Ecdysone and 20 hydroxyecdysone: new hormones for the human parasite schistosoma mansoni

Cloning and characterization of an Echinococcus granulosus ecdysteroid hormone nuclear receptor HR3-like gene

Cystic echinococcosis is an important parasitic zoonosis caused by the dog tapeworm Echinococcus granulosus. Little is known about adult worm development at the molecular level. Transcription analysis showed that the E. granulosus hormone receptor 3-like (EgHR3) gene was expressed in protoscoleces and adult worms, indicating its role in early adult development. In this study, we cloned and characterized EgHR3 showing that its cDNA contains an open reading frame (ORF) of 1890 bp encoding a 629 amino acid protein, which has a DNA-binding domain (DBD) and a ligand-binding domain (LBD). Immunolocalization revealed the protein was localized in the parenchyma of protoscoleces and adult worms. Real-time PCR analysis showed that EgHR3 was expressed significantly more in adults than in other stages of development (p<0.01) and that its expression was especially high in the early stage of adult worm development induced by bile acids. EgHR3 siRNA silenced 69–78% of the level of transcription in protoscoleces, which resulted in killing 43.6–60.9% of protoscoleces after 10 days of cultivation in vitro. EgHR3 may play an essential role in early adult worm development and in maintaining adult biological processes and may represent a novel drug or vaccine target against echinococcosis.

Nuclear receptors: emerging drug targets for parasitic diseases

Parasitic worms infect billions of people worldwide. Current treatments rely on a small group of drugs that have been used for decades. A shortcoming of these drugs is their inability to target the intractable infectious stage of the parasite. As well-known therapeutic targets in mammals, nuclear receptors have begun to be studied in parasitic worms, where they are widely distributed and play key roles in governing metabolic and developmental transcriptional networks. One such nuclear receptor is DAF-12, which is required for normal nematode development, including the all-important infectious stage. Here we review the emerging literature that implicates DAF-12 and potentially other nuclear receptors as novel anthelmintic targets.

Dynamic transcriptomes identify biogenic amines and insect-like hormonal regulation for mediating reproduction in Schistosoma japonicum

Eggs produced by the mature female parasite are responsible for the pathogenesis and transmission of schistosomiasis. Female schistosomes rely on a unique male-induced strategy to accomplish reproductive development, a process that is incompletely understood. Here we map detailed transcriptomic profiles of male and female Schistosoma japonicum across eight time points throughout the sexual developmental process from pairing to maturation. The dynamic gene expression pattern data reveal clear sex-related characteristics, indicative of an unambiguous functional division between males and females during their interplay. Cluster analysis, in situ hybridization and RNAi assays indicate that males likely use biogenic amine neurotransmitters through the nervous system to control and maintain pairing with females. In addition, the analyses indicate that reproductive development of females involves an insect-like hormonal regulation. These data sets and analyses serve as a foundation for deeper study of sexual development in this pathogen and identification of novel anti-schistosomal interventions.

The Schistosoma mansoni Cytochrome P450 (CYP3050A1) Is Essential for Worm Survival and Egg Development

Schistosomiasis affects millions of people in developing countries and is responsible for more than 200,000 deaths annually. Because of toxicity and limited spectrum of activity of alternatives, there is effectively only one drug, praziquantel, available for its treatment. Recent data suggest that drug resistance could soon be a problem. There is therefore the need to identify new drug targets and develop drugs for the treatment of schistosomiasis. Analysis of the Schistosoma mansoni genome sequence for proteins involved in detoxification processes found that it encodes a single cytochrome P450 (CYP450) gene. Here we report that the 1452 bp open reading frame has a characteristic heme-binding region in its catalytic domain with a conserved heme ligating cysteine, a hydrophobic leader sequence present as the membrane interacting region, and overall structural conservation. The highest sequence identity to human CYP450s is 22%. Double stranded RNA (dsRNA) silencing of S. mansoni (Sm)CYP450 in schistosomula results in worm death. Treating larval or adult worms with antifungal azole CYP450 inhibitors results in worm death at low micromolar concentrations. In addition, combinations of SmCYP450-specific dsRNA and miconazole show additive schistosomicidal effects supporting the hypothesis that SmCYP450 is the target of miconazole. Treatment of developing S. mansoni eggs with miconazole results in a dose dependent arrest in embryonic development. Our results indicate that SmCYP450 is essential for worm survival and egg development and validates it as a novel drug target. Preliminary structure-activity relationship suggests that the 1-(2,4-dichlorophenyl)-2-(1H-imidazol-1-yl)ethan-1-ol moiety of miconazole is necessary for activity and that miconazole activity and selectivity could be improved by rational drug design.

