A model to explain the pharmacological effects of snake venom phospholipases A2

Oral varespladib for the treatment of snakebite envenoming in India and the USA (BRAVO): a phase II randomised clinical trial

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.

Exploring the inhibitory potential of phytochemicals from Vernonia glaberrima leaves against snake venom toxins through computational simulation and experimental validation

Phospholipase A2 (PLA2) is an enzyme present in appreciable quantity in snake venoms which catalyze the hydrolysis of glycerophospholipids at sn-2 position and promote the release of lysophospholipids and fatty acids. 5-methylcoumarin-4-β-glucoside (5MC4BG) and lupeol were previously isolated from the leaves of V. glaberrima. The aim of this research was to evaluate effect of these compounds as potential inhibitors of snake venom toxins of Naja nigricollis using an in vitro and in silico studies. Antisnake venom studies was conducted using acidimetry while the molecular docking analysis against PLA2 enzyme from N. nigricollis was performed using Auto Dock Vina and ADME-Tox analysis was evaluated using swissADME and ProTox-II online servers. The two compounds (5MC4BG and Lupeol) were able to inhibit the hydrolytic actions of PLA2 enzyme with percentage inhibition ranging from 23.99 to 72.36 % and 21.97-24.82 % at 0.0625-1.00 mg/mL respectively while the standard ASV had 82.63 % at 1.00 mg/mL after 10 min incubation at 37 °C. Similar effects were observed after 30 min incubation, although there was significant increase in percentage inhibition of 5MC4BG and lupeol ranging from 66.51 to 83.73 % and 54.87-59.60 % at similar concentrations. Furthermore, the compounds were able to bind to the active site of PLA2 enzyme with high affinity (-7.7 to -6.3 kcal/mol); the standard ligand, Varespladib had a docking score of -6.9 kcal/mol and they exhibited favorable drug-likeness and pharmacokinetic properties and according to toxicity predictions, the two compounds are toxic. In conclusion, the leaf of V. glaberrima contains phytoconstituents with antisnake activity and thus, validates the hypothesis that, the phytoconstituents of V. glaberrima leaves has antisnake venom activity against N. nigricollis venom and thus, should be studied further for the development as antisnake venom agents.

Fangs and foliage: Unearthing the haemotoxic secrets of cannabis-dwelling rattlesnakes

Despite a recent surge in high-throughput venom research that has enabled many species to be studied, some snake venoms remain understudied. The long-tailed rattlesnakes (Crotalus ericsmithi, C. lannomi, and C. stejnegeri) are one group where such research lags, largely owing to the rarity of these snakes and the hazardous areas, ripe with drug (marijuana and opium) production, they inhabit in Mexico. To fill this knowledge gap, we used multiple functional assays to examine the coagulotoxic (including across different plasma types), neurotoxic, and myotoxic activity of the venom of the long-tailed rattlesnakes. All crude venoms were shown to be potently anticoagulant on human plasma, which we discovered was not due to the destruction of fibrinogen, except for C. stejnegeri displaying minor fibrinogen destruction activity. All venoms exhibited anticoagulant activity on rat, avian, and amphibian plasmas, with C. ericsmithi being the most potent. We determined the mechanism of anticoagulant activity by C. ericsmithi and C. lannomi venoms to be phospholipid destruction and inhibition of multiple coagulation factors, leading to a net disruption of the clotting cascade. In the chick biventer assay, C. ericsmithi and C. lannomi did not exhibit neurotoxic activity but displayed potential weak myotoxic activity. BIRMEX® (Faboterápico Polivalente Antiviperino) antivenom was not effective in neutralising this venom effect. Overall, this study provides an in-depth investigation of venom function of understudied long-tailed rattlesnakes and provides a springboard for future venom and ecology research on the group.

