Zinc- or cadmium-pre-induced metallothionein protects human central nervous system cells and astrocytes from radiation-induced apoptosis

Combined Effect of Gamma Radiation and Heavy Metals on Some Living Organisms

The purpose of this study was to systematise scientific publications on the combined effect of gamma radiation and heavy metals on living organisms. For this purpose, the method of analysis was applied, by means of which scientific papers in PubMed, Google Scholar, and other related databases were analysed for compliance with the inclusion criteria, where the objects of research were toxic effects of radiation and heavy metals on cells and adaptation processes. The results revealed that the study of the problem was carried out on organisms such as microalgae, fungi, weed and agricultural plants, fish, laboratory rats, and human cell cultures. In most studies, an antagonistic effect between low doses of gamma radiation and heavy metal salts was reported, which was manifested by a reduction in the cytotoxicity of isolated exposure to each agent separately. However, there are studies showing additive effects, especially in heavy metals. At the molecular level, heavy metal accumulation in combination with low doses of radiation (typically defined as less than 0.1 Gy or sievert) induces the expression of metallothionein proteins, which can bind free radicals. At the metabolic level, this is manifested by a decrease in lipid peroxidation products, activation of antioxidant enzymes, and a decrease in apoptosis. The study proved both a direct relationship between zinc and cadmium accumulation in cells and inhibition of caspases and an indirect one, by maintaining mitochondrial membrane integrity through metallothionein.

Radiation-induced neuropathies in head and neck cancer: prevention and treatment modalities

Head and neck cancer (HNC) is the sixth most common human malignancy with a global incidence of 650,000 cases per year. Radiotherapy (RT) is commonly used as an effective therapy to treat tumours as a definitive or adjuvant treatment. Despite the substantial advances in RT contouring and dosage delivery, patients suffer from various radiation-induced complications, among which are toxicities to the nervous tissues in the head and neck area. Radiation-mediated neuropathies manifest as a result of increased oxidative stress-mediated apoptosis, neuroinflammation and altered cellular function in the nervous tissues. Eventually, molecular damage results in the formation of fibrotic tissues leading to susceptible loss of function of numerous neuronal substructures. Neuropathic sequelae following irradiation in the head and neck area include sensorineural hearing loss, alterations in taste and smell functions along with brachial plexopathy, and cranial nerves palsies. Numerous management options are available to relieve radiation-associated neurotoxicities notwithstanding treatment alternatives that remain restricted with limited benefits. In the scope of this review, we discuss the use of variable management and therapeutic modalities to palliate common radiation-induced neuropathies in head and neck cancers.

The potential protective roles of zinc, selenium and glutathione on hypoxia-induced TRPM2 channel activation in transfected HEK293 cells

Hypoxia induces cell death through excessive production of reactive oxygen species (ROS) and calcium (Ca²⁺) influx in cells and TRPM2 cation channel is activated by oxidative stress. Zinc (Zn), selenium (Se), and glutathione (GSH) have antioxidant properties in several cells and hypoxia-induced TRPM2 channel activity, ROS and cell death may be inhibited by the Zn, Se, and GSH treatments. We investigated effects of Zn, Se, and GSH on lipid peroxidation (LPO), cell cytotoxicity and death through inhibition of TRPM2 channel activity in transfected HEK293 cells exposed to hypoxia defined as oxygen deficiency.We induced four groups as normoxia 30 and 60 min evaluated as control groups, hypoxia 30 and 60 min in the HEK293 cells. The cells were separately pre-incubated with extracellular Zn (100 µM), Se (150 nM) and GSH (5 mM). Cytotoxicity was evaluated by lactate dehydrogenase (LDH) release and the LDH and LPO levels were significantly higher in the hypoxia-30 and 60 min-exposed cells according to normoxia 30 and 60 min groups. Furthermore, we found that the LPO and LDH were decreased in the hypoxia-exposed cells after being treated with Zn, Se, and GSH according to the hypoxia groups. Compared to the normoxia groups, the current densities of TRPM2 channel were increased in the hypoxia-exposed cells by the hypoxia applications, while the same values were decreased in the treatment of Zn, Se, and GSH according to hypoxia group. In conclusion, hypoxia-induced TRPM2 channel activity, ROS and cell death were recovered by the Se, Zn and GSH treatments.

