Molecular mechanisms of antimony resistance in Leishmania

Interplay of human macrophage response and natural resistance of L. ( V .) panamensis to pentavalent antimony

Macrophages are the principal host cells of Leishmania spp . in human infection and play a critical role in controlling infection and enabling parasite survival and persistence. Nevertheless, understanding of drug resistance in leishmaniasis has primarily focused on the parasite. This investigation provides evidence of the significant differential macrophage response to ex vivo infection with clinical strains of L. (V . ) panamensis naturally resistant (zymodeme 2.3/zym 2.3) or sensitive (zymodeme 2.2/zym 2.2) to antimonial drug, and the distinct effect of this drug on the activation of macrophages. Transcriptome analysis of infected monocyte-derived macrophages from healthy donors revealed significant interferon responses and cytokine signaling by zym 2.3 strains compared to zym 2.2 strains. Furthermore, in the presence of antimony, macrophages infected with zym 2.3 strains, but not with zym 2.2 strains, significantly increased the expression of genes associated with M-CSF-generated macrophages (M-MØ, anti-inflammatory). Notably, macrophages infected with zym 2.3 strains exhibited elevated expression of genes associated with homeostasis and microbicidal regulation, such as the IDO1/IL4I1-Kyn-AHR pathways and superoxide dismutase, and downregulation of transporters like ABC and AQP , compared to macrophages infected with zym 2.2 strains. Remarkably, the majority of these pathways remained upregulated even in the presence of the strong modulatory effect of antimonial drug. Together, these findings demonstrate that the initial and specific parasite-host interaction influences the ex vivo macrophage response to antimony. Identification of key pathways in macrophage responses associated with natural resistance to this antileishmanial, enhances understanding of host-response mechanisms in the outcome of Leishmania infection and response to treatment.

IMPORTANCE

Drug resistance and treatment failure are increasingly recognized in human leishmaniasis. Investigation of resistance has predominantly focused on parasite-mediated mechanisms. This study examines the role of host macrophages in natural resistance to antimonial drug. Our findings reveal distinct responses by macrophages infected with Leishmania (Viannia) panamensis strains that are naturally resistant to antimonial drug versus sensitive strains, both in the presence and absence of the drug. Distinctively, resistant parasites induced regulatory pathways that modulate inflammatory responses and alter host cell transporter expression, potentially contributing to parasite survival under antimony exposure. The host cell-parasite interaction in the context of drug resistant intracellular infections presents opportunities for innovative therapeutic strategies targeting host cell responses.

Graphical abstract

Clinical strains of L. (V . ) panamensis naturally resistant or sensitive to antimonial drug (SbV) induce different profiles of human macrophage activation. L. (V . ) panamensis strains with natural SbV resistance induce a significant interferon response in macrophages, accompanied by overexpression of the IDO1 / IL4I1 - Kyn - AHR pathways and SOD2 , associated with immune homeostasis and regulation of microbicidal activity. Homeostatic regulation by the IDO1 / IL4I1 - Kyn - AHR pathways, induced in macrophages by infection with naturally SbV-resistant strains of L. (V . ) panamensis , prevails despite significant modulation of macrophage activation by antimony exposure. Antimony treatment promotes a more anti-inflammatory (M-MØ) profile in macrophages infected with naturally resistant L. (V . ) panamensis strains, while macrophages infected with sensitive strains maintain a more proinflammatory profile (GM-MØ). Infection with the zym 2.3 strains in the presence of SbV leads to downregulation of specific macrophage transporter genes, supporting the capacity of these naturally SbV-resistant parasites to elicit macrophage responses that enable antimony resistance.

Molecular Mechanisms of Drug Resistance in Leishmania spp

The protozoan parasite Leishmania causes leishmaniasis, a neglected tropical disease, that disproportionately affects underdeveloped countries. This disease has major health, economic, and social implications, particularly because of the limited treatment options, high cost, the severe side effects associated with available therapeutics, and the high rate of treatment failure caused by the parasites' growing resistance to current medications. In this review, we describe first the common strategies used by pathogens to develop drug resistance and then focus on the arsenal of available drugs to treat leishmaniasis, their modes of action, and the molecular mechanisms contributing to drug resistance in Leishmania spp., including the role of genomic, transcriptional, and translational control. We focus more specifically on our recent discovery of translational reprogramming as a major driver of drug resistance leading to coordinated changes in the translation of transcripts and orchestrating changes in metabolome and lipidome to support drug resistance. A thorough understanding of these mechanisms is essential to identify the key elements needed to combat resistance and improve leishmaniasis treatment methods.

Insights into the trypanothione system in antimony-resistant and sensitive Leishmania tropica clinical isolates

Pentavalent antimonials are the mainstay treatment against different clinical forms of leishmaniasis. The emergence of resistant isolates in endemic areas has led to treatment failure. Unraveling the underlying resistance mechanism would assist in improving the treatment strategies against resistant isolates. This study aimed to investigate the RNA expression level of glutathione synthetase (GS), Spermidine synthetase (SpS), trypanothione synthetase (TryS) genes involved in trypanothione synthesis, and thiol-dependent reductase (TDR) implicated in drug reduction, in antimony-sensitive and -resistant Leishmania tropica isolates. We investigated 11 antimony-resistant and 11 antimony-sensitive L. tropica clinical isolates from ACL patients. Drug sensitivity of amastigotes was determined in mouse macrophage cell line J774A.1. The RNA expression level in the promastigote forms was analyzed by quantitative real-time PCR. The results revealed a significant increase in the average expression of GS, SpS, and TrpS genes by 2.19, 1.56, and 2.33-fold in resistant isolates compared to sensitive ones. The average expression of TDR was 1.24-fold higher in resistant isolates, which was insignificant. The highest correlation coefficient between inhibitory concentration (IC50) values and gene expression belonged to the TryS, GS, SpS, and TDR genes. Moreover, the intracellular thiol content was increased 2.17-fold in resistant isolates compared to sensitive ones and positively correlated with IC50 values. Our findings suggest that overexpression of trypanothione biosynthesis genes and increased thiol content might play a key role in the antimony resistance of L. tropica clinical isolates. In addition, the diversity of gene expression in the trypanothione system and thiol content among L. tropica clinical isolates highlighted the phenotypic heterogeneity of antimony resistance among the parasite population.

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.

