The role of reduced glutathione and glutathione reductase in the cytotoxicity of chromium (VI) in osteoblasts

Insights into the antioxidative mechanisms of melatonin in ameliorating chromium-induced oxidative stress-mediated hepatic and renal tissue injuries in male Wistar rats

Chromium (Cr), a hazardous heavy metal, is toxic to human health and the environment. Severe detrimental effects of Cr on different physiological systems involve oxidative stress. In the current study, sodium dichromate di-hydrate was subcutaneously injected to male Wistar rats at a dose of 5 mg/kg b.w. and experimented up to 14 days to induce alterations in hepatic and renal tissues. Another group of rats was pre-treated with melatonin at three different doses (5, 10, and 20 mg/kg b.w.; orally) and 20 mg/kg b.w. dose was evidenced to provide maximal protection against Cr-induced alterations. The study demonstrated that melatonin efficiently preserved body weight, organ weight, intracellular antioxidant enzymes, and tissue morphology. Furthermore, melatonin was also found to protect organ damage markers, oxidative stress-biomarkers, activities of pro-oxidant enzymes, levels of reactive oxygen species (ROS), nitric oxide (NO), and collagen content through its antioxidative mechanisms. Moreover, melatonin effectively decreased tissue Cr content through its metal-chelating activity. Hence, the present study has established melatonin as a promising antioxidant for conserving the liver and kidney tissues from Cr-induced oxidative damage thereby strengthening the notion that this small indoleamine can act as a future therapeutic against Cr-induced oxidative stress-mediated tissue damage.

Glutathione S-Transferases in Cancer

In humans, the glutathione S-transferases (GST) protein family is composed of seven members that present remarkable structural similarity and some degree of overlapping functionalities. GST proteins are crucial antioxidant enzymes that regulate stress-induced signaling pathways. Interestingly, overactive GST proteins are a frequent feature of many human cancers. Recent evidence has revealed that the biology of most GST proteins is complex and multifaceted and that these proteins actively participate in tumorigenic processes such as cell survival, cell proliferation, and drug resistance. Structural and pharmacological studies have identified various GST inhibitors, and these molecules have progressed to clinical trials for the treatment of cancer and other diseases. In this review, we discuss recent findings in GST protein biology and their roles in cancer development, their contribution in chemoresistance, and the development of GST inhibitors for cancer treatment.

Preliminary studies of the effect of doping of chromium oxide in SiO2-CaO-P2O5 bioceramics for bone regeneration applications

Bioceramics of composition xCr₂O₃∙(43-x) CaO∙42SiO₂∙15P₂O₅ (x varying from 0 to 8 mol%) have been synthesized in the laboratory by using sol-gel technique. The morphology and structure has been determined by using Powder X-ray Diffraction, Fourier Transform Infrared and Raman spectroscopy and Field Emission Scanning Electron Microscopy. The in vitro bio mineralization behavior has been assessed by immersion in simulated body fluid for 7 days. The results obtained in our studies have indicated excellent hydroxyapatite formation ability of our samples. Drug delivery property of synthesized samples has been checked by using UV-spectroscopy of antibiotic 'gentamicin'. The in vitro drug release profile was fitted best in the Higuchi model with the highest value of coefficient of determination (R² = 0.9970). Antimicrobial properties have been evaluated from minimum inhibitory concentration and time kill assay values. The cellular response has been investigated by using human osteosarcoma MG 63 cell line. Also to check charge on the synthesized samples, Zeta potential studies have been conducted and it has been observed that samples carry negative charge when immersed in simulated body fluid. Negative surface charge provide suitable environment for cell adhesion and proliferation. Experiments have been undertaken to explore suitable composition with an objective of development of suitable implant material for bone regeneration applications.