Over 600 million people in endemic countries are at risk of contracting schistosomiasis, which results in over 200,000 deaths each year and significant illness to most people that are infected. There are concerns that the drug widely used for the treatment of schistosomiasis, praziquantel, may be losing efficacy due to evolution of drug resistant worms. Since the disease mainly affects the poor in developing countries, pharmaceutical companies have little interest in developing new drugs and none are currently being tested. In this paper we focus on a novel parasite protein, cytochrome P450, which we propose to be a new drug target. Worms are unusual in having only one cytochrome P450 gene; humans have 57 cytochrome P450 genes. By using reverse genetic and chemical approaches we found that the schistosome cytochrome P450 is essential for worm survival and egg development and, therefore, is an essential and druggable target. Drugs that target fungal cytochrome P450s and are already in use for treating several human diseases were identified as potential hits for further development for schistosomiasis treatment.

Venus Kinase Receptors at the Crossroads of Insulin Signaling: Their Role in Reproduction for Helminths and Insects

Venus kinase receptors (VKRs) are invertebrate receptor tyrosine kinases (TKs) first discovered in the human parasite Schistosoma. They contain an extracellular Venus FlyTrap module similar to the ligand-binding domain of G protein-coupled receptors of class C and an intracellular TK domain similar to that of insulin receptors. VKRs are present from cnidarians to echinoderms. They were shown to be activated by amino-acids, to induce insulin-like intracellular pathways, and to be highly expressed in larvae and in gonads of helminths and insects. The function of VKR in gametogenesis was demonstrated in schistosomes by VKR silencing and recent studies in Aedes aegypti have confirmed the importance of VKR in mosquito egg formation. AaeVKR was shown to bind to ovary ecdysteroidogenic hormone and to activate the production of ecdysteroids by the ovary, independently of signaling mediated by insulin-like peptides. These new data confirm and specify the function of VKRs in the reproduction of helminths and insects and they open interesting perspectives for elucidating the role of VKRs in other models. VKR targeting would also provide opportunities for the control of parasites and various vector-borne infectious diseases.

Male-stimulated female maturation inSchistosoma: A review

InSchistosoma mansoni and other schistosome species, pairing of the female with a male partner is necessary for the completion of reproductive morphogenesis and growth. Permanent contact with a male is also necessary for the maintenance of reproductivity in the sexually mature female. This phenomenon appears to be unique within the animal kingdom. The mechanism of male-stimulated female reproductive development in schistosomes remains unknown however. In this paper, the theories for the nature of the process are reviewed briefly, recent findings are added, and the biological and technical problems associated with its study are highlighted.

Internal chemical communication within flatworms

An understanding of reproductive function is important for control of parasitic helminths. In cestodes and trematodes virtually nothing is known about regulatory and coordinating mechanisms that control maturation, gamete formation, egg production, and related processes. Neurosecretory neurons have been reported in various species but specific modes of action of neurohormones have yet to be demonstrated. The role of ecdysone is being investigated.

Nuclear hormone receptors in parasitic helminths

Nuclear receptors (NRs) belong to a large protein superfamily that are important transcriptional modulators in metazoans. Parasitic helminths include parasitic worms from the Lophotrochozoa (Platyhelminths) and Ecdysozoa (Nematoda). NRs in parasitic helminths diverged into two different evolutionary lineages. NRs in parasitic Platyhelminths have orthologues in Deuterostomes, in arthropods or both with a feature of extensive gene loss and gene duplication within different gene groups. NRs in parasitic Nematoda follow the nematode evolutionary lineage with a feature of multiple duplication of SupNRs and gene loss.

