Gadofluorine M enhancement allows more sensitive detection of inflammatory CNS lesions than T2-w imaging: a quantitative MRI study

Brain Barriers and Multiple Sclerosis: Novel Treatment Approaches from a Brain Barriers Perspective

Multiple sclerosis (MS) is considered a prototypic organ specific autoimmune disease targeting the central nervous system (CNS). Blood-brain barrier (BBB) breakdown and enhanced immune cell infiltration into the CNS parenchyma are early hallmarks of CNS lesion formation. Therapeutic targeting of immune cell trafficking across the BBB has proven a successful therapy for the treatment of MS, but comes with side effects and is no longer effective once patients have entered the progressive phase of the disease. Beyond the endothelial BBB, epithelial and glial brain barriers establish compartments in the CNS that differ in their accessibility to the immune system. There is increasing evidence that brain barrier abnormalities persist during the progressive stages of MS. Here, we summarize the role of endothelial, epithelial, and glial brain barriers in maintaining CNS immune privilege and our current knowledge on how impairment of these barriers contributes to MS pathogenesis. We discuss how therapeutic stabilization of brain barriers integrity may improve the safety of current therapeutic regimes for treating MS. This may also allow for the development of entirely novel therapeutic approaches aiming to restore brain barriers integrity and thus CNS homeostasis, which may be specifically beneficial for the treatment of progressive MS.

Investigating the blood-spinal cord barrier in preclinical models: a systematic review of in vivo imaging techniques

STUDY DESIGN

This study is a systematic review.

OBJECTIVES

To evaluate current in vivo techniques used in the investigation of the blood-spinal cord barrier (BSCB).

METHODS

Search of English language literature for animal studies that investigated the BSCB in vivo. Data extraction included animal model/type, protocol for BSCB evaluation, and study outcomes. Descriptive syntheses are provided.

RESULTS

A total of 40 studies were included, which mainly investigated rodent models of experimental autoimmune encephalomyelitis (EAE) or spinal cord injury (SCI). The main techniques used were magnetic resonance imaging (MRI) and intravital microscopy (IVM). MRI served as a reliable tool to longitudinally track BSCB permeability changes with dynamic contrast enhancement (DCE) using gadolinium, or assess inflammatory infiltrations with targeted alternative contrast agents. IVM provided high-resolution visualization of cellular and molecular interactions across the microvasculature, commonly with either epi-fluorescence or two-photon microscopy. MRI and IVM techniques enabled the evaluation of therapeutic interventions and mechanisms that drive spinal cord dysfunction in EAE and SCI. A small number of studies demonstrated the feasibility of DCE-computed tomography, ultrasound, bioluminescent, and fluorescent optical imaging methods to evaluate the BSCB. Technique-specific limitations and multiple protocols for image acquisition and data analyses are described for all techniques.

CONCLUSION

There are few in vivo investigations of the BSCB. Additional studies are needed in less commonly studied spinal cord disorders, and to establish standardized protocols for data acquisition and analysis. Further development of techniques and multimodal approaches could overcome current imaging limitations to the spinal cord. These advancements might promote wider adoption of techniques, and can provide greater potential for clinical translation.

The blood-brain interface: a culture change

The blood-brain interface (BBI) is the subject of a new named series at Brain, Behavior, and Immunity. It is timely to reflect on a number of advances in the field within the last ten years, which may lead to an increased understanding of human behaviour and a wide range of psychiatric and neurological conditions. We cover discoveries made in solute and cell trafficking, endothelial cell and pericyte biology, extracellular matrix and emerging tools, especially those which will enable study of the human BBI. We now recognize the central role of the BBI in a number of immunopsychiatric syndromes, including sickness behaviour, delirium, septic encephalopathy, cognitive side effects of cytokine-based therapies and the frank psychosis observed in neuronal surface antibody syndromes. In addition, we find ourselves interrogating and modulating the brain across the BBI, during diagnostic investigation and treatment of brain disease. The past ten years of BBI research have been exciting but there is more to come.

The Effects of Intestinal Nematode L4 Stage on Mouse Experimental Autoimmune Encephalomyelitis

Helminths use various immunomodulatory and anti-inflammatory strategies to evade immune attack by the host. During pathological conditions, these strategies alter the course of disease by reducing immune-mediated pathology. The study examines the therapeutic effect of the nematode L4 stage based on an in vivo model of multiple sclerosis, monophasic encephalomyelitis (EAE), induced by sensitization with MOG_35-55 peptide in C57BL/6 female mice infected with the intestinal nematode Heligmosomoides polygyrus. The EAE remission was correlated with altered leukocyte number identified in the central nervous system (CNS), and temporary permeability of the blood-brain barrier at the histotrophic phase of infection. At 6 days post-infection, when the L4 stage had almost completely attenuated the clinical severity and pathological signs of EAE, CD25⁺ cell numbers expanded significantly, with parallel growth of CD8⁺ and CD4⁺, both CD25⁺Foxp3⁺ and CD25⁺Foxp3^- subsets and alternatively activated macrophages. The phenotypic changes in distinct subsets of cerebrospinal fluid cells were correlated with an inhibited proliferative response of encephalitogenic T cells and elevated levels of nerve growth factor and TGF-β. These results enhance our understanding of mechanisms involved in the inhibition of immune responses in the CNS during nematode infection.

Experimental Cerebral Malaria Spreads along the Rostral Migratory Stream

It is poorly understood how progressive brain swelling in experimental cerebral malaria (ECM) evolves in space and over time, and whether mechanisms of inflammation or microvascular sequestration/obstruction dominate the underlying pathophysiology. We therefore monitored in the Plasmodium berghei ANKA-C57BL/6 murine ECM model, disease manifestation and progression clinically, assessed by the Rapid-Murine-Coma-and-Behavioral-Scale (RMCBS), and by high-resolution in vivo MRI, including sensitive assessment of early blood-brain-barrier-disruption (BBBD), brain edema and microvascular pathology. For histological correlation HE and immunohistochemical staining for microglia and neuroblasts were obtained. Our results demonstrate that BBBD and edema initiated in the olfactory bulb (OB) and spread along the rostral-migratory-stream (RMS) to the subventricular zone of the lateral ventricles, the dorsal-migratory-stream (DMS), and finally to the external capsule (EC) and brainstem (BS). Before clinical symptoms (mean RMCBS = 18.5±1) became evident, a slight, non-significant increase of quantitative T2 and ADC values was observed in OB+RMS. With clinical manifestation (mean RMCBS = 14.2±0.4), T2 and ADC values significantly increased along the OB+RMS (p = 0.049/p = 0.01). Severe ECM (mean RMCBS = 5±2.9) was defined by further spread into more posterior and deeper brain structures until reaching the BS (significant T2 elevation in DMS+EC+BS (p = 0.034)). Quantitative automated histological analyses confirmed microglial activation in areas of BBBD and edema. Activated microglia were closely associated with the RMS and neuroblasts within the RMS were severely misaligned with respect to their physiological linear migration pattern. Microvascular pathology and ischemic brain injury occurred only secondarily, after vasogenic edema formation and were both associated less with clinical severity and the temporal course of ECM. Altogether, we identified a distinct spatiotemporal pattern of microglial activation in ECM involving primarily the OB+RMS axis, a distinct pathway utilized by neuroblasts and immune cells. Our data suggest significant crosstalk between these two cell populations to be operative in deeper brain infiltration and further imply that the manifestation and progression of cerebral malaria may depend on brain areas otherwise serving neurogenesis.

