Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases.

BACKGROUND: Avian schistosomes, the causative agents of human cercarial dermatitis (or swimmer's itch), die in mammals but the mechanisms responsible for parasite elimination are unknown. Here we examined the role of reactive nitrogen species, nitric oxide (NO) and peroxynitrite, in the immune response of mice experimentally infected with Trichobilharzia regenti, a model species of avian schistosomes remarkable for its neuropathogenicity. METHODS: Inducible NO synthase (iNOS) was localized by immunohistochemistry in the skin and the spinal cord of mice infected by T. regenti. The impact of iNOS inhibition by aminoguanidine on parasite burden and growth was then evaluated in vivo. The vulnerability of T. regenti schistosomula to NO and peroxynitrite was assessed in vitro by viability assays and electron microscopy. Additionally, the effect of NO on the activity of T. regenti peptidases was tested using a fluorogenic substrate. RESULTS: iNOS was detected around the parasites in the epidermis 8 h post-infection and also in the spinal cord 3 days post-infection (dpi). Inhibition of iNOS resulted in slower parasite growth 3 dpi, but the opposite effect was observed 7 dpi. At the latter time point, moderately increased parasite burden was also noticed in the spinal cord. In vitro, NO did not impair the parasites, but inhibited the activity of T. regenti cathepsins B1.1 and B2, the peptidases essential for parasite migration and digestion. Peroxynitrite severely damaged the surface tegument of the parasites and decreased their viability in vitro, but rather did not participate in parasite clearance in vivo. CONCLUSIONS: Reactive nitrogen species, specifically NO, do not directly kill T. regenti in mice. NO promotes the parasite growth soon after penetration (3 dpi), but prevents it later (7 dpi) when also suspends the parasite migration in the CNS. NO-related disruption of the parasite proteolytic machinery is partly responsible for this effect.

Pharmacological characterization of a homomeric nicotinic acetylcholine receptor formed by Ancylostoma caninum ACR-16.

Parasitic nematode infections are treated using anthelmintic drugs, some of which target nicotinic acetylcholine receptors (nAChRs) located in different parasite tissues. The limited arsenal of anthelmintic agents and the prevalence of drug resistance imply that future defense against parasitic infections will depend on the discovery of novel targets and therapeutics. Previous studies have suggested that Ascaris suum ACR-16 nAChRs are a suitable target for the development of antinematodal drugs. In this study, we characterized the pharmacology of the Ancylostoma caninum ACR-16 receptor using two-electrode voltage-clamp electrophysiology. This technique allowed us to study the effects of cholinergic agonists and antagonists on the nematode nAChRs expressed in Xenopus laevis oocytes. Aca-ACR-16 was not sensitive to many of the existing cholinomimetic anthelmintics (levamisole, oxantel, pyrantel, and tribendimidine). 3-Bromocytisine was the most potent agonist (> 130% of the control acetylcholine current) on the Aca-ACR-16 nAChR but, unlike Asu-ACR-16, oxantel did not activate the receptor. The mean time constants of desensitization for agonists on Aca-ACR-16 were longer than the rates observed in Asu-ACR-16. In contrast to Asu-ACR-16, the A. caninum receptor was completely inhibited by DHßE and moderately inhibited by α-BTX. In conclusion, we have successfully reconstituted a fully functional homomeric nAChR, ACR-16, from A. caninum, a model for human hookworm infections. The pharmacology of the receptor is distinct from levamisole-sensitive nematode receptors. The ACR-16 homologue also displayed some pharmacological differences from Asu-ACR-16. Hence, A. caninum ACR-16 may be a valid target site for the development of anthelmintics against hookworm infections.

Differences in protein expression associated with ivermectin resistance in Caenorhabditis elegans.

