In vitro neuromuscular activity of snake venoms

The Venom of Vipera ammodytes ammodytes: Proteomics, Neurotoxic Effect and Neutralization by Antivenom

Deep proteomic analyses identified, in total, 159 master proteins (with 1% FDR and 2 unique peptides) from 26 protein families in the venom of Vipera ammodytes ammodytes (Vaa). Data are available via ProteomeXchange with the identifier PXD056495. The relative abundance of PLA2s is 11.60% of the crude venom, of which 4.35% are neurotoxic Ammodytoxins (Atxs). The neurotoxicity of the venom of Vaa and the neutralizing effect of the antivenom were tested on the neuromuscular preparation of the diaphragm (NPD) of rats. The activity of PLA2 in the venom of Vaa and its neutralization by the antivenom were determined under in vitro conditions. The Vaa venom leads to a progressive decrease in NPD contractions. We administered pre-incubated venom/antivenom mixtures at various ratios of 1:2, 1:10 and 1:20 (w/w) and observed the effects of these mixtures on NPD contractions. The results show that the mean effective time (ET50) for NPD contractions with the 1:20 mixture is highly significantly different (p < 0.001) from the ET50 for the venom and the ET50 for the 1:2 and 1:10 mixture ratios. We also found a highly significant (p < 0.001) reduction in Na+/K+-ATPase activity in the NPD under the influence of the venom. The reduction in the activity of this enzyme was reversible by the antivenom. Under in vitro conditions, we have achieved the complete neutralization of PLA2 by the antivenom. In conclusion, the antivenom abolished the venom-induced progressive decrease in NPD contractions in a concentration-dependent manner. Antivenom with approximately the same mass proportion almost completely restores Na+/K+-ATPase activity in the NPD and completely neutralizes the PLA2 activity of the venom in vitro.

Breaking muscle: neurotoxic and myotoxic effects of Central American snake venoms and the relative efficacies of antivenom and varespladib

BACKGROUND

The snake genera Atropoides, Cerrophidion, and Metlapilcoatlus form a clade of neotropical pit vipers distributed across Mexico and Central America. This study evaluated the myotoxic and neurotoxic effects of nine species of Atropoides, Cerrophidion, and Metlapilcoatlus, and the neutralising efficacy of the ICP antivenom from Costa Rica against these effects, in the chick biventer cervicis nerve-muscle preparation. Given the prominence of PLA2s within the venom proteomes of these species, we also aimed to determine the neutralising potency of the PLA2 inhibitor, varespladib.

RESULTS

All venoms showed myotoxic and potential neurotoxic effects, with differential intra-genera and inter-genera potency. This variation was also seen in the antivenom ability to neutralise the muscle damaging pathophysiological effects observed. Variation was also seen in the relative response to the PLA2 inhibitor varespladib. While the myotoxic effects of M. mexicanus and M. nummifer venoms were effectively neutralised by varespladib, indicating myotoxicity is PLA2 mediated, those of C. godmani and M. olmec venoms were not, revealing that the myotoxicity is driven by non-PLA2 toxin types.

CONCLUSIONS

This study characterises the myotoxic and neurotoxic venom activity, as well as neutralisation of venom effects from the Atropoides, Cerrophidion, and Metlapilcoatlus clade of American crotalids. Our findings contribute significant clinical and evolutionary knowledge to a clade of poorly researched snakes. In addition, these results provide a platform for future research into the reciprocal interaction between ecological niche specialisation and venom evolution, as well as highlighting the need to test purified toxins to accurately evaluate the potential effects observed in these venoms.

Isolation and Pharmacological Characterisation of Pre-Synaptic Neurotoxins from Thai and Javanese Russell's Viper (Daboia siamensis) Venoms

The widespread geographical distribution of Russell's vipers (Daboia spp.) is associated with marked variations in the clinical outcomes of envenoming by species from different countries. This is likely to be due to differences in the quantity and potency of key toxins and, potentially, the presence or absence of some toxins in venoms across the geographical spectrum. In this study, we aimed to isolate and pharmacologically characterise the major neurotoxic components of D. siamensis venoms from Thailand and Java (Indonesia) and explore the efficacy of antivenom and a PLA2 inhibitor, Varespladib, against the neuromuscular activity. These data will provide insights into the link between venom components and likely clinical outcomes, as well as potential treatment strategies. Venoms were fractionated using RP-HPLC and the in vitro activity of isolated toxins assessed using the chick biventer cervicis nerve-muscle preparation. Two major PLA2 fractions (i.e., fractions 8 and 10) were isolated from each venom. Fraction 8 from both venoms produced pre-synaptic neurotoxicity and myotoxicity, whereas fraction 10 from both venoms was weakly neurotoxic. The removal of the two fractions from each venom abolished the in vitro neurotoxicity, and partially abolished myotoxicity, of the whole venom. A combination of the two fractions from each venom produced neurotoxic activity that was equivalent to the respective whole venom (10 µg/mL), but the myotoxic effects were not additive. The in vitro neurotoxicity of fraction 8 (100 nM) from each venom was prevented by the pre-administration of Thai Russell's viper monovalent antivenom (2× recommended concentration) or preincubation with Varespladib (100 nM). Additionally, the neurotoxicity produced by a combination of the two fractions was partially reversed by the addition of Varespladib (100-300 nM) 60 min after the fractions. The present study demonstrates that the in vitro skeletal muscle effects of Thai and Javanese D. siamensis venoms are primarily due to key PLA2 toxins in each venom.

Neurotoxic snakebites in Africa: Clinical implications, therapeutic strategies, and antivenom efficacy

Snakebite is a significant health concern in Africa, particularly due to neurotoxic envenomation which can lead to neuromuscular paralysis and respiratory failure. In Nigeria, snakes from the Elapidae family are a notable cause of envenomation cases, though these incidents are underreported. This review examined case reports of neurotoxic envenomation in Africa, highlighting the clinical impacts and the efficacy of available antivenoms. Preclinical studies showed that the polyvalent antivenom from the South African Institute for Medical Research (SAIMR) was highly effective against neurotoxicity with a protective efficacy (R) of 1346.80 mg/mL, while clinical assessment emphasized the need for high-dose antivenom therapy along with supportive measures like mechanical ventilation. Unlike hemorrhagic envenomation, where antivenom promptly resolves bleeding, neurotoxic cases often require additional interventions. The review underscores the necessity for tailored approaches in antivenom therapy to address the complexities of neurotoxic snakebites and reduce their public health burden in Africa.

