Host plasma low density lipoprotein particles as an essential source of lipids for the bloodstream forms of Trypanosoma brucei

Lipid metabolism dynamic in Triatomine Rhodnius prolixus during acute Trypanosoma rangeli infection

During its life cycle, Trypanosoma rangeli invades the hemolymph of its invertebrate host and colonizes hemocytes and salivary glands. The parasite cannot synthesize some lipid classes, and during its cycle, it depends on the uptake of these molecules from its vertebrate and invertebrate hosts to meet growth and differentiation requirements. However, until now, knowledge on how the parasite affects the lipid physiology of individual insect organs has been largely unknown. Herein, the biochemical and molecular dynamics of triatomine R. prolixus lipid metabolism in response to acute T. rangeli infection were investigated. Biochemical and microscopic assays revealed the lipid droplet profile and the levels of the different identified lipid classes. In addition, a qRT‒PCR approach was used to determine the expression profile of 6 protein-coding genes involved in the R. prolixus lipid physiology. We observed that triacylglycerol (TAG), monoacylglycerol (MAG), phosphatidylethanolamine (PE) and phosphatidylcholine (PC) levels in the fat body decreased in infected insects. On the other hand, high levels of free fatty acids were observed in the hemolymph during infection. Analysis by confocal microscopy revealed a decrease in lipid droplets size from infected fat bodies, and investigations by scanning electron microscopy revealed a significant number of parasites adhered to the surface of the organ. T. rangeli infection upregulated the transcript levels of the protein-coding gene for the acetyl-CoA carboxylase, the first enzyme in the de novo fatty acid synthesis pathway, responsible for the production of malonyl-CoA. On the other hand, downregulation of lipophorin receptor was observed. In conclusion, this study reveals a new set of molecular events that occur within the vector in response to the challenge imposed by the parasite.

How much (ATP) does it cost to build a trypanosome? A theoretical study on the quantity of ATP needed to maintain and duplicate a bloodstream-form Trypanosoma brucei cell

ATP hydrolysis is required for the synthesis, transport and polymerization of monomers for macromolecules as well as for the assembly of the latter into cellular structures. Other cellular processes not directly related to synthesis of biomass, such as maintenance of membrane potential and cellular shape, also require ATP. The unicellular flagellated parasite Trypanosoma brucei has a complex digenetic life cycle. The primary energy source for this parasite in its bloodstream form (BSF) is glucose, which is abundant in the host's bloodstream. Here, we made a detailed estimation of the energy budget during the BSF cell cycle. As glycolysis is the source of most produced ATP, we calculated that a single parasite produces 6.0 x 1011 molecules of ATP/cell cycle. Total biomass production (which involves biomass maintenance and duplication) accounts for ~63% of the total energy budget, while the total biomass duplication accounts for the remaining ~37% of the ATP consumption, with in both cases translation being the most expensive process. These values allowed us to estimate a theoretical YATP of 10.1 (g biomass)/mole ATP and a theoretical [Formula: see text] of 28.6 (g biomass)/mole ATP. Flagellar motility, variant surface glycoprotein recycling, transport and maintenance of transmembrane potential account for less than 30% of the consumed ATP. Finally, there is still ~5.5% available in the budget that is being used for other cellular processes of as yet unknown cost. These data put a new perspective on the assumptions about the relative energetic weight of the processes a BSF trypanosome undergoes during its cell cycle.

Enriched PUFA environment of Leishmania infantum promastigotes promotes the accumulation of lipid mediators and favors parasite infectivity towards J774 murine macrophages

Leishmania parasites are the causative agents of visceral or cutaneous leishmaniasis in humans and of canine leishmaniosis. The macrophage is the predilected host cell of Leishmania in which the promastigote stage is transformed into amastigote. We previously showed changes in the fatty acid composition (FA) of lipids in two strains of Leishmania donovani upon differentiation of promastigote to amastigote, including increased proportions of arachidonic acid (AA) and to a less extent of docosahexaenoic acid (DHA). Here, we carried out supplementation with AA or DHA on two Leishmania infantum strains, a visceral (MON-1) and a cutaneous (MON-24), to evaluate the role of these FA in parasite/macrophage interactions. The proportions of AA or DHA in total lipids were significantly increased in promastigotes cultured in AA- or DHA-supplemented media compared to controls. The content of FA-derived oxygenated metabolites was enhanced in supplemented strains, generating especially epoxyeicosatrienoic acids (11,12- and 14,15-EET) and hydroxyeicosatetraenoic acids (5- and 8- HETE) from AA, and hydroxydocosahexaenoic acids (14- and 17-HDoHE) from DHA. For both MON-1 and MON-24, AA-supplemented promastigotes showed higher infectivity towards J774 macrophages as evidenced by higher intracellular amastigote numbers. Higher infectivity was observed after DHA supplementation for MON-24 but not MON-1 strain. ROS production by macrophages increased upon parasite infection, but only minor change was observed between control and supplemented parasites. We propose that under high AA or DHA environment that is associated with AA or DHA enrichment of promastigote lipids, FA derivatives can accumulate in the parasite, thereby modulating parasite infectivity towards host macrophages.

Fatty acid uptake in Trypanosoma brucei: Host resources and possible mechanisms

Trypanosoma brucei spp. causes African Sleeping Sickness in humans and nagana, a wasting disease, in cattle. As T. brucei goes through its life cycle in its mammalian and insect vector hosts, it is exposed to distinct environments that differ in their nutrient resources. One such nutrient resource is fatty acids, which T. brucei uses to build complex lipids or as a potential carbon source for oxidative metabolism. Of note, fatty acids are the membrane anchoring moiety of the glycosylphosphatidylinositol (GPI)-anchors of the major surface proteins, Variant Surface Glycoprotein (VSG) and the Procyclins, which are implicated in parasite survival in the host. While T. brucei can synthesize fatty acids de novo, it also readily acquires fatty acids from its surroundings. The relative contribution of parasite-derived vs. host-derived fatty acids to T. brucei growth and survival is not known, nor have the molecular mechanisms of fatty acid uptake been defined. To facilitate experimental inquiry into these important aspects of T. brucei biology, we addressed two questions in this review: (1) What is known about the availability of fatty acids in different host tissues where T. brucei can live? (2) What is known about the molecular mechanisms mediating fatty acid uptake in T. brucei? Finally, based on existing biochemical and genomic data, we suggest a model for T. brucei fatty acid uptake that proposes two major routes of fatty acid uptake: diffusion across membranes followed by intracellular trapping, and endocytosis of host lipoproteins.

Steroidal Antimetabolites Protect Mice against Trypanosoma brucei

Trypanosoma brucei, the causative agent for human African trypanosomiasis, is an emerging ergosterol-dependent parasite that produces chokepoint enzymes, sterol methyltransferases (SMT), not synthesized in their animal hosts that can regulate cell viability. Here, we report the lethal effects of two recently described natural product antimetabolites that disrupt Acanthamoeba sterol methylation and growth, cholesta-5,7,22,24-tetraenol (CHT) and ergosta-5,7,22,24(28)-tetraenol (ERGT) that can equally target T. brucei. We found that CHT/ERGT inhibited cell growth in vitro, yielding EC₅₀ values in the low nanomolar range with washout experiments showing cidal activity against the bloodstream form, consistent with their predicted mode of suicide inhibition on SMT activity and ergosterol production. Antimetabolite treatment generated altered T. brucei cell morphology and death rapidly within hours. Notably, in vivo ERGT/CHT protected mice infected with T. brucei, doubling their survival time following daily treatment for 8-10 days at 50 mg/kg or 100 mg/kg. The current study demonstrates a new class of lead antibiotics, in the form of common fungal sterols, for antitrypanosomal drug development.

