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      Magnetic Resonance Imaging of Blood Brain/Nerve Barrier Dysfunction and Leukocyte Infiltration: Closely Related or Discordant?

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          Abstract

          Unlike other organs the nervous system is secluded from the rest of the organism by the blood brain barrier (BBB) or blood nerve barrier (BNB) preventing passive influx of fluids from the circulation. Similarly, leukocyte entry to the nervous system is tightly controlled. Breakdown of these barriers and cellular inflammation are hallmarks of inflammatory as well as ischemic neurological diseases and thus represent potential therapeutic targets. The spatiotemporal relationship between BBB/BNB disruption and leukocyte infiltration has been a matter of debate. We here review contrast-enhanced magnetic resonance imaging (MRI) as a non-invasive tool to depict barrier dysfunction and its relation to macrophage infiltration in the central and peripheral nervous system under pathological conditions. Novel experimental contrast agents like Gadofluorine M (Gf) allow more sensitive assessment of BBB dysfunction than conventional Gadolinium (Gd)-DTPA enhanced MRI. In addition, Gf facilitates visualization of functional and transient alterations of the BBB remote from lesions. Cellular contrast agents such as superparamagnetic iron oxide particles (SPIO) and perfluorocarbons enable assessment of leukocyte (mainly macrophage) infiltration by MR technology. Combined use of these MR contrast agents disclosed that leukocytes can enter the nervous system independent from a disturbance of the BBB, and vice versa, a dysfunctional BBB/BNB by itself is not sufficient to attract inflammatory cells from the circulation. We will illustrate these basic imaging findings in animal models of multiple sclerosis, cerebral ischemia, and traumatic nerve injury and review corresponding findings in patients.

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          Most cited references72

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          Cortical demyelination and diffuse white matter injury in multiple sclerosis.

          Focal demyelinated plaques in white matter, which are the hallmark of multiple sclerosis pathology, only partially explain the patient's clinical deficits. We thus analysed global brain pathology in multiple sclerosis, focusing on the normal-appearing white matter (NAWM) and the cortex. Autopsy tissue from 52 multiple sclerosis patients (acute, relapsing-remitting, primary and secondary progressive multiple sclerosis) and from 30 controls was analysed using quantitative morphological techniques. New and active focal inflammatory demyelinating lesions in the white matter were mainly present in patients with acute and relapsing multiple sclerosis, while diffuse injury of the NAWM and cortical demyelination were characteristic hallmarks of primary and secondary progressive multiple sclerosis. Cortical demyelination and injury of the NAWM, reflected by diffuse axonal injury with profound microglia activation, occurred on the background of a global inflammatory response in the whole brain and meninges. There was only a marginal correlation between focal lesion load in the white matter and diffuse white matter injury, or cortical pathology, respectively. Our data suggest that multiple sclerosis starts as a focal inflammatory disease of the CNS, which gives rise to circumscribed demyelinated plaques in the white matter. With chronicity, diffuse inflammation accumulates throughout the whole brain, and is associated with slowly progressive axonal injury in the NAWM and cortical demyelination.
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            Blood-brain barrier disruption in multiple sclerosis.

            The blood-brain barrier (BBB) is a complex organization of cerebral endothelial cells (CEC), pericytes and their basal lamina, which are surrounded and supported by astrocytes and perivascular macrophages. Collectively these cells separate and form the compartments of the cerebral vascular space and the cerebral interstitium under normal conditions. Without the BBB, the 'interior milieu' of the central nervous system (CNS) would be flooded by humoral neurotransmitters and formed blood elements that upset normal CNS functions and lead to vascular/neural injury. Dysregulation of the BBB and transendothelial migration of activated leukocytes are among the earliest cerebrovascular abnormalities seen in multiple sclerosis (MS) brains and parallel the release of inflammatory cytokines/chemokines. Mechanisms for breakdown of the BBB in MS are incompletely understood, but appear to involve direct effects of these cytokines/ chemokines on endothelial regulation of BBB components, as well as indirect cytokine/chemokine-dependent leukocyte mediated injury. Unique endothelial structural features of the BBB include highly organized endothelial tight junctions, the absence of class II major histocompatibility complex, abundant mitochondria and a highly developed transport system in CEC. Exposure of endothelium to proinflammatory cytokines (IFN-gamma, TNF-alpha and IL-1beta) interrupts the BBB by disorganizing cell-cell junctions, decreases the brain solute barrier, enhances leukocyte endothelial adhesion and migration as well as increases expression of class II MHC and promotes shedding of endothelial 'microparticles' (EMP). In this review we examine interactions between cytokines/chemokines, activated leukocytes, adhesion molecules and activated CEC in the pathogenesis of BBB failure in MS.
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              The complexity of neurobiological processes in acute ischemic stroke.

              There is an urgent need for improved diagnostics and therapeutics for acute ischemic stroke. This is the focus of numerous research projects involving in vitro studies, animal models and clinical trials, all of which are based on current knowledge of disease mechanisms underlying acute focal cerebral ischemia. Insight in the chain of events occurring during acute ischemic injury is essential for understanding current and future diagnostic and therapeutic approaches. In this review, we summarize the actual knowledge on the pathophysiology of acute ischemic stroke. We focus on the ischemic cascade, which is a complex series of neurochemical processes that are unleashed by transient or permanent focal cerebral ischemia and involves cellular bioenergetic failure, excitotoxicity, oxidative stress, blood-brain barrier dysfunction, microvascular injury, hemostatic activation, post-ischemic inflammation and finally cell death of neurons, glial and endothelial cells.
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                Author and article information

                Journal
                Front Neurol
                Front Neurol
                Front. Neur.
                Frontiers in Neurology
                Frontiers Media S.A.
                1664-2295
                26 November 2012
                21 December 2012
                2012
                : 3
                : 178
                Affiliations
                [1] 1Department of Neurology, University of Wuerzburg Wuerzburg, Germany
                [2] 2Fraunhofer Institute for Cell Therapy and Immunology Leipzig, Germany
                [3] 3Translational Center for Regenerative Medicine Leipzig, Germany
                Author notes

                Edited by: Mattias Sköld, Uppsala University, Sweden

                Reviewed by: Wolfgang J. Streit, University of Florida, USA; Bridgette D. Semple, University of California San Francisco, USA; Amade Bregy, University of Miami, USA

                *Correspondence: Gesa Weise, Department of Ischemia Research, Fraunhofer Institute for Cell Therapy and Immunology IZI, Perlickstr. 1, 04103 Leipzig, Germany. e-mail: gesa.weise@ 123456izi.fraunhofer.de

                This article was submitted to Frontiers in Neurotrauma, a specialty of Frontiers in Neurology.

                Article
                10.3389/fneur.2012.00178
                3527731
                23267343
                0b92f73a-a49c-4ce1-af83-acf6a4891a7d
                Copyright © 2012 Weise and Stoll.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.

                History
                : 16 November 2012
                : 03 December 2012
                Page count
                Figures: 4, Tables: 0, Equations: 0, References: 90, Pages: 11, Words: 10072
                Categories
                Neuroscience
                Review Article

                Neurology
                contrast-enhanced mri,gadolinium-dtpa,gadofluorine,iron oxide nanoparticles,blood brain barrier,neuroinflammation

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