Distraction osteogenesis (DO) is a surgical technique to promote bone regeneration which may require long duration for bone consolidation. Bone marrow-derived mesenchymal stem cells (MSCs) have been applied to accelerate bone formation in DO. However, the optimal time point for cell therapy in DO remains unknown. This study sought to determine the optimal time point of cell administration to achieve early bone consolidation in DO. We hypothesized that the ratio of circulating MSCs to peripheral mononuclear cells and the level of cytokines in serum might be indicators for cell administration in DO. Unilateral tibial osteotomy with an external fixator was performed in adult Sprague Dawley rats. Three days after osteotomy, the tibia was lengthened at 0.5 mm/12 h for 5 days. At first, 5 rats were used to analyze the blood components at 6 different time points (3 days before lengthening, on the day lengthening began, or 3, 6, 10, or 14 days after lengthening began) by sorting circulating MSCs and measuring serum levels of stromal cell-derived factor 1 (SDF-1) and interleukin 1β. Then, 40 rats were used for cell therapy study. A single dose of 5 × 105 allogeneic MSCs was locally injected at the lengthening site on day 3, 6, or 10 after lengthening began, or 3 doses of MSCs were injected at the three time points. Sequential X-ray radiographs were taken weekly. Endpoint examinations included micro-computed tomography analysis, mechanical testing, histomorphometry, and histology. The number of circulating MSCs and serum level of SDF-1 were significantly increased during lengthening, and then decreased afterwards. Single injection of MSCs during lengthening phase (on day 3, but not day 6 or 10) significantly increased bone volume fraction, mechanical maximum loading, and bone mineralization of the regenerate. Triple injections of MSCs at three time points also significantly increased bone volume and maximum loading of the regenerates. This study demonstrated that bone consolidation could be accelerated by a single injection of MSCs during lengthening when the ratio of peripheral MSCs to mononuclear cells and the serum SDF-1 presented at peak levels concurrently, suggesting that day 3 after lengthening began may be the optimal time point for cell therapy to promote early bone consolidation.

中文翻译：

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在延长阶段施用同种异体间充质干细胞可加快大鼠分心成骨模型的早期骨固结。

分心成骨术（DO）是一种促进骨再生的外科手术技术，可能需要长时间进行骨固结。骨髓来源的间充质干细胞（MSCs）已应用于加速DO中的骨形成。然而，在DO中进行细胞治疗的最佳时间点仍然未知。这项研究试图确定细胞给药的最佳时间点，以在DO中实现早期骨固结。我们假设循环中的MSC与外周单个核细胞的比例以及血清中的细胞因子水平可能是DO中细胞给药的指标。成年Sprague Dawley大鼠采用外固定架进行单侧胫骨截骨术。截骨后三天，以0.5 mm / 12 h的时间将胫骨延长5天。首先，通过分类循环MSC并测量血清间质水平，使用5只大鼠在6个不同的时间点（加长前3天，加长开始当天或加长后3、6、10或14天）分析血液成分细胞衍生因子1（SDF-1）和白介素1β。然后，将40只大鼠用于细胞疗法研究。在开始延长后的第3、6或10天，在延长位点局部注射单剂量的5×105同种异体MSC，或在三个时间点注射3剂MSC。每周进行连续的X射线照相。终点检查包括微计算机断层扫描分析，机械测试，组织形态计量学和组织学。在延长过程中，循环MSC的数量和SDF-1的血清水平显着增加，然后下降。在延长阶段（第3天，但不是第6天或第10天）单次注射MSCs显着增加了骨体积分数，最大机械负荷和再生的骨矿化。在三个时间点三次注射MSCs也显着增加了骨体积和再生物的最大负荷。这项研究表明，当外周MSC与单核细胞的比例和血清SDF-1同时出现在峰值水平时，在延长过程中单次注射MSC可以加速骨巩固，这表明延长开始后的第3天可能是最佳时间细胞疗法可促进早期骨骼巩固。和骨矿化的再生。在三个时间点三次注射MSCs也显着增加了骨体积和再生物的最大负荷。这项研究表明，当外周MSC与单核细胞的比例和血清SDF-1同时出现在峰值水平时，在延长过程中单次注射MSC可以加速骨巩固，这表明延长开始后的第3天可能是最佳时间细胞疗法可促进早期骨骼巩固。和骨矿化的再生。在三个时间点三次注射MSCs也显着增加了骨体积和再生物的最大负荷。这项研究表明，当外周MSC与单核细胞的比例和血清SDF-1同时出现在峰值水平时，在延长过程中单次注射MSC可以加速骨巩固，这表明延长开始后的第3天可能是最佳时间细胞疗法可促进早期骨骼巩固。