Matthew R. Lewin

Snakebite envenoming is often discussed in terms of lethality and limb loss, but local tissue injury and coagulotoxic effects of venom are significantly more common acute manifestations of snakebite envenoming (SBE). Local tissue injury and the hemorrhagic and coagulotoxic effects of venom are challenging to study in live animals and can be ethically fraught due to animal welfare concerns such that attention to the 3Rs of animal welfare motivates the development of in vitro techniques in this arena. Herein, we tested the use of a wound-healing study technique known as Electric Cell-Substrate Impedance Sensing (ECIS) to assess populations of cultured cells exposed to venom with or without sPLA₂ and/or metalloprotease inhibitors (varespladib and marimastat, respectively). For comparison, the StarMax coagulation analyzer for coagulotoxicity was further used to evaluate the venoms and the neutralizing capabilities of the abovementioned direct toxin inhibitors (DTIs) against the same venoms examined using ECIS. Three viper and three elapid venoms that were examined for their effects on H1975 cells were Agkistrodon contortrix (Eastern Copperhead), Crotalus helleri (Southern Pacific Rattlesnake), and Vipera ammodytes (Horned Viper) and Naja atra (Chinese Cobra), Naja mossambica (Mozambique Spitting Cobra), and Naja nigricollis (Black-necked Spitting Cobra), respectively. The combination of cellular and coagulation techniques appears to usefully discriminate the in vitro capabilities and limitations of specific inhibitors to inhibit specific venom effects. This study suggests that ECIS with or without concomitant coagulation testing is a feasible method to generate reproducible, meaningful preclinical data and could be used with any type of cell line. Importantly, this approach is both quantitative and has the potential of reducing animal use and suffering during the evaluation of potential therapeutics. To further evaluate the potential of this method, rescue studies should be performed.

Introduction Snakebite envenoming (SBE) results in over 500 000 deaths or disabling injuries annually. Varespladib methyl, an oral inhibitor of secretory phospholipase A2, is a nearly ubiquitous component of snake venoms. We conducted a phase II clinical trial to assess efficacy and safety of oral varespladib methyl in patients bitten by venomous snakes. Methods This double-blind, randomised, placebo-controlled trial enrolled patients in emergency departments in India and the USA. Patients with SBE were randomly assigned (1:1) to receive varespladib methyl or placebo two times per day for 1 week. All patients received standard of care, including antivenom. The primary outcome was change in the composite Snakebite Severity Score (SSS) measuring the severity of envenoming, from baseline to the average composite SSS at 6 and 9 hours. Results Among 95 patients randomised August 2021 through November 2022, the most common snakebites were from Russell’s vipers (n=29), copperheads (n=18) and rattlesnakes (n=14). The SSS improved from baseline to the average at 6 and 9 hours by 1.1 (95% CI, 0.7 to 1.6) in the varespladib group versus 1.5 (95% CI, 1.0 to 2.0) in the placebo group (difference −0.4, 95% CI, −0.8 to 0.1, p=0.13). While key secondary outcomes were not statistically different by treatment group, benefit was seen in the prespecified subgroup initiating study drug within 5 hours of bite (n=37). For this early treatment group, clinically important differences were observed for illness severity over the first week, patient-reported function on days 3 and 7 and complete recovery. No death or treatment emergent serious adverse event occurred. Conclusion For emergency department treatment of snakebites, the addition of varespladib to antivenom did not find evidence of difference for the primary outcome based on the SSS. A potentially promising signal of benefit was observed in patients initiating treatment within 5 hours of snakebite.

A field biologist was bitten by a female Nikolsky’s viper (Vipera berus nikolskii) in Kharkiv Oblast, Ukraine. Two months later, the patient began to experience cold-induced vasospasm of the affected digit diagnosed as acquired Raynaud phenomenon. The patient had more than 30 occurrences during the single winter following the bite, but the signs and symptoms of Raynaud phenomenon disappeared with the end of winter. This report describes the case and puts it into context with the literature on the topic of toxin-induced peripheral vasospastic disorders and their potential importance in snakebite envenoming.

Antivenom is currently the standard-of-care treatment for snakebite envenoming, but its efficacy is limited by treatment delays, availability, and in many cases, species specificity. Many of the rapidly lethal effects of envenoming are caused by venom-derived toxins, such as phospholipase A2 (sPLA2); therefore, small molecule direct toxin inhibitors targeting these toxins may have utility as initial and adjunct therapies after envenoming. Varespladib (intravenous, IV) and varespladib-methyl (oral) have been shown to potently inhibit sPLA2s from snake venoms in murine and porcine models, thus supporting their further study as potential treatments for snakebite envenoming. In this pilot study, we tested the ability of these compounds to reverse neurotoxic effects of venom from the Australian and Papuan taipan (Oxyuranus scutellatus) subspecies in juvenile pigs (Sus domesticus). The mean survival time for control animals receiving Australian taipan venom (0.03 mg/kg, n = 3) was 331 min ± 15 min; for those receiving Papuan taipan venom (0.15 mg/kg, n = 3) it was 178 ± 31 min. Thirteen pigs received Australian taipan venom and treatment with either IV or oral varespladib (or with IV to oral transition) and all 13 survived the duration of the study (≥96 h). Eight pigs received Papuan taipan venom followed by treatment: Briefly: Two animals received antivenom immediately and survived to the end of the study. Two animals received antivenom treatment delayed 45 min from envenoming and died within 4 h. Two animals received similarly delayed antivenom treatment and were rescued by varespladib. Two animals were treated with varespladib alone after a 45-min delay. Treatment with varespladib only was effective but required repeat dosing over the course of the study. Findings highlight both the importance of early treatment and, as well, a half-life for the investigational inhibitors now in Phase II clinical trials for snakebite. Varespladib rapidly reversed weakness even when administered many hours post-envenoming and, overall, our results suggest that varespladib and varespladib-methyl could be efficacious tools in the treatment of sPLA2-induced weakness from Oxyuranus envenoming. Further clinical study as initial therapy and as potential method of rescue from some types of antivenom-resistant envenomings are supported by these data.