Current Drug Development Overview: Targeting Voltage-Gated Calcium Channels for the Treatment of Pain.

Voltage-gated calcium channels (VGCCs) are targeted to treat pain conditions. Since the discovery of their relation to pain processing control, they are investigated to find new strategies for better pain control. This review provides an overview of naturally based and synthetic VGCC blockers, highlighting new evidence on the development of drugs focusing on the VGCC subtypes as well as mixed targets with pre-clinical and clinical analgesic effects.

Cell phone use is associated with an inflammatory cytokine profile of parotid gland saliva.

BACKGROUND: There is controversy on the effects of the non-ionizing radiation emitted by cell phones on cellular processes and the impact of such radiation exposure on health. The purpose of this study was to investigate whether cell phone use alters cytokine expression in the saliva produced by the parotid glands. METHODS: Cytokine expression profile was determined by enzyme linked immuno sorbent assay (ELISA) in the saliva produced by the parotid glands in healthy volunteers, and correlated with self-reported cell phone use and laterality. RESULTS: The following parameters were determined, in 83 Brazilian individuals in saliva produced by the parotid glands comparing the saliva from the gland exposed to cell phone radiation (ipsilateral) to that from the contralateral parotid: salivary flow, total protein concentration, interleukin 1 ß (IL-1 ß), interleukin 6 (IL-6), interleukin 10 (IL-10), interferon γ (IFN-γ), and tumor necrosis factor α (TNF-α) salivary levels by ELISA. After multiple testing correction, decreased IL-10 and increased IL-1ß salivary levels in the ipsilateral side compared with the contralateral side (P < 0.05) were detected. Subjects who used cell phones for more than 10 years presented higher differences between IL-10 levels in ipsilateral versus contralateral parotids (P = 0.0012). No difference was observed in any of the tested parameters in correlation with cell phone monthly usage in minutes. CONCLUSION: The exposure of parotid glands to cell phones can alter salivary IL-10 and IL-1ß levels, consistent with a pro-inflammatory microenvironment that may be related to heat production.

Phα1ß, a peptide from the venom of the spider Phoneutria nigriventer shows antinociceptive effects after continuous infusion in a neuropathic pain model in rats.

BACKGROUND: Neuropathic pain is a severe painful pathology that is difficult to treat. One option for its management is the continuous intrathecal (i.t.) infusion of ziconotide (the Conus magnus peptide ω-conotoxin MVIIA), which, in addition to being effective, produces serious adverse effects at analgesic doses. Single i.t. administration of Phα1ß, a peptide purified from the venom of the spider Phoneutria nigriventer, has antinociceptive effects with a greater therapeutic window than ziconotide in rodents. To further evaluate its analgesic potential, we investigated the antinociceptive and toxic effects of Phα1ß after single or continuous i.t. infusion in a rat model of neuropathic pain. METHODS: Adult male Wistar rats (200-300 g) bred in-house were used. Chronic constriction injury (CCI) of the sciatic nerve was used as the neuropathic pain model. Nociception was assessed by detecting mechanical hyperalgesia, considering a significant reduction in 50% paw withdrawal threshold values after CCI compared with baseline values. First, we assessed the antinociceptive effect of a single i.t. injection of Phα1ß (10, 30, or 100 pmol/site) in a model of neuropathic pain 8 days after nerve injury. In a different experiment, we delivered Phα1ß (60 pmol/µL/h) or vehicle (phosphate-buffered saline, 1.0 µL/h) through continuous infusion using an osmotic pump by spinal catheterization for 7 days in rats submitted to nerve injury. Behavioral adverse effects were evaluated after single or continuous Phα1ß i.t. administration, and histopathological analysis of spinal cord, brainstem, and encephalon was performed after continuous Phα1ß i.t. injection. RESULTS: We observed that CCI of the sciatic nerve but not sham surgery caused intense (reduction of approximately 2.5 times in mechanical withdrawal threshold) and persistent (up to 14 days) nociception in rats. The single i.t. injection of Phα1ß (30 or 100 pmol/site) reduced neuropathic nociception from 1 to 6 hours after administration, without showing detectable side effects. Similarly, the continuous infusion of Phα1ß (60 pmol/µL/h for 7 days) was also able to reverse nerve injury-induced nociception from 1 to 7 days, but did not cause either behavioral side effects or histopathological changes in the central nervous system. CONCLUSIONS: Thus, we have shown for the first time that the continuous i.t. delivery of Phα1ß produces analgesia disconnected from toxicity in a relevant model of neuropathic pain, indicating that it is an effective and safe drug with a great potential to treat pain.

