Opiate and acetylcholine-independent analgesic actions of crotoxin isolated from crotalus durissus terrificus venom

What Are the Neurotoxins in Hemotoxic Snake Venoms?

Snake venoms as tools for hunting are primarily aimed at the most vital systems of the prey, especially the nervous and circulatory systems. In general, snakes of the Elapidae family produce neurotoxic venoms comprising of toxins targeting the nervous system, while snakes of the Viperidae family and most rear-fanged snakes produce hemotoxic venoms directed mainly on blood coagulation. However, it is not all so clear. Some bites by viperids results in neurotoxic signs and it is now known that hemotoxic venoms do contain neurotoxic components. For example, viperid phospholipases A₂ may manifest pre- or/and postsynaptic activity and be involved in pain and analgesia. There are other neurotoxins belonging to diverse families ranging from large multi-subunit proteins (e.g., C-type lectin-like proteins) to short peptide neurotoxins (e.g., waglerins and azemiopsin), which are found in hemotoxic venoms. Other neurotoxins from hemotoxic venoms include baptides, crotamine, cysteine-rich secretory proteins, Kunitz-type protease inhibitors, sarafotoxins and three-finger toxins. Some of these toxins exhibit postsynaptic activity, while others affect the functioning of voltage-dependent ion channels. This review represents the first attempt to systematize data on the neurotoxins from "non-neurotoxic" snake venom. The structural and functional characteristic of these neurotoxins affecting diverse targets in the nervous system are considered.

Neurotoxins Acting at Synaptic Sites: A Brief Review on Mechanisms and Clinical Applications

Neurotoxins generally inhibit or promote the release of neurotransmitters or bind to receptors that are located in the pre- or post-synaptic membranes, thereby affecting physiological functions of synapses and affecting biological processes. With more and more research on the toxins of various origins, many neurotoxins are now widely used in clinical treatment and have demonstrated good therapeutic outcomes. This review summarizes the structural properties and potential pharmacological effects of neurotoxins acting on different components of the synapse, as well as their important clinical applications, thus could be a useful reference for researchers and clinicians in the study of neurotoxins.

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.

Crystal Structure of Isoform CBd of the Basic Phospholipase A2 Subunit of Crotoxin: Description of the Structural Framework of CB for Interaction with Protein Targets

Crotoxin, from the venom of the South American rattlesnake Crotalus durissus terrificus, is a potent heterodimeric presynaptic β-neurotoxin that exists in individual snake venom as a mixture of isoforms of a basic phospholipase A₂ (PLA₂) subunit (CBa₂, CBb, CBc, and CBd) and acidic subunit (CA_1-4). Specific natural mutations in CB isoforms are implicated in functional differences between crotoxin isoforms. The three-dimensional structure of two individual CB isoforms (CBa₂, CBc), and one isoform in a crotoxin (CA₂CBb) complex, have been previously reported. This study concerns CBd, which by interaction with various protein targets exhibits many physiological or pharmacological functions. It binds with high affinity to presynaptic receptors showing neurotoxicity, but also interacts with human coagulation factor Xa (hFXa), exhibiting anticoagulant effect, and acts as a positive allosteric modulator and corrector of mutated chloride channel, cystic fibrosis transmembrane conductance regulator (CFTR), implicated in cystic fibrosis. Thus, CBd represents a novel family of agents that have potential in identifying new drug leads related to anticoagulant and anti-cystic fibrosis function. We determined here the X-ray structure of CBd and compare it with the three other natural isoforms of CB. The structural role of specific amino acid variations between CB isoforms are analyzed and the structural framework of CB for interaction with protein targets is described.