Novel Toxicodynamic Model of Subcutaneous Envenomation to Characterize Snake Venom Coagulopathies and Assess the Efficacy of Site-Directed Inorganic Antivenoms

Venomous snake bite adversely affects millions of people yearly, but few animal models allow for the determination of toxicodynamic timelines with hemotoxic venoms to characterize the onset and severity of coagulopathy or assess novel, site-directed antivenom strategies. Thus, the goals of this investigation were to create a rabbit model of subcutaneous envenomation to assess venom toxicodynamics and efficacy of ruthenium-based antivenom administration. New Zealand White rabbits were sedated with midazolam via the ear vein and had viscoelastic measurements of whole blood and/or plasmatic coagulation kinetics obtained from ear artery samples. Venoms derived from Crotalus scutulatus scutulatus, Bothrops moojeni, or Calloselasma rhodostoma were injected subcutaneously, and changes in coagulation were determined over three hours and compared to samples obtained prior to envenomation. Other rabbits had ruthenium-based antivenoms injected five minutes after venom injection. Viscoelastic analyses demonstrated diverse toxicodynamic patterns of coagulopathy consistent with the molecular composition of the proteomes of the venoms tested. The antivenoms tested attenuated venom-mediated coagulopathy. A novel rabbit model can be used to characterize the onset and severity of envenomation by diverse proteomes and to assess site-directed antivenoms. Future investigation is planned involving other medically important venoms and antivenom development.

In Vitro neurotoxicity and myotoxicity of Malaysian Naja sumatrana and Naja kaouthia venoms: Neutralization by monovalent and Neuro Polyvalent Antivenoms from Thailand

Naja sumatrana and Naja kaouthia are medically important elapids species found in Southeast Asia. Snake bite envenoming caused by these species may lead to morbidity or mortality if not treated with the appropriate antivenom. In this study, the in vitro neurotoxic and myotoxic effects N. sumatrana and N. kaouthia venoms from Malaysian specimens were assessed and compared. In addition, the neutralizing capability of Cobra Antivenom (CAV), King Cobra Antivenom (KCAV) and Neuro Polyvalent Antivenom (NPAV) from Thailand were compared. Both venoms produced concentration-dependent neurotoxic and myotoxic effects in the chick biventer cervicis nerve-muscle preparation. Based on the time to cause 90% inhibition of twitches (i.e. t₉₀) N. kaouthia venom displayed more potent neurotoxic and myotoxic effects than N. sumatrana venom. All three of the antivenoms significantly attenuated venom-induced twitch reduction of indirectly stimulated tissues when added prior to venom. When added after N. sumatrana venom, at the t₉₀ time point, CAV and NPAV partially restored the twitch height but has no significant effect on the reduction in twitch height caused by N. kaouthia venom. The addition of KCAV, at the t₉₀ time point, did not reverse the attenuation of indirectly stimulated twitches caused by either venom. In addition, none of the antivenoms, when added prior to venom, prevented attenuation of directly stimulated twitches. Differences in the capability of antivenoms, especially NPAV and CAV, to reverse neurotoxicity and myotoxicity indicate that there is a need to isolate and characterize neurotoxins and myotoxins from Malaysian N. kaouthia and N. sumatrana venoms to improve neutralization capability of the antivenoms.

In Vitro Neutralization of the Myotoxicity of Australian Mulga Snake (Pseudechis australis) and Sri Lankan Russell's Viper (Daboia russelii) Venoms by Australian and Indian Polyvalent Antivenoms

We studied the neutralisation of Sri Lankan Russell's viper (Daboia russelii) and Australian mulga snake (Pseudechis australis) venom-induced myotoxicity by Indian (Vins and Bharat) and Australian (Seqirus) polyvalent antivenoms, using the in vitro chick biventer skeletal muscle preparation. Prior addition of Bharat or Vins antivenoms abolished D. russelii venom (30 µg/mL)-mediated inhibition of direct twitches, while Australian polyvalent antivenom was not protective. Bharat antivenom prevented, while Vins and Australian polyvalent antivenoms partially prevented, the inhibition of responses to exogenous KCl. Myotoxicity of Mulga venom (10 µg/mL) was fully neutralised by the prior addition of Australian polyvalent antivenom, partially neutralised by Vins antivenom but not by Bharat antivenom. Although the myotoxicity of both venoms was partially prevented by homologous antivenoms when added 5 min after the venom, with an increasing time delay between venom and antivenom, the reversal of myotoxicity gradually decreased. However, antivenoms partially prevented myotoxicity even 60 min after venom. The effect of antivenoms on already initiated myotoxicity was comparable to physical removal of the toxins by washing the bath at similar time points, indicating that the action of the antivenoms on myotoxicity is likely to be due to trapping the toxins or steric hindrance within the circulation, not allowing the toxins to reach target sites in muscles.

Isolation of Polyclonal Single-Chain Fragment Variable (scFv) Antibodies Against Venomous Snakes of Iran and Evaluation of Their Capability in Neutralizing the Venom

Several species of dangerous snakes are found in Iran and, according to the Emergency Response Center of Iran from 2002 to 2011, 53,787 Iranians have suffered from snakebite. Although the mortalities caused by snakebite are very low, snakebite-related amputations are still a major concern. Currently, anti-venom polyclonal antibodies derived from animals, such as horses are used to treat snakebites; however, in some cases they can cause anaphylactic shock and serum sickness. In line with this premise, generation of recombinant anti-venom antibodies can be considered as an alternative strategy. Single-chain fragment variable (scFv) antibodies offer several advantages compared to the whole antibodies, including ease of production, high affinity and specificity. In the present study, scFv antibodies were selected against the venom of the most poisonous snakes in Iran using phage display technology. Phage particles harboring anti-venom specific scFv were separated and scFv antibodies were produced in bacteria. In-vitro assay showed that polyclonal scFvs specifically bind to the venom. Furthermore, in-vivo experiment in mice BALB/c indicated effective toxin neutralization using 20 µg of polyclonal scFv. Our study indicates the neutralizing capacity of anti-venom polyclonal scFvs, although further neutralization assays are needed to confirm their effectiveness.

In Vitro Neurotoxicity of Chinese Krait (Bungarus multicinctus) Venom and Neutralization by Antivenoms

Bungarus multicinctus, the Chinese krait, is a highly venomous elapid snake which causes considerable morbidity and mortality in southern China. B. multicinctus venom contains pre-synaptic PLA₂ neurotoxins (i.e., β-bungarotoxins) and post-synaptic neurotoxins (i.e., α-bungarotoxins). We examined the in vitro neurotoxicity of B. multicinctus venom, and the efficacy of specific monovalent Chinese B. multicinctus antivenom, and Australian polyvalent elapid snake antivenom, against venom-induced neurotoxicity. B. multicinctus venom (1-10 μg/mL) abolished indirect twitches in the chick biventer cervicis nerve-muscle preparation as well as attenuating contractile responses to exogenous ACh and CCh, but not KCl. This indicates a post-synaptic neurotoxic action but myotoxicity was not evident. Given that post-synaptic α-neurotoxins have a more rapid onset than pre-synaptic neurotoxins, the activity of the latter in the whole venom will be masked. The prior addition of Chinese B. multicinctus antivenom (12 U/mL) or Australian polyvalent snake antivenom (15 U/mL), markedly attenuated the neurotoxic actions of B. multicinctus venom (3 μg/mL) and prevented the inhibition of contractile responses to ACh and CCh. The addition of B. multicinctus antivenom (60 U/mL), or Australian polyvalent snake antivenom (50 U/mL), at the t₉₀ time point after the addition of B. multicinctus venom (3 μg/mL), did not restore the twitch height over 180 min. The earlier addition of B. multicinctus antivenom (60 U/mL), at the t₂₀ or t₅₀ time points, also failed to prevent the neurotoxic effects of the venom but did delay the time to abolish twitches based on a comparison of t₉₀ values. Repeated washing of the preparation with physiological salt solution, commencing at the t₂₀ time point, failed to reverse the neurotoxic effects of venom or delay the time to abolish twitches. This study showed that B. multicinctus venom displays marked in vitro neurotoxicity in a skeletal muscle preparation which is not reversed by antivenom. This does not appear to be related to antivenom efficacy, but due to the irreversible/pseudo-irreversible nature of the neurotoxins.

