Functions of metallothionein

Metal and trace element concentrations in cetaceans worldwide: A review

This bibliographical review is a compilation of different scientific publications that reported data on metal concentrations in the muscle tissue of different species of cetaceans from seas and oceans around the world. Forty-nine scientific articles were selected, published over a fifteen-year period (2006-2021) with data on heavy metals and trace elements. The different groups of cetaceans considered in this study generally presented low concentrations of Cd and Pb. The same cannot be said of Hg. The highest concentrations of Hg were found in the groups of false killer whales. Similarly, the use of these groups of cetaceans as bioindicators of metal contamination shows that the Mediterranean Sea is one of the most metallically contaminated areas in the world. This may be due to the closed nature of the Mediterranean Sea and to the fact that it is also a highly populated and industrialized area.

Acquired Hyperzincaemia Due to Zinc-Laden Denture Adhesives Leading to Hypocupraemia as a Cause of Neutropenia

Introduction

Copper deficiency or hypocupraemia is a rare cause of anaemia and neutropenia.

Case description

We hereby present the case of a 34-year-old female with gastric bypass surgery who presented with neutropenic fever, abdominal pain and diarrhoea, later found to have extended-spectrum beta-lactamase resistant Escherichia coli urinary tract infection and small bowel bacterial overgrowth syndrome, with her anaemia and neutropenia being caused by copper deficiency due to hyperzincaemia induced by using zinc denture adhesive cream.

Discussion

Various causes of copper deficiency have been recognized including, but not limited to, malnutrition, gastrectomy, gastric bypass surgery, protein-losing enteropathies (coeliac disease, tropical sprue), Wilson disease and Menkes syndrome. Copper deficiency caused by zinc overuse is not very prevalent. The haematologic abnormalities associated with copper deficiency are neutropenia, sideroblastic anaemia and/or pancytopenia.

Conclusion

Because of its low prevalence and nonspecific haematologic and clinical manifestations, the diagnosis of zinc-induced copper deficiency (ZICD) can be missed.

LEARNING POINTS

Zinc toxicity is a rare cause of hypocupraemia.The bone marrow and haematological manifestations of copper deficiency are not pathognomonic but include sideroblastic anaemia, pancytopenia or neutropenia.Early detection of hypocupraemia as a cause for neutropenia will improve morbidity and mortality by avoiding untoward infections due to neutropenia, neurological decline or unnecessary interventions.

Agranulocytosis secondary to zinc excess: Clinically relevant observations, including response to G-CSF and oral copper

Anemia and leukopenia because of copper deficiency can be mistaken for myelodysplasia. Key issues, including response to G-CSF and oral copper, are discussed. This case illustrates a significant deleterious effect of excessive zinc consumption.

Cadmium exposure during pregnancy and lactation: materno-fetal and newborn repercussions of Cd(ii), and Cd-metallothionein complexes

Cadmium (Cd) is a non-physiological heavy metal that can be harmful at low concentrations. Increasing anthropogenic activities are incrementing the risk of accumulation of this heavy metal in different organs and tissues of the body. In the case of pregnant women, the threat is more serious due to the implications affecting not only their own health but also fetal development as well. Metallothioneins (MTs), small cysteine-rich proteins, are involved in zinc (Zn) and copper homeostasis in mammals but can, however, also bind with Cd if present. The accumulation of Cd in maternal tissues (e.g. placenta, maternal blood, and mammary glands) induces the synthesis of MTs, preferably MT2, in an attempt to sequester the metal to avoid toxicity. The formed Cd-MT complexes will avoid the Cd transport from the placenta to the fetus and end up accumulating in the maternal kidneys. At the same time, high concentrations of MTs will increase the formation of Zn-MT complexes, therefore decreasing the amount of Zn ions available to be transported to the fetus by means of Zn transporters such as ZnT2, ZIP14 and DMT1. Although MTs cannot transport Cd from the mother to the fetus, the divalent DMT1 transporter is suggested to carry the metal to the fetus. As a consequence, the low levels of Zn(ii) in the fetus, together with the presence of Cd(ii) coming from the mother either via the placenta and cord blood or via breast milk induce changes in the fetal development including fetal growth retardation, and low weight or height of the newborn. Likewise, the concentrations of Cd(ii) in the newborn can cause alterations such as cognitive disabilities. In summary, the presence of Cd(ii) in the maternal tissues will induce MT synthesis in an attempt to detoxify these tissues and reduce the possible toxicity of Cd in fetal and newborn tissues.

Neurodevelopmental Effects of Mercury

The toxicology of mercury (Hg) is of concern since this metal is ubiquitously distributed in the environment, and living organisms are routinely exposed to Hg at low to high levels. The toxic effects of Hg are well studied and it is known that they may differ depending on the Hg chemical species. In this chapter, we emphasize the neurotoxic effects of Hg during brain development. The immature brain is more susceptible to Hg exposure, since all the Hg chemical forms, not only the organic ones, can harm it. The possible consequences of Hg exposure during the early stages of development, the additive effects with other co-occurring neurotoxicants, and the known mechanisms of action and targets will be addressed in this chapter.

Cadmium Handling, Toxicity and Molecular Targets Involved during Pregnancy: Lessons from Experimental Models

Even decades after the discovery of Cadmium (Cd) toxicity, research on this heavy metal is still a hot topic in scientific literature: as we wrote this review, more than 1440 scientific articles had been published and listed by the PubMed.gov website during 2017. Cadmium is one of the most common and harmful heavy metals present in our environment. Since pregnancy is a very particular physiological condition that could impact and modify essential pathways involved in the handling of Cd, the prenatal life is a critical stage for exposure to this non-essential element. To give the reader an overview of the possible mechanisms involved in the multiple organ toxic effects in fetuses after the exposure to Cd during pregnancy, we decided to compile some of the most relevant experimental studies performed in experimental models and to summarize the advances in this field such as the Cd distribution and the factors that could alter it (diet, binding-proteins and membrane transporters), the Cd-induced toxicity in dams (preeclampsia, fertility, kidney injury, alteration in essential element homeostasis and bone mineralization), in placenta and in fetus (teratogenicity, central nervous system, liver and kidney).

