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.

译文

移植干细胞的体内检测是通过全面了解其治疗机制来改善基于干细胞的治疗的必要条件。磁标记细胞的MRI跟踪是非侵入性的,适用于纵向研究。摩尔迪离子若丹明-B™(MIRB) 是一种新型的超顺磁性氧化铁 (SPIO) 造影剂,专门用于细胞标记,易于被非吞噬细胞内化。这项研究表征了这种新型SPIO试剂的间充质干细胞 (MSC) 标记和MR成像特性。MIRB对MSC活力和分化以及细胞负载特性的影响评估了用浓度为5至100 μ g Fe/ml的MIRB标记的MSC。在临床1.5 T MRI上体外评估标记的MSC。根据对比度噪声比和对比度调制确定最佳扫描序列和成像参数。近似梯度回波序列的弛豫率 (1/T(2)*),并建立了理想的检测极限。MIRB标记不会影响MSC的生存能力或分化为骨骼或脂肪的能力。发现标记浓度在20 µ g Fe/ml或高于20 µ g Fe/ml时,标记效率约为95%。每个MSC的平均MIRB范围为0.7 pg Fe,用于标记5 μ g Fe/ml的MIRB浓度,并且随着标记浓度增加到100 μ g Fe/ml,渐近地接近20-25 pg Fe/MSC的值。MIRB MSC的MRI分析显示,较长的回波时间,梯度回波序列提供了最大的灵敏度。梯度回波序列的检测限被确定为小于1000 MSC,约为15 pg Fe/MSC (标记为20μgfe/ml)。这些研究为将这种造影剂用于MSC的体内MRI检测奠定了基础并确定了可行性。在这项研究中评估的特性将用作跟踪体内研究的标记MSC的参考。

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