Metformin as adjunct antituberculosis therapy

Genome-wide screen of Mycobacterium tuberculosis-infected macrophages revealed GID/CTLH complex-mediated modulation of bacterial growth

The eukaryotic Glucose Induced Degradation/C-Terminal to LisH (GID/CTLH) complex is a highly conserved E3 ubiquitin ligase involved in a broad range of biological processes. However, a role of this complex in host anti-microbial defenses has not been described. We exploited Mycobacterium tuberculosis (Mtb) induced cytotoxicity in macrophages in a FACS based CRISPR genetic screen to identify host determinants of intracellular Mtb growth restriction. Our screen identified 5 (GID8, YPEL5, WDR26, UBE2H, MAEA) of the 12 predicted members of the GID/CTLH complex as determinants of intracellular growth of both Mtb and Salmonella serovar Typhimurium. We show that the anti-microbial properties of the GID/CTLH complex knockout macrophages are mediated by enhanced GABAergic signaling, activated AMPK, increased autophagic flux and resistance to Mtb induced necrotic cell death. Meanwhile, Mtb isolated from GID/CTLH knockout macrophages are nutritionally starved and oxidatively stressed. Our study identifies the GID/CTLH complex activity as broadly suppressive of host anti-microbial responses against intracellular bacterial infections.

Synergistic role of Mycobacterium indicus pranii and human beta Defensin-2 as adjunctive therapy against Mycobacterium tuberculosis

Host-directed therapies (HDT) via modulation of specific host responses like inflammation can limit mycobacterial infection. HDTs could be included in current TB therapy as an adjunct to increase bacterial clearance and limit tissue damage to control spread. Individually, Mycobacterium indicus pranii (MIP) and human beta defensin-2 (hBD-2) are promising therapies for tuberculosis (TB). They can directly target the TB bacilli and enhance cell-mediated immune responses, which is limiting with conventional drugs. Therefore, our study investigated the combined application of MIP and hBD-2 to evaluate their efficacy in clearing infections caused by Mycobacterium smegmatis (M.smeg) and Mycobacterium tuberculosis (M.tb) (both avirulent; H37Ra and virulent strain; H37Rv) in THP-1 cells and human monocyte-derived macrophages (MDMs). A strong pro-inflammatory response was observed against the combination of MIP and hBD-2 which also correlated with a significant reduction in the bacterial load. This combination further showed protection against M.tb by enhancing pyroptosis in the infected cells. The study suggests the combined use of these potent immunomodulators, which could be employed as an effective mode of therapy as adjuvants against mycobacterial infections after validation in a suitable animal model.

Impaired fatty acid import or catabolism in macrophages restricts intracellular growth of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) infection of macrophages reprograms cellular metabolism to promote lipid retention. While it is clearly known that intracellular Mtb utilize host derived lipids to maintain infection, the role of macrophage lipid processing on the bacteria's ability to access the intracellular lipid pool remains undefined. We utilized a CRISPR-Cas9 genetic approach to assess the impact of sequential steps in fatty acid metabolism on the growth of intracellular Mtb. Our analyzes demonstrate that mutated macrophages that cannot either import, store or catabolize fatty acids restrict Mtb growth by both common and divergent anti-microbial mechanisms, including increased glycolysis, increased oxidative stress, production of pro-inflammatory cytokines, enhanced autophagy and nutrient limitation. We also show that impaired macrophage lipid droplet biogenesis is restrictive to Mtb replication, but increased induction fails to rescue Mtb growth. Our work expands our understanding of how host fatty acid homeostasis impacts Mtb growth in the macrophage.

Actionable mechanisms of drug tolerance and resistance in Mycobacterium tuberculosis

The emergence of antimicrobial resistance (AMR) across bacterial pathogens presents a serious threat to global health. This threat is further exacerbated in tuberculosis (TB), mainly due to a protracted treatment regimen involving a combination of drugs. A diversity of factors contributes to the emergence of drug resistance in TB, which is caused by the pathogen Mycobacterium tuberculosis (Mtb). While the traditional genetic mutation-driven drug resistance mechanisms operate in Mtb, there are also several additional unique features of drug resistance in this pathogen. Research in the past decade has enriched our understanding of such unconventional factors as efflux pumps, bacterial heterogeneity, metabolic states, and host microenvironment. Given that the discovery of new antibiotics is outpaced by the emergence of drug resistance patterns displayed by the pathogen, newer strategies for combating drug resistance are desperately needed. In the context of TB, such approaches include targeting the efflux capability of the pathogen, modulating the host environment to prevent bacterial drug tolerance, and activating the host anti-mycobacterial pathways. In this review, we discuss the traditional mechanisms of drug resistance in Mtb, newer understandings and the shaping of a set of unconventional approaches to target both the emergence and treatment of drug resistance in TB.

Development of inhaled moxifloxacin-metformin formulation as an alternative for pulmonary tuberculosis treatment

Resistant M. tuberculosis strains threaten pulmonary tuberculosis (P-TB) control since they limit drug options. Drug repositioning and new development strategies are urgently required to overcome resistance. Studies have already shown the beneficial role of the oral antidiabetic metformin as an anti-tuberculosis adjuvant drug. This work aimed to develop an inhalatory dry powder co-formulation of metformin and moxifloxacin to figure out a future option for P-TB treatment. Pre-formulation evaluations indicated the physicochemical compatibility of constituents, demonstrating powder crystallinity and acceptable drug content. Eight moxifloxacin-metformin dry powder formulations were produced by spray drying, and solid-state characterizations showed partial amorphization, ascribed to moxifloxacin. Four formulations containing L-leucine exhibited micromeritic and in vitro deposition profiles indicating pulmonary delivery suitability, like spherical and corrugated particle surface, geometric diameters < 5 μm, high emitted doses (>85 %), and mass median aerodynamic diameters between 1-5 μm. The use of a second spray dryer model further optimized the aerodynamic properties and yield of the best formulation, demonstrating the influence of the equipment used on the product obtained. Moreover, the final formulation showed high in vitro cell tolerability and characteristics in permeability studies indicative of good drug retention in the lungs.

Inducible antibacterial responses in macrophages

Macrophages destroy bacteria and other microorganisms through phagocytosis-coupled antimicrobial responses, such as the generation of reactive oxygen species and the delivery of hydrolytic enzymes from lysosomes to the phagosome. However, many intracellular bacteria subvert these responses, escaping to other cellular compartments to survive and/or replicate. Such bacterial subversion strategies are countered by a range of additional direct antibacterial responses that are switched on by pattern-recognition receptors and/or host-derived cytokines and other factors, often through inducible gene expression and/or metabolic reprogramming. Our understanding of these inducible antibacterial defence strategies in macrophages is rapidly evolving. In this Review, we provide an overview of the broad repertoire of antibacterial responses that can be engaged in macrophages, including LC3-associated phagocytosis, metabolic reprogramming and antimicrobial metabolites, lipid droplets, guanylate-binding proteins, antimicrobial peptides, metal ion toxicity, nutrient depletion, autophagy and nitric oxide production. We also highlight key inducers, signalling pathways and transcription factors involved in driving these different antibacterial responses. Finally, we discuss how a detailed understanding of the molecular mechanisms of antibacterial responses in macrophages might be exploited for developing host-directed therapies to combat antibiotic-resistant bacterial infections.

Discovery of anti-infective compounds against Mycobacterium marinum after biotransformation of simple natural stilbenes by a fungal secretome

Introduction

Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, remains a serious threat to human health worldwide and the quest for new anti-tubercular drugs is an enduring and demanding journey. Natural products (NPs) have played a significant role in advancing drug therapy of infectious diseases.

Methods

This study evaluated the suitability of a high-throughput infection system composed of the host amoeba Dictyostelium discoideum (Dd) and Mycobacterium marinum (Mm), a close relative of Mtb, to identify anti-infective compounds. Growth of Dd and intracellular Mm were quantified by using luminescence and fluorescence readouts in phenotypic assays. The system was first benchmarked with a set of therapeutic anti-Mtb antibiotics and then used to screen a library of biotransformed stilbenes.

Results

The study confirmed both efficacy of established antibiotics such as rifampicin and bedaquiline, with activities below defined anti-mycobacterium susceptibility breakpoints, and the lack of activity of pyrazinamide against Mm. The screening revealed the promising anti-infective activities of trans-δ-viniferins and in particular of two compounds 17 and 19 with an IC50 of 18.1 μM, 9 μM, respectively. Both compounds had no activity on Mm in broth. Subsequent exploration via halogenation and structure-activity relationship studies led to the identification of derivatives with improved selectivity and potency. The modes of action of the anti-infective compounds may involve inhibition of mycobacterial virulence factors or boosting of host defense.

