Susceptibility to praziquantel of male and female cercariae of praziquantel-resistant and susceptible isolates of Schistosoma mansoni

Fluorescent non transgenic schistosoma to decipher host-parasite phenotype compatibility

Schistosomiasis is considered as a significant public health problem, imposing a deeper understanding of the intricate interplay between parasites and their hosts. Unfortunately, current invasive methodologies employed to study the compatibility and the parasite development impose limitations on exploring diverse strains under various environmental conditions, thereby impeding progress in the field. In this study, we demonstrate the usefulness for the trematode parasite Schistosma mansoni, leveranging a fluorescence-imaging-based approach that employs fluorescein 5-chloromethylfluorescein diacetate (CMFDA) and 5-chloromethylfluorescein diacetate (CMAC) as organism tracker for intramolluscan studies involving the host snail Biomphalaria glabrata. These probes represent key tools for qualitatively assessing snail infections with unmatched accuracy and precision. By monitoring the fluorescence of parasites within the snail vector, our method exposes an unprecedented glimpse into the host-parasite compatibility landscape. The simplicity and sensitivity of our approach render it an ideal choice for evolutionary studies, as it sheds light on the intricate mechanisms governing host-parasite interactions. Fluorescent probe-based methods play a pivotal role in characterizing factors influencing parasite development and phenotype of compatibility, paving the way for innovative, effective, and sustainable solutions to enhance our understanding host-parasite immunobiological interaction and compatibility.

Anti-angiogenic and anti-proliferative activity of ziziphus leaf extract as a novel potential therapeutic agent for reducing hepatic injury in experimental hamster schistosomiasis

BACKGROUND

Schistosomiasis is one of the most prevalent helminthic infections worldwide. Praziquantel (PZQ) resistance poses a possible danger to the disease's ability to be controlled. Little is known about the role of Ziziphus spina-christi leaf extract (ZLE) in the treatment of hepatic schistosomiasis. However, no study has explored ZLE's anti-angiogenic and anti-proliferative activity as a possible mechanism for reducing hepatic injury in this context. Therefore, this study aimed to evaluate the therapeutic potential of ZLE as an anti-angiogenic, and anti-proliferative agent in hamsters infected with S. mansoni.

METHODS

Fifty hamsters were used and divided into 5 groups (10 hamsters each); noninfected untreated (controls), noninfected treated with ZLE, infected untreated, infected treated with PZQ- and infected treated with ZLE. Anti-angiogenic and anti-fibrotic effects of the drugs were assessed pathologically through the immunohistochemical expression of VEGF, Ki-67, and TGF β1 in liver sections. Some oxidative stress parameters were measured in hepatic homogenates (NO, GSH, GST, and SOD), and serum liver enzymes were also assessed.

RESULTS

A significant decrease in worm burden, granuloma size, granuloma area, and numbers in the ZLE- and PZQ-treated groups compared to the infected untreated group, and the decrease in granulomas number and tissue egg load was significantly lower in PZQ treated group compared to ZLE treated group (p<0.05). ZLE exhibited significant anti-angiogenic and anti-fibrotic effects on granulomas, illustrated by significantly lower expression of VEGF and TGF-β1 than infected untreated and PZQ-treated groups. ZLE exhibits antiproliferative activity evidenced by a significant reduction of positive Ki-67 hepatocytes percentage compared to the infected untreated group. Moreover, ZLE exhibits potent antioxidant effects evidenced by a significantly lowered NO and conservation of hepatic GSH, GST, and SOD in hepatic homogenates compared to infected untreated and PZQ-treated groups (p<0.05).

CONCLUSION

Our results point to ZLE as a promising hepatoprotective therapeutic tool in the treatment of schistosome hepatic fibrosis as it has anti-angiogenic, anti-proliferative, anti-fibrotic, and antioxidant effects in hamsters infected with S. mansoni, providing scientific support for its use in conventional medicine.

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.

