The effect of Tyloxapol on the metabolome of Mycobacterium tuberculosis.

The use of detergents when culturing Mycobacterium tuberculosis (M. tuberculosis) are essential to prevent clumping. However, these detergents may influence research outcomes by impacting bacterial morphology and metabolism. This study aimed to assess the metabolome of a M. tuberculosis H37Rv strain cultured with Tyloxapol (H37RvTyloxapol), compared to a control group of H37Rv strain cultured without detergent (H37RvControl) to evaluate Tyloxapol's suitability for metabolomic studies. Distinct metabolic alterations were observed in H37RvTyloxapol compared to H37RvControl, primarily associated with fatty acid, sugar and pentose phosphate metabolic pathways. These changes are associated with the surface stress exerted by Tyloxapol on the bacteria, prompting an adaptation of M. tuberculosis metabolism to that usually observed in stress environments. Nevertheless, the effect of Tyloxapol is less pronounced than that of a previous investigation using Tween 80, indicating its potential as the more favourable choice for culturing M. tuberculosis for metabolomic analysis, with due consideration to dosage and result interpretation.

Ergothioneine is a secreted antioxidant in Mycobacterium smegmatis.

Ergothioneine (ERG) and mycothiol (MSH) are two low-molecular-weight thiols synthesized by mycobacteria. The role of MSH has been extensively investigated in mycobacteria; however, little is known about the role of ERG in mycobacterial physiology. In this study, quantification of ERG at various points in the growth cycle of Mycobacterium smegmatis revealed that a significant portion of ERG is found in the culture media, suggesting that it is actively secreted. A mutant of M. smegmatis lacking egtD (MSMEG_6247) was unable to synthesize ERG, confirming its role in ERG biosynthesis. Deletion of egtD from wild-type M. smegmatis and an MSH-deficient mutant did not affect their susceptibility to antibiotics tested in this study. The ERG- and MSH-deficient double mutant was significantly more sensitive to peroxide than either of the single mutants lacking either ERG or MSH, suggesting that both thiols play a role in protecting M. smegmatis against oxidative stress and that ERG is able to partly compensate for the loss of MSH.

Tween 80 induces a carbon flux rerouting in Mycobacterium tuberculosis.

As a means to increase the growth rate and reduce aggregation, Tween 80 is routinely added to growth media during mycobacterial culturing. This detergent has, however, been associated with causing alterations to the morphology, pathogenicity and virulence of these bacteria. In an attempt to better understand the underlying mechanism of these alterations, we investigated the effect of Tween 80 on the metabolomes of a M. tuberculosis lab strain (H37Rv) and multidrug-resistant clinical strain (R179), using GC-GCxTOF-MS metabolomics. The metabolite markers identified indicated Tween 80-induced disparities in the central carbon metabolism of both strains, with an upregulation in the glyoxylate cycle, glucogenogenesis and the pentose phosphate pathway. The results also signified an increased production of mycobacterial biosynthetic precursors such as triacylglycerols, proteinogenic amino acids and nucleotide precursors, in the presence of the detergent. Collectively, these metabolome variations mimic the phenotypic changes observed when M. tuberculosis is grown in vivo, in a lipid rich environment. However, in addition to the increased availability of oleic acid as a carbon source from Tween 80, the observed variations, and the morphological changes associated with the detergent, could also be a result of an overall stress response in these bacteria. This study is the first to identify specific metabolome variations related to the addition of Tween 80 to the growth media during M. tuberculosis culturing. The consideration of these results during the method development and data interpretation phases of future metabolomics investigations will improve the quality of the analyses as well as the credibility of potential research outcomes. These results will also assist in the interpretation of research questions specifically aimed at aspects of mycobacterial metabolism, even when using other methodologies such as transcriptomics or fluxomics.

Preliminary Evaluation of Artemisinin-Cholesterol Conjugates as Potential Drugs for the Treatment of Intractable Forms of Malaria and Tuberculosis.

