Evaluation of fibrin-based gene-activated matrices for BMP2/7 plasmid codelivery in a rat nonunion model

Purpose: Treatment of large-segmental bone defects still is a challenge in clinical routine. Application of gene-activated matrices (GAMs) based on fibrin, bone morphogenic protein (BMP) 2/7 plasmids and nonviral transfection reagents (cationic polymers) could be an innovative treatment strategy to overcome this problem. The aim of this study was to determine the therapeutic efficacy of fibrin GAMs with or without additional transfection reagents for BMP2 and 7 plasmid codelivery in a femur nonunion rat model. Methods: In this experimental study, a critical-sized femoral defect was created in 27 rats. At four weeks after the surgery, animals were separated into four groups and underwent a second operation. Fibrin clots containing BMP2/7 plasmids with and without cationic polymer were implanted into the femoral defect. Fibrin clots containing recombinant human (rh) BMP2 served as positive and clots without supplement as negative controls. Results: At eight weeks, animals that received GAMs containing the cationic polymer and BMP2/7 plasmids showed decreased bone volume compared with animals treated with GAMs and BMP2/7 only. Application of BMP2/7 plasmids in fibrin GAMs without cationic polymer led to variable results. Animals that received rhBMP2 protein showed increased bone volume, and osseous unions were achieved in two of six animals. Conclusions: Cationic polymers decrease therapeutic efficiency of fibrin GAM-based BMP2/7 plasmid codelivery in bone regeneration. Nonviral gene transfer of BMP2/7 plasmids needs alternative promoters (e.g. by sonoporation, electroporation) to produce beneficial clinical effects

Sonoporation increases therapeutic efficacy of inducible and constitutive BMP2/7 in vivo gene delivery.

An ideal novel treatment for bone defects should provide regeneration without autologous or allogenous grafting, exogenous cells, growth factors, or biomaterials while ensuring spatial and temporal control as well as safety. Therefore, a novel osteoinductive nonviral in vivo gene therapy approach using sonoporation was investigated in ectopic and orthotopic models. Constitutive or regulated, doxycycline-inducible, bone morphogenetic protein 2 and 7 coexpression plasmids were repeatedly applied for 5 days. Ectopic and orthotopic gene transfer efficacy was monitored by coapplication of a luciferase plasmid and bioluminescence imaging. Orthotopic plasmid DNA distribution was investigated using a novel plasmid-labeling method. Luciferase imaging demonstrated an increased trend (61% vs. 100%) of gene transfer efficacy, and micro-computed tomography evaluation showed significantly enhanced frequency of ectopic bone formation for sonoporation compared with passive gene delivery (46% vs. 100%) dependent on applied ultrasound power. Bone formation by the inducible system (83%) was stringently controlled by doxycycline in vivo, and no ectopic bone formation was observed without induction or with passive gene transfer without sonoporation. Orthotopic evaluation in a rat femur segmental defect model demonstrated an increased trend of gene transfer efficacy using sonoporation. Investigation of DNA distribution demonstrated extensive binding of plasmid DNA to bone tissue. Sonoporated animals displayed a potentially increased union rate (33%) without extensive callus formation or heterotopic ossification. We conclude that sonoporation of BMP2/7 coexpression plasmids is a feasible, minimally invasive method for osteoinduction and that improvement of bone regeneration by sonoporative gene delivery is superior to passive gene delivery

The trochlear isometric point is different in patients with recurrent patellar instability compared to controls: a radiographical study

Purpose: The purpose of the study was to investigate the theoretical isometric point based of the curve of the femoral groove and relating it to the origin of the MPFL femoral tunnel on lateral radiograph by comparing a patellar instability cohort with a control cohort. Methods: From a Patellar Instability database the radiographs of 40 consecutive patients were analysed to define Schöttle’s point, and the arc of the circle of the trochlear groove. A comparison population of 20 radiographs from comparable patients with tibiofemoral joint disorders was used as a control. The distance from Schöttle’s point to the most anterior part of the groove (extension) was also compared to the distance to the distal end of the roof of the notch (flexion). Results: The trochlea was circular in the controls but not the Patellofemoral Instability cohort where trochlear dysplasia is usually present. The difference between the extension and flexion length was a mean of − 2.0 ± 0.5 mm in the controls and + 6.0 ± 0.5 mm in the patellofemoral cohort. In neither cohort did the centre of the circle correspond to Schöttle’s point. The extension distance correlated with the boss height. Conclusions: The dysplastic trochlea is not circular and the centre of the best matched circle was different to the control trochleae which were circular. The circle centres did not correlate with Schöttle’s point for either cohort, and was more proximal in the Patellofemoral Instability cohort. Clinical relevance: For the MPFL to have equal tension throughout flexion within the groove, the length should not change. In normal knees the MPFL does not behave isometrically. The change in length, as measured from Schöttle’s point to the trochlea, was greater for patellofemoral instability patients explaining why an isolated MPFL reconstruction in the presence of severe trochlear dysplasia risks poor outcomes