Schistosomiasis control: keep taking the tablets

Praziquantel inhibits Caenorhabditis elegans development and species-wide differences might be cct-8-dependent

Anthelmintic drugs are used to treat parasitic roundworm and flatworm infections in humans and other animals. Caenorhabditis elegans is an established model to investigate anthelmintics used to treat roundworms. In this study, we use C. elegans to examine the mode of action and the mechanisms of resistance against the flatworm anthelmintic drug praziquantel (PZQ), used to treat trematode and cestode infections. We found that PZQ inhibited development and that this developmental delay varies by genetic background. Interestingly, both enantiomers of PZQ are equally effective against C. elegans, but the right-handed PZQ (R-PZQ) is most effective against schistosome infections. We conducted a genome-wide association mapping with 74 wild C. elegans strains to identify a region on chromosome IV that is correlated with differential PZQ susceptibility. Five candidate genes in this region: cct-8, znf-782, Y104H12D.4, Y104H12D.2, and cox-18, might underlie this variation. The gene cct-8, a subunit of the protein folding complex TRiC, has variation that causes a putative protein coding change (G226V), which is correlated with reduced developmental delay. Gene expression analysis suggests that this variant correlates with slightly increased expression of both cct-8 and hsp-70. Acute exposure to PZQ caused increased expression of hsp-70, indicating that altered TRiC function might be involved in PZQ responses. To test if this variant affects development upon exposure to PZQ, we used CRISPR-Cas9 genome editing to introduce the V226 allele into the N2 genetic background (G226) and the G226 allele into the JU775 genetic background (V226). These experiments revealed that this variant was not sufficient to explain the effects of PZQ on development. Nevertheless, this study shows that C. elegans can be used to study PZQ mode of action and resistance mechanisms. Additionally, we show that the TRiC complex requires further evaluation for PZQ responses in C. elegans.

A review of the genetic determinants of praziquantel resistance in Schistosoma mansoni: Is praziquantel and intestinal schistosomiasis a perfect match?

Schistosomiasis is a neglected tropical disease (NTD) caused by parasitic trematodes belonging to the Schistosoma genus. The mainstay of schistosomiasis control is the delivery of a single dose of praziquantel (PZQ) through mass drug administration (MDA) programs. These programs have been successful in reducing the prevalence and intensity of infections. Due to the success of MDA programs, the disease has recently been targeted for elimination as a public health problem in some endemic settings. The new World Health Organization (WHO) treatment guidelines aim to provide equitable access to PZQ for individuals above two years old in targeted areas. The scale up of MDA programs may heighten the drug selection pressures on Schistosoma parasites, which could lead to the emergence of PZQ resistant schistosomes. The reliance on a single drug to treat a disease of this magnitude is worrying should drug resistance develop. Therefore, there is a need to detect and track resistant schistosomes to counteract the threat of drug resistance to the WHO 2030 NTD roadmap targets. Until recently, drug resistance studies have been hindered by the lack of molecular markers associated with PZQ resistance. This review discusses recent significant advances in understanding the molecular basis of PZQ action in S. mansoni and proposes additional genetic determinants associated with PZQ resistance. PZQ resistance will also be analyzed in the context of alternative factors that may decrease efficacy within endemic field settings, and the most recent treatment guidelines recommended by the WHO.

Vaccines for Human Schistosomiasis: Recent Progress, New Developments and Future Prospects

Schistosomiasis, caused by human trematode blood flukes (schistosomes), remains one of the most prevalent and serious of the neglected tropical parasitic diseases. Currently, treatment of schistosomiasis relies solely on a single drug, the anthelmintic praziquantel, and with increased usage in mass drug administration control programs for the disease, the specter of drug resistance developing is a constant threat. Vaccination is recognized as one of the most sustainable options for the control of any pathogen, but despite the discovery and reporting of numerous potentially promising schistosome vaccine antigens, to date, no schistosomiasis vaccine for human or animal deployment is available. This is despite the fact that Science ranked such an intervention as one of the top 10 vaccines that need to be urgently developed to improve public health globally. This review summarizes current progress of schistosomiasis vaccines under clinical development and advocates the urgent need for the establishment of a revolutionary and effective anti-schistosome vaccine pipeline utilizing cutting-edge technologies (including developing mRNA vaccines and exploiting CRISPR-based technologies) to provide novel insight into future vaccine discovery, design, manufacture and deployment.

A Comparative Proteomic Analysis of Praziquantel-Susceptible and Praziquantel-Resistant Schistosoma mansoni Reveals Distinct Response Between Male and Female Animals

Schistosomiasis is a chronic neglected tropical disease saddling millions of people in the world, mainly children living in poor rural areas. Praziquantel (PZQ) is currently the only drug used for the treatment and control of this disease. However, the extensive use of this drug has brought concern about the emergence of PZQ-resistance/tolerance by Schistosoma mansoni. Studies of Schistosoma spp. genome, transcriptome, and proteome are crucial to better understand this situation. In this in vitro study, we compare the proteomes of a S. mansoni variant strain stably resistant to PZQ and isogenic to its fully susceptible parental counterpart, identifying proteins from male and female adult parasites of PZQ-resistant and PZQ-susceptible strains, exposed and not exposed to PZQ. A total of 60 Schistosoma spp. proteins were identified, some of which present or absent in either strain, which may putatively be involved in the PZQ-resistance phenomenon. These proteins were present in adult parasites not exposed to PZQ, but some of them disappeared when these adult parasites were exposed to the drug. Understanding the development of PZQ-resistance in S. mansoni is crucial to prolong the efficacy of the current drug and develop markers for monitoring the potential emergence of drug resistance.

CRISPR/Cas9-mediated genome editing of Schistosoma mansoni acetylcholinesterase

CRISPR/Cas9-mediated genome editing shows cogent potential for the genetic modification of helminth parasites. We report successful gene knock-in (KI) into the genome of the egg of Schistosoma mansoni by combining CRISPR/Cas9 with single-stranded oligodeoxynucleotides (ssODNs). We edited the acetylcholinesterase (AChE) gene of S. mansoni targeting two guide RNAs (gRNAs), X5 and X7, located on exon 5 and exon 7 of Smp_154600, respectively. Eggs recovered from livers of experimentally infected mice were transfected by electroporation with a CRISPR/Cas9-vector encoding gRNA X5 or X7 combining with/ without a ssODN donor. Next generation sequencing analysis of reads of amplicon libraries spanning targeted regions revealed that the major modifications induced by CRISPR/Cas9 in the eggs were generated by homology directed repair (HDR). Furthermore, soluble egg antigen from AChE-edited eggs exhibited markedly reduced AChE activity, indicative that programed Cas9 cleavage mutated the AChE gene. Following injection of AChE-edited schistosome eggs into the tail veins of mice, an significantly enhanced Th2 response involving IL-4, -5, -10, and-13 was detected in lung cells and splenocytes in mice injected with X5-KI eggs in comparison to control mice injected with unmutated eggs. A Th2-predominant response, with increased levels of IL-4, -13, and GATA3, also was induced by X5 KI eggs in small intestine-draining mesenteric lymph node cells when the gene-edited eggs were introduced into the subserosa of the ileum of the mice. These findings confirmed the potential and the utility of CRISPR/Cas9-mediated genome editing for functional genomics in schistosomes.

Rational approach to drug discovery for human schistosomiasis

Human schistosomiasis is a debilitating, life-threatening disease affecting more than 229 million people in as many as 78 countries. There is only one drug of choice effective against all three major species of Schistosoma, praziquantel (PZQ). However, as with many monotherapies, evidence for resistance is emerging in the field and can be selected for in the laboratory. Previously used therapies include oxamniquine (OXA), but shortcomings such as drug resistance and affordability resulted in discontinuation. Employing a genetic, biochemical and molecular approach, a sulfotransferase (SULT-OR) was identified as responsible for OXA drug resistance. By crystallizing SmSULT- OR with OXA, the mode of action of OXA was determined. This information allowed a rational approach to novel drug design. Our team approach with schistosome biologists, medicinal chemists, structural biologists and geneticists has enabled us to develop and test novel drug derivatives of OXA to treat this disease. Using an iterative process for drug development, we have successfully identified derivatives that are effective against all three species of the parasite. One derivative CIDD-0149830 kills 100% of all three human schistosome species within 5 days. The goal is to generate a second therapeutic with a different mode of action that can be used in conjunction with praziquantel to overcome the ever-growing threat of resistance and improve efficacy. The ability and need to design, screen, and develop future, affordable therapeutics to treat human schistosomiasis is critical for successful control program outcomes.

