Identification and purification of a second form of Cu/Zn superoxide dismutase from Schistosoma mansoni

Two Distinct Superoxidase Dismutases (SOD) Secreted by the Helminth Parasite Fasciola hepatica Play Roles in Defence against Metabolic and Host Immune Cell-Derived Reactive Oxygen Species (ROS) during Growth and Development

The antioxidant superoxide dismutase (SOD) catalyses the dismutation of superoxide, a dangerous oxygen free radical, into hydrogen peroxide and molecular oxygen. Superoxide generation during the oxidative burst of the innate immune system is considered a key component of the host defence against invading pathogens. We demonstrate the presence and differential expression of two SODs in Fasciola hepatica, a leaderless cytosolic (FhSOD1) and an extracellular (FhSOD3) form containing a secretory signal peptide, suggesting that the parasites exploit these enzymes in distinct ways to counteract reactive oxygen species (ROS) produced by cellular metabolism and immune defences. Both enzymes are highly expressed by the infective newly excysted juvenile (NEJ) stages and are found in abundance in their excretory–secretory products (ES), but only FhSOD1 is present in adult ES, suggesting that the antioxidants have different functions and pathways of secretion, and are under separate temporal expression control during the migration, growth, and development of the parasite. Functionally, the recombinant FhSOD1 and FhSOD3 exhibit similar activity against superoxide to their mammalian counterparts. Confocal immuno-localisation studies demonstrated the presence of FhSOD1 and FhSOD3 on the NEJ tegument and parenchyma, supporting our suggestion that these enzymes are secreted during host invasion to protect the parasites from the harmful oxidative bursts produced by the activated innate immune response. By producing superoxide enzymatically in vitro, we were able to demonstrate robust killing of F. hepatica NEJ within 24 h post-excystment, and that the lethal effect of ROS was nullified with the addition of SOD and catalase (the antioxidant enzyme responsible for the dismutation of hydrogen peroxide, a by-product of the SOD reaction). This study further elucidates the mechanism by which F. hepatica protects against ROS derived from cellular metabolism and how the parasite could mitigate damage caused by the host’s immune response to benefit its survival.

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.

Proteomic analysis of adult Schistosoma mekongi somatic and excretory-secretory proteins

Schistosoma mekongi is a causative agent of human schistosomiasis. There is limited knowledge of the molecular biology of S. mekongi and very few studies have examined drug targets, vaccine candidates and diagnostic biomarkers for S. mekongi. To explore the biology of S. mekongi, computational as well as experimental approaches were performed on S. mekongi males and females to identify excretory-secretory (ES) proteins and proteins that are differentially expressed between genders. According to bioinformatic prediction, the S. mekongi ES product was approximately 4.7% of total annotated transcriptome sequences. The classical secretory pathway was the main process to secrete proteins. Mass spectrometry-based quantification of male and female adult S. mekongi proteins was performed. We identified 174 and 156 differential expression of proteins in male and female worms, respectively. The dominant male-biased proteins were involved in actin filament-based processes, microtubule-based processes, biosynthetic processes and homeostatic processes. The major female-biased proteins were related to biosynthetic processes, organelle organization and signal transduction. An experimental approach identified 88 proteins in the S. mekongi secretome. The S. mekongi ES proteins mainly contributed to nutrient uptake, essential substance supply and host immune evasion. This research identifies proteins in the S. mekongi secretome and provides information on ES proteins that are differentially expressed between S. mekongi genders. These findings will contribute to S. mekongi drug and vaccine development. In addition, the study enhances our understanding of basic S. mekongi biology.

Identification and Molecular Characterization of Superoxide Dismutases Isolated From A Scuticociliate Parasite: Physiological Role in Oxidative Stress

Philasterides dicentrarchi is a free-living microaerophilic scuticociliate that can become a facultative parasite and cause a serious parasitic disease in farmed fish. Both the free-living and parasitic forms of this scuticociliate are exposed to oxidative stress associated with environmental factors and the host immune system. The reactive oxygen species (ROS) generated by the host are neutralized by the ciliate by means of antioxidant defences. In this study we aimed to identify metalloenzymes with superoxide dismutase (SOD) activity capable of inactivating the superoxide anion (•O2-) generated during induction of oxidative stress. P. dicentrarchi possesses the three characteristic types of SOD isoenzymes in eukaryotes: copper/zinc-SOD, manganese-SOD and iron-SOD. The Cu/Zn-SOD isoenzymes comprise three types of homodimeric proteins (CSD1-3) of molecular weight (MW) 34-44 kDa and with very different AA sequences. All Cu/Zn-SODs are sensitive to NaCN, located in the cytosol and in the alveolar sacs, and one of them (CSD2) is extracellular. Mn- and Fe-SOD transcripts encode homodimeric proteins (MSD and FSD, respectively) in their native state: a) MSD (MW 50 kDa) is insensitive to H2O2 and NaN3 and is located in the mitochondria; and b) FSD (MW 60 kDa) is sensitive to H2O2, NaN3 and the polyphenol trans-resveratrol and is located extracellularly. Expression of SOD isoenzymes increases when •O2- is induced by ultraviolet (UV) irradiation, and the increase is proportional to the dose of energy applied, indicating that these enzymes are actively involved in cellular protection against oxidative stress.

