Tx3-4 a toxin from the venom of spider Phoneutria nigriventer blocks calcium channels associated with exocytosis

Neurobehavioral dysfunction in a mouse model of Down syndrome: upregulation of cystathionine β-synthase, H2S overproduction, altered protein persulfidation, synaptic dysfunction, endoplasmic reticulum stress, and autophagy

Down syndrome (DS) is a genetic condition where the person is born with an extra chromosome 21. DS is associated with accelerated aging; people with DS are prone to age-related neurological conditions including an early-onset Alzheimer's disease. Using the Dp(17)3Yey/ + mice, which overexpresses a portion of mouse chromosome 17, which encodes for the transsulfuration enzyme cystathionine β-synthase (CBS), we investigated the functional role of the CBS/hydrogen sulfide (H2S) pathway in the pathogenesis of neurobehavioral dysfunction in DS. The data demonstrate that CBS is higher in the brain of the DS mice than in the brain of wild-type mice, with primary localization in astrocytes. DS mice exhibited impaired recognition memory and spatial learning, loss of synaptosomal function, endoplasmic reticulum stress, and autophagy. Treatment of mice with aminooxyacetate, a prototypical CBS inhibitor, improved neurobehavioral function, reduced the degree of reactive gliosis in the DS brain, increased the ability of the synaptosomes to generate ATP, and reduced endoplasmic reticulum stress. H2S levels in the brain of DS mice were higher than in wild-type mice, but, unexpectedly, protein persulfidation was decreased. Many of the above alterations were more pronounced in the female DS mice. There was a significant dysregulation of metabolism in the brain of DS mice, which affected amino acid, carbohydrate, lipid, endocannabinoid, and nucleotide metabolites; some of these alterations were reversed by treatment of the mice with the CBS inhibitor. Thus, the CBS/H2S pathway contributes to the pathogenesis of neurological dysfunction in DS in the current animal model.

Transcriptome-based analyses reveal venom diversity in two araneomorph spiders, Psechrus triangulus and Hippasa lycosina

The spiders Psechrus triangulus and Hippasa lycosina are widely distributed in Yunnan Province, China, and are important natural enemies of agricultural pests, yet studies regarding the composition of their venom are lacking. In this study, cDNA libraries were constructed from venom gland tissue of P. triangulus and H. lycosina and used for transcriptomic analysis. From the analysis, 39 and 31 toxin-like sequences were predicted for P. triangulus and H. lycosina, respectively. The predicted neurotoxin sequences were categorized according to cysteine sequence motifs, and the predicted neurotoxin sequences of P. triangulus and H. lycosina could be classified into 9 and 6 toxin families, respectively. In addition, potential acetylcholinesterase, hyaluronidase, and astaxanthin-like metalloproteinases were identified through annotation. In summary, transcriptomic techniques were invaluable in mining the gene expression information from these two spider species to explore the toxin composition of their venom and determine how they differ. Studies of this type provide essential baseline data for studying the evolution and physiological activities of spider toxins and for the potential development of medicinal compounds.

Pain modulatory properties of Phoneutria nigriventer crude venom and derived peptides: A double-edged sword

Phoneutria nigriventer venom (PNV) is a complex mixture of toxins exerting multiple pharmacological effects that ultimately result in severe local pain at the site of the bite. It has been proposed that the PNV-induced pain is mediated by both peripheral and central mechanisms. The nociception triggered by PNV is peripherally mediated by the activation of B₂, 5-HT₄, NMDA, AMPA, NK₁, and NK₂ receptors, as well as TTXS-Na⁺, ASIC, and TRPV1 channels. The activation of tachykinin, glutamate and CGRP receptors along with the production of inflammatory mediators are, at least partially, responsible for the central component of pain. Despite its well established pro-nociceptive properties, PNV contains some toxins with antinociceptive activity, which have been studied in the last few years. The toxins ω-CNTX-Pn4a, ω-CNTX-Pn2a, ω-CNTX-Pn3a, κ-CNTX-Pn1a, U₇-CNTX-Pn1a, δ-CNTX-Pn1a, and Γ-CNTX-Pn1a from PNV, as well as the semi-synthetic peptide PnPP-19 have been tested in different experimental models of pain showing consistent antinociceptive properties. This review aims to discuss the pro- and antinociceptive actions of PNV and its toxins, highlighting possible mechanisms involved in these apparently dualistic properties.

Cholesterol as a key player in the balance of evoked and spontaneous glutamate release in rat brain cortical synaptosomes

Membrane rafts are domains enriched in sphingolipids, glycolipids and cholesterol that are able to compartmentalize cellular processes. Noteworthy, many proteins have been assigned to membrane rafts including those related to the control of the synaptic vesicle release machinery, which is a important step for neurotransmission between synapses. In this work, we have investigated the role of cholesterol in key steps of glutamate release in isolated nerve terminals (synaptosomes) from rat brain cortices. Incubation of synaptosomes with methyl-β-cyclodextrin (MβCD) induced glutamate release in a dose-dependent fashion. HγCD, a cyclodextrin with low affinity for cholesterol, had no significant effect on spontaneous glutamate release. When we evaluated the effects of MβCD on glutamate release induced by depolarizing stimuli, we observed that MβCD treatment inhibited the KCl-evoked glutamate release. The glutamate release induced by MβCD was not altered by treatment with EGTA nor with EGTA-AM. The KCl-evoked glutamate release was no further inhibited when synaptosomes were incubated with MβCD in the absence of calcium. We therefore investigated whether the cholesterol removal by MβCD changes intrasynaptosomal sodium and calcium levels. Our results suggested that the cholesterol removal effect on spontaneous and evoked glutamate release might be upstream to sodium and calcium entry through voltage-activated channels. We therefore tested if MβCD would have a direct effect on synaptic vesicle exocytosis and we showed that cholesterol removal by MβCD induced spontaneous exocytosis and inhibited synaptic vesicle exocytosis evoked by depolarizing stimuli. Lastly, we investigated the effect of protein kinase inhibitors on the spontaneous exocytosis evoked by MβCD and we observed a statistically significant reduction of synaptic vesicles exocytosis. In conclusion, our work shows that cholesterol removal facilitates protein kinase activation that favors spontaneous synaptic vesicles and consequently glutamate release in isolated nerve terminals.

