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Assessing Toxicokinetic Uncertainty and Variability in Risk Prioritization
Citation:
Wambaugh, J., B. Wetmore, C. Ring, C. Nicolas, R. Pearce, G. Honda, R. Dinallo, D. Angus, J. Gilbert, T. Sierra, A. Badrinarayanan, B. Snodgrass, A. Brockman, C. Strock, R. Setzer, AND R. Thomas. Assessing Toxicokinetic Uncertainty and Variability in Risk Prioritization. TOXICOLOGICAL SCIENCES. Society of Toxicology, RESTON, VA, 172(2):235-251, (2019). https://doi.org/10.1093/toxsci/kfz205
Impact/Purpose:
New chemical specific measurements of HTTK were used to assess the relative contributions of human bioavailability and measurement uncertainty in chemical risk prioritizations. New HTTK experimental measurements were made for 496 chemicals from the ToxCast HTS library. A new statistical analysis was performed to allow quantification of the chemical-specific measurement uncertainty. An updated version of the “httk” R package allows uncertainty propagation into chemical risk prioritization, including the uncertainties reported here as well as other sources such as the predictions of in silico models
Description:
High(er) throughput toxicokinetics (HTTK) encompasses in vitro measures of key determinants of chemical toxicokinetics and reverse dosimetry approaches for in vitro-in vivo extrapolation (IVIVE). With HTTK, the bioactivity identified by any in vitro assay can be converted to human equivalent doses and compared with chemical intake estimates. Biological variability in HTTK has been previously considered, but the relative impact of measurement uncertainty has not. Bayesian methods were developed to provide chemical-specific uncertainty estimates for 2 in vitro toxicokinetic parameters: unbound fraction in plasma (fup) and intrinsic hepatic clearance (Clint). New experimental measurements of fup and Clint are reported for 418 and 467 chemicals, respectively. These data raise the HTTK chemical coverage of the ToxCast Phase I and II libraries to 57%. Although the standard protocol for Clint was followed, a revised protocol for fup measured unbound chemical at 10%, 30%, and 100% of physiologic plasma protein concentrations, allowing estimation of protein binding affinity. This protocol reduced the occurrence of chemicals with fup too low to measure from 44% to 9.1%. Uncertainty in fup was also reduced, with the median coefficient of variation dropping from 0.4 to 0.1. Monte Carlo simulation was used to propagate both measurement uncertainty and biological variability into IVIVE. The uncertainty propagation techniques used here also allow incorporation of other sources of uncertainty such as in silico predictors of HTTK parameters. These methods have the potential to inform risk-based prioritization based on the relationship between in vitro bioactivities and exposures.
URLs/Downloads:
DOI: Assessing Toxicokinetic Uncertainty and Variability in Risk Prioritization
https://pubmed.ncbi.nlm.nih.gov/31532498/