Displacement of zinc and copper from copper-induced metallothionein by cadmium and by mercury: in vivo and ex vivo studies

The in vitro affinity of metals for metallothionein (MT) is Zn less than Cd less than Cu less than Hg. In a previous study Cd(II) and Hg(II) displaced Zn(II) from rat hepatic Zn7-MT in vivo and ex vivo (Day et al., 1984, Chem. Biol. Interact. 50, 159-174). The ability of Cd(II) or Hg(II) to displace Zn(II) and/or Cu(II) from metallothionein in copper-preinduced rat liver (Zn, Cu-MT) was assessed. Cd(II) and Hg(II) can displace zinc from (Zn, Cu)-MT both in vivo and ex vivo. The in vitro displacement of copper from MT by Hg(II) was not confirmed in vivo and ex vivo. Cd(II) treatment did not alter copper levels in (Zn, Cu)-MT, as expected. Hg(II) treatment, however, did not decrease copper levels in MT, but rather increased them. The sum of the copper increase and mercury incorporation into MT matched the zinc decrease under in vivo conditions and actually exceeded the zinc decrease under ex vivo conditions. Short-term exposure of rat liver to exogenous metals can result in incorporation of these metals into MT by displacement of zinc from pre-existing MT. Displacement of copper from pre-existing MT by mercury, as predicted by in vitro experiments, was not confirmed under the conditions of our in vivo and ex vivo experiments. This result is explainable based on the differing affinities and/or preferences of the two metal clusters in MT.     

Induction of metallothionein in rat tissues following subchronic exposure to mercury shown by radioimmunoassay

Although the analysis of metallothionein (MT) by radioimmunoassay (RIA) is not a common technique, its use is preferred over other methods since it offers the advantages of sensitivity and specificity. In this paper we present data on the basal levels of MT in rat tissues and physiological fluids of female Sprague-Dawley rats. The mean basal MT concentrations of the following organs and fluids were determined by RIA to be: liver (9.8 μg/g), kidney (68 μ/g), brain (0.8 μg/g), spleen (1.0 μg/g), heart (5.4 μg/g), plasma (11 ng/ml), and urine (200–300 μg/g creatinine). Following subcutaneous exposure to inorganic mercury (0.2 μmol/kg/d, 5 d a week for up to 4 wk), the metal accumulated primarily in the kidney. There was also a simultaneous accumulation of zinc in the liver and of zinc and copper in the kidney. Induction of MT did take place in liver, kidney, brain, and spleen. No increases in the MT contents of blood and urine were noted. The excess zinc and copper in the kidney of exposed animals were found to be associated predominantly with MT. No overt signs of mercury toxicity were noted in these animals and the incidence of proteinurea was nil. The data are discussed with reference to methods of MT determination in animal tissues and in relation to mercury metabolism and toxicity.     

Concentrations of cadmium,zinc, copper,iron, and metallothionein in liver and kidney of nonhuman primates

To evaluate the species specificity of Cd accumulation and the relationship of Cd with other essential metals and metallothionein (MT), the concentrations of Cd, Zn, Cu, and Fe in the liver and kidney and the MT concentrations in the soluble fractions of the liver and kidney were determined in Cd-uncontaminated nonhuman primates (11 species, 26 individuals) kept in a zoo and two wild-caught Japanese macaques. The compositions of metal-binding proteins in the soluble fractions were also investigated by high-performance liquid chromatography (HPLC). The hepatic Cd concentration was 0.03–14.0 μg/g and the renal Cd concentration was 0.35–99.0 μg/g, both varying greatly and being higher in nonhuman primates, which were more closely related to man. The hepatic Zn concentration was 24.0–176 μg/g and the renal Zn concentration was 13.5–138 μg/g, showing 7- to 10-fold differences, and a correlation (r=0.558, p<0.01) was found between renal Zn and renal Cd concentrations. It was proved that in the liver, MT is more closely correlated with Zn (r=0.795, p<0.001) than with Cd (r=0.492, p<0.01) and that in the kidney MT is correlated with both Cd (r=0.784, p<0.001) and Zn (r=0.742, p<0.001). HPLC analysis of metals bound to MT-like protein in chimpanzees, de Brazza’s monkeys, and Bolivian squirrel monkeys showed that more than 90% of Cd in both the liver and kidney, approx 40% of Zn in liver and 28–69% of Zn in kidney were bound to MT-like protein. The higher percentage Zn was bound to high-molecular protein.     

