The interactions of selenium with cadmium and mercury

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

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

Maternal micronutrient disturbance as risks of offspring metabolic syndrome

Metabolic syndrome (MetS) is defined as a constellation of individual metabolic disturbances, including central obesity, hypertension, dyslipidemia, and insulin resistance. The established pathogenesis of MetS varies extensively with gender, age, ethnic background, and nutritional status. In terms of nutritional status, micronutrients are more likely to be discounted as essential components of required nutrition than macronutrients due to the small amount required. Numerous observational studies have shown that pregnant women frequently experience malnutrition, especially in developing and low-income countries, resulting in chronic MetS in the offspring due to the urgent and increasing demands for micronutrients during gestation and lactation. Over the past few decades, scientific developments have revolutionized our understanding of the association between balanced maternal micronutrients and MetS in the offspring. Examples of successful individual, dual, or multiple maternal micronutrient interventions on the offspring include iron for hypertension, selenium for type 2 diabetes, and a combination of folate and vitamin D for adiposity. In this review, we aim to elucidate the effects of maternal micronutrient intake on offspring metabolic homeostasis and discuss potential perspectives and challenges in the field of maternal micronutrient interventions.

Determination of toxic metal burden and related risk factors in pregnant women: a biological monitoring in Sabzevar, Iran

Nowadays, the adverse effect of toxic metals on humans is well known, especially in the fetal period such as preventing cognitive development and congenital abnormalities of the central nervous system. Hence, this study aims to evaluate the toxic metal burden in mothers and newborns in Sabzevar. Obtained data can be useful for authorities in public health issues. To determine heavy metals in placental blood and umbilical cord blood, one hundred eighty blood samples were taken from ninety mothers referred to Shahidan Mobini Hospital for delivery. The amount of metals in samples was analyzed using inductively coupled plasma optical emission spectrometry (ICP OES). The results of this study revealed that 21.52%, 26.19%, and 60.71% of maternal blood samples (placental blood) and 16.47%, 56.47%, and 20% of umbilical cord blood samples were higher than the US center for disease control (CDC) recommended levels for Pb, Cd, and As respectively. According to the multiple linear regression analysis, the Pb (p = 0.054), As (p < 0.001), and Se (p < 0.001) levels had an association with the mother's living area. Also, there was a significant association between Se (0.021) and the age of the mother. However, the Se values in its optimum concentrations in the blood (60-140 μg/L) can decrease the adverse effects of toxic metals, 72.5% of the pregnant women had Se values below the 60 μg/L and only 6% of pregnant women had Se levels higher than 140 μg/L. We concluded that the mothers inhabiting the rural areas need more Se sources in their diets.

Mercury interactions with selenium and sulfur and the relevance of the Se:Hg molar ratio to fish consumption advice

Eating fish is often recommended as part of a healthful diet. However, fish, particularly large predatory fish, can contain significant levels of the highly toxic methylmercury (MeHg). Ocean fish in general also contain high levels of selenium (Se), which is reported to confer protection against toxicity of various metals including mercury (Hg). Se and Hg have a high mutual binding affinity, and each can reduce the toxicity of the other. This is an evolving area of extensive research and controversy with variable results in the animal and epidemiologic literature. MeHg is toxic to many organ systems through high affinity for -SH (thiol) ligands on enzymes and microtubules. Hg toxicity also causes oxidative damage particularly to neurons in the brain. Hg is a potent and apparently irreversible inhibitor of the selenoenzymes, glutathione peroxidases (GPX), and thioredoxin reductases (TXNRD) that are important antioxidants, each with a selenocysteine (SeCys) at the active site. Hg binding to the SeCys inhibits these enzymes, accounting in part for the oxidative damage that is an important manifestation of Hg toxicity, particularly if there is not a pool of excess Se to synthesize new enzymes. A molar excess of Se reflected in an Se:Hg molar ratio > 1 is often invoked as evidence that the Hg content can be discounted. Some recent papers now suggest that if the Se:Hg molar ratio exceeds 1:1, the fish is safe and the mercury concentration can be ignored. Such papers suggested that the molar ratio rather than the Hg concentration should be emphasized in fish advisories. This paper examines some of the limitations of current understanding of the Se:Hg molar ratio in guiding fish consumption advice; Se is certainly an important part of the Hg toxicity story, but it is not the whole story. We examine how Hg toxicity relates also to thiol binding. We suggest that a 1:1 molar ratio cannot be relied on because not all of the Se in fish or in the fish eater is available to interact with Hg. Moreover, in some fish, Se levels are sufficiently high to warrant concern about Se toxicity.

Epidemiological study of kidney health in an area with high levels of soil cadmium and selenium: Does selenium protect against cadmium-induced kidney injury?

Chronic exposure to cadmium (Cd) can cause renal dysfunction. Studies of animals, cell cultures, and plants have found that selenium (Se) can effectively alleviate the hazard generated by Cd, but there has been little study of this in general human populations. This study recruited 313 subjects from China's Hubei Province, including 160 living in areas with high soil Cd and Se (exposure group) and 153 living in clean areas (control group). The levels of the following were detected: Cd and Se in blood (B-Cd and B-Se), urine (U-Cd and U-Se), and hair (H-Cd and H-Se); N-acetyl-β-D-glucosaminidase (U-NAG), β₂-microglobulin (U-β₂-MG), and albumin (U-ALB) in urine; and malondialdehyde (S-MDA), superoxide dismutase (S-SOD), and glutathione peroxidase (S-GSH-Px) in serum. In addition, the interactions between Cd and Se were assessed. The median levels of B-Cd, B-Se, U-Cd, U-Se, H-Cd, H-Se, S-MDA, and S-GSH-Px of exposure group (2.60 ng/mL, 238.90 ng/mL, 3.13 μg/g Cr, 45.43 μg/g Cr, 0.06 μg/g, 0.70 μg/g, 5.22 nmol/mL, and 308.89 U, respectively) were significantly higher than of controls (0.95 ng/mL, 130.50 ng/mL, 1.08 μg/g Cr, 30.51 μg/g Cr, 0.04 μg/g, 0.49 μg/g, 4.71 nmol/mL, and 267.54 U, respectively), but there were no significant differences in U-NAG, U-β₂-MG, U-ALB, or S-SOD between the two groups. U-NAG levels were significantly negatively associated with the interaction between Cd and Se (B: -0.511, 95% CI: -0.886, -0.136). Additionally, changes in the direction of the estimated regression coefficient in the low and high H-Se groups were observed for U-Cd and S-MDA (from 0.018 to -0.090), U-Cd and S-GSH-Px (from -0.039 to 0.101). This study found that populations living in areas with high levels of soil Cd and Se did not show greater Cd-induced renal tubular and glomerular injuries than the control population, which could attribute to the protective effects of Se. The protective effects may be related to the peculiar function of Se that Se can combine with free Cd to activate the antioxidant enzyme system.

