Species and regional variations in the effectiveness of antivenom against the in vitro neurotoxicity of death adder (Acanthophis) venoms

From squid giant axon to automated patch-clamp: electrophysiology in venom and antivenom research

Ion channels play a crucial role in diverse physiological processes, including neurotransmission and muscle contraction. Venomous creatures exploit the vital function of ion channels by producing toxins in their venoms that specifically target these ion channels to facilitate prey capture upon a bite or a sting. Envenoming can therefore lead to ion channel dysregulation, which for humans can result in severe medical complications that often necessitate interventions such as antivenom administration. Conversely, the discovery of highly potent and selective venom toxins with the capability of distinguishing between different isoforms and subtypes of ion channels has led to the development of beneficial therapeutics that are now in the clinic. This review encompasses the historical evolution of electrophysiology methodologies, highlighting their contributions to venom and antivenom research, including venom-based drug discovery and evaluation of antivenom efficacy. By discussing the applications and advancements in patch-clamp techniques, this review underscores the profound impact of electrophysiology in unravelling the intricate interplay between ion channels and venom toxins, ultimately leading to the development of drugs for envenoming and ion channel-related pathologies.

Photoresponsive porous ZnO-based broad-spectrum venom first-aid treatment

A venomous snakebite is an emergency. However, antivenoms are rare and very similar, difficult to produce and preserve, and almost impossible to be used for emergency treatment. Therefore, it would be of great significance to develop convenient, efficient and broad-spectrum snake venom neutralizing nano-materials. In this study, inspired by boiled eggs, a new concept based on a ZnO complex (ZC) for the treatment of snake venoms is proposed. In vitro and in vivo experiments proved that ZC could widely adsorb biological (including snake) venoms and effectively reduce the concentration of toxic protein in the blood. More importantly, ZC could realize photothermal conversion under the stimulation of near-infrared (NIR) irradiation, resulting in protein hydrolyzation of venoms, thereby fundamentally prolonging survival time. In addition, ZC not only showed good biocompatibility, but also could inhibit bacterial reproduction, alleviate inflammation, and contribute to the healing of open wounds caused by biological venoms.

Variations in neurotoxicity and proteome profile of Malayan krait (Bungarus candidus) venoms

Malayan krait (Bungarus candidus) is a medically important snake species found in Southeast Asia. The neurotoxic effects of envenoming present as flaccid paralysis of skeletal muscles. It is unclear whether geographical variation in venom composition plays a significant role in the degree of clinical neurotoxicity. In this study, the effects of geographical variation on neurotoxicity and venom composition of B. candidus venoms from Indonesia, Malaysia and Thailand were examined. In the chick biventer cervicis nerve-muscle preparation, all venoms abolished indirect twitches and attenuated contractile responses to nicotinic receptor agonists, with venom from Indonesia displaying the most rapid neurotoxicity. A proteomic analysis indicated that three finger toxins (3FTx), phospholipase A2 (PLA2) and Kunitz-type serine protease inhibitors were common toxin groups in the venoms. In addition, venom from Thailand contained L-amino acid oxidase (LAAO), cysteine rich secretory protein (CRISP), thrombin-like enzyme (TLE) and snake venom metalloproteinase (SVMP). Short-chain post-synaptic neurotoxins were not detected in any of the venoms. The largest quantity of long-chain post-synaptic neurotoxins and non-conventional toxins was found in the venom from Thailand. Analysis of PLA2 activity did not show any correlation between the amount of PLA2 and the degree of neurotoxicity of the venoms. Our study shows that variation in venom composition is not limited to the degree of neurotoxicity. This investigation provides additional insights into the geographical differences in venom composition and provides information that could be used to improve the management of Malayan krait envenoming in Southeast Asia.

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.

Assessing the utility of the Oxford Nanopore MinION for snake venom gland cDNA sequencing

Portable DNA sequencers such as the Oxford Nanopore MinION device have the potential to be truly disruptive technologies, facilitating new approaches and analyses and, in some cases, taking sequencing out of the lab and into the field. However, the capabilities of these technologies are still being revealed. Here we show that single-molecule cDNA sequencing using the MinION accurately characterises venom toxin-encoding genes in the painted saw-scaled viper, Echis coloratus. We find the raw sequencing error rate to be around 12%, improved to 0–2% with hybrid error correction and 3% with de novo error correction. Our corrected data provides full coding sequences and 5′ and 3′ UTRs for 29 of 33 candidate venom toxins detected, far superior to Illumina data (13/40 complete) and Sanger-based ESTs (15/29). We suggest that, should the current pace of improvement continue, the MinION will become the default approach for cDNA sequencing in a variety of species.

