Phoneutria nigriventer toxins block tityustoxin-induced calcium influx in synaptosomes

Animal Venom Peptides as a Treasure Trove for New Therapeutics Against Neurodegenerative Disorders

BACKGROUND

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and cerebral ischemic stroke, impose enormous socio-economic burdens on both patients and health-care systems. However, drugs targeting these diseases remain unsatisfactory, and hence there is an urgent need for the development of novel and potent drug candidates.

METHODS

Animal toxins exhibit rich diversity in both proteins and peptides, which play vital roles in biomedical drug development. As a molecular tool, animal toxin peptides have not only helped clarify many critical physiological processes but also led to the discovery of novel drugs and clinical therapeutics.

RESULTS

Recently, toxin peptides identified from venomous animals, e.g. exenatide, ziconotide, Hi1a, and PcTx1 from spider venom, have been shown to block specific ion channels, alleviate inflammation, decrease protein aggregates, regulate glutamate and neurotransmitter levels, and increase neuroprotective factors.

CONCLUSION

Thus, components of venom hold considerable capacity as drug candidates for the alleviation or reduction of neurodegeneration. This review highlights studies evaluating different animal toxins, especially peptides, as promising therapeutic tools for the treatment of different neurodegenerative diseases and disorders.

An overview of Phoneutria nigriventer spider venom using combined transcriptomic and proteomic approaches

Phoneutria nigriventer is one of the largest existing true spiders and one of the few considered medically relevant. Its venom contains several neurotoxic peptides that act on different ion channels and chemical receptors of vertebrates and invertebrates. Some of these venom toxins have been shown as promising models for pharmaceutical or biotechnological use. However, the large diversity and the predominance of low molecular weight toxins in this venom have hampered the identification and deep investigation of the less abundant toxins and the proteins with high molecular weight. Here, we combined conventional and next-generation cDNA sequencing with Multidimensional Protein Identification Technology (MudPIT), to obtain an in-depth panorama of the composition of P. nigriventer spider venom. The results from these three approaches showed that cysteine-rich peptide toxins are the most abundant components in this venom and most of them contain the Inhibitor Cysteine Knot (ICK) structural motif. Ninety-eight sequences corresponding to cysteine-rich peptide toxins were identified by the three methodologies and many of them were considered as putative novel toxins, due to the low similarity to previously described toxins. Furthermore, using next-generation sequencing we identified families of several other classes of toxins, including CAPs (Cysteine Rich Secretory Protein-CRiSP, antigen 5 and Pathogenesis-Related 1-PR-1), serine proteinases, TCTPs (translationally controlled tumor proteins), proteinase inhibitors, metalloproteinases and hyaluronidases, which have been poorly described for this venom. This study provides an overview of the molecular diversity of P. nigriventer venom, revealing several novel components and providing a better basis to understand its toxicity and pharmacological activities.

Animal Toxins as Therapeutic Tools to Treat Neurodegenerative Diseases

Neurodegenerative diseases affect millions of individuals worldwide. So far, no disease-modifying drug is available to treat patients, making the search for effective drugs an urgent need. Neurodegeneration is triggered by the activation of several cellular processes, including oxidative stress, mitochondrial impairment, neuroinflammation, aging, aggregate formation, glutamatergic excitotoxicity, and apoptosis. Therefore, many research groups aim to identify drugs that may inhibit one or more of these events leading to neuronal cell death. Venoms are fruitful natural sources of new molecules, which have been relentlessly enhanced by evolution through natural selection. Several studies indicate that venom components can exhibit selectivity and affinity for a wide variety of targets in mammalian systems. For instance, an expressive number of natural peptides identified in venoms from animals, such as snakes, scorpions, bees, and spiders, were shown to lessen inflammation, regulate glutamate release, modify neurotransmitter levels, block ion channel activation, decrease the number of protein aggregates, and increase the levels of neuroprotective factors. Thus, these venom components hold potential as therapeutic tools to slow or even halt neurodegeneration. However, there are many technological issues to overcome, as venom peptides are hard to obtain and characterize and the amount obtained from natural sources is insufficient to perform all the necessary experiments and tests. Fortunately, technological improvements regarding heterologous protein expression, as well as peptide chemical synthesis will help to provide enough quantities and allow chemical and pharmacological enhancements of these natural occurring compounds. Thus, the main focus of this review is to highlight the most promising studies evaluating animal toxins as therapeutic tools to treat a wide variety of neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, brain ischemia, glaucoma, amyotrophic lateral sclerosis, and multiple sclerosis.

