N-acetyl-cysteine exhibits potent anti-mycobacterial activity in addition to its known anti-oxidative functions

Adjunctive N-Acetylcysteine and Lung Function in Pulmonary Tuberculosis

BACKGROUND

Tuberculosis remains a global health concern, and half of cured patients have permanent lung injury. N-acetylcysteine (NAC) has shown beneficial antimicrobial, antioxidant, and immunomodulatory effects in preclinical tuberculosis models. We examined its effects on tuberculosis treatment outcomes.

METHODS

This prospective, randomized, controlled trial nested within the TB SEQUEL cohort study enrolled 140 adults with moderate or far-advanced tuberculosis. Participants were randomly assigned 1:1 to standard therapy with or without 1200 mg of oral NAC twice daily for days 1 to 112. Clinical evaluations, sputum culture, and spirometry were performed at specified intervals through day 168, after which participants returned to the TB SEQUEL cohort. The primary outcome was culture conversion. Secondary outcomes included whole-blood glutathione levels and lung function.

RESULTS

Participants were predominantly young, male, and human immunodeficiency virus 1-negative and had heavy sputum Mycobacterium tuberculosis (MTB) infection burdens. NAC increased glutathione levels (NAC × day interaction, 8.48; 95% confidence interval [CI], 1.93 to 15.02) but did not increase stable culture conversion (hazard ratio, 0.84; 95% CI, 0.59 to 1.20; P=0.33). NAC treatment was associated with improved recovery of lung function (NAC × month, 0.49 [95% CI, 0.02 to 0.95] and 0.42 [95% CI, -0.06 to 0.91] for forced vital capacity and forced expiratory volume in the first second, respectively, as percentages of predicted values). The effects of NAC on lung function were greatest in participants with severe baseline lung impairment and appeared to persist beyond the period of NAC administration. Rates of serious or grade 3 to 4 nonserious adverse events did not differ between the groups.

CONCLUSIONS

Despite increasing whole-blood glutathione levels, NAC did not affect eradication of MTB infection in adults with pulmonary tuberculosis that was moderate to far advanced. Secondary outcomes of lung function showed changes that merit further investigation. (Funded by TB SEQUEL grant 01KA1613 of the German Ministry for Education and Research, the Health Africa Project, and the German Center for Infection Research; ClinicalTrials.gov number, NCT03702738.).

In vitro effects of N-acetylcysteine in combination with antifungal agents against Malassezia pachydermatis isolated from canine otitis externa

BACKGROUND

Many clinicians prescribe antifungal agents to treat canine otitis externa (OE). However, studies evaluating the antifungal effects of N-acetylcysteine (NAC) and its combinations are limited.

HYPOTHESIS/OBJECTIVES

The aim of this study was to evaluate the antifungal effects of NAC alone and in combination with other antifungal agents against Malassezia pachydermatis isolated from canine OE.

MATERIALS AND METHODS

M. pachydermatis samples were collected from 13 dogs with OE. The final concentration of the inoculum suspensions of M. pachydermatis was 1-5 × 106 colony forming units/mL. The concentrations of the test compounds ketoconazole (KTZ), terbinafine (TER), nystatin (NYS) and NAC were 0.02-300 µg/mL, 0.04-80 µg/mL, 0.16-40 µg/mL and 1.25-20 mg/mL, respectively. The minimum inhibitory concentration (MIC) was measured to evaluate the susceptibility of the M. pachydermatis to KTZ, TER, NYS and NAC. The checkerboard testing method and fractional inhibitory concentration index were used to evaluate the effect of NAC in combination with KTZ, TER and NYS against M. pachydermatis.

RESULTS

The MIC90 values of M. pachydermatis were 4.6875-9.375 µg/mL, 1.25 µg/mL, 5-10 µg/mL and 10 mg/mL for KTZ, TER, NYS and NAC, respectively. The synergistic effects of KTZ, TER and NYS with NAC were identified in 0/13, 2/13 and 0/13 isolates, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

NAC had an antifungal effect against M. pachydermatis but did not exert synergistic effects when used with KTZ, TER and NYS. Thus, the use of NAC alone as a topical solution could be considered an effective treatment option for canine OE involving M. pachydermatis.

Anti-Inflammatory and Anti-Oxidant Properties of N-Acetylcysteine: A Fresh Perspective

N-acetyl-L-cysteine (NAC) was initially introduced as a treatment for mucus reduction and widely used for chronic respiratory conditions associated with mucus overproduction. However, the mechanism of action for NAC extends beyond its mucolytic activity and is complex and multifaceted. Contrary to other mucoactive drugs, NAC has been found to exhibit antioxidant, anti-infective, and anti-inflammatory activity in pre-clinical and clinical reports. These properties have sparked interest in its potential for treating chronic lung diseases, including chronic obstructive pulmonary disease (COPD), bronchiectasis (BE), cystic fibrosis (CF), and idiopathic pulmonary fibrosis (IPF), which are associated with oxidative stress, increased levels of glutathione and inflammation. NAC's anti-inflammatory activity is noteworthy, and it is not solely secondary to its antioxidant capabilities. In ex vivo models of COPD exacerbation, the anti-inflammatory effects have been observed even at very low doses, especially with prolonged treatment. The mechanism involves the inhibition of the activation of NF-kB and neurokinin A production, resulting in a reduction in interleukin-6 production, a cytokine abundantly present in the sputum and breath condensate of patients with COPD and correlates with the number of exacerbations. The unique combination of mucolytic, antioxidant, anti-infective, and anti-inflammatory properties positions NAC as a safe, cost-effective, and efficacious therapy for a plethora of respiratory conditions.

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.

Review canine tuberculosis - An emerging concern

Canine mycobacterial disease was first recognised over 100 years ago but is now an emerging concern. All reported cases of tuberculous disease in dogs have been caused by infection with one of three Mycobacterium tuberculosis-complex (MTBC) organisms (M. tuberculosis, Mycobacterium bovis, and Mycobacterium microti). Molecular PCR and interferon-gamma release assays offer alternative or complementary diagnostic pathways to that of specialist culture, which is limited by availability, sensitivity, and the time it takes to get a result. Optimised triple antimicrobial protocols offer an excellent chance of a successful outcome in dogs where treatment can be considered and is attempted. In this review, the clinical presentation, diagnosis, treatment, and prognosis of canine tuberculosis are discussed.

BACH1 promotes tissue necrosis and Mycobacterium tuberculosis susceptibility

Oxidative stress triggers ferroptosis, a form of cellular necrosis characterized by iron-dependent lipid peroxidation, and has been implicated in Mycobacterium tuberculosis (Mtb) pathogenesis. We investigated whether Bach1, a transcription factor that represses multiple antioxidant genes, regulates host resistance to Mtb. We found that BACH1 expression is associated clinically with active pulmonary tuberculosis. Bach1 deletion in Mtb-infected mice increased glutathione levels and Gpx4 expression that inhibit lipid peroxidation. Bach1-/- macrophages exhibited increased resistance to Mtb-induced cell death, while Mtb-infected Bach1-deficient mice displayed reduced bacterial loads, pulmonary necrosis and lipid peroxidation concurrent with increased survival. Single-cell RNA-seq analysis of lungs from Mtb-infected Bach1-/- mice revealed an enrichment of genes associated with ferroptosis suppression. Bach1 depletion in Mtb-infected B6.Sst1S mice that display human-like necrotic lung pathology also markedly reduced necrosis and increased host resistance. These findings identify Bach1 as a key regulator of cellular and tissue necrosis and host resistance in Mtb infection.

