Peripheral interactions between cannabinoid and opioid systems contribute to the antinociceptive effect of crotalphine

Rattlesnake Crotalphine Analgesic Active on Tetrodotoxin-Sensitive Na+ Current in Mouse Dorsal Root Ganglion Neurons

Crotalphine is an analgesic peptide identified from the venom of the South American rattlesnake Crotalus durissus terrificus. Although its antinociceptive effect is well documented, its direct mechanisms of action are still unclear. The aim of the present work was to study the action of the crotalid peptide on the NaV1.7 channel subtype, a genetically validated pain target. To this purpose, the effects of crotalphine were evaluated on the NaV1.7 component of the tetrodotoxin-sensitive Na+ current in the dorsal root ganglion neurons of adult mice, using the whole-cell patch-clamp configuration, and on cell viability, using propidium iodide fluorescence and trypan blue assays. The results show that 18.7 µM of peptide inhibited 50% of the Na+ current. The blocking effect occurred without any marked change in the current activation and inactivation kinetics, but it was more important as the membrane potential was more positive. In addition, crotalphine induced an increase in the leakage current amplitude of approximately 150% and led to a maximal 31% decrease in cell viability at a high 50 µM concentration. Taken together, these results point out, for the first time, the effectiveness of crotalphine in acting on the NaV1.7 channel subtype, which may be an additional target contributing to the peptide analgesic properties and, also, although less efficiently, on a second cell plasma membrane component, leading to cell loss.

Wnt signaling is involved in crotalphine-induced analgesia in a rat model of neuropathic pain

The aberrant activation of Wnt/β-catenin and atypical Wnt/Ryk signaling pathways in the spinal cord is critical for the development and maintenance of neuropathic pain. Crotalphine is a structural analog to a peptide first identified in Crotalus durissus terrificus snake venom, which induces antinociception by activating kappa-opioid and CB2 cannabinoid receptors. Consistent with previous data, we showed that the protein levels of the canonical Wnt/β-catenin and the atypical Wnt/Ryk signaling pathways are increased in neuropathic rats. Importantly, the administration of crotalphine downregulates these protein levels, including its downstream cascades, such as TCF4 from the canonical pathway and NR2B glutamatergic receptor and Ca2+-dependent signals, via the Ryk receptor. The CB2 receptor antagonist, AM630, abolished the crotalphine-induced atypical Wnt/Ryk signaling pathway activation. However, the selective CB2 agonist affects both canonical and non-canonical Wnt signaling in the spinal cord. Next, we showed that crotalphine blocked hypersensitivity and significantly decreased the concentration of IL-1ɑ, IL-1β, IL-6, IL-10, IL-18, TNF-ɑ, MIP-1ɑ and MIP-2 induced by intrathecal injection of exogenous Wnt-3a agonist. Taken together, our findings show that crotalphine induces analgesia in a neuropathic pain model by down-regulating the canonical Wnt/β-catenin and the atypical Wnt/Ryk signaling pathways and, consequently controlling neuroinflammation. This effect is, at least in part, mediated by CB2 receptor activation. These results open a perspective for new approaches that can be used to target Wnt signaling in the context of chronic pain. PERSPECTIVE: Our work identified that crotalphine-induced activation of CB2 receptors plays a critical role in the impairment of Wnt signaling during neuropathic pain. This work suggests that drugs with opioid/cannabinoid activity may be a useful strategy to target Wnt signaling in the context of chronic pain.

Longitudinal changes in blood pressure are preceded by changes in albuminuria and accelerated by increasing dietary sodium intake

BACKGROUND

Dietary sodium is a well-known risk factor for cardiovascular and renal disease; however, direct evidence of the longitudinal changes that occur with aging, and the influence of dietary sodium on the age-associated alterations are scarce.