Pre-clinical evaluation of voltage-gated calcium channel blockers derived from the spider P. nigriventer in glioma progression

This study investigated the effects of P/Q- and N-type voltage-gated calcium channel (VGCC) blockers derived from P. nigriventer in glioma progression, by means of in vitro and in vivo experiments. Glioma cells M059J, U-138MG and U-251MG were used to evaluate the antiproliferative effects of P/Q- and N-type VGCC inhibitors PhTx3-3 and Phα1β from P. nigriventer (0.3-100 pM), in comparison to MVIIC and MVIIA from C. magus (0.3-100 pM), respectively. The toxins were also analyzed in a glioma model induced by implantation of GL261 mouse cells. PhTx3-3, Phα1β and MVIIA displayed significant inhibitory effects on the proliferation and viability of all tested glioma cell lines, and evoked cell death mainly with apoptosis characteristics, as indicated by Annexin V/propidium iodide (PI) positivity. The antiproliferative effects of toxins were confirmed by flow cytometry using Ki67 staining. None of the tested toxins altered the proliferation rates of the N9 non-tumor glial cell line. Noteworthy, the administration of the preferential N-type VGCC inhibitors, Phα1β (50 pmol/site; i.c.v.), its recombinant form CTK 01512-2 (50 pmol/site; i.c.v. and i.t.), or MVIIA (10 pmol/site; i.c.v.) caused significant reductions of tumor areas in vivo. N-type VGCC inhibition by Phα1β, CTK 01512-2, and MVIIA led to a marked increase of GFAP-activated astrocytes, and Iba-1-positive microglia, in the peritumoral region, which might explain, at least in part, the inhibitory effects of the toxins in tumor development. This study provides novel evidence on the potential effects of P. nigriventer-derived P/Q-, and mainly, N-type VGCC inhibitors, in glioma progression.

PhTx3-4, a Spider Toxin Calcium Channel Blocker, Reduces NMDA-Induced Injury of the Retina

The in vivo neuroprotective effect of PhTx3-4, a spider toxin N-P/Q calcium channel blocker, was studied in a rat model of NMDA-induced injury of the retina. NMDA (N-Methyl-d-Aspartate)-induced retinal injury in rats reduced the b-wave amplitude by 62% ± 3.6%, indicating the severity of the insult. PhTx3-4 treatment increased the amplitude of the b-wave, which was almost equivalent to the control retinas that were not submitted to injury. The PhTx3-4 functional protection of the retinas recorded on the ERG also was observed in the neuroprotection of retinal cells. NMDA-induced injury reduced live cells in the retina layers and the highest reduction, 84%, was in the ganglion cell layer. Notably, PhTx3-4 treatment caused a remarkable reduction of dead cells in the retina layers, and the highest neuroprotective effect was in the ganglion cells layer. NMDA-induced cytotoxicity of the retina increased the release of glutamate, reactive oxygen species (ROS) production and oxidative stress. PhTx3-4 treatment reduced glutamate release, ROS production and oxidative stress measured by malondialdehyde. Thus, we presented for the first time evidence of in vivo neuroprotection from NMDA-induced retinal injury by PhTx3-4 (-ctenitoxin-Pn3a), a spider toxin that blocks N-P/Q calcium channels.

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.

Antinociceptive effect of Brazilian armed spider venom toxin Tx3-3 in animal models of neuropathic pain

