Gyroxin fails to modify in vitro release of labelled dopamine and acetylcholine from rat and mouse striatal tissue

Snake Venom: A Promising Source of Neurotoxins Targeting Voltage-Gated Potassium Channels

The venom derived from various sources of snakes represents a vast collection of predominantly protein-based toxins that exhibit a wide range of biological actions, including but not limited to inflammation, pain, cytotoxicity, cardiotoxicity, and neurotoxicity. The venom of a particular snake species is composed of several toxins, while the venoms of around 600 venomous snake species collectively encompass a substantial reservoir of pharmacologically intriguing compounds. Despite extensive research efforts, a significant portion of snake venoms remains uncharacterized. Recent findings have demonstrated the potential application of neurotoxins derived from snake venom in selectively targeting voltage-gated potassium channels (Kv). These neurotoxins include BPTI-Kunitz polypeptides, PLA2 neurotoxins, CRISPs, SVSPs, and various others. This study provides a comprehensive analysis of the existing literature on the significance of Kv channels in various tissues, highlighting their crucial role as proteins susceptible to modulation by diverse snake venoms. These toxins have demonstrated potential as valuable pharmacological resources and research tools for investigating the structural and functional characteristics of Kv channels.

Gyroxin, a toxin from Crotalus durissus terrificus snake venom, induces a calcium dependent increase in glutamate release in mice brain cortical synaptosomes

Gyroxin is a thrombin-like toxin obtained from the venom of the South American rattlesnake, Crotalus durissus terrificus. Literature has reported "gyroxin syndrome" characterized, in mice, as series of aberrant motor behavior, known as barrel rotation, mainly after intraperitoneal administration. Despites several studies, a physiological mechanism of "gyroxin syndrome" are still not completely understood. In this context, alterations on the central nervous system (CNS), especially causing neurotoxic events, are pointed out as likely candidates. Then, we decided to investigate whether gyroxin induces alterations in glutamate release, one of the most important neurotransmitter involved in neurotoxicity. For that, we performed all experiments, in vitro, using a model of mice brain cortical synaptosomes. Notably, our results indicate that the administration of gyroxin on purified presynaptic brain cortical terminals resulted in an extracellular Ca²⁺- dependent raise in glutamate release. Indeed, our results also showed that gyroxin increases intrasynaptosomal calcium (Ca²⁺) levels through acting on voltage gated calcium channels (VGCC), specifically N and P/Q subtypes. Moreover, our data show that gyroxin increases exocytosis rate. Interestingly, these data suggest that gyroxin might induce neurotoxicity by increasing glutamate levels. However, future investigations are needed in order to elucidate the nature of the following events.

Comparative proteomic profiling and functional characterization of venom pooled from captive Crotalus durissus terrificus specimens and the Brazilian crotalic reference venom

The South American rattlesnake Crotalus durissus spp has a wide geographic distribution in Brazil. Although responsible for only a low proportion of ophidian accidents, it is considered one of the most medically important species of venomous snakes due to the high mortality rate (1.87%). Snake venom is a complex phenotype commonly subjected to individual intraspecific, ontogenetic and geographic variability. Compositional differences in pooled venom used in the immunization process may impact the efficacy of the antivenom. In order to assure standardized high-quality antivenom, the potency of each Brazilian crotalic antivenom batch is determined against the 'Brazilian Crotalic Reference Venom' (BCRV). BCRV is produced by Instituto Butantan using venom obtained from the first milking of recently wild-caught C. d. terrificus specimens brought to the Institute. The decrease in the number of snake donations experienced in recent years can become a threat to the production of future batches of BCRV. To evaluate the feasibility of using venom from long-term captive animals in the formulation of BCRV, we have compared the proteomic, biochemical and biological profiles of C. d. terrificus venom pooled from captive specimens (CVP- captive venom pool) and BCRV. Electrophoretic and venomics analyses revealed a very similar venom composition profile, but also certain differences in toxins abundance, with some low abundant protein families found only in BCRV. Enzymatic (L-amino acid oxidase, phospholipase A₂ and proteolytic) and biological (myotoxic and coagulant) activities showed higher values in CVP than in BCRV. CVP also possessed slightly higher lethal effect, although the Instituto Butantan crotalic antivenom showed equivalent potency neutralizing BCRV and CVP. Our results strongly suggest that venom from long-term captive C. d. terrificus might be a valid alternative to generate an immunization mixture of equivalent quality to the currently in use reference venom.