An Update to Novel Therapeutic Options for Combating Tuberculosis: Challenges and Future Prospectives

Drug repurposing is an ongoing and clever strategy that is being developed to eradicate tuberculosis amid challenges, of which one of the major challenges is the resistance developed towards antibiotics used in standard directly observed treatment, short-course regimen. Surpassing the challenges in developing anti-tuberculous drugs, some novel host-directed therapies, repurposed drugs, and drugs with novel targets are being studied, and few are being approved too. After almost 4 decades since the approval of rifampicin as a potent drug for drugsusceptible tuberculosis, the first drug to be approved for drug-resistant tuberculosis is bedaquiline. Ever since the urge to drug discovery has been at a brisk as this milestone in tuberculosis treatment has provoked the hunt for novel targets in tuberculosis. Host-directed therapy and repurposed drugs are in trend as their pharmacological and toxicological properties have already been researched for some other diseases making the trial facile. This review discusses the remonstrance faced by researchers in developing a drug candidate with a novel target, the furtherance in tuberculosis research, novel anti-tuberculosis agents approved so far, and candidates on trial including the host-directed therapy, repurposed drug and drug combinations that may prove to be potential in treating tuberculosis soon, aiming to augment the awareness in this context to the imminent researchers.

Selection and validation of genes related to oxidative stress production and clearance in macrophages infected with Mycobacterium tuberculosis

Background

In the fight against tuberculosis, besides chemotherapy, the regulation of oxidative stress (OS) has also aroused people's interest in host-oriented therapy. However, there is limited research on the genes involved in reactive oxygen species (ROS) production and clearance in macrophages infected with Mycobacterium tuberculosis (MTB). This study analyzes and explores this to provide a basis for exploring new targets for antituberculosis treatments.

Methods

We established a macrophage model infected with MTB, counted intracellular bacteria, and determined the ROS produced using flow cytometry. We conducted ribonucleic acid sequencing, screened differentially expressed genes through transcriptomic methods, and validated the expression of them through reverse transcription-quantitative polymerase chain reaction.

Results

The ROS of macrophages increased with intracellular bacteria at 4 h after infection with MTB and reached its peak at 48 h, surpassing the uninfected macrophages (p < 0.05). A total of 1,613 differentially expressed genes were identified after infection with MTB, of which 458 were associated with ROS, with over 50% involved in the response of organelles and biological processes to stimuli. We analyzed and identified six genes. After macrophage infection with MTB, the expression of CAMK2B increased, whereas the expression of CYBB decreased (p < 0.05). The expression of GPX3 and SOD2 increased, whereas the expression of CAT decreased (p < 0.05).

Conclusion

The ROS-related differentially expressed genes between MTB infected and uninfected macrophages may be related to some organelles and involved in various biological processes, molecular functions, and signaling pathways. Among them, CAMK2B, GPX3, and SOD2 may be related to ROS.

Excessive N-acetylcysteine exaggerates glutathione redox homeostasis and apoptosis during acetaminophen exposure in Huh-7 human hepatoma cells

Acetaminophen (APAP) hepatotoxicity is one of the biggest drawbacks of this relatively safe and widely used drug. In addition to its hepatotoxicity, APAP also cause comparable levels of toxicity on human hepatoma cells. Here we show activation of the intrinsic caspase-9/3 pathway of apoptosis followed by gasdermin E (GSDME) cleavage and subsequent ballooning in APAP (10 mM, 72 h)-treated Huh-7 human hepatocarcinoma cells. N-acetylcysteine (NAC), an antioxidant currently used as an antidote for APAP overdose, does not alleviate APAP toxicity in Huh-7 cells; NAC overdose (10 mM) rather aggravates APAP toxicity. NAC overdose not only aggravates cell death, but also decreases the cellular GSH/GSSG ratio, an indicator of redox homeostasis of glutathione. These results show for the first time that APAP-induced apoptosis in hepatoma cells is followed by secondary necrosis via the caspase-3/GSDME pathway. NAC overdose (10 mM) not only worsens the glutathione redox status, but also accelerates this pathway.

Biapenem, a Carbapenem Antibiotic, Elicits Mycobacteria Specific Immune Responses and Reduces the Recurrence of Tuberculosis

Tuberculosis (TB) still tops the list of global health burdens even after COVID-19. However, it will sooner transcend the current pandemic due to the prevailing risk of reactivation of latent TB in immunocompromised individuals. The indiscriminate misuse and overuse of antibiotics have resulted in the emergence of deadly drug-resistant variants of Mycobacterium tuberculosis (M.tb). This study aims to characterize the functionality of the carbapenem antibiotic-Biapenem (BPM) in generating long-lasting immunity against TB. BPM treatment significantly boosted the activation status of the innate immune arm-macrophages by augmenting p38 signaling. Macrophages further primed and activated the adaptive immune cells CD4+ and CD8+ T-cells in the lung and spleen of the infected mice model. Furthermore, BPM treatment significantly amplified the polarization of T lymphocytes toward inflammatory subsets, such as Th1 and Th17. The treatment also helped generate a long-lived central memory T-cell subset. The generation of central memory T lymphocyte subset upon BPM treatment in the murine model led to a significant curtailing in the recurrence of TB due to reactivation and reinfection. These results suggest the potentiality of BPM as a potent adjunct immunomodulator to improve host defense against M.tb by enriching long-term protective memory cells. IMPORTANCE Tuberculosis (TB) caused by Mycobacterium tuberculosis (M.tb) tops the list of infectious killers around the globe. The emergence of drug-resistant variants of M.tb has been a major hindrance toward realizing the "END TB" goal. Drug resistance has amplified the global burden toward the quest for novel drug molecules targeting M.tb. Host-directed therapy (HDT) offers a lucrative alternative to tackle emerging drug resistance and disease relapse by strengthening the host's immunity. Through our present study, we have tried to characterize the functionality of the carbapenem antibiotic-Biapenem (BPM). BPM treatment significantly augmented long-lasting immunity against TB by boosting the innate and adaptive immune arms. The generation of long-lived central memory T lymphocyte subset significantly improved the disease outcome and provided sterilizing immunity in the murine model of TB. The present investigation's encouraging results have helped us depict BPM as a potent adjunct immunomodulator for treating TB.

Nitric oxide-loaded nano- and microparticle platforms serving as potential new antifungal therapeutics

Fungal diseases are a leading threat to human health, especially in individuals with compromised immunity. Although there have been recent important advances in antifungal drug development, antifungal resistance, drug-drug interactions and difficulties in delivery remain major challenges. Among its pleiotropic actions, nitric oxide (NO) is a key molecule in host defense. We have developed a flexible nanoparticle platform that delivers sustained release of NO and have demonstrated the platform's efficacy against diverse bacteria as well as some fungal species. In this work, we investigate the effects of two NO-releasing particles against a panel of important human yeast. Our results demonstrate that the compounds are both effective against diverse yeast, including ascomycota and basidiomycota species, and that NO-releasing particles may be a potent addition to our armamentarium for the treatment of focal and disseminated mycoses.

N-acetylcysteine modulates redox imbalance and inflammation in macrophages and mice exposed to formaldehyde

This study aimed to evaluate the protective role of N-acetylcysteine (NAC) in cells and mice exposed to formaldehyde. For the in vitro study, J774A.1 macrophages cells were incubated for 8, 16 and 24 h with formaldehyde or NAC to assess cell viability and reactive oxygen species (ROS). In the in vivo study, C57BL/6 mice (n = 48) were divided into 6 groups: control (CG), vehicle (VG) that received saline by orogastric gavage, a group exposed to formaldehyde 1% (FG) and formaldehyde exposed groups that received NAC at doses of 100, 150 and 200 mg/Kg (FN100, FN150 and FN200) for a period of 5 days. In vitro, formaldehyde promoted a decrease in cell viability and increased ROS, while NAC reduced formaldehyde-induced ROS production. Animals exposed to formaldehyde presented higher leukocyte counts in the blood and in the bronchoalveolar lavage fluid, and promoted secretion of inflammatory markers IL-6, IL-15, and IL-10. The exposure to formaldehyde also promoted redox imbalance and oxidative damage characterized by increased activities of superoxide dismutase, catalase, decreased GSH/GSSG ratio, as well as it increased levels of protein carbonyls and lipid peroxidation. NAC administration after formaldehyde exposure attenuated oxidative stress markers, secretion of inflammatory mediators and lung inflammation. In conclusion, both in in vitro and in vivo models, NAC administration exerted protective effects, which modulated the inflammatory response and redox imbalance, thus preventing the development airway injury induced by formaldehyde exposure.