The natural compound 7-epiclusianone inhibits superoxide dismutase activity in Schistosoma mansoni

Schistosomiasis - caused by trematodes from the genus Schistosoma - affects more than 200 million people worldwide. Growing resistance to therapy with praziquantel (PZQ) has encouraged the search for novel treatments against this neglected disease. The compound 7-epiclusianone (7-epi) - isolated from 'bacupari' (the fruit of the Gracinia brasiliensis tree) - has promising activity against Schistosoma mansoni in vitro, damaging the parasite's tegument. However, the target and mechanism of action of 7-epi have not been identified. Here, we examined the possibility that 7-epi harms the tegument by inhibiting parasite superoxide dismutase (SOD), which protects the tegument from damage by reactive oxygen species produced by host immune cells. Molecular docking analysis in silico suggested strong interactions between 7-epi and S. mansoni cytosolic superoxide dismutase (SmCtSOD) at allosteric cavities. Schistosoma mansoni couples were cultivated ex vivo with 12.44-198.96 μm 7-epi for 24 h, and then parasite extracts were tested for lipid peroxidation (as a surrogate for oxidative stress), and SOD activity and expression. Lipid peroxidation levels increased after incubation with concentrations ≥99.48 μm 7-epi, and this compound reduced SOD activity at concentrations ≥24.87 μm. However, contact with 7-epi did not alter SOD expression, by quantitative real-time polymerase chain reaction (qRT-PCR). Our results show that the inhibition of SmCtSOD is partly responsible for the tegument detachment observed after incubation with 7-epi, but is not the only cause of the antiparasitic action of this compound in vitro.

Biochemical assessment of oxidative status versus liver enzymes in patients with chronic fascioliasis

The aim of this study was to examine the oxidative status in Egyptian patients suffering chronic fascioliasis. The relationship between serum malondialdehyde (MDA) levels, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) activities was investigated in relation to the level of liver enzymes; ALT and AST compared to healthy controls. Twenty patients versus ten controls were included in the study. Among cases the MDA, CAT, AST and ALT were higher than controls, while SOD and GPX higher values were present among controls. There was a highly significant difference between cases and controls as regard MDA, CAT, SOD, GPX, and AST, and a significant difference regarding ALT. The findings of increased serum lipid peroxidation and decreased antioxidant enzymes in erythrocytes of chronic fascioliasis patients indicated the presence of persistent inflammation and oxidative stress which confirms the underlying pathogenesis and reflected the stage of infection providing a baseline data for comparison between normal and infected patients guided by the level of liver enzymes in relation to oxidative status.

Protective Potential of Antioxidant Enzymes as Vaccines for Schistosomiasis in a Non-Human Primate Model

Schistosomiasis remains a major cause of morbidity in the world. The challenge today is not so much in the clinical management of individual patients, but rather in population-based control of transmission in endemic areas. Despite recent large-scale efforts, such as integrated control programs aimed at limiting schistosomiasis by improving education and sanitation, molluscicide treatment programs and chemotherapy with praziquantel, there has only been limited success. There is an urgent need for complementary approaches, such as vaccines. We demonstrated previously that anti-oxidant enzymes, such as Cu-Zn superoxide dismutase (SOD) and glutathione S peroxidase (GPX), when administered as DNA-based vaccines induced significant levels of protection in inbred mice, greater than the target 40% reduction in worm burden compared to controls set as a minimum by the WHO. These results led us to investigate if immunization of non-human primates with antioxidants would stimulate an immune response that could confer protection as a prelude study for human trials. Issues of vaccine toxicity and safety that were difficult to address in mice were also investigated. All baboons in the study were examined clinically throughout the study and no adverse reactions occurred to the immunization. When our outbred baboons were vaccinated with two different formulations of SOD (SmCT-SOD and SmEC-SOD) or one of GPX (SmGPX), they showed a reduction in worm number to varying degrees, when compared with the control group. More pronounced, vaccinated animals showed decreased bloody diarrhea, days of diarrhea, and egg excretion (transmission), as well as reduction of eggs in the liver tissue and in the large intestine (pathology) compared to controls. Specific IgG antibodies were present in sera after immunizations and 10 weeks after challenge infection compared to controls. Peripheral blood mononuclear cells, mesenteric, and inguinal node cells from vaccinated animals proliferated and produced high levels of cytokines and chemokines in response to crude and recombinant antigens compared with controls. All together, these data demonstrate the potential of antioxidants as a vaccine in a non-human primate model.

Biochemical characterization and role of the proteasome in the oxidative stress response of adult Schistosoma mansoni worms

The trematode Schistosoma mansoni, an important parasite of humans, is the principle agent of the disease schistosomiasis. In the human host, one of the most important stress factors of this parasite is the oxidative stress generated by both the metabolism of the worm and the immune system of the host. The proteasomal system is responsible for protein homeostasis during oxidative stress. The 26S proteasome is a multicatalytic protease formed by two compartments, a 20S core and regulatory particle 19S, and controls the degradation of intracellular proteins, hence regulating many cellular processes. In the present report, we describe the biochemical characterization and role of the 20S proteasome in the response of adult S. mansoni worms exposed to hydrogen peroxide. Characterization of the response to the oxidative stress included the evaluation of viability, egg production, mortality, tegument integrity, and both expression and activity of proteasome. We observed decreases in viability, egg production as well as 100% mortality at the higher concentrations of hydrogen peroxide tested. The main changes observed in the tegument of adult worms were peeling as well as the appearance of bubbles and a decrease of spines on the tubercles. Furthermore, there were increases in 26S activity to the same extent as 20S proteasome activity, although there was increase of 20S proteasome content, suggesting that degradation of protein oxidized in adult worms is due to the 20S proteasome. It was demonstrated that adult S. mansoni worms are sensitive to oxidative stress, and that a variety of processes in this parasite are altered under this condition. The work contributes to a better understanding of the mechanisms employed by S. mansoni to survive under oxidative stress.

