Oral Presentation ESA-SRB-ANZBMS 2024 in conjunction with ENSA

Mineralisation and collagen fibre compaction of recently formed bone differs between younger and older women, and is region-specific (#120)

Mary Louise Fac 1 2 , Narelle E McGregor 1 , Mark J Tobin 3 , Jitraporn (Pimm) Vongsvivut 3 , Rita Hardiman 4 , Natalie A Sims 1 2
  1. Bone Cell Biology and Disease Unit, St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia
  2. Department of Medicine at St. Vincent's Hospital, The University of Melbourne, Fitzroy, Victoria, Australia
  3. Infrared Microspectroscopy (IRM) beamline, ANSTO – Australian Synchrotron, Clayton, Victoria, Australia
  4. Melbourne Dental School, The University of Melbourne, Melbourne, Victoria, Australia

Cortical bone’s hierarchical structure contributes to its fracture resistance. On the microscale, bone fragility is characterised by high cortical porosity. This differs between regions, likely due to varying mechanical strains. On the nanoscale, mineralised collagen fibrils provide toughness and plasticity, and any imbalance compromises bone strength. We hypothesised that older women produce new bone which is defective in mineral and collagen, and that this defect shows regional variation with cortical porosity. This study sought to test that hypothesis. 

Cadaveric femoral midshaft samples from 10 healthy younger women (20-40 years old) and 10 healthy older women (77-95 years old) were obtained from the Melbourne Femur Research Collection. Cortical bone from the posterior femoral octant (which exhibits the greatest age-related increase in porosity) and lateral octant (which exhibits the least) were assessed by micro-computed tomography. Mineral accrual, collagen compaction and carbonate substitution were measured in both octants by synchrotron-based Fourier-transform infrared (FTIR) microspectroscopy in 5 recently formed osteons per subject.

At both octants and at both ages, mineral accrual, carbonate substitution and collagen compaction all increased with distance from the osteonal pore, reflecting secondary mineralisation. In older women, in both octants, collagen was more compact than in younger women. In the lateral octant, older women exhibited greater mineral accrual and carbonate substitution than younger women, consistent with greater collagen compaction. These differences in mineral were not observed in the posterior octant.

In summary, osteoblasts in older women deposit collagen which becomes more compressed than in younger women, independent of cortical porosity. In the lateral femoral octant, this was associated with more mineral containing more carbonate. However, this relationship between mineral and compressed collagen with age was disrupted in the posterior region. This suggests that older women produce poor quality bone material with region-specific variation that may relate to differences in mechanical strain.