Venoms and Isolated Toxins from Snakes of Medical Impact in the Northeast Argentina: State of the Art. Potential Pharmacological Applications

Among the ophidians that inhabit the Northeast of Argentina, the genus Bothrops such as B. alternatus and B. diporus species (also known as yararás) and Crotalus durisus terrificus (named cascabel), represent the most studied snake venom for more than thirty years. These two genera of venomous snakes account for the majority of poisonous snake envenomations and therefore, constitute a medical emergency in this region. This review presents a broad description of the compiled knowledge about venomous snakebite: its pathophysiological action, protein composition, isolated toxins, toxin synergism, toxin-antitoxin cross-reaction assays. Properties of some isolated toxins support a potential pharmacological application.

Mechanistic insights into functional characteristics of native crotamine

The chemical composition of snake venoms is a complex mixture of proteins and peptides that can be pharmacologically active. Crotamine, a cell-penetrating peptide, has been described to have antimicrobial properties and it exerts its effects by interacting selectively with different structures, inducing changes in the ion flow pattern and cellular responses. However, its real therapeutic potential is not yet fully known. Bearing in mind that crotamine is a promising molecule in therapeutics, this study investigated the action of purified molecule in three aspects: I) antibacterial action on different species of clinical interest, II) the effect of two different concentrations of the molecule on platelet aggregation, and III) its effects on isolated mitochondria. Crotamine was purified to homogeneity in a single step procedure using Heparin Sepharose. The molecular mass of the purified enzyme was 4881.4 Da, as determined by mass spectrometry. To assess antibacterial action, changes in the parameters of bacterial oxidative stress were determined. The peptide showed antibacterial activity on Escherichia coli (MIC: 2.0 μg/μL), Staphylococcus aureus (MIC: 8-16 μg/μL) and methicillin-resistant Staphylococcus aureus (MIC: 4.0-8.0 μg/μL), inducing bacterial death by lipid peroxidation and oxidation of target proteins, determined by thiobarbituric acid reactive substances and sulfhydryl groups, respectively. Crotamine induced increased platelet aggregation (IPA) at the two concentrations analyzed (0.1 and 1.4 μg/μL) compared to ADP-induced aggregation of PRP. Mitochondrial respiratory parameters and organelle structure assays were used to elucidate the action of the compound in this organelle. The exposure of mitochondria to crotamine caused a decrease in oxidative phosphorylation and changes in mitochondrial permeability, without causing damage in the mitochondrial redox state. Together, these results support the hypothesis that, besides the antimicrobial potential, crotamine acts on different molecular targets, inducing platelet aggregation and mitochondrial dysfunction.

Intrahippocampal infusion of crotamine isolated from Crotalus durissus terrificus alters plasma and brain biochemical parameters

Crotamine is one of the main constituents of the venom of the South American rattlesnake Crotalus durissus terrificus. Here we sought to investigate the inflammatory and toxicological effects induced by the intrahippocampal administration of crotamine isolated from Crotalus whole venom. Adult rats received an intrahippocampal infusion of crotamine or vehicle and were euthanized 24 h or 21 days after infusion. Plasma and brain tissue were collected for biochemical analysis. Complete blood count, creatinine, urea, glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), creatine-kinase (CK), creatine kinase-muscle B (CK-MB) and oxidative parameters (assessed by DNA damage and micronucleus frequency in leukocytes, lipid peroxidation and protein carbonyls in plasma and brain) were quantified. Unpaired and paired t-tests were used for comparisons between saline and crotamine groups, and within groups (24 h vs. 21 days), respectively. After 24 h crotamine infusion promoted an increase of urea, GOT, GPT, CK, and platelets values (p ≤ 0.01), while red blood cells, hematocrit and leukocytes values decreased (p ≤ 0.01). Additionally, 21 days after infusion crotamine group showed increased creatinine, leukocytes, TBARS (plasma and brain), carbonyl (plasma and brain) and micronucleus compared to the saline-group (p ≤ 0.01). Our findings show that crotamine infusion alter hematological parameters and cardiac markers, as well as oxidative parameters, not only in the brain, but also in the blood, indicating a systemic pro-inflammatory and toxicological activity. A further scientific attempt in terms of preserving the beneficial activity over toxicity is required.

