Correlations between complexation modes and redox activities of Ni(II)-GSH complexes

Probing the Structure and Function of the Cytosolic Domain of the Human Zinc Transporter ZnT8 with Nickel(II) Ions

The human zinc transporter ZnT8 provides the granules of pancreatic β-cells with zinc (II) ions for assembly of insulin hexamers for storage. Until recently, the structure and function of human ZnTs have been modelled on the basis of the 3D structures of bacterial zinc exporters, which form homodimers with each monomer having six transmembrane α-helices harbouring the zinc transport site and a cytosolic domain with an α,β structure and additional zinc-binding sites. However, there are important differences in function as the bacterial proteins export an excess of zinc ions from the bacterial cytoplasm, whereas ZnT8 exports zinc ions into subcellular vesicles when there is no apparent excess of cytosolic zinc ions. Indeed, recent structural investigations of human ZnT8 show differences in metal binding in the cytosolic domain when compared to the bacterial proteins. Two common variants, one with tryptophan (W) and the other with arginine (R) at position 325, have generated considerable interest as the R-variant is associated with a higher risk of developing type 2 diabetes. Since the mutation is at the apex of the cytosolic domain facing towards the cytosol, it is not clear how it can affect zinc transport through the transmembrane domain. We expressed the cytosolic domain of both variants of human ZnT8 and have begun structural and functional studies. We found that (i) the metal binding of the human protein is different from that of the bacterial proteins, (ii) the human protein has a C-terminal extension with three cysteine residues that bind a zinc(II) ion, and (iii) there are small differences in stability between the two variants. In this investigation, we employed nickel(II) ions as a probe for the spectroscopically silent Zn(II) ions and utilised colorimetric and fluorimetric indicators for Ni(II) ions to investigate metal binding. We established Ni(II) coordination to the C-terminal cysteines and found differences in metal affinity and coordination in the two ZnT8 variants. These structural differences are thought to be critical for the functional differences regarding the diabetes risk. Further insight into the assembly of the metal centres in the cytosolic domain was gained from potentiometric investigations of zinc binding to synthetic peptides corresponding to N-terminal and C-terminal sequences of ZnT8 bearing the metal-coordinating ligands. Our work suggests the involvement of the C-terminal cysteines, which are part of the cytosolic domain, in a metal chelation and/or acquisition mechanism and, as now supported by the high-resolution structural work, provides the first example of metal-thiolate coordination chemistry in zinc transporters.

Pathogenic Mechanisms and Therapeutic Implication in Nickel-Induced Cell Damage

Background:

Nickel (Ni) is mostly applied in a number of industrial areas such as printing inks, welding, alloys, electronics and electrical professions. Occupational or environmental exposure to nickel may lead to cancer, allergy reaction, nephrotoxicity, hepatotoxicity, neurotoxicity, as well as cell damage, apoptosis and oxidative stress.

Methods:

In here, we focused on published studies about cell death, carcinogenicity, allergy reactions and neurotoxicity, and promising agents for the prevention and treatment of the toxicity by Ni.

Results:

Our review showed that in the last few years, more researches have focused on reactive oxygen species formation, oxidative stress, DNA damages, apoptosis, interaction with involving receptors in allergy and mitochondrial damages in neuron induced by Ni.

Conclusion:

The collected data in this paper provide useful information about the main toxicities induced by Ni, also, their fundamental mechanisms, and how to discover new ameliorative agents for prevention and treatment by reviewing agents with protective and therapeutic consequences on Ni induced toxicity.

Biochemical, Toxicological, and Histopathological outcome in rat brain following treatment with NiO and NiO nanoparticles