Brain swelling is difficult to detect ex vivo and has recently been identified as a strong predictor of death not only in experimental cerebral malaria (ECM), but also in human cerebral malaria. As whole-brain in-vivo imaging methods have been widely underutilized in this disease model, little is known about the spatiotemporal evolution of brain swelling. To unravel this question, we monitored the evolution of ECM in vivo using high-field magnetic resonance imaging (MRI) with whole-brain coverage and have identified a distinct pattern of cerebral disease spread. Inflammatory disruption of the blood-brain-barrier and consecutive brain swelling initiates in the olfactory bulb and spreads from there along the rostral migratory stream—a neurogenic niche—deeper into the brain. When the brainstem is eventually reached, mice start to fall into a comatose state. Those findings correlate with previously published human MRI findings, which also show brain swelling of the brainstem in comatose children with cerebral malaria as well as early involvement of the striatum—recently recognized to serve neurogenesis in humans. Our study provides a novel link between neurogenic areas specifically permitting the spatiotemporal expansion of activated microglia, blood-brain-barrier disruption and consequent brain edema. Finally, the dominant role of the neurogenic axis in the transmission of inflammation may provide an explanation why children are more vulnerable to cerebral malaria.

The intrinsic pathogenic role of autoantibodies to aquaporin 4 mediating spinal cord disease in a rat passive-transfer model

Neuromyelitis optica (NMO) is causally linked to autoantibodies (ABs) against aquaporin 4 (AQP4). Here, we focused on the pathogenic effects exclusively mediated by human ABs to AQP4 in vivo. We performed cell-free intrathecal (i.th.) passive transfer experiments in Lewis rats using purified patient NMO immunoglobulin G (IgG) and various recombinant human anti-AQP4 IgG-ABs via implanted i.th. catheters. Repetitive application of patient NMO IgG fractions and of recombinant human anti-AQP4 ABs induced signs of spinal cord disease. Magnetic resonance imaging (MRI) revealed longitudinal spinal cord lesions at the site of application of anti-AQP4 IgG. Somatosensory evoked potential amplitudes were reduced in symptomatic animals corroborating the observed functional impairment. Spinal cord histology showed specific IgG deposition in the grey and white matter in the affected areas. We did not find inflammatory cell infiltration nor activation of complement in spinal cord areas of immunoglobulin deposition. Moreover, destructive lesions showing axon or myelin damage and loss of astrocytes and oligodendrocytes were all absent. Immunoreactivity to AQP4 and to the excitatory amino acid transporter 2 (EAAT2) was markedly reduced whereas immunoreactivity to the astrocytic marker glial fibrillary acid protein (GFAP) was preserved. The expression of the NMDA-receptor NR1 subunit was downregulated in areas of IgG deposition possibly induced by sustained glutamatergic overexcitation. Disease signs and histopathology were reversible within weeks after stopping injections. We conclude that in vivo application of ABs directed at AQP 4 can induce a reversible spinal cord disease in recipient rats by inducing distinct histopathological abnormalities. These findings may be the experimental correlate of "penumbra-like" lesions recently reported in NMO patients adjacent to effector-mediated tissue damage.

Multiple sclerosis: myeloperoxidase immunoradiology improves detection of acute and chronic disease in experimental model

PURPOSE

To test if MPO-Gd, a gadolinium-based magnetic resonance (MR) imaging probe that is sensitive and specific for the proinflammatory and oxidative enzyme myeloperoxidase (MPO), which is secreted by certain inflammatory cells, is more sensitive than diethylenetriaminepentaacetic acid (DTPA)-Gd in revealing early subclinical and chronic disease activity in the brain in experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis.

MATERIALS AND METHODS

The protocol for animal experiments was approved by the institutional animal care committee. A total of 61 female SJL mice were induced with EAE. Mice underwent MPO-Gd- or DTPA-Gd-enhanced MR imaging on days 6, 8, and 10 after induction, before clinical disease develops, and during chronic disease at remission and the first relapse. Brains were harvested at these time points for flow cytometric evaluation of immune cell subtypes and immunohistochemistry. Statistical analysis was performed, and P < .05 was considered to indicate a significant difference.

RESULTS

MPO-Gd helps detect earlier (5.2 vs 2.3 days before symptom onset, P = .004) and more (3.1 vs 0.3, P = .008) subclinical inflammatory lesions compared with DTPA-Gd, including in cases in which there was no evidence of overt blood-brain barrier (BBB) breakdown detected with DTPA-Gd enhancement. The number of MPO-Gd-enhancing lesions correlated with early infiltration of MPO-secreting monocytes and neutrophils into the brain (r = 0.91). MPO-Gd also helped detect more lesions during subclinical disease at remission (5.5 vs 1.3, P = .006) and at the first relapse (9.0 vs 2.7, P = .03) than DTPA-Gd, which also correlated well with the presence and accumulation of MPO-secreting inflammatory cells in the brain (r = 0.93).

CONCLUSION

MPO-Gd specifically reveals lesions with inflammatory monocytes and neutrophils, which actively secrete MPO. These results demonstrate the feasibility of detection of subclinical inflammatory disease activity in vivo, which is different from overt BBB breakdown.

