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 A2 neurotoxin (SPAN) complexes and monomers, in addition to long- and short-chain postsynaptic α-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 A2 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.