Intravenous administration of recombinant Phα1ß: Antinociceptive properties and morphine tolerance reversal in a cancer-associated pain model.

Cancer-related pain is considered one of the most prevalent symptoms for those affected by cancer, significantly influencing quality of life and treatment outcomes. Morphine is currently employed for analgesic treatment in this case, however, chronic use of this opioid is limited by the development of analgesic tolerance and adverse effects, such as digestive and neurological disorders. Alternative therapies, such as ion channel blockade, are explored. The toxin Phα1ß has demonstrated efficacy in blocking calcium channels, making it a potential candidate for alleviating cancer-related pain. This study aims to assess the antinociceptive effects resulting from intravenous administration of the recombinant form of Phα1ß (r-Phα1ß) in an experimental model of cancer-related pain in mice, tolerant or not to morphine. The model of cancer-induced pain was used to evaluate these effects, with the injection of B16F10 cells, followed by the administration of the r-Phα1ß, and evaluation of the mechanical threshold by the von Frey test. Also, adverse effects were assessed using a score scale, the rotarod, and open field tests. Results indicate that the administration of r-Phα1ß provoked antinociception in animals with cancer-induced mechanical hyperalgesia, with or without morphine tolerance. Previous administration of r-Phα1ß was able to recover the analgesic activity of morphine in animals tolerant to this opioid. r-Phα1ß was proved safe for these parameters, as no adverse effects related to motor and behavioral activity were observed following intravenous administration. This study suggests that the concomitant use of morphine and r-Phα1ß could be a viable strategy for pain modulation in cancer patients.

An evaluation of the antinociceptive effects of Phα1ß, a neurotoxin from the spider Phoneutria nigriventer, and ω-conotoxin MVIIA, a cone snail Conus magus toxin, in rat model of inflammatory and neuropathic pain.

Voltage-sensitive calcium channels (VSCCs) underlie cell excitability and are involved in the mechanisms that generate and maintain neuropathic and inflammatory pain. We evaluated in rats the effects of two VSCC blockers, ω-conotoxin MVIIA and Phα1ß, in models of inflammatory and neuropathic pain induced with complete Freund's adjuvant (CFA) and chronic constrictive injury (CCI), respectively. We also evaluated the effects of the toxins on capsaicin-induced Ca(2+) influx in dorsal root ganglion (DRG) neurons obtained from rats exposed to both models of pain. A single intrathecal injection of Phα1ß reversibly inhibits CFA and CCI-induced mechanical hyperalgesia longer than a single injection of ω-conotoxin MVIIA. Phα1ß and MVIIA also inhibited capsaicin-induced Ca(2+) influx in DRG neurons. The inhibitory effect of Phα1ß on capsaicin-induced calcium transients in DRG neurons was greater in the CFA model of pain, while the inhibitory effect of ω-conotoxin MVIIA was greater in the CCI model. The management of chronic inflammatory and neuropathic pain is still a major challenge for clinicians. Phα1ß, a reversible inhibitor of VSCCs with a preference for N-type Ca(2+) channels, has potential as a novel therapeutic agent for inflammatory and neuropathic pain. Clinical studies are necessary to establish the role of Phα1ß in the treatment of chronic pain.

ω-Phonetoxins inhibit voltage-gated calcium CaV2.2 ion channel splice isoforms of dorsal root ganglia.

