In vivo free radical generation by chromium(VI): an electron spin resonance spin-trapping investigation

Coenzyme Q10, Biochanin A and Phloretin Attenuate Cr(VI)-Induced Oxidative Stress and DNA Damage by Stimulating Nrf2/HO-1 Pathway in the Experimental Model

Hexavalent chromium [Cr(VI)] has emerged as a prevailing environmental and occupational contaminant over the past few decades. However, the knowledge is sparse regarding Cr(VI)-induced neurological aberrations, and its remediation through natural bioactive compounds has not been fully explored. This study intended to probe the possible invigorative effects of nutraceuticals such as coenzyme Q10 (CoQ10), biochanin A (BCA), and phloretin (PHL) on Cr(VI) intoxicated Swiss albino mice with special emphasis on Nrf2/HO-1/NQO1 gene expressions. Mice received potassium dichromate (75 ppm) through drinking water and were simultaneously co-treated intraperitoneally with CoQ10 (10 mg/kg), BCA, and PHL (50 mg/kg) each for 30-day treatment period. The statistics highlight the elevated levels of lipid peroxidation (LPO) and protein carbonyl content (PCC) with a concomitant reduction in the superoxide dismutase (SOD), glutathione-S-transferase (GST), reduced glutathione (GSH), total thiols (TT), catalase (CAT), and cholinesterase activities in the Cr(VI)-exposed mice. The collateral assessment of DNA fragmentation, DNA breakages, and induced histological alterations was in conformity with the above findings in conjugation with the dysregulation in the Nrf2 and associated downstream HO-1 and NQO1 gene expressions. Co-treatment with the selected natural compounds reversed the above-altered parameters significantly, thereby bringing cellular homeostasis in alleviating the Cr(VI)-induced conciliated impairments. Our study demonstrated that the combination of different bioactive compounds shields the brain better against Cr(VI)-induced neurotoxicity by revoking the oxidative stress-associated manifestations. These compounds may represent a new potential combination therapy due to their ability to modulate the cellular antioxidant responses by upregulating the Nrf2/HO-1/NQO1 signaling pathway against Cr(VI)-exposed population. HIGHLIGHTS: Cr(VI)-associated heavy metal exposure poses a significant threat to the environment, especially to living organisms. Cr(VI) exposure for 30 days resulted in the free radical's generation that caused neurotoxicity in the Swiss albino mice. Natural compounds such as coenzyme Q10, biochanin A, and phloretin counteracted the neurotoxic effect due to Cr(VI) exposure in scavenging of free radicals by enhancing Nrf2/HO-1/NQO1 gene expressions in maintaining the cellular homeostasis.

Research on the on-line determination of formaldehyde gas by the gas-liquid phase chemiluminescence method

Based on the gas-liquid phase chemiluminescence tester independently developed by our laboratory, a highly sensitive, fast and accurate on-line detection method of formaldehyde gas in ambient atmosphere is established. The chemiluminescence system and the trace formaldehyde gas in the air directly undergo an interface heterogeneous chemiluminescence reaction to obtain a strong chemiluminescence signal. Through the measurement of the chemiluminescence signal intensity, a highly sensitive, real-time and on-line method for the determination of formaldehyde in the air was established. Factors influencing the experimental results such as gallic acid, potassium dichromate, reaction medium concentration, surfactant type and concentration, pump speed, tube length, and interfering gas were discussed based on the single factor and orthogonal analysis results. Finally, the optimal detection conditions were collected, and the detection results were compared with the national standard phenol reagent method. The results show that when the concentration of the standard formaldehyde gas is in the range of 0-0.582 μg L-1, the linear equation of this method is y = 208x + 29.667, the linear coefficient is R 2 = 0.997, and the minimum detection concentration of formaldehyde is 2.327 × 10-3 μg L-1. Under the same external conditions, the comparison and analysis using the national standard phenol reagent method proved that this method has the advantages of fast detection speed, low detection limit, good sensitivity, and accurate results, which can be used for real-time and online determination of trace formaldehyde in ambient air.

