Overview for Molecular Initiating Event
When a specific MIE can be defined (i.e., the molecular target and nature of interaction is known), in addition to describing the biological state associated with the MIE, how it can be measured, and its taxonomic, life stage, and sex applicability, it is useful to list stressors known to trigger the MIE and provide evidence supporting that initiation. This will often be a list of prototypical compounds demonstrated to interact with the target molecule in the manner detailed in the MIE description to initiate a given pathway (e.g., 2,3,7,8-TCDD as a prototypical AhR agonist; 17α-ethynyl estradiol as a prototypical ER agonist). Depending on the information available, this could also refer to chemical categories (i.e., groups of chemicals with defined structural features known to trigger the MIE). Known stressors should be included in the MIE description, but it is not expected to include a comprehensive list. Rather initially, stressors identified will be exemplary and the stressor list will be expanded over time. For more information on MIE, please see pages 32-33 in the User Handbook.
TBBPA binds to PPARγ in vitro, with a Kd of 0.78 µM and in vivo in zebrafish, with a LOEL of 100 nM (Fang et al., 2015; Riu et al., 2011; Riu et al., 2014). Mild activation has also been reported in vitro in several research papers and in ToxCast assays as well, with effective doses ranging from 0.3 to 10 µM (Riu et al., 2011; Riu et al., 2014; Suzuki et al., 2013; ToxCastTM Data; Watt and Schlezinger, 2015).