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PubMed2000

Elucidating a biological role for chromium at a molecular level.

Chromium is an essential trace element for mammals and is required for maintenance of proper carbohydrate and lipid metabolism. However, elucidating its function at a molecular level has proved to be problematic. Recent research has revealed that the chromium-binding oligopeptide chromodulin may play a unique role in the autoamplification of insulin signaling. Attempts to develop chromium-containing nutritional supplements and therapeutics are described.

Carbohydrate Metabolism↗
PubMed2002

Thermal stabilization of chromium(VI) in kaolin.

Reduction of Cr(VI) by heating may be a useful detoxification mechanism for thermal immobilization. Using X-ray absorption spectroscopy, the change of speciation of chromium in 105 degrees C dried 3.7% Cr(VI)-sorbed kaolin further heated at 500, 900, or 1100 degrees C was studied. The 105 degrees C dried 3.7% Cr(VI)-sorbed kaolin sample was prepared by mixing 1.5 L of 0.257 M CrO3 solution (pH 0.71) with 0.5 kg of kaolin powder for 48 h, and then the slurry was heated (dried) at 105 degrees C until a constant weight was reached. The toxicity characteristic leaching procedure method was used to determine the percentage of leached chromium from all heated samples. In all 500-900 degrees C heated Cr(VI)-sorbed kaolin samples, Cr2O3 transformed from the hydrated Cr(VI) by a 4-h heat application was identified by the X-ray absorption near edge structure and extended X-ray absorption fine structure (EXAFS) spectroscopy as the key species that is leaching-resistant due to its low solubility. For the 1100 degrees C heated Cr(VI)-sorbed kaolin sample, the Fourier transform of its EXAFS spectrum indicates that the intensity of the peaks at 2.45 (Cr-Cr shell of Cr2O3) and 5.00 A (Cr-Cr and Cr-O shells of Cr2O3) without phase shift correction is either relatively smaller or disappearing, compared with that of the 500-900 degrees C heated Cr(VI)-sorbed kaolin samples. It is suggested that chromium octahedra were bridged to silica tetrahedra and incorporated in minerals formed at 1100 degrees C, such as mullite or sillimanite, since these phases were detected by XRD. Cr of this form is not easily leached.

Absorptiometry, Photon↗
PubMed2003

Co-removal of hexavalent chromium through copper precipitation in synthetic wastewater.

The mechanisms of hexavalent chromium [Cr(VI)] co-removal with copper [Cu(II)] during homogeneous precipitation were studied with batch tests using a synthetic solution containing Cr(VI) and Cu(II). Metal precipitation was induced by adding Na2CO3 stepwise to different pH, and the respective removals of Cu(II) and Cr(VI) were measured. At the same time, the relative quantities of Cu(II) and Cr(VI) in the precipitates were also analyzed to establish their stoichiometric relationship. The results indicated that, in a solution containing 150 mg/L Cu(II) and 60 mg/L Cr(VI), the initial co-removal of Cr(VII with Cu(II) began at pH 5.0 and completed at pH 6.2. At pH 5.0-5.2, coprecipitation took place through the formation of copper-chromium-bearing solids [such as CuCrO4 and/or CuCrO4 x 2Cu(OH)2]. Thereafter, the remaining soluble copper started to react with carbonate in a heterogeneous environment to form the negatively charged basic copper carbonate precipitates [CuCO3 x Cu(OH)2], which subsequently adsorbed additional Cr(VI) (or HCrO4-) at pH 5.2-6.2. The maximum Cr(VI) co-removal took place at pH 6.2. Between the two mechanisms, co-precipitation accounted for about 29% of the total chromium's co-removal while the remaining 71% was attributed to surface adsorption, mainly through electrostatic attraction and ligand exchange. When the solution pH was increased to beyond 7.5, a surface charge reversal took place on the basic copper carbonate solids, and this led to some Cr(VI) desorption. Thus, the extent of Cr(VI) adsorption is highly pH dependent.

Adsorption↗
PubMed2005

Formation of soluble organo-chromium(III) complexes after chromate reduction in the presence of cellular organics.

