Inflamed leukocyte-mimetic nanoparticles for molecular imaging of inflammation
Introduction
Dysregulated inflammatory responses of the host are implicated in the pathogenesis of many human diseases [1]. Acute inflammation from infection can cause sepsis [2], while chronic inflammation, and continual coexistence between acute and chronic inflammation are associated with various neurodegenerative [3] and cardiovascular diseases [4], metabolic disorders [5], and cancer [6], [7]. Accordingly, sensitive and early detection of inflammation and site-specific delivery of anti-inflammatory agents will have a wide-ranging impact on the treatment of various inflammation-related diseases. Upon induction of inflammation, a set of adhesion molecules are upregulated in endothelium, with which immune cells interact using counter adhesion molecules such as integrins to adhere to endothelium and to initiate diapedesis. Many existing studies have investigated targeted nanoparticles for the detection and treatment of inflammation employing antibodies or peptides specific to adhesion molecules such as intercellular adhesion molecule (ICAM)-1 [8], [9], [10], vascular cell adhesion molecule (VCAM)-1 [11], [12], [13], selectins [14], and collagen [15], all of which display distinct spatiotemporal responses to inflammation. Among these molecules, ICAM-1 has caught a particular interest because of its highly inducible and localized expression upon inflammatory signals, serving as a marker for inflammation despite its constitutive low level expression [16], [17].
In this study, we developed nanomicelle encapsulating super paramagnetic iron oxide (SPIO) nanoparticles, designed for facile and robust conjugation with targeting moieties and in vivo detection by optical imaging and magnetic resonance imaging (MRI). In order to design nanoparticles to mimic the behavior of inflamed leukocytes in their ability to locate to the inflamed site, SPIO nanoparticle was coated with an optimum number of high affinity inserted (I) domain of integrin called lymphocyte function-associated antigen (LFA)-1 [18], a physiological receptor for ICAM-1. Leukocyte-mimetic nanoparticles were examined for detection of ICAM-1 overexpression in tumor cells, tumor vascular microenvironment, and acute inflammation in vivo. With our recently developed MRI technique for quantitative mapping of contrast agent [19], [20], we explored the possibility of quantitative spatiotemporal mapping of iron oxide distribution in vivo using a mouse model of acute inflammation.
Section snippets
Preparation and characterization of protein coated SPIO nanomicelles
Oleic acid-capped super paramagnetic iron oxide (SPIO) nanocrystals (Ocean Nanotech, LLC) in 5 mg were suspended in 1 ml chloroform with 12 mg 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (DPPE-PEG) and 3 mg 1,2-dioleoyl-sn-glycero-3-[(N-(5-amino-1-carboxypentyl)-iminodiacetic acid)succinyl] nickel salt (DOGS-NTA) (Avanti Polar Lipids, Inc.). For radiolabeled nanoparticles, 60 μCi of L-α-Dipalmitoyl-Phosphatidylcholine, [Choline-Methyl-3H] (Perkin
Synthesis and characterization of leukocyte-mimetic nanoparticles
Selective binding of SPIO nanoparticles to overexpressed ICAM-1 was conferred by surface coating at an optimal density (∼100 molecular/particle) with the I domain of LFA-1 integrin, engineered for high affinity by mutations of F265S/F292G (denoted as F265S/F292G, KD = 6 nM) [18]. Among physiological ligands for LFA-1 such as ICAMs and junctional adhesion molecule (JAM)-1 [21], ICAM-1 is most important in the setting of leukocyte adhesion to inflamed endothelium due to its highest affinity to
Discussion
Sensitive detection of inflammation will be of high significance for diagnosis of diseases caused directly by host inflammatory response such as sepsis, allograft rejection, lupus, as well as those that are influenced by inflammation such as cardiovascular disease and cancer. In this study, we designed MRI-compatible SPIO nanoparticles, and demonstrated a successful detection of constitutive expression of ICAM-1 in tumor, as well as ICAM-1 induction in tumor-associated vasculature, where tumor
Conclusion
This study presents physiology-inspired design of SPIO nanoparticles for in vivo detection by optical imaging and MRI, mimicking activated leukocyte in its ability to recognize inflamed endothelium. Nanoparticles in vivo will experience hydrodynamic force induced by the blood flow, requiring simultaneous molecular interactions with sufficient adhesion strength with the cells for nanoparticles to remain on cell surface. Therefore, the design of nanoparticles with tunable affinity and avidity of
Acknowledgments
We thank Dickson Kirui, Sungkwon Kang, Nozomi Nishimura, Puifai Santisakultarm, Tian Liu, Warren Zipfel, and Alexander Nikitin for technical support. This work was supported by American Heart Association Scientist Development Grant and NIH R01 GM090320.
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