• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 253
  • 144
  • 102
  • 26
  • 22
  • 20
  • 20
  • 13
  • 12
  • 10
  • 10
  • 6
  • 4
  • 4
  • 4
  • Tagged with
  • 739
  • 113
  • 97
  • 60
  • 57
  • 55
  • 52
  • 50
  • 50
  • 48
  • 46
  • 46
  • 46
  • 44
  • 42
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Heart-Fatty Acid Binding Protein und α-Synuklein im Serum als mögliche Markerkandidaten für Parkinson und Demenz / Heart-fatty acid binding protein and α-synuclein in blood serum as possible biomarker candidates for Parkinson's disease and dementia

Willner, Markus 07 March 2018 (has links)
No description available.
412

Heterotopic ossification in skin:special focus on multiple miliary osteoma cutis and the role of bone morphogenetic proteins

Moilanen, R. (Riina) 07 January 2014 (has links)
Abstract Heterotopic ossification is a pathological condition in which bone forms outside the skeletal system. It can also occur in skin, which is the case in some genetic disorders. In multiple miliary osteoma cutis (MMOC), tiny bone fragments develop in the dermis and nearby subcutaneous tissue of the face and upper chest region during middle age. The etiology of the disease is poorly understood. The origin of the osteoma-forming cells is not known and also unknown are the signaling factors that direct the skin cells towards an osteogenic lineage. The purpose of this study was to investigate MMOC and the pathogenesis of ectopic bone formation by combining patient study and cell biology methods. The results from an extensive review of the literature and five new cases revealed MMOC as a distinct disease entity, where heterotopic bone formation is intramembranous. No correlation was found between MMOC and acne scars, hormonal disturbances or GNAS gene mutations. In cell culture studies mouse and human dermal fibroblasts and mouse dermal papilla (DP) cells were found to differentiate into osteoblast-like matrix mineralizing cells. The bone morphogenetic protein 4 (BMP-4) homodimer and BMP-2/7 heterodimer had significant effects on the osteogenic differentiation of the above mentioned cells. Interestingly, the BMPs enhanced the differentiation of mouse cells but reduced it in human cells. In mouse DP cells and human fibroblasts BMP-2/7 was more potent than BMP-4. The skin area affected by osteomas in patients was compared to their unaffected skin and also to the corresponding skin areas in controls with regard to osteogenic differentiation and gene expression studies. MMOC patients’ skin differs from controls both in osteoma and unaffected skin areas, which suggests MMOC is not only a local but also a systemic skin disease. The results confirm the previous findings that gene expression in skin is different in different parts of the body, which could explain why the osteomas develop in certain skin areas. The results of this study provide new information about MMOC and heterotopic ossification in skin and could be useful when developing treatments for MMOC. This study also presents new information about BMPs and their different effects in mouse and human cells, which may stimulate discussion about the generalization of mouse studies in humans and the clinical use of BMPs. / Tiivistelmä Virhesijaintinen luutuminen on patologinen tila, jossa luuta muodostuu luisen tukirangan ulkopuolelle. Tätä voi tapahtua myös ihossa, kuten käy tietyissä sairauksissa. Ihon lukuisat jyvämäiset osteoomat on tauti, jossa pieniä luujyväsiä ilmaantuu verinahkaan ja ihonalaiskudokseen keski-iässä. Taudin syytä, osteoomia muodostavien solujen alkuperää tai sitä, mitkä viestinvälittäjät saavat esiastesolut siirtymään luusolulinjalle, ei tiedetä. Tässä työssä tutkittiin ihon lukuisia jyvämäisiä osteoomia ja virhesijaintista luutumista yhdistämällä kliinisiä ja solubiologisia menetelmiä. Laajasta kirjallisuuteen perehtymisestä ja viidestä omasta potilaasta saadut tulokset osoittivat ihon lukuisten jyvämäisten osteoomien olevan oma erillinen tautinsa, jossa virhesijaintinen luutuminen tapahtuu suoran luutumisen mekanismilla. Tauti ei näytä olevan yhteydessä aknearpiin, hormonihäiriöihin tai GNAS-geenin mutaatioihin. Soluviljelykokeissa hiiren ja ihmisen verinahan fibroblastien ja hiiren karvatupen nystyn solujen havaittiin erilaistuvan osteoblastityyppisiksi soluväliainetta mineralisoiviksi soluiksi. Luun morfogeneettisillä proteiineilla (BMP) 4 ja 2/7 oli merkitsevä vaikutus yllä mainittujen solujen erilaistumisessa. Yllättävää kyllä, ne edistivät hiiren solujen, mutta vähensivät ihmisen solujen erilaistumista. Hiiren karvatupen soluille ja ihmisen fibroblasteille BMP-2/7 oli tehokkaampi kuin BMP-4. Potilaiden osteoma-aluetta verrattiin heidän terveeseen ihoalueeseensa samoin kuin vastaaviin ihoalueisiin kontrollihenkilöillä käyttäen menetelminä solujen erilaistamista luuta muodostavaan suuntaan sekä geenien ilmentymisen tutkimista. Potilaiden iho erosi kontrollien ihosta sekä osteooma-alueella että terveellä ihoalueella, mikä viittaa taudin olevan koko elimistöön vaikuttava. Tulokset vahvistavat aikaisempia löydöksiä siitä, että geenien ilmentyminen ihossa on erilaista eri puolilla kehoa. Tämä voisi selittää osteoomien esiintymisen vain tietyllä alueella. Tämän tutkimuksen tulokset antavat uutta tietoa ihon lukuisista jyvämäisistä osteoomista ja virhesijaintisesta luutumisesta ja saattavat olla hyödyksi kehitettäessä taudin hoitoa. Tutkimus antaa uutta tietoa luun morfogeneettisten proteiinien erilaisesta käyttäytymisestä hiirellä ja ihmisellä, mikä herättänee keskustelua hiirikokeiden yleistämisestä ihmiseen ja luun morfogeneettisten proteiinien kliinisestä käytöstä.
413

