Glucose Transport and Metabolism in Mammalian-stage Schistosomes

In Vivo Evaluation of an Antibody-Functionalized Lipoidal Nanosystem for Schistosomiasis Intervention

This study employed nanotechnological techniques to design and develop a praziquantel nanoliposomal (NLP) system and surface-functionalized the NLP with anti-calpain antibody (anti-calpain-NLP) for targeted praziquantel (PZQ) delivery in the treatment of schistosomiasis. Anti-calpain-NLPs were prepared and validated for their physicochemical parameters, in vitro and in vivo toxicity, drug entrapment efficiency (DEE), drug loading capacity (DLC), drug release, and parasitological cure rate. The particle sizes for the formulated nanoliposomes ranged from 88.3 to 92.7 nm (PDI = 0.17–0.35), and zeta potential ranged from −20.2 to −31.9 mV. The DLC and DEE ranged from 9.03 to 14.16 and 92.07 to 94.63, respectively. The functionalization of the nanoliposome surface was stable, uniform, and spherical. Fourier-transform infrared (FTIR), thermal behavior and X-ray powder diffraction (XRPD) analysis confirmed that the anti-calpain antibody and PZQ were attached to the surface and the nanoliposomes inner core, respectively. The drug sustained release was shown to be 93.2 and 91.1% within 24 h for NLP and anti-calpain-NLP, respectively. In the in vitro analysis study, the nanoliposome concentrations range of 30 to 120 μg/mL employed revealed acceptable levels of cell viability, with no significant cytotoxic effects on RAW 264.7 murine macrophage as well as 3T3 human fibroblast cells. Biochemical markers and histopathological analysis showed that the formulated nanoliposomes present no or minimal oxidative stress and confer hepatoprotective effects on the animals. The cure rate of the anti-calpain-NLP and PZQ was assessed by parasitological analysis, and it was discovered that treatment with 250 mg/kg anti-calpain-NLP demonstrated greater activity on the total worm burden, and ova count for both the juvenile and adult schistosomes in the intestine and liver of infected mice. The findings so obtained supported the ability of oral anti-calpain-NLP to target young and adult schistosomes in the liver and porto-mesenteric locations, resulting in improved effectiveness of PZQ.

Alternate-day fasting, a high-sucrose/caloric diet and praziquantel treatment influence biochemical and behavioral parameters during Schistosoma mansoni infection in male BALB/c mice

Schistosoma mansoni-induced granulomas result in severe damage to the host's liver, as well as neurological and metabolic disorders. We evaluated the biochemical and behavioral changes during schistosomiasis under three diet protocols: ad libitum (AL), alternate-day fasting (ADF) and a high-sucrose/caloric diet (HSD). Healthy male BALB/c mice were divided into noninfected, matched infected and infected/treated [praziquantel (PZQ)] groups. Caloric intake and energy efficiency coefficients associated with diets were measured. Behavioral (exploratory and locomotor) and biochemical (glucose, triglycerides, total cholesterol, AST, ALT, ALP, and γ-GT) tests and histological analysis were performed. Fifteen weeks postinfection, HSD and PZQ promoted weight gain, with higher caloric consumption than ADF (p < 0.05), reflecting serum glucose levels and lipid profiles. HSD and PZQ prevented liver dysfunction (AST and ALT) and significantly prevented increases in granuloma area (p < 0.05). HSD and PZQ also significantly improved mouse physical performance in exploratory and locomotor behavior (p < 0.05), reversing the impaired motivation caused by infection. These findings showed that ADF worsened the course of S. mansoni infection, while HSD and PZQ, even with synergistic effects, prevented and/or attenuated biochemical and behavioral impairment from infection.

Schistosome AMPK Is Required for Larval Viability and Regulates Glycogen Metabolism in Adult Parasites

On entering the mammalian host, schistosomes transition from a freshwater environment where resources are scarce, to an environment where there is an unlimited supply of glucose, their preferred energy substrate. Adult schistosome glycolytic activity consumes almost five times the parasite's dry weight in glucose per day to meet the parasite's energy demands, and the schistosome glycolytic enzymes and mechanisms for glucose uptake that sustain this metabolic activity have previously been identified. However, little is known of the parasite processes that regulate schistosome glucose metabolism. We previously described the Schistosoma mansoni ortholog of 5' AMP-Activated Protein Kinase (AMPK), which is a central regulator of energy metabolism in eukaryotes, and characterized the developmental regulation of its expression and activity in S. mansoni. Here we sought to explore the function of AMPK in schistosomes and test whether it regulates parasite glycolysis. Adult schistosomes mounted a compensatory response to chemical inhibition of AMPK α, resulting in increased AMPK α protein abundance and activity. RNAi inhibition of AMPK α expression, however, suggests that AMPK α is not required for adult schistosome viability in vitro. Larval schistosomula, on the other hand, are sensitive to chemical AMPK α inhibition, and this correlates with inactivity of the AMPK α gene in this life cycle stage that precludes a compensatory response to AMPK inhibition. While our data indicate that AMPK is not essential in adult schistosomes, our results suggest that AMPK regulates adult worm glycogen stores, influencing both glycogen utilization and synthesis. AMPK may therefore play a role in the ability of adult schistosomes to survive in vivo stressors such as transient glucose deprivation and oxidative stress. These findings suggest that AMPK warrants further investigation as a potential drug target, especially for interventions aimed at preventing establishment of a schistosome infection.