Schistosoma mansoni (Platyhelminthes, Trematoda) nuclear receptors: Sixteen new members and a novel subfamily

Nuclear receptors (NRs) are important transcriptional modulators in metazoans. Sixteen new NRs were identified in the Platyhelminth trematode, Schistosoma mansoni. Three were found to possess novel tandem DNA-binding domains that identify a new subfamily of NR. Two NRs are homologues of the thyroid hormone receptor that previously were thought to be restricted to chordates. This study brings the total number of identified NR in S. mansoni to 21. Phylogenetic and comparative genomic analyses demonstrate that S. mansoni NRs share an evolutionary lineage with that of arthropods and vertebrates. Phylogenic analysis shows that more than half of the S. mansoni nuclear receptors evolved from a second gene duplication. As the second gene duplication of NRs was thought to be specific to vertebrates, our data challenge the current theory of NR evolution.

Ecdysteroid concentrations through various life-stages of the meiobenthic harpacticoid copepod, Amphiascus tenuiremis and the benthic estuarine amphipod, Leptocheirus plumulosus

Endocrine function in arthropods has principally been characterized in insects and malacostracan crustaceans. However, meiofauna represent the most abundant metazoan marine taxa, with harpacticoid copepods comprising the second most abundant taxon. In addition, their diminutive biomass has made characterization of endocrine components difficult, so little is known about endocrine control of reproduction, molting, and growth in meiofauna. In this study, a sensitive fluorometric enzyme immunoassay (EIA) was utilized to quantify and compare the arthropod molting hormone, 20-hydroxyecdysone (20E), in various life-cycle and developmental stages of a laboratory reared meiobenthic copepod, Amphiascus tenuiremis, and in an amphipod, Leptocheirus plumulosus. In copepods, gravid females carrying late stage pre-hatch embryos contained significantly more 20E (390+/-252 fmol/female) than gravids carrying early (Stage-I) embryos (172+/-83 fmol/female). In contrast, ecdysteroid levels in Stage-I L. plumulosus gravid females (277+/-83 fmol/female) was greater than pre-hatch gravid females (146+/-42). Stage-I embryos of both copepods (19+/-10) and amphipods (11+/-5 fmol/embryo) possessed lower ecdysteroid content than copepod (35+/-15) and amphipod (43+/-33 fmol/embryo) pre-hatch embryos. Ecdysteroid levels were also assessed in naupliar, juvenile, adult male and non-gravid female copepod life-stages. In addition, ecdysteroids measured in field collected copepod species indicated gravid females possessed ecdysteroid levels similar to gravid A. tenuiremis. However, upon normalization of egg sac 20E content by brood size, embryos from larger broods contained lower levels of ecdysteroids when compared to embryos from smaller clutch sizes-indicating an inverse embryo/ecdysteroid relationship may exist across species.

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.

Molecular crosstalk in host-parasite relationships: schistosome- and leech-host interactions

The host-parasite relationship is based on subtle interplay between parasite survival strategies and host defense mechanisms. In this context, parasites often use the same or similar immune signaling molecules and/or molecular mimicry to escape host immunosurveillance. Both processes represent an adaptive strategy to ensure host immunocompatibility. This bidirectional communication between parasites and their hosts includes the renin-angiotensin, opioid and opiate systems. Here, Michel Salzet, André Capron and George Stefano review recent work on the interaction of common signaling mechanisms in schistosomes, leeches and their host.

Ligand binding and nuclear receptor evolution

Nuclear receptors form a superfamily of ligand-activated transcription factors that regulate various physiological functions, from development to homeostasis, in metazoans. The superfamily contains not only receptors for known ligands but also a large number of so-called orphan receptors for which ligands do not exist or have not been identified. The evolution of ligand-binding capacity of nuclear receptors may involve either secondary loss in orphan receptors, or evolutionary acquisition of ligand-binding capacity in liganded receptors. In this review, we present arguments from phylogenetic, functional and structural studies that support the hypothesis that there have been several independent gains of ligand-binding ability of nuclear receptors during metazoan evolution.

