Use of Centromeric and Telomeric DNA Probes in In Situ Hybridization for Differentiation of Micronuclei Induced by Lomefloxacin

Classification of micronuclei induced by lomefloxacin, a difluorinated quinolone bactericidal agent, in mouse bone marrow was performed by fluorescence in situ hybridization using DNA probes for the centromere repeated minor satellite DNA and the telomeric hexamer repeat (5'-TTAGGG-3'). Colchicine and mitomycin C were used as a positive control aneugen and clastogen, respectively, and these compounds produced the expected responses. Single doses of 40, 80, 160, or 320 mg/kg lomefloxacin were given via oral intubations and bone marrow was sampled at 24 and 48 hr after treatment. The micronuclei showed significant increases in both sampling times after doses of 320 mg/kg. A statistically significant increase of micronuclei frequency was also detected for 160 mg/kg lomefloxacin at 48 hr after treatment. The responses were directly correlated with bone-marrow cytotoxicity. Following treatment with 160 and 320 mg/kg lomefloxacin, 48.2 and 50.0% of the induced micronuclei, respectively, showed double labeling with centromeric signals and several telomeric signals, indicating that the induced micronuclei were composed of whole chromosomes. Similarly, 51.8 and 50.0% of the induced micronuclei, respeclively, were centromere-negative, demonstrating that lomefloxacin not only induces chromosome loss but also chromosome breakage. The results also showed that chromosomes can be enclosed in a micronucleus before and after centromere separation. Overall, this study provides the first evidence of the potential of lomefloxacin to induce aneugenic effect in mice. However, given the high doses used in this study, the clinical significance of this finding is uncertain. Environ. Mal. Mutagen. 50:394-403, 2009. (C) 2009 Wiley-Liss, Inc.