Diversity of intestinal protozoa and clinical signs associated in wild-caught Phoneutria nigriventer kept in captivity for the anti-arachnid serum production

The phylum Arthropoda comprises approximately 85% of all described animal species. The class Arachnida includes some invertebrates of great importance as they are either involved in the transmission of diseases or poses a risk of human envenomation. Spiders belonging to the genus Phoneutria sp., are the arachnids exhibiting medical importance. These animals were quarantined and maintained in captivity at the Biotério de Artrópodes of the Instituto Butantan, São Paulo, Brazil, for the production of the anti-arachnid serum. A total 509 feces samples from different Phoneutria nigriventer were analyzed, and 131 (25.73%) samples were found to be positive for flagellates and ciliates. All positive samples were subjected to DNA extraction and amplification of 18S gene. A total of 16 sequences were obtained and analyzed using BLAST. Sequences were identified as Colpoda steiini, one as Colpoda aspera, one to Colpoda sp., and one as "ciliated". Four identified as Parabodo caudatus, two as Urostipulosphaera sp., one as Helkesimastix sp., and one as a Euglena-like. The presence of clinical signs was observed in 16 spiders. The intestinal protozoa that affect armed spiders were identified for the first time as an initial step for understanding the parasitic diseases in these organisms.

Neuroprotective effects of the CTK 01512-2 toxin against neurotoxicity induced by 3-nitropropionic acid in rats

The mitochondrial inhibitor 3-nitropropionic acid (3-NP) induces excitotoxicity. The authors hypothesized that CTK 01512-2, a recombinant peptide calcium channel N-type blocker, and the TRPA1 antagonist, could show neuroprotective effects. The male Wistar rats received 3-NP [25 mg/kg (i.p.) for 7 days], and a treatment of CTK 01512-2 was delivered intrathecally (i.t.), thrice a week. The neuroprotective effects were evaluated by [18F]FDG MicroPET analysis. The CTK 01512-2 toxin was able to reestablish similar glucose uptakes on the control animals. To detect the neurobehavioral effects from 3-NP, three protocols (6.25, 12.5, 18.75 mg/kg of 3-NP (i.p.), for 3, 4, and 6 days, respectively) were evaluated by performance tests (open field test, walk footprint, elevated plus-maze, Y-maze, and the object recognition test). Important disabilities in the gait of the rats were seen, as well as memory deficits, and anxious behavior in the animals that were treated with all 3-NP protocols. The dose of 18.75 mg/kg (for 3 days) showed the most pronounced behavioral effects and lethality, while the rats treated with 12.5 mg/kg (for 4 days) showed behavioral effects similar to the 6.25 mg/kg dose (for 6 days). The third protocol was then repeated and the rats were treated with the CTK 01512-2 toxin to be evaluated behaviorally again. The recombinant peptide prevented all of the gait-evaluated parameters that were induced by 3-NP at a 6.25 mg/kg dose, which displayed an improvement in the exploratory activities. Overall, these results have reinforced the positive effects of CTK 01512-2 against the behavioral changes that were induced by the mitochondrial inhibitor 3-NP.

Phoneutria nigriventer Tx3-3 peptide toxin reduces fibromyalgia symptoms in mice

Fibromyalgia is characterized by the amplification of central nervous system pain with concomitant fatigue, sleep, mood disorders, depression, and anxiety. It needs extensive pharmacological therapy. In the present study, Swiss mice were treated with reserpine (0.25 mg/kg, s.c.) over three consecutive days, in order to reproduce the pathogenic process of fibromyalgia. On day 4, the administrations of the Tx3-3 toxin produced significant antinociception in the mechanical allodynia (87.16% ±12.7%) and thermal hyperalgesia (49.46% ± 10.6%) tests when compared with the PBS group. The effects produced by the classical analgesics (duloxetine 30 mg/kg, pramipexole 1 mg/kg, and pregabalin 30 mg/kg, p.o., respectively) in both of the tests also demonstrated antinociception. The administrations were able to increase the levels of the biogenic amines (5-HTP and DE) in the brain. The treatments with pramipexole and pregabalin, but not duloxetine, decreased the immobility time in the FM-induced animals that were submitted to the forced swimming test; however, the Tx3-3 toxin (87.45% ± 4.3%) showed better results. Taken together, the data has provided novel evidence of the ability of the Tx3-3 toxin to reduce painful and depressive symptoms, indicating that it may have significant potential in the treatment of FM.