Structure of Leishmania donovani 6-Phosphogluconate Dehydrogenase and Inhibition by Phosphine Gold(I) Complexes: A Potential Approach to Leishmaniasis Treatment

As unicellular parasites are highly dependent on NADPH as a source for reducing equivalents, the main NADPH-producing enzymes glucose 6-phosphate dehydrogenase (G6PD) and 6-phosphogluconate dehydrogenase (6PGD) of the pentose phosphate pathway are considered promising antitrypanosomatid drug targets. Here we present the biochemical characterization and crystal structure of Leishmania donovani 6PGD (Ld6PGD) in complex with NADP(H). Most interestingly, a previously unknown conformation of NADPH is visible in this structure. In addition, we identified auranofin and other gold(I)-containing compounds as efficient Ld6PGD inhibitors, although it has so far been assumed that trypanothione reductase is the sole target of auranofin in Kinetoplastida. Interestingly, 6PGD from Plasmodium falciparum is also inhibited at lower micromolar concentrations, whereas human 6PGD is not. Mode-of-inhibition studies indicate that auranofin competes with 6PG for its binding site followed by a rapid irreversible inhibition. By analogy with other enzymes, this suggests that the gold moiety is responsible for the observed inhibition. Taken together, we identified gold(I)-containing compounds as an interesting class of inhibitors against 6PGDs from Leishmania and possibly from other protozoan parasites. Together with the three-dimensional crystal structure, this provides a valid basis for further drug discovery approaches.

Comparative Proteomics and Genome-Wide Druggability Analyses Prioritized Promising Therapeutic Targets against Drug-Resistant Leishmania tropica

Leishmania tropica is a tropical parasite causing cutaneous leishmaniasis (CL) in humans. Leishmaniasis is a serious public health threat, affecting an estimated 350 million people in 98 countries. The global rise in antileishmanial drug resistance has triggered the need to explore novel therapeutic strategies against this parasite. In the present study, we utilized the recently available multidrug resistant L. tropica strain proteome data repository to identify alternative therapeutic drug targets based on comparative subtractive proteomic and druggability analyses. Additionally, small drug-like compounds were scanned against novel targets based on virtual screening and ADME profiling. The analysis unveiled 496 essential cellular proteins of L. tropica that were nonhomologous to the human proteome set. The druggability analyses prioritized nine parasite-specific druggable proteins essential for the parasite's basic cellular survival, growth, and virulence. These prioritized proteins were identified to have appropriate binding pockets to anchor small drug-like compounds. Among these, UDPase and PCNA were prioritized as the top-ranked druggable proteins. The pharmacophore-based virtual screening and ADME profiling predicted MolPort-000-730-162 and MolPort-020-232-354 as the top hit drug-like compounds from the Pharmit resource to inhibit L. tropica UDPase and PCNA, respectively. The alternative drug targets and drug-like molecules predicted in the current study lay the groundwork for developing novel antileishmanial therapies.

Antimony resistance mechanism in genetically different clinical isolates of Indian Kala-azar patients

The central theme of this enterprise is to find common features, if any, displayed by genetically different antimony (Sb)-resistant viscerotropic Leishmania parasites to impart Sb resistance. In a limited number of clinical isolates (n = 3), we studied the breadth of variation in the following dimensions: (a) intracellular thiol content, (b) cell surface expression of glycan having N-acetyl-D-galactosaminyl residue as the terminal sugar, and (c) gene expression of thiol-synthesizing enzymes (CBS, MST, gamma-GCS, ODC, and TR), antimony-reducing enzymes (TDR and ACR2), and antimonial transporter genes (AQP1, MRPA, and PRP1). One of the isolates, T5, that was genotypically characterized as Leishmania tropica, caused Indian Kala-azar and was phenotypically Sb resistant (T5-LT-SSG-R), while the other two were Leishmania donovani, out of which one isolate, AG83, is antimony sensitive (AG83-LD-SSG-S) and the other isolate, T8, is Sb resistant (T8-LD-SSG-R). Our study showed that the Sb-resistant parasites, regardless of their genotype, showed significantly higher intracellular thiol compared with Sb-sensitive AG83-LD-SSG-S. Seemingly, T5-LT-SSG-R showed about 1.9-fold higher thiol content compared with T8-LD-SSG-R which essentially mirrored cell surface N-acetyl-D-galactosaminyl expression. Except TR, the expression of the remaining thiol-synthesizing genes was significantly higher in T8-LD-SSG-R and T5-LT-SSG-R than the sensitive one, and between the Sb-resistant parasites, the latter showed a significantly higher expression. Furthermore, the genes for Sb-reducing enzymes increased significantly in resistant parasites regardless of genotype compared with the sensitive one, and between two resistant parasites, there was hardly any difference in expression. Out of three antimony transporters, AQP1 was decreased with the concurrent increase in MRPA and PRP1 in resistant isolates when compared with the sensitive counterpart. Interestingly, no difference in expression of the above-mentioned transporters was noted between two Sb-resistant isolates. The enduring image that resonated from our study is that the genetically diverse Sb-resistant parasites showed enhanced thiol-synthesizing and antimony transporter gene expression than the sensitive counterpart to confer a resistant phenotype.

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.

Pre-clinical evaluation of LASSBio-1491: From in vitro pharmacokinetic study to in vivo leishmanicidal activity

Leishmaniasis is a public health issue. It is among the top five parasitic illnesses worldwide and is one of the most neglected diseases. The current treatment disease includes limitations of toxicity, variable efficacy, high costs and inconvenient doses and treatment schedules. LASSBio-1736 was described as antileishmanial drug-candidate to cutaneous leishmaniasis, displaying plasma stability and with no preliminary signals of hepatic or renal toxicity. In this paper, we described the in vitro pharmacokinetic study of LASSBio-1491 (a less lipophilic isostere of LASSBio-1736) and it is in vitro and in vivo leishmanicidal activities. Our results demonstrated that LASSBio-1491 has high permeability, satisfactory aqueous solubility, long plasma and microsomal half-lives and low in vitro systemic clearance, suggesting a pharmacokinetic profile suitable for its use in a single daily dose. The antileishmanial effect of LASSBio-1491 was confirmed in vitro and in vivo. It exhibited no cytotoxic effect to mammalian cells and displayed good in –vivo effect against BALB/c mice infected with Leishmania major LV39 substrain, being 3 times more efficient than glucantime.

Activity of alkaloids from Aspidosperma nitidum against Leishmania (Leishmania) amazonensis

This study evaluated the morphological changes caused by fractions and subfractions, obtained from barks of Aspidosperna nitidum, against L. (L.) amazonensis promastigotes. The ethanolic extract (EE) obtained through the maceration of trunk barks was subjected to an acid-base partition, resulting the neutral (FN) and the alkaloid (FA) fractions, and fractionation under reflux, yielded hexane (FrHEX), dichloromethane (FrDCL), ethyl acetate (FrACoET), and methanol (FrMEOH) fractions. The FA was fractionated and three subfractions (SF5-6, SF8, and SF9) were obtained and analyzed by HPLC-DAD and 1H NMR. The antipromastigote activity of all samples was evaluated by MTT, after that, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for the active fractions were performed. Chromatographic analyzes suggest the presence of alkaloids in EE, FN, FA, and FrDCL. The fractionation of FA led to the isolation of the indole alkaloid dihydrocorynantheol (SF8 fractions). The SF5-6, dihydrocorynantheol and SF-9 samples were active against promastigotes, while FrDCL was moderately active. The SEM analysis revealed cell rounding and changes in the flagellum of the parasites. In the TEM analysis, the treated promastigotes showed changes in flagellar pocket and kinetoplast, and presence of lipid inclusions. These results suggest that alkaloids isolated from A. nitidum are promising as leishmanicidal.

