In vivo singlet-oxygen generation in blood of chromium(VI)-treated mice

Although it is assumed from in vitro experiments that the generation of reactive oxygen species such as the singlet oxygen (1O2), the hydroxyl radical, and the superoxide anion are responsible for chromium(VI) toxicity/carcinogenicity, no electron spin resonance (ESR) evidence for the generation of 1O2 in vivo has been reported. In this study, we have employed an ESR spin-trapping technique with 2,2,6,6-tetramethyl-4-piperidone (TMPD), a specific 1O2 trap, to detect 1O2 in blood. The ESR spectrum of the spin adduct observed in the blood of mice given 4.8 mmol Cr(VI)/kg body weight exhibited the 1:1:1 intensity pattern of three lines with a hyperfine coupling constant A(N) = 16.08 G and a g-value = 2.0066. The concentration of spin adduct detected in the blood was 1.46 microM (0.1% of total Cr concentration). The adduct production was inhibited by the addition of specific 1O2 scavengers such as 1,4-diazabicyclo[2.2.2]octane and sodium azide to the blood. The results indicate that the spin adduct is nitroxide produced by the reaction of 1O2 with TMPD. This is the first report of ESR evidence for the in vivo generation of 1O2 in mammals by Cr(VI).     

Hard X-ray microprobe studies of chromium(VI)-treated V79 Chinese hamster lung cells: intracellular mapping of the biotransformation products of a chromium carcinogen

The uptake of carcinogenic and mutagenic Cr compounds and the intracellular distribution of their biotransformation products in V79 Chinese hamster lung cells were studied by synchrotron-radiation-induced X-ray emission (SRIXE). SRIXE analysis was performed on whole cells that had been treated with either Cr(III) or Cr(V) 1,10-phenanthroline complexes, or Cr(VI). The high spatial resolution (0.3 microm) and elemental sensitivity (~10(-15) g Cr/cell) of the technique provided detailed maps of Cr and other cellular elements in thin sections prepared from Cr(VI)-treated cells. The Cr carcinogen concentrated in P-rich regions corresponding to the nucleus, as well as other areas of the cell that are likely to correspond to organelles. This is the first study that has enabled the determination of the localization of the biotransformation products of Cr(VI) carcinogens in a target lung cell.     

Uptake of chromium(III) and chromium(VI) compounds in the yeast cell structure

The study presented in this article investigated the influence of different Cr(III) and Cr(VI) compounds in the cultivation medium on the uptake and localization of chromium in the cell structure of the yeast Candida intermedia. The morphology of the yeast cell surface was observed by the scanning electron microscopy. Results demonstrated that the growth inhibitory concentration of Cr(III) in the cultivation medium induced changes in the yeast cell shape and affected the budding pattern, while inhibitory concentration of Cr(VI) did not cause any visible effects on morphological properties of the yeast cells. The amount of total accumulated chromium in yeast cells and the distribution of chromium between the yeast cell walls and spheroplasts were determined by atomic absorption spectroscopy. No significant differences were found neither in total chromium accumulation nor in the distribution of chromium in yeast cell walls and spheroplasts between the two of Cr(VI) compounds. Conversely, substantial differences between Cr(III) compounds were demonstrated in the total uptake as well as the localization of chromium in yeast cells.     

Binding of chromium(VI) to histones: implications for chromium(VI)-induced genotoxicity

The first evidence has been obtained for Cr(VI) (chromate) binding to isolated calf thymus (CT) histones under physiological conditions (pH 7.4, Cl⁻ concentration 152 mM, 310 K). No significant Cr(VI) binding under the same conditions was observed for other extracellular and intracellular proteins, including albumin, apo-transferrin and G-actin, as well as for CT DNA. The mode of Cr(VI) binding to histones was studied by vibrational, electronic and X-ray absorption (X-ray absorption near-edge structure and X-ray absorption fine structure) spectroscopies and molecular mechanics calculations. A proposed binding mechanism includes electrostatic interactions of CrO₄ ²⁻ with protonated Lys and Arg residues of histones, as well as the formation of hydrogen bonds with the protein backbone. Similarly, Cr(VI) can bind to nuclear localization signals (typically, Lys- and Arg-rich fragments) of other nuclear proteins. Selective binding of Cr(VI) to newly synthesized nuclear proteins (including histones) in the cytoplasm is likely to be responsible for the active transport of Cr(VI) into the nuclei of living cells. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Mechanism of apoptosis and determination of cellular fate in chromium(VI)-exposed populations of telomerase-immortalized human fibroblasts.