Trypanosoma cruzi modulates lipid metabolism and highjacks phospholipids from the midgut of Rhodnius prolixus

Chagas disease is potentially life-threatening and caused by the protozoan parasite Trypanosoma cruzi. The parasite cannot synthesize some lipids and depends on the uptake of these lipids from its vertebrate and invertebrate hosts. To achieve this, T. cruzi may need to modify the physiology of the insect host for its own benefit. In this study, we investigated the interaction of T. cruzi (Y strain) with its insect vector Rhodnius prolixus and how it manipulates the vector lipid metabolism. We observed a physiological change in lipid flux in of infected insects. In the fat body of infected insects, triacylglycerol levels decreased by 80.6% and lipid storage droplet-1(LSD-1) mRNA levels were lower, when compared to controls. Lipid sequestration by infected midguts led to increased levels of 5' AMP-activated protein kinase (AMPK) phosphorylation and activation in the fat body, inhibiting the synthesis of fatty acids and stimulating their oxidation. This led to reduced lipid levels in the fat body of infected insets, despite the fact that T. cruzi does not colonize this tissue. There was a 3-fold increase, in lipid uptake and synthesis in the midgut of infected insects. Finally, our results suggest that the parasite modifies the lipid flux and metabolism of its vector R. prolixus through the increase in lipid delivery from the fat body to midgut that are then scavenge by T cruzi.

Biogenesis and Breakdown of Lipid Droplets in Pathological Conditions

Lipid droplets (LD) have long been considered as mere fat drops; however, LD have lately been revealed to be ubiquitous, dynamic and to be present in diverse organelles in which they have a wide range of key functions. Although incompletely understood, the biogenesis of eukaryotic LD initiates with the synthesis of neutral lipids (NL) by enzymes located in the endoplasmic reticulum (ER). The accumulation of NL leads to their segregation into nanometric nuclei which then grow into lenses between the ER leaflets as they are further filled with NL. The lipid composition and interfacial tensions of both ER and the lenses modulate their shape which, together with specific ER proteins, determine the proneness of LD to bud from the ER toward the cytoplasm. The most important function of LD is the buffering of energy. But far beyond this, LD are actively integrated into physiological processes, such as lipid metabolism, control of protein homeostasis, sequestration of toxic lipid metabolic intermediates, protection from stress, and proliferation of tumours. Besides, LD may serve as platforms for pathogen replication and defense. To accomplish these functions, from biogenesis to breakdown, eukaryotic LD have developed mechanisms to travel within the cytoplasm and to establish contact with other organelles. When nutrient deprivation occurs, LD undergo breakdown (lipolysis), which begins with the LD-associated members of the perilipins family PLIN2 and PLIN3 chaperone-mediated autophagy degradation (CMA), a specific type of autophagy that selectively degrades a subset of cytosolic proteins in lysosomes. Indeed, PLINs CMA degradation is a prerequisite for further true lipolysis, which occurs via cytosolic lipases or by lysosome luminal lipases when autophagosomes engulf portions of LD and target them to lysosomes. LD play a crucial role in several pathophysiological processes. Increased accumulation of LD in non-adipose cells is commonly observed in numerous infectious diseases caused by intracellular pathogens including viral, bacterial, and parasite infections, and is gradually recognized as a prominent characteristic in a variety of cancers. This review discusses current evidence related to the modulation of LD biogenesis and breakdown caused by intracellular pathogens and cancer.

Raman spectroscopic analysis of skin as a diagnostic tool for Human African Trypanosomiasis

Human African Trypanosomiasis (HAT) has been responsible for several deadly epidemics throughout the 20th century, but a renewed commitment to disease control has significantly reduced new cases and motivated a target for the elimination of Trypanosoma brucei gambiense-HAT by 2030. However, the recent identification of latent human infections, and the detection of trypanosomes in extravascular tissues hidden from current diagnostic tools, such as the skin, has added new complexity to identifying infected individuals. New and improved diagnostic tests to detect Trypanosoma brucei infection by interrogating the skin are therefore needed. Recent advances have improved the cost, sensitivity and portability of Raman spectroscopy technology for non-invasive medical diagnostics, making it an attractive tool for gambiense-HAT detection. The aim of this work was to assess and develop a new non-invasive diagnostic method for T. brucei through Raman spectroscopy of the skin. Infections were performed in an established murine disease model using the animal-infective Trypanosoma brucei brucei subspecies. The skin of infected and matched control mice was scrutinized ex vivo using a confocal Raman microscope with 532 nm excitation and in situ at 785 nm excitation with a portable field-compatible instrument. Spectral evaluation and Principal Component Analysis confirmed discrimination of T. brucei-infected from uninfected tissue, and a characterisation of biochemical changes in lipids and proteins in parasite-infected skin indicated by prominent Raman peak intensities was performed. This study is the first to demonstrate the application of Raman spectroscopy for the detection of T. brucei by targeting the skin of the host. The technique has significant potential to discriminate between infected and non-infected tissue and could represent a unique, non-invasive diagnostic tool in the goal for elimination of gambiense-HAT as well as for Animal African Trypanosomiasis (AAT).

Human African Trypanosomiasis (HAT), also known as sleeping sickness, is a disease caused by the parasite Trypanosoma brucei and has been responsible for the death of millions of people across Africa in the 20^th century. It is also a major economic burden for countries endemic for trypanosomiasis, affecting livestock productivity in rural areas (Animal African Trypanosomiasis). A long-term international collaboration with the help of the World Health Organisation has resulted in the rate of human infection decreasing to less than 1000 new cases per year. However, the human disease continues to spread within remote villages. Current diagnosis is based on the detection of parasites in blood and serum samples, but this is challenging during chronic human infections with low or non-detectable parasitaemia. However, the recent discovery of extravascular skin-dwelling trypanosomes indicates that a reservoir of infection remains undetected, threatening the effort to eliminate the disease. In this study we have targeted the skin as a site for diagnosis using Raman spectroscopy and demonstrate that this method showed great promise in the laboratory, laying the foundation for field studies to examine its potential to strengthen current diagnostic strategies for detecting HAT cases.

Lipid and fatty acid metabolism in trypanosomatids

Trypanosomiases and leishmaniases are neglected tropical diseases that have been spreading to previously non-affected areas in recent years. Identification of new chemotherapeutics is needed as there are no vaccines and the currently available treatment options are highly toxic and often ineffective. The causative agents for these diseases are the protozoan parasites of the Trypanosomatidae family, and they alternate between invertebrate and vertebrate hosts during their life cycles. Hence, these parasites must be able to adapt to different environments and compete with their hosts for several essential compounds, such as amino acids, vitamins, ions, carbohydrates, and lipids. Among these nutrients, lipids and fatty acids (FAs) are essential for parasite survival. Trypanosomatids require massive amounts of FAs, and they can either synthesize FAs de novo or scavenge them from the host. Moreover, FAs are the major energy source during specific life cycle stages of T. brucei, T. cruzi, and Leishmania. Therefore, considering the distinctive features of FAs metabolism in trypanosomatids, these pathways could be exploited for the development of novel antiparasitic drugs. In this review, we highlight specific aspects of lipid and FA metabolism in the protozoan parasites T. brucei, T. cruzi, and Leishmania spp., as well as the pathways that have been explored for the development of new chemotherapies.

