Experimental chemotherapy of Schistosoma mansoni with praziquantel and oxamniquine: differential effect of single or combined formulations of drugs on various strains and on both sexes of the parasite

HGPRT and PNP: Recombinant Enzymes from Schistosoma mansoni and Their Role in Immunotherapy during Experimental Murine Schistosomiasis

Schistosomiasis is a parasitic infection caused by trematode worms (also called blood flukes) of the genus Schistosoma sp., which affects over 230 million people worldwide, causing 200,000 deaths annually. There is no vaccine or new drugs available, which represents a worrying aspect, since there is loss of sensitivity of the parasite to the medication recommended by the World Health Organization, Praziquantel. The present study evaluated the effects of the recombinant enzymes of S. mansoni Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT), Purine Nucleoside Phosphorylase (PNP) and the MIX of both enzymes in the immunotherapy of schistosomiasis in murine model. These enzymes are part of the purine salvage pathway, the only metabolic pathway present in the parasite for this purpose, being essential for the synthesis of DNA and RNA. Female mice of Swiss and BALB/c strains were infected with cercariae and treated, intraperitoneally, with three doses of 100 µg of enzymes. After the immunotherapy, the eggs and adult worms were counted in the feces; the number of eosinophils from the fluid in the peritoneal cavity and peripheral blood was observed; and the quantification of the cytokine IL-4 and the production of antibodies IgE was analyzed. The evaluation of the number of granulomas and collagen deposition via histological slides of the liver was performed. The results demonstrate that immunotherapy with the enzyme HGPRT seems to stimulate the production of IL-4 and promoted a significant reduction of granulomas in the liver in treated animals. The treatment with the enzyme PNP and the MIX was able to reduce the number of worms in the liver and in the mesenteric vessels of the intestine, to reduce the number of eggs in the feces and to negatively modulate the number of eosinophils. Therefore, immunotherapy with the recombinant enzymes of S. mansoni HGPRT and PNP might contribute to the control and reduction of the pathophysiological aspects of schistosomiasis, helping to decrease the morbidity associated with the infection in murine model.

Effects of Immunization with Recombinant Schistosoma mansoni Enzymes AK and HGPRT: Murine Infection Control

Schistosomiasis is one of the most important human helminthiases worldwide. Praziquantel is the current treatment, and no vaccine is available until the present. Thus, the presented study aimed to evaluate the immunization effects with recombinant Schistosoma mansoni enzymes: Adenosine Kinase (AK) and Hypoxanthine-Guanine Phosphoribosyltransferase (HGPRT), as well as a MIX of the two enzymes. Female Balb/c mice were immunized in three doses, and 15 days after the last immunization, animals were infected with S. mansoni. Our results showed that the group MIX presented a reduction in the eggs in feces by 30.74% and 29%, respectively, in the adult worms. The groups AK, HGPRT and MIX could produce IgG1 antibodies, and the groups AK and MIX produced IgE antibodies anti-enzymes and anti-S. mansoni total proteins. The groups AK, HGPRT and MIX induced a reduction in the eosinophils in the peritoneal cavity. Besides, the group AK showed a decrease in the number of hepatic granulomas (41.81%) and the eggs present in the liver (42.30%). Therefore, it suggests that immunization with these enzymes can contribute to schistosomiasis control, as well as help to modulate experimental infection inducing a reduction of physiopathology in the disease.

A comprehensive phytochemical and pharmacological review on sesquiterpenes from the genus Ambrosia

Sesquiterpenes are bitter secondary metabolites characteristic to the genus Ambrosia (Asteraceae) and constitute one of the most diverse classes of terpenoids. These compounds exhibit broad-spectrum bioactivities, such as antiproliferative, cytotoxic, antimicrobial, anti-inflammatory, molluscicidal, schistomicidal, larvicidal, and antiprotozoal activities. This review compiles and discusses the chemistry and pharmacology of sesquiterpenes of the Ambrosia species covering the period between 1950 and 2021. The review identified 158 sesquiterpenes previously isolated from 23 different Ambrosia species collected from across the American, African, and Asian continents. These compounds have guaiane, pseudoguaiane, seco-pseudoguaiane, daucane, germacrane, eudesmane, oplopane, clavane, and aromadendrane carbon skeletons. Most sesquiterpene compounds predominantly harbor the pseudoguaiane skeleton, whereas the eudesmanes have the most varied substituents. Antiproliferative and antiprotozoal activities are the most promising bioactivities of sesquiterpenes in Ambrosia and could lead to new pathways toward drug discovery.