Nickel oxide nanoparticle (NiO NPs) has been widely used in various fields such as catalysts, radiotherapy, and nanomedicine. The aim of this study was to compare the effects of nickel oxide (NiO) and NiO NPs on oxidative stress biomarkers and histopathological changes in brain tissue of rats. In this study, 49 male rats were randomly divided into one control group and 6 experimental groups (n = 7). The control group received normal saline and the treatment groups received NiO and NiO NPs at doses of 10, 25, and 50 mg/kg intraperitoneally for 8 days. After 8 days, animal was sacrificed, brain excised, homogenized, centrifuged, and then supernatant was collected for antioxidant assays. The results showed that activity of GST in NiO NPs groups with doses of 10, 25, and 50 mg/kg (79.42 ± 4.24, p = 0.035; 78.77 ± 8.49, p = 0.041; 81.38 ± 12.39, p = 0.042 to 47.26 ± 7.17) and catalase in NiO NPs groups with concentrations of 25 and 50 mg/kg (69.95 ± 8.65 to 39.75 ± 5.11, p = 0.02) and (68.80 ± 4.18 to 39.75 ± 5.11 p = 0.027) were significantly increased compared with the control, respectively. Total antioxidant capacity in NiONPs group with doses of 50 mg/kg was significantly decreased (345.00 ± 23.62, p = 0.015 to 496.66 ± 25.77) compared with control. The GSH level in all doses NiO and NiONPs was significantly decreased compared with the control (p = 0.002). MDA level in NiONPs and NiO groups with doses of 50 mg/kg was significantly increased (13.03 ± 1.29, p = < 0.01; 15.61 ± 1.08, p = < 0.001 to 7.32 ± 0.51) compared with the control, respectively. Our results revealed a range of histopathological changes, including necrosis, hyperemia, gliosis, and spongy changes in brain tissue. Thus, increasing level of MDA, GST, and CAT enzymes and decreasing GSH and TAC and also histopathological changes confirmed NiONPs and NiO toxicity.

Uranium(VI) Complexes of Glutathione Disulfide Forming in Aqueous Solution

The interactions between glutathione disulfide, GSSG, the redox partner and dimer of the intracellular detoxification agent glutathione, GSH, and hexavalent uranium, U(VI), were extensively studied by solution NMR (in D₂O), complemented by time-resolved laser-induced fluorescence and IR spectroscopies. As expected for the hard Lewis acid U(VI), coordination facilitates by the ligands' O-donor carboxyl groups. However, owing to the adjacent cationic α-amino group, the glutamyl-COO reveal monodentate binding, while the COO of the glycyl residues show bidentate coordination. The log K value for the reaction UO₂²⁺ + H₃GSSG^- → UO₂(H₃GSSG)⁺ (pH 3, 0.1 M NaClO₄) was determined for the first time, being 4.81 ± 0.08; extrapolation to infinite dilution gave log K^⊖ = 5.24 ± 0.08. U(VI) and GSSG form precipitates in the whole pD range studied (2-8), showing least solubility for 4 < pD < 6.5. Thus, particularly GSSG, hereby representing also other peptides and small proteins, affects the mobility of U(VI), strongly depending on the speciation of either component.

Combined effects of temperature and metal exposure on the fatty acid composition of cell membranes, antioxidant enzyme activities and lipid peroxidation in yellow perch (Perca flavescens)

The aim of this study was to investigate the combined effects of temperature and metal contamination (cadmium and nickel) on phospholipid fatty acid composition, antioxidant enzyme activities and lipid peroxidation in fish. Yellow perch were acclimated to two different temperatures (9°C and 28°C) and exposed either to Cd or Ni (respectively 4μg/L and 600μg/L) for seven weeks. Superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase activities and glutathione concentration were measured as indicators of antioxidant capacities, while malondialdehyde concentration was used as an indicator of lipid peroxidation. Poikilotherms including fish counteract the effects of temperature on phospholipid fatty acid ordering by remodelling their composition to maintain optimal fluidity. Accordingly, in our study, the fatty acid composition of yellow perch muscle at 9°C was enhanced in monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) compared to fish maintained at 28°C, in agreement with the theory of homeoviscous adaptation. Using ratios of various fatty acids as surrogates for desaturase and elongase activities, our data suggests that modification of the activity of these enzymes is responsible for the thermal acclimation of phospholipid fatty acid profiles. However, this response was altered under Ni and Cd exposure: PUFA decreased (specifically n-6 PUFA) while the proportion of saturated fatty acids increased at 9°C, whereas at 28°C, PUFA increased to proportions exceeding those observed at 9°C. Lipid peroxidation could be observed under all experimental conditions. Both enzymatic and non-enzymatic antioxidant defense systems acted cooperatively to cope with oxidative stress leading to lipid peroxidation, which was not affected by temperature acclimation as indicated by malondialdehyde concentration, in spite of a higher polyinsaturation in cold-acclimated fish which would be predicted to increase their vulnerability to peroxidation. However, in warm-acclimated, Ni-exposed fish, in which the highest proportion of PUFA was observed, lower concentrations of malondialdehyde were measured, suggesting an overcompensation of antioxidant mechanisms in these fish which could represent a substantial metabolic cost and explain their lower condition.

