Development of new antituberculous drugs based on bacterial virulence factors interfering with host cytokine networks

Inflammation-mediated changes in haemostatic variables of pulmonary tuberculosis patients during treatment

Tuberculosis (TB) disease is usually marked by inflammation which is closely linked to haemostasis both in health and disease. Close monitoring of haemostatic response to inflammatory changes during treatment is important to improve TB management. Here we studied associations between haemostatic markers and inflammatory cytokines in 60 TB-infected individuals, aged 18-65 years who received anti-TB therapy. They were recruited before commencement of therapy and followed up till completion of therapy after 6-months. The TNF-α, IL-6, IL-2 (pro-inflammatory cytokines) and P-selectin, GP IIb/IIIa, thrombopoietin (haemostatic variables) were significantly increased at 2 month into therapy compared to pre-treatment values and decreased at 6 month into therapy. Also at 6 month into therapy in comparison to 2-month into therapy, there were significant increase in IL-10 and TGF-β (anti-inflammatory cytokines) as well as a significant decline in PF-4. There were significant positive correlations between GP IIb/IIIa and TNF-α, IL-6 and PSEL, IL-6 and TPO, PF4 and TGF-β. Conclusively, the changes in the TNF-α, IL-6, IL-2 aligned with changes in the levels of P-selectin, GP IIb/IIIa, and TPO in the course of TB therapy. This may suggest that the levels of inflammatory cytokines are linked to the levels of these haemostatic variables in TB individuals.

Novel Antibacterial Activity of Febuxostat, an FDA-Approved Antigout Drug against Mycobacterium tuberculosis Infection

Accumulating evidence suggests that drug repurposing has drawn attention as an anticipative strategy for controlling tuberculosis (TB), considering the dwindling drug discovery and development pipeline. In this study, we explored the antigout drug febuxostat and evaluated its antibacterial activity against Mycobacterium species. Based on MIC evaluation, we found that febuxostat treatment significantly inhibited mycobacterial growth, especially that of Mycobacterium tuberculosis (Mtb) and its phylogenetically close neighbors, M. bovis, M. kansasii, and M. shinjukuense, but these microorganisms were not affected by allopurinol and topiroxostat, which belong to a similar category of antigout drugs. Febuxostat concentration-dependently affected Mtb and durably mediated inhibitory functions (duration, 10 weeks maximum), as evidenced by resazurin microtiter assay, time-kill curve analysis, phenotypic susceptibility test, and the Bactec MGIT 960 system. Based on these results, we determined whether the drug shows antimycobacterial activity against Mtb inside murine bone marrow-derived macrophages (BMDMs). Notably, febuxostat markedly suppressed the intracellular growth of Mtb in a dose-dependent manner without affecting the viability of BMDMs. Moreover, orally administered febuxostat was efficacious in a murine model of TB with reduced bacterial loads in both the lung and spleen without the exacerbation of lung inflammation, which highlights the drug potency. Taken together, unexpectedly, our data demonstrated that febuxostat has the potential for treating TB.

Adaptive gene profiling of Mycobacterium tuberculosis during sub-lethal kanamycin exposure

Resistance to anti-tuberculosis drugs is a formidable obstacle to effective tuberculosis (TB) treatment and prevention globally. New forms of multidrug, extensive drug and total drug resistance Mycobacterium tuberculosis (Mtb) causing a serious threat to human as well as animal's population. Mtb shows diverse adaptability under stress conditions especially antibiotic treatment, however underlying physiological mechanism remained elusive. In present study, we investigated Mtb's response and adaptation with reference to gene expression during sub-lethal kanamycin exposure. Mtb were cultured under sub-lethal drug and control conditions, where half were sub-cultured every 3-days to observe serial adaptation under same conditions and the remaining were subjected to RNA-seq. We identified 98 up-regulated and 198 down-regulated responsive genes compared to control through differential analysis, of which Ra1750 and Ra3160 were the most responsive genes. In adaptive analysis, we found Ra1750, Ra3160, Ra3161, Ra3893 and Ra2492 up-regulation at early stage and gradually showed low expression levels at the later stages of drug exposure. The adaptive expression of Ra1750, Ra3160 and Ra3161 were further confirmed by real time qPCR. These results suggested that these genes contributed in Mtb's physiological adaptation during sub-lethal kanamycin exposure. Our findings may aid to edify these potential targets for drug development against drug resistance tuberculosis.

