Trypanosoma cruzi: adrenergic modulation of cyclic AMP role in proliferation and differentiation of amastigotes in vitro

Utilization of proliferable extracellular amastigotes for transient gene expression, drug sensitivity assay, and CRISPR/Cas9-mediated gene knockout in Trypanosoma cruzi

Trypanosoma cruzi has three distinct life cycle stages; epimastigote, trypomastigote, and amastigote. Amastigote is the replication stage in host mammalian cells, hence this stage of parasite has clinical significance in drug development research. Presence of extracellular amastigotes (EA) and their infection capability have been known for some decades. Here, we demonstrate that EA can be utilized as an axenic culture to aid in stage-specific study of T. cruzi. Amastigote-like property of axenic amastigote can be sustained in LIT medium at 37°C at least for 1 week, judging from their morphology, amastigote-specific UTR-regulated GFP expression, and stage-specific expression of selected endogenous genes. Inhibitory effect of benznidazole and nifurtimox on axenic amastigotes was comparable to that on intracellular amastigotes. Exogenous nucleic acids can be transfected into EA via conventional electroporation, and selective marker could be utilized for enrichment of transfectants. We also demonstrate that CRISPR/Cas9-mediated gene knockout can be performed in EA. Essentiality of the target gene can be evaluated by the growth capability of the knockout EA, either by continuation of axenic culturing or by host infection and following replication as intracellular amastigotes. By taking advantage of the accessibility and sturdiness of EA, we can potentially expand our experimental freedom in studying amastigote stage of T. cruzi.

Megazol and its bioisostere 4H-1,2,4-triazole: comparing the trypanocidal, cytotoxic and genotoxic activities and their in vitro and in silico interactions with the Trypanosoma brucei nitroreductase enzyme

Megazol (7) is a 5-nitroimidazole that is highly active against Trypanosoma cruzi and Trypanosoma brucei, as well as drug-resistant forms of trypanosomiasis. Compound 7 is not used clinically due to its mutagenic and genotoxic properties, but has been largely used as a lead compound. Here, we compared the activity of 7 with its 4H-1,2,4-triazole bioisostere (8) in bloodstream forms of T. brucei and T. cruzi and evaluated their activation by T. brucei type I nitroreductase (TbNTR) enzyme. We also analysed the cytotoxic and genotoxic effects of these compounds in whole human blood using Comet and fluorescein diacetate/ethidium bromide assays. Although the only difference between 7 and 8 is the substitution of sulphur (in the thiadiazole in 7) for nitrogen (in the triazole in 8), the results indicated that 8 had poorer antiparasitic activity than 7 and was not genotoxic, whereas 7 presented this effect. The determination of Vmax indicated that although 8 was metabolised more rapidly than 7, it bounds to the TbNTR with better affinity, resulting in equivalent kcat/KM values. Docking assays of 7 and 8 performed within the active site of a homology model of the TbNTR indicating that 8 had greater affinity than 7.

Brazilian Green Propolis: Effects In Vitro and In Vivo on Trypanosoma cruzi

The composition of a Brazilian green propolis ethanolic extract (Et-Bra) and its effect on Trypanosoma cruzi trypomastigotes and other pathogenic microorganisms have already been reported. Here, we further investigated Et-Bra targets in T. cruzi and its effect on experimental infection of mice. The IC(50)/4 days for inhibition of amastigote proliferation was 8.5 ± 1.8 μg mL(-1), with no damage to the host cells. In epimastigotes Et-Bra induced alterations in reservosomes, Golgi complex and mitochondrion. These effects were confirmed by flow cytometry analysis. In trypomastigotes, Et-Bra led to the loss of plasma membrane integrity. The in vitro studies indicate that Et-Bra interferes in the functionality of the plasma membrane in trypomastigotes and of reservosomes and mitochondrion in epimastigotes. Acutely infected mice were treated orally with Et-Bra and the parasitemia, mortality and GPT, GOT, CK and urea levels were monitored. The extract (25-300 mg kg(-1) body weight/day for 10 days) reduced the parasitemia, although not at significant levels; increased the survival of the animals and did not induce any hepatic, muscular lesion or renal toxicity. Since Et-Bra was not toxic to the animals, it could be assayed in combination with other drugs. Et-Bra could be a potential metacyclogenesis blocker, considering its effect on reservosomes, which are an important energy source during parasite differentiation.

