A novel treatment for bone fracture repair

骨折对那些在军事训练中遭受创伤的退伍军人来说是一个重大问题。 作为一个平民的职责或流行的传染病。甲状旁腺间歇（或每日）给药 激素（PTH）是唯一FDA批准的产生骨抑制剂以治疗骨质疏松症的药物。 PTH的骨合成代谢作用是基于激素改变全身和局部因素的能力， 在刺激破骨细胞（OCL）活性之前促进成骨细胞（OB）活性， “合成代谢窗口”对骨量和结构的积极影响，以恢复骨的机械完整性。 间歇性甲状旁腺素也被证明可以促进骨折修复早期骨痂中的软骨形成 在临床前模型中。几项临床试验也证明了骨折时间歇性PTH的骨愈合作用 网站.然而，由于潜在的不良反应，其剂量仅限于低水平和短时间内- 高钙血症和诱发骨肉瘤。我们的建议旨在阐明 骨合成代谢作用和PTH的高钙作用，以设计新的策略来提高PTH 疗法提高[Ca]激活软骨细胞和OB中的细胞外钙敏感受体（CaSRs） 促进其存活和分化，并在OCL中抑制其存活和骨吸收功能。 我们推测，间歇性PTH的高钙作用对产生 骨关节炎一类别构CaSR激动剂（或拟钙剂）已在临床上用于治疗 高甲状旁腺素和高钙血症通过加强细胞外Ca诱导的PTH分泌抑制， 甲状旁腺细胞（PTCs）。在这个新的拨款申请中，我们假设这种化合物，当与 间歇性PTH，不仅会平息PTH的高钙副作用，而且还协同作用， 通过直接激活软骨细胞、OB和OCL中的CaSRs，PTH和增强骨骼紧固。我们 假设同时进行拟钙剂治疗促进软骨向骨的转变， 通过激活软骨细胞，OB， 和/或OCL以增加骨折修复能力并同时恢复其他弱化的 骷髅目的1将确定是否同时激活PTC、软骨细胞、OB中的CaSR， 通过全身联合施用R568和PTH 1 -34的OCL消除了高钙血症，并产生更多的 与单独施用PTH 1 -34或R568相比， 经受单侧胫骨中段骨折手术的骨的恢复，以及（B）增加结构性 和对侧骨的机械强度。目标2：确定（a） 软骨细胞CaSR的表达是骨折愈合所必需的，PTH 1 -34/R568的合成代谢作用对骨折愈合的影响。 通过测试软骨细胞特异性抗体的作用， 在存在或不存在那些药物的情况下，断裂的愈伤组织上的CaSR KO;和（B）表达是否 OB和/或OCL中CaSR的激活对于PTH 1 -34/R568的骨合成代谢作用是必需的 通过比较该方案对骨折和未受伤骨骼的影响， 分别在OB或OCL中消融。目标3将描绘细胞自主机制的基础， PTH 1 -34/R568对软骨-骨转变的作用，通过检查化合物对软骨-骨转变的作用， 培养愈伤组织的增殖、存活、分化、矿化功能和信号反应 缺乏CaSR和/或PTH 1 R的软骨细胞。我们的初步研究表明，间歇性联合注射 甲状旁腺素与拟钙剂，NPS-R568，（i）预防高钙血症，（ii）增强合成代谢的影响， 骨小梁和皮质骨，（iii）促进胫骨骨折愈合，和（iv）增强转分化 将骨痂软骨细胞转化为成骨细胞。成功完成这一提案将建立一个新的 和可行的方案，以恢复骨折和再生骨在大量的VA患者。

Bone fractures pose a significant problem for veterans who suffered from traumatic injury in the line of military duty or from prevalent osteoporotic diseases as a civilian. Intermittent (or daily) administration of parathyroid hormone (PTH) is the only FDA-approved pharmaceutics that produces osteoanabolism to treat osteoporosis. The osteoanabolic action of PTH is based on the ability of the hormone to alter systemic and local factors that promote osteoblast (OB) activity before its stimulation of osteoclast (OCL) activity catches up, creating an “anabolic window” of positive effects on bone mass and structure to restore mechanical integrity of the bone. Intermittent PTH has also been shown to promote chondrogenesis in calluses at early stages of fracture repair in preclinical models. Several clinical trials also demonstrated osteoanabolism of intermittent PTH at fracture sites. Its dosing is, however, limited to a low level and a short duration due to potential adverse effects -- hypercalcemia and induction of osteosarcoma. Our proposal aims to delineate mechanisms underlying the osteoanabolic actions and the hypercalcemic effects of PTH in order to devise new strategies to enhance PTH therapy. Raising [Ca] activates the extracellular calcium-sensing receptors (CaSRs) in chondrocytes and OBs to promote their survival and differentiation and in OCLs to inhibit their survival and bone-resorbing functions. We postulate that the hypercalcemic effect of intermittent PTH is essential for the production of osteoanabolism. A class of allosteric CaSR agonist (or calcimimetics) has been used clinically to treat hyperparathyroidism and hypercalcemia by potentiating extracellular Ca-induced inhibition of PTH secretion in parathyroid cells (PTCs). In this new grant application, we postulate that this compound, when co-injected with intermittent PTH, will not only subside the hypercalcemic side effects of PTH, but also synergize the effects of PTH and enhance skeletal anabolism by activating the CaSRs in chondrocytes, OBs, and OCLs directly. We hypothesize that a concurrent calcimimetic treatment promotes chondro-to-osteo transition and enhances osteoanabolism of intermittent PTH1-34 by activating the CaSRs in chondrocytes, OBs, and/or OCLs to increase fracture repair capacity and concurrently rehabilitate other weakened skeletons. Aim 1 will determine whether simultaneously activating CaSRs in PTCs, chondrocytes, OBs, and OCLs by systemic co-administration of R568 with PTH1-34 abrogates hypercalcemia and produces more robust osteoanabolism than administration of PTH1-34 or R568 alone to (a) speed up structural and functional recovery of the bone subjected to a unilateral tibial mid-shaft fracture procedure and (b) to increase structural and mechanical strength of the contralateral bone in adult and aging mice. Aim 2: determine (a) whether the expression of chondrocytic CaSR is required for fracture healing and the anabolic effects of PTH1-34/R568 on promoting chondrocyte differentiation and their transition into OBs by testing the effects of chondrocyte-specific CaSR KO on the fractured calluses in the presence or absence of those drugs; and (b) whether the expression and activation of CaSRs in OBs and/or OCLs are essential for the osteoanabolic effects of the PTH1-34/R568 treatment by comparing the effects of this regimen on fractured and uninjured skeleton in mice with their CaSR ablated in OBs or OCLs, respectively. Aim 3 will delineate the cell-autonomous mechanisms underlying the effects of PTH1-34/R568 on the chondro-to-osteo transition by examining the effects of the compounds on the proliferation, survival, differentiation, mineralizing functions, and signaling responses in cultured callus chondrocytes lacking CaSR and/or PTH1R. Our preliminary studies showed that co-injections of intermittent PTH with a calcimimetic, NPS-R568, (i) prevent hypercalcemia, (ii) enhance anabolic effects on both trabecular and cortical bone, (iii) promote healing of tibial bone fractures, and (iv) enhance transdifferentiation of callus chondrocytes into osteoblasts in mice. Successful completion of this proposal will establish a novel and feasible regimen to rehabilitate fractured and osteoporotic bones in large populations of VA patients.