Spider venom components decrease glioblastoma cell migration and invasion through RhoA-ROCK and Na+/K+-ATPase β2: potential molecular entities to treat invasive brain cancer

BACKGROUND

Glioblastoma (GB) cells have the ability to migrate and infiltrate the normal parenchyma, leading to the formation of recurrent tumors often adjacent to the surgical extraction site. We recently showed that Phoneutria nigriventer spider venom (PnV) has anticancer effects mainly on the migration of human GB cell lines (NG97 and U-251). The present work aimed to investigate the effects of isolated components from the venom on migration, invasiveness, morphology and adhesion of GB cells, also evaluating RhoA-ROCK signaling and Na⁺/K⁺-ATPase β2 (AMOG) involvement.

METHODS

Human (NG97) GB cells were treated with twelve subfractions (SFs-obtained by HPLC from PnV). Migration and invasion were evaluated by scratch wound healing and transwell assays, respectively. Cell morphology and actin cytoskeleton were shown by GFAP and phalloidin labeling. The assay with fibronectin coated well plate was made to evaluate cell adhesion. Western blotting demonstrated ROCK and AMOG levels and a ROCK inhibitor was used to verify the involvement of this pathway. Values were analyzed by the GraphPad Prism software package and the level of significance was determinate using one-way analysis of variance (ANOVA) followed by Dunnett's multiple comparisons test.

RESULTS

Two (SF1 and SF11) of twelve SFs, decreased migration and invasion compared to untreated control cells. Both SFs also altered actin cytoskeleton, changed cell morphology and reduced adhesion. SF1 and SF11 increased ROCK expression and the inhibition of this protein abolished the effects of both subfractions on migration, morphology and adhesion (but not on invasion). SF11 also increased Na⁺/K⁺-ATPase β2.

CONCLUSION

All components of the venom were evaluated and two SFs were able to impair human glioblastoma cells. The RhoA effector, ROCK, was shown to be involved in the mechanisms of both PnV components. It is possible that AMOG mediates the effect of SF11 on the invasion. Further investigations to isolate and biochemically characterize the molecules are underway.

Intravitreal injection of peptides PnPa11 and PnPa13, derivatives of Phoneutria nigriventer spider venom, prevents retinal damage

Background:

PnPa11 and PnPa13 are synthetic peptides derived from Phoneutria nigriventer spider venom, which display antinociceptive and neuroprotective properties. In this work, we evaluated the safety of intravitreal use and the neuroprotective effect of these peptides.

Methods:

The cytotoxicity and the antiangiogenic activity of these peptides were evaluated by the sulforhodamine-B method and chicken chorioallantoic membrane (CAM) assay, respectively. The in vivo safety was analyzed in Wistar rats that were intravitreally injected with different doses (0.50; 1.25; 2.50; 3.75 and 5.00 µg/mL) of these peptides (right eye, n = 6). The retinal function was assessed by electroretinography exams (ERG), intraocular pressure (IOP), and histological analyzes. In order to investigate the neuroprotective effect, Wistar rats received intravitreal injections (right eye, n = 6) of peptides at 1.25 µg/mL and then were exposed to blue LED light. In addition, the visual function and the retinal microstructure were verified.

