Properties of a novel magnetized alginate for magnetic resonance imaging

Implanting recombinant cells encapsulated in alginate microcapsules to secrete therapeutic proteins has been proven clinically effective in treating several murine models of human diseases. However, once implanted, these microcapsules cannot be assessed without invasive surgery. We now report the preparation and characterization of a novel ferrofluid to render these microcapsules visible with magnetic resonance imaging (MRI). The ferrofluid was prepared as a colloidal iron oxide stabilized in water by alginate. The presence of iron particles in the ferrofluid was verified with chemical titration, dynamic light scattering, and magnetization measurement. The microcapsules fabricated with various concentrations of the ferrofluid in the core, or on the surface of alginate microcapsules, or both, all produced microcapsules with smooth surfaces as shown with light and scanning electron microscopy. However, at the nanoscale level, as revealed with atomic force microscopy, the ferrofluid-fabricated microcapsules demonstrated increased granularity, particularly when the ferrofluid was used to laminate the surface. From the force spectroscopy measurements, these modified microcapsules showed increasing surface rigidity in the following order: traditional alginate < ferrofluid in the core < ferrofluid on the surface. Although the mechanical stability of low-concentration ferrofluid (0.1%) microcapsules was reduced, increasing concentrations, up to 20%, were able to improve stability. When these ferrofluid microcapsules were examined with MRI, their T(2) relaxation time was reduced, thereby producing increased contrast readily detectable with MRI, whereas the traditional alginate microcapsules showed no difference when compared with water. In conclusion, such ferrofluid-enhanced alginate is suitable for fabricating microcapsules that offer the potential for in vivo tracking of implanted microcapsules without invasive surgery.     

High throughput magnetic resonance imaging for evaluating targeted nanoparticle probes.

The ability to image specific molecular targets in vivo would have significant impact in allowing earlier disease detection and in tailoring molecular therapies. One of the rate-limiting steps in the development of novel compounds as reporter probes has been the lack of cell-based, biologically relevant, high throughput screening methods. Here we describe the development and validation of magnetic resonance imaging (MRI) as a technique to rapidly screen compounds that are potential MR reporter agents for their interaction with specific cellular targets. We show that MR imaging can (1) evaluate thousands of samples simultaneously and rapidly, (2) provide exceedingly accurate measurements, and (3) provide receptor binding/internalization data as validated by radioactive assays. The technique allows the screening of libraries of peptide-nanoparticle conjugates against target cells and the identification of conjugates that may be subsequently used as reporter agents in vivo. The technology should greatly accelerate the development of target-specific or cell-specific MR contrast agents.     

Synthesis and characterization of new porphyrazine-Gd(III) conjugates as multimodal MR contrast agents

Magnetic resonance imaging (MRI) has long been used clinically and experimentally as a diagnostic tool to obtain three-dimensional, high-resolution images of deep tissues. These images are enhanced by the administration of contrast agents such as paramagnetic Gd(III) complexes. Herein, we describe the preparation of a series of multimodal imaging agents in which paramagnetic Gd(III) complexes are conjugated to a fluorescent tetrapyrrole, namely, a porphyrazine (pz). Zinc metalated pzs conjugated to one, four, or eight paramagnetic Gd(III) complexes are reported. Among these conjugates, Zn-Pz-8Gd(III) exhibits an ionic relaxivity four times that of the monomeric Gd(III) agent, presumably because of increased molecular weight and a molecular relaxivity that is approximately thirty times larger, while retaining the intense electronic absorption and emission of the unmodified pz. Unlike current clinical MR agents, Zn-Pz-1Gd(III) is taken up by cells. This probe demonstrates intracellular fluorescence by confocal microscopy and provides significant contrast enhancement in MR images, as well as marked phototoxicity in assays of cellular viability. These results suggest that pz agents possess a new potential for use in cancer imaging by both MRI and near-infrared (NIR) fluorescence, while acting as a platform for photodynamic therapy.     