The Fate of Dietary Cholesterol in the Kissing Bug Rhodnius prolixus

Insects are unable to synthesize cholesterol and depend on the presence of sterols in the diet for cell membrane composition and hormone production. Thus, cholesterol absorption, transport, and metabolism are potential targets for vector and pest control strategies. Here, we investigate the dietary cholesterol absorption and tissue distribution in the kissing bug Rhodnius prolixus using radiolabeled cholesterol. Both the anterior and posterior midguts absorbed cholesterol from the ingested blood, although the anterior midgut absorbed more. We also observed esterified cholesterol labeling in the epithelium, indicating that midgut cells can metabolize and store cholesterol. Only a small amount of labeled cholesterol was found in the hemolymph, where it was mainly in the free form and associated with lipophorin (Lp). The fat body transiently accumulated cholesterol, showing a labeled cholesterol peak on the fifth day after the blood meal. The ovaries also incorporated cholesterol, but cumulatively. The insects did not absorb almost half of the ingested labeled cholesterol, and radioactivity was present in the feces. After injection of 3H-cholesterol-labeled Lp into females, a half-life of 5.5 ± 0.7 h in the hemolymph was determined. Both the fat body and ovaries incorporated Lp-associated cholesterol, which was inhibited at low temperature, indicating the participation of active cholesterol transport. These results help describe an unexplored part of R. prolixus lipid metabolism.

Multiple unbiased approaches identify oxidosqualene cyclase as the molecular target of a promising anti-leishmanial

Phenotypic screening identified a benzothiophene compound with activity against Leishmania donovani, the causative agent of visceral leishmaniasis. Using multiple orthogonal approaches, oxidosqualene cyclase (OSC), a key enzyme of sterol biosynthesis, was identified as the target of this racemic compound and its enantiomers. Whole genome sequencing and screening of a genome-wide overexpression library confirmed that OSC gene amplification is associated with resistance to compound 1. Introduction of an ectopic copy of the OSC gene into wild-type cells reduced susceptibility to these compounds confirming the role of this enzyme in resistance. Biochemical analyses demonstrated the accumulation of the substrate of OSC and depletion of its product in compound (S)-1-treated-promastigotes and cell-free membrane preparations, respectively. Thermal proteome profiling confirmed that compound (S)-1 binds directly to OSC. Finally, modeling and docking studies identified key interactions between compound (S)-1 and the LdOSC active site. Strategies to improve the potency for this promising anti-leishmanial are proposed.

•

Genetics and chemo-proteomics identify the target of a promising anti-leishmanial

•

Biochemical assays confirm the direct inhibition of oxidosqualene cyclase in cells

•

Docking and modeling studies identify key interactions between compound and target

•

Strategies to improve the potency of this benzothiophene are proposed

Lipid hijacking: a unifying theme in vector-borne diseases

Vector-borne illnesses comprise a significant portion of human maladies, representing 17% of global infections. Transmission of vector-borne pathogens to mammals primarily occurs by hematophagous arthropods. It is speculated that blood may provide a unique environment that aids in the replication and pathogenesis of these microbes. Lipids and their derivatives are one component enriched in blood and are essential for microbial survival. For instance, the malarial parasite Plasmodium falciparum and the Lyme disease spirochete Borrelia burgdorferi, among others, have been shown to scavenge and manipulate host lipids for structural support, metabolism, replication, immune evasion, and disease severity. In this Review, we will explore the importance of lipid hijacking for the growth and persistence of these microbes in both mammalian hosts and arthropod vectors.

Parasite × vector relationship in Chagas disease: does Trypanosoma cruzi (Chagas, 1909) infection affect the spermatogenesis of Triatoma infestans (Klug, 1834)?

The parasite-vector interaction of Chagas disease is still poorly understood and the understanding of this relationship can help in the development of new strategies to control Trypanosoma cruzi transmission, which is the etiological agent of this disease. Considering the need to know if T. cruzi can cause some pathology in the reproductive system of the Chagas disease vectors, we investigated the spermatogenesis of Triatoma infestans infected by T. cruzi through histological and cytogenetic analysis. Trypanosoma cruzi Bolivia strain infection was not pathogenic for the reproductive system of T. infestans, because all the analyzed males had normal spermatogenesis, with all phases (spermatocytogenesis, meiosis and spermiogenesis) happening without any change. Thus, we demonstrated that the presence of T. cruzi Bolivia strain does not have influence in the spermatogenesis of T. infestans and we suggest that the influences on reproductive system observed for other species were a result of the action of the parasite on gametogenesis of females.

Expression of a specific variant surface glycoprotein has a major impact on suramin sensitivity and endocytosis in Trypanosoma brucei

Suramin was introduced into the clinic a century ago and is still used to treat the first stage of acute human sleeping sickness. Due to its size and sixfold negative charge, uptake is mediated through endocytosis and the suramin receptor in trypanosomes is thought to be the invariant surface glycoprotein 75 (ISG75). Nevertheless, we recently identified a variant surface glycoprotein (VSGSur) that confers strong in vitro resistance to suramin in a Trypanosoma brucei rhodesiense line. In this study, we introduced VSGSur into the active bloodstream expression site of a T. b. brucei line. This caused suramin resistance and cross resistance to trypan blue. We quantified the endocytosis of different substrates by flow cytometry and showed that the expression of VSGSur strongly impairs the uptake of low-density lipoprotein (LDL) and transferrin, both imported by receptor-mediated endocytosis. However, bulk endocytosis and endocytosis of the trypanolytic factor were not affected, and the VSGSur -expressors did not exhibit a growth phenotype in the absence of suramin. Knockdown of ISG75 was synergistic with VSGSur expression, indicating that these two proteins are mediating distinct suramin resistance pathways. In conclusion, VSGSur causes suramin resistance in T. brucei bloodstream forms by decreasing specific, receptor-mediated endocytosis pathways.

Aquaglyceroporin PbAQP is required for efficient progression through the liver stage of Plasmodium infection

The discovery of aquaglyceroporins (AQP) has highlighted a new mechanism of membrane solute transport that may hold therapeutic potential for controlling parasitic infections, including malaria. Plasmodium parasites express a single AQP at the plasma membrane that functions as a channel for water, nutrients and waste into and out cells. We previously demonstrated that Plasmodium berghei targeted for PbAQP deletion are deficient in glycerol import and less virulent than wild-type parasites during the blood developmental stage. Here, we have examined the contribution of PbAQP to the infectivity of P. berghei in the liver. PbAQP is expressed in the sporozoite mosquito stage and is detected at low levels in intrahepatic parasites at the onset of hepatocyte infection. As the parasites progress to late hepatic stages, PbAQP transcription increases and PbAQP localizes to the plasma membrane of hepatic merozoites. Compared to wild-type parasites, PbAQP-null sporozoites exhibit a delay in blood stage infection due to slower replication in hepatocytes, resulting in retardation of merosome production. Furthermore, PbAQP disruption results in a significant reduction in erythrocyte infectivity by hepatocyte-derived merozoites. Hepatic merozoites incorporate exogenous glycerol into glycerophospholipids and PbAQP-null merozoites contain less phosphatidylcholine than wild-type merozoites, underlining the contribution of Plasmodium AQP to phospholipid syntheses.

Characterization and role of the 3-methylglutaconyl coenzyme A hidratase in Trypanosoma brucei

Trypanosoma brucei, the agent of African Trypanosomiasis, is a flagellated protozoan parasite that develops in tsetse flies and in the blood of various mammals. The parasite acquires nutrients such as sugars, lipids and amino acids from their hosts. Amino acids are used to generate energy and for protein and lipid synthesis. However, it is still unknown how T. brucei catabolizes most of the acquired amino acids. Here we explored the role of an enzyme of the leucine catabolism, the 3-methylglutaconyl-Coenzyme A hydratase (3-MGCoA-H). It catalyzes the hydration of 3-methylglutaconyl-Coenzyme A (3-MGCoA) into 3-hydroxymethylglutaryl-Coenzyme A (3-HMGCoA). We found that 3-MGCoA-H localizes in the mitochondrial matrix and is expressed in both insect and mammalian bloodstream forms of the parasite. The depletion of 3-MGCoA-H by RNA interference affected minimally the proliferation of both forms. However, an excess of leucine in the culture medium caused growth defects in cells depleted of 3-MGCoA-H, which could be reestablished by mevalonate, a precursor of isoprenoids and steroids. Indeed, procyclics depleted of the 3-MGCoA-H presented reduced levels of synthesized steroids relative to cholesterol that is scavenged by the parasite, and these levels were also reestablished by mevalonate. These results suggest that accumulation of leucine catabolites could affect the level of mevalonate and consequently inhibit the sterol biosynthesis, required for T. brucei growth.

