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  • 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.
11

Análise quimiométrica do extrato das folhas de Zeyheria tuberculosa (Vell) Bureau (Bignoniaceae), com atividade inibidora da linfoproliferação, por ressonância magnética nuclear / Chemometric analysis of the extract of the leaves of Zeyheria tuberculosa (Vell) Bureau (Bignoniaceae), with inhibitory activity of lymphocyte proliferation, for nuclear magnetic resonance

Tenório, Maria Amélia Lima dos Santos 19 February 2015 (has links)
Since ancient times, natural products are used as source of medicines to prevent and treat disease. Currently, high cost and time taken for analysis of natural products have been significantly reduced by the use of modern approaches such as chemometric analysis, which gives flexibility to the process of development of new products. This study aimed to chemometric analysis of the ethanol extract, fraction in chloroform and subfractions of the crude extract of leaves Zeyheria tuberculosa (Veil) Bureau (Bignoniaceae), for Nuclear Magnetic Resonance, with the characterization and quantification of the major compounds present in these, as well as construction of a model to select potentially promising extracts, serving as a guide for further isolation of the substances of interest, enabling the discovery of bioactive compounds. The fraction in chloroform which concentrated almost all the ethanol extract metabolites, showed 100% inhibitory activity lymphocyte proliferation at a concentration of 100 gg.m1:1, and is therefore chosen for characterization and quantification of the major compounds present. The NMR spectral analysis of the fraction in chloroform, including 1D experiments (1H, 13C, DEPT 90 °, DEPT135 °) and 2D (J-Resolved, HSQC and HMBC) allowed the detailed structural elucidation of two major compounds, ursolic and oleanolic acids, both identified for the first time in this species. Due to the importance of these acids in the treatment of skin diseases and various cancers, measurements were determined for these triterpenes in ethanol extract (ZTB), fraction in chloroform (ZTP2) and the subfractions, using techniques for this purpose NMR and chemometric tools (Matlab programs, AMIX and SIMCA). All spectra were processed and analyzed using the program topspin (BRUKER). The qualitative and quantitative results of the chemometrics analysis for NMR of the ethanol extract, fraction in chloroform and subfractions of Zeyheria tuberculosa showed that fractions ZTF3 (evaluated in MTT as being non-cytotoxic at concentrations of 10, 50 and 100 pg.mL-1) and ZTF6 (measured in MTT as being non-cytotoxic at the concentration of 10 pg.mL-1 and cytotoxic at concentrations of 50 and 100 pg.mL-1) are the richest of oleanolic and ursolic acids, respectively, and so are more promising for the isolation of these triterpenes. The fraction ZTF4 was second richer fraction both as oleanolic acid and ursolic acid, the most promising for the isolation of these two acids together, also considering that this fraction was evaluated in MTT as non-cytotoxic at concentrations of 10 and 50 g .mL-1, and only the cytotoxic concentration of 100 pg.mL-1. The ursolic and oleanolic acids have a range of therapeutic properties and a high commercial value, being highly relevant the qualitative and quantitative results obtained in this study, referring to these triterpenes found in the leaves of the species Zeyheria tuberculosa. The model proposed in this work was efficient, as indicated by the values of the Q parameter, and suitable for the classification of samples into groups and subgroups according to the presence of ursolic and oleanolic acids (chemical composition) and the concentration of these in the samples, and it may be useful in the identification of potentially promising extracts, serving as a guide for subsequent isolation of the substance of interest. