Submitted on May 24, 2007
Accepted on September 21, 2007
In Vivo Leukocyte Labeling with Intravenous Ferumoxides/Protamine Sulfate Complex and in vitro Characterization for Cellular Magnetic Resonance Imaging
Y. Jeffrey Wu1, Leslie L. Muldoon2, Csanad Varallyay3, Sheila Markwardt4, Richard E. Jones5, and Edward A. Neuwelt6*
1 Department of Neurology, Oregon Health & Science University, Portland, Oregon, United States
2 Department of Neurology, Oregon Health & Science University, Portland, Oregon, United States; Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, Oregon, United States
3 Department of Neurology, Oregon Health & Science University , Portland, Oregon, United States
4 Research Service, Veterans Administration Medical Center, Portland, Oregon, United States
5 Research Service, Veterans Administration Medical Center, Portland, Oregon, United States; Department of Neurology, Oregon Health & Science University , Portland, Oregon, United States
6 Research Service, Veterans Administration Medical Center, Portland, Oregon, United States; Department of Neurology, Oregon Health & Science University , Portland, Oregon, United States; Department of Neurosurgery, Oregon Health & Science University, Portland, Oregon, United States
* To whom correspondence should be addressed. E-mail: neuwelte{at}ohsu.edu.
Cellular labeling with ferumoxides (Feridex IV®) superparamagnetic iron oxide nanoparticles can be used to monitor cells in vivo by magnetic resonance imaging (MRI). The objective of this study was to use histology and MRI to evaluate an in vivo, as opposed to in vitro, technique for labeling of mononuclear leukocytes as a means of tracking inflammatory processes in the brain. Long Evans rats were intravenously (IV) injected with 20 mg/kg ferumoxides, ferumoxtran-10 or ferumoxytol with or without protamine sulfate. Leukocytes and splenocytes were evaluated by cell sorting and iron histochemistry or were implanted into brain for MRI. Injection of ferumoxides/protamine sulfate complex IV resulted in iron labeling of leukocytes (ranging from 7.4±0.5% to 12.5±0.9% with average 9.2±0.8%) compared to ferumoxides (ranging from 3.9±0.4% to 6.3±0.5% with average 5.0±0.5%) or protamine sulfate alone (ranging from 0% to 0.9±0.7% average 0.3±0.3%). Cell sorting analysis indicated that iron labeled cells were enriched for cell types positive for the myelomonocytic marker (CD11b/c), the B lymphocyte marker (CD45RA) and depleted in the T cell marker (CD3). Neither ferumoxtran-10 nor ferumoxytol with protamine sulfate labeled the leukocytes. In vivo FE-Pro-loaded leukocytes and splenocytes were detected by MRI after intracerebral injection. Ferumoxides/protamine complex labeled CD45RA-positive and CD11b/c-positive leukocytes in vivo without immediate toxicity. The dose of feumoxides in this report is much higher than the approved human dose, so additional animal studies are required before this approach could be translated to the clinic. These results might provide useful information for monitoring leukocyte trafficking into the brain.
