The heat shock protein HSP70 and heat shock cognate protein HSC70 contribute to antimony tolerance in the protozoan parasite leishmania

Leishmania spp. genetic factors associated with cutaneous leishmaniasis antimony pentavalent drug resistance: a systematic review

BACKGROUND

Leishmaniasis is a neglected zoonosis caused by parasites of Leishmania spp. The main drug used to treat cutaneous leishmaniasis (CL) is the antimoniate of meglumine. This drug, which has strong adverse and toxic effects, is usually administered intravenously, further complicating the difficult treatment. Factors such as Leishmania gene expression and genomic mutations appear to play a role in the development of drug resistance.

OBJECTIVES

This systematic review summarises the results of the literature evaluating parasite genetic markers possibly associated with resistance to pentavalent antimony in CL.

METHODS

This study followed PRISMA guidelines and included articles from PubMed, SciELO, and LILACS databases. Inclusion criteria were studies that (i) investigated mutations in the genome and/or changes in gene expression of Leishmania associated with treatment resistance; (ii) used antimony drugs in the therapy of CL; (iii) used naturally resistant strains isolated from patients. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess article quality and risk of bias.

FINDINGS

A total of 23 articles were selected, of which 18 investigated gene expression and nine genomic mutations. Of these 23 articles, four examined gene expression and genomic mutations in the same samples. Regarding gene expression, genes from the ABC transporter protein family, AQP1, MRPA, TDR1 and TRYR were most frequently associated with drug resistance. In one of the articles in which mutations were investigated, a mutation was found in HSP70 (T579A) and in three articles mutations were found in AQP1 (A516C, G562A and G700A). A limitation of this review is that in most of the included studies, parasites were isolated from cultured lesion samples and drug resistance was assessed using in vitro drug susceptibility testing. These approaches may not be ideal for accurate genetic evaluation and detection of treatment failure.

MAIN CONCLUSIONS

The development of further studies to evaluate the genetic resistance factors of Leishmania spp. is necessary to elucidate the mechanisms of the parasite and improve patient treatment and infection control.

Leishmania (Sauroleishmania) tarentolae versus pathogenic species: comparative evaluation of protease activity, glycoconjugates, resistance to complement and metabolome composition

BACKGROUND

Leishmania tarentolae is a non-pathogenic species found in lizards representing an important model for Leishmania biology. However, several aspects of this Sauroleishmania remain unknown to explain its low level of virulence.

OBJECTIVES

We reported several aspects of L. tarentolae biology including glycoconjugates, proteolytic activities and metabolome composition in comparison to pathogenic species (Leishmania amazonensis, Leishmania braziliensis, Leishmania infantum and Leishmania major).

METHODS

Parasites were cultured for extraction and purification of lipophosphoglycan (LPG), immunofluorescence probing with anti-gp63 and resistance against complement. Parasite extracts were also tested for proteases activity and metabolome composition.

FINDINGS

Leishmania tarentolae does not express LPG on its surface. It expresses gp63 at lower levels compared to pathogenic species and, is highly sensitive to complement-mediated lysis. This species also lacks intracellular/extracellular activities of proteolytic enzymes. It has metabolic differences with pathogenic species, exhibiting a lower abundance of metabolites including ABC transporters, biosynthesis of unsaturated fatty acids and steroids, TCA cycle, glycine/serine/threonine metabolism, glyoxylate/dicarboxylate metabolism and pentose-phosphate pathways.

MAIN CONCLUSIONS

The non-pathogenic phenotype of L. tarentolae is associated with alterations in several biochemical and molecular features. This reinforces the need of comparative studies between pathogenic and non-pathogenic species to elucidate the molecular mechanisms of virulence during host-parasite interactions.

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.

Mechanisms of genotoxicity and proteotoxicity induced by the metalloids arsenic and antimony

Arsenic and antimony are metalloids with profound effects on biological systems and human health. Both elements are toxic to cells and organisms, and exposure is associated with several pathological conditions including cancer and neurodegenerative disorders. At the same time, arsenic- and antimony-containing compounds are used in the treatment of multiple diseases. Although these metalloids can both cause and cure disease, their modes of molecular action are incompletely understood. The past decades have seen major advances in our understanding of arsenic and antimony toxicity, emphasizing genotoxicity and proteotoxicity as key contributors to pathogenesis. In this review, we highlight mechanisms by which arsenic and antimony cause toxicity, focusing on their genotoxic and proteotoxic effects. The mechanisms used by cells to maintain proteostasis during metalloid exposure are also described. Furthermore, we address how metalloid-induced proteotoxicity may promote neurodegenerative disease and how genotoxicity and proteotoxicity may be interrelated and together contribute to proteinopathies. A deeper understanding of cellular toxicity and response mechanisms and their links to pathogenesis may promote the development of strategies for both disease prevention and treatment.

Review of the Clinical Presentation, Pathology, Diagnosis, and Treatment of Leishmaniasis

Leishmaniasis is a vector-borne infection caused by kinetoplastid protozoans in the genera Leishmania and Endotrypanum. The disease occurs worldwide in the tropics and subtropics and can be particularly burdensome in resource-limited settings. Diseases caused by leishmaniasis range in severity from mild cutaneous lesions to life-threatening visceral and disfiguring mucocutaneous illnesses. Rapid and accurate diagnosis is needed to ensure proper clinical management of patients afflicted with this disease. Complicating matters of diagnosis and treatment are the diversity of species within these 2 genera and the variable specificity of diagnostic assays. This mini-review provides laboratory professionals with an overview of Leishmania epidemiology, biology, pathogenesis, clinical presentations, and treatments with additional emphasis placed on the nuances involved in diagnosis.

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.