Hormones and nuclear receptors in schistosome development

A substantial but disparate body of evidence suggests that hormones affect the development of schistosomes within their definitive hosts. Here, Raymond Pierce and colleagues review such evidence for host steroid and thyroid hormones, and for ecdysteroids, and link this to the expanding knowledge of the nuclear receptors for these hormones. Phylogenetic analysis of the nuclear receptor superfamily and the characterization of the first schistosome nuclear receptors suggest that steroids and thyroid hormone probably act indirectly, or by pathways not involving the control of gene transcription. However, the probability that schistosome nuclear receptors exist for a variety of unique ligands opens up exciting possibilities for targeted drug development.

Crustacean ecdysteriods in reproduction and embryogenesis

Ecdysteroids are the molting hormones in Crustacea, as in other arthropods. They also subserve functions in the control of reproduction and embryogenesis. The available evidence indicate that the ecdysteroids are sequestered into the ovary by binding to yolk precursor proteins. Steroidogenic ability of the ovary is yet to be demonstrated in Crustacea. Despite several investigations, the role of ecdysteroids in oocyte maturation is not fully known. However, the embryonic ecdysteroids undergo significant fluctuation, correlated to specific developmental stages, including the secretion of embryonic envelopes and cuticle. Ecdysteroid metabolism in the eggs seems to be active throughout embryogenesis inasmuch as the free ecdysteroids are rapidly converted into conjugates, and vice versa; in addition to their inactivation into excretory ecdysteroidic acids. Eyestalk neuropeptides such as molt inhibiting hormones have a dominant role on the ecdysteroid synthesis by Y-organ, although recent evidence suggests a stimulatory role for yet another endocrine gland, the mandibular organ on Y-organ synthesis.

Immunological system and Schistosoma mansoni: co-evolutionary immunobiology. What is the eosinophil role in parasite-host relationship?

Schistosomes, ancestors and recent species, have pervaded many hosts and several phylogenetic levels of immunity, causing an evolutionary pressure to eosinophil lineage expression and response. Schistosoma mansoni adult worms have capitalized on the apparent adversity of living within the mesenteric veins, using the dispersion of eggs and antigens to other tissues besides intestines to set a systemic activation of several haematopoietic lineages, specially eosinophils and monocytes/macrophages. This activation occurs in bone marrow, spleen, liver, lymph nodes, omental and mesenteric milky spots (activation of the old or primordial and recent or new lymphomyeloid tissue), increasing and making easy the migration of eosinophils, monocytes and other cells to the intestinal periovular granulomas. The exudative perigranulomatous stage of the periovular reaction, which present hystolitic characteristics, is then exploited by the parasites, to release the eggs into the intestinal lumen. The authors hypothesize here that eosinophils, which have a long phylogenic story, could participate in the parasite-host co-evolution, specially with S. mansoni, operating together with monocytes/macrophages, upon parasite transmission.

Sex determination and female reproductive development in the genus Schistosoma: a review

Parasites of the genus Schistosoma were among the first metazoans to develop separate sexes, which is chromosomally determined in the fertilized egg. Despite the occurrence of specific sex chromosomes, the females of most Schistosomatidae species do not complete their somatic development and reach no sexual maturity without the presence of males. Indeed, the most controversial and at the same time most fascinating aspect about the sexual development of Schistosoma females lies on discover the nature of the stimulus produced by males that triggers and controls this process. Although the nature of the stimulus (physical or chemical) is a source of controversy, there is agreement that mating is a necessary requirement for maturation to occur and for migration of the female to a definitive final site of residence in the vascular system of the vertebrate host. It has also been proposed that the stimulus is not species-specific and, in some cases, not even genus-specific. Despite a vast literature on the subject, the process or processes underlying the meeting of males and females in the circulatory system have not been determined and as yet no consensus exists about the nature of the stimulus that triggers and maintains female development. In the studies about their role, Schistosoma males have been considered, at times pejoratively, the brother, the muscles or even the liver of females. Indeed, it still remains to be determined whether the stimulus responsible for female maturation involves the transfer of hormones, nutrients, neuromediators, mere tactile stimulation or a combination of chemotactic and thigmotactic factors.

