Pseudechis species (Australian black snakes) within the Elapidae family are rich in anticoagulant PLA2 toxins, with the exception of one species (P. porphyriacus) that possesses procoagulant mutated forms of the clotting enzyme Factor Xa. Previously the mechanism of action of the PLA2 toxins' anticoagulant toxicity was said to be due to inhibition of Factor Xa, but this statement was evidence free. We conducted a series of anticoagulation assays to elucidate the mechanism of anticoagulant action produced by P. australis venom. Our results revealed that, rather than targeting FXa, the PLA2 toxins inhibited the prothrombinase complex, with FVa-alone or as part of the prothrombinase complex-as the primary target; but with significant thrombin inhibition also noted. In contrast, FXa, and other factors were inhibited only to a lesser degree were minor targets. We quantified coagulotoxic effects upon human plasma caused by all nine anticoagulant Pseudechis species, including nine localities of P. australis across Australia, and found similar anticoagulant potency across all Pseudechis species, with greater potency in P. australis and the undescribed Pseudechis species in the NT. In addition, the northern localities and eastern of P. australis were statistically significantly more potent than the central, western, and southern localities. All anticoagulant venoms responded well to Black Snake Antivenom, except P. colletti which was poorly neutralised by Black Snake Antivenom and also Tiger Snake Antivenom (the prescribed antivenom for this species). However, we found LY315920 (trade name: Varespladib), a small molecule inhibitor of PLA2 proteins, exhibited strong potency against P. colletti venom. Thus Varespladib may be a clinically viable treatment for anticoagulant toxicity exerted by this species that is not neutralised by available antivenoms. Our results provide insights into coagulotoxic venom function, and suggest future in vivo work be conducted to progress the development of a cheaper, first-line treatment option to treat PLA2-rich snake venoms globally.

中文翻译：

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黑蛇（Elapidae：Pseudechis）毒液的抗凝毒性：效力、机制和抗蛇毒血清功效

Elapidae 科中的 Pseudechis 物种（澳大利亚黑蛇）富含抗凝 PLA2 毒素，但一种物种（P. porphyriacus）除外，它具有凝血酶因子 Xa 的促凝突变形式。以前，PLA2 毒素的抗凝毒性的作用机制据说是由于抑制了因子 Xa，但这种说法是没有证据的。我们进行了一系列抗凝试验，以阐明澳大利亚青蒿毒液产生的抗凝作用机制。我们的结果表明，PLA2 毒素不是靶向 FXa，而是抑制凝血酶原酶复合物，单独使用 FVa 或作为凝血酶原酶复合物的一部分作为主要靶标；但也有明显的凝血酶抑制作用。相比之下，FXa、其他因素仅受到较小程度的抑制是次要目标。我们量化了所有 9 种抗凝 Pseudechis 物种对人体血浆的凝血毒性作用，包括澳大利亚的 9 个地区的 P. australis，并发现所有 Pseudechis 物种具有相似的抗凝效力，在 P. australis 和北领地中未描述的 Pseudechis 物种中具有更大的效力. 此外，在统计上，澳大利亚北部地区和东部地区的效力明显高于中部、西部和南部地区。所有抗凝血剂毒液对黑蛇抗蛇毒血清反应良好，除了 P. colletti 被黑蛇抗蛇毒血清和虎蛇抗蛇毒血清（该物种的规定抗蛇毒血清）中和较差。然而，我们发现了LY315920（商品名：Varespladib），PLA2 蛋白的小分子抑制剂，对 P. colletti 毒液表现出很强的效力。因此，Varespladib 可能是一种临床上可行的治疗方法，用于治疗该物种所产生的抗凝剂毒性，而这种毒性不能被可用的抗蛇毒血清中和。我们的研究结果提供了对凝固毒性毒液功能的见解，并建议未来进行体内工作以推进开发更便宜的一线治疗方案，以在全球范围内治疗富含 PLA2 的蛇毒。