The Expression Research Of BMP-2 And CD31 In The Healing Process Of Bone Xenograft

Objective:Observing the expression and tissue distribution of BMP-2 and CD31 in the process of the calf cortical with partial cancellous bone xenograft, analyzing the healing mechanism and relationship between bone remodeling and revascularization. The ideal is provide a basis for the further study of tissue engineered bone.Methods:Seventy-two New Zealand rabbits were selected as our experimental animals. They were divided into 3 groups by random numbers. Group I,II,and III all are 24 rabbits. Group I were implanted with the calf cortical with partial cancellous bone. Group II were implanted with the calf cortical bone plates and group III with the autologous iliums. Specimens were procured at 4,8,12 and 24 weeks after surgery respectively. We observed the expression and tissue distribution of BMP-2 and CD31 in the process healing by general condition,X-ray,histology and immunohistochemistry. And, we used the image analysis computer system for quantitative analysis. The extent of revascularization and remodeling was separately represented by revascularization indexes and new bone areas, studying the relationship between bone remodeling and revascularization. Results:(1) The wound was primary healing, no inflammation and toxicity reaction were observed in any groups.(2) The X-ray showed significant healing in group I , complete healing in group III while gooup II with a poor healing.(3) Histological observationBy the 4 weeks,8 weeks and 12 weeks postoperative, at the joint part , there was different amount of callus in group I,II,and III. In the cancellous bone of group I , there were new blood capillaries and osteoid deposition with calcification. By the 24 weeks postoperative, both group I and II, the grafted bone was surrounded by the compact callus. Group III had complete healing.(4) BMP-2By the 4 weeks,8 weeks and 12 weeks postoperative, the positive expression can be seen in the infant cartilage cells,osteoblastic cells,osteocytes and osteoid at the the callus of joint of group I,II,and III. Also, in the cancellous bone of grafted bone of group I; The newborn osteoblastic cells which in the enlarged haversian canals of cortical bone arrayed in "the edge" appearance also had the positive expression; By the 24 weeks postoperative, the weak positive expression can be seen in the compact callus of group I,II and Group III with complete healing. (6) CD31By the 4 weeks and 8 weeks postoperative, the strong positive expression can be seen in the peripheral soft tissue of graft bone,the callus of joint.and the periphery of cartilage nests; Much positive expression can be seen in the cancellous bone of grafted bone of group I .There can be seen some single,cord,cluster vascular endothelial cells. The positive expression can be seen in the enlarged haversian canals and periphery in every groups. By the 24 weeks postoperative, the positive expression can be seen in the enlarged haversian canals and periphery in group I andII with increasing newborn capillaries.(7) Revascularization and bone remodelingâ‘ Revascularization indexes:By the 4,8,12 and 24 weeks postoperative, there was significant difference in group I,II and III (P<0.05) . Revascularization indexes: GroupIII > Group I > Group II.â‘¡New bone areas:By the 4 weeks postoperative, there was no significant difference between group I and group II (P>0.05) . But both had significant difference with groupIII. New bone areas: GroupIII>Group I and Group II. By the 8,12 and 24 weeks postoperative, there was significant difference in group I,II and III (P<0.05) . New bone areas: GroupIII> Group I > Group II. â‘¢The correlation analysis between new bone areas and revascularizationindexes:Revascularization indexes and new bone areas showed a closely positivecorrelation in the three groups. (r_I= 0.984 , r_II =0.953 , r_III=0.992) .Conclusion:(1) The positive expression of BMP-2 can be seen in the whole process of bone xenograft and was consistent with the new bone formation. The positive expression of BMP-2 in the group of calf cortical with partial cancellous bone was better than the calf cortical bone, especially by the 4 weeks and 8 weeks.(2) The positive expression of CD31 can be seen in the whole process of bone xenograft and be different at various stage and sites. The positive expression of CD31 in the group of calf cortical with partial cancellous bone was better than the calf cortical bone.(3)The extent of revascularization of bone grafts correlated closely with that of bone remodeling, and there were better revascularization indexes and bone remodeling in the calf cortical with partial cancellous bone.(4) In the process of bone segment xenograft, the creep-subsitution was three-dimensional and mostly depending on bone conduction. The process was fulfilled in three interfaces: the joint of host bone and bone xenograft, the surface and periphery, and the haversian canals.