Zoledronate Bound to Ceramics Increases Ectopic Bone Volume Induced by rhBMP6 Delivered in Autologous Blood Coagulum in Rats

Regeneration of a Rabbit Segmental Defect with a New Bone Therapy: Autologous Blood Coagulum with Bone Morphogenetic Protein 6 and Synthetic Ceramics

Segmental defects of long bones are among the most challenging and debilitating conditions in clinical medicine. Osteogrow-C is a novel osteoinductive device composed of recombinant human bone morphogenetic protein 6 (rhBMP6) delivered within autologous blood coagulum (ABC) with calcium phosphate ceramics that was proven efficacious in preclinical models of spinal fusion. This study aimed to evaluate the efficacy of Osteogrow-C in comparison to that of other osteoinductive therapies in a clinically relevant segmental defect model in rabbits. Segmental defects (15 mm) of rabbit ulna were treated with Osteogrow-C containing different synthetic ceramic particles (tricalcium phosphate [TCP] and TCP/hydroxyapatite 40%/60%), Osteogrow (rhBMP6/ABC), Infuse (rhBMP2/absorbable collagen sponge), and control implants without bone morphogenetic proteins. Defect healing was evaluated by in vivo x-ray scans 4, 8, and 17 weeks after the surgery, and animals were killed after 17 weeks for further radiographical and histological assessment. Evaluation of x-ray images, micro-computed tomography, and histological sections revealed that both Osteogrow-C formulations as well as Osteogrow and Infuse promoted healing of the ulnar segmental defect. However, radiographic scores were higher in animals treated with Osteogrow-C than those for the other used therapies. Moreover, evaluation of in vivo x-ray scans revealed that Osteogrow-C with TCP ceramics induced the most rapid defect bridging. On the other hand, control implants (ABC/TCP and ABC/biphasic calcium phosphate) promoted limited osteogenesis without defect bridging. The findings of this study suggest that Osteogrow-C is a promising safe therapeutic solution for the treatment of large bone defects, providing relief to millions of patients suffering from this debilitating condition.

rhBMP6 in autologous blood coagulum is a preferred osteoinductive device to rhBMP2 on bovine collagen sponge in the rat ectopic bone formation assay

Osteoinductive BMPs require a suitable delivery system for treating various pathological conditions of the spine and segmental bone defects. INFUSE, the only commercially available BMP-based osteoinductive device, consisting of rhBMP2 on bovine absorbable collagen sponge (ACS) showed major disadvantages due to serious side effects. A novel osteoinductive device, OSTEOGROW, comprised of rhBMP6 dispersed within autologous blood coagulum (ABC) is a promising therapy for bone regeneration, subjected to several clinical trials for diaphysial bone repair and spinal fusion. In the present study, we have examined the release dynamics showing that the ABC carrier provided a slower, more steady BMP release in comparison to the ACS. Rat subcutaneous assay was employed to evaluate cellular events and the time course of ectopic osteogenesis. The host cellular response to osteoinductive implants was evaluated by flow cytometry, while dynamics of bone formation and maintenance in time were evaluated by histology, immunohistochemistry and micro CT analyses. Flow cytometry revealed that the recruitment of lymphoid cell populations was significantly higher in rhBMP6/ABC implants, while rhBMP2/ACS implants recruited more myeloid populations. Furthermore, rhBMP6/ABC implants more efficiently attracted early and committed progenitor cells. Dynamics of bone formation induced by rhBMP2/ACS was characterized by a delayed endochondral ossification process in comparison to rhBMP6/ABC implants. Besides, rhBMP6/ABC implants induced more ectopic bone volume in all observed time points in comparison to rhBMP2/ACS implants. These results indicate that OSTEOGROW was superior to INFUSE due to ABC's advantages as a carrier and rhBMP6 superior efficacy in inducing bone.

