Tiered screening and testing strategy for xenoestrogens and antiandrogens

Anthropogenic chemicals that disrupt endocrine function during critical stages of development can produce profound reproductive alterations in both wildlife and humans. Of the tens of thousands of chemicals in existence, few have been tested for their ability to disrupt the endocrine system. Newly enacted legislation requires that the USEPA develop a chemical screening and testing program for endocrine effects. At present, the Endocrine Disrupters Screening and Testing Advisory Committee (EDSTAC) is considering a screening battery (Tier 1) to detect (anti)estrogenic (E) (anti)androgenic (A) and antithyroid activities using in vivo and in vitro assays. In addition, the battery should detect alterations of hypothalamic-pituitary function, steroid/thyroid hormone synthesis as well as receptor-mediated effects in mammals and other taxa. Chemicals positive in Tier 1 should be labeled as potential endocrine disrupters and subjected to testing (Tier 2). The present discussion will provide examples of in vitro (receptor binding, gene expression and steroidogenesis) and in vivo assays for screening. Short-term in vivo assays which have been used to detect estrogenicity for over 70 years are still useful in this regard. Identification of (anti)androgenic activity is easily accomplished by examination of growth of androgen-dependent tissues in young castrated male rats, determination of the age at puberty (balanopreputial separation) or by examination of reproductive malformations after in utero exposure (hypospadias, testicular non-descent, retained nipples, a vaginal pouch, prostate agenesis, and reduced anogenital distance). Pubertal assays with intact animals will not only detect chemicals that alter E-A function via their nuclear receptors, but also will detect altered hormone synthesis and alterations of the hypothalamic-pituitary-gonadal axis. While in utero assays are critical for testing, presently they are not included in screening because they can be relatively long-term studies.