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Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

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Iron oxide–ferritin nanocages

Fn-Fe nanocages
, PhD
National Center for Biotechnology Information, NLM, NIH, Bethesda, MD

Created: ; Last Update: August 27, 2012.

Chemical name:Iron oxide–ferritin nanocages
Abbreviated name:Fn-Fe nanocages
Agent category:Polypeptide nanoparticle
Target category:Non-targeted
Method of detection:Magnetic resonance imaging (MRI)
Source of signal:Iron oxide
  • Checkbox In vitro
  • Checkbox Rodents
Structure is not available in PubChem.



Magnetic resonance imaging (MRI) maps information about tissues spatially and functionally. Protons (hydrogen nuclei) are widely used to create images because of their abundance in water molecules, which comprise >80% of most soft tissues. The contrast of proton MRI images depends mainly on the nuclear density (proton spins), the relaxation times of the nuclear magnetization (T1, longitudinal; T2, transverse), the magnetic environment of the tissues, and the blood flow to the tissues. However, insufficient contrast between normal and diseased tissues requires the use of contrast agents. Most contrast agents affect the T1 and T2 relaxation times of the surrounding nuclei, mainly the protons of water. T2* is the spin–spin relaxation time composed of variations from molecular interactions and intrinsic magnetic heterogeneities of tissues in the magnetic field (1). Cross-linked iron oxide nanoparticles and other iron oxide formulations affect T2 primarily and lead to a decreased signal. On the other hand, paramagnetic T1 agents, such as gadolinium (Gd3+) and manganese (Mn2+), accelerate T1 relaxation and lead to brighter contrast images.

Endothelial cells are important cells in inflammatory responses (2, 3). Bacterial lipopolysaccharides, viruses, inflammation, and tissue injury increase secretion of tumor necrosis factor α (TNFα), interleukin-1 (IL-1), and other cytokines and chemokines. Emigration of leukocytes from blood is dependent on their ability to adhere to endothelial cell surfaces. Inflammatory mediators and cytokines induce chemokine secretion from endothelial cells and other vascular cells and increase their expression of cell-surface adhesion molecules, such as intracellular adhesion molecule-1, vascular cell adhesion molecule-1, integrins, and selectins. Chemokines are chemotactic to inflammatory cells (such as leukocytes and macrophages) attracting them to sites of inflammation and tissue injury. Under atherogenic conditions, deposition of lipids on the endothelial cell surfaces of the aorta and inflammatory cells leads to the development of atherosclerotic plaques (4), which may erode and rupture.

Ferritin (Fn) is composed of 12 or 24 subunits of heavy and/or light chains, which self-assemble to form a cagelike nanoparticle (nanocage) at physiological pH (7.4) with internal and external diameters of 8 nm and 12 nm for the 24 subunit Fn (5-7), respectively. There are four or eight ion channels for directing Fe2+ ions to multiple Fe2+/O oxidoreductase (“ferroxidase”) sites in the heavy chains for Fe2O3•H2O deposition in the Fn cavity. The ion channels also control reduction, dissolution, and exit of Fe2+ from the mineral with gated pores on the surface of Fn cages. Fe2+ ions are required for protein cofactor synthesis and anti-oxidant activity after stress. Most ferritins are intracellular and tissue-specific. For applications, the outer surface of Fn can be chemically or genetically modified with ligands, and the cavity of Fn can capture metal ions with high affinity (8). Uchida et al. (9) loaded iron oxide into the cavities of human heavy chain Fn (Fn-Fe) nanocages to study the in vitro uptake of Fn-Fe nanocages by macrophages. Fn-Fe nanocages have been studied for MRI of vascular macrophages in atherosclerotic plaques in mice (10).



Recombinant human Fn subunits (heavy chains) were purified from transfected Escherichia coli cell lysates. For cage mineralization, ammonium iron(II) sulfate hexahydrate (12.5 mM) and hydrogen peroxide (4.17 mM) solutions (7.9 ml each) were added simultaneously to a solution (10 ml) of Fn nanocages (19.8 nmol, pH 8.5) over a period of ~50 min at 65°C (9). After the mineralization procedure, sodium citrate (60 mmol) was added to chelate any remaining free Fe. After dialysis, Fn-Fe nanocages were purified with column chromatography. There were ~3,000-5,000 Fe molecules per nanocage. The diameters of Fn-Fe nanocages were determined with dynamic light scattering and transmission electron microscopy (TEM) to be 13.5 nm and 12 nm, respectively. The average size of iron oxide particles inside the cage was determined with TEM to be 5.9 ± 0.9 nm. R1 and R2 relaxivity values (1.5 T) of Fn-Fe nanocages were 8.4 mM-1s-1 and 93 mM-1s-1, respectively. These values were similar to those of Ferumoxides and Ferumoxtran-10.