Metal composition of human hepatic and renal metallothionein

This article is based on data on the levels of metals (Cd, Zn, Cu) and metallothionein (MT) determined radiochemically with²⁰³Hg in renal cortex and liver of 137 autopsy cases. From this number, for 23 cases, the gel filtration of the cytoplasmic fraction of the organs was performed. The molar content of metals in the MT fraction (Sephadex G-50) amounted to 46.9, 50.2, and 2.0% for Cd, Zn, and Cu in renal cortex, respectively, and to 8.3, 83.6, and 9.1% for Cd, Zn, and Cu in the liver, respectively. In parallel with the increase of Cd and MT in renal cortex, increasing saturation was found of the MT fraction by Cd, occurring at the expense of Zn and Cu. Equimolar amounts of Cd and Zn in the MT fraction are found at Cd level of 0.5 μmol Cd/g wet wt of renal cortex. In the liver, analogous dependency (elevation of %Zn, depression of %Cd and %Cu) were observed in relation to Zn and MT levels in this organ. The basic level of Zn (not bound with MT) was estimated at 0.5 μmol/g for both renal cortex and liver. A deficit of non-MT Zn in kidneys is proposed as an alternative mechanism of toxic Cd action.     

The transfer of cadmium, mercury, methylmercury, and zinc in an intertidal rocky shore food chain

We examined the transfer of cadmium (Cd), inorganic mercury [Hg(II)], methylmercury (MeHg), and zinc (Zn) in an intertidal rocky shore food chain, namely from marine phytoplankton to suspension-feeding rock oysters (Saccostrea cucullata) and finally to predatory whelks Thais clavigera. The uptake of metals from the dissolved phase was also concurrently quantified in the oysters and the whelks. Metal uptake by the oysters was not directly proportional, whereas metal uptake by the whelks was directly proportional to metal concentration in the water. The order of uptake was MeHg>Hg(II)>Zn>Cd, and was much higher in the oysters than in the whelks. The relative uptake of Zn and Cd was comparable between oysters and whelks, whereas MeHg and Hg(II) showed disproportionally higher uptake in oysters than in whelks as compared to Zn and Cd. The assimilation efficiencies (AEs) were in the order of MeHg>Zn>Cd=Hg(II) in oysters, whereas the AEs were highest for MeHg and comparable for Zn, Cd, and Hg(II) in the whelks. Pre-exposure of the oysters to different dissolved concentrations of Cd significantly elevated the AEs of Cd and Hg(II) but not of Zn, in association with the induction of metallothioneins in the oysters. The whelks significantly assimilated Cd and Zn from various prey (barnacles, oysters, mussels, and snails) with contrasting strageties of metal sequestration and storage. There was no significant relationship between the metal AE and the metal partitioning in the soluble fraction (including metallothionein-like proteins, heat stable protein, and organelles). The insoluble fraction of metals was also available for metal assimilation. Our calculations show that the dietary uptake of metals can be dominant in the overall bioaccumulation in the oysters and whelks, and the trophic transfer factor was >1 for all metals. Thus, the four metals have a high potential of being biomagnified in the intertidal rocky shore food chain. MeHg possessed the highest and Hg(II) and Cd the lowest potential of trophic transfer among the four metals considered.     

