Synthesis of Cr(IV)-GSH, its identification and its free hydroxyl radical generation: a model compound for Cr(VI) carcinogenicity

Chromium removal from aqueous solutions using new silica gel conjugates of desferrioxamine or diethylenetriaminepentaacetic acid

Desferrioxamine (DFO) and diethylenetriaminepentaacetic acid (DTPA) conjugated with silica gel (IDFOSG and IDTPASG, respectively) were evaluated as adsorbents for chromium in aqueous solutions. Different parameters affecting adsorption such as pH, sorbent dosage, contact time, sample volume and potential of interfering ions have been optimized. The optimum pH for chromium binding was 4 for 100 mg of adsorbents at 5 min of table shaking with 5 mL sample volume of chromium solutions. Langmuir adsorption model described the removal of chromium ions. The adsorption capacity for chromium was 90% for IDFOSG and 83% for IDTPASG in single solutions, and at least 75% in multielemental solutions. Considering the removal efficacy, regeneration and stability, DFO-grafted silica gel was generally superior to its DTPA counterpart and may be applied to the removal of traces of chromium species from natural waters.

Hexavalent chromium induces reactive oxygen species and impairs the antioxidant power of human erythrocytes and lymphocytes: Decreased metal reducing and free radical quenching ability of the cells

The toxicity of hexavalent chromium [Cr(VI)] in biological systems is thought to be closely associated with the generation of free radicals and reactive oxygen species. These species are produced when Cr(VI) is reduced to its trivalent form in the cell. This process results in oxidative stress due to an imbalance between the detoxifying ability of the cell and the production of free radicals. We have studied the effect of potassium dichromate (K2Cr2O7), a [Cr(VI)] compound, on the antioxidant power of human erythrocytes and lymphocytes under in vitro conditions. Incubation of erythrocytes and lymphocytes with different concentrations of K2Cr2O7 resulted in a marked dose-dependent decrease in reduced glutathione and an increase in oxidized glutathione and reactive oxygen species levels. The antioxidant power of the cells was decreased, as determined by metal reducing and free radical quenching assays. These results show that [Cr(VI)] upregulates the generation of reactive oxygen species and, as a consequence, the cellular antioxidant defences are compromised. The resulting oxidative stress may contribute to Cr(VI)-induced cellular damage.

Toxicity of Glutathione-Binding Metals: A Review of Targets and Mechanisms

Mercury, cadmium, arsenic and lead are among priority metals for toxicological studies due to the frequent human exposure and to the significant burden of disease following acute and chronic intoxication. Among their common characteristics is chemical affinity to proteins and non-protein thiols and their ability to generate cellular oxidative stress by the best-known Fenton mechanism. Their health effects are however diverse: kidney and liver damage, cancer at specific sites, irreversible neurological damages with metal-specific features. Mechanisms for the induction of oxidative stress by interaction with the cell thiolome will be presented, based on literature evidence and of experimental findings.

Role of Bacillus subtilis error prevention oxidized guanine system in counteracting hexavalent chromium-promoted oxidative DNA damage

Chromium pollution is potentially detrimental to bacterial soil communities, compromising carbon and nitrogen cycles that are essential for life on earth. It has been proposed that intracellular reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] may cause bacterial death by a mechanism that involves reactive oxygen species (ROS)-induced DNA damage; the molecular basis of the phenomenon was investigated in this work. Here, we report that Bacillus subtilis cells lacking a functional error prevention oxidized guanine (GO) system were significantly more sensitive to Cr(VI) treatment than cells of the wild-type (WT) strain, suggesting that oxidative damage to DNA is involved in the deleterious effects of the oxyanion. In agreement with this suggestion, Cr(VI) dramatically increased the ROS concentration and induced mutagenesis in a GO-deficient B. subtilis strain. Alkaline gel electrophoresis (AGE) analysis of chromosomal DNA of WT and ΔGO mutant strains subjected to Cr(VI) treatment revealed that the DNA of the ΔGO strain was more susceptible to DNA glycosylase Fpg attack, suggesting that chromium genotoxicity is associated with 7,8-dihydro-8-oxodeoxyguanosine (8-oxo-G) lesions. In support of this notion, specific monoclonal antibodies detected the accumulation of 8-oxo-G lesions in the chromosomes of B. subtilis cells subjected to Cr(VI) treatment. We conclude that Cr(VI) promotes mutagenesis and cell death in B. subtilis by a mechanism that involves radical oxygen attack of DNA, generating 8-oxo-G, and that such effects are counteracted by the prevention and repair GO system.