Evaluation of clinical signs, parasitemia, hematologic and biochemical changes in cattle experimentally infected with Trypanosoma vivax

Abstract Infections by Trypanosoma vivax cause great losses to livestock in Africa and Central and South Americas. Outbreaks due this parasite have been occurred with increasing frequency in Brazil. Knowledge of changes caused byT. vivax during the course of this disease can be of great diagnostic value. Thus, clinical signs, parasitemia, hematologic and biochemical changes of cattle experimentally infected by this hemoparasite were evaluated. Two distinct phases were verified during the infection – an acute phase where circulating parasites were seen and then a chronic phase where fluctuations in parasitemia were detected including aparasitemic periods. A constant reduction in erythrocytes, hemoglobin and packed cell volume (PVC) were observed. White blood cells (WBC) showed pronounced changes such as severe neutropenia and lymphopenia during the acute phase of the illness. Decreases in cholesterol, albumin, aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and increases in glucose, globulin, protein, and alkaline phosphatase (ALP) were observed. The “Lins” isolate of T. vivax showed pathogenicity for cattle, and intense parasitemia was detected in the early stages of infection. Circulating parasites were detected for about two months. The most evident laboratory abnormalities were found in WBC parameters, including thrombocytopenia.

Discovery of Infection Associated Metabolic Markers in Human African Trypanosomiasis

Human African trypanosomiasis (HAT) remains a major neglected tropical disease in Sub-Saharan Africa. As clinical symptoms are usually non-specific, new diagnostic and prognostic markers are urgently needed to enhance the number of identified cases and optimise treatment. This is particularly important for disease caused by Trypanosoma brucei rhodesiense, where indirect immunodiagnostic approaches have to date been unsuccessful. We have conducted global metabolic profiling of plasma from T.b.rhodesiense HAT patients and endemic controls, using 1H nuclear magnetic resonance (NMR) spectroscopy and ultra-performance liquid chromatography, coupled with mass spectrometry (UPLC-MS) and identified differences in the lipid, amino acid and metabolite profiles. Altogether 16 significantly disease discriminatory metabolite markers were found using NMR, and a further 37 lipid markers via UPLC-MS. These included significantly higher levels of phenylalanine, formate, creatinine, N-acetylated glycoprotein and triglycerides in patients relative to controls. HAT patients also displayed lower concentrations of histidine, sphingomyelins, lysophosphatidylcholines, and several polyunsaturated phosphatidylcholines. While the disease metabolite profile was partially consistent with previous data published in experimental rodent infection, we also found unique lipid and amino acid profile markers highlighting subtle but important differences between the host response to trypanosome infections between animal models and natural human infections. Our results demonstrate the potential of metabolic profiling in the identification of novel diagnostic biomarkers and the elucidation of pathogenetic mechanisms in this disease.

Trypanosoma cruzi Epimastigotes Are Able to Manage Internal Cholesterol Levels under Nutritional Lipid Stress Conditions

Trypanosoma cruzi epimastigotes store high amounts of cholesterol and cholesteryl esters in reservosomes. These unique organelles are responsible for cellular digestion by providing substrates for homeostasis and parasite differentiation. Here we demonstrate that under nutritional lipid stress, epimastigotes preferentially mobilized reservosome lipid stocks, instead of lipid bodies, leading to the consumption of parasite cholesterol reservoirs and production of ergosterol. Starved epimastigotes acquired more LDL-NBD-cholesterol by endocytosis and distributed the exogenous cholesterol to their membranes faster than control parasites. Moreover, the parasites were able to manage internal cholesterol levels, alternating between consumption and accumulation. With normal lipid availability, parasites esterified cholesterol exhibiting an ACAT-like activity that was sensitive to Avasimibe in a dose-dependent manner. This result also implies that exogenous cholesterol has a role in lipid reservoirs in epimastigotes.

Discovery of an ergosterol-signaling factor that regulates Trypanosoma brucei growth

Ergosterol biosynthesis and homeostasis in the parasitic protozoan Trypanosoma brucei was analyzed by RNAi silencing and inhibition of sterol C24β-methyltransferase (TbSMT) and sterol 14α-demethylase [TbSDM (TbCYP51)] to explore the functions of sterols in T. brucei growth. Inhibition of the amount or activity of these enzymes depletes ergosterol from cells at <6 fg/cell for procyclic form (PCF) cells or <0.01 fg/cell for bloodstream form (BSF) cells and reduces infectivity in a mouse model of infection. Silencing of TbSMT expression by RNAi in PCF or BSF in combination with 25-azalanosterol (AZA) inhibited parasite growth and this inhibition was restored completely by adding synergistic cholesterol (7.8 μM from lipid-depleted media) with small amounts of ergosterol (1.2 μM) to the medium. These observations are consistent with the proposed requirement for ergosterol as a signaling factor to spark cell proliferation while imported cholesterol or the endogenously formed cholesta-5,7,24-trienol act as bulk membrane components. To test the potential chemotherapeutic importance of disrupting ergosterol biosynthesis using pairs of mechanism-based inhibitors that block two enzymes in the post-squalene segment, parasites were treated with AZA and itraconazole at 1 μM each (ED50 values) resulting in parasite death. Taken together, our results demonstrate that the ergosterol pathway is a prime drug target for intervention in T. brucei infection.

Effects of infection by Trypanosoma cruzi and Trypanosoma rangeli on the reproductive performance of the vector Rhodnius prolixus

The insect Rhodnius prolixus is responsible for the transmission of Trypanosoma cruzi, which is the etiological agent of Chagas disease in areas of Central and South America. Besides this, it can be infected by other trypanosomes such as Trypanosoma rangeli. The effects of these parasites on vectors are poorly understood and are often controversial so here we focussed on possible negative effects of these parasites on the reproductive performance of R. prolixus, specifically comparing infected and uninfected couples. While T. cruzi infection did not delay pre-oviposition time of infected couples at either temperature tested (25 and 30°C) it did, at 25°C, increase the e-value in the second reproductive cycle, as well as hatching rates. Meanwhile, at 30°C, T. cruzi infection decreased the e-value of insects during the first cycle and also the fertility of older insects. When couples were instead infected with T. rangeli, pre-oviposition time was delayed, while reductions in the e-value and hatching rate were observed in the second and third cycles. We conclude that both T. cruzi and T. rangeli can impair reproductive performance of R. prolixus, although for T. cruzi, this is dependent on rearing temperature and insect age. We discuss these reproductive costs in terms of potential consequences on triatomine behavior and survival.

Genome profiling of sterol synthesis shows convergent evolution in parasites and guides chemotherapeutic attack

Sterols are an essential class of lipids in eukaryotes, where they serve as structural components of membranes and play important roles as signaling molecules. Sterols are also of high pharmacological significance: cholesterol-lowering drugs are blockbusters in human health, and inhibitors of ergosterol biosynthesis are widely used as antifungals. Inhibitors of ergosterol synthesis are also being developed for Chagas's disease, caused by Trypanosoma cruzi. Here we develop an in silico pipeline to globally evaluate sterol metabolism and perform comparative genomics. We generate a library of hidden Markov model-based profiles for 42 sterol biosynthetic enzymes, which allows expressing the genomic makeup of a given species as a numerical vector. Hierarchical clustering of these vectors functionally groups eukaryote proteomes and reveals convergent evolution, in particular metabolic reduction in obligate endoparasites. We experimentally explore sterol metabolism by testing a set of sterol biosynthesis inhibitors against trypanosomatids, Plasmodium falciparum, Giardia, and mammalian cells, and by quantifying the expression levels of sterol biosynthetic genes during the different life stages of T. cruzi and Trypanosoma brucei. The phenotypic data correlate with genomic makeup for simvastatin, which showed activity against trypanosomatids. Other findings, such as the activity of terbinafine against Giardia, are not in agreement with the genotypic profile.