The cellular responses to carcinogen exposure influence cellular fate, which in turn modulates the neoplastic response. Certain hexavalent chromium [Cr(VI)] compounds are implicated as occupational respiratory carcinogens at doses that are both genotoxic and cytotoxic. We examined the mechanism of Cr(VI)-induced apoptosis in normal human fibroblasts (BJ) immortalized by human telomerase gene transfection (BJ-hTERT), and we assessed the spectrum of cumulative cellular fates [(a) regaining of replicative potential; (b) terminal growth arrest; or (c) apoptosis] for a narrow range of increasingly genotoxic doses of Cr(VI). Exposure of BJ-hTERT cells to Cr(VI) resulted in a dose-dependent increase in apoptosis that involved mitochondrial disruption as evidenced by mitochondrial membrane depolarization and cytochrome c release. The initial response to Cr(VI) exposure was inhibition of cell cycle progression. At the lowest dose tested (1 microM; 32% clonogenic survival), the cell cycle inhibition led to terminal growth arrest but no apoptosis. The fraction of terminally growth arrested cells increased as the dose was increased to 3 microM but then decreased at 4, 5, and 6 microM as apoptosis became the predominant cell fate. Our results suggest that cell populations exposed to Cr(VI) have a different spectrum of responses, depending on the extent of DNA damage, and that the regaining of replicative potential after relatively higher genotoxic exposures may be attributable to either escape from, or resistance to, terminal growth arrest or apoptosis.     

The cytotoxicity and genotoxicity of hexavalent chromium in Steller sea lion lung fibroblasts compared to human lung fibroblasts

In this study we directly compared soluble and particulate chromate cytotoxicity and genotoxicity in human (Homo sapiens) and sea lion (Eumetopias jubatus) lung fibroblasts. Our results show that hexavalent chromium induces increased cell death and chromosome damage in both human and sea lion cells with increasing intracellular chromium ion levels. The data further indicate that both sodium chromate and lead chromate are less cytotoxic and genotoxic to sea lion cells than human cells, based on an administered dose. Differences in chromium ion uptake explained some but not all of the reduced amounts of sodium chromate-induced cell death. By contrast, uptake differences could explain the differences in sodium chromate-induced chromosome damage and particulate chromate-induced toxicity. Altogether they indicate that while hexavalent chromium induces similar toxic effects in sea lion and human cells, there are different mechanisms underlying the toxic outcomes.     

Endothelin-1 induces expression of matrix-associated genes in lung fibroblasts through MEK/ERK

The endothelins are a family of endothelium-derived peptides that possess a variety of biological activities, including potent vasoconstriction. Endothelin-1 (ET-1) is up-regulated during tissue repair and pulmonary fibrosis. Here, we use genome-wide expression array analysis to show that the addition of ET-1 (100 nm, 4 h) to normal lung fibroblasts directly induces expression of matrix and matrix-associated genes, including the profibrotic protein CCN2 (connective tissue growth factor, or CTGF). ET-1 induces the MEK/ERK MAP kinase pathway in fibroblasts. Blockade of the MEK/ERK kinase pathway with U0126 abrogates the ability of ET-1 to induce expression of matrix and matrix-associated mRNAs and the CCN2 protein. The CCN2 promoter possesses an ET-1 response element, which maps to the previously identified basal control element-1 (BCE-1) site. Our results suggest that ET-1 induces a program of matrix synthesis in lung fibroblasts and that ET-1 may play a key role in connective tissue deposition during wound repair and in pulmonary fibrosis.     