Heat Shock Proteins as the Druggable Targets in Leishmaniasis: Promises and Perils

Leishmania, the causative agent of leishmaniasis, is an intracellular pathogen that thrives in the insect gut and mammalian macrophages to complete its life cycle. Apart from temperature difference (26 to 37°C), it encounters several harsh conditions, including oxidative stress, inflammatory reactions, and low pH. Heat shock proteins (HSPs) play essential roles in cell survival by strategically reprogramming cellular processes and signaling pathways. HSPs assist cells in multiple functions, including differentiation, adaptation, virulence, and persistence in the host cell. Due to cyclical epidemiological patterns, limited chemotherapeutic options, drug resistance, and the absence of a vaccine, control of leishmaniasis remains a far-fetched dream. The essential roles of HSPs in parasitic differentiation and virulence and increased expression in drug-resistant strains highlight their importance in combating the disease. In this review, we highlighted the diverse physiological importance of HSPs present in Leishmania, emphasizing their significance in disease pathogenesis. Subsequently, we assessed the potential of HSPs as a chemotherapeutic target and underlined the challenges associated with it. Furthermore, we have summarized a few ongoing drug discovery initiatives that need to be explored further to develop clinically successful chemotherapeutic agents in the future.

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.

Diversity and genome mapping assessment of disordered and functional domains in trypanosomatids

The proteins that have structural disorder exemplify a class of proteins which is part of a new frontier in structural biology that demands a new understanding of the paradigm of structure/function correlations. In order to address the location, relative distances and the functional/structural correlation between disordered and conserved domains, consensus disordered predictions were mapped together with CDD domains in Leishmania braziliensis M2904, Leishmania infantum JPCM5, Trypanosoma cruzi CL-Brener Esmeraldo-like, Trypanosoma cruzi Dm28c, Trypanosoma cruzi Sylvio X10, Blechomonas ayalai B08-376 and Paratrypanosoma confusum CUL13 predicted proteomes. Our results depicts the role of protein disorder in key aspects of parasites biology highlighting: a) statistical significant association between genome structural location of protein disordered consensus stretches and functional domains; b) that disordered protein stretches appear in greater percentage at upstream or downstream position of the predicted domain; c) a possible role of structural disorder in several gene expression, control points that includes but are not limited to: i) protein folding; ii) protein transport and degradation; and iii) protein modification. In addition, for values of protein with disorder content greater than 40%, a small percentage of protein binding sites in IDPs/IDRs, a higher hypothetical protein annotation frequency was observed than expected by chance and trypanosomatid multigene families linked with virulence are rich in protein with disorder content. SIGNIFICANCE: T. cruzi and Leishmania spp are the etiological agents of Chagas disease and leishmaniasis, respectively. Currently, no vaccine or effective drug treatment is available against these neglected diseases and the knowledge about the post-transcriptional and post-translational mechanisms of these organisms, which are key for this scenario, remain scarce. This study depicts the potential impact of the proximity between protein structural disorder and functional domains in the post-transcriptional regulation of pathogenic versus human non-pathogenic trypanosomatids. Our results revealed a significant statistical relationship between the genome structural locations of these two variables and disordered regions appearing more frequently at upstream or downstream positions of the CDD locus domain. This flexibility feature would maintain structural accessibility of functional sites for post-translational modifications, shedding light into this important aspect of parasite biology. This hypothesis is corroborated by the functional enrichment analysis of disordered proteins subset that highlight the involvement of this class of proteins in protein folding, protein transport and degradation and protein modification. Furthermore, our results pointed out: a) the impact of protein disorder in the process of genome annotation (proteins tend to be annotated as hypothetical when the disorder content reaches ~40%); b) that trypanosomatid multigenic families linked with virulence have a key protein disorder content.

Experimental Strategies to Explore Drug Action and Resistance in Kinetoplastid Parasites

Kinetoplastids are the causative agents of leishmaniasis, human African trypanosomiasis, and American trypanosomiasis. They are responsible for high mortality and morbidity in (sub)tropical regions. Adequate treatment options are limited and have several drawbacks, such as toxicity, need for parenteral administration, and occurrence of treatment failure and drug resistance. Therefore, there is an urgency for the development of new drugs. Phenotypic screening already allowed the identification of promising new chemical entities with anti-kinetoplastid activity potential, but knowledge on their mode-of-action (MoA) is lacking due to the generally applied whole-cell based approach. However, identification of the drug target is essential to steer further drug discovery and development. Multiple complementary techniques have indeed been used for MoA elucidation. In this review, the different 'omics' approaches employed to define the MoA or mode-of-resistance of current reference drugs and some new anti-kinetoplastid compounds are discussed.

Evaluation of potential drugs against leishmaniasis targeting catalytic subunit of Leishmania donovani nuclear DNA primase using ligand based virtual screening, docking and molecular dynamics approaches

Leishmania donovani, causes leishmaniasis, a global health trouble with around 89 different countries and its population under its risk. Replication initiation events have been instrumental in regulating the DNA duplication and as the small subunit of L. donovani nuclear DNA primase (Ld-PriS) inherits the catalytic site, it plays a vital role in DNA replication. In this study we have aimed Ld-PriS for the first time as a prospective target for the application of drug against Leishmania parasite. 3-D structures of Ld-PriS were built and ligand-based virtual screening was performed using hybrid similarity recognition techniques. Ligands from the ZINC database were used for the screening purposes based on known DNA primase inhibitor Sphingosine as a query. Top 150 ligands were taken into consideration for molecular docking against the query protein (Ld-PriS) using PyRx and iGEMDOCK softwares. Top five compounds with the best docking score were selected for pharmacokinetic investigation and molecular dynamic simulation. These top five screened inhibitors showed very poor binding affinity toward the catalytic subunit of human primase indicating their safety toward the host normal replication mechanism. The top five compounds showed good pharmacokinetic profiles and ADMET predictions revealed good absorption, solubility, permeability, uniform distribution, proper metabolism, minimal toxicity and good bioavailability. Simulation studies upto 50 ns revealed the three leads ZINC000009219046, ZINC000025998119 and ZINC000004677901 bind with Ld-PriS throughout the simulation and there were no huge variations in their backbone suggesting that these three may play as potential lead compounds for developing new drug against leishmaniasis.Communicated by Ramaswamy H. Sarma.

