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

Metallothionein in human immunomagnetically selected CD34(+) haematopoietic progenitor cells

Human umbilical CD34(+) immature haematopoietic cells were rapidly and efficiently obtained from light density MNC (mononuclear cells) by MACS (magnetic cell sorting). An ex vivo expanded population of CD34(+) was cultured in serum-free medium supplemented with cytokines FL (flt3 ligand), SCF (stem cell factor) and TPO (thrombopoietin) in order to obtain a sufficient number of CD34(+) cells. CD34(+) cells expanded from cord blood for 7 days were demonstrated to increase in the absolute number of CD34(+) cells by 5.12 ± 2.47-fold (mean ± S.D., n = 3). Flow cytometric analysis demonstrated that the percentage of CD34 antigen expression after expansion of the culture was 97.81 ± 1.07%, whereas it was 69.39 ± 10.37% in none-expanded CD34(+) cells (mean ± S.D., n = 3), thus defining a system that allowed extensive amplification accompanied by no maturation. MTs (metallothioneins), low molecular weight, cysteine-rich metal-binding proteins, exhibit various functions, including metal detoxification and homoeostasis. We here examined the expression pattern of functional members of the MT gene family in immature CD34(+) cells and compared it with more mature CD34(-) cells in order to strengthen the proposed function of MT in differentiation. Cells were cultured in RPMI 1640 medium, with or without different zinc supplements for 24 h. Relative quantitative expression of MT isogenes in the mature CD34(-) cells was higher than in the immature CD34(+) cells. IHC (immunohistochemical staining) revealed an increased MT protein biosynthesis in CD34(-) cells, greater than in CD34(+) cells. Therefore, the role of MT in differentiation of human haematopoietic progenitor cells from human cord blood is reported for the first time.

Dietary zinc and metallothionein on small intestinal disaccharidases activity in mice

AIM: To examine the effect of increasing dietary zinc (Zn) intake and the lack of metallothionein (MT) expression on activity of small intestinal disaccharidases.

METHODS: MT-I and II knockout (MT-/-) and wild-type (MT+/+) female mice at 3.5 wk of age were randomly fed with a diet containing 2 (2 Zn), 15 (15 Zn) or 50 (50 Zn) mg Zn/kg (n = 8/group/genotype) for 5 wk. Small intestinal segments (duodenum, jejunum and ileum) were collected and either fixed in 10% formalin for histological analysis or snap frozen in liquid nitrogen for sucrase, lactase and maltase activity analyses.

RESULTS: Plasma Zn was significantly (P < 0.05) lower (33%) in MT-/- compared with MT+/+ mice fed the 2 Zn diet. Villus height and crypt depth were increased by approximately 15% in MT+/+ mice compared with MT-/- mice. Duodenal disaccharidase activities were significantly higher in MT+/+ compared with MT-/- mice particularly in those fed the 2 Zn diet. For the 50 Zn diet, jejunal sucrase and lactase activities were significantly higher in MT-/- (13 313 ± 2314; 4107 ± 364 μmol glucose/well/min/g tissue, respectively) compared with MT+/+ mice (7054 ± 608; 1818 ± 174). Similarly, ileal lactase activities were higher in MT-/- (1480 ± 192) compared with MT+/+ (629 ± 353) mice particularly those fed the 2 Zn diet.

CONCLUSION: Increasing dietary Zn has little effect on disaccharidases activity in MT wild-type mice. The presence of MT may enhance morphological and functional development of the gut.

Hemoglobin regulates the metabolic, synthetic, detoxification, and biotransformation functions of hepatoma cells cultured in a hollow fiber bioreactor

Hepatic hollow fiber (HF) bioreactors constitute one type of extracorporeal bioartificial liver assist device (BLAD). Ideally, cultured hepatocytes in a BLAD should closely mimic the in vivo oxygenation environment of the liver sinusoid to yield a device with optimal performance. However, most BLADs, including hepatic HF bioreactors, suffer from O2 limited transport toward cultured hepatocytes, which reduces their performance. We hypothesize that supplementation of hemoglobin-based O2 carriers into the circulating cell culture medium of hepatic HF bioreactors is a feasible and effective strategy to improve bioreactor oxygenation and performance. We examined the effect of bovine hemoglobin (BvHb) supplementation (15g/L) in the circulating cell culture medium of hepatic HF bioreactors on hepatocyte proliferation, metabolism, and varied liver functions, including biosynthesis, detoxification, and biotransformation. It was observed that BvHb supplementation supported the maintenance of a higher cell mass in the extracapillary space, improved hepatocyte metabolic efficiency (i.e., hepatocytes consumed much less glucose), improved hepatocyte capacity for drug metabolism, and conserved both albumin synthesis and ammonia detoxification functions compared to controls (no BvHb supplementation) under the same experimental conditions.

Hypoxia preconditioning by cobalt chloride enhances endurance performance and protects skeletal muscles from exercise-induced oxidative damage in rats

AIM

Training under hypoxia has several advantages over normoxic training in terms of enhancing the physical performance. Therefore, we tested the protective effect of hypoxia preconditioning by hypoxia mimetic cobalt chloride against exercise-induced oxidative damage in the skeletal muscles and improvement of physical performance.

METHOD

Male Sprague-Dawley rats were randomly divided into four groups (n=8), namely control, cobalt-supplemented, training and cobalt with training. The red gastrocnemius muscle was examined for all measurements, viz. free radical generation, lipid peroxidation, muscle damage and antioxidative capacity.