An iterative process produces oxamniquine derivatives that kill the major species of schistosomes infecting humans

Currently there is only one method of treatment for human schistosomiasis, the drug praziquantel. Strong selective pressure has caused a serious concern for a rise in resistance to praziquantel leading to the necessity for additional pharmaceuticals, with a distinctly different mechanism of action, to be used in combination therapy with praziquantel. Previous treatment of Schistosoma mansoni included the use of oxamniquine (OXA), a prodrug that is enzymatically activated in S. mansoni but is ineffective against S. haematobium and S. japonicum. The oxamniquine activating enzyme was identified as a S. mansoni sulfotransferase (SmSULT-OR). Structural data have allowed for directed drug development in reengineering oxamniquine to be effective against S. haematobium and S. japonicum. Guided by data from X-ray crystallographic studies and Schistosoma worm killing assays on oxamniquine, our structure-based drug design approach produced a robust SAR program that tested over 300 derivatives and identified several new lead compounds with effective worm killing in vitro. Previous studies resulted in the discovery of compound CIDD-0066790, which demonstrated broad-species activity in killing of schistosome species. As these compounds are racemic mixtures, we tested and demonstrate that the R enantiomer CIDD-007229 kills S. mansoni, S. haematobium and S. japonicum better than the parent drug (CIDD-0066790). The search for derivatives that kill better than CIDD-0066790 has resulted in a derivative (CIDD- 149830) that kills 100% of S. mansoni, S. haematobium and S. japonicum adult worms within 7 days. We hypothesize that the difference in activation and thus killing by the derivatives is due to the ability of the derivative to fit in the binding pocket of each sulfotransferase (SmSULT-OR, ShSULT-OR, SjSULT-OR) and to be efficiently sulfated. The purpose of this research is to develop a second drug to be used in conjunction with praziquantel to treat the major human species of Schistosoma. Collectively, our findings show that CIDD-00149830 and CIDD-0072229 are promising novel drugs for the treatment of human schistosomiasis and strongly support further development and in vivo testing.

Crystal structure and chemical inhibition of essential schistosome host-interactive virulence factor carbonic anhydrase SmCA

The intravascular parasitic worm Schistosoma mansoni is a causative agent of schistosomiasis, a disease of great global public health significance. Here we identify an α-carbonic anhydrase (SmCA) that is expressed at the schistosome surface as determined by activity assays and immunofluorescence/immunogold localization. Suppressing SmCA expression by RNAi significantly impairs the ability of larval parasites to infect mice, validating SmCA as a rational drug target. Purified, recombinant SmCA possesses extremely rapid CO₂ hydration kinetics (k_cat: 1.2 × 10⁶ s^-1; k_cat/K_m: 1.3 × 10⁸ M^-1s^-1). The enzyme’s crystal structure was determined at 1.75 Å resolution and a collection of sulfonamides and anions were tested for their ability to impede rSmCA action. Several compounds (phenylarsonic acid, phenylbaronic acid, sulfamide) exhibited favorable K_is for SmCA versus two human isoforms. Such selective rSmCA inhibitors could form the basis of urgently needed new drugs that block essential schistosome metabolism, blunt parasite virulence and debilitate these important global pathogens.

Akram Da’dara et al. report the biochemical characterization of an α-carbonic anhydrase (SmCA) expressed at the surface of the parasitic worm Schistosoma mansoni. Along with the crystal structure of SmCA, they show the function of selective inhibitors in blocking essential schistosome metabolism.

Transcriptomic analysis of reduced sensitivity to praziquantel in Schistosoma mansoni

Schistosomiasis is an intravascular parasitic infection estimated to affect over 206 million people, the majority of whom live in Africa where the trematode worms Schistosoma mansoni and Schistosoma haematobium are the major causative agents. While a number of drugs have been used to treat schistosomiasis, praziquantel (PZQ) is the only one that is widely available, relatively cheap, and easy to use. The reliance on a single drug for the treatment of such a prevalent disease is a cause for concern due to the potential for resistance to render PZQ ineffective. In this study, we examine the transcriptome of three generations of a laboratory strain of S. mansoni (PR1) whose susceptibility to PZQ has been diminished across 9 passages through exposure to increasing sub-lethal doses of the drug. Miracidial susceptibility was significantly reduced after exposure to 2 × 50 mg/Kg PZQ during the first passage. Susceptibility of worms in vivo was first assessed during passage 5 when mice infected with PZQ-selected schistosomes were dosed with a lethal dose of 3 × 300 mg/kg PZQ resulting in only a 10% reduction in worm number compared to control treatment. The emergence of reduced sensitivity was marked by a shift in sex ratio from a predominantly male to a female population, a reduction in the length of females and ultimately the loss of the PZQ-selected line after passage 9. Analysis of differentially regulated transcripts did not suggest that any particular gene product or pathway was associated with drug resistance suggesting either a loss of function mutation to a single gene or an epistatic interaction of multiple gene products as the underlying cause of reduced susceptibility.

PZQ Therapy: How Close are we in the Development of Effective Alternative Anti-schistosomal Drugs?

Today schistosomiasis, caused mainly by the three major schistosome species (S. mansoni, S. haematobium and S. japonicum), has for many decades and still continues to be on a rapid and swift rise globally, claiming thousands of lives every year and leaving 800 million people at the risk of infection. Due to the high prevalence of this disease and the steady increase in the infection rates, praziquantel (PZQ) remains the only effective drug against this acute disease although it has no effect on the juvenile schistosome parasite. However, no significant approaches have been made in recent years in the discovery of new or alternative drugs and unfortunately, resistance to this drug has been reported in some parts of the world. Therefore, it is imperative to develop a new drug for this debilitating disease. In this review, a brief history of past, present, and new promising anti-schistosomal drugs is presented.

Computationally-guided drug repurposing enables the discovery of kinase targets and inhibitors as new schistosomicidal agents

The development of novel therapeutics is urgently required for diseases where existing treatments are failing due to the emergence of resistance. This is particularly pertinent for parasitic infections of the tropics and sub-tropics, referred to collectively as neglected tropical diseases, where the commercial incentives to develop new drugs are weak. One such disease is schistosomiasis, a highly prevalent acute and chronic condition caused by a parasitic helminth infection, with three species of the genus Schistosoma infecting humans. Currently, a single 40-year old drug, praziquantel, is available to treat all infective species, but its use in mass drug administration is leading to signs of drug-resistance emerging. To meet the challenge of developing new therapeutics against this disease, we developed an innovative computational drug repurposing pipeline supported by phenotypic screening. The approach highlighted several protein kinases as interesting new biological targets for schistosomiasis as they play an essential role in many parasite’s biological processes. Focusing on this target class, we also report the first elucidation of the kinome of Schistosoma japonicum, as well as updated kinomes of S. mansoni and S. haematobium. In comparison with the human kinome, we explored these kinomes to identify potential targets of existing inhibitors which are unique to Schistosoma species, allowing us to identify novel targets and suggest approved drugs that might inhibit them. These include previously suggested schistosomicidal agents such as bosutinib, dasatinib, and imatinib as well as new inhibitors such as vandetanib, saracatinib, tideglusib, alvocidib, dinaciclib, and 22 newly identified targets such as CHK1, CDC2, WEE, PAKA, MEK1. Additionally, the primary and secondary targets in Schistosoma of those approved drugs are also suggested, allowing for the development of novel therapeutics against this important yet neglected disease.

The rise of resistance through the intensive use of drugs targeted to treat specific infectious diseases means that new therapeutics are continually required. Diseases common in the tropics and sub-tropics, classified as neglected tropical diseases, suffer from a lack of new drug treatments due to the difficulty in developing new drugs and the lack of market incentive. One such disease is schistosomiasis, a major human helminth disease caused by worms from the genus Schistosoma. It is currently treated by a 40-year old drug, praziquantel, but its widespread use has led to signs of drug-resistance emerging, with no alternative effective treatments available. To meet this challenge, we have developed an innovative computational drug repurposing pipeline supported by experimental phenotypic screening. Protein kinases emerged from our pipeline as interesting new biological targets. Given that many human kinase inhibitors have been successfully applied specially in cancer therapy and kinases have conserved structures and functions, we also undertook a detailed analysis of the kinases present in all infective Schistosoma species and human host. This allowed identification of new Schistosoma-specific kinase targets and suggest approved drugs to be used for treating schistosomiasis as well as opening new avenues to treat this neglected disease.

