Pharmacokinetic Modeling of Arsenite Uptake and Metabolism in Hepatocytes—Mechanistic Insights and Implications for Further Experiments

Authors: Easterling M.R.¹; Styblo M.²; Evans M.V.³; Kenyon E.M.³

Source: Journal of Pharmacokinetics and Pharmacodynamics, Volume 29, Number 3, June 2002 , pp. 207-234(28)

Publisher: Springer

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Abstract:

Arsenic (iAs) is a known human carcinogen and widespread contaminant in drinking water. To provide a quantitative framework for experimental design and hypothesis testing, we developed a pharmacokinetic model describing the uptake and methylation of arsenite (AsIII) in primary rat hepatocytes. Measured metabolites were inorganic As (iAs), mono-methylated As (MMA), and di-methylated As (DMA) concentration in cells and media. Transport and methylation parameters were estimated from time course data for iAs, MMA, and DMA at three initial media As(III) concentrations (0.1, 0.4, 1.0 M). Inhibition of the formation DMA from MMA by As(III) was necessary to adequately describe the data. The data were consistent with multiple types of inhibition, although uncompetitive inhibition provided a slightly better fit. Model simulations indicate that cellular MMA (cMMA) is a key arsenical to measure; measurement of cMMA in the 4–6 hr time range using an initial concentration of 1.4 M AsIII would provide the best experimental conditions to distinguish uncompetitive from other types of inhibition. Due to the large number of model parameters estimated from the data, we used sensitivity analysis to determine the influential parameters. Use of sensitivity surfaces facilitated the comparison of parameters over time and across doses. Predicted model responses were most sensitive to influx and efflux parameters, suggesting that transport processes are critical in determining cellular arsenical concentrations. These high sensitivities imply that independent experiments to estimate these parameters with greater certainty may be crucial for refinement of this model and to extend this model to describe methylation and transport in human hepatocytes.

Keywords: pharmacokinetic model; arsenic; sensitivity analysis

Language: English

Document Type: Research article

Affiliations: 1: Curriculum in Toxicology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 USA 2: Department of Pediatrics, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 USA 3: U.S. Environmental Protection Agency, Office of Research and Development, NHEERL/ETD/PKB, Research Triangle Park, North Carolina 27711 USA

Publication date: 2002-06-01

Pharmacokinetic Modeling of Arsenite Uptake and Metabolism in Hepatocytes—Mechanistic Insights and Implications for Further Experiments

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