Metallothionein protects DNA from copper-induced but not iron-induced cleavage in vitro

An Assessment of MT1A (rs11076161), MT2A (rs28366003) and MT1L (rs10636) Gene Polymorphisms and MT2 Concentration in Women with Endometrial Pathologies

Several studies have indicated a relationship between metallothionein (MT) polymorphisms and the development of different pathologies, including neoplastic diseases. However, no studies thus far have been conducted on the influence of MT polymorphisms and the development of endometrial lesions, including endometrial cancer. This study included 140 patients with normal endometrial tissue, endometrial polyps, uterine myomas and endometrial cancer. The tissue MT2 concentration was determined using the ELISA method. MT1A, MT2A and MT1L polymorphisms were analyzed using TaqMan real-time PCR genotyping assays. We found no statistical difference between the tissue MT2 concentration in patients with EC vs. benign endometrium (p = 0.579). However, tissue MT2 concentration was significantly different between uterine fibromas and normal endometrial tissue samples (p = 0.019). Menopause status did not influence the tissue MT2 concentration (p = 0.282). There were no significant associations between the prevalence of MT1A, MT2A and MT1L polymorphisms and MT2 concentration. The age, menopausal status, and diabetes status of patients were identified as EC risk factors.

J-shaped association between dietary copper intake and all-cause mortality: a prospective cohort study in Chinese adults

The association between dietary Cu intake and mortality risk remains uncertain. We aimed to investigate the relationship of dietary Cu intake with all-cause mortality among Chinese adults. A total of 17 310 participants from the China Health and Nutrition Survey, a national ongoing open cohort of Chinese participants, were included in the analysis. Dietary intake was measured by three consecutive 24-h dietary recalls in combination with a weighing inventory over the same 3 d. The average intakes of the 3-d dietary macronutrients and micronutrients were calculated. The study outcome was all-cause mortality. During a median follow-up of 9·0 years, 1324 (7·6 %) participants died. After adjusting for sex, age, BMI, ever alcohol drinking, ever smoking, education levels, occupations, urban or rural residents, systolic blood pressure, diastolic blood pressure and the intakes of fat, protein and carbohydrate, the association between dietary Cu intake and all-cause mortality followed a J-shape (Pfor nonlinearity = 0·047). When dietary Cu intake was assessed as quartiles, compared with those in the first quartile (<1·60 mg/d), the adjusted hazard ratios for all-cause mortality were 0·87 (95 % CI (0·71, 1·07)), 0·98 (95 % CI (0·79, 1·21)) and 1·49 (95 % CI (1·19, 1·86)), respectively, in participants in the second (1·60–<1·83 mg/d), third (1·83–<2·09 mg/d) and fourth (≥2·09 mg/d) quartiles. A series of subgroup analyses and sensitivity analyses showed similar results. Overall, our findings emphasised the importance of maintaining optimal dietary Cu intake levels for prevention of premature death.

Particle and metal exposure in Parisian subway: Relationship between exposure biomarkers in air, exhaled breath condensate, and urine

Subway particulate toxicity results from in vitro and in vivo studies diverge and call for applied human research on outcomes from chronic exposures and potential exposure biomarkers. We aimed to (1) quantify airborne particulate matter (PM) concentrations (mass and number) and metal concentrations in exhaled breath condensate (EBC), urine, and PM; (2) investigate their associations (EBC vs. PM vs. urine); and (3) assess the relevance of EBC in biomonitoring. Nine subway workers in three jobs: station agents, locomotive operators and security guards were monitored during their 6-h shifts over two consecutive weeks. Six-hour weighed average mass concentrations expressed as PM10, PM2.5 and their metal concentrations were determined. Urine and EBC samples were collected pre- and post-shift. Ultrafine particle (UFP) number concentrations were quantified in PM and EBC samples. Metal concentrations in urine and EBC were standardized by creatinine and EBC volume, respectively, and log-transformed. Associations were investigated using Pearson correlation and linear mixed regression models, with participant's ID as random effect. PM concentrations were below occupational exposure limits (OEL) and varied significantly between jobs. Locomotive operators had the highest exposure (189 and 137 μg/m³ for PM10 and PM2.5, respectively), while station agents had the highest UFP exposure (1.97 × 10⁴ particles/cm³). Five metals (Al, Fe, Zn, Cu, and Mn) in PM2.5 and three (Al, Fe, and Zn) in PM10 were above the limit of quantification (LOQ). Fe, Cu, Al and Zn were the most abundant by mass fraction in PM. In EBC, the metal concentrations in decreasing order were: Zn > Cu > Ni > Ba > Mn. Security guards had the highest EBC metal concentrations, and in particular Zn and Cu. Urinary metal concentrations in decreasing order were: Si > Zn > Mo > Ti > Cu > Ba ≈ Ni > Co. All urinary metal concentrations from the subway workers were similar to concentrations found in the general population. A statistically significant relationship was found for ultrafine particle number concentrations in PM and in EBC. Zn and Cu concentrations in post-shift EBC were associated with Zn and Cu concentrations in PM10 and with post-shift urinary Zn and Cu concentrations. Therefore, EBC appears a relevant matrix for assessing exposure to UFP in human biomonitoring when inhalation is a primary route of exposure. We found different temporal variation patterns between particle and metal exposures in three matrices (PM, urine, EBC) quantified daily over two full weeks in subway workers. These patterns might be related to metal oxidation, particulates' solubility and size as well as their lung absorption capabilities, which need to be further explored in toxicological research. Further research should also focus on understanding possible influences of low chronic exposures to subway particulates on health in larger cohorts.

Antioxidant Defenses in the Human Eye: A Focus on Metallothioneins

The human eye, the highly specialized organ of vision, is greatly influenced by oxidants of endogenous and exogenous origin. Oxidative stress affects all structures of the human eye with special emphasis on the ocular surface, the lens, the retina and its retinal pigment epithelium, which are considered natural barriers of antioxidant protection, contributing to the onset and/or progression of eye diseases. These ocular structures contain a complex antioxidant defense system slightly different along the eye depending on cell tissue. In addition to widely studied enzymatic antioxidants, including superoxide dismutase, glutathione peroxidase, catalase, peroxiredoxins and selenoproteins, inter alia, metallothioneins (MTs) are considered antioxidant proteins of growing interest with further cell-mediated functions. This family of cysteine rich and low molecular mass proteins captures and neutralizes free radicals in a redox-dependent mechanism involving zinc binding and release. The state of the art of MTs, including the isoforms classification, the main functions described to date, the Zn-MT redox cycle as antioxidant defense system, and the antioxidant activity of Zn-MTs in the ocular surface, lens, retina and its retinal pigment epithelium, dependent on the number of occupied zinc-binding sites, will be comprehensively reviewed.