Stage-Specific Class I Nucleases of Leishmania Play Important Roles in Parasite Infection and Survival

Protozoans of the genus Leishmania are the causative agents of an important neglected tropical disease referred to as leishmaniasis. During their lifecycle, the parasites can colonize the alimentary tract of the sand fly vector and the parasitophorous vacuole of the mammalian host, differentiating into distinct stages. Motile promastigotes are found in the sand fly vector and are transmitted to the mammalian host during the insect blood meal. Once in the vertebrate host, the parasites differentiate into amastigotes and multiply inside macrophages. To successfully establish infection in mammalian hosts, Leishmania parasites exhibit various strategies to impair the microbicidal power of the host immune system. In this context, stage-specific class I nucleases play different and important roles related to parasite growth, survival and development. Promastigotes express 3’-nucleotidase/nuclease (3’-NT/NU), an ectoenzyme that can promote parasite escape from neutrophil extracellular traps (NET)-mediated death through extracellular DNA hydrolysis and increase Leishmania-macrophage interactions due to extracellular adenosine generation. Amastigotes express secreted nuclease activity during the course of human infection that may be involved in the purine salvage pathway and can mobilize extracellular nucleic acids available far from the parasite. Another nuclease expressed in amastigotes (P4/LmC1N) is located in the endoplasmic reticulum of the parasite and may be involved in mRNA stability and DNA repair. Homologs of this class I nuclease can induce protection against infection by eliciting a T helper 1-like immune response. These immunogenic properties render these nucleases good targets for the development of vaccines against leishmaniasis, mainly because amastigotes are the form responsible for the development and progression of the disease. The present review aims to present and discuss the roles played by different class I nucleases during the Leishmania lifecycle, especially regarding the establishment of mammalian host infection.

Treatment failure to sodium stibogluconate in cutaneous leishmaniasis: A challenge to infection control and disease elimination

The first-line treatment for Leishmania donovani-induced cutaneous leishmaniasis (CL) in Sri Lanka is intra-lesional sodium stibogluconate (IL-SSG). Antimony failures in leishmaniasis is a challenge both at regional and global level, threatening the ongoing disease control efforts. There is a dearth of information on treatment failures to routine therapy in Sri Lanka, which hinders policy changes in therapeutics. Laboratory-confirmed CL patients (n = 201) who attended the District General Hospital Hambantota and Base Hospital Tangalle in southern Sri Lanka between 2016 and 2018 were included in a descriptive cohort study and followed up for three months to assess the treatment response of their lesions to IL-SSG. Treatment failure (TF) of total study population was 75.1% and the majority of them were >20 years (127/151,84%). Highest TF was seen in lesions on the trunk (16/18, 89%) while those on head and neck showed the least (31/44, 70%). Nodules were least responsive to therapy (27/31, 87.1%) unlike papules (28/44, 63.6%). Susceptibility to antimony therapy seemed age-dependant with treatment failure associated with factors such as time elapsed since onset to seeking treatment, number and site of the lesions. This is the first detailed study on characteristics of CL treatment failures in Sri Lanka. The findings highlight the need for in depth investigations on pathogenesis of TF and importance of reviewing existing treatment protocols to introduce more effective strategies. Such interventions would enable containment of the rapid spread of L.donovani infections in Sri Lanka that threatens the ongoing regional elimination drive.

Antimony resistance associated with persistence of Leishmania (Leishmania) infantum infection in macrophages

Visceral leishmaniasis is a severe disease caused by protozoan parasites that include Leishmania (L.) infantum. The disease is established when parasites subvert the immune response of the host. Notably, chemotherapy-based use of antimonial compounds can partially alleviate disease burden. Unfortunately, the resistance to drug treatments is increasing in areas endemic to the disease. In this report, we investigated immune responses within macrophages infected with antimony-resistant L. infantum isolates from patients with a relapse in the disease. Results revealed that antimony-resistant parasites persist in the first 24 h of infection. Activation of macrophage or blocking of thiol production during infection shows enhanced clearance of parasites, which is coordinately associated with increased production of pro-inflammatory cytokines. Taken together, these results suggest that the mechanism of antimony resistance in L. infantum isolates may be related to a decrease in macrophage microbicidal functions.

Strike a Balance: Between Metals and Non-Metals, Metalloids as a Source of Anti-Infective Agents

Most of the commercially available anti-infective agents are organic molecules. In fact, though, during the pioneering times of modern medicine, at the beginning of the 20th century, several inorganic compounds of transition metals were used for medicinal application, to date, only a small number of inorganic drugs are used in clinical practice. Beyond the transition metals, metalloids—or semimetals—offer a rich chemistry in between that of metallic and non-metallic elements, and accordingly, peculiar features for their exploitation in medicinal chemistry. A few important examples of metalloid-based drugs currently used for the treatment of various diseases do exist. However, the use of this group of elements could be further expanded on the basis of their current applications and the clinical trials they entered. Considering that metalloids offer the opportunity to expand the “chemical-space” for developing novel anti-infective drugs and protocols, in this paper, we briefly recapitulate and discuss the current applications of B-, Si-, As-, Sb- and Te-based anti-infective drugs.

Determinants of Unresponsiveness to Treatment in Cutaneous Leishmaniasis: A Focus on Anthroponotic Form Due to Leishmania tropica

Cutaneous leishmaniasis (CL) is a curable disease; however, due to various risk factors, unresponsiveness to CL treatments is inevitable. The treatment of CL has been firmly correlated with multiple determinants, such as demographical, clinical, and environmental factors, the host’s immune response, poor treatment adherence, the parasite’s genetic make-up, and Leishmania RNA virus. This study primarily focuses on the risk factors associated with different therapeutic outcomes following meglumine antimoniate (MA; Glucantime^®) treatment and policy approaches to prevent unresponsiveness in CL patients with a focus on anthroponotic form (ACL). Findings suggest that effective preventive and therapeutic measures should be more vigorously implemented, particularly in endemic areas. Accordingly, extensive training is essential to monitor drug unresponsiveness regularly, especially in tropical regions where the disease is prevalent. Since humans are the fundamental reservoir host of ACL due to L. tropica, prompt detection, early diagnosis, and timely and effective treatment could help control this disease. Furthermore, major challenges and gaps remain: efficacious vaccine, new tools, and expert staff are crucial before CL can be definitively controlled.

