Division of Nuclear Medicine and Molecular Imaging, Department of Imaging and Pathology, KU Leuven, Leuven, Belgium.
J Nucl Med. 2013 Mar;54(3):447-54. doi: 10.2967/jnumed.112.108316. Epub 2013 Jan 25.
Because of their extended differentiation capacity, stem cells have gained great interest in the field of regenerative medicine. For the development of therapeutic strategies, more knowledge on the in vivo fate of these cells has to be acquired. Therefore, stem cells can be labeled with radioactive tracer molecules such as (18)F-FDG, a positron-emitting glucose analog that is taken up and metabolically trapped by the cells. The aim of this study was to optimize the radioactive labeling of mesenchymal stem cells (MSCs) and multipotent adult progenitor cells (MAPCs) in vitro with (18)F-FDG and to investigate the potential radiotoxic effects of this labeling procedure with a range of techniques, including transmission electron microscopy (TEM).
Mouse MSCs and rat MAPCs were used for (18)F-FDG uptake kinetics and tracer retention studies. Cell metabolic activity, proliferation, differentiation and ultrastructural changes after labeling were evaluated using an Alamar Blue reagent, doubling time calculations and quantitative TEM, respectively. Additionally, mice were injected with MSCs and MAPCs prelabeled with (18)F-FDG, and stem cell biodistribution was investigated using small-animal PET.
The optimal incubation period for (18)F-FDG uptake was 60 min. Significant early tracer washout was observed, with approximately 30%-40% of the tracer being retained inside the cells 3 h after labeling. Cell viability, proliferation, and differentiation capacity were not severely affected by (18)F-FDG labeling. No major changes at the ultrastructural level, considering mitochondrial length, lysosome size, the number of lysosomes, the number of vacuoles, and the average rough endoplasmic reticulum width, were observed with TEM. Small-animal PET experiments with radiolabeled MAPCs and MSCs injected intravenously in mice showed a predominant accumulation in the lungs and a substantial elution of (18)F-FDG from the cells.
MSCs and MAPCs can be successfully labeled with (18)F-FDG for molecular imaging purposes. The main cellular properties are not rigorously affected. TEM confirmed that the cells' ultrastructural properties are not influenced by (18)F-FDG labeling. Small-animal PET studies confirmed the intracellular location of the tracer and the possibility of imaging injected prelabeled stem cell types in vivo. Therefore, direct labeling of MSCs and MAPCs with (18)F-FDG is a suitable technique to noninvasively assess cell delivery and early retention with PET.
由于其分化能力强，干细胞在再生医学领域引起了极大的兴趣。为了开发治疗策略，必须更多地了解这些细胞在体内的命运。因此，可以用放射性示踪剂分子（如（18）F-FDG）标记干细胞，（18）F-FDG 是一种正电子发射的葡萄糖类似物，被细胞摄取并代谢性捕获。本研究的目的是优化间充质干细胞（MSCs）和多能成体祖细胞（MAPCs）的放射性标记，用（18）F-FDG 体外标记，并采用多种技术，包括透射电子显微镜（TEM），研究该标记过程的潜在放射毒性效应。
使用小鼠 MSCs 和大鼠 MAPCs 进行（18）F-FDG 摄取动力学和示踪剂保留研究。用 Alamar Blue 试剂评估细胞代谢活性、增殖、分化和标记后的超微结构变化，分别用倍增时间计算和定量 TEM。此外，用（18）F-FDG 预先标记的 MSCs 和 MAPCs 注射小鼠，并用小动物 PET 研究干细胞的体内分布。
（18）F-FDG 摄取的最佳孵育期为 60 min。标记后 3 h 观察到明显的早期示踪剂洗脱，约有 30%-40%的示踪剂保留在细胞内。（18）F-FDG 标记对细胞活力、增殖和分化能力没有严重影响。用 TEM 观察，线粒体长度、溶酶体大小、溶酶体数量、空泡数量和平均粗面内质网宽度没有明显的超微结构变化。静脉内注射标记的 MAPCs 和 MSCs 的小动物 PET 实验显示，放射性主要在肺部积聚，细胞内的（18）F-FDG 大量洗脱。
MSCs 和 MAPCs 可以成功地用（18）F-FDG 进行分子成像标记。主要细胞特性不受严格影响。TEM 证实，（18）F-FDG 标记不会影响细胞的超微结构特性。小动物 PET 研究证实了示踪剂的细胞内位置和在体内成像注射预标记的干细胞类型的可能性。因此，直接用（18）F-FDG 标记 MSCs 和 MAPCs 是一种非侵入性评估 PET 细胞递送和早期保留的合适技术。