Characterization of a second sterol-esterifying enzyme in Toxoplasma highlights the importance of cholesterol storage pathways for the parasite

Lipid bodies are eukaryotic structures for temporary storage of neutral lipids such as acylglycerols and steryl esters. Fatty acyl-CoA and cholesterol are two substrates for cholesteryl ester (CE) synthesis via the ACAT reaction. The intracellular parasite Toxoplasma gondii is incapable of sterol synthesis and unremittingly scavenges cholesterol from mammalian host cells. We previously demonstrated that the parasite expresses a cholesteryl ester-synthesizing enzyme, TgACAT1. In this article, we identified and characterized a second ACAT-like enzyme, TgACAT2, which shares 56% identity with TgACAT1. Both enzymes are endoplasmic reticulum-associated and contribute to CE formation for storage in lipid bodies. While TgACAT1 preferentially utilizes palmitoyl-CoA, TgACAT2 has broader fatty acid specificity and produces more CE. Genetic ablation of each individual ACAT results in parasite growth impairment whereas dual ablation of ACAT1 and ACAT2 is not tolerated by Toxoplasma. ΔACAT1 and ΔACAT2 parasites have reduced CE levels, fewer lipid bodies, and accumulate free cholesterol, which causes injurious membrane effects. Mutant parasites are particularly vulnerable to ACAT inhibitors. This study underlines the important physiological role of ACAT enzymes to store cholesterol in a sterol-auxotrophic organism such as Toxoplasma, and furthermore opens up possibilities of exploiting TgACAT as targets for the development of antitoxoplasmosis drugs.

Endogenous sterol biosynthesis is important for mitochondrial function and cell morphology in procyclic forms of Trypanosoma brucei

Sterol biosynthesis inhibitors are promising entities for the treatment of trypanosomal diseases. Insect forms of Trypanosoma brucei, the causative agent of sleeping sickness, synthesize ergosterol and other 24-alkylated sterols, yet also incorporate cholesterol from the medium. While sterol function has been investigated by pharmacological manipulation of sterol biosynthesis, molecular mechanisms by which endogenous sterols influence cellular processes remain largely unknown in trypanosomes. Here we analyse by RNA interference, the effects of a perturbation of three specific steps of endogenous sterol biosynthesis in order to dissect the role of specific intermediates in proliferation, mitochondrial function and cellular morphology in procyclic cells. A decrease in the levels of squalene synthase and squalene epoxidase resulted in a depletion of cellular sterol intermediates and end products, impaired cell growth and led to aberrant morphologies, DNA fragmentation and a profound modification of mitochondrial structure and function. In contrast, cells deficient in sterol methyl transferase, the enzyme involved in 24-alkylation, exhibited a normal growth phenotype in spite of a complete abolition of the synthesis and content of 24-alkyl sterols. Thus, the data provided indicates that while the depletion of squalene and post-squalene endogenous sterol metabolites results in profound cellular defects, bulk 24-alkyl sterols are not strictly required to support growth in insect forms of T. brucei in vitro.

LDL uptake by Leishmania amazonensis: involvement of membrane lipid microdomains

Leishmania amazonensis lacks a de novo mechanism for cholesterol synthesis and therefore must scavenge this lipid from the host environment. In this study we show that the L. amazonensis takes up and metabolizes human LDL(1) particles in both a time and dose-dependent manner. This mechanism implies the presence of a true LDL receptor because the uptake is blocked by both low temperature and by the excess of non-labelled LDL. This receptor is probably associated with specific microdomains in the membrane of the parasite, such as rafts, because this process is blocked by methyl-β-cyclodextrin (MCBD). Cholesteryl ester fluorescently-labeled LDL (BODIPY-cholesteryl-LDL) was used to follow the intracellular distribution of this lipid. After uptake it was localized in large compartments along the parasite body. The accumulation of LDL was analyzed by flow cytometry using FITC-labeled LDL particles. Together these data show for the first time that L. amazonensis is able to compensate for its lack of lipid synthesis through the use of a lipid importing machinery largely based on the uptake of LDL particles from the host. Understanding the details of the molecular events involved in this mechanism may lead to the identification of novel targets to block Leishmania infection in human hosts.

Lipid metabolism and other metabolic changes in vervet monkeys experimentally infected with Trypanosoma brucei rhodesiense

BACKGROUND

Human African trypanosomiasis is associated with metabolic changes which have not been well characterized.

METHODS

Chlorocebus aethiops were experimentally infected with Trypanosoma brucei rhodesiense and late-stage disease induced at 28 days post-infection. Ear prick blood for glucose determination and blood samples were obtained at weekly intervals for 56 days. Analysis was carried out using dry chemistry analysis.

RESULTS

In early infection, there was a significant increase in creatine kinase, while during early and transitional stage of infection there was a significant decrease in glucose and high-density lipoprotein and an increase in triglyceride levels. In the late stage, there was a significant increase in both total cholesterol and LDL levels.

CONCLUSIONS

Further investigations should focus on levels of total cholesterol during the follow-up period in curatively treated vervet monkeys. Apart from their importance in disease staging, the changes in lipids levels may also affect the pharmacokinetics of some trypanocides.

An expanded family of proteins with BPI/LBP/PLUNC-like domains in trypanosome parasites: an association with pathogenicity?

Trypanosomatids are protozoan parasites that cause human and animal disease. Trypanosoma brucei telomeric ESs (expression sites) contain genes that are critical for parasite survival in the bloodstream, including the VSG (variant surface glycoprotein) genes, used for antigenic variation, and the SRA (serum-resistance-associated) gene, which confers resistance to lysis by human serum. In addition, ESs contain ESAGs (expression-site-associated genes), whose functions, with few exceptions, have remained elusive. A bioinformatic analysis of the ESAG5 gene of T. brucei showed that it encodes a protein with two BPI (bactericidal/permeability-increasing protein)/LBP (lipopolysaccharide-binding protein)/PLUNC (palate, lung and nasal epithelium clone)-like domains and that it belongs to a multigene family termed (GR)ESAG5 (gene related to ESAG5). Members of this family are found with various copy number in different members of the Trypanosomatidae family. T. brucei has an expanded repertoire, with multiple ESAG5 copies and at least five GRESAG5 genes. In contrast, the parasites of the genus Leishmania, which are intracellular parasites, have only a single GRESAG5 gene. Although the amino acid sequence identity between the (GR)ESAG5 gene products between species is as low as 15-25%, the BPI/LBP/PLUNC-like domain organization and the length of the proteins are highly conserved, and the proteins are predicted to be membrane-anchored or secreted. Current work focuses on the elucidation of possible roles for this gene family in infection. This is likely to provide novel insights into the evolution of the BPI/LBP/PLUNC-like domains.

Requirement for acetyl-CoA carboxylase in Trypanosoma brucei is dependent upon the growth environment

Trypanosoma brucei, the causative agent of human African trypanosomiasis, possesses two fatty acid synthesis pathways: a major de novo synthesis pathway in the ER and a mitochondrial pathway. The 2-carbon donor for both pathways is malonyl-CoA, which is synthesized from acetyl-CoA by Acetyl-CoA carboxylase (ACC). Here, we show that T. brucei ACC shares the same enzyme architecture and moderate ∼ 30% identity with yeast and human ACCs. ACC is cytoplasmic and appears to be distributed throughout the cell in numerous puncta distinct from glycosomes and other organelles. ACC is active in both bloodstream and procyclic forms. Reduction of ACC activity by RNA interference (RNAi) resulted in a stage-specific phenotype. In procyclic forms, ACC RNAi resulted in 50-75% reduction in fatty acid elongation and a 64% reduction in growth in low-lipid media. In bloodstream forms, ACC RNAi resulted in a minor 15% decrease in fatty acid elongation and no growth defect in culture, even in low-lipid media. However, ACC RNAi did attenuate virulence in a mouse model of infection. Thus the requirement for ACC in T. brucei is dependent upon the growth environment in two different life cycle stages.