Protective Effects of Zinc on 2.45 GHz Electromagnetic Radiation-Induced Oxidative Stress and Apoptosis in HEK293 Cells

Several epidemiological studies have shown that exposure to electromagnetic radiation (EMR) can be harmful to human health. The purpose of this study was to examine oxidative parameters and apoptosis induced by EMR in human kidney embryonic cells (HEK293) and to investigate whether zinc (Zn) has protective effect on EMR-induced apoptosis in HEK293 cells. For our experiment, HEK293 cells were divided into four main groups, control, EMR, 50 μM Zn + EMR, and 100 μM Zn + EMR. HEK293 cells of EMR groups were exposed to 2.45 GHz EMR for 1 h. In Zn groups, HEK293 cells were incubated with different concentrations of Zn for 48 h before EMR exposure. Oxidative stress parameters were determined by spectrophotometric method; bcl-2 and caspase-3 were assessed immunohistochemically and TUNEL method was performed for apoptotic activity. EMR group had higher malondialdehyde (MDA) level and lower superoxide dismutase (SOD) activity compared with control group. In Zn-applied groups, MDA was decreased and SOD activity was increased compared with EMR group. The number of the apoptotic cells and caspase-3 immunopositive cells at EMR group was increased significantly compared with the control group, whereas bcl-2 was decreased. Besides, Zn-treated groups showed a significant reduction in the number of apoptotic cells and caspase-3 from that of EMR group, whereas there was an increase in bcl-2 immunopositivity. Our findings show that EMR caused oxidative stress and apoptotic activation in HEK293 cells. Zn seems to have protective effects on the EMR by increasing SOD activity and bcl-2 immunopositivity, decreasing lipid peroxidation and caspas-3 immunopositivity.

Interpopulational variability of molecular responses to ionizing radiation in freshwater bivalves Anodonta anatina (Unionidae)

Freshwater ecosystems are exposed to multiple anthropogenic stressors including chemical pollution and warming that can affect health of the resident organisms and their responses to novel challenges. We investigated the of in situ exposure history on molecular responses to a novel stressor, ionizing radiation, in unionid mollusks Anodonta anatina. Males from pristine (F-), agricultural (A-) sites and a cooling reservoir of a nuclear power plant (N-site) were exposed to acute low dose (2mGy) X-ray radiation followed by 14days of recovery (R-groups) or to control conditions (C-groups). Biomarkers of oxidative stress, geno-, cyto- and neurotoxicity were used to assess cellular injury and stress. Control group from the cooling reservoir (CN) had higher background levels of caspase-3 activity, metallothionein concentrations and nuclear lesions and lower levels of superoxide dismutase (SOD) and glutathione in the gills compared to other control groups (CF and CA). Irradiation induced cellular damage in mussels from all three sites including increased levels of nuclear lesions in hemocytes, depletion of caspase-3, suppression of superoxide dismutase and catalase activities, an increase of the lipid peroxidation and oxidized glutathione levels, as well as down-regulation of cholinesterase indicating neurotoxicity. The up-regulation of ethoxyresorufin-O-deethylase activity in the digestive gland and vitellogenin-like protein level in gonads were also found in radiation-exposed groups indicating feminization of males and disturbances of xenobiotic metabolism. The RA-group showed the greatest magnitude of radiation-induced stress responses compared to the other two groups. Overall, unionid mollusks, particularly those from a chronically polluted agricultural site, were highly sensitive to low-dose radiation (2mGy) indicating limitations of stress protection mechanisms to deal with multiple stressors.

Role of DNA methylation in the adaptive responses induced in a human B lymphoblast cell line by long-term low-dose exposures to γ-rays and cadmium

The possible involvement of epigenetic factors in health risks due to exposures to environmental toxicants and ionizing radiation is poorly understood. We have tested the hypothesis that DNA methylation contributes to the adaptive response (AR) to ionizing radiation or Cd. Human B lymphoblast cells HMy2.CIR were irradiated (0.032 Gy γ-rays) three times per week for 4 weeks or exposed to CdCl2 (0.005, 0.01, or 0.1 μM) for 3 months, and then challenged with a high dose of Cd (50 or 100 μM) or γ-rays (2 Gy). Long-term low-dose radiation (LDR) or long-term low-dose Cd exposure induced AR against challenging doses of Cd and irradiation, respectively. When the primed cells were treated with 5-aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, the ARs were eliminated. These results indicate that DNA methylation is involved in the induction of AR in HMy2.CIR cells.