Synthèse, analyses structurales et assemblage de foldamères oligoamide hydrosolubles à base de quinolines / Synthesis, structural analysis, and assembly of water soluble quinoline-based oligoamide foldamers

Hu, Xiaobo 15 June 2017 (has links)
La chimie des foldamères est un domaine de recherche en pleine expansion où les chimistes explorent la construction d’architectures artificielles variées mimant les structures repliées des biopolymères naturels. Les foldamères d’oligoamides quinoline, constituent une branche importante des foldamères montrant de nombreuses caractéristiques attractives, incluant la stabilité et la prédictibilité de leurs conformations repliées, qui en font de bons candidats pour des applications biologiques. Jusqu’à présent, la plupart des études sur les foldamères d’oligoamides quinolines ont été menées dans des solvants organiques. Cette thèse a pour objectif d’étendre leur portée au milieu aqueux et présente plusieurs méthodologies pour parvenir à leur solubilité, leur repliement, la variation de leurs chaines latérales, leur agrégation et leur capacité à former des cristaux dans l’eau.Tout d’abord, une méthode de synthèse en phase solide a été développée permettant l’accès rapide aux foldamères hybrides α-amino acide/quinoline (X/Q). Leur étude dans l’eau montre que contrairement aux foldamères hybrides de type (XQ)n, ceux de type (XQ2)n sont capables d’adopter une conformation hélicoïdale présentant un alignement des chaines α-amino acides dans l’espace. Ensuite, plusieurs chaines latérales courtes ont été identifiées pour doter les foldamères aromatiques d’une solubilité et d’une capacité à cristalliser dans l’eau. Six oligoamides quinoline ont ainsi été synthétisés pour une étude modèle. Des cristaux ont été obtenus pour toutes les séquences sauf une, présentant une excessive solubilité dans l’eau. Enfin, des efforts ont été faits pour construire des faisceaux d’hélices auto-assemblés dans l’eau à base d’effets hydrophobes et d’interactions électrostatiques. Les études RMN et cristallographiques ont indiqué que les effets hydrophobes étaient plus faibles qu’attendu et ne provoquaient pas d’agrégation forte. / Foldamer chemistry is a rapidly expanding research field where chemists explore the construction of various artificial architectures that mimic the folded structures of biopolymers found in nature. Quinoline oligoamide foldamers, as an important branch of foldamers, have been shown to possess many desirable features, including stability and predictability of their folded conformations, and are promising candidates to achieve biological applications. Up to now, most investigations of quinoline oligoamide foldamers have been carried out in organic solvents. This thesis is aimed to expand their scope in aqueous medium and presents several methodologies to achieve solubility, folding, side-chain variation, aggregation and crystal growth ability in water.First, a solid phase synthesis method was developed to enable the fast access to α-amino acid/quinoline (X/Q) hybrid oligoamide foldamers. The study of these hybrid foldamers in water showed that contrary to (XQ)n-type foldamers the (XQ2)n-type foldamers could adopt aromatic helical conformations with α-amino acid side chains aligned in space. Then, several short side chains were identified to endow aromatic foldamers with both solubility in, and crystal growth ability from water. Six quinoline oligoamides displaying these side chains were synthesized as a case study. Crystals were obtained from aqueous medium in all cases but one, exceedingly soluble in water. At last, efforts were made to construct self-assembled aromatic helix bundles in water based on hydrophobic effects and electrostatic interactions. NMR and crystallographic studies indicated that hydrophobic effects are weaker than expected and not strongly conducive of aggregation.
414

