Benzimidazole Derivatives as New and Selective Inhibitors of Arginase from Leishmania mexicana with Biological Activity against Promastigotes and Amastigotes

Leishmaniasis is a disease caused by parasites of the Leishmania genus that affects 98 countries worldwide, 2 million of new cases occur each year and more than 350 million people are at risk. The use of the actual treatments is limited due to toxicity concerns and the apparition of resistance strains. Therefore, there is an urgent necessity to find new drugs for the treatment of this disease. In this context, enzymes from the polyamine biosynthesis pathway, such as arginase, have been considered a good target. In the present work, a chemical library of benzimidazole derivatives was studied performing computational, enzyme kinetics, biological activity, and cytotoxic effect characterization, as well as in silico ADME-Tox predictions, to find new inhibitors for arginase from Leishmania mexicana (LmARG). The results show that the two most potent inhibitors (compounds 1 and 2) have an I₅₀ values of 52 μM and 82 μM, respectively. Moreover, assays with human arginase 1 (HsARG) show that both compounds are selective for LmARG. According to molecular dynamics simulation studies these inhibitors interact with important residues for enzyme catalysis. Biological activity assays demonstrate that both compounds have activity against promastigote and amastigote, and low cytotoxic effect in murine macrophages. Finally, in silico prediction of their ADME-Tox properties suggest that these inhibitors support the characteristics to be considered drug candidates. Altogether, the results reported in our study suggest that the benzimidazole derivatives are an excellent starting point for design new drugs against leishmanisis.

Micro-CT visualization of a promastigote secretory gel (PSG) and parasite plug in the digestive tract of the sand fly Lutzomyia longipalpis infected with Leishmania mexicana

Leishmaniasis is a debilitating disease of the tropics, subtropics and southern Europe caused by Leishmania parasites that are transmitted during blood feeding by phlebotomine sand flies (Diptera: Psychodidae). Using non-invasive micro-computed tomography, we were able to visualize the impact of the laboratory model infection of Lutzomyia longipalpis with Leishmania mexicana and its response to a second blood meal. For the first time we were able to show in 3D the plug of promastigote secretory gel (PSG) and parasites in the distended midgut of whole infected sand flies and measure its volume in relation to that of the midgut. We were also able to measure the degree of opening of the stomodeal valve and demonstrate the extension of the PSG and parasites into the pharynx. Although our pilot study could only examine a few flies, it supports the hypothesis that a second, non-infected, blood meal enhances parasite transmission as we showed that the thoracic PSG-parasite plug in infected flies after a second blood meal was, on average, more than twice the volume of the plug in infected flies that did not have a second blood meal.

The kinesin of the flagellum attachment zone in Leishmania is required for cell morphogenesis, cell division and virulence in the mammalian host

Leishmania parasites possess a unique and complex cytoskeletal structure termed flagellum attachment zone (FAZ) connecting the base of the flagellum to one side of the flagellar pocket (FP), an invagination of the cell body membrane and the sole site for endocytosis and exocytosis. This structure is involved in FP architecture and cell morphogenesis, but its precise role and molecular composition remain enigmatic. Here, we characterized Leishmania FAZ7, the only known FAZ protein containing a kinesin motor domain, and part of a clade of trypanosomatid-specific kinesins with unknown functions. The two paralogs of FAZ7, FAZ7A and FAZ7B, display different localizations and functions. FAZ7A localizes at the basal body, while FAZ7B localizes at the distal part of the FP, where the FAZ structure is present in Leishmania. While null mutants of FAZ7A displayed normal growth rates, the deletion of FAZ7B impaired cell growth in both promastigotes and amastigotes of Leishmania. The kinesin activity is crucial for its function. Deletion of FAZ7B resulted in altered cell division, cell morphogenesis (including flagellum length), and FP structure and function. Furthermore, knocking out FAZ7B induced a mis-localization of two of the FAZ proteins, and disrupted the molecular organization of the FP collar, affecting the localization of its components. Loss of the kinesin FAZ7B has important consequences in the insect vector and mammalian host by reducing proliferation in the sand fly and pathogenicity in mice. Our findings reveal the pivotal role of the only FAZ kinesin as part of the factors important for a successful life cycle of Leishmania.

Leishmania are flagellated trypanosomatid parasites causing worldwide human and animal diseases. As ’divergent eukaryotes’, their biology presents unique features and structures, of which the specific functions constitute potential drug targets. Among others, they possess a unique cytoskeletal structure termed the flagellum attachment zone (FAZ) attaching the base of their flagellum to one side of the flagellar pocket (FP), which is the sole site for endocytosis and exocytosis. The FP together with other unique flagellum-associated structures are crucial for parasite survival, but the functioning of this whole remains largely enigmatic. Leishmania also possess an expanded repertoire of kinesins (>55), including two trypanosomatid-specific families. Here, we show that the deletion of the sole kinesin among FAZ proteins disrupts cell morphogenesis, FP organisation and cell division. Furthermore, the ability to proliferate in the insect vector and mammalian host is reduced in parasites lacking the kinesin FAZ7B. This study helps elucidate the factors contributing to the successful lifecycle and pathogenicity of the parasite. It also highlights the functional diversification of motor proteins during evolution.

Effect of Prophylactic Vaccination with the Membrane-Bound Acid Phosphatase Gene of Leishmania mexicana in the Murine Model of Localized Cutaneous Leishmaniasis

Leishmaniasis is a disease caused by an intracellular protozoan parasite of the genus Leishmania. Current treatments for leishmaniasis are long, toxic, and expensive and are not available in some endemic regions. Attempts to develop an effective vaccine are feasible, but no vaccine is in active clinical use. In this study, the LmxMBA gene of Leishmania mexicana was selected as a possible vaccine candidate using the reverse vaccinology approach, and the prophylactic effect generated by DNA vaccination with this gene in a murine model of cutaneous leishmaniasis was evaluated. The results showed that prophylactic vaccination with pVAX1::LmxMBA significantly reduced the size of the lesion and the parasitic load on the footpad, compared to the control groups. At a histological level, a smaller number of parasites were evident in the dermis, as well as the absence of connective tissue damage. Mice immunized with plasmid pVAX1::LmxMBA induced immunity characterized by an increase in the IgG2a/IgG1 > 1 ratio and a higher rate of lymphocyte proliferation. In this study, immunization with the plasmid promoted an improvement in the macroscopic and microscopic clinical manifestations of the experimental infection by L. mexicana, with a T helper 1 response characterized by an IgG2a/IgG1 > 1 ratio and high lymphoproliferative response. These findings support immunization with the plasmid pVAX1::LmxMBA as a preventive strategy against cutaneous infection of L. mexicana.

A BONCAT-iTRAQ method enables temporally resolved quantitative profiling of newly synthesised proteins in Leishmania mexicana parasites during starvation

Adaptation to starvation is integral to the Leishmania life cycle. The parasite can survive prolonged periods of nutrient deprivation both in vitro and in vivo. The identification of parasite proteins synthesised during starvation is key to unravelling the underlying molecular mechanisms facilitating adaptation to these conditions. Additionally, as stress adaptation mechanisms in Leishmania are linked to virulence as well as infectivity, profiling of the complete repertoire of Newly Synthesised Proteins (NSPs) under starvation is important for drug target discovery. However, differential identification and quantitation of low abundance, starvation-specific NSPs from the larger background of the pre-existing parasite proteome has proven difficult, as this demands a highly selective and sensitive methodology. Herein we introduce an integrated chemical proteomics method in L. mexicana promastigotes that involves a powerful combination of the BONCAT technique and iTRAQ quantitative proteomics Mass Spectrometry (MS), which enabled temporally resolved quantitative profiling of de novo protein synthesis in the starving parasite. Uniquely, this approach integrates the high specificity of the BONCAT technique for the NSPs, with the high sensitivity and multiplexed quantitation capability of the iTRAQ proteomics MS. Proof-of-concept experiments identified over 250 starvation-responsive NSPs in the parasite. Our results show a starvation-specific increased relative abundance of several translation regulating and stress-responsive proteins in the parasite. GO analysis of the identified NSPs for Biological Process revealed translation (enrichment P value 2.47e^-35) and peptide biosynthetic process (enrichment P value 4.84e^-35) as extremely significantly enriched terms indicating the high specificity of the NSP towards regulation of protein synthesis. We believe that this approach will find widespread use in the study of the developmental stages of Leishmania species and in the broader field of protozoan biology.

