Clinical and experimental advances in treatment of visceral leishmaniasis

The Elimination Status of Visceral Leishmaniasis in Southeast Asia Region

PURPOSE

Visceral leishmaniasis (VL) is caused by an intracellular parasite that is transmitted to humans by sandfly bites. It is prevalent throughout Asia, Africa, the Americas, and the Mediterranean area, where 147 million people are at risk of contracting the illness. The manifestation of heterotrophic illness relies on both Leishmania implicated and the host's immunological response, ranging from asymptomatic to severe leishmaniasis with potentially lethal effects.

METHOD

We reviewed the literature (published till 31st December 2023) on the worldwide situation of leishmaniasis, standard and novel detection techniques, and traditional and modern treatment strategies and endeavors to eliminate VL. Moreover, epidemiological data was collected from the World Health Organization's publicly available databases. GraphPad Prism Version 8 was used to analyze and produce figures based on the epidemiological data.

RESULTS

Diagnosis of parasites in tissues or serology is commonly employed. Diagnosis by identifying parasite DNA using molecular techniques is becoming more popular. Despite recent findings of L. donovani resistance to pentavalent antimoniate medications, it continues to be the cornerstone in the medical management of VL. Amphotericin B and its lipid formulations, injectable paromomycin, and oral miltefosine are among the new therapy options being researched. The number of reported VL cases has reduced remarkably over the last decade due to human interventions made to eliminate VL. Particularly countries from the South East Asian region have experienced momentous progress in reducing VL cases and eliminating this disease from this region. Owing to the robust elimination programs, countries such as Bangladesh has eliminated VL as a public health concern. India and Nepal are on the verge of its elimination.

CONCLUSION

Rapid diagnosis, effective and inexpensive treatment, simple access to newly discovered medications, appropriate vector control, and a well-designed vaccine are all required for the elimination of this disease burden in impoverished areas of the globe.

Immunosuppressants alter the immune response associated with Glucantime® treatment for Leishmania infantum infection in a mouse model

Background

Immunosuppression is a major risk factor for the development of visceral leishmaniasis (VL). The number of patients receiving immunosuppressant drugs such as TNF antagonist (anti-TNF) and methotrexate (MTX) is increasing. In these patients, VL is more severe, their response to treatment poorer, and they are at higher risk of relapse, a consequence (largely) of the poor and inappropriate immune response they develop.

Objectives

To examine the effect of immunosuppressive treatment on the host immune response and thus gain insight into the reduced efficacy of pentavalent antimonials in these patients. Experiments were performed using BALB/c mice immunosuppressed with anti-TNF or MTX, infected with Leishmania infantum promastigotes, and then treated with Glucantime® at clinical doses.

Results

Immunosuppression with both agents impeded parasite elimination from the spleen and bone marrow. Low pro-inflammatory cytokine production by CD4+ and CD8+ T cells was detected, along with an increase in PD-1 and IL-10 expression by B and T cells in the immunosuppressed groups after treatment.

Conclusion

The immunosuppressed mice were unable to develop specific cellular immunity to the parasite, perhaps explaining the greater risk of VL relapse seen in pharmacologically immunosuppressed human patients.

Field-Deployable Treatments For Leishmaniasis: Intrinsic Challenges, Recent Developments and Next Steps

Leishmaniasis is a neglected tropical disease endemic primarily to low- and middle-income countries, for which there has been inadequate development of affordable, safe, and efficacious therapies. Clinical manifestations of leishmaniasis range from self-healing skin lesions to lethal visceral infection with chances of relapse. Although treatments are available, secondary effects limit their use outside the clinic and negatively impact the quality of life of patients in endemic areas. Other non-medicinal treatments, such as thermotherapies, are limited to use in patients with cutaneous leishmaniasis but not with visceral infection. Recent studies shed light to mechanisms through which Leishmania can persist by hiding in cellular safe havens, even after chemotherapies. This review focuses on exploring the cellular niches that Leishmania parasites may be leveraging to persist within the host. Also, the cellular, metabolic, and molecular implications of Leishmania infection and how those could be targeted for therapeutic purposes are discussed. Other therapies, such as those developed against cancer or for manipulation of the ferroptosis pathway, are proposed as possible treatments against leishmaniasis due to their mechanisms of action. In particular, treatments that target hematopoietic stem cells and monocytes, which have recently been found to be necessary components to sustain the infection and provide a safe niche for the parasites are discussed in this review as potential field-deployable treatments against leishmaniasis.

Activation of TLR-pathway to induce host Th1 immune respons eagainst visceral leishmaniasis: Involvement of galactosylated-flavonoids

Immunotherapeutic strategies against visceral leishmaniasis (VL) are pertinent because of the emergence of resistance against existing chemotherapy, coupled with their toxicity and high costs. Various bioactive components with potential immunomodulatory activity, such as alkaloids, terpenes, saponins, flavonoids obtained primarily from medicinal plants, have been screened against different disease models. Reports suggested that glycans containing terminal β-galactose can skew host immune response towards Th1 by engaging TLRs. In this study, two synthesized terminal galactose-containing flavones, Quercetin 3-d-galactoside (Q-gal) and Kaempferol 3-O-d-galactoside (K-gal), are profiled in terms of inducing host protective Th1 response in both in vitro & in vivo animal models of experimental VL individually against antimony-resistant & antimony-susceptible Leishmania donovani. Further, we explored that both Q-gal and K-gal induce TLR4 mediated Th1 response to encounter VL. Molecular docking analysis also suggested strong interaction with TLR4 for both the galactosides, with a slightly better binding potential towards Q-gal. Treatment with both Q-gal and K-gal showed significant antileishmanial efficacy. Each considerably diminished the liver and splenic parasite burden 60 days after post-infection (>90% in AG83 infected mice and >87% in GE1F8R infected mice) when administered at a 5 mg/kg/day body-weight dose for ten consecutive days. However, the treatments failed to clear the parasites in the TLR4 deficient C3H/HeJ mice. Treatment with these compounds favors the elevation of TLR4 dependent host protective Th1 cytokines and suppression of disease-promoting IL-10. Q-gal and K-gal also triggered sufficient ROS generation in macrophages to kill intracellular parasites directly.

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Galactosilated flavonoids treatment clears in-vivo drug-resistant Leishmania donovani infection.

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Quercetin 3-d-galactoside (Q-gal) & Kaempferol 3-O-d-galactoside (K-gal) induce host TLR4 pathway.

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These flavonoids up-regulate Th1 cytokines and suppress the disease-promoting IL-10.

