabolism. Special emphasis is on roles of the liver and kidney, and cellular stress responses and defenses, involving heme oxygenase-1 and -2 (HO-1 and HO-2). From heme degradation, both HO-1 and HO-2 release Fe, carbon monoxide, and a precursor substrate for producing a potent antioxidant, bilirubin. HO-2 appears to have also anti-diabetic and anti-obese actions. In old age, HO-2 deficient mice display a symptomatic spectrum of human diabetes, including hyperglycemia, insulin resistance, increased fat deposition, and hypertension.

The role of inflammation in cadmium nephrotoxicity: NF-κB comes into view

Kidney diseases are major health problem and understanding the underlined mechanisms that lead to kidney diseases are critical research points with a marked potential impact on health. Cadmium (Cd) is a heavy metal that occurs naturally and can be found in contaminated food. Kidneys are the most susceptible organ to heavy metal intoxication as it is the main route of waste excretion. The harmful effects of Cd were previously well proved. Cd induces inflammatory responses, oxidative injury, mitochondrial dysfunction and disturbs Ca²⁺ homeostasis. The nuclear factor-kappa B (NF-κB) is a cellular transcription factor that regulates inflammation and controls the expression of many inflammatory cytokines. Therefore, great therapeutic benefits can be attained from NF-κB inhibition. In this review we focused on certain compounds including cytochalasin D, mangiferin, N-acetylcysteine, pyrrolidine dithiocarbamate, roflumilast, rosmarinic acid, sildenafil, sinapic acid, telmisartan and wogonin and certain plants as Astragalus Polysaccharide, Ginkgo Biloba and Thymus serrulatus that potently inhibit NF-κB and effectively counteracted Cd-associated renal intoxication. In conclusion, the proposed NF-κB involvement in Cd-renal intoxication clarified the underlined inflammation associated with Cd-nephropathy and the beneficial effects of NF-κB inhibitors that make them the potential to substantially optimize treatment protocols for Cd-renal intoxication.

MiR-122-5p and miR-326-3p promote cadmium-induced NRK-52E cell apoptosis by downregulating PLD1

Cadmium is a toxic heavy metal distributed broadly in the environment and manufactory industry. Long-term exposure to cadmium, considered as a risk for kidney injury, leads to chronic kidney disease eventually. Phospholipase D1 (PLD1) promotes cell proliferation and inhibits apoptosis, and might be involved in cadmium-induced kidney injury. In this study, we used miRNA microarray assays and bioinformatics analysis to identify miRNAs, which may regulate PLD1 expression and exert an impact on cadmium-induced kidney injury. MiR-122-5p and miR-326-3p，selected as candidates, were explored for their regulatory functions in kidney injury, using NRK-52E cells. Both of these two miRNAs exhibited higher expression in kidneys of SD rats after exposure to cadmium for 6 weeks. Cadmium treatment also increased miR-122-5p and miR-326-3p and decreased PLD1 in NRK-52E cells. Both of miR-122-5p and miR-326-3p could downregulate PLD1 expression through targeting its 3'UTR and enhance cadmium-induced apoptosis, while inhibiting either of these two miRNAs could reverse such effects. In conclusion, our results suggest that miR-122-5p and miR-326-3p might enhance cadmium-induced NRK-52E cell apoptosis through downregulating PLD1 expression.

Renal handling of zinc in chronic kidney disease patients and the role of circulating zinc levels in renal function decline

BACKGROUND

Zinc deficiency is commonly encountered in chronic kidney disease (CKD). The aims of this study were to assess whether zinc deficiency was related to increased renal excretion of zinc and to the progression of CKD.

METHODS

Plasma and 24-h urinary zinc levels, urinary electrolytes and uromodulin were measured in 108 CKD patients and 81 individuals without CKD. Serum creatinine values were collected for 3 years to calculate the yearly change in estimated glomerular filtration rate (eGFR). Multivariable regression analysis was performed to assess the association between baseline zinc levels and yearly change in eGFR.

RESULTS

CKD patients had lower circulating zinc levels and higher 24-h urinary zinc excretion than non-CKD participants (612.4 ± 425.9 versus 479.2 ± 293.0 µg/day; P = 0.02). Fractional excretion (FE) of zinc was higher and it significantly increased at more advanced CKD stages. Zinc FE was correlated negatively with 24-h urinary uromodulin excretion (r=-0.29; P < 0.01). Lower baseline plasma zinc levels were associated with a faster yearly decline of renal function in age, gender, diabetes and hypertension adjusted models, but this relationship was no longer significant when baseline eGFR or proteinuria were included.

CONCLUSIONS

Zinc levels are lower in CKD, and not compensated by reduced renal zinc excretion. The inverse association between urinary zinc excretion and uromodulin possibly points to an impaired tubular activity, which could partly account for zinc imbalance in CKD. These data suggest that zinc status is associated with renal function decline, but further studies elucidating the underlying mechanisms and the potential role of zinc supplements in CKD are needed.

Renal bioaccumulation of trace elements in urban and rural Sri Lankan populations: A preliminary study based on post mortem tissue analysis

INTRODUCTION

Environmental pollution, especially by toxic trace elements, is a global health concern. Heavy metals such as Cadmium (Cd), Arsenic (As) and Lead (Pb) are associated with numerous disorders and are considered by some as an aetiological factor for the Chronic Kidney Disease (CKDu1) epidemic in Sri Lanka. This study explores patterns of bioaccumulation of six trace elements in kidneys obtained during forensic autopsies from urban and rural regions in Sri Lanka.

METHODS

Kidney samples obtained from one urban district (n = 13) and three rural districts (n = 18) were lyophilized, microwave digested and profiled by ICP-MS techniques.

RESULTS AND DISCUSSION

The mean age of the sampled population was 47.9 ± 11.3 yrs. Median (IQR) for Cd, As, Pb, Cr, Zn and Se were, 14.67(8.04-22.47) μg/g, 0.44(0.29-0.56) μg/g, 0.11(0.07-0.30) μg/g, 0.15(0.1096-0.3274), 25.55(17.24-39.35) μg/g and 0.52(0.37-0.84) μg/g, respectively. Cd, Zn and Se levels were significantly higher (p < 0.05) among the urban samples compared to that of the rural group. Zn and Se levels were higher among younger age groups. As, Pb and Cr did not show any significant differences between the two cohorts nor any correlations with age.

CONCLUSION

This population-specific baseline study provides an insight into the differences in exposure to toxic trace elements and essential elements between urban and rural populations. Residents in CKDu affected rural districts did not appear to be at risk of toxic heavy metal exposure, however their renal bioaccumulation of nephroprotective essential elements was lower than urban residents.

