Environmentally-relevant mixture of pharmaceutical drugs stimulates sex-steroid hormone production and modulates the expression of candidate genes in the ovary of juvenile female rainbow trout

Because of their intrinsic biological activity and ubiquitous environmental occurrence, human pharmaceutical compounds have received increasing attention from health and environmental agencies. In the present study, all-female juvenile rainbow trout (Oncorhynchus mykiss) were exposed to environmentally-realistic concentrations of a mixture of nonsteroidal pharmaceuticals for 42 days, and the effects on plasma levels of sex-steroids and the expression of genes encoding key proteins involved in ovarian development were assessed. Paracetamol, carbamazepine, diclofenac, irbesartan and naproxen were selected, as these have been detected in the Meuse River in Belgium. Fish were exposed to three concentrations of the mixture including the environmental concentration, 10- and 100-times the environmental concentration. Plasma levels of sex-steroid hormones, particularly 11-ketotestosterone, increased in a concentration-dependent way in exposed females. In addition, some key genes involved in ovarian steroidogenesis were significantly overexpressed after 7 days of exposure, such as key genes involved in the maintenance of the ovary. The steady-state mRNA level of genes implicated in germ cell fate were especially affected, such as that of foxl3 which increased by 5 fold at the highest concentration of the mixture. In conclusion, this study highlights that combined occurrence of common pharmaceutical drugs at concentrations present in surface water environments may act as endocrine-disrupting compounds in rainbow trout.