A Multidisciplinary Approach to Evaluate the Effects of Contaminants of Emerging Concern on Natural Freshwater and Brackish Water Phytoplankton Communities

Ecotoxicological assays on monospecific phytoplankton have limited application for detecting the effects of environmental pollutants on multiple species communities. With this study, we took an ecotoxicological, ecological, and biochemical approach to evaluate the effects of two contaminants of emerging concern (zinc oxide nanoparticles, ZnO NPs, and potassium dichromate, K₂Cr₂O₇) at different concentrations (K₂Cr₂O₇ 5.6-18-50 mg/L; ZnO NPs 10-100-300 mg/L) on natural freshwater and brackish water phytoplankton communities. Cell density and absorbance values decreased in freshwater and brackish water phytoplankton communities after exposure to ZnO NPs (100 mg/L and 300 mg/L only for freshwater), whereas growth rate was increased in both freshwater and brackish water phytoplankton communities after exposure to ZnO NPs 10 mg/L. Differently, there was no clear relationship between concentration and inhibition growth after exposure to K₂Cr₂O₇: the lowest cell density was recorded after exposure to 18 mg/L. Moreover, the evenness index value was lower compared to the other concentrations, indicating the growth of a few, albeit resistant species to higher K₂Cr₂O₇ concentrations. Generally, Bacillariophyceae and Dinoficee were prevalent in phytoplankton cultures after exposure to ZnO NPs and K₂Cr₂O₇. The Shannon-Wiener index was slightly higher in the negative than the positive controls, but diversity was low after all treatments in both ecotoxicological assays. The evenness index was always very close to zero, indicating the numerical predominance of one or very few species. Finally, the decrease in chlorophyll-a and pheophytin-a in both ecotoxicological assays indicated a change in photosynthetic activity. Our findings provide evidence for alterations in natural phytoplankton after exposure to emerging contaminants that can disrupt an entire ecosystem's integrity.

Novel Biochemical Properties and Physiological Role of the Flavin Mononucleotide Oxidoreductase YhdA from Bacillus subtilis

Cr(VI) is mutagenic and teratogenic and considered an environmental pollutant of increasing concern. The use of microbial enzymes that convert this ion into its less toxic reduced insoluble form, Cr(III), represents a valuable bioremediation strategy. In this study, we examined the Bacillus subtilis YhdA enzyme, which belongs to the family of NADPH-dependent flavin mononucleotide oxide reductases and possesses azo-reductase activity as a factor that upon overexpression confers protection on B. subtilis from the cytotoxic effects promoted by Cr(VI) and counteracts the mutagenic effects of the reactive oxygen species (ROS)-promoted lesion 8-OxoG. Further, our in vitro assays unveiled catalytic and biochemical properties of biotechnological relevance in YhdA; a pure recombinant His10-YhdA protein efficiently catalyzed the reduction of Cr(VI) employing NADPH as a cofactor. The activity of the pure oxidoreductase YhdA was optimal at 30°C and at pH 7.5 and displayed Km and Vmax values of 7.26 mM and 26.8 μmol·min-1·mg-1 for Cr(VI), respectively. Therefore, YhdA can be used for efficient bioremediation of Cr(VI) and counteracts the cytotoxic and genotoxic effects of oxygen radicals induced by intracellular factors and those generated during reduction of hexavalent chromium.IMPORTANCE Here, we report that the bacterial flavin mononucleotide/NADPH-dependent oxidoreductase YhdA, widely distributed among Gram-positive bacilli, conferred protection to cells from the cytotoxic effects of Cr(VI) and prevented the hypermutagenesis exhibited by a MutT/MutM/MutY-deficient strain. Additionally, a purified recombinant His10-YhdA protein displayed a strong NADPH-dependent chromate reductase activity. Therefore, we postulate that in bacterial cells, YhdA counteracts the cytotoxic and genotoxic effects of intracellular and extracellular inducers of oxygen radicals, including those caused by hexavalent chromium.

Characteristics of natural biopolymers and their derivative as sorbents for chromium adsorption: a review

Abstract

Chromium is widely used in industry, and improper disposal of wastewater and industrial residues containing excessive chromium can contaminate water and soil, endangering both environmental and human health. Natural biopolymers and their derivatives have been investigated for removal of chromium (Cr) from wastewater. Cellulose, lignin, tannin, chitin, chitosan, and polypeptides are abundant in nature, and have high potential as adsorbents due to their easy access, low cost, and the recyclability of the captured heavy metals. In order to improve their mechanical strength, recyclability, specific surface area, binding site number, and adsorption rate as adsorbents, native materials have also been modified. This review discusses the source of chromium contamination and the main species of interest, as well as their toxicity. The structures of the aforementioned biopolymers were analyzed, and the adsorption mechanism of chromium and the main influencing factors on this process are discussed. The modification methods of various adsorbents and their adsorption effects on chromium are also detailed, and the developmental direction of research on the use of biopolymer adsorption remediation to control chromium contamination is discussed.