Understanding disease processes in multiple sclerosis through magnetic resonance imaging studies in animal models

There are exciting new advances in multiple sclerosis (MS) resulting in a growing understanding of both the complexity of the disorder and the relative involvement of grey matter, white matter and inflammation. Increasing need for preclinical imaging is anticipated, as animal models provide insights into the pathophysiology of the disease. Magnetic resonance (MR) is the key imaging tool used to diagnose and to monitor disease progression in MS, and thus will be a cornerstone for future research. Although gadolinium-enhancing and T₂ lesions on MRI have been useful for detecting MS pathology, they are not correlative of disability. Therefore, new MRI methods are needed. Such methods require validation in animal models. The increasing necessity for MRI of animal models makes it critical and timely to understand what research has been conducted in this area and what potential there is for use of MRI in preclinical models of MS. Here, we provide a review of MRI and magnetic resonance spectroscopy (MRS) studies that have been carried out in animal models of MS that focus on pathology. We compare the MRI phenotypes of animals and patients and provide advice on how best to use animal MR studies to increase our understanding of the linkages between MR and pathology in patients. This review describes how MRI studies of animal models have been, and will continue to be, used in the ongoing effort to understand MS.

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MRI studies of pathology in various animal models of MS are reviewed.

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MRI phenotypes in animal models of MS and MS patients are compared.

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Animal MRI can increase understanding of links between MR and pathology in patients.

Imaging Neuroinflammation - from Bench to Bedside

Neuroinflammation plays a central role in a variety of neurological diseases, including stroke, multiple sclerosis, Alzheimer’s disease, and malignant CNS neoplasms, among many other. Different cell types and molecular mediators participate in a cascade of events in the brain that is ultimately aimed at control, regeneration and repair, but leads to damage of brain tissue under pathological conditions. Non-invasive molecular imaging of key players in the inflammation cascade holds promise for identification and quantification of the disease process before it is too late for effective therapeutic intervention. In this review, we focus on molecular imaging techniques that target inflammatory cells and molecules that are of interest in neuroinflammation, especially those with high translational potential. Over the past decade, a plethora of molecular imaging agents have been developed and tested in animal models of (neuro)inflammation, and a few have been translated from bench to bedside. The most promising imaging techniques to visualize neuroinflammation include MRI, positron emission tomography (PET), single photon emission computed tomography (SPECT), and optical imaging methods. These techniques enable us to image adhesion molecules to visualize endothelial cell activation, assess leukocyte functions such as oxidative stress, granule release, and phagocytosis, and label a variety of inflammatory cells for cell tracking experiments. In addition, several cell types and their activation can be specifically targeted in vivo, and consequences of neuroinflammation such as neuronal death and demyelination can be quantified. As we continue to make progress in utilizing molecular imaging technology to study and understand neuroinflammation, increasing efforts and investment should be made to bring more of these novel imaging agents from the “bench to bedside.”

Progress on the diagnosis and evaluation of brain tumors

Brain tumors are one of the most challenging disorders encountered, and early and accurate diagnosis is essential for the management and treatment of these tumors. In this article, diagnostic modalities including single-photon emission computed tomography, positron emission tomography, magnetic resonance imaging, and optical imaging are reviewed. We mainly focus on the newly emerging, specific imaging probes, and their potential use in animal models and clinical settings.

Imaging in sepsis-associated encephalopathy--insights and opportunities

Sepsis-associated encephalopathy (SAE) refers to a clinical spectrum of acute neurological dysfunction that arises in the context of sepsis. Although the pathophysiology of SAE is incompletely understood, it is thought to involve endothelial activation, blood-brain barrier leakage, inflammatory cell migration, and neuronal loss with neurotransmitter imbalance. SAE is associated with a high risk of mortality. Imaging studies using MRI and CT have demonstrated changes in the brains of patients with SAE that are also seen in disorders such as stroke. Next-generation imaging techniques such as magnetic resonance spectroscopy, diffusion tensor imaging and PET, as well as experimental imaging modalities, provide options for early identification of patients with SAE, and could aid in identification of pathophysiological processes that represent possible therapeutic targets. In this Review, we explore the recent literature on imaging in SAE, relating the findings of these studies to pathological data and experimental studies to obtain insights into the pathophysiology of sepsis-associated neurological dysfunction. Furthermore, we suggest how novel imaging technologies can be used for early-stage proof-of-concept and proof-of-mechanism translational studies, which may help to improve diagnosis in SAE.

Synthesis and characterization of a novel gadolinium-based contrast agent for magnetic resonance imaging of myelination

Myelin is a membrane system that fosters nervous impulse conduction in the vertebrate nervous system. Myelin sheath disruption is a common characteristic of several neurodegenerative diseases such as multiple sclerosis (MS) and various leukodystrophies. To date, the diagnosis of MS is obtained using a set of criteria in which MRI observations play a central role. However, because of the lack of specificity for myelin integrity, the use of MRI as the primary diagnostic tool has not yet been accepted. In order to improve MR specificity, we began developing MR probes targeted toward myelin. In this work we describe a new myelin-targeted MR contrast agent, Gd-DODAS, based on a stilbene binding moiety and demonstrate its ability to specifically bind to myelin in vitro and in vivo. We also present evidence that Gd-DODAS generates MR contrast in vivo in T1-weighed images and in T1 maps that correlates to the myelin content.

Neuroinflammatory imaging biomarkers: relevance to multiple sclerosis and its therapy

Magnetic resonance imaging is an established tool in the management of multiple sclerosis (MS). Loss of blood brain barrier integrity assessed by gadolinium (Gd) enhancement is the current standard marker of MS activity. To explore the complex cascade of the inflammatory events, other magnetic resonance imaging, but also positron emission tomographic markers reviewed in this article are being developed to address active neuroinflammation with increased sensitivity and specificity. Alternative magnetic resonance contrast agents, positron emission tomographic tracers and imaging techniques could be more sensitive than Gd to early blood brain barrier alteration, and they could assess the inflammatory cell recruitment and/or the associated edema accumulation. These markers of active neuroinflammation, although some of them are limited to experimental studies, could find great relevance to complete Gd information and thereby increase our understanding of acute lesion pathophysiology and its noninvasive follow-up, especially to monitor treatment efficacy. Furthermore, such accurate markers of inflammation combined with those of neurodegeneration hold promise to provide a more complete picture of MS, which will be of great benefit for future therapeutic strategies.

Magnetic resonance imaging of blood brain/nerve barrier dysfunction and leukocyte infiltration: closely related or discordant?

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.

Aquaporin-4 expression and blood–spinal cord barrier permeability in canalicular syringomyelia

Object

Noncommunicating canalicular syringomyelia occurs in up to 65% of patients with Chiari malformation Type I. The pathogenesis of this type of syringomyelia is poorly understood and treatment is not always effective. Although it is generally thought that syringomyelia is simply an accumulation of CSF from the subarachnoid space, the pathogenesis is likely to be more complex and may involve cellular and molecular processes. Aquaporin-4 (AQP4) has been implicated in numerous CNS pathological conditions involving fluid accumulation, including spinal cord edema. There is evidence that AQP4 facilitates the removal of extracellular water following vasogenic edema. The aim of this study was to investigate AQP4 expression and the structural and functional integrity of the blood–spinal cord barrier (BSCB) in a model of noncommunicating canalicular syringomyelia.

