Mycobacterium tuberculosis, a major threat to health in South Africa : intracellular survival after treatment with novel drugs designed against the mycothiol pathway

Mazorodze, James Hove (2010-12)

Thesis (MScMedSc (Biomedical Sciences))--University of Stellenbosch, 2010.

Bibliography

Thesis

ENGLISH ABSTRACT: Mycothiol (MSH) is unique to mycobacteria as the major low molecular weight cellular thiol responsible for protection of bacteria against oxidative stress. The design of drugs and inhibitors against enzymes of the mycothiol pathway was based on the premise that mycothiol is unique to mycobacteria, and is thus important for its survival. A total of 80 inhibitors designed against enzymes of the mycothiol pathway were screened for inhibition of growth on in vitro growing M. tuberculosis using the BACTEC 460TM assay. The most active compounds were further tested for inhibitory potential of M. tuberculosis within macrophages. Initial screening in the macrophage system was done using the human-like THP1 cell line and then mouse bone marrow-derived macrophages. In this investigation we established that phenothiazine can be exploited as an inhibitor of enzymes of the mycothiol pathway. Although tunicamycin significantly inhibited the growth of M. tuberculosis both in vitro and ex vivo; it was found to be cytotoxic to host macrophages. To this end we provide proof-of-concept that compounds which can inhibit the expression of mycothiol enzymes have potential as anti-tubercular drugs. The response of M. tuberculosis to stress conditions was assessed via LC-MS in which maximal levels of mycothiol were produced during the early time points of exposure to isoniazid. We used mycothiol-deficient (mshA) M. tuberculosis to investigate the role of mycothiol for survival as well as the resultant phenotype when such mutants are exposed to stress conditions. The mshA deletion mutants in M. tuberculosis were resistant to INH at concentrations which inhibited growth in the wild-type strains. We postulated that katG and inhA, the genes involved in INH metabolism, required mycothiol for their activation. Morphological alterations of M. tuberculosis within macrophages were assessed using electron microscopy approaches. In this way we attempted to follow the fate of M. tuberculosis within the phagosomes, and how mycobacteria is processed in phagosomes in terms of replication, survival and degradation. The establishment of a successful infection by M. tuberculosis depends on the initial encounter with host macrophages, which represent the first line of cellular defense against microbial invasion. At the interface between mycobacteria and macrophages, the complex outermost layer of the mycobacterial cell wall probably plays a role in facilitating host cell entry. Under normal conditions (i.e. ingestion of non pathogenic microorganisms), newly formed phagosomes intermingle contents and membrane with the successive compartments of the endocytic pathway (early endosomes, late endosomes, lysosomes) through a complex series of fusion and fission. As they are processed into phagolysosomes, they undergo gradual modifications by specific addition and removal of membrane constituents. In addition, they become acidified due to the vacuolar proton pump ATPase located in the membrane and acquire toxic constituents, including hydrolases that will ultimately destroy bacteria.

AFRIKAANSE OPSOMMING: Mycothiol (MSH) is uniek aan mycobacteria as die belangrikste lae molekulêre gewig sellulêre thiol verantwoordelik vir die beskerming van bakterieë teen oksidatiewe stres. Die ontwerp van dwelms en inhibeerders teen ensieme van die mycothiol pad is gebaseer op die veronderstelling dat mycothiol uniek is aan mycobacteria, en is dus belangrik vir sy oorlewing. 'n Totaal van 80 inhibeerders ontwerp teen ensieme van die mycothiol pad is gekeur vir die inhibisie van groei op in vitro groeiende M. tuberculosis met behulp van die BACTEC 460TM toets. Die mees aktiewe verbindings is verder getoets vir inhiberende potensiaal van M. tuberculosis binne makrofage. Aanvanklike sifting in die makrofage stelsel is gedoen met behulp van die mens-soos THP1 sel lyn dan makrofage afkomstig van muis beenmurg. In hierdie ondersoek het ons vasgestel dat fenotiasien kan gebruik word as 'n inhibitor van ensieme van die mycothiol pad. Alhoewel tunicamycin aansienlik die groei van M. tuberculosis beide in vitro en ex vivo inhibeer, was dit gevind word sitotoksies is vir makrofage. Om hierdie rede het ons bewys-van-konsep wat verbindings dat die uitdrukking van mycothiol ensieme inhibeer, die potensiaal het as anti-tuberkulose dwelms. Die reaksie van M. tuberkulose op stress is geëvalueer deur LC-MS waarin maksimum vlakke van mycothiol gedurende die vroeë tyd punte van blootstelling aan isoniasied geproduseer is. Ons gebruik mycothiol-deficient (mshA) M. tuberculosis om die rol van mycothiol vir oorlewing sowel as die gevolglike fenotipe te ondersoek wanneer sodanige mutanten blootgestel word aan stres kondisies. Die mshA-weglating mutanten van M. tuberculosis was bestand teen INH konsentrasies wat groei geïnhibeer in die wilde-tipe-stamme. Ons veronderstel dat katG en inhA, die gene wat betrokke is in INH metabolisme, mycothiol vereis vir hulle aktivering. Morfologiese veranderinge van M. tuberculosis binne makrofage is beoordeel met behulp van elektronmikroskopie. In hierdie manier waarop ons probeer om die lot van M. tuberkulose te volg binne die phagosomes, en hoe mycobacteria verwerk word in phagosomes in terme van replikasie, oorlewing en agteruitgang. Die vestiging van „n suksesvolle infeksie deur M. tuberculosis hang af van die aanvanklike ontmoeting met host makrofage, wat die eerste lyn 'n sellulêre verdediging teen mikrobiese inval verteenwoordig. Op die grens tussen mycobacteria en makrofage, speel die komplekse buitenste laag van die mikobakteriese selwand waarskynlik 'n rol in die intog van die gasheersel. Onder normale omstandighede (dws inname van non patogene mikroörganismes), nuutgevormde phagosomes meng inhoud en membraan met die opeenvolgende kompartemente van die endositiese roete (vroeë endosomes, laat endosomes, lisosome) deur 'n komplekse reeks van samesmelting en fisie. Soos hulle verwerk word tot phagolysosomes, ondergaan hulle geleidelike veranderinge deur spesifieke optel en verwydering van membraan komponente. Benewens, raak hulle versuur as gevolg van die vacuolair proton pomp ATPase geleë in die membraan en verkry giftige bestanddele, insluitend hydrolase wat uiteindelik bakterieë vernietig.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/5469
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