Mitochondrial disruption and DNA fragmentation in Trypanosoma cruzi induced by naphthoimidazoles synthesized from beta-lapachone

Three naphthoimidazoles presenting aromatic groups attached to the imidazole ring were the most active against trypomastigotes of Trypanosoma cruzi between 45 derivatives from beta-lapachone. N1 is active against the three forms of the parasite. In this work, we investigated N2 and N3 and analyzed the effect of the three derivatives on metacyclogenesis, endocytosis, and cell cycle. In epimastigotes, N2 and N3 blocked the cell cycle, inhibited succinate cytochrome c reductase, metacyclogenesis, and induced damage to mitochondrion, Golgi, and reservosomes. In treated trypomastigotes, there were alterations in the mitochondrion, nucleus and kinetoplast, and DNA fragmentation. Preincubation with cysteine protease inhibitors reversed the effect of N1, N2, and N3. Such reversion and ultrastructural alterations suggest the involvement of autophagy in parasite death. Ultrastructural, flow cytometry, and biochemical studies suggest that naphthoimidazoles interferes with the energetic metabolism and induces DNA fragmentation.

Trypanosoma cruzi epimastigotes: regulation of myo-inositol transport by effectors of protein kinases A and C

Inositol is the precursor for most Trypanosoma cruzi surface molecules, including phosphoinositides, glycosylinositolphospholipids and glycosylphosphatidylinositol anchors. As the parasite is an inositol auxotroph, the inositol transport system might be a potential target for new trypanocide drugs, as some of its properties are different from its mammalian counterpart. Here, we investigated the modulation exerted by effectors of PKA and PKC on this transport system to comply with the parasite physiology. Pre-incubation of the cells with either dibutyryl-cyclic AMP (25 microM) or forskolin (30 microM) decreased the myo-inositol uptake by half, this effect being reversed by KT5720 (PKA inhibitor). Conversely, pre-incubation of the cells with PMA (2.8 microg/ml) or serum (5%) had a approximately 50% stimulation in myo-inositol uptake, being this effect reversed by staurosporine (0.5 microM) or sphingosine (10 microM). These results allow us to conclude that the myo-inositol transport system in T. cruzi epimastigotes is inhibited by PKA and stimulated by PKC effectors.

The effect of Bulgarian propolis against Trypanosoma cruzi and during its interaction with host cells

Propolis has shown activity against pathogenic microorganisms that cause diseases in humans and animals. The ethanol (Et-Blg) and acetone (Ket-Blg) extracts from a Bulgarian propolis, with known chemical compositions, presented similar activity against tissue culture-derived amastigotes. The treatment of Trypanosoma cruzi-infected skeletal muscle cells with Et-Blg led to a decrease of infection and of the intracellular proliferation of amastigotes, while damage to the host cell was observed only at concentration 12.5 times higher than those affecting the parasite. Ultrastructural analysis of the effect of both extracts in epimastigotes revealed that the main targets were the mitochondrion and reservosomes. Et-Blg also affected the mitochondrion-kinetoplast complex in trypomastigotes, offering a potential target for chemotherapeutic agents.

Ultrastructural analysis of edelfosine-treated trypomastigotes and amastigotes of Trypanosoma cruzi

We have previously reported that epimastigote forms of Trypanosoma cruzi treated with the lysophospholipid analogues (LPAs) edelfosine (ET-18), ilmofosine, and miltefosine suffered alterations in plasma membrane, mitochondrion, and lipid synthesis. In this work, ET-18 induced membrane damage in trypomastigotes and amastigotes. Incubation of epimastigotes and trypomastigotes with the three LPAs led to membrane permeabilization, which was abolished by serum addition. Treatment for 24 h in culture medium interfered the with mitochondrial status of epimastigotes, with no effect in trypomastigotes, in agreement with ultrastructural data. LPAs induced alterations in the plasma membrane of the three forms of T. cruzi and in the mitochondria of epimastigotes, suggesting that these organelles are potential targets of these analogues.

