The effects of PAHs and N-PAHs on retinoid signaling and Oct-4 expression in vitro

Polycyclic aromatic hydrocarbons (PAHs) and their N-heterocyclic analogs (N-PAHs) are important environmental contaminants with negative effects in living organisms, including teratogenicity and embryotoxicity. Though most studies linked their embryotoxicity with aryl hydrocarbon receptor (AhR) and cytochrome P450 activation, the exact mechanism is not known. Other mechanisms such as disruption of retinoid signaling were recently suggested to be of importance. This study investigated PAHs and N-PAHs interference with retinoid signaling in vitro by modulating all-trans retinoic acid (ATRA) mediated response in a reporter gene assay using P19/A15 cell line. Further, effects on pluripotency and differentiation processes were evaluated by measuring octamer-4 (Oct-4), an important pluripotency marker and master differentiation factor. Two of the studied compounds, benz[a]anthracene and benz[c]acridine significantly up-regulated ATRA-mediated response in the co-exposure with a range of ATRA concentrations. Another structural N-PAH variant, 1,7-phenanthroline, downregulated ATRA-mediated response at most of tested ATRA concentrations and exposure times. Interesting concentration-dependent biphasic effects (i.e. downregulation with subsequent up-regulation to control levels) were observed at co-exposures of ATRA and parent PAH phenanthrene. Non significant Oct-4 modulation in co-exposure with ATRA was observed at compounds, which potentiated ATRA-mediated effects in the reporter gene assay. On the other hand, 1,7-phenanthroline and phenanthrene significantly suppressed Oct-4 levels in higher tested concentrations. Our results further extend the knowledge of PAH and N-PAH in vitro effects and indicate that these environmental toxicants may have influence on differentiation process and embryonic development by interfering with ATRA signaling and by modulating levels of Oct-4. (C) 2010 Elsevier Ireland Ltd. All rights reserved.