Simulation of mouse and rat spermatogenesis to inform genotoxicity testing using OECD test guideline 488
- DOI
- Language of the publication
- English
- Date
- 2018-06-01
- Type
- Article
- Author(s)
- Marchetti, Francesco
- Aardema, Marilyn
- Beevers, Carol
- van Benthem, Jan van
- Douglas, George R.
- Godschalk, Roger
- Yauk, Carole L.
- Young, Robert
- Williams, Andrew
- Publisher
- Elsevier
Abstract
The Organisation for Economic Co-operation and Development Test Guideline (TG) 488 for the transgenic rodent (TGR) mutation assay recommends two sampling times for assessing germ cell mutagenicity following the required 28-day exposure period: 28 + > 49 days for mouse sperm and 28 + >70 days for rat sperm from the cauda epididymis, or three days (i.e., 28 + 3d) for germ cells from seminiferous tubules (hereafter, tubule germ cells) plus caudal sperm for mouse and rat. Although the latter protocol is commonly used for mutagenicity testing in somatic tissues, it has several shortcomings for germ cell testing because it provides limited exposure of the proliferating phase of spermatogenesis when mutations are fixed in the transgene. Indeed, analysis of sperm at 28 + 3d has generated negative results with established germ cell mutagens, while the analysis of tubule germ cells has generated both positive and either negative or equivocal results. The Germ Cell workgroup of the Genetic Toxicology Technical Committee of the Health and Environmental Sciences Institute modelled mouse and rat spermatogenesis to better define the exposure history of the cell population collected from seminiferous tubules. The modelling showed that mouse tubule germ cells at 28 + 3d receive, as a whole, 42% of the total exposure during the proliferating phase. This percentage increases to 99% at 28 + 28d and reaches 100% at 28 + 30d. In the rat, these percentages are 22% and 80% at 28 + 3d and 28 + 28d, reaching 100% at 28 + 44d. These results show that analysis of tubule germ cells at 28 + 28d may be an effective protocol for assessing germ cell mutagenicity in mice and rats using TG 488. Since TG 488 recommends the 28 + 28d protocol for slow dividing somatic tissues, this appears to be a better compromise than 28 + 3d when slow dividing somatic tissues or germ cells are the critical tissues of interest.
Plain language summary
Health Canada supports the development of the Organisation for the Economic Co-operation and Development (OECD) test guidelines (TG) for identifying chemicals that cause mutations (changes in the DNA sequence). Recently, OECD endorsed TG 488 for simultaneously detecting mutations in somatic (non-reproductive) cells and germ (reproductive) cells using genetically modified rodent models. However, follow-up analysis indicated that the recommended protocol was unreliable for detecting mutations in germ cells. Therefore, Health Canada scientists together with scientists from other international governments, academia and industry developed a computational model of spermatogenesis (the process that produces sperm, the male germ cell) to characterize the exposure history of germ cells following three different experimental designs included in TG 488. Results of the modelling indicated that one of the three designs in TG 488, that is, 28 days of exposure followed by tissue sampling 28 days later, offers a better compromise for the simultaneous assessment of mutagenicity in both somatic cells and germ cells that the currently recommended design of collecting tissues three days after the end of the exposure. This work contributes to identifying the optimal experimental design for detecting mutations in germ cells and forms the basis for revising and updating OECD TG 488. Furthermore, it assures that germ cell data submitted for regulatory purposes are robust and allow regulators to make appropriate risk assessment/risk management decisions.
Subject
- Health,
- Health and safety