Modulation of gene expression in human macrophages treated with the anti-leishmania pentavalent antimonial drug sodium stibogluconate

Induced pluripotent stem cell-derived human macrophages as an infection model for Leishmania donovani

The parasite Leishmania donovani is one of the species causing visceral leishmaniasis in humans, a deadly infection claiming up to 40,000 lives each year. The current drugs for leishmaniasis treatment have severe drawbacks and there is an urgent need to find new anti-leishmanial compounds. However, the search for drug candidates is complicated by the intracellular lifestyle of Leishmania. Here, we investigate the use of human induced pluripotent stem cell (iPS)-derived macrophages (iMACs) as host cells for L. donovani. iMACs obtained through embryoid body differentiation were infected with L. donovani promastigotes, and high-content imaging techniques were used to optimize the iMACs seeding density and multiplicity of infection, allowing us to reach infection rates up to 70% five days after infection. IC50 values obtained for miltefosine and amphotericin B using the infected iMACs or mouse peritoneal macrophages as host cells were comparable and in agreement with the literature, showing the potential of iMACs as an infection model for drug screening.

Transcriptomic Analysis in Human Macrophages Infected with Therapeutic Failure Clinical Isolates of Leishmania infantum

Leishmaniasis is one of the neglected tropical diseases with a worldwide distribution, affecting humans and animals. In the absence of an effective vaccine, current treatment is through the use of chemotherapy; however, existing treatments have frequent appearance of drug resistance and therapeutic failure (TF). The identification of factors that contribute to TF in leishmaniasis will provide the basis for a future therapeutic strategy more efficient for the control of this disease. In this article, we have evaluated the transcriptomic changes in the host cells THP-1 after infection with clinical Leishmania infantum isolates from leishmaniasis patients with TF. Our results show that distinct L. infantum isolates differentially modulate host cell response, inducing phenotypic changes that probably may account for parasite survival and TF of patients. Analysis of differential expression genes (DEGs), with a statistical significance threshold of a fold change ≥ 2 and a false discovery rate value ≤ 0.05, revealed a different number of DEGs according to the Leishmanialine. Globally, there was a similar number of genes up- and downregulated in all the infected host THP-1 cells, with exception of Hi-L2221, which showed a higher number of downregulated DEGs. We observed a total of 58 DEGs commonly modulated in all infected host cells, including upregulated (log₂FC ≥ 1) and downregulated (log₂FC ≤ -1) genes. Based on the results obtained from the analysis of RNA-seq, volcano plot, and GO enrichment analysis, we identified the most significant transcripts of relevance for their possible contribution to the TF observed in patients with leishmaniasis.

New Insights on Drug-Resistant Clinical Isolates of Leishmania infantum-Infected Human Macrophages as Determined by Comparative Transcriptome Analyses

Leishmaniasis is the second most important neglected tropical parasitic disease after malaria. This disease is distributed worldwide and can be present in a variety of clinical forms, depending on the parasite species and host's genetic background. As chemotherapy is the only effective weapon whose effectiveness is limited by the frequent appearance of drug resistance and therapeutic failure, new therapeutic strategies are required. To better understand the factors that contribute to therapeutic failure and drug resistance in leishmaniasis, we studied the transcriptomic changes in host THP-1 cells after infection with clinical Leishmania infantum isolates with different susceptibilities to antileishmanial drugs by RNA-seq. Analysis of the differentially expressed genes (DEGs) in infected host cells revealed variations in DEG numbers in the THP-1-infected cells depending on the Leishmania line. A key conclusion of this study is that the modulation of host cells is Leishmania line dependent. Gene ontology enrichment analyses of DEGs indicated that certain biological processes were modulated in the infected host cells, specifically related to cellular metabolism, immune response, defense response, signaling pathways, and cell proliferation and apoptosis. Furthermore, this study provides new potential therapeutic markers and insights into the THP-1 host transcriptomic changes that occur after late infection with drug-resistant L. infantum clinical isolates.