Comparative Transcriptome Analyses of Schistosoma japonicum Derived From SCID Mice and BALB/c Mice: Clues to the Abnormality in Parasite Growth and Development

Schistosomiasis, caused by the parasitic flatworms called schistosomes, remains one of the most prevailing parasitic diseases in the world. The prodigious oviposition of female worms after maturity is the main driver of pathology due to infection, yet our understanding about the regulation of development and reproduction of schistosomes is limited. Here, we comparatively profiled the transcriptome of Schistosoma japonicum recovered from SCID and BALB/c mice, which were collected 35 days post-infection, when prominent morphological abnormalities could be observed in schistosomes from SCID mice, by performing RNA-seq analysis. Of the 11,183 identified genes, 62 differentially expressed genes (DEGs) with 39 upregulated and 23 downregulated messenger RNAs (mRNAs) were found in male worms from SCID mice (S_M) vs. male worms from BALB/c mice (B_M), and 240 DEGs with 152 upregulated and 88 downregulated mRNAs were found in female worms from SCID mice (S_F) vs. female worms from BALB/c mice (B_F). We also tested nine DEGs with a relatively higher expression abundance in the gonads of the worms (ovary, vitellaria, or testis), suggesting their potential biological significance in the development and reproduction of the parasites. Gene ontology (GO) enrichment analysis revealed that GO terms such as “microtubule-based process,” “multicellular organismal development,” and “Rho protein signal transduction” were significantly enriched in the DEGs in S_F vs. B_F, whereas GO terms such as “oxidation–reduction process,” “response to stress,” and “response to DNA damage stimulus” were significantly enriched in the DEGs in S_M vs. B_M. These results revealed that the differential expression of some important genes might contribute to the morphological abnormalities of worms in SCID mice. Furthermore, we selected one DEG, the mitochondrial prohibitin complex protein 1 (Phb1), to perform double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) in vivo targeting the worms in BALB/c mice, and we found that it was essential for the growth and reproductive development of both male and female S. japonicum worms. Taken together, these results provided a wealth of information on the differential gene expression profiles of schistosomes from SCID mice when compared with those from BALB/c mice, which were potentially involved in regulating the growth and development of schistosomes. These findings contributed to an understanding of parasite biology and provided a rich resource for the exploitation of antischistosomal intervention targets.

HSPA8/HSC70 in Immune Disorders: A Molecular Rheostat that Adjusts Chaperone-Mediated Autophagy Substrates

HSPA8/HSC70 is a molecular chaperone involved in a wide variety of cellular processes. It plays a crucial role in protein quality control, ensuring the correct folding and re-folding of selected proteins, and controlling the elimination of abnormally-folded conformers and of proteins daily produced in excess in our cells. HSPA8 is a crucial molecular regulator of chaperone-mediated autophagy, as a detector of substrates that will be processed by this specialized autophagy pathway. In this review, we shortly summarize its structure and overall functions, dissect its implication in immune disorders, and list the known pharmacological tools that modulate its functions. We also exemplify the interest of targeting HSPA8 to regulate pathological immune dysfunctions.

Transcriptional responses of Leishmania (Leishmania) amazonensis in the presence of trivalent sodium stibogluconate

Background

In the last decade, resistance to antimonials has become a serious problem due to the emergence of drug-resistant strains. Therefore, understanding the mechanisms used by Leishmania parasites to survive under drug pressure is essential, particularly for species of medical-veterinary importance such as L. amazonensis.

Methods

Here, we used RNA-seq technology to analyse transcriptome profiles and identify global changes in gene expression between antimony-resistant and -sensitive L. amazonensis promastigotes.

Results

A total of 723 differentially expressed genes were identified between resistant and sensitive lines. Comparative transcriptomic analysis revealed that genes encoding proteins involved in metabolism (fatty acids) and stress response, as well as those associated with antimony resistance in other Leishmania species, were upregulated in the antimony-resistant line. Most importantly, we observed upregulation of genes encoding autophagy proteins, suggesting that in the presence of trivalent stibogluconate (Sb^III) L. amazonensis can activate these genes either as a survival strategy or to induce cell death, as has been observed in other parasites.

Conclusions

This work identified global transcriptomic changes in an in vitro-adapted strain in response to Sb^III. Our results provide relevant information to continue understanding the mechanism used by parasites of the subgenus Leishmania (L. amazonensis) to generate an antimony-resistant phenotype.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3603-8) contains supplementary material, which is available to authorized users.

The Hsp70/J-protein machinery of the African trypanosome, Trypanosoma brucei

The etiological agent of the neglected tropical disease African trypanosomiasis, Trypanosoma brucei, possesses an expanded and diverse repertoire of heat shock proteins, which have been implicated in cytoprotection, differentiation, as well as progression and transmission of the disease. Hsp70 plays a crucial role in proteostasis, and inhibition of its interactions with co-chaperones is emerging as a potential therapeutic target for numerous diseases. In light of genome annotations and the release of the genome sequence of the human infective subspecies, an updated and current in silico overview of the Hsp70/J-protein machinery in both T. brucei brucei and T. brucei gambiense was conducted. Functional, structural, and evolutionary analyses of the T. brucei Hsp70 and J-protein families were performed. The Hsp70 and J-proteins from humans and selected kinetoplastid parasites were used to assist in identifying proteins from T. brucei, as well as the prediction of potential Hsp70-J-protein partnerships. The Hsp70 and J-proteins were mined from numerous genome-wide proteomics studies, which included different lifecycle stages and subcellular localisations. In this study, 12 putative Hsp70 proteins and 67 putative J-proteins were identified to be encoded on the genomes of both T. brucei subspecies. Interestingly there are 6 type III J-proteins that possess tetratricopeptide repeat-containing (TPR) motifs. Overall, it is envisioned that the results of this study will provide a future context for studying the biology of the African trypanosome and evaluating Hsp70 and J-protein interactions as potential drug targets.

J-binding protein 1 and J-binding protein 2 expression in clinical Leishmania major no response-antimonial isolates

Cutaneous leishmaniasis (CL) is a major disease in many parts of the world. Since no vaccine has been developed, treatment is the best way to control it. In most areas, antimonial resistance whose mechanisms have not been completely understood has been reported. The main aim of this study is gene expression assessing of J-binging protein 1 and J-binding protein 2 in clinical Leishmania major isolates. The patients with CL from central and north Iran were considered for this study. The samples were transferred in RNAlater solution and stored in - 20 °C. RNA extraction and cDNA synthesis were performed. The gene expression analysis was done with SYBR Green real-time PCR using ∆∆CT. Written informed consent forms were filled out by patients, and then, information forms were filled out based on the Helsinki Declaration. Statistical analysis was done with SPSS (16.0; SPSS Inc, Chicago) using independent t test, Shapiro-Wilk, and Pearson's and Spearman's rank correlation coefficients. P ≤ 0.05 was considered significant. The gene expression of JBP1 and JBP2 had no relation with sex and age. The JBP1 gene expression was high in sensitive isolates obtained from north of the country. The JBP2 gene expression was significant in sensitive and no response-antimonial isolates from the north, but no significant differences were detected in sensitive and resistant isolates from central Iran. Differential gene expression of JBP1 and JBP2 in various clinical resistances isolates in different geographical areas shows multifactorial ways of developing resistance in different isolates.

