Evidence for the involvement of hydroxyl radicals in nickel mediated enhancement of lipid peroxidation: implications for nickel carcinogenesis

Nickel tolerance is channeled through C-4 methyl sterol oxidase Erg25 in the sterol biosynthesis pathway

Nickel (Ni) is an abundant element on Earth and it can be toxic to all forms of life. Unlike our knowledge of other metals, little is known about the biochemical response to Ni overload. Previous studies in mammals have shown that Ni induces various physiological changes including redox stress, hypoxic responses, as well as cancer progression pathways. However, the primary cellular targets of nickel toxicity are unknown. Here, we used the environmental fungus Cryptococcus neoformans as a model organism to elucidate the cellular response to exogenous Ni. We discovered that Ni causes alterations in ergosterol (the fungal equivalent of mammalian cholesterol) and lipid biosynthesis, and that the Sterol Regulatory Element-Binding transcription factor Sre1 is required for Ni tolerance. Interestingly, overexpression of the C-4 methyl sterol oxidase gene ERG25, but not other genes in the ergosterol biosynthesis pathway tested, increases Ni tolerance in both the wild type and the sre1Δ mutant. Overexpression of ERG25 with mutations in the predicted binding pocket to a metal cation cofactor sensitizes Cryptococcus to nickel and abolishes its ability to rescue the Ni-induced growth defect of sre1Δ. As overexpression of a known nickel-binding protein Ure7 or Erg3 with a metal binding pocket similar to Erg25 does not impact on nickel tolerance, Erg25 does not appear to simply act as a nickel sink. Furthermore, nickel induces more profound and specific transcriptome changes in ergosterol biosynthetic genes compared to hypoxia. We conclude that Ni targets the sterol biosynthesis pathway primarily through Erg25 in fungi. Similar to the observation in C. neoformans, Ni exposure reduces sterols in human A549 lung epithelial cells, indicating that nickel toxicity on sterol biosynthesis is conserved.

Protective effect of luteolin against chemical and natural toxicants by targeting NF-κB pathway

Humans are continuously exposed to environmental, occupational, consumer and household products, food, and pharmaceutical substances. Luteolin, a flavone from the flavonoids family of compounds, is found in different fruits and vegetables. LUT is a strong anti-inflammatory (via inhibition of NF-κB, ERK1/2, MAPK, JNK, IL-6, IL-8, and TNF-α) and antioxidant agent (reducing ROS and enhancement of endogenous antioxidants). LUT can chelate transition metal ions responsible for ROS generation and consequently repress lipoxygenase. It has been proven that NF-κB, as a commom cellular pathway plays a considerable role in the progression of inflammatory process and stimulates the expression of genes encoding inducible pro-inflammatory enzymes (iNOS and COX-2) and cytokines including IL-1β, IL-6, and TNF-α. This review summarizes the available literature discussing LUT and its potential protective role against pharmaceuticals-, metals-, and environmental compounds-induced toxicities. Furthermore, the review explains the involved protective mechanisms, especially inhibition of the NF-κB pathway.

Ni exposure impacts the pool of free Fe and modifies DNA supercoiling via metal-induced oxidative stress in Escherichia coli K-12

The biology of nickel has been widely studied in mammals because of its carcinogenic properties, whereas few studies have been performed in microorganisms. In the present work, changes accompanying stress caused by nickel were evaluated at the cellular level using RNA-Seq in Escherichia coli K-12. Interestingly, a very large number of genes were found to be deregulated by Ni stress. Iron and oxidative stress homeostasis maintenance were among the most highly enriched functional categories, and genes involved in periplasmic copper efflux were among the most highly upregulated. These results suggest that the deregulation of Fe and Cu homeostatic genes is caused by a release of free Cu and Fe ions in the cell which in turn activate the Cu and Fe homeostatic systems. The content of Cu was not significantly affected upon the addition of Ni to the growth medium, nor were the Cus and CopA Cu-efflux systems important for the survival of bacteria under Ni stress In contrast the addition of Ni slightly decreased the amount of cellular Fe and activated the transcription of Fur regulated genes in a Fur-dependent manner. Cu or Fe imbalance together with oxidative stress might affect the structure of DNA. Further experiments revealed that Ni alters the state of DNA folding by causing a relaxed conformation, a phenomenon that is reversible by addition of the antioxidant Tiron or the Fe chelator Dip. The Tiron-reversible DNA relaxation was also observed for Fe and to a lesser extent with Cu but not with Co. DNA supercoiling is well recognized as an integral aspect of gene regulation. Moreover our results show that Ni modifies the expression of several nucleoid-associated proteins (NAPs), important agents of DNA topology and global gene regulation. This is the first report describing the impact of metal-induced oxidative on global regulatory networks.

Identification of two nickel ion-induced genes, NCI16 and PcGST1, in Paramecium caudatum

Here, we describe the isolation of two nickel-induced genes in Paramecium caudatum, NCI16 and PcGST1, by subtractive hybridization. NCI16 encoded a predicted four-transmembrane domain protein (∼16 kDa) of unknown function, and PcGST1 encoded glutathione S-transferase (GST; ∼25 kDa) with GST and glutathione peroxidase (GPx) activities. Exposing cells to cobalt chloride also caused the moderate upregulation of NCI16 and PcGST1 mRNAs. Both nickel sulfate and cobalt chloride dose dependently induced NCI16 and PcGST1 mRNAs, but with different profiles. Nickel treatment caused a continuous increase in PcGST1 and NCI16 mRNA levels for up to 3 and 6 days, respectively, and a notable increase in H₂O₂ concentrations in P. caudatum. NCI16 expression was significantly enhanced by incubating cells with H₂O₂, implying that NCI16 induction in the presence of nickel ions is caused by reactive oxygen species (ROS). On the other hand, PcGST1 was highly induced by the antioxidant tert-butylhydroquinone (tBHQ) but not by H2O2, suggesting that different mechanisms mediate the induction of NCI16 and PcGST1. We introduced a luciferase reporter vector with an ∼0.42-kb putative PcGST1 promoter into cells and then exposed the transformants to nickel sulfate. This resulted in significant luciferase upregulation, indicating that the putative PcGST1 promoter contains a nickel-responsive element. Our nickel-inducible system also may be applicable to the efficient expression of proteins that are toxic to host cells or require temporal control.

Goldfish brain and heart are well protected from Ni²⁺-induced oxidative stress

After 96 h goldfish exposure to 10, 25 or 50 mg/L of Ni(2+) no Ni accumulation was found in the brain, but lipid peroxide concentration was by 44% elevated in the brain, whereas carbonyl protein content was by 45-45% decreased in the heart. High molecular mass thiol concentration was enhanced by 30% in the heart, while in the brain low molecular mass thiol concentration increased by 28-88%. Superoxide dismutase activity was by 27% and 35% increased in the brain and heart, respectively. Glutathione peroxidase activity was lowered to 38% and 62% of control values in both tissues, whereas catalase activity was increased in the heart by 15-45%, accompanied by 18-29% decreased glutathione reductase activity. The disturbances of free radical processes in the brain and heart might result from Ni-induced injuries to other organs with more prominent changes in the heart, because of close contact of this organ with blood, whereas the blood-brain barrier seems to protect the brain.

