Amphiphilic core-shell nanoparticles with poly(ethylenimine) shells as potential gene delivery carriers.

Spherical, well-defined core-shell nanoparticles that consist of poly(methyl methacrylate) (PMMA) cores and branched poly(ethylenimine) shells (PEI) were synthesized via a graft copolymerization of methyl methacrylate from branched PEI induced by a small amount of tert-butyl hydroperoxide. The PMMA-PEI core-shell nanoparticles were between 130 to170 nm in diameter and displayed zeta-potentials near +40 mV at pH 7 in 1 mM aqueous NaCl. Plasmid DNA (pDNA) was mixed with nanoparticles and formed complexes of approximately 120 nm in diameter and was highly monodispersed. The complexes were characterized with respect to their particle size, zeta-potential, surface morphology, and DNA integrity. The complexing ability of the nanoparticles was strongly dependent on the molecular weight of the PEI and the thickness of the PEI shells. The stability of the complexes was influenced by the loading ratio of the pDNA and the nanoparticles. The condensed pDNA in the complexes was significantly protected from enzymatic degradation by DNase I. Cytotoxity studies using MTT colorimetric assays suggested that the PMMA-PEI (25 kDa) core-shell nanoparticles were three times less toxic than the branched PEI (25 kDa). Their transfection efficiencies were also significantly higher. Thus, the PEI-based core-shell nanoparticles show considerable potential as carriers for gene delivery.

Recombinant human bone morphogenetic protein-4 (rhBMP-4) enhanced posterior spinal fusion without decortication.

In posterior spinal fusion, insufficient decortication may decrease the number of bone marrow derived ostoprogenitor stem cells and affect the success of bony fusion. The finding of bone formation through interaction between rhBMP-4 and non-marrow derived mesenchymal cells constituted the basis of the current study. The aim is to investigate the possibility of molecular enhancement of posterior spinal fusion by site-specific application of rhBMP-4 with or without surgical decortication. Eighteen adult rabbits underwent single level bilateral posterior intertransverse process spinal fusion at L5-L6. one side with decortication, and the other side without decortication. Two animals underwent sham operation without bone grafts, the other 16 animals were randomly allocated into three groups, using hydroxyapatite-tricalcium phosphate (HA-TCP) ceramic blocks augmented with 0, 125 and 5 micromg [corrected] of rhBMP-4 respectively. Spinal fusion morphology was evaluated with sequential X-ray, microradiography and histomorphology. At week 7, complete bony fusion was achieved in none of the groups without rhBMP-4 irrespective of whether the bony contact surface was decorticated or not. In the groups with low dose rhBMP-4, complete fusion occurred in two of six un-decorticated sites (33%) and in three of six (50%) decorticated sites. 100% complete fusion was found in the high dose rhBMP-4 group independent of surgical decortication. The dorsal cortices of the un-decorticated transverse processes were replaced by newly formed trabecular bone through biological remodeling. This study suggested that rhBMP-4 can induce non-marrow derived mesenchymal cells to differentiate into osteogenic cells and thus enhance the high success rate of pesterior spinal fusion in both the decorticated and un-decorticated model.

How does recombinant human bone morphogenetic protein-4 enhance posterior spinal fusion?

STUDY DESIGN: A rabbit posterolateral intertransverse process fusion model was used to evaluate the effect that different doses of recombinant human bone morphogenetic protein-4 delivered in a porous hydroxyapatite-tricalcium phosphate ceramic had on osteogenesis and spinal fusion. OBJECTIVE: To study the biologic effect and threshold dose of recombinant human bone morphogenetic protein-4 in enhancing spinal fusion. SUMMARY OF BACKGROUND DATA: Biologic manipulation for spinal fusion is an area undergoing active research. The enhancing effects of recombinant human bone morphogenetic proteins 2 and 7 on spinal fusion have been proved, and clinical trials of their application are in progress. Recombinant human bone morphogenetic protein-4 is another osteoinductive protein that has the ability to induce heterotopic bone formation, and its potential for enhancing spinal fusion has not yet been studied. METHODS: For this study, 24 adult New Zealand white rabbits underwent single-level unilateral posterior intertransverse process spinal fusion at L5-L6. The animals were divided into four groups using different graft materials: allograft as well as hydroxyapatite-tricalcium phosphate augmented with 0, 1.25, and 5 microgram of recombinant human bone morphogenetic protein-4, respectively. The local changes were evaluated by sequential radiograph, manual palpation, histomorphology, and microradiography. RESULTS: At week 7, ossification in the intertransverse process area ceased in groups without recombinant human bone morphogenetic protein-4, whereas active multicentric endochondral bone formation was demonstrated in groups with this growth factor. The success rate of contiguous bony bridging was found to correlate positively with the dose of recombinant human bone morphogenetic protein-4. CONCLUSIONS: Recombinant human bone morphogenetic protein-4 effectively enhances new bone formation and accelerates fusion in the rabbit posterolateral posterior spinal fusion model. The effective dose of recombinant human bone morphogenetic protein-4 is 10 times lower than the reported dosage of recombinant human bone morphogenetic proteins 2 and 7.