Plasmodium salvages cholesterol internalized by LDL and synthesized de novo in the liver

Our previous morphological studies illustrated the association of sterols with Plasmodium infecting hepatocytes. Because malaria parasites cannot synthesize sterols, they must scavenge these lipids from the host. In this paper, we have examined the source/s of sterols for intrahepatic Plasmodium and evaluated the importance of sterols for liver stage development. We show that Plasmodium continuously diverts cholesterol from hepatocytes until release of merozoites. Removal of plasma lipoproteins from the medium results in a 70% reduction of cholesterol content in hepatic merozoites but these parasites remain infectious in animals. Plasmodium salvages cholesterol that has been internalized by low-density lipoprotein but reduced expression of host low-density lipoprotein receptors by 70% does not influence liver stage burden. Plasmodium is also able to intercept cholesterol synthesized by hepatocytes. Pharmacological blockade of host squalene synthase or downregulation of the expression of this enzyme by 80% decreases by twofold the cholesterol content of merozoites without further impacting parasite development. These data enlighten that, on one hand, malaria parasites have moderate need of sterols for optimal development in hepatocytes and, on the other hand, they can adapt to survive in cholesterol-restrictive conditions by exploitation of accessible sterols derived from alternative sources in hepatocytes to maintain proper infectivity.

The essential neutral sphingomyelinase is involved in the trafficking of the variant surface glycoprotein in the bloodstream form of Trypanosoma brucei

Sphingomyelin is the main sphingolipid in Trypanosoma brucei, the causative agent of African sleeping sickness. In vitro and in vivo characterization of the T. brucei neutral sphingomyelinase demonstrates that it is directly involved in sphingomyelin catabolism. Gene knockout studies in the bloodstream form of the parasite indicate that the neutral sphingomyelinase is essential for growth and survival, thus highlighting that the de novo biosynthesis of ceramide is unable to compensate for the loss of sphingomyelin catabolism. The phenotype of the conditional knockout has given new insights into the highly active endocytic and exocytic pathways in the bloodstream form of T. brucei. Hence, the formation of ceramide in the endoplasmic reticulum affects post-Golgi sorting and rate of deposition of newly synthesized GPI-anchored variant surface glycoprotein on the cell surface. This directly influences the corresponding rate of endocytosis, via the recycling endosomes, of pre-existing cell surface variant surface glycoprotein. The trypanosomes use this coupled endocytic and exocytic mechanism to maintain the cell density of its crucial variant surface glycoprotein protective coat. TbnSMase is therefore genetically validated as a drug target against African trypanosomes, and suggests that interfering with the endocytic transport of variant surface glycoprotein is a highly desirable strategy for drug development against African trypanosomasis.

A standardizable protocol for infection of Rhodnius prolixus with Trypanosoma rangeli, which mimics natural infections and reveals physiological effects of infection upon the insect

Trypanosoma rangeli is a protozoan parasite that shares hosts - mammals and triatomines - with Trypanosoma cruzi, the etiological agent of Chagas disease. Although T. rangeli is customarily considered to be non-pathogenic to human hosts, it is able to produce pathologies in its invertebrate hosts. However, advances are hindered by a lack of standardization of infection procedures and these pathologies need documentation. To establish a suitable, and standardizable, infection protocol, the duration of the fourth instar was evaluated in nymphs infected by injection into the thorax with different concentrations of parasites, and compared with nymphs infected naturally (i.e. orally). We demonstrate that delays in moult were attributable to the presence of the parasite in the haemolymph (vs. the gut) and propose that the protocol presented here simulates closely natural infections. This methodology was then used for the evaluation of physiological parameters and several hitherto unreported effects of T. rangeli infection on Rhodnius prolixus were revealed. Haemolymph volume was greater in infected than uninfected nymphs but this alteration could not be attributed to water retention, since infected insects lost the same amount of water as controls. However, we found that lipid content and fat body weight were both increased in insects infected by T. rangeli. We propose that this is due to the parasite's sequestration of host blood lipids and carrier proteins. With these findings, we have taken a few first steps to unravelling physiological details of the host-parasite interaction. We suggest future directions towards a fuller understanding of mechanistic and adaptive aspects of triatomine-trypanosomatid interactions.

Novel roles for ATP-binding cassette G transporters in lipid redistribution in Toxoplasma

Toxoplasma is a protozoan parasite proficiently adapted to thrive in a parasitophorous vacuole (PV) formed in the cytoplasm of a large variety of mammalian cells. As an actively dividing organism, the parasite must adjust the lipid composition of its membranes to preserve organelle vitality and expand the size of the PV membrane to accommodate growing progeny. We showed that Toxoplasma takes up host lipids and can expel major lipids in an ATP-dependent process. In order to provide detailed mechanistic insights into lipid trafficking phenomena relevant to Toxoplasma biology, we characterized six parasite ATP-binding cassette (ABC) G family transporters and investigated their potential contribution to lipid homeostatic processes. All these transporters are expressed in the parasite and five of them are upregulated upon exposure to sterols. Four ABCG are localized to secretory organelles and the plasma membrane, and promote cholesterol and phospholipid efflux, reflecting the importance in exportation of large amounts of lipids into the PV. Interestingly, one ABCG that is associated with vesicles in the PV and the plasma membrane acts as a cholesterol importer. This last finding expands our current view on the role of some ABCG transporters in eukaryotic sterol influx.

The major insect lipoprotein is a lipid source to mosquito stages of malaria parasite

Once mosquito midgut barrier was crossed malaria parasite faces a extensive metabolic developmental program in order to ensure its transmission. In the hemolymph of the mosquito the dynamics of lipid metabolism is conducted by a major lipoprotein, lipophorin (Lp). It was recently shown that Lp is engaged in the mosquito immune response to parasite infection. However, it is not clear if Lp is uptaken by the parasite. Here, we show that oocysts are able to uptake mosquito Lp. The uptake of FITC-labeled Lp was demonstrated in midgut-associated oocysts. Alternatively, to confirm Lp incorporation by oocysts we have conducted another set of experiments with iodinated Lp ((125)I-Lp). Oocysts were able to incorporate (125)I-Lp and the process is both time and temperature dependent. This set of results indicated that no matter oocysts are attached to mosquito midgut wall they bear a lipid sequestering machinery from its surroundings. Phospholipid transfer to sporozoites was also demonstrated. In conclusion, these results demonstrate for the first time that malaria parasite undergoes lipid uptake while in the invertebrate host.

Role of an ancestral d-bifunctional protein containing two sterol-carrier protein-2 domains in lipid uptake and trafficking in Toxoplasma

The inability to synthesize cholesterol is universal among protozoa. The intracellular pathogen Toxoplasma depends on host lipoprotein-derived cholesterol to replicate in mammalian cells. Mechanisms of cholesterol trafficking in this parasite must be important for delivery to proper organelles. We characterized a unique d-bifunctional protein variant expressed by Toxoplasma consisting of one N-terminal d-3-hydroxyacyl-CoA dehydrogenase domain fused to two tandem sterol carrier protein-2 (SCP-2) domains. This multidomain protein undergoes multiple cleavage steps to release free SCP-2. The most C-terminal SCP-2 carries a PTS1 that directs the protein to vesicles before processing. Abrogation of this signal results in SCP-2 accumulation in the cytoplasm. Cholesterol specifically binds to parasite SCP-2 but with 10-fold lower affinity than phosphatidylcholine. In mammalian cells and Toxoplasma, the two parasite SCP-2 domains promote the circulation of various lipids between organelles and to the surface. Compared with wild-type parasites, TgHAD-2SCP-2-transfected parasites replicate faster and show enhanced uptake of cholesterol and oleate, which are incorporated into neutral lipids that accumulate at the basal end of Toxoplasma. This work provides the first evidence that the lipid transfer capability of an ancestral eukaryotic SCP-2 domain can influence the lipid metabolism of an intracellular pathogen to promote its multiplication in mammalian cells.