Cytotoxiciy of Naja nubiae (Serpentes: Elapidae) and Echis ocellatus (Serpentes: Viperidae) Venoms from Sudan

In Sudan, as in many African countries, no local specific antivenom is manufactured resulting in snake bite victims being treated by antivenoms imported from abroad. In the present work we measured the cytotoxic effect of the recently described spitting cobra (Naja nubiae) and the carpet viper (Echis ocellatus) snake venoms using a cell based assay. We also investigated the efficacy of four antivenoms CSL (Australia), SAIMR (South Africa), snake venom antiserum (India), and EchiTAb-Plus-ICP (Cost Rica) to neutralize the cytotoxic effect of the two venoms. The venoms resulted in a remarkable inhibition of cell viability with N. nubiae being more cytotoxic than E. ocellatus. The four antivenoms studied were effective in neutralizing N. nubiae cytotoxicity. However, only partial efficacy in neutralizing the cytotoxic effect of E. ocellatus was achieved using CSL (Australia) and SVA (India) antivenoms. Based on the cross neutralization by the four antivenoms, the Sudanese N. nubiae venom most likely has homologous epitopes with similar snakes from Australia, South Africa, India, and Cost Rica, while E. ocellatus venom from Sudan shares little homology with similar snakes from other countries.

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.

Vintage venoms: proteomic and pharmacological stability of snake venoms stored for up to eight decades

For over a century, venom samples from wild snakes have been collected and stored around the world. However, the quality of storage conditions for "vintage" venoms has rarely been assessed. The goal of this study was to determine whether such historical venom samples are still biochemically and pharmacologically viable for research purposes, or if new sample efforts are needed. In total, 52 samples spanning 5 genera and 13 species with regional variants of some species (e.g., 14 different populations of Notechis scutatus) were analysed by a combined proteomic and pharmacological approach to determine protein structural stability and bioactivity. When venoms were not exposed to air during storage, the proteomic results were virtually indistinguishable from that of fresh venom and bioactivity was equivalent or only slightly reduced. By contrast, a sample of Acanthophis antarcticus venom that was exposed to air (due to a loss of integrity of the rubber stopper) suffered significant degradation as evidenced by the proteomics profile. Interestingly, the neurotoxicity of this sample was nearly the same as fresh venom, indicating that degradation may have occurred in the free N- or C-terminus chains of the proteins, rather than at the tips of loops where the functional residues are located. These results suggest that these and other vintage venom collections may be of continuing value in toxin research. This is particularly important as many snake species worldwide are declining due to habitat destruction or modification. For some venoms (such as N. scutatus from Babel Island, Flinders Island, King Island and St. Francis Island) these were the first analyses ever conducted and these vintage samples may represent the only venom ever collected from these unique island forms of tiger snakes. Such vintage venoms may therefore represent the last remaining stocks of some local populations and thus are precious resources. These venoms also have significant historical value as the Oxyuranus venoms analysed include samples from the first coastal taipan (Oxyuranus scutellatus) collected for antivenom production (the snake that killed the collector Kevin Budden), as well as samples from the first Oxyuranus microlepidotus specimen collected after the species' rediscovery in 1976. These results demonstrate that with proper storage techniques, venom samples can retain structural and pharmacological stability. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

BIOLOGICAL SIGNIFICANCE

Death adder envenoming causes neurotoxicity not reversed by antivenom--Australian Snakebite Project (ASP-16)

BACKGROUND

Death adders (Acanthophis spp) are found in Australia, Papua New Guinea and parts of eastern Indonesia. This study aimed to investigate the clinical syndrome of death adder envenoming and response to antivenom treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Definite death adder bites were recruited from the Australian Snakebite Project (ASP) as defined by expert identification or detection of death adder venom in blood. Clinical effects and laboratory results were collected prospectively, including the time course of neurotoxicity and response to treatment. Enzyme immunoassay was used to measure venom concentrations. Twenty nine patients had definite death adder bites; median age 45 yr (5-74 yr); 25 were male. Envenoming occurred in 14 patients. Two further patients had allergic reactions without envenoming, both snake handlers with previous death adder bites. Of 14 envenomed patients, 12 developed neurotoxicity characterised by ptosis (12), diplopia (9), bulbar weakness (7), intercostal muscle weakness (2) and limb weakness (2). Intubation and mechanical ventilation were required for two patients for 17 and 83 hours. The median time to onset of neurotoxicity was 4 hours (0.5-15.5 hr). One patient bitten by a northern death adder developed myotoxicity and one patient only developed systemic symptoms without neurotoxicity. No patient developed venom induced consumption coagulopathy. Antivenom was administered to 13 patients, all receiving one vial initially. The median time for resolution of neurotoxicity post-antivenom was 21 hours (5-168). The median peak venom concentration in 13 envenomed patients with blood samples was 22 ng/mL (4.4-245 ng/mL). In eight patients where post-antivenom bloods were available, no venom was detected after one vial of antivenom.

CONCLUSIONS/SIGNIFICANCE

Death adder envenoming is characterised by neurotoxicity, which is mild in most cases. One vial of death adder antivenom was sufficient to bind all circulating venom. The persistent neurological effects despite antivenom, suggests that neurotoxicity is not reversed by antivenom.