Etude de la propreté inclusionnaire des lingots VAR - Application aux alliages de titane / Study of inclusional cleanliness of VAR lingots - Application to titanium alloys

Ghazal, Ghassan 15 April 2010 (has links)
L’apparition d’inclusions exogènes demeure un problème majeur pour les élaborateurs de titane. Afin d’améliorer la propreté inclusionnaire des lingots élaborés par le procédé de refusion à l’arc sous vide (Vacuum Arc Remelting), une étude numérique et expérimentale a été réalisée. La partie numérique de la thèse consiste à modéliser le comportement d’un défaut hard-α provenant de l’électrode consommable et tombant dans le puits liquide du lingot. Un modèle décrivant le processus de dissolution prédit l’évolution de la taille d’une inclusion durant son séjour dans le puits liquide. La trajectoire est déterminée à l’aide d’un modèle lagrangien tenant compte de la turbulence de l’écoulement en modifiant le coefficient de trainée. Les deux modèles ont été couplés et implémentés dans le logiciel SOLAR, qui simule la croissance d’un lingot VAR.Les résultats mettent en évidence la difficulté d’éliminer une inclusion hard-α avec une seule refusion, principalement à cause de la croissance d’une couche de phase β pendant les premiers moments de l’immersion. Le comportement global du défaut dépend fortement de l’hydrodynamique du puits et des caractéristiques de l’inclusion.Pour étudier la dissolution expérimentalement, des défautssynthétiques (hard-α et HDI) ont été immergés dans un bain de titane liquide chauffé dans un four à bombardement électronique. Les vitesses de dissolution ont été déterminées en mesurant les dimensions des défauts avant et après les expériences et ont été ensuite utilisées pour valider les modèles numériques. Par ailleurs, nous avons mis en évidence la grande influence de la température et de la vitesse de l’écoulement sur les cinétiques de dissolution / The presence of exogeneous inclusions has always been a major concern for the titanium industry. To help improve the inclusional cleanliness of VAR (Vacuum Arc Remelting) titanium ingots, a numerical and experimental study was undertaken.The numerical model is capable of predicting the motion and dissolution of a hard-α defect falling from the electrode tip into the ingot melt pool during vacuum arc remelting. It is implemented in SOLAR, a CFD code that simulates the ingot growth and solidification. The dissolution of the inclusion is governed by nitrogen diffusion from the defect towards the surrounding molten metal. A model describing this phenomenon predicts the particle size evolution and the nitrogen profile at each moment. The motion of the spherical particle is tracked using a Lagrangian model and the influence of turbulence is accounted for by a modification of the drag coefficient.Results show that inclusion removal is difficult with a single melt since the growth of a β-phase layer leads to an initial increase in the defect size. The inclusion behaviour is highly dependent on the pool hydrodynamics and on inclusion characteristics.In order to clarify dissolution aspects of these defects and to measure their dissolution kinetics, synthetically processed defects were introduced into molten titanium heated in an electron beam melting furnace. Dissolution rates were calculated by measuring the size of the defects before and after the experiments and the results were used to validate the numerical models. Furthermore, the experiments show that dissolution kinetics highly depend on fluid motion and temperature
415

Etudes des impacts de la réactivité en phase aqueuse atmosphérique sur la formation et le vieillissement des Aérosols Organiques Secondaires sous conditions simulées

