Chemical structure of FR and morphological changes of BM-MSCs upon exposure to FR and subsequent antagonistic effects of CH 223191 every 24 hours for up to 72 hours. FR is a polycyclic aromatic hydrocarbon (PAH) that is formed by the fusion of naphthalene and benzene connected by a five-membered ring (A). Morphological changes of BM-MSCs after FR exposure revealed that cells were elongated, detached from the subsurface, and had loosened cell-to-cell attachments. These morphological alterations were partially rescued after co-treatment with an AHR antagonist (CH223191) in a dose-dependent manner (B).