多功能磁共振造影剂研究进展

磁共振成像技术因对人体无创、任意方向断层扫描三维图像且分辨率较高、提供形态与功能两方面诊断评价等突出优点,成为了临床上用于疾病诊断的重要手段之一。临床上使用磁共振造影剂可以提高成像的分辨率和灵敏度,提高图像质量,增强对比度和可读性。但是,各种成像技术由于实现原理不同,具有各自的优势和缺陷,靠传统单一的诊断模式无法提供疾病的全面信息,因而在对各种复杂疾病进行诊断时会受到一定的限制。因此,将磁共振成像与其他成像技术如CT成像、超声成像等联合起来使用,则可以达到优势互补的效果,能为疾病的临床诊断提供更快捷精确的信息,同时可将磁共振成像与各种治疗方式结合在一起,即开发基于磁共振成像的诊断治疗一体化试剂,以实现对疾病的即时治疗和实时监控。本文主要介绍了磁共振成像造影剂的原理和种类,并且综述了目前国内外在基于磁共振成像的多功能造影剂/诊疗制剂这一领域的研究进展,最后就未来可能的研究方向进行了展望。     

In vivo visualization of gene expression using magnetic resonance imaging

High-resolution in vivo imaging of gene expression is not possible in opaque animals by existing techniques. Here we present a new approach for obtaining such images by magnetic resonance imaging (MRI) using an MRI contrast agent that can indicate reporter gene expression in living animals. We have prepared MRI contrast agents in which the access of water to the first coordination sphere of a chelated paramagnetic ion is blocked with a substrate that can be removed by enzymatic cleavage. Following cleavage, the paramagnetic ion can interact directly with water protons to increase the MR signal. Here, we report an agent where galactopyranose is the blocking group. This group renders the MRI contrast agent sensitive to expression of the commonly used marker gene, beta-galactosidase. To cellular resolution, regions of higher intensity in the MR image correlate with regions expressing marker enzyme. These results offer the promise of in vivo mapping of gene expression in transgenic animals and validate a general approach for constructing a family of MRI contrast agents that respond to biological activity.     

Development of Bifunctional Gadolinium-Labeled Superparamagnetic Nanoparticles (Gd-MnMEIO) for In Vivo MR Imaging of the Liver in an Animal Model

Liver tumors are common and imaging methods, particularly magnetic resonance imaging (MRI), play an important role in their non-invasive diagnosis. Previous studies have shown that detection of liver tumors can be improved by injection of two different MR contrast agents. Here, we developed a new contrast agent, Gd-manganese-doped magnetism-engineered iron oxide (Gd-MnMEIO), with enhancement effects on both T1- and T2-weighted MR images of the liver. A 3.0T clinical MR scanner equipped with transmit/receiver coil for mouse was used to obtain both T1-weighted spoiled gradient-echo and T2-weighted fast spin-echo axial images of the liver before and after intravenous contrast agent injection into Balb/c mice with and without tumors. After pre-contrast scanning, six mice per group were intravenously injected with 0.1 mmol/kg Gd-MnMEIO, or the control agents, i.e., Gd-DTPA or SPIO. The scanning time points for T1-weighted images were 0.5, 5, 10, 15, 20, 25, and 30 min after contrast administration. The post-enhanced T2-weighted images were then acquired immediately after T1-weighted acquisition. We found that T1-weighted images were positively enhanced by both Gd-DTPA and Gd-MnMEIO and negatively enhanced by SPIO. The enhancement by both Gd-DTPA and Gd-MnMEIO peaked at 0.5 min and gradually declined thereafter. Gd-MnMEIO (like Gd-DTPA) enhanced T1-weighted images and (like SPIO) T2-weighted images. Marked vascular enhancement was clearly visible on dynamic T1-weighted images with Gd-MnMEIO. In addition, the T2 signal was significantly decreased at 30 min after administration of Gd-MnMEIO. Whereas the effects of Gd-MnMEIO and SPIO on T2-weighted images were similar (p = 0.5824), those of Gd-MnMEIO and Gd-DTPA differed, with Gd-MnMEIO having a significant T2 contrast effect (p = 0.0086). Our study confirms the feasibility of synthesizing an MR contrast agent with both T1 and T2 shortening effects and using such an agent in vivo. This agent enables tumor detection and characterization in single liver MRI sections.     