Synthesis of sp2-Iminosugar Selenoglycolipids as Multitarget Drug Candidates with Antiproliferative, Leishmanicidal and Anti-Inflammatory Properties

sp²-Iminosugar glycolipids (sp²-IGLs) represent a consolidated family of glycoconjugate mimetics encompassing a monosaccharide-like glycone moiety with a pseudoamide-type nitrogen replacing the endocyclic oxygen atom of carbohydrates and an axially-oriented lipid chain anchored at the pseudoanomeric position. The combination of these structural features makes them promising candidates for the treatment of a variety of conditions, spanning from cancer and inflammatory disorders to parasite infections. The exacerbated anomeric effect associated to the putative sp²-hybridized N-atom imparts chemical and enzymatic stability to sp²-IGLs and warrants total α-anomeric stereoselectivity in the key glycoconjugation step. A variety of O-, N-, C- and S-pseudoglycosides, differing in glycone configurational patterns and lipid nature, have been previously prepared and evaluated. Here we expand the chemical space of sp²-IGLs by reporting the synthesis of α-d-gluco-configured analogs with a bicyclic (5N,6O-oxomethylidene)nojirimycin (ONJ) core incorporating selenium at the glycosidic position. Structure-activity relationship studies in three different scenarios, namely cancer, Leishmaniasis and inflammation, convey that the therapeutic potential of the sp²-IGLs is highly dependent, not only on the length of the lipid chain (linear aliphatic C₁₂ vs. C₈), but also on the nature of the glycosidic atom (nitrogen vs. sulfur vs. selenium). The ensemble of results highlights the α-dodecylseleno-ONJ-glycoside as a promising multitarget drug candidate.

Heme oxygenase-1 in protozoan infections: A tale of resistance and disease tolerance

Heme oxygenase (HO-1) mediates the enzymatic cleavage of heme, a molecule with proinflammatory and prooxidant properties. HO-1 activity deeply impacts host capacity to tolerate infection through reduction of tissue damage or affecting resistance, the ability of the host to control pathogen loads. In this Review, we will discuss the contribution of HO-1 in different and complex protozoan infections, such as malaria, leishmaniasis, Chagas disease, and toxoplasmosis. The complexity of these infections and the pleiotropic effects of HO-1 constitute an interesting area of study and an opportunity for drug development.

Post kala-azar dermal leishmaniasis: A threat to elimination program

Leishmaniasis remains a public health concern around the world that primarily affects poor folks of the developing world spanning across 98 countries with mortality of 0.2 million to 0.4 million annually. Post kala-azar dermal leishmaniasis (PKDL) is the late skin manifestation of visceral leishmaniasis (VL). It has been reported that about 2.5% to 20% of patients recovered from VL develop PKDL having stilted macular or nodular lesions with parasites. In the Indian subcontinent (ISC), it manifests a few months after recovery from VL, though in Africa it can occur simultaneously with VL or a little later. New cases of PKDL are also observed without prior VL in the ISC. These individuals with PKDL represent an important but largely neglected reservoir of infection that perpetuates anthroponotic Leishmania donovani transmission in the ISC and can jeopardize the VL elimination program as these cases can infect the sand flies and spread the endemic. Therefore, it becomes imperative to eradicate PKDL as a part of the VL elimination program. With the limited treatment options besides little knowledge on PKDL, this review stands out in focusing on different aspects that should be dealt for sustained VL elimination.

