Kinetic analysis of furan biotransformation by F-344 rats in vivo and in vitro.

Furan is both hepatotoxic and hepatocarcinogenic in rats. The kinetics of furan biotransformation by male F-344 rats were studied in vivo and in vitro in order to understand target tissue dosimetry. A physiologically based pharmacokinetic (PBPK) model for furan in rats was developed from gas uptake studies using initial furan concentrations of 100, 500, 1050, and 3850 ppm. Tissue partition coefficients for furan were determined in vitro using vial equilibration techniques. Furan gas uptake kinetics in vivo were described by a single saturable process with a Vmax of 27.0 mumol/hr/250 g rat and a KM of 2.0 microM. Furan metabolism in vivo was inhibited by pyrazole. The furan PBPK model adequately simulated blood and liver furan concentrations following 4-hr inhalation exposures to 52, 107, and 208 ppm furan. The biotransformation of furan was studied in freshly isolated rat hepatocytes in vitro and compared to biotransformation in vivo. Furan biotransformation by isolated rat hepatocytes exhibited a KM of 0.4 microM and a Vmax of 0.018 mumol/hr/10(6) cells. Inhibition and induction studies indicated that cytochrome P450 was the catalyst of furan oxidation. Acetone pretreatment of the rats produced a five-fold increase in the rate of the hepatocyte oxidation of furan, suggesting an important role for cytochrome P450 2E1. The Vmax determined in hepatocytes in vitro extrapolated to 23.0 mumol/hr/250 g rat, assuming 128 x 10(6) hepatocytes/g liver. Incorporation of the in vitro hepatocyte kinetic parameters into the PBPK model for furan accurately simulated in vivo pharmacokinetics. These results suggest that freshly isolated hepatocytes are a valuable in vitro system for predicting chemical pharmacokinetics in vivo.