The indiscriminate administration of synthetic anthelmintics such as ivermectin contributes to the selection of subpopulations capable of resisting the drugs' effects. To understand the mechanisms of ivermectin resistance in Caenorhabditis elegans, this study attempted to identify molecular targets. C. elegans lineages that were sensitive and resistant to ivermectin were used. Collected nematodes were added to an extraction buffer and macerated in liquid nitrogen for protein extraction. The extracted proteins were separated according to molecular weight by SDS-PAGE to verify their integrity. Subsequently, proteins from both lineages were separated using two-dimensional electrophoresis. The gels were analyzed and the relevant spots were excised and identified by mass spectrometry (NanoESI-Q-TOF and MASCOT®) and subsequently assessed by GO enrichment and STRING® analyses. The increased expression of proteins associated with high metabolic activity, such as ATP-2 and ENOL-1, which are responsible for ATP synthesis, was observed. Furthermore, proteins with involvement in mediating muscular function (MLC-1, ACT-1, and PDI-2), signaling (FAR-1 and FAR-2), and embryo development (VHA-2) were identified. Protein interaction analysis indicated that the majority of the identified proteins in the resistant lineages participated in the same reaction triggered by ivermectin.

Differences in protein expression associated with ivermectin resistance in Caenorhabditis elegans / Diferenças na expressão de proteínas associadas à resistência à ivermectina em Caenorhabditis elegans

Abstract The indiscriminate administration of synthetic anthelmintics such as ivermectin contributes to the selection of subpopulations capable of resisting the drugs' effects. To understand the mechanisms of ivermectin resistance in Caenorhabditis elegans, this study attempted to identify molecular targets. C. elegans lineages that were sensitive and resistant to ivermectin were used. Collected nematodes were added to an extraction buffer and macerated in liquid nitrogen for protein extraction. The extracted proteins were separated according to molecular weight by SDS-PAGE to verify their integrity. Subsequently, proteins from both lineages were separated using two-dimensional electrophoresis. The gels were analyzed and the relevant spots were excised and identified by mass spectrometry (NanoESI-Q-TOF and MASCOT®) and subsequently assessed by GO enrichment and STRING® analyses. The increased expression of proteins associated with high metabolic activity, such as ATP-2 and ENOL-1, which are responsible for ATP synthesis, was observed. Furthermore, proteins with involvement in mediating muscular function (MLC-1, ACT-1, and PDI-2), signaling (FAR-1 and FAR-2), and embryo development (VHA-2) were identified. Protein interaction analysis indicated that the majority of the identified proteins in the resistant lineages participated in the same reaction triggered by ivermectin.

Resumo A administração indiscriminada de anti-helmínticos sintéticos, como a ivermectina, contribui para a seleção de subpopulações capazes de resistir ao efeito das drogas. Para entender os mecanismos de resistência à ivermectina em Caenorhabditis elegans, este estudo visou identificar alvos moleculares. Portanto, linhagens de C. elegans sensíveis e resistentes à ivermectina foram utilizadas. Os nematóides coletados foram adicionados ao tampão de extração e macerados em nitrogênio líquido para obtenção das proteínas. As proteínas extraídas foram separadas por peso molecular em SDS-PAGE para verificar sua integridade. Posteriormente, as proteínas de ambas as linhagens foram separadas por eletroforese bidimensional. Os géis foram analisados, os spots relevantes foram excisados e identificados por espectrometria de massa (NanoESI-Q-TOF e MASCOT®), em seguida, analisados ​​em seus termos de GO e STRING®. A expressão aumentada de proteínas associadas à alta atividade metabólica, como as proteínas ATP-2 e ENOL-1, responsáveis ​​pela síntese de ATP, foi observada. Além disso, foram identificadas as proteínas responsáveis ​​pelo controle da função muscular (MLC-1, ACT-1 e PDI-2), sinalização (FAR-1 e FAR-2) e desenvolvimento embrionário (VHA-2). A análise das interações proteicas indicou que a maioria das proteínas identificadas na cepa resistente participa da mesma reação desencadeada pela ivermectina.

Nicotine-sensitive acetylcholine receptors are relevant pharmacological targets for the control of multidrug resistant parasitic nematodes.

