Species-specific antimonial sensitivity in Leishmania is driven by post-transcriptional regulation of AQP1

Promising aryl selenoate derivatives as antileishmanial agents and their effects on gene expression

Leishmaniasis remains one of the main public health problems worldwide, with special incidence in the poorest populations. Selenium and its derivatives can be potent therapeutic options against protozoan parasites. In this work, 17 aryl selenoates were synthesized and screened against three species of Leishmania (Leishmania major, Leishmania amazonensis, and Leishmania infantum). Initial screening in promastigotes showed L. infantum species was more sensitive to selenoderivatives than the others. The lead Se-(2-selenocyanatoethyl) thiophene-2-carboselenoate (16) showed a half-maximal effective concentration of 3.07 µM and a selectivity index > 32.57 against L. infantum promastigotes. It was also the most effective of all 17 compounds, decreasing the infection ratio by 90% in L. infantum-infected macrophages with amastigotes at 10 µM. This aryl selenoate did not produce a hemolytic effect on human red blood cells at the studied doses (10-100 µM). Furthermore, the gene expression of infected murine macrophages related to cell death, the cell cycle, and the selenoprotein synthesis pathway in amastigotes was altered, while no changes were observed in their murine homologs, supporting the specificity of Compound 16 against the parasite. Therefore, this work reveals the possible benefits of selenoate derivatives for the treatment of leishmaniasis.

Antimony resistance and gene expression in Leishmania: spotlight on molecular and proteomic aspects

Leishmaniasis is a vector-borne parasitic disease caused by Leishmania parasites with a spectrum of clinical manifestations, ranging from skin lesions to severe visceral complications. Treatment of this infection has been extremely challenging with the concurrent emergence of drug resistance. The differential gene expression and the discrepancies in protein functions contribute to the appearance of 2 distinct phenotypes: resistant and sensitive, but the current diagnostic tools fail to differentiate between them. The identification of gene expression patterns and molecular mechanisms coupled with antimony (Sb) resistance can be leveraged to prompt diagnosis and select the most effective treatment methods. The present study attempts to use comparative expression of Sb resistance-associated genes in resistant and sensitive Leishmania, to disclose their relative abundance in clinical or in vitro selected isolates to gain an understanding of the molecular mechanisms of Sb response/resistance. Data suggest that the analysis of resistance gene expression would verify the Sb resistance or susceptibility only to a certain extent; however, none of the individual expression patterns of the studied genes was diagnostic as a biomarker of Sb response of Leishmania. The findings highlighted will be useful in bridging the knowledge gap and discovering innovative diagnostic tools and novel therapeutic targets.

Leishmanicidal activity of the venoms of the Scorpions Brotheas amazonicus and Tityus metuendus

Leishmaniasis is a vector-transmitted zoonosis caused by different species of the genus Leishmania, with a wide clinical spectrum. It is a public health problem aggravated by a series of limitations regarding treatment. In the search for new therapeutic alternatives, scorpion venoms are a source of multifunctional molecules that act against the natural resistance of pathogens. This work evaluated the antileishmanial potential of Brotheas amazonicus and Tityus metuendus venoms against the promastigote forms of Leishmania amazonensis e Leishmania guyanensis. The venoms of B. amazonicus and T. metuendus were evaluated for their constituents using Fourier Transform Infrared (FTIR). Growth inhibition and death of promastigotes were evaluated in the presence of diferente crude venom concentrations (100 µg/mL, 50 µg/mL, 10 µg/mL, 1 µg/mL) after one hour of incubation at 25 °C. The FTIR spectra of both venoms exhibited bands in approximate regions, revealing that both exhibit similar functional groups. Crude venom from both scorpion species showed similar or superior leishmanicidal effects to the standart drug N-methylglucamine antimoniate. At the highest concentration of 100 µg/mL, cultures of L. guyanensis treated with the venom of B. amazonicus showed the highest mortality percentages, above 28%, while T. metuendus venom showed the highest activity against L. amazonensis, with mortality above 7%. This preliminar study demonstrates that B. amazonicus and T. metuendus venoms can be important tools in the search for new drugs Against leishmaniasis. Next step involves evaluating the activity against the amastigote forms and purifying the venom proteins in order to identify the best anti-leishmania candidates.

Further Investigations of Nitroheterocyclic Compounds as Potential Antikinetoplastid Drug Candidates

Due to the lack of specific vaccines, management of the trypanosomatid-caused neglected tropical diseases (sleeping sickness, Chagas disease and leishmaniasis) relies exclusively on pharmacological treatments. Current drugs against them are scarce, old and exhibit disadvantages, such as adverse effects, parenteral administration, chemical instability and high costs which are often unaffordable for endemic low-income countries. Discoveries of new pharmacological entities for the treatment of these diseases are scarce, since most of the big pharmaceutical companies find this market unattractive. In order to fill the pipeline of compounds and replace existing ones, highly translatable drug screening platforms have been developed in the last two decades. Thousands of molecules have been tested, including nitroheterocyclic compounds, such as benznidazole and nifurtimox, which had already provided potent and effective effects against Chagas disease. More recently, fexinidazole has been added as a new drug against African trypanosomiasis. Despite the success of nitroheterocycles, they had been discarded from drug discovery campaigns due to their mutagenic potential, but now they represent a promising source of inspiration for oral drugs that can replace those currently on the market. The examples provided by the trypanocidal activity of fexinidazole and the promising efficacy of the derivative DNDi-0690 against leishmaniasis seem to open a new window of opportunity for these compounds that were discovered in the 1960s. In this review, we show the current uses of nitroheterocycles and the novel derived molecules that are being synthesized against these neglected diseases.

