The role of chromatin damage in nickel-induced carcinogenesis. A review of recent developments

A selective colorimetric chemosensor for detecting Ni(II) in aqueous solutions based on 4-[{[4-(3-chlorophenyl)-1,3-thiazol-2-yl]hydrazono}methyl]phenyl 4-methyl benzene sulfonate (CTHMBS)

Among the toxic heavy metals, Ni(II) can cause a variety of side effects on human health, such as allergy, cardiovascular and kidney diseases, lung fibrosis, lung, and nasal cancer. It is therefore critical from a public health and environmental perspective to determine and monitor Ni(II) ions in drinking water, foods, and environmental samples. In this study, a novel selective chemosensor (4-[{[4-(3-Chlorophenyl)-1,3-Thiazol-2-yl]Hydrazono}Methyl]phenyl4-methylBenzene Sulfonate (CTHMBS) was developed for the colorimetric detection of Ni(II) in aqueous medium. The presence of Ni(II) led to a distinct naked-eye color change from yellow to reddish-brown in aqueous solution. To examine the binding mechanism of CTHMBS to Ni(II), UV-vis spectroscopy analysis and DFT calculations were conducted. The detection limit of CTHMBS for Ni(II) was 11.87 µM, and the sensing ability of CTHMBS for Ni(II) was successfully carried out in real water samples.

Chronic nickel exposure alters extracellular vesicles to mediate cancer progression via sustained NUPR1 expression

Cancer cells release extracellular vesicles (EVs) that participate in altering the proximal tumor environment and distal tissues to promote cancer progression. Chronic exposure to nickel (Ni), a human group I carcinogen, results in epigenetic changes that promotes epithelial to mesenchymal transition (EMT). Cells that undergo EMT demonstrate various molecular changes, including elevated levels of the mesenchymal cadherin N-cadherin (N-CAD) and the transcription factor Zinc finger E-box binding homeobox 1 (ZEB1). Moreover, the molecular changes following EMT induce changes in cellular behavior, including anchorage-independent growth, which contributes to cancer cells detaching from tumor bulk during the metastatic process. Here, we present data demonstrating that EVs from Ni-exposed cells induce EMT in recipient BEAS-2B cells in the absence of Ni. Moreover, we show evidence that the EVs from Ni-altered cells package the transcription factor nuclear protein 1 (NUPR1), a transcription factor associated with Ni exposure and cancer progression. Moreover, our data demonstrates that the NUPR1 in the EVs becomes part of the recipient cell proteomic milieu and carry the NUPR1 to the nuclear space of the recipient cell. Interestingly, knockdown of NUPR1 in Ni-transformed cells suppressed NUPR1 packaging in the EVs, and nanoparticle tracking analysis (NTA) demonstrated decreased EV release. Reduction of NUPR1 in EVs resulted in diminished EMT capacity that resulted in decreased anchorage independent growth. This study is the first to demonstrate the role of NUPR1 in extracellular vesicle-mediate cancer progression.

Fluorescent and chromogenic organic probes to detect group 10 metal ions: design strategies and sensing applications

Group 10 metals including Ni, Pd and Pt have been extensively applied in various essential aspects of human social life, material science, industrial manufactures, medicines and biology. The ionic forms of these metals are involved in several biologically important processes due to their strong binding capability towards different biomolecules. However, the mishandling or overuse of such metals has been linked to serious contamination of our ecological system, more specifically in soil and water bodies with acute consequences. Therefore, the detection of group 10 metal ions in biological as well as environmental samples is of huge significance from the human health point of view. Related to this, considerable efforts are underway to develop adequately efficient and facile methods to achieve their selective detection. Optical sensing of metal ions has gained increasing attention of researchers, particularly in the environmental and biological settings. Innovatively designed optical probes (fluorescent or colorimetric) are usually comprised of three basic components: an explicitly tailored receptor unit, a signalling unit and a clearly defined reporter unit. This review deals with the recent progress in the design and fabrication of fluorescent or colorimetric organic sensors for the detection of group 10 metal ions (Ni(II), Pd(II) and Pt(II)), with attention to the general aspects for design of such sensors.