Reverse Epidemiology: An Experimental Framework to Drive Leishmania Biomarker Discovery in situ by Functional Genetic Screening Using Relevant Animal Models

Leishmania biomarker discovery remains an important challenge that needs to be revisited in light of our increasing knowledge on parasite-specific biology, notably its genome instability. In the absence of classical transcriptional regulation in these early-branching eukaryotes, fluctuations in transcript abundance can be generated by gene and chromosome amplifications, which have been linked to parasite phenotypic variability with respect to virulence, tissue tropism, and drug resistance. Conducting in vitro evolutionary experiments to study mechanisms of Leishmania environmental adaptation, we recently validated the link between parasite genetic amplification and fitness gain, thus defining gene and chromosome copy number variations (CNVs) as important Leishmania biomarkers. These experiments also demonstrated that long-term Leishmania culture adaptation can strongly interfere with epidemiologically relevant, genetic signals, which challenges current protocols for biomarker discovery, all of which rely on in vitro expansion of clinical isolates. Here we propose an experimental framework independent of long-term culture termed “reverse” epidemiology, which applies established protocols for functional genetic screening of cosmid-transfected parasites in animal models for the identification of clinically relevant genetic loci that then inform targeted field studies for their validation as Leishmania biomarkers.

High-throughput Cos-Seq screen with intracellular Leishmania infantum for the discovery of novel drug-resistance mechanisms

Increasing drug resistance towards first line antimony-derived compounds has forced the introduction of novel therapies in leishmaniasis endemic areas including amphotericin B and miltefosine. However, their use is threatened by the emergence and spread of drug-resistant strains. In order to discover stage-dependent resistance genes, we have adapted the Cos-Seq approach through the introduction of macrophage infections in the pipeline. A L. infantum intracellular amastigote population complemented with a L. infantum cosmid library was submitted to increasing concentrations of miltefosine, amphotericin B and pentavalent antimonials in experimental infections of THP-1 cells. For each step of selection, amastigotes were extracted and cosmids were isolated and submitted to next-generation sequencing, followed by subsequent gene-enrichment analyses. Cos-Seq screen in amastigotes revealed four highly enriched loci for antimony, five for miltefosine and one for amphotericin B. Of these, a total of seven cosmids were recovered and tested for resistance in both promastigotes and amastigotes. Candidate genes within the pinpointed genomic regions were validated using single gene overexpression in wild-type parasites and/or gene disruption by means of a CRISPR-Cas9-based approach. This led to the identification and validation of a stage-independent antimony-resistance gene (LinJ.06.1010) coding for a putative leucine rich repeat protein and a novel amastigote-specific miltefosine-resistance gene (LinJ.32.0050) coding for a member of the SEC13 family of WD-repeat proteins. This study further reinforces the power of Cos-Seq approach to discover novel drug-resistance genes, some of which are life-stages specific.

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The Cos-Seq led to the discovery of several new genomic regions selected with drugs.

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This work led to the validation of novel drug-resistance genes in Leishmania.

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Gene LinJ.06.1010 is involved in antimony resistance in both life stages of the parasite.

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Gene LinJ.32.0050 is involved in miltefosine resistance in amastigotes.

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The amastigote screen is labour intensive but complements screens in promastigotes.

Leishmania infections: Molecular targets and diagnosis

Progress in the diagnosis of leishmaniases depends on the development of effective methods and the discovery of suitable biomarkers. We propose firstly an update classification of Leishmania species and their synonymies. We demonstrate a global map highlighting the geography of known endemic Leishmania species pathogenic to humans. We summarize a complete list of techniques currently in use and discuss their advantages and limitations. The available data highlights the benefits of molecular markers in terms of their sensitivity and specificity to quantify variation from the subgeneric level to species complexes, (sub) species within complexes, and individual populations and infection foci. Each DNA-based detection method is supplied with a comprehensive description of markers and primers and proposal for a classification based on the role of each target and primer in the detection, identification and quantification of leishmaniasis infection. We outline a genome-wide map of genes informative for diagnosis that have been used for Leishmania genotyping. Furthermore, we propose a classification method based on the suitability of well-studied molecular markers for typing the 21 known Leishmania species pathogenic to humans. This can be applied to newly discovered species and to hybrid strains originating from inter-species crosses. Developing more effective and sensitive diagnostic methods and biomarkers is vital for enhancing Leishmania infection control programs.

A mitochondrial HSP70 (HSPA9B) is linked to miltefosine resistance and stress response in Leishmania donovani

Background

Protozoan parasites of the genus Leishmania are responsible for leishmaniasis, a neglected tropical disease affecting millions worldwide. Visceral leishmaniasis (VL), caused by Leishmania donovani, is the most severe form of leishmaniasis with high rates of mortality if left untreated. Current treatments include pentavalent antimonials and amphotericin B. However, high toxicity and emergence of resistance hinder the success of these options. Miltefosine (HePC) is the first oral treatment available for leishmaniasis. While treatment with HePC has proven effective, higher tolerance to the drug has been observed, and experimental resistance is easily developed in an in vitro environment. Several studies, including ours, have revealed that HePC resistance has a multi-factorial origin and this work aims to shed light on this complex mechanism.

Methods

2D-DIGE quantitative proteomics comparing the soluble proteomes of sensitive and HePC resistant L. donovani lines identified a protein of interest tentatively involved in drug resistance. To test this link, we employed a gain-of-function approach followed by mutagenesis analysis. Functional studies were complemented with flow cytometry to measure HePC incorporation and cell death.

