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Clinical Chemistry 0: clinchem.2006.080143v1, 2007; 10.1373/clinchem.2006.080143
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Received on ,
Accepted on ,

Technical Briefs

Natural Calcium Isotopic Composition of Urine as a Marker of Bone Mineral Balance

Joseph Skulan 1*, Thomas Bullen 2, Ariel Anbar 3, J. Edward Puzas 4, Linda Shackelford 5, Adrian LeBlanc 6, Scott M. Smith 5

1 Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI
2 Branch of Regional Research, Water Resources Discipline, US Geological Survey, Menlo Park, CA
3 School of Earth and Space Exploration and Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ
4 Department of Orthopaedics, University of Rochester School of Medicine and Dentistry, Rochester, NY
5 Human Adaptation and Countermeasures Division, NASA Johnson Space Center, Houston, TX
6 Department of Medicine, Baylor College of Medicine, Houston, TX

* To whom correspondence should be addressed. E-mail: jlskulan{at}geology.wisc.edu.

Background: 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.

Methods: Calcium isotopic compositions are expressed as {delta}44Ca, or the difference in parts per thousand between the 44Ca/40Ca of a sample and the 44Ca/40Ca of a standard reference material. {delta}44Ca 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.

Results: Urine {delta}44Ca 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.

Conclusion: 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.




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