In vitro characterization of two different ultrasmall iron oxide particles for magnetic resonance cell tracking

RATIONALE AND OBJECTIVES. Comparison of two different ultrasmall superparamagnetic iron oxide (USPIO) particles in terms of their intracellular cell-labeling properties of macrophages and subsequent visualization by MR imaging. MATERIALS AND METHODS. Cultures containing the macrophage cell line P-388D1 were incubated with a neutral carboxydextran-coated USPIO preparation (DDM 43/34/103) or an acidic citrate-coated USPIO (VSOP-C125). Experiments were performed in which incubation concentration and duration were varied and phagocytosis and pinocytosis suppressed by specific inhibitors. In cell culture specimens iron content was measured quantitatively and signal intensities determined by in vitro MR imaging. RESULTS. VSOP-C125 is incorporated by cells much faster than DDM 43/34/103 and produces significantly higher final intracellular iron concentrations per cell (3420 vs. 727 ng/million cells). Both preparations show similar signal-reducing effects at MR imaging relative to the Fe content per cell. Intracellular USPIO has a much lower detection threshold at MR imaging (50/80 mumol/L) than extracellular USPIO in free solution (300 mumol/L). CONCLUSIONS. Citrate-coated USPIO particles VSOP-C125 appear to have more favorable properties for magnetic labeling of macrophages than the carboxydextran-coated USPIO preparation DDM 43/34/103.