Genomic organisation and transcription characterisation of the gene encoding Leishmania (Leishmania) amazonensis arginase and its protein structure prediction

Computer-aided drug design approaches applied to screen natural product's structural analogs targeting arginase in Leishmania spp

Introduction: Leishmaniasis is a disease with high mortality rates and approximately 1.5 million new cases each year. Despite the new approaches and advances to fight the disease, there are no effective therapies. Methods: Hence, this study aims to screen for natural products' structural analogs as new drug candidates against leishmaniasis. We applied Computer-aided drug design (CADD) approaches, such as virtual screening, molecular docking, molecular dynamics simulation, molecular mechanics-generalized Born surface area (MM-GBSA) binding free estimation, and free energy perturbation (FEP) aiming to select structural analogs from natural products that have shown anti-leishmanial and anti-arginase activities and that could bind selectively against the Leishmania arginase enzyme. Results: The compounds 2H-1-benzopyran, 3,4-dihydro-2-(2-methylphenyl)-(9CI), echioidinin, and malvidin showed good results against arginase targets from three parasite species and negative results for potential toxicities. The echioidinin and malvidin ligands generated interactions in the active center at pH 2.0 conditions by MM-GBSA and FEP methods. Conclusions: This work suggests the potential anti-leishmanial activity of the compounds and thus can be further in vitro and in vivo experimentally validated.

Exploring the antileishmanial activity of N1,N2-disubstituted-benzoylguanidines: synthesis and molecular modeling studies

In this report, we describe the synthesis and evaluation of nine N¹,N²-disubstituted-benzoylguanidines against promastigotes and amastigotes forms of Leishmania amazonensis. The derivatives 2g and 2i showed low IC₅₀ values against promastigote form (90.8 ± 0.05 µM and 68.4 ± 0.03 µM, respectively), low cytotoxicity profile (CC₅₀ 396 ± 0.02 µM and 857.9 ± 0.06 µM) for peritoneal macrophages cells and SI of 5.5 and 12.5, respectively. Investigations about the mechanism of action of 2g and 2i showed that both compounds cause mitochondrial depolarization, increase in ROS levels, and generation of autophagic vacuoles on free promastigotes forms. These compounds were also capable of reducing the number of infected macrophages with amastigotes forms (59.5% ± 0.08% and 98.1% ± 0.46%) and the number of amastigotes/macrophages (79.80% ± 0.05% and 96.0% ± 0.16%), through increasing induction of microbicide molecule NO. Additionally, ADMET-Tox in silico predictions showed drug-like features and free of toxicological risks. The molecular docking studies with arginase and gp63 showed that relevant intermolecular interactions could explain the experimental results. Therefore, these results reinforce that benzoylguanidines could be a starting scaffold for the search for new antileishmanial drugs.Communicated by Ramaswamy H. Sarma.

Inhibiting Human and Leishmania Arginases Using Cannabis sativa as a Potential Therapy for Cutaneous Leishmaniasis: A Molecular Docking Study

Cutaneous leishmaniasis (CL), a vector-borne parasitic disease caused by the Leishmania protozoan, is a serious public health problem in Morocco. The treatment of this disease is still based on pentavalent antimonials as the primary therapy, but these have associated side effects. Thus, the development of effective, risk-free alternative therapeutics based on natural compounds against leishmaniasis is urgent. Arginase, the key enzyme in the polyamine biosynthetic pathway, plays a critical role in leishmaniasis outcome and has emerged as a potential therapeutic target. The objective of this study was to test Cannabis sativa's phytochemical components (cannabinoids and terpenoids) through molecular docking against Leishmania and human arginase enzymes. Our results showed that delta-9-tetrahydrocannabinol (THC) possessed the best binding energies of -6.02 and -6.35 kcal/mol with active sites of Leishmania and human arginases, respectively. Delta-9-THC interacted with Leishmania arginase through various amino acids including His139 and His 154 and linked to human arginase via His 126. In addition to delta-9-THC, caryophyllene oxide and cannabidiol (CBD) also showed a good inhibition of Leishmania and human arginases, respectively. Overall, the studied components were found to inhibit both arginases active sites via hydrogen bonds and hydrophobic interactions. These components may serve as therapeutic agents or in co-administrated therapy for leishmaniasis.

An Update on Arginase Inhibitors and Inhibitory Assays

Arginase, which converts arginine into ornithine and urea, is a promising therapeutic target. Arginase is involved in cardiovascular diseases, parasitic infections and, through a critical role in immunity, in some cancers. There is a need to develop effective arginase inhibitors and therefore efforts to identify and optimize new inhibitors are increasing. Several methods of evaluating arginase activity are available, but few directly measure the product. Radiometric assays need to separate urea and dying reactions require acidic conditions and sometimes heating. Hence, there are a variety of different approaches available, and each approach has its own limits and benefits. In this review, we provide an update on arginase inhibitors, followed by a discussion on available arginase assays and alternative methods, with a focus on the intrinsic biases and parameters that are likely to impact results.

Thiohydantoins as anti-leishmanial agents: n vitro biological evaluation and multi-target investigation by molecular docking studies

Leishmaniasis is a neglected tropical disease caused by protozoa of the genus Leishmania. The first-line treatment of this disease is still based on pentavalent antimonial drugs that have a high toxicity profile, which could induce parasitic resistance. Therefore, there is a critical need to discover more effective and selective novel anti-leishmanial agents. In this context, thiohydantoins are a versatile class of substances due to their simple synthesis and several biological activities. In this work, thiohydantoins 1a-l were evaluated in vitro for antileishmania activity. Among them, four derivatives (1c, 1e, 1h and 1l) showed promising IC₅₀ values around 10 µM against promastigotes forms of Leishmania amazonensis and low cytotoxicity profile for peritoneal macrophages cells. Besides, these compounds induce oxidative stress through an increase in ROS production and the labeling of annexin-V and propidium iodide, indicating that promastigotes were undergoing a late apoptosis-like process. Additionally, molecular consensual docking analysis was carried out against two important targets to L. amazonensis: arginase and trypanothione reductase enzymes. Docking results suggest that thiohydantoin ring could be a pharmacophoric group due to its binding affinity by hydrogens bond interactions with important amino acid residues at the active site of both enzymes. These results demonstrate that compounds 1c, 1e, 1h and 1l may are promising in future advance studies.Communicated by Ramaswamy H. Sarma.