Microbial reduction of hexavalent chromium [Cr(VI)] to trivalent chromium [Cr(III)] has been investigated as a method for bioremediation of Cr(VI) contaminated environments. The produced Cr(III) is thought to be insoluble Cr(OH)3; however, recent reports suggested a more complex fate of Cr(III). A bacterial enzyme system, using NADH as the reductant, converts Cr(VI)to a soluble NAD+-Cr(III) complex, and cytochrome c-mediated Cr(VI) reduction produces cytochrome c-Cr(III) adducts. In this study, Cr(VI) reduction in the presence of cellular organic metabolites formed both soluble and insoluble organo-Cr(III) end-products. Several soluble end-products were characterized by absorbance spectroscopy and electron paramagnetic resonance spectrometry as organo-Cr(III) complexes, similar to the known ascorbate-Cr(III) complex. The complexes remained soluble and stable upon dialysis against distilled H20 and over a broad pH range. The ready formation of stable organo-Cr(III) complexes suggests that organo-Cr(III) complexes are rather common, likely representing an integral part of the natural cycling of chromium. Thus, organo-Cr(III) complexes may account for the mobile form of Cr(II) detected in the environment.

Ascorbic Acid↗
PubMed2006

Synthesis and structure characterization of chromium oxide prepared by solid thermal decomposition reaction.

Mesoporous chromium oxide (Cr2O3) nanocrystals were first synthesized by the thermal decomposition reaction of Cr(NO3)3.9H2O using citric acid monohydrate (CA) as the mesoporous template agent. The texture and chemistry of chromium oxide nanocrystals were characterized by N2 adsorption-desorption isotherms, FTIR, X-ray diffraction (XRD), UV-vis, and thermoanalytical methods. It was shown that the hydrate water and CA are the crucial factors in influencing the formation of mesoporous Cr2O3 nanocrystals in the mixture system. The decomposition of CA results in the formation of a mesoporous structure with wormlike pores. The hydrate water of the mixture provides surface hydroxyls that act as binders, making the nanocrystals aggregate. The pore structures and phases of chromium oxide are affected by the ratio of precursor-to-CA, thermal temperature, and time.

Chromium Compounds↗
PubMed2004

Lead chromate-induced chromosome damage requires extracellular dissolution to liberate chromium ions but does not require particle internalization or intracellular dissolution.

Hexavalent chromium [Cr(VI)] is a well-established human lung carcinogen. Water solubility has proven to be a key factor in the carcinogenicity of Cr(VI), with the water insoluble or "particulate" compounds the more potent carcinogens. Pathology studies indicate that chromates target cells at bronchial bifurcation sites in human lungs. However, it is uncertain what roles particle internalization and dissolution play in the genotoxicity of these compounds to human lung cells. We investigated these mechanisms in a human lung cell line after exposure to particulate lead chromate. We found that lead chromate was clastogenic in a concentration-dependent manner with 0.1, 0.5, and 1 microg/cm(2), while 5 and 10 microg/cm(2) caused complete cell cycle arrest. We also found concentration-dependent increases in intracellular and extracellular chromium ion levels. We investigated particle internalization by using transmission electron microscopy and found an apparent relative increase with concentration but no apparent particle internalization at the lowest concentration (0.1 microg/cm(2)) even after 24 h. Furthermore, we found no lysosomal association with the vacuoles containing particles, further suggesting that intracellular dissolution did not occur. Cotreating the cells with lead chromate and vitamin C eliminated both the uptake of ionic chromium and the clastogenic activity of lead chromate but had no effect on particle internalization. These data indicate that in human bronchial cells lead chromate clastogenesis is mediated by the extracellular dissolution of the particles and not their internalization. These findings have important implications for our understanding of the physicochemical mechanism of particulate chromates as they contradict previous indirect data from human bronchial epithelial cells, which suggest that particles dissolve inside those cells. Thus, these new data suggest that there may be different mechanisms of genotoxicity for epithelial cells and fibroblasts exposed to chromate particles.

Ascorbic Acid↗
PubMed1997

Direct and hydrogen peroxide-induced chromium(V) oxidation of deoxyribose in single-stranded and double-stranded calf thymus DNA.