Results:

Cytotoxicity analyses demonstrated that the peptides did not present any toxicity over ARPE-19 (adult retinal pigmented epithelial) cell line and the antiangiogenic study highlighted that the peptides promoted the reduction of blood vessels. The intravitreal injection did not cause major changes, neither induced any irreversible damage. In the retinal degeneration assay, the ERG records demonstrated that the prior treatment with PnPa11 and PnPa13 protected the retina from damage. Morphological analyses confirmed the ERG findings. Immunoblotting analyses revealed that PnPa11 increased Erk1/2, NR2A, and NR2B retinal expression after the light stress model, but did not cause Akt1 activation, while PnPa13 prevented Erk1/2 and Akt1 dephosphorylation.

Conclusions:

The intraocular administration of these peptides was well tolerated and presented protective activity against retinal degeneration, suggesting the potential use of these peptides as neuroprotectors in the ophthalmological field.

Analgesic effects of the CTK 01512-2 toxin in different models of orofacial pain in rats

BACKGROUND

Orofacial pain is clinically challenging, having therapeutic failures and side effects. This study evaluated the antinociceptive activities of the CTK 01512-2 toxin, the TRPA1 channel antagonist, and the selective inhibitor of the N-type voltage-gated calcium channels (N-type VGCC), in different pain models.

MATERIALS AND METHODS

The trigeminal ganglia were stimulated in vitro with capsaicin. The in vivo models received subcutaneous (sc) injections of formalin into the upper lip of the rats, Freund's Complete Adjuvant (FCA) into the temporomandibular joint (TMJ), and infraorbital nerve constrictions (IONC). CTK 01512-2 at concentrations of 30, 100, and 300 pmol/site, intrathecally (ith), and MVIIA at 10, 30, and 100 pmol/site in the formalin test, guided the doses for the models. The glutamate levels in the CSF of the rats that were submitted to IONC were analyzed.

RESULTS

CTK 01512-2 decreased the nociceptive behavior in the inflammatory phase of the formalin test (65.94 ± 7.35%) and MVIIA in the neurogenic phase (81.23 ± 3.36%). CTK 01512-2 reduced facial grooming with FCA in the TMJ (96.7 ± 1.6%), and in the IONC neuropathy model, it decreased heat hyperalgesia (100%) and cold hyperalgesia (81.61 ± 9.02%). The levels of glutamate in the trigeminal ganglia in vitro (81.40 ± 8.59%) and in the CSF in vivo (70.0 ± 9.2%) were reduced.

CONCLUSIONS

The roles of TRPA1 in pain transduction and the performance of CTK 01512-2 in the inhibition of the N-type VGCCs were reinforced. This dual activity may represent an advantage in clinical treatments.

Antinociceptive effect of PnTx4(5-5), a peptide from Phoneutria nigriventer spider venom, in rat models and the involvement of glutamatergic system

Background:

The venom of Phoneutria nigriventer spider is a source of numerous bioactive substances, including some toxins active in insects. An example is PnTx4(5-5) that shows a high insecticidal activity and no apparent toxicity to mice, although it inhibited NMDA-evoked currents in rat hippocampal neurons. In this work the analgesic activity of PnTx4(5-5) (renamed Γ-ctenitoxin-Pn1a) was investigated.

Methods:

The antinociceptive activity was evaluated using the paw pressure test in rats, after hyperalgesia induction with intraplantar injection of carrageenan or prostaglandin E₂ (PGE₂).

Results:

PnTx4(5-5), subcutaneously injected, was able to reduce the hyperalgesia induced by PGE₂ in rat paw, demonstrating a systemic effect. PnTx4(5-5) administered in the plantar surface of the paw caused a peripheral and dose-dependent antinociceptive effect on hyperalgesia induced by carrageenan or PGE₂. The hyperalgesic effect observed in these two pain models was completely reversed with 5 µg of PnTx4(5-5). Intraplantar administration of L-glutamate induced hyperalgesic effect that was significantly reverted by 5 μg of PnTx4(5-5) injection in rat paw.