Human serum activates the tegument of female schistosomes and supports recovery from Praziquantel

Schistosomiasis is one of the most devastating parasitic disease in the world. Schistosoma spp. survive for decades within the vasculature of their human hosts. They have evolved a vast array of mechanisms to avoid the immune reaction of the host. Due to their sexual dimorphism, with the female worm lying within the gynecophoric canal of the male worm, it is the male that is exposed to the immediate environment and the soluble parts of the host’s immune response. To understand how the worms are so successful in fending off the immune attacks of the host, comparative analyses of both worm sexes in human serum (with or without Praziquantel) were performed using scanning electron microscopy, transmission electron microscopy, and immunohistochemistry. Further, gene expression analyses of tegument-specific genes were performed. Following the incubation in human serum, males and females out of pairs show morphological changes such as an altered structure of the pits below the surface and an increased number of pits per area. In addition, female schistosomes presented a marked tuft-like repulsion of their opsonized surface. The observed resistance of females to Praziquantel seemed to depend on active proteins in the human serum. Moreover, different expression profiles of tegument-specific genes indicate different functions of female_single and male_single teguments in response to human serum. Our results indicate that female schistosomes developed different evasion strategies toward the host’s immune system in comparison to males that might lead to more robustness and has to be taken into account for the development of new anti-schistosomal drugs.

Pharmacological inhibition of lysine-specific demethylase 1 (LSD1) induces global transcriptional deregulation and ultrastructural alterations that impair viability in Schistosoma mansoni

Treatment and control of schistosomiasis still rely on only one effective drug, praziquantel (PZQ) and, due to mass treatment, the increasing risk of selecting for schistosome strains that are resistant to PZQ has alerted investigators to the urgent need to develop novel therapeutic strategies. The histone-modifying enzymes (HMEs) represent promising targets for the development of epigenetic drugs against Schistosoma mansoni. In the present study, we targeted the S. mansoni lysine-specific demethylase 1 (SmLSD1), a transcriptional corepressor, using a novel and selective synthetic inhibitor, MC3935, which was used to treat schistosomula and adult worms in vitro. By using cell viability assays and optical and electron microscopy, we showed that treatment with MC3935 affected parasite motility, egg-laying, tegument, and cellular organelle structures, culminating in the death of schistosomula and adult worms. In silico molecular modeling and docking analysis suggested that MC3935 binds to the catalytic pocket of SmLSD1. Western blot analysis revealed that MC3935 inhibited SmLSD1 demethylation activity of H3K4me1/2. Knockdown of SmLSD1 by RNAi recapitulated MC3935 phenotypes in adult worms. RNA-Seq analysis of MC3935-treated parasites revealed significant differences in gene expression related to critical biological processes. Collectively, our findings show that SmLSD1 is a promising drug target for the treatment of schistosomiasis and strongly support the further development and in vivo testing of selective schistosome LSD1 inhibitors.

In vitro and in vivo activities of multi-target phtalimido-thiazoles on Schistosomiasis mansoni

Schistosomicidal activity of six phthalimido-thiazoles derivatives with substitutions at the position three of the thiazole ring were analyzed in an experimental model. The substituents biphenyl (2i) and 2- naphthyl (2j) at a concentration of 80 µg/mL caused 100% mortality of the parasite in culture after 24 h and 48 h respectively. An evaluation of ultrastructural parasites showed damage in the tegument, formation of bubbles and partial destruction of the tubercles. The in vivo anti-parasitic activity with the derivate 2i was performed by administering it orally and intraperitoneally in a 400 mg/kg/5days regimen. Decreases in the number of eggs in the gut (45.1%) and a reduction of the percentage of mature (23.7%) and increased unviable (53.8%) eggs were observed. Our results also showed a reduction in the number of recovered worms after treatment with 2i (oral administration: 81, 25%). The results demonstrated that the prototypes which were tested had a significant anti-schistosomal effect against S. mansoni, suggesting that these derivatives are promising candidates for further research into the chemotherapy of schistosomiasis.