Nanotechnology-aided diagnosis, treatment and prevention of leishmaniasis

Leishmaniasis is a prevalent parasitic infection belonging to neglected tropical diseases. It is caused by Leishmania protozoan parasites transmitted by sandflies and it is responsible for increased morbidity/mortality especially in low- and middle-income countries. The lack of cheap, portable, easy to use diagnostic tools exhibiting high efficiency and specificity impede the early diagnosis of the disease. Furthermore, the typical anti-leishmanial agents are cytotoxic, characterized by low patient compliance and require long-term regimen and usually hospitalization. In addition, due to the intracellular nature of the disease, the existing treatments exhibit low bioavailability resulting in low therapeutic efficacy. The above, combined with the common development of resistance against the anti-leishmanial agents, denote the urgent need for novel therapeutic strategies. Furthermore, the lack of effective prophylactic vaccines hinders the control of the disease. The development of nanoparticle-based biosensors and nanocarrier-aided treatment and vaccination strategies could advance the diagnosis, therapy and prevention of leishmaniasis. The present review intends to highlight the various nanotechnology-based approaches pursued until now to improve the detection of Leishmania species in biological samples, decrease the side effects and increase the efficacy of anti-leishmanial drugs, and induce enhanced immune responses, specifically focusing on the outcome of their preclinical and clinical evaluation.

Involvement of Leishmania Phosphatases in Parasite Biology and Pathogeny

In the Leishmania lifecycle, the motile promastigote form is transmitted from the sand fly vector to a mammalian host during a blood meal. Inside vertebrate host macrophages, the parasites can differentiate into the amastigote form and multiply, causing leishmaniasis, one of the most significant neglected tropical diseases. Leishmania parasites face different conditions throughout their development inside sand flies. Once in the mammalian host, the parasites have to overcome the microbicide repertoire of the cells of the immune system to successfully establish the infection. In this context, the expression of protein phosphatases is of particular interest. Several members of the serine/threonine-specific protein phosphatase (STP), protein tyrosine phosphatase (PTP), and histidine acid phosphatase (HAcP) families have been described in different Leishmania species. Although their physiological roles have not been fully elucidated, many studies suggest they have an involvement with parasite biology and pathogeny. Phosphatases play a role in adaptation to nutrient starvation during parasite passage through the sand fly midgut. They are also important to parasite virulence, mainly due to the modulation of host cytokine production and impairment of the microbiocidal potential of macrophages. Furthermore, recent whole-genome expression analyses have shown that different phosphatases are upregulated in metacyclic promastigotes, the infective form of the mammalian host. Leishmania phosphatases are also upregulated in drug-resistant strains, probably due to the increase in drug efflux related to the activation of ABC transporters. Throughout this review, we will describe the physiological roles that have been attributed to Leishmania endogenous phosphatases, including their involvement in the adaptation, survival, and proliferation of the parasites inside their hosts.

Nanotechnology based solutions for anti-leishmanial impediments: a detailed insight

As a neglected tropical disease, Leishmaniasis is significantly instigating morbidity and mortality across the globe. Its clinical spectrum varies from ulcerative cutaneous lesions to systemic immersion causing hyperthermic hepato-splenomegaly. Curbing leishmanial parasite is toughly attributable to the myriad obstacles in existing chemotherapy and immunization. Since the 1990s, extensive research has been conducted for ameliorating disease prognosis, by resolving certain obstacles of conventional therapeutics viz. poor efficacy, systemic toxicity, inadequate drug accumulation inside the macrophage, scarce antigenic presentation to body's immune cells, protracted length and cost of the treatment. Mentioned hurdles can be restricted by designing nano-drug delivery system (nano-DDS) of extant anti-leishmanials, phyto-nano-DDS, surface modified-mannosylated and thiolated nano-DDS. Likewise, antigen delivery with co-transportation of suitable adjuvants would be achievable through nano-vaccines. In the past decade, researchers have engineered nano-DDS to improve the safety profile of existing drugs by restricting their release parameters. Polymerically-derived nano-DDS were found as a suitable option for oral delivery as well as SLNs due to pharmacokinetic re-modeling of drugs. Mannosylated nano-DDS have upgraded macrophage internalizing of nanosystem and the entrapped drug, provided with minimal toxicity. Cutaneous Leishmaniasis (CL) was tackling by the utilization of nano-DDS designed for topical delivery including niosomes, liposomes, and transfersomes. Transfersomes, however, appears to be superior for this purpose. The nanotechnology-based solution to prevent parasitic resistance is the use of Thiolated drug-loaded and multiple drugs loaded nano-DDS. These surfaces amended nano-DDS possess augmented IC50 values in comparison to conventional drugs and un-modified nano-DDS. Phyto-nano-DDS, another obscure horizon, have also been evaluated for their anti-leishmanial response, however, more intense assessment is a prerequisite. Impoverished Cytotoxic T-cells response followed by Leishmanial antigen proteins delivery have also been vanquished using nano-adjuvants. The eminence of nano-DDS for curtailment of anti-leishmanial chemotherapy and immunization associated challenges are extensively summed up in this review. This expedited approach is ameliorating the Leishmaniasis management successfully. Alongside, total to partial eradication of this disease can be sought along with associated co-morbidities.

Drug-Induced Lipid Remodeling in Leishmania Parasites

Leishmania parasites efficiently develop resistance against several types of drugs including antimonials, the primary antileishmanial drug historically implemented. The resistance to antimonials is considered to be a major risk factor for effective leishmaniasis treatment. To detect biomarkers/biopatterns for the differentiation of antimony-resistant Leishmania strains, we employed untargeted global mass spectrometry to identify intracellular lipids present in antimony sensitive and resistant parasites before and after antimony exposure. The lipidomic profiles effectively differentiated the sensitive and resistant phenotypes growing with and without antimony pressure. Resistant phenotypes were characterized by significant downregulation of phosphatidylcholines, sphingolipid decrease, and lysophosphatidylcholine increase, while sensitive phenotypes were characterized by the upregulation of triglycerides with long-chain fatty acids and a tendency toward the phosphatidylethanolamine decrease. Our findings suggest that the changes in lipid composition in antimony-resistant parasites contribute to the physiological response conducted to combat the oxidative stress unbalance caused by the drug. We have identified several lipids as potential biomarkers associated with the drug resistance.

Sand Fly Studies Predict Transmission Potential of Drug-resistant Leishmania

Leishmania parasites have the capacity to rapidly adapt to changing environments in their digenetic life cycle which alternates between a vertebrate and an invertebrate host. Emergence of resistance following drug exposure can evoke phenotypic alterations that affect several aspects of parasite fitness in both hosts. Current studies of the impact of resistance are mostly limited to interactions with the mammalian host and characterization of in vitro parasite growth and differentiation. Development in the vector and transmission capacity have been largely ignored. This review reflects on the impact of drug resistance on its spreading potential with specific focus on the use of the sand fly infection model to evaluate parasite development in the vector and the ensuing transmission potential of drug-resistant phenotypes.

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.