A comprehensive and critical overview of schistosomiasis vaccine candidates

A digenetic platyhelminth Schistosoma is the causative agent of schistosomiasis, one of the neglected tropical diseases that affect humans and animals in numerous countries in the Middle East, sub-Saharan Africa, South America and China. Several control methods were used for prevention of infection or treatment of acute and chronic disease. Mass drug administration led to reduction in heavy-intensity infections and morbidity, but failed to decrease schistosomiasis prevalence and eliminate transmission, indicating the need to develop anti-schistosome vaccine to prevent infection and parasite transmission. This review summarizes the efficacy and protective capacity of available schistosomiasis vaccine candidates with some insights and future prospects.

Revisiting the Schistosoma japonicum life cycle transcriptome for new insights into lung schistosomula development

Schistosome parasites are complex trematode blood flukes responsible for the disease schistosomiasis; a global health concern prevalent in many tropical and sub-tropical countries. While established transcriptomic databases are accessed ad hoc to facilitate studies characterising specific genes or gene families, a more comprehensive systematic updating of gene annotation and survey of the literature to aid in annotation and context is rarely addressed. We have reanalysed an online transcriptomic dataset originally published in 2009, where seven life cycle stages of Schistosoma japonicum were examined. Using the online pathway analysis tool Reactome, we have revisited key data from the original study. A key focus of this study was to improve the interpretation of the gene expression profile of the developmental lung-stage schistosomula, since it is one of the principle targets for worm elimination. Highly enriched transcripts, associated with lung schistosomula, were related to a number of important biological pathways including host immune evasion, energy metabolism and parasitic development. Revisiting large transcriptomic databases should be considered in the context of substantial new literature. This approach could aid in the improved understanding of the molecular basis of parasite biology. This may lead to the identification of new targets for diagnosis and therapies for schistosomes, and other helminths.

A Review of Nanotechnology for Targeted Anti-schistosomal Therapy

Schistosomiasis is one of the major parasitic diseases and second most prevalent among the group of neglected diseases. The prevalence of schistosomiasis may be due to environmental and socio-economic factors, as well as the unavailability of vaccines for schistosomiasis. To date, current treatment; mainly the drug praziquantel (PZQ), has not been effective in treating the early forms of schistosome species. The development of drug resistance has been documented in several regions globally, due to the overuse of PZQ, rate of parasitic mutation, poor treatment compliance, co-infection with different strains of schistosomes and the overall parasite load. Hence, exploring the schistosome tegument may be a potential focus for the design and development of targeted anti-schistosomal therapy, with higher bioavailability as molecular targets using nanotechnology. This review aims to provide a concise incursion on the use of various advance approaches to achieve targeted anti-schistosomal therapy, mainly through the use of nano-enabled drug delivery systems. It also assimilates the molecular structure and function of the schistosome tegument and highlights the potential molecular targets found on the tegument, for effective specific interaction with receptors for more efficacious anti-schistosomal therapy.

The human blood parasite Schistosoma mansoni expresses extracellular tegumental calpains that cleave the blood clotting protein fibronectin

Schistosomes are intravascular, parasitic flatworms that cause debilitating disease afflicting >200 million people. Proteins expressed at the host-parasite interface likely play key roles in modifying the worm's local environment to ensure parasite survival. Proteomic analysis reveals that two proteases belonging to the calpain family (SmCalp1 and SmCalp2) are expressed in the Schistosoma mansoni tegument. We have cloned both; while highly conserved in domain organization they display just 31% amino acid sequence identity. Both display high relative expression in the parasite's intravascular life forms. Immunolocalization and activity based protein profiling experiments confirm the presence of the enzymes at the host-parasite interface. Living parasites exhibit surface calpain activity that is blocked in the absence of calcium and in the presence of calpain inhibitors (E64c, PD 150606 and calpastatin). While calpains are invariably reported to be exclusively intracellular (except in diseased or injured tissues), our data show that schistosomes display unique, constitutive, functional extracellular calpain activity. Furthermore we show that the worms are capable of cleaving the host blood clotting protein fibronectin and that this activity can be inhibited by E64c. We hypothesize that SmCalp1 and/or SmCalp2 perform this cleavage function to impede blood clot formation around the worms in vivo.

Molecular cloning and functional characterization of a glucose transporter (CsGLUT) in Clonorchis sinensis

A complementary DNA (cDNA) encoding a glucose transporter of Clonorchis sinensis (CsGLUT) was isolated from the adult C. sinensis cDNA library. The open reading frame of CsGLUT cDNA consists of 1653 base pairs that encode a 550-amino acid residue protein. Hydropathy analysis suggested that CsGLUT possess 12 putative membrane-spanning domains. The Northern blot analysis result using poly(A)(+)RNA showed a strong band at ~2.1 kb for CsGLUT. When expressed in Xenopus oocytes, CsGLUT mediated the transport of radiolabeled deoxy-D-glucose in a time-dependent but sodium-independent manner. Concentration-dependency results showed saturable kinetics and followed the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 588.5 ± 53.0 μM and a Vmax value of 1500.0 ± 67.5 pmol/oocyte/30 min for [1,2-(3)H]2-deoxy-D-glucose. No trans-uptakes of bile acid (taurocholic acid), amino acids (tryptophan and arginine), or p-aminohippuric acid were observed. CsGLUT-mediated transport of deoxyglucose was significantly and concentration-dependently inhibited by radio-unlabeled deoxyglucose and D-glucose. 3-O-Methylglucose at 10 and 100 μM inhibited deoxyglucose uptake by ~50 % without concentration dependence. No inhibitory effects by galactose, mannose, and fructose were observed. This work may contribute to the molecular biological study of carbohydrate metabolism and new drug development of C. sinensis.

