Uptake of citrate-coated iron oxide nanoparticles into atherosclerotic lesions in mice occurs via accelerated transcytosis through plaque endothelial cells

Wolfram C Poller,Konstantin Möller,Evelyn Ramberger,Norbert Löwa,Eyk Schellenberger,Verena Stangl,Antje Ludwig,Gert Baumann,Karl Stangl,Philipp Boehm-Sturm,Susanne Wagner,Matthias Taupitz,Susanne Mueller,Frank Wiekhorst

doi:10.1007/s12274-016-1220-9

Abstract

AbstractVery small superparamagnetic iron oxide nanoparticles (VSOPs) rapidly accumulate in atherosclerotic lesions, thereby enabling plaque visualization by magnetic resonance imaging (MRI). This study was performed to identify the uptake mechanisms of VSOPs into atherosclerotic plaques. Low-density lipoprotein receptor-deficient (LDLR−/−) mice with advanced atherosclerosis were analyzed using MRI and transmission electron microscopy (TEM) at various time points after intravenous administration of VSOPs. Post-mortem MRI detected VSOP labeling of atherosclerotic plaques 10 min after injection, and the signal increased over the first 3 h. TEM revealed that the intensive plaque labeling was mediated by accelerated transcytosis of VSOPs through endothelial cells overlaying atherosclerotic lesions. Experiments with endocytosis inhibitors and small interfering RNA (siRNA) revealed a dynamin-dependent mechanism involving both clathrin- and caveolin-mediated processes. In cell culture experiments, endothelial VSOP uptake was enhanced under proatherogenic flow and TNFα stimulation, conditions that are both present in plaque areas. Our study demonstrates that VSOPs enable non-invasive MRI assessment of accelerated endothelial transcytosis, an important pathomechanism in atherosclerotic plaque formation.

Highlights

Atherosclerosis is the leading cause of death in human society [1]
The uptake mechanisms underlying the rapid accumulation of Very small superparamagnetic iron oxide nanoparticles (VSOPs) in plaques were analyzed by combining magnetic resonance imaging (MRI) and transmission electron microscopy (TEM) in LDLR−/− mice with advanced atherosclerosis
We recorded T2*-weighted in situ and ex vivo MRI scans of the thoracic aorta at time points ranging from 10 min to 24 h after intravenous injection of VSOPs

Summary

Introduction

Atherosclerosis is the leading cause of death in human society [1]. Endothelial dysfunction promotes extravasation of lipids and leucocytes, proliferation of smooth muscle cells, and the formation of atherosclerotic plaques [2, 3]. Plaque analyses in atherosclerotic rabbits confirmed VSOP accumulation in macrophages and uncovered GAGcontaining microvesicles as additional imaging targets [18]. In agreement with these instability-associated targets, the loss of MRI signal caused by VSOPs was reported to correlate with histological plaque instability criteria [18]. A study comparing VSOP variants stabilized with different monomeric organic acids detected VSOP-filled vesicular structures in the cytoplasm of plaque endothelial cells (ECs) 3 h after VSOP injection [17]. This observation adds an important new aspect to the discussion on potential VSOP uptake mechanisms. VSOP-based MRI was correlated with electron microscopic analyses of VSOP uptake into plaques at various time points after VSOP injection

Methods

Results

Conclusion