Identification of poorly immunodepleted phospholipase A2 (PLA2) proteins of Bungarus fasciatus venom from Assam, India and evaluation of Indian polyvalent antivenom using third-generation antivenomics

Bungarus fasciatus also referred to as the Banded krait is a snake which possesses venom and belongs to the Elapidae family. It is widely distributed across the Indian subcontinent and South East Asian countries and is responsible for numerous snakebites in the population. B. fasciatus possesses a neurotoxic venom and envenomation by the snake results in significant morbidity and occasional morbidity in the victim if not treated appropriately. In this study, the efficacy of Indian polyvalent antivenom (Premium Serums polyvalent antivenom) was evaluated against the venom of B. fasciatus from Guwahati, Assam (India) employing the Third-generation antivenomics technique followed by identification of venom proteins from three poorly immunodepleted peaks (P5, P6 and P7) using LC-MS/MS analysis. Seven proteins were identified from the three peaks and all these venom proteins belonged to the phospholipase A2 (PLA2) superfamily. The identified PLA2 proteins were corroborated by the in vitro enzymatic activities (PLA2 and Anticoagulant activity) exhibited by the three peaks and previous reports of pathological manifestation in the envenomated victims. Neutralization of enzymatic activities by Premium Serums polyvalent antivenom was also assessed in vitro for crude venom, P5, P6 and P7 which revealed moderate to poor inhibition. Inclusion of venom proteins/peptides, which are non-immunodepleted or poorly immunodepleted, into the immunization mixture of venom used for antivenom production may help in enhancing the efficacy of the polyvalent antivenom.

Viper Venom Phospholipase A2 Database: The Structural and Functional Anatomy of a Primary Toxin in Envenomation

Viper venom phospholipase A2 enzymes (vvPLA2s) and phospholipase A2-like (PLA2-like) proteins are two of the principal toxins in viper venom that are responsible for the severe myotoxic and neurotoxic effects caused by snakebite envenoming, among other pathologies. As snakebite envenoming is the deadliest neglected tropical disease, a complete understanding of these proteins' properties and their mechanisms of action is urgently needed. Therefore, we created a database comprising information on the holo-form, cofactor-bound 3D structure of 217 vvPLA2 and PLA2-like proteins in their physiologic environment, as well as 79 membrane-bound viper species from 24 genera, which we have made available to the scientific community to accelerate the development of new anti-snakebite drugs. In addition, the analysis of the sequenced, 3D structure of the database proteins reveals essential aspects of the anatomy of the proteins, their toxicity mechanisms, and the conserved binding site areas that may anchor universal interspecific inhibitors. Moreover, it pinpoints hypotheses for the molecular origin of the myotoxicity of the PLA2-like proteins. Altogether, this study provides an understanding of the diversity of these toxins and how they are conserved, and it indicates how to develop broad, interspecies, efficient small-molecule inhibitors to target the toxin's many mechanisms of action.

In Vitro Efficacy of Antivenom and Varespladib in Neutralising Chinese Russell's Viper (Daboia siamensis) Venom Toxicity

The venom of the Russell's viper (Daboia siamensis) contains neurotoxic and myotoxic phospholipase A₂ toxins which can cause irreversible damage to motor nerve terminals. Due to the time delay between envenoming and antivenom administration, antivenoms may have limited efficacy against some of these venom components. Hence, there is a need for adjunct treatments to circumvent these limitations. In this study, we examined the efficacy of Chinese D. siamensis antivenom alone, and in combination with a PLA₂ inhibitor, Varespladib, in reversing the in vitro neuromuscular blockade in the chick biventer cervicis nerve-muscle preparation. Pre-synaptic neurotoxicity and myotoxicity were not reversed by the addition of Chinese D. siamensis antivenom 30 or 60 min after venom (10 µg/mL). The prior addition of Varespladib prevented the neurotoxic and myotoxic activity of venom (10 µg/mL) and was also able to prevent further reductions in neuromuscular block and muscle twitches when added 60 min after venom. The addition of the combination of Varespladib and antivenom 60 min after venom failed to produce further improvements than Varespladib alone. This demonstrates that the window of time in which antivenom remains effective is relatively short compared to Varespladib and small-molecule inhibitors may be effective in abrogating some activities of Chinese D. siamensis venom.