To evaluate the feasibility of developing drugs that may be active against both malaria and tuberculosis (TB) by using in part putative cholesterol transporters in the causative pathogens and through enhancement of passive diffusion in granulomatous TB, artemisinin-cholesterol conjugates were synthesized by connecting the component molecules through various linkers. The compounds were screened in vitro against Plasmodium falciparum (Pf) and Mycobacterium tuberculosis (Mtb). Antimalarial activities (IC50 ) against Pf drug-sensitive NF54, and drug-resistant K1 and W2 strains ranged from 0.03-2.6, 0.03-1.9, and 0.02-1.7 µm. Although the compounds are less active than the precursor artemisinin derivatives, the cholesterol moiety renders the compounds relatively insoluble in the culture medium, and variation in solubilities among the different compounds may reflect in the range of efficacies observed. Activities against Mtb H37Rv were assessed using a standardized colony-forming unit (CFU) assay after 24 h pretreatment of cultures with each of the compounds. Percentage inhibition ranged from 3-38 % and 18-52 % at 10 and 80 µm, respectively. Thus, in contrast to the comparator drug artemether, the conjugates display enhanced activities. The immediate aims include the preparation of conjugates with enhanced aqueous solubilities, assays against malaria and TB in vivo, and for TB, assays using an infected macrophage model and assessment of granuloma influx.

RNAseq reveals hypervirulence-specific host responses to M. tuberculosis infection.

The distinguishing factors that characterize the host response to infection with virulent Mycobacterium tuberculosis (M.tb) are largely confounding. We present an infection study with 2 genetically closely related M.tb strains that have vastly different pathogenic characteristics. The early host response to infection with these detergent-free cultured strains was analyzed through RNAseq in an attempt to provide information on the subtleties which may ultimately contribute to the virulent phenotype. Murine bone marrow derived macrophages (BMDMs) were infected with either a hyper- (R5527) or hypovirulent (R1507) Beijing M. tuberculosis clinical isolate. RNAseq revealed 69 differentially expressed host genes in BMDMs during comparison of these 2 transcriptomes. Pathway analysis revealed activation of the stress-induced and growth inhibitory Gadd45 signaling pathway in hypervirulent infected BMDMs. Upstream regulators of interferon activation such as and IRF3 and IRF7 were predicted to be upregulated in hypovirulent-infected BMDMs. Additional analysis of the host immune response through ELISA and qPCR included the use of human THP-1 macrophages where a robust proinflammatory response was observed after infection with the hypervirulent strain. RNAseq revealed 2 early-response genes (ier3 and saa3) and 2 host-defense genes (oasl1 and slpi) that were significantly upregulated by the hypervirulent strain. The role of these genes under M.tb infection conditions are largely unknown but here we provide validation of their presence with use of qPCR and Western blot. Further analysis into their biological role during infection with virulent M.tb is required.

The Host Response to a Clinical MDR Mycobacterial Strain Cultured in a Detergent-Free Environment: A Global Transcriptomics Approach.

During Mycobacterium tuberculosis (M.tb) infection, the initial interactions between the pathogen and the host cell determines internalization and innate immune response events. It is established that detergents such as Tween alter the mycobacterial cell wall and solubilize various lipids and proteins. The implication of this is significant since induced changes on the cell wall affect macrophage uptake and the immune response to M.tb. Importantly, during transmission between hosts, aerosolized M.tb enters the host in its native form, i.e. in a detergent-free environment, thus in vitro and in vivo studies should mimic this as closely as possible. To this end, we have optimized a procedure for growing and processing detergent-free M.tb and assessed the response of murine macrophages (BMDM) infected with multi drug-resistant M.tb (R179 Beijing 220 clinical isolate) using RNAseq. We compared the effects of the host response to M.tb cultured under standard laboratory conditions (Tween 80 containing medium -R179T), or in detergent-free medium (R179NT). RNAseq comparisons reveal 2651 differentially expressed genes in BMDMs infected with R179T M.tb vs. BMDMs infected with R179NT M.tb. A range of differentially expressed genes involved in BMDM receptor interaction with M.tb (Mrc1, Ifngr1, Tlr9, Fpr1 and Itgax) and pro-inflammatory cytokines/chemokines (Il6, Il1b, Tnf, Ccl5 and Cxcl14) were selected for analysis through qPCR. BMDMs infected with R179NT stimulate a robust inflammatory response. Interestingly, R179NT M.tb induce transcription of Fpr1, a receptor which detects bacterial formyl peptides and initiates a myriad of immune responses. Additionally we show that the host components Cxcl14, with an unknown role in M.tb infection, and Tlr9, an emerging role player, are only stimulated by infection with R179NT M.tb. Taken together, our results suggest that the host response differs significantly in response to Tween 80 cultured M.tb and should therefore not be used in infection experiments.

