Annexin A5-Functionalized Bimodal Lipid-Based Contrast Agents for the Detection of Apoptosis

Abstract

Apoptosis, or programmed cell death, plays an important role in the etiology of a variety of diseases, including cancer and myocardial infarction. Visualization of apoptosis would allow both early detection of therapy efficiency and evaluation of disease progression. To that aim, we synthesized two types of lipid-based bimodal contrast agents that enable the detection of apoptotic cells with both MRI and optical techniques. MR contrast was provided either by entrapment of iron oxide particles within pegylated micelles or by incorporation of Gd-DTPA-bis(stearylamide) (Gd-DTPA-BSA) lipids within the lipid bilayer of pegylated liposomes. The resulting contrast agents were approximately 10 and 100 nm in diameter, respectively. Additional fluorescent lipids were incorporated in the lipid (bi)layer of the contrast agents to allow parallel detection with optical methods. Multiple human recombinant annexin A5 molecules were covalently coupled to introduce specificity for apoptotic cells. Both annexin A5-conjugated contrast agents were shown to significantly increase the relaxation rates of apoptotic cell pellets compared to untreated control cells and apoptotic cells that were treated with nonfunctionalized nanoparticles. Increased relaxation rates were confirmed to originate from association of the contrast agents to apoptotic cells by confocal microscopy. The targeted nanoparticles presented in this study, which differ both in size and in magnetic properties, may have applications for the in vivo detection of apoptosis.

Nanoparticles in magnetic resonance imaging: from simple to dual contrast agents

“…The resulting contrast agent increased the relaxation rates of apoptotic cell pellets compared with untreated control cells and apoptotic cells that were treated with nonfunctionalized nanoparticles. 92 Although recent research has progressed in the preparation and formulation of applications of paramagnetic liposomes for nanoparticle imaging systems, the use of liposomes as contrast agents is mainly based on superparamagnetic liposomes.…”

Quantum Dots with a Paramagnetic Coating as a Bimodal Molecular Imaging Probe

“…Next to the ligand used in this study, other ligands can be conjugated to the pQDs for multimodality imaging of other markers of angiogenesis and also for imaging processes such as inflammation, 6 atherosclerosis, 32 and apoptosis. 33 The bare particle without ligand may be used to study vascular permeability with both MRI and fluorescence microscopy. 13,14,34 In conclusion, we have shown the synthesis of quantum dots with a water-soluble and paramagnetic micellular coating as a molecular imaging probe for both fluorescence microscopy and MRI.…”

Visual Recognition and Efficient Isolation of Apoptotic Cells with Fluorescent-Magnetic-Biotargeting Multifunctional Nanospheres

“…Our understanding of the progression of apoptosis and analyses of the associated changes in DNA, proteins, or organelles would greatly benefit from the ability to visualize and isolate cells at various stages of apoptosis. Schellenberger et al (32,33 ) and van Tilborg et al (34 ) synthesized a series of functionalized magnetic-fluorescent nanoparticle conjugates that recognize apoptotic cells. The fluorophores involved in these bioconjugates, however, were not QDs but fluorescein isothiocyanate (FITC), which might limit the applications for these bioconjugates because of the disadvantages of this organic dye.…”