Cell-specific alternative splicing of Cacna1b pre-mRNA generates functionally distinct voltage-gated CaV2.2 channels. CaV2.2 channels mediate the release of glutamate from nociceptor termini in the dorsal horn spinal cord and they are implicated in chronic pain. One alternatively spliced exon in Cacna1b, e37a, is highly expressed in dorsal root ganglia, relative to other regions of the nervous system, and it is particularly important in inflammatory hyperalgesia. Here we studied the effects of two ω-phonetoxins, PnTx3-4 and Phα1ß, derived from the spider Phoneutria nigriventer on CaV2.2 channel isoforms of dorsal root ganglia (CaV2.2 e37a and CaV2.2 e37b). Both PnTx3-4 and Phα1ß are known to have analgesic effects in rodent models of pain and to inhibit CaV2.2 channels. CaV2.2 e37a and CaV2.2 e37b isoforms expressed in a mammalian cell line were inhibited by PnTx3-4 and Phα1ß with similar potency and with similar timecourse, although CaV2.2 e37a currents were slightly, but consistently more sensitive to toxin inhibition compared to CaV2.2 e37b. The inhibitory effects of PnTx3-4 and Phα1ß on CaV2.2-e37a and CaV2.2-e37b channels were voltage-dependent, and both occlude the inhibitory effects of ω-conotoxin GVIA, consistent with a common site of action. The potency of PnTx3-4 and Phα1ß on both major splice isoforms in dorsal root ganglia constribute to understanding the analgesic actions of these ω-phonetoxins.

Preclinical study in a postoperative pain model to investigate the action of ketamine, lidocaine, and ascorbic acid in reversing fentanyl-induced, non-glutamate-dependent hyperalgesia.

Introduction: Opioid-induced hyperalgesia (OIH) is a paradoxical phenomenon in which exposure to opioids can increase sensitivity to painful stimuli. Currently, several drugs have been used in an attempt to prevent OIH. We design this study to address the effect of preemptive treatment with ketamine, lidocaine, and ascorbic acid in a rat preclinical model of perioperative opioid-induced hyperalgesia. Methods: To reproduce OIH in a model of postoperative pain, rats received successive doses of fentanyl subcutaneously and underwent an incision in the paw. In an attempt to prevent OIH, ketamine, lidocaine, and ascorbic acid were administered before treatment with fentanyl. The von Frey test and the hot-plate test were used to evaluate mechanical allodynia and thermal hyperalgesia, respectively, with a follow-up period from 1 hour up to 7 days after surgery. Spinal cord nerve terminals (synaptosomes) were used to assess glutamate release under our experimental conditions. Results: Consecutive fentanyl injections increased the postoperative pain as indicated by increased thermal hyperalgesia and allodynia 48 hours after incision. Ketamine, lidocaine, and the combination of ketamine + lidocaine were able to prevent thermal hyperalgesia but not mechanical allodynia. Ascorbic acid did not prevent the hyperalgesia induced by fentanyl. We found no correlation between spinal glutamate release and the pharmacological treatments. Conclusion: Fentanyl induced a hyperalgesic effect that last few days in a postoperative model of pain. Hyperalgesic effect was not totally inhibited by ketamine and lidocaine in rats. Increased glutamate release was not the main molecular mechanism of fentanyl-induced hyperalgesia.

Ion Channels-related Neuroprotection and Analgesia Mediated by Spider Venom Peptides.

Ion channels play critical roles in generating and propagating action potentials and in neurotransmitter release at a subset of excitatory and inhibitory synapses. Dysfunction of these channels has been linked to various health conditions, such as neurodegenerative diseases and chronic pain. Neurodegeneration is one of the underlying causes of a range of neurological pathologies, such as Alzheimer's disease (AD), Parkinson's disease (PD), cerebral ischemia, brain injury, and retinal ischemia. Pain is a symptom that can serve as an index of the severity and activity of a disease condition, a prognostic indicator, and a criterion of treatment efficacy. Neurological disorders and pain are conditions that undeniably impact a patient's survival, health, and quality of life, with possible financial consequences. Venoms are the best-known natural source of ion channel modulators. Venom peptides are increasingly recognized as potential therapeutic tools due to their high selectivity and potency gained through millions of years of evolutionary selection pressure. Spiders have been evolving complex and diverse repertoires of peptides in their venoms with vast pharmacological activities for more than 300 million years. These include peptides that potently and selectively modulate a range of targets, such as enzymes, receptors, and ion channels. Thus, components of spider venoms hold considerable capacity as drug candidates for alleviating or reducing neurodegeneration and pain. This review aims to summarize what is known about spider toxins acting upon ion channels, providing neuroprotective and analgesic effects.