Graphical abstract

Biosorption and biotransformation of hexavalent chromium [Cr(VI)]: A comprehensive review

Chromium (VI) is one of the most common environmental contaminant due to its tremendous industrial applications. It is non-biodegradable as it is a heavy metal, and hence, of major concern. Therefore, it is pertinent that the remediation method should be such that brings chromium within permissible limits before the effluent is discharged. Several different strategies are adopted by microorganisms for Cr (VI) removal mostly involving biosorption and biotransformation or both. These mechanisms are based on the surface nature of the biosorbent and the availability of reductants. This review article focuses on chromium pollution problem, its chemistry, sources, effects, remediation strategies by biological agents and detailed chromium detoxification mechanism in microbial cell. A summary of applied in situ and ex situ chromium bioremediation technologies is also listed. This can be helpful for developing technologies to be more efficient for Cr (VI) removal thereby bridging the gap between laboratory findings and industrial application for chromium remediation.

Effects of hexavalent chromium on phytoplankton and bacterioplankton of the Río de la Plata estuary: an ex-situ assay

We examined the responses of the phytoplankton and the bacterioplankton of the freshwater zone of the Río de la Plata estuary when exposed to an addition of hexavalent chromium (Cr⁺⁶). The planktonic community from a coastal site was exposed to a chromium increase of 80 μg L^-1 for 72 h in laboratory conditions. The results showed a decrease in the concentration of Cr⁺⁶ by 33% in the treatments, along with significant decreases in chlorophyll-a (63%), the chlorophyll-a:pheophytin-a ratio (33%), oxygen production (37%), and in the total density of the phytoplankton (15%). The relative abundance of chlorophytes and diatoms decreased, while the cyanobacteria thrived. Finally, the total bacterial density and the density of viable bacteria decreased. These results show that even small increments in Cr⁺⁶ can cause significant effects on the phytoplankton and bacterioplankton, which could potentially affect other trophic levels of the community, risking alterations of the entire ecosystem.

Selenium Administration Alleviates Toxicity of Chromium(VI) in the Chicken Brain

Selenium (Se) can play a protective role against heavy metal toxicity. This experiment aims to evaluate the effect of Se supplementation at different doses on the chicken brains. Oxidative stress was induced in the chicken brains by chromium(VI). A total of 105 Hyland brown male chickens were randomly divided into seven groups, including the control group, poisoned group [6%LD₅₀ K₂Cr₂O₇ body weight (B.W.)], and detoxification groups K₂Cr₂O₇ (6%LD₅₀) + Se (0.31, 0.63, 1.25, 2.50, and 5.00 Na₂SeO₃ mg/kg B.W.) orally in water for 42 days. The chickens were detected by the activities of mitochondrial membrane potential, 2'-benzoyloxycinnamaldehyde, superoxide dismutase (SOD), malondialdehyde (MDA), glutathione (GSH), and Ca²⁺-ATPase. Cr(VI) administration caused histopathological damage. In addition, changes in oxidative stress indicators were observed in the chicken's brains. Se supplement increased the levels of GSH, mitochondrial membrane potential (MMP), and Ca²⁺-ATPase and reduced MDA activity in the detoxification groups. However, the high-dose Se supplementation groups of 2.50 and 5.00 mg/kg reduced the activities of GSH, MMP, and Ca²⁺-ATPase; increased the brain-body ratio; and increased SOD activity. In conclusion, Cr(VI) exposure caused oxidative stress. Se exerted a remission effect on toxic responses in the chicken brains. However, a high Se concentration was synergistic to the toxic effect of Cr(VI).

Cytotoxicity assays to evaluate tannery effluents treated by photoelectrooxidation

The advanced oxidation process (AOP) is used to increase the treatment efficiency of effluents however, it is necessary to compare the toxicity of treated and untreated effluents to evaluate if the decontamination process does not cause any biological harm. Cultured cells have been previously used to assess the genotoxic and cytotoxic potential of various compounds. Hence, the aim of this work was to assess the applicability of cytotoxicity assays to evaluate the toxicity related to the AOP treatment. Samples of an industrial effluent were collected after their treatment by a conventional method. Cytotoxicity of standard and AOP treated effluents was assessed in CRIB and HEp-2 cell line using the MTT and neutral red assays. We observed decrease at cell viability in the both assays (50% MTT and 13% NRU) when cells were exposed to the AOP treatment in the highest concentration. Thus, cytotoxic assays in cultured cells can be explored as an useful method to evaluate toxicity as well as to optimize effluents treatment process.

Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: a review

Chromium is a highly toxic non-essential metal for microorganisms and plants, and its occurrence is rare in nature. Lower to higher chromium containing effluents and solid wastes released by activities such as mining, metal plating, wood preservation, ink manufacture, dyes, pigments, glass and ceramics, tanning and textile industries, and corrosion inhibitors in cooling water, induce pollution and may cause major health hazards. Besides, natural processes (weathering and biochemical) also contribute to the mobility of chromium which enters in to the soil affecting the plant growth and metabolic functions of the living species. Generally, chemical processes are used for Cr- remediation. However, with the inference derived from the diverse Cr-resistance mechanism displayed by microorganisms and the plants including biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux, bioremediation is emerging as a potential tool to address the problem of Cr(VI) pollution. This review focuses on the chemistry of chromium, its use, and toxicity and mobility in soil, while assessing its concentration in effluents/wastes which becomes the source of pollution. In order to conserve the environment and resources, the chemical/biological remediation processes for Cr(VI) and their efficiency have been summarised in some detail. The interaction of chromium with various microbial/bacterial strains isolated and their reduction capacity towards Cr(VI) are also discussed.

Attenuation of chromium toxicity by bioremediation technology

Chromium is an important toxic environmental pollutant. Chromium pollution results largely from industrial activities, but other natural and anthropogenic sources also contribute to the problem. Plants that are exposed to environmental contamination by chromium are affected in diverse ways, including a tendency to suffer metabolic stress. The stress imposed by Cr exposure also extends to oxidative metabolic stress in plants that leads to the generation of active toxic oxygen free radicals. Such active free radicals degrade essential biomolecules and distort plant biological membranes. In this chapter, we describe sources of environmental chromium contamination, and provide information about the toxic impact of chromium on plant growth and metabolism. In addition, we address different phytoremediation processes that are being studied for use worldwide, in contaminated regions, to address and mitigate Cr pollution. There has been a long history of attempts to successfully mitigate the toxic effects of chromium-contaminated soil on plants and other organisms. One common approach, the shifting of polluted soil to landfills, is expensive and imposes environmental risks and health hazards of its own. Therefore, alternative eco-friendly bioremediation approaches are much in demand for cleaning chromium-polluted areas. To achieve its cleaning effects, bioremediation utilizes living organisms (bacteria, algae, fungi, and plants) that are capable of absorbing and processing chromium residues in ways which amend or eliminate it. Phytoremediation (bioremediation with plants) techniques are increasingly being used to reduce heavy metal contamination and to minimize the hazards of heavy metal toxicity. To achieve this, several processes, viz., rhizofiltration, phytoextraction, phytodetoxification, phytostabilization, and phytovolatilization, have been developed and are showing utility in practice, or promise. Sources of new native hyperaccumulator plants for use at contaminated sites are needed and constitute a key goal of ongoing phytoremediation research programs. Such new plants are needed to enhance the attractiveness of phytoremediation as an effective, affordable, and eco-friendly technique to achieve successful clean-up of metal-contaminated sites worldwide.

Chromium III exposure inhibits brain Na+K+ATPase activity of Clarias batrachus L. involving lipid peroxidation and deficient mitochondrial electron transport chain activity

The present study elucidated the role of lipid peroxidation and diminished mitochondrial electron transport chain activity in partial dysfunction of brain Na+K+ATPase of Clarias batrachus exposed to chromium III ions. The fish were exposed to 10% and 20% of the derived 96 h LC50 value, 5.69 mg/L and 11.38 mg/L, respectively, and sampled on 20, 40 and 60 days. Exposure to chromium III on fish brain demonstrated an increased lipid peroxidation, production of protein carbonyl and reactive oxygen species and loss of protein thiol groups in synaptosomal fraction with decreased activity of Na+K+ATPase, partial inactivation of mitochondrial electron transport chain activity and energy depletion.

Potassium dichromate induced cytotoxicity, genotoxicity and oxidative stress in human liver carcinoma (HepG2) cells

