Redox regulation of copper-metallothionein

Copper homeostasis dysregulation in respiratory diseases: a review of current knowledge

Cu is an essential micronutrient for various physiological processes in almost all human cell types. Given the critical role of Cu in a wide range of cellular processes, the local concentrations of Cu and the cellular distribution of Cu transporter proteins in the lung are essential for maintaining a steady-state internal environment. Dysfunctional Cu metabolism or regulatory pathways can lead to an imbalance in Cu homeostasis in the lungs, affecting both acute and chronic pathological processes. Recent studies have identified a new form of Cu-dependent cell death called cuproptosis, which has generated renewed interest in the role of Cu homeostasis in diseases. Cuproptosis differs from other known cell death pathways. This occurs through the direct binding of Cu ions to lipoylated components of the tricarboxylic acid cycle during mitochondrial respiration, leading to the aggregation of lipoylated proteins and the subsequent downregulation of Fe-S cluster proteins, which causes toxic stress to the proteins and ultimately leads to cell death. Here, we discuss the impact of dysregulated Cu homeostasis on the pathogenesis of various respiratory diseases, including asthma, chronic obstructive pulmonary disease, idiopathic interstitial fibrosis, and lung cancer. We also discuss the therapeutic potential of targeting Cu. This study highlights the intricate interplay between copper, cellular processes, and respiratory health. Copper, while essential, must be carefully regulated to maintain the delicate balance between necessity and toxicity in living organisms. This review highlights the need to further investigate the precise mechanisms of copper interactions with infections and immune inflammation in the context of respiratory diseases and explore the potential of therapeutic strategies for copper, cuproptosis, and other related effects.

A Peptoid-Chelator Selective to Cu2+ That Can Extract Copper from Metallothionein-2 and Lead to the Production of ROS

Copper is an essential metal ion that is involved in critical cellular processes, but which can also exhibit toxic effects through its ability to catalyze reactive oxygen species (ROS) formation. Dysregulation of copper homeostasis has been implicated in the progression of several diseases, including cancer. A novel therapeutic approach, extensively studied in recent years, is to capitalize on the increased copper uptake and dependency exhibited by cancer cells and to promote copper-associated ROS production within the tumor microenvironment, leading to the apoptosis of cancer cells. Such an effect can be achieved by selectively chelating copper from copper-bearing metalloproteins in cancer cells, thereby forming a copper-chelator complex that produces ROS and, through this, induces oxidative stress and initiates apoptosis. Herein, we describe a peptoid chelator, TB, that is highly suitable to carry this task. Peptoids are N-substituted glycine oligomers that can be efficiently synthesized on a solid support and are also biocompatible; thus, they are considered promising drug candidates. We show, by rigorous spectroscopic techniques, that TB is not only selective for Cu(II) ions, but can also effectively extract copper from metallothionein-2, and the formed complex CuTB can promote ROS production. Our findings present a promising first example for the future development of peptoid-based chelators for applications in anti-cancer chelation therapy, highlighting the potential for the prospect of peptoid chelators as therapeutics.

Fluid shear stress affects the metabolic and toxicological response of the rainbow trout gill cell line RTgill-W1

The Rainbow trout gill cell-line (RTgill-W1) has been accepted by the Organisation for Economic Co-operation and Development (OECD TG249) as a replacement for fish in acute toxicity tests. In these tests cells are exposed under static conditions. In contrast, in vivo, water moves over fish gills generating fluid shear stress (FSS) that alters cell physiology and response to toxicants. The current study uses a specialised 3D printed chamber designed to house inserts and allows for the flow (0.2 dynes cm²) of water over the cells. This system was used to assess RTgill-W1 cell responses to FSS in the absence and presence of copper (Cu) over 24 h. FSS caused increased gene expression of mechanosensitive channel peizo1 and the Cu-transporter atp7a, elevated reactive oxygen species generation and increased expression of superoxidase dismutase. Cell metabolism was unaffected by Cu (0.163 μM to 2.6 μM Cu) under static conditions but significantly reduced by FSS + Cu above 1.3 μM. Differential expression of metallothionein (mt) a and b was observed with increased expression of mta under static conditions and mtb under FSS on exposure to Cu. These findings highlight toxicologically relevant mechanosensory responses by RTgill-W1 to FSS that may influence toxicological responses.

pCO2-driven seawater acidification affects aqueous-phase copper toxicity in juvenile flounder Paralichthys olivaceus: Metal accumulation, antioxidant defenses and detoxification in livers

Ocean acidification potentially influences the biotoxicity of metals and the antioxidant defense systems of marine organisms. This study investigated how pCO₂-driven seawater acidification (SA) affected aqueous-phase copper (Cu) toxicity in the juvenile flounder Paralichthys olivaceus from the perspective of hepatic oxidative stress and damage to better understand the mechanisms underlying the biological effects produced by the two stressors. Fish were exposed to aqueous-phase Cu at relevant ambient and polluted concentrations (0, 5, 10, 50, 100 and 200 μg L^-1) at different pH levels (no SA: pH 8.10; moderate SA: pH 7.70, pCO₂ ∼1353.89 μatm; extreme SA: pH 7.30, pCO₂ ∼3471.27 μatm) for 28 days. A battery of biomarkers in the livers was examined to investigate their roles in antioxidant defense and detoxification in response to coexposure. Hepatic Cu accumulation (30.22-184.90 mg kg^-1) was positively correlated with Cu concentrations. The biomarkers responded adaptively to different redox states following SA and Cu exposure. In unacidified seawater, increases in Cu concentrations significantly induced hepatic lipid peroxidation (LPO, by up to 27.03 %), although compensatory responses in antioxidant defenses and detoxification were activated. Moderate SA helped maintain hepatic redox homeostasis and alleviated LPO through different defense strategies, depending on Cu concentrations. Under extreme SA, antioxidant-based defenses were activated to cope with oxidative stress at ambient-low Cu concentrations but failed to defend against Cu toxicity at polluted Cu levels, and LPO (by up to 63.90 %) was significantly induced. Additionally, thiols (GSH and MT) responded actively to cope with Cu toxicity under SA. SOD, CAT, EROD, and GST were also sensitively involved in defending against hepatic oxidative stress during coexposure. These findings highlight the notable interactive effects of SA and Cu and provide a basis for understanding antioxidant-based defenses in marine fish confronting environmental challenges.

The Role of Copper Homeostasis in Brain Disease

In the human body, copper is an important trace element and is a cofactor for several important enzymes involved in energy production, iron metabolism, neuropeptide activation, connective tissue synthesis, and neurotransmitter synthesis. Copper is also necessary for cellular processes, such as the regulation of intracellular signal transduction, catecholamine balance, myelination of neurons, and efficient synaptic transmission in the central nervous system. Copper is naturally present in some foods and is available as a dietary supplement. Only small amounts of copper are typically stored in the body and a large amount of copper is excreted through bile and urine. Given the critical role of copper in a breadth of cellular processes, local concentrations of copper and the cellular distribution of copper transporter proteins in the brain are important to maintain the steady state of the internal environment. The dysfunction of copper metabolism or regulatory pathways results in an imbalance in copper homeostasis in the brain, which can lead to a myriad of acute and chronic pathological effects on neurological function. It suggests a unique mechanism linking copper homeostasis and neuronal activation within the central nervous system. This article explores the relationship between impaired copper homeostasis and neuropathophysiological progress in brain diseases.