Synthesis of polyfluoroalkyl sp2-iminosugar glycolipids and evaluation of their immunomodulatory properties towards anti-tumor, anti-leishmanial and anti-inflammatory therapies

Immunomodulatory glycolipids, among which α-galactosylceramide (KRN7000) is an iconic example, have shown strong therapeutic potential in a variety of conditions ranging from cancer and infection to autoimmune or neurodegenerative diseases. A main difficulty for those channels is that they often provoke a cytokine storm comprising both pro- and anti-inflammatory mediators that antagonize each other and negatively affect the immune response. The synthesis of analogues with narrower cytokine secretion-inducing capabilities is hampered by the intrinsic difficulty at controlling the stereochemical outcome in glycosidation reactions, particularly if targeting the α-anomer, which seriously hampers drug optimization strategies. Here we show that replacing the monosaccharide glycone by a sp²-iminosugar glycomimetic moiety allows accessing N-linked sp²-iminosugar glycolipids (sp²-IGLs) with total α-stereocontrol in a single step with no need of protecting groups or glycosidation promotors. The lipid tail has been then readily tailored by incorporating polyfluoroalkyl segments of varied lengths in view of favouring binding to the lipid binding site of the master p38 mitogen activated protein kinase (p38 MAPK), thereby polarizing the immune response in a cell-context dependent manner. The compounds have been evaluated for their antiproliferative, anti-leishmanial and anti-inflammatory activities in different cell assays. The size of the fluorous segment was found to be critical for the biological activity, probably by regulating the aggregation and membrane-crossing properties, whereas the hydroxylation profile (gluco or galacto-like) was less relevant. Biochemical and computational data further support a mechanism of action implying binding to the allosteric lipid binding site of p38 MAPK and subsequent activation of the noncanonical autophosphorylation route. The ensemble of results provide a proof of concept of the potential of sp²-IGLs as immunoregulators.

Thiol-ene "Click" Synthesis and Pharmacological Evaluation of C-Glycoside sp2-Iminosugar Glycolipids

The unique stereoelectronic properties of sp2-iminosugars enable their participation in glycosylation reactions, thereby behaving as true carbohydrate chemical mimics. Among sp2-iminosugar conjugates, the sp2-iminosugar glycolipids (sp2-IGLs) have shown a variety of interesting pharmacological properties ranging from glycosidase inhibition to antiproliferative, antiparasitic, and anti-inflammatory activities. Developing strategies compatible with molecular diversity-oriented strategies for structure-activity relationship studies was therefore highly wanted. Here we show that a reaction sequence consisting in stereoselective C-allylation followed by thiol-ene "click" coupling provides a very convenient access to α-C-glycoside sp2-IGLs. Both the glycone moiety and the aglycone tail can be modified by using sp2-iminosugar precursors with different configurational profiles (d-gluco or d-galacto in this work) and varied thiols, as well as by oxidation of the sulfide adducts (to the corresponding sulfones in this work). A series of derivatives was prepared in this manner and their glycosidase inhibitory, antiproliferative and antileishmanial activities were evaluated in different settings. The results confirm that the inhibition of glycosidases, particularly α-glucosidase, and the antitumor/leishmanicidal activities are unrelated. The data are also consistent with the two later activities arising from the ability of the sp2-IGLs to interfere in the immune system response in a cell line and cell context dependent manner.

Model-based Evaluation of Gene Expression Changes in Response to Leishmania Infection

Since the development of high-density microarray technology in the late 1990s, global host gene expression changes in response to various stimuli have been extensively studied. More than a dozen peer-reviewed publications have investigated the effect of Leishmania infection in various models since 2001. This review covers the transcriptional changes in macrophage models induced by various Leishmania species and summarizes the resulting impact these studies have on our understanding of the host response to leishmaniasis in vitro. Characterization of the similarities and differences between various model systems will not only further our understanding of Leishmania-induced changes to macrophage gene expression but also identify potential therapeutic targets in the future.

