Uptake and incorporation of choline by Schistosoma mansoni adults

Functional characterization of Clonorchis sinensis choline transporter

Clonorchis sinensis is commonly found in East Asian countries. Clonorchiasis is prevalent in these countries and can lead to various clinical symptoms. In this study, we used overlap extension polymerase chain reaction (PCR) and the Xenopus laevis oocyte expression system to isolate a cDNA encoding the choline transporter of C. sinensis (CsChT). We subsequently characterized recombinant CsChT. Expression of CsChT in X. laevis oocytes enabled efficient transport of radiolabeled choline, with no detectable uptake of arginine, α-ketoglutarate, p-aminohippurate, taurocholate, and estrone sulfate. Influx and efflux experiments showed that CsChT-mediated choline uptake was time- and sodium-dependent, with no exchange properties. Concentration-dependent analyses of revealed saturable kinetics consistent with the Michaelis-Menten equation, while nonlinear regression analyses revealed a Km value of 8.3 μM and a Vmax of 61.0 pmol/oocyte/h. These findings contribute to widen our understanding of CsChT transport properties and the cascade of choline metabolisms within C. sinensis.

Drug effects on metabolic profiles of Schistosoma mansoni adult male parasites detected by 1H-NMR spectroscopy

Schistosomiasis is one of the most devastating neglected tropical parasitic diseases caused by trematodes of the genus Schistosoma. Praziquantel (PZQ) is today the only drug used in humans and animals for the treatment of schistosomiasis but unfortunately it is poorly effective on larval and juvenile stages of the parasite. Therefore, it is urgent the discovery of new drug targets and compounds. We have recently showed that the anti-anginal drug perhexiline maleate (PHX) is very active on multiple developmental stages of Schistosoma mansoni in vitro. It is well known that PHX impacts the lipid metabolism in mammals, but the final target on schistosomes still remains unknown. The aim of this study was to evaluate the ability of 1H nuclear magnetic resonance (NMR) spectroscopy in revealing metabolic perturbations due to PHX treatment of S. mansoni adult male worms. The effects of PHX were compared with the ones induced by vehicle and gambogic acid, in order to detect different metabolic profiles and specificity of the PHX action. Remarkably a list of metabolites associated to PHX-treatment was identified with enrichment in several connected metabolic pathways including also the Kennedy pathway mediating the glycerophospholipid metabolism. Our study represents the first 1H-NMR metabolomic approach to characterize the response of S. mansoni to drug treatment. The obtained "metabolic fingerprint" associated to PHX treatment could represent a strategy for displaying cellular metabolic changes for any given drug and to compare compounds targeting similar or distinct biochemical pathways.

The transport of choline

Choline has many physiological functions throughout the body that are dependent on its available local supply. However, since choline is a charged hydrophilic cation, transport mechanisms are required for it to cross biological membranes. Choline transport is required for cellular membrane construction and is the rate-limiting step for acetylcholine production. Transport mechanisms include: (1) sodium-dependent high-affinity uptake mechanism in synaptosomes, (2) sodium-independent low-affinity mechanism on cellular membranes, and (3) unique choline uptake mechanisms (e.g., blood-brain barrier choline transport). A comprehensive overview of choline transport studies is provided. This review article examines landmark and current choline transport studies, molecular mapping, and molecular identification of these carriers. Information regarding the choline-binding site is presented by reviewing choline structural analog (hemicholinium-3 and 15, and other nitrogen/methyl-hydroxyl compounds) inhibition studies. Choline transport in Alzheimer's disease, brain ischemic events, and aging is also discussed. Emphasis throughout the article is placed on targeting the choline transporter in disease and use of this carrier as a drug delivery vector.