Methods

A kaolin-induced model of canalicular syringomyelia was used to investigate BSCB permeability and AQP4 expression in 27 adult male Sprague-Dawley rats. Control groups consisted of nonoperated, laminectomy-only, and saline-injected animals. The structural integrity of the BSCB was assessed using immunoreactivity to endothelial barrier antigen. Functional integrity of the BSCB was assessed by extravasation of systemically injected horseradish peroxidase (HRP) at 1, 3, 6, or 12 weeks after surgery. Immunofluorescence was used to assess AQP4 and glial fibrillary acidic protein (GFAP) expression at 12 weeks following syrinx induction.

Results

Extravasation of HRP was evident surrounding the central canal in 11 of 15 animals injected with kaolin, and in 2 of the 5 sham-injected animals. No disruption of the BSCB was observed in laminectomy-only controls. At 12 weeks the tracer leakage was widespread, occurring at every level rostral to the kaolin injection. At this time point there was a decrease in EBA expression in the gray matter surrounding the central canal from C-5 to C-7. Aquaporin-4 was expressed in gray- and white-matter astrocytes, predominantly at the glia limitans interna and externa, and to a lesser extent around neurons and blood vessels, in both control and syrinx animals. Expression of GFAP and APQ4 directly surrounding the central canal in kaolin-injected animals was variable and not significantly different from expression in controls.

Conclusions

This study demonstrated a prolonged disruption of the BSCB directly surrounding the central canal in the experimental model of noncommunicating canalicular syringomyelia. The disruption was widespread at 12 weeks, when central canal dilation was most marked. Loss of integrity of the barrier with fluid entering the interstitial space of the spinal parenchyma may contribute to enlargement of the canal and progression of syringomyelia. Significant changes in AQP4 expression were not observed in this model of canalicular syringomyelia. Further investigation is needed to elucidate whether subtle changes in AQP4 expression occur in canalicular syringomyelia.

Interstitial MR lymphography in mice: comparative study with gadofluorine 8, gadofluorine M, and gadofluorine P

PURPOSE

We investigated the characteristics and capability of interstitial MR lymphography in mice using gadofluorine 8, gadofluorine M, and gadofluorine P.

METHODS

We injected healthy mice with 0.5 µmol of Gd gadofluorine 8, gadofluorine M, or gadofluorine P subcutaneously into the right rear footpad and assessed the time courses of contrast enhancement in the lymph nodes. Six mice were studied for each contrast agent. We also used gadofluorine M to assess the lymphatic pathway from the right and left rear feet or tail.

RESULTS

Contrast enhancement was demonstrated for the right popliteal, sacral, and iliac lymph nodes in all mice 5 minutes after injection of each of the 3 agents and decreased gradually. Enhancement in the lymph nodes was still detectable 30 minutes after injection of gadofluorine 8 or gadofluorine M. Enhancement became obscure sooner after gadofluorine P injection and was mildly stronger with the other 2 contrast agents. Clear differences were found in the hepatobiliary and urinary kinetics of the 3 agents. Gadofluorine M injected into various sites delineated the lymphatic pathway from the site of injection.

CONCLUSION

Interstitial MR lymphography using gadofluorine 8, gadofluorine M, and gadofluorine P offered clear visualization of the lymphatic pathway in healthy mice during a sufficient imaging time window, and allowed repeated assessment of the pathway and clarification of the lymphatic system.

Lymph node metastases from gastric cancer: gadofluorine M and gadopentetate dimeglumine MR imaging in a rabbit model

PURPOSE

To compare the diagnostic performance of gadofluorine M with that of gadopentetate dimeglumine in the diagnosis of lymph node metastases with magnetic resonance (MR) imaging in a rabbit model of gastric cancer.

MATERIALS AND METHODS

The study protocol was approved by the institutional animal care committee. VX2 carcinomas were inoculated into the wall of the stomach in 20 rabbits. Gadopentetate dimeglumine-enhanced MR imaging was performed 4-6 weeks after inoculation, and gadofluorine M-enhanced MR imaging was performed approximately 24 hours later. Both MR imaging sets were analyzed separately and independently by four radiologists with respect to confidence level regarding the presence of metastases in lymph nodes and lymph node conspicuity. Statistical analysis was performed by using multiple-reader multiple-case (MRMC) receiver operating characteristic curve analysis and the Wilcoxon signed rank test.

RESULTS

Metastases were confirmed at pathologic analysis in 32 of 104 lymph nodes from 16 rabbits. The area under the receiver operating characteristic curve (AUC) for confidence regarding the presence of metastases in lymph nodes was significantly greater for gadofluorine M than for gadopentetate dimeglumine (AUC, 0.947 vs 0.894; P = .009). However, most (81%, 25 of 32) metastatic nodes were necrotic, and no significant difference was obtained in nonnecrotic nodes. For lymph node conspicuity, the gadofluorine M MR imaging set was assigned a significantly higher score than was the gadopentetate dimeglumine MR imaging set by all readers (P < .001).

CONCLUSION

Gadofluorine M showed significantly higher accuracy and better conspicuity than gadopentetate dimeglumine in the diagnosis of metastatic nodes, most of which were necrotic, in this animal model of gastric cancer.

Myelin imaging compound (MIC) enhanced magnetic resonance imaging of myelination

The vertebrate nervous system is characterized by myelination, a fundamental biological process that protects the axons and facilitates electric pulse transduction. Damage to myelin is considered a major effect of autoimmune diseases such as multiple sclerosis (MS). Currently, therapeutic interventions are focused on protecting myelin integrity and promoting myelin repair. These efforts need to be accompanied by an effective imaging tool that correlates the disease progression with the extent of myelination. To date, magnetic resonance imaging (MRI) is the primary imaging technique to detect brain lesions in MS. However, conventional MRI cannot differentiate demyelinated lesions from other inflammatory lesions and therefore cannot predict disease progression in MS. To address this problem, we have prepared a Gd-based contrast agent, termed MIC (myelin imaging compound), which binds to myelin with high specificity. In this work, we demonstrate that MIC exhibits a high kinetic stability toward transmetalation with promising relaxometric properties. MIC was used for in vivo imaging of myelination following intracerebroventricular infusion in the rat brain. MIC was found to distribute preferentially in highly myelinated regions and was able to detect regions of focally induced demyelination.