RESULTS

Hypoxic preconditioning with cobalt along with training significantly increased physical performance (33%, P<0.01) in rats compared with training-only rats. Cobalt supplementation activated cellular oxygen sensing system in rat skeletal muscle. It also protected against training-induced oxidative damage as observed by an increase in the GSH/GSSG ratio (36%, P<0.001; 28%, P<0.01 respectively) and reduced lipid peroxidation (15%, P<0.01; 31%, P<0.01 respectively) in both trained and untrained rats compared with their respective controls. Cobalt supplementation along with training enhanced the expression of antioxidant proteins haem oxygenase-1 (HO-1; 1.2-fold, P<0.05) and metallothionein (MT; 4.8-fold, P<0.001) compared with training only. A marked reduction was observed in exercise-induced muscle fibre damage as indicated by decreased necrotic muscle fibre, decreased lipofuscin content of muscle and plasma creatine kinase level (16%, P<0.01) in rats preconditioned with cobalt.

CONCLUSION

Our study provides strong evidence that hypoxic preconditioning with cobalt chloride enhances physical performance and protects muscle from exercise-induced oxidative damage via GSH, HO-1 and MT-mediated antioxidative capacity.

Comprehensive analysis of expressed sequence tags from the pulp of the red mutant 'Cara Cara' navel orange (Citrus sinensis Osbeck)

Expressed sequence tag (EST) analysis of the pulp of the red-fleshed mutant 'Cara Cara' navel orange provided a starting point for gene discovery and transcriptome survey during citrus fruit maturation. Interpretation of the EST datasets revealed that the mutant pulp transcriptome held a high section of stress responses related genes, such as the type III metallothionein-like gene (6.0%), heat shock protein (2.8%), Cu/Zn superoxide dismutase (0.8%), late embryogenesis abundant protein 5 (0.8%), etc. 133 transcripts were detected to be differentially expressed between the red mutant and its orange-color wild genotype 'Washington' via digital expression analysis. Among them, genes involved in metabolism, defense/stress and signal transduction were statistical overrepresented. Fifteen transcription factors, composed of NAM, ATAF, and CUC transcription factor (NAC); myeloblastosis (MYB); myelocytomatosis (MYC); basic helix-loop-helix (bHLH); basic leucine zipper (bZIP) domain members, were also included. The data reflected the distinct expression profile and the unique regulatory module associated with these two genotypes. Eight differently expressed genes analyzed in digital were validated by quantitative real-time polymerase chain reaction. For structural polymorphism, both simple sequence repeats and single nucleotide polymorphisms (SNP) loci were surveyed; dinucleotide presentation revealed a bias toward AG/GA/TC/CT repeats (52.5%), against GC/CG repeats (0%). SNPs analysis found that transitions (73%) outnumbered transversions (27%). Seventeen potential cultivar-specific and 387 heterozygous SNP loci were detected from 'Cara Cara' and 'Washington' EST pool.

Gold compounds as anticancer agents: chemistry, cellular pharmacology, and preclinical studies

Gold compounds are a class of metallodrugs with great potential for cancer treatment. During the last two decades, a large variety of gold(I) and gold(III) compounds are reported to possess relevant antiproliferative properties in vitro against selected human tumor cell lines, qualifying themselves as excellent candidates for further pharmacological evaluation. The unique chemical properties of the gold center confer very interesting and innovative pharmacological profiles to gold-based metallodrugs. The primary goal of this review is to define the state of the art of preclinical studies on anticancer gold compounds, carried out either in vitro or in vivo. The available investigations of anticancer gold compounds are analyzed in detail, and particular attention is devoted to underlying molecular mechanisms. Notably, a few biophysical studies reveal that the interactions of cytotoxic gold compounds with DNA are generally far weaker than those of platinum drugs, implying the occurrence of a substantially different mode of action. A variety of alternative mechanisms were thus proposed, of which those involving either direct mitochondrial damage or proteasome inhibition or modulation of specific kinases are now highly credited. The overall perspectives on the development of gold compounds as effective anticancer drugs with an innovative mechanism of action are critically discussed on the basis of the available experimental evidence.

Role of metallothionein in cadmium traffic and toxicity in kidneys and other mammalian organs

Metallothioneins are cysteine-rich, small metal-binding proteins present in various mammalian tissues. Of the four common metallothioneins, MT-1 and MT-2 (MTs) are expressed in most tissues, MT-3 is predominantly present in brain, whereas MT-4 is restricted to the squamous epithelia. The expression of MT-1 and MT-2 in some organs exhibits sex, age, and strain differences, and inducibility with a variety of stimuli. In adult mammals, MTs have been localized largely in the cell cytoplasm, but also in lysosomes, mitochondria and nuclei. The major physiological functions of MTs include homeostasis of essential metals Zn and Cu, protection against cytotoxicity of Cd and other toxic metals, and scavenging free radicals generated in oxidative stress. The role of MTs in Cd-induced acute and chronic toxicity, particularly in liver and kidneys, is reviewed in more details. In acute toxicity, liver is the primary target, whereas in chronic toxicity, kidneys are major targets of Cd. The intracellular MTs bind Cd ions and form CdMT. In chronic intoxication, Cd stimulates de novo synthesis of MTs; it is assumed that toxicity in the cells starts when loading with Cd ions exceeds the buffering capacity of intracellular MTs. CdMT, released from the Cd-injured organs, or when applied parenterally for experimental purposes, reaches the kidneys via circulation, where it is filtered, endocytosed in the proximal tubule cells, and degraded in lysosomes. Liberated Cd can immediately affect the cell structures and functions. The resulting proteinuria and CdMT in the urine can be used as biomarkers of tubular injury.