The paradigm of intracellular parasite survival and drug resistance in leishmanial parasite through genome plasticity and epigenetics: Perception and future perspective

Leishmania is an intracellular, zoonotic, kinetoplastid eukaryote with more than 1.2 million cases all over the world. The leishmanial chromosomes are divided into polymorphic chromosomal ends, conserved central domains, and antigen-encoding genes found in telomere-proximal regions. The genome flexibility of chromosomal ends of the leishmanial parasite is known to cause drug resistance and intracellular survival through the evasion of host defense mechanisms. Therefore, in this review, we discuss the plasticity of Leishmania genome organization which is the primary cause of drug resistance and parasite survival. Moreover, we have not only elucidated the causes of such genome plasticity which includes aneuploidy, epigenetic factors, copy number variation (CNV), and post-translation modification (PTM) but also highlighted their impact on drug resistance and parasite survival.

Down the membrane hole: Ion channels in protozoan parasites

Parasitic diseases caused by protozoans are highly prevalent around the world, disproportionally affecting developing countries, where coinfection with other microorganisms is common. Control and treatment of parasitic infections are constrained by the lack of specific and effective drugs, plus the rapid emergence of resistance. Ion channels are main drug targets for numerous diseases, but their potential against protozoan parasites is still untapped. Ion channels are membrane proteins expressed in all types of cells, allowing for the flow of ions between compartments, and regulating cellular functions such as membrane potential, excitability, volume, signaling, and death. Channels and transporters reside at the interface between parasites and their hosts, controlling nutrient uptake, viability, replication, and infectivity. To understand how ion channels control protozoan parasites fate and to evaluate their suitability for therapeutics, we must deepen our knowledge of their structure, function, and modulation. However, methodological approaches commonly used in mammalian cells have proven difficult to apply in protozoans. This review focuses on ion channels described in protozoan parasites of clinical relevance, mainly apicomplexans and trypanosomatids, highlighting proteins for which molecular and functional evidence has been correlated with their physiological functions.

Global distribution of treatment resistance gene markers for leishmaniasis

Background

Pentavalent antimonials (Sb(V)) such as meglumine antimoniate (Glucantime®) and sodium stibogluconate (Pentostam®) are used as first‐line treatments for leishmaniasis, either alone or in combination with second‐line drugs such as amphotericin B (Amp B), miltefosine (MIL), methotrexate (MTX), or cryotherapy. Therapeutic aspects of these drugs are now challenged because of clinical resistance worldwide.

Methods

We reviewedthe recent original studies were assessed by searching in electronic databases such as Scopus, Pubmed, Embase, and Web of Science.

Results

Studies on molecular biomarkers involved in drug resistance are essential for monitoring the disease. We reviewed genes and mechanisms of resistance to leishmaniasis, and the geographical distribution of these biomarkers in each country has also been thoroughly investigated.

Conclusion

Due to the emergence of resistant genes mainly in anthroponotic Leishmania species such as L. donovani and L. tropica, as the causative agents of ACL and AVL, respectively, selection of an appropriate treatment modality is essential. Physicians should be aware of the presence of such resistance for the selection of proper treatment modalities in endemic countries.

Tackling Drug Resistance and Other Causes of Treatment Failure in Leishmaniasis

Leishmaniasis is a tropical infectious disease caused by the protozoan Leishmania parasite. The disease is transmitted by female sand flies and, depending on the infecting parasite species, causes either cutaneous (stigmatizing skin lesions), mucocutaneous (destruction of mucous membranes of nose, mouth and throat) or visceral disease (a potentially fatal infection of liver, spleen and bone marrow). Although more than 1 million new cases occur annually, chemotherapeutic options are limited and their efficacy is jeopardized by increasing treatment failure rates and growing drug resistance. To delay the emergence of resistance to existing and new drugs, elucidating the currently unknown causes of variable drug efficacy (related to parasite susceptibility, host immunity and drug pharmacokinetics) and improved use of genotypic and phenotypic tools to define, measure and monitor resistance in the field are critical. This review highlights recent progress in our understanding of drug action and resistance in Leishmania, ongoing challenges (including setbacks related to the COVID-19 pandemic) and provides an overview of possible strategies to tackle this public health challenge.

New Vistas in the Biology of the Flagellum—Leishmania Parasites

Like other kinetoplastid protozoa, the flagellum in Leishmania parasites plays central roles throughout the life cycle. Discoveries over the past decade have begun to elucidate flagellar functions at the molecular level in both the insect vector stage promastigotes and intra-macrophage amastigotes. This focused review will highlight recent advances that contribute to understanding flagellar function in the various biological contexts encountered by Leishmania parasites.

