Leishmaniasis: current status of available drugs and new potential drug targets

Transmission of leishmaniasis from human to other vertebrates: a rapid zooanthroponotic evolution

Research regarding zoonotic diseases often focuses on those diseases that are transferred from animals to humans. However, humans are also transmitting pathogens to animals but research on this topic is not given priority and importance. I have tried to draw the attention of researchers to this area also which is equally important. The aim of this letter was to provide a brief overview of published literature regarding reverse zoonoses or zooanthroponosis in the field of leishmaniasis and highlight the need for future work in this area. Scientific research must be conducted in the field of reverse zoonoses to provide an enriched understanding of emerging disease threats to animals and should not be neglected.

Efflux pumps and antimicrobial resistance: Paradoxical components in systems genomics

Efflux pumps play a major role in the increasing antimicrobial resistance rendering a large number of drugs of no use. Large numbers of pathogens are becoming multidrug resistant due to inadequate dosage and use of the existing antimicrobials. This leads to the need for identifying new efflux pump inhibitors. Design of novel targeted therapies using inherent complexity involved in the biological network modeling has gained increasing importance in recent times. The predictive approaches should be used to determine antimicrobial activities with high pathogen specificity and microbicidal potency. Antimicrobial peptides, which are part of our innate immune system, have the ability to respond to infections and have gained much attention in making resistant strain sensitive to existing drugs. In this review paper, we outline evidences linking host-directed therapy with the efflux pump activity to infectious disease.

In-vitro and In-vivo Antileishmanial Activity of a Compound Derived of Platinum, Oxaliplatin, against Leishmania Major

This study aimed to evaluate the antileishmanial efficacy of oxaliplatin against Leishmania major (L. major) both in-vitro and in-vivo. The IC50, CC50, and SI of oxaliplatin against promastigotes, murine macrophages, Raw 264.7 cells, and intramacrophage amastigotes of L. major were investigated in-vitro. The effects of this drug on intracellular amastigotes were also assayed, and the percentage of infectivity and IIR were calculated. Flow cytometry was performed to assay apoptosis, using 50 and 100 µg/mL of oxaliplatin in the promastigotes and macrophages. In-vivo, the BALB/c mice were classified into three groups, receiving oxaliplatin, glucantime, and phosphate-buffered saline for one month, respectively. The lesion size, IFN-γ, and IL-4 levels, and parasite burden were also evaluated in the animals. After 72 h, the IC50 and CC50 of oxaliplatin against promastigotes and macrophages were respectively 0.5 and 66.78 µg/mL. The apoptosis of promastigotes and macrophages using 50 µg/mL of oxaliplatin was 7.25% and 2.14%, respectively, while apoptosis induced at 100 µg/mL was 15.48% and 2.80%, respectively. Similar to the glucantime group, the mice treated with oxaliplatin showed a lower parasite burden and smaller lesions, compared with the PBS group (p < 0.01). Furthermore, higher IFN-γ levels were reported in mice receiving oxaliplatin in comparison with those receiving PBS (p < 0.01). The current findings indicated the efficacy of oxaliplatin against promastigote and amastigote forms of Leishmania and L. major-induced leishmaniasis.

Effective Tetradentate Compound Complexes against Leishmania spp. that Act on Critical Enzymatic Pathways of These Parasites

The spectrum and efficacy of available antileishmanial drugs is limited. In the present work we evaluated in vitro the antiproliferative activity of 11 compounds based on tetradentate polyamines compounds against three Leishmania species (L. braziliensis, L. donovani and L. infantum) and the possible mechanism of action. We identified six compounds (3, 5, 6, 7, 8 and 10) effective against all three Leishmania spp both on extracellular and intracellular forms. These six most active leishmanicidal compounds also prevent the infection of host cells. Nevertheless, only compound 7 is targeted against the Leishmania SOD. Meanwhile, on the glucose metabolism the tested compounds have a species-specific effect on Leishmania spp.: L. braziliensis was affected mainly by 10 and 8, L. donovani by 7, and L. infantum by 5 and 3. Finally, the cellular ultrastructure was mainly damaged by 11 in the three Leishmania spp. studied. These identified antileishmania candidates constitute a good alternative treatment and will be further studied.

Antimicrobial activity of an antimicrobial peptide against amastigote forms of Leishmania major

Zoonotic cutaneous leishmaniasis caused by Leishmania major is a most common type of vector-borne disease in Iran. The pentavalent antimonial drugs have been used in the treatment of cutaneous leishmaniasis for a long time, but drug resistance and some of serious side effects have been reported. Thus, discovery and development of new therapeutic candidates are needed. The CM11 peptide is one of these peptides that its anti-bacterial activity has been proven. This peptide is a short cecropin–melittin hybrid peptide obtained through a sequence combination approach. The aim of this study was to evaluate in vitro anti-leishmanial activity of CM11 peptide against amastigote forms of Leishmania major. In this study, amastigote forms of Iranian strain of L. major (MRHO/IR/75/ER) were cultured in the presence of different concentrations of meglumine antimoniate (Glucantime^®) to find the most appropriate in vitro concentration of Glucantime^® against L. major amastigotes. Then, the anti-leishmanial activities of various concentrations of CM11 peptide (8, 16, 32 and 64 µM) were evaluated for 24, 48 and 72 hr by DAPI staining. In addition, MTT assay was used to determine the cytotoxic effects of CM11 peptide on murine fibroblast cell line. The results showed that CM11 peptide has antimicrobial activity against Iranian isolate of L. major in the laboratory conditions. It seems that the CM11 peptide has significant potential to be used as a new anti-leishmanial agent.

Antileishmanial activity and cytotoxicity of ent-beyerene diterpenoids

We describe the in vitro activity of two natural isomeric ent-beyerene diterpenes, several derivatives and synthetic intermediates. Beyerenols 1 and 2 showed EC₅₀ of 4.6 ± 9.4 and 5.3 ± 9.4 μg/mL against amastigotes of L. (V) brazilensis, with SI of 5.1 and 7.7, respectively. Beyerenol 1 was synthesized from stevioside. In vivo experiments with bereyenols showed cure in 50% of hamsters infected with L. (V) brazilensis topically applied as Cream I (beyerenol 1, 0.81%, w/w) and Cream III (beyerenol 2, 1.96%, w/w). These results suggest that beyerenols are potential candidates for cutaneous leishmaniasis chemotherapy by topical application. In vitro assays of amastigotes of L. (V) brazilensis showed EC₅₀ of 1.1 ± 0.1 and 1.3 ± 0.04 μg/mL, with SI of 3.1 and 3.5 for hydrazone intermediates 10 and 11, respectively.