A pyridine dicarboxylate based hydrazone Schiff base for reversible colorimetric recognition of Ni2+ and PPi

A pyridine dicarboxylate Schiff-base DAS was synthesized for cascade colorimetric recognition of Ni²⁺ and PPi. The selectivity and sensitivity of chemosensor DAS was investigated through colorimetric and UV-vis studies in MeOH-PBS (5 : 1, v/v, pH = 7.4). The chemosensor formed a 2 : 1 complex with Ni²⁺ metal ions with a binding constant of K_a = 3.07 × 10³ M^-2. Besides, a plausible sensing mechanism is confirmed by single crystal X-ray diffraction (SC-XRD), Job's plot and Benesi-Hildebrand plot (B-H plot) experiments. Furthermore, the DAS-Ni²⁺ ensemble formed 'in situ' was used to selectively recognise PPi. The limit of detection (LOD) of DAS for Ni²⁺ was found to be 0.14 μM and that of the DAS-Ni²⁺ ensemble for PPi was found to be 0.33 μM. Also, the potential of the chemosensor has been applied for solid state detection of Ni²⁺ as well as to mimic the 'INHIBIT' logic gate on the addition of Ni²⁺ ions and PPi.

A Molecular Mechanism to Explain the Nickel-Induced Changes in Protamine-like Proteins and Their DNA Binding Affecting Sperm Chromatin in Mytilus galloprovincialis: An In Vitro Study

Nickel is associated with reproductive toxicity, but little is known about the molecular mechanisms of nickel-induced effects on sperm chromatin and protamine-like proteins (PLs). In the present work, we analyzed PLs from Mytilus galloprovincialis by urea-acetic acid polyacrylamide gel electrophoresis (AU-PAGE) and SDS-PAGE and assessed their binding to DNA by Electrophoretic Mobility Shift Assay (EMSA) after exposing mussels to 5, 15, and 35 µM NiCl2 for 24 h. In addition, a time course of digestion with MNase and release of PLs from sperm nuclei by the NaCl gradient was performed. For all exposure doses, in AU-PAGE, there was an additional migrating band between PL-III and PL-IV, corresponding to a fraction of PLs in the form of peptides detected by SDS-PAGE. Alterations in DNA binding of PLs were observed by EMSA after exposure to 5 and 15 µM NiCl2, while, at all NiCl2 doses, increased accessibility of MNase to sperm chromatin was found. The latter was particularly relevant at 15 µM NiCl2, a dose at which increased release of PLII and PLIII from sperm nuclei and the highest value of nickel accumulated in the gonads were also found. Finally, at all exposure doses, there was also an increase in PARP expression, but especially at 5 µM NiCl2. A possible molecular mechanism for the toxic reproductive effects of nickel in Mytilus galloprovincialis is discussed.

A Sol-gel Membrane Utilized Cellulose Paper Doped with α-furil Dioxime for Colorimetric Determination of Nickel

A simple and sensitive colorimetric sensor for nickel(II) ions has been successfully prepared by immobilizing α-furil dioxime reagent in the sol-gel matrix with a solid supporting filter paper medium. The sensor was developed using tetraethyl orthosilicate (TEOS) precursors with 4 days aging time, the mole ratio of water: precursor was 4:1, and reagent concentration at 0.10%. The sensor was quantified by utilizing the Red (R), Green (G), and Blue (B) values ​​of the colors that were successfully displayed after the detection process. The RGB value is confirmed by the Euclidean Distance (ED) equation to determine the optimum conditions. There was no observed degree of leaching in plain sight, and the result of leaching investigation by the double dyeing method did not show any significant change. The linear range was ​​0.10 to 2.8 ppm with an R² of 0.9964. The values of LOD and LOQ were 0.1 ppm and 0.4 ppm, respectively. In addition, the sensor was free from interfering species and had a percent recovery around 90 to 110%.

