In vivo metabolism of butadiene by mice and rats: a comparison of physiological model predictions and experimental data

Abstract

1,3-Butadiene (BD), a rodent carcinogen, is metabolized to mutagenic and potentially DNA-reactive epoxides, including butadiene monoepoxide (BMO) and butadiene diepoxide. A physiological model containing five tissue groups (liver, lung, fat, slowly perfused tissues and rapidly perfused tissues) and blood was developed to describe uptake and metabolism of inhaled BD and BMO. Maximal rates for hepatic and pulmonary metabolism of BD and hepatic metabolism of BMO incorporated into the model were extrapolated from in vitro data (Csanády et al., Carcinogenesis, 13, 1143-1153, 1992). Apparent enzyme affinities used in the model were identified to the values measured in vitro. Model stimulations for BD and BMO uptake were compared to results from experiments in which groups of male Sprague-Dawley rats and B6C3F1 mice were exposed to initial concentrations of 50-5000 p.p.m. BD in closed chamber experiments and published data on BMO uptake by rats and mice. Metabolic rate constants extrapolated from in vitro data stimulated both BMO and BD uptake from closed chambers. The Vmax for hepatic metabolism of BD extrapolated from in vitro studies was 62 mumol/kg/h for rats and 340 mumol/kg/h for mice, while the Vmax for pulmonary metabolism of BD was 1.0 and 22 for rats and mice, respectively. These results demonstrate the usefulness of data derived in vitro for predicting in vivo behavior. Model simulations were also conducted in which only hepatic metabolism of BD was incorporated. These simulations underestimated BD uptake for mice, but not rats. Inclusion of in vitro-derived rates of pulmonary metabolism of BD into the model improved the fit to the data for mice. Since mice, but not rats, develop lung tumors after exposure to BD, these results point to the need for further characterize the metabolic capacity and target cells in the lung for BD and its metabolites. Once characterized, these models can be extended to predict in vivo behavior of BD in humans.

Human cancer risk and exposure to 1,3-butadiene - a tale of mice and men

“…Since that time 2 physiologically-based pharmacokinetic models have been published which incorporate in vitro data on the metabolism of BD in humans (29,30). These models represent an effort to improve the risk assessment process for BD by utilizing scientific data rather than generic assumptions regarding interspecies scaling.…”

Prediction of in vivo developmental toxicity of all-trans-retinoic acid based on in vitro toxicity data and in silico physiologically based kinetic modeling

“…For the rat model, kinetic constants on ATRA metabolism obtained using liver, kidney, lung and brain fractions were used, whereas for the human model, kinetic constants on ATRA metabolism obtained using specific cytochrome P450 (CYP) and uridine 5′-diphospho-glucuronosyltransferase (UGT) enzymes were used (supplementary Table 3). The reported apparent K m values were applied in the PBK model, whereas the apparent V max values were scaled to a complete organ using a microsomal protein per gram of liver (MPPGL) of 35 mg for rat liver (Medinsky et al 1994), a MPPGK of 7 mg for rat kidney (Beierschmitt and Weiner 1986), a MPPGLu of 20 mg for rat lung (Medinsky et al 1994), a MPPGB of 4 mg for rat brain (Ravindranath and Anandatheerthavarada 1990), and a MPPGL for human liver as generated by PopGen (supplementary Table 2). …”

A Multicompartment Liver-based Pharmacokinetic Model for Benzene and its Metabolites in Mice

“…Unlike in the previous SCL model where C MP was estimated, the value of C MP found by Medinsky et al [26] was used. The kidney contains approximately 10% of the concentration of CYP2E1 found in the liver [7].…”

“…The value of C CP obtained by Medinsky et al [26] was used. The metabolism of hydroquinone to its conjugates is assumed occur in zone 3 since the glucuronidation capacity is greater in this region [25].…”