Buffalo casein derived peptide can alleviates H2O2 induced cellular damage and necrosis in fibroblast cells

Oxidative stress is one of a critical pathogenic factor in the progression of aging and chronic diseases such as cancer, myocardial inflammation and diabetes. In the present scenario, peptides with short half life and more biological specificities are gaining much attention as prodrugs. Thus, the present investigation carried out to screen potential antioxidative peptide, VLPVPQK to cope with the cellular oxidative damage. Our results showed that treatment of rat fibroblast cells with 0.2mM H₂O₂ for 6h significantly declined different oxidative stress biomarkers such as SOD, CAT, GSH, and promoted LDH activity. In addition, ROS and TNF-α levels were also increased upon H₂O₂ exposure for 6h and thereby, it induced cell death. Amazingly, pretreatment of the peptide (VLPVPQK) significantly elevated cell survivability, by reversing all H₂O₂ induced alterations in fibroblast cells. Therefore, our results indicated that, the peptide (VLPVPQK) acted as a potential cytoprotective agent, who restored redox balance and cell homeostasis in cultured fibroblast cells, even after H₂O₂ exposure, suggesting that the peptide can be valuable as an effective remedy in treatment of oxidative stress related diseases and skin inflammation related disorders.

Protective effects of casein-derived peptide VLPVPQK against hydrogen peroxide–induced dysfunction and cellular oxidative damage in rat osteoblastic cells

Oxidative stress inhibits osteoblast differentiation and function that lead to the development of osteoporosis. Casein-derived peptide VLPVPQK (PEP), a potent antioxidant, was isolated from β-casein of buffalo milk. We used an in vitro oxidative stress model induced by hydrogen peroxide (H2O2) in rat osteoblastic cells to investigate the protective effects of PEP against H2O2-induced dysfunction and oxidative damage. Cells were pretreated with PEP (50–200 ng/mL) for 2, 7 or 21 days followed by 0.3 mM H2O2 treatment for 24 h and then markers of osteogenic development, oxidative damage and apoptosis were examined. PEP significantly increased the viability and differentiation markers of osteoblast cells such as alkaline phosphatase and calcium mineralization. Moreover, PEP suppressed the production of reactive oxygen species (ROS), lipid peroxidation and ameliorated H2O2-induced reduction in glutathione, superoxide dismutase and catalase activities. In addition, PEP partially inhibited caspase-9 and-3 activities and reduced propidium iodide–positive cells. Altogether, our results demonstrated that PEP could protect rat osteoblast against H2O2-induced dysfunction and oxidative damage by reduction of ROS production, lipid peroxidation and increased antioxidant enzyme activities. Thus, our data suggest that PEP might be a valuable protective agent against oxidative stress–related diseases such as osteoporosis.

Metal-Based Combinations That Target Protein Synthesis by Fungi

A wide range of fungicides (or antifungals) are used in agriculture and medicine, with activities against a spectrum of fungal pathogens. Unfortunately, the evolution of fungicide resistance has become a major issue. Therefore, there is an urgent need for new antifungal treatments. Certain metals have been used for decades as efficient fungicides in agriculture. However, concerns over metal toxicity have escalated over this time. Recent studies have revealed that metals like copper and chromate can impair functions required for the fidelity of protein synthesis in fungi. This occurs through different mechanisms, based on targeting of iron-sulphur cluster integrity or competition for uptake with amino acid precursors. Moreover, chromate at least acts synergistically with other agents known to target translation fidelity, like aminoglycoside antibiotics, causing dramatic and selective growth inhibition of several fungal pathogens of humans and plants. As such synergy allows the application of decreased amounts of metals for effective inhibition, it lessens concerns about nonspecific toxicity and opens new possibilities for metal applications in combinatorial fungicides targeting protein synthesis.

Luteolin inhibits Cr(VI)-induced malignant cell transformation of human lung epithelial cells by targeting ROS mediated multiple cell signaling pathways