Crotalus Neutralizing Factor (CNF) inhibits the toxic effects of Crotoxin at mouse neuromuscular preparations

Crotalus Neutralizing Factor (CNF) was the first phospholipase A₂ inhibitor isolated from the plasma of the South American rattlesnake (Crotalus durissus terrificus). Previous biochemical and biophysical studies demonstrate an interaction of CNF with Crotoxin (CTX), the main toxic component in the venom of these snakes. CTX promotes the blockade of neuromuscular transmission by a sum of neurotoxic and myotoxic activities. However, the ability of CNF to inhibit these activities has not been shown until the present study. We performed a myographic study to compare the neuromuscular effects of CTX and the mixture CTX plus CNF in mice phrenic nerve-diaphragm muscle preparations. CTX (5 μg/mL) alone, or pre-incubated with CNF (5, 20 or 50 μg/mL) for 15 min was added to the preparations and maintained throughout the experimentation period. Myotoxicity was assessed by light microscopic analysis of diaphragm muscle after myographic study. CTX (5 μg/mL) blocked both indirectly and directly evoked twitches in neuromuscular preparations. In addition, CTX induced histological alterations in diaphragm muscle. Pre-incubation with CNF (50 μg/mL) abolished both the muscle-paralyzing and muscle-damaging activities of CTX. Therefore, the present study confirms, through functional studies, the antiophidic potential of CNF.

In-Vitro Neutralization of the Neurotoxicity of Coastal Taipan Venom by Australian Polyvalent Antivenom: The Window of Opportunity

Coastal taipan (Oxyuranus scutellatus) envenoming causes life-threatening neuromuscular paralysis in humans. We studied the time period during which antivenom remains effective in preventing and arresting in vitro neuromuscular block caused by taipan venom and taipoxin. Venom showed predominant pre-synaptic neurotoxicity at 3 µg/mL and post-synaptic neurotoxicity at 10 µg/mL. Pre-synaptic neurotoxicity was prevented by addition of Australian polyvalent antivenom before the venom and taipoxin and, reversed when antivenom was added 5 min after venom and taipoxin. Antivenom only partially reversed the neurotoxicity when added 15 min after venom and had no significant effect when added 30 min after venom. In contrast, post-synaptic activity was fully reversed when antivenom was added 30 min after venom. The effect of antivenom on pre-synaptic neuromuscular block was reproduced by washing the bath at similar time intervals for 3 µg/mL, but not for 10 µg/mL. We found an approximate 10–15 min time window in which antivenom can prevent pre-synaptic neuromuscular block. This time window is likely to be longer in envenomed patients due to the delay in venom absorption. Similar effectiveness of antivenom and washing with 3 µg/mL venom suggests that antivenom most likely acts by neutralizing pre-synaptic toxins before they interfere with neurotransmission inside the motor nerve terminals.

An Examination of the Neutralization of In Vitro Toxicity of Chinese Cobra (Naja atra) Venom by Different Antivenoms

The Chinese Cobra (Naja atra) is an elapid snake of major medical importance in southern China. We describe the in vitro neurotoxic, myotoxic, and cytotoxic effects of N. atra venom, as well as examining the efficacy of three Chinese monovalent antivenoms (N. atra antivenom, Gloydius brevicaudus antivenom and Deinagkistrodon acutus antivenom) and an Australian polyvalent snake antivenom. In the chick biventer cervicis nerve-muscle preparation, N. atra venom (1–10 µg/mL) abolished indirect twitches in a concentration-dependent manner, as well as abolishing contractile responses to exogenous acetylcholine chloride (ACh) and carbamylcholine chloride (CCh), indicative of post-synaptic neurotoxicity. Contractile responses to potassium chloride (KCl) were also significantly inhibited by venom indicating myotoxicity. The prior addition of Chinese N. atra antivenom (0.75 U/mL) or Australian polyvalent snake antivenom (3 U/mL), markedly attenuated the neurotoxic actions of venom (3 µg/mL) and prevented the inhibition of contractile responses to ACh, CCh, and KCl. The addition of Chinese antivenom (0.75 U/mL) or Australian polyvalent antivenom (3 U/mL) at the t₉₀ time point after the addition of venom (3 µg/mL), partially reversed the inhibition of twitches and significantly reversed the venom-induced inhibition of responses to ACh and CCh, but had no significant effect on the response to KCl. Venom (30 µg/mL) also abolished direct twitches in the chick biventer cervicis nerve-muscle preparation and caused a significant increase in baseline tension, further indicative of myotoxicity. N. atra antivenom (4 U/mL) prevented the myotoxic effects of venom (30 µg/mL). However, G. brevicaudus antivenom (24 U/mL), D. acutus antivenom (8 U/mL) and Australian polyvalent snake antivenom (33 U/mL) were unable to prevent venom (30 µg/mL) induced myotoxicity. In the L6 rat skeletal muscle myoblast cell line, N. atra venom caused concentration-dependent inhibition of cell viability, with a half maximal inhibitory concentration (IC₅₀) of 2.8 ± 0.48 μg/mL. N. atra antivenom significantly attenuated the cytotoxic effect of the venom, whereas Australian polyvalent snake antivenom was less effective but still attenuated the cytotoxic effects at lower venom concentrations. Neither G. brevicaudus antivenom or D. acutus antivenom were able to prevent the cytotoxicity. This study indicates that Chinese N. atra monovalent antivenom is efficacious against the neurotoxic, myotoxic and cytotoxic effects of N. atra venom but the clinical effectiveness of the antivenom is likely to be diminished, even if given early after envenoming. The use of Chinese viper antivenoms (i.e., G. brevicaudus and D. acutus antivenoms) in cases of envenoming by the Chinese cobra is not supported by the results of the current study.