Upregulation of epithelial metallothioneins by metal-rich ultrafine particulate matter from an underground railway

Airborne particulate matter (PM) is a leading cause of mortality and morbidity. However, understanding of the range and mechanisms of effects of PM components is poor. PM generated in underground railways is rich in metals, especially iron. In the ultrafine (UFPM; <0.1 μm diameter) fraction, the combination of small size and metal enrichment poses an unknown health risk. This study aimed to analyse transcriptomic responses to underground UFPM in primary bronchial epithelial cells (PBECs), a key site of PM deposition. The oxidation state of iron in UFPM from an underground station was determined by X-ray absorption near edge structure (XANES) spectroscopy. Antioxidant response was assayed using a reporter cell line transfected with an antioxidant response element (ARE)-luciferase construct. Differentiated PBECs were exposed to UFPM for 6 h or 24 h for RNA-Seq and RT-qPCR analysis. XANES showed predominance of redox-active Fe3O4, with ROS generation confirmed by induction of ARE-luciferase expression. 6 h exposure of PBECs to UFPM identified 52 differentially expressed genes (DEGs), especially associated with epithelial maintenance, whereas 24 h exposure yielded 23 DEGs, particularly involved with redox homeostasis and metal binding. At both timepoints, there was upregulation of members of the metallothionein family, low molecular weight proteins with antioxidant activity whose main function is binding and homeostasis of zinc and copper ions, but not iron ions. This upregulation was partially inhibited by metal chelation or ROS scavenging. These data suggest differential regulation of responses to metal-rich UFPM depending on exposure period, and highlight novel pathways and markers of PM exposure, with the role of metallothioneins warranting further investigation.

Molecular effects of copper on the reproductive system of mytilus galloprovincialis

This study aims to assess the effects induced by 24 hr exposure to a subtoxic copper concentration on the reproductive system (gonads, spermatozoa, and protamine-like [PL] proteins) of Mytilus galloprovincialis. Inductively coupled plasma-mass spectrometry indicated accumulation of this metal in gonads, spermatozoa, and PL proteins of exposed mussels. Further, real-time polymerase chain reaction analyses showed altered expression levels of mt10 and PL proteins genes in spermatozoa and gonads, respectively, of exposed mussels. Protamine-like proteins, which represent the main basic component of sperm chromatin of this organism, showed a higher DNA binding affinity and a different DNA binding mode in exposed mussels. Moreover, an increased amount of NaCl was required for the release from sperm nuclei of PL-III, the main PL protein component. Finally, PL proteins extracted from exposed mussels promoted DNA oxidative damage in the presence of H ₂ O _2. These results demonstrate that the tolerable copper amount could also affect the properties of PL proteins and determine the negative effects on the reproductive system of this organism. These analyses could be useful to develop quick and efficient chromatin-based genotoxicity tests for pollution biomonitoring programs.

Relevance of arginine residues in Cu(II)-induced DNA breakage and Proteinase K resistance of H1 histones

This work analyzes the involvement of arginines in copper/H₂O₂-induced DNA breakage. Copper is a highly redox active metal which has been demonstrated to form compounds with arginines. For this aim we used mixtures of pGEM3 DNA plasmid and two types of H1 histones which differ only in their arginine content. The sperm H1 histone from the annelid worm Chaetopterus variopedatus (arginine content 12.6 mol% K/R ratio 2) and the somatic H1 histone from calf thymus (arginine content 1.8 mol% and K/R ratio 15). Copper/H₂O₂-induced DNA breakage was observed only in presence of sperm H1 histones, but it was more relevant for the native molecule than for the deguanidinated derivative (K/R ratio 14), in which 80% of arginine residues were converted to ornithine. Further, copper induced proteinase K resistance and increase of DNA binding affinity on native sperm H1 histones. These observations are consistent with a copper induced reorganization of the side-chains of arginine residues. Copper, instead, did not affect DNA binding affinity of somatic and deguanidinated H1 histones, which show similar K/R ratio and DNA binding mode. These results indicate that arginine residues could affect these H1 histones properties and provide new insights into copper toxicity mechanisms.

Effects of co-exposure to imidacloprid and gibberellic acid on redox status, kidney variables and histopathology in adult rats

Data on the individual nephrotoxic effects of imidacloprid (IMI) and gibberellic acid (GA₃) are scarce. Moreover, there is a lack of information about their combined effects on the renal tissue. Our study investigated the effects of IMI and GA₃ separately or together on rats kidney. IMI (64 mg/kg bw) was given for 3 weeks by gavage either individually or in combination with GA₃ (200 mg/L) via drinking water. IMI associated or no with GA₃ increased the levels of kidney malondialdehyde, advanced oxidation protein products, protein carbonyls and metallothionein, plasma creatinine, urea, blood urea nitrogen and lactate dehydrogenase activity. A decline of kidney uric acid level and antioxidant status was also observed. All these changes were supported by histopathological observations. Our results highlighted the role of IMI and/or GA₃-induced nephrotoxicity. Co-exposure to IMI and GA₃ exhibited synergism in biochemical kidney variables and histopathology and antagonism in physical and morphological parameters.

ABC294640, A Novel Sphingosine Kinase 2 Inhibitor, Induces Oncogenic Virus-Infected Cell Autophagic Death and Represses Tumor Growth

Kaposi sarcoma-associated herpes virus (KSHV) is the etiologic agent of several malignancies, including Kaposi sarcoma and primary effusion lymphoma (PEL), which preferentially arise in HIV⁺ patients and lack effective treatment. Sphingosine kinase 2 (SphK2) is a key factor within sphingolipid metabolism, responsible for the conversion of proapoptotic ceramides to antiapoptotic sphingosine-1-phosphate (S1P). We have previously demonstrated that targeting SphK2 using a novel selective inhibitor, ABC294640, leads to the accumulation of intracellular ceramides and induces apoptosis in KSHV-infected primary endothelial cells and PEL tumor cells but not in uninfected cells. In this study, we found that ABC294640 induces autophagic death instead of apoptosis in a KSHV long-term-infected immortalized endothelial cell-line, TIVE-LTC, but not in uninfected TIVE cells, through the upregulation of LC3B protein. Transcriptomic analysis indicates that many genes related to cellular stress responses, cell cycle/proliferation, and cellular metabolic process are altered in TIVE-LTC exposed to ABC294640. One of the candidates, Egr-1, was found to directly regulate LC3B expression and was required for the ABC294640-induced autophagic death. By using a Kaposi sarcoma-like nude mice model with TIVE-LTC, we found that ABC294640 treatment significantly suppressed KSHV-induced tumor growth in vivo, which indicates that targeting sphingolipid metabolism, especially SphK2, may represent a promising therapeutic strategy against KSHV-related malignancies. Mol Cancer Ther; 16(12); 2724-34. ©2017 AACR.