Schistosome feeding and regurgitation

Schistosomes are parasitic flatworms that infect >200 million people worldwide, causing the chronic, debilitating disease schistosomiasis. Unusual among parasitic helminths, the long-lived adult worms, continuously bathed in blood, take up nutrients directly across the body surface and also by ingestion of blood into the gut. Recent proteomic analyses of the body surface revealed the presence of hydrolytic enzymes, solute, and ion transporters, thus emphasising its metabolic credentials. Furthermore, definition of the molecular mechanisms for the uptake of selected metabolites (glucose, certain amino acids, and water) establishes it as a vital site of nutrient acquisition. Nevertheless, the amount of blood ingested into the gut per day is considerable: for males ∼100 nl; for the more actively feeding females ∼900 nl, >4 times body volume. Ingested erythrocytes are lysed as they pass through the specialized esophagus, while leucocytes become tethered and disabled there. Proteomics and transcriptomics have revealed, in addition to gut proteases, an amino acid transporter in gut tissue and other hydrolases, ion, and lipid transporters in the lumen, implicating the gut as the site for acquisition of essential lipids and inorganic ions. The surface is the principal entry route for glucose, whereas the gut dominates amino acid acquisition, especially in females. Heme, a potentially toxic hemoglobin degradation product, accumulates in the gut and, since schistosomes lack an anus, must be expelled by the poorly understood process of regurgitation. Here we place the new observations on the proteome of body surface and gut, and the entry of different nutrient classes into schistosomes, into the context of older studies on worm composition and metabolism. We suggest that the balance between surface and gut in nutrition is determined by the constraints of solute diffusion imposed by differences in male and female worm morphology. Our conclusions have major implications for worm survival under immunological or pharmacological pressure.

Revisiting glucose uptake and metabolism in schistosomes: new molecular insights for improved schistosomiasis therapies

A better understanding of the molecular mechanisms required for schistosomes to take up glucose, the major nutritional source exploited by these blood flukes from their mammalian hosts and the subsequent metabolism required to fuel growth and fecundity, can provide new avenues for developing novel interventions for the control of schistosomiasis. This aspect of parasitism is particularly important to paired adult schistosomes, due to their considerable requirements for the energy needed to produce the extensive numbers of eggs laid daily by the female worm. This review describes recent advances in characterizing glucose metabolism in adult schistosomes. Potential intervention targets are discussed within the insulin signaling and glycolysis pathways, both of which play critical roles in the carbohydrate and energy requirements of schistosomes.

Induction of protective immune responses against schistosomiasis using functionally active cysteine peptidases

Each year schistosomiasis afflicts up to 600 million people in 74 tropical and sub-tropical countries, predominantly in the developing world. Yet we depend on a single drug, praziquantel, for its treatment and control. There is no vaccine available but one is urgently needed especially since praziquantel-resistant parasites are likely to emerge at some time in the future. The disease is caused by several worm species of the genus Schistosoma. These express several classes of papain-like cysteine peptidases, cathepsins B and L, in various tissues but particularly in their gastrodermis where they employ them as digestive enzymes. We have shown that sub-cutaneous injection of recombinant and functionally active Schistosoma mansoni cathepsin B1 (SmCB1), or a cathepsin L from a related parasite Fasciola hepatica (FhCL1), elicits highly significant protection (up to 73%) against an experimental challenge worm infection in murine models of schistosomiasis. The immune modulating properties of this subcutaneous injection can boost protection levels (up to 83%) when combined with other S. mansoni vaccine candidates, glyceraldehyde 3-phosphate dehydrogenase (SG3PDH) and peroxiredoxin (PRX-MAP). Here, we discuss these data in the context of the parasite's biology and development, and provide putative mechanism by which the native-like cysteine peptidase induce protective immune responses.

Novel therapeutic and prevention approaches for schistosomiasis: review

Schistosomiasis is a debilitating disease affecting approximately 600 million people in 74 developing countries, with 800 million, mostly children at risk. To circumvent the threat of having praziquantel (PZQ) as the only drug used for treatment, several PZQ derivatives were synthesized, and drugs destined for other parasites were used with success. A plethora of plant-derived oils and extracts were found to effectively kill juvenile and adult schistosomes, yet none was progressed to pre- and clinical studies except an oleo-gum resin extracted from the stem of Commiphora molmol, myrrh, which action was challenged in several trials. We have proposed an essential fatty acid, a component of our diet and cells, the polyunsaturated fatty acid arachidonic acid (ARA) as a remedy for schistosomiasis, due to its ability to activate the parasite tegument-bound neutral sphingomyelinase, with subsequent hydrolysis of the apical lipid bilayer sphingomyelin molecules, allowing access of specific antibody molecules, and eventual worm attrition. This concept was convincingly supported using larval and adult Schistosoma mansoni and Schistosoma haematobium worms in in vitro experiments, and in vivo studies in inbred mice and outbred hamsters. Even if ARA proves to be an entirely effective and safe therapy for schistosomiasis, it will not prevent reinfection, and accordingly, the need for developing an effective vaccine remains an urgent priority. Our studies have supported the status of S. mansoni calpain, glutathione-S-transferase, aldolase, triose phosphate isomerase, glyceraldehyde 3-phosphate dehydrogenase, enolase, and 2-cys peroxiredoxin as vaccine candidates, as they are larval excreted-secreted products and, contrary to the surface membrane molecules, are entirely accessible to the host immune system effector elements. We have proposed that the use of these molecules, in conjunction with Th2 cytokines-inducing adjuvants for recruiting and activating eosinophils and basophils, will likely lead to development and implementation of a sterilizing vaccine in a near future.

