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Intracellular SPIO labeling of microglia: high field considerations and limitations for MR microscopy
Jens T Rosenberg1, Afi Sachi-Kocher, Michael W Davidson
1Chemical and Biomedical Engineering, The Florida State University, 2525 Pottsdamer Street, Tallahassee, FL 32310, USA.
Abstract:
The purpose of this study is to investigate MRI contrast as a function of magnetic field strength for microglia labeled with superparamagnetic iron oxide (SPIO) nanoparticles. A rat microglia cell line, Bv2, was incubated with SPIOs for 6 h. In two separate experiments conducted at 11.75 and 21.1 T, the impact of SPIO loading and cell count on T(1) , T(2) and T(2) * contrast were evaluated: (a) cells were incubated with 1, 2 or 5 µl of Feridex; and (b) cells incubated with 5 µl of Feridex were used to form layers of 25 000, 50 000, 100 000 or 200 000 cells. Intracellular iron was analyzed with ICP-MS and histological staining while cell viability was evaluated by Trypan blue dye exclusion. Bv2 cells displayed increases in intracellular iron concentration with SPIO exposure, with the highest labeling yielding 0.83 pg of Fe per cell. Although no differences were identified for T(1) mechanisms, both fields displayed trends toward increasing T(2) and T(2) * contrast with increasing SPIO loading or cell count, with few differences evident between fields. Bv2 cells can be labeled readily with commercially available SPIOs, with the potential of increasing the intracellular iron content over short incubation times without impacting viability. This phagocytotic cell line not only provides direct SPIO uptake but also plays a critical role in inflammation after brain injury, providing a possible neurodegeneration biomarker. With few differences between field strengths and limited ability to quantify intracellular iron content and cell count, this study demonstrates only a slight benefit of SPIO-based contrast agent at high fields based on susceptibility-based contrast and detection, necessitating unique agents for such applications.
Insights
Superparamagnetic iron oxide (SPIO) nanoparticles effectively labeled microglia cells, enhancing MRI contrast. However, high magnetic field strengths showed minimal benefit for SPIO-based contrast agents.
Area of Science:
- Biomedical Imaging
- Nanotechnology
- Cell Biology
Background:
- Microglia play a critical role in brain inflammation and injury.
- Superparamagnetic iron oxide (SPIO) nanoparticles are used as MRI contrast agents.
- Assessing SPIO effectiveness at different magnetic field strengths is crucial for developing advanced imaging techniques.
Purpose of the Study:
- To investigate MRI contrast enhancement using SPIO-labeled microglia at varying magnetic field strengths (11.75 and 21.1 T).
- To evaluate the impact of SPIO loading and cell count on MRI relaxation times (T1, T2, T2*).
- To determine the suitability of Bv2 microglia cells as a model for SPIO-based contrast agent development.
Main Methods:
- Bv2 microglia cells were incubated with SPIOs (Feridex) at different concentrations.
- Cells were analyzed for intracellular iron content using ICP-MS and histological staining.
- MRI contrast was evaluated at 11.75 T and 21.1 T based on SPIO loading and cell density.
- Cell viability was assessed using Trypan blue dye exclusion.
Main Results:
- Bv2 cells readily incorporated SPIOs, increasing intracellular iron content up to 0.83 pg Fe per cell without affecting viability.
- Increasing SPIO loading and cell count led to enhanced T2 and T2* contrast at both magnetic field strengths.
- No significant differences in T1 contrast mechanisms were observed between the field strengths.
- Minimal differences in T2/T2* contrast were noted between the 11.75 T and 21.1 T fields.
Conclusions:
- Bv2 microglia can be effectively labeled with SPIOs, offering potential as a biomarker for neurodegeneration.
- High magnetic field strengths provide only a slight benefit for SPIO-based contrast agents due to susceptibility effects.
- Development of novel contrast agents is necessary for improved SPIO detection and quantification at high fields.
