Cardiovascular, haematological and neurological effects of the venom of the Papua New Guinean small-eyed snake (Micropechis ikaheka) and their neutralisation with CSL polyvalent and black snake antivenoms

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.

Single Domain Antibodies as New Biomarker Detectors

Biomarkers are defined as indicators of biological processes, pathogenic processes, or pharmacological responses to a therapeutic intervention. Biomarkers have been widely used for early detection, prediction of response after treatment, and for monitoring the progression of diseases. Antibodies represent promising tools for recognition of biomarkers, and are widely deployed as analytical tools in clinical settings. For immunodiagnostics, antibodies are now exploited as binders for antigens of interest across a range of platforms. More recently, the discovery of antibody surface display and combinatorial chemistry techniques has allowed the exploration of new binders from a range of animals, for instance variable domains of new antigen receptors (V_NAR) from shark and variable heavy chain domains (V_HH) or nanobodies from camelids. These single domain antibodies (sdAbs) have some advantages over conventional murine immunoglobulin owing to the lack of a light chain, making them the smallest natural biomarker binders thus far identified. In this review, we will discuss several biomarkers used as a means to validate diseases progress. The potential functionality of modern singe domain antigen binders derived from phylogenetically early animals as new biomarker detectors for current diagnostic and research platforms development will be described.

Preclinical efficacy of Australian antivenoms against the venom of the small-eyed snake, Micropechis ikaheka, from Papua New Guinea: an antivenomics and neutralization study

There is no specific antivenom for the treatment of envenoming by the small-eyed snake, Micropechis ikaheka, a dangerous fossorial species endemic to Papua New Guinea, Irian Jaya (West Papua) and neighbouring islands. This study evaluated one marine (sea snake) and four terrestrial (tiger snake, brown snake, black snake and polyvalent) antivenoms, manufactured in Australia by bioCSL Limited, for their ability to immunoreact ('antivenomic' analysis) and neutralize enzymatic and toxic activities of M. ikaheka venom. All antivenoms neutralized lethality of the venom and attenuated, dose-dependently, myotoxic activity. The polyvalent antivenom also neutralized cardiotoxic activity. In contrast, antivenoms were ineffective in the neutralization of phospholipase A₂ (PLA₂) and anticoagulant activities. Antivenomics outcomes were in concordance with neutralization tests, for chromatographic peaks corresponding to α-neurotoxins of the three finger family, responsible for lethality, were quantitatively retained in the immunoaffinity columns, whereas peaks corresponding to PLA₂s were immunocaptured only to a partial extent. The ability of antivenoms to neutralize lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom, which represent the most relevant clinical manifestations of envenoming, suggests that these antivenoms may provide paraspecific protection in humans, although the poor neutralization of PLA₂ supports the need for well-designed clinical studies to not only determine which antivenoms are most appropriate for treatment of M. ikaheka envenoming, but to also fully describe the syndrome of envenoming caused by this beautiful, but lethal species.

BIOLOGICAL SIGNIFICANCE

Snakebite by the small-eyed snake, Micropechis ikaheka, in Papua New Guinea can be life-threatening. The predominant clinical features in this envenoming are neurotoxicity and systemic myotoxicity. Although it accounts for only a small proportion of snakebites on the mainland, 40% of snakebites on Karkar Island are attributed to bites by the Ikaheka snake. However, no specific antivenom is available for the treatment of M. ikaheka envenoming in Papua New Guinea. This study evaluated a panel of Australian bioCSL antivenoms for their paraspecific immunoreaction and neutralization of the toxic activities of M. ikaheka venom. All antivenoms exhibited strong immunorecognition of α-neurotoxins of the 3FTx family and neutralized the lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom. However, these antivenoms exhibited poor neutralization of PLA₂ and anticoagulant activities. This study suggests that the Australian antivenoms may provide paraspecific protection against M. ikaheka venom in humans, a hypothesis that demands studies aimed at assessing whether these antivenoms neutralize neurotoxicity and myotoxicity in the clinical setting.

