Effect of Tail Suspension on Apatite Crystallites of Mouse Femur

Objectives: In recent years, bone quality has garnered attention in addition to bone mineral density (BMD) as a parameter for evaluating bone strength. In particular, the alignment of biological apatite (BAp) crystallites responds to local stress, and assessment of BAp crystalline orientation can therefore be used to identify the direction and regions subjected to mechanical stress. The aim of the present study is to elucidate the influence of hindlimb unloading on BMD and BAp crystalline orientation using tail suspension mouse that are used as bone atrophy osteoporosis model.
Methods: Hindlimb unloading (HLU) was conducted using male C57BL6 mouse of 12 weeks-age. The animals were randomized into two groups: control group and HLU group with six animals each group. For HLU group, the tail of animals was suspended for 21 days. After the experiment, the femur of mouse was equally divided into ten slices of cortical bone with 150-μm thick by cutting perpendicular to the long axis of femurs. These slices of cortical bone were subjected to measurement of BMD and BAp crystalline orientation. BMD value was measured using TRI-3D-BON-BMD (RATOC System Engineering, Tokyo, Japan) and BAp crystalline orientation was evaluated using a micro region X-ray diffractometer (RINT RARID-CMF, Rigaku, Tokyo, Japan). Statistical analysis was performed using one-way ANOVA followed by Tukey’s multiple comparison. This study was conducted under the Tokyo Dental College’s Ethical Review Board (Approval Number 290102).
Results: The BMD values decreased in the femurs on the HLU group compared to control group at all regions of the slice. On the other hand, the BAp crystalline orientation showed the lower value on the HLU group at diaphysial center of the slice compared to control group.
Conclusions: These results indicated that determining BAp crystalline orientation is important in the evaluation of bone quality against mechanical stress in addition to BMD.