The Urinary Metabolites of DINCH Have an Impact on the Activities of the Human Nuclear Receptors ERα, ERβ, AR, PPARα and PPARγ

DINCH (di-isononyl cyclohexane-1,2-dicarboxylate) is a non-phthalate plasticizer that has been developed to replace phthalate plasticizers such as DEHP (di-2-ethylhexyl phthalate) or DINP (di-isononyl phthalate). DINCH is metabolized to its corresponding monoester and subsequently to oxidized monoester derivatives. These are conjugated to glucuronic acid and subject to urinary excretion. In contrast to DINCH, there are almost no toxicological data available regarding its primary and secondary metabolites. The present study aimed at the characterization of potential endocrine properties of DINCH and five DINCH metabolites by using reporter gene assays to monitor the activity of the human nuclear receptors ERα, ERβ, AR, PPARα and PPARγ in vitro. DINCH itself did not have any effect on the activity of these receptors whereas DINCH metabolites were shown to activate all these receptors. In the case of AR, DINCH metabolites predominantly enhanced dihydrotestosterone-stimulated AR activity. In the H295R steroidogenesis assay, neither DINCH nor any of its metabolites affected estradiol or testosterone synthesis. In conclusion, primary and secondary DINCH metabolites exert different effects at the molecular level compared to DINCH itself. All these in vitro effects of DINCH metabolites, however, were only observed at high concentrations such as 10 μM or above which is about three orders of magnitude above reported DINCH metabolite concentrations in human urine. Thus, the in vitro data do not support the notion that DINCH or any of the investigated metabolites may exert considerable endocrine effects in vivo at relevant human exposure levels.