Discussion

The study highlights the potential of biotransformation and NP-inspired derivatization approaches for drug discovery and underscores the utility of the Dd-Mm infection system in identifying novel anti-infective compounds.

Metformin modulates corticosteroids hormones in adrenals cells promoting Mycobacterium tuberculosis elimination in human macrophages

Research suggests that both tuberculosis (TB) and type 2 diabetes mellitus (T2DM) have an immuno-endocrine imbalance characterized by dysregulated proinflammatory molecules and hormone levels (high cortisol/DHEA ratio), impeding an effective immune response against Mycobacterium tuberculosis (Mtb) driven by cytokines, antimicrobial peptides (AMPs), and androgens like DHEA. Insulin, sulfonylurea derivatives, and metformin are commonly used glucose-lowering drugs in patients suffering from TB and T2DM. For this comorbidity, metformin is an attractive target to restore the immunoendocrine mechanisms dysregulated against Mtb. This study aimed to assess whether metformin influences cortisol and DHEA synthesis in adrenal cells and if these hormones influence the expression of proinflammatory cytokines and AMPs in Mtb-infected macrophages. Our results suggest that metformin may enhance DHEA synthesis while maintaining cortisol homeostasis. In addition, supernatants from metformin-treated adrenal cells decreased mycobacterial loads in macrophages, which related to rising proinflammatory cytokines and AMP expression (HBD-2 and 3). Intriguingly, we find that HBD-3 and LL-37 can modulate steroid synthesis in adrenal cells with diminished levels of cortisol and DHEA, highlighting the importance of crosstalk communication between adrenal hormones and these effectors of innate immunity. We suggest that metformin's effects can promote innate immunity against Mtb straight or through modulation of corticosteroid hormones.

Comparative risk of infection of medications used for type 2 diabetes

INTRODUCTION

Glucose-lowering drugs pose a potential infection risk among individuals with type 2 diabetes. The U.S. Food and Drug Administration has issued safety warnings regarding increased risks of urinary tract infections (UTIs) and genital infections with sodium-glucose cotransporter 2 (SGLT2) inhibitors. However, the infection risk associated with other glucose-lowering drugs remains unclear. We conducted a PubMed database search to review the infection risk of glucose-lowering drugs, focusing on meta-analysis of randomized controlled trials.

AREAS COVERED

We described the infection risks associated with SGLT2 inhibitors, dipeptidyl peptidase-4 (DPP-4) inhibitors, glucose-like peptide-1 receptor agonists, metformin, and thiazolidinediones, covering infections of the genitourinary, respiratory, and gastrointestinal systems, including skin and soft tissue infections (SSTIs).

EXPERT OPINION

SGLT2 inhibitors are associated with a higher genital infection risk, while their UTI risk remains inconclusive. DPP-4 inhibitors could be a treatment option for those intolerant to SGLT2 inhibitors, given their lower genital infection risk compared to placebo. Uncertainty persists regarding the risks of respiratory infections, gastroenteritis, and SSTIs with SGLT2 inhibitors. Limited evidence is available regarding the impact of DPP-4 inhibitors on respiratory infections. Additional research is needed to determine the comparative infection risk of other glucose-lowering drugs.

Effect of Metformin on systemic chemokine responses during anti-tuberculosis chemotherapy

BACKGROUND

Metformin (MET), by boosting immunity, has been suggested as a host-adjunctive therapy to anti-tuberculosis treatment (ATT).

METHODS

We evaluated whether adding MET to the standard ATT can alter the host chemokine response. We investigated the influence of metformin on the plasma levels of a wide panel of chemokines in a group of active tuberculosis patients before treatment, at 2nd month of ATT and at 6-months of ATT as part of our clinical study to examine the effect of metformin on ATT.

RESULTS

Our results demonstrated that addition of metformin resulted in diminished CC (CCL1 and CCL3) and CXC (CXCL-2 and CXCL-10) chemokines in MET arm as compared to non-MET arm at the 2nd month and 6th month of ATT. In addition to this, MET arm showed significantly diminished chemokines in individuals with high bacterial burden and cavitary disease.

CONCLUSION

Our current data suggest that metformin alters chemokines responses that could potentially curb excessive inflammation during ATT.

Elongation of Very Long-Chain Fatty Acids (ELOVL) in Atopic Dermatitis and the Cutaneous Adverse Effect AGEP of Drugs

Atopic dermatitis (AD) is a common inflammatory skin disease, in particular among infants, and is characterized, among other things, by a modification in fatty acid and ceramide composition of the skin's stratum corneum. Palmitic acid and stearic acid, along with C16-ceramide and 2-hydroxy C16-ceramide, occur strikingly in AD. They coincide with a simultaneous decrease in very long-chain ceramides and ultra-long-chain ceramides, which form the outermost lipid barrier. Ceramides originate from cellular sphingolipid/ceramide metabolism, comprising a well-orchestrated network of enzymes involving various ELOVLs and CerSs in the de novo ceramide synthesis and neutral and acid CERase in degradation. Contrasting changes in long-chain ceramides and very long-chain ceramides in AD can be more clearly explained by the compartmentalization of ceramide synthesis. According to our hypothesis, the origin of increased C16-ceramide and 2-hydroxy C16-ceramide is located in the lysosome. Conversely, the decreased ultra-long-chain and very long-chain ceramides are the result of impaired ELOVL fatty acid elongation. The suggested model's key elements include the lysosomal aCERase, which has pH-dependent long-chain C16-ceramide synthase activity (revaCERase); the NADPH-activated step-in enzyme ELOVL6 for fatty acid elongation; and the coincidence of impaired ELOVL fatty acid elongation and an elevated lysosomal pH, which is considered to be the trigger for the altered ceramide biosynthesis in the lysosome. To maintain the ELOVL6 fatty acid elongation and the supply of NADPH and ATP to the cell, the polyunsaturated PPARG activator linoleic acid is considered to be one of the most suitable compounds. In the event that the increase in lysosomal pH is triggered by lysosomotropic compounds, compounds that disrupt the transmembrane proton gradient or force the breakdown of lysosomal proton pumps, non-HLA-classified AGEP may result.

Host-directed therapy with amiodarone in preclinical models restricts mycobacterial infection and enhances autophagy

Mycobacterium tuberculosis (Mtb) as well as nontuberculous mycobacteria are intracellular pathogens whose treatment is extensive and increasingly impaired due to the rise of mycobacterial drug resistance. The loss of antibiotic efficacy has raised interest in the identification of host-directed therapeutics (HDT) to develop novel treatment strategies for mycobacterial infections. In this study, we identified amiodarone as a potential HDT candidate that inhibited both intracellular Mtb and Mycobacterium avium in primary human macrophages without directly impairing bacterial growth, thereby confirming that amiodarone acts in a host-mediated manner. Moreover, amiodarone induced the formation of (auto)phagosomes and enhanced autophagic targeting of mycobacteria in macrophages. The induction of autophagy by amiodarone is likely due to enhanced transcriptional regulation, as the nuclear intensity of the transcription factor EB, the master regulator of autophagy and lysosomal biogenesis, was strongly increased. Furthermore, blocking lysosomal degradation with bafilomycin impaired the host-beneficial effect of amiodarone. Finally, amiodarone induced autophagy and reduced bacterial burden in a zebrafish embryo model of tuberculosis, thereby confirming the HDT activity of amiodarone in vivo. In conclusion, we have identified amiodarone as an autophagy-inducing antimycobacterial HDT that improves host control of mycobacterial infections.

IMPORTANCE

Due to the global rise in antibiotic resistance, there is a strong need for alternative treatment strategies against intracellular bacterial infections, including Mycobacterium tuberculosis (Mtb) and non-tuberculous mycobacteria. Stimulating host defense mechanisms by host-directed therapy (HDT) is a promising approach for treating mycobacterial infections. This study identified amiodarone, an antiarrhythmic agent, as a potential HDT candidate that inhibits the survival of Mtb and Mycobacterium avium in primary human macrophages. The antimycobacterial effect of amiodarone was confirmed in an in vivo tuberculosis model based on Mycobacterium marinum infection of zebrafish embryos. Furthermore, amiodarone induced autophagy and inhibition of the autophagic flux effectively impaired the host-protective effect of amiodarone, supporting that activation of the host (auto)phagolysosomal pathway is essential for the mechanism of action of amiodarone. In conclusion, we have identified amiodarone as an autophagy-inducing HDT that improves host control of a wide range of mycobacteria.

