Neutralization of the Principal Toxins from the Venoms of Thai Naja kaouthia and Malaysian Hydrophis schistosus: Insights into Toxin-Specific Neutralization by Two Different Antivenoms

Abstract

Antivenom neutralization against cobra venoms is generally low in potency, presumably due to poor toxin-specific immunoreactivity. This study aimed to investigate the effectiveness of two elapid antivenoms to neutralize the principal toxins purified from the venoms of the Thai monocled cobra (Naja kaouthia, Nk-T) and the Malaysian beaked sea snake (Hydrophis schistosus, Hs-M). In mice, N. kaouthia Monovalent Antivenom (NKMAV) neutralization against Nk-T long neurotoxin (LNTX) and cytotoxin was moderate (potency of 2.89–6.44 mg toxin/g antivenom protein) but poor against the short neurotoxin (SNTX) (1.33 mg/g). Its cross-neutralization against Hs-M LNTX of Hs-M is compatible (0.18 mg/g) but much weaker against Hs-M SNTX (0.22 mg/g). Using CSL (Seqirus Limited) Sea Snake Antivenom (SSAV), we observed consistently weak neutralization of antivenom against SNTX of both species, suggesting that this is the limiting factor on the potency of antivenom neutralization against venoms containing SNTX. Nevertheless, SSAV outperformed NKMAV in neutralizing SNTXs of both species (0.61–2.49 mg/g). The superior efficacy of SSAV against SNTX is probably partly attributable to the high abundance of SNTX in sea snake venom used as immunogen in SSAV production. The findings indicate that improving the potency of cobra antivenom may be possible with a proper immunogen formulation that seeks to overcome the limitation on SNTX immunoreactivity.

Revisiting Notechis scutatus venom: on shotgun proteomics and neutralization by the “bivalent” Sea Snake Antivenom

“…By incorporating N. scutatus venom in the immunogen, the neutralization of H. schistosus venom by SSAV is likely improved with the additional antibody titer raised against its myotoxic, basic PLA 2 s; however, the overall potency of the antivenom appears to remain limited by the weak neutralization of short neurotoxins which are present in a very large amount in sea snake venom [15]. This is in agreement with recent reports on the consistently weak neutralization of antivenoms against short neurotoxins isolated from Asiatic cobra venoms (Naja naja, Naja kaouthia and Naja sputatrix) [37][38][39]. On the other hand, the neutralization of N. scutatus venom is attributable primarily to SSAV neutralizing the abundant PLA 2 s, and enhanced by the additional anti-titers against the coagulant enzymes and alpha-neurotoxins.…”

Comparative venom gland transcriptomics ofNaja kaouthia(monocled cobra) from Malaysia and Thailand: elucidating geographical venom variation and insights into sequence novelty

“…These SNTXs are highly lethal α-neurotoxins in rodents although some studies suggested that cobra venom SNTXs exhibit a weaker affinity towards the nicotinic acetylcholine receptor (nAChR) as compared to LNTXs, due to the lack of the fifth disulphide bridge in its structure (Barber, Isbister & Hodgson, 2013; Servent et al, 1997, 2000). The weaker affinity of SNTX towards nAChR, however, does not compromise its lethal potency (having compatible LD 50 with LNTX), but has important practical concern as its poor antigenicity is a contributing factor to low neutralisation efficacy of antivenom against SNTX-predominated venoms (Leong et al, 2015; Tan et al, 2015b, 2016a). …”

“…Substantial venom variations were noted across the geographical samples; notably the Thai N. kaouthia venom contains a much higher amount of long-chain neurotoxin (LNTX, ∼33%) as compared to the Malaysian (∼4%) and the Vietnamese specimens (not detected), respectively. The proteomic variation was further demonstrated at functional levels through studies on venom lethality, neuromuscular depressant activity and immunological neutralisation using antivenom (Tan et al, 2016a, 2016b). The molecular diversity and the genetic variability of the toxins in the venom, however have not been comprehensively investigated.…”

Assessing SABU (Serum Anti Bisa Ular), the sole Indonesian antivenom: A proteomic analysis and neutralization efficacy study

“…This is in agreement with the higher content of alpha-neurotoxins in N. sumatrana venom compared to N. sputatrix venom, which has a much higher content of cytotoxins26. The LD 50 value of cobra cytotoxin is about 10-fold higher (hence less lethal) than the alpha-neurotoxin when administered intravenously92728. On the other hand, krait venoms are known to exhibit high lethality (LD 50  < 0.2 μg/g, including Indonesian B. candidus ), except for B. fasciatus of Thailand which has an exceptionally higher venom LD 50 exceeding 1.0 μg/g1829.…”

“…The neutralization potency is a more direct indicator of antivenom neutralizing capacity, and is theoretically unaffected by the number of LD 50 in the challenge dose. For comparative purpose, the P values of different antivenoms were normalized by their respective protein amount and expressed as milligram of venom neutralized per gram of antivenom protein27.…”