Impact of selenium co-administration on methylmercury exposed eleutheroembryos and adult zebrafish (Danio rerio): Changes in bioaccumulation and gene expression

Mercury still represents one of the most hazardous threats for the aquatic ecosystem due to its high toxicity, and the fact that it can be easily incorporated into the food chain by accumulation in fish as MeHg. On the other hand, selenium is a micronutrient that is part of different antioxidant enzymes that regulate the cellular redox state, and whose complex interaction with Hg has been extensively studied from a toxicological point of view. In order to evaluate the protective effect of Se(IV) co-administration against MeHg accumulation and toxicity, we have selected an in-vivo model at two developmental stages: zebrafish eleutheroembryos and adult fish. Embryos were exposed during 48 h to MeHg (5 or 25 μg/l) and a concentration of Se (IV) representing a molar ratio close to one (2.5 or 12.5 μg/l), while adult zebrafish were exposed during 72 h to either 25 μg/l of MeHg alone or co-exposed with 12.5 μg/l of Se (IV). A significant decrease in MeHg bioaccumulation factor was observed in eleutheroembryos co-exposed to Se(IV). A time-dependent accumulation of MeHg was observed in all the analyzed organs and tissues of adult fish, which was significantly reduced in the muscular tissue and the intestine by Se(IV) co-administration. However, such protection against MeHg bioaccumulation was not maintained in the brain and liver. The data derived from the gene expression analysis also demonstrated the protective effect of Se(IV) against MeHg-induced oxidative stress and the activation of different defense mechanisms by Se(IV) co-administration.

Vascular Dysfunction Induced by Mercury Exposure

Methylmercury (MeHg) causes severe damage to the central nervous system, and there is increasing evidence of the association between MeHg exposure and vascular dysfunction, hemorrhage, and edema in the brain, but not in other organs of patients with acute MeHg intoxication. These observations suggest that MeHg possibly causes blood-brain barrier (BBB) damage. MeHg penetrates the BBB into the brain parenchyma via active transport systems, mainly the l-type amino acid transporter 1, on endothelial cell membranes. Recently, exposure to mercury has significantly increased. Numerous reports suggest that long-term low-level MeHg exposure can impair endothelial function and increase the risks of cardiovascular disease. The most widely reported mechanism of MeHg toxicity is oxidative stress and related pathways, such as neuroinflammation. BBB dysfunction has been suggested by both in vitro and in vivo models of MeHg intoxication. Therapy targeted at both maintaining the BBB and suppressing oxidative stress may represent a promising therapeutic strategy for MeHg intoxication. This paper reviews studies on the relationship between MeHg exposure and vascular dysfunction, with a special emphasis on the BBB.

Metals and metalloids in blood and feathers of common moorhens (Gallinula chloropus) from wetlands that receive treated wastewater

We addressed the hypothesis that birds in eutrophic wetlands receiving wastewater treatment plant (WWTP) effluents are exposed to high levels of metals and metalloids and this may drive an ecological trap in some species attracted to these highly productive ecosystems. Levels of metals and metalloids were determined in sediment and in blood and feathers of common moorhens (Gallinula chloropus) from two wetlands in Central Spain: Navaseca Pond, which receives directly the effluent of a WWTP; and Tablas de Daimiel National Park, which is a floodplain less affected by urban discharges. Sediment concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb were higher in Navaseca Pond than in Tablas de Daimiel; only Se was higher in Tablas de Daimiel than in Navaseca. Blood levels of Hg and Se were higher in moorhens from Tablas de Daimiel than those from Navaseca. In the case of Hg these levels were below the threshold of adverse effect, but Se levels in 24% of moorhens from Tablas de Daimiel were above the threshold value associated with Se toxicity in birds (1000 ng/mL). In feathers, Hg, Se, Mn, Cu and As levels were higher in Tablas de Daimiel than in Navaseca. Body condition of moorhens was negatively associated with blood Se levels in the moorhens from Tablas de Daimiel. We can reject the hypothesis of a higher accumulation of metals and metalloids in birds associated with the WWTP effluent, but Se levels may need further research considering the nature of the floodplain of Tablas de Daimiel National Park.

Concentrations of mercury (Hg) and selenium (Se) in afterbirth and their relations with various factors

The aim of the study was to evaluate Hg and Se concentrations and Se:Hg molar ratios in the placenta, umbilical cord and fetal membranes, and to examine the relationship between the concentrations of the elements and selected factors. The study material consisted of the placenta, umbilical cord and fetal membranes obtained from 91 healthy women from northwestern and central Poland. In our study mean Hg and Se concentrations in afterbirth were ~ 0.01 mg/kg dry weight (dw) and ≤ 0.5 mg/kg dw, respectively. Correlation analysis showed negative relationships between placenta weight and Se concentration in the placenta and umbilical cord, as well as between placenta length and Se levels in the umbilical cord. We found negative correlations between THg concentration in the placenta and birth weight and between Se concentration in the placenta and umbilical cord and the morphological parameters of the placenta. Furthermore, we noted new types of interactions in specific parts of the afterbirth. In our study, Se:THg molar ratios ranged from 5 to 626; these values indicate protection against Hg toxicity.

Selenium supplementation prevents metabolic and transcriptomic responses to cadmium in mouse lung

BACKGROUND

The protective effect of selenium (Se) on cadmium (Cd) toxicity is well documented, but underlying mechanisms are unclear.

METHODS

Male mice fed standard diet were given Cd (CdCl₂, 18 μmol/L) in drinking water with or without Se (Na₂SeO_4, 20 μmol/L) for 16 weeks. Lungs were analyzed for Cd concentration, transcriptomics and metabolomics. Data were analyzed with biostatistics, bioinformatics, pathway enrichment analysis, and combined transcriptome-metabolome-wide association study.

RESULTS

Mice treated with Cd had higher lung Cd content (1.7 ± 0.4 pmol/mg protein) than control mice (0.8 ± 0.3 pmol/mg protein) or mice treated with Cd and Se (0.4 ± 0.1 pmol/mg protein). Gene set enrichment analysis of transcriptomics data showed that Se prevented Cd effects on inflammatory and myogenesis genes and diminished Cd effects on several other pathways. Similarly, Se prevented Cd-disrupted metabolic pathways in amino acid metabolism and urea cycle. Integrated transcriptome and metabolome network analysis showed that Cd treatment had a network structure with fewer gene-metabolite clusters compared to control. Centrality measurements showed that Se counteracted changes in a group of Cd-responsive genes including Zdhhc11, (protein-cysteine S-palmitoyltransferase), Ighg1 (immunoglobulin heavy constant gamma-1) and associated changes in metabolite concentrations.

CONCLUSION

Co-administration of Se with Cd prevented Cd increase in lung and prevented Cd-associated pathway and network responses of the transcriptome and metabolome. Se protection against Cd toxicity in lung involves complex systems responses.

GENERAL SIGNIFICANCE

Environmental Cd stimulates proinflammatory and profibrotic signaling. The present results indicate that dietary or supplemental Se could be useful to mitigate Cd toxicity.

Interactive effects of chronic dietary selenomethionine and cadmium exposure in rainbow trout (Oncorhynchus mykiss): A preliminary study

The present study investigated the interactive effects of dietary cadmium (Cd) and selenium (Se) on the tissue-specific (liver, kidney, and muscle) accumulation of these two elements, hepatic oxidative stress response, and morphometrics in rainbow trout (Oncorhynchus mykiss) during chronic exposure. Fish were exposed to elevated dietary Cd (45 μg g^-1 dry wt.), and medium (10 μg g^-1 dry wt.) or high (45 μg g^-1 dry wt.) dietary selenium (added as selenomethionine), both alone and in combination, for 30 days. Exposure to dietary Cd alone caused oxidative stress in fish as reflected by reduced thiol redox (GSH:GSSG), increased lipid peroxidation, and induction of anti-oxidative enzymes (catalase, superoxide dismutase, and glutathione peroxidase) in the liver. Also, an increase in tissue-specific Cd burden and impaired morphometrics (hepato-somatic index and condition factor) were also recorded in fish following exposure to dietary Cd. In contrast, the dietary co-exposure to Cd and Se (at both medium and high doses) resulted in a decrease in Cd burden in the liver and kidney of fish. However, co-exposure to medium, but not high, dose of dietary Se completely alleviated Cd-induced oxidative stress and impaired morphometrics in fish, indicating that the reduced Cd tissue burden might not have been the primary factor behind the amelioration of Cd toxicity by Se. Overall, our study demonstrated that the protective effect of Se against the chronic Cd toxicity in fish is mainly mediated by the anti-oxidative properties of Se, but this protective effect is dose-specific and occurs only at a moderate exposure dose.