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

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

Tellurides Bearing Sulfonamides as Novel Inhibitors of Leishmanial Carbonic Anhydrase with Potent Antileishmanial Activity

We report for the first time a novel series of tellurides bearing sulfonamide as selective and potent inhibitors of the β-class carbonic anhydrase (CA; EC 4.2.1.1) enzyme expressed in Leishmania donovani protozoa. Such derivatives showed high activity against axenic amastigotes, and among them, compound 5g (4-(((3,4,5-trimethoxyphenyl)tellanyl)methyl)benzenesulfonamide) showed an IC₅₀ of 0.02 μM being highly selective for the parasites over THP-1 cells with a selectivity index of 300. The in vitro and in vivo toxicity experiments showed compound 5g to possess a safe profile and thus paving the way for tellurium-containing compounds as novel drug entities.

Enzymatic, antimicrobial, and leishmanicidal bioactivity of gram-negative bacteria strains from the midgut of Lutzomyia evansi, an insect vector of leishmaniasis in Colombia

Knowledge regarding new compounds, peptides, and/or secondary metabolites secreted by bacteria isolated from the intestine of phebotominae has the potential to control insect vectors and pathogens (viruses, bacteria, and parasites) transmitted by them. In this respect, twelve Gram-negative bacteria isolated from the intestine of Lutzomyia evansi were selected and screened for their enzymatic, antimicrobial, and leishmanicidal activity. E. cancerogenus, E. aerogenes, P. otitidis, E. cloacae, L. soli, and P. ananatis exhibited enzymatic activity. 83.3% of the isolates displayed lipolytic and nitrate reductase activity and 58.3% of the isolates displayed protease activity. Hemolytic activity (17%) was identified only in E. hormaechei, and P. ananatis. E. cancerogenus, A. calcoaceticus, and P. otitidis showed cellulolytic activity. A. gyllenbergii, P. aeruginosa, and E. hormaechei showed amylolytic activity. In general, the totality of methanolic extracts exhibited antimicrobial activity, where E. hormaechei, A. calcoaceticus, and E. cancerogenus presented the highest activity against the evaluated reference bacteria strains. Cell-free supernatants (CFSS) of the Gram-negative bacteria showed higher growth inhibitory activity against the reference Gram-positive bacteria. The CFS of A. gyllenbergii was the most active antimicrobial in this study, against S. aureus (AAODs = 95.12%) and E. faecalis (AAODs = 86.90%). The inhibition percentages of CFS against Gram-positive bacteria showed statistically significant differences (repeated measure ANOVA df= 2; F= 6.095; P= 0.007832). The E. hormaechei methanolic extract showed leishmanicidal activity (CE-50 μg/ml = 47.7 + 3.8) against metacyclic promastigotes of Leishmania braziliensis (UA301). Based on this finding, we discuss the possible implications of these bacteria in digestion and physiological processes in the Lu. evansi intestine. P. ananatis, E. cloacae, E. hormaechei, and P. otitidis were considered the most promising bacteria in this study and they could potentially be used for biological control.

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.

Drug transporter and oxidative stress gene expression in human macrophages infected with benznidazole-sensitive and naturally benznidazole-resistant Trypanosoma cruzi parasites treated with benznidazole

Background

Chagas disease is a potentially life-threatening disease caused by the protozoan parasite Trypanosoma cruzi. Current therapeutic management is limited to treatment with nitroheterocyclic drugs, such as nifurtimox (NFX) and benznidazole (BZ). Thus, the identification of affordable and readily available drugs to treat resistant parasites is urgently required worldwide. To analyse the effects of BZ on human macrophage gene expression, a quantitative PCR (qPCR) array analysis was performed using drug transporter and oxidative stress pathway genes to compare the gene expression profiles of human differentiated THP-1 macrophage (THP-1 MΦ) cells infected or not with benznidazole-sensitive (CL Brener) and naturally benznidazole-resistant (Colombiana) T. cruzi parasites followed by treatment with BZ.

Results

The gene expression analysis indicated that the expression levels of 62 genes were either up- or downregulated at least 3-fold in the host upon infection with CL Brener and BZ treatment, of which 46 were upregulated and 16 were downregulated. Moreover, the expression level of 32 genes was altered in THP-1 MФ cells infected with Colombiana and treated with BZ, of which 29 were upregulated and 3 were downregulated. Our results revealed that depending on the specific condition, human THP-1 MΦ cells infected with T. cruzi strains with sensitive or resistant phenotypes and treated with BZ expressed high mRNA levels of AQP1, AQP9 and ABCB1 (MDR1) compared to those of the control cells.

Conclusions

Our findings suggest that the proteins encoded by AQP1, AQP9 and ABCB1 may be implicated in benznidazole detoxification. Therefore, studies on gene expression are required to better understand the host response to pathogens and drug treatment integrated with functional and metabolic data to identify potentially novel targets for the treatment of this important and neglected tropical disease.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3485-9) contains supplementary material, which is available to authorized users.

Active Essential Oils and Their Components in Use against Neglected Diseases and Arboviruses

The term neglected diseases refers to a group of infections caused by various classes of pathogens, including protozoa, viruses, bacteria, and helminths, most often affecting impoverished populations without adequate sanitation living in close contact with infectious vectors and domestic animals. The fact that these diseases were historically not considered priorities for pharmaceutical companies made the available treatments options obsolete, precarious, outdated, and in some cases nonexistent. The use of plants for medicinal, religious, and cosmetic purposes has a history dating back to the emergence of humanity. One of the principal fractions of chemical substances found in plants are essential oils (EOs). EOs consist of a mixture of volatile and hydrophobic secondary metabolites with marked odors, composed primarily of terpenes and phenylpropanoids. They have great commercial value and were widely used in traditional medicine, by phytotherapy practitioners, and in public health services for the treatment of several conditions, including neglected diseases. In addition to the recognized cytoprotective and antioxidative activities of many of these compounds, larvicidal, insecticidal, and antiparasitic activities have been associated with the induction of oxidative stress in parasites, increasing levels of nitric oxide in the infected host, reducing parasite resistance to reactive oxygen species, and increasing lipid peroxidation, ultimately leading to serious damage to cell membranes. The hydrophobicity of these compounds also allows them to cross the membranes of parasites as well as the blood-brain barrier, collaborating in combat at the second stage of several of these infections. Based on these considerations, the aim of this review was to present an update of the potential of EOs, their fractions, and their chemical constituents, against some neglected diseases, including American and African trypanosomiasis, leishmaniasis, and arboviruses, specially dengue.

