Depression of hydrogen peroxide dependent killing of schistosomula in vitro by peritoneal exudate cells from Schistosoma mansoni infected mice

Thiazinoquinones as New Promising Multistage Schistosomicidal Compounds Impacting Schistosoma mansoni and Egg Viability

Schistosomiasis is the most significant neglected tropical parasitic disease caused by helminths in terms of morbidity and mortality caused by helminths. In this work, we present the antischistosomal activity against Schistosoma mansoni of a rationally selected small set of thiazinoquinone derivatives, some of which were previously found to be active against Plasmodium falciparum and others synthesized ad hoc. The effects on larvae, juvenile, and adult parasite viability as well as on egg production and development were investigated, resulting in the identification of new multistage antischistosomal hit compounds. The most promising compounds 6, 8, 13, and 14 with a LC₅₀ value on schistosomula from ∼5 to ∼15 μM also induced complete death of juvenile (28 days old) and adult worm pairs (7 weeks old) and a detrimental effect on egg production and development in vitro. Structure-activity relationships (SARs) were analyzed by means of computational studies leading to the hypothesis of a redox-based mechanism of action with a one-electron reduction bioactivation step and the subsequent formation of a toxic semiquinone species, similarly to what was previously observed for the antiplasmodial activity. Our results also evidenced that the selective toxicity against mammalian cells or parasites as well as specific developmental stages of a parasite can be addressed by varying the nature of the introduced substituents.

Comparative analysis of transcriptional profiles of Schistosoma japonicum adult worms derived from primary-infected and re-infected water buffaloes

BACKGROUND

Schistosoma japonicum (S. japonicum) is an important zoonotic parasite that is prevalent in China and parts of Southeast Asia. Water buffaloes are an important reservoir and the main transmission sources of S. japonicum. However, self-curing and resistance to re-infection have been observed in water buffaloes.

RESULTS

In this study, we compared the morphometry and differences in transcriptional expression of adult S. japonicum worms recovered from primary-infected and re-infected water buffaloes using Illumina RNA-sequencing (RNA-Seq) technology. Results of morphometry analysis revealed that adult S. japonicum worms recovered from re-infected water buffaloes were runtish with smaller organs. The ventral length of male worms was shorter in re-infected buffaloes (328 ± 13 vs 273 ± 8 µm, P < 0.05), and in female worms the oral sucker length (44 ± 3 vs 33 ± 5 µm, P < 0.05), ovary length (578 ± 23 vs 297 ± 27 µm, P < 0.05) and width (150 ± 8 vs 104 ± 9 µm, P < 0.05) were shorter, with fewer eggs in the uteri (41 ± 2 vs 12 ± 1, P < 0.05). Of 13,605 identified genes, 112 were differentially expressed, including 51 upregulated and 61 downregulated genes, in worms from re-infected compared with primary-infected water buffaloes. Gene ontology (GO) enrichment analysis revealed that GO terms such as "oxidation-reduction process", "calcium-dependent phospholipid binding", "lipid binding" and "calcium ion binding" were significantly enriched in downregulated genes, whereas GO terms related to metabolism and biosynthesis were significantly enriched in upregulated genes. The results revealed that the downregulation of some important genes might contribute to a reduction in worm numbers and maldevelopment of surviving worms in re-infected water buffaloes. Furthermore, upregulation of genes related to metabolic processes and biosynthesis might be a compensatory mechanism of worms in disadvantageous environments.

CONCLUSIONS

To our knowledge, our results present the first large-scale transcriptional expression study identifying the differences between adult S. japonicum worms from primary-infected and re-infected water buffaloes, and particularly emphasize differential expression that may affect the survival and growth of worms in re-infected water buffalo. This will provide new insight into screening for anti-schistosome targets and vaccine candidates.