Oxilipin, a New Anti-cancer Phospholipase A2-like Protein from Iranian Caspian Cobra, Naja Naja Oxiana

The discovery of novel anti-cancer agents from natural resources is highly necessary. Concerning the above problem, the purpose of this study was to discover an anti-cancer compound from Caspian cobra venom. Fractionation of Caspian cobra venom was performed by gel filtration and IEX chromatography. The results showed an anti-cancer protein nominated as Oxilipin. Activity and toxicity of Oxilipin were studied on the colon SW480 cancer cell line using MTT, LDH release, PI staining, morphological cell analysis, hemolysis, and anti-proliferation assays. Oxilipin, an 11kDa protein purified from the venom of the Caspian cobra. LC/MS/MS analysis of obtained protein showed homology with Phospholipase A2 from ‎Naja naja oxiana. 40 µg/ml of Oxilipin can induce an apoptotic effect in SW480 cell line up to 90%; meanwhile, this amount can induce only one-third of cytotoxicity on a normal cell. In this study, Iranian cobra venom was found to have cytotoxic effects on SW480 colon cancer tumor cells, with the least cytotoxicity on normal cells on HEK-293. Given that Oxilipin has slight toxicity on normal cells, it can be hypothesized that the obtained peptide can be considered as a drug lead in an animal model study of colon cancer.

Dynamics of action of a Lys-49 and an Asp-49 PLA2s on inflammasome NLRP3 activation in murine macrophages

Phospholipases A₂ (PLA₂s) are proteins found in snake venoms with hemolytic, anticoagulant, myotoxic, edematogenic, bactericidal and inflammatory actions. In Bothrops jararacussu snake venom were isolated a Lys49-PLA₂ (BthTX-I) and an Asp49-PLA₂ (BthTX-II) with myotoxic and inflammatory actions. Both PLA₂s can activate the NLRP3 inflammasome, an intracytoplasmic platform that recognizes molecules released when tissue is damaged liberating IL-1β that contributes to the inflammatory response observed in envenoming. The dynamic of action of BthTX-I and BthTX-II in both thioglycollate (TG)-elicited macrophages and C2C12 myoblasts and the involvement of EP1 and EP2 receptors, and PGE₂ in NLRP3 inflammasome activation were evaluated. Both toxins induced PGE₂ liberation and inflammasome components (NLRP3, Caspase-1, ASC, IL-1β, and IL18), IL-6, P2X7, COX-1, COX-2, EP2 and EP4 gene expression in TG-elicited macrophages but not in C2C12 myoblasts. EP2 (PF04418948) and EP4 (GW627368X) inhibitors abolished this effect. Both PLA₂s also induced NLRP3 inflammasome protein expression that was abolished with the inhibitors used. Immunofluorescence and IL-1β assays confirmed the NLRP3 activation in TG-elicited macrophages with the participation of both EP2 and EP4 receptors confirming their involvement in this effect. All in all, BthTX-I and BthTX-II activate macrophages and induce the NLRP3 inflammasome complex activation with the participation of the PGE₂ via COX pathway and EP2 and EP4, both PGE₂ receptors, contributing to the local inflammatory effects observed in envenoming.

The chemistry of snake venom and its medicinal potential

The fascination and fear of snakes dates back to time immemorial, with the first scientific treatise on snakebite envenoming, the Brooklyn Medical Papyrus, dating from ancient Egypt. Owing to their lethality, snakes have often been associated with images of perfidy, treachery and death. However, snakes did not always have such negative connotations. The curative capacity of venom has been known since antiquity, also making the snake a symbol of pharmacy and medicine. Today, there is renewed interest in pursuing snake-venom-based therapies. This Review focuses on the chemistry of snake venom and the potential for venom to be exploited for medicinal purposes in the development of drugs. The mixture of toxins that constitute snake venom is examined, focusing on the molecular structure, chemical reactivity and target recognition of the most bioactive toxins, from which bioactive drugs might be developed. The design and working mechanisms of snake-venom-derived drugs are illustrated, and the strategies by which toxins are transformed into therapeutics are analysed. Finally, the challenges in realizing the immense curative potential of snake venom are discussed, and chemical strategies by which a plethora of new drugs could be derived from snake venom are proposed.

