Tegumental changes in 21-day-old Schistosoma mansoni harboured in mice treated with artemether

Antischistosomal effects of Ficus carica leaves extract and/or PZQ on Schistosoma mansoni infected mice

Currently, praziquantel (PZQ) is the only drug of choice used for treatment of human schistosomes because of its safety and broad-spectrum activity. It is reported that the repeated chemotherapy is complicated by the occurrence of drug resistance to schistosomiasis. So there is an urgent need to develop new drug combinations therapy. The current study aimed to evaluate antischistosomal activity of F. carica leaves extract alone or in combination with PZQ on Schistosoma mansoni infected mice. Mice were experimentally infected with Schistosoma mansoni and orally administrated 6 weeks' post-infection with Fig leaves extract and/or PZQ. Schistosoma mansoni (S. mansoni)-infected mice were separated into four groups: untreated (I), treated with PZQ in dose of 200 mg/kg bw (II), treated with Fig leaves extract dose of 400 mg/kg bw (III). Group IV was treated with dose of Fig leaves extract-PZQ as in groups II and III, respectively. The effect was detected parasitologically using ova count technique and oogram pattern in intestine and liver. The greatest antischistosomal effect was achieved using orally administered Fig leaves extract-PZQ as indicated by total worm burden, tissue egg count and oogram pattern. Fig leaves extract + PZQ induced the therapeutic efficacy over the PZQ dose alone in intestine and liver as shown by a complete absence of immature worms, a very high reduction in the total numbers of tissue egg load (59.81% vs. 61.43% & 67.96% vs. 73.46%), mature eggs (37.86 ± 1.4 vs. 34.14 ± 1.9) and increasing in the total number of dead eggs (62.14 ± 1.4vs.67.29 ± 1.76). The results suggested the curcumin in combination with PZQ as a strong schistosomicidal regimen against S. mansoni. In addition, F. carica leaves extract is a promising for PZQ potentiating its antischistosomal action in animal model infected with S. mansoni. Therefore, the present work conclude that combined treatment has a synergetic effect and could be more promising in the management of schistosomiasis.

Drug Discovery and Target Identification against Schistosomiasis: a Reality Check on Progress and Future Prospects

Schistosomiasis ranks among the most important infectious diseases, with over 200 million people currently being infected and > 280,000 deaths reported annually. Chemotherapeutic treatment has relied on one drug, praziquantel, for four decades, while other drugs, such as oxamniquine and metrifonate, are no longer preferred for clinical use due to their narrow spectrum of activity - these are only active against S. mansoni and S. haematobium, respectively. Despite being cheap, safe, and effective against all schistosome species, praziquantel is ineffective against immature worms, which may lead to reinfections and treatment failure in endemic areas; a situation that necessitates repeated administration besides other limitations. Therefore, novel drugs are urgently needed to overcome this situation. In this paper, an up to date review of drug targets identified and validated against schistosomiasis while also encompassing promising clinical and preclinical candidate drugs is presented. While there are considerable efforts aimed at identifying and validating drug targets, the pipeline for new antischistosomals is dry. Moreover, the majority of compounds evaluated preclinically are not really advanced because most of them were evaluated in very small preclinical species such as mice alone. Overall, it appears that although a lot of research is going on at discovery phases, unfortunately, it does not translate to advanced preclinical and clinical evaluation.

Licochalcone A-loaded solid lipid nanoparticles improve antischistosomal activity in vitro and in vivo

Aim: To isolate licochalcone A (LicoA) from licorice, prepare LicoA-loaded solid lipid nanoparticles (L-SLNs) and evaluate the L-SLNs in vitro and in vivo against Schistosoma mansoni. Materials & methods: LicoA was obtained by chromatographic fractionation and encapsulated in SLNs by a modified high shear homogenization method. Results: L-SLNs showed high encapsulation efficiency, with satisfactory particle size, polydispersity index and Zeta potential. Transmission electron microscopy revealed that L-SLNs were rounded and homogenously distributed. Toxicity studies revealed that SLNs decreased the hemolytic and cytotoxic properties of LicoA. Treatment with L-SLNs showed in vivo efficacy against S. mansoni. Conclusion: L-SLNs are efficient in reducing worm burden and SLNs may be a promising delivery system for LicoA to treat S. mansoni infections.

Ginger (Zingiber Officinale)-derived nanoparticles in Schistosoma mansoni infected mice: Hepatoprotective and enhancer of etiological treatment

BACKGROUND

Nanotechnology has been manufactured from medicinal plants to develop safe, and effective antischistosmal alternatives to replace today's therapies. The aim of the study is to evaluate the prophylactic effect of ginger-derived nanoparticles (GNPs), and the therapeutic effect of ginger aqueous extract, and GNPs on Schistosoma mansoni (S. mansoni) infected mice compared to praziquantel (PZQ), and mefloquine (MFQ).

METHODOLOGY/PRINCIPAL FINDINGS

Eighty four mice, divided into nine different groups, were sacrificed at 6th, 8th, and 10th week post-infection (PI), with assessment of parasitological, histopathological, and oxidative stress parameters, and scanning the worms by electron microscope. As a prophylactic drug, GNPs showed slight reduction in worm burden, egg density, and granuloma size and number. As a therapeutic drug, GNPs significantly reduced worm burden (59.9%), tissue egg load (64.9%), granuloma size, and number at 10th week PI, and altered adult worm tegumental architecture, added to antioxidant effect. Interestingly, combination of GNPs with PZQ or MFQ gave almost similar or sometimes better curative effects as obtained with each drug separately. The highest therapeutic effect was obtained when ½ dose GNPs combined with ½ dose MFQ which achieved 100% reduction in both the total worm burden, and ova tissue density as early as the 6th week PI, with absence of detected eggs or tissue granuloma, and preservation of liver architecture.

CONCLUSIONS/SIGNIFICANCE

GNPs have a schistosomicidal, antioxidant, and hepatoprotective role. GNPs have a strong synergistic effect when combined with etiological treatments (PZQ or MFQ), and significantly reduced therapeutic doses by 50%, which may mitigate side effects and resistance to etiological drugs, a hypothesis requiring further research. We recommend extending this study to humans.

