Nanocrystal core high-density lipoproteins: a multimodality contrast agent platform

Abstract

High density lipoprotein (HDL) is an important natural nanoparticle that may be modified for biomedical imaging purposes. Here we developed a novel technique to create unique multimodality HDL mimicking nanoparticles by incorporation of gold, iron oxide, or quantum dot nanocrystals for computed tomography, magnetic resonance, and fluorescence imaging, respectively. By including additional labels in the corona of the particles, they were made multifunctional. The characteristics of these nanoparticles, as well as their in vitro and in vivo behavior, revealed that they closely mimic native HDL.

Figure 1. Nanocrystal core high density lipoprotein

A schematic depiction of the different agents in this study. B summary of the synthesis procedure of the agents where 1, the phospholipids and nanocrystal in chloroform are added to water, 2, apoA-I is added and 3, the ‘empty’ particles are removed. C and D negative stain TEM images of FeO-HDL and FeO-PEG. E emission and absorption spectrum of the QD-HDL. F photograph of the QD-HDL in normal light (left) and under UV illumination (right). G, H, I phantoms of Au-HDL imaged using fluorescence, CT and MRI, respectively.

Figure 2. Uptake of Au-HDL by macrophage cells in vitro

A confocal microscopy of cells incubated for 2 hours with Au-HDL or B Au-PEG, which appear red (rhodamine) and the nuclei are stained with DAPI (blue). C TEM image where black circles indicate areas of particle uptake. D CT images of the different cell pellets. E graph of the increase in CT attenuation of the cell pellets compared to media only incubated cells vs. time of incubation. F T1-weighted MR image of cell pellets.

Figure 3. Uptake of FeO-HDL by macrophage cells in vitro

Confocal microscopy of cells incubated for 2 hours with A FeO-HDL and B FeO-PEG, where uptake is indicated by red (rhodamine) and the nuclei are stained with DAPI. C TEM of cells incubated with FeO-HDL, areas containing iron oxide are highlighted by circles. D T2-weighted MR image of cells incubated with FeO-HDL, FeO-PEG or media only for 4 hours.

Figure 4. Uptake of QD-HDL by macrophage cells in vitro

Confocal microscopy of macrophage cells incubated for 2 hours, where A QD-HDL and B QD-PEG uptake is indicated by red and the nuclei are blue. C T1-weighted MR image of pellets of cells incubated for 4 hrs. D TEM image of QD-HDL uptake, QDs are highlighted with black rings. Photographs of the cell pellets taken under E ambient light and F UV irradiation. G chart of fluorescent intensity of the cell pellets, with a typical fluorescent image inset.

Figure 5. Multimodality imaging of atherosclerosis using nanocrystal high density lipoprotein

T1-weighted MR images of the aorta of apoE KO mice pre- (A, B) and 24 hours post-injection (D, E) with Au-HDL or QD-HDL. Arrows indicate areas enhanced in the post images. C, F T2*-weighted images of an apoE KO mouse pre- and 24 hours post-injection with FeO-HDL. G, H, I confocal microscopy images of aortic sections of mice injected with nanocrystal HDL. Red is nanocrystal HDL, macrophages are green and nuclei and blue. Yellow indicates co-localization of nanocrystal HDL with macrophages and is indicated by arrowheads. J fluorescence image of aortas of mice injected with QD-HDL, QD-PEG and saline. K ex vivo sagittal CT images of the aortas of mice injected with Au-HDL, Au-PEG and saline.