Transcriptional analysis of a unique set of genes involved in Schistosoma mansoni female reproductive biology

Schistosomiasis affects more than 200 million people globally. The pathology of schistosome infections is due to chronic tissue inflammation and damage from immune generated granulomas surrounding parasite eggs trapped in host tissues. Schistosoma species are unique among trematode parasites because they are dioecious; females require paring with male parasites in order to attain reproductive maturity and produce viable eggs. Ex vivo cultured females lose the ability to produce viable eggs due to an involution of the vitellarium and loss of mature oocytes. In order to better understand schistosome reproductive biology we used data generated by serial analysis of gene expression (SAGE) to identify uncharacterized genes which have different transcript abundance in mature females, those that have been paired with males, and immature females obtained from unisexual infections. To characterize these genes we used bioinformatics, transcript localization, and transcriptional analysis during the regression of in vitro cultured females. Genes transcribed exclusively in mature females localize primarily in the vitellocytes and/or the ovary. Genes transcribed exclusively in females from single sex infections localize to vitellocytes and subtegumental cells. As female reproductive tissues regress, eggshell precursor proteins and genes involved in eggshell synthesis largely have decreased transcript abundance. However, some genes with elevated transcript abundance in mature adults have increased gene expression following regression indicating that the genes in this study function both in eggshell biology as well as vitellogenesis and maintenance of female reproductive tissues. In addition, we found that genes enriched in females from single sex infections have increased expression during regression in ex vivo females. By using these transcriptional analyses we can direct research to examine the areas of female biology that are both relevant to understanding the overall process of female development and worm pairing while determining novel therapeutic approaches directed at the maturation of female schistosomes.

Schistosomiasis is a chronic, debilitating disease that affects over 200 million people globally. The pathology associated with schistosomiasis is caused by host immune responses to parasite eggs. Therefore, it is imperative to identify pathways responsible for controlling worm reproductive biology. Schistosome females must be in constant contact with male parasites in order to achieve reproductive maturity. The process of pairing and reproductive maturation in female worms is poorly understood, in part, because it does not occur outside of the host. In addition, when female schistosomes are removed from their mammalian host they regress to an immature state. In this study our goal was to characterize a unique set of genes in Schistosoma mansoni whose transcript abundance differs in mature and immature female worms. We found that the genes with higher transcript abundance in sexually mature female worms were expressed in female reproductive tissues, while those transcripts enriched in sexually immature worms were present in sub-surface somatic cells. Transcript abundance of the selected genes changed dramatically when females were removed from their host. These findings inform new approaches to study female worm biology and will provide insights into the processes of worm pairing and reproductive maturation.

Schistosoma tegument proteins in vaccine and diagnosis development: an update

The development of a vaccine against schistosomiasis and also the availability of a more sensitive diagnosis test are important tools to help chemotherapy in controlling disease transmission. Bioinformatics tools, together with the access to parasite genome, published recently, should help generate new knowledge on parasite biology and search for new vaccines or therapeutic targets and antigens to be used in the disease diagnosis. Parasite surface proteins, especially those expressed in schistosomula tegument, represent interesting targets to be used in vaccine formulations and in the diagnosis of early infections, since the tegument represents the interface between host and parasite and its molecules are responsible for essential functions to parasite survival. In this paper we will present the advances in the development of vaccines and diagnosis tests achieved with the use of the information from schistosome genome focused on parasite tegument as a source for antigens.

The redox biology of schistosome parasites and applications for drug development

Schistosomiasis caused by Schistosoma spp. is a serious public health concern, especially in sub-Saharan Africa. Praziquantel is the only drug currently administrated to treat this disease. However, praziquantel-resistant parasites have been identified in endemic areas and can be generated in the laboratory. Therefore, it is essential to find new therapeutics. Antioxidants are appealing drug targets. In order to survive in their hosts, schistosomes are challenged by reactive oxygen species from intrinsic and extrinsic sources. Schistosome antioxidant enzymes have been identified as essential proteins and novel drug targets and inhibition of the antioxidant response can lead to parasite death. Because the organization of the redox network in schistosomes is significantly different from that in humans, new drugs are being developed targeting schistosome antioxidants. In this paper the redox biology of schistosomes is discussed and their potential use as drug targets is reviewed. It is hoped that compounds targeting parasite antioxidant responses will become clinically relevant drugs in the near future.

Superoxide Dismutase (SOD) Enzyme Activity Assay in Fasciola spp. Parasites and Liver Tissue Extract

BACKGROUND

The purpose of this comparative study was to detect superoxide dismutase (SOD) activities in Fasciola hepatica, F. gigantica parasites, infected and healthy liver tissues in order to determine of species effects and liver infection on SODs activity level.

METHODS

Fasciola spp. parasites and sheep liver tissues (healthy and infected liver tissues), 10 samples for each, were collected, homogenized and investigated for protein measurement, protein detection and SOD enzyme activity assay. Protein concentration was measured by Bradford method and SODs band protein was detected on SDS-PAGE. SODs activity was determined by iodonitrotetrazolium chloride, INT, and xanthine substrates. Independent samples t-test was conducted for analysis of SODs activities difference.

RESULTS

Protein concentration means were detected for F. hepatica 1.3 mg/ ml, F. gigantica 2.9 mg/ml, healthy liver tissue 5.5 mg/ml and infected liver tissue 1.6 mg/ml (with similar weight sample mass). Specific enzyme activities in the samples were obtained 0.58, 0.57, 0.51, 1.43 U/mg for F. hepatica, F. gigantica, healthy liver and infected liver respectively. Gel electrophoresis of Fasciola spp. and sheep liver tissue extracts revealed a band protein with MW of 60 kDa. The statistical analysis revealed significant difference between SOD activities of Fasciola species and also between SOD activity of liver tissues (P<.05).

CONCLUSION

Fasciola species and liver infection are effective causes on SOD enzyme activity level.

