Diabetes Research Institute, University of Miami School of Medicine, FL 33101, USA.
Contrast Media Mol Imaging. 2011 Jan-Feb;6(1):7-18. doi: 10.1002/cmmi.396. Epub 2010 Aug 5.
In vivo detection of transplanted stem cells is requisite for improving stem cell-based treatments by developing a thorough understanding of their therapeutic mechanisms. MRI tracking of magnetically labeled cells is non-invasive and is suitable for longitudinal studies. Molday ION Rhodamine-B™ (MIRB) is a new superparamagnetic iron oxide (SPIO) contrast agent specifically formulated for cell labeling and is readily internalized by non-phagocytic cells. This investigation characterizes mesenchymal stem cell (MSC) labeling and MR imaging properties of this new SPIO agent. Effects of MIRB on MSC viability and differentiation as well as cellular loading properties were assessed for MSC labeled with MIRB at concentrations from 5 to 100 µg Fe/ml. Labeled MSC were evaluated, in vitro, on a clinical 1.5 T MRI. Optimal scanning sequences and imaging parameters were determined based on contrast-to-noise ratio and contrast modulation. Relaxation rates (1/T(2)*) for gradient-echo sequences were approximated and an idealized limit of detection was established. MIRB labeling did not affect MSC viability or the ability to differentiate into either bone or fat. Labeling efficiency was found to be approximately 95% for labeling concentrations at or above 20 µg Fe/ml. Average MIRB per MSC ranged from 0.7 pg Fe for labeling MIRB concentration of 5 µg Fe/ml and asymptotically approached a value of 20-25 pg Fe/MSC as labeling concentration increased to 100 µg Fe/ml. MRI analysis of MIRB MSC revealed long echo time, gradient echo sequences to provide the most sensitivity. Limit of detection for gradient echo sequences was determined to be less than 1000 MSC, with approximately 15 pg Fe/MSC (labeled at 20 µg Fe/ml). These investigations have laid the groundwork and established feasibility for the use of this contrast agent for in vivo MRI detection of MSC. Properties evaluated in this study will be used as a reference for tracking labeled MSC for in vivo studies.
在体内检测移植的干细胞对于通过深入了解其治疗机制来改进基于干细胞的治疗方法是必需的。磁共振成像（MRI）追踪磁性标记的细胞是一种非侵入性的方法，适用于纵向研究。Molday ION Rhodamine-B（MIRB）是一种新型超顺磁性氧化铁（SPIO）造影剂，专门用于细胞标记，并且很容易被非吞噬细胞内化。本研究对这种新型 SPIO 造影剂标记的间充质干细胞（MSC）及其 MRI 成像特性进行了表征。研究了 MIRB 对 MSC 活力和分化的影响，以及 MIRB 浓度为 5 至 100μgFe/ml 时的细胞加载特性。用 MIRB 标记的 MSC 在临床 1.5T MRI 上进行了体外评估。根据对比噪声比和对比调制来确定最佳扫描序列和成像参数。通过近似梯度回波序列的弛豫率（1/T2*）并建立理想化的检测极限来确定弛豫率。MIRB 标记不会影响 MSC 的活力或分化为骨或脂肪的能力。标记效率约为 95%，标记浓度为 20μgFe/ml 或更高。对于标记浓度为 5μgFe/ml 的 MIRB 标记，每个 MSC 的平均 MIRB 量为 0.7pgFe，并且随着标记浓度增加到 100μgFe/ml，逐渐接近 20-25pgFe/MSC 的值。MIRB-MSC 的 MRI 分析表明，长回波时间的梯度回波序列提供了最大的灵敏度。梯度回波序列的检测极限确定为小于 1000 个 MSC，每个 MSC 约 15pgFe（标记浓度为 20μgFe/ml）。这些研究为使用这种造影剂进行体内 MRI 检测 MSC 奠定了基础并确定了可行性。本研究中评估的特性将作为体内研究中标记 MSC 跟踪的参考。