Small Molecule Targeting PPM1A Activates Autophagy for Mycobacterium tuberculosis Host-Directed Therapy

Mycobacterium tuberculosis (Mtb), the infectious agent of tuberculosis (TB), causes over 1.5 million deaths globally every year. Host-directed therapies (HDT) for TB are desirable for their potential to shorten treatment and reduce the development of antibiotic resistance. Previously, we described a modular biomimetic strategy to identify SMIP-30, targeting PPM1A (IC50 = 1.19 μM), a metal-dependent phosphatase exploited by Mtb to survive intracellularly. SMIP-30 restricted the survival of Mtb in macrophages and lungs of infected mice. Herein, we redesigned SMIP-30 to create SMIP-031, which is a more potent inhibitor for PPM1A (IC50 = 180 nM). SMIP-031 efficiently increased the level of phosphorylation of S403-p62 and the expression of LC3B-II to activate autophagy, resulting in the dose-dependent clearance of Mtb in infected macrophages. SMIP-031 possesses a good pharmacokinetic profile and oral bioavailability (F = 74%). In vivo, SMIP-031 is well tolerated up to 50 mg/kg and significantly reduces the bacteria burden in the spleens of infected mice.

Exploring necrosis-associated mitochondrial gene signatures: revealing their role in prognosis and immunotherapy of renal clear cell carcinoma

Mitochondrial dysfunction and necrotic apoptosis, pivotal in therapeutic strategies for multiple diseases, lack comprehensive understanding in the context of renal clear cell carcinoma (ccRCC). This study explores their potential as valuable tools for ccRCC prediction, prevention, and personalized medical care. Transcriptomic and clinical datasets were acquired from the Cancer Genome Atlas (TCGA) repository. Mitochondrial and necrosis-associated gene sets were sourced from MitoCarta3.0 and the KEGG Pathway databases, respectively. Six necrosis-related mitochondrial genes (nc-MTGs) with prognostic significance were analyzed and screened, and a prognostic model was constructed. The accuracy of the model was verified using external data (E-MTAB-1980). TISCH was used to explore nc-MTGs at the cellular level. Finally, the expression level of BH3 interacting domain death agonist (BID) in ccRCC cell line was detected by real-time fluorescence quantitative polymerase chain reaction (RT-qPCR), and the effect of BID down-regulation on tumor cell migration was verified by transwell assays and wound-healing experiments. We established and validated a prognostic model for clear cell renal cell carcinoma (ccRCC) utilizing six necrosis-related mitochondrial genes (nc-MTGs), affirming its efficacy in evaluating tumor progression. RT-PCR results showed that BID expression was up-regulated in ccRCC tissues compared with controls and exhibited oncogenic effects. In vitro cell function experiments showed that BID may be an important factor affecting the migration of ccRCC. Our study is the first to elucidate the biological functions and prognostic significance of mitochondrial molecules related to necroptosis, providing a new way to evaluate mitochondrial therapeutics in patients with ccRCC.

Metabolic requirements of CD160 expressing memory-like NK cells in Gram-negative bacterial infection

Objective

Unique metabolic requirements accompany the development and functional fates of immune cells. How cellular metabolism is important in natural killer (NK) cells and their memory-like differentiation in bacterial infections remains elusive.

Methods

Here, we utilise our established NK cell memory assay to investigate the metabolic requirement for memory-like NK cell formation and function in response to the Gram-negative intracellular bacteria Burkholderia pseudomallei (BP), the causative agent of melioidosis.

Results

We demonstrate that CD160+ memory-like NK cells upon BP stimulation upregulate glucose and amino acid transporters in a cohort of recovered melioidosis patients which is maintained at least 3-month post-hospital admission. Using an in vitro assay, human BP-specific CD160+ memory-like NK cells show metabolic priming including increased expression of glucose and amino acid transporters with elevated glucose uptake, increased mTOR activation and mitochondrial membrane potential upon BP re-stimulation. Antigen-specific and cytokine-induced IFN-γ production of this memory-like NK cell subset are highly dependent on oxidative phosphorylation (OXPHOS) with some dependency on glycolysis, whereas the formation of CD160+ memory-like NK cells in vitro is dependent on fatty acid oxidation and OXPHOS and further increased by metformin.

Conclusion

This study reveals the link between metabolism and cellular function of memory-like NK cells, which can be exploited for vaccine design and for monitoring protection against Gram-negative bacterial infection.

Backtranslation of human RNA biosignatures of tuberculosis disease risk into the preclinical pipeline is condition dependent

It is not clear whether human progression to active tuberculosis disease (TB) risk signatures are viable endpoint criteria for evaluations of treatments in clinical or preclinical development. TB is the deadliest infectious disease globally and more efficacious vaccines are needed to reduce this mortality. However, the immune correlates of protection for either preventing infection with Mycobacterium tuberculosis or preventing TB disease have yet to be completely defined, making the advancement of candidate vaccines through the pipeline slow, costly, and fraught with risk. Human-derived correlate of risk (COR) gene signatures, which identify an individual's risk to progressing to active TB disease, provide an opportunity for evaluating new therapies for TB with clear and defined endpoints. Though prospective clinical trials with longitudinal sampling are prohibitively expensive, characterization of COR gene signatures is practical with preclinical models. Using a 3Rs (Replacement, Reduction and Refinement) approach we reanalyzed heterogeneous publicly available transcriptional datasets to determine whether a specific set of COR signatures are viable endpoints in the preclinical pipeline. We selected RISK6, Sweeney3 and BATF2 human-derived blood-based RNA biosignatures because they require relatively few genes to assign a score and have been carefully evaluated across several clinical cohorts. Excitingly, these data provide proof-of-concept that human COR signatures seem to have high fidelity across several tissue types in the preclinical TB model pipeline and show best performance when the model most closely reflected human infection or disease conditions. Human-derived COR signatures offer an opportunity for high-throughput preclinical endpoint criteria of vaccine and drug therapy evaluations.

One Sentence Summary

Human-derived biosignatures of tuberculosis disease progression were evaluated for their predictive fidelity across preclinical species and derived tissues using available public data sets.

The advances in adjuvant therapy for tuberculosis with immunoregulatory compounds

Tuberculosis (TB) is a chronic bacterial disease, as well as a complex immune disease. The occurrence, development, and prognosis of TB are not only related to the pathogenicity of Mycobacterium tuberculosis (Mtb), but also related to the patient's own immune state. The research and development of immunotherapy drugs can effectively regulate the body's anti-TB immune responses, inhibit or eliminate Mtb, alleviate pathological damage, and facilitate rehabilitation. This paper reviews the research progress of immunotherapeutic compounds for TB, including immunoregulatory compounds and repurposing drugs, and points out the existing problems and future research directions, which lays the foundation for studying new agents for host-directed therapies of TB.

Host stress drives tolerance and persistence: The bane of anti-microbial therapeutics

Antibiotic resistance, typically associated with genetic changes within a bacterial population, is a frequent contributor to antibiotic treatment failures. Antibiotic persistence and tolerance, which we collectively term recalcitrance, represent transient phenotypic changes in the bacterial population that prolong survival in the presence of typically lethal concentrations of antibiotics. Antibiotic recalcitrance is challenging to detect and investigate-traditionally studied under in vitro conditions, our understanding during infection and its contribution to antibiotic failure is limited. Recently, significant progress has been made in the study of antibiotic-recalcitrant populations in pathogenic species, including Mycobacterium tuberculosis, Staphylococcus aureus, Salmonella enterica, and Yersiniae, in the context of the host environment. Despite the diversity of these pathogens and infection models, shared signals and responses promote recalcitrance, and common features and vulnerabilities of persisters and tolerant bacteria have emerged. These will be discussed here, along with progress toward developing therapeutic interventions to better treat recalcitrant pathogens.

Host Cell Death and Modulation of Immune Response against Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), a prevalent infectious disease affecting populations worldwide. A classic trait of TB pathology is the formation of granulomas, which wall off the pathogen, via the innate and adaptive immune systems. Some key players involved include tumor necrosis factor-alpha (TNF-α), foamy macrophages, type I interferons (IFNs), and reactive oxygen species, which may also show overlap with cell death pathways. Additionally, host cell death is a primary method for combating and controlling Mtb within the body, a process which is influenced by both host and bacterial factors. These cell death modalities have distinct molecular mechanisms and pathways. Programmed cell death (PCD), encompassing apoptosis and autophagy, typically confers a protective response against Mtb by containing the bacteria within dead macrophages, facilitating their phagocytosis by uninfected or neighboring cells, whereas necrotic cell death benefits the pathogen, leading to the release of bacteria extracellularly. Apoptosis is triggered via intrinsic and extrinsic caspase-dependent pathways as well as caspase-independent pathways. Necrosis is induced via various pathways, including necroptosis, pyroptosis, and ferroptosis. Given the pivotal role of host cell death pathways in host defense against Mtb, therapeutic agents targeting cell death signaling have been investigated for TB treatment. This review provides an overview of the diverse mechanisms underlying Mtb-induced host cell death, examining their implications for host immunity. Furthermore, it discusses the potential of targeting host cell death pathways as therapeutic and preventive strategies against Mtb infection.