Cadmium stress stimulates tissue turnover in Helix pomatia: increasing cell proliferation from metal tolerance to exhaustion in molluscan midgut gland

In terrestrial pulmonate snails, cadmium (Cd) uptake leads to the induction of a Cd-specific metallothionein isoform (Cd-MT) that protects against adverse interactions of this toxic metal ion. Increasing concentrations of Cd cause increased individual mortality possibly linked to pathological alterations in the snail midgut gland. Histological, immuno-histochemical, and electron-microscopic methods in combination with tissue metal analyses and quantification of MT induction parameters were applied to the midgut gland of Cd-exposed Roman snails (Helix pomatia). Conspicuous concentration-dependent alterations occurred in this organ, including the metal-induced increase of Cd-MT concentration and manifestation of Cd-MT mRNA precipitations in all midgut gland cell types. The most evident alteration was an increase of cellular turnover reflected by enhanced cell proliferation. Intensified vesiculation of endoplasmic reticulum was noted in basophilic cells and an increasing formation of lipofuscin granules in excretory cells. At the highest Cd concentrations, mitochondrial membranes were disrupted in basophilic cells, and lipofuscin granules were released from excretory cells into the midgut gland tubular system. Some of these alterations (e.g., increased cell proliferation rate, vesiculation of endoplasmic reticulum) detected at low Cd concentrations were interpreted as adaptive response processes enhancing the tolerance of exposed individuals to metal stress. Cellular alterations at higher Cd concentrations (e.g., mitochondrial structural damage) clearly represented ongoing irreversible cellular disruption. Combined evaluation of cellular biomarkers and MT saturation levels indicated that the transition from stress resistance to depletion of resistance capacity occurred above a threshold of 0.8 micromol Cd/g dry weight in the midgut gland of H. pomatia. At these Cd concentrations, Cd-MT was saturated with Cd(2+) ions, whereas at the cellular level, structural alterations turned into pathological deterioration.

Antifibrotic activity of anthocyanidin delphinidin in carbon tetrachloride-induced hepatotoxicity in mice

The aim of this study was to investigate the hepatoprotective effects of anthocyanidin delphinidin in carbon tetrachloride (CCl(4))-induced liver fibrosis in mice. Male Balb/C mice were treated with CCl(4) dissolved in olive oil (20%, v/v, 2mL/kg) intraperitoneally (i.p.), twice a week for 7 weeks. Delphinidin was administered i.p. once daily for next 2 weeks, in doses of 10 and 25mg/kg of body weight. The CCl(4) control group has been observed for spontaneous reversion of fibrosis. CCl(4)-administration induced an elevation in serum transaminase and alkaline phosphatase levels and increased oxidative stress in the liver. Delphinidin has successfully attenuated oxidative stress, increased matrix metalloproteinase-9 and metallothionein I/II expression and restored hepatic architecture. Furthermore, the overexpression of tumor necrosis factor-alpha and transforming growth factor-beta1 has been withdrawn by delphinidin. Concomitantly, the expression of alpha-smooth muscle actin indicated returning of hepatic stellate cells (HSC) into inactive state. Our results suggest the therapeutic effects of delphinidin in CCl(4)-induced liver fibrosis by promoting extracellular matrix degradation, HSC inactivation and down-regulation of fibrogenic stimuli, with strong enhancement of hepatic regenerative capability.

Responses of wild small mammals to a pollution gradient: host factors influence metal and metallothionein levels

We investigated how host factors (species, age, gender) modulated Cd, Pb, Zn, and Cu concentrations, metallothionein levels (MTs) and their relationships in 7 sympatric small mammal species along a pollution gradient. Cd concentrations in liver and kidneys increased with age in all species. Age effect on other metals and MTs differs among species. Gender did not influence metal and MT levels except in the bank vole. Three patterns linking internal metal concentrations and MTs were observed along the gradient: a low metal accumulation with a (i) high (wood mouse) or (ii) low (bank vole) level of MTs accompanied by a slight or no increase of MTs with Cd accumulation; (iii) an elevated metal accumulation with a sharp increase of MTs (common and pygmy shrews). In risk assessment and biomonitoring perspectives, we conclude that measurements of MTs and metals might be associated because they cannot be interpreted properly when considered separately.

Protective role of metallothionein in benzo[a]pyrene-induced DNA damage

Metallothionein (MT) is known to reduce chemical carcinogenesis. Carcinogenesis induced by benzo[a]pyrene (B[a]P) which is an environmental chemical carcinogen is related to DNA adduct formation and oxidative damage through metabolic activation. Ten-week-old male MT-I/II null mice and wild-type mice were given a single injection of B[a]P (250 mg/kg, p.o.), and B[a]P-induced DNA damage was evaluated at 6-48 hr later. The frequencies of micronucleated reticulocytes (MNRET) in MT-I/II null mice were significantly increased compared with that of wild-type mice at 48 hr after B[a]P administration. At 48 hr after B[a]P administration, comet scores were significantly increased in MT-I/II null mice but not in wild-type mice. 8-Hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, was significantly increased in liver of MT-I/II null mice at 6 and 12 hr after B[a]P administration, although that of wild-type mice was only slightly changed. Because cytochrome P450 (CYP) plays a major role in the process of B[a]P metabolic activation, we attempted to reveal the effect of MT on metabolic activation of B[a]P. Although CYP1A activities were elevated in the livers of MT-I/II null mice and wild-type mice treated with B[a]P, it was not different between both strains of mice. In addition, MT levels in the livers of wild-type mice were significantly increased by the B[a]P treatment, whereas MT was not detected in livers of MT-I/II null mice with or without B[a]P treatment. These results demonstrate that MT acts as an endogenous defensive factor against B[a]P-induced DNA damage.

Automated brain tumor biopsy prediction using single-labeling cDNA microarrays-based gene expression profiling

AIMS

Gene signatures obtained from microarray experiments may be of use to improve the prediction of brain tumor diagnosis. Nevertheless, automated and objective prediction with accuracy comparable to or better than the gold standard should be convincingly demonstrated for possible clinician uptake of the new methodology. Herewith, we demonstrate that primary brain tumor types can be discriminated using microarray data in an automated and objective way.

METHODS

Postsurgical biopsies from 35 patients [17 glioblastoma multiforme (Gbm) and 18 meningothelial meningioma (Mm)] were stored in liquid nitrogen, total RNA was extracted, and cDNA was labeled with Cy3 fluorochrome and hybridized onto a cDNA-based microarray containing 11,500 cDNA clones representing 9300 loci. Scanned data were preprocessed, normalized, and used for predictor development. The predictive functions were fitted to a subset of samples and their performance evaluated with an independent subset. Expression results were validated by means of real time-polymerase chain reaction.