Conclusion:

The antinociceptive effect for PnTx4(5-5) was demonstrated against different rat pain models, i.e. induced by PGE₂, carrageenan or glutamate. We suggest that the antinociceptive effect of PnTx4(5-5) may be related to an inhibitory activity on the glutamatergic system.

Immunodetection of toxins in historesin-embedded sections of Phoneutria nigriventer venom glands using laser confocal scanning microscopy

In the last decades, main advances were achieved in the identification, structural and pharmacological characterization of Phoneutria nigriventer toxins. However, studies on the venom-producing apparatus are rare. Presently, we applied immunolabeling to historesin-embedded cross-sections of P. nigriventer venom glands. Toxins and toxin-secreting cells were successfully located in situ, using laser confocal scanning microscopy. The methodological strategy was successful and may be applied in future studies on venom glands and other secreting tissues, in general.

Acute Toxicity of the Recombinant and Native Phα1β Toxin: New Analgesic from Phoneutria nigriventer Spider Venom

Phα1β, a purified peptide from the venom of the spider Phoneutria nigriventer, and its recombinant form CTK 01512-2 are voltage-dependent calcium channel (Ca_V) blockers of types N, R, P/Q, and L with a preference for type N. These peptides show analgesic action in different pain models in rats. The aim of this study was to evaluate the acute intrathecal toxicity of the native and recombinant Phα1β toxin in Wistar rats. Clinical signs, serum biochemistry, organ weight, and histopathological alterations were evaluated in male and/or female rats. Dyspnea was observed in males, hyporesponsiveness in females, and Straub tail and tremors in both genders. There were no significant differences in male organ weight, although significant differences in the female relative weight of the adrenal glands and spleen have been observed; these values are within the normal range. Serum biochemical data revealed a significant reduction within the physiological limits of species related to urea, ALT, AST, and FA. Hepatic and renal congestion were observed for toxin groups. In renal tissue, glomerular infiltrates were observed with increased glomerular space. These histological alterations were presented in focal areas and in mild degree. Therefore, Phα1β and CTK 01512-2 presented a good safety profile with transient toxicity clinical signals in doses higher than used to obtain the analgesic effect.

Phoneutria nigriventer Spider Toxin PnTx2-1 (δ-Ctenitoxin-Pn1a) Is a Modulator of Sodium Channel Gating

Spider venoms are complex mixtures of biologically active components with potentially interesting applications for drug discovery or for agricultural purposes. The spider Phoneutria nigriventer is responsible for a number of envenomations with sometimes severe clinical manifestations in humans. A more efficient treatment requires a comprehensive knowledge of the venom composition and of the action mechanism of the constituting components. PnTx2-1 (also called δ-ctenitoxin-Pn1a) is a 53-amino-acid-residue peptide isolated from the venom fraction PhTx2. Although PnTx2-1 is classified as a neurotoxin, its molecular target has remained unknown. This study describes the electrophysiological characterization of PnTx2-1 as a modulator of voltage-gated sodium channels. PnTx2-1 is investigated for its activity on seven mammalian Na_V-channel isoforms, one insect Na_V channel and one arachnid Na_V channel. Furthermore, comparison of the activity of both PnTx2-1 and PnTx2-6 on Na_V1.5 channels reveals that this family of Phoneutria toxins modulates the cardiac Na_V channel in a bifunctional manner, resulting in an alteration of the inactivation process and a reduction of the sodium peak current.

