Longitudinal changes of bone microstructure and biomechanical properties of vertebral trabeculae in OVX rats

Abstract

Objective To characterize the longitudinal changes of cancellous bone microstructural deterioration of vertebral trabeculae and to investigate the possible adaptative compensations in OVX rats.Methods 50 Female Sprague -Dawley rats of seven-month-old were ovariectomized(OVX),SHAM-operated(SHAM) or left unoperated(baseline control).The vertebral bodies and artery blood samples were harvested at baseline,3 and 15 weeks postoperatively.The compressive test was performed on L_5 vertebral body,and micro-computed tomography(μ-CT) assessment was performed to estimate 3D bone mineral density(BMD) and microstructure parameters of the L_6 vertebral body.After fatigue damage testing,L_6 vertebral body was bulk-stained in 1%basic fuchsin and embedded in methylmethacrylate.Mounted bone slices were used to measure osteocyte density(Ot.N/T.Ar).Blood samples were used to analyze serum tartrate-resistant acid phosphatase 5b(TRAP-5b).Results At 3 weeks postoperatively,apparent BMD,trabecular volume fraction(TV/ BV),trabecular thickness(Tb.Th),trabecular number(Tb.N),tartrate-resistant acid phosphatase 5b(TRAP-5b), maximum load(ML),elastic modulus(EM) and osteocyte density(Ot.N/T.Ar) were significantly decreased in OVX rats than those of SHAM and baseline control rats.Degree of anisotropy(DA) was significantly decreased in OVX rat than those of baseline control group.Bone area density(BS/BV),trabecular separation(Tb.Sp) and trabecular model index (SMI) were significantly increased in OVX rat than those of SHAM and baseline control rats.There were no significant differences between OVX and SHAM rats with regard to DA,trabecular connectivity density(Conn.D),ML,EM,Ot N/ T.Ar and TRAP-5b.There was no significant difference with regard to Conn.D between OVX and baseline control rats. At 15 weeks postoperatively,apparent BMD,TV/BV,Conn.D,Tb.N,TRAP-5b,ML and Ot N/T.Ar were significantly decreased in OVX rat than those of SHAM and baseline control rats.SMI,Tb.Sp and DA were significantly increased in OVX rat than that of SHAM and baseline control rats.There were no significant differences with regard to BS/BV and Tb.Th.between OVX,SHAM and baseline control rats.BS/BV,Conn.D and Tb.N of OVX rat were significandy decreased at 15 weeks postoperatively than those at 3 weeks postoperatively.Ot N/T.Ar,Tb.Sp and DA of OVX group were significantly increased at 15 weeks postoperatively than those at 3 weeks postoperatively.Conclusion In early ovariectomized rats,bone mass of lumbar vertebra lost rapidly while the microstructure of spongy bone deteriorated gradually.A decrease in serum TRAP-5b,and an increase in osteocyte density,trabecular degree of anisotropy and trabecular thickness might represent the adaptive changes to the attenuated bone quality accounting for maintenance of the strength and integrity of cancellous bone in OVX rats.