Praziquantel has no direct effect on (Na(+)+K+)-ATPases and (Ca2(+)-Mg2+)ATPases of Schistosoma mansoni

Considering ivermectin for treatment of schistosomiasis

Because of recent reports of praziquantel resistance in schistosome infections, there have been suggestions to employ ivermectin as a possible alternative, especially as its chemical composition is different from that of praziquantel, so cross-resistance is not expected. In order to ascertain possible damage and elimination of worms, we used ivermectin by oral gavage in infected mice, at a high dose (30.1 mg/kg, bordering toxicity). We also tested the efficacy of the drug at various times postinfection (PI), to check on possible effect on young and mature stages of the parasites. Thus, we treated mice on days 21 and 22 or on days 41 and 42 and even on days 21, 22, 41, and 42 PI. None of the treatment regimens resulted in cure rates or signs of lessened pathology in the mice. We also compared the effect of ivermectin to that of artemisone, an artemisinin derivative which had served us in the past as an effective anti-schistosome drug, and there was a stark difference in the artemisone's efficacy compared to that of ivermectin; while ivermectin was not effective, artemisone eliminated most of the worms, prevented egg production and granulomatous inflammatory response. We assume that the reported lack of activity of ivermectin, in comparison with praziquantel and artemisinins, originates from the difference in their mode of action. In wake of our results, we suggest that ivermectin is not a suitable drug for treatment of schistosomiasis.

Calcium and Ca2+/Calmodulin-dependent kinase II as targets for helminth parasite control

In eukaryotes, effective calcium homeostasis is critical for many key biological processes. There is an added level of complexity in parasites, particularly multicellular helminth worms, which modulate calcium levels while inhabiting the host microenvironment. Parasites ensure efficient calcium homeostasis through gene products, such as the calmodulin-dependent kinases (CaMK), the main focus of this review. The importance of CaMK is becoming increasingly apparent from recent functional studies of helminth and protozoan parasites. Investigations on the molecular regulation of calcium and the role of CaMK are important for both supplementing current drug regimens and finding new antiparasitic compounds. Whereas calcium regulators, including CaMK, are well characterised in mammalian systems, knowledge of their functional properties in parasites is increasing but is still in its infancy.

New insight into praziquantel against various developmental stages of schistosomes

Praziquantel, due to high efficacy, excellent tolerability, few and transient side effects, simple administration, and competitive cost, is virtually the only drug of choice for treatment of human schistosomiasis. Treatment of schistosomiasis has shown great advances with the introduction of the drug into the therapeutic arsenal in areas that are endemic for the parasite. However, the drug presents various efficacies against different developmental stages of schistosomes, appearing an oddity intermitted mode. The present review article reviews the effects and mechanism of action of praziquantel against schistosomes briefly and suggests the research on this oddity phenomenon.

Chemotherapy of schistosomiasis: an update

No major changes have occurred during the past 20 years regarding the therapeutic tools available to the clinician for the treatment of schistosomiasis. If anything, the two drugs (oxamniquine and metrifonate) that are valuable alternatives to the drug of choice (praziquantel) have become more difficult to procure in some African countries. Here, Donato Cioli summarizes some of the most recent and interesting laboratory studies on potential antischistosomal compounds, and then reviews recent developments related to the mechanism of action of praziquantel and to the possible emergence of praziquantel-resistant schistosomes.

Ca2+ signalling, voltage-gated Ca2+ channels and praziquantel in flatworm neuromusculature

Transient changes in calcium (Ca2+) levels regulate a wide variety of cellular processes, and cells employ both intracellular and extracellular sources of Ca2+ for signalling. Praziquantel, the drug of choice against schistosomiasis, disrupts Ca2+ homeostasis in adult worms. This review will focus on voltage-gated Ca2+ channels, which regulate levels of intracellular Ca2+ by coupling membrane depolarization to entry of extracellular Ca2+. Ca2+ channels are members of the ion channel superfamily and represent essential components of neurons, muscles and other excitable cells. Ca2+ channels are membrane protein complexes in which the pore-forming alpha1 subunit is modulated by auxiliary subunits such as beta and alpha2delta. Schistosomes express two Ca2+ channel beta subunit subtypes: a conventional subtype similar to beta subunits found in other vertebrates and invertebrates and a novel variant subtype with unusual structural and functional properties. The variant schistosome beta subunit confers praziquantel sensitivity to an otherwise praziquantel-insensitive mammalian Ca2+ channel, implicating it as a mediator of praziquantel action.

Are Ca2+ channels targets of praziquantel action?

Praziquantel is the current drug of choice for the control of schistosomiasis. It is highly effective against all species of schistosomes and shows minimal adverse effects. Though introduced for the treatment of schistosomiasis more than 20 years ago, the mode of action of praziquantel remains to be elucidated. This review will focus on advances in defining the molecular target of praziquantel action, with particular emphasis on recent work indicating an important role for voltage-gated calcium channels.

Schistosoma mansoni Ca2+-ATPase SMA2 restores viability to yeast Ca2+-ATPase-deficient strains and functions in calcineurin-mediated Ca2+ tolerance

The sarco(endo)plasmic reticulum of animal cells contains an ATP-powered Ca2+ pump that belongs to the P-type family of membrane-bound cation-translocating enzymes. In Schistosoma mansoni, the sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is encoded by the SMA1 and SMA2 genes. A full-length SMA2 cDNA clone was isolated, sequenced, and expressed into a yeast Ca2+-ATPase-deficient strain requiring plasmid-borne rabbit SERCA1a for viability. The S. mansoni Ca2+-ATPase supports growth of mutant cells lacking SERCA1a, indicating functional expression in yeast and a role in calcium sequestration. Subcellular fractionation showed that the SMA2 ATPase is localized in yeast internal membranes. SMA2 expression was found to be associated with thapsigargin-sensitive, Ca2+-dependent ATPase activity. The activity increased 2-fold upon calcineurin inactivation, which correlates with in vivo stimulated contribution of SMA2 in calcium tolerance. These results suggest that calcineurin controls calcium homeostasis by inhibiting Ca2+-ATPase activity in an internal compartment.

Evidence for ryanodine receptors in Schistosoma mansoni

The present study investigated the presence of ryanodine receptors in the trematode Schistosoma mansoni. [3H]Ryanodine specific binding sites were found in the four subcellular fractions of S. mansoni; however, more binding sites were recovered in the heterogeneous fraction P1 and the microsomal fraction P4, as was thapsigargin-sensitive (Ca2+-Mg2+)ATPase activity, marking the sarco/endoplasmic reticulum calcium ATPase (SERCA) pumps. This binding had an equilibrium dissociation constant (Kd) in the nanomolar range, an apparent maximal number of receptors (Bmax) of about 80 fmol/mg of protein, and was modulated by ions (Ca2+, Mg2+) and some pharmacological tools such as caffeine. Ryanodine was able to accelerate the rate of 45Ca2+ release from actively loaded vesicles, and also to induce a transient contraction of the whole worm. We conclude that ryanodine-sensitive Ca2+ release channels are present in S. mansoni, with properties very similar to the ones present in higher animals.