Anti-snake venom activities of extracts and fractions from callus cultures of Sapindus saponaria

CONTEXT

Sapindus saponaria L. (Sapindaceae) bark, root, and fruits are used as sedatives and to treat gastric ulcer and also demonstrate diuretic and expectorant effects.

OBJECTIVE

The anti-snake venom properties of callus of S. saponaria are investigated here for the first time.

MATERIALS AND METHODS

In vitro cultivated callus of Sapindus saponaria were lyophilized, and the extracts were prepared with different solvents, before submitting to phytochemical studies and evaluation of the anti-ophidian activity. Crude extracts were fractionated by liquid-liquid partition and the fractions were monitored by thin layer chromatography (TLC). Subsequently, anti-ophidian activities were analyzed toward Bothrops jararacussu Lacerda (Viperidae), B. moojeni Hoge (Viperidae), B. alternates Duméril (Viperidea) and Crotalus durissus terrificus Lineu (Viperidae) venoms and isolated myotoxins and phospholipase A(2) (PLA(2)).

RESULTS

Fractions A1, A2 and the extract in MeOH:H(2)O (9:1) significantly inhibited the toxic and pharmacological activities induced by snake venoms and toxins, when compared to other extracts and fractions. The lethal, clotting, phospholipase, edema-inducing, hemorrhagic and myotoxic activities were partially inhibited by the different extracts and fractions. TLC profiles of the crude extracts (B and C) and fractions (A1 and A2) showed β-sitosterol and stigmasterol as their main compounds. Stigmasterol exhibited inhibitory effects on enzymatic and myotoxic activities of PLA(2).

DISCUSSION AND CONCLUSION

Sapindus saponaria extracts and fractions presented anti-ophidian activity and could be used as an adjuvant to serum therapy or for its supplementation, and in addition, as a rich source of potential inhibitors of enzymes involved in several pathophysiological human and animal diseases.

Validation of a cell-based assay to differentiate between the cytotoxic effects of elapid snake venoms

INTRODUCTION

Acanthophis genus (i.e. death adders) and the Naja genus (i.e. cobras) belong to the family elapidae. The current study compared the in vitro cytotoxicity of venoms from four Acanthophis spp. and three Naja spp. on rat aortic smooth muscle cells, A7r5, and rat skeletal muscle cells, L6. The ability of CSL death adder antivenom and SAIMR antivenom, for Acanthophis spp. and Naja spp. venom respectively, to negate the cytotoxicity was also examined.

METHODS

A cell proliferation assay was used to determine cell viability following treatment with venom in the presence or absence of antivenom. Sigmoidal growth curves were obtained, and IC(50) values were determined.

RESULTS

Acanthophis spp. and Naja spp. venoms produced concentration-dependent inhibition of cell proliferation in both cell lines. Naja spp. venoms were significantly more cytotoxic than the most potent Acanthophis venom (i.e. A. antarcticus) in both cell lines. Naja spp. venoms also displayed higher sensitivity in L6 cells. SAIMR antivenom significantly inhibited the cytotoxic actions of all Naja spp. venoms in both A7r5 and L6 cells. However, death adder antivenom (CSL Ltd) was unable to negate the cytotoxic effects of Acanthophis spp. venoms.

DISCUSSION

Concentrations of the predominantly cytotoxic Naja spp. venoms used were approximately three times less than the predominantly neurotoxic Acanthophis spp. venoms. SAIMR antivenom was partially effective in neutralising the effects of Naja spp. venoms. Death adder antivenom (CSL Ltd) was not effective in negating the cytotoxic effects of venom from Acanthophis spp. These results indicate that the cell-based assay is suited to the examination of cytotoxic snake venoms and may be used in conjunction with organ bath experiments to pharmacologically characterise snake venoms. Furthermore, the results suggest that the use of a skeletal muscle cell line is likely to be more clinically relevant for the examination of cytotoxic snake venoms.

Isolation and characterisation of P-EPTX-Ap1a and P-EPTX-Ar1a: pre-synaptic neurotoxins from the venom of the northern (Acanthophis praelongus) and Irian Jayan (Acanthophis rugosus) death adders

