Pathophysiologic mechanisms of biosphosphonate related osteonecrosis of the jaws

描述（由申请人提供）：双膦酸盐（bp）是治疗原发性和转移性骨癌以及骨质疏松症的常用药物。虽然bp可以改善骨密度，降低骨折风险，降低恶性肿瘤的高钙血症，但许多患者发生颌骨骨坏死。BP相关性颌骨骨坏死（BRONJ）是一种毁灭性的并发症，临床上表现为颌面部骨外露超过8周。BRONJ与严重疼痛、肿胀、感染、瘘管和颌骨骨折相关，这些都会显著影响患者的生活质量。尽管自2003年首次报道以来，BRONJ病例数量不断增加，但该疾病的病理生理机制在很大程度上仍然未知。探索BRONJ病因存在两个主要障碍。首先，我们关于牙槽骨（AB）细胞功能和分化的许多假设都是从使用其他骨骼部位细胞的实验模型中推断出来的。其次，没有完善的BRONJ动物模型来研究疾病发生和进展的体内参数。在这个应用程序中，我们解决了这两个问题。我们建立了一种分离AB骨髓基质细胞（MSCs）的方法，并证明了AB骨髓基质细胞与长骨（LB）骨髓基质细胞成骨潜能的差异，为研究颅面和阑尾骨骼的差异提供了相关的体外模型。此外，与LB相比，AB MSCs表达更低的RANKL mRNA水平，对氧化应激更敏感。已发表的研究和我们自己的初步数据表明，口腔疾病在BRONJ的病理生理中起着重要作用。令人兴奋的是，我们开发了一种啮齿类动物BRONJ模型。我们的目标是通过研究AB MSC在培养中的分化模型和BRONJ动物模型，探索BRONJ的分子和细胞机制。根据我们的初步数据，我们假设bp可以有效地抑制牙周炎症区域的AB吸收。炎症病灶周围的高氧化应激环境强烈降低AB愈合能力，增加细胞凋亡。这些过程的最终结果是AB坏死，临床表现为BRONJ。为了实现我们的目标并验证我们的假设，我们提出了三个具体目标：(1)探索双膦酸盐治疗和牙周病对大鼠BRONJ发育的必要和充分要求；(2)研究在存在或不存在双膦酸盐的情况下，AB和LB骨髓支持破骨细胞发生的能力；(3)研究双膦酸盐存在或不存在时，AB和LB间充质干细胞对氧化应激的敏感性。拟议的研究将开始揭示BRONJ的病理生理机制，并将为BP和齿科疾病参与BRONJ的发病率提供证据。了解口腔环境对氧化应激敏感的机制和骨重塑的BP抑制可能会导致新的治疗方法来减少BRONJ的频率、进展和严重程度。公共卫生相关性：双磷酸盐是用于治疗癌症患者骨转移和骨质疏松症的药物。然而，使用双膦酸盐会导致严重的口腔并发症，包括颌骨暴露、脓肿和颌骨骨折。目前还没有治疗这些并发症的方法，因为我们不了解它们的发展机制。在本应用中，我们探讨了双膦酸盐相关颌骨坏死的机制，并建立了该疾病的动物模型。这项研究的结果可能会导致新的治疗方法，可以减少BRONJ的发病率、严重程度和进展。

DESCRIPTION (provided by applicant): Bisphosphonates (BPs) are commonly used medications to treat primary and metastatic bone cancer, as well as osteoporosis. Though BPs improve bone mineral density, reduce fracture risk, and reduce hypercalcemia of malignancy, many patients develop osteonecrosis of the jaws. BP related osteonecrosis of the jaws (BRONJ) is a devastating complication, presenting as clinically exposed bone in the maxillofacial region for more than 8 weeks. BRONJ is associated with severe pain, swelling, infection, fistulae, and jaw fracture, all of which significantly impact patients' quality of life. Despite the increasing number of BRONJ cases since the first report in 2003, the pathophysiology of the disease remains largely unknown. Two major impediments in exploring BRONJ etiology exist. First, many of our assumptions concerning alveolar bone (AB) cell function and differentiation are extrapolated from experimental models using cells from other skeletal sites. Second, there is no well-established BRONJ animal model to study the in vivo parameters of disease initiation and progression. In this application, we have addressed these two gaps. We have established a method for isolating AB marrow stromal cells (MSCs) and have demonstrated differences in the osteoblastic potential of AB vs. long bone (LB) MSCs, providing a relevant in vitro model to study differences between the craniofacial and appendicular skeleton. Moreover, AB MSCs express lower RANKL mRNA levels and are more sensitive to oxidative stress than their LB counterparts. Published studies and our own preliminary data demonstrate a significant role for dental disease in the pathophysiology of BRONJ. Excitingly, we have developed a rodent model of BRONJ. Equipped both with a model to study AB MSC differentiation in culture and with a BRONJ animal model, our objective is to explore molecular and cellular mechanisms of BRONJ. Based on our preliminary data, we hypothesize that BPs robustly suppress AB resorption at the area of periodontal inflammation. The high oxidative stress environment around the inflammatory nidus strongly decreases AB healing capacity and increases cell apoptosis. The net result of these processes is AB necrosis that presents clinically as BRONJ. To achieve our objective and test our hypothesis, we propose three specific aims: (1) To explore the necessary and sufficient requirement of bisphosphonate treatment and periodontal disease for BRONJ development in the rat; (2) To investigate the ability of AB vs. LB marrow to support osteoclastogenesis in the presence or absence of bisphosphonates; and (3) To investigate the AB vs. LB MSC sensitivity to oxidative stress in the presence or absence of bisphosphonates. The proposed studies will begin uncovering the mechanisms underlying BRONJ pathophysiology and will provide evidence for BP and dental disease involvement in BRONJ incidence. Understanding the mechanisms by which the oral environment is sensitive to oxidative stress and BP inhibition of bone remodeling may lead to novel therapeutic approaches to reduce BRONJ frequency, progression, and severity. PUBLIC HEALTH RELEVANCE: Bisphosphonates are drugs used to treat bone metastasis in cancer patients and osteoporosis. However, bisphosphonate use has been associated with significant oral complications including exposure of the jaw bone, abscesses and jaw fractures. No treatment for these complications exists, because we do not understand the mechanisms of their development. In this application, we explore mechanisms of bisphosphonate related jaw necrosis and establish an animal model of the disease. Results of this research can potentially lead to novel therapeutic approaches that can reduce the incidence, severity, and progression of BRONJ.