Periodic nutrient scarcity plays crucial roles in the life cycle of the protozoan parasite Leishmania spp. Although adaptation to nutrient stress has a pivotal role in Leishmania biology, the underlying mechanisms remain poorly understood. In a period of nutrient starvation, the parasite responds by decreasing its protein production to conserve nutrient resources and to prevent formation of toxic proteins. However, even during severe starvation, the parasite generates certain essential quality control and rescue proteins. Differential identification of the complete repertoire of these proteins synthesised during starvation from the pre-existing proteins in the parasite holds the key to understanding the starvation adaptation mechanisms. This has been challenging to accomplish due to technical limitations. Using a combination of chemical labelling techniques and protein mass-spectrometry, we selectively identified and measured the proteins generated in the starving Leishmania parasite. Our results show a starvation time-dependent differential expression of important protein synthesis regulators in the parasite. This will serve as an important dataset for a holistic understanding of the starvation adaptation mechanisms in Leishmania. We also believe that this method will find widespread applications in the field of protozoa and other parasites causing Neglected Tropical Diseases.

Effect of Two Different Isolates of Leishmania mexicana in the Production of Cytokines and Phagocytosis by Murine Dendritic Cells

Species of the genus Leishmania are the causal agents of leishmaniasis, a disease with diametrically different clinical manifestations that have been attributed to the species and host immune response. Some Leishmania species, including Leishmania mexicana, are capable of causing both localized cutaneous leishmaniasis (LCL) and diffuse cutaneous leishmaniasis (DCL). Therefore, it is possible that intraspecific differences may exist that contribute to the development of distinct clinical forms. Dendritic cells (DC) are important host cells of Leishmania spp. parasites, and cytokine production and phagocytosis upon infection with the parasite are significant for the outcome of the disease. In the present study we analyzed the production of IL-12, TNF-α, and IL-10 by DC infected with L. mexicana amastigotes isolated from a patient with LCL (amastigote = Lac) and from a patient with DCL (amastigote = Diact) by murine DC. Furthermore, we compared the frequency of phagocytosis of L. mexicana amastigotes of each isolate by fluorescence and optical microscopy and by flow cytometry. We show that the infection of DC with Diact amastigotes elicited the secretion of IL-10, TNF-α, and IL-12 by DC to a major extent as compared to the infection with Lac amastigotes. On the other hand, Lac and Diact amastigotes were similarly phagocytosed by DC, but interestingly there were more vacuoles in DC infected with Diact amastigotes. Our results suggest that isolates from a same species of Leishmania, such as L. mexicana, with different degrees of virulence according to the clinical manifestation they cause, differ in their capacity to elicit cytokine production and form vacuoles in DC.

Development of NanoLuc-PEST expressing Leishmania mexicana as a new drug discovery tool for axenic- and intramacrophage-based assays

The protozoan parasite Leishmania causes leishmaniasis; a spectrum of diseases of which there are an estimated 1 million new cases each year. Current treatments are toxic, expensive, difficult to administer, and resistance to them is emerging. New therapeutics are urgently needed, however, screening the infective amastigote form of the parasite is challenging. Only certain species can be differentiated into axenic amastigotes, and compound activity against these does not always correlate with efficacy against the parasite in its intracellular niche. Methods used to assess compound efficacy on intracellular amastigotes often rely on microscopy-based assays. These are laborious, require specialist equipment and can only determine parasite burden, not parasite viability. We have addressed this clear need in the anti-leishmanial drug discovery process by producing a transgenic L. mexicana cell line that expresses the luciferase NanoLuc-PEST. We tested the sensitivity and versatility of this transgenic strain, in comparison with strains expressing NanoLuc and the red-shifted firefly luciferase. We then compared the NanoLuc-PEST luciferase to the current methods in both axenic and intramacrophage amastigotes following treatment with a supralethal dose of Amphotericin B. NanoLuc-PEST was a more dynamic indicator of cell viability due to its high turnover rate and high signal:background ratio. This, coupled with its sensitivity in the intramacrophage assay, led us to validate the NanoLuc-PEST expressing cell line using the MMV Pathogen Box in a two-step process: i) identify hits against axenic amastigotes, ii) screen these hits using our bioluminescence-based intramacrophage assay. The data obtained from this highlights the potential of compounds active against M. tuberculosis to be re-purposed for use against Leishmania. Our transgenic L. mexicana cell line is therefore a highly sensitive and dynamic system suitable for Leishmania drug discovery in axenic and intramacrophage amastigote models.

The protozoan parasite Leishmania causes a spectrum of diseases collectively known as leishmaniasis. The parasite is transmitted to humans by the bite of its vector, the sand fly, following which the parasite invades host white blood cells, particularly macrophages. Leishmaniasis is classified as a neglected tropical disease, and is endemic in 97 countries. Symptoms of the disease depend on the species of Leishmania. These include skin lesions, destruction of the mucosal membranes, and the visceral form which is usually fatal if untreated. Current therapeutic options for leishmaniasis have a number of associated problems that include toxicity, the development of drug resistance and poor patient compliance due to lengthy and painful treatment regimens. New therapeutics are therefore urgently needed. The ability to screen potential drug candidates requires robust screening assays. Currently, screening the intracellular parasite relies on microscopy-based techniques that require expensive equipment, are time consuming and only detect parasite burden, not viability. By using a transgenic cell line that expresses the NanoLuc-PEST luciferase, we show that we have a parasite-specific viability marker that can be used to measure the efficacy of compounds against the intracellular parasite. We validate the potential of this cell line by screening the MMV Pathogen Box.

In vitro antileishmanial and cytotoxicity activities of essential oils from Haplophyllum tuberculatum A. Juss leaves, stems and aerial parts

BACKGROUND

Plants used for traditional medicine produce diverse and complex secondary metabolites exhibiting various medicinal properties. The medicinal plant Haplophyllum tuberculatum is used by native people against malaria and parasitic infections.

METHODS

In this study and in order to contribute for the search of new natural drugs for leishmaniasis, the essential oils of H. tuberculatum leaves, stems and aerial parts (leaves+stems) collected in two different periods, 2013 and 2015, and their components by GC/FID and GC/MS analyses were investigated. Those collected in 2013 were also re-analyzed two years later. The extracted oils were screened in vitro for anti-leishmanial activity on Leishmania mexicana mexicana (L.m.m.) promastigotes and cytotoxicity on the Chinese Hamster Ovary (CHO) cell line. Limonene (1.5 - 8%), its isomers (R- (+)-limonene and S-(-)-limonene), linalool and octanol were also tested.

RESULTS

Results showed that the chemical composition varied according to the year of collection. Though major compounds remain almost the same, qualitative and quantitative variations in the composition of the EOs can be observed between the two years of collection, with some minor compounds identified only in one type of samples. Variation in the composition were also observed in the re-analyzed volatile oils, showing stability concerns. The essential oils and R-(+)-limonene showed moderate anti-leishmanial activity. Their IC50 range from 6.48 to 50.28 μg/ml. Cytotoxicity assays for theses volatile extracts, R- (+)-limonene and S- (-)-limonene on CHO cells showed relatively potent cytotoxicity with a selectivity index <10. Their CC50 range from 27.79 to 82.56 μg/ml.

CONCLUSIONS

The findings of the present study demonstrated that H. tuberculatum might not be considered as a natural source for production of new anti-leishmanial agents without further analyzing its eventual in vivo toxicity as well as that of major pure compounds.