Effects of Fructose and Stress on Rat Renal Copper Metabolism and Antioxidant Enzymes Function

The effects of a fructose-rich diet and chronic stress on copper metabolism in the kidneys are still understudied. We investigated whether fructose and/or chronic unpredictable stress modulate copper metabolism in a way that affects redox homeostasis, thus contributing to progression of metabolic disturbances in the kidney. We determined protein level of copper transporters, chaperones, and cuproenzymes including cytochrome c oxidase, as well as antioxidant enzymes function in the kidneys of male Wistar rats subjected to 20% liquid fructose supplementation and/or chronic stress. Liquid fructose supplementation increased level of copper chaperone of superoxide dismutase and decreased metallothionein level, while rendering the level of copper importer and copper chaperones involved in copper delivery to mitochondria and trans Golgi network unaffected. Stress had no effect on renal copper metabolism. The activity and expression of renal antioxidant enzymes remained unaltered in all experimental groups. In conclusion, fructose, independently of stress, decreased renal copper level, and modulated renal copper metabolism as to preserve vital cellular function including mitochondrial energy production and antioxidative defense, at the expense of intracellular copper storage.

Genetics of metallothioneins in Drosophilamelanogaster

Metallothioneins (MTs) are ubiquitous metal-chelating proteins involved in cellular metal homeostasis. MTs were found to be related with almost all the biological processes and their malfunctioning is responsible for a lot of important human diseases. Invertebrate MTs were also used broadly as biomarkers of metal contamination due to their inducible expression by metal exposure. MT system plays a significant role in maintaining human health and ecological stability. Drosophila melanogaster, the vinegar fly, is a perfect model for studying insect MT systems. Six MTs were identified in D. melanogaster, and were designated MtnA to F. All the MTs are considered as Cu-thioneins except for MtnF, which is putatively a Zn-thionein. Expression of all the MTs are regulated by MTF-1/MRE system, thus being able to be induced by heavy metal exposure. The expression pattern and function of separated MTs are partially overlapped and partially distinct. In this work, we made a summary of all the studies on D. melanogaster MTs. From this review, we noted that, compared with studies on mammalian MTs, the understanding of the MT system of D. melanogaster and other invertebrates, especially the regulation mechanism for MT expression and protein-protein interaction with them, is still in a low level.

The Bioinorganic Chemistry of Mammalian Metallothioneins

The functions, purposes, and roles of metallothioneins have been the subject of speculations since the discovery of the protein over 60 years ago. This article guides through the history of investigations and resolves multiple contentions by providing new interpretations of the structure-stability-function relationship. It challenges the dogma that the biologically relevant structure of the mammalian proteins is only the one determined by X-ray diffraction and NMR spectroscopy. The terms metallothionein and thionein are ambiguous and insufficient to understand biological function. The proteins need to be seen in their biological context, which limits and defines the chemistry possible. They exist in multiple forms with different degrees of metalation and types of metal ions. The homoleptic thiolate coordination of mammalian metallothioneins is important for their molecular mechanism. It endows the proteins with redox activity and a specific pH dependence of their metal affinities. The proteins, therefore, also exist in different redox states of the sulfur donor ligands. Their coordination dynamics allows a vast conformational landscape for interactions with other proteins and ligands. Many fundamental signal transduction pathways regulate the expression of the dozen of human metallothionein genes. Recent advances in understanding the control of cellular zinc and copper homeostasis are the foundation for suggesting that mammalian metallothioneins provide a highly dynamic, regulated, and uniquely biological metal buffer to control the availability, fluctuations, and signaling transients of the most competitive Zn(II) and Cu(I) ions in cellular space and time.

The Role of Zinc and Copper in Gynecological Malignancies

Zinc (Zn) and copper (Cu) are essential microelements, which take part in cellular metabolism, feature in enzymatic systems, and regulate enzyme activity. Homeostasis of these micronutrients is tightly regulated by multiple compensatory mechanisms that balance their concentrations including transporters, importers, and metallothioneins. An altered intake of only one of these trace elements may cause an imbalance in their levels and result in their competition for absorption. Relatively low levels of zinc and increased levels of copper may result in an increased level of oxidative stress and impair the antioxidant properties of multiple enzymes. Altered levels of trace elements were discovered in various pathologies including immunological, degenerative, and inflammatory diseases. Moreover, due to the role of Zn and Cu in oxidative stress and chronic inflammation, they were found to influence cancerogenesis. We review the roles of zinc and copper and their mechanisms in tumor growth, metastasis potential, microenvironment remodeling, and drug resistance. We highlight their role as potential biomarkers for cancer diagnosis, treatment, and prognosis, concentrating on their impact on gynecological malignancies.

ATP7B knockout disturbs copper and lipid metabolism in Caco-2 cells

Intestinal cells control delivery of lipids to the body by adsorption, storage and secretion. Copper (Cu) is an important trace element and has been shown to modulate lipid metabolism. Mutation of the liver Cu exporter ATP7B is the cause of Wilson disease and is associated with Cu accumulation in different tissues. To determine the relationship of Cu and lipid homeostasis in intestinal cells, a CRISPR/Cas9 knockout of ATP7B (KO) was introduced in Caco-2 cells. KO cells showed increased sensitivity to Cu, elevated intracellular Cu storage, and induction of genes regulating oxidative stress. Chylomicron structural protein ApoB48 was significantly downregulated in KO cells by Cu. Apolipoproteins ApoA1, ApoC3 and ApoE were constitutively induced by loss of ATP7B. Formation of small sized lipid droplets (LDs) was enhanced by Cu, whereas large sized LDs were reduced. Cu reduced triglyceride (TG) storage and secretion. Exposure of KO cells to oleic acid (OA) resulted in enhanced TG storage. The findings suggest that Cu represses intestinal TG lipogenesis, while loss of ATP7B results in OA-induced TG storage.