Snake three-finger α-neurotoxins and nicotinic acetylcholine receptors: molecules, mechanisms and medicine

Snake venom three-finger α-neurotoxins (α-3FNTx) act on postsynaptic nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction (NMJ) to produce skeletal muscle paralysis. The discovery of the archetypal α-bungarotoxin (α-BgTx), almost six decades ago, exponentially expanded our knowledge of membrane receptors and ion channels. This included the localisation, isolation and characterization of the first receptor (nAChR); and by extension, the pathophysiology and pharmacology of neuromuscular transmission and associated pathologies such as myasthenia gravis, as well as our understanding of the role of α-3FNTxs in snakebite envenomation leading to novel concepts of targeted treatment. Subsequent studies on a variety of animal venoms have yielded a plethora of novel toxins that have revolutionized molecular biomedicine and advanced drug discovery from bench to bedside. This review provides an overview of nAChRs and their subtypes, classification of α-3FNTxs and the challenges of typifying an increasing arsenal of structurally and functionally unique toxins, and the three-finger protein (3FP) fold in the context of the uPAR/Ly6/CD59/snake toxin superfamily. The pharmacology of snake α-3FNTxs including their mechanisms of neuromuscular blockade, variations in reversibility of nAChR interactions, specificity for nAChR subtypes or for distinct ligand-binding interfaces within a subtype and the role of α-3FNTxs in neurotoxic envenomation are also detailed. Lastly, a reconciliation of structure-function relationships between α-3FNTx and nAChRs, derived from historical mutational and biochemical studies and emerging atomic level structures of nAChR models in complex with α-3FNTxs is discussed.

Actividad neurotóxica del veneno de serpientes del género Micrurus y métodos para su análisis. Revisión de la literatura

Introducción. Las serpientes del género Micrurus son animales de hábitos fosoriales, de temperamento pasivo y escasa producción de un potente veneno con características neurotóxicas que bloquean la transmisión sináptica en la placa neuromuscular.Objetivo. Presentar un panorama general de la neurotoxicidad del veneno de las serpientes Micrurus y su caracterización funcional mediante métodos de análisis ex vivo.Materiales y métodos. Se realizó una revisión de la literatura en MedLine y ScienceDirect usando términos específicos y sus combinaciones. Estrategia de búsqueda: tipo de estudios: artículos sobre la neurotoxicidad del veneno de serpientes Micrurus y técnicas para determinar su actividad neurotóxica mediante modelos in vitro, in vivo y ex vivo; periodo de publicación: sin limite inicial a junio de 2018; idiomas: inglés y español.Resultados. De los 88 estudios identificados en la búsqueda inicial, se excluyeron 28 por no cumplir los criterios de inclusión (basándose en la lectura de títulos y resúmenes); además, se incluyeron 8 documentos adicionales (libros e informes), que, a criterio de los autores, complementaban la información reportada por las referencias seleccionadas. Los estudios incluidos en la revisión (n=68) correspondieron a las siguientes tipologías: investigaciones originales (n=44), artículos de revisión (n=16) y capítulos de libros, informes, guías y consultas en internet (n=8).Conclusiones. Los estudios que describen el uso de preparaciones ex vivo de músculo y nervio para evaluar el efecto de neurotoxinas ofrecen un buen modelo para la caracterización del efecto presináptico y postsináptico del veneno producido por las serpientes Micrurus.

Snake Venoms in Drug Discovery: Valuable Therapeutic Tools for Life Saving

Animal venoms are used as defense mechanisms or to immobilize and digest prey. In fact, venoms are complex mixtures of enzymatic and non-enzymatic components with specific pathophysiological functions. Peptide toxins isolated from animal venoms target mainly ion channels, membrane receptors and components of the hemostatic system with high selectivity and affinity. The present review shows an up-to-date survey on the pharmacology of snake-venom bioactive components and evaluates their therapeutic perspectives against a wide range of pathophysiological conditions. Snake venoms have also been used as medical tools for thousands of years especially in tradition Chinese medicine. Consequently, snake venoms can be considered as mini-drug libraries in which each drug is pharmacologically active. However, less than 0.01% of these toxins have been identified and characterized. For instance, Captopril^® (Enalapril), Integrilin^® (Eptifibatide) and Aggrastat^® (Tirofiban) are drugs based on snake venoms, which have been approved by the FDA. In addition to these approved drugs, many other snake venom components are now involved in preclinical or clinical trials for a variety of therapeutic applications. These examples show that snake venoms can be a valuable source of new principle components in drug discovery.

Neuromuscular effect of venoms from adults and juveniles of Crotalus durissus cumanensis (Humboldt, 1811) from Guajira, Colombia

A toxinological study was performed to compare the neuromuscular effect of venom from adult and juvenile specimens from Crotalus durissus cumanensis from Guajira, Colombia. Both venoms exhibited neurotoxic activity in chick biventer cervicis nerve-muscle preparation. In addition, venom from juveniles was faster than adults to produce a neuromuscular blockade. In the contrary to the venom from juvenile's, at high doses, adult's venom affected the ACh and KCl contractures, indicating a myotoxic effect.

A novel in vitro potency assay of antisera against Thai Naja kaouthia based on nicotinic acetylcholine receptor binding

Snake envenomation is an important medical problem. One of the hurdles in antivenom development is the in vivo assay of antivenom potency which is expensive, gives variable results and kills many animals. We report a novel in vitro assay involving the specific binding of the postsynaptic neurotoxins (PSNTs) of elapid snakes with purified Torpedo californica nicotinic acetylcholine receptor (nAChR). The potency of an antivenom is determined by its antibody ability to bind and neutralize the PSNT, thus preventing it from binding to nAChR. The PSNT of Naja kaouthia (NK3) was immobilized on microtiter wells and nAChR was added to bind with it. The in vitro IC50 of N. kaouthia venom that inhibited 50% of nAChR binding to the immobilized NK3 was determined. Varying concentrations of antisera against N. kaouthia were separately pre-incubated with 5xIC50 of N. kaouthia venom. The remaining free NK3 were incubated with nAChR before adding to the NK3 coated plates. The in vitro and in vivo median effective ratio, ER50s of 12 batches of antisera showed correlation (R 2) of 0.9809 (p < 0.0001). This in vitro assay should be applicable to antisera against other elapid venoms and should reduce the use of live animals and accelerate development of life-saving antivenoms.

Prediction of presynaptic and postsynaptic neurotoxins by combining various Chou's pseudo components

Presynaptic and postsynaptic neurotoxins are two groups of neurotoxins. Identification of presynaptic and postsynaptic neurotoxins is an important work for numerous newly found toxins. It is both costly and time consuming to determine these two neurotoxins by experimental methods. As a complement, using computational methods for predicting presynaptic and postsynaptic neurotoxins could provide some useful information in a timely manner. In this study, we described four algorithms for predicting presynaptic and postsynaptic neurotoxins from sequence driven features by using Increment of Diversity (ID), Multinomial Naive Bayes Classifier (MNBC), Random Forest (RF), and K-nearest Neighbours Classifier (IBK). Each protein sequence was encoded by pseudo amino acid (PseAA) compositions and three biological motif features, including MEME, Prosite and InterPro motif features. The Maximum Relevance Minimum Redundancy (MRMR) feature selection method was used to rank the PseAA compositions and the 50 top ranked features were selected to improve the prediction accuracy. The PseAA compositions and three kinds of biological motif features were combined and 12 different parameters that defined as P1-P12 were selected as the input parameters of ID, MNBC, RF, and IBK. The prediction results obtained in this study were significantly better than those of previously developed methods.