Investigating Immunization With Nucleotide Enzymes of Schistosoma mansoni: Nucleoside Diphosphate Kinase and Adenylosuccinate Lyase as New Antigenic Targets Against Schistosomiasis

Schistosomiasis, caused by Schistosoma mansoni trematode worm, affects more than 1.5 million people in Brazil. The current treatment consists in the administration of Praziquantel, the only medicine used for treatment for more than 40 years. Some of the limitations of this drug consist in its inactivity against schistosomula and parasite eggs, the appearance of resistant strains and non-prevention against reinfection. Thus, the objective of this study was to evaluate the effect of immunization with recombinant functional enzymes of the purine salvage pathway of S. mansoni, Nucleoside Diphosphate Kinase (NDPK) and Adenylosuccinate Lyase (ADSL), to evaluate the host immune response, as well as the parasite load after vaccination. For this, Balb/c mice were divided into 5 groups: control (uninfected and untreated), non-immunized/infected, NDPK infected, ADSL infected, and NDPK + ADSL infected. Immunized groups received three enzyme dosages, with a 15-day interval between each dose, and after 15 days of the last application the animals were infected with 80 cercariae of S. mansoni. On the 47th day after the infection, fecal eggs were counted and, on the 48th day after the infection, the evaluation of leukocyte response, parasite load, antibody production, cytokines quantification, and histopathological analysis were performed. The results showed that immunizations with NDPK, ADSL or NDPK + ADSL promoted a discreet reduction in eosinophil counts in lavage of peritoneal cavity. All immunized animals showed increased production and secretion of IgG1, IgG2a, and IgE antibodies. Increased production of IL-4 was observed in the group immunized with the combination of both enzymes (NDPK + ADSL). In addition, in all immunized groups there were reductions in egg counts in the liver and intestine, such as reductions in liver granulomas. Thus, we suggest that immunizations with these enzymes could contribute to the reduction of schistosomiasis transmission, besides being important in immunopathogenesis control of the disease.

Current and Novel Therapies Against Helminthic Infections: The Potential of Antioxidants Combined with Drugs

Infections caused by Schistosoma haematobium and Opisthorchisviverrini are classified as Group 1 biological carcinogen and it has been postulated that parasites produce oxysterol and estrogen-like metabolites that might be considered as initiators of infection-associated carcinogenesis. Chemotherapy for these helminthic infections relies on a single drug, praziquantel, (PZQ) that mainly targets the parasite. Additionally, PZQ has some major drawbacks as inefficacy against juvenile form and alone it is not capable to counteract pathologies associated to infections or prevent carcinogenesis. There is an urgent need to develop novel therapeutic approaches that not only target the parasite but also improve the pathologies associated to infection, and ultimately, counteract or/and prevent the carcinogenesis processes. Repurposing the drug in combination of compounds with different modes of action is a promising strategy to find novel therapeutics approaches against these helminthic infections and its pathologies. Here, we emphasized that using antioxidants either alone or combined with anthelmintic drugs could ameliorate tissue damage, infection-associated complications, moreover, could prevent the development of cancer associated to infections. Hence, antioxidants represent a potential adjuvant approach during treatment to reduce morbidity and mortality. Despite the success of some strategies, there is a long way to go to implement novel therapies for schistosomiasis.

A novel praziquantel solid lipid nanoparticle formulation shows enhanced bioavailability and antischistosomal efficacy against murine S. mansoni infection

Background

Schistosomiasis is responsible for a considerable global disease burden. This work aimed to improve the therapeutic outcome of the only available antischistosomal drug worldwide, praziquantel (PZQ), by incorporating it into a novel carrier, “solid lipid nanoparticles (SLNs)”, to enhance its solubility, bioavailability and efficacy. A simple, cost-effective method was used to prepare SLN-PZQ.

Results

Compared to market PZQ (M-PZQ), SLN-PZQ was more bioavailable, as denoted by higher serum concentrations in both normal and infected mice where elevated K_a, AUC_0–24, C_max, and t_1/2e with a decrease in k_el were demonstrated. The AUC_0–24 for SLN-PZQ in normal and Schistosoma mansoni-infected groups was almost nine- and eight-fold higher, respectively, than that for M-PZQ in corresponding groups. In normal and S. mansoni-infected mice, SLN-PZQ was detectable in serum at 24 h, while M-PZQ completely vanished 8 h post-treatment. Additionally, enhanced absorption with extended residence time was recorded for SLN-PZQ. Compared to M-PZQ, SLN-PZQ revealed superior antischistosomal activity coupled with enhanced bioavailability in all treated groups where higher percentages of worm reduction were recorded with all dosages tested. This effect was especially evident at the lower dose levels. The ED₉₅ of SLN-PZQ was 5.29-fold lower than that of M-PZQ, with a significantly higher reduction in both the hepatic and intestinal tissue egg loads of all treated groups and almost complete disappearance of immature deposited eggs (clearly evident at the low dose levels).

Conclusions

SLN-PZQ demonstrated enhanced PZQ bioavailability and antischistosomal efficacy with a safe profile despite the prolonged residence in the systemic circulation.

