CXCR4-targeted and MMP-responsive iron oxide nanoparticles for enhanced magnetic resonance imaging

MRI offers high spatial resolution with excellent tissue penetration but it has limited sensitivity and the commonly administered contrast agents lack specificity. In this study, two sets of iron oxide nanoparticles (IONPs) were synthesized that were designed to selectively undergo copper-free click conjugation upon sensing of matrix metalloproteinase (MMP) enzymes, thereby leading to a self-assembled superparamagnetic nanocluster network with T2 signal enhancement properties. For this purpose, IONPs with bioorthogonal azide and alkyne surfaces masked by polyethylene glycol (PEG) layers tethered to CXCR4-targeted peptide ligands were synthesized and characterized. The IONPs were tested in vitro and T2 signal enhancements of around 160 % were measured when the IONPs were incubated with cells expressing MMP2/9 and CXCR4. Simultaneous systemic administration of the bioorthogonal IONPs in tumor-bearing mice demonstrated the signal-enhancing ability of these ‘smart’ self-assembling nanomaterials

In vivo fluorescence lifetime tomography of a FRET probe expressed in mouse

Förster resonance energy transfer (FRET) is a powerful biological tool for reading out cell signaling processes. In vivo use of FRET is challenging because of the scattering properties of bulk tissue. By combining diffuse fluorescence tomography with fluorescence lifetime imaging (FLIM), implemented using wide-field time-gated detection of fluorescence excited by ultrashort laser pulses in a tomographic imaging system and applying inverse scattering algorithms, we can reconstruct the three dimensional spatial localization of fluorescence quantum efficiency and lifetime. We demonstrate in vivo spatial mapping of FRET between genetically expressed fluorescent proteins in live mice read out using FLIM. Following transfection by electroporation, mouse hind leg muscles were imaged in vivo and the emission of free donor (eGFP) in the presence of free acceptor (mCherry) could be clearly distinguished from the fluorescence of the donor when directly linked to the acceptor in a tandem (eGFP-mCherry) FRET construct

Evaluation of 3D T1-weighted imaging at 3T across scanner vendors and models

Volumetric analyses of 3D T1-weighted images has become an integral part of the clinical work-up and research studies. Variation between scanners, in both vendors and models, is a major confound in combining imaging-derived biomarkers across sites. In this work, we analyse test-retest data from di×erent days on six 3 T scanners from three vendors to quantify this inter-scanner variability compared to intra-scanner variability. Contrast-to-noise ratios as well as volumetric analyses are performed showing between-scanner variation in total brain volumes – indicating di×erent scanner calibrations – but also tissue-speciÒc di×erences – possibly arising from di×erent e×ective contrasts

Age-dependent effects of chronic fluoxetine treatment on the serotonergic system one week following treatment

Abstract Rationale Selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine are increasingly used for the treatment of depression in children. Limited data are, however, available on their effects on brain development and their efficacy remains debated. Moreover, previous experimental studies are seriously hampered in their clinical relevance. Objectives The aim of the present study was to investigate putative age-related effects of a chronic treatment with fluoxetine (5 mg/kg, either orally or i.p. for 3 weeks, 1 week washout) using conventional methods (behavioral testing and binding assay using [ 123 I]β-CIT) and a novel magnetic resonance imaging (MRI) approach. Methods Behavior was assessed, as well as serotonin transporter (SERT) availability and function through ex vivo binding assays and in vivo pharmacological MRI (phMRI) with an acute fluoxetine challenge (10 mg/kg oral or 5 mg/kg i.v.) in adolescent and adult rats. Results Fluoxetine caused an increase in anxiety-like behavior in treated adult, but not adolescent, rats. On the binding assays, we observed increased SERT densities in most cortical brain regions and hypothalamus in adolescent, but not adult, treated rats. Finally, reductions in brain activation were observed with phMRI following treatment, in both adult and adolescent treated animals. Conclusion Collectively, our data indicate that the shortterm effects of fluoxetine on the 5-HT system may be agedependent. These findings could reflect structural and functional rearrangements in the developing brain that do not occur in the matured rat brain. phMRI possibly will be well suited to study this important issue in the pediatric population

Heart rate reduction with ivabradine promotes shear stress-dependent anti-inflammatory mechanisms in arteries

Blood flow generates wall shear stress (WSS) which alters endothelial cell (EC) function. Low WSS promotes vascular inflammation and atherosclerosis whereas high uniform WSS is protective. Ivabradine decreases heart rate leading to altered haemodynamics. Besides its cardio-protective effects, ivabradine protects arteries from inflammation and atherosclerosis via unknown mechanisms. We hypothesised that ivabradine protects arteries by increasing WSS to reduce vascular inflammation. Hypercholesterolaemic mice were treated with ivabradine for seven weeks in drinking water or remained untreated as a control. En face immunostaining demonstrated that treatment with ivabradine reduced the expression of pro-inflammatory VCAM-1 (p<0.01) and enhanced the expression of anti-inflammatory eNOS (p<0.01) at the inner curvature of the aorta. We concluded that ivabradine alters EC physiology indirectly via modulation of flow because treatment with ivabradine had no effect in ligated carotid arteries in vivo, and did not influence the basal or TNFα-induced expression of inflammatory (VCAM-1, MCP-1) or protective (eNOS, HMOX1, KLF2, KLF4) genes in cultured EC. We therefore considered whether ivabradine can alter WSS which is a regulator of EC inflammatory activation. Computational fluid dynamics demonstrated that ivabradine treatment reduced heart rate by 20 % and enhanced WSS in the aorta. In conclusion, ivabradine treatment altered haemodynamics in the murine aorta by increasing the magnitude of shear stress. This was accompanied by induction of eNOS and suppression of VCAM-1, whereas ivabradine did not alter EC that could not respond to flow. Thus ivabradine protects arteries by altering local mechanical conditions to trigger an anti-inflammatory response

