Effects of a toxic fraction, PhTx2, from the spider Phoneutria nigriventer on the sodium current

From the PnTx2-6 Toxin to the PnPP-19 Engineered Peptide: Therapeutic Potential in Erectile Dysfunction, Nociception, and Glaucoma

The venom of the “armed” spider Phoneutria nigriventer comprises several potent toxins. One of the most toxic components from this venom is the neurotoxin PnTx2-6 (LD50 = ∼ 0.7 μg/mouse, 48 residues, five disulfide bridges, MW = 5,289.31 Da), which slows down the inactivation of various Na+ channels. In mice and rats, this toxin causes priapism, an involuntary and painful erection, similar to what is observed in humans bitten by P. nigriventer. While not completely elucidated, it is clear that PnTx2-6 potentiates erectile function via NO/cGMP signaling, but it has many off-target effects. Seeking to obtain a simpler and less toxic molecule able to retain the pharmacological properties of this toxin, we designed and synthesized the peptide PnPP-19 (19 residues, MW = 2,485.6 Da), representing a discontinuous epitope of PnTx2-6. This synthetic peptide also potentiates erectile function via NO/cGMP, but it does not target Na+ channels, and therefore, it displays nontoxic properties in animals even at high doses. PnPP-19 effectively potentiates erectile function not only after subcutaneous or intravenous administration but also following topical application. Surprisingly, PnPP-19 showed central and peripheral antinociceptive activity involving the opioid and cannabinoid systems, suggesting applicability in nociception. Furthermore, considering that PnPP-19 increases NO availability in the corpus cavernosum, this peptide was also tested in a model of induced intraocular hypertension, characterized by low NO levels, and it showed promising results by decreasing the intraocular pressure which prevents retinal damage. Herein, we discuss how was engineered this smaller active non-toxic peptide with promising results in the treatment of erectile dysfunction, nociception, and glaucoma from the noxious PnTx2-6, as well as the pitfalls of this ongoing journey.

Spider Knottin Pharmacology at Voltage-Gated Sodium Channels and Their Potential to Modulate Pain Pathways

Voltage-gated sodium channels (Na_Vs) are a key determinant of neuronal signalling. Neurotoxins from diverse taxa that selectively activate or inhibit Na_V channels have helped unravel the role of Na_V channels in diseases, including chronic pain. Spider venoms contain the most diverse array of inhibitor cystine knot (ICK) toxins (knottins). This review provides an overview on how spider knottins modulate Na_V channels and describes the structural features and molecular determinants that influence their affinity and subtype selectivity. Genetic and functional evidence support a major involvement of Na_V subtypes in various chronic pain conditions. The exquisite inhibitory properties of spider knottins over key Na_V subtypes make them the best lead molecules for the development of novel analgesics to treat chronic pain.

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.

Partial Characterization of Venom from the Colombian Spider Phoneutria Boliviensis (Aranae:Ctenidae)

We report on the first studies on the characterization of venom from Phoneutria boliviensis (Aranae:Ctenidae) (F. O. Pickard-Cambridge, 1897), done with Colombian species. After the electrostimulation extraction process, the venom showed physicochemical properties corresponding to a colorless and water-soluble liquid with a density of 0.86 mg/mL and 87% aqueous content. P. boliviensis venom and RP-HPLC fractions showed hemolytic activity and hydrolyzed the synthetic substrate 4-nitro-3-octanoyloxy-benzoic acid, indicating the presence of phospholipases A₂ enzymes. The electrophoretic profile showed an important protein content with molecular masses below 14 kDa, and differences between male and female protein content were also revealed. The RP-HPLC venom profile exposes differences between males and female content consistent with the electrophoretic profile. Five fractions collected from the RP-HPLC displayed significant larvicidal activity. Mass analysis indicates the presence of peptides ranging from 1047.71 to 3278.07 Da. Two peptides, Ctenitoxin-Pb48 and Ctenitoxin-Pb53, were partially identified using HPLC-nESI-MS/MS, which showed a high homology with other Ctenitoxins (family Tx3) from Phoneutria nigriventer, Phoneutria keyserlingi and Phoneutria reidyi affecting voltage-gated calcium receptors (Cav 1, 2.1, 2.2 and 2.3) and NMDA-glutamate receptors.

Mechanisms involved in the nociception triggered by the venom of the armed spider Phoneutria nigriventer

BACKGROUND

The frequency of accidental spider bites in Brazil is growing, and poisoning due to bites from the spider genus Phoneutria nigriventer is the second most frequent source of such accidents. Intense local pain is the major symptom reported after bites of P. nigriventer, although the mechanisms involved are still poorly understood. Therefore, the aim of this study was to identify the mechanisms involved in nociception triggered by the venom of Phoneutria nigriventer (PNV).