Cinnamides Target Leishmania amazonensis Arginase Selectively

Caffeic acid and related natural compounds were previously described as Leishmania amazonensis arginase (L-ARG) inhibitors, and against the whole parasite in vitro. In this study, we tested cinnamides that were previously synthesized to target human arginase. The compound caffeic acid phenethyl amide (CAPA), a weak inhibitor of human arginase (IC₅₀ = 60.3 ± 7.8 μM) was found to have 9-fold more potency against L-ARG (IC₅₀ = 6.9 ± 0.7 μM). The other compounds that did not inhibit human arginase were characterized as L-ARG, showing an IC₅₀ between 1.3–17.8 μM, and where the most active was compound 15 (IC₅₀ = 1.3 ± 0.1 μM). All compounds were also tested against L. amazonensis promastigotes, and only the compound CAPA showed an inhibitory activity (IC₅₀ = 80 μM). In addition, in an attempt to gain an insight into the mechanism of competitive L-ARG inhibitors, and their selectivity over mammalian enzymes, we performed an extensive computational investigation, to provide the basis for the selective inhibition of L-ARG for this series of compounds. In conclusion, our results indicated that the compounds based on cinnamoyl or 3,4-hydroxy cinnamoyl moiety could be a promising starting point for the design of potential antileishmanial drugs based on selective L-ARG inhibitors.

Synthesis, In Silico, and In Vitro Evaluation of Anti-Leishmanial Activity of Oxadiazoles and Indolizine Containing Compounds Flagged against Anti-Targets

Due to the lack of approved vaccines against human leishmaniasis and the limitations of the current chemotherapy inducing side effects and drug resistance, development of new, effective chemotherapeutic agents is essential. This study describes the synthesis of a series of novel oxadiazoles and indolizine-containing compounds. The compounds were screened in silico using an EIIP/AQVN filter followed by ligand-based virtual screening and molecular docking to parasite arginase. Top hits were further screened versus human arginase and finally against an anti-target battery to tag their possible interactions with proteins essential for the metabolism and clearance of many substances. Eight candidate compounds were selected for further experimental testing. The results show measurable in vitro anti-leishmanial activity for three compounds. One compound with an IC₅₀ value of 2.18 µM on Leishmania donovani intramacrophage amastigotes is clearly better positioned than the others as an interesting molecular template for further development of new anti-leishmanial agents.

Molecular characterization of recombinant arginase of Leishmania donovani

Arginase catalyzes the first committed step in the biosynthesis of polyamines that enable cell growth and hence potential drug target for the treatment of leishmaniasis. The arginase from Leishmania donovani (LdARG) was cloned, overexpressed and characterized. Analysis of the deduced amino acid sequence of LdARG with homologous enzyme from other trypanosomatids arginases identified a non-conserved 12 residues long segment VWGLIERTFLSA from position 161-172. This counter segment in L. mexicana arginase exhibits a different conformation compared with human arginase I. The pH and temperature optima of LdARG were 9.0 and 37 °C, respectively. Biochemical studies revealed that the K_M for the substrate L-arginine was 24.76 ± 0.06 mM. Molecular modeling of LdARG studies revealed that the glutamic acid residue at position 288 plays a role in substrate binding. The importance of this glutamic acid residue was validated by constructing a mutant variant of LdARG (E288Q-LdARG) by replacing glutamic acid with glutamine through site-directed mutagenesis. The K_M value of mutant variant for L-arginine was found to be 107 ± 0.18 mM. The increase in K_M value of E288Q-LdARG as compared to LdARG suggested that substrate binding was significantly affected which could be exploited further. Studies on biochemical and structural characterization of recombinant LdARG will help in evaluating this enzyme as a potential drug target for visceral leishmaniasis.

Isolation, leishmanicidal evaluation and molecular docking simulations of piperidine alkaloids from Senna spectabilis

Leishmaniasis is one of the most important neglected tropical diseases (NTDs) that are especially common among low-income populations in developing regions of Africa, Asia, and the Americas. Many natural products, particularly alkaloids, have been reported to have inhibitory activity against arginase, the key enzyme in the pathology caused by Leishmania sp. In this way, piperidine alkaloids (-)-cassine (1), (-)-spectaline (2), (-)-3-O-acetylcassine (3), and (-)-3-O-acetylspectaline (4) were isolated from Senna spectabilis flowers. These compounds (1/2 and 3/4) initially present as homologous mixtures were separated by high performance liquid chromatography and evaluated against the promastigote phase of Leishmania amazonensis. In addition, molecular docking simulations were implemented in order to probe the binding modes of the ligands 1-4 to the amino acids in the active site of L. amazonensis arginase. Alkaloid 2 (IC₅₀ 15.81 μg mL^-1) was the most effective against L. amazonensis. Compounds 2 and 4, with larger side chain, were more effective against the parasite than compounds 1 and 3. The cell viability test on Vero cells revealed that compound 2 (CC₅₀ 66.67 μg mL^-1) was the most toxic. The acetyl group in the 3-O position of the parent structures reduced the leishmanicidal activity and the toxicity of the alkaloids. Further, molecular docking suggested that Asn143 is essential for arginase to interact with (-)-spectaline-derived compounds, which agreed with the IC₅₀ measurements. Our findings revealed that S. spectabilis is an important source of piperidine alkaloids with leishmanicidal activity. Moreover, the natural compound 3 has been isolated for the first time. Experimental investigation combined with theoretical study advances knowledge about the enzyme binding site mode of interaction and contributes to the design of new bioactive drugs against Leishmania infection.