Venoms peptides have produced exceptional sources for drug development to treat pain. In this study we examined the antinociceptive and side effects of Tx3-3, a peptide toxin isolated from Phoneutria nigriventer venom, which inhibits high-voltage-dependent calcium channels (VDCC), preferentially P/Q and R-type VDCC. We tested the effects of Tx3-3 in animal models of nociceptive (tail-flick test), neuropathic (partial sciatic nerve ligation and streptozotocin-induced diabetic neuropathy), and inflammatory (intraplantar complete Freund's adjuvant) pain. In the tail-flick test, both intrathecal (i.t.) and intracerebroventricular (i.c.v.) injection of Tx3-3 in mice caused a short-lasting effect (ED(50) and 95% confidence intervals of 8.8 [4.1-18.8] and 3.7 [1.6-8.4] pmol/site for i.t. and i.c.v. injection, respectively), without impairing motor functions, at least at doses 10-30 times higher than the effective dose. By comparison, ω-conotoxin MVIIC, a P/Q and N-type VDCC blocker derived from Conus magus venom, caused significant motor impairment at doses close to efficacious dose in tail flick test. Tx3-3 showed a long-lasting antinociceptive effect in neuropathic pain models. Intrathecal injection of Tx3-3 (30 pmol/site) decreased both mechanical allodynia produced by sciatic nerve injury in mice and streptozotocin-induced allodynia in mice and rats. On the other hand, i.t. injection of Tx3-3 did not alter inflammatory pain. Taken together, our data show that Tx3-3 shows prevalent antinociceptive effects in the neuropathic pain models and does not cause adverse motor effects at antinociceptive efficacious doses, suggesting that this peptide toxin holds promise as a novel therapeutic agent for the control of neuropathic pain. The Brazilian armed spider Tx3-3, a new P/Q and R-type calcium channel blocker, effectively alleviates allodynia in animal neuropathic pain models.

Intrahippocampal injection of TsTX-I, a beta-scorpion toxin, causes alterations in electroencephalographic recording and behavior in rats

AIMS

TsTX-I scorpion toxin, also known as γ-toxin, is a β-toxin which binds to site 4 of the sodium channel, shifting its activation potential. There are few studies about its pharmacological action in the central nervous system. The objective of this work was to determine the electroencephalographic, behavioral and histopathological effects of intrahippocampal injection of TsTX-I.

MAIN METHODS

Rats were anesthetized and fitted with cannulae for injection into the hippocampus and with electrodes for cerebral recording. The animals were treated with Ringer solution, some doses of TsTX-I, DMSO 0.1% or veratridine. Behavioral and electrographic recordings were observed for 4 hours after the injection. After 7 days, the rats were perfused, and their brains removed for histological analysis.

KEY FINDINGS

Increasing doses of the toxin evoked epileptic-like discharges, wet dog shakes, and in some cases hind limb paralysis and intense respiratory difficulty followed by death. The histopathological analysis demonstrated no cell loss. Animals injected with veratridine developed epileptiform activity in the electrographic recording and neuronal loss.

SIGNIFICANCE

The results suggest that TsTX-I toxin may be responsible, at least in part, for the epileptic and behavioral effects observed with the crude venom, and although veratridine and TsTX-I act on Na-channel, the differences between them are remarkable, demonstrating that toxins can have different functional effects depending on the site of action in the channel. Thus, animal neurotoxins are often highly selective and may be useful for the identification of the sequence of events underlying neurotransmission.

Leftward shift in the voltage-dependence for Ca2+ currents activation induced by a new toxin from Phoneutria reidyi (Aranae, Ctenidae) venom

Various neurotoxins have been described from the venom of the Brazilian spider Phoneutria nigriventer, but little is known about the venoms of the other species of this genus. In the present work, we describe the purification and some structural and pharmacological features of a new toxin (PRTx3-7) from Phoneutria reidyi that causes flaccid paralysis in mice. The observed molecular mass (4627.26 Da) was in accordance with the calculated mass for the amidated form of the amino acid sequence (4627.08 Da). The presence of an alpha-amidated C-terminus was confirmed by MS/MS analysis of the C-terminal peptide, isolated after enzymatic digestion of the native protein with Glu-C endoproteinase. The purified protein was injected (intracerebro-ventricular) into mice at dose levels of 5 microg/mouse causing immediate agitation and clockwise gyration, followed by the gradual development of general flaccid paralysis. PRTx3-7 at 1 microM inhibited by 20% the KCl-induced increase on [Ca2+]i in rat brain synaptosomes. The HEK cells permanently expressing L, N, P/Q and R HVA Ca2+ channels were also used to better characterize the pharmacological features of PRTx3-7. To our surprise, PRTx3-7 shifted the voltage-dependence for activation towards hyperpolarized membrane potentials for L (-4 mV), P/Q (-8 mV) and R (-5 mV) type Ca2+ currents. In addition, the new toxin also affected the steady state of inactivation of L-, N- and P/Q-type Ca2+ currents.

