Altered behaviour of carbohydrate-bound molecules and lipids in areas of the tegument of adult Schistosoma mansoni worms damaged by praziquantel

Activation of transient receptor potential channel Sm.(Schistosoma mansoni)TRPMPZQ by PZQ, enhanced Ca++ influx, spastic paralysis, and tegumental disrupture-the deadly cascade in parasitic schistosomes, other trematodes, and cestodes

After almost 50 years of praziquantel (PZQ) research, Park and Marchant (Trends Parasitol 36:182-194, 2020) described the Ca++-permeable transient receptor potential (TRP) channel Sm.TRPMPZQ in Schistosoma mansoni as target of PZQ. Here we describe the deadly cascade in schistosomes which is induced by the (R)-PZQ enantiomer that includes contemporaneous stereoselective activation of Sm.TRPMPZQ-mediated Ca++ influx, disturbed Ca++ homeostasis, Ca++-dependent spastic paralysis, and Ca++- and PZQ-dependent disruption of parasitic teguments. Under normal conditions, there is a reversible balance between bilayer, isotropic, and HII phases in biological membranes (Jouhet 2013). In vitro, we could observe an irreversible but not stereoselective transition to the HII phase in liposomes consisting of phosphatidylethanolamine (PE) and phosphatidylserine (PS), two naturally occurring phospholipids in schistosomes, by the concerted action of Ca++ and PZQ (Harder 2013). HII structures are a prerequisite for induction of fusion processes (Jouhet 2013), which, indeed, become visible as blebs, vacuolation processes, and large balloon-like surface exudates in a large variety of PZQ-sensitive parasitic flukes and cestodes after PZQ treatment. These tegument damages are irreversible. As homologs of Sm.TRPMPZQ are also present in the other trematodes S. japonicum, S. haematobium, or Clonorchis sinensis and cestodes Taenia solium, Echinococcus multilocularis, or Hymenolepis microstoma (Park and Marchant, Trends Parasitol 36:182-194, 2020), it is suggested that a similar deadly cascade will be operating generally in PZQ-sensitive parasites.

Novel therapeutic and prevention approaches for schistosomiasis: review

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

Morphological tegument alterations of adult Schistosoma mansoni, harbored in non anti-helminthic treated, high-immune-tolerogenic and low-inflammatory mice

The present study exhibits original results of S. mansoni tegumental alterations due to contact with the immune system of non anti-helminthic treated mice. We compared, by SEM, the tegument of adult worms recovered from strains of mice genetically selected to extreme phenotypes of resistance (TR strain) and susceptibility (TS strain) to egg-albumin oral tolerance (OT). The parasites recovered from TR mice displayed no morphologic alteration, while specimens collected from TS mice presented tubercle swelling with blunted and shortened spines in lower density, increased sensory organelle numbers, fusion and tegumental ridge peeling. These tegument alterations were similar to those described for Artemether or Praziquantel treatment, supporting observations that the host immune system influences the development and function of the tegument of worms harbored in both anti-helminthic treated and non-treated mice. Our results are indicative that the development and function of the worm tegument depend on the immune regulatory capacity of each individual host.

Use of fluorescent probes as a useful tool to identify resistantSchistosoma mansoniisolates to praziquantel

The use of chemotherapy on a mass scale in endemic areas may lead to the appearance of resistant isolates through the mechanism of selective drug pressure. Studies have demonstrated that praziquantel (PZQ) is able to inhibit the excretory activity and to cause tegumental damage inSchistosoma mansoniadult worms. The use of the probe resorufin to evaluate excretory activity, as well as the probe Hoechst 33258 to detect tegumental damage in adult worms, may represent a method to identify resistant (or less susceptible) isolates. The purpose of the present work was to compare the changes caused by PZQ in the function of the excretory system and in the integrity of the tegument of adult worms from the LE isolate (susceptible to PZQ) and the LE-PZQ isolate (less susceptible to PZQ). Worms from the isolate LE-PZQ showed less severe tegumental lesions, in bothin vitroandin vivoexperiments, detected by labelling with Hoechst 33258 and continued to have a functional excretory system as shown by labelling with resorufinin vitro.

The effects of drugs, ions, and poly-l-lysine on the excretory system of Schistosoma mansoni

We have been able to label the excretory system of cercariae and all forms of schistosomula, immature and adult worms with the highly fluorescent dye resorufin. We have shown that the accumulation of the resorufin into the excretory tubules and collecting ducts of the male adult worm depends on the presence of extracellular calcium and phosphate ions. In the adult male worms, praziquantel (PZQ) prevents this accumulation in RPMI medium and disperses resorufin from tubules which have been prelabelled. Female worms and all other developmental stages are much less affected either by the presence of calcium and phosphate ions, or the disruption caused by PZQ. The male can inhibit the excretory system in paired female. Fluorescent PZQ localises in the posterior gut (intestine) region of the male adult worm, but not in the excretory system, except for the anionic carboxy fluorescein derivative of PZQ, which may be excreted by this route. All stages of the parasite can recover from damage by PZQ treatment in vitro. The excretory system is highly sensitive to damage to the surface membrane and may be involved in vesicle movement and damage repair processes. In vivo the adult parasite does not recover from PZQ treatment, but what is inhibiting recovery is unknown, but likely to be related to immune effector molecules.