Effects of the Environment on Developmental Plasticity and Infection Success of Schistosoma Parasites - An Epigenetic Perspective

Evidence of how environmental cues affect the phenotypes of, and compatibility between Schistosoma mansoni and their hosts come from studies in environmental parasitology and research on host diet and chemotherapeutic treatment. Schistosomes deal with a multitude of signals from the water environment as well as cues that come from their hosts, particularly in response to molecules that serve to recognize and destroy them, i.e., those molecules that arise from their hosts' immune systems. These interactions shape, not only the parasite's morphology, metabolism and behavior in the short-term, but also their infection success and development into different stage-specific phenotypes later in their life cycle, through the modification of the parasite's inheritance system. Developmental phenotypic plasticity of S. mansoni is based on epigenetic mechanisms which are also sensitive to environmental cues, but are poorly understood. Here, we argue that specific cues from the environment could lead to changes in parasite development and infectivity, and consequently, environmental signals that come from environmental control measures could be used to influence S. mansoni dynamics and transmission. This approach poses a challenge since epigenetic modification can lead to unexpected and undesired outcomes. However, we suggest that a better understanding of how environmental cues are interpreted by epigenome during schistosome development and host interactions could potentially be applied to control parasite's virulence. We review evidence about the role of environmental cues on the phenotype of S. mansoni and the compatibility between this parasite and its intermediate and definitive hosts.

Inhibition of histone methyltransferase EZH2 in Schistosoma mansoni in vitro by GSK343 reduces egg laying and decreases the expression of genes implicated in DNA replication and noncoding RNA metabolism

Background

The possibility of emergence of praziquantel-resistant Schistosoma parasites and the lack of other effective drugs demand the discovery of new schistosomicidal agents. In this context the study of compounds that target histone-modifying enzymes is extremely promising. Our aim was to investigate the effect of inhibition of EZH2, a histone methyltransferase that is involved in chromatin remodeling processes and gene expression control; we tested different developmental forms of Schistosoma mansoni using GKS343, a selective inhibitor of EZH2 in human cells.

Methodology/Principal findings

Adult male and female worms and schistosomula were treated with different concentrations of GSK343 for up to two days in vitro. Western blotting showed a decrease in the H3K27me3 histone mark in all three developmental forms. Motility, mortality, pairing and egg laying were employed as schistosomicidal parameters for adult worms. Schistosomula viability was evaluated with propidium iodide staining and ATP quantification. Adult worms showed decreased motility when exposed to GSK343. Also, an approximate 40% reduction of egg laying by GSK343-treated females was observed when compared with controls (0.1% DMSO). Scanning electron microscopy showed the formation of bulges and bubbles throughout the dorsal region of GSK343-treated adult worms. In schistosomula the body was extremely contracted with the presence of numerous folds, and growth was markedly slowed. RNA-seq was applied to identify the metabolic pathways affected by GSK343 sublethal doses. GSK343-treated adult worms showed significantly altered expression of genes related to transmembrane transport, cellular homeostasis and egg development. In females, genes related to DNA replication and noncoding RNA metabolism processes were downregulated. Schistosomula showed altered expression of genes related to cell adhesion and membrane synthesis pathways.

Conclusions/Significance

The results indicated that GSK343 presents in vitro activities against S. mansoni, and the characterization of EZH2 as a new potential molecular target establishes EZH2 inhibitors as part of a promising new group of compounds that could be used for the development of schistosomicidal agents.

Schistosomiasis is a chronic and debilitating disease caused by a trematode of the genus Schistosoma. The current strategy for the control of the disease involves treatment with praziquantel, the only available drug. The development of new drugs is therefore a top priority. Drugs that inhibit histone modifying enzymes have been used in cancer, altering gene expression, replication, repair and DNA recombination. Schistosoma parasites have some characteristics similar to malignant tumors, such as intense cell division and high levels of metabolic activity. Here we evaluate in Schistosoma mansoni the effect of GSK343, an inhibitor of the histone methyltransferase EZH2 that had been shown to arrest or reduce the growth of human cancer cells. We show that GSK343 causes damage to the parasite tegument and reduces egg laying in vitro, concomitant with a decrease in levels of H3K27me3, the histone mark put in place by EZH2. RNA-seq and proteomic analyses of treated parasites showed changes in the expression of hundreds of genes involved in important metabolic processes. In females, a marked decrease was observed in the expression of genes related to processes such as DNA replication and noncoding RNA metabolism. In conclusion, the histone methyltransferase EZH2 seems to be a promising novel drug target against schistosomiasis.