METHODS

C57BL/6 mice were maintained for 13 months on a low (LS, 0.02 % Na+), normal (NS, 0.3 % Na+) or high (HS, 1.6 % Na+) salt diet. We assessed 1) the longitudinal trajectories for two markers of cardiovascular and renal dysfunction (blood pressure (BP) and albuminuria), as well as hormonal changes, and 2) end-of-study cardiac and renal parameters.

RESULTS

The effect of aging on BP and kidney damage did not reach significance levels in the LS group; however, relative to baseline, there were significant increases in these parameters for animals maintained on NS and HS diets, starting as early as month 7 and month 5, respectively. Furthermore, changes in albuminuria preceded the changes in BP relative to baseline, irrespective of the diet. Circulating aldosterone and plasma renin activity displayed the expected decreasing trends with age and dietary sodium loading. As compared to LS - higher dietary sodium consumption associated with increasing trends in left ventricular mass and volume indices, consistent with an eccentric dilated phenotype. Functional and molecular markers of kidney dysfunction displayed similar trends with increasing long-term sodium levels: higher renovascular resistance, increased glomerular volumes, as well as higher levels of renal angiotensin II type 1 and mineralocorticoid receptors, and lower renal Klotho levels.

CONCLUSION

Our study provides a timeline for the development of cardiorenal dysfunction with aging, and documents that increasing dietary salt accelerates the age-induced phenotypes. In addition, we propose albuminuria as a prognostic biomarker for the future development of hypertension. Last, we identified functional and molecular markers of renal dysfunction that associate with long-term dietary salt loading.

Biological and Medical Aspects Related to South American Rattlesnake Crotalus durissus (Linnaeus, 1758): A View from Colombia

In Colombia, South America, there is a subspecies of the South American rattlesnake Crotalus durissus, C. d. cumanensis, a snake of the Viperidae family, whose presence has been reduced due to the destruction of its habitat. It is an enigmatic snake from the group of pit vipers, venomous, with large articulated front fangs, special designs on its body, and a characteristic rattle on its tail. Unlike in Brazil, the occurrence of human envenomation by C. durisus in Colombia is very rare and contributes to less than 1% of envenomation caused by snakes. Its venom is a complex cocktail of proteins with different biological effects, which evolved with the purpose of paralyzing the prey, killing it, and starting its digestive process, as well as having defense functions. When its venom is injected into humans as the result of a bite, the victim presents with both local tissue damage and with systemic involvement, including a diverse degree of neurotoxic, myotoxic, nephrotoxic, and coagulopathic effects, among others. Its biological effects are being studied for use in human health, including the possible development of analgesic, muscle relaxant, anti-inflammatory, immunosuppressive, anti-infection, and antineoplastic drugs. Several groups of researchers in Brazil are very active in their contributions in this regard. In this work, a review is made of the most relevant biological and medical aspects related to the South American rattlesnake and of what may be of importance for a better understanding of the snake C. d. cumanensis, present in Colombia and Venezuela.

Crotalphine Modulates Microglia M1/M2 Phenotypes and Induces Spinal Analgesia Mediated by Opioid-Cannabinoid Systems

Pain is a worldwide public health problem and its treatment is still a challenge since clinically available drugs do not completely reverse chronic painful states or induce undesirable effects. Crotalphine is a 14 amino acids synthetic peptide that induces a potent and long-lasting analgesic effect on acute and chronic pain models, peripherally mediated by the endogenous release of dynorphin A and the desensitization of the transient receptor potential ankyrin 1 (TRPA1) receptor. However, the effects of crotalphine on the central nervous system (CNS) and the signaling pathway have not been investigated. Thus, the central effect of crotalphine was evaluated on the partial sciatic nerve ligation (PSNL)-induced chronic neuropathic pain model. Crotalphine (100 µg/kg, p.o.)-induced analgesia on the 14th day after surgery lasting up to 24 h after administration. This effect was prevented by intrathecal administration of CB1 (AM251) or CB2 (AM630) cannabinoid receptor antagonists. Besides that, crotalphine-induced analgesia was reversed by CTOP, nor-BNI, and naltrindole, antagonists of mu, kappa, and delta-opioid receptors, respectively, and also by the specific antibodies for β-endorphin, dynorphin-A, and met-enkephalin. Likewise, the analgesic effect of crotalphine was blocked by the intrathecal administration of minocycline, an inhibitor of microglial activation and proliferation. Additionally, crotalphine decreased the PSNL-induced IL-6 release in the spinal cord. Importantly, in vitro, crotalphine inhibited LPS-induced CD86 expression and upregulated CD206 expression in BV-2 cells, demonstrating a polarization of microglial cells towards the M2 phenotype. These results demonstrated that crotalphine, besides activating opioid and cannabinoid analgesic systems, impairs central neuroinflammation, confirming the neuromodulatory mechanism involved in the crotalphine analgesic effect.