Crotoxin Conjugated to SBA-15 Nanostructured Mesoporous Silica Induces Long-Last Analgesic Effect in the Neuropathic Pain Model in Mice

Neuropathic pain is a disease caused by structural and functional plasticity in central and peripheral sensory pathways that produce alterations in nociceptive processing. Currently, pharmacological treatment for this condition remains a challenge. Crotoxin (CTX), the main neurotoxin of Crotalus durissus terrificus rattlesnake venom, has well described prolonged anti-inflammatory and antinociceptive activities. In spite of its potential benefits, the toxicity of CTX remains a limiting factor for its use. SBA-15 is an inert nanostructured mesoporous silica that, when used as a vehicle, may reduce toxicity and potentiate the activity of different compounds. Based on this, we propose to conjugate crotoxin with SBA-15 (CTX:SBA-15) in order to investigate if when adsorbed to silica, CTX would have its toxicity reduced and its analgesic effect enhanced in neuropathic pain induced by the partial sciatic nerve ligation (PSNL) model. SBA-15 enabled an increase of 35% of CTX dosage. Treatment with CTX:SBA-15 induced a long-lasting reduction of mechanical hypernociception, without modifying the previously known pathways involved in antinociception. Moreover, CTX:SBA-15 reduced IL-6 and increased IL-10 levels in the spinal cord. Surprisingly, the antinociceptive effect of CTX:SBA-15 was also observed after oral administration. These data indicate the potential use of the CTX:SBA-15 complex for neuropathic pain control and corroborates the protective potential of SBA-15.

Effects of crotoxin, a neurotoxin from Crotalus durissus terrificus snake venom, on human endothelial cells

Vascular endothelium plays an important modulatory role due to the production of molecules that mediate vasomotricity, inflammation, and leukocyte adhesion and rolling. Here we addressed whether crotoxin (25-200 μg/mL) - the main component of Crotalus durissus terrificus snake venom - interferes with cell viability, apotosis/necrosis, and cell response to oxidative stress in human umbilical vein endothelial cells (HUVEC) in vitro. We also examined whether crotoxin alters the levels of interleukins, adhesion molecules, and endothelial vasoactive factors in HUVEC cells treated or not with lipopolysaccharide (LPS; 1 μg/mL; 24 h). Crotoxin was not cytotoxic towards HUVEC cells, and downregulated the LPS-induced production of adhesion molecules (VCAM-1, ICAM-1, and E-selectin), vasoactive factors (endothelin-1 and prostaglandin I2), and interleukins (IL-6, IL-8, and IL1β), as well as protected cells against H₂O₂-induced oxidative stress. Hence, crotoxin played anti-inflammatory, antioxidant, immunomodulating, and vasoactive actions on HUVEC cells, in vitro. Considering that the initial stages of atherosclerosis is characterized by vasoconstriction, increased levels of adhesion molecules, inflammatory cytokines, and oxidative stress in the vascular endothelium; and crotoxin downmodulated all these events, our findings indicate that the actions of crotoxin here demonstrated suggest that it may have an anti-atherogenic action in vivo, which deserves to be tested in future studies.

Secreted Phospholipases A₂ from Animal Venoms in Pain and Analgesia

Animal venoms comprise a complex mixture of components that affect several biological systems. Based on the high selectivity for their molecular targets, these components are also a rich source of potential therapeutic agents. Among the main components of animal venoms are the secreted phospholipases A₂ (sPLA₂s). These PLA₂ belong to distinct PLA₂s groups. For example, snake venom sPLA₂s from Elapidae and Viperidae families, the most important families when considering envenomation, belong, respectively, to the IA and IIA/IIB groups, whereas bee venom PLA₂ belongs to group III of sPLA₂s. It is well known that PLA₂, due to its hydrolytic activity on phospholipids, takes part in many pathophysiological processes, including inflammation and pain. Therefore, secreted PLA₂s obtained from animal venoms have been widely used as tools to (a) modulate inflammation and pain, uncovering molecular targets that are implicated in the control of inflammatory (including painful) and neurodegenerative diseases; (b) shed light on the pathophysiology of inflammation and pain observed in human envenomation by poisonous animals; and, (c) characterize molecular mechanisms involved in inflammatory diseases. The present review summarizes the knowledge on the nociceptive and antinociceptive actions of sPLA₂s from animal venoms, particularly snake venoms.