Cinnamic acids derived compounds with antileishmanial activity target Leishmania amazonensis arginase

This study describes the activity of five natural hydroxycinnamic acids and derived compound: caffeic (1), rosmarinic (2), chlorogenic (3), and cryptochlorogenic (4), acids and isoverbascoside (5). All compounds inhibited Leishmania amazonensis arginase with IC₅₀ -in range of 1.5-11 μM. Compounds 2 and 5 also showed activity against promastigotes of L. amazonensis with IC₅₀  = 61 (28-133) μM and IC₅₀  = 14 (9-24) μM, respectively. Further computational studies applying molecular docking simulations were performed on the competitive inhibitors to gain insight into the molecular basis for arginase inhibition and could be exploited to the development of new antileishmanials drug targeting parasite arginase.

Arginine and Polyamines Fate in Leishmania Infection

Leishmania is a protozoan parasite that alternates its life cycle between the sand fly and the mammalian host macrophages, involving several environmental changes. The parasite responds to these changes by promoting a rapid metabolic adaptation through cellular signaling modifications that lead to transcriptional and post-transcriptional gene expression regulation and morphological modifications. Molecular approaches such as gene expression regulation, next-generation sequencing (NGS), microRNA (miRNA) expression profiling, in cell Western blot analyses and enzymatic activity profiling, have been used to characterize the infection of murine BALB/c and C57BL/6 macrophages, as well as the human monocytic cell-lineage THP-1, with Leishmania amazonensis wild type (La-WT) or arginase knockout (La-arg^-). These models are being used to elucidate physiological roles of arginine and polyamines pathways and the importance of arginase for the establishment of the infection. In this review, we will describe the main aspects of Leishmania-host interaction, focusing on the arginine and polyamines pathways and pointing to possible targets to be used for prognosis and/or in the control of the infection. The parasite enzymes, arginase and nitric oxide synthase-like, have essential roles in the parasite survival and in the maintenance of infection. On the other hand, in mammalian macrophages, defense mechanisms are activated inducing alterations in the mRNA, miRNA and enzymatic profiles that lead to the control of infection. Furthermore, the genetic background of both parasite and host are also important to define the fate of infection.

Arginase activity of Leishmania isolated from patients with cutaneous leishmaniasis

Cutaneous leishmaniasis (CL) is one of the most important vector-borne parasitic diseases, highly endemic in Iran, and its prevalence is increasing all over the country. Arginase (ARG) activity in isolated Leishmania parasites from CL patients is yet to be explored. This study aimed to compare the ARG activity of isolated Leishmania promastigotes from CL patients with a standard strain of Leishmania major and its influences on the disease pathogenesis. We recruited 16 confirmed CL patients from Qom Province, in central Iran; after detection of Leishmania species using PCR-RFLP, we assessed the levels of ARG in the isolated promastigotes and determined the parasites' growth rate. Only L. major was identified from CL patients. The level of ARG activity in the isolated Leishmania promastigotes from CL patients was significantly higher than that obtained from the standard strain of L. major. No significant correlations between ARG activity and lesion size, number or duration were observed; in contrast, a significant negative correlation was seen between ARG level and Leishmania' growth rate. The obtained results suggest that increased ARG expression and activity in the isolated Leishmania promastigotes might contribute to the higher parasite infectivity and play a major role in the pathogenicity of the CL.

Arginase expression modulates nitric oxide production in Leishmania (Leishmania) amazonensis

BACKGROUND

Arginase is an enzyme that converts L-arginine to urea and L-ornithine, an essential substrate for the polyamine pathway supporting Leishmania (Leishmania) amazonensis replication and its survival in the mammalian host. L-arginine is also the substrate of macrophage nitric oxide synthase 2 (NOS2) to produce nitric oxide (NO) that kills the parasite. This competition can define the fate of Leishmania infection.

METHODOLOGY/PRINCIPAL FINDINGS

The transcriptomic profiling identified a family of oxidoreductases in L. (L.) amazonensis wild-type (La-WT) and L. (L.) amazonensis arginase knockout (La-arg-) promastigotes and axenic amastigotes. We highlighted the identification of an oxidoreductase that could act as nitric oxide synthase-like (NOS-like), due to the following evidences: conserved domain composition, the participation of NO production during the time course of promastigotes growth and during the axenic amastigotes differentiation, regulation dependence on arginase activity, as well as reduction of NO amount through the NOS activity inhibition. NO quantification was measured by DAF-FM labeling analysis in a flow cytometry.

CONCLUSIONS/SIGNIFICANCE

We described an arginase-dependent NOS-like activity in L. (L.) amazonensis and its role in the parasite growth. The increased detection of NO production in the mid-stationary and late-stationary growth phases of La-WT promastigotes could suggest that this production is an important factor to metacyclogenesis triggering. On the other hand, La-arg- showed an earlier increase in NO production compared to La-WT, suggesting that NO production can be arginase-dependent. Interestingly, La-WT and La-arg- axenic amastigotes produced higher levels of NO than those observed in promastigotes. As a conclusion, our work suggested that NOS-like is expressed in Leishmania in the stationary growth phase promastigotes and amastigotes, and could be correlated to metacyclogenesis and amastigotes growth in a dependent way to the internal pool of L-arginine and arginase activity.

L-arginine availability and arginase activity: Characterization of amino acid permease 3 in Leishmania amazonensis

BACKGROUND

Leishmania uses the amino acid L-arginine as a substrate for arginase, enzyme that produces urea and ornithine, last precursor of polyamine pathway. This pathway is used by the parasite to replicate and it is essential to establish the infection in the mammalian host. L-arginine is not synthesized by the parasite, so its uptake occurs through the amino acid permease 3 (AAP3). AAP3 is codified by two copies genes (5.1 and 4.7 copies), organized in tandem in the parasite genome. One copy presents the expression regulated by L-arginine availability.