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

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

Leishmania mexicana promastigotes down regulate JNK and p-38 MAPK activation: Role in the inhibition of camptothecin-induced apoptosis of monocyte-derived dendritic cells

Dendritic cells (DC) are one of the principal host cells of the obligate intracellular parasite Leishmania. Inhibition of host cell apoptosis is a strategy employed by multiple pathogens to ensure their survival in the infected cell. We have previously shown that the infection of monocyte-derived dendritic cells (moDC) with Leishmania mexicana inhibits campthotecin-induced apoptosis. Nevertheless, the mechanisms involved in the inhibition of apoptosis of dendritic cells by Leishmania have not been established. Mitogen-activated protein kinases (MAPK) are key participants in the process of apoptosis and different species of Leishmania have been shown to regulate these kinases. In the present study, we analyzed the effect of L. mexicana promastigotes in the activation of JNK and p38 MAP kinase and their participation in the inhibition of apoptosis. The infection of moDC with L. mexicana promastigotes diminished significantly the phosphorylation of the MAP kinases JNK and p38. The inhibition of both kinases diminished DNA fragmentation, but in a major extent was the reduction of DNA fragmentation when JNK was inhibited. The capacity of L. mexicana promastigotes to diminish MAP kinases activation is probably one of the strategies employed to delay apoptosis induction in the infected moDC and may have implications for Leishmania pathogenesis by favoring the invasion of its host and the persistence of the parasite in the infected cells.

Intracellular Survival of Leishmania major Depends on Uptake and Degradation of Extracellular Matrix Glycosaminoglycans by Macrophages

Leishmania parasites replicate within the phagolysosome compartment of mammalian macrophages. Although Leishmania depend on sugars as a major carbon source during infections, the nutrient composition of the phagolysosome remains poorly described. To determine the origin of the sugar carbon source in macrophage phagolysosomes, we have generated a N-acetylglucosamine acetyltransferase (GNAT) deficient Leishmania major mutant (∆gnat) that is auxotrophic for the amino sugar, N-acetylglucosamine (GlcNAc). This mutant was unable to grow or survive in ex vivo infected macrophages even when macrophages were cultivated in presence of exogenous GlcNAc. In contrast, the L. major ∆gnat mutant induced normal skin lesions in mice, suggesting that these parasites have access to GlcNAc in tissue macrophages. Intracellular growth of the mutant in ex vivo infected macrophages was restored by supplementation of the macrophage medium with hyaluronan, a GlcNAc-rich extracellular matrix glycosaminoglycan. Hyaluronan is present and constitutively turned-over in Leishmania-induced skin lesions and is efficiently internalized into Leishmania containing phagolysosomes. These findings suggest that the constitutive internalization and degradation of host glycosaminoglycans by macrophages provides Leishmania with essential carbon sources, creating a uniquely favorable niche for these parasites.

Encapsulation of Living Leishmania Promastigotes in Artificial Lipid Vacuoles

After phagocytosis by mammalian macrophages, promastigote forms of Leishmania parasites settle inside intracellular parasitophorous vacuoles (PVs) in which they transform into amastigote forms and replicate. Here, using a variant of the 'inverted emulsion' method, we succeeded in encapsulating living L. amazonensis parasites in giant artificial liposomes that serve as model PVs. We were able to control the size of liposomes, the pH and the composition of their internal volume, and the number of internalized parasites per liposome. L. amazonensis promastigotes encapsulated in liposomes filled with RPMI-Dextran solution at pH 7.5 or 6.5 survived up to 96 h at 24°C. At 37°C and pH 5.5, parasites survived 48h. This method paves the way to identifying certain effectors secreted by the parasite and to unraveling specific mechanisms of fusion between the PV and intracellular vesicles of the host cell. This method will also facilitate the study of the temporal evolution of biophysical properties of the PV during its maturation.

Scanning and three-dimensional electron microscopy methods for the study of Trypanosoma brucei and Leishmania mexicana flagella

Three-dimensional electron microscopy tools have revolutionized our understanding of cell structure and molecular complexes in biology. Here, we describe methods for studying flagellar ultrastructure and biogenesis in two unicellular parasites-Trypanosoma brucei and Leishmania mexicana. We describe methods for the preparation of these parasites for scanning electron microscopy cellular electron tomography, and serial block face scanning electron microscopy (SBFSEM). These parasites have a highly ordered cell shape and form, with a defined positioning of internal cytoskeletal structures and organelles. We show how knowledge of these can be used to dissect cell cycles in both parasites and identify the old flagellum from the new in T. brucei. Finally, we demonstrate the use of SBFSEM three-dimensional models for analysis of individual whole cells, demonstrating the excellent potential this technique has for future studies of mutant cell lines.

Characterization of metabolically quiescent Leishmania parasites in murine lesions using heavy water labeling

Information on the growth rate and metabolism of microbial pathogens that cause long-term chronic infections is limited, reflecting the absence of suitable tools for measuring these parameters in vivo. Here, we have measured the replication and physiological state of Leishmania mexicana parasites in murine inflammatory lesions using ²H₂O labeling. Infected BALB/c mice were labeled with ²H₂O for up to 4 months, and the turnover of parasite DNA, RNA, protein and membrane lipids estimated from the rate of deuterium enrichment in constituent pentose sugars, amino acids, and fatty acids, respectively. We show that the replication rate of parasite stages in these tissues is very slow (doubling time of ~12 days), but remarkably constant throughout lesion development. Lesion parasites also exhibit markedly lower rates of RNA synthesis, protein turnover and membrane lipid synthesis than parasite stages isolated from ex vivo infected macrophages or cultured in vitro, suggesting that formation of lesions induces parasites to enter a semi-quiescent physiological state. Significantly, the determined parasite growth rate accounts for the overall increase in parasite burden indicating that parasite death and turnover of infected host cells in these lesions is minimal. We propose that the Leishmania response to lesion formation is an important adaptive strategy that minimizes macrophage activation, providing a permissive environment that supports progressive expansion of parasite burden. This labeling approach can be used to measure the dynamics of other host-microbe interactions in situ.

Microbial pathogens can adapt to changing conditions in their hosts by switching between different growth and physiological states. However, current methods for measuring microbial physiology in vivo are limited, hampering detailed dissection of host-pathogen interactions. Here we have used heavy water labeling to measure the growth rate and physiological state of Leishmania parasites in murine lesions. Based on the rate of in situ labeling of parasite DNA, RNA, protein, and lipids, we show that the growth rate of intracellular parasite stages is very slow, and that these stages enter a semi-quiescent state characterized by very low rates of RNA, protein, and membrane turnover. These changes in parasite growth and physiology are more pronounced than in in vitro differentiated parasites, suggesting that they are induced in part by the lesion environment. Despite their slow growth, the parasite burden in these lesions progressively increases as a result of low rates of parasite death and host cell turnover. We propose that these changes in Leishmania growth and physiology contribute to the development of a relatively benign tissue environment that is permissive for long term parasite expansion. This approach is suitable for studying the dynamics of other host-pathogen systems.

Reprogramming neutral lipid metabolism in mouse dendritic leucocytes hosting live Leishmania amazonensis amastigotes

Background

After loading with live Leishmania (L) amazonensis amastigotes, mouse myeloid dendritic leucocytes/DLs are known to undergo reprogramming of their immune functions. In the study reported here, we investigated whether the presence of live L. amazonensis amastigotes in mouse bone marrow-derived DLs is able to trigger re-programming of DL lipid, and particularly neutral lipid metabolism.

Methodology/Principal Findings

Affymetrix-based transcriptional profiles were determined in C57BL/6 and DBA/2 mouse bone marrow-derived DLs that had been sorted from cultures exposed or not to live L. amazonensis amastigotes. This showed that live amastigote-hosting DLs exhibited a coordinated increase in: (i) long-chain fatty acids (LCFA) and cholesterol uptake/transport, (ii) LCFA and cholesterol (re)-esterification to triacyl-sn-glycerol (TAG) and cholesteryl esters (CE), respectively. As these neutral lipids are known to make up the lipid body (LB) core, oleic acid was added to DL cultures and LB accumulation was compared in live amastigote-hosting versus amastigote-free DLs by epi-fluorescence and transmission electron microscopy. This showed that LBs were both significantly larger and more numerous in live amastigote-hosting mouse dendritic leucocytes. Moreover, many of the larger LB showed intimate contact with the membrane of the parasitophorous vacuoles hosting the live L. amazonensis amastigotes.