Literature review of the role of hydroxyl radicals in chemically-induced mutagenicity and carcinogenicity for the risk assessment of a disinfection system utilizing photolysis of hydrogen peroxide

We have developed a new disinfection system for oral hygiene, proving that hydroxyl radicals generated by the photolysis of 1 M hydrogen peroxide could effectively kill oral pathogenic microorganisms. Prior to any clinical testing, the safety of the system especially in terms of the risk of carcinogenicity is examined by reviewing the literature. Previous studies have investigated indirectly the kinds of reactive oxygen species involved in some sort of chemically-induced mutagenicity in vitro by using reactive oxygen species scavengers, suggesting the possible involvement of hydroxyl radicals. Similarly, possible involvement of hydroxyl radicals in some sort of chemically-induced carcinogenicity has been proposed. Notably, it is suggested that the hydroxyl radical can play a role in heavy metal-induced carcinogenicity that requires chronic exposure to the carcinogen. In these cases, hydroxyl radicals produced by Fenton-like reactions may be involved in the carcinogenicity. Meanwhile, potential advantages have been reported on the use of the hydroxyl radical, being included in host immune defense by polymorphonuclear leukocytes, and medical applications such as for cancer treatment and antibiotics. From these, we conclude that there would seem to be little to no risk in using the hydroxyl radical as a disinfectant for short-term treatment of the oral cavity.

Review of chromium (VI) apoptosis, cell-cycle-arrest, and carcinogenesis

Hexavalent chromium combines with glutathione in chloride intracellular channel carrier to form tetravalent and pentavalent chromium in plasma and organelle membranes. It also combines with NADH/NADPH to form pentavalent chromium in mitochondria. Tetravalent- and pentavalent- chromium (directly and indirectly) mediated DNA double strand breaks activate DNA damage signaling sensors: DNA-dependent-protein-kinase signals p53-dependent intrinsic mitochondrial apoptosis, and ataxia-telangiectasia-mutated and ataxia-telangiectasia-Rad3-related signal cell-arrest for DNA repair. Tetravalent chromium may be the most potent species since it causes DNA breaks and somatic recombination, but not apoptosis. Upon further failure of apoptosis and senescence/DNA-repair, damaged cells may become immortal with loss-of-heterozygosity and genetic plasticity.

Cr(VI) induces mitochondrial-mediated and caspase-dependent apoptosis through reactive oxygen species-mediated p53 activation in JB6 Cl41 cells

Cr(VI) compounds are known to cause serious toxic and carcinogenic effects. Cr(VI) exposure can lead to a severe damage to the skin, but the mechanisms involved in the Cr(VI)-mediated toxicity in the skin are unclear. The present study examined whether Cr(VI) induces cell death by apoptosis or necrosis using mouse skin epidermal cell line, JB6 Cl41 cells. We also investigated the cellular mechanisms of Cr(VI)-induced cell death. This study showed that Cr(VI) induced apoptotic cell death in a dose-dependent manner, as demonstrated by the appearance of cell shrinkage, the migration of cells into the sub-G1 phase, the increase of Annexin V positively stained cells, and the formation of nuclear DNA ladders. Cr(VI) treatment resulted in the increases of mitochondrial membrane depolarization and caspases activation. Electron spin resonance (ESR) and fluorescence analysis revealed that Cr(VI) increased intracellular levels of reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion radical in dose-dependent manner. Blockage of p53 by si-RNA transfection suppressed mitochondrial changes of Bcl-2 family composition, mitochondrial membrane depolarization, caspase activation and PARP cleavage, leading to the inhibition of Cr(VI)-induced apoptosis. Further, catalase treatment prevented p53 phosphorylation stimulated by Cr(VI) with the concomitant inhibition of caspase activation. These results suggest that Cr(VI) induced a mitochondrial-mediated and caspase-dependent apoptosis in skin epidermal cells through activation of p53, which are mainly mediated by reactive oxidants generated by the chemical.

Chromate causes sulfur starvation in yeast

Chromate is a widespread pollutant as a waste of human activities. However, the mechanisms underlying its high toxicity are not clearly understood. In this work, we used the yeast Saccharomyces cerevisiae to analyse the physiological effects of chromate exposure in a eukaryote cell model. We show that chromate causes a strong decrease of sulfate assimilation and sulfur metabolite pools suggesting that cells experience sulfur starvation. As a consequence, nearly all enzymes of the sulfur pathway are highly induced as well as enzymes of the sulfur-sparing response such as Pdc6, the sulfur-poor pyruvate decarboxylase. The induction of Pdc6 was regulated at the mRNA level and dependent upon Met32, a coactivator of Met4, the transcriptional activator of the sulfur pathway. Finally, we found that chromate enters the cells mainly through sulfate transporters and competitively inhibits sulfate uptake. Also consistent with a competition between the two substrates, sulfate supplementation relieves chromate toxicity. However, the data suggest that the chromate-mediated sulfur depletion is not simply due to this competitive uptake but would also be the consequence of competitive metabolism between the two compounds presumably at another step of the sulfur assimilation pathway.