Treatment of Cutaneous Leishmaniasis and Insights into Species-Specific Responses: A Narrative Review

Cutaneous leishmaniasis (CL) is a complex skin infection that has imposed a heavy burden on many developing countries and is caused by more than 20 Leishmania species. This disease is predominantly associated with disfiguring scars and major social stigma upon infection. The severity of the disease seemingly depends on many factors including the species of parasite, the host, region of endemicity, socio-economic status and the accessibility to health facilities. Despite myriad studies that have been performed on current and novel therapies, the treatment outcomes of CL remain contentious, possibly because of the knowledge gaps that still exist. The differential responses to the current CL therapies have become a major drawback in disease control, and the dearth of information on critical analyses of outcomes of such studies is a hindrance to the overall understanding. On the basis of currently available literature on treatment outcomes, we discuss the most effective doses, drug susceptibilities/resistance and treatment failures of the Leishmania genus for both monotherapy and combination therapy. This review focuses on the available treatment modalities for CL caused by different Leishmania species, with insights into their species-specific efficacies, which would inform the selection of appropriate drugs for the treatment and control of leishmaniasis.

The Search for Putative Hits in Combating Leishmaniasis: The Contributions of Natural Products Over the Last Decade

Despite advancements in the areas of omics and chemoinformatics, potent novel biotherapeutic molecules with new modes of actions are needed for leishmaniasis. The socioeconomic burden of leishmaniasis remains alarming in endemic regions. Currently, reports from existing endemic areas such as Nepal, Iran, Brazil, India, Sudan and Afghanistan, as well as newly affected countries such as Peru, Bolivia and Somalia indicate concerns of chemoresistance to the classical antimonial treatment. As a result, effective antileishmanial agents which are safe and affordable are urgently needed. Natural products from both flora and fauna have contributed immensely to chemotherapeutics and serve as vital sources of new chemical agents. This review focuses on a systematic cross-sectional view of all characterized anti-leishmanial compounds from natural sources over the last decade. Furthermore, IC50/EC50, cytotoxicity and suggested mechanisms of action of some of these natural products are provided. The natural product classification includes alkaloids, terpenes, terpenoids, and phenolics. The plethora of reported mechanisms involve calcium channel inhibition, immunomodulation and apoptosis. Making available enriched data pertaining to bioactivity and mechanisms of natural products complement current efforts geared towards unraveling potent leishmanicides of therapeutic relevance.

Advances in Understanding Leishmania Pathobiology: What Does RNA-Seq Tell Us?

Leishmaniasis is a vector-borne disease caused by a protozoa parasite from over 20 Leishmania species. The clinical manifestations and the outcome of the disease vary greatly. Global RNA sequencing (RNA-Seq) analyses emerged as a powerful technique to profile the changes in the transcriptome that occur in the Leishmania parasites and their infected host cells as the parasites progresses through their life cycle. Following the bite of a sandfly vector, Leishmania are transmitted to a mammalian host where neutrophils and macrophages are key cells mediating the interactions with the parasites and result in either the elimination the infection or contributing to its proliferation. This review focuses on RNA-Seq based transcriptomics analyses and summarizes the main findings derived from this technology. In doing so, we will highlight caveats in our understanding of the parasite’s pathobiology and suggest novel directions for research, including integrating more recent data highlighting the role of the bacterial members of the sandfly gut microbiota and the mammalian host skin microbiota in their potential role in influencing the quantitative and qualitative aspects of leishmaniasis pathology.

Phenotypical and genotypical differences among Leishmania (Leishmania) amazonensis isolates that caused different clinical frames in humans and dogs: A systematic review

Leishmania (Leishmania) amazonensis is an important etiological agent of American cutaneous leishmaniasis (ACL) in Brazil. The species causes a large spectrum of clinical manifestations in humans and dogs, ranging from cutaneous, cutaneous diffuse, mucocutaneous, and visceral involvement, however, the factors that drive the development of different disease forms by the same species are not yet fully known. In the present work, it was systematically reviewed the studies addressing phenotypic and genotypic characteristics of Leishmania (L.) amazonensis isolates causing cutaneous and visceral clinical frames in humans and dogs, comparing the results observed. For this, four research databases were searched for the following keywords: (Leishmania amazonensis AND visceral leishmaniasis) AND (tropism OR virulence OR visceralization OR adaptations OR mutation OR clinical presentation OR resistance OR survival OR wide spectrum). The results revealed that the complexity disease seems to involve the combination of genetic factors of the parasite (as modifications in molecules related to the virulence and metabolism) and also of the host's immune background and status. Nonetheless, the exact mechanism that leads to different clinical manifestations between strains of the same species is still uncertain and future studies must be developed to better elucidate this phenomenon.

Leishmania: Responding to environmental signals and challenges without regulated transcription

Here we describe the non-canonical control of gene expression in Leishmania, a single-cell parasite that is responsible for one of the major neglected tropical diseases. We discuss the lack of regulated RNA synthesis, the post-transcriptional gene regulation including RNA stability and regulated translation. We also show that genetic adaptations such as mosaic aneuploidy, gene copy number variations and DNA sequence polymorphisms are important means for overcoming drug challenge and environmental diversity. These mechanisms are discussed in the context of the unique flow of genetic information found in Leishmania and related protists.