Sexual Preferences in Nutrient Utilization Regulate Oxygen Consumption and Reactive Oxygen Species Generation in Schistosoma mansoni: Potential Implications for Parasite Redox Biology

Schistosoma mansoni, one of the causative agents of human schistosomiasis, has a unique antioxidant network that is key to parasite survival and a valuable chemotherapeutic target. The ability to detoxify and tolerate reactive oxygen species increases along S. mansoni development in the vertebrate host, suggesting that adult parasites are more exposed to redox challenges than young stages. Indeed, adult parasites are exposed to multiple redox insults generated from blood digestion, activated immune cells, and, potentially, from their own parasitic aerobic metabolism. However, it remains unknown how reactive oxygen species are produced by S. mansoni metabolism, as well as their biological effects on adult worms. Here, we assessed the contribution of nutrients and parasite gender to oxygen utilization pathways, and reactive oxygen species generation in whole unpaired adult S. mansoni worms. We also determined the susceptibilities of both parasite sexes to a pro-oxidant challenge. We observed that glutamine and serum importantly contribute to both respiratory and non-respiratory oxygen utilization in adult worms, but with different proportions among parasite sexes. Analyses of oxygen utilization pathways revealed that respiratory rates were high in male worms, which contrast with high non-respiratory rates in females, regardless nutritional sources. Interestingly, mitochondrial complex I-III activity was higher than complex IV specifically in females. We also observed sexual preferences in substrate utilization to sustain hydrogen peroxide production towards glucose in females, and glutamine in male worms. Despite strikingly high oxidant levels and hydrogen peroxide production rates, female worms were more resistant to a pro-oxidant challenge than male parasites. The data presented here indicate that sexual preferences in nutrient metabolism in adult S. mansoni worms regulate oxygen utilization and reactive oxygen species production, which may differently contribute to redox biology among parasite sexes.

Gnathostoma spinigerum: immunodepression in experimental infected mice

Mice were infected with 8- or 25-infective worms of advanced third stage Gnathostoma spinigerum larvae (L3) which were obtained from natural infected eels. On day 14, 60 and 200 post infections (PI), spleen cells of infected mice were tested for lymphoproliferative responses in vitro against the mitogen and specific L3 somatic antigen in order to clarify the cellular immune status of the host upon this nematode infection. Reduced responsiveness to Con A was observed in infected mice. These depressed responses were more pronounced in chronically infected mice (day 200, PI) than in day 14 and day 60, PI. There was no significant difference of lymphoproliferative response between groups of high (25 L3) and low (8 L3)-infective dose in the chronic readily stage. Regarding to the L3 somatic Ag stimulation, the depressed response was obviously detected in high dose and chronic infection. Our results demonstrated that in this G. spinigerum-mouse system T-cell response is defective. The depression could be reversible and was associated with active infection because it was abolished by anthelmintic (ivermectin) treatment. This study shows the involvement of Th-2 response to this nematode in regulating T cell proliferation.

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.

Evidence for the presence of active cytochrome P450 systems in Schistosoma mansoni and Schistosoma haematobium adult worms

Extracts of the adult worms of both Schistosoma mansoni and Schistosoma haematobium can metabolise some typical P450 substrates but to differing degrees. S. mansoni worm extracts displayed a approximately 12-fold higher specific activity for an aminopyrine substrate than rat liver microsomes. At 4 mM substrate concentration the demethylation reaction with N-nitrosodimethylamine (NDMA) (5 nmol HCHO/mg protein/min) was only half that of rat liver microsomes, whereas in extracts of S. haematobium, no detectable activity was found towards NDMA. Using ethylmorphine as substrate the demethylation activity of S. mansoni extracts (1.82 nmol HCHO/mg protein/min) was 5.5-fold lower than that of rat liver microsomes. Benzphetamine demethylase activity was also readily detectable in S. mansoni worm extracts at 6.79 nmol HCHO/mg protein/min compared with 10.20 nmol HCHO/mg protein/min in the case of rat liver microsomes. When aniline was used as substrate, surprisingly, no activity was found in worm extracts of either S. mansoni or S. haematobium, whereas rat liver microsomes showed high activity towards this amine. The anti-P450 2E1 and 2B1/2 cross-reacted with both worm homogenates and gave a specific band corresponding to a protein of molecular weight of approximately 50.0 kDa. A study with anti-P450 IVA antibody revealed that while this protein was strongly expressed in S. haematobium worm extracts, no immunoreactivity was observed with extracts of S. mansoni. Immunoblotting analyses with anti-P450 IIIA and P450 1A1 did not detect immunoreactive protein in either S. mansoni or S. haematobium.

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.

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.