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TLR4 deficient C3H/HeJ mice are unresponsive towards Q-gal and K-gal treatment.

Synthesis of Tellurium Oxide (TeO2) Nanorods and Nanoflakes and Evaluation of Its Efficacy Against Leishmania major In Vitro and In Vivo

PURPOSE

Today, the use of natural products and nanostructures has increased. Given the reports on beneficial effects of various organotellurane compounds on types of visceral leishmaniasis, we decided to investigate the effect of TeO₂ NPs on Leishmania major (L. major). Tellurium can cause cell apoptosis in cancer cells without activating the caspase-pathway.

METHODS

TeO₂ NPs at first synthesized and the structure was checked by XRD, SEM and EDS tests. The cytotoxic effect of TeO₂ NPs against L. major promastigotes, amastigotes and macrophages was assessed by MTT test or counting. The possible apoptosis of L. major by TeO₂ NPs was evaluated by flow cytometry test. For in vivo assay, the lesions of infected BALB/c mice with L. major promastigotes were treated with TeO₂ NPs, then the lesion size and survival rate were evaluated.

RESULTS

The synthesis of TeO₂ with tetragonal structure was confirmed by XRD. The combination of nanorods and nanoflakes and the presence of Te were proven by SEM and EDS, respectively. According the effects of nanoparticle on promastigotes and amastigotes, the IC₅₀ values of TeO₂ after 72 h of incubation were 15.13 and 52.22 µg/ml, respectively. TeO₂ NPs induced apoptosis in about 41% of promastigotes. The ulcer greatly healed and survival rate was higher in treated mice compared to those in control group.

CONCLUSION

Based on the data, favorable anti-leishmanial properties were observed by using TeO₂ NPs. TeO₂ NPs have cytotoxic impacts on L. major promastigotes and amastigotes in vitro and in vivo and may be regarded as a therapy option.

Immunomodulatory role of Th17 pathway in experimental visceral leishmaniasis

Visceral leishmaniasis (VL) or Kala-azar is a vector borne protozoan infection caused by Leishmania donovani in the Indian subcontinent mainly India, Nepal and Bangladesh. It is a major public health problem in these countries mostly affecting the socio-economically poor population. Leishmaniasis ranks the third most important disease after malaria and filariasis but is still considered as one of the neglected tropical diseases of the world. For development of better therapeutic agents and effective vaccine against VL, there is a need to understand host immunological changes that play a vital role during course of infection. Therefore, we investigated the role of Th17 pathway in Balb/c mice during Leishmania donovani infection and treatment with amphotericin B. Mice were divided in four groups i.e. Control, Infected, Uninfected treated and Infected treated. The cytokine levels were estimated in the spleen of Balb/c mice on days 1, 3, 7, 14, 17, 21, 28, 35, 45 and 60 post infection and during course of treatment. The mRNA levels of the Th17 pathway during active Leishmania donovani infection and after treatment were determined by real time polymerase chain reaction (RT-PCR) and protein levels by flow cytometry and ELISA. Results of our study revealed that active infection was associated with low levels of Th17 cytokines IL-17, IL-22 and IL-23 and elevated levels of IL-6, IL-1β and TGF-β. Amphotericin B treatment restored production of pro-inflammatory cytokines IL-17 and IL-22. The levels of transcription factor RORγt were found to correlate with the levels of IL-17 during infection and also after chemotherapy whereas STAT3 levels were elevated during infection and vice versa after treatment. The findings of this study suggest that Th17 cytokines IL-17 and IL-22 are associated with protection against VL infection and development of any interventions or chemotherapeutic agents targeting Th17 pathway could be an important approach for VL treatment.

Discovery and Validation of Lmj_04_BRCT Domain, a Novel Therapeutic Target: Identification of Candidate Drugs for Leishmaniasis

Since many of the currently available antileishmanial treatments exhibit toxicity, low effectiveness, and resistance, search and validation of new therapeutic targets allowing the development of innovative drugs have become a worldwide priority. This work presents a structure-based drug discovery strategy to validate the Lmj_04_BRCT domain as a novel therapeutic target in Leishmania spp. The structure of this domain was explored using homology modeling, virtual screening, and molecular dynamics studies. Candidate compounds were validated in vitro using promastigotes of Leishmania major, L. amazonensis, and L. infantum, as well as primary mouse macrophages infected with L. major. The novel inhibitor CPE2 emerged as the most active of a group of compounds against Leishmania, being able to significantly reduce the viability of promastigotes. CPE2 was also active against the intracellular forms of the parasites and significantly reduced parasite burden in murine macrophages without exhibiting toxicity in host cells. Furthermore, L. major promastigotes treated with CPE2 showed significant lower expression levels of several genes (α-tubulin, Cyclin CYCA, and Yip1) related to proliferation and treatment resistance. Our in silico and in vitro studies suggest that the Lmj_04_BRCT domain and its here disclosed inhibitors are new potential therapeutic options against leishmaniasis.

Computational study to discover potent phytochemical inhibitors against drug target, squalene synthase from Leishmania donovani

AIMS

The parasite, Leishmania donovani is responsible for lethal visceral leishmaniasis (VL) in humans. There is a need to investigate novel medicines as antileishmanial drugs, as medication currently introduced for leishmaniasis may cause resistance, serious side-effects, chemical instability and high cost. Therefore, this computational study was designed to explore potential phytochemical inhibitors against Leishmania donovani squalene synthase (LdSQS) enzyme, a drug target.

MAIN METHODS

Multiple sequence alignment was carried to detect conserved regions across squalene synthases from different Leishmania spp. Their evolutionary relationships were studied by generating phylogenetic tree. Homology modeling method was used to build a three dimensional model of the protein. The validated model was explored by docking simulation with the phytochemicals of interest to identify the most potent inhibitors. Two reported inhibitors were used as references in the virtual screening. The top hit compounds (binding energy less than -9 kcal/mol) were further subjected to intermolecular interaction analysis, pharmacophore modeling, pharmacokinetic and toxicity prediction.

KEY FINDINGS

Seven phytochemicals displayed binding energies less than -9 kcal/mol hence demonstrating ability to be strongly bound to the active site of LdSQS to inhibit the enzymatic activity. Ancistrotanzanine B demonstrated the lowest binding affinity of -9.83 kcal/mol superior to reported inhibitors in literature. Conserved two aspartate rich regions and two signatory motifs were found in the L. donovani squalene synthase by multiple sequence alignment. In addition, study of pharmacophore modeling confirmed that top hit phytochemicals and the reported inhibitor (E5700) share common chemical features for their biochemical interaction with LdSQS. Among seven phytochemicals, 3-O-methyldiplacol showed admissible physicochemical, pharmacokinetic and toxicity predictions compared to the reported inhibitors. All seven phytochemicals satisfied in silico prediction criteria for oral bioavailability.