Age- and tissue-dependent metallothionein and cytosolic metal distribution in a native Mediterranean fish, Mullus barbatus, from the Eastern Adriatic Sea

The levels of metallothionein (MT), a biomarker of metal exposure, and of cytosolic metals (Zn, Cu, Cd), known as MT inducers, were investigated as variables of age (1 to 8 years) and tissue mass (liver, kidney, brain) of red mullet (Mullus barbatus). Within the age from 1 to 8 years the most significant increase is evident for cytosolic Cd in liver (43-fold) and in kidney (5-fold). MT and essential metals are constant with age or slightly increased. Over the growth period, statistically significant MT and metal increase is evident only between 1 and 6-8 years old specimens, while for Cd in liver and kidney cytosol significant increase already exists at 4 years old specimens. Metal distribution in all tissues follows the order: Zn>Cu>Cd, with even 500-800 times lower Cd levels than essential metal levels. Consequently, MTs follow the levels of essential metals, Zn and Cu, indicating MT involvement in homeostasis of essential metals. In contrast to kidney and brain, hepatic MT levels are not age-dependent. Inclusion of hepatic MT measurements and the associated cytosolic metals will be useful in the assessment of long-term metal effects in demersal fish M. barbatus.     

On metallothionein,cadmium, copper and zinc relationships in the liver and kidney of adult rats

1. A short-term exposure of adult Wistar rats to Cu (50 μg/ml) and Cd (10.0 μg/ml drinking water) caused significant changes in the subcellular concentrations of Cd, Cu, Zn and metallothionein (MT) in the liver and kidney; the concentrations were close to the physiological values, however.2. To establish a relationship between these changes in the subcellular concentrations of Cd, Cu, Zn and the level of MT in the post-mitochondrial fraction of the liver and kidney, the analytical data (N = 42) were subjected to the multiple regression analysis.3. The analysis showed that MT synthesis in the liver was principally induced by small amounts of Cd (0.32–1.4 μg/g wet wt) whereas in the kidney a level of MT in the post-mitochondrial fraction correlated positively with the renal Cd and Cu, as well as with the level of this protein in the liver.4. The above results together with the positive correlation between the level of MT in the post-mitochondrial fraction and the concentration of Cu in this fraction, as well as the fact that under normal physiological conditions the capacity of MT (β-domain) in the liver and kidney was sufficient to bind 50–100% of the total post-mitochondrial Cu suggest that MT, first induced by small amounts of Cd, may be involved in the metabolism of Cu.     

Heavy metal intracellular balance and relationship with metallothionein induction in the liver of carp after contamination by silver,cadmium and mercury following or not pretreatment by zinc

Determination of metal levels (copper, zinc, cadmium, silver and mercury) in soluble and insoluble fractions of liver homogenates has been performed after 7 days exposure of carps (Cyprinus carpio) to moderate concentrations of cadmium, silver and mercury in water. Metallothionein (MT) levels have been quantified by a polarographic method before and after the contamination and a subsequent decontamination phase (7 days). The influence of pretreatment by zinc (7 days) has also been evaluated. MT level variations have been interpreted as having regard to inter-related flows of metal between subcellular fractions. Special interest has been focused on heat-stable compound (HSC)-bound heavy metal flows within the cytosol, taking in account that MT is the major component of these ligands. Our data showed differences between the ability of metals to bind cytosolic ligands and HSCs, and their respective potency for MT induction in liver. Regardless of pretreatment, mercury gave the highest increase of liver MT, but the MT level decreased during the decontamination step, especially after pretreatment by zinc. Cadmium and silver gave similar increases, but a significant difference with the control appeared only after the decontamination step with cadmium, while 1 week of contamintion was enough for silver. However, silver binding with MT was achieved only by the end of the decontamination step, while cadmium depicted the highest ratio for HSC-bound toxic metals after the contamination. Our experimental conditions gave the following order of potency for MT induction in liver: mercury silver > cadmium > zinc. Results are discussed comparatively with data obtained with carp gills.     