Suppression of Inflammation and Arthritis by Orally Administrated Cardiotoxin from Naja naja atra

Cardiotoxin (CTX) from Naja naja atra venom (NNAV) reportedly had analgesic effect in animal models but its role in inflammation and arthritis was unknown. In this study, we investigated the analgesic, anti-inflammatory, and antiarthritic actions of orally administered CTX-IV isolated from NNAV on rodent models of inflammation and adjuvant arthritis. CTX had significant anti-inflammatory effects in models of egg white induced nonspecific inflammation, filter paper induced rat granuloma formation, and capillary osmosis tests. CTX significantly reduced the swelling of paw induced by egg white, the inflammatory exudation, and the formation of granulomas. CTX reduced the swelling of paw, the AA clinical scores, and pathological alterations of joint. CTX significantly decreased the number of the CD4 T cells and inhibited the expression of relevant proinflammatory cytokines IL-17 and IL-6. CTX significantly inhibited the secretion of proinflammatory cytokine IL-6 and reduced the level of p-STAT3 in FLS. These results suggest that CTX inhibits inflammation and inflammatory pain and adjuvant-induced arthritis. CTX may be a novel therapeutic drug for treatment of arthritis.

Nicotinic acetylcholine receptor α7 subunit is involved in the cobratoxin-induced antinociception in an animal model of neuropathic pain

In this study we report that cobratoxin (CbTX), a long-chain postsynaptic α-neurotoxin isolated from the Thailand cobra, Naja naja kaouthia, has antinociceptive effect in rats with neuropathic pain. The neuropathic pain model was established in rats with partial sciatic nerve ligature (PSNL) method. The pain response was examined behaviorally with mechanical paw withdrawal and thermal paw withdrawal method. Different doses (0.56, 1.12 and 4.50 μg/kg) of CbTX were injected intrathecally. Injection of CbTX resulted in a significant dose-dependent antinociception as evidenced by increased mechanical withdrawal threshold and thermal withdrawal latency. CbTX also induces a significant dose-dependent inhibition of pain-evoked unit discharges of thalamic parafascicular neurons. Both the behavioral mechanical and thermal antinociception and the inhibition of pain-evoked discharges of neurons in thalamic parafascicular nucleus in PSNL model could be mimicked by PUN282987, selective α7 nicotinic AChR (α7 nAChR) agonist and reversed by methyllycaconitine (MLA) selective α7 nAChR antagonist. In summary, these results suggested that AChR α7 subunit was involved in the antinociceptive action of CbTX for neuropathic pain and might be the candidate target for analgesic drug design.

Antitumoral activity of snake venom proteins: new trends in cancer therapy

For more than half a century, cytotoxic agents have been investigated as a possible treatment for cancer. Research on animal venoms has revealed their high toxicity on tissues and cell cultures, both normal and tumoral. Snake venoms show the highest cytotoxic potential, since ophidian accidents cause a large amount of tissue damage, suggesting a promising utilization of these venoms or their components as antitumoral agents. Over the last few years, we have studied the effects of snake venoms and their isolated enzymes on tumor cell cultures. Some in vivo assays showed antineoplastic activity against induced tumors in mice. In human beings, both the crude venom and isolated enzymes revealed antitumor activities in preliminary assays, with measurable clinical responses in the advanced treatment phase. These enzymes include metalloproteases (MP), disintegrins, L-amino acid oxidases (LAAOs), C-type lectins, and phospholipases A2 (PLA2s). Their mechanisms of action include direct toxic action (PLA2s), free radical generation (LAAOs), apoptosis induction (PLA2s, MP, and LAAOs), and antiangiogenesis (disintegrins and lectins). Higher cytotoxic and cytostatic activities upon tumor cells than normal cells suggest the possibility for clinical applications. Further studies should be conducted to ensure the efficacy and safety of different snake venom compounds for cancer drug development.

