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Dose-Response Analysis of Early MicroRNA Alterations Linked to PPAR-alpha Activation
Citation:
Chorley, B., G. Carswell, G. Nelson, V. Bhat, AND C. Wood. Dose-Response Analysis of Early MicroRNA Alterations Linked to PPAR-alpha Activation. 2018 SOT Annual meeting, San Antonio, TX, March 11 - 15, 2018.
Impact/Purpose:
The incorporation of epigenetic-based measurements into toxicological studies and chemical risk assessment has been a recent source of discussion and debate. Most researchers agree that more data is needed to clearly link epigenetic measurements to health and ecological outcomes of regulatory concern. In this study, we measure a type of epigenetic measurement, non-coding microRNAs, in a short term mouse study who has been exposed to a well-characterized liver tumorigen. The overall purpose is to begin to link these measurements to know toxicologic responses and examine the overall utility and usefulness of these measurements within a risk assessment context.
Description:
MicroRNAs (miRNAs) are short non-coding RNA species that play a critical role in post-transcriptional regulation of gene expression. MiRNAs also serve as a promising source of early predictive biomarkers for different types of health outcomes, although there is limited information on target pathways linked to specific miRNAs and associated dose response metrics. In this case study, we measured liver miRNA alterations using next generation sequencing in male B6C3F1 mice that were exposed to a known liver tumorigen, di(2-ethylhexyl) phthalate (DEHP), for 7 and 28 days at doses of 0, 0.75K, 1.5K, 3K, or 6K ppm in feed. At the highest dose tested, DEHP altered 61 miRNAs after 7 days and 171 miRNAs after 28 days of exposure, with 48 overlapping miRNAs. Analysis of these 48 common miRNAs indicated enrichment in pathways related to liver injury and cancer, most notably peroxisome proliferator-activated receptor alpha (PPARα) activation, which is the known tumorigenic mode-of-action for DEHP. Of the 48 persistent miRNAs, 10 exhibited a dose trend (two-tailed Jonckheere-Terpstra test pBBP>DNOP and DEHP>DNOP>BBP for miR-182-5p and -378a-3p, respectively, correctly identifying DEHP as having the greatest potency of the test exposures. Point-of-departure (POD) dose estimates for DEHP based on these miRNAs (average 163; range 126-202 mg/kg-day) were higher on average than previously calculated values for PPARα target genes (average 74; range 29-183 mg/kg-day) and liver tumor incidence derived from the 2-year tumor data (hepatocellular carcinoma BMD = 71 mg/kg-day; hepatocellular adenoma + carcinoma = 35 mg/kg-day). These findings identify putative miRNA markers of PPARα activation and suggest that early miRNA changes may correctly stratify chemicals based on transcriptional potency. However, miRNA BMDT estimates were less sensitive compared to most target genes and tumorigenic outcome. This abstract does not represent EPA policy.