Metabolite movement across the schistosome surface

Intravascular schistosome parasites are covered by an unusual double lipid bilayer. Nutrients, such as glucose and amino acids, as well as other metabolites, are known to be transported across this surface via specific transporter proteins. For instance, the glucose transporter protein SGTP4 is found in the host-interactive tegumental membranes. A second glucose transporter, SGTP1, localizes to the tegumental basal membrane (and internal tissues). Following expression in Xenopus oocytes, SGTP1 and SGTP4 both function as facilitated-diffusion sugar transporters. Suppressing the expression of SGTP1 and SGTP4 in juvenile schistosomes using RNA interference (RNAi) impairs the parasite's ability to import glucose and severely decreases worm viability. Amino acids can also be imported into schistosomes across their surface and an amino acid transporter (SPRM1lc) has been localized in the parasite surface membranes (as well as internally). In Xenopus oocytes, SPRM1lc can import the basic amino acids arginine, lysine and histidine as well as leucine, phenylalanine, methionine and glutamine. To function, this protein requires the assistance of a heavy-chain partner (SPRM1hc) which acts as a chaperone. Water is transported across the tegument of schistosomes via the aquaporin protein SmAQP. Suppressing SmAQP gene expression makes the parasites less able to osmoregulate and decreases their viability. In addition, SmAQP-suppressed adult parasites have been shown to be impaired in their ability to excrete lactate. Analysis of tegumental transporter proteins, as described in this report, is designed to generate a comprehensive understanding of the role of such proteins in promoting parasite survival by controlling the movement of metabolites into and out of the worms.

Tracing of the Bile-chemotactic migration of juvenile Clonorchis sinensis in rabbits by PET-CT

Background

Adult Clonorchis sinensis live in the bile duct and cause clonorchiasis. It is known that the C. sinensis metacercariae excyst in the duodenum and migrate up to the bile duct through the common bile duct. However, no direct evidence is available on the in vivo migration of newly excysted C. sinensis juveniles (CsNEJs). Advanced imaging technologies now allow the in vivo migration and localization to be visualized. In the present study, we sought to determine how sensitively CsNEJs respond to bile and how fast they migrate to the intrahepatic bile duct using PET-CT.

Methodology/Principal Findings

CsNEJs were radiolabeled with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG). Rabbits with a gallbladder contraction response to cholecystokinin-8 (CCK-8) injection were pre-screened using cholescintigraphy. In these rabbits, gallbladders contracted by 50% in volume at an average of 11.5 min post-injection. The four rabbits examined were kept anesthetized and a catheter inserted into the mid duodenum. Gallbladder contraction was stimulated by injecting CCK-8 (20 ng/kg every minute) over the experiment. Anatomical images were acquired by CT initially and dynamic PET was then carried out for 90 min with a 3-min acquisition per frame. Twelve minutes after CCK-8 injection, about 3,000 ¹⁸F-FDG-labeled CsNEJs were inoculated into the mid duodenum through the catheter. Photon signals were detected in the liver 7–9 min after CsNEJs inoculation, and these then increased in the whole liver with stronger intensity in the central area, presenting that the CsNEJs were arriving at the intrahepatic bile ducts.

Conclusion

In the duodenum, CsNEJs immediately sense bile and migrate quickly with bile-chemotaxis to reach the intrahepatic bile ducts by way of the ampulla of Vater.

Clonorchis sinensis adults habituating in the bile duct cause clonorchiasis endemic in East Asian countries, in which about 15–20 million people are supposedly infected. It has previously been reported that C. sinensis metacercariae excyst in the duodenum and that the juvenile flukes migrate to the bile duct through the ampulla of Vater in 4–7 hours. Recently advanced imaging technologies have enabled visualization of movements and localizations of parasites in mammalian hosts. From present study, we found the following: newly excysted C. sinensis juveniles (CsNEJs) were efficiently in vitro radiolabeled with ¹⁸F-FDG since CsNEJs have glucose transporters; CCK-8-induced gallbladder contraction was various rabbit to rabbit; CsNEJs promptly recognized bile and migrated up the duodenum to reach the intrahepatic bile ducts by way of the ampulla of Vater and the common bile duct as early as 7–9 minutes after inoculation. Some CsNEJs responding slowly to the bile delayed arriving at the distal bile capillaries. It was visualized for the first time that the CsNEJs migrate quickly within 10–20 minutes from the duodenum to the intrahepatic bile duct. These findings provide fundamental information on the migration of parasites living in the biliary passages of mammals.

Manipulation of vascular function by blood flukes?

Schistosomes (blood flukes) are long lived, intravascular parasites that afflict ~200 million people worldwide. Here we review the potential ability of these parasites to exert control on local vascular physiology. We examine schistosome kallikrein-like proteins that drive vasodilation. We review biogenic amine metabolism in the parasites that involve the vasodilator histamine and its receptors and the vasoconstrictor serotonin and its receptor. Schistosomes can trigger the release of histamine from host cells and can import serotonin. We consider the ability of schistosomes to generate and release the eicosanoid vasodilators PGD(2) and PGE(2) and the vasoconstrictors LTB(4) and LTC(4). The literature on nitric oxide metabolism in these blood flukes is assessed. Finally the potential impact of other schistosome metabolic processes (e.g. exogenous adenosine generation and acetylcholine degradation) on vascular function is appraised. An increased understanding of these processes could lead to novel anti-parasitics as well as new therapies to treat vascular dysfunction.

