The efficient delivery of nanomaterials to specific targets for in vivo biomedical imaging is hindered by rapid sequestration by the reticuloendothelial system (RES) and consequent short circulation times. To overcome these two problems, we have prepared a new stealth PEG polymer conjugate containing a terminal 1,1-bisphosphonate (BP) group for strong and stable binding to the surface of ultrasmall-superparamagnetic oxide nanomaterials (USPIOs). This polymer, PEG(5)-BP, can be used to exchange the hydrophobic surfactants commonly used in the synthesis of USPIOs very efficiently and at room temperature using a simple method in 1 h. The resulting nanoparticles, PEG(5)-BP-USPIOs are stable in water or saline for at least 7 months and display a near-zero ζ-potential at neutral pH. The longitudinal (r1) and transverse (r2) relaxivities were measured at a clinically relevant magnetic field (3 T), revealing a high r1 of 9.5 mM–1 s–1 and low r2/r1 ratio of 2.97, making these USPIOs attractive as T1-weighted MRI contrast agents at high magnetic fields. The strong T1-effect was demonstrated in vivo, revealing that PEG(5)-BP-USPIOs remain in the bloodstream and enhance its signal 6-fold, allowing the visualization of blood vessels and vascular organs with high spatial definition. Furthermore, the optimal relaxivity properties allow us to inject a dose 4 times lower than with other USPIOs. PEG(5)-BP-USPIOs can also be labeled using a radiolabeled-BP for visualization with single photon emission computed tomography (SPECT), and thus affording dual-modality contrast. The SPECT studies confirmed low RES uptake and long blood circulation times (t1/2 = 2.97 h). These results demonstrate the potential of PEG(5)-BP-USPIOs for the development of targeted multimodal imaging agents for molecular imaging.

Background-Endothelial dysfunction promotes atherosclerosis and precedes acute cardiovascular events. We investigated whether in vivo magnetic resonance imaging with the use of an albumin-binding contrast agent, gadofosveset, could detect endothelial damage associated with atherosclerosis in apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) mice. Furthermore, we tested whether magnetic resonance imaging could noninvasively assess endothelial function by measuring the endothelial-dependent vasodilation in response to acetylcholine. Methods and Results-ApoEϪ/Ϫ mice were imaged at 4, 8, and 12 weeks after commencement of a high-fat diet. Statin-treated ApoE Ϫ/Ϫ mice were scanned after 12 weeks of a high-fat diet. Wild-type mice were imaged before and 48 hours after injection of Russell's viper venom, an endothelial toxin. Delayed enhancement magnetic resonance imaging and T1 mapping of the brachiocephalic artery, 30 minutes after injection of gadofosveset, showed increased vessel wall enhancement and relaxation rate (R 1 ) with progression of atherosclerosis in ApoE (R 1 ϭ3.0Ϯ0.65) mice showed less enhancement. Uptake of gadofosveset correlated with Evans blue staining, morphological changes of endothelial cells, and widening of the cell-cell junctions, suggesting that uptake occurs in regions of increased vascular permeability. Endothelial-dependent vasomotor responses showed vasoconstriction of the arteries of the ApoE Ϫ/Ϫ (Ϫ22.22Ϯ7.95%) and Russell's viper venom-injected (Ϫ10.37Ϯ17.60%) mice compared with wild-type mice (32.45Ϯ12.35%). Statin treatment improved endothelium morphology and function (Ϫ8.12Ϯ8.22%). Conclusions-We demonstrate the noninvasive assessment of endothelial permeability and function with the use of an albumin-binding magnetic resonance contrast agent. Blood albumin leakage could be a surrogate marker for the in vivo evaluation of interventions that aim to restore the endothelium. (Circulation. 2012;126:707-719.)Key Words: atherosclerosis Ⅲ endothelial dysfunction Ⅲ gadofosveset Ⅲ magnetic resonance imaging Ⅲ permeability A therosclerosis is a chronic disease of the vessels and a major cause of death in Western societies. Dysfunction of the vascular endothelium triggers leukocyte transmigration, platelet activation, smooth muscle cell proliferation, and vasoconstriction, which collectively promote the development of atherosclerosis. 1 Additionally, damaged endothelium can precipitate the complications of atherosclerosis through vasospasm and thrombosis, causing life-threatening cardiovascular events. Clinical Perspective on p 719Transport across the normal endothelium occurs between endothelial cells (ECs) (intercellular pathway) and/or through the ECs (transcytosis). Intercellular junctions with a diameter of Ϸ2 nm allow transport of small water-soluble molecules up to that diameter, 2 whereas breaks in the tight junctions with a diameter of Ϸ20 nm 3,4 accommodate the influx of albumin (diameter of Ϸ6 nm) and Evans blue dye (EBD). At the molecular level, oxidized low-density lipoprotein (1) decreases...