Results

We identified a mitochondrial HSP70 (HSPA9B) downregulated in HePC-resistant L. donovani promastigotes. The overexpression of HSPA9B in WT lines confers an increased sensitivity to HePC, regardless of whether the expression is ectopic or integrative. Moreover, the increased sensitivity to HePC is specific to the HSPA9B overexpression since dominant negative mutant lines were able to restore HePC susceptibility to WT values. Interestingly, the augmented susceptibility to HePC did not correlate with an increased HePC uptake. Leishmania donovani promastigotes overexpressing HSPA9B were subjected to different environmental stimuli. Our data suggest that HSPA9B is capable of protecting cells from stressful conditions such as low pH and high temperature. This phenotype was further corroborated in axenic amastigotes overexpressing HSPA9B.

Conclusions

The results from this study provide evidence to support the involvement of a mitochondrial HSP70 (HSPA9B) in experimental HePC resistance, a mechanism that is not yet fully understood, and reveal potential fundamental roles of HSPA9B in the biology of Leishmania. Overall, our findings are relevant for current and future antileishmanial chemotherapy strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1904-8) contains supplementary material, which is available to authorized users.

A Telomeric Cluster of Antimony Resistance Genes on Chromosome 34 of Leishmania infantum

The mechanisms underlying the drug resistance of Leishmania spp. are manifold and not completely identified. Apart from the highly conserved multidrug resistance gene family known from higher eukaryotes, Leishmania spp. also possess genus-specific resistance marker genes. One of them, ARM58, was first identified in Leishmania braziliensis using a functional cloning approach, and its domain structure was characterized in L. infantum Here we report that L. infantum ARM58 is part of a gene cluster at the telomeric end of chromosome 34 also comprising the neighboring genes ARM56 and HSP23. We show that overexpression of all three genes can confer antimony resistance to intracellular amastigotes. Upon overexpression in L. donovani, ARM58 and ARM56 are secreted via exosomes, suggesting a scavenger/secretion mechanism of action. Using a combination of functional cloning and next-generation sequencing, we found that the gene cluster was selected only under antimonyl tartrate challenge and weakly under Cu(2+) challenge but not under sodium arsenite, Cd(2+), or miltefosine challenge. The selective advantage is less pronounced in intracellular amastigotes treated with the sodium stibogluconate, possibly due to the known macrophage-stimulatory activity of this drug, against which these resistance markers may not be active. Our data point to the specificity of these three genes for antimony resistance.

Species- and Strain-Specific Adaptation of the HSP70 Super Family in Pathogenic Trypanosomatids

All eukaryotic genomes encode multiple members of the heat shock protein 70 (HSP70) family, which evolved distinctive structural and functional features in response to specific environmental constraints. Phylogenetic analysis of this protein family thus can inform on genetic and molecular mechanisms that drive species-specific environmental adaptation. Here we use the eukaryotic pathogen Leishmania spp. as a model system to investigate the evolution of the HSP70 protein family in an early-branching eukaryote that is prone to gene amplification and adapts to cytotoxic host environments by stress-induced and chaperone-dependent stage differentiation. Combining phylogenetic and comparative analyses of trypanosomatid genomes, draft genome of Paratrypanosoma and recently published genome sequences of 204 L. donovani field isolates, we gained unique insight into the evolutionary dynamics of the Leishmania HSP70 protein family. We provide evidence for (i) significant evolutionary expansion of this protein family in Leishmania through gene amplification and functional specialization of highly conserved canonical HSP70 members, (ii) evolution of trypanosomatid-specific, non-canonical family members that likely gained ATPase-independent functions, and (iii) loss of one atypical HSP70 member in the Trypanosoma genus. Finally, we reveal considerable copy number variation of canonical cytoplasmic HSP70 in highly related L. donovani field isolates, thus identifying this locus as a potential hot spot of environment–genotype interaction. Our data draw a complex picture of the genetic history of HSP70 in trypanosomatids that is driven by the remarkable plasticity of the Leishmania genome to undergo massive intra-chromosomal gene amplification to compensate for the absence of regulated transcriptional control in these parasites.

Drug resistance in eukaryotic microorganisms

Eukaryotic microbial pathogens are major contributors to illness and death globally. Although much of their impact can be controlled by drug therapy as with prokaryotic microorganisms, the emergence of drug resistance has threatened these treatment efforts. Here, we discuss the challenges posed by eukaryotic microbial pathogens and how these are similar to, or differ from, the challenges of prokaryotic antibiotic resistance. The therapies used for several major eukaryotic microorganisms are then detailed, and the mechanisms that they have evolved to overcome these therapies are described. The rapid emergence of resistance and the restricted pipeline of new drug therapies pose considerable risks to global health and are particularly acute in the developing world. Nonetheless, we detail how the integration of new technology, biological understanding, epidemiology and evolutionary analysis can help sustain existing therapies, anticipate the emergence of resistance or optimize the deployment of new therapies.

HSP70 of Leishmania amazonensis alters resistance to different stresses and mitochondrial bioenergetics

The 70 kDa heat shock protein (HSP70) is a molecular chaperone that assists the parasite Leishmania in returning to homeostasis after being subjected to different types of stress during its life cycle. In the present study, we evaluated the effects of HSP70 transfection of L. amazonensis promastigotes (pTEX-HSP70) in terms of morphology, resistance, infectivity and mitochondrial bioenergetics. The pTEX-HSP70 promastigotes showed no ultrastructural morphological changes compared to control parasites. Interestingly, the pTEX-HSP70 promastigotes are resistant to heat shock, H2O2-induced oxidative stress and hyperbaric environments. Regarding the bioenergetics parameters, the pTEX-HSP70 parasites had higher respiratory rates and released less H2O2 than the control parasites. Nevertheless, the infectivity capacity of the parasites did not change, as verified by the infection of murine peritoneal macrophages and human macrophages, as well as the infection of BALB/c mice. Together, these results indicate that the overexpression of HSP70 protects L. amazonensis from stress, but does not interfere with its infective capacity.