METHODOLOGY/PRINCIPAL FINDINGS

Twenty microliters of PNV or PBS was injected into the mouse paw (intraplantar, i.pl.). The time spent licking the injected paw was considered indicative of the level of nociception. I.pl. injection of PNV produced spontaneous nociception, which was reduced by arachnid antivenin (ArAv), local anaesthetics, opioids, acetaminophen and dipyrone, but not indomethacin. Boiling or dialysing the venom reduced the nociception induced by the venom. PNV-induced nociception is not dependent on glutamate or histamine receptors or on mast cell degranulation, but it is mediated by the stimulation of sensory fibres that contain serotonin 4 (5-HT4) and vanilloid receptors (TRPV1). We detected a kallikrein-like kinin-generating enzyme activity in tissue treated with PNV, which also contributes to nociception. Inhibition of enzymatic activity or administration of a receptor antagonist for kinin B2 was able to inhibit the nociception induced by PNV. PNV nociception was also reduced by the blockade of tetrodotoxin-sensitive Na(+) channels, acid-sensitive ion channels (ASIC) and TRPV1 receptors.

CONCLUSION/SIGNIFICANCE

Results suggest that both low- and high-molecular-weight toxins of PNV produce spontaneous nociception through direct or indirect action of kinin B2, TRPV1, 5-HT4 or ASIC receptors and voltage-dependent sodium channels present in sensory neurons but not in mast cells. Understanding the mechanisms involved in nociception caused by PNV are of interest not only for better treating poisoning by P. nigriventer but also appreciating the diversity of targets triggered by PNV toxins.

Increased cavernosal relaxation by Phoneutria nigriventer toxin, PnTx2-6, via activation at NO/cGMP signaling

Erectile dysfunction mechanisms in diabetic patients are multifactorial and often lead to resistance to current therapy. Animal toxins have been used as pharmacological tools to study penile erection. Human accidents involving the venom of Phoneutria nigriventer spider are characterized by priapism. We hypothesize that PnTx2-6 potentiates cavernosal relaxation in diabetic mice by increasing cGMP. This effect is nNOS dependent. Cavernosal strips were contracted with phenylephrine (10⁻⁵ M) and relaxed by electrical field stimulation (EFS, 20V, 1–32 Hz) in the presence or absence of PnTx2-6 (10⁻⁸ M).Cavernosal strips from nNOS and eNOS knocaut (KO) mice, besides nNOS inhibitor (10⁻⁵M), were used to evaluate the role of this enzyme in the potentiation effect evoked by PnTx2-6. Tissue cGMP levels were determined after stimulation with PnTx2-6 in presence or absence of L-NAME (10⁻⁴M) and ω-conotoxin GVIA (10⁻⁶M), an N-type calcium channel inhibitor. Results showed PnTx2-6 enhanced cavernosal relaxation in diabetic mice (65%) and eNOS KO mice, but not in nNOS KO mice. The toxin effect in the cavernosal relaxation was abolished by nNOS inhibitor. cGMP levels are increased by PnTx2-6, however L-NAME abolished this enhancement as well as ω-conotoxin GVIA. We conclude PnTx2-6 facilitates penile relaxation in diabetic mice through a mechanism dependent on nNOS, probably via increasing NO/cGMP production.

Nitric oxide-induced vasorelaxation in response to PnTx2-6 toxin from Phoneutria nigriventer spider in rat cavernosal tissue

INTRODUCTION

Priapism is one of several symptoms observed in accidental bites by the spider Phoneutria nigriventer. The venom of this spider is comprised of many toxins, and the majority has been shown to affect excitable ion channels, mainly sodium (Na(+) ) channels. It has been demonstrated that PnTx2-6, a peptide extracted from the venom of P. nigriventer, causes erection in anesthetized rats and mice.

AIM

We investigated the mechanism by which PnTx2-6 evokes relaxation in rat corpus cavernosum.

MAIN OUTCOME MEASURES

PnTx2-6 toxin potentiates nitric oxide (NO)-dependent cavernosal relaxation.

