Development of a generic high-throughput screening assay for profiling snake venom protease activity after high-resolution chromatographic fractionation

Compendium of medically important snakes, venom activity and clinical presentations in Ghana

BACKGROUND

Snake bite envenoming (SBE) is one neglected tropical disease that has not received the needed attention. The sequelae of burdensome disability and mortality impact the socioeconomic life of communities adversely with little documentation of SBE in health facility records in Ghana. This study details SBE and snake distribution, habits/habitats, type of venom expressed and clinical manifestations.

METHODOLOGY

We conducted a structured thematic desk review of peer reviewed papers, books and reports from repositories including PubMed, World Health Organization (WHO) and Women's & Children's Hospital (WCH) Clinical Toxinology Resources using bibliographic software EndNote and search engine Google Scholar with the following key words; snakes, medical importance, snake bites, venom and venom type, envenomation, symptoms and signs, vaccines, venom expenditure, strike behaviour and venom-metering + Ghana, West Africa, Africa, World. We also reviewed data from the District Health Information Management System (DHIMS) of the Ghana Health Service (GHS). Outcome variables were organized as follows: common name (s), species, habitat/habit, species-specific toxin, clinical manifestation, antivenom availability, WHO category.

FINDINGS

Snake bites and SBE were grouped by the activity of the expressed venom into neurotoxic, cardiotoxic, haemorrhagic, cytotoxic, myotoxic, nephrotoxic and procoagulants. Neurotoxic snake bites were largely due to elapids. Expressed venoms with cardiotoxic, haemorrhagic, nephrotoxic and procoagulant activities principally belonged to the family Viperidae. Snakes with venoms showing myotoxic activity were largely alien to Ghana and the West African sub-region. Venoms showing cytotoxic activity are expressed by a wide range of snakes though more prevalent among the Viperidae family. Snakes with neurotoxic and haemorrhagic venom activities are prevalent across all the agro-ecological zones in Ghana.

CONCLUSION/SIGNIFICANCE

Understanding the characteristics of snakes and their venoms is useful in the management of SBE. The distribution of snakes by their expressed venoms across the agro-ecological zones is also instructive to species identification and diagnosis of SBE.

Application of an Extracellular Matrix-Mimicking Fluorescent Polymer for the Detection of Proteolytic Venom Toxins

The cytotoxicity caused by snake venoms is a serious medical problem that greatly contributes to the morbidity observed in snakebite patients. The cytotoxic components found in snake venoms belong to a variety of toxin classes and may cause cytotoxic effects by targeting a range of molecular structures, including cellular membranes, the extracellular matrix (ECM) and the cytoskeleton. Here, we present a high-throughput assay (384-well plate) that monitors ECM degradation by snake venom toxins via the application of fluorescent versions of model ECM substrates, specifically gelatin and collagen type I. Both crude venoms and fractionated toxins of a selection of medically relevant viperid and elapid species, separated via size-exclusion chromatography, were studied using the self-quenching, fluorescently labelled ECM-polymer substrates. The viperid venoms showed significantly higher proteolytic degradation when compared to elapid venoms, although the venoms with higher snake venom metalloproteinase content did not necessarily exhibit stronger substrate degradation than those with a lower one. Gelatin was generally more readily cleaved than collagen type I. In the viperid venoms, which were subjected to fractionation by SEC, two (B. jararaca and C. rhodostoma, respectively) or three (E. ocellatus) active proteases were identified. Therefore, the assay allows the study of proteolytic activity towards the ECM in vitro for crude and fractionated venoms.

Revisiting the potential of South American rattlesnake Crotalus durissus terrificus toxins as therapeutic, theranostic and/or biotechnological agents

The potential biotechnological and biomedical applications of the animal venom components are widely recognized. Indeed, many components have been used either as drugs or as templates/prototypes for the development of innovative pharmaceutical drugs, among which many are still used for the treatment of human diseases. A specific South American rattlesnake, named Crotalus durissus terrificus, shows a venom composition relatively simpler compared to any viper or other snake species belonging to the Crotalus genus, although presenting a set of toxins with high potential for the treatment of several still unmet human therapeutic needs, as reviewed in this work. In addition to the main toxin named crotoxin, which is under clinical trials studies for antitumoral therapy and which has also anti-inflammatory and immunosuppressive activities, other toxins from the C. d. terrificus venom are also being studied, aiming for a wide variety of therapeutic applications, including as antinociceptive, anti-inflammatory, antimicrobial, antifungal, antitumoral or antiparasitic agent, or as modulator of animal metabolism, fibrin sealant (fibrin glue), gene carrier or theranostic agent. Among these rattlesnake toxins, the most relevant, considering the potential clinical applications, are crotamine, crotalphine and gyroxin. In this narrative revision, we propose to organize and present briefly the updates in the accumulated knowledge on potential therapeutic applications of toxins collectively found exclusively in the venom of this specific South American rattlesnake, with the objective of contributing to increase the chances of success in the discovery of drugs based on toxins.

