Nicolau Beckmann

High resolution magnetic resonance angiography non-invasively reveals mouse strain differences in the cerebrovascular anatomy in vivo

High resolution magnetic resonance angiography (MRA) revealed highly variable arterial cerebrovascular structures in mice from different strains and within the same strain. C57Black/6 mice presented small unilateral anastomoses between the posterior cerebral and the superior cerebellar arteries. Well developed, either unilateral or bilateral, posterior communicating arteries (PcomA) were detected on CBA mice. The arterial structure of CD1 mice ranged from no detectable anastomoses to well developed, unilateral PcomAs. SV‐129 mice showed significantly shorter middle cerebral arteries compared to the other strains, and clear bilateral anastomoses between the posterior cerebral and the superior cerebellar arteries. Because of its non‐invasiveness, MRA may be of importance in murine stroke studies by enabling the selection of animals and/or the side for performing the surgical intervention, and the verification of its success. Magn Reson Med 44:252–258, 2000.

In vivo magnetic resonance methods in pharmaceutical research: current status and perspectives.

In the last decade, in vivo MR methods have become established tools in the drug discovery and development process. In this review, several successful and potential applications of MRI and MRS in stroke, rheumatoid and osteo‐arthritis, oncology and cardiovascular disorders are dealt with in detail. The versatility of the MR approach, allowing the study of various pathophysiological aspects in these disorders, is emphasized. New indication areas, for the characterization of which MR methods have hardly been used up to now, such as respiratory, gastro‐intestinal and skin diseases, are outlined in a subsequent section. A strength of MRI, being a non‐invasive imaging modality, is the ability to provide functional, i.e. physiological, readouts. Functional MRI examples discussed are the analysis of heart wall motion, perfusion MRI, tracer uptake and clearance studies, and neuronal activation studies. Functional information may also be derived from experiments using target‐specific contrast agents, which will become important tools in future MRI applications. Finally the role of MRI and MRS for characterization of transgenic and knock‐out animals, which have become a key technology in modern pharmaceutical research, is discussed. The advantages of MRI and MRS are versatility, allowing a comprehensive characterization of a diseased state and of the drug intervention, and non‐invasiveness, which is of relevance from a statistical, economical and animal welfare point of view. Successful applications in drug discovery exploit one or several of these aspects. In addition, the link between preclinical and clinical studies makes in vivo MR methods highly attractive methods for pharmaceutical research. Copyright

Pulmonary edema induced by allergen challenge in the rat: noninvasive assessment by magnetic resonance imaging.

The course of pulmonary edema formation after an intratracheal (i.t.) instillation of ovalbumin was followed noninvasively by magnetic resonance imaging ( MRI ) in actively sensitized Brown Norway (BN) rats. Changes in edema volume assessed by MRI mimicked the results from the analysis of the number and activation of inflammatory cells recovered from the broncho‐alveolar lavage (BAL) fluid. Rats treated with budesonide did not develop edema following challenge with ovalbumin, and these animals showed a significant decrease in BAL fluid inflammatory cell numbers and eosinophil peroxidase and myeloperoxidase activities. Thus, following lung edema formation by MRI provides a reliable means of assessing pulmonary inflammation after allergen challenge. Unlike BAL fluid analysis, which requires killing animals at each time point, this method is noninvasive. MRI could be of importance for the noninvasive profiling of anti‐inflammatory drugs in animal models of asthma and in the clinic. Magn Reson Med 45:88–95, 2001.

Capillary cerebral amyloid angiopathy is associated with vessel occlusion and cerebral blood flow disturbances

The role of cerebral amyloid angiopathy (CAA) in the pathogenesis of Alzheimers disease (AD) is not fully understood. Here, we studied whether CAA is associated with alterations in microvascularisation in transgenic mouse models and in the human brain. APP23 mice at 25-26 months of age exhibited severe CAA in thalamic vessels whereas APP51/16 mice did not. Wild-type littermates were free of CAA. We found CAA-related capillary occlusion within the thalamus of APP23 mice but not in APP51/16 and wild-type mice. Magnetic resonance angiography (MRA) showed blood flow alterations in the thalamic vessels of APP23 mice. CAA-related capillary occlusion in the branches of the thalamoperforating arteries of APP23 mice, thereby, corresponded to the occurrence of blood flow disturbances. Similarly, CAA-related capillary occlusion was observed in the human occipital cortex of AD cases but less frequently in controls. These results indicate that capillary CAA can result in capillary occlusion and is associated with cerebral blood flow disturbances providing an additional mechanism for toxic effects of the amyloid beta-protein in AD.

Macrophage infiltration into the rat knee detected by MRI in a model of antigen-induced arthritis

Three‐dimensional (3D) MR images were obtained from the knees of rats in a model of antigen‐induced arthritis, elicited by the intraarticular administration of methylated bovine serum albumin (mBSA) to previously immunized rats. Superparamagnetic particles of iron oxide (SPIO) were administered i.v. 24 hr before each imaging session. Starting 4 days postantigen injection, images from arthritic knees exhibited distinctive signal attenuation in the synovium. This signal attenuation was significantly smaller in knees from animals treated with dexamethasone, a glucocorticosteroid, and completely absent in contralateral knees that had been challenged with vehicle. A significant negative correlation was found between the MRI signal intensity in the synovium and the histologically determined iron content in macrophages located in the same region. These results suggest the feasibility of detecting macrophage infiltration into the knee synovium in this model of antigen‐induced arthritis by labeling the cells with SPIO. This readout could provide an early marker of disease progression, before more aggressive changes like cartilage and bone erosion take place. Monitoring early changes associated with arthritis can have an impact in preclinical studies by shortening the duration of the experimental period and by facilitating the investigation of novel immunomodulatory therapies acting on macrophages. Also, the approach can be potentially adapted to clinical studies. Magn Reson Med 49:1047–1055, 2003.