Sesquiterpenes evaluation on Schistosoma mansoni: Survival, excretory system and membrane integrity

The main challenge in schistosomiasis control has been the emergence of drug-resistant parasites. Since the 1970's, praziquantel (PZQ) is the single drug for treatment. This fact highlights the importance to research news chemotherapeutic agents. In the last years, S. mansoni excretory system and tegument have been major targets for drug development. The purpose of this study was to evaluate the effect of sesquiterpenes, alpha-humulene and trans-caryophyllene on S. mansoni survival, excretory system and membrane integrity, after in vitro exposure. The in vitro studies, showed that sesquiterpenes reduced egg production and motor activity of worms at sublethal concentrations, and caused death in a concentration-dependent manner (100 and 200μg/mL). Tegumental analysis by Scanning Electron Microscopy (SEM), showed tegument damage. Additionally, it was possible to observe lesions, evidenced by intense marking trough Hoechst probe, in the tegument and suckers of worms exposed to 200μg/mL. In this study, we also showed that resorufin is only capable of identifying the interaction of sesquiterpenes in males excretory system, Pgp expression and inferring that females are more tolerant to treatments. Thus, the present study results contribute to an understanding of alpha-humulene and trans-caryophyllene effect over these targets, contributing for the development of schistosomicidal drugs.

Barbatic Acid Offers a New Possibility for Control of Biomphalaria Glabrata and Schistosomiasis

This study evaluated the biological activity of an ether extract and barbatic acid (BAR) from Cladia aggregata on embryos and adult mollusks of Biomphalaria glabrata, cercariae of Schistosoma mansoni and the microcrustacean Artemia salina. The ether extract and BAR were obtained by successive extractions with diethyl ether. The obtained extracts were analyzed using thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), proton nuclear magnetic resonance (¹H-NMR) and infrared (IR) spectroscopy. The results demonstrated that the ether extract exerted embryotoxic effects at 50 and 100 µg/mL and molluscicidal effects at 20 and 25 µg/mL. BAR exhibited no embryotoxicity, and its molluscicidal concentration was equal to that of the ether extract. However, after 60 min of exposure, 1 µg/mL BAR presented cercaricidal activity against the parasite S. mansoni at the second larval stage. Neither substance induced toxicity against A. salina. These results indicate the potential molluscicidal activities of the ether extract and BAR against B. glabrata and S. mansoni cercariae. In addition to these effects, there was a lack of toxicity against the aquatic environment and no damage to the biota, indicating the potential of these products for large-scale control and/or eradication of schistosomiasis.

In vivo study of schistosomicidal action of 1-benzyl-4-[(4-fluoro-phenyl)-hydrazono]-5-thioxo-imidazolidin-2-one

Praziquantel has been the drug most widely used therapy against different forms of schistosomiasis around the world. However, this treatment has shown ineffective in humans and in experimental models of Schistosoma mansoni. New therapeutic alternatives have been tested, including the imidazolidine derivative LPSF/PT-09, which has shown high therapeutic potential in vitro. In this work, we tested the schistosomal activity of this derivative in doses of 250mg/kg and 200mg/kg in mice experimentally infected with a high parasite load of S. mansoni. Parasitological evaluations related to the number of S. mansoni worms and their oviposition were performed during the acute phase of the disease and have demonstrated moderate effectiveness of 30-54,4%. However, LPSF/PT-09 did not influence oviposition of the parasites or the embryonic development of the eggs. The results obtained in this model showed that the imidazolidine derivative LPSF/PT-09 presented significant antischistosomal activity in vivo, posing as a potential candidate for this class of drugs. However, a better understanding of the pharmacokinetics and pharmacodynamics of the imidazolidine derivative LPSF/PT-09 is needed.

