Coagulotoxic Cobras: Clinical Implications of Strong Anticoagulant Actions of African Spitting Naja Venoms That Are Not Neutralised by Antivenom but Are by LY315920 (Varespladib)

Abstract

Snakebite is a global tropical disease that has long had huge implications for human health and well-being. Despite its long-standing medical importance, it has been the most neglected of tropical diseases. Reflective of this is that many aspects of the pathology have been underinvestigated. Snakebite by species in the Elapidae family is typically characterised by neurotoxic effects that result in flaccid paralysis. Thus, while clinically significant disturbances to the coagulation cascade have been reported, the bulk of the research to date has focused upon neurotoxins. In order to fill the knowledge gap regarding the coagulotoxic effects of elapid snake venoms, we screened 30 African and Asian venoms across eight genera using in vitro anticoagulant assays to determine the relative inhibition of the coagulation function of thrombin and the inhibition of the formation of the prothrombinase complex through competitive binding to a nonenzymatic site on Factor Xa (FXa), thereby preventing FXa from binding to Factor Va (FVa). It was revealed that African spitting cobras were the only species that were potent inhibitors of either clotting factor, but with Factor Xa inhibited at 12 times the levels of thrombin inhibition. This is consistent with at least one death on record due to hemorrhage following African spitting cobra envenomation. To determine the efficacy of antivenom in neutralising the anticoagulant venom effects, for the African spitting cobras we repeated the same 8-point dilution series with the addition of antivenom and observed the shift in the area under the curve, which revealed that the antivenom performed extremely poorly against the coagulotoxic venom effects of all species. However, additional tests with the phospholipase A2 inhibitor LY315920 (trade name: varespladib) demonstrated a powerful neutralisation action against the coagulotoxic actions of the African spitting cobra venoms. Our research has important implications for the clinical treatment of cobra snakebites and also sheds light on the molecular mechanisms involved in coagulotoxicity within Naja. As the most coagulotoxic species are also those that produce characteristic extreme local tissue damage, future research should investigate potential synergistic actions between anticoagulant toxins and cytotoxins.

Mechanisms Responsible for the Anticoagulant Properties of Neurotoxic Dendroaspis Venoms: A Viscoelastic Analysis

“…4 14.5-16. 3 3.4-6.7 Dendroaspis jamesoni [13] 80. 3 15.1 0.5 Dendroaspis viridis [13] 77.7 15.2 2.7…”

“…While the coagulopathic effects of hemotoxic venoms derived from venomous snakes have been of great scientific interest for several decades [1], it is only recently that investigation has intensified on the effects of neurotoxic venoms on coagulation [2][3][4][5][6][7]. Specifically, utilizing the thrombelastograph, the effects of neurotoxic venoms containing proteolytic and lipolytic enzymes on human plasma-based coagulation or isolated human thrombin-fibrinogen systems have been defined in venoms obtained from snakes within the Elapidae and Viperidae families [2][3][4][5][6][7]. Of interest, the venoms containing neurotoxic phospholipase A 2 (PLA 2 ) that were investigated were found to have their anticoagulant effects inhibited by either specific phospholipase A 2 inhibitors or tricarbonyldichlororuthenium (II) dimer (CORM-2) [3][4][5][6][7].…”

“…Specifically, utilizing the thrombelastograph, the effects of neurotoxic venoms containing proteolytic and lipolytic enzymes on human plasma-based coagulation or isolated human thrombin-fibrinogen systems have been defined in venoms obtained from snakes within the Elapidae and Viperidae families [2][3][4][5][6][7]. Of interest, the venoms containing neurotoxic phospholipase A 2 (PLA 2 ) that were investigated were found to have their anticoagulant effects inhibited by either specific phospholipase A 2 inhibitors or tricarbonyldichlororuthenium (II) dimer (CORM-2) [3][4][5][6][7]. Critically, these preliminary investigations exploited the ability to assess Table 1.…”

Enzymatic Activity And Brine Shrimp Lethality Of Venom From The Large Brown Spitting Cobra (Naja Ashei) And Its Neutralization By Antivenom

“…B. arietans venom was non-toxic after 24 hours but toxic after 48 and 72 hours. Table 2.Discussion svPLA 2 make up to 30% of viperid and elapid venoms[28,29], and the local effects of venomous snakebite in sub-Saharan Africa have been linked to svPLA 2 's[12,[30][31][32][33]. Our results suggest that the Eastern forest cobra had the highest svPLA 2 activity while mamba venoms had the least activity.This observation seems to corroborate clinical reports on venomous snakebite in Sub-Saharan Africa where cobra bites are associated with severe muscle and tissue damage, and painful progressive swelling which are generally absent in mamba bites[30,[34][35][36][37][38][39].…”

“…Both antivenoms had poor neutralization capacity against the svPLA 2 activity of N. ashei venom. It is no surprise therefore that research into compounds like varespladib, methylvarespladib, and medicinal plant extracts continue to be pursued as possible adjuncts in the management of svPLA 2 -induced effects of viper and elapid venoms[20,28,31,40,41].To the best of our knowledge, this is the first report to establish that the non-spitting Eastern forest cobra (N. subfulva) is more potent than the red spitting cobra (N. pallida) and the large brown spitting cobra (N. ashei) in as far as svPLA 2 activity is concerned. However, considering that both the Eastern forest cobra (N. subfulva) and the Egyptian cobra (N. haje) are non-spitting cobras, it is not clear why they have varying svPLA 2 activity.…”