Effects of Macrophage Depletion and Transplantation on Bisphosphonate-related Osteonecrosis of the Jaw-like Lesions in Mice

Abstract Background: Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a potentially intractable disease with no definitive pathophysiology and treatment and prevention strategies. Cell-based therapy is one of the useful methods for resolving intractable diseases. This study aimed to investigate whether time-selective depletion and transplantation of macrophages worsens and ameliorates, respectively, BRONJ-like lesions in mice. Methods: A murine model of high-prevalence BRONJ-like lesions in combination with zoledronate/chemotherapeutic drug administration and tooth extraction was created according to our previous studies. Daily submucosal administration of clodronate-loaded liposomes and systemic transplantation of cultured M2 macrophages induced by macrophage colony-stimulation factor and interleukin-4 and interleukin-10 were performed immediately after tooth extraction. Spleens, femora, tibiae, and maxillae were dissected 2 weeks after extraction to evaluate BRONJ-like lesions and systemic conditions by micro-computed tomography analysis, followed by histomorphometric and immunofluorescent analyses, and serum was assessed with ELISA. Results: Depletion of macrophages significantly decreased the numbers of local and systemic macrophages, which markedly worsened osseous healing with increased necrotic bone and empty lacunae and soft tissue healing with decreased collagen production and increased infiltration of polymorphonuclear cells. Interestingly, depletion of macrophages significantly shifted macrophage polarization to M1 macrophages by increased M1 macrophages and decreased M2 macrophages. On the other hand, transplantation of M2 macrophages significantly increased the number of local macrophages, but not systemic macrophages, resulting in amelioration and/or cure of early-stage BRONJ-like lesions by promoting osseous and soft tissue healing, with increased distributions of blood and lymphatic vessels and shifting macrophage polarization to M2 macrophages in the connective tissue of the early stages of BRONJ-like lesions. Conclusions: These data demonstrated that polarization shifting of macrophages is one of the essential factors for development or healing of BRONJ. Cell-based therapy using M2 macrophages could become a useful treatment and/or prevention strategy for BRONJ if safe procedures are established.