Effect of Metformin on Plasma Exposure of Rifampicin, Isoniazid, and Pyrazinamide in Patients on Treatment for Pulmonary Tuberculosis

BACKGROUND

To evaluate the effect of metformin on the plasma levels of rifampicin, isoniazid, and pyrazinamide in patients with drug-sensitive pulmonary tuberculosis being treated with first-line antituberculosis treatment (ATT) and to assess the influence of gene polymorphisms on the metabolic pathway of metformin and plasma levels of antitubercular drugs.

METHODS

Nondiabetic adults aged 18-60 years with pulmonary tuberculosis were randomized to either the standard ATT (ATT group) or ATT plus metformin (METRIF group) groups in a phase IIB clinical trial. An intensive pharmacokinetic study with blood collection at 0 hour (predosing), followed by 1, 2, 4, 6, 8, and 12 hours after dosing was conducted during the first month of treatment in a subset of 60 study participants after a minimum of 14 doses. Plasma concentrations of rifampicin, isoniazid, pyrazinamide, and metformin were measured by high-performance liquid chromatography using validated methods, and pharmacokinetic parameters and OCT1 and MATE1 gene polymorphisms were compared between the groups.

RESULTS

Significant increases in the clearance of rifampicin, isoniazid, and pyrazinamide were observed in patients in the METRIF group (n = 29) compared with those in the ATT group (n = 31). The AA genotypes of the single-nucleotide polymorphism of rs2289669 ( MATE1 ) in the METRIF group showed a significantly decreased area under the concentration-time curve to the last observation point and increased clearance of rifampicin.

CONCLUSIONS

Metformin altered rifampicin and isoniazid plasma concentrations in patients receiving antituberculosis treatment for pulmonary tuberculosis with little effect on sputum conversion at the end of treatment. Studies with larger sample sizes are needed to understand host drug-drug interactions.

Genome-wide screen of Mycobacterium tuberculosis- infected macrophages identified the GID/CTLH complex as a determinant of intracellular bacterial growth

The eukaryotic GID/CTLH complex is a highly conserved E3 ubiquitin ligase involved in a broad range of biological processes. However, a role of this complex in host antimicrobial defenses has not been described. We exploited Mycobacterium tuberculosis ( Mtb ) induced cytotoxicity in macrophages in a FACS based CRISPR genetic screen to identify host determinants of intracellular Mtb growth restriction. Our screen identified 5 ( GID8 , YPEL5 , WDR26 , UBE2H , MAEA ) of the 10 predicted members of the GID/CTLH complex as determinants of intracellular growth of both Mtb and Salmonella serovar Typhimurium. We show that the antimicrobial properties of the GID/CTLH complex knockdown macrophages are mediated by enhanced GABAergic signaling, activated AMPK, increased autophagic flux and resistance to cell death. Meanwhile, Mtb isolated from GID/CTLH knockdown macrophages are nutritionally starved and oxidatively stressed. Our study identifies the GID/CTLH complex activity as broadly suppressive of host antimicrobial responses against intracellular bacterial infections.

Graphical abstract

The antimicrobial activity of innate host-directed therapies: A systematic review

Intracellular human pathogens are the deadliest infectious diseases and are difficult to treat effectively due to their protection inside the host cell and the development of antimicrobial resistance (AMR). An emerging approach to combat these intracellular pathogens is host-directed therapies (HDT), which harness the innate immunity of host cells. HDT rely on small molecules to promote host protection mechanisms that ultimately lead to pathogen clearance. These therapies are hypothesized to: (1) possess indirect yet broad, cross-species antimicrobial activity, (2) effectively target drug-resistant pathogens, (3) carry a reduced susceptibility to the development of AMR and (4) have synergistic action with conventional antimicrobials. As the field of HDT expands, this systematic review was conducted to collect a compendium of HDT and their characteristics, such as the host mechanisms affected, the pathogen inhibited, the concentrations investigated and the magnitude of pathogen inhibition. The evidential support for the main four HDT hypotheses was assessed and concluded that HDT demonstrate robust cross-species activity, are active against AMR pathogens, clinical isolates and laboratory-adapted pathogens. However, limited information exists to support the notion that HDT are synergistic with canonical antimicrobials and are less predisposed to AMR development.

Modulating the antibacterial effect of the existing antibiotics along with repurposing drug metformin

Owing to the extensive prevalence of resistant bacteria to numerous antibiotic classes, antimicrobial resistance (AMR) poses a well-known hazard to world health. As an alternate approach in the field of antimicrobial drug discovery, repurposing the available medications which are also called antibiotic resistance breakers has been pursued for the treatment of infections with antimicrobial resistance pathogens. In this study, we used Haloperidol, Metformin and Hydroxychloroquine as repurposing drugs in in vitro (Antibacterial Antibiotic Sensitivity Test and Minimum Inhibitory Concentration-MIC) and in vivo (Shigellosis in Swiss albino mice) tests in combination with traditional antibiotics (Oxytetracycline, Erythromycin, Doxycycline, Gentamicin, Ampicillin, Chloramphenicol, and Penicillin) against a group of AMR resistance bacteria (Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Shigella boydii). After observing the results of the conducted in vitro experiments we studied the effects of the above non antibiotic drugs in combination with the said antibiotics. As an repurposing adjuvant antibiotic drug, Metformin exhibited noteworthy activity in almost all in vitro, in vivo and in silico tests (Zone of inhibition for 30 to 43 mm for E.coli in combination with Doxycycline; MIC value decreased 50 µM to 0.781 µM with Doxycycline on S. boydii).In rodents Doxycycline and Metformin showed prominent against Shigellosis in White blood cell count (6.47 ± 0.152 thousand/mm3) and Erythrocyte sedimentation rate (10.5 ± 1.73 mm/hr). Our findings indicated that Metformin and Doxycycline combination has a crucial impact on Shigellosis. The molecular docking study was performed targeting the Acriflavine resistance protein B (AcrB) (PDB ID: 4CDI) and MexA protein (PDB ID: 6IOK) protein with Metformin (met8) drug which showed the highest binding energy with - 6.4 kcal/mol and - 5.5 kcal/mol respectively. Further, molecular dynamics simulation revealed that the docked complexes were relatively stable during the 100 ns simulation period. This study suggest Metformin and other experimented drugs can be used as adjuvants boost up antibiosis but further study is needed to find out the safety and efficacy of this non-antibiotic drug as potent antibiotic adjuvant.

Dependency on host vitamin B12 has shaped Mycobacterium tuberculosis Complex evolution

Human and animal tuberculosis is caused by the Mycobacterium tuberculosis Complex (MTBC), which has evolved a genomic decay of cobalamin (vitamin B12) biosynthetic genes. Accordingly, and in sharp contrast to environmental, opportunistic and ancestor mycobacteria; we demonstrate that M. tuberculosis (Mtb), M. africanum, and animal-adapted lineages, lack endogenous production of cobalamin, yet they retain the capacity for exogenous uptake. A B12 anemic model in immunocompromised and immunocompetent mice, demonstrates improved survival, and lower bacteria in organs, in B12 anemic animals infected with Mtb relative to non-anemic controls. Conversely, no differences were observed between mice groups infected with M. canettii, an ancestor mycobacterium which retains cobalamin biosynthesis. Interrogation of the B12 transcriptome in three MTBC strains defined L-methionine synthesis by metE and metH genes as a key phenotype. Expression of metE is repressed by a cobalamin riboswitch, while MetH requires the cobalamin cofactor. Thus, deletion of metE predominantly attenuates Mtb in anemic mice; although inactivation of metH exclusively causes attenuation in non-anemic controls. Here, we show how sub-physiological levels of B12 in the host antagonizes Mtb virulence, and describe a yet unknown mechanism of host-pathogen cross-talk with implications for B12 anemic populations.

Relationship between metformin use and mortality in tuberculosis patients with diabetes: a nationwide cohort study

BACKGROUND/AIMS

To determine whether metformin, which is considered a host-directed therapy for tuberculosis (TB), is effective in improving the prognosis of patients with TB and diabetes mellitus (DM), who have higher mortality than those without DM.