Clinical and Evolutionary Implications of Dynamic Coagulotoxicity Divergences in Bothrops (Lancehead Pit Viper) Venoms

Despite coagulotoxicity being a primary weapon for prey capture by Bothrops species (lancehead pit vipers) and coagulopathy being a major lethal clinical effect, a genus-wide comparison has not been undertaken. To fill this knowledge gap, we used thromboelastography to compare 37 venoms, from across the full range of geography, taxonomy, and ecology, for their action upon whole plasma and isolated fibrinogen. Potent procoagulant toxicity was shown to be the main venom effect of most of the species tested. However, the most basal species (B. pictus) was strongly anticoagulant; this is consistent with procoagulant toxicity being a novel trait that evolved within Bothrops subsequent to their split from anticoagulant American pit vipers. Intriguingly, two of the arboreal species studied (B. bilineatus and B. taeniatus) lacked procoagulant venom, suggesting differential evolutionary selection pressures. Notably, some terrestrial species have secondarily lost the procoagulant venom trait: the Mogi Mirim, Brazil locality of B. alternatus; San Andres, Mexico locality of B. asper; B. diporus; and the São Roque of B. jararaca. Direct action on fibrinogen was extremely variable; this is consistent with previous hypotheses regarding it being evolutionary decoupled due to procoagulant toxicity being the primary prey-capture weapon. However, human patients live long enough for fibrinogen depletion to be clinically significant. The extreme variability may be reflective of antivenom variability, with these results thereby providing a foundation for such future work of clinical relevance. Similarly, the venom diversification trends relative to ecological niche will also be useful for integration with natural history data, to reconstruct the evolutionary pressures shaping the venoms of these fascinating snakes.

A New Approach to Inhibiting Triple-Negative Breast Cancer: In Vitro, Ex Vivo and In Vivo Antiangiogenic Effect of BthTx-II, a PLA2-Asp-49 from Bothrops jararacussu Venom

Phospholipases A2 (PLA2) represent a superfamily of enzymes widely distributed in living organisms, with a broad spectrum of pharmacological activities and therapeutic potential. Anti-angiogenic strategies have become one of the main tools in fighting cancer. In this sense, the present work reports the inhibition of tumor angiogenesis induced by Asp-49 BthTX-II using in vitro, ex vivo and in vivo approaches. We demonstrate that BthTx-II inhibited cell adhesion, proliferation, and migration of human umbilical vein endothelial cells (HUVEC), as well as caused a reduction in the levels of endothelial growth factor (VEGF) during in vitro angiogenesis assays. BthTx-II was also able to inhibit the sprouting angiogenic process, by the ex vivo germination assay of the aortic ring; in addition, this toxin inhibited the migration and proliferation of HUVEC in co-culture with triple-negative breast cancer cells (e.g., MDA-MB-231 cells). Finally, in vivo tumor suppression and anti-angiogenic activities were analyzed using MDA-MB-231 cells with Matrigel injected into the chorioallantoic membrane of chicken embryo (CAM) for 7 days treatment with BthTx-II, showing a considerable reduction in vessel caliber, on the size and weight of tumors. Together, these results suggest an important antiangiogenic and antitumor role for BthTx-II, as a potential prototype for the development of new tools and antitumor drugs in cancer therapy.