Chromium is a widespread industrial waste. The soluble hexavalent chromium Cr (VI) is an environmental contaminant widely recognized to act as a carcinogen, mutagen and teratogen towards humans and animals. The fate of chromium in the environment is dependent on its oxidation state. Hexavalent chromium primarily enters the cells and undergoes metabolic reduction to trivalent chromium, resulting in the formation of reactive oxygen species together with oxidative tissue damage and a cascade of cellular events. However, the results from in vitro studies are often conflicting. The aim of this study was to develop a model to establish relationships between cytotoxicity, genotoxicity and oxidative stress, in human liver carcinoma [HepG2] cells exposed to potassium dichromate. HepG2 cells were cultured following standard protocols and exposed to various concentrations [0–50 μM] of potassium dichromate [K₂Cr₂O₇]. Following exposure to the toxic metal, the MTT assay was performed to assess the cytotoxicity, the thiobarbituric acid test to evaluate the degree of lipid peroxidation as an indicator of oxidative stress and the alkaline comet assay was used to assess DNA damage to study genotoxicity. The results of the study indicated that potassium dichromate was cytotoxic to HepG2 cells. The LD₅₀ values of 8.83 ± 0.89 μg/ml, 6.76 ± 0.99 μg/ml, respectively, for cell mortality at 24 and 48 hrs were observed, indicating a dose- and time-dependent response with regard to the cytotoxic effects of potassium dichromate. A statistically significant increase in the concentration of malondialdehyde [MDA], an indicator of lipid peroxidation, was recorded in exposed cells [15.9 – 69.9 μM] compared to control [13 μM]. Similarly, a strong dose-response relationship (p<0.05) was also obtained with respect to potassium dichromate induced DNA damage (comet assay) in HepG2 cells exposed [3.16 ± 0.70 – 24.84 ± 1.86 microns – mean comet tail length]; [12.4 ± 1.45% – 76 ± 1.49% – % tail DNA] to potassium dichromate than control [3.07 ± 0.26 microns – mean comet tail length]; [2.69 + 0.19% – % Tail DNA], respectively. The results demonstrated that potassium dichromate was highly cytotoxic to HepG2 cells, and its cytotoxicity seems to be mediated by oxidative stress and DNA damage.

Oxidative stress, DNA damage, and antioxidant enzyme activity induced by hexavalent chromium in Sprague-Dawley rats

Chromium is a widespread industrial compound. The soluble hexavalent chromium Cr (VI) is an environmental contaminant widely recognized as carcinogen, mutagen, and teratogen toward humans and animals. The fate of chromium in the environment is dependent on its oxidation state. The reduction of Cr (VI) to Cr (III) results in the formation of reactive intermediates leading to oxidative tissue damage and cellular injury. In the present investigation, Potassium dichromate was given intraperitoneally to Sprague-Dawley rats for 5 days with the doses of 2.5, 5.0, 7.5, and 10 mg/kg body weight per day. Oxidative stress including the level of reactive oxygen species (ROS), the extent of lipid peroxidation and the activity of antioxidant enzymes in both liver and kidney was determined. DNA damage in peripheral blood lymphocytes was determined by single-cell gel electrophoresis (comet assay). The results indicated that administration of Cr (VI) had caused a significant increase of ROS level in both liver and kidney after 5 days of exposure, accompanied with a dose-dependent increase in superoxide dismutase and catalase activities. The malondialdehyde content in liver and kidney was elevated as compared with the control animals. Dose- and time-dependent effects were observed on DNA damage after 24, 48, 72, and 96 h posttreatment. The results obtained from the present study showed that Cr (VI) could induce dose- and time-dependent effects on DNA damage, both liver and kidney show defense against chromium-induced oxidative stress by enhancing their antioxidant enzyme activity. However, liver was found to exhibit more antioxidant defense than the kidney.

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.

Effect of chromate stress on Escherichia coli K-12

The nature of the stress experienced by Escherichia coli K-12 exposed to chromate, and mechanisms that may enable cells to withstand this stress, were examined. Cells that had been preadapted by overnight growth in the presence of chromate were less stressed than nonadapted controls. Within 3 h of chromate exposure, the latter ceased growth and exhibited extreme filamentous morphology; by 5 h there was partial recovery with restoration of relatively normal cell morphology. In contrast, preadapted cells were less drastically affected in their morphology and growth. Cellular oxidative stress, as monitored by use of an H2O2-responsive fluorescent dye, was most severe in the nonadapted cells at 3 h postinoculation, lower in the partially recovered cells at 5 h postinoculation, and lower still in the preadapted cells. Chromate exposure depleted cellular levels of reduced glutathione and other free thiols to a greater extent in nonadapted than preadapted cells. In both cell types, the SOS response was activated, and levels of proteins such as SodB and CysK, which can counter oxidative stress, were increased. Some mutants missing antioxidant proteins (SodB, CysK, YieF, or KatE) were more sensitive to chromate. Thus, oxidative stress plays a major role in chromate toxicity in vivo, and cellular defense against this toxicity involves activation of antioxidant mechanisms. As bacterial chromate bioremediation is limited by the toxicity of chromate, minimizing oxidative stress during bacterial chromate reduction and bolstering the capacity of these organisms to deal with this stress will improve their effectiveness in chromate bioremediation.