Use of Digital Droplet PCR to Detect Mycobacterium tuberculosis DNA in Whole Blood-Derived DNA Samples from Patients with Pulmonary and Extrapulmonary Tuberculosis

Tuberculosis (TB) is a chronic infectious disease that has been threatening public health for many centuries. The clinical diagnostic procedure for TB is time-consuming and laborious. In the last 20 years, real-time fluorescence-based quantitative PCR (real-time PCR) has become a better alternative for TB diagnosis in clinics due to its sensitivity and specificity. Recently, digital droplet PCR (ddPCR) has been developed, and it might be an ideal alternative to conventional real-time PCR for microorganism detection. In this study, we aimed to assess the capacity of ddPCR and real-time PCR for detecting low levels of circulating Mycobacterium tuberculosis (MTB) DNA. The study involved testing whole blood samples for an MTB DNA target (known as IS6110). Blood samples were obtained from 28 patients with pulmonary TB, 28 patients with extrapulmonary TB, and 28 healthy individuals. The results show that ddPCR could be used to measure low levels of MTB DNA, and it has the potential to be used to diagnose pulmonary and extrapulmonary TB based on clinical samples.

Host Transcriptional Profiles and Immunopathologic Response following Mycobacterium avium subsp. paratuberculosis Infection in Mice

Paratuberculosis or Johne’s disease is a chronic granulomatous enteropathy in ruminants caused by Mycobacterium avium subsp. paratuberculosis (MAP) infection. In the present study, we examined the host response to MAP infection in spleens of mice in order to investigate the host immunopathology accompanying host-pathogen interaction. Transcriptional profiles of the MAP-infected mice at 3 and 6 weeks p.i. showed severe histopathological changes, whereas those at 12 weeks p.i. displayed reduced lesion severity in the spleen and liver. MAP-infected mice at 3 and 6 weeks p.i. showed up-regulation of interferon-related genes, scavenger receptor, and complement components, suggesting an initial innate immune reaction, such as macrophage activation, bactericidal activity, and macrophage invasion of MAP. Concurrently, MAP-infected mice at 3 and 6 weeks p.i. were also suggested to express M2 macrophage phenotype with up-regulation of Mrc1, and Marco and down-regulation of MHC class II, Ccr7, and Irf5, and canonical pathways related to the T cell response including ICOS-ICOSL signaling in T helper cells, calcium-induced T lymphocyte apoptosis, and CD28 signaling in T helper cell. These results provide information which furthers the understanding of the immunopathologic response to MAP infection in mice, thereby providing insights valuable for research into the pathogenesis for MAP infection.

Exploring the potential of adjunct therapy in tuberculosis

A critical unmet need for treatment of drug-resistant tuberculosis (TB) is to find novel therapies that are efficacious, safe, and shorten the duration of treatment. Drug discovery approaches for TB primarily target essential genes of the pathogen Mycobacterium tuberculosis (Mtb) but novel strategies such as host-directed therapies and nonmicrobicidal targets are necessary to bring about a paradigm shift in treatment. Drugs targeting the host pathways and nonmicrobicidal proteins can be used only in conjunction with existing drugs as adjunct therapies. Significantly, host-directed adjunct therapies have the potential to decrease duration of treatment, as they are less prone to drug resistance, target the immune responses, and act via novel mechanism of action. Recent advances in targeting host-pathogen interactions have implicated pathways such as eicosanoid regulation and angiogenesis. Furthermore, several approved drugs such as metformin and verapamil have been identified that appear suitable for repurposing for the treatment of TB. These findings and the challenges in the area of host- and/or pathogen-directed adjunct therapies and their implications for TB therapy are discussed.

Mycobacterial phylogenomics: an enhanced method for gene turnover analysis reveals uneven levels of gene gain and loss among species and gene families

Species of the genus Mycobacterium differ in several features, from geographic ranges, and degree of pathogenicity, to ecological and host preferences. The recent availability of several fully sequenced genomes for a number of these species enabled the comparative study of the genetic determinants of this wide lifestyle diversity. Here, we applied two complementary phylogenetic-based approaches using information from 19 Mycobacterium genomes to obtain a more comprehensive view of the evolution of this genus. First, we inferred the phylogenetic relationships using two new approaches, one based on a Mycobacterium-specific amino acid substitution matrix and the other on a gene content dissimilarity matrix. Then, we utilized our recently developed gain-and-death stochastic models to study gene turnover dynamics in this genus in a maximum-likelihood framework. We uncovered a scenario that differs markedly from traditional 16S rRNA data and improves upon recent phylogenomic approaches. We also found that the rates of gene gain and death are high and unevenly distributed both across species and across gene families, further supporting the utility of the new models of rate heterogeneity applied in a phylogenetic context. Finally, the functional annotation of the most expanded or contracted gene families revealed that the transposable elements and the fatty acid metabolism-related gene families are the most important drivers of gene content evolution in Mycobacterium.

