Difference in Soft Tissue Response Between Immediate and Delayed Delivery Suggests a New Mechanism for Recombinant Human Bone Morphogenetic Protein 2 Action in Large Segmental Bone Defects

• Published in: Tissue engineering. Part A 2012-03, Vol.18 (5-6), p.665-675
• Main Authors: Hussein, Khaled A., Zakhary, Ibrahim E., Elawady, Ahmed R., Emam, Hany A., Sharawy, Mohamed, Baban, Babak, Akeel, Sara, Al-Shabrawey, Mohamed, Elsalanty, Mohammed E.
• Format: Article
• Language: English
• Subjects: Animals; Bone growth; Bone morphogenetic protein 2; Bone Morphogenetic Protein 2 - biosynthesis; Bone Morphogenetic Protein 2 - pharmacology; Bone Regeneration - drug effects; Bones; Collagen; Craniofacial Abnormalities - drug therapy; Craniofacial Abnormalities - pathology; Craniofacial syndromes; Disease Models, Animal; Dogs; Dose-Response Relationship, Drug; Endothelial cells; Gene expression; Gene Expression Regulation - drug effects; Humans; Lipoproteins; Lipoproteins, LDL - metabolism; Mandible; Mandibular Fractures - drug therapy; Mandibular Fractures - pathology; Morphometry; Original Articles; Periosteum; Periosteum - metabolism; Periosteum - pathology; Polymerase chain reaction; Proteins; Reconstruction; Regeneration; Soft tissues; Surgery; Time Factors; Tissue engineering; Vascular endothelial growth factor; Vascular Endothelial Growth Factor A - biosynthesis
• ISSN: 1937-3341; 1937-335X
• DOI: 10.1089/ten.tea.2011.0148

The ability of recombinant human bone morphogenetic protein 2 on absorbable collagen sponge (rh BMP2 /ACS) to regenerate bone in segmental defect has been well characterized. However, clinical results of rh BMP2 /ACS constructs in secondary reconstruction of large mandibular and craniofacial defects have not been consistent. We hypothesized that rh BMP2 delivery triggers an endogenous response in the soft tissues surrounding the defect, in the form of expression of BMP2 and vascular endothelial growth factor ( VEGF ). Such osteogenic response will occur only after immediate, as opposed to delayed, rh BMP2 delivery, suggesting a new explanation to the difference in bone regeneration between the two settings. A 35-mm segmental bone and periosteum defect was created on one side of the mandible in 16 dogs divided in three groups. Group 1 (Gp1, n =6) ACS was loaded with 8 mL of rh BMP2 (0.2 mg/mL). In Gp2 ( n =5) the same dose of rh BMP2 /ACS was delivered into the defect 4 weeks after surgery. In Gp3 (control; n =5) the defect was reconstructed using ACS loaded with 8 mL of buffer only (devoid of rh BMP2 ). Tissues were collected after 12 weeks of reconstruction in all groups. Direct measurement of physical dimensions of regenerates and bone morphometry was performed to evaluate bone regeneration. The mRNA expression of both BMP2 and VEGF in the soft tissue surrounding the defect was evaluated using real-time quantitative PCR. Both BMP2 and VEGF proteins were quantified in immunostained sections. Immunoflurescence colocalization of BMP2 and acetylated low density lipoprotein ( AcLDL ) was done to detect the source of BMP2 . Immediate delivery yielded better bone regeneration. Both BMP2 and VEGF mRNA expression was upregulated only in Gp1 (+7.3, p =0.001; +1.53, p =0.001, respectively). BMP2 protein was significantly higher in the immediate reconstruction group; however, VEGF protein was undetected in the examined sections. Immediate delivery of rh BMP2 seemed to induce endogenous release of BMP2 from the surrounding soft tissues, an effect that was lacking in delayed delivery and may explain the variability of clinical results associated with BMP2 use. Colocalization of BMP2 and endothelial cells (ECs) suggested that ECs could be the source of endogenous BMP2 .