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Desde os tempos antigos, os produtos naturais são utilizados como fonte de medicamentos, para prevenir e tratar doenças. Atualmente, o alto custo e o tempo despendido para as análises de produtos naturais têm sido significativamente reduzidos pelo uso de abordagens modernas, como a análise quimiométrica, que dão agilidade ao processo de desenvolvimento de novos produtos. Este trabalho teve como objetivo a análise quimiométrica do extrato etanólico, da fração em clorofórmio e subfrações do extrato bruto das folhas de Zeyheria tuberculosa (Vell) Bureau (Bignoniaceae), por Ressonância Magnética Nuclear, com a caracterização e quantificação dos compostos majoritários presentes nestes, além da construção de um modelo capaz de selecionar extratos potencialmente promissores, servindo como guia para um posterior isolamento das substâncias de interesse, viabilizando a descoberta de compostos bioativos. A fração em clorofórmio que concentrou a quase totalidade dos metabólitos do extrato bruto, apresentou 100 % de atividade inibitória da linfoproliferação, sendo por isso escolhida para caracterização e quantificação dos compostos majoritários presentes. A análise espectral de RMN da fração em clorofórmio, incluindo experimentos 1D (1H, 13C, DEPT 90°, DEPT 135°) e 2D (J-Resolvido, HSQC e HMBC) permitiu a elucidação estrutural detalhada de dois compostos majoritários, os Ácidos Ursólico e Oleanólico, ambos identificados pela primeira vez nesta espécie. Devido à importância desses ácidos no tratamento de doenças da pele e vários tipos de câncer, foram determinadas as quantificações relativas destes triterpenos no extrato bruto (ZTB), na fração em clorofórmio (ZTP2) e nas subfrações, utilizando-se para este fim técnicas de RMN e ferramentas quimiométricas (programas Matlab, AMIX e SIMCA). Todos os espectros foram processados e analisados utilizando o programa TOPSPIN (BRUKER). Os resultados quantitativos e qualitativos da análise quimiométrica por RMN do extrato bruto, fração clorofórmica e subfrações de Z. tuberculosa mostraram que as frações ZTF3 (avaliada no teste MTT como sendo átoxica nas concentrações de 10, 50 e 100 pg.mL-1) e ZTF6 (avaliada no teste MTT como sendo atóxica na concentração de 10 pg.mL-1 e citotóxica nas concentrações de 50 e 100 pg.mL-1) são as mais ricas dos ácidos oleanólico e ursólico, respectivamente, e por isso são as mais promissoras para o isolamento destes triterpenos. Já a fração ZTF4 foi a segunda fração mais rica tanto em ácido ursólico como em ácido oleanólico, sendo a mais promissora para o isolamento destes dois ácidos juntos, considerando ainda que esta fração foi avaliada no teste MTT como atóxica nas concentrações de 10 e 50 pg.mL-1, e citotóxica apenas na concentração de 100 pg.mL-1. Os ácidos ursólico e oleanólico possuem uma gama de propriedades terapêuticas e um alto valor comercial, sendo de grande relevância os resultados qualitativos e quantitativos, obtidos neste trabalho, referentes a esses triterpenos encontrados nas folhas da espécie Zeyheria tuberculosa. O modelo proposto neste trabalho foi eficiente, conforme indicado pelos valores do parâmetro Q, e satisfatório para a classificação das amostras em grupos e subgrupos, segundo a presença dos ácidos ursólico e oleanólico (composição química) e a concentração destes nas amostras, podendo ser de grande utilidade na identificação de extratos potencialmente promissores, servindo como guia para um posterior isolamento da(s) substância(s) de interesse.
12