Oxidative metabolism in the cardiorespiratory system after an acute exposure to nickel-doped nanoparticles in mice

There is an increasing concern over the harmful effects that metallic nanoparticles (NP) may produce on human health. Due to their redox properties, nickel (Ni) and Ni-containing NP are particularly relevant. Hence, the aim of this study was to establish the toxicological mechanisms in the cardiorespiratory oxidative metabolism initiated by an acute exposure to Ni-doped-NP. Mice were intranasally instilled with silica NP containing Ni (II) (Ni-NP) (1 mg Ni (II)/kg body weight) or empty NP as control, and 1 h after exposure lung, plasma, and heart samples were obtained to assess the redox metabolism. Results showed that, NP were mainly retained in the lungs triggering a significantly increased tissue O₂ consumption rate, leading to Ni-NP-increased reactive oxygen species production by NOX activity, and mitochondrial H₂O₂ production rate. In addition, an oxidant redox status due to an altered antioxidant system showed by lung GSH/GSSG ratio decreased, and SOD activity increased, resulting in an increased phospholipid oxidation. Activation of circulating polymorphonuclear leukocytes, along with GSH/GSSG ratio decreased, and phospholipid oxidation were found in the Ni-NP-group plasma samples. Consequently, in distant organs such as heart, Ni-NP inhalation alters the tissue redox status. Our results showed that the O₂ metabolism analysis is a critical area of study following Ni-NP inhalation. Therefore, this work provides novel data linking the redox metabolisms alterations elicited by exposure to Ni (II) adsorbed to NP and cardiorespiratory toxicity.

Assessing reference levels of nickel and chromium in cord blood, maternal blood and placenta specimens from Ankara, Turkey

Objective:

Placenta is a temporary organ that connects the developing fetus and the mother. However, it cannot protect the embryo against chromium (Cr) and nickel (Ni) exposure. Quantification of Cr and Ni in biological and ecological subjects is challenging. Thus, the first goal of this study was to provide a validated Graphite Furnace Atomic Absorption Spectrometry (GFAAS) method to determine Cr and Ni in mother-newborn specimens. The second goal was to assess the reference Ni and Cr contents in cord blood, maternal blood, and placenta samples in a population from Ankara.

Material and Methods:

Biological samples were collected from 100 healthy mother-newborn pairs. Metal levels were quantified by GFAAS. Method validation of this toxicological analysis was performed by the use of certified reference materials, and assessed through accuracy, precision, specificity, range, quantitation, and detection limits.

Results:

Mean Cr levels of maternal blood, placentas, and cord blood were 0.337±0.222 μg/L, 0.221±0.160 μg/kg, 0.121±0.096 μg/L, respectively while mean Ni concentrations were 0.128±0.093 μg/L, 0.124±0.067 μg/kg, 0.099±0.067 μg/L, respectively. The method showed linearity with excellent correlation coefficients (r²) for Cr (0.9994) and Ni (0.9999). Satisfactory recovery and coefficient of variation for Cr and Ni were 102.85% and 102.35%; 1.75% and 2.91%, respectively. Relative error did not exceed 3%, demonstrating the accuracy of the method. Control charts were drawn to assess inter-day stability. The predicted reference ranges for Cr and Ni concentrations in maternal blood, placenta and cord blood were: Cr 0.033-0.75 μg/L; 0.032-0.526 μg/kg; 0.031-0.309 μg/L and for Ni were 0.011-0.308 μg/L; 0.024-0.251 μg/kg; 0.066-0.209 μg/L, respectively.

Conclusion:

The reported reference values of biological specimens in this paper will provide complementary aid to health professionals in terms of assessment of environmental and occupational exposure.

Metal nickel exposure increase the risk of congenital heart defects occurrence in offspring: A case-control study in China

BACKGROUND

Previous studies have investigated heavy metal exposure could increase the occurrence of congenital heart defects (CHDs). However, there are limited data regarding the relationship between exposure to nickel and CHDs occurrence in offspring. The aim of this study was to analyze the association between nickel exposure in mothers and the risk of CHDs in offspring.