Mercury Exposure and Heart Diseases

Environmental contamination has exposed humans to various metal agents, including mercury. It has been determined that mercury is not only harmful to the health of vulnerable populations such as pregnant women and children, but is also toxic to ordinary adults in various ways. For many years, mercury was used in a wide variety of human activities. Nowadays, the exposure to this metal from both natural and artificial sources is significantly increasing. Recent studies suggest that chronic exposure, even to low concentration levels of mercury, can cause cardiovascular, reproductive, and developmental toxicity, neurotoxicity, nephrotoxicity, immunotoxicity, and carcinogenicity. Possible biological effects of mercury, including the relationship between mercury toxicity and diseases of the cardiovascular system, such as hypertension, coronary heart disease, and myocardial infarction, are being studied. As heart rhythm and function are under autonomic nervous system control, it has been hypothesized that the neurotoxic effects of mercury might also impact cardiac autonomic function. Mercury exposure could have a long-lasting effect on cardiac parasympathetic activity and some evidence has shown that mercury exposure might affect heart rate variability, particularly early exposures in children. The mechanism by which mercury produces toxic effects on the cardiovascular system is not fully elucidated, but this mechanism is believed to involve an increase in oxidative stress. The exposure to mercury increases the production of free radicals, potentially because of the role of mercury in the Fenton reaction and a reduction in the activity of antioxidant enzymes, such as glutathione peroxidase. In this review we report an overview on the toxicity of mercury and focus our attention on the toxic effects on the cardiovascular system.

Phenylselenolate Mercury Alkyl Compounds, PhSeHgMe and PhSeHgEt: Molecular Structures, Protolytic Hg-C Bond Cleavage and Phenylselenolate Exchange

The phenylselenolate mercury alkyl compounds, PhSeHgMe and PhSeHgEt, have been structurally characterized by X-ray diffraction, thereby demonstrating that both compounds are monomeric with approximately linear coordination geometries; the mercury centers do, nevertheless, exhibit secondary Hg•••Se intermolecular interactions that serve to increase the coordination number in the solid state. The ethyl derivative, PhSeHgEt, undergoes facile protolytic cleavage of the Hg-C bond to release ethane at room temperature, whereas PhSeHgMe exhibits little reactivity under similar conditions. Interestingly, the cleavage of the Hg-C bond of PhSeHgEt is also more facile than that of the thiolate analogue, PhSHgEt, which demonstrates that coordination by selenium promotes protolytic cleavage of the mercury-carbon bond. The phenylselenolate compounds PhSeHgR (R = Me, Et) also undergo degenerate exchange reactions with, for example, PhSHgR and RHgCl. In each case, the alkyl groups preserve coupling to the 199Hg nuclei, thereby indicating that the exchange process involves metathesis of the Hg-SePh/Hg-X groups rather than metathesis of the Hg-R/Hg-R groups.

Protolytic cleavage of Hg-C bonds induced by 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone: synthesis and structural characterization of mercury complexes

Multinuclear ((1)H, (77)Se, and (199)Hg) NMR spectroscopy demonstrates that 1-methyl-1,3-dihydro-2H-benzimidazole-2-selone, H(sebenzim(Me)), a structural analogue of the selenoamino acid, selenoneine, binds rapidly and reversibly to the mercury centers of HgX2 (X = Cl, Br, I), while X-ray diffraction studies provide evidence for the existence of adducts of composition [H(sebenzim(Me))]xHgX2 (X = Cl, x = 2, 3, 4; X = I, x = 2) in the solid state. H(sebenzim(Me)) also reacts with methylmercury halides, but the reaction is accompanied by elimination of methane resulting from protolytic cleavage of the Hg-C bond, an observation that is of relevance to the report that selenoneine demethylates CysHgMe, thereby providing a mechanism for mercury detoxification. Interestingly, the structures of [H(sebenzim(Me))]xHgX2 exhibit a variety of different hydrogen bonding patterns resulting from the ability of the N-H groups to form hydrogen bonds with chlorine, iodine, and selenium.

Effectiveness of (PhSe)2 in protect against the HgCl2 toxicity

This work investigated the preventive effect of diphenyl diselenide [(PhSe)2] on renal and hepatic toxicity biomarkers and oxidative parameters in adult mice exposed to mercury chloride (HgCl2). Selenium (Se) and mercury (Hg) determination was also carried out. Mice received a daily oral dose of (PhSe)2 (5.0mg/kg/day) or canola oil for five consecutive days. During the following five days, the animals were treated with a daily subcutaneous dose of HgCl2 (5.0mg/kg/day) or saline (0.9%). Twenty-four hours after the last HgCl2 administration, the animals were sacrificed and biological material was obtained. Concerning toxicity biomarkers, Hg exposure inhibited blood δ-aminolevulinic acid dehydratase (δ-ALA-D), serum alanine aminotransferase (ALT) activity and also increased serum creatinine levels. (PhSe)2 partially prevented blood δ-ALA-D inhibition and totally prevented the serum creatinine increase. Regarding the oxidative parameters, Hg decreased kidney TBARS levels and increased kidney non-protein thiol levels, while (PhSe)2 pre-treatment partially protected the kidney thiol levels increase. Animals exposed to HgCl2 presented Hg content accumulation in blood, kidney and liver. The (PhSe)2 pre-treatment increased Hg accumulation in kidney and decreased in blood. These results show that (PhSe)2 can be efficient in protecting against these toxic effects presented by this Hg exposure model.

Organotropism of persistent organic pollutants and heavy metals in the Greenland shark Somniosus microcephalus in NE Greenland

The Greenland shark Somniosus microcephalus is an opportunistic feeder, a top predator, and a very long-lived species. The brain, liver, red and white muscle, gonads, fat, skin, pancreas, and spleen of Greenland sharks from NE Greenland fjords were analysed for PCBs, PCDDs/DFs, PBDEs; DDT isomers; HCH isomers; dieldrin; endrin; HCB; Cd, Hg, Pb, and Se. PCBs (2.01-103 ng/g wet wt) and PBDEs (7.9-3050 pg/g wet wt) were detected in most of the samples. PCDDs/DFs showed high values when detected. DDTs, HCB and HCHs were only detected in some tissues. The ΣTEQ was 5.76 pg/g in muscle. Cadmium mainly accumulated in the pancreas and liver (19.6 and 10.7 mg/kg dry wt, respectively); mercury in red muscle (4.10-6.91 mg/kg dry wt); selenium in the pancreas (3.57 mg/kg dry wt) and spleen (1.95 mg/kg dry wt); lead in the skin (0.358 mg/kgd ry wt). The selenium-mercury ratio in the liver was also evaluated.

