Abstract
In this study we compared the response of the Pig-a gene mutation assay to that of the lacZ transgenic rodent mutation assay, and demonstrated that multiple endpoints can be measured in a 28-day repeat dose study. Muta™Mouse were dosed daily for 28 days with benzo[a]pyrene (BaP; 0, 25, 50 and 75 mg/kg body weight/day) by oral gavage. Micronucleus (MN) frequency was determined in reticulocytes (RETs) 48 hr following the last dose. 72 h following the last dose, mice were euthanized, and tissues (glandular stomach, small intestine, bone marrow and liver) were collected for lacZ mutation and DNA adduct analysis, and blood was evaluated for Pig-a mutants. BaP-derived DNA adducts were detected in all tissues examined and significant dose-dependent increases in mutant Pig-a phenotypes (i.e., RETCD24- and RBC CD24-) and lacZ mutants were observed. We estimate that mutagenic efficiency (i.e., rate of conversion of adducts into mutations) was much lower for Pig-a compared to lacZ, and speculate that this difference is likely explained by differences in repair capacity between the gene targets, and differences in the cell populations sampled for Pig-a versus lacZ. The BaP doubling doses for both gene targets, however, were comparable, suggesting that similar mechanisms are involved in the accumulation of gene mutations. Significant dose-related increases in % MN were also observed; however, the doubling dose was considerably higher for this endpoint. The similarity in dose response kinetics of Pig-a and lacZ provides further evidence for the mutational origin of glycosylphosphatidylinositol (GPI)-anchor deficiencies detected in the Pig-a assay. Environ. Mol. Mutagen. 2011. © 2011 Wiley-Liss, Inc.
Highlights
Data for the induction of gene mutations in vivo form an increasingly important component of hazard and risk assessment
Transgenic mice were exposed to BaP daily for 28 days via oral gavage, and simultaneous measurements of DNA adduct frequency, micronucleus frequency, lacZ
Mutant frequency, and the frequency of mutant Pig-a phenotypes were carried out in an effort to better understand the responsiveness of Pig-a phenotype frequency relative to other established genotoxicity endpoints for the prototypical polycyclic aromatic hydrocarbon BaP
Summary
Data for the induction of gene mutations in vivo form an increasingly important component of hazard and risk assessment. One widely used and well-validated system for assessment of gene mutations in vivo is the transgenic rodent (TGR) mutation assay system (for review see [Lambert et al, 2005; OECD, 2009]). Used versions of the TGR assays include the lacZ bacteriophage. Arlt are currently at MRC-HPA Centre for Environment and Health, School of Biomedical Sciences, King’s College London, London, United Kingdom
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