MATERIALS AND METHODS

To explore the association of nickel exposure and occurrence of CHD, a case-control study with 490 controls and 399 cases with CHDs in China were developed. The concentrations of nickel in hair of pregnant woman and fetal placental tissue were measured and used a logistic regression analysis to explore the relationship between nickel exposure and risk of CHD.

RESULTS

The median concentrations of nickel were 0.629 ng/mg, P < .05 (adjusted odds ratio [aOR], 1.326; 95% CI, 1.003-1.757) and 0.178 ng/mg, P < .05 (aOR, 2.204; 95% CI, 0.783-6.206), in maternal hair and in fetal placental tissue in the CHD group, respectively. Significant differences in the level of nickel in hair were also found in the different CHD subtypes including septal defects (P < .05), conotruncal defects (P < .05), right ventricular outflow tract obstruction (P < .01), and left ventricular outflow tract obstruction (P < .05). Dramatically different nickel concentrations in fetal placenta tissue were found in cases with other heart defects (P < .05).

CONCLUSIONS

The finding suggested that the occurrence of CHDs may be associated with nickel exposure.

Nickle(II) ions exacerbate bleomycin-induced pulmonary inflammation and fibrosis by activating the ROS/Akt signaling pathway

Nickle (Ni) is a heavy metal found in particulate matter. We previously reported that Ni ions are strongly associated with high apoptosis rates and high expression of IL-1β in human bronchial epithelial cells following exposure to PM2.5; however, the effects of Ni ions on pulmonary fibrosis have not been fully elucidated. In the current study, we evaluated whether Ni ions can exacerbate bleomycin (BLM)-induced pulmonary fibrosis in a mouse model and illustrated the potential mechanism. Ni ions inhibited cell proliferation and induced apoptosis in A549 and MRC-5 cells. BLM-induced lung injury and fibrosis in mice were significantly enhanced by nickel treatment, and these findings were also supported by inflammatory cell accumulation in bronchoalveolar lavage fluid and elevated levels of pro-inflammatory cytokines in lung tissues. Ni ions also increased extracellular matrix protein levels, including those of type I collagen and MMP9 in mouse lung tissues and cell lines. Moreover, Ni ions promoted the phosphorylation of AKT in this mouse model. The effect of increased collagen levels and MMP9 expression was inhibited by blocking the AKT phosphorylation. Together, these findings suggest AKT activation as a critical contributor to this Ni-exacerbated pulmonary fibrotic process.

Interaction of three new tetradentates Schiff bases containing N2O2 donor atoms with calf thymus DNA

Interaction of 1,3-bis(2-hydroxy-benzylidene)-urea (H2L1), 1,3-bis(2-hydroxy-3-methoxy-benzylidene)-urea (H2L2) and 1,3-bis(2-hydroxy-3-methoxy-benzylidene)-urea nickel(II) (NiL2) with calf-thymus DNA were investigated by UV-vis absorption, fluorescence emission and circular dichroism (CD) spectroscopy as well as cyclic voltammetry, viscosity measurements, molecular docking and molecular dynamics simulation. Binding constants were determined using UV-vis absorption and fluorescence spectra. The results indicated that studied Schiff-bases bind to DNA in the intercalative mode in which the metal derivative is more effective than non metals. Their interaction trend is further determined by molecular dynamics (MD) simulation. MD results showed that Ni derivative reduces oligonucleotide intermolecular hydrogen bond and increases solvent accessible surface area more than other compounds.

Ni(ii) ions cleave and inactivate human alpha-1 antitrypsin hydrolytically, implicating nickel exposure as a contributing factor in pathologies related to antitrypsin deficiency

Ni(ii) ions cleave AAT hydrolytically, inactivating the protein.

