Cell internalization of anionic maghemite nanoparticles: quantitative effect on magnetic resonance imaging

Area of Science:

• Biomedical Engineering
• Materials Science
• Nanotechnology

Background:

• Anionic iron oxide nanoparticles are utilized for biomedical applications.
• Macrophages efficiently internalize nanoparticles into endosomes.
• Intracellular nanoparticle localization affects magnetic properties.

Purpose of the Study:

• To investigate the magnetic properties of anionic maghemite nanoparticles after internalization by macrophages.
• To compare MRI contrast enhancement between intracellularly labeled macrophages and dispersed nanoparticles.
• To understand the impact of endosomal confinement on nanoparticle relaxivity.

Main Methods:

• Quantification of nanoparticle uptake using electron spin resonance (ESR).
• Acquisition of MRI spin-echo sequences with varying echo times (TEs) and repetition times (TRs).
• Comparison of contrast enhancement in agarose phantoms containing either dispersed nanoparticles or magnetically labeled macrophages.

Main Results:

• Intracellular confinement of maghemite nanoparticles in micrometric endosomes significantly decreases longitudinal relaxivity.
• A moderate decrease in transverse relaxivity was observed for intracellular nanoparticles compared to dispersed ones.
• Endosomal magnetic labeling results in negative contrast on T1-weighted images, irrespective of ferrite concentration.

Conclusions:

• The intracellular localization of anionic iron oxide nanoparticles within macrophages alters their magnetic relaxivity.
• Endosomal confinement leads to distinct MRI contrast signatures, enabling differentiation from extracellular nanoparticles.
• This finding has implications for developing targeted MRI contrast agents and understanding nanoparticle biodistribution.