A novel bifunctional chelator combines a dithiocarbamate group for binding the positron‐emitter 64Cu (red spheres) for PET imaging and a bisphosphonate group (green ellipsoids) for strong binding to several inorganic materials, such as MRI contrast agents based on superparamagnetic iron oxide nanoparticles and rare‐earth metal oxides. The dual PET–MR imaging capabilities of this approach are demonstrated in vivo by imaging lymph nodes using both imaging modalities.

Cardiac remodelling and contractile dysfunction occur during both acute and chronic disease processes including the accumulation of insoluble aggregates of misfolded amyloid proteins that are typical features of Alzheimer's, Parkinson's and Huntington's disease (HD). While HD has been described mainly as a neurological disease, multiple epidemiological studies have shown that HD patients exhibit a high incidence of cardiovascular events leading to heart failure, and that this is the second highest cause of death. Given that huntingtin is ubiquitously expressed, cardiomyocytes may be at risk of an HD-related dysfunction. In mice, the forced expression of an expanded polyQ repeat under the control of a cardiac specific promoter led to severe heart failure followed by reduced lifespan. However the mechanism leading to cardiac dysfunction in the clinical and pre-clinical HD settings remains unknown. To unravel this mechanism, we employed the R6/2 transgenic and HdhQ150 knock-in mouse models of HD. We found that pre-symptomatic animals developed connexin-43 relocation and a significant deregulation of hypertrophic markers and Bdnf transcripts. In the symptomatic animals, pronounced functional changes were visualised by cardiac MRI revealing a contractile dysfunction, which might be a part of dilatated cardiomyopathy (DCM). This was accompanied by the re-expression of foetal genes, apoptotic cardiomyocyte loss and a moderate degree of interstitial fibrosis. To our surprise, we could identify neither mutant HTT aggregates in cardiac tissue nor a HD-specific transcriptional dysregulation, even at the end stage of disease. We postulate that the HD-related cardiomyopathy is caused by altered central autonomic pathways although the pathogenic effects of mutant HTT acting intrinsically in the heart may also be a contributing factor.

The combination of radionuclide-based imaging modalities such as single photon emission computed tomography (SPECT) and positron emission tomography (PET) with magnetic resonance imaging (MRI) is likely to become the next generation of clinical scanners. Hence, there is a growing interest in the development of SPECT- and PET-MRI agents. To this end, we report a new class of dual-modality imaging agents based on the conjugation of radiolabeled bisphosphonates (BP) directly to the surface of superparamagnetic iron oxide (SPIO) nanoparticles. We demonstrate the high potential of BP-iron oxide conjugation using (⁹⁹m)Tc-dipicolylamine(DPA)-alendronate, a BP-SPECT agent, and Endorem/Feridex, a liver MRI contrast agent based on SPIO. The labeling of SPIOs with (⁹⁹m)Tc-DPA-alendronate can be performed in one step at room temperature if the SPIO is not coated with an organic polymer. Heating is needed if the nanoparticles are coated, as long as the coating is weakly bound as in the case of dextran in Endorem. The size of the radiolabeled Endorem (⁹⁹m)Tc-DPA-ale-Endorem) was characterized by TEM (5 nm, Fe₃O₄ core) and DLS (106 ± 60 nm, Fe₃O₄ core + dextran). EDX, Dittmer-Lester, and radiolabeling studies demonstrate that the BP is bound to the nanoparticles and that it binds to the Fe₃O₄ cores of Endorem, and not its dextran coating. The bimodal imaging capabilities and excellent stability of these nanoparticles were confirmed using MRI and nanoSPECT-CT imaging, showing that (⁹⁹m)Tc and Endorem co-localize in the liver and spleen In Vivo, as expected for particles of the composition and size of (⁹⁹m)Tc-DPA-ale-Endorem. To the best of our knowledge, this is the first example of radiolabeling SPIOs with BP conjugates and the first example of radiolabeling SPIO nanoparticles directly onto the surface of the iron oxide core, and not its coating. This work lays down the basis for a new generation of SPECT/PET-MR imaging agents in which the BP group could be used to attach functionality to provide targeting, stealth/stability, and radionuclides to Fe₃O₄ nanoparticles using very simple methodology readily amenable to GMP.

