Measurement of Androgen-Sensitive Preweaning Developmental Landmarks in Rodents: Best Practices and Toxicological Significance

Background

Anogenital distance and nipple/areola(e) retention are biomarkers for monitoring normal age-appropriate masculinization of male offspring required by U.S. EPA and OECD guidelines for chemicals. OECD Guidance Document 150 considers both landmarks as sensitive, apical endpoints. For the last century, it has been known that nipple regression in male rodents is complete by late gestation and there are no external or microscopic traces of a nipple at the time of birth. Adverse effects of antiandrogen exposures in humans are well documented, and AGD/NR serve as surrogates for effects on physical and sexual development, although the human relevance of these individual endpoints and endocrine disruption in rodents continues to be debated. The European Chemicals Agency (ECHA) published its reports on the EOGRTS Review Project and ranked 37% AGD and 83% NR datasets across 72 studies as limited or of unacceptable quality.

Methods

We retrospectively analyzed AGD/NR data from 142 rodent studies based on sound scientific principles and per the agency's scoring criteria.

Results and Conclusion

For AGD, our data met standards for precision, variability, and separation of sexes. For NR, our data demonstrated that spontaneous nipple/areolae retention is far less common than asserted by the agency. We propose that the 5-point rating scale used by ECHA to rate NR data has considerable limitations as it is based on data from a single publication that evaluated a limited number of litters/studies. Based on our review of the literature, ECHA recommendations, and the data presented herein, we put forth best practice recommendations for data collection, analysis, and reporting in an effort to improve future data quality, interpretation, and coherence for regulatory review.