Mechanism of chromium(VI) carcinogenesis

Since chromium(VI) is unreactive toward DNA under physiological conditions in vitro, the ability of carcinogenic chromium(VI) compounds to damage DNA depends on the presence of cellular redox components that reduce chromium(VI) to reactive species capable of interacting with DNA. We have examined the role of glutathione and hydrogen peroxide in chromium(VI)-induced DNA damage in vitro. Upon reaction with chromium(VI), glutathione produced chromium(V) and glutathione thiyl radical reactive intermediates, whereas hydrogen peroxide produced chromium(V) and hydroxyl radical. Reaction of DNA with chromium(VI) in the presence of glutathione resulted in binding of chromium and glutathione to DNA with little or no DNA strand breakage. Reaction of DNA with chromium(VI) in the presence of hydrogen peroxide produced the 8-hydroxydeoxy-guanosine adduct and extensive DNA strand breakage in the absence of significant Cr-DNA adduct formation. These results suggest that the nature of chromium(VI)-induced DNA damage will be strongly dependent on reactive intermediates such as chromium(V), glutathione thiyl radical, and hydroxyl radical, produced by cellular components active in chromium(VI) metabolism. In order to assess the ability of chromium(VI)-induced DNA damage to affect the normal template function of DNA, we investigated the effects of chromium(VI) on steady-state mRNA levels of various genes in chick embryo liver in vivo, and compared the effects to the levels of DNA damage observed. Chromium(VI) induced DNA-protein and DNA interstrand cross-links in chick embryo liver in vivo and suppressed the induction of 5-aminolevulinic acid synthase and cytochrome P-450 mRNA expression by porphyrinogenic drugs. In contrast, chromium(VI) increased the basal levels of expression of these two inducible genes, but had little or no effect on the expression of the constitutive albumin, β-actin, and conalbumin genes. Comparison of the time course of formation and repair of DNA damage with that of changes in gene expression suggests that chromium(VI) may form a mono-adduct prior to formation of DNA cross-links, and that chromium(VI)-induced DNA lesions may target certain classes of genes and lead to changes in their expression.     

Carcinogenic chromium(VI) induces cross-linking of vitamin C to DNA in vitro and in human lung A549 cells

Reductive activation of carcinogenic Cr(VI) is required for the induction of DNA damage and mutations. Here, we examined the formation of Cr-DNA adducts in the reactions of Cr(VI) with its dominant biological reducer, vitamin C (ascorbate). Reductive conversion of Cr(VI) to Cr(III) by ascorbate produced stable Cr-DNA adducts, of which approximately 25% constituted ascorbate-Cr(III)-DNA cross-links. No evidence was found for the involvement of Cr(V) or Cr(IV) intermediates in the formation of either binary or ternary adducts. The cross-linking reaction was consistent with the attack of DNA by transient Cr(III)-ascorbate complexes. The yield of Cr(III)-DNA adducts was similar on dsDNA and AGT, ACT, or CT oligonucleotides and was strongly inhibited by Mg(2+), suggesting predominant coordination of Cr(III) to DNA phosphate oxygens. We also detected cross-linking of ascorbate to DNA in Cr(VI)-exposed human lung A549 cells that were preincubated with dehydroascorbic acid to create normal levels of intracellular ascorbate. Ascorbate-Cr-DNA cross-links accounted for approximately 6% of the total Cr-DNA adducts in A549 cells. Shuttle-vector experiments showed that ascorbate-Cr-DNA cross-links were mutagenic in human cells. Our results demonstrate that in addition to reduction of Cr(VI) to DNA-reactive Cr(III), vitamin C contributes to the genotoxicity of Cr(VI) via a direct chemical modification of DNA. The absence of Asc in A549 and other human cultured cells indicates that cells maintained under the usual in vitro conditions lack the most important reducing agent for Cr(VI) and would primarily display slow thiol-dependent activation of Cr(VI).     

Time-dependent uptake, distribution and biotransformation of chromium(VI) in individual and bulk human lung cells: application of synchrotron radiation techniques

Chromium(VI) is a human carcinogen, primarily affecting the respiratory tract probably via active transport into cells, followed by the reduction to Cr(III) with the formation of DNA-damaging intermediates. Distribution of Cr and endogenous elements within A549 human lung adenocarcinoma epithelial cells, following treatment with Cr(VI) (100 M, 20 min or 4 h) were studied by synchrotron-radiation-induced X-ray emission (SRIXE) of single freeze-dried cells. After the 20-min treatment, Cr was confined to a small area of the cytoplasm and strongly co-localized with S, Cl, K, and Ca. After the 4-h treatment, Cr was distributed throughout the cell, with higher concentrations in the nucleus and the cytoplasmic membrane. This time-dependence corresponded to ~100% or 0% clonogenic survival of the cells following the 20-min or 4-h treatments, respectively, and could potentially be explained by a new cellular protective mechanism. Such processes may also be important in reducing the potential hazards of Cr(III) dietary supplements, for which there is emerging evidence that they exert their anti-diabetic effects via biological oxidation to Cr(VI). The predominance of Cr(III) was confirmed by micro-XANES spectroscopy of intracellular Cr hotspots. X-ray absorption spectroscopy (XANES and EXAFS, using freeze-dried cells after the 0–4-h treatments) was used to gain insight into the chemical structures of Cr(III) complexes formed during the intracellular reduction of Cr(VI). The polynuclear nature of such complexes (probably with a combination of carboxylato and hydroxo bridging groups and O-donor atoms of small peptides or proteins) was established by XAFS data analyses.Electronic Supplementary Material Supplementary material is available for this article at     

