Sodium oleate, arachidonate, and linoleate enhance fibrinogenolysis by Russell's viper venom proteinases and inhibit FXIIIa; a role for phospholipase A2 in venom induced consumption coagulopathy

Comparative functional characterization and in vitro immunological cross-reactivity studies on Daboia russelii and Craspedocephalus malabaricus venom

BACKGROUND

Snake venom is a complex mixture of organic and inorganic constituents, including proteins and peptides. Several studies showed that antivenom efficacy differs due to intra- and inter-species venom variation.

METHODS

In the current study, comparative functional characterization of major enzymatic proteins present in Craspedocephalus malabaricus and Daboia russelii venom was investigated through various in vitro and immunological cross-reactivity assays.

RESULTS

The enzymatic assays revealed that hyaluronidase and phospholipase A2 activities were markedly higher in D. russelii. By contrast, fibrinogenolytic, fibrin clotting and L-amino acid oxidase activities were higher in C. malabaricus venom. ELISA results suggested that all the antivenoms had lower binding potential towards C. malabaricus venom. For D. russelii venom, the endpoint titration value was observed at 1:72 900 for all the antivenoms. In the case of C. malabaricus venom, the endpoint titration value was 1:2700, except for Biological E (1:8100). All these results, along with the avidity assays, indicate the strength of venom-antivenom interactions. Similarly, the western blot results suggest that all the antivenoms showed varied efficacies in binding and detecting the venom antigenic epitopes in both species.

CONCLUSIONS

The results highlight the need for species-specific antivenom to better manage snakebite victims.

The Need for Next-Generation Antivenom for Snakebite Envenomation in India

The limitations posed by currently available antivenoms have emphasized the need for alternative treatments to counteract snakebite envenomation. Even though exact epidemiological data are lacking, reports have indicated that most global snakebite deaths are reported in India. Among the many problems associated with snakebite envenomation, issues related to the availability of safer and more efficient antivenoms are of primary concern. Since India has the highest number of global snakebite deaths, efforts should be made to reduce the burden associated with snakebite envenoming. Alternative methods, including aptamers, camel antivenoms, phage display techniques for generating high-affinity antibodies and antibody fragments, small-molecule inhibitors, and natural products, are currently being investigated for their effectiveness. These alternative methods have shown promise in vitro, but their in vivo effectiveness should also be evaluated. In this review, the issues associated with Indian polyvalent antivenoms in neutralizing venom components from geographically distant species are discussed in detail. In a nutshell, this review gives an overview of the current drawbacks of using animal-derived antivenoms and several alternative strategies that are currently being widely explored.

The BRAVO Clinical Study Protocol: Oral Varespladib for Inhibition of Secretory Phospholipase A2 in the Treatment of Snakebite Envenoming

INTRODUCTION

Snakebite is an urgent, unmet global medical need causing significant morbidity and mortality worldwide. Varespladib is a potent inhibitor of venom secretory phospholipase A2 (sPLA2) that can be administered orally via its prodrug, varespladib-methyl. Extensive preclinical data support clinical evaluation of varespladib as a treatment for snakebite envenoming (SBE). The protocol reported here was designed to evaluate varespladib-methyl for SBE from any snake species in multiple geographies.

METHODS AND ANALYSIS

BRAVO (Broad-spectrum Rapid Antidote: Varespladib Oral for snakebite) is a multicenter, randomized, double-blind, placebo-controlled, phase 2 study to evaluate the safety, tolerability, and efficacy of oral varespladib-methyl plus standard of care (SoC) vs. SoC plus placebo in patients presenting with acute SBE by any venomous snake species. Male and female patients 5 years of age and older who meet eligibility criteria will be randomly assigned 1:1 to varespladib-methyl or placebo. The primary outcome is the Snakebite Severity Score (SSS) that has been modified for international use. This composite outcome is based on the sum of the pulmonary, cardiovascular, nervous, hematologic, and renal systems components of the updated SSS.

ETHICS AND DISSEMINATION

This protocol was submitted to regulatory authorities in India and the US. A Clinical Trial No Objection Certificate from the India Central Drugs Standard Control Organisation, Drug Controller General-India, and a Notice to Proceed from the US Food and Drug Administration have been obtained. The study protocol was approved by properly constituted, valid institutional review boards or ethics committees at each study site. This study is being conducted in compliance with the April 1996 ICH Guidance for Industry GCP E6, the Integrated Addendum to ICH E6 (R2) of November 2016, and the applicable regulations of the country in which the study is conducted. The trial is registered on Clinical trials.gov, NCT#04996264 and Clinical Trials Registry-India, 2021/07/045079 000062.