Magnetic resonance imaging in the differential diagnosis of chronic endometritis: capacities and methodic features

By examining 83 females aged 17-48 years by magnetic resonance imaging (MRI), the authors conclude that the specificity and sensitivity of the technique without MR contrast agents in detecting chronic endometritis (CE) and chronic metroendometritis (CME) are 75.3 and 95.9%, respectively. On the MRI scans, hypertrophic and atrophic forms of CE have rather specific MR signs and appear as changes not only in the functional layer of the endometrium and transitional area, but also in the proper myometrium in CME. This all permits evaluating the degree of uterine wall involvement in the pathological process. Overall, the MRI criteria proposed by the authors can identify the signs of a chronic inflammatory process and its sequels and make a differential diagnosis this condition with female genital diseases to a high accuracy.     

Improvement of MRI probes to allow efficient detection of gene expression

Recently, it has been demonstrated that magnetic resonance imaging (MRI) utilizing monocrystalline iron oxide nanoparticles (MIONs) targeted to an engineered transferrin receptor enables imaging of gene expression. However, the relatively high doses of iron oxides used indicated the need for improved MR imaging probes to monitor changes in gene expression in vivo. Using alternative conjugation chemistries to link targeting ligands and iron oxide nanoparticles, we present the development and characterization as well as improved receptor binding and MRI detection of a novel imaging probe. Iron oxide nanoparticles with a cross-linked dextran coat were conjugated to transferrin (Tf) through the linker molecule N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) to yield Tf-S-S-CLIO. The characteristics of this conjugate were evaluated in comparison to Tf-MION and Tf-CLIO generated by oxidative activation of the dextran-coat with subsequent reduction of Schiff's base. SPDP conjugation allowed approximately a 4-fold increase in the number of Tf molecules attached per iron oxide nanoparticle and resulted in a more than 10-fold improvement of binding and uptake by cells. This translated into an imaging probe that was 16 times better for imaging gene expression in a cellular MRI assay. This novel probe for MRI may substantially increase the sensitivity for the detection of endogenous or genetically induced transferrin receptor expression in small numbers of cells and may significantly reduce the imaging dose from over 100 mg/kg to doses of iron oxides that are currently used in clinical imaging.     

海藻酸钠漂浮微囊的制备以及载药应用研究

目的:本文研究了一种海藻酸钠漂浮微囊的制备方法用以实现胃部持续给药。方法:采用微胶囊发生器制备海藻酸钠漂浮微囊,壁材为海藻酸钠,芯材为食用油的漂浮微囊,衡量不同的制备参数对微囊的理化特性影响;采用克拉霉素作为模型脂溶性药物,测量漂浮药物递送系统的控制释放性质、以及微囊载药特性和小鼠体内漂浮验证。结果:成功制备出了具有漂浮特性的海藻酸钠微囊,其中泵送速度对微囊性质的影响最大。制备出的微囊具有低细胞毒性,可以实现90%的药物包埋率。此外,微囊可以在小鼠的胃中保存超过6小时,具有良好的漂浮特性。结论:海藻酸钠漂浮微囊是一种有效的胃部药物递送系统,可明显延长药物在胃部的滞留时间。     