Mechanotransduction Activity Facilitates Hair Cell Toxicity Caused by the Heavy Metal Cadmium

Hair cells are sensitive to many insults including environmental toxins such as heavy metals. We show here that cadmium can consistently kill hair cells of the zebrafish lateral line. Disrupting hair cell mechanotransduction genetically or pharmacologically significantly reduces the amount of hair cell death seen in response to cadmium, suggesting a role for mechanotransduction in this cell death process, possibly as a means for cadmium uptake into the cells. Likewise, when looking at multiple cilia-associated gene mutants that have previously been shown to be resistant to aminoglycoside-induced hair cell death, resistance to cadmium-induced hair cell death is only seen in those with mechanotransduction defects. In contrast to what was seen with mechanotransduction, significant protection was not consistently seen from other ions previously shown to compete for cadmium uptake into cells or tissue including zinc and copper. These results show that functional mechanotransduction activity is playing a significant role in cadmium-induced hair cell death.

Biological and molecular modifications induced by cadmium and arsenic during breast and prostate cancer development

Breast and prostate cancer are two of the most common malignancies worldwide. Both cancers can develop into hormone -dependent or -independent subtypes and are associated to environmental exposure in the context of an inherited predisposition. As and Cd have been linked to the onset of both cancers, with the exception of As, which lacks a definitive association with breast carcinogenesis. The two elements exert an opposite effect dependent on acute versus chronic exposure. High doses of As or Cd were shown to induce cell death in acute experimental exposure, while chronic exposure triggers cell proliferation and viability, which is no longer limited by telomere shortening and apoptosis. The chronically exposed cells also increase their invasion capacity and tumorigenic potential. At molecular level, malignant transformation is evidenced mainly by up-regulation of BCL-2, MMP-2, MMP-9, VIM, Snail, Twist, MT, MLH and down-regulation of Casp-3, PTEN, E-CAD, and BAX. The signaling pathways most commonly activated are KRAS, p53, TGF-β, TNF-α, WNT, NRF2 and AKT. This knowledge could potentially raise public awareness over the health risks faced by the human population living or working in a polluted environment and smokers. Human exposure to As and Cd should be minimize as much as possible. Healthcare policies targeting people belonging to these risk categories should include analysis of: DNA damage, oxidative stress, molecular alterations, and systemic level of heavy metals and of essential minerals. In this review, we present the literature regarding cellular and molecular alterations caused by exposure to As or Cd, focusing on the malignant transformation of normal epithelial cells after long-term intoxication with these two carcinogens.

The Source and Pathophysiologic Significance of Excreted Cadmium

In theory, the identification of the source of excreted cadmium (Cd) might elucidate the pathogenesis of Cd-induced chronic kidney disease (CKD). With that possibility in mind, we studied Thai subjects with low, moderate, and high Cd exposure. We measured urine concentrations of Cd, ([Cd]_u); N-acetyl-β-d-glucosaminidase, a marker of cellular damage ([NAG]_u); and β₂-microglobulin, an indicator of reabsorptive dysfunction ([β₂MG]_u). To relate excretion rates of these substances to existing nephron mass, we normalized the rates to creatinine clearance, an approximation of the glomerular filtration rate (GFR) (E_Cd/C_cr, E_NAG/C_cr, and E_β2MG/C_cr). To link the loss of intact nephrons to Cd-induced tubular injury, we examined linear and quadratic regressions of estimated GFR (eGFR) on E_Cd/C_cr, eGFR on E_NAG/C_cr, and E_NAG/C_cr on E_Cd/C_cr. Estimated GFR varied inversely with both ratios, and E_NAG/C_cr varied directly with E_Cd/C_cr. Linear and quadratic regressions of E_β2MG/C_cr on E_Cd/C_cr and E_NAG/C_cr were significant in moderate and high Cd-exposure groups. The association of E_NAG/C_cr with E_Cd/C_cr implies that both ratios depicted cellular damage per surviving nephron. Consequently, we infer that excreted Cd emanated from injured tubular cells, and we attribute the reduction of eGFR to the injury. We suggest that E_Cd/C_cr, E_NAG/C_cr, and eGFR were associated with one another because each parameter was determined by the tubular burden of Cd.

The Association Between Renal Tubular Dysfunction and Zinc Level in a Chinese Population Environmentally Exposed to Cadmium

Studies in vivo and in vitro have shown a protective effect of zinc against renal dysfunction caused by cadmium exposure. However, limited human data is available. In this study, we evaluated the association between renal tubular dysfunction and body zinc burden in a Chinese population exposed to cadmium. A total of 331 subjects (170 women and 161 men) living in control and cadmium-polluted area were included. Blood cadmium (BCd), urinary cadmium (UCd), serum zinc (SZn), zinc in hair (HZn), Zn/Cd ratio, and urinary β₂Microglobulin (UBMG) were measured. The median UCd, BCd, SZn, and HZn were 2.8 and 13.6 μg/g cr, 1.3 and 12.2 μg/L, 1.31 and 1.12 mg/L, and 0.14 and 0.12 mg/g in subjects living in control and polluted areas. The UBMG level of subjects living in the polluted area was significantly higher than that of the control (0.27 vs 0.11 mg/g cr, p < 0.01). SZn, HZn, and Zn/Cd ratios were negatively correlated with UBMG (p < 0.05 or 0.01). Subjects with high SZn concentrations (≥ 1.62 mg/L) had reduced risks of elevated UBMG [(odds ratio (OR) = 0.26, 95% confidence interval (CI) 0.07-0.99)] after controlling for multiple covariates compared with those with lower zinc levels. A similar result was observed in subjects with high HZn (OR = 0.09, 95% CI 0.02-0.48). The ORs of the second, third, and fourth quartiles of Zn/Cd ratio were 0.40 (95% CI 0.19-0.84), 0.14 (95% CI 0.06-0.37), and 0.01 (95% CI 0.02-0.18) for renal dysfunction compared with those of the first quartile, respectively. For those subjects with high level of UCd, high level of SZn and HZn also had reduced risks of elevated UBMG. The results of the present study show that high zinc body burden is associated with a decrease risk of renal tubular dysfunction induced by cadmium. Zinc nutritional status should be considered in evaluating cadmium-induced renal damage.

Effect of tramadol addiction alone and its co-abuse with cannabis on urinary excretion of Copper, Zinc, and Calcium among Egyptian addicts

BACKGROUND

The use of illicit drugs has become a worldwide health problem. Substances with the potential to be abused may have direct or indirect effects on physiologic mechanisms that lead to organ system dysfunction and diseases.

OBJECTIVE

The present study aims to investigate the structural and reabsorption integrity of the nephron among Egyptian addicts of tramadol alone and coabused with cannabis.

METHODS

Sixty-five males were included in the study, they were classified into control group (G1=19), tramadol addicts group (G2=18), and tramadol coabused with cannabis addicts group (G3=28). Parameters investigated for structural integrity were urinary levels ofleucineaminopeptidase and N-acetyl-β-D-glucosaminidase, and urinary parameters for reabsorption integrity were levels of copper and zinc as well as calcium, also urinary creatinine was measured. In addition, urinary levels of tramadol and tetrahydrocannabinol were estimated.

RESULTS

Among the two addicted groups, all measured parameters were not significantly different in comparison with the control group except for urinary calcium excretion which was found to be significantly increased among the two addicted groups.