Cytotoxicity studies of chromium(III) complexes on human dermal fibroblasts

The cytotoxicity of certain Cr(III) complexes, such as [Cr(salen)(H(2)O)(2)](+), [Cr(edta)(H(2)O)](-), [Cr(en)(3)](3+), [Cr(ox)(3)](3-), [Cr(pic)(3)], and CrCl(3), which differ in ionic character and ligand environment in human dermal skin fibroblasts, has been studied. After 72 h of exposure to 100 microM doses of chromium(III) complexes, the order in which the complexes had an inhibitory effect on cell viability was [Cr(en)(3)](3+) > [Cr(salen)(H(2)O)(2)](+) > [Cr(ox)(3)](3-) > [Cr(edta)(H(2)O)](-) > [Cr(pic)(3)] > CrCl(3). Based on viability studies it was confirmed that [Cr(en)(3)](3+), a triply charged cation, inhibits cell proliferation, and therefore, it was chosen to carry out further investigations. [Cr(en)(3)](3+), at a dose of 50 microM, was found to bring about surface morphological changes, evidenced by cellular blebbing and spike formation accompanied by nuclear damage. TEM analysis revealed substantial intracellular damage to fibroblasts in terms of the formation of apoptotic bodies and chromatin condensation, thus reflecting cell death. FACS analysis further revealed DNA damage by formation of a sub-G(1) peak with 84.2% DNA as aneuploid DNA and arrest of the G(2) / M phase of the cell cycle. Cellular DNA damage was confirmed by agarose gel electrophoresis with the characteristic appearance of a DNA streak in DNA isolated from [Cr(en)(3)](3+)-treated fibroblasts. The proposed mechanism suggests the plausible role of Cr(V), formed as a result of oxidation of Cr(III) by cellular oxidative enzymes, in the cytotoxic response. Consequently, any Cr(III) complex that is absorbed by cells and can be oxidized to Cr(V) must be considered a potential carcinogen. This has potential implications for the increased use of Cr(III) complexes as dietary supplements and highlights the need to consider the cytotoxicity and genotoxicity of a variety of Cr(III) complexes and to understand the potential hazards of Cr(III) complexes encountered in research laboratories.     

Oxidative damage induced by chromium (VI) in rat erythrocytes: protective effect of selenium

Excess chromium (Cr) exposure is associated with various pathological conditions including hematological dysfunction. The generation of oxidative stress is one of the plausible mechanisms behind Cr-induced cellular deteriorations. The efficacy of selenium (Se) to combat Cr-induced oxidative damage in the erythrocytes of adult rats was investigated in the current study. Female Wistar rats were randomly divided into four groups of six each: group I served as controls which received standard diet, group II received in drinking water K₂Cr₂O₇ alone (700 ppm), group III received both K₂Cr₂O₇ and Se (0.5 Na₂SeO₃ mg/kg of diet), and group IV received Se (0.5 mg/kg of diet) for 3 weeks. Rats exposed to K₂Cr₂O₇ showed an increase of malondialdehyde and protein carbonyl levels and a decrease of sulfhydryl content, glutathione, non-protein thiol, and vitamin C levels. A decrease of enzyme activities like catalase, glutathione peroxidase, and superoxide dismutase activities was also noted. Co-administration of Se with K₂Cr₂O₇ restored the parameters cited above to near-normal values. Therefore, our investigation revealed that Se was a useful element preventing K₂Cr₂O₇-induced erythrocyte damages.     

Sulfate transport in human lung fibroblasts (IMR-90)

Sulfate transport in a fibroblast cell line derived from human lung (IMR-90) occurred mainly via high- and low-affinity, SITS-sensitive pathways and to a lesser extent by an SITS-insensitive mechanism. In low-ionic-strength media (sucrose substituted for salts) the apparent Km of the carrier-mediated sulfate influx was 1 mM. At 0.3 mM, the sulfate concentration normally found in human serum, the contribution of the SITS-insensitive pathway was negligible. In physiological salts solution, an SITS-sensitive, high-affinity (Km 34 +/- 14 microM) sulfate influx system was observed at extracellular sulfate concentrations less than 100 microM. Between 100 and 500 microM sulfate, the range normally found in human serum, sulfate influx occurred via an SITS-sensitive, low-affinity pathway and to a small extent by an SITS-insensitive mechanism. Extracellular chloride inhibited the influx and stimulated the efflux of sulfate. Bicarbonate and thiosulfate inhibited sulfate influx but had no effect on sulfate efflux. Phosphate, arsenate, or Na+ did not affect sulfate uptake. These results indicate that in human lung fibroblast IMR-90 cells sulfate is transported mainly via an SO4(2-)/Cl- exchange system independent of the phosphate or Na+ transport. Since sulfate concentration as high as 50 mM only slightly increased sulfate efflux, SO4(2-)/SO4(2-) exchange is probably a minor component of sulfate uptake.     

