You are here:
Development of Short-term Molecular Thresholds to Predict Long-term Mouse Liver Tumor Outcomes: Phthalate Case Study
Citation:
Lake, A., S. Hester, V. Bhat, G. Carswell, B. Chorley, C. McQueen, J. Simmons, AND C. Wood. Development of Short-term Molecular Thresholds to Predict Long-term Mouse Liver Tumor Outcomes: Phthalate Case Study. Tamburro Liver Symposium, Louisville, KY, September 10 - 12, 2014.
Impact/Purpose:
To be presented at the Tamburro Symposium in Louisville, KY
Description:
Short-term molecular profiles are a central component of strategies to model health effects of environmental chemicals. In this study, a 7 day mouse assay was used to evaluate transcriptomic and proliferative responses in the liver for a hepatocarcinogenic phthalate, di (2-ethylhexyl) phthalate (DEHP), and two non-carcinogenic phthalates, di-n-octyl phthalate (DNOP) and n-butyl-benzyl phthalate (BBP). Phthalates were given in feed at four different doses to adult male B6C3F1 mice (n=10/group). Our goal was to establish early gene expression and proliferation thresholds related to liver tumor incidence observed at 2 years. Global genomic profiles using Illumina bead arrays showed clear activation of peroxisome proliferator-activated receptor alpha (PPARα) genes for phthalate-treated mouse liver samples (DEHP>BBP>DNOP). Robust increases for phthalate response genes were validated using PrimePCR SYBR assays. Monotonically increasing dose response profiles for DEHP-treated livers were observed for all PPARα target genes. Only high-dose BBP and DNOP exhibited significant gene fold elevations for PPARα response genes such as Cyp4a10, Cyp4a31, Cyp4a12b, Cyp4a14, and Acot, while Pdk4, a marker of pyruvate dehydrogenase kinase was only significantly elevated among high dose DEHP-treated livers. Liver cell proliferation measured by Ki-67 labeling index (LI) at 7 days was significantly increased only for DEHP. Fold-change (FC) thresholds for gene expression and proliferation at 7 days corresponding to a significant increase in liver tumor incidence (30%) at 2 years were estimated across all phthalates for PPARα target genes and proliferation. A wide range of threshold gene expression values were identified, from 3.2x for Pdk4 to 335x for Cyp4a14. In comparison, a threshold value of 2.0x was identified for liver cell proliferation LI. Using a case study approach, these results reveal short-term quantitative effect thresholds for early receptor-mediated events in liver. Our findings indicate the importance of both proximate transcriptomic as well as functional outcomes for these types of models. Disclaimer: The research described in this article has been reviewed by the National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, and approved for publication. Approval does not signify that the contents necessarily reflect the views and the policies of the Agency.