The Chemotherapy of Chagas Disease: An Overview

The review presents: a) a brief description of the disease; b) a summary of the most important metabolic targets so far identified in Trypanosome cruzi (T. cruzi) along with corresponding inhibitor compounds; c) the current state of knowledge on the trypanothione reductase system of trypanosomatids with reference to oxidative stress defenses; d) detailed discussions on T. cruzi trypanothione reductase inhibitors such as nitrofuranes, naphthoquinones and phenothiazines. As yet, the chemotherapy of Chagas' disease remains an unsolved problem. Further search for new drugs must continue by means of nucleating existing chemotherapy efforts.

Bisphosphonates as chemotherapeutic agents against trypanosomatid and apicomplexan parasites

Trypanosomatid and apicomplexan parasites remain an important health problem in developing countries. Advances are being made in parts of the world in blocking transmission from insect vectors, but more effective chemotherapy is urgently needed. This is especially important since development of resistance is a growing problem. The rational development of new drugs depends on the identification of differences between human metabolism and that of the parasites. Recent developments in the study of the basic biochemistry of these parasites have resulted in the discovery that bisphosphonates, drugs widely used in the treatment of benign and malignant diseases characterized by increased bone resorption, could have a role as lead antiparasitic agents.

Antiparasitic activity in Asteraceae with special attention to ethnobotanical use by the tribes of Odisha, India

The purpose of this review is to survey the antiparasitic plants of the Asteraceae family and their applicability in the treatment of parasites. This review is divided into three major parts: (a) literature on traditional uses of Asteraceae plants for the treatment of parasites; (b) description of the major classes of chemical compounds from Asteraceae and their antiparasitic effects; and (c) antiparasitic activity with special reference to flavonoids and terpenoids. This review provides detailed information on the reported Asteraceae plant extracts found throughout the world and on isolated secondary metabolites that can inhibit protozoan parasites such as Plasmodium, Trypanosoma, Leishmania, and intestinal worms. Additionally, special attention is given to the Asteraceae plants of Odisha, used by the tribes of the area as antiparasitics. These plants are compared to the same plants used traditionally in other regions. Finally, we provide information on which plants identified in Odisha, India and related compounds show promise for the development of new drugs against parasitic diseases. For most of the plants discussed in this review, the active compounds still need to be isolated and tested further.

In vitro antiprotozoal activities and cytotoxicity of some selected Cameroonian medicinal plants

Eight extracts from seven selected Cameroonian medicinal plants, traditionally used to treat malaria and other protozoal diseases, were tested in vitro for their antiprotozoal activities against Plasmodium falciparum K1 chloroquine-resistant strain, Leishmania donovani, Trypanosoma cruzi and Trypanosoma brucei rhodesiense, protozoa responsible for malaria, visceral leishmaniasis, Chagas disease and African trypanosomiasis, respectively. The most active extract against Plasmodium falciparum K1 strain and Trypanosoma brucei rhodesiense was the methanolic extract of Albizia zygia (Fabaceae) stem bark with IC(50) values of 1.0 microg/ml and 0.2 microg/ml, respectively. Five extracts showed IC(50) values below 5mug/ml against Leishmania donovani, with the methanolic seed extract of Harungana madagascarensis showing the highest activity, but only the methanolic extract of Albizia zygia showed activity against Trypanosoma cruzi. Cytotoxicity and selectivity indexes were estimated for the most active extracts. The best ratio of cytotoxicity to antiplasmodial activity (SI(a)=14) was established for the methanolic leaf extract of Symphonia globulifera (Clusiaceae), while the methanolic stem bark extract of Albizia zygia showed the best ratio of cytotoxicity to antitrypanosomal activity (SI(b)=22.5).