The intrahippocampal infusion of crotamine from Crotalus durissus terrificus venom enhances memory persistence in rats

Previous research has shown that crotamine, a toxin isolated from the venom of Crotalus durissus terrificus, induces the release of acetylcholine and dopamine in the central nervous system of rats. Particularly, these neurotransmitters are important modulators of memory processes. Therefore, in this study we investigated the effects of crotamine infusion on persistence of memory in rats. We verified that the intrahippocampal infusion of crotamine (1 μg/μl; 1 μl/side) improved the persistence of object recognition and aversive memory. By other side, the intrahippocampal infusion of the toxin did not alter locomotor and exploratory activities, anxiety or pain threshold. These results demonstrate a future prospect of using crotamine as potential pharmacological tool to treat diseases involving memory impairment, although it is still necessary more researches to better elucidate the crotamine effects on hippocampus and memory.

Beneficial effect of crotamine in the treatment of myasthenic rats

INTRODUCTION

Crotamine is a basic, low-molecular-weight peptide that, at low concentrations, improves neurotransmission in isolated neuromuscular preparations by modulating sodium channels. In this study, we compared the effects of crotamine and neostigmine on neuromuscular transmission in myasthenic rats.

METHODS

We used a conventional electromyographic technique in in-situ neuromuscular preparations and a 4-week treadmill program.

RESULTS

During the in-situ electromyographic recording, neostigmine (17 μg/kg) caused short-term facilitation, whereas crotamine induced progressive and sustained twitch-tension enhancement during 140 min of recording (50 ± 5%, P < 0.05). On the treadmill evaluation, rats showed significant improvement in exercise tolerance, characterized by a decrease in the number of fatigue episodes after 2 weeks of a single-dose treatment with crotamine.

CONCLUSIONS

These results indicate that crotamine is more efficient than neostigmine for enhancing muscular performance in myasthenic rats, possibly by improving the safety factor of neuromuscular transmission.

Gyroxin increases blood-brain barrier permeability to Evans blue dye in mice

Gyroxin is a serine protease enzyme component of the South American rattlesnake (Crotalus durissus terrificus) venom. This toxin displays several activities, including the induction of blood coagulation (fibrinogenolytic activity), vasodilation and neurotoxicity, resulting in an effect called barrel rotation. The mechanisms involved in this neurotoxic activity are not well known. Because gyroxin is a member of a potentially therapeutic family of enzymes, including thrombin, ancrod, batroxobin, trypsin and kallicrein, the identification of the mechanism of gyroxin's action is extremely important. In this study, gyroxin was isolated from crude venom by affinity and molecular exclusion chromatography. Analysis of the isolated gyroxin via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a single protein band with a molecular weight of approximately 28 kDa, confirming the identity of the molecule. Furthermore, intravenous administration of purified gyroxin (0.25 μg/g of body weight) to mice resulted in symptoms compatible with barrel rotation syndrome, confirming the neurotoxic activity of the toxin. Mice treated with gyroxin showed an increase in the concentration of albumin-Evans blue in brain extracts, indicating an increase in the blood-brain barrier (BBB) permeability. This gyroxin-induced increase in BBB permeability was time-dependent, reaching a peak within 15 min after exposure, similar to the time span in which the neurotoxic syndrome (barrel rotation) occurs. This work provides the first evidence of gyroxin's capacity to temporarily alter the permeability of the BBB.

Biochemistry of the envenomation response-A generator theme for interdisciplinary integration

The understanding of complex physiological processes requires information from many different areas of knowledge. To meet this interdisciplinary scenario, the ability of integrating and articulating information is demanded. The difficulty of such approach arises because, more often than not, information is fragmented through under graduation education in Health Sciences. Shifting from a fragmentary and deep view of many topics to joining them horizontally in a global view is not a trivial task for teachers to implement. To attain that objective we proposed a course herein described-Biochemistry of the envenomation response-aimed at integrating previous contents of Health Sciences courses, following international recommendations of interdisciplinary model. The contents were organized by modules with increasing topic complexity. The full understanding of the envenoming pathophysiology of each module would be attained by the integration of knowledge from different disciplines. Active-learning strategy was employed focusing concept map drawing. Evaluation was obtained by a 30-item Likert-type survey answered by ninety students; 84% of the students considered that the number of relations that they were able to establish as seen by concept maps increased throughout the course. Similarly, 98% considered that both the theme and the strategy adopted in the course contributed to develop an interdisciplinary view.

