On the hydroxyl radical formation in the reaction between hydrogen peroxide and biologically generated chromium(V) species

Overlooked role of aqueous chromate (VI) as a photosensitizer in enhancing the photochemical reactivity of ferrihydrite and production of hydroxyl radical

The reactive oxygen species (ROS) photochemically generated from natural iron minerals have gained significant attention. Amidst the previous studies on the impact of heavy metal ions on ROS generation, our study addresses the role of the anion Cr(VI), with its intrinsic photoactivity, in influencing ROS photochemical generation with the co-presence of minerals. We investigated the transformation of inorganic/organic pollutants (Cr(VI) and benzoic acid) at the ferrihydrite interface, considering sunlight-mediated conversion processes (300-1000 nm). Increased photochemical reactivity of ferrihydrite was observed in the presence of aqueous Cr(VI), acting as a photosensitizer. Meanwhile, a positive correlation between hydroxyl radical (•OH) production and concentrations of aqueous Cr(VI) was observed, with a 650% increase of •OH generation at 50 mg L-1 Cr(VI) compared to systems without Cr(VI). Our photochemical batch experiments elucidated three potential pathways for •OH photochemical production under varying wet chemistry conditions: (1) ferrihydrite hole-mediated pathway, (2) chromium intermediate O-I-mediated pathway, and (3) chromium intermediates CrIV/V-mediated pathway. Notably, even in the visible region (> 425 nm), the promotion of aqueous Cr(VI) on •OH accumulation was observed in the presence of ferrihydrite and TiO2 suspensions, attributed to Cr(VI) photosensitization at the mineral interface. This study sheds light on the overlooked role of aqueous Cr(VI) in the photochemical reactivity of minerals, thereby enhancing our understanding of pollutant fate in acid mining-impacted environments.

Implantation of Bacillus pseudomycoides Chromate Transporter Increases Chromate Tolerance in Bacillus subtilis

Chromium of anthropogenic origin contaminates the environment worldwide. The toxicity of chromium, a group I human carcinogen, is greatest when it is in a hexavalent oxidation state, Cr(VI). Cr(VI) is actively transported into the cell, triggering oxidative damage intracellularly. Due to the abundance of unspecific intracellular reductants, any microbial species is capable of bio-transformation of toxic Cr(VI) to innocuous Cr(III), however, this process is often lethal. Only some bacterial species are capable of sustaining the vegetative growth in the presence of a high concentration of Cr(VI) and thus operate as self-sustainable bioremediation agents. One of the successful microbial Cr(VI) detoxification strategies is the activation of chromate efflux pumps. This work describes transplantation of the chromate efflux pump from the potentially pathogenic but highly Cr resistant Bacillus pseudomycoides environmental strain into non-pathogenic but only transiently Cr tolerant Bacillus subtilis strain. In our study, we compared the two Bacillus spp. strains harboring evolutionarily diverged chromate efflux proteins. We have found that individual cells of the Cr-resistant B. pseudomycoides environmental strain accumulate less Cr than the cells of B. subtilis strain. Further, we found that survival of the B. subtilis strain during the Cr stress can be increased by the introduction of the chromate transporter from the Cr resistant environmental strain into its genome. Additionally, the expression of B. pseudomycoides chromate transporter ChrA in B. subtilis seems to be activated by the presence of chromate, hinting at versatility of Cr-efflux proteins. This study outlines the future direction for increasing the Cr-tolerance of non-pathogenic species and safe bioremediation using soil bacteria.

Transcriptome Analysis Reveals Cr(VI) Adaptation Mechanisms in Klebsiella sp. Strain AqSCr

Klebsiella sp. strain AqSCr, isolated from Cr(VI)-polluted groundwater, reduces Cr(VI) both aerobically and anaerobically and resists up 34 mM Cr(VI); this resistance is independent of the ChrA efflux transporter. In this study, we report the whole genome sequence and the transcriptional profile by RNA-Seq of strain AqSCr under Cr(VI)-adapted conditions and found 255 upregulated and 240 downregulated genes compared to controls without Cr(VI) supplementation. Genes differentially transcribed were mostly associated with oxidative stress response, DNA repair and replication, sulfur starvation response, envelope-osmotic stress response, fatty acid (FA) metabolism, ribosomal subunits, and energy metabolism. Among them, genes not previously associated with chromium resistance, for example, cybB, encoding a putative superoxide oxidase (SOO), gltA2, encoding an alternative citrate synthase, and des, encoding a FA desaturase, were upregulated. The sodA gene encoding a manganese superoxide dismutase was upregulated in the presence of Cr(VI), whereas sodB encoding an iron superoxide dismutase was downregulated. Cr(VI) resistance mechanisms in strain AqSCr seem to be orchestrated by the alternative sigma factors fecl, rpoE, and rpoS (all of them upregulated). Membrane lipid analysis of the Cr(IV)-adapted strain showed a lower proportion of unsaturated lipids with respect to the control, which we hypothesized could result from unsaturated lipid peroxidation followed by degradation, together with de novo synthesis mediated by the upregulated FA desaturase-encoding gene, des. This report helps to elucidate both Cr(VI) toxicity targets and global bacterial response to Cr(VI).

Cr(VI) Sorption from Aqueous Solution: A Review

Hexavalent chromium (Cr(VI)) in water systems is a major hazard for living organisms, including humans. The most popular technology currently used to remove Cr(VI) from polluted water is sorption for its effectiveness, ease of use, low cost and environmental friendliness. The electrostatic interactions between chromium species and the sorbent matrix are the main determinants of Cr(VI) sorption. The pH plays a central role in the process by affecting chromium speciation and the net charge on sorbent surface. In most cases, Cr(VI) sorption is an endothermic process whose kinetics is satisfactorily described by the pseudo second-order model. A critical survey of the recent literature, however, reveals that the thermodynamic and kinetic parameters reported for Cr(VI) sorption are often incorrect and/or erroneously interpreted.

