A Critical Assessment of the Requirement for a Single Time Point Vaginal Cytology on the Day of Necropsy in Rats.

For toxicology testing of (agro)chemicals, different study types are being performed with general and/or reproductive toxicity endpoints (see Organisation for Economic Co-operation and Development guidelines). In most of these rat studies, vaginal cytology is performed on serial samples (collected by lavage) for evaluation of cycle regularity and evidence of mating, and/or on a single sample collected on the day of necropsy for information on the estrous cycle stage and allowing correlation with histopathology. In the latter case, the utility of vaginal cytology can be argued. In this article, estrous cycle stages based on vaginal cytology of samples taken on the day of necropsy and histopathology of ovaries, uterus, and vagina (gold standard for estrous cycle stage assessment) were compared. The agreement was generally low. Disagreement between the two methods could be explained by time differences between lavage and necropsy, by manipulation of vaginal epithelium during lavage which may impact epithelial morphology on histology, and by misinterpretation of vaginal cytology during or shortly after lactation. Based on the results of estrous staging within different study types, we strongly discourage vaginal cytology from samples collected on the day of necropsy since there is no added value, vaginal manipulation can be stressful and may complicate the histologic diagnosis.

Is there a rationale for direct dosing of chemicals to nursing pups in the EOGRTS (OECD 443)?

In OECD guideline 443 - Extended One Generation Reproductive Toxicity Study (EOGRTS) - to be used for testing industrial and agrochemicals, it has been indicated that careful consideration of benefits and disadvantages should be made prior to conducting direct-dosing studies in nursing pups. Nursing pups will not be directly dosed in dietary and drinking water studies whereas in oral gavage studies this possibility exists. Besides the risk of intubation trauma and overdosing due to direct exposure and exposure via the mother's milk, direct dosing could lead to a different hazard assessment of chemicals depending on the choice of the route of administration. In addition, in case of industrial and agrochemicals used in industrial or professional settings only, there will never be direct exposure of newborns. Moreover, direct dosing of nursing pups is an artificial, non-physiological, route of exposure and as such it would hamper risk assessment. It should therefore only be considered in exceptional cases and justified on a case-by-case approach.

A critical evaluation of thyroid hormone measurements in OECD test guideline studies: Is there any added value?

Recently several OECD test guidelines were updated to include thyroid hormone measurements for assessing endocrine disruptor potency, which led to an imperative need to align interpretation of these results by the different stakeholders. We therefore evaluated 124 repro screening studies, which showed in 38% of the studies a statistical significant finding for T4 in at least one treatment group, probably due to disturbances of normal homeostasis causing high variation. Consequently, for a thorough evaluation it is extremely important to take the historical control range into account. In conclusion, the current testing approach is not providing specific information needed to assess endocrine disruption, as too often a statistical significant finding is noted and as down-stream adverse effects are not evaluated. Therefore, major modifications are urgently needed. Instead of extending the in vivo experiments, it should be investigated if in vitro assessments will provide more relevant information on human endocrine disruptor potential.

Best practices for developmental toxicity assessment for classification and labeling.

Many chemicals are going through a hazard-based classification and labeling process in Europe. Because of the significant public health implications, the best science must be applied in assessing developmental toxicity data. The European Teratology Society and Health and Environmental Sciences Institute co-organized a workshop to consider best practices, including data quality and consistency, interpretation of developmental effects in the presence of maternal toxicity, human relevance of animal data, and limits of chemical classes. Recommendations included larger historical control databases, more pharmacokinetic studies in pregnant animals for dose setting and study interpretation, generation of mechanistic data to resolve questions about whether maternal toxicity is causative of developmental toxicity, and more rigorous specifications for what constitutes a chemical class. It is our hope that these recommendations will form the basis for subsequent consensus workshops and other scientific activities designed to improve the scientific robustness of data interpretation for classification and labeling.

Guidance on the selection of cohorts for the extended one-generation reproduction toxicity study (OECD test guideline 443).

The extended one-generation reproduction toxicity study (EOGRTS; OECD test guideline 433) is a new and technically complex design to evaluate the putative effects of chemicals on fertility and development, including effects upon the developing nervous and immune systems. In addition to offering a more comprehensive assessment of developmental toxicity, the EOGRTS offers important improvements in animal welfare through reduction and refinement in a modular study design. The challenge to the practitioner is to know how the modular aspects of the study should be triggered on the basis of prior knowledge of a particular chemical, or on earlier findings in the EOGRTS itself, requirements of specific regulatory frameworks notwithstanding. The purpose of this document is to offer guidance on science-based triggers for these extended evaluations.