Oxidative DNA damage by a model Cr(V) complex, [CrO(ehba)2]-, with and without added H2O2, was investigated for the formation of base and sugar products derived from C1', C4', and C5' hydrogen atom abstraction mechanisms. EPR studies with 5,5-dimethylpyrroline N-oxide (DMPO) have shown that Cr(V)-ehba alone can oxidize the spin trap via a direct chromium pathway, whereas reactions of Cr(V)-ehba in the presence of H2O2 generated the hydroxyl radical. Direct (or metal-centered) Cr(V)-ehba oxidation of single-stranded (ss) and double-stranded (ds) calf thymus DNA demonstrated the formation of thiobarbituric acid-reactive species (TBARS) and glycolic acid in an O2-dependent manner, consistent with abstraction of the C4' H atom. A minor C1' H atom abstraction mechanism was also observed for direct Cr(V) oxidation of DNA, but no C5' H atom abstraction product was observed. Direct Cr(V) oxidation of ss- and ds-DNA also caused the release of all four nucleic acid bases with a preference for the pyrimidines cytosine and thymine in ds-DNA, but no base release preference was observed in ss-DNA. This base release was O2-independent and could not be accounted for by the H atom abstraction mechanisms in this study. Reaction of Cr(V)-ehba with H2O2 and DNA yielded products consistent with all three DNA oxidation pathways measured, namely, C1', C4', and C5' H atom abstractions. Cr(V)-ehba and H2O2 also mediated a nonpreferential release of DNA bases with the exception of the oxidatively sensitive purine, guanine. Direct and H2O2-induced Cr(V) DNA oxidation had opposing substrate preferences, with direct Cr(V) oxidation favoring ss-DNA while H2O2-induced Cr(V) oxidative damage favored ds-DNA. These results may help explain the carcinogenic mechanism of chromium(VI) and serve to highlight the differences and similarities in DNA oxidation between high-valent chromium and oxygen-based radicals.

Animals↗
PubMed1998

Hypervalent chromium mimics reactive oxygen species as measured by the oxidant-sensitive dyes 2',7'-dichlorofluorescin and dihydrorhodamine.

Intracellular metabolism of the carcinogen chromate [Cr(VI)] produces the oxidative stress and oxidative DNA damage associated with its genotoxicity. Such oxidative stress has previously been measured by fluorescence using oxidant-sensitive dyes and attributed to the formation of reactive oxygen species (ROS). However, metabolism of Cr(VI) also produces Cr(IV) and Cr(V) which can directly damage biological macromolecules without forming ROS. We used the high-valence chromium species, bis(2-ethyl-2-hydroxybutyrato)oxochromate(V) [Cr(V)-EHBA], to test whether high-valence chromium would also react with the oxidant-sensitive dyes 2',7'-dichlorofluorescin (DCFH) and dihydrorhodamine (DHR). Cr(V)-EHBA caused both dyes to fluoresce over a wide dynamic range and under conditions which indicated that Cr(V) had reacted directly with both dyes without first forming a diffusible radical species. Dimethylthiourea (DMTU) and ethanol did not affect Cr(V)-induced fluorescence in vitro or Cr(VI)-induced fluorescence in A549 cells. Under the same conditions, ethanol and DMTU increased the extent of hydrogen peroxide-induced fluorescence. As chromium-induced fluorescence was unaffected by radical scavengers and was qualitatively different from hydrogen peroxide-induced fluorescence, we conclude that DCF and R123 fluorescence in chromate-treated A549 cells is a qualitative and cumulative measure of intracellular Cr(V) formation and not ROS.

Chromium↗
PubMed1999

Analysis of EDTA-chelatable proteins from DNA-protein crosslinks induced by a carcinogenic chromium(VI) in cultured intact human cells.

