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Comparison of SPIO and USPIO for in vitro labeling of human monocytes: MR detection and cell function
Raoul D Oude Engberink1, Susanne M A van der Pol, Ed A Döpp
1Image Sciences Institute, University Medical Center Utrecht, Utrecht, the Netherlands. raoul@invivonmr.uu.nl
Purpose:
To label human monocytes with superparamagnetic iron oxide (SPIO) and compare labeling efficiency with that of ultrasmall SPIO (USPIO) and evaluate the effect of iron incorporation on cell viability, migratory capacity, and proinflammatory cytokine production.
Materials And Methods:
The study was approved by the institutional ethics committee; informed consent was obtained from donors. Freshly isolated human monocytes were labeled with iron particles of two sizes, USPIOs of 30 nm and SPIOs of 150 nm, for 1.5 hours in culture medium containing 0.1, 0.5, 1.0, and 3.7 mg of iron per milliliter. Labeling efficiency was determined with relaxation time magnetic resonance (MR) imaging (4.7 T) and Prussian blue staining for presence of intracellular iron. Cell viability was monitored; migratory capacity of monocytes after labeling was evaluated by using an in vitro assay with monolayers of brain endothelial cells. Levels of proinflammatory cytokines, interleukin (IL) 1 and IL-6, were measured with enzyme-linked immunosorbent assay 24 hours after labeling. Data were analyzed with Student t test or two-way analysis of variance followed by a multiple-comparison procedure.
Results:
R2 relaxation rates increased for cell samples incubated with SPIOs, whereas rates were not affected for samples incubated with highest concentration of USPIOs. Labeling monocytes with SPIOs (1.0 mg Fe/mL) resulted in an R2 of 13.1 sec(-1) +/- 0.8 (standard error of the mean) (7 sec(-1) +/- 0.2 for vehicle-treated cells, P < .05) and had no effect on cell viability. On the basis of T2 relaxation times, the in vitro MR detection limit of 58 labeled monocytes per 0.05 microL was calculated. Migration of labeled monocytes was not different from that of vehicle-treated cells. Intracellular iron had no effect on production of IL-1 and IL-6 24 hours after labeling.
Conclusion:
In vitro labeling of human monocytes is effective by using SPIOs, not USPIOs. Incubation with SPIOs (1.0 mg Fe/mL) results in efficient labeling detectable on MR images and does not affect cellular viability and activation markers such as cell migration and cytokine production.
Insights
Superparamagnetic iron oxide (SPIO) effectively labels human monocytes for MRI detection without impacting cell function. Ultrasmall SPIO (USPIO) showed limited labeling efficiency in this study.
Area of Science:
- Biomedical Engineering
- Cell Biology
- Magnetic Resonance Imaging
Background:
- Monocyte labeling with superparamagnetic iron oxide nanoparticles (SPIONs) is crucial for in vivo tracking using magnetic resonance imaging (MRI).
- Comparing the efficacy of different SPION sizes, such as superparamagnetic iron oxide (SPIO) and ultrasmall SPIO (USPIO), is essential for optimizing labeling protocols.
Purpose of the Study:
- To evaluate the efficiency of labeling human monocytes with SPIO compared to USPIO.
- To assess the impact of iron incorporation on monocyte viability, migratory capacity, and proinflammatory cytokine production.
Main Methods:
- Human monocytes were incubated with SPIO (150 nm) and USPIO (30 nm) at various iron concentrations (0.1–3.7 mg/mL).
- Labeling efficiency was quantified using MRI relaxation time measurements and Prussian blue staining.
- Cell viability, in vitro migration, and cytokine (IL-1, IL-6) production were assessed post-labeling.
Main Results:
- SPIO labeling significantly increased R2 relaxation rates, indicating effective iron incorporation, while USPIO showed minimal effect at high concentrations.
- Optimal SPIO labeling (1.0 mg Fe/mL) enhanced MRI detectability without compromising cell viability or migratory function.
- No significant changes in IL-1 and IL-6 production were observed 24 hours after SPIO labeling.
Conclusions:
- In vitro labeling of human monocytes with SPIO is highly effective and suitable for MRI detection.
- SPIO labeling at 1.0 mg Fe/mL provides excellent contrast enhancement on MRI without adverse effects on cellular functions.
- USPIOs demonstrated lower labeling efficiency compared to SPIOs under the tested conditions.
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