Phytochemical and Antimicrobial Screening of Flavanones and Chalcones from Galenia africana and Dicerothamnus rhinocerotis.

This study focused on an 80% ethanol:water extract of Galenia africana and Dicerothamnus rhinocerotis in which a phytochemical study revealed the presence of flavonoids as the major secondary plant metabolites. Eleven pure flavonoids viz., (E)-2',4'-dihydroxychalcone 1, (S)-7-hydroxyflavanone 2, (E)-2',4'-dihydroxy-2,3-dihydrochalcone 3, (S)-5,7-dihydroxyflavanone 4, (S)-2',5,7,-trihydroxyflavanone 5, (S)-5,7-dihydroxy-2'-methoxyflavanone 6, 5,7-dihydroxy-4H-chromen-4-one 7, (S)-5-hydroxy-7-methoxyflavanone 8 and (E)-2-hydroxy-3',6'-dimethoxychalcone 9 were isolated from G. africana, while [sakuranetin] (S)-4',5-dihydroxy-7-methoxyflavanone 10 and [eriodictyol-3',7-dimethyl ether] (S)-4',5-dihydroxy-3',7-dimethoxyflavanone 11 were isolated from D. rhinocerotis. Compounds 6 and 9 are new while this is the first reported isolation of 1, 2, 3, 4, 5, 7, 8, 10 and 11 from these plants. All isolated compounds were tested for their antimycobacterial activity against the reference strain Mtb H37Rv. The most active compound, 9, demonstrated a MIC99 of 5 µM against Mtb H37Rv American Type Culture (ATCC) and (ATCC27294), which were also sensitive to Isoniazid (INH) and Rifampicin. The antibacterial activity of 9 might be ascribed to the presence of features such as the α,ß-unsaturated ketone and the substitution patterns on the A and B rings.

Mycolic acids, a promising mycobacterial ligand for targeting of nanoencapsulated drugs in tuberculosis.

The appearance of drug-resistant strains of Mycobacterium tuberculosis (Mtb) poses a great challenge to the development of novel treatment programmes to combat tuberculosis. Since innovative nanotechnologies might alleviate the limitations of current therapies, we have designed a new nanoformulation for use as an anti-TB drug delivery system. It consists of incorporating mycobacterial cell wall mycolic acids (MA) as targeting ligands into a drug-encapsulating Poly dl-lactic-co-glycolic acid polymer (PLGA), via a double emulsion solvent evaporation technique. Bone marrow-derived mouse macrophages, either uninfected or infected with different mycobacterial strains (Mycobacterium avium, Mycobacterium bovis BCG or Mtb), were exposed to encapsulated isoniazid-PLGA nanoparticles (NPs) using MA as a targeting ligand. The fate of the NPs was monitored by electron microscopy. Our study showed that i) the inclusion of MA in the nanoformulations resulted in their expression on the outer surface and a significant increase in phagocytic uptake of the NPs; ii) nanoparticle-containing phagosomes were rapidly processed into phagolysosomes, whether MA had been included or not; and iii) nanoparticle-containing phagolysosomes did not fuse with non-matured mycobacterium-containing phagosomes, but fusion events with mycobacterium-containing phagolysosomes were clearly observed.