Transcriptional and biochemical biomarker responses in a freshwater mussel (Anodonta anatina) under environmentally relevant Cu exposure

Molecular biomarkers, like gene transcripts or enzyme activities, are potentially powerful tools for early warning assessment of pollution. However, a thorough understanding of response and baseline variation is required to distinguish actual effects from pollution. Here, we assess the freshwater mussel Anodonta anatina as a biomarker model species for freshwater ecosystems, by testing responses of six transcriptional (cat, gst, hsp70, hsp90, mt, and sod) and two biochemical (AChE and GST) biomarkers to environmentally relevant Cu water concentrations. Mussels (n = 20), collected from a stream free from point source pollution, were exposed in the laboratory, for 96 h, to Cu treatments (< 0.2 μg/L, 0.77 ± 0.87 μg/L, and 6.3 ± 5.4 μg/L). Gills and digestive glands were extracted and analyzed for transcriptional and biochemical responses. Biological and statistical effect sizes from Cu treatments were in general small (mean log₂ fold-change ≤ 0.80 and Cohen's f ≤ 0.69, respectively), and no significant treatment effects were observed. In contrast, four out of eight biomarkers (cat, gst, hsp70, and GST) showed a significant sex:tissue interaction, and additionally one (sod) showed significant overall effects from sex. Specifically, three markers in gills (cat, mt, GST) and one in digestive gland (AChE) displayed significant sex differences, independent of treatment. Results suggest that sex or tissue effects might obscure low-magnitude biomarker responses and potential early warnings. Thus, variation in biomarker baselines and response patterns needs to be further addressed for the future use of A. anatina as a biomarker model species.

The Copper Homeostasis Transcription Factor CopR Is Involved in H2O2 Stress in Lactobacillus plantarum CAUH2

Transcriptional factors (TFs) play important roles in the responses to oxidative, acid, and other environmental stresses in Gram-positive bacteria, but the regulatory mechanism of TFs involved in oxidative stress remains unknown in lactic acid bacteria. In the present work, homologous overexpression strains with 43 TFs were constructed in the Lactobacillus plantarum CAUH2 parent strain. The strain overexpressing CopR displayed the highest sensitivity and a 110-fold decrease in survival rate under H₂O₂ challenge. The importance of CopR in the response to H₂O₂ stress was further confirmed by a 10.8-fold increase in the survival of a copR insertion mutant. In silico analysis of the genes flanking copR revealed putative CopR-binding “cop box” sequences in the promoter region of the adjacent gene copB encoding a Cu²⁺-exporting ATPase. Electrophoretic mobility shift assay (EMSA) analysis demonstrated the specific binding of CopR with copB in vitro, suggesting copB is a target gene of CopR in L. plantarum. The role of CopB involved in oxidative stress was verified by the significantly decreased survival in the copB mutant. Furthermore, a growth defect in copper-containing medium demonstrated that CopB functions as an export ATPase for copper ions. Furthermore, EMSAs revealed that CopR functions as a regulator that negatively regulates copB gene and Cu²⁺ serves as inducer of CopR to activate the expression of CopB in response to H₂O₂ stress in L. plantarum CAUH2. Our findings indicated that CopR plays an important role in enhancing oxidative resistance by regulating copB to modulate copper homeostasis.

Basal and copper-induced expression of metallothionein isoform 1,2 and 3 genes in epithelial cancer cells: The role of tumor suppressor p53

Metallothioneins (MTs) are a ubiquitous low-molecular weight, cysteine rich proteins with a high affinity for metal ions. The expression and induction of MTs have been associated with protection against DNA damage, oxidative stress, and apoptosis. Our past research had shown that p53 is an important factor in metal regulation of MTs. The present study was undertaken to explore further the interrelationship between p53 and MTs. We investigated whether silencing of p53 could affect expression pattern of basal and copper induced metallothioneins. The silencing of wild-type p53 (wt-p53) in epithelial breast cancer MCF7 cells affected the basal level of MT-2A RNA, whereas the levels of MT-1A and MT-1X RNA remained largely unchanged. The expression of MT-3 was undetectable in MCF7 with either functional or silenced p53. MCF7 cells with silenced wt-p53 failed to upregulate MT-2A in response to copper and showed a reduced sensitivity toward copper induced cell apoptotic death. Similarly in MCF7-E6 and MDA-MB-231 cells, the presence of inactive/mutated p53 halted MT-1A and MT-2A gene expression in response to copper. Constitutive expression of MT-3 RNA was detectable in the presence of mutated p53 (mtp53). Transient transfection of MDA-MB-231 cells with wt-p53 enabled copper induced upregulation of both MT-1A and MT-2A but not basal level of MT-2A, MT-1E, MT-1X and MT-3. Inactivation of p53 in HepG2 cells amplified the basal expression of studied MT isoforms, including MT-3, as well as copper-induced mRNA expression of MTs except MT-1H and MT-3. Presented data demonstrate a direct relation between p53 and MT-1A and MT-2A and they also indicate that wt-p53 might be a negative regulator of MT-3 in epithelial cancer cells.

Redox-implications associated with the formation of complexes between copper ions and reduced or oxidized glutathione

Binding of copper by reduced glutathione (GSH) is generally seen as a mechanism to lower, if not abolish, the otherwise high electrophilicity and redox activity of its free ions. In recent years, however, this concept has been contradicted by new evidence revealing that, rather than stabilizing free copper ions, its binding to GSH leads to the formation of a Cu(I)-[GSH]2 complex capable of reducing molecular oxygen into superoxide. It is now understood that, under conditions leading to the removal of such radicals, the Cu(I)-[GSH]2 complex is readily oxidized into Cu(II)-GSSG. Interestingly, in the presence of a GSH excess, the latter complex is able to regenerate the superoxide-generating capacity of the complex it originated from, opening the possibility that a GSH-dependent interplay exists between the reduced and the oxidized glutathione forms of these copper-complexes. Furthermore, recent evidence obtained from experiments conducted in non-cellular systems and intact mitochondria indicates that the Cu(II)-GSSG complex is also able to function in a catalytic manner as an efficient superoxide dismutating- and catalase-like molecule. Here we review and discuss the most relevant chemical and biological evidence on the formation of the Cu(I)-[GSH]2 and Cu(II)-GSSG complexes and on the potential redox implications associated with their intracellular occurrence.

Cd, Cu, Zn, Se, and metallothioneins in two amphibians, Necturus maculosus (Amphibia, Caudata) and Bufo bufo (Amphibia, Anura)

