Nakajima Arata, Shimoji Naoshi, Shiomi Koji, Shimizu Sumito, Moriya Hideshige, Einhorn Thomas A, Yamazaki Masashi
Department of Orthopedic Surgery, Chiba University Graduate School of Medicine, Japan.
J Bone Miner Res. 2002 Nov;17(11):2038-47. doi: 10.1359/jbmr.2002.17.11.2038.
Recent reports have demonstrated that intermittent treatment with parathyroid hormone (1-34) [PTH(1-34)] increases callus formation and mechanical strength in experimental fracture healing. However, little is known about the optimal dose required for enhancement of fracture repair or the molecular mechanisms by which PTH regulates the healing process. In this study, we analyzed the underlying molecular mechanisms by which PTH affects fracture healing and tested the hypothesis that intermittent low-dose treatment with human PTH(1-34) can increase callus formation and mechanical strength. Unilateral femoral fractures were produced and a daily subcutaneous injection of 10 microg/kg of PTH(1-34) was administered during the entire healing period. Control animals were injected with vehicle solution alone. The results showed that on day 28 and day 42 after fracture, bone mineral content (BMC), bone mineral density (BMD), and ultimate load to failure of the calluses were significantly increased in the PTH-treated group compared with controls (day 28, 61, 46, and 32%; day 42, 119, 74, and 55%, respectively). The number of proliferating cell nuclear antigen (PCNA)-positive subperiosteal osteoprogenitor cells was significantly increased in the calluses of the PTH-treated group on day 2, and TRAP+ multinucleated cells were significantly increased in areas of callus cancellous bone on day 7. The levels of expression of type I collagen (COLlA1), osteonectin (ON), ALP, and osteocalcin (OC) mRNA were increased markedly in the PTH-treated group and accompanied by enhanced expression of insulin-like growth factor (IGF)-I mRNA during the early stages of healing (days 4-7). The increased expression of COL1A1, ON, ALP, and OC mRNA continued during the later stages of healing (days 14-21) despite a lack of up-regulation of IGF-I mRNA. These results suggest that treatment of fractures with intermittent low dose PTH(1-34) enhances callus formation by the early stimulation of proliferation and differentiation of osteoprogenitor cells, increases production of bone matrix proteins, and enhances osteoclastogenesis during the phase of callus remodeling. The resultant effect to increase callus mechanical strength supports the concept that clinical investigations on the ability of injectable low-dose PTH(1-34) to enhance fracture healing are indicated.
近期报告显示，甲状旁腺激素（1-34）[PTH(1-34)]间歇性治疗可增加实验性骨折愈合中的骨痂形成及机械强度。然而，对于增强骨折修复所需的最佳剂量，或PTH调节愈合过程的分子机制，人们知之甚少。在本研究中，我们分析了PTH影响骨折愈合的潜在分子机制，并验证了间歇性低剂量人PTH(1-34)治疗可增加骨痂形成及机械强度这一假说。制作单侧股骨骨折模型，并在整个愈合期每日皮下注射10μg/kg的PTH(1-34)。对照动物仅注射赋形剂溶液。结果显示，骨折后第28天和第42天，与对照组相比，PTH治疗组的骨矿物质含量（BMC）、骨矿物质密度（BMD）以及骨痂的极限破坏载荷均显著增加（第28天分别增加61%、46%和32%；第42天分别增加119%、74%和55%）。在第2天，PTH治疗组骨痂中增殖细胞核抗原（PCNA）阳性的骨膜下骨祖细胞数量显著增加，在第7天，骨痂松质骨区域的抗酒石酸酸性磷酸酶（TRAP）阳性多核细胞显著增加。在愈合早期（第4 - 7天），PTH治疗组I型胶原蛋白（COL1A1）、骨连接蛋白（ON）、碱性磷酸酶（ALP）和骨钙素（OC）mRNA的表达水平显著升高，并伴有胰岛素样生长因子（IGF）-I mRNA表达增强。尽管IGF-I mRNA缺乏上调，但在愈合后期（第14 - 21天），COL1A1、ON、ALP和OC mRNA的表达持续增加。这些结果表明，间歇性低剂量PTH(1-34)治疗骨折可通过早期刺激骨祖细胞增殖和分化来增强骨痂形成，增加骨基质蛋白的产生，并在骨痂重塑阶段增强破骨细胞生成。增加骨痂机械强度的最终效应支持了对可注射低剂量PTH(1-34)增强骨折愈合能力进行临床研究的观点。