Schistosoma mansoni: susceptibility differences between male and female mice can be mediated by testosterone during early infection

In murine Schistosoma mansoni infections, fewer adult worms develop in male than in female mice infected with the same number of cercariae. To evaluate a potential role for testosterone in this phenomenon, testosterone levels were manipulated in groups of CBA/J mice that were then infected and monitored for survival rates, worm burdens, organomegaly, and egg production. By 16 weeks of infection, more than 80% of mice in groups with low levels of testosterone (untreated females, castrated males, or carrier-treated castrates) were dead, while less than 40% of those in groups with high levels of testosterone (sham-castrated males, testosterone-treated castrates, or testosterone-treated female mice) succumbed to infection. The mean number of worms recovered from mice in the low testosterone level groups was comparable among groups, and significantly greater than that from those in high-testosterone-level groups. The degree of organomegaly observed correlated strongly with worm burden, but the number of hepatic eggs per female worm did not differ significantly between groups. When male mice were castrated or sham-castrated 5 weeks after S. mansoni infection, no significant differences in host survival occurred. Furthermore, female mice treated with testosterone demonstrated reduced worm burdens if the testosterone was given 10 days prior to infection but not if the testosterone was given 10 days or 5 weeks after infection. Thus, the host sex bias observed in parallel-infected male and female mice appears to be related to the presence of male gonadal tissue or testosterone early in infection, during the development of immature schistosomules.

F-10 nuclear binding proteins of Schistosoma mansoni: structural and functional features

By incubating total protein extracts of Schistosoma mansoni with 3H-17-beta-estradiol and 20-hydroxyecdysone, steroid binding proteins were detected in both male and female worms. The interaction of nuclear proteins with a restriction fragment of the gender and stage-specific gene F-10 was investigated using the 'band-shift' technique. Male and female nuclear proteins bound in a distinct way to the fragment of this gene containing putative regulatory consensus motifs. Among the nuclear proteins, only those rich in cysteine residues bound to DNA. In vitro incubation of live worms with the oestrogen antagonist Tamoxifen, altered the pattern of the DNA binding proteins, producing in females a profile similar to that obtained with male worm protein extracts. This effect of Tamoxifen could not be correlated to inhibition of protein biosynthesis. These results suggest that the regulation of transcription of the F-10 gene might involve steroid receptors.

Protein interactions with a gender-specific gene of Schistosoma mansoni: characterization by DNase I footprinting, band shift and UV cross-linking

A schistosome gender specific gene (F-10), was used as a probe to characterize DNA binding proteins from adult male and female Schistoma mansoni. Using the band-shift and DNase I footprinting methods, it was found that proteins from male and female worms bound to the intact F-10 gene and to restriction fragments corresponding to different domains of the gene, generating relatively long protected sites. Clear differences between male and female proteins were only observed when nuclear proteins were tested. Thus, gender-specific binding was detected in fragments corresponding to the 5' and 3' ends. UV-induced cross-linking between schistosome proteins and a synthetic oligonucleotide bearing a steroid response element present in the 3' untranslated end of the F-10 gene, revealed a major DNA binding protein with a molecular mass of 30 kDa, in both male and female worms. These results suggested that the activation of transcription of the F-10 gene may depend essentially on nuclear proteins.

Evolution of the nuclear receptor gene superfamily

Nuclear receptor genes represent a large family of genes encoding receptors for various hydrophobic ligands such as steroids, vitamin D, retinoic acid and thyroid hormones. This family also contains genes encoding putative receptors for unknown ligands. Nuclear receptor gene products are composed of several domains important for transcriptional activation, DNA binding (C domain), hormone binding and dimerization (E domain). It is not known whether these genes have evolved through gene duplication from a common ancestor or if their different domains came from different independent sources. To test these possibilities we have constructed and compared the phylogenetic trees derived from two different domains of 30 nuclear receptor genes. The tree built from the DNA binding C domain clearly shows a common progeny of all nuclear receptors, which can be grouped into three subfamilies: (i) thyroid hormone and retinoic acid receptors, (ii) orphan receptors and (iii) steroid hormone receptors. The tree constructed from the central part of the E domain which is implicated in transcriptional regulation and dimerization shows the same distribution in three subfamilies but two groups of receptors are in a different position from that in the C domain tree: (i) the Drosophila knirps family genes have acquired very different E domains during evolution, and (ii) the vitamin D and ecdysone receptors, as well as the FTZ-F1 and the NGF1B genes, seem to have DNA binding and hormone binding domains belonging to different classes. These data suggest a complex evolutionary history for nuclear receptor genes in which gene duplication events and swapping between domains of different origins took place.