EDTA Chelation Therapy to Reduce Cardiovascular Events in Persons with Diabetes

The Trial to Assess Chelation Therapy (TACT) was a randomized double-blind placebo-controlled trial enrolling patients age ≥50 years with prior myocardial infarction. TACT used a 2 × 2 factorial design to study ethylene diamine tetraacetic acid (EDTA) chelation and high-dose vitamin supplementation. Chelation provided a modest but significant reduction in cardiovascular endpoints. The benefit was stronger and significant among participants with diabetes but absent in those without diabetes. Mechanisms by which chelation might reduce cardiovascular risk in persons with diabetes include the effects of EDTA chelation on transition and toxic metals. Transition metals, particularly copper and iron, play important roles in oxidative stress pathways. Toxic metals, in particular cadmium and lead, are toxic for the cardiovascular system. This review discusses the epidemiologic evidence and animal and human studies supporting the role of these metals in the development of diabetes and ischemic heart disease and potential ways by which EDTA chelation could confer cardiovascular benefit.

Metallothionein - immunohistochemical cancer biomarker: a meta-analysis

Metallothionein (MT) has been extensively investigated as a molecular marker of various types of cancer. In spite of the fact that numerous reviews have been published in this field, no meta-analytical approach has been performed. Therefore, results of to-date immunohistochemistry-based studies were summarized using meta-analysis in this review. Web of science, PubMed, Embase and CENTRAL databases were searched (up to April 30, 2013) and the eligibility of individual studies and heterogeneity among the studies was assessed. Random and fixed effects model meta-analysis was employed depending on the heterogeneity, and publication bias was evaluated using funnel plots and Egger's tests. A total of 77 studies were included with 8,015 tissue samples (4,631 cases and 3,384 controls). A significantly positive association between MT staining and tumors (vs. healthy tissues) was observed in head and neck (odds ratio, OR 9.95; 95% CI 5.82-17.03) and ovarian tumors (OR 7.83; 1.09-56.29), and a negative association was ascertained in liver tumors (OR 0.10; 0.03-0.30). No significant associations were identified in breast, colorectal, prostate, thyroid, stomach, bladder, kidney, gallbladder, and uterine cancers and in melanoma. While no associations were identified between MT and tumor staging, a positive association was identified with the tumor grade (OR 1.58; 1.08-2.30). In particular, strong associations were observed in breast, ovarian, uterine and prostate cancers. Borderline significant association of metastatic status and MT staining were determined (OR 1.59; 1.03-2.46), particularly in esophageal cancer. Additionally, a significant association between the patient prognosis and MT staining was also demonstrated (hazard ratio 2.04; 1.47-2.81). However, a high degree of inconsistence was observed in several tumor types, including colorectal, kidney and prostate cancer. Despite the ambiguity in some tumor types, conclusive results are provided in the tumors of head and neck, ovary and liver and in relation to the tumor grade and patient survival.

The role of metallothionein in oxidative stress

Free radicals are chemical particles containing one or more unpaired electrons, which may be part of the molecule. They cause the molecule to become highly reactive. The free radicals are also known to play a dual role in biological systems, as they can be either beneficial or harmful for living systems. It is clear that there are numerous mechanisms participating on the protection of a cell against free radicals. In this review, our attention is paid to metallothioneins (MTs) as small, cysteine-rich and heavy metal-binding proteins, which participate in an array of protective stress responses. The mechanism of the reaction of metallothioneins with oxidants and electrophilic compounds is discussed. Numerous reports indicate that MT protects cells from exposure to oxidants and electrophiles, which react readily with sulfhydryl groups. Moreover, MT plays a key role in regulation of zinc levels and distribution in the intracellular space. The connections between zinc, MT and cancer are highlighted.

Molecular functions of metallothionein and its role in hematological malignancies

Metallothionein (MT) was reported to be a potential negative regulator of apoptosis, and various reports have suggested that it may play roles in carcinogenesis and drug resistance, in at least a portion of cancer cells. The author summarizes the current understanding of the molecular functions of MT for tumor cell growth and drug resistance. These activities are regulated through intracellular metal ion modulation and free radical scavenging. Compared with analyses of solid tumors, few studies have analyzed the roles of MT in hematological malignancies. This review mainly describes the functions of MT in hematopoietic cells. Furthermore, through expression analyses of leukemias and lymphomas, the roles of MT in the biology of these diseases are particularly focused upon.

Trace and toxic element patterns in nonsmoker patients with noninsulin-dependent diabetes mellitus, impaired glucose tolerance, and fasting glucose

PROJECT:

Noninsulin dependent diabetes mellitus is supposed to be associated with fluctuations in the plasma levels of several trace elements. There is accumulating evidence that the metabolism of several trace elements is altered in patients with noninsulin dependent diabetes mellitus and that these nutrients might have specific roles in the pathogenesis and progression of this disorder.

PROCEDURE:

The aim of the present study is to compare the levels of essential trace and toxic elements including lead (Pb), arsenic (As), cadmium (Cd), chromium (Cr), aluminium (Al), nickel (Ni), cobalt (Co), iron (Fe), copper (Cu), selenium (Se), zinc (Zn), vanadium (V), manganese (Mn), barium (Ba), silver (Ag), and mercury (Hg) in patients with noninsulin dependent diabetes mellitus (n = 31), impaired glucose tolerance (n = 20), impaired fasting glucose (n = 14), and healthy controls (n = 22). Plasma concentrations of the elements were measured by using inductively coupled plasma mass spectrometry.

RESULTS:

The results indicated that values of lead, nickel, aluminium, copper, and chromium were significantly higher, but not above toxic levels, in the plasma of nonsmoker patients with noninsulin dependent diabetes mellitus (P < 0.05). The values for these elements were found to be significantly higher (P < 0.05) in patients with impaired fasting glucose than in controls. Moreover, a statistically significant correlation was found between plasma levels of glycated hemoglobin and of some trace elements like lead, nickel, aluminium, copper, chromium, cadmium, and mercury.

CONCLUSIONS

Thus, it was concluded that chronic complications of glucose metabolism disorders might be associated with alterations in the levels of some trace elements. Nevertheless, some more timely and extensive studies are required to clarify the exact mechanisms of each of these changes.

The "magic numbers" of metallothionein

Metallothioneins (MT) are a family of small cysteine rich proteins, which since their discovery in 1957, have been implicated in a range of roles including toxic metal detoxification, protection against oxidative stress, and as a metallochaperone involved in the homeostasis of both zinc and copper. The most well studied member of the family is the mammalian metallothionein, which consists of two domains: a β-domain with 9 cysteine residues, which sequesters 3 Cd(2+) or Zn(2+) or 6 Cu(+) ions, and an α-domain with 11 cysteine residues and, which sequesters 4 Cd(2+) or Zn(2+) or 6 Cu(+) ions. Despite over half a century of research, the exact functions of MT are still unknown. Much of current research aims to elucidate the mechanism of metal binding, as well as to isolate intermediates in metal exchange reactions; reactions necessary to maintain homeostatic equilibrium. These studies further our understanding of the role(s) of this remarkable and ubiquitous protein. Recently, supermetallated forms of the protein, where supermetallation describes metallation in excess of traditional levels, have been reported. These species may potentially be the metal exchange intermediates necessary to maintain homeostatic equilibrium. This review focuses on recent advances in the understanding of the mechanistic properties of metal binding, the implications for the metal induced protein folding reactions proposed for metallothionein metallation, the value of "magic numbers", which we informally define as the commonly determined metal-to-protein stoichiometric ratios and the significance of the new supermetallated states of the protein and the possible interpretation of the structural properties of this new metallation status. Together we provide a commentary on current experimental and theoretical advances and frame our consideration in terms of the possible functions of MT.