Suppressing glucose transporter gene expression in schistosomes impairs parasite feeding and decreases survival in the mammalian host

Adult schistosomes live in the host's bloodstream where they import nutrients such as glucose across their body surface (the tegument). The parasite tegument is an unusual structure since it is enclosed not by the typical one but by two closely apposed lipid bilayers. Within the tegument two glucose importing proteins have been identified; these are schistosome glucose transporter (SGTP) 1 and 4. SGTP4 is present in the host interactive, apical tegumental membranes, while SGTP1 is found in the tegumental basal membrane (as well as in internal tissues). The SGTPs act by facilitated diffusion. To examine the importance of these proteins for the parasites, RNAi was employed to knock down expression of both SGTP genes in the schistosomula and adult worm life stages. Both qRT-PCR and western blotting analysis confirmed successful gene suppression. It was found that SGTP1 or SGTP4-suppressed parasites exhibit an impaired ability to import glucose compared to control worms. In addition, parasites with both SGTP1 and SGTP4 simultaneously suppressed showed a further reduction in capacity to import glucose compared to parasites with a single suppressed SGTP gene. Despite this debility, all suppressed parasites exhibited no phenotypic distinction compared to controls when cultured in rich medium. Following prolonged incubation in glucose-depleted medium however, significantly fewer SGTP-suppressed parasites survived. Finally, SGTP-suppressed parasites showed decreased viability in vivo following infection of experimental animals. These findings provide direct evidence for the importance of SGTP1 and SGTP4 for schistosomes in importing exogenous glucose and show that these proteins are important for normal parasite development in the mammalian host.

Schistosomula, pre-adults and adults of Schistosoma mansoni ingest fluorescence-labelled albumin in vitro and in vivo: implication for a drug-targeting model

SUMMARY OBJECTIVE

Bilharziosis is one of the most important helminthal infections in humans and is caused by blood flukes of the genus Schistosoma. Three different life stages of the parasite occur within the mammalian host: schistosomula located in the skin, pre-adults located in the lung and adult worms located in the portal venous system. Erythrocytes are a major source of nutrient supply for adults. However, sources of nutrition for the developing stages are still unclear.

METHODS

To investigate whether schistosomula, pre-adults and adults of Schistosoma mansoni ingest human serum albumin (HSA) in vitro, these life stages were incubated with aminofluorescein-labelled human serum albumin (Afl-HSA) for 5 h. To test the uptake of albumin in vivo, the albumin conjugate was given intravenously to S. mansoni infected NMRI mice 24 h before harvesting the 3 life stages.

RESULTS

In comparison to the control group schistosomula, pre-adults, and adults showed an accumulation of Afl-HSA within the oesophagus and intestinal caecum in vitro and in vivo.

CONCLUSION

Our findings suggest that albumin seems to be a major source of energy supply for the early schistosomal life stages and an additive energy support for adult worms. Since albumin has been used successfully as a drug carrier for chemotherapeutic substances against malignant disorders, further studies will focus on albumin as a carrier for anthelminthics in a drug-targeting model.

The tegument of the human parasitic worm Schistosoma mansoni as an excretory organ: the surface aquaporin SmAQP is a lactate transporter

Adult schistosomes are intravascular parasites that metabolize imported glucose largely via glycolysis. How the parasites get rid of the large amounts of lactic acid this generates is unknown at the molecular level. Here, we report that worms whose aquaporin gene (SmAQP) has been suppressed using RNAi fail to rapidly acidify their culture medium and excrete less lactate compared to controls. Functional expression of SmAQP in Xenopus oocytes demonstrates that this protein can transport lactate following Michaelis-Menten kinetics with low apparent affinity (Km = 41+/-5. 8 mM) and with a low energy of activation (E(a) = 7.18+/-0.7 kcal/mol). Phloretin, a known inhibitor of lactate release from schistosomes, also inhibits lactate movement in SmAQP-expressing oocytes. In keeping with the substrate promiscuity of other aquaporins, SmAQP is shown here to be also capable of transporting water, mannitol, fructose and alanine but not glucose. Using immunofluorescent and immuno-EM, we confirm that SmAQP is localized in the tegument of adult worms. These findings extend the proposed functions of the schistosome tegument beyond its known capacity as an organ of nutrient uptake to include a role in metabolic waste excretion.

A comparative proteomic study of the undeveloped and developed Schistosoma mansoni egg and its contents: the miracidium, hatch fluid and secretions

The schistosome egg is the key agent responsible both for transmission of the parasite from human to molluscan host, and is the primary cause of pathogenesis in schistosomiasis. Characterisation of its proteome is a crucial step in understanding the egg's interactions with the mammalian host. We devised a scheme to isolate undeveloped eggs from mature schistosome eggs by Percoll gradient and then fractionate the mature egg into miracidial, hatch fluid and secreted protein preparations. The soluble proteins contained within the five preparations were separated by two-dimensional electrophoresis and their spot patterns compared by image analysis. Large numbers of representative spots were then excised and subjected to tandem mass spectrometry to obtain identities. In this way, the principal components of each sub-proteome were established. Chaperones were the most abundant category, with heat shock protein 70 (HSP70) dominant in the undeveloped egg and Schistosoma mansoni protein 40 (Smp-40) in the miracidium. Cytoskeletal proteins were expressed at similar levels in the undeveloped egg and miracidium, with tubulins the most abundant. The proteins of energy metabolism reflected the change from anaerobic to aerobic metabolism as the miracidium developed. None of the above categories was abundant in the hatch fluid but this peri-miracidial compartment was highly enriched for defence proteins such as thioredoxin. Hatch fluid also contained several host proteins and schistosome proteins of unknown function, highlighting its distinct nature and potentially its role. The egg secretions could not be compared with the other preparations due to their unique composition featuring the previously characterised IL-4-inducing principal of S. mansoni eggs (IPSE), Omega-1, egg secreted protein 15 (ESP15), a micro-exon gene 2 (MEG-2) protein and two members of the recently described MEG-3 family. This last preparation contains the subset of egg proteins that probably enables eggs to escape from host tissues and may also initiate granuloma formation, emphasising the need to establish fully the roles of its components in schistosome biology.