Visceral leishmaniasis and HIV coinfection: current perspectives

Visceral leishmaniasis (VL) is caused by Leishmania donovani and Leishmania infantum. The burden of VL is concentrated in tropical and subtropical areas; however, HIV infection has spread VL over a hyperendemic area. Several outcomes are observed as a result of VL–HIV coinfection. Impacts are observed in immunopathogenesis, clinical manifestation, diagnosis, and therapeutic response. Concerning clinical manifestation, typical and unusual manifestation has been observed during active VL in HIV-infected patient, as well as alteration in immunoresponse, inducing greater immunosuppression by low CD4 T-lymphocyte count or even by induction of immunoactivation, with cell senescence. Serological diagnosis of VL in the HIV-infected is poor, due to low humoral response, characterized by antibody production, so parasitological methods are more recommended. Another important and even more challenging point is the definition of the best therapeutic regimen for VL in HIV-coinfected patients, because in this population there is greater failure and consequently higher mortality. The challenge of better understanding immunopathogenesis in order to obtain more effective therapies is one of the crucial points to be developed. The combination of drugs and the use of secondary prophylaxis associated with highly active antiretroviral therapy may be the best tool for treatment of HIV coinfection. Some derivatives from natural sources have action against Leishmania; however, studies have been limited to in vitro evaluation, without clinical trials.

Exploitation of Mangrove Endophytic Fungi for Infectious Disease Drug Discovery

There is an acute need for new and effective agents to treat infectious diseases. We conducted a screening program to assess the potential of mangrove-derived endophytic fungi as a source of new antibiotics. Fungi cultured in the presence and absence of small molecule epigenetic modulators were screened against Mycobacterium tuberculosis and the ESKAPE panel of bacterial pathogens, as well as two eukaryotic infective agents, Leishmania donovani and Naegleria fowleri. By comparison of bioactivity data among treatments and targets, trends became evident, such as the result that more than 60% of active extracts were revealed to be selective to a single target. Validating the technique of using small molecules to dysregulate secondary metabolite production pathways, nearly half (44%) of those fungi producing active extracts only did so following histone deacetylase inhibitory (HDACi) or DNA methyltransferase inhibitory (DNMTi) treatment.

Transforming Growth Factor Beta (TGFβ1) and Epidermal Growth Factor (EGF) as Biomarkers of Leishmania (V) braziliensis Infection and Early Therapeutic Response in Cutaneous Leishmaniasis: Studies in Hamsters

Introduction: In cutaneous leishmaniasis, the host immune response is responsible for the development of skin injuries but also for resolution of the disease especially after antileishmanial therapy. The immune factors that participate in the regulation of inflammation, remodeling of the extracellular matrix, cell proliferation and differentiation may constitute biomarkers of diseases or response to treatment. In this work, we analyzed the production of the growth factors EGF, TGFβ1, PDGF, and FGF during the infection by Leishmania parasites, the development of the injuries and the early response to treatment. Methodology: Golden hamsters were infected with L. (V) braziliensis. The growth factors were detected in skin scrapings and biopsies every 2 weeks after infected and then at day 7 of treatment with different drug candidates by RT-qPCR. The parasitic load was also quantified by RT-qPCR in skin biopsies sampled at the end of the study. Results: The infection by L. (V) braziliensis induced the expression of all the growth factors at day 15 of infection. One month after infection, EGF and TGFβ1 were expressed in all hamsters with inverse ratio. While the EGF and FGF levels decreased between day 15 and 30 of infection, the TGFβ1 increased and the PGDF levels did not change. The relative expression of EGF and TGFβ1 increased notably after treatment. However, the increase of EGF was associated with clinical cure while the increase of TGFβ1 was associated with failure to treatment. The amount of parasites in the cutaneous lesion at the end of the study decreased according to the clinical outcome, being lower in the group of cured hamsters and higher in the group of hamsters that had a failure to the treatment. Conclusions: A differential profile of growth factor expression occurred during the infection and response to treatment. Higher induction of TGFβ1 was associated with active disease while the higher levels of EGF are associated with adequate response to treatment. The inversely EGF/TGFβ1 ratio may be an effective biomarker to identify establishment of Leishmania infection and early therapeutic response, respectively. However, further studies are needed to validate the utility of the proposed biomarkers in field conditions.

Active Natural Product Scaffolds against Trypanosomatid Parasites: A Review

Neglected tropical diseases caused by trypanosomatid parasites are a continuing and escalating problem, which devastate the less economically developed cultures in countries in which they are endemic by impairing both human and animal health. Current drugs for these diseases are regarded as out-of-date and expensive, with unacceptable side-effects and mounting parasite resistance, meaning there is an urgent need for new therapeutics. Natural products have long been a source of potent, structurally diverse bioactive molecules. Herein are reviewed natural products with reported trypanocidal activity, which have been clustered based on core structural similarities, to aid the future discovery of new trypanocidal core motifs with potential routes to synthetically accessible natural product cores suggested.

Challenges in drug discovery targeting TriTryp diseases with an emphasis on leishmaniasis

Tritryps diseases are devastating parasitic neglected infections caused by Leishmania spp., Trypanosoma cruzi and Trypanosoma brucei subspecies. Together, these parasites affect more than 30 million people worldwide and cause high mortality and morbidity. Leishmaniasis comprises a complex group of diseases with clinical manifestation ranging from cutaneous lesions to systemic visceral damage. Antimonials, the first-choice drugs used to treat leishmaniasis, lead to high toxicity and carry significant contraindications limiting its use. Drug-resistant parasite strains are also a matter for increasing concern, especially in areas with very limited resources. The current scenario calls for novel and/or improvement of existing therapeutics as key research priorities in the field. Although several studies have shown advances in drug discovery towards leishmaniasis in recent years, key knowledge gaps in drug discovery pipelines still need to be addressed. In this review we discuss not only scientific and non-scientific bottlenecks in drug development, but also the central role of public-private partnerships for a successful campaign for novel treatment options against this devastating disease.