Cloning of serine protease cDNAs from Crotalus durissus terrificus venom gland and expression of a functional Gyroxin homologue in COS-7 cells

Gyroxin is one of main serine proteases of Crotalus durissus terrificus venom, representing about 2% of the protein content in the crude venom. It is a 33 kDa glycoprotein with 3.8% by weight of sugar moiety. This toxin induces hemotoxicity in mice and a neurological condition called barrel rotation syndrome. In the present work, we report the molecular cloning of five new nucleotide sequences from a cDNA library of the venom glands of a single specimen of C. d. terrificus. These sequences have been analyzed in silico with respect to their cDNA organization and similarity with other snake venom serine proteases (SVSPs). We also describe a rapid and efficient method for screening vectors for mammalian cell expression, based on the fact that SVSPs are difficult-to-express toxins due to the presence of several disulfide bonds and glycosylation in their structures. Thus, one of the Gyroxin cDNAs was subcloned into pSectag2 HygroA and pED vectors and used to transfect COS-7 cells. Expression of the functional recombinant Gyroxin isoform was achieved with this cell line with esterase activity in the conditioned culture medium, as revealed by immunoblot of secreted protein and standard anti-crotalic serum from Butantan Institute.

Glycine stimulates the release of labeled acetylcholine but not dopamine nor glutamate from superfused rat striatal tissue

Glycine is known as an inhibitory neurotransmitter in the spinal cord and forebrain but its precise role in the forebrain is largely overlooked. This investigation evaluated whether glycine alters acetylcholine, glutamate or dopamine release from striatal tissue using an in vitro approach. We observed that while glycine induced a robust (3)H-acetylcholine release ((3)H-ACh) from superfused striatal tissue, it failed at releasing (3)H-glutamate or (3)H-dopamine. Glycine stimulated (3)H-ACh release in a dose- and calcium-dependent manner (EC(50)=69 microM). Tetrodotoxin (1 microM) inhibited about 75% of the release demonstrating a predominant dendritic and cell body location of glycine receptors. The prototypical glycine receptor antagonist strychnine at 10 microM completely abolished (3)H-ACh release. To further characterize the role of striatal glycine receptors in (3)H-ACh release we examined glycine effects after in vivo treatment with Haloperidol-decanoate (HD). Treatment for 30 days or more with HD decreased maximal glycine-stimulated release of (3)H-ACh suggesting a non-competitive inhibition. After 30 days of washout release parameters did not return to vehicle-treated levels. The glutamate agonist NMDA also stimulated acetylcholine release but showed slightly different behavior in HD-treated striatal tissue. These effects could be attributed to changes in chloride transporters expressed in the giant striatal cholinergic cell as well as glycine receptor subunit composition and finally, GABA/glycine co-release in this tissue.

Neurotoxicological effects of a thrombin-like enzyme isolated from Crotalus durissus terrificus venom (preliminary study)

A thrombin-like enzyme, purified from the venom of Crotalus durissus terrificus by gel filtration and affinity chromatography, showed a single protein band in Sodium dodecyl sulfate-polyacrilamide gel electrophoresis (SDS-PAGE) with a molecular weight of about 33kDa. Clear cellular morphological changes, deep ganglioside level modifications in some brain areas and behavioral alterations in pup rats injected with this protein were detected. Ganglioside composition, one of the chemical markers of brain maturation, was altered specially in the hypothalamus, hippocampus and prefrontal cortex. The most reliable behavioral effects were a delayed, maturation of the righting reflex, posture and motor response after treatment. These effects were consistent with the histological changes revealed in the cerebellum and prefrontal cortex of treated neonate rats, areas related to motor activities.

Isolation of a new l-amino acid oxidase from Crotalus durissus cascavella venom

A novel l-amino acid oxidase (LAO) (Casca LAO) from Crotalus durissus cascavella venom was purified to a high degree of molecular homogeneity using a combination of molecular exclusion and ion-exchange chromatography system. The purified monomer of LAO presented a molecular mass of 68 kDa and pI estimated in 5.43, which were determined by two-dimensional electrophoresis. The 71st N-terminal amino acid sequence of the LAO from Crotalus durissus cascavella presented a high amino acid sequence similarities with other LAOs from Colloselasma rhosostoma, Crotalus adamanteus, Agkistrodon h. blomhoffi, Agkistrodon h. halys and Trimeresurus stejnegeri. LAO displayed a Michaelis-Menten behavior with a kilometer of 46.7 microM and an optimum pH for enzymatic activity of 6.5. Casca LAO induced a dose-dependent platelet aggregation, which was abolished by catalase and inhibited by indomethacin and aspirin. These results suggest that the production of H2O2 is involved in subsequent activation of inflammatory enzymes, such as thromboxane. Casca LAO also inhibited the bacterial growth of Gram-negative (Xanthomonas axonopodis pv passiflorae) and Gram-positive (S. mutans) strains. Electron microscopy assessments of both bacterial strains suggest that the hydrogen peroxide produced by LAO induce bacterial membrane rupture and consequently loss of cytoplasmatic content. This LAO exhibited a high antileishmanic activity against the promastigote of Leishmania amazonensis in vitro, its activity was dependent on the production of hydrogen peroxide, and the 50% inhibitory concentration was estimated in 2.39 microg/ml.