The impact of cinnarizine and griseofulvin on juvenile and adult stages of Schistosoma mansoni

Schistosomiasis affects millions globally. There is no vaccine, and treatment depends entirely on praziquantel (PZQ). Field isolates exhibit reduced susceptibility to PZQ, and resistance has been experimentally induced, suggesting that reliance on a single treatment is particularly dangerous. The present study investigated the value of cinnarizine and griseofulvin against Schistosoma mansoni through their in vitro effects on adult worms and oviposition as well as in vivo evaluation in early and late infection, compared to PZQ, in a preliminary experimental model. In vitro, both cinnarizine and griseofulvin showed uncoupling, sluggish worm movement and complete absence of ova at 100 μg/ml. In early infection, cinnarizine showed a significant reduction in the number of porto-mesenteric couples compared to the griseofulvin and control groups, a finding similar to PZQ. Remarkably, cinnarizine significantly exceeded PZQ and griseofulvin in reducing the total worm burden. In late infection, cinnarizine and griseofulvin showed results similar to PZQ by significantly reducing the numbers of hepatic and porto-mesenteric couples and total worm burden compared to controls. Cinnarizine performed better than griseofulvin by reducing hepatic and intestinal ovum counts, and it led to complete disappearance of the first two immature stages. The current work suggests the possibility of using cinnarizine and griseofulvin, mainly in late S. mansoni infection, especially cinnarizine, which showed similar results to PZQ and surpassed it in early infection. Further studies are required to elucidate their exact mechanisms of action and particularly their synergistic effect with PZQ.

In vitro schistosomicidal activity of tamoxifen and its effectiveness in a murine model of schistosomiasis at a single dose

Schistosomiasis is a neglected tropical disease affecting 220 million people worldwide. Praziquantel has proven to be effective against this parasitic disease, though there are increasing concerns regarding tolerance/resistance that calls for new drugs. Repurposing already existing and well-known drugs has been a desirable approach since it reduces time, costs, and ethical concerns. The anti-cancer drug tamoxifen (TAM) has been used worldwide for several decades to treat and prevent breast cancer. Previous reports stated that TAM affects Schistosoma hormonal physiology; however, no controlled schistosomicidal in vivo assays have been conducted. In this work, we evaluated the effect of TAM on female and male Schistosoma mansoni morphology, motility, and egg production. We further assessed worm survival and egg production in S. mansoni-infected mice. TAM induced morphological alterations in male and female parasites, as well as in eggs in vitro. Furthermore, in our in vivo experiments, one single dose of intraperitoneal TAM citrate reduced the total worm burden by 73% and led to a decrease in the amount of eggs in feces and low percentages of immature eggs in the small intestine wall. Eggs obtained from TAM citrate-treated mice were reduced in size and presented hyper-vacuolated structures. Our results suggest that TAM may be repurposed as a therapeutic alternative against S. mansoni infections.

Epiisopilosine alkaloid has activity against Schistosoma mansoni in mice without acute toxicity

Schistosomiasis is a disease caused by parasites of the genus Schistosoma, currently affecting more than 200 million people. Among the various species of this parasite that infect humans, S. mansoni is the most common. Pharmacological treatment is limited to the use of a single drug, praziquantel (PZQ), despite reports of parasite resistance and low efficacy. It is therefore necessary to investigate new potential schistosomicidal compounds. In this study, we tested the efficacy of epiisopilosine (EPIIS) in a murine model of schistosomiasis. A single dose of EPIIS (100 or 400 mg/kg) administered orally to mice infected with adult S. mansoni resulted in reduced worm burden and egg production. The treatment with the lower dose of EPIIS (100 mg/kg) significantly reduced total worm burden by 60.61% (P < 0.001), as well as decreasing hepatosplenomegaly and egg excretion. Scanning electron microscopy revealed morphological changes in the worm tegument after treatment. Despite good activity of EPIIS in adult S. mansoni, oral treatment with single dose of EPIIS 100 mg/kg had only moderate effects in mice infected with juvenile S. mansoni. In addition, we performed cytotoxicity and toxicological studies with EPIIS and found no in vitro cytotoxicity (in HaCaT, and NIH-3T3 cells) at a concentration of 512 μg/mL. We also performed in silico analysis of toxicological properties and showed that EPIIS had low predicted toxicity. To confirm this, we investigated systemic acute toxicity in vivo by orally administering a 2000 mg/kg dose to Swiss mice. Treated mice showed no significant changes in hematological, biochemical, or histological parameters compared to non-treated animals. Epiisopilosine showed potential as a schistosomicidal drug: it did not cause acute toxicity and it displayed an acceptable safety profile in the animal model.

