Drug targets and mechanisms of resistance in the anaerobic protozoa

Anti-protozoal activity of diamine derivatives

Ten N-monoalkylated diamines were synthesized and evaluated for in vitro activities against Trichomonas vaginalis and Giardia lamblia. Several compounds displayed a good inhibition of parasite growth, with MIC less or equal to 20μg/mL. N-hexadecil-1,4-butanediamine was found to be the most active compound in vitro against T. vaginalis with MIC of 2.5μg/mL, twice more active in comparison to the reference drug metronidazole (MTZ). Seven of the studied compounds showed a better anti-G. lamblia activity than MTZ.

Towards a systematic characterization of the antiprotozoal activity landscape of benzimidazole derivatives

Parasitic infections caused by the protozoa Trichomonas vaginalis and Giardia intestinalis still represent a major problem in developing countries. Despite the fact that benzimidazoles are promising compounds with activity against both protozoa, systematic studies to characterize and compare their structure-activity relationships (SAR) are limited. Herein, we report a systematic characterization of the SAR of 32 benzimidazoles with activity against T. vaginalis and G. intestinalis. The analysis was based on pairwise comparisons of the activity similarity and molecular similarity using different molecular representations. Radial, MACCS keys, TGD and piDAPH3 fingerprints were used to develop consensus models of the landscape. The landscapes contained continuous regions and activity cliffs. Two 'deep consensus activity cliffs' and several pairs of compounds in smooth regions of the SAR were identified in the landscape of T. vaginalis. In contrast, a number of 'apparent and shallow cliffs' were found for G. intestinalis. Several compounds active for both parasites showed similar SAR suggesting a common mechanism of action. We also identified pairs of structurally similar molecules with dramatic changes in selectivity. Results suggested that while substitution at position 2 on the benzimidazole moiety plays an important role in increasing the potency against both parasites, substitutions at positions 4-7 could influence selectivity. This study represents a first step towards the systematic characterization of the antiprotozoal activity landscape of benzimidazoles, and has direct implications in the future development of other types of quantitative models. The landscape of larger data sets with other biological endpoints can be analyzed using the general approaches used in this work.

Protective potential of L. acidophilus in murine giardiasis

This study describes the in vivo activity of Lactobacillus acidophilus in Giardia lamblia infected BALB/c mice. Experimentally, it was observed that daily administration of lactobacilli 7 days before or in simultaneous inoculation with Giardia trophozoites efficiently reduced G. lamblia infection in mice. More specifically, excretion of Giardia cysts were reduced significantly in probiotic-treated groups, and resolution of infection was observed by day 21 post-inoculation. It was also observed that the lactobacillus count increased tremendously and continuously in faeces of all probiotic-fed mice, and was significantly higher as compared with that in control mice. Histological analysis of microvilli membrane integrity revealed that probiotic administration also protected mice against parasite-induced mucosal damage, whereas Giardia-infected mice had severe villous atrophy, oedema, vacuolation and ileitis. Immunologically, the anti-Giardia serum IgG level was not stimulated significantly by probiotic treatment administered both prior to and simultaneous with Giardia infection, but remained high after the infection peak. Taken together, the data demonstrates the anti-giardial effect of the probiotic in vivo by modulation of the intestinal epithelial cells, inhibiting the colonization of Giardia trophozoites and thereby reducing the severity of Giardia infection.

Two atypical L-cysteine-regulated NADPH-dependent oxidoreductases involved in redox maintenance, L-cystine and iron reduction, and metronidazole activation in the enteric protozoan Entamoeba histolytica

We discovered novel catalytic activities of two atypical NADPH-dependent oxidoreductases (EhNO1/2) from the enteric protozoan parasite Entamoeba histolytica. EhNO1/2 were previously annotated as the small subunit of glutamate synthase (glutamine:2-oxoglutarate amidotransferase) based on similarity to authentic bacterial homologs. As E. histolytica lacks the large subunit of glutamate synthase, EhNO1/2 were presumed to play an unknown role other than glutamine/glutamate conversion. Transcriptomic and quantitative reverse PCR analyses revealed that supplementation or deprivation of extracellular L-cysteine caused dramatic up- or down-regulation, respectively, of EhNO2, but not EhNO1 expression. Biochemical analysis showed that these FAD- and 2[4Fe-4S]-containing enzymes do not act as glutamate synthases, a conclusion which was supported by phylogenetic analyses. Rather, they catalyze the NADPH-dependent reduction of oxygen to hydrogen peroxide and L-cystine to L-cysteine and also function as ferric and ferredoxin-NADP(+) reductases. EhNO1/2 showed notable differences in substrate specificity and catalytic efficiency; EhNO1 had lower K(m) and higher k(cat)/K(m) values for ferric ion and ferredoxin than EhNO2, whereas EhNO2 preferred L-cystine as a substrate. In accordance with these properties, only EhNO1 was observed to physically interact with intrinsic ferredoxin. Interestingly, EhNO1/2 also reduced metronidazole, and E. histolytica transformants overexpressing either of these proteins were more sensitive to metronidazole, suggesting that EhNO1/2 are targets of this anti-amebic drug. To date, this is the first report to demonstrate that small subunit-like proteins of glutamate synthase could play an important role in redox maintenance, L-cysteine/L-cystine homeostasis, iron reduction, and the activation of metronidazole.

A new-generation 5-nitroimidazole can induce highly metronidazole-resistant Giardia lamblia in vitro

The 5-nitroimidazole (NI) compound C17, with a side chain carrying a remote phenyl group in the 2-position of the imidazole ring, is at least 14-fold more active against the gut protozoan parasite Giardialamblia than the 5-NI drug metronidazole (MTR), with a side chain in the 1-position of the imidazole ring, which is the primary drug for the treatment of giardiasis. Over 10 months, lines resistant to C17 were induced in vitro and were at least 12-fold more resistant to C17 than the parent strains. However, these lines had ID(90) values (concentration of drug at which 10% of control parasite ATP levels are detected) for MTR of >200 microM, whilst lines induced to be highly resistant to MTR in vitro have maximum ID(90) values around 100 microM (MTR-susceptible isolates typically have an ID(90) of 5-12.8 microM). The mechanism of MTR activation in Giardia apparently involves reduction to toxic radicals by the activity of pyruvate:ferredoxin oxidoreductase (PFOR) and the electron acceptor ferredoxin. MTR-resistant Giardia have decreased PFOR activity, which is consistent with decreased activation of MTR in these lines, but C17-resistant lines have normal levels of PFOR. Therefore, an alternative mechanism of resistance in Giardia must account for these super-MTR-resistant cells.