Chelation in metal intoxication. XXVIII: Effect of thiochelators on mercury (II) toxicity: pre- and post treatment

The effect of treatment with alpha-mercapto-beta-(2-furyl)acrylic acid (MFA), N-(N-mercaptopropionyl) glycine (MPG) and N-acetylcysteine (NAC) compared to spironolactone (SPL), a steroid, before and after 203 mercury (II) exposure, on the disposition of Hg and induction of tissue metallothionein (MT), was investigated in rats. The pretreatment with SPL, MFA and MPG enhanced faecal elimination of Hg and reduced its accumulation in liver particularly, the "heat stable fraction" resulting in lowered hepatic MT induction. Neither the renal uptake of Hg nor induction of tissue MT was affected by pre-treatment with the chelating agents; SPL and MFA causing re-distribution of Hg among the renal sub-cellular fractions. The post-Hg exposure treatment with MFA enhanced the faecal and MPG the urinary excretion of Hg. However, both the chelating agents increased the hepatic burden of Hg as reflected in the subcellular fractions and increased MT contents indicating mobilization of Hg from other tissue binding sites. The post-treatment with MPG however, depleted renal Hg as reflected by the sub-cellular distribution, without affecting renal MT levels. The results show that MFA and MPG are more promising preventive than therapeutic agents in Hg intoxication acting as metal chelators.     

Metal accumulation and metallothionein in brown trout, Salmo trutta, from two Norwegian rivers differently contaminated with Cd, Cu and Zn

In this work we have studied the accumulation of heavy metals in two brown trout (Salmo trutta) populations in their natural environment and the participation of metal binding to metallothionein (MT) in this process. Cd, Cu and Zn concentrations, total MT (including Cu MT) and Cd/Zn MT were measured in the gills, liver and kidney of trout inhabiting two rivers, one Cu-contaminated and the other Cd/Zn-contaminated, located at Røros, Central Norway. In both populations, high levels of Cu were found in the liver, whereas Cd was accumulated in liver and particularly in the kidney. The proportions of Cd/Zn MT and Cu MT in liver and kidney, but not in gills, reflected the accumulated and the environmental concentrations of these metals. The total Cu MT concentrations in the investigated tissues, however, were highest in trout from the river with the lowest ambient Cu concentration. It is suggested that MTs are of less importance in Cu-acclimated trout. The data also suggest that acclimation to a Cu-rich environment involves reduced Cu accumulation or increased Cu elimination. In trout from the Cd-rich environment, this metal was mainly bound to MT, whereas in trout from the Cu-rich environment Cd was also associated with non-MT proteins. These findings emphasize the importance to determine both Cd/Zn MT and Cu MT levels, when the participation of this protein in metal handling in trout tissues is investigated.     

Nephrotoxicity of simultaneous exposure to mercury and uranium in comparison to individual effects of these metals in rats

Both inorganic mercury and uranium are known nephrotoxicants in mammals. In this study, the renal toxicity of a concurrent exposure to inorganic mercury and uranium was compared with the nephrotoxic effects of the individual metals in a rat model. Eight groups of rats, 10 animals per group, were subcutaneously given a single administration of mercuric chloride (HgCl₂, 0.34 mg/kg and 0.68 mg/kg), uranyl acetate dihydrate (UAD, 2.5 mg/kg and 5 mg/kg), or combinations of both compounds at the same doses. A ninth group of rats received sc injections of 0.9% saline and was designated as the control group. Necrosis of proximal tubules, which was observed in all experimental groups, was the most relevant morphologic abnormality. Marked changes, which were remarkably greater than those induced by the individual elements, were noted in some urinary parameters in the groups concurrently exposed to HgCl₂ and UAD. It could be an indicator of a synergistic interaction between mercury and uranium. In contrast, compared with the urinary levels found after individual administration of the highest doses of mercury and uranium, significant reductions in the urinary concentrations of these elements were noted following simultaneous exposure to both metals. At these doses, the reduction in the urinary metal excretion was also accompanied by significant decreases in the renal content of mercury and uranium. Whereas the results of some parameters pointed out a possible synergistic interaction between mercury and uranium, other measures hinted that an antagonistic interaction between these elements is also present.     

