Molecular cloning, expression and characterization of a recombinant glutathione S-transferase from Echinococcus multilocularis

Molecular characteristics of glutathione transferase gene family in a neglect medical Spirometra tapeworm

The Spirometra mansoni is a neglect medical tapeworm, its plerocercoid larvae can parasitize in humans and animals, causing sparganosis. In this study, 17 new members of the glutathione transferase (GST) family were sequenced and characterized in S. mansoni. Clustering analysis displayed the categorization of SmGSTs into two main clades. RT-qPCR illustrated that 7 GST genes were highly expressed in the plerocercoid stage while 8 GSTs were highly expressed in the adult. rSmGST has the typical C- and N-terminal double domains of glutathione transferase. Immunolocalization revealed that natural SmGST is mainly located in the epidermis and parenchyma of plerocercoid, and in the epidermis, parenchyma, uterus and egg shell of adult worm. The optimum activity for rSmGST was found to be pH 6.5 and 25°C. The evolutionary tree showed a high level of diversity of cestodes GSTs. SmGSTs contained both conserved family members and members in the process of further diversification. The findings in this study will lay a foundation to better explore the underlying mechanisms of GSTs involved in Spirometra tapeworms.

Assessment of Electronic Sensing Techniques for the Rapid Identification of Alveolar Echinococcosis through Exhaled Breath Analysis

Here we present a proof-of-concept study showing the potential of a chemical gas sensors system to identify the patients with alveolar echinococcosis disease through exhaled breath analysis. The sensors system employed comprised an array of three commercial gas sensors and a custom gas sensor based on WO₃ nanowires doped with gold nanoparticles, optimized for the measurement of common breath volatile organic compounds. The measurement setup was designed for the concomitant measurement of both sensors DC resistance and AC fluctuations during breath samples exposure. Discriminant Function Analysis classification models were built with features extracted from sensors responses, and the discrimination of alveolar echinococcosis was estimated through bootstrap validation. The commercial sensor that detects gases such as alkane derivatives and ethanol, associated with lipid peroxidation and intestinal gut flora, provided the best classification (63.4% success rate, 66.3% sensitivity and 54.6% specificity) when sensors’ responses were individually analyzed, while the model built with the AC features extracted from the responses of the cross-reactive sensors array yielded 90.2% classification success rate, 93.6% sensitivity and 79.4% specificity. This result paves the way for the development of a noninvasive, easy to use, fast and inexpensive diagnostic test for alveolar echinococcosis diagnosis at an early stage, when curative treatment can be applied to the patients.

Unraveling oxidative stress response in the cestode parasite Echinococcus granulosus

Cystic hydatid disease (CHD) is a worldwide neglected zoonotic disease caused by Echinococcus granulosus. The parasite is well adapted to its host by producing protective molecules that modulate host immune response. An unexplored issue associated with the parasite's persistence in its host is how the organism can survive the oxidative stress resulting from parasite endogenous metabolism and host defenses. Here, we used hydrogen peroxide (H₂O₂) to induce oxidative stress in E. granulosus protoescoleces (PSCs) to identify molecular pathways and antioxidant responses during H₂O₂ exposure. Using proteomics, we identified 550 unique proteins; including 474 in H₂O₂-exposed PSCs (H-PSCs) samples and 515 in non-exposed PSCs (C-PSCs) samples. Larger amounts of antioxidant proteins, including GSTs and novel carbonyl detoxifying enzymes, such as aldo-keto reductase and carbonyl reductase, were detected after H₂O₂ exposure. Increased concentrations of caspase-3 and cathepsin-D proteases and components of the 26S proteasome were also detected in H-PSCs. Reduction of lamin-B and other caspase-substrate, such as filamin, in H-PSCs suggested that molecular events related to early apoptosis were also induced. We present data that describe proteins expressed in response to oxidative stress in a metazoan parasite, including novel antioxidant enzymes and targets with potential application to treatment and prevention of CHD.

Treatment of echinococcosis: albendazole and mebendazole--what else?