A comparative study of hollow copper sulfide nanoparticles and hollow gold nanospheres on degradability and toxicity

Gold and copper nanoparticles have been widely investigated for photothermal therapy of cancer. However, degradability and toxicity of these nanoparticles remain concerns. Here, we compare hollow CuS nanoparticles (HCuSNPs) with hollow gold nanospheres (HAuNS) in similar particle sizes and morphology following intravenous administration to mice. The injected pegylated HCuSNPs (PEG-HCuSNPs) are eliminated through both hepatobiliary (67 percentage of injected dose, %ID) and renal (23 %ID) excretion within one month postinjection. By contrast, 3.98 %ID of Au is excreted from liver and kidney within one month after iv injection of pegylated HAuNS (PEG-HAuNS). Comparatively, PEG-HAuNS are almost nonmetabolizable, while PEG-HCuSNPs are considered biodegradable nanoparticles. PEG-HCuSNPs do not show significant toxicity by histological or blood chemistry analysis. Principal component analysis and 2-D peak distribution plots of data from matrix-assisted laser desorption ionization-time-of-flight imaging mass spectrometry (MALDI-TOF IMS) of liver tissues demonstrated a reversible change in the proteomic profile in mice receiving PEG-HCuSNPs. This is attributed to slow dissociation of Cu ion from CuS nanoparticles along with effective Cu elimination for maintaining homeostasis. Nonetheless, an irreversible change in the proteomic profile is observed in the liver from mice receiving PEG-HAuNS by analysis of MALDI-TOF IMS data, probably due to the nonmetabolizability of Au. This finding correlates with the elevated serum lactate dehydrogenase at 3 months after PEG-HAuNS injection, indicating potential long-term toxicity. The comparative results between the two types of nanoparticles will advance the development of HCuSNPs as a new class of biodegradable inorganic nanomaterials for photothermal therapy.

Metallothionein 1 h tumour suppressor activity in prostate cancer is mediated by euchromatin methyltransferase 1

Metallothioneins (MTs) are a group of metal binding proteins thought to play a role in the detoxification of heavy metals. Here we showed by microarray and validation analyses that MT1h, a member of MT, is down-regulated in many human malignancies. Low expression of MT1h was associated with poor clinical outcomes in both prostate and liver cancer. We found that the promoter region of MT1h was hypermethylated in cancer and that demethylation of the MT1h promoter reversed the suppression of MT1h expression. Forced expression of MT1h induced cell growth arrest, suppressed colony formation, retarded migration, and reduced invasion. SCID mice with tumour xenografts with inducible MT1h expression had lower tumour volumes as well as fewer metastases and deaths than uninduced controls. MT1h was found to interact with euchromatin histone methyltransferase 1 (EHMT1) and enhanced its methyltransferase activity on histone 3. Knocking down of EHMT1 or a mutation in MT1h that abrogates its interaction with EHMT1 abrogated MT1h tumour suppressor activity. This demonstrates tumour suppressor activity in a heavy metal binding protein that is dependent on activation of histone methylation.

Determination of trace elements in Rheum moorcroftianum by AAS

Micro and macro elements such as Zn, Cu, Mn, Fe, Co, Na, K, Ca and Li were detected from Rheum moorcroftianum Royle, a plant used in folk medicines. Altitudinal and seasonal variation of these trace elements in cultivated and wild roots and leaves of R. moorcroftianum were quantified by atomic absorption spectroscopy. The highest concentrations of Zn, Cu, Mn, Fe, Co, Na, K, Ca and Li were found to be 376.0 ± 0.9, 83.0 ± 4.6, 322.0 ± 6.0, 920.0 ± 1.9, 72.0 ± 1.5, 402.0 ± 7.8, 10,235.0 ± 7.0, 12,336.0 ± 2.6 and 59.9 ± 0.3  mg kg(-1), respectively, in all the samples analysed.

Sex, age, and tissue specific accumulation of eight metals, arsenic, and selenium in the European hedgehog (Erinaceus europaeus)

Many insectivores have been shown to be sensitive to heavy metals and therefore suitable for biomonitoring purposes. In Finland, the hibernation period of the European hedgehog (Erinaceus europaeus) is long, and during hibernation the stress caused by environmental toxins may be crucial. Concentrations of cadmium (Cd), copper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), arsenic (As), and selenium (Se) were measured in a population of hedgehogs in the town of Joensuu in eastern Finland during the summers of 2004 and 2005. The analyzed tissues were kidney, liver, hair, and spine. The sampled hedgehogs (n = 65) were mainly road-killed animals. As expected, the concentrations of heavy metals were low because the hedgehogs were living in a comparatively unpolluted area. Significant increases with age were found in Cd concentrations (kidney, liver, and spine) and some essential elements (Se in spine, kidney, and liver; Mo in kidney and liver; Cu in spine; Fe in liver; and Mn in spine). Age accumulation and correlations between Se and Cd and between Mo and Cd may indicate the protective roles of Se and Mo against Cd toxicity in hedgehogs, in which Cd is already at comparatively low concentrations. Sex had no significant effect on concentrations of the elements studied. In conclusion, age is an important parameter to be taken into account when studying heavy-metal concentrations in hedgehogs and other insectivores.

Tumours from a Cell Strain with a High Content of Metallothionein Show Enhanced Resistance against Cis-Dichlorodiammineplatinum

Cultured cells with a high content of the extremely cysteine-rich protein metallothionein (MT) have previously been shown to exhibit resistance when exposed to otherwise lethal doses of cis-dichlorodiammineplatinum (cis-DDP), chlorambucil or prednimustine, and to have a significant proportion of intracellular drug associated with MT after such treatment. In order to study this protective mechanism in vivo, cells from a MT-rich variant of a murine fibroblast line resistant to cis-DDP and its parent sensitive line with only trace amounts of MT, were injected subcutaneously into nude mice (24 animals in each group), and tumour growth was compared during cis-DDP treatment. Animals in the treatment groups received 3 intravenous doses of either 4 mg/kg or 8 mg/kg of cis-DDP on day 12, 26 and 33 after inoculation of cells, whereas the control groups received saline. The 8 mg/kg dose produced an almost complete growth inhibition of the tumours derived from the parent cells, as well as from the MT-rich variant. However, following the injections with 4 mg/kg of cis-DDP, tumour volume was reduced by approximately 80% in tumours from the parent cells, whereas the tumours from MT-rich cells were almost completely resistant. This study provides for the first time evidence that metallothionein-conferred protection against cis-DDP toxicity also is mediated in tumours in vivo.