The antioxidant and pro-oxidant activity of vitamin C and trolox in vitro: a comparative study

The antioxidant and pro-oxidant properties of ascorbic acid (vitamin C) and the water-soluble analogue of alpha-tocopherol (trolox) were compared. Trolox has advantages over alpha-tocopherol, the latter being only lipid-soluble due to the presence of a carboxyl group in lieu of a phytol chain which imparts trolox with water solubility. Trolox is used as a standard antioxidant in biochemical studies against which the antioxidant capacity of compounds is compared. Although ascorbic acid and tocopherols possess strong antioxidant properties, they might also exhibit pro-oxidant properties in the presence of free transition metals. Thus, reactions detailed in this study were performed in the presence of Cr(VI) in an effort to investigate the potential of ascorbic acid and trolox to generate hydroxyl radicals in a Fenton-like reaction. Results obtained were derived from reactions containing the same concentration of ascorbic acid and trolox under identical experimental conditions. Hydroxyl radical formation was observed in the reaction of Cr(VI) with ascorbic acid resulting from ascorbic acid auto-oxidation and H2O2 formation. Hydroxyl radical formation was only detected in the reaction mixture containing Cr(VI) and trolox following the addition of H2O2.

Release of chromium from orthopaedic arthroplasties

Many orthopaedic implants are composed of alloys containing chromium. Of particular relevance is the increasing number of Cobalt Chromium bearing arthroplasies being inserted into young patients with osteoarthritis. Such implants will release chromium ions. These patients will be exposed to the released chromium for over 50 years in some cases. The subsequent chromium ion metabolism and redistribution in fluid and tissue compartments is complex. In addition, the potential biological effects of chromium are also controversial, including DNA and chromosomal damage, reduction in CD8 lymphocyte levels and possible hypersensitivity reactions (ALVAL). The establishment of these issues and the measurement of chromium in biological fluids is the subject of this review.

S-allylcysteine scavenges singlet oxygen and hypochlorous acid and protects LLC-PK1 cells of potassium dichromate-induced toxicity

It has been found that S-allylcysteine (SAC), a garlic-derived compound, has in vivo and in vitro antioxidant properties. In addition, it is known that SAC is able to scavenge different reactive oxygen or nitrogen species including superoxide anion (O(2)(-)), hydrogen peroxide (H(2)O(2)), hydroxyl radical (OH()), and peroxynitrite anion (ONOO(-)) although the IC(5O) values for each reactive species has not been calculated and the potential ability of SAC to scavenge singlet oxygen ((1)O(2)) and hypochlorous acid (HOCl) has not been explored. The purposes of this work was (a) to explore the potential ability of SAC to scavenge (1)O(2) and HOCl, (b) to further characterize the O(2)(-), H(2)O(2), OH(), and ONOO(-) scavenging ability of SAC by measuring the IC(50) values using in vitro assays, and (c) to explore the potential ability of SAC to ameliorate the potassium dichromate (K(2)Cr(2)O(7))-induced cytotoxicity in LLC-PK1 cells in which oxidative stress is involved. The scavenging activity was compared against the following reference compounds: N-acetylcysteine for O(2)(-), sodium pyruvate for H(2)O(2), dimethylthiourea for OH(), lipoic acid and glutathione for (1)O(2), lipoic acid for HOCl, and penicillamine for ONOO(-). It was found that SAC was able to scavenge concentration-dependently all the species assayed with the following IC(5O) (mean+/-SEM, mM): O(2)(-) (14.49+/-1.67), H(2)O(2) (68+/-1.92), OH() (0.68+/-0.06), (1)O(2) (1.93+/-0.27), HOCl (2.86+/-0.15), and ONOO(-) (0.80+/-0.05). When the ability of SAC to scavenge these species was compared to those of the reference compounds it was found that the efficacy of SAC (a) to scavenge O(2)(-), H(2)O(2), OH(), and ONOO(-) was lower, (b) to scavenge HOCl was similar, and (c) to scavenge (1)O(2) was higher. In addition, it was found that SAC was able to prevent K(2)Cr(2)O(7)-induced toxicity in LLC-PK1 cells in culture. It was showed for the first time that SAC is able to scavenge (1)O(2) and HOCl and to ameliorate the K(2)Cr(2)O(7)-induced toxicity.

Protective effects of garlic powder against potassium dichromate-induced oxidative stress and nephrotoxicity

Potassium dichromate (K(2)Cr(2)O(7))-induced nephrotoxicity is associated with oxidative stress. In the present work the effect of garlic powder, a recognized antioxidant, on K(2)Cr(2)O(7)-induced nephrotoxicity and oxidative stress was studied. Rats were fed a 2% garlic powder diet for 1 month. A single injection of K(2)Cr(2)O(7) (15 mg/kg) to rats induced tubule interstitial damage and an increase in the following markers of renal injury 2 days later: blood urea nitrogen (4.6-fold), serum creatinine (9.7-fold), proteinuria (35.9-fold), urinary excretion of N-acetyl-beta-d-glucosaminidase (12.9-fold) and glutathione-S-transferase (2.3-fold) and a decrease of 65% in serum glutathione peroxidase activity. In addition, K(2)Cr(2)O(7) injection increased the following nitrosative and oxidative stress markers in kidney: 3-nitrotyrosine (1.9-fold), 4-hydroxy-2-nonenal (2.1-fold), malondialdehyde (1.8-fold) and protein carbonyl content (1.7-fold). It was found that garlic powder feeding was able to prevent by 44-71% the alterations in the markers of renal injury studied, by 55% the histological damage, and by 47-100% the increase in markers of oxidative and nitrosative stress. It is concluded that the ability of garlic powder to ameliorate K(2)Cr(2)O(7)-induced renal injury is associated with its antioxidant properties. Our data support the use of garlic powder as a renoprotective agent.