Hexavalent chromium [Cr(VI)] is a well-known human carcinogen associated with the incidence of lung cancer. Inhibition of metal induced carcinogenesis by a dietary antioxidant is a novel approach. Luteolin, a natural dietary flavonoid found in fruits and vegetables, possesses potent antioxidant and anti-inflammatory activity. We found that short term exposure of human bronchial epithelial cells (BEAS-2B) to Cr(VI) (5μM) showed a drastic increase in ROS generation, NADPH oxidase (NOX) activation, lipid peroxidation, and glutathione depletion, which were significantly inhibited by the treatment with luteolin in a dose dependent manner. Treatment with luteolin decreased AP-1, HIF-1α, COX-2, and iNOS promoter activity induced by Cr(VI) in BEAS-2B cells. In addition, luteolin protected BEAS-2B cells from malignant transformation induced by chronic Cr(VI) exposure. Moreover, luteolin also inhibited the production of pro-inflammatory cytokines (IL-1β, IL-6, IL-8, TNF-α) and VEGF in chronic Cr(VI) exposed BEAS-2B cells. Western blot analysis showed that luteolin inhibited multiple gene products linked to survival (Akt, Fak, Bcl-2, Bcl-xL), inflammation (MAPK, NF-κB, COX-2, STAT-3, iNOS, TNF-α) and angiogenesis (HIF-1α, VEGF, MMP-9) in chronic Cr(VI) exposed BEAS-2B cells. Nude mice injected with BEAS-2B cells chronically exposed to Cr(VI) in the presence of luteolin showed reduced tumor incidence compared to Cr(VI) alone treated group. Overexpression of catalase (CAT) or SOD2, eliminated Cr(VI)-induced malignant transformation. Overall, our results indicate that luteolin protects BEAS-2B cells from Cr(VI)-induced carcinogenesis by scavenging ROS and modulating multiple cell signaling mechanisms that are linked to ROS. Luteolin, therefore, serves as a potential chemopreventive agent against Cr(VI)-induced carcinogenesis.

Ginsenoside Rh1 induces mouse osteoblast growth and differentiation through the bone morphogenetic protein 2/runt-related gene 2 signalling pathway

Objectives

This study aimed to investigate the stimulative and pharmacological effects of ginsenoside Rh1 (hereinafter referred to as: Rh1) on differentiation and mineralization of osteoblast and its possible mechanism of action on the expression of bone morphogenetic protein 2 (BMP-2)/Runt-related gene 2 (Runx2) signalling pathways using mouse preosteoblastic MC3T3-E1 cell line as in-vitro model.

Methods

An in-vitro stimulative activity of Rh1 was assessed by analyzing alkaline phosphatase activity (ALP), type-I collagen (Coll-I) synthesis, mineralization and glutathione content. Its antioxidant activity was measured by evaluating the reactive oxygen species (ROS) production in the presence of antimycin A (AMA), one of the mitochondrial dysfunction factors. The level of BMP-2/Runx2 signal-regulated osteoblast-specific proteins such as osteocalcin (OCN), Coll-I and ALP were detected using Western blot analysis.

Key findings

Rh1 was capable to stimulate cell growth, ALP activity, Coll-I synthesis, mineralization and glutathione content in the MC3T3-E1 cells. BMP-2 and Runx2 expression were also increased by Rh1 concentration dependently. Additionally, Rh1 also showed inhibitory action on the level of ROS production enhanced by AMA in MC3T3-E1 cells. Rh1 could increase the expression level of BMP-2/Runx2 signal-regulated osteogenic markers such as ALP, Coll-I and OCN.

Conclusions

Rh1, a protopanaxatriol type's active ingredients of Panax ginseng Meyer, possesses osteoblast differentiation, osteogenic stimulatory and anti-oxidative activity.