Antischistosomal properties of aurone derivatives against juvenile and adult worms of Schistosoma mansoni

Schistosomiasis is a neglected disease caused by helminth flatworms of the genus Schistosoma, affecting over 240 million people in more than 70 countries. The treatment relies on a single drug, praziquantel, making urgent the discovery of new compounds. Aurones are a natural type of flavonoids that display interesting pharmacological activities, particularly as chemotherapeutic agents against parasites. In pursuit of treatment alternatives, the present work conducted an in vitro and in vivo antischistosomal investigation with aurone derivatives against Schistosoma mansoni. After preparation of aurone derivatives and their in vitro evaluation on adult schistosomes, the three most active aurones were evaluated in cytotoxicity and haemolytic assays, as well as in confocal laser-scanning microscope studies, showing tegumental damage in parasites in a concentration-dependent manner with no haemolytic or cytotoxic potential toward mammalian cells. In a mouse model of schistosomiasis, at a single oral dose of 400 mg/kg, the selected aurones showed worm burden reductions of 35% to 65.0% and egg reductions of 25% to 70.0%. The most active thiophenyl aurone derivative 18, unlike PZQ, had efficacy in mice harboring juvenile S. mansoni, also showing significant inhibition of oviposition by parasites, giving support for the antiparasitic potential of aurones as lead compounds for novel antischistosomal drugs.

Assessment of the In Vitro Antischistosomal Activities of the Extracts and Compounds from Solidago Microglossa DC (Asteraceae) and Aristolochia Cymbifera Mart. & Zucc. (Aristolochiaceae)

Schistosomiasis, caused by helminth flatworms of the genus Schistosoma, is a neglected tropical disease that afflicts over 230 million people worldwide. Currently, treatment is achieved with only one drug, praziquantel (PZQ). In this regard, the roots of Solidago microglossa (Asteraceae) and Aristolochia cymbifera (Aristolochiaceae) are popularly used as anthelmintic. Despite their medicinal use against helminthiasis, such as schistosomiasis, A. cymbifera, and S. microglossa have not been evaluated against S. mansoni. Then, in this work, the in vitro antischistosomal activity of the crude extracts of A. cymbifera (Ac) and S. microglossa (Sm) and their isolated compounds were investigated against S. mansoni adult worms. Sm (200 μg/mL) and Ac (100–200 μg/mL) were lethal to all male and female worms at the 24 h incubation. In addition, Sm (10–50 μg/mL) and Ac (10 μg/mL) caused significant reduction in the parasite's movements, showing no significant cytotoxicity to Vero cells at the same range of schistosomicidal concentrations. Confocal laser scanning microscopy revealed that Sm and Ac caused tegumental damages and reduced the numbers of tubercles of male schistosomes. Chromatographic fractionation of Sm leads to isolation of bauerenol, α-amirin, and spinasterol, while populifolic acid, cubebin, 2-oxopopulifolic acid methyl ester, and 2-oxopopulifolic acid were isolated from Ac. At concentrations of 25–100 μM, bauerenol, α-amirin, spinasterol, populifolic acid, and cubebin showed significant impact on motor activity of S. mansoni. 2-oxopopulifolic acid methyl ester and 2-oxopopulifolic acid caused 100% mortality and decreased the motor activity of adult schistosomes at 100 μM. This study has reported, for the first time, the in vitro antischistosomal effects of S. microglossa and A. cymbifera extracts, also showing promising compounds against adult schistosomes.

Single oral fixed-dose praziquantel-miltefosine nanocombination for effective control of experimental schistosomiasis mansoni

Background

The control of schistosomiasis has been centered to date on a single drug, praziquantel, with shortcomings including treatment failure, reinfection, and emergence of drug resistance. Drug repurposing, combination therapy or nanotechnology were explored to improve antischistosomal treatment. The aim of the present study was to utilize a novel combination of the three strategies to improve the therapeutic profile of praziquantel. This was based on a fixed-dose nanocombination of praziquantel and miltefosine, an antischistosomal repurposing candidate, co-loaded at reduced doses into lipid nanocapsules, for single dose oral therapy.

Methods

Two nanocombinations were prepared to provide 250 mg praziquantel-20 mg miltefosine/kg (higher fixed-dose) or 125 mg praziquantel-10 mg miltefosine/kg (lower fixed-dose), respectively. Their antischistosomal efficacy in comparison with a non-treated control and their praziquantel or miltefosine singly loaded counterparts was assessed in murine schistosomiasis mansoni. A single oral dose of either formulation was administered on the initial day of infection, and on days 21 and 42 post-infection. Scanning electron microscopic, parasitological, and histopathological studies were used for assessment. Preclinical data were subjected to analysis of variance and Tukeyʼs post-hoc test for pairwise comparisons.

Results

Lipid nanocapsules (~ 58 nm) showed high entrapment efficiency of both drugs (> 97%). Compared to singly loaded praziquantel-lipid nanocapsules, the higher nanocombination dose showed a significant increase in antischistosomal efficacy in terms of statistically significant decrease in mean worm burden, particularly against invasive and juvenile worms, and amelioration of hepatic granulomas (P ≤ 0.05). In addition, scanning electron microscopy examination showed extensive dorsal tegumental damage with noticeable deposition of nanostructures.

Conclusions

The therapeutic profile of praziquantel could be improved by a novel multiple approach integrating drug repurposing, combination therapy and nanotechnology. Multistage activity and amelioration of liver pathology could be achieved by a new praziquantel-miltefosine fixed-dose nanocombination providing 250 mg praziquantel-20 mg miltefosine/kg. To the best of our knowledge, this is the first report of a fixed-dose nano-based combinatorial therapy for schistosomiasis mansoni. Further studies are needed to document the nanocombination safety and explore its prophylactic activity and potential to hinder the onset of resistance to the drug components.

