Coagulotoxic effects by brown snake (Pseudonaja) and taipan (Oxyuranus) venoms, and the efficacy of a new antivenom.

Snakebite is a neglected tropical disease that disproportionately affects the poor. Antivenom is the only specific and effective treatment for snakebite, but its distribution is severely limited by several factors, including the prohibitive cost of some products. Papua New Guinea (PNG) is a snakebite hotspot but the high costs of Australian antivenoms (thousands of dollars per treatment) makes it unaffordable in PNG. A more economical taipan antivenom has recently been developed at the Instituto Clodomiro Picado (ICP) in Costa Rica for PNG and is currently undergoing clinical trials for the treatment of envenomations by coastal taipans (Oxyuranus scutellatus). In addition to potentially having the capacity to neutralise the effects of envenomations of non-PNG taipans, this antivenom may have the capacity to neutralise coagulotoxins in venom from closely related brown snakes (Pseudonaja spp.) also found in PNG. Consequently, we investigated the cross-reactivity of taipan antivenom across the venoms of all Oxyuranus and Pseudonaja species. In addition, to ascertain differences in venom biochemistry that influence variation in antivenom efficacy, we tested for relative cofactor dependence. We found that the new ICP taipan antivenom exhibited high selectivity for Oxyuranus venoms and only low to moderate cross-reactivity with any Pseudonaja venoms. Consistent with this genus level distinction in antivenom efficacy were fundamental differences in the venom biochemistry. Not only were the Pseudonaja venoms significantly more procoagulant, but they were also much less dependent upon the cofactors calcium and phospholipid. There was a strong correlation between antivenom efficacy, clotting time and cofactor dependence. This study sheds light on the structure-function relationships of the procoagulant toxins within these venoms and may have important clinical implications including for the design of next-generation antivenoms.

Zdenek CN ，Hay C ，Arbuckle K ，Jackson TNW ，Bos MHA ，Op den Brouw B ，Debono J ，Allen L ，Dunstan N ，Morley T ，Herrera M ，Gutiérrez JM ，Williams DJ ，Fry BG ... -  《-》

Clinical implications of convergent procoagulant toxicity and differential antivenom efficacy in Australian elapid snake venoms.

Australian elapid snakes are some of the most venomous snakes in the world and are unique among venomous snakes in having mutated forms of the blood clotting factor X in an activated form (FXa) as a key venom component. In human bite victims, an overdose of this activated clotting enzyme results in the systemic consumption of fibrinogen due to the large amounts of endogenous thrombin generated by the conversion of prothrombin to thrombin by venom FXa. Within Australian elapids, such procoagulant venom is currently known from the tiger snake clade (Hoplocephalus, Notechis, Paroplocephalus, and Tropidechis species), brown/taipan (Oxyuranus and Pseudonaja species) clade, and the red-bellied black snake Pseudechis porphyriacus. We used a STA-R Max coagulation analyser and TEG5000 thromboelastographers to test 47 Australian elapid venoms from 19 genera against human plasma in vitro. In addition to activity being confirmed in the two clades above, FXa-driven potent procoagulant activity was found in four additional genera (Cryptophis, Demansia, Hemiaspis, and Suta). Ontogenetic changes in procoagulant function was also identified as a feature of Suta punctata venom. Phylogenetic analysis of FX sequences confirmed that snake venom FXa toxins evolved only once, that the potency of these toxins against human plasma has increased in a stepwise fashion, and that multiple convergent amplifications of procoagulant activity within Australian elapid snakes have occurred. Cofactor dependence tests revealed all procoagulant venoms in our study, except those of the tiger snake clade, to be highly calcium-dependent, whereas phospholipid dependence was less of a feature but still displayed significant variation between venoms. Antivenom testing using CSL Tiger Snake Antivenom showed broad but differential cross-reactivity against procoagulant venoms, with P. porphyriacus and S. punctata extremely well neutralised but with Cryptophis, Demansia, and Hemiaspis less well-neutralised. The relative variation was not in accordance to genetic relatedness of the species used in antivenom production (Notechis scutatus), which underscores a fundamental principle that the rapid evolution characteristic of venoms results in organismal phylogeny being a poor predictor of antivenom efficacy. Our results have direct and immediate implications for the design of clinical management plans in the event of snakebite by such lesser known Australian elapid snake species that have been revealed in this study to be as potent as the better studied, and proven lethal, species.