The accumulation of cadmium, its affinity for metallothioneins (MTs), and its relation to copper, zinc, and selenium were investigated in the experimental mudpuppy Necturus maculosus and the common toad Bufo bufo captured in nature. Specimens of N. maculosus were exposed to waterborne Cd (85 μg/L) for up to 40 days. Exposure resulted in tissue-dependent accumulation of Cd in the order kidney, gills > intestine, liver, brain > pancreas, skin, spleen, and gonads. During the 40-day exposure, concentrations increased close to 1 μg/g in kidneys and gills (0.64-0.95 and 0.52-0.76; n = 4), whereas the levels stayed below 0.5 in liver (0.14-0.29; n = 4) and other organs. Cd exposure was accompanied by an increase of Zn and Cu in kidneys and Zn in skin, while a decrease of Cu was observed in muscles and skin. Cytosol metallothioneins (MTs) were detected as Cu,Zn-thioneins in liver and Zn,Cu-thioneins in gills and kidney, with the presence of Se in all cases. After exposure, Cd binding to MTs was clearly observed in cytosol of gills as Zn,Cu,Cd-thionein and in pellet extract of kidneys as Zn,Cu,Cd-thioneins. The results indicate low Cd storage in liver with almost undetectable Cd in liver MT fractions. In field trapped Bufo bufo (spring and autumn animals), Cd levels were followed in four organs and found to be in the order kidney > liver (0.56-5.0 μg/g >0.03-0.72 μg/g; n = 11, spring and autumn animals), with no detectable Cd in muscle and skin. At the tissue level, high positive correlations between Cd, Cu, and Se were found in liver (all r > 0.80; α = 0.05, n = 5), and between Cd and Se in kidney (r = 0.76; n = 5) of autumn animals, possibly connected with the storage of excess elements in biologically inert forms. In the liver of spring animals, having higher tissue level of Cd than autumn ones, part of the Cd was identified as Cu,Zn,Cd-thioneins with traces of Se. As both species are special in having liver Cu levels higher than Zn, the observed highly preferential Cd load in kidney seems reasonable. The relatively low Cd found in liver can be attributed to its excretion through bile and its inability to displace Cu from MTs. The associations of selenium observed with Cd and/or Cu (on the tissue and cell level) point to selenium involvement in the detoxification of excessive cadmium and copper through immobilization.

Efficient metal-specific transcription activation by Drosophila MTF-1 requires conserved cysteine residues in the carboxy-terminal domain

MTF-1 is a sequence-specific DNA binding protein that activates the transcription of metal responsive genes. The extent of activation is dependent on the nature of the metal challenge. Here we identify separate regions within the Drosophila MTF-1 (dMTF-1) protein that are required for efficient copper- versus cadmium-induced transcription. dMTF-1 contains a number of potential metal binding regions that might allow metal discrimination including a DNA binding domain containing six zinc fingers and a highly conserved cysteine-rich C-terminus. We find that four of the zinc fingers in the DNA binding domain are essential for function but the DNA binding domain does not contribute to the metal discrimination by dMTF-1. We find that the conserved C-terminus of the cysteine-rich domain provides cadmium specificity while copper specificity maps to the previously described copper-binding region (Chen et al.). In addition, both metal specific domains are autorepressive in the absence of metal and contribute to the low level of basal transcription from metal inducible promoters.

Metallothionein-like gene from Cicer microphyllum is regulated by multiple abiotic stresses

Cicer microphyllum, a wild relative of cultivated chickpea, is a high altitude cold desert-adapted species distributed in western and trans-Himalayas. A complementary DNA (cDNA) encoding metallothionein-like protein has been identified from a cold-induced subtraction cDNA library from C. microphyllum. The sequence of the cloned metallothionein gene from C. microphyllum (GQ900702) contains 240-bp-long open reading frame and encodes predicted 79-amino acid protein of 7.9 kDa. Sequence analysis identified the motifs characteristic of type II metallothionein and designated as CmMet-2. Southern hybridization confirms a single copy of the CmMet-2 gene in C. microphyllum genome. In situ hybridization indicated spatial transcript regulation of CmMet-2 in root and aerial parts and also confirmed through real-time PCR-based quantitative transcript analysis. The data revealed a significantly low level of transcript in the aerial parts than the roots. Quantitative analysis using real-time PCR assay revealed induction of transcript in all parts of plants in response to cold stress at 4°C. The transcript abundance was found to increase exponentially with time course from 6 to 24 h after exposure. Further, regulation of transcript accumulation in response to abscisic acid application, polyethylene glycol (100 μM)-induced osmotic stress, or ZnSO(4) (1 μM) foliar spray indicated by Northern hybridization suggests the involvement of CmMet-2 in multiple stress response.

Proteomic and physiological responses of Kineococcus radiotolerans to copper

Copper is a highly reactive, toxic metal; consequently, transport of this metal within the cell is tightly regulated. Intriguingly, the actinobacterium Kineococcus radiotolerans has been shown to not only accumulate soluble copper to high levels within the cytoplasm, but the phenotype also correlated with enhanced cell growth during chronic exposure to ionizing radiation. This study offers a first glimpse into the physiological and proteomic responses of K. radiotolerans to copper at increasing concentration and distinct growth phases. Aerobic growth rates and biomass yields were similar over a range of Cu(II) concentrations (0–1.5 mM) in complex medium. Copper uptake coincided with active cell growth and intracellular accumulation was positively correlated with Cu(II) concentration in the growth medium (R² = 0.7). Approximately 40% of protein coding ORFs on the K. radiotolerans genome were differentially expressed in response to the copper treatments imposed. Copper accumulation coincided with increased abundance of proteins involved in oxidative stress and defense, DNA stabilization and repair, and protein turnover. Interestingly, the specific activity of superoxide dismutase was repressed by low to moderate concentrations of copper during exponential growth, and activity was unresponsive to perturbation with paraquot. The biochemical response pathways invoked by sub-lethal copper concentrations are exceptionally complex; though integral cellular functions are preserved, in part, through the coordination of defense enzymes, chaperones, antioxidants and protective osmolytes that likely help maintain cellular redox. This study extends our understanding of the ecology and physiology of this unique actinobacterium that could potentially inspire new biotechnologies in metal recovery and sequestration, and environmental restoration.

Change of zinc, copper, and metallothionein concentrations and the copper-zinc superoxide dismutase activity in patients with pancreatitis

OBJECTIVES

The aims of the present studies were to measure the concentrations of zinc (Zn), copper (Cu), and metallothionein and the Cu/Zn superoxide dismutase activity as elements engaged in an essential manner in the prooxidative and antioxidative balance of organism and to demonstrate the degree to which metallothionein and Cu/Zn superoxide dismutase are involved in the inflammatory processes occurring in the pancreas.

METHODS

The concentration of metallothionein was measured by immunoenzymatic method. Serum Cu/Zn superoxide dismutase activity was determined using a commercial test. The measurements of Zn and Cu concentrations in serum were assessed with the use of flame atomic absorption spectrometry.

RESULTS

Lowered serum Zn concentration and higher Cu level were observed in the serum of patients with chronic exacerbated pancreatitis and chronic pancreatitis. The significant increase of metallothionein concentration and Cu/Zn superoxide dismutase activity was observed in the blood of patients with chronic exacerbated pancreatitis and chronic pancreatitis. In slices of the pancreas during pancreatitis, we observed in immunohistochemical reaction the variable involvement of Cu/Zn superoxide dismutase and metallothionein.

CONCLUSIONS

The results presented in these studies indicate an essential and variable involvement of antioxidants such Cu/Zn superoxide dismutase and metallothionein and disordered Cu and Zn homeostasis depending on the progression of inflammatory processes in patients with pancreatitis.