Bioassay-based Corchorus capsularis L. leaf-derived β-sitosterol exerts antileishmanial effects against Leishmania donovani by targeting trypanothione reductase

Leishmaniasis, a major neglected tropical disease, affects millions of individuals worldwide. Among the various clinical forms, visceral leishmaniasis (VL) is the deadliest. Current antileishmanial drugs exhibit toxicity- and resistance-related issues. Therefore, advanced chemotherapeutic alternatives are in demand, and currently, plant sources are considered preferable choices. Our previous report has shown that the chloroform extract of Corchorus capsularis L. leaves exhibits a significant effect against Leishmania donovani promastigotes. In the current study, bioassay-guided fractionation results for Corchorus capsularis L. leaf-derived β-sitosterol (β-sitosterol_CCL) were observed by spectroscopic analysis (FTIR, ¹H NMR, ¹³C NMR and GC–MS). The inhibitory efficacy of this β-sitosterol_CCL against L. donovani promastigotes was measured (IC₅₀ = 17.7 ± 0.43 µg/ml). β-Sitosterol_CCL significantly disrupts the redox balance via intracellular ROS production, which triggers various apoptotic events, such as structural alteration, increased storage of lipid bodies, mitochondrial membrane depolarization, externalization of phosphatidylserine and non-protein thiol depletion, in promastigotes. Additionally, the antileishmanial activity of β-sitosterol_CCL was validated by enzyme inhibition and an in silico study in which β-sitosterol_CCL was found to inhibit Leishmania donovani trypanothione reductase (LdTryR). Overall, β-sitosterol_CCL appears to be a novel inhibitor of LdTryR and might represent a successful approach for treatment of VL in the future.

Leishmanicidal Potential of Hardwickiic Acid Isolated From Croton sylvaticus

Leishmania is a parasitic protozoon responsible for the neglected tropical disease Leishmaniasis. Approximately, 350 million people are susceptible and close to 70,000 death cases globally are reported annually. The lack of effective leishmanicides, the emergence of drug resistance and toxicity concerns necessitate the pursuit for effective antileishmanial drugs. Natural compounds serve as reservoirs for discovering new drugs due to their chemical diversity. Hardwickiic acid (HA) isolated from the stembark of Croton sylvaticus was evaluated for its leishmanicidal potential against Leishmania donovani and L. major promastigotes. The susceptibility of the promastigotes to HA was determined using the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide/phenazine methosulfate colorimetric assay with Amphotericin B serving as positive control. HA showed a significant antileishmanial activity on L. donovani promastigotes with an IC₅₀ value of 31.57± 0.06 µM with respect to the control drug, amphotericin B with IC₅₀ of 3.35 ± 0.14 µM). The cytotoxic activity was observed to be CC₅₀ = 247.83 ± 6.32 µM against 29.99 ± 2.82 µM for curcumin, the control, resulting in a selectivity index of SI = 7.85. Molecular modeling, docking and dynamics simulations of selected drug targets corroborated the observed antileishmanial activity of HA. Novel insights into the mechanisms of binding were obtained for trypanothione reductase (TR), pteridine reductase 1 (PTR1), and glutamate cysteine ligase (GCL). The binding affinity of HA to the drug targets LmGCL, LmPTR1, LdTR, LmTR, LdGCL, and LdPTR1 were obtained as -8.0, -7.8, -7.6, -7.5, -7.4 and -7.1 kcal/mol, respectively. The role of Lys16, Ser111, and Arg17 as critical residues required for binding to LdPTR1 was reinforced. HA was predicted as a Caspase-3 stimulant and Caspase-8 stimulant, implying a possible role in apoptosis, which was shown experimentally that HA induced parasite death by loss of membrane integrity. HA was also predicted as antileishmanial molecule corroborating the experimental activity. Therefore, HA is a promising antileishmanial molecule worthy of further development as a biotherapeutic agent.

Outwitting an Old Neglected Nemesis: A Review on Leveraging Integrated Data-Driven Approaches to Aid in Unraveling of Leishmanicides of Therapeutic Potential

The global prevalence of leishmaniasis has increased with skyrocketed mortality in the past decade. The causative agent of leishmaniasis is Leishmania species, which infects populations in almost all the continents. Prevailing treatment regimens are consistently inefficient with reported side effects, toxicity and drug resistance. This review complements existing ones by discussing the current state of treatment options, therapeutic bottlenecks including chemoresistance and toxicity, as well as drug targets. It further highlights innovative applications of nanotherapeutics-based formulations, inhibitory potential of leishmanicides, anti-microbial peptides and organometallic compounds on leishmanial species. Moreover, it provides essential insights into recent machine learning-based models that have been used to predict novel leishmanicides and also discusses other new models that could be adopted to develop fast, efficient, robust and novel algorithms to aid in unraveling the next generation of anti-leishmanial drugs. A plethora of enriched functional genomic, proteomic, structural biology, high throughput bioassay and drug-related datasets are currently warehoused in both general and leishmania-specific databases. The warehoused datasets are essential inputs for training and testing algorithms to augment the prediction of biotherapeutic entities. In addition, we demonstrate how pharmacoinformatics techniques including ligand-, structure- and pharmacophore-based virtual screening approaches have been utilized to screen ligand libraries against both modeled and experimentally solved 3D structures of essential drug targets. In the era of data-driven decision-making, we believe that highlighting intricately linked topical issues relevant to leishmanial drug discovery offers a one-stop-shop opportunity to decipher critical literature with the potential to unlock implicit breakthroughs.

