Crosstalk Between Sphingomyelinases and Reactive Oxygen Species in Mycobacterial Infection

Reactive oxygen species trigger inflammasome activation after intracellular microbial interaction

The intracellular production of reactive oxygen species (ROS), composed of oxygen-reduced molecules, is important not only because of their lethal effects on microorganisms but also due to their potential inflammatory and metabolic regulation properties. The ROS pro-inflammatory properties are associated with the second signal to inflammasome activation, leading to cleaving pro-IL-1β and pro-IL18 before their secretion, as well as gasdermin-D, leading to pyroptosis. Some microorganisms can modulate NLRP3 and AIM-2 inflammasomes through ROS production: whilst Mycobacterium bovis, Mycobacterium kansasii, Francisella novicida, Brucella abortus, Listeria monocytogenes, Influenza virus, Syncytial respiratory virus, Porcine reproductive and respiratory syndrome virus, SARS-CoV, Mayaro virus, Leishmania amazonensis and Plasmodium sp. enhance inflammasome assembly, Hepatitis B virus, Mycobacterium marinum, Mycobacterium tuberculosis, Francisella tularensis and Leishmania sp. disrupt it. This process represents a recent cornerstone in our knowledge of the immunology of intracellular pathogens, which is reviewed in this mini-review.

Types and functions of heterogeneity in mycobacteria

The remarkable ability of Mycobacterium tuberculosis to survive attacks from the host immune response and drug treatment is due to the resilience of a few bacilli rather than a result of survival of the entire population. Maintenance of mycobacterial subpopulations with distinct phenotypic characteristics is key for survival in the face of dynamic and variable stressors encountered during infection. Mycobacterial populations develop a wide range of phenotypes through an innate asymmetric growth pattern and adaptation to fluctuating microenvironments during infection that point to heterogeneity being a vital survival strategy. In this Review, we describe different types of mycobacterial heterogeneity and discuss how heterogeneity is generated and regulated in response to environmental cues. We discuss how this heterogeneity may have a key role in recording memory of their environment at both the single-cell level and the population level to give mycobacterial populations plasticity to withstand complex stressors.

Radical Releasing Anti-Tuberculosis Agents and the Treatment of Mycobacterial Tuberculosis Infections - An Overview

The treatment and management of tuberculosis (TB) is a major global concern. Approved drugs for the treatment of TB to date displayed various modes of action which can be grouped into radical releasing and non-radical releasing anti TB agents. Radical releasing agents are of special interest because they diffuse directly into the mycobacterium cell wall, interact with the host cell DNA causing DNA strand breakages and fatal destabilization of the DNA helix inhibiting nucleic acid synthase. As a therapeutic agent with aforementioned activity, nitroimidazoles and most especially bicyclic nitroimidazoles are currently in clinical use for the treatment of tuberculosis. However, the approved drugs, pretomanid (PR) and delamanid (DE) are limited in their nitric oxide radical (NO•) releasing abilities to cause effective bactericidity. It is believed that their bactericidal activity can be improved by harnessing alternative strategies to increase NO• release. The last decade has witness the strategic inclusion of NO-donors into native drugs to improve their activities and/or reverse resistance. The rationale behind this strategy is the targeting of NO• release at specific therapeutic sites. This review therefore aims to highlight various radical releasing agents that may be effective in the treatment of TB. The review also investigates various structural modification to PR and DE and suggests alternative strategies to improve NO• release as well as some applications where NO-donor hybrid drugs have been used with good therapeutic effect.

Role of Oxidative Stress in the Pathology and Management of Human Tuberculosis

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, is the leading cause of mortality worldwide due to a single infectious agent. The pathogen spreads primarily via aerosols and especially infects the alveolar macrophages in the lungs. The lung has evolved various biological mechanisms, including oxidative stress (OS) responses, to counteract TB infection. M. tuberculosis infection triggers the generation of reactive oxygen species by host phagocytic cells (primarily macrophages). The development of resistance to commonly prescribed antibiotics poses a challenge to treat TB; this commonly manifests as multidrug resistant tuberculosis (MDR-TB). OS and antioxidant defense mechanisms play key roles during TB infection and treatment. For instance, several established first-/second-line antitubercle antibiotics are administered in an inactive form and subsequently transformed into their active form by components of the OS responses of both host (nitric oxide, S-oxidation) and pathogen (catalase/peroxidase enzyme, EthA). Additionally, M. tuberculosis has developed mechanisms to survive high OS burden in the host, including the increased bacterial NADH/NAD⁺ ratio and enhanced intracellular survival (Eis) protein, peroxiredoxin, superoxide dismutases, and catalases. Here, we review the interplay between lung OS and its effects on both activation of antitubercle antibiotics and the strategies employed by M. tuberculosis that are essential for survival of both drug-susceptible and drug-resistant bacterial subtypes. We then outline potential new therapies that are based on combining standard antitubercular antibiotics with adjuvant agents that could limit the ability of M. tuberculosis to counter the host's OS response.

Bioactive Lipids and Redox Signaling: Molecular Mechanism and Disease Pathogenesis

The actions of bioactive lipids and reactive oxygen species (ROS) are usually coupled, and their interplay is a common and important mechanism mediating tissue injury, inflammation, and other pathologies. Understanding the interplay of ROS and lipid mediators will extend horizons for researchers to clarify the pathogenesis of different diseases and help identify therapeutic targets for treatment of these diseases. Some bioactive lipids are converted into oxidized lipids during cell or tissue oxidative stress such as isoprostanes and isoketals, which are even more bioactive than their precursors. Moreover, many enzymes that produce lipid mediators such as prostaglandin H synthases, lipoxygenases, and cytochrome P450 isoforms may catalyze the production of ROS. Bioactive lipids-lysophospholipids, sphingolipids, or deposited lipids in cells-are shown to stimulate redox enzymes to produce ROS. In addition, a lipid-channel-ROS axis in different organelles may be associated with the crosstalk of ROS and bioactive lipids. This Forum focuses on the crosstalk of ROS with sphingolipids, P450 eicosanoids, lysophospholipids, and deposited plasma lipids and related novel signaling pathway in their reciprocal actions, which is expected to provide novel insights into the pathogenesis of different diseases associated with the participation of these lipid mediators. It is imperative to further understand the molecular mechanism mediating the crosstalk of ROS with specific lipid mediators and to develop more effective therapeutic strategies to target the interplay of ROS and lipid mediators for treatment specific to different organ diseases. Antioxid. Redox Signal. 28, 911-915.