A novel protein phosphatase 2A (PP2A) is involved in the transformation of human protozoan parasite Trypanosoma cruzi

Here we provide evidence for a critical role of PP2As (protein phosphatase 2As) in the transformation of Trypanosoma cruzi. In axenic medium at pH 5.0, trypomastigotes rapidly transform into amastigotes, a process blocked by okadaic acid, a potent PP2A inhibitor, at concentrations as low as 0.1 microM. 1-Norokadaone, an inactive okadaic acid analogue, did not affect the transformation. Electron microscopy studies indicated that okadaic acid-treated trypomastigotes had not undergone ultrastructural modifications, reinforcing the idea that PP2A inhibits transformation. Using a microcystin-Sepharose affinity column we purified the native T. cruzi PP2A. The enzyme displayed activity against 32P-labelled phosphorylase a that was inhibited in a dose-dependent manner by okadaic acid. The protein was also submitted to MS and, from the peptides obtained, degenerate primers were used to clone a novel T. cruzi PP2A enzyme by PCR. The isolated gene encodes a protein of 303 amino acids, termed TcPP2A, which displayed a high degree of homology (86%) with the catalytic subunit of Trypanosoma brucei PP2A. Northern-blot analysis revealed the presence of a major 2.1-kb mRNA hybridizing in all T. cruzi developmental stages. Southern-blot analysis suggested that the TcPP2A gene is present in low copy number in the T. cruzi genome. These results are consistent with the mapping of PP2A genes in two chromosomal bands by pulsed-field gel electrophoresis and chromoblot hybridization. Our studies suggest that in T. cruzi PP2A is important for the complete transformation of trypomastigotes into amastigotes during the life cycle of this protozoan parasite.

Molecular cloning and expression of the catalytic subunit of protein kinase A from Trypanosoma cruzi

The activation of protein kinase A (cyclic adenosine monophosphate-dependent protein kinase) by cyclic adenosine monophosphate is believed to play an important role in regulating the growth and differentiation of Trypanosoma cruzi. A PCR using degenerate oligonucleotide primers against conserved motifs in the VIb and VIII subdomains of the ACG family of serine/threonine protein kinases was utilised to amplify regions corresponding to the parasite homologue of the protein kinase A catalytic subunit. This putative protein kinase A fragment was used to isolate the entire gene from T. cruzi genomic libraries. The deduced 329 amino acid sequence of this gene contained all of the signature motifs of known protein kinase A catalytic subunit proteins. The recombinant protein expressed in Escherichia coli was shown to phosphorylate Kemptide, a synthetic peptide substrate of protein kinase A, in a protein kinase inhibitor (PKI)-inhibitory manner. Immunoprecipitation with polyclonal antisera raised against recombinant protein of this gene was able to pull-down PKI-inhibitory phosphotransferase activity from epimastigote lysates. Immunoblot and Northern blot analyses, in combination with enzyme activity assays, revealed that this gene was a stage-regulated enzyme in T. cruzi with higher levels and activity being present in epimastigotes compared with amastigotes or trypomastigotes. Overall these studies indicate that the cloned gene encodes an authentic protein kinase A catalytic subunit from T. cruzi and are the first demonstration of PKI-inhibitory phosphotransferase activity in an expressed protozoan protein kinase A catalytic subunit.

Effect of the alkyl-lysophospholipids on the proliferation and differentiation of Trypanosoma cruzi

