In Vivo PET Imaging of HDL in Multiple Atherosclerosis Models

Abstract

Objectives Our aim was to develop and validate a non-invasive imaging tool to visualize HDL’s in vivo behavior by positron emission tomography (PET), with an emphasis on its plaque targeting abilities. Background High-density lipoprotein (HDL) is a natural nanoparticle that interacts with atherosclerotic plaque macrophages to facilitate reverse cholesterol transport. HDL-cholesterol concentration in blood is inversely associated with risk of coronary heart disease and remains one of the strongest independent predictors of incident cardiovascular events. Methods Discoidal HDL nanoparticles were prepared by reconstitution of its components apolipoprotein A-I (APOA1) and the phospholipid DMPC. For radiolabeling with Zirconium-89 (89Zr), the chelator DFO was introduced by conjugation to APOA1 or as a phospholipid-chelator (DSPE-DFO). Radiolabeled HDL’s biodistribution and plaque targeting was studied in established murine, rabbit and porcine atherosclerosis models by PET combined with computed tomography (PET/CT) or with magnetic resonance imaging (PET/MRI). Ex vivo validation was conducted by radioactivity counting, autoradiography and near infrared fluorescence imaging. Flow cytometric assessment of cellular specificity in different tissues was performed in the murine model. Results We observed distinct pharmacokinetic profiles for the two 89Zr-HDL nanoparticles. Both APOA1- and phospholipid-labeled HDL mainly accumulated in kidneys, liver and spleen with some marked quantitative differences in radioactivity uptake values. Radioactivity concentrations in rabbit atherosclerotic aortas were 3–4-fold higher than in controls at 5 days p.i. for both 89Zr-HDL nanoparticles. In the porcine model, we observed increased accumulation of radioactivity in lesions by in vivo PET imaging. Irrespective of the radiolabel’s location we found HDL nanoparticles to preferentially target plaque macrophages and monocytes. Conclusions 89Zr labeling of HDL allows studying its in vivo behavior by non-invasive PET imaging, including visualization of its accumulation in advanced atherosclerotic lesions. The different labeling strategies provide insight on the pharmacokinetics and biodistribution of HDL’s main components, i.e. phospholipids and APOA1.

PET/MR Imaging of Malondialdehyde-Acetaldehyde Epitopes With a Human Antibody Detects Clinically Relevant Atherothrombosis

“…In a clinical scenario, however, target-to-blood ratios could compensate for these effects, which is not possible in rabbits. Although currently limited to research purposes, PET/MR imaging use for evaluating atherosclerosis is superior to PET/CT without compromising accuracy as we have shown with a significant positive correlation between ex vivo and in vivo uptake of 89 Zr-LA25 in rabbit aortas, and previously for other agents (32,51). …”

“…DCE-MR imaging was used to evaluate vascular permeability, which was numerically higher in atherosclerotic rabbits compared with control rabbits (4.29 ± 1.61 vs. 1.82 ± 1.33; p = 0.11) (Figure 6E). We also used a fluorescently labeled reconstituted high-density lipoprotein (rHDL) nanoparticle as a macrophage mapping agent that was injected 24 h before sacrifice, as previously described (32). After euthanasia, all aortas were imaged by near infrared fluorescence (NIRF), which revealed approximately 100-fold higher fluorescence intensity in atherosclerotic aortas compared with control aortas (98 ± 16 × 10 9 vs. 1.14 ± 0.18 × 10 9 μW/cm 2 ; p = 0.03) (Figure 6F).…”

Invasive or non-invasive imaging for detecting high-risk coronary lesions?

“…These include 18 F-fluorodeoxymannose, the somatostatin receptor subtype-2 PET ligand 68 Ga-DOTATATE, 11 F-fluorocholine, and transient receptor protein receptor tracers, including 11 C-PK11195 [128][129][130][131]. Aside from inflammation, several other pathogenic mechanisms of atherosclerosis can be imaged using PET, including microcalcification, hypoxia, neo-angiogenesis, hematopoiesis, and HDL accumulation [126,[132][133][134][135]. For example, early vascular calcification occurring in response to intense plaque inflammation, and below the resolution of CT, can be detected using 18 F-sodium fluoride (NaF) PET.…”

A Comprehensive Procedure to Evaluate the <em>In Vivo</em> Performance of Cancer Nanomedicines

“…Remove the blood in mouse tissues by first cutting open the right atrium and then injecting 20 mL PBS into the left ventricle, and subsequently collect the relevant tissues such as tumor, liver, spleen, lung, kidney, muscle, and others 16 .…”