Combined in silico and in vitro studies of phthalates and organophosphorus compounds: effects on peroxisome proliferator-activated receptors (PPARs) signaling pathways

Increasing evidence suggests that some environmental contaminants, including known endocrine disrupting chemicals (EDCs), are able to interfere with metabolic pathways by interacting with nuclear receptors. Recently, it has been demonstrated that phthalates and organometallic compounds bind to peroxisome proliferator activated receptors (PPARs) resulting in modulation of lipid metabolism at both the systemic and peripheral level. However, little is known about the metabolic impact of these pollutants on fish. In this context, we performed an in silico docking screen of an EDCs database to identify a set of ligands with conveniently high affinity for the PPARs. Kd values in the nanomolar to micromolar range, generated by the in silico model, suggest that piscine PPARs may be activated by phthalates (e.g. di-isononylphpthalate -DiNP; Di-isodecyl phthalate-DiDP) and some organophosphorus compounds (e.g. tri-m-cresyl phosphate-TmCP) at concentrations similar to those activating the homologous mammalian receptors. Because natural endogenous ligands for PPARs are involved in lipid homeostasis, we assessed the effects of compounds identified using in silico screening on Sparus aurata hepatocytes primary cultures. Generally, exposure of hepatocytes to 0.1, 1 or 10 microM of DiNP, DiDP or TmCP consistently increased both PPAR and its heterodimeric partner Retinoid X Receptor (RXR) mRNA levels at 48 h. In addition, all compounds investigated produced significant increases in the expression of the PPAR target genes, carnitine palmitoyltransferase (CPT) isoforms. In general our data show that phthalates and TmCP modulated PPAR signaling in the seabream in vitro system. The results also suggest the potential involvement of these pollutants in the modulation of mitochondrial fatty acid oxidation.