Zinc protects human kidney cells from depleted uranium-induced apoptosis

Depleted uranium (DU) is a weak radioactive heavy metal, and zinc (Zn) is an effective antidote to heavy metal poisoning. However, the effect of Zn on DU-induced cytotoxicity and apoptosis is not completely understood. The purpose of this study was to evaluate the effect of Zn on DU-induced cell apoptosis in human kidney cells (HK-2) and explore its molecular mechanism. Pre-treatment with Zn significantly inhibited DU-induced apoptosis. It reduced the formation of reactive oxygen species in the cells, increased the catalase (CAT) and glutathione (GSH) concentrations, suppressed the DU-induced soluble Fas receptor (sFasR) and soluble Fas ligand (sFasL) overexpression, suppressed the release of cytochrome c and apoptosis inhibitor factor (AIF) from mitochondria to cytoplasm, inhibited the activation of caspase-9, caspase-8 and caspase-3, and induced metallothionein (MT) expression. Furthermore, exogenous MT effectively inhibited DU-induced cell apoptosis. In conclusion, mitochondrial and FasR-mediated apoptosis pathways contribute to DU-induced apoptosis in HK-2 cells. Through independent mechanisms, such as indirect antioxidant effects, inhibition of the activation of caspase-9, caspase-8 and caspase-3, and induction of MT expression, Zn inhibits DU-induced apoptosis.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

The new radiobiology: returning to our roots

In 2005, two expert advisory bodies examined the evidence on the effects of low doses of ionizing radiation. The U.S. National Research Council concluded that current scientific evidence is consistent with the linear no-threshold dose-response relationship (NRCNA 2005) while the French National Academies of Science and Medicine concluded the opposite (Aurengo et al. 2005). These contradictory conclusions may stem in part from an emphasis on epidemiological data (a "top down" approach) versus an emphasis on biological mechanisms (a "bottom up" approach). In this paper, the strengths and limitations of the top down and bottom up approaches are discussed, and proposals for strengthening and reconciling them are suggested. The past seven years since these two reports were published have yielded increasing evidence of nonlinear responses of biological systems to low radiation doses delivered at low dose-rates. This growing body of evidence is casting ever more doubt on the extrapolation of risks observed at high doses and dose-rates to estimate risks associated with typical environmental and occupational exposures. This paper compares current evidence on low dose, low dose-rate effects against objective criteria of causation. Finally, some questions for a post-LNT world are posed.

Mammalian metallothionein in toxicology, cancer, and cancer chemotherapy

The present paper centers on mammalian metallothionein 1 and 2 in relationship to cell and tissue injury beginning with its reaction with Cd²⁺ and then considering its role in the toxicology and chemotherapy of both metals and non-metal electrophiles and oxidants. Intertwined is a consideration of MTs role in tumor cell Zn²⁺ metabolism. The paper updates and expands on our recent review by Petering et al. (Met Ions Life Sci 5:353-398, 2009).

Up-regulation of metallothionein gene expression in parkinsonian astrocytes

The role of glial cells in Parkinson's disease (PD) is unclear. We have previously reported a striking up-regulation of DnaJB6 heat shock protein in PD substantia nigra astrocytes. Whole genome transcriptome analysis also indicated increased expression of metallothionein genes in substantia nigra and cortex of sporadic PD cases. Metallothioneins are metal-binding proteins in the CNS that are released by astrocytes and associated with neuroprotection. Metallothionein expression was investigated in 18 PD cases and 15 non-PD controls using quantitative real-time polymerase chain reaction (qRT-PCR), in situ hybridisation (ISH) and immunocytochemistry (ICC). We observed a strong increase in the expression of metallothioneins MT1E, MT1F, MT1G, MT1H, MT1M, MT1X and MT2A in both PD nigra and frontal cortex. Expression of LRP2 (megalin), the neuronal metallothionein receptor was also significantly increased. qRT-PCR confirmed metallothionein up-regulation. Astrocytes were found to be the main source of metallothioneins 1 and 2 based on ISH results, and this finding was confirmed by ICC. Our findings demonstrate metallothionein expression by reactive astrocytes in PD nigra and support a neuroprotective role for these cells. The traditional view that nigral astrocytes are non-reactive in PD is clearly incorrect. However, it is possible that astrocytes are themselves affected by the disease process which may explain their comparatively modest and previously overlooked response.