Biological and ecological factors related to trace element levels in harbour porpoises (Phocoena phocoena) from European waters

Selected trace elements (Cd, Cu, Hg, Se, Zn) were measured in the kidneys and the liver of 104 harbour porpoises (Phocoena phocoena) stranded along the coasts of France, Galicia (Spain), Ireland, Scotland (UK), and the Netherlands. Generally, relatively low concentrations of toxic elements were encountered in the tissues of European porpoises, except for two individuals, which displayed high hepatic Hg concentrations. Also, elevated Cd levels obtained in Scottish porpoises could be related to their feeding preferences and this result suggests an increase of the proportion of cephalopods in their diet with latitude. Moreover, significant geographical differences were seen in hepatic Zn concentrations; the elevated Zn concentrations displayed by porpoises from the Netherlands may relate their poor health status. Variation in metal concentrations within porpoises from the North Sea is likely to reflect a long-term segregation between animals from northern (Scotland) and southern areas (the Netherlands), making trace elements powerful ecological tracers.

Accumulation of cadmium and its effects on liver and kidney functions in rats given diet containing cadmium-polluted radish bulb

The aim of this study was to examine the accumulation of cadmium (Cd) incorporated in radish bulb and its effects on liver and kidney functions in male rats. Control animals were given diet containing ordinary radish bulb for 4, 8 and 12 weeks, while contaminated animals were given diet containing Cd-polluted radish bulb (1.1 microg Cd/g of diet) for the same periods as in controls. At each time point, rats were killed and plasma was collected, and the liver and the kidneys were removed. Results indicated that body weight gain of contaminated rats was identical to that of control rats. Cd concentration in the liver and the kidney increased significantly and gradually from the 4th to the 12th week of treatment. Plasma alanine aminotrasfase (ALT) and lactate dehydrogenase (LDH) activities increased significantly after 8 and 12 weeks of treatment, while plasma alkaline phosphatase (ALP) activity was increased significantly only after 12 weeks. Plasma urea concentration was comparable in the two groups during the experimental period, while plasma creatinine concentration increased significantly after 12 weeks of treatment.

Characterization of calcineurin-dependent response element binding protein and its involvement in copper-metallothionein gene expression in Neurospora

In continuation of our recent observations indicating the presence of a lone calcineurin-dependent response element (CDRE) in the -3730bp upstream region of copper-induced metallothionein (CuMT) gene of Neurospora [K.S. Kumar, S. Dayananda, C. Subramanyam, Copper alone, but not oxidative stress, induces copper-metallothionein gene in Neurospora crassa, FEMS Microbiol. Lett. 242 (2005) 45-50], we isolated and characterized the CDRE-binding protein. The cloned upstream region of CuMT gene was used as the template to specifically amplify CDRE element, which was immobilized on CNBr-activated Sepharose 4B for use as the affinity matrix to purify the CDRE binding protein from nuclear extracts obtained from Neurospora cultures grown in presence of copper. Two-dimensional gel electrophoresis of the affinity purified protein revealed the presence of a single 17kDa protein, which was identified and characterized by MALDI-TOF. Peptide mass finger printing of tryptic digests and analysis of the 17kDa protein matched with the regulatory beta-subunit of calcineurin (Ca(2+)-calmodulin dependent protein phosphatase). Parallel identification of nuclear localization signals in this protein by in silico analysis suggests a putative role for calcineurin in the regulation of CuMT gene expression.

Orally administrated rare earth element cerium induces metallothionein synthesis and increases glutathione in the mouse liver

The influence of oral administration of rare earth element cerium (Ce) was studied in relation to metallothionein (MT) and glutathione (GSH) content in the organs of ICR mice, which were administered heavy metal cadmium (Cd) for comparison. Male ICR mice were divided into 9 groups: 1 control group, 4 cerium groups and 4 cadmium groups, each with 4 mice, for a total of 36 mice. Ce groups included a 20 ppm CeCl3 diet (Ce-low) group and a 200 ppm CeCl3 diet (Ce-high) group, as did Cd groups, i.e., a 20 ppm CdCl2 diet (Cd-low) group and a 200 ppm CdCl2 diet (Cd-high) group. Each group was subdivided in 2 groups except a control group: 6-week administration group and 12-week administration group. The level of plasma aspartate aminotransferase(AST) activity, plasma alanine aminotransferase(ALT) activity, plasma cholesterol and plasma triglyceride in the Ce-low, Cd-low, Ce-high, and Cd-high group were higher than that of control group, although there were no significant differences (p > 0.05). By contrast, both Ce and Cd groups had higher levels of MT and GSH in hepatic cells compared to the control group (p < 0.05) and decreased liver tissue level of lipoperoxide (p < 0.05). These groups also had decreased plasma superoxide dismutase (SOD) activity (p < 0.05), and increased plasma level of lipoperoxide (p > 0.05). In conclusion, it is suggested that orally administered Ce increases MT and GSH as an antioxidant in the mouse liver, and these reaction are probably caused by increases in the oxidative stress with Ce.

Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination

Copper deficiency is a rare cause of sideroblastic anemia and neutropenia that often is not suspected clinically. The morphologic findings in bone marrow, while not pathognomonic, are sufficiently characteristic to suggest the diagnosis, leading to further testing to establish the correct diagnosis. Excess zinc ingestion is among the causes of copper deficiency. We present 3 cases of zinc-induced copper deficiency in which the diagnosis first was suggested on the basis of bone marrow examination. The first patient was a 47-year-old man with a debilitating peripheral neuropathy that had progressed during the previous 18 months, mild anemia, and severe neutropenia. The second was a 21-year-old man receiving zinc supplementation for acrodermatitis enteropathica in whom moderate normocytic anemia and neutropenia developed. The third patient was a 42-year-old man with anemia, severe neutropenia, and a peripheral neuropathy that had progressed during 8 months. The bone marrow findings in all cases suggested copper deficiency, which was confirmed by further laboratory testing and determined to be due to zinc excess. The morphologic features, clinical manifestations, differential diagnosis, and pathogenetic mechanisms are discussed.