SIGNIFICANCE

Based on the current study, these hits can be further structurally optimized and validated under laboratory conditions to develop antileishmanial drugs.

A "Golden Age" for the discovery of new antileishmanial agents: Current status of leishmanicidal gold complexes and prospective targets beyond the trypanothione system

Leishmaniasis is one of the most neglected diseases worldwide and is considered a serious public health issue. The current therapeutic options have several disadvantages that make the search for new therapeutics urgent. Gold compounds are emerging as promising candidates based on encouraging in vitro and limited in vivo results for several Au^I and Au^III complexes. The antiparasitic mechanisms of these molecules remain only partially understood. However, a few studies have proposed the trypanothione redox system as a target, similar to the mammalian thioredoxin system, pointed out as the main target for several gold compounds with significant antitumor activity. In this review, we present the current status of the investigation and design of gold compounds directed at treating leishmaniasis. In addition, we explore potential targets in Leishmania parasites beyond the trypanothione system, taking into account previous studies and structure modulation performed for gold-based compounds.

Combination of Subtherapeutic Doses of Tretazicar and Liposomal Amphotericin B Suppresses and Cures Leishmania major-Induced Cutaneous Lesions in Murine Models

Cutaneous leishmaniasis (CL) is the most common form of leishmaniasis affecting human populations, yet CL remains largely ignored in drug discovery programs. CL causes disfiguring skin lesions and often relapses after "clinical cure" using existing therapeutics. To expand the pool of anti-CL lead candidates, we implemented an integrated screening platform comprising three progressive Leishmania parasite life cycle forms. We identified tretazicar (CB1954, 5-(aziridin-1-yl)-2,4-dinitrobenzamide) as a potent inhibitor of Leishmania parasite viability across multiple Leishmania species, which translated into complete and prolonged in vivo suppression of CL lesion formation in BALB/c mice when used as a monotherapy and which was superior to liposomal amphotericin B. In addition, oral twice a day administration of tretazicar healed the majority of existing Leishmania major (L. major) cutaneous lesions. In drug combination studies, there was a strong potentiation when subtherapeutic doses of liposomal amphotericin B and tretazicar were simultaneously administered. This drug combination decreased L. major lesion size in mice earlier than individual monotherapy drug treatments and maintained all animals lesion free for up to 64 days after treatment cessation. In contrast, administration of subtherapeutic doses of tretazicar or amphotericin B as monotherapies resulted in no or partial lesion cures, respectively. We propose that tretazicar should be explored as a component of a systemic CL combination therapy and potentially for other diseases where amphotericin B is a first line therapy.

The balance between IL-12/IL4 in renal tissue switches the inflammatory response arm and shows relationship with the clinical signs in Leishmania-infected dogs

The pathogenesis of Canine leishmaniosis (CanL) is associated with altered cytokine expression and parasitic tissue shows a lot of inflammation. The aim of this study was to assess the renal inflammation and cytokine expression in eight symptomatic and eight asymptomatic Leishmania- infected dogs, and seven uninfected control dogs. Kidney fragments were stained with hematoxylin and eosin for morphometric evaluation. mRNA expression levels of interferon gamma (IFN-γ), tumor necrosis factor alpha (TNF-α), interleukin (IL)-2, IL-4, IL-10, and IL-12 were assessed in the kidney fragments using quantitative real time-polymerase chain reaction. Inflammation, quantified by the average area of the infiltrated immune cells, was greater in symptomatic dogs than in those asymptomatic, whereas asymptomatic dogs exhibited higher inflammation than the control dogs (p > 0.05, Tukey's test). Expression levels of IFN-γ, TNF-α, IL-4, IL-10, and IL-12 were upregulated in symptomatic dogs and downregulated in asymptomatic dogs compared with those of the uninfected group. Furthermore, IL-4 showed higher expression in symptomatic dogs than in asymptomatic ones (p < 0.05, Mann-Whitney test), which was directly associated with clinical manifestations (p < 0.05, Chi-square test). However, IL-12 was predominantly expressed in symptomatic dogs, shifting the balance from IL-12/IL-4 to IL-12, which elicits a change in the inflammatory response. Leishmania was not found in the renal tissues in any one of the studied groups. Our data suggests that the balance between IL-12 and IL-4 plays an important role in the regulation of inflammation in renal tissue and clinical presentations in CanL.

Leishmanial CpG DNA nanovesicles: A propitious prophylactic approach against visceral leishmaniasis

Unmethylated CpG motifs with phosphothioate backbone trigger TLR9 to elicit innate immune response characterized by the production of Th1 cytokines. The use of CpG DNA as an adjuvant has established its role in potentiating the humoral and cell mediated vaccine specific immune response. However, none of the synthetic oligodeoxynucleotides (ODNs) know and used till date are associated with the parasite itself. Our group identified a novel CG rich sequence of 14 base pairs from Leishmania donovani genome (Ld CpG ODN) and established it as a TLR9 agonist. The present study was designed to ascertain the adjuvanticity of Ld CpG ODN with soluble leishmanial antigen in experimental model of L. donovani. During the study Schizophyllan (SPG), a fungal polymer was used for encapsulating Ld CpG ODN for efficient endosomal delivery. The synthesized nanovehicles were of nearly 100 nm and localized within endosomes as confirmed by confocal microscopy. Immunization studies displayed the superior ability of synthesized nanovehicles co-administered with parasite antigen in augmenting innate immune response in comparison to ODN, nanoparticles or soluble antigen alone. The response included generation of ROS, NO and iNOS expression followed by proinflammatory cytokine milieu with reduced parasitic load within liver, spleen and bone marrow. These immune-tailored particles in combination with parasitic antigens elicited significant generation of cell mediated response owing to the presence of high levels of CD8⁺ T-cells and lymphocyte proliferation. Moreover, vaccination regime with synthesized adjuvant also activated humoral immunity by escalating the levels of IgG2 followed by reduced levels of anti-leishmanial IgG and IgG1 antibodies. The findings support the efficacy of Ld CpG ODN as a potential adjuvant against visceral leishmaniasis.