Conclusions/Significance

As leucocyte LBs are known to be more than simple neutral lipid repositories, we set about addressing two related questions. Could LBs provide lipids to live amastigotes hosted within the DL parasitophorous vacuole and also deliver? Could LBs impact either directly or indirectly on the persistence of L. amazonensis amastigotes in rodent skin?

Once they have gained entry to mammals, live Leishmania (L) amazonensis amastigotes are known to subvert both macrophages and dendritic leucocytes (DLs) as host cells. These L. amazonensis amastigotes then may or may not proliferate in these two phagocytic leucocyte lineages, but in both cases the otherwise versatile differentiation program of these lineages is known to be rapidly remodeled. Here, we describe the rapid reprogramming of C57BL/6 and DBA/2 mouse bone marrow-derived DLs, with a special focus on cytosolic lipid bodies (LBs) that are known to store neutral lipids such as triacyl-sn-glycerol (TAG) and cholesteryl esters (CE). After extracting RNA from carefully sorted amastigote-free DLs and L. amazonensis amastigote-hosting DLs, an Affymetrix-based analysis clearly showed a singular and coordinated increase in DL transcripts involved in (i) long-chain fatty acid uptake, transport and esterification to TAG and (ii) cholesterol uptake and esterification to cholesteryl esters. Oleic acid was added to check that neutral lipid metabolism was both rapidly increased and reprogrammed in amastigote-hosting DLs. It should be noted that the LBs in live amastigote-hosting DLs were more numerous, and that the largest of these LBs were in contact with live amastigote- hosting parasitophorous vacuoles. We further discuss these findings in the context of live L. amazonensis amastigote-rodent host interactions.

[Effect of Leishmania mexicana, RANTES and TNF alpha on splenic dendritic cells of newborn and adult BALB/c mice: phenotypic characteristics and migratory properties]

Dendritic cells (DCs) are essential in the development and regulation of the immune response (IR). The inherent potential of DCs to induce a specific immune response in the neonatal period is controversial. It has been suggested that the specific IR in neonates depends on the quantitative relation of DC/T lymphocytes, as well as on the neonatal or adult age at which the interaction antigen/DC/T lymphocytes occurs. This suggests that this contact has an influence on the phenotypic and/or biological properties of DCs, which modifies its behavior. Therefore, the effects of Leishmania mexicana (L. mexicana) and of TNFalpha and RANTES cytokines on immunophenotypical characteristics were evaluated on spleen DCs, from neonate and adult BALB/c mice, by using flow cytometry and in vitro migratory properties with a Boyden Chamber. In basal conditions, neonate and adult DCs express the same molecules (CD40, CD86, MHCII and CD54). When the DCs interact with the antigen L. mexicana, the expression of these molecules are similar in adults and in neonates, with the exception of CD40 whose intensity of expression was raised (P < 0.05) in both groups. The rate of migration of the DCs in a culture medium conditioned of L. mexicana, RANTES and TNFalpha was higher in adults than in newborn mice. These observations suggest that neonatal and adult mice DCs have similar phenotypic characteristics. Under the effect of the same stimulus they respond differently; suggesting that other factors are involved in the higher susceptibility that newborns have to infections.

Inhibition profile of Leishmania mexicana arginase reveals differences with human arginase I

Arginase (ARG), the enzyme that catalyzes the conversion of arginine to ornithine and urea, is the first and committed step in polyamine biosynthesis in Leishmania. The creation of a conditionally lethal Δarg null mutant in Leishmania mexicana has established that ARG is an essential enzyme for the promastigote form of the parasite and that the enzyme provides an important defense mechanism for parasite survival in the eukaryotic host. Furthermore, human ARGI (HsARGI) has also been implicated as a key factor in parasite proliferation. Thus, inhibitors of ARG offer a rational paradigm for drug design. To initiate a search for inhibitors of the L. mexicana ARG (LmARG), recombinant LmARG and HsARGI enzymes were purified from Escherichia coli. Both LmARG and HsARGI were specific for l-arginine and exhibited no activity with either d-arginine or agmatine as possible substrates. LmARG exhibited a K(m) of 25±4mM for l-arginine, a pH optimum ∼9.0, and was dependent upon the presence of a divalent cation, preferentially manganese. A K(m) of 13.5 ± 2mM for l-arginine was calculated for the HsARGI. A collection of 37 compounds was evaluated against both enzymes. Twelve of these compounds were identified as being either strong inhibitors of both LmARG and HsARGI or differential inhibitors between the two enzymes. Of the 12 compounds, six were selected for further analysis and the type and extent of inhibition determined.

In vitro initial immune response against Leishmania amazonensis infection is characterized by an increased production of IL-10 and IL-13

The initial encounter of Leishmania with its host's immune system is important in the outcome of infection. Previous studies have shown that PBMCs from healthy volunteers (HV) exposed to Leishmania differ in IFN-γ production. We have expanded such observations evaluating the profile and kinetics of cytokines (IFN-γ, IL-12p70, IL-10, IL-13), chemokines (CCL5, CCL3, CCL4, CXCL10), and chemokine receptors (CCR1,CCR5, CXCR3, CCR4) in vitro L. amazonensis-stimulated of HV's PBMCs. HVs were divided in groups of high (HR) or low (LR) IFN-γ responders. In both groups, HR and LR, after L. amazonensis infection there was a predominance of IL-10 and IL-13 over IFN-γ production, while IL-12 was produced in similar amount. Regarding chemokines, a more striking difference was observed for CCL3 expression that was lower at 12 hours and 48 hours post infection in LR than in HR. Interestingly, a downregulation of CCR5 and a greater expression of CCR4 were found in low IFN-γ responders. These data suggest that early after L. amazonensis infection there is a cytokine milieu dominated by IL-13 and IL-10, and despite of this environment, IFN-γ is produced, supporting the complexity of the response. It is noteworthy that the pattern of immune response is mounted in first hours after Leishmania stimulation, with the definition of the differentiation of Th1 versus Th2 cells. It remains to be determined if such an in vitro difference has an in vivo counterpart in terms of susceptibility to infection.

Proteophosophoglycans regurgitated by Leishmania-infected sand flies target the L-arginine metabolism of host macrophages to promote parasite survival

All natural Leishmania infections start in the skin; however, little is known of the contribution made by the sand fly vector to the earliest events in mammalian infection, especially in inflamed skin that can rapidly kill invading parasites. During transmission sand flies regurgitate a proteophosphoglycan gel synthesized by the parasites inside the fly midgut, termed promastigote secretory gel (PSG). Regurgitated PSG can exacerbate cutaneous leishmaniasis. Here, we show that the amount of Leishmania mexicana PSG regurgitated by Lutzomyia longipalpis sand flies is proportional to the size of its original midgut infection and the number of parasites transmitted. Furthermore, PSG could exacerbate cutaneous L. mexicana infection for a wide range of doses (10–10,000 parasites) and enhance infection by as early as 48 hours in inflamed dermal air pouches. This early exacerbation was attributed to two fundamental properties of PSG: Firstly, PSG powerfully recruited macrophages to the dermal site of infection within 24 hours. Secondly, PSG enhanced alternative activation and arginase activity of host macrophages, thereby increasing L-arginine catabolism and the synthesis of polyamines essential for intracellular parasite growth. The increase in arginase activity promoted the intracellular growth of L. mexicana within classically activated macrophages, and inhibition of macrophage arginase completely ablated the early exacerbatory properties of PSG in vitro and in vivo. Thus, PSG is an essential component of the infectious sand fly bite for the early establishment of Leishmania in skin, which should be considered when designing and screening therapies against leishmaniasis.

