Inhibition of the in-vitro growth of Mycobacterium tuberculosis by a phytosiderophore

Iron Supplementation Therapy, A Friend and Foe of Mycobacterial Infections?

Iron is an essential element that is required for oxygen transfer, redox, and metabolic activities in mammals and bacteria. Mycobacteria, some of the most prevalent infectious agents in the world, require iron as growth factor. Mycobacterial-infected hosts set up a series of defense mechanisms, including systemic iron restriction and cellular iron distribution, whereas mycobacteria have developed sophisticated strategies to acquire iron from their hosts and to protect themselves from iron’s harmful effects. Therefore, it is assumed that host iron and iron-binding proteins, and natural or synthetic chelators would be keys targets to inhibit mycobacterial proliferation and may have a therapeutic potential. Beyond this hypothesis, recent evidence indicates a host protective effect of iron against mycobacterial infections likely through promoting remodeled immune response. In this review, we discuss experimental procedures and clinical observations that highlight the role of the immune response against mycobacteria under various iron availability conditions. In addition, we discuss the clinical relevance of our knowledge regarding host susceptibility to mycobacteria in the context of iron availability and suggest future directions for research on the relationship between host iron and the immune response and the use of iron as a therapeutic agent.

Mycobacterial siderophore: A review on chemistry and biology of siderophore and its potential as a target for tuberculosis

Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis is known to secrete low molecular mass compounds called siderophores especially under low iron conditions to chelate iron from host environment. Iron is essential for growth and other essential processes to sustain life of the bacterium in the host. Hence targeting siderophore is considered to be an alternative approach to prevent further virulence of bacterium into the host. This review article presents classification of siderophores, their role in transporting iron into the tubercular cell, biosynthesis of mycobactins, viability of siderophore as a therapeutic target and also focuses on overview on various approaches to target siderophore. The approaches encompass mutation effect on genes involved in siderophore recycling, synthetic as well as natural compounds that can inhibit further spread of bacterium by targeting siderophore.

Preliminary evaluation of anti-tuberculosis potential of siderophores against drug-resistant Mycobacterium tuberculosis by mycobacteria growth indicator tube-drug sensitivity test

Background

Alternative treatment strategies have become essential in overcoming the problem of drug-resistant Mycobacterium tuberculosis (Mtb). In this preliminary in vitro study, the anti-tuberculosis (anti-TB) activity of exogenous iron chelators (xenosiderophores) such as Exochelin-MS (Exo-MS) and Deferoxamine-B (DFO-B) was evaluated against ten multi-drug-resistant (MDR) and seven pyrazinamide-resistant (PZA^R) Mtb isolates.

Methods

Mycobacteria Growth Indicator Tube-Drug Susceptibility Test was used to assess the anti-TB effect of Exo-MS or DFO-B individually and their combinations with isoniazid (INH), rifampicin (RIF) and pyrazinamide (PZA).

Results

For the MDR-Mtb isolates, Exo-MS alone inhibited two out of the five isolates tested. Whereas, DFO-B alone inhibited nine out of the ten MDR isolates tested. For PZA-resistant Mtb isolates, both Exo-MS and DFO-B individually inhibited five out of the seven isolates. The MIC of Exo-MS in combination with INH, RIF and PZA remained the same. The MIC of DFO-B decreased when tested in combination with INH, RIF and PZA.

Conclusions

Exo-MS and DFO-B were shown to have activity against drug-resistant Mtb isolates. Therefore, these xenosiderophores may be useful adjuncts to antibiotics in overcoming the problem of drug-resistant Mtb in clinical setting.

Screening of antihelminthic effects of Indian plant extracts: a preliminary report

INTRODUCTION

The purpose of the present study was to evaluate the antihelminthic effect of plants from the Ayurvedic system of medicine traditionally used in India.

MATERIALS AND METHODS

Six plant extracts were assayed for their activity against free-living nematodes. Inhibitory effects on free-living nematodes were evaluated in vitro using aqueous or ethanolic extracts.

CONCLUSIONS

Of six plants assayed, Momordica charantia yielded the best results, its crude extract producing 96% mortality.

Iron and iron chelating agents modulate Mycobacterium tuberculosis growth and monocyte-macrophage viability and effector functions

Excess of iron promotes Mycobacterium tuberculosis infection, its replication and progression to clinical disease and death from tuberculosis. Chelation of iron may reduce M. tuberculosis replication, restore host defence mechanisms and it could constitute an application in the prevention and treatment strategies where both iron overload and tuberculosis are prevalent. We investigated the effect of iron and iron chelating agents, like desferrioxamine and silybin, individually and in combination with iron on mycobacterial number, viability in culture and after recovery from monocyte-macrophages, together with monocyte-macrophages viability and oxidative defence. Mycobacterial number and viability in culture were assessed using real-time quantitative PCR of H37Rv IS6110 DNA, 16S rRNA and 85B mRNA, whereas the microplate AlamarBlue(TM) assay was used to detect viability in culture post-infection. Mitochondrial membrane potential and phosphatidyl serine exposure of monocyte-macrophages, detected using Mitotracker Red fluorescence and Annexin V binding, respectively, served as indicators of host cell viability. Superoxide generation served as marker of monocyte-macrophage effector functions. Extracellular H37Rv showed a significant increase in number and viability in presence of excess iron and, by large, a significant decrease in number and viability in presence of the iron chelating agents, silybin and desferrioxamine, compared to cultivation without supplementation. Intracellularly, excess iron increased H37Rv viability significantly but reduced monocyte-macrophages mitochondrial membrane potential and compromised superoxide production. Desferrioxamine had little influence on intracellular parameters, but consistently prevented effects of excess iron, while silybin significantly altered most intracellular parameters and mostly failed to prevent effects of excess iron. These findings suggest that chelation therapy should be considered in conditions of iron overload and that effective chelating agents like desferrioxamine, with limited intracellular access might need to be used in combination with lypophilic chelating agents.

Iron, mycobacteria and tuberculosis

The role of iron in the growth and metabolism of M. tuberculosis and other mycobacteria is discussed in relation to the acquisiton of iron from host sources, such as transferrin, lactoferrin and ferritin, and its subsequent assimilation and utilization by the bacteria. Key components involved in the acquisition of iron (as ferric ion) and its initial transport into the mycobacterial cell are extracellular iron binding agents (siderophores) which, in pathogenic mycobacteria, are the carboxymycobactins and, in saprophytic mycobacteria, are the exochelins. In both cases, iron may be transferred to an intra-envelope, short-term storage molecule, mycobactin. For transport across the cell membrane, a reductase is used which converts FeIII-mycobactin to the FeII form. The ferrous ion, possibly complexed with salicylic acid, is then shuttled across the membrane either for direct incorporation into various porphyrins and apoproteins or, for storage of iron within the bacterial cytoplasm, bacterioferritin. The overall process of iron acquisition and its utilization is under very genetic tight control. The importance of iron in the virulence of mycobacteria is discussed in relationship to the development of tuberculosis. The management of dietary iron can therefore be influential in aiding the outcome of this disease. The role of the old anti-TB compound, p-aminosalicylate (PAS), is discussed in its action as an inhibitor of iron assimilation, together with the prospects of being able to synthesize further selective inhibitors of iron metabolism that may be useful as future chemotherapeutic agents.