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Gas Phase Probe Molecules for Assessing In vitro Metabolism to Infer an In vivo Response
Citation:
Angrish, M., M. Madden, AND J. Pleil. Gas Phase Probe Molecules for Assessing In vitro Metabolism to Infer an In vivo Response. EPA's Chemical Safety Research: Second ToxCast Data Summit, Research Triangle Park, NC, September 29 - 30, 2014.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA mission to protect human health and the environment. HEASD research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Description:
Efficient and accurate in vitro high-throughput screening (HTS) methods use cellular and molecular based adverse outcome pathways (AOPs) as central elements for exposure assessment and chemical prioritization. However, not all AOPs are based on human or animal systems biology, but rather supported by in vitro to in vivo extrapolation and other computational modeling. The challenge is to develop unambiguous quantitative links between in vitro responses and corresponding in vivo effects. The use of gas phase probe molecules (PrMs) supported by relevant human exposure studies and pharmacokinetic (PK) parameters may address this gap. Furthermore, existing HTS assays that require liquid handling robotics would becomplemented by quantitative ultrasensitive gas phase PrM assays. We previously determined the kinetic parameters for methyl-tertiary butyl ether (MTBE) metabolism to tertiary butyl alcohol (TBA) via CYP2A6 and sevoflurane metabolism to hexafluoroisopropanol via CYP2E1 pathways in the liver from human empirical data. In this study, we constructed a one-compartment PK model based on differential equations to estimate MTBE and SEV probe pathways for establishing steady state in vitro liver function. Because the MTBE and SEV metabolic pathways are well characterized from in vivo data, we can use them as PrM to explore the effects of chemicals of interest on their respective CYP pathways. We found that the PrMconcept may provide a quantitative real time measurement from air of an in vitro response with a well defined and corresponding in vivo effect. PrM methodology could be easily applied to a broad range of in vitro cell models and would provide a novel approach to assess chemicals of concern including endocrine disruptors, air toxics, and particulate matter.
