Neuro-metabolite profiles of rodent models of psychiatric dysfunctions characterised by MR spectroscopy.

Neuroimaging endophenotypes in animal models provide an objective and translationally-relevant alternative to cognitive/behavioral traits in human psychopathologies. Metabolic alterations, such as those involved in the glutamate-cycle, have been proposed to play a preponderant role in both depression and schizophrenia. Chronic Mild Unpredictable Stress (CMUS) and sub-chronic administration of NMDA receptor antagonist generate animal models of depression and schizophrenia, respectively. The models are based on etiologically-relevant factors related to the induction and support of these psychopathologies. To test metabolic alterations within the glutamate-cycle and in other major neurochemicals, single-voxel Magnetic Resonance Spectroscopy was recorded within the hippocampus in both rat models and control animals. Surprisingly, altered glutamate-related metabolites were observed in the CMUS model, but not NMDA-based model, as indicated by decreased glutamine and increased GABA levels. However, both models presented elevated total visible choline and inositol levels relative to controls. These results indicate the presence cell membrane metabolic alterations and inflammatory processes shared in both models, comparable to evidence presented in schizophrenia and depression and other comparable animal models. These translationally-relevant biomarkers may thus form the basis for drug-development targets in both psychopathologies.

Biocompatible Peptide-Coated Ultrasmall Superparamagnetic Iron Oxide Nanoparticles for In Vivo Contrast-Enhanced Magnetic Resonance Imaging.

The biocompatibility and performance of reagents for in vivo contrast-enhanced magnetic resonance imaging (MRI) are essential for their translation to the clinic. The quality of the surface coating of nanoparticle-based MRI contrast agents, such as ultrasmall superparamagnetic iron oxide nanoparticles (USPIONs), is critical to ensure high colloidal stability in biological environments, improved magnetic performance, and dispersion in circulatory fluids and tissues. Herein, we report the design of a library of 21 peptides and ligands and identify highly stable self-assembled monolayers on the USPIONs' surface. A total of 86 different peptide-coated USPIONs are prepared and selected using several stringent criteria, such as stability against electrolyte-induced aggregation in physiological conditions, prevention of nonspecific binding to cells, and absence of cellular toxicity and contrast-enhanced in vivo MRI. The bisphosphorylated peptide 2PG-S*VVVT-PEG4-ol provides the highest biocompatibility and performance for USPIONs, with no detectable toxicity or adhesion to live cells. The 2PG-S*VVVT-PEG4-ol-coated USPIONs show enhanced magnetic resonance properties, r1 (2.4 mM-1·s-1) and r2 (217.8 mM-1·s-1) relaxivities, and greater r2/ r1 relaxivity ratios (>90) when compared to those of commercially available MRI contrast agents. Furthermore, we demonstrate the utility of 2PG-S*VVVT-PEG4-ol-coated USPIONs as a T2 contrast agent for in vivo MRI applications. High contrast enhancement of the liver is achieved as well as detection of liver tumors, with significant improvement of the contrast-to-noise ratio of tumor-to-liver contrast. It is envisaged that the reported peptide-coated USPIONs have the potential to allow for the specific targeting of tumors and hence early detection of cancer by MRI.

Imaging vulnerable plaques by targeting inflammation in atherosclerosis using fluorescent-labeled dual-ligand microparticles of iron oxide and magnetic resonance imaging.

