title: Development of an inhalation physiologically based pharmacokinetic (PBPK) model for 2,2, 4-trimethylpentane (TMP) in male Long-Evans rats using gas uptake experiments.
abstract: 2,2,4-Trimethylpentane (TMP) is a volatile colorless liquid used primarily to increase the octane rating of combustible fuels. TMP is released in the environment through the manufacture, use, and disposal of products associated with the gasoline and petroleum industry. Short-term inhalation exposure to TMP (< 4 h; > 1000 ppm) caused sensory and motor irritations in rats and mice. Like many volatile hydrocarbons, acute exposure to TMP may also be expected to alter neurological functions. To estimate in vivo metabolic kinetics of TMP and to predict its target tissue dosimetry during inhalation exposures, a physiologically based pharmacokinetic (PBPK) model was developed for the chemical in Long-Evans male rats using closed-chamber gas-uptake experiments. Gas-uptake experiments were conducted in which rats (80-90 days old) were exposed to targeted initial TMP concentrations of 50, 100, 500, and 1000 ppm. The model consisted of compartments for the closed uptake chamber, lung, fat, kidney, liver, brain, and rapidly and slowly perfused tissues. Physiological parameters were obtained from literature. Partition coefficients for the model were experimentally determined for air/blood, fat, liver, kidney, muscle, and brain using vial equilibration methods. Common to other hydrocarbons, metabolism of TMP via oxidative reactions is assumed to mainly occur in the liver. The PBPK model simulations of the closed chamber data were used to estimate in vivo metabolic parameters for TMP in male Long-Evans rats.
authors.affiliation: Integrated Systems Toxicology Divison, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27709, USA. el-masri.hisham@epa.gov
authors.forename: Hisham A
authors.initials: HA
authors.lastname: El-Masri
authors.forename: Sean
authors.initials: S
authors.lastname: Dowd
authors.forename: Rex A
authors.initials: RA
authors.lastname: Pegram
authors.forename: Randy
authors.initials: R
authors.lastname: Harrison
authors.forename: Sisouphanh J
authors.initials: SJ
authors.lastname: Yavanhxay
authors.forename: Jane Ellen
authors.initials: JE
authors.lastname: Simmons
authors.forename: Marina
authors.initials: M
authors.lastname: Evans
mesh_terms: D000393:Air Pollutants / Q000493:pharmacokinetics* / Q000633:toxicity; D000818:Animals; D001273:Atmosphere Exposure Chambers; D001711:Biotransformation; D002849:Chromatography, Gas; D005740:Gases; D019570:Inhalation Exposure; D008297:Male; D008954:Models, Biological; D009795:Octanes / Q000493:pharmacokinetics* / Q000633:toxicity; D010084:Oxidation-Reduction; D051381:Rats; D020318:Rats, Long-Evans; D014018:Tissue Distribution
chemical_list: D000393:Air Pollutants; D005740:Gases; D009795:Octanes; C045798:2,2,4-trimethylpentane