The search for novel therapeutic options to cure alveolar echinococcosis (AE), due to the metacestode of Echinococcus multilocularis, is ongoing, and these developments could also have a profound impact on the treatment of cystic echinococcosis (CE), caused by the closely related Echinococcus granulosus s.l. Several options are being explored. A viable strategy for the identification of novel chemotherapeutically valuable compounds includes whole-organism drug screening, employing large-scale in vitro metacestode cultures and, upon identification of promising compounds, verification of drug efficacy in small laboratory animals. Clearly, the current focus is targeted towards broad-spectrum anti-parasitic or anti-cancer drugs and compound classes that are already marketed, or that are in development for other applications. The availability of comprehensive Echinococcus genome information and gene expression data, as well as significant progress on the molecular level, has now opened the door for a more targeted drug discovery approach, which allows exploitation of defined pathways and enzymes that are essential for the parasite. In addition, current in vitro and in vivo models that are used to assess drug efficacy should be optimized and complemented by methods that give more detailed information on the host-parasite interactions that occur during drug treatments. The key to success is to identify, target and exploit those parasite molecules that orchestrate activities essential to parasite survival.

Biochemical analysis of a recombinant glutathione transferase from the cestode Echinococcus granulosus

Glutathione transferases (GSTs) are believed to be a major detoxification system in helminths. We describe the expression and functional analysis of EgGST, a cytosolic GST from Echinococcus granulosus, related to the Mu-class of mammalian enzymes. EgGST was produced as an enzymatically active dimeric protein (rEgGST), with highest specific activity towards the standard substrate 1-chloro-2,4-dinitrobenzene (CDNB; 2.5 micromol min(-1)mg(-1)), followed by ethacrynic acid. Interestingly, rEgGST displayed glutathione peroxidase activity (towards cumene hydroperoxide), and conjugated reactive carbonyls (trans-2-nonenal and trans,trans-2,4-decadienal), indicating that it may intercept damaging products of lipid peroxidation. In addition, classical GST inhibitors (cybacron blue, triphenylthin chloride and ellagic acid) and a number of anthelmintic drugs (mainly, hexachlorophene and rafoxanide) were found to interfere with glutathione-conjugation to CDNB; suggesting that they may bind to EgGST. Considered globally, the functional properties of rEgGST are similar to those of putative orthologs from Echinococcus multilcularis and Taenia solium, the other medically important cestodes. Interestingly, our results also indicate that differences exist between these closely related cestode GSTs, which probably reflect specific biological functions of the molecules in each parasitic organism.

Application of an in vitro drug screening assay based on the release of phosphoglucose isomerase to determine the structure-activity relationship of thiazolides against Echinococcus multilocularis metacestodes

OBJECTIVES

The disease alveolar echinococcosis (AE), caused by the larval stage of the cestode Echinococcus multilocularis, is fatal if treatment is unsuccessful. Current treatment options are, at best, parasitostatic, and involve taking benzimidazoles (albendazole, mebendazole) for the whole of a patient's life. In conjunction with the recent development of optimized procedures for E. multilocularis metacestode cultivation, we aimed to develop a rapid and reliable drug screening test, which enables efficient screening of a large number of compounds in a relatively short time frame.

METHODS

Metacestodes were treated in vitro with albendazole, the nitro-thiazole nitazoxanide and 29 nitazoxanide derivatives. The resulting leakage of phosphoglucose isomerase (PGI) activity into the medium supernatant was measured and provided an indication of compound efficacy.

RESULTS

We show that upon in vitro culture of E. multilocularis metacestodes in the presence of active drugs such as albendazole, the nitro-thiazole nitazoxanide and 30 different nitazoxanide derivatives, the activity of PGI in culture supernatants increased. The increase in PGI activity correlated with the progressive degeneration and destruction of metacestode tissue in a time- and concentration-dependent manner, which allowed us to perform a structure-activity relationship analysis on the thiazolide compounds used in this study.

CONCLUSIONS

The assay presented here is inexpensive, rapid, can be used in 24- and 96-well formats and will serve as an ideal tool for first-round in vitro tests on the efficacy of large numbers of antiparasitic compounds.

Enzymatic antioxidant systems in helminth parasites

Parasitic helminths have a coexistence with mammalian hosts whereby they survive for several years in known hostile conditions of their hosts. Many explanations exist describing how these parasitic helminths are able to survive. In the last years, a lot of studies have focused on both enzymatic and non-enzymatic antioxidant systems now shown to exist in these parasites and which may serve as defence tactics against the host-generated oxygen radicals. The relevance of antioxidant enzymes is confirmed by the fact that some of these molecules represent putative protective anti-parasite vaccines (i.e. in schistosomiasis). This review tries to compile what is known to date of the enzymatic antioxidant systems in selected parasitic helminths.