OBJECTIVE: Identification of patients with high-risk asymptomatic carotid plaques remains an elusive but essential step in stroke prevention. Inflammation is a key process in plaque destabilization and a prelude to clinical sequelae. There are currently no clinical imaging tools to assess the inflammatory activity within plaques. This study characterized inflammation in atherosclerosis using dual-targeted microparticles of iron oxide (DT-MPIO) as a magnetic resonance imaging (MRI) probe. METHODS: DT-MPIO were used to detect and characterize inflammatory markers, vascular cell adhesion molecule 1 (VCAM-1). and P-selectin on (1) tumor necrosis factor-α-treated cells by immunocytochemistry and (2) aortic root plaques of apolipoprotein-E deficient mice by in vivo MRI. Furthermore, apolipoprotein E-deficient mice with focal carotid plaques of different phenotypes were developed by means of periarterial cuff placement to allow in vivo molecular MRI using these probes. The association between biomarkers and the magnetic resonance signal in different contrast groups was assessed longitudinally in these models. RESULTS: Immunocytochemistry confirmed specificity and efficacy of DT-MPIO to VCAM-1 and P-selectin. Using this in vivo molecular MRI strategy, we demonstrated (1) the DT-MPIO-induced magnetic resonance signal tracked with VCAM-1 (r = 0.69; P = .014), P-selectin (r = 0.65; P = .022), and macrophage content (r = 0.59; P = .045) within aortic root plaques and (2) high-risk inflamed plaques were distinguished from noninflamed plaques in the murine carotid artery within a practical clinical imaging time frame. CONCLUSIONS: These molecular MRI probes constitute a novel imaging tool for in vivo characterization of plaque vulnerability and inflammatory activity in atherosclerosis. Further development and translation into the clinical arena will facilitate more accurate risk stratification in carotid atherosclerotic disease in the future.

MRI detection of endothelial cell inflammation using targeted superparamagnetic particles of iron oxide (SPIO).

BACKGROUND: There is currently no clinical imaging technique available to assess the degree of inflammation associated with atherosclerotic plaques. This study aims to develop targeted superparamagnetic particles of iron oxide (SPIO) as a magnetic resonance imaging (MRI) probe for detecting inflamed endothelial cells. METHODS: The in vitro study consists of the characterisation and detection of inflammatory markers on activated endothelial cells by immunocytochemistry and MRI using biotinylated anti-P-selectin and anti-VCAM-1 (vascular cell adhesion molecule 1) antibody and streptavidin conjugated SPIO. RESULTS: Established an in vitro cellular model of endothelial inflammation induced with TNF-α (tumor necrosis factor alpha). Inflammation of endothelial cells was confirmed with both immunocytochemistry and MRI. These results revealed both a temporal and dose dependent expression of the inflammatory markers, P-selectin and VCAM-1, on exposure to TNF-α. CONCLUSION: This study has demonstrated the development of an in vitro model to characterise and detect inflamed endothelial cells by immunocytochemistry and MRI. This will allow the future development of contrast agents and protocols for imaging vascular inflammation in atherosclerosis. This work may form the basis for a translational study to provide clinicians with a novel tool for the in vivo assessment of atherosclerosis.

Microcapsules engineered to support mesenchymal stem cell (MSC) survival and proliferation enable long-term retention of MSCs in infarcted myocardium.

The limited efficacy of cardiac cell-based therapy is thought to be due to poor cell retention within the myocardium. Hence, there is an urgent need for biomaterials that aid in long-term cell retention. This study describes the development of injectable microcapsules for the delivery of mesenchymal stem cells (MSCs) into the infarcted cardiac wall. These microcapsules comprise of low concentrations of agarose supplemented with extracellular matrix (ECM) proteins collagen and fibrin. Dextran sulfate, a negatively charged polycarbohydrate, was added to mimic glycosaminoglycans in the ECM. Cell viability assays showed that a combination of all components is necessary to support long-term survival and proliferation of MSCs within microcapsules. Following intramyocardial transplantation, microcapsules degraded slowly in vivo and did not induce a fibrotic foreign body response. Pre-labeling of encapsulated MSCs with iron oxide nanoparticles allowed continued cell-tracking by MRI over several weeks following transplantation into infarcted myocardium. In contrast, MSCs injected as cell suspension were only detectable for two days post transplantation by MRI. Histological analysis confirmed integration of transplanted cells at the infarct site. Therefore, microcapsules proved to be suitable for stem cell delivery into the infarcted myocardium and can overcome current limitations of poor cell retention in cardiac cell-based therapy.

"Smart" theranostic lanthanide nanoprobes with simultaneous up-conversion fluorescence and tunable T1-T2 magnetic resonance imaging contrast and near-infrared activated photodynamic therapy.