Drug Repurposing for Schistosomiasis: Combinations of Drugs or Biomolecules

Schistosomiasis is a major neglected tropical disease. Control of schistosomiasis currently relies on a single drug, praziquantel, and despite its efficacy against the all schistosome species that parasitize humans, it displays some problematic drawbacks and alone is ineffective in counteracting adverse pathologies associated with infection. Moreover, due to the development of the potential emergence of PZQ-resistant strains, the search for additional or alternative antischistosomal drugs have become a public health priority. The current drug discovery for schistosomiasis has been slow and uninspiring. By contrast, repurposing of existing approved drugs may offer a safe, rapid and cost-effective alternative. Combined treatment with PZQ and other drugs with different mode of action, i.e., antimalarials, shows promise results. In addition, a combination of anthelminthic drugs with antioxidant might be advantageous for modulating oxidative processes associated with schistosomiasis. Herein, we review studies dealing with combination therapies that involve PZQ and other anthelminthic drugs and/or antioxidant agents in treatment of schistosomiasis. Whereas PZQ combined with antioxidant agents might or might not interfere with anthelminthic efficacy, combinations may nonetheless ameliorate tissue damage and infection-associated complications. In fact, alone or combine with other drugs, antioxidants might be a valuable adjuvant to reduce morbidity and mortality of schistosomiasis. Therefore, attempting new combinations of anthelmintic drugs with other biomolecules such as antioxidants provides new avenues for discovery of alternatives to PZQ.

Structural and Functional Characterization of the Enantiomers of the Antischistosomal Drug Oxamniquine

Background

For over two decades, a racemic mixture of oxamniquine (OXA) was administered to patients infected by Schistosoma mansoni, but whether one or both enantiomers exert antischistosomal activity was unknown. Recently, a ~30 kDa S. mansonisulfotransferase (SmSULT) was identified as the target of OXA action.

Methodology/Principal Findings

Here, we separate the OXA enantiomers using chromatographic methods and assign their optical activities as dextrorotary [(+)-OXA] or levorotary [(-)-OXA]. Crystal structures of the parasite enzyme in complex with optically pure (+)-OXA and (-)-OXA) reveal their absolute configurations as S- and R-, respectively. When tested in vitro, S-OXA demonstrated the bulk of schistosomicidal activity, while R-OXA had antischistosomal effects when present at relatively high concentrations. Crystal structures R-OXA•SmSULT and S-OXA•SmSULT complexes reveal similarities in the modes of OXA binding, but only the S-OXA enantiomer is observed in the structure of the enzyme exposed to racemic OXA.

Conclusions/Significance

Together the data suggest the higher schistosomicidal activity of S-OXA is correlated with its ability to outcompete R-OXA binding the sulfotransferase active site. These findings have important implications for the design, syntheses, and dosing of new OXA-based antischistosomal compounds.

Schistosomes, parasites that cause the disease schistosomiasis in humans, are blood flukes that infect an estimated 200 million people in 76 countries. Control of schistosomiasis is currently based on repeated doses of the drug praziquantel (PZQ). Parasites showing reduced susceptibility to PZQ have been recovered from patients that failed PZQ treatment and have been obtained by experimental selection. New anti-schistosomal drugs are therefore needed that can be used with PZQ to minimize the probability of resistance. The older anti-schistosomal drug oxamniquine (OXA) has an excellent efficacy and safety record but is only active against one of the three species infecting humans. Recently, a combination of genetic and structural analyses resulted in the determination of the structure of OXA in complex with its target enzyme in the parasite, providing opportunity for structure-guided modifications of OXA to make it more effective against all three schistosome species. Synthesis of OXA results in a racemic mixture. Here, we isolate OXA enantiomers and find that one is more effective than the other at killing schistosomes. Crystal structures of both OXA enantiomers bound to the target enzyme suggest a molecular basis for this observation that should be considered in ongoing and future OXA-based drug design efforts.

Effectiveness of hyperbaric oxygen for experimental treatment of schistosomiasis mansoni using praziquantel-free and encapsulated into liposomes: assay in adult worms and oviposition

The treatment of schistosomiasis depends on a single drug: praziquantel (PZQ). However, this treatment presents limitations such as low and/or erratic bioavailability that can contribute to cases of tolerance. Improvements to the available drug are urgently needed and studies with a controlled system of drug release, like liposomes, have been gaining prominence. The present study evaluated the activity and synergy between liposomal-praziquantel (lip.PZQ) and hyperbaric oxygen therapy (HBO). Mice received doses of 60 or 100mg/kg PZQ or lip.PZQ, 50 days post-infection, and after the treatment, were exposed to HBO (3 atmosphere absolute - ATA) for 1h. The viability of adult worms and oviposition were analyzed, by necropsy and Kato-Katz examination performed after 15 days of treatment. A concentration of 100mg/kg of lip.PZQ+HBO was more effective (48.0% reduction of worms, 83.3% reduction of eggs/gram of feces) and 100% of the mice had altered of oograms (indicating interruption of oviposition) compared to other treatments and to the Control group (infected and untreated). It is known that PZQ requires participation of the host immune system to complete its antischistosomal activity and that HBO is able to stimulate the immune system. The drug became more available in the body when incorporated into liposomes and, used with HBO, the HBO worked as an adjuvant. This explains the decreases of oviposition and worms recovered form hepatic portal system.

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 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.

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.