The cytotoxicity study of praziquantel enantiomers

Praziquantel (PZQ) is prescribed as a racemic mixture (racemic-PZQ, rac-PZQ), which is composed of (R)-PZQ and (S)-PZQ. In this work, the cytotoxicity of rac-PZQ and its two enantiomers (R)-PZQ and (S)-PZQ on eight cell lines (L-02, HepG2, prf-plc-5, SH-SY5Y, HUVEC, A549, HCT-15, Raw264.7) was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphe-nyltetrazolium bromide and lactate dehydrogenase assays. The morphology of apoptotic cells was studied by fluorescence microscope using Hoechst 33342 staining, and the cytotoxicity of the compounds was also tested by lactate dehydrogenase assay. Results revealed that (R)-PZQ had negligible cytotoxicity against L-02, SH-SY5Y, HUVEC, A549, HCT-15, and Raw264.7 cells but selectively inhibited tumor cell lines (prf-plc-5 and HepG2). However, in contrast to (R)-PZQ, the (S)-isomer showed higher cytotoxicity against L-02 cells and lower inhibition on prf-plc-5 and HepG2 cells. Besides, (R)-PZQ showed lower cytotoxicity on SH-SY5Y cells than (S)-PZQ. Meanwhile, (R)-PZQ at <80 μM concentration could promote proliferation of macrophage cells (Raw264.7). Our research revealed that (R)-PZQ has lower cytotoxicity than (S)-PZQ and has similar cytotoxicity with rac-PZQ. (S)-PZQ is the principal enantiomer to cause side effects on human definitive hosts. These findings gave the reasonable reasons for World Health Organization to produce (R)-PZQ as a replacement for rac-PZQ for the treatment of schistosomiasis.

ULTRASTRUCTURAL CHANGES IN Schistosoma mansoni MALE WORMS AFTER in vitro INCUBATION WITH THE ESSENTIAL OIL OF Mentha x villosa Huds

INTRODUCTION

The essential oil Mentha x villosa (MVEO) has a wide range of actions, including antibacterial, antifungal, antiprotozoal and schistosomicidal actions. The present study aimed to investigate the ultrastructural changes of MVEO on the tegument of adult Schistosoma mansoni.

MATERIALS AND METHODS

Different concentrations of MVEO were tested on S. mansoni adult worms in vitro. Ultrastructural changes on the tegument of these adult worms were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

The MVEO caused the death of all worms at 500 μg mL(-1) after 24 h. After 24h of 500 μg mL(-1) MVEO treatment, bubble lesions were observed over the entire body of worms and they presented loss of tubercles in some regions of the ventral portion. In the evaluation by TEM, S. mansoni adult worms treated with MVEO, 500 μg mL(-1), presented changes in the tegument and vacuoles in the syncytial matrix region. Glycogen granules close to the muscle fibers were visible.

CONCLUSION

The ability of MVEO to cause extensive ultrastructural damage to S. mansoni adult worms correlates with its schistosomicidal effects and confirms earlier findings with S. mansoni.

The Role of Efflux Pumps in Schistosoma mansoni Praziquantel Resistant Phenotype

BACKGROUND

Schistosomiasis is a neglected disease caused by a trematode of the genus Schistosoma that is second only to malaria in public health significance in Africa, South America, and Asia. Praziquantel (PZQ) is the drug of choice to treat this disease due to its high cure rates and no significant side effects. However, in the last years increasingly cases of tolerance to PZQ have been reported, which has caused growing concerns regarding the emergency of resistance to this drug.