PKCζ-Mitogen-Activated Protein Kinase Signaling Mediates Crotalphine-Induced Antinociception

Crotalphine (CRP) is a structural analogue to a peptide that was first identified in the crude venom from the South American rattlesnake Crotalus durissus terrificus. This peptide induces a potent and long-lasting antinociceptive effect that is mediated by the activation of peripheral opioid receptors. The opioid receptor activation regulates a variety of intracellular signaling, including the mitogen-activated protein kinase (MAPK) pathway. Using primary cultures of sensory neurons, it was demonstrated that crotalphine increases the level of activated ERK1/2 and JNK-MAPKs and this increase is dependent on the activation of protein kinase Cζ (PKCζ). However, whether PKCζ-MAPK signaling is critical for crotalphine-induced antinociception is unknown. Here, we biochemically demonstrated that the systemic crotalphine activates ERK1/2 and JNK and decreases the phosphorylation of p38 in the lumbar spinal cord. The in vivo pharmacological inhibition of spinal ERK1/2 and JNK, but not of p38, blocks the antinociceptive effect of crotalphine. Of interest, the administration of a PKCζ pseudosubstrate (PKCζ inhibitor) prevents crotalphine-induced ERK activation in the spinal cord, followed by the abolishment of crotalphine-induced analgesia. Together, our results demonstrate that the PKCζ-ERK signaling pathway is involved in crotalphine-induced analgesia. Our study opens a perspective for the PKCζ-MAPK axis as a target for pain control.

Revisiting the potential of South American rattlesnake Crotalus durissus terrificus toxins as therapeutic, theranostic and/or biotechnological agents

The potential biotechnological and biomedical applications of the animal venom components are widely recognized. Indeed, many components have been used either as drugs or as templates/prototypes for the development of innovative pharmaceutical drugs, among which many are still used for the treatment of human diseases. A specific South American rattlesnake, named Crotalus durissus terrificus, shows a venom composition relatively simpler compared to any viper or other snake species belonging to the Crotalus genus, although presenting a set of toxins with high potential for the treatment of several still unmet human therapeutic needs, as reviewed in this work. In addition to the main toxin named crotoxin, which is under clinical trials studies for antitumoral therapy and which has also anti-inflammatory and immunosuppressive activities, other toxins from the C. d. terrificus venom are also being studied, aiming for a wide variety of therapeutic applications, including as antinociceptive, anti-inflammatory, antimicrobial, antifungal, antitumoral or antiparasitic agent, or as modulator of animal metabolism, fibrin sealant (fibrin glue), gene carrier or theranostic agent. Among these rattlesnake toxins, the most relevant, considering the potential clinical applications, are crotamine, crotalphine and gyroxin. In this narrative revision, we propose to organize and present briefly the updates in the accumulated knowledge on potential therapeutic applications of toxins collectively found exclusively in the venom of this specific South American rattlesnake, with the objective of contributing to increase the chances of success in the discovery of drugs based on toxins.