Inhibition of VEGF-Flk-1 binding induced profound biochemical alteration in the hippocampus of a rat model of BBB breakdown by spider venom. A preliminary assessment using FT-IR spectroscopy

Phoneutria nigriventer spider venom (PNV) contains ion channels-acting neuropeptides that in rat induces transitory blood-brain barrier breakdown (BBBb) in hippocampus in parallel with VEGF upregulation. We investigated whether VEGF has a neuroprotective role by inhibiting its binding to receptor Flk-1 by itraconazole (ITZ). FT-IR spectroscopy examined the biochemical status of hippocampus and evaluated BBBb in rats administered PNV or ITZ/PNV at periods with greatest toxicity (1-2h), recovery (5h) and visual absence of symptoms (24h), and compared to saline and ITZ controls. The antifungal treatment before venom intoxication aggravated the venom effects and increased BBB damage. FT-IR spectra of venom, hippocampi of controls, PNV and ITZ-PNV showed a 1400 cm^-1 band linked to symmetric stretch of carboxylate and 1467 cm^-1 band (CH₂ bending: mainly lipids) that were considered biomarker and reference bands, respectively. Inhibition of VEGF/Flk-1 binding produced marked changes in lipid/protein stability at 1-2h. The largest differences were observed in spectra regions assigned to lipids, both symmetric (2852 cm^-1) and asymmetric (2924 and 2968 cm^-1). Quantitative analyses showed greatest increases in the 1400 cm^-1/1467 cm^-1 ratio also at 1h. Such changes at period of rats' severe intoxication referred to wavenumber region from 3106 cm^-1 to 687 cm^-1 assigning for C-H and N-H stretching of protein, Amide I, C=N cytosine, N-H adenine, Amide II, CH₂ bending: mainly lipids, C-O stretch: glycogen, polysaccharides, glycolipids, z-type DNA, C-C, C-O and CH out-of-plane bending vibrations. We conclude that VEGF has a neuroprotective role and can be a therapeutic target in PNV envenomation. FT-IR spectroscopy showed to be instrumental for monitoring biochemical changes in this model of P. nigriventer venom-induced BBB disruption.

The Peptide PnPP-19, a Spider Toxin Derivative, Activates μ-Opioid Receptors and Modulates Calcium Channels

The synthetic peptide PnPP-19 comprehends 19 amino acid residues and it represents part of the primary structure of the toxin δ-CNTX-Pn1c (PnTx2-6), isolated from the venom of the spider Phoneutria nigriventer. Behavioural tests suggest that PnPP-19 induces antinociception by activation of CB1, μ and δ opioid receptors. Since the peripheral and central antinociception induced by PnPP-19 involves opioid activation, the aim of this work was to identify whether this synthetic peptide could directly activate opioid receptors and investigate the subtype selectivity for μ-, δ- and/or κ-opioid receptors. Furthermore, we also studied the modulation of calcium influx driven by PnPP-19 in dorsal root ganglion neurons, and analyzed whether this modulation was opioid-mediated. PnPP-19 selectively activates μ-opioid receptors inducing indirectly inhibition of calcium channels and hereby impairing calcium influx in dorsal root ganglion (DRG) neurons. Interestingly, notwithstanding the activation of opioid receptors, PnPP-19 does not induce β-arrestin2 recruitment. PnPP-19 is the first spider toxin derivative that, among opioid receptors, selectively activates μ-opioid receptors. The lack of β-arrestin2 recruitment highlights its potential for the design of new improved opioid agonists.

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.

A spider derived peptide, PnPP-19, induces central antinociception mediated by opioid and cannabinoid systems

Background

Some peptides purified from the venom of the spider Phoneutria nigriventer have been identified as potential sources of drugs for pain treatment. In this study, we characterized the antinociceptive effect of the peptide PnPP-19 on the central nervous system and investigated the possible involvement of opioid and cannabinoid systems in its action mechanism.

Methods

Nociceptive threshold to thermal stimulation was measured according to the tail-flick test in Swiss mice. All drugs were administered by the intracerebroventricular route.