Parasites are known to manipulate their arthropod vectors for increased transmission, yet little is known about the manipulator-molecules involved. The protozoan parasite Leishmania secrete a proteophosphoglycan-rich gel (termed promastigote secretory gel, PSG) to block the sand fly midgut to force the regurgitation of parasites and gel into the skin. Here we show that the amount of PSG and dose of Leishmania transmitted by individual sand flies strongly correlate with the size of the original midgut infection. Regurgitated PSG exacerbated both low and high dose mouse infections, resulting from the gel's ability to augment the recruitment of its principal host cell, the macrophage, to the site of injury and induce the upregulation of macrophage arginase activity. The infecting parasites take advantage of the increased arginase-mediated L-arginine catabolism and the increased pool of polyamines available within these macrophages for their early nutrition and growth. This resulted in enhanced survival and growth of Leishmania in macrophages. Since arginase plays a crucial role in orchestrating wound repair in skin, it would appear that through the generation of PSG, Leishmania has evolved to exploit the wound response to the bite of the sand fly for its early survival.

Leishmania amazonensis infection may affect the ability of the host macrophage to be activated by altering their outward potassium currents

Understanding the impact of intracellular pathogens on the behaviour of their host cells is key to designing new interventions. We are interested in how Leishmania alters the electrical functioning of the plasma membrane of the macrophage it infects. The specific question addressed here is whether Leishmania amazonensis infection alters the macrophage's outward currents and what the consequences of such changes might be. Using the whole cell configuration of the patch clamp technique, we show that outward peak current density remains constant over the period studied but that time to peak and sensitivity to inhibitors vary during infection. Infected cells take 40% longer to activate and are more sensitive to the potassium channel inhibitor tetraethyl ammonium, compared to control cells, indicating increased potassium outward current activity. Activation of macrophages is associated with increases of nitric oxide production and membrane area, depolarization of the macrophage membrane, down regulation of inward potassium and up regulation of outward currents. After Leishmania infection, macrophage activation is characterised by a reduction of nitric oxide production and of outward current density. We therefore suggest that this reflects a weaker activation.

Leishmania amazonensis infection impairs differentiation and function of human dendritic cells

Dendritic cells (DCs) are of utmost importance in initiating an immune response and may also function as targets for pathogens. The presence of pathogens inside DCs is likely to impair their functions and thus, influence immune responses. In the present report, we evaluated the impact of the presence of Leishmania amazonensis during differentiation and maturation of human monocyte-derived DCs. The presence of live L. amazonensis parasites during DC differentiation led to a significant decrease in CD80 (92%) and CD1a (56%) expression and an increase in CD86 (56%) cell surface expression. Phenotypic changes were accompanied by a lower secretion of IL-6, observed after 6 days of DC differentiation in the presence of L. amazonensis. DCs differentiated in the presence of L. amazonensis were used as APC in an autologous coculture, and lower amounts of IFN-gamma were obtained compared with control DCs differentiated in the absence of parasites. The effect of heat-killed parasites, but not of Leishmania antigen, during DC differentiation and maturation was similar to that observed with viable parasites. During maturation, the presence of live L. amazonensis parasites, but not of soluble Leishmania antigen, led to a decrease in IL-6 and IL-10 production. In this way, we observed that the parasite is able to abrogate full DC differentiation, causing a delay in the immune response and likely, favoring its establishment in human hosts.

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.

Leishmania amazonensis: multiple receptor-ligand interactions are involved in amastigote infection of human dendritic cells

In their mammalian hosts, Leishmania are obligate intracellular parasites that reside in macrophages and dendritic cells (DCs). In the present study, we have investigated in vitro the mechanisms of entry into human DCs of Leishmania amazonensis amastigotes isolated from lesions in nude mice (Am nude). The DC infection rate with Am nude was approximately 36%, while opsonization of Am nude with normal human serum and infected human serum increased the DC infection rates to 60% and 62%, respectively. Heat inactivation and depletion of antibodies in sera brought the DC infection rate down to 40%. The DC infection rate was inhibited after pre-treatment of Am nude with heparin. We were unable to implicate mannose-fucose receptors in the uptake of Am nude by DCs. Our data suggest that the ability of L. amazonensis amastigotes to infect human DCs involves the participation of at least three multiple receptor-ligand interactions, antibodies/FcR, complement components/CR and proteoglycans/heparin-binding protein.

Leukotrienes are essential for the control of Leishmania amazonensis infection and contribute to strain variation in susceptibility

Leukotrienes (LTs) are known to be produced by macrophages when challenged with Leishmania, but it is not known whether these lipid mediators play a role in host defense against this important protozoan parasite. In this study, we investigated the involvement of LTs in the in vitro and in vivo response to Leishmania amazonensis infection in susceptible (BALB/c) and resistant (C3H/HePAS) mice. Pharmacologic or genetic deficiency of LTs resulted in impaired leishmanicidal activity of peritoneal macrophages in vitro. In contrast, addition of LTB4 increased leishmanicidal activity and this effect was dependent on the BLT1 receptor. LTB4 augmented NO production in response to L. amazonensis challenge, and studies with a NO synthesis inhibitor revealed that NO was critical for the enhancement of macrophage leishmanicidal activity. Interestingly, macrophages from resistant mice produced higher levels of LTB4 upon L. amazonensis challenge than did those from susceptible mice. In vivo infection severity, as assessed by footpad swelling following s.c. promastigote inoculation, was increased when endogenous LT synthesis was abrogated either pharmacologically or genetically. Taken together, these results for the first time reveal an important role for LTB4 in the protective response to L. amazonensis, identify relevant leishmanicidal mechanisms, and suggest that genetic variation in LTB4 synthesis might influence resistance and susceptibility patterns to infection.

Cysteine peptidases CPA and CPB are vital for autophagy and differentiation in Leishmania mexicana

In the past, ultrastructural investigations of Leishmania mexicana amastigotes revealed structures that were tentatively identified as autophagosomes. This study has now provided definitive data that autophagy occurs in the parasite during differentiation both to metacyclic promastigotes and to amastigotes, autophagosomes being particularly numerous during metacyclic to amastigote form transformation. Moreover, the results demonstrate that inhibiting two major lysosomal cysteine peptidases (CPA and CPB) or removing their genes not only interferes with the autophagy pathway but also prevents metacyclogenesis and transformation to amastigotes, thus adding support to the hypothesis that autophagy is required for cell differentiation. The study suggests that L. mexicana CPA and CPB perform similar roles to the aspartic peptidase PEP4 and the serine peptidase PRB1 in Saccharomyces cerevisiae. The results also provide an explanation for why L. mexicana CPA/CPB-deficient mutants transform to amastigotes very poorly and lack virulence in macrophages and mice.

Leishmania amazonensis: Chemotaxic and osmotaxic responses in promastigotes and their probable role in development in the phlebotomine gut

Taxic responses may play a role in development of Leishmania in their phlebotomine sand fly vectors. They are possibly responsible for movement of the parasites towards the anterior regions of the gut, from where they would be transmitted to the vertebrate host. A methodology capable to distinguish chemotaxic from osmotaxic responses was described and used to characterise taxic responses in Leishmania promastigotes. These were able to respond to chemotaxic as well as to osmotaxic stimuli. Like bacteria, promastigotes were capable to undergo "adaptation," a phenomenon by which they stop responding to a continuos stimulus. A model capable to explain how a relatively small number of different receptors works to perceive gradients in chemotaxic responses was proposed. According to this model, these receptors possess low specificity and a wide range of affinities varying from high to low. A low specificity makes the same receptor able to bind to a large number of different but structurally related molecules and; a wide range of affinities (considering a population of receptors), implies that the number of receptors "occupied" by attractant molecules along a gradient would go growing step by step.

Characterisation of a Leishmania mexicana knockout lacking guanosine diphosphate-mannose pyrophosphorylase

In eukaryotes, the enzyme GDP-mannose pyrophosphorylase (GDP-MP) is essential for the formation of GDP-mannose, the donor of activated mannose for all glycosylation reactions. Unlike other eukaryotes, where deletion of GDP-mannose pyrophosphorylase is lethal, deletion of this gene in Leishmania mexicana has no effect on viability, but leads to the generation of avirulent parasites. In this study, we show that the null mutants have a perturbed morphology and cytokinesis, retarded growth and increased adherence to the substratum where they form large colonies. The null mutants attach avidly to mouse macrophages, but unlike the wild type organisms, they do not bind to the complement receptor 3 and are slow to induce phagocytosis. Once internalised, they localise to the phagolysosome, but in contrast to wild type organisms which transform into the intracellular amastigote and establish in the macrophage, they are cleared by 24 h in culture and by 5 h in vivo. The null mutants are hypersensitive to human but not mouse complement and to temperature and acidic pH. Surprisingly, in view of the lack of several known host-protective antigens, injection of the mutant parasites into BALB/c mice confers significant and long lasting protection against infection, suggesting that these temperature sensitive mutants are an attractive candidate for a live attenuated vaccine.