The tropical brown alga Lobophora variegata: a source of antiprotozoal compounds

Lobophora variegata, a brown alga collected from the coast of the Yucatan peninsula, Mexico, was studied for antiprotozoal activity against Giardia intestinalis, Entamoeba histolytica and Trichomonas vaginalis. The whole extract showed the highest activity against T. vaginalis, with an IC(50) value of 3.2 microg/mL. For the fractions, the best antiprotozoal activity was found in non-polar fractions. The chloroform fraction of the extract contained a major sulfoquinovosyldiacylglycerol (SQDG), identified as 1-O-palmitoyl-2-O-myristoyl-3-O-(6'''-sulfo-alpha-D-quinovopyranosyl)-glycerol (1), together with small amounts of 1,2-di-O-palmitoyl-3-O-(6'''-sulfo-alpha-D-quinovopyranosyl)-glycerol (2) and a new compound identified as 1-O-palmitoyl-2-O-oleoyl-3-O-(6'''-sulfo-alpha-D-quinovopyranosyl)-glycerol (3). Their structures were elucidated on the basis of chemical and enzymatic hydrolysis and careful analysis of FAB-MS and NMR spectroscopic data. This is the first report on the isolation of SQDGs from L. variegata. The mixture of 1-3 showed good activity against E. histolytica and moderate activity against T. vaginalis with IC(50s) of 3.9 and 8.0 microg/mL, respectively, however, the activity of 1-3 is not as effective as metronidazole. These results afford ground information for the potential use of the whole extract and fractions of this species in protozoal infections.

Metronidazole resistance in Trichomonas vaginalis from highland women in Papua New Guinea

BACKGROUND

The prevalence of the sexually transmissible protozoan parasite Trichomonas vaginalis in the highlands of Papua New Guinea (PNG) has been reported to be as high as 46% and although not previously studied in Papua New Guinea, clinical resistance against metronidazole (Mz), the drug most commonly used to treat trichomoniasis, is well documented worldwide. This study was primarily aimed at assessing resistance to Mz in T. vaginalis strains from the Goroka region.

METHODS

Consenting patients presenting at the Goroka Base Hospital Sexually Transmitted Diseases (STD) Clinic and local women were asked to provide two vaginal swabs: one for culturing of the parasite; and one for polymerase chain reaction detection of T. vaginalis, Chlamydia trachomatis and Neisseria gonorrhoeae. T. vaginalis isolates were assayed for Mz susceptibility and a selection was genotyped.

RESULTS

The prevalence of T. vaginalis was determined to be 32.9% by culture and polymerase chain reaction of swabs among 82 local women and patients from the STD clinic. An unexpectedly high level of in vitro Mz resistance was determined with 17.4% of isolates displaying unexpectedly high resistance to Mz. The ability to identify isolates of T. vaginalis by genotyping was confirmed and the results revealed a more homogeneous T. vaginalis population in Papua New Guinea compared with isolates from elsewhere.

CONCLUSION

T. vaginalis is highly prevalent in the Goroka region and in vitro Mz resistance data suggest that clinical resistance may become an issue.

Could giardiasis be a risk factor for low zinc status in schoolchildren from northwestern Mexico? A cross-sectional study with longitudinal follow-up

Background

Both giardiasis and zinc deficiency are serious health problems worldwide. In Mexico, the prevalence of G. intestinalis was estimated at 32% in 1994. It remains a health problem in northwestern Mexico. Recent surveys (1987, 1995, and 1999) reported zinc deficiency in the Mexican population. The association of giardiasis and malabsorption of micronutrients has been well documented, although the association with zinc remains controversial. This study investigated the association between giardiasis and zinc deficiency in schoolchildren from northwestern Mexico.

Methods

We combined a cross-sectional design with a longitudinal follow-up six months after parasite treatment. The baseline sample consisted of 114 schoolchildren (mean age 8.8 yr) from seven suburban public schools, grouped as Giardia-free (n = 65, 57%) and Giardia-infected (n = 49, 43%). Three stool analyses per child were done using Faust's method. Children with giardiasis received secnidazole. Serum zinc was determined by atomic absorption spectrophotometry. Height and weight were measured. Socioeconomic information was obtained in an oral questionnaire, and daily zinc intake was assessed using 24 hour-recalls. Pearson's correlation and ANCOVA and paired t-test analyses were used to determine the association between giardiasis and zinc status.

Results

Longitudinal analysis demonstrated a significant increase of the mean serum zinc levels in the Giardia-infected group six months after treatment (13.78 vs. 19.24 μmol/L μmol/L; p = 0.001), although no difference was found between the Giardia-free and the Giardia-infected groups (p = 0.86) in the baseline analysis. Z scores for W/A and H/A were lower in the Giardia-infected than in the Giardia-free group (p < 0.05). No difference was observed in the socioeconomic characteristics and mean daily intakes of zinc between the groups (p > 0.05).

Conclusions

Giardiasis may be a risk factor for zinc deficiency in schoolchildren from northwestern Mexico.

The flavin inhibitor diphenyleneiodonium renders Trichomonas vaginalis resistant to metronidazole, inhibits thioredoxin reductase and flavin reductase, and shuts off hydrogenosomal enzymatic pathways

Infections with the microaerophilic protozoan parasite Trichomonas vaginalis are commonly treated with metronidazole, a 5-nitroimidazole drug. Metronidazole is selectively toxic to microaerophiles and anaerobes because reduction at the drug's nitro group, which is a precondition for toxicity, occurs only quantitatively in these organisms. In our previous work we identified the flavin enzyme thioredoxin reductase as an electron donor to 5-nitroimidazole drugs in T. vaginalis and observed that highly metronidazole-resistant cell lines lack thioredoxin reductase and flavin reductase activities. In this study we added the flavin inhibitor diphenyleneiodonium (DPI) to T. vaginalis cultures in order to test our hypothesis that metronidazole reduction is catalyzed by flavin enzymes, e.g. thioredoxin reductase, and intracellular free flavins. Indeed, within hours, DPI rendered T. vaginalis insensitive to metronidazole concentrations as high as 1mM and prevented the formation of metronidazole adducts with proteins. Thioredoxin reductase activity was absent from DPI-treated cells and flavin reductase activity was sharply decreased. In addition, DPI-treated cells also upregulated the expression of antioxidant enzymes, i.e. thioredoxin peroxidases and superoxide dismutases, and displayed a fundamentally altered metabolism caused by inactivation of pyruvate:ferredoxin oxidoreductase (PFOR) and concomitant upregulation of lactate dehydrogenase (LDH) activity. Thus, the disruption of the cellular flavin metabolism by DPI mediated metabolic steps which are similar to that of cells with metronidazole resistance induced in vitro. Finally, we present direct evidence that the increased expression of antioxidant enzymes is dispensable for acquiring resistance to metronidazole.

Giardiasis--why do the symptoms sometimes never stop?

