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. 2017 May;91(5):2045-2065.
doi: 10.1007/s00204-016-1886-5. Epub 2016 Dec 7.

Recommended approaches in the application of toxicogenomics to derive points of departure for chemical risk assessment

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Recommended approaches in the application of toxicogenomics to derive points of departure for chemical risk assessment

Reza Farmahin et al. Arch Toxicol. 2017 May.

Abstract

There is increasing interest in the use of quantitative transcriptomic data to determine benchmark dose (BMD) and estimate a point of departure (POD) for human health risk assessment. Although studies have shown that transcriptional PODs correlate with those derived from apical endpoint changes, there is no consensus on the process used to derive a transcriptional POD. Specifically, the subsets of informative genes that produce BMDs that best approximate the doses at which adverse apical effects occur have not been defined. To determine the best way to select predictive groups of genes, we used published microarray data from dose-response studies on six chemicals in rats exposed orally for 5, 14, 28, and 90 days. We evaluated eight approaches for selecting genes for POD derivation and three previously proposed approaches (the lowest pathway BMD, and the mean and median BMD of all genes). The relationship between transcriptional BMDs derived using these 11 approaches and PODs derived from apical data that might be used in chemical risk assessment was examined. Transcriptional BMD values for all 11 approaches were remarkably aligned with corresponding apical PODs, with the vast majority of toxicogenomics PODs being within tenfold of those derived from apical endpoints. We identified at least four approaches that produce BMDs that are effective estimates of apical PODs across multiple sampling time points. Our results support that a variety of approaches can be used to derive reproducible transcriptional PODs that are consistent with PODs produced from traditional methods for chemical risk assessment.

Keywords: BMD; BMDL; LOAEL; Microarray; NOAEL; Point of departure; Risk assessment; Toxicogenomics; Transcriptomics.

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Figures

Fig. 1
Fig. 1
Study method overview. White boxes show animal exposures, necropsies, histology and microarray procedures that were conducted in previous studies (Dodd et al. , , , , , ; Thomas et al. 2013a, b). Blue boxes represent procedures that were conducted in the current study (color figure online)
Fig. 2
Fig. 2
Box and whisker plots of the BMDt means for all approaches for all chemicals at the 5-, 14-, 28-, and 90-day time points. Colored horizontal lines represent the NOAEL (blue line), LOAEL (red line), lowest time-point-matched BMDa value (gray line), the lowest overall BMDa values (i.e., any time) across all time points (green line), and cancer (black line). The box boundaries and lines represent the interquartile ranges and means, respectively. The whiskers represent 10 and 90 percentiles (color figure online)
Fig. 3
Fig. 3
BMD(L)ts relative to apical PODs for the 5-day time point. Threefold and tenfold ranges from the apical POD are within the shaded area and the dashed horizontal lines, respectively. a The BMDts derived from each approach were divided by the corresponding apical POD values for every chemical; b data from a shown separately for each chemical; c the BMDLts derived from each approach were divided by NOAEL and LOAEL; d data from c shown separately for each chemical

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