Cadmium and mercury accumulation in rat hepatocytes: interactions with other metal ions

DNA hypomethylation-associated transcriptional rewiring enables resistance to heavy metal mercury (Hg) stress in rice

Mercury (Hg) is an important hazardous pollutant that can cause phytotoxicity and harm human health through the food chain. Recently, rice (Oryza sativa L.) has been confirmed as a potential Hg bioaccumulator. Although the genetic and molecular mechanisms involved in heavy metal absorption and translocation in rice have been investigated for several heavy metals, Hg is largely neglected. Here, we analyzed one Hg-resistant line in rice (RHg) derived from a DNA methyltransferase-coding gene, OsMET1-2 heterozygous mutant. Compared with its isogenic wild-type (WT), RHg exhibited a significantly higher survival rate after Hg treatment, ameliorated oxidative damage, and lower Hg uptake and translocation. RNAseq-based comparative transcriptomic analysis identified 34 potential Hg resistance-related genes involved in phytohormone signaling, abiotic stress response, and zinc (Zn) transport. Importantly, the elevated expression of Hg resistance-related genes in RHg was highly correlated with DNA hypomethylation in their putative promoter regions. An ionomic analysis unraveled a negative correlation between Zn and Hg in roots. Moreover, Hg concentration was effectively decreased by exogenous application of Zn in Hg-stressed rice plants. Our findings indicate an epigenetic basis of Hg resistance and reveal an antagonistic relationship between Hg and Zn, providing new hints towards Hg detoxification in plants. ENVIRONMENTAL IMPLICATION: Mercury (Hg) as an important hazardous pollutant adversely impacts the environment and jeopardizes human health, due to its chronicity, transferability, persistence, bioaccumulation and toxicity. In this paper, we identified 34 potential genes that may significantly contribute to Hg resistance in rice. We find the expression of Hg resistance-related genes was highly correlated with DNA hypomethylation in their putative promoter regions. Our results also revealed an antagonistic relationship between Hg and Zinc (Zn), providing new hints towards Hg detoxification in plants. Together, findings of this study extend our current understanding of Hg tolerance in rice and are informative to breed seed non-accumulating rice cultivars.

More Effective Mobilization of Hg2+ from Human Serum Albumin Compared to Cd2+ by L-Cysteine at Near-Physiological Conditions

Although chronic low-level exposure to Hg²⁺ and Cd²⁺ causes human nephrotoxicity, the bioinorganic processes that deliver them to their target organs are poorly understood. Since the plasma protein human serum albumin (HSA) has distinct binding sites for these metal ions, we wanted to gain insight into these translocation processes and have employed size-exclusion chromatography coupled on-line to an inductively coupled plasma atomic emission spectrometer using phosphate-buffered saline mobile phases. When HSA 'labeled' with Hg²⁺ and Cd²⁺ (1:0.1:0.1) using 300 μM of L-methionine was analyzed, the co-elution of a single C, S, Cd, and Hg peak was observed, which implied the intact bis-metalated HSA complex. Since human plasma contains small molecular weight thiols and sulfur-containing metabolites, we analyzed the bis-metalated HSA complex with mobile phases containing 50-200 µM of L-cysteine (Cys), D,L-homocysteine (hCys), or glutathione (GSH), which provided insight into the comparative mobilization of each metal from their respective binding sites on HSA. Interestingly, 50 µM Cys, hCys, or GSH mobilized Hg²⁺ from its HSA binding site but only partially mobilized Cd²⁺ from its binding site. Since these findings were obtained at conditions simulating near-physiological conditions of plasma, they provide a feasible explanation for the higher 'mobility' of Hg²⁺ and its concomitant interaction with mammalian target organs compared to Cd²⁺. Furthermore, 50 µM Cys resulted in the co-elution of similar-sized Hg and Cd species, which provides a biomolecular explanation for the nephrotoxicity of Hg²⁺ and Cd²⁺.

Structural Characterization of Toxicologically Relevant Cd2+-L-Cysteine Complexes

The exposure of humans to Cd exerts adverse human health effects at low chronic exposure doses, but the underlying biomolecular mechanisms are incompletely understood. To gain insight into the toxicologically relevant chemistry of Cd²⁺ in the bloodstream, we employed an anion-exchange HPLC coupled to a flame atomic absorption spectrometer (FAAS) using a mobile phase of 100 mM NaCl with 5 mM Tris-buffer (pH 7.4) to resemble protein-free blood plasma. The injection of Cd²⁺ onto this HPLC-FAAS system was associated with the elution of a Cd peak that corresponded to [CdCl₃]^-/[CdCl₄]^2- complexes. The addition of 0.1-10 mM L-cysteine (Cys) to the mobile phase significantly affected the retention behavior of Cd²⁺, which was rationalized by the on-column formation of mixed CdCys_xCl_y complexes. From a toxicological point of view, the results obtained with 0.1 and 0.2 mM Cys were the most relevant because they resembled plasma concentrations. The corresponding Cd-containing (~30 μM) fractions were analyzed by X-ray absorption spectroscopy and revealed an increased sulfur coordination to Cd²⁺ when the Cys concentration was increased from 0.1 to 0.2 mM. The putative formation of these toxicologically relevant Cd species in blood plasma was implicated in the Cd uptake into target organs and underscores the notion that a better understanding of the metabolism of Cd in the bloodstream is critical to causally link human exposure with organ-based toxicological effects.

Heavy Metals Content in Selected Medicinal Plants Produced and Consumed in Serbia and Their Daily Intake in Herbal Infusions

The heavy metals content (HMs) was investigated in 14 different medicinal plants collected from the three regions in Central Serbia, Zlatar, Sokobanja, and Kopaonik. The concentrations of Cd, Cr, Ni, Hg and Pb were determined: Cd (<0.03-2.72 mg/kg); Cr (<0.08-12.1 mg/kg); Ni (<0.08-12.2 mg/kg); Pb (0.6-49.0 mg/kg); the Hg concentration was below the detection limit of 0.06 mg/kg in all samples. The daily intake of HMs due to ingestion of 200 mL of herbal infusion was in all cases below the recommended limit prescribed by the World Health Organization. The estimated daily intake values were below the values for the oral reference dose regulated by the U.S. Environmental Protection Agency (USA EPA). The target hazard quotient and hazard index for Cd, Cr Ni, and Pb were below 1. Nevertheless, due to the tendency of heavy metals to accumulate in the organism, attention should be paid to the daily intake of herbal infusion during long-term usage. Specifically, it is recommended to consume not more than one cup (200 mL) of infusion per day made from thyme (Mt. Zlatar) and blueberry (Mt. Kopaonik), and not more than two cups per day for other herbs.

Mechanisms underlying mercury detoxification in soil-plant systems after selenium application: a review

Feasible countermeasures to mitigate mercury (Hg) accumulation and its deleterious effects on crops are urgently needed worldwide. Selenium (Se) fertilizer application is a cost-effective strategy to reduce Hg concentrations, promote agro-environmental sustainability and food safety, and decrease the public health risk posed by Hg-contaminated soils and its accumulation in food crops. This holistic review focuses on the processes and detoxification mechanisms of Hg in whole soil-plant systems after Se application. The reduction of Hg bioavailability in soil, the formation of inert HgSe or/and HgSe-containing proteinaceous complexes in the rhizosphere and/or roots, and the reduction of plant root uptake and translocation of Hg in plant after Se application are systemically discussed. In addition, the positive responses in plant physiological and biochemical processes to Se application under Hg stress are presented to show the possible mechanisms for protecting the plant. However, application of high levels Se showed synergistic toxic effect with Hg and inhibited plant growth. The effectiveness of Se application methods, rates, and species on Hg detoxification is compared. This review provides a good approach for plant production in Hg-contaminated areas to meet food security demands and reduce the public health risk.