CONCLUSION

Both tramadol addiction alone or coabused with cannabis causes increased urinary excretion of calcium, indicating reabsorption dysfunction of calcium without affecting structural integrity along the nephron.

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.

Dietary Cadmium Intake and Its Effects on Kidneys

Cadmium (Cd) is a food-chain contaminant that has high rates of soil-to-plant transference. This phenomenon makes dietary Cd intake unavoidable. Although long-term Cd intake impacts many organ systems, the kidney has long been considered to be a critical target of its toxicity. This review addresses how measurements of Cd intake levels and its effects on kidneys have traditionally been made. These measurements underpin the derivation of our current toxicity threshold limit and tolerable intake levels for Cd. The metal transporters that mediate absorption of Cd in the gastrointestinal tract are summarized together with glomerular filtration of Cd and its sequestration by the kidneys. The contribution of age differences, gender, and smoking status to Cd accumulation in lungs, liver, and kidneys are highlighted. The basis for use of urinary Cd excretion to reflect body burden is discussed together with the use of urinary N-acetyl-β-d-glucosaminidase (NAG) and β2-microglobulin (β2-MG) levels to quantify its toxicity. The associations of Cd with the development of chronic kidney disease and hypertension, reduced weight gain, and zinc reabsorption are highlighted. In addition, the review addresses how urinary Cd threshold levels have been derived from human population data and their utility as a warning sign of impending kidney malfunction.

Chronic exposure to low-level cadmium induced zinc-copper dysregulation

BACKGROUND AND OBJECTIVES

Exposure to cadmium (Cd) has been associated with aberrant zinc and copper homeostasis. This study investigated if Cd exposure impairs renal reabsorption of metals.

METHODS

Renal tubular reabsorption of metals were calculated from urine to serum metal ratios and analyzed for an independent association with Cd exposure levels, using data from 100 men and 100 women, aged 16-60 years.

RESULTS

The smoking prevalence was 30% in men and 0% in women. The male and female means (SD) for urine Cd were 0.54 (0.43) and 0.62 (0.43) μg/g creatinine. The mean (SD) for fractional zinc reabsorption was 77.2 (23) % in men and 87.7 (13.3) % in women, while the copper reabsorption was 100% in both men and women. Lower zinc reabsorption levels were associated with higher Cd exposure (P<0.001), higher serum copper to zinc ratios (P=0.007) and higher tubular impairment levels (P=0.024). Reduced zinc reabsorption was particularly severe in smokers as those with high Cd exposure had 44.9% and 37.2% (P<0.001) lower zinc reabsorption than those with low and moderate exposures. The mean zinc reabsorption in male non-smokers with high Cd exposure was 25.8% (P<0.001) and 18.2% (P=0.003) lower than those with low and moderate exposures, while the corresponding figure for female non-smokers was 17% (P<0.001), and 12.8% (P=0.013), respectively.

CONCLUSIONS

This is the first report demonstrating Cd-dose dependent reduction in renal zinc reabsorption and high serum copper to zinc ratios.

Environmental toxin-induced acute kidney injury

Human beings are exposed to various potentially toxic agents and conditions in their natural and occupational environments. The kidney, due to its concentrating ability and excretory function, is highly vulnerable to the effects of environmental toxins. Identifying the precise cause and mechanisms of environmentally induced renal injury remains a challenge for which various scientific disciplines need to be involved. Investigations in this field are confronted with the apparent infinite types of toxins, their mutual interaction, handling/metabolization by the body, ways of exposure, etc. Although interdisciplinary efforts and persistence are required to identify, mechanistically unravel and tackle environmental toxin-induced pathologies, research eventually pays off in ameliorated working/living conditions and development of preventive/therapeutic strategies. This review was compiled to particularly emphasize the need for a maintained awareness of environmental threats in general and those targeting the kidney. Different mechanisms of renal toxicity are illustrated and discussed, thereby focusing on three types of environmental toxins, namely aristolochic acid, melamine and heavy metals.

Chronic Kidney Disease and Exposure to Nephrotoxic Metals

Chronic kidney disease (CKD) is a common progressive disease that is typically characterized by the permanent loss of functional nephrons. As injured nephrons become sclerotic and die, the remaining healthy nephrons undergo numerous structural, molecular, and functional changes in an attempt to compensate for the loss of diseased nephrons. These compensatory changes enable the kidney to maintain fluid and solute homeostasis until approximately 75% of nephrons are lost. As CKD continues to progress, glomerular filtration rate decreases, and remaining nephrons are unable to effectively eliminate metabolic wastes and environmental toxicants from the body. This inability may enhance mortality and/or morbidity of an individual. Environmental toxicants of particular concern are arsenic, cadmium, lead, and mercury. Since these metals are present throughout the environment and exposure to one or more of these metals is unavoidable, it is important that the way in which these metals are handled by target organs in normal and disease states is understood completely.

Urinary metals in a spontaneous canine model of calcium oxalate urolithiasis

Calcium oxalate urolithiasis is a common and painful condition in people. The pathogenesis of this disease is complex and poorly understood. Laboratory animal and in vitro studies have demonstrated an effect of multiple trace metals in the crystallization process, and studies in humans have reported relationships between urinary metal concentrations and stone risk. Dogs are a spontaneous model of calcium oxalate urolithiasis, and the metal content of canine calcium oxalate stones mirrors that of human stones. The aim of this study was to test for a relationship between urinary metals and calcium oxalate urolithiasis in dogs. We hypothesized that urinary metals would differ between dogs with and without calcium oxalate urolithiasis. Urine from 122 dogs (71 cases and 51 stone-free controls) was analyzed for calcium and 12 other metals. The cases had higher urinary calcium, copper, iron, and vanadium and lower urinary cobalt. Higher urinary vanadium in the cases was associated with being fed a therapeutic stone-prevention diet. Urinary calcium had a strong positive correlation with strontium and moderate positive correlations with chromium, nickel, and zinc. The results of this study complement the findings of similar human studies and suggest a potential role of trace metals in calcium oxalate urolithiasis. Further investigation into how trace metals may affect stone formation is warranted.

Targeting eIF5A Hypusination Prevents Anoxic Cell Death through Mitochondrial Silencing and Improves Kidney Transplant Outcome

The eukaryotic initiation factor 5A (eIF5A), which is highly conserved throughout evolution, has the unique characteristic of post-translational activation through hypusination. This modification is catalyzed by two enzymatic steps involving deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Notably, eIF5A may be involved in regulating the lifespan of Drosophila during long-term hypoxia. Therefore, we investigated the possibility of a link between eIF5A hypusination and cellular resistance to hypoxia/anoxia. Pharmacologic targeting of DHPS by N1-guanyl-1,7-diaminoheptane (GC7) or RNA interference-mediated inhibition of DHPS or DOHH induced tolerance to anoxia in immortalized mouse renal proximal cells. Furthermore, GC7 treatment of cells reversibly induced a metabolic shift toward glycolysis as well as mitochondrial remodeling and led to downregulated expression and activity of respiratory chain complexes, features characteristic of mitochondrial silencing. GC7 treatment also attenuated anoxia-induced generation of reactive oxygen species in these cells and in normoxic conditions, decreased the mitochondrial oxygen consumption rate of cultured cells and mice. In rats, intraperitoneal injection of GC7 substantially reduced renal levels of hypusinated eIF5A and protected against ischemia-reperfusion-induced renal injury. Finally, in the preclinical pig kidney transplant model, intravenous injection of GC7 before kidney removal significantly improved graft function recovery and late graft function and reduced interstitial fibrosis after transplant. This unconventional signaling pathway offers an innovative therapeutic target for treating hypoxic-ischemic human diseases and organ transplantation.