Liu, Yao 25 February 2011 (has links)
Cette étude se focalise sur les impacts de la réactivité en phase aqueuse de la méthacroléïne et de la méthyl vinyl cétone sur la formation des nouveaux aérosols organiques secondaires (AOS), et les impacts de la réactivité en phase aqueuse sur le vieillissement des AOS formés par l’isoprène, α-pinène et 1,3,5-triméthylbenzène en phase gazeuse. Les études de la réactivité en phase aqueuse ont été étudiées vis-à-vis des radicaux OH. Dans le but d’identifier et quantifier les produits d’oxydation des différents précurseurs d’intérêt, les échantillons en phase aqueuse ont été analysés par différents systèmes analytiques. Les résultats montrent clairement la formation de petits composés primaires et secondaires qui ont été expliqués par les mécanismes réactionnels. On a observé également la formation de composés à haute masse moléculaire par rapport à leurs précurseurs. Ces produits ont été supposés être très peu volatils et pourraient induire la formation des AOS lors de l’évaporation de l’eau. Leur capacité à former des AOS a été montrée expérimentalement par les expériences de nébulisation des solutions aqueuses à différents temps de réaction. Les résultats montrent qu’au moins une part de ces produits à haute masse moléculaire reste en phase particulaire lors de l’évaporation de l’eau, et contribue à la formation des AOS. L’ensemble de ces résultats met en évidence le fait que la réactivité en phase aqueuse atmosphérique peut induire des effets importants sur la formation et le vieillissement des AOS atmosphériques, qui peut induire une modification des propriétés physico-chimiques des aérosols. / This work focused on the impacts of aqueous phase OH-oxidation of methacrolein, methyl vinyl ketone on the SOA formation, and impacts of aqueous phase OH-oxidation on aging of SOA that are formed by isoprene, -pinene and 1,3,5-trimethylbenzene in gas phase. The chemical characterization of aqueous phase was performed by different analytical techniques. The results show the formation of small primary and secondary reaction products that were explained by suitable chemical reaction mechanisms. The formation of oligomers with high molecular mass (compared with their precursors) has also been observed during the OH-oxidation. These oligomers might be low volatile compounds that induce the formation of SOA during water evaporation. Their capacity to form SOA was experimentally demonstrated by nebulizing the aqueous phase solution at different reaction times. The results show that at least a part of oligomers remains in the particle phase during water evaporation, and contributes to the SOA formation. All of these results highlight that aqueous phase reactivity could induce important effects on the formation and aging of atmospheric SOA, which can induce modification of physico-chemical properties of SOA.
416

Desenvolvimento de sistemas multifuncionais nanoestruturados para a liberação de fármacos administrados por via nasal no tratamento de glioblastoma /

Naddeo, Natália Noronha Ferreira January 2020 (has links)
Orientador: Maria Palmira Daflon Gremião / Resumo: Glioblastomas (GBM) representam 77% dos tumores malignos do sistema nervoso central (SNC) e ainda hoje, apesar de todos os avanços na terapia, continua com prognóstico limitado. A existência de barreiras fisiológicas como a barreira hematoencefálica (BHE) representa o principal obstáculo que impede que concentrações adequadas do fármaco atinjam o local de ação. Por suas vantagens anatômicas, uma estratégia proposta para a administração de fármacos destinados ao SNC consiste no uso da via nasal. Além disso, o uso de terapias combinadas utilizando fármacos capazes de agir em diferentes alvos moleculares deve ser considerada para o tratamento de doenças complexas como GBM. O candidato a fármaco ácido alfa-ciano-4-hidroxicinâmico (CHC) e o anticorpo monoclonal cetuximab (CTX) já são explorados devido à capacidade de agir em diferentes alvos moleculares nas células tumorais e aplicados em conjunto, como uma nova abordagem combinada, podem melhorar os resultados terapêuticos. De forma complementar, a utilização de sistemas de liberação baseados em nanotecnologia trará inevitavelmente ganhos terapêuticos à combinação proposta, permitindo que atributos específicos sejam agregados ao sistema e possibilite não somente a administração nasal, como também a associação de diferentes fármacos em um único carreador. Assim, o presente estudo propõe o desenvolvimento de diferentes plataformas poliméricas baseadas em poli(ácido láctico-co-glicólico) (PLGA) e quitosana trimetilada (TMC) ou quito... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Glioblastomas (GBM) account for 77% of malignant tumors in the central nervous system (SNC), and today, despite all advances in therapy, remains with a limited prognosis. The existence of physiological barriers as the blood brain barrier (BBB) represents the main obstacle that limits appropriate concentrations of drugs designed to therapy. Due to their anatomical advantages, a strategy proposed for direct delivery to SNC involves the use of the nose-to-brain route. Besides, combination therapy that uses multiple drugs against different molecular targets should be considered for complex diseases such as GBM. Drugs like alpha-cyano-4-hydroxycinnamic acid (CHC) and the monoclonal antibody cetuximab (CTX) are already explored for their capacity to act against different hallmarks of cancer and applied together, as a novel combining approach, might improve therapeutic outcomes. Therefore, advances in nanotechnology-based delivery systems will inevitably bring therapeutic gains to the proposed combination since they enable acquisition of important characteristics desired and also the association of different drugs into a single carrier. Thus, the current study proposes the development of different polymeric platforms based on poly(lactic-co-glycolic acid) (PLGA) and trimethyl chitosan (TMC) /chitosan oligosaccharide (OCS) for CHC encapsulation. Both CHC-loaded developed systems (PLGA/TMC and PLGA/OCS) exhibited nanostructure organization of about 300 to 400 nm, containing chitosan o... (Complete abstract click electronic access below) / Doutor
417

