ToxSci Advance Access originally published online on April 10, 2007
Toxicological Sciences 2007 98(1):43-56; doi:10.1093/toxsci/kfm082
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Published by Oxford University Press 2007.
Predicting Age-Appropriate Pharmacokinetics of Six Volatile Organic Compounds in the Rat Utilizing Physiologically Based Pharmacokinetic Modeling
* US Environmental Protection Agency, Office of Research and Development, National Center for Computational Toxicology, Research Triangle Park, North Carolina 27711
AFRL/HEPB, Wright-Patterson Air Force Base, Ohio 45433
ManTech Environmental Technology, Inc., Dayton, Ohio 45437
US Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, Cincinnati, Ohio
1 To whom correspondence should be addressed at National Center for Computational Toxicology, B205-1, Office of Research and Development, US EPA, 109 TW Alexander Drive, Research Triangle Park, NC 27711. Fax: (919) 541-1194. E-mail: barton.hugh{at}epa.gov.
Received October 13, 2006; accepted March 23, 2007
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Abstract |
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The capability of physiologically based pharmacokinetic models to incorporate age-appropriate physiological and chemical-specific parameters was utilized to predict changes in internal dosimetry for six volatile organic compounds (VOCs) across different ages of rats. Typical 6-h animal inhalation exposures to 50 and 500 ppm perchloroethylene, trichloroethylene, benzene, chloroform, methylene chloride, or methyl ethyl ketone (MEK) were simulated for postnatal day 10 (PND10), 2-month-old (adult), and 2-year-old (aged) rats. With the exception of MEK, predicted venous blood concentrations of VOCs in the aged rat were equal or up to 1.5-fold higher when compared to the adult rat at both exposure levels, whereas levels were predicted to be up to 3.8-fold higher in the case of PND10 at 50 ppm. Predicted blood levels of MEK were similar in the adult and aged rat, but were more than 5-fold and 30-fold greater for PND10 rats at 500 and 50 ppm, respectively, reflecting high water solubility along with lower metabolic capability and faster ventilation rate per unit body weight (BW) of PND10 animals. Steady-state blood levels of VOCs, simulated by modeling constant exposure, were predicted to be achieved in the order PND10 > adult > aged, largely due to increasing fat volume. The dose metric, total amount metabolized per unit liver volume was generally much lower in PND10 than in adult rats. The blood:air partition coefficient, fat volume, and fat blood flow were identified as critical determinants for the predicted differences in venous blood concentrations between the adult and aged. The lower metabolic capability, largely due to a smaller liver size, and faster ventilation rate per unit BW of PND10 animals contribute the most to the differences between PND10 and adult rats. This study highlights the pharmacokinetic differences and the relevant parameters that may contribute to differential susceptibility to the toxic effects of VOCs across life stages of the rat.
Key Words: volatile organic compounds (VOCs); physiologically based pharmacokinetic (PBPK) modeling; rat; age-dependent pharmacokinetics.
Disclaimer: This manuscript has been subjected to review by the National Center for Computational Toxicology and approved for publication. Approval does not signify that the contents reflect the views of the Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.