Although giardiasis is considered by most medical practitioners to be an easily treated infection, prolonged symptoms due to, or following, Giardia duodenalis infection can have a significant impact on quality of life. Symptom recurrence, including abdominal symptoms and fatigue, can result from re-infection, treatment failure, disturbances in the gut mucosa or post-infection syndromes. In developed countries, these sequelae can have an enormous impact on quality of life; in developing countries, particularly in children, they add yet another burden to populations that are already disadvantaged. Here, we outline current knowledge, based on individual case sequelae from sporadic infections, observations of population effects following outbreaks and studies of phenotypic and genotypic diversity between morphologically identical isolates of parasites. We also raise further questions, looking for clues as to why giardiasis sometimes becomes an intrusive, long-term problem.

Effects of Essential Oils on the Growth of Giardia lamblia Trophozoites

Giardia lamblia is one of the most important worldwide causes of intestinal infections produced by protozoa. Current therapy for giardiasis is unsatisfactory due to high incidence of undesirable side effects and significant failure in clearing parasites from the gastrointestinal tract. In the search for new therapeutic agents, we report on the effect of several essential oils on G. lamblia growth. Among eighteen tested essential oils, those with phenolic compositions were the most active, particularly if containing high contents of carvacrol, such as Thymbra capitata and Origanum virens (IC50 values of 71 and 85 μg.mL−1, respectively). The oils from Syzygium aromaticum and Thymus zygis subsp. sylvestris (IC50 values from 100 to 200 μg.mL−1), as well as, those from Mentha x piperita and Lippia graveolens (IC50 values over 200 μg.mL−1) were less active. Results support the concept that several essential oils or some of their constituents may be useful in the clinical management of Giardia infections.

New hopes from old drugs: revisiting DNA-binding small molecules as anticancer agents

Most of the anticancer chemotherapeutic drugs that are broadly and successfully used today are DNA-damaging agents. Targeting of DNA has been proven to cause relatively potent and selective destruction of tumor cells. However, the clinical potential of DNA-damaging agents is limited by the adverse side effects and increased risk of secondary cancers that are consequences of the agents' genotoxicity. In this review, we present evidence that those agents capable of targeting DNA without inducing DNA damage would not be limited in these ways, and may be as potent as DNA-damaging agents in the killing of tumor cells. We use as an example literature data and our own research of the well-known antimalarial drug quinacrine, which binds to DNA without inducing DNA damage, yet modulates a number of cellular pathways that impact tumor cell survival.

Pathema: a clade-specific bioinformatics resource center for pathogen research

Pathema (http://pathema.jcvi.org) is one of the eight Bioinformatics Resource Centers (BRCs) funded by the National Institute of Allergy and Infectious Disease (NIAID) designed to serve as a core resource for the bio-defense and infectious disease research community. Pathema strives to support basic research and accelerate scientific progress for understanding, detecting, diagnosing and treating an established set of six target NIAID Category A-C pathogens: Category A priority pathogens; Bacillus anthracis and Clostridium botulinum, and Category B priority pathogens; Burkholderia mallei, Burkholderia pseudomallei, Clostridium perfringens and Entamoeba histolytica. Each target pathogen is represented in one of four distinct clade-specific Pathema web resources and underlying databases developed to target the specific data and analysis needs of each scientific community. All publicly available complete genome projects of phylogenetically related organisms are also represented, providing a comprehensive collection of organisms for comparative analyses. Pathema facilitates the scientific exploration of genomic and related data through its integration with web-based analysis tools, customized to obtain, display, and compute results relevant to ongoing pathogen research. Pathema serves the bio-defense and infectious disease research community by disseminating data resulting from pathogen genome sequencing projects and providing access to the results of inter-genomic comparisons for these organisms.

Development of Drug Resistance in Trichomonas vaginalis and its Overcoming with Natural Products

Trichomoniasis is an infectious disease afflicting women worldwide. The protozoan parasite Trichomonas vaginalis is the causative agent of this sexually-transmitted disease, including also men in its infection cycle. The disease is usually not life-threatening, but has been associated with the development of cervical cancer and increased susceptibility to HIV. Approved drugs are 5-nitroimidazoles, with metronidazole being the drug of first choice. These drugs act via induction of oxidative stress and DNA-damage, leading to cell death in the parasite. Nevertheless, with the development of resistant T. vaginalis strains the treatment of the disease becomes exceedingly difficult. Mechanisms of drug resistance are characterized by reduced expression or even loss of proteins necessary for drug activation and a decreased reductive nature in the parasite. A promising strategy for research into new drugs and moreover, to overcome drug resistance, are compounds derived from natural sources. The present study provides a summary of all so far investigated small molecules with antitrichomonal activity; promisingly, some also show efficacy against resistant strains. Whereas the list of chemically characterized compounds derived from plants is rather short, literature provides immense applications of crude plant extracts tested against T. vaginalis. This demonstrates the absence of studies in this field aimed to identify and isolate single natural products exhibiting antitrichomonal features. Likewise, elucidating their mode of action on a molecular basis is of paramount importance

In vitro activity of pyrvinium pamoate against Entamoeba histolytica and Giardia intestinalis using radiolabelled thymidine incorporation and an SYBR Green I-based fluorescence assay

OBJECTIVES

To assess the in vitro activity of the FDA-approved antihelminthic drug pyrvinium pamoate against Entamoeba histolytica and Giardia intestinalis.

METHODS

A head-to-head comparison of a standard radiolabelled thymidine incorporation assay and the SYBR Green I-based fluorescence assay for determination of in vitro inhibition by pyrvinium and metronidazole was performed.

RESULTS

The 50% inhibitory concentration (IC(50)) for treatment of E. histolytica with pyrvinium was 4-5 microM for both assays compared with 1-2 microM for metronidazole. For pyrvinium treatment of G. intestinalis, an IC(50) of approximately 12 microM was determined by the radiolabelled thymidine assay alone, with maximum inhibition around 60%. In contrast, the IC(50) for metronidazole treatment using this assay was approximately 2 microM.

CONCLUSIONS

Pyrvinium is a potential gut lumen agent for treatment of intestinal amoebiasis, but possibly not for giardiasis. SYBR Green I is an alternative screening method for E. histolytica, but not G. intestinalis.

Synthesis and electrochemistry of 2-ethenyl and 2-ethanyl derivatives of 5-nitroimidazole and antimicrobial activity against Giardia lamblia

Infections with the diarrheagenic pathogen, Giardia lamblia, are commonly treated with the 5-nitroimidazole (5-NI) metronidazole (Mz), and yet treatment failures and Mz resistance occur. Using a panel of new 2-ethenyl and 2-ethanyl 5-NI derivatives, we found that compounds with a saturated bridge between the 5-NI core and a pendant ring system exhibited only modestly increased antigiardial activity and could not overcome Mz resistance. By contrast, olefins with a conjugated bridge connecting the core and a substituted phenyl or heterocyclic ring showed greatly increased antigiardial activity without toxicity, and several overcame Mz resistance and were more effective than Mz in a murine giardiasis model. Determination of the half-wave potential of the initial one-electron transfer by cyclic voltammetry revealed that easier redox activation correlated with greater antigiardial activity and capacity to overcome Mz resistance. These studies show the potential of combining systematic synthetic approaches with biological and electrochemical evaluations in developing improved 5-NI drugs.