Alkyl-lysophospholipids (ALPs), designed as potential immunomodulators, have been shown to be cytotoxic for a variety of tumour cells and are under clinical studies for cancer chemotherapy. ET-18-OCH(3), hexadecylphosphocholine and ilmofosine were assayed against the three forms of Trypanosoma cruzi. Incubation with bloodstream trypomastigotes resulted, under different experimental conditions, in higher activity of the compounds in comparison with crystal violet. The ED(50)/24 h values were 13.4+/-2.8 microM and 11. 7+/-0.6 microM for amastigotes and epimastigotes, respectively. ET-18-OCH(3) (0.3 and 0.6 microM) inhibited the differentiation of epimastigotes to trypomastigotes (Dm28C clone) in the range 40-57%. This drug (3.75-15 microM) also caused a time- and dose-dependent inhibition of the intracellular proliferation of amastigotes in heart muscle cells with ED(50) values of 14.3+/-4.2, 8.9+/-1.9 and 6. 8+/-0.4 microM, after 1, 2 and 3 days of treatment. Pre-treatment of the parasite with this drug inhibited its interiorization into the host cell. Interestingly, the intracellular differentiation of amastigotes to trypomastigotes was not hampered by the drug. The present results demonstrate the lytic effect of ALPs on the three forms of T. cruzi, as well as the inhibition of both the differentiation to the infective form and the proliferation of parasites interiorized in heart cells. Ultrastructural analysis of epimastigotes treated with the three ALPs showed extensive blebing of the flagellar membrane. As described in tumour cells, the membrane seems to be a primary target of the drugs.

Characterization of cyclic AMP phosphodiesterases in Leishmania mexicana and purification of a soluble form

The cyclic AMP phosphodiesterase (PDE) activity in Leishmania mexicana is mainly located (>95%) in the soluble fraction of the cell. The intact parasite, as well as plasma membranes, showed PDE activity, probably indicating that at least part of the activity in the particulate fraction resides on the parasite cell surface, with its catalytic domain facing the extracellular moiety. For the first time, a highly specific cAMP phosphodiesterase (PDE) was purified from the soluble fraction to apparent homogeneity after a single step 2239-fold purification using pseudo-affinity chromatography on Cibacron Blue 3GA agarose. The enzyme was identified as a 61-kDa protein on SDS-PAGE, with a K(m) of 277 microM at 30 degrees C (optimum temperature). The native enzyme protein showed an apparent molecular size of approximately 200000 estimated by molecular sieve chromatography on Sephacryl S-300. Further characterization of the PDE activity present in the soluble fraction shows that the enzyme requires Mg(2+) for maximal activity. Furthermore, no activity was detected when assayed at pHs below 6.0, but above this value it increased dramatically, reaching the optimum at pH 7.2. On the basis of the K(m) and PDE activity in presence of specific drugs or modulators such as rolipram, OPC-3911, cGMP, IBMX, zaprinast, theophylline, caffeine and Ca(2+)/calmodulin, this enzyme does not seem to conform to any of the ten previously described Class I PDE families but to the PDE class II (or non-mammalian PDEs) similar to the those found in Candida albicans, Dictyostelium discoideum, Saccharomyces cerevisiae or Vibrio fischeri.

Identification of novel serine/threonine protein phosphatases in Trypanosoma cruzi: a potential role in control of cytokinesis and morphology

We cloned two novel Trypanosoma cruzi proteins by using degenerate oligonucleotide primers prepared against conserved domains in mammalian serine/threonine protein phosphatases 1, 2A, and 2B. The isolated genes encoded proteins of 323 and 330 amino acids, respectively, that were more homologous to the catalytic subunit of human protein phosphatase 1 than to those of human protein phosphatase 2A or 2B. The proteins encoded by these genes have been tentatively designated TcPP1alpha and TcPP1beta. Northern blot analysis revealed the presence of a major 2.3-kb mRNA transcript hybridizing to each gene in both the epimastigote and metacyclic trypomastigote developmental stages. Southern blot analysis suggests that each protein phosphatase 1 gene is present as a single copy in the T. cruzi genome. The complete coding region for TcPP1beta was expressed in Escherichia coli by using a vector, pTACTAC, with the trp-lac hybrid promoter. The recombinant protein from the TcPP1beta construct displayed phosphatase activity toward phosphorylase a, and this activity was preferentially inhibited by calyculin A (50% inhibitory concentration [IC(50)], approximately 2 nM) over okadaic acid (IC(50), approximately 100 nM). Calyculin A, but not okadaic acid, had profound effects on the in vitro replication and morphology of T. cruzi epimastigotes. Low concentrations of calyculin A (1 to 10 nM) caused growth arrest. Electron microscopic studies of the calyculin A-treated epimastigotes revealed that the organisms underwent duplication of organelles, including the flagellum, kinetoplast, and nucleus, but were incapable of completing cell division. At concentrations higher than 10 nM, or upon prolonged incubation at lower concentrations, the epimastigotes lost their characteristic elongated spindle shape and had a more rounded morphology. Okadaic acid at concentrations up to 1 microM did not result in growth arrest or morphological alterations to T. cruzi epimastigotes. Calyculin A, but not okadaic acid, was also a potent inhibitor of the dephosphorylation of (32)P-labeled phosphorylase a by T. cruzi epimastigotes and metacyclic trypomastigote extracts. These inhibitor studies suggest that in T. cruzi, type 1 protein phosphatases are important for the completion of cell division and for the maintenance of cell shape.