Aquaporin 1 is located on the intestinal basolateral membrane in Toxocara canis and might play a role in drug uptake

Background

Aquaporins (AQPs) are a family of integral membrane channel proteins that facilitate the transport of water and other small solutes across cell membranes. AQPs appear to play crucial roles in parasite survival and represent possible drug targets for novel intervention strategy. In this work, we investigated the tissue distribution and biological roles of an aquaporin TcAQP1 in the neglected parasitic nematode Toxocara canis.

Methods

Recombinant C-terminal hydrophilic domain of AQP1 of T. canis (rTcAQP1c) and polyclonal antibody against rTcAQP1c were produced to analyse the tissue expression of native TcAQP1 in adult (female and male) worms using an immunohistochemical approach. RNA interference (RNAi), quantitative real-time PCR (qRT-PCR) and nematocidal assays were performed to investigate the functional roles of TcAQP1 in the adult stage of T. canis.

Results

Immunofluorescence analysis showed that TcAQP1 was localised predominantly in the epithelial linings of the reproductive tract and basolateral membrane of the intestine in the adult stage (female and male) of T. canis, indicating important roles in reproduction, nutrient absorption and/or osmoregulation. Treatment with silencing RNA for 24 h resulted in a significant reduction of Tc-aqp-1 mRNA level in adult T. canis, though no phenotypical change was observed. The efficient gene knockdown compromised the nematocidal activity of albendazole in vitro, suggesting the role of TcAQP1 in drug uptake.

Conclusions

The findings of this study provide important information about tissue expression and functional roles of TcAQP1 protein in adult T. canis. Understanding the biological functions of this protein in other developmental stages of T. canis and related parasitic nematodes would contribute to the discovery of novel diagnostic or anthelmintic targets.

Insights about resveratrol analogs against trypanothione reductase of Leishmania braziliensis: Molecular modeling, computational docking and in vitro antileishmanial studies

In this work, we combined molecular modeling, computational docking and in vitro analysis to explore the antileishmanial effect of some resveratrol analogs (ResAn), focusing on their pro-oxidant effect. The molecular target was the trypanothione reductase of Leishmania braziliensis (LbTryR), an essential component of the antioxidant defenses in trypanosomatid parasites. Three-dimensional structures of LbTryR were modeled and molecular docking studies of ResAn1-5 compounds showed the following affinity: ResAn1 > ResAn2 > ResAn4 > ResAn5 > ResAn3. Positive correlation was observed between these compounds' affinity to the LbTryR and the IC₅₀ values against Leishmania sp (ResAn1 < ResAn2 < ResAn4), which allows for TryR being considered an important target for them. As the compound ResAn1 showed the best antileishmanial activity, and docking studies showed its high affinity for NADP binding site (NS) of TryR, plus having been able to induce ROS production in L. braziliensis promastigotes treated, ResAn1 probably occupies NS interfering in the electron transfer processes responsible for the catalytic reaction. The in silico prediction of ADMET properties suggests that ResAn1 may be a promising drug candidate with properties to cross biological membranes and high gastrointestinal absorption, not violating Lipinski's rules. Ultimately, the antileishmanial effect of ResAn can be associated with a pro-oxidant effect which, in turn, can be exploited as an antimicrobial agent. Communicated by Ramaswamy H. Sarma.

Ammonium trichloro [1,2-ethanediolato-O,O']-tellurate cures experimental visceral leishmaniasis by redox modulation of Leishmania donovani trypanothione reductase and inhibiting host integrin linked PI3K/Akt pathway

In an endeavor to search for affordable and safer therapeutics against debilitating visceral leishmaniasis, we examined antileishmanial potential of ammonium trichloro [1,2-ethanediolato-O,O']-tellurate (AS101); a tellurium based non toxic immunomodulator. AS101 showed significant in vitro efficacy against both Leishmania donovani promastigotes and amastigotes at sub-micromolar concentrations. AS101 could also completely eliminate organ parasite load from L. donovani infected Balb/c mice along with significant efficacy against infected hamsters (˃93% inhibition). Analyzing mechanistic details revealed that the double edged AS101 could directly induce apoptosis in promastigotes along with indirectly activating host by reversing T-cell anergy to protective Th1 mode, increased ROS generation and anti-leishmanial IgG production. AS101 could inhibit IL-10/STAT3 pathway in L. donovani infected macrophages via blocking α4β7 integrin dependent PI3K/Akt signaling and activate host MAPKs and NF-κB for Th1 response. In silico docking and biochemical assays revealed AS101's affinity to form thiol bond with cysteine residues of trypanothione reductase in Leishmania promastigotes leading to its inactivation and inducing ROS-mediated apoptosis of the parasite via increased Ca2+ level, loss of ATP and mitochondrial membrane potential along with metacaspase activation. Our findings provide the first evidence for the mechanism of action of AS101 with excellent safety profile and suggest its promising therapeutic potential against experimental visceral leishmaniasis.

