TRABECULAR BONE ADAPTATION TO LOW-MAGNITUDE HIGH-FREQUENCY LOADING AT MICRO-GRAVITY

Antonia Torcasio,Katharina Jähn,Maarten Van Guyse,Pieter Spaepen,Andrea E Tami,Jos Vander Sloten,David B Jones,Martin J Stoddart,G Harry Van Lenthe

doi:10.1016/s0021-9290(12)70532-8

Abstract

Exposure to microgravity causes loss of lower body bone mass in some astronauts. Low-magnitude high-frequency loading can stimulate bone formation on earth. Here we hypothesized that low-magnitude high-frequency loading will also stimulate bone formation under microgravity conditions. Two groups of six bovine cancellous bone explants were cultured at microgravity on a Russian Foton-M3 spacecraft and were either loaded dynamically using a sinusoidal curve or experienced only a static load. Comparable reference groups were investigated at normal gravity. Bone structure was assessed by histology, and mechanical competence was quantified using mCT and FE modelling; bone remodelling was assessed by fluorescent labelling and secreted bone turnover markers. Statistical analyses on morphometric parameters and apparent stiffness did not reveal significant differences between the treatment groups. The release of bone formation marker from the groups cultured at normal gravity increased significantly from the first to the second week of the experiment by 90.4% and 82.5% in response to static and dynamic loading, respectively. Bone resorption markers decreased significantly for the groups cultured at microgravity by 7.5% and 8.0% in response to static and dynamic loading, respectively. We found low strain magnitudes to drive bone turnover when applied at high frequency, and this to be valid at normal as well as at microgravity. In conclusion, we found the effect of mechanical loading on trabecular bone to be regulated mainly by an increase of bone formation at normal gravity and by a decrease in bone resorption at microgravity. Additional studies with extended experimental time and increased samples number appear necessary for a further understanding of the anabolic potential of dynamic loading on bone quality and mechanical competence. Citation: Torcasio A, Jahn K, Van Guyse M, Spaepen P, Tami AE, et al. (2014) Trabecular Bone Adaptation to Low-Magnitude High-Frequency Loading in Microgravity. PLoS ONE 9(5): e93527. doi:10.1371/journal.pone.0093527 Editor: Ali Al-Ahmad, University Hospital of the Albert-Ludwigs-University Freiburg, Germany Received May 22, 2013; Accepted March 7, 2014; Published May 2, 2014 Copyright: 2014 Torcasio et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was financially supported by grant C90346 (Belgium PRODEX-9 project) and the ESA MAP grant #AO99-122. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: harry.vanlenthe@mech.kuleuven.be

Highlights

One of the effects resulting from the exposure to microgravity is the loss of bone mass in the lower limbs and spine in some astronauts [1,2]
During a space mission at the Mir, areal bone mineral density of some astronauts was reduced by a monthly rate of 0.3% from the total skeleton, with 97% of that loss occurring in the pelvis and legs [3]
The bone resorption data (Figure 4) indicated a decrease in NTx release in the second week from the explants cultured at microgravity in response to static and dynamic loading; on average, the decrease was 7.5% and 8.0% for the static and dynamic loading group, respectively; the change in NTx release from explants cultured at normal gravity was not significant

Summary

Introduction

One of the effects resulting from the exposure to microgravity is the loss of bone mass in the lower limbs and spine in some astronauts [1,2]. During a space mission at the Mir, areal bone mineral density (aBMD) of some astronauts was reduced by a monthly rate of 0.3% from the total skeleton, with 97% of that loss occurring in the pelvis and legs [3]. Computed Tomography (CT) measurements in combination with DXA (dual energy X-ray absorptiometry) revealed that bone is lost in cancellous as well as in cortical bone volumes. These effects on bones might not have immediate implications for the astronauts, but could lead to increased fracture risk because of an associated loss in bone strength as well as to an early onset of age-related osteoporosis in the more advanced age

Methods

Results

Conclusion