The TCP1γ subunit of Leishmania donovani forms a biologically active homo-oligomeric complex

Chaperonins are a class of molecular chaperons that encapsulate nascent or stress-denatured proteins and assist their intracellular assembly and folding in an ATP-dependent manner. The ubiquitous eukaryotic chaperonin, TCP1 ring complex is a hetero-oligomeric complex comprising two rings, each formed of eight subunits that may have distinct substrate recognition and ATP hydrolysis properties. In Leishmania, only the TCP1γ subunit has been cloned and characterized. It exhibited differential expression at various growth stages of promastigotes. In the present study, we expressed the TCP1γ subunit in Escherichia coli to investigate whether it forms chaperonin-like complexes and plays a role in protein folding. LdTCP1γ formed high-molecular-weight complexes within E. coli cells as well as in Leishmania cell lysates. The recombinant protein is arranged into two back-to-back rings of seven subunits each, as predicted by homology modelling and observed by negative staining electron microscopy. This morphology is consistent with that of the oligomeric double-ring group I chaperonins found in mitochondria. The LdTCP1γ homo-oligomeric complex hydrolysed ATP, and was active as assayed by luciferase refolding. Thus, the homo-oligomer performs chaperonin reactions without partner subunit(s). Further, co-immunoprecipitation studies revealed that LdTCP1γ interacts with actin and tubulin proteins, suggesting that the complex may have a role in maintaining the structural dynamics of the cytoskeleton of parasites.

Molecular Chaperones of Leishmania: Central Players in Many Stress-Related and -Unrelated Physiological Processes

Molecular chaperones are key components in the maintenance of cellular homeostasis and survival, not only during stress but also under optimal growth conditions. Folding of nascent polypeptides is supported by molecular chaperones, which avoid the formation of aggregates by preventing nonspecific interactions and aid, when necessary, the translocation of proteins to their correct intracellular localization. Furthermore, when proteins are damaged, molecular chaperones may also facilitate their refolding or, in the case of irreparable proteins, their removal by the protein degradation machinery of the cell. During their digenetic lifestyle, Leishmania parasites encounter and adapt to harsh environmental conditions, such as nutrient deficiency, hypoxia, oxidative stress, changing pH, and shifts in temperature; all these factors are potential triggers of cellular stress. We summarize here our current knowledge on the main types of molecular chaperones in Leishmania and their functions. Among them, heat shock proteins play important roles in adaptation and survival of this parasite against temperature changes associated with its passage from the poikilothermic insect vector to the warm-blooded vertebrate host. The study of structural features and the function of chaperones in Leishmania biology is providing opportunities (and challenges) for drug discovery and improving of current treatments against leishmaniasis.

Identifying vaccine targets for anti-leishmanial vaccine development

Leishmaniasis is a neglected tropical disease spread by an arthropod vector. It remains a significant health problem with an incidence of 0.2–0.4 million visceral leishmaniasis and 0.7–1.2 million cutaneous leishmaniasis cases each year. There are limitations associated with the current therapeutic regimens for leishmaniasis and the fact that after recovery from infection the host becomes immune to subsequent infection therefore, these factors force the feasibility of a vaccine for leishmaniasis. Publication of the genome sequence of Leishmania has paved a new way to understand the pathogenesis and host immunological status therefore providing a deep insight in the field of vaccine research. This review is an effort to study the antigenic targets in Leishmania to develop an anti-leishmanial vaccine.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

No stress--Hsp90 and signal transduction in Leishmania

SUMMARY Hsp90 (a.k.a. Hsp83) plays a significant role in the life cycle control of the protozoan parasite Leishmania donovani. Rather than protecting Leishmania spp. against adverse and stressful environs, Hsp90 is required for the maintenance of the motile, highly proliferative insect stage, the promastigote. However, Hsp90 is also essential for survival and proliferation of the intracellular mammalian stage, the amastigote. Moreover, recent evidence shows Hsp90 and other components of large multi-chaperone complexes as substrates of stage-specific protein phosphorylation pathways, and thus as likely effectors of the signal transduction pathways in Leishmania spp. Future efforts should be directed towards the identification of the protein kinases and the critical phosphorylation sites as targets for novel therapeutic approaches.

A novel marker, ARM58, confers antimony resistance to Leishmania spp

Protozoa of the Leishmania genus cause a variety of disease forms that rank at the top of the list of neglected tropical diseases. Anti-leishmanial drugs based on pentavalent antimony have been the mainstay of therapy for over 60 years and resistance against them is increasingly encountered in the field. The biochemical basis for this is poorly understood and likely diverse. No stringent correlation between genetic markers and antimony resistance has so far been shown, prompting us to use a functional cloning approach to identify markers of resistance. Using gene libraries derived from drug-resistant and drug-sensitive Leishmania braziliensis clinical isolates in a functional cloning strategy, we repeatedly selected one gene locus located on chromosome 20 whose amplification confers increased antimony (III) resistance in vitro to an otherwise sensitive L. braziliensis clone. The gene responsible for the effect encodes a previously hypothetical protein that we dubbed LbrARM58. It comprises four repeats of a domain of unknown function, DUF1935, one of them harbouring a potential trans-membrane domain. The gene is so far unique to the Leishmania genus, while a structurally related gene without antimony resistance functionality is also found in Trypanosoma spp. Overexpression of LbrARM58 also confers antimony resistance to promastigotes and intracellular amastigotes of the related species Leishmania infantum, indicating a conserved function in Old World and New World Leishmania species. Our results also show that in spite of their RNAi system, L. braziliensis promastigotes can serve as acceptor cells for episomally propagated cosmid libraries, at least for the initial stages of functional cloning efforts.

Antimony transport mechanisms in resistant leishmania parasites

Antimonial compounds have been used for more than a century in the treatment of the parasitic disease leishmaniasis. Although pentavalent antimonials are still first-line drugs in several developing countries, this class of drugs is no longer recommended in the Indian sub-continent because of the emergence of drug resistance. The precise mechanisms involved in the resistance of leishmania parasites to antimony are still subject to debate. It is now well documented that drug resistance in leishmania parasites is a multifactorial phenomenon involving multiple genes whose expression pattern synergistically leads to the resistance phenotype. The reduction of intracellular antimony accumulation is a frequent change observed in resistant leishmania cells; however, no comprehensive transport model has been presented so far to explain this change and its contribution to Leishmania resistance. The present review firstly covers the actual knowledge on the metabolism of antimonial drugs, the mechanisms of their transmembrane transport and intracellular processing in Leishmania. It further describes both the functional and molecular changes associated with Sb resistance in this organism. Possible transport models based on the actual knowledge are then presented, as well as their functional implications. Biophysical and pharmacological strategies are finally proposed for the precise identification of the transport pathways.