Site-Selective Peptide/Protein Cleavage

Site-selective peptide/protein degradation through chemical cleavage methods is an important modification of biologically relevant macromolecules which complements enzymatic hydrolysis. In this review, recent progress in chemical, site-selective peptide bond cleavage is overviewed, with an emphasis on postulated mechanisms and their implications on reactivity, selectivity, and substrate scope.

Assaying environmental nickel toxicity using model nematodes

Although nickel exposure results in allergic reactions, respiratory conditions, and cancer in humans and rodents, the ramifications of excess nickel in the environment for animal and human health remain largely undescribed. Nickel and other cationic metals travel through waterways and bind to soils and sediments. To evaluate the potential toxic effects of nickel at environmental contaminant levels (8.9-7,600 µg Ni/g dry weight of sediment and 50-800 µg NiCl₂/L of water), we conducted assays using two cosmopolitan nematodes, Caenorhabditis elegans and Pristionchus pacificus. We assayed the effects of both sediment-bound and aqueous nickel upon animal growth, developmental survival, lifespan, and fecundity. Uncontaminated sediments were collected from sites in the Midwestern United States and spiked with a range of nickel concentrations. We found that nickel-spiked sediment substantially impairs both survival from larval to adult stages and adult longevity in a concentration-dependent manner. Further, while aqueous nickel showed no adverse effects on either survivorship or longevity, we observed a significant decrease in fecundity, indicating that aqueous nickel could have a negative impact on nematode physiology. Intriguingly, C. elegans and P. pacificus exhibit similar, but not identical, responses to nickel exposure. Moreover, P. pacificus could be tested successfully in sediments inhospitable to C. elegans. Our results add to a growing body of literature documenting the impact of nickel on animal physiology, and suggest that environmental toxicological studies could gain an advantage by widening their repertoire of nematode species.

Nickel alloys in the oral environment

The use of nickel casting alloys for long-term restorations in dentistry has long been controversial. A 'tug-of-war' between economic, engineering and biological considerations is central to this controversy; nickel-casting alloys have low costs and favorable physical properties, but are corrosion-prone in the oral environment. Clinicians and researchers have questioned the safety of nickel-containing dental alloys because several nickel compounds are known to cause adverse biological effects in vivo and in vitro in contexts outside of dentistry. The debate revolves around the extent to which corrosion products from oral restorations cause intraoral or systemic biological problems. Current evidence suggests that nickel alloys may be used successfully and safely in dentistry if clinical risks are taken into account. However, these alloys may cause significant clinical problems, primarily allergenic and inflammatory, if the risks are ignored.

The role of cadmium and nickel in estrogen receptor signaling and breast cancer: metalloestrogens or not?

During the past half-century, incidences of breast cancer have increased globally. Various factors--genetic and environmental--have been implicated in the initiation and progression of this disease. One potential environmental risk factor that has not received a lot of attention is the exposure to heavy metals. While several mechanisms have been put forth describing how high concentrations of heavy metals play a role in carcinogenesis, it is unclear whether chronic, low-level exposure to certain heavy metals (i.e., cadmium and nickel) can directly result in the development and progression of cancer. Cadmium and nickel have been hypothesized to play a role in breast cancer development by acting as metalloestrogens--metals that bind to estrogen receptors and mimic the actions of estrogen. Since the lifetime exposure to estrogen is a well-established risk factor for breast cancer, anything that mimics its activity will likely contribute to the etiology of the disease. However, heavy metals, depending on their concentration, are capable of binding to a variety of proteins and may exert their toxicities by disrupting multiple cellular functions, complicating the analysis of whether heavy metal-induced carcinogenesis is mediated by the estrogen receptor. The purpose of this review is to discuss the various epidemiological, in vivo, and in vitro studies that show a link between the heavy metals, cadmium and nickel, and breast cancer development. We will particularly focus on the studies that test whether these two metals act as metalloestrogens in order to assess the strength of the data supporting this hypothesis.