Interconversion of sphingomyelin and ceramide in adult Schistosoma mansoni

Fluorescent lipid analogues of the lipids ceramide and sphingomyelin, namely BODIPY FL C5-ceramide ((N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-sindacene-3-pentanoyl) sphingosine) and BODIPY C5-sphingomyelin ((N-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-pentanoyl) sphingosyl phosphocholine), respectively, were used to investigate the presence of a sphingomyelin cycle in Schistosoma mansoni adult males. The parasites were able to convert BODIPY FL C5-ceramide into a fluorescent sphingomyelin analogue, and traffic it to the outer monolayer where it was lost to the medium. The vesicular trafficking inhibitors Brefeldin A and monensin were found, however, to have no effect on either the rate of sphingomyelin synthesis or its trafficking to the surface. Parasites were also shown to break BODIPY FL sphingomyelin down, forming a fluorescent ceramide analogue. Inhibitors of lysosomal function, NH4Cl, desipramine and perhexiline, did not inhibit this breakdown, suggesting that endocytosis and trafficking to lysosomes was not involved. In addition, assays carried out on parasite homogenates for sphingomyelinase activity were unable to detect sphingomyelin breakdown at acidic pH, but did detect activity at pH 7.4. This activity was stimulated by arachidonic acid and MgCl2. The results are discussed with respect to tegument synthesis and turnover, and cellular signalling.

Novel benzamil-sensitive sodium-independent choline transport in the cestode Hymenolepis diminuta: evidence for sodium channels uptake at low pH

The uptake of choline by the tegument of Hymenolepis diminuta was investigated. The Q10 at pH 7.0 was 1.7, with an Ea of 90 kJ.mol-1. Choline transport was pH sensitive: At pH 5.0, a Na(+)-independent mechanism predominated, which was inhibited by 100 nM benzamil, 130 mM Na+, and 300 microM verapamil. At pH 7.0, the Na(+)-independent mechanism was inhibited by 130 mM Na+, amiloride, and EIPA with IC50's of 130 microM and 30 microM, respectively, and by benzamil with IC50's of 100 pM (high-potency Benzamil Sensitive Component; HBSC) and 70 microM (low-potency Benzamil Sensitive Component; LBSC). Calcium-free saline enhanced choline uptake non-specifically. Lanthanum3+, Gd3+, gramicidin, nigericin, and high-K+ did not affect choline uptake at pH 5.0 or pH 7.0, and 10 microM verapamil was without effect at pH 5.0, suggesting no significant role for the electrical potential difference across the brush-border membrane, a Na+/H+ antiporter, a Na+/Ca2+ antiporter, or Ca2+ channels in choline uptake. Under physiological conditions, the HBSC accounts for approximately 25% of the total choline taken up at pH 5.0, while the LBSC accounts for approximately 55% of the choline taken up at pH 7.0. The data suggest novel choline transporting mechanisms; an HBSC which displays properties in common with apical Na+ channels, and a unique LBSC of choline transport.

Transport of neurotransmitter precursors in a syncytial epithelium

1. Tegumental transport of choline at concentrations ranging from 0.005-5.0 mM provided no evidence for saturable, carrier-mediated entry of this amine in the tegument of the rat tapeworm (Hymenolepis diminuta). 2. In contrast, the large neutral amino acid tryptophan appears to be taken up via a high-affinity transporter. In the 1st quartile of 17-day-old tapeworms (Km = 0.033 mM, Vmax = 0.7 nmol.min-1.g-1), in the 2nd quartile (Km = 0.015 mM, Vmax = 0.3 nmol.min-1.g-1), in the 3rd quartile (Km = 0.022 mM, Vmax = 0.5 nmol.min-1.g-1) and in the 4th quartile (Km = 0.025 mM, Vmax = 0.5 nmol.min-1.g-1) saturable tryptophan transport was kinetically characterized. 3. The non-saturable diffusion component (Kd) for tryptophan transport ranged from 3.8-10.2 microliters.min-1.g-1. 4. These studies suggest choline does not appear to be transported across the tapeworm tegument. Saturable transport of tryptophan via a high-affinity carrier is reported, and no regional variations in indole amino acid uptake were detected.

Unique roles for lipids in Schistosoma mansoni

The dynamic interplay among lipids has been exploited by S. mansoni to evolve some unique processes that are vital for its long-term survival within the mammalian host. Lipids are required by the parasite not only to maintain its surface integrity and structural requirements but also for egg production and cell-cell signalling. However, S. mansoni is incapable of synthesizing essential lipids and must obtain these from its host. In this review, Stephen Furlong describes the roles and routes of acquisition o f lipids by this parasite.