Re-evaluating the induction of bone formation in primates

Area of Science:

• Regenerative Medicine
• Skeletal Biology
• Biomaterials Science

Background:

• Recombinant human bone morphogenetic/osteogenic proteins (hBMPs/OPs) have shown limited clinical success in bone tissue engineering, often requiring supra-physiological doses and incurring high costs.
• Previous pre-clinical studies prematurely suggested hBMPs/OPs would translate effectively to clinical bone regeneration, but this has not been realized, leading to complications and performance failures.
• The clinical need for effective alternatives to hBMPs/OPs is critical, especially given their substandard regeneration of clinical defects and the high cost associated with their use.

Purpose of the Study:

• To investigate the potential of transforming growth factor-beta 3 (TGF-β3) as an initiator of bone formation, questioning the sole reliance on hBMPs/OPs.
• To elucidate the molecular and morphological mechanisms underlying bone induction by hTGF-β3 in a primate model and its potential clinical applications.
• To explore novel frontiers in bone tissue engineering by combining hTGF-β3 with biomaterial scaffolds for enhanced bone regeneration.

Main Methods:

• Administration of hTGF-β3 in heterotopic intramuscular sites in Chacma baboons (Papio ursinus) to assess bone induction.
• Analysis of molecular markers (TGF-β1, TGF-β3, BMP-2, BMP-3, OP-1, RUNX-2, Osteocalcin) and morphological changes including osteoblastic activity, osteoid synthesis, and angiogenesis.
• Clinical translation involving implantation of hTGF-β3 with human demineralized bone matrix in a pediatric patient with a large mandibular defect.

Main Results:

• Rapid induction of bone formation by hTGF-β3 in baboons, accompanied by upregulation of BMPs/OPs, RUNX-2, and Osteocalcin, alongside increased osteoblastic activity, osteoid synthesis, and angiogenesis.
• Evidence suggests hTGF-β3 induces bone via the BMPs/OPs pathway by regulating Noggin expression, potentially overcoming the inhibitory effects seen with direct hBMP/OP application.
• Successful clinical application in a pediatric patient, demonstrating radiographic evidence of mandibular reconstruction, including the coronoid process, 30 months post-implantation.

Conclusions:

• hTGF-β3 is a potent initiator of bone formation, acting upstream in the cascade and potentially overcoming the limitations of direct hBMP/OP application.
• The mechanism involves regulating endogenous BMPs/OPs expression and potentially bypassing Noggin-mediated inhibition, offering a more effective clinical strategy.
• The combination of hTGF-β3 with biomaterial scaffolds represents a novel and effective frontier for clinical bone tissue engineering, as demonstrated by the successful mandibular reconstruction.