Effects Of 1, 25-dihydroxyvitamin D₃ On Osteoporosis In Simulated Weightlessness Rats.

BackgroundWeightlessness is the object shows only for the quality but not for the weight in the microgravity(10^-6～10^-9g).In the weightlessness flying,the regulation of bone metabolism would be disequilibrium and the lost of bone mass might keep developing after return to the earth and result in Osteoporosis.Osteoporosis was considered as dysostosis disorder due to the damage of microstructure of bony tissues,the persistent decreasing of bony matrixes and mineral bones,thinness of sclerotin,the decrease of the number of trabecular bones,and the increase of bony fragility and the risk of fracture.The weightlessness osteoporosis occurrence is mainly the bone formation decreased which leads to the bone loss.Strengthens the research of bone metabolism in microgravity environment,and to provide a new thinking prevention and cure in disuse osteoporosis,at the same time 1,25-dihydroxyvitamin D₃(1,25-D)is a kind of active vitamin D,which not only increase Ca absorption but also promote ossein and bone matrix synthesis.1,25-D stimulates bone formation directly.The research confirmed that exogenous 1,25-D prevented unloading induced bone loss,but still lacked the correlation of morphology material. ObjectiveTo evaluate the effects of 1,25-D treatment on osteoporosis of in simulated weightlessness rats by means of bone micromorphology,DEXA and bone biomechanics.MethodsIn successful model experiment foundation,thirty-six 3-month-old male SD rats were purchased and acclimated to condition for 1 week.The animals were randomly divided into 4 groups:one free control group(group A)and three tail-suspended simulatied weightlessness groups(group B,C and D).Group D treated with 1,25-D, 0.05μg/kg·d,group C treated with the same dose of 1a-D.After 4 weeks,all animals were sacrificed.Blood samples were obtained before sacrifice to determine the serum Ca,ALP,BGP and TRAP.The femur were prepared for DEXA,SEM and bone biomechanical measurement with femoral shaft three-point bending test(after measuring BMD),a vertebral body compression and indentation test were performed on the lumbar vertebra.Statistical methodsAll data were reported as mean±standard error,SPSS 10.0 software was used for these analyses.Group A and group B comparisons were run using independent-samples T test,and when a significant difference was revealed(P＜0.05);group C and group D assays performed were analyzed by one-way ANOVA and when significance was revealed(P＜0.05).Results1.Osteoporosis model established by simulated weightlessness:All rats gained substantial body weight,significant differences were not found in two groups(t= 1.404,P=0.191).Serum BGP and ALP were significantly lower than in group A (P=0.000;t=2.712,P=0.022;t=3.878,P=0.003),serum Ca were significantly higher than in group A(t=4.191,P=0.002),serum TRAP were not found significant differences in two groups(t=1.969,P=0.077);the BMD of the right femur were significantly lower than in group A(t=4.774,P=0.001);the max load and rigidity were significantly lower than in group A(t=8.031,P=0.000;t=0.327,P=0.000;t =4.774,P=0.003;t=4.289,P=0.002).2,Effects of 1,25-D on osteoporosis in simulated weightlessness rats:(1).In DEXA BMD measurements of the right femur were found significant differences in all groups(F=29.140;P=0.000).Group B were significantly lower than in group A(P=0.000);group D were significantly higher than in group B (P=0.000),but no found significant difference between group D and group A (P=0.070);there were no found significant difference between group B and group C (P=0.077).(2).In SEM observation,bone trabecula of the femur were found with normal network structure and collagenous fibers with regular arrangement in group A;bone trabecula of the femur were manifested with fewness,fragility,microcrack and collagen fibers displaced by absorption lacuna in group B;destructing network structure of bone trabecular and collagenous fibers were seen with fluffy arrangement in group C;bone trabecula getting more,network structure getting better,resorption surface decreased and collagenous fiber were much more regular in group D.(3).The cancellous bone biomechanical property like the max load and rigidity of vertebral body indentation and compression test were found significant differences in four groups(F=10.958,11.075,13.531,15.251;P=0.000).Group B were significantly lower than in group A(P=0.000);group D were significantly higher than in group B (P=0.005,0.003,0.002,0.001),but lower in group A(P=0.029,0.044,0.046, 0.041);no significant difference were found between group B and group C(P=0.299, 0.252,0.714,0.537).The cortical bone biomechanical property such as the elastic load,max load,rigidity,and max deformation of femoral shaft three-point bending test,four groups were found significant differences(F=12.707,55.841,11.076,8.277; P=0.000).Group B were significantly lower than in group A(P=0.000);group D were significantly higher than in group B(P=0.001,0.000,0.003,0.007),but lower in group A(P=0.045,0.026,0.046,0.047);there were no found significant difference between group B and group C(P=0.218,0.108,0.265,0.405).Conclusion1.Bone formation and bone mass decreased,microarchitectural destructive in simulated weightlessness rats,accompanied with decreased of biomechanical competence.The rat osteoporosis models were successful established.2.1a-D has a weak effect on reducing bone loss in simulated weightlessness.3.1,25-dihydroxyvitamin D₃ has a powerful effect on preventing osteoporosis in simulated weightlessness rats.1,25-D can promote bone formation,reduce bone loss, improve bone microarchitectural and enhance bone trabecula quality.