Crotalphine Attenuates Pain and Neuroinflammation Induced by Experimental Autoimmune Encephalomyelitis in Mice

Multiple sclerosis (MS) is a demyelinating disease of inflammatory and autoimmune origin, which induces sensory and progressive motor impairments, including pain. Cells of the immune system actively participate in the pathogenesis and progression of MS by inducing neuroinflammation, tissue damage, and demyelination. Crotalphine (CRO), a structural analogue to a peptide firstly identified in Crotalus durissus terrificus snake venom, induces analgesia by endogenous opioid release and type 2 cannabinoid receptor (CB2) activation. Since CB2 activation downregulates neuroinflammation and ameliorates symptoms in mice models of MS, it was presently investigated whether CRO has a beneficial effect in the experimental autoimmune encephalomyelitis (EAE). CRO was administered on the 5th day after immunization, in a single dose, or five doses starting at the peak of disease. CRO partially reverted EAE-induced mechanical hyperalgesia and decreased the severity of the clinical signs. In addition, CRO decreases the inflammatory infiltrate and glial cells activation followed by TNF-α and IL-17 downregulation in the spinal cord. Peripherally, CRO recovers the EAE-induced impairment in myelin thickness in the sciatic nerve. Therefore, CRO interferes with central and peripheral neuroinflammation, opening perspectives to MS control.

PnAn13, an antinociceptive synthetic peptide inspired in the Phoneutria nigriventer toxin PnTx4(6-1) (δ-Ctenitoxin-Pn1a)

Animal venoms are an almost inexhaustible source for promising molecules with biological activity and the venom of Phoneutria nigriventer spider is a good example of this. Among several other toxins obtained from this venom, PnTx4(6–1), also called δ-Ctenitoxin-Pn1a, was isolated and initially described as an insect toxin that binds to the site 3 of sodium channels in cockroach nerve cord synaptosomes (Periplaneta americana) and slows down sodium current inactivation in isolated axons of this animal. This toxin did not cause any apparent toxicity to mice when intracerebroventricularly injected (30 μg). Subsequently, it was demonstrated that PnTx4(6–1) has an antinociceptive effect in three different pain models: inflammatory, induced by carrageenan; nociceptive, induced by prostaglandin E₂ and neuropathic, induced by sciatic nerve constriction. Using diverse antagonists from receptors, it was shown that the cannabinoid system, via the CB₁ receptor, and the opioid system, through the μ and δ receptors, are both involved in the antinociceptive effect of PnTx4(6–1). In the present work, it was synthesized a peptide, named PnAn13, based on the amino acid sequence of PnTx4(6–1) in order to try to reproduce or increase the analgesic effect of the toxin. As it was seen for the toxin, PnAn13 had antinociceptive activity, when intrathecally injected, and this effect involved the cannabinoid and opioid systems. In addition, when it was evaluated the peripheral effect of PnAn13, via intraplantar administration, this peptide was able to reverse the hyperalgesic threshold, evoked by prostaglandin E₂. Therefore, using different pharmacological tools, it was shown the participation of cannabinoid and opioid systems in this effect.

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A synthetic peptide PnAn13, reproduced the antinociceptive effects of the PnTx4(6-1) (δ-Ctenitoxin-Pn1a) toxin.

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PnAn13 showed a clear analgesic effect in the nociceptive in vivo rat pain model, both centrally and peripherally.

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The antinociceptive effect of PnAn13 involves cannabinoid and opioid systems.