New concepts in characterization of ischemically injured myocardium by MRI

New concepts regarding the assessment of ischemic myocardial injuries have been addressed in this Minireview using magnetic resonance imaging (MRI). MRI, with its different techniques, brings not only anatomic, but also physiologic, information on ischemic heart disease. It has the ability to measure identical parameters in preclinical and clinical studies. MRI techniques provide the ideal package for repeated and noninvasive assessment of myocardial anatomy, viability, perfusion, and function. MR contrast agents can be applied in a variety of ways to improve MRI sensitivity for detecting and assessing ischemically injured myocardium. With MR contrast agents protocol, it becomes possible to identify ischemic, acutely infarcted, and peri-infarcted myocardium in occlusive and reperfused infarctions. Necrosis specific and nonspecific extracellular contrast-enhanced MRI has been used to assess myocardial viability. Contrast-enhanced perfusion MRI can explore the disturbances in large (angiography) and small coronary arteries (myocardial perfusion) as the underlying cause of myocardial dysfunction. Perfusion MRI has been used to measure myocardial perfusion (ml/min/g) and to demonstrate the difference in transmural myocardial blood flow. Information on no-reflow phenomenon is derived from dynamic changes in regional signal intensity after bolus injection of MR contrast agents. Another development is the near future availability of blood pool MR contrast agents. These agents are able to assess microvascular permeability and integrity and are advantageous in MR angiography (MRA) due to their persistence in the blood. Noncontrast-enhanced MRI such as cine MRI at rest/stress, sodium MRI, and MR spectroscopy also have the potential to noninvasively assess myocardial viability in patients. Futuristic applications for MRI in the heart will focus on identifying coronary artery disease at an early stage and the beneficial effects of new therapeutic agents such as intra-arterial gene therapy. MR techniques will have great future in the drug discovery process and in testing the effects of drugs on myocardial biochemistry, physiology, and morphology. Molecular imaging is going to bloom in this decade.     

Paramagnetic liposomes as innovative contrast agents for magnetic resonance (MR) molecular imaging applications

This article illustrates some innovative applications of liposomes loaded with paramagnetic lanthanide-based complexes in MR molecular imaging field. When a relatively high amount of a Gd(III) chelate is encapsulated in the vesicle, the nanosystem can simultaneously affect both the longitudinal (R(1)) and the transverse (R(2)) relaxation rate of the bulk H2O H-atoms, and this finding can be exploited to design improved thermosensitive liposomes whose MRI response is not longer dependent on the concentration of the probe. The observation that the liposome compartmentalization of a paramagnetic Ln(III) complex induce a significant R(2) enhancement, primarily caused by magnetic susceptibility effects, prompted us to test the potential of such agents in cell-targeting MR experiments. The results obtained indicated that these nanoprobes may have a great potential for the MR visualization of cellular targets (like the glutamine membrane transporters) overexpressing in tumor cells. Liposomes loaded with paramagnetic complexes acting as NMR shift reagents have been recently proposed as highly sensitive CEST MRI agents. The main peculiarity of CEST probes is to allow the MR visualization of different agents present in the same region of interest, and this article provides an illustrative example of the in vivo potential of liposome-based CEST agents.     

Molecular magnetic resonance imaging with targeted contrast agents

Magnetic resonance imaging (MRI) produces high-resolution three-dimensional maps delineating morphological features of the specimen. Differential contrast in soft tissues depends on endogenous differences in water content, relaxation times, and/or diffusion characteristics of the tissue of interest. The specificity of MRI can be further increased by exogenous contrast agents (CA) such as gadolinium chelates, which have been successfully used for imaging of hemodynamic parameters including blood perfusion and vascular permeability. Development of targeted MR CA directed to specific molecular entities could dramatically expand the range of MR applications by combining the noninvasiveness and high spatial resolution of MRI with specific localization of molecular targets. However, due to the intrinsically low sensitivity of MRI (in comparison with nuclear imaging), high local concentrations of the CA at the target site are required to generate detectable MR contrast. To meet these requirements, the MR targeted CA should recognize targeted cells with high affinity and specificity. They should also be characterized by high relaxivity, which for a wide variety of CA depends on the number of contrast-generating groups per single molecule of the agent. We will review different designs and applications of targeted MR CA and will discuss feasibility of these approaches for in vivo MRI.     