RESULTS

Some gene expression-based predictors achieved 100% accuracy both in training resampling validation and independent testing. One of them, composed of GFAP, PTPRZ1, GPM6B and PRELP, produced a 100% prediction accuracy for both training and independent test datasets. Furthermore, the gene signatures obtained, increased cell detoxification, motility and intracellular transport in Gbm, and increased cell adhesion and cytochrome-family genes in Mm, agree well with the expected biologic and pathologic characteristics of the studied tumors.

CONCLUSIONS

The ability of gene signatures to automate prediction of brain tumors through a fully objective approach has been demonstrated. A comparison of gene expression profiles between Gbm and Mm may provide additional clues about patterns associated with each tumor type.

Effects of exogenous metallothionein against thallium-induced oxidative stress in rat liver

Metallothionein (MT) is a low-molecular weight sulfur-rich protein that plays role in metal homeostasis/detoxification and radical scavenging. The following study investigated the ability of exogenous MT to protect against oxidative damage induced by thallium (TI) in rat liver. Male Wistar rats were divided into four groups; a control and three experimental groups. The control group received physiological saline. Group 1 animals were injected with thallium acetate intraperitoneally (i.p.) at a single dose of LD(50) (32 mg/kg). In group 2 and group 3, metallothionein I was administrated once at two different doses (1 or 2.5mg/kg i.p., respectively) 1h before TI intoxication. Levels of endogenous antioxidants, oxidative stress markers were measured and histopathological examinations were performed 4 days after TI administration. TI accumulation in liver decreased related to the dose of MT. Mostly all of the alterations in the levels antioxidants restored to normal levels in MT administrated animals. H(2)O(2) levels and lipid peroxidation decreased, integrity of hepatocytes and membranous structures inside the cells were preserved. The toxic effects of TI were modulated in MT administrated animals particularly at the dose of 2.5mg/kg. These findings suggest an active role of exogenous MT against TI-induced oxidative stress in rat liver.

2'-Benzoyloxycinnamaldehyde inhibits tumor growth in H-ras12V transgenic mice via downregulation of metallothionein

Cinnamaldehydes have been reported to induce apoptosis in human carcinomas through the generation of reactive oxygen species (ROS). 2'-benzoyloxycinnamaldehyde (BCA) has been reported to inhibit tumor formation in H-ras12V transgenic mice. To see the antitumor effects of BCA, BCA was administrated intraperitoneally (50 mg/kg) to H-ras12V transgenic mice for 3 wk, and it was found that the hepatic tumor volume and the total number of tumors were decreased in BCA-treated mice as compared to control H-ras12V transgenic mice. To identify possible target genes responsible for BCA antitumor effects in H-ras12V transgenic mice, cDNA microarray analyses were performed comparing gene expression between BCA treated and control transgenic mice. We found that 42 genes were downregulated, and 40 genes were upregulated in the BCA-treated transgenic mice. The downregulated genes included several genes involved in ROS regulation and immune response (aconitase, metallothionein-1, metallothionein-2, and purine nucleoside phosphorylase). The expression of ROS-related genes, metallothionein 1 and metallothionein 2, was decreased more than twofold with BCA treatment (P < 0.001). It was confirmed by RT-PCR and immunohistochemical analyses. The inhibition of tumor formation and growth in H-ras12V transgenic mice by BCA was mediated through inhibition of the expression of the ROS scavengers metallothionein 1 and metallothionein 2.

Mechanism of cadmium-mediated inhibition of Msh2-Msh6 function in DNA mismatch repair

The observation that Cadmium (Cd(2+)) inhibits Msh2-Msh6, which is responsible for identifying base pair mismatches and other discrepancies in DNA, has led to the proposal that selective targeting of this protein and consequent suppression of DNA repair or apoptosis promote the carcinogenic effects of the heavy metal toxin. It has been suggested that Cd(2+) binding to specific sites on Msh2-Msh6 blocks its DNA binding and ATPase activities. To investigate the mechanism of inhibition, we measured Cd(2+) binding to Msh2-Msh6, directly and by monitoring changes in protein structure and enzymatic activity. Global fitting of the data to a multiligand binding model revealed that binding of about 100 Cd(2+) ions per Msh2-Msh6 results in its inactivation. This finding indicates that the inhibitory effect of Cd(2+) occurs via a nonspecific mechanism. Cd(2+) and Msh2-Msh6 interactions involve cysteine sulfhydryl groups, and the high Cd(2+):Msh2-Msh6 ratio implicates other ligands such as histidine, aspartate, glutamate, and the peptide backbone as well. Our study also shows that cadmium inactivates several unrelated enzymes similarly, consistent with a nonspecific mechanism of inhibition. Targeting of a variety of proteins, including Msh2-Msh6, in this generic manner would explain the marked broad-spectrum impact of Cd(2+) on biological processes. We propose that the presence of multiple nonspecific Cd(2+) binding sites on proteins and their propensity to change conformation on interaction with Cd(2+) are critical determinants of the susceptibility of corresponding biological systems to cadmium toxicity.

Zinc and diabetes--clinical links and molecular mechanisms

Zinc is an essential trace element crucial for the function of more than 300 enzymes and it is important for cellular processes like cell division and apoptosis. Hence, the concentration of zinc in the human body is tightly regulated and disturbances of zinc homeostasis have been associated with several diseases including diabetes mellitus, a disease characterized by high blood glucose concentrations as a consequence of decreased secretion or action of insulin. Zinc supplementation of animals and humans has been shown to ameliorate glycemic control in type 1 and 2 diabetes, the two major forms of diabetes mellitus, but the underlying molecular mechanisms have only slowly been elucidated. Zinc seems to exert insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Furthermore, zinc might play a role in the development of diabetes, since genetic polymorphisms in the gene of zinc transporter 8 and in metallothionein (MT)-encoding genes could be demonstrated to be associated with type 2 diabetes mellitus. The fact that antibodies against this zinc transporter have been detected in type 1 diabetic patients offers new diagnostic possibilities. This article reviews the influence of zinc on the diabetic state including the molecular mechanisms, the role of the zinc transporter 8 and MT for diabetes development and the resulting diagnostic and therapeutic options.