A novel ecto-phosphatase activity of Herpetomonas muscarum muscarum inhibited by platelet-activating factor

In the present work ecto-phosphatase activity in Herpetomonas muscarum muscarum has been characterized using live parasites. This enzyme hydrolyzed p-nitrophenylphosphate at a rate of 4.27 nmol Pi/mg of protein.min. A pH curve was generated, in which these intact flagellates showed the highest phosphatase activity at pH 6.5. Classical inhibitors for acid phosphatase, such as sodium orthovanadate, sodium tartrate, and ammonium molybdate, were used in the experiments and showed different patterns of inhibition. Lithium fluoride, aluminum chloride, and fluoroaluminate complexes were also tested. Although lithium fluoride and fluoroaluminate complexes were capable of inhibiting the phosphatase activity, aluminum chloride stimulated this enzyme. Cytochemical analysis showed the localization of this enzyme on the parasite surface. This ecto-phosphatase activity was also significantly diminished when the parasites were treated with 10(-6) M platelet-activating factor (PAF), a potent phospholipid mediator that promoted cellular differentiation in this parasite.

Prolylisoxazoles: potent inhibitors of prolyloligopeptidase with antitrypanosomal activity

Prolylprolylisoxazoles and prolylprolylisoxazolines were synthesized through a 1,3-dipolar cycloaddition reaction. These compounds are potent inhibitors of human and trypanosomal prolyloligopeptidase. They were shown to inhibit Trypanosoma cruzi and Trypanosoma b. brucei in in vitro systems with ED(50)'s in the lower microM range.

Screening Marine Natural Products for New Drug Leads against Trypanosomatids and Malaria

Neglected Tropical Diseases (NTD) represent a serious threat to humans, especially for those living in poor or developing countries. Almost one-sixth of the world population is at risk of suffering from these diseases and many thousands die because of NTDs, to which we should add the sanitary, labor and social issues that hinder the economic development of these countries. Protozoan-borne diseases are responsible for more than one million deaths every year. Visceral leishmaniasis, Chagas disease or sleeping sickness are among the most lethal NTDs. Despite not being considered an NTD by the World Health Organization (WHO), malaria must be added to this sinister group. Malaria, caused by the apicomplexan parasite Plasmodium falciparum, is responsible for thousands of deaths each year. The treatment of this disease has been losing effectiveness year after year. Many of the medicines currently in use are obsolete due to their gradual loss of efficacy, their intrinsic toxicity and the emergence of drug resistance or a lack of adherence to treatment. Therefore, there is an urgent and global need for new drugs. Despite this, the scant interest shown by most of the stakeholders involved in the pharmaceutical industry makes our present therapeutic arsenal scarce, and until recently, the search for new drugs has not been seriously addressed. The sources of new drugs for these and other pathologies include natural products, synthetic molecules or repurposing drugs. The most frequent sources of natural products are microorganisms, e.g., bacteria, fungi, yeasts, algae and plants, which are able to synthesize many drugs that are currently in use (e.g. antimicrobials, antitumor, immunosuppressants, etc.). The marine environment is another well-established source of bioactive natural products, with recent applications against parasites, bacteria and other pathogens which affect humans and animals. Drug discovery techniques have rapidly advanced since the beginning of the millennium. The combination of novel techniques that include the genetic modification of pathogens, bioimaging and robotics has given rise to the standardization of High-Performance Screening platforms in the discovery of drugs. These advancements have accelerated the discovery of new chemical entities with antiparasitic effects. This review presents critical updates regarding the use of High-Throughput Screening (HTS) in the discovery of drugs for NTDs transmitted by protozoa, including malaria, and its application in the discovery of new drugs of marine origin.

Calcium mobilization by arachidonic acid in trypanosomatids

A recent report (Eintracht J, Maathai R, Mellors A, Ruben L. Calcium entry in Trypanosoma brucei is regulated by phospholipase A, and arachidonic acid, Biochem J 1998:336:659-66) provided evidence that calcium entry in Trypanosoma brucei bloodstream trypomastigotes is regulated via a signaling pathway involving phospholipase A2-mediated generation of arachidonic acid and stimulation of a plasma membrane-located calcium channel. Here we show that Ca2+ influx in T. brucei procyclic trypomastigotes, Leishmania donovani promastigotes and T. cruzi amastigotes was also stimulated in a dose-dependent manner (50-400 nM) by the amphiphilic peptide melittin. This effect was blocked by the phospholipase A, inhibitor 3-(4-octadecyl)-benzoylacrylic acid. The unsaturated fatty acid arachidonic acid, in the range of 10-75 microM, induced Ca2+ entry by a mechanism sensitive to LaCl3. However, both melittin and arachidonic acid induced an increase in [Ca2+]i in T. brucei procyclic trypomastigotes incubated in Ca2+-free medium implying Ca2+ mobilization from intracellular stores. This hypothesis was supported by experiments showing that arachidonic acid promoted Ca2+ release from the acidocalcisomes of these cells. The results showing changes in mitochondrial membrane potential, release of acridine orange and Ca2+ from the acidocalcisomes and Ca2+ transport across the plasma membrane suggest that in addition to the possible stimulation of a Ca2+ channel-mediated process, arachidonic acid, in the range of concentrations used here, have other nonspecific effects on the trypanosomatids membranes.