Myricetin Possesses Anthelmintic Activity and Attenuates Hepatic Fibrosis via Modulating TGFβ1 and Akt Signaling and Shifting Th1/Th2 Balance in Schistosoma japonicum-Infected Mice

Schistosomiasis is a zoonotic and debilitating parasitic disease caused by Schistosoma japonicum. Praziquantel remains the choice for treating schistosomiasis, but its efficacy could be hampered by emergence of resistance. In this study, using large-scale drug screening, we selected out myricetin, a natural flavonol compound, having a good anti-schistosome effect. We found that myricetin exhibited dose and time-dependent insecticidal effect on S. japonicum in vitro, with an LC₅₀ of 600 μM for 24 h, and inhibited female spawning. The drug mainly destroyed the body structure of the worms and induced apoptosis of the worm cells, which in turn led to death. In addition, oral administration of myricetin in mice infected with S. japonicum showed a deworming effect in vivo, as evidenced by a significant reduction in the liver egg load. H&E staining, quantitative RT-PCR, and Western blotting assays showed that myricetin significantly alleviated liver fibrosis in mice infected with S. japonicum. Myricetin also effectively inhibited the expression of TGFβ1, Smad2, phospho-Smad2, Smad3, phospho-Smad3, ERK, phospho-ERK, Akt, and phospho-Akt in the liver of infected mice, suggesting that myricetin attenuated liver fibrosis in mice via modulating TGFβ1 and Akt signaling. Flow cytometric analysis of Th subtypes (Th1/Th2/Th17/Treg) in the mouse spleen further revealed that myricetin significantly increased the percentage Th1 cells in infected mice and reduced the proportion of Th2 cells and Th17 cells. Immunology multiplex assay further showed that myricetin attenuated S. japonicum-induced rise in the plasma levels of IL-4, IL-5, IL-10, IL-13, and IL-17A in infected mice while increasing the plasma contents of IFN-γ, IL-12, and IL-7. In conclusion, our study provides the first direct evidence that myricin possesses potent anti-schistosome activities in vitro and in vivo, and offers new insights into the mechanisms of action by myricetin. The present findings suggest that myricetin could be further explored as a therapeutic agent for S. japonicum.

Assessment of the potential therapeutic effects of omeprazole in Schistosoma mansoni infected mice

Schistosomiasis is a neglected chronic parasitic disease with a significant lasting morbidity. Currently, praziquantel (PZQ) is the most efficient drug for schistosomiasis worldwide. However, the possibility of the occurrence of resistance to PZQ is increasing. Therefore, there is a vital need to find new antischistosomal drugs or to increase the efficacy of the existing ones. Omeprazole is a proton pump inhibitor which is reported to have antiparasitic properties. Thus, the aim of this study was to assess the potential therapeutic effects of omeprazole in experimental Schistosoma mansoni infection either alone or in combination with PZQ. For this aim, 80 laboratory bred mice were divided into 3 groups; uninfected control, infected untreated control, and infected and treated at tenth week P.I. The last group was divided into three subgroups that received either PZQ alone, omeprazole alone, or both drugs. The effectiveness of treatment was assessed by adult worm counts, liver egg count, scanning electron microscopy of adult worms, histopathological, and immunohistochemical (GFAP) examination. There was significant reduction of adult worm counts, liver egg counts, size, diameter of hepatic granulomas, hepatic fibrosis, and GFAP expression in the group that received combined treatment as compared to PZQ group. Moreover, the tegumental changes were more evident in the group that received combined treatment. In conclusion, the administration of omeprazole with PZQ improved the efficacy of PZQ in the treatment of Schistosomiasis mansoni.

Immunization with adult Schistosoma mansoni tegument, treated with sub-curative praziquantel, partially protects mice against the infection

The tegument of schistosomes is a source of many potential anti-Schistosoma vaccine molecules. This work aimed to assess the protective effects of the adult Schistosoma mansoni tegument treated (TT) with sub-curative praziquantel (PZQ), whether in vivo (in vivo TT) or in vitro (in vitro TT), in murine schistosomiasis. In vitro TT and in vivo TT showed great similarity, and they differed from untreated tegument antigen (Teg) in terms of quantity and quality of protein bands on SDS-PAGE. Two immunization trials were performed, each with 50 mice, divided randomly into five groups of 10 mice each: (1) uninfected control mice (UC), (2) infected mice given phosphate buffer saline + adjuvant (PBS + adjuvant), (3) infected, Teg vaccinated, (4) infected, in vivo TT vaccinated, and (5) infected, in vitro TT vaccinated. All the immunizations with antigens induced mixed Th1/Th2 immune responses, as indicated by significantly high (P < 0.001) specific IgG2a and IgG1 levels, with Th1 predominating, as shown by a diminished IgG1/IgG2a ratio, as well as a high serum concentration of IFN-γ, an absence of IL-4 and increased IL-10. In vitro TT gave the most pronounced response. With respect to reduction of total worm burden, relative to PBS + adjuvant mice, in vitro TT achieved the highest significant (P < 0.001) results, followed by in vivo TT and Teg (51.8-57.04%, 44.6-50.2% and 35.2-39.3%, respectively). In scanning electron microscopy studies, all the tested antigens caused tegumental changes in adult worms, with the worst occurring with in vitro TT, such as retracted ventral sucker, an effect on the gynaecophoric canal, and changes to tubercles. In conclusion, in vitro TT, which is cheap to prepare, could be a potential vaccine against S. mansoni.

In vitro and in vivo evaluation of six artemisinin derivatives against Schistosoma mansoni

Schistosomiasis is a tropical neglected disease whose socioeconomic impact is surpassed only by malaria. Until recently, praziquantel (PZQ) has been the only available drug, raising concerns that tolerant/resistant strains may appear. Since the discovery of the schistosomicidal potential of artemisinin (ART), new derivatives have been produced and evaluated. In this work, we evaluated the activity of ART derivatives against Schistosoma mansoni, both in vitro and in vivo. In the in vitro assay, worm survival, oviposition, and morphological alterations were evaluated. Further analysis of morphological alterations and membrane integrity was conducted using scanning electron microscopy and a cell-permeable, benzimidazole dye (Hoescht 33258) that binds to the minor groove of double stranded DNA. For the in vivo assay, artesunic acid (AcART) and dihydroartemisinin acetate (AcDQHS) were selected, since they showed the best in vitro results. Infected mice treated 21, 45, or 60 days post-infection (dpi), with a concentration of 100 mg/kg of either AcART or AcDQHS, showed a significant worm reduction (particularly in females), fewer eggs eliminated in feces, and a decrease of immature eggs in the intestinal tissues. Our results indicate that AcART and AcDQHS have some schistosomicidal activity against juvenile and adult stages of S. mansoni.