Results

PnPP-19 induced central antinociception in mice in the doses of 0.5 and 1 μg. The non-selective opioid receptor antagonist naloxone (2.5 and 5 μg), μ-opioid receptor antagonist clocinnamox (2 and 4 μg), δ-opioid receptor antagonist naltrindole (6 and 12 μg) and CB₁ receptor antagonist AM251 (2 and 4 μg) partially inhibited the antinociceptive effect of PnPP-19 (1 μg). Additionally, the anandamide amidase inhibitor MAFP (0.2 μg), the anandamide uptake inhibitor VDM11 (4 μg) and the aminopeptidase inhibitor bestatin (20 μg) significantly enhanced the antinociception induced by a low dose of PnPP-19 (0.5 μg). In contrast, the κ-opioid receptor antagonist nor-binaltorphimine (10 μg and 20 μg) and the CB₂ receptor antagonist AM630 (2 and 4 μg) do not appear to be involved in this effect.

Conclusions

PnPP-19-induced central antinociception involves the activation of CB₁ cannabinoid, μ- and δ-opioid receptors. Mobilization of endogenous opioids and cannabinoids might be required for the activation of those receptors, since inhibitors of endogenous substances potentiate the effect of PnPP-19. Our results contribute to elucidating the action of the peptide PnPP-19 in the antinociceptive pathway.

δ-Ctenitoxin-Pn1a, a Peptide from Phoneutria nigriventer Spider Venom, Shows Antinociceptive Effect Involving Opioid and Cannabinoid Systems, in Rats

PnTx4(6-1), henceforth renamed δ-Ctenitoxin-Pn1a (δ-CNTX-Pn1a), a peptide from Phoneutria nigriventer spider venom, initially described as an insect toxin, binds to site 3 of sodium channels in nerve cord synaptosomes and slows down sodium current inactivation in isolated axons in cockroaches (Periplaneta americana). δ-CNTX-Pn1a does not cause any apparent toxicity to mice, when intracerebroventricularly injected (30 μg). In this study, we evaluated the antinociceptive effect of δ-CNTX-Pn1a in three animal pain models and investigated its mechanism of action in acute pain. In the inflammatory pain model, induced by carrageenan, δ-CNTX-Pn1a restored the nociceptive threshold of rats, when intraplantarly injected, 2 h and 30 min after carrageenan administration. Concerning the neuropathic pain model, δ-CNTX-Pn1a, when intrathecally administered, reversed the hyperalgesia evoked by sciatic nerve constriction. In the acute pain model, induced by prostaglandin E₂, intrathecal administration of δ-CNTX-Pn1a caused a dose-dependent antinociceptive effect. Using antagonists of the receptors, we showed that the antinociceptive effect of δ-CNTX-Pn1a involves both the cannabinoid system, through CB₁ receptors, and the opioid system, through μ and δ receptors. Our data show, for the first time, that δ-Ctenitoxin-Pn1a is able to induce antinociception in inflammatory, neuropathic and acute pain models.

Are Synchronized Changes in Connexin-43 and Caveolin-3 a Bystander Effect in a Phoneutria nigriventer Venom Model of Blood-Brain Barrier Breakdown?

Upregulation of caveolin-3 (Cav-3) or connexin-43 (Cx43) in astrocytes has been associated with important brain pathologies. We used Phoneutria nigriventer spider venom (PNV), which induces blood-brain barrier breakdown in rats, in order to investigate Cav-3 and Cx43 expression in the cerebellum over critical periods of rat envenomation. By immunofluorescence, western blotting (WB), and transmission electron microscopy (TEM), we assessed changes at 1, 2, 5, 24, and 72 h post-venom. WB showed immediate increases in Cav-3 and Cx43 at 1 h (interval of greatest manifestations of envenomation) that persisted at 5 h (when there were signs of recovery) and peaked at 24 h when no signs of envenomation were detectable. At 2 and 72 h, Cav-3 was downregulated and Cx43 had returned to baseline. PNV markedly intensified Cx43 in molecular, Purkinje and granular layers and Cav-3 in astrocytes whose colocalization to increased GFAP suggests interaction between reactive astrogliosis and Cav-3 upregulation. TEM showed swollen perivascular astrocytic end-feet and synaptic contact alterations that had generally resolved by 72 h. It is uncertain whether such PNV-induced synchronized changes are an interactive effect between Cav-3 and Cx43, or a bystander effect. Evidences indicate that Cav-3 downregulation coupled to Cx43 return to baseline at 72 h when no signs of envenomation were visible, suggesting homeostasis reestablishment. This experimental model is relevant to studying mechanisms involved in neurological disorders associated with Cav-3 overexpression.