Kinetic mechanisms by which nickel alters the calcium (Ca2+) transport in intact rat liver

In the present work, the multiple-indicator dilution (MID) technique was used to investigate the kinetic mechanisms by which nickel (Ni²⁺) affects the calcium (Ca²⁺) transport in intact rat liver. ⁴⁵Ca²⁺ and extra- and intracellular space indicators were injected in livers perfused with 1 mM Ni²⁺, and the outflow profiles were analyzed by a mathematical model. For comparative purposes, the effects of norepinephrine were measured. The influence of Ni²⁺ on the cytosolic Ca²⁺ concentration ([Ca²⁺]_c) in human hepatoma Huh7 cells and on liver glycogen catabolism, a biological response sensitive to cellular Ca²⁺, was also evaluated. The estimated transfer coefficients of ⁴⁵Ca²⁺ transport indicated two mechanisms by which Ni²⁺ increases the [Ca²⁺]_c in liver under steady-state conditions: (1) an increase in the net efflux of Ca²⁺ from intracellular Ca²⁺ stores due to a stimulus of Ca²⁺ efflux to the cytosolic space along with a diminution of Ca²⁺ re-entry into the cellular Ca²⁺ stores; (2) a decrease in Ca²⁺ efflux from the cytosolic space to vascular space, minimizing Ca²⁺ loss. Glycogen catabolism activated by Ni²⁺ was transient contrasting with the sustained activation induced by norepinephrine. Ni²⁺ caused a partial reduction in the norepinephrine-induced stimulation in the [Ca²⁺]_c in Huh7 cells. Our data revealed that the kinetic parameters of Ca²⁺ transport modified by Ni²⁺ in intact liver are similar to those modified by norepinephrine in its first minutes of action, but the membrane receptors or Ca²⁺ transporters affected by Ni²⁺ seem to be distinct from those known to be modulated by norepinephrine.

Mercury-Tolerant Ensifer medicae Strains Display High Mercuric Reductase Activity and a Protective Effect on Nitrogen Fixation in Medicago truncatula Nodules Under Mercury Stress

Mercury (Hg) is extremely toxic for all living organisms. Hg-tolerant symbiotic rhizobia have the potential to increase legume tolerance, and to our knowledge, the mechanisms underlying Hg tolerance in rhizobia have not been investigated to date. Rhizobial strains of Ensifer medicae, Rhizobium leguminosarum bv. trifolii and Bradyrhizobium canariense previously isolated from severely Hg-contaminated soils showed different levels of Hg tolerance. The ability of the strains to reduce mercury Hg²⁺ to Hg⁰, a volatile and less toxic form of mercury, was assessed using a Hg volatilization assay. In general, tolerant strains displayed high mercuric reductase activity, which appeared to be inducible in some strains when grown at a sub-lethal HgCl₂ concentration. A strong correlation between Hg tolerance and mercuric reductase activity was observed for E. medicae strains, whereas this was not the case for the B. canariense strains, suggesting that additional Hg tolerance mechanisms could be playing a role in B. canariense. Transcript abundance from merA, the gene that encodes mercuric reductase, was quantified in tolerant and sensitive E. medicae and R. leguminosarum strains. Tolerant strains presented higher merA expression than sensitive ones, and an increase in transcript abundance was observed for some strains when bacteria were grown in the presence of a sub-lethal HgCl₂ concentration. These results suggest a regulation of mercuric reductase in rhizobia. Expression of merA genes and mercuric reductase activity were confirmed in Medicago truncatula nodules formed by a sensitive or a tolerant E. medicae strain. Transcript accumulation in nodules formed by the tolerant strain increased when Hg stress was applied, while a significant decrease in expression occurred upon stress application in nodules formed by the Hg-sensitive strain. The effect of Hg stress on nitrogen fixation was evaluated, and in our experimental conditions, nitrogenase activity was not affected in nodules formed by the tolerant strain, while a significant decrease in activity was observed in nodules elicited by the Hg-sensitive bacteria. Our results suggest that the combination of tolerant legumes with tolerant rhizobia constitutes a potentially powerful tool in the bioremediation of Hg-contaminated soils.

Differential gene expression profile of male and female copepods in response to cadmium exposure

In this study, the whole transcriptome and sex-specific differential gene expression of the copepod Pseudodiaptomus annandalei exposed to cadmium (Cd) were investigated. P. annandalei were exposed to 40 μg/L Cd from the naupliar stage to male and female adults. High-throughput transcriptome sequencing (RNA-seq) was performed with copepod samples using an Illumina Hiseq™ 2000 platform. TransDecoder analysis found 32,625 putative open reading frame contigs. At p-values of <0.001, a total of 4756 differentially expressed genes (DEGs) (2216 up-regulated and 2540 down-regulated genes) were found in male copepods. Whereas a total of 2879 DEGs (2007 up-regulated and 872 down-regulated genes) were found in female copepods. A few selected cellular stress response genes, involved in xenobiotic metabolism, energy metabolism, growth, and development as a result of Cd exposure in the copepods were discussed. The study showed that most of these processes were changed in a sex-specific manner, accounting for the different sensitivities of male and female copepods. Results suggest and reinforce that sex is an important factor to be considered in ecotoxicogenomics.

Linking molecular targets of Cd in the bloodstream to organ-based adverse health effects

The chronic exposure of human populations to toxic metals remains a global public health concern. Although chronic Cd exposure is linked to kidney damage, osteoporosis and cancer, the underlying biomolecular mechanisms remain incompletely understood. Since other diseases could also be causally linked to chronic Cd exposure, a systems toxicology-based approach is needed to gain new insight into the underlying exposure-disease relationship. This approach requires one to integrate the cascade of dynamic bioinorganic chemistry events that unfold in the bloodstream after Cd enters with toxicological events that unfold in target organs over time. To this end, we have conducted a systematic literature search to identify all molecular targets of Cd in plasma and in red blood cells (RBCs). Based on this information it is impossible to describe the metabolism of Cd and the toxicological relevance of it binding to molecular targets in/on RBCs is elusive. Perhaps most importantly, the role that peptides, amino acids and inorganic ions, including HCO₃^-, Cl^- and HSeO₃^- play in terms of mediating the translocation of Cd to target organs and its detoxification is poorly understood. Causally linking human exposure to this metal with diseases requires a much better integration of the bioinorganic chemistry of Cd that unfolds in the bloodstream with target organs. This from a public health point of view important goal will require collaborations between scientists from different disciplines to untangle the complex mechanisms which causally link Cd exposure to disease.

The effects of pretreatment with lithium metaborate dihydrate on lipid peroxidation and Ca, Fe, Mg, and K levels in serum of Wistar albino male rats exposed to Cd

Boron and boron compounds have beneficial biological effects. Lithium metaborate dihydrate (LMBDH) is used in many branches of industry. Despite its wide industrial use, there is limited information about its biological effects on antioxidant defense system and trace element homeostasis. Therefore, the aim of this study was to evaluate the in vivo protective effects of LMBDH against CdCl₂-induced oxidative stress and imbalance of some bioelements for the first time. In the study, totally 20 Wistar albino male rats were used. The rats were fed with pellet food and water ad libitum and divided into four groups including five rats in each. Group I was control group (standard pellet food + water + normal saline), Group II was CdCl₂ (4.58 mg/kg/body weight/intraperitoneally/single dose), Group III was LMBDH (15 mg/kg/body weight/day orally, for 5 days), Group IV was CdCl₂ (4.58 mg/kg/body weight/intraperitoneally/single dose in fifth day), and LMBDH (15 mg/kg/body weight/day orally for 5 days). The results showed that CdCl₂ treatment increased blood MDA level and decreased antioxidant enzyme activities and the level of blood GSH compared to control group. Pretreatment with LMBDH significantly decreased MDA levels and increased SOD activity (p < 0.05). In addition, Ca, Fe, and K levels decreased in LMBDH pretreatment group in different statistically levels. However, Mg levels showed an increase in LMBDH pretreatment group. As a result, LMBDH pretreatment decreased MDA status and supported antioxidant system by increasing SOD activity. In addition, it did not exhibit an ameliorative effect on measured bioelement homeostasis.

