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Redox Disrupting Potential of ToxCast™Chemicals Ranked by Activity in Mouse Embryonic Stem Cells
Citation:
CHANDLER, K. J., E. S. HUNTER, M. L. HOOPES, S. C. JEFFAY, H. P. NICHOLS, N. KLEINSTREUER, AND T. Knudsen. Redox Disrupting Potential of ToxCast™Chemicals Ranked by Activity in Mouse Embryonic Stem Cells. Presented at Society of Toxicology (SOT) Annual Meeting, San Francisco, CA, March 11 - 15, 2012.
Impact/Purpose:
Here, we developed a weight-of-evidence ToxPi ranking for the 309 chemicals across 19 ToxCast™ assays selected for cellbased and biochemical features that can be tied to cellular redox balance
Description:
Little is known regarding the adverse outcome pathways responsible for developmental toxicity following exposure to chemicals. An evaluation of Toxoast™ Phase I chemicals in an adherent mouse embryonic stem cell (mESC) assay revealed a redox sensitive pathway that correlated with altered myocardial differentiation. Here, we developed a weight-of-evidence ToxPi ranking for the 309 chemicals across 19 ToxCast™assays selected for cell-based and biochemical features that can be tied to cellular redox balance. Among the highest putative redox disrupting (pRDC) chemicals were mitochondrial disruptors such as rotenone, azoxystrobin, pyraclostrobln, fluoxastrobin, and trifloxystrobin. For these five chemicals, the ToxPi ranking followed their rank order potency in developmental toxicity (ToxRefDB). For the entire 309 chemical library, those that produced a 50% change in stem cell differentiation (AC50) were grouped with the more potent pRDCs whereas chemicals that altered cell number by 50%) were evenly distributed throughout the redox ToxPi ranking (Wilcoxon rank sum, p=0.03). To test the putative redox disrupting activity of pRDCs, 2',7'-dichlorodihydrofluorescein diacetate fluorochroming was used to measure ROS in exposed mESCs. H202 at concentrations <300uM produced concentration and temporally dependent ROS levels. ROS was 30% lower on Day 3 than Day 7, indicating a decline in antioxidant capacity with mESC differentiation. Thus, more differentiated mESCs may have decreased antioxidant capabilities. This finding indicates the importance of temporal considerations in the mESC differentiation assay when interpreting the pRDC ToxPi ranking of ToxCast™ chemicals on oxidative stress signaling/altered redox pathways. In sum, altered redox potential may be an adverse outcome pathway linked to altered differentiation in mESCs and developmental toxicity in vivo. Identification of pRDCs may be useful in prioritizing chemicals as potential developmental toxicants. This abstract does not necessarily reflect US EPA policy.