Neurotoxins from Australo-Papuan elapids: a biochemical and pharmacological perspective

Most of the medically important snakes in Papua New Guinea and Australia belong to the family Elapidae and are referred to as "Australo-Papuan" elapids. Neurotoxicity is often a life-threatening symptom of envenoming by these snakes; therefore, much attention has been paid to the isolation and detailed pharmacological and biochemical characterization of the presynaptic (beta) and postsynaptic (alpha) neurotoxins from these elapid venoms. These studies have highlighted the potential for these toxins to be used as highly potent and selective probes for biomedical research and, perhaps, the potential for their use as lead compounds for the development of pharmaceutical agents. Historically, the potency of neurotoxins/crude venoms has been determined using murine LD50 (lethal dose) assays. However, a different rank order of potency often results when crude venoms/toxins are ranked based on their in vitro pharmacological parameters (e.g., t90 values). The lack of neurotoxicity following envenoming by brown snakes, despite the presence of a potent neurotoxin in their venom, has puzzled clinical toxinologists for years. This paradox also appears to include envenoming by the Stephen's banded snake. Lastly, the in vitro studies examining the effectiveness of antivenoms as well as the potential for alternative compounds to reverse/prevent neurotoxicity are discussed. This review presents for the first time a detailed comparative analysis of the pharmacology and biochemistry of neurotoxins isolated from the Australo-Papuan elapids, placing emphasis on the time taken for onset of action, receptor binding parameters, reversibility, and the methods for determining potency.