Update in tuberculosis and nontuberculous mycobacterial disease 2010

Matrix metalloproteinases: Expression, regulation and role in the immunopathology of tuberculosis

Mycobacterium tuberculosis (Mtb) leads to approximately 1.5 million human deaths every year. In pulmonary tuberculosis (TB), Mtb must drive host tissue destruction to cause pulmonary cavitation and dissemination in the tissues. Matrix metalloproteinases (MMPs) are endopeptidases capable of degrading all components of pulmonary extracellular matrix (ECM). It is well established that Mtb infection leads to upregulation of MMPs and also causes disturbance in the balance between MMPs and tissue inhibitors of metalloproteinases (TIMPs), thus altering the extracellular matrix deposition. In TB, secretion of MMPs is mainly regulated by NF-κB, p38 and MAPK signalling pathways. In addition, recent studies have demonstrated the immunomodulatory roles of MMPs in Mtb pathogenesis. Researchers have proposed a new regimen of improved TB treatment by inhibition of MMP activity to hinder matrix destruction and to minimize the TB-associated morbidity and mortality. The proposed regimen involves adjunctive use of MMP inhibitors such as doxycycline, marimastat and other related drugs along with front-line anti-TB drugs to reduce granuloma formation and bacterial load. These findings implicate the possible addition of economical and well-tolerated MMP inhibitors to current multidrug regimens as an attractive mean to increase the drug potency. Here, we will summarize the recent advancements regarding expression of MMPs in TB, their immunomodulatory role, as well as their potential as therapeutic targets to control the deadly disease.

[Clinical pathology of granulomatous inflammation : With special emphasis on the lungs and central nervous system]

CLINICAL ISSUE

Granulomatous diseases are not rare in routine daily diagnostics. Granulomas are an indication of a sufficiently functioning immune system. In the absence of granulomas, a possible immunodeficiency should also be considered (e.g. in tuberculosis) in the diagnostic procedure. Many types of diseases with different etiologies can cause granulomatous manifestations.

DIAGNOSTICS

Diagnostic procedures should be oriented to the clinical symptoms and should include blood analyses, radiography, especially computed tomography (CT) and magnetic resonance imaging (MRI) and sampling for histology or cytology. In the case of proven granulomatous inflammation an infectious etiology should first be excluded. The diagnosis of a granulomatous disease should always be confirmed by histopathology when possible.

ACHIEVEMENTS

In this study the origins and general histopathological classification of granulomatous diseases are presented. In addition to the most common granulomatous diseases, some special and rare forms are discussed, which should also be considered in the differential diagnostic process.

PRACTICAL RECOMMENDATIONS

The diagnosis of a granulomatous disease should always be made in an interdisciplinary cooperation and requires close collaboration between radiologists, internists, pathologists and specialists in laboratory parameters.

Biochemical and structural characterization of mycobacterial aspartyl-tRNA synthetase AspS, a promising TB drug target

The human pathogen Mycobacterium tuberculosis is the causative agent of pulmonary tuberculosis (TB), a disease with high worldwide mortality rates. Current treatment programs are under significant threat from multi-drug and extensively-drug resistant strains of M. tuberculosis, and it is essential to identify new inhibitors and their targets. We generated spontaneous resistant mutants in Mycobacterium bovis BCG in the presence of 10× the minimum inhibitory concentration (MIC) of compound 1, a previously identified potent inhibitor of mycobacterial growth in culture. Whole genome sequencing of two resistant mutants revealed in one case a single nucleotide polymorphism in the gene aspS at ⁵³⁵GAC>⁵³⁵AAC (D179N), while in the second mutant a single nucleotide polymorphism was identified upstream of the aspS promoter region. We probed whole cell target engagement by overexpressing either M. bovis BCG aspS or Mycobacterium smegmatis aspS, which resulted in a ten-fold and greater than ten-fold increase, respectively, of the MIC against compound 1. To analyse the impact of inhibitor 1 on M. tuberculosis AspS (Mt-AspS) activity we over-expressed, purified and characterised the kinetics of this enzyme using a robust tRNA-independent assay adapted to a high-throughput screening format. Finally, to aid hit-to-lead optimization, the crystal structure of apo M. smegmatis AspS was determined to a resolution of 2.4 Å.

Rapid detection and differentiation of mycobacterial species using a multiplex PCR system

INTRODUCTION

The early diagnosis of mycobacterial infections is a critical step for initiating treatment and curing the patient. Molecular analytical methods have led to considerable improvements in the speed and accuracy of mycobacteria detection.