Evidence for a potential role of metallothioneins in inflammatory bowel diseases

Inflammatory bowel diseases (IBDs) are a group of chronic, relapsing, immune-mediated disorders of the intestine, including Crohn's disease and ulcerative colitis. Recent studies underscore the importance of the damaged epithelial barrier and the dysregulated innate immune system in their pathogenesis. Metallothioneins (MTs) are a family of small proteins with a high and conserved cysteine content that are rapidly upregulated in response to an inflammatory stimulus. Herein, we review the current knowledge regarding the expression and potential role of MTs in IBD. MTs exert a central position in zinc homeostasis, modulate the activation of the transcription factor nuclear factor (NF)-kappaB, and serve as antioxidants. In addition, MTs could be involved in IBD through their antiapoptotic effects or through specific immunomodulating extracellular effects. Reports on MT expression in IBD are contradictory but clearly demonstrate a deviant MT expression supporting the idea that these aberrations in IBD require further clarification.

Functional characterization of the 5'-upstream region of MTT5 metallothionein gene from Tetrahymena thermophila

Metallothioneins are ubiquitous small, cysteine-rich, metal-binding proteins that play important roles in intracellular metal homeostasis and detoxification. Very few data are available on the promoter region and the mechanism of metallothionein transcription in Protozoa. In this study, we focused on Tetrahymena thermophila MTT5 5'-flanking region. To define the sequence elements underlying the metal-responsiveness of this promoter, we constructed a series of deletions and mutations starting with a 1777 bp fragment immediately upstream of the start codon of MTT5. As a reporter gene we used the previously tested IAG52B surface antigen from the protozoan fish parasite Ichthyophthirius multifiliis. The results suggest that a region spanning between -300 bp and -274 bp, dubbed Tetrahymena thermophila Cadmium-Response-Element (TtCdRE), is necessary to elicit high-level expression of the transgene following induction with cadmium. This is the first demonstration by in vivo analyses of a regulatory element essential for Cd-mediated control of protozoan metallothionein gene expression, where the sequence GATA appears to be involved.

Influence of NH-Sgamma bonding interactions on the structure and dynamics of metallothioneins

Mammalian metallothioneins ([Formula: see text]) show a clustered arrangement of the metal ions and a nonregular protein structure. The solution structures of Cd(3)-thiolate cluster containing beta-domain of mouse beta-MT-1 and rat beta-MT-2 show high structural similarities, but widely differing structure dynamics. Molecular dynamics simulations revealed a substantially increased number of NH-Sgamma hydrogen bonds in beta-MT-2, features likely responsible for the increased stability of the Cd(3)-thiolate cluster and the enfolding protein domain. Alterations in the NH-Sgamma hydrogen-bonding network may provide a rationale for the differences in dynamic properties encountered in the beta-domains of MT-1, -2, and -3 isoforms, believed to be essential for their different biological function.

Association between metallothionein genes polymorphisms and sporadic amyotrophic lateral sclerosis in a Japanese population

Amyotrophic lateral sclerosis (ALS) is a progressive, lethal neurodegenerative disease that selectively affects motor neurons. Reactive oxygen species (ROS) are assumed to be involved in the pathogenesis of ALS. Metallothioneins (MTs) are self-protective, multifunctional proteins that scavenge ROS. In particular, metallothionein-III (MT-III) has a strong scavenging effect on hydroxyl radicals. MTs have been suggested to have important roles in the pathophysiology of ALS. Therefore we investigated single nucleotide polymorphisms (SNPs) of the MT-III and the metallothionein-IIA (MT-IIA) promoter region in 37 Japanese SALS cases and 206 sex-matched healthy controls using polymerase chain reaction (PCR)-direct sequencing or PCR-temporal temperature gradient gel electrophoresis (TTGE). We detected no SNPs of the MT-III gene in SALS cases and controls, and no detectable association between SALS phenotypes and a SNP of the MT-IIA promoter region. We conclude that gene polymorphisms of MT-IIA promoter region and MT-III gene are not associated with SALS phenotypes in a Japanese population.

Metallothionein-I+II in neuroprotection

Metallothionein (MT)-I+II synthesis is induced in the central nervous system (CNS) in response to practically any pathogen or disorder, where it is increased mainly in reactive glia. MT-I+II are involved in host defence reactions and neuroprotection during neuropathological conditions, in which MT-I+II decrease inflammation and secondary tissue damage (oxidative stress, neurodegeneration, and apoptosis) and promote post-injury repair and regeneration (angiogenesis, neurogenesis, neuronal sprouting and tissue remodelling). Intracellularly the molecular MT-I+II actions involve metal ion control and scavenging of reactive oxygen species (ROS) leading to cellular redox control. By regulating metal ions, MT-I+II can control metal-containing transcription factors, zinc-finger proteins and p53. However, the neuroprotective functions of MT-I+II also involve an extracellular component. MT-I+II protects the neurons by signal transduction through the low-density lipoprotein family of receptors on the cell surface involving lipoprotein receptor-1 (LRP1) and megalin (LRP2). In this review we discuss the newest data on cerebral MT-I+II functions following brain injury and experimental autoimmune encephalomyelitis.

