Thioredoxin glutathione reductase as a novel drug target: evidence from Schistosoma japonicum

Inhibitory effects and analysis of RNA interference on thioredoxin glutathione reductase expression in Schistosoma japonicum

Schistosomes infect around 280 million people worldwide. The worms survive in the veins of the final host, where thioredoxin glutathione reductase (TGR) activity helps the parasites to survive in the aerobic environment. In the present study, we synthesized 4 small interfering RNAs (siRNA S1, S2, S3, and S4) targeting the Schistosoma japonicum (Sj) TGR gene and used them to knockdown the TGR gene. The knockdown effects of the siRNAs on SjTGR, and the thioredoxin reductase (TrxR) activity of SjTGR, were evaluated in vitro. The results of transfection with the siRNAs via the soaking method in vitro were confirmed by flow cytometry. S2 siRNA at a final concentration of 200 nM partially inhibited the expression of SjTGR at both the transcript and protein levels in vitro. TrxR-activity was lower in worms in the S2 siRNA-treated group compared with the control groups. Further analysis revealed that purified recombinant SjTGR could remove oxygen free radicals but not H(2)O(2) directly, which may explain the incomplete effects of RNA interference on SjTGR. The results of this study indicate that SjTGR may play an important role in the clearance of oxygen free radicals and protection of S. japonicum parasites against oxidative damage.

Expression, crystallization and preliminary X-ray diffraction analysis of thioredoxin glutathione reductase from Schistosoma japonicum in complex with FAD

Thioredoxin glutathione reductase from Schistosoma japonicum (SjTGR), a multifunctional enzyme, plays a vital role in antioxidant pathways and is considered to be a potential drug target for the development of antischistosomal chemotherapy. In this study, two constructs of a truncated form of SjTGR without the last two residues (Sec597-Gly598) were cloned, overexpressed and purified using wild-type and codon-optimized genes. Only SjTGR from the wild-type gene was found to form a complex with flavin adenine dinucleotide (FAD), which could be crystallized in the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 84.185, b = 86.47, c = 183.164 Å, at 295 K using the hanging-drop vapour-diffusion method. One dimer was present in the crystallographic asymmetric unit and the calculated Matthews coefficient (VM) and solvent content were 2.6 Å(3) Da(-1) and 52.8%, respectively. Structural determination of SjTGR is in progress using the molecular-replacement method.

Antioxidant, antibacterial and antischistosomal activities of extracts from Grateloupia livida (Harv). Yamada

The present study was designated to evaluate the antioxidant, antibacterial and antischistosomal activities of Grateloupia livida (GL) extracts in vitro. A GL Ethanol extract (EE) was separated into petroleum ether (PE), ethyl acetate (EA), n-butyl alcohol (BuOH) and aqueous (AQ) fractions to fractionate the polar and non-polar compounds in the EE. Extracts antioxidant activities were evaluated in vitro by DPPH radical-scavenging, deoxyribose radical scavenging, and β-carotene bleaching assays, all using butylated hydroxytoluene (BHT) as the reference antioxidant compound. The most effective antioxidant properties were observed in the PE fraction in all three assays. Antimicrobial testing showed that the PE fraction exhibited broad-spectrum antimicrobial activity, with the PE fraction also exhibiting strong activity against the human pathogenic trematode S. japonicum adult worm. In order to investigate the relationships between bioactivity and chemical composition, the chemical composition of the PE fraction was analyzed by gas chromatography-mass spectrometry (GC-MS). In total, 25 components were identified in the PE fraction, most of which have known antioxidant and antimicrobial activities. However, none of the compounds have reported activity against Schistosoma, suggesting that the schistosomicidal activity of the PE fraction may be related to minor constituents present in the extract, or governed by more intricate synergistic or additive relationships. Finally, fractions with the greatest biological activity displayed neither cellular cytotoxicity, at concentrations up to 100 ug/ml, or acute oral toxicity in mice, at doses up to 2000 mg/kg. Based on antioxidant, antimicrobial, antischistosomal activities, and low toxicity, the PE fraction possesses properties useful for food preservation and overall improvement of human health.

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.

Synthesis and SAR studies of praziquantel derivatives with activity against Schistosoma japonicum

The synthesis and structure-activity relationship (SAR) studies of praziquantel derivatives with activity against adult Schistosoma japonicum are described. Several of them showed better worm killing activity than praziquantel and could serve as leads for further optimization.

