Low frequency electron paramagnetic resonance investigation on metabolism of chromium (VI) by whole live mice

Detection of Cr(V) in the reduction of Cr(VI) by whole live mice and its characterization were carried out by low frequency electron paramagnetic resonance (EPR). Intravenous injection of Cr(VI) to mice generated Cr(V). The Cr(V) was found predominantly in the liver with a small amount in the blood. Liver homogenates from Cr(VI) treated mice generated essentially the same Cr(V) spectrum as that obtained from the whole live mice. This Cr(V) species was identified to be a Cr(V)-nicotinamide adenine dinucleotide (NAD) (P)H complex with an oxygen bond to Cr(V). Pretreatment of the mice with ascorbic acid and glutathione reduced the Cr(V) formation, while pretreatment with reduced nicotinamide adenine dinucleotide (NADH) enhanced it. Metal chelators, ethylenediaminetetraacetic acid (EDTA), 1,10-phenanthroline, and diethylenetriaminepentaacetic acid (DTPA) inhibited the intensity of the Cr(V) signal. The results suggest that Cr(V) generated in the whole body of a live animal is a Cr(V)-NAD(P)H complex and NAD(P)H/flavoenzymes and not glutathione or ascorbate as the major one-electron Cr(VI) reductant responsible for observed formation of Cr(V)-NAD(P)H complex in vivo.