Utilisation of compounds from venoms in drug discovery

Difficult drug targets are becoming the normal course of business in drug discovery, sometimes due to large interacting surfaces or only small differences in selectivity regions. For these, a different approach is merited: compounds lying somewhere between the small molecule and the large antibody in terms of many properties including stability, biodistribution and pharmacokinetics. Venoms have evolved over millions of years to be complex mixtures of stable molecules derived from other somatic molecules, the stability comes from the pressure to be ready for delivery at a moment's notice. Snakes, spiders, scorpions, jellyfish, wasps, fish and even mammals have evolved independent venom systems with complex mixtures in their chemical arsenal. These venom-derived molecules have been proven to be useful tools, such as for the development of antihypotensive angiotensin converting enzyme (ACE) inhibitors and have also made successful drugs such as Byetta® (Exenatide), Integrilin® (Eptifibatide) and Echistatin. Only a small percentage of the available chemical space from venoms has been investigated so far and this is growing. In a new era of biological therapeutics, venom peptides present opportunities for larger target engagement surface with greater stability than antibodies or human peptides. There are challenges for oral absorption and target engagement, but there are venom structures that overcome these and thus provide substrate for engineering novel molecules that combine all desired properties. Venom researchers are characterising new venoms, species, and functions all the time, these provide great substrate for solving the challenges presented by today's difficult targets.

Anticoagulant Activity of Naja nigricollis Venom Is Mediated by Phospholipase A2 Toxins and Inhibited by Varespladib

Bites from elapid snakes typically result in neurotoxic symptoms in snakebite victims. Neurotoxins are, therefore, often the focus of research relating to understanding the pathogenesis of elapid bites. However, recent evidence suggests that some elapid snake venoms contain anticoagulant toxins which may help neurotoxic components spread more rapidly. This study examines the effects of venom from the West African black-necked spitting cobra (Naja nigricollis) on blood coagulation and identifies potential coagulopathic toxins. An integrated RPLC-MS methodology, coupled with nanofractionation, was first used to separate venom components, followed by MS, proteomics and coagulopathic bioassays. Coagulation assays were performed on both crude and nanofractionated N. nigricollis venom toxins as well as PLA₂s and 3FTx purified from the venom. Assays were then repeated with the addition of either the phospholipase A₂ inhibitor varespladib or the snake venom metalloproteinase inhibitor marimastat to assess whether either toxin inhibitor is capable of neutralizing coagulopathic venom activity. Subsequent proteomic analysis was performed on nanofractionated bioactive venom toxins using tryptic digestion followed by nanoLC-MS/MS measurements, which were then identified using Swiss-Prot and species-specific database searches. Varespladib, but not marimastat, was found to significantly reduce the anticoagulant activity of N. nigricollis venom and MS and proteomics analyses confirmed that the anticoagulant venom components mostly consisted of PLA₂ proteins. We, therefore, conclude that PLA₂s are the most likely candidates responsible for anticoagulant effects stimulated by N. nigricollis venom.

Convergent evolution of pain-inducing defensive venom components in spitting cobras

Convergent evolution provides insights into the selective drivers underlying evolutionary change. Snake venoms, with a direct genetic basis and clearly defined functional phenotype, provide a model system for exploring the repeated evolution of adaptations. While snakes use venom primarily for predation, and venom composition often reflects diet specificity, three lineages of cobras have independently evolved the ability to spit venom at adversaries. Using gene, protein, and functional analyses, we show that the three spitting lineages possess venoms characterized by an up-regulation of phospholipase A2 (PLA2) toxins, which potentiate the action of preexisting venom cytotoxins to activate mammalian sensory neurons and cause enhanced pain. These repeated independent changes provide a fascinating example of convergent evolution across multiple phenotypic levels driven by selection for defense.