Induction of haem oxygenase-1 increases infection of dog macrophages by L. infantum

We aimed to induce and inhibit HO-1, ascertaining its effect on infection rate, parasite load and the levels of superoxide, reactive oxygen species (ROS), nitric oxide (NO), TNF-alpha and IL-10 in cultured macrophages from healthy dogs infected by Leishmania infantum. Macrophages obtained from 15 healthy dogs were cultured alone or infected with L. infantum, with or without association of HO-1 inducer and inhibitor. The infection rate and the parasite load were determined by the number of infected macrophages and number of promastigotes per macrophage, respectively. HO-1 levels and gene expression, as well as IL-10 and TNF-alpha levels were also measured in these cultures. Superoxide, ROS and NO levels in macrophages were measured through flow cytometry. Induction of HO-1 increased the infection rate and parasite load, while its inhibition decreased the infection rate and IL-10 production. There was a positive correlation between HO-1 and infection rate or parasite load. Increased infection rate was associated with decreased superoxide, ROS and NO levels. Induction of HO-1 metabolism in dogs infected by L. infantum is possibly one of the mechanisms responsible for increasing the infection of macrophages, mainly through reduction in the oxidative and nitrosative metabolisms of these cells.

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.

Snapshot Profiling of the Antileishmanial Potency of Lead Compounds and Drug Candidates against Intracellular Leishmania donovani Amastigotes, with a Focus on Human-Derived Host Cells

This study characterized the in vitro potencies of antileishmanial agents against intracellular Leishmania donovani amastigotes in primary human macrophages, obtained with or without CD14-positive monocyte enrichment, phorbol 12-myristate 13-acetate (PMA)-differentiated THP-1 cells, and mouse peritoneal exudate macrophages (PEMs). Host cell-dependent potency was confirmed for pentavalent and trivalent antimony. Fexinidazole was inactive against intracellular amastigotes across the host cell panel. Fexinidazole sulfone, (R)-PA-824, (S)-PA-824, and VL-2098 displayed similar potency in all of the host cells tested.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

Antileishmanial activity of sp2-iminosugar derivatives

sp²-iminosugar S-linked pseudoglycosides selectively inhibit growth of the intracellular form of Leishmania donovani.

Mechanisms of action of substituted β-amino alkanols on Leishmania donovani

Leishmaniasis is the protozoan disease second in importance for human health, superseded only by malaria; however, the options for chemotherapeutic treatment are increasingly limited due to drug resistance and toxicity. Under this perspective, a quest for new chemical compounds is urgently needed. An N-substituted 2-aminoalkan-1-ol scaffold has been shown to be a versatile scaffold for antiparasitic activity. Knowledge about its mechanism of action is still rather limited. In this work, we endeavored to define the leishmanicidal profile of such β-amino alkanol derivatives using a set of 15 N-mono- and disubstituted surrogates, tested on Leishmania donovani promastigotes and intracellular amastigotes. The best compound (compound 5), 2-ethylaminododecan-1-ol, had a 50% effective concentration (EC50) of 0.3 μM and a selectivity index of 72 for infected THP-1 cells and was selected for further elucidation of its leishmanicidal mechanism. It induced fast depletion of intracellular ATP content in promastigotes in the absence of vital dye intracellular entry, ruling out plasma membrane permeabilization as its origin. Confocal and transmission electron microscopy analyses showed that compound 5 induced severe mitochondrial swelling and vesiculation. Polarographic analysis using an oxygen electrode demonstrated that complex II of the respiratory chain (succinate reductase) was strongly inhibited by compound 5, identifying this complex as one of the primary targets. Furthermore, for other β-amino alkanols whose structures differed subtly from that of compound 5, plasma membrane permeabilization or interference with membrane traffic was also observed. In all, N-substituted β-amino alkanols were shown as appealing leishmanicidal candidates deserving further exploration.