Response to chromate challenge by marine Staphylococcus sp. NIOMR8 evaluated by differential protein expression

Liquid Chromatography-Mass Spectrometry-Quadrupole Time of Flight (LC/MS QToF) protein profiling of marine-derived Staphyloccous gallinarum NIOMR8 was carried out to evaluate proteins conferring chromate (Cr⁶⁺) resistance and possible metabolic pathways that were altered as a result. Expressional (up or down-regulation) responses to varying Cr⁶⁺ (0, 50, 100, 150, and 200 µg mL^- 1) concentrations varied, with as many as 346 proteins identified. Most number of proteins-their numbers in parentheses-were up-regulated when grown in medium with 50 µg mL^- 1 (162) and, down-regulated in medium with 100 (281) or 200 µg mL^- 1 Cr⁶⁺ (280). Among these, eight proteins were commonly up-regulated, while 58 were commonly down-regulated across all conditions of Cr⁶⁺. Expression of protein moieties in metabolic pathways like translation (38), transcription (14), replication (18) and repair (4), metabolism of carbohydrates (26), amino acids (27), nucleotides (17), and membrane transport (21) was evidenced. Up-regulation patterns suggest that reduction of molecular oxygen (5), DNA repair (4) and peptide misfolding (7) were the potential protective mechanisms employed to counter Cr⁶⁺ stress. Additionally, proteins associated with biofilm and cell wall biogenesis highlight their hypothetical involvement in toxicity tolerance. Results also indicate that at higher concentrations of Cr⁶⁺, down-regulation of functional proteins impedes normal cellular functions.

Melatonin protects against chromium (VI) induced hepatic oxidative stress and toxicity: Duration dependent study with realistic dosage

The present study was undertaken to assess the degree of oxidative stress and toxic effects induced by chromium on hepatic tissue in male Wistar rats exposed to a realistic dosage of Cr(VI) (20 mg/kg/b.w./day) through drinking water, based on the levels of these metals found in the environment, for a duration of 15, 30 and 60 days. The protective effect of melatonin (10 mg/kg) was also studied by simultaneous administration with the metal. Levels of enzymatic and non-enzymatic antioxidants as well as lipid peroxidation were assessed. There was a significant decrease in enzymatic as well as non-enzymatic antioxidants and an increase in the lipid peroxidation level, which were prevented and maintained at near-normal levels by the administration of melatonin in all treatment periods. Metal accumulation was maximal at 15 days, with gradual decreases till 60 days. Histopathological observations also demonstrated the fact that Cr (VI) exposure leads to cytological lesions in the hepatic tissue promoting cellular necrotic/apoptotic changes, while melatonin was able to counteract insults induced by Cr (VI) at all treatment periods. It also prevented alterations in insulin and glucose levels. Overall, the present study suggests a duration-dependent effect of Cr on hepatic oxidative stress and cytotoxicity and shows the potent activity of melatonin in preventing the negative effects of Cr (VI).

Contaminant-induced oxidative stress in fish: a mechanistic approach

The presence of reactive oxygen species (ROS) in living organisms was described more than 60 years ago and virtually immediately it was suggested that ROS were involved in various pathological processes and aging. The state when ROS generation exceeds elimination leading to an increased steady-state ROS level has been called "oxidative stress." Although ROS association with many pathological states in animals is well established, the question of ROS responsibility for the development of these states is still open. Fish represent the largest group of vertebrates and they inhabit a broad range of ecosystems where they are subjected to many different aquatic contaminants. In many cases, the deleterious effects of contaminants have been connected to induction of oxidative stress. Therefore, deciphering of molecular mechanisms leading to such contaminant effects and organisms' response may let prevent or minimize deleterious impacts of oxidative stress. This review describes general aspects of ROS homeostasis, in particular highlighting its basic aspects, modification of cellular constituents, operation of defense systems and ROS-based signaling with an emphasis on fish systems. A brief introduction to oxidative stress theory is accompanied by the description of a recently developed classification system for oxidative stress based on its intensity and time course. Specific information on contaminant-induced oxidative stress in fish is covered in sections devoted to such pollutants as metal ions (particularly iron, copper, chromium, mercury, arsenic, nickel, etc.), pesticides (insecticides, herbicides, and fungicides) and oil with accompanying pollutants. In the last section, certain problems and perspectives in studies of oxidative stress in fish are described.

Algal photosynthetic responses to toxic metals and herbicides assessed by chlorophyll a fluorescence

Chlorophyll a fluorescence is established as a rapid, non-intrusive technique to monitor photosynthetic performance of plants and algae, as well as to analyze their protective responses. Apart from its utility in determining the physiological status of photosynthesizers in the natural environment, chlorophyll a fluorescence-based methods are applied in ecophysiological and toxicological studies to examine the effect of environmental changes and pollutants on plants and algae (microalgae and seaweeds). Pollutants or environmental changes cause alteration of the photosynthetic capacity which could be evaluated by fluorescence kinetics. Hence, evaluating key fluorescence parameters and assessing photosynthetic performances would provide an insight regarding the probable causes of changes in photosynthetic performances. This technique quintessentially provides non-invasive determination of changes in the photosynthetic apparatus prior to the appearance of visible damage. It is reliable, economically feasible, time-saving, highly sensitive, versatile, accurate, non-invasive and portable; thereby comprising an excellent alternative for detecting pollution. The present review demonstrates the applicability of chlorophyll a fluorescence in determining photochemical responses of algae exposed to environmental toxicants (such as toxic metals and herbicides).

Molecular mechanisms of Cr(VI) resistance in bacteria and fungi

Hexavalent chromium [Cr(VI)] contamination is one of the main problems of environmental protection because the Cr(VI) is a hazard to human health. The Cr(VI) form is highly toxic, mutagenic, and carcinogenic, and it spreads widely beyond the site of initial contamination because of its mobility. Cr(VI), crossing the cellular membrane via the sulfate uptake pathway, generates active intermediates Cr(V) and/or Cr(IV), free radicals, and Cr(III) as the final product. Cr(III) affects DNA replication, causes mutagenesis, and alters the structure and activity of enzymes, reacting with their carboxyl and thiol groups. To persist in Cr(VI)-contaminated environments, microorganisms must have efficient systems to neutralize the negative effects of this form of chromium. The systems involve detoxification or repair strategies such as Cr(VI) efflux pumps, Cr(VI) reduction to Cr(III), and activation of enzymes involved in the ROS detoxifying processes, repair of DNA lesions, sulfur metabolism, and iron homeostasis. This review provides an overview of the processes involved in bacterial and fungal Cr(VI) resistance that have been identified through 'omics' studies. A comparative analysis of the described molecular mechanisms is offered and compared with the cellular evidences obtained using classical microbiological approaches.