Antinociceptive effect of a novel armed spider peptide Tx3-5 in pathological pain models in mice

The venom of the Brazilian armed spider Phoneutria nigriventer is a rich source of biologically active peptides that have potential as analgesic drugs. In this study, we investigated the analgesic and adverse effects of peptide 3-5 (Tx3-5), purified from P. nigriventer venom, in several mouse models of pain. Tx3-5 was administered by intrathecal injection to mice selected as models of postoperative (plantar incision), neuropathic (partial sciatic nerve ligation) and cancer-related pain (inoculation with melanoma cells) in animals that were either sensitive or tolerant to morphine. Intrathecal administration of Tx3-5 (3-300 fmol/site) in mice could either prevent or reverse postoperative nociception, with a 50 % inhibitory dose (ID50) of 16.6 (3.2-87.2) fmol/site and a maximum inhibition of 87 ± 10 % at a dose of 30 fmol/site. Its effect was prevented by the selective activator of L-type calcium channel Bay-K8644 (10 μg/site). Tx3-5 (30 fmol/site) also produced a partial antinociceptive effect in a neuropathic pain model (inhibition of 67 ± 10 %). Additionally, treatment with Tx3-5 (30 fmol/site) nearly abolished cancer-related nociception with similar efficacy in both morphine-sensitive and morphine-tolerant mice (96 ± 7 and 100 % inhibition, respectively). Notably, Tx3-5 did not produce visible adverse effects at doses that produced antinociception and presented a TD50 of 1125 (893-1418) fmol/site. Finally, Tx3-5 did not alter the normal mechanical or thermal sensitivity of the animals or cause immunogenicity. Our results suggest that Tx3-5 is a strong drug candidate for the treatment of painful conditions.

Differential effects of the recombinant toxin PnTx4(5-5) from the spider Phoneutria nigriventer on mammalian and insect sodium channels

The toxin PnTx4(5-5) from the spider Phoneutria nigriventer is extremely toxic/lethal to insects but has no macroscopic behavioral effects observed in mice after intracerebral injection. Nevertheless, it was demonstrated that it inhibits the N-methyl-d-aspartate (NMDA) - subtype of glutamate receptors of cultured rat hippocampal neurons. PnTx4(5-5) has 63% identity to PnTx4(6-1), another insecticidal toxin from P. nigriventer, which can slow down the sodium current inactivation in insect central nervous system, but has no effect on Nav1.2 and Nav1.4 rat sodium channels. Here, we have cloned and heterologous expressed the toxin PnTx4(5-5) in Escherichia coli. The recombinant toxin rPnTx4(5-5) was tested on the sodium channel NavBg from the cockroach Blatella germanica and on mammalian sodium channels Nav1.2-1.6, all expressed in Xenopus leavis oocytes. We showed that the toxin has different affinity and mode of action on insect and mammalian sodium channels. The most remarkable effect was on NavBg, where rPnTx4(5-5) strongly slowed down channel inactivation (EC50 = 212.5 nM), and at 1 μM caused an increase on current peak amplitude of 105.2 ± 3.1%. Interestingly, the toxin also inhibited sodium current on all the mammalian channels tested, with the higher current inhibition on Nav1.3 (38.43 ± 8.04%, IC50 = 1.5 μM). Analysis of activation curves on Nav1.3 and Nav1.5 showed that the toxin shifts channel activation to more depolarized potentials, which can explain the sodium current inhibition. Furthermore, the toxin also slightly slowed down sodium inactivation on Nav1.3 and Nav1.6 channels. As far as we know, this is the first araneomorph toxin described which can shift the sodium channel activation to more depolarized potentials and also slows down channel inactivation.