Phospholipid signalling pathways in Trypanosoma cruzi growth control

The role of phospholipids (PLs) in the signal transduction pathways that are activated by a mitogenic stimulus (foetal calf serum) in Trypanosoma cruzi epimastigotes (EPI) was investigated. Only phosphatidylinositol-bis-phosphate was significantly altered in this process. Other phosphoinositides, including major PLs such as phosphatidylcholine and phosphatidylethanolamine, were unaltered. Lysophosphatidic acid, reported to be the primary active substance in effects of serum in other systems, had no mitogenic activity when added to epimastigote cultures. Involvement of phosphoinositide-specific phospholipase C was established using the inhibitors ET-18-OCH3 and U73122, which prevented phosphatidylinositol-bis-phosphate hydrolysis; the latter compound decreased T. cruz proliferation. The intracellular signalling downstream to the phospholipase C was mediated by Ca2+/PL-dependent protein kinase and Ca2+/calmodulin-dependent protein kinase II, judging from the marked decrease in replication caused by the specific inhibitors staurosporine, derythro-sphingosine and KN-93. Previous reports have demonstrated a dual control of cell growth in EPI, whose proliferation is stimulated by the activation of a phospholipase C system and inhibited by activation of an adenylate cyclase system. Investigating this 'cross-talk' phenomenon, we observed that an increase in intracellular cAMP inhibited growth mediated by a cAMP-dependent protein kinase, but did not cause PL alterations, and also did not prevent the effect of serum on them.

Propolis extracts are effective against Trypanosoma cruzi and have an impact on its interaction with host cells

Propolis, a natural resin produced by honey bees, that displays strong antimicrobial activity, has been used as a chemotherapeutic agent since ancient times. The anti-protozoan properties of different propolis extracts were studied regarding T. cruzi and its interaction with host cells. Ethanolic (EEP) and dimethylsulphoxide extracts (DEP) were both active against the three forms of the parasite, with the former being more active than the latter against the vertebrate forms, amastigotes and trypomastigotes. Total lysis of bloodstream trypomastigotes was observed after 24 h in the presence of EEP at a concentration of 100 micrograms/ml. The effect was found to be temperature dependent. Treatment of infected peritoneal macrophages and heart muscle cells with EEP strongly inhibited infection levels. The utilization of propolis as a possible antitrypanosomal agent is discussed.

Cellular response of protozoan parasites to host-derived cytokines

Cytokines are extracellular signalling molecules, produced by different cell types and displaying a wide range of activities such as the induction or inhibition of target cell survival, proliferation and differentiation. When directly interacting with different parasites, cytokines exert similar activities, acting as growth factors and, in one of the examples given here, also enhancing parasite survival. The importance of this interaction in the natural history of parasitic diseases as well as the selective forces maintaining functional cytokine 'receptors' in protozoan parasites is discussed in this review by Marcello Barcinski and Maria Elisabete Costa-Moreira.

Signal transduction in Trypanosoma cruzi: opposite effects of adenylcyclase and phospholipase C systems in growth control

Fetal calf serum (FCS), which is mitogenic for the pathogenic protozoa T. cruzi, inhibits cAMP production in basal and forskolin-stimulated epimastigotes. It also activates phosphoinositides hydrolysis yielding diacylglycerol and inositol phosphates (Ins-P). Ins-P production is enhanced by AlF4-, GTP or beta-gamma-methylene-GTP, thus implying G proteins mediation in the phenomenon. An enzyme with phospholipase C activity which may be involved in the phospholipid metabolism was partially characterized.