The influence of metallothionein on exposure to metals: an in vitro study on cellular models

In the present study, the interactions between zinc (Zn) and copper (Cu) or iron (Fe) have been examined. Rat hepatoma cell line H4-II-E-C3, fibroblast cell line mutant MT-/-, and wild-type MT+/+ cells treated with ZnSO4 or CuSO4 or FeSO4 or CuSO4+ZnSO4 or ZnSO4+FeSO4 for different times have been employed to study the effect of metallothionein (MT), glutathione (GSH) and metal (Cu, Fe and Zn) accumulation during cellular adaptation to supraphysiological metal concentrations. To investigate the different biological functions in the processes of metal homeostasis and detoxification, the levels of both MT-1 and MT-2 mRNAs have been evaluated. The three cell lines responded differently to metal treatments suggesting that the uptake and storage of these metals are affected by the specific cellular model and MT presence. In particular, Zn treatment significantly decreased Fe accumulation (p<0.05), whereas MT induced by Zn increased intracellular Cu content (p<0.05). Moreover, in H4-II-E-C3 cells administration of metals resulted in a rapid and transient induction of MT (p<0.05) and in GSH accumulation (p<0.05) suggesting synergistic interactions in which both appear essential for a protective regulatory function against the redox activity of metals. Taken together these results demonstrate that Zn affects the cellular levels of Cu and Fe by competition with the same ligand sites and/or by coordinate regulation of MT and GSH content.

Metal binding and antioxidant properties of chimeric tri- and tetra-domained metallothioneins

An unusual tri-domained (alpha-beta-beta) natural oyster metallothionein (MT) is known, and non-oxidative MT dimers occur in vivo in mollusk species and in mammals. To assess the respective role of the MT domains, two chimeric MTs were constructed: a tetra-domained oyster MT corresponding to the alpha-beta-alpha-beta structure, in order to mimic the natural non-oxidative dimeric form, and a tri-domained alpha-beta-alpha oyster MT. Metal binding and putative antioxidant properties of these two chimeric MTs were investigated using expression of the related genes in the bacteria Escherichia coli. In a wild-type strain these MTs could efficiently bind Cd. In a superoxide dismutase (sodA sodB) null mutant, the tri-domained MT was found to exacerbate Cd toxicity whereas the tetra-domained MT efficiently protected bacteria from Cd. The paradoxical toxicity displayed by the tri-domained MT upon Cd contamination was linked to the generation of superoxide radicals generated by a mechanism which most probably involves a copper-redox cycling reaction, since a Cd-contaminated sodA sodB strain expressing this MT produced 4 times more O2(-) than the control bacteria, and MT toxicity disappeared in the presence of bathocuproine disulfonic acid, a copper chelator. In contrast, the tetra-domained form did not. Interestingly, in bacteria producing superoxide dismutase but hypersensitive to oxidative stress due to either mutations in thioredoxin and glutathione reductase pathways (WM104 mutant) or to a lack of gamma-glutamylcysteine synthetase (gshA mutant), both chimeric MTs were protecting against Cd toxicity. However, an unexpected lack of antioxidant function was observed for both chimeric MTs, which were found to enhance the toxicity of hydrogen peroxide in WM104, or that of menadione in QC1726. Altogether, our results suggest that superoxide dismutase activity counteracts the potential prooxidative effect of the tri-domained MT mediated by Cu ions and that the tetra-domained form is a very efficient protector against metal toxicity in vivo.

Role of metallothioneins in superoxide radical generation during copper redox cycling: Defining the fundamental function of metallothioneins

In order to demonstrate the in vivo antioxidant properties of metallothioneins (MTs), the bacteria Escherichia coli was used as a cell reactor in which we compared the metal binding and antioxidative functions of MTs from different species, with different structures and polypeptide lengths. No protective effects of cytoplasmic MTs from cadmium (Cd) or zinc (Zn) contamination were observed in a wild-type E. coli strain, although these MTs can efficiently bind both Cd and Zn. To test their antioxidant properties, MTs were expressed within the cytoplasm of a sodA sodB deficient mutated strain (QC1726). However, a paradoxical MT toxicity was found when this strain was contaminated with Cd and Zn, suggesting that in a wild-type strain, superoxide dismutase counteracts MT toxicity. The most toxic MT was the one with the strongest Cd and Zn binding capacities. This toxic effect was linked to the generation of superoxide radicals, since a Cd-contaminated QC1726 strain expressing oyster MT isoforms produced 75-85% more O(2)*(-) than the control QC1726 strain. Conversely, under anaerobiosis or in the presence of a copper chelator, MTs protected QC1726 strain from Cd and Zn contamination. A model is proposed to explain the observed MT toxicity.

Zinc, antioxidant systems and metallothionein in metal mediated-apoptosis: biochemical and cytochemical aspects

Copper, zinc and iron are essential metals for different physiological functions, even though their excess can lead to biological damage. This review provides a background of toxicity related to copper, iron and zinc excess, biological mechanisms of their homeostasis and their respective roles in the apoptotic process. The antioxidant action of metallothionein has been highlighted by summarizing the most important findings that confirm the role of zinc in cellular protection in relation to metallothionein expression and apoptotic processes. In particular, we show that a complex and efficient antioxidant system, the induction of metallothionein and the direct action of zinc have protective roles against oxidative damage and the resulting apoptosis induced by metals with redox proprieties. In addition, to emphasize the protective effects of Zn and Zn-MT in Cu and Fe-mediated oxidative stress-dependent apoptosis, some aspects of apoptotic cell death are shown. The most widely used cytochemical techniques also have been examined in order to critically evaluate the available data from a methodological point of view. The observations on the role of Zn and MT could potentially develop new applications for this metal and MT in biomedical research.

Alteration of biological samples in speciation analysis of metalloproteins

For investigations of metalloproteins by speciation analysis, the integrity of the protein-metal complexes before and during separation is crucial. Knowledge about potential alterations of the samples is thus essential to avoid misinterpretations of the analytical results. Chromatographic element profiles of different cytosolic samples from animal tissues were measured repeatedly to estimate the sample stability. The dependence of the signals on the dwell time of the sample in an autosampling device at 4 degrees C for a period of 10 h was observed. Alterations in the element content of different metal-containing fractions were quantified by means of recovery values. Some metalloprotein fractions (e.g. approximately 27-kDa arsenic, approximately 27-kDa iron and different zinc fractions) were stable or only minor alterations were observed and for their investigation an autosampling device is therefore suitable. However, most of the other metalloprotein fractions, especially nickel-containing proteins, showed major alterations: these samples should therefore be analysed immediately after preparation or directly after thawing.