Physiologically relevant plasma d,l-homocysteine concentrations mobilize Cd from human serum albumin

Although low-level chronic exposure of humans to cadmium (Cd(2+)) can result in a variety of adverse health effects, little is known about the role that its interactions with plasma proteins and small molecular weight (SMW) ligands in the bloodstream may play in delivering this metal to its target organs. To gain insight, a Cd-human serum albumin (HSA) 1:1 (molar ratio) complex was analyzed by size exclusion chromatography (SEC) coupled on-line to a flame atomic absorption spectrometer (FAAS). Using a phosphate buffered saline (PBS)-buffer mobile phase, the stability of the Cd-HSA complex was investigated in the presence of 2.0mM of SMW ligands, including taurine, acetaminophen, l-methionine, l-cysteine (Cys), d,l-homocysteine (hCys) or l-cysteine methyl-ester (Cys-Me). While taurine, acetaminophen and l-methionine did not affect its integrity, Cys, hCys and Cys-Me completely abstracted Cd from HSA. Subsequent investigations into the effect of 1.5, 1.0 and 0.5mM Cys and hCys on the integrity of the Cd-HSA complex revealed clear differences with regard to the nature of the eluting SMW-Cd species between these structurally related endogenous thiols. Interestingly, the Cd-specific chromatograms that were obtained for 0.5mM hCys revealed the elution of an apparent mixture of the parent Cd-HSA complex with a significant contribution of a structurally uncharacterized CdxhCysy species. Since this hCys concentration is encountered in blood plasma of hyperhomocysteinemia patients and since previous studies by others have revealed that a SH-containing carrier mediates the uptake of Cd into hepatocytes, our results suggest that plasma hCys may play a role in the toxicologically relevant translocation of Cd from the bloodstream to mammalian target organs.

Protective effect of diallylsulphide against mercuric chloride-induced hepatic injury in rats

The present study was undertaken to evaluate the effect of diallylsulphide (DAS) against mercuric chloride (HgCl₂)-induced oxidative stress in rat livers. Rats were randomly divided into four groups of six rats each and exposed to HgCl₂ (50 mg/kg/body weight (b.w.)) intraperitoneally and/or DAS (200 mg/kg/b.w.) by gavage. HgCl₂ administration enhanced alanine aminotransferase (AST) and aspartate aminotransferase (ALT) levels (p < 0.05) with reduction in the levels of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px). However, treatment with DAS markedly attenuated HgCl₂-induced biochemical alterations in liver and serum transaminases (AST and ALT; p < 0.05). Further, biochemical results were confirmed by histopathological changes as compared to HgCl₂-intoxicated rats. Histopathology of liver also showed that administration of DAS significantly reduced the damage generated by HgCl₂ The present study suggests that DAS shows antioxidant activity and plays a protective role against mercury-induced oxidative damage in the rat livers.

Essential and nonessential elements in nestling rooks Corvus frugilegus from eastern Poland with a special emphasis on their high cadmium contamination

Concentration of minerals (sodium, potassium, calcium [Ca], magnesium, iron [Fe], copper, zinc [Zn], manganese [Mn], and cobalt) as well as toxic metals (cadmium [Cd], lead [Pb]) were determined in five tissues (liver, lung, kidney, muscle, and bone) of nestling rooks (Corvus frugilegus; 1 to 13 days old) found dead in seven breeding colonies in eastern Poland. Cd concentration in all analyzed tissues was in the narrow range of 17.0-17.2 mg/kg dry weight (dw) Cd, which in the light of the literature data indicates acute contamination by this toxic metal. Similarly, we found increased levels of Pb, which in all tissues ranged between 5.0 and 6.2 mg/kg dw. Results of multivariate general linear model (GLM) testing of the effect of three variables (tissue type, colony, and nestling age) on tissue concentrations of various metals showed significance for Fe, Cu, Zn, and Mn. Only concentrations of Ca, Fe, and Zn differed significantly between the analyzed tissues. GLM analysis did not show any statistically significant differences in tissue levels of minerals and both toxic metals among examined rookeries, which indicates the widespread presence of nonpoint Cd and Pb pollution linked to agricultural activity and similar levels of these inorganic contaminants on crop fields (feeding grounds) around breeding colonies. We concluded that high levels of both toxic metals, Cd and Pb, probably resulting from the diet of nestling rooks, are based mainly on a diet of ground-dwelling beetles gathered on crop fields.

Assimilation of elements and digestion in grass shrimp pre-exposed to dietary mercury

Grass shrimp Palaemonetes pugio were fed mercury (Hg)-contaminated oligochaetes for 15 days and analyzed for Hg, cadmium (Cd), and carbon assimilation efficiencies (AE) as well as toxicological end points related to digestion. Disproportionate increases in stable Hg concentrations in shrimp did not appear to be related to partitioning to trophically available Hg in worms. Hg AE by pre-exposed shrimp reached a plateau (approximately 53 %), whereas Cd AE varied (approximately 40-60 %) in a manner that was not dose-dependent. Carbon AE did not differ among treatments (approximately 69 %). Gut residence time was not impacted significantly by Hg pre-exposure (grand median approximately 465 min), however, there was a trend between curves showing percentages of individuals with markers in feces over time versus treatment. Feces-elimination rate did not vary with dietary pre-exposure. Extracellular protease activity varied approximately 1.9-fold but did not exhibit dose-dependency. pH increased over the range of Hg pre-exposures within the anterior (pH approximately 5.33-6.51) and posterior (pH approximately 5.29-6.25) regions of the cardiac proventriculus and Hg assimilation exhibited a negative relationship to hydrogen ion concentrations. The results of this study indicate that previous Hg ingestion can elicit post-assimilatory impacts on grass shrimp digestive physiology, which may, in turn, influence Hg assimilation during subsequent digestive cycles.

Phytotoxicity of Mercury in Plants: A Review

With the advent of the industrial revolution, heavy metal contamination has become an ever increasing concern. Thus, it is of major importance to understand the extent of the toxicity in plants and animals and the consequences from the ingestion of contaminated food. Hg is easily modified into several oxidation states, and it can be spread in many ecosystems. Due to the recurrence of Hg pollution and due to the lack of knowledge about the effects of this heavy metal in plants, the aim of the present text is to provide a comprehensive review of the literature regarding Hg phytotoxicity.

Proliferation potential of human amniotic fluid stem cells differently responds to mercury and lead exposure

There are considerable gaps in our knowledge on cell biological effects induced by the heavy metals mercury (Hg) and lead (Pb). In the present study we aimed to explore the effects of these toxicants on proliferation and cell size of primary human amniotic fluid stem (AFS) cells. Monoclonal human AFS cells were incubated with three dosages of Hg and Pb (single and combined treatment; ranging from physiological to cytotoxic concentrations) and the intracellular Hg and Pb concentrations were analyzed, respectively. At different days of incubation the effects of Hg and Pb on proliferation, cell size, apoptosis, and expression of cyclins and the cyclin-dependent kinase inhibitor p27 were investigated. Whereas we found Hg to trigger pronounced effects on proliferation of human AFS cells already at low concentrations, anti-proliferative effects of Pb could only be detected at high concentrations. Exposure to high dose of Hg induced pronounced downregulation of cyclin A confirming the anti-proliferative effects observed for Hg. Co-exposure to Hg and Pb did not cause additive effects on proliferation and size of AFS cells, and on cyclin A expression. Our here presented data provide evidence that the different toxicological effects of Pb and Hg on primary human stem cells are due to different intracellular accumulation levels of these two toxicants. These findings allow new insights into the functional consequences of Pb and Hg for mammalian stem cells and into the cell biological behavior of AFS cells in response to toxicants.