Interaction of dietary zinc and intracellular binding protein metallothionein in postnatal bone growth

Zinc and its binding protein, metallothionein (MT), are important in regulating growth and development, and yet it is unclear how dietary Zn and MT interact in regulating bone growth. Here, 3.5-week female MT-I&II knockout (MT(-/-)) and wild type (MT(+/+)) mice were fed diets containing 2.5 (limiting, Zn-L), 15 or 50 mg Zn/kg (Zn adequate) for 5 or 9 weeks, and effects were analysed on structure and function of growth plate and metaphysis, two structures important for bone growth. Zn limitation did not affect bone growth in MT(+/+) mice. However, MT(-/-) mice, having lower Zn concentrations in plasma and long bone, showed growth retardation as demonstrated by lower body length gain, shorter and smaller tibia/femur, lower chondrocyte proliferation, reduced metaphysis heights, but increased osteoclast densities on trabecular bone, particularly in mice fed Zn-L diet. Interestingly, mRNA expression of MT-I&II was induced in the growth plate of MT(+/+) mice fed the Zn-L diet possibly compensating for Zn limitation. Growth plate MT-III expression increased in MT(-/-) mice fed the adequate Zn diet, whereas metaphyseal MT-III was significantly upregulated in MT(-/-) mice fed Zn-L diet, possibly as a compensatory mechanism or exacerbating effects of Zn limitation. Consistent with the increased osteoclast numbers, a higher ratio of RANKL/OPG gene expression was found in bone of mutant mice fed lower Zn diets. These results indicate that interaction between dietary Zn and endogenous MT is important for maximal bone growth, and MT is particularly important in the regulation of Zn pool for bone growth during moderate Zn limitation.

Expression of metallothionein mRNAs on mouse cerebellum microglia cells by thimerosal and its metabolites

Effects of thimerosal and its metabolites, ethyl mercury and thiosalicylate, on the expression of metallothionein (MT) mRNAs in mouse cerebellum microglia cell line, C8-B4 cells, were studied. The level of MT-1 mRNA significantly decreased at early hours and recovered time-dependently 24h after thimerosal was added to the C8-B4 cells. However, MT-2 and MT-3 mRNA expressions did not change from the control group. In contrast, the expression of MT-1 mRNA increased in a mouse neuroblastoma cell line 6h after incubation with thimerosal. In addition, the level of MT-1 mRNA decreased in C8-B4 cells 6h after the addition of thiosalicylate, but ethyl mercury induced MT-1 mRNA expression. When cell viability was compared with thimerosal, thiosalicylate, and ethyl mercury, the viability of C8-B4 cells decreased dose-dependently 24h after either thimerosal or ethyl mercury was added; however, the viability increased dose-dependently until 15 microM thiosalicylate was added. From the present results, it is concluded that the expression of MT-1 mRNA may be mediated by different factors than the expression of MT-2 mRNA in C8-B4 cells. The reduction of MT-1 mRNA level by thiosalicylate may affect the proliferation of C8-B4 cells.

The role of zinc in the homeostasis of human organism

Az emberi szervezet sejtjei különböző kompartmentjeinek nyomelem-koncentrációi pontosan szabályozottak (homeosztázis). A fémelemek raktározásának vagy kiürülésének rendellenességei jól karakterizált betegségekhez vezetnek. Ez az összefoglaló a cink metabolizmusával, továbbá az ennek szabályozására szolgáló folyamatokkal foglalkozik, amelyek biztosítják, hogy a cinkionok intracelluláris és extracelluláris szintje azokon a fiziológiai határokon belül maradjon, amelyek között a biológiai funkciók normálisak. Patológiás állapotban a metabolizmus folyamatai is megváltoznak. A cinkionoknak a kompartmenteket elválasztó membránokon és a citoszólon való átjutását, a fémionok szekvesztrálását génregulációk irányítják. A cink hatására kialakuló sejt- és szövetkárosodási folyamatokat, valamint a nyomelemhiányok szimptómáit is részletesen elemezzük.

Changes in metallothionein level in rat hepatic tissue after administration of natural mouldy wheat

Mycotoxins are secondary metabolites produced by microfungi that are capable of causing disease and death in humans and other animals. This work was aimed at investigation of influence of mouldy wheat contaminated by pathogenic fungi producing mycotoxins on metallothionein levels in hepatic tissue of rats. The rats were administrating feed mixtures with different contents of vitamins or naturally mouldy wheat for 28 days. It was found that the wheat contained deoxynivalenol (80 +/- 5 microg per kg of mouldy wheat), zearalenone (56 +/- 3 microg/kg), T2-toxin (20 +/- 2 microg/kg) and aflatoxins as a sum of B1, B2, G1 and G2 (3.9 +/- 0.2 microg/kg). Rats were fed diets containing 0, 33, 66 and 100% naturally moulded wheat. Control group 0, 33, 66 and 100% contained vitamins according to Nutrient Requirements of Rats (NRC). Other four groups (control group with vitamins, vit33, vit66 and vit100%) were fed on the same levels of mouldy wheat, also vitamins at levels 100% higher than the previous mixtures. We determined weight, feed conversion and performed dissection to observe pathological processes. Changes between control group and experimental groups exposed to influence of mouldy wheat and experimental groups supplemented by higher concentration of vitamins and mouldy wheat were not observed. Livers were sampled and did not demonstrate significant changes in morphology compared to control either. In the following experiments the levels of metallothionein as a marker of oxidative stress was determined. We observed a quite surprising trend in metallothionein levels in animals supplemented with increased concentration of vitamins. Its level enhanced with increasing content of mouldy wheat. It was possible to determine a statistically significant decline (p<0.05) between control group and groups of animals fed with 33, 66 and 100% mouldy wheat. It is likely that some mycotoxins presented in mouldy wheat are able to block the mechanism of metallothionein synthesis.

