ABSTRACT
Objective To determine the feasibility of magnetically labeling and tracking mesenchymal stem cells(MSCs)in vitro by using a gadolinium and fluorescent bi-functionally transfection agent of polyethylenimine.Methods A gadolinium bifunctional transfection reagent complex was obtained after the linear polyethylenimine derivative(JetPEI-FluoR)was incubated with Gd-DTPA.Mesenchymal stem cells isolated from the bone marrows of SD rats were cultured and expanded.The mesenchymal stem cells were incubated with the bi-functional labeling agents.After labeling,the MSCs were examined with fluoroscope and electron microscope and the biological characters were detected including trypan blue exclusion test,MTT,and apoptosis detection.On a 1.5 T MR system,the labeled MSCs were examined with spin echo T1 WI and T2 WI and T1 measurement with mixed sequence.After labeling,the cells were cultured and undergone routine passage.Prior MR examinations were repeated for each passage of labeled cells.All data was statistically prolessed with SPSS for Windows.Results Of 5×105 MSCs incubated with the bi-functional agents,4.25×105 MSCs were successfully labeled,the percentage of labeled MSCs was 85% fluoroscopically.The high density electron particles of gadolinium observed electron microscopically existed around cellular apparatuses,especially around Golgi apparatus.In trypan blue exclusion test,the exclusion rate of labeled MSCs with incubation duration of 3,6,12,24 h was(96.55±2.90)%,(94.17±2.56)%,(97.16±3.12)% and(94.23±2.67)%,respectively.The corresponding exclusion rate of unlabeled MSCs was(95.86±2.67)%,(92.04±2.21)%,(93.38±3.64)%and(92.12±2.53)%,respectively.There was no statistical difference of trypan blue exclusion rate between labeled cells and control unlabeled cells within 24 hours of incubation(F=4.523,P＞0.05).In the proliferation test,the optical absorption value of labeled MSC with 2.5,5.0,10.0,20.0,30.0 and 40.0 μl bi-functional labeling agent was(0.1884±0.0151),(0.1878±0.0190),(0.1741±0.0160),(0.1135±0.0215),(0.1079±0.0145)and(0.0811±0.0079),respectively.The corresponding optical absorption value of unlabeled MSCs was(0.1940±0.0116).The optical absorption value of labeled cells was not affected in case of less than 30.0 μl of Gd-DTPA(q'=0.2225-0.9458,P＞0.05).The apoptosis index for labeled cells and unlabeled cells were 5.08% and 3.86%,respectively.On T1 WI,the signal intensity and T1 relaxation time of unlabeled cells and labeled cells were 240.3±24.7 and(2457±56)ms,336.2±20.7 and(1102±64)ms,respectively,and there were significant statistical difference(t=12.656,17.889,P＜0.01).The minimal amount of cells which was detectable for T1 WI was 5×103.After routine passage,the gadolinium in the cells gradually decreased and could be tracked by MRI until the fifth passage.Conclusions The gadolinium and fluorescent bi-functionally labeling rat bone marrow mesenchymal stem cell by using the transfection agent of polyethylenimine is feasible,efficient and safe.The labeled cells could be tracked in vitro on MR imaging.