The current work reports a type of "smart" lanthanide-based theranostic nanoprobe, NaDyF4:Yb(3+)/NaGdF4:Yb(3+),Er(3+), which is able to circumvent the up-converting poisoning effect of Dy(3+) ions to give efficient near infrared (980 nm) triggered up-conversion fluorescence, and offers not only excellent dark T2-weighted MR contrast but also tunable bright and T1-weighted MR contrast properties. Due to the efficient up-converted energy transfer from the nanocrystals to chlorin e6 (Ce6) photosensitizers loaded onto the nanocrystals, cytotoxic singlet oxygen was generated and photodynamic therapy was demonstrated. Therefore, the current multifunctional nanocrystals could be potentially useful in various image-guided diagnoses where bright or dark MRI contrast could be selectively tuned to optimize image quality, but also as an efficient and more penetrative near-infrared activated photodynamic therapy agent.

A comparison of PET imaging agents for the assessment of therapy efficacy in a rodent model of glioma.

The aim of the current study was to assess the ability of PET imaging agents to detect early response to therapy in an orthotopic experimental rodent model of glioma. Clinically, MRI and [(18)F]FDG PET are routinely used but their ability to assess early therapeutic response can be limited. In this study, nude rats were implanted with U87-MG tumors orthotopically and imaged with either [(18)F]FDG or [(18)F]FLT to determine which tracer acts as the most sensitive biomarker for evaluation of treatment response in animals undergoing anti-angiogenic therapy with sunitinib, a receptor tyrosine kinase (RTK) inhibitor. Of the radiopharmaceuticals tested, [(18)F]FLT proved to be the most sensitive biomarker in the proliferating glioma, based on tumour-to-normal tissue radiotracer uptake (TNR ~17) in comparison to [(18)F]FDG (TNR ~1.7). Furthermore, [(18)F]FLT displayed earlier assessment of therapy efficacy, than either tumour volume measured by MRI or [(18)F]FDG PET imaging. Overall, longitudinal molecular imaging with [(18)F]FLT provides earlier detection of therapy response than either of the commonly used clinical imaging modalities potentially improving patient management.

Design, synthesis and in vitro characterization of fluorescent and paramagnetic CXCR4-targeted imaging agents.

The G-protein coupled C-X-C chemokine receptor type 4 (CXCR4) is highly overexpressed in a range of cancers and is therefore an excellent biomarker for cancer imaging. To this end targeted iron oxide nanoparticles were developed and utilised for in vitro imaging of MDA-MB-231 breast cancer cells overexpressing the CXCR4 receptor. Nanoparticles comprising an iron oxide core, encapsulated in a stabilising epichlorohydrin crossed-linked dextran polymer, were conjugated to a cyclopentapeptide with affinity to the CXCR4 receptor. The particles were characterized for their size, surface charge and r2 relaxivity at 4.7 T. MR imaging of the CXCR4 receptor with targeted iron oxide nanoparticles revealed an approximately 3-fold increase in T2 signal enhancement of MDA-MB-231 cells compared to non-targeted controls. Prussian blue staining of labeled MDA-MB-231 cells revealed darker and more intense staining of the cellular membrane. This study demonstrates the potential of targeted iron oxide nanoparticles for the imaging of the CXCR4 receptor by magnetic resonance imaging (MRI).

Stratification of 18F-labeled PET imaging agents for the assessment of antiangiogenic therapy responses in tumors.