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Treatment options targeting TriTryp diseases are limited.

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Scientific and non-scientific bottlenecks need to be unveiled for the development of new treatments.

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Private and public sector partnership is key to allow advances in bench-to-bedside science.

Bovine serum albumin nanoparticles containing amphotericin B were effective in treating murine cutaneous leishmaniasis and reduced the drug toxicity

Cutaneous leishmaniasis is the most common form of leishmaniasis and the available chemotherapy causes serious side effects, justifying the search for new therapies. This study investigated the antileishmanial activity of bovine serum albumin (BSA) nanoparticles containing amphotericin B (AmB) against Leishmania amazonensis. The antiproliferative activity against promastigotes and amastigotes was assessed and the cytotoxicity was determined and compared to commercial AmB-deoxycholate (AmB-D). In vivo antileishmania activity was evaluated in murine cutaneous leishmaniasis model. BSA nanoparticles showed spherical shape, mean size about 180 nm, zeta potential of ≈ -45 mV and AmB encapsulation efficiency >95%. AmB-D was effective in promastigote and amastigote forms, while AmB-loaded BSA nanoparticles were more effective against amastigotes than promastigotes. AmB-D was more effective than AmB-loaded BSA nanoparticles in both forms, however, the lowest cytotoxicity against macrophages was achieved by AmB-nanoparticles. BALB/c mice treated with AmB-D or AmB-loaded BSA nanoparticles showed a significant decrease in the lesion thickness at the infected footpad. Histopathological analysis after 3 weeks of treatment revealed AmB-D-related toxicity in heart, spleen, lung, liver and kidneys, while treatment with AmB-loaded BSA nanoparticles did not reveal tissue toxicity. The antileishmanial efficacy and the reduced toxicity become BSA nanoparticles containing AmB a potential candidate for treating cutaneous leishmaniasis.

Feature optimization in high dimensional chemical space: statistical and data mining solutions

Objectives

The primary goal of this experiment is to prioritize molecular descriptors that control the activity of active molecules that could reduce the dimensionality produced during the virtual screening process. It also aims to: (1) develop a methodology for sampling large datasets and the statistical verification of the sampling process, (2) apply screening filter to detect molecules with polypharmacological or promiscuous activity.

Results

Sampling from large a dataset and its verification were done by applying Z-test. Molecular descriptors were prioritized using principal component analysis (PCA) by eliminating the least influencing ones. The original dimensions were reduced to one-twelfth by the application of PCA. There was a significant improvement in statistical parameter values of virtual screening model which in turn resulted in better screening results. Further improvement of screened results was done by applying Eli Lilly MedChem rules filter that removed molecules with polypharmacological or promiscuous activity. It was also shown that similarities in the activity of compounds were due to the molecular descriptors which were not apparent in prima facie structural studies.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3535-y) contains supplementary material, which is available to authorized users.

Antileishmanial Activity of Amphotericin B-loaded-PLGA Nanoparticles: An Overview

In recent decades, nanotechnology has made phenomenal strides in the pharmaceutical field, favouring the improvement of the biopharmaceutical properties of many active compounds. Many liposome-based formulations containing antitumor, antioxidant and antifungal compounds are presently on the market and are used daily (for example Doxil^®/Caelyx^® and Ambisome^®). Polymeric nanoparticles have also been used to entrap many active compounds with the aim of improving their pharmacological activity, bioavailability and plasmatic half-life while decreasing their side effects. The modulation of the structural/morphological properties of nanoparticles allows us to influence various technological parameters, such as the loading capacity and/or the release profile of the encapsulated drug(s). Amongst the biocompatible polymers, poly(D,L-lactide) (PLA), poly(D,L-glycolide) (PLG) and their co-polymers poly(lactide-co-glycolide) (PLGA) are the most frequently employed due to their approval by the FDA for human use. The aim of this review is to provide a description of the foremost recent investigations based on the encapsulation of amphotericin B in PLGA nanoparticles, in order to furnish an overview of the technological properties of novel colloidal formulations useful in the treatment of Leishmaniasis. The pharmacological efficacy of the drug after nanoencapsulation will be compared to the commercial formulations of the drug (i.e., Fungizone^®, Ambisome^®, Amphocil^® and Abelcet^®).

In vitro 4-Aryloxy-7-chloroquinoline derivatives are effective in mono- and combined therapy against Leishmania donovani and induce mitocondrial membrane potential disruption

The present study evaluates in vitro the effect of two synthetic compounds of the 7-chloro-4-aryloxyquinoline series, QI (C₁₇H₁₂ClNO₃) and QII (C₁₈H₁₅ClN₄O₂S), on Leishmania donovani parasites. The results obtained demonstrate that these compounds are able to inhibit the proliferation of L. donovani promastigotes in a dose-dependent way (QI IC₅₀ = 13.03 ± 3.4 and QII IC₅₀ = 7.90 ± 0.6 μM). Likewise, these compounds significantly reduced the percentage of macrophage infection by amastigotesand the number of amastigotes within macrophage phagolysosomes, the clinical relevant phase of these parasites. Compound QI showed an IC₅₀ value of 0.66 ± 0.2 μM, while for derivative QII, the corresponding IC₅₀ was 1.02 ± 0.17 μM. Interestingly, the amastigotes were more susceptible to the drug treatment when compared to promastigotes. Furthermore, no cytotoxic effect of these compounds was observed on the macrophage cell line at the concentrations tested. The combination of these compounds with miltefosine and amphotericin B on both parasite morphotypes was evaluated. The isobolograms showed a synergistic effect for both combinations; with a Fractional Inhibitory Concentration (FIC) Index lower than 1 for promastigotes and less than 0.3 for intracellular amastigotes. The effect of QI and QII on mitochondrial membrane potential was also studied. The combination of quinolone derivatives compounds with miltefosine and amphotericin B showed 5-8-fold stronger depolarization of membrane mitochondrial potential when compared to drugs alone. The present work validates the combination of drugs as an effective alternative to potentiate the action of anti-Leishmania agents and points to the quinoline compounds studied here as possible leishmanicidal drugs.