METHODS

Rat cavernosal strips were incubated with bretylium (3 × 10(-5) M) and contracted with phenylephrine (PE; 10(-5) M). Relaxation responses were evoked by electrical field stimulation (EFS) or sodium nitroprusside (SNP) before and after 4 minutes of incubation with PnTx2-6 (10(-8) M). The effect of PnTx2-6 on relaxation induced by EFS was also tested in the presence of atropine (10(-6) M), a muscarinic receptor antagonist, N-type Ca(2+) channel blockers (ω-conotoxin GVIA, 10(-6) M) and sildenafil (3 × 10(-8) M). Technetium99m radiolabeled PnTx2-6 subcutaneous injection was administrated in the penis.

RESULTS

Whereas relaxation induced by SNP was not affected by PnTx2-6, EFS-induced relaxation was significantly potentiated by this toxin as well as PnTx2-6 plus SNP. This potentiating effect was further increased by sildenafil, not altered by atropine, however was completely blocked by the N-type Ca(2+) channels. High concentrated levels of radiolabeled PnTx2-6 was specifically found in the cavernosum tissue, suggesting PnTx2-6 is an important toxin responsible for P. nigriventer spider accident-induced priapism.

CONCLUSION

We show that PnTx2-6 slows Na(+) channels inactivation in nitrergic neurons, allowing Ca(2+) influx to facilitate NO/cGMP signalling, which promotes increased NO production. In addition, this relaxation effect is independent of phosphodiesterase enzyme type 5 inhibition. Our data displays PnTx2-6 as possible pharmacological tool to study alternative treatments for erectile dysfunction.

Tx2-6 toxin of the Phoneutria nigriventer spider potentiates rat erectile function

The venom of the spider Phoneutria nigriventer contains several toxins that have bioactivity in mammals and insects. Accidents involving humans are characterized by various symptoms including penile erection. Here we investigated the action of Tx2-6, a toxin purified from the P. nigriventer spider venom that causes priapism in rats and mice. Erectile function was evaluated through changes in intracavernosal pressure/mean arterial pressure ratio (ICP/MAP) during electrical stimulation of the major pelvic ganglion (MPG) of normotensive and deoxycorticosterone-acetate (DOCA)-salt hypertensive rats. Nitric oxide (NO) release was detected in cavernosum slices with fluorescent dye (DAF-FM) and confocal microscopy. The effect of Tx2-6 was also characterized after intracavernosal injection of a non-selective nitric oxide synthase (NOS) inhibitor, L-NAME. Subcutaneous or intravenous injection of Tx2-6 potentiated the elevation of ICP/MAP induced by ganglionic stimulation. L-NAME inhibited penile erection and treatment with Tx2-6 was unable to reverse this inhibition. Tx2-6 treatment induced a significant increase of NO release in cavernosum tissue. Attenuated erectile function of DOCA-salt hypertensive rats was fully restored after toxin injection. Tx2-6 enhanced erectile function in normotensive and DOCA-salt hypertensive rats, via the NO pathway. Our studies suggest that Tx2-6 could be important for development of new pharmacological agents for treatment of erectile dysfunction.

Promiscuous and reversible blocker of presynaptic calcium channels in frog and crayfish neuromuscular junctions from Phoneutria nigriventer spider venom

Peptide channel blockers found in venoms of many predators are useful pharmacological tools and potential therapeutic agents. The venom of the Brazilian spider Phoneutria nigriventer contains a fraction, omega-phonetoxin-IIA (omega-Ptx-IIA, 8360 MW), which blocks Ca2+ channels. At frog neuromuscular junctions (NMJ) bathed in normal Ca2+ (1.8 mM) saline, omega-Ptx IIA did not affect spontaneous transmitter release but reversibly reduced evoked transmitter release by 75 and 95% at 12 and 24 nM, respectively. In contrast, toxin effects were irreversible in low-Ca2+ (0.5 mM) saline. Ca2+ imaging in normal-Ca2+ saline showed that omega-Ptx-IIA partially blocked stimulus-dependent presynaptic Ca2+ signals, and the blockade was almost completely reversible. Increases in spontaneous release frequency induced by high extracellular K+ were blocked by omega-Ptx-IIA. Therefore omega-Ptx-IIA blocks N-type Ca2+ channels, which admit Ca2+ that triggers transmitter release at the frog NMJ. Additional evidence predicts that omega-Ptx-IIA binds to N-type Ca2+ channels at a different site from that of omega-Conotoxin-GVIA. omega-Ptx-IIA also gave a low-affinity partial blockade of transmitter release and presynaptic Ca2+ signals at crayfish NMJs where P-type channels are blocked by omega-agatoxin-IVA. The Ca2+-dependent reversibility and promiscuity of this toxin may make it highly useful experimentally and therapeutically.