Protective Immune Responses Generated in a Murine Model Following Immunization with Recombinant Schistosoma japonicum Insulin Receptor

There is a pressing need to develop vaccines for schistosomiasis given the current heavy dependency on praziquantel as the only available drug for treatment. We previously showed the ligand domain of the Schistosoma japonicum insulin receptor 1 and 2 (rSjLD1 and 2) fusion proteins conferred solid protection in mice against challenge infection with S. japonicum. To improve vaccine efficacy, we compared the immunogenicity and protective efficacy of rSjLD1 on its own and in combination with S. japonicum triose-phosphate isomerase (SjTPI), formulated with either of two adjuvants (QuilA and montanide ISA 720VG) in murine vaccine trials against S. japonicum challenge. The level of protection was higher in mice vaccinated only with rSjLD1 formulated with either adjuvant; rSjTPI or the rSjTPI-rSjLD1 combination resulted in a lower level of protection. Mirroring our previous results, there were significant reductions in the number of female worms (30–44%), faecal eggs (61–68%), liver eggs (44–56%), intestinal eggs (46–48%) and mature intestinal eggs (58–63%) in the rSjLD1-vaccinated mice compared with the adjuvant only groups. At 6-weeks post-cercarial challenge, a significantly increased production of interferon gamma (IFNγ) in rSjLD1-stimulated splenic CD4⁺ T cells was observed in the rSjLD1-vaccinated mice suggesting a Th1-type response is associated with the generated level of protective efficacy.

Identification of 170 New Long Noncoding RNAs in Schistosoma mansoni

Long noncoding RNAs (lncRNAs) are transcripts generally longer than 200 nucleotides with no or poor protein coding potential, and most of their functions are also poorly characterized. Recently, an increasing number of studies have shown that lncRNAs can be involved in various critical biological processes such as organism development or cancer progression. Little, however, is known about their effects in helminths parasites, such as Schistosoma mansoni. Here, we present a computational pipeline to identify and characterize lncRNAs from RNA-seq data with high confidence from S. mansoni adult worms. Through the utilization of different criteria such as genome localization, exon number, gene length, and stability, we identified 170 new putative lncRNAs. All novel S. mansoni lncRNAs have no conserved synteny including human and mouse. These closest protein coding genes were enriched in 10 significant Gene Ontology terms related to metabolism, transport, and biosynthesis. Fifteen putative lncRNAs showed differential expression, and three displayed sex-specific differential expressions in praziquantel sensitive and resistant adult worm couples. Together, our method can predict a set of novel lncRNAs from the RNA-seq data. Some lncRNAs are shown to be differentially expressed suggesting that those novel lncRNAs can be given high priority in further functional studies focused on praziquantel resistance.

Menthol and Menthone Associated with Acetylsalicylic Acid and Their Relation to the Hepatic Fibrosis in Schistosoma mansoni Infected Mice

Schistosomiasis is an important parasitic disease caused by Schistosoma mansoni, an intravascular trematode. Schistosomiasis treatment is limited to just one drug, Praziquantel (PZQ). Thus, studies on new antischistosomal compounds are of fundamental importance to disease control. Here we report on the effects of Mentha piperita L. compounds - menthol and menthone - in association with acetylsalicylic acid (ASA) in the regulation of hepatic fibrosis caused by schistosomiasis granulomas. Six different groups of Swiss rats were infected with 80 cercariae. Two groups received only menthol and menthol treatment at different concentrations (30 and 50 mg/kg); two groups received treatment with the same concentration of menthol and menthol, but associated the ASA. All groups received treatment for 14 consecutive days from the 35 days after the parasitic infection. In addition, three other groups were used: uninfected and untreated group, infected and untreated group and infected group treated with the commercial drug (single dose). Parasitological, cytological and histological analyses were performed. Results showed a significant reduction on the number of eosinophils found in the peritoneal cavity lavage (LPC) in all treated groups and on the number of eosinophils found in the blood of PZQ treated group, in the blood of the group treated with 30 mg/kg of Mentaliv® and in the blood of group treated with 50 mg/kg Mentaliv® + ASA when compared to the infected group. All treated groups presented a reduction in the parasite load, represented by the number of S. mansoni eggs, in the experimental group treated with 30 mg/kg of menthol and menthone a 62.80% reduction was observed and in the experimental group treated with 50 mg/kg of menthol and menthone + ASA a reduction of 64.21% was observed. In the liver histological analysis we observed that all Mentaliv® treated groups expressed a unique cytological profile, with diffused cells through the granuloma. In the experimental group treated with 50 mg/kg of Mentaliv® + ASA it was possible to observe the formation of type III collagen fibers, a typical wound healing characteristic. Our data strongly suggest that both the hepatic fibrosis and the inflammatory process were regulated through the schistosomiasis granulomatous process after treatment with menthol and menthone associated with ASA.

Treatment of Schistosoma mansoni with miltefosine in vitro enhances serological recognition of defined worm surface antigens

Background

Miltefosine, an anti-cancer drug that has been successfully repositioned for treatment of Leishmania infections, has recently also shown promising effects against Schistosoma spp targeting all life cycle stages of the parasite. The current study examined the effect of treating Schistosoma mansoni adult worms with miltefosine on exposure of worm surface antigens in vitro.

Methodology/Principal findings

In an indirect immunofluorescence assay, rabbit anti-S.mansoni adult worm homogenate and anti-S. mansoni infection antisera gave strong immunofluorescence of the S. mansoni adult worm surface after treatment with miltefosine, the latter antiserum having previously been shown to synergistically enhance the schistosomicidal activity of praziquantel. Rabbit antibodies that recognised surface antigens exposed on miltefosine-treated worms were recovered by elution off the worm surface in low pH buffer and were used in a western immunoblotting assay to identify antigenic targets in a homogenate extract of adult worms (SmWH). Four proteins reacting with the antibodies in immunoblots were purified and proteomic analysis (MS/MS) combined with specific immunoblotting indicated they were the S. mansoni proteins: fructose-1,6 bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. These antibodies were also found to bind to the surface of 3-hour schistosomula and induce immune agglutination of the parasites, suggesting they may have a role in immune protection.

Conclusion/Significance

This study reveals a novel mode of action of miltefosine as an anti-schistosome agent. The immune-dependent hypothesis we investigated has previously been lent credence with praziquantel (PZQ), whereby treatment unmasks parasite surface antigens not normally exposed to the host during infection. Antigens involved in this molecular mechanism could have potential as intervention targets and antibodies against these antigens may act to increase the drug’s anti-parasite efficacy and be involved in the development of resistance to re-infection.

Schistosomiasis (Bilharzia) is a serious public health problem caused by a parasite of genus Schistosoma. There is an increasing concern about development of parasite resistance to the only drug available for treatment, praziquantel (PZQ). Miltefosine, a repurposed anti-cancer drug for treatment of Leishmania infection, was shown to have activity against Schistosoma in animal models at all the parasite’s life cycle stages. In this work, we examined the potential that miltefosine could act to expose parasite surface antigens that are normally hidden during natural infection as a way to avoid lethal effects of host immunity. We used two immunobinding techniques, immunofluorescence and western immunoblotting, and a protein identification technique, namely mass spectrometry, to identify proteins exposed on the worm surface following incubation with miltefosine. Four S. mansoni proteins were shown to be exposed by miltefosine treatment: fructose-bisphosphate aldolase (SmFBPA), Sm22.6, alkaline phosphatase and malate dehydrogenase. Antibodies specific for these antigens recognised and bound to the surface of early-stage schistosome larvae and antibodies specific for SmFBPA induced clumping of the larvae, suggesting a potential role in early parasite killing and protection against infection. These antibodies may be utilised to increase miltefosine’s anti-parasite efficacy and may be involved in resistance to re-infection.

