Elucidating the Venom Diversity in Sri Lankan Spectacled Cobra (Naja naja) through De Novo Venom Gland Transcriptomics, Venom Proteomics and Toxicity Neutralization

Abstract

Inadequate effectiveness of Indian antivenoms in treating envenomation caused by the Spectacled Cobra/Indian Cobra (Naja naja) in Sri Lanka has been attributed to geographical variations in the venom composition. This study investigated the de novo venom-gland transcriptomics and venom proteomics of the Sri Lankan N. naja (NN-SL) to elucidate its toxin gene diversity and venom variability. The neutralization efficacy of a commonly used Indian antivenom product in Sri Lanka was examined against the lethality induced by NN-SL venom in mice. The transcriptomic study revealed high expression of 22 toxin genes families in NN-SL, constituting 46.55% of total transcript abundance. Three-finger toxins (3FTX) were the most diversely and abundantly expressed (87.54% of toxin gene expression), consistent with the dominance of 3FTX in the venom proteome (72.19% of total venom proteins). The 3FTX were predominantly S-type cytotoxins/cardiotoxins (CTX) and α-neurotoxins of long-chain or short-chain subtypes (α-NTX). CTX and α-NTX are implicated in local tissue necrosis and fatal neuromuscular paralysis, respectively, in envenomation caused by NN-SL. Intra-species variations in the toxin gene sequences and expression levels were apparent between NN-SL and other geographical specimens of N. naja, suggesting potential antigenic diversity that impacts antivenom effectiveness. This was demonstrated by limited potency (0.74 mg venom/ml antivenom) of the Indian polyvalent antivenom (VPAV) in neutralizing the NN-SL venom. A pan-regional antivenom with improved efficacy to treat N. naja envenomation is needed.

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

“…N. naja venom showed postsynaptic neurotoxicity in the indirectly stimulated chick biventer nerve-muscle preparation as indicated by the concentration-dependent inhibition of indirect twitches and reduction in contractile responses to external nicotinic agonists. This observation is consistent with proteomic analyses indicating a large abundance of postsynaptic neurotoxins and absence of pre-synaptic neurotoxins in the venom ( Wong et al, 2021 ). The potency of the neurotoxic effects of the venom was moderate (i.e., t 90 of 42 min at 10 μg/ml) compared with the potency of other elapid venoms we have previously studied using the same techniques.…”

“…Combined with the relative abundance of peak 1, the components of N. naja venom with postsynaptic neurotoxicity, constitute approximately 9% of the venom protein content. This closely matches the findings by Wong et al (2021) , reporting that short- and long-chain neurotoxins constitute approximately 10% of N. naja venom from Sri Lanka. The α-neurotoxins in peak 1 could not be further purified using our chromatographic methods.…”

“…Neuromuscular paralysis is a well-known sequalae of envenoming by N. naja , so the pharmacological characterization of the neurotoxins with potential clinical relevance is of high importance. Recent proteomic studies suggest the dominance of three-finger toxins (3FTx) in the composition of N. naja venom from India and Sri Lanka ( Senji Laxme et al, 2021 ; Wong et al, 2021 ). These toxins include both the neurotoxic and cytotoxic 3FTx’s, which have varying relative abundances depending on the biogeographic region of the venom.…”

“…The percentage of neurotoxic 3FTx’s in N. naja venom from India can range between 30 and 80% ( Senji Laxme et al, 2021 ). Despite these disparities, postsynaptic neurotoxins are the only toxins in N. naja venom that cause neuromuscular paralysis ( Wong et al, 2021 ), and neurotoxicity seen in envenomed patients could be entirely attributed to the postsynaptic neurotoxins. Postsynaptic neurotoxins inhibit neurotransmission at the neuromuscular junction by competitively binding with the two acetylcholine binding sites of the nicotinic acetylcholine receptors (nAChRs) of the motor-end plate ( Barber et al, 2013 ).…”

Clinical study of anti-snake venom blockade in the treatment of local tissue necrosis caused by Chinese cobra (Naja atra) bites

“…Commonly used drugs are chymotrypsin and pancreatic enzymes. It is important to note that patients bitten by Chinese cobra must use the corresponding anti-snake venom, not geographically diverse snake anti-snake venoms since antigenicities of anti-snake venoms have been found to vary from one species to another, whose titer may be very low or even ineffective [26][27][28][29].…”