Nanosized Drug Delivery Systems to Fight Tuberculosis

Tuberculosis (TB) is currently the second deadliest infectious disease. Existing antitubercular therapies are long, complex, and have severe side effects that result in low patient compliance. In this context, nanosized drug delivery systems (DDSs) have the potential to optimize the treatment's efficiency while reducing its toxicity. Hundreds of publications illustrate the growing interest in this field. In this review, the main challenges related to the use of drug nanocarriers to fight TB are overviewed. Relevant publications regarding DDSs for the treatment of TB are classified according to the encapsulated drugs, from first-line to second-line drugs. The physicochemical and biological properties of the investigated formulations are listed. DDSs could simultaneously (i) optimize the therapy's antibacterial effects; (ii) reduce the doses; (iii) reduce the posology; (iv) diminish the toxicity; and as a global result, (v) mitigate the emergence of resistant strains. Moreover, we highlight that host-directed therapy using nanoparticles (NPs) is a recent promising trend. Although the research on nanosized DDSs for TB treatment is expanding, clinical applications have yet to be developed. Most studies are only dedicated to the development of new formulations, without the in vivo proof of concept. In the near future, it is expected that NPs prepared by "green" scalable methods, with intrinsic antibacterial properties and capable of co-encapsulating synergistic drugs, may find applications to fight TB.

Use of N-acetylcysteine as treatment adjuvant regulates immune response in visceral leishmaniasis: Pilot clinical trial and in vitro experiments

This investigation aimed to assess the effect of N-acetylcysteine (NAC) as an adjuvant treatment to alleviate visceral leishmaniasis (VL). The present work includes both blinded randomized clinical intervention and experimental in vitro studies. The clinical trial included 60 patients with VL randomly allocated into two groups: a test group (n = 30) treated with meglumine antimoniate plus NAC (SbV + NAC) and a control group (n = 30) treated with meglumine antimoniate only (SbV). The primary outcome was clinical cure (absence of fever, spleen and liver sizes reduction, and hematological improvement) in 180 days. The cure rate did not differ between the groups; both groups had similar results in all readout indices. The immunological parameters of the patients treated with SbV + NAC showed higher sCD40L in sera during treatment, and the levels of sCD40L were negatively correlated with Interleukin-10 (IL-10) serum levels. In addition, data estimation showed a negative correlation between the sCD40L levels and the spleen size in patients with VL. For the in vitro experiments, peripheral blood mononuclear cells (PBMCs) or PBMC-derived macrophages from healthy donors were exposed to soluble Leishmania antigen (SLA) or infected with stationary promastigotes of Leishmania infantum in the presence or absence of NAC. Results revealed that NAC treatment of SLA-stimulated PBMCs reduces the frequency of monocytes producing IL-10 and lowers the frequency of CD4+ and CD8+ T cells expressing (pro-)inflammatory cytokines. Together, these results suggest that NAC treatment may modulate the immune response in patients with VL, thus warranting additional investigations to support its case use as an adjuvant to antimony therapy for VL.

Modulating macrophage function to reinforce host innate resistance against Mycobacterium avium complex infection

Mycobacterium avium complex (MAC) is the main causative agent of infectious diseases in humans among nontuberculous mycobacteria (NTM) that are ubiquitous organisms found in environmental media such as soil as well as in domestic and natural waters. MAC is a primary causative agent of NTM-lung disease that threaten immunocompromised or structural lung disease patients. The incidence and the prevalence of M. tuberculosis infection have been reduced, while MAC infections and mortality rates have increased, making it a cause of global health concern. The emergence of drug resistance and the side effects of long-term drug use have led to a poor outcome of treatment regimens against MAC infections. Therefore, the development of host-directed therapy (HDT) has recently gained interest, aiming to accelerate mycobacterial clearance and reversing lung damage by employing the immune system using a novel adjuvant strategy to improve the clinical outcome of MAC infection. Therefore, in this review, we discuss the innate immune responses that contribute to MAC infection focusing on macrophages, chief innate immune cells, and host susceptibility factors in patients. We also discuss potential HDTs that can act on the signaling pathway of macrophages, thereby contributing to antimycobacterial activity as a part of the innate immune response during MAC infection. Furthermore, this review provides new insights into MAC infection control that modulates and enhances macrophage function, promoting host antimicrobial activity in response to potential HDTs and thus presenting a deeper understanding of the interactions between macrophages and MACs during infection.

Impact of N-Acetyl Cysteine (NAC) on Tuberculosis (TB) Patients-A Systematic Review

Sustained TB infection overproduces reactive oxygen species (ROS) as a host defense mechanism. Research shows ROS is destructive to lung tissue. Glutathione (GSH) neutralizes ROS, although it is consumed. NAC is a precursor of GSH synthesis, and administering an appropriate dose of NAC to patients with respiratory conditions may enhance lung recovery and replenish GSH. The present review searched for articles reporting on the effects of NAC in TB treatment from 1960 to 31 May 2022. The PICO search strategy was used in Google Scholar, PubMed, SciFinder, and Wiley online library databases. The COVIDENCE tool was used to delete inappropriate content. We eventually discovered five clinical trials, one case report, seven reviews, in vitro research, and four experimental animal studies from the twenty-four accepted articles. The use of NAC resulted in increased GSH levels, decreased treatment time, and was safe with minimal adverse events. However, the evidence is currently insufficient to estimate the overall effects of NAC, thus the study warrants more NAC clinical trials to demonstrate its effects in TB treatment.

GPX4 regulates cellular necrosis and host resistance in Mycobacterium tuberculosis infection

Cellular necrosis during Mycobacterium tuberculosis (Mtb) infection promotes both immunopathology and bacterial dissemination. Glutathione peroxidase-4 (Gpx4) is an enzyme that plays a critical role in preventing iron-dependent lipid peroxidation-mediated cell death (ferroptosis), a process previously implicated in the necrotic pathology seen in Mtb-infected mice. Here, we document altered GPX4 expression, glutathione levels, and lipid peroxidation in patients with active tuberculosis and assess the role of this pathway in mice genetically deficient in or overexpressing Gpx4. We found that Gpx4-deficient mice infected with Mtb display substantially increased lung necrosis and bacterial burdens, while transgenic mice overexpressing the enzyme show decreased bacterial loads and necrosis. Moreover, Gpx4-deficient macrophages exhibited enhanced necrosis upon Mtb infection in vitro, an outcome suppressed by the lipid peroxidation inhibitor, ferrostatin-1. These findings provide support for the role of ferroptosis in Mtb-induced necrosis and implicate the Gpx4/GSH axis as a target for host-directed therapy of tuberculosis.

Gene expression, levels and polymorphism (Ala16Val) of Mitochondrial Superoxide Dismutase in Tuberculosis patients of Rajasthan

BACKGROUND

Infectious diseases cause redox imbalance and oxidative stress (OS) in host. Superoxide Dismutases(SOD) decrease this OS. SOD2 gene polymorphism can influence the expression and levels of enzyme.

AIM

To investigate the association of genetic polymorphism of MnSOD with enzyme levels and mRNA expression in TB patients.

METHODS

A total of 87 TB patients and 85 healthy individuals participated in the study. The serum SOD2 levels were measured by ELISA. Gene polymorphism was analysed using PCR-RFLP with BsaW1 as the restriction enzyme. Expression was studied by Real-TimePCR. Statistical significance was determined using the Mann-Whitney, Chi-square and Kruskal-Wallis tests and p value < 0.05 was considered statistically significant.

RESULTS

The median(IQR) serum SOD2 levels of TB patients were lower than those of healthy subjects (4.64(6.48) vs 11.35(20.36)ng/mL respectively,p < 0.001). SOD2 expression was significantly down-regulated in TB patients with a fold change value of 0.312. The Val/Val genotype was higher in the patient group than healthy subjects (36.8% vs 23.5%). However, the difference observed between serum SOD2 levels and mRNA expression in the different genotypes were statistically non-significant.

CONCLUSION

Significant difference was found between levels and expression of SOD2 in TB patients and healthy controls, but not for SOD2 gene polymorphism.