Iron transport in the kidney: implications for physiology and cadmium nephrotoxicity

The kidney has recently emerged as an organ with a significant role in systemic iron (Fe) homeostasis. Substantial amounts of Fe are filtered by the kidney, which have to be reabsorbed to prevent Fe deficiency. Accordingly Fe transporters and receptors for protein-bound Fe are expressed in the nephron that may also function as entry pathways for toxic metals, such as cadmium (Cd), by way of "ionic and molecular mimicry". Similarities, but also differences in handling of Cd by these transport routes offer rationales for the propensity of the kidney to develop Cd toxicity. This critical review provides a comprehensive update on Fe transport by the kidney and its relevance for physiology and Cd nephrotoxicity. Based on quantitative considerations, we have also estimated the in vivo relevance of the described transport pathways for physiology and toxicology. Under physiological conditions all segments of the kidney tubules are likely to utilize Fe for cellular Fe requiring processes for metabolic purposes and also to contribute to reabsorption of free and bound forms of Fe into the circulation. But Cd entering tubule cells disrupts metabolic pathways and is unable to exit. Furthermore, our quantitative analyses contest established models linking chronic Cd nephrotoxicity to proximal tubular uptake of metallothionein-bound Cd. Hence, Fe transport by the kidney may be beneficial by preventing losses from the body. But increased uptake of Fe or Cd that cannot exit tubule cells may lead to kidney injury, and Fe deficiency may facilitate renal Cd uptake.

The Effect of Exposure to Cd and Pb in the Form of a Drinking Water or Feed on the Accumulation and Distribution of These Metals in the Organs of Growing Wistar Rats

The degree of accumulation and distribution of Cd and Pb in the organs of young animals compared to the amount taken in with water or feed have not been thoroughly investigated yet. The experiment aimed to verify whether the source of toxic metals (feed, drinking water) administered to growing rats orally has an influence on the degree of accumulation of Cd and Pb in the organs (brain, spleen, lungs, heart, liver and kidneys). The rats received Cd and/or Pb respectively in the amount of 7 mg and/or 50 mg per 1 kg of feed or per 1 L of distilled water. The rats' organs accumulated in total about 0.5 % Cd and about 0.71 % Pb consumed with water and about 0.46 % Cd and about 0.63 % Pb taken in with feed. More than 60 % of Cd and more than 70 % of Pb absorbed by the studied organs was accumulated in the liver, and more than 30 % of Cd and 26-29 % of Pb in the kidneys and less than 1 % in other organs. The relationship between the distribution percentage of Cd in the studied organs can be presented as: liver > kidneys > brain > lungs > heart > spleen. The relationship between the distribution percentage of Pb can be presented as: liver > kidneys > brain > spleen > heart > lungs. Significantly (P < 0.05), more Cd and Pb were accumulated in total in the organs of rats receiving the metals in drinking water.

Zinc Intake Is Associated with Lower Cadmium Burden in U.S. Adults

BACKGROUND

Cadmium is a toxic transition metal whose absorption and accumulation might depend on zinc intake.

OBJECTIVE

We sought to determine whether zinc intake and serum zinc would be inversely associated with cadmium exposure.

METHODS

This study used data from NHANES 2003-2012, from which there were 6678 and 6488 participants with urinary and blood cadmium data, respectively, and 1195 participants with serum zinc data. Mean blood and urinary cadmium were reported by quintiles of zinc intake and by the dose and duration of zinc supplement use. The associations between zinc intake from diet and supplements, serum zinc, and blood and urinary cadmium were determined using multiple regression. Analyses were adjusted for age, body mass index, race/ethnicity, gender, income-to-poverty ratio, education, smoking status, and mean intakes of energy, calcium, and iron.

RESULTS

Urinary cadmium concentrations were 0.04 μg/g creatinine lower among participants in the highest compared with lowest quintile of total zinc intake (P-trend = 0.0041). Zinc supplement dose and duration were inversely associated with blood cadmium (P = 0.0372) and serum zinc (P-trend = 0.0017), respectively. In adjusted regression models, a 10% increase in total zinc intake corresponded to a predicted decrease in blood cadmium of 0.42% (95% CI: -0.79%, -0.06%; P = 0.0260) and in urinary cadmium of 0.42% (95% CI: -0.81%, -0.04%; P = 0.0340). A 10% increase in serum zinc was associated with a predicted 1.99% (95% CI: -3.17%, -0.81%; P = 0.0012) decrease in blood cadmium and a predicted 4.09% (95% CI: 2.14%, 6.04%, P = 0.0001) increase in urinary cadmium.

CONCLUSIONS

Dietary and serum zinc in US adults are associated with cadmium exposure, presumably by influencing the absorption and accumulation of cadmium. Whether the degree of reduction in cadmium exposure from greater zinc intake and status is causal or relevant from a public health perspective needs further investigation.

Cadmium transporters in the kidney and cadmium-induced nephrotoxicity

Among the organs in which the environmental pollutant cadmium causes toxicity, the kidney has gained the most attention in recent years. Numerous studies have sought to unravel the exact pathways by which cadmium enters the renal epithelial cells and the mechanisms by which it causes toxicity in the kidney. The purpose of this review is to present the progress made on the mechanisms of cadmium transport in the kidney and the role of transporter proteins in cadmium-induced nephrotoxicity.

Cumulative rate and distribution of Cd and Pb in the organs of adult male Wistar rats during oral exposure

The degree of accumulation of Cd and Pb in the brains, spleens, lungs, hearts, livers and kidneys of adult Wistar rats was compared both for separate (Cd or Pb) and combined (Cd+Pb) oral exposure. In addition, the metals were administered either with liquids or with solid feed. Rats were exposed to low doses of metals (7mg Cd and 50mg Pb/kg feed or L of distilled water) over 6 or 12 weeks. In total the organs of rats accumulated about 0.3-0.5% Cd and 0.4-0.6% Pb supplied with food or drink. The presented studies demonstrated that the distribution of Cd and Pb in the organs is affected by: the type of exposure (separate or combined), the source of metals (feed or drinks) and the duration of exposure. It was found that simultaneous exposure to low doses of Cd and Pb supplied with food is much more hazardous than exposure to such metals supplied with water.