MRP proteins as potential mediators of heavy metal resistance in zebrafish cells

Acquired resistance of mammalian cells to heavy metals is closely relevant to enhanced expression of several multidrug resistance-associated proteins (MRP), but it remains unclear whether MRP proteins confer resistance to heavy metals in zebrafish. In this study, we obtained zebrafish (Danio rerio) fibroblast-like ZF4 cells with resistance to toxic heavy metals after chronic cadmium exposure and selection for 6months. These cadmium-resistant cells (ZF4-Cd) were maintained in 5μM cadmium and displayed cross-resistance to cadmium, mercury, arsenite and arsenate. ZF4-Cd cells remained the resistance to heavy metals after protracted culture in cadmium-free medium. In comparison with ZF4-WT cells, ZF4-Cd cells exhibited accelerated rate of cadmium excretion, enhanced activity of MRP-like transport, elevated expression of abcc2, abcc4 and mt2 genes, and increased content of cellular GSH. Inhibition of MRP-like transport activity, GSH biosynthesis and GST activity significantly attenuated the resistance of ZF4-Cd cells to heavy metals. The results indicate that some of MRP transporters are involved in the efflux of heavy metals conjugated with cellular GSH and thus play crucial roles in heavy metal detoxification of zebrafish cells.

Effects of cadmium and zinc ions on purified lamb kidney cortex glucose-6-phosphate dehydrogenase activity

Glucose-6-phosphate dehydrogenase (G-6-PD) is the first enzyme in the pentose phosphate pathway. Cadmium is a toxic heavy metal that inhibits several enzymes. Zinc is an essential metal but overdoses of zinc have toxic effects on enzyme activities. In this study G-6-PD from lamb kidney cortex was competitively inhibited by zinc both with respect to glucose-6-phosphate (G-6-P) and NADP+ with Ki values of 1.066 +/- 0.106 and 0.111 +/- 0.007 mM respectively whereas cadmium was a non-competitive inhibitor with respect to both G-6-P and NADP+ Ki values of 2.028 +/- 0.175 and 2.044 +/- 0.289 mM respectively.

Zinc or magnesium supplementation modulates cd intoxication in blood, kidney, spleen, and bone of rabbits

The objective of this study was to examine the influence of oral supplementation with Zn or Mg on Cd content in the blood and organs of rabbits exposed to prolonged Cd intoxication. Rabbits were divided into the following groups: Cd group-received orally every day for 4 weeks 10 mg Cd/kg body weight (b.w.), Cd+Zn group and Cd+Mg group-exposed to Cd and supplemented with 20 mg Zn/kg b.w. or 40 mg Mg/kg b.w. 1 h after Cd treatment. Cd content in biological material was determined by atomic absorption spectrophotometry. Blood Cd concentration was determined in all investigated groups at time 0 and after 10, 14, 18, 22, 25, and 28 days, whereas Cd content in the brain, heart, lungs, liver, kidney, spleen, pancreas, skeletal muscle, and bone was determined after 28 days. Blood Cd concentration was significantly increased in all groups from the 14th day of Cd intoxication and lasted till the end of the experiment. Zn or Mg supplementation significantly reduced blood Cd content on the 18th and 25th days. Supplementation with Zn or Mg significantly decreased Cd concentration in the kidney, spleen, and bone and, in addition, Zn reduced Cd content in the brain. Supplementation with Zn or Mg in Cd-intoxicated rabbits caused similar reduction of blood Cd concentration; however, reduction of tissue Cd content was more pronounced in Zn- than in Mg-supplemented group.

Cadmium, zinc and iron interactions in the tissues of bank vole Clethrionomys glareolus after exposure to low and high doses of cadmium chloride

In present study, bank voles Clethrionomys glareolus were peritioneally injected with different doses of cadmium, 0, 1.5, 3.0 mg Cd/kg body mass. Animals were sacrificed on the 21st day after cadmium exposure and the liver and kidney were obtained for cadmium, zinc and iron analysis using atomic absorption spectrometry. Results showed that cadmium had accumulated in the tissues according to dosage and sex. Cadmium affected the survival and body masses of dosed females. Cadmium decreased the iron concentrations in the liver of voles, whereas zinc concentrations increased in both the kidney and liver.

Cadmium accumulation and interactions with zinc, copper, and manganese, analysed by ICP-MS in a long-term Caco-2 TC7 cell model

The influence of long-term exposure to cadmium (Cd) on essential minerals was investigated using a Caco-2 TC7 cells and a multi-analytical tool: microwave digestion and inductively coupled plasma mass spectrometry. Intracellular levels, effects on cadmium accumulation, distribution, and reference concentration ranges of the following elements were determined: Na, Mg, Ca, Cr, Fe, Mn, Co, Ni, Cu, Zn, Mo, and Cd. Results showed that Caco-2 TC7 cells incubated long-term with cadmium concentrations ranging from 0 to 10 micromol Cd/l for 5 weeks exhibited a significant increase in cadmium accumulation. Furthermore, this accumulation was more marked in cells exposed long-term to cadmium compared with controls, and that this exposure resulted in a significant accumulation of copper and zinc but not of the other elements measured. Interactions of Cd with three elements: zinc, copper, and manganese were particularly studied. Exposed to 30 micromol/l of the element, manganese showed the highest inhibition and copper the lowest on cadmium intracellular accumulation but Zn, Cu, and Mn behave differently in terms of their mutual competition with Cd. Indeed, increasing cadmium in the culture medium resulted in a gradual and significant increase in the accumulation of zinc. There was a significant decrease in manganese from 5 micromol Cd/l exposure, and no variation was observed with copper.

Reciprocal inhibition of Cd and Pb sulfocomplexes for uptake in Caco-2 cells

Cadmium-lead interactions for uptake were studied in the TC7 clone of human enterocytic-like Caco-2 cells as a function of inorganic metal speciation. We have previously shown that Cd uptake in these cells involves both the free cation Cd2+ and chlorocomplex (CdCln(2-n)) species. Here we show 1.9 times higher uptake levels for 109CdCln(2-n) compared to 210PbCln(2-n). Reciprocal inhibitions of chlorocomplexes were observed with a much higher inhibitory effect of Cd compared to Pb. Replacing Cl- by NO3- increased both the level of aquo ion 109Cd2+ and 109Cd accumulation. In contrast, higher levels of 210Pb2+ did not favor 210Pb uptake. For both metals, higher uptake data were recorded in the presence of SO4(2-), leading to sulfocomplex formation, compared with Cl-. Reciprocal inhibitions were minimal at high-cation levels but were significant and comparable in the presence of sulfo-complexes. We conclude that, in addition to Cd2+ (but not Pb2+), sulfocomplexes of both metals would preferentially be taken up compared to chlorocomplexes. NRAMP2 is not involved in Pb2+ uptake, and the NRAMP2-mediated Cd2+ uptake is insensitive to Pb. Uptake of Pb chlorocomplexes could involve specific mechanisms but of very low affinity, whereas uptake of Pb sulfocomplexes occurs with high affinity.