Identification of free and conjugated ecdysteroids in cercariae of the schistosome Trichobilharzia ocellata

Extracts of cercariae of the avian schistosome Trichobilharzia ocellata were analysed for the presence of ecdysteroids by radioimmunoassay, high-performance liquid chromatography monitoring fractions by radioimmunoassay, and gas chromatography/mass spectrometry (selected ion monitoring). Both free ecdysteroids and polar conjugated ecdysteroids were detected in the cercarial extracts. The free ecdysteroid fraction, as well as the hydrolysed polar conjugated ecdysteroid fraction, contained both ecdysone and 20-hydroxyecdysone in approximately equal amounts. The amount of ecdysteroids detected is comparable to those found in other platyhelminths. A possible role for the ecdysteroids in the development of the parasite and/or the interactions between the parasite and its intermediate host, the freshwater snail Lymnaea stagnalis, is discussed.

A monoclonal antibody blocking the Schistosoma mansoni 28-kDa glutathione S-transferase activity reduces female worm fecundity and egg viability

The protective effects of two different monoclonal antibodies (mAb) raised against the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm 28 GST) were investigated. Two mAb of the same isotype (IgM) have been selected according to the blocking effect on Sm 28 GST enzymatic activity (S13) or the lack of blockade (H12). When passively transferred into Fischer rats, both S13 and H12 significantly reduced the worm burden. In BALB/c mice clear effects on female worm fecundity and egg viability were observed when the S13 mAb was transferred; these effects included significantly reduced loads of intestinal eggs, reduced egg hatching rates and an increased proportion of non-living eggs. No effect on egg production and egg hatching was observed in H12-treated mice. In addition, worm pairs recovered from S13-but not H12-treated mice laid significantly fewer eggs in vitro, and normal worm pairs incubated in vitro with the S13 mAb produced significantly fewer eggs than those incubated with H12 mAb. The impairment of egg hatching ability was also reproduced in vitro by the S13 mAb. These data suggest the existence of two different effector mechanisms induced by immunization with Sm 28 GST. The effect on the schistosome worm burden appears to be independent of GST activity whereas the effect on S. mansoni female fecundity and egg viability seems to be significantly linked to the inactivation of the enzymatic site.

The effect of ecdysteroids on the microfilarial production of Brugia pahangi and the control of meiotic reinitiation in the oocytes of Dirofilaria immitis

The effects of the ecdysteroids ecdysone and 20-hydroxyecdysone on microfilarial release in Brugia pahangi and on meiotic reinitiation in the oocytes of Dirofilaria immitis were studied. Ecdysone was found to stimulate microfilarial release at 2 x 10(-6) M, but this effect was reduced at higher and lower concentrations. 20-Hydroxyecdysone was found to have no such effect. In D. immitis, ecdysone at 10(-5) M was also found to overcome the period of meiotic arrest that occurs during the pachytene stage of prophase 1. This effect was reduced when 10(-6) M ecdysone was used. These results help support the theory that the ecdysteroids play a hormonal role in filarial worms similar to that found in insects.

Ecdysteroids in urine of African patients infected with helminths

The insect molting hormone and related compounds (ecdysteroids) have been found in patients infected with helminths. To investigate this phenomenon, we quantified and analyzed the urinary ecdysteroids in Malian subjects suffering from various helminthiases, as well as in Europeans. Very high titers (up to 100 nM) were found in some patients, whereas healthy persons had a basic level of 4 nM only. The high RIA activity was mainly due to two compounds. One of them was remarkable for being present in all the positive samples; it comigrated with the 20-hydroxyecdysone standard, both in HPLC and in TLC. The origin and the physiological significance of these compounds are questionable, since there was no clear relationship between their levels and the severity of the diseases. Numerous patients who were heavily infected had normal titers. Nevertheless, there is no doubt that high concentrations of ecdysteroid-like compounds in human urine indicate a pathological condition.

