铁羧葡胺标记猪间充质干细胞的体内外磁共振成像研究

In vitro and in vivo MR imaging of SHU 555A-labelled swine bone marrow mesenchymal stem cells

目的探讨铁羧葡胺-多聚赖氨酸复合物标记猪骨髓间充质干细胞（MSC）的体外和活体心脏内MR成像的特点。方法分离培养猪MSC，用含铁羧葡胺-多聚赖氨酸复合物标记细胞24h。分别于标记后0、4、8、12、16、20d行普鲁士蓝染色观察细胞内铁，原子吸收分光光度仪测定细胞内含铁量，锥虫蓝排除试验检测细胞活力。对不同时间点、不同细胞数的磁标记干细胞进行1．5T MR仪体外成像，并对植入猪心肌内的标记细胞进行体内MR成像。结果①MSC标记后见胞质中大量普鲁士蓝着色颗粒，标记率达100％，铁离子含量平均为（13．13±2．30）pg／细胞；随细胞的分裂增殖，细胞内铁离子含量逐渐减少，16d时铁离子含量下降到（0．68±0．20）pg／细胞，接近标记前水平[（0．21±0．06）pg／细胞，P〉0．051。干细胞磁标记后各时间点的锥虫蓝拒染率与未标记细胞无统计学差异（P〉0．05）。②3种成像序列中GRE T2＊WI信号改变最为明显，成像细胞数量越多，信号强度变化越明显。1×10^6个细胞进行MR成像，发现随着标记后体外培养时间延长，T2＊WI磁标低信号逐渐消失，12d以后信号强度和标记前无差异（P〉0．05）。体外MR成像最少能检测到5×10^4～1×10^5个标记的猪MSC。③标记细胞心肌内移植后1周MR成像显示低信号区。结论应用铁羧葡胺-多聚赖氨酸复合物标记猪MSC安全、高效；体外MR信号强度能一定程度上反映磁标记细胞的数量及增殖情况；1．5T临床MR成像仪可对植入心脏的磁标记细胞进行活体显像示踪。

Objective To detect the feasibility of magnetically labeled swine bone marrow mesenchymal stem cells （MSCs） with SHU 555A combined with poly-L-arginine （PLL）, under MR imaging in vitro and in vivo. Methods Swine mesenchymal stem cells were isolated and culture-expanded 3 passages in vitro, then magnetically labeled by incubation with SHU 555A （25 μg Fe/ml, Resovist, Schering） for 24 hours with 750 ng/mL poly-L-lysine （PLL; average MW_275 kDa） added 1 hour before incubation. Cellular iron incorporation and detention at 0 d, 4 d, 8 d, 12 d, 16 d, 20 d after labeling was qualitatively assessed using Prussian blue and quantified at atomic absorption spectrometry. Cell viability was assessed by trypan-blue exclusion test. Cell suspensions underwent MR imaging with T1-and T2-weighted spin-echo and fast field-echo sequences on a clinical 1.5 T MR system. At last, 1×10^6 SHU 555A labeled and unlabeled MSCs were transextracardially implanted into the infracted and normal myocardium approximately 2 week following the ligation of left anterior descending coronary artery in 1 swine respectively, and finally performed 1.5-T MRI within 1 week after infarction. Results ① Intracytoplasmic particles stained with Prussian blue stain were detected for all cells with mean cellular iron content of （13.13±2.30） pg per cell. With division of stem cells, the stained particles decreased gradually with iron content （0.68±0.20） pg per cell at 16 days after labeling, approximately to the prelabeled baseline values.（0.21±0.06） pg per cell （P 〉 0.05）. The viability of the labeled cells at various time points were not significantly different with that of nonlabeled cells （P 〉 0.05）. ② MR images showed signal intensity changed most obviouly in T2＊WI in vitro. The percentage change of signal intensity increased with increasing cell numbers, and decreased with the time. As few as 5×10^4 - 1×10^5 cells could be detected by using this approach. ③ Two injected sites containing MR-MSCs were detected in vivo, presentingas low signal intensity areas with the T2＊WI scanning sequence. Conclusion Swine bone marrow MSCs can be labeled with SHU555A-PLL and depicted with a standard 1.5-T MR imager in vitro and in vivo.