Metals distribution and interactions in tissues of shrews (Sorex spp.) from copper- and zinc-contaminated areas in Poland

To assess the risk from heavy metal accumulation to insectivorous species exposed to different pollutants, shrews [Sorex araneus (Linnaeus 1758) and Sorex minutus (Linnaeus 1766)] were collected in the Olkuski Ore Region (OOR; a Zn and Cd smelter area), Legnicko-Głogowski Copper Mine Region (LGCR; a copper ore-mining area), and Białowieza Forest (BF; a control area). A few sites were chosen in each region and a total of 57 animals were collected from them. The liver and kidneys were dissected from the animals, dried, and digested in a 4:1 mixture of HNO3 (nitric acid) and HClO4 (perchloric acid). Cadmium, lead, zinc, copper, and iron were determined in the samples by flame or flameless atomic absorption spectrometry. The interactions between toxic and essential metals were calculated for each tissue. The data showed that accumulation of metals by insectivores is high; shrews accumulated much higher amounts of cadmium and lead than bank voles, studied by other researchers, from the same areas. The expected high tissue accumulation of copper at LGCR and zinc at OOR was not seen, but the levels of both elements were higher in the tissues of shrews from OOR than from LGCR. The lowest copper concentrations were in the tissues of shrews from BF. The highest cadmium and lead concentrations were found in the tissues of shrews from OOR. Some significant correlations were found between the tissue concentrations of xenobiotic and essential metals (e.g., between cadmium and zinc and between lead and iron).

Molecular and ionic mimicry and the transport of toxic metals

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

Cadmium uptake in isolated adrenocortical cells of rainbow trout and yellow perch

Cadmium uptake was studied in isolated adrenocortical cells of rainbow trout (Oncorhynchus mykiss) and yellow perch (Perca flavescens) to test the hypothesis that the greater sensitivity of trout cells to Cd-induced disruption of cortisol secretion observed in previous studies is correlated to higher level of metal accumulation. There was no evidence for interspecies differences in accumulation level, and a specific transport mechanism of similar affinity has been characterized in both fish species. However, inhibition of Cd uptake by calcium was observed in rainbow trout exclusively. The free metal ion Cd(2+) and chlorocomplexes CdCl(n)(2-n) both contribute to Cd accumulation with different level of contribution between fish species. We conclude that interspecies differences in sensitivity to Cd endocrine disrupting effect are not necessarily related to different levels of metal accumulation but would rather be linked to transport pathways and metal speciation. Cadmium/calcium competition for uptake could be a determinant of the early Cd-induced impaired cortisol secretion in trout but not perch cells.

Cadmium uptake in rat hepatocytes in relation to speciation and to complexation with metallothionein and albumin

Cadmium (Cd) uptake has been studied in primary cultures of rat hepatocytes focusing on the impact of inorganic and organic speciation. Uptake time-course studies over a 60-min exposure to 0.3 microM (109)Cd revealed a zero-time uptake and a slower process of accumulation which proceeds within minutes. (109)Cd uptake showed saturation kinetics (K(m) = 3.5 +/- 0.8 microM), and was highly sensitive to inhibition by Zn and Hg. There was no evidence for sensitivity to the external pH nor for any preferential transport of the free cation Cd(2+) over CdCl(n) (2-n) chloro-complexes. According to the assumption that only inorganic metal species are available, metal uptake decreased upon albumin (BSA) addition to the exposure media. In contrast, higher levels of (109)Cd accumulation were obtained under optimal conditions for Cd complexation by MT. Comparison among uptake data obtained under inorganic and organic conditions revealed that Cd-MT would be taken up 0.4 times as rapidly as Cd(inorg). We conclude that uptake of Cd in rat hepatocytes involves specific transport mechanism(s) subjected to Zn or Hg interactions. Uptake of inorganic Cd is not proportional to the levels of free Cd(2+) and does not involve the divalent cation transporter DCT1 nor the co-transporter Fe(2+)-H(+) NRAMP2. We found Cd-MT but not Cd-BSA to be available for the liver cells, and have estimated a binding affinity four orders of magnitude higher for Cd complexation with MT compared to BSA; MT may have a significant role in Cd delivery to the liver.

Different transport mechanisms for cadmium and mercury in Caco-2 cells: inhibition of Cd uptake by Hg without evidence for reciprocal effects

Cadmium/Hg interactions have been studied in the TC7 clone of the enterocytic-like Caco-2 cells to test the hypothesis that these metals may compete for intestinal transport. Comparison of the kinetic parameter values for 203Hg(II) and 109Cd(II) uptake in a serum-free medium revealed that Hg is accumulated much more rapidly and to higher concentrations. The very rapid uptake/binding step and the initial uptake rate of 109Cd were both significantly inhibited by an excess of unlabeled Cd or Hg (apparent K(i) for Hg of 9.3 +/- 1.2 microM) without reciprocal effects. 109cadmium uptake was highly sensitive to temperature and a significant fraction of accumulation (12%) was EDTA extractable. 203Hg uptake remained insensitive to temperature or the EDTA washing procedure. However, the uptake of both tracers was half-decreased when an excess of the respective unlabeled metal was added in the stop solution, suggesting an exchange mechanism for adsorption. Cell pretreatment with N-ethylmaleimide (NEM) led to a 30% decrease or a 73% increase in the 3-min specific transport of 109Cd when NEM was still present in or removed from the uptake medium, respectively. NEM had no effect on 203Hg uptake. Overall our results suggest the involvement of a saturable specific mechanism for Cd, which is highly sensitive to inhibition by Hg and NEM under some conditions, and a nonspecific passive diffusion for Hg. The Hg- or NEM-induced inhibition of Cd uptake likely involves a thiol-mediated reaction, but our results suggest that NEM pretreatment may activate other cellular mechanisms leading to a stimulatory effect.

Involvement of calcium channels in the sexual dimorphism of cadmium-induced hepatotoxicity

Cadmium toxicity has been evaluated in a number of in vivo and in vitro toxicological studies. In vivo Cd toxicity exhibits sexual dimorphism with females being more susceptible to Cd uptake, accumulation, and toxicity in the liver. Research to date does not explain why females are more sensitive to Cd-induced hepatotoxicity. Recent studies demonstrate that progesterone sensitizes female F(344) rats and TRL-1215 cells to Cd toxicity, however the mode of action is still unclear. Approximately one half of the Cd entering the cytoplasm does so through receptor operated Ca(2+) channels. Progesterone treatment of human spermatozoa and Xenopus laevis oocytes causes a rapid influx of Ca(2+) suggesting a possible mechanism. Since hepatocytes have progesterone receptors on their cellular membrane and Ca(2+) influx into the cytoplasm occurs following progesterone treatment we evaluated the hypothesis that progesterone facilitates the uptake and accumulation of Cd via Ca(2+) channels, leading to enhanced toxicity. Primary isolated rat hepatocytes were treated with Cd, progesterone, and/or verapamil for 4 h and cytolethality was measured. Pretreatment with the Ca(2+) channel blocker verapamil increased the Cd concentration producing 50% lethality (LC(50)) by 2-fold, thus decreasing Cd cytolethality. In contrast, pretreatment with progesterone decreased the Cd LC(50) by 2-fold resulting in enhanced Cd cytolethality. Verapamil treatment reversed the progesterone enhanced Cd cytolethality. Verapamil and/or progesterone in the absence of Cd did not affect hepatocyte viability. Overall, the results of this study demonstrate that inhibition of progesterone-induced Ca(2+) influx with the Ca(2+) channel blocker verapamil, decreases Cd cytolethality in primary isolated rat hepatocytes. These findings indicate that progesterone activation of receptor-mediated Ca(2+) channels is involved in the sexually dimorphic hepatotoxicity seen following acute Cd exposure.