Pro-oxidative vs antioxidative properties of ascorbic acid in chromium(VI)-induced damage: an in vivo and in vitro approach

The effect of antioxidant ascorbic acid (vitamin C) pretreatment on chromium(VI)-induced damage was investigated using the yeast Saccharomyces cerevisiae as a model organism. The objective of this study was to pretreat yeast cells with the antioxidant ascorbic acid in an effort to increase cell tolerance against reactive chromium intermediates and reactive oxygen species formed during chromium(VI) reduction. Intracellular oxidation was estimated using the fluorescence indicators dihidro-2,7-dichlorofluorescein, dihydroethidium and dihydrorhodamine 123. The role of ascorbic acid pretreatment on chromium(VI) toxicity was determined by measuring mitotic gene conversion, reverse mutations, 8-OHdG, hydroxyl radical, superoxide anion and chromium(V) formation. The chromium content in the biomass was determined by flame atomic absorption spectrometry. In the absence of chromium, ascorbic acid effectively protected the cells against endogenous reactive oxygen species formed during normal cellular metabolism. In vitro measurements employing EPR and the results of supercoiled DNA cleavage revealed that the pro-oxidative action of ascorbic acid during Cr(VI) reduction was concentration-dependent and that harmful hydroxyl radical and Cr(V) had formed following Cr(VI) reduction. However, the in vivo results highlighted the important role of increased cytosol reduction capacity related to modification of Cr(V) formation, increased chromium accumulation, better scavenging ability of superoxide anions and hydrogen peroxide, and consequently decreased cytotoxicity and genotoxicity in ascorbic acid pretreated cells. Ascorbic acid influenced Cr(VI) toxicity both as a reducing agent, by decreasing Cr(V) persistence, and as an antioxidant, by decreasing intracellular superoxide anion and hydrogen peroxide formation and by quenching free radicals formed during Cr(VI) to Cr(III) reduction. Increased 8-OHdG and decreased reduced glutathione in ascorbic acid-treated cells might induce an endogenous antioxidant defense system and thus increase cell tolerance against subsequent Cr-induced stress.

Lung carcinogenesis: pivotal role of metals in tobacco smoke

Although significant progress has been made in unraveling the molecular mechanisms responsible for tobacco smoke toxicity and carcinogenicity, only limited information is available concerning the mechanisms by which tar particles and the gaseous phase constituents of tobacco smoke participate and contribute to carcinogenic processes in lung cancer. The present review critically evaluates how metals contained in the tar particles and the gaseous phase of tobacco smoke play a leading role in the carcinogenic process, taking into consideration the physiology and pathophysiology of the bronchial epithelium. Overwhelmingly, the published data indicate that the bronchopulmonary epithelial cells may represent the first and most critical line of defense against cigarette smoke.

Pro-oxidative versus antioxidative reactions between Trolox and Cr(VI): The role of H(2)O(2)

The effect of the Vitamin E model compound Trolox in reactions with Cr(VI) in the presence or absence of hydrogen peroxide was investigated. The aim of this study was to establish and discuss potential Trolox-mediated pro-oxidative reactions. The importance of the Trolox:Cr(VI) ratio in the Cr(VI) reduction process was determined from the EPR spectra and DNA cleavage reactions. In the absence of hydrogen peroxide, reduction of Cr(VI) occurred with concomitant oxidation of Trolox to the phenoxyl radical. In the presence of hydrogen peroxide, Cr(V), produced by the reduction of Cr(VI), reduced hydrogen peroxide to the hydroxyl radical. The latter was detected by spin-trapping the methyl radical following reaction with N-methyl sulfoxide. During Cr(VI) reduction with Trolox, DNA single- or double-strand breaks due to Trolox radical formation were not observed. Relaxed DNA appeared only when H(2)O(2) was added to Trolox/Cr(VI) mixtures most probably due to hydroxyl radical formation during the redox cycling of Cr(V/IV)-species. Fenton-like reactions do not play a significant role in the Trolox/Cr(VI) system in the absence of added H(2)O(2).