Mercury and selenium intake by seafood from the Ionian Sea: A risk evaluation

The subject of the present study is the evaluation of the concentrations of mercury (Hg) and selenium (Se) in fish and shellfish from the Gulf of Catania (Ionian Sea) and the assessment of related risk-based consumption limits per single contaminant in adults and children. In contrast to the potential harm from Hg, Se is an essential element that is normally found in high levels in seafood. If the amount of Hg is high enough, it could bind Se and irreversibly inhibit selenium-dependent enzymes. Thus, adequate levels of Se need to be available to replace the amount of Se lost to Hg sequestration, thereby maintaining normal selenoprotein synthesis. Hg analysis was conducted using a flow injection analysis system coupled with an atomic adsorption spectrometer, and Se analysis was conducted using an inductively coupled plasma mass spectrometry (ICP-MS). Of the trace elements investigated, only Hg has a limit set by the European Community for human consumption, and this was never exceeded. Nevertheless, based on Target Hazard Quotient (THQ) over 1, and on the Estimated Daily Intake per meal (EDIm) higher than the Provisional Tolerable Intake (PTI) suggested by the Joint FAO/WHO Expert Committee on Food Additive (JECFA), Hg oral exposure derived from consumption of the benthonic fish and of the bigger pelagic fish species analyzed, could follow the occurrence of systemic effects. Se was found always in molar excess respect to Hg in all pelagic fish and in the shellfish, nearly equimolar in the benthonic fish. Determining the evidence that foods, such as pelagic fish, with high molar excess of Se, could contribute to replace the amount of Se bound to Hg and thereby maintaining normal selenoprotein synthesis, is useful for a better understanding of the seafood safety.

Mercury toxicity and neurodegenerative effects

Mercury is among the most toxic heavy metals and has no known physiological role in humans. Three forms of mercury exist: elemental, inorganic and organic. Mercury has been used by man since ancient times. Among the earliest were the Chinese and Romans, who employed cinnabar (mercury sulfide) as a red dye in ink (Clarkson et al. 2007). Mercury has also been used to purify gold and silver minerals by forming amalgams. This is a hazardous practice, but is still widespread in Brazil's Amazon basin, in Laos and in Venezuela, where tens of thousands of miners are engaged in local mining activities to find and purify gold or silver. Mercury compounds were long used to treat syphilis and the element is still used as an antiseptic,as a medicinal preservative and as a fungicide. Dental amalgams, which contain about 50% mercury, have been used to repair dental caries in the U.S. since 1856.Mercury still exists in many common household products around the world.Examples are: thermometers, barometers, batteries, and light bulbs (Swain et al.2007). In small amounts, some organo mercury-compounds (e.g., ethylmercury tiosalicylate(thimerosal) and phenylmercury nitrate) are used as preservatives in some medicines and vaccines (Ballet al. 2001).Each mercury form has its own toxicity profile. Exposure to Hg0 vapor and MeHg produce symptoms in CNS, whereas, the kidney is the target organ when exposures to the mono- and di-valent salts of mercury (Hg+ and Hg++, respectively)occur. Chronic exposure to inorganic mercury produces stomatitis, erethism and tremors. Chronic MeHg exposure induced symptoms similar to those observed in ALS, such as the early onset of hind limb weakness (Johnson and Atchison 2009).Among the organic mercury compounds, MeHg is the most biologically available and toxic (Scheuhammer et a!. 2007). MeHg is neurotoxic, reaching high levels of accumulation in the CNS; it can impair physiological function by disrupting endocrine glands (Tan et a!. 2009).The most important mechanism by which mercury causes toxicity appears to bemitochondrial damage via depletion of GSH (Nicole et a!. 1998), coupled with binding to thiol groups ( -SH), which generates free radicals. Mercury has a high affinity for thiol groups ( -SH) and seleno groups ( -SeH) that are present in amino acids as cysteine and N-acetyl cysteine, lipoic acid, proteins, and enzymes. N-acetylcysteine and cysteine are precursors for the biosynthesis of GSH, which is among the most powerful intracellular antioxidants available to protect against oxidative stress and inflammation.Mercury and methylmercury induce mitochondrial dysfunction, which reduces ATP synthesis and increases lipid, protein and DNA peroxidation. The content of metallothioneines, GSH, selenium and fish high in omega-3 fatty acids appear to be strongly related with degree of inorganic and organic mercury toxicity, and with the protective detoxifying mechanisms in humans. In conclusion, depletion of GSH,breakage of mitochondria, increased lipid peroxidation, and oxidation of proteins and DNA in the brain, induced by mercury and his salts, appear to be important factors in conditions such as ALS and AD (Bains and Shaw 1997; Nicole eta!. 1998;Spencer eta!. 1998; Alberti et a!. 1999).

Mercury distribution and speciation in different brain regions of beluga whales (Delphinapterus leucas)

The toxicokinetics of mercury (Hg) in key species of Arctic ecosystem are poorly understood. We sampled five brain regions (frontal lobe, temporal lobe, cerebellum, brain stem and spinal cord) from beluga whales (Delphinapterus leucas) harvested in 2006, 2008, and 2010 from the eastern Beaufort Sea, Canada, and measured total Hg (HgT) and total selenium (SeT) by inductively coupled plasma mass spectrometry (ICP-MS), mercury analyzer or cold vapor atomic absorption spectrometry, and the chemical forms using a high performance liquid chromatography ICP-MS. At least 14% of the beluga whales had HgT concentrations higher than the levels of observable adverse effect (6.0 mg kg(-1) wet weight (ww)) in primates. The concentrations of HgT differed between brain regions; median concentrations (mgkg(-1) ww) were 2.34 (0.06 to 22.6, 81) (range, n) in temporal lobe, 1.84 (0.12 to 21.9, 77) in frontal lobe, 1.84 (0.05 to 16.9, 83) in cerebellum, 1.25 (0.02 to 11.1, 77) in spinal cord and 1.32 (0.13 to 15.2, 39) in brain stem. Total Hg concentrations in the cerebellum increased with age (p<0.05). Between 35 and 45% of HgT was water-soluble, of which, 32 to 41% was methyl mercury (MeHg) and 59 to 68% was labile inorganic Hg. The concentration of MeHg (range: 0.03 to 1.05 mg kg(-1) ww) was positively associated with HgT concentration, and the percent MeHg (4 to 109%) decreased exponentially with increasing HgT concentration in the spinal cord, cerebellum, frontal lobe and temporal lobe. There was a positive association between SeT and HgT in all brain regions (p<0.05) suggesting that Se may play a role in the detoxification of Hg in the brain. The concentration of HgT in the cerebellum was significantly associated with HgT in other organs. Therefore, HgT concentrations in organs that are frequently sampled in bio-monitoring studies could be used to estimate HgT concentrations in the cerebellum, which is the target organ of MeHg toxicity.

2-Seleno-1-alkylbenzimidazoles and their Diselenides: Synthesis and Structural Characterization of a 2-Seleno-1-methylbenzimidazole Complex of Mercury

2-Seleno-1-methylbenzimidazole, H(sebenzimMe), can be synthesized from 1-methylbenzimidazole by sequential treatment with (i) BunLi, (ii) elemental selenium and (iii) HCl(aq). This method is also applicable to the synthesis of 2-seleno-1-t-butylbenzimidazole, H(sebenzimBut ). Single crystal X-ray diffraction and NMR spectroscopic data demonstrate that H(sebenzimMe) and H(sebenzimBut ) exist as the selone rather than the selenol tautomers, which is in accord with the results of density functional theory (B3LYP) calculations. The data also indicate that the selone is best represented as a C+-Se- zwitterion rather than as a C=Se doubly bonded species. Aerobic oxidation of H(sebenzimMe) and H(sebenzimBut ) in the presence of Et3N yields the diselenides, (sebenzimMe)2 and (sebenzimBut )2. In addition, H(sebenzimMe) reacts with HgCl2 to give [H(sebenzimMe)]2HgCl2, the first structurally characterized example of a 2-seleno-1-alkylimidazole mercury complex.