Effect of chromium (VI) exposure on antioxidant defense status and trace element homeostasis in acute experiment in rat

Occupational exposure to hexavalent chromium (Cr(VI)) compounds is of concern in many Cr-related industries and their surrounding environment. Cr(VI) is a proven toxin and carcinogen. The Cr(VI) compounds are easily absorbed, can diffuse across cell membranes, and have strong oxidative potential. Despite intensive studies of Cr(VI) pro-oxidative effects, limited data exist on the influence of Cr(VI) on selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx)-important components of antioxidant defense system. This study investigates the effect of Cr(VI) exposure on antioxidant defense status, with focus on these selenoenzymes, and on trace element homeostasis in an acute experiment in rat. Male Wistar rats (130-140g) were assigned to two groups of 8 animals: I. control; and II. Cr(VI) treated. The animals in Cr(VI) group were administered a single dose of K2Cr2O7 (20 mg /kg, intraperitoneally (ip)). The control group received saline solution. After 24 h, the animals were sacrificed and the liver and kidneys were examined for lipid peroxidation (LP; thiobarbituric acid reactive substances (TBARS) concentration), the level of reduced glutathione (GSH) and the activities of GPx-1, TrxR-1, and glutathione reductase (GR). Samples of tissues were also used to estimate Cr accumulation and alterations in zinc, copper, and iron levels. The acute Cr(VI) exposure caused an increase in both hepatic and renal LP (by 70%, p < 0.01 and by 15%, p < 0.05, respectively), increased hepatic GSH level and GPx-1 activity, and decreased renal GPx-1 activity. The activity of GR was not changed. A significant inhibitory effect of Cr(VI) was found on TrxR-1 activity in both the liver and the kidneys. The ability of Cr(VI) to cause TrxR inhibition could contribute to its cytotoxic effects. Further investigation of oxidative responses in different in vivo models may enable the development of strategies to protect against Cr(VI) oxidative damage.

Strategies for chromium bioremediation of tannery effluent

Bioremediation offers the possibility of using living organisms (bacteria, fungi, algae,or plants), but primarily microorganisms, to degrade or remove environmental contaminants, and transform them into nontoxic or less-toxic forms. The major advantages of bioremediation over conventional physicochemical and biological treatment methods include low cost, good efficiency, minimization of chemicals, reduced quantity of secondary sludge, regeneration of cell biomass, and the possibility of recover-ing pollutant metals. Leather industries, which extensively employ chromium compounds in the tanning process, discharge spent-chromium-laden effluent into nearby water bodies. Worldwide, chromium is known to be one of the most common inorganic contaminants of groundwater at pollutant hazardous sites. Hexavalent chromium poses a health risk to all forms of life. Bioremediation of chromium extant in tannery waste involves different strategies that include biosorption, bioaccumulation,bioreduction, and immobilization of biomaterial(s). Biosorption is a nondirected physiochemical interaction that occurs between metal species and the cellular components of biological species. It is metabolism-dependent when living biomass is employed, and metabolism-independent in dead cell biomass. Dead cell biomass is much more effective than living cell biomass at biosorping heavy metals, including chromium. Bioaccumulation is a metabolically active process in living organisms that works through adsorption, intracellular accumulation, and bioprecipitation mechanisms. In bioreduction processes, microorganisms alter the oxidation/reduction state of toxic metals through direct or indirect biological and chemical process(es).Bioreduction of Cr6+ to Cr3+ not only decreases the chromium toxicity to living organisms, but also helps precipitate chromium at a neutral pH for further physical removal,thus offering promise as a bioremediation strategy. However, biosorption, bioaccumulation, and bioreduction methods that rely on free cells for bioremediation suffer from Cr6 toxicity, and cell damage. Therefore, immobilization of microbial cell biomass enhances bioremediation and renders industrial bioremediation processes more economically viable from reduced free-cells toxicity, easier separation of biosorbents from the tannery effluent, ability to achieve multiple biosorption cycles, and desorption (elution) of metal(s) from matrices for reuse. Thus, microbial bioremediation can be a cost competitive strategy and beneficial bioresource for removing many hazardous contaminants from tannery and other industrial wastes.

Characterization of stress processes of Phaffia rhodozyma stress-resistant mutant

A carotenoid-less Phaffia rhodozyma mutant (MCP 325) exhibited significantly higher resistance to oxidative stressors such as menadione, H2O2 and K2Cr2O7 than its astaxanthin-producing parental strain (MCP 324). The absence of carotenoids in the mutant did not explain this phenomenon. The cause of the decreased superoxide, hydroxyl radical and glutathione contents, the increased peroxide concentration and the elevated specific activity of catalase under uninduced conditions may be a second mutation. Peroxide treatment induced specific catalase activity in the mutant but not in the parental strain. Regulation of these processes led to the result that, in spite of the mutations, the two strains exhibited the same multiplication rate and generation time.

The dual roles of c-Jun NH2-terminal kinase signaling in Cr(VI)-induced apoptosis in JB6 cells

Occupational exposure to chromium (Cr) compounds has been shown to cause serious toxic and carcinogenic effects. The skin is an important target for the compounds in industrially exposed Cr workers. c-Jun NH(2)-terminal kinase (JNK) regulates cell proliferation, apoptosis, and differentiation. This protein's effects on cellular response depend upon the cell type and stimuli. The mechanisms by which hexavalent chromium (Cr(VI)) leads to apoptosis in the skin are unclear at present. The aim of this study is to examine whether JNK regulates apoptosis in Cr(VI)-exposed mouse JB6 epidermal cells. The present study showed that Cr(VI) induced apoptotic cell death through JNK activation. The blockage of JNK by small interference RNA (si-RNA) transfection suppressed Cr(VI)-induced apoptotic cell death with the concomitant downregulation of antiapoptotic Bcl-2 family proteins, mitochondrial membrane depolarization (Δψm), caspase activation, and poly (ADP-ribose) polymerase cleavage. However, inhibition of c-Jun expression by si-RNA transfection enhanced cytotoxicity, which corresponded to increasing apoptosis and Δψm. This phenomenon is associated with p53 activation caused by increasing reactive oxygen species (ROS) levels because of the downregulation of superoxide dismutase expression in si-c-Jun-transfected cells. Taken together, Cr(VI) induces apoptosis via JNK-mediated signaling, whereas c-Jun activation acts as an inhibitor of apoptotic signaling. Additionally, ROS generated by Cr(VI) is a pivotal regulator of JNK.

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.

