应用基准剂量法估算硝酸钕急性染毒致小鼠遗传毒效应阈值
Estimation of genotoxicity threshold induced by acute exposure to neodymium nitrate in mice using benchmark dose
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摘要:
背景 基准剂量（BMD）法是根据特定剂量-反应关系，求得引起某一反应特定改变所对应的剂量，与传统的未观察到有害作用剂量（NOAEL）法比较，BMD法有许多优点，其单侧95%可信区间下限值（BMDL）通常可代替NOAEL用于生物接触限值推导。目前尚无任何权威机构得出基于健康的稀土元素指导值。
目的 应用微核试验和彗星试验，采用BMD法估算硝酸钕急性染毒致小鼠遗传毒效应的阈值。
方法 将90只SPF级昆明种小鼠随机分为9组：7个硝酸钕染毒组、1个对照组（蒸馏水）和1个阳性对照组（200 mg·kg−1甲基磺酸乙酯），每组10只，雌雄各半。7个剂量组分别以灌胃的方式给予不同浓度的硝酸钕溶液（雄：14、27、39、55、77、109、219 mg·kg−1；雌：24、49、69、97、138、195、389 mg·kg−1）2次，间隔21 h。于末次染毒3 h后，颈椎脱臼处死动物，取小鼠股骨骨髓观察骨髓细胞微核率，取肝脏和胃进行彗星试验。
结果 硝酸钕致雌、雄小鼠的骨髓嗜多染红细胞微核细胞率升高的最佳拟合模型分别为exponential 4模型、hill模型，计算得出雌性小鼠的BMD和BMDL分别为31.37 mg·kg−1和21.90 mg·kg−1，雄性小鼠的BMD和BMDL分别为58.62 mg·kg−1和54.31 mg·kg−1。硝酸钕致雌、雄小鼠肝细胞DNA损伤的最佳拟合模型分别为exponential 5模型、exponential 4模型，计算得出BMD和BMDL分别为27.15 mg·kg−1、11.99 mg·kg−1，以及16.28 mg·kg−1、10.47 mg·kg−1。硝酸钕致雌、雄小鼠胃腺细胞DNA损伤的最佳拟合模型均为hill模型，计算得出BMD和BMDL分别为36.73 mg·kg−1、19.92 mg·kg−1，以及24.74 mg·kg−1、14.08 mg·kg−1。
结论 以骨髓细胞微核率、肝细胞和胃腺细胞DNA损伤作为遗传毒性终点事件，硝酸钕的BMDL为10.47 mg·kg−1，可以此作为硝酸钕急性染毒致小鼠遗传毒效应的阈值。
Abstract:Background The benchmark dose (BMD) method calculates the dose associated with a specific change in response based on a specific dose-response relationship. Compared with the traditional no observed adverse effect level (NOAEL) method, the BMD method has many advantages, and the 95% lower confidence limit of benchmark dose lower limit (BMDL) is recommended to replace NOAEL in deriving biological exposure limits. No authority has yet published any health-based guideline for rare earth elements.
Objective To evaluate genotoxicity threshold induced by acute exposure to neodymium nitrate in mice using BMD modeling through micronucleus test and comet assay.
Methods SPF grade mice (
n =90) were randomly divided into nine groups, including seven neodymium nitrate exposure groups, one control group (distilled water), and one positive control group (200 mg·kg−1 ethyl methanesulfonate), 10 mice in each group, half male and half female. The seven dose groups were fed by gavage with different concentrations of neodymium nitrate solution (male: 14, 27, 39, 55, 77, 109, and 219 mg·kg−1; female: 24, 49, 69, 97, 138, 195, and 389 mg·kg−1) twice at an interval of 21 h. Three hours after the last exposure, the animals were neutralized by cervical dislocation. The bone marrow of mice femur was taken to calculate the micronucleus rate of bone marrow cells, and the liver and stomach were taken for comet test.Results The best fitting models for the increase of polychromatophil micronucleus rate in bone marrow of female and male mice induced by neodymium nitrate were the exponential 4 model and the hill model, respectively. The BMD and the BMDL of female mice were calculated to be 31.37 mg·kg−1 and 21.90 mg·kg−1, and those of male mice were calculated to be 58.62 mg·kg−1 and 54.31 mg·kg−1, respectively. The best fitting models for DNA damage induced by neodymium nitrate in female and male mouse hepatocytes were the exponential 5 model and the exponential 4 model, respectively, and the calculated BMD and BMDL were 27.15 mg·kg−1 and 11.99 mg·kg−1 for female mice, and 16.28 mg·kg−1 and 10.47 mg·kg−1 for male mice, respectively. The hill model was the best fitting model for DNA damage of gastric adenocytes in both female and male mice, and the calculated BMD and BMDL were 36.73 mg·kg−1 and 19.92 mg·kg−1 for female mice, and 24.74 mg·kg−1 and 14.08 mg·kg−1 for male mice, respectively.
Conclusion Taken the micronucleus rate of bone marrow cells, DNA damage of liver cells and gastric gland cells as the end points of genotoxicity, the BMDL of neodymium nitrate is 10.47 mg·kg−1, which can be used as the threshold of genotoxic effects induced by acute exposure to neodymium nitrate in mice.
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