The effect of dimethyl sulfoxide on the induction of DNA strand breaks in plasmid DNA and colony formation of PC Cl3 mammalian cells by alpha-, beta-, and Auger electron emitters 223Ra, 188Re, and 99mTc

Runge, Roswitha, Oehme, Liane, Kotzerke, Jörg, Freudenberg, Robert 16 January 2017 (has links)
BACKGROUND: DNA damage occurs as a consequence of both direct and indirect effects of ionizing radiation. The severity of DNA damage depends on the physical characteristics of the radiation quality, e.g., the linear energy transfer (LET). There are still contrary findings regarding direct or indirect interactions of high-LET emitters with DNA. Our aim is to determine DNA damage and the effect on cellular survival induced by (223)Ra compared to (188)Re and (99m)Tc modulated by the radical scavenger dimethyl sulfoxide (DMSO). METHODS: Radioactive solutions of (223)Ra, (188)Re, or (99m)Tc were added to either plasmid DNA or to PC Cl3 cells in the absence or presence of DMSO. Following irradiation, single strand breaks (SSB) and double strand breaks (DSB) in plasmid DNA were analyzed by gel electrophoresis. To determine the radiosensitivity of the rat thyroid cell line (PC Cl3), survival curves were performed using the colony formation assay. RESULTS: Exposure to 120 Gy of (223)Ra, (188)Re, or (99m)Tc leads to maximal yields of SSB (80 %) in plasmid DNA. Irradiation with 540 Gy (223)Ra and 500 Gy (188)Re or (99m)Tc induced 40, 28, and 64 % linear plasmid conformations, respectively. DMSO prevented the SSB and DSB in a similar way for all radionuclides. However, with the α-emitter (223)Ra, a low level of DSB could not be prevented by DMSO. Irradiation of PC Cl3 cells with (223)Ra, (188)Re, and (99m)Tc pre-incubated with DMSO revealed enhanced survival fractions (SF) in comparison to treatment without DMSO. Protection factors (PF) were calculated using the fitted survival curves. These factors are 1.23 ± 0.04, 1.20 ± 0.19, and 1.34 ± 0.05 for (223)Ra, (188)Re, and (99m)Tc, respectively. CONCLUSIONS: For (223)Ra, as well as for (188)Re and (99m)Tc, dose-dependent radiation effects were found applicable for plasmid DNA and PC Cl3 cells. The radioprotection by DMSO was in the same range for high- and low-LET emitter. Overall, the results indicate the contribution of mainly indirect radiation effects for each of the radionuclides regarding DNA damage and cell survival. In summary, our findings may contribute to fundamental knowledge about the α-particle induced DNA damage.
418

Should Skin Biopsies Be Performed in Patients Suspected of Having Parkinson’s Disease?