Alveolar and cystic echinococcosis: towards novel chemotherapeutical treatment options

Echinococcus granulosus and Echinococcus multilocularis are cestode parasites, of which the metacestode (larval) stages cause the neglected diseases cystic echinococcosis (CE) and alveolar echinococcosis (AE), respectively. The benzimidazoles albendazole and mebendazole are presently used for the chemotherapeutical treatment, alone or prior to and after surgery. However, in AE these benzimidazoles do not appear to be parasiticidal in vivo. In addition, failures in drug treatments as well as the occurrence of side-effects have been reported, leading to discontinuation of treatment or to progressive disease. Therefore, new drugs are needed to cure AE and CE. Strategies that are currently employed in order to identify novel chemotherapeutical treatment options include in vitro and in vivo testing of broad-spectrum anti-infective drugs or drugs that interfere with unlimited proliferation of cancer cells. The fact that the genome of E. multilocularis has recently been sequenced has opened other avenues, such as the selection of novel drugs that interfere with the parasite signalling machinery, and the application of in silico approaches by employing the Echinococcus genome information to search for suitable targets for compounds of known mode of action.

Glutathione transferases from parasites: a biochemical view

The glutathione transferase (GST) system of parasites represents the main detoxification mechanism of hydrophobic and electrophilic compounds. Parasites lack the CYP450 activity, hence part of its function has been taken over by other enzymes including GSTs. Cytosolic GSTs (cGSTs) are found in this system and constitute a versatile and numerous group that in parasites display many peculiarities in contrast to mammalian cGSTs. This review summarizes aspects of the biochemistry of parasite cGSTs such as substrate specificities, inhibitor sensitivities, classification, kinetics and catalysis, as well as some aspects of their protective role.

Brugia malayi and Wuchereria bancrofti: gene comparison and recombinant expression of pi-class related glutathione S-transferases

The nucleotide sequences for Brugia malayi and Wuchereria bancrofti GST have been submitted to EMBL, GenBank, and DDBJ Nucleotide Sequence Databases under Accession Nos. Y12788 and AY195867.

Molecular cloning and characterization of a mu-class glutathione S-transferase from Clonorchis sinensis

In biliary passages, Clonorchis sinensis causes epithelial hyperplasia and is assumed to promote carcinogenesis. Glutathione S-transferase (GST) is an antioxidant enzyme involved in phase II defense in trematodes. A clone (pcsGSTM1) encoding a GST was identified by screening a C. sinensis cDNA library with a PCR-synthesized cDNA probe. The predicted amino acid sequence encoded by pcsGSTM1 cDNA had a high degree of sequence identity and folding topology similar to the mu-class GSTs. The estimated molecular mass of the protein, 26 kDa, was consistent with an expression by pcsGSTM1 cDNA. The bacterially expressed recombinant csGSTM1 protein possessed an enzymatic GST activity and conjugated GSH to reactive carbonyls of lipid peroxidation. The recombinant csGSTM1 protein did not share antigenic epitope(s) with GSTs of Fasciola hepatica, Paragonimus westermani and Schistosoma japonicum. The csGSTM1 was identified to a mu-class GST in C. sinensis.

Molecular cloning and enzymatic expression of the 28-kDa glutathione S-transferase of Schistosoma japonicum: evidence for sequence variation but lack of consistent vaccine efficacy in the murine host

Glutathione S-transferases (GSTs) have long been regarded as attractive vaccine (and drug) targets in schistosomes due to their suspected role in detoxification processes. Indeed, the 28-kDa GST of Schistosoma mansoni (SmGST28) has proven efficacy as an antigen for protective immunity reducing worm burden, female fecundity and egg viability. In contrast, the vaccinating effects of the bacterial expressed homologue of Philippine S. japonicum (SjpGST28) have proved disappointing, possibly because this recombinant form was an incomplete sequence, lacking five N-terminal amino acids which may have affected its vaccination efficacy. Here we describe the cloning and functional enzymatic expression of a complete cDNA encoding SjpGST28. We report also on the immunogenicity and vaccine efficacy of this molecule as a purified recombinant protein and as a DNA plasmid vaccine in the murine model. We further describe the cloning of several complete cDNAs encoding the Chinese homologue of SjpGST28 and the identification of 3 SjcGST28 sequence variants which are probably encoded by distinct alleles.