Effects of nickel exposure on testicular function, oxidative stress, and male reproductive dysfunction in Spodoptera litura Fabricius

Nickel is an environmental pollutant that adversely affects the male reproductive system. In the present study, the effects of nickel exposure on Spodoptera litura Fabricius were investigated by feeding larvae artificial diets containing different doses of nickel for three generations. Damage to testes and effects on male reproduction were examined. The amount of nickel that accumulated in the testes of newly emerged males increased as the nickel dose in the diet increased during a single generation. Nickel exposure increased the amount of thiobarbituric acid reactive substances and decreased the amount of glutathione in treatment groups compared with the control. The activity levels of the antioxidant response indices superoxide dismutases, catalase, and glutathione peroxidase in the testes showed variable dose-dependent relationships with nickel doses and duration of exposure. Nickel doses also disrupted the development of the testes by decreasing the weight and volume of testes and the number of eupyrene and apyrene sperm bundles in treatment groups compared with the control. When the nickel-treated males mated with normal females, fecundity was inhibited by the higher nickel doses in all three generations, but fecundity significantly increased during the second generation, which received 5 mg kg(-1) nickel. Hatching rates in all treatments significantly decreased in a dose-dependent manner in the three successive generations. The effects of nickel on these parameters correlated with the duration of nickel exposure. Results indicate assays of testes may be a novel and efficient means of evaluating the effects of heavy metals on phytophagous insects in an agricultural environment.

M2L4 coordination capsules with tunable anticancer activity upon guest encapsulation

Guest encapsulation can modulate the cytotoxicity of anthracene-based nano-capsules and broaden their applications from metallodrugs to biocompatible delivery systems.

Research Advances on Pathways of Nickel-Induced Apoptosis

High concentrations of nickel (Ni) are harmful to humans and animals. Ni targets a number of organs and produces multiple toxic effects. Apoptosis is important in Ni-induced toxicity of the kidneys, liver, nerves, and immune system. Apoptotic pathways mediated by reactive oxygen species (ROS), mitochondria, endoplasmic reticulum (ER), Fas, and c-Myc participate in Ni-induced cell apoptosis. However, the exact mechanism of apoptosis caused by Ni is still unclear. Understanding the mechanism of Ni-induced apoptosis may help in designing measures to prevent Ni toxicity.

Salinity-dependent nickel accumulation and oxidative stress responses in the euryhaline killifish (Fundulus heteroclitus)

The mechanisms of nickel (Ni) toxicity in marine fish remain unclear, although evidence from freshwater (FW) fish suggests that Ni can act as a pro-oxidant. This study investigated the oxidative stress effects of Ni on the euryhaline killifish (Fundulus heteroclitus) as a function of salinity. Killifish were exposed to sublethal levels (5, 10, and 20 mg L(-1)) of waterborne Ni for 96 h in FW (0 ppt) and 100 % saltwater (SW) (35 ppt). In general, SW was protective against both Ni accumulation and indicators of oxidative stress [protein carbonyl formation and catalase (CAT) activity]. This effect was most pronounced at the highest Ni exposure level. For example, FW intestine showed increased Ni accumulation relative to SW intestine at 20 mg Ni L(-1), and this was accompanied by significantly greater protein carbonylation and CAT activity in this tissue. There were exceptions, however, in that although liver of FW killifish at the highest exposure concentration showed greater Ni accumulation relative to SW liver, levels of CAT activity were greatly decreased. This may relate to tissue- and salinity-specific differences in oxidative stress responses. The results of the present study suggest (1) that there was Ni-induced oxidative stress in killifish, (2) that the effects of salinity depend on differences in the physiology of the fish in FW versus SW, and (3) that increased levels of cations (sodium, calcium, potassium, and magnesium) and anions (SO4 and Cl) in SW are likely protective against Ni accumulation in tissues exposed to the aquatic environment.

NiCl2-down-regulated antioxidant enzyme mRNA expression causes oxidative damage in the broiler(')s kidney