New view on crotamine, a small basic polypeptide myotoxin from South American rattlesnake venom

Crotamine is a toxin from the Crotalus durissus terrificus venom, composed of 42 amino acid residues and three disulfide bridges. It belongs to a toxin family previously called Small Basic Polypeptide Myotoxins (SBPM) whose members are widely distributed through the Crotalus snake venoms. Comparison of SBPM amino acid sequences shows high similarities. Crotamine induces skeletal muscle spasms, leading to spastic paralysis of the hind limbs of mice, by interacting with sodium channels on muscle cells. The crotamine gene with 1.8 kbp is organized into three exons, which are separated by a long phase-1 and short phase-2 introns and mapped to chromosome 2. The three-dimensional structure of crotamine was recently solved and shares a structural topology with other three disulfide bond-containing peptide similar to human beta-defensins and scorpion Na+ channel toxin. Novel biological activities have been reported, such as the capacity to penetrate undifferentiated cells, to localize in the nucleus, and to serve as a marker of actively proliferating living cells.

Ionotropic glutamate receptors regulating labeled acetylcholine release from rat striatal tissue in vitro: possible involvement of receptor modulation in magnesium sensitivity

This study evaluated the role of glutamate ionotropic receptors on the control of [3H]acetylcholine ([3H]ACh) release by the intrinsic striatal cholinergic cells. [3H]-choline previously taken up by chopped striatal tissue and converted to [3H]ACh, was released under stimulation by glutamate, N-methyl-d-aspartate (NMDA), kainate and a-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA). Experiments were conducted in the absence of choline uptake inhibitors or acetylcholinesterase inhibitors. A paradigm of two stimulations was employed, the first in control conditions and the second after 9 min of perfusion with the test agents MK-801, 2-amino-5-phosphonopentanoic acid (AP-5), tetrodotoxin (TTX), 6,7-dinitroquinoxaline-2,3-dione (DNQX), 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo-[f]quinoxaline-7-sulfonamide (NBQX), glycine and magnesium. Our results support that (1) in the absence of Mg2+, NMDA is the most effective agonist to stimulate [3H]ACh release from striatal slices (2) magnesium effectively antagonized kainate and AMPA stimulation suggesting that at least part of the kainate and AMPA effects might be attributed to glutamate release (3) besides NMDA, kainate receptors showed a more direct involvement in [3H]ACh release control based on the smaller dependence on Mg2+ and less inhibition by TTX and (4) stimulation of ionotropic glutamate receptors may induce long lasting biochemical changes in receptor/ion channel function since the effects of TTX and/or Mg2+ ions on [3H]ACh release were modified by previous exposure of the tissue to agonists.

Determination of Crotalus durissus cascavella venom components that induce renal toxicity in isolated rat kidneys

Envenomation by Crotalus durissus terrificus leads to coagulation disorders, myotoxicity, neurotoxicity and acute renal failure (ARF). The most serious systemic change and primary cause of death is ARF. In this work, we used RP-HPLC to isolate crotoxin, convulxin and gyroxin from venom of the related subspecies Crotalus durissus cascavella and investigated the effects of these toxins on renal function in the isolated rat kidneys perfused with Krebs-Henseleit solution containing 6% of bovine serum albumin. The parameters studied included perfusion pressure (PP), renal vascular resistance (RVR), glomerular filtration rate (GFR), urinary flow (UF), percent of sodium tubular transport (%TNa(+)), percent of potassium tubular transport (%TK(+)) and percent of chloride tubular transport (%TCl(-)). Crotoxin (5 microg/ml) increased the PP, RVR, GFR, UF and decreased %TNa(+), %TK(+) and %TCl(-), with gyroxin (5 micro g/ml) the GFR remained stable during the 120 min of perfusion, whereas PP and RVR increased significantly and the %TNa(+), %TK(+) and %TCl(-) decreased significantly. Convulxin (5 micro g/ml) had no effect on renal function. Crotoxin caused alterations in all renal parameters. Gyroxin produced a minor effect compared to crotoxin. These results indicated that crotoxin is the main componenet responsible for acute nephrotoxicity caused by C. d. cascavella venom.