Stimulative effect of ginsenosides Rg5:Rk1 on murine osteoblastic MC3T3-E1 cells

Panax ginseng C.A. Meyer (P. ginseng), hereafter referred to as P. ginseng, is known to exert a wide range of pharmacological effects both in vitro and in vivo; however, few studies have investigated the effects of ginseng on bone metabolism. We therefore investigated the potential antiosteoporotic properties of ginseng on the growth and differentiation of murine MC3T3-E1 cells. Rg5:Rk1 is a mixture of protopanaxadiol-type ginsenosides, isolated from fresh P. ginseng root, via a repetitive steaming and drying process. In this study, we examined the stimulatory effects of Rg5:Rk1 on the differentiation and mineralization of MC3T3-E1 cells. Undifferentiated cells were treated with a range of concentrations of Rg5:Rk1 (1-50 µg/mL), and cell viability was measured with the 3-(4,5-dimethyl-thiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Treatment with Rg5:Rk1 significantly increased cell viability in a dose-dependent manner. To investigate the possible mechanisms by which Rg5:Rk1 affects the early differentiation phase of MC3T3-E1 cells, the cells were treated with Rg5:Rk1 for 14-24 days before assessing the levels of multiple osteoblastic markers. The markers examined included alkaline phosphatase (ALP) activity type I collagen content (Coll-I), calcium deposition (by Alizarin Red S staining), extracellular mRNA expression of bone morphogenetic protein-2 (BMP-2), and the level of Runt-related transcription factor 2 (Runx2). Rg5:Rk1 treatment also increased the activities of proteins associated with osteoblast growth and differentiation in a dose-dependent manner. Overall, we found that the Rg5:Rk1 mixture of ginsenosides improved the osteoblastic function of MC3T3-E1 cells by increasing their proliferative capacity. This improvement is due to the action of Rg5:Rk1 on BMP-2, which is mediated by Runx2-dependent pathways.

Protection by salidroside against bone loss via inhibition of oxidative stress and bone-resorbing mediators

Oxidative stress is a pivotal pathogenic factor for bone loss in mouse model. Salidroside, a phenylpropanoid glycoside extracted from Rhodiola rosea L, exhibits potent antioxidative effects. In the present study, we used an in vitro oxidative stress model induced by hydrogen peroxide (H₂O₂) in MC3T3-E1 cells and a murine ovariectomized (OVX) osteoporosis model to investigate the protective effects of salidroside on bone loss and the related mechanisms. We demonstrated that salidroside caused a significant (P<0.05) elevation of cell survival, alkaline phosphatase (ALP) staining and activity, calcium deposition, and the transcriptional expression of Alp, Col1a1 and Osteocalcin (Ocn) in the presence of H₂O₂. Moreover, salidroside decreased the production of intracellular reactive oxygen species (ROS), and osteoclast differentiation inducing factors such as receptor activator of nuclear factor-kB ligand (RANKL) and IL-6 induced by H₂O₂. In vivo studies further demonstrated that salidroside supplementation for 3 months caused a decrease in malondialdehyde (MDA) and an increase in reduced glutathione (GSH) concentration in blood of ovariectomized mouse (P<0.05), it also improved trabecular bone microarchitecture and bone mineral density in the fourth lumbar vertebra and distal femur. Our study indicated that the protection provided by salidroside in alleviating bone loss was mediated, at least in part, via inhibition of the release of bone-resorbing mediators and oxidative damage to bone-forming cells, suggesting that salidroside can be used as an effective remedy in the treatment or prevention of osteoporosis.

Effect of magnolol on the function of osteoblastic MC3T3-E1 cells

Objectives. In the present study, the ability of magnolol, a hydroxylated biphenyl compound isolated from Magnolia officinalis, to stimulate osteoblast function and inhibit the release of bone-resorbing mediators was investigated in osteoblastic MC3T3-E1 cells. Methods. Osteoblast function was measured by cell growth, alkaline phosphatase activity, collagen synthesis, and mineralization. Glutathione content was also measured in the cells. Bone-resorbing cytokines, receptor activator of nuclear factor-κB ligand (RANKL), TNF-α, and IL-6 were measured with an enzyme immunoassay system. Results. Magnolol caused a significant elevation of cell growth, alkaline phosphatase activity, collagen synthesis, mineralization, and glutathione content in the cells (P < 0.05). Skeletal turnover is orchestrated by a complex network of regulatory factors. Among cytokines, RANKL, TNF-α, and IL-6 were found to be key osteoclastogenetic molecules produced by osteoblasts. Magnolol significantly (P < 0.05) decreased the production of osteoclast differentiation inducing factors such as RANKL, TNF-α, and IL-6 in the presence of antimycin A, which inhibits mitochondrial electron transport and has been used as an ROS generator. Conclusion. Magnolol might be a candidate as an agent for the prevention of bone disorders such as osteoporosis.

