Background:

Tendon-bone interface (TBI) healing is a clinical dilemma that is closely relevant to new bone formation and remodeling at the repair site. Previous studies showed that metformin is an osteogenic inducer for stem cells in vitro and capable of stimulating bone regeneration in vivo.

Hypothesis:

Metformin would be effective for promoting TBI healing by enhancing new bone formation and remodeling.

Study Design:

Controlled laboratory study.

Methods:

Canine bone marrow stem cells (BMSCs) were cultured with various concentrations of metformin (0, 10, 50, 100, 200 μM). The effect of metformin on the osteogenic differentiation of canine BMSCs was evaluated via alizarin red staining and osteogenic gene expression. Eighteen mature beagles were included in a bilateral Achilles tendon–calcaneus (ATC) interface injury model. The right interface was reattached via surgical repair only, while the left was surgically reattached after implanting a fibrin glue containing metformin. At postoperative week 4 or 8, the healing quality of the wounded ATC interfaces was evaluated.

Results:

In vitro experiments determined that metformin was an osteogenic inducer for canine BMSCs. In vivo experiments showed that the metformin-treated ATC interfaces were repaired with significantly greater failure load and stiffness than was the no-metformin control site (P < .05 for all). Micro–computed tomography analysis showed that the metformin-treated specimens presented significantly higher bone volume/total volume and trabecular thickness than did the no-metformin control specimens (P < .05 for all), as confirmed via hematoxylin and eosin staining. Immunohistochemical staining showed that significantly more osteocalcin-positive cells were located at the newly formed bones treated with metformin than at the no-metformin control site at week 4 (P < .05). Masson trichrome staining showed that significantly more oriented collagen fibers anchored into the newly formed bone of the metformin-treated site than the no-metformin control site (P < .05).

Conclusion:

Metformin induced the osteogenesis of canine BMSCs in vitro, and local administration of metformin provided an improvement of bone microarchitecture at the calcaneus as well as an increase in the tensile properties of the repaired ATC interfaces in canines.

Clinical Relevance:

Findings of the study indicate that local administration of metformin may be an effective strategy for TBI healing in clinic.

中文翻译：

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局部给药二甲双胍可改善犬跟腱-跟骨界面破裂愈合过程中的骨微结构和生物力学特性

背景：

肌腱-骨界面 (TBI) 愈合是一种临床困境，与修复部位的新骨形成和重塑密切相关。先前的研究表明，二甲双胍在体外是干细胞的成骨诱导剂，能够在体内刺激骨再生。

假设：

二甲双胍可通过促进新骨形成和重塑来有效促进 TBI 愈合。

学习规划：

受控实验室研究。

方法：

犬骨髓干细胞 (BMSCs) 与不同浓度的二甲双胍 (0, 10, 50, 100, 200 μM) 一起培养。通过茜素红染色和成骨基因表达评估二甲双胍对犬骨髓间充质干细胞成骨分化的影响。18 只成熟的小猎犬被纳入双侧跟腱-跟骨 (ATC) 界面损伤模型。右侧接口仅通过手术修复重新连接，而左侧接口在植入含有二甲双胍的纤维蛋白胶后通过手术重新连接。在术后第 4 周或第 8 周，评估受伤的 ATC 接口的愈合质量。

结果：

体外实验确定二甲双胍是犬骨髓间充质干细胞的成骨诱导剂。体内实验表明，经二甲双胍处理的 ATC 界面修复后的失效载荷和刚度明显高于未使用二甲双胍的对照部位（所有P < .05）。显微计算机断层扫描分析显示，经苏木精和伊红染色证实，二甲双胍治疗的标本的骨体积/总体积和骨小梁厚度显着高于未使用二甲双胍的对照标本（所有P < .05）。免疫组化染色显示，在第 4 周，用二甲双胍处理的新形成的骨骼中的骨钙素阳性细胞明显多于未使用二甲双胍的对照部位（P< .05)。Masson 三色染色显示，与未使用二甲双胍的对照部位相比，二甲双胍治疗部位新形成的骨中锚定的定向胶原纤维明显更多 ( P < .05)。

结论：

二甲双胍在体外诱导犬骨髓间充质干细胞的成骨，二甲双胍的局部给药改善了跟骨的骨微结构，并增加了修复的犬 ATC 界面的拉伸特性。

临床相关性：

研究结果表明，二甲双胍的局部给药可能是临床治疗 TBI 的有效策略。