Modulation of the immune response and infection pattern to Leishmania donovani in visceral leishmaniasis due to arsenic exposure: An in vitro study

The arsenic contamination of ground water in visceral leishmaniasis (VL) endemic areas in Bihar, India leads to human exposure through drinking water. Possibly, the consumed arsenic (As) accumulates in the tissues of VL patients, who subsequently internalize intracellular amastigotes to confer resistance against chemotherapy to the parasite, leading to modulation in the host’s immune response. This hypothesis appears to be consistent with the in vitro findings that in arsenic-exposed parasites, the mitochondrial membrane potential became depolarized, whereas the reduced thiol and lactate production was overexpressed with enhanced glucose consumption; therefore, the reduced thiol possibly supports an immunosuppressive state in the host cells. This observation was well supported by the down-regulated expression of pro-inflammatory cytokines (IL-2, IL-12, IFN-γ, and TNF-α) with a suppressed anti-leishmanial function of macrophage (NO, ROS). In contrast, the pathophysiological mechanism of VL has received ample support by the promotion of Th2 cytokines (IL-4 and IL-10) in the presence of arsenic-exposed Leishmania parasites (Ld^AS). Dysfunction of mitochondria and the overexpression of lactate production raise the possibility of the Warburg effect being operative through the up-regulation of glucose consumption by parasites to enhance the energy production, possibly augmenting virulence. Therefore, we surmise from our data that arsenic exposure to Leishmania donovani modulates the immune response and infection pattern by impairing parasite function, which may affect the anti-leishmanial effect in VL.

Drug Resistance in Protozoan Parasites: An Incessant Wrestle for Survival

Nowadays, drug resistance in parasites is considered to be one of the foremost concerns in health and disease management. It is interconnected worldwide and undermines the health of millions of people, threatening to grow worse. Unfortunately, it does not receive serious attention from every corner of society. Consequently, drug resistance in parasites is gradually complicating and challenging the treatment of parasitic diseases. In this context, we have dedicated ourselves to review the incidence of drug resistance in the protozoan parasites Plasmodium, Leishmania, Trypanosoma, Entamoeba and Toxoplasma gondii. Moreover, understanding the role of ATP-binding cassette (ABC) transporters in drug resistance is essential in the control of parasitic diseases. Therefore, we also focused on the involvement of ABC transporters in drug resistance, which will be a superior approach to find ways for better regulation of diseases caused by parasitic infections.

Resistance of Leishmania (Viannia) Panamensis to Meglumine Antimoniate or Miltefosine Modulates Neutrophil Effector Functions

Leishmania (Viannia) panamensis (L. (V.) p.) is the main causative agent of cutaneous leishmaniasis in Colombia and is usually treated with either meglumine antimoniate (MA) or miltefosine (MIL). In recent years, there has been increasing evidence of the emergence of drug-resistance against these compounds. Neutrophils are known to play an important role in immunity against Leishmania. These cells are rapidly recruited upon infection and are also present in chronic lesions. However, their involvement in the outcome of infection with drug-resistant Leishmania has not been examined. In this study, human and murine neutrophils were infected in vitro with MA or MIL drug-resistant L. (V.) p. lines derived from a parental L. (V.) p. drug-susceptible strain. Neutrophil effector functions were assessed analyzing the production of reactive oxygen species (ROS), the formation of neutrophil extracellular trap (NET) and the expression of cell surface activation markers. Parasite killing by neutrophils was assessed using L. (V.) p. transfected with a luciferase reporter. We show here that MA and MIL-resistant L. (V.) p. lines elicited significantly increased NET formation and MA-resistant L. (V.) p. induced significantly increased ROS production in both murine and human neutrophils, compared to infections with the parental MIL and MA susceptible strain. Furthermore, neutrophils exposed to drug-resistant lines showed increased activation, as revealed by decreased expression of CD62L and increased expression of CD66b in human neutrophils yet presented higher survival within neutrophils than the drug-susceptible strain. These results provide evidence that parasite drug-susceptibility may influences neutrophil activation and function as well as parasite survival within neutrophils. Further investigaton of the inter-relationship of drug susceptibility and neutrophil effector function should contribute to better understanding of the factors involved in susceptibility to anti-Leishmania drugs.

Growth arrested live-attenuated Leishmania infantum KHARON1 null mutants display cytokinesis defect and protective immunity in mice

There is no safe and efficacious vaccine against human leishmaniasis available and live attenuated vaccines have been used as a prophylactic alternative against the disease. In order to obtain an attenuated Leishmania parasite for vaccine purposes, we generated L. infantum KHARON1 (KH1) null mutants (ΔLikh1). This gene was previously associated with growth defects in L. mexicana. ΔLikh1 was obtained and confirmed by PCR, qPCR and Southern blot. We also generate a KH1 complemented line with the introduction of episomal copies of KH1. Although ΔLikh1 promastigote forms exhibited a growth pattern similar to the wild-type line, they differ in morphology without affecting parasite viability. L. infantum KH1-deficient amastigotes were unable to sustain experimental infection in macrophages, forming multinucleate cells which was confirmed by in vivo attenuation phenotype. The cell cycle analysis of ΔLikh1 amastigotes showed arrested cells at G₂/M phase. ΔLikh1-immunized mice presented reduced parasite burden upon challenging with virulent L. infantum, when compared to naïve mice. An effect associated with increased Li SLA-specific IgG serum levels and IL-17 production. Thus, ΔLikh1 parasites present an infective-attenuated phenotype due to a cytokinesis defect, whereas it induces immunity against visceral leishmaniasis in mouse model, being a candidate for antileishmanial vaccine purposes.

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

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

Unresponsiveness to meglumine antimoniate in anthroponotic cutaneous leishmaniasis field isolates: analysis of resistance biomarkers by gene expression profiling

BACKGROUND

Resistance to antimonials is a fundamental determinant of treatment failure in anthroponotic cutaneous leishmaniasis (ACL). Detection of reliable molecular markers to distinguish unresponsive and responsive parasites is critical for consolidating strategies to monitor drug efficacy.

METHODS

We analysed the expression of five major antimony resistance-associated genes that is aquaglyceroporin1 (AQP1), γ-glutamylcysteine synthetase (γ-GCS), multidrug resistance protein A (MRPA), trypanothione reductase (TR) and thiol-dependent reductase 1 (TDR1), in unresponsive and responsive Leishmania tropica field isolates by quantitative real-time PCR in comparison with sensitive and resistant reference strains.

RESULTS

Gene expression analysis showed the down-regulation of AQP1, γ-GCS and TDR1 by a factor of 1.9, 1.7 and 3.55, respectively, in unresponsive isolates vs. responsive ones. The average RNA expression level of MRPA increased by a factor of 1.9 in the unresponsive group. Isolates exhibited a strong positive linear correlation between gene expression of AQP1 and γ-GCS. A negative correlation between the AQP1 and γ-GCS expression level and lesion duration in responsive patients indicated the potential role in diagnosing drug-unresponsive parasites in endemic areas of ACL.

CONCLUSION

In cases of inconclusive outcomes of resistance tests in clinical isolates, expression analysis of a set of influential genes can be beneficial to identify distinctive biomarkers between antimony-unresponsive and responsive parasites.