Exposure-dose-response of Anadara trapezia to metal contaminated estuarine sediments: 3. Selenium spiked sediments

Selenium enters near shore marine environments from the activities of coal-fired power stations. Although selenium is an essential element, at elevated concentrations it can cause genotoxic damage. The relationship between selenium exposure dose and response was investigated in Anadara trapezia exposed to selenium spiked sediment (5 μg/g and 20 μg/g dry mass) for 56 days. A. trapezia reached an equilibrium selenium tissue concentration (2 μg/g and 10 μg/g respectively) by day 42. Gills had significantly more selenium than the hepatopancreas and haemolymph. Between 12 and 21% of accumulated selenium in the gill and hepatopancreas was detoxified and in the metal rich granule. Most of the biologically active selenium in both tissues was in the mitochondrial fraction. Glutathione peroxidase activity and mean total glutathione concentrations for selenium exposed organisms were not significantly different to controls. The ratio of reduced to oxidised glutathione and the total antioxidant capacity were significantly reduced in selenium exposed organisms compared to control organisms. Increased selenium exposure resulted in significant increases in lipid peroxidation, lysosomal destabilisation and an increased frequency of micronuclei. A significant exposure-dose-response relationship for A. trapezia exposed to selenium enriched sediments indicates that elevated sediment selenium concentrations can increased biologically active selenium burdens and cause impairment of cellular processes and cell integrity.

Cadmium-induced changes in trace element bioaccumulation and proteomics perspective in four marine bivalves

Bivalves are employed widely as biomonitors of metal pollution and proteomics has increasingly been applied to solve ecotoxicological issues. This study aimed to investigate the effects of Cd exposure on the bioaccumulation of other trace elements and reveal the molecular mechanisms using proteomics technologies. The results showed that Cd exposure resulted in remarkable changes in body concentrations of Zn, Cu, Ag, Co, Ni, Pb, and Se in four marine bivalves (scallop Chlamys nobilis, clam Ruditapes philippinarum, mussel Perna viridis, and oyster Saccostrea cucullata). Generally, the bivalves exposed to higher Cd concentration accumulated higher concentrations of Zn, Cu, and Se, but a lower concentration of Co. The accumulation of Ag, Ni, and Pb was specific for different species. The data strongly suggest that the influences of one metal exposure on the bioaccumulation of other metals/metalloids need to be considered in interpreting body concentrations of the elements in the biomonitors. Cd exposure had little effect on bivalve proteomes, and the identified proteins were insufficient to explain the observed disruption of trace element metabolism. However, protein expression signatures composed of the altered proteins could distinguish the clams and the mussels with different body Cd levels. The strong up-regulation of galectin in Cd-exposed oysters indicated the protein as a novel biomarker in environmental monitoring.

Biogenic and toxic elements in feathers, eggs, and excreta of Gentoo penguin (Pygoscelis papua ellsworthii) in the Antarctic

Feathers, eggs, and excreta of Gentoo penguin (Pygoscelis papua ellsworthii), adults, from Livingston Island (South Shetlands), chosen as bioindicators, were used to test the quality of the Antarctic environment. Sex was not examined. The bioaccumulations of toxic trace elements (Cd, Pb, Al, and As), essential trace elements (Fe, Cu, Zn, Mn, Cr, V, Ni, and Sr), and major essential elements (Na, K, Mg, Ca, P, and S) were established. For the first time data about the element contents in Gentoo eggs is provided. Two hypotheses were tested: (1) there are differences in the metal levels among eggs and feathers; and (2) the element concentrations are highest in the excreta. The hypotheses were confirmed at 0.01-0.05 confidence levels. The concentrations of almost all trace elements were significantly higher in the feathers compared to those in the eggs. The following values of the concentrations ratio Fe/Zn were obtained: in the embryo, Fe/Zn = 1.5, and in the feathers, Fe/Zn = 0.5. The concentration of Pb in the embryo and excreta was below 0.4 μg/g, and Cd and As in eggs were below 0.05 and 0.3 μg/g, respectively. This indicates that there is no toxic risk for penguin offspring. Arsenic could be considered as a potential pollutant for Antarctic soil due to its relative high concentration in excreta, 5.13 μg/g. The present data (year 2007) were compared to the data for years 2002 and 2003. No trend of toxic element contamination was established. The concentrations of Pb, Cd, and As in representatives from the top of the food chain in the Antarctic (the present study) and Arctic (literature data) were compared. The data supports the hypothesis that there is an abnormality in cadmium levels in polar marine areas. Regarding Pb, the South Shetlands displayed 3-fold lower level compared to the Aleutians.

In vivo formation and binding of SeHg complexes to the erythrocyte surface

The in vivo dynamics of selenium (Se) and mercury (Hg) interaction was studied in mouse tissues using direct visualization of individual Se, Hg, and SeHg particles on the surface of circulating erythrocytes. This high-resolution detection of Se and Hg was obtained by scanning electron microscopy coupled to X-ray microanalysis. BALB/c mice were injected in the peritoneal cavity with Se and Hg salts, and the animals were sacrificed 3 min after the Hg injection. Only a minority (9%) of the metal dots seen on mouse liver erythrocytes were SeHg complexes when Se and Hg salts were mixed together before injection. In contrast, the majority (73%) of metal dots on liver erythrocytes were SeHg complexes if Se was injected at least 5 min before Hg injection. All metal dots on liver erythrocytes were of SeHg complexes if Se was injected 9 or 12 min before the Hg injection. We conclude that the formation of stable in vivo SeHg complexes requires preliminary interaction of Se with a putative serum factor before complexes between Se and Hg are formed and are bound to the erythrocyte cell surface.

On the chalcogenophilicity of mercury: evidence for a strong Hg-Se bond in [Tm(Bu(t))]HgSePh and its relevance to the toxicity of mercury

One of the reasons for the toxic effects of mercury has been attributed to its influence on the biochemical roles of selenium. For this reason, it is important to understand details pertaining to the nature of Hg-Se interactions and this has been achieved by comparison of a series of mercury chalcogenolate complexes that are supported by tris(2-mercapto-1-t-butyl-imidazolyl)hydroborato ligation, namely [Tm(Bu(t))]HgEPh (E = S, Se, Te). In particular, X-ray diffraction studies on [Tm(Bu(t))]HgEPh demonstrate that although the Hg-S bonds involving the [Tm(Bu(t))] ligand are longer than the corresponding Cd-S bonds of [Tm(Bu(t))]CdEPh, the Hg-EPh bonds are actually shorter than the corresponding Cd-EPh bonds, an observation which indicates that the apparent covalent radii of the metals in these compounds are dependent on the nature of the bonds. Furthermore, the difference in Hg-EPh and Cd-EPh bond lengths is a function of the chalcogen and increases in the sequence S (0.010 A) < Se (0.035 A) < Te (0.057 A). This trend indicates that the chalcogenophilicity of mercury increases in the sequence S < Se < Te. Thus, while mercury is often described as being thiophilic, it is evident that it actually has a greater selenophilicity, a notion that is supported by the observation of facile selenolate transfer from zinc to mercury upon treatment of [Tm(Bu(t))]HgSCH(2)C(O)N(H)Ph with [Tm(Bu(t))]ZnSePh. The significant selenophilicity of mercury is in accord with the aforementioned proposal that one reason for the toxicity of mercury is associated with it reducing the bioavailability of selenium.