Phytomonas serpens: cysteine peptidase inhibitors interfere with growth, ultrastructure and host adhesion

In this study, we report the ultrastructural and growth alterations caused by cysteine peptidase inhibitors on the plant trypanosomatid Phytomonas serpens. We showed that the cysteine peptidase inhibitors at 10 microM were able to arrest cellular growth as well as promote alterations in the cell morphology, including the parasites becoming short and round. Additionally, iodoacetamide induced ultrastructural alterations, such as disintegration of cytoplasmic organelles, swelling of the nucleus and kinetoplast-mitochondrion complex, which culminated in parasite death. Leupeptin and antipain induced the appearance of microvillar extensions and blebs on the cytoplasmic membrane, resembling a shedding process. A 40 kDa cysteine peptidase was detected in hydrophobic and hydrophilic phases of P. serpens cells after Triton X-114 extraction. Additionally, we have shown through immunoblotting that anti-cruzipain polyclonal antibodies recognised two major polypeptides in P. serpens, including a 40 kDa component. Flow cytometry analysis confirmed that this cruzipain-like protein has a location on the cell surface. Ultrastructural immunocytochemical analysis demonstrated the presence of the cruzipain-like protein on the surface and in small membrane fragments released from leupeptin-treated parasites. Furthermore, the involvement of cysteine peptidases of P. serpens in the interaction with explanted salivary glands of the phytophagous insect Oncopeltus fasciatus was also investigated. When P. serpens cells were pre-treated with either cysteine peptidase inhibitors or anti-cruzipain antibody, a significant reduction of the interaction process was observed. Collectively, these results suggest that cysteine peptidases participate in several biological processes in P. serpens including cell growth and interaction with the invertebrate vector.

Biological effects of extracts obtained from Stryphnodendron adstringens on Herpetomonas samuelpessoai

We report the effect of Stryphnodendron adstringens on the trypanosomatid Herpetomonas samuelpessoai. The parasites were grown at 28 degrees C in a chemically defined medium containing crude extract and fractions at concentrations from 100 to 5000 microg/ml obtained from S. adstringens. Concentrations of 500, 1000, 2500, and 5000 microg/ml both crude extract and semi-purified fraction progressively inhibited the protozoans' growth. At a concentration of 100 microg/ml, crude extract or a semi-purified (F3) fraction did not affect the growth of the protozoans. The F3-9 - F3-12 sub-fractions, at a concentration of 1000 microg/ml, also showed increased inhibitory activity on H. samuelpessoai. The IC50 of the crude extract and the F3 fraction were 538 and 634 microg/ml, respectively. Ultrastructural and enzymatic alterations in the trypanosomatids were also evaluated. H. samuelpessoai cultivated in the presence of IC50 crude extract showed considerable ultrastructural alterations, such as marked mitochondrial swelling with a large number of cristae and evident Golgi complex vesiculation, as observed by transmission electron microscopy. Cells exposed to 538 microg/ml of crude extract at 28 degrees C for 72 h, showed decreased activity of the enzyme succinate cytochrome c reductase, a typical mitochondrion marker, as compared to untreated cells.