Construction of a subtractive library from hexavalent chromium treated winter flounder (Pseudopleuronectes americanus) reveals alterations in non-selenium glutathione peroxidases

Chromium is released during several industrial processes and has accumulated in some estuarine areas. Its effects on mammals have been widely studied, but relatively little information is available on its effects on fish. Gene expression changes are useful biomarkers that can provide information about toxicant exposure and effects, as well as the health of an organism and its ability to adapt to its surroundings. Therefore, we investigated the effects of Cr(VI) on gene expression in the sediment dwelling fish, winter flounder (Pseudopleuronectes americanus). Winter flounder ranging from 300 to 360 g were injected i.p. with Cr(VI) as chromium oxide at 25 microg/kg chromium in 0.15N KCl. Twenty-four hours following injections, winter flounder were euthanized with MS-222 and the livers were excised. Half of the livers were used to make cytosol and the other half were used to isolate mRNA for subtractive hybridization. Subtractive clones obtained were spotted onto nylon filters, which revealed several genes with potentially altered expression due to Cr(VI), including an alpha class GST, 1-Cys peroxiredoxin (a non-selenium glutathione peroxidase), a P-450 2X subfamily member, two elongation factors (EF-1 gamma and EF-2), and complement component C3. Semi-quantitative RT-PCR was performed and confirmed that Cr(VI) down-regulated complement component C3, an EST, and two potential glutathione peroxidases, GSTA3 and 1-Cys peroxiredoxin. In addition, cytosolic GSH peroxidase activity was reduced, and silver stained SDS-PAGE gels from glutathione-affinity purified cytosol demonstrated that a 27.1 kDa GSH-binding protein was down-regulated greater than 50%. Taken together, Cr(VI) significantly altered the expression of several genes including two potential glutathione peroxidases in winter flounder.

Oxidative Stress,hogg1Expression and NF‐κB Activity in Cells Exposed to Low Level Chromium

Chromium compounds are carcinogenic to the human lung, although the detailed biochemical mechanism is still unclear. To understand the carcinogenic mechanism in cells exposed to low level hexavalent chromium, we measured the generation of reactive oxygen species (ROS) and 8-hydroxydeoxyguanosine (8-OH-dG), the transcription of hogg1, which encodes an 8-OH-dG repair protein, and NF-kappaB activation levels in the A549 human lung epithelial cell line after exposure to Cr (VI) at concentrations of 12.5 to 800 microM. In A549 cells, ROS levels and DNA binding by NF-kappaB increased in proportion to the concentration of Cr (VI). These increases were diminished by pretreatment with catalase, superoxide dismutase, or D-mannitol, but the levels of 8-OH-dG and expression of hogg1 did not change significantly with Cr (VI) exposure. These results suggest that the induction of ROS and the activation of NF-kappaB are important in the carcinogenic mechanism of Cr (VI), but it is unlikely that Cr (VI) concentrations below 800 microM increase 8-OH-dG levels or the expression of hogg1.

Characterization of the initial carbon-centered pentadienyl radical and subsequent radicals in lipid peroxidation: identification via on-line high performance liquid chromatography/electron spin resonance and mass spectrometry

The previously reported combination of an on-line high-performance liquid chromatography (LC)/electron spin resonance (ESR) system with mass spectrometric analysis (MS) created a unique technique to identify a variety of lipid-derived radicals ((.)L(d)) formed from in vitro lipid peroxidation (Iwahashi et al. [20]). To improve the sensitivity, resolution, and reliability of this method for in vitro and in vivo studies, we have investigated the effects of mobile phase pH, modifiers, and columns on the chromatographic separation of linoleic acid-derived radical adducts. Using tetrahydrofuran (THF) and 0.1% glacial acetic acid (HOAc) in an H(2)O/acetonitrile (ACN) mobile phase greatly increased the resolution and retention reproducibility of lipid radical adducts in LC/ESR. In addition, these modifications allowed the elimination of an ESR tuning problem and the synchronization of UV and ESR detection of radical adducts in on-line LC/ESR, neither of which had been possible previously. Analyte purity was therefore increased, thus increasing the reliability of radical detection via on-line LC/ESR as well as radical identification via MS analysis. For the first time, POBN adducts of linoleic carbon-centered pentadienyl radicals (L(.)) were detected and identified. The optimization of chromatography in the LC/ESR and MS combination provided a reliable and sensitive way for the detection and identification of expected radical adducts in vitro and in vivo.