Artemether and Praziquantel: Origin, Mode of Action, Impact, and Suggested Application for Effective Control of Human Schistosomiasis

The stumbling block for the continued, single-drug use of praziquantel (PZQ) against schistosomiasis is less justified by the risk of drug resistance than by the fact that this drug is inactive against juvenile parasites, which will mature and start egg production after chemotherapy. Artemisinin derivatives, currently used against malaria in the form of artemisinin-based combination therapy (ACT), provide an opportunity as these drugs are not only active against malaria plasmodia, but surprisingly also against juvenile schistosomes. An artemisinin/PZQ combination would be complementary, and potentially additive, as it would kill two schistosome life cycle stages and thus confer a transmission-blocking modality to current chemotherapy. We focus here on single versus combined regimens in endemic settings. Although the risk of artemisinin resistance, already emerging with respect to malaria therapy in Southeast Asia, prevents use in countries where ACT is needed for malaria care, an artemisinin-enforced praziquantel treatment (APT) should be acceptable in regions of North Africa (including Egypt), the Middle East, China, and Brazil that are not endemic for malaria. Thanks to recent progress with respect to high-resolution diagnostics, based on circulating schistosome antigens in humans and molecular approaches for snail surveys, it should be possible to keep areas scheduled for schistosomiasis elimination under surveillance, bringing rapid response to bear on problems arising. The next steps would be to investigate where and for how long APT should be applied to make a lasting impact. A large-scale field trial in an area with modest transmission should tell how apt this approach is.

Praziquantel-lipid nanocapsules: an oral nanotherapeutic with potential Schistosoma mansoni tegumental targeting

Purpose

Lipid nanocapsules (LNCs) have shown potential to increase the bioavailability and efficacy of orally administered drugs. However, their intestinal translocation to distal target sites and their implication in pharmacokinetic (PK)–pharmacodynamic (PD) relationships are yet to be elucidated. In this study, the effect of LNCs on the PD activity and pharmacokinetics of praziquantel (PZQ), the mainstay of schistosomiasis chemotherapy, was investigated.

Materials and methods

The composition of LNCs was modified to increase PZQ payload and to enhance membrane permeability. PZQ–LNCs were characterized in vitro for colloidal properties, entrapment efficiency (EE%), and drug release. PD activity of the test formulations was assessed in Schistosoma mansoni-infected mice 7 days post-oral administration of a single 250 mg/kg oral dose. Pharmacokinetics of the test formulations and their stability in simulated gastrointestinal (GI) fluids were investigated to substantiate in vivo data.

Results

PZQ–LNCs exhibited good pharmaceutical attributes in terms of size (46–62 nm), polydispersity index (0.01–0.08), EE% (>95%), and sustained release profiles. Results indicated significant efficacy enhancement by reduction in worm burden, amelioration of liver pathology, and extensive damage to the fluke suckers and tegument. This was partly explained by PK data determined in rats. In addition, oral targeting of the worms was supported by the stability of PZQ–LNCs in simulated GI fluids and scanning electron microscopy (SEM) visualization of nanostructures on the tegument of worms recovered from mesenteric/hepatic veins. Cytotoxicity data indicated tolerability of PZQ–LNCs.

Conclusion

Data obtained provide evidence for the ability of oral LNCs to target distal post-absorption sites, leading to enhanced drug efficacy. From a practical standpoint, PZQ–LNCs could be suggested as a potential tolerable single lower dose oral nanomedicine for more effective PZQ mass chemotherapy.

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.

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.

Dose-response relationship in Schistosoma mansoni juvenile and adult stages following limonin treatment in experimentally infected mice

Preventive chemotherapy with praziquantel is the mainstay of schistosomiasis control. However, drug resistance is an imminent threat, particularly with large-scale administration of praziquantel, in addition to much less efficacy against young schistosomes. Several biological activities of limonin have been explored such as insecticidal, insect antifeedant, and growth-regulating activity on insects as well as antimalarial, antiviral, anticancer, cholesterol-lowering, and antioxidant activities. This study investigates limonin as an alternative antischistosomal compound using two novel, single, oral dose regimens. In the current work, the therapeutic efficacy of different limonin dosing protocols was evaluated in experimentally infected mice harboring Schistosoma mansoni (Egyptian strain) juvenile or adult stages. Oral administration of limonin in a single dose of 50 or 100 mg/kg on day 21 post-infection (p.i.) resulted in a significant worm burden reduction of 70.0 and 83.33 %, respectively. The same dose given on day 56 p.i. reduced total worm burdens by 41.09 and 60.27 %, respectively. In addition, significant reductions of 34.90 and 47.16 % in the hepatic and 46.67 and 56.1 % in the intestinal tissue egg loads, respectively, associated with significant alterations in the oogram pattern with elevated dead egg levels. Limonin produced ameliorations of hepatic pathology with reduction in dimensions and number of granulomas. Limonin also produced a variety of tegumental alterations in treated worms including tubercular disruption, edema, blebbing, and ulcerations. Results obtained by this work elucidated promising limonin bioactivity against S. mansoni juvenile and adult stages and provided a basis for subsequent experimental and clinical trials.

Antiparasitic peptides

: The most important parasitic diseases, malaria, leishmaniasis, trypanosomiasis, and schistosomiasis, are a great burden to mankind, threatening the life of millions of people worldwide and mostly affecting the poorest. Because drug resistance is increasing and vaccines are rarely available, novel chemotherapeutic compounds are necessary in order to treat these devastating diseases. Insects serve as vectors of many human parasitic diseases and have been shown to express a huge variety of antimicrobial peptides (AMPs). Therefore, research activity on insect-derived AMPs has been increasing in the last 40 years. This chapter summarizes the current state of research on the possible role of AMPs as potential chemotherapeutic compounds against human parasitic diseases. As a representative antimicrobial peptide with antiparasitic activity, the structure of insect defensin A is shown [PDB accession code: 1ICA]. The molecule is surrounded by schematic representations of the human pathogenic parasites Plasmodium, Leishmania and Trypanosoma.