The control of parasitic nematodes impacting animal health relies on the use of broad spectrum anthelmintics. However, intensive use of these drugs has led to the selection of resistant parasites in livestock industry. In that respect, there is currently an urgent need for novel compounds able to control resistant parasites. Nicotine has also historically been used as a de-wormer but was removed from the market when modern anthelmintics became available. The pharmacological target of nicotine has been identified in nematodes as acetylcholine-gated ion channels. Nicotinic-sensitive acetylcholine receptors (N-AChRs) therefore represent validated pharmacological targets that remain largely under-exploited. In the present study, using an automated larval migration assay (ALMA), we report that nicotinic derivatives efficiently paralyzed a multiple (benzimidazoles/levamisole/pyrantel/ivermectin) resistant field isolate of H. contortus. Using C. elegans as a model we confirmed that N-AChRs are preferential targets for nornicotine and anabasine. Functional expression of the homomeric N-AChR from C. elegans and the distantly related horse parasite Parascaris equorum in Xenopus oocytes highlighted some striking differences in their respective pharmacological properties towards nicotine derivative sensitivity. This work validates the exploitation of the nicotine receptors of parasitic nematodes as targets for the development of resistance-breaking compounds.

Structure-Based Design and Synthesis of Novel Inhibitors Targeting HDAC8 from Schistosoma mansoni for the Treatment of Schistosomiasis.

Schistosomiasis is a major neglected parasitic disease that affects more than 265 million people worldwide and for which the control strategy consists of mass treatment with the only available drug, praziquantel. In this study, a series of new benzohydroxamates were prepared as potent inhibitors of Schistosoma mansoni histone deacetylase 8 (smHDAC8). Crystallographic analysis provided insights into the inhibition mode of smHDAC8 activity by these 3-amidobenzohydroxamates. The newly designed inhibitors were evaluated in screens for enzyme inhibitory activity against schistosome and human HDACs. Twenty-seven compounds were found to be active in the nanomolar range, and some of them showed selectivity toward smHDAC8 over the major human HDACs (1 and 6). The active benzohydroxamates were additionally screened for lethality against the schistosome larval stage using a fluorescence-based assay. Four of these showed significant dose-dependent killing of the schistosome larvae and markedly impaired egg laying of adult worm pairs maintained in culture.

Drug targets for lymphatic filariasis: a bioinformatics approach.

This review article discusses the current scenario of the national and international burden due to lymphatic filariasis (LF) and describes the active elimination programmes for LF and their achievements to eradicate this most debilitating disease from the earth. Since, bioinformatics is a rapidly growing field of biological study, and it has an increasingly significant role in various fields of biology. We have reviewed its leading involvement in the filarial research using different approaches of bioinformatics and have summarized available existing drugs and their targets to re-examine and to keep away from the resisting conditions. Moreover, some of the novel drug targets have been assembled for further study to design fresh and better pharmacological therapeutics. Various bioinformatics-based web resources, and databases have been discussed, which may enrich the filarial research.

Interactions of anthelmintic drugs in Caenorhabditis elegans neuro-muscular ion channel mutants.

Due to the increasing development of anthelmintic resistance in nematodes worldwide, it is important to search for anthelmintic compounds with new modes of action and also to investigate the possibility to combine compounds with possible synergistic effects. There might also be the chance to take advantage of the fact that nematode populations which have developed resistance against one anthelmintic class might respond hypersusceptibly to another drug class. The aim of this study was to investigate responses of Caenorhabditis elegans populations with mutations in neuro-muscular ion channels to different anthelmintic classes. Furthermore, potential synergistic effects between two anthelmintic compounds from different classes, i.e. emodepside and tribendimidine, were studied. Although there was neither a synergistic nor an antagonistic effect between emodepside and tribendimidine, other types of interactions could be identified. The C. elegans GABAA-receptor (GABAA-R) unc-49 mutants, showing decreased emodepside susceptibility, were more susceptible to tribendimidine than wild-type C. elegans. In contrast, the reverse phenomenon - hypersusceptibility to emodepside in tribendimidine resistant acetylcholine-receptor (AChR) loss of function mutants - was not observed. Moreover, the slo-1 mutant strain (completely emodepside resistant) also showed hypersusceptibility to piperazine. Interestingly, neither the GABAA-R unc-49 mutants nor the AChR mutants showed decreased susceptibility against piperazine, although there were some studies that indicated an involvement of GABAA-R or AChR in the piperazine mode of action. In conclusion, the present study provides evidence suggesting that interactions between commercially available anthelmintic drugs with different modes of action might be a relatively common phenomenon but this has to be carefully worked out for each anthelmintic and each anthelmintic drug combination. Moreover, results obtained in C. elegans will have to be confirmed using parasitic nematodes in the future.

