Prevention of Medication-Related Osteonecrosis of the Jaw in a Rat Animal Model

Medication-related osteonecrosis of the jaw (MRONJ) still poses an enigma for clinicians and researchers alike, with a pathogenesis that is still shrouded in mystery. MRONJ is known to occur in patients taking oral or intravenous bisphosphonates following an invasive dental procedure of the bone yet, can also present rarely without any obvious inciting trauma. At present, there is no accepted preventative intervention of the the condition however, a variety of novel methods have been proposed ranging from the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) to the use of platelet rich fibrin (PRF) once MRONJ occurs. Currently, clinicians rely on prevention of the condition which revolves around identification of at-risk patients and minimization of exodontia or traumatic dental procedures involving bone after the commencement of bisphosphonate therapy. If MRONJ occurs, treatment is then dictated by the degree of bone exposure and spread to adjacent structures, through the use of antibiotics, antimicrobial mouthrinses or finally, surgery¹. This study evaluated the efficacy of a novel polyethylene glycol-heparin hydrogel² (starPEG-heparin) incorporating arginylglycylaspartic acid (RGD) coupled with rhBMP-2 for the prevention of MRONJ development at the time of dentoalveolar surgery. Twenty-four (24) skeletally mature rats were divided into three equal groups (n=8) receiving two doses of intravenous zoledronic acid (0.1mg/Kg) at weeks two and five of the housing period prior to surgery. In all animals, the right first molar of the mandible was extracted and the gingiva sutured close using 6/0 prolene. Group 1 animals had the sockets left empty following extraction, while those in group 2 had starPEG-heparin/RGD hydrogel (15μL) without rhBMP-2 placed into the extraction socket. Animals in group 3 had starPEG-heparin /RGD hydrogel (15μL) with rhBMP-2 (5μg) placed in the extraction socket. Eight weeks after surgery specimens containing the right lower mandibular socket and contralateral equivalent were harvested and analyzed. Levels of c-terminal telopeptide (CTX) from serum taken periodically from the animals were evaluated using enzyme linked immunosorbent assays (ELISA). This demonstrated a linear downward trend in the bone turnover from week 1 to the final week of housing confirming the efficacy of the administered zoledronic acid. µCT analysis of samples showed a greater degree of bone formation in group 3 and the least bone formation in Group 1, as expected (P <0.05). Histological analysis of samples using H&E staining from group 1 displayed empty lacunae, or areas of karyorrhexis and pyknosis in the bone surrounding the extraction socket, consistent with MRONJ. Tartrate resistant acid phosphatase staining displayed an increase in osteoclastic action in groups 2 and 3 compared to group 1 (P <0.05). Although, increased angiogenesis was seen in groups 2 and 3 compared to group 1 throughout all the angiogenesis markers (anti-CD31, anti-CD34, anti-Von Willebrands Factor), these results were not significant. Scanning electron microscopic analysis of samples confirmed increased osteocyte density surrounding the extraction socket in groups 2 and 3 compared to group 1 (P <0.05). These results indicate that the use of a starPEG-heparin/RGD hydrogel combined with rhBMP-2 can stimulate increased osteoclastic action, localized angiogenesis and increased bone healing compared to both hydrogel-alone, or no intervention in a MRONJ rat animal model. Further work is required to evaluate if this novel intervention is translatable to an animal model with bone biology more similar to the human species.

1. Ruggiero, Salvatore L., et al. "American Association of Oral and Maxillofacial Surgeons position paper on medication-related osteonecrosis of the jaw—2014 update." Journal of Oral and Maxillofacial Surgery 72.10 (2014): 1938-1956.
2. Freudenberg, Uwe, et al. "A star-PEG–heparin hydrogel platform to aid cell replacement therapies for neurodegenerative diseases." Biomaterials 30.28 (2009): 5049-5060.