Protective capacity of cercarial transformation fluid alone or in combination with crude cercarial antigen against challenge infections of Schistosoma mansoni in mice

Schistosomiasis is the second major parasitic disease in the world after malaria. It affects 201.5 million cases in Africa alone. The aim of this research was to explore alternative vaccination strategies against experimental schistosomiasis mansoni. We assessed the effect of cercarial transformation fluid (CTF) singly and in combination with crude cercarial antigen (CCA) using alum as an adjuvant. The combined antigens gave the best results, as evidenced by a significant reduction in the worm load (62.07%), tissue egg count (78.16%, 86.46%) in liver and intestine respectively, and hepatic granuloma size (29.96%). Scanning electron microscopy revealed changes in the tegument, in the form of roughness and appearance of vesicles and furrows between the tegumental tubercles. Also, resorption of the ventral sucker and dimples replacing its spines were observed. The female tegument was irregular and its posterior end showed loss of spines and sensory bulbs. Moreover, there was a significant decrease in liver enzymes (alanine transaminase (ALT) and aspartate transaminase (AST)) compared to infected control mice. A significant elevation in CD4+T-lymphocytes, denoting amelioration of the immune status, in mice that received combined antigens was also observed. It can be concluded that combined antigens demonstrate potential as a vaccine against Schistosoma mansoni.

In vitro and in vivo anti-schistosomal activity of the alkylphospholipid analog edelfosine

Background

Schistosomiasis is a parasitic disease caused by trematodes of the genus Schistosoma. Five species of Schistosoma are known to infect humans, out of which S. haematobium is the most prevalent, causing the chronic parasitic disease schistosomiasis that still represents a major problem of public health in many regions of the world and especially in tropical areas, leading to serious manifestations and mortality in developing countries. Since the 1970s, praziquantel (PZQ) is the drug of choice for the treatment of schistosomiasis, but concerns about relying on a single drug to treat millions of people, and the potential appearance of drug resistance, make identification of alternative schistosomiasis chemotherapies a high priority. Alkylphospholipid analogs (APLs), together with their prototypic molecule edelfosine (EDLF), are a family of synthetic antineoplastic compounds that show additional pharmacological actions, including antiparasitic activities against several protozoan parasites.

Methodology/Principal Findings

We found APLs ranked edelfosine> perifosine> erucylphosphocholine> miltefosine for their in vitro schistosomicidal activity against adult S. mansoni worms. Edelfosine accumulated mainly in the worm tegument, and led to tegumental alterations, membrane permeabilization, motility impairment, blockade of male-female pairing as well as induction of apoptosis-like processes in cells in the close vicinity to the tegument. Edelfosine oral treatment also showed in vivo schistosomicidal activity and decreased significantly the egg burden in the liver, a key event in schistosomiasis.

Conclusions/Significance

Our data show that edelfosine is the most potent APL in killing S. mansoni adult worms in vitro. Edelfosine schistosomicidal activity seems to depend on its action on the tegumental structure, leading to tegumental damage, membrane permeabilization and apoptosis-like cell death. Oral administration of edelfosine diminished worm and egg burdens in S. mansoni-infected CD1 mice. Here we report that edelfosine showed promising antischistosomal properties in vitro and in vivo.

Present-day anthelmintics and perspectives on future new targets

In absence of vaccines for the majority of helminths, chemotherapy is still the mainstay for controlling human helminthiases. However, a limited number of drugs are available in the market to combat parasitic helminths in human. Besides, the development and spread of drug resistance have declined the use of most currently available anthelmintics. Clearly, availability of new anthelmintic agents will be essential in the next few years. More research into the mechanisms of drug actions and their targets are eminent for the discovery and development of novel anthelmintic agents. Recent drug discovery techniques mostly rely on mechanism-based screening of compounds on heterologously expressed targets in bacterial, mammalian or yeast cells. Although this is usually a successful approach, it is money- and time-consuming; meanwhile, pharmaceutical companies prefer the tested target that is chosen based on basic research. The nervous system is the site of action of several chemotherapeutics including pesticides and antinematode drugs; accordingly, the nervous system continues to be a promising target. Recent advances in exploring helminths' nervous system, neurotransmitters and receptors have paved the way for the development of potential agents targeting the nervous system and its components.

Antischistosomal effect of holothurin extracted from some Egyptian sea cucumbers

CONTEXT

Holothuria polii (H. polii) Linnaeus (Holothuriidae), Actinopyga mauritiana (A. mauritiana) Quoy & Gaimard (Holothuriidae) and Bohadschia vitiensis (B. vitiensis) Semper (Holothuriidae) are sea cucumbers inhabiting the coasts of Egypt. Their tegument and the cuvierian gland contained a substance called holothurin that was used in traditional medicine. These three species are abundant in the Egyptian coast, however there are no reports about their efficacy as antiparasitic agent.

OBJECTIVE

The antischistosomal effect of the holothurin extracted from the three species of sea cucumber is investigated.

MATERIALS AND METHODS

The ethanol extract was made from the tegument of both H. polii and A. mauritiana while it was made from the cuvierian gland of B. vitiensis. The body wall (or cuvierian gland) of the sea cucumber was blended with 95% ethanol in a volume = 4 × tissue weight. Extraction was done at room temperature for one day then filtered. The ethanol was removed by evaporation using Rotavapour (BÜCHI 461 water bath REIII) at 40°C. Later the aqueous residue was placed in a vacuum oven at 20°C for about 48 h to remove water. The resulting dried mass was then stored at -4°C until use. The percentage yield and the LD₅₀ were calculated for each extract. Each extract was administered orally to Shistosoma mansoni infected mice in acute and chronic phases of infection. The dose of one-tenth of LD₅₀ of each extract was administrated to mice (5.4, 62.2, and 10 mg/kg body weight/mouse for H. polii extract (HPE), A. mauritiana extract (AME), and cuvierian gland of B. vitiensis, respectively) for 24 h. The effects of each extract on the worm burden and total egg count was studied. The effects of each extract on the worm tegument using scanning electron microscope (SEM) were investigated in vivo and in vitro.