The role and characterization of phospholipase A1 in mediating lysophosphatidylcholine synthesis in Trypanosoma brucei

Lysophospholipids are ubiquitous intermediates in a variety of metabolic and signalling pathways in eukaryotic cells. We have reported recently that lysoglycerophosphatidylcholine (lyso-GPCho) synthesis in the insect form of the ancient eukaryote Trypanosoma brucei is mediated by a novel phospholipase A1 (TbPLA1). In the present study, we show that despite equal levels of TbPLA1 gene expression in wild-type insect and bloodstream trypomastigotes, both TbPLA1 enzyme levels and lysoGPCho metabolites are approx. 3-fold higher in the bloodstream form. Both of these parasite stages synthesize identical molecular species of lysoGPCho. TbPLA1 null mutants in the bloodstream form of the parasite are viable, but are deficient in lysoGPCho synthesis, a defect that can be overcome by the expression of an ectopic copy of TbPLA1. The biochemical attributes of TbPLA1-mediated lysoGPCho synthesis were examined in vitro using recombinant TbPLA1. Although TbPLA1 possesses an active-site serine residue, it is insensitive to serine-modifying reagents, such as di-isopropyl fluorophosphate and PMSF, a characteristic shared by lipases that possess lid-sheltered catalytic triads. TbPLA1 does not require metal co-factors for activity, but it does require interfacial activation prior to catalysis. Results from size-exclusion chromatography and binding kinetics analysis revealed that TbPLA1 activation by Triton X-100/GPCho mixed micelle surfaces was not specific and did not require the pre-formation of a specific enzyme-substrate complex to achieve surface binding.

A fatty-acid synthesis mechanism specialized for parasitism

Most cells use either a type I or type II synthase to make fatty acids. Trypanosoma brucei, the sleeping sickness parasite, provides the first example of a third mechanism for this process. Trypanosomes use microsomal elongases to synthesize fatty acids de novo, whereas other cells use elongases to make long-chain fatty acids even longer. The modular nature of the pathway allows synthesis of different fatty-acid end products, which have important roles in trypanosome biology. Indeed, this newly discovered mechanism seems ideally suited for the parasitic lifestyle.

Comparative proteomics of glycosomes from bloodstream form and procyclic culture form Trypanosoma brucei brucei

Peroxisomes are present in nearly every eukaryotic cell and compartmentalize a wide range of important metabolic processes. Glycosomes of Kinetoplastid parasites are peroxisome-like organelles, characterized by the presence of the glycolytic pathway. The two replicating stages of Trypanosoma brucei brucei, the mammalian bloodstream form (BSF) and the insect (procyclic) form (PCF), undergo considerable adaptations in metabolism when switching between the two different hosts. These adaptations involve also substantial changes in the proteome of the glycosome. Comparative (non-quantitative) analysis of BSF and PCF glycosomes by nano LC-ESI-Q-TOF-MS resulted in the validation of known functional aspects of glycosomes and the identification of novel glycosomal constituents.

Adaptations in the lipid metabolism of the protozoan parasite Trypanosoma brucei

Trypanosomes are unicellular parasites and like all decent parasites, they try to obtain from the host as much material as possible, including lipids. However, the needs of a parasite are not always the same as those of the host, and therefore, mostly, some biosynthetic work still has to be done by the parasite itself. Very often at least modifications of the lipid components that are acquired from the host have to be made. Furthermore, next to the lipids Trypanosoma brucei indeed obtains from the host, some other lipid components have to be synthesized de novo. Especially the processes where the metabolism of T. brucei differs from that of the host, will be discussed, as at least some of them are excellent targets for the development of urgently needed new chemotherapeutics.

Novel antitrypanosomal agents

Trypanosomes are the causative agents of Chagas' disease in Central and South America and sleeping sickness in sub-Saharan Africa. The current chemotherapy of the human trypanosomiases relies on only six drugs, five of which were developed > 30 years ago. In addition, these drugs display undesirable toxic side effects and the emergence of drug-resistant trypanosomes has been reported. Therefore, the development of new drugs in the treatment of Chagas' disease and sleeping sickness is urgently required. This article summarises the recent progress in identifying novel lead compounds for antitrypanosomal chemotherapy. Particular emphasis is placed on those agents showing promising, selective antitrypanosomal activity.

Peculiarities of host cholesterol transport to the unique intracellular vacuole containing Toxoplasma

The intracellular protozoan Toxoplasma gondii is auxotrophic for low-density lipoprotein (LDL)-derived cholesterol (C). We previously showed that T. gondii scavenges this essential lipid from host endolysosomal compartments and that C delivery to the parasitophorous vacuole (PV) does not require transit through host Golgi or endoplasmic reticulum. In this study, we explore the itinerary of C from the host endolysosomes to the PV. Labeled C incorporated into LDL is rapidly detected in intravacuolar parasites and partially esterified by the parasites. In contrast to diverse mammalian organelles, the post-endolysosomal transfer of C to the PV does not involve the host plasma membrane as an intermediate. Nevertheless, the PV membrane is accessible to extracellular sterol acceptors, suggesting C trafficking from intracellular parasites to host plasma membrane. C movement to the PV requires temperatures permissive for vesicular transport, metabolic energy and functional microtubules. Host caveolae vesicles and the sterol carrier protein-2 do not participate in this process. Proteolytic treatment of purified PV or free parasites abolishes C acquisition by the parasites. Altogether, these results support a vesicular transport system from host endolysosomes to the PV, and a requirement for PV membrane and parasite plasma membrane proteins in C delivery to T. gondii.

Trypanosoma rangeli: characterization of a Mg-dependent ecto ATP-diphosphohydrolase activity

In this work we describe the ability of living Trypanosoma rangeli to hydrolyze extracellular ATP. In these intact parasites whose viability was assessed before and after the reactions by motility and by Trypan blue dye exclusion, there was a low level of ATP hydrolysis in the absence of any divalent metal (1.53+/-0.12 nmol P(i)/h x 10(7) cells). The ATP hydrolysis was stimulated by MgCl(2) and the Mg-dependent ecto-ATPase activity was 5.24+/-0.64 nmol P(i)/h x 10(7) cells. The Mg-dependent ecto-ATPase activity was linear with cell density and with time for at least 60 min. This stimulatory effect on the ATP hydrolysis was also observed when MgCl(2) was replaced by MnCl(2), but not by CaCl(2), SrCl(2), and ZnCl(2). The apparent K(m) for Mg-ATP2- was 0.53+/-0.11 mM. The optimum pH for the T. rangeli Mg-dependent ecto-ATPase activity lies in the alkaline range. This ecto-ATPase activity was insensitive to inhibitors of other ATPase and phosphatase activities, such as oligomycin, sodium azide, bafilomycin A1, ouabain, furosemide, vanadate, molybdate, sodium fluoride, tartrate, and levamizole. To confirm that this Mg-dependent ATPase was an ecto-ATPase, we used an impermeant inhibitor, DIDS (4, 4'-diisothiocyanostylbene 2'-2'-disulfonic acid) as well as suramin, an antagonist of P2 purinoreceptors and inhibitor of some ecto-ATPases. These two reagents inhibited the Mg(2+)-dependent ATPase activity in a dose-dependent manner. This ecto-ATPase activity was stimulated by carbohydrates involved in the attachment/invasion of salivary glands of Rhodnius prolixus and by lipophorin, an insect lipoprotein circulating in the hemolymph.