Toward a Drug Against All Kinetoplastids: From LeishBox to Specific and Potent Trypanothione Reductase Inhibitors

Leishmaniasis, Chagas disease, and sleeping sickness affect millions of people worldwide and lead to the death of about 50 000 humans per year. These diseases are caused by the kinetoplastids Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, respectively. These parasites share many general features, including gene conservation, high amino acid identity among proteins, the presence of subcellular structures as glycosomes and the kinetoplastid, and genome architecture, that may make drug development family specific, rather than species-specific, i.e., on the basis of the inhibition of a common, conserved parasite target. However, no optimal molecular targets or broad-spectrum drugs have been identified to date to cure these diseases. Here, the LeishBox from GlaxoSmithKline high-throughput screening, a 192-molecule set of best antileishmanial compounds, based on 1.8 million compounds, was used to identify specific inhibitors of a validated Leishmania target, trypanothione reductase (TR), while analyzing in parallel the homologous human enzyme glutathione reductase (GR). We identified three specific highly potent TR inhibitors and performed docking on the TR solved structure, thereby elucidating the putative molecular basis of TR inhibition. Since TRs from kinetoplastids are well conserved, and these compounds inhibit the growth of Leishmania, Trypanosoma cruzi, and Trypanosoma brucei, the identification of a common validated target may lead to the development of potent antikinetoplastid drugs.

Synthesis and In vitro Leishmanicidal Activities of Six Quercetin Derivatives

Background:

Today, leishmaniasis is a widespread, infectious parasitic disease caused by Leishmania spp. Natural-derived compounds are likely to provide a valuable source of new pharmaceuticals, and among them, quercetin derivatives may have antileishmanial effects. The antileishmanial activity of 3,5,7,3’,4’-pentahydroxyflavonol (quercetin) derivatives is partly attributed to the position and pKa of phenolic or catechol hydroxyl groups. Therefore, to optimize their leishmanicidal effect, the structural features of quercetin and its derivatives were improved by acylation or alkylation of hydroxyl groups and changing their pKa and consequently their activities.

Materials and Methods:

In this study, during a regioselective method, quercetin derivatives were synthesized. The structures of synthesized compounds were confirmed by mass, IR, ¹H-, and ¹³C-NMR spectral data. The antileishmanial activities of compounds 1–6 were compared with glucantime as the standard drug against promastigotes of Leishmania major using standard cell-based leishmanicidal assay.

Results:

In this study, during a regioselective method, two 7-O-quercetin derivatives (5 and 6), and three quercetin acetate derivatives (2, 3, and 4) were synthesized. In detail, the IC₅₀ values found against L. major were (1) 2.5 ± 0.92; (2) 2.85 ± 0.99; (3) 15.5 ± 1.95; (4) 13.5 ± 3.5; (5) 2.6 ± 0.57; and (6) 1.3 ± 0.35 μM while IC₅₀ value of glucantime as the standard drug was 88.5 ± 9.47 μM.

Conclusions:

The present study showed an effective antileishmanial activity of quercetin semisynthetic compounds (1–6) against in vitro promastigotes of L. major. Among them, quercetin analogs with more lipophilic and iron-chelating activity showed more antiparasite activity.

Centrin-Deleted Leishmania donovani Parasites Help CD4+ T Cells to Acquire Th1 Phenotype and Multi-Functionality Through Downregulation of CD200-CD200R Immune Inhibitory Axis

The protozoan parasite Leishmania has evolved several strategies to undermine host defense mechanisms by inducing Th2-type adaptive immunity and suppressing effector functions of Th1 phenotype. In our earlier studies, using centrin gene-deleted Leishmania (LdCen^−/−) parasites as an immunogen, we have shown induction of an effective Th1-type immunity and robust memory responses that mediate protection against virulent challenge. However, role of inhibitory signals in Leishmania vaccine induced immunity in general, and LdCen^−/− in particular has not been studied. Herein, we report that immunization with LdCen^−/− parasites produces more functional Th1-type CD4⁺ T cells via downregulation of CD200–CD200R immune inhibitory axis compared to wild-type infection. We found that expression of CD200 and CD200R was significantly reduced in LdCen^−/− infection compared to wild-type infection. Diminished CD200–CD200R signaling in LdCen^−/− infection enabled proliferation of CD4⁺ T cells and resulted in the induction of pro-inflammatory cytokines and suppression of anti-inflammatory response. The effects of diminished CD200–CD200R signaling by LdCen^−/− were most evident in the suppression of IL-10-producing CD4⁺ T cells that helped enhance more Th1 cytokine producing and multi-functional T cells compared to wild-type infection. In vivo blocking of CD200 expression with anti-CD200 treatment in wild-type infected mice limited Th2 response as indicated by reduction of IL-10-producing Tr1 cells and reduced parasite burden. On the other hand, treatment with anti-CD200 improved the LdCen^−/− vaccine-induced multifunctional response and reduction in splenic parasite load upon challenge. Taken together, these studies demonstrate the role of CD200–CD200R signals in the protection induced by LdCen^−/− parasites.

Homology modelling, molecular docking, and molecular dynamics simulations reveal the inhibition of Leishmania donovani dihydrofolate reductase-thymidylate synthase enzyme by Withaferin-A

Objective

Present in silico study was carried out to explore the mode of inhibition of Leishmania donovani dihydrofolate reductase-thymidylate synthase (Ld DHFR-TS) enzyme by Withaferin-A, a withanolide isolated from Withania somnifera. Withaferin-A (WA) is known for its profound multifaceted properties, but its antileishmanial activity is not well understood. The parasite’s DHFR-TS enzyme is diverse from its mammalian host and could be a potential drug target in parasites.