DNA-protein crosslinks (DPCs) were induced in intact human leukemic T-lymphocyte MOLT4 cells or isolated nuclei by treatment with potassium chromate, chromium(III) chloride hexahydrate or x-rays. The proteins complexed to DNA were analyzed by two-dimensional SDS-polyacrylamide gel electrophoresis (PAGE). A group of identical non-histone proteins was crosslinked to DNA by any of the three treatments, except that a 51 kDa basic protein was additionally complexed to DNA when either potassium chromate or chromium(III) chloride hexahydrate was the crosslinking agent. Treatment of chromate-induced DNA-protein crosslinks with EDTA or thiourea followed by ultracentifugation dissociated the major proteins from the complex indicating that these proteins were crosslinked to DNA by direct participation of a EDTA-chelatable form of chromium such as Cr(III) through sulfur containing amino acid residues. The 51 kDa protein was not seen in the post-EDTA pellet but was present in the post-thiourea pellet, indicating that it was also crosslinked to DNA by Cr(III) through non-sulfur-containing amino acids. Digestion of x-rays-induced DPCs by DNase I also revealed this protein on two-dimensional gels indicating that the same protein was also crosslinked by oxidative mechanisms. The involvement of oxidative mechanisms in the crosslinking process was indicated as the majority of the proteins in chromate-induced DPCs were resistant to EDTA and thiourea treatment, and were found to crosslink to DNA when x-rays were used as the crosslinking agent. These results suggest that the chromate-induced DPCs are formed by the generation of reactive oxygen species during the intracellular chromate reduction as well as by the biologically generated Cr(III). About 19% of DNA-protein crosslinks actually involve Cr(III) crosslinking DNA to proteins, of which about 14% involve Cr(III) crosslinking DNA to proteins through non-sulfhydryl containing moieties and about 5% involve Cr(III) crosslinking DNA to sulfhydryl groups on proteins. The remaining 81% of DNA-protein crosslinks appear to be oxidatively crosslinked out of which about 45% appear to be through sulfhydryl groups and another 36% appear to be through non-sulfhydryl groups.

Carcinogens, Environmental↗
PubMed2001

Long-term effects of chromium, grape seed extract, and zinc on various metabolic parameters of rats.

Progressive insulin resistance may contribute to both enhanced glycosylation of proteins and nucleic acids and augmented free radical damage commonly associated with aging. Accordingly, ingestion of chromium and antioxidants which improve insulin sensitivity and/or lessen free radical formation could theoretically ameliorate these basic disorders and lessen signs and symptoms of chronic age-related disorders. However, this supposition is based primarily upon acute rather than chronic data. Therefore, we divided 104 F344/BN rats into 2 groups: a control group receiving a basic diet and a test group receiving the same diet with added chromium polynicotinate (5 ppm), zinc monomethionine (18 ppm elemental zinc), and a grape seed extract high in flavonoids (250 ppm). Initial mean systolic blood pressures (SBP) of both control and test groups were 122 mm Hg. Over the first 7 months, the SBP of the control animals steadily increased to 140 mm Hg and remained at this level for the next 7-8 months. In contrast, the SBP of the test animals initially decreased over the first 4 months to as low as 110-114 mm Hg. The SBP then increased over the following months, essentially reaching the starting value of 120 mm Hg. This was still significantly lower than control (p < 0.001). In 12 control and 12 test rats, hepatic TBARS formation, an estimate of lipid peroxidation/free radical formation, was significantly lower after 1 year ingesting the test diet (p < 0.04); and HbA1C was also statistically significantly lower in the test group (5.4 vs. 4.8%, p < 0.003). Circulating levels of cholesterol, HDL, and triglycerides were similar between the two groups. Body, kidney, and liver weights were not different after 1 year ingesting the different diets; but epididymal fat pad weight was less in the group receiving supplements. We conclude that after prolonged supplementation a combination of agents known to sensitize insulin response and act as antioxidants (chromium polynicotinate, grape seed extract, and zinc monomethionine) can markedly lower SBP in normotensive rats, lessen oxidative damage to fats as suggested by decreased TBARS formation, and lower HbA1C without showing signs of toxicity.

Aging↗
PubMed2004

Mechanisms of chromium-induced suppression of RNA synthesis in cellular and cell-free systems: relationship to RNA polymerase arrest.

Chromium(VI) (Cr(VI)) can suppress both DNA replication and transcription as a result of chromium (Cr)-induced DNA damage. While progress has been made in the characterization of Cr-induced DNA polymerase arresting lesions, very little information is available on the inhibition of transcription by this metal. The aim of the present study was to identify the molecular mechanisms involved in the reduction of RNA synthesis by Cr. Following treatment with a moderately cytotoxic dose (approximately LC50) of Cr(VI) (150 microM for 2 h), total RNA synthesis was initially suppressed in CHO cells and recovered to control levels within 72 h post-treatment. In vitro nuclear run-on transcription assays of nuclei isolated from Cr(VI)-treated cells showed a similar amount of RNA synthesis suppression as observed in intact cells. Qualitative analysis of nascent transcripts revealed a general, concentration-dependent reduction in size suggesting that transcriptional elongation was inhibited following Cr-treatment. Transcriptional initiation in these nuclei was also reduced. To better determine whether transcriptional suppression was related to Cr-induced DNA damage we examined the transcriptional activity of T7 RNA polymerase on Cr(III)-treated plasmid DNA. Treatment of pGEM3Z-TS DNA with Cr(III) resulted in transcriptional arrest which occurred primarily at GC-rich and palindromic regions. However, in contrast to the cellular data, transcriptional initiation was unaffected in the in vitro transcription arrest assays. Taken together, these results suggest that the suppression of RNA synthesis by Cr is related to chromium-induced template DNA damage which prevents elongation leading to premature RNA polymerase arrest.