Genome wide comparison of Ethiopian Leishmania donovani strains reveals differences potentially related to parasite survival

Leishmania donovani is the main cause of visceral leishmaniasis (VL) in East Africa. Differences between northern Ethiopia/Sudan (NE) and southern Ethiopia (SE) in ecology, vectors, and patient sensitivity to drug treatment have been described, however the relationship between differences in parasite genotype between these two foci and phenotype is unknown. Whole genomic sequencing (WGS) was carried out for 41 L. donovani strains and clones from VL and VL/HIV co-infected patients in NE (n = 28) and SE (n = 13). Chromosome aneuploidy was observed in all parasites examined with each isolate exhibiting a unique karyotype. Differences in chromosome ploidy or karyotype were not correlated with the geographic origin of the parasites. However, correlation between single nucleotide polymorphism (SNP) and geographic origin was seen for 38/41 isolates, separating the NE and SE parasites into two large groups. SNP restricted to NE and SE groups were associated with genes involved in viability and parasite resistance to drugs. Unique copy number variation (CNV) were also associated with NE and SE parasites, respectively. One striking example is the folate transporter (FT) family genes (LdBPK_100390, LdBPK_100400 and LdBPK_100410) on chromosome 10 that are single copy in all 13 SE isolates, but either double copy or higher in 39/41 NE isolates (copy number 2-4). High copy number (= 4) was also found for one Sudanese strain examined. This was confirmed by quantitative polymerase chain reaction for LdBPK_100400, the L. donovani FT1 transporter homolog. Good correlation (p = 0.005) between FT copy number and resistance to methotrexate (0.5 mg/ml MTX) was also observed with the haploid SE strains examined showing higher viability than the NE strains at this concentration. Our results emphasize the advantages of whole genome analysis to shed light on vital parasite processes in Leishmania.

Drug resistance and treatment failure in leishmaniasis: A 21st century challenge

Reevaluation of treatment guidelines for Old and New World leishmaniasis is urgently needed on a global basis because treatment failure is an increasing problem. Drug resistance is a fundamental determinant of treatment failure, although other factors also contribute to this phenomenon, including the global HIV/AIDS epidemic with its accompanying impact on the immune system. Pentavalent antimonials have been used successfully worldwide for the treatment of leishmaniasis since the first half of the 20th century, but the last 10 to 20 years have witnessed an increase in clinical resistance, e.g., in North Bihar in India. In this review, we discuss the meaning of “resistance” related to leishmaniasis and discuss its molecular epidemiology, particularly for Leishmania donovani that causes visceral leishmaniasis. We also discuss how resistance can affect drug combination therapies. Molecular mechanisms known to contribute to resistance to antimonials, amphotericin B, and miltefosine are also outlined.

Chemotherapy is central to the control and management of leishmaniasis. Antimonials remain the primary drugs against different forms of leishmaniasis in several regions. However, resistance to antimony has necessitated the use of alternative medications, especially in the Indian subcontinent (ISC). Compounds, notably the orally available miltefosine (MIL), parenteral paromomycin, and amphotericin B (AmB), are increasingly used to treat leishmaniasis. Although treatment failure (TF) has been observed in patients treated with most anti-leishmanials, its frequency of appearance may be important in patients treated with MIL, which has replaced antimonials within the kala-azar elimination program in the ISC. AmB is highly efficacious, and the associated toxic effects—when administered in its free deoxycholate form—are somewhat ameliorated in its liposomal formulation. Regrettably, laboratory experimentation has demonstrated a risk of resistance towards AmB as well. The rise of drug resistance impacts treatment outcome, and understanding its causes, spread, and impact will help us manage the risks it imposes. Here, we review the problem of TF in leishmaniasis and the contribution of drug resistance to the problem. Molecular mechanisms causing resistance to anti-leishmanials are discussed along with the appropriate use of additional available drugs, as well as the urgent need to consolidate strategies to monitor drug efficacy, epidemiological surveillance, and local policies. Coordination of these activities in national and international programs against leishmaniasis might represent a successful guide to further research and prevention activities.

Mannosylated thiolated polyethylenimine nanoparticles for the enhanced efficacy of antimonial drug against Leishmaniasis

AIM

Our aim was to inhibit trypanothione reductase (TR) and P-gp efflux pump of Leishmania by the use of thiolated polymers. Thus, increasing the intracellular accumulation and therapeutic effectiveness of antimonial compounds.

METHODS

Mannosylated thiolated chitosan and mannosylated thiolated chitosan-polyethyleneimine graft were synthesized and characterized. Meglumine antimoniate-loaded nanoparticles were prepared and evaluated for TR and P-gp efflux pump inhibition, biocompatibility, macrophage uptake and antileishmanial potential.

RESULTS

Thiomers inhibited TR with Ki 2.021. The macrophage uptake was 33.7- and 18.9-fold higher with mannosylated thiolated chitosan-polyethyleneimine graft and mannosylated thiolated chitosan nanoparticles, respectively, as compared with the glucantime. Moreover, the in vitro antileishmanial activity showed 14.41- and 7.4-fold improved IC₅₀ for M-TCS-g-PEI and M-TCS, respectively as compared with glucantime.

CONCLUSION

These results encouraged the concept that TR and P-gp inhibition by the use of thiomers improves the therapeutic efficacy of antimonial drugs.

ABCI3 Is a New Mitochondrial ABC Transporter from Leishmania major Involved in Susceptibility to Antimonials and Infectivity

We have identified and characterized ABCI3 as a new mitochondrial ABC transporter from Leishmania major Localization studies using confocal microscopy, a surface biotinylation assay, and trypsin digestion after digitonin permeabilization suggested that ABCI3 presents a dual localization in both mitochondria and the plasma membrane. From studies using parasites with a single knockout of ABCI3 (ABCI3^+/-), we provide evidence that ABCI3 is directly involved in susceptibility to the trivalent form of antimony (SbIII) and metal ions. Attempts to obtain parasites with a double knockout of ABCI3 were unsuccessful, suggesting that ABCI3 could be an essential gene in L. majorABCI3^+/- promastigotes were 5-fold more resistant to Sb^III than the wild type, while ABCI3^+/- amastigotes were approximately 2-fold more resistant to pentavalent antimony (Sb^V). This resistance phenotype was associated with decreased Sb^III accumulation due to decreased Sb^III uptake. ABCI3^+/- parasites presented higher ATP levels and generated less mitochondrial superoxide after Sb^III incubation. Finally, we observed that ABCI3^+/- parasites showed a slightly higher infection capacity than wild-type and add-back ABCI3^+/-::3×FABCI3 parasites; however, after 72 h the number of ABCI3^+/- intracellular parasites per macrophage increased significantly. Our results show that ABCI3 is responsible for Sb^III transport inside mitochondria, where it contributes to enhancement of the general toxic effects caused by Sb^III To our knowledge, ABCI3 is the first ABC transporter which is involved in susceptibility toward antimony, conferring Sb^III resistance to parasites when it is partially deleted.