The neurotoxicity observed following death adder envenoming has been thought to be solely due to the presence of potent post-synaptic neurotoxins. Clinically, these effects are often poorly reversed by death adder antivenom or anticholinesterase, particularly when patients present with established paralysis. This suggests that either the post-synaptic neurotoxins are irreversible/'pseudo' irreversible, or the venom contains pre-synaptic neurotoxins that do not respond to antivenom. To support the later hypothesis, a pre-synaptic neurotoxin (P-EPTX-Aa1a) has recently been isolated from the venom of Acanthophis antarcticus. We examined Acanthophis praelongus and Acanthophis rugosus venoms for the presence of pre-synaptic neurotoxins. P-EPTX-Ap1a (40,719Da) and P-EPTX-Ar1a (40,879Da) were isolated from A. praelongus and A. rugosus venoms, respectively. P-EPTX-Ap1a and P-EPTX-Ar1a are comprised of three different subunits, alpha, beta1 and beta2. The two toxins displayed similar levels of PLA(2) activity which was almost solely attributed to the alpha subunit in both toxins. P-EPTX-Ap1a (20-100nM) and P-EPTX-Ar1a (20-100nM) caused inhibition of indirect twitches of the skeletal muscle preparation without affecting contractile responses to nicotinic receptor agonists. Interestingly, only the alpha subunit of both toxins (300nM) displayed neurotoxic activity. Inhibition of PLA(2) activity markedly reduced the effect of the toxins on muscle twitch height. These results confirm that P-EPTX-Ap1a and P-EPTX-Ar1a are pre-synaptic neurotoxins and represent the second and third such toxins to be isolated from death adder venom. The presence of pre-synaptic neurotoxins in Acanthophis sp. venoms indicates that treatment strategies for envenoming by these snakes needs to be reassessed given the likelihood of irreversible neurotoxicity.

Presence of presynaptic neurotoxin complexes in the venoms of Australo-Papuan death adders (Acanthophis spp.)

Australo-papuan death adders (Acanthophis spp.) are a cause of serious envenomations in Papua New Guinea and northern Australia often resulting in neurotoxic paralysis. Furthermore, victims occasionally present with delayed-onset neurotoxicity that sometimes responds poorly to antivenom or anticholinesterase treatment. This clinical outcome could be explained by the presence of potent snake presynaptic phospholipase A(2) neurotoxin (SPAN) complexes and monomers, in addition to long- and short-chain postsynaptic alpha-neurotoxins, that bind irreversibly, block neurotransmitter release and result in degeneration of the nerve terminal. The present study therefore aimed to determine within-genus variations in expression of high molecular mass SPAN complexes in the venoms of six major species of Acanthophis, four geographic variants of Acanthophis antarcticus. Venoms were separated by size-exclusion liquid chromatography under non-denaturing conditions and fractions corresponding to proteins in the range of 22 to >60 kDa were subjected to pharmacological characterization using the isolated chick biventer cervicis nerve-muscle (CBCNM) preparation. All venoms, except Acanthophis wellsi and Acanthophis pyrrhus, contained high mass fractions with phospholipase A(2) activity that inhibited twitch contractions of the CBCNM preparation. This inhibition was of slow onset, and responses to exogenous nicotinic agonists were not blocked, consistent with the presence of SPAN complexes. The results of the present study indicate that clinicians may need to be aware of possible prejunctional neurotoxicity following envenomations from A. antarcticus (all geographic variants except perhaps South Australia), Acanthophis praelongus, Acanthophis rugosus and Acanthophis. laevis species, and that early antivenom intervention is important in preventing further development of toxicity.

Geographic variation in venom allelic composition and diets of the widespread predatory marine gastropod Conus ebraeus

Background

Members of the predatory gastropod genus Conus use a venom comprised of a cocktail of peptide neurotoxins, termed conotoxins or conopeptides, to paralyze prey and conotoxin gene family members diversify via strong positive selection. Because Conus venoms are used primarily to subdue prey, the evolution of venoms is likely affected by predator-prey interactions.

Methodology/Principal Findings

To identify the selective forces that drive the differentiation of venoms within species of Conus, we examined the distribution of alleles of a polymorphic O-superfamily conotoxin locus of Conus ebraeus at Okinawa, Guam and Hawaii. Previous analyses of mitochondrial cytochrome oxidase I gene sequences suggest that populations of C. ebraeus, a worm-eating Conus, are not structured genetically in the western and central Pacific. Nonetheless, because the sample size from Guam was relatively low, we obtained additional data from this location and reexamined patterns of genetic variation at the mitochondrial gene at Okinawa, Guam and Hawaii. We also utilized a DNA-based approach to identify prey items of individuals of C. ebraeus from Guam and compared this information to published data on diets at Okinawa and Hawaii. Our results show that conotoxin allelic frequencies differ significantly among all three locations, with strongest differentiation at Hawaii. We also confirm previous inferences that C. ebraeus exhibits no genetic differentiation between Okinawa, Guam and Hawaii at the mitochondrial locus. Finally, DNA-based analyses show that eunicid polychaetes comprise the majority of the prey items of C. ebraeus at Guam; while this results compares well with observed diet of this species at Okinawa, C. ebraeus preys predominantly on nereid polychaetes at Hawaii.

Conclusions/Significance

These results imply that strong selection pressures affect conotoxin allelic frequencies. Based on the dietary information, the selection may derive from geographic variation in dietary specialization and local coevolutionary arms races between Conus and their prey.

