[Show abstract][Hide abstract] ABSTRACT: Phagocytic cells produce reactive oxygen and nitrogen species (ROS & RNS) as the most common arsenal to kill intracellular pathogens. Leishmania, an obligate intracellular pathogen also confronts this antimicrobial assault during the early phase of infection but nevertheless is able to survive these attacks and proliferate in macrophage. Adaptation of Leishmania to the toxic effects of ROS and RNS, involves a rapid change in the parasite proteome to combat the host defense response that macrophage mount in combating pathogen. To understand the events associated with combating ROS and RNS species, we performed a proteomic analysis of L. donovani promastigotes treated with sub-lethal doses of menadione (ROS), S-nitroso-N-acetylpenicillamine (RNS) or combination of both compounds. Proteomic changes triggered by these reagents were evaluated by iTRAQ labeling and subsequent LC-MALDI-TOF/TOF-MS analysis. Across the 3 stress conditions, the quantitative analysis identified changes in the proteins which encompass ~20% of the parasite proteome. Major changes were observed in enzymatic machinery of pathways involved in maintaining redox homeostasis, trypanothione metabolism, oxidative phosphorylation, superoxide metabolism, mitochondrial respiration process and other essential metabolic pathways. These observations shed light on how Leishmania promastigotes counter ROS and RNS affects during the initial stage of infection.
Full-text · Article · Jan 2013 · Journal of Proteomics
[Show abstract][Hide abstract] ABSTRACT: The clinical value of amphotericin B, the mainstay therapy for visceral leishmaniasis in sodium antimony gluconate-nonresponsive zones of Bihar, India, is now threatened by the emergence of acquired drug resistance, and a comprehensive understanding of the underlying mechanisms is the need of the hour. We have selected an amphotericin B-resistant clinical isolate which demonstrated 8-fold-higher 50% lethal doses (LD(50)) than an amphotericin B-sensitive strain to explore the mechanism of amphotericin B resistance. Fluorimetric analysis demonstrated lower anisotropy in the motion of the diphenylhexatriene fluorescent probe in the resistant strain, which indicated a higher fluidity of the membrane for the resistant strain than for the sensitive strain. The expression patterns of the two transcripts of S-adenosyl-l-methionine:C-24-Δ-sterol methyltransferase and the absence of ergosterol, replaced by cholesta-5,7,24-trien-3β-ol in the membrane of the resistant parasite, indicate a decreased amphotericin B affinity, which is evidenced by decreased amphotericin B uptake. The expression level of MDR1 is found to be higher in the resistant strain, suggesting a higher rate of efflux of amphotericin B. The resistant parasite also possesses an upregulated tryparedoxin cascade and a more-reduced intracellular thiol level, which helps in better scavenging of reactive oxygen species produced by amphotericin B. The resistance to amphotericin B was partially reverted by the thiol metabolic pathway and ABC transporter inhibitors. Thus, it can be concluded that altered membrane composition, ATP-binding cassette transporters, and an upregulated thiol metabolic pathway have a role in conferring amphotericin B resistance in clinical isolates of Leishmania donovani.
Full-text · Article · Nov 2011 · Antimicrobial Agents and Chemotherapy
[Show abstract][Hide abstract] ABSTRACT: Visceral leishmaniasis (VL), caused by Leishmania donovani, is a major health concern in India. It represents T-helper type 2 (Th2) bias of cytokines in active state and Th1 bias at cure. However, the role of the parasite in regulating Toll-like receptor (TLR)-mediated macrophage activation in VL patients remains elusive. In this report, we demonstrated that later stages of L. donovani infection rendered tolerance to macrophages, leading to incapability for the production of inflammatory cytokines like tumor necrosis factor (TNF)-α and interleukin (IL)-1β in response to TLR stimulation. Overexpression of transforming growth factor (TGF)-β(1), but not IL-10, resulted in suppressed lipopolysaccharide (LPS)-induced production of TNF-α and downregulation of TLR4 expression in L. donovani-infected macrophages. Recombinant human (rh)TGF-β(1) markedly enhanced tyrosine phosphatase (Src homology region 2 domain-containing phosphatase-1) activity, but inhibited IL-1 receptor-activated kinase (IRAK)-1 activation. Addition of neutralizing TGF-β(1) antibody reversed these effects, and thus suggesting the pivotal role of TGF-β(1) in promoting refractoriness for LPS in macrophages. Surprisingly, the use of a tyrosine phosphatase inhibitor (sodium orthovanadate, Na(3)VO(4)) promoted IRAK-1 activation, confirming the negative inhibitory role of tyrosine phosphatase in macrophage activation. Furthermore, rhTGF-β(1) induced tolerance in infected macrophages by reducing inhibitory protein (IκBα) degradation in a time-dependent manner. In addition, short interfering RNA studies proved that overexpression of A20 ubiquitin-editing protein complex induced inhibitory activity of TGF-β(1) on LPS-mediated nuclear factor-κB activation. Thus, these findings suggest that TGF-β(1) promotes overexpression of A20 through tyrosine phosphatase activity that ensures transient activation of inflammatory signaling pathways in macrophages in active L. donovani infection.
Full-text · Article · Oct 2011 · Immunology and Cell Biology