The selenium-independent inherent pro-oxidant NADPH oxidase activity of mammalian thioredoxin reductase and its selenium-dependent direct peroxidase activities

Mammalian thioredoxin reductase (TrxR) is an NADPH-dependent homodimer with three redox-active centers per subunit: a FAD, an N-terminal domain dithiol (Cys(59)/Cys(64)), and a C-terminal cysteine/selenocysteine motif (Cys(497)/Sec(498)). TrxR has multiple roles in antioxidant defense. Opposing these functions, it may also assume a pro-oxidant role under some conditions. In the absence of its main electron-accepting substrates (e.g. thioredoxin), wild-type TrxR generates superoxide (O ), which was here detected and quantified by ESR spin trapping with 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO). The peroxidase activity of wild-type TrxR efficiently converted the O adduct (DEPMPO/HOO(*)) to the hydroxyl radical adduct (DEPMPO/HO(*)). This peroxidase activity was Sec-dependent, although multiple mutants lacking Sec could still generate O . Variants of TrxR with C59S and/or C64S mutations displayed markedly reduced inherent NADPH oxidase activity, suggesting that the Cys(59)/Cys(64) dithiol is required for O generation and that O is not derived directly from the FAD. Mutations in the Cys(59)/Cys(64) dithiol also blocked the peroxidase and disulfide reductase activities presumably because of an inability to reduce the Cys(497)/Sec(498) active site. Although the bulk of the DEPMPO/HO(*) signal generated by wild-type TrxR was due to its combined NADPH oxidase and Sec-dependent peroxidase activities, additional experiments showed that some free HO(*) could be generated by the enzyme in an H(2)O(2)-dependent and Sec-independent manner. The direct NADPH oxidase and peroxidase activities of TrxR characterized here give insights into the full catalytic potential of this enzyme and may have biological consequences beyond those solely related to its reduction of thioredoxin.

Interference of chromium with biological systems in yeasts and fungi: a review

This paper deals with the interactions of chromium (Cr) with biological systems, focusing in particular on yeasts and fungi. These interactions are analysed with primarily regard to biochemical functions, but higher levels of organization are also considered. Thus, the morphological and cytological characteristics of selected microorganisms in response to exposure to chromium ions are evaluated. The different oxidation states of chromium and reactive oxygen species (ROS) generated in redox reactions with chromium ions are presented and characterized. The interactions of the most exposed subcellular structures, including the cell wall, plasma membrane and nuclei, have been deeply investigated in recent years, for two major reasons. The first is the toxicity of chromium ions and their strong impact on the metabolism of many species, ranging from microbes to humans. The second is the still disputed usefulness of chromium ions, and in particular trivalent chromium, in the glucose and fat metabolisms. Chromium pollution is still an important issue in many regions of the world, and various solutions have been proposed for the bioremediation of soil and water with selected microbial species. Yeasts and especially moulds have been most widely investigated from this aspect, and the biosorption and bioaccumulation of chromium for bioremediation purposes have been demonstrated. Accordingly, the mechanisms of chromium tolerance or resistance of selected microbes are of particular importance in both bioremediation and waste water treatment technologies. The mechanisms of chromium toxicity and detoxification have been studied extensively in yeasts and fungi, and some promising results have emerged in this area.

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.

Determinants of urinary 8-hydroxy-2'-deoxyguanosine in Chinese children with acute leukemia

The 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidized nucleoside of DNA, not only is a widely used biomarker for the measurement of endogenous oxidative DNA damage, but might also be a risk factor for many diseases including cancer. Elevated level of urinary 8-OHdG has been detected in patients with various malignancies. In the present study, the level of urinary 8-OHdG was examined in 116 Chinese children with acute leukemia (94 acute lymphoid leukemia, ALL, 22 acute myeloid leukemia, AML), and its correlation with urinary metal elements was investigated. Our result showed that the level of urinary 8-OHdG in children with acute leukemia before treatment was significantly elevated compared with that in normal controls (11.92 +/- 15.42 vs. 4.03 +/- 4.70 ng/mg creatinine, P < 0.05). In particular, urinary 8-OHdG was higher in children with acute leukemia aged under 3 years (20.86 +/- 21.75 ng/mg creatinine) than in those aged 3-15 years (8.09 +/- 9.65 ng/mg creatinine), whereas no differences were shown in terms of gender, parental smoking and education, household income, place of residence, and use of paracetamol. In addition, urinary 8-OHdG levels were similar among different subtypes of acute lymphoid leukemia (ALL) patients. Furthermore, linear regression analysis revealed a significant correlation between urinary 8-OHdG and urinary Cr, but not Fe or As, in group aged <3 years compared with group aged 3-15 years (P = 0.041), indicating that the metal elements may be involved in increasing urinary 8-OHdG level in younger children with acute leukemia. Our results suggest that children with acute leukemia undergo an increased risk of oxidative DNA damage, which may be correlated with high level of Cr exposure in Chinese children with acute leukemia.

Chromium(III) induces oxidative stress in goldfish liver and kidney

In the environment chromium is found mainly in two valence states-hexavalent chromium (Cr6+) and trivalent chromium (Cr3+). The present study evaluates the effects of Cr3+ exposure on goldfish by analyzing parameters of oxidative stress and antioxidant defense in liver and kidney of fish given 96 h exposures to Cr3+ concentrations of 1, 2.5, 5 or 10 mg/l in aquarium water. Cr3+ exposure did not alter two parameters of oxidative stress-protein carbonyl content and lipid peroxide concentrations in either organ. However, Cr3+ exposure did decrease total glutathione concentration in liver by 34-69% and in kidney to 36-49% of the respective control values. Oxidized GSSG content fell by similar percentages so that the ratio [GSSG]/[total glutathione] remained constant at all Cr3+ exposure levels except in liver under the highest, 10 mg/l, exposure level. In liver, exposure to 1-5 mg/l Cr3+ led to a decrease in the activity of superoxide dismutase (SOD) by 29-36%, and at 10 mg/l Cr3+ the reduction was 54%, whereas in kidney approximately 30% reductions in SOD activity were seen at concentrations 1 and 10 mg/l Cr3+. Catalase activity was not significantly affected by 1-5 mg/l Cr3+, but was reduced by 57 and 42% in liver and kidney, respectively. Chromium exposure also reduced the activity of glutathione-S-transferase in both organs by 17-50% but did not affect glutathione reductase or glucose-6-phosphate dehydrogenase activities. A comparison of Cr3+ effects on goldfish liver and kidney metabolism indicates that the trivalent ion induces stronger oxidative stress than Cr6+ at the same concentrations.