METHODS

This cohort study included patients who were registered as having TB in the National Tuberculosis Surveillance System. The medical and death records of matched patients were obtained from the National Health Information Database and Statistics Korea, respectively, and data from 2011 to 2017 were collected retrospectively. We classified patients according to metformin use among participants who used diabetes drugs for more than 28 days. The primary outcome was all-cause mortality during TB treatment. Double propensity score adjustment was applied to reduce the effects of confounding and multivariable Cox proportional hazard models were used to estimate adjusted hazard ratio (aHR) with 95% confidence interval (CI).

RESULTS

The all-cause mortality rate during TB treatment was lower (9.5% vs. 12.4%, p < 0.01) in the metformin user group. The hazard of death due to all causes after double propensity score adjustment was also lower in the metformin user group (aHR 0.76, 95% CI 0.67-0.86, p < 0.01). There was no significant difference in mortality between metformin users and non-users for TB-related deaths (p = 0.22); however, there was a significant difference in the non-TB-related deaths (p < 0.01).

CONCLUSION

Metformin use in patients with TB-DM co-prevalence is associated with reduced all-cause mortality, suggesting the potential for metformin adjuvant therapy in these patients.

Mutational Dynamics Related to Antibiotic Resistance in M. tuberculosis Isolates from Serial Samples of Patients with Tuberculosis and Type 2 Diabetes Mellitus

Genetic variation in tuberculosis is influenced by the host environment, patients with comorbidity, and tuberculosis-type 2 diabetes mellitus (TB-T2DM) and implies a higher risk of treatment failure and development of drug resistance. Considering the above, this study aimed to evaluate the influence of T2DM on the dynamic of polymorphisms related to antibiotic resistance in TB. Fifty individuals with TB-T2DM and TB were initially characterized, and serial isolates of 29 of these individuals were recovered on day 0 (diagnosis), 30, and 60. Genomes were sequenced, variants related to phylogeny and drug resistance analyzed, and mutation rates calculated and compared between groups. Lineage X was predominant. At day 0 (collection), almost all isolates from the TB group were sensitive, apart from four isolates from the TB-T2DM group showing the mutation katG S315T, from which one isolate had the mutations rpoB S450L, gyrA A90G, and gyrA D94G. This pattern was observed in a second isolate at day 30. The results provide a first overview of the dynamics of mutations in resistance genes from individuals with TB-T2DM, describing an early development of resistance to isoniazid and a rapid evolution of resistance to other drugs. Although preliminary, these results help to explain the increased risk of drug resistance in individuals with TB and T2DM.

Natural products in anti-tuberculosis host-directed therapy

Given that the disease progression of tuberculosis (TB) is primarily related to the host's immune status, it has been gradually realized that chemotherapy that targets the bacteria may never, on its own, wholly eradicate Mycobacterium tuberculosis, the causative agent of TB. The concept of host-directed therapy (HDT) with immune adjuvants has emerged. HDT could potentially interfere with infection and colonization by the pathogens, enhance the protective immune responses of hosts, suppress the overwhelming inflammatory responses, and help to attain a state of homeostasis that favors treatment efficacy. However, the HDT drugs currently being assessed in combination with anti-TB chemotherapy still face the dilemmas arising from side effects and high costs. Natural products are well suited to compensate for these shortcomings by having gentle modulatory effects on the host immune responses with less immunopathological damage at a lower cost. In this review, we first summarize the profiles of anti-TB immunology and the characteristics of HDT. Then, we focus on the rationale and challenges of developing and implementing natural products-based HDT. A succinct report of the medications currently being evaluated in clinical trials and preclinical studies is provided. This review aims to promote target-based screening and accelerate novel TB drug discovery.

Host-directed therapy against mycobacterium tuberculosis infections with diabetes mellitus

Tuberculosis (TB) is caused by the bacterial pathogen Mycobacterium tuberculosis (MTB) and is one of the principal reasons for mortality and morbidity worldwide. Currently, recommended anti-tuberculosis drugs include isoniazid, rifampicin, ethambutol, and pyrazinamide. TB treatment is lengthy and inflicted with severe side-effects, including reduced patient compliance with treatment and promotion of drug-resistant strains. TB is also prone to other concomitant diseases such as diabetes and HIV. These drug-resistant and complex co-morbid characteristics increase the complexity of treating MTB. Host-directed therapy (HDT), which effectively eliminates MTB and minimizes inflammatory tissue damage, primarily by targeting the immune system, is currently an attractive complementary approach. The drugs used for HDT are repositioned drugs in actual clinical practice with relative safety and efficacy assurance. HDT is a potentially effective therapeutic intervention for the treatment of MTB and diabetic MTB, and can compensate for the shortcomings of current TB therapies, including the reduction of drug resistance and modulation of immune response. Here, we summarize the state-of-the-art roles and mechanisms of HDT in immune modulation and treatment of MTB, with a special focus on the role of HDT in diabetic MTB, to emphasize the potential of HDT in controlling MTB infection.

Metformin has immunomodulatory effects which support its potential use as adjunctive therapy in tuberculosis

Metformin is the preferred oral medication for patients with type 2 diabetes mellitus, and this blood glucose-lowering and insulin-sensitizing drug has immunomodulatory effects that could contribute to the management of patients with various other autoimmune and infectious diseases. Tuberculosis is one such infection, and it remains prevalent worldwide, largely due to the successful evasion of the host's immune responses by the infecting pathogen, Mycobacterium tuberculosis. This review focuses on the possible mechanisms relevant to metformin's modulation of innate and adaptive immune responses to Mycobacterium tuberculosis and its potential use as an adjunctive drug in the treatment of tuberculosis. Current data suggest that metformin increases autophagy, phagocytosis, and mitochondrial reactive oxygen species production, while limiting excess inflammation and tissue destruction. This multifaceted drug also augments cell-mediated immune responses by maintaining CD8+ T cell metabolic homeostasis and improving immunological memory. Several murine models have demonstrated that metformin can reduce tuberculosis severity and tissue pathology, and two in vitro human studies confirmed enhanced immune responses in metformin-treated cells. These studies provide convincing evidence supporting the use of metformin to augment immune responses in patients with tuberculosis.

Interactive effect of oral anti-hyperglycaemic or anti-hypertensive drugs on the inhibitory and bactericidal activity of first line anti-TB drugs against M. tuberculosis

Co-existence of life style disorders, like, Diabetes or Hypertension, increases risk of, treatment failure, deaths and developing drug-resistant TB. Concomitant administration of drugs to treat dual/multi-morbidities may alter their effectiveness, in additive/synergistic or adverse/antagonistic manner. We evaluated interactive effect of 7 anti-hyperglycaemic (HG) and 6 anti-hypertensive (HT) drugs on the inhibitory (MICs) and bactericidal (% killing of intracellular bacilli) activities of anti-TB drugs, Isoniazid (INH), Rifampicin (RFM), Ethambutol (EMB) and Streptomycin (STR) against M. tuberculosis. Five anti-HG drugs, namely, Acarbose, Acetohexamide, Glyburide, Repaglinide and Sitagliptin imparted either 'additive' or 'no effect' on the activities (inhibition or % killing) of all the four anti-TB drugs, as evident by their lower FICs (Fractional Inhibitory concentrations) and higher bacterial killing in combination. Metformin and Rosiglitazone, however, exerted adverse effect on the Ethambutol (FICs >2.0). All the six anti-HT drugs, namely, Atenolol, Hydrochlorothiazide, Ramipril, Valsartan, Nifedipine and Verapamil exerted either 'additive'/'synergistic' or 'no effect' on the activities of anti-TB drugs. These findings may help clinicians to select safe and helpful anti-HG or anti-HT drugs for TB patients, if, suffering with diabetes or hypertension like co-morbidities and receiving DOTs (a set regimen for the treatment of TB based on the WHO guidelines).