Gene Expression in Leishmania Is Regulated Predominantly by Gene Dosage

Leishmania tropica, a unicellular eukaryotic parasite present in North and East Africa, the Middle East, and the Indian subcontinent, has been linked to large outbreaks of cutaneous leishmaniasis in displaced populations in Iraq, Jordan, and Syria. Here, we report the genome sequence of this pathogen and 7,863 identified protein-coding genes, and we show that the majority of clinical isolates possess high levels of allelic diversity, genetic admixture, heterozygosity, and extensive aneuploidy. By utilizing paired genome-wide high-throughput DNA sequencing (DNA-seq) with RNA-seq, we found that gene dosage, at the level of individual genes or chromosomal "somy" (a general term covering disomy, trisomy, tetrasomy, etc.), accounted for greater than 85% of total gene expression variation in genes with a 2-fold or greater change in expression. High gene copy number variation (CNV) among membrane-bound transporters, a class of proteins previously implicated in drug resistance, was found for the most highly differentially expressed genes. Our results suggest that gene dosage is an adaptive trait that confers phenotypic plasticity among natural Leishmania populations by rapid down- or upregulation of transporter proteins to limit the effects of environmental stresses, such as drug selection.IMPORTANCELeishmania is a genus of unicellular eukaryotic parasites that is responsible for a spectrum of human diseases that range from cutaneous leishmaniasis (CL) and mucocutaneous leishmaniasis (MCL) to life-threatening visceral leishmaniasis (VL). Developmental and strain-specific gene expression is largely thought to be due to mRNA message stability or posttranscriptional regulatory networks for this species, whose genome is organized into polycistronic gene clusters in the absence of promoter-mediated regulation of transcription initiation of nuclear genes. Genetic hybridization has been demonstrated to yield dramatic structural genomic variation, but whether such changes in gene dosage impact gene expression has not been formally investigated. Here we show that the predominant mechanism determining transcript abundance differences (>85%) in Leishmania tropica is that of gene dosage at the level of individual genes or chromosomal somy.

Antileishmanial activity and tubulin polymerization inhibition of podophyllotoxin derivatives on Leishmania infantum

Leishmania microtubules play an important role not only in cell division, but also in keeping the shape of the parasite and motility of its free-living stages. Microtubules result from the self-assembly of alpha and beta tubulins, two phylogenetically conserved and very abundant eukaryotic proteins in kinetoplastids. The colchicine binding domain has inspired the discovery and development of several drugs currently in clinical use against parasites. However, this domain is less conserved in kinetoplastids and may be selectively targeted by new compounds. This report shows the antileishmanial effect of several series of compounds (53), derived from podophyllotoxin (a natural cyclolignan isolated from rhizomes of Podophyllum spp.) and podophyllic aldehyde, on a transgenic, fluorescence-emitting strain of Leishmania infantum. These compounds were tested on both promastigotes and amastigote-infected mouse splenocytes, and in mammalian – mouse non-infected splenocytes and liver HepG2 cells – in order to determine selective indexes of the drugs. Results obtained with podophyllotoxin derivatives showed that the hydroxyl group at position C-7α was a structural requisite to kill the parasites. On regards podophyllic aldehyde, derivatives with C9-aldehyde group integrated into a bicyclic heterostructure displayed more potent antileishmanial effects and were relatively safe for host cells. Docking studies of podophyllotoxin and podophyllic aldehyde derivatives showed that these compounds share a similar pattern of interaction at the colchicine site of Leishmania tubulin, thus pointing to a common mechanism of action. However, the results obtained suggested that despite tubulin is a remarkable target against leishmaniasis, there is a poor correlation between inhibition of tubulin polymerization and antileishmanial effect of many of the compounds tested, fact that points to alternative pathways to kill the parasites.

Effectiveness of Short-Course Meglumine Antimoniate (Glucantime®) for Treatment of Visceral Leishmaniasis: A 13-Year, Multistage, Non-Inferiority Study in Iran

The World Health Organization's (WHO) recommendation is 28-day course of meglumine antimoniate (Glucantime^®, Sanofi Aventis, France) for the treatment of visceral leishmaniasis (VL). The aim of this study was to evaluate the effectiveness of a shorter duration of treatment in regions with low level of resistance to Glucantime. During 13 years, this study was conducted in three phases on 392 patients. In the pilot first phase, we performed splenic punctures in seven patients to assess the correlation between the changes in the parasite load during treatment with Glucantime and defervescence. With defervescence, parasite density was dramatically dropped (P = 0.014), propounding defervescence as a marker of parasitological response. On the basis of the results, we conducted a randomized trial on 75 patients, comparing the efficacy of continuation of Glucantime therapy for 1, 2, or 3 weeks after defervescence. The treatment course of 1 week after defervescence (mean = 11.7 days) was non-inferior to that of 3 weeks (final cure rate, 96% versus 100%; P = 0.023). The third phase was a retrospective cohort study of 302 patients treated either with the WHO's regimen or for 7 days after defervescence (intervention group). Relapse was detected in 8.3% patients of the intervention group and in 5% patients following the WHO's regimen (P = 0.006 for non-inferiority). The final duration of treatment in intervention group was significantly shorter than standard course (13.3 ± 2.6 versus 28 days; P < 0.001). In summary, treatment of VL with Glucantime for 1 week after defervescence was non-inferior to and appears to be an acceptable alternative to the standard 28-day course for patients in Iran who show a response to antimonial therapy.

