Kasahara Y, Wakata A, Nakai Y, Yuno K, Miura D, Yagi K, Hirabayashi K, Makita T
Safety Research Department, 2nd Bio-Medical Research Laboratories, Teijin Ltd., Tokyo, Japan.
Mutat Res. 1992 Feb-Mar;278(2-3):145-51.
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.
在两个实验室中，使用小鼠外周血网织红细胞检测了甲氨蝶呤（MTX）诱导微核的情况。在使用骨髓细胞的微核试验中，MTX单次处理时是一种弱诱导剂，并且是少数显示多次处理效应的化学物质之一（CSGMT/JEMS.MMS，1990）。在我们的初步实验中，用100 mg/kg的MTX单次处理后，网织红细胞与总红细胞的比例大幅下降，因此选择较低剂量水平的MTX进行外周血微核试验。在0、10、20、40和80 mg/kg的剂量水平下进行了全面试验，采样时间为0、24、48、72和96小时。微核网织红细胞（MNRETs）的频率在72小时时呈剂量依赖性增加，最高约为1%；由于网织红细胞与总红细胞的比例严重下降，无法检测从高剂量动物获得的一些样本。在0.5 - 4.0 mg/kg的剂量下，多次处理与单次处理的效果不明确，最大反应水平也没有太大差异。由于MTX单次处理后在外周血网织红细胞中诱导了明显的阳性反应，外周血中的网织红细胞似乎是更敏感的靶点。