Trivalent chromium induces oxidative stress in goldfish brain

Although information on the effects of Cr(6+) in biological systems is abundant, Cr(3+) has received less attention. Toxic effects of chromium compounds are partially associated with activation of redox processes. Recently we found that Cr(6+) induced oxidative stress in goldfish tissues and the glutathione system was shown to play a protective role. The present study aimed to investigate free radical processes in brain of goldfish exposed to CrCl(3). Trivalent chromium at a concentration of 50 mg L(-1) was lethal and therefore we chose to examine sublethal dosages of 1.0-10.0 mg L(-1) in aquarium water. The levels of lipid peroxides and protein carbonyls (measures of oxidative damage to lipids and proteins) in brain increased after 96 h exposure of goldfish to Cr(3+). However, exposure to 1.0-10.0 mg L(-1) Cr(3+) decreased total glutathione concentration in brain by approximately 50-60%. Oxidized glutathione levels also fell by approximately 40-60% except at the 10.0 mg L(-1) dosage where they decreased by 85%. Therefore, 10.0 mg L(-1) Cr(3+) significantly reduced the ratio [GSSG]/[totalGSH] to 35% of the control value. Chromium treatment did not affect the activity of superoxide dismutase, but reduced the activities of catalase by 55-62% and glutathione-S-transferase by 14-21%. The activities of glucose-6-phosphate dehydrogenase and glutathione reductase were unchanged under any experimental conditions used. Therefore, it can be concluded that although Cr(3+) exposure induced oxidative stress in goldfish brain, it failed to enhance the efficiency of the antioxidant system in the organ.

Urinary level of nickel and acute leukaemia in Chinese children

The 8-hydroxy-2′-deoxyguanosine (8-OHdG), an oxidized nucleoside of DNA, not only is a widely used biomarker for the measurement of endogenous oxidative DNA damage but might also be a risk factor for many diseases including cancer. Metal exposure may play an important role in oxidative DNA damage among children. However, few studies on urinary 8-OHdG and metals have been conducted in children with acute leukemia. In the present study, urinary Ni and 8-OHdG were examined in 116 children with acute leukaemia (94 acute lymphoid leukaemia [ALL] and 22 acute myeloid leukaemia [AML]) and 51 healthy child controls. Our result showed that urinary Ni in acute leukaemia patients (ALL: 68.40 ± 133.98, AML: 41.48 ± 76.31 ng/mg creatinine) was significantly higher than that in controls (62.47 ± 124.90 vs 17.63 ± 46.17 ng/mg creatinine, P < 0.05). Similarly, the pretherapy level of urinary 8-OHdG in patients (ALL: 11.83 ± 16.23, AML: 12.36 ± 11.36 ng/mg creatinine) was significantly elevated compared with controls (11.92 ± 15.42 vs 4.03 ± 4.70 ng/mg creatinine, P < 0.05). Moreover, urinary 8-OHdG and urinary Ni showed a weak but significant association with increased risk of childhood leukaemia. The present study suggests that Ni may be an etiologic factor for childhood acute leukaemia by oxidative DNA damage.

Toxic Effects of Chromium(VI) on Anaerobic and Aerobic Growth of Shewanella oneidensis MR-1

Cr(VI) was added to early- and mid-log-phase Shewanella oneidensis (S. oneidensis) MR-1 cultures to study the physiological state-dependent toxicity of Cr(VI). Cr(VI) reduction and culture growth were measured during and after Cr(VI) reduction. Inhibition of growth was observed when Cr(VI) was added to cultures of MR-1 growing aerobically or anaerobically with fumarate as the terminal electron acceptor. Under anaerobic conditions, there was immediate cessation of growth upon addition of Cr(VI) in early- and mid-log-phase cultures. However, once Cr(VI) was reduced below detection limits (0.002 mM), the cultures resumed growth with normal cell yield values observed. In contrast to anaerobic MR-1 cultures, addition of Cr(VI) to aerobically growing cultures resulted in a gradual decrease of the growth rate. In addition, under aerobic conditions, lower cell yields were also observed with Cr(VI)-treated cultures when compared to cultures that were not exposed to Cr(VI). Differences in response to Cr(VI) between aerobically and anaerobically growing cultures indicate that Cr(VI) toxicity in MR-1 is dependent on the physiological growth condition of the culture. Cr(VI) reduction has been previously studied in Shewanella spp., and it has been proposed that Shewanella spp. may be used in Cr(VI) bioremediation systems. Studies of Shewanella spp. provide valuable information on the microbial physiology of dissimilatory metal reducing bacteria; however, our study indicates that S. oneidensis MR-1 is highly susceptible to growth inhibition by Cr(VI) toxicity, even at low concentrations [0.015 mM Cr(VI)].

Addition of DNA to Cr(VI) and cytochrome b5 containing proteoliposomes leads to generation of DNA strand breaks and Cr(III) complexes

Chromium (Cr) is a cytotoxic metal that can be associated with a variety of types of DNA damage, including Cr-DNA adducts and strand breaks. Prior studies with purified human cytochrome b(5) and NADPH:P450 reductase in reconstituted proteoliposomes (PLs) demonstrated rapid reduction of Cr(VI) (hexavalent chromium, as CrO(4)(2-), and the generation of Cr(V), superoxide (O(2)(*-)), and hydroxyl radical (HO(*)). Studies reported here examined the potential for the species produced by this system to interact with DNA. Strand breaks of purified plasmid DNA increased over time aerobically, but were not observed in the absence of O(2). Cr(V) is formed under both conditions, so the breaks are not mediated directly by Cr(V). The aerobic strand breaks were significantly prevented by catalase and EtOH, but not by the metal chelator diethylenetriaminepentaacetic acid (DTPA), suggesting that they are largely due to HO(*) from Cr-mediated redox cycling. EPR was used to assess the formation of Cr-DNA complexes. Following a 10-min incubation of PLs, CrO(4)(2-), and plasmid DNA, intense EPR signals at g=5.7 and g=5.0 were observed. These signals are attributed to specific Cr(III) complexes with large zero field splitting (ZFS). Without DNA, the signals in the g=5 region were weak. The large ZFS signals were not seen, when Cr(III)Cl(3) was incubated with DNA, suggesting that the Cr(III)-DNA interactions are different when generated by the PLs. After 24 h, a broad signal at g=2 is attributed to Cr(III) complexes with a small ZFS. This g=2 signal was observed without DNA, but it was different from that seen with plasmid. It is concluded that EPR can detect specific Cr(III) complexes that depend on the presence of plasmid DNA and the manner in which the Cr(III) is formed.