Effect of praziquantel on the differential expression of mouse hepatic genes and parasite ATP binding cassette transporter gene family members during Schistosoma mansoni infection

Schistosomiasis is a chronic parasitic disease caused by sexually dimorphic blood flukes of the genus Schistosoma. Praziquantel (PZQ) is the only drug widely available to treat the disease but does not kill juvenile parasites. Here we report the use of next generation sequencing to study the transcriptional effect of PZQ on murine hepatic inflammatory, immune and fibrotic responses to Schistosoma mansoni worms and eggs. An initial T helper cell 1 (Th1) response is induced against schistosomes in mice treated with drug vehicle (Vh) around the time egg laying begins, followed by a T helper cell 2 (Th2) response and the induction of genes whose action leads to granuloma formation and fibrosis. When PZQ is administered at this time, there is a significant reduction in egg burden yet the hepatic Th1, Th2 and fibrotic responses are still observed in the absence of granuloma formation suggesting some degree of gene regulation may be induced by antigens released from the dying adult worms. Quantitative real-time PCR was used to examine the relative expression of 16 juvenile and adult S. mansoni genes during infection and their response to Vh and PZQ treatment in vivo. While the response of stress genes in adult parasites suggests the worms were alive immediately following exposure to PZQ, they were unable to induce transcription of any of the 9 genes encoding ATP-binding cassette (ABC) transporters tested. In contrast, juvenile schistosomes were able to significantly induce the activities of ABCB, C and G family members, underscoring the possibility that these efflux systems play a major role in drug resistance.

Synergistic effects of in vitro combinations of piplartine, epiisopiloturine and praziquantel against Schistosoma mansoni

Schistosomiasis is a world health problem, and praziquantel is the only drug currently used for the treatment. There is some evidence that extensive monotherapy of praziquantel may be leading to drug resistance in the parasite. In order to find alternative treatments, the effects of the combination of epiisopiloturine (EPI), piplartine (PPT) and praziquantel (PZQ) were evaluated. Similarity analysis of these compounds was performed using optimized molecular structures to compare the shape and the charge modeling of combinations between PZQ and EPI or PPT. Supported by this data, in vitro association of PZQ-PPT, PZQ-EPI, and EPI-PPT was carried out, and the activity of these combinations against Schistosoma mansoni was assessed. The results showed synergistic activity with a combination index (CI) of 0.42 for the treatment with PZQ-PPT. Both PZQ-EPI and EPI-PPT combinations also showed synergistic effects, with CI values of 0.86 and 0.61, respectively. Surface alterations in the tegument of adult schistosomes after the treatments were observed using laser confocal microscopy and scanning electron microscopy. Additionally, the association of EPI-PPT decreased the cytotoxicity when compared with both isolated compounds in three different lines of mammalian cells. Thus, synergistic combinations of PZQ-PPT, PZQ-EPI, and EPI-PPT create the possibility of reduced doses to be used against Schistosoma mansoni.

Moving from control to elimination of schistosomiasis in sub-Saharan Africa: time to change and adapt strategies

Schistosomiasis is a water borne parasitic disease of global importance and with ongoing control the disease endemic landscape is changing. In sub-Saharan Africa, for example, the landscape is becoming ever more heterogeneous as there are several species of Schistosoma that respond in different ways to ongoing preventive chemotherapy and the inter-sectoral interventions currently applied. The major focus of preventive chemotherapy is delivery of praziquantel by mass drug administration to those shown to be, or presumed to be, at-risk of infection and disease. In some countries, regional progress may be uneven but in certain locations there are very real prospects to transition from control into interruption of transmission, and ultimately elimination. To manage this transition requires reconsideration of some of the currently deployed diagnostic tools used in surveillance and downward realignment of existing prevalence thresholds to trigger mass treatment. A key challenge will be maintaining and if possible, expanding the current donation of praziquantel to currently overlooked groups, then judging when appropriate to move from mass drug administration to selective treatment. In so doing, this will ensure the health system is adapted, primed and shown to be cost-effective to respond to these changing disease dynamics as we move forward to 2020 targets and beyond.

Prevalence of Schistosoma mansoni infection and the therapeutic efficacy of praziquantel among school children in Manna District, Jimma Zone, southwest Ethiopia

Background

Intestinal schistosomiasis is one of the neglected tropical parasitic diseases caused by Schistosoma mansoni. Currently, the control measures for the disease are mainly based on mass drug administration (MDA) with praziquantel (PZQ) targeting the school-age children. In Ethiopia, the potential foci for schistosomiasis and therapeutic efficacy of PZQ among school-age children remain poorly explored. Therefore, we determined both the prevalence and intensity of S. mansoni infection and the therapeutic efficacy of PZQ among school children in the Manna District (new foci for S. mansoni), Jimma Zone, southwest Ethiopia.

Methods

A cross-sectional study was conducted among the school children aged between 6 and 18 years in three primary schools in Manna district from March to April 2014. For diagnosis of S. mansoni, a single stool sample was obtained from each child and processed using single Kato Katz and examined under light microscopy. A questionnaire was used to collect demographic information of the school children participated in the study. School children excreting eggs of S. mansoni were administered with 40 mg/kg of PZQ and re-examined after three weeks post-treatment. The therapeutic efficacy of PZQ against S. mansoni was evaluated by means of cure rate and egg reduction rate.

Results

The overall prevalence of S. mansoni among the school children in the three primary schools in Manna District was 24.0 %. Higher prevalence was recorded for males 25.6 % (61/238) than for females 22.5 % (59/262). Majority (27.5 %) of infection intensity was light with mean faecal egg count (FEC) of 202 eggs per gram (EPG). The therapeutic efficacy of PZQ at a dose of 40 mg/kg was highly efficient (cure rate of 99.1 % and egg reduction rate of 99.9 %) among the school children in the three primary schools in Manna District.

Conclusions

The school children in the three primary schools of Manna District, Jimma Zone were at moderate risk of the morbidity caused by S. mansoni (prevalence > 10 % and < 50 % according to WHO threshold), and hence a biannual MDA with PZQ is required. PZQ available on the local market was found efficient and can be recommended for individual treatment in absence of MDA. The therapeutic efficacy of PZQ at 40 mg/kg against S. mansoni was high in the study area.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1833-6) contains supplementary material, which is available to authorized users.

Discovery of New Anti-Schistosomal Hits by Integration of QSAR-Based Virtual Screening and High Content Screening

Schistosomiasis is a debilitating neglected tropical disease, caused by flatworms of Schistosoma genus. The treatment relies on a single drug, praziquantel (PZQ), making the discovery of new compounds extremely urgent. In this work, we integrated QSAR-based virtual screening (VS) of Schistosoma mansoni thioredoxin glutathione reductase (SmTGR) inhibitors and high content screening (HCS) aiming to discover new antischistosomal agents. Initially, binary QSAR models for inhibition of SmTGR were developed and validated using the Organization for Economic Co-operation and Development (OECD) guidance. Using these models, we prioritized 29 compounds for further testing in two HCS platforms based on image analysis of assay plates. Among them, 2-[2-(3-methyl-4-nitro-5-isoxazolyl)vinyl]pyridine and 2-(benzylsulfonyl)-1,3-benzothiazole, two compounds representing new chemical scaffolds have activity against schistosomula and adult worms at low micromolar concentrations and therefore represent promising antischistosomal hits for further hit-to-lead optimization.

TRP channels in schistosomes

Praziquantel (PZQ) is effectively the only drug currently available for treatment and control of schistosomiasis, a disease affecting hundreds of millions of people worldwide. Many anthelmintics, likely including PZQ, target ion channels, membrane protein complexes essential for normal functioning of the neuromusculature and other tissues. Despite this fact, only a few classes of parasitic helminth ion channels have been assessed for their pharmacological properties or for their roles in parasite physiology. One such overlooked group of ion channels is the transient receptor potential (TRP) channel superfamily. TRP channels share a common core structure, but are widely diverse in their activation mechanisms and ion selectivity. They are critical to transducing sensory signals, responding to a wide range of external stimuli. They are also involved in other functions, such as regulating intracellular calcium and organellar ion homeostasis and trafficking. Here, we review current literature on parasitic helminth TRP channels, focusing on those in schistosomes. We discuss the likely roles of these channels in sensory and locomotor activity, including the possible significance of a class of TRP channels (TRPV) that is absent in schistosomes. We also focus on evidence indicating that at least one schistosome TRP channel (SmTRPA) has atypical, TRPV1-like pharmacological sensitivities that could potentially be exploited for future therapeutic targeting.

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We provide an overview of transient receptor potential (TRP) channels in schistosomes and other parasitic helminths.

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TRP channels are important for sensory signaling, ion homeostasis, organellar trafficking, and a host of other functions.

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Very little work has been done on TRP channels in parasitic helminths.