Praziquantel binds Schistosoma mansoni adult worm actin

Praziquantel (PZQ) is widely used for the treatment of schistosomiasis. It induces worm muscle contractions and tegumental disruption, followed by exposure of parasite surface membrane antigens to the host immunological defence mechanisms. It may be assumed that PZQ, like cholesterol, is too hydrophobic to traverse the schistosome outer lipid bilayers by passive diffusion and probably requires binding to a surface membrane protein carrier for distribution throughout the worm. However, the PZQ binding site on the schistosome surface and the precise mechanism of action are not yet known. The Claisen condensation reaction was used to bind PZQ on cellulose acetate membranes. Triton-insoluble surface membrane antigens of Schistosoma mansoni adult worms were allowed to bind to the PZQ column. The identity of the bound molecules was examined by amino acid microsequencing and immunogenicity in outbred and inbred mice. The PZQ column was found to bind molecules of 45 kDa selectively from the Triton-insoluble surface membrane antigens of S. mansoni adult worms. Amino acid microsequencing revealed that the 45 kDa species consist predominantly of schistosome actin. This finding was supported by the poor immunogenicity of the 45 kDa molecules in outbred and inbred mice. PZQ was also shown to bind bovine actin but not bovine serum albumin. However, pre-incubation with bovine actin did not impair the effect of PZQ on adult worms in vitro. The study represents an attempt to understand how PZQ distributes across schistosome outer lipid bilayers.

Antibody response in mice infected with Mesocestoides vogae (syn. Mesocestoides corti) tetrathyridia after treatment with praziquantel and liposomised glucan

The therapeutic effect of praziquantel (PZQ) involves synergy with the humoral immune response during helminth infections, which is modulated by parasitic antigens. During experimental murine infections with the larval stage of cestoda Mesocestoides vogae (syn. M. corti), dynamic changes in the IgG and IgM antibody serum levels to both soluble somatic and secretory larval antigens were investigated after administration of PZQ alone and after its co-administration with the immunomodulator (l-->3)-beta-D-glucan entrapped in liposomes (lip.glucan). During the 2 weeks of follow-up after termination of therapy, specific IgG and IgM serum levels to the somatic antigens (enzyme-linked immunosorbent assay test) significantly decreased, whereas concentrations of the antibodies to the secretory antigens moderately increased, both in comparison with the control. Moreover, the number of immunogenic larval antigens (analysed by Western blot) was higher after combined therapy in comparison with single drug administration, which correlated with the intensity of reduction of the larval counts in the liver and peritoneal cavity of mice. Our data showed that administration of PZQ alone and in combination with lip.glucan resulted in marked changes in the dynamics of IgG and IgM antibodies to the somatic larval antigens, which were probably induced by the newly exposed antigens. In this respect, glucan can enhance chemotherapeutic activity of PZQ against larval cestodes by means of stimulation of the macrophage/monocyte effector functions, which seemed to contribute to the more intense larval damage.

Improvement of in vitro efficacy of a novel schistosomicidal drug by incorporation into nanoemulsions

The aim of this article included the development and evaluation of the capacity of nanoemulsions to improve the activity of the novel schistosomicidal drug-2-(butylamino)-1-phenyl-1-ethanethiosulfuric acid (BphEA). BphEA is a compound with a poor solubility in water, which makes its application as a drug difficult. Nanoemulsion formulations presenting anionic (NANOSTOA, NANOST and NANOLP) and cationic (NANOSTE) interfacial charges were prepared to encapsulate BphEA. These formulations were characterized by the encapsulation rate, diameter, and zeta potential. NANOSTOA, NANOST, and NANOLP presented an entrapment efficiency and zeta potential of 18.7+/-1.8% and -33.6+/-1.2 mV; 20.5+/-3.0% and -31.5+/-5.7 mV; as well as 33.8+/-7.2% and -62.6+/-1.3 mV, respectively. NANOSTE presented an entrapment efficiency of 51.8+/-5.0% and a zeta potential of 25.7+/-3.9 mV. The mean droplet size (between 200 and 252 nm) and polydispersity index (between 0.158 and 0.294) were similar for all formulations. The stability study showed no alteration in these formulations' zeta potential and size. The in vitro schistosomicidal activity of BphEA was higher with the use of NANOSTE than with free BphEA. In addition, release studies revealed a good stability of NANOSTE containing BphEA in a biological medium. These results indicate that cationic nanoemulsions can represent an interesting delivery system for the pharmaceutical formulation of BphEA.