Accumulation of heme oxygenase-1 (HSP32) in Xenopus laevis A6 kidney epithelial cells treated with sodium arsenite, cadmium chloride or proteasomal inhibitors

The present study examined the effect of sodium arsenite, cadmium chloride, heat shock and the proteasomal inhibitors MG132, withaferin A and celastrol on heme oxygenase-1 (HO-1; also known as HSP32) accumulation in Xenopus laevis A6 kidney epithelial cells. Immunoblot analysis revealed that HO-1 accumulation was not induced by heat shock but was enhanced by sodium arsenite and cadmium chloride in a dose- and time-dependent fashion. Immunocytochemistry revealed that these metals induced HO-1 accumulation in a granular pattern primarily in the cytoplasm. Additionally, in 20% of the cells arsenite induced the formation of large HO-1-containing perinuclear structures. In cells recovering from sodium arsenite or cadmium chloride treatment, HO-1 accumulation initially increased to a maximum at 12h followed by a 50% reduction at 48 h. This initial increase in HO-1 levels was likely the result of new synthesis as it was inhibited by cycloheximide. Interestingly, treatment of cells with a mild heat shock enhanced HO-1 accumulation induced by low concentrations of sodium arsenite and cadmium chloride. Finally, we determined that HO-1 accumulation was induced in A6 cells by the proteasomal inhibitors, MG132, withaferin A and celastrol. An examination of heavy metal and proteasomal inhibitor-induced HO-1 accumulation in amphibians is of importance given the presence of toxic heavy metals in aquatic habitats.

The RPTEC/TERT1 cell line models key renal cell responses to the environmental toxicants, benzo[a]pyrene and cadmium

We have characterized initial canonical responses to two environmental toxicants, cadmium (Cd) and benzo[a]pyrene (B[a]P), in a novel in vitro model derived from renal proximal tubule epithelial cells (RPTEC) of a healthy human donor. The RPTEC/TERT1 cell line has been immortalized using the human telomerase reverse transcriptase (hTERT) subunit only and does not exhibit chromosomal abnormalities. RPTEC/TERT1 cells were exposed to single-compound and binary mixtures of Cd and B[a]P, known or suspected renal toxicants respectively. Cells exhibited cytotoxicity to concentrations of B[a]P and Cd as low as 1 nm and 3 μM, respectively. RPTEC/TERT1 cells exhibited compound-specific gene expression responses when exposed to 0.01-1 μM B[a]P and 0.1-10 μM Cd. A significant increase in the expression of genes coding for B[a]P metabolizing enzymes (CYP1A1, CYP1B1) occurred in a dose and time dependent manner at 3, 6, and 24 h post exposure. Likewise, a significant increase in the heavy metal responsive gene MT2A was observed following exposure to Cd. The EROD activity assay confirmed significant increases in CYP1(A/B) activity after 24 h of exposure to B[a]P which was not affected by the presence of Cd. Co-exposure to low concentrations of Cd and B[a]P were consistent with changes in gene expression as seen with single-compound exposures. These experiments are the first to provide information regarding toxicological responses in the RPTEC/TERT1 cell line that model those of the target tissue. We conclude that these cells can provide a useful tool for future toxicological studies.

Enhanced HSP30 and HSP70 accumulation in Xenopus cells subjected to concurrent sodium arsenite and cadmium chloride stress

Heat shock proteins (HSPs) are molecular chaperones that aid in protein folding, translocation and in preventing stress-induced protein aggregation. The present study examined the effect of simultaneous sodium arsenite and cadmium chloride treatment on the pattern of HSP30 and HSP70 accumulation in A6 kidney epithelial cells of the frog, Xenopus laevis. Immunoblot analysis revealed that HSP30 and HSP70 accumulation in concurrent stressor treatments were significantly higher than the sum of HSP30 or HSP70 accumulation in individual treatments. This finding suggested a synergistic action between sodium arsenite and cadmium chloride. KNK437 inhibitor studies indicated that the combined stressor-induced accumulation of HSPs may be regulated, at least in part, at the level of transcription. Immunocytochemistry revealed that simultaneous treatment of cells with the two stressors induced HSP30 accumulation primarily in the cytoplasm in a punctate pattern with some dysregulation of F-actin structure. Increased ubiquitinated protein accumulation was observed with combined sodium arsenite and cadmium chloride treatment compared to individual stressors suggesting an impairment of the ubiquitin proteasome degradation system. The addition of a mild heat shock further enhanced the accumulation of HSP30 and HSP70 in response to relatively low concentrations of sodium arsenite plus cadmium chloride.

Tight junction proteins and oxidative stress in heavy metals-induced nephrotoxicity

Kidney is a target organ for heavy metals. They accumulate in several segments of the nephron and cause profound alterations in morphology and function. Acute intoxication frequently causes acute renal failure. The effects of chronic exposure have not been fully disclosed. In recent years increasing awareness of the consequences of their presence in the kidney has evolved. In this review we focus on the alterations induced by heavy metals on the intercellular junctions of the kidney. We describe that in addition to the proximal tubule, which has been recognized as the main site of accumulation and injury, other segments of the nephron, such as glomeruli, vessels, and distal nephron, show also deleterious effects. We also emphasize the participation of oxidative stress as a relevant component of the renal damage induced by heavy metals and the beneficial effect that some antioxidant drugs, such as vitamin A (all-trans-retinoic acid) and vitamin E (α-tocopherol), depict on the morphological and functional alterations induced by heavy metals.

Roles of ZIP8, ZIP14, and DMT1 in transport of cadmium and manganese in mouse kidney proximal tubule cells

Chronic exposure to cadmium causes preferential accumulation of cadmium in the kidney, leading to nephrotoxicity. In the process of renal cadmium accumulation, the cadmium bound to a low-molecular-weight metal-binding protein, metallothionein, has been considered to play an important role in reabsorption by epithelial cells of proximal tubules in the kidney. However, the role and mechanism of the transport of Cd(2+) ions in proximal tubule cells remain unclear. Zinc transporters such as Zrt, Irt-related protein 8 (ZIP8) and ZIP14, and divalent metal transporter 1 (DMT1) have been reported to have affinities for Cd(2+) and Mn(2+). To examine the roles of these metal transporters in the absorption of luminal Cd(2+) and Mn(2+) into proximal tubule cells, we utilized a cell culture system, in which apical and basolateral transport of metals can be separately examined. The uptake of Cd(2+) and Mn(2+) from the apical side of proximal tubule cells was inhibited by simultaneous addition of Mn(2+) and Cd(2+), respectively. The knockdown of ZIP8, ZIP14 or DMT1 by siRNA transfection significantly reduced the uptake of Cd(2+) and Mn(2+) from the apical membrane. The excretion of Cd(2+) and Mn(2+) was detected predominantly in the apical side of the proximal tubule cells. In situ hybridization of these transporters revealed that ZIP8 and ZIP14 are highly expressed in the proximal tubules of the outer stripe of the outer medulla. These results suggest that ZIP8 and ZIP14 expressed in the S3 segment of proximal tubules play significant roles in the absorption of Cd(2+) and Mn(2+) in the kidney.