Comparative transcript expression analysis of miltefosine-sensitive and miltefosine-resistant Leishmania donovani

Leishmania donovani is the causative agent of anthroponotic visceral leishmaniasis in the Indian subcontinent. Oral miltefosine therapy has recently replaced antimonials in endemic areas. However, the drug is at risk of emergence of resistance due to unrestricted use, and, already, there are indications towards decline in treatment efficacy. Hence, understanding the mechanism of miltefosine resistance in the parasite is crucial. We employed genomic microarray analysis to compare the gene expression patterns of miltefosine-resistant and miltefosine-sensitive L. donovani. Three hundred eleven genes, representing ∼3.9% of the total Leishmania genome, belonging to various functional categories including metabolic pathways, transporters, and cellular components, were differentially expressed in miltefosine-resistant parasite. Results in the present study highlighted the probable mechanisms by which the parasite sustains miltefosine pressure including (1) compromised DNA replication/repair mechanism, (2) reduced protein synthesis and degradation, (3) altered energy utilization via increased lipid degradation, (4) increased ABC 1-mediated drug efflux, and (5) increased antioxidant defense mechanism via elevated trypanothione metabolism. The study provided the comprehensive insight into the underlying mechanism of miltefosine resistance in L. donovani that may be useful to design strategies to increase lifespan of this important oral antileishmanial drug.

Reduced antimony accumulation in ARM58-overexpressing Leishmania infantum

Antimony-based drugs are still the mainstay of chemotherapy against Leishmania infections in many countries where the parasites are endemic. The efficacy of antimonials has been compromised by increasing numbers of resistant infections, the basis of which is not fully understood and likely involves multiple factors. By using a functional cloning strategy, we recently identified a novel antimony resistance marker, ARM58, from the parasite Leishmania braziliensis that protects the parasites against antimony-based antileishmanial compounds. Here we show that the Leishmania infantum homologue also confers resistance against antimony but not against other antileishmanial drugs and that its function depends critically on one of four conserved domains of unknown function. This critical domain requires at least two hydrophobic amino acids and is predicted to form a transmembrane structure. Overexpression of ARM58 in antimony-exposed parasites reduces the intracellular Sb accumulation by over 70%, indicating a role for ARM58 in Sb extrusion pathways, but without involvement of energy-dependent transporter proteins.

Proteomic and genomic analyses of antimony resistant Leishmania infantum mutant

BACKGROUND

Antimonials remain the primary antileishmanial drugs in most developing countries. However, drug resistance to these compounds is increasing and our understanding of resistance mechanisms is partial.

METHODS/PRINCIPAL FINDINGS

In the present study, quantitative proteomics using stable isotope labelling of amino acids in cell culture (SILAC) and genome next generation sequencing were used in order to better characterize in vitro generated Leishmania infantum antimony resistant mutant (Sb2000.1). Using the proteomic method, 58 proteins were found to be differentially regulated in Sb2000.1. The ABC transporter MRPA (ABCC3), a known marker of antimony resistance, was observed for the first time in a proteomic screen. Furthermore, transfection of its gene conferred antimony resistance in wild-type cells. Next generation sequencing revealed aneuploidy for 8 chromosomes in Sb2000.1. Moreover, specific amplified regions derived from chromosomes 17 and 23 were observed in Sb2000.1 and a single nucleotide polymorphism (SNP) was detected in a protein kinase (LinJ.33.1810-E629K).

CONCLUSION/SIGNIFICANCE

Our results suggest that differentially expressed proteins, chromosome number variations (CNVs), specific gene amplification and SNPs are important features of antimony resistance in Leishmania.

Assessment of drug resistance related genes as candidate markers for treatment outcome prediction of cutaneous leishmaniasis in Brazil

The great public health problem posed by leishmaniasis has substantially worsened in recent years by the emergence of clinical failure. In Brazil, the poor prognosis observed for patients infected by Leishmania braziliensis (Lb) or L. guyanensis (Lg) may be related to parasite drug resistance. In the present study, 19 Lb and 29 Lg isolates were obtained from infected patients with different treatment outcomes. Translated amino acid sequence polymorphisms from four described antimony resistance related genes (AQP1, hsp70, MRPA and TRYR) were tested as candidate markers for antimonial treatment failure prediction. Possibly due to the low intraspecific variability observed in Lg samples, none of the prediction models had good prognosis values. Most strikingly, one mutation (T579A) found in hsp70 of Lb samples could predict 75% of the antimonial treatment failure clinical cases. Moreover, a multiple logistic regression model showed that the change from adenine to guanine at position 1735 of the hsp70 gene, which is responsible for the T579A mutation, significantly increased the chance of Lb clinical isolates to be associated with treatment failure (OR=7.29; CI 95%=[1.17, 45.25]; p=0.0331). The use of molecular markers to predict treatment outcome presents practical and economic advantages as it allows the development of rapid assays to monitor the emergence of drug resistant parasites that can be clinically applied to aid the prognosis of cutaneous leishmaniasis in Brazil.

Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.

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

The control of Leishmania infection relies primarily on chemotherapy till date. Resistance to pentavalent antimonials, which have been the recommended drugs to treat cutaneous and visceral leishmaniasis, is now widespread in Indian subcontinents. New drug formulations like amphotericin B, its lipid formulations, and miltefosine have shown great efficacy to treat leishmaniasis but their high cost and therapeutic complications limit their usefulness. In addition, irregular and inappropriate uses of these second line drugs in endemic regions like state of Bihar, India threaten resistance development in the parasite. In context to the limited drug options and unavailability of either preventive or prophylactic candidates, there is a pressing need to develop true antileishmanial drugs to reduce the disease burden of this debilitating endemic disease. Notwithstanding significant progress of leishmanial research during last few decades, identification and characterization of novel drugs and drug targets are far from satisfactory. This review will initially describe current drug regimens and later will provide an overview on few important biochemical and enzymatic machineries that could be utilized as putative drug targets for generation of true antileishmanial drugs.

Leishmaniasis: vaccine candidates and perspectives

Leishmania is a protozoan parasite and a causative agent of the various clinical forms of leishmaniasis. High cost, resistance and toxic side effects of traditional drugs entail identification and development of therapeutic alternatives. The sound understanding of parasite biology is key for identifying novel drug targets, that can induce the cell mediated immunity (mainly CD4+ and CD8+ IFN-gamma mediated responses) polarized towards a Th1 response. These aspects are important in designing a new vaccine along with the consideration of the candidates with respect to their ability to raise memory response in order to improve the vaccine performance. This review is an effort to identify molecules according to their homology with the host and their ability to be used as potent vaccine candidates.

