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H. B. Raju, Y. Hu, K. R. Padgett, J. L. Goldberg; Investigation of Nanoparticles Using Magnetic Resonance Imaging After Intravitreal Injection. Invest. Ophthalmol. Vis. Sci. 2010;51(13):423.
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Magnetic nanoparticles (MNPs) may be used for delivery for cell replacement therapy, focal delivery of plasmids or drugs, and other applications. Previously, we have shown that intravitreal or anterior chamber injections of MNPs showed little to no signs of toxicity on retinal structure, photoreceptor function or interference with aqueous drainage from the eye. In the present study, we determined whether MNPs (50 nm and 4 µm in diameter) could be detected in vivo at different time points after intravitreal injection by magnetic resonance imaging (MRI).
Adult SD rats were injected intravitreally with an equal volume (3 µl) of 50 nm or 4 µm magnetic particles into the left eye, with an equal volume of PBS into the right eye (as controls). Animals were examined by MRI at 1 hr, 1 day and 5 weeks after injection. Eyes were enucleated and the brain, liver, spleen and kidney were dissected out for high-resolution ex vivo MRI scanning.
In vivo MRI, at 1 hr and 1 day, more clearly detected magnetic particles in the 4 µm group compared to the 50 nm group. 50 nm particles could be seen more clearly in ex vivo high-resolution MRI. 5 weeks after intravitreal injection, MRI still could clearly detect 4 µm particles inside the eye, but by this time point, 50 nm particles could not be detected either in vivo or ex vivo with high-resolution MRI. No magnetic particles were detected in any other organ.
Our results also suggest that MRI could be used to track MNPs in the eye. Clearance of nanoparticles varies depending on size, i.e. 50 nm particles cleared more quickly compared to 4 µm particles. Thus nanoparticles may provide advantages over micron-scale particles when considering risks associated with long-term persistence.
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