RESULTS

The percentage yield of cuvierian gland extract (CGE) was higher (70%) than the tegument AME (33.4%) and HPE (9.3%). The 24 h LD₅₀ of investigated sea cucumber ethanol extracts were 54.46, 627, and 100 mg/kg body weight/mouse for HPE, AME, and CGE. Oral administration of HPE caused decrease in male and female worm burden of 30-day infected mice to reach 60 and 90%, respectively. HPE decreased the egg count significantly in those mice with 30-day (1.75 egg counts/g tissue, p < 0.05) and 45-day (3.25 egg counts/g tissue, p < 0.05) infections. SEM studies of recovered worms from treated mice with all extracts showed different tegumental changes like formation of blebs, wrinkling, formation of numerous pores, and rupturing of some tubercles. These effects were more pronounced in those worms treated in vitro represented by severe shrinkage of the tegument, deformation of spines, rupturing, and collapsing of tubercles.

DISCUSSION AND CONCLUSION

Results support the hypothesis that holothurin is a promising antischistosomal agent.

Structural changes of Schistosoma mansoni adult worms recovered from C57BL/6 mice treated with radiation-attenuated vaccine and/or praziquantel against infection

Although the current treatment of schistosomiasis relies largely on praziquantel (PZQ), it has not significantly reduced the overall number of disease cases, perhaps due to inevitable resistance to PZQ. Previous studies showed that radiation-attenuated vaccine gives protection levels for Schistosoma mansoni in host various species. In the present study, we evaluated the effect of various vaccination strategies in C57BL/6 mice, including single or multiple vaccination strategy, subcurative dose (20 mg/kg) of PZQ, and a combination of single vaccination with subcurative dose of PZQ. Groups of five mice were sacrificed postinfection in 42 days and schistosomes were collected by perfusion and examined by scanning electron microscopy. Treatment either with subcurative dose of PZQ or with a single vaccination of attenuated cercariae (500 per mouse), caused significant reduction in total worm burden, hepatic and intestinal ova counts 43.03%, 73.2%, 59.5% and 37.97%, 52.02%, 26.3%, respectively. Furthermore, tegumental changes were observed, including severe swelling, fusion of tegumental folds, vesicle formation, and loss or shortening of the spines on the tubercles. However, multiple vaccination strategy resulted in much higher reduction in total worm burden, hepatic and intestinal ova count. However, multiple vaccination strategy resulted in high reduction of worm burden, hepatic and intestinal ova counts 72.5%, 90.7%, 65.79%, respectively, and further causing swollen, disruption of tubercles teguments and erosion, extensive peeling, fusion of tegumental folds. Our findings suggest that multiple vaccination strategy is the most effective strategy to clear schistosomal infection, indicating its potential in guiding the design of appropriate therapeutic strategy against schistosomes.

Antischistosomal activity of ginger (Zingiber officinale) against Schistosoma mansoni harbored in C57 mice

The repeated chemotherapy of schistosomiasis has resulted in the emergence of drug-resistant schistosome strains. The development of such resistance has drawn the attention of many authors to alternative drugs. Many medicinal plants were studied to investigate their antischistosomal potency. The present work aimed to evaluate antischistosomal activity of crude aqueous extract of ginger against Schistosoma mansoni. Sixteen mice of C57 strain were exposed to 100 ± 10 cercariae per mouse by the tail immersion method; the mice were divided into two groups: untreated group and ginger-treated one. All mice were sacrificed at the end of 10th week post-infection. Worm recovery and egg counting in the hepatic tissues and faeces were determined. Surface topography of the recovered worms was studied by scanning electron microscopy. Histopathological examination of liver and intestine was done using routine histological procedures. The worm burden and the egg density in liver and faeces of mice treated with ginger were fewer than in non-treated ones. Scanning electron microscopical examination revealed that male worms recovered from mice treated with ginger lost their normal surface architecture, since its surface showed partial loss of tubercles' spines, extensive erosion in inter-tubercle tegumental regions and numerous small blebs around tubercles. Histopathological data indicated a reduction in the number and size of granulomatous inflammatory infiltrations in the liver and intestine of treated mice compared to non-treated mice. The results of the present work suggested that ginger has antischistosomal activities and provided a basis for subsequent experimental and clinical trials.

Schistosoma mansoni: In vitro schistosomicidal activity of piplartine

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

Further assessment of Mirazid as antischistosomal drug in experimental schistosomiasis hematobium

Conflicting reports are found in the literature about the efficacy of Mirazid (MZ), which is a special formulation of myrrh obtained from the stem of Commiphora molmol (Nees), Engl. tree (Burseraceae), as an antischistosomal drug. This initiated the present study to further assess this drug in experimental schistosomiasis hematobium. The drug was administered orally to hamsters infected with Schistosoma hematobium ( Bilharz, 1852 ) using 500 mg/kg body weight for six successive days on an empty stomach. The drug effect was examined after three periods: 4, 8 and 12 weeks post-treatment. Emphasis was given to certain parameters such as change in worm load, number of ova/mg tissue, oogram pattern and number of ova/g stool, and tegumental changes in the worms by electron microscopy after prolonged observation periods. The results showed very slight 3.4% worm reduction by MZ after the longest evaluation period (12 weeks), versus very high reduction (100%) by the reference drug praziquantel (PZQ). In comparison with the untreated control no change was found in the number of ova/mg tissue in MZ-treated hamsters regardless of the date of observation (4-12 weeks), versus significantly high reduction (99.6%) observed in the case of PZQ treatment. However, a significant decrease (22%) in the ratio of immature and increase in dead ova in tissues of MZ-treated hamsters was obvious at 12 weeks post treatment. In MZ-treated animals, a slight reduction (18.3%) in the number of stool eggs versus absence of eggs in PZQ-treated animals 12 weeks after treatment. Scanning electron microscopic examination of S. hematobium worms revealed intact tubercles, spines and sensory bulbs and no effect of the ventral side after MZ treatment. Meanwhile, PZQ treatment revealed extensive disruption of the tegument worm. Therefore, this experimental study gives extra support to previously reported negative evaluation about the effectiveness of this drug in the treatment of schistosomiasis against many other published positive results. This controversy about the efficacy of MZ may be attributed to inconsistency of its material which is obtained from natural origin.