Elucidating the function of hypothetical PE_PGRS45 protein of Mycobacterium tuberculosis as an oxido-reductase: a potential target for drug repurposing for the treatment of tuberculosis

Mycobacterium tuberculosis (Mtb) encodes a total of 67 PE_PGRS proteins and definite functions of many of them are still unknown. This study reports PE_PGRS45 (Rv2615c) protein from Mtb as NADPH dependent oxido-reductase having substrate specificity for fatty acyl Coenzyme A. Computational studies predicted PE_PGRS45 to be an integral membrane protein of Mtb. Expression of PE_PGRS45 in non-pathogenic Mycobacterium smegmatis, which does not possess PE_PGRS genes, confirmed its membrane localization. This protein was observed to have NADPH binding motif. Experimental validation confirmed its NADPH dependent oxido-reductase activity (Km value = 34.85 ± 9.478 μM, Vmax = 96.77 ± 7.184 nmol/min/mg of protein). Therefore, its potential to be targeted by first line anti-tubercular drug Isoniazid (INH) was investigated. INH was predicted to bind within the active site of PE_PGRS45 protein and experiments validated its inhibitory effect on the oxido-reductase activity of PE_PGRS45 with IC50/Ki values of 5.66 μM. Mtb is resistant to first line drugs including INH. Therefore, to address the problem of drug resistant TB, docking and Molecular Dynamics (MD) simulation studies between PE_PGRS45 and three drugs (Entacapone, Tolcapone and Verapamil) which are being used in Parkinson's and hypertension treatment were performed. PE_PGRS45 bound the three drugs with similar or better affinity in comparison to INH. Additionally, INH and these drugs bound within the same active site of PE_PGRS45. This study discovered Mtb's PE_PGRS45 protein to have an oxido-reductase activity and could be targeted by drugs that can be repurposed for TB treatment. Furthermore, in-vitro and in-vivo validation will aid in drug-resistant TB treatment. HIGHLIGHTSIn-silico and in-vitro studies of hypothetical protein PE_PGRS45 (Rv2615c) of Mycobacterium tuberculosis (Mtb) reveals it to be an integral membrane proteinPE_PGRS45 protein has substrate specificity for fatty acyl Coenzyme A (fatty acyl CoA) and possess NADPH dependent oxido-reductase activityDocking and simulation studies revealed that first line anti-tubercular drug Isoniazid (INH) and other drugs with anti-TB property have strong affinity for PE_PGRS45 proteinOxido-reductase activity of PE_PGRS45 protein is inhibited by INHPE_PGRS45 protein could be targeted by drugs that can be repurposed for TB treatmentCommunicated by Ramaswamy H. Sarma.

Exploring and exploiting the host cell autophagy during Mycobacterium tuberculosis infection

Tuberculosis, caused by Mycobacterium tuberculosis, is a fatal infectious disease that prevails to be the second leading cause of death from a single infectious agent despite the availability of multiple drugs for treatment. The current treatment regimen involves the combination of several drugs for 6 months that remain ineffective in completely eradicating the infection because of several drawbacks, such as the long duration of treatment and the side effects of drugs causing non-adherence of patients to the treatment regimen. Autophagy is an intracellular degradative process that eliminates pathogens at the early stages of infection. Mycobacterium tuberculosis's unique autophagy-blocking capability makes it challenging to eliminate compared to usual pathogens. The present review discusses recent advances in autophagy-inhibiting factors and mechanisms that could be exploited to identify autophagy-inducing chemotherapeutics that could be used as adjunctive therapy with the existing first-line anti-TB agent to shorten the duration of therapy and enhance cure rates from multidrug-resistant tuberculosis (MDR-TB) and extreme drug-resistant tuberculosis (XDR-TB).

Mycobacterium tuberculosis: Pathogenesis and therapeutic targets

Tuberculosis (TB) remains a significant public health concern in the 21st century, especially due to drug resistance, coinfection with diseases like immunodeficiency syndrome (AIDS) and coronavirus disease 2019, and the lengthy and costly treatment protocols. In this review, we summarize the pathogenesis of TB infection, therapeutic targets, and corresponding modulators, including first-line medications, current clinical trial drugs and molecules in preclinical assessment. Understanding the mechanisms of Mycobacterium tuberculosis (Mtb) infection and important biological targets can lead to innovative treatments. While most antitubercular agents target pathogen-related processes, host-directed therapy (HDT) modalities addressing immune defense, survival mechanisms, and immunopathology also hold promise. Mtb's adaptation to the human host involves manipulating host cellular mechanisms, and HDT aims to disrupt this manipulation to enhance treatment effectiveness. Our review provides valuable insights for future anti-TB drug development efforts.

Mitochondrial reactive oxygen species: double agents in Mycobacterium tuberculosis infection

In addition to housing the major energy-producing pathways in cells, mitochondria are active players in innate immune responses. One critical way mitochondria fulfill this role is by releasing damage-associated molecular patterns (mtDAMPs) that are recognized by innate sensors to activate pathways including, but not limited to, cytokine expression, selective autophagy, and cell death. Mitochondrial reactive oxygen species (mtROS) is a multifunctional mtDAMP linked to pro- and antimicrobial immune outcomes. Formed as a by-product of energy generation, mtROS links mitochondrial metabolism with downstream innate immune responses. As a result, altered cellular metabolism can change mtROS levels and impact downstream antimicrobial responses in a variety of ways. MtROS has emerged as a particularly important mediator of pathogenesis during infection with Mycobacterium tuberculosis (Mtb), an intracellular bacterial pathogen that continues to pose a significant threat to global public health. Here, we will summarize how Mtb modulates mtROS levels in infected macrophages and how mtROS dictates Mtb infection outcomes by controlling inflammation, lipid peroxidation, and cell death. We propose that mtROS may serve as a biomarker to predict tuberculosis patient outcomes and/or a target for host-directed therapeutics.

Role of Oxidative Stress in Tuberculosis Meningitis Infection in Diabetics

Tuberculosis meningitis (TBM) is a result of the invasion of the meninges with the bacilli of Mycobacterium tuberculosis (Mtb), leading to inflammation of the meninges around the brain or spinal cord. Oxidative stress occurs when the body's cells become overwhelmed with free radicals, particularly reactive oxygen species (ROS). ROS plays a significant role in the pathogenesis of TBM due to their toxic nature, resulting in impairment of the body's ability to fight off infection. ROS damages the endothelial cells and impairs the defense mechanisms of the blood-brain barrier (BBB), which contributes to CNS susceptibility to the bacteria causing TBM. Diabetes mellitus (DM) is a common condition that is characterized by the impairment of the hormone insulin, which is responsible for modulating blood glucose levels. The increased availability of glucose in individuals with diabetes results in increased cellular activity and metabolism, leading to heightened ROS production and, in turn, increased susceptibility to TBM. In this review, we summarize our current understanding of oxidative stress and its role in both TBM and DM. We further discuss how increased oxidative stress in DM can contribute to the likelihood of developing TBM and potential therapeutic approaches that may be of therapeutic value.

Impaired resolution of blood transcriptomes through tuberculosis treatment with diabetes comorbidity

BACKGROUND

People with diabetes are more likely to develop tuberculosis (TB) and to have poor TB-treatment outcomes than those without. We previously showed that blood transcriptomes in people with TB-diabetes (TB-DM) co-morbidity have excessive inflammatory and reduced interferon responses at diagnosis. It is unknown whether this persists through treatment and contributes to the adverse outcomes.

METHODS

Pulmonary TB patients recruited in South Africa, Indonesia and Romania were classified as having TB-DM, TB with prediabetes, TB-related hyperglycaemia or TB-only, based on glycated haemoglobin concentration at TB diagnosis and after 6 months of TB treatment. Gene expression in blood at diagnosis and intervals throughout treatment was measured by unbiased RNA-Seq and targeted Multiplex Ligation-dependent Probe Amplification. Transcriptomic data were analysed by longitudinal mixed-model regression to identify whether genes were differentially expressed between clinical groups through time. Predictive models of TB-treatment response across groups were developed and cross-tested.

RESULTS

Gene expression differed between TB and TB-DM patients at diagnosis and was modulated by TB treatment in all clinical groups but to different extents, such that differences remained in TB-DM relative to TB-only throughout. Expression of some genes increased through TB treatment, whereas others decreased: some were persistently more highly expressed in TB-DM and others in TB-only patients. Genes involved in innate immune responses, anti-microbial immunity and inflammation were significantly upregulated in people with TB-DM throughout treatment. The overall pattern of change was similar across clinical groups irrespective of diabetes status, permitting models predictive of TB treatment to be developed.

CONCLUSIONS

Exacerbated transcriptome changes in TB-DM take longer to resolve during TB treatment, meaning they remain different from those in uncomplicated TB after treatment completion. This may indicate a prolonged inflammatory response in TB-DM, requiring prolonged treatment or host-directed therapy for complete cure. Development of transcriptome-based biomarker signatures of TB-treatment response should include people with diabetes for use across populations.

Immune Responses in Lung Granulomas during Mtb/HIV Co-Infection: Implications for Pathogenesis and Therapy

HIV and TB are the cause of significant worldwide mortality and pose a grave danger to the global public health. TB is the leading cause of death in HIV-infected persons, with one in four deaths attributable to TB. While the majority of healthy individuals infected with M. tuberculosis (Mtb) are able to control the infection, co-infection with HIV increases the risk of TB infection progressing to TB disease by over 20-fold. While antiretroviral therapy (ART), the cornerstone of HIV care, decreases the incidence of TB in HIV-uninfected people, this remains 4- to 7-fold higher after ART in HIV-co-infected individuals in TB-endemic settings, regardless of the duration of therapy. Thus, the immune control of Mtb infection in Mtb/HIV-co-infected individuals is not fully restored by ART. We do not fully understand the reasons why Mtb/HIV-co-infected individuals maintain a high susceptibility to the reactivation of LTBI, despite an effective viral control by ART. A deep understanding of the molecular mechanisms that govern HIV-induced reactivation of TB is essential to develop improved treatments and vaccines for the Mtb/HIV-co-infected population. We discuss potential strategies for the mitigation of the observed chronic immune activation in combination with both anti-TB and anti-retroviral approaches.