Purified Splenic amastigotes of Leishmania donovani-Immunoproteomic approach for exploring Th1 stimulatory polyproteins

Visceral leishmaniasis (VL) represents one of the most challenging infectious diseases worldwide. The reason that once infected, patient develops immunity against Leishmania parasite has paved way to develop prophylactic vaccines against disease, but only some of these have moved ahead for clinical trials. Herein, the study to explore novel and potential vaccine candidates was extended to pathogenic form of parasite, that is, amastigote form which is less explored due to complexity of its purification process. Methods and results. Classical protocol of purification of splenic amastigotes was modified to obtain highly pure amastigotes which was confirmed by Western blotting in support with proteomics studies. Fractionation and sub-fractionation of purified splenic amastigotes revealed four sub-fractions, belonging to 97 to 68 kDa and 68 to 43 kDa ranges, which showed long-lasting protection with remarkable Th1-type cellular responses in hamsters vaccinated with these sub-fractions (LTT, NO, QRT-PCR). Further proteomics analysis, to identify and understand the precise nature and function of these protective protein sub-fractions, identified a total of 47 proteins including twenty-five hypothetical proteins/unknowns. Amastigote stage has potential Th1-stimulatory vaccine candidates, notably, among identified proteins, major were uncharacterized proteins/hypothetical proteins, which once characterized may serve as novel and potential vaccine candidates/drug targets.

Modified solid lipid nanoparticles encapsulated with Amphotericin B and Paromomycin: an effective oral combination against experimental murine visceral leishmaniasis

The development of an effective oral therapeutics is an immediate need for the control and elimination of visceral leishmaniasis (VL). We exemplify the preparation and optimization of 2-hydroxypropyl-β-cyclodextrin (HPCD) modified solid lipid nanoparticles (SLNs) based oral combinational cargo system of Amphotericin B (AmB) and Paromomycin (PM) against murine VL. The emulsion solvent evaporation method was employed to prepare HPCD modified dual drug-loaded solid lipid nanoparticles (m-DDSLNs). The optimized formulations have a mean particle size of 141 ± 3.2 nm, a polydispersity index of 0.248 ± 0.11 and entrapment efficiency for AmB and PM was found to be 96% and 90% respectively. The morphology of m-DDSLNs was confirmed by scanning electron microscopy and transmission electron microscopy. The developed formulations revealed a sustained drug release profile upto 57% (AmB) and 21.5% (PM) within 72 h and were stable at both 4 °C and 25 °C during short term stability studies performed for 2 months. Confocal laser scanning microscopy confirmed complete cellular internalization of SLNs within 24 h of incubation. In vitro cytotoxicity study against J774A.1 macrophage cells confirmed the safety and biocompatibility of the developed formulations. Further, m-DDSLNs did not induce any hepatic/renal toxicities in Swiss albino mice. The in vitro simulated study was performed to check the stability in simulated gastric fluids and simulated intestinal fluids and the release was found almost negligible. The in vitro anti-leishmanial activity of m-DDSLNs (1 µg/ml) has shown a maximum percentage of inhibition (96.22%) on intra-cellular amastigote growth of L. donovani. m-DDSLNs (20 mg/kg × 5 days, p.o.) has significantly (P < 0.01) reduced the liver parasite burden as compared to miltefosine (3 mg/kg × 5 days, p.o.) in L. donovani-infected BALB/c mice. This work suggests that the superiority of as-prepared m-DDSLNs as a promising approach towards the oral delivery of anti-leishmanial drugs.

Can We Harness Immune Responses to Improve Drug Treatment in Leishmaniasis?

Leishmaniasis is a vector-borne parasitic disease that has been neglected in priority for control and eradication of malaria, tuberculosis, and HIV/AIDS. Collectively, over one seventh of the world’s population is at risk of being infected with 0.7–1.2 million new infections reported annually. Clinical manifestations range from self-healing cutaneous lesions to fatal visceral disease. The first anti-leishmanial drugs were introduced in the 1950′s and, despite several shortcomings, remain the mainstay for treatment. Regardless of this and the steady increase in infections over the years, particularly among populations of low economic status, research on leishmaniasis remains under funded. This review looks at the drugs currently in clinical use and how they interact with the host immune response. Employing chemoimmunotherapeutic approaches may be one viable alternative to improve the efficacy of novel/existing drugs and extend their lifespan in clinical use.

Synthesis and Biological Activity of Some Aminothiazole Derivatives as Antileishmanial Agents

Background:

Leishmaniasis is a major health problem which is caused by the protozoan parasite of the genus Leishmania. Cutaneous leishmaniasis is one type of leishmaniasis and selflimited in most of the cases. However, when the lesions come with scars, they make a deep lifelong stigma. Despite being WHO's research priority, the optimum treatment for this disease has not been found yet. The current study aimed to synthesize and assess the activity of some new aminothiazole compounds against Leishmania major-induced cutaneous leishmaniasis in BALB/c mice.

Methods:

Eight new aminothiazole derivatives were synthesized and their chemical structures were characterized by spectral data 1H-NMR spectroscopy, Mass spectrophotometry and elemental analysis. L. major parasites were inoculated into the tail base of BALB/c mice and the induced lesions were treated every other day with three different doses of the synthesized compounds against meglumine antimoniate as the drug reference for two weeks. Size of the lesions was observed for three weeks and the collected data were analyzed by SPSS software. Also, these compounds are docked into the active site of 14- α-demethylase as the targets in the treatment of leishmaniasis.

Results:

Among the synthesized aminothiazole derivatives, compounds 1, 2, 3, 4, and 7 had good leishmanicidal effects. Docking binding energies showed that the synthesized compounds could act as inhibitors for 14- α-demethylase.

Conclusions:

Among the synthesized compounds, compound 3, (N-((4-chlorophenyl)(phenyl) methyl)thiazol-2-amine) was the most promising one which deserves future studies for the treatment of leishmaniasis.

Relationship of Serum Antileishmanial Antibody With Development of Visceral Leishmaniasis, Post-kala-azar Dermal Leishmaniasis and Visceral Leishmaniasis Relapse

Introduction

To sustain the achievement of kala-azar elimination program (KEP), early detection and treatment of the visceral leishmaniasis (VL) cases and associated modalities such as treatment failure (TF), relapse VL (RVL), and Post-kala-azar dermal leishmaniasis (PKDL) is the cornerstone. A predictive biomarker for VL development and related complications could also play a crucial role in curtailing disease incidence and transmission. Investigations to find a biomarker with prospective capabilities are, however, scarce. Using samples and known clinical outcomes generated within two previous longitudinal cohort studies, we aimed to determine if fluctuations in serum anti-rK39 antibody levels could provide such predictive value.