Protective effect of metallothionein on oxidative stress-induced DNA damage

Metallothioneins (MTs) are a family of low molecular weight proteins with a high cysteine and metal ion content. They are found in most cells and tissues and can be induced by a number of substances, including various forms of oxidative stress. MTs play a central role in essential trace element homeostasis and in metal detoxification. Because of their peculiar structure, characterized by a large content of thiol groups, MTs also act as a potent antioxidant by protecting against various injuries resulting from reactive oxygen (ROS) or nitrogen species (RNS). In this review, the involvement of MT in the protection of DNA against oxidative stress is discussed.

Selective degeneration of central photoreceptors after hyperbaric oxygen in normal and metallothionein-knockout mice

PURPOSE

Metallothioneins (MTs) in the brain and retina are believed to bind metals and reduce free radicals, thereby protecting neurons from oxidative damage. This study was undertaken to investigate whether retinal photoreceptor (PR) cells lacking MTs are more susceptible to hyperbaric oxygen (HBO)-induced cell death in vivo.

METHODS

Wild-type (WT) and MT-knockout (MT-KO) mice lacking metallothionein (MT)-1 and MT-2 were exposed to three atmospheres of 100% oxygen for 3 hours, 3 times per week for 1, 3, or 5 weeks. The control animals were not exposed. Histologic analysis of PR viability was performed by counting rows of nuclei in the outer nuclear layer (ONL). Ultrastructure studies verified PR damage.

RESULTS

HBO exposure produced a major loss of PR cells in the central retinas of WT and MT-KO mice, with no effect on the peripheral retina even at the longest (5 weeks) exposures. The degree of PR damage and cell death increased with duration of HBO exposure. One week of HBO exposure was insufficient to cause PR death, but tissue damage was observed in the inner and outer segments. At 3 weeks, the rows of PR nuclei in the central retina were significantly reduced by 38% in WT and 28% in MT-KO animals. At 5 weeks, PR loss was identical in WT (34%) and MT-KO (34%) animals and was comparable to that in WT at 3 weeks.

CONCLUSIONS

The data suggest that MT-1 and -2 alone are not sufficient for protecting PRs against HBO-induced cell death. The selective degeneration of central PRs may provide clues to mechanisms of oxidative damage in retinal disease.

The role of zinc, copper and iron in the pathogenesis of diabetes and diabetic complications: therapeutic effects by chelators

Zinc (Zn), copper (Cu) and iron (Fe) are essential minerals that are required for a variety of biomolecules to maintain the normal structure, function, and proliferation of cells. These metals can be toxic in excessive amounts, especially in certain genetic disorders. The homeostasis of these trace elements results from a tightly coordinated regulation by different proteins involved in their uptake, excretion and intracellular storage/trafficking. Through the Fenton reaction, Cu and Fe under a non protein-binding condition, can generate various reactive oxygen species, damaging tissues or cells. Abnormal metabolism of Zn, Cu and Fe can lead to several chronic pathogenesis, such as diabetes or diabetic complications. These pathogenic conditions appear to be prevalent in Zn and Cu deficiency, as well as Cu and Fe overload. In the Fe and Cu overloading conditions, Fe and Cu chelating drugs could be used to control diabetes and diabetic complications. The essentiality, toxicity and roles of these metals in the pathogenesis of diabetes and diabetic complications are discussed.

Mapping of oxidative stress responses of human tumor cells following photodynamic therapy using hexaminolevulinate

Background

Photodynamic therapy (PDT) involves systemic or topical administration of a lesion-localizing photosensitizer or its precursor, followed by irradiation of visible light to cause singlet oxygen-induced damage to the affected tissue. A number of mechanisms seem to be involved in the protective responses to PDT, including activation of transcription factors, heat shock proteins, antioxidant enzymes and apoptotic pathways.

Results

In this study, we address the effects of a destructive/lethal hexaminolevulinate (HAL) mediated PDT dose on the transcriptome by using transcriptional exon evidence oligo microarrays. Here, we confirm deviations in the steady state expression levels of previously identified early defence response genes and extend this to include unreported PDT inducible gene groups, most notably the metallothioneins and histones. HAL-PDT mediated stress also altered expression of genes encoded by mitochondrial DNA (mtDNA). Further, we report PDT stress induced alternative splicing. Specifically, the ATF3 alternative isoform (deltaZip2) was up-regulated, while the full-length variant was not changed by the treatment. Results were independently verified by two different technological microarray platforms. Good microarray, RT-PCR and Western immunoblotting correlation for selected genes support these findings.

Conclusion

Here, we report new insights into how destructive/lethal PDT alters the transcriptome not only at the transcriptional level but also at post-transcriptional level via alternative splicing.

The Physiological Significance of Metallothionein in Oxidative Stress

Metallothionein (MT), a ubiquitous family of low-molecular weight metal-binding proteins, comprises 30% cysteine residues. Although all of the thiol residues in MT are bound to metals, it still remains active to reactive oxygen species. Each cysteine residue in MT is more effective at protecting DNA from hydroxyl radical attack than the glutathione cysteine in vitro. Prooxidative agents such as paraquat and carbon tetrachloride induce MT synthesis mediated by some responsive elements. MT demonstrates strong antioxidant properties, yet the physiological relevance of its antioxidant action is not clear. An injection of ferric nitrilotriacetate (Fe-NTA), which produces reactive oxygen species, caused transcriptional induction of MT synthesis in the liver and kidney. Pretreatment of mice with Zn attenuated nephrotoxicity induced by Fe-NTA. After a Fe-NTA injection, a loss of Cd-binding properties of preinduced MT was observed only in kidneys of Zn-pretreated mice but not in liver. MT-enriched hepatocytes are resistant to Fe-NTA toxicity, oxidative DNA, and cell damage during conditions of glutathione depletion. In glutathione-depleted cells, but not in non-treated cells, Cd-binding properties of cellular MT decreased with increasing concentration of Fe-NTA. Moreover, Cd released from MT after an injection of Fe-NTA induced new MT protein again. Thus MT may act as a secondary antioxidant in cellular protection system against oxidative stress.