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TRPV channels, found throughout the Metazoa, appear not to be present in parasitic platyhelminths.

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TRP channels in schistosomes appear to have atypical pharmacology, perhaps an entrée for therapeutic targeting.

Global Assessment of Schistosomiasis Control Over the Past Century Shows Targeting the Snail Intermediate Host Works Best

BACKGROUND

Despite control efforts, human schistosomiasis remains prevalent throughout Africa, Asia, and South America. The global schistosomiasis burden has changed little since the new anthelmintic drug, praziquantel, promised widespread control.

METHODOLOGY

We evaluated large-scale schistosomiasis control attempts over the past century and across the globe by identifying factors that predict control program success: snail control (e.g., molluscicides or biological control), mass drug administrations (MDA) with praziquantel, or a combined strategy using both. For data, we compiled historical information on control tactics and their quantitative outcomes for all 83 countries and territories in which: (i) schistosomiasis was allegedly endemic during the 20th century, and (ii) schistosomiasis remains endemic, or (iii) schistosomiasis has been "eliminated," or is "no longer endemic," or transmission has been interrupted.

PRINCIPAL FINDINGS

Widespread snail control reduced prevalence by 92 ± 5% (N = 19) vs. 37 ± 7% (N = 29) for programs using little or no snail control. In addition, ecological, economic, and political factors contributed to schistosomiasis elimination. For instance, snail control was most common and widespread in wealthier countries and when control began earlier in the 20th century.

CONCLUSIONS/SIGNIFICANCE

Snail control has been the most effective way to reduce schistosomiasis prevalence. Despite evidence that snail control leads to long-term disease reduction and elimination, most current schistosomiasis control efforts emphasize MDA using praziquantel over snail control. Combining drug-based control programs with affordable snail control seems the best strategy for eliminating schistosomiasis.

QSAR-Driven Discovery of Novel Chemical Scaffolds Active against Schistosoma mansoni

Schistosomiasis is a neglected tropical disease that affects millions of people worldwide. Thioredoxin glutathione reductase of Schistosoma mansoni (SmTGR) is a validated drug target that plays a crucial role in the redox homeostasis of the parasite. We report the discovery of new chemical scaffolds against S. mansoni using a combi-QSAR approach followed by virtual screening of a commercial database and confirmation of top ranking compounds by in vitro experimental evaluation with automated imaging of schistosomula and adult worms. We constructed 2D and 3D quantitative structure-activity relationship (QSAR) models using a series of oxadiazoles-2-oxides reported in the literature as SmTGR inhibitors and combined the best models in a consensus QSAR model. This model was used for a virtual screening of Hit2Lead set of ChemBridge database and allowed the identification of ten new potential SmTGR inhibitors. Further experimental testing on both shistosomula and adult worms showed that 4-nitro-3,5-bis(1-nitro-1H-pyrazol-4-yl)-1H-pyrazole (LabMol-17) and 3-nitro-4-{[(4-nitro-1,2,5-oxadiazol-3-yl)oxy]methyl}-1,2,5-oxadiazole (LabMol-19), two compounds representing new chemical scaffolds, have high activity in both systems. These compounds will be the subjects for additional testing and, if necessary, modification to serve as new schistosomicidal agents.

Effect of neem (Azadirachta indica A. Juss) leaf extract on resistant Staphylococcus aureus biofilm formation and Schistosoma mansoni worms

ETHNOPHARMACOLOGICAL RELEVANCE

There are ethnopharmacological reports supporting the use of neem (Azadirachta indica A. Juss) leaf against bacterial and worm infections. However there is a lack of studies about its effect on bacterial biofilm formation and Schistosoma mansoni worms. This study reports the in vitro effects of neem leaf ethanolic extract (Neem EE) on Methicillin-resistant Staphylococcus aureus (MRSA) biofilm and planktonic aggregation formation, and against S. mansoni worms.

MATERIALS AND METHODS

Quantification of the Azadirachtin (AZA), thought to be one of their main compounds related to biological effects, was performed. The effect of sub-inhibitory concentrations of Neem EE on biofilm formation and planktonic aggregates of S. aureus was tested using the crystal violet dye method and atomic force microscopy (AFM) analysis, respectively. Changes in S. mansoni motor activity and death of worms were analyzed in vitro after exposition to the extract. Treated schistosomes were also examined using confocal laser scanning microscopy.

RESULTS

It was observed the presence of AZA in the extract (0.14 ± 0.02 mg/L). Testing Neem EE sub-inhibitory concentrations, a significant biofilm adherence inhibition from 62.5 µg/mL for a sensitive S. aureus and 125 µg/mL for two MRSA strains was observed. AFM images revealed that as the Neem EE concentration increases (from 250 to 1000 µg/mL) decreased ability of a chosen MRSA strain to form large aggregates. In relation of anti-schistosoma assay, the extract caused 100% mortality of female worms at a concentration of 50 µg/mL at 72 h of incubation, while 300 µg/mL at 24h of incubation was required to achieve 100% mortality of male worms. The extract also caused significant motor activity reduction in S. mansoni. For instance, at 96 h of incubation with 100 µg/mL, 80% of the worms presented significant motor activity reduction. By the confocal microscopy analysis, the dorsal surface of the tegument of worms exposed to 300 µg/mL (male) and 100 µg/mL (female) of the extract showed severe morphological changes after 24h of treatment.

CONCLUSIONS

Neem leaf ethanolic extract presented inhibitory effect on MRSA biofilm and planktonic aggregation formation, and anthelmintic activity against S. mansoni worms.

Anthelmintic activity in vivo of epiisopiloturine against juvenile and adult worms of Schistosoma mansoni

Schistosomiasis is a serious disease currently estimated to affect more that 207 million people worldwide. Due to the intensive use of praziquantel, there is increasing concern about the development of drug-resistant strains. Therefore, it is necessary to search for and investigate new potential schistosomicidal compounds. This work reports the in vivo effect of the alkaloid epiisopiloturine (EPI) against adults and juvenile worms of Schistosoma mansoni. EPI was first purified its thermal behavior and theoretical solubility parameters charaterised. In the experiment, mice were treated with EPI over the 21 days post-infection with the doses of 40 and 200 mg/kg, and 45 days post-infection with single doses of 40, 100 and 300 mg/kg. The treatment with EPI at 40 mg/kg was more effective in adult worms when compared with doses of 100 and 300 mg/kg. The treatment with 40 mg/kg in adult worms reduced parasite burden significantly, lead to reduction in hepatosplenomegaly, reduced the egg burden in faeces, and decreased granuloma diameter. Scanning electron microscopy revealed morphological changes to the parasite tegument after treatment, including the loss of important features. Additionally, the in vivo treatment against juvenile with 40 mg/kg showed a reduction of the total worm burden of 50.2%. Histopathological studies were performed on liver, spleen, lung, kidney and brain and EPI was shown to have a DL50 of 8000 mg/kg. Therefore EPI shows potential to be used in schistosomiasis treatment. This is the first time that schistosomicidal in vivo activity of EPI has been reported.

Inhibition or knockdown of ABC transporters enhances susceptibility of adult and juvenile schistosomes to Praziquantel

Parasitic flatworms of the genus Schistosoma cause schistosomiasis, a neglected tropical disease that affects hundreds of millions. Treatment of schistosomiasis depends almost entirely on the drug praziquantel (PZQ). Though essential to treating and controlling schistosomiasis, a major limitation of PZQ is that it is not active against immature mammalian-stage schistosomes. Furthermore, there are reports of field isolates with heritable reductions in PZQ susceptibility, and researchers have selected for PZQ-resistant schistosomes in the laboratory. P-glycoprotein (Pgp; ABCB1) and other ATP binding cassette (ABC) transporters remove a wide variety of toxins and xenobiotics from cells, and have been implicated in multidrug resistance (MDR). Changes in ABC transporter structure or expression levels are also associated with reduced drug susceptibility in parasitic helminths, including schistosomes. Here, we show that the activity of PZQ against schistosome adults and juveniles ex vivo is potentiated by co-administration of either the highly potent Pgp inhibitor tariquidar or combinations of inhibitors targeting multiple ABC multidrug transporters. Adult worms exposed to sublethal PZQ concentrations remain active, but co-administration of ABC transporter inhibitors results in complete loss of motility and disruption of the tegument. Notably, juvenile schistosomes (3–4 weeks post infection), normally refractory to 2 µM PZQ, become paralyzed when transporter inhibitors are added in combination with the PZQ. Experiments using the fluorescent PZQ derivative (R)-PZQ-BODIPY are consistent with the transporter inhibitors increasing effective intraworm concentrations of PZQ. Adult worms in which expression of ABC transporters has been suppressed by RNA interference show increased responsiveness to PZQ and increased retention of (R)-PZQ-BODIPY consistent with an important role for these proteins in setting levels of PZQ susceptibility. These results indicate that parasite ABC multidrug transporters might serve as important targets for enhancing the action of PZQ. They also suggest a potentially novel and readily-available strategy for overcoming reduced PZQ susceptibility of schistosomes.

