Identifying germ cell mutagens using OECD test guideline 488 (transgenic rodent somatic and germ cell gene mutation assays) and integration with somatic cell testing
- DOI
- Language of the publication
- English
- Date
- 2018-05-29
- Type
- Article
- Author(s)
- Marchetti, Francesco
- Aardema, Marilyn J.
- Beevers, Carol
- van Benthem, Jan
- Godschalk, Roger
- Williams, Andrew
- Yauk, Carole L.
- Young, Robert
- Douglas, George R.
- Publisher
- Elsevier
Abstract
The Organisation for Economic Co-operation and Development Test Guideline 488 (TG 488) provides recommendations for assessing germ cell and somatic cell mutagenicity using transgenic rodent (TGR) models. However, important data gaps exist for selecting an optimal approach for simultaneously evaluating mutagenicity in both cell types. It is uncertain whether analysis of germ cells from seminiferous tubules (hereafter, tubule germ cells) or caudal sperm within the recommended design for somatic tissues (i.e., 28 days of exposure plus three days of fixation time, 28 + 3d) has enough sensitivity to detect an effect as compared with the analysis of sperm within the recommended design for germ cells (i.e., 28 + 49d and 28 + 70d for mouse and rat, respectively). To address these data gaps, the Germ Cell workgroup of the Genetic Toxicology Technical Committee of the Health and Environmental Sciences Institute reviewed the available TGR mutagenicity data in male germ cells, and, characterized the exposure history of tubule germ cells for different sampling times to evaluate its impact on germ cell mutagenicity testing using TG 488. Our analyses suggest that evaluating mutant frequencies in: i) sperm from the cauda epididymis at 28 + 3d does not provide meaningful mutagenicity data; ii), tubule germ cells at 28 + 3d provides reliable mutagenicity data only if the results are positive; and iii) tubule germ cells at 28 + 28d produces reliable positive and negative results in both mice and rats. Thus, the 28 + 28d regimen may provide an approach for simultaneously assessing mutagenicity in somatic tissues and germ cells from the same animals. Further work is required to support the 28 + 28d protocol for tissues other than slowly proliferating tissues as per current TG 488. Finally, recommendations are provided to guide the experimental design for germ cell mutagenicity data for regulatory submission, as well as other possible approaches to increase the reliability of the TGR assay.
Plain language summary
Health Canada supports the development of test guidelines for the Organisation for the Economic Co-operation and Development (OECD). These guidelines are routinely used for assessing the safety of chemicals before they come on the market. One of these guidelines (TG 488) uses genetically-modified mouse models, called transgenic rodents (TGR), that allow the detection of mutations (changes in the sequence of the DNA) in any tissue in the body. The guideline recommends a common protocol for detecting mutations in both somatic (non-reproductive) and germ (reproductive) cells. However, recent data suggests that this protocol is unreliable for detecting mutations in germ cells. Thus, Health Canada scientists together with scientists from other international governments, academia and industry, have reviewed the available data on the induction of mutations in relation to sperm (the male germ cell) development together with modelling of spermatogenesis (the process that produces the sperm) to identify the optimal experimental design for detecting mutations in germ cells. Results indicate that an alternative design in TG 488 offers a better compromise for the simultaneous assessment of mutagenicity in both cell types. Furthermore, recommendations are provided to guide the experimental design used to generate germ cell mutagenicity data and update TG 488. This work contributes to reducing the number of laboratory animals that are used for research purposes by developing an optimal approach for the comprehensive evaluation of the mutagenicity of environmental chemicals in somatic cells and germ cells to impact their risk assessment and guide subsequent regulatory decisions.
Subject
- Health,
- Health and safety