Results

A 3D model of Ld DHFR-TS enzyme was built and verified using Ramachandran plot and SAVES tools. The protein was docked with WA-the ligand, methotrexate (MTX)-competitive inhibitor of DHFR, and dihydrofolic acid (DHFA)-substrate for DHFR-TS. Molecular docking studies reveal that WA competes for active sites of both Hu DHFR and TS enzymes whereas it binds to a site other than active site in Ld DHFR-TS. Moreover, Lys 173 residue of DHFR-TS forms a H-bond with WA and has higher binding affinity to Ld DHFR-TS than Hu DHFR and Hu TS. The MD simulations confirmed the H-bonding interactions were stable. The binding energies of WA with Ld DHFR-TS were calculated using MM-PBSA. Homology modelling, molecular docking and MD simulations of Ld DHFR-TS revealed that WA could be a potential anti-leishmanial drug.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3354-1) contains supplementary material, which is available to authorized users.

Genomic and transcriptomic alterations in Leishmania donovani lines experimentally resistant to antileishmanial drugs

Leishmaniasis is a serious medical issue in many countries around the World, but it remains largely neglected in terms of research investment for developing new control and treatment measures. No vaccines exist for human use, and the chemotherapeutic agents currently used are scanty. Furthermore, for some drugs, resistance and treatment failure are increasing to alarming levels. The aim of this work was to identify genomic and trancriptomic alterations associated with experimental resistance against the common drugs used against VL: trivalent antimony (Sb^III, S line), amphotericin B (AmB, A line), miltefosine (MIL, M line) and paromomycin (PMM, P line). A total of 1006 differentially expressed transcripts were identified in the S line, 379 in the A line, 146 in the M line, and 129 in the P line. Also, changes in ploidy of chromosomes and amplification/deletion of particular regions were observed in the resistant lines regarding the parental one. A series of genes were identified as possible drivers of the resistance phenotype and were validated in both promastigotes and amastigotes from Leishmania donovani, Leishmania infantum and Leishmania major species. Remarkably, a deletion of the gene LinJ.36.2510 (coding for 24-sterol methyltransferase, SMT) was found to be associated with AmB-resistance in the A line. In the P line, a dramatic overexpression of the transcripts LinJ.27.T1940 and LinJ.27.T1950 that results from a massive amplification of the collinear genes was suggested as one of the mechanisms of PMM resistance. This conclusion was reinforced after transfection experiments in which significant PMM-resistance was generated in WT parasites over-expressing either gene LinJ.27.1940 (coding for a D-lactate dehydrogenase-like protein, D-LDH) or gene LinJ.27.1950 (coding for an aminotransferase of branched-chain amino acids, BCAT). This work allowed to identify new drivers, like SMT, the deletion of which being associated with resistance to AmB, and the tandem D-LDH-BCAT, the amplification of which being related to PMM resistance.

Successful Treatment of Disseminated Cutaneous Leishmaniasis With Liposomal Amphotericin B and Miltefosine in an Eight-year-old Girl

This case report presents an 8-year-old girl, from Fars province in Iran, diagnosed with cutaneous leishmaniasis in the form of multiple nodular, ulcerative and crusted lesions disseminated on the face, trunk and extremities. The result of direct smear of ulcers was positive for Leishmania parasite. The patient had no immunodeficiency or relevant family history making her susceptible for disseminated cutaneous leishmaniasis. The skin lesions failed to respond to multiple treatment courses of meglumine antimoniate or amphotericin B but were successfully treated with simultaneous miltefosine and liposomal amphotericin B.

Decanethiol functionalized silver nanoparticles are new powerful leishmanicidals in vitro

We evaluated, for the first time, the leishmanicidal potential of decanethiol functionalized silver nanoparticles (AgNps-SCH) on promastigotes and amastigotes of different strains and species of Leishmania: L. mexicana and L. major isolated from different patients suffering from localized cutaneous leishmaniasis (CL) and L. mexicana isolated from a patient suffering from diffuse cutaneous leishmaniasis (DCL). We recorded the kinetics of promastigote growth by daily parasite counting for 5 days, promastigote mobility, parasite reproduction by CFSE staining's protocol and promastigote killing using the propidium iodide assay. We also recorded IC₅₀'s of promastigotes and amastigotes, therapeutic index, and cytotoxicity by co-culturing macrophages with AgNps-SCH or sodium stibogluconate (Sb) used as reference drug. We used Sb as a reference drug since it is used as the first line treatment for all different types of leishmaniasis. At concentrations 10,000 times lower than those used with Sb, AgNps-SCH had a remarkable leishmanicidal effect in all tested strains of parasites and there was no toxicity to J774A.1 macrophages since > 85% were viable at the concentrations used. Therapeutic index was about 20,000 fold greater than the corresponding one for Sb treated cells. AgNps-SCH inhibited > 80% promastigote proliferation in all tested parasites. These results demonstrate there is a high leishmanicidal potential of AgNps-SCH at concentrations of 0.04 µM. Although more studies are needed, including in vivo testing of AgNps-SCH against different types of leishmaniasis, they can be considered a potential new treatment alternative.

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.

Identification of novel leishmanicidal molecules by virtual and biochemical screenings targeting Leishmania eukaryotic translation initiation factor 4A

Leishmaniases are neglected parasitic diseases in spite of the major burden they inflict on public health. The identification of novel drugs and targets constitutes a research priority. For that purpose we used Leishmania infantum initiation factor 4A (LieIF), an essential translation initiation factor that belongs to the DEAD-box proteins family, as a potential drug target. We modeled its structure and identified two potential binding sites. A virtual screening of a diverse chemical library was performed for both sites. The results were analyzed with an in-house version of the Self-Organizing Maps algorithm combined with multiple filters, which led to the selection of 305 molecules. Effects of these molecules on the ATPase activity of LieIF permitted the identification of a promising hit (208) having a half maximal inhibitory concentration (IC50) of 150 ± 15 μM for 1 μM of protein. Ten chemical analogues of compound 208 were identified and two additional inhibitors were selected (20 and 48). These compounds inhibited the mammalian eIF4I with IC50 values within the same range. All three hits affected the viability of the extra-cellular form of L. infantum parasites with IC50 values at low micromolar concentrations. These molecules showed non-significant toxicity toward THP-1 macrophages. Furthermore, their anti-leishmanial activity was validated with experimental assays on L. infantum intramacrophage amastigotes showing IC50 values lower than 4.2 μM. Selected compounds exhibited selectivity indexes between 19 to 38, which reflects their potential as promising anti-Leishmania molecules.