Dietary nickel chloride induces oxidative stress, apoptosis and alters Bax/Bcl-2 and caspase-3 mRNA expression in the cecal tonsil of broilers

The purpose of this study was to investigate the effects of dietary NiCl2 on antioxidant function, apoptosis, and the protein expression, mRNA expression and contents of the bcl-2, bax and caspase-3 in the cecal tonsil of broilers. 280 one-day-old avian broilers were divided into four groups and fed on a corn-soybean basal diet as control diet or the same basal diet supplemented with 300, 600 and 900 mg/kg of NiCl2 for 42 days. The activities of SOD, CAT and GSH-Px, and the ability to inhibit hydroxy radical, and GSH content were significantly decreased in all experimental groups. MDA content was significantly increased. The protein expression, mRNA expression and contents of bcl-2 were decreased, and bax and caspase-3 were increased in all experimental groups. The percentages of apoptotic lymphocytes were significantly increased. In conclusion, dietary NiCl2 in excess of 300 mg/kg caused oxidative stress, and then induced decreased the protein expression, mRNA expression and the contents of bcl-2, and increased protein expression, mRNA expression and the contents of bax and caspase-3 proteins in the cecal tonsil. The local intestinal mucosal immunity could finally be impaired due to the oxidative stress and apoptosis in the cecal tonsil caused by NiCl2.

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.

Binding of nickel to testicular glutamate-ammonia ligase inhibits its enzymatic activity

Exposure to nickel has been shown to cause damage to the testis in several animal models. It is not known if the testis expresses protein(s) that can bind nickel. To test this, we used a nickel-binding assay to isolate testicular nickel-binding proteins. We identified glutamate-ammonia ligase (GLUL) as a prominent nickel-binding protein by mass spectrometry. Protein analysis and reverse transcriptase polymerase chain reaction showed that GLUL is expressed in the testis, predominantly in interstitial cells. We determined that GLUL has a higher affinity for nickel than for its regular co-factor manganese. We produced an enzymatically active, recombinant GLUL protein. Upon binding, nickel interferes with the manganese-catalyzed enzymatic activity of recombinant GLUL protein. We also determined that GLUL activity in testes of animals exposed to nickel sulfate is reduced. Our results identify testicular GLUL as the first testicular protein shown to be affected by nickel exposure.

Cytoplasmic membrane response to copper and nickel in Acidithiobacillus ferrooxidans

Metal tolerance has been found to vary among Acidithiobacillus ferrooxidans strains and this can impact the efficiency of biomining practices. To explain observed strain variability for differences in metal tolerance we examined the effects of Cu(2+) and Ni(2+) concentrations (1-200 mM) on cytoplasmic membrane properties of two A. ferrooxidans type strains (ATCC 23270 and 19859) and four strains isolated from AMD water around Sudbury, Ontario, Canada. Growth rate, membrane fluidity and phase, determined from the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), and fatty acid profiles indicated that three different modes of adaptation were present and could separate between strains showing moderate, or high metal tolerance from more sensitive strains. To compensate for the membrane ordering effects of the metals, significant remodelling of the membrane was used to either maintain homeoviscous adaptation in the moderately tolerant strains or to increase membrane fluidity in the sensitive strains. Shifts in the gel-to-liquid crystalline transition temperature in the moderately tolerant strains led to multiple phase transitions, increasing the potential for phase separation and compromised membrane integrity. The metal-tolerant strain however, was able to tolerate increases in membrane order without significant compensation via fatty acid composition. Our multivariate analyses show a common adaptive response which involves changes in the abundant 16:0 and 18:1 fatty acids. However, fatty acid composition and membrane properties showed no difference in response to either copper or nickel suggesting that adaptive response was non-specific and tolerance dependent. We demonstrate that strain variation can be evaluated using differences in membrane properties as intrinsic determinants of metal susceptibility.

Oral Keratinocyte Responses to Nickel-based Dental Casting Alloys In Vitro

Adverse reactions of oral mucosa to nickel-based dental casting alloys are probably due to corrosion metal ion release. We exposed H400 oral keratinocytes to two Ni-based dental alloys (Matchmate and Dsign10) as well as NiCl 2 (1—40 μg/mL Ni2+). Alloy derived Ni2+ media concentrations were determined. Direct culture on both alloys resulted in inhibited growth with a greater effect observed for Dsign10 (higher ion release). Indirect exposure of cells to conditioned media from Dsign10 negatively affected cell numbers (~64% of control by 6 days) and morphology while Matchmate-derived media did not. Exposure to increasing NiCl2 negatively affected cell growth and morphology, and the Granulocyte-macrophage colony-stimulating factor (GM-CSF) transcript was significantly up-regulated in cells following direct and indirect exposure to Dsign10. NiCl2 exposure up-regulated all cytokine transcripts at 1 day. At day 6, IL-1β and IL-8 transcripts were suppressed while GM-CSF and IL-11 increased with Ni2+ dose. Accumulation of Ni2+ ions from alloys in oral tissues may affect keratinocyte viability and chronic inflammation.

The involvement of transition metal ions on iron-dependent lipid peroxidation

The metals iron (Fe) and copper (Cu) are considered trace elements, and the metals cobalt (Co) and nickel (Ni) are known as ultra-trace elements, considering their presence in low to very low quantity in humans. The biologic activity of these transition metals is associated with the presence of unpaired electrons that favor their participation in redox reactions. They are part of important enzymes involved in vital biologic processes. However, these transition metals become toxic to cells when they reach elevated tissue concentrations and produce cellular oxidative damage. Phospholipid liposomes (0.5 mg/ml, phosphatidylcholine (PC)/phosphatidylserine (PS), 60/40) were incubated for 60 min at 37 degrees C with 25 microM of Fe2+ in the absence and in the presence of Cu2+, Co2+, and Ni2+ (0-100 microM) with and without the addition of hydrogen peroxide (H2O2, 5-50 microM). Iron-dependent lipid peroxidation in PC/PS liposomes was assessed by thiobarbituric acid-reactive substances (TBARS) production. Metal transition ions promoted lipid peroxidation by H2O2 decomposition and direct homolysis of endogenous hydroperoxides. The Fe2+-H2O2-mediated lipid peroxidation takes place by a pseudo-second order process, and the Cu2+-mediated process by a pseudo-first order reaction. Co2+ and Ni2+ alone do not induce lipid peroxidation. Nevertheless, when they are combined with Fe2+, Fe2+-H2O2-mediated lipid peroxidation was stimulated in the presence of Ni2+ and was inhibited in the presence of Co2+. The understanding of the effects of transition metal ions on phospholipids is relevant to the prevention of oxidative damage in biologic systems.

Oxidative stress in the pathogenesis of skin disease

Skin is the largest body organ that serves as an important environmental interface providing a protective envelope that is crucial for homeostasis. On the other hand, the skin is a major target for toxic insult by a broad spectrum of physical (i.e. UV radiation) and chemical (xenobiotic) agents that are capable of altering its structure and function. Many environmental pollutants are either themselves oxidants or catalyze the production of reactive oxygen species (ROS) directly or indirectly. ROS are believed to activate proliferative and cell survival signaling that can alter apoptotic pathways that may be involved in the pathogenesis of a number of skin disorders including photosensitivity diseases and some types of cutaneous malignancy. ROS act largely by driving several important molecular pathways that play important roles in diverse pathologic processes including ischemia-reperfusion injury, atherosclerosis, and inflammatory responses. The skin possesses an array of defense mechanisms that interact with toxicants to obviate their deleterious effect. These include non-enzymatic and enzymatic molecules that function as potent antioxidants or oxidant-degrading systems. Unfortunately, these homeostatic defenses, although highly effective, have limited capacity and can be overwhelmed thereby leading to increased ROS in the skin that can foster the development of dermatological diseases. One approach to preventing or treating these ROS-mediated disorders is based on the administration of various antioxidants in an effort to restore homeostasis. Although many antioxidants have shown substantive efficacy in cell culture systems and in animal models of oxidant injury, unequivocal confirmation of their beneficial effects in human populations has proven elusive.