Morphological effects and tegumental alterations induced by mefloquine on schistosomula and adult flukes of Schistosoma mansoni

There is a pressing need to develop novel anti-schistosomal drugs, as current treatment relies largely on praziquantel (PZQ). To further strengthen current evidence of the anti-schistosomal properties of mefloquine (MQ), we studied the temporal effect of this compound in vitro and in vivo, and examined alterations on the tegumental surface of schistosomula and adults of S. mansoni by means of scanning electron microscopy (SEM). Schistosomula and adults were each incubated in vitro using MQ over a wide concentration range (1-100 microg/ml). In addition, mice infected with adult S. mansoni were treated with a single oral dose of 400 mg/kg MQ, and worms were recovered 24, 48, 72, 96 and 120 h following treatment. MQ showed a rapid onset of action on schistosomula in vitro; 100 and 75 microg/ml of MQ killed schistosomula immediately; the minimal lethal and effective concentrations of MQ on schistosomula after 1 h were 25 and 5 microg/ml, respectively. Adult worms incubated with 100 and 10 microg/ml of MQ were dead after 1 h and 24 h of incubation, respectively. A hepatic shift of adult schistosomes was observed in mice already 24 h after treatment, and 120 h following treatment >98% of all worms had translocated to the liver. SEM observations revealed extensive tegumental destruction, including blebbing, shrinking and sloughing, particularly following in vitro incubation and on the tegument of female worms.

Current chemotherapy arsenal for schistosomiasis mansoni: alternatives and challenges

Schistosomiasis still represents a major health problem in many tropical and subtropical countries despite continuing control efforts. Due to the unavailability of a vaccine that is practically applicable to humans, the use of chemotherapy is the mainstay of schistosomiasis-associated morbidity control. This paper attempts to review the antischistosomal drugs currently used in the treatment of intestinal schistosomiasis caused by Schistosoma mansoni. Their antischistosomal properties, advantages, and disadvantages as well as issues regarding the evidence for drug resistance and combination studies are reviewed in a simple manner. The recent trends towards the identification of specific chemotherapeutic targets for the treatment of schistosomes are also discussed briefly.

Schistosoma mekongi: the in vitro effect of praziquantel and artesunate on the adult fluke

The efficacy and tolerance of 80 microg/ml praziquantel (PZQ) and 40 microg/ml artesunate (ATS) against adult stage Schistosoma mekongi in vitro were investigated after 3, 6, 12, and 24h incubation by monitoring worm motility and compared tegumental changes using scanning electron microscopy (SEM). Thirty mice were infected with S. mekongi cercaria for 49 days. Adult worms were collected by perfusion method and prepared for in vitro study. Contraction and decreased motor activity were observed after as little as 3h incubation with PZQ and ATS. Some of the worms were immobile 12h after exposure, and died within 24h. The tegument of S. mekongi showed severe swelling, vacuolization and disruption, fusion of the tegumental ridges, collapse and peeling. After 12-24h incubation, PZQ induced similar but they less severe, tegumental changes to those observed after exposure to ATS. The direct observation of the fluke motility and SEM study suggest that ATS is more effective than PZQ in causing tegumental damage in adult S. mekongi, and provides a basis for subsequent clinical trials.

Development of antischistosomal drugs in China, with particular consideration to praziquantel and the artemisinins

Remarkable achievements have been made in the control of schistosomiasis in China, with chemotherapy playing a seminal role. From the early 1950s through the early 1980s, Chinese scientists made considerable progress in discovery and development of compounds with antischistosomal properties, including antimonials, non-antimonials and various effective principles stemming from traditional herbs. However, only few compounds entered clinical testing, while others were abandoned mainly due to their toxicity and poor efficacy. The advent of praziquantel in the 1970s changed the landscape of research and development of drugs for treatment and morbidity control of schistosomiasis. The main Chinese contributions to enhance the understanding of the antischistosomal drug praziquantel are reviewed here, including issues of metabolism, antibody-dependency, host immune factors, stage-specific susceptibility and resistance. Over the past 25 years, researchers from China successfully developed artemether and artesunate, two derivatives from the antimalarial artemisinin, as promising drugs against Schistosoma japonicum. Laboratory investigations showed that the artemisinins display their highest activity against the juvenile stages of the parasite. These findings were consistently confirmed in randomised controlled trials; repeated oral administration of artemether or artesunate was safe and efficacious in the prevention of patent S. japonicum infections. The key findings are reviewed here, and emphasis is placed on how it stimulated research outside of China on other human schistosome species.

Effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice

The effects of praziquantel and artesunate on the tegument of adult Schistosoma mekongi harboured in mice were compared using scanning electron microscopy (SEM). Forty-two mice infected with S. mekongi for 49 days were treated intragastrically with either 300 mg/kg praziquantel or 300 mg/kg artesunate. Mice were sacrificed 1 or 3 days post-treatment. Worms were collected by perfusion and examined by SEM. One to 3 days after administration of artesunate, the tegument of S. mekongi showed severe swelling, vacuolization, fusion of the tegumental ridges and loss or shortening of the spines on the trabeculae, collapse and peeling. Praziquantel induced similar tegumental alterations as those observed after administration of artesunate, but they were less severe. Three days post-treatment, there was evidence of recovery only in the case of praziquantel. The results of our study suggest that artesunate is more effective than praziquantel in causing tegumental damage in adult S. mekongi, and provides a basis for subsequent clinical trials.

