Bhat VS, Hester SD, Nesnow S, Eastmond DA. 2013. Concordance of transcriptional and apical benchmark dose levels for conazole-induced liver effects in CD-1 mice. Toxicol Sci 136:205-215.
The ability to anchor chemical class–based gene expression changes to phenotypic lesions and to describe these changes as a function of dose and time informs mode-of-action determinations and improves quantitative risk assessments. Previous global expression profiling identified a 330-probe cluster differentially expressed and commonly responsive to 3 hepatotumorigenic conazoles (cyproconazole, epoxiconazole, and propiconazole) at 30 days. Extended to 2 more conazoles (triadimefon and myclobutanil), the present assessment encompasses 4 tumorigenic and 1 nontumorigenic conazole. Transcriptional benchmark dose levels (BMDLT) were estimated for a subset of the cluster with dose-responsive behavior and a ≥ 5-fold increase or decrease in signal intensity at the highest dose. These genes primarily encompassed CAR/RXR activation, P450 metabolism, liver hypertrophy- glutathione depletion, LPS/IL-1-mediated inhibition of RXR, and NRF2-mediated oxidative stress pathways. Median BMDLT estimates from the subset were concordant (within a factor of 2.4) with apical benchmark doses (BMDLA) for increased liver weight at 30 days for the 5 conazoles. The 30-day median BMDLT estimates were within one-half order of magnitude of the chronic BMDLA for hepatocellular tumors. Potency differences seen in the dose-responsive transcription of certain phase II metabolism, bile acid detoxification, and lipid oxidation genes mirrored each conazole’s tumorigenic potency. The 30-day BMDLT corresponded to tumorigenic potency on a milligram per kilogram day basis with cyproconazole > epoxiconazole > propiconazole > triadimefon > myclobutanil (nontumorigenic). These results support the utility of measuring short-term gene expression changes to inform quantitative risk assessments from long-term exposures.