Expression and Purification of glutathione transferase-small ubiquitin-related modifier-metallothionein fusion protein and its neuronal and hepatic protection against D-galactose-induced oxidative damage in mouse model

The present study aimed to produce and pathophysiologically evaluate the metallothionein (MT) fusion protein. A recombinant plasmid containing DNA segment coding the pET-glutathione transferase (GST)-small ubiquitin-related modifier (SUMO)-MT fusion protein was inserted into Escherichia coli for expression. The expression level of the fusion protein was very high, reaching to 38.4% of the total supernatant proteins from the organism. Subsequent filtration through glutathione Sepharose 4B gel and Sephadex G-25 yielded an MT fusion protein with purity more than 95%. When exposed to metals, E. coli containing the GST-SUMO-MT fusion protein showed an increased accumulation of Cd(2+), Zn(2+), or Cu(2+) at approximately 4.2, 4.0, or 1.6 times higher, respectively, than those containing the control protein. Administration of GST-SUMO-MT to mice that were also treated with D-galactose to induce neuronal and hepatic damage showed a significant improvement of animal learning and memory capacity, which was depressed in mice treated by D-galactose alone. Administration of MT fusion protein also prevented D-galactose-increased malondialdehyde contents and histopathological changes in the brain and liver. Furthermore, supplement of the fusion protein significantly prevented D-galactose-increased nitric oxide contents and -decreased superoxide dismutase activity in the brain, liver, and serum. The fusion protein was also able to prevent ionizing radiation-induced DNA damage of the mouse thymus. The present study indicates that GST-SUMO-MT has a normal metal binding feature and also significantly protects the multiple tissues against oxidative damage in vivo caused by chronic exposure to D-galactose and by ionizing radiation. Therefore, GST-SUMO-MT may be a potential candidate to be developed for the clinical application.

Metallothionein Toxicology: Metal Ion Trafficking and Cellular Protection

The literature is replete with reports about the involvement of metallothionein in host defense against injurious chemical, biological, and physical agents. Yet, metallothionein's functional roles are still being debated. This review addresses the issues that have left the physiological significance of metallothionein in doubt and moves on to assess the MT's importance in cell toxicology. It is evident that the protein is broadly involved in protecting cells from injury due to toxic metal ions, oxidants, and electrophiles. Attention is focused on MT's structural and chemical properties that confer this widespread role in cell protection. Particular emphasis is placed on the implications of finding that metal ion unsaturated metallothionein is commonly present in many cells and tissues and the question, how does selectivity of reaction with metallothionein take place in the cellular environment that includes large numbers of competing metal binding sites and high concentrations of protein and glutathione sulfhydryl groups?

The role of metallothionein in oncogenesis and cancer prognosis

The antiapoptotic, antioxidant, proliferative, and angiogenic effects of metallothionein (MT)-I+II has resulted in increased focus on their role in oncogenesis, tumor progression, therapy response, and patient prognosis. Studies have reported increased expression of MT-I+II mRNA and protein in various human cancers; such as breast, kidney, lung, nasopharynx, ovary, prostate, salivary gland, testes, urinary bladder, cervical, endometrial, skin carcinoma, melanoma, acute lymphoblastic leukemia (ALL), and pancreatic cancers, where MT-I+II expression is sometimes correlated to higher tumor grade/stage, chemotherapy/radiation resistance, and poor prognosis. However, MT-I+II are downregulated in other types of tumors (e.g. hepatocellular, gastric, colorectal, central nervous system (CNS), and thyroid cancers) where MT-I+II is either inversely correlated or unrelated to mortality. Large discrepancies exist between different tumor types, and no distinct and reliable association exists between MT-I+II expression in tumor tissues and prognosis and therapy resistance. Furthermore, a parallel has been drawn between MT-I+II expression as a potential marker for prognosis, and MT-I+II's role as oncogenic factors, without any direct evidence supporting such a parallel. This review aims at discussing the role of MT-I+II both as a prognostic marker for survival and therapy response, as well as for the hypothesized role of MT-I+II as causal oncogenes.