Analysis of fluorescent MRI contrast agent behavior in the liver and thoracic aorta of mice

OBJECTIVE: To characterize the behavior of magnetofluorescent products injected in mice intravenously. STUDY DESIGN: The magnetic resonance imaging (MRI) products were labelled with fluorescent molecules to examine the biodistribution process in vivo and observe them at the cellular level by means of confocal microscopy. Three-dimensional (3D) sequences of images were obtained by spectral analysis of sample preparations in a multiphoton confocal microscope and analyzed by the factor analysis of medical image sequence algorithm, which provides factor curves. Factor images are the result of image-processing methods that utilize information from emission spectra. Preparations are also screened in the counting mode to provide fluorescent lifetime imaging microscopy (FLIM) characterizations. RESULTS: Factor images and FLIM images can help to analyze MRI targeting inside the liver and thoracic aorta of mice. They show positive detection of Fe-Texas red and BOPTA-Eu in the liver and positive detection of Fe-Texas red and negative detection of BOPTA-Eu inside the thoracic aorta. CONCLUSION: This investigation established the utility of fluorescent MRI contrast agents as in vivo staining tools for cellular sites.     

Cellular MR imaging

Cellular MR imaging is a young field that aims to visualize targeted cells in living organisms. In order to provide a different signal intensity of the targeted cell, they are either labeled with MR contrast agents in vivo or prelabeled in vitro. Either (ultrasmall) superparamagnetic iron oxide [(U)SPIO] particles or (polymeric) paramagnetic chelates can be used for this purpose. For in vivo cellular labeling, Gd3+- and Mn2+-chelates have mainly been used for targeted hepatobiliary imaging, and (U)SPIO-based cellular imaging has been focused on imaging of macrophage activity. Several of these magnetopharmaceuticals have been FDA-approved or are in late-phase clinical trials. As for prelabeling of cells in vitro, a challenge has been to induce a sufficient uptake of contrast agents into nonphagocytic cells, without affecting normal cellular function. It appears that this issue has now largely been resolved, leading to an active research on monitoring the cellular biodistribution in vivo following transplantation or transfusion of these cells, including cell migration and trafficking. New applications of cellular MR imaging will be directed, for instance, towards our understanding of hematopoietic (immune) cell trafficking and of novel guided (stem) cell-based therapies aimed to be translated to the clinic in the future.     

Production of cell-enclosing hollow-core agarose microcapsules via jetting in water-immiscible liquid paraffin and formation of embryoid body-like spherical tissues from mouse ES cells enclosed within these microcapsules

We developed agarose microcapsules with a single hollow core templated by alginate microparticles using a jet-technique. We extruded an agarose aqueous solution containing suspended alginate microparticles into a coflowing stream of liquid paraffin and controlled the diameter of the agarose microparticles by changing the flow rate of the liquid paraffin. Subsequent degradation of the inner alginate microparticles using alginate lyase resulted in the hollow-core structure. We successfully obtained agarose microcapsules with 20-50 microm of agarose gel layer thickness and hollow cores ranging in diameter from ca. 50 to 450 microm. Using alginate microparticles of ca. 150 microm in diameter and enclosing feline kidney cells, we were able to create cell-enclosing agarose microcapsules with a hollow core of ca. 150 microm in diameter. The cells in these microcapsules grew much faster than those in alginate microparticles. In addition, we enclosed mouse embryonic stem cells in agarose microcapsules. The embryonic stem cells began to self-aggregate in the core just after encapsulation, and subsequently grew and formed embryoid body-like spherical tissues in the hollow core of the microcapsules. These results show that our novel microcapsule production technique and the resultant microcapsules have potential for tissue engineering, cell therapy and biopharmaceutical applications.     

Molecular aspects of magnetic resonance imaging and spectroscopy

Magnetic resonance imaging (MRI) is a well known diagnostic tool in radiology that produces unsurpassed images of the human body, in particular of soft tissue. However, the medical community is often not aware that MRI is an important yet limited segment of magnetic resonance (MR) or nuclear magnetic resonance (NMR) as this method is called in basic science. The tremendous morphological information of MR images sometimes conceal the fact that MR signals in general contain much more information, especially on processes on the molecular level. NMR is successfully used in physics, chemistry, and biology to explore and characterize chemical reactions, molecular conformations, biochemical pathways, solid state material, and many other applications that elucidate invisible characteristics of matter and tissue. In medical applications, knowledge of the molecular background of MRI and in particular MR spectroscopy (MRS) is an inevitable basis to understand molecular phenomenon leading to macroscopic effects visible in diagnostic images or spectra. This review shall provide the necessary background to comprehend molecular aspects of magnetic resonance applications in medicine. An introduction into the physical basics aims at an understanding of some of the molecular mechanisms without extended mathematical treatment. The MR typical terminology is explained such that reading of original MR publications could be facilitated for non-MR experts. Applications in MRI and MRS are intended to illustrate the consequences of molecular effects on images and spectra.     