Cross-neutralisation of the neurotoxic effects of Egyptian cobra venom with commercial tiger snake antivenom

Cross-neutralisation has been demonstrated for haemorrhagic venoms including Echis spp. and Cerastes spp. and for Australia elapid procoagulant toxins. A previous study showed that commercial tiger snake antivenom (TSAV) was able to neutralise the systemic effects of the Egyptian cobra, Naja haje, in vivo but it is unclear if this was true cross-neutralisation. The aim of the current study was to determine whether TSAV can neutralise the in vitro neurotoxic effects of N. haje venom. Both Notechis scutatus (10 μg/ml) and N. haje (10 μg/ml) venoms caused inhibition of indirect (supramaximal V, 0.1 Hz, 0.2 msec.) twitches of the chick biventer cervicis nerve-muscle preparation with t(90) values (i.e. the time to produce 90% inhibition of the original twitch height) of 26 ± 1 min. (n = 4) and 36 ± 4 min.; (n = 4). This effect at 10 μg/ml was significantly attenuated by the prior addition of TSAV (5 U/ml). A comparison of the reverse-phase HPLC profiles of both venoms showed some similarities with peak elution times, and SDS-PAGE analysis elucidated comparable bands across both venoms. Further analysis using Western immunoblotting indicated TSAV was able to detect N. haje venom, and enzyme immunoassay showed that in-house biotinylated polyclonal monovalent N. scutatus antibodies were able to detect N. haje venom. These findings demonstrate cross-neutralisation between different and geographically separated snakes supporting potential immunological similarities in snake toxin groups for a large range of snakes. This provides more evidence that antivenoms could be developed against specific toxin groups to cover a large range of snakes.

Pilot studies of pressure-immobilization bandages for rattlesnake envenomations

STUDY OBJECTIVE

Pressure-immobilization bandages sequester venom in extremities and are recommended for snakebites without local toxicity. Pilot studies were performed to determine the time of onset of toxicity and efficacy of pressure-immobilizations bandages in a porcine model of rattlesnake envenomation.

METHODS

After IACUC approval, anesthetized pigs were injected subcutaneously in a distal hind leg with 200 mg of Crotalus atrox venom. After 1 min, pigs received either a pressure-immobilization bandage (N = 3) or no treatment (N = 3). At 24 h, surviving pigs received antivenin and then the pressure-immobilization bandages were removed. Surviving subjects were followed for 1 week. Chi-square analysis and paired t-test were used.

RESULTS

Pigs with pressure-immobilization bandages survived for 24 h, whereas untreated pigs died at 13.68 +/- 3.42 h (p = 0.014). Surviving pigs walked on the extremity at 7 days. Potassium rose from 4.033 +/- 0.252 at baseline to 17.767 +/- 5.218 mEq/L (p < 0.0001) at time of death in untreated pigs but was normal at 24 h in treated subjects. Widespread tissue necrosis was seen in the untreated group but only local necrosis in the treatment group.

CONCLUSIONS

Pressure-immobilization bandages prevented death from severe C. atrox envenomations with a 24 h delay to treatment. Surviving pigs had recovery of limb use at 1 week.

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 use of therapeutic plasmapheresis in the treatment of poisoned and snake bite victims: An academic emergency department's experiences

The objective of this study is to describe the clinical status, procedural interventions, and outcomes of critically ill patients with poisoning and snake bite injuries presenting to a tertiary-care emergency department for treatment with therapeutic plasmapheresis. Records of 20 patients who presented to our academic emergency department over a 2-year period and who underwent plasmapheresis for poisoning or snake bite were retrospectively reviewed. Plasmapheresis was performed using centrifugation technology via an intravenous antecubital venous or subclavian vein catheter access. Human albumin or fresh frozen plasma were used as replacement fluids. Data extracted from the patient record included demographic data, clinical status, and outcome measures. Sixteen patients underwent plasmapheresis because of toxicity from snake bite. Three patients were treated for drug poisoning (phenytoin, theophylline, bipyridene HCl) and one patient for mushroom poisoning. Haematologic parameters such as platelet count, PT, and INR resolved rapidly in victims of snake bite injuries after treatment with plasmapheresis. Loss of limbs did not occur in these cases. Seven patients required admission to the intensive care unit. One patient with mushroom poisoning died. Mean length of hospital stay was 14.3 days (range 3-28 days) for all cases. Plasmapheresis was a clinically effective and safe approach in the treatment of snake bite envenomation and other drug poisoning victims especially in the management of hematologic problems and in limb preservation/salvage strategies. In addition to established conventional therapies, emergency physicians should consider plasmapheresis among the therapeutic options in treatment strategies for selected toxicologic emergencies.

Pressure-Immobilization Bandages Delay Toxicity in a Porcine Model of Eastern Coral Snake (Micrurus fulvius fulvius) Envenomation

STUDY OBJECTIVES

Pressure-immobilization bandages are used in countries where neurotoxic snake envenomations are common. They impede lymphatic egress from the bite site and delay systemic venom toxicity. The effectiveness of these devices has not been evaluated in coral snake envenomations. We investigated the efficacy of pressure-immobilization bandages in delaying the onset of systemic toxicity in a porcine model of coral snake envenomation.