Stress response in Cu2+ and Cd2+ exposed oysters (Crassostrea gigas): an immunohistochemical approach

Localization of heat shock proteins (HSPs) and metallothioneins (MTs) was investigated in a marine bivalve (Crassostrea gigas) by immunohistochemical methods. Differential protein expression was demonstrated in digestive gland, gonad and gills, using a polyclonal antibody against C. gigas proteins. Application of this technique showed the cellular and tissue immunolabelling specificity of the two proteins. HSPs and MTs were localized in the epithelium of the digestive gland and gills in contact with the palleal compartment. For the first time, localization of MTs was observed in mature gametes of bivalve molluscs. Our results establish a basis for the use of immmunodetection techniques to study the tissue-specific localization of stress proteins in marine bivalves exposed to metal stress.

Oxidative stress is involved in inhibition of copper on histone acetylation in cells

Our previous study demonstrates that copper induces histone hypoacetylation by inhibiting histone acetyltransferase (HAT) activity. However, it lacks direct evidences whether copper-inhibited histone acetylation right contributes to the toxicity of copper. Exposure of human leukemia cells (HL-60) to Cu2+ resulted in cell proliferation arrest and a concentration- and time-dependent decrease of histone acetylation. At the same time, Cu2+-induced significant increase of H2O2 and O2.- generation via a concentration- and time-dependent manner too. The histone acetylation was efficiently suppressed by exogenous H2O2, and enhanced by superoxide dismutase (the scavenger of O2.-), catalase (the scavenger of H2O2) or the combination of both, indicating that Cu2+ at least partially inhibited histone acetylation through triggering oxidative stress. Further studies found that sodium butyrate, the inhibitor of histone deacetylase (HDAC), which had no obvious effect on oxidative stress but increased histone acetylation at the concentration of 50 microM, attenuated Cu2+-inhibited cell proliferation, indicating that histone acetylation inhibition is simultaneously involved in the cytotoxicity of Cu2+. Considering the important role of histone acetylation in gene transcription and regulation of cell fate, the present study may open a new door to further understand the mechanism of Cu2+-induced toxicity.

Increased metallothionein in light damaged mouse retinas

Oxidative stress plays a role in human age-related macular degeneration and in the light damage model of retinal degeneration. Metallothionein (MT), an antioxidant, has been reported to protect retinal pigment epithelial cells against apoptosis and oxidative stress. The purpose of this study was to evaluate changes in MT expression level and retinal localization following light damage. To accomplish this, Balb/c mice were exposed to cool white fluorescent light (10,000 lx) for 7 hr. In three independent experiments, at several intervals after the light injury, retinal MTs were studied at the protein level by immunohistochemistry (IHC) and Western analysis, and at the mRNA level by quantitative PCR with isoform-specific primers. Western analysis and IHC indicated an increase in metallothionein protein following light damage. MT localized to the retinal pigment epithelium and several layers of neural retina. Quantitative PCR identified the expression of MT I-III isoforms, not the MT IV isoform in the mouse retina, and, following light damage, showed increased expression of retinal MT-I and MT-II mRNAs by 8- and 22-fold, respectively. Increased expression of the antioxidant MT in the light damaged mouse retina suggests that upregulation of MT is an important acute retinal response to photo-oxidative stress.

Metal contents of liver parenchyma after percutaneous ethanol injection or radiofrequency ablation in patients with hepatocellular carcinoma before and after trientine hydrochloride therapy

We administered trientine hydrochloride, a drug used in the treatment of Wilson's disease, to patients with hepatocellular carcinoma after radical treatment with percutaneous ethanol injection or radiofrequency ablation, and examined its effect on the reduction of liver-tissue copper content. We enrolled 24 patients with 3 or fewer primary lesions of Child class A or B hepatocellular carcinoma with diameters of 3 cm or less who had undergone radical treatment with percutaneous ethanol injection or radiofrequency ablation. Trientine hydrochloride was orally administered in a single daily dose of 250 mg to 12 patients before a meal (at fasting, group 1) or at a total daily dosage of 750 mg, divided into 3 doses, to 12 patients (group 2). This study was a randomized between-groups comparative study of 12 weeks' duration. We used the particle-induced x-ray-emission method to determine liver-tissue mineral content. Urine copper and serum mineral levels were also measured, and transaminase levels were examined. Liver-tissue copper content decreased significantly, to 160.1 microg/g dry weight, after treatment, compared with the pretreatment level of 306.8 microg/g dry weight (P <.05). We detected no significant difference in iron or zinc content before and after treatment. The copper content was significantly reduced after treatment in both groups (P <.05). The urine copper level was significantly increased after 1 week of treatment but decreased thereafter. Serum copper levels were significantly reduced after treatment (P <.01). We detected no significant difference in transaminase level before and after treatment. Iron-deficiency anemia in 1 patient after 12 weeks' treatment was the only adverse reaction, and it was improved by the administration of an iron product. We noted no other overt adverse reactions. In patients with hepatocellular carcinoma, trientine hydrochloride therapy may significantly reduce copper content in liver tissue.

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

We have shown the protection of human central nervous system (CNS) cultures by zinc (Zn) or cadmium (Cd)-pre-induced metallothionein (MT) synthesis from radiation-induced cytotoxicity (lactate dehydrogenase (LDH) release and neuronal dendritic injury). The present study is to further define the types of cell death induced by different dose levels of radiation and investigate the effect of MT induction (by Zn or Cd) on radiation-induced apoptosis in primary human CNS and astrocyte cultures. Apoptosis was detected by fragmented DNA electrophoresis, TUNEL technique, and propidium iodide staining. Expression of MT protein was examined by immunofluorescent staining. Results showed that exposure of primary human CNS cultures to 15 and 30 Gy gamma-radiation predominantly induced apoptotic cell death, while exposure to 60 Gy gamma-radiation predominantly induced necrotic cell death. Normal primary human CNS cultures showed weak MT staining, while primary human CNS cultures exposed to Zn or Cd showed intense MT staining. The induced apoptotic cell death by exposure to 30 Gy gamma-radiation increased to a maximum level at 12 and 24 h, and was reduced significantly by Zn or Cd pre-induced MT. Using primary human astrocytes, the induction of MT protein by Zn or Cd was further confirmed. The enhanced MT expression also afforded a significant protection from 30 Gy gamma-ray-induced apoptosis in the primary human astrocytes. These results suggest that MT protected human CNS cells from apoptosis following ionizing radiation, probably through its antioxidant property.