Avaliação do potencial terapêutico e perfil imunológico de triterpenos ácidos na fase crônica da infecção experimental por Trypanosoma cruzi / Evaluation of therapeutic and immunological potential of acid triterpenes in the chronic phase of experimental infection by Trypanosoma cruzi

Mariana Rosa da Silva 23 August 2013 (has links)
A doença de Chagas é um problema de saúde pública, com dados preocupantes referentes ao número de pessoas contaminadas e daquelas que ainda permanecem expostas ao risco de infecção. A dificuldade do combate a Trypanosoma cruzi, agente etiológico da doença, está intimamente relacionada às interações existentes entre o parasito e o hospedeiro, sendo que até o momento, nenhum medicamento ou substância tem demonstrado real eficácia ao combate ao parasito. Em estudos recentes realizados por nosso grupo de pesquisa, os ácidos ursólico e oleanólico demonstraram um bom potencial tripanocida, além de um efeito imunomodulatório, promovendo a inibição da produção de IFN-? quando de suas utilizações por via intraperitoneal em elevadas concentrações. Considerando essas evidências encontradas em relação a essas substâncias e os efeitos promovidos no processo de avaliação biológica, propusemos como objetivo avaliar o potencial terapêutico dos triterpenos ácido ursólico e ácido oleanólico na fase crônica da infecção chagásica e suas associações ao benzonidazol, fármaco referência indicado ao tratamento da parasitose, verificando a possibilidade de geração de benefícios sobre a patogênese da infecção crônica experimental. A quantificação de linfócitos T CD4+ e T CD8+, e das citocinas IL-2, IL-10, IL-12, IFN-? e TNF-??pela técnica de citometria de fluxo, utilizando o kit BD Cytometric Bead Array®, indicaram que essas substâncias não apresentam efeitos imunomodulatórios significativos sobre a resposta Th1 e Th2 nessa fase da doença, na comparação entre grupos infectados e tratados e aquele que recebeu apenas solvente. O parasitismo tecidual determinado por Real Time PCR e as observações realizadas em cortes histológicos, mostraram, respectivamente, baixo número de cópias de DNA de T. cruzi, e ausência de ninhos amastigotas, porém, com marcante presença de infiltrado inflamatório em todos os grupos. Assim, os dados obtidos levam à conclusão de que apesar da atividade apresentada pelos triterpenos ácidos em estudo na fase aguda da doença de Chagas, o mesmo não ocorre na fase crônica, como seria desejável para favorecer uma melhora do quadro patológico, mesmo não havendo a cura da doença, considerando as conseqüências da infecção de longo prazo. / Chagas disease is a public health problem, with disturbing data about the number of infected people and those who remain at risk of infection. The difficulty of eliminating Trypanosoma cruzi, etiologic agent of the disease is closely related to the interactions between the parasite and the host, and until now, no medicine or substance has demonstrated real effectiveness against the parasite. In recent studies by our research group, the ursolic and oleanolic acids revealed considerable trypanocidal activity, and an immunomodulatory effect, promoting the inhibition of IFN-? with intraperitoneal administration in high concentrations. Considering these evidences and the effects observed during the biological evaluation, our objective was to evaluate the biological potential of the triterpenoids ursolic acid and oleanolic acid in the chronic phase of chagasic infection and their associations to benznidazole, the reference drug indicated for the treatment of this disease, verifying the possibility of benefits on the pathogenesis of experimental chronic infection. Quantification of T CD4+ and T CD8+ cells and of the cytokines IL-2, IL-10, IL-12, IFN-? and TNF-? by flow cytometry using the kit BD cytometric Bead Array®, indicated that these substances do not exhibit significant immunomodulatory effects on Th1 and Th2 responses in this stage of the disease, comparing infected and treated groups and that who received only solvent. The tissue parasitism determined by Real Time PCR and in histological observations showed, respectively, low copy number of T. cruzi DNA, and absence of amastigote nests, however, with marked inflammatory infiltration in all groups. Thus, our data lead to the conclusion that despite the activity presented by the triterpene acids studied in the acute phase of Chagas disease, the same does not occur in the chronic phase, as would be desirable to the reduction of the pathological conditions, even if there is no cure of the disease, considering the consequences of long term infection.
13

Avaliação neurofarmacológica das atividades tipo ansiolítica e/ou antidepressiva da fração diclorometano, ácido oleanólico e (E)-metilisoeugenol das folhas de pimenta pseudocaryophyllus (Gomes) L. R. Landrum (Myrtaceae) quimiotipo (E)-metilisoeugenol / Neuropharmacological evaluation of anxiolytic and/or antidepressant like activities of dichloromethane fraction, oleanolic acid and (E)-metilisoeugenol of the leaves of pimenta pseudocaryophyllus (Gomes) L. R. Landrum (Myrtaceae) Chemotype (E)- metilisoeugenol

