Skulan Joseph, Bullen Thomas, Anbar Ariel D, Puzas J Edward, Shackelford Linda, LeBlanc Adrian, Smith Scott M
Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI 53706, USA.
Clin Chem. 2007 Jun;53(6):1155-8. doi: 10.1373/clinchem.2006.080143. Epub 2007 Apr 26.
We investigated whether changes in the natural isotopic composition of calcium in human urine track changes in net bone mineral balance, as predicted by a model of calcium isotopic behavior in vertebrates. If so, isotopic analysis of natural urine or blood calcium could be used to monitor short-term changes in bone mineral balance that cannot be detected with other techniques.
Calcium isotopic compositions are expressed as delta(44)Ca, or the difference in parts per thousand between the (44)Ca/(40)Ca of a sample and the (44)Ca/(40)Ca of a standard reference material. delta(44)Ca was measured in urine samples from 10 persons who participated in a study of the effectiveness of countermeasures to bone loss in spaceflight, in which 17 weeks of bed rest was used to induce bone loss. Study participants were assigned to 1 of 3 treatment groups: controls received no treatment, one treatment group received alendronate, and another group performed resistive exercise. Measurements were made on urine samples collected before, at 2 or 3 points during, and after bed rest.
Urine delta(44)Ca values during bed rest were lower in controls than in individuals treated with alendronate (P <0.05, ANOVA) or exercise (P <0.05), and lower than the control group baseline (P <0.05, t-test). Results were consistent with the model and with biochemical and bone mineral density data.
Results confirm the predicted relationship between bone mineral balance and calcium isotopes, suggesting that calcium isotopic analysis of urine might be refined into a clinical and research tool.
我们研究了人类尿液中钙的天然同位素组成变化是否能追踪净骨矿物质平衡的变化，这是根据脊椎动物钙同位素行为模型预测的。如果是这样，天然尿液或血钙的同位素分析可用于监测骨矿物质平衡的短期变化，而其他技术无法检测到这些变化。
钙同位素组成用δ(44)Ca表示，即样品的(44)Ca/(40)Ca与标准参考物质的(44)Ca/(40)Ca之间的千分差。对10名参与太空飞行骨质流失应对措施有效性研究的人员的尿液样本进行了δ(44)Ca测量，该研究中采用17周卧床休息来诱发骨质流失。研究参与者被分配到3个治疗组中的1组：对照组不接受治疗，一个治疗组接受阿仑膦酸盐治疗，另一组进行阻力运动。在卧床休息前、期间的2或3个时间点以及之后收集的尿液样本上进行测量。
卧床休息期间，对照组的尿液δ(44)Ca值低于接受阿仑膦酸盐治疗的个体（方差分析，P<0.05）或进行运动的个体（P<0.05），且低于对照组基线（t检验，P<0.05）。结果与模型以及生化和骨密度数据一致。
结果证实了骨矿物质平衡与钙同位素之间的预测关系，表明尿液钙同位素分析可能会发展成为一种临床和研究工具。