Long-term assessment of contrast effects of gadofluorine M and gadofluorine P in magnetic resonance imaging of mice

PURPOSE

To investigate the long-term time course of the contrast effects after the intravenous injection of gadofluorine M or gadofluorine P in mice.

MATERIALS AND METHODS

Magnetic resonance images were acquired longitudinally after intravenous injection of 0.1 μmol Gd/g gadofluorine M into BALB/c mice. The contrast effects were also assessed in C57BL/6J mice injected with gadofluorine M, BALB/c mice injected with gadofluorine P, and BALB/c mice injected with a double dose of gadopentetate dimeglumine.

RESULTS

The injection of gadofluorine M into BALB/c mice caused prolonged contrast effects in the blood and other organs. The liver enhancement was especially long-lasting and still evident 6 days after injection. Strain-related differences in contrast kinetics of gadofluorine M were not observed between BALB/c mice and C57BL/6J mice. In comparison with gadofluorine M, clearances from the blood, liver, and kidney were more rapid and contrast enhancement in the spleen was generally lower for gadofluorine P. The enhancement in the gallbladder cavity, indicating biliary excretion, was evident only after gadofluorine P injection. Blood enhancement at 10 min was much weaker for gadopentetate dimeglumine.

CONCLUSION

Both gadofluorine M and gadofluorine P appear to be applicable to blood pool imaging and liver imaging in mice.

Gadofluorine M enhanced MRI in experimental glioma: superior and persistent intracellular tumor enhancement compared with conventional MRI

PURPOSE

To compare conventional magnetic resonance imaging (MRI) techniques (T2-w and Gadolinium-DTPA-enhanced T1-w images) and Gadofluorine-M (GfM), a novel contrast agent in MRI, in murine gliomas.

MATERIALS AND METHODS

Growth monitoring of murine gliomas (induced in mice) was performed on a 2.3 Tesla Bruker Biospec MRI unit. First all animals were investigated with conventional MRI techniques. In group I GfM was applied at an early stage of disease, in group II at a later stage. After injection of GfM follow-up MRI was performed without further injection of contrast agent. On MR images tumor size and signal intensities were assessed. Animals were killed for histological evaluation.

RESULTS

In both groups GfM delineated tumor extents larger and more precisely than conventional MRI techniques. The difference between GfM and conventional MRI techniques reached level of significance at both tumor stages. Follow-up MRI after singular injection of GfM showed persistence of GfM in tumor tissue. On tissue sections GfM-enhancing areas corresponded closely to vital tumor tissue. GfM showed a mainly intracellular accumulation.

CONCLUSION

Application of GfM resulted in superior delineation of experimental glioma compared with conventional MRI techniques. Thus, GfM bears a high potential in clinical application.

Novel frontiers in ultra-structural and molecular MRI of the brain

PURPOSE OF REVIEW

Recent developments in the MRI of the brain continue to expand its use in basic and clinical neuroscience. This review highlights some areas of recent progress.

RECENT FINDINGS

Higher magnetic field strengths and improved signal detectors have allowed improved visualization of the various properties of the brain, facilitating the anatomical definition of function-specific areas and their connections. For example, by sensitizing the MRI signal to the magnetic susceptibility of tissue, it is starting to become possible to reveal the laminar structure of the cortex and identify millimeter-scale fiber bundles. Using exogenous contrast agents, and innovative ways to manipulate contrast, it is becoming possible to highlight specific fiber tracts and cell populations. These techniques are bringing us closer to understanding the evolutionary blueprint of the brain, improving the detection and characterization of disease, and help to guide treatment.

SUMMARY

Recent MRI techniques are leading to more detailed and more specific contrast in the study of the brain.

Examination of the role of magnetic resonance imaging in multiple sclerosis: A problem-orientated approach

Magnetic Resonance Imaging (MRI) has brought in several benefits to the study of Multiple Sclerosis (MS). It provides accurate measurement of disease activity, facilitates precise diagnosis, and aid in the assessment of newer therapies. The imaging guidelines for MS are broadly divided in to approaches for imaging patients with suspected MS or clinically isolated syndromes (CIS) or for monitoring patients with established MS. In this review, the technical aspects of MR imaging for MS are briefly discussed. The imaging process need to capture the twin aspects of acute MS viz. the autoimmune acute inflammatory process and the neurodegenerative process. Gadolinium enhanced MRI can identify acute inflammatory lesions precisely. The commonly applied MRI marker of disease progression is brain atrophy. Whole brain magnetization Transfer Ratio (MTR) and Magnetic Resonance Spectroscopy (MRS) are two other techniques use to monitor disease progression. A variety of imaging techniques such as Double Inversion Recovery (DIR), Spoiled Gradient Recalled (SPGR) acquisition, and Fluid Attenuated Inversion Recovery (FLAIR) have been utilized to study the cortical changes in MS. MRI is now extensively used in the Phase I, II and III clinical trials of new therapies. As the technical aspects of MRI advance rapidly, and higher field strengths become available, it is hoped that the impact of MRI on our understanding of MS will be even more profound in the next decade.

Magnetic resonance enhancement pattern and diagnostic accuracy of gadofluorine M in a rabbit VX2 tumor model: Comparison with gadopentetate dimeglumine

OBJECTIVE

The purpose of this study was to evaluate the enhancement pattern and the diagnostic accuracy of gadofluorine M in comparison with gadopentetate dimeglumine in a rabbit VX2 tumor model.

MATERIALS AND METHODS

Thirteen rabbits with experimentally induced VX2 carcinomas in the thighs underwent sequential T1-weighted enhancement MR imaging using a 3.0T MR imager, first with gadopentetate dimeglumine, and then 24 (n=4) or 4h (n=9) later with gadofluorine M. In 4 rabbits with 13 tumors, the time-percentage enhancement (PE; i.e., percentage of signal intensity increase) curve was obtained for up to 24h for each contrast agent. In 9 rabbits with 49 tumors (random numbers of VX2 tumors were inoculated at random sites in the thigh), 3 readers unaware of the histopathologic results interpreted the MR images and determined the number and conspicuity level of the detected tumors. The reference standard was the histopathology of the specimen.