Secreted Phospholipases A2 - not just Enzymes: Revisited

Secreted phospholipases A₂ (sPLA₂s) participate in a very broad spectrum of biological processes through their enzymatic activity and as ligands for membrane and soluble receptors. The physiological roles of sPLA₂s as enzymes have been very well described, while their functions as ligands are still poorly known. Since the last overview of sPLA₂-binding proteins (sPLA₂-BPs) 10 years ago, several important discoveries have occurred in this area. New and more sensitive analytical tools have enabled the discovery of additional sPLA₂-BPs, which are presented and critically discussed here. The structural diversity of sPLA₂-BPs reveals sPLA₂s as very promiscuous proteins, and we offer some structural explanations for this nature that makes these proteins evolutionarily highly advantageous. Three areas of physiological engagement of sPLA₂-BPs have appeared most clearly: cellular transport and signalling, and regulation of the enzymatic activity of sPLA₂s. Due to the multifunctionality of sPLA₂s, they appear to be exceptional pharmacological targets. We reveal the potential to exploit interactions of sPLA₂s with other proteins in medical terms, for the development of original diagnostic and therapeutic procedures. We conclude this survey by suggesting the priority questions that need to be answered.

BthTX-II from Bothrops jararacussu venom has variants with different oligomeric assemblies: An example of snake venom phospholipases A2 versatility

Phospholipases A₂ (PLA₂s) are found in almost every venomous snake family. In snakebites, some PLA₂s can quickly cause local myonecrosis, which may lead to permanent sequelae if antivenom is administered belatedly. They hydrolyse phospholipids in membranes through a catalytic calcium ions-dependent mechanism. BthTX-II is a basic PLA₂ and the second major component in the venom of Bothrops jararacussu. Herein, using the software SEQUENCE SLIDER, which integrates crystallographic, mass spectrometry and genetic data, we characterized the primary, tertiary and quaternary structure of two BthTX-II variants (called a and b), which diverge in 7 residues. Crystallographic structure BthTX-IIa is in a Tense-state with its distorted calcium binding loop buried in the dimer interface, contrarily, the novel BthTX-IIb structure is a monomer in a Relax-state with a fatty acid in the hydrophobic channel. Structural data in solution reveals that both variants are monomeric in neutral physiological conditions and mostly dimeric in an acidic environment, being catalytic active in both situations. Therefore, we propose two myotoxic mechanisms for BthTX-II, a catalytic one associated with the monomeric assembly, whereas the other has a calcium independent activity related to its C-terminal region, adopting a dimeric conformation similar to PLA₂-like proteins.

Advances in the Therapeutic Application of Small-Molecule Inhibitors and Repurposed Drugs against Snakebite

The World Health Organization has declared snakebite as a neglected tropical disease. Antivenom administration is the sole therapy against venomous snakebite; however, several limitations of this therapy reinforce the dire need for an alternative and/or additional treatment against envenomation. Inhibitors against snake venoms have been explored from natural resources and are synthesized in the laboratory; however, repurposing of small-molecule therapeutics (SMTs) against the principal toxins of snake venoms to inhibit their lethality and/or obnoxious effect of envenomation has been garnering greater attention owing to their established pharmacokinetic properties, low-risk attributes, cost-effectiveness, ease of administration, and storage stability. Nevertheless, SMTs are yet to be approved and commercialized for snakebite treatment. Therefore, we have systematically reviewed and critically analyzed the scenario of small synthetic inhibitors and repurposed drugs against snake envenomation from 2005 to date and proposed novel approaches and commercialization strategies for the development of efficacious therapies against snake envenomation.

Panacea within a Pandora's box: the antiparasitic effects of phospholipases A2 (PLA2s) from snake venoms

Parasitic diseases affect millions of individuals worldwide, mainly in low-income regions. There is no cure for most of these diseases, and the treatment relies on drugs that have side effects and lead to drug resistance, emphasizing the urgency to find new treatments. Snake venom has been gaining prominence as a rich source of molecules with antiparasitic potentials, such as phospholipases A₂ (PLA₂s). Here, we compile the findings involving PLA₂s with antiparasitic activities against helminths, Plasmodium, Toxoplasma, and trypanosomatids. We indicate their molecular features, highlighting the possible antiparasitic mechanisms of action of these proteins. We also demonstrate interactions between PLA₂s and some parasite membrane components, shedding light on potential targets for drug design that may provide better treatment for the illnesses caused by parasites.

