A Leukocyte-Mimetic Magnetic Resonance Imaging Contrast Agent Homes Rapidly to Activated Endothelium and Tracks With Atherosclerotic Lesion Macrophage Content

Abstract

Objective Endothelial cell activation is an important mediator of monocyte recruitment to sites of vascular inflammation. We hypothesised that high-affinity dual-ligand microparticles of iron oxide, targeted to P-selectin and vascular cell adhesion molecule-1 (VCAM-1) (PV-MPIO), would identify activated endothelial cells during atherosclerosis progression. Methods and Results In vivo MRI in apolipoprotein E-deficient mice showed rapid binding of PV-MPIO to the aortic root, which was maximal 30 minutes post-MPIO injection and maintained at 60 minutes. Minimal binding was observed for control IgG-MPIO. Intensely low MR signal areas, corresponding to PV-MPIO binding, were detected early (14 weeks), during foam cell formation. Contrast effects increased at 20 weeks during fibrofatty lesion development (P < 0.05), but reduced by 30 weeks (P < 0.01). Across all lesion severities, MRI contrast effects correlated with lesion macrophage area quantified by immunohistochemistry (R = 0.53; P < 0.01). Near-infrared fluorescently labeled PV-MPIO were shown, by flow cytometry, to bind only activated endothelial cells, and not to macrophages. Using en face immunofluorescence, we further demonstrate selective PV-MPIO accumulation at atherosclerosis-susceptible sites, with minimal binding to atherosclerosis-spared regions. Conclusions This high affinity leukocyte mimetic MRI agent reveals endothelial activation. PV-MPIO demonstrate exceptionally rapid in vivo steady state accumulation, providing conspicuous MR contrast effects that can be objectively quantified. In atherosclerosis progression, PV-MPIO tracked closely with the burden and distribution of plaque macrophages, not merely plaque size. On a biocompatible platform, this approach has potential for quantitative MRI of inflammatory disease activity.

Molecular magnetic resonance imaging discloses endothelial activation after transient ischaemic attack

“…68 Ga-Fucoidan) or by coupling contrast agents to ligands (e.g. fucoidan, antibodies, sialyl Lewis X ) (Jin et al, 2009;McAteer et al, 2012;Beziere et al, 2014;Farr et al, 2014;Li et al, 2014). In a stroke/neuroinflammation context, Pselectin has been targeted in molecular MRI studies, with disappointing results: P-selectin targeted USPIOs (ultrasmall particles of iron oxide) had a limited sensitivity and specificity in a mouse ischaemic stroke model (Jin et al, 2009) and a dual antibody-conjugated MPIOs, targeting both VCAM1 and P-selectin, did not show better images over single VCAM1 antibody-conjugated MPIOs in a model of acute inflammation in mice .…”

Nanomedicine for the molecular diagnosis of cardiovascular pathologies

“…After injection of an iron dose of 0.56 mg Fe/kg, MRI was performed at 7.4 T. A contrast uptake was observed after 30 min. Non-biodegradable tosyl-activated polystyrene-coated superparamagnetic MP (Dynabeads ® , Life Technologies) with a covalent grafting of P-selectin antibody were shown to accumulate onto activated endothelium at most during fibrous cap formation [40].…”

Inflammation and Neovascularization Intertwined in Atherosclerosis

“…Microparticles of iron oxide (MPIOs) dually targeting VCAM-1 and P-selectin in aortic plaques have been reported to have significantly increased binding compared to P-selectin or VCAM-1 only targeted MPIOs, with significantly increased MR signal ex vivo compared to control agent 34 . By further reducing the size of this MPIO to micron size, efficacy of this CM to image activated endothelium and different stages of development of atheroma has been demonstrated 35 .…”