157 research outputs found

    Radiopharmaceuticals for PET imaging of neuroinflammation - Les radiopharmaceutiques pour l’imagerie TEP de la neuroinflammation

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    Abstract Recently, accumulating evidence has revealed that neuroinflammation appears to be the cornerstone of many neurological diseases including stroke, multiple sclerosis, Alzheimer's disease or Parkinson's disease. Neuroinflammation causes neuronal damages by activation of numerous cells and molecular mediators in diseases involving the inflammatory process. In this article, we focus on noninvasive molecular imaging of radioligands that target inflammatory cells and molecules involved in neuroinflammation. PET is in fact one of the most promising imaging techniques to visualize and quantify neuroinflammation in vivo. We have also summarized the potential neuroinflammation imaging targets and corresponding PET radioligands. Résumé Des données scientifiques récentes et de plus en plus nombreuses ont mis en évidence le rôle central joué par le processus de neuroinflammation dans la physiopathologie de nombreuses maladies neurologiques, telles que l’accident vasculaire cérébral, la sclérose en plaques, la maladie d’Alzheimer ou encore la maladie de Parkinson. Dans ces maladies impliquant le processus inflammatoire, la neuro-inflammation cause en effet des dommages neuronaux par activation de nombreuses cellules et médiateurs moléculaires. L’imagerie par tomographie par émission de positons (TEP) apparaît comme une approche prometteuse pour visualiser et quantifier in vivo la neuro-inflammation de façon non invasive, grâce en particulier au développement de radioligands ciblant spécifiquement diverses molécules impliquées dans cette réaction inflammatoire cérébrale. Dans cette revue sont présentés les cibles moléculaires potentielles pour l’imagerie TEP de la neuro-inflammation ainsi que les médicaments radiopharmaceutiques correspondants

    Current paradigm of the 18-kDa translocator protein (TSPO) as a molecular target for PET imaging in neuroinflammation and neurodegenerative diseases

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    Neuroinflammation is a process characterised by drastic changes in microglial morphology and by marked upregulation of the 18-kDa translocator protein (TSPO) on the mitochondria. The continual increase in incidence of neuroinflammation and neurodegenerative diseases poses a major health issue in many countries, requiring more innovative diagnostic and monitoring tools. TSPO expression may constitute a biomarker for brain inflammation that could be monitored by using TSPO tracers as neuroimaging agents. From medical imaging perspectives, this review focuses on the current concepts related to the TSPO, and discusses briefly on the status of its PET imaging related to neuroinflammation and neurodegenerative diseases in humans

    Novel PET Imaging of Inflammatory Targets and Cells for the Diagnosis and Monitoring of Giant Cell Arteritis and Polymyalgia Rheumatica

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    Giant cell arteritis (GCA) and polymyalgia rheumatica (PMR) are two interrelated inflammatory diseases affecting patients above 50 years of age. Patients with GCA suffer from granulomatous inflammation of medium- to large-sized arteries. This inflammation can lead to severe ischemic complications (e.g., irreversible vision loss and stroke) and aneurysm-related complications (such as aortic dissection). On the other hand, patients suffering from PMR present with proximal stiffness and pain due to inflammation of the shoulder and pelvic girdles. PMR is observed in 40-60% of patients with GCA, while up to 21% of patients suffering from PMR are also affected by GCA. Due to the risk of ischemic complications, GCA has to be promptly treated upon clinical suspicion. The treatment of both GCA and PMR still heavily relies on glucocorticoids (GCs), although novel targeted therapies are emerging. Imaging has a central position in the diagnosis of GCA and PMR. While [18F]fluorodeoxyglucose (FDG)-positron emission tomography (PET) has proven to be a valuable tool for diagnosis of GCA and PMR, it possesses major drawbacks such as unspecific uptake in cells with high glucose metabolism, high background activity in several non-target organs and a decrease of diagnostic accuracy already after a short course of GC treatment. In recent years, our understanding of the immunopathogenesis of GCA and, to some extent, PMR has advanced. In this review, we summarize the current knowledge on the cellular heterogeneity in the immunopathology of GCA/PMR and discuss how recent advances in specific tissue infiltrating leukocyte and stromal cell profiles may be exploited as a source of novel targets for imaging. Finally, we discuss prospective novel PET radiotracers that may be useful for the diagnosis and treatment monitoring in GCA and PMR.</p