AM. High-frequency speckle tracking echocardiography in the assessment of left ventricular function and remodeling after murine myocardial infarction. Am J Physiol Heart Circ Physiol 306: H1371-H1383, 2014. First published February 15, 2014 doi:10.1152/ajpheart.00553.2013.-The objectives of this study were to assess the feasibility and accuracy of high-frequency speckle tracking echocardiography (STE) in a murine model of myocardial infarction (MI). STE is used clinically to quantify global and regional cardiac function, but its application in mice is challenging because of the small cardiac size and rapid heart rates. A high-frequency microultrasound system with STE (Visualsonics Vevo 2100) was compared against magnetic resonance imaging (MRI) for the assessment of global left ventricular (LV) size and function after murine MI. Animals subjected to coronary ligation (n ϭ 46) or sham ligation (n ϭ 27) were studied 4 wk postoperatively. Regional and global deformation were also assessed. STE-derived LV ejection fraction (EF) and mass correlated well with MRI indexes (r ϭ 0.93, 0.77, respectively; P Ͻ 0.001), as did STE-derived mass with postmortem values (r ϭ 0.80, P Ͻ 0.001). Higher STE-derived volumes correlated positively with MRI-derived infarct size (P Ͻ 0.01). Global strain parameters were significantly reduced after MI (all P Ͻ 0.001) and strongly correlated with LV mass and MRI-derived infarct size as promising surrogates for the extent of remodeling and infarction, respectively (both P Ͻ 0.05). Regional strain analyses showed that radial strain and strain rate were relatively preserved in anterior basal segments after MI compared with more apical segments (P Ͻ 0.001); however, longitudinal strain and strain rate were significantly impaired both basally and distally (P Ͻ 0.001). Strain-derived parameters of dyssynchrony were significantly increased in the MI group (P Ͻ 0.01). Analysis time for STE was 210 Ϯ 45 s with acceptable inter-and intraobserver variability. In conclusion, high-frequency STE enables quantitative assessment of regional and global function in the remodeling murine LV after MI. mouse; myocardial infarction; strain; echocardiography; left ventricular function COMPARED WITH CLINICAL IMAGING, echocardiography in mouse models remains relatively challenging, primarily because of the exceptional spatial and temporal resolution required to image such a small, rapidly beating heart. Research studies involving gene-modified mouse models commonly use clinical echocardiography systems (with transducer frequencies of up to 15 MHz) and tend to rely on rather simple measures of LV size and function, for example from M-mode tracings. These measures provide relatively crude estimates of global LV size and function, especially in remodeled hearts (e.g., after MI) where the geometric assumptions of symmetry are likely to be inaccurate. In clinical practice, such measures have largely been superseded, and the last decade has seen the introduction of several advanced echocardiography techniques to improve...

A sound theoretical rationale for the design of a magnetic nanocarrier capable of magnetic capture in vivo after intravenous administration could help elucidate the parameters necessary for in vivo magnetic tumor targeting. In this work, we utilized our long-circulating polymeric magnetic nanocarriers, encapsulating increasing amounts of superparamagnetic iron oxide nanoparticles (SPIONs) in a biocompatible oil carrier, to study the effects of SPION loading and of applied magnetic field strength on magnetic tumor targeting in CT26 tumor-bearing mice. Under controlled conditions, the in vivo magnetic targeting was quantified and found to be directly proportional to SPION loading and magnetic field strength. Highest SPION loading, however, resulted in a reduced blood circulation time and a plateauing of the magnetic targeting. Mathematical modeling was undertaken to compute the in vivo magnetic, viscoelastic, convective, and diffusive forces acting on the nanocapsules (NCs) in accordance with the Nacev-Shapiro construct, and this was then used to extrapolate to the expected behavior in humans. The model predicted that in the latter case, the NCs and magnetic forces applied here would have been sufficient to achieve successful targeting in humans. Lastly, an in vivo murine tumor growth delay study was performed using docetaxel (DTX)-encapsulated NCs. Magnetic targeting was found to offer enhanced therapeutic efficacy and improve mice survival compared to passive targeting at drug doses of ca. 5-8 mg of DTX/kg. This is, to our knowledge, the first study that truly bridges the gap between preclinical experiments and clinical translation in the field of magnetic drug targeting.

Purpose: To investigate myocardial infarction (MI), late gadolinium (Gd) enhancement (LGE), cardiovascular magnetic resonance imaging (CMRI) is used as the current gold standard for the in vivo diagnosis in patients and preclinical studies. While inversion recovery (IR) fast gradient echo LGE imaging is the preferred technique at clinical field strengths it remains to be investigated which is the best sequence at higher field strength. We therefore compared the IR technique against cine fast low shot angle (cine-FLASH) for the quantification of MI size in mice at 7T in vivo.Materials and Methods: Five mice were used to optimize cine-FLASH and IR parameters. Nine mice were subsequently imaged with optimized parameters using both techniques 2-3 days after MI and %30 minutes post Gd injection. Results:The difference in infarct size values was within 3.3% between the two CMRI techniques and within 7.5% of histological values by Bland-Altman analysis. Contrast-to-noise-ratio between infarcted and normal tissue as well as blood was higher for cine-FLASH with the additional benefit of a 2-time-fold shorter scan time than with the IR method. Furthermore, left ventricular function/volumes could be calculated from cine-FLASH images before as well as after Gd injection. Conclusion:In conclusion, cine-FLASH LGE MRI represents an attractive alternative to IR LGE MRI for infarct size assessment in mice at high field strengths because it provides similar accuracy while being more robust, faster, and less user dependent.