Study of Interactions between Metallothionein and Cisplatin by using Differential Pulse Voltammetry Brdickás reaction and Quartz Crystal Microbalance

Treatment strategies for tumour diseases are progressively focusing on personalization of medicine. However, this focus requires methods revealing the early general biological mechanisms, including the formation anti-cancer drugs’ resistance. The low molecular mass protein metallothionein is thought to be the crucial for the formation of resistance in tumour treatment based on the platinum-cytostatics. The interactions between metallothionein (MT) and cisplatin were determined by the adsorptive transfer stripping technique coupled with the differential pulse votlammetry Brdickás reaction. The signals related to the MT-cisplatin complex appeared at −0.9 V. The formation of this complex depended on the time of interaction between cisplatin and MT. The complex formation was consequently confirmed by quartz crystal microbalance analyses. The formation of this complex was detectable even after a 20 s long interaction. Moreover, we detected presence of MT-cisplatin complex in the blood of male rats treated with this drug.

Role of metallothionein as a protective factor against radiation carcinogenesis

In order to elucidate the involvement of metallothionein (MT) in radiation carcinogenesis, we examined the susceptibility of MT-I/II null mice to carcinogenesis and oxidative DNA damage resulting from X-irradiation. Eight-week-old female MT-I/II null mice and wild-type mice were exposed to whole-body X-irradiation at doses of 1.0, 1.5 or 2.0 Gy once a week for 6 weeks. Incidence of thymic lymphoma was determined at 24 weeks after the first exposure to X-irradiation. The frequency of thymic lymphomas induced by X-irradiation (at 1.5 and 2.0 Gy) was significantly higher in MT-I/II null mice than in wild-type mice. In addition, although the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG) were increased in the serum and urine of both strains of mice 24 hr after exposure to a single bout of whole body X-irradiation, these increases were significantly greater in the MT-I/II null mice than in the wild-type mice. Thus, the present results suggest that MT plays a protective role against carcinogenesis and oxidative DNA damage caused by X-irradiation.

Differential regulation of zebrafish metallothionein-II (zMT-II) gene transcription in ZFL and SJD cell lines by metal ions

Two alleles of a zebrafish metallothionein II gene (zMT-II) promoter (zMT-IIA and zMT-IIB) containing 10 MREs in the 5'-flanking region (1514bp) were identified in zebrafish. These putative MREs were confirmed via electrophoretic mobility shift assay (EMSA) to have binding activities from the cellular and nuclear extracts of a zebrafish cell line, ZFL. Transient gene expression studies using zebrafish liver (ZFL) and caudal fin (SJD) cell lines also confirmed that the most distal cluster of MREs contributed to the maximal induction of zMT-IIA activity by Zn(2+) and that this Zn(2+) induction was dose-dependent. Further transient gene expression assay of the zMT-IIA gene promoter was carried out to study the effects of various metal ions (Zn(2+), Cd(2+), Cu(2+), Hg(+), As(3+), As(5+), Cr(3+) and Cr(6+)), and Zn(2+) and Cd(2+) were found to be the most efficient MT gene inducers of zMT-II. As(3+) was a weak inducer of zMT-II in the two cell lines, and Hg(+) caused significant induction only in the SJD cells. No significant induction was found in the other metal ion exposures. EMSA also identified transcription factor(s) of two different sizes from the cytoplasmic and nuclear extracts of the ZFL cells that were able to bind with the MREs, but no increase in MRE binding was detected in the extracts of these cells after Zn(2+) or Cd(2+) treatment, compared with untreated control cells. The mechanisms of MT gene transcription induction via metal ions are discussed herein.

Protective role of metallothionein in bone marrow injury caused by X-irradiation

In order to elucidate the role of metallothionein (MT) in preventing the adverse effects of X-ray irradiation, we examined the susceptibility of MT-I/II null mice to bone marrow injury caused by X-irradiation and effects of pretreatment with MT-inducing metals on X-ray injury. Eight-week-old male mice were exposed to a single bout of whole-body X-irradiation at a dose between 0.1 and 6.0 Gy. The numbers of leukocytes, reticulocytes with micronuclei (MNRET) in the blood, and polychromatic erythrocytes with micronuclei (MNPCE) in the bone marrow were determined 24 hr after X-irradiation. X-irradiation significantly decreased the total number of leukocytes in MT-I/II null mice and wild-type mice in a dose-dependent manner, but the total number of leukocytes was significantly lower in MT-I/II null mice than in wild-type mice at a low dose of irradiation, between 0.1 and 1.0 Gy. X-irradiation (0.1 and 0.5 Gy) significantly increased the appearance of MNRET and MNPCE in both strains, but the increase was greater in the MT-I/II null mice than in the wild-type mice. Additional groups of mice were pre-administered bismuth nitrate or zinc sulfate to induce MT in the bone marrow cells prior to X-irradiation; the X-ray injury was prevented by such treatments in wild-type mice only. Thus, the present results suggest that MT plays a protective role against a low dose of X-ray injury.

Metallothionein-2 gene from the mandarin fish Siniperca chuatsi: cDNA cloning, tissue expression, and immunohistochemical localization

The metallothionein-2 (MT-2) gene was isolated from the mandarin fish, one of the most important industrial aquatic animals in China, by using rapid amplification of cDNA ends (RACE). The deduced amino acid sequence of MT-2 comprised 60 amino acids and showed approximately 62.3% identity to human metallothionein. Its promoter region was amplified by thermal asymmetric interlaced polymerase chain reaction (TAIL-PCR). The MT-2 gene consists of 3 exons and 2 introns, extending approximately 900 bp of genomic sequence. Phylogenetic analysis clearly demonstrated that MT-2 formed a clade with fish metallothionein. The promoter region contained 5 putative metal-regulatory elements (MREs) and 1 TATA box. Real-time quantitative RT-PCR analysis revealed that MT-2 transcripts were significantly increased in the brain and gills and were stable in the muscles, liver, and trunk kidney in Cd(2+)-stimulated fish. Western blotting analysis demonstrated that the protein of the MT-2 gene was expressed mainly in the gills, liver, heart, trunk kidney, muscle, and intestine; it was weakly detected in the brain and head kidney. Moreover, the MT-2 protein was immunohistochemically detected in the cytoplasm in the liver and trunk kidney. All the above results revealed that the mandarin fish MT-2 would be a useful biomarker for metal pollution.