Secreted phosphatase activity induced by dimethyl sulfoxide in Herpetomonas samuelpessoai

A phosphatase activity of the trypanosomatid parasite Herpetomonas samuelpessoai was characterized using intact living cells. The effects of dimethyl sulfoxide (DMSO) on this activity were investigated. This phosphatase activity (2.53+/-0.01 nmol P(i)/mg protein x min) was linear with cell density and with time for at least 60 min. The optimum pH for the H. samuelpessoai phosphatase lies in the acid range. This phosphatase activity was inhibited by metal chelators and classical phosphatase inhibitors. A robust stimulation of the phosphatase activity was observed when the flagellates were grown in the presence of 4% DMSO, both when intact flagellates and when culture supernatant from those cells were assayed, as observed by biochemical and cytochemical analysis. We also demonstrate that DMSO induced the secretion and/or shedding of this phosphatase to the extracellular medium, with a possible involvement of protein kinase C in this process.

Cytotoxicity of three new triazolo-pyrimidine derivatives against the plant trypanosomatid: Phytomonas sp. isolated from Euphorbia characias

There is no effective chemotherapy against diseases caused by Phytomonas sp., a plant trypanosomatid responsible for economic losses in major crops. We tested three triazolo-pyrimidine complexes [two with Pt(II), and another with Ru(III)] against promastigotes of Phytomonas sp. isolated from Euphorbia characias. The incorporation of radiolabelled precursors, ultrastructural alterations and changes in the pattern of metabolite excretion were examined. Different degrees of toxicity were found for each complex: the platinum compound showed an inhibition effect on nucleic acid synthesis, provoking alterations on the levels of mitochondria, nucleus and glycosomes. These results, together with others reported previously in our laboratory about the activity of pyrimidine derivatives, reflect the potential of these compounds as agents in the treatment of Phytomonas sp.

The effect of topoisomerase II inhibitors on the kinetoplast ultrastructure

Topoisomerases from trypanosomatids play key functions in the replication and organization of kinetoplast DNA (kDNA). Hence, they are considered as potential targets for anti-parasite drugs. In this paper, the effect of topoisomerase II inhibitors, such as nalidixic acid, novobiocin and etoposide, on the ultrastructure of trypanosomatids that present distinct kDNA arrangements was evaluated. Prokaryotic topoisomerase II inhibitors were more effective on growth arrest and ultrastructure changes than etoposide, a eukaryotic topoisomerase II inhibitor. With the exception of novobiocin, drug concentrations which inhibited cell proliferation also promoted kinetoplast ultrastructure alterations, including the redistribution of topoisomerase II. The data reinforce the concept that prokaryotic topoisomerase II inhibitors may offer greater selectivity in drug therapy of trypanosomatid infections.

Sensitivity of trypanosomatid protozoa to DFMO and metabolic turnover of ornithine decarboxylase

alpha-Difluoromethylornithine (DFMO), the specific and irreversible inhibitor of ornithine decarboxylase (ODC), was able to induce the arrest of proliferation in Leishmania mexicana and ODC-transformed Trypanosoma cruzi cultures grown in a semi-defined medium essentially free of polyamines. Conversely, Crithidia fasciculata and Phytomonas 274 were not affected by the inhibitor. The drug-resistance of Crithidia and Phytomonas was neither caused by an impairment of DFMO uptake nor by a decrease of the enzyme affinity for the inhibitor. We were also able to rule out the possibility of ODC overexpression in the drug-tolerant parasites. The measurements of ODC metabolic turnover indicated that the enzymes from Crithidia and Phytomonas have a short half-life of 20-40 min, while ODC from Leishmania and transgenic Trypanosoma cruzi are rather stable with a half-life longer than 6 hours. Analyses of polyamine internal pools under different growth conditions have shown that DFMO was able to markedly decrease the levels of putrescine and spermidine in all parasites, but the depletion of spermidine was higher in trypanosomatids containing an ODC with slow turnover. Our results suggest that in these parasites cultivated in the presence of the drug, spermidine might decrease below critical levels needed to maintain trypanothione concentrations or other conditions essential for normal proliferation.

The TryPIKinome of five human pathogenic trypanosomatids: Trypanosoma brucei, Trypanosoma cruzi, Leishmania major, Leishmania braziliensis and Leishmania infantum--new tools for designing specific inhibitors

Phosphatidylinositol (PI) kinases are at the heart of one of the major pathways of intracellular signal transduction. Herein, we present the first report on a survey made by similarity searches against the five human pathogenic trypanosomatids Trypanosoma brucei, Trypanosoma cruzi, Leishmania major, Leishmania braziliensis and Leishmania infantum genomes available to date for phosphatidylinositol- and related-kinases (TryPIKs). In addition to generating a panel called "The TryPIKinome", we propose a model of signaling pathways for these TryPIKs. The involvement of TryPIKs in fundamental pathways, such as intracellular signal transduction and host invasion processes, makes the study of TryPIKs an important area for further inquiry. New subtype-specific inhibitors are expected to work on individual members of the PIK family and, therefore, can presumably neutralize trypanosomatid invasion processes.