Microanalysis of metals in barbs of a snow petrel (Pagodroma Nivea) from the Antarctica using synchrotron radiation X-ray fluorescence

For the first time synchrotron radiation X-ray fluorescence (SR-XRF) microanalysis was performed throughout the total length of 4 single barbs from the primaries and secondaries of a snow petrel (Pagodroma Nivea) collected in the Antarctica. Thirteen elements (S, Mg, K, Ca, Fe, Ni, Cu, Zn, Se, Sr, Ba, Hg and Pb) were detected somewhere in the barbs. Variations in levels of these elements within and among the barbs were obvious, indicating nonuniform microscale distributions. Factors influencing the fluctuations of the levels of the elements were investigated using a multivariate statistical analysis method. Five factors (F1 being associated with high loadings of Ca, Sr, and Ni, F2 with high loadings of Fe and Ba, F3 with high loadings of Se and Hg, F4 with high loadings of Ca and K, and F5 with high loadings of Zn and Pb) were found to explain about 80% of the total variance. Results from the factor analysis suggested external contamination of Fe, Ba, Pb, Zn and Hg on the feathers of the snow petrel.

Selenium in placenta predicts birth weight in normal but not intrauterine growth restriction pregnancy

Placental selenium, lead and cadmium concentrations were determined in a group of pregnancies with birth weight appropriate for gestational age and in a group of intrauterine growth restriction cases. Following adjustment for a number of confounding variables, selenium was found to be a significant predictor of newborn weight only in the group of pregnancies with birth weights appropriate for gestational age. Placental lead and cadmium levels were not associated with birth weight in either group.

Trace metal concentrations in the hair of Zalophus californianus pups and their relation to feeding habits

The levels of six trace metals (Hg, Se, Pb, Cu, Fe, and Zn) were measured in the hair of California sea lion pups from eight rookeries in the Gulf of California, with the aim of relating these levels with the animals feeding habits, trophic level, and delta(15)N signatures at each locality. Trace metal levels were seen to vary significantly between sample sites as were tendencies associated with feeding habits. Mercury concentrations showed a clear positive correlation with trophic level (r = 0.73, p = 0.06) as well as the delta(15)N values of the rookeries (r = 0.79, p = 0.033). This was explainable via the process of biomagnification, although other elements did not follow the same tendency. High Cu concentrations in the hair (18 and 47 microg g(-1); ANOVA, p < 0.05) were observed at San Pedro Mártir and San Esteban, where the consumption of squid is higher than at other localities (approximately 17% and approximately 27% of the diet, respectively). Se and Hg concentrations correlated positively (r = 0.73, p = 0.038), probably the result of detoxification processes, a phenomenon previously reported in marine mammals. In light of the high degree of philopatry among sea lions in the Gulf and their pups' dependence exclusively upon their mother's milk during the first months of life, the analysis of trace metals in the easily sampled hair of the pups, offers an indirect way of monitoring the toxicology of the sea lion populations.

Facile and sensitive determination of selenium (IV) in pharmaceutical formulations by flow injection spectrophotometry

An automated flow injection spectrophotometric method has been developed for the rapid, simple, selective, and sensitive determination of selenium (IV) from various pharmaceutical multivitamin and mineral formulations. The method was based on the oxidation of 4-aminoantipyrine (4-amino-l,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazole-3-one; 4-AAP) by selenium in presence of acidic medium and the coupling with N-(naphthalen-l-yl)ethane-1,2-diamine dihydrochloride (NEDA) to give a violet color derivative. Gilson P2 mini pulse peristaltic pump has been used for introducing the selenium (IV), dilute HCl, 4-AAP and NEDA solutions into reaction coil by an automatic system. The absorbance of the 4-AAP-NEDA color derivative was measured at 563 nm after a reaction time of 3 min in stop flow of 4-AAP-NEDA. Beer's law was obeyed for selenium in the concentration range 0.05-5.0 microg mL(-1) and Sandell's sensitivity was found to be 0.00286 microg cm2. The performance of the present method was compared with the official method in terms of Student's F- and t-tests, and no significant difference was observed. This method was found to be suitable for estimating the selenium (IV) concentration in various pharmaceutical multivitamin and mineral formulations such as tablets and capsules.

Oral administration of lycopene reverses cadmium-suppressed body weight loss and lipid peroxidation in rats

Cadmium (Cd) exposure has been recognized to result in a wide variety of cellular responses, including oxidative stress and body weight loss. The aim of the present study was to examine the effect of lycopene supplementation on the antioxidant defense system, lipid peroxidation (LPO) level, nitric oxide (NO), tumor necrosis factor alpha (TNF-alpha) production, and body weight in Cd-exposed rats. Animals were divided into four groups (n = 7): control, Cd-treated, Cd plus lycopene-treated, and lycopene-treated. Cadmium (as CdCl2) was administrated orally for 20 days (6.6 mg kg(-1) day(-1)), and lycopene (10 mg kg(-1) day(-1)) was similarly administered. Lycopene administration significantly suppressed Cd-induced LPO in plasma and kidney homogenates. Lycopene also reversed Cd-decreased body weight compared to the control. Cadmium treatment had diverse effects on the antioxidant enzyme activities. Although antioxidant superoxide dismutase activity was unchanged, glutathione peroxidase activity was decreased, and catalase activity was elevated in kidney homogenates of Cd-administrated group. However, lycopene treatment reversed Cd-changed enzyme activities to the control level. Xanthine oxidase activity and TNF-alpha concentration were not altered by Cd administration, indicating that superoxide anion production and inflammation were not stimulated. Cadmium did not change NO levels in kidney homogenates but decreased those in plasma, and this effect was not prevented by lycopene supplementation. The result suggests that consumption of adequate levels of lycopene may be useful to prevent heavy-metal-induced LPO and body weight loss.

Role of selenium in mercury intoxication in mice

Studies were conducted to examine the effect of pre and post-treatment of selenium in mercury intoxication (20 micromole/ kg b.w. each given intraperitoneally) in mice in terms of lipid peroxidation (LPO), glutathione (GSH) content, activities of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and mercury concentration in liver, kidney and brain. No significant alteration was observed in all the organs examined after mercury or selenium treatment in LPO and GSH but administration of selenium (pre and post) resulted in an increase in the level of LPO and GSH. The activity of SOD was depleted in liver and kidney while that of GPx was lowered in liver of mercury exposed animals. Selenium administration resulted in restoration of the depletion of these enzymatic activities. The activity of CAT in liver and brain was enhanced both in mercury and selenium treated animals. Administration of selenium significantly arrested enhanced CAT activity. Kidney showed the highest mercury concentration among the organs examined. Administration of selenium resulted in further enhancement of mercury concentration in the tissues. An increase in selenium level in liver was observed after mercury treatment, which was also restored by mercury selenium co-administration. Our results indicate that the prooxidant effect of selenium was greater by its pretreatment.

Mercury in seafood: mechanisms of accumulation and consequences for consumer health

Mercury is a largely uncontrollable heavy metal contaminant in that it is globally ubiquitous, and environmentally persistent. The element has the potential for global mobilization following liberation from environmental stores, which can occur as a consequence of either anthropogenic activities or natural processes. Furthermore, organic forms like methylmercury accumulate in biological tissues with an exceptionally long biological half-life, facilitating the magnification of this toxin along trophic food chains. Bioaccumulation is particularly evident in aquatic environments, in which long-lived piscivorous fishes and marine mammals are reported with a mercury burden one-million times that of the surrounding water body, typically attaining mercury burdens exceeding 1 microg g(-1). Mercury levels in other seafood, however, are typically reported in the range of 0.1 to 0.2 microg g(-1) and usually less then 0.5 microg g(-1). The primary source of human exposure to environmental mercury is through seafood consumption. The dangers associated with the consumption of large amounts of methylmercury accumulated in seafood are well recognized from past poisoning incidents, in which fish with mercury burdens in the range of 9 to 24 microg g(-1) were consumed. Nevertheless, the toxicological consequence of chronic low-level mercury exposure from habitual seafood consumption is an area of contention. This review discusses the mechanisms of mercury accumulation and distribution in fish tissues and the toxicological consequences of mercury exposure from seafood consumption with regard to international safety guidelines.