The Search for Natural and Synthetic Inhibitors That Would Complement Antivenoms as Therapeutics for Snakebite Envenoming

A global strategy, under the coordination of the World Health Organization, is being unfolded to reduce the impact of snakebite envenoming. One of the pillars of this strategy is to ensure safe and effective treatments. The mainstay in the therapy of snakebite envenoming is the administration of animal-derived antivenoms. In addition, new therapeutic options are being explored, including recombinant antibodies and natural and synthetic toxin inhibitors. In this review, snake venom toxins are classified in terms of their abundance and toxicity, and priority actions are being proposed in the search for snake venom metalloproteinase (SVMP), phospholipase A2 (PLA2), three-finger toxin (3FTx), and serine proteinase (SVSP) inhibitors. Natural inhibitors include compounds isolated from plants, animal sera, and mast cells, whereas synthetic inhibitors comprise a wide range of molecules of a variable chemical nature. Some of the most promising inhibitors, especially SVMP and PLA2 inhibitors, have been developed for other diseases and are being repurposed for snakebite envenoming. In addition, the search for drugs aimed at controlling endogenous processes generated in the course of envenoming is being pursued. The present review summarizes some of the most promising developments in this field and discusses issues that need to be considered for the effective translation of this knowledge to improve therapies for tackling snakebite envenoming.

Inhibition of key enzymes linked to snake venom induced local tissue damage by kolaviron

OBJECTIVES

Snakebite envenoming is an important public health problem that threatens the lives of healthy individuals especially in many tropical countries like Nigeria. Antivenins, the only efficient approach for snakebite envenoming, are limited in their efficacy in the neutralization of local tissue damage. Snake venom phospholipase A₂ (PLA₂), protease, hyaluronidase and l-amino acid oxidase (LAAO) are the major hydrolytic enzymes involve in local tissue damage. Therefore, this study evaluates the inhibitory effect of kolaviron (KV) against Naja n. nigricollis (NNN) snake venom hydrolytic enzymes involved in local tissue damage.

METHODS

Kolaviron was evaluated for its ability to inhibit the hydrolytic enzyme activities of NNN venom phospholipase A₂ (PLA₂), protease, hyaluronidase and l-amino acid oxidase (LAAO). Present study also deals with the neutralization of NNN venom enzyme(s) induced complications such as myotoxic, edemic, hemolytic and procoagulant effects.

RESULTS

Kolaviron inhibited the PLA₂, protease, hyaluronidase and LAAO enzyme activities of NNN venom in a dose-dependent manner. Furthermore, myotoxic, edemic, hemolytic and procoagulant effects induced by NNN venom enzyme were neutralized significantly (p<0.05) when different doses of KV were pre-incubated with venom before assays.

CONCLUSIONS

These findings clearly present kolaviron as a potent inhibitor against NNN venom hydrolytic enzymes involved in local tissue damage and may act by either forming an inhibitor-enzyme complex that restricts the substrate availability to the enzyme or direct binding to the enzyme active site that affects the enzyme activity thereby mitigating venom-induced toxicity.

Biochemical and functional characterization of a new recombinant phospholipase A2 inhibitor from Crotalus durissus collilineatus snake serum

Phospholipase A₂ plays an important role in many diseases. Thus, the production of bioactive molecules, which can modulate PLA₂ activity, became an important target for the pharmaceutical industry. Previously, we demonstrated the inhibitory and anti-angiogenic effect of γCdcPLI, the natural PLA₂inhibitor from Crotalus durissus collilineatus. The aim of the present study was to recombinantly express the γCdcPLI inhibitor and analyze its biochemical and functional characteristics. Based on the amino acid sequence from the natural protein, we designed a synthetic gene for production of a non-tagged recombinant recγCdcPLI using the pHis-Parallel2 vector. To enable disulfide bond formation, protein expression was performed using E. coli Rosetta-gamiB. The protein was purified by anion and affinity chromatography with a yield of 5 mg/L. RecγCdcPLI showed similar secondary structure in CD and FTIR, revealing predominately β-strands. Analogous to the natural protein, recγCdcPLI was able to form oligomers of ~5.5 nm. The inhibitor was efficiently binding to PLA₂ from honeybee (Kd = 1.48 μM) and was able to inhibit the PLA₂ activity. Furthermore, it decreased the vessel formation in HUVEC cells, suggesting an anti-angiogenic potential. Heterologous production of recγCdcPLI is highly efficient and thus enables enhanced drug design for treatment of diseases triggered by PLA₂ activity.