Animals↗
PubMed1989

The qualitative assessment of cobalt-chromium castings for partial dentures.

Criteria for objective assessment of cobalt-chromium castings have been developed. A random sample of 21 commercial dental laboratories specialising in the production of cobalt-chromium castings was selected. Identical casts and instructions for the construction of a lower partial denture framework were sent to each of them. The resultant castings were assessed according to specific criteria relating to detailed design features. Only one laboratory produced a casting which conformed completely with the design instructions. Significant defects were found in a high proportion of castings. The range of charges was from 28 pounds to 85 pounds. The results of the qualitative assessments suggest only a very weak relationship between laboratory charges and the quality of cobalt-chromium castings. Suggestions are made for minimum standards that may be applied in clinical practice.

Chromium Alloys↗
PubMed2001

Monitoring the species of arsenic, chromium and nickel in milled coal, bottom ash and fly ash from a pulverized coal-fired power plant in western Canada.

The concentration of As, Cr and Ni and their speciation (As3+;5+, Cr3+;6+ and Ni0;2+) in milled coal, bottom ash and ash collected by electrostatic precipitator (ESP) from a coal fired-power plant in western Canada were determined using HGAAS, ICP-AES and XANES. The chemical fractionation of these elements was also determined by a sequential leaching procedure, using deionized water, NH4OAC and HCI as extracting agents. The leachate was analyzed by ICP-AES. Arsenic in the milled coal is mostly associated with organic matter, and 67% of this arsenic is removed by ammonium acetate. This element is totally removed from milled coal after extraction with HCI. Arsenic occurs in both the As3+ and the As5+ oxidation states in the milled coal, while virtually all (>90%) of the arsenic in bottom ash and fly ash appears to be in the less toxic arsenate (As5+) form. Both Ni and Cr in the milled coal are extracted by HCI, indicating that water can mobilize Ni and Cr in an acidic environment. The chromium is leached by water from fly ash as a result of the high pH of the water, which is induced during the leaching. Ammonium acetate removes Ni from bottom ash through an ion exchange process. Chromium in milled coal is present entirely as Cr3+, which is an essential human trace nutrient. The Cr speciation in bottom ash is a more accentuated version of the milled coal and consists mostly of the Cr3+ species. Chromium in fly ash is mostly Cr3+, with significant contamination by stainless-steel from the installation itself.

Air Pollution↗
PubMed2002

A novel approach for speciation of airborne chromium by convective-interaction media fast-monolithic chromatography with electrothermal atomic-absorption spectrometric detection.

A new analytical procedure using an anion-exchange separation support based on convective-interaction media (CIM) was developed for the speciation of chromium. The separation of Cr(VI) was performed on a weak anion-exchange CIM diethylamine (DEAE) fast-monolithic chromatographic disc. Buffer A (0.005 mol dm(-3) TRIS-HCl, pH 8.0) and buffer B (buffer A plus 3 mol dm(-3) NH4NO3) were employed in the separation procedure. The separated chromium species were determined 'off-line' by ETAAS in 0.5 cm3 fractions. The applicability of the CIM DEAE-ETAAS procedure was investigated for the determination of airborne Cr(VI) at a plasma cutting workplace. Aerosols were collected on polycarbonate membrane filters of 8 and 0.4 microm pore size (inhalable and respirable aerosols). Alkaline extraction of filters in a heated ultrasonic bath was applied to leach chromium. Good repeatability of measurement (+/-3.0%) of the alkaline extracts was obtained for Cr(VI). The LOD (3s) was found to be 0.30 microg m(-3) Cr(VI), when 0.25 m3 of air was collected on the filter. The validation of the procedure was performed by spiking filters with Cr(VI) and by the analysis of the standard reference material CRM 545, Cr(VI) in welding dust loaded on a filter. Good recoveries for spiked samples (101-102%) and good agreement between Cr(VI) found and the reported certified value for CRM 545 were obtained. The extracts were also analysed by the FPLC-ETAAS technique. Good agreement between two techniques (r2 = 0.9978) confirmed the reliability of the CIM DEAE-ETAAS procedure developed. The main advantage of the procedure lies in the speed of the chromatographic separation (chromatographic run completed in 15 min).