Siepmann, Timo, Penzlin, Ana Isabel, Illigens, Ben Min-Woo, Reichmann, Heinz 06 June 2018 (has links)
In patients with Parkinson’s disease (PD), the molecularly misfolded form of α-synuclein was recently identified in cutaneous autonomic nerve fibers which displayed increased accumulation even in early disease stages. However, the underlying mechanisms of synucleinopathic nerve damage and its implication for brain pathology in later life remain to be elucidated. To date, specific diagnostic tools to evaluate small fiber pathology and to discriminate neurodegenerative proteinopathies are rare. Recently, research has indicated that deposition of α-synuclein in cutaneous nerve fibers quantified via immunohistochemistry in superficial skin biopsies might be a valid marker of PD which could facilitate early diagnosis and monitoring of disease progression. However, lack of standardization of techniques to quantify neural α-synuclein deposition limits their utility in clinical practice. Additional challenges include the identification of potential distinct morphological patterns of intraneural α-synuclein deposition among synucleinopathies to facilitate diagnostic discrimination and determining the degree to which structural damage relates to dysfunction of nerve fibers targeted by α-synuclein. Answering these questions might improve our understanding of the pathophysiological role of small fiber neuropathy in Parkinson’s disease, help identify new treatment targets, and facilitate assessment of response to neuroprotective treatment.
419

Phenotypic Variability in a Family with Aicardi-Goutières Syndrome Due to the Common A177T RNASEH2B Mutation

Tüngler, Victoria, Schmidt, Franziska, Hieronimus, Steve, Reyes-Velasco, Claudio, Lee-Kirsch, Min Ae 09 July 2014 (has links)
Aicardi-Goutières syndrome (AGS) is a rare inflammatory encephalopathy mimicking in utero acquired viral infection. Cardinal findings comprise leukodystrophy, basal ganglia calcifications and cerebral atrophy along with cerebrospinal fluid lymphocytosis and elevated interferon-α. In the majority of cases AGS is inherited as an autosomal recessive trait and caused by mutations in six genes including RNASEH2A, RNASEH2B, RNASEH2C, TREX1, SAMHD1 and ADAR1, all of which encode enzymes acting on nucleic acid species. Most patients present with first neurological signs in early infancy and experience severe global developmental delay. Here, we report on the unusual divergent phenotype of two siblings who both carry the most frequent AGS causing p.A177T (c.529G > A) RNASEH2B mutation in the homozygous state. While one sibling showed a typical AGS presentation with early onset and severe statomotor and mental impairment, the older sibling was intellectually completely normal. She was only diagnosed because of mild spasticity of the legs and serological signs of autoimmunity. These findings highlight the phenotypic variability of AGS and suggest that AGS may be underdiagnosed among children with mild cerebral palsy.
420

Synthèse de prodrogues de l’[aza(p-MeO)F⁴]-GHRP-6, α-acyloxyéthyl carbamates, pour réguler le récepteur CD36