Interactions of chromium with microorganisms and plants

Chromium is a highly toxic non-essential metal for microorganisms and plants. Due to its widespread industrial use, chromium (Cr) has become a serious pollutant in diverse environmental settings. The hexavalent form of the metal, Cr(VI), is considered a more toxic species than the relatively innocuous and less mobile Cr(III) form. The presence of Cr in the environment has selected microbial and plant variants able to tolerate high levels of Cr compounds. The diverse Cr-resistance mechanisms displayed by microorganisms, and probably by plants, include biosorption, diminished accumulation, precipitation, reduction of Cr(VI) to Cr(III), and chromate efflux. Some of these systems have been proposed as potential biotechnological tools for the bioremediation of Cr pollution. In this review we summarize the interactions of bacteria, algae, fungi and plants with Cr and its compounds.

Redox-modulated pathways in inflammatory skin diseases

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

In vitro and in vivo assessment of the irritation potential of different spin traps in human skin

No clinical data are available on the acute cutaneous toxicity of spin traps which are frequently used in combination with the electron paramagnetic resonance (EPR) technique for detection of free radicals and reactive oxygen/nitrogen species. The purpose of this study was to evaluate the acute dermatotoxicity of the following spin traps in human skin: C-phenyl-N-tert.-butyl nitrone (PBN), C-(4-pyridinyl-N-oxide)-N-tert.-butylnitrone (POBN), 5, 5-dimethyl-l-pyrroline-N-oxide(DMPO), 5 diethoxyphosphoryl-5-methyl-l-pyrroline-N-oxide (DEPMPO), diethyldithiocarbamate (DDC) and N-methyl-D-glucamine dithiocarbamate (MGD). The corrosivity of the test substances was first assessed in human skin in vitro by measurement of transcutaneous electrical resistance (TER). In this assay all spin traps were non-corrosive at 500 mM concentration. Subsequently cutaneous irritation of the spin traps was determined at different concentrations (50, 250 and 500 mM) in human skin according to a routine four h human patch test in comparison to the standardized irritant sodium laurylsulfate (SLS, 20%). The response was evaluated clinically as well as by a biophysical method analyzing transepidermal water loss (TEWL). PBN and DEPMPO caused a transient and weak inflammatory reaction at 500 mM in four of 17 and in two of 17 volunteers, respectively. DMPO, POBN, DDC, MGID, and the iron complexes of DDC and MGD were clinically non-irritant at all concentrations tested and no delayed-acute inflammatory reactions were observed. However, the TEWL values were significantly increased by all spin traps except DMPO at 500 mM, indicating disturbed epidermal barrier function. We conclude that the spin traps investigated have a low potential to cause acute skin toxicity and may be used safely for in vivo EPR studies in human skin.

Metabolism of acetaldehyde to methyl and acetyl radicals: in vitro and in vivo electron paramagnetic resonance spin-trapping studies

Acetaldehyde oxidation by enzymes and cellular fractions has been previously shown to produce radicals that have been characterized as superoxide anion, hydroxyl, and acetyl radicals. Here, we report that acetaldehyde metabolism by xanthine oxidase, submitochondrial particles and whole rats produces both the acetyl and the methyl radical, although only the latter was unambiguously identified in vivo. Electron paramagnetic resonance (EPR) characterization of both radicals was possible by the use of two spin traps, 5,5-dimethyl 1-pyrroline N-oxide (DMPO) and alpha-(4-pyridyl 1-oxide)-N-t-butylnitrone (POBN), and of acetaldehyde labeled with (13)C. The POBN-acetyl radical adduct proved to be unstable, but POBN was employed to monitor acetaldehyde metabolism by Sprague-Dawley rats because previous studies have shown its usefulness for in vivo spin trapping. EPR analysis of the bile collected from treated and control rats showed the presence of the POBN-methyl and of an unidentified, biomolecule-derived, POBN adduct. Because decarbonylation of the acetyl radical is one of the routes for methyl radical formation from acetaldehyde, detection of the latter in bile provides strong evidence for the production of both radicals in vivo. The results may be relevant to understanding the toxic effects of acetaldehyde itself and of its more relevant biological precursor, ethanol.