Expression of a recombinant Phoneutria toxin active in calcium channels

PnTx3-4 is a toxin isolated from the venom of the spider Phoneutria nigriventer that blocks N-, P/Q-, and R-type voltage-gated calcium channels and has great potential for clinical applications. In this report we used the SUMO system to express large amounts of recombinant PnTx3-4 peptide, which was found in both soluble and insoluble fractions of bacterial extracts. We purified the recombinant toxin from both fractions and showed that the recombinant peptide showed biological activity similar to the native PnTx3-4. In silico analysis of the primary sequence of PnTx3-4 indicated that the peptide conforms to all the criteria of a knottin scaffold. Additionally, circular dichroism spectrum analysis of the recombinant PnTx3-4 predicted that the toxin structure is composed of approximately 53% turns/unordered, 31% α-helix and 16% β-strand, which is consistent with predicted model of the PnTx3-4 knottin scaffold available at the knottin database (http://knottin.cbs.cnrs.fr). These studies provide the basis for future large scale production and structure-function investigation of PnTx3-4.

Phoneutria spider toxins block ischemia-induced glutamate release and neuronal death of cell layers of the retina

PURPOSE

To investigate the effect of calcium channel blockers, spider toxins, on cell viability and the glutamate content of ischemic retinal slices.

METHODS

Rat retinal slices were subjected to ischemia via exposure to oxygen-deprived low-glucose medium for 45 minutes. Slices were either treated or not treated with the toxins PhTx3, Tx3-3, and Tx3-4. After oxygen-deprived low-glucose insult, glutamate content and cell viability were assessed in the slices by confocal and optical microscopy.

RESULTS

In the retinal ischemic slices that were treated with PhTx3, Tx3-3, and Tx3-4, confocal imaging showed a decrease in cell death of 79.5 ± 3.1%, 75.5 ± 5.8%, and 61 ± 3.8%, respectively. Neuroprotective effects were also observed 15, 30, 60, and 90 minutes after the onset of the retinal ischemic injury. As a result of the ischemia, glutamate increased from 6.2 ± 1.0 nMol/mg protein to 13.2 ± 1.0 nMol/mg protein and was inhibited by PhTx3, Tx3-3, and Tx3-4 to 8.6 ± 0.7, 8.8 ± 0.9, and 7.4 ± 0.8 nMol/mg protein, respectively. Histologic analysis of the live cells in the outer, inner, and ganglion cell layers of the ischemic slices showed a considerable reduction in cell death by the toxin treatment.

CONCLUSION

Spider toxins reduced glutamate content and cell death of retinal ischemic slices.

Peptide neurotoxins that affect voltage-gated calcium channels: a close-up on ω-agatoxins

Peptide neurotoxins found in animal venoms have gained great interest in the field of neurotransmission. As they are high affinity ligands for calcium, potassium and sodium channels, they have become useful tools for studying channel structure and activity. Peptide neurotoxins represent the clinical potential of ion-channel modulators across several therapeutic fields, especially in developing new strategies for treatment of ion channel-related diseases. The aim of this review is to overview the latest updates in the domain of peptide neurotoxins that affect voltage-gated calcium channels, with a special focus on ω-agatoxins.

Flow cytometric assessment of distinct physiological stages withinCryptosporidium parvumsporozoites post-excystation

Cryptosporidium parvumare protozoan parasites responsible for outbreaks of gastrointestinal disease worldwide. Within the apical complex of this organism reside numerous vesicular secretory organelles and their discharge has been identified as essential for sporozoite motility, cell attachment and penetration. Traditionally, investigation of apical organelle discharge has relied on microscopic and immunochemical hybridization techniques. In this study we demonstrate for the first time how flow cytometry, in combination with vital dye staining, provides an avenue for discrimination of distinct physiological events occurring withinCryptosporidiumsporozoites post-excystation. Time-course studies of freshly excysted sporozoites were carried out at 37°C in cell-free medium, stained with the fluorescent dyes SYTO9/PI, DiBAC4(3), Fluo-4 AM or FM1-43 and analysed by flow cytometry. Significant decreases in sporozoite plasma membrane permeability and increased membrane depolarization were found to be accompanied by concomitant increases in intracellular calcium. Subsequent to these changes, large increases in exocytosed vesicular membrane were apparent. In addition, by measuring side and forward angle light scatter we were able to assess changes in internal granularity and size of sporozoites post-excystation. These observations were suggestive of rapid mobilization, utilization and discharge of apical organelles within sporozoites, which we relate to changes in sporozoite infectivity, ATP levels and total secreted soluble protein.