Direct labeling of hMSC with SPIO: the long-term influence on toxicity, chondrogenic differentiation capacity, and intracellular distribution.

<bold>Purpose: </bold>The purpose of this study was to evaluate the long-term cellular toxicity, labeling efficiency, chondrogenic differentiation capacity, and intracellular distribution following direct superparamagnetic iron oxide (SPIO) nanoparticle labeling of human mesenchymal stem cells (hMSCs) in the absence of transfection agents.<bold>Procedures: </bold>hMSCs were incubated with a SPIO, Ferucarbotran, at concentrations of 0, 1, 10, and 100 μg Fe/ml for 24 or 72 h. The cell granularity and size change, reactive oxygen species generation, and mitochondria membrane potential were measured by flow cytometry. The differentiation capacity of the cells into chondrocytes was determined by Alcian blue and Safranin-O staining, immunocytochemical analysis, and reverse transcription polymerase chain reaction.<bold>Results: </bold>The intracellular distribution of the internalized particles was visualized via confocal microscopy. No significant difference was found in the toxicity of labeled cells relative to controls. Successful chondrogenesis of Ferucarbotran-labeled hMSCs was confirmed. The intracellular SPIO nanoparticles were located within the lysosomes.<bold>Conclusions: </bold>In conclusion, we have demonstrated the feasibility of direct labeling with Ferucarbotran without impairment of cellular function, toxicity, or inhibition of differentiation capacity. Furthermore, lysosomal metabolism takes place after intracellular uptake of Ferucarbotran. [ABSTRACT FROM AUTHOR]