The kidney serves as a major organ of nickel (Ni) excretion and is a target organ for acute Ni toxicity due to Ni accumulation. There are no studies on the Ni or Ni compound-regulated antioxidant enzyme mRNA expression in animals and human beings at present. This study was conducted to investigate the pathway of nickel chloride (NiCl2)-caused renal oxidative damage by the methods of biochemistry, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay. Two hundred and eighty one-day-old broilers were randomly divided into four groups and fed on a control diet and three experimental diets supplemented with 300, 600, and 900 mg/kg of NiCl2 for 42 days. Dietary NiCl2 elevated the malondialdehyde (MDA), nitric oxide (NO), 8-hydroxy-2'-deoxyguanosine (8-OHdG) contents, and reduced the ability to inhibit hydroxy radical in the NiCl2-treated groups. Also, the renal inducible nitric oxide synthase (iNOS) activity and mRNA expression levels were increased. The total antioxidant (T-AOC) and activities of antioxidant enzymes including copper zinc superoxide dismutase (CuZn-SOD), manganese superoxide dismutase (Mn-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and glutathione-s-transferase (GST) were decreased, and the glutathione (GSH) contents as well were decreased in the kidney. Concurrently, the renal CuZn-SOD, Mn-SOD, CAT, GSH-Px, GST, and GR mRNA expression levels were decreased. The above-mentioned results showed that dietary NiCl2 in excess of 300 mg/kg caused renal oxidative damage by reducing mRNA expression levels and activities of antioxidant enzymes, and then enhancing free radicals generation, lipid peroxidation, and DNA oxidation.

Antioxidant system efficiently protects goldfish gills from Ni(2+)-induced oxidative stress

Fish gills are target organs for waterborne metal ions and this work aimed to investigate the effects of waterborne Ni(2+) (10, 25 and 50 mg L(-1)) on goldfish gills. A special focus was on the relationship between Ni uptake and the homeostasis of reactive oxygen species (ROS) in the gills, the tissue, in direct contact with the metal pollutant. Ni-accumulation in the gills occurred as a function of exposure concentration (R(2)=0.98). The main indices of oxidative stress, namely carbonyl proteins (CP) and lipid peroxides (LOOH), decreased by 21-33% and 21-24%, as well as the activities of principal antioxidant enzymes superoxide dismutase and glutathione-dependent peroxidase, by 29-47% and 41-46%, respectively, in gills of Ni-exposed fish. One of the main players in the antioxidant defense of gills seems to be catalase, which increased by 23-53% in Ni-treated fish, and low molecular mass thiol-containing compounds (L-SH), exceeding untreated controls by 73-105% after fish exposure to 10-50 mg L(-1) of Ni(2+). The increased level of L-SH, mainly represented by reduced glutathione, was supported by enhanced activities of glutathione reductase (by 27-38%), glutathione-S-transferase (56-141%) and glucose-6-phosphate dehydrogenase (by 96-117%) and demonstrates the ability of the antioxidant system of gills to resist Ni-induced oxidative stress.

Tissue specificity in nickel uptake and induction of oxidative stress in kidney and spleen of goldfish Carassius auratus, exposed to waterborne nickel

Toxic and carcinogenic effects of nickel compounds are suggested to result from nickel-mediated oxidative damage to macromolecules and/or inhibition of cellular antioxidant defenses. We investigated the effects of waterborne Ni(2+) (10, 25 and 50 mg/L) on the blood and blood-producing tissues (kidney and spleen) of goldfish to identify relationships between Ni accumulation and oxidative stress. Whereas the main hematological parameters (total hemoglobin and hematocrit) were unaffected, Ni(2+) exposure had substantial influence on goldfish immune system, causing lymphopenia. Ni accumulation increased renal iron content (by 49-78%) and resulted in elevated lipid peroxide (by 29%) and protein carbonyl content (by 274-278%), accompanied by suppression of the activities of superoxide dismutase (by 50-53%), glutathione peroxidase (15-45%), glutathione reductase (31-37%) and glucose-6-phosphate dehydrogenase (20-44%), indicating development of oxidative stress in kidney. In contrast to kidney, in spleen the activation of glutathione peroxidase (by 34-118%), glutathione-S-transferase (by 41-216%) and glutathione reductase (by 47%), as well as constant levels of low molecular mass thiols and metals together with enhanced activity of glucose-6-phosphate dehydrogenase (by 41-94%) speaks for a powerful antioxidant potential that counteracts Ni-induced ROS production. Further, as Ni accumulation in this organ was negligible, Ni-toxicity in spleen may be minimized by efficient exclusion of this otherwise toxic metal.

