A Dual Delivery of Substance P and Bone Morphogenetic Protein-2 for Mesenchymal Stem Cell Recruitment and Bone Regeneration

Abstract

Implantation of ex vivo expanded and osteogenically differentiated mesenchymal stem cells (MSCs) for bone regeneration has drawbacks for clinical applications, such as poor survival of implanted cells and increased treatment expenses. As a new approach for bone regeneration that can circumvent these limitations, we propose dual delivery of substance P (SP) and bone morphogenetic protein-2 (BMP-2) to facilitate endogenous stem cell recruitment to bone defects by SP and subsequent in situ osteogenic differentiation of those cells by BMP-2. A heparin-conjugated fibrin (HCF) gel enabled dual delivery with fast release of SP and slow release of BMP-2, which would be ideal for prompt recruitment of endogenous stem cells in the first stage and time-consuming osteogenic differentiation of the recruited stem cells in the second stage. The HCF gels with SP and/or BMP-2 were implanted into mouse calvarial defects for 8 weeks. Local delivery of SP to the calvarial defects using HCF gel was more effective in recruiting MSCs to the calvarial defects than intraperitoneal or intravenous administration of SP. Many of the cells recruited by SP underwent osteogenic differentiation through local delivery of BMP-2. The efficacy of in vivo bone regeneration was significantly higher in the SP/BMP-2 dual delivery group. The dual delivery of SP and BMP-2 using the HCF gel therefore has potential as an effective bone regeneration strategy.