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

Heuser, Alexander and Frings-Meuthen, Petra and Rittweger, Jörn and Galer, Stephen 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, 10 (12), pp. 1-11. Frontiers Media S.A. DOI: 10.3389/fphys.2019.00012 ISSN 1664-042X

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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), headdown-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.

Item URL in elib:https://elib.dlr.de/126259/
Document Type:Article
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
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Heuser, AlexanderSteinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität BonnUNSPECIFIED
Frings-Meuthen, PetraPetra.Frings-Meuthen (at) dlr.deUNSPECIFIED
Rittweger, JörnJoern.Rittweger (at) dlr.dehttps://orcid.org/0000-0002-2223-8963
Galer, Stephen J.G.Max-Planck-Institut für Chemie, Abteilung Klimageochemie, MainzUNSPECIFIED
Date:25 January 2019
Journal or Publication Title:Frontiers in Physiology
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:10
DOI :10.3389/fphys.2019.00012
Page Range:pp. 1-11
Publisher:Frontiers Media S.A
ISSN:1664-042X
Status:Published
Keywords:calcium isotopes; Urine; renal Ca reabsorption; Ca metabolism; bone loss; bed rest
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Research under Space Conditions
DLR - Research area:Raumfahrt
DLR - Program:R FR - Forschung unter Weltraumbedingungen
DLR - Research theme (Project):R - Vorhaben Systemphysiologie
Location: Köln-Porz
Institutes and Institutions:Institute of Aerospace Medicine > Muscle and Bone Metabolism
Deposited By: Becker, Christine
Deposited On:05 Feb 2019 08:55
Last Modified:05 Feb 2019 08:55

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