Chem. Res. Toxicol. 1992,5, 461-463
461
Communications Production of Activated Species of Oxygen during the Chromate(V1)-Ascorbate Reaction: Implication in Carcinogenesis Yves Lefebvre and Henri PBzerat* Laboratoire de rkactiuitk de surface et structure, Uniuersitk Pierre et Marie Curie, 4, place Jussieu, 75252 Paris Ckdex 05, France Receiued March 2, 1992
The reaction of chromate and ascorbate in a 1:l molar ratio at p H 7.4 and 37 "C produces a Cr(V) signal observable by EPR at g = 1.980. When this reaction is carried out in aerated media and in the presence of formate, carboxylate radicals (COO*-1 can be trapped as DMPO-COO' spin adducts (DMPO, 5,5-dimethyl-l-pyrroline N-oxide). The use of a known complexant of Cr(V), 2-ethyl-2-hydroxybutyricacid, produces a different Cr(V) signal at g = 1.978 and a decrease of the DMPO-COO' - signal. Hydroxyl radicals are not detected in the media. The oxidizing behavior is suggested to be produced by activation of molecular oxygen present in the reaction mixture.
Introduction The carcinogenicity of chromate compounds is now largely suspected to be due to chromium(V)intermediates produced by the reaction of chromate with hydrogen peroxide and/or suitable biological reductants (1-3). The reaction of chromate with ascorbate at neutral pH has received much less attention than it merits probably because the lack of a characteristic Cr(V)-ascorbate complex observable by EPRl(4). On the other hand, glutathione, which forms numerous complexes (5, 61,has received greater attention. Our results show that reaction of chromate with ascorbate in aerated media produces oxygen-activated species leading to a strong oxidizing behavior toward formate anion, with hydrogen abstraction. This very electrophilic species is probably implicated in chromate carcinogenesis.
gassed and kept under argon, and reactions were immediately carried out under argon atmosphere.
Results and Discussion
Chemicals. NazCrO4, NaHC02, K2HP04 (
