Leibniz-Institut für Meereswissenschaften, IFM-GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany.
Bone. 2010 Apr;46(4):889-96. doi: 10.1016/j.bone.2009.11.037. Epub 2009 Dec 11.
We explored the possibility of using natural calcium (Ca) isotope variations in the urine (delta(44/40)Ca(urine)) as a proxy for the Ca balance in the human body. We chose two test persons extremely different in their health status, gender and age (4-year-old healthy boy and a 60-year-old woman known to suffer from osteoporosis). During a 5 day interval the Ca isotope composition of the individual diet (delta(44/40)Ca(diet)) was monitored for both test persons to be in general agreement to the Ca isotope composition of the normal western European diet ( approximately -1.02+/-0.1 per thousand). However, measurements showed that (1) delta(44/40)Ca(urine) of both test persons are approximately 1.37 and approximately 2.49 per thousand, respectively, heavier than delta(44/40)Ca(diet) and that (2) the delta(44/40)Ca(urine-boy) is approximately 1.1 per thousand heavier when compared to the value of the woman. The individual offset between diet and test persons is interpreted to reflect individual Ca reabsorption rates in the kidneys being the result of Rayleigh type Ca isotope fractionation related to the partitioning of Ca between the glomerular filtrate and filtered residue. The relative difference between delta(44/40)Ca(urine-boy) and delta(44/40)Ca(urine-woman) of approximately 1.1 per thousand may reflect individual differences in the balance of bone mineralization and demineralization processes related to age, gender and health status. By arbitrarily defining an equilibrium value for Delta(44/40)Ca(diet-urine) of -1.93 per thousand being the arithmetic mean of delta(44/40)Ca(urine) for both test persons the measured delta(44/40)Ca(urine) values may be applied to model the individual bone mineralization and demineralization processes in a qualitative way. Note, second order influences of intestinal Ca absorption during sequestration of Ca between intestine and blood have to be subject of further studies.
我们探讨了利用尿液中天然钙（Ca）同位素变化（δ(44/40)Ca(urine)）作为人体钙平衡的替代指标的可能性。我们选择了两个在健康状况、性别和年龄方面差异极大的测试对象（4 岁健康男孩和一位已知患有骨质疏松症的 60 岁女性）。在 5 天的时间间隔内，监测了两个测试对象的个体饮食中 Ca 同位素组成（δ(44/40)Ca(diet)），其结果与正常的西欧饮食 Ca 同位素组成基本一致（约为-1.02±0.1‰）。然而，测量结果表明：（1）两个测试对象的 δ(44/40)Ca(urine)分别比 δ(44/40)Ca(diet)重约 1.37‰和 2.49‰；（2）与女性相比，男孩的 δ(44/40)Ca(urine-boy)重约 1.1‰。个体饮食与测试对象之间的偏移被解释为反映了肾脏中 Ca 重吸收率的个体差异，这是由于肾小球滤过液和滤过残渣之间 Ca 分配的瑞利型 Ca 同位素分馏导致的。δ(44/40)Ca(urine-boy)与 δ(44/40)Ca(urine-woman)之间的相对差异约为 1.1‰，可能反映了与年龄、性别和健康状况相关的骨矿化和脱矿化过程的个体差异。通过任意定义一个平衡值（即，δ(44/40)Ca(diet-urine)为-1.93‰，是两个测试对象的 δ(44/40)Ca(urine)的算术平均值），可将测量得到的 δ(44/40)Ca(urine)值应用于定性地模拟个体骨矿化和脱矿化过程。需要注意的是，肠道 Ca 吸收的二级影响在肠和血液之间的 Ca 螯合过程中需要进一步研究。