The old and new therapeutic approaches to the treatment of giardiasis: where are we?

Giardia lamblia is the causative agent of giardiasis, one of the most common parasitic infections of the human intestinal tract. This disease most frequently affects children causing abdominal pain, nausea, vomiting, acute or chronic diarrhea, and malabsorption syndrome. In undernourished children, giardiasis is a determining factor in retarded physical and mental development. Antigiardial chemotherapy focuses on the trophozoite stage. Metronidazole and other nitroimidazoles have been used for decades as the therapy of choice against giardiasis. In recent years many other drugs have been proposed for the treatment of giardiasis. Therefore, several synthetic and natural substances have been tested in search of new giardicidal compounds. This study is a review of drugs used in in vitro and in vivo tests, and also drugs tested in clinical trials (nonrandomized and randomized).

In vitro resistance to 5-nitroimidazoles and benzimidazoles in Giardia duodenalis: variability and variation in gene expression

The susceptibility of Giardia duodenalis trophozoites exposed in vitro to sublethal concentrations of metronidazole (MTZ) and albendazole (ABZ) may exhibit inter-culture (variability) and intra-culture (variation) differences in drug susceptibility. It was previously reported that MTZ-resistant trophozoites may display changes in pyruvate:ferredoxin oxidoreductase (PFOR) expression while changes at the beta-tubulin molecule are apparently absent in ABZ-resistant cultures. To assess the levels of gene expression of these molecules, we obtained cloned cultures growing at concentrations up to 23 microM MTZ (WBRM23) and up to 8muM ABZ (WBRA8) and gene sequence and expression of pfor and beta-tubulin loci were compared with these of drug-susceptible clone WB1. Neither the pfor nor the beta-tubulin genes showed changes at sequence level but the MTZ-resistant clones WBRM21 and WBRM23 showed up-regulation of the pfor RNA using the gdh gene as reference. By using WB1 and WBRA8 clones in representational difference analyses of gene expression (RDA) an insert referred to as ARR-VSP was selected and sequenced. It showed the highest homology to one VSP molecule in the Giardia Genome Database (orf GL50803_101765). This isogene was up-regulated in five ABZ-resistant clones and the clone WBRA8 exhibited the highest RNA expression level. When successive progenies of clones WB1, WBRM23 and WBRA8 were analyzed in Northern blot assays to detect pfor and ARR-VSP RNAs respectively, the expression patterns showed variation for both genes but it was much lower in the clone WBRA8. These results suggest that G. duodenalis cultures either susceptible or resistant to MTZ and ABZ may display variability and variation at RNA expression levels albeit these were more marked in the MTZ-resistant parasites. These data might have further implications defining major mechanisms involved in drug resistance of Giardia.

The role of ATP-binding cassette (ABC) proteins in protozoan parasites

The ATP-binding cassette (ABC) superfamily is one of the largest protein families with representatives in all kingdoms of life. Members of this superfamily are involved in a wide variety of transport processes with substrates ranging from small ions to relatively large polypeptides and polysaccharides, but also in cellular processes such as DNA repair, translation or regulation of gene expression. For many years, the role of ABC proteins was mainly investigated for their implication in drug resistance. However, recent studies focused rather on their physiological functions for the parasite. In this review, we present an overview of ABC proteins in major protozoan parasites including Leishmania, Trypanosoma, Plasmodium, Toxoplasma, Cryptosporidium and Entamoeba species. We will also discuss the role of characterized ABC transporters in the biology of the parasite and in drug resistance.

Trichomonas vaginalis: metronidazole and other nitroimidazole drugs are reduced by the flavin enzyme thioredoxin reductase and disrupt the cellular redox system. Implications for nitroimidazole toxicity and resistance

Infections with the microaerophilic parasite Trichomonas vaginalis are treated with the 5-nitroimidazole drug metronidazole, which is also in use against Entamoeba histolytica, Giardia intestinalis and microaerophilic/anaerobic bacteria. Here we report that in T. vaginalis the flavin enzyme thioredoxin reductase displays nitroreductase activity with nitroimidazoles, including metronidazole, and with the nitrofuran drug furazolidone. Reactive metabolites of metronidazole and other nitroimidazoles form covalent adducts with several proteins that are known or assumed to be associated with thioredoxin-mediated redox regulation, including thioredoxin reductase itself, ribonucleotide reductase, thioredoxin peroxidase and cytosolic malate dehydrogenase. Disulphide reducing activity of thioredoxin reductase was greatly diminished in extracts of metronidazole-treated cells and intracellular non-protein thiol levels were sharply decreased. We generated a highly metronidazole-resistant cell line that displayed only minimal thioredoxin reductase activity, not due to diminished expression of the enzyme but due to the lack of its FAD cofactor. Reduction of free flavins, readily observed in metronidazole-susceptible cells, was also absent in the resistant cells. On the other hand, iron-depleted T. vaginalis cells, expressing only minimal amounts of PFOR and hydrogenosomal malate dehydrogenase, remained fully susceptible to metronidazole. Thus, taken together, our data suggest a flavin-based mechanism of metronidazole activation and thereby challenge the current model of hydrogenosomal activation of nitroimidazole drugs.

Giardia lamblia: a report of drug effects under cell differentiation

The Giardia lamblia life cycle is characterized by two phases during which two major cell differentiation processes take place: encystation and excystation. During encystation, the trophozoites transform into cysts, the resistance form. Once ingested by a susceptible host, the cysts are stimulated to excyst in the stomach, and the excysted trophozoites adhere to the epithelium of the upper small intestine. Our work analyses the effects of four benzimidazole derivatives during Giardia differentiation into cysts and evaluates the excystation efficiency of water resistant cysts. Albendazole (AB) showed the most significant results by inhibiting encystation about 30% and a decreasing rate of excystation efficiency. The ultrastructural organization of the cyst adhesive disk was notably affected by AB treatment. Although other benzimidazoles showed some effect on encystation, they were not able to inhibit the excystation process. It is known that the benzimidazoles affect the cytoskeleton of many organisms but how it interferes in Giardia differentiation processes is our main focus. The importance of studying Giardia's differentiation under drug action is reinforced by the following arguments: (1) Cysts eliminated by hosts undergoing treatment could still be potentially infective; (2) once the host has been treated, it would be desirable that the shedding of cysts into the environment is avoided; (3) the prevention of Giardia dissemination is a question of extreme importance mainly in underdeveloped countries, where poor sanitary conditions are related to high rates of giardiasis. This report concerns the importance of keeping the environment free from infective cysts and on Giardia's drug resistance and differentiating abilities.