Inhibitory mechanisms of metallothionein on platelet aggregation in in vitro and platelet plug formation in in vivo experiments

Metallothionein (MT) is a low-molecular-weight, cysteine-rich protein that contains heavy metals such as cadmium and zinc. The biological function of MT in platelets is not yet understood. Therefore, the aim of this study was to systematically examine the inhibitory mechanisms of metallothionein in platelet aggregation. In this study, metallothionein concentration-dependently (1-8 microM) inhibited platelet aggregation in human platelets stimulated by agonists. Metallothionein (4 and 8 microM) inhibited phosphoinositide breakdown in [3H]-inositol-labeled platelets, intracellular Ca+2 mobilization in Fura-2 AM-loaded platelets, and thromboxane A2 formation stimulated by collagen. In addition, metallothionein (4 and 8 microM) significantly increased the formation of cyclic GMP but not cyclic AMP in human platelets. Rapid phosphorylation of a protein of Mr 47,000 (P47), a marker of protein kinase C activation, was triggered by PDBu (100 nM). This phosphorylation was markedly inhibited by metallothionein (4 and 8 microM) in phosphorus-32-labeled platelets. In an in vivo thrombotic study, platelet thrombus formation was induced by irradiation of mesenteric venules in mice pretreated with fluorescein sodium. Metallothionein (6 microg/g) significantly prolonged the latency period for inducing platelet plug formation in mesenteric venules. These results indicate that the antiplatelet activity of metallothionein may involve the following pathways: (1) metallothionein may inhibit the activation of phospholipase C, followed by inhibition of phosphoinositide breakdown and thromboxane A2 formation, thereby leading to inhibition of intracellular Ca+2 mobilization; (ii) Metallothionein also activated the formation of cyclic GMP in human platelets, resulting in inhibition of platelet aggregation. The results strongly indicate that metallothionein provides protection against thromboembolism.

Trace elements in human physiology and pathology: zinc and metallothioneins

Zinc is one of the most abundant nutritionally essential elements in the human body. It is found in all body tissues with 85% of the whole body zinc in muscle and bone, 11% in the skin and the liver and the remaining in all the other tissues. In multicellular organisms, virtually all zinc is intracellular, 30-40% is located in the nucleus, 50% in the cytoplasm, organelles and specialized vesicles (for digestive enzymes or hormone storage) and the remainder in the cell membrane. Zinc intake ranges from 107 to 231 micromol/d depending on the source, and human zinc requirement is estimated at 15 mg/d. Zinc has been shown to be essential to the structure and function of a large number of macromolecules and for over 300 enzymic reactions. It has both catalytic and structural roles in enzymes, while in zinc finger motifs, it provides a scaffold that organizes protein sub-domains for the interaction with either DNA or other proteins. It is critical for the function of a number of metalloproteins, inducing members of oxido-reductase, hydrolase ligase, lyase family and has co-activating functions with copper in superoxide dismutase or phospholipase C. The zinc ion (Zn(++)) does not participate in redox reactions, which makes it a stable ion in a biological medium whose potential is in constant flux. Zinc ions are hydrophilic and do not cross cell membranes by passive diffusion. In general, transport has been described as having both saturable and non-saturable components, depending on the Zn(II) concentrations involved. Zinc ions exist primarily in the form of complexes with proteins and nucleic acids and participate in all aspects of intermediary metabolism, transmission and regulation of the expression of genetic information, storage, synthesis and action of peptide hormones and structural maintenance of chromatin and biomembranes.

Zinc-metallothionein protects from DNA damage induced by radiation better than glutathione and copper- or cadmium-metallothioneins

Protection of radiation-induced DNA damage by metallothionein (MT) has been documented, but there is no detailed information about its efficiency compared to other antioxidants or the effect of metals which bind to MT on the protective effect of MT in radiation-induced DNA damage. In this study, we used a cell-free system to investigate the effect of MT with other antioxidants, such as albumin and glutathione and we compared the efficiency of MT bound to different metals on radiation-induced DNA damage. DNA damage was measured by loss in ethidium bromide/DNA fluorescence and increased mobility of DNA on gel electrophoresis. Gamma rays at 30 Gy induced significant DNA damage and zinc-MT showed a significant higher protection from radiation-induced DNA damage than both glutathione and albumin. Metallothionein bound to other metals, such as copper and cadmium, also showed protection of radiation-induced DNA damage, but the protective effect by zinc-MT was the highest. These results suggest that MT, in particular bound to zinc, is a high-capacity antioxidant to protect radiation-induced DNA damage.

Potential role of p53 on metallothionein induction in human epithelial breast cancer cells

The expression and induction of metallothionein has been associated with protection against oxidative stress and apoptosis. This study examines the effect of tumour suppressor protein p53 on metallothionein expression following CdCl2 treatment in eight human epithelial breast cancer cell lines differing in p53 and oestrogen-receptor status. Cells were treated with 10 microM CdCl2 for 24 h and metallothionein protein levels were measured by cadmium binding assay. MCF7 cells which are p53-positive (p53+) and oestrogen-receptor-positive showed a large induction in metallothionein synthesis by 10.79+/-1.36-fold. Other breast cancer cell lines which are p53-negative (p53-) and oestrogen-receptor-negative or weakly oestrogen-receptor-positive showed a small induction ranging from 1.40+/-0.10 to 3.65+/-0.30-fold. RT-PCR analysis showed an induction of metallothionein mRNA in MCF7 cells by about 1.61+/-0.08-fold, while in HCC1806 cells (p53-, oestrogen-receptor-negative) by 1.11+/-0.13-fold, and in MDA-MB-231 (p53-, oestrogen-receptor-negative) by 1.25+/-0.06-fold. Metallothionein localisation was determined by immunohistochemical staining. Prior to metal treatment, metallothionein was localised mainly in the cytoplasm of MCF7 and MDA-MB-231 cells. After treatment with 10 microM CdCl2 for 24 h, MCF7 cells showed intense nuclear and cytoplasmic staining for metallothionein, while MDA-MB-231 cells showed staining in the cytoplasm with weak nuclear staining. Apoptosis induced by 10-40 microM CdCl2 at time points between 4 and 48 h was examined with TUNEL assay. In MCF7 cells, apoptosis increased with higher concentrations of CdCl2, it peaked at 6-8 h and appeared again at 48 h for all concentrations of CdCl2 tested. In MDA-MB-231 cells, apoptosis remained at low levels for 10-40 microM CdCl2 at all time points. Studies on cadmium uptake showed similar uptake and accumulation of cadmium at 8 and 24 h in all the cell lines. The data demonstrate that treatment of epithelial breast cancer cells with 10 microM CdCl2 for 24 h caused a greater induction of metallothionein protein and mRNA expression in p53+ and oestrogen-receptor-positive cells as compared to p53- and oestrogen-receptor-negative or weakly oestrogen-receptor-positive cells. This effect may be associated with the occurrence of apoptosis and suggests a role for p53 and oestrogen-receptor on the expression and induction of metallothionein in epithelial cells.