Toxic effect of nickel in an in vitro model of human oral epithelium

Nickel is a metal widely employed in dental alloys, and due to peculiar properties of certain nickel-based materials, it cannot be substituted with other metals in some applications. The release of nickel ions from dental alloys placed into long-term contact with mouth soft tissues is alarming because of the toxic, immunological and carcinogenic effects which have been well documented for some nickel compounds. Our study was focussed on the toxic effects induced "in vitro" on human oral epithelium by the exposure to low concentrations of nickel chloride. In view of this, we adopted a three-dimensional model of epithelial cultures, reconstituted from TR 146 cells, resembling the physiological environment of the oral cavity and useful for biocompatibility testing. The effects on cell viability, apoptosis, cellular content of reduced and oxidized glutathione (GSH and GSSG) and release of prostaglandin E(2) (PGE(2)), interleukin-8 (IL-8) and interleukin-6 (IL-6) were investigated following topical application of a NiCl(2) solution ranging from 7.6mM to 0.05 mM for 72 h. Our findings show that nickel concentrations, which do not significantly modify cell viability and inflammation mediator release, can affect the redox equilibrium and stimulate apoptosis in oral epithelium cells. Further studies are needed to demonstrate the hypothesis that the oxidative imbalance induced by nickel might be implicated in the induction of apoptosis.

Effects of nickel poisoning on expression pattern of the 72/73 and 94 kDa stress proteins in rat organs and in the COS-7, HepG2, and A549 cell lines

The present study deals with the effects of Ni on the expression level of three stress proteins, namely, the cytosolic HSP72 and HSP73, and the reticulum-associated GRP94. Experiments were carried out on "Wistar'' female rats daily injected with 4 mg NiCl2 per kg body weight for 1, 3, 5, and 10 days. Another set of experiments were carried out using cell lines, derived from the monkey kidney (COS-7), and from human tumors of the lung (A549) and liver (HepG2). Cells were cultured for 4 days in the permanent presence of 100, 200, or 400 microM NiCl2. In control rats, stress proteins pattern was found to be tissue specific: two protein bands of 96 and 94 kDa were immunodetected with the anti-GRP94 antibody in kidney and liver extracts, whereas only the 96 kDa band was present in ovary extracts. HSP73 was present in kidney, liver, and ovary whereas HSP72 was only found in kidney. In kidney of nickel-treated animals, HSP73 and the 96 kDa proteins were overexpressed whereas HSP72 was strongly down regulated. No such effect was observed in liver or ovary. Similarly, in nickel-treated cell lines, HSP72 was downregulated and GRP94 (96 kDa protein) was overexpressed. HSP73 expression appeared moderately increased in A549 cells but decreased in COS-7 cells. Because long-term caloric restriction was reported to reduce free radical generation in cells, the effect of 1 month food restriction (50%) was tested in rats as a possible way to lower oxidative damages induced by Ni. No significant effect on HSP expression was observed.

Nickel-induced oxidative stress in testis of mice: evidence of DNA damage and genotoxic effects

Oxidative stress (OS) mechanisms are speculated to play a significant role in nickel-induced toxic effects and their carcinogenic potency. Although nickel-induced oxidative damage in somatic tissues is well demonstrated, evidence of the involvement of a similar mechanism(s) in nickel-induced testicular dysfunction and associated genotoxic effects is scarce. Hence, the present study aimed to investigate the nickel-induced OS response in testis and the associated genotoxic implications in vivo. Initially, the toxicity profile of nickel chloride was determined in adult albino mice (CFT-Swiss) following administration (intraperitoneal) of single doses. Subsequently, multiple sublethal doses (1.25, 2.5, and 5.0 micromol/100 g of body weight per day for 3 days) were used to characterize effects on testicular histoarchitecture, lipid peroxidation (LPO) in testis (homogenates, microsomal or mitochondrial fractions) and epididymal sperm, DNA damage, induction of apoptosis in testis, and incidence of sperm head abnormalities. Although short-term doses of nickel induced only a minimal LPO response, multiple doses elicited a moderate (15% to 30%) increase in LPO in whole homogenates and higher dose-related increases in both mitochondrial (20% to 50%) and microsomal fractions (25% to 60%). This was associated with a significant increase in DNA damage in the testis as evidenced by increased single-strand breaks (fluorimetric analysis of DNA unwinding assay). Further, at higher doses, nickel-induced apoptosis was demonstrable in the testis biochemically. Although caudal sperm counts determined at all sampling weeks showed no alterations, analysis for head abnormalities revealed a nearly 3- to 4-fold increase in the percentage of abnormal sperms among the nickel-treated males during the first 3 weeks. Furthermore, mating of nickel-treated (2.5 micromol/100 g of body weight per day for 5 days) males sequentially for a period of 5 weeks with untreated females resulted in a significant increase in male-mediated dominant lethal-type mutations (the frequency of dead implantations) during the first 3 weeks, suggesting a stage-specific effect on postmeiotic germ cells. These findings suggest that testicular toxicity of nickel compounds may be related to enhanced production of reactive oxygen species, probably mediated through oxidative damage to macromolecules, including damage to DNA.

Ni2+ enhances Fe2+/peroxide-induced oxidation of arachidonic acid and formation of geno/cytotoxic 4-hydroxynonenal: a possible contributory mechanism in nickel toxicity and allergenicity

Ni(2+), a toxic, carcinogenic and allergenic agent, affected both the kinetic and chemical courses of the Fe(2+)-induced oxidation of arachidonic acid (AA) in 0.05 M phosphate buffer (pH 7.4) and at 37 degrees C. At 10 microM concentration, Ni(2+) decreased the rate of oxidation of peroxide-free AA (200 microM) promoted by 50 microM Fe(2+), as determined by measurement of thiobarbituric acid reactive species (TBARS) and 1H NMR analysis. However, in the presence of low levels of peroxides (e.g. 2%), Ni(2+) exerted a significant stimulatory effect on Fe(2+)-induced AA oxidation and TBARS formation. 1H NMR analysis showed that Ni(2+) (10 microM) enhanced formation of genotoxic alkenals including 4-hydroxy-2-nonenal (4-HNE, GC/MS evidence) by Fe(2+)-promoted degradation of both AA and 15-hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) methyl esters. The observed stimulatory effects of Ni(2+) on peroxide breakdown and cytotoxic aldehyde formation provide an attractive explanation to the enhanced sensitization capacity of nickel in inflammatory states compared to normal states.

