抄録
Snake venoms are one of the most complicated drug targets due to the complex nature of their toxin proteins, which can be highly variable across different species or even within the same species. This study aimed to unravel the compositional details, pharmacological activities and immunological responses of the venoms of medically important snake species in Asia and Africa, including 15 major cobras (Naja) species found in the world for insights into the improvement of antivenom treatment.
The venoms were first decomplexed using C18-reverse-phase high performance liquid chromatography, and the protein fractions were trypsin-digested, followed by nano-ESI liquid chromatography-tandem mass spectrometry and data mining. De novo venom-gland transcriptomes of selected species were also analyzed to enhance the deep profiling of the venom proteomes. The venom/toxin toxicity (neurotoxicity and lethality) and the neutralization were tested ex vivo (chick biventer-cervicis nerve-muscle model) and in vivo (mouse model). Modified venom immunogen with enriched short neurotoxins was used to raise experimental horse anti-cobra antserum to test for neutralization efficacy improvement.
Cobra venoms exhibit a high degree of plasticity, displaying a diverse composition of neurotoxins that correlated strongly with the venom toxicity. Notably, the Pakistani black cobra (Naja naja), Thai monocled cobra (Naja kaouthia), Philippines spitting cobra (Naja philippinensis) and Egyptian cobra (Naja haje) have highly lethal venoms (LD50 = 0.1-0.3 µg/g) driven by the abundant alpha-neurotoxins (>25% of total venom proteins). This has important medical implication as it influences the effectiveness of antivenoms and the choice thereof. Further protein purification study, toxin-specific characterization through isolated nerve-muscle preparations and in vivo neurotoxicity mouse model revealed that the short three-finger alpha-neurotoxins are the culprit lethal components. Unfortunately, they were consistently weak in immunoreactivity evidenced by poor immunorecognition on enzyme-linked immunosorbent assay (ELISA), and they were poorly neutralized by antivenoms available in the region. Using a revised immunization protocol where venom immunogen was enriched with neurotoxins, the antisera raised experimentally from horses showed promising neutralization efficacy against the different cobra venoms including those with abundant short-chain neurotoxins. Together, in-depth venom protemics combined with pharmacological study and immunological innovation may pave the path to improve treatment for snakebite envenomation.
