Scavenger Receptor-AI–Targeted Iron Oxide Nanoparticles for In Vivo MRI Detection of Atherosclerotic Lesions

Abstract

Objective-In search of molecular imaging modalities for specific detection of inflammatory atherosclerotic plaques, we explored the potential of targeting scavenger receptor-AI (SR-AI), which is highly expressed by lesional macrophages and linked to effective internalization machinery. Approach and Results-Ultrasmall superparamagnetic iron oxide particles were conjugated to a peptidic SR-AI ligand (0.371 mol Fe/L and 0.018 mol PP1/L). In vitro incubation of human or murine macrophages with SR-AI-targeted USPIO led to significantly higher iron uptake in vitro than with nontargeted USPIO, as judged by quantitative atomic absorption spectroscopy and Perl's staining. Incremental uptake was strictly mediated by SRs. SR-AI-targeted USPIO displayed accelerated plasma decay and a 3.5-fold increase (P=0.01) in atherosclerotic plaque accumulation on intravenous injection into apolipoprotein E-deficient mice compared with nontargeted USPIO. In addition, atherosclerotic humanized LDLr −/− chimeras with leukocyte expression of human SR-AI showed a significant improvement in contrast-to-noise ratio (2.7-fold; P=0.003) in the atherosclerotic aortic arch plaques 24 hours after injection of SR-AI-targeted USPIO compared with chimeras with leukocyte SR-AI deficiency. Conclusions-Collectively, our data provide several lines of evidence that SR-AI-targeted molecular imaging of USPIO-based contrast agents holds great promise for in situ detection of inflammatory plaques in manifest atherosclerosis. Segers et al SR-AI-Targeted Molecular Imaging of Atherosclerosis 1813screening that displayed high affinity and specificity for SR-AI in vitro in murine and human macrophages. In vivo, PP1 has been shown to accumulate in macrophage-rich organs where it colocalized with F4/80+ macrophages and in atherosclerotic plaques. Furthermore, intravenous injected PP1-coupled fluorescent nanocrystals were successfully accumulated in advanced atherosclerotic plaques of apolipoprotein E-deficient (apoE −/− ) mice. 19In the current study, we report development and validation of SR-AI-targeted USPIO (T-USPIO) functionalized with the aforementioned SR-AI-specific peptide. The T-USPIO was validated in vitro on different mouse and human cell types found in atherosclerotic lesions and also in vivo in an established mouse model for atherosclerosis, as well as in a humanized model of atherosclerosis. Materials and MethodsMaterials and Methods are available in the online-only Supplement. Results Relaxivity AnalysisThe contrast agent relaxivities were measured at 37°C at 20, 60, and 400 MHz, respectively (Table). The transverse relaxivities of the SR-A1 and control particle did not differ significantly nor did the longitudinal relaxivity. Increased Scavenger Receptor-AI-Mediated Uptake of T-USPIO In VitroThe kinetics of basal uptake, processing, and detection of USPIO in vitro and in vivo by macrophages have been the subject of numerous studies. 9 Here, we sought to investigate whether USPIO uptake by (plaque associated) macrophages could be augmented by conju...

Recommendation on Design, Execution, and Reporting of Animal Atherosclerosis Studies: A Scientific Statement From the American Heart Association

“…Experimental atherosclerosis has been quantified and characterized by several modalities, including ultrasound, 202 magnetic resonance imaging, 203,204 and positron emission tomography, sometimes in combination with computed tomography. 205,206 There have also been applications to experimental atherosclerosis using multimodality imaging such as positron emission tomography/magnetic resonance imaging.…”

Human macrophage responses to metal-oxide nanoparticles: a review

“…SR-A also mediated the uptake of dextran-coated SPIONs (120-180 nm) by THP-1-derived macrophages (PMAdifferentiated) [40]. A peptidic SR-A type I ligand conjugated in USPIONs (15-30 nm) increased the uptake of these particles by macrophages (PMA-differentiated THP-1 and U937 cells) in the study of Segers et al [41] reinforcing the involvement of this receptor in the internalization of some SPIONs used as magnetic resonance contrasts.…”

Nanoparticle uptake by macrophages in vulnerable plaques for atherosclerosis diagnosis

“…In vivo visualization by MRI Tumor tracking (mouse) [94][95][96] Septic arthritis (rabbit) [97] AS (mouse, rat, rabbit) [98][99][100] Inflammatory bowel disease (mouse) [101] Fluorescent particles Analysis by microscopy and/or flow cytometry Evaluation and quantification of macrophage phagocytosis (in vitro) [102][103][104] depth and high background noise from surrounding tissues.…”