The challenge of Chagas' disease chemotherapy: an update of drugs assayed against Trypanosoma cruzi

The chemotherapy of Chagas' disease remains an unsolved problem, and the search for alternative drugs continues. Only two nitroheterocyclic drugs are in clinical use at the present time, and these have severely restricted applicability for chronic patients, as well as being highly toxic. This review covers drugs tested in the last 12 years. A large number of different compounds have been assayed in a variety of ways, most commonly in terms of their capacity to inhibit epimastigote proliferation. Allopurinol has emerged for the treatment of chronic cases. However, only with greater knowledge of the biochemistry of the parasite and in particular of its peculiarities, will it be possible to shift the emphasis of drug research away from random screenings onto a more rational footing. This is exemplified by recent studies carried out using purine derivatives and trypanothione reductase inhibitors.

Absence of transitory [Ca2+]i flux during early in vitro metacyclogenesis of Trypanosoma cruzi

The phorbol ester TPA (phorbol 12-myristate 13-acetate) substitutes for CO2 as an agonist for transforming Trypanosoma cruzi epimastigotes to the metacyclic trypomastigote stage in a starvation medium consisting of phosphate buffered saline + 10 mM proline, 10 mM sodium acetate and 0.035% NaHCO3. Since TPA is thought to stimulate protein kinase C by mimicking the activity of the secondary messenger diacylglycerol, the above result suggested that T. cruzi metacyclogenesis could be activated by a Ca(2+)-dependent protein kinase C signal induction pathway. Accordingly, cytosolic calcium flux ([Ca2+]i) in epimastigotes, activated with 5% CO2 or TPA (10(-7) M), was measured with the Ca2+ molecular probe, fluo-3AM. In addition, [Ca2+]i was measured in cells incubated with putative metacyclogenic agonists (e.g. proline, glutamate, bioamines, ionophores and catecholamines). None of the compounds studies, except for EGTA, affected cytosolic Ca2+ levels. Control assays with 11 microM thapsigargin, which mobilizes noncytoplasmic Ca2+ stores by inhibiting endoplasmic reticulum Ca(2+)-ATPase, validated our fluorometric assay procedure. Although thapsigargin significantly increases cytoplasmic Ca2+ fluorescence, it has no effect on transformation. The protein kinase C inhibitors staurosporine, H-7 and HA 1004 were tested for their effect on T. cruzi metacyclogenesis. Low concentrations of staurosporine and HA 1004 significantly elevated Peru strain transformation while H-7 had no effect on Peru strain metacyclogenesis. Inhibitor H-7 did significantly depress CL transformation. The results indicate that induction of T. cruzi metacyclic trypomastigote formation by CO2 and TPA is not accompanied by changes in cytosolic Ca2+ and do not provide supporting evidence for participation of a protein kinase C-mediated phosphoinositide cascade in metacyclogenesis.

Trypanosoma cruzi: alteration of cAMP metabolism following infection of human endothelial cells

We have previously reported that Trypanosoma cruzi infection of endothelial cells results in alterations in the metabolism of Ca2+, inositol triphosphate (IP3), and prostacycline (PGI2). In this report, we demonstrate that infection also alters the metabolism of cAMP. Infection of endothelial cells does not significantly alter beta-adrenergic receptor density or affinity, adenylate cyclase activity, and whole-cell cAMP levels. However, incubation of infected endothelial cells with the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) resulted in less than a 60% increase in cell cAMP in contrast to the greater than a 100% increase observed in uninfected endothelial cells under otherwise identical reaction conditions. Infected endothelial cells demonstrated a twofold increase in phosphodiesterase activity when measured directly. Moreover, homogenates prepared from infected endothelial cells previously incubated with isoproterenol for 20 min showed little or no change in PDE activity. In contrast, homogenates prepared from uninfected endothelial cells treated under otherwise identical reaction conditions showed a 5.7-fold increase in PDE activity. In the presence of IBMX, isoproterenol-dependent stimulation of cAMP levels in infected endothelial cells reached a maximum level at 5 min of incubation, and thereafter rapidly declined. In contrast, cAMP levels in uninfected endothelial cells reached a maximum at 2 min of incubation, and thereafter remained elevated throughout the duration of the incubation. Infection-associated changes in isoproterenol dependent stimulation of cAMP accumulation appear to relate, in part, to changes in PDE activity.