Apparent isocitrate lyase activity in Leishmania amazonensis

Early reports have demonstrated the occurrence of glyoxylate cycle enzymes in several Leishmania species. However, these results have been underestimated because genes for the two key enzymes of the cycle, isocitrate lyase (ICL) and malate synthase (MS), are not annotated in Leishmania genomes. We have re-examined this issue in promastigotes of Leishmania amazonensis. Enzyme activities were assayed spectrophotometrically in cellular extracts and characterized partially. A 40 kDa band displaying ICL activity was visualized on zymograms of the extracts. By immunoblotting with mouse antibodies against ICL from Bacillus stearothermophilus, a band of approximately 40 kDa was identified, coincident with the relative molecular mass of the activity band revealed on zymograms. Indirect immunofluorescence of intact promastigotes showed that the recognized antigen is distributed as a punctuated pattern, mainly distributed beneath the subpellicular microtubules, over a diffused cytoplasmic stain. These results clearly demonstrate the existence of an apparent ICL activity in L. amazonensis promastigotes, which is associated to a 40 kDa polypeptide and distributed both diffused and as punctuate aggregates in the cytoplasm. The relevance of this activity is discussed.

Leishmania infantum 5'-Methylthioadenosine Phosphorylase presents relevant structural divergence to constitute a potential drug target

BACKGROUND

The 5'-methylthioadenosine phosphorylase (MTAP), an enzyme involved in purine and polyamine metabolism and in the methionine salvage pathway, is considered as a potential drug target against cancer and trypanosomiasis. In fact, Trypanosoma and Leishmania parasites lack de novo purine pathways and rely on purine salvage pathways to meet their requirements. Herein, we propose the first comprehensive bioinformatic and structural characterization of the putative Leishmania infantum MTAP (LiMTAP), using a comparative computational approach.

RESULTS

Sequence analysis showed that LiMTAP shared higher identity rates with the Trypanosoma brucei (TbMTAP) and the human (huMTAP) homologs as compared to the human purine nucleoside phosphorylase (huPNP). Motifs search using MEME identified more common patterns and higher relatedness of the parasite proteins to the huMTAP than to the huPNP. The 3D structures of LiMTAP and TbMTAP were predicted by homology modeling and compared to the crystal structure of the huMTAP. These models presented conserved secondary structures compared to the huMTAP, with a similar topology corresponding to the Rossmann fold. This confirmed that both LiMTAP and TbMTAP are members of the NP-I family. In comparison to the huMTAP, the 3D model of LiMTAP showed an additional α-helix, at the C terminal extremity. One peptide located in this specific region was used to generate a specific antibody to LiMTAP. In comparison with the active site (AS) of huMTAP, the parasite ASs presented significant differences in the shape and the electrostatic potentials (EPs). Molecular docking of 5'-methylthioadenosine (MTA) and 5'-hydroxyethylthio-adenosine (HETA) on the ASs on the three proteins predicted differential binding modes and interactions when comparing the parasite proteins to the human orthologue.

CONCLUSIONS

This study highlighted significant structural peculiarities, corresponding to functionally relevant sequence divergence in LiMTAP, making of it a potential drug target against Leishmania.

Dataset generated for Dissection of mechanisms of Trypanothione Reductase and Tryparedoxin Peroxidase through dynamic network analysis and simulations in leishmaniasis

Leishmaniasis is the second largest parasitic killer disease caused by the protozoan parasite Leishmania, transmitted by the bite of sand flies. It's endemic in the eastern India with 165.4 million populations at risk with the current drug regimen. Three forms of leishmaniasis exist in which cutaneous is the most common form caused by Leishmania major. Trypanothione Reductase (TryR), a flavoprotein oxidoreductase, unique to thiol redox system, is considered as a potential target for chemotherapy for trypanosomatids infection. It is involved in the NADPH dependent reduction of Trypanothione disulphide to Trypanothione. Similarly, is Tryparedoxin Peroxidase (Txnpx), for detoxification of peroxides, an event pivotal for survival of Leishmania in two disparate biological environment. Fe-S plays a major role in regulating redox balance. To check for the closeness between human homologs of these proteins, we have carried the molecular clock analysis followed by molecular modeling of 3D structure of this protein, enabling us to design and test the novel drug like molecules. Molecular clock analysis suggests that human homologs of TryR i.e. Glutathione Reductase and Txnpx respectively are highly diverged in phylogenetic tree, thus, they serve as good candidates for chemotherapy of leishmaniasis. Furthermore, we have done the homology modeling of TryR using template of same protein from Leishmania infantum (PDB ID: 2JK6). This was done using Modeller 9.18 and the resultant models were validated. To inhibit this target, molecular docking was done with various screened inhibitors in which we found Taxifolin acts as common inhibitors for both TryR and Txnpx. We constructed the protein-protein interaction network for the proteins that are involved in the redox metabolism from various Interaction databases and the network was statistically analysed.

Evaluation of a new set of recombinant antigens for the serological diagnosis of human and canine visceral leishmaniasis

Current strategies for the control of zoonotic visceral leishmaniasis (VL) rely on its efficient diagnosis in both human and canine hosts. The most promising and cost effective approach is based on serologic assays with recombinant proteins. However, no single antigen has been found so far which can be effectively used to detect the disease in both dogs and humans. In previous works, we identified Leishmania infantum antigens with potential for the serodiagnosis of VL. Here, we aimed to expand the panel of the available antigens for VL diagnosis through another screening of a genomic expression library. Seven different protein-coding gene fragments were identified, five of which encoding proteins which have not been previously studied in Leishmania and rich in repetitive motifs. Poly-histidine tagged polypeptides were generated from six genes and evaluated for their potential for diagnosis of VL by ELISA (Enzyme Linked ImmunoSorbent Assay) with sera from infected humans and dogs. None of those was valid for the detection of human VL (26–52% sensitivity) although their performance was increased in the canine sera (48–91% sensitivity), with one polypeptide useful for the diagnosis of canine leishmaniasis. Next, we assayed a mixture of three antigens, found to be best for human or canine VL, among 13 identified through different screenings. This “Mix” resulted in similar levels of sensitivity for both human (84%) and canine (88%) sera. With improvements, this validates the use of multiple proteins, including antigens identified here, as components of a single system for the diagnosis of both forms of leishmaniasis.