Effects of lead on Na(+)-K(+) ATPase and Ca(+2) ATPase activities and lipid peroxidation in blood of workers

Lead is considered one of the major environmental toxicants that causes hematological, neurological, and gastrointestinal dysfunction. In this study, the authors examined the relationship between lead and lipid peroxidation, lead and Na(+)-K(+) ATPase activity, and lead and Ca(+2) ATPase activity in blood of workers. The working group consisted of 30 male workers occupationally exposed to lead at least for 10 years. The control group consisted of 20 healthy male individuals not involved with job-related lead exposures. Blood lead content of the control group and the working group were 10.0 +/- 1.8 microg/dl and 317.3 +/- 47.6 microg/dl, respectively. Malondialdehyde (MDA) value of the working group (0.57 +/- 0.30 nmol MDA/ml) was significantly greater than MDA value of the control goup (0.17 +/- 0.02 nmol MDA/ml). In the working group, both Na(+)-K(+) ATPase activity (105.0 +/- 47.0 nmol Pi. mg protein(-1) x h(-1)) and Ca(+2) ATPase activity (58.0 +/- 40.0 nmol Pi. mg protein(-1) x h(-1)) were lower compared with the corresponding values of Na(+)-K(+) ATPase activity (247.0 +/- 41.0 nmol Pi. mg protein(-1) x h(-1)) and Ca(+2) ATPase activity (230.0 +/- 41.0 nmol Pi. mg protein(-1) x h(-1)) of normal controls. The results show that lead exposure causes inhibition of Na(+)-K(+) ATPase and Ca(+2) ATPase activities and also results in increased lipid peroxidation.

Alterations of the glutathione-redox balance induced by metals in CHO-K1 cells

The effects of cadmium (Cd(2+)), mercury (Hg(2+)), lead (Pb(2+)), copper (Cu(2+)) and nickel (Ni(2+)) on the glutathione (GSH)-redox cycle were assessed in CHO-K1 by the neutral red uptake inhibition (NR) assay (NR(6.25), NR(12.5) and NR(25)). Mercury proved to be the most and lead the least toxic of the metals tested. The effects on GSH content and intracellular specific activities of enzymes involved in the GSH-redox balance were measured after a 24-h exposure. Total GSH content increased significantly in cultures exposed to the lowest metal concentration assayed (NR(6.25)), but fell to below control values when exposed to concentrations equivalent to NR(25). Oxidised glutathione content dropped significantly at NR(6.25), while somewhat higher values were obtained for cultures exposed to higher doses. Glutathione peroxidase (Gpx) activities were 1.2-, 1.5-, 1.6-, 2.0- and 2.5-fold higher than untreated controls for cadmium, copper, mercury, nickel and lead, respectively, at concentrations equivalent to NR(6.25). Gpx activity declined at metal concentrations equivalent to NR(12.5) and NR(25). Glutathione reductase activity remained almost unchanged except at low doses of mercury, nickel and lead. Glutathione-S-transferase activity decreased at rising metal concentrations. The results suggest that a homeostatic defence mechanism was activated when cells were exposed to doses equivalent to NR(6.25) while the ability of the cells to respond weakened as the dose increased. A close relationship was also observed between metal cytotoxicity, total GSH content and the dissociation energy of the sulphur-metal bonds. These facts confirm the involvement of antioxidant defence mechanisms in the toxic action of these ions.

The role of oxidative stress in mechanisms of metal-induced carcinogenesis

Metals are necessary for the normal functioning of cells and the survival of organisms. However, exposure to higher than the physiological levels of several metals may lead to tumor development. Although the exact molecular mechanism(s) of metal-induced carcinogenesis is not clear, a vast body of evidence indicates that metal-induced generation of reactive oxygen species (ROS) may play a central role in this process. Two main pathways of ROS-induced effects are discussed in this chapter: (i) increased DNA damage induced either directly or indirectly by impeding DNA repair, and (ii) modulation of nuclear transcriptional factor activities, such as NF-kappaB and AP-1, through mitogen-activated protein kinases signal transduction mechanisms.

Role of oxidative stress and thiol antioxidant enzymes in nickel toxicity and resistance in strains of the green alga Scenedesmus acutus f. alternans

Treatment with Ni(NO3)2 leads to the formation of reactive oxygen species (ROS) in the green alga Scenedesmus acutus f. alternans, causing lipid peroxidation. This effect was stronger in a Ni-sensitive strain, UTEX72, than in a Ni-resistant strain, B4. In the resistant strain, Ni induced an increased ratio of reduced to oxidized glutathione (GSH:GSSG), whereas it caused a lowered ratio in the sensitive strain. Enzymes involved in the control of ROS were studied in these strains as well as two others that have shown different degrees of nickel resistance. The resistant strain, B4, which grows while containing large amounts of internal Ni, had much higher levels of glutathione reductase and catalase than the other strains. The sensitive strain, UTEX72, had higher levels of glutathione peroxidase, superoxide dismutase, and glucose-6-phosphate dehydrogenase than did strain B4. The resistant strains, Ni-Tol and Cu-Tol, derived from strain UTEX72, which are partly able to exclude Ni, had enzyme profiles that resembled that of UTEX72 more closely than that of B4. Treatment with 10 and 100 microM Ni for 4 or 22 h had complex effects on enzyme levels in all four strains. Ni decreased glutathione reductase in B4, slightly increased it in Ni-Tol and Cu-Tol, and did not affect the low levels of this enzyme in UTEX72. Ni lowered glutathione peroxidase in B4 and either did not affect it or slightly raised it in the other strains. Ni lowered catalase in B4 and did not affect the other strains. Superoxide dismutase was raised in B4 and Ni-Tol and lowered in Cu-Tol and UTEX72, and glucose-6-phosphate dehydrogenase was lowered in all four strains. These results suggest that one major mechanism of Ni resistance, especially in strain B4, may be the ability to combat the formation of ROS when exposed to this metal, likely by maintaining a high GSH:GSSG ratio.

Ni(2+), a double-acting inhibitor of neuronal nitric oxide synthase interfering with L-arginine binding and Ca(2+)/calmodulin-dependent enzyme activation

Ni(2+), a toxic and carcinogenic pollutant and one of the leading causes of contact dermatitis, is shown to inhibit neuronal nitric oxide synthase (nNOS) in a competitive, reversible manner with respect to the substrate l-arginine (K(i) = 30 +/- 4 microM). The IC(50) values were dependent on calmodulin (CaM) concentration, but proved independent of Ca(2+), tetrahydrobiopterin (BH(4)) and other essential cofactors. Ni(2+) also inhibited CaM-dependent cytochrome c reduction, NADPH oxidation, and H(2)O(2) production by nNOS. Overall, the action profile of Ni(2+) was suggestive of an unusual, double-acting inhibitor of nNOS affecting l-arginine-binding and Ca(2+)/CaM-dependent enzyme activation.

Redox-modulated pathways in inflammatory skin diseases

Inflammatory skin diseases account for a large proportion of all skin disorders and constitute a major health problem worldwide. Contact dermatitis, atopic dermatitis, and psoriasis represent the most prevalent inflammatory skin disorders and share a common efferent T-lymphocyte mediated response. Oxidative stress and inflammation have recently been linked to cutaneous damage in T-lymphocyte mediated skin diseases, particularly in contact dermatitis. Insights into the pathophysiology responsible for contact dermatitis can be used to better understand the mechanism of other T-lymphocyte mediated inflammatory skin diseases, and may help to develop novel therapeutic approaches. This review focuses on redox sensitive events in the inflammatory scenario of contact dermatitis, which comprise for example, several kinases, transcription factors, cytokines, adhesion molecules, dendritic cell surface markers, the T-lymphocyte receptor, and the cutaneous lymphocyte-associated antigen (CLA). In vitro and animal studies clearly point to a central role of several distinct but interconnected redox-sensitive pathways in the pathogenesis of contact dermatitis. However, clinical evidence that modulation of the skin's redox state can be used therapeutically to modulate the inflammatory response in contact dermatitis is presently not convincing. The rational for this discrepancy seems to be multi-faceted and complex and will be discussed.

