The tegumental surface membranes of Schistosoma mansoni are enriched in parasite-specific phospholipid species

The complex surface structure of adult Schistosoma mansoni, the tegument, is essential for survival of the parasite. This tegument is syncytial and is covered by two closely-apposed lipid bilayers that form the interactive surface with the host. In order to identify parasite-specific phospholipids present in the tegument, the species compositions of the major glycerophospholipid classes, phosphatidylcholine, phosphatidylserine, phosphatidylethanolamine and phosphatidylinositol, including lysophospholipid species, were analysed in adult S. mansoni worms, isolated tegumental membranes and hamster blood cells. It was shown that there are large differences in species composition in all four phospholipid classes between the membranes of S. mansoni and those of the host blood cells. The species compositions of phosphatidylserine and phosphatidylcholine were strikingly different in the tegument compared with the whole worm. The tegumental membranes are especially enriched in lysophospholipids, predominantly eicosenoic acid (20:1)-containing lyso-phosphatidylserine and lyso-phosphatidylethanolamine species. Furthermore, the tegument was strongly enriched in phosphatidylcholine that contained 5-octadecenoic acid, an unusual fatty acid that is not present in the host. As we have shown previously that lysophospholipids from schistosomes affect the parasite-host interaction, excretion of these tegument-specific phospholipid species was examined in vitro and in vivo. Our experiments demonstrated that these lysophospholipids are not significantly secreted during in vitro incubations and are not detectable in peripheral blood of infected hosts. However, these analyses demonstrated a substantial decrease in PI content of blood plasma from schistosome-infected hamsters, which might indicate that schistosomes influence exosome formation by the host.

Target Immobilization as a Strategy for NMR-Based Fragment Screening

Fragment-based drug discovery (FBDD) has become a widely accepted tool that is complementary to high-throughput screening (HTS) in developing small-molecule inhibitors of pharmaceutical targets. Because a fragment campaign can only be as successful as the hit matter found, it is critical that the first stage of the process be optimized. Here the authors compare the 3 most commonly used methods for hit discovery in FBDD: high concentration screening (HCS), solution ligand-observed nuclear magnetic resonance (NMR), and surface plasmon resonance (SPR). They selected the commonly used saturation transfer difference (STD) NMR spectroscopy and the proprietary target immobilized NMR screening (TINS) as representative of the array of possible NMR methods. Using a target typical of FBDD campaigns, the authors find that HCS and TINS are the most sensitive to weak interactions. They also find a good correlation between TINS and STD for tighter binding ligands, but the ability of STD to detect ligands with affinity weaker than 1 mM KD is limited. Similarly, they find that SPR detection is most suited to ligands that bind with KD better than 1 mM. However, the good correlation between SPR and potency in a bioassay makes this a good method for hit validation and characterization studies.

Development of surface plasmon resonance biosensor assays for primary and secondary screening of acetylcholine binding protein ligands

Surface plasmon resonance (SPR) biosensors recently gained an important place in drug discovery. Here we present a primary and secondary SPR biosensor screening methodology. The primary screening method is based on a direct binding assay with covalent immobilized drug target proteins. For the secondary screening method, a sequential competition assay has been developed where the captured protein is first exposed to an unknown test compound, followed directly by an exposure to a high-molecular-weight reporter ligand. Using the high-molecular-weight reporter ligand to probe the remaining free binding site on the sensor, a significant signal enhancement is obtained. Furthermore, this assay format allows the validation of the primary direct binding assay format, efficiently revealing false positive data. As a model system, acetylcholine binding protein (AChBP), which is a soluble model protein for neuronal nicotinic acetylcholine receptors, has been used. The secondary assay is lower in throughput than the primary assay; however, the signal-to-noise ratio is two times higher compared with the direct assay, and it has a z' factor of 0.96. Using both assays, we identified the compound tacrine as a ligand for AChBP.

Combined TLR2 and TLR4 ligation in the context of bacterial or helminth extracts in human monocyte derived dendritic cells: molecular correlates for Th1/Th2 polarization

BACKGROUND

Recognition of pathogens by dendritic cells (DCs) through interaction with pattern recognition receptors, including Toll like receptors (TLR), is crucial for the initiation of appropriate polarized T helper (Th) cell responses. Yet, the characteristics and differences in molecular profiles of DCs with different T cell polarizing capacities are still poorly defined. To address this issue, the molecular profile of human monocyte derived DCs was characterized after exposure to TLR4 ligand LPS in combination with the Th1 promoting bacterial extracts from Listeria monocytogenes and Escherichia coli or the Th2 promoting helminth derived phospholipids from Schistosoma mansoni and Ascaris lumbricoides, all with TLR2 activating capacity.

RESULTS

With regard to the signalling pathways activated upon exposure to LPS and the TLR2 activating compounds, we find that the ratio of activated Mitogen Activated Protein Kinases (MAPK) p-ERK/p-p38 is lower in DCs stimulated with the bacterial products compared to DCs stimulated with the helminth products, which correlates with the Th1 and Th2 polarizing capacity of these compounds. Furthermore, analysis of the mRNA expression levels of a set of 25 carefully selected genes potentially involved in modulation of T cell polarization revealed that the mRNA expression of notch ligand delta-4 and transcription factor c-fos are differentially regulated and show a strong correlation with Th1 and Th2 polarization, respectively.

CONCLUSION

This study shows that combined TLR2 and TLR4 activation in the context of different antigen sources can induce very distinct molecular profiles in DCs and suggests that the Th1/Th2 polarizing capacity of compounds can be predicted with the molecular signature they induce in DCs.

