The August 2017 Editor's Choice article is, "Applying the erythrocyte Pig-a assay concept to rat epididymal sperm for germ cell mutagenicity evaluation," by Zhiying Ji and Matthew LeBaron.
Efficient methods of evaluating germ cell mutagenicity are urgently needed for human health risk assessment. In the August 2017 issue of Environmental and Molecular Mutagenesis, Zhiying Ji and Matthew LeBaron from the Dow Chemical Company, describe an assay capable detecting mutagens in rat epididymal sperm. The standard Pig-a assay identifies mutants with altered cell surface markers (e.g. CD59 protein) and is typically conducted using peripheral blood samples. Spermatozoa (sperm) also bear CD59 on their surface thus holding the promise of detecting Pig-a mutations in sperm samples. This was investigated in the article using two examples. Following initial optimization through spike-in experiments, in which rat sperm was labelled with anti-rat CD59 antibody while unlabelled sperm served as a mutant-mimic, authors conducted a five-day oral gavage study in F344/DuCrl rats using a prototypical mutagen N-ethyl-N-nitrosourea (ENU) and a 28-day oral gavage study with clofibrate, a non-genotoxic rat carcinogen and lipid-lowering drug. Peripheral blood was collected on day -5 for both studies, as well as on day 29 (clofibrate) and day 63 (ENU). Epididymal sperm were collected on day 63 (ENU) and day 85 (clofibrate) to account for the duration of spermatogenesis in rats subsequent to the final gavage dose. For both compounds, there was a good correlation between the erythrocyte and sperm Pig-a assays with both assays yielding negative results for clofibrate and a positive response for ENU. In addition, important biological questions (e.g., whether the absence of CD59 on the surface of epididymal sperm is equal to Pig-a gene mutation in germ cells) and technical parameters (e.g., flow rate and sperm density) were identified that may affect data quality and further assay applicability. Overall, the paper demonstrates the potential of the sperm Pig-a assay for detecting germ cell mutagens using two case study chemicals. The assay’s relatively high-throughput, animal-saving (if integrated into standard animal studies), and potential application in chemical safety assessment, strongly suggest that the utility of the sperm Pig-a assay for routine assessments of germ cell mutagenicity should be investigated further.
Environ. Mol. Mutagen. 58:485–493, 2017. © 2017 Wiley Periodicals, Inc.