METHODOLOGY/PRINCIPAL FINDINGS

RNA-seq data revealed 14 amino acid transporters differentially expressed in the comparison of La-WT vs. La-arg- promastigotes and axenic amastigotes. The 5.1 and 4.7 aap3 transcripts were down-regulated in La-WT promastigotes vs. axenic amastigotes, and in La-WT vs. La-arg- promastigotes. In contrast, transcripts of other transporters were up-regulated in the same comparisons. The amount of 5.1 and 4.7 aap3 mRNA of intracellular amastigotes was also determined in sample preparations from macrophages, obtained from BALB/c and C57BL/6 mice and the human THP-1 lineage infected with La-WT or La-arg-, revealing that the genetic host background is also important. We also determined the aap3 mRNA and AAP3 protein amounts of promastigotes and axenic amastigotes in different environmental growth conditions, varying pH, temperature and L-arginine availability. Interestingly, the increase of temperature increased the AAP3 level in plasma membrane and consequently the L-arginine uptake, independently of pH and L-arginine availability. In addition, we demonstrated that besides the plasma membrane localization, AAP3 was also localized in the glycosome of L. amazonensis promastigotes and axenic amastigotes.

CONCLUSIONS/SIGNIFICANCE

In this report, we described the differential transcriptional profiling of amino acids transporters from La-WT and La-arg- promastigotes and axenic amastigotes. We also showed the increased AAP3 levels under amino acid starvation or its decrease in L-arginine supplementation. The differential AAP3 expression was determined in the differentiation of promastigotes to amastigotes conditions, as well as the detection of AAP3 in the plasma membrane reflecting in the L-arginine uptake. Our data suggest that depending on the amino acid pool and arginase activity, Leishmania senses and could use an alternative route for the amino acid transport in response to stress signaling.

Arginase activity in pathogenic and non-pathogenic species of Leishmania parasites

Proliferation of Leishmania (L.) parasites depends on polyamine availability, which can be generated by the L-arginine catabolism and the enzymatic activity of arginase (ARG) of the parasites and of the mammalian hosts. In the present study, we characterized and compared the arginase (arg) genes from pathogenic L. major and L. tropica and from non-pathogenic L. tarentolae. We quantified the level of the ARG activity in promastigotes and macrophages infected with pathogenic L. major and L. tropica and non-pathogenic L. tarentolae amastigotes. The ARG's amino acid sequences of the pathogenic and non-pathogenic Leishmania demonstrated virtually 98.6% and 88% identities with the reference L. major Friedlin ARG. Higher ARG activity was observed in all pathogenic promastigotes as compared to non-pathogenic L. tarentolae. In vitro infection of human macrophage cell line (THP1) with pathogenic and non-pathogenic Leishmania spp. resulted in increased ARG activities in the infected macrophages. The ARG activities present in vivo were assessed in susceptible BALB/c and resistant C57BL/6 mice infected with L. major, L. tropica and L. tarentolae. We demonstrated that during the development of the infection, ARG is induced in both strains of mice infected with pathogenic Leishmania. However, in L. major infected BALB/c mice, the induction of ARG and parasite load increased simultaneously according to the time course of infection, whereas in C57BL/6 mice, the enzyme is upregulated solely during the period of footpad swelling. In L. tropica infected mice, the footpads' swellings were slow to develop and demonstrated minimal cutaneous pathology and ARG activity. In contrast, ARG activity was undetectable in mice inoculated with the non-pathogenic L. tarentolae. Our data suggest that infection by Leishmania parasites can increase ARG activity of the host and provides essential polyamines for parasite salvage and its replication. Moreover, the ARG of Leishmania is vital for parasite proliferation and required for infection in mice. ARG activity can be used as one of the main marker of the disease severity.

Leishmania (Leishmania) amazonensis induces macrophage miR-294 and miR-721 expression and modulates infection by targeting NOS2 and L-arginine metabolism

Leishmania (Leishmania) amazonensis is an intracellular protozoan parasite responsible for the cutaneous leishmaniasis. The parasite replicates inside mammalian macrophage to establish infection. Host-pathogen interactions result in microRNA-mediated post-transcriptional regulation of host genes involved in inflammatory immune response. We analyzed macrophage miRNA profiles during L. (L.) amazonensis infection. The regulation of macrophage miRNA expression by the parasite correlates with/depends on parasite arginase activity during infection. L. (L.) amazonensis (La-WT) presented significant miRNA profile alteration (27%) compared to L. (L.) amazonensis arginase knockout (La-arg⁻) (~40%) in relation to uninfected-macrophages. We observed that 78% of the altered miRNAs were up-regulated in La-WT infection, while only 32% were up-regulated in La-arg⁻-infected macrophages. In contrast to La-WT, the lack of L. (L.) amazonensis arginase led to the inhibition of miR-294 and miR-721 expression. The expression of miR-294 and miR-721 was recovered to levels similar to La-WT in La-arg⁻ addback mutant. The inhibition of miR-294/Nos2 and miR721/Nos2 interactions increased NOS2 expression and NO production, and reduced L. (L.) amazonensis infectivity, confirming Nos2 as target of these miRNAs. The role of miR-294 and miR-721 in the regulation of NOS2 expression during Leishmania replication in infected macrophages pointing these miRNAs as potential new targets for drug development.

Arginase Flavonoid Anti-Leishmanial in Silico Inhibitors Flagged against Anti-Targets

Arginase, a drug target for the treatment of leishmaniasis, is involved in the biosynthesis of polyamines. Flavonoids are interesting natural compounds found in many foods and some of them may inhibit this enzyme. The MetIDB database containing 5667 compounds was screened using an EIIP/AQVN filter and 3D QSAR to find the most promising candidate compounds. In addition, these top hits were screened in silico versus human arginase and an anti-target battery consisting of cytochromes P450 2a6, 2c9, 3a4, sulfotransferase, and the pregnane-X-receptor in order to flag their possible interactions with these proteins involved in the metabolism of substances. The resulting compounds may have promise to be further developed for the treatment of leishmaniasis.