    Positron emissiontomography imaging of neuroinflammation in Multiple Sclerosis with a second generation translocator protein PET radioligand

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    This thesis describes a new approach for molecular imaging of neuroinflammation in Multiple Sclerosis (MS). My aim was to use the 2nd generation TSPO radioligand 18F-PBR111 to explore the potential of Positron Emission Tomography (PET) targeting the 18-kDa Translocator Protein (TSPO), as an in vivo biomarker of activated microglia in MS patients. This thesis addresses three research objectives. First, I characterised 18F-PBR111 PET signal in healthy controls’ brains and tested how it is affected by the TSPO gene polymorphism at rs6971. Second, I measured 18F-PBR111 uptake across white matter volumes segmented using structural MRI measures related to MS neuropathology. Third, I explored how 18F-PBR111 uptake in the hippocampus correlated with depressive symptoms and to the brain functional connectivity of the hippocampus. Eleven patients with relapsing-remitting MS and 22 age-matched healthy controls underwent 18F-PBR111 PET and MRI scans. Structural and functional MRI sequences were used to define conventional MS neuropathological markers and for the assessment of functional connectivity, respectively. I discovered that white matter 18F-PBR111 PET signal in healthy volunteers varied with TSPO genotype and correlated positively with age. In patients with MS, signal intensity in MRI-defined lesions was higher than that in normal-appearing white matter and correlated with the historical rate of progression of their disability. Hippocampal 18F-PBR111 uptake was higher in the MS patient group than in healthy volunteers and correlated with both depressive symptoms and functional connectivity of the hippocampus with frontal, temporal and parietal cortex. I thus discovered that this 2nd generation TSPO PET radiotracer, used in humans for the first time in our study, is sensitive to MS neuropathology consistent with recognized patterns of microglial activation and that differences between subjects can be related to disability progression. I also have discovered a novel relationship between this measure of hippocampal microglial activation and affective symptoms of MS.Open Acces

    QUANTITATIVE METHODS FOR ANALYSIS OF TSPO AVAILABILITY IN PROGRESSIVE MULTIPLE SCLEROSIS, USING BRAIN PET IMAGING WITH RADIOLIGAND 11C-PBR28

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    Background – The translocator protein 18kDA (TSPO) is closely related to diffuse inflammatory demyelinating injury and hence represents an ideal target for brain imaging in progressive-MS pathology in vivo. However, quantification of the TSPO is associated with number of challenges corresponding to its genetic polymorphism and localization in the CNS and surroundings. Subsequent inaccuracy in TSPO quantification with plasma concentration or anatomical brain reference region proposes for implementation of alternative quantification approaches that are hypothesized to compensate the shortcomings. Objectives – This study has tried to perform a comparative evaluation of novel quantification approaches for analyzing neuroinflammation using 11C-PBR28 tracer in MR-PET brain imaging of the patients with SPMS versus healthy control participants. Methods – Nine secondary progressive MS and 11 healthy controls have been examined in 3Tesla MR and (11C-PBR28) PET brain imaging in Turku PET Centre (TPC). Brain segmentation and image preprocessing were fulfilled using Freesurfer v.5.3 and SPM12 toolset in MATLAB. Lesion and ROIs delineation was performed via in house software. Tracer binding activity was measured, and volume of distribution was quantified via 2TCM compartmental model. Four brain reference regions were considered for normalization of the values, consisted of three anatomical reference regions in addition to one supervised clustering pseudo-references modified version of the algorithm developed in the Harvard university for similar aim. Results – The results of this study obtained via examination of several kinetic models, data and partial volume correction steps aimed at narrowing down the selected approaches and accounting the apparently most robust method for the higher-level analysis and the statistical examination. However, through neither of the steps any result represented a significant support for the H1 hypothesis in this study. The low signal to noise ratio of the PET imaging data with the utilized radioligand and the diffusivity of the TSPO in the MS brain, along with the complexity of quantification caused by the polymorphism genotype and the affinity binding of the radiotracer in MS brains and blood plasma are the greatest obstacles challenging the analysis of the PET-MR imaging data in the pathological studies of the MS in vivo