Proteomic characterization of larval and adult developmental stages in Echinococcus granulosus reveals novel insight into host-parasite interactions

Cystic hydatid disease is an important zoonosis caused by Echinococcus granulosus infection. The expression profiles of its parasitic life stages and host-Echinococcus interactions remain to be elucidated. Here, we identified 157 adult and 1588 protoscolex proteins (1610 in all), including 1290 novel identifications. Paramyosins and an antigen B (AgB) were the dominant adult proteins. Dog proteins (30) identified in adults indicated diminished local inflammation caused by adult infection. The protoscolex expresses proteins that have been reported to be antigens in other parasites, such as 6-phosphofructokinase and calcineurin B. Pathway analyses suggested that E. granulosus uses both aerobic and anaerobic carbohydrate metabolisms to generate ATP. E. granulosus expresses proteins involved in synthesis and metabolism of lipids or steroids. At least 339 of 390 sheep proteins identified in protoscolex were novel identifications not seen in previous analyses. IgGs and lambda light chains were the most abundant antibody species. Sheep proteins were enriched for detoxification pathways, implying that host detoxification effects play a central role during host-parasite interactions. Our study provides valuable data on E. granulosus expression characteristics, allowing novel insights into the molecular mechanisms involved in host-parasite interactions.

BIOLOGICAL SIGNIFICANCE

In this study, the Echinococcus granulosus adult worm proteome was analyzed for the first time. The protein identification of E. granulosus protoscoleces was extended dramatically. We also identified the most abundant host proteins co-purified with Echinococcus. The results provide useful information pertaining to the molecular mechanisms behind host-Echinococcus interaction and Echinococcus biology. This data also increases the potential for identifying vaccine candidates and new therapeutic targets, and may aid in the development of protein probes for selective and sensitive diagnosis of echinococcosis infection. In addition, the data collected here represents a valuable proteomic resource for subsequent genome annotation.

Gene gun bombardment with DNA-coated golden particles enhanced the protective effect of a DNA vaccine based on thioredoxin glutathione reductase of Schistosoma japonicum

Schistosomiasis, caused by infection with Schistosoma species, remains an important parasitic zoonosis. Thioredoxin glutathione reductase of Schistosoma japonicum (SjTGR) plays an important role in the development of the parasite and for its survival. Here we present a recombinant plasmid DNA vaccine, pVAX1/SjTGR, to estimate its protection against S. japonicum in BALB/c mice. The DNA vaccine administrated by particle bombardment induced higher protection than by intramuscular injection. All animals vaccinated with pVAX1/SjTGR developed significant specific anti-SjTGR antibodies than control groups. Moreover, animals immunized by gene gun exhibited a splenocyte proliferative response, with an increase in IFN-γ and IL-4. The recombinant plasmid administrated by gene gun achieved a medium protective efficacy of 27.83–38.83% (P < 0.01) of worm reduction and 40.38–44.51% (P < 0.01) of liver egg count reduction. It suggests that different modes of administering a DNA vaccine can influence the protective efficacy induced by the vaccine. Interestingly, from the enzymatic activity results, we found that worms obtained from pVAX1/SjTGR-vaccinated animals expressed lower enzymatic activity than the control group and the antibodies weakened the enzymatic activity of SjTGR in vitro, too. It implies that the high-level antibodies may contribute to the protective effects.

Molecular cloning and characterization of Schistosoma japonicum aldose reductase

Antioxidant defense is an essential mechanism for schistosomes to cope with damage from host immune-generated reactive oxygen species. The evaluation of the effects of aldose reductase, an important enzyme that may be involved in this system, has long been neglected. In the present study, aldose reductase of Schistosoma japonicum (SjAR) was cloned and characterized. The activity of SjAR was assessed in vitro and was suppressed by the reported inhibitor, epalrestat. RT-PCR analysis revealed that SjAR was expressed at each of the development stages analyzed with increased levels in cercariae. The results also showed that SjAR was expressed at higher levels in adult male worms than in adult female worms. Indirect enzyme-linked immunosorbent assay and western blot analysis indicated that the purified recombinant SjAR (rSjAR) protein displayed a significant level of antigenicity. Immunolocalization analysis revealed that SjAR was mainly distributed in the gynecophoral canal of adult male worms. BALB/c mice immunized with rSjAR induced a 32.91 % worm reduction compared to the adjuvant group (P < 0.01). Moreover, a 28.27 % reduction in egg development in the liver (P > 0.05) and a 42.75 % reduction in egg development in the fecal samples (P < 0.05) were also observed. These results suggested that SjAR may be a potential new drug target or vaccine candidate for schistosomes.