Molecular imaging of myocardial infarction with Gadofluorine P - A combined magnetic resonance and mass spectrometry imaging approach

State-of-the-art mass spectrometry imaging applications in biomedical research

Mass spectrometry imaging has advanced from a niche technique to a widely applied spatial biology tool operating at the forefront of numerous fields, most notably making a significant impact in biomedical pharmacological research. The growth of the field has gone hand in hand with an increase in publications and usage of the technique by new laboratories, and consequently this has led to a shift from general MSI reviews to topic-specific reviews. Given this development, we see the need to recapitulate the strengths of MSI by providing a more holistic overview of state-of-the-art MSI studies to provide the new generation of researchers with an up-to-date reference framework. Here we review scientific advances for the six largest biomedical fields of MSI application (oncology, pharmacology, neurology, cardiovascular diseases, endocrinology, and rheumatology). These publications thereby give examples for at least one of the following categories: they provide novel mechanistic insights, use an exceptionally large cohort size, establish a workflow that has the potential to become a high-impact methodology, or are highly cited in their field. We finally have a look into new emerging fields and trends in MSI (immunology, microbiology, infectious diseases, and aging), as applied MSI is continuously broadening as a result of technological breakthroughs.

Next-generation pathology practices with mass spectrometry imaging

Mass spectrometry imaging (MSI) is a powerful technique that reveals the spatial distribution of various molecules in biological samples, and it is widely used in pathology-related research. In this review, we summarize common MSI techniques, including matrix-assisted laser desorption/ionization and desorption electrospray ionization MSI, and their applications in pathological research, including disease diagnosis, microbiology, and drug discovery. We also describe the improvements of MSI, focusing on the accumulation of imaging data sets, expansion of chemical coverage, and identification of biological significant molecules, that have prompted the evolution of MSI to meet the requirements of pathology practices. Overall, this review details the applications and improvements of MSI techniques, demonstrating the potential of integrating MSI techniques into next-generation pathology practices.

Fingerprints of Element Concentrations in Infective Endocarditis Obtained by Mass Spectrometric Imaging and t-Distributed Stochastic Neighbor Embedding

Staphylococcus aureus-induced infective endocarditis (IE) is a life-threatening disease. Differences in virulence between distinct S. aureus strains, which are partly based on the molecular mechanisms during bacterial adhesion, are not fully understood. Yet, distinct molecular or elemental patterns, occurring during specific steps in the adhesion process, may help to identify novel targets for accelerated diagnosis or improved treatment. Here, we use laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) of post-mortem tissue slices of an established mouse model of IE to obtain fingerprints of element distributions in infected aortic valve tissue. Three S. aureus strains with different virulence due to deficiency in distinct adhesion molecules (fibronectin-binding protein A and staphylococcal protein A) were used to assess strain-specific patterns. Data analysis was performed by t-distributed stochastic neighbor embedding (t-SNE) of mass spectrometry imaging data, using manual reference tissue classification in histological specimens. This procedure allowed for obtaining distinct element patterns in infected tissue for all three bacterial strains and for comparing those to patterns observed in healthy mice or after sterile inflammation of the valve. In tissue from infected mice, increased concentrations of calcium, zinc, and magnesium were observed compared to noninfected mice. Between S. aureus strains, pronounced variations were observed for manganese. The presented approach is sensitive for detection of S. aureus infection. For strain-specific tissue characterization, however, further improvements such as establishing a database with elemental fingerprints may be required.

Emerging methods for the characterization of ischemic heart disease: ultrafast Doppler angiography, micro-CT, photon-counting CT, novel MRI and PET techniques, and artificial intelligence

After an ischemic event, disruptive changes in the healthy myocardium may gradually develop and may ultimately turn into fibrotic scar. While these structural changes have been described by conventional imaging modalities mostly on a macroscopic scale-i.e., late gadolinium enhancement at magnetic resonance imaging (MRI)-in recent years, novel imaging methods have shown the potential to unveil an even more detailed picture of the postischemic myocardial phenomena. These new methods may bring advances in the understanding of ischemic heart disease with potential major changes in the current clinical practice. In this review article, we provide an overview of the emerging methods for the non-invasive characterization of ischemic heart disease, including coronary ultrafast Doppler angiography, photon-counting computed tomography (CT), micro-CT (for preclinical studies), low-field and ultrahigh-field MRI, and ¹¹C-methionine positron emission tomography. In addition, we discuss new opportunities brought by artificial intelligence, while addressing promising future scenarios and the challenges for the application of artificial intelligence in the field of cardiac imaging.

Multimodal Imaging Mass Spectrometry: Next Generation Molecular Mapping in Biology and Medicine

Imaging mass spectrometry has become a mature molecular mapping technology that is used for molecular discovery in many medical and biological systems. While powerful by itself, imaging mass spectrometry can be complemented by the addition of other orthogonal, chemically informative imaging technologies to maximize the information gained from a single experiment and enable deeper understanding of biological processes. Within this review, we describe MALDI, SIMS, and DESI imaging mass spectrometric technologies and how these have been integrated with other analytical modalities such as microscopy, transcriptomics, spectroscopy, and electrochemistry in a field termed multimodal imaging. We explore the future of this field and discuss forthcoming developments that will bring new insights to help unravel the molecular complexities of biological systems, from single cells to functional tissue structures and organs.