Nickel induces hyperglycemia and glycogenolysis and affects the antioxidant system in liver and white muscle of goldfish Carassius auratus L

The toxicity of nickel to mammals is well studied, whereas information on nickel effects on fish is scant. Goldfish exposure to 10-50 mg L(-1) of waterborne Ni(2+) for 96 h showed reduced glycogen levels by 27-33% and 37-40% in liver and white muscle, respectively, accompanied by substantial increases in blood glucose levels (by 15-99%). However, indices of oxidative damage to proteins (carbonyl proteins) and lipids (lipid peroxides) were largely unaffected by nickel exposure. In liver, the activities of antioxidant enzymes, superoxide dismutase (SOD) and glutathione peroxidase (GPx), were not affected by Ni(2+) treatment, while catalase activity was elevated by 26%. In white muscle, however, substantial increases in SOD (by 38-147%) and GPx (by 2.5-5.5-fold) activities appeared to compensate for decreased catalase activity (by 59-69%) in order to resist Ni-induced oxidative perturbations. Both hepatic and muscular glutathione reductase activities were suppressed by 10-30% and 12-21%, respectively, after goldfish exposure to all Ni(2+) concentrations used. However, the activity of glucose-6-phosphate dehydrogenase was remarkably enhanced (by 1.6-5.4-fold) in white muscle of Ni-exposed fish, indicating a strong potential increase in NADPH production under Ni exposure. Thus, the exposure of goldfish to 10-50 mg L(-1) of Ni(2+) for 96 h induces glycogenolysis and hyperglycemia, showing some similarities with a hypoxia response, and leads to a substantial activation of defense systems against reactive oxygen species in liver and white muscle in tissue-specific and concentration-dependent manner.

Oxidative stress level in the testes of mice and rats during nickel intoxication

The genotioxic and carcinogenic effect of nickel probably results from its capacity to produce reactive oxygen species (ROS) and disturb the redox balance. The aim of the study was to find out if rats lacking spermatic protamine 2 are less susceptible to Ni(II) than mice. Consequently, the levels of malondialdehyde + 4 hydroxynonenal (MDA+4HDA) − markers of lipid peroxidation, as well as the level of reduced glutathione (GSH) were measured within the rat and mouse testes. Our results showed that the levels of lipid peroxidation markers were elevated in testicular homogenates of intoxicated mice without any changes in rats. GSH level was lower in the group of intoxicated mice comparing to the control without statistically significant changes in rats' homogenates. Moreover, the level of GSH in the testes of intoxicated mice was lower than in rats. On the basis of our results, it appears that Ni(II) can initiate oxidative stress in the testes of mice but not of rats and can reduce GSH level. Consequently, the antioxidative defense of the testes is reduced. Ni(II) that causes oxidative stress in the testes may also contribute to infertility.

Aqueous photoreduction of oxidized mercury species in presence of selected alkanethiols

Mercury is a global environmental contaminant with severe toxicity impact. The chemical processes resulting in the transformation of oxidized mercury species (Hg2+) to elemental mercury (Hg0), greatly affects the fate and transport of mercury in the natural environment. We hereby provide the first study on the photochemistry of Hg2+ with selected alkanethiols (R-SH) as model compounds to represent thiols and thiol-type binding sites on humic substances in natural waters because of the common sulfhydryl functional group (-SH). Kinetic studies were performed using cold vapor atomic fluorescence spectroscopy (CVAFS), the formation of Hg2+-thiol complexes (Hg(SR)2) were confirmed by UV-visible spectrometry and Atmospheric Pressure Chemical Ionization-Mass Spectrometry (APCI-MS), and the reaction products were analyzed using Electron Impact-Mass Spectrometry (EI-MS) and Solid Phase Microextraction coupled with Gas Chromatography-Mass Spectrometry (SPME/GC-MS). Our results indicated that the photoreduction of Hg2+ by selected alkanethiols may be mediated by Hg2+-thiol complexes to produce Hg0. Under our experimental conditions, the apparent first order rate constants obtained for 1-propanethiol, 1-butanethiol, and 1-pentanethiol were (2.0±0.2)×10(-7) s(-1), (1.4±0.1)×10(-7) s(-1), (8.3±0.5)×10(-8) s(-1), respectively. The effects of ionic strength, dissolved oxygen or chloride ion on reaction rates were found to be minimal under our experimental conditions. The identified products of the reaction between oxidized mercury species with selected alkanethiols (C3-C5) were Hg0 and disulfides (RS-SR). The potential environmental implications are herein discussed.