From anatomy to the target: Contributions of magnetic resonance imaging to preclinical pharmaceutical research

In recent years, in vivo magnetic resonance (MR) methods have become established tools in the drug discovery and development process. In this article, the role of MR imaging (MRI) in the preclinical evaluation of drugs in animal models of diseases is illustrated on the basis of selected examples. The individual sections are devoted to applications of anatomic, physiologic, and “molecular” imaging providing, respectively, structural‐morphological, functional, and target‐specific information. The impact of these developments upon clinical drug evaluation is also briefly addressed. The main advantages of MRI are versatility, allowing a comprehensive characterization of a disease state and of the corresponding drug intervention; high spatial resolution; and noninvasiveness, enabling repeated measurements. Successful applications in drug discovery exploit one or several of these aspects. Additionally, MRI is contributing to strengthen the link between preclinical and clinical drug research. Anat Rec (New Anat) 265:85–100, 2001.

Macrophage labeling by SPIO as an early marker of allograft chronic rejection in a rat model of kidney transplantation.

Anatomical and functional information (renography, perfusion) was obtained by MRI in a life‐supporting transplantation model, in which Lewis rats received kidneys from Fisher 344 donors. Renography and perfusion analyses were carried out with Gd‐DOTA and small particles of iron oxide (SPIO), respectively. Starting 12 weeks posttransplantation, images from grafts of untreated recipients exhibited distinctive signal attenuation in the cortex. Animals treated with cyclosporin (Sandimmune Neoral; Novartis Pharma, Basel, Switzerland) to prevent acute rejection showed a signal attenuation in the cortex at 33 weeks posttransplantation, while kidneys from rats treated additionally with everolimus (Certican; Novartis), a rapamycin derivative, had no changes in anatomical appearance. A significant negative correlation was found between the MRI cortical signal intensity and the histologically determined iron content in macrophages located in the cortex. Renography revealed a significantly reduced functionality of the kidneys of untreated controls 33 weeks after transplantation, while no significant changes in perfusion were observed in any group of rats. These results suggest the feasibility, by labeling macrophages with SPIO, of detecting signs of graft rejection significantly earlier than when changes in function occur. Monitoring early changes associated with chronic rejection can have an impact in preclinical studies by shortening the duration of the experimental period and by facilitating the investigation of novel immunomodulatory therapies for transplantation. Magn Reson Med 49:459–467, 2003.

Magnetic resonance angiography of the rat cerebrovascular system without the use of contrast agents.

We describe and discuss the application of three‐dimensional (3D) time‐of‐flight (TOF) magnetic resonance angiography (MRA) to visualize non‐invasively the cerebral vasculature of the rat. MR angiograms of healthy spontaneously hypertensive rats were obtained without the use of contrast agents. Total imaging time ranged from 1 to 50 min for a 3D data set. The influences of the data matrix and the inflow delay on the image quality and the total imaging time are assessed and discussed. Varying the inflow delay yielded in addition semiquantitative information on hemodynamics. The method was applied to obtain angiograms in rat models of permanent and temporal middle cerebral artery occlusion. Occlusion and reopening of the vessel could easily be verified byMRA. However, after reperfusion a slight reduction in blood flow was observed. Copyright

In vivo visualization of macrophage infiltration and activity in inflammation using magnetic resonance imaging.

Because macrophages play a key role on host defense, visualization of the migration of these cells is of high relevance for both diagnostic purposes and the evaluation of therapeutic interventions. The present article addresses the use of iron oxide and gadolinium-based particles for the noninvasive in vivo detection of macrophage infiltration into inflamed areas by magnetic resonance imaging (MRI). A general introduction on the functions and general characteristics of macrophages is followed by a discussion of some of the agents and acquisition schemes currently used to track the cells in vivo. Attention is then devoted to preclinical and clinical applications in the following disease areas: atherosclerosis and myocardial infarction, stroke, multiple sclerosis, rheumatoid arthritis, and kidney transplantation.

Administration of bleomycin via the oropharyngeal aspiration route leads to sustained lung fibrosis in mice and rats as quantified by UTE-MRI and histology.

Pulmonary fibrosis can be experimentally induced in small rodents by bleomycin. The antibiotic is usually administered via the intratracheal or intranasal routes. In the present study, we investigated the oropharyngeal aspiration of bleomycin as an alternative route for the induction of lung fibrosis in rats and mice. The development of lung injury was followed in vivo by ultrashort echo time magnetic resonance imaging (UTE-MRI) and by post-mortem analyses (histology of collagen, hydroxyproline determination, and qRT-PCR). In C57BL/6 mice, oropharyngeal aspiration of bleomycin led to more prominent lung fibrosis as compared to intranasal administration. Consequently, the oropharyngeal aspiration route allowed a dose reduction of bleomycin and, therewith, a model refinement. Moreover, the distribution of collagen after oropharyngeal aspiration of bleomycin was more homogenous than after intranasal administration: for the oropharyngeal aspiration route, fibrotic areas appeared all over the lung lobes, while for the intranasal route fibrotic lesions appeared mainly around the largest superior airways. Thus, oropharyngeal aspiration of bleomycin induced morphological changes that were more comparable to the human disease than the intranasal administration route did. Oropharyngeal aspiration of bleomycin led to a homogeneous fibrotic injury also in rat lungs. The present data suggest oropharyngeal aspiration of bleomycin as a less invasive means to induce homogeneous and sustained fibrosis in the lungs of mice and rats.