RESULTS

The time-to-peak PE for gadopentetate dimeglumine was 1min and gadopentetate dimeglumine showed a rapid washout pattern. The time-to-peak PE for gadofluorine M was 30min and gadofluorine M showed a plateau enhancement pattern for up to 24h. The peak PE of gadofluorine M was approximately twice that of the same dose of gadopentetate dimeglumine (108.2±14.8 vs. 51.5±24.0). The sensitivities for detecting VX2 tumors by 3 readers were 89.8% (44/49), 85.7% (42/49), and 95.9% (47/49) for gadopentetate dimeglumine-enhanced MR imaging, and 87.8% (43/49), 89.8% (44/49), and 89.8% (44/49) for gadofluorine M-enhanced MR imaging. No significant differences in the sensitivities existed between the two contrast agents for any reader. However, the conspicuity level of tumors was superior with gadofluorine M-enhanced MR imaging for two readers and similar for the other reader.

CONCLUSION

Gadofluorine M showed strong and plateau enhancement of tumors for up to 24h. In the reader study, gadofluorine M showed better conspicuity for VX2 tumors than gadopentetate dimeglumine, but had a similar sensitivity.

Magnetic resonance imaging techniques in white matter disease: potentials and limitations

OBJECTIVES

excellent soft tissue contrast, noninvasiveness, assessment of multiple structural and functional parameters, and absence of radiation are the essential properties of magnetic resonance imaging explaining why this modality is the technique of choice for the assessment of cerebral white matter (WM).

METHODS

the present review discusses various standard and advance magnetic resonance imaging techniques with respect to WM assessment in a clinical context. Techniques assessing predominantly structure are T2, fluid-attenuated inversion recovery, echo-gradient T2*, and susceptibility weighted imaging. Techniques assessing a mix between structure and function are diffusion-weighted and diffusion tensor imaging to investigate WM tracts, magnetization transfer to assess bound and free water pool, and magnetic resonance spectroscopy investigating brain metabolites. Finally, functional techniques are perfusion-weighted imaging and perfusion reserve imaging to assess cerebral perfusion and cerebral perfusion reserve, respectively.

CONCLUSIONS

magnetic resonance imaging may assess various and complementary WM parameters. Because acquisition time is limited in the clinical setting, MR techniques must be adapted to the primary question asked. The basic imaging of WM might include axial T2, diffusion-weighted imaging, and coronal fluid-attenuated inversion recovery. This provides an excellent overview in a relatively short time and 2 imaging planes. The remaining MR techniques can add complementary information, for example, PWI/perfusion reserve imaging in vascular disease, T2*/susceptibility weighted imaging in degenerative disease (iron deposition) and head trauma (microbleeds), magnetic resonance spectroscopy (metabolic disease and neoplasm), magnetization transfer (demyelinating disease), and diffusion tensor imaging (degenerative diseases, presurgical evaluation).

Gadofluorine M-enhanced MRI shows involvement of circumventricular organs in neuroinflammation

Background

Circumventricular organs (CVO) are cerebral areas with incomplete endothelial blood-brain barrier (BBB) and therefore regarded as "gates to the brain". During inflammation, they may exert an active role in determining immune cell recruitment into the brain.

Methods

In a longitudinal study we investigated in vivo alterations of CVO during neuroinflammation, applying Gadofluorine M- (Gf) enhanced magnetic resonance imaging (MRI) in experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. SJL/J mice were monitored by Gadopentate dimeglumine- (Gd-DTPA) and Gf-enhanced MRI after adoptive transfer of proteolipid-protein-specific T cells. Mean Gf intensity ratios were calculated individually for different CVO and correlated to the clinical disease course. Subsequently, the tissue distribution of fluorescence-labeled Gf as well as the extent of cellular inflammation was assessed in corresponding histological slices.

Results

We could show that the Gf signal intensity of the choroid plexus, the subfornicular organ and the area postrema increased significantly during experimental autoimmune encephalomyelitis, correlating with (1) disease severity and (2) the delay of disease onset after immunization. For the choroid plexus, the extent of Gf enhancement served as a diagnostic criterion to distinguish between diseased and healthy control mice with a sensitivity of 89% and a specificity of 80%. Furthermore, Gf improved the detection of lesions, being particularly sensitive to optic neuritis. In correlated histological slices, Gf initially accumulated in the extracellular matrix surrounding inflammatory foci and was subsequently incorporated by macrophages/microglia.

Conclusion

Gf-enhanced MRI provides a novel highly sensitive technique to study cerebral BBB alterations. We demonstrate for the first time in vivo the involvement of CVO during the development of neuroinflammation.

New approaches to neuroimaging of central nervous system inflammation

PURPOSE OF REVIEW

Inflammation is an important component not only in autoimmune but also in ischemic/degenerative disorders of the central nervous system (CNS). We here review magnetic resonance imaging (MRI)-based techniques to visualize neuroinflammation in vivo.

RECENT FINDINGS

Iron oxide particles such as superparamagnetic iron oxide (SPIO) and ultrasmall SPIO (USPIO) are phagocytosed by hematogeneous macrophages upon systemic application into the circulation and allow in-vivo tracking of infiltration to the CNS due to their paramagnetic effect by MRI in experimental CNS disorders, and also in multiple sclerosis and stroke. Thereby, the size and application scheme of the iron particles is critical for interpretation of the MRI data which in addition to neuroinflammation involves passive diffusion and intravascular trapping. Targeting of inflammatory, activation-dependent enzymes such as myeloperoxidase or immune function molecules by MR contrast agents represents a molecular approach to visualize critical steps of lesion development caused by neuroinflammation. Clinical studies with Gd-DTPA in conjunction with experimental investigations employing more sensitive MR contrast agents such as gadofluorine revealed that breakdown of the blood-brain barrier and SPIO/USPIO-related macrophage infiltration occur mostly independently.

SUMMARY

Cellular and targeted molecular MRI provides important insights into the dynamics of neuroinflammation.

Inflammation induced neurological handicap processes in multiple sclerosis: new insights from preclinical studies

Multiple sclerosis (MS) is described as originating from incompletely explained neuroinflammatory processes, dysfunction of neuronal repair mechanisms and chronicity of inflammation events. Blood-borne immune cell infiltration and microglia activation are causing both neuronal destruction and myelin loss, which are responsible for progressive motor deficiencies, organic and cognitive dysfunctions. MRI as a non-invasive imaging method offers various ways to visualise de- and remyelination, neuronal loss, leukocyte infiltration, blood-brain barrier modification and new sensors are emerging to detect inflammatory lesions at an early stage. We describe studies performed on experimental autoimmune encephalomyelitis (EAE) animal models of MS that shed new light on mechanisms of functional impairments to understand the neurological handicap in MS. We focus on examples of neuroinflammation-mediated inhibition of CNS repair involving adult neurogenesis in the sub-ventricular zone and hippocampus and such experimentally observed inhibitions could reflect deficient plasticity and activation of compensatory mechanisms in MS. In parallel with cognitive decline, organic deficits such as bladder dysfunction are described in most of MS patients. Neuropharmacological interventions, electrical stimulation of nerves, MRI and histopathology follow-up studies helped in understanding the operating events to remodel the neurological networks and to compensate the inflammatory lesions both in spinal cord and in cortical regions. At the molecular level, the local production of reactive products is a well-described phenomenon: oxidative species disturb cellular physiology and generate new molecular epitopes that could further promote immune reactions. The translational research from EAE animal models to MS patient cohorts helps in understanding the mechanisms of the neurological handicap and in development of new therapeutic concepts in MS.