Antivenom for Neuromuscular Paralysis Resulting From Snake Envenoming

Antivenom therapy is currently the standard practice for treating neuromuscular dysfunction in snake envenoming. We reviewed the clinical and experimental evidence-base for the efficacy and effectiveness of antivenom in snakebite neurotoxicity. The main site of snake neurotoxins is the neuromuscular junction, and the majority are either: (1) pre-synaptic neurotoxins irreversibly damaging the presynaptic terminal; or (2) post-synaptic neurotoxins that bind to the nicotinic acetylcholine receptor. Pre-clinical tests of antivenom efficacy for neurotoxicity include rodent lethality tests, which are problematic, and in vitro pharmacological tests such as nerve-muscle preparation studies, that appear to provide more clinically meaningful information. We searched MEDLINE (from 1946) and EMBASE (from 1947) until March 2017 for clinical studies. The search yielded no randomised placebo-controlled trials of antivenom for neuromuscular dysfunction. There were several randomised and non-randomised comparative trials that compared two or more doses of the same or different antivenom, and numerous cohort studies and case reports. The majority of studies available had deficiencies including poor case definition, poor study design, small sample size or no objective measures of paralysis. A number of studies demonstrated the efficacy of antivenom in human envenoming by clearing circulating venom. Studies of snakes with primarily pre-synaptic neurotoxins, such as kraits (Bungarus spp.) and taipans (Oxyuranus spp.) suggest that antivenom does not reverse established neurotoxicity, but early administration may be associated with decreased severity or prevent neurotoxicity. Small studies of snakes with mainly post-synaptic neurotoxins, including some cobra species (Naja spp.), provide preliminary evidence that neurotoxicity may be reversed with antivenom, but placebo controlled studies with objective outcome measures are required to confirm this.

Cross-Neutralisation of In Vitro Neurotoxicity of Asian and Australian Snake Neurotoxins and Venoms by Different Antivenoms

There is limited information on the cross-neutralisation of neurotoxic venoms with antivenoms. Cross-neutralisation of the in vitro neurotoxicity of four Asian and four Australian snake venoms, four post-synaptic neurotoxins (α-bungarotoxin, α-elapitoxin-Nk2a, α-elapitoxin-Ppr1 and α-scutoxin; 100 nM) and one pre-synaptic neurotoxin (taipoxin; 100 nM) was studied with five antivenoms: Thai cobra antivenom (TCAV), death adder antivenom (DAAV), Thai neuro polyvalent antivenom (TNPAV), Indian Polyvalent antivenom (IPAV) and Australian polyvalent antivenom (APAV). The chick biventer cervicis nerve-muscle preparation was used for this study. Antivenom was added to the organ bath 20 min prior to venom. Pre- and post-synaptic neurotoxicity of Bungarus caeruleus and Bungarus fasciatus venoms was neutralised by all antivenoms except TCAV, which did not neutralise pre-synaptic activity. Post-synaptic neurotoxicity of Ophiophagus hannah was neutralised by all antivenoms, and Naja kaouthia by all antivenoms except IPAV. Pre- and post-synaptic neurotoxicity of Notechis scutatus was neutralised by all antivenoms, except TCAV, which only partially neutralised pre-synaptic activity. Pre- and post-synaptic neurotoxicity of Oxyuranus scutellatus was neutralised by TNPAV and APAV, but TCAV and IPAV only neutralised post-synaptic neurotoxicity. Post-synaptic neurotoxicity of Acanthophis antarcticus was neutralised by all antivenoms except IPAV. Pseudonaja textillis post-synaptic neurotoxicity was only neutralised by APAV. The α-neurotoxins were neutralised by TNPAV and APAV, and taipoxin by all antivenoms except IPAV. Antivenoms raised against venoms with post-synaptic neurotoxic activity (TCAV) cross-neutralised the post-synaptic activity of multiple snake venoms. Antivenoms raised against pre- and post-synaptic neurotoxic venoms (TNPAV, IPAV, APAV) cross-neutralised both activities of Asian and Australian venoms. While acknowledging the limitations of adding antivenom prior to venom in an in vitro preparation, cross-neutralization of neurotoxicity means that antivenoms from one region may be effective in other regions which do not have effective antivenoms. TCAV only neutralized post-synaptic neurotoxicity and is potentially useful in distinguishing pre-synaptic and post-synaptic effects in the chick biventer cervicis preparation.

Isolation and Pharmacological Characterization of α-Elapitoxin-Ot1a, a Short-Chain Postsynaptic Neurotoxin from the Venom of the Western Desert Taipan, Oxyuranus temporalis

Taipans (Oxyuranus spp.) are elapids with highly potent venoms containing presynaptic (β) and postsynaptic (α) neurotoxins. O. temporalis (Western Desert taipan), a newly discovered member of this genus, has been shown to possess venom which displays marked in vitro neurotoxicity. No components have been isolated from this venom. We describe the characterization of α-elapitoxin-Ot1a (α-EPTX-Ot1a; 6712 Da), a short-chain postsynaptic neurotoxin, which accounts for approximately 30% of O. temporalis venom. α-Elapitoxin-Ot1a (0.1–1 µM) produced concentration-dependent inhibition of indirect-twitches, and abolished contractile responses to exogenous acetylcholine and carbachol, in the chick biventer cervicis nerve-muscle preparation. The inhibition of indirect twitches by α-elapitoxin-Ot1a (1 µM) was not reversed by washing the tissue. Prior addition of taipan antivenom (10 U/mL) delayed the neurotoxic effects of α-elapitoxin-Ot1a (1 µM) and markedly attenuated the neurotoxic effects of α-elapitoxin-Ot1a (0.1 µM). α-Elapitoxin-Ot1a displayed pseudo-irreversible antagonism of concentration-response curves to carbachol with a pA₂ value of 8.02 ± 0.05. De novo sequencing revealed the main sequence of the short-chain postsynaptic neurotoxin (i.e., α-elapitoxin-Ot1a) as well as three other isoforms found in O. temporalis venom. α-Elapitoxin-Ot1a shows high sequence similarity (i.e., >87%) with other taipan short-chain postsynaptic neurotoxins.

Structural and functional evidence for membrane docking and disruption sites on phospholipase A2-like proteins revealed by complexation with the inhibitor suramin

Local myonecrosis resulting from snakebite envenomation is not efficiently neutralized by regular antivenom administration. This limitation is considered to be a significant health problem by the World Health Organization. Phospholipase A2-like (PLA2-like) proteins are among the most important proteins related to the muscle damage resulting from several snake venoms. However, despite their conserved tertiary structure compared with PLA2s, their biological mechanism remains incompletely understood. Different oligomeric conformations and binding sites have been identified or proposed, leading to contradictory data in the literature. In the last few years, a comprehensive hypothesis has been proposed based on fatty-acid binding, allosteric changes and the presence of two different interaction sites. In the present study, a combination of techniques were used to fully understand the structural–functional characteristics of the interaction between suramin and MjTX-II (a PLA2-like toxin).In vitroneuromuscular studies were performed to characterize the biological effects of the protein–ligand interaction and demonstrated that suramin neutralizes the myotoxic activity of MjTX-II. The high-resolution structure of the complex identified the toxin–ligand interaction sites. Calorimetric assays showed two different binding events between the protein and the inhibitor. It is demonstrated for the first time that the inhibitor binds to the surface of the toxin, obstructing the sites involved in membrane docking and disruption according to the proposed myotoxic mechanism. Furthermore, higher-order oligomeric formation by interaction with interfacial suramins was observed, which may also aid the inhibitory process. These results further substantiate the current myotoxic mechanism and shed light on the search for efficient inhibitors of the local myonecrosis phenomenon.