Lactating and non-lactating rats differ in sensitivity to HgCl2: Protective effect of ZnCl2

This work investigated zinc (Zn) and mercury (Hg) effects on oxidative parameters, markers of toxicity and metal levels in different tissues from non-lactating rats (NLR) and lactating rats (LR). Adult NLR and LR received ZnCl₂ (27 mg/kg) or saline (0.9%) subcutaneously and after 24 h they received HgCl₂ (5 mg/kg) or saline (0.9%). Twenty four hours later, they were sacrificed and the preparation of biological material and biochemical analyses were performed. With respect to oxidative parameters, Hg exposure decreased kidney total SH levels from NLR and LR and hepatic catalase activity (not statistically significant) in NLR. Zinc pre-treatment partly prevented the decrease of kidney total SH levels in LR. Zinc per se increased hepatic non-protein SH levels of NLR and LR. Regarding toxicity markers, Hg exposure inhibited the δ-aminolevulinic acid dehydratase (δ-ALA-D) activity from kidney and liver of NLR, inhibited serum alanine aminotransferase (ALT) activity of LR and increased serum creatinine and urea levels of NLR and LR. Zinc pre-exposure prevented the enzymatic alterations caused by Hg. NLR and LR Hg exposed presented accumulation of mercury in the kidney, liver, blood and urine. Zinc pre-treatment prevented this accumulation partly in NLR liver and blood and completely in LR kidney and liver. These results show that NLR and LR are differently sensitive to HgCl₂ and that ZnCl₂ showed a promising effect against Hg toxicity.     

Simian virus 40-transformed metallothionein null cells showed increased sensitivity to cadmium but not to zinc, copper, mercury or nickel

Primary cultured embryonic cells derived from mice with disrupted metallothionein (MT) I and II genes and from control mice were transformed with a plasmid encoding the simian virus 40 (SV40) large T antigen. The resulting MT-/- and MT+/+ cell strains showed similar cell morphology, cell cycle and no significant differences in glutathione levels or in the activities of glutathione-related enzymes and antioxidant enzymes. The MT-/- cells were more sensitive to Cd than MT+/+ cells, though no increase in the sensitivity to Zn, Cu, Hg or Ni were observed in MT-/- cells. MT+/+ cells accumulated more Cd than MT-/- cells but showed less lesion, suggesting the role of MT induced by Cd in MT+/+ cells as a scavenger of toxic Cd ion. These results suggest a dominant protective role of MT against Cd compared with other metals. SV40-transformed MT-/- cells seem to be a useful tool for the investigation of cellular function of MT.     

Urinary excretion of mercury, copper and zinc in subjects exposed to mercury vapour

The excretion of mercury, copper and zinc in urine, and mercury in whole blood andplasma, was determined in 40 chloralkali workers exposed to mercury vapour and 40age-matched referents. The Hg concentrations in whole blood, plasma and urine werehigher in the exposed group (35 nmol l, 30 nmol l,and 11.5 nmol mmol creatinine, respectively) in comparison with thereference group (15 nmol l, 6.3 nmol l, and 1.8nmol mmol creatinine, respectively). The urinary copper excretionwas similar in the two groups, while U-Zn excretion was significantly higher (P = 0.04)in the exposed group, median 0.83 mmol mmol creatinine versus 0.76mnmol mmol creatinine in the reference group. In a subgroup of exposedworkers with current U-Hg above 11.5 nmol lmmolcreatinine (20 mg g creatinine) the medianU-Zn was 1.1 mmol mmol creatinine. In both groups smokers had highU-Zn levels than non smokers. When both U-Hg and smoking were taken into account in alinear regression model, there was a significant association between U-Hg and U-Zn inthe combined group of exposed and referents (P = 0.002). This study indicates thatmercury exposure in humans, as in animals, causes increased urinary excretion of zinc.The mechanisms may be induced synthesis of metallothionein in the kidneys, displacementof Zn from preexisting metallothionein by Hg, or a decreased reabsorption of zinc in thekidneys owing to a slight tubular dysfunction.     