Varespladib in the Treatment of Snakebite Envenoming: Development History and Preclinical Evidence Supporting Advancement to Clinical Trials in Patients Bitten by Venomous Snakes

The availability of effective, reliably accessible, and affordable treatments for snakebite envenoming is a critical and long unmet medical need. Recently, small, synthetic toxin-specific inhibitors with oral bioavailability used in conjunction with antivenom have been identified as having the potential to greatly improve outcomes after snakebite. Varespladib, a small, synthetic molecule that broadly and potently inhibits secreted phospholipase A2 (sPLA2s) venom toxins has renewed interest in this class of inhibitors due to its potential utility in the treatment of snakebite envenoming. The development of varespladib and its oral dosage form, varespladib-methyl, has been accelerated by previous clinical development campaigns to treat non-envenoming conditions related to ulcerative colitis, rheumatoid arthritis, asthma, sepsis, and acute coronary syndrome. To date, twenty-nine clinical studies evaluating the safety, pharmacokinetics (PK), and efficacy of varespladib for non-snakebite envenoming conditions have been completed in more than 4600 human subjects, and the drugs were generally well-tolerated and considered safe for use in humans. Since 2016, more than 30 publications describing the structure, function, and efficacy of varespladib have directly addressed its potential for the treatment of snakebite. This review summarizes preclinical findings and outlines the scientific support, the potential limitations, and the next steps in the development of varespladib's use as a snakebite treatment, which is now in Phase 2 human clinical trials in the United States and India.

Hypocholesterolaemia as a prognostic factor in venomous snakebite: a retrospective study from a single centre in Kerala, India

BACKGROUND

Studies have suggested a association between serum cholesterol values and severity of envenoming. The objective of the study was to correlate the serum cholesterol levels with severity of envenoming in victims of snakebite, across snake species in our patient population.

METHODS

Retrospective secondary data analysis of health records of a cohort of snakebite victims treated at Little Flower Hospital, Angamaly, Kerala during June 2006-January 2008 was performed. The cholesterol values were assessed in 205 consecutive patients admitted with snakebite envenoming, within 24 h of admission and 10 h of overnight fasting. Lipid fractions were estimated from fasting serum through the standard CHOD-PAP method on a Hitachi analyzer. The cholesterol level was compared between victims with mild and serious envenoming to assess the proportion among each category with a low cholesterol (defined as ≤150 mg/dl as per institutional criteria). In addition, low cholesterol as a marker of severity was compared with other laboratory parameters suggesting severe envenoming such as low fibrinogen, low platelet count, neutrophilia, elevated creatinine, d-dimer, hepatic transaminases and albuminuria.

RESULTS

Of the 146 victims with serious degree of snakebite envenoming 116 (79%) had low cholesterol values ≤150 mg%, while 30 (21%) had values >150 mg%. Of the patients with low cholesterol, 116 (78%) had serious envenoming, while 22% had mild envenoming. By contrast, 30 patients (21%) had values >150 mg%. The risk of moderate-severe envenoming with low cholesterol was 2.7 times (170%) that of victims with normal or high cholesterol on admission.

CONCLUSIONS

A low cholesterol on admission in victims of snake envenoming suggested a more severe degree of envenoming and likelihood of complications.

Cerebral Complications of Snakebite Envenoming: Case Studies

There are an estimated 5.4 million snakebite cases every year. People with snakebite envenoming suffer from severe complications, or even death. Although some review articles cover several topics of snakebite envenoming, a review of the cases regarding cerebral complications, especially rare syndromes, is lacking. Here, we overview 35 cases of snakebite by front-fanged snakes, including Bothrops, Daboia, Cerastes, Deinagkistrodon, Trimeresurus, and Crotalus in the Viperidae family; Bungarus and Naja in the Elapidae family, and Homoroselaps (rare cases) in the Lamprophiidae family. We also review three rare cases of snakebite by rear-fanged snakes, including Oxybelis and Leptodeira in the Colubridae family. In the cases of viper bites, most patients (17/24) were diagnosed with ischemic stroke and intracranial hemorrhage, leading to six deaths. We then discuss the potential underlying molecular mechanisms that cause these complications. In cases of elapid bites, neural, cardiac, and ophthalmic disorders are the main complications. Due to the small amount of venom injection and the inability to deep bite, all the rear-fanged snakebites did not develop any severe complications. To date, antivenom (AV) is the most effective therapy for snakebite envenoming. In the six cases of viper and elapid bites that did not receive AV, three cases (two by viper and one by elapid) resulted in death. This indicates that AV treatment is the key to survival after a venomous snakebite. Lastly, we also discuss several studies of therapeutic agents against snakebite-envenoming-induced complications, which could be potential adjuvants along with AV treatment. This article organizes the diagnosis of hemotoxic and neurotoxic envenoming, which may help ER doctors determine the treatment for unidentified snakebite.

