Fig. 2. Schematic adverse outcome pathway (AOP) framework. (A) The AOP consist of a molecular initiating event (MIE), key event (KE), key event relationship (KER), and an adverse outcome (AO). Arrows indicate KERs and a dotted arrow is the naKER, that is, the non-adjacent (indirect) KER. Basically, a KER is the relationship between the two adjacent KEs, but the relationship between non-adjacent KEs is also possible. One AOP has one MIE and AO, and there is no limit to the number of KE and KER. (B) Since each component of an AOP exists independently, even different AOPs can contain the same component. Arrows also mean KER and the indication is omitted for convenience.

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