Molecular characterization and expression analysis of extracellular copper-zinc superoxide dismutase gene from swimming crab Portunus trituberculatus

An extracellular CuZnSOD cDNA was cloned from the haemocytes of swimming crab Portunus trituberculatus by a reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA end (RACE) method. Analysis of the nucleotide sequence revealed that the ecCuZnSOD full-length cDNA consisted of 965 bp with an open reading frame of 579 bp. It encoded a polypeptide of 192 amino acids which had a predicted molecular weight of 20.0 kDa and with an estimated pI of 6.23. The deduced amino acid sequence contained a putative signal peptide of 31 amino acids. It is predicted to possess all the expected features of CuZnSOD members, including amino acids responsible for binding Cu and Zn, two putative CuZnSOD signatures, two cysteines and one N-linked glycosylation site. Sequence comparison showed that the CuZnSOD deduced amino acid sequence of P. trituberculatus has similarity of 80%, 76%, 55% and 50% to that of blue crab Callinectes sapidus, mud crab Scylla serrata, crayfish Pacifastacus leniusculus and freshwater prawn Macrobrachium rosenbergii, respectively. The ecCuZnSOD transcripts expressed in all examined tissues, including haemocytes, hepatopancreas, heart, stomach, intestine, gill, ovary and muscle. RT-PCR analysis indicated that ecCuZnSOD transcripts both in haemocytes and hepatopancreas increased in the first 3 h after Vibrio alginolyticus challenging, as the bacterial infection progressed, the challenged crabs decreased to levels significantly lower than control by 96 h post-infection. These facts indicated that ecCuZnSOD was potentially involved in the acute response against invading bacteria in P. trituberculatus.

Anti-schistosomal intervention targets identified by lifecycle transcriptomic analyses

Background

Novel methods to identify anthelmintic drug and vaccine targets are urgently needed, especially for those parasite species currently being controlled by singular, often limited strategies. A clearer understanding of the transcriptional components underpinning helminth development will enable identification of exploitable molecules essential for successful parasite/host interactions. Towards this end, we present a combinatorial, bioinformatics-led approach, employing both statistical and network analyses of transcriptomic data, for identifying new immunoprophylactic and therapeutic lead targets to combat schistosomiasis.

Methodology/Principal Findings

Utilisation of a Schistosoma mansoni oligonucleotide DNA microarray consisting of 37,632 elements enabled gene expression profiling from 15 distinct parasite lifecycle stages, spanning three unique ecological niches. Statistical approaches of data analysis revealed differential expression of 973 gene products that minimally describe the three major characteristics of schistosome development: asexual processes within intermediate snail hosts, sexual maturation within definitive vertebrate hosts and sexual dimorphism amongst adult male and female worms. Furthermore, we identified a group of 338 constitutively expressed schistosome gene products (including 41 transcripts sharing no sequence similarity outside the Platyhelminthes), which are likely to be essential for schistosome lifecycle progression. While highly informative, statistics-led bioinformatics mining of the transcriptional dataset has limitations, including the inability to identify higher order relationships between differentially expressed transcripts and lifecycle stages. Network analysis, coupled to Gene Ontology enrichment investigations, facilitated a re-examination of the dataset and identified 387 clusters (containing 12,132 gene products) displaying novel examples of developmentally regulated classes (including 294 schistosomula and/or adult transcripts with no known sequence similarity outside the Platyhelminthes), which were undetectable by the statistical comparisons.

Conclusions/Significance

Collectively, statistical and network-based exploratory analyses of transcriptomic datasets have led to a thorough characterisation of schistosome development. Information obtained from these experiments highlighted key transcriptional programs associated with lifecycle progression and identified numerous anti-schistosomal candidate molecules including G-protein coupled receptors, tetraspanins, Dyp-type peroxidases, fucosyltransferases, leishmanolysins and the netrin/netrin receptor complex.

Despite the implementation of focused and well-funded chemotherapeutic control initiatives over the last decade, schistosomiasis remains a significant cause of morbidity and mortality within countries of the developing world. There is, therefore, an urgent need for the rapid translation of genomic information into viable vaccines or new drug classes capable of eradicating the parasitic schistosome worms responsible for this neglected tropical disease. In our effort to identify potential targets for novel chemotherapeutic and immunoprophylactic interventions, we detail a combined bioinformatics approach, comprising exploratory statistical and network analyses, to thoroughly describe the transcriptional progression of Schistosoma mansoni across three environmental niches. Our results indicate that, although schistosomes are masters at host deception and survival, there are numerous exploitable candidate molecules displaying either differential or constitutive expression throughout the parasite's lifecycle. Importantly, some of these transcripts represent gene families not commonly found outside—or expanded within—the phylum Platyhelminthes, and thus represent priority targets. Many of the candidates identified herein will be subjected to ongoing and future hypothesis-led functional investigations. The completion of such specific examinations ultimately will contribute to the successful development of novel control strategies useful in the alleviation of schistosome-induced immunopathologies, morbidities and mortalities.

Enzymatic antioxidant systems in helminth parasites

Parasitic helminths have a coexistence with mammalian hosts whereby they survive for several years in known hostile conditions of their hosts. Many explanations exist describing how these parasitic helminths are able to survive. In the last years, a lot of studies have focused on both enzymatic and non-enzymatic antioxidant systems now shown to exist in these parasites and which may serve as defence tactics against the host-generated oxygen radicals. The relevance of antioxidant enzymes is confirmed by the fact that some of these molecules represent putative protective anti-parasite vaccines (i.e. in schistosomiasis). This review tries to compile what is known to date of the enzymatic antioxidant systems in selected parasitic helminths.

Molecular characterization of two superoxide dismutases from Hydra vulgaris

Apparent full-length cDNA sequences coding for manganese superoxide dismutase (HvMnSOD) and extracellular superoxide dismutase (HvEC-SOD) were isolated from Hydra vulgaris in order to understand their expression and 3D structures; and explore their possibility of being used as for biomarkers for environmental stress and toxicity. The deduced HvMnSOD protein consists of 219 amino acids of which first 21 amino acids constitute a presumed mitochondria-targeting signal peptide whereas HvEC-SOD protein consists of 189 amino acids of which first 19 amino acids constitute a presumed signal peptide. Molecular model generated for HvMnSOD displayed the N-terminal long alpha antiparallel hairpin and the C-terminal mixed alpha/beta fold characteristic of MnSODs and that for HvEC-SOD displayed the characteristic CuZnSOD â-barrel fold. Hydrae subjected to thermal, starvation, metal and oxidative stress responded by regulating MnSOD and EC-SOD mRNA transcription. These results indicated that these genes are involved in the cellular stress response and (anti)oxidative processes triggered by stressor and contaminant exposure. Hence the expression of these SODs in hydra may have potential as molecular biomarkers for assessing stress, toxicity and pro-oxidant quality of chemicals and aquatic environmental quality.

