Purification, kinetics and inhibition by antimonials of recombinant phosphofructokinase from Schistosoma mansoni

Proteomic analysis of Ascocotyle longa (Trematoda: Heterophyidae) metacercariae

Ascocotyle longa is parasitic trematode with wide distribution throughout America, Europe, Africa, and Middle East. Despite the fact that this fish-borne pathogen has been considered an agent of human heterophyiasis in Brazil, the molecules involved in the host-parasite interaction remain unknown. The present study reports the proteome profile of A. longa metacercariae collected from the fish Mugil liza from Brazil. This infective stage for humans, mammals and birds was analyzed using nLC-MS/MS approach. We identified a large repertoire of proteins, which are mainly involved in energy metabolism and cell structure. Peptidases and immunogenic proteins were also identified, which might play roles in host-parasite interface. Our data provided unprecedented insights into the biology of A. longa and represent a first step to understand the natural host-parasite interaction. Moreover, as the first proteome characterized in this trematode, it will provide an important resource for future studies.

Thioredoxin glutathione reductase-dependent redox networks in platyhelminth parasites

SIGNIFICANCE

Platyhelminth parasites cause chronic infections that are a major cause of disability, mortality, and economic losses in developing countries. Maintaining redox homeostasis is a major adaptive problem faced by parasites and its disruption can shift the biochemical balance toward the host. Platyhelminth parasites possess a streamlined thiol-based redox system in which a single enzyme, thioredoxin glutathione reductase (TGR), a fusion of a glutaredoxin (Grx) domain to canonical thioredoxin reductase (TR) domains, supplies electrons to oxidized glutathione (GSSG) and thioredoxin (Trx). TGR has been validated as a drug target for schistosomiasis.

RECENT ADVANCES

In addition to glutathione (GSH) and Trx reduction, TGR supports GSH-independent deglutathionylation conferring an additional advantage to the TGR redox array. Biochemical and structural studies have shown that the TR activity does not require the Grx domain, while the glutathione reductase and deglutathionylase activities depend on the Grx domain, which receives electrons from the TR domains. The search for TGR inhibitors has identified promising drug leads, notably oxadiazole N-oxides.

CRITICAL ISSUES

A conspicuous feature of platyhelminth TGRs is that their Grx-dependent activities are temporarily inhibited at high GSSG concentrations. The mechanism underlying the phenomenon and its biological relevance are not completely understood.

FUTURE DIRECTIONS

The functional diversity of Trxs and Grxs encoded in platyhelminth genomes remains to be further assessed to thoroughly understand the TGR-dependent redox network. Optimization of TGR inhibitors and identification of compounds targeting other parasite redox enzymes are good options to clinically develop relevant drugs for these neglected, but important diseases.

A portrait of the transcriptome of the neglected trematode, Fasciola gigantica--biological and biotechnological implications

Fasciola gigantica (Digenea) is an important foodborne trematode that causes liver fluke disease (fascioliasis) in mammals, including ungulates and humans, mainly in tropical climatic zones of the world. Despite its socioeconomic impact, almost nothing is known about the molecular biology of this parasite, its interplay with its hosts, and the pathogenesis of fascioliasis. Modern genomic technologies now provide unique opportunities to rapidly tackle these exciting areas. The present study reports the first transcriptome representing the adult stage of F. gigantica (of bovid origin), defined using a massively parallel sequencing-coupled bioinformatic approach. From >20 million raw sequence reads, >30,000 contiguous sequences were assembled, of which most were novel. Relative levels of transcription were determined for individual molecules, which were also characterized (at the inferred amino acid level) based on homology, gene ontology, and/or pathway mapping. Comparisons of the transcriptome of F. gigantica with those of other trematodes, including F. hepatica, revealed similarities in transcription for molecules inferred to have key roles in parasite-host interactions. Overall, the present dataset should provide a solid foundation for future fundamental genomic, proteomic, and metabolomic explorations of F. gigantica, as well as a basis for applied outcomes such as the development of novel methods of intervention against this neglected parasite.

Fasciola gigantica (Digenea) is a socioeconomically important liver fluke of humans and other mammals. It is the predominant cause of fascioliasis in the tropics and has a serious impact on the lives of tens of millions of people and other animals; yet, very little is known about this parasite and its relationship with its hosts at the molecular level. Here, advanced sequencing and bioinformatic technologies were employed to explore the genes transcribed in the adult stage of F. gigantica. From >20 million raw reads, >30,000 contiguous sequences were assembled. Relative levels of transcription were estimated; and molecules were characterized based on homology, gene ontology, and/or pathway mapping. Comparisons of the transcriptome of F. gigantica with those of other trematodes, including F. hepatica, showed similarities in transcription for molecules predicted to play roles in parasite-host interactions. The findings of the present study provide a foundation for a wide range of fundamental molecular studies of this neglected parasite, as well as research focused on developing new methods for the treatment, diagnosis, and control of fascioliasis.