Review of the evidence regarding the carcinogenicity of hexavalent chromium in drinking water

Recent analyses have revealed that 38% of municipal sources of drinking water in California have detectable levels of hexavalent chromium. This observation provided new impetus to characterize the carcinogenic risk associated with oral exposure to hexavalent chromium in drinking water. Notwithstanding the well-characterized increases in cancer associated with inhalation exposure to this chemical, the marked reduction of hexavalent chromium to trivalent chromium in the stomach suggests that exposure to hexavalent chromium in drinking water may not pose a carcinogenic risk. A reevaluation of studies that investigated the toxicokinetics, the genotoxicity, and the mechanism of carcinogenicity of hexavalent chromium, as well as the available human and animal cancer studies, was undertaken to determine if there is evidence that exposure to this chemical in drinking water may pose a carcinogenic risk. Mechanistic studies suggest the potential for a carcinogenic response if hexavalent chromium enters cells. Both toxicokinetic and genotoxicity studies indicate that a portion of an orally administered dose of hexavalent chromium is absorbed and gets into cells of several tissues, causing DNA damage. The only lifetime oral study of hexavalent chromium in animals conducted thus far yielded a statistically significant increase in stomach tumors compared to controls. Also, in a limited-term cancer study, co-exposure to hexavalent chromium in drinking water and ultraviolet light produced skin tumors in mice. The only available cancer study of humans exposed to hexavalent chromium in drinking water revealed a statistically significant increase in stomach tumors. Moreover, a meta-analysis of occupational studies also revealed a statistically significant increase in stomach cancers. The increases in stomach tumors in both human and animal studies, along with the toxicokinetic, genotoxic, and mechanistic data, suggest that oral exposure to this agent appears to pose a carcinogenic risk.

Time course study of oxidative and nitrosative stress and antioxidant enzymes in K2Cr2O7-induced nephrotoxicity

Background

Potassium dichromate (K₂Cr₂O₇)-induced nephrotoxicity is associated with oxidative and nitrosative stress. In this study we investigated the relation between the time course of the oxidative and nitrosative stress with kidney damage and alterations in the following antioxidant enzymes: Cu, Zn superoxide dismutase (Cu, Zn-SOD), Mn-SOD, glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT).

Methods

Nephrotoxicity was induced in rats by a single injection of K₂Cr₂O₇. Groups of animals were sacrificed on days 1,2,3,4,6,8,10, and 12. Nephrotoxicity was evaluated by histological studies and by measuring creatinine clearance, serum creatinine, blood urea nitrogen (BUN), and urinary excretion of N-acetyl-β-D-glucosaminidase (NAG) and total protein. Oxidative and nitrosative stress were measured by immunohistochemical localization of protein carbonyls and 3-nitrotyrosine, respectively. Cu, Zn-SOD, Mn-SOD, and CAT were studied by immunohistochemical localization. The activity of total SOD, CAT, GPx, and GR was also measured as well as serum and kidney content of chromium and urinary excretion of NO₂ ^-/NO₃^-. Data were compared by two-way analysis of variance followed by a post hoc test.

Results

Serum and kidney chromium content increased reaching the highest value on day 1. Nephrotoxicity was made evident by the decrease in creatinine clearance (days 1–4) and by the increase in serum creatinine (days 1–4), BUN (days 1–6), urinary excretion of NAG (days 1–4), and total protein (day 1–6) and by the structural damage to the proximal tubules (days 1–6). Oxidative and nitrosative stress were clearly evident on days 1–8. Urinary excretion of NO₂^-/NO₃^- decreased on days 2–6. Mn-SOD and Cu, Zn-SOD, estimated by immunohistochemistry, and total SOD activity remained unchanged. Activity of GPx decreased on days 3–12 and those of GR and CAT on days 2–10. Similar findings were observed by immunohistochemistry of CAT.

Conclusion

These data show the association between oxidative and nitrosative stress with functional and structural renal damage induced by K₂Cr₂O₇. Renal antioxidant enzymes were regulated differentially and were not closely associated with oxidative or nitrosative stress or with kidney damage. In addition, the decrease in the urinary excretion of NO₂^-/NO₃^- was associated with the renal nitrosative stress suggesting that nitric oxide was derived to the formation of reactive nitrogen species involved in protein nitration.

Genetic and cellular mechanisms in chromium and nickel carcinogenesis considering epidemiologic findings

Genetic and environmental interactions determine cancer risks but some cancer incidence is primarily a result of inherited genetic deficits alone. Most cancers have an occupational, viral, nutritional, behavioral or iatrogenic etiology. Cancer can sometimes be controlled through broad public health interventions including industrial hygiene and engineering controls. Chromium and nickel are two human carcinogens associated with industrial exposures where public health measures apparently work. Carcinogenic mechanisms of these metals are examined by electron-spin-resonance-spectroscopy and somatic-mutation-and-recombination in Drosophila melanogaster in this report. Both metals primarily affect initiation processes in cancer development suggesting important theoretical approaches to prevention and followup.

Crystalline and water soluble Cr(4+) and Cr(5+) model compounds for chromium toxicity studies

We discuss two complexes of Cr(4+) for their possible utility as models for Cr toxicity studies. They are Cr(dien)(O2)2(.)H2O (dien = diethylenetriamine) and Cr(NH3)3(O2)2, which have been recently characterized by x-ray diffraction and magnetic techniques. We present their optical and infrared absorption spectra as quick aids in their identification procedure. We also summarize the general properties of some well-characterized Cr(5+) compounds. All of these compounds are water soluble with the Cr(5+) samples being fairly stable in basic solutions. They can all be prepared as pure crystals with a shelf life of over 2 years when stored in a refrigerator.

Protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity in rats: the indispensability of HO-1 preinduction and lack of association with some antioxidant enzymes

We have shown that the ameliorative effect of stannous chloride (SnCl2) pretreatment on potassium dichromate (K2Cr2O7)-induced renal damage 24 h after K2Cr2O7 injection was associated with the induction of heme oxygenase-1 (HO-1). In this work we evaluated: (a) if the protective effect of SnCl2 (given 12 h before K2Cr2O7) is associated with changes in the renal activity of HO-1, superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and catalase (CAT) 24 and 48 h after K2Cr2O7 injection, and (b) if HO-1 induction is indispensable before K2Cr2O7 injection. It was found that the protective effect of SnCl2 on renal function was observed both at 24 and 48 h reaching its maximum at 24 h when HO-1 expression was higher. Cu,Zn-SOD, Mn-SOD, and GR activities remained unchanged whereas GPx and CAT activities decreased at 48 h in K2Cr2O7-treated rats. The activity of Cu,Zn-SOD, Mn-SOD, GPx, CAT, and GR was unchanged in the SnCl2-treated rats. To fulfill the objective (b) groups of rats treated with K2Cr2O7 and SnCl2 (given at the same time or 12 h after K2Cr2O7) were studied 24 h after K2Cr2O7-injection. The simultaneous injections of SnCl2 and K2Cr2O7 had no protective effect whereas the injection of SnCl2 12 h after K2Cr2O7 exacerbated renal damage. In conclusion, the protective effect of SnCl2 on K2Cr2O7-induced nephrotoxicity is associated with HO-1 induction and not with other antioxidant enzymes (Cu,Zn-SOD, Mn-SOD, GPx, GR, and CAT) and SnCl2 has a preventive and not a therapeutic effect on renal damage induced by K2Cr2O7.

HO-1 induction attenuates renal damage and oxidative stress induced by K2Cr2O7

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme; its inducible isozyme HO-1 protects against some types of acute tissue injury. The expression and functional role of HO-1 in rats with renal injury induced by potassium dichromate (K(2)Cr(2)O(7)) was investigated in this work. Rats were studied 24 h after a single injection of K(2)Cr(2)O(7). To address the possible protective effect of HO-1 in this experimental model, this enzyme was induced by an injection of stannous chloride (SnCl(2)) 12 h before K(2)Cr(2)O(7) administration. The functional role of HO-1 in K(2)Cr(2)O(7) + SnCl(2)-treated animals was tested by inhibiting HO activity with an injection of zinc (II) protoporphyrin IX (ZnPP) 18 h before K(2)Cr(2)O(7). In K(2)Cr(2)O(7)-treated rats: (i) renal HO-1 content, measured by Western blot, increased 2.6-fold; and, (ii) renal nitrotyrosine and protein carbonyl content, markers of oxidative stress, increased 3.5- and 1.36-fold, respectively. Renal damage and oxidative stress were ameliorated and HO-1 content was increased in the K(2)Cr(2)O(7) + SnCl(2) group. The attenuation of renal injury and oxidative stress was lost by the inhibition of HO activity in K(2)Cr(2)O(7) + SnCl(2) + ZnPP-treated animals. Our data suggest that HO-1 overexpression induced by SnCl(2) is responsible for the attenuation of renal damage and oxidative stress induced by K(2)Cr(2)O(7).

New genes involved in chromate resistance in Ralstonia metallidurans strain CH34

Chromate resistance in Ralstonia metallidurans CH34 is based on chromate efflux catalyzed by ChrA efflux pumps. The bacterium harbors two chromate resistance determinants, the previously known chr(1) on plasmid pMOL28 (genes chrI, chrB(1), chrA(1), chrC, chrE, chrF(1)) and chr(2) on the chromosome (genes chrB(2), chrA(2), chrF(2)). Deletion of the genes chrI, chrC, chrA(2), chrB(2) and chrF(2) influenced chromate resistance and transcription from a chrBp(1) ::lacZ fusion. Deletion of the plasmid-encoded gene chrB(1) did not change chromate resistance or chrBp(1) regulation. Northern hybridization and primer-extension experiments were used to study transcription of the plasmid-encoded chr(1) determinant. Transcription of chrB(1), chrA(1) and chrC was induced by chromate. The presence of sulfate influenced transcription positively. The chrBp(1), chrAp(1) and chrCppromoters showed some similarity to heat-shock promoters. Transcription of the gene rpoH encoding a putative heat-shock sigma factor was also induced by chromate, but rpoH was not essential for chromate resistance. The ChrC protein was purified as a homotetramer and exerted superoxide dismutase activity. Thus, possible regulators for chromate resistance (ChrI, ChrB(1), ChrB(2), ChrF(1), and ChrF(2)) and an additional detoxification system (ChrC) were newly identified as parts of chromate resistance in R. metallidurans.