In Vitro Studies: Testing in Cells and Tissues


Uchida et al. (9) performed cellular uptake studies of Fn-Fe nanocages (0.165 mg Fe/ml), Ferumoxides (0.165 mg Fe/ml), and Ferumoxtran-10 (0.165 mg Fe/ml) in murine macrophage cells (RAW). Internalization of Fn-Fe nanocages by RAW cells was similar to that of Ferumoxides as measured with Prussian blue staining of Fe after 24 h of incubation, whereas Ferumoxtran-10 showed little staining at the same time point. Quantitative analysis of Fe uptake as measured with inductively coupled plasma mass spectrometry showed that cellular uptake values were 116 pg Fe/cell, 152 pg Fe/cell, and 3 pg Fe/cell at 72 h of incubation for Fn-Fe nanocages, Ferumoxides, and Ferumoxtran-10, respectively. There were slight decreases (~10%) in cell viability of treated RAW cells, but these decreases were not statistically significant (P > 0.05).

Animal Studies



Terashima et al. (10) performed MRI (7 T) of macrophages in atherosclerotic carotid arteries in streptozotocin (STZ)-induced diabetic mice. At day 14 after STZ injection, the left common carotid artery (LCA) was ligated in 5 mice and sham-operated in 3 mice. Fn-Fe nanocages (25 mgFe/kg) were injected intravenously. MRI images of both LCA and right common carotid artery (RCA) were obtained at 24 h and 48 h after injection. There was a clear T2* signal loss in the macrophage-rich ligated LCA, but not in the control RCA or in either artery in sham-operated mice. Quantitative analysis showed that the T2*-induced reduction in lumen contrast was significant at both 24 h and 48 h in the ligated LCA compared to contralateral RCA and sham controls (P < 0.01). Immunohistochemical analysis showed macrophage infiltration in the ligated LCA but not in the non-ligated RCA. Fn-Fe nanocages were co-localized with macrophages in the neointima of the ligated LCA but not in the RCA or sham-operated arteries.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

NIH Support

R01 HL078678, R21 EB005364


Wang Y.X., Hussain S.M., Krestin G.P. Superparamagnetic iron oxide contrast agents: physicochemical characteristics and applications in MR imaging. Eur Radiol. 2001;11(11):2319–31. [PubMed: 11702180]
Cybulsky M.I., Gimbrone M.A. Jr. Endothelial expression of a mononuclear leukocyte adhesion molecule during atherogenesis. Science. 1991;251(4995):788–91. [PubMed: 1990440]
Lowe J.B. Glycosylation in the control of selectin counter-receptor structure and function. Immunol Rev. 2002;186:19–36. [PubMed: 12234359]
Libby P. Inflammation in atherosclerosis. Nature. 2002;420(6917):868–74. [PubMed: 12490960]
Maham A., Tang Z., Wu H., Wang J., Lin Y. Protein-based nanomedicine platforms for drug delivery. Small. 2009;5(15):1706–21. [PubMed: 19572330]
Uchida M., Kang S., Reichhardt C., Harlen K., Douglas T. The ferritin superfamily: Supramolecular templates for materials synthesis. Biochim Biophys Acta. 2010;1800(8):834–45. [PMC free article: PMC3763752] [PubMed: 20026386]
Theil E.C. Ferritin protein nanocages use ion channels, catalytic sites, and nucleation channels to manage iron/oxygen chemistry. Curr Opin Chem Biol. 2011;15(2):304–11. [PMC free article: PMC3074017] [PubMed: 21296609]
Uchida M., Flenniken M.L., Allen M., Willits D.A., Crowley B.E., Brumfield S., Willis A.F., Jackiw L., Jutila M., Young M.J., Douglas T. Targeting of cancer cells with ferrimagnetic ferritin cage nanoparticles. J Am Chem Soc. 2006;128(51):16626–33. [PubMed: 17177411]
Uchida M., Terashima M., Cunningham C.H., Suzuki Y., Willits D.A., Willis A.F., Yang P.C., Tsao P.S., McConnell M.V., Young M.J., Douglas T. A human ferritin iron oxide nano-composite magnetic resonance contrast agent. Magn Reson Med. 2008;60(5):1073–81. [PubMed: 18956458]
Terashima M., Uchida M., Kosuge H., Tsao P.S., Young M.J., Conolly S.M., Douglas T., McConnell M.V. Human ferritin cages for imaging vascular macrophages. Biomaterials. 2011;32(5):1430–7. [PMC free article: PMC3012961] [PubMed: 21074263]
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