Experimental Study About Application Of Both Osteoprotegerin And Calcium Phosphate Cement For The Augmentation Of Mechanical Properties In The Osteoporotic Femoral Intertrochanteric Area

ObjectiveThe percentage of intertrochanteric region in old persons increased oftentime,which add hard burned to both families and society.It is of important to pretect old persons from suffering osteoporotic fractures in femoral intertrochanteric area previously. Osteoprotegerin is an inhibitory factor of Osteoclasts,can decrease the absorption of bone and increase bone volume.People have get the good clinic effect in treating postmenopausal osteoporosis with OPG.In this study, we used the methylotrophic yeast Pichia pastoris-SMD1168 to rebuild SMD1168/OPG-Fc system and acquire the rhOPG-Fc protein;To determine the feasibility of Calcium phosphate cement(CPC) injected into the intertrochanteric region of cadaveric femur and its effect on the mechanical properties. Elucidate the degradation and the osteogenic response of CPC injected into the intertro- chanteric region of rats with experimentally induced osteoporosis.MethodsWe choosed the functional segment(D1-D4) of OPG as the purpose gene 1,choosed the Fc1 segment of IgG as the purpose gene 2, and got the coding gene of OPG and Fc segment through the RT-PCR technique. Further we built the excretive expression carrier pPICZα/OPG-Fc, and we used the methyl-otrophic yeast Pichia pastoris-SMD1168 to rebuild SMD1168/OPG-Fc system, and we got the rhOPG-Fc protein through zymosis.Six pairs of cadaver femurs were mechanically tested. From each pair, one femur was augmented in intertrochanteric region with CPC, with the contralateral femur serving as a control. In a load to failure test, the compressi- on rigidity and the fracture load were recorded and calculated. The differences between the ehnanced femurs and the native controls were detected.Osteoporotic animal model: Twenty female mature Sprague-Dawley rats were weight matched before ovariectomy (Ovx) or Sham surgery (Sham). Rats were euthanized at 3 and 6 monthes after surgery, and had received fluorochrome bone markers at 10 and 3 days prior to euthanasia. All rats were also scanned for bone mineral parameters by DEXA before euthanasia. Proximal femurs were used for bone histomorphometry.Osteogenic response of application of both OPG and CPC in osteoporotic bone:Thirty osteoporotic rats were divided into three groups:CPC injection, both CPC injection and OPG injection, and comparison. Rats were were injectived with rhOPG-Fc protein at 3mg/kg/d for fourteen days. CPC was injected into the intertrochanteric region of rats. Rats were euthanized at 1,3,7days and 1,3,6 monthes after injection of CPC, and had received specimens of proximal femur. The degradation and the osteogenic response of CPC were evaluated histomorphologically in nondecalcified section. At the same time, the integration of CPC and osteoporotic bone was observed under SEM (scanning electron microscope).ResultsThe purpose gene were expanded successfully and we built the excretive expression carrier pPICZα/OPG-Fc and transferred it to rebuild SMD1168/ OPG-Fc, and we got the rhOPG-Fc protein through zymosis.18-25 ml of CPC (mean, 21.2ml) could be injected into each femur and distributing equally. Compression rigidity has significance different in the groups. Compression strength was increased by 24% after CPC was injected into the intertrochanteric region. The peak fracture load was significantly higher in the groups injected with CPC than the contral group (P<0.01).Osteoporotic animal model:Mineral density was significantly higher in the Sham rats relative to Ovx animals. Ovariectomy reduced trabecular number and thickness, and increased trabecular separation. The structure of the remaining trabeculae was dramatically changed. Cortical thickness in Ovx rats was reduced because of the high endocortical resorption, which, in addition to cancellous bone resorption, resulted in fewer endocortico-trabecular connec-tions.Osteogenic response of application of both CPC and OPG in osteoporotic bone:There was significant bone conduction of CPC in the intertrochanteric region of these osteoporotic rats. There were more osteoblast and osteoclast in the CPC injection side. The trabecula area was significantly higher in the groups injected with CPC than the contral group at 6 months. New trabecular bone contact impact with cement. CPC resorption was corresponding to the new bone formation. Osteogenic response of application of both CPC and OPG in is much obvious while the observation under the microscope and the scanning electron microscope is much closer to the normal bone.ConclusionThe OPG gene were can be built with the excretive expression carrier pPICZα/OPG-Fc and transferred rebuild SMD1168/OPG-Fc. The feasibility and mechanical effectiveness of CPC injected into the intertrochanteric region could be demonstrated. Osteogenic response of application of both CPC and OPG could occur in osteoporotic intertrochanteric region.