Materials and Methods

Serum samples collected at four different time points (Baseline, 12, 18, and 24 months) from 16 patients who had developed VL within the monitoring period and 15 of their asymptomatic healthy controls counterparts were investigated. To investigate potential prediction of VL related complications, serum samples of 32 PKDL, 10 RVL, 07 TF, and 38 cured VL from a single dose AmBisome trial were analyzed. Of this second panel, all patients were monitored for 5 years and sera were collected at four time points (Baseline then 1, 6, and 12 months after treatment). The level of anti-rK39 antibodies in archived samples was measured by a semi-quantitative ELISA.

Results

The mean antibody level was significantly higher in VL patients compared to their asymptomatic healthy counterparts at each time point. Likewise, we observed a trend toward elevations in antibody levels for PKDL, RVL, TF relative to the reducing levels observed in cured VL. Receiver operating characteristic (ROC) analysis found a promising predictive power of rK39 antibody levels to reveal progression from asymptomatic Leishmania donovani infection stage to VL, defined as 87.5% sensitive and 95% specific. Following treatment, rk39 antibody notably showed 100% sensitivity and 95% specificity in predicting TF.

Conclusion

Our data indicate that the relative quantity of serum anti-rK39 antibody has promise within either a predictive or prognostic algorithm for VL and VL-related modalities. These could enable VL control programs to implement more effective measures to eliminate the disease. Further research is, however, imperative to standardize the rK39 antibody ELISA between sites prior to broader use.

Behavior of two Leishmania infantum strains-evaluation of susceptibility to antimonials and expression of microRNAs in experimentally infected J774 macrophages and in BALB/c mice

Strains of the same Leishmania parasite species, isolated from different host organisms, may exhibit unique infection profiles and induce a change in the expression of microRNAs among host macrophages and in model host mice. MicroRNAs (MiR) are endogenous molecules of about 22 nucleotides that are involved in many regulatory processes, including the vertebrate host immune response. In this respect, the infectivity and susceptibility to antimonials of two L. infantum strains, BH46, isolated from human, and OP46, isolated from symptomatic dog, were characterized in J774 macrophages and BALB/c mice. Parasite burden was assessed in the liver, spleen, and bone marrow using the serial limiting dilution technique. A higher parasite burden was observed in the spleen and bone marrow of animals infected with OP46 compared to BH46 strain. Our results also showed that OP46 was less susceptible to the antimonials. In addition, miR-122 and miR-155 expression was evaluated in the liver and J774 macrophages, and in spleens from infected animals, respectively. An increase was observed in the expression of miR-155 in J774 macrophages infected with both strains compared to uninfected cells, with a higher expression in cells infected with OP46. However, no difference in the expression of miR-122 and miR-155 was observed in the infected animals. Thus, this study shows that OP46 was more infective for mice, it caused a higher increase in miR-155 expression in infected macrophages and was less susceptible to the antimonials evaluated. These data suggest that alteration in miR-155 level likely plays a role in regulating the response to L. infantum.

Efficacy of Four Solanum spp. Extracts in an Animal Model of Cutaneous Leishmaniasis

Background: Leishmaniasis is a complex protozoa disease caused by Leishmania genus (Trypanosomatidae family). Currently, there have been renewed interests worldwide in plants as pharmaceutical agents. In this study, the in vivo efficacy of Solanum spp. is assessed in an L. amazonensis BALB/c mice model for experimental cutaneous leishmaniasis. Methods: Animals were infected with 5 × 10⁶ metacyclic promastigotes and 30-day post-infection, a treatment with 30 mg/kg of Solanum extracts or Glucantime^® (GTM) was applied intralesionally every four days to complete 5 doses. Results: Neither death nor loss of weight higher than 10% was observed. All the tested extracts were able to control the infection, compared with the infected and untreated group. Solanum havanense Jacq. extract showed the highest efficacy and was superior (p < 0.05) to GTM. Solanum myriacanthum Dunal., S. nudum Dunal. and S. seaforthianum Andr. extracts demonstrated a similar effect (p > 0.05) to GTM. An increase of IFN-γ (p < 0.05) was displayed only by animals treated with S. nudum compared to the group treated with a vehicle, while no differences (p > 0.05) were observed for IL-12. Conclusions:In vivo effects of Solanum extracts were demonstrated, suggesting that this genus could be further explored as a new antileishmanial alternative.

Emerging therapeutic targets for treatment of leishmaniasis

INTRODUCTION

Parasitic diseases that pose a threat to human life include leishmaniasis - caused by protozoan parasite Leishmania species. Existing drugs have limitations due to deleterious side effects like teratogenicity, high cost and drug resistance. This calls for the need to have an insight into therapeutic aspects of disease. Areas covered: We have identified different drug targets via. molecular, imuunological, metabolic as well as by system biology approaches. We bring these promising drug targets into light so that they can be explored to their maximum. In an effort to bridge the gaps between existing knowledge and prospects of drug discovery, we have compiled interesting studies on drug targets, thereby paving the way for establishment of better therapeutic aspects. Expert opinion: Advancements in technology shed light on many unexplored pathways. Further probing of well established pathways led to the discovery of new drug targets. This review is a comprehensive report on current and emerging drug targets, with emphasis on several metabolic targets, organellar biochemistry, salvage pathways, epigenetics, kinome and more. Identification of new targets can contribute significantly towards strengthening the pipeline for disease elimination.

Safety Analysis of Leishmania Vaccine Used in a Randomized Canine Vaccine/Immunotherapy Trial

In Leishmania infantum-endemic countries, controlling infection within dogs, the domestic reservoir, is critical to public health. There is a need for safe vaccines that prevent canine progression with disease and transmission to others. Protective vaccination against Leishmania requires mounting a strong, inflammatory, Type 1 response. Three commercially available canine vaccines on the global veterinary market use saponin or inflammatory antigen components (Letifend) as a strong pro-inflammatory adjuvant. There is very little information detailing safety of saponin as an adjuvant in field trials. Safety analyses for the use of vaccine as an immunotherapeutic in asymptomatically infected animals are completely lacking. Leishmania infantum, the causative agent of canine leishmaniasis, is enzootic within U.S. hunting hounds. We assessed the safety of LeishTec^® after use in dogs from two different clinical states: 1) without clinical signs and tested negative on polymerase chain reaction and serology or 2) without clinical signs and positive for at least one Leishmania diagnostic test. Vaccine safety was assessed after all three vaccinations to quantify the number and severity of adverse events. Vaccinated animals had an adverse event rate of 3.09%, whereas placebo animals had 0.68%. Receiving vaccine was correlated with the occurrence of mild, site-specific, reactions. Occurrence of severe adverse events was not associated with having received vaccine. Infected, asymptomatic animals did not have a higher rate of adverse events. Use of vaccination is, therefore, likely to be safe in infected, asymptomatic animals.