Ellagic acid ameliorates nickel induced biochemical alterations: diminution of oxidative stress

Nickel, a major environmental pollutant is known for its clastogenic, toxic and carcinogenic potentials. The present investigation shows that ellagic acid proves to be exceptional in the amelioration of the nickel-induced biochemical alterations in serum, liver and kidney. Administration of nickel (250 micromol Ni/kg body wt) to female Wistar rats, resulted in increase in the reduced glutathione (GSH) content [kidney (*P<0.05) and liver (**P<0.001)] and Glutathione-S-transferase (GST) and glutathione reductase (GR) activities [kidney and liver, (**P<0.001)]. Ellagic acid treatment to the intoxicated rats leads to the formation of soluble ellagic acid-metal complex which facilitates excretion of nickel from the cell or tissue, thus ameliorating nickel-induced toxicity, as evident from the down regulation of GSH content, GST and GR activities with concomitant restoration of glutathione peroxidase (GPx) activity in liver and kidney. Our data shows that ellagic acid maintains cell membrane integrity through sequestration of metal ions from the extracellular fluid, as evident from the alleviated levels of serum glutamate oxaloacetate transaminase, (SGOT), serum glutamate pyruvate transaminase (SGPT) and lactate dehydrogenase (LDH) when compared to nickel treated group. Similarly, the enhanced blood urea nitrogen (BUN) and serum creatinine levels that are indicative of renal injury showed a reduction of about 45 and 40%, respectively. The data also show that treatment of ellagic acid after 30 min of nickel administration exhibits maximum inhibition in a dose-dependent manner. In summary, our data suggests that ellagic acid act as an effective chelating agent in suppressing nickel-induced renal and hepatic biochemical alterations.

Role of oxidative stress in nickel chloride-induced cell injury in rat renal cortical slices

Nickel chloride (NiCl2) induced lactate dehydrogenase (LDH) release and lipid peroxidation (LPO) in rat renal cortical slices in vitro in a concentration- (0-2 mM) and time- (0-4 hr) dependent manner, with initial significant LDH release occurring as early as 1 hr, whereas significant increase in LPO started 3 hr after exposure, suggesting that LPO results from renal cell injury. Both NiCl2-induced LDH release and LPO were prevented significantly by glutathione and dithiothreitol, suggesting that NiCl2-induced renal cell injury is dependent on thiols. However, such injury is not dependent solely on thiols, because (a) these thiols failed to inhibit completely the uptake of Ni2+ by the renal cortex, and (b) diethylmaleate pretreatment failed to increase NiCl2-induced cell injury further. Superoxide dismutase partially reduced the NiCl2-induced LDH release without affecting LPO and glutathione, whereas catalase did not affect such LDH release and LPO. Dimethylthiourea and DMSO completely prevented NiCl2-induced LPO, but only partially reduced LDH release. Deferoxamine prevented NiCl2-induced renal cell injury without affecting LPO and without significantly reducing Ni2+ uptake by the renal cortex, suggesting that nickel chelation is not important in such prevention of injury. NiCl2-induced inhibition of para-aminohippurate uptake was prevented significantly by thiols, deferoxamine, and dimethylthiourea. NiCl2-induced loss of cellular glutathione content was prevented significantly by thiols and deferoxamine, but not by superoxide dismutase and dimethylthiourea. These results suggest that LPO was not related to NiCl2-induced lethal renal cell injury, whereas such injury may be caused by the induction of the Fenton reaction, generating hydroxyl radicals.

Age-dependent renal accumulation of 4-hydroxy-2-nonenal (HNE)-modified proteins following parenteral administration of ferric nitrilotriacetate commensurate with its differential toxicity: implications for the involvement of HNE-protein adducts in oxidative stress and carcinogenesis

In this study, we show that the toxicity of ferric nitrilotriacetate (Fe-NTA) can be correlated with the tissue accumulation of 4-hydroxy-2-nonenal (HNE)-modified protein adducts. It is observed that the toxic manifestations of Fe-NTA gradually increase with the increasing age of animals. A dose of Fe-NTA which produces almost 100% mortality in aged rats causes 70% mortality in adults, 30% in pups, 20% in litters, and less than 10% in neonates. The age-dependent increase in its toxicity is also evident from the data of renal microsomal lipid peroxidation and hydrogen peroxide generation. No significant difference in the generation of H2O2 and induction of renal microsomal lipid peroxidation between saline- and Fe-NTA-treated neonates, litters, and pups could be observed. However, in adult rats, a significant increase in both of the parameters was observed which was even greater in aged rats. On the contrary, renal glutathione levels in these animals show an inverse relationship with the oxidant generation. In neonates, litters, and pups the maximum decrease of glutathione was up to 22%, whereas in adult and aged rats, the depletion was more than 60% of their respective saline-treated controls. Parallel to this data, blood urea nitrogen and creatinine, the indicators of renal damage, show a significant increase in Fe-NTA-treated adult and aged rats only, whereas no significant alterations were observed in other groups. Similarly, the magnitude of ODC induction and [3H]thymidine incorporation was much higher in aged and adult rats in comparison to other groups of animals after Fe-NTA treatment. Additionally, the immunohistochemical localization studies show a significant increase in HNE-modified protein adducts in kidney of adult and aged rats, whereas no significant staining was observed in other groups. A similar increase in the level of protein carbonyls has also been observed with the increasing age of rats. These data suggest that the toxicity of Fe-NTA increases with the increasing age of rats and correlates with the accumulation of HNE-modified protein adducts. It may also be speculated that Fe-NTA-mediated renal toxicity leading to carcinogenesis may be related to the tissue accumulation of HNE-modified protein adducts. However, further studies are needed to establish a definite role of HNE-modified proteins in Fe-NTA-mediated carcinogenesis.

Nickel-catalyzed N-terminal oxidative deamination in peptides containing histidine at position 2 coupled with sulfite oxidation

Peptides containing histidine at position 2 were observed to undergo spontaneous N-terminal oxidative deamination in aqueous solution in the presence of Ni(II), sulfite, and ambient oxygen. The reaction resulted in the formation of a free carbonyl on the N-terminal alpha-carbon (alpha-ketoamide) and was catalytic with respect to nickel. This oxidative deamination was confirmed by 13C NMR, 1H NMR, mass spectrometry, and chemical tests. No evidence of modification of histidine was found. It was demonstrated that the nickel-dependent N-terminal oxidative deamination also occurred in His-2 peptides using potassium peroxymonosulfate (oxone) as an oxidant. When oxone was used, oxygen was not required for the deamination to proceed. The results suggest that both nickel-catalyzed reactions (sulfite and oxygen, and oxone) produce an imine intermediate that spontaneously hydrolyzes to form the free carbonyl. These findings may provide a physiologically relevant model for oxidative carbonyl formation in vivo, as well as a useful method for producing a site-specific carbonyl on peptides and proteins.

Potassium bromate (KBrO3) induces renal proliferative response and damage by elaborating oxidative stress

Many chemical compounds which induce oxidative stress in the tissue produce carcinogenesis either alone or act as a tumor promoter in carcinogen-initiated animals after prolonged exposure. Here, we report that potassium bromate (KBrO3) induces renal proliferative response and damage by elaborating oxidative stress. KBrO3 administration dose dependently induced renal ornithine decarboxylase (ODC) activity several fold compared to its activity in saline-treated rats. Similarly renal DNA synthesis which has been measured as [3H]thymidine incorporation in DNA also increases. KBrO3 administration also depleted the level of renal glutathione and glutathione reductase activity in a time dependent manner. The maximum depletion in the levels of renal glutathione and glutathione reductase activity was observed 3 h after KBrO3 treatment which was 60 and 40%, respectively, of saline-treated controls. Parallel to these changes, a sharp increase in the blood urea nitrogen and serum creatinine levels was observed which is indicative of the concurrent renal damage. These results suggest that oxidant generating KBrO3 acts as a potent proliferator of kidney and acts by producing oxidative damage.