Cadmium distribution and toxicity in tissues of small rodents

The aim of the present paper is to discuss the accumulation and distribution of cadmium (Cd) in the various tissues of animals, the interactions of cadmium with other elements, and the damage to tissues caused by this metal. Cadmium is not physiologically or biochemically essential to an organism. It is absorbed via the gastrointestinal tract and lungs and accumulated in various tissues, mainly the kidneys and liver. The distribution of cadmium between various tissues depends on many endogenous and exogenous factors. Cadmium is bound to a low-molecular-weight protein, metallothionein (MT), and to high-molecular-weight proteins. This metal has a great affinity to thiol groups. Cadmium binds also to O- and N-containing ligands. The distribution of cadmium between organs differs markedly depending on the chemical form of administered Cd and the duration of exposure. Acute exposure results in a different distribution pattern throughout the body than does chronic exposure. Long-term exposure to high doses of cadmium may cause biochemical and functional changes in some critical organs. Cadmium can influence the absorption and distribution of essential elements and can replace them in enzymes. Metallothionein and glutathione play important roles in the transport of metals and in detoxification processes. Reported findings are mainly the results of experiments on laboratory animals. The lack of data concerning the localization of cadmium in various tissues of wild species is noticeable and there is a great need for such data.

Evidence for cadmium uptake through Nramp2: metal speciation studies with Caco-2 cells

The specific uptake of 0.3 microM (109)Cd by the TC7 clone of the human enterocytic-like Caco-2 cells increased 4-fold as the pH(out) was lowered from 7.5 to 5.5; the stimulatory effect of acidic media being more pronounced when the level of the free ion (109)Cd(2+), relative to total (109)Cd, was increased. The initial uptake rate was 12-fold higher under conditions, optimizing (109)Cd(2+) accumulation over that of (109)CdCl(2-n)(n) (NO(-)(3)/pH(out) 5.5); a saturable system of transport has been characterized (K(m) = 1.1 +/- 0.1 microM, V(max) = 87 +/- 3 pmol/3 min/mg protein). An excess of Fe(2+) failed to affect (109)Cd uptake when the pH(out) was 7.4, whereas a strong inhibition was observed under NO(-)(3)/pH(out) 5.5 conditions. In contrast, the maximal inhibitory effect of Zn(2+) was observed under Cl(-)/pH(out) 7.4 conditions. This results strongly suggest that Fe(2+) may compete with Cd(2+) for Nramp2, whereas Zn and CdCl(2-n)(n) compete for another system of transport that has yet to be identified.

Uncoupling effect of mercuric chloride on mitochondria isolated from an hepatic cell line

A human fetal hepatic cell line (WRL-68) was used as a model to study the damage produced by mercury. The Hg(II) uptake by WRL-68 cells was found to be in a biphasic manner with a rapid initial uptake phase lasting about 5 min, followed by a sustained phase of slower accumulation. Distribution of mercury was studied and mitochondria were found to be the major target for mercury in this cell line (48%), followed by nuclei (38%), cytosol (8%) and microsomes (7%). Mitochondrial morphological damage after mercury treatment was observed by transmission electron microscopy. To determine if the toxic effect of mercury on mitochondrial bioenergetics was direct or indirect, mitochondria were isolated from WRL-68 cells after 1 h of pre-incubation with 0.5 microM HgCl(2). Oxygen consumption was quantified in two sets of experiments: in the presence of classical mitochondrial respiratory inhibitors; and in the presence of oligomycin. No significant difference was found in respiration with classical inhibitors, indicating that mercury does not affect directly the mitochondrial respiratory chain. However, mitochondria of Hg-treated cells were not inhibited when oligomycin was added, probably due to an uncoupling effect. This effect was prevented with dithiothreitol (DTT) treatment. A possible explanation for mercury's effect on mitochondria and its relation with oxidative stress is presented.

The effects of sulfhydryl blockers and metal ions on nickel accumulation by rat primary hepatocyte cultures

Previously, we found that nickel (Ni) accumulation by rat hepatocytes involves Ca channel transport processes. However, other mechanisms responsible for Ni accumulation are still unclear. Therefore, in the present study we examined the effects of sulfhydryl (SH) blockers on Ni accumulation by hepatocytes. Hepatocytes were exposed to various concentrations of N-ethylmaleimide (NEM) (0.5, 1 or 2 mM) or monoiodoacetic acid (MIA) (0.1, 0.25 or 0.5 mM), potent blockers of SH ligands, for 30 min and subsequently exposed to 10 microM NiCl(2) for an additional 60 min. Pretreatment with NEM and MIA enhanced the Ni accumulation by hepatocytes to maximum of 156 and 73%, respectively. The effects of essential and nonessential metal ions on Ni accumulation were also investigated. Pretreatment with 10 microM of Cu, Zn, Co, Cd and Mn, decreased Ni accumulation by 46, 30, 20, 18 and 11%, respectively. In contrast, pretreatment with Hg (10 and 20 microM) enhanced the Ni accumulation by almost 81 and 140%, respectively. Furthermore, significant decrease in SH concentration in the hepatocyte membrane was observed by the treatment with NEM, MIA and Hg, but not with Cu, Zn and Cd. These results suggest that Ni accumulation by hepatocytes does not appear to be dependent on the SH carrier-mediated transport processes, and that to block the SH ligands in the plasma membrane may facilitate the Ni crossing of the cell membrane.

gamma-Glutamyl transpeptidase and l-cysteine regulate methylmercury uptake by HepG2 cells, a human hepatoma cell line

Mechanisms of methylmercury (MeHg) and inorganic mercury (Hg) uptake were examined in HepG2 cells, a human hepatoma-derived cell line. MeHg uptake was faster when it was present as the l-cysteine complex, as compared to the glutathione (GSH), CysGly, gamma-GluCys, d-cysteine, N-acetylcysteine, l-penicillamine, or albumin complexes. Uptake of MeHg-l-cysteine was independent of Na(+), stereoselective, and was inhibited by the amino acid transport system l substrates l-leucine, l-valine, and l-phenylalanine (5 mM). Moreover, [(3)H]l-leucine uptake was inhibited by MeHg-l-cysteine, suggesting that MeHg-l-cysteine is transported into HepG2 cells by an l-type amino acid carrier. Uptake of MeHg as the GSH complex (MeHg-SG) was dependent on the extracellular GSH concentration, and was diminished when cellular gamma-glutamyl transpeptidase activity was inhibited. Inorganic mercury uptake was slower than that of MeHg, but was also sensitive to the type of thiol ligand present. These findings demonstrate that mercury uptake by HepG2 cells is dependent on the chemical structure of the mercury compound, the thiol ligand, and the activity of gamma-glutamyl transpeptidase. gamma-Glutamyl transpeptidase appears to play a key role in the disposition of MeHg-SG by facilitating the formation of MeHg-l-cysteine, which is readily transported into the cells on an amino acid-type carrier.

Transport of toxic heavy metals across cell membranes

Membrane transport of nonessential toxic heavy metals (type D heavy metals) not only controls their access to intracellular target sites but also helps determine their uptake, distribution, and excretion from the body. The critical role of membranes in the toxicology of class D metals has attracted the attention of many investigators, and extensive information has been collected on the mechanism(s) of metal transfer across membranes. Characteristics of metal transport in different cells, or even on opposite sides of the same cell, or under different physiological conditions, are not identical, and no unitary hypothesis has been formulated to explain this process in all cells. However, it seems possible that the mechanisms proposed for different cells represent variations on a few common themes.

