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Heuser A, Frings-Meuthen P, Rittweger J, et al. Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest. Front Physiol. 2019;10:12doi: 10.3389/fphys.2019.00012.
Heuser, A., Frings-Meuthen, P., Rittweger, J., & Galer, S. J. G. (2019). Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest. Frontiers in physiology, 1012. https://doi.org/10.3389/fphys.2019.00012
Heuser, Alexander, et al. "Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest." Frontiers in physiology vol. 10 (2019): 12. doi: https://doi.org/10.3389/fphys.2019.00012
Heuser A, Frings-Meuthen P, Rittweger J, Galer SJG. Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest. Front Physiol. 2019 Jan 25;10:12. doi: 10.3389/fphys.2019.00012. eCollection 2019. PMID: 30740058; PMCID: PMC6355708.
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Front Physiol. 2019 Jan 25;10:12. doi: 10.3389/fphys.2019.00012. eCollection 2019.

Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest.

Frontiers in physiology

Alexander Heuser, Petra Frings-Meuthen, Jörn Rittweger, Stephen J G Galer

Affiliations

  1. Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Bonn, Germany.
  2. Institute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, Germany.
  3. Department of Pediatrics and Adolescent Medicine, University of Cologne, Cologne, Germany.
  4. Max-Planck-Institut für Chemie, Abteilung Klimageochemie, Mainz, Germany.

PMID: 30740058 PMCID: PMC6355708 DOI: 10.3389/fphys.2019.00012

Abstract

The calcium (Ca) isotopic composition in urine during bed rest has been demonstrated to be systematically light, indicating a negative bone mineral balance (i.e., bone loss). Here we present new Ca isotope data on urine during the "nutritional countermeasures" (NUC) bed rest study. We analyzed the Ca isotopic composition of 24 h pooled urine samples from seven healthy male subjects during baseline data collection (BDC), head-down-tilt bed rest and recovery. Additionally, we analyzed urine from two follow-up examinations after the regeneration phase. We observed a change in Ca isotopic composition during the bed rest phase, indicative of bone loss with a time delay of 10 to 21 days. We also observe that the Ca isotopic composition of urine is strongly dependent on the individual Ca metabolism and varies between subjects. We relate this individuality in Ca metabolism to differences in the amounts of Ca being recycled in the kidneys. Previous studies have shown that the more Ca is reabsorbed in the kidneys the more enriched the urine becomes in heavy isotopes of calcium. The Ca isotopic composition of urine is thus modified by more than one process and cannot be used in a straightforward manner to monitor net bone mineral balance. To overcome this problem, we propose a new baseline approach for using Ca isotopes, which effectively cancels out the effects of individual renal Ca reabsorption. This allows us to detect bone loss in patients without ambiguity by combining measurements of the Ca isotopic composition of urine and daily Ca excretion rate and comparing these to data collected on healthy individuals with a normal steady-state bone balance.

Keywords: Ca metabolism; bed rest; bone loss; calcium isotopes; renal Ca reabsorption; urine

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