Air Pollutants↗
PubMed2002

Serum levels of cobalt and chromium in a complex modular total hip arthroplasty system.

There is concern that modularity in a total hip arthroplasty system increases serum cobalt and chromium ion levels. This study measures the serum cobalt and chromium levels in patients with an Oxford Universal Hip (Corin, Cirencester, United Kingdom), which has a modular sliding mechanism; patients with a similarly manufactured hip with no sliding mechanism; and a control group. Loosening was excluded clinically and radiologically. Arthroplasty patients had statistically higher levels of serum cobalt and chromium than controls, but there was no significant difference in levels between the implanted groups.

Arthroplasty, Replacement, Hip↗
PubMed1996

[Squamous epithelial carcinoma of the tongue after occupational exposure to chromium VI compounds].

BACKGROUND: The major key risk factors of head and neck cancer are chronic alcohol and tobacco consumption. There ist further increasing evidence that exposure to hazardous occupational agents increases the cancer risk substantially. CASE REPORT: By means of a case report and an overview of the literature, the role of occupational exposure to hexavalent chromium compounds as a risk factor of head and neck cancer is analysed. RESULTS AND CONCLUSIONS: The mechanisms of chromium carcinogenesis are outlined. Possible interactions of life-style factors and occupational factors which may influence the cancer risk in a synergistic manner are also discussed. Critical analysis of the literature provides evidence of a possible role of occupational exposition to hexavalent chromium compounds as a risk factor for oral squamous cell cancer.

Carcinogens, Environmental↗
PubMedDate not supplied

[The role of the alloy-specific elements iron, cobalt, chromium and nickel in aseptic loosening of total hip joint prosthesis].

The cause of aseptic loosening of total hip joint prostheses is still largely unexplained. In addition to mechanical forces, material factors may also be instrumental. In 16 patients with loosened hip prostheses who underwent re-operation (8 X Huggler-Weber, 8 X McKee-Farrar), the concentration of the alloy-specific elements cobalt, chromium, nickel and iron were determined in 58 tissue samples by means of neutron activation and emission spectrum analysis. An increase in the element concentrations was found in all the tissue samples, and this was unrelated to the time elapsed since implantation. The chromium concentration in particular was significantly elevated in all the tissue samples, in some patients with McKee-Farrar prostheses up to 10,000 times the norm. In view of the known toxicity of cobalt, chromium and nickel in high doses it seems that the presence of unphysiologically high concentrations of these elements in the vicinity of total hip joint prostheses represents an explanation of some of the loosened prostheses.

Chromium Alloys↗
PubMed2001

Mechanical characteristics of various tempers of as-received cobalt-chromium archwires.

The mechanical characteristics of 24 of the 36 wire cross-sectional configurations were investigated in the as-received state from among the 4 tempers of a cobalt-chromium product. After engineering mechanics were used to validate the efficacy of the span combinations, each wire was measured in flexure to determine its elastic modulus and in tension to determine its yield strength, ultimate tensile strength, and ductility. Other combined characteristics were evaluated, including flexibility, resilience, and the yield strength criterion. In these as-received materials the formability sometimes followed expectations, but the flexibility and resilience characteristics were variable and independent of temper. And although the elastic modulus was independent of testing parameters, it was affected by the loss of material at the corners of rectangular wires. Overall, the stiffnesses of cobalt-chromium wires in round configurations were comparable to those of multi- and single-stranded stainless steel wires but were 3 and 6 times greater than the stiffnesses of beta-titanium and nickel-titanium wires, respectively. In the final analysis, these as-received wires do not meet their potential as a variably formable and variably resilient alternative to stainless steel. Perhaps this is why cobalt-chromium wires have never had the impact on the profession that was expected from them several years ago.

Algorithms↗