Evaluation of microbubbles as contrast agents for ultrasonography and magnetic resonance imaging

Background

Microbubbles (MBs) can serve as an ultrasound contrast agent, and has the potential for magnetic resonance imaging (MRI). Due to the relatively low effect of MBs on MRI, it is necessary to develop new MBs that are more suitable for MRI. In this study, we evaluate the properties of SonoVue® and custom-made Fe₃O₄-nanoparticle-embedded microbubbles (Fe₃O₄-MBs) in terms of contrast agents for ultrsonography (US) and MRI.

Methodology/Principal Findings

A total of 20 HepG2 subcutaneous-tumor-bearing nude mice were randomly assigned to 2 groups (i.e., n = 10 mice each group), one for US test and the other for MRI test. Within each group, two tests were performed for each mouse. The contrast agent for the first test is SonoVue®, and the second is Fe₃O₄-MBs. US was performed using a Technos^MPX US system (Esaote, Italy) with a contrast-tuned imaging (CnTI™) mode. MRI was performed using a 7.0T Micro-MRI (PharmaScan, Bruker Biospin GmbH, Germany) with an EPI-T₂* sequence. The data of signal-to-noise ratio (SNR) from the region-of-interest of each US and MR image was calculated by ImageJ (National Institute of Health, USA). In group 1, enhancement of SonoVue® was significantly higher than Fe₃O₄-MBs on US (P<0.001). In group 2, negative enhancement of Fe₃O₄-MBs was significantly higher than SonoVue® on MRI (P<0.001). The time to peak showed no significant differences between US and MRI, both of which used the same MBs (P>0.05). The SNR analysis of the enhancement process reveals a strong negative correlation in both cases (i.e., SonoVue® r = −0.733, Fe₃O₄-MBs r = −0.903, with P<0.05).

Conclusions

It might be important to change the Fe₃O₄-MBs'' shell structure and/or the imagining strategy of US to improve the imaging quality of Fe₃O₄-MBs on US. As an intriguing prospect that can be detected by US and MRI, MBs are worthy of further study.     

Dual contrast magnetic resonance imaging tracking of iron-labeled cells in vivo

Negative-contrast magnetic resonance imaging (MRI) methods utilizing magnetic susceptibility contrast agents have become one of the most widely used approaches in cellular imaging research. However, visualizing and tracking super-paramagnetic iron oxide nanoparticle (SPIO)-labeled cells on the basis of negative-contrast can limit specificity and sensitivity. Therefore, there has been a strong motivation to explore MRI methods for cellular imaging with either positive or dual contrast (both positive and negative) for identifying labeled cells; these methods offer the potential to improve significantly the sensitivity and specificity of MRI-based cell-tracking approaches. In this review, current state-of-the-art positive- and dual-contrast MRI techniques and contrast agents are described specifically for applications involving in vivo cellular tracking and imaging.     

Emerging concepts in molecular MRI

Molecular magnetic resonance imaging (MRI) offers the potential to image some events at the cellular and subcellular level and many significant advances have recently been witnessed in this field. The introduction of targeted MR contrast agents has enabled the imaging of sparsely expressed biological targets in vivo. Furthermore, high-throughput screens of nanoparticle libraries have identified nanoparticles that act as novel contrast agents and which can be targeted with enhanced diagnostic specificity and range. Another class of magnetic nanoparticles have also been designed to image dynamic events; these act as 'switches' and could be used in vitro, and potentially in vivo, as biosensors. Other specialized MR probes have been developed to image enzyme activity in vivo. Lastly, the use of chemical exchange and off-resonance techniques have been developed, adding another dimension to the broad capabilities of molecular MRI and offering the potential of multispectral imaging. These and other advances in molecular MRI offer great promise for the future and have significant potential for clinical translation.