Characterization of the NAD(P)H oxidase and metronidazole reductase activities of the RdxA nitroreductase of Helicobacter pylori

Metronidazole (MTZ) is widely used in combination therapies against the human gastric pathogen Helicobacter pylori. Resistance to this drug is common among clinical isolates and results from loss-of-function mutations in rdxA, which encodes an oxygen-insensitive nitroreductase. The RdxA-associated MTZ-reductase activity of H. pylori is lost upon cell disruption. Here we provide a mechanistic explanation for this phenomenon. Under aerobic conditions, His6-tagged RdxA protein (purified from Escherichia coli), catalyzed NAD(P)H-dependent reductions of nitroaromatic and quinone substrates including nitrofurazone, nitrofurantoin, furazolidone, CB1954 and 1,4-benzoquinone, but not MTZ. Unlike other nitroreductases, His6-RdxA exhibited potent NAD(P)H-oxidase activity (k(cat) = 2.8 s(-1)) which suggested two possible explanations for the role of oxygen in MTZ reduction: (a) NAD(P)H-oxidase activity promotes cellular hypoxia (nonspecific reduction of MTZ), and (b) molecular oxygen out-competes MTZ for reducing equivalents. The first hypothesis was eliminated upon finding that rdxA expression, although increasing MTZ toxicity in both E. coli and H. pylori constructs, did not increase paraquat toxicity, even though both are of similar redox potential. The second hypothesis was confirmed by demonstrating NAD(P)H-dependent MTZ-reductase activity (apparent K(m) = 122 +/- 58 microM, k(cat) = 0.24 s(-1)) under strictly anaerobic conditions. The MTZ-reductase activity of RdxA was 60 times greater than for NfsB (E. coli NTR), but 10 times lower than the NADPH-oxidase activity. Whether molecular oxygen directly competes with MTZ or alters the redox state of the FMN cofactors is discussed.

Changes in beta-giardin sequence of Giardia intestinalis sensitive and resistant to albendazole strains

Giardia intestinalis can develop resistance to albendazole, although the molecular mechanism is not understood. The aim of this study was to investigate the differences and permanent mutation in the beta-giardin gene of G. intestinalis strains: sensitive, resistant, or recovered-resistance to albendazole. The beta-giardin gene was amplified by nested polymerase chain reaction. The IC(50) values varied from 0.29 to 0.38 microg/mL for strains sensitive to albendazole. For resistant strains, the IC(50) range was 1.31-2.12 microg/mL. Recovered-sensitivity albendazole strains' IC(50) values were 0.33-0.49 microg/mL, and for strains with recovered-resistance, the IC(50) was 1.42-2.74 microg/mL. beta-giardin amplicon (720 bp) was sequenced and analysis sequence revealed several amino acid mutations from resistant and recovered-sensitive strains of G. intestinalis. Most of the mutations were located in the ROD domain of beta-giardin with a change from the sequence "TIARERA" in sensitive strains instead "IDRPRE" in resistant strains. A comparative sequence analysis in resistant, recovered-sensitive, and resistant-recovered strains revealed permanent mutation. This is the first report of combinatorial serine-proline-arginine repeats in the ROD domain of beta-giardin, whereas such repeats have been reported previously in the HEAD domain of SF-assemblin proteins. This is the first time that the resistance to albendazole correlates with genetics but it is not necessarily caused by mutations in the beta-giardin gene of G. intestinalis.

Lipidomic analysis reveals that phosphatidylglycerol and phosphatidylethanolamine are newly generated phospholipids in an early-divergent protozoan, Giardia lamblia

The pathogenic protozoan Giardia lamblia is known to not synthesize membrane lipids de novo. Therefore, it is possible that lipids in the small intestine, where trophozoites colonize, play key roles in regulating the growth and differentiation of this important pathogen. The focus of the current study is to conduct a complete lipidomic analysis and to test the hypothesis that Giardia has some ability to generate new phospholipids (PLs). Using mass spectrometry, now we show that phosphatidylglycerols (PGs) are major PLs followed by phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) in non-encysting and encysting trophozoites, as well in cysts. The fatty acids attached to these PLs consist mostly of palmitate, palmitoleate, oleate, and linoleate. Results also indicate that PGs and PEs, unlike PCs, are not present in bovine bile and serum, the major sources of lipids of the culture medium, and that they could therefore be produced by fatty acid and headgroup remodeling reactions, circumventing the synthesis of entirely new PLs via de novo pathways. Genomic and transcriptional analyses show the presence of giardial phosphatidylglycerolphosphate synthase (gpgps) and phosphatidylserine decarboxylase (gpsd) genes, which are expressed throughout the life cycle. Bioinformatic and phylogenetic analyses further indicated that both genes are of prokaryotic origin and that they have undergone duplication in the course of evolution. Our studies suggest that the abundance of PG in Giardia is unique among eukaryotes and that its synthesis thus could serve as a potential target for developing new therapies against this waterborne parasite.

Treatment of metronidazole-resistant Trichomonas vaginalis

A 58-year-old Caucasian woman presented with a 14-month history of persistent trichomoniasis not responsive to numerous courses of metronidazole and tinidazole. Vaginal secretion samples were obtained for sensitivity testing and treatment recommendations. In vitro susceptibility testing revealed the patient’s Trichomonas vaginalis isolate was highly resistant to both metronidazole and tinidazole. She was treated with topical furazolidone and experienced a complete symptomatic cure and culture remained negative 35 days post furazolidone treatment.

Inhibitory effects of Iranian Thymus vulgaris extracts on in vitro growth of Entamoeba histolytica

One of the most common drugs used against a wide variety of anaerobic protozoan parasites is metronidazole. However, this drug is mutagenic for bacteria and is a potent carcinogen for rodents. Thymus vulgaris is used for cough suppression and relief of dyspepsia. Also it has antibacterial and antifungal properties. The aim of this study was to investigate antiamebic effect of Thymus vulgaris against Entamoeba histolytica in comparison with metronidazole. One hundred gram air-dried T. vulgaris plant was obtained and macerated at 25 degrees C for 14 days using n-hexane and a mixture of ethanol and water. For essential oil isolation T. vulgaris was subjected to hydrodistillation using a clevenger-type apparatus for 3 hr. E. histolytica, HM-1: IMSS strain was used in all experiments. It was found that the minimal inhibitory concentration (MIC) for T. vulgaris hydroalcoholic, hexanic extracts, and the essential oil after 24 hr was 4 mg/mL, 4 mg/mL, and 0.7 mg/mL, respectively. After 48 hr the MIC for T. vulgaris hydroalcoholic and hexanic extracts was 3 and 3 mg/mL, respectively. Therefore, it can be concluded that the Iranian T. vulgaris is effective against the trophozoites of E. histolytica.

