The micronucleus test using peripheral blood reticulocytes from methotrexate-treated mice.
The induction of micronuclei by methotrexate (MTX) was examined in two laboratories using mouse peripheral blood reticulocytes. MTX was a weak inducer in the micronucleus test using bone marrow cells and single treatments, and was one of the few chemicals showing a multiple-treatment effect (CSGMT/JEMS.MMS, 1990). In our preliminary experiments, the ratio of reticulocytes to total erythrocytes decreased greatly after a single treatment with MTX at 100 mg/kg, so lower dose levels of MTX were selected to carry out the micronucleus test in peripheral blood. Full-scale tests were performed at dose levels of 0, 10, 20, 40, and 80 mg/kg, with five sampling times of 0, 24, 48, 72, and 96 h. Frequencies of micronucleated reticulocytes (MNRETs) increased dose-dependently at 72 h, to a maximum of approximately 1%; some preparations obtained from the animals at higher doses could not be examined because the ratio of reticulocytes to total erythrocytes had decreased severely. At doses of 0.5-4.0 mg/kg, the effect of multiple treatments vs. single treatments was not clear, nor was the maximum level of response much different. Since MTX induced a clear positive response in peripheral blood reticulocytes after a single treatment, the reticulocytes in peripheral blood seem a more sensitive target.
Safety Research Department, 2nd Bio-Medical Research Laboratories, Teijin Ltd., Tokyo, Japan.
Y
Y
Kasahara
A
A
Wakata
Y
Y
Nakai
K
K
Yuno
D
D
Miura
K
K
Yagi
K
K
Hirabayashi
T
T
Makita
D000165:Acridine Orange; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D008297:Male; D008727:Methotrexate / Q000633:toxicity*; D051379:Mice; D008815:Mice, Inbred Strains; D015162:Micronucleus Tests / Q000379:methods; D016685:Mitomycin / Q000633:toxicity; D009153:Mutagens / Q000633:toxicity*; D012156:Reticulocytes / Q000187:drug effects*
D009153:Mutagens; D016685:Mitomycin; D000165:Acridine Orange; D008727:Methotrexate