Biological reactive intermediates that mediate chromium (VI) toxicity

1. Addition of Cr VI (dichromate) to isolated rat hepatocytes results in rapid glutathione oxidation, reactive oxygen species (ROS) formation, lipid peroxidation, decreased mitochondrial membrane potential and lysosomal membrane rupture before hepatocyte lysis occurred. 2. Cytotoxicity was prevented by "ROS" scavengers, antioxidants, and glutamine (ATP generator). Hepatocyte dichlorofluorescin oxidation (to determine ROS/Cr V formation) was inhibited by mannitol (a hydroxyl radical scavenger) or butylated hydroxyanisole and butylated hydroxytoluene (antioxidants). 3. The Cr VI reductive mechanism required for toxicity are not known. Cytotoxicity was also prevented by cytochrome P450 inhibitors, particularly CYP 2E1 inhibitors, but not inhibitors of DT diaphorase or glutathione reductase. This suggests that P450 reductase and/or reduced cytochrome P450 contributes to Cr VI reduction to Cr IV. 4. Glutathione depleted hepatocytes were resistant to Cr (VI) toxicity and much less dichlorofluorescin oxidation occurred. Reduction of dichromate by glutathione or cysteine in vitro was also accompanied by oxygen uptake and was inhibited by Mn II (a Cr IV reductant ). Cr VI induced cytotoxicity and ROS formation was also inhibited by Mn II which suggests that Cr IV and Cr IV.GSH mediate "ROS" formation in isolated hepatocytes. 5. In conclusion Cr VI cytotoxicity is associated with mitochondrial/lysosomal toxicity by the biological reactive intermediates Cr IV and "ROS".

Combining Drosophila melanogaster somatic-mutation-recombination and electron-spin-resonance-spectroscopy data to interpret epidemiologic observations on chromium carcinogenicity

Lung cancers are significantly increased among workers exposed to chromate (Cr6+, Cr3+), chromium pigments (Cr6+) and chromium plating (Cr6+). Chromium lung burdens and cancer risk increase proportionately with duration of employment at long latencies. However, this epidemiologic information alone is insufficient in determining whether Cr6+ or Cr3+ are equally important in causing cancer. We have attempted to combine epidemiologic data with data from the Drosophila melanogaster somatic-mutation-recombination-test and from the in vitro electron-spin-resonance spectroscopy study to demonstrate that following somatic recombination plays a more important role than somatic mutation in chromium carcinogenesis. Cr4+ is more important than Cr5+ or Cr6+ in inducing somatic recombination while Cr6+ produces more and bigger clones than Cr4+ in somatic mutation. Cr3+ produces negative results in this fruit-fly wing-spot-assay. When the larvae and flies exposed to Cr6+ and Cr4+ are examined by ESR, only Cr5+ and Cr3+ are found. Thermodynamic parameters deltaE, deltaH, and deltaS are also estimated from these latter experiments to explain the relative importance of Cr6+, Cr4+, Cr3+ in chromium carcinogenesis among exposed industrial workers.

Role of reactive oxygen species and p53 in chromium(VI)-induced apoptosis

Apoptosis is a programmed cell death mechanism to control cell number in tissues and to eliminate individual cells that may lead to disease states. The present study investigates chromium(VI) (Cr(VI))-induced apoptosis and the role of reactive oxygen species (ROS) and p53 in this response. Treatment of human lung epithelial cells (A549) with Cr(VI) caused apoptosis as measured by DNA fragmentation, mitochondria damage, and cell morphology. Cr(VI)-induced apoptosis is contributed to ROS generation, resulting from cellular reduction of Cr(VI) as measured by flow cytometric analysis of the stained cells, oxygen consumption, and electron spin resonance spin trapping. Scavengers of ROS, such as catalase, aspirin, and N-acetyl-L-cysteine, decreased Cr(VI)-induced apoptosis, whereas NADPH and glutathione reductase, enhancers of Cr(VI)-induced ROS generation, increased it. p53 is activated by Cr(VI), mostly by ROS-mediated free radical reactions. Cr(VI)-induced ROS generation occurred within a few minutes after Cr(VI) treatment of the cells, whereas p53 induction took at least 5 h. The level of Cr(VI)-induced apoptosis was similar in both p53-positive cells and p53-negative cells independent of p53 status in the early stage (0-3 h) of Cr(VI) treatment. However, at the later stage (3-24 h), the level of the apoptosis is higher in p53-positive cells than in p53-negative cells. These results suggest that ROS generated through Cr(VI) reduction is responsible to the early stage of apoptosis, whereas p53 contributes to the late stage of apoptosis and is responsible for the enhancement of Cr(VI)-induced apoptosis at this stage.