Examination of the role of MRI in multiple sclerosis: a problem orientated approach

Current multiple sclerosis (MS) is generally thought to consist of two general pathological processes; acute inflammation and degeneration. The relationship between these two components is not understood. What is clear, however, is that the measures of acute inflammation are a poor predictor of long-term disability. Although some have suggested that inflammation may not contribute directly to the essential pathology in MS or that it is secondary to tissue degeneration, most students of the disease believe that the two processes are linked. Therefore, applications of MRI to measure both components of the disease are important. As most readers know, considerable success has been achieved in measuring acute inflammation and very little success has been obtained in identifying measures that correlate with disability and the prediction of future disability has not been achieved. In this review, we will examine the successes and failures of MRI in measuring these two components of the disease process. Consequently, we will not attempt to provide a detailed review of each MRI technique or sequence that has been applied to MS (a number of excellent reviews are available) but rather discuss how these techniques have been applied to answer specific questions. We will provide some comments on the use of MRI in clinical trials as well as in clinical practice. Finally, we will end with a brief discussion of future challenges.

Role of intraspinal steroid application in patients with multiple sclerosis

Clinical trials on patients with progressive multiple sclerosis (MS) have shown no clear evidence of an effective symptomatic treatment with improving disability. Immunomodulatory compounds efficaciously reduce the relapse rate. Numerous earlier papers exist on the pros and cons and/or on the efficacy of intrathecal administration of differing dosages of various conventional released steroids. Furthermore, this treatment approach was nearly abondoned owing to a debate on side effects and a missing proven superiority over intravenous systemic high dosage steroid administration. However, recent open-label studies in progressive MS patients with predominant spinal symptomatology investigated the repeated intraspinal application of the sustained-release compound triamcinolone acetonide (TCA). A distinct improvement of walking distance and MS scores in the short term and stabilization of this beneficial effect after repeat TCA application every 6-12 weeks was found. Moreover, patients with a relapse with acute onset of painful sensations showed a marked pain improvement after repeated TCA application following prior unsuccessful treatment with intravenous steroids. The available data from open studies ask for the performance of a randomized clinical trial, comparing intravenous with intrathecal steroid administration, to confirm the higher efficacy of the more invasive therapy with repeated lumbar puncture.

Magnetic resonance imaging in multiple sclerosis

OBJECTIVES

multiple sclerosis (MS) is an inflammatory disease of unknown origin affecting the central nervous system. Magnetic resonance imaging (MRI) plays an increasingly important role in its diagnosis and further monitoring of disease progress.

METHODS

the typical MRI appearance of MS on conventional MRI sequences and current diagnostic criteria for MS are discussed. Advanced imaging techniques are reviewed with respect to application in MS. Finally, the atypical variants of MS are briefly reviewed.

CONCLUSIONS

although MRI is not intended and will not replace clinical assessment in MS, the recognized MRI criteria may aid in establishing an earlier and more accurate diagnosis of MS in the context of a clinical suspicion or clinically isolated syndrome. In addition, MRI might contribute to rule out differential diagnoses for MS. Moreover, MRI may be used to monitor the evolution of MS and in pharmaceutical trials. Advanced imaging techniques might, in the future, further characterize MS lesion subtypes and potentially guide tailored therapy.

Beyond blood brain barrier breakdown - in vivo detection of occult neuroinflammatory foci by magnetic nanoparticles in high field MRI

Background

Gadopentate dimeglumine (Gd-DTPA) enhanced magnetic resonance imaging (MRI) is widely applied for the visualization of blood brain barrier (BBB) breakdown in multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). Recently, the potential of magnetic nanoparticles to detect macrophage infiltration by MRI was demonstrated. We here investigated a new class of very small superparamagnetic iron oxide particles (VSOP) as novel contrast medium in murine adoptive-transfer EAE.

Methods

EAE was induced in 17 mice via transfer of proteolipid protein specific T cells. MR images were obtained before and after application of Gd-DTPA and VSOP on a 7 Tesla rodent MR scanner. The enhancement pattern of the two contrast agents was compared, and correlated to histology, including Prussian Blue staining for VSOP detection and immunofluorescent staining against IBA-1 to identify macrophages/microglia.

Results

Both contrast media depicted BBB breakdown in 42 lesions, although differing in plaques appearances and shapes. Furthermore, 13 lesions could be exclusively visualized by VSOP. In the subsequent histological analysis, VSOP was localized to microglia/macrophages, and also diffusely dispersed within the extracellular matrix.

Conclusion

VSOP showed a higher sensitivity in detecting BBB alterations compared to Gd-DTPA enhanced MRI, providing complementary information of macrophage/microglia activity in inflammatory plaques that has not been visualized by conventional means.

TASK1 modulates inflammation and neurodegeneration in autoimmune inflammation of the central nervous system

We provide evidence that TWIK-related acid-sensitive potassium channel 1 (TASK1), a member of the family of two-pore domain potassium channels relevant for setting the resting membrane potential and balancing neuronal excitability that is expressed on T cells and neurons, is a key modulator of T cell immunity and neurodegeneration in autoimmune central nervous system inflammation. After induction of experimental autoimmune encephalomyelitis, an experimental model mimicking multiple sclerosis, TASK1(-/-) mice showed a significantly reduced clinical severity and markedly reduced axonal degeneration compared with wild-type controls. T cells from TASK1(-/-) mice displayed impaired T cell proliferation and cytokine production, while the immune repertoire is otherwise normal. In addition to these effects on systemic T cell responses, TASK1 exhibits an independent neuroprotective effect which was demonstrated using both a model of acutely prepared brain slices cocultured with activated T cells as well as in vitro cultivation experiments with isolated optic nerves. Anandamide, an endogenous cannabinoid and inhibitor of TASK channels, reduced outward currents and inhibited effector functions of T cells (IFN-gamma production and proliferation); an effect completely abrogated in TASK1(-/-) mice. Accordingly, preventive blockade of TASK1 significantly ameliorated experimental autoimmune encephalomyelitis after immunization. Therapeutic application of anandamide significantly reduced disease severity and was capable of lowering progressive loss of brain parenchymal volume as assessed by magnetic resonance imaging. These data support the identification and characterization of TASK1 as potential molecular target for the therapy of inflammatory and degenerative central nervous system disorders.