Zinc supplementation alleviates heat stress in laying Japanese quail

The study was conducted to determine whether zinc supplementation could alleviate the detrimental effects of high ambient temperature (34 degrees C) on egg production, digestibility of nutrients and antioxidant status in laying Japanese quail. Quail (n = 180; 52 d old) were divided into six groups (n = 30/group) and were fed a basal diet or the basal diet supplemented with 30 or 60 mg of zinc (ZnSO(4). H(2)O)/kg diet. Birds were kept at 22 degrees C and 58% relative humidity (RH). At 13 wk of age, the thermoneutral (TN) groups remained at the same temperature, whereas the heat-stress (HS) groups were kept in an environmentally controlled room at 34 degrees C and 42% RH for 3 wk. Heat exposure decreased egg production in birds fed the basal diet (P = 0.001). Linear increases in feed intake (P = 0.01) and egg production (P = 0.004) and improved feed efficiency (P = 0.01) and egg quality variables (P <or= 0.05) occurred in zinc-supplemented groups reared under HS conditions. Heat exposure decreased digestibility of nutrients (P = 0.001), and these decreases were ameliorated by zinc supplementation (P <or= 0.05). Serum vitamin C (P = 0.05), vitamin E (P = 0.01) and zinc (P = 0.001) concentrations increased linearly, whereas malondialdehyde concentrations decreased (P = 0.002) as dietary zinc supplementation increased. No significant differences in any values were observed in the TN groups (P > 0.05). Results of the present study suggest that supplementation with 60 mg zinc/kg diet protects quail by reducing the negative effects of heat stress.

Antioxidant property of metallothionein in fasted mice

Metallothionein (MT) is a low-molecular-weight and sulfur-rich protein that is induced by not only heavy metals but also physiological stresses such as fasting and restraint stresses. Although MT plays a role as a radical scavenger and a regulator of metabolism of metals, the biological function of MT induced by fasting stress has not been elucidated. In this study, we investigated the antioxidative role of MT in fasted mice. In fasted mice, the lipid peroxidation level of the liver was elevated by 24-h fasting stress, and pre-induction of hepatic MT by Zn diminished hepatic lipid peroxidation. Although 24-h fasting stress induced MT synthesis in the liver, other antioxidants such as catalase, manganese-superoxide dismutase (Mn-SOD), and glutathione peroxidase (GSHPx) were not activated in the liver. Moreover, the hepatic MT level was still elevated by fasting stress after seven cycles of repetition of alternate fasting and feeding every 24 h, but the activities of catalase, Mn-SOD and GSHPx were unchanged. These results indicate that MT induced by fasting stress plays partly as an antioxidant.

Risk factors for gallbladder cancer: a reappraisal

Carcinoma of the gallbladder has a very unusual geographical distribution with pockets of high incidence seen in Chile, Poland, India, Japan and Israel; it occurs rarely in the rest of the world. It is a common malignancy in the Western Bihar and Eastern Uttar Pradesh regions of India. Patients present with extremes of clinical symptoms, indicating benign biliary diseases on the one hand and incurable malignant disease on the other. Laboratory and roentgenographic data tend to confirm the clinical diagnosis of the advanced incurable disease at presentation, in most cases. Various aetiopathological agents have been proposed but none has stood the test of time. In this article, we have reviewed the aetiopathological agents proposed from time to time over the past two centuries, with special emphasis on the developments made in the last 25 years.

Metabolic activation of 3-hydroxyanisole by isolated rat hepatocytes

A tyrosinase-directed therapeutic approach for malignant melanoma therapy uses the depigmenting phenolic agents such as 4-hydroxyanisole (4-HA) to form cytotoxic o-quinones. However, renal and hepatic toxicity was reported as side effects in a recent 4-HA clinical trial. In search of novel therapeutics, the cytotoxicity of the isomers 4-HA, 3-HA and 2-HA were investigated. In the following, the order of the HAs induced hepatotoxicity in mice, as measured by increased in vivo plasma transaminase activity, or in isolated rat hepatocytes, as measured by trypan blue exclusion, was 3-HA > 2-HA > 4-HA. Hepatocyte GSH depletion preceded HA induced cytotoxicity and a 4-MC-SG conjugate was identified by LC/MS/MS mass spectrometry analysis when 3-HA was incubated with NADPH/microsomes/GSH. 3-HA induced hepatocyte GSH depletion or GSH depletion when 3-HA was incubated with NADPH/microsomes was prevented by CYP 2E1 inhibitors. Dicumarol (an NAD(P)H: quinone oxidoreductase inhibitor) potentiated 3-HA- or 4-methoxycatechol (4-MC) induced toxicity whereas sorbitol (an NADH generating nutrient) greatly prevented cytotoxicity indicating a quinone-mediated cytotoxic mechanism. Ethylendiamine (an o-quinone trap) largely prevented 3-HA and 4-MC-induced cytotoxicity indicating that o-quinone was involved in cytotoxicity. Dithiothreitol (DTT) greatly reduced 3-HA and 4-MC induced toxicity. The ferric chelator deferoxamine slightly decreased 3-HA and 4-MC induced cytotoxicity whereas the antioxidants pyrogallol or TEMPOL greatly prevented the toxicity suggesting that oxidative stress contributed to 3-HA induced cytotoxicity. In summary, ring hydroxylation but not O-demethylation/epoxidation seems to be the bioactivation pathway for 3-HA in rat liver. The cytotoxic mechanism for 3-HA and its metabolite 4-MC likely consists cellular protein alkylation and oxidative stress. These results suggest that 3-HA is not suitable for treatment of melanoma.

