OBJECTIVETo investgate the expression patterns of bone morphogenetic protein-2 (BMP-2) in the distraction area following plRES-hBMP2-VEGFI65 gene transfection at different time during mandibular distraction osteogenesis in a rabbit model.

METHODS48 New-Zeland rabbits were employed to underwent osteotomy and distraction devices implantation on mandible bilaterly. After 3 days of latency period, the devices were activated at the rate of 0. 8 mm per day for 10 days. The rabbits were randomly divided into 4 groups (group A, B, C and D). Group A, B and C were transfected recombinant plasmids pIRES-hBMP2-hVEGF165 via electroporation-mediated approach at latency period, distraction period, consolidation period respectively. Group D was used as control group without gene transfection. Three rabbits in each group were sacrificed at 1, 2, 4 weeks of consolidation respectively. The mandibles were harvested for immunohistochemical staining detection of BMP-2 expression respectively, which were analyzed by CMIAS series multifunction color quantitative analysis of pathological image analysis system.

RESULTSBMP-2 expression was found to be mainly located in the monocyte, fibroblast of the granulation tissue, the osteoblasts, osteocyte on the surface of new formed trabecular, and the connective tissues surrounding the new formed bone. The expression in group B was superior to other groups. Image analysis showed that, at the first week and second week of consolidation, the expression abosordbance A in group B (0. 58 ± 0. 03 and 0. 34 ± 0. 02) was relatively higher, when compared with that in group A (0. 42 ± 0. 02 and. 31 ±0.01), C(0.32 ±0.01 and 0.30 ±0.01)and D(0.27 ±0.01 and 0.23 ±0.02), showing a significant difference(P <0. 05). It was also relatively higher in group A(0. 42 ± 0. 02 and 0. 31 ± 0. 01) and C(0. 32 ± 0.01 and 0.30 ± 0.01), when compared with that in group D(0. 27 ±0.01 and 0.23 ± 0. 02), showing a significant difference( P < 0. 05) , but there was no significant difference ( P > 0. 05) between group A and group C. At the fourth week of consolidation, the expression decreased and there was no significant difference among group A, B, C, D.

CONCLUSIONSThe electroporation-mediated gene transfection which is transfected at the beginning of traction can promote BMP-2 expression effectively, stimulate bone marrix synthesis and induce proliferation and differentiation of fibroblasts, osteoblasts, endothelial cells, which further effectively promote the new bone formation. It suggests that the distraction stage is the optimal time for gene therapy.