Osteoinduction by microbubble-enhanced transcutaneous sonoporation of human bone morphogenetic protein-2

Bone morphogenetic protein-2 (BMP-2) is believed to participate in bone healing and regeneration. Previous studies using BMP-2 in clinical applications have encountered difficulties that include the lack of an efficient, safe and simple delivery system, and expensive proteins and matrices. The gene transfer approach is a promising option for utilizing BMP-2. Viral vector-mediated gene transfer is efficient, but safety concerns prevent its clinical application for common diseases. Sonoporation is a simple and inexpensive method that only requires a plasmid and a sonoporation device.

We used a plasmid-based human BMP-2 construct (pCAGGS-BMP-2) and examined the induction of bone in the skeletal muscle of mice after plasmid transfer by transcutaneous sonoporation. First, an in vitro study was performed to confirm the expression of BMP-2 after gene transfer by sonoporation using pCAGGS-BMP-2. Next, the BMP-2 gene was transferred into the skeletal muscle of mice by transcutaneous sonoporation using pCAGGS-BMP-2. BMP-2 production was assessed via immunohistochemistry, and osteoinduction was verified by radiography, histology and biochemical assays.

The presence of human BMP-2, alkaline phosphatase and osteocalcin mRNA and the production of the alkaline phosphatase were observed in vitro. Moreover, mature bone was observed in mice sonoporated with pCAGGS-BMP-2, confirming that transcutaneous sonoporation with pCAGGS-BMP-2 caused osteoinduction in the skeletal muscle of mice.

These results suggest the possibility of the effective clinical use of human BMP-2 gene therapy using transcutaneous sonoporation, and should facilitate clinical applications of BMP-2 gene therapy.