The in vitro neurotoxic and myotoxic effects of the venom from the Suta genus (curl snakes) of elapid snakes

Australia has a tremendous diversity of elapid snakes, including many unique smaller sized species of this venomous snake family. However, little if anything is known about the majority of the venoms of these lesser studied snakes. In the current study, the venoms of Suta suta (curl snake) and Suta punctata (spotted-curl snake) were examined for in vitro activity using a skeletal muscle preparation (i.e. chick biventer cervicis nerve-muscle preparation). Both venoms caused concentration-dependent (3-10 microg/ml) inhibition of nerve-mediated twitches, and inhibited responses to exogenous acetylcholine and carbachol, indicating the presence of postsynaptic neurotoxins. These effects were prevented by prior addition of CSL Ltd. polyvalent snake antivenom (5 units/ml) but only partially reversed by the addition of antivenom (5 units/ml) at the t(90) time-point (i.e. time at which twitches were inhibited by 90%). Suta punctata venom (10 microg/ml) was also myotoxic as indicated by the inhibition of direct twitches of the chick biventer cervicis nerve-muscle preparation. This effect was not reversed by antivenom (5 units/ml). This study highlights the danger of underestimating the potential severe clinical effects posed by these small but highly venomous snakes.

Snake venoms and their toxins: An Australian perspective

Australia is home to a vast collection of highly venomous terrestrial and marine snakes. As such, Australia has proven to be an excellent source of investigative material for both local and international toxinologists. Research on snake venoms initially focussed on identifying the most lethal species, and the venom components responsible for the lethality, so that treatment strategies could be implemented. Since then, the focus of research has included the isolation and characterisation of toxins (primarily neurotoxins), examination of the efficacy of commercially available antivenoms and, more recently, the use of liquid chromatography/mass spectrometry (LCMS) to aid in the analysis of whole venoms. Given the vast quantity of research undertaken over the past 70 yr we have tried to provide a short insight into some of this excellent work and identify areas requiring further examination.

The good, the bad and the ugly: Australian snake taxonomists and a history of the taxonomy of Australia's venomous snakes

The Australian snake fauna is unique in harbouring more venomous species than non-venomous ones. Although taxonomic research on the elapid snakes of Australia goes back to the late 18th century, in stark contrast to other developed regions of the world (e.g. the continental USA), Australian snake taxonomy is very much in its infancy. Despite this, or perhaps because of this, the taxonomy of Australian snakes has been extraordinarily controversial, and many of the taxonomists involved correspondingly colourful. In this review, we explore the sometimes-tortured history of the taxonomic exploration of the venomous snake fauna of Australia, looking at some of the more colourful and notable contributors and highlighting systematic pitfalls that persist even today.

Treatment of snakebite in Australia: the current evidence base and questions requiring collaborative multicentre prospective studies

Despite the wealth of anecdotes and case reports there are fundamental questions of management of snakebite in Australia that remain unresolved or for which the current evidence is limited. The efficacy in the field, potential limitations and possibility of improvements in pressure immobilisation first aid need objective studies in humans. Optimal bandage sizes, stretch and pressure for different sized limbs need further evaluation, as does the use of pressure pads. Better definitions of specific clinical envenoming syndromes attributable to individual snake species are required, including elucidation of within-genus variations, similarities and differences. Venom studies suggest this is especially important for species within the brown snake (Pseudonaja) and death adder (Acanthophis) genera. Appropriate antivenom types, doses and dosing intervals for individual snake species should be more formally studied in patients. Especially important are confirmation of the need for higher doses of brown snake antivenom, while possibly limiting unnecessarily high doses, confirmation of the critical importance of early antivenom use to prevent pre-synaptic neurotoxicity in Taipan and tiger snake bites and ascertainment of whether larger doses of antivenom are unhelpful in Taipan bites after specified time delays. Confirmation of clinical efficacy and dosing recommendations for use of tiger snake (Notechis) antivenom in envenoming from Australian copperhead (Austrelaps spp.), broad headed (Hoplocephalus spp.) and rough-scaled snakes (Tropidechis carinatus) also require formal study in patients. Other examples of clinical relevance of cross-specificity of current and future monospecific antivenoms and whether there are geographical variations in antivenom responses within species will require elucidation. Prospective multicentre collaborative studies with predefined data collection and serial venom level assays are proposed as the way forward in Australia to help resolve therapeutic uncertainties and to establish a firmer evidence base for best-practice treatment guidelines for Australasian elapid snakebite.

Four cases of snake envenomation responsive to death adder antivenom

Death adder envenomation is rare in humans and there is only one brief report previously in dogs. This paper details three cases of canine common death adder (Acanthophis antarcticus) envenomation and one case of bardick (Echiopsis curta) envenomation which were responsive to death adder antivenom. The available literature on death adder envenomations is also reviewed. The main clinical sign in the four dogs was severe lower motor neuron paralysis. There was no clinical evidence of coagulopathy or myopathy. Use of a snake venom detection kit was essential for selection of appropriate antivenom. Death adder and bardick envenomation in dogs potentially has a good prognosis if sufficient antivenom is administered and intensive supportive care is available.

