Integration of sperm DNA damage assessment into OECD test guidelines for genotoxicity testing using the MutaMouse model
- DOI
- Language of the publication
- English
- Date
- 2018-08-27
- Type
- Article
- Author(s)
- Maurice, Clotilde
- O'Brien, Jason M.
- Yauk, Carole L.
- Marchetti, Francesco
- Publisher
- Elsevier
Abstract
The Organisation for Economic Co-operation and Development (OECD) endorses test guidelines (TG) for identifying chemicals that are genotoxic, such as the transgenic rodent gene mutation assay (TG 488). Current OECD TG do not include assays for sperm DNA damage resulting in a critical testing gap. We evaluated the performance of the Sperm Chromatin Structure Assay (SCSA) and the Terminal Deoxynucleotidyl Transferase-Mediated Deoxyuridine Triphosphate Nick end Labeling (TUNEL) assay to detect sperm DNA damage within the recommended TG 488 protocol. MutaMouse males received 0, 0.5, 1, or 2 mg/kg/day triethylenemelamine (TEM), a multifunctional alkylating agent, for 28 days orally and tissues were collected two (blood) and three (sperm and bone marrow) days later. TEM significantly increased the frequency of lacZ mutants in bone marrow, and of micronuclei (MN) in both reticulocytes (%MN-RET) and normochromatic erythrocytes (%MN-NCE) in a dose-dependent manner (P < 0.05). The percentage of DNA fragmentation index (%DFI) and %TUNEL positive cells demonstrated dose-related increases in sperm (P < 0.05), and the two assay results were strongly correlated (R = 0.9298). Within the same animal, a good correlation was observed between %MN-NCE and %DFI (R = 0.7189). Finally, benchmark dose modelling (BMD) showed comparable BMD10 values among the somatic and germ cell assays. Our results suggest that sperm DNA damage assays can be easily integrated into standard OECD designs investigating genotoxicity in somatic tissues to provide key information on whether a chemical is genotoxic in germ cells and impact its risk assessment.
Plain language summary
Health Canada supports the development, validation and improvement of test guidelines for the Organisation for the Economic Co-operation and Development (OECD), given its responsibility to assess and manage potential health risks associated with exposure to chemicals in the environment. These guidelines are routinely used for assessing chemicals for mutagenicity (changes in the sequence of the DNA) or clastogenicity (induction of breaks in the DNA). One of these guidelines (TG 488) uses genetically-modified mouse models, called transgenic rodents, that allow the detection of mutations in any tissue in the body. However, the recommended protocol in TG 488 for detecting mutations in somatic cells (non-reproductive cells) is not appropriate for detecting mutations in mature male germ cells (sperm). In the present study, Health Canada scientists used the recommended protocol in TG 488 to show that triethylenemelamine, a model compound used for chemotherapy, induced mutations in the bone marrow and micronuclei (a measure of DNA breaks) in red blood cells of transgenic rodents. At the same time, analysis of sperm from these mice using two assays that detect DNA breaks in sperm demonstrated a dose-related increase in this type of damage. These results show that assays that detect DNA breaks in sperm can be easily integrated within the standard protocol in TG 488 for somatic cells to obtain information on the ability of the tested chemical to affect germ cells. This work contributes to reducing the number of laboratory animals that are used for research purposes by developing an approach for the comprehensive evaluation of the mutagenicity and clastogenicity of environmental chemicals in somatic cells and germ cells to impact their risk assessment and guide subsequent regulatory decisions.
Subject
- Health,
- Health and safety