Phosphatidylinositol-and related-kinases: a genome-wide survey of classes and subtypes in the Schistosoma mansoni genome for designing subtype-specific inhibitors

Phosphatidylinositol kinases (PIK) are at the heart of one of the major pathways of intracellular signal transduction. The signals made by PIK influence a wide variety of cellular functions, including cell growth, differentiation and survival, glucose metabolism and cytoskeletal organization. Wortmannin strongly binds in vitro to all PIK subtypes and it is therefore an effective antiproliferative agent. This study is the first report on a survey made by similarity searches against Schistosoma mansoni genome available to date for phosphatidylinositol- and related-kinases (SmPIKs). We classified the SmPIKs according to five models (1-5). SmPIK sequences were retrieved from GeneDB (http://www.genedb.org) by means of a combinatorial approach which uses terms defined in genome annotation associated with PFAM (Protein Families) domains, BLAST analysis and COGs (Clusters of Orthologous Groups of proteins). This approach detects the kinase (catalytic) domain structure and also the recently described FAT and FATC motifs.

Schistosoma spp.: Isolation of microtubule associated proteins in the tegument and the definition of dynein light chains components

Schistosomes are parasitic blood flukes that reside in human mesenteric veins or urinary bladder veins, depending on species of the parasite. The syncytial tegument of these parasites represents a dynamic interface that regulates nutritional and immunological interactions between the parasite and the host. It is known that the components for biogenesis and maintenance of the tegument are supplied via vesicles from the nucleated cell bodies beneath the syncytium and muscle layer. To investigate the common motor components of vesicular transport in the tegument of schistomes, we extracted Schistosoma mansoni tegumental microtubule associated proteins utilizing detergent/high-salt procedure and raised antiserum against these proteins. The antiserum was applied to screen Schistosoma haematobium lambda gt11 expression library and some of the isolated clones were sequenced. Blast search for the sequences against NCBI database identified clones that are dynein light chains and myosin genes. Further analysis of schistosome dynein genes in the databases identified three families of dynein light chains (Dlcs). The Tctex family protein sequences are significantly different from the mammalian homologs and, therefore, offer a potential vaccine/drug target against schistosomes.

Amino acid transport in schistosomes: Characterization of the permeaseheavy chain SPRM1hc

Schistosomes are human parasitic flatworms that constitute an important public health problem globally. Adult parasites live in the bloodstream where they import nutrients such as amino acids across their body surface (the tegument). One amino acid transporter, Schistosome Permease 1 light chain, SPRM1lc, a member of the glycoprotein-associated family of transporters (gpaAT), has been characterized in schistosomes. Only a single member of the SLC3 family of glycoproteins that associate with gpaATs is found following extensive searching of the genomes of Schistosoma mansoni and S. japonicum. In this report, we characterize this schistosome permease heavy chain (SPRM1hc) gene and protein. The 72-kDa gene product is predicted to possess a single transmembrane domain, a (betaalpha)(8) (TIM barrel) conformation and a catalytic triad. Xenopus oocytes functionally expressing SPRM1hc with SPRM1lc import phenylalanine, arginine, lysine, alanine, glutamine, histidine, tryptophan, and leucine. Biochemical characterization demonstrates that in Xenopus extracts and in schistosome extracts SPRM1hc is associated into a high molecular weight complex with SPRM1lc that is disrupted by reducing agents. Quantitative real-time PCR and Western analysis demonstrate that SPRM1hc is expressed in each schistosome life stage examined (eggs, cercariae, schistosomula, adult males and females). SPRM1hc is widely distributed throughout adult male and female worms as determined by immunolocalization. Consistent with the hypothesis that SPRM1hc functions to facilitate nutrient uptake from host blood, immunogold electron microscopy confirms that the protein is distributed on the host-interactive tegumental membranes. We propose that surface-exposed, host-interactive, nutrient-transporting proteins like the SPRM1 heterodimer are promising vaccine candidates.

Biology of the schistosome lung-stage schistosomulum

Past and more recent research has examined the ultrastructure, metabolism, cell biology, genomics and post-genomics of schistosome schistosomula. These areas are considered and discussed in this review with particular emphasis on (1) the early migration phases through the host, (2) interaction of the host immune response with the parasite surface, (3) glucose uptake mechanisms, and (4) defining the transcriptional profiles of lung-stage schistosomula compared with other developmental stages using microarrays. The microarray profiling studies suggest caution is required when considering the use of schistosomes obtained by in vitro means for molecular or biochemical studies.

Making sense of the schistosome surface

The syncytial cytoplasmic layer, termed the tegument, which covers the entire surface of adult schistosomes, is a major interface between the parasite and its host. Since schistosomes can survive for decades within the host bloodstream, they are clearly able to evade host immune responses, and their ability is dependent on the properties of the tegument surface. We review here the molecular organization and biochemical functions of the tegument, combining the extensive literature over the last three decades with recent proteomic studies. We have interpreted the organization of the tegument surface as bounded by a conventional plasma membrane overlain by a membrane-like secretion, the membranocalyx, with which host molecules can associate. The range of parasite proteins, glycans and lipids found in the surface complex is evaluated, together with the host molecules detected. We consider the way in which the tegument surface is formed after cercarial penetration into the skin, and changes that occur as parasites develop to maturity. Lastly, we review the evidence on surface dynamics and turnover.