Antinociceptive activity of crotoxin in the central nervous system: a functional Magnetic Resonance Imaging study

Crotoxin, the main neurotoxic component of the venom of South American rattlesnake (Crotalus durissus terrificus), is reported to have potent antinociceptive activity. Several authors have shown mainly in behavioral pain models that crotoxin induces antinociceptive effects, supposed to be mediated by actions on the central nervous system. The antinociceptive effects of crotoxin (45 μg/kg ip) in rats were verified in this study by increased response latencies in a Hargreaves test and tail flick test. In addition, it was demonstrated that crotoxin does not lead to motor impairments during a rotarod test and open field test. The main objective, carried out by blood oxygen level dependent functional Magnetic Resonance Imaging (BOLD fMRI) in anesthetized rats, was to determine which specific brain structures are involved in these antinociceptive effects. Moreover, potential antihyperalgesic effects were investigated by inducing a local hyperalgesia on the left hind paw. Therefore, antinociceptive effects (right paw) and antihyperalgesic effects (left paw) of crotoxin were able to be differentiated. As a result, crotoxin exhibited dominant antihyperalgesic but also antinociceptive effects during pain stimulation. Reductions of BOLD signal already occurred in brain input structures but were most prominent in primary and secondary somatosensory cortices. In conclusion, BOLD fMRI in anesthetized rats proved to be a helpful tool in toxinology, particularly in unraveled mechanisms of modulating nociception in the central nervous system by (potential) analgesics like crotoxin.

Antinociceptive activity and pathway of the pallanalgesin isolated from venom of Agkistrodon halys (Pallas)

CONTEXT

Venom of Agkstrodon halys (Pallas) is a traditional Chinese medicine for the control of severe pain, but its analgesic mechanism is not clear.

OBJECTIVE

To isolate the analgesic fraction from the venom, evaluate the profile of its action on pain using preclinical nociceptive tests and determine the involvement of neurotransmitters in its action.

MATERIALS AND METHODS

Venom was separated with SPXL resin, and further purified by Superdex 75 and Superdex 30 resin. Its biochemical characteristics were analyzed including molecular weight (MW), isoelectric point (pI) and amino acid sequence. Animal pain models were applied including the hot plate test, acetic acid-induced writhing test, formalin test, Randall-Selitto pressure test, antagonistic test, spinalized rats test and intracerebral injection test. The endogenous neuropeptides leucine-enkephalin, β-endorphin and P substance were determined by HPLC in the tissues of brain and spinal cord.

RESULTS

An analgesic protein named pallanalgesin (MW 16.6 kDa, pI 8.8) was obtained from the venom of A. halys. It had significant antinociceptive activity in different animal pain models of thermal, chemical and mechanical stimulation. It effects both central and peripheral nerve systems, and it is related to opiate receptors and monoamines rather than acetylcholine receptors. Pallanalgesin could modulate the levels of neuropeptides in the brain and spinal cord, which contributes to the recovery of nerve injury and pain control.

CONCLUSION

As a novel analgesic, pallanalgesin has been found to explain the function of the venom of A. halys on severe pain control in traditional uses, and can be used as a new analgesic in the future.

Autophagy and cathepsin L are involved in the antinociceptive effect of DMBC in a mouse acetic acid-writhing model

AIM

2-(3',5'-Dimethoxybenzylidene) cyclopentanone (DMBC) is a novel synthetic compound with antinociceptive activities. The aim of this study was to investigate the roles of the autophagic-lysosomal pathway in the antinociceptive effect of DMBC in a mouse acetic acid-writhing model.

METHODS

Mouse acetic acid-writhing test and hotplate test were used to assess the antinociceptive effects of DMBC, 3-MA (autophagy inhibitor) and Clik148 (cathepsin L inhibitor). The drugs were administered peripherally (ip) or centrally (icv).

