Cell therapy based on human adipose derived stem cells (hADSCs) is a known potential therapeutic approach to induce angiogenesis in ischemic diseases. However, the therapeutic efficacy of direct hADSC injection is limited by a low cell viability and poor cell engraftment after administration. To improve the outcomes of this kind of approach, various types of nanoparticles have been utilized to improve the therapeutic efficacy of hADSC transplantation. Despite their advantages, the adverse effects of nanoparticles, such as genetic damage and potential oncogenesis based on non-degradable property of nanoparticles prohibit the application of nanoparticles toward the clinical applications. Herein, we designed a transition metal based inorganic nanocluster able of pH-selective degradation (ps-TNC), with the aim of enhancing an hADSC based treatment of mouse hindlimb ischemia. Our ps-TNC was designed to undergo degradation at low pH conditions, thus releasing metal ions only after endocytosis, in the endosome. To eliminate the limitations of both conventional hADSC injection and non-degradable property of nanoparticles, we have collected conditioned medium (CM) from the ps-TNC treated hADSCs and administrated it to the ischemic lesions. We found that intracellular increment of transition metal ion upregulated the hypoxia-inducible factor 1α, which can induce vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) expressions. Based on the molecular mechanism, the secretion of VEGF and bFGF by ps-TNC treated hADSCs showed a significant improvement compared to that of untreated cells. Injecting the CM collected from ps-TNC treated hADSCs into the mouse hindlimb ischemia model (ps-TNC-CM group) showed significantly improved angiogenesis in the lesions, with improved limb salvage and decreased muscle degeneration compared to the group injected with CM collected from normal hADSCs (CM group). This study suggests a novel strategy, combining a known angiogenesis molecular mechanism with both an improvement on conventional stem cell therapy and the circumvention of some limitations still present in modern approaches based on nanoparticles.

中文翻译：

---

利用 pH 敏感的无机纳米团簇调节细胞内过渡金属离子水平，通过富集从人类脂肪干细胞中提取的条件培养基来改善治疗性血管生成

基于人类脂肪干细胞（hADSC）的细胞疗法是一种已知的诱导缺血性疾病血管生成的潜在治疗方法。然而，直接注射 hADSC 的治疗效果受到细胞活力低和给药后细胞植入差的限制。为了改善这种方法的结果，各种类型的纳米颗粒已被用来提高 hADSC 移植的治疗效果。尽管纳米颗粒具有优点，但其不利影响，例如基于纳米颗粒不可降解特性的遗传损伤和潜在的肿瘤发生，阻碍了纳米颗粒的临床应用。在此，我们设计了一种能够进行 pH 选择性降解的基于过渡金属的无机纳米簇 (ps-TNC)，旨在增强基于 hADSC 的小鼠后肢缺血治疗。我们的 ps-TNC 被设计为在低 pH 条件下发生降解，因此仅在内体中进行胞吞作用后才释放金属离子。为了消除传统 hADSC 注射和纳米颗粒不可降解特性的局限性，我们从 ps-TNC 处理的 hADSC 中收集了条件培养基 (CM)，并将其施用到缺血性病变处。我们发现细胞内过渡金属离子的增加上调缺氧诱导因子1α，从而诱导血管内皮生长因子（VEGF）和碱性成纤维细胞生长因子（bFGF）的表达。基于分子机制，ps-TNC处理的hADSCs的VEGF和bFGF的分泌与未处理的细胞相比显示出显着的改善。将从 ps-TNC 处理的 hADSC 收集的 CM 注射到小鼠后肢缺血模型（ps-TNC-CM 组）中，与注射从正常人收集的 CM 的组相比，病变中的血管生成显着改善，肢体挽救得到改善，肌肉退化减少hADSC（CM 组）。这项研究提出了一种新策略，将已知的血管生成分子机制与传统干细胞疗法的改进相结合，并规避基于纳米粒子的现代方法中仍然存在的一些局限性。