PnPP-19, a Synthetic and Nontoxic Peptide Designed from a Phoneutria nigriventer Toxin, Potentiates Erectile Function via NO/cGMP

PURPOSE

We designed a peptide, PnPP-19, comprising the potential active core of the Phoneutria nigriventer native toxin PnTx2-6. We investigated its role on erectile function, and its toxicity and immunogenicity.

MATERIALS AND METHODS

Erectile function was evaluated by the intracavernous pressure-to-mean arterial pressure ratio during electrical field stimulation on rat pelvic ganglia. Cavernous strips were contracted with phenylephrine and relaxation was induced by electrical field stimulation with or without PnPP-19 (10(-8) M). Activity on sodium channels was evaluated by electrophysiological screening of transfected channels on Xenopus oocytes and dorsal root ganglion cells. Antibodies were detected by indirect enzyme-linked immunosorbent assay in mice previously treated with the peptide. Histopathological studies were performed with mouse organs treated with different doses of PnPP-19.

RESULTS

PnPP-19 was able to potentiate erection at 4 and 8 Hz in vivo and ex vivo. It showed no toxicity and low immunogenicity in mice, and did not affect sodium channels or rat hearts. PnPP-19 increased cyclic guanosine monophosphate levels at 8 Hz. This effect was inhibited by L-NAME (10(-4) M). Erectile function was partially inhibited by 7-nitroindazole (10(-5) M), a selective inhibitor of neuronal nitric oxide synthase.

CONCLUSIONS

PnPP-19 potentiates erection in vivo and ex vivo via the nitric oxide/cyclic guanosine monophosphate pathway. It does not affect sodium channels or rat hearts and shows no toxicity and low immunogenicity. These findings make it a promising candidate as a novel drug in the therapy of erectile dysfunction.

Effect of ω-conotoxin MVIIA and Phα1β on paclitaxel-induced acute and chronic pain

The treatment with the chemotherapeutic agent paclitaxel produces a painful peripheral neuropathy, and is associated with an acute pain syndrome in a clinically significant number of patients. However, no standard therapy has been established to manage the acute pain or the chronic neuropathic pain related to paclitaxel. In the present study, we evaluated the analgesic potential of two N-type voltage-gated calcium channel (VGCC) blockers, ω-conotoxin MVIIA and Phα1β, on acute and chronic pain induced by paclitaxel. Adult male rats were treated with four intraperitoneal injections of paclitaxel (1+1+1+1mg/kg, in alternate days) and the development of mechanical hyperalgesia was evaluated 24h (acute painful stage) or 15days (chronic painful stage) after the first paclitaxel injection. Not all animals showed mechanical hyperalgesia 24h after the first paclitaxel injection, but those that showed developed a more intense mechanical hyperalgesia at the chronic painful stage. Intrathecal administration (i.t.) of ω-conotoxin MVIIA (3-300pmol/site) or Phα1β (10-300pmol/site) reduced the mechanical hyperalgesia either at the acute or at the chronic painful stage induced by paclitaxel. When administered at the acute painful stage, ω-conotoxin MVIIA (300pmol/site, i.t.) and Phα1β (300pmol/site, i.t.) prevented the worsening of chronic mechanical hyperalgesia. Furthermore, Phα1β (30-300pmol/site, i.t.) elicited less adverse effects than ω-conotoxin MVIIA (10-300 pmol/site, i.t.). Taken together, our data evidence the involvement of N-type VGCC in pain sensitization induced by paclitaxel and point out the potential of Phα1β as a safer alternative than ω-conotoxin MVIIA to treat the pain related to paclitaxel.