Sativa seeds against Schistosoma mansoni different stages

The schistosomicidal properties of Nigella sativa seeds were tested in vitro against Schistosoma mansoni miracidia, cercariae, and adult worms. Results indicate its strong biocidal effects against all stages of the parasite and also showed an inhibitory effect on egg-laying of adult female worms. In the present work we also studied the effects of crushed seeds on some antioxidant enzymes; which have a role in protection of adult worms against host oxidant killing; as well as some enzymes of glucose metabolism; which have a crucial role in the survival of adult worms inside their hosts. The data revealed that the used drug induce an oxidative stress against adult worms which indicated by a decrease in the activities of both antioxidant enzymes, superoxide dismutase, glutathione peroxidase, and glutathione reductase and enzymes of glucose metabolism, hexokinase and glucose-6-phosphate dehydrogenase. Disturbing of such enzymes of adult worms using N. sativa seeds could in turn render the parasite vulnerable to damage by the host and may play a role in the antischistosomal potency of the used drug.

Isolation and analysis of partial cDNA sequence coding for superoxide dismutase in Wuchereria bancrofti

Molecular characterization of Wuchereria bancrofti is essential to develop suitable anti-filarial drugs and vaccines. We describe here isolation, sequence analysis and cloning of a partial cDNA of an enzyme superoxide dismutase from this parasite. The immunoscreening of a lambda zap W. bancrofti microfilarial (Mf) cDNA library with microfilaremic sera had resulted in the isolation of several seroreactive clones including, WbSOD. This clone contained a 309 bp insert and showed significant nucleotide and deduced amino acid sequence homologies to the superoxide dismutases of other nematode parasites. The antioxidant property of this enzyme may have important contribution in the defense mechanism of the parasite against host immune response.

An oligonucleotide microarray for transcriptome analysis of Schistosoma mansoni and its application/use to investigate gender-associated gene expression

Global profiling transcriptomes of parasitic helminths offers the potential to simultaneously identify co-ordinately expressed genes, novel genetic programs and uniquely utilized metabolic pathways, which together provide an extensive and new resource for vaccine and drug discovery. We have exploited this post-genomic approach to fabricate the first oligonucleotide DNA microarray for gene expression analysis of the parasitic trematode Schistosoma mansoni. A total of 17,329 S. mansoni DNA sequences were used to design a microarray consisting of 7335 parasite elements or approximately 50% of this parasite's transcriptome. Here, we describe the design of this new microarray resource and its evaluation by extending studies into gender-associated gene expression in adult schistosomes. We demonstrate a high degree of reproducibility in detecting transcriptional differences among biologically replicated experiments and the ability of the microarray to distinguish between the expression of closely related gene family members. Importantly, for issues related to sexual dimorphism, labour division, gamete production and drug target discovery, 197 transcripts demonstrated a gender-biased pattern of gene expression in the adult schistosome, greatly extending the number of sex-associated genes. These data demonstrate the power of this new resource to facilitate a greater understanding into the biological complexities of schistosome development and maturation useful for identifying novel intervention strategies.

MOLECULAR CLONING AND CHARACTERIZATION OF COPPER/ZINC-SUPEROXIDE DISMUTASE OF PARAGONIMUS WESTERMANI

Superoxide dismutases (SODs; EC 1.15.1.1) play important roles in the protection of the parasites against cellular oxygen-mediated killing of the hosts. A copper/zinc-containing SOD (Cu/Zn-SOD) was identified previously from lung fluke, Paragonimus westermani. To expand our understanding of P. westermani SOD, we isolated a complementary DNA encoding a Cu/Zn-SOD, expressed the active enzyme in Escherichia coli, and characterized its biochemical properties. The deduced amino acid (aa) sequence of the gene shared up to 73.7% identities with Cu/Zn-SODs of other helminths and shared well-conserved characteristic motifs and essential aa residues involved in coordinating copper and zinc enzymatic functions. Recombinant Cu/ Zn-SOD exhibited comparable biochemical properties with that of the native enzyme, including pH optima and potassium cyanide-and hydrogen peroxide-sensitive inhibition profiles. The active enzyme consisted of 2 identical subunits covalently linked by disulfide bonds. The enzyme was constitutively expressed throughout various developmental stages of the parasite. The levels increased as P. westermani matured and plateaued in adult stage. Our result suggests the enzyme might play an important role for parasites to survive in the hosts through its superoxide anion-detoxifying function.

Molecular cloning and characterization of the copper/zinc and manganese superoxide dismutase genes from the human parasiteClonorchis sinensis

A copper/zinc superoxide dismutase (Cu/ZnSOD) gene and a manganese superoxide dismutase (MnSOD) gene of the human parasiteClonorchis sinensishave been cloned and their gene products functionally characterized. GenesCu/ZnSODandMnSODencode proteins of 16 kDa and 25·4 kDa, respectively. The deduced amino acid sequences of the two genes contained highly conserved residues required for activity and secondary structure formation of Cu/ZnSOD and MnSOD, respectively, and show up to 73·7% and 75·4% identities with their counterparts in other animals. The genomic DNA sequence analysis of Cu/ZnSOD gene revealed this as an intronless gene. Inhibitor studies with purified recombinant Cu/ZnSOD and MnSOD, both of which were functionally expressed inEscherichia coli, confirmed that they are copper/zinc and manganese-containing SOD, respectively. Immunoblots showed that bothC. sinensisCu/ZnSOD and MnSOD should be antigenic for humans, and both, especially theC. sinensisMnSOD, exhibit extensive cross-reactions with sera of patients infected by other trematodes or cestodes. RT-PCR and SOD activity staining of parasite lysates indicate that there are no significant differences in mRNA level or SOD activity for both species of SOD, indicating cytosolic Cu/ZnSOD and MnSOD might play a comparatively important role in theC. sinensisantioxidant system.