METHODS

The purpose of this study was to evaluate a multiplex polymerase chain reaction system using mycobacterial strains as an auxiliary tool in the differential diagnosis of tuberculosis and diseases caused by nontuberculous mycobacteria (NTM) RESULTS: Forty mycobacterial strains isolated from pulmonary and extrapulmonary origin specimens from 37 patients diagnosed with tuberculosis were processed. Using phenotypic and biochemical characteristics of the 40 mycobacteria isolated in LJ medium, 57.5% (n=23) were characterized as the Mycobacterium tuberculosis complex (MTBC) and 20% (n=8) as nontuberculous mycobacteria (NTM), with 22.5% (n=9) of the results being inconclusive. When the results of the phenotypic and biochemical tests in 30 strains of mycobacteria were compared with the results of the multiplex PCR, there was 100% concordance in the identification of the MTBC and NTM species, respectively. A total of 32.5% (n=13) of the samples in multiplex PCR exhibited a molecular pattern consistent with NTM, thus disagreeing with the final diagnosis from the attending physician.

CONCLUSIONS

Multiplex PCR can be used as a differential method for determining TB infections caused by NTM a valuable tool in reducing the time necessary to make clinical diagnoses and begin treatment. It is also useful for identifying species that were previously not identifiable using conventional biochemical and phenotypic techniques.

[Granulomatous lung and systemic diseases]

Granuloma formation occurs in the human body if there is a particle which persists in phagocytes and which the immune system cannot eliminate. The immune reaction of granuloma formation evolved in order to combat mycobacteria with the aim of localizing mycobacteria and to avoid spreading of mycobacteria throughout the body. Granulomatous lung diseases are often accompanied by severe, systemic inflammation. However, acute phase proteins may be only slightly elevated. The spectrum of granulomatous lung diseases is broad. Sarcoidosis is the most common granulomatous lung disease. To diagnose sarcoidosis, other infectious granulomatous lung diseases such as tuberculosis, atypical mycobacterial and fungal infection have to be ruled out. Pulmonary granuloma also evolve in the context of autoimmune diseases such as rheumatoid arthritis, granulomatosis with polyangiitis (GBA, Wegener's) and eosinophilic granulomatosis with polyangiitis (EGPA, Churg-Strauss syndrome). Furthermore, immunodeficiencies such as common variable immunodeficiency (CVID) and immune reconstitution syndrome in HIV can be associated with systemic granulomatous inflammation. Finally, occupational lung disease, particularly hypersensitivity pneumonitis, silicosis, hard metal lung, and chronic berylliosis are associated with pulmonary granuloma formation.

Identification of novel imidazo[1,2-a]pyridine inhibitors targeting M. tuberculosis QcrB

Mycobacterium tuberculosis is a major human pathogen and the causative agent for the pulmonary disease, tuberculosis (TB). Current treatment programs to combat TB are under threat due to the emergence of multi-drug and extensively-drug resistant TB. Through the use of high throughput whole cell screening of an extensive compound library a number of imidazo[1,2-a]pyridine (IP) compounds were obtained as potent lead molecules active against M. tuberculosis and Mycobacterium bovis BCG. The IP inhibitors (1-4) demonstrated minimum inhibitory concentrations (MICs) in the range of 0.03 to 5 µM against a panel of M. tuberculosis strains. M. bovis BCG spontaneous resistant mutants were generated against IP 1, 3, and 4 at 5× MIC and subsequent whole genome sequencing identified a single nucleotide polymorphism (937)ACC>(937)GCC (T313A) in qcrB, which encodes the b subunit of the electron transport ubiquinol cytochrome C reductase. This mutation also conferred cross-resistance against IP 1, 3 and 4 demonstrating a common target. Gene dosage experiments confirmed M. bovis BCG QcrB as the target where over-expression in M. bovis BCG led to an increase in MIC from 0.5 to >8 µM for IP 3. An acute murine model of TB infection established bacteriostatic activity of the IP series, which await further detailed characterization.

Association between CD209 -336A/G and -871A/G polymorphisms and susceptibility of tuberculosis: a meta-analysis

Background

The association between CD209 promoter polymorphisms (-336A/G, -871A/G) and tuberculosis (TB) risk has been widely reported, but results of previous studies remain controversial and ambiguous. To assess the association between CD209 polymorphisms and TB risk, a meta-analysis was performed.

Methods

Based on comprehensive searches of the PubMed, Embase, Web of Science, Weipu, and CBM databases, we identified outcome data from all articles estimating the association between CD209 polymorphisms and TB risk. The pooled odds ratio (OR) with 95% confidence intervals (CIs) were calculated.