Costs of gestation in an Arctic ruminant: copper reserves in muskoxen

The transfer of trace minerals between mother and fetus may be critical for survival of young ruminants especially among species at high latitudes, which gestate during a long winter and grow through a brief summer. We examined the distribution of copper and metalloproteins (ceruloplasmin and metallothionein) in muskoxen and their fetuses, three times during gestation. Hepatic levels of copper were high in mothers (179 microg g(-1) whole tissue) and did not change through gestation, whereas fetuses accumulated large reserves of Cu (>300 microg g(-1)), likely stored in proteins such as metallothionein, during the last third of gestation. The effect of fetal Cu demands on the pregnant female was tested by supplementation of Cu by subcutaneous injections of Cu gluconate (30 mg Cu/week) during pregnancy. Maternal copper supplementation did not significantly increase hepatic Cu in newborns (412 microg g(-1) for supplemented vs. 303 microg g(-1) for unsupplemented neonates), probably because the diet was already adequate in copper (14 microg g(-1) dry matter). Ceruloplasmin activity declined in pregnant muskoxen that had not received injections of Cu and suggested increased systemic demands for copper during late gestation. Supplies of Cu to the fetus could be limited either by low levels of Cu in the maternal liver, or in the maternal diet during late winter when fetal gains in mass and liver Cu are greatest.

Maternal-to-fetus transfer of mercury in metallothionein-null pregnant mice after exposure to mercury vapor

This study examined the role of placenta metallothionein (MT) in maternal-to-fetal mercury transfer in MT-null and wild-type mice after exposure to elemental mercury (Hg(0)) vapor. Both strains were exposed to Hg(0) vapor at 5.5-6.7 mg/m(3) for 3 h during late gestation. Twenty-four hours after exposure to Hg(0) vapor, accumulation of mercury in the major organs, except the brain, of MT-null maternal mice was significantly lower than that in organs of wild-type mice. In contrast to mercury levels in maternal organs, fetal mercury levels were significantly higher in MT-null mice than in wild-type mice. In placenta, mercury concentrations were not significantly different between the two strains. Although MT levels in major organs, except the brain, of wild type mice were markedly elevated after the exposure to Hg(0) vapor, the placental MT levels were not elevated. However, endogenous MT level in the placenta is significantly higher than that in other organs, except the liver. Gel filtration profile of the placental cytosol in the wild-type mice revealed that a large amount of placental mercury was associated with MT. In MT-null mice, mercury in placental cytosol appeared mainly in the high-molecular-weight protein fractions. Mercury in the placenta was localized mainly in the yolk sac and decidual cells in the deep layer of the decidua in both mouse strains. The similar localization of MT was found in the placenta of wild type mice. These results suggest that MT in the placenta has a defensive role in preventing maternal-to-fetal mercury transfer.

Effect of cadmium and aluminum intake on the antioxidant status and lipid peroxidation in rat tissues

This work aimed to study the relationship between the accumulation of cadmium (Cd) or aluminum (Al) in certain tissues and the levels of lipid peroxides as well as tissue antioxidants. To carry out such investigations, CdCl2 was given to rats in two dose levels; 0.5 or 2.0 mg/kg i.p for 1 day or daily repeated doses for 2 weeks. Al was given as AlCl3 either in a single dose of 100 mg/kg or daily repeated doses of 20 mg/kg for 2 and 4 weeks. The measured parameters were tissue malondialdehyde (MDA, index of lipid peroxidation) and reduced glutathione (GSH) levels as well as the activities of glutathione peroxidase (GSH-PX), glutathione reductase (GSSG-R), and glucose-6-phosphate dehydrogenase (G-6-PDH) enzymes. Liver and kidney functions were assessed by measuring serum alanine aminotransferase (ALT) and alkaline phosphatase (ALP) activities as well as serum urea and creatinine concentrations. Cd and Al concentrations in the studied tissues were also measured. Results indicated that tissue Cd was significantly increased after administration of either Cd doses. After a single dose of 0.5 or 2.0 mg/kg CdCl2, the increase in tissue Cd levels were accompanied by an increase in MDA and a decrease in GSH levels. On the other hand, after repeated administration of Cd, tissue Cd accumulation was accompanied by increased hepatic and renal GSH levels with decrease in MDA content and a decrease in GSH-PX activity in liver. Liver function was affected at all dose regimens, whereas kidney function was affected only after 2 weeks administration of the higher dose. In Al treated rats, Al concentration was shown to be increased in liver much more than in brain. This was accompanied by a slight decrease in hepatic GSH level after 2 weeks and a decrease in GSH-PX activity after 4 weeks. Liver function was affected only after repeated injection of Al for 2 or 4 weeks. In general, Al administration exhibited safer pattern than Cd.

Placental to fetal transfer of mercury and fetotoxicity

Mercury vapor is known penetrate the placental barrier more easily than inorganic mercury. A relative amount of mercury accumulates in the fetus after exposure of pregnant animals to mercury vapor. Mercury concentration in fetal organs is much lower than that in maternal organs except the liver, and fetal liver shows significantly higher mercury concentrations than maternal liver. In fetal liver, a substantial portion of mercury is bound to metallothionein (MT), which plays an important role as a reservoir of mercury during the prenatal period. The mercury retained in fetal liver is redistributed to other organs, such as the brain and kidney, with diminishing MT levels during postnatal development. Consequently, an increase in mercury concentration in the brain and kidney of the neonate is observed. In studies on animal offspring in utero exposed to mercury vapor, behavioral changes, such as radial arm maze, morris maze and lever-press durations, are observed when the levels of mercury vapor exceed the threshold limit value (TLV).

Cadmium-containing granules in kidney tissue of the Atlantic white-sided dolphin (Lagenorhyncus acutus) off the Faroe Islands

Top predators from the northern sub-polar and polar areas exhibit high cadmium concentrations in their tissues. In the aim to reveal possible adverse effects, samples of five Atlantic white-sided dolphins Lagenorhyncus acutus have been collected on the occasion of the drive fishery in the Faroe Islands, for ultrastructural investigations and energy dispersive X-ray microanalyses. Cadmium concentrations were less than the limit of detection in both immature individuals and ranged from 22.7 to 31.1 microg x g(-1) wet weight in the mature individuals. Two individuals with the highest cadmium concentrations exhibited electron dense mineral concretions in the basal membranes of the proximal tubules. They are spherocrystals made up of numerous strata mineral deposit of calcium and phosphorus together with cadmium. Cadmium has been detected with a molar ratio of Ca:Cd of 10:1 in the middle of these concretions. To our knowledge, this is the first report of such granules in a wild vertebrate. The role of these granules in the detoxification of the metal and the possible pathological effects are considered.