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 decreases Schistosoma mansoni genetic diversity in experimental infections

BACKGROUND

Schistosomiasis has a considerable impact on public health in many tropical and subtropical areas. In the new world, schistosomiasis is caused by the digenetic trematode Schistosoma mansoni. Chemotherapy is the main measure for controlling schistosomiasis, and the current drug of choice for treatment is praziquantel (PZQ). Although PZQ is efficient and safe, its repetitive large-scale use in endemic areas may lead to the selection of resistant strains. Isolates less susceptible to PZQ have been found in the field and selected for in the laboratory. The impact of selecting strains with a decreased susceptibility phenotype on disease dynamics and parasite population genetics is not fully understood. This study addresses the impact of PZQ pressure on the genetics of a laboratory population by analyzing frequency variations of polymorphic genetic markers.

METHODOLOGY

Infected mice were treated with increasing PZQ doses until the highest dose of 3 × 300 mg/Kg was reached. The effect of PZQ treatment on the parasite population was assessed using five polymorphic microsatellite markers. Parasitological and genetic data were compared with those of the untreated control. After six parasite generations submitted to treatment, it was possible to obtain a S. mansoni population with decreased susceptibility to PZQ. In our experiments we also observed that female worms were more susceptible to PZQ than male worms.

CONCLUSIONS

The selective pressure exerted by PZQ led to decreased genetic variability in S. mansoni and increased endogamy. The understanding of how S. mansoni populations respond to successive drug pressure has important implications on the appearance and maintenance of a PZQ resistance phenotype in endemic regions.

Liposomal-praziquantel: efficacy against Schistosoma mansoni in a preclinical assay

Currently, schistosomiasis mansoni is treated clinically with praziquantel (PZQ). Nevertheless, cases of tolerance and resistance to this drug have been reported, creating the need to develop new drugs or to improve existing drugs. Considering the small number of new drugs against Schistosoma mansoni, the design of nanotechnology-based drug delivery systems is an important strategy in combating this disease. The aim of this study was to evaluate the activity of PZQ containing liposome (lip.PZQ) on S. mansoni, BH strain. Mice were treated orally with different concentrations of PZQ and lip.PZQ 30 and 45 days following infection. The number of worms, recovered by perfusion of the hepatic portal system, and the number of eggs found in the intestine and liver were analysed. Parasite egg counts were also performed. The most active formulation for all parameters was 300mg/kg of lip.PZQ, since as it decreased the total number of worms by 68.8%, the number of eggs in the intestine by 79%, and the number of hepatic granulomas by 98.4% compared to untreated controls. In addition, this concentration decreased egg counts by 55.5%. The improved efficacy of the treatment with lip.PZQ, especially when administered 45 days following infection, compared with the positive-control group (untreated) and the groups that received free PZQ, can be explained by greater bioavailability in the host organism; the preferred target of lip.PZQ is the liver, and lip.PZQ is better absorbed by the tegument of S. mansoni, which has an affinity for phospholipids.

Susceptibility of a Brazilian wild rodent isolate of Schistosoma mansoni to praziquantel in mice

The therapeutic effects of praziquantel (PZQ) against a Schistosoma mansoni isolate derived from Nectomys squamipes (isolate R) and a susceptible isolate (BH) were analyzed in Swiss mice by fecal egg counting, adult worm reduction and oogram pattern. Infected mice were orally administrated with 62.5mg/kg (group 1), 125mg/kg (group 2), 250mg/kg (group 3) and 500mg/kg (group 4), each dose divided over 3 days (49, 50 and 51 days after infection). The data were analyzed using one-way analysis of variance (ANOVA). In regard to isolate R, no fecal eggs were observed with 250 mg/Kg and 500 mg/kg (p<0.05), whereas BH excretion reached zero with all doses. Mean worm burden reduction was significantly (p<0.05) higher at the two highest concentrations, regardless of isolate. At 62.5mg/kg, the percentage of immature eggs varied from 17% (isolate R) to 38% (isolate BH). At 125 mg/kg, the percentage of immature eggs varied from 20% (isolate R) to 16% (isolate BH). At 250 mg/kg, immature eggs dropped significantly to 1% (isolate R) and 4% (isolate BH). At 500 mg/kg, no immature eggs were found in isolate R, whereas in BH was 8%. No dosage significantly (p>0.05) affected the percentage of mature eggs, regardless of isolate. There was a large increase (p<0.001) in the percentages of dead eggs in all treated groups of 62% and 64% in groups 3 and 4, respectively (isolate R). The percentage of dead eggs rose from 34% (group 1) to 58% (group 3) in isolate BH. Although group 4 showed lowest increase in the percentage of dead eggs (46%), it was higher (p<0.001) compared to the 8% in the control. Our findings indicate that the wild isolate from N. squamipes is susceptible to PZQ.