Human dendritic cells exhibit a pronounced type I IFN signature following Leishmania major infection that is required for IL-12 induction

Leishmania major-infected human dendritic cells (DCs) exhibit a marked induction of IL-12, ultimately promoting a robust Th1-mediated response associated with parasite killing and protective immunity. The host cell transcription machinery associated with the specific IL-12 induction observed during L. major infection remains to be thoroughly elucidated. In this study, we used Affymetrix GeneChip (Affymetrix) to globally assess the host cell genes and pathways associated with early L. major infection in human myeloid-derived DCs. Our data revealed 728 genes were significantly differentially expressed and molecular signaling pathway revealed that the type I IFN pathway was significantly enriched. Addition of a neutralizing type I IFN decoy receptor blocked the expression of IRF7 and IL-12p40 during DC infection, indicating the L. major-induced expression of IL-12p40 is dependent upon the type I IFN signaling pathway. In stark contrast, IL-12p40 expression is not elicited by L. donovani, the etiological agent of deadly visceral leishmaniasis. Therefore, we examined the gene expression profile for several IFN response genes in L. major versus L. donovani DC infections. Our data revealed that L. major, but not L. donovani, induces expression of IRF2, IRF7, and IFIT5, implicating the regulation of type I IFN-associated signaling pathways as mediating factors toward the production of IL-12.

4-amino bis-pyridinium derivatives as novel antileishmanial agents

The antileishmanial activity of a series of bis-pyridinium derivatives that are analogues of pentamidine have been investigated, and all compounds assayed were found to display activity against promastigotes and intracellular amastigotes of Leishmania donovani and Leishmania major, with 50% effective concentrations (EC50s) lower than 1 μM in most cases. The majority of compounds showed similar behavior in both Leishmania species, being slightly more active against L. major amastigotes. However, compound VGP-106 {1,1'-(biphenyl-4,4'-diylmethylene)bis[4-(4-bromo-N-methylanilino)pyridinium] dibromide} exhibited significantly higher activity against L. donovani amastigotes (EC50, 0.86 ± 0.46 μM) with a lower toxicity in THP-1 cells (EC50, 206.54 ± 9.89 μM). As such, VGP-106 was chosen as a representative compound to further elucidate the mode of action of this family of inhibitors in promastigote forms of L. donovani. We have determined that uptake of VGP-106 in Leishmania is a temperature-independent process, suggesting that the compound crosses the parasite membrane by diffusion. Transmission electron microscopy analysis showed a severe mitochondrial swelling in parasites treated with compound VGP-106, which induces hyperpolarization of the mitochondrial membrane potential and a significant decrease of intracellular free ATP levels due to the inhibition of ATP synthesis. Additionally, we have confirmed that VGP-106 induces mitochondrial ROS production and an increase in intracellular Ca(2+) levels. All these molecular events can activate the apoptotic process in Leishmania; however, propidium iodide assays gave no indication of DNA fragmentation. These results underline the potency of compound VGP-106, which may represent a new avenue for the development of novel antileishmanial compounds.

Post kala-azar dermal leishmaniasis: an unresolved mystery

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Sodium antimony gluconate contributes towards the pathogenesis of PKDL.

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UV light plays a pivotal role in the development of PKDL.

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Development of PKDL can be viewed as a reinfection or activation of latent Leishmania parasites.

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PKDL can be resolved by mounting an effective tissue-specific memory T cell response.

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Host genetic factors play a contributory role.

Post kala-azar dermal leishmaniasis (PKDL), a cutaneous sequela of visceral leishmaniasis (VL), develops in some patients alongside but more commonly after apparent cure from VL. In view of the pivotal role of PKDL patients in the transmission of VL, here we review clinical, epidemiological, parasitological, and immunological perspectives of this disease, focusing on five hypotheses to explain the development of PKDL: (i) the role of antimonial drugs; (ii) UV-induced skin damage; (iii) reinfection; (iv) organ specific failure of memory T cell responses; and (v) genetic susceptibility of the host. This review will enable researchers and clinicians to explore the unresolved mystery of PKDL and provide a framework for future application of ‘omic’ approaches for the control and eventual elimination of VL.

Leishmania panamensis infection and antimonial drugs modulate expression of macrophage drug transporters and metabolizing enzymes: impact on intracellular parasite survival

OBJECTIVES

Treatment failure is multifactorial. Despite the importance of host cell drug transporters and metabolizing enzymes in the accumulation, distribution and metabolism of drugs targeting intracellular pathogens, their impact on the efficacy of antileishmanials is unknown. We examined the contribution of pharmacologically relevant determinants in human macrophages in the antimony-mediated killing of intracellular Leishmania panamensis and its relationship with the outcome of treatment with meglumine antimoniate.