Ion-pair chromatography for simultaneous analysis of ethionamide and pyrazinamide from their porous microparticles

Ethionamide (ETA) and pyrazinamide (PZA) are considered the drugs of choice for the treatment of multidrug-resistant tuberculosis. Current methods available in the literature for simultaneous determination of ETA and PZA have low sensitivity or involve column modifications with lipophilic cations. The aim of this study was to develop a simple and validated reversed-phase ion-pair HPLC method for simultaneous determination of ETA and PZA for the characterization of polymeric-based porous inhalable microparticles in in vitro and spiked human serum samples. Chromatographic separation was achieved on a Phenomenex C18 column (250 mm × 4.6 mm) using a Shimadzu LC 10 series HPLC. The mobile phase consisted of A: 0.01% trifluoroacetic acid in distilled water and B: ACN/MeOH at 1:1 v/v. Gradient elution was run at a flow rate of 1.5 mL/min and a fixed UV wavelength of 280 nm. The validation characteristics included accuracy, precision, linearity, analytical range, and specificity. Calibration curves at seven levels for ETA and PZA were linear in the analytical range of 0.1-3.0 μg/mL with correlation coefficient of r (2) > 0.999. Accuracy for both ETA and PZA ranged from 94 to 106% at all quality control (QC) standards. The method was precise with relative standard deviation less than 2% at all QC levels. Limits of quantitation for ETA and PZA were 50 and 70 ng/mL, respectively. There was no interference from either the polymeric matrix ions or the biological matrix in the analysis of ETA and PZA.

The polyphosphate kinase gene ppk2 is required for Mycobacterium tuberculosis inorganic polyphosphate regulation and virulence

The Mycobacterium tuberculosis gene Rv3232c/MT3329 (ppk2) encodes a class II polyphosphate kinase, which hydrolyzes inorganic polyphosphate (poly P) to synthesize GTP. We assessed the role of ppk2 in M. tuberculosis poly P regulation, antibiotic tolerance, and virulence. A ppk2-deficient mutant (ppk2::Tn) and its isogenic wild-type (WT) and complemented (Comp) strains were studied. For each strain, the intrabacillary poly P content, MIC of isoniazid, and growth kinetics during infection of J774 macrophages were determined. Multiplex immunobead assays were used to evaluate cytokines elaborated during macrophage infection. The requirement of ppk2 for M. tuberculosis virulence was assessed in the murine model. The ppk2::Tn mutant was found to have significantly increased poly P content and a 4-fold increase in the MIC of isoniazid relative to the WT and Comp strains. The ppk2::Tn mutant showed reduced survival at day 7 in activated and naive J774 macrophages relative to the WT. Naive ppk2::Tn mutant-infected macrophages showed increased expression of interleukin 2 (IL-2), IL-9, IL-10, IL-12p70, and gamma interferon (IFN-γ) relative to WT-infected macrophages. The ppk2::Tn mutant exhibited significantly lower lung CFU during acute murine infection compared to the control groups. ppk2 is required for control of intrabacillary poly P levels and optimal M. tuberculosis growth and survival in macrophages and mouse lungs.

Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is a highly successful human pathogen because it has developed mechanisms to multiply and survive in the lungs by circumventing the immune system. Identification of virulence factors responsible for M. tuberculosis growth and persistence in host tissues may assist in the development of novel strategies to treat TB. In this study, we found that the mycobacterial enzyme polyphosphate kinase 2 (PPK2) is required for controlling intracellular levels of important regulatory molecules and for maintaining susceptibility to the first-line anti-TB drug isoniazid. In addition, PPK2 was found to be required for M. tuberculosis growth in the lungs of mice, at least in part by suppressing the expression of certain key cytokines and chemokines by inactivated lung macrophages.

Foxp3 expression and nitric oxide production in peripheral blood mononuclear cells of communicants with pulmonary tuberculosis

The understanding of the mechanisms involved in the immune response is of significant relevance to the control of tuberculosis (TB), especially in individuals living with patients with TB. To characterize the nitric oxide (NO) production and the Foxp3 marker expression in this population, peripheral blood mononuclear cells of intradomiciliary contacts of individuals with pulmonary tuberculosis with (CTb, susceptible) and without (STb, resistant) previous history of active infection were stimulated in vitro with Mycobacterium tuberculosis antigen (TbAg) and with the mitogen Concanavalin A for 24 and 48 h. The groups analysed did not present significant difference in the Foxp3 mRNA expression nor in the NO production. Negative correlation (P = 0.09) between NO and Foxp3 after a 48-h stimulation with TbAg was observed in the STb group. In this group, after a 24-h culture stimulated with TbAg (P = 0.03), this same correlation was observed. In comparison with the cytokines previously studied by our group (Cavalcanti et al., 2009), a positive correlation was observed between IL-10 and Foxp3 after a 48-h culture of cells from communicants susceptible to tuberculosis (STb) stimulated with TbAg (P = 0.04). Evaluating the entire population, a positive correlation was observed between the cytokine TNF-α and the Foxp3 marker in the cultures stimulated for 24 (P = 0.03) and 48 (P = 0.02) hours with TbAg. Therefore, considering the similarity in the exposure and the individual capacity of responding to the contact with M. tuberculosis, the present study contributes to the comprehension of the immune regulation in individuals living with patients with TB.

