A study on the changes of bone structure and properties in female rats under simulated weightlessness as osteoporosis models

Objective To study the changes of bone mineral density( BMD) of cancellous bone, trabecular bone structure, bone tissue morphology, bone metabolic biochemical markers and mechanical properties in tailsuspended female rats under simulated weightlessness, so as to provide certain theoretical support for the research on bone mass changes in female astronauts after the fl ight and aerospace medicine. Methods Twenty 3-month-old female Sprague-Dawley( SD) rats were randomly divided into 2 groups. The tails of the rats in group A( n=10) were suspended for 4 weeks, and the other rates were taken as blank control group( n=10). All the rates were continuously fed for 4 weeks, and their general conditions were recorded, including activities, eating and drinking, defecation, weight, unhairing or not, death and tail falling off. All the rats were sacrificed at predetermined time points. The BMD of the L4 vertebral body and femoral condyle was evaluated by dual-energy X-ray absorption( DEXA). Micro computed tomography( Micro-CT) was applied to analyze the trabecular bone. Bone tissue slice staining was conducted by using ponceau. Serum bone metabolic biochemical markers were detected by Enzymelinked immunosorbent assay( ELISA), and biochemical properties were investigated. Results At 4 weeks after the establishment of osteoporosis models, the activities, eating and drinking and defecation of the rats in group A were normal, and the differences in weight gain were not statistically significant between the 2 groups( P0.05). No unhairing, death or tail falling off was noticed in either group. When compared with that in blank control group, the BMD of the L4 vertebral body and femoral condyle in group A was reduced by 29% and 30%( P0.05). The bone volume / total volume( BV/TV), bone surface/bone volume( BS/BV), trabecular thickness( Tb.Th) and trabecular number( Tb.N) of the L4 vertebral body in group A was reduced by 40%, 15%, 30% and 33% when compared with that in blank control group( P0.05). The BV/TV, BS/BV, Tb.Th and Tb.N of the femoral condyle in group A was reduced by 21%, 25%, 50% and 19% when compared with that in blank control group( P0.05). The trabecular separation( Tb.Sp) of the L4 vertebral body and femoral condyle in group A was increased by 92% and 33% respectively( P0.05) when compared with that in blank control group( P0.05). The 3-dimensional( 3 D) reconstruction of the trabecular bone in region of interest( ROI) of lumbar cancellous bone showed group A was not as good as blank control group in the intensity, real volume, size and continuity of the trabecular bone in the lumbar vertebral body. Honeycomblike structure was detected and obvious osteoporosis and 3D structural damage were noticed. The osteoporotic bone changes and incontinuity, diminution and enlarged space of the trabecular bone were observed in group A under the microscope( 50X). The human bone alkaline phosphatase( BALP) and tartrate resistant acid phosphatase( TRAP) in group A was 4.5 and 3.1 times higher than that in blank control group( P0.05). The maximal compressive load and maximal compressive stress of the lumbar vertebral body and the maximal fl exural load of the femur in group A were decreased by 36%, 33% and 34% when compared with that of blank control group( P0.05). Conclusions The significant decrease of the BMD of cancellous bone, 3 D structural damage of the trabecular bone, morphological destruction of bone tissues, bone metabolism imbalance and obvious reduction of mechanical strength of the vertebral body and femur are detected in the tail-suspended rats at 4 weeks after the establishment of osteoporosis models. The visible signs of osteoporosis are observed, and the risk of fracture is increased theoretically. A full understanding of bone mass loss and fracture risk in female astronauts should be developed.