In vivo antileishmanial activity and histopathological evaluation in Leishmania infantum infected hamsters after treatment with a furoxan derivative

N-oxide derivatives compounds such as furoxan and benzofuroxan are promising scaffolds for designing of new antileishmanial drugs. A series of furoxan (1,2,5-oxadiazole 2-N-oxide) (compounds 4a-b, and 14a-f) and benzofuroxan (benzo[c][1,2,5]oxadiazole1-N-oxide) (compounds 8a-c) derivatives were evaluated against in vitro cultured L. infantum promastigotes and amastigotes. The compounds exhibited activity against promastigote and intracellular amastigote forms with EC₅₀ values ranging from 2.9 to 71.2μM and 2.1 to 18.2μM, respectively. The most promising compound, 14e, showed good antileishmanial activity (EC₅₀=3.1μM) against intracellular amastigote forms of L. infantum with a selectivity index, based on murine macrophages (SI=66.4), almost 3-times superior to that presented by the standard drug amphotericin B (AmpB). The efficacy of 14e to eliminate the parasites in vivo was also demonstrated. Treatment of L. infantum-infected hamsters with compound 14e at 3.0mg/Kg/day led to a meaningful reduction of parasite load in spleen (49.9%) and liver (54.2%), respectively; these data were corroborated by histopathological analysis, which also revealed reduction in the number of inflammatory cells in the liver of the treated animals. Moreover, histological analysis of the spleen and kidney of treated animals did not reveal alterations suggestive of toxic effects. The parasite load reduction might be related to NO production, since this molecule is a NO-donor. We observed neither side effects nor elevation of hepatic/renal biomarker levels in the plasma. The data herein presented suggest that the compound should be considered in the development of new drugs for treatment of visceral leishmaniasis.

Identification of two natural compound inhibitors of Leishmania donovani Spermidine Synthase (SpdS) through molecular docking and dynamic studies

Visceral leishmaniasis caused by the protozoan Leishmania donovani is the most severe form of leishmaniasis and it is potentially lethal if untreated. Despite the availability of drugs for treating the disease, the current drug regime suffers from drawbacks like antibiotic resistance and toxicity. New drugs have to be discovered in order to overcome these limitations. Our aim is to identify natural compounds from plant sources as putative inhibitors considering the occurrence of structural diversity in plant sources. Spermidine Synthase (SpdS) was chosen as the target enzyme as it plays a vital role in growth, survival, and due to its contribution in virulence. Our initial investigation started with a literature survey in identifying natural compounds that showed antileishmanial activity. Subsequently, we identified two monoterpenoid compounds, namely Geraniol and Linalool, that were structurally analogous to one of the substrates (putrescine) of SpdS. In the present study, homology model of L. donovani SpdS was generated and the binding affinity of the identified compounds was analyzed and also compared with the putrescine through molecular docking and dynamic studies. The pharmacokinetic properties of the identified compounds were validated and the binding efficiency of these ligands over the original substrate has been demonstrated. Based on these studies, Geraniol and Linalool can be considered as lead molecules for future investigations targeting SpdS. This study further emphasizes the choice of natural compounds as a good source of therapeutic agents.

Efficacy of a Binuclear Cyclopalladated Compound Therapy for Cutaneous Leishmaniasis in the Murine Model of Infection with Leishmania amazonensis and Its Inhibitory Effect on Topoisomerase 1B

Leishmaniasis is a disease found throughout the (sub)tropical parts of the world caused by protozoan parasites of the Leishmania genus. Despite the numerous problems associated with existing treatments, pharmaceutical companies continue to neglect the development of better ones. The high toxicity of current drugs combined with emerging resistance makes the discovery of new therapeutic alternatives urgent. We report here the evaluation of a binuclear cyclopalladated complex containing Pd(II) and N,N'-dimethylbenzylamine (Hdmba) against Leishmania amazonensis The compound [Pd(dmba)(μ-N3)]2 (CP2) inhibits promastigote growth (50% inhibitory concentration [IC50] = 13.2 ± 0.7 μM) and decreases the proliferation of intracellular amastigotes in in vitro incubated macrophages (IC50 = 10.2 ± 2.2 μM) without a cytotoxic effect when tested against peritoneal macrophages (50% cytotoxic concentration = 506.0 ± 10.7 μM). In addition, CP2 was also active against T. cruzi intracellular amastigotes (IC50 = 2.3 ± 0.5 μM, selective index = 225), an indication of its potential for use in Chagas disease therapy. In vivo assays using L. amazonensis-infected BALB/c showed an 80% reduction in parasite load compared to infected and nontreated animals. Also, compared to amphotericin B treatment, CP2 did not show any side effects, which was corroborated by the analysis of plasma levels of different hepatic and renal biomarkers. Furthermore, CP2 was able to inhibit Leishmania donovani topoisomerase 1B (Ldtopo1B), a potentially important target in this parasite. (This study has been registered at ClinicalTrials.gov under identifier NCT02169141.).

Achievement of constitutive fluorescent pLEXSY-egfp Leishmania braziliensis and its application as an alternative method for drug screening in vitro

BACKGROUND

Gene reporter-fluorescent cells have emerged as alternative method for drug screening.

OBJECTIVE

Achievement of constitutive expression of fluorescent protein GFP by Leishmania braziliensis as alternative method for drug screening.

METHODS

L. braziliensis-GFP was generated using Leishmania tarentolae pLEXSY-egfp for constitutive expression of GFP. Fluorescent cells were selected and subjected to standardisation tests of anti-promastigote and anti-intracellular amastigote assays.

FINDINGS

Our results showed that L. braziliensis-GFP method is faster and more sensitive than Allamar Blue-resazurin.

MAIN CONCLUSION

Transfected parasites maintained stable fluorescence after successive in vitro passages and pLEXSY system can be used to achieve non-L. tarentolae fluorescent cells.