Associação da concentração plasmática de cobre com metaloproteínas cobre-dependentes em atletas de elite

O cobre é um elemento-traço essencial para a manutenção de vários processos biológicos, tais como metabolismo energético, homeostase de ferro e mecanismos de proteção antioxidante através da atividade da cobre-zinco superóxido dismutase (Cu-Zn SOD), da ceruloplasmina e da metalotioneína. No entanto, o cobre também participa de reações oxidativas que promovem a liberação de radicais livres, podendo prejudicar a integridade e a funcionalidade celular. A atividade física afeta a homeostase do cobre e promove maior utilização de oxigênio, favorecendo a instalação do estresse oxidativo quando mecanismos naturais de proteção antioxidante, incluindo os dependentes de cobre, não atuam adequadamente. Não há relatos na literatura sobre a associação de diferentes níveis de concentração plasmática de cobre com indicadores antioxidantes cobre-dependentes em atletas de elite. O presente estudo objetivou verificar a associação entre diferentes níveis plasmáticos de cobre e metaloproteínas cobre-dependentes, com atividade antioxidante, em atletas de elite. Os indicadores bioquímicos (metalotioneína e Cu-Zn SOD eritrocitárias, ceruloplasmina e cobre plasmáticos) foram avaliados em 50 atletas, homens e adultos, utilizando metodologias já consolidadas. Os resultados mostraram que 32% dos atletas apresentaram níveis de cobre plasmático inferiores a 11µmol/L, 38% entre 11-13µmol/L e 30% > 13µmol/L. As associações encontradas entre cobre plasmático e ceruloplasmina (r = 0,31; p = 0,04) e Cu-Zn SOD (r = 0,32, p = 0,02); metalotioneína eritrocitária e ceruloplasmina (r = 0,40, p = 0,006) e Cu-Zn SOD (0,73, p = 0,001) e entre Cu-Zn SOD e ceruloplasmina (r = 0,37, p < 0,001) demonstraram que a atividade da Cu-Zn SOD e a concentração de metalotioneína eritrocitárias são sensíveis a menor concentração, enquanto que a ceruloplasmina é sensível a elevadas concentrações plasmáticas de cobre, sugerindo que há um equilíbrio homeostático entre antioxidantes, cobre-dependentes, intra e extracelulares em atletas de elite.

Effect of Zn treatment on wild type and MT-null cell lines in relation to apoptotic and/or necrotic processes and on MT isoform gene expression

It has been shown in various systems that zinc is able to antagonize the catalytic properties of the redox-active transition metals iron and copper, although the process is still unclear. Probably, the protective effect of Zn against oxidative stress is mainly due to the induction of a scavenger metal binding protein such as metallothionein (MT), rather than a direct action. To support this hypothesis, in this study, the effects of Zn, Cu, Fe, Zn + Cu and Zn + Fe treatments were investigated in a fibroblast cell line corresponding to an SV40-transformed MT-1/-2 mutant (MT-/-), and in wild type (MT+/+), by valuing metal concentrations and apoptotic and/or necrotic processes. We also investigated the synthesis of MT and the levels of both MT-1 and MT-2 mRNAs. In MT+/+ cells, co-treatment with Zn + Fe caused a decrease in Fe content compared to treatment with Fe alone. After Zn and Zn + Cu exposure the expression of MT-1 and MT-2 isoforms increased with a concomitant increase in MT synthesis. Annexin V-FITC and propidium iodide staining revealed necrotic or apoptotic cells in terminal stages, especially after Fe treatments. Immunofluorescent staining with an anti-ssDNA Mab and annexin detected a lower signal in co-treated cells compared to the single treatments in both cell lines. The intensity and quantity of fluorescence resulting from anti-ssDNA and Annexin V staining of MT null cells was higher compared to wild type cells. These results suggest that Zn alone does not completely exert an anti-oxidant effect against Cu and Fe toxicity, but that induction of MT is necessary.

Nitric oxide and zinc homeostasis in acute lung injury

Among putative small molecules that affect sensitivity to acute lung injury, zinc and nitric oxide are potentially unique by virtue of their interdependence and dual capacities to be cytoprotective or injurious. Nitric oxide and zinc appear to be linked via an intracellular signaling pathway involving S-nitrosation of metallothoinein--itself a small protein known to be an important inducible gene product that may modify lung injury. In the present article, we summarize recent efforts using genetic and fluorescence optical imaging techniques to: (1) demonstrate that S-nitrosation of metallothionein affects intracellular zinc homeostasis in intact pulmonary endothelial cells; and (2) reveal a protective role for this pathway in hyperoxic and LPS-induced injury.

Copper, oxidative stress, and human health

Copper (Cu), a redox active metal, is an essential nutrient for all species studied to date. During the past decade, there has been increasing interest in the concept that marginal deficits of this element can contribute to the development and progression of a number of disease states including cardiovascular disease and diabetes. Deficits of this nutrient during pregnancy can result in gross structural malformations in the conceptus, and persistent neurological and immunological abnormalities in the offspring. Excessive amounts of Cu in the body can also pose a risk. Acute Cu toxicity can result in a number of pathologies, and in severe cases, death. Chronic Cu toxicity can result in liver disease and severe neurological defects. The concept that elevated ceruloplasmin is a risk factor for certain diseases is discussed. In this paper, we will review recent literature on the potential causes of Cu deficiency and Cu toxicity, and the pathological consequences associated with the above. Finally, we will review some of the potential biochemical lesions that might underlie these pathologies. Given that oxidative stress is a characteristic of Cu deficiency, the role of Cu in the oxidative defense system will receive special attention. The concept that excess Cu may be a precipitating factor in Alzheimer's disease is discussed.

The role of metallothionein in the pathogenesis of acute lung injury

Often fatal, acute lung injury has a complicated etiology. Previous studies from our laboratory in mice have demonstrated that survival during acute lung injury is a complex trait governed by multiple loci. We also found that the increase in metallothionein (MT) is one of the greatest noted in transcriptome-wide analyses of gene expression. To assess the role of MT in nickel-induced acute lung injury, the survival of Mt-transgenic, Mt1/2(+/+), and Mt1/2(-/-) mice was compared. Pulmonary inflammation and global gene expression were compared in Mt1/2(+/+) and Mt1/2(-/-) mice. Gene-targeted Mt1/2(-/-) mice were more susceptible than Mt1/2(+/+) mice to nickel-induced inflammation, surfactant-associated protein B transcript loss, and lethality. Similarly, Mt-transgenic mice exhibited increased survival. MAPPFinder analyses also noted significant decreases in genes involved in protein processing (e.g., ubiquitination, folding), which were greater in Mt1/2(-/-) mice as compared with Mt1/2(+/+) mice early in the progression of acute lung injury, possibly due to a zinc-mediated transcript destabilization. In contrast, transcript levels of genes associated with the inflammatory response, extracellular matrix regulation, and coagulation/fibrinolysis were increased more in Mt1/2(-/-) mice as compared with Mt1/2(+/+) mice late in the development of acute lung injury. Thus, MT ultimately improves survival in the progression of acute lung injury in mice. Transcriptome-wide analysis suggests that this survival may be mediated through changes in the destabilization of transcripts associated with protein processing, the subsequent augmentation of transcripts controlling inflammation, extracellular matrix regulation, coagulation/fibrinolysis, and disruption of surfactant homeostasis.