Acute temperature and cadmium stress response characterization of small heat shock protein 27 in large yellow croaker, Larimichthys crocea

Small heat shock proteins (sHSPs) are a group of molecular chaperones and play a crucial role in cell response to various stresses. In this study, we cloned and sequenced a small heat shock protein 27 (LcHSP27) cDNA from large yellow croaker, Larimichthys crocea. The full-length cDNA of LcHSP27 was 1227 bp, including a 5'-terminal untranslated region (UTR) of 54 bp, a 3'-terminal UTR of 561 bp and an open reading frame (ORF) of 612 bp encoding a polypeptide of 203 amino acids. Three conserved phosphorylation sites of serine were identified in the deduced LcHSP27 amino acid sequence at positions 15, 91 and 95 respectively, and a typical α-crystallin domain was at positions 96-193. Phylogenetic analysis revealed that LcHSP27 was categorized together with the HSP27 obtained from other fish. And a closer phylogenetic relationship of HSP27 was found with HSP22, then HSP30. Quantitative real-time reverse transcription PCR (qRT-PCR) analysis indicated the strongest expression of LcHSP27 in heart. However, expression of LcHSP27 in other examined tissues including muscle, brain, liver, spleen, kidney, gill, and blood was very weak. The impact of temperature and cadmium (Cd(2+)) stress on LcHSP27 expression was tested in liver and brain. The results showed that the levels of LcHSP27 expression increased significantly after low temperature (19°C) and high temperature (27°C and 31°C) stress both in liver and brain. And low temperature stress induced a higher LcHSP27 expression in liver. More important, LcHSP27 expression showed a dramatic up-regulation after a combined stress of temperature and cadmium (p<0.05). These results reveal that HSP27 may play an important role in the large yellow croaker response to temperature and cadmium stress.

Low doses of cadmium chloride and methallothionein-1-bound cadmium display different accumulation kinetics and induce different genes in cells of the human nephron

Background/Aims

The present study was conducted to investigate the renal tubular handling of inorganic cadmium (Cd²⁺) by exposing primary human tubular cell cultures to physiologically relevant doses of cadmium chloride (CdCl₂). Furthermore, the cellular accumulation of Cd²⁺ was compared to that of metallothionein-1-bound Cd (Cd7MT-1). Finally, this study aimed to investigate the effect of the accumulation of Cd (both Cd²⁺ and Cd7MT-1) in renal cells on the expression of genes relevant to nephrotoxic processes.

Methods

Cd concentration was measured using atomic absorption spectrometry. mRNA expression was evaluated by quantitative real-time RT-PCR.

Results

Cd²⁺ accumulated into human tubular cells in a concentration- and time-dependent way. Furthermore, cellular accumulation of Cd²⁺ was different from the cellular accumulation of Cd7MT-1, indicative for different uptake routes. Finally, mRNA expression of the genes encoding the anti-oxidative proteins metallothionein-1 (MT-1) and heme-oxygenase-1 (HO-1) as well as the pro-apoptotic Bcl-2-associated X protein (Bax) were upregulated by CdCl₂ and not by Cd7MT1.

Conclusion

In the presence of physiologically relevant Cd concentrations, tubular accumulation of the element in its inorganic form is different from that of Cd7MT-1. Furthermore, the tubular accumulation of inorganic Cd induces mRNA expression of genes of which the protein products may play a role in Cd-associated renal toxicity.

Cadmium Toxicity Revisited: Focus on Oxidative Stress Induction and Interactions with Zinc and Magnesium

Discovered in late 1817, cadmium is currently one of the most important occupational and environmental pollutants. It is associated with renal, neurological, skeletal and other toxic effects, including reproductive toxicity, genotoxicity, and carcinogenicity. There is still much to find out about its mechanisms of action, biomarkers of critical effects, and ways to reduce health risks. At present, there is no clinically efficient agent to treat cadmium poisoning due to predominantly intracellular location of cadmium ions. This article gives a brief review of cadmium-induced oxidative stress and its interactions with essential elements zinc and magnesium as relevant mechanisms of cadmium toxicity. It draws on available literature data and our own results, which indicate that dietary supplementation of either essential element has beneficial effect under condition of cadmium exposure. We have also tackled the reasons why magnesium addition prevails over zinc and discussed the protective role of magnesium during cadmium exposure. These findings could help to solve the problem of prophylaxis and therapy of increased cadmium body burden.

Cadmium and transport of ions and substances across cell membranes and epithelia

Toxic metals such as cadmium (Cd(2+)) pose serious risks to human health. However, even though the importance of Cd(2+) as environmental health hazards is now widely appreciated, the specific mechanisms by which it produces its adverse effects have yet to be fully elucidated. Cd(2+) is known to enter cells, it binds and interacts with a multitude of molecules, it may indirectly induce oxidative stress and interfere with gene expression and repair of DNA. It also interacts with transport across cell membranes and epithelia and may therefore disturb the cell's homeostasis and function. Interaction with epithelial transport, especially in the kidney and the liver, may have serious consequences in general health. A lot of research still needs to be done to understand the exact way in which Cd(2+) interferes with these transport phenomena. It is not always clear whether Cd(2+) has primary or secondary effects on cell membrane transport. In the present review we try to summarize the work that has been done up to now and to critically discuss the relevance of the experimental work in vitro with respect to the in vivo situation.

Potential mechanisms involved in the absorptive transport of cadmium in isolated perfused rabbit renal proximal tubules

Lumen-to-cell transport, cellular accumulation, and toxicity of cadmium as ionic cadmium (Cd(2+)) or as the L-cysteine (Cys) or D,L-homocysteine (Hcy) S-conjugate of cadmium (Cys-S-Cd-S-Cys, Hcy-S-Cd-S-Hcy) were studied in isolated, perfused rabbit proximal tubular segments. When Cd(2+) (0.73 microM) or Cys-S-Cd-S-Cys (0.73 microM) was perfused through the lumen of S(2) segments of the proximal tubule, no visual evidence of cellular pathological changes was detected during 30 min of study. Cd(2+)-transport was temperature-dependent and was inhibited by Fe(2+), Zn(2+), and elevated concentrations of Ca(2+). Luminal uptake of Cys-S-Cd-S-Cys was also temperature-dependent and was inhibited by the amino acids L-cystine and L-arginine, while stimulated by L-methionine. Neither L-aspartate, L-glutamate, the synthetic dipeptide, Gly-Sar nor Zn(2+) had any effect on the rate of Cys-S-Cd-S-Cys transport.

CONCLUSIONS

When delivered to the luminal compartment, Cd(2+) appears to be capable of utilizing certain transporter(s) of Zn(2+) and some transport systems sensitive to Ca(2+) and Fe(2+). In addition, Cys-S-Cd-S-Cys and Hcy-S-Cd-S-Hcy appear to be transportable substrates of one or more amino acid transporters participating in luminal absorption of the amino acid L-cystine (such as system b(0,+)). These findings indicate that multiple mechanisms could be involved in the luminal absorption of cadmium (Cd) in proximal tubular segments depending on its form. These findings provide a focus for future studies of Cd absorption in the proximal tubule.