Antibiofilm Activity of Acidic Phospholipase Isoform Isolated from Bothrops erythromelas Snake Venom

Introduction: Bacterial resistance is a worldwide public health problem, requiring new therapeutic options. An alternative approach to this problem is the use of animal toxins isolated from snake venom, such as phospholipases A₂ (PLA₂), which have important antimicrobial activities. Bothropserythromelas is one of the snake species in the northeast of Brazil that attracts great medical-scientific interest. Here, we aimed to purify and characterize a PLA₂ from B. erythromelas, searching for heterologous activities against bacterial biofilms. Methods: Venom extraction and quantification were followed by reverse-phase high-performance liquid chromatography (RP-HPLC) in C18 column, matrix-assisted ionization time-of-flight (MALDI-ToF) mass spectrometry, and sequencing by Edman degradation. All experiments were monitored by specific activity using a 4-nitro-3-(octanoyloxy) benzoic acid (4N₃OBA) substrate. In addition, hemolytic tests and antibacterial tests including action against Escherichiacoli, Staphylococcusaureus, and Acinetobacterbaumannii were carried out. Moreover, tests of antibiofilm action against A. baumannii were also performed. Results: PLA₂, after one purification step, presented 31 N-terminal amino acid residues and a molecular weight of 13.6564 Da, with enzymatic activity confirmed in 0.06 µM concentration. Antibacterial activity against S. aureus (IC₅₀ = 30.2 µM) and antibiofilm activity against A. baumannii (IC₅₀ = 1.1 µM) were observed. Conclusions: This is the first time that PLA₂ purified from B. erythromelas venom has appeared as an alternative candidate in studies of new antibacterial medicines.

Snake three-finger α-neurotoxins and nicotinic acetylcholine receptors: molecules, mechanisms and medicine

Snake venom three-finger α-neurotoxins (α-3FNTx) act on postsynaptic nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction (NMJ) to produce skeletal muscle paralysis. The discovery of the archetypal α-bungarotoxin (α-BgTx), almost six decades ago, exponentially expanded our knowledge of membrane receptors and ion channels. This included the localisation, isolation and characterization of the first receptor (nAChR); and by extension, the pathophysiology and pharmacology of neuromuscular transmission and associated pathologies such as myasthenia gravis, as well as our understanding of the role of α-3FNTxs in snakebite envenomation leading to novel concepts of targeted treatment. Subsequent studies on a variety of animal venoms have yielded a plethora of novel toxins that have revolutionized molecular biomedicine and advanced drug discovery from bench to bedside. This review provides an overview of nAChRs and their subtypes, classification of α-3FNTxs and the challenges of typifying an increasing arsenal of structurally and functionally unique toxins, and the three-finger protein (3FP) fold in the context of the uPAR/Ly6/CD59/snake toxin superfamily. The pharmacology of snake α-3FNTxs including their mechanisms of neuromuscular blockade, variations in reversibility of nAChR interactions, specificity for nAChR subtypes or for distinct ligand-binding interfaces within a subtype and the role of α-3FNTxs in neurotoxic envenomation are also detailed. Lastly, a reconciliation of structure-function relationships between α-3FNTx and nAChRs, derived from historical mutational and biochemical studies and emerging atomic level structures of nAChR models in complex with α-3FNTxs is discussed.