Knockdown of Host Antioxidant Defense Genes Enhances the Effect of Glucantime on Intracellular Leishmania braziliensis in Human Macrophages

Leishmaniasis is a neglected tropical disease that affects millions of people worldwide and represents a major public health problem. Information on protein expression patterns and functional roles within the context of Leishmania-infected human monocyte-derived macrophages (MDMs) under drug treatment conditions is essential for understanding the role of these cells in leishmaniasis treatment. We analyzed functional changes in the expression of human MDM genes and proteins during in vitro infection by Leishmania braziliensis and treatment with Glucantime (Sb^V), using quantitative PCR (qPCR) arrays, Western blotting, confocal microscopy, and small interfering RNA (siRNA) human gene inhibition assays. Comparison of the results from gene transcription and protein expression analyses revealed that glutathione S-transferase π1 (GSTP1), glutamate-cysteine ligase modifier subunit (GCLM), glutathione reductase (GSR), glutathione synthetase (GSS), thioredoxin (TRX), and ATP-binding cassette, subfamily B, member 5 (ABCB5), were strongly upregulated at both the mRNA and protein levels in human MDMs that were infected and treated, compared to the control group. Subcellular localization studies showed a primarily phagolysosomal location for the ABCB5 transporter, indicating that this protein may be involved in the transport of Sb^V By inducing a decrease in L. braziliensis intracellular survival in THP-1 macrophages, siRNA silencing of GSTP1, GSS, and ABCB5 resulted in an increased leishmanicidal effect of Sb^V exposure in vitro Our results suggest that human MDMs infected with L. braziliensis and treated with Sb^V express increased levels of genes participating in antioxidant defense, whereas our functional analyses provide evidence for the involvement of human MDMs in drug detoxification. Therefore, we conclude that GSS, GSTP1, and ABCB5 proteins represent potential targets for enhancing the leishmanicidal activity of Glucantime.

Voacamine alters Leishmania ultrastructure and kills parasite by poisoning unusual bi-subunit topoisomerase IB

Indole alkaloids possess a large spectrum of biological activities including anti-protozoal action. Here we report for the first time that voacamine, isolated from the plant Tabernaemontana coronaria, is an antiprotozoal agent effective against a large array of trypanosomatid parasites including Indian strain of Leishmania donovani and Brazilian strains of Leishmania amazonensis and Trypanosoma cruzi. It inhibits the relaxation activity of topoisomerase IB of L. donovani (LdTop1B) and stabilizes the cleavable complex. Voacamine is probably the first LdTop1B-specific poison to act uncompetitively. It has no impact on human topoisomerase I and II up to 200μM concentrations. The study also provides a thorough insight into ultrastructural alterations induced in three kinetoplastid parasites by a specific inhibitor of LdTop1B. Voacamine is also effective against intracellular amastigotes of different drug unresponsive field isolates of Leishmania donovani obtained from endemic zones of India severely affected with visceral leishmaniasis. Most importantly, this is the first report demonstrating the efficacy of a compound to reduce the burden of drug resistant parasites, unresponsive to SAG, amphotericin B and miltefosine, in experimental BALB/c mice model of visceral leishmaniasis. The findings cumulatively provide a strong evidence that voacamine can be a promising drug candidate against trypanosomatid infections.

Glucose-6-phosphate dehydrogenase and Trypanothione reductase interaction protects Leishmania donovani from metalloid mediated oxidative stress

Exploration of metabolons as viable drug target is rare in kinetoplastid biology. Here we present a novel protein-protein interaction among Glucose-6-phosphate dehydrogenase (LdG6PDH) and Trypanothione reductase (LdTryR) of Leishmania donovani displaying interconnection between central glucose metabolism and thiol metabolism of this parasite. Digitonin fractionation patterns observed through immunoblotting indicated localisation of both LdG6PDH and LdTryR in cytosol. In-silico and in-vitro interaction observed by size exclusion chromatography, co-purification, pull-down assay and spectrofluorimetric analysis revealed LdG6PDH and LdTryR physically interact with each other in a NADPH dependent manner. Coupled enzymatic assay displayed that NADPH generation was severely impaired by addition of Sb^III, As^III and Te^IV extraneously, which hint towards metalloid driven structural changes of the interacting proteins. Co-purification patterns and pull-down assays also depicted that metalloids (Sb^III, As^III and Te^IV) hinder the in-vitro interaction of these two enzymes. Surprisingly, metalloids at sub-lethal concentrations induced the in-vivo interaction of LdG6PDH and LdTryR, as analyzed by pull-down assays and fluorescence microscopy signifying protection against metalloid mediated ROS. Inhibition of LdTryR by thioridazine in LdG6PDH^-/- parasites resulted in metalloid induced apoptotic death of the parasites due to abrupt fall in reduced thiol content, disrupted NADPH/NADP⁺ homeostasis and lethal oxidative stress. Interestingly, clinical isolates of L.donovani resistant to SAG exhibited enhanced interaction between LdG6PDH and LdTryR and showed cross resistivity towards As^III and Te^IV. Thus, our findings propose the metabolon of LdG6PDH and LdTryR as an alternate therapeutic target and provide mechanistic insight about metalloid resistance in Visceral Leishmaniasis.

Treatment Outcome of the Drug-resistant Zoonotic Cutaneous Leishmaniasis by Glucantime

BACKGROUND

Resistance of Leishmania species to antimonial drugs has increased. Hence, in the present study Leishmania major isolates were collected from patients with resistance phenotype and the presence/absence of resistance to Glucantime was investigated.

MATERIALS AND METHODS

Samples were taken from 10 cutaneous leishmaniasis (CL) patients who had not responded to chemotherapy with Glucantime. Nested polymerase chain reaction (PCR) was performed to identify the isolated species. Stationary phase promastigotes were added to the grown, adhesive J774 macrophages. Values obtained from standard strain were compared with the test cultures after exposure to the medicine. In vivo, the effects of Glucantime were assessed by comparing the sizes and the parasite burden of the lesions on mouse model.

RESULTS

The results of amplified band on agarose gel demonstrated all samples were L. major. After exposure to medicine, a reduction of intracellular amastigotes to half was detected. In vivo, the parasite was eliminated in 90% of mice with lesions caused by both isolates of patients and standard L. major, and their lesions became smaller significantly.

CONCLUSION

Pentavalent antimonial (SbV) salts are the main component of chemotherapy against leishmaniasis. However, the medicine has been found ineffective. In the present study, isolates from patients with no response to treatment had no significant difference from the standard L. major strain (as the sensitive strain). Therefore, in patients with resistance phenotype to Glucantime, the parasites did not actually have intrinsic resistance, i.e., environmental and host factors prevented the successful treatment of the disease.

Rapid synthesis for monodispersed gold nanoparticles in kaempferol and anti-leishmanial efficacy against wild and drug resistant strains

Synthesis of monodispersed gold nanoparticles using kaempferol and antileishmanial activity with high macrophage uptake capacity.