Effects of in vitro exposures to cadmium, mercury, zinc, and 1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane on steroidogenesis by dispersed interrenal cells of rainbow trout (Oncorhynchus mykiss)

Numerous environmental xenobiotics can act as endocrine disrupters in wildlife species. Fish chronically exposed to pollutants exhibit a deficiency in the synthesis of cortisol, a glucocorticosteroid hormone secreted by interrenal steroidogenic cells in response to ACTH by a mechanism mediated by cAMP. The capacity of a series of heavy metals (CdCl2, ZnCl2, HgCl2, and CH3HgCl) and 1-(2-chlorophenyl)-1-(4-chlorophenyl)-2,2-dichloroethane (o,p'-DDD) to disrupt cortisol secretion was determined in dispersed interrenal cells of rainbow trout (Oncorhynchus mykiss) exposed in vitro to the toxicant, by measuring cortisol secretion stimulated with ACTH or dibutiryl-cAMP (dbcAMP) and by assessing cell viability. The effect of cadmium in presence of zinc on the interrenal cells was also determined. The median lethal concentration (LC50, dose that kills 50% of the cells), median effective concentration (EC50, dose that inhibits cortisol secretion by 50%), and LC50/EC50 ratio were determined for each chemical to compare its endocrine toxicity and to test the specificity of the toxicants to act as endocrine disrupters. HgCl2 had the lowest EC50 and LC50; it was the most toxic of the chemicals tested. The LC50/EC50 ratio was the highest for ZnCl2 and CdCl2, indicating that these toxicants had the most specific endocrine toxicity. The mechanism of toxicity of heavy metals on cortisol-secreting cells involves a site situated downstream from the step generating cAMP, while o,p'-DDD seemed to impair a step located between adenyl cyclase activation and the ACTH binding. No evidence for a protector effect of zinc against cadmium toxicity was found.

Cadmium uptake and defense mechanism in insect cells

The uptake of cadmium and the defense mechanism against this heavy metal were studied in the Aedes albopictus C6/36 cell line. The internalization of cadmium was a very quick process and exhibited saturation kinetics over the metal concentration gradient (1.37 to 131 micromol/L). Cd toxicity and influx were both shown to be temperature dependent. The uptake was not influenced by a 2, 4-dinitrophenol pretreatment but was significantly decreased by the Ca2+ antagonist verapamil. These data suggest that cadmium is readily taken up through mediated transport, not requiring metabolic energy. A considerable amount of the metal passes through the Ca2+ channels, but probably (an)other transporting molecule(s) also play(s) an important role in the uptake process. The remarkable, nonsigmoid viability pattern of Cd-treated cultures suggests that CdCl2 concentrations above 33 micromol/L induce a cellular defense system. This phenomenon went together with increased protein synthesis. We found a major induction of a group consisting of 71-, 75-, and 78-kDa proteins, probably belonging to the HSP70 family, as similar proteins were induced by heat shock. A slight induction of a 120-kDa protein also occurred. At the highest Cd concentrations 98-, 108-, and 110-kDa proteins were induced. These data suggest that heat shock proteins may play an important role in the Aedes cell protection against Cd insult.

Uptake, cellular distribution and DNA damage produced by mercuric chloride in a human fetal hepatic cell line

A human hepatic cell line (WRL-68 cells) was employed to investigate the uptake of the toxic heavy metal mercury. Hg accumulation in WRL-68 cells is a time and concentration dependent process. A rapid initial phase of uptake was followed by a second slower phase. The transport does not require energy and at low HgCl2 concentrations (<50 microM) Hg transport occurs by temperature-insensitive processes. Subcellular distribution of Hg was: 48% in mitochondria, 38% in nucleus and only 8% in cytosolic fraction and 7% in microsomes. Little is known at the molecular level concerning the genotoxic effects following the acute exposure of eucaryotic cells to low concentrations of Hg. Our results showed that Hg induced DNA single-strand breaks or alkali labile sites using the single-cell gel electrophoresis assay (Comet assay). The percentage of damaged nucleus and the average length of DNA migration increased as metal concentration and time exposure increased. Lipid peroxidation, determined as malondialdehyde production in the presence of thiobarbituric acid, followed the same tendency, increased as HgCl2 concentration and time of exposure increased. DNA damage recovery took 8 h after partial metal removed with PBS-EGTA.

Cytotoxicity of cadmium and characteristics of its transport in cardiomyocytes

Cadmium (Cd) is reported to produce cardiotoxicity at doses and exposure conditions that cause no effect in kidney or liver. The purpose of the present investigation was to examine the cytotoxicity of Cd to neonatal rat cardiomyocytes in primary culture and to elucidate the transport characteristics of Cd in these cells at a nontoxic concentration. Cd concentrations of 0.1 microM and higher that are well tolerated by hepatocytes and renal cortical epithelial cells were toxic to the cardiomyocyte. The plot of initial uptake rate of Cd at various concentrations was nonlinear suggesting that, in addition to simple diffusion, other processes may also be involved. These processes required metabolic energy as pretreatment with dinitrophenol or sodium fluoride inhibited 58 and 59% of the Cd uptake, respectively. The uptake of Cd was also affected by the incubation temperature and lowering the temperature from 37 to 4 degreesC reduced Cd uptake over 30 min by 61%. Cd uptake required interaction with membrane sulfhydryl groups; pretreatment with p-chloromercuribenzenesulfonic acid or mercuric chloride reduced Cd uptake by 46 and 58%, respectively. Cd utilized the transport pathways for calcium (Ca), zinc (Zn), and copper (Cu). Coincubation with 1.26 mM Ca competitively inhibited Cd uptake by 77%. In the presence of Ca, 30 microM Zn or Cu further inhibited Cd accumulation competitively by as much as 63 and 32%, respectively. Cd could enter the cardiomyocytes through Ca channels and Ca channel blocker, verapamil, inhibited up to 76% of Cd uptake. From the above results it can be concluded that Cd is highly toxic to the cardiomyocytes. A majority of Cd enters these cells through transport processes that exist for Ca, Zn, and Cu. The transport processes utilized by Cd are temperature sensitive and dependent on metabolic energy. Furthermore, these involve membrane sulfhydryl groups and include Ca channels.

Accumulation of cadmium in and its effect on bank vole tissues after chronic exposure

Cadmium is one of many metals that are not physiologically or biochemically essential to organisms. This element is extremely dangerous as it is easily absorbed and remains in tissues for a long time. Long exposure to high doses of cadmium may cause biochemical and functional changes in some critical organs. In this study, wheat grains contaminated with cadmium chloride were used to test the influence of cadmium on male bank voles (Clethrionomys glareolus). Doses used in the experiment were environmentally realistic: 0.25 microg g-1 (control), 15 microg g-1, and 40 microg g-1 cadmium (dry weight). The animals were given cadmium-contaminated food and clean water ad libitum for 3 and 6 months. After these exposures, the animals were killed and the kidneys, liver, and testes from each vole were collected for analyses. The concentrations of Cd, Cu, Zn, and Fe in the tissues were determined with an atomic absorption spectrophotometer. The formalin-fixed testes, kidneys, and part of the liver were embedded in paraffin and then stained with hematoxylin and eosin. Cadmium accumulation in the tissues was directly proportional to dose. The highest cadmium concentrations were found in the kidneys of animals fed the highest dose of cadmium. Histological examination of the tissues revealed some pathological changes in the structure of kidneys, liver, and testes.