Towards prenatal biomonitoring in North Carolina: assessing arsenic, cadmium, mercury, and lead levels in pregnant women

Exposure to toxic metals during the prenatal period carries the potential for adverse developmental effects to the fetus, yet such exposure remains largely unmonitored in the United States. The aim of this study was to assess maternal exposure to four toxic metals (arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb)) in a cohort of pregnant women in North Carolina. We analyzed blood samples submitted to the North Carolina Department of Health and Human Services for blood typing to assess toxic metal levels in pregnant women (n = 211) across six North Carolina counties. Whole blood metal concentrations were measured by inductively coupled plasma mass spectrometry. The association between maternal characteristics, including county of residence, age, and race, and metal exposure was analyzed using multiple linear regression analysis. A large fraction of the blood samples showed detectable levels for each of the four metals. Specifically, As (65.7%), Cd (57.3%), Hg (63.8%), and Pb (100%) were detected in blood samples. Moreover, compared with adult females participating in the Fourth National Report on Human Exposure to Environmental Chemicals and guidelines for pregnant women, some women in the sample population exceeded benchmark levels of Cd, Hg, and Pb. Evidence from this pilot study indicates that pregnant women in North Carolina are exposed to As, Cd, Hg, and Pb and suggests that factors related to maternal county of residence and race may impact maternal exposure levels. As increased levels of one or more of these metals in utero have been associated with detrimental developmental and reproductive outcomes, further study is clearly warranted to establish the impacts to newborns.     

Increased urinary excretion of zinc and copper by mercuric chloride injection in rats

The effects of HgCl₂ on urinary excretion of Zn, Cu and metallothionein at different time intervals were observed in male Wistar rats. The rats were given a daily intraperitoneal injection of²⁰³HgCl₂ (0.5 or 1.0 mg Hg kg^–1) for 2 days.²⁰³Hg, Zn, Cu and metallothionein in urine, kidney and liver were analyzed. Significant increases in urinary Zn and Cu concentrations were found in HgCl₂-dosed groups. Elevated urinary Zn and Cu concentrations were accompanied by an increased metallothionein excretion in urine at different time periods. Zn concentration in urine remained elevated during the entire observation period of 7 days. There were also increased concentrations of Cu and Zn in the renal cortex in one of the two exposed groups. The results indicate that urinary Cu and Zn are related to the manifestation of renal toxicity and/or the synthesis of metallothionein in kidney induced by mercury.     

Properties of metallothionein induced by zinc, copper and cadmium in the frog, Xenopus laevis

1. Repeated injections of zinc (Zn) and copper (Cu) into the frog Xenopus laevis caused accumulations of the respective metals in the liver and kidney. 2. The accumulated metals in the liver supernatant fractions were present as Zn- and Cu-binding proteins of the same properties as that of metallothionein (MT) induced by cadmium (Cd) injections. 3. The affinity of Zn, Cu and Cd ions to the metal-binding protein was in the decreasing order of Cu, Cd and Zn. 4. The Xenopus MT induced by Cd was unstable and disrupted easily to give two peaks as if the MT consists of two isometallothioneins.     

Zinc and N-acetylcysteine modify mercury distribution and promote increase in hepatic metallothionein levels

This study investigated the ability of zinc (Zn) and N-acetylcysteine (NAC) in preventing the biochemical alterations caused by mercury (Hg) and the retention of this metal in different organs. Adult female rats received ZnCl₂ (27 mg/kg) and/or NAC (5 mg/kg) or saline (0.9%) subcutaneously and after 24 h they received HgCl₂ (5 mg/kg) or saline (0.9%). Twenty-four hours after, they were sacrificed and analyses were performed. Hg inhibited hepatic, renal, and blood δ-aminolevulinic acid dehydratase (δ-ALA-D) activity, decreased renal total thiol levels, as well as increased serum creatinine and urea levels and aspartate aminotransferase activity. HgCl₂-exposed groups presented an important retention of Hg in all the tissues analyzed. All pre-treatments demonstrated tendency in preventing hepatic δ-ALA-D inhibition, whereas only ZnCl₂ showed this effect on blood enzyme. Moreover, the combination of these compounds completely prevented liver and blood Hg retention. The exposure to Zn and Hg increased hepatic metallothionein levels. These results show that Zn and NAC presented promising effects against the toxicity caused by HgCl₂.     

