Background

[PubMed]

Optical fluorescence imaging is increasingly used to monitor biological functions of specific targets in small animals (1-3). However, the intrinsic fluorescence of biomolecules poses a problem when fluorophores that absorb visible light (350–700 nm) are used. Near-infrared (NIR) fluorescence (700–1,000 nm) detection avoids the background fluorescence interference of natural biomolecules, providing a high contrast between target and background tissues. NIR fluorophores have a wider dynamic range and minimal background as a result of reduced scattering compared with visible fluorescence detection. They also have high sensitivity, resulting from low fluorescence background, and high extinction coefficients, which provide high quantum yields. The NIR region is also compatible with solid-state optical components, such as diode lasers and silicon detectors. NIR fluorescence (NIRF) imaging is becoming a noninvasive alternative to radionuclide imaging in small animals (4).

Endothelial cells are important cells in inflammatory responses (5, 6). 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 (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 (7), which may erode and rupture.

Ferritin (Fn) is composed of 24 subunits of heavy and 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 (8, 9), respectively. 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 (10). Terashima et al. (11) chemically coupled Cy5.5 onto human heavy chain Fn (Cy5.5-Fn) nanocages. Cy5.5-Fn nanocages have been studied for NIRF imaging of vascular macrophages in atherosclerotic plaques in mice.

Synthesis

[PubMed]

Recombinant human Fn subunits were purified from transfected Escherichia coli cell lysates. Cy5.5-Fn was prepared by incubation of Cy5.5-NHS ester with Fn (pH 8.2) for 1 h at room temperature, followed by overnight incubation at 4°C. Cy5.5-Fn was isolated with column chromatography (11). There were four Cy5.5 molecules per Fn nanocage.

In Vitro Studies: Testing in Cells and Tissues

[PubMed]

The external diameters of Cy5.5-Fn nanocages and unlabeled Fn-nanocages were determined to be ~12 nm with transmission electron microscopy at pH 7.4 (11).

Animal Studies

Human Studies

[PubMed]

No publication is currently available.

NIH Support

R01 HL078678, R21 EB005364

References

1.

Achilefu S. Lighting up tumors with receptor-specific optical molecular probes. Technol Cancer Res Treat. 2004;3(4):393–409. [PubMed: 15270591]

2.

Ntziachristos V., Bremer C., Weissleder R. Fluorescence imaging with near-infrared light: new technological advances that enable in vivo molecular imaging. Eur Radiol. 2003;13(1):195–208. [PubMed: 12541130]

3.

Becker A., Hessenius C., Licha K., Ebert B., Sukowski U., Semmler W., Wiedenmann B., Grotzinger C. Receptor-targeted optical imaging of tumors with near-infrared fluorescent ligands. Nat Biotechnol. 2001;19(4):327–31. [PubMed: 11283589]

4.

Tung C.H. Fluorescent peptide probes for in vivo diagnostic imaging. Biopolymers. 2004;76(5):391–403. [PubMed: 15389488]

5.

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]

6.

Lowe J.B. Glycosylation in the control of selectin counter-receptor structure and function. Immunol Rev. 2002;186:19–36. [PubMed: 12234359]

7.

Libby P. Inflammation in atherosclerosis. Nature. 2002;420(6917):868–74. [PubMed: 12490960]

8.

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]

9.

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]

10.

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]

11.

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]