Functional analysis of a Douglas-fir metallothionein-like gene promoter: transient assays in zygotic and somatic embryos and stable transformation in transgenic tobacco

Douglas-fir (Pseudotsuga menziesii [Mirb] Franco) metallothionein (PmMT) cDNA encodes a novel cysteine- and serine-rich MT, indicating a new subtype or prototype MT from which other plant MTs may have evolved. A genomic library of Douglas-fir was screened using MT cDNA probes, and genomic sequences that mediate tissue-specific, temporal as well as inducible expression of the embryo-specific MT-gene were analyzed. The promoter region of the PmMT genomic clone (gPmMT) contained a hexameric G-box, two putative ethylene-responsive elements and an inverted repeat of a motif similar to the core metal regulatory element. Interestingly, comparison of the upstream region of Douglas-fir gPm2S1 and gPmMTa genes revealed a conserved motif, CATTATTGA, not found in any known angiosperm gene promoter. Chimeric gene constructs containing a series of deletions in the gPmMTa promoter fused to the uidA reporter gene were assayed in Douglas-fir and transgenic tobacco (Nicotiana tabacum L.). Transient-expression assays in Douglas-fir megagametophyte and zygotic embryos indicated that the sequence -190 to +88 of gPmMTa was sufficient to drive the expression of the reporter gene and that the 225-bp fragment (-677 to -453) contained sequences necessary for high-level expression. In transgenic tobacco seedlings the beta-glucuronidase activity was localized in the vacuolar tissue and proliferating tissue of the auxiliary buds and stem elongation zone. The gPmMTa promoter was not active in the seeds of transgenic tobacco or in the roots of seedlings up to 3 weeks old. Detailed studies of transient expression and stable transformation provided important information on evolutionary conservation as well as novel features found in the conifer promoter. This is the first report of an MT-like gene promoter from conifers.

Low micromolar concentrations of copper augment the impairment of endothelium-dependent relaxation of aortae from diabetic rabbits

Both diabetes mellitus (DM) and elevated plasma copper concentrations are risk factors for cardiovascular disease (CVD). DM is associated with impaired endothelial nitric oxide (NO) and with excess superoxide (O2*-) formation. Copper is also elevated in DM and is also associated with the generation of O2*-. To explore possible interactions between DM and copper, the effect of exogenous copper (CuCl2) on endothelium-dependent relaxation and cyclic guanosine monophosphate (GMP) formation was investigated in aortae from diabetic rabbits. Rabbits were rendered diabetic by intravenous injection of alloxan. Six months after induction of DM, the aortae were excised, cut into rings, and mounted in an organ bath for isometric measurement of acetylcholine (Ach)-evoked relaxation in rings precontracted with phenylephrine (PE). In parallel studies, cyclic (c)GMP formation by aortic rings following stimulation with Ach, calcium ionophore A23187 (A23187) and sodium nitroprusside (SNP) was assessed using radioimmunoassay. The effect of copper on these parameters was then studied using the same methods. Ach-evoked relaxation and Ach- and A23187-evoked cGMP formation were significantly impaired in aortae from diabetic rabbits compared to controls, effects that were reversed with superoxide dismutase (SOD) and catalase (CAT). In contrast, there were no significant differences in SNP-stimulated relaxation or cGMP formation in aortae from diabetic rabbits compared to controls. Copper (1 to 10 micromol/L) promoted a further significant inhibition of Ach-stimulated relaxation in aortae from diabetic but not control rabbits. This reduction by copper was again reversed by SOD and CAT. We conclude that copper augments the reduction of NO bioavailability, which is already impaired in aortae from diabetic rabbits due to excess production of O2*- and H2O2. These results indicate that patients with DM may be susceptible to copper-mediated vasculopathy at much lower concentrations than those that promote vasculopathy in nondiabetic patients.

CZE-ICP-MS separation of metallothioneins in human brain cytosols: comparability of electropherograms obtained from different sample matrices

Capillary zone electrophoresis, with its high resolution capability in the separation of different compounds, is well suited for the investigation of metal-containing proteins, especially when elemental detection is conducted using hyphenated inductively coupled plasma-mass spectrometry. A major problem in the separation of proteins in body fluids is caused by the effects of different sample matrix composition. The migration time of proteins varies significantly, depending on the nature of the matrix. Electropherograms are consequently difficult to compare and the peak identification is uncertain. Pre-analytical steps for the reduction of matrix compounds enhance the quality of the data, but the results are still unsatisfactory. This paper describes a technique for obtaining electropherograms that can be used for comparison purposes by correction of the data with the aid of time markers. A mixture of five substances (caesium chloride, arsenocholine, arsenobetaine, dimethylarsinic acid and monomethylarsonic acid) was added in a separate injection step. Ionic caesium eluted at the start of the separation and the other four markers appeared throughout and at the end of the electropherogram. All electropherograms were normalized to a reference run by recalculation of the time axis using the time markers. The method was applied to the analysis of human brain cytosols. Samples were separated after different pre-treatment steps and were compared, with special emphasis on the detection of the isoform metallothionein-3.

Molecular cloning of two metallothionein-like protein genes with differential expression patterns from sweet potato (Ipomoea batatas) leaves

Metallothionein (MT) is a group of proteins with low molecular masses and high cysteine contents, and is classified into different types, which in general contains two domains (domain 1 and domain 2) with typical amino acid sequences (Rauser 1999). In this report two full-length cDNAs (Y459 and G14) encoding MT-like proteins were isolated from leaves of sweet potato (Ipomoea batatas). Their open reading frames contained 249 and 195 nucleotides (82 and 64 amino acids) for Y459 and G14, respectively, and exhibited a relatively low amino acid sequence similarity (ca. 25.8%). Gene structure studies showed that Y459 had the conserved domain 1 region of type 2 MT; however, the domain 2 region was not conserved and contained additional amino acids between the CxC and CxC spacing. G14 had conserved domains 1 and 2 of type 4 MT except that the last CxC of domain 2 was changed to RxC. Semi-quantitative RT-PCR showed that Y459 was expressed in significant quantity in roots and stems, but was much less in green leaves. During natural and induced (with dark and ethephon, an ethylene-releasing compound, treatments) leaf senescence, Y459 gene expression was significantly enhanced. In contrast, relatively constant gene expression levels were found for G14 in all tissues or treatments analyzed. In conclusion, the two MT-like protein genes of sweet potato display differential gene structures and gene expression patterns, which may be associated with the diverse roles and functions they play in plant physiology in order to cope with particular developmental and environmental cues.