Lowering effects of onion intake on oxidative stress biomarkers in streptozotocin-induced diabetic rats

The protective effect of onion against oxidative stress in streptozotosin-induced diabetic rats was investigated in comparison with that of quercetin aglycone. We measured oxidative stress biomarkers involving the susceptibility of the plasma against copper ion-induced lipid peroxidation, which was estimated by the amounts of thiobarbituric acid-reactive substances (TBARS) and cholesteryl ester hydroperoxides, and urine TBARS and 8-hydroxydeoxyguanosine contents. After the 12-week feeding period, plasma glucose levels and these biomarkers increased in diabetic rats compared to normal rats. In diabetic rats fed a 6.0% onion diet (quercetin equivalent: 0.023%), quercetin metabolites accumulated in the plasma at concentrations of approximately 35 microM. Onion intake decreased plasma glucose levels and lowered the oxidative stress biomarkers. On the other hand, quercetin metabolites in the plasma of rats fed a diet with 0.023% quercetin aglycone were found at lower concentrations (14.2 microM) than the rats fed the onion diet. Furthermore, oxidative stress biomarkers were higher in the quercetin diet group compared to the onion diet group. These results strongly suggest that onion intake suppresses diabetes-induced oxidative stress more effectively than the intake of the same amount of quercetin aglycone alone.

Evaluation of the potential cytotoxicity of metals associated with implanted biomaterials (I)

The present assessments of potential toxicity of metal ions (Al, Ni, Cr, V, and Ag) that construct the metallic biomaterials were carried out in vitro. By measurements of cell alkaline phosphatase (ALP) activity and reduction ability of cell methyl tetrazolium (MTT), the cytotoxicity of prevalence metallic biomaterials has been investigated. Furthermore, the poison and erosion of metal ions and atoms on human tissue are discussed. Research results indicated that trace Cr(VI) showed serious cytotoxicity and Ni as well as V are cytotoxic if the ion concentration in culture medium is over 100 micromol x L(-1) and 1 micromol x L(-1), respectively. A strange phenomenon is that Ag also is cytotoxic if the ion concentration is higher than 500 micromol x L(-1). Al ion is biphasic in cytotoxicity. At low ion concentration (< 10 micromol x L(-1)), Al ions can stimulate cell proliferation, whereas at concentrations over 1,000 micromol x L(-1), cytotoxicity increases.

Release of chromium from orthopaedic arthroplasties

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

The central role of glutathione in the pathophysiology of human diseases

Reduced glutathione (L-gamma-glutamyl-L-cysteinyl-glycine, GSH) is the prevalent low-molecular-weight thiol in mammalian cells. It is formed in a two-step enzymatic process including, first, the formation of gamma-glutamylcysteine from glutamate and cysteine, by the activity of the gamma-glutamylcysteine synthetase; and second, the formation of GSH by the activity of GSH synthetase which uses gamma-glutamylcysteine and glycine as substrates. While its synthesis and metabolism occur intracellularly, its catabolism occurs extracellularly by a series of enzymatic and plasma membrane transport steps. Glutathione metabolism and transport participates in many cellular reactions including: antioxidant defense of the cell, drug detoxification and cell signaling (involved in the regulation of gene expression, apoptosis and cell proliferation). Alterations in its concentration have also been demonstrated to be a common feature of many pathological conditions including diabetes, cancer, AIDS, neurodegenerative and liver diseases. Additionally, GSH catabolism has been recently reported to modulate redox-sensitive components of signal transduction cascades. In this manuscript, we review the current state of knowledge on the role of GSH in the pathogenesis of human diseases with the aim to underscore its relevance in translational research for future therapeutic treatment design.

The interaction of chromium (VI) with macrophages: Depletion of glutathione and inhibition of glutathione reductase

There are reports of alterations in the number and functions of the cells of the immune system in patients with metal-on-metal (MOM) orthopaedic implants. These effects have been correlated with elevated chromium levels in the patients' blood. We have investigated the interactions of clinically relevant concentrations of Cr VI with macrophages in vitro, and the mechanisms responsible for its toxicity. Cr VI causes a concentration dependent decrease in macrophage viability above 1 microM as measured by the MTT and Neutral Red assays. This falls well within the range of circulating chromium serum concentrations measured in patients with MOM. Intracellular reduced glutathione (GSH) levels fall as a result, and most of the loss (86%) is accounted for by oxidation to the dimer, GSSG. Prior depletion of GSH does not sensitise the cells to Cr VI toxicity, implying that it is not involved in protecting the cells against the effects of Cr VI. During the metabolism of Cr VI, glutathione reductase activity is inhibited. In contrast, the activities of catalase and superoxide dismutase are not significantly altered. Prior inhibition of glutathione reductase activity protects against the toxicity of Cr VI to a significant extent, suggesting that it reduces Cr VI to a toxic metabolite.