Zdenek CN ，den Brouw BO ，Dashevsky D ，Gloria A ，Youngman NJ ，Watson E ，Green P ，Hay C ，Dunstan N ，Allen L ，Fry BG ... -  《-》

Mud in the blood: Novel potent anticoagulant coagulotoxicity in the venoms of the Australian elapid snake genus Denisonia (mud adders) and relative antivenom efficacy.

Due to their potent coagulotoxicity, Australian elapid venoms are unique relative to non-Australian members of the Elapidae snake family. The majority of Australian elapids possess potent procoagulant venom, while only a few species have been identified as possessing anticoagulant venoms. The majority of research to-date has concentrated on large species with range distributions overlapping major city centres, such as brown snakes (Pseudonaja spp.) and taipans (Oxyuranus spp.). We investigated the venom from the poorly studied genus Denisonia and documented anticoagulant activities that were differentially potent on amphibian, avian, and human plasmas. Both species were potently anticoagulant upon amphibian plasma, consistent with these snakes preying upon frogs as their primary food source. While D. devisi was only relatively weakly active on avian and human plasma, D. maculata was potently anticoagulant to amphibian, avian, and human plasma. The mechanism of anticoagulant action was determined to be the inhibition of prothrombin activation by Factor Xa by blocking the formation of the prothrombinase complex. Fractionation of D. maculata venom followed by MS sequencing revealed that the toxins responsible were Group I phospholipase A2. As no antivenom is produced for this species or its near relatives, we examined the ability of Seqirus Australian snake polyvalent antivenom to neutralise the anticoagulant effects, with this antivenom shown to be effective. These results contribute to the body of knowledge regarding adaptive evolution of venom, revealing a unique taxon-specific anticoagulant effect for D. devisi venom. These results also reveal the potential effects and mechanisms behind envenomation by the potently acting D. maculata venom on human plasma, while the discovery of the efficacy of an available antivenom provides information crucial to the design of snakebite management strategies.

Youngman NJ ，Zdenek CN ，Dobson JS ，Bittenbinder MA ，Gillett A ，Hamilton B ，Dunstan N ，Allen L ，Veary A ，Veary E ，Fry BG ... -  《-》

Antivenomic characterization of two antivenoms against the venom of the taipan, Oxyuranus scutellatus, from Papua New Guinea and Australia.

Antivenoms manufactured by bioCSL Limited (Australia) and Instituto Clodomiro Picado (Costa Rica) against the venom of the taipan snakes (Oxyuranus scutellatus) from Australia and Papua New Guinea (PNG), respectively, were compared using antivenomics, an analytical approach that combines proteomics with immunoaffinity chromatography. Both antivenoms recognized all venom proteins present in venom from PNG O. scutellatus, although a pattern of partial recognition was observed for some components. In the case of the Australian O. scutellatus venom, both antivenoms immunorecognized the majority of the components, but the CSL antivenom showed a stronger pattern of immunoreactivity, which was revealed by the percentage of retained proteins in the immunoaffinity column. Antivenoms interacted with taipoxin in surface plasmon resonance. These observations on antivenomics agree with previous neutralization studies.

Herrera M ，Paiva OK ，Pagotto AH ，Segura A ，Serrano SM ，Vargas M ，Villalta M ，Jensen SD ，León G ，Williams DJ ，Gutiérrez JM ... -  《-》

The effects of antivenom on the in vitro neurotoxicity of venoms from the taipans Oxyuranus scutellatus, Oxyuranus microlepidotus and Oxyuranus scutellatus canni.

Crachi MT ，Hammer LW ，Hodgson WC 《-》