Giardia, Entamoeba, and Trichomonas enzymes activate metronidazole (nitroreductases) and inactivate metronidazole (nitroimidazole reductases)

Infections with Giardia lamblia, Entamoeba histolytica, and Trichomonas vaginalis, which cause diarrhea, dysentery, and vaginitis, respectively, are each treated with metronidazole. Here we show that Giardia, Entamoeba, and Trichomonas have oxygen-insensitive nitroreductase (ntr) genes which are homologous to those genes that have nonsense mutations in metronidazole-resistant Helicobacter pylori isolates. Entamoeba and Trichomonas also have nim genes which are homologous to those genes expressed in metronidazole-resistant Bacteroides fragilis isolates. Recombinant Giardia, Entamoeba, and Trichomonas nitroreductases used NADH rather than the NADPH used by Helicobacter, and two recombinant Entamoeba nitroreductases increased the metronidazole sensitivity of transformed Escherichia coli strains. Conversely, the recombinant nitroimidazole reductases (NIMs) of Entamoeba and Trichmonas conferred very strong metronidazole resistance to transformed bacteria. The Ehntr1 gene of the genome project HM-1:IMSS strain of Entamoeba histolytica had a nonsense mutation, and the same nonsense mutation was present in 3 of 22 clinical isolates of Entamoeba. While ntr and nim mRNAs were variably expressed by cultured Entamoeba and Trichomonas isolates, there was no relationship to metronidazole sensitivity. We conclude that microaerophilic protists have bacterium-like enzymes capable of activating metronidazole (nitroreductases) and inactivating metronidazole (NIMs). While Entamoeba and Trichomonas displayed some of the changes (nonsense mutations and gene overexpression) associated with metronidazole resistance in bacteria, these changes did not confer metronidazole resistance to the microaerophilic protists examined here.

Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection

Blastocystis is a prevalent enteric protozoan that infects a variety of vertebrates. Infection with Blastocystis in humans has been associated with abdominal pain, diarrhea, constipation, fatigue, skin rash, and other symptoms. Researchers using different methods and examining different patient groups have reported asymptomatic infection, acute symptomatic infection, and chronic symptomatic infection. The variation in accounts has lead to disagreements concerning the role of Blastocystis in human disease, and the importance of treating it. A better understanding of the number of species of Blastocystis that can infect humans, along with realization of the limitations of the existing clinical laboratory diagnostic techniques may account for much of the disagreement. The possibility that disagreement was caused by the emergence of particular pathogenic variants of Blastocystis is discussed, along with the potential role of Blastocystis infection in irritable bowel syndrome (IBS). Findings are discussed concerning the role of protease-activated receptor-2 in enteric disease which may account for the presence of abdominal pain and diffuse symptoms in Blastocystis infection, even in the absence of fever and endoscopic findings. The availability of better diagnostic techniques and treatments for Blastocystis infection may be of value in understanding chronic gastrointestinal illness of unknown etiology.

Effect of Lactobacillus casei as a probiotic on modulation of giardiasis

The present study was designed with the aim to study the modulation of giardiasis with natural intervention, i.e., Lactobacillus casei--a probiotic, in a murine model. Probiotics are viable microorganisms having a beneficial effect on the prevention and treatment of specific pathological conditions. Various dairy products such as curd, lassi, and kulfi were employed particularly to isolate live organisms (probiotics). Out of five isolated strains only one was found to be similar to a standard strain--Lactobacillus delbrueckii. Experimentally, it was observed that oral feeding of isolated strain A, 7 days prior to inoculation with Giardia lamblia trophozoites, was not as efficient as L. casei in eliminating Giardia infection from BALB/c mice. Interestingly, it was observed that L. casei fed 7 days prior to Giardia infection was more effective and efficient in eliminating the infection from mice. On histological examination, it was observed that probiotic-fed mice had less atrophied villi and infiltrating cells in the small intestine compared to the control. Ultrastructural studies by scanning electron microscopy further confirmed the protection of the mice dosed with L. casei 7 days prior to Giardia infection and also when simultaneously infected with Giardia. It is felt that probiotics, particularly L. casei, modulate Giardia infection by minimizing or preventing the adherence of Giardia trophozoites to the mucosal surface, suggesting that probiotics offer a safe and effective mode to prevent and treat Giardia infection.

Experimental validation of metabolic pathway modeling

In the search for new drug targets in the human parasite Entamoeba histolytica, metabolic control analysis was applied to determine, experimentally, flux control distribution of amebal glycolysis. The first (hexokinase, hexose-6-phosphate isomerase, pyrophosphate-dependent phosphofructokinase (PP(i)-PFK), aldolase and triose-phosphate isomerase) and final (3-phosphoglycerate mutase, enolase and pyruvate phosphate dikinase) glycolytic segments were reconstituted in vitro with recombinant enzymes under near-physiological conditions of pH, temperature and enzyme proportion. Flux control was determined by titrating flux with each enzyme component. In parallel, both glycolytic segments were also modeled by using the rate equations and kinetic parameters previously determined. Because the flux control distribution predicted by modeling and that determined by reconstitution were not similar, kinetic interactions among all the reconstituted components were experimentally revised to unravel the causes of the discrepancy. For the final segment, it was found that 3-phosphoglycerate was a weakly competitive inhibitor of enolase, whereas PP(i) was a moderate inhibitor of 3-phosphoglycerate mutase and enolase. For the first segment, PP(i) was both a strong inhibitor of aldolase and a nonessential mixed-type activator of amebal hexokinase; in addition, lower V(max) values for hexose-6-phosphate isomerase, PP(i)-PFK and aldolase were induced by PP(i) or ATP inhibition. It should be noted that PP(i) and other metabolites were absent from the 3-phosphoglycerate mutase and enolase or aldolase and hexokinase kinetics experiments, but present in reconstitution experiments. Only by incorporating these modifications in the rate equations, modeling predicted values of flux control distribution, flux rate and metabolite concentrations similar to those experimentally determined. The experimentally validated segment models allowed 'in silico experimentation' to be carried out, which is not easy to achieve in in vivo or in vitro systems. The results predicted a nonsignificant effect on flux rate and flux control distribution by adding parallel routes (pyruvate kinase for the final segment and ATP-dependent PFK for the first segment), because of the much lower activity of these enzymes in the ameba. Furthermore, modeling predicted full flux-control by 3-phosphoglycerate mutase and hexokinase, in the presence of low physiological substrate and product concentrations. It is concluded that the combination of in vitro pathway reconstitution with modeling and enzyme kinetics experimentation permits a more comprehensive understanding of the pathway behavior and control properties.

Identification of differentially expressed genes in a Giardia lamblia WB C6 clone resistant to nitazoxanide and metronidazole

OBJECTIVES

The characterization of differential gene expression in Giardia lamblia WB C6 strain C4 resistant to metronidazole and nitazoxanide using microarray technology and quantitative real-time PCR.

METHODS

In a previous study, we created and characterized the G. lamblia WB C6 clone C4 resistant to nitazoxanide and metronidazole. In this study, using a microarray-based approach, we have identified open-reading frames (ORFs) that were differentially expressed in C4 when compared with its wild-type WB C6. Using quantitative real-time PCR, we have validated the expression patterns of some of those ORFs, focusing on chaperones such as heat-shock proteins in wild-type and C4 trophozoites. In order to induce an antigenic shift, trophozoites of both strains were subjected to a cycle of en- and excystation. Expression of selected genes and resistance to nitazoxanide and metronidazole were investigated after this cycle.