RESULTS

Peripheral administration of 3-MA (7.5-30 mg/kg) or Clik148 (10-80 mg/kg) produced potent antinociceptive effect in acetic acid-writhing test. Central administration of 3-MA or Clik148 (12.5-50 nmol/L) produced comparable antinociceptive effect in acetic acid-writhing test. Peripheral administration of DMBC (25-50 mg/kg) produced potent antinociceptive effects in both acetic acid-writhing and hotplate tests. Furthermore, the antinociceptive effect produced by peripheral administration of DMBC (50 mg/kg) in acetic acid-writhing test was antagonized by low doses of 3-MA (3.75 mg/kg) or Clik148 (20 mg/kg) peripherally administered, but was not affected by 3-MA or Clik148 (25 nmol/L) centrally administered.

CONCLUSION

Activation of central autophagy and cathepsin L is involved in nociception in mice, whereas peripheral autophagy and cathepsin L contributes, at least in part, to the antinociceptive effect of DMBC in mice.

Anti-inflammatory effects of Neurotoxin-Nna, a peptide separated from the venom of Naja naja atra

Background

Neurotoxin-Nna (NT), an analgesic peptide separated from the venom of Naja naja atra, has reported to have an exceptional specificity to block transmission of the nerve impulse by binding to the α- subunit of the nicotinic acetylcholine receptor in the membrane. However, little information is available on the anti-inflammatory effects of NT. Therefore, the anti-inflammatory activity of Neurotoxin-Nna was investigated in this study.

Methods

The anti-inflammatory effects of NT were evaluated by measuring its influence on several crucial factors in inflammatory pathways, including total antioxidant activity, antinociceptive effects in vivo, nuclear factor kappa B (NF-κB), polymorphonuclear cells (PMN), inducible nitric oxide synthase (iNOS), adhesion molecule (ICAM-1) and tactile hyperalgesia.

Results

NT treatment decreased the levels of tumor necrosis factor alpha (TNF-α) and interleukin 1 beta (IL-1β). NT treatment decreased the total antioxidant status (TAOS) and reduced CFA-induced tactile hyperalgesia in a dose-dependent manner. NT significantly inhibited regulation of NF-kappaB activation and the production of IL-1β, TNF-α, iNOS and CAM-1. Moreover, NT suppressed infiltration of PMN.

Conclusions

Our results showed that NT reduced CFA-induced tactile hyperalgesia through inhibition inflammatory pathways in experimental inflammatory rats.

The effect of acetylcholine on pain-related electric activities in the hippocampal CA3 of rats

Acetylcholine (ACh) regulates pain perception in the central nervous system. However, the mechanism of action of ACh on pain-related neurons in the hippocampal CA3 is not clear. The present study aimed to determine the effect of ACh, muscarinic ACh receptors (mAChRs) agonist pilocarpine and mAChRs antagonist atropine on the pain-evoked responses of pain-excited neuron (PEN) and pain-inhibited neuron (PIN) in the hippocampal CA3 of normal rats. The trains of electric impulses applied to the sciatic nerve were used as noxious stimulation. The electric activities of PEN or PIN in the hippocampal CA3 were recorded by using a glass microelectrode. Our results showed that, in the hippocampal CA3, the intra-CA3 microinjection of ACh (2 μg/1 μl) or pilocarpine (2 μg/1 μl) decreased the discharge frequency and prolonged firing latency of PEN, and increased the discharge frequency and shortened firing inhibitory duration (ID) of PIN, i.e. exhibiting the analgesic effect of ACh or pilocarpine. The intra-CA3 administration of atropine (0.5 μg/1 μl) produced an opposite effect. On the basis of the above-mentioned findings, we can deduce that ACh and mAChRs in the hippocampal CA3 are involved in the modulation of nociceptive response by regulating the electric activities of PEN and PIN.

K+ATP Channels-Independent Analgesic Action of Crotalus durissus cumanensis venom

The effect was investigated of the K+ channel blocker, glibenclamide, on the ability of Crotalus durissus cumanensis venom (CDCM) to promote peripheral antinociception. This was measured by formalin-induced nociception in male Swiss mice. CDCM (200 and 300 μg/kg) produced an antinociceptive effect during phase 2 in the formalin test. The effect of CDCM (200 μg/kg) was unaffected by the ATP-sensitive K+ channel blocker glibenclamide (2 mg/kg). These results suggest that CDCM is effective against acute pain. However, the ATP-sensitive K+ channels pathway is not contribuable to the antinociceptive mechanism of CDCM.