Ecdysteroid-like compounds in the serum and urine of African patients infected with Loa loa and Mansonella perstans microfilariae

Ecdysteroids are compounds related to 20-hydroxyecdysone, the insect moulting hormone. Surprisingly, they have been found in serum and urine of patients infected with helminths. In these cases, the substances are assumed to be produced by the parasites and, therefore, might be used as a marker of parasitic infection. Thus, we need to know exactly which species, at which developmental stage, can release ecdysteroids in such large quantities that they could be detected in the biological fluids of the host. Large-scale investigations must, accordingly, be devoted to the major species of helminths. In the present study, we examined 100 African patients with Loa loa and/or Mansonella perstans microfilaraemia. About 70 of them had high levels of ecdysteroid-like materials in serum or urine. In contrast, uninfected patients and European controls had much lower concentrations. However, the ecdysteroid titres did not reflect the concentration of microfilariae actually present in the blood, and some heavily infected patients were even negative. Nevertheless, the most important point was that high ecdysteroid levels in man were always associated with a pathological condition. The precise significance of the phenomenon should be determined.

Investigation of ecdysteroid excretion by adult Dirofilaria immitis and Brugia pahangi

The excretion of ecdysteroids by the filarial nematode species, Dirofilaria immitis and Brugia pahangi, was examined both in vitro, by the analysis of culture medium, and in vivo, through analysis of serum samples from experimentally infected hosts. There was no evidence of ecdysteroid excretion by intact parasites of either species in vitro. Free ecdysteroids were detected in the serum of ferrets and dogs infected with D. immitis, but concentrations would be at or below the limit of detection in sub-millilitre serum samples. The detection of ecdysteroids in the serum of potential hosts is unlikely to be of value in the diagnosis of filarial infections due to a combination of low titre in the presence of current infection and measurable titre in its absence. Ecdysteroids of dietary origin may contribute to the latter.

DNA binding proteins of Schistosoma mansoni recognizing a hexanucleotide motif occurring in genes regulated by steroids

1. Schistosome proteins interacting with a gene (F-10), which is only expressed in adult females, were investigated. 2. These were also tested using a synthetic oligonucleotide of 20 bp bearing a defined sequence derived from the F-10 gene and containing a hexanucleotide motif, TGTCCT, occurring in genes responsive to steroids. 3. Schistosome proteins (male and female) bound to the F-10 DNA, but only the male proteins bound to the synthetic oligonucleotide with high affinity. 4. The other preparations each produced different binding patterns, although this seemed to lack specificity. 5. These results indicated that the F-10 gene binds different proteins along its structure and suggested that proteins present in the male schistosomes may regulate its expression.

Echinococcus granulosus: occurrence of ecdysteroids in protoscoleces and hydatid cyst fluid

Both free ecdysteroids and hydrolysable polar conjugated ecdysteroids were detected in protoscoleces of Echinococcus granulosus from the equine host, and in hydatid cyst fluid from the same source. Comparisons were made of hydatid cyst fluid from E. granulosus infections of three intermediate host species: horses, sheep and humans. Ecdysone and 20-hydroxyecdysone were identified in both protoscoleces and hydatid cyst fluids by high-performance liquid chromatography monitoring fractions by radioimmunoassay, and by capillary gas chromatography/mass spectrometry (selected ion monitoring). The free ecdysteroid fractions of hydatid cyst fluid from horses and sheep also contained several unidentified, chromatographically unique, immunoreactive compounds which were refractory to hydrolysis with a crude Helix pomatia aryl sulphatase enzyme preparation.

Schistosoma mansoni: comparison of a Caribbean and African strain and experimental crossing based on compatibility with intermediate hosts and Rattus rattus