Arginase in Leishmania

The presence of different sets of several enzymes that participate in the Krebs-Henseleit cycle has been used to identify several genera of trypanosomatids. One of these enzymes is arginase (L-arginine amidinohydrolase, E.C. 3.5.3.1), a metalloenzyme that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. Arginase activity has been detected in Leishmania, Crithidia and Leptomonas but not in Trypanosoma, Herpetomonas or Phytomonas. The ureotelic behavior of some trypanosomatids is not due to urea excretion but to the production of ornithine to supply the polyamine pathway, which is essential for replication. Leishmania is found inside macrophages in the mammalian host and to live in these cells, the parasite must escape from several microbicidal mechanisms, such as nitric oxide (NO) production mediated by inducible nitric oxide synthase (iNOS). Since arginase and iNOS use the L-arginine as substrate, the amount of this amino acid available for both pathways is critical for parasite replication. In both promastigotes and amastigotes, arginase is located in the glycosome indicating that arginine trafficking in the cell is used to provide the optimal concentration of substrate for arginase. Arginine uptake by the parasite is also important in supplying the arginase substrate. Leishmania responds to arginine starvation by increasing the amino acid uptake. In addition to the external supply, the internal L-arginine pool also governs the uptake of this amino acid, and the size of this internal pool is modulated by arginase activity. Thus, arginine uptake and arginase activity are important in establishing and maintaining Leishmania infection.

Inhibition of Leishmania (Leishmania) amazonensis and rat arginases by green tea EGCG, (+)-catechin and (-)-epicatechin: a comparative structural analysis of enzyme-inhibitor interactions

Epigallocatechin-3-gallate (EGCG), a dietary polyphenol (flavanol) from green tea, possesses leishmanicidal and antitrypanosomal activity. Mitochondrial damage was observed in Leishmania treated with EGCG, and it contributed to the lethal effect. However, the molecular target has not been defined. In this study, EGCG, (+)-catechin and (−)-epicatechin were tested against recombinant arginase from Leishmania amazonensis (ARG-L) and rat liver arginase (ARG-1). The compounds inhibit ARG-L and ARG-1 but are more active against the parasite enzyme. Enzyme kinetics reveal that EGCG is a mixed inhibitor of the ARG-L while (+)-catechin and (−)-epicatechin are competitive inhibitors. The most potent arginase inhibitor is (+)-catechin (IC₅₀ = 0.8 µM) followed by (−)-epicatechin (IC₅₀ = 1.8 µM), gallic acid (IC₅₀ = 2.2 µM) and EGCG (IC₅₀ = 3.8 µM). Docking analyses showed different modes of interaction of the compounds with the active sites of ARG-L and ARG-1. Due to the low IC₅₀ values obtained for ARG-L, flavanols can be used as a supplement for leishmaniasis treatment.

Leishmanicidal activity of Cecropia pachystachya flavonoids: arginase inhibition and altered mitochondrial DNA arrangement

The plant Cecropia pachystachya Trécul is widely used in Brazilian ethnomedicine to treat hypertension, asthma, and diabetes. Arginase is an enzyme with levels that are elevated in these disorders, and it is central to Leishmania polyamine biosynthesis. The aims of this study were to evaluate antileishmanial activity and inhibition of the arginase enzyme by C. pachystachya extracts, and to study changes in cellular organization using electron microscopy. The ethanol extract of C. pachystachya was tested on Leishmania (Leishmania) amazonensis promastigote survival/proliferation and arginase activity in vitro. Qualitative ultrastructural analysis was also used to observe changes in cell organization. The major bioactive molecules of the ethanol extract were characterized using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS). The ethyl acetate fraction of the ethanol extract diminished promastigote axenic growth/survival, inhibited arginase activity, and altered a mitochondrial kinetoplast DNA (K-DNA) array. The bioactive compounds of C. pachystachya were characterized as glucoside flavonoids. Orientin (9) (luteolin-8-C-glucoside) was the main component of the methanol-soluble ethyl acetate fraction obtained from the ethanol extract and is an arginase inhibitor (IC50 15.9 μM). The ethyl acetate fraction was not cytotoxic to splenocytes at a concentration of 200 μg/mL. In conclusion, C. pachystachya contains bioactive compounds that reduce the growth of L. (L.) amazonensis promastigotes, altering mitochondrial K-DNA arrangement and inhibiting arginase.

Arginase activity - a marker of disease status in patients with visceral leishmaniasis in ethiopia

The underlying mechanisms resulting in the profound immune suppression characteristic of human visceral leishmaniasis (VL) are not fully understood.

Here, we tested the hypothesis that arginase, an enzyme associated with immunosuppression, is higher in patients with VL and contributes to impaired T cell responses. We recruited patients with VL before and after treatment and healthy controls and measured the arginase metabolism in the blood of these individuals. Our results show that arginase activity is significantly higher in the blood of patients with active VL as compared to controls. These high levels of arginase decline considerably once the patients are successfully treated. We identified the phenotype of arginase-expressing cells among PBMCs as neutrophils and show that their frequency was increased in PBMCs of patients before treatment; this coincides with reduced levels of L-arginine in the plasma and decreased expression levels of CD3ζ in T cells.