Venomous and poisonous Australian animals of veterinary importance: a rich source of novel therapeutics

Envenomation and poisoning by terrestrial animals (both vertebrate and invertebrate) are a significant economic problem and health risk for domestic animals in Australia. Australian snakes are some of the most venomous animals in the world and bees, wasps, ants, paralysis ticks, and cane toads are also present as part of the venomous and poisonous fauna. The diagnosis and treatment of envenomation or poisoning in animals is a challenge and can be a traumatic and expensive process for owners. Despite the potency of Australian venoms, there is potential for novel veterinary therapeutics to be modeled on venom toxins, as has been the case with human pharmaceuticals. A comprehensive overview of envenomation and poisoning signs in livestock and companion animals is provided and related to the potential for venom toxins to act as therapeutics.

Comparative studies of the venom of a new Taipan species, Oxyuranus temporalis, with other members of its genus

Taipans are highly venomous Australo-Papuan elapids. A new species of taipan, the Western Desert Taipan (Oxyuranus temporalis), has been discovered with two specimens housed in captivity at the Adelaide Zoo. This study is the first investigation of O. temporalis venom and seeks to characterise and compare the neurotoxicity, lethality and biochemical properties of O. temporalis venom with other taipan venoms. Analysis of O. temporalis venom using size-exclusion and reverse-phase HPLC indicated a markedly simplified "profile" compared to other taipan venoms. SDS-PAGE and agarose gel electrophoresis analysis also indicated a relatively simple composition. Murine LD50 studies showed that O. temporalis venom is less lethal than O. microlepidotus venom. Venoms were tested in vitro, using the chick biventer cervicis nerve-muscle preparation. Based on t90 values, O. temporalis venom is highly neurotoxic abolishing indirect twitches far more rapidly than other taipan venoms. O. temporalis venom also abolished responses to exogenous acetylcholine and carbachol, indicating the presence of postsynaptic neurotoxins. Prior administration of CSL Taipan antivenom (CSL Limited) neutralised the inhibitory effects of all taipan venoms. The results of this study suggest that the venom of the O. temporalis is highly neurotoxic in vitro and may contain procoagulant toxins, making this snake potentially dangerous to humans.

Anterior Segment Ischemia in Viper Bite

PURPOSE

To describe the clinical and histopathological features of post viper bite anterior segment ischemia.

METHODS

Seven patients with ocular complications following viper bite referred to uveitis clinic had slit-lamp examination, intraocular pressure (IOP) measurement, and fundus evaluation. Iris and fundus fluorescein angiography was performed on 2 patients. Histopathological examination was performed on iris tissues collected during cataract surgery.

RESULTS

Strikingly similar clinical findings were noted, including circumpupillary superficial iris atrophy, mid dilated fixed pupil, marked pigment dispersion, low IOP, and cataract. All clinical signs were noted only in the anterior segment; the posterior segment was normal. Histopathology of iris revealed atrophy of iris stroma, necrotic iris pigment epithelium, and infiltration of T lymphocytes and fibrous membrane. Poor visual outcome was noted in patients with low IOP.

CONCLUSION

Viper bite victims presented with clinical and histopathological signs of anterior segment ischemia and secondary inflammatory signs mimicking uveitis.

In-vitro neurotoxicity of two Malaysian krait species (Bungarus candidus and Bungarus fasciatus) venoms: neutralization by monovalent and polyvalent antivenoms from Thailand

Bungarus candidus and Bungarus fasciatus are two species of krait found in Southeast Asia. Envenoming by these snakes is often characterized by neurotoxicity and, without treatment, causes considerable morbidity and mortality. In this study, the in vitro neurotoxicity of each species, and the effectiveness of two monovalent antivenoms and a polyvalent antivenom, against the neurotoxic effects of the venoms, were examined in a skeletal muscle preparation. Both venoms caused concentration-dependent inhibition of indirect twitches, and attenuated responses to exogenous nicotinic receptor agonists, in the chick biventer preparation, with B. candidus venom being more potent than B. fasciatus venom. SDS-PAGE and western blot analysis indicated different profiles between the venoms. Despite these differences, most proteins bands were recognized by all three antivenoms. Antivenom, added prior to the venoms, attenuated the neurotoxic effect of the venoms. Interestingly, the respective monovalent antivenoms did not neutralize the effects of the venom from the other Bungarus species indicating a relative absence of cross-neutralization. Addition of a high concentration of polyvalent antivenom, at the t₉₀ time point after addition of venom, partially reversed the neurotoxicity of B. fasciatus venom but not B. candidus venom. The monovalent antivenoms had no significant effect when added at the t₉₀ time point. This study showed that B. candidus and B. fasciatus venoms display marked in vitro neurotoxicity in the chick biventer preparation and administration of antivenoms at high dose is necessary to prevent or reverse neurotoxicity.

Comparative analysis of the venom proteome of four important Malaysian snake species

BACKGROUND

Naja kaouthia, Ophiophagus hannah, Bungarus fasciatus and Calloselasma rhodostoma are four venomous snakes indigenous to Malaysia. In the present study, their proteomic profile by two-dimensional gel electrophoresis (2-DE) have been separated and compared.

RESULTS

The 2-DE of venoms of the four species snake demonstrated complexity and obvious interspecies differences in proteome profiles. A total of 63 proteins were identified in the four species: C. rhodostoma - 26, N. kaouthia - 16, O. hannah - 15 and B. fasciatus - 6.

CONCLUSIONS

Despite the identifications of major proteins in the four snake species, a large number of protein spots from the 2-DE were unidentified even though the spots displayed high-quality MALDI-TOF-MS spectra. Those identified included phospholipase A2 proteins in all four venoms, long neurotoxins in both cobra species and the C. rhodostoma venom found with the most varied types of peptidases, i.e. metalloproteinase kistomin, halystase and L-amino acid oxidase.