Schistosomes are parasitic flatworms that cause schistosomiasis, a tropical disease affecting hundreds of millions worldwide. Praziquantel (PZQ) is the current drug of choice against schistosomiasis, and, indeed, is the only approved antischistosomal treatment available in most parts of the world. Though effective overall, PZQ has limitations, including its lack of activity against immature schistosomes. Furthermore, reported cure rates in the field are often below optimal levels, and there is increasing evidence that schistosomes can become resistant to the drug. ABC transporters such as P-glycoprotein are efflux transporters that mediate detoxification of cells via removal of toxins and xenobiotics, including drugs. They underlie multidrug resistance in mammalian cells, and are also associated with drug resistance in parasitic worms, including schistosomes. Here, we show that compounds that inhibit these efflux transporters potentiate the activity of PZQ against schistosomes, including normally PZQ-insensitive juvenile worms. Similarly, suppressing expression of these transporters also increases adult worm responsiveness to PZQ. Our experiments may provide insights into the role of these drug transporters in PZQ action, and could also translate into new therapeutic strategies for augmenting treatment of schistosome infections and overcoming drug resistance.

Praziquantel sensitivity of Kenyan Schistosoma mansoni isolates and the generation of a laboratory strain with reduced susceptibility to the drug

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We isolated S. mansoni miracidia from 72 Kenyan adults and children.

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We found no evidence of S. mansoni with reduced praziquantel sensitivity.

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An S. mansoni lab isolate with reduced praziquantel sensitivity was established.

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The potential for the emergence of praziquantel resistance remains.

Schistosomiasis is a neglected tropical disease caused by blood-dwelling flukes of the genus Schistosoma. While the disease may affect as many as 249 million people, treatment largely relies on a single drug, praziquantel. The near exclusive use of this drug for such a prevalent disease has led to concerns regarding the potential for drug resistance to arise and the effect this would have on affected populations. In this study, we use an in vitro assay of drug sensitivity to test the effect of praziquantel on miracidia hatched from eggs obtained from fecal samples of Kenyan adult car washers and sand harvesters as well as school children. Whereas in a previous study we found the car washers and sand harvesters to harbor Schistosoma mansoni with reduced praziquantel sensitivity, we found no evidence for the presence of such strains in any of the groups tested here. Using miracidia derived from seven car washers to infect snails, we used the shed cercariae to establish a strain of S. mansoni with significantly reduced praziquantel sensitivity in mice. This was achieved within 5 generations by administering increasing doses of praziquantel to the infected mice until the parasites could withstand a normally lethal dose. This result indicates that while the threat of praziquantel resistance may have diminished in the Kenyan populations tested here, there is a strong likelihood it could return if sufficient praziquantel pressure is applied.

Metabolic profiling of praziquantel enantiomers

Praziquantel (PZQ), prescribed as a racemic mixture, is the most readily available drug to treat schistosomiasis. In the present study, ultra-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC-ESI-QTOFMS) based metabolomics was employed to decipher the metabolic pathways and enantioselective metabolic differences of PZQ. Many phase I and four new phase II metabolites were found in urine and feces samples of mice 24h after dosing, indicating that the major metabolic reactions encompassed oxidation, dehydrogenation, and glucuronidation. Differences in the formation of all these metabolites were observed between (R)-PZQ and (S)-PZQ. In an in vitro phase I incubation system, the major involvement of CYP3A, CYP2C9, and CYP2C19 in the metabolism of PZQ, and CYP3A, CYP2C9, and CYP2C19 exhibited different catalytic activity toward the PZQ enantiomers. Apparent Km and Vmax differences were observed in the catalytic formation of three mono-oxidized metabolites by CYP2C9 and CYP3A4 further supporting the metabolic differences for PZQ enantiomers. Molecular docking showed that chirality resulted in differences in substrate location and conformation, which likely accounts for the metabolic differences. In conclusion, in silico, in vitro, and in vivo methods revealed the enantioselective metabolic profile of praziquantel.

Design and synthesis of molecular probes for the determination of the target of the anthelmintic drug praziquantel

Schistosomiasis is a highly prevalent neglected tropical disease caused by blood-dwelling helminths of the genus Schistosoma. Praziquantel (PZQ) is the only drug available widely for the treatment of this disease and is administered in racemic form, even though only the (R)-isomer has significant anthelmintic activity. Progress towards the development of a second generation of anthelmintics is hampered by a lack of understanding of the mechanism of action of PZQ. In this Letter, we report an efficient protocol for the small-scale separation of enantiomers of 2 (hydrolyzed PZQ) using supercritical fluid chromatography (SFC). The enantiopure 2 was then used to develop several molecular probes, which can potentially be used to help identify the protein target of PZQ and study its mode of action.

Gene expression analysis distinguishes tissue-specific and gender-related functions among adult Ascaris suum tissues

Over a billion people are infected by Ascaris spp. intestinal parasites. To clarify functional differences among tissues of adult A. suum, we compared gene expression by various tissues of these worms by expression microarray methods. The A. suum genome was sequenced and assembled to allow generation of microarray elements. Expression of over 40,000 60-mer elements was investigated in a variety of tissues from both male and female adult worms. Nearly 50 percent of the elements for which signal was detected exhibited differential expression among different tissues. The unique profile of transcripts identified for each tissue clarified functional distinctions among tissues, such as chitin binding in the ovary and peptidase activity in the intestines. Interestingly, hundreds of gender-specific elements were characterized in multiple non-reproductive tissues of female or male worms, with most prominence of gender differences in intestinal tissue. A. suum genes from the same family were frequently expressed differently among tissues. Transcript abundance for genes specific to A. suum, by comparison to Caenorhabditis elegans, varied to a greater extent among tissues than for genes conserved between A. suum and C. elegans. Analysis using C. elegans protein interaction data identified functional modules conserved between these two nematodes, resulting in identification of functional predictions of essential subnetworks of protein interactions and how these networks may vary among nematode tissues. A notable finding was very high module similarity between adult reproductive tissues and intestine. Our results provide the most comprehensive assessment of gene expression among tissues of a parasitic nematode to date.

Transcriptional analysis of Schistosoma mansoni treated with praziquantel in vitro

Schistosomiasis is one of the foremost health problems in developing countries and has been estimated to account for the loss of up to 56 million annual disability-adjusted life years. Control of the disease relies almost exclusively on praziquantel (PZQ) but this drug does not kill juvenile worms during the early stages of infection or prevent post-treatment reinfection. As the use of PZQ continues to grow, there are fears that drug resistance may become problematic thus there is a need to develop a new generation of more broadly effective anti-schistosomal drugs, a task that will be made easier by having an understanding of why PZQ kills sexually mature worms but fails to kill juveniles. Here, we describe the exposure of mixed-sex juvenile and sexually mature male and female Schistosoma mansoni to 1 μg/mL PZQ in vitro and the use of microarrays to observe changes to the transcriptome associated with drug treatment. Although there was no significant difference in the total number of genes expressed by adult and juvenile schistosomes after treatment, juveniles differentially regulated a greater proportion of their genes. These included genes encoding multiple drug transporter as well as calcium regulatory, stress and apoptosis-related proteins. We propose that it is the greater transcriptomic flexibility of juvenile schistosomes that allows them to respond to and survive exposure to PZQ in vivo.

Calcium channels of schistosomes: unresolved questions and unexpected answers

Parasitic flatworms of the genus Schistosoma are the causative agents of schistosomiasis, a highly prevalent, neglected tropical disease that causes significant morbidity in hundreds of millions of people worldwide. The current treatment of choice against schistosomiasis is praziquantel (PZQ), which is known to affect Ca(2+) homeostasis in schistosomes, but which has an undefined molecular target and mode of action. PZQ is the only available antischistosomal drug in most parts of the world, making reports of PZQ resistance particularly troubling. Voltage-gated Ca(2+) (Ca(v)) channels have been proposed as possible targets for PZQ, and, given their central role in the neuromuscular system, may also serve as targets for new anthelmintic therapeutics. Indeed, ion channels constitute the majority of targets for current anthelmintics. Ca(v) channel subunits from schistosomes and other platyhelminths have several unique properties that make them attractive as potential drug targets, and that could also provide insights into structure-function relationships in, and evolution of, Ca(v) channels.