The role of tegumental aquaporin from the human parasitic worm, Schistosoma mansoni, in osmoregulation and drug uptake

Schistosomes are parasitic platyhelminths that constitute an important public health problem globally. Infection is characterized by the presence of adult worms within the vasculature of their hosts, where they can reside for many years. The worms are covered by an unusual dual lipid bilayer through which they import nutrients. How the parasites import other vital molecules, such as water, is not known. Recent proteomic analysis of the schistosome tegumental membranes revealed the presence of an aquaporin homologue at the host-interactive surface whose cDNA we have cloned and characterized. The cDNA encodes a predicted 304-aa protein (SmAQP) that is found largely in the parasite tegument by immunolocalization and is most highly expressed in the intravascular life stages. Treatment of parasites with short interfering RNAs targeting the SmAQP gene results in potent (>90%) suppression. These suppressed parasites resist swelling when placed in hypotonic medium, unlike their control counterparts, which rapidly double in volume. In addition, SmAQP-suppressed parasites, unlike controls, resist shrinkage when incubated in hyperosmotic solution. While suppressed parasites exhibit lower viability in culture relative to controls and exhibit a stunted appearance following prolonged suppression, they are nonetheless more resistant to killing by the drug potassium antimonyl tartrate (PAT). This is likely because SmAQP acts as a conduit for this drug, as is the case for aquaporins in other systems. These experiments reveal a heretofore unrecognized role of the schistosome tegument in controlling water and drug movement into the parasites and highlight the importance of the tegument in parasite osmoregulation and drug uptake.

Thioredoxin glutathione reductase from Schistosoma mansoni: an essential parasite enzyme and a key drug target

BACKGROUND

Schistosomiasis--infection with helminth parasites in the genus Schistosoma, including S. mansoni--is a widespread, devastating tropical disease affecting more than 200 million people. No vaccine is available, and praziquantel, the only drug extensively utilized, is currently administered more than 100 million people yearly. Because praziquantel resistance may develop it is essential to identify novel drug targets. Our goal was to investigate the potential of a unique, selenium-containing parasite enzyme thioredoxin glutathione reductase (TGR) as a drug target.

METHODS AND FINDINGS

Using RNA interference we found that TGR is essential for parasite survival; after silencing of TGR expression, in vitro parasites died within 4 d. We also found that auranofin is an efficient inhibitor of pure TGR (Ki = 10 nM), able to kill parasites rapidly in culture at physiological concentrations (5 microM), and able to partially cure infected mice (worm burden reductions of ~60%). Furthermore, two previously used antischistosomal compounds inhibited TGR activity, suggesting that TGR is a key target during therapy with those compounds.

CONCLUSIONS

Collectively, our results indicate that parasite TGR meets all the major criteria to be a key target for antischistosomal chemotherapy. To our knowledge this is the first validation of a Schistosoma drug target using a convergence of both genetic and biochemical approaches.

Drugs, their targets and the nature and number of drug targets

What is a drug target? And how many such targets are there? Here, we consider the nature of drug targets, and by classifying known drug substances on the basis of the discussed principles we provide an estimation of the total number of current drug targets.

Schistosoma mansoni: biochemical characterization of lactate transporters or similar proteins

While in medium containing glucose, schistosomes exhibit homolactic fermentation. Accumulation of lactate acid in tissue fluid causes lowering of pH and a resultant inhibition of metabolic pathways. This requires lactate transporter protein in homolactic fermentors to facilitate the translocation of lactate(-) and [H(+)] across their plasma membrane. The ex-vivo experiment assessed lactic acid secretion by adult worms in absence and the presence of lactic acid transporter protein inhibitors. Phloretin and alpha-cyano-4-hydroxycinnamate caused a combined 25-35% inhibition of lactic acid secretion and probenecid increased this inhibition to 65% of control values. The removal of inhibitors resulted in 80% recovery of lactic acid secretion. In the in-vitro studies using vesicles isolated from adult worms and from schistosomula, the effects of phloretin and alpha-cyano-4-hydroxycinnamate were greater, each causing approximately 80% inhibition independently. The data obtained in this study demonstrate the presence of lactic acid transporters or similar proteins in Schistosoma mansoni.