Synthesis and Evaluation of Methyl 4-(7-Hydroxy-4,4,8-Trimethyl-3-Oxabicyclo[3.3.1]Nonan-2-yl)Benzoate as an Antileishmanial Agent and Its Synergistic Effect with Miltefosine

In our interest in oxabicyclic compounds as potent antileishmanial agents, the present work deals with the chemical synthesis of a new oxabicyclic derivative, methyl 4-(7-hydroxy-4,4,8-trimethyl-3-oxabicyclo[3.3.1]nonan-2-yl)benzoate (PS-207). This oxabicyclic derivative showed a good antileishmanial effect on the parasite, on both the promastigote and the amastigote. The mode of parasitic death from PS-207 seemed to be apoptosis-like. Interestingly, the combination of PS-207 with a low dose of miltefosine showed a synergistic effect against the parasite.

To evaluate efficacy and safety of amphotericin B in two different doses in the treatment of post kala-azar dermal leishmaniasis (PKDL)

Background

Post kala-azar dermal leishmaniasis (PKDL) is a skin disorder that usually occurs among patients with a past history of visceral leishmaniasis (VL). Cases are also reported without a history of VL. There is no satisfactory treatment regimen available at present. We aimed to compare the efficacy and safety of amphotericin B in two different doses (0.5mg/kg vs 1mg/kg) in a prospective randomized trial in 50 PKDL patients.

Methods

In this open label study 50 patients with PKDL, aged between 5–60 years were randomized in two groups. Group A received amphotericin B in the dose of 0.5 mg/kg in 5% dextrose, daily for 20 infusions for 3 courses at an interval of 15 days between each course and Group B received amphotericin B in the dose of 1mg/kg in 5% dextrose on alternate days, 20 infusions for 3 courses an interval of 15 days between each course and followed up for one year.

Results

A total of 50 patients were enrolled, 25 in each of group A and group B. Two patients lost to follow up and three patients withdrew consent due to adverse events. The initial cure rate was 92% in group A and 88% in group B by intention to treat analysis and final cure rate by per protocol analysis was 95.65% and 95.45% in group A and group B respectively. Two patients each from either group relapsed. Nephrotoxicity was the most common adverse event occurring in both the groups.

Conclusion

The lower dose appears to have fewer adverse events however, nephrotoxicity remains a problem in both regimens. The 0.5mg/kg regimen may be considered instead of the higher dosage however safer treatments remain critical for PKDL treatment.

Glycyrrhizic acid attenuates growth of Leishmania donovani by depleting ergosterol levels

In the present study, glycyrrhizic acid (GA) the main component of Glycyrrhiza glabra was evaluated for its efficacy as antileishmanial agent and its mode of action explored. GA inhibits promastigotes and intracellular amastigotes in a dose dependent manner at an IC₅₀ value of 34 ± 3.0 μM and 20 ± 4.2 μM respectively. GA was non-toxic against THP-1 macrophage host cell line. GA was found to inhibit recombinant Leishmania donovani HMG-CoA reductase (LdHMGR) enzyme at the half-maximum inhibitory concentration of 24 ± 4.3 μM indicating the sensitivity and specificity of GA towards the enzyme. However, GA could cause only 30% reduction in HMGR activity when measured in Leishmania promastigotes treated with 34 μM of GA. Interestingly western blot analysis revealed fivefold reduced HMGR expression in GLA treated promastigotes. To further study the mode of action of GA, we used transgenic parasites overexpressing LdHMGR. Results indicated that ∼2 fold resistance was exhibited by LdHMGR overexpressing promastigotes to GA with an IC₅₀ value of 74 μM compared to the wild type parasite. This explained the specific binding of GA to LdHMGR enzyme. There was ∼2 fold depletion in ergosterol levels in wild type promastigotes compared to the HMGR overexpressors. This data was further validated by exogenous supplementation of GA treated cells with ergosterol and 40% reversal of growth inhibition was observed. The results obtained suggested that GA kills the parasite by affecting sterol biosynthetic pathway, especially by inhibiting the L. donovani HMGR and altering ergosterol levels. The finding from the current study shows that GA is a potential antileishmanial chemotherapeutic agent.

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Glycyrrhizic acid (GA) kills both promastigote and amastigote forms of Leishmania donovani (Ld).

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It inhibits recombinant LdHMGR enzyme and native promastigote enzyme.

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It depletes ergosterol levels in Leishmania promastigotes.

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Ergosterol supplementation partially rescues GA inhibited promastigotes.

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HMGR overexpressors are 2 fold resistant to GA.

Recovery of antigen-specific T cell responses from dogs infected with Leishmania (L.) infantum by use of vaccine associated TLR-agonist adjuvant

Visceral leishmaniasis (VL), caused by infection with the obligate intracellular protozoan parasite Leishmania infantum, is a fatal disease of dogs and humans. Protection against VL requires a T helper 1 (Th1) skewed CD4⁺ T response, but despite this knowledge, there are currently no approved-to-market vaccines for humans and only three veterinary-use vaccines globally. As VL progresses from asymptomatic to symptomatic, L. infantum-specific interferon gamma (IFNγ) driven-Th1 responses become dampened and a state of immune exhaustion established. T cell exhaustion and other immunoregulatory processes, starting during asymptomatic disease, are likely to hinder vaccine-induced responses if vaccine is administered to infected, but asymptomatic and seronegative, individuals. In this study we evaluated how immune exhaustion, shown previously by our group to worsen in concert with VL progression, effected the capacity of vaccine candidate antigen/toll-like receptor (TLR) agonist combinations to promote protective CD4⁺ T cell responses during progressive VL. In conjunction with Th1 responses, we also evaluated concomitant stimulation of immune-balanced IL-10 regulatory cytokine production by these vaccine products in progressive VL canine T cells. Vaccine antigen L111f in combination with TLR agonists significantly recovered CD4⁺ T cell IFNγ intracellular production in T cells from asymptomatic VL dogs. Vaccine antigen NS with TLR agonists significantly recovered CD4⁺ T cell production in both endemic control and VL dogs. Combinations of TLR agonists and vaccine antigens overcame L. infantum induced cellular exhaustion, allowing robust Th1 CD4⁺ T cell responses from symptomatic dogs that previously had dampened responses to antigen alone. Antigen-agonist adjuvants can be utilized to promote more robust vaccine responses from infected hosts in endemic areas where vaccination of asymptomatic, L. infantum-infected animals is likely.