Depletion of iron and ascorbate in rodents diminishes lung injury after silica

Exposures of the lung to iron chelates can be associated with an injury. The catalysis of oxygen-based free radicals is postulated to participate in this injury. Such oxidant generation by mineral oxide particles can be dependent on availability of both iron and a reductant. We tested the study hypothesis that lung injury after silica is associated with the availability of both iron and ascorbate in the host by depleting this metal and reductant in the lungs of rats and guinea pigs, respectively. Rats were fed either a normal diet or a diet deficient of iron. After 30 days, animals were instilled with either saline or 1.0 mg Minusil-5 silica. Relative to saline, silica significantly increased neutrophils and lavage protein. Iron depletion significantly diminished both the cellular influx and injury but only at 1 week after silica exposure. Guinea pigs were provided either a normal diet supplemented with 1,000 ppm vitamin C or a diet deficient in ascorbate. After 14 days, the guinea pigs were instilled with either saline or 1.0 mg silica. Silica exposure significantly increased neutrophils and lavage protein. Ascorbate depletion significantly diminished the influx of inflammatory cells and injury at both 1 day and 1 week after silica exposure. We conclude that host concentrations of both iron and ascorbate can affect lung injury after silica exposure.

Lipid peroxidation in liver of mice administrated with nickel chloride: with special reference to trace elements and antioxidants

The relationship between Ni-induced hepatic lipid peroxidation (LPO) and the concentrations of Ni and trace elements was investigated in male ICR mice. The protective effects of antioxidants were also examined. Hepatic LPO and the concentrations of Ni, Fe, Cu, and Zn in the liver were enhanced after an ip injection of nickel chloride (NiCl2). Dose-response studies were conducted on male mice with different groups being injected with 50, 85, and 170 micromol Ni/kg. LPO increased significantly in a dose-dependent manner. In time-course studies, mice were administrated NiCl2 (170 micromol Ni/kg) and killed at intervals of 6, 12, 24, and 48 h after injection. Both LPO and the accumulation of Ni, Fe, Cu, and Zn in the liver showed a significantly positive time-course relationship after NiCl2 injection. At 1 h and 24 h after a single ip injection of 170 micromol Ni/kg, the mice were given an ip injection of ascorbic acid (vit C), glutathione (GSH), and selenium (Se). Vit C and GSH significantly decreased both the level of hepatic LPO and the concentration of Ni in the liver, but did not decrease the accumulation of Fe, Cu, and Zn. However, LPO in the experimental group of mice was different significantly from that in the control group. In conclusion, the results suggest that Ni-induced hepatic LPO may result from increasing the amounts of Ni, Fe, and Cu, since these elements are involved in the generation of hydroxyl radical by inducing the Fenton reaction, thus instigating the Ni-mediated hepatic LPO. The protective effects of vit C and GSH in hepatic LPO result not only from removing the oxygen reactive species, but also from decreasing the Ni concentration.

Biochemical and clinical aspects of nickel toxicity

Nickel is an important metal in the automobile industry, in electronics, as a catalyst in chemical processes, in nickel-cadmium batteries and accumulators, in many household products, and in cheap jewelry. Almost everyone in the industrially developed countries may be in daily contact with nickel. Cutaneous nickel allergy (contact dermatitis) is very common, as typically 15% to 20% of the population have positive results in epicutaneous testing. Nickel sensitization may be avoided by restricting contact with objects that release nickel ions through sweat on skin. Because nickel is also carcinogenic to man, causing upper respiratory tract and lung malignancies, advanced control of exposure at workplaces is necessary. Control can be accomplished either by measuring the exposure in the occupational environment or through urinary nickel analysis by applying so-called biological monitoring. As covalent nickel adducts have not been found in DNA, the carcinogenic effect of nickel is probably related to its lipid-peroxidation properties, which induce DNA-strand gaps and breaks and DNA-protein crosslinks. The negative effect of nickel ions on glycoprotein metabolism may explain the nephrotoxic effects of excessive exposure.

The detection of pollutant impact in marine environments: condition index, oxidative DNA damage, and their associations with metal bioaccumulation in the Sydney rock oyster Saccostrea commercialis

Specimens of the Sydney rock oyster Saccostrea commercialis were deployed for a 3-month period at control and sewage disturbed marine locations in the Hunter Region, New South Wales, Australia. The DNA damage product,8-hydroxyguanine, was measured by GC/MS-SIM from chromatin extracts of the gill tissues of oysters to assess oxidative damage. The levels ranged from 11.5 to 18.8 modified bases per 10(7) guanine bases. Although the condition indices were significantly different between the Redhead control site (178.3+/-3. 6) and the Burwood sewage disturbed location (140.4+/-4.4), no significant differences in 8-hydroxyguanine concentrations were detected between the sites, and the concentration of 8-hydroxyguanine was not correlated to condition index. However, levels of the DNA base modification were correlated with the concentrations of bioaccumulated lead (r=0.84, P=0.036). This association provides in vivo evidence that the bioaccumulation of lead results in oxidative damage to DNA. An additional control and sewage disturbed site were included to investigate the relationship between heavy metal bioaccumulation and the condition index of deployed oysters. After the 3-month deployment period, the condition index was negatively correlated to concentrations of bioaccumulated mercury (r=-0.80, P<0.001), cobalt (r=-0.65, P<0.01), and nickel (r=-0.69, P<0.01), suggesting a strong negative influence of these metals at relatively low concentrations on the physiological condition of the oysters.

Modulation of cellular antioxidant defense activities by sodium arsenite in human fibroblasts

Many studies have shown that oxygen radicals can be produced during arsenic metabolism. We report here that in human fibroblasts (HFW cells) sodium arsenite exposure caused increased formation of fluorescent dichlorofluorescein (DCF) by oxidation of the nonfluorescent form. The enhanced DCF fluorescence was inhibited by a radical scavenger, butylated hydroxytoluene. The effects of sodium arsenite treatment on cellular antioxidant activities were then examined. Treatment of HFW cells with sodium arsenite resulted in a significant increase in heme oxygenase activity and ferritin level. Sodium arsenite-enhanced heme oxygenase synthesis was inhibited by co-treatment of cells with the antioxidants sodium azide and dimethyl sulfoxide. Furthermore, sodium arsenite treatment did not apparently affect glucose-6-phosphate dehydrogenase activity, but resulted in significantly increased glutathione levels and superoxide dismutase activity, slightly decreased glutathione peroxidase activity, and significantly decreased catalase activity. Sodium arsenite toxicity was partly reduced by addition of catalase to the culture medium. These results imply that arsenite can enhance oxidative stress in HFW cells.

Crude extracts of hepatoprotective plants, Solanum nigrum and Cichorium intybus inhibit free radical-mediated DNA damage

The presence of plant extracts of Solanum nigrum and Cichorium intybus in the reaction mixture containing calf thymus DNA and free radical generating system protect DNA against oxidative damage to its deoxyribose sugar moiety. The effect was dependent on the concentration of plant extracts. However, the effect of Cichorium intybus was much pronounced as compared to the effect of Solanum nigrum. These studies suggest that the observed hepatoprotective effect of these crude plant extracts may be due to their ability to suppress the oxidative degradation of DNA in the tissue debris.