Targeting Cannabinoid Receptors: Current Status and Prospects of Natural Products

Cannabinoid receptors (CB1 and CB2), as part of the endocannabinoid system, play a critical role in numerous human physiological and pathological conditions. Thus, considerable efforts have been made to develop ligands for CB1 and CB2, resulting in hundreds of phyto- and synthetic cannabinoids which have shown varying affinities relevant for the treatment of various diseases. However, only a few of these ligands are clinically used. Recently, more detailed structural information for cannabinoid receptors was revealed thanks to the powerfulness of cryo-electron microscopy, which now can accelerate structure-based drug discovery. At the same time, novel peptide-type cannabinoids from animal sources have arrived at the scene, with their potential in vivo therapeutic effects in relation to cannabinoid receptors. From a natural products perspective, it is expected that more novel cannabinoids will be discovered and forecasted as promising drug leads from diverse natural sources and species, such as animal venoms which constitute a true pharmacopeia of toxins modulating diverse targets, including voltage- and ligand-gated ion channels, G protein-coupled receptors such as CB1 and CB2, with astonishing affinity and selectivity. Therefore, it is believed that discovering novel cannabinoids starting from studying the biodiversity of the species living on planet earth is an uncharted territory.

The Role of Toxins in the Pursuit for Novel Analgesics

Chronic pain is a major medical issue which reduces the quality of life of millions and inflicts a significant burden on health authorities worldwide. Currently, management of chronic pain includes first-line pharmacological therapies that are inadequately effective, as in just a portion of patients pain relief is obtained. Furthermore, most analgesics in use produce severe or intolerable adverse effects that impose dose restrictions and reduce compliance. As the majority of analgesic agents act on the central nervous system (CNS), it is possible that blocking pain at its source by targeting nociceptors would prove more efficient with minimal CNS-related side effects. The development of such analgesics requires the identification of appropriate molecular targets and thorough understanding of their structural and functional features. To this end, plant and animal toxins can be employed as they affect ion channels with high potency and selectivity. Moreover, elucidation of the toxin-bound ion channel structure could generate pharmacophores for rational drug design while favorable safety and analgesic profiles could highlight toxins as leads or even as valuable therapeutic compounds themselves. Here, we discuss the use of plant and animal toxins in the characterization of peripherally expressed ion channels which are implicated in pain.

Chemical Tools for Studying Lipid-Binding Class A G Protein-Coupled Receptors

Cannabinoid, free fatty acid, lysophosphatidic acid, sphingosine 1-phosphate, prostanoid, leukotriene, bile acid, and platelet-activating factor receptor families are class A G protein-coupled receptors with endogenous lipid ligands. Pharmacological tools are crucial for studying these receptors and addressing the many unanswered questions surrounding expression of these receptors in normal and diseased tissues. An inherent challenge for developing tools for these lipid receptors is balancing the often lipophilic requirements of the receptor-binding pharmacophore with favorable physicochemical properties to optimize highly specific binding. In this study, we review the radioligands, fluorescent ligands, covalent ligands, and antibodies that have been used to study these lipid-binding receptors. For each tool type, the characteristics and design rationale along with in vitro and in vivo applications are detailed.

Crotalphine desensitizes TRPA1 ion channels to alleviate inflammatory hyperalgesia

Crotalphine is a structural analogue to a novel analgesic peptide that was first identified in the crude venom from the South American rattlesnake Crotalus durissus terrificus. Although crotalphine's analgesic effect is well established, its direct mechanism of action remains unresolved. The aim of the present study was to investigate the effect of crotalphine on ion channels in peripheral pain pathways. We found that picomolar concentrations of crotalphine selectively activate heterologously expressed and native TRPA1 ion channels. TRPA1 activation by crotalphine required intact N-terminal cysteine residues and was followed by strong and long-lasting desensitization of the channel. Homologous desensitization of recombinant TRPA1 and heterologous desensitization in cultured dorsal root ganglia neurons was observed. Likewise, crotalphine acted on peptidergic TRPA1-expressing nerve endings ex vivo as demonstrated by suppression of calcitonin gene-related peptide release from the trachea and in vivo by inhibition of chemically induced and inflammatory hypersensitivity in mice. The crotalphine-mediated desensitizing effect was abolished by the TRPA1 blocker HC030031 and absent in TRPA1-deficient mice. Taken together, these results suggest that crotalphine is the first peptide to mediate antinociception selectively and at subnanomolar concentrations by targeting TRPA1 ion channels.