Trend in cumulative cases and mortality rate among visceral leishmaniasis patients in Eastern Sudan: a 14-year registry, 2002-2015

BACKGROUND

Leishmaniasis is one of the neglected infectious diseases of the world. This disease largely affects individuals of low socio-economic level, mainly in developing countries.

METHODS

The aim of this study was to investigate the cumulative number of cases, case fatality rate, and trend in incidence and mortality rate of visceral leishmaniasis (VL) in Eastern Sudan. A retrospective descriptive study was performed through analysis of the database managed by the Ministry of Health in Gadarif State, which includes all cases of VL.

RESULTS

Over the 14-year study period (2002-2015), a total of 51773 patients were registered in Gadarif State with clinical and laboratory evidence of proven VL. The trend in VL was considerably higher over the years 2003-2005 as compared to the last 5 years of 2011-2015. The highest fatality rate was observed in 2002 (4.8%) and it had declined in 2014 (1.1%) and 2015 (1.7%). Rural residence was statistically associated with death related to VL (p=0.021).

CONCLUSIONS

This study showed a high number of cumulative cases of VL in Eastern Sudan. The fatality rate was found to be highest among rural residents and has declined in the last 5 years. Thus immediate interventions are needed in terms of health education and the implementation of preventive measures, with a specific focus on people residing in rural areas.

SLA-PGN-primed dendritic cell-based vaccination induces Th17-mediated protective immunity against experimental visceral leishmaniasis: a crucial role of PKCβ

Emergence of drug resistance during visceral leishmaniasis (VL) is a major obstacle imposed during successful therapy. An effective vaccine strategy against this disease is therefore necessary. Our present study exploited the SLA (soluble leishmanial antigen) and PGN (peptidoglycan) stimulated bone marrow-derived dendritic cells (DCs) as a suitable vaccine candidate during experimental VL. SLA-PGN-stimulated DCs showed a significant decrease in hepatic and splenic parasite burden, which were associated with increased production of nitric oxide and pro-inflammatory cytokines such as IL-12, IFN-γ and IL-17. Elevated level of IL-17 was accompanied with the generation of more Th17 cells. Further studies on DC provided the evidence that these SLA-PGN-stimulated DCs played an important role in providing necessary cytokines such as IL-6, IL-23 and TGF-β for the generation of Th17 cells. Interestingly, inhibition of protein kinase C-β (PKCβ) in DCs led to decreased production of Th17 polarizing cytokines, causing reduction of the Th17 population size. Altogether, our finding highlighted the important role of DC-based PKCβ in regulation of the function and generation of Th17 cells.

Leishmania genome analysis and high-throughput immunological screening identifies tuzin as a novel vaccine candidate against visceral leishmaniasis

Leishmaniasis is a neglected tropical disease caused by Leishmania species. It is a major health concern affecting 88 countries and threatening 350 million people globally. Unfortunately, there are no vaccines and there are limitations associated with the current therapeutic regimens for leishmaniasis. The emerging cases of drug-resistance further aggravate the situation, demanding rapid drug and vaccine development. The genome sequence of Leishmania, provides access to novel genes that hold potential as chemotherapeutic targets or vaccine candidates. In this study, we selected 19 antigenic genes from about 8000 common Leishmania genes based on the Leishmania major and Leishmania infantum genome information available in the pathogen databases. Potential vaccine candidates thus identified were screened using an in vitro high throughput immunological platform developed in the laboratory. Four candidate genes coding for tuzin, flagellar glycoprotein-like protein (FGP), phospholipase A1-like protein (PLA1) and potassium voltage-gated channel protein (K VOLT) showed a predominant protective Th1 response over disease exacerbating Th2. We report the immunogenic properties and protective efficacy of one of the four antigens, tuzin, as a DNA vaccine against Leishmania donovani challenge. Our results show that administration of tuzin DNA protected BALB/c mice against L. donovani challenge and that protective immunity was associated with higher levels of IFN-γ and IL-12 production in comparison to IL-4 and IL-10. Our study presents a simple approach to rapidly identify potential vaccine candidates using the exhaustive information stored in the genome and an in vitro high-throughput immunological platform.

Progress in the treatment of a neglected infectious disease: visceral leishmaniasis

Visceral leishmaniasis (kala-azar) is a disseminated intracellular protozoal infection. Most cases (90%) occur in the rural regions of five countries: India, Sudan, Nepal, Bangladesh and Brazil. As with other infectious diseases embedded in high-level poverty, developing and/or delivering new treatments for visceral leishmaniasis had been painfully slow or nonexistent. However, despite persistent unresolved obstacles (e.g., drug affordability), renewed interest in visceral leishmaniasis and numerous successful treatment trials have combined to turn a therapeutic corner in the past 5 years, yielding new alternatives to conventional pentavalent antimony. Advances include the use of low-cost generic pentavalent antimony, rediscovery of amphotericin B, short-course regimens via lipid formulations of amphotericin B, retesting injectible paromyomycin and, of clear-cut importance, identifying miltefosine (Impavido, Zentaris) as the first effective oral therapy for this neglected disease.

Nanonization increases the antileishmanial efficacy of amphotericin B: an ex vivo approach

With widespread resistance to pentavalent antimonial in the endemic eastern terai belt of Nepal and Bihar, India, Amphotericin B deoxycholate is now the first-line antileishmanial drug for the treatment of visceral leishmaniasis (VL). However, universal occurrence of infusion-related fever and rigors with amphotericin B (AmB), occasional serious life-threatening toxicities like cardiotoxicity, anaphylaxis, hypokalemia, and nephrotoxicity are major barriers to its use in areas with limited medical facilities. Liposomal amphotericins, however, are devoid of adverse effects, high cost makes it unaffordable. We had formulated nanoparticles (10-20 nm) from amphotericin B deoxycholate (1-2 μm) applying high pressure (150 atm) milling homogenization in argon atmosphere and tested its ex vivo efficacy in Leishmania infected J774A cell line and peritoneal macrophage. The ex vivo ED50 for intracellular amastigotes in peritoneal macrophage by nano-amphotericin was 0.0027 ± 0.001 μg/mL which was significantly less (p = 0.0029) than the required dose of amphotericin B (0.0426 ± 0.003 μg/mL). Similarly, in J774A cell line, 50 % of intracellular amastigotes were cleared by 0.0038 ± 0.001 μg/mL of nano-amphotericin while the dose was a bit more for AmB (0.0196 ± 0.001 μg/mL) illustrating the significant difference (p value, 0.0122). The nanoformulation has also shown high efficacy (ED50, 0.0028-0.0035 μg/mL) in inhibition of infected macrophage count. The new formulation accumulated to spleen, the targeted organ, 7 days after inoculation of drug to the infected hamster as traced in vivo by TEM convincing it as potential drug. Given a favorable safety profile and very low cost of production contemplated, it may prove to be a feasible alternative for conventional amphotericin B.