Chromium(VI) induces oxidative stress in the mouse brain

Potassium dichromate was given to female Swiss mice (25 mg/kg per day) orally in water for 1-3 days. Brain homogenates were prepared to evaluate the occurrence of oxidative stress in this organ through the measurement of the antioxidant defense levels, and the extent of lipid peroxidation. In addition, mitochondrial fractions were isolated from brain homogenates to determine the production of reactive oxygen species in this subcellular fraction. The administration of potassium dichromate for 3 days caused increases of 72 and 74% in superoxide dismutase and catalase activities, respectively, in the homogenates. The treatment with this metal for 3 days increased brain homogenate chemiluminescence and thiobarbituric acid-reactive substances by 34 and 29%, respectively. The brain contents of the non-enzymatic antioxidants alpha-tocopherol and sulfhydryl groups decreased by 35 and 32%, respectively. Ascorbic acid levels were not modified by the administration of potassium dichromate. Finally, there was a significant increment in the mitochondrial production of oxidants in the brain of treated mice as compared with controls. These results suggest that chromium(VI) produces an increased formation of reactive oxygen species and brain lipid peroxidation. The increase in the antioxidant enzyme activities reflects an adaptive response against oxidative stress, while the reduction in the levels of non-enzymatic antioxidants might be due to their reaction with reactive oxygen species generated during the metabolism of chromium(VI).

A comparison of the in vitro genotoxicity of tri- and hexavalent chromium

Chromium can be found in the environment in two main valence states: hexavalent (Cr(VI)) and trivalent (Cr(III)). Cr(VI) salts are well known human carcinogens, but the results from in vitro studies are often conflicting. Cr(VI) primarily enters the cells and undergoes metabolic reduction; however, the ultimate product of this reduction, Cr(III) predominates within the cell. In the present work, we compared the effects of tri- and hexavalent chromium on the DNA damage and repair in human lymphocytes using the alkaline single cell gel electrophoresis (comet assay). Potassium dichromate induced DNA damage in the lymphocytes, measured as the increase in comet tail moment. The effect was dose-dependent. Treated cells were able to recover within a 120-min incubation. Cr(III) caused greater DNA migration than Cr(VI). The lymphocytes did not show measurable DNA repair. Vitamin C at 50 microM reduced the extent of DNA migration. This was either due to a decrease in DNA strand breaks and/or alkali labile sites induced by Cr(VI) or to the formation of DNA crosslinks by Cr(VI) in the presence of vitamin C. Vitamin C, however, did not modify the effects of Cr(III). Catalase, an enzyme inactivating hydrogen peroxide, decreased the extent of DNA damage induced by Cr(VI) but not the one induced by Cr(III). Lymphocytes exposed to Cr(VI) and treated with endonuclease III, which recognizes oxidized pyrimidines, displayed greater extent of DNA damage than those not treated with the enzyme. Such an effect was not observed when Cr(III) was tested. The results obtained suggest that reactive oxygen species and hydrogen peroxide may be involved in the formation of DNA lesions by hexavalent chromium. The comet assay did not indicate the involvement of oxidative mechanisms in the DNA-damaging activity of trivalent chromium and we speculate that its binding to cellular ligands may play a role in its genotoxicity.

Blood chemistry changes in the rat induced by high doses of nitronyl free radical spin traps

For greatest efficacy, it is desirable to use spin trapping agents in the highest concentrations possible. Fifty-four male Sprague-Dawley rats were used to explore the relative toxicity of four representative nitronyl spin traps at doses chosen on the basis of earlier lethality studies. Most studies were confined to the 3- to 6-h period following drug injection, because the behavioral signs of toxicity are most evident early after injection and because spin trapping studies would typically be performed within this time frame. Doses of spin trap were dissolved in a corn oil/buffer vehicle and injected intraperitoneally (i.p.). Toxic signs were recorded periodically, and at the time of euthanasia or spontaneous death a blood sample was collected by cardiac puncture for clinical chemistry analysis and a necropsy was performed. Both gross pathology and histopathological examination of the major organs were essentially negative in all cases, with no obvious evidence of cellular damage being observed. Neither DMPO (232 mg/100 g b.wt.) nor PBN (100 mg/100 g b.wt.) were lethal in the present study, while both M4PO (20 and 40 mg/ 100 g b.wt.) and PyOBN (100 and 200 mg/100 g b.wt.) were lethal. Abnormal clinical chemistry findings were generally confined to those animals that died spontaneously or were euthanized early for humane reasons. In most cases, death was associated with marked seizure activity and impaired respiration, and deaths occurred within a few min to a few hours. The mechanism of toxicity was unclear due to the lack of histopathological evidence and the wide range of abnormal serum analytes in those rats killed by either M4PO or PyOBN. In conclusion, during the first 6 h after IP administration there is little indication of tissue damage by the nitrone spin traps until the dose is increased to a lethal level, at which point an acute, rapidly occurring, wide-spread disruption of tissue integrity seems to occur.