coli Periplasmic Space: Its Characterization and Preclinical Testing

Human BMP-2, a homodimeric protein that belongs to the TGF- β family, is a recognized osteoinductor due to its capacity of inducing bone regeneration and ectopic bone formation. The administration of its recombinant form is an alternative to autologous bone grafting. A variety of E. coli-derived hBMP-2 has been synthesized through refolding of cytoplasmic inclusion bodies. The present work reports the synthesis, purification, and characterization of periplasmic hBMP-2, obtained directly in its correctly folded and authentic form, i.e., without the initial methionine typical of the cytoplasmic product that can induce undesired immunoreactivity. A bacterial expression vector was constructed including the DsbA signal peptide and the cDNA of hBMP-2. The periplasmic fluid was extracted by osmotic shock and analyzed via SDS-PAGE, Western blotting, and reversed-phase high-performance liquid chromatography (RP-HPLC). The purification was carried out by heparin affinity chromatography, followed by high-performance size-exclusion chromatography (HPSEC). HPSEC was used for qualitative and quantitative analysis of the final product, which showed >95% purity. The classical in vitro bioassay based on the induction of alkaline phosphatase activity in myoblastic murine C2C12 cells and the in vivo bioassay consisting of treating calvarial critical-size defects in rats confirmed its bioactivity, which matched the analogous literature data for hBMP-2.

Novel Synthesized Nanofibrous Scaffold Efficiently Delivered hBMP-2 Encoded in Adenoviral Vector to Promote Bone Regeneration

Treatment of bone defect, especially large bone defect, is still a challenge for physicians clinically. Bone morphogenetic protein 2 (BMP-2) can induce osteoblast differentiation and promote new bone formation. Recently, nanomaterials have been widely used as a carrier to hold and deliver biomolecules, like human bone morphogenetic protein 2 gene (hBMP-2) in target cells/tissues. Most nanomethods, however, need further modification in order to work more reliably in clinical applications. Therefore, in this study, we created a novel poly(lactic-co-glycolic acid [PLGA]) nanofibrous scaffold using an electrospinning technique; then, using a lyophilization process to allow nanofibrous scaffold to adsorb hBMP-2 adenoviral vector, AdCMV-hBMP2. Results indicate that the lyophilized poly(lactic-co-glycolic acid) nanofibrous scaffold/AdCMVhBMP2 can efficiently release and transduce cells in vitro and in vivo, and secrete functional hBMP-2 to promote osteogenic differentiation in vitro, and new bone generation in vivo. Importantly, the amount of newly formed bone covered >80% of the bone defect area 8 weeks post-implantation in vivo, in which the defect could not be repaired without any treatment in general. Our data demonstrate that the lyophilized PLGA nanofibrous scaffold/AdCMV-hBMP2 created herein stably and efficiently release functional viral vector to transduce local cells, resulting in secretion of hBMP-2 and promote new bone formation in vivo. Our new nanodelivery method has potential clinical application for the repair of large bone defects.