Fluoroquinolone heteroresistance, antimicrobial tolerance, and lethality enhancement

With tuberculosis, the emergence of fluoroquinolone resistance erodes the ability of treatment to interrupt the progression of MDR-TB to XDR-TB. One way to reduce the emergence of resistance is to identify heteroresistant infections in which subpopulations of resistant mutants are likely to expand and make the infections fully resistant: treatment modification can be instituted to suppress mutant enrichment. Rapid DNA-based detection methods exploit the finding that fluoroquinolone-resistant substitutions occur largely in a few codons of DNA gyrase. A second approach for restricting the emergence of resistance involves understanding fluoroquinolone lethality through studies of antimicrobial tolerance, a condition in which bacteria fail to be killed even though their growth is blocked by lethal agents. Studies with Escherichia coli guide work with Mycobacterium tuberculosis. Lethal action, which is mechanistically distinct from blocking growth, is associated with a surge in respiration and reactive oxygen species (ROS). Mutations in carbohydrate metabolism that attenuate ROS accumulation create pan-tolerance to antimicrobials, disinfectants, and environmental stressors. These observations indicate the existence of a general death pathway with respect to stressors. M. tuberculosis displays a variation on the death pathway idea, as stress-induced ROS is generated by NADH-mediated reductive stress rather than by respiration. A third approach, which emerges from lethality studies, uses a small molecule, N-acetyl cysteine, to artificially increase respiration and additional ROS accumulation. That enhances moxifloxacin lethality with M. tuberculosis in culture, during infection of cultured macrophages, and with infection of mice. Addition of ROS stimulators to fluoroquinolone treatment of tuberculosis constitutes a new direction for suppressing the transition of MDR-TB to XDR-TB.

Host-directed therapies in pulmonary tuberculosis: Updates on anti-inflammatory drugs

Tuberculosis (TB) is a lethal disease and remains one of the top ten causes of mortality by an infectious disease worldwide. It can also result in significant morbidity related to persistent inflammation and tissue damage. Pulmonary TB treatment depends on the prolonged use of multiple drugs ranging from 6 months for drug-susceptible TB to 6-20 months in cases of multi-drug resistant disease, with limited patient tolerance resulting from side effects. Treatment success rates remain low and thus represent a barrier to TB control. Adjunct host-directed therapy (HDT) is an emerging strategy in TB treatment that aims to target the host immune response to Mycobacterium tuberculosis in addition to antimycobacterial drugs. Combined multi-drug treatment with HDT could potentially result in more effective therapies by shortening treatment duration, improving cure success rates and reducing residual tissue damage. This review explores the rationale and challenges to the development and implementation of HDTs through a succinct report of the medications that have completed or are currently being evaluated in ongoing clinical trials.

Heme oxygenase-1 modulates ferroptosis by fine-tuning levels of intracellular iron and reactive oxygen species of macrophages in response to Bacillus Calmette-Guerin infection

Macrophages are the host cells and the frontline defense against Mycobacterium tuberculosis (Mtb) infection, and the form of death of infected macrophages plays a pivotal role in the outcome of Mtb infections. Ferroptosis, a programmed necrotic cell death induced by overwhelming lipid peroxidation, was confirmed as one of the mechanisms of Mtb spread following infection and the pathogenesis of tuberculosis (TB). However, the mechanism underlying the macrophage ferroptosis induced by Mtb infection has not yet been fully understood. In the present study, transcriptome analysis revealed the upregulation of heme oxygenase-1 (HMOX1) and pro-ferroptosis cytokines, but downregulation of glutathione peroxidase 4 (GPX4) and other key anti-lipid peroxidation factors in the peripheral blood of both patients with extra-pulmonary tuberculosis (EPTB) and pulmonary tuberculosis (PTB). This finding was further corroborated in mice and RAW264.7 murine macrophage-like cells infected with Bacillus Calmette-Guerin (BCG). A mechanistic study further demonstrated that heme oxygenase-1 protein (HO-1) regulated the production of reactive oxygen species (ROS) and iron metabolism, and ferroptosis in BCG-infected murine macrophages. The knockdown of Hmox1 by siRNA resulted in a significant increase of intracellular ROS, Fe2+, and iron autophagy-mediated factor Ncoa4, along with the reduction of antioxidant factors Gpx4 and Fsp1 in macrophages infected with BCG. The siRNA-mediated knockdown of Hmox1 also reduced cell survival rate and increased the release of intracellular bacteria in BCG-infected macrophages. By contrast, scavenging ROS by N-acetyl cysteine led to the reduction of intracellular ROS, Fe2+, and Hmox1 concentrations, and subsequently inhibited ferroptosis and the release of intracellular BCG in RAW264.7 cells infected with BCG. These findings suggest that HO-1 is an essential regulator of Mtb-induced ferroptosis, which regulates ROS production and iron accretion to alter macrophage death against Mtb infections.

Moxifloxacin-Mediated Killing of Mycobacterium tuberculosis Involves Respiratory Downshift, Reductive Stress, and Accumulation of Reactive Oxygen Species

Moxifloxacin is central to treatment of multidrug-resistant tuberculosis. Effects of moxifloxacin on the Mycobacterium tuberculosis redox state were explored to identify strategies for increasing lethality and reducing the prevalence of extensively resistant tuberculosis. A noninvasive redox biosensor and a reactive oxygen species (ROS)-sensitive dye revealed that moxifloxacin induces oxidative stress correlated with M. tuberculosis death. Moxifloxacin lethality was mitigated by supplementing bacterial cultures with an ROS scavenger (thiourea), an iron chelator (bipyridyl), and, after drug removal, an antioxidant enzyme (catalase). Lethality was also reduced by hypoxia and nutrient starvation. Moxifloxacin increased the expression of genes involved in the oxidative stress response, iron-sulfur cluster biogenesis, and DNA repair. Surprisingly, and in contrast with Escherichia coli studies, moxifloxacin decreased expression of genes involved in respiration, suppressed oxygen consumption, increased the NADH/NAD⁺ ratio, and increased the labile iron pool in M. tuberculosis. Lowering the NADH/NAD⁺ ratio in M. tuberculosis revealed that NADH-reductive stress facilitates an iron-mediated ROS surge and moxifloxacin lethality. Treatment with N-acetyl cysteine (NAC) accelerated respiration and ROS production, increased moxifloxacin lethality, and lowered the mutant prevention concentration. Moxifloxacin induced redox stress in M. tuberculosis inside macrophages, and cotreatment with NAC potentiated the antimycobacterial efficacy of moxifloxacin during nutrient starvation, inside macrophages, and in mice, where NAC restricted the emergence of resistance. Thus, NADH-reductive stress contributes to moxifloxacin-mediated killing of M. tuberculosis, and the respiration stimulator (NAC) enhances lethality and suppresses the emergence of drug resistance.

