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
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The Samar Cobra, , is endemic to the southern Philippines and is a WHO-listed Category 1 venomous snake species of medical importance. Envenomation caused by results in neurotoxicity, while there is no species-specific antivenom available for its treatment. The composition and neutralization of venom remain largely unknown to date. This study thus aimed to investigate the venom proteome of 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 C 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 A 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 (LD) of 0.18 μg/g in mice. The high abundance and low LD support the potent lethal activity of venom. The hetero-specific antivenom, Philippine Cobra Antivenom (PCAV, raised against ) 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 . The findings support the potential para-specific use of PCAV in treating envenomation caused by while underscoring the need to improve the potency of its neutralization activity, especially against the highly lethal alpha-neurotoxins.
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