Phoneutria nigriventer spider venom activates 5-HT4 receptors in rat-isolated vagus nerve

1. The venom of Phoneutria nigriventer spider (PNV) causes intense pain and inflammation following an attack. We have investigated the involvement of capsaicin-sensitive nerve fibres by utilizing an in vitro nerve preparation. Extracellular DC potential recordings were made from the rat-isolated vagus nerve, a preparation that is rich in capsaicin-sensitive, that is, nociceptive, C-fibres. 2. PNV (1-10 microg ml(-1)), capsaicin (0.03-0.3 microM) or 5-hydroxytriptamine (5-HT) (0.3-3 microM) induced dose-dependent depolarizations of vagus nerve fibres. Depolarizing responses to capsaicin were blocked by ruthenium red (RR, 10 microM), but responses to PNV were not. Depolarizing responses to PNV or veratridine (50 microM) were inhibited by tetrodotoxin (TTX, 10 microM), but those to capsaicin were not. This suggests that capsaicin and PNV depolarize the nerve fibres by distinct mechanisms. 3. Depolarization in response to 5-HT (3 microM) was reduced by the 5-HT(3) receptor antagonists Y25130 (0.5 micro M) and tropisetron (10 nM) or, to a lesser extent, by the 5-HT(4) receptor antagonist RS39604 (1 or 10 microM). Depolarizing responses to PNV were not affected significantly by Y25130 or tropisetron, but were blocked by RS39604. 4. These data show that 5-HT(4) receptors play a significant role in the activation of nociceptive sensory nerve fibres by PNV and suggest that this is of importance in the development of the pain and inflammation associated with bites from the P. nigriventer spider.

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.

Cloning of cDNAS encoding neurotoxic peptides from the spider Phoneutria nigriventer

A cDNA library made from venom glands of the spider Phoneutria nigriventer was constructed and used to clone neurotoxic peptides. A cDNA of about 360 nucleotides encoding the precursor for the toxin Tx2-1 active on mammals has been isolated. The deduced amino acid sequence for the mature polypeptide confirms the polypeptide sequence previously published. In addition, two new putative toxins called Pn2-1A and Pn2-5A have been characterized and their complete amino acid sequence show 92% similarity to Tx2-1 and 94% similarity to Tx2-5 respectively. The cDNAs revealed that the precursors contain signal peptides characterized by a very hydrophobic core and a propeptide interposed between the signal sequence and the peptide toxin.

A novel tool for the investigation of glutamate release from rat cerebrocortical synaptosomes: the toxin Tx3-3 from the venom of the spider Phoneutria nigriventer

The present experiments investigated the effect of some of the toxic components present in the venom of the spider Phoneutria nigriventer on the release of neurotransmitter. The toxic fraction, Phoneutria nigriventer toxin-3 (PhTx3), abolished Ca2+-dependent glutamate release, but did not alter Ca2+-independent secretion of glutamate when rat brain cortical synaptosomes were depolarized with 33 mM KCl. This effect was most likely due to interference with the entry of calcium through voltage-gated calcium channels, because PhTx3 reduced by 50% the increase in intrasynaptosomal free calcium induced by membrane depolarization, and did not affect the release of glutamate evoked by a calcium ionophore (ionomycin). A polypeptide (Tx3-3) present in the PhTx3 fraction reproduced the effects of the PhTx3 fraction on transmitter release and intrasynaptosomal free calcium in the low nanomolar range. We compared the alterations produced by the Tx3-3 with the actions of toxins known to block calcium channels coupled to exocytosis: the results indicated that the Tx3-3 inhibition of glutamate release and intrasynaptosomal calcium resemble that observed with omega-conotoxin MVIIC. We suggest that the Tx3-3 is a calcium-channel antagonist that blocked glutamate exocytosis.

Blockade of acetylcholine release at the motor endplate by a polypeptide from the venom of Phoneutria nigriventer