Oxidative stress-related lung dysfunction by chromium(VI): alleviation by Citrus aurantium L.

Chromium(VI), a very strong oxidant, causes high cytotoxicity through oxidative stress in tissue systems. Our study investigated the potential ability of ethanolic Citrus aurantium L., family Rutaceae extract, used as a nutritional supplement, to alleviate lung oxidative damage induced by Cr(VI). A high-performance liquid chromatography coupled with a mass spectrometer method was developed to separate and identify flavonoids in C. aurantium L. Six flavonoids were identified, as (1) poncirin, (2) naringin, (3) naringenin, (4) quercetin, (5) isosinensetin, and (6) tetramethyl-o-isoscutellarein. Adult Wistar rats, used in this study, were divided into six groups of six animals each: group I served as controls which received standard diet, group II received via drinking water K₂Cr₂O₇ alone (700 ppm), groups III and IV were pretreated for 10 days with ethanol extract of C. aurantium L. at doses of 100 and 300 mg/kg body weight/day, respectively, and then K₂Cr₂O₇ was administrated during 3 weeks, and groups V and VI received during 10 days only C. aurantium L. ethanol extract at doses of 100 and 300 mg/kg/day, respectively. Ethanol extract of C. aurantium L. was administered orally. Rats exposed to Cr(VI) showed in lung an increase in malondialdehyde and protein carbonyl levels and a decrease in sulflydryl content, glutathione, nonprotein thiol, and vitamins C and E levels. Decreases in enzyme activities such as in Na⁺K⁺ ATPase, catalase, glutathione peroxidase, and superoxide dismutase were noted. Pretreatment with C. aurantium L. of chromium-treated rats ameliorated all biochemical parameters. Lung histological studies confirmed the biochemical parameters and the beneficial role of C. aurantium L.     

Lack of genotoxic effects in hematopoietic and gastrointestinal cells of mice receiving chromium(VI) with the drinking water

Chromium(VI) is genotoxic when tested in vitro or injected parenterally in such a way to escape detoxification mechanisms. However, its genotoxicity and potential carcinogenicity are lost, depending on dose and administration route, due to efficient reduction in body fluids and nontarget cells. Chromium(VI) is a Group 1 IARC carcinogen, but only in the respiratory tract and in well-defined occupational settings that involved heavy exposures. Recently, concern has been expressed that oral chromium(VI) may be a gastric carcinogen. We demonstrated that administration of very high doses of chromium(VI) with the drinking water does not induce any clastogenic effect in hematopoietic cells of adult mice and their fetuses. Thereafter, we investigated whether administration of chromium(VI) with the drinking water may induce local genotoxic effects in the gastrointestinal tract. Sodium dichromate dihydrate was administered to mice for 9 consecutive months, at doses corresponding to 5 and 20 mg chromium(VI)/l, which exceed drinking water standards by 100 and 400 times, respectively. Under these conditions, chromium(VI) failed to enhance the frequency of DNA-protein crosslinks and did not cause oxidative DNA damage, measured in terms of 8-oxo-2'-deoxyguanosine, in the forestomach, glandular stomach and duodenum. When cells from the same organs were isolated and challenged in vitro with chromium(VI), as positive controls, the same genotoxicity biomarkers were evidently affected. Thus, consistently with the knowledge accumulated in 50 years of research on chromium(VI) kinetics and metabolism, oral chromium(VI) appears to be devoid of genotoxicity in the gastrointestinal tract. After 9 months, we did not observe any variation of tumor yield in skin, lung, forestomach, glandular stomach, and duodenum of chromium(VI)-treated mice. These results are discussed in the light of literature data, also including a recent 2-year carcinogenicity study performed by the National Toxicology Program.     