TREM2 Promotes Immune Evasion by Mycobacterium tuberculosis in Human Macrophages

Macrophage surface receptors are critical for pathogen defense, as they are the gatekeepers for pathogen entry and sensing, which trigger robust immune responses. TREM2 (triggering receptor expressed on myeloid cells 2) is a transmembrane surface receptor that mediates anti-inflammatory immune signaling. A recent study showed that TREM2 is a receptor for mycolic acids in the mycobacterial cell wall and inhibits macrophage activation. However, the underlying functional mechanism of how TREM2 regulates the macrophage antimycobacterial response remains unclear. Here, we show that Mycobacterium tuberculosis, the causative agent for tuberculosis, specifically binds to human TREM2 to disable the macrophage antibacterial response. Live but not killed mycobacteria specifically trigger the upregulation of TREM2 during macrophage infection through a mechanism dependent on STING (the stimulator of interferon genes). TREM2 facilitated uptake of M. tuberculosis into macrophages and is responsible for blocking the production of tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and reactive oxygen species (ROS), while enhancing the production of interferon-β (IFN-β) and IL-10. TREM2-mediated blockade of ROS production promoted the survival of M. tuberculosis within infected macrophages. Consistent with this, genetic deletion or antibody-mediated neutralization of TREM2 reduced the intracellular survival of M. tuberculosis through enhanced production of ROS. Importantly, inhibition of type I IFN signaling in TREM2-overexpressing macrophages restored the ability of these cells to produce inflammatory cytokines and ROS, resulting in normal levels of intracellular bacteria killing. Collectively, our study identifies TREM2 as an attractive host receptor for host-directed antimycobacterial therapeutics. IMPORTANCE Mycobacterium tuberculosis is one of the most ancient bacterial pathogens and remains the leading cause of death from a single bacterial agent. The success of M. tuberculosis relies greatly on its ability to parasitize and disable its host macrophages. Previous studies have found that M. tuberculosis uses its unique cell wall lipids to manipulate the immune response by binding to specific surface receptors on macrophages. Our study reveals that M. tuberculosis binds to TREM2, an immunomodulatory receptor expressed on macrophages, to facilitate a "silent" mode of entry. Increased levels of TREM2 triggered by intracellular sensing of M. tuberculosis promoted the intracellular survival of M. tuberculosis through type I IFN-driven inhibition of reactive oxygen species (ROS) and proinflammatory cytokine production. Importantly, deletion of TREM2 reversed the effects of "silent" entry and resulted in increased production of inflammatory cytokines, generation of ROS, and cell death. As such, antibody-mediated or pharmacological targeting of TREM2 could be a promising strategy for novel treatments against M. tuberculosis infection.

The Impact of Alcohol Use Disorder on Tuberculosis: A Review of the Epidemiology and Potential Immunologic Mechanisms

Globally, an estimated 107 million people have an alcohol use disorder (AUD) leading to 2.8 million premature deaths each year. Tuberculosis (TB) is one of the leading causes of death globally and over 8% of global TB cases are estimated to be attributable to AUD. Social determinants of health such as poverty and undernutrition are often shared among those with AUD and TB and could explain the epidemiologic association between them. However, recent studies suggest that these shared risk factors do not fully account for the increased risk of TB in people with AUD. In fact, AUD has been shown to be an independent risk factor for TB, with a linear increase in the risk for TB with increasing alcohol consumption. While few studies have focused on potential biological mechanisms underlying the link between AUD and TB, substantial overlap exists between the effects of alcohol on lung immunity and the mechanisms exploited by Mycobacterium tuberculosis (Mtb) to establish infection. Alcohol misuse impairs the immune functions of the alveolar macrophage, the resident innate immune effector in the lung and the first line of defense against Mtb in the lower respiratory tract. Chronic alcohol ingestion also increases oxidative stress in the alveolar space, which could in turn facilitate Mtb growth. In this manuscript, we review the epidemiologic data that links AUD to TB. We discuss the existing literature on the potential mechanisms by which alcohol increases the risk of TB and review the known effects of alcohol ingestion on lung immunity to elucidate other mechanisms that Mtb may exploit. A more in-depth understanding of the link between AUD and TB will facilitate the development of dual-disease interventions and host-directed therapies to improve lung health and long-term outcomes of TB.

TB patients: Is sputum disinfection important?

BACKGROUND

Patients with pulmonary tuberculosis (TB) may produce large amount of infectious sputum which needs to be handled carefully both in health care and household settings. As mycobacteria may survive for long duration in sputum; proper collection, disinfection and disposal is necessary to avoid potential disease transmission. We aimed to assess the efficacy of bedside disinfectant treatment of sputum produced by TB patients using easily available disinfectants that can be used both in TB wards and household settings, to sterilize the infected sputum and compared it with sputum without disinfectant treatment.

METHODS

It was a prospective case control study. Sputum of total 95 patients with sputum smear positive pulmonary tuberculosis was collected in sputum containers with lids. Patients on anti-tubercular treatment for more than 2 weeks were excluded. Each patient was given 3 sterile sputum containers to expectorate, Container A containing 5% Phenol solution, Container B containing 4.8% Chloroxylenol and Container C without any disinfectant, acting as a control. Thick sputum was liquified with Mucolytic agent N-acetyl cysteine (NAC). Aliquots of the sputum were sent for culture in Lowenstein-Jensen medium on day 0 (to confirm alive mycobacteria) and on day 1 i.e., after 24 hours (to evaluate effective sterilization). Drug resistance testing was done on all grown mycobacteria.

RESULTS

If the samples on day 0 did not grow mycobacteria (indicating non-viable mycobacteria) or day 1 sample grew contaminants in any of the three containers, they were excluded from the analysis (15/95). In remaining 80 patients, bacilli were alive on day 0 and remained alive even after 24 hours (day 1) in control samples (without disinfectants). The sputum was effectively disinfected resulting in no growth after 24 hours (day 1) in 71/80 (88.75%) containing 5% Phenol and 72/80 (90%) with 4.8% Chloroxylenol. The efficacy of disinfection was 71/73 (97.2%) and 72/73 (98.6%) for drug sensitive mycobacteria respectively. The mycobacteria however remained alive with these disinfectants in all 7 samples of drug-resistant mycobacteria with an efficacy of 0%.

CONCLUSION

We recommend use of simple disinfectants like 5% Phenol or 4.8% Chloroxylenol for safe disposal of sputum of pulmonary tuberculosis patients. It is necessary as sputum collected without disinfection remained infectious after 24 hours. Resistance of all drug resistant mycobacteria to disinfectants was a novel chance finding. This needs further confirmatory studies.

Inhalation potential of N-Acetylcysteine loaded PLGA nanoparticles for the management of tuberculosis: In vitro lung deposition and efficacy studies

Several studies have stated that mucus is a critical hurdle for drug delivery to the mucosal tissues. As a result, Polymeric nanoparticles that can overcome mucus barriers are gaining popularity for controlled drug delivery into intra-macrophages to attain high intracellular drug concentration. The present study was aimed to fabricate inhalable N-acetylcysteine (NAC) modified PLGA mucus penetrating particles using the double emulsion method (w/o/w) for target delivery to alveolar macrophages and minimize the dose-related adverse effects, efficiently encapsulate hydrophilic drug, sustain the release profile and prolong the retention time for the management of tuberculosis. Among the numerous formulations, the drug/polymer ratio of 1:10 with 0.50% PVA concentration and sonication time for 2 ​min ​s was chosen for further research. The formulated nanoparticles had a mean particle size of 307.50 ​± ​9.54 ​nm, PDI was 0.136 ​± ​0.02, zeta potential about -11.3 ​± ​0.4 ​mV, decent entrapment efficiency (55.46 ​± ​2.40%), drug loading (9.05 ​± ​0.22%), and excellent flowability. FTIR confirmed that NAC and PLGA were compatible with each other. SEM graphs elucidated that the nanoparticles were spherically shaped with a slightly rough surface whereas TEM analysis ensured the nanometer size nanoparticles and coating of lipid over NPs surface. PXRD spectrum concluded the transformation of the drug from crystalline to amorphous state in the formulation. In vitro release pattern was biphasic started with burst release (64.67 ​± ​1.53% within 12hrs) followed by sustained release over 48hrs thus enabling the prolonged replenishing of NAC. In vitro lung deposition study pronounced that coated NAC-PLGA-MPPs showed favorable results in terms of emitted dose (86.67 ​± ​2.52%), MMAD value (2.57 ​± ​0.12 ​μm), GSD value (1.55 ​± ​0.11 ​μm), and FPF of 62.67 ​± ​2.08% for the deposition and targeting the lungs. Finally, in vitro efficacy studies demonstrated that NAC-PLGA-MPPs presented more prominent antibacterial activity against MTB H37Rv strain as compared to NAC. Hence, PLGA based particles could be a better strategy to deliver the NAC for lung targeting.

The Role of NRF2 in Mycobacterial Infection

The incidence of pulmonary nontuberculous mycobacterial (NTM) infection is increasing worldwide, and its clinical outcomes with current chemotherapies are unsatisfactory. The incidence of tuberculosis (TB) is still high in Africa, and the existence of drug-resistant tuberculosis is also an important issue for treatment. To discover and develop new efficacious anti-mycobacterial treatments, it is important to understand the host-defense mechanisms against mycobacterial infection. Nuclear erythroid 2 p45-related factor-2 (NRF2) is known to be a major regulator of various antioxidant response element (ARE)-driven cytoprotective gene expressions, and its protective role has been demonstrated in infections. However, there are not many papers or reviews regarding the role of NRF2 in mycobacterial infectious disease. Therefore, this review focuses on the role of NRF2 in the pathogenesis of Mycobacterium tuberculosis and Mycobacterium avium infection.