Comparison of rotational thromboelastometry parameters with 20-minute whole blood clotting test as a predictor of envenoming in Russell's viper bite patients

BACKGROUND

Coagulopathy is an important and common systemic clinical syndrome caused by snake envenoming. The major clinical effect of Russell's viper (RV) envenoming is haematotoxicity. The 20-min whole blood clotting test (WBCT20) is the standard test for identification of envenoming in resource-limited settings. However, its reliability as a diagnostic test has been questioned. Rotational thromboelastometry (ROTEM) assays different phases of clot formation from initiation to fibrinolysis. Our objective was to compare parameters of ROTEM with WBCT20 and the international normalized ratio (INR) as predictors of envenoming in RV bite patients.

METHODS

Fifty-three patents with RV bite presenting to Anuradhapura Hospital, Sri Lanka were recruited. Epidemiological and clinical data were obtained. Venous blood samples were collected at admission for ROTEM, INR and WBCT20.

RESULTS

A total of 46 of 53 patients with RV bites received antivenom serum (AVS); 74% had a non-clottable WBCT20. All 46 had at least one abnormal ROTEM parameter and 93% had a prolonged EXTEM clotting time (EXTEM-CT). The sensitivity of a prolonged INR was only 55%.

CONCLUSIONS

EXTEM-CT is a better predictor of envenoming and the need for AVS than WBCT20 in RV bites (p=0.02). It provides a numerical value that can be used post-AVS to objectively assess the response and decide on further treatment.

Assessment of snakebite burdens, clinical features of envenomation, and strategies to improve snakebite management in Vietnam

The sheer paucity of scientific documentation of herpetofauna in Vietnam and the rudimentary healthcare response to snakebite have stimulated this review. Over six decades of data culled from public data bases and search engines, have been used to assess snakebite burdens, clinical features of envenomation, and strategies for snakebite management in Vietnam. In addition, biochemical and proteomic analyses to decipher venom composition, rapid analytical techniques to be used for clinical diagnosis of snakebite in Vietnam have been discussed in detail. The assessment of efficacy, safety, and quality of commercial antivenom produced in Vietnam and improvement of antivenom production to meet the national requirement has been critically examined. It is apparent that snake bite incidence in Vietnam is exacerbated by mismatch in demand and supply of antivenom therapy, insufficient medical facilities, preference for traditional healers and poor management of clinical records. The impediments arising from geographical and species-specific variation in venom composition can be overcome by the 'Omics approach', and scientific documentation of pathophysiological manifestations post envenomation. The development of next generation of therapeutics, encouraging clinical research, novel approaches and social awareness against snakebite and its treatments have been suggested to significantly reduce the snakebite mortality and morbidity in this region.

Biogeographic venom variation in Russell's viper (Daboia russelii) and the preclinical inefficacy of antivenom therapy in snakebite hotspots

BACKGROUND

Snakebite in India results in over 58,000 fatalities and a vast number of morbidities annually. The majority of these clinically severe envenomings are attributed to Russell's viper (Daboia russelii), which has a near pan-India distribution. Unfortunately, despite its medical significance, the influence of biogeography on the composition and potency of venom from disparate D. russelii populations, and the repercussions of venom variation on the neutralisation efficacy of marketed Indian antivenoms, remain elusive.

METHODS

Here, we employ an integrative approach comprising proteomic characterisation, biochemical analyses, pharmacological assessment, and venom toxicity profiling to elucidate the influence of varying ecology and environment on the pan-Indian populations of D. russelii. We then conducted in vitro venom recognition experiments and in vivo neutralisation assays to evaluate the efficacy of the commercial Indian antivenoms against the geographically disparate D. russelii populations.

FINDINGS

We reveal significant intraspecific variation in the composition, biochemical and pharmacological activities and potencies of D. russelii venoms sourced from five distinct biogeographic zones across India. Contrary to our understanding of the consequences of venom variation on the effectiveness of snakebite therapy, commercial antivenom exhibited surprisingly similar neutralisation potencies against the majority of the investigated populations, with the exception of low preclinical efficacy against the semi-arid population from northern India. However, the ability of Indian antivenoms to counter the severe morbid effects of Daboia envenoming remains to be evaluated.

CONCLUSION

The concerning lack of antivenom efficacy against the north Indian population of D. russelii, as well as against two other 'big four' snake species in nearby locations, underscores the pressing need to develop pan-India effective antivenoms with improved efficacy in high snakebite burden locales.