Redox sensor function of metallothioneins

In summary, the redox conversions of MT cysteines are likely to be the principal mechanisms for regulation of metal binding and release by this protein. Oxidative and/or nitrosative challenges can serve to promote metal ion release from MT to render their delivery to specific target proteins. It is tempting to consider the potential roles of MTs as redox sensors because of their high sensitivity to cysteine modification, as well as their potential to amplify signals by releasing multiple metal ions. In other words, MTs may act early in a biological signaling cascade that triggers metal-dependent biochemical and cellular responses. Alternatively, uncontrolled release of metals by excessive oxidative stress may contribute to metal toxicity. Because oxidative and nitrosative signaling is ubiquitous within cells, the physiological function of MT demands that efficient recycling of modified cysteines be operative. Little is known regarding the potential mechanisms for the regeneration of MT after oxidative/nitrosative modification, but they may involve endogenous dithiols, such as thioredoxin, and pharmacologically relevant dithiols, such as dihydrolipoate.

Influence of age, sex and body condition on zinc, copper, cadmium and metallothioneins in common guillemots (Uria aalge) stranded at the Belgian coast

The common guillemots, Uria aalge, found stranded at the Belgian coast, display high levels of Cu in both liver and kidneys. The condition index of the animals, defined as the ratio of liver to kidneys mass (Wenzel & Adelung, 1996, The suitability of oiled Guillemots (Uria aalge) as monitoring organisms for geographical comparisons of trace element contaminants. Archives of Environmental Contamination and Toxicology, 31, 368-377), influences both the metal concentration and its binding to metallothioneins (MT): the lower the condition index, the more emaciated the animals, and the higher the total Cu concentration and the concentration of Cu bound to MT. In less robust individuals, our results suggest that Cu could displace Zn from MT, rendering the Zn ions available to induce a new MT synthesis. Sex-related effects also emerged as significantly higher hepatic MT as well as Cu- and Zn-MT concentrations were found in emaciated male guillemots compared to females. In both organs, Cd concentrations remained low and typically demonstrated an age-dependent renal accumulation, with no noticeable effect of the condition index. As a whole, these results suggest that, for guillemots found stranded at the Belgian coast. Cu binding to hepatic and renal MT could function as a protective mechanism, rendering the metal ions unavailable to exert any cytotoxic activity.

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.

The importance of proteins in defense against oxidation

Free radicals are a normal feature of cellular oxygen metabolism. However, free radical-associated damage is an important factor in many pathological and toxicological processes. For a long time, lipid peroxidation, mediated by oxygen-derived free radicals, was probably the most extensively investigated process. From more recent studies, it has become evident that proteins are also the targets of free radicals, and this has important implication for their activity, unfolding, and degradation, as well as in cell functioning. After giving a brief overview of the key role of proteins in the overall antioxidant defense, this review examines their role as targets of oxidation reactions, taking into account the reactivity of amino acid residues and some of their oxidation products. In light of recent data, we then consider the specific role of sulfur-containing amino acids in protein degradation and their possible interplay with the reversal of limited oxidative lesions. The participation of proteins in the overall antioxidant defense is also discussed, specifically the role of metallothionein as an intracellular antioxidant and that of albumin as a circulating antioxidant.

Nitric oxide-dependent pro-oxidant and pro-apoptotic effect of metallothioneins in HL-60 cells challenged with cupric nitrilotriacetate

Intracellular safeguarding functions of metallothioneins (MTs) include sequestering transition and heavy metals, scavenging free radicals and protecting against electrophiles. We report that MT protection against Cu-induced cytotoxicity can be reversed and pro-oxidant and pro-apoptotic effects can be induced in HL-60 cells exposed to NO. We demonstrate that in ZnCl(2)-pretreated HL-60 cells loaded with copper nitrilotriacetate (Cu-NTA), exposure to an NO donor, S-nitroso-N-acetyl penicillamine, resulted in S-nitrosylation and oxidation of MT cysteines. This disruption of MT Cu-binding thiolate clusters caused loosening and release of redox-active Cu, enhanced redox-cycling activity of Cu and increased peroxidation of major classes of membrane phospholipids. We also found that Cu-induced oxidative stress in ZnCl(2)-pretreated/Cu-NTA-loaded HL-60 cells was accompanied by apoptosis documented by characteristic changes of nuclear morphology, internucleosomal DNA cleavage, externalization of phosphatidylserine, release of cytochrome c from mitochondria into cytosol and activation of caspase-3. We conclude that in Cu-challenged cells, NO can reverse the protective role of MTs and convert them into pro-oxidant, pro-apoptotic implements.

Ceruloplasmin enhances DNA damage induced by hydrogen peroxide in vitro

Ceruloplasmin (Cp) was found to promote the oxidative damage to DNA, as evidenced by the formation of 8-hydroxy-2'-deoxyguanosine and strand breaks, when incubated with H2O2 in vitro. The capacity of Cp to enhance oxidative damage to DNA was inhibited by hydroxyl radical scavengers such as sodium azide and mannitol, a metal chelator, diethylenetriaminepentaacetic acid, and catalase. Although the oxidized protein resulted in an increase in the content of carbonyl groups, the ferroxidase activity and the proteolytic susceptibility were not significantly altered. The release of a portion of Cu from Cp was observed, and conformational alterations were indicated by the changes in fluorescence spectra. Based on these results, we suggest that damage to DNA is mediated in the H2O2/Cp system via the generation of *OH by released Cu2+ and/or loosely bound Cu exposed from oxidatively damaged Cp through the conformational change. The release of Cu from Cp during oxidative stress could enhance the formation of reactive oxygen species and could also potentiate cellular damage.

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

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

Copper, zinc superoxide dismutase enhances DNA damage and mutagenicity induced by cysteine/iron

Oxidative DNA damage caused by a cysteine metal-catalyzed oxidation system (Cys-MCO) comprised of Fe(3+), O(2), and a cysteine as an electron donor was enhanced by copper, zinc superoxide dismutase (CuZnSOD) in a concentration-dependent manner, as reflected by the formation of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and strand breaks. Unlike CuZnSOD, manganese SOD (MnSOD) as well as iron SOD (FeSOD) did not enhance DNA damage. The capacity of CuZnSOD to enhance damage to DNA was inhibited by a spin-trapping agent, 5, 5-dimethyl-1-pyrroline N-oxide (DMPO) and a metal chelator, diethylenetriaminepentaacetic acid (DETAPAC). The deoxyribose assay showed that hydroxyl free radicals were generated in the reaction of CuZnSOD with Cys-MCO. We found that the Cys-MCO system caused the release of free copper from CuZnSOD. CuZnSOD also caused the two-fold enhancement of a mutation in the pUC18 lacZ' gene in the presence of Cys-MCO when measured as a loss of alpha-complementation. Based on these results, we interpret the effects of CuZnSOD on Cys-MCO-induced DNA damage and mutation as due to reactive oxygen species, probably hydroxyl free radicals, formed by the reaction of free Cu(2+), released from oxidatively damaged CuZnSOD, and H(2)O(2) produced by the Cys-MCO system.