Mycobacterium tuberculosis Exploits Focal Adhesion Kinase to Induce Necrotic Cell Death and Inhibit Reactive Oxygen Species Production

Tuberculosis is a deadly, contagious respiratory disease that is caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb). Mtb is adept at manipulating and evading host immunity by hijacking alveolar macrophages, the first line of defense against inhaled pathogens, by regulating the mode and timing of host cell death. It is established that Mtb infection actively blocks apoptosis and instead induces necrotic-like modes of cell death to promote disease progression. This survival strategy shields the bacteria from destruction by the immune system and antibiotics while allowing for the spread of bacteria at opportunistic times. As such, it is critical to understand how Mtb interacts with host macrophages to manipulate the mode of cell death. Herein, we demonstrate that Mtb infection triggers a time-dependent reduction in the expression of focal adhesion kinase (FAK) in human macrophages. Using pharmacological perturbations, we show that inhibition of FAK (FAKi) triggers an increase in a necrotic form of cell death during Mtb infection. In contrast, genetic overexpression of FAK (FAK⁺) completely blocked macrophage cell death during Mtb infection. Using specific inhibitors of necrotic cell death, we show that FAK-mediated cell death during Mtb infection occurs in a RIPK1-depedent, and to a lesser extent, RIPK3-MLKL-dependent mechanism. Consistent with these findings, FAKi results in uncontrolled replication of Mtb, whereas FAK⁺ reduces the intracellular survival of Mtb in macrophages. In addition, we demonstrate that enhanced control of intracellular Mtb replication by FAK⁺ macrophages is a result of increased production of antibacterial reactive oxygen species (ROS) as inhibitors of ROS production restored Mtb burden in FAK⁺ macrophages to same levels as in wild-type cells. Collectively, our data establishes FAK as an important host protective response during Mtb infection to block necrotic cell death and induce ROS production, which are required to restrict the survival of Mtb.

Melanin Produced by Bordetella parapertussis Confers a Survival Advantage to the Bacterium during Host Infection

Bordetella parapertussis causes respiratory infection in humans, with a mild pertussis (whooping cough)-like disease. The organism produces a brown pigment, the nature and biological significance of which have not been elucidated. Here, by screening a transposon library, we demonstrate that the gene encoding 4-hydroxyphenylpyruvate dioxygenase (HppD) is responsible for production of this pigment. Our results also indicate that the brown pigment produced by the bacterium is melanin, because HppD is involved in the biosynthesis of a type of melanin called pyomelanin, and homogentisic acid, the monomeric precursor of pyomelanin, was detected by high-performance liquid chromatography-mass spectrometry analyses. In an infection assay using macrophages, the hppD-deficient mutant was internalized by THP-1 macrophage-like cells, similar to the wild-type strain, but was less able to survive within the cells, indicating that melanin protects B. parapertussis from intracellular killing in macrophages. Mouse infection experiments also showed that the hppD-deficient mutant was eliminated from the respiratory tract more rapidly than the wild-type strain, although the initial colonization levels were comparable between the two strains. In addition, melanin production by B. parapertussis was not regulated by the BvgAS two-component system, which is the master regulator for the expression of genes contributing to the bacterial infection. Taken together, our findings indicate that melanin produced by B. parapertussis in a BvgAS-independent manner confers a survival advantage to the bacterium during host infection.

IMPORTANCE In addition to the Gram-negative bacterium Bordetella pertussis, the etiological agent of pertussis, Bordetella parapertussis also causes respiratory infection in humans, with a mild pertussis-like disease. These bacteria are genetically closely related and share many virulence factors, including adhesins and toxins. However, B. parapertussis is clearly distinguished from B. pertussis by its brown pigment production, the bacteriological significance of which remains unclear. Here, we demonstrate that this pigment is melanin, which is known to be produced by a wide range of organisms from prokaryotes to humans and helps the organisms to survive under various environmental stress conditions. Our results show that melanin confers a survival advantage to B. parapertussis within human macrophages through its protective effect against reactive oxygen species and eventually contributes to respiratory infection of the bacterium in mice. This study proposes melanin as a virulence factor involved in the increased survival of B. parapertussis during host infection.

Shooting yourself in the foot: How immune cells induce antibiotic tolerance in microbial pathogens

Antibiotic treatment failure of infection is common and frequently occurs in the absence of genetically encoded antibiotic resistance mechanisms. In such scenarios, the ability of bacteria to enter a phenotypic state that renders them tolerant to the killing activity of multiple antibiotic classes is thought to contribute to antibiotic failure. Phagocytic cells, which specialize in engulfing and destroying invading pathogens, may paradoxically contribute to antibiotic tolerance and treatment failure. Macrophages act as reservoirs for some pathogens and impede penetration of certain classes of antibiotics. In addition, increasing evidence suggests that subpopulations of bacteria can survive inside these cells and are coerced into an antibiotic-tolerant state by host cell activity. Uncovering the mechanisms that drive immune-mediated antibiotic tolerance may present novel strategies to improving antibiotic therapy.

Understanding the Reciprocal Interplay Between Antibiotics and Host Immune System: How Can We Improve the Anti-Mycobacterial Activity of Current Drugs to Better Control Tuberculosis?

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) infection, remains a global health threat despite recent advances and insights into host-pathogen interactions and the identification of diverse pathways that may be novel therapeutic targets for TB treatment. In addition, the emergence and spread of multidrug-resistant Mtb strains led to a low success rate of TB treatments. Thus, novel strategies involving the host immune system that boost the effectiveness of existing antibiotics have been recently suggested to better control TB. However, the lack of comprehensive understanding of the immunomodulatory effects of anti-TB drugs, including first-line drugs and newly introduced antibiotics, on bystander and effector immune cells curtailed the development of effective therapeutic strategies to combat Mtb infection. In this review, we focus on the influence of host immune-mediated stresses, such as lysosomal activation, metabolic changes, oxidative stress, mitochondrial damage, and immune mediators, on the activities of anti-TB drugs. In addition, we discuss how anti-TB drugs facilitate the generation of Mtb populations that are resistant to host immune response or disrupt host immunity. Thus, further understanding the interplay between anti-TB drugs and host immune responses may enhance effective host antimicrobial activities and prevent Mtb tolerance to antibiotic and immune attacks. Finally, this review highlights novel adjunctive therapeutic approaches against Mtb infection for better disease outcomes, shorter treatment duration, and improved treatment efficacy based on reciprocal interactions between current TB antibiotics and host immune cells.

The mechanism of action of N-acetylcysteine (NAC): The emerging role of H2S and sulfane sulfur species

Initially adopted as a mucolytic about 60 years ago, the cysteine prodrug N-acetylcysteine (NAC) is the standard of care to treat paracetamol intoxication, and is included on the World Health Organization's list of essential medicines. Additionally, NAC increasingly became the epitome of an "antioxidant". Arguably, it is the most widely used "antioxidant" in experimental cell and animal biology, as well as clinical studies. Most investigators use and test NAC with the idea that it prevents or attenuates oxidative stress. Conventionally, it is assumed that NAC acts as (i) a reductant of disulfide bonds, (ii) a scavenger of reactive oxygen species and/or (iii) a precursor for glutathione biosynthesis. While these mechanisms may apply under specific circumstances, they cannot be generalized to explain the effects of NAC in a majority of settings and situations. In most cases the mechanism of action has remained unclear and untested. In this review, we discuss the validity of conventional assumptions and the scope of a newly discovered mechanism of action, namely the conversion of NAC into hydrogen sulfide and sulfane sulfur species. The antioxidative and cytoprotective activities of per- and polysulfides may explain many of the effects that have previously been ascribed to NAC or NAC-derived glutathione.

