Effect Of Gene Transfecting At Different Time On Mandibular Distraction Osteogenesis

Background:Since McCarthy reported that correction the human mandible malformation with distraction osteogenesis in 1992, this technology has been achieved remarkable progresses in craniomaxillofacial surgery. With the clinical application experience accumulation, we have known more and more about distraction osteogenesis. Clinically, many people realized that the technology provided a new method to treat severe craniomaxillifacial deformities and bone defects, which are difficult to manage with common operations, however, there are some problems may occur during the long time for distraction, such as loose of the fixation, infection, as well as bone fracture, all those because of the long period of the instruments placed introral or extroral, these would be the main hamper to further clinical application. Therefore, how to promote new bone formation, shorten treatment period and reduce the complications, has become a hot spot and challenge in craniomaxillofacial surgery research.Objective:Based on previous research, We employed New Zealand rabbits bilateral mandibular distraction model and used electroporation mediate recombinant plasmid pIRES-hBMP2-hVEGF165 transfect into the distraction gap at the beginning of latency period,distraction period and consolidation period respectively, to explore the optimal time for gene therapy and obtain a better effect.Methods:48 New-Zealand rabbits were employed, mandibles were osteotomy bilaterly under general anaesthesia, the distraction devices were fixed by titanium screws at the ends of bone gap. The arms of distractors are placed percutaneously outside the oral and the wound was closed layer by layer. The rabbits were randomly divided into 4 groups:Group A:2μg (0.1μg/μl) recombinant plasmids pIRES-hBMP2-hVEGF165 were injected into distraction area instantly after operation; Group B:2μg (0.1μg/μl) recombinant plasmids pIRES-hBMP2-hVEGF165 were injected into distraction area at the beginning of distraction; Group C:2μg (0.1μg/μl) recombinant plasmids pIRES-hBMP2-hVEGF165 were injected into distraction area after the completion of distraction. Each group was employed electroporation 5 minutes after the injection of plasmids (electric impulses parameters:200V in voltage,10μF in capacitance,0.2Hz in frequency,2.5ms in average pulse width,6 single pulses, change the positive and negative poles after 3 pulses). Group D:only distracted without gene transfection. In each group, after a 3 days of latency period, the device were activated at the rate of 1mm per day and rhythm of once per day for 10 days. Three rabbits of each group were sacrificed at lwk,2wk,4wk and 8wk of consolidation respectively. The mandibles were harvested and the left subject to X-ray examination for bone healing, and quantitative computed tomography (QCT) dectection for the density of newly formed bone in the distraction gap. The biomechanical properties of the new generation bone at 4th and 8th week of consolidation of each group were detected by three point bending test. The newly formed tissue in the distraction area of the right mandible was harvested for histology examination and histomorphometry analysis.Results:The bone mineral density and the biomechanical strength of newly formed bone increased with the pass of the consolidation time in each group. After 1 week of consolidation, there is no significant difference of BMD among group A, group B, group C; But the BMD of group A, B and C is higher than that of group D. After 2wk,4wk and 8wk of consolidation, the BMD of group B is significantly higher than those of group A, C, and D. The biomechanical parameters are also higher in group B than those of group A, C and D after four and eight weeks of consolidation. The amounts of newly formed vessel,osteoblast and mesenchymal cell of group B were greater than those of group A,group B and group D. The new bone volume and width of bone trabecula of distraction area in group B were higher than those of group A,group B and group D at 1wk,2wk,4wk and 8wk of consolidation respectively. Conclusion:It is better to transfect gene at the beginning of traction (distraction period) than at other stages of DO, in this way, we can obtain more remarkable effect on new bone formation. It suggests that the distraction stage is the optimal time for gene therapy.