Neuroprotective effect on brain injury by neurotoxins from the spider Phoneutria nigriventer

The role of calcium channels blockers in ischemic condition has been well documented. The PhTx3 neurotoxic fraction of the spider Phoneutria nigriventer venom is a broad-spectrum calcium channel blocker that inhibits glutamate release, calcium uptake and also glutamate uptake in synaptosomes. In the present study we describe the effect of PhTx3 (1.0 microg/mL), omega-conotoxin GVIA (1.0 micromol/L) and omega-conotoxin MVIIC (100 nmol/L) on neuroprotection of hippocampal slices and SN56 cells subjected to ischemia by oxygen deprivation and low glucose insult (ODLG). After the insult, cell viability in the slices and SN56 cells was assessed by confocal microscopy and epifluorescence, using live/dead kit containing calcein-AM and ethidium homodimer. Confocal images of CA1 region of the rat hippocampal slices subjected to ischemia insult and treated with omega-conotoxin GVIA, omega-conotoxin MVIIC and PhTx3 showed a percentage of dead cells of 68%, 54% and 18%, respectively. The SN56 cells subjected to ischemia were almost completely protected from damage by PhTx3 while with omega-conotoxin GVIA or omega-conotoxin MVIIC the cell protection was only partial. Thus, PhTx3 provided robust ischemic neuroprotection showing potential as a novel class of agents that targets multiple components and exerts neuroprotection in in vitro model of brain ischemia.

Comparison of the partial proteomes of the venoms of Brazilian spiders of the genus Phoneutria

The proteomes of the venoms of the Brazilian wandering "armed" spiders Phoneutria nigriventer, Phoneutria reidyi, and Phoneutria keyserlingi, were compared using two-dimensional gel electrophoresis. The venom components were also fractionated using a combination of preparative reverse phase HPLC on Vydac C4, analytical RP-HPLC on Vydac C8 and C18 and cation exchange FPLC on Resource S at pH 6.1 and 4.7, or anion exchange HPLC on Synchropak AX-300 at pH 8.6. The amino acid sequences of the native and S-pyridyl-ethylated proteins and peptides derived from them by enzymatic digestion and chemical cleavages were determined using a Shimadzu PPSQ-21(A) automated protein sequencer, and by MS/MS collision induced dissociations. To date nearly 400 peptides and proteins (1.2-27 kDa) have been isolated in a pure state and, of these, more than 100 have had their complete or partial amino acid sequences determined. These sequences demonstrate, as might be expected, that the venoms of P. reidyi and P. keyserlingi (Family: Ctenidae) both contain a similar range of isoforms of the neurotoxins as those previously isolated from P. nigriventer which are active on neuronal ion (Ca(2+), Na(+) and K(+)) channels and NMDA-type glutamate receptors. In addition two new families of small (3-4 kDa) toxins, some larger protein (>10 kDa) components, and two serine proteinases of the venom of P. nigriventer are described. These enzymes may be responsible for some of the post-translational modification observed in some of the venom components.

Effects of alpha-scorpion toxin, tityustoxin on the release of [3H] dopamine of rat brain prefrontal cortical slices

The effect of tityustoxin (TsTX) on the release of [3H] dopamine in rat brain prefrontal cortical slices was investigated. The stimulatory effect of TsTX was dependent on incubation time and TsTX concentration with an EC50 of 0.05 microM. The release of [3H] dopamine stimulated by TsTX is dependent of Na+ channels and thus, was completely, inhibited by tetrodotoxin. Tityustoxin-induced release of [3H] dopamine was not blocked by ethylene glycol-bis(beta-aminoethyl) ether (EGTA) and thus was independent of extracellular calcium. However, [3H] dopamine release induced by TsTX was inhibited by 52% by BAPTA, a calcium chelator. Moreover, dantrolene (100 microM) and tetracaine (500 microM) partially inhibited by 38 and 29%, respectively, the tityustoxin-induced release of [3H] dopamine from prefrontal cortical slices suggesting a role from intracellular calcium increase. In conclusion, part of the TsTX-induced release [3H] dopamine may be due to an effect of the toxin on the reversal of the dopamine transporter (DAT), but the majority of the toxin stimulated release of [3H] dopamine involves the mobilization of intracellular calcium stores.