Leishmaniases, a group of diseases caused by a parasite, Leishmania, belong to the most neglected tropical diseases: they are mainly found in low-income countries and affect the poorest populations. These parasites infect cells of the immune system called macrophages, which can kill the intracellular parasites when they receive the right signals from other cells of the immune system, the lymphocytes. During the active phase of visceral leishmaniasis, it has been shown that lymphocytes lose their capacity to instruct the macrophages to kill the intracellular parasites. Here, we show that the levels of an enzyme, arginase, are significantly increased in the blood of patients with visceral leishmaniasis, but decrease to the same levels as those of healthy controls following successful treatment. Arginase has the capacity to deplete an amino acid, L-arginine, which is crucial for the activation of lymphocytes. Indeed, our results show that the levels of this amino acid are considerably decreased in patients with visceral leishmaniasis. Our results suggest that during the active phase of visceral leishmaniasis, increased arginase results in the depletion of L-arginine, which is responsible for the incapacity of lymphocytes to send the adequate signals to the macrophages.

Parasite-derived arginase influences secondary anti-Leishmania immunity by regulating programmed cell death-1-mediated CD4+ T cell exhaustion

The breakdown of L-arginine to ornithine and urea by host arginase supports Leishmania proliferation in macrophages. Studies using arginase-null mutants show that Leishmania-derived arginase plays an important role in disease pathogenesis. We investigated the role of parasite-derived arginase in secondary (memory) anti-Leishmania immunity in the resistant C57BL/6 mice. We found that C57BL/6 mice infected with arginase-deficient (arg(-)) L. major failed to completely resolve their lesion and maintained chronic pathology after 16 wk, a time when the lesion induced by wild-type L. major is completely resolved. This chronic disease was associated with impaired Ag-specific proliferation and IFN-γ production, a concomitant increase in programmed cell death-1 (PD-1) expression on CD4(+) T cells, and failure to induce protection against secondary L. major challenge. Treatment with anti-PD-1 mAb restored T cell proliferation and IFN-γ production in vitro and led to complete resolution of chronic lesion in arg(-) L. major-infected mice. These results show that infection with arg(-) L. major results in chronic disease due in part to PD-1-mediated clonal exhaustion of T cells, suggesting that parasite-derived arginase contributes to the overall quality of the host immune response and subsequent disease outcome in L. major-infected mice. They also indicate that persistent parasites alone do not regulate the quality of secondary anti-Leishmania immunity in mice and that the quality of the primary immune response may be playing a hitherto unrecognized dominant role in this process.

Untargeted metabolomics reveals a lack of synergy between nifurtimox and eflornithine against Trypanosoma brucei

A non-targeted metabolomics-based approach is presented that enables the study of pathways in response to drug action with the aim of defining the mode of action of trypanocides. Eflornithine, a polyamine pathway inhibitor, and nifurtimox, whose mode of action involves its metabolic activation, are currently used in combination as first line treatment against stage 2, CNS-involved, human African trypanosomiasis (HAT). Drug action was assessed using an LC-MS based non-targeted metabolomics approach. Eflornithine revealed the expected changes to the polyamine pathway as well as several unexpected changes that point to pathways and metabolites not previously described in bloodstream form trypanosomes, including a lack of arginase activity and N-acetylated ornithine and putrescine. Nifurtimox was shown to be converted to a trinitrile metabolite indicative of metabolic activation, as well as inducing changes in levels of metabolites involved in carbohydrate and nucleotide metabolism. However, eflornithine and nifurtimox failed to synergise anti-trypanosomal activity in vitro, and the metabolomic changes associated with the combination are the sum of those found in each monotherapy with no indication of additional effects. The study reveals how untargeted metabolomics can yield rapid information on drug targets that could be adapted to any pharmacological situation.

Leishmania amazonensis arginase compartmentalization in the glycosome is important for parasite infectivity

In Leishmania, de novo polyamine synthesis is initiated by the cleavage of L-arginine to urea and L-ornithine by the action of arginase (ARG, E.C. 3.5.3.1). Previous studies in L. major and L. mexicana showed that ARG is essential for in vitro growth in the absence of polyamines and needed for full infectivity in animal infections. The ARG protein is normally found within the parasite glycosome, and here we examined whether this localization is required for survival and infectivity. First, the localization of L. amazonensis ARG in the glycosome was confirmed in both the promastigote and amastigote stages. As in other species, arg⁻ L. amazonensis required putrescine for growth and presented an attenuated infectivity. Restoration of a wild type ARG to the arg⁻ mutant restored ARG expression, growth and infectivity. In contrast, restoration of a cytosol-targeted ARG lacking the glycosomal SKL targeting sequence (argΔSKL) restored growth but failed to restore infectivity. Further study showed that the ARGΔSKL protein was found in the cytosol as expected, but at very low levels. Our results indicate that the proper compartmentalization of L. amazonensis arginase in the glycosome is important for enzyme activity and optimal infectivity. Our conjecture is that parasite arginase participates in a complex equilibrium that defines the fate of L-arginine and that its proper subcellular location may be essential for this physiological orchestration.

Infection with arginase-deficient Leishmania major reveals a parasite number-dependent and cytokine-independent regulation of host cellular arginase activity and disease pathogenesis

The balance between the products of L-arginine metabolism in macrophages regulates the outcome of Leishmania major infection. L-arginine can be oxidized by host inducible NO synthase to produce NO, which contributes to parasite killing. In contrast, L-arginine hydrolysis by host arginase blocks NO generation and provides polyamines, which can support parasite proliferation. Additionally, Leishmania encode their own arginase which has considerable potential to modulate infectivity and disease pathogenesis. In this study, we compared the infectivity and impact on host cellular immune response in vitro and in vivo of wild-type (WT) L. major with that of a parasite arginase null mutant (arg(-)) L. major. We found that arg(-) L. major are impaired in their macrophage infectivity in vitro independent of host inducible NO synthase activities. As with in vitro results, the proliferation of arg(-) L. major in animal infections was also significantly impaired in vivo, resulting in delayed onset of lesion development, attenuated pathology, and low parasite burden. Despite this attenuated pathology, the production of cytokines by cells from the draining lymph node of mice infected with WT and arg(-) L. major was similar at all times tested. Interestingly, in vitro and in vivo arginase levels were significantly lower in arg(-) than in WT-infected cases and were directly correlated with parasite numbers inside infected cells. These results suggest that Leishmania-encoded arginase enhances disease pathogenesis by augmenting host cellular arginase activities and that contrary to previous in vitro studies, the host cytokine response does not influence host arginase activity.