Nucleic acid vaccination with Schistosoma mansoni antioxidant enzyme cytosolic superoxide dismutase and the structural protein filamin confers protection against the adult worm stage

Schistosomiasis remains a worldwide endemic cause of chronic and debilitating illness. There are two paradigms that exist in schistosome immunology. The first is that the schistosomule stages are the most susceptible to immune killing, and the second is that the adult stage, through evolution of defense mechanisms, can survive in the hostile host environment. One mechanism that seems to aid the adult worm in evading immune killing is the expression of antioxidant enzymes to neutralize the effects of reactive oxygen and nitrogen species. Here, we challenge one paradigm by targeting adult Schistosoma mansoni worms for immune elimination in an experimental mouse model using two S. mansoni antioxidants, cytosolic superoxide dismutase (SmCT-SOD) and glutathione peroxidase (SmGPX), and a partial coding sequence for a structural protein, filamin, as DNA vaccine candidates. DNA vaccination with SmCT-SOD induced a mean of 39% protection, filamin induced a mean of 50% protection, and SmGPX induced no protection compared to controls following challenge with adult worms by surgical transfer. B- and T-cell responses were analyzed in an attempt to define the protective immune mechanism(s) involved in adult worm killing. SmCT-SOD-immunized mice presented with a T1 response, and filamin-immunized mice showed a mixed T1-T2 response. We provide evidence for natural boosting after vaccination. Our results demonstrate that adult worms can be targeted for immune elimination through vaccination. This represents an advance in schistosome vaccinology and allows for the development of a therapeutic as well as a prophylactic vaccine.

Molecular characterization of two CuZn-superoxide dismutases in a sea anemone

Cnidarians living in symbiosis with photosynthetic cells--called zooxanthellae--are submitted to high oxygen levels generated by photosynthesis. To cope with this hyperoxic state, symbiotic cnidarians present a high diversity of superoxide dismutases (SOD) isoforms. To understand better the mechanism of resistance of cnidarian hosts to hyperoxia, we studied copper- and zinc-containing SOD (CuZnSOD) from Anemonia viridis, a temperate symbiotic sea anemone. We cloned two CuZnSOD genes that we call AvCuZnSODa and AvCuZnSODb. Their molecular analysis suggests that the AvCuZnSODa transcript encodes an extracellular form of CuZnSOD, whereas the AvCuZnSODb transcript encodes an intracellular form. Using in situ hybridization, we showed that both AvCuZnSODa and AvCuZnSODb transcripts are expressed in the endodermal and ectodermal cells of the sea anemone, but not in the zooxanthellae. The genomic flanking sequences of AvCuZnSODa and AvCuZnSODb revealed different putative binding sites for transcription factors, suggesting different modes of regulation for the two genes. This study represents a first step in the understanding of the molecular mechanisms of host animal resistance to permanent hyperoxia status resulting from the photosynthetic symbiosis. Moreover, AvCuZnSODa and AvCuZnSODb are the first SODs cloned from a diploblastic animal, contributing to the evolutionary understanding of SODs.

Gender-associated gene expression in two related strains of Schistosoma japonicum

Host inflammatory responses directed against eggs laid by sexually-mature Schistosoma japonicum female worms instigate lesion formation and associated clinical pathologies during infection. To identify parasite gene transcripts that associate with egg production and to characterise sexually-mature adult gene expression profiles of two related Chinese strains, S. japonicum cDNA microarrays were fabricated using 457 ESTs originating from three parasite developmental stages. Twenty-two female-associated and 8 male-associated gene transcripts were identified in the adult Anhui strain whereas 21 female-associated and 7 male-associated gene transcripts were revealed in the adult Zhejiang strain. RT-PCR analysis, in situ enzyme localisation studies and enzymatic assays confirmed the cDNA microarray results, and importantly, provided information previously unappreciated in schistosome conjugal biology. Specifically, our novel findings include the female-specific expression of genes putatively involved in haemoglobin digestion and eggshell formation including extracellular superoxide dismutase, two histidine-rich proteins, a large blood-brain barrier amino acid transporter and two tyrosinase orthologues. In contrast, transcripts involved in mechanical support (actin), cytoskeletal infrastructure (e.g. dynein light chain 3 and myosin regulatory light chain) and tegumental biology (e.g. TM4SF and Sj25) were more highly represented in adult male schistosomes. Together these data establish a transcriptional basis for adult schistosome labour division and expands the list of novel S. japonicum gender-associated gene transcripts that may be considered targets for improved intervention strategies.

Protection against Schistosoma mansoni utilizing DNA vaccination with genes encoding Cu/Zn cytosolic superoxide dismutase, signal peptide-containing superoxide dismutase and glutathione peroxidase enzymes

Protection against Schistosoma mansoni infection in C57BL/6 female mice was evaluated by two DNA vaccination strategies. Mice were either vaccinated by intramuscular injection with pcDNAI/Amp constructs encoding either Cu/Zn cytosolic superoxide dismutase (CT-SOD), signal peptide-containing SOD (SP-SOD), glutathione peroxidase (GPX(bb)) or a mutated form of GPX (GPX(m)), or primed with naked DNA constructs and boosted with recombinant vaccinia virus (RVV) containing the same genes. Animals were then challenged with S. mansoni and the level of protection was assessed as the reduction in worm burden. CT-SOD showed significant levels of protection compared to the control group, ranging between 44 and 60%, while SP-SOD exhibited from 22 to 45%. GPX(bb) showed levels of protection (23-55%) higher than GPX(m) (25-34%). The prime-boost strategy gave the same results as naked DNA or recombinant vaccinia virus alone except in the case of GPX, where the protection was 85%.

