A testing strategy for the identification of mammalian, systemic endocrine disruptors with particular focus on steroids.

Most endocrine disruptors interact with hormone receptors or steroid biosynthesis and metabolism, thereby modifying the physiological function of endogenous hormones. Here, we present an alternative testing paradigm for detection of endocrine modes of action that replace and reduce animal testing through refinement. Receptor mediated endocrine effects were assessed using the yeast-based receptor-mediated transcriptional activation YES/YAS assays and effects on steroid hormone biosynthesis were assessed using the human cell line H295R in the steroidogenesis assay. In our testing paradigm we propose to complement the in vitro assays with a single in vivo repeated dose study in which plasma samples are analyzed for their metabolome profile in addition to classical parameters such as histopathology. The combination of these methods does not only contribute to refinement and reduction of animal testing, but also has significantly increased the efficient allocation of resources and allows for a sound assessment of the endocrine disruption potential of compounds. Thus, this proposal constitutes a potentially attractive alternative to EPA's Endocrine Disruptor Screening Program to identify mammalian, systemic endocrine modes of action. Data on 14 reference substances for which the in vitro YES/YAS and steroidogenesis assays and the in vivo metabolome analysis were performed to assess their putative endocrine modes of action are presented here.