Evaluation of the cytotoxicity and genotoxicity of extracts of mussels originating from Moroccan Atlantic coast, in human colonic epithelial cells Caco-2

Industrial processing of phosphates generates chemical wastes which are, without any treatment, discharged directly into the Atlantic Ocean at Jorf Lasfar (JL), located 120 km south of Casablanca (Morocco) were shellfish are also collected by people without any control. Marine bivalves concentrate these pollutants by filtration and serve as vectors in human's exposure. The objective of this study was to test and compare in vitro on human intestinal cells (Caco-2) the cytotoxicity and genotoxicity of mussels (Mytilus galloprovincialis) extracts (either hydrophilic or lipophilic) collected at two coastal sites; JL (neighboring a phosphate processing plat-form) and Oualidia (OL) (a vegetable growing area) located 160 km south of Casablanca (i.e. 40 km south of JL). Using Caco-2 cells, the following end-points have been evaluated, cytotoxicity as measured by MTS test, inhibition of cellular macromolecules syntheses (DNA and protein) and genotoxicity evaluated by DNA fragmentation in agarose gel electrophoresis. The results indicated, that hydrophilic and lipophilic OL mussels extracts are cytotoxic and inhibit cellular macromolecules syntheses. Moreover these extracts damage the DNA in Caco-2 cells. The lipophilic JL mussels extract is cytotoxic, inhibits cellular macromolecules syntheses, and damages the DNA in Caco-2 cells whereas the hydrophilic extract of JL mussels fails to inhibit protein synthesis and does not damage the DNA. This extract rather enhances protein synthesis, suggesting possible metallothioneins induction by metal ions. Altogether these in vitro data indicate that mussels collected from OL could be more harmful than those from JL even though the later is closer to the pollution site than OL. Nevertheless consumption of mussels from all these areas may present a risk for humans. Epidemiological studies will be needed for global risk assessment in humans living in these areas especially those consuming see food regularly.

Effects of zinc compound on body weight and recovery of bone marrow in mice treated with total body irradiation

This study aimed to investigate if zinc compound would have effects on body weight loss and bone marrow suppression induced by total body irradiation (TBI). ICR mice were divided randomly into two groups and treated with test or control compounds. The test compound contained zinc (amino acid chelated with bovine prostate extract), and the control was reverse osmosis pure water (RO water). One week after receiving the treatment, mice were unirradiated, or irradiated with 6 or 3 Gy by 6 MV photon beams to the total body. Body weight changes were examined at regular intervals. Three and 5 weeks after the radiation, animals were sacrificed to examine the histologic changes in the bone marrow. Lower body weight in the period of 1-5 weeks after radiation and poor survival rate were found after the 6 Gy TBI, as compared with the 3 Gy groups. The median survival time after 6 Gy and 3 Gy TBI for mice given the test compound were 26 and 76 days, respectively, and the corresponding figures were 14 and 70 days, respectively, for mice given the control compound (p < 0.00001). With zinc supplement, the mean body weight in mice which received the same dose of radiation was 7-8 g heavier than in the water-supplement groups during the second and third weeks (p < 0.05). Hence, there was no statistically significant difference in survival rate between zinc and water supplement in mice given the same dose of irradiation. Histopathologically, there was less recovery of bone marrow cells in the 6 Gy groups compared with the 3 Gy groups. In the 3 Gy water-supplement group, the nucleated cells and megakaryocytes were recovered in the fifth week when recovery was still not seen in the 6 Gy group. With zinc supplement, these cells were recovered in the third week. In this study, we found that zinc is beneficial to body weight in mice treated with TBI. Histologic examination of bone marrow showed better recovery of bone marrow cells in groups of mice fed with zinc. This study suggests that zinc can be used as supplements in cancer patients receiving radiotherapy to reduce radiation-induced complications.