The role of free radicals in toxicity and disease

Free radicals are defined as atoms or molecules that contain one or more unpaired electrons. The toxicity of many xenobiotics is associated with the metabolic activation of foreign compounds to form free radicals or with the production of reactive oxygen species as superoxide anion, hydroxyl radicals or hydrogen peroxide which are responsible for the tissue damaging effects as lipid peroxidation, and DNA and protein damage. Oxidative stress associated with production of reactive oxygen species is believed to be involved not only in the toxicity of xenobiotics but also in the pathophysiology of aging, and various age-related diseases, including cataracts, atherosclerosis, neoplastic diseases, diabetes, diabetic retinopathy, chronic inflammatory diseases of the gastrointestinal tract, aging of skin, diseases associated with cartilage, Alzheimer's disease, and other neurologic disorders. The cellular sources of free radicals and reactive oxygen species, the biological targets of free radicals, and clinical conditions which are associated with free radical production and tissue damage are reviewed. In addition, potential therapeutic approaches to the prevention of free radical damage are considered. Free radical-induced injury can explain many clinical conditions.

Possible role of oxidative damage in metal-induced carcinogenesis

This review presents and evaluates evidence relevant to the mechanisms of metal carcinogenicity with special emphasis on the emerging hypothesis of the oxidative nature of metals' effect on DNA. The carcinogenic transition metals are capable of in vivo binding with the cell nucleus and causing promutagenic damage that includes DNA base modifications, inter- and intramolecular crosslinking of DNA and proteins, DNA strand breaks, rearrangements, and depurination. The chemistry of that damage and the resulting mutations observed in vitro and in metal-induced tumors are both characteristic for oxidative attack on DNA. The underlying mechanism involves various kinds of active oxygen and other radical species arising from metal-catalyzed redox reactions of O2, H2O2, lipid peroxides, and others, with certain amino acids, peptides, and proteins. Other metal-mediated pathogenic effects, such as enhancement of lipid peroxidation, stimulation of inflammation, inhibition of cellular antioxidant defenses, and inhibition of DNA repair, may also contribute to that mechanism. Thus far, published data revealing the oxidative character of metal-induced promutagenic DNA alterations are particularly strong for two of the most powerful human metal carcinogens, chromium and nickel. However, without excluding contribution of other effects, the promotion of oxidative damage tends to take the leading role in explaining mechanisms of carcinogenicity and acute toxicity of certain other metals as well.

Effect of nickel(II) and tetraglycine on hydroxylation of the guanine moiety in 2'-deoxyguanosine, DNA, and nucleohistone by hydrogen peroxide

The purpose of this study was to determine whether the Ni(II)-tetraglycine complex system (NiG4) that is known to disproportionate H2O2 at pH > or = 8 can catalyze oxidation of the guanine residues in 2'-deoxyguanosine (dG), calf thymus DNA, and calf thymus nucleohistone (NH) by H2O2 at physiological pH. Incubation of dG with H2O2 in the presence of NiG4 at 37 degrees C, produced two effects: (a) formation of 8-hydroxy-2'-deoxyguanosine (8-OH-dG) and (b) decomposition of dG to 2,6-diamino-4-hydroxy-5-formamidopyrimidine and several low molecular weight unidentified products. The magnitude of both effects depended on incubation time (1-48 h), H2O2 concentration (7.5-40 mM), NiG4 concentration (0.1 or 1 mM), and pH (6.0-8.0). The effects were not detected below pH 6 and above pH 8.0. For 0.1 mM NiG4 and 7.5 mM H2O2, production of 8-OH-dG from dG (0.75 mM) during 24 h at 37 degrees C was significantly lower than from NH (1 mg/ml) or DNA (0.5 mg/ml), indicating possible specific effects that might be related to the strength of interaction of NiG4 with dG, NH, or DNA. The results indicate production of hydroxyl radical or other oxidizing species in the reaction of H2O2 with NiG4 at pH 7-8. Reactions like this may be relevant to the mechanisms of Ni(II)-mediated oxidative damage, observed in vitro and in vivo, which may contribute to the toxic and carcinogenic effects of this metal.

Generation of free radicals from lipid hydroperoxides by Ni2+ in the presence of oligopeptides

The generation of free radicals from lipid hydroperoxides by Ni2+ in the presence of several oligopeptides was investigated by electron spin resonance (ESR) utilizing 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap. Incubation of Ni2+ with cumene hydroperoxide or t-butyl hydroperoxide did not generate any detectable free radical. In the presence of glycylglycylhistidine (GlyGlyHis), however, Ni2+ generated cumene peroxyl (ROO.) radical from cumene hydroperoxide, with the free radical generation reaching its saturation level within about 3 min. The reaction was first order with respect to both cumene hydroperoxide and Ni2+. Similar results were obtained using t-butyl hydroperoxide, but the yield of t-butyl peroxyl radical generation was about 7-fold lower. Other histidine-containing oligopeptides such as beta-alanyl-L-histidine (carnosine), gamma-aminobutyryl-L-histidine (homocarnosine), and beta-alanyl-3-methyl-L-histidine (anserine) caused the generation of both cumene alkyl (R.) and cumene alkoxyl (RO.) radicals in the reaction of Ni2+ with cumene hydroperoxide. Similar results were obtained using t-butyl hydroperoxide. Glutathione also caused generation of R. and RO. radicals in the reaction of Ni2+ with cumene hydroperoxide but the yield was approximately 25-fold greater than that produced by the histidine-containing peptides, except GlyGlyHis. The ratio of DMPO/R. and DMPO/RO. produced with glutathione and cumene hydroperoxide was approximately 3:1. Essentially the same results were obtained using t-butyl hydroperoxide except that the ratio of DMPO/R. to DMPO/RO. was approximately 1:1. The free radical generation from cumene hydroperoxide reached its saturation level almost instantaneously while in the case of t-butyl hydroperoxide, the saturation level was reached in about 3 min. In the presence of oxidized glutathione, the Ni2+/cumene hydroperoxide system caused DMPO/.OH generation from DMPO without forming free hydroxyl radical. Since glutathione, carnosine, homocarnosine, and anserine are considered to be cellular antioxidants, the present work suggests that instead of protecting against oxidative damage, these oligopeptides may facilitate the Ni(2+)-mediated free radical generation and thus may participate in the mechanism(s) of Ni2+ toxicity and carcinogenicity.

The relationship between nickel chloride-induced peroxidation and DNA strand breakage in rat liver

Inorganic nickel chloride induces hepatic DNA strand breaks, chromosome aberrations, and lipid peroxidation under in vitro and in vivo conditions. The objective of this research was to determine if a relationship exists between NiCl2 genotoxicity and lipid peroxidation in vivo. Male Sprague-Dawley rats (210-250 g) were dosed with 0.56 or 0.75 mmol/kg NiCl2 subcutaneously and euthanized after specific time periods, ranging from 30 min to 24 hr. Livers were perfused and excised for the measurement of nickel content using atomic absorption spectrometry, lipid peroxidation using a thiobarbituric acid assay, and DNA strand breakage using single-stranded DNA extraction and the diaminobenzoic acid assay. The lower dose (0.56 mmol/kg) did not induce lipid peroxidation or strand breakage. The higher dose (0.75 mmol/kg) induced DNA strand breakage at 4 hr and lipid peroxidation at 12 hr in rat liver. Nickel was seen to accumulate in liver nuclei of rats receiving 0.75 mmol/kg. Deferoxamine (1 g/kg, ip, 15 min before the NiCl2 injection) completely inhibited DNA strand breakage at 4 hr but had no effect on lipid peroxidation. This suggests that lipid peroxidation is not causally related to genetic damage. NiCl2-induced DNA strand breakage may be caused by the induction of the Fenton reaction, generating hydroxyl radicals.