Exploration of 2, 4-diaminopyrimidine and 2, 4-diamino-s-triazine derivatives as potential antifilarial agents.

In view of the mandate from the World Health Organization (WHO) for developing novel drug candidates against human lymphatic filariasis, dihydrofolate reductase (DHFR) inhibitors are explored as potential antifilarial agents. The in vitro biological evaluation of an in-house library of 12 diverse antifolate compounds with 2,4-diaminopyrimidine and 2,4-diamino-s-triazine structural features against Brugia malayi is reported. To confirm the DHFR inhibitory potential of these compounds, reversal studies using folic acid and folinic acid were undertaken. Inhibition of DHFR can induce apoptosis; in this light, preliminary evidence of apoptosis by test compounds was detected using ethidium bromide-acridine orange staining and the poly(adenosine diphosphate-ribose) polymerase (PARP) inhibition assay. Among the evaluated compounds, 3 showed significant activity against both microfilariae and adult worms. The effects of 2 of these compounds were mostly reversed by folic acid, validating DHFR inhibitory activity. Partial reversal of the effect of 2 compounds by folinic acid and non-reversal of the effect of the third compound both by folic and folinic acids are discussed. This study opens new avenues for the discovery of lead molecules by exploiting the folate pathway against one of the major neglected tropical diseases, filariasis.

Current drug targets for helminthic diseases.

More than 2 billion people are infected with helminth parasites across the globe. The burgeoning drug resistance against current anthelmintics in parasitic worms of humans and livestock requires urgent attention to tackle these recalcitrant worms. This review focuses on the advancements made in the area of helminth drug target discovery especially from the last few couple of decades. It highlights various approaches made in this field and enlists the potential drug targets currently being pursued to target economically important helminth species both from human as well as livestock to combat disease pathology of schistosomiasis, onchocerciasis, lymphatic filariasis, and other important macroparasitic diseases. Research in the helminths study is trending to identify potential and druggable targets through genomic, proteomic, biochemical, biophysical, in vitro experiments, and in vivo experiments in animal models. The availability of major helminths genome sequences and the subsequent availability of genome-scale functional datasets through in silico search and prioritization are expected to guide the experimental work necessary for target-based drug discovery. Organized and documented list of drug targets from various helminths of economic importance have been systematically covered in this review for further exploring their use and applications, which can give physicians and veterinarians effective drugs in hand to enable them control worm infections.

Nicotinic acetylcholine receptors: a comparison of the nAChRs of Caenorhabditis elegans and parasitic nematodes.

Nicotinic acetylcholine receptors (nAChRs) play a key role in the normal physiology of nematodes and provide an established target site for anthelmintics. The free-living nematode, Caenorhabditis elegans, has a large number of nAChR subunit genes in its genome and so provides an experimental model for testing novel anthelmintics which act at these sites. However, many parasitic nematodes lack specific genes present in C. elegans, and so care is required in extrapolating from studies using C. elegans to the situation in other nematodes. In this review the properties of C. elegans nAChRs are reviewed and compared to those of parasitic nematodes. This forms the basis for a discussion of the possible subunit composition of nAChRs from different species of parasitic nematodes. Currently our knowledge on this is largely based on studies using heterologous expression and pharmacological analysis of receptor subunits in Xenopus laevis oocytes. It is concluded that more information is required regarding the subunit composition and pharmacology of endogenous nAChRs in parasitic nematodes.

Apoptosis phenomenon in the schistosomulum and adult worm life cycle stages of Schistosoma japonicum.

Apoptosis is an important aspect of a number of biological processes, from embryogenesis to the stress-injury response. It plays a central role in balancing cell proliferation and tissue remodeling activity in many organisms. In the present study, apoptosis in 14 days post infection schistosomula was evaluated using TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assays and DAPI staining. Additionally, flow cytometry using the Annexin V-FITC/propidium iodide (PI) (Annexin V/PI) assay confirmed the percentage of early apoptotic, late apoptotic, and necrotic cells in 14 and 23 days post infection worms. Conserved Domain Database (CDD) BLAST analysis and alignment analysis of known schistosome proteins demonstrated the feasibility of detecting the activity of caspase-3 and -7 using the caspase-3/7 Glo analysis assay. Analysis of caspase-3 and -7 activities in schistosome demonstrated that both caspases were active in each developmental stage of Schistosoma japonicum, but was highest in the 14 days post infection schistosomula. Additionally, the caspase peptide inhibitor (Z-VAD-FMK) inhibited the caspase-3/7 activity at all developmental stages examined. Therefore, we hypothesized that two main signaling pathways are involved in apoptosis in S. japonicum, the caspase cascade and the mitochondrial-initiated pathway. We have constructed a model of these two pathways, including how they may interact and their biological outcomes. qRT-PCR analyses of the gene expression profiles of apoptosis-related genes supported our hypothesis of the relationship between the apoptotic pathway and parasite development. The data presented here demonstrates that apoptosis is an important biological process for the survival and development of the schistosome, and identifies potential novel therapeutic targets.