Apoptotic rate and metallothionein levels in the tissues of cadmium- and copper-exposed rats

It is well known that cadmium (Cd) has toxic and carcinogenic effects in rodents and humans, but the effects of Cd on apoptosis are still not clear. Although some studies have shown that Cd has apoptotic potential, other studies have shown that Cd can be antiapoptotic. Parameters such as sensitivity of the exposed organism or cells and the exposure conditions should be important in delineating the effect of Cd on apoptosis. In the present study, we aimed to determine the apoptotic index (AI) of Sprague-Dawley rat tissues that are loaded at a lower Cd concentration than the critical concentration (50 microg/g) for its toxic effects. Metallothionein (MT) levels of tissues were also determined and the experiments repeated with copper (Cu)-exposed rats. We detected decreases in the apoptotic index in liver and lung tissues of Cd-exposed groups accompanied with an increase in MT levels. Also, decreases of AI were detected in the liver tissues of Cu-exposed groups. These findings indicate that Cd can suppress apoptosis in vivo. The possible role of MT expression on the suppression of apoptosis and the importance of free-Cd ion concentration on switching antiapoptotic effects to proapoptotic effects are also discussed.

The effects of prophylactic zinc and melatonin application on experimental spinal cord ischemia–reperfusion injury in rabbits: experimental study

STUDY DESIGN

Experimental study.

OBJECTIVES

To determine the neuroprotective effects of zinc and melatonin on spinal cord ischemia-reperfusion (I/R) injuries of rabbits.

SETTING

The Experimental Research Centre of Selçuk University, Konya, Turkey.

METHODS

Twenty-four male rabbits underwent spinal cord ischemia by clamping the thoraco-abdominal aorta for 20 min. Twenty minutes before the aortic clamping, animals received zinc, melatonin or a combination of both. Neurological examination of the animals was performed three times during reperfusion period. The animals were killed 24 h after reperfusion. Spinal cord samples were taken for biochemical and histopathological evaluation.

RESULTS

Pre-treated animals with zinc, melatonin or combination displayed better neurological outcomes than the I/R group (P<0.05). Zinc, melatonin and combined treatment prevented spinal cord injury by reducing apoptosis rate (P<0.05) and preserving intact ganglion cell numbers (P<0.05). Zinc pre-treatment protected spinal cord by preventing malondialdehyde (MDA) formation (P=0.002), increasing glutathione peroxidase (GPx) activity (P=0.002) and decreasing xanthine oxidase enzyme activity (P=0.026) at molecular level. Melatonin treatment also resulted with MDA formation (P=0.002), increased GPx activity (P=0.002) and decreased xanthine oxidase activity (P=0.026).

CONCLUSION

The results of the study showed that prophylactic zinc and melatonin use in spinal cord I/R not only suppressed lipid peroxidation by activating antioxidant systems but also had significant neuroprotective effects by specifically improving the neurological and histopathological situation.

In vitro free radical scavenging activity of hepatic metallothionein induced in an Indian freshwater fish, Channa punctata Bloch

Mammalian metallothioneins (MT) have been reported to scavenge free radicals. There is no experimental evidence to show that fish MT has a similar property. In the present study cadmium-induced MT (Cd-MT) from the liver of an Indian freshwater fish Channa punctata Bloch was investigated for its free radical scavenging activity using three different in vitro assays. Exposure to cadmium chloride (0.2 mg/kg body weight; three doses on alternate days) resulted in a marked induction of Cd-MT in liver. Only a single isoform of Cd-MT was found to be induced. Molecular weight of Cd-MT was found to be 14 kDa as deduced by SDS-PAGE analysis. The purified Cd-MT effectively scavenged the following free radicals: superoxide radical (O2*-), 2,2'-azinobis 3-ethylbenzothiazoline-6-sulfonic acid (ABTS*+) and 1,1-diphenyl-picrylhydrazyl radical (DPPH*). The radical scavenging effect was found to be concentration-dependent. Also, the purified MT exhibited an inhibitory effect on ferric nitrilotriacetate (Fe-NTA) induced oxidative DNA damage in vitro. The cysteine residues of MT are proposed to be the main candidate for its radical scavenging activity. Findings of the present study strongly suggest a free radical scavenging role for fish MT. Present study adds to the little existing knowledge about fish MT and its possible biological functions.

