Les maladies neurodégénératives sont un sujet de santé publique majeur. La maladie de Parkinson (MP), la démence à corps de Lewy (DCL) et l'atrophie multisystématisée (AMS) font partie d'une famille liées à l'accumulation pathologique d'une protéine : l'α-synucléine (α-syn), appelées les synucléinopathies. Il n'existe pas méthode de diagnostic formel pre-mortem de ces pathologies. À ce jour, la confirmation définitive de synucléinopathies n'est possible que sur des études post-mortem. Le mécanisme de survenue reste incompris. L'exploration des systèmes de neurotransmission et des voies métaboliques pourrait permettre d'élucider ces mécanismes. Les travaux effectués au cours de cette thèse se positionnent dans une optique de développement d'un outil de diagnostic précoce et de compréhension des mécanismes physiopathologiques grâce à l'imagerie TEP. Dans une première partie, nous avons caractérisé et validé un modèle murin de synucléinopathies. Nous avons conclu que le [18F]BF227 ne pouvait être employé comme radiotraceur des agrégats d'α-syn. La seconde partie a permis la mise au point d'une technique d'évaluation de l'affinité de molécules pour une cible donnée. Douze ligands froids ont pu être testés in vitro. Actuellement, aucun composé ne semble présenter les critères pour être un radiotraceur idéal. Enfin, la dernière partie a mis en évidence un hypométabolisme glucidique ainsi qu'une surexpression des récepteurs 5-HT1A à un stade précoce de la pathologie. Au final, cette étude a montré l'intérêt et les limites de l'imagerie TEP et des modèles animaux pour le développement d'un nouveau radiotraceur ainsi que pour l'exploration des mécanismes physiopathologiques / Neurodegenerative diseases are a major public health issue. Parkinson's disease (PD), dementia with Lewy bodies (DLB) and multiple system atrophy (MSA) are part of a family related to the pathological accumulation of a protein, α-synuclein (α- syn), and called synucleinopathies. To date, there is no pre-mortem formal diagnosis method for these diseases and the final confirmation only relies on postmortem studies. While the occurrence mechanisms remain unclear, exploration of neurotransmitter systems and metabolic pathways could bring more information on the underlying pathophysiological processes. The aims of this PhD work were (1) to develop the first radioligand targeting α-syn as an early diagnostic tool and (2) to investigate, with PET imaging, how neurotransmitter systems relates to pathophysiological mechanisms in an accelerated mouse model of synucleinopathy. In the first part of this study, we demonstrated the inability of in vivo PET imaging with [18F]BF227 to label α-syn aggregates in a model of synucleinopathy. The second part allowed the development of a competitive radioligand binding assay to determine α-syn binding parameters of non-radioactive candidate molecules. Twelve ligands were tested in vitro. Currently, no compound appears to present ideal α-syn binding properties. The last part of this study highlighted a serotoninergic hypometabolism and the overexpression of 5-HT1A receptors at an early stage of the disease in the synucleinopathy mouse model. Finally, this study demonstrated the advantages and limitations of PET imaging and animal models for the development of radiotracer and for the exploration of pathophysiological mechanisms

<p>In this study, we have addressed the serotonergic and the opioid system within the CNS. Both systems are of outmost importance in the etiology of disease states, especially mental disorders. </p><p>In our investigation of the serotonergic system, we have synthesized novel enantiomerically pure 6-aryl-3-amino- and 8-aryl-3-aminochromans as ligands for the 5-HT₇ receptor. One reason for the lack of understanding of the physiological functionality of the serotonin 5-HT₇ receptor, the most recently discovered member of the serotonin receptor family, is the absence of partial agonists and agonists. In this series, we have identified partial agonists with more than189 fold selectivity over the 5-HT_1Areceptor and one agonist with 29 fold greater selectivity over the serotonin 5-HT_1Areceptor. Thus the present series constitutes a starting point for developing highly selective ligands for the 5-HT₇ receptor. </p><p>In our investigation of the opioid system, our focus has been on the natural product salvinorin A, which is a highly selective kappa opioid receptor agonist. In the total synthesis of salvinorin A, we have accomplished the synthesis of a key intermediate, 6-(3-furyl)-4-methyl-5,6-dihydro-pyran-2-one via ring closing metathesis. Furthermore, synthetic methodologies have been developed as a part of the total synthesis. Several lipases have been screeened for their ability to generate enantiomerically pure 1-(3-Furyl)-3-buten-1-ol via bio-catalyzed hydrolysis of the corresponding acetate. The lipase from <i>Pseudomonas fluorescens</i> was identified as having stereoselectivity high enough to generate a % <i>ee </i>value above 98%. We have also developed a route for the introduction of a hydroxyl functionality in the γ position of α,β-unsaturated cyclic ketones by the regioselective oxidation of 1-silyloxy-1,3-dienes using dimethyldioxirane. We have initiated the investigation of the pharmacophore responsible for the kappa opioid activity by synthesizing simplified analogues of salvinorin A. A synthetic route providing easy access to simplified analogues of salvinorin A have been established.</p>