METHODS

Patients with cutaneous leishmaniasis who failed (n = 8) or responded (n =8) to treatment were recruited. Gene expression profiling of pharmacological determinants in primary macrophages was evaluated by quantitative RT-PCR and correlated to the drug-mediated intracellular parasite killing. Functional validation was conducted through short hairpin RNA gene knockdown.

RESULTS

Survival of L. panamensis after exposure to antimonials was significantly higher in macrophages from patients who failed treatment. Sixteen macrophage drug-response genes were modulated by infection and exposure to meglumine antimoniate. Correlation analyses of gene expression and intracellular parasite survival revealed the involvement of host cell metallothionein-2A and ABCB6 in the survival of Leishmania during exposure to antimonials. ABCB6 was functionally validated as a transporter of antimonial compounds localized in both the cell and phagolysosomal membranes of macrophages, revealing a novel mechanism of host cell-mediated regulation of intracellular drug exposure and parasite survival within phagocytes.

CONCLUSIONS

These results provide insight into host cell mechanisms regulating the intracellular exposure of Leishmania to antimonials and variations among individuals that impact parasite survival. Understanding of host cell determinants of intracellular pharmacokinetics/pharmacodynamics opens new avenues to improved drug efficacy for intracellular pathogens.

Oxidative stress in mice treated with antileishmanial meglumine antimoniate

In order to improve the understanding of the toxicity of pentavalent antimony (Sb(V)), we investigated the acute effects of meglumine antimoniate (MA) on the oxidative stress in heart, liver, kidney, spleen and brain tissue of mice. Levels of lipoperoxidation and protein carbonylation were measured to evaluate the oxidative status, whereas superoxide dismutase/catalase activity and glutathione levels were recorded to examine the antioxidative status. We observed that MA caused significant protein carbonylation in the heart, spleen and brain tissue. Increased lipoperoxidation was found in the liver and brain tissue. An imbalance between superoxide dismutase and catalase activities could be observed in heart, liver, spleen and brain tissue. Our results suggest that MA causes oxidative stress in several vital organs of mice. This indicates that the production of highly reactive oxygen and nitrogen species induced by MA might be involved in some of its toxic adverse effects.

High content analysis of primary macrophages hosting proliferating Leishmania amastigotes: application to anti-leishmanial drug discovery

BACKGROUND/OBJECTIVES

Human leishmaniases are parasitic diseases causing severe morbidity and mortality. No vaccine is available and numerous factors limit the use of current therapies. There is thus an urgent need for innovative initiatives to identify new chemotypes displaying selective activity against intracellular Leishmania amastigotes that develop and proliferate inside macrophages, thereby causing the pathology of leishmaniasis.

METHODOLOGY/PRINCIPAL FINDINGS

We have developed a biologically sound High Content Analysis assay, based on the use of homogeneous populations of primary mouse macrophages hosting Leishmania amazonensis amastigotes. In contrast to classical promastigote-based screens, our assay more closely mimics the environment where intracellular amastigotes are growing within acidic parasitophorous vacuoles of their host cells. This multi-parametric assay provides quantitative data that accurately monitors the parasitic load of amastigotes-hosting macrophage cultures for the discovery of leishmanicidal compounds, but also their potential toxic effect on host macrophages. We validated our approach by using a small set of compounds of leishmanicidal drugs and recently published chemical entities. Based on their intramacrophagic leishmanicidal activity and their toxicity against host cells, compounds were classified as irrelevant or relevant for entering the next step in the drug discovery pipeline.