Reductive activation of hexavalent chromium by human lung epithelial cells: generation of Cr(V) and Cr(V)-thiol species

Chromium(VI) compounds (e.g. chromates) are cytotoxic, mutagenic, and potentially carcinogenic. The reduction of Cr(VI) can yield reactive intermediates such as Cr(V) and reactive oxygen species. Bronchial epithelial cells are the primary site of pulmonary exposure to inhaled Cr(VI) and are the primary cells from which Cr(VI)-associated human cancers arise. BEAS-2B cells were used here as a model of normal human bronchial epithelium for studies on the reductive activation of Cr(VI). Cells incubated with Na(2)CrO(4) exhibited two Cr(V) ESR signals, g=1.979 and 1.985, which persisted for at least 1h. The g=1.979 signal is similar to that generated in vitro by human microsomes and by proteoliposomes containing P450 reductase and cytochrome b(5). Unlike many cells in culture, these cells continued to express P450 reductase and cytochrome b(5). Studies with the non-selective thiol oxidant diamide indicated that the g=1.985 signal was thiol-dependent whereas the g=1.979 signal was not. Pretreatment with phenazine methosulfate eliminated both Cr(V) signals suggesting that Cr(V) generation is largely NAD(P)H-dependent. ESR spectra indicated that a portion of the Cr(VI) was rapidly reduced to Cr(III). Cells incubated with an insoluble chromate, ZnCrO(4), also generated both Cr(V) signals, whereas Cr(V) was not detected with insoluble PbCrO(4). In clonogenic assays, the cells were very sensitive to Na(2)CrO(4) and ZnCrO(4), but considerably less sensitive to PbCrO(4).

Superoxide-mediated proteasomal degradation of Bcl-2 determines cell susceptibility to Cr(VI)-induced apoptosis

Hexavalent chromium [Cr(VI)] compounds are redox cycling environmental carcinogens that induce apoptosis as the primary mode of cell death. Defects in apoptosis regulatory mechanisms contribute to carcinogenesis induced by Cr(VI). Activation of apoptosis signaling pathways is tightly linked with the generation of reactive oxygen species (ROS). Likewise, ROS have been implicated in the regulation of Cr(VI)-induced apoptosis and carcinogenicity; however, its role in Cr(VI)-induced apoptosis and the underlying mechanism are largely unknown. We report that ROS, specifically superoxide anion (.O(-)(2), mediates Cr(VI)-induced apoptosis of human lung epithelial H460 cells. H460 rho(0) cells that lack mitochondrial DNA demonstrated a significant decrease in ROS production and apoptotic response to Cr(VI), indicating the involvement of mitochondrial ROS in Cr(VI)-induced apoptosis. In agreement with this observation, we found that Cr(VI) induces apoptosis mainly through the mitochondrial death pathway via caspase-9 activation, which is negatively regulated by the antiapoptotic protein Bcl-2. Furthermore, .O(-)(2) induced apoptosis in response to Cr(VI) exposure by downregulating and degrading Bcl-2 protein through the ubiquitin-proteasomal pathway. This study reveals a novel mechanism linking .O(-)(2) with Bcl-2 stability and provides a new dimension to ROS-mediated Bcl-2 downregulation and apoptosis induction.

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.

Mechanisms of bacterial resistance to chromium compounds

Chromium is a non-essential and well-known toxic metal for microorganisms and plants. The widespread industrial use of this heavy metal has caused it to be considered as a serious environmental pollutant. Chromium exists in nature as two main species, the trivalent form, Cr(III), which is relatively innocuous, and the hexavalent form, Cr(VI), considered a more toxic species. At the intracellular level, however, Cr(III) seems to be responsible for most toxic effects of chromium. Cr(VI) is usually present as the oxyanion chromate. Inhibition of sulfate membrane transport and oxidative damage to biomolecules are associated with the toxic effects of chromate in bacteria. Several bacterial mechanisms of resistance to chromate have been reported. The best characterized mechanisms comprise efflux of chromate ions from the cell cytoplasm and reduction of Cr(VI) to Cr(III). Chromate efflux by the ChrA transporter has been established in Pseudomonas aeruginosa and Cupriavidus metallidurans (formerly Alcaligenes eutrophus) and consists of an energy-dependent process driven by the membrane potential. The CHR protein family, which includes putative ChrA orthologs, currently contains about 135 sequences from all three domains of life. Chromate reduction is carried out by chromate reductases from diverse bacterial species generating Cr(III) that may be detoxified by other mechanisms. Most characterized enzymes belong to the widespread NAD(P)H-dependent flavoprotein family of reductases. Several examples of bacterial systems protecting from the oxidative stress caused by chromate have been described. Other mechanisms of bacterial resistance to chromate involve the expression of components of the machinery for repair of DNA damage, and systems related to the homeostasis of iron and sulfur.

Molecular mechanisms of resistance to heavy metals in the protist Euglena gracilis

The biochemical mechanisms of resistance to several heavy metals, which are associated with their accumulation (binding by high-affinity chelating molecules such as thiol-compounds together with their compartmentalization into organelles), are analyzed for the photosynthetic, free-living protist Euglena gracilis. The complete understanding of these mechanisms may facilitate the rational design of strategies for bioremediation of heavy metal polluted water and soil systems.