Critical Pronociceptive Role of Family 2 Voltage-Gated Calcium Channels in a Novel Mouse Model of HIV-Associated Sensory Neuropathy.

Some people living with HIV present painful sensory neuropathy (HIV-SN) that is pharmacoresistant, sex-associated, and a major source of morbidity. Since the specific mechanisms underlying HIV-SN are not well understood, the aim of our study was to characterize a novel model of painful HIV-SN by combining the HIV-1 gp120 protein and the antiretroviral stavudine (d4T) in mice and to investigate the pronociceptive role of the family 2 voltage-gated calcium channel (VGCC) α1 subunit (Cav2.X channels) in such a model. HIV-SN was induced in male and female C57BL/6 mice by administration of gp120 and/or d4T and detected by a battery of behavior tests and by immunohistochemistry. The role of Cav2.X channels was assessed by the treatment with selective blockers and agonists as well as by mRNA detection. Repeated administration with gp120 and/or d4T produced long-lasting touch-evoked painful-like behaviors (starting at 6 days, reaching a maximum on day 13, and lasting up to 28 days after treatment started), with a greater intensity in female mice treated with the combination of gp120 + d4T. Moreover, gp120 + d4T treatment reduced the intraepidermal nerve fibers and well-being of female mice, without altering other behaviors. Mechanistically, gp120 + d4T treatment induced Cav2.1, 2.2, and 2.3 transcriptional increases in the dorsal root ganglion and the Cav2.X agonist-induced nociception. Accordingly, intrathecal selective Cav2.2 blockade presented longer and better efficacy in reversing the hyperalgesia induced by gp120 + d4T treatment compared with Cav2.1 or Cav2.3, but also presented the worst safety (inducing side effects at effective doses). We conclude that the family 2 calcium channels (Cav2.X) exert a critical pronociceptive role in a novel mouse model of HIV-SN.

Targeting N-type calcium channels in young-onset of some neurological diseases.

Calcium (Ca 2+) is an important second messenger in charge of many critical processes in the central nervous system (CNS), including membrane excitability, neurotransmission, learning, memory, cell proliferation, and apoptosis. In this way, the voltage-gated calcium channels (VGCCs) act as a key supply for Ca2+ entry into the cytoplasm and organelles. Importantly, the dysregulation of these channels has been reported in many neurological diseases of young-onset, with associated genetic factors, such as migraine, multiple sclerosis, and Huntington's disease. Notably, the literature has pointed to the role of N-type Ca2+ channels (NTCCs) in controlling a variety of processes, including pain, inflammation, and excitotoxicity. Moreover, several Ca2+ channel blockers that are used for therapeutic purposes have been shown to act on the N-type channels. Therefore, this review provides an overview of the NTCCs in neurological disorders focusing mainly on Huntington's disease, multiple sclerosis, and migraine. It will discuss possible strategies to generate novel therapeutic strategies.

Systemic, Intrathecal, and Intracerebroventricular Antihyperalgesic Effects of the Calcium Channel Blocker CTK 01512-2 Toxin in Persistent Pain Models.

CTK 01512-2 toxin is a recombinant peptide of the Phα1ß version derived from the venom of the Phoneutria nigriventer spider. It acts as an N-type voltage-gated calcium channel (VGCC) blocker and shows a prolonged effect on preventing and reducing nociception. Herein, CTK 01512-2 was tested on two models of persistent pain, the chronic post-ischemia pain (CPIP) and the paclitaxel-induced peripheral neuropathy, to evaluate its systemic, intrathecal, and intracerebroventricular effects on mechanical hypersensitivity and thermal allodynia. Glial cell viability was also investigated using the MTT test. The results showed that CTK 01512-2 intrathecal and systemic treatments reduced the mechanical hypersensitivity induced by CPIP, mainly between 1-4 h after its administration. Additionally, intrathecal treatment reduced the CPIP-induced thermal allodynia. In its turn, the intracerebroventricular treatment showed mechanical antihyperalgesic and thermal antiallodynic effects in the paclitaxel-induced peripheral neuropathy. These data reinforce the therapeutic potential of CTK 01512-2 to treat persistent pain conditions and offer a perspective to use the systemic route. Moreover, CTK 01512-2 increased the glial cell viability in the MTT reduction assay, and it may indicate a new approach to managing chronic pain. The results found in this study help to pave new perspectives of pain relief treatments to patients affected by chronic pain.

