The effect of matrix bound parathyroid hormone on bone regeneration

Introduction: Autogenous bone is the most successful bone-grafting material; however, multiple disadvantages continue to drive developments of improved methods for bone regeneration. Aim: The aim of the present study was to test the hypothesis that an arginine-glycine-aspartic acid (RGD) modified polyethylene glycol-based matrix (PEG) containing covalently bound peptides of the parathyroid hormone (PTH1-34) enhances bone regeneration to a degree similar to autogenous bone. Material and methods: Six American foxhounds received a total of 48 cylindrical titanium implants placed in the mandible between the first premolar and the second molar. Five, respectively, 7 months following tooth extraction, implants were placed into the center of surgically created defects. This resulted in a circumferential bone defect simulating an alveolar defect with a circular gap of 1.5 mm. Four treatment modalities were randomly allocated to the four defects per side: (1) PEG-matrix containing 20 mu g/ml of PTH1-34, and 350 mu g/ml cys-RGD peptide, (2) PEG alone, (3) autogenous bone and (4) empty defects. Histomorphometric analysis was performed 4 and 12 weeks after implantation. The area fraction of newly formed bone was determined within the former defect and the degree of bone-to-implant contact (BIC) was evaluated both in the defect region and in the apical region of the implant. For statistical analysis ANOVA and subsequent pairwise Student's t-test were applied. Results: Healing was uneventful and all implants were histologically integrated. Histomorphometric analysis after 4 weeks showed an average area fraction of newly formed bone of 41.7 +/- 1.8% for matrix-PTH, 26.6 +/- 4.1% for PEG alone, 43.9 +/- 4.5% for autogenous bone, and 28.9 +/- 1.5% for empty defects. After 12 weeks, the respective values were 49.4 +/- 7.0% for matrix-PTH, 39.3 +/- 5.7% for PEG alone, 50.5 +/- 3.4% for autogenous bone and 38.7 +/- 1.9% for empty defects. Statistical analysis after 4 and 12 weeks revealed significantly more newly formed bone in the PTH1-34 group compared with PEG alone or empty defects, whereas no difference could be detected against autogenous bone. Regarding BIC no significant difference was observed between the four treatment groups neither at 4 nor at 12 weeks. Conclusion: It is concluded that an RGD-modified PEG hydrogel containing PTH1-34 is an effective matrix system to obtain bone regeneration.