| A result of osteoporosis in the long-term space flight has become one of the biggest threat to the health of astronauts, due to decreased bone mineral density, increased bone fragility, can easily lead to the occurrence of osteoporotic fractures, serious impact on their work in space and the quality of life after return to the ground. Growth and metabolism of human bone depend on the role of the Earth’s gravitational field, exposure to the weightless environment as an astronaut into space, will lead structural and functional changes of the skeletal system (especially the load-bearing parts of the spine, limbs, pelvis, etc.) causing the loss of bone mass, bone demineralization, bone mechanical properties decreased to a negative calcium balance. It’s a serious threat to the astronauts’ health and the smooth implementation of space missions. Tail suspended hindlimb-unloaded (tail-suspended, TS) rat model simulates an astronaut in the weightless environment. It’s one of the most commonly used classical model in simulated weightlessness in rats, widely recognized all over the world. Micro-computed tomography (Micro-CT) from the trabecular level evaluation of the structure and function of the bone, has been applied in a foreign country. However, this technology used in the tail-suspended rat model has not been reported in China. The existing data is insufficient to support the domestic conditions of the further study. In this study, the SD rats as subjects, We did bone mineral density scan, Micro-CT analysis and histological observation, observed the changes of BMD and trabecular bone’s3D micro-structural of TS rats. At the same time, bone biochemical markers determination and biomechanical testing were taken, relevant data results provided a basis for predicting the risk of osteoporotic fractures.Objective:To observe the changes of bone mineral density, trabecular bone structure, serum bone biochemical markers and bone mechanical changes in simulated weightlessness TS rat model.Method:603-month-old male SD rats randomly divided into five groups: tail-suspended7d group,14d group,21d group,28d group and a blank control group. Samples of the serum,fourth and fifth lumbar vertebral body and left femoral condyle were collected after the rats were sacrificed at predetermined time points. The serum bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase (TRAP) content were tested, the Ponceau staining of the L5vertebral body were observed, the BMD, structure and mechanical properties of the L4vertebral body and femoral condyle were evaluated.Results:The BMD of the lumbar vertebra and femoral condyle from the two suspension groups were significantly lower than those from the control group (P<0.05). Furthermore the BMD decreased with the extension of suspension. The bone volume fraction (BV/TV), trabecular bone thickness (Tb. Th) and trabecular bone number (Tb. N) of the suspension groups were significantly lower than those of the control group (P<0.05). However, the bone surface to bone volume (BS/BV) and trabecular separation (Tb. Sp) of the suspension groups were significantly higher than the control (P<0.05). Serological test results show that the rat bone alkaline phosphatase (BALP), tartrate-resistant acid phosphatase (TRAP) of TS groups increased significantly than blank control group (P<0.05), The consolidated results suggest that increased bone turnover rate. By biomechanical testing, we found that maximal compressive stress of lumbar vertebra from the suspension7d,14d,21d and28d groups decreased respectively5.1%,14.3%,20.8%and27.6%compared to the blank control group. Furthermore, the flexural load of femoral condyle in group7d,14d,21d and28d decreased7.9%,13.9%18.8%and24.8%compared to the blank control group.Conclusion:The BMD of tail-suspended rats decreased, it can be diagnosed as a reduction of bone mass from14day, and it was closed to the diagnostic criteria of osteoporosis in28days. Trabecular bone structure damaged, the mechanical properties of vertebrae and femur declined, and develop with time extension. Mechanical properties and the levels of BALP, TRAP showed a negative correlation. Bone biochemical markers suggest rats bone turnover increased, which theoretically increases the risk of fracture. |
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