N-Acetylcysteine (NAC): Impacts on Human Health

N-acetylcysteine (NAC) is a medicine widely used to treat paracetamol overdose and as a mucolytic compound. It has a well-established safety profile, and its toxicity is uncommon and dependent on the route of administration and high dosages. Its remarkable antioxidant and anti-inflammatory capacity is the biochemical basis used to treat several diseases related to oxidative stress and inflammation. The primary role of NAC as an antioxidant stems from its ability to increase the intracellular concentration of glutathione (GSH), which is the most crucial biothiol responsible for cellular redox imbalance. As an anti-inflammatory compound, NAC can reduce levels of tumor necrosis factor-alpha (TNF-α) and interleukins (IL-6 and IL-1β) by suppressing the activity of nuclear factor kappa B (NF-κB). Despite NAC's relevant therapeutic potential, in several experimental studies, its effectiveness in clinical trials, addressing different pathological conditions, is still limited. Thus, the purpose of this chapter is to provide an overview of the medicinal effects and applications of NAC to human health based on current therapeutic evidence.

New roles for glutathione: Modulators of bacterial virulence and pathogenesis

Low molecular weight (LMW) thiols contain reducing sulfhydryl groups that are important for maintaining antioxidant defense in the cell. Aside from the traditional roles of LMW thiols as redox regulators in bacteria, glutathione (GSH) has been reported to affect virulence and bacterial pathogenesis. The role of GSH in virulence is diverse, including the activation of virulence gene expression and contributing to optimal biofilm formation. GSH can also be converted to hydrogen sulfide (H₂S) which is important for the pathogenesis of certain bacteria. Besides GSH, some bacteria produce other LMW thiols such as mycothiol and bacillithiol that affect bacterial virulence. We discuss these newer reported functions of LMW thiols modulating bacterial pathogenesis either directly or indirectly and via modulation of the host immune system.

Ferroptosis in infection, inflammation, and immunity

Ferroptosis is a type of regulated necrosis that is triggered by a combination of iron toxicity, lipid peroxidation, and plasma membrane damage. The upstream inducers of ferroptosis can be divided into two categories (biological versus chemical) and activate two major pathways (the extrinsic/transporter versus the intrinsic/enzymatic pathways). Excessive or deficient ferroptotic cell death is implicated in a growing list of physiological and pathophysiological processes, coupled to a dysregulated immune response. This review focuses on new discoveries related to how ferroptotic cells and their spilled contents shape innate and adaptive immunity in health and disease. Understanding the immunological characteristics and activity of ferroptotic death not only illuminates an intersection between cell death and immunity but may also lead to the development of novel treatment approaches for immunopathological diseases.

The promises and limitations of N-acetylcysteine as a potentiator of first-line and second-line tuberculosis drugs

N-acetylcysteine (NAC) is most commonly used for the treatment of acetaminophen overdose and acetaminophen-induced liver injury. In patients infected with Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), NAC is given to treat hepatotoxicity induced by TB drugs. We had previously shown that cysteine, a derivative of NAC, potentiated the activity of isoniazid, a first-line TB drug, by preventing the emergence of INH resistance and persistence in M. tuberculosis in vitro. Herein, we demonstrate that in vitro, NAC has the same boosting activity with various combinations of first- and second-line TB drugs against drug-susceptible and multidrug-resistant M. tuberculosis strains. Similar to cysteine, NAC increased M. tuberculosis respiration. However, in M. tuberculosis-infected mice, the addition of NAC did not augment the activity of first- or second-line TB drugs. A comparison of the activity of NAC combined with TB drugs in murine and human macrophage cell lines revealed that studies in mice might not be recapitulated during host infection in vivo.

From infection niche to therapeutic target: the intracellular lifestyle of Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is an obligate human pathogen killing millions of people annually. Treatment for tuberculosis is lengthy and complicated, involving multiple drugs and often resulting in serious side effects and non-compliance. Mtb has developed numerous complex mechanisms enabling it to not only survive but replicate inside professional phagocytes. These mechanisms include, among others, overcoming the phagosome maturation process, inhibiting the acidification of the phagosome and inhibiting apoptosis. Within the past decade, technologies have been developed that enable a more accurate understanding of Mtb physiology within its intracellular niche, paving the way for more clinically relevant drug-development programmes. Here we review the molecular biology of Mtb pathogenesis offering a unique perspective on the use and development of therapies that target Mtb during its intracellular life stage.

The Interplay Between Systemic Inflammation, Oxidative Stress, and Tissue Remodeling in Tuberculosis

Significance: Excessive and prolonged proinflammatory responses are associated with oxidative stress, which is commonly observed during chronic tuberculosis (TB). Such condition favors tissue destruction and consequently bacterial spread. A tissue remodeling program is also triggered in chronically inflamed sites, facilitating a wide spectrum of clinical manifestations. Recent Advances: Since persistent and exacerbated oxidative stress responses have been associated with severe pathology, a number of studies have suggested that the inhibition of this augmented stress response by improving host antioxidant status may represent a reasonable strategy to ameliorate tissue damage in TB. Critical Issues: This review summarizes the interplay between oxidative stress, systemic inflammation and tissue remodeling, and its consequences in promoting TB disease. We emphasize the most important mechanisms associated with stress responses that contribute to the progression of TB. We also point out important host immune components that may influence the exacerbation of cellular stress and the subsequent tissue injury. Future Directions: Further research should reveal valuable targets for host-directed therapy of TB, preventing development of severe immunopathology and disease progression. Antioxid. Redox Signal. 34, 471-485.

Adjunct N-Acetylcysteine Treatment in Hospitalized Patients With HIV-Associated Tuberculosis Dampens the Oxidative Stress in Peripheral Blood: Results From the RIPENACTB Study Trial

Tuberculosis (TB) still causes significant morbidity and mortality worldwide, especially in persons living with human immunodeficiency virus (HIV). This disease is hallmarked by persistent oxidative stress and systemic inflammation. N-acetylcysteine (NAC), a glutathione (GSH) precursor, has been shown in experimental models to limit Mycobacterium tuberculosis infection and disease both by suppression of the host oxidative response and through direct antimicrobial activity. In a recent phase II randomized clinical trial (RIPENACTB study), use of NAC as adjunct therapy during the first two months of anti-TB treatment was safe. Whether adjunct NAC therapy of patients with TB-HIV coinfection in the context of anti-TB treatment could directly affect pro-oxidation and systemic inflammation has not been yet formally demonstrated. To test this hypothesis, we leveraged existing data and biospecimens from the RIPENACTB trial to measure a number of surrogate markers of oxidative stress and of immune activation in peripheral blood of the participants at pre-treatment and at the day 60 of anti-TB treatment. Upon initiation of therapy, we found that the group of patients undertaking NAC exhibited significant increase in GSH levels and in total antioxidant status while displaying substantial reduction in lipid peroxidation compared to the control group. Only small changes in plasma concentrations of cytokines were noted. Pharmacological improvement of the host antioxidant status appears to be a reasonable strategy to reduce TB-associated immunopathology.

Reactive Oxygen Species in Pathogen Clearance: The Killing Mechanisms, the Adaption Response, and the Side Effects

Reactive oxygen species (ROS) are attractive weapons in both antibiotic-mediated killing and host-mediated killing. However, the involvement of ROS in antibiotic-mediated killing and complexities in host environments challenge the paradigm. In the case of bacterial pathogens, the examples of some certain pathogens thriving under ROS conditions prompt us to focus on the adaption mechanism that pathogens evolve to cope with ROS. Based on these, we here summarized the mechanisms of ROS-mediated killing of either antibiotics or the host, the examples of bacterial adaption that successful pathogens evolved to defend or thrive under ROS conditions, and the potential side effects of ROS in pathogen clearance. A brief section for new antibacterial strategies centered around ROS was also addressed.

Repeated bouts of pulmonary tuberculosis in a hunting cat: reinfection or recrudescence?