Molecular cloning and characterization of Phoneutria nigriventer toxins active on calcium channels

The aim of the present study was the molecular cloning of toxins active on calcium channels expressed by the spider Phoneutria nigriventer. Clones encoding the toxins Pn3-3A, Pn3-4A, Tx3-5, Pn3-5A, Tx3-6, Pn3-6A and Pn3-6B were identified from a cDNA library derived from the venom gland of this spider, revealing toxins of 49, 76, 45, 39, 55 and 58 amino acids residues, respectively, with polypeptide precursors being composed of three major portions: a signal peptide, a propeptide and finally, the mature toxin. A high degree of homology with the amino acid sequence was found between Pn3-3A and the neurotoxin Tx3-3 (identity of 79%), and between Pn3-4A and the neurotoxin Tx3-4 (identity of 95%). The deduced amino acid sequence for the mature polypeptides Tx3-5 and Tx3-6 confirms the polypeptide sequence previously published for these neurotoxins. In addition, the toxin Pn3-5A showed 58% identity to the Tx3-5 amino acid sequence, and the toxins Pn3-6A and Pn3-6B showed 85 and 33% identity, respectively, to the Tx3-6 amino acid sequence.

Expression of a functional recombinant Phoneutria nigriventer toxin active on K+ channels

PnTx3-1 is a peptide isolated from the venom of the spider Phoneutria nigriventer that specifically inhibits A-type K(+) currents (I(A)) in GH(3) cells. Here we used a bacterial expression system to produce an NH(2)-extended mutant of PnTx3-1 (ISEF-PnTx3-1) and tested whether the toxin is functional. The recombinant toxin was purified from bacterial extracts by a combination of affinity and ion-exchange chromatography. The recombinant toxin blocked A-type K(+) currents in GH(3) cells in a fashion similar to that observed with the wild-type toxin purified from the spider venom. These results suggest that recombinant cDNA methods provide a novel source for the production of functional Phoneutria toxins. The recombinant ISEF-PnTx3-1 should be useful for further understanding of the role of A-type K(+) currents in biological processes.

PnTx3-6 a spider neurotoxin inhibits K+-evoked increase in [Ca2+](i) and Ca2+-dependent glutamate release in synaptosomes

The present experiments investigated the effect of a neurotoxin purified from the venom of the spider Phoneutria nigriventer. This toxic component, P. nigriventer toxin 3-6 (PnTx3-6), abolished Ca(2+)-dependent glutamate release with an IC(50) of 74.4nM but did not alter Ca(2+)-independent secretion of glutamate when brain cortical synaptosomes were depolarized by KCl (33mM). This effect was most likely due to interference with the entry of calcium through voltage activated calcium channels (VACC), reducing the increase in the intrasynaptosomal free calcium induced by membrane depolarization with an IC(50) of 9.5nM. We compared the alterations induced by PnTx3-6 with the actions of toxins known to block calcium channels coupled to exocytosis. Our results indicate that PnTx3-6 inhibition of glutamate release and intrasynaptosomal calcium involves P/Q type calcium channels and this toxin can be a valuable tool in the investigation of calcium channels.

Phoneutria nigriventer venom: a cocktail of toxins that affect ion channels

1. We review the pharmacological actions of toxins present in the venom of the aggressive spider Phoneutria nigriventer. 2. This venom is rich in toxins that affect ion channels and neurotransmitter release. Voltage-gated sodium, calcium, and potassium channels have been described as the main targets of these toxins. 3. In addition to these classical actions Phoneutria toxins have also been shown to affect glutamate transporter. 4. It is expected that molecular genetics in addition to biochemical, biophysical and pharmacological approaches will help to further define Phoneutria toxins and their mechanisms of action in the near future.

Modulation of Na+-channels by neurotoxins produces different effects on [3H]ACh release with mobilization of distinct Ca2+-channels