Possible role of metal redistribution, hepatotoxicity and oxidative stress in chelating agents induced hepatic and renal metallothionein in rats

A study was planned to investigate possible role of oxidative stress, hepato- and nephrotoxicity and essential metal redistribution following administration of amino and thiol chelating agents on hepatic and renal metallothionein (MT) and the levels of some metalloenzymes in male rats. Animals were administered 50 mg/kg, intraperitoneally, twice daily for 15 consecutive days; a dose of three amino and four thiol chelators and were sacrificed 24 h after the last dose. The results indicate no evidence of oxidative stress in hepatic and renal tissues of rats administered thiol and amino chelators, except for some marginal changes in the animals treated with calcium disodium ethylenediaminetetraacetic acid (EDTA) and D-penicillamine (DPA). Redistribution of essential metal (particularly zinc), hepato- and nephrotoxicity seems to play a significant role in influencing the MT induction by amino chelators. Redistribution of essential metals may also be playing a significant role in a number of metalloenzymes, especially by amino chelators compared to thiol chelators. It can thus be concluded that toxic effects of chelating agents, including metal redistribution and hepatotoxicity, might be playing a crucial role in the metallothionein induction.

Immunohistochemical demonstration of metallothionein in eyes with choroidal melanomas

PURPOSE

The since immunohistochemically detectable metallothionein (MT) overexpression has been described in a variety of human tumours, including skin melanomas, in relation to different stages of tumour development and progression.

MATERIALS AND METHODS

We used a monoclonal antibody to investigate the distribution of MT in 18 formalin-fixed, paraffin-embedded, surgically enucleated eyes with choroidal melanomas, from 18 patients (8 male, 10 female; age range 30-83 years, mean 58.7). Clinico-pathological details and follow-up data (2-124 months, mean 36.1) were also available. MT immunoreactivity was recorded and the percentage of stained cells was graded for semiquantitative purposes. Correlations between immunohistochemical data and morphological characteristics of melanomas were investigated using non-parametric methods; survival analysis was done by the Kaplan-Meier method and the survival curves were compared by the Mantel-Cox log-rank test.

RESULTS

MT immunoexpression was found in 15/18 cases (83.3%) with staining scores from 1 to 3; MT staining varied in intensity and was mainly localized in the cytoplasm, although a combined nuclear/cytoplasmic reactive pattern was seen in neoplastic elements. No differences in MT immunostaining were seen in relation to age or sex, tumour size, histotype and amount of pigment; univariate analysis of survival data showed no prognostic significance regarding MT expression.

CONCLUSIONS

The immunohistochemical evidence of MT in neoplastic elements could be related to the production of this scavenging protein in the tumour for cell defense mechanisms against hydroxyl free radicals, and to act as a Zn donor, since Zn is required for the synthesis of DNA and DNA-repair enzymes.

Induction, regulation, degradation, and biological significance of mammalian metallothioneins

MTs are small cysteine-rich metal-binding proteins found in many species and, although there are differences between them, it is of note that they have a great deal of sequence and structural homology. Mammalian MTs are 61 or 62 amino acid polypeptides containing 20 conserved cysteine residues that underpin the binding of metals. The existence of MT across species is indicative of its biological demand, while the conservation of cysteines indicates that these are undoubtedly central to the function of this protein. Four MT isoforms have been found so far, MT-1, MT-2, MT-3, and MT-4, but these also have subtypes with 17 MT genes identified in man, of which 10 are known to be functional. Different cells express different MT isoforms with varying levels of expression perhaps as a result of the different function of each isoform. Even different metals induce and bind to MTs to different extents. Over 40 years of research into MT have yielded much information on this protein, but have failed to assign to it a definitive biological role. The fact that multiple MT isoforms exist, and the great variety of substances and agents that act as inducers, further complicates the search for the biological role of MTs. This article reviews the current knowledge on the biochemistry, induction, regulation, and degradation of this protein in mammals, with a particular emphasis on human MTs. It also considers the possible biological roles of this protein, which include participation in cell proliferation and apoptosis, homeostasis of essential metals, cellular free radical scavenging, and metal detoxification.

The influence of nutrition on methyl mercury intoxication

This article reviews progress in the research of methyl mercury (MeHg) and nutrient interactions during the past two decades. Special emphasis is placed on the following three major areas: a) effects on kinetics, b) effects on toxicity, and c) possible mechanisms. Dietary information is not usually collected in most epidemiologic studies examining of the effects of MeHg exposure. However, inconsistency of the MeHg toxicity observed in different populations is commonly attributed to possible effects of dietary modulation. Even though the mechanisms of interaction have not been totally elucidated, research in nutritional toxicology has provided insights into the understanding of the effects of nutrients on MeHg toxicity. Some of this information can be readily incorporated into the risk assessment of MeHg in the diets of fish-eating populations. It is also clear that there is a need for more studies designed specifically to address the role of nutrition in the metabolism and detoxification of MeHg. It is also important to collect more detailed dietary information in future epidemiologic studies of MeHg exposure.

Correlations between cadmium treatment, oxygen uptake and metallothionein response in liver and kidney from two mice strains

Oxygen uptake was determined in liver and kidney slices from Balb/C and C3H/HeJ mice at various time points related to a 4-day cadmium (Cd) i.p. injection regime, the latter strain being not only the higher metallothionein (MT) responder, but also more Cd sensitive. In both strains Cd injections caused an increase in O2 uptake in the tissues, being more expressed in the higher MT responsive C3H/HeJ strain. An ability for fast, additional increase of O2 uptake in response to subsequent Cd exposure was also induced during the injection regime. Maximal obtainable MT levels in the two strains were estimated by forced overwhelming pneumococcal infection challenge, giving induction values above those obtained for the Cd injections in the Balb/C strain and equal to those obtained for Cd in the more responsive C3H/HeJ strain. Together with direct defendants against harmful oxygen radicals, MT may act complementary as a radical scavenger and by Cd inactivation, but to a higher degree in the C3H/HeJ compared to the Balb/C strain.