Alteration of metallothionein mRNA in bay scallop Argopecten irradians under cadmium exposure and bacteria challenge

Metallothionein (MT) is a superfamily of cysteine-rich proteins contributing to metal metabolism, detoxification of heavy metals, and immune response such as protecting against ionizing radiation and antioxidant defense. A metallothionein (designated AiMT2) gene was identified and cloned from bay scallop, Argopecten irradians. The full length cDNA of AiMT2 consisted of an open reading frame (ORF) of 333 bp encoding a protein of 110 amino acids, with nine characteristic Cys-X-Cys, five Cys-X-X-Cys, five Cys-X-X-X-Cys and two Cys-Cys motif arrangements and a conserved structural pattern Cys-x-Cys-x(3)-Cys-Tyr-x(3)-Cys-x-Cys-x(3)-Cys-x-Cys-Arg at the C-terminus. The cloned AiMT showed about 50% identity in the deduced amino acid sequence with previously published MT sequences of mussels and oysters. The conserved structural pattern and the close phylogenetic relationship of AiMT2 shared with MTs from other mollusc especially bivalves indicated that AiMT2 was a new member of molluscan MT family. The mRNA transcripts in hemolymph of AiMT2 under cadmium (Cd) exposure and bacteria challenge were examined by real-time RT-PCR. The mRNA expression of AiMT2 was up-regulated to 3.99-fold at 2 h after Listonella anguillarum challenge, and increased drastically to 66.12-fold and 126.96-fold at 16 and 32 h post-challenge respectively. Cadmium ion exposure could induce the expression of AiMT2, and the expression level increased 2.56-fold and 6.91-fold in hemolymph respectively after a 10-day exposure of 100 microg L(- 1) and 200 microg L(- 1) CdCl(2). The sensitivity of AiMT2 to bacteria challenge and cadmium stress indicated it was a new Cd-dependent MT in bay scallop and also regulated by an immune challenge. The changes in the expression of AiMT2 could be used as an indicator of exposure to metals in pollution monitoring programs and oxidative stress, and bay scallop as a potential sentinel organism for the cadmium contamination in aquatic environment.

[Characteristics of MT-IV in sheep and goat]

Metallothioneins (MTs) was characterized by its low molecular weight (6 to 7 kDa), high metal content, high content of conserved cysteine(Cys) residues and absence of aromatic amino acids. In mammals there are four isoforms (MT-I-IV), MT-IV was expressed exclusively in stratified squamous epithelia. In this study, according to other animal MT-IV gene sequence from GenBank, a pair of special primers (MT-IVSP1 and MT-IVSP2) were designed for cloning the coding sequence of MT-IV from rumen organ in both sheep and goat. The MT-IV coding sequence in goat and sheep were 189bp, and be submitted to GenBank under Accession Numbers EF470251 and EF624067, respectively. Both goat and sheep MT-IV gene coded 62 AAs, including 20 Cys residues in sheep, 19 Cys residues in goat, the 61st conserved Cys was replaced by Trp in goat. MT-IV in goat and sheep both have characteristic Cys-x-Cys, Cys-x-y-Cys, and Cys-Cys sequences of MTs , where x and y were non-cysteine amino acids, no aromatic AAs, no cross membrane area, and no signal peptide, these information showed MT-IV in goat and sheep was a cytoplasmic protein. The second structure of MT-IV was coil, except sheet structure in 7-9 AAs and 49-51AAs. The 3 dimension structure was composed by a-and b-domain, the beta-domain structure was same between sheep and goat, and same with other species, but a- domain structure in goat was difference with sheep and other species, because it less one Cys in goat than other animals,the structure change maybe alter the biological function, it is necessary to study further.

Functional analysis of avian metallothionein isoforms: an ecotoxicological approach for assessing potential tolerability to element exposure

To assess the inducibility of avian metallothionein (MT) genes and potential tolerability of their protiens to element exposure, we investigated the transcriptional inducibilities of cormorant (Phalacrocorax carbo) and mallard (Anas platyrhynchos) MT genes in CV-1 cells by elements and detoxification potencies of their in vitro synthesized MT proteins. About 1.3 kb of 5'-upstream regions were sequenced for cormorant MT1 and 2 genes, where two metal-responsive elements were identified. Both cormorant MT promoters were dose dependently activated by Cd, Zn, Cu, and CH3Hg, whereas no transactivation was detected by Pb, TI, Ag, inorganic Hg, Cr(VI), Cr(III), As(V), As(III), Ni, Co, Rb, and Bi, suggesting a shared transactivational mechanism of both MTs for specific elements. These findings support our previous results, where Cu and Zn concentrations were shown to be positively correlated with hepatic MT1/2 mRNA levels in wild cormorants. Comparison of EC50 and LOEL (lowest observed effect level) for each element revealed that Cd was the most potent inducer of MT1/2 promoters, followed by CH3Hg, Zn, and Cu. Since LOELs of CH3Hg for both MT promoters were higher than the hepatic levels in wild cormorants, hepatic CH3Hg concentration may not be high enough to induce MT mRNA in the wild population. Although LOELs of Cd were much lower than the hepatic concentrations detected in wild cormorants, no significant correlation was observed between hepatic Cd levels and MT mRNAs. This may be due to the masking effect of multiple elements, probably by Zn and/or Cu that were highly accumulated in wild cormorants. Cotreatment of Cd with Zn supported a possible suppression of Cd-induced MT expression by Zn in wild cormorants. MT1 and 2 proteins of cormorant and mallard endowed Escherichia coli with significantly higher growth rate than control to Cd exposure (500-1000 microM), implying that avian MTs could be involved in the detoxification of intracellular Cd. This study provides the first evidence on the inducibility of avian MT isoforms by specific elements and functional significance of each avian MT isoform in detoxifying intracellular heavy metals. Our in vitro approaches demonstrate their validity in predicting the response of MTs to element exposure in a wild avian population.