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Hoer D, Barton HA, Paini A, Bartels M, Ingle B, Domoradzki J, Fisher J, Embry M, Villanueva P, Miller D, Nguyen J, Zhang Q, Edwards SW, Tan YM. Predicting nonlinear relationships between external and internal concentrations with physiologically based pharmacokinetic modeling. Toxicol Appl Pharmacol 2022; 440:115922. [PMID: 35176293 PMCID: PMC10519136 DOI: 10.1016/j.taap.2022.115922] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 01/19/2022] [Accepted: 02/10/2022] [Indexed: 11/20/2022]
Abstract
Although external concentrations are more readily quantified and often used as the metric for regulating and mitigating exposures to environmental chemicals, the toxicological response to an environmental chemical is more directly related to its internal concentrations than the external concentration. The processes of absorption, distribution, metabolism, and excretion (ADME) determine the quantitative relationship between the external and internal concentrations, and these processes are often susceptible to saturation at high concentrations, which can lead to nonlinear changes in internal concentrations that deviate from proportionality. Using generic physiologically-based pharmacokinetic (PBPK) models, we explored how saturable absorption or clearance influence the shape of the internal to external concentration (IEC) relationship. We used the models for hypothetical chemicals to show how differences in kinetic parameters can impact the shape of an IEC relationship; and models for styrene and caffeine to explore how exposure route, frequency, and duration impact the IEC relationships in rat and human exposures. We also analyzed available plasma concentration data for 2,4-dichlorophenoxyacetic acid to demonstrate how a PBPK modeling approach can be an alternative to common statistical methods for analyzing dose proportionality. A PBPK modeling approach can be a valuable tool used in the early stages of a chemical safety assessment program to optimize the design of longer-term animal toxicity studies or to interpret study results.
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Affiliation(s)
- Daniel Hoer
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Durham, NC, USA
| | | | - Alicia Paini
- European Commission, Joint Research Centre, Ispra, Italy.
| | | | - Brandall Ingle
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Durham, NC, USA
| | | | | | - Michelle Embry
- Health and Environmental Sciences Institute, Washington, DC, USA
| | - Philip Villanueva
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Washington, DC, USA
| | - David Miller
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Washington, DC, USA
| | - James Nguyen
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Washington, DC, USA
| | - Qiang Zhang
- Gangarosa Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA, USA
| | | | - Yu-Mei Tan
- U.S. Environmental Protection Agency, Office of Pesticide Programs, Durham, NC, USA.
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