The penguin feathers as bioindicator of Antarctica environmental state

Concentrations of biogenic and toxic elements (Na, K, Mg, Ca, P, S, Fe, Cu, Zn, Co, Mn, Se, Ni, Sr, Al, Cd, Pb, As) were determined for the first time in feathers of gentoo penguin (Pygoscelis papua) and chinstrap penguin (Pygoscelis antarctica) from Antarctica. A comparison of element levels was performed among these species in years 2002-2003. Penguins molt annually and this fact allows defining precisely the concentrations of accumulated toxic elements and heavy metals in plumage every year. A continual environmental biomonitoring could establish a possible trend to contamination of the Antarctica sea zones. The penguin feather is an excellent subject for monitoring because penguins have long life span, permanent ecological niche and dominate the aviafauna in Antarctica. Because of its remoteness, Antarctica is believed to be unpolluted. The relatively elevated levels of Cd established are due to the Cd-enrichment of the Antarctic marine food chain. Because of great bioaccumulation of lead in feathers, the concentration of Pb in penguin feather was higher (4-8 times) compared to that of Cd. In both penguin species the levels of Zn were 1.9 times higher than respective Fe levels. The concentrations of most of the investigated elements were significantly higher in P. papua than in P. antarctica and this probably could be explained by the different diet and feeding habit of these species.

Beneficial role of monoesters of meso-2,3-dimercaptosuccinic acid in the mobilization of lead and recovery of tissue oxidative injury in rats

We investigated the therapeutic efficacy of meso-2,3-dimercaptosuccinic acid (DMSA) and two of its analogues, monomethyl dimercaptosuccinic acid (MmDMSA) and mono-cyclohexyl dimercaptosuccinic acid (MchDMSA) in reducing lead concentration in blood and soft tissues, and in recovering lead induced oxidative stress in rats. Male wistar rats were exposed to lead acetate in drinking water for 20 weeks, followed by 5 days of oral treatment with DMSA (100mg/kg, oral, once daily), MmDMSA or MchDMSA (50 and 100mg/kg). Biochemical variables indicative of oxidative stress along with lead, zinc and copper concentration were evaluated in blood and other soft tissues. Exposure to lead caused a significant decrease in blood delta-aminolevulinic acid dehydratase (ALAD) activity and glutathione (GSH) level. These changes were accompanied by inhibition of kidney ALAD and an increase in delta-aminolevulinic acid synthatase (ALAS) activity in liver and kidneys. Also seen were a pronounced depletion of brain GSH, glutathione peroxidase (GPx), glutathione-S-transferase (GST) and decreased superoxide dismutase (SOD) activity and an increase in thiobarbituric acid reactive substances (TBARS) and reactive oxygen species (ROS) levels. These biochemical changes were correlated with an increased uptake of lead in blood and soft tissues. Blood and kidneys zinc concentration decreased significantly following lead exposure while, copper concentration remained unchanged. No effect of chelation on hepatic zinc concentration was noted, only liver copper concentration showed significant depletion on treatment with DMSA and MmDMSA (100mg/kg). Treatment with DMSA, MmDMSA and MchDMSA provided significant recovery in altered biochemical variables and brain DNA damage besides significant depletion of tissue lead burden. Among the chelating agents used, MchDMSA and MmDMSA provided better recovery in altered biochemical variables and depletion of lead concentration in tissues compared to DMSA. The above results suggest DMSA monoesters to be a better treatment option than DMSA in eliciting recovery to the altered biochemical variables and in the depletion of body lead burden.

Lead-induced oxidative stress and hematological alterations and their response to combined administration of calcium disodium EDTA with a thiol chelator in rats

The therapeutic efficacy of calcium disodium ethylenediaminetetracetic acid (CaNa(2)EDTA) and the two thiol chelators, 2,3-dimercaptopropane 1-sulfonate (DMPS) and monoisoamyl dimercaptosuccinic acid (MiADMSA) was studied, both individually and in combination, in reducing lead concentration in blood and soft tissues and in restoring lead induced altered biochemical variables in rats. Exposure to subacute dose of lead implicated a critical role of reactive oxygen species (ROS) and oxidative stress in altering the normal values of these variables. Exposure to lead caused a significant inhibition of blood delta-aminolevulinic acid dehydratase (ALAD), an important enzyme in the haem synthesis pathway and glutathione (GSH) level. These changes were also accompanied by inhibition of ALAD activity in kidney, delta-aminolevulinic acid synthase (ALAS) activities in liver and changes in platelet counts in whole blood suggesting disturbed haem synthesis pathway. Lead exposure also led to a pronounced depletion of brain GSH contents, superoxide dismutase (SOD) activity, an increase in thiobarbituric acid reactive substances (TBARS), and activity of glutathione S-transferase (GST). Specific activities of membrane-bound enzymes, acetylcholinesterase (AChE) and monoamine oxidase (MAO), were significantly inhibited on lead exposure. These biochemical changes were correlated with increased uptake of lead in blood and soft tissues. Post lead exposure treatment with MiADMSA in particular provided significant recovery in altered biochemical variables besides significant depletion of tissue lead burden. Treatment with CaNa(2)EDTA and DMPS individually had only moderate beneficial effects on tissue oxidative stress, although they were equally effective in the removal of tissue lead burden. Tissue zinc and copper levels did not depict any significant depletion, although changes like marked depletion of zinc following CaNa(2)EDTA and copper after MiADMSA administration were of some concern. Combined administration of CaNa(2)EDTA, particularly with MiADMSA, was the most effective treatment protocol compared to all other treatments. It can be concluded from our present results that combined therapy with CaNa(2)EDTA and MiADMSA proved significantly better in restoring biochemical and clinical variables over monotherapy with these chelating agents against subacute lead exposure in adult rats.

Chemical forms of mercury and cadmium accumulated in marine mammals and seabirds as determined by XAFS analysis

Marine mammals and seabirds tend to exhibit high accumulations of mercury, cadmium, and selenium in their livers and kidneys. In this study, chemical forms of mercury, cadmium, and selenium accumulated in the livers and kidneys of northern fur seal (Callorhinus ursinus), Risso's dolphin (Grampus griseus), and black-footed albatross (Diomedea nigripes) were studied by extended X-ray absorption fine structure (EXAFS) spectroscopy to reveal the detoxification mechanisms of these metals. It was found that mercury and selenium exist in the form of HgSe in the liver of northern fur seal. Mercury levels were found to be higher than those of Se, based on their molar ratio, in black-footed albatross. XAFS analysis disclosed an existence of chalcogenide containing both Hg-Se and the Hg-S bonds, suggesting the existence of a solid solution Hg(Se, S) as granules in black-footed albatross. In contrast, Cd concentrations in the kidney were higher than those in the liver for northern fur seal, black-footed albatross, and Risso's dolphin. It was found that Cd was bound to sulfur, which was probably derived from the metallothionein. The Cd-O bond was observed in the tissues of northern fur seal.

Selenium in pregnancy: is selenium an active defective ion against environmental chemical stress?