CONCLUSIONS/SIGNIFICANCE

Our assay represents a new screening platform that overcomes several limitations in anti-leishmanial drug discovery. First, the ability to detect toxicity on primary macrophages allows for discovery of compounds able to cross the membranes of macrophage, vacuole and amastigote, thereby accelerating the hit to lead development process for compounds selectively targeting intracellular parasites. Second, our assay allows discovery of anti-leishmanials that interfere with biological functions of the macrophage required for parasite development and growth, such as organelle trafficking/acidification or production of microbicidal effectors. These data thus validate a novel phenotypic screening assay using virulent Leishmania amastigotes growing inside primary macrophage to identify new chemical entities with bona fide drug potential.

Human macrophage response to L. (Viannia) panamensis: microarray evidence for an early inflammatory response

Background

Previous findings indicate that susceptibility to Leishmania (Viannia) panamensis infection of monocyte-derived macrophages from patients and asymptomatically infected individuals were associated with the adaptive immune response and clinical outcome.

Methodology/Principal Findings

To understand the basis for this difference we examined differential gene expression of human monocyte-derived macrophages following exposure to L. (V.) panamensis. Gene activation profiles were determined using macrophages from healthy volunteers cultured with or without stationary phase promastigotes of L. (V.) panamensis. Significant changes in expression (>1.5-fold change; p<0.05; up- or down-regulated) were identified at 0.5, 4 and 24 hours. mRNA abundance profiles varied over time, with the highest level of activation occurring at earlier time points (0.5 and 4 hrs). In contrast to observations for other Leishmania species, most significantly changed mRNAs were up- rather than down-regulated, especially at early time points. Up-regulated transcripts over the first 24 hours belonged to pathways involving eicosanoid metabolism, oxidative stress, activation of PKC through G protein coupled receptors, or mechanism of gene regulation by peroxisome proliferators via PPARα. Additionally, a marked activation of Toll-receptor mediated pathways was observed. Comparison with published microarray data from macrophages infected with L. (Leishmania) chagasi indicate differences in the regulation of genes involved in signaling, motility and the immune response.

Conclusions

Results show that the early (0.5 to 24 hours) human monocyte-derived macrophage response to L. (Viannia) panamensis is not quiescent, in contrast to published reports examining later response times (48–96 hours). Early macrophage responses are important for the developing cellular response at the site of infection. The kinetics and the mRNA abundance profiles induced by L. (Viannia) panamensis illustrate the dynamics of these interactions and the distinct biologic responses to different Leishmania species from the outset of infection within their primary host cell.

Leishmania parasites cause a spectrum of diseases (cutaneous, visceral and the deforming forms—chronic cutaneous and mucocutaneous) known as leishmaniasis. The macrophage, a key cell in the immune system, is the cellular target of Leishmania parasites in the mammalian host. Previous studies showed the responses of monocytederived macrophages from naturally infected humans to infection with Leishmania (Viannia) panamensis were key to adaptive immune responses and clinical outcome. Consequently, an mRNA microarray approach was employed to assess the changes in macrophage gene expression over time (0.5 to 24 hours) induced by L. panamensis. The highest level of gene expression induction occurred early (0.5–4 hours); the early pathways (groups of genes) activated included those involved in the innate immune response (signaling, phagocytosis, TLR activation, and inflammatory). Early gene activation is presumed to be important for the developing cellular milieu at the site of infection. By 24 hours post-infection the dominant pathways involved metabolic functions. However, a comparison of the macrophage response to L. (V.) panamensis to that of L. (L.) chagasi (causative agent of visceral leishmaniasis) at 24 hours revealed a differential up-regulation of genes (cell adhesion, signaling, and inflammation) in response to these species. These observations underscore the distinct biology of different Leishmania species from the outset of infection.

