Objective:
The aim of this study was to label human umbilical cord blood mesenchymal stem cells (mscs) with poly-l-lysine (pll)-conjugated superparamagnetic iron oxide particles and to obtain magnetic resonance (mr) images of the labeled mscs' suspension at 1.5 t.
Material and methods:
Pll was conjugated with iron oxide to form superparamagnetic particles called fe(2)o(3)-pll. human umbilical cord blood mscs were isolated, purified, expanded and incubated with fe(2)o(3)-pll. prussian blue stain was performed to show intracellular iron; spectrometry was used to quantify iron uptake within cells. tetrazolium salt (mtt) assay was applied to evaluate toxicity and proliferation of mscs labeled with various concentrations of fe(2)o(3)-pll. the cell apoptosis rate was determined by annexin v/propichium iodide (pi) double staining method. vials containing cells underwent mr imaging (mri) with t(1), t(2) and t(2)* weighted mri.
Results:
Iron-containing intracytoplasmatic vesicles could be observed clearly with prussian blue staining in all samples except the unlabeled control. the iron content per cell determined by spectrometry was 64.51+/-10.32 pg. among mscs with and without labeling of various concentrations of fe(2)o(3)-pll, mtt values of light absorption had no statistically significant difference (kruskal-wallis test, chi(2)=10.35, p=.17). a concentration at 20 mug/ml of iron appeared most suitable for incubating cells. of labeled and unlabeled mscs, the early [annexin v-fluorescein isothiocyanate (fitc)-positive/pi-negative] and late (annexin v-fitc-positive/pi-positive) apoptotic cells were 10.34+/-0.43%/11.36+/-1.30% and 4.01+/-1.76%/2.98+/-1.37%, respectively, and there were no significant differences between them (p>.05). t(2) weighted image (wi) and t(2)*wi demonstrated significant decrease of signal intensity (si) in vials containing 1 x 10(6) (1 day), 1x10(6) (8 days) and 5 x 10(5) labeled cells, in comparison with unlabeled cells (p<.05). the percentage change of si (deltasi) was significantly higher in 10(6) labeled cells after 1-day culture than that in the same number of labeled cells after 8-day culture and that in 5 x 10(5) labeled cells, particularly on t(2)*wi (p<.05). among pulse sequences, t(2)*wi demonstrated the highest deltasi (p<.05).
Conclusion:
The human umbilical cord blood mscs can be labeled with fe(2)o(3)-pll without significant change in viability and apoptosis. the suspension of labeled mscs can be imaged with standard 1.5-t mr equipment.