Hexadecylphosphocholine (Miltefosine) stabilized chitosan modified Ampholipospheres as prototype co-delivery vehicle for enhanced killing of L. donovani

Lipid nanoparticles are stable, biodegradable and biocompatible carriers offering excellent therapeutic efficacy. Here, a novel effort has been made to develop Miltefosine (HePC- hexadecylphosphocholine) stabilized chitosan anchored nanostructured lipid carriers (NLC) of Amphotericin B (AmB) as co-delivery vehicle to enhance killing of L. donovani. The entrapment efficiency of AmB was achieved upto 85.3% for HePC-AmB-CNLCs with mean particle size of 150.8±8.4nm, and zeta potential value of +28.2±1.1mV, respectively. The cumulative amount of AmB released at even after the 24h was less than 65% from HePC-AmB-CNLCs and Tween-80-AmB-CNLCs. Intravenous administration of HePC-AmB-CNLCs revealed the significantly increased localization of AmB in both liver and spleen when estimated. FACS study represented enhanced uptake of FITC-HePC-CNLCs over FITC-HePC-NLCs in J774A.1 cell lines. Highly significant in vitro and in vivo anti-leishmanial activity (p<0.05 compared with Tween 80-AmB-CNLCs) was observed with HePC-AmB-CNLCs when tested against VL in Leishmania donovani-infected hamsters. The haemolysis and cytotoxicity studies showed the safety of HePC-AmB-CNLCs and Tween 80-AmB-CNLCs. The findings suggested that it would be preferable to deliver AmB through HePC stabilized chitosan anchored nanostructured lipid carriers for rapid and effective treatment with decreased adverse effects.

Skin parasite landscape determines host infectiousness in visceral leishmaniasis

Increasing evidence suggests that the infectiousness of patients for the sand fly vector of visceral leishmaniasis is linked to parasites found in the skin. Using a murine model that supports extensive skin infection with Leishmania donovani, spatial analyses at macro-(quantitative PCR) and micro-(confocal microscopy) scales indicate that parasite distribution is markedly skewed. Mathematical models accounting for this heterogeneity demonstrate that while a patchy distribution reduces the expected number of sand flies acquiring parasites, it increases the infection load for sand flies feeding on a patch, increasing their potential for onward transmission. Models representing patchiness at both macro- and micro-scales provide the best fit with experimental sand fly feeding data, pointing to the importance of the skin parasite landscape as a predictor of host infectiousness. Our analysis highlights the skin as a critical site to consider when assessing treatment efficacy, transmission competence and the impact of visceral leishmaniasis elimination campaigns.

Parasitemia has been considered the main determinant of visceral leishmaniasis transmission. By combining imaging, qPCR and experimental xenodiagnoses with mathematical models, Doehl et al. argue that the patchy landscape of parasites in the skin is necessary to explain infectiousness.

Probing the efficacy of a heterologous Leishmania/L. Viannia braziliensis recombinant enolase as a candidate vaccine to restrict the development of L. infantum in BALB/c mice

In the present study, the Leishmania braziliensis enolase protein was evaluated as a vaccine candidate against visceral leishmaniasis (VL). The DNA sequence was cloned and the recombinant protein (rEnolase) was evaluated as a vaccine, associated with saponin, as an immune adjuvant. The protective efficacy of the rEnolase plus saponin combination was investigated in BALB/c mice against Leishmania infantum infection. The results revealed that the vaccine induced higher levels of IFN-γ, IL-12, and GM-CSF when a capture ELISA and flow cytometry were performed, as well as an antileishmanial nitrite production after using in vitro stimulation with rEnolase and an antigenic Leishmania preparation. The vaccinated animals, when compared to the control groups, showed a lower parasite burden in the liver, spleen, bone marrow, and paws' draining lymph nodes when both a limiting dilution technique and RT-PCR assay were performed. In addition, these mice showed low levels of antileishmanial IL-4, IL-10, and anti-Leishmania IgG1 isotype antibodies. Partial protection was associated with IFN-γ production, which was mainly mediated by CD4⁺ T cells. In conclusion, the present study's data showed that the L. braziliensis enolase protein could be considered a vaccine candidate that offers heterologous protection against VL.

In Vitro and In Vivo Evaluation of Essential Oil from Artemisia absinthium L. Formulated in Nanocochleates against Cutaneous Leishmaniasis

Background: Leishmaniasis is a zoonotic disease caused by protozoan parasites from Leishmania genus. Currently, there are no effective vaccines available and the available therapies are far from ideal. In particular, the development of new therapeutic strategies to reduce the infection caused by Leishmania amazonensis could be considered desirable. Different plant-derived products have demonstrated antileishmanial activity, including the essential oil (EO) from Artemisia absinthium L. (EO-Aa), Asteraceae. Methods: In the present study, the EO-Aa formulated in nanocochleates (EO-Aa-NC) was investigated in vitro against intracellular amastigotes of L. amazonensis and non-infected macrophages from BALB/c mice. In addition, the EO-Aa-NC was also evaluated in vivo against on experimental cutaneous leishmaniasis, which body weight, lesion progression, and parasite load were determined. Results: EO-Aa-NC displayed IC₅₀ values of 21.5 ± 2.5 μg/mL and 27.7 ± 5.6 μg/mL against intracellular amastigotes of L. amazonensis and non-infected peritoneal macrophage, respectively. In the animal model, the EO-Aa-NC (30 mg/kg/intralesional route/every 4 days 4 times) showed no deaths or weight loss greater than 10%. In parallel, the EO-Aa-NC suppressed the infection in the murine model by approximately 50%, which was statistically superior (p < 0.05) than controls and mice treated with EO-Aa. In comparison with Glucantime^®, EO-Aa-NC inhibited the progression of infection as efficiently (p > 0.05) as administration of the reference drug. Conclusions: Encochleation of EO-Aa resulted in a stable, tolerable, and efficacious antileishmanial formulation, facilitating systemic delivery of EO, with increased activity compared to administration of the free EO-Aa. This new formulation shows promising potential to future studies aimed at a new therapeutic strategy to treat leishmaniasis.