Role of oral mucosa in bisphosphonate related osteonecrosis of the jaw

描述（由申请人提供）：双膦酸盐（bp）是一种有效的抗骨吸收药物，广泛用于治疗骨质疏松症和转移性骨病。长期服用bp的人患颌骨骨坏死（ONJ）的风险更高。双膦酸盐相关性颌骨骨坏死（BRONJ）的病因被认为是由于其对破骨细胞的抑制作用，破骨细胞是骨重塑和愈合的重要骨吸收细胞。然而，仅凭这一点不足以解释BRONJ的病理生理，因为口腔环境中的伤口愈合是一个多因素和复杂的过程，需要包括口腔粘膜细胞在内的不同细胞类型的协调努力。BRONJ通常发生在以前拔牙或其他手术干预的部位，临床定义为暴露的坏死骨伴未愈合和开放的口腔黏膜。尽管如此，口腔黏膜在BRONJ病理生理中的确切作用尚不完全清楚。为了更好地了解bp对口腔黏膜细胞的影响，我们建立了三维口腔黏膜伤口愈合模型，发现bp能显著抑制角质形成细胞的增殖和迁移。与离体模型类似，我们的体外研究也显示bp对原代正常人口腔角质形成细胞（NHOK）的增殖和迁移有明显的抑制作用。我们最近建立的再现BA-ONJ的动物模型也显示了伤口愈合受损，并伴有潜在的暴露和坏死骨。根据我们的初步数据，我们假设BP通过靶向甲羟戊酸途径直接损害口腔黏膜的再上皮化（如增殖和迁移）。为此，我们提出：1)在体外和离体实验中研究法尼基焦磷酸合成酶（FPPS）和RhoA在bp处理的NHOK中的作用；2)在动物模型中研究伤口愈合相关蛋白的空间表达模式。临床结果和益处大于使用bp的不良影响。因此，bp将继续用于治疗骨质疏松症和转移性骨病，正确治疗和预防BRONJ仍将是牙科和医疗实践中重要的临床问题。我们的研究将为BRONJ以口腔特异性方式发生的原因提供可能的解释，并为今后BRONJ的管理和治疗的临床应用奠定基础。当前项目的成功完成可能会导致R01拨款机制，重点是将研究结果应用于临床环境。

DESCRIPTION (provided by applicant): Bisphosphonate (BPs) are potent anti-resorptive agents that are widely used to treat osteoporosis and metastatic bone diseases. Long-term users of BPs are at the higher risk of developing osteonecrosis of the jaw (ONJ). The etiology of bisphosphonate-related osteonecrosis of the jaw (BRONJ) is thought to be due to its inhibitory effects on osteoclasts, bone resorbing cells important for bone remodeling and healing. However, this alone is insufficient to explain the pathophysiology of BRONJ because wound healing in oral environment is a multi-factorial and complex process that requires orchestrated efforts of different cell types including oral mucosal cells. BRONJ commonly occurs at the site of previous tooth extraction or other surgical interventions and is clinically defined as exposed necrotic bone with unhealed and open oral mucosa. Nonetheless, the exact role of oral mucosa in the pathophysiology of BRONJ is not fully understood. To better understand effects of BPs on oral mucosal cells, we established a 3 dimensional (3D) oral mucosal wound healing model and found that BPs drastically inhibit proliferation and migration of keratinocytes. Similar to this ex vivo model, our in vitro studies also showed the marked inhibition of proliferation and migration by BPs specific to primary normal human oral keratinocytes (NHOK). Our recently developed animal model which recapitulates BA-ONJ also revealed the impaired wound closure with underlying exposed and necrotic bone. Based on our preliminary data, we hypothesize that BP directly impairs reepithelialization (e.g., proliferation and migration) of oral mucosa by targeting the mevalonate pathway. To this end, we propose 1) to examine roles of farnesyl pyrophosphate synthase (FPPS) and RhoA in BP-treated NHOK in vitro and ex vivo, and 2) to examine spatial expression patterns of wound healing-associated proteins in vivo using animal model. The clinical outcomes and benefits outweigh the adverse effects of using BPs. Therefore, BPs will continually be used to manage osteoporosis and metastatic bone diseases, and proper treatment and prevention of BRONJ will remain important and relevant clinical issues in dental and medical practices. Our proposal will provide possible explanations as to why BRONJ occurs in oral-cavity specific manner, and will establish a basis for the future clinical applications in managing and treating BRONJ. Successful completions of the current project will likely lead to R01 grant mechanism focusing on the application of findings to the clinical settings. PUBLIC HEALTH RELEVANCE: With the increasing use of bisphosphonates due to its effectiveness in multiple clinical settings, bisphosphonate-related osteonecrosis of the jaw (BRONJ) has been surfaced as a significant dental and medical problem because no definitive prevention and treatment are currently available. Although BRONJ is clinically defined as exposed bone with unhealed and opened overlaying oral mucosa, the exact role of oral mucosa in the pathophysiology of BRONJ is not fully understood. In this proposal, we will investigate direct effects of bisphosphonates on the oral mucosal cells, and our results are expected to contribute significantly on managing long-term bisphosphonate users by improving treatment and prevention modalities.