Metallothionein protects against oxidative stress-induced lysosomal destabilization

The introduction of apo-ferritin or the iron chelator DFO (desferrioxamine) conjugated to starch into the lysosomal compartment protects cells against oxidative stress, lysosomal rupture and ensuing apoptosis/necrosis by binding intralysosomal redox-active iron, thus preventing Fenton-type reactions and ensuing peroxidation of lysosomal membranes. Because up-regulation of MTs (metallothioneins) also generates enhanced cellular resistance to oxidative stress, including X-irradiation, and MTs were found to be capable of iron binding in an acidic and reducing lysosomal-like environment, we propose that these proteins might similarly stabilize lysosomes following autophagocytotic delivery to the lysosomal compartment. Here, we report that Zn-mediated MT up-regulation, assayed by Western blotting and immunocytochemistry, results in lysosomal stabilization and decreased apoptosis following oxidative stress, similar to the protection afforded by fluid-phase endocytosis of apo-ferritin or DFO. In contrast, the endocytotic uptake of an iron phosphate complex destabilized lysosomes against oxidative stress, but this was suppressed in cells with up-regulated MT. It is suggested that the resistance against oxidative stress, known to occur in MT-rich cells, may be a consequence of autophagic turnover of MT, resulting in reduced iron-catalysed intralysosomal peroxidative reactions.

Cardiac metallothionein induction plays the major role in the prevention of diabetic cardiomyopathy by zinc supplementation

BACKGROUND

Our previous studies showed that transgenic mice that overexpress cardiac-specific metallothionein (MT) are highly resistant to diabetes-induced cardiomyopathy. Zinc is the major metal that binds to MT under physiological conditions and is a potent inducer of MT. The present study therefore explored whether zinc supplementation can protect against diabetic cardiomyopathy through cardiac MT induction.

METHODS AND RESULTS

Diabetes was induced in mice (C57BL/6J strain) by a single injection of streptozotocin. Half were supplemented intraperitoneally with zinc sulfate (5 mg/kg) every other day for 3 months. After zinc supplementation, mice were maintained for 3 more months and then examined for cardiomyopathy by functional and morphological analysis. Significant increases in cardiac morphological impairment, fibrosis, and dysfunction were observed in diabetic mice but not in diabetic mice supplemented with zinc. Zinc supplementation also induced a significant increase in cardiac MT expression. The role of MT in cardiac protection by zinc supplementation was examined in cultured cardiac cells that were directly exposed to high levels of glucose (HG) and free fatty acid (FFA) (palmitate), treatment that mimics diabetic conditions. Cell survival rate was significantly decreased for cells exposed to HG/FFA but did not change for cells exposed to HG/FFA and pretreated with zinc or low-dose cadmium, each of which induces significant MT synthesis. When MT expression was silenced with the use of MT small-interfering RNA, the preventive effect of pretreatment with zinc or low-dose cadmium was abolished.

CONCLUSIONS

These results suggest that the prevention of diabetic cardiomyopathy by zinc supplementation is predominantly mediated by an increase in cardiac MT.

Zinc and the diabetic heart

Zinc (Zn) is an essential mineral that is required for various cellular functions. Its abnormal metabolism is related to certain disorders such as diabetic complications. Oxidative stress has been considered as the major causative factor for diabetic cardiomyopathy. Zn has a critical antioxidant action in protecting the heart from various oxidative stresses. Zn deficiency was found to be a risk factor for cardiac oxidative damage and supplementation with Zn provides a significant prevention of oxidative damage to the heart. Diabetes causes a significant systemic oxidative stress and also often is accompanied by Zn deficiency that increases the susceptibility of the heart to oxidative damage. Therefore, there is a strong rationale to consider the strategy of Zn supplementation to prevent or delay diabetic cardiomyopathy. This short article collects the preliminary evidence, based on our own studies and those by others, for a preventive effect of Zn supplementation on diabetes-induced injury to the heart in animals and under in vitro conditions. Possible mechanisms by which Zn supplementation prevents diabetic heart disease are discussed. They include an antioxidant action of Zn, insulin function and metallothionein induction. In the final section, the future of Zn supplementation for diabetic patients is also briefly discussed. Although Zn supplementation has not been clinically used to prevent diabetic complications, because several issues need to be addressed, the fact that Zn supplementation is being used clinically for other disorders encourages us to explore its direct clinical application for the prevention of diabetic cardiomyopathy.