Reduction of hexavalent chromium by human cytochrome b5: generation of hydroxyl radical and superoxide

The reduction of hexavalent chromium, Cr(VI), can generate reactive Cr intermediates and various types of oxidative stress. The potential role of human microsomal enzymes in free radical generation was examined using reconstituted proteoliposomes (PLs) containing purified cytochrome b(5) and NADPH:P450 reductase. Under aerobic conditions, the PLs reduced Cr(VI) to Cr(V) which was confirmed by ESR using isotopically pure (53)Cr(VI). When 5-diethoxyphosphoryl-5-methyl-1-pyrroline-N-oxide (DEPMPO) was included as a spin trap, a very prominent signal for the hydroxyl radical (HO()) adduct was observed as well as a smaller signal for the superoxide (O(2)(-)) adduct. These adducts were observed even at very low Cr(VI) concentrations (10 muM). NADPH, Cr(VI), O(2), and the PLs were all required for significant HO() generation. Superoxide dismutase eliminated the O(2)(-) adduct and resulted in a 30% increase in the HO() adduct. Catalase largely diminished the HO() adduct signal, indicating its dependence on H(2)O(2). Some sources of catalase were found to have Cr(VI)-reducing contaminants which could confound results, but a source of catalase free of these contaminants was used for these studies. Exogenous H(2)O(2) was not needed, indicating that it was generated by the PLs. Adding exogenous H(2)O(2), however, did increase the amount of DEPMPO/HO() adduct. The inclusion of formate yielded the carbon dioxide radical adduct of DEPMPO, and experiments with dimethyl sulfoxide (DMSO) plus the spin trap alpha-phenyl-N-tert-butylnitrone (PBN) yielded the methoxy and methyl radical adducts of PBN, confirming the generation of HO(). Quantification of the various species over time was consistent with a stoichiometric excess of HO() relative to the net amount of Cr(VI) reduced. This also represents the first demonstration of a role for cytochrome b(5) in the generation of HO(). Overall, the simultaneous generation of Cr(V) and H(2)O(2) by the PLs and the resulting generation of HO() at low Cr(VI) concentrations could have important implications for Cr(VI) toxicity.

Elemental profile of cerebrospinal fluid in patients with Parkinson's disease

To ascertain the potential role of chemical elements (namely, Al, Ba, Be, Bi, Ca, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Ni, Pb, Sb, Si, Sn, Sr, Tl, V, W, Zn and Zr) as markers in the Parkinson's disease (PD), the elemental concentration of cerebrospinal fluid (CSF) of 42 patients with PD and 20 age-matched controls was assessed. Analyses were performed by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS). Significantly lower levels of Co, Cr, Fe, Pb, Si and Sn were observed in the CSF of PD patients compared with those in controls, with a percentage of depletion up to 50% for Cr and Pb. No such variations were detected for all the other elements. Results suggested that Pb, Cr, Fe were the most suitable elements to distinguish between normality and PD. Different cut-off concentrations for these elements could be tentatively proposed as a predictive tool for the PD condition.

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.

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).

Evaluation of Urinary 8-Hydroxydeoxyguanine inHealthy Japanese People

The urinary concentration of 8-hydroxydeoxyguanine (8-OHdG), which is a biomarker of oxidative DNA damage, was measured in 248 healthy Japanese, and its correlations with life style, urinary metal elements, serum antioxidants, and other plasma or serum factors were investigated. The mean urinary concentration of 8-OHdG was 15.2+/-5.71 ng/mg creatinine. Mean urinary 8-OHdG was not significantly different in terms of age (<45, >or=45), gender, smoking (no, <20, >or=20), and alcohol consumption (no, occasionally, sometimes and usually). Moreover, multiple regression analysis showed a significant association between urinary 8-OHdG and urinary arsenic (As) or chromium (Cr), and a tendency for association between the former and aluminum (Al) and nickel (Ni). Age, gender and plasma or serum factors including antioxidants, lipid peroxide, HbA1c, BUN, and iron did not show such an association. The present study suggests that natural exposure to toxic metal elements such as As, Cr, and Ni may influence oxidative DNA damage in healthy people under usual environmental management. Therefore, the measurement of urinary metals such as As, Ni and Cr is prerequisite for the study of the relationship between urinary 8-OHdG and other variable factors.

Biochemical study on the protective role of folic acid in rabbits treated with chromium (VI)

Deleterious effects of chromium (VI) compounds are diversified affecting almost all the organ systems in a wide variety of animals. Therefore, the present study was carried out to determine the effectiveness of folic acid (FA) in alleviating the toxicity of chromium (VI) on certain biochemical parameters, lipid peroxidation, and enzyme activities of male New Zealand white rabbits. Six rabbits per group were assigned to one of four treatment groups: 0 mg FA and 0 mg Cr(VI)/kg BW (control); 8.3 microg FA/kg BW; 5 mg Cr(VI)/kg BW; 5 mg Cr(VI) plus 8.3 microg FA/kg BW, respectively. Rabbits were orally administered their respective doses every day for 10 weeks. Results obtained showed that Cr(VI) significantly (P < 0.05) increased the levels of free radicals and the activity of glutathione S-transferase (GST), and decreased the content of sulfhydryl groups (SH groups) in liver, testes, brain, kidney, and lung. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (AlP), acid phosphatase (AcP), and lactate dehydrogenase (LDH) were significantly decreased in liver and testes due to Cr(VI) administration. Also, AlP and AcP activities were significantly decreased in kidney and lung. The activity of acetylcholinesterase (AChE) was significantly decreased in brain and plasma. Contrariwise, the activities of AST and ALT were significantly increased in plasma, while AlP and AcP decreased. Chromium (VI) treatment caused a significant decrease in plasma total protein (TP) and globulin, and increased total lipids (TL), cholesterol, glucose, urea, creatinine, and bilirubin concentrations. Folic acid alone significantly decreased the levels of free radicals in liver, brain, and kidney, and increased the content of SH-group. The activities of AST, ALT, and LDH in liver; AST, ALT, AlP, AcP, and LDH in testes; AcP in kidney; AlP and AcP in lung, and LDH in brain were significantly increased. Plasma TP and albumin were increased, while urea and creatinine were decreased. The presence of FA with Cr(VI) restored the changes in enzyme activities and biochemical parameters. In conclusion, folic acid could be effective in the protection of chromium-induced toxicity.