Quinoline derivatives: Synthesis, leishmanicidal activity and involvement of mitochondrial oxidative stress as mechanism of action

Leishmaniasis comprise a spectrum of diseases caused by protozoa parasites from the genus Leishmania, affecting millions of people worldwide, mainly in subtropical countries. Most antileishmanial drugs are highly toxic, present resistance issues or require long-term treatment. Consequently, new drugs are urgently needed. Quinoline-containing compounds have displayed an impressive array of biological properties over the years, including antileishmanial activity. In the present study, we report the synthesis and evaluation of novel quinoline derivatives (QuinDer) against Leishmania species and cytotoxic effect on mammalian cells. The ROS production and mitochondrial membrane potential analyses were also studied. The compound QuinDer1 showed activity on L. amazonensis and L. braziliensis promastigotes and this compound exhibited a strong inhibition of the proliferation of L. amazonensis amastigotes at nM concentration (IC₅₀ of 0.0911 μM), being 139 times more active than miltefosine (IC₅₀ of 12.7 μM), used as reference drug. This compound presents low cytotoxicity toward murine macrophages and human erythrocytes. In addition, promastigotes of L. amazonensis treated with the compound QuinDer1 present high generation of ROS levels with low alterations in mitochondrial membrane potential and maintenance of parasite membrane integrity. No substantial NO production in infected-macrophages treated with this compound was detected. These results suggest that the compound QuinDer 1 is a potent and selective antileishmanial agent by mitochondrial oxidative stress.

Plasticity of the Leishmania genome leading to gene copy number variations and drug resistance

Leishmania has a plastic genome, and drug pressure can select for gene copy number variation (CNV). CNVs can apply either to whole chromosomes, leading to aneuploidy, or to specific genomic regions. For the latter, the amplification of chromosomal regions occurs at the level of homologous direct or inverted repeated sequences leading to extrachromosomal circular or linear amplified DNAs. This ability of Leishmania to respond to drug pressure by CNVs has led to the development of genomic screens such as Cos-Seq, which has the potential of expediting the discovery of drug targets for novel promising drug candidates.

Diagnostic Efficacy of Molecular Techniques for Detection and Identification of Leishmania Species in Human Whole Blood and Skin Samples from Ecuador

Microscopic examination is the standard method for diagnosis of cutaneous and mucocutaneous leishmaniasis despite its low sensitivity. This study compared the diagnosis efficacy of microscopic examination versus polymerase chain reaction (PCR)-based methods and DNA sequencing using whole blood and skin lesion samples from patients with suspected leishmaniasis. The presence of Leishmania was determined by microscopy and amplification of 18S ribosomal RNA gene from blood and skin samples of 22 patients. Twenty individuals were positive for leishmaniasis. Microscopic analysis identified 85%, whereas PCR identified 100% of positive cases from skin and 90% from blood. Cytochrome b gene (cyt-b) amplification and sequencing identified Leishmania guyanensis, Leishmania shawi, and Leishmania naiffi from skin and blood samples. This study demonstrated the usefulness of whole blood and molecular techniques for the diagnosis and species identification of leishmaniasis.

Silver and Nitrate Oppositely Modulate Antimony Susceptibility through Aquaglyceroporin 1 in Leishmania (Viannia) Species

Antimony (Sb) resistance in leishmaniasis chemotherapy has become one of the major challenges to the control of this spreading worldwide public health problem. Since the plasma membrane pore-forming protein aquaglyceroporin 1 (AQP1) is the major route of Sb uptake in Leishmania, functional studies are relevant to characterize drug transport pathways in the parasite. We generated AQP1-overexpressing Leishmania guyanensis and L. braziliensis mutants and investigated their susceptibility to the trivalent form of Sb (Sb(III)) in the presence of silver and nitrate salts. Both AQP1-overexpressing lines presented 3- to 4-fold increased AQP1 expression levels compared with those of their untransfected counterparts, leading to an increased Sb(III) susceptibility of about 2-fold. Competition assays using silver nitrate, silver sulfadiazine, or silver acetate prior to Sb(III) exposure increased parasite growth, especially in AQP1-overexpressing mutants. Surprisingly, Sb(III)-sodium nitrate or Sb(III)-potassium nitrate combinations showed significantly enhanced antileishmanial activities compared to those of Sb(III) alone, especially against AQP1-overexpressing mutants, suggesting a putative nitrate-dependent modulation of AQP1 activity. The intracellular level of antimony quantified by graphite furnace atomic absorption spectrometry showed that the concomitant exposure to Sb(III) and nitrate favors antimony accumulation in the parasite, increasing the toxicity of the drug and culminating with parasite death. This is the first report showing evidence of AQP1-mediated Sb(III) susceptibility modulation by silver in Leishmania and suggests the potential antileishmanial activity of the combination of nitrate salts and Sb(III).

