Venom Evolution Lab, School of Biological Science, University of Queensland, St. Lucia, QLD, Australia; Department of Biochemistry & Microbiology, North South University, Dhaka, Bangladesh.
Ophirex Inc., Corte Madera, CA, 94925, USA; California Academy of Sciences, San Francisco, CA, 94118, USA.
Toxicon. 2022 Oct 30;218:19-24. doi: 10.1016/j.toxicon.2022.08.017. Epub 2022 Aug 31.
Venoms are evolutionary novelties that have real-world implications due to their impact upon human health. However, relative to the abundant studies of elapid and viperid snake venoms, fewer investigations have been undertaken on those of rear-fanged snakes as they are more problematic for obtaining venom. While most rear-fanged venomous snakes are not considered to be of great medical importance, several species are capable of producing fatalities. Most notable among these are snakes from the genus Rhabdophis, the Asian "keelback" snakes. Prior work have described potent procoagulant toxicity suggesting Factor X and prothrombin activation, but did not investigate the ability to activate other clotting factors. Here we show that in addition to activating both Factor X and prothrombin (with prothrombin twice that of FX), the venom of Rhabdophis subminiatus is able to more potently activate Factor VII (ten times that of prothrombin), while also activating FXII and FIX equipotently to prothrombin, and with FXI also activated but at a much lower level. The ability to activate FVII represents a third convergent evolution of this trait. The Australian elapid clade of [Oxyuranus (taipans) + Pseudonaja (brown snakes)] was the first identified to have evolved this trait. and only recently was it shown to be independently present in another lineage (the Central American viperid species Porthidium volcanicum). In addition, the abilities to activate FXI and FXII are also convergent between R. subminiatus and P. volcanicum, but with R. subminiatus being much more potent. By testing across amphibian, avian, and mammalian plasmas we demonstrate that the venom is potently procoagulant across diverse plasma types. However, consistent with dietary preference, R. subminiatus venom was most potent upon amphibian plasma. While a Rhabdophis antivenom is produced in Japan to treat R. tigrinus envenomings, it is scarce even within Japan and is not exported. As this genus is very wide-ranging in Asia, alternate treatment options are in need of development. Hence we tested the ability of candidate, broad-spectrum enzyme inhibitors to neutralize R. subminiatus venom: marimastat was more effective than prinomastat but both marimastat and prinomastat were significantly more effective than DMPS (2,3-Dimercapto-1-propanesulfonic acid). The findings of this study shed light on the evolution of these fascinating rear-fanged snakes as well as explored their systemic effects upon blood coagulation and point to potential treatment options for the rare, but potentially lethal encounters.
毒液是进化的新产物，由于其对人类健康的影响，具有实际意义。然而，与大量研究的眼镜蛇和蝰蛇毒液相比，对后齿蛇类的毒液研究较少，因为后齿蛇类的毒液更难获得。虽然大多数后齿毒蛇并不被认为具有重要的医学意义，但有几种蛇类能够致人死亡。其中最著名的是 Rhabdophis 属的蛇，即亚洲“龙骨蛇”。先前的研究已经描述了强效的促凝血毒性，表明因子 X 和凝血酶原的激活，但没有研究其激活其他凝血因子的能力。在这里，我们表明，除了激活因子 X 和凝血酶原（凝血酶原是因子 X 的两倍）外，Rhabdophis subminiatus 的毒液还能够更有效地激活因子 VII（是凝血酶原的十倍），同时还能够等效力地激活因子 XII 和 FIX，而对凝血酶原的激活作用则较弱。激活因子 VII 的能力代表了该特性的第三次趋同进化。澳大利亚眼镜蛇科的[Oxyuranus ( taipans) + Pseudonaja (brown snakes)]是第一个被发现具有这种特性的科。直到最近，才发现它在另一个谱系（中美洲蝰蛇种 Porthidium volcanicum）中独立存在。此外，R. subminiatus 和 P. volcanicum 之间也存在 FXI 和 FXII 的激活能力的趋同进化，但 R. subminiatus 的作用要强得多。通过在两栖动物、鸟类和哺乳动物的血浆中进行测试，我们证明了毒液在不同的血浆类型中都具有很强的促凝血作用。然而，与饮食偏好一致，R. subminiatus 毒液在两栖动物血浆中最为有效。虽然日本生产了一种抗 Rhabdophis 蛇毒的抗蛇毒血清来治疗 R. tigrinus 的蛇伤，但即使在日本，这种抗蛇毒血清也很稀缺，而且没有出口。由于这个属在亚洲分布非常广泛，因此需要开发替代的治疗选择。因此，我们测试了候选的广谱酶抑制剂中和 R. subminiatus 毒液的能力：marimastat 比 prinomastat 更有效，但 marimastat 和 prinomastat 都比 DMPS（2,3-二巯基-1-丙磺酸）更有效。这项研究的结果揭示了这些迷人的后齿蛇类的进化，以及它们对血液凝固的系统影响，并为罕见但可能致命的遭遇提供了潜在的治疗选择。