ESR characterization and metallokinetic analysis of Cr(V) in the blood of rats given carcinogen chromate(VI) compounds

It has been shown that bio-trace metal elements are related to many diseases and the aging process. For many years, carcinogen hexavalent chromium (VI) has been known to be toxic to animals, but its dynamic toxicological mechanism is not sufficiently elucidated. Bioinorganic chemistry in terms of metallokinetic analysis of beneficial or toxic metal ions and their complexes is an important investigation for understanding their biochemical and physiological roles. We have tried to examine the real-time behavior of paramagnetic metal ions and complexes in animals, in which electron spin resonance (ESR) was capable of measuring paramagnetic species in chemical and biological systems. On the basis of our previous results on stable nitroxide spin probes, we have developed the in vivo blood circulation monitoring-electron spin resonance (BCM-ESR) method to analyze time-dependent ESR signal changes due to paramagnetic metal ions and their complexes in real time. When K2Cr2O7 or Na2Cr2O7 in saline was intravenously administered to rats, two ESR signals due to pentavalent chromium(V) were detectable in the circulating blood of rats. Cr(V) detected in the blood was indicated to be in the CrO(O4) and CrO(S2O2) coordination modes after the study on model complexes. From the changes of ESR signal intensities due to Cr(V) in the blood, the metallokinetic parameters were obtained using the pharmacokinetic analysis and the curve-fitting methods. The obtained results are important for understanding carcinogen chromate in terms of the formation of Cr(V) in animals. In addition, we propose the BCM-ESR method, which is useful to analyze the disposition of paramagnetic metal species in the blood of living animals.

Cr(IV) causes activation of nuclear transcription factor-kappa B, DNA strand breaks and dG hydroxylation via free radical reactions

Electrophoretic mobility shift, DNA strand breakage assays and electron spin resonance (ESR) spin trapping were used to investigate the activation of nuclear transcription factor (NF)-kappa B, DNA strand breakage and 2'-deoxyguanosine hydroxylation induced by Cr(IV), as well the role of free radical reactions in these processes. Incubation of synthesized Cr(IV)-glutathione complex with cultured Jurkat cells resulted in activation of DNA binding activity of NF-kappa B. Cr(VI) is also able to induce NF-kappa B activation through Cr(V) and Cr(IV) intermediates generated during the reduction of Cr(VI) by the cells. Cr(III) did not cause observable NF-kappa B activation due to its inability to cross cell membranes. Cr(IV)-induced NF-kappa B activation is dose-dependent. Catalase inhibited the activation while superoxide dismutase enhanced it. The metal chelator, deferoxamine, and hydroxyl (.OH) radical scavengers, sodium formate and aspirin, also inhibited the NF-kappa B activation. Electrophoretic assays using lambda Hind III linear DNA showed that, in the presence of H2O2, Cr(IV) is capable of causing DNA strand breaks. Deferoxamine, sodium formate and aspirin inhibited the DNA strand breaks. HPLC measurements also show that .OH radical generated by the Cr(IV)-mediated reaction with H2O2 was capable of causing 2'-deoxyguanosine (dG) hydroxylation to generate 8-hydroxyguanosine (8-OHdG). The relative magnitude of 8-OHdG formation correlated with the generation of .OH radicals. ESR spin trapping measurements showed that reaction of Cr(IV) with H2O2 generated .OH radicals, which were inhibited by deferoxamine, sodium formate and aspirin. The results show that Cr(IV) can cause NF-kappa B activation, DNA strand breaks and dG hydroxylation through .OH radical-initiated reactions. This reactive chromium intermediate may play an important role in the mechanism of Cr(VI)-induced carcinogenesis. The results also suggest that the Cr(IV)-glutathione complex may be used as a model compound to study the role of Cr(IV) in Cr(VI) carcinogenicity.

Hydroxopentaamminechromium(III) promoted phosphorylation of bovine serum albumin: its potential implications in understanding biotoxicity of chromium

Evidence for chromium(III) induced phosphorylation of a biomarker protein bovine serum albumin (BSA) is presented. Radiolabelled adenosine 5'-triphosphate (ATP) was reacted with BSA in the presence of various Cr(III) salts. While [Cr(NH3)5(H2O)]3+ brought about phosphorylation of BSA, several Cr(III) complexes, viz. [Cr(bpy)3]3+, [Cr(phen)3]3+, [Cr(en)3]3+, [Cr(salen)(H2O)2]+ and [Cr(salprn)(H2O)2]+, did not phosphorylate BSA. The Cr(III) mediated the transfer of gamma- and alpha-phosphates but not the adenine and the sugar moieties of the ATP molecule to BSA. The observed stoichiometry was 0.75 mol Pi to mol BSA for the gamma-phosphate and 0.5 mol Pi to mol BSA for the alpha-phosphate of ATP. The presence of serine phosphate and threonine phosphate was detected in the hydrolysate of phosphorylated BSA by means of comparison of Rf values with authentic samples of phosphoserine and phosphothreonine after chromatographic separation and autoradiography. [Cr(NH3)5(H2O)]3+ at pH 7.4 is known to exist as the conjugate base [Cr(NH3)5(OH)]2+ and is capable of ligand substitution involving metal-oxygen bond retention. Such anation reaction of [Cr(NH3)5(OH)]2+ with ATP subsequently leads to the esterification of alcoholic hydroxyl groups of serine and threonine of BSA. Possible consequences of chromium(III) induced in vivo phosphorylation of proteins are discussed.