ARTEMETHER AS ADJUVANT THERAPY TO PRAZIQUANTEL IN MURINE EGYPTIAN SCHISTOSOMIASIS MANSONI

We investigated the activity of artemether (ART) against different developmental stages of schistosomes alone and in addition to praziquantel (PZQ). ART was administered orally (400 mg/kg) 4 and 6 wk postinfection (PI), 4 and 5 wk PI, or 4 or 6 wk PI alone and in addition to oral PZQ (500 x 2 mg/kg) 6 wk PI. Mice were killed in parallel to infected untreated controls 8 wk PI. Parasitological parameters and histological changes in the liver were studied. ART given 4 and 6 wk PI reduced worm burdens by 59 and 55% and tissue egg load by 96 and 90%, respectively. Moreover, eggs in different developmental stages were not found. The reduction in worm and egg burden (63 and 58%, and 96 and 99%, respectively) in mice treated with ART 4 and 5 wk or 4 and 6 wk PI was comparable with that in ART-treated mice at 4 or 6 wk PI. Compared with PZQ alone, combined treatment of PZQ and ART (4 and 5 wk or 4 and 6 wk PI) did not enhance worm eradication, but there was a complete absence of parasite eggs. Livers revealed no granulomata when ART was given 4 and 5 wk or 4 and 6 wk PI, with minimal central necrosis in those treated 4 and 6 wk PI. In conclusion, combined treatment of ART (4 and 6 wk PI) and PZQ resulted in >90% worm eradication and amelioration of Schistosoma mansoni eggs from the tissues, with minor histological changes in the liver.

Ultrastructural alterations in adult Schistosoma mansoni caused by artemether

Progress has been made over the last decade with the development and clinical use of artemether as an agent against major human schistosome parasites. The tegument has been identified as a key target of artemether, implying detailed studies on ultrastructural damage induced by this compound. We performed a temporal examination, employing a transmission electron microscope to assess the pattern and extent of ultrastructural alterations in adult Schistosoma mansoni harboured in mice treated with a single dose of 400 mg/kg artemether. Eight hours post-treatment, damage to the tegument and subtegumental structures was seen. Tegumental alterations reached a peak 3 days after treatment and were characterized by swelling, fusion of distal cytoplasma, focal lysis of the tegumental matrix and vacuolisation. Tubercles and sensory organelles frequently degenerated or collapsed. Typical features of subtegumental alterations, including muscle fibres, syncytium and parenchyma tissues, were focal or extensive lysis, vacuolisation and degeneration of mitochondria. Severe alterations were also observed in gut epithelial cells and vitelline cells of female worms. Our findings of artemether-induced ultrastructural alterations in adult S. mansoni confirm previous results obtained with juvenile S. mansoni and S. japonicum of different ages.

Transmission electron microscopic observations on ultrastructural damage in juvenile Schistosoma mansoni caused by artemether

Artemether, a derivative of the antimalarial artemisinin, has been shown to induce rapid and extensive alteration to the tegument of juvenile Schistosoma japonicum, S. mansoni and S. haematobium. Less is known with regard to ultrastructural damage caused by artemether; therefore, the present work was designed to assess the damage in juvenile S. mansoni. Mice infected with S. mansoni were treated intragastrically with a single dose of 400 mg/kg artemether 21 days post-infection. Between 8 h and 14 days after treatment groups of two mice were sacrificed, and schistosomula recovered for transmission electron microscopic observations. Ultrastructural damage was seen in the tegument, subtegumental musculature, parenchymal tissues and gastrodermis. It was already apparent 8 h after drug administration and increased gradually to reach a peak, 7 days post-treatment. Tegumental alterations were characterised by swelling, vesiculation and degeneration of sensory structures. Damage in subtegumental musculature, parenchymal tissues and gastrodermis included swelling, focal or extensive lysis, and decrease in granular endoplasmatic reticulum. Fourteen days after treatment ultrastructural damage was still seen in most schistosomula, however, there was partial repair in some specimens. The ability of artemether to cause extensive ultrastructural damage to juvenile S. mansoni correlates with its schistosomicidal effects and confirms earlier findings with S. japonicum.

The potential of artemether for the control of schistosomiasis

Schistosomiasis continues to rank--following malaria--at the second position of the world's parasitic diseases in terms of the extent of endemic areas and the number of infected people. There is yet no vaccine available and the current mainstay of control is chemotherapy with praziquantel used as the drug of choice. In view of concern about the development of tolerance and/or resistance to praziquantel, there is a need for research and development of novel drugs for the prevention and cure of schistosomiasis. Interestingly, derivatives of artemisinin, which are already effectively used in the treatment of malaria, also exhibit antischistosomal properties. Significant advances have been made with artemether, the methyl ether derivative of artemisinin. We review the discovery of the antischistosomal activity of artemether by Chinese scientists two decades ago; the detailed laboratory studies of the susceptibility of, and effect on, the different developmental stages of Schistosoma japonicum, Schistosoma mansoni and Schistosoma haematobium to artemether; the possible mechanism of action and the potential long-term toxicity. Finally, we look at the effect of combined treatment with artemether and praziquantel; and clinical findings thus far obtained from randomised controlled trials with oral artemether for the prevention of patent infections and morbidity. The review intends to create a forum for strategic discussion of how these laboratory and clinical findings could be translated into public health actions. We conclude that artemether--as part of integrated current control measures and adapted to specific socio-ecological and epidemiological settings--has considerable potential to significantly reduce the current burden of schistosomiasis in many parts of the world.

Tegumental alterations in juvenile Schistosoma haematobium harboured in hamsters following artemether treatment

We report the findings of a detailed temporal study on tegumental alterations in juvenile Schistosoma haematobium, induced by artemether, using scanning electron microscopy. Hamsters infected with S. haematobium cercariae for 28 days were treated intragastrically with a single dose of 300 mg/kg artemether. Groups of two hamsters were killed 24 h, 72 h and 7 days after treatment, and schistosomula were recovered from livers by perfusion and subsequent systematic examination of the tissue, before routinely processing for scanning electron microscopic examination. Most schistosomula collected 24 h after artemether administration showed severe tegumental damage, usually including swelling, fusion, vesiculation, peeling and collapse of enlarged sensory structures. After 72 h, tegumental damage had increased and schistosomula generally showed contraction with extensive swelling, erosion and peeling of the tegument. Seven days post-treatment, severe tegumental damage was only seen in a single male specimen with swelling of the worm body and destruction of the oral sucker. The other schistosomula showed only light to moderate damage, suggesting that schistosomula surviving the treatment began to recover. Our findings of tegumental damage following artemether treatment correlate with the efficacy of this novel antischistosomal drug in killing the juvenile stages of S. haematobium and complement recent findings with S. japonicum and S. mansoni.