Zn(II) complexes of glutathione disulfide: structural basis of elevated stabilities

Glutathione disulfide (GSSG), a long disregarded redox partner of glutathione (GSH), is thought to participate in intracellular zinc homeostasis. We performed a concerted potentiometric and NMR spectroscopic study of protonation and Zn(II) binding properties of GSSG ((γECG)(2)) and a series of its nine analogs with C-terminal modifications, tripeptide disulfides: (γECS)(2), (γECE)(2), (γECG-NH(2))(2), (γECG-OEt)(2), and (γEcG)(2); dipeptide disulfides, (γEC)(2) and (γEC-OEt)(2); and mixed disulfides, γECG-γEC and γECG-γEC-OEt. The acid-base and Zn(II) complexation properties in this group of compounds are strictly correlated to average C-terminal electrostatic charges. In particular, it was demonstrated that GSSG assumes a bent (head-to-tail) conformation in solution at neutral pH, which is controlled by electrostatic attraction between the protonated γ-amino groups of the Glu residue and the deprotonated C-terminal Gly carboxylates. This interaction modulates the ability of GSSG to coordinate Zn(II), both indirectly, by affecting the basicities of the amino groups, and directly, through the participation of the Gly carboxylates in the outer coordination sphere of the Zn(II) ion. A specific coiled structure of the major [Zn-GSSG](2-) complex is additionally stabilized by the formation of hydrogen bonds between glycinyl carboxylates and two Zn(II)-coordinated water molecules. The elevated stability of Zn(II)-GSSG complexes was demonstrated by competition with FluoZin-3, a fluorescent sensor with high Zn(II) affinity, commonly used in in vitro and in vivo studies. The potential biological functions and reactivity of GSSG complexes of Zn(II) ions are discussed.

Investigation on the Interactions of NiCR and NiCR-2H with DNA

We report here a biophysical and biochemical approach to determine the differences in interactions of NiCR and NiCR-2H with DNA. Our goal is to determine whether such interactions are responsible for the recently observed differences in their cytotoxicity toward MCF-7 cancer cells. Viscosity measurement and fluorescence displacement titration indicated that both NiCR and NiCR-2H bind weakly to duplex DNA in the grooves. The coordination of NiCR-2H with the N-7 of 2'-deoxyguanosine 5'-monophosphate (5'-dGMP) is stronger than that of NiCR as determined by (1)H NMR. NiCR-2H, like NiCR, can selectively oxidize guanines present in distinctive DNA structures (e.g., bulges), and notably, NiCR-2H oxidizes guanines more efficiently than NiCR. In addition, UV and (1)H NMR studies revealed that NiCR is oxidized into NiCR-2H in the presence of KHSO(5) at low molar ratios with respect to NiCR (</=4).

DNA oxidative cleavage induced by the novel peptide derivatives of 3-(quinoxalin-6-yl)alanine in combination with Cu(II) or Fe(II) ions

Three model dipeptides containing 3-(2,3-di(pyridin-2-yl)quinoxalin-6-yl)alanine, 3-(dipyrido[3,2-a:2,3-c]phenazin-11-yl)alanine, and 3-(2,3-diphenylquinoxalin-6-yl)alanine were studied with respect to their ability to bind selected transition metal ions, such as Cu(II), Fe(II), Ni(II), Co(II), Mn(II), and Cr(III). It was found that only Cu(II) and Fe(II) ions could form stable complex species with the studied compounds. The ability to form the complexes correlated well with DNA damage experiments. Only the ferrous and cupric complexes are capable of generating both single- and double-strand scissions. However, double-strand breakages appear to be dominating lesions in the presence of hydrogen peroxide, especially for copper(II) containing systems. The quantity of breakage products in the presence of N-(3-(dipyrido[3,2-a:2,3-c]phenazine-11-yl)alanyl)glycine complexes was the highest as compared to the complexes of the remaining compounds. Moreover, this ligand was the only one that cleaved DNA in the absence of either Cu(II) or Fe(II) ions.

Aminothiol receptors for decorporation of intravenously administered (60)Co in the rat

This report provides a comparison of the oral decorporation efficacy of L-glutathione (GSH), L-cysteine (Cys), and a liposomal GSH formulation (ReadiSorb) toward systemic (60)Co to that observed following intravenous administration of GSH and Cys in F344 rats. Aminoacid L-histidine (His) containing no thiol functionality was tested intravenously to compare in vivo efficacy of the aminothiol (GSH, Cys) chelators with that of the aminoimidazole (His) chelator. In these studies, (60)Co was administered to animals by intravenous injection, followed by intravenous or oral gavage doses of a chelator repeated at 24-h intervals for a total of 5 doses. The results suggest that GSH and Cys are potent decorporation agents for (60)Co in the rat model, although the efficacy of treatment depends largely on the systemic availability of the chelator. The intravenous route of administration of GSH or Cys was most effective in reducing tissue (60)Co levels and in increasing excretion of radioactivity compared to control animals. Liposomal encapsulation was found to markedly enhance the oral bioavailability of GSH compared to non-formulated GSH. The oral administration of liposomal GSH reduced (60)Co levels in nearly all tissues by 12-43% compared to that observed for non-formulated GSH. Efficacy of oral Cys was only slightly reduced in comparison with intravenous Cys. Further studies to optimize the dosing regimen in order to maximize decorporation efficiency are warranted.