Genetic influence on the working memory circuitry: behavior, structure, function and extensions to illness

Working memory is a highly heritable complex cognitive trait that is critical for a number of higher-level functions. However, the neural substrates of this behavioral phenotype are intricate and it is unknown through what precise biological mechanism variation in working memory is transmitted. In this review we explore different functional and structural components of the working memory circuitry, and the degree to which each of them is contributed to by genetic factors. Specifically, we consider dopaminergic function, glutamatergic function, white matter integrity and gray matter structure all of which provide potential mechanisms for the inheritance of working memory deficits. In addition to discussing the overall heritability of these measures we also address specific genes that may play a role. Each of these heritable components has the potential to uniquely contribute to the working memory deficits observed in genetic disorders, including 22q deletion syndrome, fragile X syndrome, phenylketonuria (PKU), and schizophrenia. By observing the individual contributions of disruptions in different components of the working memory circuitry to behavioral performance, we highlight the concept that there may be many routes to a working memory deficit; even though the same cognitive measure may be a valid endophenotype across different disorders, the underlying cause of, and treatment for, the deficit may differ. This has implications for our understanding of the transmission of working memory deficits in both healthy and disordered populations.

Genomic organization of leishmania species

Leishmania is a protozoan parasite belonging to the family Trypanosomatidae, which is found among 88 different countries. The parasite lives as an amastigote in vertebrate macrophages and as a promastigote in the digestive tract of sand fly. It can be cultured in the laboratory using appropriate culture media. Although the sexual cycle of Leishmania has not been observed during the promastigote and amastigote stages, it has been reported by some researchers. Leishmania has eukaryotic cell organization. Cell culture is convenient and cost effective, and because posttranslational modifications are common processes in the cultured cells, the cells are used as hosts for preparing eukaryotic recombinant proteins for research. Several transcripts of rDNA in the Leishmania genome are suitable regions for conducting gene transfer. Old World Leishmania spp. has 36 chromosomes, while New World Leishmania spp. has 34 or 35 chromosomes. The genomic organization and parasitic characteristics have been investigated. Leishmania spp. has a unique genomic organization among eukaryotes; the genes do not have introns, and the chromosomes are smaller with larger numbers of genes confined to a smaller space within the nucleus. Leishmania spp. genes are organized on one or both DNA strands and are transcribed as polycistronic (prokaryotic-like) transcripts from undefined promoters. Regulation of gene expression in the members of Trypanosomatidae differs from that in other eukaryotes. The trans-splicing phenomenon is a necessary step for mRNA processing in lower eukaryotes and is observed in Leishmania spp. Another particular feature of RNA editing in Leishmania spp. is that mitochondrial genes encoding respiratory enzymes are edited and transcribed. This review will discuss the chromosomal and mitochondrial (kinetoplast) genomes of Leishmania spp. as well as the phenomenon of RNA editing in the kinetoplast genome.

The role of reduced pterins in resistance to reactive oxygen and nitrogen intermediates in the protozoan parasite Leishmania

During its life cycle, the protozoan parasite Leishmania experiences oxidative stress when interacting with macrophages. Reduced pterins are known scavengers of reactive oxygen and nitrogen intermediates. Leishmania has a pteridine reductase, PTR1, whose main function is to provide reduced pterins. We investigated the role of PTR1 in resistance to oxidative and nitrosative stress in Leishmania tarentolae, Leishmania infantum, and Leishmania major PTR1(-/-) mutants. The PTR1(-/-) cells of the three species were more sensitive to H2O2- and NO-induced stress. Using a fluorescent probe allowing ROI quantification, we demonstrated an increase in intracellular oxidant molecules in the PTR1(-/-) mutants. The disruption of PTR1 increased metacyclogenesis in L. infantum and L. major. We purified metacyclic parasites from PTR1(-/-) mutants and control cells and tested their intracellular survival in the J774 mouse cell line and in human monocyte-derived macrophages. Our results showed that PTR1(-/-) null mutants survived less in both macrophage models compared to control cells and this decrease was more pronounced in macrophages activated for oxidant production. This study demonstrates that one physiological role of reduced pterins in Leishmania is to deal with oxidative and nitrosative species, and a decreased ability to provide reduced pterins leads to decreased intracellular survival.