Mass Spectrometry Imaging of atherosclerosis-affine Gadofluorine following Magnetic Resonance Imaging

Abstract

Molecular imaging of atherosclerosis by Magnetic Resonance Imaging (MRI) has been impaired by a lack of validation of the specific substrate responsible for the molecular imaging signal. We therefore aimed to investigate the additive value of mass spectrometry imaging (MSI) of atherosclerosis-affine Gadofluorine P for molecular MRI of atherosclerotic plaques. Atherosclerotic Ldlr −/− mice were investigated by high-field MRI (7 T) at different time points following injection of atherosclerosis-affine Gadofluorine P as well as at different stages of atherosclerosis formation (4, 8, 16 and 20 weeks of HFD). At each imaging time point mice were immediately sacrificed after imaging and aortas were excised for mass spectrometry imaging: Matrix Assisted Laser Desorption Ionization (MALDI) Imaging and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) imaging. Mass spectrometry imaging allowed to visualize the localization and measure the concentration of the MR imaging probe Gadofluorine P in plaque tissue ex vivo with high spatial resolution and thus adds novel and more target specific information to molecular MR imaging of atherosclerosis. Visualization of atherosclerosis using MR imaging is an emerging tool to gain deeper and more dynamic insights into biological processes of atherosclerosis with a high spatial and temporal resolution as well as high sensitivity. An advantage of MR imaging is the ability to acquire anatomical, functional and biological information simultaneously. Noninvasive characterization and assessment of plaque burden, characterization of plaque features (molecular and anatomical) and monitoring of plaque progression are crucial to predict plaque rupture, which causes myocardial infarction or stroke. Various molecular MRI approaches have tried to characterize specific aspects of atherosclerosis. Endothelial permeability, one of the key features of early vascular dysfunction, can be assessed by using albumin-affine gadolinium (Gd) chelates such as Gadofosveset trisodium 1,2. Influx of inflammatory cells such as proinflammatory macrophages can be traced by using iron-oxide nanoparticles, which has been similarly successful both in mice and humans. Additionally, the complex process of vascular remodeling has been successfully investigated by targeting tropoelastin, elastin and other extracellular proteins by more or less specific gadolinium agents in mice and rabbits 3-5. All approaches rely on alteration of the MR signal induced either by shortening T1 relaxation (in case of gadolinium) or shortening T2* (in case of iron-oxide nanoparticles), generated by accumulation of a

Comparative lipid profiling of murine and human atherosclerotic plaques using high-resolution MALDI MSI

“…In the context of atherosclerosis, recent studies use MSI as a novel strategy to visualize atherosclerotic plaque localization in the aorta of atherosclerotic mice such as LDL receptor knockout (LDLR –/– ) fed a cholesterol-rich diet or apolipoprotein E knockout (ApoE –/– ) mice [ 7 , 31 ], and to evaluate treatment effects on plaque formation and remodelling of the complex lipid components [ 7 ]. These animal studies define several lipid markers for a deeper understanding of the causes and underlying mechanisms of plaque progression.…”

A novel calibration strategy based on internal standard–spiked gelatine for quantitative bio-imaging by LA-ICP-MS: application to renal localization and quantification of uranium

“…In this work, in-house solid matrix-matched standards were prepared from uranium-spiked kidney homogenate. Nevertheless, further calibration strategies are found in the literature including the solution-based calibration [27], fabrication xerogel solid calibration standards which are more suitable for the calibration of glasses and silicate matrices [28], the synthesis of metal-spiked polymer films [29], the use of dried droplets or dried matrix spots (DMS) deposited on different substrates [30][31][32][33][34], and the spiking and sectioning of gelatine droplets, whose use has increased noticeably in recent years for the quantitative analysis of biological tissues [35][36][37][38][39][40][41]. For internal standardization, three different approaches are mainly described in the literature for the quantitative elemental imaging of biological samples: (i) the simultaneous nebulization of a standard solution [42], (ii) the use of an element naturally occurring in the sample [43][44][45], and (iii) the addition of an internal standard-spiked layer between the sample and support or on the sample [46][47][48][49][50][51].…”

Evaluation of Plaque Characteristics and Inflammation Using Magnetic Resonance Imaging

“…Furthermore, Woodside et al have visualized overall inflammatory cell burden in different regions of the aorta in ApoE −/− mice at clinically relevant field strengths by using a targeted gadolinium contrast agent binding to the integrin α4β1, which is involved in the recruitment of inflammatory cells to atherosclerotic plaques [ 144 ]. Moreover, a recent study showed gadofluorine P accumulation in aortic atherosclerotic plaques of low density lipoprotein receptor deficient (Ldlr −/− ) mice with MRI, followed by ex vivo mass spectrometry imaging to quantify the contrast agent to validate its local accumulation [ 145 ].…”