METHODOLOGY/PRINCIPAL FINDINGS

Here we describe the selection of a parasitic strain that has a stable resistance phenotype to PZQ. It has been reported that drug resistance in helminths might involve efflux pumps such as members of ATP-binding cassette transport proteins, including P-glycoprotein and multidrug resistance-associated protein families. Here we evaluate the role of efflux pumps in Schistosoma mansoni resistance to PZQ, by comparing the efflux pumps activity in susceptible and resistant strains. The evaluation of the efflux activity was performed by an ethidium bromide accumulation assay in presence and absence of Verapamil. The role of efflux pumps in resistance to PZQ was further investigated comparing the response of susceptible and resistant parasites in the absence and presence of different doses of Verapamil, in an ex vivo assay, and these results were further reinforced through the comparison of the expression levels of SmMDR2 RNA by RT-PCR.

CONCLUSIONS/SIGNIFICANCE

This work strongly suggests the involvement of Pgp-like transporters SMDR2 in Praziquantel drug resistance in S. mansoni. Low doses of Verapamil successfully reverted drug resistance. Our results might give an indication that a combination therapy with PZQ and natural or synthetic Pgp modulators can be an effective strategy for the treatment of confirmed cases of resistance to PZQ in S. mansoni.

Evaluation of a method for induction of praziquantel resistance in Schistosoma mansoni

CONTEXT

Praziquantel (PZQ) is a highly efficacious anthelmintic against many flatworms including schistosomes. PZQ has been in use for more than 25 years, and concern is increasing that resistance has emerged in human schistosomes in Egypt and other endemic countries.

OBJECTIVE

The current study was designed to evaluate a recently described method for induction of PZQ resistance in Schistosoma mansoni.

MATERIALS AND METHODS

Successive subcurative drug treatments of Biomphalaria alexandrina snails infected with an Egyptian strain of S. mansoni were undertaken. Cercariae shed from snails exposed and unexposed to PZQ were used to infect mice. Forty-five days after infection, mice were treated with a single oral dose of PZQ in 2% aqueous solution of Cremophor-EL®. The concentration of PZQ was 0, 200, 400, or 800 mg/kg. Thirty-three days after treatment, all groups of mice were dissected to collect the S. mansoni worms by the perfusion technique. In addition, the oogram pattern was examined to study the production, maturity, and death of S. mansoni eggs in the different groups of mice.

RESULTS

The present study has shown that the sublethal dose for induction of PZQ resistance in the intra-molluscan S. mansoni stages was 500 mg/kg. The worm count and the percentage of immature eggs in different groups of mice were significantly affected by the intra-molluscan exposure to PZQ and the drug concentration used to treat infected mice.

DISCUSSION AND CONCLUSION

The results obtained herein confirm the possibility of using successive drug treatments of infected B. alexandrina to induce PZO resistance in S. mansoni.

Anthelmintic activity in vitro and in vivo of Baccharis trimera (Less) DC against immature and adult worms of Schistosoma mansoni

Although its efficiency against all Schistosoma species, praziquantel (PZQ) shows low efficacy against schistosomula and juvenile stages. The potential for development of resistance to PZQ has justified the search for new alternative chemotherapies. In this scenario, studies to new formulations, more comprehensive and without adverse effects, are being conducted. One viable and promising treatment is the study of medicinal plants as a new approach to the experimental treatment for Schistosomiasis. Amongst all the variety of the medicinal species studied, we can highlight Baccharis trimera (Less) DC, known as "Carqueja-amarga". This paper not only describes the effect of crude dichloromethane extract (DE) and aqueous fraction (AF) obtained from B. trimera, in vitro but also is the first one that investigates the in vivo efficacy of B. trimera against schistosomula, juvenile and adult worms of Schistosoma mansoni BH strain. In the experiment, mice were treated with DE, AF and PZQ (40 and 200mg/kg) over the period of larval development (3 and 30 post-infection; pi), and adult worms (60days post-infection; pi). The in vitro results show that the DE and AF effects are dose-dependents, being the 130μg/mL the most effective one in a shorter period of incubation. The exposure of the in vitro samples over adult parasites were able to inhibit 100% of the oviposition in females. Likewise caused the mortality of the parasites with morphological alterations on the tegument, on the suckers, oral and acetabulum, in both males and females after 6-72h of exposure. Additionally, the in vivo treatments against juvenile and adult infection were more effective compared to the control group untreated. Administrations of AF and DE in day 30pi (juvenile worms) show female worm total burden reductions of 75% and 68% respectively. At the same period of infection reductions of respectively 98% and 97% egg/g in the faeces were seen. In relation to the different egg developmental stages (oogram), the results showed significant reductions, due to the reduction in the number of worms, especially the females. In conclusion, B. trimera exhibits major schistosomicidal effects in vivo against immature and adult worms of S. mansoni, opening up perspectives for future researches on substance or compound isolation and the elucidation of its mechanisms of action.