Heat shock protein Hsp70 expression and DNA damage in Baikalian sponges exposed to model pollutants and wastewater from Baikalsk Pulp and Paper Plant

Lake Baikal, a unique habitat for a great number of endemic species, is the largest freshwater reservoir in the world which is still largely unaffected by anthropogenic pollution, except for some shore regions with industrial activity. The expressions of a biomarker of exposure (heat shock protein Hsp70) and a biomarker of effect (DNA single-strand breaks) were measured for the first time in endemic Baikalian sponge species (Baikalospongia intermedia, Lubomirskia fusifera, and Lubomirskia abietina). Tissue cubes of B. intermedia and dissociated cells of L. fusifera and L. abietina reacted to temperature stress (10-16 degrees C above ambient temperature) with a time-dependent increase in expression of Hsp70. In B. intermedia, the effects of model pollutants (lead, copper, and zinc, and the organochlorines tetrachloroguaiacol, TCG, and pentachlorophenol, PCP) and of the wastewater from the final refinement and aeration reservoirs of the Baikalsk Pulp and Paper Plant (BPPP), located at the shore of the southern basin of Lake Baikal, on the expression of Hsp70 and the extent of DNA damage were investigated. It was found that lead and zinc but not copper cause a strong induction of Hsp70 in this sponge, while the frequency of DNA single-strand breaks increased after exposure to all these heavy metals tested. Induction of DNA single-strand breaks was also observed after exposure to TCG and PCP, but these compounds did not (consistently) enhance Hsp70 expression. Wastewater taken from the final water aeration pond of BPPP caused a concentration-dependent increase in Hsp70 expression in B. intermedia. However, there was no difference in the basal levels of Hsp70 between sponges collected in the shallow water at an unpolluted site near Baikalsk City and at a polluted site where the wastewaters of BPPP are discharged into the lake. There was also no clear difference in the wastewater concentration-dependent induction of Hsp70 expression between sponges collected at these sites, indicating no adaptation to continuous stress exposure.

Metallothionein 1+2 protect the CNS during neuroglial degeneration induced by 6-aminonicotinamide

6-Aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray matter astrocytes. Metallothionein 1+2 (MT-1+2) are neuroprotective factors in the central nervous system (CNS), and to determine the roles for MT after 6-AN, we have examined transgenic mice overexpressing MT-1 (TgMTI* mice) after an i.p. injection with 6-AN. In control mice injected with 6-AN, astrocytes in specific gray matter areas of the brainstem showed degeneration. Reactive astrocytes surrounded the degenerated areas, which were heavily infiltrated by macrophages and T lymphocytes. MT-1+2 expression was significantly decreased in the damaged brainstem areas, but it increased in reactive astrocytes surrounding these areas and also in infiltrating macrophages. The levels of oxidative stress, as determined by immunoreactivity for inducible nitric-oxide synthase (iNOS), malondialdehyde (MDA), and nitrotyrosine (NITT), and the number of terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine triphosphate [dUTP]-digoxigenin nick end labeling-positive (TUNEL+), caspase-3+ apoptotic cells were significantly increased in the brainstem of normal mice after 6-AN. In the TgMTI* mice, the 6-AN-induced tissue damage was decreased in comparison to control mice, and they showed significantly reduced numbers of recruited macrophages and T lymphocytes, and a drastic reduction of oxidative stress and apoptotic cell death. In addition, the accompanying reactive astrogliosis was increased in the transgenic mice. To further study the potential protective role of MT, we administered intraperitoneally Zn-MT-2 to 6-AN-injected normal mice and found essentially the same results as those obtained in TgMTI* mice. Thus, we hereby report that endogenous MT-1 overexpression and exogenous MT-2 treatment have significant neuroprotective roles during CNS pathological conditions.

Iron enhancement of oxidative DNA damage and neuronal cell death induced by salsolinol

A group of naturally occurring isoquinoline alkaloids have been detected in certain regions of mammalian brain. One such compound is salsolinol (SAL; 1-methyl-6, 7-dihydroxy-1,2,3,4-tetrahydroisoquinoline). This endogenous isoquinoline derivative has been considered to be implicated in the pathophysiology of chronic alcoholism and Parkinsonism. The present study deals with the DNA strand scission induced by SAL in the presence of iron. Incubation of phiX174 DNA with SAL and ferric ion led to conversion of the supercoiled DNA to open circular and linear forms, which was inhibited by the iron chelator deferoxamine, catalase, and scavengers of reactive oxygen species. SAL in combination with Fe(III) also produced 8-hydroxydeoxyguanosine in calf thymus DNA. Exposure of PC12 cells to SAL produced concentration-dependent reduction in viability, which was exacerbated by iron and ameliorated by deferoxamine.

Reduction of copper and metallothionein in toxic milk mice by tetrathiomolybdate, but not deferiprone

Copper is both essential for life and toxic. Aberrant regulation of copper at the level of intracellular transport has been associated with inherited diseases, including Wilson's disease (WND) in humans. WND results in accumulation of copper and the copper and zinc-binding protein metallothionein (MT) in liver and other tissues, liver degeneration, and neurological dysfunction. The toxic milk (TX) mutation in mice results in a phenotype that mimics human WND, and TX has been proposed to be a model of the disease. We characterized TX mice as a model of altered metal ion and MT levels during development, and after treatment with the metal ion chelators tetrathiomolybdate (TTM) and deferiprone (L1). We report that hepatic, renal and brain copper and MT are elevated in TX mice at 3 and 12 months of age. Zinc was significantly higher in TX mouse liver, but not brain and kidney, at both time points. Nodules appeared spontaneously in TX mouse livers at 8-12 months that maintained high copper levels, but with more normal morphology and decreased MT levels. Treatment of TX mice with TTM significantly reduced elevated hepatic copper and MT. Transient increases in blood and kidney copper accompanied TTM treatment and indicated that renal excretion was a significant route of removal. Treatment with L1, on the other hand, had no effect on liver or kidney copper and MT, but resulted in increased brain copper and MT levels. These data indicate that TTM, but not L1, may be useful in treating diseases of copper overload including WND.

Different protective roles in vitro of alpha- and beta-domains of growth inhibitory factor (GIF) on neuron injuries caused by oxygen free radicals

It was well known that beta-amyloid (Abeta) and tau protein play an important role in pathological procedure of Alzheimer's disease (AD), a senile dementia. The growth inhibitory factor (GIF, also named metallothionein-3, MT-3) had been demonstrated to inhibit the outgrowth of cortex neurons in the medium with extract of the AD patient brain. In our experiments, it was found that the neurons of cortex and the PC12 (pheochromocytoma) cells could be protected from the cytotoxicity of beta-amyloid 25-35 in presence of GIF and its domains. Additionally, GIF can scavenge the hydroxyl radical efficiently in CytC-VitC radical producing system and its alpha-domain shown more effective potentials than its beta-domain. The electron paramagnetic resonance spectra also show that the alpha-domain has more potential ability for eliminating reactive oxygen free radicals than its beta-domain. The results suggest that GIF could act as an efficient scavenger against free radicals in vitro and the alpha-domain in GIF molecule shows more potential in protecting against reactive oxygen species injury than the beta-domain.