Molecular cloning and expression of Cu/Zn-containing superoxide dismutase from Fasciola hepatica

The cytosolic superoxide dismutase (SOD) of Fasciola hepatica, a causative agent of fascioliasis, was purified and characterized. The enzyme consists of two identical subunits, each with an apparent molecular mass of 17.5 kDa. An analysis of the enzyme's primary structure and inhibition studies revealed that the enzyme is a copper/zinc-containing SOD (Cu/Zn-SOD). The enzyme activity was relatively stable in a broad pH range, from pH 7.0 to 10.0, and the enzyme showed maximum activity at pH 7.5. This enzyme also displayed strong antigenicity against sera of bovine and human subjects with fascioliasis. The SOD gene fragment was amplified by PCR with degenerate oligonucleotide primers derived from amino acid sequences conserved in the Cu/Zn-SODs of other organisms. An F. hepatica cDNA library was screened with the SOD gene fragment as a probe. As a result, a complete gene encoding the Cu/Zn-SOD was identified, and its nucleotide sequence was determined. The gene had an open reading frame of 438 bp and 146 deduced amino acids. Comparison of the deduced amino acid sequence of the enzyme with previously reported Cu/Zn-SOD amino acid sequences revealed considerably high homologies. The coding region of the F. hepatica Cu/Zn-SOD was cloned and expressed in Escherichia coli. Staining of native polyacrylamide gel for SOD activity of the expressed protein revealed SOD activity that was inactivated by potassium cyanide and hydrogen peroxide but not by sodium azide. This means that the presence of the recombinant fusion protein is indicative of Cu/Zn-SOD. The expressed protein also reacted with sera of bovine and human subjects with fascioliasis, but it did not react with sera of uninfected bovine and human subjects.

Effect of Fasciola gigantica somatic extracts and excretory/secretory products on superoxide production by activated neutrophils

Somatic extracts and excretory/secretory (ES) products from Fasciola gigantica suppress the release of toxic oxygen intermediates by activated sheep neutrophils. At the concentrations used both the somatic extracts and ES products had no effect on neutrophil viability and in both cases the inhibitory effect was reversible. In the somatic extracts, heating or treatment with trypsin destroyed the inhibitory effect. However, the ES products contained at least two immunomodulatory factors. One was less than 10 kDa, the other greater than 50 kDa and both factors were heat and trypsin stable. By acting locally and only causing temporary inhibition of neutrophil function F. gigantica can protect itself from immune mediated oxidative damage without compromising the host's response elsewhere.

Copper-zinc superoxide dismutase from the marine yeast Debaryomyces hansenii

We have isolated the cytosolic form of Cu-Zn superoxide dismutase (SOD) from the marine yeast Debaryomyces hansenii. This enzyme has a subunit mass of 18 kDa. The preparation was found to be heterogeneous by IF electrophoresis with two pI ranges: 5.14-4.0 and 1.6-1.8. The enzyme preparation had a remarkably strong stability at pH 6.0-7.0, surviving boiling for 10 min without losing more than 60% of activity. On Western blots, this enzyme was recognized by antibodies raised in rabbits against D. hansenii extracts, while only a weak cross-reaction could be detected using antibodies generated against either Saccharomyces cerevisiae or bovine erythrocyte Cu-Zn SODs. In sequencing analysis, a peptide obtained by trypsin digestion was found to have 85% identity to the S. cerevisiae Cu-Zn SOD.

Do Antioxidants Play a Role in Schistosome Host–Parasite Interactions?

Schistosoma mansoni, an intravascular parasite, lives in a hostile environment in close contact with host humoral and cellular cytotoxic factors. To establish itself in the host, the schistosome has evolved a number of immune evasion mechanisms. Here, Philip LoVerde discusses evidence suggesting that antioxidant enzymes provide one such mechanism used by adult schistosomes. Antioxidant enzymes may thus represent a target for immune elimination of adult worms.

Schistosoma mansoni: the developmental regulation and immunolocalization of antioxidant enzymes

Antioxidant enzymes from S. mansoni, cytosolic Cu-Zn superoxide dismutase (CT-SOD), signal-peptide-containing SOD (SP-SOD), glutathione peroxidase (GPX), and glutathione transferase (GST) were compared for their relative levels of transcript expression throughout development in a semiquantitative reverse transcriptase-polymerase chain reaction assay. All of the antioxidant enzymes exhibited a similar pattern of developmental regulation. Adult worms have the highest level of specific mRNA compared with larval stages. GST shows the highest level of expression, being approximately 10-fold more abundant than CT-SOD and SP-SOD and 100-fold more abundant than GPX. This order of expression was nearly consistent for all the developmental stages studied. To localize the antioxidant enzymes, immunofluorescence staining was performed on 3-hr schistosomula and adult worms. GPX, SP-SOD, and CT-SOD were all found to be associated with the adult tegument and gut epithelium. SP-SOD was also associated with organelle and cell membranes of parenchymal cells and interestingly with the spines of adult worms. Schistosomula, on the other hand, showed little immunofluorescence. These studies further demonstrate the developmental regulation of antioxidant enzymes and localize them to the host-parasite interface, supporting the notion that they have a role in allowing adult worms to evade immune attack.

Expression and characterization of glutathione peroxidase activity in the human blood fluke Schistosoma mansoni

Antioxidants may play an important role in immune evasion by schistosome parasites. Previous studies have focused on the roles of superoxide dismutase and glutathione S-transferase. In the present study, glutathione peroxidase (GPX) activity was measured in different fractions of worm extracts from several developmental stages of Schistosoma mansoni. The enzyme activity was shown to be developmentally regulated, with higher specific activities being found in the tegument-enriched Nonidet P-40 extract of adult worms (the stage least susceptible to immune killing) than in the larval stages (which are most susceptible to immune elimination). In all extracts tested, the activity against cumene hydroperoxide, even when glutathione S-transferase activity was removed, was higher than that for hydrogen peroxide. The expression of GPX cDNA in pGEX-2T by bacteria produced a 50-kDa fusion protein and a 32-kDa truncated protein. The latter was due to termination at the internal UGA codon that codes for selenocysteine. GPX activity was detected in the recombinantly produced GPX but not with Sj26-glutathione S-transferase from the vector. Mutating the TGA codon to TGT produced a full-length product, GPXm (19 kDa), that was used to produce 19 monoclonal antibodies. Anti-GPXm monoclonal antibodies recognized a 19-kDa molecule in adult-worm extract which, upon removal by immunoprecipitation, resulted in the loss of over 90% of the GPX activity, suggesting that a single form of GPX exists in the schistosome.