Zinc finger proteins as templates for metal ion exchange and ligand reactivity. Chemical and biological consequences

Zinc finger reactions with inorganic ions and coordination compounds are as diverse as the zinc fingers themselves. Use of metal ions such as Co(2+) and Cd(2+) has given structural, thermodynamic and kinetic information on zinc fingers and zinc-finger-DNA/RNA interactions. It is a general truism that alteration of the coordination sphere in the finger environment will disrupt the recognition with DNA/RNA and this has implications for mechanism of toxicity and carcinogenesis of metal ions. Structural zinc fingers are susceptible to electrophilic attack and the recognition that the coordination sphere of inorganic compounds may be modulated for control of electrophilic attack on zinc fingers raises the possibility of systematic studies of zinc fingers as drug targets using inorganic chemistry. Some inorganic compounds such as those of As(III) and Au(I) may exert their biological effects through inactivation of zinc fingers and novel approaches to specifically attack the zinc-bound ligands using Co(III)-Schiff bases and Platinum(II)-Nucleobase compounds have been proposed. The genomic importance of zinc fingers suggests that the "coordination chemistry" of zinc fingers themselves is ripe for exploration to design new targets for medicinal inorganic chemistry.

Epigenetics in metal carcinogenesis: nickel, arsenic, chromium and cadmium

Although carcinogenic metals have been known to disrupt a wide range of cellular processes the precise mechanism by which these exert their carcinogenic effects is not known. Over the last decade or two, studies in the field of metal carcinogenesis suggest that epigenetic mechanisms may play a role in metal-induced carcinogenesis. In this review we summarize the evidence demonstrating that exposure to carcinogenic metals such as nickel, arsenic, chromium, and cadmium can perturb DNA methylation levels as well as global and gene specific histone tail posttranslational modification marks. We also wish to emphasize the importance in understanding that gene expression can be regulated by both genetic and epigenetic mechanisms and both these must be considered when studying the mechanism underlying the toxicity and cell-transforming ability of carcinogenic metals and other toxicants, and aberrant changes in gene expression that occur during disease states such as cancer.

Effects of mixing metal ions on oxidative DNA damage mediated by a Fenton-type reduction

The formation of 8-hydroxy-deoxyguanosine (8-OHdG) and strand breaks in DNA by Fenton-type reactions by mixtures of two of five metal ions, iron (II), cadmium (II), nickel (II), chromium (III) or copper (II), has been investigated and compared to their formation by each single metal ion. Salmon sperm DNA and pBluescript K+ plasmid were each incubated with hydrogen peroxide and metal ions. The formation of 8-OHdG declined in the Fe (II) or Cu (II) Fenton reaction upon addition of Cd (II) or Ni (II) ion. In contrast, the Fe (II) reaction upon addition of Cr (III) ion showed an additive influence on the formation of 8-OHdG. Furthermore, the Cu (II) plus Cr (III) reaction showed a synergistic effect. These influences relate to the interaction of metal ions with DNA, the potentials of the metal ions to generate activated oxygen and electron transfer between metal ions. The formation of DNA strand breaks was investigated in plasmid DNA by agarose gel electrophoresis and subsequent densitometry. The formation of DNA strand breaks in the Fe (II) or Cu (II) Fenton reaction decreased upon the addition of Ni (II) ion, as with the formation of 8-OHdG mediated by these metal ions. On the other hand, the formation of DNA strand breaks in the Fe (II) reaction decreased upon addition of Cr (III) ion, and the Cu (II) plus Cr (III) reaction did not show the synergistic influence on DNA strand breaks. These results suggest that interactions between two metal ions can influence the generation of 8-OHdG and the formation of DNA strand breaks and demonstrate that these lesions can arise by different mechanisms.

