AUTHOR=Huynh Tam M. , Silva Anjana , Isbister Geoffrey K. , Hodgson Wayne C. 

TITLE=Isolation and Characterization of Two Postsynaptic Neurotoxins From Indian Cobra (Naja Naja) Venom

JOURNAL=Frontiers in Pharmacology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2022.815079

DOI=10.3389/fphar.2022.815079

ISSN=1663-9812

ABSTRACT=<p>The Indian Cobra (<italic>Naja naja</italic>) is among the “Big Four” responsible for most of the snakebite envenoming cases in India. Although recent proteomic studies suggest the presence of postsynaptic neurotoxins in <italic>N. naja</italic> venom, little is known about the pharmacology of these toxins. We isolated and characterized α-Elapitoxin-Nn2a (α-EPTX-Nn2a; 7020 Da) and α-Elapitoxin-Nn3a (α-EPTX-Nn3a; 7807 Da), a short-chain and long-chain postsynaptic neurotoxin, respectively, which constitute 1 and 3% of <italic>N. naja</italic> venom. α-EPTX-Nn2a (100–300 nM) and α-EPTX-Nn3a (100–300 nM) both induced concentration-dependent inhibition of indirect twitches and abolished contractile responses of tissues to exogenous acetylcholine and carbachol, in the chick biventer cervicis nerve-muscle preparation. The prior incubation of tissues with Indian polyvalent antivenom (1 ml/0.6 mg) prevented the <italic>in vitro</italic> neurotoxic effects of α-EPTX-Nn2a (100 nM) and α-EPTX-Nn3a (100 nM). The addition of Indian polyvalent antivenom (1 ml/0.6 mg), at the t<sub>90</sub> time point, could not reverse the <italic>in vitro</italic> neurotoxicity of α-EPTX-Nn2a (100 nM). The <italic>in vitro</italic> neurotoxicity of α-EPTX-Nn3a (100 nM) was partially reversed by the addition of Indian polyvalent antivenom (1 ml/0.6 mg), as well as repeated washing of the tissue. α-EPTX-Nn2a displayed non-competitive antagonism of concentration-response curves to carbachol, with a pA<sub>2</sub> of 8.01. In contrast, α-EPTX-Nn3a showed reversible antagonism of concentration-response curves to carbachol, with a pA<sub>2</sub> of 8.17. <italic>De novo</italic> sequencing of α-EPTX-Nn2a and α-EPTX-Nn3a showed a short-chain and long-chain postsynaptic neurotoxin, respectively, with 62 and 71 amino acids. The important observation made in this study is that antivenom can reverse the neurotoxicity of the clinically important long-chain neurotoxin, but not the short-chain neurotoxin, from <italic>N. naja</italic> venom.</p>