Crystallization and preliminary X-ray diffraction analysis of crotoxin B from Crotalus durissus collilineatus venom

Crotoxin B is a basic phospholipase A(2) found in the venom of several Crotalus durissus ssp. rattlesnakes and is one of the subunits that constitute crotoxin, the main component of the venom of these snakes. This heterodimeric toxin is related to important envenomation effects such as neurological disorders, myotoxicity and renal failure. Although crotoxin was first crystallized in 1938, the first structural data only became available in 2007 (for crotoxin B from C. durissus terrificus) and showed an ambiguous result for the biological assembly, which could be either dimeric or tetrameric. In this work, the crystallization, X-ray diffraction data collection at 2.2 A resolution and molecular-replacement solution of a dimeric complex formed by two crotoxin B isoforms from C. durissus collilineatus venom is presented.

Peripheral and spinal antihyperalgesic activity of najanalgesin isolated from Naja naja atra in a rat experimental model of neuropathic pain

Snake venoms are a rich source of various compounds that have applications in medicine and biochemistry. Recently, it has been demonstrated that najanalgesin isolated from the venom of Naja naja atra exerts analgesic effects on acute pain in mice. The objective of this study was to evaluate the antinociceptive effect of najanalgesin in a rat model of neuropathic pain, induced by L5 spinal nerve ligation and transaction. We observed that intraperitoneal (i.p.) administration of najanalgesin produced significant increase in hind paw withdrawal latency (HWL) in response to both mechanical and thermal stimulation. Moreover, a single dose of najanalgesin was able to induce antinociceptive activity that lasted for 1 week. Intrathecal injection of najanalgesin increased the HWL in response to mechanical stimuli. The antinociceptive effect of najanalgesin administered intrathecally was partly inhibited by intrathecal injection of naloxone or atropine. These results demonstrate that najanalgesin has antinociceptive effects on the central and peripheral system in the rat neuropathic pain model. The opioid receptor and muscatinic receptor are involved in najanalgesin-induced antinociception in the spinal cord. This research supports the possibility of using najanalgesin as a novel pharmacotherapeutic agent for neuropathic pain.

Cobratoxin inhibits pain-evoked discharge of neurons in thalamic parafascicular nucleus in rats: involvement of cholinergic and serotonergic systems

The present study investigated the inhibitory effect of cobratoxin (CTX) on pain-evoked discharge of neurons in thalamic parafascicular nucleus (Pf) of rats and analyzed some of the mechanisms involved in this effect. Intracerebroventricular injection (icv) of CTX at 0.56, 1.12 and 4.50 microg/kg resulted in a dose-dependent inhibitory effect on the pain-evoked discharges of Pf neurons. The inhibition of pain-evoked discharges of Pf neurons by CTX at high dose (4.50 microg/kg) persisted at least for 2h, while the inhibitory effect of morphine (40 microg) persisted no longer than 30 min. The inhibitory effect of CTX was reversed by pretreatment with atropine (icv, 5 microg). In contrast, icv injection of naloxone (4 microg) had no effect on CTX-induced inhibition. Furthermore, pretreatment with parachlorophenylalanine, a specific inhibitor of tryptophan hydroxylase, also significantly attenuated the inhibitory effect of CTX. The results suggested that: (a) CTX has a dose-dependent inhibitory effect on pain-evoked discharges of Pf neurons, confirming electrophysiologically the antinociceptive action of CTX; (b) the inhibitory effect of CTX has a longer duration compared to that of morphine; (c) central cholinergic and serotonergic systems, but not opioidergic system, are involved in the inhibitory effect of CTX.