METHODS

A randomized controlled trial of pressure-immobilization bandages was conducted in a university animal care center. Subjects were 12 anesthetized, spontaneously breathing pigs, ranging from 9.1 to 11.4 kg. After injection with 10 mg of Micrurus fulvius fulvius venom in the subcutaneous tissue of the distal foreleg, subjects were randomized to receive no treatment or application of a pressure-immobilization bandage at 1 minute after injection. Treated animals had elastic bandages applied to the extremity and splinting for immobilization. Vital signs and quality of respirations were recorded. Outcome was the onset of respiratory failure or survival to 8 hours. Necropsies and histologic analysis of the envenomation site was performed.

RESULTS

One animal from each group was removed because of the discovery of pre-existing respiratory pathology. Four of 5 pigs in the treatment group survived to 8 hours, but none in the control group survived. Mean time to onset of respiratory compromise was 170.4 +/- 33.3 minutes in the control group. None of the pigs had histologic changes at the envenomation site consistent with ischemia or pressure-related injury.

CONCLUSION

Pressure-immobilization bandages delayed the onset of systemic toxicity in our porcine model of M fulvius envenomation.

Phospholipase A2-dependent effects of the venom from the new guinean small-eyed snakeMicropechis ikaheka

The New Guinean small-eyed snake (Micropechis ikaheka) is a cause of life-threatening envenoming. Previous studies on M. ikaheka venom have indicated the presence of neurotoxins as well as myotoxins. This study examined the in vitro myotoxic effects of M. ikaheka venom and the efficacy of a polyvalent antivenom in neutralizing these effects. Venom (50 microg/ml) produced a slowly developing contracture and inhibition of direct twitches of the chick biventer cervicis nerve-muscle preparation in the presence of tubocurarine (10 microM). Myotoxicity was confirmed by subsequent histological examination of tissues. This myotoxicity was prevented by the prior addition of polyvalent snake antivenom (30 U/ml). However, the addition of antivenom (30 U/ml) 1 h after venom administration failed to reverse or prevent the further inhibition of direct twitches. In addition, venom (1-10 microg/ml) produced concentration-dependent contractions of the guinea-pig isolated ileum. These effects were dependent on phospholipase A2 (PLA2) activity of the venom as evidenced by the ability of the PLA2 inhibitor 4-bromophenacyl bromide (4-BPB; 1.8 mM) to prevent this activity. This study indicates that M. ikaheka venom causes significant myotoxicity and that polyvalent snake antivenom may be a potential treatment for the myotoxic effects in patients envenomed by this species.

The efficacy of two antivenoms against the in vitro myotoxic effects of black snake (Pseudechis) venoms in the chick biventer cervicis nerve-muscle preparation

Neurotoxicity is rarely seen following human systemic envenoming by Australasian black snakes (genus Pseudechis) with myotoxicity being the most prominent feature following bites by some species. This study investigated the in vitro myotoxicity of venoms from seven species of Australasian Pseudechis and determined the efficacy of CSL black and tiger snake antivenoms. All Pseudechis venoms (10 microg/ml) significantly inhibited direct twitches of the chick biventer cervicis nerve-muscle preparation (p<0.05, one-way ANOVA). Prior addition of black snake antivenom (5 U/ml) prevented the inhibitory effects of all Pseudechis venoms (p<0.05, one-way ANOVA), except Pseudechis butleri. Prior addition of tiger snake antivenom (5 U/ml) prevented the venom-induced reduction in direct twitches to Notechis scutatus venom and all Pseudechis venoms (p<0.05, one-way ANOVA), with the exception of Pseudechis australis and Pseudechis colletti venoms. Black or tiger snake antivenom (5 U/ml) added 1 h after the addition of venom inhibited further reduction of direct twitches by N. scutatus and most Pseudechis venoms, but did not significantly restore twitch height. PLA2 activity was found in all venoms with the following rank order: Pseudechis porphyriacus>P. australis>Pseudechis papuanus>P. butleri>Pseudechis guttatus> or =Pseudechis pailsii>P. colletti>N. scutatus. The results of the present study suggest that Australasian Pseudechis venoms possess variable myotoxic activity. The ability of black or tiger snake antivenom to prevent or inhibit further venom-induced effects varied across the genus.