Prognostic evaluation of metallothionein expression in human colorectal neoplasms

AIM

To investigate the role of metallothionein in colorectal tumours and the possible relation with other factors associated with tumour progression: expression of cathepsin D (CD), CD44, p53, Rb, bcl-2, c-erbB-2, epidermal growth factor receptor (EGFR), proliferation indices (Ki-67, proliferating cell nuclear antigen (PCNA)), and conventional clinicopathological variables.

METHODS

The immunohistochemical expression of metallothionein was investigated in 23 cases of colorectal adenoma and 94 adenocarcinomas. Metallothionein expression was examined by the avidinbiotin peroxidase immunoperoxidase (ABC) using the monoclonal mouse antibody E9, on formalin fixed, paraffin embedded tissue.

RESULTS

Positive metallothionein expression (> 5% of neoplastic cells) was observed in 30.4% of adenomas and 25.5% of adenocarcinomas, while 8.7% of adenomas and 14.9% carcinomas showed focal metallothionein positivity. In contrast, 60.9% of adenomas and 59.6% of carcinomas almost completely lacked metallothionein expression. In the series of adenocarcinomas, metallothionein expression was inversely correlated with CD44 in neoplastic cells (p = 0.01). There was no statistically significant difference of metallothionein expression, or the other variables examined, between adenocarcinomas and adenomas.

CONCLUSIONS

Metallothionein expression does not seem to indicate aggressive biological behaviour in colorectal adenocarcinomas, in comparison with the other types of carcinoma. The inverse correlation with CD44 could suggest that the decreased metallothionein expression may contribute to the metastatic spread of the lymph node involvement in colorectal cancer. Metallothionein expression does not seem to represent an independent prognostic marker in colorectal cancer.

Distribution and retention of mercury in metallothionen-null mice after exposure to mercury vapor

We studied the role of metallothionein (MT) in the distribution and retention of mercury in the brain, lung, liver and kidney of MT-null and wild-type mice after exposure to mercury (Hg0) vapor. Mice were exposed to Hg0 vapor at 5.5-6.7 mg/m3 for 3 h and killed at 1, 24, 72 or 168 h after exposure. One hour after exposure to Hg0 vapor, there were no differences in mercury concentrations in these organs from MT-null and wild-type mice. However, the elimination rate of mercury from the organs, except the brain, were remarkably faster in MT-null mice than in wild-type mice. MT-I and -II levels in the lung and kidney were increased significantly in wild-type mice but not in MT-null mice at 24 h after exposure to Hg0 vapor. At this time point, over 65% of the mercury was retained in the MT fraction of the cytosol of organs from wild-type mice. In contrast, mercury appeared mainly in the high-molecular-weight protein fractions in the cytosol of organs from MT-null mice. In the brain, a large amount of mercury was bound to MT in both strains of mice immediately after exposure. No difference was observed in the elimination rate of mercury from the brain between both strains of mice. Brain MT levels were elevated slightly in wild-type mice at 168 h after exposure but could not be detected in MT-null mice. These data suggest that no detectable MT-I and -II levels were found in the brain of MT-null mice and that mercury was apparently bound to MT-III. Using MT-null mice, we showed also that MT-III may play an important role in the retention of mercury in the brain.

Heavy metal content in liver and kidneys of grey seals (Halichoerus grypus) in various life stages correlated with metallothionein levels: Some metal-binding characteristics of this protein

Liver and kidneys from grey seals (Halichoerus grypus) in their natural habitats in Norwegian waters contain high levels of Cd and Hg as well as metallothionein (MT). The data show significant placental transfer of heavy metals in seals. The MT concentrations were higher in fetus liver and kidneys than in the liver and kidneys of juveniles and adults. A significantly higher proportion of the total Cd and Cu, as compared to Zn and Hg, in fetal liver was associated with MT. Only low amounts of metals and MT were found in juveniles. In kidneys, little metal was associated with MT, although high amounts of Cd were bound in fetal stages. Positive correlations were found between total metal, MT content, and MT-bound metals, particularly for Cd and Zn. Grey seal MT may have higher affinity to Zn than to Cd. The use of seal MT as a biomarker for environmental heavy metal exposure seems promising.

Pulmonary toxicity caused by acute exposure to mercury vapor is enhanced in metallothionein-null mice

This study examined the protective role of metallothionein (MT) against pulmonary damage caused by acute exposure to metallic mercury (Hg0) vapor using MT-null and wild-type mice. Both strains of mice were exposed to Hg0 at 6.6 to 7.5 mg/m3 for 4 hr each day for 3 consecutive days. This dosing protocol was lethal to over 60% of MT-null mice but did not kill any wild-type mice. More severe pulmonary damage was found by histopathological observation in MT-null mice than in wild-type mice. MT levels in the lung were elevated in wild-type mice after Hg0 vapor exposure, and gel filtration of the lung cytosol revealed that most of the mercury was associated with MT. In MT-null mice, MT levels were below the limit of detection (0.2 microg/g tissue) for the MT assay even after exposure. After exposure to Hg0 vapor for 3 consecutive days, the pulmonary mercury levels in wild-type mice were significantly higher than in MT-null mice. These findings suggest that MT plays a protective role against the acute pulmonary toxicity of Hg0 vapor.

Oxidative stress as a mechanism of chronic cadmium-induced hepatotoxicity and renal toxicity and protection by antioxidants

The role of oxidative stress in chronic cadmium (Cd) toxicity and its prevention by cotreatment with antioxidants was investigated. Adult female Sprague-Dawley rats were injected sc with 5 micromol CdCl2/kg/day, 5 times a week, for up to 22 weeks. Serum alanine amino transferase and lactate dehydrogenase activities were elevated after 9 weeks of Cd administration, indicating hepatic damage. Renal toxicity, indicated by elevation in urinary lactate dehydrogenase activity and protein, was also observed around this time. Chronic Cd administration resulted in a gradual rise in hepatic as well as renal cortex glutathione levels. In spite of this, lipid peroxidation increased in both tissues, particularly during the second half of the Cd exposure period. Depletion of glutathione following buthionine sulfoximine administration at the end of Week 5, or inhibition of catalase by aminotriazole at the end of Week 7, resulted in the development of acute nephrotoxicity within 6 h. Coadministration of antioxidants, N-acetylcysteine (50-100 mg/kg, sc), or vitamin E (100-150 mg/kg, sc) with Cd, starting from the early phases of Cd exposure, controlled Cd-induced lipid peroxidation and protected the animals against hepatic as well as renal toxicity. A Japanese hepatoprotective drug, Stronger Neo-Minophagen C, containing glycyrrhizin, glycine, and cysteine, was also effective in reducing the chronic Cd nephrotoxicity. In conclusion, oxidative stress appears to play a major role in chronic Cd-induced hepatic and renal toxicity since inhibition of components of the antioxidant defense system accelerated and administration of antioxidants protected against Cd toxicity.

