Snake Venom Proteomics of Samar Cobra (Naja samarensis) from the Southern Philippines: Short Alpha-Neurotoxins as the Dominant Lethal Component Weakly Cross-Neutralized by the Philippine Cobra Antivenom.

Praneetha Palasuberniam,Choo Hock Tan,Yi Wei Chan,Kae Yi Tan

doi:10.3389/fphar.2021.727756

Abstract

The Samar Cobra, Naja samarensis, is endemic to the southern Philippines and is a WHO-listed Category 1 venomous snake species of medical importance. Envenomation caused by N. samarensis results in neurotoxicity, while there is no species-specific antivenom available for its treatment. The composition and neutralization of N. samarensis venom remain largely unknown to date. This study thus aimed to investigate the venom proteome of N. samarensis for a comprehensive profiling of the venom composition, and to examine the immunorecognition as well as neutralization of its toxins by a hetero-specific antivenom. Applying C18 reverse-phase high-performance liquid chromatography (RP-HPLC) and tandem mass spectrometry (LC-MS/MS), three-finger toxins (3FTx) were shown to dominate the venom proteome by 90.48% of total venom proteins. Other proteins in the venom comprised snake venom metalloproteinases, phospholipases A2, cysteine-rich secretory proteins, venom nerve growth factors, L-amino acid oxidases and vespryn, which were present at much lower abundances. Among all, short-chain alpha-neurotoxins (SαNTX) were the most highly expressed toxin within 3FTx family, constituting 65.87% of the total venom proteins. The SαNTX is the sole neurotoxic component of the venom and has an intravenous median lethal dose (LD50) of 0.18 μg/g in mice. The high abundance and low LD50 support the potent lethal activity of N. samarensis venom. The hetero-specific antivenom, Philippine Cobra Antivenom (PCAV, raised against Naja philippinensis) were immunoreactive toward the venom and its protein fractions, including the principal SαNTX. In efficacy study, PCAV was able to cross-neutralize the lethality of SαNTX albeit the effect was weak with a low potency of 0.20 mg/ml (defined as the amount of toxin completely neutralized per milliliter of the antivenom). With a volume of 5 ml, each vial of PCAV may cross-neutralize approximately 1 mg of the toxin in vivo. The findings support the potential para-specific use of PCAV in treating envenomation caused by N. samarensis while underscoring the need to improve the potency of its neutralization activity, especially against the highly lethal alpha-neurotoxins.

Highlights

Each year, about 5.4 million snakebites occur worldwide, resulting in 1.8–2.7 million cases of envenomation
Between 80 and 140 min, the elution profiles of N. samarensis venom and the commercially supplied N. philippinensis venom (Latoxan) were comparable, whereas variation was noticed in the wild-caught N. philippinensis venom in which proteins eluted had a higher abundance
In N. samarensis venom, the dominance of low molecular weight proteins is similar to the venom of N. philippinensis (Tan et al, 2019b), and several other medically important Asiatic cobras reported including N. kaouthia (Tan et al, 2015d; Xu et al, 2017), Naja siamensis (Liu et al, 2017), Naja sputatrix (Tan et al, 2017c), Naja atra (Huang et al, 2015) and Naja naja (Sintiprungrat et al, 2016; Chanda et al, 2018; Wong et al, 2018)

Summary

Introduction

About 5.4 million snakebites occur worldwide, resulting in 1.8–2.7 million cases of envenomation. 81,000 to 138,000 people die due to the toxic effects of snake venom, with three times as many continue to suffer long-term complications of various physical and mental sequelae (Kasturiratne et al, 2008; World Health Organization [WHO], 2019). South Asia, sub-Saharan Africa and Southeast Asia are the regional trio that features the highest prevalence and mortality of snakebite envenomation. This public health crisis heavily affects the impoverished populations in the rural areas, where health resources are scarce, venomous snakes are abundant and human-snake interaction is common due to extensive agricultural practice (World Health Organization [WHO], 2016; Gutiérrez et al, 2017; Ralph et al, 2019). Species-specific antivenoms are still lacking in many regions

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