The effect of spider toxin PhTx3-4, ω-conotoxins MVIIA and MVIIC on glutamate uptake and on capsaicin-induced glutamate release and [Ca2+]i in spinal cord synaptosomes.

In spinal cord synaptosomes, the spider toxin PhTx3-4 inhibited capsaicin-stimulated release of glutamate in both calcium-dependent and -independent manners. In contrast, the conus toxins, ω-conotoxin MVIIA and xconotoxin MVIIC, only inhibited calcium-dependent glutamate release. PhTx3-4, but not ω-conotoxin MVIIA or xconotoxin MVIIC, is able to inhibit the uptake of glutamate by synaptosomes, and this inhibition in turn leads to a decrease in the Ca(2+)-independent release of glutamate. No other polypeptide toxin so far described has this effect. PhTx3-4 and ω-conotoxins MVIIC and MVIIA are blockers of voltage-dependent calcium channels, and they significantly inhibited the capsaicin-induced rise of intracellular calcium [Ca(2+)](i) in spinal cord synaptosomes, which likely reflects calcium entry through voltage-gated calcium channels. The inhibition of the calcium-independent glutamate release by PhTx3-4 suggests a potential use of the toxin to block abnormal glutamate release in pathological conditions such as pain.

Effect of intravenous anesthetic propofol on synaptic vesicle exocytosis at the frog neuromuscular junction.

AIM: To investigate the presynaptic effects of propofol, a short-acting intravenous anesthetic, in the frog neuromuscular junction. METHODS: Frog cutaneous pectoris nerve muscle preparations were prepared. A fluorescent tool (FM1-43) was used to visualize the effect of propofol on synaptic vesicle exocytosos in the frog neuromuscular junction. RESULTS: Low concentrations of propofol, ranging from 10 to 25 µmol/L, enhanced spontaneous vesicle exocytosis monitored by FM1-43 in a Ca(2+)-dependent and Na(+)-independent fashion. Higher concentrations of propofol (50, 100, and 200 µmol/L) had no effect on spontaneous exocytosis. By contrast, higher concentrations of propofol inhibited the Na(+)-dependent exocytosis evoked by 4-aminopyridine but did not affect the Na(+)-independent exocytosis evoked by KCl. This action was similar and non-additive with that observed by tetrodotoxin, a Na(+) channel blocker. CONCLUSION: Our data suggest that propofol has a dose-dependent presynaptic effect at the neuromuscular transmission which may help to understand some of the clinical effects of this agent on neuromuscular function.

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.

Mapping of Brain Activity in the Analgesia Induced by Phα1ß and Morphine.

Preclinical evidence suggests the potential of Phα1ß, a toxin obtained from the venom of spider Phoneutria nigriventer, as a new analgesic drug. Molecular brain imaging techniques have afforded exciting opportunities to examine brain processes in clinical pain conditions. This paper aims to study the brain regions involved in the analgesic effects of Phα1ß compared with Morphine, in a model of acute pain induced by formalin in Sprague Dawley rats. We used 18F-fluorodeoxyglucose as a metabolic radiotracer to perform brain imaging of rats pretreated with Phα1ß or Morphine in a model of acute inflammatory pain caused by intraplantar injection of formalin. The rats' hind paw's formalin stimulation resulted in a brain metabolic increase at the bilateral motor cortex, visual cortex, somatosensory cortex, thalamus, and cingulate cortex.In rats treated with Phα1ß, selective inhibition of unilateral motor cortex and cingulate cortex was observed. Morphine treatment leads to small and selective inhibition at the bilateral amygdala striatum and accumbens. Our results indicate that the analgesic effect of Phα1ß and Morphine possesses a differential profile of central processing in the pain state.