RESULTS

Forty of a total of 9115 ORFs were found to be up-regulated and 46 to be down-regulated in C4 when compared with wild-type. After a cycle of en- and excystation, resistance of C4 to nitazoxanide and metronidazole was lost. Resistance formation and en-/excystation were correlated with changes in expression of ORFs encoding for major surface antigens such as the variant surface protein TSA417 or AS7 ('antigenic shift'). Moreover, expression patterns of the cytosolic heat-shock protein HSP70 B2, HSP40, and of the previously identified nitazoxanide-binding proteins nitroreductase and protein disulphide isomerase PDI4 were correlated with resistance and loss of resistance after en-/excystation. C4 trophozoites had a higher thermotolerance level than wild-type trophozoites. After en-/excystation, this tolerance was lost.

CONCLUSIONS

These results suggest that resistance formation in Giardia to nitazoxanide and metronidazole is correlated with altered expression of genes involved in stress response such as heat-shock proteins.

Nitroimidazole action in Entamoeba histolytica: a central role for thioredoxin reductase

Metronidazole, a 5-nitroimidazole drug, has been the gold standard for several decades in the treatment of infections with microaerophilic protist parasites, including Entamoeba histolytica. For activation, the drug must be chemically reduced, but little is known about the targets of the active metabolites. Applying two-dimensional gel electrophoresis and mass spectrometry, we searched for protein targets in E. histolytica. Of all proteins visualized, only five were found to form adducts with metronidazole metabolites: thioredoxin, thioredoxin reductase, superoxide dismutase, purine nucleoside phosphorylase, and a previously unknown protein. Recombinant thioredoxin reductase carrying the modification displayed reduced enzymatic activity. In treated cells, essential non-protein thiols such as free cysteine were also affected by covalent adduct formation, their levels being drastically reduced. Accordingly, addition of cysteine allowed E. histolytica to survive in the presence of otherwise lethal metronidazole concentrations and reduced protein adduct formation. Finally, we discovered that thioredoxin reductase reduces metronidazole and other nitro compounds, suggesting a new model of metronidazole activation in E. histolytica with a central role for thioredoxin reductase. By reducing metronidazole, the enzyme renders itself and associated thiol-containing proteins vulnerable to adduct formation. Because thioredoxin reductase is a ubiquitous enzyme, similar processes could occur in other eukaryotic or prokaryotic organisms.

The protist parasites Entamoeba histolytica, Trichomonas vaginalis, and Giardia intestinalis grow in environments with low oxygen concentration. Infections with these parasites are commonly treated with metronidazole, a nitroimidazole drug that must be reduced for activation, resulting in several toxic metabolites. We examined the soluble proteome of metronidazole-treated E. histolytica cells for target proteins of these metabolites, applying two-dimensional gel electrophoresis and mass spectrometry. Of about 1,500 proteins visualized, only five formed covalent adducts with metronidazole metabolites, including thioredoxin, thioredoxin reductase, and superoxide dismutase. Metronidazole-bound thioredoxin reductase displayed diminished activity. In addition to these proteins, small thiol molecules, including cysteine, formed adducts with metronidazole. Supplementation with cysteine allowed the cells to survive otherwise lethal metronidazole concentrations. Finally, we discovered that one of the modified proteins, thioredoxin reductase, reduces metronidazole, suggesting a central role for this enzyme with regard to metronidazole toxicity. Taken together, our work reveals a new area of molecular interactions of activated metronidazole with cellular components. Because thioredoxin reductase is a ubiquitous enzyme, similar processes could also occur in other eukaryotic or prokaryotic organisms.

Metronidazole is used for treatment of infections with microaerophilic protist parasites. Here, a new model of metronidazole activation is proposed, with a central role for thioredoxin reductase.

Characterization of a Giardia lamblia WB C6 clone resistant to the isoflavone formononetin

Giardia lamblia is a common intestinal-dwelling protozoan and causes diarrhoea in humans and animals worldwide. For several years, a small number of drugs such as the 5-nitroimidazole metronidazole (MET) or the thiazolide nitazoxanide (NTZ) have been used for chemotherapy against giardiasis. However, various pre-clinical and clinical investigations revealed that antigiardial chemotherapy may be complicated by emergence of giardial resistance to these drugs. The present study addressed the question if isoflavones with antigiardial activity, such as daidzein (DAI) or formononetin (FOR), may serve as alternative compounds for treatment of giardiasis. For this purpose, the potential of G. lamblia clone WB C6 to form resistance to FOR and related isoflavones was tested in vitro. In the line of these experiments, a clone (C3) resistant to isoflavones, but sensitive to MET and NTZ, was generated. Affinity chromatography on DAI-agarose using cell-free extracts of G. lamblia trophozoites resulted in the isolation of a polypeptide of approximately 40 kDa, which was identified by mass spectrometry as a nucleoside hydrolase (NH) homologue (EAA37551.1). In a nucleoside hydrolase assay, recombinant NH hydrolysed all nucleosides with a preference for purine nucleosides and was inhibited by isoflavones. Using quantitative RT-PCR, the expression of genes that are potentially involved in resistance formation was analysed, namely NH and genes encoding variant surface proteins (VSPs, TSA417). The transcript level of the potential target NH was found to be significantly reduced in C3. Moreover, drastic changes were observed in VSP gene expression. This may indicate that resistance formation in Giardia against isoflavones is linked to, and possibly mediated by, altered gene expression. Taken together, our results suggest FOR or related isoflavones as an alternative antigiardial agent to overcome potential problems of resistance to drugs like MET or NTZ. However, the capacity of Giardia to develop resistance to isoflavones can potentially interfere with this alternative treatment of the disease.

Tonic shock induces detachment of Giardia lamblia

BACKGROUND

The parasite Giardia lamblia must remain attached to the host small intestine in order to proliferate and subsequently cause disease. However, little is known about the factors that may cause detachment in vivo, such as changes in the aqueous environment. Osmolality within the proximal small intestine can vary by nearly an order of magnitude between host fed and fasted states, while pH can vary by several orders of magnitude. Giardia cells are known to regulate their volume when exposed to changes in osmolality, but the short-timescale effects of osmolality and pH on parasite attachment are not known.

METHODOLOGY AND PRINCIPAL FINDINGS

We used a closed flow chamber assay to test the effects of rapid changes in media osmolality, tonicity, and pH on Giardia attachment to both glass and C2(Bbe)-1 intestinal cell monolayer surfaces. We found that Giardia detach from both surfaces in a tonicity-dependent manner, where tonicity is the effective osmolality experienced by the cell. Detachment occurs with a characteristic time constant of 25 seconds (SD = 10 sec, n = 17) in both hypo- and hypertonic media but is otherwise insensitive to physiologically relevant changes in media composition and pH. Interestingly, cells that remain attached are able to adapt to moderate changes in tonicity. By exposing cells to a timed pattern of tonicity variations and adjustment periods, we found that it is possible to maximize the tonicity change experienced by the cells, overcoming the adaptive response and resulting in extensive detachment.