Isolation and characterisation of acanmyotoxin-2 and acanmyotoxin-3, myotoxins from the venom of the death adder Acanthophis sp. Seram

Death adder (genus Acanthophis) venoms display neurotoxic activity but were thought to be devoid of myotoxic components. Studies from our laboratory have shown that some species (i.e. Acanthophis rugosus and Acanthophis sp. Seram) possess venom with myotoxic activity [Wickramaratna JC, Fry BG, Aguilar M, Kini RM, Hodgson WC. Isolation and pharmacological characterisation of a phospholipase A2 myotoxin from the venom of the Irian Jayan death adder (A. rugosus). Br J Pharmacol 2003;138:333-342; Wickramaratna JC, Fry BG, Hodgson WC. Species-dependent variations in the in vitro myotoxicity of death adder (Acanthophis) venoms. Toxicol Sci 2003;74:352-360]. The present study describes the isolation and characterisation of two myotoxins (acanmyotoxin-2 and acanmyotoxin-3) from A. sp. Seram venom. Venom was fractionated into approximately 12 major peaks using reverse phase high performance liquid chromatography. Two components caused concentration (0.1-1 microM) dependent inhibition of direct (2 ms, 0.1 Hz, supramaximal V) twitches and an increase in baseline tension in the chick biventer cervicis nerve-muscle. Histological examination of the muscle confirmed damage. PLA2 activity was detected in both acanmyotoxin-2 (390.2+/-19.7 micromol/(min mg); n=4) and acanmyotoxin-3 (14.2+/-7.7 micromol/(min mg); n=4). In comparison, A. sp. Seram whole venom had a specific activity of 461.3+/-90.4 micromol/(min mg) (n=3). Mass spectrometry analysis indicated acanmyotoxin-2 had a mass of 13,082 Da and acanmyotoxin-2 13,896 Da. Acanmyotoxin-2 and acanmyotoxin-3 accounted for approximately 7 and 4% of total venom composition, respectively. N-terminal sequencing of the first 30 amino acids of each toxin indicated they shared some sequence homology with known myotoxins. In conclusion, clinicians should be aware that symptoms of envenoming by some species of death adder may include signs of myotoxicity as well as neurotoxicity. Future studies will investigate the efficacy of the current antivenom treatment against the myotoxic components of A. sp. Seram venom.

Toxins not neutralized by brown snake antivenom

The Australian snakes of the genus Pseudonaja (dugite, gwardar and common brown) account for the majority of snake bite related deaths in Australia. Without antivenom treatment, the risk of mortality is significant. There is an accumulating body of evidence to suggest that the efficacy of the antivenom is limited. The current study investigates the protein constituents recognized by the antivenom using 2-DE, immuno-blot techniques and rat tracheal organ bath assays. The 2-DE profiles for all three snake venoms were similar, with major species visualized at 78-132 kDa, 32-45 kDa and 6-15 kDa. Proteins characterized by LC-MS/MS revealed a coagulant toxin ( approximately 42 kDa) and coagulant peptide ( approximately 6 kDa), as well as two PLA(2) ( approximately 14 kDa). Peptides isolated from approximately 78 kDa and 15-32 kDa protein components showed no similarity to known protein sequences. Protein recognition by the antivenom occurred predominantly for the higher molecular weight components with little recognition of 6-32 kDa MW species. The ability of antivenom to neutralize venom activity was also investigated using rat tracheal organ bath assays. The venoms of Pseudonaja affinis affinis and Pseudonaja nuchalis incited a sustained, significant contraction of the trachea. These contractions were attributed to PLA(2) enzymatic activity as pre-treatment with the PLA(2) inhibitor 4-BPB attenuated the venom-induced contractions. The venom of Pseudonaja textilis incited tracheal contractility through a non-PLA(2) enzymatic activity. Neither activity was attenuated by the antivenom treatment. These results represent the first proteomic investigation of the venoms from the snakes of the genus Pseudonaja, revealing a possible limitation of the brown snake antivenom in binding to the low MW protein components.

Isolation and characterization at cholinergic nicotinic receptors of a neurotoxin from the venom of the Acanthophis sp. Seram death adder

