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Xenobiotic-Metabolizing Enzyme and Transporter Gene Expression in Primary Cultures of Human Hepatocytes Modulated by Toxcast Chemicals
Citation:
ROTROFF, D., A. L. BEAM, D. J. DIX, A. FARMER, K. M. FREEMAN, K. A. HOUCK, R. JUDSON, E. L. LECLUYSE, M. T. MARTIN, D. REIF, AND S. S. FERGUSON. Xenobiotic-Metabolizing Enzyme and Transporter Gene Expression in Primary Cultures of Human Hepatocytes Modulated by Toxcast Chemicals. JOURNAL OF TOXICOLOGY AND ENVIRONMENTAL HEALTH - PART B: CRITICAL REVIEWS. Taylor & Francis, Inc., Philadelphia, PA, 1(2-4):329-346, (2010).
Impact/Purpose:
The bioactivity of the 309 unique chemicals currently in the ToxCast library was characterized in cultures of primary human hepatocytes over concentration and time-course measurements. Many of these chemicals induced the expression of these human genes, providing distinct bioactivity profiles that may be useful in classifying and ranking these chemicals based on their potential to impact xenobiotic metabolism pathways regulated by nuclear receptors and often associated with toxicity. In addition, direct associations were observed between the activation of key human receptor pathways and specific and relevant rodent in vivo toxicity endpoints. These findings indicate the potential of metabolically competent, in vitro hepatocyte culture systems for generating data useful in predictive toxicity modeling, and identify putative human toxicity pathways for specific disease endpoints.
Description:
Primary human hepatocyte cultures are useful in vitro model systems of human liver because when cultured under appropriate conditions the hepatocytes retain liver-like functionality such as metabolism, transport, and cell signaling. This model system was used to characterize the concentration- and time-response of the 320 ToxCast chemicals for changes in expression of genes regulated by nuclear receptors. Fourteen gene targets were monitored in quantitative nuclease protection assays: six representative cytochromes P-450, four hepatic transporters, three Phase II conjugating enzymes, and one endogenous metabolism gene involved in cholesterol synthesis. These gene targets are sentinels of five major signaling pathways: AhR, CAR, PXR, FXR, and PPAR. Besides gene expression, the relative potency and efficacy for these chemicals to modulate cellular health and enzymatic activity were assessed. Results demonstrated that the culture system was an effective model of chemical-induced responses by prototypical inducers such as phenobarbital and rifampicin. Gene expression results identified various ToxCast chemicals that were potent or efficacious inducers of one or more of the 14 genes, and by inference the 5 nuclear receptor signaling pathways. Significant relative risk associations with rodent in vivo chronic toxicity effects are reported for the five major receptor pathways. These gene expression data are being incorporated into the larger ToxCast predictive modeling effort.