Responses of the surface membrane and excretory system of Schistosoma mansoni to damage and to treatment with praziquantel and other biomolecules

Damage to the surface membrane of adult Schistosoma mansoni, and the activity of the excretory system, as shown by resorufin fluorescence, was observed following treatment with praziquantel and incubation with other molecules. Praziquantel treatment induced damage to the surface membrane as measured by the use of a variety of fluorescent compounds. The excretory system of the male worm was inhibited immediately after praziquantel treatment, but fully recovered after culture for 2 h following removal of praziquantel. The excretory system of the female, observed to be minimally active in untreated worm pairs, was often greatly activated in paired females, as shown by intense resorufin labelling, after praziquantel treatment, and this continued during recovery of the male excretory system. In experiments with normal worm pairs, the female could be activated by inhibiting the metabolic rate of the pair by a cooling procedure. The effects on the excretory system of changes in culture conditions (such as changes in pH, concentrations of bacterial lipopolysaccharide, cytokines, reactive oxygen species, compounds which remove cholesterol, such as beta-methyl cyclodextrin, and damaging basic poly-L-lysine) were also assessed. It is concluded that the extensive excretory system of the adult worm is responsive to drug treatment and to certain changes in environmental conditions. Its activity seems to be strongly linked to the integrity of the surface membrane.

Tegumental changes in adult Schistosoma mansoni harbored in mice treated with artemether

A detailed temporal examination was made of alterations induced by artemether in the tegument of adult Schistosoma mansoni worms using scanning electron microscopy (SEM). Mice infected with S. mansoni cercariae 42 days previously were treated intragastrically with artemether at a single dose of 400 mg/kg. Groups of 3 mice were killed at 24 hr, 72 hr, and 7 days after treatment; the worms were collected by perfusion and examined by SEM. Twenty-four hours after artemether treatment, focal damage to the tubercles on the tegumental surface of male worms was seen. In both male and female worms, there was focal swelling and fusion of tegumental ridges, and sometimes peeling. After 72 hr, the damage to the tegument had increased, especially in female worms, with extensive swelling, fusion, and peeling of the tegumental ridges. In the most severely damaged worms, host leukocytes were seen to be adhered to the damaged tegument. Damage to the oral sucker was also occasionally seen in both male and female worms. Seven days after treatment, the appearance of the tegument had returned to normal in some male and female worms, whereas others still showed apparent damage. The results demonstrate that artemether damages the tegument of adult S. mansoni, and the intensity of damage is more severe in female worms than in males.

Genotoxic activity of praziquantel

Praziquantel is a synthetic drug with a remarkable activity against parasites, particularly treamatodes and cestodes. Initial genotoxicity tests used a spectrum of endpoints including tests in bacteria, yeasts, mammalian cells and Drosophila and each one gave negative results. Effects on reproductive cells of mice were negative as well. However, host mediated studies in mice and humans were contradictory and a comutagenic effect with several mutagens and carcinogens was found. Later studies, including monitoring in humans and pigs have shown that Praziquantel induces a greater frequency of hyperploid lymphocytes as well as structural chromosomal aberrations, but not in all the individuals treated. In vitro studies have demonstrated that Praziquantel can induce micronuclei in syrian hamster embryonic (SHE) cells and in lymphocytes of some individuals. The same was found about structural chromosomal aberrations. Fetal death and fetal resorption were found when Praziquantel was administered in high doses to pregnant rats between the 6th and 10th day of gestation. Due to its efficiency as a parasiticide, Praziquantel is in use in Latin-American, Asiatic, African and East-European countries where infections by trematodes and cestodes are frequent. However, the extensive use of Praziquantel in multiple reinfections, in non-infected and non-diagnosed individuals for prevention, in higher doses or repeated doses for cysticercosis treatment and in individuals exposed to environmental mutagens, in conjunction with new findings about its metabolism and genotoxic properties, make it necessary to further evaluate the potential of this drug not only to be mutagenic per se, but to contribute in the development of neoplasm.

Distribution and biophysical properties of fluorescent lipids on the surface of adult Schistosoma mansoni

The properties of 4 fluorescent lipid compounds in the surface membrane of adult male Schistosoma mansoni worms were examined by fluorescent microscopy and fluorescent recovery after photobleaching (FRAP). The data suggest that the probes N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s- indacene-3-pentanoyl) sphingosine (BODIPY FL ceramide) and PKH2 pass through the outer membrane and enter structures in or below the membrane. In contrast 5-(N-octadecanoyl)aminofluorescein (AF18) and N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s- indacene-3-pentanoyl) sphingosylphosphocholine (BODIPY FL sphingomyelin) insert into the outer monolayer. The DL values of these latter 2 compounds, 8:83 +/- 2.35 x 10(-9)cm(2)s(-1) and 2.76 +/- 0.53 x 10(-9)cm(2)s(-1), respectively, suggest that they enter different domains. Furthermore, it was observed that both BODIPY FL ceramide and BODIPY FL sphingomyelin entered particular structures in or under the surface membrane. The possible nature of these particles is discussed.

Praziquantel: An urgent and exciting challenge

The anthelmintic drug praziquantel has proved useful in the treatment of schistosomiasis. The precise mechanism by which praziquantel kills the parasites has yet to be elucidated. Here, John Kusel and colleagues review the current theories on praziquantel action and suggest future avenues for research, which becomes urgent in the light of some reports of drug resistance.