Neuromuscular activity of Micrurus laticollaris (Squamata: Elapidae) venom in vitro

In this work, we have examined the neuromuscular activity of Micrurus laticollaris (Mexican coral snake) venom (MLV) in vertebrate isolated nerve-muscle preparations. In chick biventer cervicis preparations, the MLV induced an irreversible concentration- and time-dependent (1–30 µg/mL) neuromuscular blockade, with 50% blockade occurring between 8 and 30 min. Muscle contractures evoked by exogenous acetylcholine were completely abolished by MLV, whereas those of KCl were also significantly altered (86% ± 11%, 53% ± 11%, 89% ± 5% and 89% ± 7% for one, three, 10 and 30 µg of venom/mL, respectively; n = 4; p < 0.05). In mouse phrenic nerve-diaphragm preparations, MLV (1–10 µg/mL) promoted a slight increase in the amplitude of twitch-tension (3 µg/mL), followed by neuromuscular blockade (n = 4); the highest concentration caused complete inhibition of the twitches (time for 50% blockade = 26 ± 3 min), without exhibiting a previous neuromuscular facilitation. The venom (3 µg/mL) induced a biphasic modulation in the frequency of miniature end-plate potentials (MEPPs)/min, causing a significant increase after 15 min, followed by a decrease after 60 min (from 17 ± 1.4 (basal) to 28 ± 2.5 (t₁₅) and 12 ± 2 (t₆₀)). The membrane resting potential of mouse diaphragm preparations pre-exposed or not to d-tubocurarine (5 µg/mL) was also significantly less negative with MLV (10 µg/mL). Together, these results indicate that M. laticollaris venom induces neuromuscular blockade by a combination of pre- and post-synaptic activities.

Preliminary results of the in vivo and in vitro characterization of a tentacle venom fraction from the jellyfish Aurelia aurita

The neurotoxic effects produced by a tentacle venom extract and a fraction were analyzed and correlated by in vivo and in vitro approaches. The tentacle venom extract exhibited a wide range of protein components (from 24 to >225 kDa) and produced tetanic reactions, flaccid paralysis, and death when injected into crabs. Two chromatography fractions also produced uncontrolled appendix movements and leg stretching. Further electrophysiological characterization demonstrated that one of these fractions potently inhibited ACh-elicited currents mediated by both vertebrate fetal and adult muscle nicotinic acetylcholine receptors (nAChR) subtypes. Receptor inhibition was concentration-dependent and completely reversible. The calculated IC(50) values were 1.77 μg/μL for fetal and 2.28 μg/μL for adult muscle nAChRs. The bioactive fraction was composed of a major protein component at ~90 kDa and lacked phospholipase A activity. This work represents the first insight into the interaction of jellyfish venom components and muscle nicotinic receptors.

Neurotoxicity in snakebite--the limits of our knowledge

Snakebite is classified by the WHO as a neglected tropical disease. Envenoming is a significant public health problem in tropical and subtropical regions. Neurotoxicity is a key feature of some envenomings, and there are many unanswered questions regarding this manifestation. Acute neuromuscular weakness with respiratory involvement is the most clinically important neurotoxic effect. Data is limited on the many other acute neurotoxic manifestations, and especially delayed neurotoxicity. Symptom evolution and recovery, patterns of weakness, respiratory involvement, and response to antivenom and acetyl cholinesterase inhibitors are variable, and seem to depend on the snake species, type of neurotoxicity, and geographical variations. Recent data have challenged the traditional concepts of neurotoxicity in snake envenoming, and highlight the rich diversity of snake neurotoxins. A uniform system of classification of the pattern of neuromuscular weakness and models for predicting type of toxicity and development of respiratory weakness are still lacking, and would greatly aid clinical decision making and future research. This review attempts to update the reader on the current state of knowledge regarding this important issue.

In vitro comparison of enzymatic effects among Brazilian Bothrops spp. venoms

In various types of snake venom, the major toxic components are proteinases and members of the phospholipase A2 family, although other enzymes also contribute to the toxicity. In this study, we evaluated the proteolytic, phospholipase, and L-Amino acid oxidase activities in the venom of five Bothrops species-Bothrops jararaca, Bothrops jararacussu, Bothrops moojeni, Bothrops neuwiedi, and Bothrops alternatus-all of which are used in the production of commercial antivenom, prepared in horses. The enzymatic activities of each species' venom were classified as high, moderate, or low. B. moojeni venom demonstrated the highest enzymatic activity profile, followed by the venom of B. neuwiedi, B. jararacussu, B. jararaca, and B. alternatus. To our knowledge, this is the first study to compare all of these enzymes from multiple species, which is significant in view of the activity of L-amino acid oxidase across Bothrops species.

Identification and characterization of a taxon-specific three-finger toxin from the venom of the Green Vinesnake (Oxybelis fulgidus; family Colubridae)

Snake venoms contain a variety of protein and peptide toxins, and the three-finger toxins (3FTxs) are among the best characterized family of venom proteins. The compact nature and highly conserved molecular fold of 3FTxs, together with their abundance in many venoms, has contributed to their utility in structure-function studies. Although many target the nicotinic acetylcholine receptor of vertebrate skeletal muscle, often binding with nanomolar Kds, several non-conventional 3FTxs show pronounced taxon-specific neurotoxic effects. Here we describe the purification and characterization of fulgimotoxin, a monomeric 3FTx from the venom of Oxybelis fulgidus, a neotropical rear-fanged snake. Fulgimotoxin retains the canonical 5 disulfides of the non-conventional 3FTxs and is highly neurotoxic to lizards; however, mice are unaffected, demonstrating that this toxin is taxon-specific in its effects. Analysis of structural features of fulgimotoxin and other colubrid venom 3FTxs indicate the presence of a "colubrid toxin motif" (CYTLY) and a second conserved segment (WAVK) found in Boiga and Oxybelis taxon-specific 3FTxs, both in loop II. Because specific residues in loop II conventional α-neurotoxic 3FTxs are intimately associated with receptor binding, we hypothesize that this loop, with its highly conserved substitutions, confers taxon-specific neurotoxicity. These findings underscore the importance of rear-fanged snake venoms for understanding the evolution of toxin molecules and demonstrate that even among well-characterized toxin families, novel structural and functional motifs may be found.

Population divergence in venom bioactivities of elapid snake Pseudonaja textilis: role of procoagulant proteins in rapid rodent prey incapacitation

This study looked at how toxic proteins in venoms of adult Australian eastern Brown snakes Pseudonaja textilis from South Australian and Queensland populations interact with physiological functions of the lab SD rat Rattus norvegicus. Circulatory collapse and incoagulable blood occurred instantly after injection of venom under the dorsal skin of anaesthetised and mechanically ventilated rats in an imitation of a P. textilis bite. Intravenous injection of purified P. textilis (Mackay, QLD) venom prothrombin activator proteins caused instant failure of circulation, testifying of high toxicity of these proteins and suggesting their role in rapid incapacitation of rodent prey. The hypothesis is further supported by circulatory collapse occurring instantly despite artificial respiration in envenomed rats and the finding of extremely high venom procoagulant potency in rat plasma. LC-MS and physiology assays revealed divergent venom composition and biological activity of South Australian (Barossa locality) and Queensland (Mackay locality) populations, which may be driven by selection for different prey. The Queensland venom of P. textilis was found to be more procoagulant and to exhibit predominately presynaptic neurotoxicity, while the South Australian venom contained diverse postsynaptic type II and III α-neurotoxins in addition to the presynaptic neurotoxins and caused significantly faster onset of neuromuscular blockade in the rat phrenic nerve-diaphragm preparation. LC-MS analysis found evidence of multiple coagulation factor X-like proteins in P. textilis venoms, including a match to P. textilis coagulation factor X isoform 2, previously known to be expressed only in the liver.