The two cytoplasmic dynein-2 isoforms in Leishmania mexicana perform separate functions

Eukaryotic organisms with cilia or flagella typically express two non-axonemal or "cytoplasmic" dyneins, dynein-1 and dynein-2. Interestingly, we find that Leishmania mexicana is unusual and contains two distinct cytoplasmic dynein-2 heavy chain genes (designated LmxDHC2.1 and LmxDHC2.2) along with a single dynein-1 heavy chain (LmxDHC1). Disruption of LmxDHC2.2 resulted in immotile parasites that had a rounded cell body. Although they assume amastigote morphology, immunoblot analysis of these cells demonstrates protein expression consistent with the promastigote stage. Ultrastructural analysis revealed non-emergent flagella that lacked the paraflagellar rod and an axoneme with deficiencies in several components. We confirmed the absence of paraflagellar rod proteins PFR1 and PFR2. These results show that LmxDHC2.2 is required for flagellar assembly and also participates in the maintenance of promastigote cell shape. In contrast to the results with LmxDHC2.2, we were unable to generate homologous disruptions of LmxDHC2.1. This result suggests that, unlike LmxDHC2.2, LmxDHC2.1 is an essential gene in Leishmania. Together, these findings demonstrate that the two dynein-2 heavy chain isoforms in Leishmania perform distinct functions. The observation that the genomes of Leishmania major, Leishmania infantum and Trypanosoma brucei also contain two dynein-2 isoforms suggests that this unusual aspect of cytoplasmic dynein is a conserved feature of the kinetoplastids.

Heterologous expression of the filarial nematode alt gene products reveals their potential to inhibit immune function

Background

Parasites exploit sophisticated strategies to evade host immunity that require both adaptation of existing genes and evolution of new gene families. We have addressed this question by testing the immunological function of novel genes from helminth parasites, in which conventional transgenesis is not yet possible. We investigated two such novel genes from Brugia malayi termed abundant larval transcript (alt), expression of which reaches ~5% of total transcript at the time parasites enter the human host.

Results

To test the hypothesis that ALT proteins modulate host immunity, we adopted an alternative transfection strategy to express these products in the protozoan parasite Leishmania mexicana. We then followed the course of infection in vitro in macrophages and in vivo in mice. Expression of ALT proteins, but not a truncated mutant, conferred greater infectivity of macrophages in vitro, reaching 3-fold higher parasite densities. alt-transfected parasites also caused accelerated disease in vivo, and fewer mice were able to clear infection of organisms expressing ALT. alt-transfected parasites were more resistant to IFN-γ-induced killing by macrophages. Expression profiling of macrophages infected with transgenic L. mexicana revealed consistently higher levels of GATA-3 and SOCS-1 transcripts, both associated with the Th2-type response observed in in vivo filarial infection.

Conclusion

Leishmania transfection is a tractable and informative approach to determining immunological functions of single genes from heterologous organisms. In the case of the filarial ALT proteins, our data suggest that they may participate in the Th2 bias observed in the response to parasite infection by modulating cytokine-induced signalling within immune system cells.

Transmission of cutaneous leishmaniasis by sand flies is enhanced by regurgitation of fPPG

Sand flies are the exclusive vectors of the protozoan parasite Leishmania, but the mechanism of transmission by fly bite has not been determined nor incorporated into experimental models of infection. In sand flies with mature Leishmania infections the anterior midgut is blocked by a gel of parasite origin, the promastigote secretory gel. Here we analyse the inocula from Leishmania mexicana-infected Lutzomyia longipalpis sand flies. Analysis revealed the size of the infectious dose, the underlying mechanism of parasite delivery by regurgitation, and the novel contribution made to infection by filamentous proteophosphoglycan (fPPG), a component of promastigote secretory gel found to accompany the parasites during transmission. Collectively these results have important implications for understanding the relationship between the parasite and its vector, the pathology of cutaneous leishmaniasis in humans and also the development of effective vaccines and drugs. These findings emphasize that to fully understand transmission of vector-borne diseases the interaction between the parasite, its vector and the mammalian host must be considered together.

EFFECT OF HYPOXIA ON MACROPHAGE INFECTION BY LEISHMANIA AMAZONENSIS

In the present study, we compared the effect of 5% oxygen tension (hypoxia) with a normal tension of 21% oxygen (normoxia) on macrophage infection by the protozoan parasite Leishmania amazonensis. Macrophages from different sources (human cell line U937, murine cell line J774, and murine peritoneal macrophages) exposed to hypoxia showed a reduction of the percentage of infected cells and the number of intracellular parasites per cell. Observations on the kinetics of infection indicated that hypoxia did not depress L. amazonensis phagocytosis but induced macrophages to reduce intracellular parasitism. Furthermore, hypoxia did not act synergistically with gamma-interferon and bacterial lipopolysaccharides in macrophages to induce killing of parasites. Experiments also indicated no correlation between nitric oxide production and control of infection in macrophages under hypoxic condition. Thus, we have provided the first evidence that hypoxia, which occurs in various pathological conditions, can alter macrophage susceptibility to a parasitic infection.

[Infection of skin fibroblasts in animals with different levels of sensitivity to Leishmania infantum and Leishmania mexicana (Kinetoplastida: Trypanosomatidae)]

Infection and multiplication of Leishmania infantum and L. mexicana inside of skin fibroblasts from hamsters, mice and rats was achieved. This process was demonstrated either by counting parasites inside the stained cells or by electronic microscopy studies. In addition multiplication rate differences in the cells from these rodent species were determined, for L. infantum as well as for L. mexicana. Parasite development in hamsters and mice fibroblasts was evident but there was not multiplication in rat cells showing that apparently they are refractory to Leishmania infection. These results suggest that the parasite affinity for each animal, as well as any intracellular environment resistance, could involve genetic factors in the parasite multiplication. On the other hand, presence of amastigote multiplication inside of parasitophorus vacuole, showed by electronic microscopy images, probes a true parasite transformation. Therefore it is suggested that fibroblasts could work as host cells for parasite survival and permanency in the infected animals.

Cryopreservation of protozoan parasites

Conventional methods for the propagation and preservation of parasites in vivo or in vitro have some limitations, including the need for labor, initial isolation and loss of strains, bacterial, and fungal contamination, and changes in the original biological and metabolic characteristics. All these disadvantages are considerably reduced by cryopreservation. In this study, we examined the effects of various freezing conditions on the survival of several protozoan parasites after cryopreservation. The viability of Entamoeba histolytica was improved by seeding (p < 0.05, chi2 test), while this was not so effective for Trichomonas vaginalis. Of six cryoprotectants examined, dimethyl sulfoxide (Me(2)SO), and glycerol showed the strongest cryoprotective effects. The optimum conditions for using Me(2)SO were a concentration of 10% with no equilibration, and those for glycerol were a concentration of 15% with equilibration for 2h. The optimum cooling rate depended on the parasite species. Trypanosoma brucei gambiense and Leishmania amazonensis were successfully cryopreserved over a wide range of cooling rates, whereas the survival rates of E. histolytica, T. vaginalis, Pentatrichomonas hominis, and Blastocystis hominis were remarkably decreased when frozen at improper rates. Unlike the cooling rate, exposure of the protozoans to a rapid thawing method produced better motility for all parasites.

