Carcinogenesis, Vol 18, 611-625, Copyright © 1997 by Oxford University Press
LM Sweeney, PM Schlosser, MA Medinsky and JA Bond
1,3-Butadiene (BD) is a more potent tumor inducer in mice than in rats. BD
also shows striking differences in metabolic activation, with substantially
higher blood concentrations of 1,2:3,4-diepoxybutane (butadiene diepoxide;
BDE) in BD-exposed mice than in similarly exposed rats. The objective of
this study was to develop a single mechanistic model structure capable of
describing BD disposition in both species. To achieve this objective, known
pathways of 1,2-epoxy-3-butene (butadiene monoepoxide; BMO) and BDE
metabolism were incorporated into a physiologically based pharmacokinetic
model by scaling rates determined in vitro. With this model structure,
epoxide clearance was underestimated for both rats and mice. Improved
simulation of blood epoxide concentrations was achieved by addition of
first-order metabolism in the slowly perfused tissues, verified by
simulation of data on the time course for BMO elimination after i.v.
injection of BMO. Blood concentrations of BD were accurately predicted for
mice and rats exposed by inhalation to constant concentrations of BD.
However, if all BD was assumed to be metabolized to BMO, blood
concentrations of BMO were overpredicted. By assuming that only a fraction
of BD metabolism produces BMO, blood concentrations of BMO could be
predicted over a range of BD exposure concentrations for both species. In
vitro and in vivo studies suggest an alternative cytochrome P-450-mediated
pathway for BD metabolism that does not yield BMO. Including an alternative
pathway for BD metabolism in the model also gave accurate predictions of
blood BDE concentrations after inhalation of BD. Blood concentrations of
BMO and BDE observed in both mice and rats are best explained by the
existence of an alternative pathway for BD metabolism which does not
produce BMO.
ARTICLES
Physiologically based pharmacokinetic modeling of 1,3-butadiene, 1,2- epoxy-3-butene, and 1,2:3,4-diepoxybutane toxicokinetics in mice and rats
Chemical Industry Institute of Toxicology, Research Triangle Park, NC 27709, USA.
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