1. Voltage-gated Na+ channels are responsible for initiation and conduction of action potentials. The arrival of an action potential at nerve terminal increases intracellular Na+ and Ca2+ concentrations. Calcium entry into neurons through voltage-dependent calcium channels is associated with a variety of intracellular processes. Scorpion neurotoxins have been used as tools to investigate mechanisms involved in neurotransmitter release. Tityustoxin (TsTX) is an alpha-type toxin that delays Na+-channel inactivation. Toxin-gamma (TiTX-gamma) is a beta-type toxin that induces Na+-channel activation at resting potentials. 2. In the present work, we describe the effects of both toxins on [3H]acetylcholine ([3H]ACh) release from rat cerebrocortical synaptosomes, in the presence or absence of the calcium channels blockers: omega-conotoxin-GVIA (omega-CgTx), 1 microM; omega-agatoxin-IVA (omega-Aga), 30 nM; omega-conotoxin-MVIIC (omega-MVIIC), 1 microM; or verapamil, 1 microM. 3. TsTX evokes [3H]ACh release in a concentration-dependent manner with a gradual increase up to saturation at concentrations of 500 nM. However, release of ACh evoked by TiTX-gamma was not linear regarding the toxin concentration. The [3H]-ACh release evoked by TsTX or TiTX-gamma was partially inhibited by omega-CgTx or omega-Aga, and blocked with omega-MVIIC. Verapamil (1 microM) had no effect. Tetrodotoxin blocked [3H]ACh release evoked by both toxins. 4. These results show that different actions on Na+-channels produce different effects on [3H]ACh release with involvement of distinct presynaptic Ca2+-channels, which supports the idea that sodium channels may modulate neurotransmitter release.

Release of gamma-[(3)H]aminobutyric acid in rat brain cortical slices by alpha-scorpion toxin

In this paper, the effect of the alpha-scorpion toxin tityustoxin (TsTX) in the release of gamma-[(3)H]aminobutyric acid ([(3)H]GABA) from rat brain cortical slices is described. The TsTX-stimulatory effect on the release of [(3)H]GABA was dependent on incubation time and TsTX concentration, having an EC(50) of 0.33 microM. Tetrodotoxin (TTX) completely inhibited the TsTX action on [(3)H]GABA release. The scorpion toxin effect was calcium-dependent and involves P/Q calcium channels. beta-Alanine also induces the release of [(3)H]GABA that was not inhibited by TTX but was additive in the presence of TsTX. The data suggest a neuronal origin for the release of [(3)H]GABA by TsTX.

Phoneutria nigriventer omega-phonetoxin IIA blocks the Cav2 family of calcium channels and interacts with omega-conotoxin-binding sites

omega-Phonetoxin IIA (omegaPtxIIA), a peptide from spider venom (Phoneutria nigriventer), inhibits high threshold voltage-dependent calcium currents in neurons. To define its pharmacological specificity, we have used patch-clamp methods in cell lines expressing recombinant Ca(v)2.1, Ca(v)2.2, and Ca(v)2.3 channels (P/Q-, N-, and R-type currents, respectively). Calcium currents generated by Ca(v)2.1 and Ca(v)2.2 were blocked almost irreversibly by 3 nm omegaPtxIIA, whereas Ca(v)2.3 showed partial and readily reversible inhibition. Binding assays with mono[(125)I]iodo-omegaPtxIIA indicated that membranes expressing recombinant Ca(v)2.1 or Ca(v)2.2 channels showed a single class of sites with similar affinity (K(D) approximately 50 pm), whereas low affinity interactions were detectable with Ca(v)2.3. Kinetic, saturation, and displacement assays demonstrated that rat brain synaptosomes displayed multiple classes of binding sites for (125)I-omegaPtxIIA. High affinity binding of (125)I-omegaPtxIIA was totally displaced by omegaPtxIIA (K(i) = 100 pm), but only partially by omega-conotoxin GVIA (25% inhibition) and omega-conotoxin MVIIC (50% inhibition at 0.3 microm). (125)I-omegaPtxIIA thus defines a unique high affinity binding site that is predominantly associated with Ca(v)2.1 or Ca(v)2.2 channels.

Pharmacology and biochemistry of spider venoms

Spider venoms represent an incredible source of biologically active substances which selectively target a variety of vital physiological functions in both insects and mammals. Many toxins isolated from spider venoms have been invaluable in helping to determine the role and diversity of neuronal ion channels and the process of exocytosis. In addition, there is enormous potential for the use of insect specific toxins from animal sources in agriculture. For these reasons, the past 15-20 years has seen a dramatic increase in studies on the venoms of many animals, particularly scorpions and spiders. This review covers the pharmacological and biochemical activities of spider venoms and the nature of the active components. In particular, it focuses on the wide variety of ion channel toxins, novel non-neurotoxic peptide toxins, enzymes and low molecular weight compounds that have been isolated. It also discusses the intraspecific sex differences in given species of spiders.