Fajemiroye, James Oluwagbamigbe 16 October 2015 (has links)
Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2017-06-08T20:21:50Z No. of bitstreams: 2 Tese - James Oluwagbamigbe Fajemiroye - 2015.pdf: 1734029 bytes, checksum: c1790bce6e7eace236dd1d68cec686a8 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-06-09T11:42:36Z (GMT) No. of bitstreams: 2 Tese - James Oluwagbamigbe Fajemiroye - 2015.pdf: 1734029 bytes, checksum: c1790bce6e7eace236dd1d68cec686a8 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-06-09T11:42:36Z (GMT). No. of bitstreams: 2 Tese - James Oluwagbamigbe Fajemiroye - 2015.pdf: 1734029 bytes, checksum: c1790bce6e7eace236dd1d68cec686a8 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2015-10-16 / Depression and anxiety are widely acclaimed as psychiatric disorders of global concern. These disorders are among the leading causes of disability worldwide. Unsatisfactory responses of patients to the available pharmacotherapy make the search for new drugs a necessity. Medicinal plants remain important source of new drugs and new chemical entities. The ethnopharmacological knowledge and previous data have revealed calming and anxiolytic like effects of the organic leaf extract of Pimenta pseudocaryophyllus (Gomes) L.R. Landrum. The present study sought to investigate antidepressive like effect of dichloromethane fraction (DF) of the ethanolic leaf extract of Pimenta pseudocaryophyllus as well as anxiolytic and antidepressive like effects of oleanolic acid (OA), (E) methyl isoeugenol (MIE) and possible mechanisms of action that are involved. Animal models like barbiturate-induced sleep, light dark box test (LDB), elevated plusmaze (EPM), open field (OF), wire hanging test, pentylenetetrazol-induced convulsion test, forced swimming test (FST), tail suspension test (TST) were conducted to evaluate behavioural alterations that were elicited by the administrations of vehicle, DF, OA, MIE or reference drugs. Bioassays (ex vivo and in vitro) of monoamine oxidase (MAO) and quantification of hippocampal level of brain derived neurotrophic factor (BDNF) were conducted in an attempt to elucidate possible mechanisms of action. Oral administration of DF 125, 250 or 500 mg/kg (potentiated the hypnotic effect of sodium pentobarbital). In the TST and FST, DF 125 or 250 mg/kg induced antidepressant-like response. The data obtained in the OF suggest sedative effect of DF at 500 mg/kg. Pretreatment (i.p) with pchlorophenylalanine methyl ester (PCPA) 100 mg/kg (serotonin depletor) or 𝛼-methyl-ptyrosine (AMPT) 100 mg/kg (catecholamine depletor) blocked anti-immobility effect of DF viii in the FST. The enzymatic activity of MAO remained unaltered by DF. Oral administration of OA (5-20 mg/kg) increased the duration of barbiturate - induced sleep and demonstrated anxiolytic like effect in both LDB and EPM. In the FST and TST, OA 5-20 mg/kg elicited antidepressant like effect without altering locomotion activity of the animals. The antidepressant like effect of OA was attenuated by NAN-190 (non-selective antagonist of 5-HT1A), AMPT, PCPA, WAY and PRAZ. Chronic administration of OA increased hippocampal level of BDNF. Oral administration of MIE 250 or 500 mg/kg potentiated hypnotic effect of sodium pentobarbital without protecting mice against PTZ - induced convulsion. The parameters evaluated in the LDB, EPM and OF demonstrated anxiolytic like property of MIE. This effect was blocked by WAY (selective antagonist of 5-HT1A) pretreatment. MIE 125 or 250 mg/kg showed antidepressant like effect in the FST. Locomotion activity of the animal in the OF remained unaltered by MIE administration at 125 or 250 mg/kg. Pretreatment of mice with PCPA attenuated