Nickel(II) complexes of biologically active glutathione: spectroscopic, kinetics of thermal decomposition and XRPD studies

Nickel(II) complexes of reduced glutathione (GSH) of general composition Na[Ni(L)(X)]H(2)O, where H(2)L=GSH; X=NO(3)(-), SCN(-), CH(3)CO(2)(-), Cl(-) have been synthesized and characterized by elemental analysis, infrared spectra, electronic spectra, magnetic susceptibility measurements, thermal and X-ray powder diffraction studies. Infrared spectra indicate deprotonation and coordination of cysteinyl sulphur and carboxylate oxygen of glycine residue with nickel ions. It indicates the presence of water molecule in all the complexes which has been supported by TG/DTA. The thermal behavior of complexes shows that water molecule is removed in first step-followed removal of anions and then decomposition of the ligand molecule in subsequent steps. General mechanisms describing the decomposition of the solid complexes are suggested. Kinetic and thermodynamic parameters were computed from the thermal decomposition data. The room temperature magnetic moment values for all the complexes lie in the range of 2.2-2.4BM, indicating departure from spin only values due to second order Zeeman effect. The electronic spectra indicate planar coordination geometry for all the complexes. Crystal data for Na[Ni(L)(CH(3)CO(2)(-))]H(2)O: tetragonal, space group P4/m, a=8.2004A, b=8.2004A, c=16.0226A, V=1077.47A(3), Z=2. Crystal data for Na[Ni(L)(Cl(-))]H(2)O: cubic, space group Pm3, a=16.1055A, b=16.1055A, c=16.1055A, V=4178.38A(3), Z=6. Crystal data for Na[Ni(L)(NO(3)(-))]H(2)O: tetragonal, space group P4/m, a=7.2121A, b=7.2121A, c=12.0200A, V=625.22A(3), Z=2.

The role of ascorbate in the modulation of HIF-1alpha protein and HIF-dependent transcription by chromium(VI) and nickel(II)

Molecular oxygen is involved in hydroxylation and subsequent degradation of HIF-1alpha, a subunit of HIF-1 transcription factor; therefore oxygen shortage (hypoxia) stabilizes this protein. However, HIF-1alpha can also be stabilized by transition metal ions in the presence of oxygen, suggesting that a different mechanism is involved in metal-induced hypoxic stress. Recently, we showed that the depletion of intracellular ascorbate by metals may lead to the inhibition of hydroxylases. Because nickel(II) has similarity to iron(II), an alternative hypothesis suggests that iron substitution for nickel in the enzyme inhibits hydroxylase activity. Here we investigated the induction of HIF-1 by another metal, chromium, which cannot replace iron in the enzyme. We show that chromium(VI), but not chromium(III), can oxidize ascorbate both in cells and in a cell-free system. In agreement with these data chromium(VI) stabilizes HIF-1alpha protein in cells only until it is reduced to chromium(III). In contrast, nickel(II) was found to be a catalyst, which facilitated continuous oxidation of ascorbate by ambient oxygen. These data correlate with extended stabilization of HIF-1alpha after acute exposure to nickel(II). The HIF-1-dependent reporter assays revealed that 20-24 h was required to fully develop the HIF-1 transcriptional response, and the acute exposure to nickel(II), but not chromium(VI), meets this requirement. However, repeated (chronic) exposure to chromium(VI) can also lead to extended stabilization of HIF-1alpha. Thus, the obtained data emphasize the important role of ascorbate in regulation of HIF-1 transcriptional activity in metal-exposed human lung cells.

Metal ion selectivity of oligopeptides

Metal binding affinity and selectivity of peptides are reviewed with a special emphasis on the high structural variety of peptide complexes. The most common structural type of these complexes is built up by the deprotonation and metal ion coordination of subsequent amide groups in the form of fused five-membered chelate rings. The metal ion selectivity of this process and the role of various anchoring groups are discussed in detail. The highest metal binding affinity of peptides is connected to the presence of two anchoring groups in appropriate location (the "double anchor"): e.g. the NH2-Xaa-Xaa-His/Cys/Asp/Met-Xaa sequence. Among the side chain donor functions, the imidazole of histidyl and thiolate of cysteinyl residues are the most effective ligating groups and their involvement in metal binding results in a great variety of different macrochelate or loop structures and/or formation of various polynuclear complexes. Examples of these structural motifs and their possible applications have been thoroughly discussed.