Increase of striatal dopamine release by cadmium in nursing rats and its prevention by dexamethasone-induced metallothionein

Repeated daily intraperitoneal (i.p.) administrations of cadmium (CdCl2, 1 mg/kg per day for 5 days) increased striatal dopamine (DA) release (180% of controls) and turnover (150% of controls) in 13-day-old rats. Cd treatment also increased striatal metallothionein (MT) content (161%), Cd (127%) and lipid peroxidation (LPO, 190%). In addition, Cd treatment decreased striatal tyrosine hydroxylase (TH) activity (-28%), and such an effect may result from D-2 receptor blockade as a consequence of excessive dopamine release, since sulpiride (a specific D-2 receptor antagonist) administration to Cd-treated rats abolished the effect of Cd on TH. No effect was observed on striatal monoamine oxidase (MAO) activity. Dexamethasone (Dx) treatment increased striatal MT content and caused no effect on either DA release or turnover. However, Dx administration prevented the effects caused by Cd, including the increased DA release and enhanced striatal lipid peroxidation. These results indicate that toxic effects on the brain are to be expected as a result of Cd exposure and that Dx administration can attenuate them.

Induction of drug resistance to gold sodium thiomalate in a monocyte cell line, THP-1

The expression of metallothionein, an intracellular heavy-metal-binding protein, and p-glycoprotein, an energy-dependent drug efflux pump, was examined to study the mechanism of cell resistance to gold sodium thiomalate (GST). THP-1, one of the monocyte-derived cell lines, was cultured for 6 months and resistance to 25 microg/ml of GST (GST-resistant cells) was thus induced. The GST-resistant cells were then cultured with bucillamine to examine the presence of cross-resistance. The intracellular GST concentration was examined by flameless atomic absorption spectroscopy. The cell viability was determined by the uptake of 3-4,5 dimethylthiazole-2,5 diphenyl tetrazolium bromide (MTT). The expression of p-glycoprotein was detected by Western blotting using monoclonal anti-p-glycoprotein antibody. The expression of metallothionein was detected using the indirect immunofluorescence technique. GST-resistant cells did not show any cross-resistance to bucillamine. The rate of cytoplasmic GST accumulation decreased in the GST-resistant cells, while the rate of GST efflux also decreased. The expression of p-glycoprotein in the GST-resistant cells was not significantly different from that in the cells not treated with GST. On the other hand, the GST-resistant cells showed a higher expression of metallothionein than cells not treated with GST. These findings suggest that the induced resistance to GST might partly be due to an induction of metallothionein.

Age-dependent changes in metallothionein levels in liver and kidney of the Japanese

Samples of liver, renal cortex, and medulla were obtained from 55 forensic autopsies (0- to 95-yr-old Japanese). Metallothionein (MT) was determined by the Ag-hem or Cd-hem method. Zinc (Zn), copper (Cu), and cadmium (Cd) were determined by atomic absorption spectrophotometry. The mean levels of MT were 250 micrograms/g in the liver, and 394 micrograms/g (cortex) and 191 micrograms/g (medulla) in the kidney. Age-dependent changes were observed in both the liver and kidney. In the liver, MT level decreased during infancy and increased thereafter with age. Similar age-dependent changes in the levels of Zn and Cu were observed. In the kidney cortex, MT level increased with age, although no correlation was found after middle age. The levels of Cd and Zn also increased with age until middle age; however, they decreased thereafter. These results suggest that age-dependent changes in renal MT levels are associated with accumulation of Cd.

Efficacy of amphipathic dithiocarbamates in intracellular cadmium mobilization and in modulation of hepatic and renal metallothionein in cadmium pre-exposed rat

Forty-eight hours after an intraperitoneal injection of cadmium chloride (1.5 mg Cd/kg) to female albino rats, Cd was mainly localized in the hepatic and renal supernatant cytosolic fraction (SCF). Seventy-two hours later, the total hepatic burden remained unchanged but the total renal burden was enhanced, showing its tendency to accumulate in the kidney. A single dose (0.4 mmol/kg, i.p.) of sodium N-benzyl-D-glucamine dithiocarbamate (BG.DTC) or sodium N-(4-methoxybenzyl)-D-glucamine dithiocarbamate (MeO.BG.DTC), 24 h after Cd injection, efficiently mobilized Cd from hepatic SCF, apparently from cadmium-metallothionein (Cd-MT); MeO.BG.DTC also removed Cd from hepatic nuclear mitochondrial fraction. This treatment, however, increased the renal burden of Cd, indicating that the chelating agents, at least partly, transport Cd from the liver and possibly from other sites into the kidney. Three doses of the chelators further enhanced mobilization of Cd from hepatic as well as renal SCF, as corroborated by its enhanced urinary and, to a greater extent, fecal excretion. Hepatic and renal MT were induced several-fold above normal after a single dose of Cd as well as single or repeated doses of BG.DTC or MeO.BG.DTC. Seventy-two hours after a Cd injection, the hepatic MT declined to half of the induced level while the renal MT remained elevated. Administration of BG.DTC or MeO.BG.DTC in Cd pre-treated rats produced an additive response in hepatic MT, but the response in renal MT was less than additive at one dose and slightly declined after three doses. Hepatic Zn and Cu and renal Zn increased on treatment with Cd but were depleted after a single or repeated injection of BG.DTC or MeO.BG.DTC in normal as well as in Cd pre-exposed animals. The results indicate that intracellular access of amphipathic dithiocarbamates effectively mobilizes MT-bound Cd, which is preferentially excreted in the feces, and helps avoid further burden on the kidney and consequent nephrotoxicity. Additionally, MeO.BG.DTC was a better inducer of hepatic MT to help increased capture of toxic metal from the initial circulation and consequent toxicity.