antidepressant like property of MIE. In conclusion, our findings demonstrated anxiolytic and/or antidepressant like effects of dichloromethane fraction, oleanolic acid and (E) methyl isoeugenol, thereby suggesting the involvement of monoaminergic pathway. / Ansiedade e depressão são transtornos psiquiátricos de interesse global. Estes transtornos estão entre as principais causas da incapacidade laboral das pessoas. Apesar de uma gama de farmacoterapias disponíveis, os resultados clínicos mostram que os fármacos não produziram efeitos terapêuticos desejados e se faz necessário a busca de novos fármacos. As plantas medicinais continuam sendo uma das fontes mais importantes para a descoberta de novos fármacos e entidades químicas. Estudos anteriores mostraram efeito calmante e ansiolítico da fração orgânica do extrato das folhas de Pimenta pseudocaryophyllus (Gomes) L. R. Landrum (Myrtaceae). O presente estudo buscou investigar a atividade tipo antidepressiva da fração diclorometano (FD) do extrato etanólico das folhas desta espécie, bem como antidepressiva e ansiolítica do ácido oleanólico (AO), (E)-metilisoeugenol (MIE) e os possíveis mecanismos de ações envolvidos. Modelos experimentais como o sono induzido por barbitúricos, caixa claro escuro (CCE), labirinto em cruz elevado (LCE), campo aberto (CA), teste de arame, teste de convulsão induzida por pentilenotetrazol, teste de natação forçada (TNF) e teste de suspensão pela cauda (TSC) foram realizados para avaliar alterações comportamentais induzidas pela administração do veículo, FD, AO, MIE ou fármacos de referência. Na tentativa de elucidar os possíveis mecanismos de ação, foram realizados bioensaios (ex vivo e in vitro) da monoamina oxidase (MAO) e do fator neurotrófico derivado do cérebro (BDNF do hipocampo). A administração oral da FD 125, 250 ou 500 mg/kg potencializou o efeito hipnótico de pentobarbital sódico. No TNF e TSC, a FD 125 ou 250 mg/kg induziu efeito tipo antidepressivo. Os dados obtidos no campo aberto sugerem efeito sedativo da fração vi diclorometano na dose de 500 mg/kg. O pré-tratamento (i.p) com p - clorofenilalanina metil éster (PCPA) 100 mg/kg (depletor de serotonina) ou α - metil - p - tirosina (AMPT) 100 mg/kg (depletor de catecolamina) bloqueou o efeito tipo antidepressivo da FD no TNF. O bioensaio da atividade enzimática mostrou que a FD não alterou a atividade da MAO. A administração oral do AO (5-20 mg/kg) aumentou a duração do sono induzido por pentobarbital sódico e demonstrou efeito tipo ansiolítico no CCE e LCE. O AO 5-20 mg/kg demonstrou efeito tipo antidepressivo no TNF e TSC sem alterar a atividade locomotora dos animais. O efeito tipo antidepressivo do AO foi atenuado por prétratamento com NAN-190 (antagonista não-seletivo do receptor 5-HT1A), AMPT, PCPA e PRAZ-prazosin (antagonista do receptor α1 adrenérgico). A administração crônica do AO aumentou o nível de BDNF no hipocampo. A administração oral do MIE 250 ou 500 mg/kg potencializou o efeito hipnótico de pentobarbital sódico sem proteger os animais contra a convulsão induzida por PTZ. Os parâmetros avaliados na CCE e LCE sugerem que MIE têm efeito tipo ansiolítico. Este efeito foi bloqueado pelo pré-tratamento com WAY100635 (antagonista seletivo do receptor 5-HT1A). MIE 125 ou 250 mg/kg apresentou efeito tipo antidepressivo no TNF. Não houve alteração na atividade locomotora dos animais no CA após a administração do MIE 125 ou 250 mg/kg. O prétratamento com PCPA atenuou o efeito tipo antidepressivo do MIE no TNF. Os resultados demonstraram efeito tipo ansiolítico e/ou antidepressivo da fração diclorometano, ácido oleanólico e (E)-metilisoeugenol, sugerindo o envolvimento de vias monoaminérgicas nestes efeitos.
14