CASE SUMMARY

A 7-year-old neutered male Siamese cat was referred for investigation of weight loss and hypercalcaemia (3.3 mmol/l; reference interval 2-3 mmol/l). Haematology, serum biochemistry, thoracic imaging, bronchoalveolar lavage (BAL), Ziehl-Neelsen staining of the BAL fluid and interferon gamma release assay (IGRA) were compatible with pneumonia caused by the less pathogenic member of the Mycobacterium tuberculosis complex, that is, M microti (the 'vole bacillus'), which is common in cats in the UK. Treatment with azithromycin, rifampicin and marbofloxacin was given for 2 months, followed by 4 months of azithromycin and marbofloxacin. Treatment recommendations for tuberculous pneumonia have since changed. The cat remained asymptomatic for 1 year but went on to develop M microti pneumonia on five other occasions, and was treated for 6-12 months on each occasion. The patient's clinical signs, hypercalcaemia and radiographic/CT pulmonary pathology always resolved completely, and the IGRA became negative, before antimycobacterial treatment was stopped. This suggests cure followed by reinfection owing to avid hunting behaviour. Alternatively, this could represent recrudescence of dormant disease. This case has previously been included in a study that described a series of cases of feline tuberculosis.

RELEVANCE AND NOVEL INFORMATION

This case shows that M microti infection in cats can present as recurrent episodes of pneumonia, even after prolonged treatment courses.

Mitchell J, Lodzinska J, Cazzini P, Varjonen K, Gunn-Moore DA. Systemic Mycobacterium kansasii Infection in Two Related Cats

Mycobacterial infections are a major concern in veterinary medicine because of the difficulty achieving an etiological diagnosis, the challenges and concerns of treatment, and the potential zoonotic risk. Mycobacterium kansasii, a slow-growing non-tuberculous mycobacteria, causes disease in both humans and animals. While infections have been well described in humans, where it may be misdiagnosed as tuberculosis, there are fewer reports in animals. Only four cases have been reported in the domestic cat. This case report describes systemic M. kansasii infection in two sibling indoor-only cats that presented two and half years apart with cutaneous disease that was found to be associated with osteolytic and pulmonary pathology. Infection with M. kansasii was confirmed in both cats by polymerase chain reaction on fine-needle aspirate of a lumbosacral soft tissue mass in one cat and on a tissue punch biopsy of a skin lesion in the other; interferon-gamma release assay inferred M. avium-complex and M. tuberculosis-complex infection in the two cats, respectively. Both patients made a full recovery following antimicrobial therapy with rifampicin, azithromycin, and pradofloxacin (plus N-acetyl cysteine in cat 2). This report highlights successful treatment of systemic M. kansasii mycobacteriosis in the cat and the challenge of accurately diagnosing this infection.

Hydroxyurea treatment is associated with reduced degree of oxidative perturbation in children and adolescents with sickle cell anemia

Sickle cell anemia (SCA) is the most common inherited hemolytic anemia worldwide. Here, we performed an exploratory study to investigate the systemic oxidative stress in children and adolescents with SCA. Additionally, we evaluated the potential impact of hydroxyurea therapy on the status of oxidative stress in a case–control study from Brazil. To do so, a panel containing 9 oxidative stress markers was measured in plasma samples from a cohort of 47 SCA cases and 40 healthy children and adolescents. Among the SCA patients, 42.5% were undertaking hydroxyurea. Multidimensional analysis was employed to describe disease phenotypes. Our results demonstrated that SCA is associated with increased levels of oxidative stress markers, suggesting the existence of an unbalanced inflammatory response in peripheral blood. Subsequent analyses revealed that hydroxyurea therapy was associated with diminished oxidative imbalance in SCA patients. Our findings reinforce the idea that SCA is associated with a substantial dysregulation of oxidative responses which may be dampened by treatment with hydroxyurea. If validated by larger prospective studies, our observations argue that reduction of oxidative stress may be a main mechanism through which hydroxyurea therapy attenuates the tissue damage and can contribute to improved clinical outcomes in SCA.

N-acetyl-cysteine mediates protection against Mycobacterium avium through induction of human β-defensin-2 in a mouse lung infection model

Mycobacterium avium complex is a causative organism for refractory diseases. In this study, we examined the effects of N-acetyl-cysteine on M. avium infection in vitro and in vivo. N-acetyl-cysteine treatment suppressed the growth of M. avium in A549 cells in a concentration-dependent manner. This effect was related to the induction of the antibacterial peptide human β-defensin-2. In a mouse model, N-acetyl-cysteine treatment significantly reduced the number of bacteria in the lungs and induced murine β-defensin-3. In interleukin-17-deficient mice, the effects of N-acetyl-cysteine disappeared, indicating that these mechanisms may be mediated by interleukin-17. Moreover, an additional reduction in bacterial load was observed in mice administered N-acetyl-cysteine in combination with clarithromycin. Our findings demonstrate the potent antimycobacterial effects of N-acetyl-cysteine against M. avium by inducing antimicrobial peptide, suggesting that N-acetyl-cysteine may have applications as an alternative to classical treatment regimens.

Thiol/disulfide homeostasis as a novel indicator of oxidative stress during the treatment process of patients with septic arthritis

Objectives

This study aims to investigate dynamic thiol/disulfide homeostasis as a novel indicator of oxidative stress and to find out its association with standard inflammatory markers during the treatment of patients with septic arthritis (SA).

Patients and methods

In this prospective study, a new colorimetric method for measuring thiol/disulfide homeostasis was assessed between May 2013 and October 2014 in 24 patients with SA (14 males, 10 females; mean age 14.5±19.1 years; range, 1 to 80 years) at baseline and the end of the third week of the treatment, and in 24 healthy controls (14 males, 10 females; mean age 12.5±18.7 years; range, 1 to 85 years). Also, standard inflammatory markers such as C-reactive protein (CRP), erythrocyte sedimentation rate, and white blood cell count were evaluated.

Results

At baseline, serum disulfide was higher in SA group compared to the control group, whereas native thiol was lower (p<0.05 for all). At the end of the third week of the treatment, serum disulfide level was lower, whereas the native thiol was higher compared to baseline (p<0.05 for all). In addition, serum disulfide level was positively correlated with CRP (r=0.736, p<0.001) and disulfide/native thiol ratio (r=0.779, p<0.001). Furthermore, in multiple regression analyses, the disulfide level was independently associated with CRP (β=0.226, p=0.005).

Conclusion

Our results suggest that the elevated levels of serum disulfide and standard inflammatory markers at baseline in patients with SA and decreased levels of these parameters are related with oxidative stress. This homeostasis shifted towards disulfide formation due to thiol oxidation. Therefore, thiol/ disulfide homeostasis may be a helpful biomarker for the follow- up in patients with SA.

Possible role for acetylcysteine as a treatment for acute liver failure secondary to antitubercular medication use

PURPOSE

Drug-induced liver injury (DILI) that progresses to acute liver failure (ALF) has a high mortality rate, and therapeutic options are limited. Acetylcysteine has a labeled indication for use as an antidote for acetaminophen toxicity and has also been used with limited success in treatment of non-acetaminophen-induced liver injury, with small clinical trials indicating an increase in transplant-free survival. Recommendations for management of non-acetaminophen-induced DILI include withdrawal of the offending agent and supportive care. Treatment guidelines generally discourage a rechallenge with an offending medication, except in cases where there are no other therapeutic options for management of a serious disease, such as active tuberculosis (TB).

SUMMARY

This case report describes the reversal of ALF due to DILI in a patient receiving antitubercular agents for active TB. After withdrawal of initially prescribed antitubercular agents, the patient was switched to a less hepatotoxic anti-TB regimen and intravenous acetylcysteine pending results of antimicrobial susceptibility testing. After stabilization of the patient's liver enzyme levels, intravenous acetylcysteine was discontinued and oral acetylcysteine was continued for 5 days without an increase in hepatic enzyme levels or clinical deterioration. After 5 days, oral acetylcysteine was discontinued due to patient-reported nausea and vomiting.

CONCLUSION

Given the limited number of therapeutic interventions shown to be beneficial in ALF and data suggesting a protective effect against DILI with initiation of acetylcysteine at the start of treatment with anti-TB medications, acetylcysteine can be considered for patients with anti-TB - associated DILI.