In this study, we have addressed the serotonergic and the opioid system within the CNS. Both systems are of outmost importance in the etiology of disease states, especially mental disorders. In our investigation of the serotonergic system, we have synthesized novel enantiomerically pure 6-aryl-3-amino- and 8-aryl-3-aminochromans as ligands for the 5-HT7 receptor. One reason for the lack of understanding of the physiological functionality of the serotonin 5-HT7 receptor, the most recently discovered member of the serotonin receptor family, is the absence of partial agonists and agonists. In this series, we have identified partial agonists with more than189 fold selectivity over the 5-HT1A receptor and one agonist with 29 fold greater selectivity over the serotonin 5-HT1A receptor. Thus the present series constitutes a starting point for developing highly selective ligands for the 5-HT7 receptor. In our investigation of the opioid system, our focus has been on the natural product salvinorin A, which is a highly selective kappa opioid receptor agonist. In the total synthesis of salvinorin A, we have accomplished the synthesis of a key intermediate, 6-(3-furyl)-4-methyl-5,6-dihydro-pyran-2-one via ring closing metathesis. Furthermore, synthetic methodologies have been developed as a part of the total synthesis. Several lipases have been screeened for their ability to generate enantiomerically pure 1-(3-Furyl)-3-buten-1-ol via bio-catalyzed hydrolysis of the corresponding acetate. The lipase from Pseudomonas fluorescens was identified as having stereoselectivity high enough to generate a % ee value above 98%. We have also developed a route for the introduction of a hydroxyl functionality in the γ position of α,β-unsaturated cyclic ketones by the regioselective oxidation of 1-silyloxy-1,3-dienes using dimethyldioxirane. We have initiated the investigation of the pharmacophore responsible for the kappa opioid activity by synthesizing simplified analogues of salvinorin A. A synthetic route providing easy access to simplified analogues of salvinorin A have been established.

Positron emission tomography (PET) is a functional imaging method that allows studying physiological, biochemical or pharmacological processes in vivo. PET is being used in both research and clinical practice. In the brain, it has been used to investigate metabolism, receptor binding, and alterations in regional blood flow. This thesis involves both preclinical and clinical dual-tracer PET imaging studies of different neurological disorders. In this way, different radiotracers were used along the projects. The first project focused on the implementation and in vivo validation of the simultaneous dual-tracer PET imaging technique on the rat brain and its applications in the study of cerebral ischemia. In particular, in this project two biological processes were studied at the same time: cerebral blood flow and cerebral glucose metabolism. The second project consisted in a clinical correlation study of the GABAergic and serotonin systems in a population with Essential Tremor (ET), the most commonly movement disorders. / La tomografia per emissió de positrons (PET) és un mètode d'imatge funcional que permet l'estudi in vivo de processos fisiològics, bioquímics i farmacològics. La PET s'utilitza tant en la pràctica clínica com en la recerca. Al cervell, s'ha utilitzat per investigar el metabolisme, la neurotransmissió, i les alteracions en el flux sanguini regional. Aquesta tesi implica estudis preclínics i clínics de la tècnica PET en diversos trastorns neurològics. D'aquesta manera, es van utilitzar diferents radiotraçadors al llarg dels projectes. El primer projecte es va centrar en la implementació i validació in vivo de la tècnica PET del doble-marcador simultani en el cervell de rata i les seves aplicacions en l'estudi de la isquèmia cerebral. En particular, en aquest projecte es van estudiar en el mateix moment dos processos biològics: el flux sanguini cerebral i el metabolisme cerebral de la glucosa. El segon projecte va consistir en un estudi clínic de correlació dels sistemes GABAèrgic i serotoninèrgic en una població amb tremolor essencial (TE), el trastorn del moviment més comú

The purpose of this study was the investigation of several transport systems expressed at the BBB. The identification and functional characterization of such transport systems is essential to provide a basis for strategies to regulate drug disposition into the brain. Immortalized rat brain endothelial cells (RBE4 cells) have been used in this study as an in vitro model of the BBB. The present study has shown that the RBE4 cells are a suitable model of the BBB for transporter studies. These cells do express the amino acid transport systems L and y+, which are known to be present at the BBB. The uptake of L-tryptophan, a neutral amino acid transported by system L, exhibited a half saturation constant (Kt) of 31 µM and a maximal velocity rate (Vmax) of about 1 nmol/mg/min in RBE4 cells. The kinetic constants of the L-arginine uptake, representing system y+ transport activity, into RBE4 cells were determined with a Kt value of about 55 µM and a Vmax of 0.56 nmol/mg/min. Furthermore the expression of two sodium dependent transporters, the 5-HT transporter (SERT) and the organic cation/carnitine transporter OCTN2, was shown at the RBE4 cells. Uptake studies with radiolabeled 5-HT exhibited a saturable, sodium dependent transport at RBE4 cells with a Kt value of about 0.40 µM and a Vmax of about 52 fmol/mg/min. L-carnitine and TEA (tetraethylammonium) are known to be transported by the OCTN2 transporter. The uptake of L-carnitine into RBE4 cells was shown to be sodium dependent and saturable with a Kt value of 54 µM and a maximal velocity of about 3.6 pmol/mg/min. In contrast, the organic cation TEA follows a sodium independent uptake mechanism at RBE4 cells. Also a sodium independent choline uptake into the cells was discovered but the molecular identity remained unknown. This saturable choline transport exhibited a Kt value of about 22 µM and a maximal velocity of about 52 pmol/mg/min.