Carcinogen-mediated oxidant formation and oxidative DNA damage

This article reviews the experimental data that points to formation of reactive oxygen species (ROS) and oxidative DNA base damage as being important contributors to cancer development. Particular emphasis is placed on the role they play in genetic changes occurring during tumor promotion. A number of structurally different anticarcinogenic agents inhibit ROS production and oxidative DNA damage as they inhibit inflammation and tumor promotion. This underlines the importance of ROS and oxidative genetic damage to the carcinogenic process. It also points to the possibility that some types of cancer may be preventable if the cycles of tumor promotion can be interrupted.

Nickel-induced renal lipid peroxidation in different strains of mice: concurrence with nickel effect on antioxidant defense systems

Lipid peroxidation (LPO) and active oxygen-detoxifying enzymes, catalase (CAT), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD), as well as glutathione (GSH) and some related enzymes, glutathione-S-transferase (GST) and glutathione reductase (GSSG-R) were assayed in kidneys of BALB/cAnNCr (BALB/c), C3H/HeNCr-MTV- (C3H), B6C3F1, and C57BL/6NCr (C57BL) mice 3-48 h after a single intraperitoneal injection of 170 mumol nickel (II) acetate (NiAcet)/kg body wt. In control mice that received 340 mumol sodium acetate/kg, the levels of enzymes and GSH did not significantly vary in time but were different in various strains. The basal activities of CAT and SOD in in the controls were highest in BALB/c and lowest in C57BL mice (1.8:1.0 and 1.4:1.0 respectively) in contrast to that of GSH-Px which was highest in B6CF1 and lowest in BALB/c (1.3:1.0; P less than 0.05). The strain ranking of control concentrations of renal GSH was B6C3F1 greater than C3H greater than or equal to C57BL greater than BALB/c (2.8:2.4:2.3:1.0), and that of GSSG-R was C3H greater than or equal to BALB/c greater than B6C3F1 greater than or equal to C57BL [corrected] (1.5:1.4:1.1:1.0). The basal activity of renal GST in control mice was 25% lower in C3H than in any of the other 3 strains. The renal LPO levels in the control mice did not vary among strains. Nickel treatment transiently increased renal LPO levels in the control mice did not vary among strains. Nickel treatment transiently increased renal LPO in the BALB/c mice by 100%, in B6C3F1 by 30%, and in C57BL by 20% (P less than 0.05), with no significant effect in C3H mice. Thus, the magnitude of nickel-induced renal LPO was greatest in the strain that is lowest in GSH and GSH-Px, but not in CAT and SOD. Nickel effects on GSH and the enzymes were time-dependent and included transient inhibition or enhancement of different proportions with no apparent strain- and/or base level-related patterns, or concurrence with LPO. The results emphasize the importance of GSH and GSH-Px for preventing nickel-induced oxidative cell damage.

Nickel (II) as a temporary catalyst for hydroxyl radical generation

Many in vivo studies show peroxidative damage during nickel toxicity, suggesting the generation of oxygen-activated species. Using the murexide (5,5'-nitrilodibarbituric acid ammonium salt) bleaching technique, we attempted to spectroscopically determine whether there are any histidylpeptides-Ni (II) complexes able to catalyze a nickel-dependent reduction of hydrogen peroxide leading to free oxygen radical production. We show that peptides containing the glycyl-glycyl-L-histidyl sequence trigger nickel-dependent production of oxygen radicals which can damage proteins, cause a rapid loss of tryptophan and a significant production of bityrosine and also induce peroxidation of polyunsaturated fatty acids. During the reaction, the histidine residue in the peptide is selectively damaged and breakdown of the peptide switches off hydroxyl-radical production.

Nickel induced lipid peroxidation in the rat: correlation with nickel effect on antioxidant defense systems

Lipid peroxidation (LPO) and alterations in cellular systems protecting against oxidative damage were determined in the liver, kidney and skeletal muscle of male F344/NCr rats, 1 h to 3 days after a single intraperitoneal (i.p.) injection of 107 mumol nickel(II)acetate per kg body weight. At 3 h, when tissue nickel concentrations were highest, the following significant (at least, P less than 0.05) effects were observed: in kidney, increased LPO (by 43%), increased renal iron (by 24%), decreased catalase (CAT) and glutathione peroxidase (GSH-Px) activities (both by 15%), decreased glutathione (GSH) concentration (by 20%), decreased glutathione reductase (GSSG-R) activity (by 10%), and increased glutathione-S-transferase (GST) activity (by 44%); the activity of superoxide dismutase (SOD) and gamma-glutamyl transferase (GGT), as well as copper concentration, were not affected. In the liver, nickel effects included increased LPO (by 30%), decreased CAT and GSH-Px activities (both by 15%), decreased GSH level (by 33%), decreased GSSG-R activity (by 10%) and decreased GST activity (by 35%); SOD, GGT, copper, and iron remained unchanged. In muscle, nickel treatment decreased copper content (by 43%) and the SOD activity (by 30%) with no effects on other parameters. In blood, nickel had no effect on CAT and GSH-Px, but increased the activities of alanine-(ALT) and aspartate-(AST) transaminases to 330% and 240% of the background level, respectively. In conclusion, nickel treatment caused profound cell damage as indicated by increased LPO in liver and kidney and leakage of intracellular enzymes, ALT and AST to the blood. The time pattern of the resulting renal and hepatic LPO indicated a possible contribution to its magnitude from an increased concentration of nickel and concurrent inhibition of CAT, GSH-Px and GSSG-R, but not from increased iron or copper levels. The oxidative damage expressed as LPO was highest in the kidney and lowest in the muscle, which concurs with the corresponding ranking of nickel uptake by these tissues.

Effects of nickel on catalase activity in vitro and in vivo

The decomposition of H2O2 by catalase (CAT) was measured in a cell-free in vitro system in the presence of 0-24 mM Ni(II) or Mg(II) as well as in red blood cells (RBCs), and in post-mitochondrial fractions of liver and kidney of rats injected i.p. with 95 mumol/kg of nickel acetate. In vitro, immediately after addition of Ni(II), the inhibition of the catalytic activity of CAT (at 25 degrees C and pH 7.2) was directly proportional to Ni(II) concentration while Mg(II) had no effect. Following in vivo treatment, activity of CAT in the RBCs was decreased by 12% at 16 h, but had returned to control level by 48 h post injection. Hepatic CAT activity remained unchanged during the first 24 h after the injection but subsequently decreased by 25% at 48 h. Renal CAT first increased by 17% above the control levels at 16 h, returned to the control level at 24 h, and finally decreased by 27% at 48 h post injection. These changes neither concurred with the corresponding tissue concentrations of Ni(II) nor resembled the concentration/effect relationships observed in vitro. Thus, the mechanism by which Ni(II) inhibits CAT activity in vivo is more complex than that in vitro and cannot be solely related to direct Ni(II)-CAT interaction.