Schistosoma mansoni: biochemical characterization of lactate transporters or similar proteins

While in medium containing glucose, schistosomes exhibit homolactic fermentation. Accumulation of lactate acid in tissue fluid causes lowering of pH and a resultant inhibition of metabolic pathways. This requires lactate transporter protein in homolactic fermentors to facilitate the translocation of lactate(-) and [H(+)] across their plasma membrane. The ex-vivo experiment assessed lactic acid secretion by adult worms in absence and the presence of lactic acid transporter protein inhibitors. Phloretin and alpha-cyano-4-hydroxycinnamate caused a combined 25-35% inhibition of lactic acid secretion and probenecid increased this inhibition to 65% of control values. The removal of inhibitors resulted in 80% recovery of lactic acid secretion. In the in-vitro studies using vesicles isolated from adult worms and from schistosomula, the effects of phloretin and alpha-cyano-4-hydroxycinnamate were greater, each causing approximately 80% inhibition independently. The data obtained in this study demonstrate the presence of lactic acid transporters or similar proteins in Schistosoma mansoni.

Impact of interleukin-1 and interleukin-6 in murine primary schistosomiasis

BACKGROUND

Immunization with schistosome antigens invariably elicits a plethora of cytokines and, hence, it is reasonable to assume that these cytokines influence host responses to challenge lung-stage larvae and, consequently, the adult worm burden, and may be responsible for the erratic data generally observed in protection studies against schistosome infection.

METHODS

Schistosoma mansoni-infected mice were administered with recombinant interleukin (IL)-1beta or IL-6 to evaluate the impact of cytokines in host responses to lung-stage schistosomula, and subsequent effects on adult worm parameters. Plasma lipid levels were assayed by colorimetric enzymatic tests and antibody responses by ELISA. Cytokine profile in peripheral blood mononuclear cells was evaluated by RT-PCR.

RESULTS

S. mansoni infection elicited, at the time of parasite residency in the lung, significant increase in free fatty acids (FA) and decrease in cholesterol plasma levels in C57BL/6 and CD1 mice, and stimulation of mRNA expression for cytokines of T helper type (Th) 2 in BALB/c, Th1 in C57BL/6, and Th1/Th2 in CD1 mice. However, no specific antibody production was evident in any mouse strain. In BALB/c mice, exogenous IL-1beta-related plasma free FA level significant increase, stimulation of expression of IL-1 and IL-12 mRNA, and considerable increase in percent of specific antibody-producing mice were associated with significant reduction in adult worm burden and egg load. In contrast, exogenous IL-1beta elicited decrease in free FA plasma levels, and down-regulation of cytokines' mRNA expression in C57BL/6 and CD1 mice, changes associated with aggravation of the worm burden. Likewise, exogenous IL-6 failed to stimulate increase in plasma free FA levels or percent of antibody-producing mice except in BALB/c mice, effects that were protective for the host in BALB/c and for the parasite in C57BL/6 and CD1 mice.

CONCLUSION

These findings were discussed in relation to the erratic data of protection experiments with schistosome subunit antigens in different mouse strains.

A new description of the reproductive system of Schistosoma mansoni (Trematoda: Schistosomatidae) analyzed by confocal laser scanning microscopy

Classical schemes of the adult Schistosoma mansoni reproductive system have been described. In our study, whole adult worms derived from unisexual or mixed infections and stained with carmine chlorine were virtually and tomographically analyzed under confocal laser scanning microscopy. We found that: (1) there were morphological differences in the ovary, vitteline glands and testicular lobes between specimens derived from unisexual or mixed infections; (2) there was always a single lobed ovary (three or four lobes), presenting differentiation from the anterior to the posterior lobes, where the most mature oocytes were located; (3) the proximal segment of oviduct was connected to an ampullary dilatation, full of tailed spermatozoa, characterizing a seminal receptacle; (4) there was no long vitelline duct, but a short one that begins at the end of the proximal region of the vitelline gland; (5) long cells of Mehlis' gland placed radially around the ootype were not observed. Otherwise, the ootype was only lined by thick cuboidal epithelial cells with plaited bases and nuclei with flabby chromatin, making a clear distinction from the uterine epithelium. This morphological feature suggests that each cell represents a gland. (6) In coupled males, the specimens located inside the gynaecophoric canal had smaller testicular lobes, suckers, and body length and width when compared to their partners. Our results show that the reproductive system does not follow a unique pattern within flatworms. Due to its better resolution, confocal laser scanning microscopy, using a reflected mode with tomographic sections, allows new interpretations, modifying the adopted and current descriptions of the internal morphological structures of S. mansoni adult worms.

The cytoskeleton and motor proteins of human schistosomes and their roles in surface maintenance and host-parasite interactions

Schistosomes are parasitic blood flukes, responsible for significant human disease in tropical and developing nations. Here we review information on the organization of the cytoskeleton and associated motor proteins of schistosomes, with particular reference to the organization of the syncytial tegument, a unique cellular adaptation of these and other neodermatan flatworms. Extensive EST databases show that the molecular constituents of the cytoskeleton and associated molecular systems are likely to be similar to those of other eukaryotes, although there are potentially some molecules unique to schistosomes and platyhelminths. The biology of some components, particular those contributing to host-parasite interactions as well as chemotherapy and immunotherapy are discussed. Unresolved questions in relation to the structure and function of the tegument relate to dynamic organization of the syncytial layer.