Generation of G protein-coupled receptor antibodies differentially sensitive to conformational states

The N-terminal region of G protein-coupled receptors can be efficiently targeted for the generation of receptor-selective antibodies. These antibodies are useful for the biochemical characterization of the receptors. In this study, we developed a set of criteria to select the optimal epitope and applied them to generate antibodies to the N-terminal region of 34 different G protein-coupled receptors. The antibody characterization revealed that a subset of antibodies exhibited increased recognition of the receptor following agonist treatment and this increase could be blocked by treatment with the receptor antagonist. An analysis of the epitopes showed that those antibodies that exhibit increased recognition are on average twelve residues long, have an overall net negative charge and are enriched in aspartic and glutamic acids. These antibodies are useful since they facilitate studies examining dose dependent increases in recognition of receptors in heterologous cells as well as in native tissue. Another interesting use of these antibodies is that they facilitate measuring changes in receptor recognition in brain following peripheral drug administration; for example, systemic administration of cocaine, a blocker of dopamine transporter that increases local dopamine levels at the synapse, was found to lead to increases in antibody recognition of dopamine receptors in the brain. Taken together these studies, in addition to describing novel tools to study native receptors, provide a framework for the generation of antibodies to G protein-coupled receptors that can detect ligand-induced conformational changes.

Hyperalgesic and hypoalgesic mechanisms evoked by the acute administration of CCL5 in mice

We show here that the intraplantar administration of CCL5 in mice produces hyperalgesia at low doses but activates compensatory antinociceptive mechanisms at doses slightly higher. Thus, the injection of 3-10ng of CCL5 evoked thermal hyperalgesia through the activation of CCR1 and CCR5 receptors, as demonstrated by the inhibitory effect exerted by the selective antagonists J113863 (0.01-0.1μg) and DAPTA (0.3-3μg), respectively. The prevention of this hyperalgesia by diclofenac (1-10μg), the inhibitors of COX-1 SC-560 (0.1-1μg) or COX-2 celecoxib (1-5μg), the TRPV1 antagonist capsazepine (0.03-0.3μg) or the TRPA1 antagonist HC030031 (10-50μg) demonstrates the involvement of prostaglandin synthesis and TRP sensitization in CCL5-evoked hyperalgesia. Doses of CCL5 higher than 17μg did not evoke hyperalgesia. However, this effect was restored by the administration of naloxone-methiodide (5μg), nor-binaltorphimine (10mg/kg) or an anti-dynorphin A antibody (0.62-2.5ng). The administration of 30ng of CCL5 also induced hyperalgesia in mice with reduced number of circulating white blood cells in response to cyclophosphamide or with selective neutrophil depletion induced by an anti-Ly6G antibody. In fact, the number of neutrophils present in paws treated with 30ng of CCL5 was greater than in paws receiving the administration of the hyperalgesic dose of 10ng. Finally, the expression of the endogenous opioid peptide dynorphin A was demonstrated by double immunofluorescence assays in these neutrophils attracted by CCL5. These results support previous data describing the hyperalgesic properties of CCL5 and constitute the first indication that a chemokine of the CC group can activate endogenous analgesic mechanisms.

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.

PnPP-19, a spider toxin peptide, induces peripheral antinociception through opioid and cannabinoid receptors and inhibition of neutral endopeptidase

BACKGROUND AND PURPOSE

The synthetic peptide PnPP-19 has been studied as a new drug candidate to treat erectile dysfunction. However, PnTx2-6, the spider toxin from which the peptide was designed, induces hyperalgesia. Therefore, we intended to investigate the role of PnPP-19 in the nociceptive pathway.