The present study describes the isolation of the first neurotoxin (acantoxin IVa) from Acanthophis sp. Seram death adder venom and an examination of its activity at nicotinic acetylcholine receptor (nAChR) subtypes. Acantoxin IVa (MW 6815; 0.1-1.0 microM) caused concentration-dependent inhibition of indirect twitches (0.1 Hz, 0.2 ms, supramaximal V) and inhibited contractile responses to exogenous nicotinic agonists in the chick biventer cervicis nerve-muscle, confirming that this toxin is a postsynaptic neurotoxin. Acantoxin IVa (1-10 nM) caused pseudo-irreversible antagonism at skeletal muscle nAChR with an estimated pA2 of 8.36+/-0.17. Acantoxin IVa was approximately two-fold less potent than the long-chain (Type II) neurotoxin, alpha-bungarotoxin. With a pKi value of 4.48, acantoxin IVa was approximately 25,000 times less potent than alpha-bungarotoxin at alpha7-type neuronal nAChR. However, in contrast to alpha-bungarotoxin, acantoxin IVa completely inhibited specific [3H]-methyllycaconitine (MLA) binding in rat hippocampus homogenate. Acantoxin IVa had no activity at ganglionic nAChR, alpha4beta2 subtype neuronal nAChR or cytisine-resistant [3H]-epibatidine binding sites. While long-chain neurotoxin resistant [3H]-MLA binding in hippocampus homogenate requires further investigation, we have shown that a short-chain (Type I) neurotoxin is capable of fully inhibiting specific [3H]-MLA binding.

Species-dependent variations in the in vitro myotoxicity of death adder (Acanthophis) venoms

Based on early studies on Acanthophis antarcticus (common death adder) venom, it has long been thought that death adder snake venoms are devoid of myotoxicity. However, a recent clinical study reported rhabdomyolysis in patients following death adder envenomations, in Papua New Guinea, by a species thought to be different to A. antarcticus. Subsequently, a myotoxic phospholipase A2 component was isolated from A. rugosus (Irian Jayan death adder) venom. The present study examined the venoms of A. praelongus (northern), A. pyrrhus (desert), A. hawkei (Barkly Tableland), A. wellsi (black head), A. rugosus, A. sp. Seram and the regional variants of A. antarcticus for in vitro myotoxicity. Venoms (10-50 microg/ml) were examined for myotoxicity using the chick directly (0.1 Hz, 2 ms, supramaximal V) stimulated biventer cervicis nerve-muscle preparation. A significant contracture of skeletal muscle and/or inhibition of direct twitches were considered signs of myotoxicity. This was confirmed by histological examination. All venoms displayed high phospholipase A2 activity. The venoms (10-50 microg/ml) of A. sp. Seram, A. praelongus, A. rugosus,and A. wellsi caused a significant inhibition of direct twitches and an increase in baseline tension compared to the vehicle (n=4-6; two-way ANOVA, p<0.05). Furthermore, these venoms caused dose-dependent morphological changes in skeletal muscle. In contrast, the venoms (10-50 microg/ml; n=3-6) of A. hawkei, A. pyrrhus, and regional variants of A. antarcticus were devoid of myotoxicity. Prior incubation (10 min) of CSL death adder antivenom (5 U/ml) prevented the myotoxicity caused by A. sp. Seram, A. praelongus, A. rugosus, and A. wellsi venoms (50 microg/ml; n=4-7). In conclusion, clinicians may need to be mindful of possible myotoxicity following envenomations by A. praelongus, A. rugosus, A. sp. Seram, and A. wellsi species.

Comparison of the in vitro neuromuscular activity of venom from three Australian snakes (Hoplocephalus stephensi, Austrelaps superbus and Notechis scutatus): efficacy of tiger snake antivenom

1. Tiger snake antivenom, raised against Notechis scutatus venom, is indicated not only for the treatment of envenomation by this snake, but also that of the copperhead (Austrelaps superbus) and Stephen's banded snake (Hoplocephalus stephensi). The present study compared the neuromuscular pharmacology of venom from these snakes and the in vitro efficacy of tiger snake antivenom. 2. In chick biventer cervicis muscle and mouse phrenic nerve diaphragm preparations, all venoms (3-10 microg/mL) produced inhibition of indirect twitches. In the biventer muscle, venoms (10 micro g/mL) inhibited responses to acetylcholine (1 mmol/L) and carbachol (20 micromol/L), but not KCl (40 mmol/L). The prior (10 min) administration of 1 unit/mL antivenom markedly attenuated the neurotoxic effects of A. superbus and N. scutatus venoms (10 microg/mL), but was less effective against H. stephensi venom (10 microg/mL); 5 units/mL antivenom attenuated the neurotoxic activity of all venoms. 3. Administration of 5 units/mL antivenom at t90 partially reversed, over a period of 3 h, the inhibition of twitches produced by N. scutatus (10 microg/mL; 41% recovery), A. superbus (10 microg/mL; 25% recovery) and H. stephensi (10 microg/mL; 50% recovery) venoms. All venoms (10-100 microg/mL) also displayed signs of in vitro myotoxicity. 4. The results of the present study indicate that all three venoms contain neurotoxic activity that is effectively attenuated by tiger snake antivenom.