CONCLUSIONS AND SIGNIFICANCE

These results, conducted with human-infecting Giardia on human intestinal epithelial monolayers, highlight the ability of Giardia to adapt to the changing intestinal environment and suggest new possibilities for treatment of giardiasis by manipulation of tonicity in the intestinal lumen.

A sphingolipid inhibitor induces a cytokinesis arrest and blocks stage differentiation in Giardia lamblia

Sphingolipid biosynthesis pathways have recently emerged as a promising target for therapeutic intervention against pathogens, including parasites. A key step in the synthesis of complex sphingolipids is the glucosylation of ceramide, mediated by glucosylceramide (GlcCer) synthase, whose activity can be inhibited by PPMP (1-phenyl-2-palmitoylamino-3-morpholino-1-propanol). In this study, we investigated whether PPMP inhibits the proliferation and differentiation of the pathogenic parasite Giardia lamblia, the major cause of parasite-induced diarrhea worldwide. PPMP was found to block in vitro parasite replication in a dose-dependent manner, with a 50% inhibitory concentration of 3.5 muM. The inhibition of parasite replication was irreversible at 10 muM PPMP, a concentration that did not affect mammalian cell metabolism. Importantly, PPMP inhibited the completion of cell division at a specific stage in late cytokinesis. Microscopic analysis of cells incubated with PPMP revealed the aberrant accumulation of cellular membranes belonging to the endoplasmic reticulum network in the caudal area of the parasites. Finally, PPMP induced a 90% reduction in G. lamblia differentiation into cysts, the parasite stage responsible for the transmission of the disease. These results show that PPMP is a powerful inhibitor of G. lamblia in vitro and that as-yet-uncharacterized sphingolipid biosynthetic pathways are potential targets for the development of anti-G. lamblia agents.

Kinetic modeling can describe in vivo glycolysis in Entamoeba histolytica

Glycolysis in the human parasite Entamoeba histolytica is characterized by the absence of cooperative modulation and the prevalence of pyrophosphate-dependent (over ATP-dependent) enzymes. To determine the flux-control distribution of glycolysis and understand its underlying control mechanisms, a kinetic model of the pathway was constructed by using the software gepasi. The model was based on the kinetic parameters determined in the purified recombinant enzymes, and the enzyme activities, and steady-state fluxes and metabolite concentrations determined in amoebal trophozoites. The model predicted, with a high degree of accuracy, the flux and metabolite concentrations found in trophozoites, but only when the pyrophosphate concentration was held constant; at variable pyrophosphate, the model was not able to completely account for the ATP production/consumption balance, indicating the importance of the pyrophosphate homeostasis for amoebal glycolysis. Control analysis by the model revealed that hexokinase exerted the highest flux control (73%), as a result of its low cellular activity and strong AMP inhibition. 3-Phosphoglycerate mutase also exhibited significant flux control (65%) whereas the other pathway enzymes showed little or no control. The control of the ATP concentration was also mainly exerted by ATP consuming processes and 3-phosphoglycerate mutase and hexokinase (in the producing block). The model also indicated that, in order to diminish the amoebal glycolytic flux by 50%, it was required to decrease hexokinase or 3-phosphoglycerate mutase by 24% and 55%, respectively, or by 18% for both enzymes. By contrast, to attain the same reduction in flux by inhibiting the pyrophosphate-dependent enzymes pyrophosphate-phosphofructokinase and pyruvate phosphate dikinase, they should be decreased > 70%. On the basis of metabolic control analysis, steps whose inhibition would have stronger negative effects on the energy metabolism of this parasite were identified, thus becoming alternative targets for drug design.

Application of two-dimensional electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry for proteomic analysis of the sexually transmitted parasite Trichomonas vaginalis

Trichomonas vaginalis is a sexually transmitted protozoan parasite that infects the human urogenital tract causing trichomoniasis, a worldwide disease. In this work, a fresh clinical isolate of T. vaginalis was used for study of the protein expression in this species. Two-dimensional gel electrophoresis (2-DE) and MALDI-TOF/TOF mass spectrometry (MS) were employed to create a reference map of soluble proteins in the pH range 4-7. A set of 116 proteins belonging to functional classes expressed in high and low abundance was identified by peptide mass fingerprinting and tandem MS. These identifications corresponded to 67 different proteins, suggesting that post-translational modifications are common phenomena in T. vaginalis. Identified proteins were classified into 16 groups according to biological processes. Among detected proteins we identified the major enzymes involved in both cytosolic and hydrogenosomal metabolic pathways, as well as putative protein targets for new drug design. In addition, this analysis allows validation of previous gene predictions confirming the expression of 15 hypothetical proteins. Finally, the findings here reported represent the first reference proteome map of T. vaginalis and the first steps towards the description of a comprehensive proteome map of this parasite.

Azasterols impair Giardia lamblia proliferation and induces encystation

The effects of sterol biosynthesis inhibitors on growth and fine structure of Giardia lamblia P1 strain cultures were analyzed. Azasterols demonstrated high efficacy in killing cells. The IC(50) values for 22,26-azasterol and 24(R,S),25-epiminolanosterol were 7muM and 170nM, respectively. Morphological analysis showed that azasterols induced changes in G. lamblia ultrastructure. The most significant alterations were: (a) considerable increase of the size of the peripheral vesicles, which are part of the parasite endosomal-lysosomal system; (b) appearance of autophagosomal structures; and (c) induction of differentiation, followed by an abnormal enlargement of encystation secretory vesicles. We propose that azasterols are effective chemotherapeutic drugs against Giardia lamblia in vitro and may have another target in cells besides sterol biosynthesis.

Effect of Mexican medicinal plant used to treat trichomoniasis on Trichomonas vaginalis trophozoites

Crude methanolic extracts from 22 Mexican medicinal plants were screened for antitrichomonal activity against Trichomonas vaginalis, which is the etiological agent of trichomoniasis. Among the plants tested Carica papaya and Cocos nucifera showed the best antitrichomonal activity with IC(50) values of 5.6 and 5.8 microg/ml, respectively. The extracts of Bocconia frutescens, Geranium mexicanum, and Lygodium venustum showed moderate activity with IC(50) values ranging from 30.9 to 60.9 microg/ml. All the other plant extracts were inactive (IC(50)>100 microg/ml). All extracts tested were less active than metronidazole (IC(50) 0.037 microg/ml), an antiprotozoal drug used as positive control. The results of the antiprotozoal screening support the popular uses of five of the plants tested for the treatment of some urogenital tract disorders in Mexican traditional medicine. However, seeds of Carica papaya and aerial parts of Bocconia frutescens should be used in herbal medicine with care to avoid toxicity.