Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest
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 C...
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Frontiers Media S.A.
2019-01-01
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| Series: | Frontiers in Physiology |
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| Online Access: | https://www.frontiersin.org/article/10.3389/fphys.2019.00012/full |
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| author | Alexander Heuser Petra Frings-Meuthen Jörn Rittweger Jörn Rittweger Stephen J. G. Galer |
| author_facet | Alexander Heuser Petra Frings-Meuthen Jörn Rittweger Jörn Rittweger Stephen J. G. Galer |
| author_sort | Alexander Heuser |
| collection | DOAJ |
| description | 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. |
| first_indexed | 2024-12-11T13:48:18Z |
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| institution | Directory Open Access Journal |
| issn | 1664-042X |
| language | English |
| last_indexed | 2024-12-11T13:48:18Z |
| publishDate | 2019-01-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Physiology |
| spelling | doaj.art-697b88b137bc4cc9b55c977277da76e92022-12-22T01:04:22ZengFrontiers Media S.A.Frontiers in Physiology1664-042X2019-01-011010.3389/fphys.2019.00012432313Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed RestAlexander Heuser0Petra Frings-Meuthen1Jörn Rittweger2Jörn Rittweger3Stephen J. G. Galer4Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Bonn, GermanyInstitute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, GermanyInstitute of Aerospace Medicine, German Aerospace Center (DLR), Cologne, GermanyDepartment of Pediatrics and Adolescent Medicine, University of Cologne, Cologne, GermanyMax-Planck-Institut für Chemie, Abteilung Klimageochemie, Mainz, GermanyThe 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.https://www.frontiersin.org/article/10.3389/fphys.2019.00012/fullcalcium isotopesurinerenal Ca reabsorptionCa metabolismbone lossbed rest |
| spellingShingle | Alexander Heuser Petra Frings-Meuthen Jörn Rittweger Jörn Rittweger Stephen J. G. Galer 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 calcium isotopes urine renal Ca reabsorption Ca metabolism bone loss bed rest |
| title | Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest |
| title_full | Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest |
| title_fullStr | Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest |
| title_full_unstemmed | Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest |
| title_short | Calcium Isotopes in Human Urine as a Diagnostic Tool for Bone Loss: Additional Evidence for Time Delays in Bone Response to Experimental Bed Rest |
| title_sort | calcium isotopes in human urine as a diagnostic tool for bone loss additional evidence for time delays in bone response to experimental bed rest |
| topic | calcium isotopes urine renal Ca reabsorption Ca metabolism bone loss bed rest |
| url | https://www.frontiersin.org/article/10.3389/fphys.2019.00012/full |
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