Trabecular bone adaptation to low-magnitude high-frequency loading in microgravity

PLoS One. 2014 May 2;9(5):e93527. doi: 10.1371/journal.pone.0093527. eCollection 2014.

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 μCT 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Physiological*
  • Animals
  • Biomarkers / metabolism
  • Biomechanical Phenomena
  • Bone and Bones / cytology
  • Bone and Bones / diagnostic imaging
  • Bone and Bones / metabolism
  • Bone and Bones / physiology*
  • Cattle
  • Finite Element Analysis
  • Materials Testing
  • Stress, Mechanical
  • Weight-Bearing*
  • Weightlessness*
  • X-Ray Microtomography

Substances

  • Biomarkers

Grants and 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.