Pi inhibits intracellular accumulation of methylglyoxal in promastigote form of L. donovani

Similar to their mammalian counterpart, protozoan parasites including Leishmania donovani detoxify methylglyoxal (MG),(1) a toxic ubiquitous product generated in glycolysis pathway. However, it differs in one or more way(s) from the humans. It is known that MG is eliminated either through glyoxalase (GLO)(2) pathway and/or excreted across the cell membrane. This toxic metabolic by-product is known to be detoxified predominantly by the GLO pathway and excretion across the cell membrane is never considered to be a significant pathway for its detoxification. We have tried to modulate these pathways under various physiological conditions to find ways that may lead to accumulation of MG in L. donovani. Besides targeting the GLO pathway, we intend to understand the mechanism of MG release across the cell membrane and possible ways to inhibit its exclusion from parasites. In our study, it was found that inorganic phosphate (Pi)(3) in the presence of glucose inhibits the production of MG as well as promotes the expulsion of MG from the cell. Moreover, the trivalent form of antimony (Sb(III)) inhibits GLO pathway and thus detoxification of MG. Inhibition of Pi transport, which is a Na(+)/H(+) dependent process, restores the Pi mediated abrogation of MG production. Thus, Sb(III) along with inhibitors of Pi transporter may be a therapeutic advancement for treatment of antimony resistant cases of human visceral leishmaniasis. However, it requires further validation using specific inhibitor(s) of Pi transporter.

Functional role of lysine 12 in Leishmania major AQP1

Leishmania major aquaglyceroporin (AQP1) is an adventitious metalloid channel that allows the bidirectional movement of arsenite and antimonite. Here we demonstrate that AQP1 is subjected to proteasome-dependent degradation. Treatment of Leishmania promastigotes with the proteasome inhibitor MG132 resulted in increased AQP1 accumulation. Site-directed mutagenesis in AQP1 revealed that alteration of lysine 12 to either alanine or arginine improves protein stability. AQP1 expression is stabilized by mitogen-activated protein kinase 2 (MPK2). Cells expressing a dominant-negative MPK2 mutant exhibited severely reduced AQP1 expression, which could be reversed upon addition of MG132. Interestingly, the dominant-negative MPK2 mutant could not destabilize either AQP1K12A or AQP1K12R. While stabilization of AQP1 by MPK2 leads to its relocalization from flagellum to the entire surface of the parasite, altered AQP1K12A or AQP1K12R was restricted to flagellum only. Our data demonstrate that lysine 12 is targeted for proteasomal degradation of AQP1 and plays an integral role in subcellular localization of AQP1 as well as its interaction with MPK2. This work also raises the possibility that a strategy combining antimonial with a proteasome inhibitor may be an effective combination regimen against diverse forms of leishmaniasis.

Number and regulation of protozoan aquaporins reflect environmental complexity

Protozoa are a diverse group of unicellular eukaryotes. Evidence has accumulated that protozoan aquaporin water and solute channels (AQP) contribute to adaptation in changing environments. Intracellular protozoan parasites live a well-sheltered life. Plasmodium spp. express a single AQP, Toxoplasma gondii two, while Trypanosoma cruzi and Leishamnia spp. encode up to five AQPs. Their AQPs are thought to import metabolic precursors and simultaneously to dispose of waste and to help parasites survive osmotic stress during transmission to and from the insect vector or during kidney passages. Trypanosoma brucei is a protozoan parasite that swims freely in the human blood. Expression and intracellular localization of the three T. brucei AQPs depend on the stage of differentiation during the life cycle, suggesting distinct roles in energy generation, metabolism, and cell motility. Free-living amoebae are in direct contact with the environment, encountering severe and sudden changes in the availability of nutrition, and in the osmotic conditions due to rainfall or drought. Amoeba proteus expresses a single AQP that is present in the contractile vacuole complex required for osmoregulation, whereas Dictyostelium discoideum expresses four AQPs, of which two are present in the single-celled amoeboidal stage and two more in the later multicellular stages preceding spore formation. The number and regulation of protozoan aquaporins may reflect environmental complexity. We highlight the gated AqpB from D. discoideum as an example of how life in the wild is challenged by a complex AQP structure-function relationship.

Generation of an aquaglyceroporin AQP1 null mutant in Leishmania major

The Leishmania aquaglyceroporin AQP1 plays an important physiological role in water and uncharged polar solutes transport, volume regulation, osmotaxis, and is a key determinant of antimony resistance. By targeted gene disruption, we generated a Leishmania major promastigote AQP1 null mutant. This required several attempts but a chromosomal null AQP1 mutant was obtained by loss of heterozygosity in the presence of a rescue plasmid encoding AQP1. Growth in the absence of selection led to the loss of the rescuing plasmid, indicating that AQP1 is not essential for Leishmania viability. The AQP1-null mutant was resistant to antimonyl tartrate (SbIII) and arsenite (AsIII) due to a decrease import of these metalloids. It also exhibited alterations in its osmoregulation abilities compared with wild-type cells. This is the first report of the generation of a genetic AQP1 null mutant in Leishmania parasite, confirming its physiological function and role in resistance to antimonials, the therapeutic mainstay against Leishmania.