Alpha neurotoxins

α-Neurotoxins have been isolated from hydrophid, elapid and, more recently, colubrid snake venoms. Also referred to as postsynaptic neurotoxins or 'curare mimetic' neurotoxins, they play an important role in the capture and/or killing of prey by binding to the nicotinic acetylcholine receptor on the skeletal muscle disrupting neurotransmission. They are also thought to cause respiratory paralysis in envenomed humans. This review will discuss the historical background into the discovery, isolation, structure and mechanism of action of the α-neurotoxins, including targets and cellular outcomes, and then will examine the potential uses of α-neurotoxins as pharmacological tools and/or as drug leads.

In vitro neurotoxic effects of Pseudechis spp. venoms: A comparison of avian and murine skeletal muscle preparations

Two common in vitro skeletal muscle preparations used for the study of venom neurotoxicity are the indirectly stimulated chick isolated biventer cervicis nerve-muscle preparation and the rat isolated phrenic nerve-diaphragm preparation. The aim of the current study was to compare the in vitro neurotoxicity of six Pseudechis spp. (Black snakes) venoms in both avian (chicken) and mammalian (rat) skeletal muscle preparations to determine differences in sensitivity. All Pseudechis spp. venoms significantly inhibited indirect twitches, in both preparations, indicating the presence of post synaptic neurotoxins. The inhibitory effects of all venoms were more rapid in the avian preparation, except for Pseudechis colletti venom where no significant difference was seen between the murine and avian muscles. Time taken to produce 50% reduction in stimulated twitches (i.e. t(50)) was markedly shorter in the avian preparation. We have shown that the avian in vitro preparation is more sensitive to the neurotoxic activity of Pseudechis spp. than the murine preparation. This difference is likely to be due to species differences in the interaction between the neurotoxins and the nicotinic receptor binding sites as well as differences in the 'safety factor' between the preparations.

Biochemistry of envenomation

Venoms and toxins are of significant interest due to their ability to cause a wide range of pathophysiological conditions that can potentially result in death. Despite their wide distribution among plants and animals, the biochemical pathways associated with these pathogenic agents remain largely unexplored. Impoverished and underdeveloped regions appear especially susceptible to increased incidence and severity due to poor socioeconomic conditions and lack of appropriate medical treatment infrastructure. To facilitate better management and treatment of envenomation victims, it is essential that the biochemical mechanisms of their action be elucidated. This review aims to characterize downstream envenomation mechanisms by addressing the major neuro-, cardio-, and hemotoxins as well as ion-channel toxins. Because of their use in folk and traditional medicine, the biochemistry behind venom therapy and possible implications on conventional medicine will also be addressed.

Solving the 'Brown snake paradox': in vitro characterisation of Australasian snake presynaptic neurotoxin activity

Pseudonaja textilis (Eastern Brown snake) and Oxyuranus scutellatus scutellatus (Coastal taipan) are clinically important Australian elapid snakes, whose potent venoms contain the presynaptic (β) neurotoxins, textilotoxin and taipoxin, respectively, and a number of postsynaptic neurotoxins. However, while taipan envenoming frequently results in neurotoxicity, Brown snake envenoming causes an isolated coagulopathy and neurotoxicity is rare. This phenomenon is called the 'Brown snake paradox'. This study compared the pharmacology of both venoms and their respective presynaptic neurotoxins to investigate this phenomenon. From size-exclusion high performance liquid chromatography (HPLC) analysis textilotoxin represents a significantly smaller proportion (5.7%) of P. textilis venom compared to taipoxin in O. s. scutellatus venom (20.4%). In the chick biventer cervicis nerve-muscle (CBCNM) preparation both venoms caused concentration-dependent neurotoxicity, with P. textilis venom being significantly more potent than O. s. scutellatus venom. Conversely, taipoxin was significantly more potent than textilotoxin when compared at the same concentration. Textilotoxin only partially contributed to the overall neurotoxicity of P. textilis venom, while taipoxin accounted for the majority of the neurotoxicity of O. s. scutellatus venom in the CBCNM preparation. Compared with taipoxin, textilotoxin is less potent and constitutes a smaller proportion of the venom. This is likely to be the reason for the absence of neurotoxicity in envenomed humans thus explaining the 'Brown snake paradox'.

Neuromuscular activity of the venoms of the Colombian coral snakes Micrurus dissoleucus and Micrurus mipartitus: an evolutionary perspective

The venoms of coral snakes (genus Micrurus) are known to induce a broad spectrum of pharmacological activities. While some studies have investigated their potential human effects, little is known about their mechanism of action in terms of the ecological diversity and evolutionary relationships among the group. In the current study we investigated the neuromuscular blockade of the venom of two sister species Micrurus mipartitus and Micrurus dissoleucus, which exhibit divergent ecological characteristics in Colombia, by using the chick biventer cervicis nerve-muscle preparation. We also undertook a phylogenetic analysis of these species and their congeners, in order to provide an evolutionary framework for the American coral snakes. The venom of M. mipartitus caused a concentration-dependant inhibition (3-10 μg/ml) of nerve-mediated twitches and significantly inhibited contractile responses to exogenous ACh (1 mM), but not KCl (40 mM), indicating a postsynaptic mechanism of action. The inhibition of indirect twitches at the lower venom dose (3 μg/ml) showed to be triphasic and the effect was further attenuated when PLA2 was inhibited. M. dissoleucus venom (10-50 μg/ml) failed to produce a complete blockade of nerve-mediated twitches within a 3 h time period and significantly inhibited contractile responses to exogenous ACh (1 mM) and KCl (40 mM), indicating both postsynaptic and myotoxic mechanisms of action. Myotoxic activity was confirmed by morphological studies of the envenomed tissues. Our results demonstrate a hitherto unsuspected diversity of pharmacological actions in closely related species which exhibit divergent ecological characteristics; these results have important implications for both the clinical management of Coral snake envenomings and the design of Micrurus antivenom.

Mojave toxin-type ascending flaccid paralysis after an envenomation by a Southern Pacific Rattlesnake in a dog

OBJECTIVE

To describe the clinical presentation and case management of a dog that developed ascending flaccid paralysis after being envenomated by a Southern Pacific rattlesnake.

CASE SUMMARY

A dog was presented after it was bitten by a Southern Pacific rattlesnake. Only mild local edema and a minor coagulapathy developed, which is atypical for the Southern Pacific envenomation where hemotoxic effects are more commonly observed. Instead, a severe, rapidly progressing, ascending flaccid paralysis leading to acute respiratory failure, consistent with Mojave toxin, was seen. The patient was treated with repeated doses of antivenin and supported with mechanical ventilation. Despite clinical improvement of the paralysis over subsequent 3 days and successful weaning off the ventilator, the dog decompensated and succumbed to acute respiratory distress syndrome.

NEW OR UNIQUE INFORMATION PROVIDED

The geographic region where this envenomation occurred has a documented population of Southern Pacific rattlesnakes with Mojave toxin in their venom. To the knowledge of the authors, this is the first reported case in the veterinary literature of an ascending flaccid paralysis, consistent with Mojave toxin, developing after an envenomation by a Southern Pacific rattlesnake.