Effectiveness of synthetic trioxolane OZ78 against Schistosoma japonicum in mice and rabbits

Antischistosomal activities of a synthetic peroxide OZ78 (an ozonide carboxylic acid) against Schistosoma japonicum have been studied in mice and rabbits. Among 132 mice used, 30 of them were infected with 80-100 S. japonicum cercariae for collection of juvenile and adult schistosomes applied in in vitro tests. The remaining 102 mice were infected with 40 schistosome cercariae used for experimental treatment. Other 13 rabbits infected each with 200 schistosome cercariae were treated orally with OZ78 42 days post-infection. Most treated mice and rabbits were sacrificed 4 weeks post-treatment to collect residual schistosomes for evaluation of the drug efficacy. OZ78 and its sodium salt (OZ78-Na salt) 10-60 μg/mL alone exhibited no in vitro effect against day 14, day 21 schistosomula, and day 35 adult schistosomes. But OZ78 and OZ78-Na salt 10 and 20 μg/mL together with hemin 80 μg/mL showed decrease in worm motor activity and severe damage to the worm tegument and intestine, and all worms died within 3 days post-incubation. After infected mice were treated orally with OZ78 at a single dose of 400 mg/kg for 1 day, 34.9% of the worms shifted to the liver. Three and 7 days post-treatment, 100% of the worms were recovered from the liver. Fourteen days post-treatment, 92.3% of the worms still remained in the liver and 7.7% of the worms returned back to the mesenteric veins. Male and female worms shifted to the liver revealed in apparent shrinkage, degeneration of worm body, depigmentation in gut, and disappearance of ova in the uterus of some female worms. Meanwhile, dead worm and dead worm fragments were found in the liver tissues. In mice infected with various stages of schistosomes and treated orally with single OZ78 400 mg/kg, moderate or potential effect of the drug against day 0 (3-h-old worm), day 7, day 14, and day 21 juvenile worms and day 28, day 35 as well as day 42 adult worms were observed, the differences of total or female worm burdens between each treated group and control group were statistically significant (P < 0.01 or P < 0.05). Among the various stages of juveniles, day 7 worms were more susceptible to OZ78 with worm reduction of 83.8%, while the effect of OZ78 against day 28 to day 42 adult worms were similar. Finally, rabbits infected with adult schistosomes and treated with OZ78 at a single dose of 45 mg/kg or a daily dose of 35 mg/kg for three consecutive days resulted in significantly lower total and female worm burdens in comparison with that of control (P < 0.05) with total and female worm reductions of 84.1% and 84.7% as well as 74.3% and 77.4%, respectively. The results demonstrate that OZ78 possesses effect against both juvenile and adult S. japonicum in mouse model, and also shows effect against adult schistosomes in rabbits.

Bioactivity Evaluation of Plant Extracts Used in Indigenous Medicine against the Snail, Biomphalaria glabrata, and the Larvae of Aedes aegypti

This investigation examined the molluscicidal and larvicidal activity of eight plants that are used in the traditional medicine of the Pankararé indigenous people in the Raso da Catarina region, Bahia state, Brazil. The tested plants were chosen based on the results of previous studies. Only those plants that were used either as insect repellents or to treat intestinal parasitic infections were included in the study. Crude extracts (CEs) of these plants were tested for their larvicidal activity (against Aedes aegypti larvae in the fourth instar) and molluscicidal activity (against the snail Biomphalaria glabrata). The plant species Scoparia dulcis and Helicteres velutina exhibited the best larvicidal activities (LC₅₀ 83.426 mg/L and LC₅₀ 138.896 mg/L, resp.), and Poincianella pyramidalis, Chenopodium ambrosoides, and Mimosa tenuiflora presented the best molluscicidal activities (LC₅₀ 0.94 mg/L, LC₅₀ 13.51 mg/L, and LC₅₀ 20.22 mg/L, resp.). As we used crude extracts as the tested materials, further study is warranted to isolate and purify the most active compounds.

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

Praziquantel (PZQ) is now widely used for the treatment of human schistosomiasis. However, in recent years, there has been a growing concern about the resistance of Schistosoma to PZQ. The mechanisms of PZQ action against Schistosoma and resistance of Schistosoma to PZQ are poorly understood. Here, we report differential susceptibilities to PZQ between male and female cercariae in the PZQ-susceptible and PZQ-resistant isolates of Schistosoma mansoni, using tail loss as a measurement of PZQ action. The miracidia were collected by hatching eggs collected from faeces of infected mice. Single-sex cercaria lines were made by infecting a single Biomphalaria glabrata snail with a single miracidium. The sex of each single-sex cercaria line was identified by a direct W1-specific polymerase chain reaction (PCR) technique. Single-sex cercariae of two isolates were exposed to four different concentrations of PZQ, respectively. The tail shedding of cercariae was observed under a dissecting microscope for five time points up to 100 min after adding PZQ. The results showed that male cercariae have higher tail-shedding rates than that of female cercariae when PZQ-susceptible isolates of S. mansoni are exposed to the same concentration of PZQ. But this phenomenon was not observed in the PZQ-resistant isolates. This sexual differential resistance phenomenon of S. mansoni suggests that resistance to PZQ is induced by decreasing the PZQ susceptibility of male worms. The experiment described here may also be useful for developing tests to detect PZQ resistance in the field.