UNLABELLED: Successful antiangiogenic therapies have been developed for the treatment of various cancers, but not all patients respond. Therefore, the early determination of therapy efficacy is essential for patient management. This study was done to evaluate the utility of various PET imaging biomarkers for early determination of the response to therapy with the antiangiogenic agent axitinib, a multiple receptor tyrosine kinase inhibitor, in tumors with diverse biologic characteristics. METHODS: Mice bearing U87-MG and MDA-MB-231 subcutaneous tumors were treated with axitinib (25 mg/kg intraperitoneally daily for 10 d), and tumor volumes were assessed with caliper measurements. The animals were concurrently imaged longitudinally with (18)F-FDG, 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT), and 2-(18)F-fluoroethyl-triazolyl conjugated c(RGDyK) peptide ((18)F-FtRGD) to determine the optimal radiopharmaceutical for measuring the early treatment response in the 2 tumor types. RESULTS: Daily administration of axitinib successfully retarded the growth of both U87-MG and MDA-MB-231 subcutaneous tumors, with significant differences in tumor volumes being observed from day 7 after therapy on. (18)F-FDG revealed a treatment efficacy response only at day 10 after treatment in both U87-MG tumor-bearing and MDA-MB-231 tumor-bearing animals. (18)F-FLT afforded earlier detection of the therapy response, revealing a significant difference between drug- and vehicle-treated animals at day 3 for animals bearing U87-MG tumors and at day 7 for animals bearing the more slowly growing MDA-MB-231 tumors. (18)F-FtRGD showed a rapid change in tumor retention that reached significance by day 7 in U87-MG tumor-bearing animals; in contrast, no significant difference in tumor retention was observed in MDA-MB-231 tumor-bearing animals. CONCLUSION: Longitudinal imaging with different radiopharmaceuticals displays various characteristics in different tumor types, depending on their biologic characteristics. Such studies may provide clinically important information to guide patient management and monitor the response to antiangiogenic therapy with the optimum noninvasive imaging agent in the relevant cancer type.

Design and synthesis of polymer-functionalized NIR fluorescent dyes--magnetic nanoparticles for bioimaging.

The fluorescent probes having complete spectral separation between absorption and emission spectra (large Stokes shift) are highly useful for solar concentrators and bioimaging. In bioimaging application, NIR fluorescent dyes have a greater advantage in tissue penetration depth compared to visible-emitting organic dyes or inorganic quantum dots. Here we report the design, synthesis, and characterization of an amphiphilic polymer, poly(isobutylene-alt-maleic anhyride)-functionalized near-infrared (NIR) IR-820 dye and its conjugates with iron oxide (Fe3O4) magnetic nanoparticles (MNPs) for optical and magnetic resonance (MR) imaging. Our results demonstrate that the Stokes shift of unmodified dye can be tuned (from ~106 to 208 nm) by the functionalization of the dye with polymer and MNPs. The fabrication of bimodal probes involves (i) the synthesis of NIR fluorescent dye (IR-820 cyanine) functionalized with ethylenediamine linker in high yield, >90%, (ii) polymer conjugation to the functionalized NIR fluorescent dye, and (iii) grafting the polymer-conjugated dyes on iron oxide MNPs. The resulting uniform, small-sized (ca. 6 nm) NIR fluorescent dye-magnetic hybrid nanoparticles (NPs) exhibit a wider emissive range (800-1000 nm) and minimal cytotoxicity. Our preliminary studies demonstrate the potential utility of these NPs in bioimaging by means of direct labeling of cancerous HeLa cells via NIR fluorescence microscopy and good negative contrast enhancement in T2-weighted MR imaging of a murine model.

Tuning sub-10 nm single-phase NaMnF3 nanocrystals as ultrasensitive hosts for pure intense fluorescence and excellent T1 magnetic resonance imaging.

We report ultrasensitive sub-10 nm NaMnF(3) nanocrystals codoped with Yb(3+), Er(3+)/Tm(3+) ions, and their intense pure red and near-infrared upconversion emissions in the presence of Mn(2+). The nanocrystals showed excellent T(1) contrast in 7 T MRI, implying their potential as single-phase contrast agents for fluorescent deep tissue and MR imaging.

A metabonomic analysis of organ specific response to USPIO administration.

As ultrasmall superparamagnetic particles of iron oxides (USPIO) have been widely used in clinical medicine as MRI contrast agents, hence their potential toxicity and adverse effects following administration have attracted particular attention. In the present study, high resolution magic-angle-spinning (1)H NMR spectroscopy coupled with multivariate statistical analysis was used to directly determine the metabolic consequences of specific-tissues, including kidney, liver and spleen following the intravenous administration of USPIO. Alterations of renal, hepatic and splenic function were reflected by changes in a number of metabolic pathways including small molecules involved in energy, lipid, glucose, and amino acids metabolism. The toxicological potential and metabolic fate of USPIO seems to be linked to their surface chemistry and particle size. Hierarchical principal component analysis was used to explore the multidimensional metabolic relationships between various biological matrices such as kidney, liver, spleen, plasma and urine. Information on the involvement of USPIO in transportation, absorption, biotransformation, biodistribution and secretion was derived from metabolic correlation analysis between different organs and biofluids. Such a metabonomic strategy provides methodology for investigating the potential adverse biological effects of similar nanoparticles on the environmental and human health and assessing the drug interventions on the targeted organ.