    Imaging Neuroinflammation in Progressive Multiple Sclerosis

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    Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system CNS), where inflammation and neurodegeneration lead to irreversible neuronal damage. In MS, a dysfunctional immune system causes auto‐reactive lymphocytes to migrate into CNS where they initiate an inflammatory cascade leading to focal demyelination, axonal degeneration and neuronal loss. One of the hallmarks of neuronal injury and neuroinflammation is the activation of microglia. Activated microglia are found not only in the focal inflammatory lesions, but also diffusely in the normal‐appearing white matter (NAWM), especially in progressive MS. The purine base, adenosine is a ubiquitous neuromodulator in the CNS and also participates in the regulation of inflammation. The effect of adenosine mediated via adenosine A2A receptors has been linked to microglial activation, whereas modulating A2A receptors may exert neuroprotective effects. In the majority of patients, MS presents with a relapsing disease course, later advancing to a progressive phase characterised by a worsening, irreversible disability. Disease modifying treatments can reduce the severity and progression in relapsing MS, but no efficient treatment exists for progressive MS. The aim of this research was to investigate the prevalence of adenosine A2A receptors and activated microglia in progressive MS by using in vivo positron emission tomography (PET) imaging and [11C]TMSX and [11C](R)‐PK11195 radioligands. Magnetic resonance imaging (MRI) with diffusion tensor imaging (DTI) was performed to evaluate structural brain damage. Non‐invasive input function methods were also developed for the analyses of [11C]TMSX PET data. Finally, histopathological correlates of [11C](R)‐PK11195 radioligand binding related to chronic MS lesions were investigated in post‐mortem samples of progressive MS brain using autoradiography and immunohistochemistry. [11C]TMSX binding to A2A receptors was increased in NAWM of secondary progressive MS (SPMS) patients when compared to healthy controls, and this correlated to more severe atrophy in MRI and white matter disintegration (reduced fractional anisotropy, FA) in DTI. The non‐invasive input function methods appeared as feasible options for brain [11C]TMSX images obviating arterial blood sampling. [11C](R)‐PK11195 uptake was increased in the NAWM of SPMS patients when compared to patients with relapsing MS and healthy controls. Higher [11C](R)‐PK11195 binding in NAWM and total perilesional area of T1 hypointense lesions was associated with more severe clinical disability, increased brain atrophy, higher lesion load and reduced FA in NAWM in the MS patients. In autoradiography, increased perilesional [11C](R)‐PK11195 uptake was associated with increased microglial activation identified using immunohistochemistry. In conclusion, brain [11C]TMSX PET imaging holds promise in the evaluation of diffuse neuroinflammation in progressive MS. Being a marker of microglial activation, [11C](R)‐ PK11195 PET imaging could possibly be used as a surrogate biomarker in the evaluation of the neuroinflammatory burden and clinical disease severity in progressive MS.Siirretty Doriast

    Kinetic modeling and parameter estimation of TSPO PET imaging in the human brain

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    PURPOSE: Translocator protein 18-kDa (TSPO) imaging with positron emission tomography (PET) is widely used in research studies of brain diseases that have a neuro-immune component. Quantification of TSPO PET images, however, is associated with several challenges, such as the lack of a reference region, a genetic polymorphism affecting the affinity of the ligand for TSPO, and a strong TSPO signal in the endothelium of the brain vessels. These challenges have created an ongoing debate in the field about which type of quantification is most useful and whether there is an appropriate simplified model. METHODS: This review focuses on the quantification of TSPO radioligands in the human brain. The various methods of quantification are summarized, including the gold standard of compartmental modeling with metabolite-corrected input function as well as various alternative models and non-invasive approaches. Their advantages and drawbacks are critically assessed. RESULTS AND CONCLUSIONS: Researchers employing quantification methods for TSPO should understand the advantages and limitations associated with each method. Suggestions are given to help researchers choose between these viable alternative methods
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