Roles of vitamin C in radiation-induced DNA damage in presence and absence of copper

Exposure to either ionizing radiation or certain transition metals results in generation of reactive oxygen species that induce DNA damage, mutation, and cancer. Vitamin C (a reactive oxygen scavenger) is considered to be a dietary radioprotective agent. However, it has been reported to be genotoxic in the presence of certain transition metals, including copper. In order to explore the capacity of vitamin C to protect DNA from radiation-induced damage, and the influence of the presence of copper on this protection, we investigated vitamin C-mediated protection against radiation-induced damage to calf thymus DNA in vitro in the presence or absence of copper(II). Vitamin C (0.08-8.00 mM, pH 7.0) significantly reduced DNA damage induced by gamma-irradiation (30-150 Gy) by 30-50%, similar to the protective effect of glutathione. However, vitamin C plus copper (50 microM) significantly enhanced gamma-radiation-induced DNA damage. Low levels of added copper (5 microM), or chelation of copper with 1-N-benzyltriethylenetetraine tetrahydrochloride (BzTrien) and bathocuprinedisulfonic acid (BCSA), abolished the enhanced damage without diminishing the protective effect of vitamin C. These results indicate that vitamin C can act as: (1) an antioxidant to protect DNA damage from ionizing radiation; and (2) a reducing agent in the presence of copper to induce DNA damage. These effects are important in assessing the role of vitamin C, in the presence of mineral supplements or radioprotective therapeutic agents, particularly in patients with abnormally high tissue copper levels.

Metallothionein treatment reduces proinflammatory cytokines IL-6 and TNF-alpha and apoptotic cell death during experimental autoimmune encephalomyelitis (EAE)

Experimental autoimmune encephalomyelitis (EAE) is an animal model for the human autoimmune disease multiple sclerosis (MS). Proinflammatory cytokines such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) are considered important for induction and pathogenesis of EAE/MS disease, which is characterized by significant inflammation and neuroglial damage. We have recently shown that the exogenous administration of the antioxidant protein zinc-metallothionein-II (Zn-MT-II) significantly decreased the clinical symptoms, mortality, and leukocyte infiltration of the CNS during EAE. However, it is not known how EAE progression is regulated nor how cytokine production and cell death can be reduced. We herewith demonstrate that treatment with Zn-MT-II significantly decreased the CNS expression of IL-6 and TNF-alpha during EAE. Zn-MT-II treatment could also significantly reduce apoptotic cell death of neurons and oligodendrocytes during EAE, as judged by using TUNEL and immunoreactivity for cytochrome c and caspases 1 and 3. In contrast, the number of apoptotic lymphocytes and macrophages was less affected by Zn-MT-II treatment. The Zn-MT-II-induced decrease in proinflammatory cytokines and apoptosis during EAE could contribute to the reported diminution of clinical symptoms and mortality in EAE-immunized rats receiving Zn-MT-II treatment. Our results demonstrate that MT-II reduces the CNS expression of proinflammatory cytokines and the number of apoptotic neurons during EAE in vivo and that MT-II might be a potentially useful factor for treatment of EAE/MS.

Cu-metallothioneins (Cu(I)8-MTs) in LEC rat livers 13 weeks after birth still act as antioxidants

Redox properties of metallothioneins (MTs) and Cu in the cytosol from Long-Evans Cinnamon (LEC) rat livers 13 weeks after birth were investigated. MTs from LEC rat livers contain 8 g atoms of Cu and 1 g atom of Zn per mole of protein (Cu(I)8-MTs). Titration of Cu(I)8-MTs with CuCl2 indicates that Cu(I)8-MTs were able to reduce further 2-g atoms of cupric ions per mole MTs as bound form. Hg2+-induced hydroxyl radical generation from Cu(I)8-MTs was demonstrated by ESR using the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). The intensity of DMPO-OH signal from Cu-loaded MTs was increased with the increasing number of Cu in MTs. The used cytosol fraction contained 1.37 mM total Cu and 5 mM DTNB titrable-SH groups has a potential to reduce 2 mM CuCl2. No ESR signal due to Cu2+ was also detected with LEC rat liver cytosol, whereas strong Cu2+ signal appeared by the addition of HgCl2. The rate constants for the reaction of Cu(I)8-MTs with superoxide and hydroxyl radicals were estimated to be 2 x 10(6) and > or = 10(12) M(-1)s(-1), respectively, from competition kinetics. Cu2+-catalyzed oxidation of DNA was strongly inhibited both in the presence of Cu-unsaturated MTs and GSH. The results suggest that Cu(I)8-MTs from LEC rat livers just before hepatitis still act as antioxidants.

Induction of metallothionein by exposure to normobaric 100% oxygen atmosphere in rats with different zinc supply

The objective of this study was to determine the effects of an oxygen enriched environment on the induction of the metalloprotein metallothionein (MT) and its relation to zinc metabolism in rats supplied with different levels of dietary zinc. Male albino rats were fed purified diets based on maize starch, egg white, saccharose and soybean oil differing in the concentration of zinc (1; 20; 100; 500 mg Zn/kg diet). At a dietary zinc supply of 1 mg/kg, the rats developed a zinc deficiency indicated by visual and biochemical parameters. At the end of the 37-day feeding period, half of the rats were exposed to 100% oxygen for 12 h. The oxygen treatment significantly reduced plasma zinc in the zinc supplemented rats and reduced it in tendency in the zinc deficient rats. The MT concentration was increased in the zinc supplemented groups in the liver, kidney and lung. The oxygen treatment elevated the metallothionein concentration in the two high zinc supplemented groups (100 and 500 mg Zn/kg diet) in the liver. The response of the zinc concentration in plasma and of hepatic metallothionein levels to oxygen exposure indicates a role of metallothionein in zinc distribution or interactions with other trace elements to support antioxidant capacity, rather than an impact on direct scavenging activity of free radicals.

Metallothionein inhibits peroxynitrite-induced DNA and lipoprotein damage

Previous studies have demonstrated that metallothionein functions as an antioxidant that protects against oxidative DNA, protein, and lipid damage induced by superoxide anion, hydrogen peroxide, hydroxyl radical, and nitric oxide. The present study was undertaken to test the hypothesis that metallothionein also protects from DNA and lipoprotein damage induced by peroxynitrite, an important reactive nitrogen species that causes a diversity of pathological processes. A cell-free system was used. DNA damage was detected by the mobility of plasmid DNA in electrophoresis. Oxidation of low density lipoprotein was measured by a thiobarbituric acid-reactive substance, which was confirmed by lipid hydroperoxide assay. Plasmid DNA damage and low density lipoprotein oxidation were induced by 3-morpholinosydnomine, which produces peroxynitrite through the reaction between nitric oxide and superoxide anion or by synthesized peroxynitrite directly. DNA damage by 3-morpholinosydnomine was prevented by both metallothionein and superoxide dismutase, whereas the damage caused by peroxynitrite was prevented by metallothionein only. The oxidation of low density lipoprotein by 3-morpholinosydnomine and peroxynitrite was also significantly inhibited by metallothionein. This study thus demonstrates that metallothionein may react directly with peroxynitrite to prevent DNA and lipoprotein damage induced by this pathological reactive nitrogen species.