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

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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 (40,719 Da) and P-EPTX-Ar1a (40,879 Da) were isolated from A. praelongus and A. rugosus venoms, respectively. P-EPTX-Ap1a and P-EPTX-Ar1a are comprised of three different subunits, α, β1 and β2. The two toxins displayed similar levels of PLA2 activity which was almost solely attributed to the α subunit in both toxins. P-EPTX-Ap1a (20-100 nM) and P-EPTX-Ar1a (20-100 nM) caused inhibition of indirect twitches of the skeletal muscle preparation without affecting contractile responses to nicotinic receptor agonists. Interestingly, only the α subunit of both toxins (300 nM) displayed neurotoxic activity. Inhibition of PLA2 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.

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