Results

A total of 14 studies with 3,610 cases and 3,539 controls were identified. There was no significant association between CD209 -336A/G polymorphism and TB risk (OR = 1.04, 95% CI = 0.91–1.19 for G vs. A; OR = 1.13, 95% CI = 0.84–1.53 for GG vs. AA; OR = 1.04, 95% CI = 0.87–1.24 for GG+AG vs. AA; OR = 1.11, 95% CI = 0.88–1.39 for GG vs. AG+AA). However, the significant association was revealed for Asians in GG vs. AA (OR = 2.48, 95% CI = 1.46–4.22, P = 0.0008) and GG vs. AG+AA (OR = 2.10, 95% CI = 1.33–3.32, P = 0.001). For the CD209 -871A/G polymorphism, lack of an association was also found (OR = 0.81, 95% CI = 0.70–0.95 for G vs. A; OR = 1.00, 95% CI = 0.52–1.93 for GG vs. AA; OR = 0.73, 95% CI = 0.60–0.89 for GG+AG vs. AA; OR = 1.09, 95% CI = 0.57–2.10 for GG vs. AG+AA).

Conclusion

The present meta-analysis suggested that CD209 promoter polymorphisms (-336A/G, -871A/G) were unlikely to substantially contribute to TB susceptibility. However, the GG genotype of CD209 -336A/G polymorphism might be a genetic risk factor that increases TB susceptibility for Asians in GG vs. AA and GG vs. AG+AA.

Bacillus Calmette-Guérin (BCG) complications associated with primary immunodeficiency diseases

Primary immunodeficiency diseases (PIDs) are a group of inherited disorders, characterized by defects of the immune system predisposing individuals to variety of manifestations, including recurrent infections and unusual vaccine complications. There are a number of PIDs prone to Bacillus Calmette-Guérin (BCG) complications. This review presents an update on our understanding about the BCGosis-susceptible PIDs, including severe combined immunodeficiency, chronic granulomatous disease, and Mendelian susceptibility to mycobacterial diseases.

Identification of novel Mt-Guab2 inhibitor series active against M. tuberculosis

Tuberculosis (TB) remains a leading cause of mortality worldwide. With the emergence of multidrug resistant TB, extensively drug resistant TB and HIV-associated TB it is imperative that new drug targets be identified. The potential of Mycobacterium tuberculosis inosine monophosphate dehydrogenase (IMPDH) as a novel drug target was explored in the present study. IMPDH exclusively catalyzes the conversion of inosine monophosphate (IMP) to xanthosine monophosphate (XMP) in the presence of the cofactor nicotinamide adenine dinucleotide (NAD⁺). Although the enzyme is a dehydrogenase, the enzyme does not catalyze the reverse reaction i.e. the conversion of XMP to IMP. Unlike other bacteria, M. tuberculosis harbors three IMPDH-like genes, designated as Mt-guaB1, Mt-guaB2 and Mt-guaB3 respectively. Of the three putative IMPDH's, we previously confirmed that Mt-GuaB2 was the only functional ortholog by characterizing the enzyme kinetically. Using an in silico approach based on designed scaffolds, a series of novel classes of inhibitors was identified. The inhibitors possess good activity against M. tuberculosis with MIC values in the range of 0.4 to 11.4 µg mL⁻¹. Among the identified ligands, two inhibitors have nanomolar K_is against the Mt-GuaB2 enzyme.

Doxycycline and HIV infection suppress tuberculosis-induced matrix metalloproteinases

RATIONALE

Tuberculosis kills more than 1.5 million people per year, and standard treatment has remained unchanged for more than 30 years. Tuberculosis (TB) drives matrix metalloproteinase (MMP) activity to cause immunopathology. In advanced HIV infection, tissue destruction is reduced, but underlying mechanisms are poorly defined and no current antituberculous therapy reduces host tissue damage.

OBJECTIVES

To investigate MMP activity in patients with TB with and without HIV coinfection and to determine the potential of doxycycline to inhibit MMPs and decrease pathology.

METHODS

Concentrations of MMPs and cytokines were analyzed by Luminex array in a prospectively recruited cohort of patients. Modulation of MMP secretion and Mycobacterium tuberculosis growth by doxycycline was studied in primary human cells and TB-infected guinea pigs.

MEASUREMENTS AND MAIN RESULTS

HIV coinfection decreased MMP concentrations in induced sputum of patients with TB. MMPs correlated with clinical markers of tissue damage, further implicating dysregulated protease activity in TB-driven pathology. In contrast, cytokine concentrations were no different. Doxycycline, a licensed MMP inhibitor, suppressed TB-dependent MMP-1 and -9 secretion from primary human macrophages and epithelial cells by inhibiting promoter activation. In the guinea pig model, doxycycline reduced lung TB colony forming units after 8 weeks in a dose-dependent manner compared with untreated animals, and in vitro doxycycline inhibited mycobacterial proliferation.

CONCLUSIONS

HIV coinfection in patients with TB reduces concentrations of immunopathogenic MMPs. Doxycycline decreases MMP activity in a cellular model and suppresses mycobacterial growth in vitro and in guinea pigs. Adjunctive doxycycline therapy may reduce morbidity and mortality in TB.