Some Activities of the Oxidant Chromate
Hexavalent chromium [Cr(VI)] compounds are recognized mutagens and carcinogens (IARC, 1980), although the mechanism of action is unknown. Chromium compounds commonly exist in the Cr(VI) and trivalent ([Cr(III)] states, with the Cr(III) state as the most stable form of chromium. Cr(III) compounds differ from Cr(VI) not only in that they are more stable but they exist as cations in octahedral form (with six ligands) and cannot cross membranes readily. They are considered to be non-bioavailable and non-carcinogenic. Cr(VI) compounds, which exist as the oxides or the oxyanions and thus readily cross membranes, are rapidly reduced in the body (both intra- and extracellularly) to the stable Cr(III) via Cr(V) and Cr(IV). Some synthetic Cr(III) complexes, with lipid soluble organic anions as ligands such as the picolinate, cross membranes fairly readily. Cr(III) complexes formed in situ gain entry to the nucleus, as only Cr(III) is detected bound to DNA. Thus it may be that only the Cr(III) formed in situ is toxic. Cr(VI) compounds are not mutagenic without metabolic reduction, (Petrilli and De Flora, 1978). The intermediates, Cr(V) and Cr(IV), are being investigated as putative toxins/carcinogens of Cr(VI). Cr(V) has been detected by electron paramagnetic resonance (EPR) on reduction of Cr(VI) in cells in culture and in vitro (O’Brien et al., 1981; Goodgame and Joy, 1986; Shi and Dalai, 1988; Aiyar et al., 1988;Sugiyama, 1991; Witmer et al., 1994). Both Cr(V) and Cr(IV) can disproportionate so that the reduction of Cr(VI) is not a straightforward process, A two-electron reduction of Cr(VI) is catalyzed by DT diaphorase, which also decreases the mutagenicity of Cr(VI) in vitro.
KeywordsReactive Oxygen Species Electron Paramagnetic Resonance A549 Cell Reactive Oxygen Species Production Hexavalent Chromium
Unable to display preview. Download preview PDF.
- Faria, E.C., Sadrieh, N. and Witmer, CM. (1993) Effects of hexavalent chromium [Cr(VI)] on cytochrome P-450 isozymes. The Toxicologist 13: 8.Google Scholar
- Faria, E., Sadrieh, N. Thomas, P.E. and Witmer, CM. (1995). Sex and organ specific effects of hexavalent chromium [Cr(VI)] on cytochrome P450 (P450) isozymes. The Toxicologist 15: 312.Google Scholar
- Granger, D.N., Hollwarth, M. A., and Parks, D.A. (1982). Ischemia reperfusion injury: Role of oxygen-derived free radicals. Acta Physiol. Scand. 126, Suppl 548: 47–63.Google Scholar
- IARC (1980). Chromium and chromium compounds. In: IARC monographs for carcinogenic risk of chemicals to humans; Some metals and metallic compounds. Lyon: International Agency for Research on Cancer; 23: 205–323.Google Scholar
- Manning, F.C.R., Blankenship, L.J., Wise, J.P., Xu, J., Bridgewater, L.C., and Patierno, S.P. (1994). Environ. Hlth. Perspect. 102 (Suppl. 3): 159–167.Google Scholar
- Shi, X., Mao, Y, Knapton, A.D., Ding, M., Rojanasakul, Y., Gannett, P.M., Dalai, N. and Liu, K. (1994). Reaction of Cr(VI) with ascorbate and hydrogen peroxide generates hydroxyl radicals and causes DNA damage: Role of a Cr(IV)-mediated Fenton-like reaction. Carcinogenesis 15: 2475–2478.PubMedCrossRefGoogle Scholar
- Sugiyama, M.(1991). Effects of vitamins on Cr(VI)-induced damage. Environ. Health perspect. 92: 63–71.Google Scholar
- Witmer, C., Faria, E., Park, H.S., Sadrieh, N., Yurkow, E., O’Connell, S., Sirak, A. and Schleyel, H. (1994). In Vivo Effects of Chromium. Environ. Health Persepct. 102: 169–176.Google Scholar