Effects of zinc and copper on cadmium uptake by brush border membrane vesicles

The effects of essential metals, zinc (Zn) and copper (Cu), on cadmium (Cd) uptake were investigated in brush border membrane vesicles (BBMV) isolated from the rat renal cortex and LLC-PK1 cells. BBMV were incubated with Cd in the presence or absence of Zn or Cu, and then washed with a chelating agent, EGTA, to remove Cd bound to the outer surface of BBMV. Co-incubation with Zn or Cu decreased Cd accumulation in these BBMV in a concentration-dependent manner. Kinetic analysis of the initial accumulation of Cd suggested that Cd is taken up into rat BBMV via an unsaturable component and a saturable component (K(m) = 13.8 microM, V(max) = 1.44 nmol/mg protein/min), and co-incubation with Zn significantly increased the K(m) of the saturable component without affecting the V(max), whereas Cu significantly increased the K(m)-value and decreased the V(max)-value. Increasing the osmolarity of the incubation medium slightly decreased Cd accumulation in the absence of Zn or Cu, whereas it did not decrease Cd accumulation in the presence of these metals. These results suggest the possibility that, in addition to passive diffusion, Cd is also taken up from the renal brush border membrane via carrier-mediated mechanisms that are inhibited by Zn competitively and by Cu non-competitively. Furthermore, these results suggest that: (1) Cd binds externally and internally to BBMV, (2) little Cd is transported into the intravesicular space, and (3) both Zn and Cu decrease the binding and transport of Cd.

Study of the interactions of cadmium and zinc ions with cellular calcium homoeostasis using 19F-NMR spectroscopy

The effects of the heavy-metal ions Cd2+ and Zn2+ on the homoeostasis of intracellular free Ca2+ in E367 neuroblastoma cells were examined using 19F-NMR spectroscopy with the fluorinated chelator probe 1,2-bis-(2-amino-5-fluorophenoxy)ethane-N,N,N', N'-tetra-acetic acid (5F-BAPTA). First, the technique was used to quantify the uptake and intracellular free concentrations of the heavy metals after treatment of the cells with 20 microM CdCl2 or 100 microM ZnCl2. Secondly, metal-induced transients in intracellular free Ca2+ were recorded. Addition of 20 microM CdCl2, but not 100 microM ZnCl2, evoked a transient increase in Ca2+ from a resting level of 84 nM to approx. 190 nM within 15 min after addition of the metal. Zn2+ at 20 microM completely prevented the induction of a Ca2+ transient by Cd2+. Ca2+ was mobilized by Cd2+ from intracellular organelles, since depletion of these stores by thapsigargin abolished the effect of the toxic metal. Furthermore, 20 microM Cd2+ evoked a transient rise in cellular Ins(1,4,5)P3, reaching a maximum level within 5 min after addition of the metal. These results demonstrate that perturbation of the Ins(1,4,5)P3/Ca2+ messenger system is an early and discrete cellular effect of Cd2+.

Protective effect of metallothionein on intracellular pH changes induced by cadmium

In order to gain further insight into the protective mechanism of metallothionein (MT) against Cd cytotoxicity, the effects of in vivo Zn- or Cd-pretreatment on the cytotoxicity and alteration in cellular pH induced by Cd were examined in isolated rat hepatocytes and testicular Leydig cells. These pretreatments both induced the synthesis of MT in the hepatocytes, but not in the Leydig cells. Both pretreatments alleviated Cd cytotoxicity in the hepatocytes. Cd- or Zn-pretreatment was also effective in preventing Cd-induced cellular acidification in hepatocytes but neither pretreatment was effective in Leydig cells. In fact, Cd-pretreatment stimulated acidification in Leydig cells. Exposure in vitro of hepatocytes from untreated rats to probenecid, an inhibitor of HCO3-/Cl- exchange, also ameliorated Cd-induced cellular acidification, suggesting an involvement of HCO3-/Cl- exchange in the preventive action of MT against Cd-induced acidification. These results suggest that Cd cytotoxicity in various cells may be initiated by alterations in plasma membrane ion transport systems such as the HCO3-/Cl- exchange and consequential cellular acidification. Induction of MT, therefore, may prevent Cd cytotoxicity, at least in rat hepatocytes, by preventing an alteration in ion transport at the plasma membrane as well as by intracytoplasmic binding of the metal molecules.

Fluctuation of trace elements during methylmercury toxication and chelation therapy

The aim of the present investigation was to check the fluctuation in essential elements, such as Na, K, Mg, Mn, Cu, Zn, Cr and Ni in the brain, spinal cord, liver and kidney of mice during methylmercury chloride (MMC) toxication and therapy with monothiols (N-acetyl-DL-homocysteine thiolactone and glutathione) and vitamins (vitamin B complex and E). Mercury deposition and its elimination during chelation therapy were also screened for comparative purposes. The animals were dosed for 7 days with MMC 1 mg/kg/d and some were then kept without treatment for a further. 7 days. Other MMC-treated animals were immediately given one of the above antidotes for 7 days. All the animals were sacrificed on the 15th day. There was a decrease in all elements during MMC toxication with few exceptions, for example, copper was increased in the liver as was sodium in the kidney. Treatment with the thiols and vitamins restored the levels of these elements in certain tissues towards normal, but their concentrations remained abnormal in most instances. The fluctuations in the concentration of these elements were attributed to their association with various macromolecules.

Cytotoxicity and accumulation of Hg, Ag, Cd, Cu, Pb and Zn in human peripheral T and B lymphocytes and monocytes in vitro

1. The cytotoxic effects of various heavy metals were assayed by trypan blue exclusion in vitro in human peripheral immune cells separated to high purity. T and B lymphocytes and monocytes were equally sensitive to metals. The individual metals could be ranked in the following decreasing order of cytotoxic potency, Hg approximately Ag > Cd approximately Cu > Pb approximately Zn, based on exposure time and concentration needed to give a particular percentage of dead cells. 2. The cytotoxic effects became irreversible after about 13 hr of metal exposure. 3. Examination by scanning electron microscopy showed that the heavy metals caused serious destruction of the cell membranes. 4. Solubility and uptake of metals into the cells were studied and discussed in relation to the cytotoxic effects. It was concluded that metal binding to cell surfaces or precipitate formation could inhibit ordinary uptake, thereby affecting cytotoxicity. For Pb in monocytes this appeared to lead to uptake of non-toxic complexes, probably by phagocytosis.

Interaction of inorganic mercury salts with model and red cell membranes: importance of lipid binding sites

The effect of two mercury salts, HgCl2 and Hg(NO3)2, on the thermotropic properties of phosphatidylserine (PS) model membranes and sonicated rat red cell membranes was investigated by fluorescence polarization. Both Hg(II) salts abolished the phase transition and decreased the membrane fluidity by interacting with PS. Maximal effect was observed at a Hg/PS ratio of 2.5-5 for mercuric chloride and at 1.5 for the nitrate salt. For both mercury compounds, 10 mM NaCl protected model membranes from the effects of Hg(II). HgCl2 and Hg(NO3)2 also decreased the fluidity of rat red cell membranes. Maximal effect was observed for 0.4 mM HgCl2 and 0.6 mM Hg(NO3)2, with 0.0125 mg protein/ml. Addition of NaCl to the Hg(II)-red cell system decreased the Hg(II)-induced perturbation of the thermotropic properties. For both membrane systems, the effects observed with Hg(NO3)2 were greater than those with HgCl2, which can be accounted for by the absence of competition with chloride ions in samples containing Hg(NO3)2.[Cl-] governs the availability of Hg(II) by determining its chemical speciation: increasing [Cl-] generates HgCl3- and HgCl4(2-), which do not interact with lipid binding sites. These results indicate that besides protein thiol groups, Hg(II)-lipid binding sites play an important role in the interaction of Hg(II) with red cell membranes that is qualitatively different from Hg(II) binding to protein thiol groups.