Polymorphism associated with the Schistosoma mansoni tetraspanin-2 gene

A vaccine against schistosomiasis would contribute significantly to reducing the 3-70 million disability-adjusted life years lost annually to the disease. Towards this end, inoculation with the large extracellular loop (EC-2) of Schistosoma mansoni tetraspanin-2 protein (Sm-TSP-2) has proved effective in reducing worm and egg burdens in S. mansoni-infected mice. The EC-2 loop of Schistosoma japonicum TSP-2, however, has been found to be highly polymorphic, perhaps diminishing the likelihood that this antigen can be used for vaccination against this species. Here, we examine polymorphism of the EC-2 of Sm-TSP-2 in genetically unique worms derived from six individuals from Kisumu, Kenya.

Vaccines to combat the neglected tropical diseases

The neglected tropical diseases (NTDs) represent a group of parasitic and related infectious diseases such as amebiasis, Chagas disease, cysticercosis, echinococcosis, hookworm, leishmaniasis, and schistosomiasis. Together, these conditions are considered the most common infections in low- and middle-income countries, where they produce a level of global disability and human suffering equivalent to better known conditions such as human immunodeficiency virus/acquired immunodeficiency syndrome and malaria. Despite their global public health importance, progress on developing vaccines for NTD pathogens has lagged because of some key technical hurdles and the fact that these infections occur almost exclusively in the world's poorest people living below the World Bank poverty line. In the absence of financial incentives for new products, the multinational pharmaceutical companies have not embarked on substantive research and development programs for the neglected tropical disease vaccines. Here, we review the current status of scientific and technical progress in the development of new neglected tropical disease vaccines, highlighting the successes that have been achieved (cysticercosis and echinococcosis) and identifying the challenges and opportunities for development of new vaccines for NTDs. Also highlighted are the contributions being made by non-profit product development partnerships that are working to overcome some of the economic challenges in vaccine manufacture, clinical testing, and global access.

Pharmacology and potential physiological significance of schistosome multidrug resistance transporters

Schistosomes are the causative agents of schistosomiasis, a neglected tropical disease affecting hundreds of millions worldwide and a major global health burden. Current control of schistosomiasis depends largely on a single drug, praziquantel (PZQ). One potential physiological target for new antischistosomal drugs is the parasite's excretory system, which removes wastes and xenobiotics. Multidrug resistance (MDR) transporters that are members of the ATP-binding cassette (ABC) superfamily of proteins are ATP-dependent efflux pumps involved in removal of toxins and xenobiotics from cells. They mediate the phenomenon of multidrug resistance, in which cells resistant to one drug show cross-resistance to a broad range of other agents, and are also associated with reduced drug susceptibility in parasitic helminths. In this review, we survey the different types of ABC transporter genes present within the schistosome genome, and examine recent evidence indicating that at least some of these transporters may play a role in fine-tuning susceptibility of schistosomes to PZQ. Disruption of their function may therefore provide a strategy for enhancing drug action or overcoming or attenuating drug resistance. Furthermore, dissection of the roles these transporters may play in normal schistosome physiology could potentially lead to identification of highly "druggable" targets for new antischistosomals.

Schistosoma mansoni: In vitro schistosomicidal activity of piplartine

Schistosomiasis is one of the world's greatly neglected tropical diseases, and its control is largely dependent on a single drug, praziquantel. Here, we report the in vitro effect of piplartine, an amide isolated from Piper tuberculatum (Piperaceae), on Schistosoma mansoni adult worms. A piplartine concentration of 15.8 μM reduced the motor activity of worms and caused their death within 24h in a RPMI 1640 medium. Similarly, the highest sub-lethal concentration of piplartine (6.3 μM) caused a 75% reduction in egg production in spite of coupling. Additionally, piplartine induced morphological changes on the tegument, and a quantitative analysis carried out by confocal microscopy revealed an extensive tegumental destruction and damage in the tubercles. This damage was dose-dependent in the range of 15.8-630.2 μM. At doses higher than 157.6 μM, piplartine induced morphological changes in the oral and ventral sucker regions of the worms. It is the first time that the schistosomicidal activity has been reported for piplartine.

Discovery of new inhibitors of Schistosoma mansoni PNP by pharmacophore-based virtual screening

Schistosomiasis is considered the second most important tropical parasitic disease, with severe socioeconomic consequences for millions of people worldwide. Schistosoma mansoni , one of the causative agents of human schistosomiasis, is unable to synthesize purine nucleotides de novo, which makes the enzymes of the purine salvage pathway important targets for antischistosomal drug development. In the present work, we describe the development of a pharmacophore model for ligands of S. mansoni purine nucleoside phosphorylase (SmPNP) as well as a pharmacophore-based virtual screening approach, which resulted in the identification of three thioxothiazolidinones (1-3) with substantial in vitro inhibitory activity against SmPNP. Synthesis, biochemical evaluation, and structure-activity relationship investigations led to the successful development of a small set of thioxothiazolidinone derivatives harboring a novel chemical scaffold as new competitive inhibitors of SmPNP at the low-micromolar range. Seven compounds were identified with IC(50) values below 100 μM. The most potent inhibitors 7, 10, and 17 with IC(50) of 2, 18, and 38 μM, respectively, could represent new potential lead compounds for further development of the therapy of schistosomiasis.

Health seeking behaviour and utilization of health facilities for schistosomiasis-related symptoms in ghana

BACKGROUND

Schistosomiasis causes long-term illness and significant economic burden. Morbidity control through integration within existing health care delivery systems is considered a potentially sustainable and cost-effective approach, but there is paucity of information about health-seeking behaviour.

METHODS

A questionnaire-based study involving 2,002 subjects was conducted in three regions of Ghana to investigate health-seeking behaviour and utilization of health facilities for symptoms related to urinary (blood in urine and painful urination) and intestinal schistosomiasis (diarrhea, blood in stool, swollen abdomen and abdominal pain). Fever (for malaria) was included for comparison.

RESULTS

Only 40% of patients with urinary symptoms sought care compared to >70% with intestinal symptoms and >90% with fever. Overall, about 20% of schistosomiasis-related symptoms were reported to a health facility (hospital or clinic), compared to about 30% for fever. Allopathic self-medication was commonly practiced as alternative action. Health-care seeking was relatively lower for patients with chronic symptoms, but if they took action, they were more likely to visit a health facility. In a multivariate logistic regression analysis, perceived severity was the main predictor for seeking health care or visiting a health facility. Age, socio-economic status, somebody else paying for health care, and time for hospital visit occasionally showed a significant impact, but no clear trend. The effect of geographic location was less marked, although people in the central region, and to a lesser extent the north, were usually less inclined to seek health care than people in the south. Perceived quality of health facility did not demonstrate impact.

CONCLUSION

Perceived severity of the disease is the most important determinant of seeking health care or visiting a health facility in Ghana. Schistosomiasis control by passive case-finding within the regular health care delivery looks promising, but the number not visiting a health facility is large and calls for supplementary control options.

Crystal structure of Schistosoma purine nucleoside phosphorylase complexed with a novel monocyclic inhibitor

A novel inhibitor of Schistosoma PNP was identified using an "in silico" approach allied to enzyme inhibition assays. The compound has a monocyclic structure which has not been previously described for PNP inhibitors. The crystallographic structure of the complex was determined and used to elucidate the binding mode within the active site. Furthermore, the predicted pose was very similar to that determined crystallographically, validating the methodology. The compound Sm_VS1, despite its low molecular weight, possesses an IC(50) of 1.3 microM, surprisingly low when compared with purine analogues. This is presumably due to the formation of eight hydrogen bonds with key residues in the active site E203, N245 and T244. The results of this study highlight the importance of the use of multiple conformations for the target during virtual screening. Indeed the Sm_VS1 compound was only identified after flipping the N245 side chain. It is expected that the structure will be of use in the development of new highly active non-purine based compounds against the Schistosoma enzyme.