Evaluation of the effect of oxamniquine, praziquantel and a combination of both drugs on the intramolluscan phase of Schistosoma mansoni

The activity of oxamniquine (OXA), praziquantel (PZQ), and a combination of both drugs was evaluated at the intramolluscan phase of Schistosoma mansoni. Biomphalaria glabrata snails infected with S. mansoni were treated with 500 mg/kg OXA, 1000 mg/kg PZQ or with 250 mg/kg OXA and 500 mg/kg PZQ, in association, at the pre-patent and patent phases of infection. The results showed that either treatments with OXA or PZQ, alone, at the pre-patent period, delayed the parasite's development, increasing the pre-patent period by approximately 10 days. At the same pre-patent period, treatment with a combination of OXA/PZQ delayed the parasite's development even more, extending the pre-patent period up to 56 days. At the patent period, treatment with OXA and PZQ, alone, interrupted cercarial shedding. When the snails were treated with 1000 mg/kg PZQ, the cercarial production was re-established 15 days after treatment, but in lower numbers than those obtained before treatment, whereas the snails treated with 500 mg/kg OXA were able to shed cercariae in similar quantities to those observed before treatment. The association 250 mg/kg OXA+500 mg/kg PZQ, at the patent period, not only discontinued cercarial shedding, but also led to the "cure" of the snails, showing a synergistic effect of this combination of drugs. These results suggest that this model will be useful for selection of resistant parasites, as well as for screening new antischistosomal drugs.

Preliminary characterization of an adult worm “vomit” preparation of Schistosoma mansoni and its potential use as antigen for diagnosis

Schistosoma mansoni is a parasitic trematode of the portal-mesenteric veins with a closed-end intestine. Adult worms regurgitate their intestinal content after digestion, together with constituents of the lining gut. Some of these molecules circulate in the blood and are antigenic. We obtain a "vomit" preparation and preliminary evaluate its biochemical composition and antigenic capacity. The "vomit" preparation was obtained after changes in temperature and solutions of incubation of adult worms between 4 and 37 degrees C. Supernatant was assayed for protein, carbohydrate concentration and enzymatic activities associated to the intestine and to the worm tegument. The antigenicity of the product was evaluated using Western blot (WB) analysis against sera of experimentally infected mice, before and after drug cure, sera from people infected with S. mansoni and from individuals infected with other parasitoses. More carbohydrate than protein was detected in the preparations. Cysteine proteinase (CP), N-acetyl-beta-D: -glucosaminidase and alkaline phosphatase activities were detected. The latter enzyme activity is a marker of the tegument, suggesting that in spite of careful conditions used to avoid the presence of tegumental material, manipulation of the worms always resulted in the release of tegumental molecules. Cationic exchange chromatography was useful to separate various components of this "vomit" preparation, particularly enzymes responsible for CP activity. Two highly immunogenic and specific duplets were observed in the WB analysis, 31/32- and 38/40-kDa components, the former probably referring to the intestinal CPs Sm31/Sm32. None of the two duplets disappeared after successful chemotherapy during the time of evaluation in mice or humans.

The efficacy of human schistosomicide treatment may depend on the rate of transmission

The efficacy of different treatment protocols in humans infected with Schistosoma mansoni at sites with different transmission conditions was evaluated by the disappearance of anti-worm intestine IgM antibodies in an indirect fluorescence antibody test (IgM-IFT) and anti-egg antibodies in the circumoval precipitin test (COPT). Patient sera coming from sites of active low transmission (ALT), active high transmission (AHT) and low interrupted transmission (LIT) from Venezuela were studied. Chemotherapy protocols were (1) ALT, 60 mg/kg praziquantel (Pzq60); (2) AHT, one dose of 40 mg/kg Pzq followed by one dose of 20 mg/kg oxamniquine for one group and one dose of 40 mg/kg Pzq alone for the other group; (3) LIT, one dose of 40 mg/kg Pzq repeated every 3 months up to three doses. Cure rates occurred mostly between 3 and 12 months with the exception of Pzq60-ALT where it was evident before 3 months. Higher cure rates were evident in both places of low transmission (ALT and LIT) and the lowest in the AHT regardless of the treatment protocol. Cure was more evident with COPT compared to IgM-IFT. The rate of serological cure appears then to depend on the previous state of transmission. The differential cure rate evaluated by both techniques is probably due to the persistence of antibodies against antigens in different stages of the parasite.

Sexual Biology of Schistosomes

Schistosomes are unusual, together with some of the didymozoidae, in that they are dioecious instead of being hermaphrodite. This gonochorism is accompanied with morphological, ecological, behavioural and molecular differences between the male and the female parasites all through their life cycle. This review is an overview of the sexual biology of schistosomes and aims to provide the most recent information that may help to build future control strategies against these parasites. It proposes a new view of the life cycle of schistosomes, taking into account the sexual status of each developmental stage. It presents the relevant information available on the genetic and phenotypic sexual dimorphisms of these parasites; it proposes a comparison between the host-male parasite and the host-female parasite interactions in both the molluscan intermediate and the mammalian definitive hosts; it exposes the male-female parasite interactions that exist in both the mollusc and the mammalian hosts at the parasite individual and populational levels. This review highlights the domains of research that are still unexplored but that would be of great interest for a better knowledge of the sexual way of life of the parasites which are still responsible for one of the most important human parasitic diseases in the world.