Chromatographic and electrophoretic methods for analysis of superoxide dismutases

A brief overview of the family of superoxide dismutase (SOD) enzymes and their biomedical significance is presented. Methodology for the purification and electrophoretic analysis of superoxide dismutases is reviewed and discussed, with emphasis on the specific problems raised by the separation of individual superoxide dismutase isoenzymes. Purification methods and their performance, as reported in the literature are summarised in table form. Generally used methods for measuring SOD activity in vitro and SOD visualisation after electrophoresis are outlined, particularly those relevant to the monitoring of progress of SOD purification.

How schistosomes profit from the stress responses they elicit in their hosts

Results obtained with the model Trichobilharzia ocellata-Lymnaea stagnalis have confirmed the hypothesis that the physiological effects evoked by schistosomes in their snail host--castration and giant growth--are brought about by them interfering with the neuroendocrine systems (NES) regulating the physiological processes concerned. As soon as differentiating cercariae are present in the daughter sporocysts a factor can be detected in the haemolymph of the snail host, called schistosomin, which acts both at the central and the peripheral parts of the NES involved in regulation of reproduction and growth. Schistosomin appears to be a host-derived factor, which is probably released by cells of the internal defence system, the haemocytes, and by connective tissue cells, the telo-glial cells. It meets the criteria of having a cytokine-like function although its molecular structure does not show sequence homology with any of the vertebrate-type cytokines identified to date. Its cytokine nature explains why schistosomin can interfere with different neuroendocrine regulatory systems both at the central and peripheral--target--level, namely after binding to its own receptor. Schistosomin is probably not only responsible for the effects exerted by the parasite on female reproduction but also for those on male reproduction and on growth so that energy and space become available for the continuous production of cercariae. The nature of the humoral cercarial factor, which induces schistosomin release, is as yet unknown. Based on its hydrophobic character and on the fact that it can pass through the wall of the daughter sporocyst, it is supposed to be a diffusible molecule or a protonephridial excretion product. It does not seem to be a vertebrate-type steroid, an ecdysteroid or an eicosanoid. Results obtained in vitro have indicated that schistosomin might have a suppressive effect on haemocyte activity. Plasma from snails 5-6 weeks post-exposure showed a tendency to inhibit phagocytic activity of haemocytes from non-infected snails, that is preparatory to the escape and migration of cercariae. Once shedding has started this effect of schistosomin is overrruled by a strong activation of haemocyte activity coinciding with the tissue damage that the cercariae cause in the host. The cercariae escape from being attacked by masking their surface coat with host molecules. As the physiological effects caused by schistosomes resemble those observed during stress in mammals, experiments were carried out to find out whether schistosomin is also released in non-parasitized snails during stress resulting in an inhibiting effect on reproduction.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular variation in the human schistosomes

It is now recognised that intraspecific variation is widespread in the human schistosome species. This review evaluates recent advances in the detection and characterisation of variants within the human schistosomes and the implications of this variation in terms of infectivity and development in intermediate and definitive hosts, drug responsiveness, pathogenicity and immunogenicity. It also examines advances in the methods used to detect variation and highlights the use of genetic approaches, notably enzyme electrophoresis and, especially, the recent application of DNA methods. Molecular techniques, such as restriction fragment length polymorphism (RFLP) analysis, polymerase chain reaction (PCR) and DNA sequencing are now proving invaluable for distinguishing species and strains of schistosomes and recent progress in this remarkably dynamic area is emphasised.

Immunity to helminths: Ready to tip the biochemical balance?

Using data from recent laboratory and field studies, Peter Brophy and David Pritchard here summarize our current understanding of the approximate sequence of events leading to protective immune responses against some chronic parasitic helminth infections.

Schistosoma mansoni: cloning of a complementary DNA encoding a cytosolic Cu/Zn superoxide dismutase and high-yield expression of the enzymatically active gene product in Escherichia coli

We recently purified a 16-kDa cytosolic Cu/Zn superoxide dismutase (CT Cu/Zn-SOD) from Schistosoma mansoni, a human parasite. Three peptide sequences were obtained, one from the unblocked N-terminal and two from internal peptides which were generated by digestions with trypsin and cyanogen bromide. These sequences were aligned to the corresponding sequences of 19 cytosolic Cu/Zn-SODs from various species. Degenerate oligonucleotides were then designed according to the sequence and the position of each peptide. The oligonucleotides were used to amplify a complete cDNA using the polymerase chain reaction with either adult schistosome total RNA or a cercariae lambda gt11 phage cDNA library as the template. The protein encoded by the cDNA has 153 amino acids with a calculated molecular weight of 15,693. It also has 60-65% homology to 19 cytosolic Cu/Zn-SOD from various species. All of the copper/zinc binding sites and SOD activity sites are conserved. Computer analysis predicts that the Cu/Zn-SOD has a pI value of 6.6, which is very close to the experimental results of IEF analysis (6.0 and 6.3). The entire coding sequence from the cDNA was cloned into a bacterial alkaline phosphatase cytosolic expression vector and a large amount of soluble product was expressed and purified to homogeneity. We compared the bacterially expressed Cu/Zn-SOD with the native enzyme derived from schistosomes and found that they are identical by the following criteria: (1) They focus at the same positions on IEF gels; (2) they form dimers in solution as measured by gel filtration; (3) they have the same unblocked N-terminal sequence; (4) they both are enzymatically active with comparable specific activities. The specific activity of the bacterially derived enzyme was increased somewhat (approximately 10%) by incubation with copper and zinc ions.