Ni(II) affects ubiquitination of core histones H2B and H2A

The molecular mechanisms of nickel-induced malignant cell transformation include effects altering the structure and covalent modifications of core histones. Previously, we found that exposure of cells to Ni(II) resulted in truncation of histones H2A and H2B and thus elimination of some modification sites. Here, we investigated the effect of Ni(II) on one such modification, ubiquitination, of histones H2B and H2A in nuclei of cultured 1HAEo- and HPL1D human lung cells. After 1-5 days of exposure, Ni(II) up to 0.25 mM stimulated mono-ubiquitination of both histones, while at higher concentrations a suppression was found. Di-ubiquitination of H2A was not affected except for a drop after 5 days at 0.5 mM Ni(II). The decrease in mono-ubiquitination coincided with the appearance of truncated H2B that lacks the K120 ubiquitination site. However, prevention of truncation did not avert the decrease of H2B ubiquitination, indicating mechanistic independence of these effects. The changes in H2B ubiquitination did not fully coincide with concurrent changes in the nuclear levels of the ubiquitin-conjugating enzymes Rad6 and UbcH6. Overall, our results suggest that dysregulation of H2B ubiquitination is a part of Ni(II) adverse effects on gene expression and DNA repair which may assist in cell transformation.

Ternary Nickel(II) Complexes as Hydrolytic DNA-Cleavage Agents

A series of small model complexes made from Ni(II) and the ligands ethylenediamine (en), histamine (hist), and histidylleucine (HisLeu) were prepared and studied as potential hydrolytic DNA-cleavage agents. The stability constants and species-distribution curves for these complexes were determined as a function of pH. The 1 : 1 : 1 ternary complexes [Ni(II)(en)(HisLeu)] (1) and [Ni(II)(hist)(HisLeu)] (2) were the only major species present at the physiologically relevant pH of 6-7, as further corroborated by ESI-MS analysis. The complex geometries of 1 and 2 were analyzed by UV/VIS experiments and molecular dynamics (MD) simulations. Both ternary complexes were found to intercalate with DNA, as shown by UV/VIS, thermal-denaturation, and fluorescence-titration studies with ethidium bromide (EB). The intrinsic binding constants (K(b)) for the bound complexes 1DNA and 2DNA were determined as 150 and 290, resp. Gel-electrophoresis experiments revealed that 1 and 2 cleave supercoiled (type-I) to nicked-circular (type-II) DNA at physiological pH, with rate constants of 0.64 and 0.75 h(-1), resp. A tentative mechanism for this hydrolytic cleavage is proposed.

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.

Oxidative reactivity of Cu–TESHHK– and its alanine analogues

Redox properties of Cu(II) complexes of the terminally blocked hexapeptide -TESHHK- and a series of its alanine substituted analogs: -TASHHK-, -TEAHHK-, -TESAHK-, -TESHAK-, were investigated in their reactions with hydrogen peroxide in solution and by cyclic voltammetry in a broad range of pH. The formation of reactive oxygen species was followed with the use of spectrophotometric indicators, NDMA and NBT. The results indicate that the ability of these complexes to generate hydroxyl-like radicals correlates with the formation of active Cu(III) complexes resulting from the oxidation of Cu(II) by H2O2, which interact with further H2O2 molecules specifically.

Study of Ni(II) ion–DNA interactions with methylene blue as fluorescent probe

Spectroscopic studies of the interactions of Ni(II) ion with herring sperm DNA have been performed in this contribution using methylene blue (MB) as the fluorescent probe molecule. MB binds to double helical DNA via the intercalative mode, and its fluorescence is efficiently quenched by the DNA nucleobases. The fluorescence intensity of the probe molecule increases distinctly when Ni(II) ion is added to the MB-DNA solution system. These results indicate that the Ni(II) ions may be complexed with the DNA helix and probably bind at N-7 of adenine or guanine; consequently, some intercalated MB molecules are released due to the binding of Ni(II) ions to N-7 nitrogen of the purines. The Ni(II) ion-DNA interactions are further investigated by performing the photobleaching experiments of the MB-DNA complex in the presence and absence of Ni(II) ion. The bi-exponential decay functions of the fluorescence intensity have been observed in both cases and the shortening of the slow decay component when added Ni(II) ion also agrees with the release of MB from the DNA duplex.