To elucidate changes relative to compatibility with intermediate and definitive hosts affecting Schistosoma mansoni since it was introduced to the New World, the compatibility of S. mansoni from Africa (the Cameroons), from the Caribbean (Guadeloupe), and those resulting from experimental crosses with the gastropods Biomphalaria glabrata and B. pfeifferi has been studied. Results show that S. mansoni, regardless of its origin or its usual snail host, always infects B. pfeifferi more successfully than B. glabrata. The success rate with B. pfeifferi is 100% with 5 miracidia of S. mansoni from Guadeloupe and 97% with 5 miracidia from the Cameroons. On the other hand, in B. glabrata infection rate was 54% with 5 miracidia from Guadeloupe and 0% with 5 miracidia from the Cameroons (a rate of 19% is reached when using 10 miracidia). Hybrid miracidia infect B. pfeifferi and B. glabrata with a success rate of 60 and 86%, respectively, which are intermediate between those of the parent strains. Studies of S. mansoni development in Rattus rattus show that there is better infectivity and survival for the Caribbean strain than the Cameroon strain: the percentage worm recovery 4 weeks after exposure in 34% for S. mansoni from Guadeloupe, 14% for S. mansoni from the Cameroons, and 31% for the hybrids. The mortality rate between 4 and 12 weeks after exposure is 51% for S. mansoni from Guadeloupe, 87% for S. mansoni from the Cameroons, and 31% for the hybrids.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunocytochemical localization of ecdysteroids in the life history stages of Schistosoma mansoni

Sporocysts, cercariae and adults of S. mansoni exhibit focal immunoreactivity against anti-ecdysone serum in an indirect immunofluorescence assay. In adult males immunoreactivity is limited to cell bodies and linear connections in the parenchyma surrounding the intestinal caeca. In both unisexual and paired mature females part of the lining of the ootype is reactive, especially near the entrance of the vitelline duct; this demonstrates that females can make ecdysteroids without mal contact. Adult worms cultured completely in vitro show a similar pattern of reactivity. Immunoreactivity is strong in cercariae, but is essentially absent in miracidia.

Transfer of [14C] cholesterol and its metabolites between adult male and female worms of Schistosoma mansoni

Adult male and female worms of Schistosoma mansoni are able to incorporate [14C]cholesterol and convert it into several metabolites. Schistosomula on the other hand cannot convert the incorporated cholesterol. Male worms are able to transfer the [14C]cholesterol and labelled metabolites to female worms but labelled female worms can transfer cholesterol but are unable to transfer the conversion products of cholesterol to male worms. Uptake by female worms of labelled products shed by male worms seems to occur more efficiently in the presence of serum than in its absence.

Unisexual murine schistosomiasis: portal hepatitis in subacute infections

Liver changes induced by unisexual male infection with S. mansoni were studied in mice during 2-20 weeks post-infection, in order to distinguish changes related to released worm substances from changes related to schistosome egg deposition. In subacute unisexual infection the venous wall appears as the target for inflammation which remains focal for a long time and affects limited segments of the main portal veins. Schistosomal pigment deposited in the lobule does not induce inflammatory or fibrogenic reactions.

Renewal of the membrane complex of Schistosoma mansoni is closely associated with lipid metabolism

Metabolic pathways leading to lipid biosynthesis in four different developmental stages of Schistosoma mansoni were explored and quantified by incubation in the presence of labeled precursors in a chemically defined medium. At the schistosomulum stage and in male, female, or paired worms, glycerol and oleate incorporation into neutral lipids, mainly in the form of triacylglycerols, was greater than into phospholipids, whereas in 11-and 15-day-old worms, synthesis mainly led to phospholipids. Incorporation into phospholipids was recovered largely in phosphatidylcholine, and distribution into other phospholipids depended on the developmental stage. Incorporation of choline and ethanolamine into their respective phospholipids represented up to 15% of the parasitic phospholipid content. The formation of phosphatidylcholine by phosphatidylethanolamine methylation occurred mainly in the immature parasitic stages. Inositol incorporation was also measurable, whereas [14C]serine incorporation was low or undetectable. Addition of 1-palmitoyl-2-[14C]oleyl phosphatidylcholine revealed a very high uptake of this phospholipid by the immature stages but further metabolism was not detectable. In contrast, adult S. mansoni were completely unable to take up or absorb this exogenous phospholipid. The most striking aspect of this study was the relatively high metabolic activity in 11-day-old worms and the lower but sustained activity on day 15 and at the schistosomulum stage. By comparison, biosynthetic activity in adult S. mansoni, on which research studies have been focused until now, was very low. We also discuss the participation of lipid metabolism in the constant renewal of the membrane complex which is essential to parasitism by S. mansoni.