Gene therapy using non-viral vectors that are safe and efficient at transfecting target cells is an effective approach to overcome the shortcomings of delivery of growth factors in protein form. The objective of this study was to develop and test a non-viral gene delivery system for bone regeneration utilizing a collagen scaffold carrying polyethylenimine (PEI)-plasmid DNA (pDNA) complexes.
Two different pDNA were used: pDNA encoding platelet derived growth factor-B (PDGF-B) and pDNA encoding vascular endothelial growth factor (VEGF). The complexes were fabricated at an amine (N) to phosphate (P) ratio of 10 and then characterized for size, surface charge, as well as in vitro cytotoxicity and transfection efficacy in human bone marrow stromal cells (BMSCs). The influence of the PEI-pPDGF-B complex-loaded collagen scaffold on cellular attachment and recruitment was evaluated in vitro using microscopy techniques. The in vivo regenerative capacity of the gene delivery system, using PEI-pPDGF-B and PEI-pVEGF complexes, was assessed in 5 mm diameter critical-sized calvarial defects in Fisher 344 rats. A different biomaterial, chitosan, loaded with copper was also evaluated in vivo.
The complexes were ∼100 nm in size with a positive surface charge. Complexes prepared at an N/P ratio of 10 displayed low cytotoxicity as assessed by a cell viability assay. High magnification scanning electron microscopy imaging demonstrated the recruitment and attachment of BMSCs into the collagen scaffold containing PEI-pPDGF-B complexes. Confocal microscopy revealed significant proliferation of BMSCs on PEI-pPDGF-B complex-loaded collagen scaffolds compared to empty scaffolds. In vivo studies showed significantly higher new bone volume/total volume (BV/TV) % in calvarial defects treated with the PEI-pPDGF-B complex-activated collagen scaffolds following 4 weeks of implantation when compared to the other treatment groups. Together these findings suggest that non-viral PDGF-B gene-activated collagen scaffolds effectively promote bone regeneration and are an attractive gene delivery system with significant potential for clinical translation.