Effective use of the <i>Pig-a</i> gene mutation assay for mutagenicity screening: measuring CD59-deficient red blood cells in rats treated with genotoxic chemicals

Abstract

The Pig-a gene mutation assay using perpherial blood erythrocytes is being investigated as a screening tool for assessing mutagenicity in vivo. In this study, we evaluated two distinct approaches for performing the Pig-a assay in rats. We used antibodies to CD45 or the erythroid marker HIS49 to identify red blood cells (RBCs), and then monitored the kinetics of Pig-a mutant frequency, as measured by the frequency of CD59-deficient RBCs, in rats treated with the genotoxic chemicals, N-ethyl-N-nitrosourea, cyclophosphamide, 4-nitroquinoline-1-oxide, and ethylmethanesulfonate. In some instances, micronucleus frequency also was measured in the same animals. Time- and dose-related increases in Pig-a mutant frequency were found in all the chemical-treated groups, except for the groups treated with cyclophosphamide, which was a potent inducer of micronuclei. The two different approaches we employed were comparable for measuring induced mutant frequencies, but our historical data showed that the mean background frequencies for the CD45/CD59 method and the HIS49/CD59 method were 12.7 × 10(-6) and 5.5 ×10(-6), respectively. The relatively low, stable background mutant frequency associated with the HIS49/CD59 method indicates that it may have greater power for discriminating weak induced responses. These results suggest that the HIS49/CD59 method is a promising tool for measuring Pig-a mutant RBCs. In addition, differences in their manifestation kinetics and in their relative sensitivity for detecting different test compounds suggest that the combination of the Pig-a assay and the micronucleus assay may be effective in identifying in vivo genotoxicity.