The interaction of cysteine with chromium(VI) ions under UV irradiation

In 0.1 M phosphate buffer (pH 7.2), the interaction of chromium(VI) with cysteine in the presence and absence of UV irradiation was studied by cyclic voltammetry and electronic spectroscopy techniques. The reduction of Cr(VI) by cysteine takes place through the formation of Cr(VI)-thioester intermediate. On the cyclic voltammograms of cysteine and Cr(VI) mixture, the peaks at -0.315 and -0.800 V were observed, and these peaks are corresponding to the reduction of Cr(VI)-thioester and thiyl radical, respectively. In the cysteine solution exposed to UV irradiation, the formation of free cystine was observed at -0.792 V. In the cysteine and Cr(VI) mixture exposed to UV irradiation, the peak current of thiyl radical increases while the peak current of Cr(VI)-thioester reaches a maximum at 15 min and then decreases by increasing UV irradiation time. The formation of the thioester in the reaction between Cr(VI) and cysteine in aqueous media has been studied by monitoring the decrease of Cr(VI) at 370 nm. It was observed that the reaction is catalyzed by the UV irradiation of the Cr(VI) and cysteine mixture.

Zinc has ambiguous effects on chromium (VI)-induced oxidative stress and apoptosis

Zinc is an important cellular antioxidant. We investigated its role in chromium-induced oxidative stress and apoptosis in human tumor cell line Hep-2. The measured parameters included intracellular labile zinc content (Zinquin-E fluorescence), cell viability (WST-1 assay), oxidative stress (spectrophotometry), mitochondrial potential (flow cytometry), caspase-3 activity, and PARP cleavage (immunofluorescence). We found that Hep-2 cells contain abundant labile zinc stores that may be depleted by the ionophore TPEN or increased by external zinc supplementation. Chromium (VI)-induced cytotoxicity and apoptosis were enhanced in zinc-depleted cells after 24 h, in particular at chromium (VI) concentrations of 50 and 150 micromol/l. On the other hand, elevated levels of labile zinc were able to protect against apoptosis induced by 10 micromol/l chromium (VI) but at higher chromium (VI) concentrations (50 and 150 micromol/l) acted synergistically, significantly enhancing oxidative stress and the course of apoptosis, possibly through oxidative stress and mitochondrial damage.

Damage to F-actin and cell death induced by chromium VI and nickel in primary monolayer cultures of rat hepatocytes

The toxicity of hexavalent chromium and nickel was investigated using primary cultures of hepatocytes as an in vitro system. Cr VI and Ni are widely used in the steel and orthopaedic implant industry. Although their toxicity has been extensively investigated, the mechanism(s) of action is/are not fully understood. Monolayer cultures of hepatocytes (10(5) cells/cm2) were exposed to various concentrations of Cr VI and Ni for 24 h. Cells were stained with phalloidin-FITC for the detection of the cytoskeletal component, F-actin, and Annexin V-FITC and propidium iodide for the detection of the mode of cell death. Exposure of cells to Cr VI (1, 5, 10 and 50 microM) resulted in the loss of the cell cytoskeleton, and this was accompanied by membrane blebbing and shrinking of the cell. Ni, on the other hand, induced detectable damage to the cytoskeleton only at 500 microM. Staining of the cells with Annexin V and propidium iodide showed that Cr VI induces apoptosis at low concentrations (5 microM), and necrosis at higher concentrations (25 and 50 microM). Ni almost exclusively induced necrosis at 500 microM with very few cells undergoing apoptosis. Below this concentration it had no discernable effect on hepatocytes. Damage to the cell cytoskeleton caused by Cr VI may be an early indication of apoptosis in hepatocytes.