Hypoxia impedes the formation of chromium DNA-adducts in a cell-free system

The metabolic reduction of hexavalent chromium [Cr(VI)] in the presence of DNA generates several lesions which impede DNA replication and gene transcription. However, the relative contribution of molecular oxygen to Cr-induced genetic damage is unclear. To elucidate the role of dioxygen in Cr genotoxicity, we studied the formation of Cr-induced lesions in DNA treated with either Cr(VI) and the physiological reductant, ascorbic acid (Asc), or Cr(III), under ambient and hypoxic (<1% oxygen) conditions. We found that hypoxia did not impede the reduction of Cr(VI) by Asc throughout a 2 h treatment. In contrast, Cr-DNA binding under these conditions was reduced up to 70% by hypoxia, and a 50-90% decrease in the frequency of Cr-induced Taq polymerase-arresting DNA adducts was also observed. In the presence of Cr(VI)/Asc, formation of Cr-DNA interstrand crosslinks (ICLs) under hypoxia was 50% or less of that under ambient conditions. Kinetic studies found that hypoxia reduced the rate at which Cr interacted with DNA, but not the ultimate steady state level of Cr-DNA binding. The inhibitory effect of hypoxia on Cr(VI)/Asc genotoxicity could not be explained solely by alterations in the reactivity of intermediate Cr(V) species because Cr(III)-DNA binding and Cr(III)-induced ICL formation were also impaired by hypoxia. Moreover, Cr(V) was generated to similar levels in ambient and hypoxic reactions. Hypoxia did not affect ICL formation by the inorganic chemotherapeutic agent cisplatin, suggesting that these effects were specific for Cr(III). Taken together, these results support a role for dioxygen in facilitating the formation of Cr-DNA coordination complexes.

Uptake, distribution, and speciation of chromium in Brassica juncea

Brassica juncea (Indian mustard) has been widely used in phytoremediation because of its capacity to accumulate high levels of chromium (Cr) and other metals. The present study was conducted to investigate mechanism(s) involved in Cr binding and sequestration by B. juncea. The plants were grown under greenhouse conditions in field-moist or air-dried soils, amended with 100 mg kg(-1) of Cr (III) or VI). The plant concentrated Cr mainly in the roots. B. juncea removed an average of 48 and 58 microg Cr per plant from Cr (III) and Cr (VI)-treated soils, respectively. The uptake of Cr was not affected by the moisture status of the soils. X-ray absorption near-edge spectroscopy measurements showed only Cr (III) bound predominantly to formate and acetate ligands, in the bulk and rhizosphere soils, respectively. In the plant tissues, Cr (III) was detected, primarily as acetate in the roots and oxalate in the leaves. X-ray microprobe showed the sites of Cr localization, and probably sequestration, in epidermal and cortical cells in the roots and epidermal and spongy mesophyll cells in the leaves. These findings demonstrate the ability of B. juncea to detoxify more toxic Cr (VI), thereby making this plant a potential candidate for phytostabilization.

Metal-induced oxidative stress and signal transduction

Occupational and environmental exposures to metals are associated with the development of various cancers. Although carcinogenesis caused by metals has been intensively investigated, the mechanisms of action, especially at the molecular level, are still unclear. Accumulating evidence indicates that reactive oxygen species generated by metals may play an important role in the etiology of disease. This review covers recent advances in (1) metal-induced generation of reactive oxygen species; (2) the receptors, kinases, and nuclear transcription factors affected by metals and metal-induced oxidative stress, including growth factor receptors, src kinase, ras signaling, mitogen-activated protein kinases, the phosphoinositide 3-phosphate/Akt pathway, nuclear transcription factor kappaB, activator protein 1, p53, nuclear factor of activated T cells, and hypoxia-inducible factor 1; and (3) global cellular phenomena (signal transduction, cell cycle regulation, and apoptosis) associated with metal-induced ROS production and gene expression.

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.

Arsenite induces HIF-1alpha and VEGF through PI3K, Akt and reactive oxygen species in DU145 human prostate carcinoma cells

Arsenite is widely distributed environmental toxicant in water, food and air. It is a known human carcinogen, which is strongly associated with human cancers originated from liver, nasal cavity, lung, skin, bladder, kidney, and prostate. In this study, we investigated whether arsenite induces expression of hypoxia-inducible factor 1 (HIF-1). HIF-1 is a heterodimeric basic helix-loop-helix transcription factor, composed of HIF-1alpha and HIF-1beta/ARNT subunits; and is involved in tumor growth and angiogenesis. Here we demonstrate that arsenite induces the expression of HIF-1alpha but not HIF-1beta subunit in DU145 human prostate carcinoma cells. Arsenite also increases the expression of VEGF through the induction of HIF-1. We also found that arsenite activates PI3K and Akt that are required for arsenite-induced expression of HIF-1alpha and VEGF. The induction of HIF-1 and VEGF by arsenite can not be inhibited by MAP kinase inhibitors. Arsenite causes production of reactive oxygen species (ROS). The major species of ROS required for the induction of HIF-1 and VEGF is H2O2. These data indicate that the arsenite-induced activation of PI3K/Akt signaling and the expression of HIF-1 and VEGF through the generation of ROS could be an important mechanism in the arsenite-induced carcinogenesis.

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.

Oxidative stress and apoptosis in metal ion-induced carcinogenesis

Epidemiological evidence suggests that exposure to certain metals causes carcinogenesis. The mechanisms of metal-induced carcinogenesis have been pursued in chemical, biochemical, cellular, and animal models. Significant evidence has accumulated that oxidative stress may be a common pathway in cellular responses to exposure to different metals. For example, in the last few years evidence in support of a correlation between the generation of reactive oxygen species, DNA damage, tumor promotion, and arsenic exposure has strengthened. This article summarizes the current literature on metal-mediated oxidative stress, apoptosis, and their relation to metal-mediated carcinogenesis, concentrating on arsenic and chromium.

Status of antioxidant defense system in chromium-induced Swiss mice tissues

Based on epidemiological studies, chromium(VI) compounds are considered as more toxic and carcinogenic than chromium(III) compounds. The deleterious effects of chromium(VI) compounds are diversified affecting almost all the organ systems in a wide variety of animals. The present study, describes the cytotoxic effects of chromium trioxide, a well-known chromium(VI) compound in three tissues (liver, kidney, lungs) of male Swiss mice during post-treatment phase (5th-8th week after treatment). Lipid peroxidation, an index of oxidative stress, was determined as thiobarbituric acid-reactive substances (TBA-Rs) in mice tissues dosed with a single intraperitoneal injection of chromium trioxide (1mg/kg body weight). Tissue specific and statistically significant increases in TBA-Rs was observed in chromium-treated mice groups compared to controls in all the weeks of post-treatment. Endogenous ascorbic acid (vit-C) content of tissues which happens to be one of the stable antioxidants, declined significantly due to chromium-induction. Activity of antioxidative enzymes like superoxide dismutase (SOD), catalase (CT) and peroxidase (PD) was significantly inhibited among chromium-injected mice groups compared to respective controls. Protective role of ascorbic acid and the antioxidative enzymes in chromium-induced cytotoxicity in mice is discussed.