EXPERIMENTAL APPROACH

Nociceptive thresholds were measured by paw pressure test. PnPP-19 was administered intraplantarly alone or with selective cannabinoid or opioid receptor antagonists. The hydrolysis of PnPP-19 by neutral endopeptidase (NEP) (EC 3.4.24.11), an enzyme that cleaves enkephalin, was monitored by HPLC and the cleavage sites were deduced by LC-MS. Inhibition by PnPP-19 and Leu-enkephalin of NEP enzyme activity was determined spectrofluorimetrically.

KEY RESULTS

PnPP-19 (5, 10 and 20 μg per paw) induced peripheral antinociception in rats. Specific antagonists of μ opioid receptors (clocinnamox), δ opioid receptors (naltrindole) and CB1 receptors (AM251) partly inhibited the antinociceptive effect of PnPP-19. Inhibition of fatty acid amide hydrolase by MAFP or of anandamide uptake by VDM11 enhanced PnPP-19-induced antinociception. NEP cleaved PnPP-19 only after a long incubation, and Ki values of 35.6 ± 1.4 and 14.6 ± 0.44 μmol·L(-1) were determined for PnPP-19 and Leu-enkephalin respectively as inhibitors of NEP activity.

CONCLUSIONS AND IMPLICATIONS

Antinociception induced by PnPP-19 appears to involve the inhibition of NEP and activation of CB1, μ and δ opioid receptors. Our data provide a greater understanding of the antinociceptive effects of PnPP-19. This peptide could be useful as a new antinociceptive drug candidate.

Harnessing the knowledge of animal toxins to generate drugs

Animal toxins present high selectivity and specificity for their molecular targets, and have long been considered as prototypes for developing novel drugs, with some successful cases. In this regard, the variety of molecules found in animal venoms, which can be capable of affecting vital physiological systems, have providing the development of studies focusing on turning those molecules (toxins) into therapeutics to treat several diseases, such as chronic pain, hypertension, thrombosis, cancer, and so on. However, some important issues have been responsible for disrupting the toxin-based drug discovery projects. In this review, we have briefly highlighted the development of drugs based on animal toxins, discussing some successful cases as well as the main causes of failure, pointing out the recent strategies applied to overcome the difficulties related to the translational process in this kind of development scenario.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Toxins and drug discovery

Components from venoms have stimulated many drug discovery projects, with some notable successes. These are briefly reviewed, from captopril to ziconotide. However, there have been many more disappointments on the road from toxin discovery to approval of a new medicine. Drug discovery and development is an inherently risky business, and the main causes of failure during development programmes are outlined in order to highlight steps that might be taken to increase the chances of success with toxin-based drug discovery. These include having a clear focus on unmet therapeutic needs, concentrating on targets that are well-validated in terms of their relevance to the disease in question, making use of phenotypic screening rather than molecular-based assays, and working with development partners with the resources required for the long and expensive development process.

Ultrapure ajulemic acid has improved CB2 selectivity with reduced CB1 activity

Ajulemic acid, a side-chain analog of Δ(8)-THC-11-oic acid, was designed as a potent therapeutic agent free of the psychotropic adverse effects typical of most cannabinoids. Subsequent studies of ajulemic acid have yielded widely divergent findings on the occurrence of these adverse effects. To help resolve these discrepancies, we have prepared highly purified ajulemic acid using a different synthetic method than previously reported in the literature and compared its cannabinoid receptor binding constants with those obtained using several other preparations from different sources. Whereas CB2 binding did not vary greatly among all of the samples, the CB1 binding showed a wide range of affinities. The highly purified product (JBT-101) reported here had the weakest affinity for CB1 while the original preparation (HU-239) showed the strongest affinity for CB1. The CB1/CB2 ratio of affinities was 12.3 for JBT-101 whereas that for HU-239 was 0.19, a 65-fold difference. Functional responses such as catalepsy and hypothermia using JBT-101 versus HU-239 displayed reduced CB1 activity in keeping with the receptor binding data. Thus, earlier conclusions on the limited therapeutic index for ajulemic acid need to be reconsidered in the light of the data now obtained using JBT-101.