Transportation of selenium from mother to fetus and its possible effects on mother's zinc, copper, cadmium, and mercury levels were studied together during the first trimester and at term in 216 mothers. Mothers came from three geographical places with different selenium intakes. The role of selenium as a biomarker for the vital function was estimated by studying the associations between tissue or blood selenium content and placental cytochrome P450 enzyme activities and the newborn's birth weight. Regardless of the selenium intake of the mothers, higher concentrations were found in the cord blood than in mother's blood reflecting active transportation of selenium to the fetus. Active smoking was associated with higher placental selenium concentrations like it is associated with higher placental zinc concentrations. When the cadmium concentrations were high in placenta, as in smokers, the transfer of selenium from blood to placenta was increased, decreasing the selenium levels in blood. On the other hand, the high selenium concentrations in blood were connected to lower cadmium concentrations in placenta also in nonsmokers. Selenium had correlations with copper and zinc. ECOD activity in placental tissue, mercury in mothers' hair, mothers' age, and selenium concentrations in cord blood and placental selenium all seem to have connections with xenobiotic-metabolizing enzymes linked effects among mothers. These data suggest that selenium has an active role in the mother's defense systems against the toxicity of environmental pollutants and the constituents of cigarette smoke.

Effects of Se and Zn supplementation on the antagonism against Pb and Cd in vegetables

The antagonistic effects of supplementation of Zn and Se to the soil on vegetables were studied in this work. In the pot experiment, Se (Se4+) and Zn (Zn2+) were applied, respectively, to the soil, in which the Chinese cabbage (Brassica rapa) and the lettuce (Lactuca sativa L.) were planted. As a result, Se and Zn were enriched evidently in the two vegetables. The contents of Pb and Cd in the two vegetables were decreased markedly while contents of some healthy mineral elements, like Mn and Mg, were increased to some extent when Se and Zn were applied. The antagonism of Se and Zn against Pb and Cd in plants was suggested. The farmland experiment on the lettuce was conducted to explore further the effect of supplementation of Zn and Se under the actual field conditions. Result came out to be that the enrichment of Zn and Se restrained the accumulation of Pb and Cd in the lettuce remarkably, as well as enhanced the absorption of some other nutritional elements, like Fe, Mn, Cu, Ca and Mg. Therefore, application of Se and Zn was proved to be an effective and feasible method to improve trace elements nutrition in the vegetables.

In vitro cytogenetic testing of an organoselenium compound and its sulfur analogue in cultured rat bone marrow cells

Background

Selenium (Se) is a non-metal element, occurring in varying degrees in the environment and it has been found to be a component of several enzymes. Different selenium compounds have been associated with carcinogenicity, toxicity, modification of metal toxicity and prevention of cancer. Organoselenium compounds had substantially greater bioavailability and less toxicity than that of inorganic selenium. From a chemical point of view, Se resembles sulfur (S) in many of its properties, thus, Se and S may be considered to be isosteric. The ability of a synthetic organoselenium compound; cyclopenta-dienyldicarbonyl ironselenoterephthalic acid (CSe) and its sulfur analogue (CS) in the range of 10^-8 to 10^-5 M, to induce sister-chormatid exchanges (SCE) and alter cell division expressed as mitotic index (MI) as well as cell survival has been investigated.

Methods

Rat bone marrow cells were cultured in the presence of CSe and CS in the range of 10^-8 to 10^-5 M with a total exposure time of 4, 16 or 28 h at 37°C. Fluorescence-plus-Giemsa (FPG) technique was used to visualize chromosomes for SCE analysis and MI determination. Trypan blue exclusion technique was used to determine cell viability.

Results

At the three exposure times, cell survival progressively decreased with increasing concentration, but the effect of either chemical was not significant (ANOVA; P < 0.05) as compared to the negative control. Significant reductions in MI were calculated at the highest concentration (10^-5 M) when either chemical was applied for 16 or 28 h. Furthermore, the mean SCE increased with longer exposure times and, in general, CSe had slightly greater effect on cell survival and caused higher frequencies of SCE than CS. The exception was the 10^-8 M treatment. However, both CSe and CS failed to induce 2-fold SCE as that of the negative control and therefore they are not considered as mutagens.

Conclusion

Both CSe and CS in the range of 10^-8 to 10^-5 M could not double the SCE rate of the negative control and therefore not considered as mutagens at these experimental conditions.

Mechanisms of the inhibitory effects of selenium and mercury on the activity of delta-aminolevulinate dehydratase from mouse liver, kidney and brain

Mercury is known to interact with selenite and when the two are co-administered, one reduces the toxicity of the other. The main goal of this study was to investigate the simultaneous in vitro effects of sodium selenite (Se(4+)) and mercuric chloride (Hg(2+)) on the activity of hepatic, renal and cerebral delta-aminolevulinate dehydratase (delta-ALA-D) of adult male mice (Swiss albino). Hg(2+) inhibited delta-ALA-D from tissue supernatants and the IC(50) values for hepatic, renal and cerebral enzyme inhibition were 38+/-4.2, 67.5+/-4.3 and 46.2+/-3.7 microM, respectively. Se(4+) displayed a higher inhibitory action toward delta-ALA-D activity than Hg(2+). Simultaneous addition of Se(4+) and Hg(2+) to the delta-ALA-D assay increased the inhibition of the enzyme. Se(4+) and Hg(2+) oxidized total -SH groups from hepatic, renal and cerebral supernatants, although the effect of Se(4+) decreased in the presence of increasing concentrations of Hg(2+). The oxidation of -SH groups from a dithiol (DTT), a monothiol glutathione (GSH) and a protein (albumin) increased in the presence of Hg(2+). Only DTT was oxidized by Se(4+) and the oxidation decreased in the presence of Hg(2+), suggesting the formation of a chemical complex. This complex did not inhibit delta-ALA-D. These results suggest a similar inhibitory mechanism of Se(4+) and Hg(2+) on delta-ALA-D in which oxidation of sulfhydryl groups located at the active site of the enzyme is an essential step. Furthermore, decreasing oxidative effects of selenite on sulfhydryl groups from DTT in the presence of mercury are believed to occur as the result of the formation of an inactive ternary complex of the thiol-Hg-Se type, which does not inhibit delta-ALA-D.

Profile of nonprotein thiols, lipid peroxidation and delta-aminolevulinate dehydratase activity in mouse kidney and liver in response to acute exposure to mercuric chloride and sodium selenite

The effects of mercury (Hg(2+)) and selenite (Se(4+)) on delta-aminolevulinic acid dehydratase (delta-ALA-D) activity, 2-thiobarbituric acid reactive substances (TBARS) and nonprotein sulfhydryl content (NPSH) in mouse kidney and liver were investigated. Male mice were given a single i.p. injection of Hg(2+) and/or Se(4+) (25 micromol/kg) and were killed at 6, 12, 24 and 48 h after treatment. Hg(2+) inhibited renal delta-ALA-D at 6 and 12 h after treatment. Se(4+) abolished the inhibitory effect of mercury on renal delta-ALA-D at 12 h after treatment. Renal and hepatic NPSH content decreased after Hg(2+) exposure and selenite inhibited, at least in part, the Hg-induced oxidation of renal and hepatic NPSH. Se(4+) and Hg(2+), when injected alone, did not alter hepatic or renal TBARS levels; however, simultaneous exposure to these compounds increased hepatic and renal TBARS levels at 12 and 48 h after treatment, respectively. Present results suggest that selenium abolishes the interaction of Hg(2+) with sulfhydryl groups of protein and nonprotein sources.