Expression of immune-regulatory genes, arginase-2 and inducible nitric oxide synthase (iNOS), in two rainbow trout (Oncorhynchus mykiss) strains following exposure to Myxobolus cerebralis

The present endeavor was conducted to evaluate the role of activated macrophage in the susceptibility of two different rainbow trout (Oncorhynchus mykiss) strains, a susceptible American (T) and a more resistant German (H), to infection with Myxobolus cerebralis. Arginase-2 and inducible nitric oxide synthase (iNOS) genes were used as references to the alternative and classical pathway of macrophage activation. The expression level of both genes was measured using quantitative real-time polymerase chain reaction. The expression level of arginase-2 was significantly upregulated in strain T at 2 h and 8 days post exposure in the strain H. In case of iNOS, the expression level was significantly upregulated from 24 h to 8 days p.e. in strain T and only in 8 days p.e. in strain H. During this study also, the influence of nitric oxide (NO) on the viability of the triactinomyxon spores (TAMs) of M. cerebralis was evaluated using the NO-donor S-nitroso-N-acetyl-penicillamine (SNAP). Rising final concentrations of SNAP from 0.25 to 1 mM at 2, 4, and 24 h resulted in increasing numbers of propidium iodide-positive TAMs detected. The results of this study suggest an inability of strain T to react with an effective immune response against infection with M. cerebralis. Furthermore, the TAMs of M. cerebralis react with significant decrease of viable spores to rising concentration of SNAP and longer incubation, but there is also evidence for some resistance to NO activity.

Leishmania major lacking arginase (ARG) are auxotrophic for polyamines but retain infectivity to susceptible BALB/c mice

Polyamines are essential metabolites in eukaryotes participating in a variety of proliferative processes, and in trypanosomatid protozoa play an additional role in the synthesis of the critical thiol trypanothione. Whereas the polyamine biosynthesis arising from L-ornithine has been well studied in protozoa, the metabolic origin(s) of L-ornithine have received less attention. Arginase (EC 3.5.3.1) catalyzes the enzymatic hydrolysis of L-arginine to L-ornithine and urea, and we tested the role of arginase in polyamine synthesis by the generation of an arg(?) knockout in Leishmania major by double targeted gene replacement. This mutant lacked arginase activity and required the nutritional provision of polyamines or L-ornithine for growth. A complemented line (arg(?)/+ARG) expressing arginase from a multi-copy expression vector showed 30-fold elevation of arginase activity, similar polyamine and ornithine levels as the wild-type, and resistance to the inhibitors ?-difluoromethylornithine (DFMO) and N(?)-hydroxy-l-arginine (NOHA). This established that arginase is the major route of polyamine synthesis in promastigotes cultured in vitro. The arg(?) parasites retained the ability to differentiate normally to the infective metacyclic stage, and were able to induce progressive disease following inoculation into susceptible BALB/c mice, albeit less efficiently than WT parasites. These data suggest that the infective amastigote form of Leishmania, which normally resides within an acidified parasitophorous vacuole, can survive in vivo through salvage of host polyamines and/or other molecules, aided by the tendency of acidic compartments to concentrate basic metabolites. This may thus contribute to the relative resistance of Leishmania to ornithine decarboxylase (ODC) inhibitors. The availability of infective, viable, arginase-deficient parasites should prove useful in dissecting the role of l-arginine metabolism in both pro- and anti-parasitic responses involving host nitric oxide synthase, which requires L-arginine to generate NO.

In vitro sodium nitroprusside-mediated toxicity towards Leishmania amazonensis promastigotes and axenic amastigotes

Leishmania parasites survive despite exposure to the toxic nitrosative oxidants during phagocytosis by the host cell. In this work, the authors investigated comparatively the resistance of Leishmania amazonensis promastigotes and axenic amastigotes to a relatively strong nitrosating agent that acts as a nitric oxide (NO) donor, sodium nitroprusside (SNP). Results demonstrate that SNP is able to decrease, in vitro, the number of L. amazonensis promastigotes and axenic amastigotes in a dose-dependent maner. Promastigotes, cultured in the presence of 0.25, 0.5, and 1 mmol L(-1) SNP for 24 h showed about 75% growth inhibition, and 97-100% when the cultures were treated with >2 mmol L(-1) SNP. In contrast, when axenic amastigotes were growing in the presence of 0.25-8 mM SNP added to the culture medium, 50% was the maximum of growth inhibition observed. Treated promastigotes presented reduced motility and became round in shape further confirming the leishmanicidal activity of SNP. On the other hand, axenic amastigotes, besides being much more resistant to SNP-mediated cytotoxicity, did not show marked morphological alteration when incubated for 24 h, until 8 mM concentrations of this nitrosating agent were used. The cytotoxicity toward L. amazonensis was attenuated by reduced glutathione (GSH), supporting the view that SNP-mediated toxicity triggered multiple oxidative mechanisms, including oxidation of thiols groups and metal-independent oxidation of biomolecules to free radical intermediates.

L-arginine metabolism and its impact on host immunity against Leishmania infection

Leishmaniasis is a vector-borne disease found in many countries worldwide. The causative agent of the disease, Leishmania spp., lives as an obligate intracellular parasite within mammalian hosts. Since tissue macrophages are major target cells for parasite replication, the outcome of infection depends largely on the activation status of these cells. L-arginine is a crucial amino acid required for both nitric oxide (NO)-mediated parasite killing and polyamine-mediated parasite replication. This review highlights the significance of L-arginine as a factor determining the outcomes of Leishmania infection in vitro and its influences on host immune responses in vivo. Various therapeutic approaches targeting L-arginine metabolic pathways during infections with Leishmania are also discussed.