Effects of a Lasiodora spider venom on Ca2+ and Na+ channels

The venom of a Brazilian spider, Lasiodora sp (Mygalomorphae, Theraphosidae), was screened for activity against ion channels using Ca2+ imaging and whole-cell patch clamp in GH3 cells. When tetrodotoxin (TTX) was present to block Na+ channels, the venom abolished the Ca2+ oscillations that are normally present in these cells and reduced the basal level of intracellular Ca2+. Under patch clamp, the venom reduced the L-type Ca2+ channel conductance and caused a positive shift in its voltage dependence of activation. In addition to these effects, when applied without TTX, the venom also caused a slow and noisy increase in intracellular Ca2+. The sensitivity of this second effect to TTX suggested an effect on Na+ channels, which was tested using patch clamp. Control Na+ currents inactivated completely as a single exponential. Treatment with the venom did not affect the amplitude of I(Na), but caused it to divide in two slower exponential components plus a sustained component, all of which were suppressed by TTX. The venom also caused a negative shift in the voltage dependence of activation and steady-state inactivation of I(Na). The observed effects of this venom on whole-cell currents explain the changes it causes in intracellular Ca2+ in GH3 cells and demonstrate that the venom of this spider is a source of toxins active against ion channels.

Spider neurotoxins block the beta scorpion toxin-induced calcium uptake in rat brain cortical synaptosomes

In this paper we describe the effects of the beta scorpion toxin Tityus gamma (TiTX gamma) and spider neurotoxins Tx3-3 and Tx3-4 in the (45)Ca(2+) uptake in synaptosomes. The TiTX gamma-stimulatory effect on (45)Ca(2+) uptake in synaptosomes was inhibited omega-Conotoxin MVIIC (omega-CgTX MVIIC) (0.1 microM) and omega-Agatoxin IVA (0.1 microM) by 70% and 41%, respectively. omega-CgTX MVIIC (1.0 microM) almost completely blocked the TiTX gamma-induced (45)Ca(2+) uptake in synaptosomes. Verapamil (1.0 microM) and omega-Conotoxin GVIA (0.1 microM) had no effect in the scorpion toxin-induced (45)Ca(2+) influx. The spider neurotoxins Tx3-3 and Tx3-4 inhibited the TiTX gamma-induced calcium uptake with an IC(50) of 10.0 and 30.0 nM, respectively. It is suggested that spider neurotoxins Tx3-3 and Tx3-4 blocking effect in the TiTX gamma-induced calcium uptake involves P/Q-type calcium channels.

Inhibition of neuronal high-voltage activated calcium channels by the omega-phoneutria nigriventer Tx3-3 peptide toxin

We have investigated the effect of omega-PnTx3-3 (referred to in previous papers simply as Tx3-3), a peptide toxin from the venom of the spider Phoneutria nigriventer, on neuronal high-voltage activated (HVA) Ca(2+) channels, using whole-cell patch-clamp. omega-PnTx3-3 (120 nM) blocked 74+/-8% of the total HVA Ca(2+) currents of cerebellar granule neurones, without affecting the low-voltage activated (LVA) current. P/Q/R-type currents in cerebellar granule neurones, isolated using 4 microM nicardipine and 100 nM omega-conotoxin GVIA, were markedly (79+/-6%) inhibited by 60 nM omega-PnTx3-3. R-type currents, isolated either by additional application of 0.5-1 microM of omega-agatoxin IVA or by pre-incubation with 5 microM omega-conotoxin MVIIC were inhibited almost totally by 120 nM of omega-PnTx3-3. omega-PnTx3-3 reversibly altered the kinetics of the P/Q/R current, increasing the degree of inactivation that occurred during a 50 ms pulse from 20% to 40%. N-type currents, recorded from neuroblastoma N18 cells, were partially (34+/-2%) inhibited by 320 nM omega-PnTx3-3. L-type currents, recorded from GH3 cells, were partially (45+/-12%) inhibited by 80 nM omega-PnTx3-3. We conclude that omega-PnTx3-3 inhibits all known HVA Ca(2+) channels, and most effectively the P/Q- and R-type currents.