Peptidases and gp63-like proteins in Herpetomonas megaseliae: possible involvement in the adhesion to the invertebrate host

The cell-associated and extracellular peptidases of Herpetomonas megaseliae grown in brain-heart infusion and in modified Roitman's complex media were analyzed by measuring peptidase activity on gelatin, casein and hemoglobin in zymograms. Casein was the best proteinaceous substrate for the peptidase detection on both growth conditions. However, no proteolytic activity was detected when hemoglobin was used. Our results showed that cellular cysteine peptidase (115-100, 40 and 35 kDa) and metallopeptidase (70 and 60 kDa) activities were detected on both media in casein and gelatin zymograms. Additionally, the use of casein in the gel revealed a distinct acidic metallopeptidase of 50 kDa when the parasite was cultured in the modified Roitman's complex medium. Irrespective of the culture medium composition, H. megaseliae released metallopeptidases exclusively in the extracellular environment. The presence of gp63-like molecules on the H. megaseliae surface was shown by flow cytometry using anti-gp63 antibody raised against recombinant gp63 from Leishmania mexicana. The pre-treatment of parasites with phospholipase C reduced the number of gp63-positive cells, suggesting that these molecules were glycosylphosphatidylinositol-anchored to the surface. Additionally, the supernatant obtained from phospholipase C-treated cells and probed with anti-cross-reacting determinant confirmed that at least a 52 kDa gp63-like molecule is glycosylphosphatidylinositol-anchored. Furthermore, we assessed a possible function for the gp63-like molecules in H. megaseliae on the interaction with explanted guts of its original host, Megaselia scalaris, and with an experimental model employing Aedes aegypti. Parasites pre-treated with either anti-gp63 antibody or phospholipase C showed a significant reduction in the adhesion to M. scalaris and A. aegypti guts. Similarly, the pre-treatment of the explanted guts with purified gp63 diminished the interaction process. Collectively, these results corroborate the ubiquitous existence of gp63 homologues in insect trypanosomatids and the potential adhesion of these molecules to invertebrate host tissues.

Effect of platelet-activating factor on the process of cellular differentiation of Herpetomonas muscarum muscarum

The effects of platelet-activating factor (PAF), at doses ranging from 10(-6) M to 10(-10) M, on cell growth and on cell differentiation of Herpetomonas muscarum muscarum were investigated. Cell differentiation was evaluated by both light and electron microscopy. At the concentrations used, PAF did not interfere with the protozoan growth. However, parasites grown in the presence of PAF (10(-6) M) were significantly more differentiated than those grown in the absence of PAF, since the first day of culture. On the first two days of culture, PAF doses ranging from 10(-10) M to 10(-7) M, did not significantly interfere with the differentiation of these parasites, although after the third day of culture, all PAF doses used significantly increased the protozoan differentiation. Specific PAF receptor antagonists totally abrogated (WEB 2086 and WEB 2170) or significantly decreased (BN 52021) PAF effect on cell differentiation. These findings indicate PAF triggers the process of cell differentiation in Herpetomonas muscarum muscarum and suggest these parasites have receptors for PAF.

Biochemical and ultrastructural alterations caused by newly synthesized 1,2,4-triazole[1,5a]pyrimidine derivatives against Phytomonas staheli (Trypanosomatidae)

Six compounds, all newly synthesized triazole-pyrimidine derivatives that proved inhibitory of in in vitro growth of epimastigotes in Trypanosoma cruzi and of promastigotes of Leishmania donovani and Phytomonas staheli, were studied to investigate their toxic effects. As a biological model, the plant trypanosome P. staheli, which causes sudden wilt in the oil palm and Hartrot in the coconut palm, was used. The six compounds markedly inhibited macromolecule synthesis (nucleic acids and proteins) by the parasite. The cells treated with these compounds present severe damage in their ultrastructure-intense 'vacuolization, and appearance of lysosomes as well as other residual bodies. The mitochondrial section appeared larger in size. with a swollen matrix. In addition, these compounds changed the excretion of end metabolites, primarily affecting ethanol and acetate excretion, possibly by directly influencing certain enzymes (alcohol dehydrogenase and acetate synthetase) or their synthesis. 2000 Elsevier Science Ltd.

