Administration of allogeneic mesenchymal stem cells in lengthening phase accelerates early bone consolidation in rat distraction osteogenesis model

Abstract

Background 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. Methods 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. Results 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. Conclusion 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.

Local administration of allogeneic or autologous bone marrow-derived mesenchymal stromal cells enhances bone formation similarly in distraction osteogenesis

“…Each rat was operated on under general anesthesia with a solution of 0.2% (v/v) xylazine and 1% (v/v) ketamine in saline. A transverse 5-mm osteotomy was performed on the mid-shaft of the right tibia as previously described [1,48,49]. A monolateral external fixator (Tianjin Xinzhong Medical Devices Co., Ltd., Tianjin, China) with four stainless steel pins was used to fix the bone segments.…”

“…Micro-structural change within the distraction regeneration area in the rat was quantitatively assessed using micro-computed tomography (micro-CT) after 28 days of consolidation as previously described [1,50]. Briefly, all specimens (n = 10 per group) were imaged using a high-resolution micro-CT (Scanco Medical, Bassersdorf, Switzerland) at a custom isotropic resolution of 8 mm isometric voxel size with a voltage of 70 kV and a current of 114 mA.…”

“…Distraction osteogenesis (DO) is a powerful technique for tissue regeneration that has been commonly applied to the treatment of limb discrepancy, bone defect, nonunion, infection and malformation [1,2]. Although tremendous achievements have been made, a major limitation for its clinical application is the long treatment duration, which places great physical and economic burdens on patients [3].…”

“…Although tremendous achievements have been made, a major limitation for its clinical application is the long treatment duration, which places great physical and economic burdens on patients [3]. Multiple therapeutic strategies, such as gene therapy [4], small-molecule therapy [5], growth factor-based therapy [6], scaffold-based therapy [7,8] and stem cell-based therapy [1,9], have been developed to accelerate DO-mediated bone healing.…”

“…Recently, the authors' group reported that administration of allogeneic MSCs during the distraction phase, but not the consolidation phase, accelerated bone consolidation in a rat DO model, providing an optimized time point for stem cell therapy in DO [1]. Regarding stem cell therapy in bone healing, the literature shows various results, ranging from superior effect on bone formation to equally efficient bone regeneration using autologous MSCs compared with allogeneic MSCs [19,32].…”