Selective effect of the anthelmintic bephenium on Haemonchus contortus levamisole-sensitive acetylcholine receptors.

Acetylcholine receptors (AChRs) are pentameric ligand-gated ion channels involved in the neurotransmission of both vertebrates and invertebrates. A number of anthelmintic compounds like levamisole and pyrantel target the AChRs of nematodes producing spastic paralysis of the worms. The muscle AChRs of nematode parasites fall into three pharmacological classes that are preferentially activated by the cholinergic agonists levamisole (L-type), nicotine (N-type) and bephenium (B-type), respectively. Despite a number of studies of the B-type AChR in parasitic species, this receptor remains to be characterized at the molecular level. Recently, we have reconstituted and functionally characterized two distinct L-AChR subtypes of the gastro-intestinal parasitic nematode Haemonchus contortus in the Xenopus laevis oocyte expression system by providing the cRNAs encoding the receptor subunits and three ancillary proteins (Boulin et al. in Br J Pharmacol 164(5):1421-1432, 2011). In the present study, the effect of the bephenium drug on Hco-L-AChR1 and Hco-L-AChR2 subtypes was examined using the two-microelectrode voltage-clamp technique. We demonstrate that bephenium selectively activates the Hco-L-AChR1 subtype made of Hco-UNC-29.1, Hco-UNC-38, Hco-UNC-63, Hco-ACR-8 subunits that is more sensitive to levamisole than acetylcholine. Removing the Hco-ACR-8 subunit produced the Hco-L-AChR2 subtype that is more sensitive to pyrantel than acetylcholine and partially activated by levamisole, but which was bephenium-insensitive indicating that the bephenium-binding site involves Hco-ACR-8. Attempts were made to modify the subunit stoichiometry of the Hco-L-AChR1 subtype by injecting five fold more cRNA of individual subunits. Increased Hco-unc-29.1 cRNA produced no functional receptor. Increasing Hco-unc-63, Hco-unc-38 or Hco-acr-8 cRNAs did not affect the pharmacological characteristics of Hco-L-AChR1 but reduced the currents elicited by acetylcholine and the other agonists. Here, we provide the first description of the molecular composition and functional characteristics of any invertebrate bephenium-sensitive receptor.

An UNC-49 GABA receptor subunit from the parasitic nematode Haemonchus contortus is associated with enhanced GABA sensitivity in nematode heteromeric channels.

We have identified two genes from the parasitic nematode Haemonchus contortus, Hco-unc-49B and Hco-unc-49C that encode two GABA-gated chloride channel subunits. Electrophysiological analysis revealed that this channel has properties similar to those of the UNC-49 channel from the free-living nematode Caenorhabditis elegans. For example, the Hco-UNC-49B subunit forms a functional homomeric channel that responds to GABA and is highly sensitive to picrotoxin. Hco-UNC-49C alone does not respond to GABA but can assemble with Hco-UNC-49B to form a heteromeric channel with a lower sensitivity to picrotoxin. However, we did find that the Hco-UNC-49B/C heteromeric channel is significantly more responsive to agonists compared to the Hco-UNC-49B homomeric channel, which is the opposite trend to what has been found previously for the C. elegans channel. To investigate the subunit requirements for high agonist sensitivity, we generated cross-assembled channels by co-expressing the H. contortus subunits with UNC-49 subunits from C. elegans (Cel-UNC-49). Co-expressing Cel-UNC-49B with Hco-UNC-49C produced a heteromeric channel with a reduced sensitivity to GABA compared to that of the Cel-UNC-49B homomeric channel. In contrast, co-expressing Hco-UNC-49B with Cel-UNC-49C produced a heteromeric channel that, like the Hco-UNC-49B/C heteromeric channel, exhibits an increased sensitivity to GABA. These results suggest that the Hco-UNC-49B subunit is the key determinant for the high agonist sensitivity of heteromeric channels.

