Differential modulation of xenobiotic metabolizing enzymes by vanadium during diethylnitrosamine-induced hepatocarcinogenesis in Sprague-Dawley rats.

Effect of vanadium on hepatic xenobiotic biotransformation in rats exposed to diethylnitrosamine (DENA, 200 mg/kg body weight, intraperitoneally) was investigated to elucidate a possible mechanism of vanadium mediated prevention of chemical carcinogenesis. Vanadium supplementation (0.5 ppm ad libitum with drinking water), at different phases before and after DENA treatment, significantly modulated the decrease in contents of total cytochrome P-450, cytochrome b5, activity of nicotinamide adenine dinucleotide phosphate (NADPH), (reduced form) cytochrome reductase, and uridine diphospho-glucuronyl transferase (UDPGT) in microsomal fractions of whole liver, hyperplastic nodules (HNs) and non nodular surrounding parenchyma (NNSP) as induced by DENA, 20 weeks following its administration. Supplementary vanadium had also substantial influence on the activities of cytosolic enzymes, like, uridine diphospho (UDP)-glucose dehydrogenase and NAD(P)H: quinone oxidoreductase (DT-diaphorase) in the concerned tissue which were observed to be remarkably decreased as a result of DENA treatment in comparison to that of the control counterparts. However, vanadium was found to have little or no effect on the lowering ofaryl hydrocarbon hydroxylase (AHH) activity by DENA administration. On the basis of significant modulation of DENA induced alterations in cytosolic and microsomal enzyme activity it can be presumed that the chemoprotective effect of vanadium might be mediated through elevation of phase II conjugating enzymes which in turn, lead to a move and shift of metabolic profile that reduces the intracellular concentration of carcinogen derived reactive intermediates.