1. The mechanisms underlying the muscle relaxation effect of a fraction (PF3) isolated from the Phoneutria nigriventer spider venom were assessed on mouse diaphragm and chick biventer cervicis muscle preparations. 2. PF3 (0.25-4 micrograms ml-1) produced a concentration-dependent blockade of the nerve-elicited muscle twitch of the mouse diaphragm (IC50 = 0.8 micrograms ml-1) without affecting the directly induced muscle twitch. In similar preparations, the crude venom (1-10 micrograms ml-1) produced muscle contracture and blocked both the direct and indirectly induced muscle twitches. 3. In the chick biventer cervicis muscle, PF3 (1-5 micrograms ml-1) blocked the nerve stimulated muscle twitch (IC50 = 1.26 micrograms ml-1), but did not alter the postjunctional response to exogenous acetylcholine (ACh, 10 microM-10 mM). 4. PF3 (2-8 micrograms ml-1) reduced the frequency of miniature endplate potentials (m.e.p.ps) recorded intracellularly from the mouse diaphragm muscle fibers by 58 to 64%, and diminished the amplitude of m.e.p.ps by 20 to 40% of control. The relationship between log m.e.p.p. frequency and log [Ca2+]o was shifted rightwards in the presence of 4 micrograms ml-1 PF3. 5. Raising the frequency of m.e.p.ps with high K+ medium or theophylline (3 mM) did not prevent the toxin-induced depression of spontaneous ACh release. 6. The quantal content of e.p.ps (m), determined in cut-diaphragm muscle fibres, was reduced by 53% and 77% of control by 1 and 4 micrograms ml-1 PF3, respectively. At 1 microgram ml-1 the toxin shifted the relationship between log m and log [Ca2+]o towards higher values without apparent change of the slope. 7. E.p.p. trains elicited at 10 to 50 Hz in the presence of PF3 (1 microgram ml-1) exhibited irregular amplitudes and facilitation related to the frequency of nerve stimulation. 8. It is concluded that PF3 blocks neuromuscular transmission by acting prejunctionally and reducing the nerve-evoked transmitter release. The effect was related to a diminished Ca2+ entry into the nerve terminal associated with inhibition of exocytosis.

Modulation of Ca(2+)-stimulated glutamate release from synaptosomes by Na+ entry through tetrodotoxin-sensitive channels

Tityustoxin (TsTX), a toxin obtained from the venom of the Brazilian scorpion Tityus serrulatus, stimulates Na+ influx through tetrodotoxin (TTX)-sensitive Na+ channels which, in turn, promotes both Ca(2+)-dependent and Ca(2+)-independent release of glutamate from rat cerebrocortical synaptosomes. The level of Ca(2+)-dependent glutamate release after addition of 0.5 microM TsTX is greater than that produced by a maximally depolarizing concentration of KCl. This effect of TsTX, which is entirely dependent on Na+ entry, suggests that Na+ has a role in modulating Ca2+ entry and glutamate release that is not simply related to membrane depolarization. In order to investigate possible modulatory role(s) of Na+ on Ca(2+)-dependent glutamate release, we compared the effects of TsTX with those of KCl and the Na+ ionophore gramicidin D. When used alone, 100 nM gramicidin D produced a larger increase in intrasynaptosomal free Na+ than did 0.5 microM TsTX, and a similar rise in intrasynaptosomal free Ca2+, but was much less effective in promoting glutamate release. Even the combination of membrane depolarization (by 33 mM KCl) and elevation of intrasynaptosomal free Na+ (by 100 nM gramicidin) was still less effective than TsTX at causing Ca(2+)-dependent glutamate release. These data suggest that localized Na+ entry, through TTX-sensitive Na+ channels, exerts a modulatory role on Ca(2+)-dependent glutamate release from nerve endings in the cerebral cortex.

Rat cortical synaptosomes have more than one mechanism for Ca2+ entry linked to rapid glutamate release: studies using the Phoneutria nigriventer toxin PhTX2 and potassium depolarization

PhTX2, one of the components of the venom of the South American spider Phoneutria nigriventer, inhibits the closure of voltage-sensitive Na+ channels. Incubation of cerebral-cortical synaptosomes with PhTX2 causes a rapid increase in the intrasynaptosomal free Ca2+ concentration and a dose-dependent release of glutamate. This release is made up of a slow component, which appears to be due to reversal of Na(+)-dependent glutamate uptake, and more rapid component that is dependent on the entry of extrasynaptosomal Ca2+. It has previously been shown that membrane depolarization using KCl can cause rapid Ca(2+)-dependent release of glutamate from synaptosomes. This requires Ca2+ entry through a specific type of Ca2+ channel that is sensitive to Aga-GI, a toxic component of the venom of the spider Agelenopsis aperta. We have compared the effects of PhTX2 and KCl on elevation of intrasynaptosomal free Ca2+ and glutamate release, and a number of differences have emerged. Firstly, PhTX2-mediated Ca2+ influx and glutamate release, but not those caused by KCl, are inhibited by tetrodotoxin. Secondly, KCl produces a clear additional increase in Ca2+ and glutamate release following those elicited by PhTX2. Finally, 500 microM MnCl2 abolishes PhTX2-mediated, but not KCl-mediated, glutamate release. These findings suggest that more than one mechanism of Ca2+ entry may be coupled to glutamate release from nerve endings.