Host cell lipids control cholesteryl ester synthesis and storage in intracellular Toxoplasma

The intracellular protozoan Toxoplasma gondii lacks a de novo mechanism for cholesterol synthesis and therefore must scavenge this essential lipid from the host environment. In this study, we demonstrated that T. gondii diverts cholesterol from low-density lipoproteins for cholesteryl ester synthesis and storage in lipid bodies. We identified and characterized two isoforms of acyl-CoA:cholesterol acyltransferase (ACAT)-related enzymes, designated TgACAT1alpha and TgACAT1beta in T. gondii. Both proteins are coexpressed in the parasite, localized to the endoplasmic reticulum and participate in cholesteryl ester synthesis. In contrast to mammalian ACAT, TgACAT1alpha and TgACAT1beta preferentially incorporate palmitate into cholesteryl esters and present a broad sterol substrate affinity. Mammalian ACAT-deficient cells transfected with either TgACAT1alpha or TgACAT1beta are restored in their capability of cholesterol esterification. TgACAT1alpha produces steryl esters and forms lipid bodies after transformation in a Saccharomyces cerevisiae mutant strain lacking neutral lipids. In addition to their role as ACAT substrates, host fatty acids and low-density lipoproteins directly serve as Toxoplasma ACAT activators by stimulating cholesteryl ester synthesis and lipid droplet biogenesis. Free fatty acids significantly increase TgACAT1alpha mRNA levels. Selected cholesterol esterification inhibitors impair parasite growth by rapid disruption of plasma membrane. Altogether, these studies indicate that host lipids govern neutral lipid synthesis in Toxoplasma and that interference with mechanisms of host lipid storage is detrimental to parasite survival in mammalian cells.

Both of the Rab5 subfamily small GTPases of Trypanosoma brucei are essential and required for endocytosis

Endocytosis is an essential process in Trypanosoma brucei and all evidence suggests it is exclusively clathrin-mediated. The trypanosome genome encodes two Rab5 proteins, small GTPases that play a role in very early stages of endocytosis. In the mammalian bloodstream stage TbRAB5A localises to compartments containing internalised antibody, variant surface glycoprotein (VSG) and transferrin, whilst TbRAB5B localises to compartments containing the transmembrane protein ISG(100). Dominant-active forms of TbRAB5A stimulate endocytosis in procyclic forms and alter the kinetics of anti-VSG antibody and transferrin turnover in bloodstream stages. Similar mutants of TbRAB5B increase fluid phase uptake in procyclic cells but do not significantly affect endocytosis in bloodstream forms. Here, we use RNA interference to evaluate the relative importance of TbRAB5A and TbRAB5B and show that both GTPases are essential in the bloodstream form. Depletion of either TbRAB5A or TbRAB5B results in morphological abnormalities, including enlargement of the flagellar pocket, consistent with a potent block to endocytosis. Also, RNAi compromises transferrin accumulation in both cases but induces distinct patterns of mislocalisation of endosomal markers. Finally, RNAi of either TbRAB5A or TbRAB5B results in a decrease in levels of clathrin. Taken together, these data indicate that both TbRAB5A and TbRAB5B are required for endocytosis in trypanosomes and demonstrate that there are multiple essential endocytic routes in this organism.

Trypanosoma rangeli uptakes the main lipoprotein from the hemolymph of its invertebrate host

During its life cycle Trypanosoma rangeli crosses the hemolymph of its invertebrate host. In the present study, we demonstrate for the first time the uptake of lipophorin (Lp), the main lipid-transporting particle of insect hemolymph. We observed that living T. rangeli parasites uptake lipids from both 32P- and 3H-, or 125I-labeled Lp. However, the parasites do not uptake any other hemolymphatic protein such as 32P-labeled vitellogenin. The presence of a specific receptor to Lp in the parasite surface is suggested based on experiments using 125I-Lp. We also investigated the intracellular fate of lipids using Texas Red-labeled phosphatidylethanolamine-Lp. Parasites were observed under confocal microscope and displayed fluorescent-labeled lipids close to the flagellar pocket and in vesicles at the posterior region. In conclusion, this study raises a novel set of molecular events which takes place during vector-parasite interaction.

Perkinsus marinus, a protozoan parasite of the Eastern oyster (Crassostrea virginica): effects of temperature on the uptake and metabolism of fluorescent lipid analogs and lipase activities

The effects of temperature on the uptake and metabolism of fluorescent labeled palmitic acid (FLC16) and phosphatidylcholine (FLPC) and lipase activities in the oyster protozoan parasite, Perkinsus marinus, meront stage were tested at 10, 18, and 28 degrees C. Temperature significantly affected not only the uptake, assimilation, and metabolism of both FLC16 and FLPC in P. marinus, but also its triacylglycerol (TAG) lipase activities. The incorporation of both FLC16 and FLPC increased with temperature and paralleled the increase in the amount of total fatty acids in P. marinus meront cultures. The incorporation of FLC16 was higher than FLPC at all temperatures. The percentage of FLC16 metabolized to TAG was significantly higher at higher temperatures. Trace amounts of incorporated FLC16 were detected in monoacylglycerol (MAG) and PC at 18 and 28 degrees C. P. marinus meronts metabolized FLPC to TAG, diacylglycerol (DAG), monoacylglycerol (MAG), free fatty acids (FFA), phosphatidylethanolamine (PE), and cardiolipin (CL). The conversion of FLPC to TAG and PE was highest at 28 degrees C. The relative proportions of individual fatty acids and total saturated, monounsaturated and polyunsaturated fatty acids changed with temperatures. While total saturated fatty acids (SAFAs) increased with temperature, total monounsaturated fatty acids (MUFAs) decreased with temperature. Total polyunsaturated fatty acids (PUFAs) increased from 28 to 18 degrees C. The findings of increase of total SAFAs and decrease of total MUFAs with the increase of temperatures and upward shift of total PUFAs from 28 to 18 degrees C suggest that, as in other organisms, P. marinus is capable of adapting to changes in environmental temperatures by modifying its lipid metabolism. Generally, higher lipase activities were noted at higher cultivation temperatures. Both TAG lipase and phospholipase activities were detected in P. marinus cells and their extra cellular products (ECP), but phospholipase activities in both the cell pellets and ECP were very low. Also, lipase activities were much lower in ECP than in the cells. The observations of low metabolism, bioconversion of incorporated fluorescent lipid analogs and lipase activities at low temperatures are consistent with the low in vitro growth rate and low infectivity of P. marinus at low temperatures.

Host but not parasite cholesterol controls Toxoplasma cell entry by modulating organelle discharge

Host cell cholesterol is implicated in the entry and replication of an increasing number of intracellular microbial pathogens. Although uptake of viral particles via cholesterol-enriched caveolae is increasingly well described, the requirement of cholesterol for internalization of eukaryotic pathogens is poorly understood and is likely to be partly organism specific. We examined the role of cholesterol in active host cell invasion by the protozoan parasite Toxoplasma gondii. The parasitophorous vacuole membrane (PVM) surrounding T. gondii contains cholesterol at the time of invasion. Although cholesterol-enriched parasite apical organelles termed rhoptries discharge at the time of cell entry and contribute to PVM formation, surprisingly, rhoptry cholesterol is not necessary for this process. In contrast, host plasma membrane cholesterol is incorporated into the forming PVM during invasion, through a caveolae-independent mechanism. Unexpectedly, depleting host cell plasma membrane cholesterol blocks parasite internalization by reducing the release of rhoptry proteins that are necessary for invasion. Cholesterol back-addition into host plasma membrane reverses this inhibitory effect of depletion on parasite secretion. These data define a new mechanism by which host cholesterol specifically controls entry of an intracellular pathogen.