In vitro responses of praziquantel-resistant and -susceptible Schistosoma mansoni to praziquantel

The resistance status of five praziquantel-susceptible and five praziquantel-resistant isolates was confirmed by chemotherapy in CD(1) mice with 3 x 200mg/kg micronised praziquantel. Micronised praziquantel had higher efficacy than two other praziquantel formulations (prepared without milling). The five resistant isolates were less responsive to praziquantel than the five susceptible isolates (59-74% reduction in worm burden in resistant isolates compared with 92-100% in susceptible isolates). Observations were made on the in vitro responses of different stages of 10 isolates to praziquantel. There were different in vitro responses to praziquantel at the egg, miracidial, cercarial and adult stages of Schistosoma mansoni between praziquantel-resistant and praziquantel-susceptible isolates. There were differences in the response of resistant and susceptible isolates following exposure of freshly hatched miracidia to 10(-6)M praziquantel for 1 min and observing the percent change in shape. Using this test it should be possible to determine whether failed therapy in patients infected with S. mansoni is due to the presence of praziquantel-resistant worms. Similarly, by exposing freshly shed cercariae to 4 x 10(-7)M praziquantel and observing the percent of tail shedding over 80 min it should be possible to monitor for the presence of praziquantel-resistant worms in snails collected in the field.

Schistosome resistance to praziquantel: Fact or artifact?

Praziquantel is the current drug of choice for human schistosomiasis. Recent reports from laboratory and field studies concerning reduced praziquantel efficacy against Schistosoma mansoni have generated some controversy. The prevailing question is whether the emergence of strains of schistosome resistant to praziquantel is a fact, or an artifact resulting from erroneous field or laboratory experimentation. In this article, Padraic Fallon, Liang-feng Tao, Magdi Ismail and James Bennett examine the available evidence for schistosome resistance to praziquantel. Contributory factors to the schistosomicidal activity of praziquantel, which may interfere with evaluation of drug efficacy or resistance, are also considered.

Efficacy of treatment of murine Schistosoma mansoni infections with praziquantel and oxamniquine correlates with infection intensity: role of host antibody

The reduction in worm burden obtained by treatment of Schistosoma mansoni with praziquantel and oxamniquine was greater in mice with heavy infections than in relatively lightly infected animals. The reduction in worm burden achieved by each drug correlated with the size of the pre-treatment worm burden (r2 = 0.82 and 0.81 for praziquantel and oxamniquine, respectively). Intensity of infection did not affect the degree of tegumental damage and drug-induced antigen exposure on worms recovered soon after treatment with praziquantel. However, praziquantel-treated worms from mice with heavy infections had significantly more murine antibody attached to the treated-worm surface than worms from praziquantel-treated lightly infected mice. Heavily infected mice had greater levels of circulating anti-worm antibodies than lighter infected mice. The correlation between infection intensity and cure rates achieved by praziquantel and oxamniquine may thus be a reflection of the higher titres of relevant antibody in heavily infected mice mediating death of drug-treated worms.

Evaluation of the activity of Ambrosia maritima L. against Schistosoma mansoni infection in mice

Two groups of mice, showing a patent infection of Schistosoma mansoni, were orally treated with an alcoholic extract of Ambrosia maritima leaves. One group received a single dose, equivalent to 15 g leaves/kg body weight, whereas the other received 5 consecutive doses. The schistosomicidal activity of the plant extract was evaluated 1 week after treatment using 4 parameters: worm load, motility of the worms, oogram and the number of eggs in the liver and intestinal wall. In comparison to the control group no effect at all was observed in the mice who received one single dose of A. maritima. In the group receiving 5 consecutive daily doses, however, the percentage of immature eggs in the intestinal wall had slightly decreased as compared to the controls, but this was compensated by an increase in the number of eggs in the liver. Given the high doses of plant extract used, it is concluded that oral administration of A. maritima has a negligible effect on S. mansoni in mice.

Praziquantel-induced exposure of Schistosoma mansoni alkaline phosphatase: drug-antibody synergy which acts preferentially against female worms

The efficacy of praziquantel-treatment of murine Schistosoma mansoni-infections can be enhanced by concurrent administration of rabbit anti-sera with specificity for parasite antigens. Monospecific rabbit serum raised against S. mansoni worm alkaline phosphatase, that was reactive with the enzyme on the drug-treated female surface, was found to significantly and preferentially increase the mortality of female worms by PZQ. Immunoglobulins purified from the anti-alkaline phosphatase antiserum inhibited 54% of schistosome alkaline phosphatase enzymatic activity on the surface of praziquantel-treated worms. We propose that synergistic antibody-mediated death of drug-damaged worms is a consequence of the inhibition of drug-exposed alkaline phosphatase on the female worm surface by passively transferred antibody.