Molecular targeting of breast cancer: imaging and therapy.

Breast cancer is increasing at an alarming rate in women around the world, where medical biology is confronted by this disease on two crucial fronts. The first step is the early accurate diagnosis, which is very critical and the second step involves the appropriate clinical management. The current trend in molecular imaging of breast cancer provides not only an excellent tool in diagnosing the disease but also useful in validating the potentiality targeted of a pharmaceutical interventions. This review addresses the effectiveness of imaging technologies to resolve the molecular characterization and pathological evidences in breast cancer. The focus is on the present practices in breast cancer imaging, specifically targeting cellular machineries such as hormone receptors and angiogenic factors.

Bimodal magnetic-fluorescent probes for bioimaging.

Fluorescent optical probes have been intensively used in the area of bio-imaging. In this review article, we describe the recent advancements in the synthesis and application of bimodal magnetic-fluorescent probes for bioimaging. The bimodal probes consist of fluorescent [semiconducting quantum dots (e.g., CdSe/ZnS) or rare-earth doped (e.g., NaYF(4) :Yb,Er)] nanoparticles (NPs) and magnetic (iron oxide or gadolinium based) NPs for optical and magnetic resonance (MR) imaging.

Homing of stem cells to sites of inflammatory brain injury after intracerebral and intravenous administration: a longitudinal imaging study.

INTRODUCTION: This study aimed to determine the homing potential and fate of epidermal neural crest stem cells (eNCSCs) derived from hair follicles, and bone marrow-derived stem cells (BMSCs) of mesenchymal origin, in a lipopolysaccharide (LPS)-induced inflammatory lesion model in the rat brain. Both eNCSCs and BMSCs are easily accessible from adult tissues by using minimally invasive procedures and can differentiate into a variety of neuroglial lineages. Thus, these cells have the potential to be used in autologous cell-replacement therapies, minimizing immune rejection, and engineered to secrete a variety of molecules. METHODS: Both eNCSCs and BMSCs were prelabeled with iron-oxide nanoparticles (IO-TAT-FITC) and implanted either onto the corpus callosum in healthy or LPS-lesioned animals or intravenously into lesioned animals. Both cell types were tracked longitudinally in vivo by using magnetic resonance imaging (MRI) for up to 30 days and confirmed by postmortem immunohistochemistry. RESULTS: Transplanted cells in nonlesioned animals remained localized along the corpus callosum. Cells implanted distally from an LPS lesion (either intracerebrally or intravenously) migrated only toward the lesion, as seen by the localized MRI signal void. Fluorescence microscopy of the FITC tag on the nanoparticles confirmed the in vivo MRI data, CONCLUSIONS: This study demonstrated that both cell types can be tracked in vivo by using noninvasive MRI and have pathotropic properties toward an inflammatory lesion in the brain. As these cells differentiate into the glial phenotype and are derived from adult tissues, they offer a viable alternative autologous stem cell source and gene-targeting potential for neurodegenerative and demyelinating pathologies.

Gadolinium oxide ultranarrow nanorods as multimodal contrast agents for optical and magnetic resonance imaging.

We demonstrate a simple synthetic strategy for the fabrication of single-phase rare earth (RE) doped gadolinium oxide (Gd(2)O(3):RE where RE = terbium (Tb), ytterbium (Yb), and erbium (Er)) nanorods (NRs) as multimodal imaging probes. The NRs are ultranarrow and exhibit both emission and magnetic characteristics. The Tb-doped and Yb/Er-codoped Gd(2)O(3) NRs exhibit down- and up-conversion fluorescence respectively, and also exhibit paramagnetism. Importantly, these codoped NRs possess excellent magnetic characteristics, as shown in their longitudinal relaxation time (T1) -weighted image contrast, which is closer to that of commercial Gadovist for magnetic resonance imaging (MRI) applications. This property opens up new avenues in the development of contrast agents.