Insights into the role of oligomeric state on the biological activities of crotoxin: crystal structure of a tetrameric phospholipase A2 formed by two isoforms of crotoxin B from Crotalus durissus terrificus venom

Crotoxin B (CB or Cdt PLA(2)) is a basic Asp49-PLA(2) found in the venom of Crotalus durissus terrificus and it is one of the subunits that constitute the crotoxin (Cro). This heterodimeric toxin, main component of the C. d. terrificus venom, is completed by an acidic, nontoxic, and nonenzymatic component (crotoxin A, CA or crotapotin), and it is related to important envenomation effects such as neurological disorders, myotoxicity, and renal failure. Although Cro has been crystallized since 1938, no crystal structure of this toxin or its subunits is currently available. In this work, the authors present the crystal structure of a novel tetrameric complex formed by two dimers of crotoxin B isoforms (CB1 and CB2). The results suggest that these assemblies are stable in solution and show that Ser1 and Glu92 of CB1 and CB2, respectively, play an important role in the oligomerization. The tetrameric and dimeric conformations resulting from the association of the isoforms may increase the neurotoxicity of the toxin CB by the creation of new binding sites, which could improve the affinity of the molecular complexes to the presynaptic membrane.

Purification and characterization of a novel antinociceptive toxin from Cobra venom (Naja naja atra)

Snake venoms have demonstrated antinociceptive activity, and certain isolated neurotoxins have demonstrated significant analgesia in animal models. Here we report a novel analgesic toxin which was isolated from Naja naja atra and was given the name 'najanalgesin'. The LD(50) of the crude venom and najanalgesin were 0.89mg/kg and 2.69mg/kg, respectively. We used the writhing test and hot plate test to evaluate the antinociceptive properties of the crude venom and najanalgesin after intraperitoneal (ip) administration. The analgesic mechanism of najanalgesin was also studied. The response latency time was significantly prolonged in the hot plate test after ip administration of the crude venom of Naja naja atra (0.111-0.445mg/kg) in a dose-dependent manner. Najanalgesin (1mg/kg) elicited almost the same antinociceptive effect as that of the crude venom of Naja naja atra at the dose of 0.445mg/kg and remained for 6h after intraperitoneal injection, shown by hot plate test. The percentage of increase in the latency time for the venom and the najanalgesin 3h after drug administration was 96.2% and 112%, respectively. The number of writhes decreased to almost 1/3, 1/6, and 1/12 of the NS (physiological saline) group after intraperitoneal administration of najanalgesin at 0.25, 0.5, and 1.0mg/kg, respectively. Pretreatment with atropine (1mg/kg) or naloxone (3mg/kg) blocked the antinociception of najanalgesin in the hot plate test. Based on the sequence information, najanalgesin is found to be highly homologous with the conventional CTXs (cardiotoxins). To our knowledge, no study had previously reported that a toxin which was homologous with CTXs possessed the antinociceptive activity. Thus, this is the first report that the antinociceptive effect induced by najanalgesin is mediated by cholinergic and opioidergic mechanisms.

Crotalphine, a novel potent analgesic peptide from the venom of the South American rattlesnake Crotalus durissus terrificus

We have shown that the venom of the South American rattlesnake Crotalus durissus terrificus induces a long-lasting antinociceptive effect mediated by activation of kappa- and delta-opioid receptors. Despite being mediated by opioid receptors, prolonged treatment with the crotalid venom does not cause the development of peripheral tolerance or abstinence symptoms upon withdrawal. In the present study, we have isolated and chemically characterized a novel and potent antinociceptive peptide responsible for the oral opioid activity of this crotalid venom. The amino acid sequence of this peptide, designated crotalphine, was determined by mass spectrometry and corroborated by solid-phase synthesis to be <EFSPENCQGESQPC, where <E is pyroglutamic acid and the two cysteine residues forming a disulfide bond. This 14-amino-acid residue sequence is identical to the gamma-chain sequence of crotapotin, a non-toxic component of this snake venom. Crotalphine, when orally administered (0.008-25mug/kg), induces antinociceptive effect in the prostaglandin E(2)- and carrageenin-induced mechanical hyperalgesia models in rats and in the hot-plate test in mice. Crotalphine was also effective when administered by intravenous (0.0032-0.04mug/kg) or intraplantar (s.c., 0.00006-0.3mug/paw) routes. In the mechanical hyperalgesia models, crotalphine shows a long-lasting (5 days) antinociceptive effect. d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr amide (CTOP) and N,N-diallyl-Tyr-Aib-Aib-Phe-Leu (ICI 174,864), antagonists of mu- and delta-opioid receptors, respectively, did not alter the antinociceptive effect of the peptide, whereas nor-binaltorphimine, an antagonist of kappa-opioid receptors, blocked this effect. These results indicate that crotalphine induces antinociception mediated by activation of kappa-opioid receptors and may contribute to the antinociceptive effect of the crotalid venom.

