科技日报讯据物理学家组织网7月17日报道，美国埃默里大学和佐治亚理工大学研究人员合作，证明让干细胞携带氧化铁纳米粒子，通过静脉注射到小鼠体内后，用磁铁能吸引这些细胞到达身体特定位置。相关论文近期将发表在纳米科技杂志《Small》上。
以往研究中也曾用过纳米粒子，但那些粒子涂层有毒，或者会改变干细胞性质。新粒子的涂层是聚乙二醇，内部为直径约15纳米的氧化铁核，能保护细胞免受伤害。“纳米粒子的涂层是独特的，因此细胞生存能力不受影响；我们也没有发现干细胞的分化能力等特征有任何改变。”论文第一作者、埃默里大学医学院医学与生物医学工程教授、心脏病学分部主管罗伯特·泰勒说。
实验所用细胞是间叶干细胞。它能很容易地从成熟组织中取得，如骨髓或脂肪，能变成骨髓、脂肪和软骨细胞，但不能变成肌肉、脑等类型的细胞。它们能分泌多种营养和抗炎症因子，在治疗心血管病或自身免疫紊乱方面是极有价值的工具。
在细胞的溶酶体中，粒子会变黏，能停驻在细胞中至少一个星期而不被觉察。研究人员检测了细胞中携带的铁成分，确定每个细胞吸收了大约150万个粒子。给干细胞“装入”氧化铁粒子后，他们分别在培养细胞和活动物身上测试了用磁力驱动细胞的能力。
在小鼠实验中，研究人员将条形稀土磁铁放在尾部靠近身体的地方，吸引注射的干细胞到达小鼠尾部，并给干细胞做了荧光染色标记用于跟踪。一般情况下，大部分间叶干细胞会在肺部或肝脏沉积下来，而使用磁铁时，到达小鼠尾部的干细胞数量是原来的6倍。此外，氧化铁粒子本身也可用于跟踪细胞在体内的进程。
“这是关键的原理实验证据。最终，我们将把这些专门用于特定肢体、异常血管，甚至心脏。”泰勒说，“下一步，我们打算重点研究在动物模型上的治疗应用，用磁铁引导这些细胞到达精确部位，影响新血管的修复和再生。”
总编辑圈点
生活中，鲜活农产品要通过长途运输而不变质，就必须对运输车辆进行改造，加装制冷或输氧等设备。医学上，纳米氧化铁粒子就是一种备受关注的运输工具，作为一种新型靶向给药系统，它可在外加磁场控制下，将药物准确运到患处，实现使命必达。然而，如果把死的药物变成了活的干细胞，并让干细胞在生物体内的长途旅行中保持活力，就必须对载体进行表面改性，以增强其稳定性和生物相容性等，这便是本成果的核心价值所在。（生物谷 Bioon.com）
生物谷推荐的英文摘要
Small DOI: 10.1002/smll.201300570
Magnetic Targeting of Human Mesenchymal Stem Cells with Internalized Superparamagnetic Iron Oxide Nanoparticles
Natalia Landázuri, Sheng Tong, Jin Suo, Giji Joseph, Daiana Weiss, Diane J. Sutcliffe, Don P. Giddens, Gang Bao, W. Robert Taylor
Cell therapies offer exciting new opportunities for effectively treating many human diseases. However, delivery of therapeutic cells by intravenous injection, while convenient, relies on the relatively inefficient process of homing of cells to sites of injury. To address this limitation, a novel strategy has been developed to load cells with superparamagnetic iron oxide nanoparticles (SPIOs), and to attract them to specific sites within the body by applying an external magnetic field. The feasibility of this approach is demonstrated using human mesenchymal stem cells (hMSCs), which may have a significant potential for regenerative cell therapies due to their ease of isolation from autologous tissues, and their ability to differentiate into various lineages and modulate their paracrine activity in response to the microenvironment. The efficient loading of hMSCs with polyethylene glycol-coated SPIOs is achieved, and it is found that SPIOs are localized primarily in secondary lysosomes of hMSCs and are not toxic to the cells. Further, the key stem cell characteristics, including the immunophenotype of hMSCs and their ability to differentiate, are not altered by SPIO loading. Through both experimentation and mathematical modeling, it is shown that, under applied magnetic field gradients, SPIO-containing cells can be localized both in vitro and in vivo. The results suggest that, by loading SPIOs into hMSCs and applying appropriate magnetic field gradients, it is possible to target hMSCs to particular vascular networks.