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

Our laboratories previously isolated a putative extracellular or membrane-associated Cu/Zn superoxide dismutase (Cu/Zn-SOD) gene, designated a signal peptide-containing (SP) Cu/Zn-SOD, from Schistosoma mansoni. SOD activity was thus investigated throughout the life cycle of S. mansoni and found in all stages: eggs, miracidia, cercariae, schistosomula, lung-stage worms, and adult worms. The adult worms had the highest SOD activity (53 +/- 9 nitrite units), which was five times higher than that of eggs or miracidia and twice as high as that of 3-h-old mechanically transformed schistosomula. Cu/Zn-SOD constituted over 95% of the total SOD activity found in S. mansoni, compared with that of Mn-SOD. Most of Cu/Zn-SOD specific activity was associated with a detergent-extractable fraction of the parasite. Isoelectric focusing gel electrophoresis analysis revealed that there were four major pI variants of Cu/Zn-SOD present in the adult worms. Only two of these Cu/Zn-SOD pI variants were present in the 3-h-old mechanically transformed schistosomula. Fast protein liquid chromatography gel filtration fractionation of adult parasite extract was carried out to correlate the SP Cu/Zn-SOD with the SOD activity by using anti-SP Cu/Zn-SOD monoclonal antibodies, which separated the immunoreactive gene product and the SOD activity into different fractions. Quantitative tissue fractionation also revealed a discordant distribution of the gene product compared with that of Cu/Zn-SOD activity. These results indicated the existence of another Cu/Zn-SOD(s) in the parasite. Purification of the Cu/Zn-SOD activity from the adult worms showed that it represented the two lower-pI variants found in both adult worms and 3-h-old schistosomula. Peptide sequence analysis of the purified Cu/Zn-SOD confirmed that there is a second form of Cu/Zn-SOD in the parasite.

Identification of a Schistosoma mansoni sporocyst excretory-secretory antioxidant molecule and its effect on superoxide production by Biomphalaria glabrata hemocytes

Excretory-secretory (E-S) products obtained during in vitro Schistosoma mansoni miracidium-to-sporocyst transformation were found to contain a 108-kDa polypeptide capable of scavenging both exogenously produced and M-line Biomphalaria glabrata hemocyte-derived superoxide (O2-) anions. Separation of crude transformation E-S products using HPLC and ion exchange chromatography resulted in the separation of two isoforms of the 108-kDa molecule. Using an in vitro phagocytosis assay, both isoforms were found to be capable of reducing O2- production by phagocytically stimulated M-line B. glabrata hemocytes without cell loss and without a concomitant reduction in phagocytosis. Although parasite antioxidant molecules appear to play a role in the evasion of host oxidative defense systems in several parasite-vertebrate systems, no previous reports of a parasite antioxidant capability against the potential of oxidative killing by invertebrate defense systems has been reported. In conjunction with the previously confirmed production of O2- by B. glabrata hemocytes and reports of reactive oxygen metabolite production by hemocytes from several molluscan species, these results indicate that reactive forms of oxygen and parasite antioxidant systems may play an important role in the determination of compatibility in the trematode-mollusc relationship.

Schistosoma mansoni: levels of antioxidants and resistance to oxidants increase during development

The effects of cell-free generated oxidants on migrating and developing stages of Schistosoma mansoni were investigated and the levels of antioxidant enzymes and of glutathione were determined for each stage. Schistosomula and 2-week-old parasites recovered from the livers of infected mice showed similar susceptibility to killing by added hydrogen peroxide and t-butylhydroperoxide. However, when glucose (0.5 mM)-glucose oxidase (2.5 mU ml-1) and xanthine (0.5 mM) or hypoxanthine (0.5 mM)-xanthine oxidase (5.0 mU ml-1) systems were used to generate hydrogen peroxide and oxygen free-radicals, schistosomula were more susceptible to oxidative killing than the 2-week-old parasites. The 4- and 8-week-old worms were more resistant to oxidants than all of the younger stages. High levels of superoxide dismutase (16.2-24.8 U mg-1 protein) were present in all stages. Catalase was not detected. Glutathione peroxidase activity with cumene hydroperoxide as substrate was not detectable in the schistosomula but the activity was present in the 2-week-old parasites. However, hydrogen peroxide-sensitive glutathione peroxidase activity was present in all the stages with a threefold difference in activity between schistosomula and the adult stages. Glutathione-s-transferase activity was significantly lower in the schistosomula, lung stages, and the 2-week-old parasites than in the older stages. Progressive increases in the levels of glutathione reductase and glutathione were also observed with development. The differences in the levels of antioxidants between different stages of development may partly explain the increase in resistance to oxidant-mediated damage as the parasite develops.