L-arginine and cationic amino acid transporter 2B regulate growth and survival of Leishmania amazonensis amastigotes in macrophages

Leishmania spp. are obligate intracellular parasites, requiring a suitable microenvironment for their growth within host cells. We previously reported that the growth of Leishmania amazonensis amastigotes in murine macrophages (Mphis) was enhanced in the presence of gamma interferon (IFN-gamma), a Th1 cytokine normally associated with classical Mphi activation and killing of intracellular pathogens. In this study, we provided several lines of evidence suggesting that IFN-gamma-mediated parasite growth enhancement was associated with L-arginine transport via mouse cationic amino acid transporter 2B (mCAT-2B). (i) mRNA expression of Slc7A2, the gene encoding for mCAT-2B, as well as L-arginine transport was increased in IFN-gamma-treated Mphis. (ii) Supplementation of L-arginine in Mphi cultures increased parasite growth. (iii) Parasite growth enhancement in wild-type Mphis was inhibited in the presence of nonmetabolized L-arginine analogues. (iv) IFN-gamma-mediated parasite growth was absent in Mphis derived from mCAT-2B-deficient mice. Although we detected a clear upregulation of mCAT-2B and L-arginine transport, no measurable iNOS or arginase activities were observed in IFN-gamma-treated, infected Mphis. Together, these data suggest an involvement of a novel L-arginine usage independent of iNOS and arginase activities during IFN-gamma-mediated parasite growth enhancement. A possible role of mCAT-2B in supplying L-arginine directly to the parasites for their proliferation is discussed.

Evolutionary conservation of alternative activation of macrophages: structural and functional characterization of arginase 1 and 2 in carp (Cyprinus carpio L.)

Classically activated macrophages (caMF) play an important role in type-I immune responses and alternatively activated macrophages (aaMF) function in type-II immune responses. While the classical activation of fish macrophages has been well described, the existence of aaMF has not yet been described for teleosts. Arginase is the characteristic enzyme in aaMF and two isoforms have been described for mammals. To study the presence of aaMF in a primitive vertebrate species we cloned arginase 1 and 2 cDNA of common carp. Carp arginase 1 is a 340 aa protein with 63% aa sequence identity to human arginase 1. Carp arginase 2 is a 347 aa protein with 63% aa sequence identity to human arginase 2. Three highly homologous arginase 2 genes were found, each showing only single non-synonymous substitutions. Basal arginase 1 expression is mainly found in carp mid kidney. In contrast, arginase 2 was expressed in all organs examined with the highest basal gene expression in liver. Cultured carp head kidney-derived macrophages were used to study aaMF in vitro. Carp macrophages showed significant arginase activity which could be induced by dibutyryl cyclic adenosine mono phosphate (cAMP) and specifically inhibited by NG-hydroxy-L-arginine (NOHA). At the gene level, arginase 2 gene expression was upregulated by cAMP stimulation, while arginase 1 gene expression was not influenced. LPS stimulation did not alter the arginase 1 or 2 expression, inducible nitric oxide synthase (iNOS) expression was, however, upregulated. This expression of iNOS was used as a measure of classical activation of carp macrophages. Thus, in contrast to mammals, fish arginase 2 and not arginase 1 is differentially regulated and likely involved in the alternative activation of fish macrophages. Our data suggest there may be an evolutionary conservation of the presence of aaMF down to teleost fish.

Pre-mRNA trans-splicing: from kinetoplastids to mammals, an easy language for life diversity

Since the discovery that genes are split into intron and exons, the studies of the mechanisms involved in splicing pointed to presence of consensus signals in an attempt to generalize the process for all living cells. However, as discussed in the present review, splicing is a theme full of variations. The trans-splicing of pre-mRNAs, the joining of exons from distinct transcripts, is one of these variations with broad distribution in the phylogenetic tree. The biological meaning of this phenomenon is discussed encompassing reactions resembling a possible noise to mechanisms of gene expression regulation. All of them however, can contribute to the generation of life diversity.

Arginase plays a pivotal role in polyamine precursor metabolism in Leishmania. Characterization of gene deletion mutants

The polyamine pathway of protozoan parasites has been successfully targeted in anti-parasitic therapies and is significantly different from that of the mammalian host. To gain knowledge into the metabolic routes by which parasites synthesize polyamines and their precursors, the arginase gene was cloned from Leishmania mexicana, and Deltaarg null mutants were created by double targeted gene replacement and characterized. The ARG sequence exhibited significant homology to ARG proteins from other organisms and predicted a peroxisomal targeting signal (PTS-1) that steers proteins to the glycosome, an organelle unique to Leishmania and related parasites. ARG was subsequently demonstrated to be present in the glycosome, whereas the polyamine biosynthetic enzymes, in contrast, were shown to be cytosolic. The Deltaarg knockouts expressed no ARG activity, lacked an intracellular ornithine pool, and were auxotrophic for ornithine or polyamines. The ability of the Deltaarg null mutants to proliferate could be restored by pharmacological supplementation, either with low putrescine or high ornithine or spermidine concentrations, or by complementation with an arginase episome. Transfection of an arg construct lacking the PTS-1 directed the synthesis of an arg that mislocalized to the cytosol and notably also complemented the genetic lesion and restored polyamine prototrophy to the Deltaarg parasites. This molecular, biochemical, and genetic dissection of ARG function in L. mexicana promastigotes establishes: (i) that the enzyme is essential for parasite viability; (ii) that Leishmania, unlike mammalian cells, expresses only one ARG activity; (iii) that the sole vital function of ARG is to provide polyamine precursors for the parasite; and (iv) that ARG is present in the glycosome, but this subcellular milieu is not essential for its role in polyamine biosynthesis.