Calcium phosphate ceramics combined with rhBMP6 within autologous blood coagulum promote posterolateral lumbar fusion in sheep

Posterolateral spinal fusion (PLF) is a procedure used for the treatment of degenerative spine disease. In this study we evaluated Osteogrow-C, a novel osteoinductive device comprised of recombinant human Bone morphogenetic protein 6 (rhBMP6) dispersed in autologous blood coagulum with synthetic ceramic particles, in the sheep PLF model. Osteogrow-C implants containing 74-420 or 1000-1700 µm ceramic particles (TCP/HA 80/20) were implanted between L4-L5 transverse processes in sheep (Ovis Aries, Merinolaandschaf breed). In the first experiment (n = 9 sheep; rhBMP6 dose 800 µg) the follow-up period was 27 weeks while in the second experiment (n = 12 sheep; rhBMP6 dose 500 µg) spinal fusion was assessed by in vivo CT after 9 weeks and at the end of the experiment after 14 (n = 6 sheep) and 40 (n = 6 sheep) weeks. Methods of evaluation included microCT, histological analyses and biomechanical testing. Osteogrow-C implants containing both 74-420 and 1000-1700 µm ceramic particles induced radiographic solid fusion 9 weeks following implantation. Ex-vivo microCT and histological analyses revealed complete osseointegration of newly formed bone with adjacent transverse processes. Biomechanical testing confirmed that fusion between transverse processes was complete and successful. Osteogrow-C implants induced spinal fusion in sheep PLF model and therefore represent a novel therapeutic solution for patients with degenerative disc disease.

Comparison of synthetic ceramic products formulated with autologous blood coagulum containing rhBMP6 for induction of bone formation

PURPOSE

Osteogrow, an osteoinductive device containing recombinant human Bone Morphogenetic Protein 6 (rhBMP6) in autologous blood coagulum, is a novel therapeutic solution for bone regeneration. This study aimed to evaluate different commercially available calcium phosphate synthetic ceramic particles as a compression-resistant matrix (CRM) added to Osteogrow implants to enhance their biomechanical properties.

METHODS

Osteogrow implants with the addition of Vitoss, ChronOs, BAM, and Dongbo ceramics (Osteogrow-C, where C stands for ceramics) were evaluated in the rodent subcutaneous ectopic bone formation assay. Osteogrow-C device was prepared as follows: rhBMP6 was added to blood, and blood was mixed with ceramics and left to coagulate. Osteogrow-C was implanted subcutaneously in the axillary region of Sprague-Dawley rats and the outcome was analyzed 21 days following implantation using microCT, histology, morphometric analyses, and immunohistochemistry.

RESULTS

Osteogrow-C implants with all tested ceramic particles induced the formation of the bone-ceramic structure containing cortical bone, the bone between the particles, and bone at the ceramic surfaces. The amount of newly formed bone was significant in all experimental groups; however, the highest bone volume was measured in Osteogrow-C implants with highly porous Vitoss ceramics. The trabecular number was highest in Osteogrow-C implants with Vitoss and ChronOs ceramics while trabeculae were thicker in implants containing BAM and Dongbo ceramics. The immunological response and inflammation were comparable among ceramic particles evaluated in this study.

CONCLUSION

Osteogrow-C bone regenerative device was effective with a broad range of commercially available synthetic ceramics providing a promising therapeutic solution for the regeneration of long bone fracture nonunion, large segmental defects, and spinal fusion surgeries.

Long-term posterolateral spinal fusion in rabbits induced by rhBMP6 applied in autologous blood coagulum with synthetic ceramics

Autologous bone graft substitute (ABGS) containing rhBMP6 in autologous blood coagulum (Osteogrow) is a novel therapeutic solution for bone regeneration. This study is aimed to investigate the long-term outcome of ABGS with synthetic ceramics (Osteogrow-C) in rabbit posterolateral spinal fusion (PLF) model. Osteogrow-C implants were implanted bilaterally between rabbit lumbar transverse processes. We compared the outcome following implantation of ABGS with ceramic particles of different chemical composition (TCP and biphasic ceramics containing both TCP and HA) and size (500–1700 µm and 74–420 µm). Outcome was analyzed after 14 and 27 weeks by microCT, histology, and biomechanical analyses. Successful bilateral spinal fusion was observed in all animals at the end of observation period. Chemical composition of ceramic particles has impact on the PLF outcome via resorption of TCP ceramics, while ceramics containing HA were only partially resorbed. Moreover, persistence of ceramic particles subsequently resulted with an increased bone volume in implants with small particles containing high proportion of HA. ABGS (rhBMP6/ABC) with various synthetic ceramic particles promoted spinal fusion in rabbits. This is the first presentation of BMP-mediated ectopic bone formation in rabbit PLF model with radiological, histological, and biomechanical features over a time course of up to 27 weeks.