[Magnetic resonance imaging of central nervous system inflammation]

Magnetic resonance imaging (MRI) is widely used to explore central nervous system inflammatory disorders, especially multiple sclerosis (MS). Advanced MRI methods are bringing more sensitive and specific tools for each step of the inflammatory process. In this review, we discuss the different MRI approaches for inflammatory disorders exploration, especially MS. We give particular emphasize on sensibility and specificity of each MRI approach and we also discuss the current knowledge concerning biological and histopathological substratum that could explain MRI signal with each modality.

Comparison of gadofluorine-M and Gd-DTPA for noninvasive staging of atherosclerotic plaque stability using MRI

BACKGROUND

Inflammation and neovascularization play critical roles in the stability of atherosclerotic plaques. Whole-body quantitative assessment of these plaque features may improve patient risk-stratification for life-threatening thromboembolic events and direct appropriate intervention. In this report, we determined the utility of the MR contrast agent gadofluorine-M (GdF) for staging plaque stability and compared this to the conventional agent Gd-DTPA.

METHODS AND RESULTS

Five control and 7 atherosclerotic rabbits were sequentially imaged after administration of Gd-DTPA (0.2 mmol/kg) and GdF (0.1 mmol/kg) using a T(1)-weighted pulse sequence on a 3-T MRI scanner. Diseased aortic wall could be distinguished from normal wall based on wall-to-muscle contrast-to-noise values after GdF administration. RAM-11 (macrophages) and CD-31 (endothelial cells) immunostaining of MR-matched histological sections revealed that GdF accumulation was related to the degree of inflammation at the surface of plaques and the extent of core neovascularization. Importantly, an MR measure of GdF accumulation at both 1 and 24 hours after injection but not Gd-DTPA at peak enhancement was shown to correlate with a quantitative histological morphology index related to these 2 plaque features.

CONCLUSIONS

GdF-enhanced MRI of atherosclerotic plaques allows noninvasive quantitative information about plaque composition to be acquired at multiple time points after injection (within 1 and up to 24 hours after injection). This dramatically widens the imaging window for assessing plaque stability that is currently attainable with clinically approved MR agents, therefore opening the possibility of whole-body (including coronary) detection of unstable plaques in the future and potentially improved mitigation of cataclysmic cardiovascular events.

Defining the therapeutic window of vertebral photodynamic therapy in a murine pre-clinical model of breast cancer metastasis using the photosensitizer BPD-MA (Verteporfin)

Breast cancer is known to cause metastatic lesions in the bone, which can lead to skeletal-related events. Currently, radiation therapy and surgery are the treatment of choice, but the success rate varies and additional adjuncts are desirable. Photodynamic therapy (PDT) has been applied successfully as a non-radiative treatment for numerous cancers. Earlier work has shown that the athymic rat model is suitable to investigate the effect of PDT on bone metastasis and benzoporphyrin-derivative monoacid ring A (BPD-MA; verteporfin) has been shown to be a selective photosensitizer. The aim of this study was to define the therapeutic window of photosensitizer with regard to drug and light dose. Human breast carcinoma cells (MT-1)-stable transfected with the luciferase gene-were injected intra-cardiacally into athymic rats. At 14 days, the largest vertebral lesion by bioluminescence imaging was targeted for single treatment PDT. A drug escalating-de-escalating scheme was used (starting drug dose and light energy of 0.2 mg/kg and 50 J, respectively). Outcomes included 48 h post-treatment bioluminescence of remaining viable tumour, histomorphometric assessment of tumour burden, and neurologic evaluation. The region of effect by bioluminescence and histology increased with increasing drug dose and light energy. A safe and effective drug-light dose combination in this model appears to be 0.5 mg/kg BPD-MA and applied light energy of less than 50 J for the thoracic spine and 1.0 mg/kg and 75 J for the lumbar spine. For translation to clinical use, it is an advantage that BPD-MA (verteporfin), a second-generation photosensitizer, is already approved to treat age-related macular degeneration. Overall, PDT represents an exciting potential new minimally-invasive local, safe and effective therapy in the management of patients with spinal metastases.

Imaging of inflammation in the peripheral and central nervous system by magnetic resonance imaging

Inflammation plays a central role in the pathophysiology of numerous disorders of the nervous system, but is also pivotal for repair processes like peripheral nerve regeneration. In this review we summarize recent advances in cellular magnetic resonance imaging (MRI) while nuclear imaging methods to visualize neuroinflammation are covered by Wunder et al. [Wunder A, Klohs J, Dirnagl U (2009) Non-invasive imaging of central nervous system inflammation with nuclear and optical imaging. Neuroscience, in press]. Use of iron oxide-contrast agents allows assessment of inflammatory processes in living organisms. Upon systemic application, circulating small (SPIO) and ultrasmall particles of iron oxide (USPIO) are preferentially phagocytosed by monocytes before clearance within the reticuloendothelial system of the liver, spleen and lymph nodes. Upon acute migration into the diseased nervous system these iron oxide-laden macrophages become visible on MRI by the superparamagnetic effects of iron oxide resulting in a signal loss on T2-w and/or bright contrast on T1-w MRI. There is an ongoing controversy, however, to what extent SPIO/USPIO also diffuses passively into the brain after disruption of the blood-brain barrier pretending macrophage invasion. Other confounding factors include circulating SPIO/USPIO particles within the blood pool, local hemorrhages, and intrinsic iron oxide-loading of phagocytes. These uncertainties can be overcome by in vitro preloading of cells with iron oxide contrast agents and consecutive systemic application into animals. Iron oxide-contrast-enhanced MRI allowed in vivo visualization of cellular inflammation during wallerian degeneration, experimental autoimmune neuritis and encephalomyelitis, and stroke in rodents, but also in patients with multiple sclerosis and stroke. Importantly, cellular MRI provides additional information to gadolinium-DTPA-enhanced MRI since cellular infiltration and breakdown of the blood-brain barrier are not closely linked. Coupling of antibodies to iron oxide particles opens new avenues for molecular MRI and has been successfully used to visualize cell adhesion molecules guiding inflammation.