Safe and efficient magnetic resonance imaging of acute myocardial infarction with gadolinium-doped carbon dots

Aim: The magneto-fluorescent gadolinium-doped carbon dots (Gd-CDs) were developed as a cardiac MR imaging contrast agent to detect the infarcted myocardium on a myocardial ischemia/reperfusion (I/R) mice model. Materials & methods: The chemophysical features, cardiac MR imaging effect, biodistribution and biocompatibility of Gd-CDs were studied. Results: The ultrasmall size and good aqueous dispersibility endows Gd-CDs with high longitudinal relaxivity, intense fluorescence, excellent physiological stability and superior biocompatibility. More importantly, Gd-CDs preferentially target the infarcts as determined by the confocal microscopy and MR imaging on the I/R mice at the acute stage of myocardial infarction. Conclusion: Gd-CDs manifest great potential for development as an MR imaging contrast agent to facilitate accurate visualization and image-guided therapy of acute myocardial infarction.

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

Mass spectrometry imaging (MSI) using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been employed for the elemental bio-distribution and quantification of uranium (U) in histological tissue sections of rodent kidneys. Kidneys were immediately immersed into 4% paraformaldehyde (PFA) solution for 24 h, Tissue-Tek O.C.T. Compound embedded and stored at - 80 °C until cutting in a cryostat, and mounted in gel-covered glass slides. In order to assure complete ablation of sample, sample preparation and laser conditions were carefully optimized. In this work, a new analytical methodology is presented for performing quantitative laser ablation analyses based on internal standard (thulium, Tm)-spiked gelatine (10% m/v) for correction of matrix effects, lack of tissue homogeneity, and instrumental drift. In parallel, matrix-matched laboratory standards, dosed at different concentrations of U, were prepared from a pool of rat kidneys. The quantitative images of cryo-sections revealed heterogeneous distribution of uranium within the renal tissue, because the cortical concentration was up to 120-fold higher than the medullary concentration. Graphical abstract.

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

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.

Tagged cine magnetic resonance imaging to quantify regional mechanical changes after acute myocardial infarction

PURPOSE

The conventional volumetric approaches of measuring cardiac function are load-dependent, and are not able to discriminate functional changes in the infarct, transition and remote myocardium. We examined phase-dependent regional mechanical changes in the infarct, transition and remote regions after acute myocardial infarction (MI) in a preclinical mouse model using cardiovascular magnetic resonance imaging (CMR).

METHODS

We induced acute MI in six mice with left anterior descending coronary artery ligation. We then examined cardiac (infarct, transition and remote-zone) morphology and function utilizing 9.4 T high field CMR before and 2 weeks after the induction of acute MI. Myocardial scar tissue was evaluated by using CMR with late gadolinium enhancement (LGE). After determining global function through volumetric analysis, regional wall motion was evaluated by measuring wall thickening and radial velocities. Strain rate imaging was performed to assess circumferential contraction and relaxation at the myocardium, endocardium, and epicardium.

RESULTS

There was abnormal LGE in the anterior walls after acute MI suggesting a successful MI procedure. The transition zone consisted of a mixed signal intensity, while the remote zone contained viable myocardium. As expected, the infarct zone had demonstrated severely decreased myocardial velocities and strain rates, suggesting reduced contraction and relaxation function. Compared to pre-infarct baseline, systolic and diastolic velocities (v_S and v_D) were significantly reduced at the transition zone (v_S: -1.86 ± 0.16 cm/s vs -0.68 ± 0.13 cm/s, P < 0.001; v_D: 1.86 ± 0.17 cm/s vs 0.53 ± 0.06 cm/s, P < 0.001) and remote zone (v_S: -1.86 ± 0.16 cm/s vs -0.65 ± 0.12 cm/s, P < 0.001; v_D: 1.86 ± 0.16 cm/s vs 0.51 ± 0.04 cm/s, P < 0.001). Myocardial peak systolic and diastolic strain rates (SR_S and SR_D) were significantly lower in the transition zone (SR_S: -4.2 ± 0.3 s^-1 vs -1.3 ± 0.2 s^-1, P < 0.001; SR_D: 3.9 ± 0.3 s^-1 vs 1.3 ± 0.2 s^-1, P < 0.001) and remote zone (SR_S: -3.8 ± 0.3 s^-1 vs -1.4 ± 0.3 s^-1, P < 0.001; SR_D: 3.5 ± 0.2 s^-1 vs 1.5 ± 0.4 s^-1, P = 0.006). Endocardial and epicardial SR_S and SR_D were similarly reduced in the transition and remote zones compared to baseline.

CONCLUSIONS

This study, for the first time, utilized state-of-the art high-field CMR algorithms in a preclinical mouse model for a comprehensive and controlled evaluation of the regional mechanical changes in the transition and remote zones, after acute MI. Our data demonstrate that CMR can quantitatively monitor dynamic post-MI remodeling in the transition and remote zones, thereby serving as a gold standard tool for therapeutic surveillance.

MRI micelles self-assembled from synthetic gadolinium-based nano building blocks

Synthetic self-assembled stealth Gd-micelles are a new blood pool contrast agent for magnetic resonance imaging.

MRI demonstrates glutamine antagonist-mediated reversal of cerebral malaria pathology in mice

The deadliest complication of Plasmodium falciparum infection is cerebral malaria (CM), with a case fatality rate of 15 to 25% in African children despite effective antimalarial chemotherapy. No adjunctive treatments are yet available for this devastating disease. We previously reported that the glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON) rescued mice from experimental CM (ECM) when administered late in the infection, a time by which mice had already suffered blood-brain barrier (BBB) dysfunction, brain swelling, and hemorrhaging. Herein, we used longitudinal MR imaging to visualize brain pathology in ECM and the impact of a new DON prodrug, JHU-083, on disease progression in mice. We demonstrate in vivo the reversal of disease markers in symptomatic, infected mice following treatment, including the resolution of edema and BBB disruption, findings usually associated with a fatal outcome in children and adults with CM. Our results support the premise that JHU-083 is a potential adjunctive treatment that could rescue children and adults from fatal CM.