Biological behavior of Leishmania (L.) amazonensis isolated from a human diffuse cutaneous leishmaniasis in inbred strains of mice

After a subcutaneous injection of 100000 purified amastigotes of an isolate from a diffuse case of cutaneous leishmaniasis caused by the MHOM/BR/76/Ma-5 strain of Leishmania amazonensis, three inbred mouse strains developed a progressive nodular lesion, which evolved to an ulcerated lesion. Based on these data, mice of BALB/c, C57BL/6 or C57BL/10 could be classified as susceptible. The majority of mice developed metastases in the footpads, ear, tail, nose and oral mucosa. Amputation of the members related to the primary lesion was frequent. Experiments using the limiting dilution analysis showed that there was no correlation between lesion and parasite load. It has been demonstrated that these mouse strains could be considered excellent models for mucocutaneous leishmaniasis when infected with L. amazonensis. Metastatic lesions caused destruction of the nasal region with many parasitized macrophages under the epithelial surface of the nasal mucosa. Bone destruction occurred with an extensive inflammatory reaction presenting macrophages heavily parasitized by amastigotes. The parasites also spread to the periodontal ligament and other structures of the oral cavity, which could induce a severe inflammatory process. This study indicates that both nasal and oral lesions in mice infected by L. amazonensis were characterized by an inflammatory reaction with the presence of a high parasite load within macrophages.

Sigma 1- and mu 1-Adaptin homologues of Leishmania mexicana are required for parasite survival in the infected host

The sorting of membrane-bound proteins from the trans-Golgi network to lysosomal/endosomal compartments is achieved by preferential inclusion into clathrin-coated vesicles. Contained within the cytoplasmic domains of such proteins, specific sequence motifs have been identified (tyrosine-based and/or di-leucine-based) that are essential for targeting and are recognized by a family of heterotetrameric adaptor complexes, which then recruit clathrin. These cytosolic protein complexes, which have been found in a wide variety of higher eukaryotic organisms, are essential for the development of multicellular organisms. In trypanosomatids, the adaptin-mediated sorting of proteins is largely uncharacterized. In order to identify components of the adaptor-complex machinery, this study reports the cloning and characterization of sigma 1- and mu 1-adaptin gene homologues from the eukaryotic protozoan parasite, Leishmania mexicana. Generation of sigma 1- and mu 1-adaptin gene deletion mutants shows that these promastigote parasites are viable in culture, but are unable to establish infection of macrophages or mice, indicating that adaptin function is crucial for pathogenesis in these unicellular organisms.

Effect of itraconazole and terbinafine on Leishmania promastigotes

The antiproliferative effect induced in vitro by two antifungal compounds, the azole itraconazole and the allylamine terbinafine on Leishmania major, L. donovani and L. mexicana promastigotes are reported. Treatment of promastigotes cultures with itraconazole or with terbinafine induced growth arrest with L. major but neither with L. donovani nor with L. mexicana. Concentrations of 0.75 microl/l or more of itraconazole induced cell lysis after 72 hours with L. major. However, even relatively large concentrations of terbinafine (2.0 microl/l) did not induce cell lysis. For L. major, the IC 50 for itraconazole and terbinafine were 0.31 microl/l and 3.3 microl/l respectively.

Growth phase and medium ph modulate the expression of proteinase activities and the development of megasomes in axenically cultivated Leishmania (Leishmania) amazonensis amastigote-like organisms

Leishmania (Leishmania) amazonensis LV79 (MPRO/BR/72/M1841) has been adapted to grow at 33 C as amastigote-like (AL) organisms in modified UM-54 medium initially adjusted to a pH of 4.8-5.0. Axenic cultures could be routinely restarted from parasites recovered from footpad lesions obtained by inoculation of BALB/c mice with preadapted culture stages. Morphological features, proteinase activities, and infectivity of AL organisms were examined during the in vitro growth cycle, and differences were found between log- and stationary-phase parasites. Stationary-phase AL organisms were morphologically similar to lesion amastigotes, did not react with a paraflagellar rod-specific monoclonal antibody in western blots, and contained proteinase activities resolving identically to the enzymes of lesion amastigotes in gelatin gels. Whereas typical megasomes could be identified in about a third of the stationary-phase AL population, the organelles were rarely seen in log-phase organisms. Azocaseinolytic activity progressively increased during the exponential growth phase and reached its highest values (approximately 65-70% of those determined in lesion amastigotes) at the stationary phase; the association of total proteinase activity with increased expression of cysteine proteinases was indicated by the strong inhibition of azocasein hydrolysis by E-64, the intensified banding of the 28-, 31-, and 35-kDa proteinases in gelatin gels, and the higher susceptibility of stationary-phase AL organisms to L-leucine methyl ester. Although overall axenic amastigotes were less infective to BALB/c mice than were lesion-derived parasites, stationary-phase AL organisms were more infective than were log-phase parasites. Medium pH increased during the exponential growth phase, but dropped in the stationary phase, when the observed morphological, biochemical, and biological changes became apparent.

Leishmania mexicana: promastigotes migrate through osmotic gradients

During the insect phase of the parasite lifecycle, Leishmania promastigotes move from the midgut to the anterior regions of the alimentary tract of their sandfly vector. Chemotaxis of Leishmania promastigotes towards sugars has been reported, and the putative presence of sugar gradient in the insect foregut has been suggested to play a role in promastigote development in the insect. We have further investigated the potential of Leishmania mexicana promastigotes to respond to chemical stimulii. We find that promastigotes move towards concentrations of all substances tested and that this taxis requires the presence of an osmotic gradient. Our results indicate that behaviour that has previously been interpreted as chemotaxis is better understood as osmotaxis. The implications of this observation are discussed in the context of promastigote development.

Leishmania RAB7: characterisation of terminal endocytic stages in an intracellular parasite

Leishmania species are intracellular parasites that inhabit a parasitophorous vacuole (PV) within host macrophages and engage with the host endo-membrane network to avoid clearance from the cell. Intracellular Leishmania amastigotes exhibit a high degree of proteolytic/lysosomal activity that may assist degradation of MHC class II molecules and subsequent interruption of antigen presentation. As an aid to further analysis of the endosomal/lysosomal events that could facilitate this process, we have characterised a Leishmania homologue of the late endosomal marker, Rab7, thought to be involved in the terminal steps of endocytosis and lysosomal delivery. The Leishmania major Rab7 (LmRAB7) protein is expressed throughout the life-cycle, shows 73 and 64% identity to Trypanosoma cruzi and Trypanosoma brucei Rab7s (TcRAB7 and TbRAB7), respectively, and includes a kinetoplastid-specific insertion. The recombinant protein binds GTP and polyclonal antibodies raised against this antigen recognise structures in the region of the cell between the nucleus and kinetoplast. By immunoelectron microscopy of axenic amastigotes, Leishmania mexicana Rab7 (LmexRAB7) is found juxtaposed to and overlapping membrane structures labelled for the megasomal marker, cysteine proteinase B, confirming a late-endosomal/lysosomal localisation.

Regulated degradation of an endoplasmic reticulum membrane protein in a tubular lysosome in Leishmania mexicana

The cell surface of the human parasite Leishmania mexicana is coated with glycosylphosphatidylinositol (GPI)-anchored macromolecules and free GPI glycolipids. We have investigated the intracellular trafficking of green fluorescent protein- and hemagglutinin-tagged forms of dolichol-phosphate-mannose synthase (DPMS), a key enzyme in GPI biosynthesis in L. mexicana promastigotes. These functionally active chimeras are found in the same subcompartment of the endoplasmic reticulum (ER) as endogenous DPMS but are degraded as logarithmically growing promastigotes reach stationary phase, coincident with the down-regulation of endogenous DPMS activity and GPI biosynthesis in these cells. We provide evidence that these chimeras are constitutively transported to and degraded in a novel multivesicular tubule (MVT) lysosome. This organelle is a terminal lysosome, which is labeled with the endocytic marker FM 4-64, contains lysosomal cysteine and serine proteases and is disrupted by lysomorphotropic agents. Electron microscopy and subcellular fractionation studies suggest that the DPMS chimeras are transported from the ER to the lumen of the MVT via the Golgi apparatus and a population of 200-nm multivesicular bodies. In contrast, soluble ER proteins are not detectably transported to the MVT lysosome in either log or stationary phase promastigotes. Finally, the increased degradation of the DPMS chimeras in stationary phase promastigotes coincides with an increase in the lytic capacity of the MVT lysosome and changes in the morphology of this organelle. We conclude that lysosomal degradation of DPMS may be important in regulating the cellular levels of this enzyme and the stage-dependent biosynthesis of the major surface glycolipids of these parasites.