Herpetomonas samuelpessoai: dimethylsulfoxide-induced differentiation is influenced by proteinase expression

In this study, we analyzed the influence of proteinase expression on the cellular differentiation of Herpetomonas samuelpessoai. Along cellular differentiation, which was induced by dimethylsulfoxide (DMSO), the trypanosomatids secreted several molecules with variable proteolytic activity. All of them were inhibited by 10 m M 1,10-phenanthroline, suggesting that they are zinc-metalloproteinases. Analysis of parasite extracts revealed the occurrence of a 63-kDa metalloproteinase and a 45-kDa cysteine proteinase. After extraction with Triton X-114 followed by water-detergent partition, the 63-kDa component was present in both aqueous and detergent phases, which indicated that this enzyme may be distributed over different cellular compartments including membrane domains. The 45-kDa component, however, presented hydrophilic properties and was predominantly expressed by DMSO non-treated parasites, suggesting that proteinases may be involved in the process of cellular differentiation in H. samuelpessoai. This was confirmed by the fact that a cysteine proteinase inhibitor abrogated parasite differentiation. The role of proteinases and their relevance in the differentiation of H. samuelpessoai are discussed.

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi in Triatoma infestans (Insecta, Hemiptera)

The effect of azadirachtin on Blastocrithidia triatomae and Trypanosoma cruzi, which colonise the intestinal tract of the blood-sucking bug Triatoma infestans, was investigated. In established infections of controls without azadirachtin treatment, the small intestine of fifth-instar T. infestans contained up to 7 x l0(6) B. triatomae and the rectum 3 x 10(6). In comparison to this homoxenous flagellate, the population densities of T. cruzi in the respective regions were 99.3 and 76% lower. Treatment with azadirachtin (1 microg ml(-1)) via a blood meal and a concurrent infection with B. triatomae resulted in an increase of the population density (3 weeks p.i.), caused mainly by the mastigote stages in the rectum. In an established B. triatomae infection (12 weeks p.i.), feeding of azadirachtin did not affect the population density and composition. In an optimal T. cruzi-vector system, i.e. parasite and bug originate from the same locality, the treatment with azadirachtin at 20 weeks p.i. strongly reduced the population density in the small intestine of all bugs up to 100 days after treatment, but only in a minor percentage of the bugs in the rectum. Trypanosoma (cruzi incubated for up to 24 h in faeces of azadirachtin-treated bugs were not affected, indicating that the rectum of these bugs contained no toxic substances. The importance of these findings is that investigations of the mechanisms of action of azadirachtin offer a possibility to identify vector-derived compounds, which are necessary for the development of T. cruzi, thereby, giving us a possible new strategy to combat Chagas' disease.

Changes in cell surface anionogenic groups during differentiation of Herpetomonas samuelpessoai mediated by dimethylsulfoxide

The surface anionic groups of untreated or dimethyl sulfoxide (DMSO)-treated Herpetomonas samuelpessoai cells were analyzed by cell electrophoresis, ultrastructural cytochemistry, and identification of sialic acids using thin-layer chromatography. Differentiation of H. samuelpessoai induced by DMSO treatment caused a significant increase in the net negative surface charge. In flagellates exposed to DMSO, more cationized ferritin, colloidal iron hydroxide, and sendai virus particles bound to the cell surface. Treatment of both untreated and DMSO-treated flagellates with neuraminidase decreased markedly the EPM of cells to the cathodic pole. These findings suggest that sialic acid residues are the major anionogenic groups exposed on the surface of H. samuelpessoai. Thin-layer chromatography showed that N-acetyl and N,O-diacylneuraminic acids, in equal proportions, were present in H. samuelpessoai. However, N-acetylneuraminic acid predominates in DMSO-treated cells.