Praziquantel treatment in trematode and cestode infections: an update

Status and emerging issues in the use of praziquantel for treatment of human trematode and cestode infections are briefly reviewed. Since praziquantel was first introduced as a broadspectrum anthelmintic in 1975, innumerable articles describing its successful use in the treatment of the majority of human-infecting trematodes and cestodes have been published. The target trematode and cestode diseases include schistosomiasis, clonorchiasis and opisthorchiasis, paragonimiasis, heterophyidiasis, echinostomiasis, fasciolopsiasis, neodiplostomiasis, gymnophalloidiasis, taeniases, diphyllobothriasis, hymenolepiasis, and cysticercosis. However, Fasciola hepatica and Fasciola gigantica infections are refractory to praziquantel, for which triclabendazole, an alternative drug, is necessary. In addition, larval cestode infections, particularly hydatid disease and sparganosis, are not successfully treated by praziquantel. The precise mechanism of action of praziquantel is still poorly understood. There are also emerging problems with praziquantel treatment, which include the appearance of drug resistance in the treatment of Schistosoma mansoni and possibly Schistosoma japonicum, along with allergic or hypersensitivity reactions against praziquantel treatment. To cope with and overcome these problems, combined use of drugs, i.e., praziquantel and other newly introduced compounds such as triclabendazole, artemisinins, and tribendimidine, is being tried.

Contribution of silver ions to the inhibition of infectivity of Schistosoma japonicum cercariae caused by silver nanoparticles

Blockage of pathogen transmission through water decontamination is considered an important strategy for the prevention of schistosome infection. Many believe that this strategy is feasible, but it has yet to be achieved. Silver has a long history of use as a disinfectant. With the emergence of nanotechnology, silver can be shaped into nanoparticles which have been found to possess superb antimicrobial activities. In this light, we investigated the effects of silver nanoparticles (AgNPs) on Schistosoma japonicum cercariae. AgNPs rapidly induced cercarial tail-shedding, agitated behaviour and a decrease in cercarial secretion in a dose-dependent manner. Prolonged treatment was found to be cercariocidal, which nevertheless might be attributable to AgNP-induced cercarial tail loss rather than to toxicity. Higher concentrations of AgNPs (125 μg mL-1 and above) completely blocked cercarial infectivity. Despite decreased infectivity, cercariae exposed to lower concentrations of AgNPs for 30 min were still found capable of infecting hosts even without their tails, suggesting that tail loss does not necessarily signify a total loss of infective ability. We also found that silver ions (Ag+) were heavily involved in the observed cercarial responses of AgNPs. Our observations provide insight into the interactions between the larvae of helminth parasites and nanoparticles.

Susceptibility or resistance of praziquantel in human schistosomiasis: a review

Since praziquantel was developed in 1970s, it has replaced other antischistosomal drugs to become the only drug of choice for treatment of human schistosomiases, due to high efficacy, excellent tolerability, few and transient side effects, simple administration, and competitive cost. Praziquantel-based chemotherapy has been involved in the global control strategy of the disease and led to the control strategy shifting from disease control to morbidity control, which has greatly reduced the prevalence and intensity of infections. Given that the drug has been widely used for morbidity control in endemic areas for more than three decades, the emergence of resistance of Schistosoma to praziquantel under drug selection pressure has been paid much attention. It is possible to induce resistance of Schistosoma mansoni and Schistosoma japonicum to praziquantel in mice under laboratorial conditions, and a reduced susceptibility to praziquantel in the field isolates of S. mansoni has been found in many foci. In addition, there are several schistosomiasis cases caused by Schistosoma haematobium infections in which repeated standard treatment fails to clear the infection. However, in the absence of exact mechanisms of action of praziquantel, the mechanisms of drug resistance in schistosomes remain unclear. The present review mainly demonstrates the evidence of drug resistance in the laboratory and field and the mechanism of praziquantel resistance and proposes some strategies for control of praziquantel resistance in schistosomes.