N'guessan, Ginette 09 1900 (has links)
Les prodrogues sont des dérivés biologiquement inactifs d’un principe actif qui, après administration à un organisme, subissent une transformation chimique ou enzymatique pour libérer le principe actif au site d’action. Elles améliorent les propriétés physicochimiques du principe actif pour permettre un meilleur transport à travers les barrières biologiques et pour augmenter l’activité in vivo. Elles sont utilisées pour améliorer la formulation et l’administration, accroître la perméabilité et l’absorption, modifier le profil de distribution et éviter le métabolisme et la toxicité. Cette approche est très utile pour améliorer l'administration de principes actifs. Il existe deux types de prodrogues : les prodrogues liées à un transporteur et les bioprécurseurs. Dans le premier cas, la molécule active est liée par une liaison covalente à un groupement temporaire, ce qui fournit une nouvelle molécule, qui est inactive. Le groupement temporaire libéré ne doit pas avoir, par lui-même, d'action pharmacologique ni de toxicité. Dans le second cas, le principe actif est transformé métaboliquement ou chimiquement par réaction d’hydratation, d’oxydation ou de réduction. Les azapeptides sont des mimes peptidiques dans lesquels un ou plusieurs carbones de la chaîne peptidique sont remplacés par des atomes d’azote. Ce remplacement augmente la rigidité de la chaîne peptidique et favorise le repliement de type β. Le repliement β des azapeptides est associé à plusieurs propriétés thérapeutiques. Certains azapeptides ont montré une meilleure activité, une meilleure sélectivité et une plus grande stabilité comparativement aux peptides parents ce qui prolonge leur durée d'action et les rend plus résistants aux dégradations métaboliques. Ce mémoire s’intéresse particulièrement à l’azapeptide : [aza(p-MeO)F⁴]-GHRP-6. Celui-ci est un analogue du peptide sécréteur d’hormone de croissance 6 (GHRP-6, H-His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂), qui possède une affinité pour deux récepteurs distincts : les récepteurs de growth hormone secretagogue receptor 1a (GHS-R1a) et le récepteur cluster of differentiation 36 (CD36). L’[aza(p-MeO)F⁴]-GHRP-6 démontre une sélectivité envers le récepteur CD36 offrant des possibilités de traitement de maladies telles que l’athérosclérose et la dégénérescence maculaire liée à l’âge (DMLA). De plus, le récepteur CD36 peut interagir avec un corécepteur toll-like receptor 2 (TLR2), et l’[aza(p-MeO)F⁴]-GHRP-6 peut réduire des réponses immunitaires innées. La stratégie des prodrogues a été utilisée dans ce mémoire pour augmenter la durée d’action de l’azapeptide [aza(p-MeO)F⁴]-GHRP-6. Plus précisément, cinq analogues des prodrogues α-acyloxyéthylcarbamates de l’aza(p-MeO)F⁴-GHRP-6 ont été synthétisées. Ce mémoire présente la première synthèse de prodrogues α-acyloxyéthylcarbamates à caractère PEG de l’[aza(p-MeO)F⁴]-GHRP-6. / A prodrug is a biologically inactive derivative of a drug which after administration undergoes chemical or enzymatic modification to release the active drug at targeted sites of activity. Prodrugs improve physicochemical properties to enable better transport through biological barriers and enhance activity. They are used to improve formulation and administration, to enhance permeability and absorption, to modify distribution profiles and to avoid metabolism and toxicity. The prodrug approach is useful for improving drug delivery. Prodrugs are classified into two types: carrier-linked prodrugs and bio-precursors. In the first case, the parent drug is linked by a covalent bond to an inert carrier or transport moiety. The carrier should not be active or toxic. The active drug is released by a chemical or enzymatic cleavage in vivo. In the second case, the parent drug is converted metabolically or chemically by hydration, oxidation or reduction reactions. Azapeptides employ a semicarbazide as an amino amide surrogate in a peptide analog in which the backbone α-CH is replaced by nitrogen. Through electronic interactions, the semicarbazide favors backbone β-turn geometry due to a combination of urea planarity and hydrazine nitrogen lone pair – lone pair repulsion. Azapeptides have proven therapeutic utility. Some of them exhibit better selectivity, activity and stability than the parent peptides with increased duration of action and improved metabolic stability. Growth hormone releasing peptide-6 (GHRP-6, H-His-D-Trp-Ala-Trp-D-Phe-Lys-NH₂) is a synthetic peptide possessing an affinity for two different receptors: growth hormone secretagogue receptor 1a (GHS-R1a) and cluster of differentiation receptor 36 (CD36). The GHRP-6 azapeptide analogue, [aza(p-MeO)F⁴]-GHRP-6, has exhibited good affinity for CD36 and reduced nitric oxide overproduction in macrophage cells stimulated with the TLR-2 agonist R-FSL-1. Azapeptide ligands of CD36, such as [aza(p-MeO)F⁴]-GHRP-6, offers potential as prototypes for developing treatments of diseases such as atherosclerosis and age-related macular degeneration. A prodrug strategy has been pursued to improve the pharmacokinetic properties, such as duration of action, of [aza(p-MeO)F⁴]-GHRP-6. The first examples of α-acyloxyethyl carbamate peptides have been prepared. Five α-acyloxyethyl carbamate analogues of [aza(p-MeO)F⁴]-GHRP-6 have been synthesized by routes featuring acylation of the resin-bound peptide using different activated α-acyloxyethyl carbonates prior to resin cleavage and side chain deprotection. The evaluation of the activity of the pharmacokinetic properties of the [aza(p-MeO)F⁴]-GHRP-6 prodrugs is currently in progress and will be reported in due time.

Page generated in 0.0425 seconds