Triterpene Carboxylic Acids as Cortisol Lowering Agents and Synthesis of Hexadeuterated Beta-Ionone

Mogg, Trevor January 2012 (has links)
In part one, betulinic acid (1) was isolated from the American Sycamore (Platanus occidentalis) in 1.6% yield, while ursolic acid (3) was isolated from Fuji and McIntosh apple peels in 1.0% and 0.8% crude yields, respectively. Oleanolic (4) and dehydrocanophyllic (6) acids were previously available, along with several analogs. Additional analogs of 1, 3 and 4 were prepared, including 9 new compounds, for a total of 51 compounds. Compounds were initially screened for cortisol lowering properties in vitro using a fish head kidney cell assay. Platanic acid (43) was selected for in vivo study in rats, along with 1 and a blend of Platanus occidentalis and Souroubea sympetela. No significant cortisol lowering was observed in vivo. In part two, β-ionone-d6 (75) was synthesized in 6.5% yield from ethyl 2-oxo-cyclohexane carboxylate (77). Total deuterium incorporation was 99.85%, with 0.03% d0 analog. 75 was converted to retinoic acid-d6 (93) in 2.2% yield.
15

Implication of Ca2+ signaling in fat taste perception : modulation by planttriterpenoids and a chemical GPR120 agonist / Implication de la signalisation Ca2 + dans la perception du goût du gras : modulation par plante triterpénoïdes et un agoniste chimique du GPR120

Murtaza, Babar 14 May 2019 (has links)
En dépit des efforts déployés, l'incidence de l'obésité est en augmentation dans le monde entier où la consommation d‘aliments moins coûteux et hyperénergétiquesriches en matières grasses, représente la principale cause. Des études récentes ont révélé l'existence d'un goût de gras et que l'envie de le satisfaire pourrait être responsable de l‘excès des prises alimentaires et de l'attirance pour les aliments riches en gras. Différentes stratégies ont été utilisées pour réduire la teneur engraisse des aliments ou pour la remplacer par des mimétiques et des substituts de graisse. Dans cette thèse, nous avons non seulement exploré des mécanismes de signalisation tels que le rôle des canaux TRPC3 Ca2+ dans les cellules du bourgeon gustatif, mais nous avons également tenté de rechercher de nouvelles classes de molécules artificielles et naturelles, d‘origines végétales, qui pourraient agir comme exhausteurs de goût ou comme activateurs du goût. Sur la base des résultats obtenus par des études biochimiques et comportementales au cours de la thèse actuelle, nous proposons que Zizyphine purifié à partir de Zizyphus lotus, d‘acide oléanolique et de TUG891 (un agoniste chimique de GPR120) puissent être un candidat novateur et prometteur pour le traitement et la prévention de l'obésité et du syndrome métabolique qui lui est associé. / Despite efforts, the incidence of obesity is on a rise throughout the world andconsumption of less expensive fat rich and high energy diet remains the major cause.Recent studies have successfully unveiled the existence of a fat taste, and that theurge to satisfy it might be responsible for the overeating behaviour and attractiontowards fat rich foods. Different strategies have been used to reduce fat content offood or replace it with fat mimetics and fat replacers. In this dissertation, we have not only explored signalling mechanisms like role of TRPC3 Ca2+ channels in taste bud cells but also tried to search for newer classes of molecules from botanical and chemical origin that might either act as fat taste enhancers, or fat taste activators. Based on the result of various biochemical and behavioural studies during the current dissertation, we propose that Zizyphin purified from Zizyphus lotus,Oleanolic acid and TUG891 (a chemical agonist of GPR120), might be novel andpromising candidates for the treatment and prevention of obesity and associatedmetabolic syndrome.
16

Inhibition du mécanisme de quorum sensing et de la formation de biofilm chez Pseudomonas aerugionsa par des composés bioactifs de Dalbergia trichocarpa (Fabaceae) / Dalbergia trichocarpa, source of natural compounds which affect quorum sensing mechanism and biofilm formation in Pseudomonas aeruginosa

