Finding maximal transcriptome differences between reprotoxic and non-reprotoxic phthalate responses in rat testis

The chemical legislation of the EU, Registration, Evaluation, and Authorization of Chemicals (REACH), stipulates that about 30 000 chemical substances are to be assessed on their possible risks. Toxicological evaluation of these compounds will at least partly be based on animal testing. In particular, the assessment of reproductive toxicity is a very complicated, time‐consuming and animal‐demanding process. Introducing microarray‐based technologies can potentially refine in vivo toxicity testing. If compounds of a distinct chemical class induce reproducible gene‐expression responses with a recognizable overlap, these gene‐expression signatures may indicate intrinsic features of certain compounds, including specific toxicity. In the present study, we have set out the first steps towards this approach for the reproductive toxicity of phthalates. Male rats were treated with a single dose of either reprotoxic or non‐reprotoxic phthalates, and were analyzed 24 h afterwards. Subsequently, histopathological and gene‐expression profiling analyses were performed. Despite ambiguous histopathological observations, we were able to identify genes with differential expression profiles between the reprotoxic phthalates and the non‐reprotoxic counterparts. This shows that differences in gene‐expression profiles, indicative of the type of exposure, may be detected earlier, or at lower doses, than classical pathological endpoints. These findings are promising for ‘early warning’ biomarker analyses and for using toxicogenomics in a category approach. Ultimately, this could lead to a more cost‐effective approach for prioritizing the toxicity testing of large numbers of chemicals in a short period of time in hazard assessment of chemicals, which is one of the objectives of the REACH chemical legislation. Copyright © 2010 John Wiley & Sons, Ltd.