Accumulation,regulation and toxicity of copper,zinc, lead and mercury in Hyalella azteca

Zinc, lead and mercury accumulation in the amphipod Hyalella azteca increases with increasing exposure to metals. During 10 week chronic toxicity tests, metal accumulated at the highest non-toxic/lowest toxic concentration was 126/136 µg Zn g^–1, 7.1/16 µg Pb g^–1 and 56/90 µg Hg g^–1 dry weight. Concentrations of lead and mercyry in control animals were substantially lower (1.3 µg Pb g^–1 and 0.4 µg Hg g^–1), but concentrations of zinc in controls (74 µg g^–1) were about one half those of the lowest toxic concentration. Copper was completely regulated. Accumulated copper concentrations after 10 weeks exposure to all waterborne copper concentrations resulting in less than 100% mortality were not significantly different from controls (79 µg g^–1). Lead and mercury concentrations in wild H. azteca should be useful indicators of potential toxicity. Zinc accumulation may also be a useful indicator of zinc toxicity, but careful comparison with control or reference animals is necessary because of the small differences between toxic and control concentrations. Copper is not accumulated by H. azteca under chronic exposure conditions and body burdens of field animals cannot be used as an indicator of exposure or potential toxic effects. Short term exposures to copper, however, result in elevated copper concentrations in H. azteca, even at concentrations below those causing chronic toxicity. Short term bioaccumulation studies might, therefore, provide a useful indication of potential chronic copper toxicity.     

Metal interactions in mice under environmental stress

A metallomic analytical approach based on the use of size exclusion chromatography coupled to ICP-MS has been used to obtain metal profiles related to overexpression or inhibition of metal-binding biomolecules, which is connected to exposure experiment of laboratory mice Mus musculus to toxic metals, such as Cd, Hg and As. Exposure to Cd induces the formation of Cd-metallothionein in liver that reveals the protective role of this organ; however, exposure to Hg reduces the intensity of the peak associated to Cu-superoxide dismutase (Cu-SOD) while Hg-SOD peak increases, which suggests the competence of Cu and Hg for the active sites of SOD in liver that causes mercury translocation to kidney, in which the concentration of Hg as Hg-metallothionein increases drastically to be excreted by urine. It has been also observed the protective effect of selenium on mercury toxicity in blood plasma, which produces decreasing of the intensity of Se-protein in plasma with Hg exposure and correlative increases of Hg-albumin that transport mercury to kidney for excretion. Finally, arsenic exposure provokes the accumulation of small metabolites of this element, such as dimethylarsenic and monomethylarsenic for excretion. The application of the metallomic approach to liver extracts from free-living mouse Mus spretus shows the overexpression of Cu, Zn and Cd-peaks at 7 kDa (related to metal-metallothionein) in environmental contaminated sites, as well as the increase of peaks related to Cu- and Zn-SOD and Zn-albumin. However, in kidney, can be checked the presence of high concentration of arsenic small metabolites in contaminated areas, similarly to results found in exposure experiments. In addition, the application of a metabolomic approach based on direct infusion mass spectrometry to organ extracts (liver, kidney and serum) from mice (M. musculus) exposed to arsenic reveals important metabolic changes related to antioxidative activity, membrane cell damage, energy metabolism and arsenic elimination. Similar results were obtained from free-living mouse (M. spretus) from areas contaminated with arsenic. The integration of metallomics and metabolomics results provides a more comprehensive evaluation about the biological response in exposure experiments to toxic metals as well as in environmental assessment of contamination.