Isobolographic analysis reveals antinociceptive synergism between Phα1ß recombinant toxin and morphine in a model of cancer pain in C57BL/6J mice.

BACKGROUND: Phoneutria nigriventer venom contains Phα1ß. This toxin and its recombinant form have a remarkable analgesic potential that is associated with blockage of voltage-gated calcium channels and TRPA1 receptors. Although morphine is a mainstay drug to treat moderate and severe pain related to cancer, it has serious and dose-limiting side effects. Combining recombinant Phα1ß and morphine to treat pain is an interesting approach that has been gaining attention. Therefore, a quantitative and reliable method to establish the strength of the antinociceptive interaction between these two substances is necessary. The present study was designed to investigate the nature of the functional antinociceptive (analgesic) interaction between Phα1ß recombinant toxin and morphine in a model of cancer pain. METHODS: Melanoma was produced by intraplantar inoculation of B16-F10 cells into the right paw of C57BL/6J mice. Von Frey filaments measured the paw-withdrawal threshold after intrathecal administration of morphine, recombinant Phα1ß, and their combination. Thermal hyperalgesia was assessed using Hargreaves apparatus. The degree of interaction was evaluated using isobolographic analysis. Spontaneous and forced motor performance was assessed with the open-field and rotarod tests, respectively. RESULTS: Co-administration of recombinant Phα1ß and morphine synergistically reverses the melanoma-induced mechanical hyperalgesia. The potency of the mixture, measured as the effective dose to reach 50% of maximum possible effect (MPE) in ameliorating mechanical hyperalgesia, was about twice fold higher than expected if the interaction between morphine and recombinant Phα1ß was merely additive. Treatment with the combination at doses necessary to reach 50% of MPE caused no spontaneous nor forced motor alterations. CONCLUSION: The combinatorial use of recombinant Phα1ß and morphine allows significant and effective dose reduction of both agents, which has translational potential for opioid-sparing approaches in pain management related to cancer.

Effects of intravenous administration of recombinant Phα1ß toxin in a mouse model of fibromyalgia.

This study investigated the effects of intravenous (iv) administration of recombinant Phα1ß toxin, pregabalin, and diclofenac by the intrathecal route using an animal model fibromyalgia (FM). The reserpine administration (0.25 mg/kg s. c) once daily for three consecutive days significantly induced hyperalgesia, immobility time, and sucrose consumption in mice on the 4th day. Reserpine caused hyperalgesia on the mechanical and thermal hyperalgesia on the 4th day was reverted by recombinant Phα1ß (0.2 mg/kg iv) and pregabalin (1.25 µmol/site i. t) treatments. In contrast, diclofenac (215 nmol/site i. t) was ineffective. Recombinant Phα1ß toxin, pregabalin, and diclofenac did not affect the depressive-like behavioural effect induced by reserpine on mice during the forced swim and sucrose consumption tests. The data confirmed the analgesic effect of the recombinant Phα1ß toxin administered intravenously in a fibromyalgia mouse model.

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.

Analgesic effects of Phα1ß toxin: a review of mechanisms of action involving pain pathways.

Phα1ß is a neurotoxin purified from spider venom that acts as a high-voltage-activated (HVA) calcium channel blocker. This spider peptide has shown a high selectivity for N-type HVA calcium channels (NVACC) and an analgesic effect in several animal models of pain. Its activity was associated with a reduction in calcium transients, glutamate release, and reactive oxygen species production from the spinal cord tissue and dorsal ganglia root (DRG) in rats and mice. It has been reported that intrathecal (i.t.) administration of Phα1ß to treat chronic pain reverted opioid tolerance with a safer profile than ω-conotoxin MVIIA, a highly selective NVACC blocker. Following a recent development of recombinant Phα1ß (CTK 01512-2), a new molecular target, TRPA1, the structural arrangement of disulphide bridges, and an effect on glial plasticity have been identified. CTK 01512-2 reproduced the antinociceptive effects of the native toxin not only after the intrathecal but also after the intravenous administration. Herein, we review the Phα1ß antinociceptive activity in the most relevant pain models and its mechanisms of action, highlighting the impact of CTK 01512-2 synthesis and its potential for multimodal analgesia.

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.