Comparison of fathead minnow ovary explant and H295R cell-based steroidogenesis assays for identifying endocrine-active chemicals

An in vitro steroidogenesis assay using H295R human adenocarcinoma cells has been suggested as a possible alternative to gonad explant assays for use as a Tier I screening assay to detect endocrine active chemicals capable of modulating steroid hormone synthesis. This study is one of the first to investigate the utility of the H295R assay for predicting effects and/or understanding mechanisms of action across species and tissues. Six chemicals, including one selective aromatase inhibitor (fadrozole), four fungicides (fenarimol, ketoconazole, prochloraz, and vinclozolin), and one herbicide (prometon), were tested in both the H295R steroidogenesis assay, and an in vitro steroidogenesis assay using fathead minnow ovary explants. All six chemicals caused significant alterations in 17β-estradiol (E2) and/or testosterone (T) production in vitro. Effects of ketoconazole, prochloraz, and prometon were similar in both assays. However, there were differences in the profile of responses for T for fadrozole and fenarimol, and for T and E2 for vinclozolin. In terms of sensitivity, steroid production in the H295R assay was most sensitive for detecting the effects of fadrozole, fenarimol, and prochloraz, but was less sensitive than the fathead minnow ovary explant assay to the effects of ketoconazole and vinclozolin. The H295R assay was consistently less variable (among replicates) than the fathead minnow ovary explant assay. However, the ovary explant assay was more predictive of in vivo effects of the six chemicals on fathead minnows than the H295R system. Further characterization of autoregulatory capacities, interaction of steroid-hormone receptor pathways with steroidogenesis, and metabolic capabilities of each system are needed for either system to provide clear and informative insights regarding a chemicalʹs mechanism of action. Overall, however, results of this study suggest that both the H295R and fathead minnow ovary explant assays have utility for identifying endocrine-active chemicals in screening-type applications.