Rasamiravaka, Tsiry 13 June 2014 (has links)
Depuis quelques décennies, les bactéries pathogènes multi-résistantes aux antibiotiques sont de plus en plus répandues dans le monde. Cette situation a suscité le besoin et l'intérêt de trouver des médicaments antibactériens avec de nouvelles cibles potentiels. La découverte des systèmes de communication de type quorum sensing (QS) régulant la virulence bactérienne représente une des cibles privilégiées pour contrôler les bactéries pathogènes autrement qu’en interférant avec leur croissance bactérienne. Dans l’écosystème naturel, un grand nombre d'organismes (Eucaryotes et Procaryotes) co-existent en synthétisant chacun de leur côté des métabolites secondaires. Les plantes, étant en permanence en contact avec des bactéries, synthétisent des métabolites secondaires capables d’inhiber l’expression des gènes de virulence chez les bactéries sans pour autant affecter ni leur croissance ni leur viabilité. Notre objectif a été de contribuer à la valorisation de la biodiversité malgache en identifiant des plantes et en y isolant les composés actifs présentant une capacité à perturber le mécanisme de QS chez P. aeruginosa PAO1, une bactérie pathogène opportuniste de l’homme, des animaux et des plantes. Dans ce but, nous avons tout d’abord réalisé un criblage d’activité anti-QS de différents flavonoïdes commerciaux. De ce criblage, la narigenine et la naringine ont été sélectionnées pour être les molécules de contrôle positif et négatif des tests d’activité anti-QS, respectivement. Par la suite, 4 espèces de Dalbergia endémique de Madagascar ont fait l’objet de criblage pour leur activité anti-QS. Ce travail a fait ressortir l’activité anti-QS très intéressante de l’écorce de D. trichocarpa à partir de laquelle nous avons isolée le composé actif nommé la coumarate de l’aldéhyde-oléanolique (OALC). Le contrôle naringénine et l’OALC ne présente aucun effets inhibiteurs sur la croissance bactérienne de P. aeruginosa PAO1 et sur l’expression du gène QS-indépendant aceA suggérant une activité d’inhibition spécifiquement liée au QS. Cependant, ces deux molécules présentent des spectres d’inhibition différente. En effet, les deux molécules diffèrent dans le sens que la naringenine n’inhibe pas l’expression du gène gacA et la motilité de type twitching contrairement à l’OALC. Ces résultats suggèrent que l’OALC et la naringénine représente des candidats potentiels pour des investigations in vivo quant à leur effet anti-QS et anti-biofilm sur des modèles infectieux d’organismes supérieurs. Par ailleurs, ils démontrent la richesse des plantes malgaches comme sources de nouvelles molécules anti-virulence ainsi que l’importance de telle investigation afin de renforcer notre arsenal thérapeutique en composé antibactérienne dans la lutte continuelle contre les bactéries pathogènes/Since few decades, multidrug resistant bacteria spread all over the world. This situation gives rise to the need and interest in finding antibacterial drugs with novel potent target. Discovery of communication system termed Quorum Sensing (QS) which regulate bacterial virulence factor represent privileged target in another way than interfering with bacterial growth. In natural ecosystem, many organisms (Eukaryotes and Prokaryotes) produce secondary metabolites. As plants are permanently in contact with bacteria, they have synthetized secondary metabolites which inhibit bacterial virulence gene expression without affecting bacterial viability. Our goal was to contribute to the valorization of Malagasy biodiversity and specifically to identify plants and isolate bioactive compound presenting ability to disrupt QS mechanism in P. aeruginosa, opportunistic pathogen bacteria in plants, animals and human. In this purpose, screening of commercial available flavonoids has been firstly carried out. From this screening, naringenin and naringin have been selected to be used as positive and negative QS inhibitor controls, respectively. Subsequently, Four Malagasy endemic Dalbergia species have been screened for their anti-QS activity. This work pointed out the interesting anti-QS activity of D. trichocarpa bark extract which led to the isolation of oleanolic aldehyde coumarate (OALC) as one major bioactive compound. At the concentration tested, naringenin and OALC did not affect P. aeruginosa PAO1 viability and didn’t reduce QS-independent aceA gene expression suggesting a specific anti-QS activity. However, these two compounds present different inhibition spectrum. Indeed, naringenin didn’t inhibit gacA gene expression and twitching motility contrarily to OALC. These results suggest that OALC and naringenin represent potent candidates for in vivo investigations in their anti-QS and anti-biofilm activity onto eukaryotes infectious model. Besides, this finding demonstrated the potent source for novel anti-virulence compounds of Malagasy flora and the importance of this kind of research to strengthen our antimicrobial therapeutic arsenal with the ongoing struggle against bacterial infection. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

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