Structure mechanism insights and the role of nitric oxide donation guide the development of oxadiazole-2-oxides as therapeutic agents against schistosomiasis

Schistosomiasis is a chronic parasitic disease affecting hundreds of millions of individuals worldwide. Current treatment depends on a single agent, praziquantel, raising concerns of emergence of resistant parasites. Here, we continue our explorations of an oxadiazole-2-oxide class of compounds we recently identified as inhibitors of thioredoxin glutathione reductase (TGR), a selenocysteine-containing flavoenzyme required by the parasite to maintain proper cellular redox balance. Through systematic evaluation of the core molecular structure of this chemotype, we define the essential pharmacophore, establish a link between the nitric oxide donation and TGR inhibition, determine the selectivity for this chemotype versus related reductase enzymes, and present evidence that these agents can be modified to possess appropriate drug metabolism and pharmacokinetic properties. The mechanistic link between exogenous NO donation and parasite injury is expanded and better defined. The results of these studies verify the utility of oxadiazole-2-oxides as novel inhibitors of TGR and as efficacious antischistosomal agents.

Reduced susceptibility to praziquantel among naturally occurring Kenyan isolates of Schistosoma mansoni

Background

The near exclusive use of praziquantel (PZQ) for treatment of human schistosomiasis has raised concerns about the possible emergence of drug-resistant schistosomes.

Methodology/Principal Findings

We measured susceptibility to PZQ of isolates of Schistosoma mansoni obtained from patients from Kisumu, Kenya continuously exposed to infection as a consequence of their occupations as car washers or sand harvesters. We used a) an in vitro assay with miracidia, b) an in vivo assay targeting adult worms in mice and c) an in vitro assay targeting adult schistosomes perfused from mice. In the miracidia assay, in which miracidia from human patients were exposed to PZQ in vitro, reduced susceptibility was associated with previous treatment of the patient with PZQ. One isolate (“KCW”) that was less susceptible to PZQ and had been derived from a patient who had never fully cured despite multiple treatments was studied further. In an in vivo assay of adult worms, the KCW isolate was significantly less susceptible to PZQ than two other isolates from natural infections in Kenya and two lab-reared strains of S. mansoni. The in vitro adult assay, based on measuring length changes of adults following exposure to and recovery from PZQ, confirmed that the KCW isolate was less susceptible to PZQ than the other isolates tested. A sub-isolate of KCW maintained separately and tested after three years was susceptible to PZQ, indicative that the trait of reduced sensitivity could be lost if selection was not maintained.

Conclusions/Significance

Isolates of S. mansoni from some patients in Kisumu have lower susceptibility to PZQ, including one from a patient who was never fully cured after repeated rounds of treatment administered over several years. As use of PZQ continues, continued selection for worms with diminished susceptibility is possible, and the probability of emergence of resistance will increase as large reservoirs of untreated worms diminish. The potential for rapid emergence of resistance should be an important consideration of treatment programs.

The emergence of drug resistant pathogens is a great challenge to the control of infectious diseases. Schistosomiasis is one of the world's greatest neglected tropical diseases, and it is primarily controlled with the drug praziquantel. This drug is often used by repeatedly treating patients to maintain reduced worm burdens, an ideal situation to encourage the evolution of resistant worms. Although drug based control programs are increasing, monitoring efforts for drug resistance remain rare. We measured drug susceptibility of schistosomes from a cohort of patients in Kenya who are enrolled in a longitudinal study in which they are repeatedly treated with praziquantel. We found that schistosomes from previously treated patients were significantly less susceptible than those that were not. Also, schistosomes derived from a single patient who had been treated with praziquantel 18 times showed marked resistance. Although the findings of this study indicated that reduced drug susceptibility occurs in this population of schistosomes, this trait does not seem to be spreading widely or creating clinical levels of resistance. We hypothesize that the trait remains at low frequency because of the large population of schistosomes that are not exposed to the drug and/or potential fitness costs associated with reduced susceptibility.

A wake up call for urinary schistosomiasis: reconciling research effort with public health importance

This review considers the current status of urinary schistosomiasis, caused by infection with Schistosoma haematobium, and argues that greater research effort and focus are needed to improve understanding of this neglected tropical disease (NTD). The inappropriateness of relying solely on data concerning the much more extensively studied intestinal form of schistosomiasis caused by S. mansoni is highlighted. The current lack of genome and transcriptome information for S. haematobium is directly hindering further targeted research and must be quickly rectified. Recent molecular phylogenies caution the expectation of similarities between schistosome species and highlight the close relationships of species within the S. haematobium group. Treatment, current and prospective drugs and vaccines, together with diagnosis are considered, highlighting the differences associated with urinary schistosomiasis. This infection has a significant and specific impact on the urino-genital system and has a strong association with bladder cancer, leading to severe and chronic morbidity. There is a clear need for new clinical initiatives in this area to better quantify the disease burden. Furthermore, emerging associations with HIV and other pathogens need to be closely monitored. Research is urgently needed to improve current knowledge in order to develop the next generation of control tools.

Schistosoma mansoni P-glycoprotein levels increase in response to praziquantel exposure and correlate with reduced praziquantel susceptibility

One potential physiological target for new antischistosomals is the parasite's system for excretion of wastes and xenobiotics. P-glycoprotein (Pgp), a member of the ATP-binding-cassette superfamily of proteins, is an ATP-dependent efflux pump involved in transport of toxins and xenobiotics from cells. In vertebrates, increased expression of Pgp is associated with multidrug resistance in tumor cells. Pgp may also play a role in drug resistance in helminths. In this report, we examine the relationship between praziquantel (PZQ), the current drug of choice against schistosomiasis, and Pgp expression in Schistosoma mansoni. We show that levels of RNA for SMDR2, a Pgp homolog from S. mansoni, increase transiently in adult male worms following exposure to sub-lethal concentrations (100-500 nM) of PZQ. A corresponding, though delayed, increase in anti-Pgp immunoreactive protein expression occurs in adult males following exposure to PZQ. The level of anti-Pgp immunoreactivity in particular regions of adult worms also increases in response to PZQ. Adult worms from an Egyptian S. mansoni isolate with reduced sensitivity to PZQ express increased levels of SMDR2 RNA and anti-Pgp-immunoreactive protein, perhaps indicating a role for multidrug resistance proteins in development or maintenance of PZQ resistance.

Imaging schistosomes in vivo

Schistosomes are intravascular, parasitic helminths that cause a chronic, often debilitating disease afflicting over 200 million people in over 70 countries. Here we describe novel imaging methods that, for the first time, permit visualization of live schistosomes within their living hosts. The technology centers on fluorescent agent uptake and activation in the parasite's gut, and subsequent detection and signal quantitation using fluorescence molecular tomography (FMT). There is a strong positive correlation between the signal detected and parasite number. Schistosoma mansoni parasites of both sexes recovered from infected experimental animals exhibit vivid fluorescence throughout their intestines. Likewise, the remaining important human schistosome parasites, S. japonicum and S. hematobium, also exhibit gut fluorescence when recovered from infected animals. Imaging has been used to efficiently document the decline in parasite numbers in infected mice treated with the antischistosome drug praziquantel. This technology will provide a unique opportunity both to help rapidly identify much-needed, novel antischistosome therapies and to gain direct visual insight into the intravascular lives of the major schistosome parasites of humans.

Praziquantel: its use in control of schistosomiasis in sub-Saharan Africa and current research needs

Treatment with praziquantel (PZQ) has become virtually the sole basis of schistosomiasis control in sub-Saharan Africa and elsewhere, and the drug is reviewed here in the context of the increasing rate that it is being used for this purpose. Attention is drawn to our relative lack of knowledge about the mechanisms of action of PZQ at the molecular level, the need for more work to be done on schistosome isolates that have been collected recently from endemic areas rather than those maintained in laboratory conditions for long periods, and our reliance for experimental work mainly on Schistosoma mansoni, little work having been done on S. haematobium. There is no evidence that resistance to PZQ has been induced in African schistosomes as a result of its large-scale use on that continent to date, but there is also no assurance that PZQ and/or schistosomes are in any way unique and that resistant organisms will not be selected as a result of widespread drug usage. The failure of PZQ to produce complete cures in populations given a routine treatment should therefore solicit considerable concern. With few alternatives to PZQ currently available and/or on the horizon, methods to monitor drug-susceptibility in African schistosomes need to be devised and used to help ensure that this drug remains effective for as long a time as possible.