Halothane enhances exocytosis of [3H]-acetylcholine without increasing calcium influx in rat brain cortical slices

1. The effect of halothane on the release of [3H]-acetylcholine ([3H]-ACh) in rat brain cortical slices was investigated. 2. Halothane (0.018 mM) did not significantly affect the basal and the electrical field stimulation induced release of [3H]-ACh. However, halothane (0.063 mM) significantly increased the basal release of [3H]-ACh and this effect was additive with the electrical field stimulation induced release of [3H]-ACh. 3. The release of [3H]-ACh induced by 0.063 mM halothane was independent of the extracellular sodium and calcium ion concentration and was decreased by tetracaine, an inhibitor of Ca(2+)-release from intracellular stores or dantrolene, an inhibitor of Ca(2+)-release from ryanodine-sensitive stores 4. Using 2-(4-phenylpiperidino)-cyclohexanol (vesamicol), a drug that blocks the storage of ACh in synaptic vesicles, we investigated whether exocytosis of this neurotransmitter is involved in the effect of halothane. Vesamicol significantly decreased the release of [3H]-ACh evoked by halothane. 5. It is suggested that halothane may cause a Ca2+ release from intracellular stores that increases [3H]-ACh exocytosis in rat brain cortical slices.

Phoneutria nigriventer toxin Tx3-1 blocks A-type K+ currents controlling Ca2+ oscillation frequency in GH3 cells

GH3 cells present spontaneous Ca2+ action potentials and oscillations of intracellular Ca2+, which can be modified by altering the activity of K+ or Ca2+ channels. We took advantage of this spontaneous activity to screen for effects of a purified toxin (Tx3-1) from the venom of Phoneutria nigriventer on ion channels. We report that Tx3-1 increases the frequency of Ca2+ oscillations, as do two blockers of potassium channels, 4-aminopyridine and charybdotoxin. Whole-cell patch clamp experiments show that Tx3-1 reversibly inhibits the A-type K+ current (I(A)) but does not block other K+ currents (delayed-rectifying, inward-rectifying, and large-conductance Ca2+-sensitive) or Ca2+ channels (T and L type) in these cells. In addition, we describe the sequence of a full cDNA clone of Tx3-1, which shows that Tx3-1 has no homology to other known blockers of K+ channels and gives insights into the processing of this neurotoxin. We conclude that Tx3-1 is a selective inhibitor of I(A), which can be used to probe the role of this channel in the control of cellular function. Based on the effect of Tx3-1, we suggest that I(A) is an important determinant of the frequency of Ca2+ oscillations in unstimulated GH3 cells.

The effect of calcium channels blockers in the K+-evoked release of [3H]adenine nucleotides from rat brain cortical synaptosomes

The role of L-,N-, P- and Q-type voltage-dependent calcium channels in K+-induced release of [3H]adenine nucleotides from rat brain cortical synaptosomes was investigated. Cd2+, a non-specific blocker of calcium channels, inhibited by 69% the release of the nucleotides induced by 33 mM K+. Nifedipine, omega-Conotoxin GVIA and omega-Agatoxin IVA had no effect whereas omega-Conotoxin MVIIC inhibited by 62% the K+ induced release of adenine nucleotides in rat brain cortical synaptosomes. It is concluded that Q-type calcium channels are directly involved in the release of adenine nucleotides in rat brain cortical synaptosomes.

Cloning, cDNA sequence analysis and patch clamp studies of a toxin from the venom of the armed spider (Phoneutria nigriventer)

The cDNAs (Tx3-2 and Pn3A) encoding precursor of toxin Tx3-2 and an isoform called Pn3A have been isolated from a library constructed from stimulated venom glands of the spider Phoneutria nigriventer. The cDNA of Tx3-2 reveals the presence of a signal peptide of 21 amino acids and of an intervening propeptide (with 16 amino acids) preceding the toxin sequence, which was followed by additional amino acid residues at the C-terminus (C-terminal peptide), implying post-translational modifications of the synthesised peptide. The deduced amino acid sequence for the mature toxin confirms the previous sequence published. In addition, by using the whole-cell patch clamp technique, we have determined that purified Tx3-2 decreases L-type currents present in GH3 cells. Finally, the presence of the cDNA Pn3A, with high sequence identity with Tx3-2, reveals the existence of a putative new toxin showing, at the cDNA level, 85.4% identity in its whole segment.