Iron transport and the kidney

Over the last decade there has been an explosion in our understanding of the proteins that modulate iron homeostasis. Much research has focused on the tissues classically associated with iron absorption and metabolism, namely the duodenum, the liver and the reticulo-endothelial system. Expression profiling has highlighted that many of the components associated with iron homeostasis, are also expressed in tissues which hitherto have received relatively little attention in terms of iron research. These include, testis, lung and, the subject of this review, the kidney. The latter is of great interest because other than a source of erythropoietin, a function that is of course of utmost importance for iron homeostasis, the kidney is regarded as more or less irrelevant in terms of iron handling. However, the fact that the kidneys of our favourite subjects, namely rats, mice and humans, contain many if not all of the proteins that are central to iron balance, that in some cases are expressed in considerable amounts, implies that the kidney handles iron in some way that has demanded evolutionary conservation and therefore is likely to be of importance. This review will document the evidence of iron transporter expression in the kidney, detail data showing the expression of other proteins associated with iron homeostasis and discuss the relevance of renal iron transport to pathophysiological states. Based on these data, a hypothetical model of renal iron handling will be presented.

Acute effect of cadmium treatment on the kidney of rats: biochemical and ultrastructural studies

The present study was designed to explore the nephrotoxic effect of intraperitoneal acute administration of CdCl2 (2.5 and 5 mg kg(-1) b.w.) in rats. A number of toxicological parameters in kidney were examined including malondialdehyde (MDA) and endogenous antioxidants, e.g., catalase (CAT), superoxide dismutase (SOD) and Glutathione Peroxidase (GPx). The parameters that indicate tissue damage such as serum urea and creatinine were also determined, along with the ultrastructural changes of kidneys. A correlation was found between the dose and the intensity of changes. The results demonstrated that cadmium administration increased renal MDA but decreased CAT, SOD and GPx activities. In parallel, serum creatinine and urea elevated. The glomerular ultrastructural changes observed in cadmium-treated rats included narrowing of the capillary lumen and swelling of the capillary endothelium with occasional loss of fenestrae. The mesangium was wide with increased mesangial matrix. Loss of homogenous appearance of basement membrane displaying ondulation and thickening in many areas and deterioration of the slit membrane structures formed by the podocytes were also noted. The effects of cadmium on proximal cell ultrastructure were focal loss of brush border, nuclear membrane damage, chromatin condensation, swelling of the mitochondria with regression of mitochondrial cristae, degranulation and disintegration of protein-synthesizing structures such as rough endoplasmic reticulum, increased number of lysosomes and ultimately cell death.

FK506, a Calcineurin Inhibitor, Prevents Cadmium-Induced Testicular Toxicity in Mice

Cadmium, a ubiquitous environmental contaminant, damages several major organs in humans and other mammals. The molecular mechanisms for damage are not known. At high doses (5 mg/kg cadmium chloride or higher), testicular damage in mice, rats, and other rodents includes interstitial edema, hemorrhage, and changes in the seminiferous tubules affecting spermatogenesis. Necrosis is evident by 48 h. The goal of this study was to fine map and identify the cdm gene, a gene that when mutated prevents cadmium-induced testicular toxicity in mouse strains with a mutation in this gene. A serine-threonine phosphatase, calcineurin (CN), subunit A, alpha isoform (Ppp3ca), was one of the seven candidates in the cdm region that was narrowed from 5.6 to 2.0 Mb on mouse chromosome 3. An inhibitor of CN, the immunosuppressant, FK506, prevented cadmium-induced testicular damage in five pathological categories, including vascular endothelial and seminiferous epithelial endpoints. Inductively coupled plasma-mass spectrometry revealed that FK506 protected without lowering the amount of cadmium in the testes. Ppp3ca(-/-) mice were investigated but were found to exhibit endogenous testicular abnormalities, making them an inappropriate model for determining whether the inactivation of the Ppp3ca gene would afford protection from cadmium-induced testicular toxicity. The protection afforded by FK506, found by the current study, indicated that CN is likely to be important in the mechanism of cadmium toxicity in the testis and possibly other organs.

ICP/OES application for assessing cadmium uptake (or toxicity) in glomerular cells: influence of extracellular calcium

The risks of metals for health are highlighted by their chemical stability and their persistence in the environment. Chronic exposure to low cadmium (Cd) concentrations results in renal dysfunction mainly. Cd has been regarded primarily as a renal tubular toxicant, but glomerular structures may also be affected. Since the cellular environment may influence metal toxicity, differences concerning Cd uptake and toxicity were evaluated according to calcium (Ca) medium concentrations. An optimized inductively coupled plasma emission spectrometry method (ICP/OES) was developed under defined conditions, as a selective analytical tool to determine cadmium uptake in glomerular mesangial cells. The performance characteristics of the analytical system were evaluated for both Cd and Ca by calibration (50 to 250 microg/L and 1 to 5 mg/L), linearity (r2 .9968 and .9943), limits of detection (1 microg/L and 0.1 mg/L) and quantitation (3 microg/L and 0.3 mg/L), accuracy with spiking, and repeatability (1.2 and 2.9%) with matrix matched standards. Total intracellular Cd content was significantly threefold lower in 0.175 mM Ca medium (Ca-free Eagle's minimum essential medium [EMEM] medium with 5% fetal bovine serum [FBS]) than in EMEM medium (1.8 mM Ca) with respectively 0.16 and 0.37 microg/mg proteins after 24 h of Cd (1 microM) exposure. Similar differences were obtained in cytotoxicity studies with a fourfold reduction in the mortality index (IC50). Complementary assays using Ca-spiked medium reinforced that Cd cytotoxicity and uptake were significantly dependent on the concentration of extracellular Ca. These findings suggest direct link between Cd uptake and toxicity, underlining the relevance of the analytical method.

Human glomerular mesangial IP15 cell line as a suitable model for in vitro cadmium cytotoxicity studies

Cadmium represents a major environmental pollutant that may induce severe damage, especially in the kidney where cadmium accumulates. While cadmium is known to severely impair renal tubular functions, glomerular structures are also potential targets. Owing to their contractile properties, glomerular mesangial cells play a major role in the control of glomerular hemodynamics and influence the ultrafiltration coefficient. Cell cultures provide alternative and fruitful models for study of in vitro toxicology. However, the use of primary human mesangial cell cultures is hampered by their limited survival span and their rapid dedifferentiation during passages. This study presents a human stable immortalized mesangial cell line, designated IP15. Cell characteristics were investigated by the detection of known mesangial markers, as well as their ability to contract in response to angiotensin II. IP15 cells were used to investigate cadmium uptake and morphological changes such as cell contraction and cytoskeleton protein expression. The IC(50) cytotoxicity index was obtained with 3.55 micromol/L using neutral red assay for 24 h. After cadmium exposure (1 micromol/L, determined as nonlethal concentration), 0.38 microg Cd/mg protein was internalized by the cells as evaluated by inductively coupled plasma optical emission spectrometry (ICP/OES). Cadmium induced a significant cell surface reduction that correlated with smooth-muscle alpha-actin disorganization. Thus, the IP15 cell line is a suitable model for study of in vitro cadmium cytotoxicity in mesangial cells and allows sufficient material to be obtained for future studies of the intracellular effects of cadmium exposure.