New insight into praziquantel against various developmental stages of schistosomes

Praziquantel, due to high efficacy, excellent tolerability, few and transient side effects, simple administration, and competitive cost, is virtually the only drug of choice for treatment of human schistosomiasis. Treatment of schistosomiasis has shown great advances with the introduction of the drug into the therapeutic arsenal in areas that are endemic for the parasite. However, the drug presents various efficacies against different developmental stages of schistosomes, appearing an oddity intermitted mode. The present review article reviews the effects and mechanism of action of praziquantel against schistosomes briefly and suggests the research on this oddity phenomenon.

Resolution of praziquantel

Background

Praziquantel remains the drug of choice for the worldwide treatment and control of schistosomiasis. The drug is synthesized and administered as a racemate. Use of the pure active enantiomer would be desirable since the inactive enantiomer is associated with side effects and is responsible for the extremely bitter taste of the pill.

Methodology/Principal Findings

We have identified two resolution approaches toward the production of praziquantel as a single enantiomer. One approach starts with commercially available praziquantel and involves a hydrolysis to an intermediate amine, which is resolved with a derivative of tartaric acid. This method was discovered through an open collaboration on the internet. The second method, identified by a contract research organisation, employs a different intermediate that may be resolved with tartaric acid itself.

Conclusions/Significance

Both resolution procedures identified show promise for the large-scale, economically viable production of praziquantel as a single enantiomer for a low price. Additionally, they may be employed by laboratories for the production of smaller amounts of enantiopure drug for research purposes that should be useful in, for example, elucidation of the drug's mechanism of action.

The drug praziquantel (PZQ) is used very widely in both animal and human medicine, where it is the mainstay of the treatment of the neglected tropical disease schistosomiasis. The drug is currently manufactured and administered as a racemate (1∶1 mixture of enantiomers) but for various reasons the large-scale production of PZQ as the single active enantiomer is very desirable. We describe here the preparation of praziquantel as a single enantiomer using classical resolution. The protocols are experimentally simple and inexpensive. One method was found and validated by an unusual research mechanism—open science—where the details of the collaboration (involving academic and industrial partners) and all research data were available on the web as they were acquired, and anyone could participate. The other route was found in parallel by a contract research organisation. Besides being possible routes by which praziquantel may be produced in large quantities for the affected communities, it is also hoped that these methods can be used for the production of smaller quantities of enantiopure PZQ for pharmacological studies.

In vitro praziquantel test capable of detecting reduced in vivo efficacy in Schistosoma mansoni human infections

Although great reductions in human schistosomiasis have been observed after praziquantel (PZQ) mass drug administration (MDA), some individuals remain infected after multiple treatments. Many MDA programs now require monitoring for drug efficacy as a key component. No molecular tools for PZQ resistance currently exist and investigations into the dose of PZQ required to kill 50% of adult worms in vivo (ED(50)) present ethical, logistical, and temporal restraints. We, therefore, assessed the feasibility and accuracy of a rapid, inexpensive in vitro PZQ test in the laboratory and directly in the field in Uganda under MDA in conjunction with highly detailed infection intensity, clearance, and reinfection data. This test strongly differentiated between subsequently cleared and uncleared infections as well as differences between parasite populations pre- and post-PZQ treatments, advocating its use for on-the-spot monitoring of PZQ efficacy in natural foci. After only a few treatments, uncleared parasites were identified to be phenotypically different from drug-sensitive parasites, emphasizing the urgent need for monitoring of these repeatedly PZQ-treated populations.