Metformin: update on mechanisms of action and repurposing potential

Currently, metformin is the first-line medication to treat type 2 diabetes mellitus (T2DM) in most guidelines and is used daily by >200 million patients. Surprisingly, the mechanisms underlying its therapeutic action are complex and are still not fully understood. Early evidence highlighted the liver as the major organ involved in the effect of metformin on reducing blood levels of glucose. However, increasing evidence points towards other sites of action that might also have an important role, including the gastrointestinal tract, the gut microbial communities and the tissue-resident immune cells. At the molecular level, it seems that the mechanisms of action vary depending on the dose of metformin used and duration of treatment. Initial studies have shown that metformin targets hepatic mitochondria; however, the identification of a novel target at low concentrations of metformin at the lysosome surface might reveal a new mechanism of action. Based on the efficacy and safety records in T2DM, attention has been given to the repurposing of metformin as part of adjunct therapy for the treatment of cancer, age-related diseases, inflammatory diseases and COVID-19. In this Review, we highlight the latest advances in our understanding of the mechanisms of action of metformin and discuss potential emerging novel therapeutic uses.

Macrophage targeted polymeric curcumin nanoparticles limit intracellular survival of Mycobacterium tuberculosis through induction of autophagy and augment anti-TB activity of isoniazid in RAW 264.7 macrophages

Rapid emergence of antibiotic resistance in tuberculosis has left us with limited resources to treat and manage multi drug resistant (MDR) cases of tuberculosis, prompting the development of novel therapeutics. Mycobacterium tuberculosis (MTB) perturbs the host protective pathways for its survival, therefore host directed therapeutic (HDT) interventions offer an attractive alternative strategy. Curcumin (CMN), the principle curcuminoid from Curcuma longa is known to have anti-TB activity against MDR strains of MTB in macrophages. We discovered that treatment of CMN induced autophagy in uninfected and MTB infected macrophages which was evident by conversion of LC3-I to LC3-II and degradation of p62. Inhibition of autophagy by a pharmacological inhibitor 3-MA resulted in significant inhibition of intracellular killing activity of CMN, suggesting the involvement of autophagy in intracellular clearance of MTB. Moreover, annexin v-FITC/PI staining data suggested induction of apoptosis in uninfected and MTB infected macrophages post CMN treatment. This finding was further corroborated by up-regulated expression of pro-apoptotic proteins, Bax, cleaved caspase-3 and PARP and diminished expression of anti-apoptotic protein Bcl-2 as evaluated by immunoblotting. Using GFP-MTB H37Rv and Lysotracker Red staining we demonstrated co-localization of GFP-MTB H37Rv containing phagosome to lysosome after CMN treatment, indicating enhanced phagosome lysosome fusion. Due to poor bioavailability of CMN, its clinical use is limited, therefore to overcome this issue, CMN was encapsulated in Poly(lactic-co-glycolic) acid (PLGA) shell, resulting in polymeric CMN nano particles (ISCurNP). Flow cytometric evaluation suggested >99% uptake of ISCurNP after 3h of treatment. In BALB/c mice, oral dose of ISCurNP resulted in 6.7-fold increase in the bioavailability compared to free CMN. Moreover, ISCurNP treatment resulted in significant decrease in the intracellular survival of MTB H37Rv through induction of autophagy. Adjunct action of ISCurNP and CMN in combination with isoniazid (INH) revealed >99% decrease in intracellular survival of MTB in macrophage as compared to ISCurNP, CMN or INH alone. In conclusion, our findings suggest the role of ISCurNP as novel host directed formulation to combat both sensitive and MDR strains of MTB by induction of autophagy.

Stratification of Nontuberculous Mycobacterial Disease Risk in Type 2 Diabetes Based on Metformin Use: a Population-Based Cohort Study in South Korea

In a 1:4 case-control matched analysis of data from a nationwide population-based cohort in South Korea, we evaluated whether metformin use mitigates the risk of nontuberculous mycobacterial disease in patients with type 2 diabetes. Multivariable analysis revealed no significant association of metformin use with a diminished risk for incident nontuberculous mycobacterial disease in patients with type 2 diabetes.

Metformin Increases Cell Viability and Regulates Pro-Inflammatory Response to Mtb

Introduction

Current TB treatment regimens are pathogen-directed and can be severely compromised by the development of drug resistance. Metformin has been proposed as an adjunctive therapy for TB, however relatively little is known about how metformin modulates the cellular interaction between Mtb and macrophages. We aimed to characterize how metformin modulates Mtb growth within macrophages.

Methods

We utilized live cell tracking through time-lapse microscopy to better understand the biological effect of metformin in response to Mtb infection. Furthermore, the potent first-line anti-TB drug, isoniazid, was used as a comparator and as a companion drug.

Results

Metformin caused a 14.2-fold decrease in Mtb growth compared to the untreated control. Metformin combined with isoniazid controlled Mtb growth is slightly better than isoniazid alone. Metformin demonstrated the ability to regulate the cytokine and chemokine response over a 72 hour period, better than isoniazid only.

Conclusion

We provide novel evidence that metformin controls mycobacterial growth by increasing host cell viability, and a direct and independent pro-inflammatory response to Mtb. Understanding the impact of metformin on Mtb growth within macrophages will advance our current knowledge on metformin as an adjunctive therapy, providing a new host-directed approach to TB treatment.

Advances in immunomodulatory strategies for host-directed therapies in combating tuberculosis

Tuberculosis (TB) maintains its infamous status regarding its detrimental effect on global health, causing the highest mortality by a single infectious agent. The presence of resistance and immune compromising disease favours the disease in maintaining its footing in the health care burden despite various anti-TB drugs used to fight it. Main factors contributing to resistance and difficulty in treating disease include prolonged treatment duration (at least 6 months) and severe toxicity, which further leads to patient non-compliance, and thus a ripple effect leading to therapeutic non-efficacy. The efficacy of new regimens demonstrates that targeting host factors concomitantly with the Mycobacterium tuberculosis (M.tb) strain is urgently required. Due to the huge expenses and time required of up to 20 years for new drug research and development, drug repurposing may be the most economical, circumspective, and conveniently faster journey to embark on. Host-directed therapy (HDT) will dampen the burden of the disease by acting as an immunomodulator, allowing it to defend the body against antibiotic-resistant pathogens whilst minimizing the possibility of developing new resistance to susceptible drugs. Repurposed drugs in TB act as host-directed therapies, acclimatizing the host immune cell to the presence of TB, improving its antimicrobial activity and time taken to get rid of the disease, whilst minimizing inflammation and tissue damage. In this review, we, therefore, explore possible immunomodulatory targets, HDT immunomodulatory agents, and their ability to improve clinical outcomes whilst minimizing the risk of drug resistance, through various pathway targeting and treatment duration reduction.

The effect of metformin on influenza vaccine responses in nondiabetic older adults: a pilot trial

BACKGROUND

Aging is associated with progressive declines in immune responses leading to increased risk of severe infection and diminished vaccination responses. Influenza (flu) is a leading killer of older adults despite availability of seasonal vaccines. Geroscience-guided interventions targeting biological aging could offer transformational approaches to reverse broad declines in immune responses with aging. Here, we evaluated effects of metformin, an FDA approved diabetes drug and candidate anti-aging drug, on flu vaccination responses and markers of immunological resilience in a pilot and feasibility double-blinded placebo-controlled study.

RESULTS

Healthy older adults (non-diabetic/non-prediabetic, age: 74.4 ± 1.7 years) were randomized to metformin (n = 8, 1500 mg extended release/daily) or placebo (n = 7) treatment for 20 weeks and were vaccinated with high-dose flu vaccine after 10 weeks of treatment. Peripheral blood mononuclear cells (PBMCs), serum, and plasma were collected prior to treatment, immediately prior to vaccination, and 1, 5, and 10 weeks post vaccination. Increased serum antibody titers were observed post vaccination with no significant differences between groups. Metformin treatment led to trending increases in circulating T follicular helper cells post-vaccination. Furthermore, 20 weeks of metformin treatment reduced expression of exhaustion marker CD57 in circulating CD4 T cells.

