There is an increase in the risk of bone fracture with aging and the onset of diabetes, and this increase cannot be solely explained by changes in bone mineral density (BMD). As such, clinical assessment of fracture resistance should also include quantitative characteristics of collagen. Moreover, lowering fracture risk for the elderly and those individuals with diabetes requires a complete understanding of the biophysical basis for the changes in bone that decrease fracture resistance. Addressing these needs, the proposal aims to determine the extent to which water that is bound to the bone matrix and water residing in bone pores, as determined by Nuclear Magnetic Resonance (NMR), explain bone's resistance to fracture with respect to aging and disease. NMR underlies clinical Magnetic Resonance Imaging (MRI), and the proposed mechanical tests characterize the ability of bone to resist fracture, not just bone strength.
Aim 1 will determine whether NMR-measurable attributes - including those quantifiable by clinical MRI - contribute to the age-related decreases in the post-yield toughness, fatigue life, crack initiation toughness, and crack growth toughness of human cortical and trabecular bone, and do so in relation to other explanatory factors.
Aim 2 will examine potential determinants of bound water through series of manipulations experiments that will affect matrix-water interactions and the fracture properties of bone. Specimens for Aims 1 and 2 will be extracted from cadaveric femurs that are acquired from donors of varying age (23 to 100 years of age). Then, using pre-clinical, rat models of disease, Aim 3 will determine whether NMR properties can explain 1) the deleterious effect of type-2 diabetes on the fracture resistance of bone and 2) the protective effect of bisphosphonate treatment on ovariectomy-induced decrease in fracture resistance. In addition, it will be determined if the NMR attributes can explain whole bone strength and brittleness in relation to bone structure. To explore the biophysical basis for the changes in the NMR and fracture properties in each aim, a number of characteristics of bone will be measured. Micro-Computed Tomography will quantify volumetric BMD and structure and architecture;high performance liquid chromatography will quantify the concentration of mature crosslinks and collagen content as well as fraction of denatured collagen;thermal gravimetric analysis will quantify the collagen, mineral, and water fractions;Raman spectroscopy will quantify mineral structure;microscopy (light and electron) will quantify osteonal architecture and collagen fibril orientation. Statistical models will determine the relatie contribution of the NMR-derived properties to the fracture properties of bone. This will address the relevance of measuring matrix-bound water and porosity by NMR to improving bone health. The long-term goal is to identify the factors affecting the important determinants of fracture resistance and developing accurate, MRI-based diagnostic assessments of fracture risk.

Public Health Relevance

Current clinical diagnosis of osteoporosis is only sensitive to changes in mineral density and content as well as structure, ignoring important factors such as collagen and porosity to fracture risk. The proposed research therefore uses clinically translatable NMR techniques to elucidate the changes in bone tissue that determine the fracture resistance of bone. In doing so, this research will potentially reveal new targets for improving fracture resistance as well as properly diagnosing a loss in fracture resistance.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Skeletal Biology Structure and Regeneration Study Section (SBSR)
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Lester, Gayle E
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Vanderbilt University Medical Center
Schools of Medicine
United States
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Granke, Mathilde; Coulmier, Aurélie; Uppuganti, Sasidhar et al. (2014) Insights into reference point indentation involving human cortical bone: sensitivity to tissue anisotropy and mechanical behavior. J Mech Behav Biomed Mater 37:174-85
Makowski, Alexander J; Pence, Isaac J; Uppuganti, Sasidhar et al. (2014) Polarization in Raman spectroscopy helps explain bone brittleness in genetic mouse models. J Biomed Opt 19:117008
Makowski, Alexander J; Uppuganti, Sasidhar; Wadeer, Sandra A et al. (2014) The loss of activating transcription factor 4 (ATF4) reduces bone toughness and fracture toughness. Bone 62:1-9
Nyman, Jeffry S; Gorochow, Lacey E; Adam Horch, R et al. (2013) Partial removal of pore and loosely bound water by low-energy drying decreases cortical bone toughness in young and old donors. J Mech Behav Biomed Mater 22:136-45