Phenotypic plasticity in adult worms of Schistosoma mansoni (Trematoda:Schistosomatidae) evidenced by brightfield and confocal laser scanning microscopies

A comparative morphometric study was performed to identify host-induced morphological alterations in Schistosoma mansoni adult worms. A wild parasite population was obtained from a naturally infected rodent (Nectomys squamipes) and then recovered from laboratory infected C3H/He mice. Furthermore, allopatric worm populations maintained for long-term under laboratory conditions in Swiss Webster mice were passed on to N. squamipes. Suckers and genital system (testicular lobes, uterine egg, and egg spine) were analyzed by a digital system for image analysis. Confocal laser scanning microscopy (CLSM) showed details of the genital system (testicular lobes, vitelline glands, and ovary) and the tegument just below the ventral sucker. Significant morphological changes (p < 0.05) were detected in male worms in all experimental conditions, with no significant variability as assessed by CLSM. Significant changes (p < 0.05) were evident in females from the wild population related to their ovaries and vitelline glands, whereas allopatric females presented differences only in this last character. We conclude that S. mansoni worms present the phenotypic plasticity induced by modifications in the parasite's microenvironment, mainly during the first passage under laboratory conditions.

Biochemical and immunological adaptation in schistosome parasitism

The objective of this review is to clarify aspects of immunological and biochemical adaptations of schistosomes to their intermediate and final mammalian hosts. Adaptations to the mammalian hosts are traced in relation to cercarial penetration of mammalian skin, glucose transport and metabolism. The unusual ability of schistosome surface membrane to escape immune recognition and damage are reviewed. Moreover, the behavioural changes induced in the intermediate hosts by schistosomes are considered. The evolutionary adaptation to molluscan hosts aims to increase the probability of transmission of the parasite into its mammalian host. This review inspires more hope for further design of anti-schistosome drugs through disturbing aspects of biochemical and immunological adaptations in schistosome parasitism.

A comparative parasitologic study on Biomphalaria glabrata snail and C3H/He mice infected with human and murine isolates of Schistosoma mansoni derived from Sumidouro, Rio de Janeiro, Brazil

Experiments were carried out to analyze the biological characteristics of two sympatric isolates of Schistosoma mansoni derived from humans and murines in a low endemic transmission area (Sumidouro county, state of Rio de Janeiro, Brazil). Sympatric reared-laboratory Biomphalaria glabrata and C3H/He mice were used as experimental hosts. Parameters assessed comprised: precercarial period, infectivity and mortality (snails), prepatent period, infectivity (percentage of cercariae maturation into adult worm) and intestinal egg count (mice). The murine isolate showed a shorter precercarial period and higher infectivity than human isolate (p<0.05). This biological heterogenicity did not correspond to the vertebrate data because any biological parameter presented significant difference (p>0.05). These data suggest that both isolates are local sub-populations, providing support for the hypotheses that in a same biotope mixed populations or sub-populations circulate among their main host (human beings) and/or rodent as an anfixenous infection.

Morphometric study of Schistosoma mansoni adult worms recovered from Undernourished infected mice

Some unfavourable effects of malnutrition of the host on Schistosoma mansoni worm biology and structure have been reported based upon brigthfield microscopy. This paper aims to study by morphometric techniques, some morphological parameters in male and female adult worms recovered from undernourished albino mice in comparison with parasites recovered from well-fed infected mice. Undernourished animals were fed a multideficient and essentially low protein diet (RBD diet) and compared to well-fed control mice fed with the commercial diet NUVILAB. Seventy-five days post-infection with 80 cercarie (BL strain) animals were sacrificed. All adult worms were fixed in 10% formalin and stained with carmine chloride. One hundred male and 60 female specimens from each group (undernourished and control) were examined using an image system analysis Leica Quantimet 500C and the Sigma Scan Measurement System. The following morphometrical parameters were studied: body length and width, oral and ventral suckers, number and area of testicular lobes, length and width of ovary and uterine egg. For statistical analysis, the Student's t test for unpaired samples was applied. Significant differences (p < 0.05) were detected in body length and width, in parameters of suckers, uterine egg width, ovary length and area of testicular lobes, with lower values for specimens from undernourished mice. The nutritional status of the host has negative influence on S. mansoni adult worms, probably through unavailability of essential nutrients to the parasites.

Phenotypic characterization of Schistosoma mansoni adult worms recovered from undernourished mice: a morphometric study focusing on the reproductive system

A morphometric study focusing on some features of the reproductive system of Schistosoma mansoni adult worms was performed, aiming to complete previously reported data concerning the effects of undernourishment of the host on the parasites. Male worms were significantly affected (p<0.05) regarding the testicular lobes.

Effects of carnosine on bilharzial infestation in hamsters: biochemical and histochemical studies

We tested the ability of carnosine to improve some liver disorders induced by Schistosoma mansoni parasite in hamsters (Mesocricetus auratus). Results indicate that parasitic infestation induced elevation in serum alkaline phosphatase, gamma-glutamyl transferase, aspartate aminotransferase and procollagen III peptide as a marker of liver fibrosis. Administration of carnosine (10 mg/day) for 15 days either concurrent with infection, 2 and 4 weeks post-infestation was effective in reducing differential worm burden. It was also effective in renormalizing blood glucose level depending on the time course. The most evident effect of carnosine was on serum procollagen III peptide level, which was lowered in infested groups treated with carnosine. Histopathological studies confirmed the potential use of carnosine for intervention in schistosomiasis.

Schistosome male-female interaction: induction of germ-cell differentiation

Male and female schistosomes are permanently paired while they live in the bloodstream of their vertebrate hosts. Female schistosomes produce eggs only when they are in intimate association with a male. Here, I combine classical cytological knowledge about the cellular processes in the female that are affected by the male with recent molecular results that are beginning to allow speculation about the signalling events involved.