Paragonimus westermani: a cytosolic glutathione S-transferase of a sigma-class in adult stage

We purified cytosolic glutathione S-transferase (GST) of adult Paragonimus westermani monitoring its activity with 1-chloro-2,4-dinitrobenzene (CDNB). The enzyme was purified 18.4-fold to electrophoretic homogeneity with 21% recovery rate through a three-step procedure. The purified enzyme (Pw28GST) has a subunit molecular weight of 28 kDa with an isoelectric point at 4.6. Monoclonal antibody (anti-Pw28GST) against Pw28GST did not cross-react with GSTs from other helminths. cDNA library was constructed in lambdaZAP II bacteriophage and screened with anti-Pw28GST. The corresponding gene containing a single open reading frame of 804 bp encoded 211 amino acids. The predicted amino acid sequence exhibited a higher homology with catalytic domain near N-terminus of class sigma GSTs (58%) than with schistosome 28-kDa GSTs (45-41%) or with class sigma GSTs themselves (33-31%). The sequence contained both Tyr-6 and Tyr-10 that are highly conserved in mammalian and helminth GSTs. The apparent K(m) value of a recombinant enzyme was 0.78 mM. Both native and recombinant enzymes showed the highest activity against CDNB, relatively weak activity against ethacrynic acid and reactive carbonyls, and no activity against epoxy-3-(p-nitrophenoxy)-propane. The activities were inhibited by bromosulfophthalein, cibacron blue, and albendazole, but not by praziquantel. These findings indicate that adult P. westermani has a class sigma GST.

Application of molecular biology in veterinary parasitology

The number of applications of molecular biology in veterinary parasitology is increasing rapidly. The techniques used with eukaryotic cells are generally applicable to the study of parasites and their hosts. The polymerase chain reaction is particularly important for identification and diagnosis of parasites, as well as for many other applications. With species and type specific probes or primers, sensitivities and specificities unheard of with conventional techniques can be achieved. The accumulation of more information on the DNA sequences of parasites will reveal many more unique sequences which can be used for identification, diagnosis, molecular epidemiology, vaccine development and for studying the evolutionary biology and the physiology of parasites and the host-parasite relationship. Similarly, the completion of genome projects on host organisms will greatly assist efforts to select for hosts that are genetically resistant to parasite infection. The study of the molecular biology of antiparasitic drug receptors, potential targets for chemotherapy, and the molecular genetics of drug resistance will allow molecular screens to be used with combinatorial chemistry in the search for new antiparasitic drugs, improvements to existing chemotherapeutic families and better diagnosis and monitoring of drug resistance. While there is a proliferation of molecular biology techniques, the availability of simple kits and of automated techniques and services for sequencing, library construction and oligonucleotide synthesis and other procedures is making it easier for non-specialists to apply many of the common techniques of molecular biology. Molecular biology and the benefits from its application are relevant for veterinary parasitologists in developing countries as well as developed countries and we should introduce aspects of molecular biology to the teaching and training of veterinary parasitologists.

Structural and functional analysis of a glutathione S-transferase from Ascaris suum

A recombinant glutathione S-transferase (GST) (EC 2.5.1.18) from the parasitic nematode Ascaris suum (AsGST1) displays specific activity with a variety of model substrates and secondary products of lipid peroxidation. The AsGST1 interacts with a range of model inhibitors, haematin-related compounds, bile acids and anthelminthics. The reported variations in biochemical activity correlate with structural differences observed by homology modelling. Here, differences in the topography of the proposed substrate binding site between the AsGST1 and the host GSTs were identified. A rabbit polyclonal antiserum was raised against the glutathione-binding proteins of A. suum and specific antibodies against AsGST1 were affinity-purified using the recombinant protein. These antibodies were used to localize the AsGST1 in adult worms by immunohistochemical staining. The strongest immunostaining for AsGST1 was localized in the intestine in all worms examined. This suggests that the enzyme may be responsible for the metabolism of materials that are incorporated from the environment, as well as for molecules that are excreted or secreted from the parasite to the environment. It also demonstrates the accessibility of the enzyme to an inhibitor or blocking antibody. In addition, the structure and sequence of the gene encoding AsGST1 have been determined. Southern-blot analyses of the AsGST1 gene suggests that it is a single-copy gene. The nucleotide sequence analysis revealed that the gene is composed of four exons and three introns, and potential regulatory elements were identified in the 5' flanking sequence.