Granulocyte-macrophage colony-stimulating factor is a growth-factor for promastigotes of Leishmania mexicana amazonensis

In this paper we show that murine lung conditioned medium (LCM) displays, in addition to its already described colony-stimulating activity on bone marrow cells, a potent growth-stimulating activity on promastigotes of Leishmania mexicana amazonesis. Immunoprecipitation of LCM with an antibody specific for murine granulocyte-macrophage colony stimulating factor (GM-CSF) abrogates both activities, indicating that the leishmanial growth-promoting activity is due to the presence of GM-CSF on LCM. Furthermore, recombinant GM-CSF (rGM-CSF) added to the culture medium or to the immunoprecipitated LCM is able to respectively induce or to partially recover the growth-promoting activity of the LCM. Sequential in vitro passages of the parasite induces a progressive loss of sensitivity to the growth-factor. Parasite forms recently collected from lesions are significantly more responsive to the growth-factor than forms already adapted to grow in culture. Since it has been shown that several different microorganisms display receptors for vertebrate-like hormones and that GM-CSF is able to enhance a cutaneous leishmanial lesion, our results permit us to raise the hypothesis that a direct interaction between a host-derived hormone and a pathogenic microorganism can be of importance in defining the fate of an infection. The fact that GM-CSF is produced by cells that actively participate in a leishmanial infection (T-lymphocytes and macrophages) reinforces our hypothesis.

Trypanosoma cruzi proliferation and differentiation are blocked by topoisomerase II inhibitors

Bacterial topoisomerase II inhibitors (ofloxacin and its commercial derivative Tarivid, nalidixic acid, and novobiocin) were tested as blockers of Trypanosoma cruzi differentiation and proliferation. The transformation of either epimastigotes into metacyclic trypomastigotes or amastigotes into trypomastigotes was inhibited by the drugs in a dose-dependent manner. The inhibition of epimastigote differentiation was also dependent on the time of drug addition to the medium. Proliferation of T. cruzi was also blocked in a dose-dependent manner by the drugs, with the exception of novobiocin, which did not inhibit epimastigote replication and resulted in cell lysis when it was used at high concentrations. On the other hand, the transformation of amastigotes into epimastigotes in axenic culture was not inhibited; this process did not require either kinetoplast (mitochondrial) DNA replication or changes in the DNA network organization. Electron microscopy of cells treated with Tarivid (ofloxacin) showed damage to the kinetoplast, suggesting that this organelle might be the target of the drug. These results indicate that a bacterial-like topoisomerase II plays an important role in T. cruzi proliferation and differentiation.

Trypanosoma cruzi: killing and enhanced uptake by resident peritoneal macrophages treated with alpha-2-macroglobulin

We report that alpha-2-macroglobulin (A2M), the physiologically important plasma protease inhibitor and suspected immunomodulator, alters the functional ability of murine resident peritoneal macrophages (RM) to ingest and kill the infective trypomastigote stage of Trypanosoma cruzi, the aetiological agent of Chagas' disease. Treatment of RM with 500 micrograms/ml A2M for 30 min enhanced the uptake of trypomastigotes, epimastigotes, and amastigotes by 125%, 46%, and 300%, respectively. The same treatment also increased the phagocytosis of sheep erythrocytes opsonized with complement and IgG as well as of galactosylated asialoerythrocytes. After 60-90 min parasite-cell interaction, epi- and amastigotes were killed by the RM, whereas the infection with trypomastigotes was controlled only after 24 h. Other protease inhibitors, bovine serum albumin, and LPS showed no such effect. The production of hydrogen peroxide was not affected by A2M treatment, but the ultrastructural aspects showed trypomastigote damage and enhancement of macrophage membrane ruffling, indicative of macrophage activation. These results suggest that A2M has the ability to modulate, at least functionally, certain receptor-mediated endocytic pathways that, in concert with an activation of possibly oxygen-independent microbicidal mechanisms, could contribute to resistance against the parasite.