Responses to Nickel in the Proteome of the Hyperaccumulator Plant Alyssum lesbiacum

A proteomic analysis of the Ni hyperaccumulator plant Alyssum lesbiacum was carried out to identify proteins that may play a role in the exceptional degree of Ni tolerance and accumulation characteristic of this metallophyte. Of the 816 polypeptides detected in root tissue by 2D SDS-PAGE, eleven increased and one decreased in abundance relative to total protein after 6-week-old plants were transferred from a standard nutrient solution containing trace concentrations of Ni to a moderately high Ni treatment (0.3 mM NiSO4) for 48 h. These polypeptides were identified by tandem mass spectrometry and the majority were found to be involved in sulphur metabolism (consistent with a re-allocation of sulphur towards cysteine and glutathione), protection against reactive oxygen species, or heat-shock response. In contrast, very few polypeptides were found to change in abundance in root or shoot tissue after plants were exposed for 28 days to 0.03 mM NiSO4, a concentration representing the optimum for growth of this species but sufficient to lead to hyperaccumulation of Ni in the shoot. Under these conditions, constitutively expressed genes in this highly Ni-tolerant species may be sufficient to allow for effective chelation and sequestration of Ni without the need for additional protein synthesis.

Coordination mode and oxidation susceptibility of nickel(II) complexes with 2'-deoxyguanosine 5'-monophosphate and l-histidine

The formation of binary and ternary complexes of Ni(II) with two biologically relevant molecules, 2'-deoxyguanosine 5'-monophosphate (dGMP) and l-histidine (histidine or His) was characterized by potentiometry and UV-visible spectroscopy. For dGMP, the mononuclear complexes with stoichiometries NiH(2)L(+), NiHL and NiL(-) were found. In the mixed system the ternary complexes NiH(2)LA, NiHLA(-) and NiLA(2-) were detected. In binary systems, the Ni(II) ion coordinates to dGMP through the N-7 atom of its purine ring and indirectly through a water molecule bonded to the phosphate group, while in ternary complexes Ni(II) is bonded to all three histidine donors and directly to the phosphate group of dGMP. Both binary and ternary complexes are susceptible to oxidation by H(2)O(2), with the increased formation of 8-oxo-dGMP in the ternary system. The toxicological relevance of these findings stems from possible disturbance by the major biological Ni(II)-His complex of the nucleotide pools homeostasis through the formation of ternary species and oxidation promotion, as well as from 8-oxo-dGMP capacity to inhibit enzymatic elimination of promutagenic oxidized nucleotides from such pools.

Determination of the stability constants and oxidation susceptibility of nickel(II) complexes with 2'-deoxyguanosine 5'-triphosphate and L-histidine

The formation of binary Ni(II) complexes with 2'-deoxyguanosine 5'-triphosphate (dGTP, L) as well as ternary complexes thereof with L-histidine (His, A) was studied with the use of potentiometry and electronic absorption spectroscopy. In the binary and ternary systems, the complexes with stoichiometries NiH2L-, NiHL2-, NiL3- and NiH2LA2-, NiHLA3-, NiLA4- respectively, were detected. The ternary complexes are very stable at pH 7.4 and thus may constitute biologically relevant Ni(II) carriers in the cell. In the presence of hydrogen peroxide, the binary and ternary systems both generate hydroxyl radical-like species and undergo dGTP degradation with the formation of the 8-oxo-dGTP intermediate. The latter, along with dGTP complexation and degradation, may lead to mutagenesis and carcinogenesis due to base-mispairing properties of 8-oxoguanine and the disturbance in the physiological balance among the four canonical triphosphodeoxynucleotide substrates for DNA synthesis.

Structure-function relationships in glutathione and its analogues

The results are presented of measurements of protonation constants (potentiometry and NMR), UV spectroscopic properties and redox potentials of GSH and its five analogues, which are modified at the C-terminal glycine residue (gammaGlu-Cys-X, X = Gly, Gly-NH2, Gly-OEt, Ala, Glu, Ser). Strong linear correlations were found between various properties of the thiol and other functions of these peptides. These results allow discussion of the relationships between the structures and properties in glutathione and its analogues, and provide a novel chemical background for the issue of control of GSH reactivity.