Discovery of factors linked to antimony resistance in Leishmania panamensis through differential proteome analysis

The rate of treatment failure to antileishmanial chemotherapy in Latin America is up to 64%. Parasite drug resistance contributes to an unknown proportion of treatment failures. Identification of clinically relevant molecular mechanisms responsible for parasite drug resistance is critical to the conservation of available drugs and to the discovery of novel targets to reverse the resistant phenotype. We conducted comparative proteomic-based analysis of Leishmania (Viannia) panamensis lines selected in vitro for resistance to trivalent antimony (Sb(III)) to identify factors associated with antimony resistance. Using 2-dimensional gel electrophoresis, two distinct sub-proteomes (soluble in NP-40/urea and Triton X-114, respectively) of promastigotes of WT and Sb(III)-resistant lines were generated. Overall, 9 differentially expressed putative Sb-resistance factors were detected and identified by mass spectrometry. These constituted two major groups: (a) proteins involved in general stress responses and (b) proteins with highly specific metabolic and transport functions, potentially directly contributing to the Sb-resistance mechanism. Notably, the sulfur amino acid-metabolizing enzymes S-adenosylmethionine synthetase (SAMS) and S-adenosylhomocysteine hydrolase (SAHH) were over-expressed in Sb(III)-resistant lines and Sb(III)-resistant clinical isolates. These enzymes play a central role in the upstream synthesis of precursors of trypanothione, a key molecule involved in Sb-resistance in Leishmania parasites, and suggest involvement of epigenetic regulation in response to drug exposure. These data re-enforce the importance of thiol metabolism in Leishmania Sb resistance, reveal previously unrecognized steps in the mechanism(s) of Sb tolerance, and suggest a cross-talk between drug resistance, metabolism and virulence.

Antimony resistance in leishmania, focusing on experimental research

Leishmaniases are parasitic diseases that spread in many countries with a prevalence of 12 million cases. There are few available treatments and antimonials are still of major importance in the therapeutic strategies used in most endemic regions. However, resistance toward these compounds has recently emerged in areas where the replacement of these drugs is mainly limited by the cost of alternative molecules. In this paper, we reviewed the studies carried out on antimonial resistance in Leishmania. Several common limitations of these works are presented before prevalent approaches to evidence antimonial resistance are related. Afterwards, phenotypic determination of resistance is described, then confronted to clinical outcome. Finally, we detail molecular mechanisms and targets involved in resistance and already identified in vitro within selected mutant strains or in clinical isolates.

Paromomycin affects translation and vesicle-mediated trafficking as revealed by proteomics of paromomycin -susceptible -resistant Leishmania donovani

Leishmania donovani is a protozoan parasite that causes visceral leishmaniasis (VL) and is responsible for significant mortality and morbidity. Increasing resistance towards antimonial drugs poses a great challenge in chemotherapy of VL. Paromomycin is an aminoglycosidic antibiotic and is one of the drugs currently being used in the chemotherapy of cutaneous and visceral leishmaniasis. To understand the mode of action of this antibiotic at the molecular level, we have investigated the global proteome differences between the wild type AG83 strain and a paromomycin resistant (PRr) strain of L. donovani. Stable isotope labeling of amino acids in cell culture (SILAC) followed by quantitative mass spectrometry of the wild type AG83 strain and the paromomycin resistant (PRr) strain identified a total of 226 proteins at ≥95% confidence. Data analysis revealed upregulation of 29 proteins and down-regulation of 21 proteins in the PRr strain. Comparative proteomic analysis of the wild type and the paromomycin resistant strains showed upregulation of the ribosomal proteins in the resistant strain indicating role in translation. Elevated levels of glycolytic enzymes and stress proteins were also observed in the PRr strain. Most importantly, we observed upregulation of proteins that may have a role in intracellular survival and vesicular trafficking in the PRr strain. Furthermore, ultra-structural analysis by electron microscopy demonstrated increased number of vesicular vacuoles in PRr strain when compared to the wild-type strain. Drug affinity pull-down assay followed by mass spectrometery identified proteins in L. donovani wild type strain that were specifically and covalently bound to paromomycin. These results provide the first comprehensive insight into the mode of action and underlying mechanism of resistance to paromomycin in Leishmania donovani.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.

Strict sex-specific mtDNA segregation in the germ line of the DUI species Venerupis philippinarum (Bivalvia: Veneridae)

Doubly Uniparental Inheritance (DUI) is one of the most striking exceptions to the common rule of standard maternal inheritance of metazoan mitochondria. In DUI, two mitochondrial genomes are present, showing different transmission routes, one through eggs (F-type) and the other through sperm (M-type). In this paper, we report results from a multiplex real-time quantitative polymerase chain reaction analysis on the Manila clam Venerupis philippinarum (formerly Tapes philippinarum). We quantified M- and F-types in somatic tissues, gonads, and gametes. Nuclear and external reference sequences were used, and the whole experimental process was designed to avoid any possible cross-contamination. In most male somatic tissues, the M-type is largely predominant: This suggests that the processes separating sex-linked mitochondrial DNAs (mtDNAs) in somatic tissues are less precise than in other DUI species. In the germ line, we evidenced a strict sex-specific mtDNA segregation because both sperm and eggs do carry exclusively M- and F-types, respectively, an observation that is in contrast with a previous analysis on Mytilus galloprovincialis. More precisely, whereas two mtDNAs are present in the whole gonad, only the sex-specific one is detected in gametes. Because of this, we propose that the mtDNA transmission is achieved through a three-checkpoint process in V. philippinarum. The cytological mechanisms of male mitochondria segregation in males and degradation in females during the embryo development (here named Checkpoint #1 and Checkpoint #2) are already well known for DUI species; a Checkpoint #3 would act when primordial germ cells (PGCs) are first formed and would work in both males and females. We believe that Checkpoint #3 is a mere variation of the "mitochondrial bottleneck" in species with standard maternal inheritance, established when their PGCs separate during embryo cleavage.