Isolation and pharmacological characterization of a phospholipase A2 myotoxin from the venom of the Irian Jayan death adder (Acanthophis rugosus)

1. It has long been thought that death adder venoms are devoid of myotoxic activity based on studies done on Acanthophis antarcticus (Common death adder) venom. However, a recent clinical study reported rhabdomyolysis in patients following death adder envenomations, in Papua New Guinea, by a species thought to be different to A. antarcticus. Consequently, the present study examined A. rugosus (Irian Jayan death adder) venom for myotoxicity, and isolated the first myotoxin (acanmyotoxin-1) from a death adder venom. 2. A. rugosus (10-50 micro g ml(-1)) and acanmyotoxin-1 (MW 13811; 0.1-1 micro M) were screened for myotoxicity using the chick directly (0.1 Hz, 2 ms, supramaximal V) stimulated biventer cervicis nerve-muscle (CBCNM) preparation. A significant contracture of skeletal muscle and/or inhibition of direct twitches were considered signs of myotoxicity. This was confirmed by histological examination. 3. High phospholipase A(2) (PLA(2)) activity was detected in both A. rugosus venom (140.2+/-10.4 micro mol min(-1) mg(-1); n=6) and acanmyotoxin-1 (153.4+/-11 micro mol min(-1) mg(-1); n=6). Both A. rugosus venom (10-50 micro g ml(-1)) and acanmyotoxin-1 (0.1-1 micro M) caused dose-dependent inhibition of direct twitches and increase in baseline tension (n=4-6). In addition, dose-dependent morphological changes in skeletal muscle were observed. 4. Prior incubation (10 min) of CSL death adder antivenom (5 units ml(-1); n=4) or inactivation of PLA(2) activity with 4-bromophenacyl bromide (1.8 mM; n=4) prevented the myotoxicity caused by acanmyotoxin-1 (1 micro M). 5. Acanmyotoxin-1 (0.1 micro M; n=4) displayed no significant neurotoxicity when it was examined using the indirectly (0.1 Hz, 0.2 ms, supramaximal V) stimulated CBCNM preparation. 6. In conclusion, clinicians may need to be mindful of possible myotoxicity following death adder envenomation in Irian Jaya.

In vitro neuromuscular activity of snake venoms

1. Snake venoms consist of a multitude of pharmacologically active components used for the capture of prey. Neurotoxins are particularly important in this regard, producing paralysis of skeletal muscles. These neurotoxins can be classified according to their site of action (i.e. pre- or post-synaptic). 2. Presynaptic neurotoxins, which display varying phospholipase A2 activities, have been identified in the venoms of the four major families of venomous snakes (i.e. Crotalidae, Elapidae, Hydrophiidae and Viperidae). The blockade of transmission produced by these toxins is usually characterized by a triphasic effect on acetylcholine release. Considerable work has been directed at identifying the binding site(s) on the presynaptic nerve terminal for these toxins, although their mechanism of action remains unclear. 3. Post-synaptic neurotoxins are antagonists of the nicotinic receptor on the skeletal muscle. Depending on their sequence, post-synaptic toxins are subdivided into short- and long-chain toxins. These toxins display different binding kinetics and different affinity for subtypes of nicotinic receptors. Post-synaptic neurotoxins have only been identified in venoms from the families Elapidae and Hydrophiidae. 4. Due to the high cost of developing new antivenoms and the reluctance of many companies to engage in this area of research, new methodologies are required to test the efficacy of existing antivenoms to ensure their optimal use. While chicken eggs have proven useful for the examination of haemorrhagic venoms, this procedure is not suited to venoms that primarily display neurotoxic activity. The chick biventer cervicis muscle has proven useful for this procedure, enabling the rapid screening of antivenoms against a range of venoms. 5. Historically, the lethality of snake venoms has been based on murine LD50 studies. Due to ethical reasons, these studies are being superseded by in vitro studies. Instead, the time taken to produce 90% inhibition of nerve-mediated twitches (i.e. t90) in skeletal muscle preparations can be determined. However, these two procedures result in different rank orders because they are measuring two different parameters. While murine LD50 determinations are based on "quantity", t90 values are based on how "quick" a venom acts. Therefore, knowledge of both parameters is still desirable. 6. In vitro neuromuscular preparations have proven to be invaluable tools in the examination of snake venoms and isolated neurotoxins. They will continue to play a role in further elucidating the mechanism of action of these highly potent toxins. Further study of these toxins may provide more highly specific research tools or lead compounds for pharmaceutical agents.

Electrospray liquid chromatography/mass spectrometry fingerprinting of Acanthophis (death adder) venoms: taxonomic and toxinological implications

Death adders (genus Acanthophis) are unique among elapid snakes in both morphology and venom composition. Despite this genus being among the most divergent of all elapids, the venom has been historically regarded as relatively quite simple. In this study, liquid chromatography/mass spectrometry (LC/MS) analysis has revealed a much greater diversity in venom composition, including the presence of molecules of novel molecular weights that may represent a new class of venom component. Furthermore, significant variation exists between species and populations, which allow for the LC/MS fingerprinting of each species. Mass profiling of Acanthophis venoms clearly demonstrates the effectiveness of this technique which underpins fundamental studies ranging from chemotaxonomy to drug design.