A longitudinal study of patients with cirrhosis treated with L-ornithine L-aspartate, examined with magnetization transfer, diffusion-weighted imaging and magnetic resonance spectroscopy

The presence of overt hepatic encephalopathy (HE) is associated with structural, metabolic and functional changes in the brain discernible by use of a variety of magnetic resonance (MR) techniques. The changes in patients with minimal HE are less well documented. Twenty-two patients with well-compensated cirrhosis, seven of whom had minimal HE, were examined with cerebral 3 Tesla MR techniques, including T1- and T2-weighted, magnetization transfer and diffusion-weighted imaging and proton magnetic resonance spectroscopy sequences. Studies were repeated after a 4-week course of oral L-ornithine L-aspartate (LOLA). Results were compared with data obtained from 22 aged-matched healthy controls. There was no difference in mean total brain volume between patients and controls at baseline. Mean cerebral magnetization transfer ratios were significantly reduced in the globus pallidus and thalamus in the patients with cirrhosis irrespective of neuropsychiatric status; the mean ratio was significantly reduced in the frontal white matter in patients with minimal HE compared with healthy controls but not when compared with their unimpaired counterparts. There were no significant differences in either the median apparent diffusion coefficients or the mean fractional anisotropy, calculated from the diffusion-weighted imaging, or in the mean basal ganglia metabolite ratios between patients and controls. Psychometric performance improved in 50% of patients with minimal HE following LOLA, but no significant changes were observed in brain volumes, cerebral magnetization transfer ratios, the diffusion weighted imaging variables or the cerebral metabolite ratios. MR variables, as applied in this study, do not identify patients with minimal HE, nor do they reflect changes in psychometric performance following LOLA

Liver fat content and T2*: simultaneous measurement by using breath-hold multiecho MR imaging at 3.0 T--feasibility.

Research ethics committee approval was obtained for this study, and written informed consent was obtained from all participants. The purpose was to prospectively evaluate the feasibility of breath-hold multiecho in- and out-of-phase magnetic resonance (MR) imaging for simultaneous lipid quantification and T2* measurement. A spoiled gradient-echo sequence with seven echo times alternately in phase and out of phase was used at 3.0 T. Imaging was performed in a lipid phantom, in five healthy volunteers (all men; mean age, 37 years), and in five obese individuals with hyperlipidemia or diabetes (four men, one woman; mean age, 53 years). A biexponential curve-fitting model was used to derive the relative signal contributions from fat and water, and these results were compared with results of liver proton MR spectroscopy, the reference standard. There was a significant correlation between multiecho and spectroscopic measurements of hepatic lipid concentration (r2 = 0.99, P < .001). In vivo, the T2* of water was consistently longer than that of fat and reliably enabled the signal components to be correctly assigned. In the lipid phantom, the multiecho method could be used to determine the fat-to-water ratio and the T2* values of fat and water throughout the entire range of fat concentrations. Multiecho imaging shows promise as a method of simultaneous fat and T2* quantification

Imaging of the vulnerable carotid plaque: biological targeting of inflammation in atherosclerosis using iron oxide particles and MRI.

OBJECTIVES: Identification of those 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 the propensity of atherosclerotic lesions to cause clinical sequelae. There is currently no clinical imaging technique available to assess the degree of inflammation associated with plaques. This study aims at visualizing and characterizing atherosclerosis using antibody-conjugated superparamagnetic iron oxide (SPIO) particles as an MRI probe to assess inflammation in human atherosclerotic plaques. METHODS: Atherosclerotic plaques were collected from 20 consecutive patients (n=10 from symptomatic patients, n=10 from asymptomatic patients) undergoing carotid endarterectomy (CEA) for extracranial high-grade internal carotid artery (ICA) stenosis (&gt;70% luminal narrowing). Inflammatory markers on human atherosclerotic plaques were detected and characterized by ex vivo magnetic resonance imaging (MRI) using anti-VCAM-1 antibody and anti-E-selectin antibody-conjugated SPIO with confirmatory immunohistochemistry. RESULTS: Inflammation associated with human ex vivo atherosclerotic plaques could be imaged using dual antibody-conjugated SPIO by MRI. Symptomatic plaques could be distinguished from asymptomatic ones by the degree of inflammation, and the MR contrast effect was significantly correlated with the degree of plaque inflammation (r=.64, p&lt;.001). The asymptomatic plaque population exhibited heterogeneity in terms of inflammation. The dual-targeted SPIO-induced MR signal not only tracked closely with endothelial activation (i.e. endothelial expression of VCAM-1 and E-selectin), but also reflected the macrophage burden within plaque lesions, offering a potential imaging tool for quantitative MRI of inflammatory activity in atherosclerosis. CONCLUSIONS: These functional molecular MRI probes constitute a novel imaging tool for ex vivo characterization of atherosclerosis at a molecular level. Further development and translation into the clinical arena will facilitate more accurate risk stratification in carotid artery disease in the future

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.This study was funded by The Health and Medical Research Fund from The Food and Health Bureau, The Government of The Hong Kong Special Administrative Region. The Food and Health Bureau, The Government of The Hong Kong Special Administrative Region had no involvement in the study design; collection, analysis, and interpretation of data; manuscript writing; or the decision to submit the manuscript for publication