Inhibitory effect of crotoxin on the pain-evoked discharge of neurons in thalamic parafascicular nucleus in rats

Crotoxin (Cro), the principal neurotoxic component of Crotalus durissus terrificus, has been previously reported to have a behavioral analgesic effect in rats and mice. The present study investigated electrophysiologically the effect of Cro on pain-evoked unit discharge of neurons in thalamic parafascicular nucleus (Pf) and underlying mechanisms of its effect. The electrical discharge of Pf neurons was recorded with the microelectrode technique in rats. Intracerebroventricular (i.c.v.) injection of Cro at 0.25, 0.45 and 0.65 microg/kg resulted in a dose-dependent inhibitory effect on the pain-evoked discharge of Pf neurons. The discharge frequency and the discharge duration significantly (P<0.05) decreased after Cro administration. This inhibitory effect was significantly (P<0.05) attenuated after pretreatment with para-chlorophenylalanine (pCPA), or electrolytic lesion of dorsal raphe (DR) nucleus. In contrast, i.c.v. injection of atropine (muscarinic receptor antagonist, 5 microg) or naloxone (opioid receptor antagonist, 4 microg) had no effect on Cro-induced inhibition of discharge of Pf neurons. The results suggested that Cro has an analgesic effect, which is mediated, at least partially, by the central serotonergic system.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Preliminary X-ray crystallographic studies of a tetrameric phospholipase A2 formed by two isoforms of crotoxin B from Crotalus durissus terrificus venom

Crotoxin B is a basic phospholipase A2 found in the venom of Crotalus durissus terrificus and is one of the subunits that constitute crotoxin. This heterodimeric toxin, which is the main component of C. d. terrificus venom, is completed by an acidic, nontoxic and non-enzymatic component (crotoxin A) and is involved in important envenomation effects, such as neurological disorders, myotoxicity and renal failure. Although crotoxin was first crystallized in 1938, no crystal structure is currently available for crotoxin, crotoxin A or crotoxin B. In this work, the crystallization, X-ray diffraction data collection to 2.28 A resolution and molecular-replacement solution of a novel tetrameric complex formed by two dimers of crotoxin B isoforms (CB1 and CB2) is presented.

Crystallization and preliminary X-ray crystallographic analysis of the heterodimeric crotoxin complex and the isolated subunits crotapotin and phospholipase A2

Crotoxin, a potent neurotoxin from the venom of the South American rattlesnake Crotalus durissus terrificus, exists as a heterodimer formed between a phospholipase A(2) and a catalytically inactive acidic phospholipase A(2) analogue (crotapotin). Large single crystals of the crotoxin complex and of the isolated subunits have been obtained. The crotoxin complex crystal belongs to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 38.2, b = 68.7, c = 84.2 A, and diffracted to 1.75 A resolution. The crystal of the phospholipase A(2) domain belongs to the hexagonal space group P6(1)22 (or its enantiomorph P6(5)22), with unit-cell parameters a = b = 38.7, c = 286.7 A, and diffracted to 2.6 A resolution. The crotapotin crystal diffracted to 2.3 A resolution; however, the highly diffuse diffraction pattern did not permit unambiguous assignment of the unit-cell parameters.