Manganese is highly effective in protecting cells from cadmium intoxication

Cadmium poisoning results in cell death. Although several intracellular pathways have been identified in this response, transport systems responsible for cadmium entry into cells remain poorly understood and controversial. Here, we analyzed the effects of several divalent cations on cadmium toxicity in different cell types. We found that zinc, previously reported as a protective agent against cadmium poisoning, is actually much less efficient than manganese. We show that manganese dramatically reduces cadmium intake, and that this is associated with the inhibition of our recently reported sustained activation of ERK, characteristic of cadmium intoxication. Finally, we show that this inhibition of cadmium entry and ERK-sustained activation perfectly correlates with a high cellular resistance to cadmium exposure. Our results, together with previously published data, support the idea that the yet to be characterized manganese transporter system(s) may be responsible for cadmium entry into cells.

In vivo protective effect of melatonin on cadmium-induced changes in redox balance and gene expression in rat hypothalamus and anterior pituitary

Cadmium (Cd) is widely used in industrial applications and is an important side contaminant of agricultural products. As an endocrine disruptor, Cd modifies pituitary hormone release. It has been shown that this metal causes oxidative stress in primary cultures of anterior pituitary cells. To examine whether Cd induces redox damage in the hypothalamic-pituitary axis in vivo and to evaluate the efficacy of the antioxidant molecule melatonin to prevent Cd activity, rats were exposed to Cd (5 p.p.m. in drinking water) with or without melatonin (3 microg/mL drinking water) for 1 month. In the anterior pituitary, Cd increased lipid peroxidation and mRNA levels for heme oxygenase-1 (HO-1) at both time intervals tested (09:00 and 01:00 hr, beginning of rest span and middle of activity span, respectively). Melatonin administration prevented the Cd-induced increase in both parameters. In the hypothalamus, Cd affected the levels of mRNA for HO-1 by decreasing it in the evening. Melatonin reduced hypothalamic HO-1 gene expression. Cd treatment augmented gene expression of nitric oxide synthase (NOS)1 and NOS2 in the pituitary whereas melatonin decreased it, impairing the activity of Cd. Exposure to Cd increased the levels of hypothalamic NOS1 mRNA at 09:00 hr and decreased the levels of NOS2 mRNA at 01:00 hr, with melatonin treatment preventing Cd effects. Cd treatment decreased plasma thyroid-stimulating hormone levels at both examined times, while melatonin reversed the effect of Cd at 09:00 hr and partially counteracted the effect at 01:00 hr. There were important variations between day and night in the expression of all the genes tested in both tissues. Melatonin treatment was effective reducing all examined effects of Cd, documenting its effectiveness to protect the rat hypothalamic-pituitary axis from the toxic metal effects.

Effects of cadmium exposure during pregnancy on trace elements in fetal rat liver and kidney

Female rats were exposed by intragastric administration with a cannula 1mg/kg/day or 10mg/kg/day CdCl2 for the 11 days from the 9th to 19th day of pregnancy, and the effects of Cd exposure on eight elements, Na, K, Ca, Mg, P, Fe, Zn, and Cu in fetal liver, kidney, brain, fetal membrane and placenta then examined. We found that: (1) although Cd was not detected in fetal kidney and brain, significant Cd accumulation was found in fetal liver, fetal membrane and placenta in the 10 mg/kg Cd group, (2) the Zn and Fe concentrations in fetal liver in the 10 mg/kg Cd group were significantly lower than those in the control group, but no difference was found in the placenta, (3) the Cu concentrations in the placenta, fetal membrane and liver in the 10 mg Cd groups were significantly lower than those in the control group, (4) Na/K ratio in the placenta and fetal kidney and the Ca concentration in the placenta in the 10 mg/kg Cd group were lower than those in the controls. These results suggest that Cd exposure inhibits Zn and Fe transportation from the placenta to fetus, as well as Cu, Ca, Na and K uptake and transportation across the placenta, possibly influencing fetal growth and metabolism.

Zinc and Cadmium Interactions in a Renal Cell Line Derived from Rabbit Proximal Tubule

BACKGROUND

The aim of this work was to characterize the relationship between zinc (Zn(2+)) and cadmium (Cd(2+)) and the toxic effects of Cd(2+) in immortalized renal proximal tubule cells RP1.

METHODS

An RP1 cell line was developed from primary cultures of microdissected S1 and S2. Uptakes of (65)Zn and (109)Cd and competitive experiments with Cd(2+) and Zn(2+) were performed and kinetic parameters were determined. Oxygen consumption, metallothionein synthesis, and necrotic and apoptotic phenomena were studied.

RESULTS

Kinetic parameters indicate that (65)Zn (Km = 71.8 +/- 10.6 microM) and (109)Cd (Km = 23.3 +/- 2.0 microM) were both transported by a saturable carrier-mediated process. Competition between Cd(2+) and Zn(2+) uptake was reciprocal. Cd(2+) induced an increase in necrosis and apoptosis, and a decrease in oxygen consumption, depending on Cd(2+) concentrations. Concomitant addition of Zn(2+) (10 microM) reduced the number of necrotic and apoptotic cells and maintained oxygen consumption at control levels. Cd(2+) alone, or in the presence of Zn(2+), increased metallothionein levels, whereas Zn(2+) alone did not.

CONCLUSION

Zn(2+) and Cd(2+) probably share the same transporter in the proximal tubule. Cd(2+) caused necrotic and apoptotic cell death. Cd(2+) toxicity may occur through an effect on the mitochondrial electron transport chain and not on metallothionein synthesis. Zn(2+) protects against the renal cell toxicity of Cd(2+).

Effect of heavy metals on, and handling by, the kidney

Heavy metals such as cadmium (Cd), mercury (Hg), lead (Pb), chromium (Cr) and platinum (Pt) are a major environmental and occupational hazard. Unfortunately, these non-essential elements are toxic at very low doses and non-biodegradable with a very long biological half-life. Thus, exposure to heavy metals is potentially harmful. Because of its ability to reabsorb and accumulate divalent metals, the kidney is the first target organ of heavy metal toxicity. The extent of renal damage by heavy metals depends on the nature, the dose, route and duration of exposure. Both acute and chronic intoxication have been demonstrated to cause nephropathies, with various levels of severity ranging from tubular dysfunctions like acquired Fanconi syndrome to severe renal failure leading occasionally to death. Very varied pathways are involved in uptake of heavy metals by the epithelium, depending on the form (free or bound) of the metal and the segment of the nephron where reabsorption occurs (proximal tubule, loop of Henle, distal tubule and terminal segments). In this review, we address the putative uptake pathways involved along the nephron, the mechanisms of intracellular sequestration and detoxification and the nephropathies caused by heavy metals. We also tackle the question of the possible therapeutic means of decreasing the toxic effect of heavy metals by increasing their urinary excretion without affecting the renal uptake of essential trace elements. We have chosen to focus mainly on Cd, Hg and Pb and on in vivo studies.