Autophagy in Mycobacterium tuberculosis infection: a passepartout to flush the intruder out?

Tuberculosis is a global health calamity. The causative agent, Mycobacterium tuberculosis (M. tuberculosis), has evolved elaborate survival mechanisms in humans, allowing it to remain in a clinically latent infection state, constantly engaging the immune system, with the possibility to progress to active disease. Autophagy is a cellular process responsible for the degradation of intracellular components, including invading pathogens, playing an important role in both innate and adaptive immunity. In this review, we describe the molecular mechanisms employed by M. tuberculosis to avoid autophagic degradation and exploit this process to its own advantage. Moreover, we discuss the multiple roles played by autophagy in the immune responses to M. tuberculosis, and its unforeseen contribution to the antibacterial activity of tuberculosis-specific drugs.

Role of TNF-Alpha, IFN-Gamma, and IL-10 in the Development of Pulmonary Tuberculosis

Host immune response against Mycobacterium tuberculosis is mediated by cellular immunity, in which cytokines and Th1 cells play a critical role. In the process of control of the infection by mycobacteria, TNF-alpha seems to have a primordial function. This cytokine acts in synergy with IFN-gamma, stimulating the production of reactive nitrogen intermediates (RNIs), thus mediating the tuberculostatic function of macrophages, and also stimulating the migration of immune cells to the infection site, contributing to granuloma formation, which controls the disease progression. IFN-gamma is the main cytokine involved in the immune response against mycobacteria, and its major function is the activation of macrophages, allowing them to exert its microbicidal role functions. Different from TNF-alpha and IFN-gamma, IL-10 is considered primarily an inhibitory cytokine, important to an adequate balance between inflammatory and immunopathologic responses. The increase in IL-10 levels seems to support the survival of mycobacteria in the host. Although there is not yet conclusive studies concerning a clear dichotomy between Th1 and Th2 responses, involving protective immunity and susceptibility to the disease, respectively, we can suggest that the knowledge about this responses based on the prevailing cytokine profile can help to elucidate the immune response related to the protection against M. tuberculosis.

Dual mechanism for Mycobacterium tuberculosis cytotoxicity on lung epithelial cells

Mycobacterium tuberculosis strains CDC1551 and Erdman were used to assess cytotoxicity in infected A549 human alveolar epithelial cell monolayers. Strain CDC1551 was found to induce qualitatively greater disruption of A549 monolayers than was strain Erdman, although total intracellular and cell-associated bacterial growth rates over the course of the infections were not significantly different. Cell-free culture supernatants from human monocytic cells infected with either of the 2 M. tuberculosis strains produced a cytotoxic effect on A549 cells, correlating with the amount of tumor necrosis factor alpha (TNF-α) released by the infected monocytes. The addition of TNF-α-neutralizing antibodies to the supernatants from infected monocyte cultures did prevent the induction of a cytotoxic effect on A549 cells overlaid with this mixture but did not prevent the death of epithelial cells when added prior to infection with M. tuberculosis bacilli. Thus, these data agree with previous observations that lung epithelial cells infected with M. tuberculosis bacilli are rapidly killed in vitro. In addition, the data indicate that some of the observed epithelial cell killing may be collateral damage; the result of TNF-α released from M. tuberculosis-infected monocytes.

Characteristics of suppressor macrophages induced by mycobacterial and protozoal infections in relation to alternatively activated M2 macrophages

In the advanced stages of mycobacterial infections, host immune systems tend to change from a Th1-type to Th2-type immune response, resulting in the abrogation of Th1 cell- and macrophage-mediated antimicrobial host protective immunity. Notably, this type of immune conversion is occasionally associated with the generation of certain types of suppressor macrophage populations. During the course of Mycobacterium tuberculosis (MTB) and Mycobacterium avium-intracellulare complex (MAC) infections, the generation of macrophages which possess strong suppressor activity against host T- and B-cell functions is frequently encountered. This paper describes the immunological properties of M1- and M2-type macrophages generated in tumor-bearing animals and those generated in hosts with certain microbial infections. In addition, this paper highlights the immunological and molecular biological characteristics of suppressor macrophages generated in hosts with mycobacterial infections, especially MAC infection.