Contrasting Effects of Metal Ions on S-Nitrosoglutathione, Related to Coordination Equilibria: GSNO Decomposition Assisted by Ni(II) vs Stability Increase in the Presence of Zn(II) and Cd(II)

Complex formation between nitrosoglutathione (GSNO) and Zn(II), Cd(II), and Ni(II) ions was studied by potentiometry and spectroscopic techniques. GSNO forms simple ML and ML2 type complexes (L = GSNO) with these ions. The stability of GSNO in HEPES buffer solution, pH 7.4, increased in the presence of both Zn(II) and Cd(II), due to an indirect mechanism. A concentration-dependent destabilization of GSNO by Ni(II) ions was found to be linearly dependent on the NiL complex concentration. NiL forms ternary complexes readily. The NiLA- stoichiometry was found for l-His, and NiHLB3- and NiLB4- complexes were detected for GSSG as the second ligand. The formation of these complexes was found to inhibit GSNO decay, by limiting the concentration of the NiL complex. The mechanism of Ni(II)-assisted GSNO decomposition contains several steps, with a hypothetical ternary complex with GSH as a likely active form. These results provide experimental evidence for the stabilization of GSNO in solution by metal ions, which may provide an additional level of control and/or impairment of cellular redox signaling. The Ni(II)-dependent destabilization of GSNO may constitute a novel epigenetic mechanism in nickel carcinogenesis.

Bulk and trace element analysis of spices: the applicability of k0-standardization and energy dispersive X-ray fluorescence

Methodology has been developed for the bulk and trace element analysis of spices such as curry powder and turmeric powder originated from Sri Lanka by the k0-standardization method (INAA-k0) and by energy dispersive X-ray fluorescence (EDXRF). SRM 1572 citrus leaves was used to check the accuracy of the results obtained by the two nuclear techniques. The elements determined quantitatively in these matrices by the EDXRF analysis were bromine, calcium, copper, iron, potassium, magnesium, manganese, phosphorus, rubidium, sulphur, strontium and zinc. The results obtained by the two techniques are comparable, although a few inconsistencies were detected, requiring adequate attention for their correction, whenever possible, in future studies.

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

The formation of Ni(II) complexes of GSH in conditions of 4-fold GSH excess over Ni(II) was studied by potentiometric titrations, UV-vis and CD spectroscopies, and magnetic susceptibility measurements. The following set of complexes was obtained in the pH range of 6-12: NiHL, Ni(2)L(2)(2)(-), NiHL(2)(3)(-), NiL(2)(4)(-), and NiH(-)(1)L(2)(5)(-). The first of these is an octahedral species, coordinated through the donors of the Glu moiety of GSH, while the remaining ones are largely square-planar, with participation of the thiol in Ni(II) coordination. Magnetic moments indicate the presence of a spin equilibrium for Ni(2)L(2)(2)(-), NiHL(2)(3)(-), and NiL(2)(4)(-) complexes. Phosphate ions apparently decompose the Ni(2)L(2)(2)(-) complex, converting it into a monomeric, high spin, ternary species. Among the molecular forms of GSH, HL(2)(-) is the one most susceptible to air oxidation, due to a presence of ionic interactions between its protonated amine and deprotonated thiol moieties. The complexation of Ni(II) accelerates air oxidation of GSH in alkaline solutions by a factor of 4, but this effect is absent at neutral pH. The damage to plasmid DNA by H(2)O(2) is facilitated by Ni(II) ions and inhibited by excess of GSH. However, the analysis of the concentration profile of this process indicates that octahedral Ni(II) complexes with GSH are involved in the formation of double strand breaks. Finally, numerical simulations of intracellular Ni(II) distribution, made possible by the determination of stability constants of Ni(II) complexes of GSH, indicate that histidine and ATP, rather than GSH, may act as ligands for Ni(II) in vivo. Altogether, our results suggest that the direct impact of GSH on Ni(II) toxicity may be of a limited character.