Activation of the glycosylphosphatidylinositol-anchored membrane proteinase upon release from Herpetomonas samuelpessoai by phospholipase C

We have analyzed the effects of exogenous phospholipase C (PLC) on the cell-surface polypeptides and proteinases of Herpetomonas samuelpessoai grown in chemically defined conditions by SDS-PAGE gels. Live parasites treated with PLC released into the extracellular medium a complex profile of glycosylphosphatidylinositol (GPI)-anchored polypeptides ranging from 15 to 100 kDa, some of them with proteolytic activity. Two major metalloproteinases with apparent molecular masses of 63 and 115 kDa were observed after PLC hydrolysis. Interestingly, only the PLC-released soluble form of the 115-kDa metalloenzyme, and not the membrane-anchored form, displayed proteolytic activity, demonstrating that cleavage of the GPI anchor can lead to enzymatic activation.

Developmentally regulated protein expression mediated by dimethylsulfoxide in Herpetomonas samuelpessoai

We have analyzed the total cell extract, cell surface, and secretory protein profiles related to cellular differentiation triggered by dimethylsulfoxide in the insect trypanosomatid Herpetomonas samuelpessoai. The flagellates were cultivated in chemically defined conditions in the absence or in the presence of 4% DMSO, and the resolved protein bands were detected by SDS-PAGE gels and avidin-Western blotting. The cell-associated proteins showed a complex pattern of around 40 silver-staining bands ranging from 15 to 150 kDa. There were generally minor quantitative differences in the protein profile between the non-treated and the DMSO-treated cells. The cell-surface protein profile revealed by the incubation of live parasites with biotin showed a decrease in the expression of the 120 kDa biotinylated polypeptide observed in the DMSO-treated cells when compared with untreated ones. However, control samples of both systems showed an endogenous biotinylated polypeptide of 63 kDa which also presented gelatinolytic activity. The trypanosomatids released at least 10 polypeptides to the culture medium. A low molecular mass exopolypeptide (35 kDa) was found exclusively in untreated cells, whereas a high-molecular-mass exopolypetide (250 kDa) was preferentially found in DMSO-treated cells.

Chemotherapeutic approaches to protozoa: kinetoplastida--current level of knowledge and outlook

The possibilities for treating haemoflagellate infections (African trypanosomiasis) are very limited (Table 1; Mehlhorn and Schrevel 1995; Croft 1997; Hunter 1997; Wang 1997; Trouiller and Olliaro 1998). All the available drugs have severe side-effects in humans and animals. Vaccination is not really an option, in view of the wide antigen variability. At present, there are several drug combinations in clinical trials: suramin/eflornithine, suramin/metronidazole, suramin/pentamidine, melarsoprol/pentamidine, melarsoprol/nifurtimox and nifurtimox/eflornithine. Some of these combinations were successful in treating resistant Trypanosoma brucei rhodesiense and/or T. b. gambiense infections (Keiser et al. 2001). In leishmaniasis, the tendency is still to resort to the old antimony compounds, with their severe side effects. At present, miltefosine is in clinical phase and is the first oral drug against visceral leishmaniasis (Jha et al. 1999). Two drugs are currently used against Chagas' disease, although these do not cure chronic effects. There is no prospect of novel drugs in this indication either (Pecoul et al. 1999; Morel 2000).

Targeting metabolic pathways in microbial pathogens: oxidative stress and anti-folate drug resistance in trypanosomatids

The large quantity of genomic, biochemical and metabolic data on microbial pathogens provides information that helps us to select biological problems of interest and to identify targets, metabolic pathways or constituent enzymes, for therapeutic intervention. One area of potential use in developing novel anti-parasitic agents concerns the regulation of oxidative stress, and we have targeted the trypanothione peroxidase pathway in this respect. In order to characterize this pathway, we have determined crystal structures for each of its components, and are now studying enzyme-ligand complexes of the first enzyme, trypanothione reductase. Also with regard to trypanosomatids, a question that arose was: why do anti-folates not provide useful therapies? The enzyme pteridine reductase has been shown to contribute to anti-folate drug resistance, and we have determined the enzyme structure and mechanism to understand this aspect of drug resistance.