Reduction of chromium(VI) by D-galacturonic acid and formation of stable chromium(V) intermediates

The interaction of dichromate with D-galacturonic acid in aqueous solution, as a function of pH, is described. The reaction involves the reduction of Cr(VI) to Cr(III), but the reaction rate is remarkably dependent on pH. In fact, the reduction of Cr(VI) to Cr(III) proceeds rather quickly in strongly acidic solutions, while it is slow in neutral or moderately acidic media. In all cases, according to the ESR evidence, Cr(V) species are found as intermediates. The stability of the Cr(V) species increases with increasing pH, so that it may be suggested that the overall reaction rate is controlled by the Cr(V) to Cr(III) conversion.     

Effects of chromium(VI) and chromium(III) on energy charge and oxygen consumption in rat thymocytes

The cytotoxic effects of chromium compounds in two oxidation states have been studied in rat thymocytes. endogenous nucleotide levels and oxygen consumption were examined as relevant parameters of the physiological state of the cell. Incubation of rat thymocytes with Cr(VI) produced a marked unbalance of endogenous purine nucleotide pool and a parallel decrease in oxygen consumption. A close correlation between the reduction of oxygen consumption and ATP level in rat thymocytes treated with increasing concentrations of Cr(VI) has been found. In rat thymocytes permeabilized with digitonin and in isolated rat liver mitochondria both Cr(VI) and Cr(III) showed, at different range of concentrations, a marked inhibition of maximal oxygen consumption rate (uncoupled respiration). The effects observed were depending on chromium oxidation state and on different mitochondrial sites of substrate oxidation.     

Estimates of heavy metal tolerance and chromium(VI) reducing ability of Pseudomonas aeruginosa CCTCC AB93066: chromium(VI) toxicity and environmental parameters optimization

The potential role of parameters in the reduction of hexavalent chromium [Cr(VI)] by Pseudomonas aeruginosa is not well documented. In this study, laboratory batch studies were conducted to assess the effect of a variety of factors, e.g., carbon sources, salinity, initial Cr(VI) concentrations, co-existing ions and a metabolic inhibitor, on microbial Cr(VI) reduction to Cr(III) by P. aeruginosa AB93066. Strain AB93066 tolerated up to 400 mg/L of Cr(VI) in nutrient broth medium compared to only 150 mg/L of Cr(VI) in nutrient agar. This bacteria exhibited different levels of resistance against Pb(II) (200 mg/L), Cd(II) (100 mg/L), Ni(II) (100 mg/L), Cu(II) (100 mg/L), Co(II) (50 mg/L) and Hg(II) (5 mg/L). Cr(VI) reduction was significantly promoted by the addition of glucose and glycerine but was strongly inhibited by the presence of methanol and phenol. The rate of Cr(VI) reduction increased with increasing concentrations of Cr(VI) and then decreased at higher concentrations. The presence of Ni(II) stimulated Cr(VI) reduction, while Pb(II), Co(II) and Cd(II) had adverse impact on reduction ability of this strain. Cr(VI) reduction was also inhibited by high levels of NaCl, various concentrations of sodium azide and 20 mM of SO₄ ^2?, MoO₄ ^2?, NO₃ ^?, PO₄ ^3?. No significant relationship was observed between Cr(VI) reduction and redox potential of the culture medium. Scanning electron microscopy showed visible morphological changes in the cells due to chromate stress. Fourier transform infrared spectroscopy analysis revealed chromium species was likely to form complexes with certain functional groups such as carboxyl and amino groups on the surface of P. aeruginosa AB93066. Overall, above results are beneficial to the bioremediation of chromate-polluted industrial wastewaters.     

Response of antioxidant defense system to chromium (VI)-induced cytotoxicity in human diploid cells

The aim of this study is to establish antioxidant indicators of chromium toxicity in fetal human lung fibroblasts (HLF). The results obtained corroborate and develop our earlier observation of low-dose and long-term action of Cr(VI) on human cells in culture. In the case of a nontoxic chromium dose, temporary oxidative stress is overcome by increased activity of the antioxidant system with correlation to cell cycle re-entry. The toxic concentrations misbalance the cell antioxidant defense systems and cause irreversible growth arrest and massive cell death by apoptosis. Sub-toxicity is defined as toxicity stretched in time. The activity of GPx (glutathione peroxidase) is proposed as a biomarker of oxidative stress caused by Cr(VI), and the GR (glutathione reductase) inhibition is considered as a marker of the toxicity developed under the complex Cr(VI) action. In HLF cells the glutathione dependent defense system is the first system destroyed in response to toxic chromium action. Only the balance between SOD (superoxide dismutase) and H₂O₂ degrading enzymes (catalase and GPx), should play an important role in the fate of a cell, not individual enzymes.