An in vivo multimodal imaging study using MRI and PET of stem cell transplantation after myocardial infarction in rats.

PURPOSE: The purpose of the study is to track iron-oxide nanoparticle-labelled adult rat bone marrow-derived stem cells (IO-rBMSCs) by magnetic resonance imaging (MRI) and determine their effect in host cardiac tissue using 2-deoxy-2-[F-18]fluoro-D: -glucose-positron emission tomography (FDG-PET). PROCEDURES: Infarcted rats were randomised to receive (1) live IO-rBMSCs by direct local injection, or (2) dead IO-rBMSCs as controls; (3) sham-operated rats received live IO-rBMSCs. The rats were then imaged from 2 days to 6 weeks post-cell implantation using both MRI at 9.4T and FDG-PET. RESULTS: Implanted IO-rBMSCs were visible in the heart by MRI for the duration of the study. Histological analysis confirmed that the implanted IO-rBMSCs were present for up to 6 weeks post-implantation. At 1 week post-IO-rBMSC transplantation, PET studies demonstrated an increase in FDG uptake in infarcted regions implanted with live IO-rBMSC compared to controls. CONCLUSIONS: Noninvasive multimodality imaging allowed us to visualise IO-rBMSCs and establish their affect on cardiac function in a rat model of myocardial infarction (MI).

Assessment of myocardial infarction in mice by late gadolinium enhancement MR imaging using an inversion recovery pulse sequence at 9.4T.

PURPOSE: To demonstrate the feasibility of using an inversion recovery pulse sequence and to define the optimal inversion time (TI) to assess myocardial infarction in mice by late gadolinium enhancement (LGE) MRI at 9.4T, and to obtain the maximal contrast between the infarcted and the viable myocardium. METHODS: MRI was performed at 9.4T in mice, two days after induction of myocardial infarction (n = 4). For cardiovascular MR imaging, a segmented magnetization-prepared fast low angle shot (MP-FLASH) sequence was used with varied TIs ranging from 40 to 420 ms following administration of gadolinium-DTPA at 0.6 mmol/kg. Contrast-to-noise (CNR) and signal-to-noise ratio (SNR) were measured and compared for each myocardial region of interest (ROI). RESULTS: The optimal TI, which corresponded to a minimum SNR in the normal myocardium, was 268 ms +/- 27.3. The SNR in the viable myocardium was significantly different from that found in the infarcted myocardium (17.2 +/- 2.4 vs 82.1 +/- 10.8; p = 0.006) leading to a maximal relative SI (Signal Intensity) between those two areas (344.9 +/- 60.4). CONCLUSION: Despite the rapid heart rate in mice, our study demonstrates that LGE MRI can be performed at 9.4T using a protocol similar to the one used for clinical MR diagnosis of myocardial infarction.

The human mirror system: a motor resonance theory of mind-reading.

Electrophysiological data confirm the existence of neurons that respond to both motor and sensory events in the macaque brain. These mirror neurons respond to execution and observation of goal-orientated actions. It has been suggested that they comprise a neural basis for encoding an internal representation of action. In this paper the evidence for a parallel system in humans is reviewed and the implications for human theory of mind processing are discussed. Different components of theory of mind are discussed; the evidence for mirror activity within subtypes is addressed. While there is substantial evidence for a human mirror system, there are weaknesses in the attempts to localize such a system in the brain. Preliminary evidence indicates that mirror neurons may be involved in theory of mind; however, these data by their very nature are reliant on the presence, and precise characterization, of the human mirror system.

Imaging molecular and cellular events in transplantation.

Imaging methods such as nuclear medicine (including positron emission tomography), magnetic resonance imaging, ultrasound, and optical imaging can be used to provide information about the expression of genes, and the location of molecules and cells in intact animals or patients. In the setting of transplantation, this will allow monitoring of inflammatory responses, as well as the state of the graft. In this review, the advantages and disadvantages of different approaches to imaging will be discussed, as well as their potential application to transplantation.