Novel trends in endocrine disruptor testing: the H295R Steroidogenesis Assay for identification of inducers and inhibitors of hormone production.

Over the past two decades, there has been increasing concern about the possible impacts of exposure to chemicals in the environment on endocrine and reproductive systems in humans and wildlife [1]. To address these concerns, national and international programs have been initiated to develop new guidelines for the screening and testing of potential endocrine-disrupting chemicals (EDCs) in vertebrates [2, 3]. The focus of these multi-tiered programs was to develop in vitro and in vivo assays to identify and classify chemicals relative to their potential interaction with endocrine systems (Tier 1), and then to develop concentration–response relationships in animal models (Tier 2) [2]. In this article we will focus on a new in vitro bioassay to test for the potential of chemicals to interfere with steroid hormone production. This assay is currently being developed as part of Tier 1 of the USEPA Endocrine Disruptor Screening Program and an Organization for Economic Cooperation and Development (OECD) test method validation program [4]. Most of the efforts to develop screening assays for endocrine disruptor testing have been focused on the development and validation of in vitro hormone receptorbinding assays including the estrogen receptor (ER) and the androgen receptor (AR) [5–7]. However, it should be acknowledged that there are a number of non-receptormediated processes that may also alter endocrine function [8]. These include chemical-induced modulation of the enzymes involved in the production, transformation, or elimination of steroid hormones, which can result in alterations of the absolute and relative concentrations of hormones in blood and tissues [9]. Often, these nonreceptor-mediated effects are caused indirectly via alterations of common signal-transduction pathways [10], or through direct competitive or non-competitive inhibition of the enzyme. Steroid sex hormones are key factors involved in the regulation of reproduction in vertebrates and are also involved in numerous other processes that are related to development and growth [11]. Thus, chemicals that can disrupt the production of sex steroids may be directly linked to adverse outcomes for these processes. To address the potential issues of exposure to chemicals that may result in the disturbance of sex steroid homeostasis, therefore, several in vivo test systems have been evaluated. These tests include the pubertal male and female rat assays, the fish reproductive screen, and the frog thyroid assay. Furthermore, several in vitro screening methods have been developed including the microsomal aromatase assay and a rodent minced-testis assay [2]. Some of these assays such as the rodent minced-testis have shown some promise regarding their potential to identify effects on androgen production. However, a number of questions have been raised about the utility of rodent–based explant assays in that they were found to yield high rates of false positive or Anal Bioanal Chem DOI 10.1007/s00216-007-1657-5