Effect of a second bloodmeal on the oesophagus colonization by Leishmania mexicana complex in Lutzomyia evansi (Diptera: Psychodidae)

Migration and colonization of the oesophagus by Leishmania mexicana parasites were enhanced after digestion of a second bloodmeal intake in Lutzomyia evansi. This event has epidemiological significance since it affects the infection susceptibility of this sand fly species, which is a proven vector of L. chagasi in Colombian and Venezuelan visceral leishmaniasis foci. Also, it may explain the host seeking behaviour displayed by some partially bloodfed flies found inside houses.

Hexose transport in asexual stages of Plasmodium falciparum and kinetoplastidae

The hexose sugar, glucose, is a vital energy source for most organisms and an essential nutrient for asexual stages of Plasmodium falciparum. Kinetoplastid organisms (e.g. Trypanosoma and Leishmania spp) also require glucose at certain critical stages of their life cycles. Although phylogenetically unrelated, these organisms share many common challenges during the mammalian stages of a parasitic life cycle, and possess hexose uptake mechanisms that are amenable to study using similar methods. Defining hexose permeation pathways into parasites might expose an Achilles' heel at which both antidisease and antiparasite measures can be aimed. Understanding the mode of entry of glucose also presents a good general model for substrate acquisition in multicompartment systems. In this review, Sanjeev Krishna and colleagues summarize current understanding of hexose transport processes in P. falciparum and provide a comparison with data obtained from kinetoplastids.

Analysis of the roles of cysteine proteinases of Leishmania mexicana in the host-parasite interaction

Promastigotes of Leishmania mexicana mutants lacking the multicopy CPB cysteine proteinase genes (deltaCPB) are markedly less able than wild-type parasites to infect macrophages in vitro. deltaCPB promastigotes invade macrophages in large numbers but are unable to survive in the majority of the cells. In contrast, deltaCPB amastigotes invade and survive within macrophages in vitro. This extreme in vitro stage-specific difference was not mimicked in vivo; both promastigotes and amastigotes of deltaCPB produced lesions in BALB/c mice, but in each case the lesions grew considerably more slowly than those caused by wild-type parasites and only small lesions resulted. Inhibition of CPB in situ using cell-permeant peptidyl-diazomethylketones had no measurable effect on parasite growth or differentiation axenically in vitro. In contrast, N-benzoyloxycarbonyl-phe-ala-diazomethylketone reduced the infectivity of wild-type parasites to macrophages by 80%. Time-course experiments demonstrated that application of the inhibitor caused effects not seen with deltaCPB, suggesting that CPB may not be the prime target of this inhibitor. The data show that the CPB genes of L. mexicana encode enzymes that have important roles in intracellular survival of the parasite and more generally in its interaction with its mammalian host.

Lipophosphoglycan is not required for infection of macrophages or mice by Leishmania mexicana

Cell surface lipophosphoglycan (LPG) is commonly regarded as a multifunctional Leishmania virulence factor required for survival and development of these parasites in mammals. In this study, the LPG biosynthesis gene lpg1 was deleted in Leishmania mexicana by targeted gene replacement. The resulting mutants are deficient in LPG synthesis but still display on their surface and secrete phosphoglycan-modified molecules, most likely in the form of proteophosphoglycans, whose expression appears to be up-regulated. LPG-deficient L.mexicana promastigotes show no significant differences to LPG-expressing parasites with respect to attachment to, uptake into and multiplication inside macrophages. Moreover, in Balb/c and C57/BL6 mice, LPG-deficient L.mexicana clones are at least as virulent as the parental wild-type strain and lead to lethal disseminated disease. The results demonstrate that at least L. mexicana does not require LPG for experimental infections of macrophages or mice. Leishmania mexicana LPG is therefore not a virulence factor in the mammalian host.

Leishmania amazonensis infection does not inhibit systemic nitric oxide levels elicited by lipopolysaccharide in vivo

Leishmaniasis is a parasitic disease that leads to chronic inflammation. Macrophages, depending on their activation state, are either hosts or killers of the parasites. Downregulation of nitric oxide (NO) synthesis by the parasite infecting the macrophages has been proposed to be an important evading mechanism based on in vitro studies. We confirmed inhibition of NO release by macrophages infected with Leishmania amazonensis in vitro. To examine the role of the parasite in regulating NO production in vivo, we monitored systemic NO levels elicited by challenging naive and L. amazonensis-infected BALB/c mice with lipopolysaccharide (LPS). Animals were challenged after 1, 2, 6, and 9 wk of infection. NO production was monitored by electron paramagnetic resonance spectroscopy as the levels of hemoglobin nitrosyl complexes (HbNO) present in the animal's blood. No significant differences in HbNO levels were observed between LPS-treated naive and inoculated mice at any time during infection. To control for increased macrophage numbers in infected mice, naive mice were injected with a macrophage cell line before LPS challenge; this treatment did not increase produced NO levels. The results argue against a major role for the parasite in downregulating NO production in vivo.

Filamentous proteophosphoglycan secreted by Leishmania promastigotes forms gel-like three-dimensional networks that obstruct the digestive tract of infected sandfly vectors

Development of Leishmania parasites in the digestive tract of their sandfly vectors involves several morphological transformations from the intracellular mammalian amastigote via a succession of free and gut wall-attached promastigote stages to the infective metacyclic promastigotes. At the foregut midgut transition of Leishmania-infected sandflies a gel-like plug of unknown origin and composition is formed, which contains high numbers of parasites, that occludes the gut lumen and which may be responsible for the often observed inability of infected sandflies to draw blood. This "blocked fly" phenotype has been linked to efficient transmission of infectious metacyclic promastigotes from the vector to the mammalian host. We show by immunofluorescence and immunoelectron microscopy on two Leishmania/sandfly vector combinations (Leishmania mexicana/Lutzomyia longipalpis and L. major/Phlebotomus papatasi) that the gel-like mass is formed mainly by a parasite-derived mucin-like filamentous proteophosphoglycan (fPPG) whereas the Leishmania polymeric secreted acid phosphatase (SAP) is not a major component of this plug. fPPG forms a dense three-dimensional network of filaments which engulf the promastigote cell bodies in a gel-like mass. We propose that the continuous secretion of fPPG by promastigotes in the sandfly gut, that causes plug formation, is an important factor for the efficient transmission to the mammalian host.

Status of respiration and ATP content in arsenite resistant Leishmania mexicana amazonensis

Cellular ATP and rate of respiration are important for the cell survival. We have analyzed both the parameters in wild type and arsenite resistant Leishmania mexicana amazonensis. There was no significant change observed in the rate of respiration and cellular ATP content between drug resistant cells (resistance to 30 microM of sodium arsenite) and wild type cells. Further, we have tested the effect of higher concentrations (i.e. 100 microM and 500 microM) of sodium arsenite on the ATP content of the cells. An elevated level of ATP was observed only in wild type cells after short term exposure (2 h) to 100 microM of the drug, whereas, drug resistant cells initially resist with higher toxic dosage of drug (i.e. 500 microM) but failed to maintain the normal ATP level. In conclusion, respiration and ATP is not a prime event associated with drug resistance in Leishmania. Resistance to metals like arsenic and antimony in Leishmania is multifactorial events.

Transformation, development, and transmission of axenically cultured amastigotes of Leishmania mexicana in vitro and in Lutzomyia longipalpis

Axenic cultures of Leishmania mexicana amastigotes were transformed to promastigotes in vitro and in vivo in Lutzomyia longipalpis. In vitro, both exponential phase and stationary phase amastigotes were capable of transforming and growing as promastigotes, but exponential phase amastigotes completed this transition more quickly. In vivo, both populations were capable of establishing infections in sand flies by membrane feeding and could be transmitted to BALB/c mice via bite. A variety of morphologic forms could be observed in vivo, including putative metacyclic promastigotes. Infection rates in sandflies with axenic amastigotes were comparable with those achieved with lesion-derived amastigotes, supporting the use of these cultured forms in studies of parasite biology.