Organotin(iv) carboxylate derivatives as a new addition to anticancer and antileishmanial agents: design, physicochemical characterization and interaction with Salmon sperm DNA

The compounds interact with DNA via the intercalative mode of interaction. They show strong antibacterial, anticancer and antileishmanial activities.

Ecology- and Bioassay-Guided Drug Discovery for Treatments of Tropical Parasitic Disease: 5α,8α-Epidioxycholest-6-en-3β-ol Isolated from the Mollusk Dolabrifera dolabrifera Shows Significant Activity against Leishmania donovani

An ecology- and bioassay-guided search employed to discover compounds with activity against tropical parasitic diseases and cancer from the opisthobranch mollusk, Dolabrifera dolabrifera, led to the discovery of antileishmanial properties in the known compound, 5α,8α-epidioxycholest-6-en-3β-ol (1). Compound 1 was identified through nuclear magnetic resonance spectroscopy (1H, 13C) and mass spectrometry. The compound was concentrated in the digestive gland of D. dolabrifera, but was not detected in other body parts, fecal matter or mucus. Compound 1 showed an IC50 of 4.9 μM towards the amastigote form of Leishmania donovani compared with an IC50 of 281 μM towards the control Vero cell line, a 57.3-fold difference, and demonstrated no measurable activity against Plasmodium falciparum, Trypanosoma cruzi, and the breast cancer cell line, MCF-7.

Antidermatophytic and antileishmanial activities of essential oils from Lippia gracilis Schauer genotypes

Lippia gracilis, popularly known in Brazil as 'alecrim-de-tabuleiro', is used for many purposes, especially antimicrobial and antiseptic activities. The leaves of three L. gracilis genotypes, including LGRA-106, LGRA-109 and LGRA-110 were collected from the Active Germplasm Bank located in the "Campus Rural da UFS" research farm at the São Cristóvão country, Sergipe State, Brazil. The essential oils were obtained from leaves of L. gracilis plants by hydrodistillation. Chemical analysis of the essential oils was performed by gas chromatography-mass spectrometry (GC-MS). The susceptibility of Trichophyton rubrum strains, MYA3108 and TruMDR2, to the two L. gracilis genotypes (LGRA-106 and LGRA-109) essential oils was determined by the serial microdilution method. Leishmanicidal activity of essential oil from LGRA-106 and LGRA-110 was assayed by tetrazolium-dye (MTT) colorimetric method. The oxygenated monoterpene thymol was the main component of the essential oil from genotype LGRA-106, while Carvacrol was more abundant in LGRA-109 and LGRA-110. The concentrations of LGRA-106 and LGRA-109 essential oils that completely eliminate the fungi were determined and these concentrations were similar to those observed for fluconazole, a common antifungal drug. Among the genotype tested, LGRA-106 essential oil exhibited the best fungicidal activity at 46.87μgmL(-1). Regarding to leishmanicidal activity, the IC50, for LGRA-106 and LGRA-110, was 86.32 and 77.26μgmL(-1), respectively. The results showed that L. gracilis essential oil, rich in thymol and thymol itself presented best antidermatophytic activity, while the best leishmanicidal activity was obtained with essential oil from genotype rich in Carvacrol and Carvacrol itself.

Molecular characterization of the MRPA transporter and antimony uptake in four New World Leishmania spp. susceptible and resistant to antimony

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Level of expression of Pgp is increased in the SbIII-resistant L. guyanensis and L. amazonensis lines.

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Incorporation of antimony was reduced in the SbIII-resistant L. guyanensis, L. amazonensis and L. braziliensis lines.

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Down-regulation of AQP1 protein was observed in the SbIII-resistant L. guyanensis and L. amazonensis lines.

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Rates of SbIII efflux are higher in the SbIII-resistant lines of L. guyanensis and L. braziliensis.

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Mechanisms of antimony-resistance of the MRPA gene are different among species of Leishmania analyzed.

ATP-binding cassette (ABC) transporters have been associated with drug resistance in various diseases. The MRPA gene, a transporter of ABCC subfamily, is involved in the resistance by sequestering metal-thiol conjugates in intracellular vesicles of Leishmania parasite. In this study, we performed the molecular characterization of the MRPA transporter, analysis of P-glycoprotein (Pgp) and aquaglyceroporin-1 (AQP1) expression, and determination of antimony level in antimony-susceptible and -resistant lines of L. (V.) guyanensis, L. (L.) amazonensis, L. (V.) braziliensis and L. (L.) infantum. PFGE analysis revealed an association of chromosomal amplification of MRPA gene with the drug resistance phenotype in all SbIII-resistant Leishmania lines analyzed. Levels of mRNA from MRPA gene determined by real-time quantitative RT-PCR showed an increased expression of two fold in SbIII-resistant lines of Leishmania guyanensis, Leishmania amazonensis and Leishmania braziliensis. Western blot analysis revealed that Pgp is increased in the SbIII-resistant L. guyanensis and L. amazonensis lines. The intracellular level of antimony quantified by graphite furnace atomic absorption spectrometry showed a reduction in the accumulation of this element in SbIII-resistant L. guyanensis, L. amazonensis and L. braziliensis lines when compared to their susceptible counterparts. Interestingly, a down-regulation of AQP1 protein was observed in the SbIII-resistant L. guyanensis and L. amazonensis lines, contributing for decreasing of SbIII entry in these lines. In addition, efflux experiments revealed that the rates of SbIII efflux are higher in the SbIII-resistant lines of L. guyanensis and L. braziliensis, that may explain also the low SbIII concentration within of these parasites. The BSO, an inhibitor of γ-glutamylcysteine synthetase enzyme, reversed the SbIII-resistance phenotype of L. braziliensis and caused an increasing in the Sb intracellular level in the LbSbR line. Our data indicate that the mechanisms of antimony-resistance are different among species of Leishmania analyzed in this study.