Modulation of a Schistosoma mansoni multidrug transporter by the antischistosomal drug praziquantel.

P-glycoprotein (Pgp) is an ATP-dependent efflux pump involved in transport of xenobiotics from cells that, when overexpressed, can mediate multidrug resistance in mammalian cells. Pgp may be a candidate target for new anthelmintics, as it plays critical roles in normal cell physiology, in removal of drugs from cells, and potentially in the development of drug resistance. Schistosomes are parasitic flatworms that cause schistosomiasis, which affects hundreds of millions of people worldwide. Here, we express SMDR2, a Pgp homologue from Schistosoma mansoni (Platyhelminthes), in Chinese hamster ovary (CHO) cells and use fluorescence-based assays to examine the functional and pharmacological properties of this transporter. Membrane vesicles from stably transfected CHO cells expressing recombinant SMDR2 show significant increases in rhodamine transport and ATP hydrolysis compared with those from control cells or cells transfected with empty vector. SMDR2-mediated transport is inhibited by the Pgp modulators verapamil (IC(50)=12.1 muM) and nifedipine, and also by praziquantel, the current drug of choice against schisotosomiasis (IC(50)=17.4 muM). Efflux measurements of a fluorescent analog of praziquantel indicate that it is also a substrate for SMDR2. The interaction of praziquantel with SMDR2 may offer new strategies for potentiating the action of praziquantel and possibly overcoming drug resistance.

A combined bioinformatics and chemoinformatics approach for the development of new antiparasitic drugs.

A modern concept for the development of novel antiparasitic drugs is the combination of bioinformatics and chemoinformatics approaches. This covers, for example, the identification of target proteins serving as molecular points of attack for parasiticides--the idea is that, owing to some essential role, inhibition of a target protein should eradicate the parasite. To prevent toxicity problems for vertebrate host organisms, it is advantageous that these proteins show significant differences from their vertebrate counterparts. In the present work, we identified potential target proteins in parasitic nematodes (Ascaris suum, Brugia malayi, and Haemonchus contortus) and arthropods (Boophilus microplus and Rhipicephalus appendiculatus) using bioinformatic sequence comparison methods on expressed sequence tags. Interesting target proteins (e.g., S-adenosyl-l-methionine synthetase) were characterized in detail by subjecting them to in-depth bioinformatic analysis. S-Adenosyl-l-methionine synthetase was also used to elucidate chemoinformatics approaches like homology modeling and docking, which represent appropriate methods for generating valuable data for the development of new drug candidates.

Fluoride exposure inhibits protein expression and enzyme activity in the lung-stage larvae of Ascaris suum.

Sodium fluoride (NaF) is an anion that has been previously shown to block the moulting process of Ascaris suum larvae. This study describes moulting and development-specific protein expression profiles of A. suum lung-stage L3 (AsLL3) following NaF exposure. AsLL3s cultured in the presence or absence of NaF were prepared for protein analysis using two-dimensional (2D) electrophoresis. NaF exposure inhibited at least 22 proteins in AsLL3 compared with moulted larvae (i.e. AsLL4). A further comparison of AsLL4 with those of pre-cultured AsLL3 and NaF-exposed AsLL3 revealed 8 stage-specifically and 4 over-expressed proteins. Immunoblot analysis revealed an inhibition by NaF of 19 immunoreactive proteins. Enzyme assay and immunochemical data showed an inhibition of the moulting-specific inorganic pyrophosphatase activity by 41% and a decreased expression in NaF-treated larvae, indicating its significance in the moulting process. A protein spot associated with NaF inhibition was isolated and identified by peptide mass spectrometry and bioinformatics approaches to be a member of 3-hydroxyacyl-CoA dehydrogenase/short-chain dehydrogenase enzyme families. These results have implications for the identification of proteins specific to the moulting process as potential chemotherapeutic targets.

Molecular characterization of a family of metalloendopeptidases from the intestinal brush border of Haemonchus contortus.

