Chromate-Induced Chromium(V) Formation in Live Mice and Its Control by Cellular Antioxidants: An L-Band Electron Paramagnetic Resonance Study

A recent note from our laboratory reported that L-band (1.2 GHz) electron paramagnetic resonance spectroscopy can be utilized in detecting the formation of Cr(V) intermediates from chromate-treated whole mice. Since Cr(V) is thought to be one of the key species in the mechanism of chromate's toxicity, we carried out additional measurements with improved sensitivity. The new spectra show partially resolved hyperfine structure from protons that suggests that the Cr(V) ion is ligated to NAD(P)H moieties via oxygens. Using laboratory-synthesized Cr(V) (K3CrO8) as a standard, the yield of Cr(V) formation was estimated to be 153 +/- 12 nmol after intravenous injection of 100 microliters of 100 mM sodium dichromate into mice. Pretreatment of the mice with ascorbic acid and glutathione significantly reduced the Cr(V) formation yield in a dose-related manner, while pretreatment with NADH had the opposite effect. Injection of ascorbic acid also had the effect of enhancing the rate of Cr(V) disappearance in vivo. By comparing these results with in vitro results utilizing L-band as well as X-band (9.6 GHz) measurements, we conclude that L-band spectroscopy can indeed be effectively utilized for following the metabolism of Cr(V) in live mice and that Cr(V) formation can be controlled by utilizing cellular antioxidants in vivo.