A simple and universal method for the separation and identification of phospholipid molecular species

One of the major challenges in lipidomics is to obtain as much information about the lipidome as possible. Here, we present a simple yet universal high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS/MS) method to separate molecular species of all phospholipid classes in one single run. The method is sensitive, robust and allows lipid profiling using full scan mass spectrometry, as well as lipid class specific scanning in positive and negative ionisation mode. This allows high-throughput processing of samples for lipidomics, even if different types of MS analysis are required. Excellent separation of isobaric and even isomeric species is achieved, and original levels of lyso-lipids can be determined without interference from lyso-lipids formed from diacyl species by source fragmentation. As examples of application of this method, more than 400 phospholipid species were identified and quantified in crude phospholipid extracts from rat liver and the parasitic helminth Schistosoma mansoni.

Immunologic activity of schistosomal and bacterial TLR2 ligands in Gabonese children

Schistosomes carry lipid moieties that interact with the immune system. To understand the consequence of interactions in terms of polarizing the cytokine profiles, the effect of two Toll-like receptor-2 (TLR2) activating schistosomal lipid fractions was studied on whole blood from Gabonese children living in a schistosomiasis endemic area. One fraction contained lysophosphatidylserine [monoacylglycerophosphoserine (lysoGPSer)] plus diacylphosphatidylserine [diacylglycerophosphoserine (GPSer)] while the other contained lysoGPSer and only a trace of GPSer. The effect of these schistosomal lipid fractions was compared with the known bacterial TLR2 ligands PAM3CSK4 and MALP-2. PAM3CSK4 and MALP-2 had preferential IL-10-activating capacities, while the fraction containing lysoGPSer plus GPSer had a strong TNF-alpha-inducing capacity. The fraction containing lysoGPSer was neutral with respect to pro- vs. anti-inflammatory effects. When Th1 and Th2 cytokines were analysed, the schistosomal lipid fraction containing lysoGPSer plus GPSer showed a stronger Th2 response compared to PAM3CSK4, MALP-2 and lysoGPSer alone. Therefore, the study indicates that not only TLR2 ligands derived from bacteria or from parasites can generate distinct cytokine profiles but also that the composition of lipid entities reaching the immune system can be important in leading to different immune outcomes. This information may be important for exploitation of immune modulatory molecules.

Antibody responses to Ascaris-derived proteins and glycolipids: the role of phosphorylcholine

In addition to proteins, glycolipids can be targets of antibody responses and contribute to host-pathogen interaction. Following the structural analysis of Ascaris lumbricoides-derived glycolipids, the antibody responses of a group of children with no, light and heavy infections were analysed. The role of the phosphorylcholine moiety, present on Ascaris glycoproteins and glycolipids, in antibody reactivity of these infected individuals was determined. Children carrying heavy infections showed highest IgG reactivity to glycolipids compared to lightly or non-infected children. Substantial IgG antibody reactivity to both (glyco)proteins and glycolipids was found to be directed to the phosphorylcholine moiety as determined by either removal of this group or a competition assay. This was most pronounced for glycolipids, where removal of the phosphorylcholine moieties by hydrofluoric acid treatment abrogated IgG antibody reactivity. Measurement of IgG4 and IgE isotypes showed no IgG4 reactivity to Ascaris glycolipids, but raised IgE responses were detected in subjects with light or no Ascaris infections, suggesting that IgE responses to glycolipids may play a role in controlling parasite burden. Differences found in antibody profiles to glycolipids and (glyco)proteins, indicate that these different classes of compounds may have distinct roles in shaping of and interacting with humoral immune responses.

Functions of the tegument of schistosomes: clues from the proteome and lipidome

The tegumental outer-surface of schistosomes is a unique double membrane structure that is of crucial importance for modulation of the host response and parasite survival. Although several tegumental proteins had been identified by classical biochemical approaches, knowledge on the entire molecular composition of the tegument was limited. The Schistosoma mansoni genome project, together with recently developed proteomic and lipidomic techniques, allowed studies on detailed characterisation of the proteins and lipids of the tegumental membranes. These studies identified tegumental proteins and lipids that confirm the function of the tegument in nutrient uptake and immune evasion. However, these studies also demonstrated that compared to the complete worm, the tegument is enriched in lipids that are absent in the host. The tegument is also enriched in proteins that share no sequence similarity to any sequence present in databases of species other than schistosomes. These results suggest that the unique tegumental structures comprise multiple unique components that are likely to fulfil yet unknown functions. The tegumental proteome and lipidome, therefore, imply that many unknown molecular mechanisms are employed by schistosomes to survive within their host.

Responses to Toll-like receptor ligands in children living in areas where schistosome infections are endemic

To study the effect of repeated challenge of the innate immune system with pathogen-associated molecular patterns, cytokine responses to schistosomal lipids and bacterial lipopolysaccharide (LPS) were analyzed in schoolchildren living in an area in Gabon where schistosomiasis, a helminth infection that is chronic in nature, is endemic. A schistosomal phosphatidylserine (PS) fraction containing the Toll-like receptor (TLR)-2 ligand lyso-PS stimulated the production of interleukin (IL)-8, IL-10, IL-6, and tumor necrosis factor (TNF)-alpha in children without Schistosoma haematobium infection. However, in infected children, the responses to this stimulus were lower, in particular for production of IL-8 and TNF-alpha. Responses to the TLR4 ligand, LPS, followed a similar pattern. In contrast, schistosomal adult worm glycolipids that did not stimulate any of the TLRs tested induced IL-8 and IL-6 responses that were significantly higher in schistosome-infected children than in schistosome-uninfected children. These results indicate that relentless exposure to pathogens can lead to altered responses to TLR ligands.