Substantial protection against the economically important parasitic nematode Haemonchus contortus has been achieved by immunizing sheep with a glycoprotein fraction isolated from the intestinal membranes of the worm (H-gal-GP). Previous studies showed that one of the major components of H-gal-GP is a family of at least 4 zinc metalloendopeptidases, designated MEPs 1-4. This paper describes aspects of the molecular architecture of this protease family, including the proteomic analysis of the MEP fraction of the H-gal-GP complex. These enzymes belong to the M13 zinc metalloendopeptidase family (EC 3.4.24.11), also known as neutral endopeptidases or neprilysins. The sequences of MEPs 1 and 3 suggested a typical Type II integral membrane protein structure, whilst MEPs 2 and 4 had putative cleavable signal peptides, typical of secreted proteins. Proteomic analysis of H-gal-GP indicated that the extracellular domain of all 4 MEPs had been cleaved close to the transmembrane region/signal peptide with additional cleavage sites mid-way along the polypeptide. MEP3 was present as a homo-dimer in H-gal-GP, whereas MEP1 or MEP2 formed hetero-dimers with MEP4. It was found that expression of MEP3 was confined to developing 4th-stage larvae and to adult worms, the stages of Haemonchus which feed on blood. MEP-like activity was detected in the H-gal-GP complex over a broad pH range (5-9). Since all 4 MEPs must share a similar microenvironment in the complex, this suggests that each might have a different substrate specificity.

Molecular cloning and characterization of a novel lactate dehydrogenase gene from Clonorchis sinensis.

From a Clonorchis sinensis adult worm cDNA library, we isolated a cDNA clone encoding a novel lactate dehydrogenase (LDH) gene which encoded a putative protein with a predicted molecular weight of 35.6 kDa. The optimum pH and temperature for the enzyme were 7.5 and 50 degrees C in the pyruvate reduction while 11 and 80 degrees C in the lactate oxidation reaction, respectively. CsLDH showed no substrate inhibition by high lactate and NAD(+) concentration, and the optimal pyruvate and optimal NADH concentrations were 10 and 0.5 mmol/l, respectively. The relative activities of these 2-oxocarboxylic acids were pyruvic acid>2-ketobutyrate>oxalacetic acid>alpha-ketoglutaric acid>phenylpyruvate. The cofactor 3-acetylpyridine adenine dinucleotide was much more effective than NAD(+). The cofactor analogs in which the nicotinamide ring is replaced by 3-pyridinealdehyde were lower activity cofactors, while the nicotinamide ring is replaced by nicotinic acid or thionicotinamide which is not a cofactor to CsLDH. The succinic acid and malic acid are not substrates of CsLDH. Cu(2+), Fe(2+), and Zn(2+) greatly inhibited the CsLDH activity both in the direction of pyruvate reduction and in the direction of lactate oxidation. The inhibition of CsLDH by gossypol may make gossypol a potential therapy drug or a lead compound for C. sinensis. Accordingly, the CsLDH may be a novel potential drug target.

Oral administration of a live Aro attenuated Salmonella vaccine strain expressing 14-kDa Schistosoma mansoni fatty acid-binding protein induced partial protection against experimental schistosomiasis.

We report the oral vaccination of SWISS mice with an Aro attenuated Salmonella enterica var. Typhimurium vaccine strain expressing the 14-kDa Schistosoma mansoni antigen, Sm14. Bacterial adjuvants, including (i) Lactococcus lactis expressing interleukin-12 (IL-12) and (ii) Lactobacillus delbrueckii UFV-H2b20, were also employed in oral immunization assays. Detection assays to specific IgG and IgA anti-Sm14 antibodies were performed to evaluate humoral immune responses in vaccinated mice. An increase in specific IgG titers was observed; however, no IgA production was detected. The protection levels against schistosomiasis (34.9-49.5%) obtained with all experimental formulations in this work were very similar to values reported by previous studies, which used purified recombinant Sm14 for parenteral vaccination of mice. There was a slight reduction in hepatic granulomas of mice vaccinated with Salmonella. Oogram studies showed diminished numbers of S. mansoni eggs in the intestinal wall of vaccinated mice, but individual female worm fecundity did not seem to be affected by our immunization protocol.