CONCLUSIONS

Pre-vaccination metformin treatment improved some components of flu vaccine responses and reduced some markers of T cell exhaustion without serious adverse events in nondiabetic older adults. Thus, our findings highlight the potential utility of metformin to improve flu vaccine responses and reduce age-related immune exhaustion in older adults, providing improved immunological resilience in nondiabetic older adults.

Metformin Use Is Associated With Lower Mortality in Veterans With Diabetes Hospitalized With Pneumonia

BACKGROUND

Recent studies suggest that metformin use may be associated with improved infectious disease-related outcomes, whereas other papers suggest potentially worse outcomes in serious bacterial infections. Our purpose was to examine the association of prior outpatient prescription of metformin on 30- and 90-day mortality for older veterans with pre-existing diabetes hospitalized with pneumonia.

METHODS

We conducted a retrospective cohort study using national Department of Veterans Affairs data of patients ≥65 years with a prior history of diabetes who were hospitalized with pneumonia over a 10-year period (fiscal years 2002-2012.) For our primary analysis, we created a propensity score and matched metformin users to nonusers 1:1.

RESULTS

We identified 34 759 patients who met the inclusion criteria, 20.3% of whom were prescribed metformin. Unadjusted 30-day mortality was 9.6% for those who received metformin versus 13.9% in nonusers (P < .003), and 90-day mortality was 15.8% for those who received metformin versus 23.0% for nonusers (P < .0001). For the propensity score model, we matched 6899 metformin users to 6899 nonusers. After propensity matching, both 30-day (relative risk [RR]: .86; 95% confidence interval [CI]: .78-.95) and 90-day (RR: .85; 95% CI: .79-.92) mortality was significantly lower for metformin users.

CONCLUSIONS

Prior receipt of metformin was associated with significantly lower mortality after adjusting for potential confounders. Additional research is needed to examine the safety and potential benefits of metformin use in patients with respiratory infections.

Host-directed immunotherapy of viral and bacterial infections: past, present and future

The advent of COVID-19 and the persistent threat of infectious diseases such as tuberculosis, malaria, influenza and HIV/AIDS remind us of the marked impact that infections continue to have on public health. Some of the most effective protective measures are vaccines but these have been difficult to develop for some of these infectious diseases even after decades of research. The development of drugs and immunotherapies acting directly against the pathogen can be equally challenging, and such pathogen-directed therapeutics have the potential disadvantage of selecting for resistance. An alternative approach is provided by host-directed therapies, which interfere with host cellular processes required for pathogen survival or replication, or target the host immune response to infection (immunotherapies) to either augment immunity or ameliorate immunopathology. Here, we provide a historical perspective of host-directed immunotherapeutic interventions for viral and bacterial infections and then focus on SARS-CoV-2 and Mycobacterium tuberculosis, two major human pathogens of the current era, to indicate the key lessons learned and discuss candidate immunotherapeutic approaches, with a focus on drugs currently in clinical trials.

Human alveolar macrophage metabolism is compromised during Mycobacterium tuberculosis infection

Pulmonary macrophages have two distinct ontogenies: long-lived embryonically-seeded alveolar macrophages (AM) and bone marrow-derived macrophages (BMDM). Here, we show that after infection with a virulent strain of Mycobacterium tuberculosis (H37Rv), primary murine AM exhibit a unique transcriptomic signature characterized by metabolic reprogramming distinct from conventional BMDM. In contrast to BMDM, AM failed to shift from oxidative phosphorylation (OXPHOS) to glycolysis and consequently were unable to control infection with an avirulent strain (H37Ra). Importantly, healthy human AM infected with H37Ra equally demonstrated diminished energetics, recapitulating our observation in the murine model system. However, the results from seahorse showed that the shift towards glycolysis in both AM and BMDM was inhibited by H37Rv. We further demonstrated that pharmacological (e.g. metformin or the iron chelator desferrioxamine) reprogramming of AM towards glycolysis reduced necrosis and enhanced AM capacity to control H37Rv growth. Together, our results indicate that the unique bioenergetics of AM renders these cells a perfect target for Mtb survival and that metabolic reprogramming may be a viable host targeted therapy against TB.

Urinary excretion of metformin in diabetic patients with and without tuberculosis

BACKGROUND

Patients with concurrent diabetes mellitus (DM) and tuberculosis (TB) pose an increased risk of treatment failure in TB and management of DM is complicated. Anti-diabetic and anti-TB drugs may interact with on another other when co-administered. The role of anti-TB drugs on the excretion of metformin in urine has not been studied. Therefore, we carried out a study in DM patients with and without TB to compare the percentage of metformin excreted in urine.

METHODS

A total of 52 DMTB and 17 DM patients were recruited in this study from the Chennai Corporation Centres. DM and DM - TB patients were administered the prescribed anti-TB and anti-diabetic drugs (metformin (MET), glipizide (GLP),glimepiride (GLM),glibenclamide (GLB),rifampicin (RMP),isoniazid (INH), pyrazinamide (PZA) and ethambutol (EMB). DM and DMTB patients received metformin (MET) alone and in combination with sulphonylureas as diabetic drugs. The urine samples were collected from 0 to 8 hours after drug administration. Urine MET excreted in DM and DMTB patients were estimated by high performance liquid chromatography (HPLC) and percent dose was calculated.

RESULTS

The percent dose of MET excreted in urine in DMTB patients was significantly higher when compared to DM patients. There is significant difference in the percent dose of MET excreted among DM patients with and without sulphonylureas, values being 23.3 and 17.7% respectively (p = 0.044).

CONCLUSION

This is the first study to report on the percent dose of MET excretion in urine in patients with DM and DMTB receiving MET along with anti-TB drugs.

Inflammation-mediated tissue damage in pulmonary tuberculosis and host-directed therapeutic strategies

Treatment of tuberculosis (TB) involves the administration of anti-mycobacterial drugs for several months. The emergence of drug-resistant strains of Mycobacterium tuberculosis (Mtb, the causative agent) together with increased disease severity in people with co-morbidities such as diabetes mellitus and HIV have hampered efforts to reduce case fatality. In severe disease, TB pathology is largely attributable to over-exuberant host immune responses targeted at controlling bacterial replication. Non-resolving inflammation driven by host pro-inflammatory mediators in response to high bacterial load leads to pulmonary pathology including cavitation and fibrosis. The need to improve clinical outcomes and reduce treatment times has led to a two-pronged approach involving the development of novel antimicrobials as well as host-directed therapies (HDT) that favourably modulate immune responses to Mtb. HDT strategies incorporate aspects of immune modulation aimed at downregulating non-productive inflammatory responses and augmenting antimicrobial effector mechanisms to minimise pulmonary pathology and accelerate symptom resolution. HDT in combination with existing antimycobacterial agents offers a potentially promising strategy to improve the long-term outcome for TB patients. In this review, we describe components of the host immune response that contribute to inflammation and tissue damage in pulmonary TB, including cytokines, matrix metalloproteinases, lipid mediators, and neutrophil extracellular traps. We then proceed to review HDT directed at these pathways.

The Changing Paradigm of Drug-Resistant Tuberculosis Treatment: Successes, Pitfalls, and Future Perspectives

Drug-resistant tuberculosis (DR-TB) remains a global crisis due to the increasing incidence of drug-resistant forms of the disease, gaps in detection and prevention, models of care, and limited treatment options. The DR-TB treatment landscape has evolved over the last 10 years. Recent developments include the remarkable activity demonstrated by the newly approved anti-TB drugs bedaquiline and pretomanid against Mycobacterium tuberculosis. Hence, treatment of DR-TB has drastically evolved with the introduction of the short-course regimen for multidrug-resistant TB (MDR-TB), transitioning to injection-free regimens and the approval of the 6-month short regimens for rifampin-resistant TB and MDR-TB. Moreover, numerous clinical trials are under way with the aim to reduce pill burden and shorten the DR-TB treatment duration. While there have been apparent successes in the field, some challenges remain. These include the ongoing inclusion of high-dose isoniazid in DR-TB regimens despite a lack of evidence for its efficacy and the inclusion of ethambutol and pyrazinamide in the standard short regimen despite known high levels of background resistance to both drugs. Furthermore, antimicrobial heteroresistance, extensive cavitary disease and intracavitary gradients, the emergence of bedaquiline resistance, and the lack of biomarkers to monitor DR-TB treatment response remain serious challenges to the sustained successes. In this review, we outline the impact of the new drugs and regimens on patient treatment outcomes, explore evidence underpinning current practices on regimen selection and duration, reflect on the disappointments and pitfalls in the field, and highlight key areas that require continued efforts toward improving treatment approaches and rapid biomarkers for monitoring treatment response.