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High Throughput Determinations of Critical Dosing Parameters (IVIVE workshop)
Citation:
Nicolas, C., B. Ingle, M. Bacolod, J. Gilbert, B. Wetmore, C. Ring, Woodrow Setzer, R. Tornero-Velez, M. Martin, AND J. Wambaugh. High Throughput Determinations of Critical Dosing Parameters (IVIVE workshop). Presented at IVIVE for HT Prioritization and Decision Making, Durham, NC, February 17 - 18, 2016. https://doi.org/10.23645/epacomptox.5189194
Impact/Purpose:
Poster presentation on HTTK at IVIVE workshop in RTP, NC. High throughput toxicokinetics (HTTK) is an approach that allows for rapid estimations of TK for hundreds of environmental chemicals.
Description:
High throughput toxicokinetics (HTTK) is an approach that allows for rapid estimations of TK for hundreds of environmental chemicals. HTTK-based reverse dosimetry (i.e, reverse toxicokinetics or RTK) is used in order to convert high throughput in vitro toxicity screening (HTS) data into predicted human equivalent doses, which can be linked with biologically relevant exposure scenarios. Therefore, HTTK provides critical data in order to prioritize the risk for thousands of chemicals that lack TK data. The unbound fraction of a chemical in plasma (Fub) is a critical HTTK parameter that can be measured in vitro. However, for current methods whereby Fub is measured at 100% plasma concentration, Fub is below the limits of quantitation (LOQ) for high throughput analytical chemistry for chemicals that bind strongly to plasma, and therefore cannot be quantified. In order to quantify Fub, a novel method was implemented for 85 strategically selected chemicals: Fub was measured at 10%, 30%, and 100% of physiological plasma concentrations using rapid equilibrium dialysis assays. Chemicals were selected based on their capacity to be potent in vitro estrogen signaling disruptors (Rotroff et al. 2014), having NHANES data, or either having no HTTK data or a failed Fub assay. Including plasma concentrations substantially lower than physiological levels allows the direct measurement of unbound chemical concentrations. The consequent Fub estimates at lower protein concentration can be extrapolated to physiological levels. At 100% plasma concentration, assays yielded values below LOQ for 34 chemicals. Fub could be quantified for 12 of these 34 chemicals at 10% and/or 30% plasma concentrations, which suggests that assay failure at 100% plasma concentration was caused by plasma protein binding for these chemicals. For the remaining 22 chemicals, assay failure may be due to chemical insolubility, susceptibility to enzymatic or other degradation, and ability to bind to RED device constituents such as assay plate walls or dialysis membrane. As a result of using this new approach, ~35% of missing Fub values were captured and would have been missing with the use of previous HTTK protocols. This abstract does not necessarily reflect U.S. EPA policy.