Role of different valence states of chromium in the elicitation of allergic contact dermatitis

Chromium, a known contact sensitizer, is present at high levels in certain detergent bars (40-50 p.p.m.) sold in India. A concern was whether chromium present in such detergent bars could sensitize users or their use lead to the elicitation of allergic contact dermatitis. Chromium present in detergent bars was analyzed for its valence state. It was found to be trivalent [Cr (III)] and not hexavalent [Cr (VI)]. An elicitation test on normal volunteers, as well as on volunteers who were sensitive to chromium, was carried out to determine the elicitation potential of chromium (III) in the bars. Of the 48 volunteers who completed the study, 30 did not show any positive response to either potassium dichromate, the positive control, or the detergent bar containing chromium (III). 18 volunteers who were identified as chromium-sensitive showed a positive response to potassium dichromate but not to the detergent bar containing trivalent chromium. This study clearly showed that the detergent bar with 40-50 p.p.m. of trivalent chromium did not elicit any allergic contact dermatitis even in individuals known to be chromium-sensitive. Hexavalent chromium (potassium dichromate) did however, elicit allergic contact dermatitis in these subjects.

Pretreatment of rats with the inducing agents phenobarbitone and 3-methylcholanthrene ameliorates the toxicity of chromium (VI) in hepatocytes

To exert cytotoxicity chromium VI (Cr(VI)) has to be reduced inside cells. This is achieved through both enzymatic and non-enzymatic mechanisms. Enzymatic mechanisms include DT-diaphorase, cytochrome P450, and NADPH cytochrome c reductase, and non-enzymatic mechanisms involve reduced glutathione (GSH) and ascorbic acid. The extent of cytotoxicity of Cr(VI) may thus be influenced by the availability of non-enzymatic reductants, and by the activities of the reductase enzymes. In the present paper we have investigated the effect of pretreatment with the inducing agents, phenobarbitone (PB) and 3-methylcholanthrene (3-MC), on the response of rat hepatocytes to Cr(VI). Pretreatment with PB increased the activity of NADPH cytochrome c reductase, and 3-MC increased DT-diaphorase activity in hepatocytes. Both inducers increased cytochrome P450 content, while neither influenced intracellular GSH content or the activity of glutathione reductase. Pretreatment with either PB or 3-MC resulted in amelioration of Cr(VI) toxicity both in terms of hepatocyte viability, and to a greater extent, in terms of Cr(VI) induced GSH loss. We propose that the inducing agents increase the amount of enzymatic reduction of Cr(VI) relative to non-enzymatic reduction. Thus, less GSH is used in the reduction of Cr(VI), and intracellular GSH does not fall as rapidly as in cells from control animals therefore cell integrity is better maintained. Exposure to environmental inducing agents in vivo may also alter the response of human tissues to Cr(VI).

The role of glutathione reductase in the cytotoxicity of chromium (VI) in isolated rat hepatocytes

Chromium (VI) is an environmental and occupational carcinogen, and it is accepted that intracellular reduction is necessary for DNA damage and cytotoxicity. We have investigated the interaction of Cr(VI) with hepatocytes in vitro to determine the contribution of various hepatic enzymes to the reduction of Cr(VI). Cr(VI) caused a dose-dependent decrease in cell viability and intracellular reduced glutathione (GSH) levels between 100 and 500 microM within 3 h exposure of hepatocytes. Both DT-diaphorase and cytochrome P450 play only a minor role in detoxifying Cr(VI) and/or its metabolites. (GSH) appears to act as a non-enzymatic reductant, reducing Cr(VI) to a toxic form. The evidence for this is two-fold. Firstly, GSH was depleted during the metabolism of Cr(VI) and, secondly, pretreatment of the cells with diethylmaleate to deplete GSH levels, partially protected the cells from Cr(VI) toxicity. Glutathione reductase appears to play an important role in the enzymatic reduction of Cr(VI) as inhibition of this enzyme by carmustine (BCNU) markedly protected the cells from cytotoxicity.