Insights into the antiviral activity of phospholipases A2 (PLA2s) from snake venoms

Viruses are associated with several human diseases that infect a large number of individuals, hence directly affecting global health and economy. Owing to the lack of efficient vaccines, antiviral therapy and emerging resistance strains, many viruses are considered as a potential threat to public health. Therefore, researches have been developed to identify new drug candidates for future treatments. Among them, antiviral research based on natural molecules is a promising approach. Phospholipases A₂ (PLA₂s) isolated from snake venom have shown significant antiviral activity against some viruses such as Dengue virus, Human Immunodeficiency virus, Hepatitis C virus and Yellow fever virus, and have emerged as an attractive alternative strategy for the development of novel antiviral therapy. Thus, this review provides an overview of remarkable findings involving PLA₂s from snake venom that possess antiviral activity, and discusses the mechanisms of action mediated by PLA₂s against different stages of virus replication cycle. Additionally, molecular docking simulations were performed by interacting between phospholipids from Dengue virus envelope and PLA₂s from Bothrops asper snake venom. Studies on snake venom PLA₂s highlight the potential use of these proteins for the development of broad-spectrum antiviral drugs.

Varespladib Inhibits the Phospholipase A2 and Coagulopathic Activities of Venom Components from Hemotoxic Snakes

Phospholipase A2 (PLA2) enzymes are important toxins found in many snake venoms, and they can exhibit a variety of toxic activities including causing hemolysis and/or anticoagulation. In this study, the inhibiting effects of the small molecule PLA2 inhibitor varespladib on snake venom PLA2s was investigated by nanofractionation analytics, which combined chromatography, mass spectrometry (MS), and bioassays. The venoms of the medically important snake species Bothrops asper, Calloselasma rhodostoma, Deinagkistrodon acutus, Daboia russelii, Echis carinatus, Echis ocellatus, and Oxyuranus scutellatus were separated by liquid chromatography (LC) followed by nanofractionation and interrogation of the fractions by a coagulation assay and a PLA2 assay. Next, we assessed the ability of varespladib to inhibit the activity of enzymatic PLA2s and the coagulopathic toxicities induced by fractionated snake venom toxins, and identified these bioactive venom toxins and those inhibited by varespladib by using parallel recorded LC-MS data and proteomics analysis. We demonstrated here that varespladib was not only capable of inhibiting the PLA2 activities of hemotoxic snake venoms, but can also effectively neutralize the coagulopathic toxicities (most profoundly anticoagulation) induced by venom toxins. While varespladib effectively inhibited PLA2 toxins responsible for anticoagulant effects, we also found some evidence that this inhibitory molecule can partially abrogate procoagulant venom effects caused by different toxin families. These findings further emphasize the potential clinical utility of varespladib in mitigating the toxic effects of certain snakebites.

Toxinology provides multidirectional and multidimensional opportunities: A personal perspective

In nature, toxins have evolved as weapons to capture and subdue the prey or to counter predators or competitors. When they are inadvertently injected into humans, they cause symptoms ranging from mild discomfort to debilitation and death. Toxinology is the science of studying venoms and toxins that are produced by a wide variety of organisms. In the past, the structure, function and mechanisms of most abundant and/or most toxic components were characterized to understand and to develop strategies to neutralize their toxicity. With recent technical advances, we are able to evaluate and determine the toxin profiles using transcriptomes of venom glands and proteomes of tiny amounts of venom. Enormous amounts of data from these studies have opened tremendous opportunities in many directions of basic and applied research. The lower costs for profiling venoms will further fuel the expansion of toxin database, which in turn will provide greater exciting and bright opportunities in toxin research.

An Appetite for Destruction: Detecting Prey-Selective Binding of α-Neurotoxins in the Venom of Afro-Asian Elapids

Prey-selective venoms and toxins have been documented across only a few species of snakes. The lack of research in this area has been due to the absence of suitably flexible testing platforms. In order to test more species for prey specificity of their venom, we used an innovative taxonomically flexible, high-throughput biolayer interferometry approach to ascertain the relative binding of 29 α-neurotoxic venoms from African and Asian elapid representatives (26 Naja spp., Aspidelaps scutatus, Elapsoidea boulengeri, and four locales of Ophiophagus hannah) to the alpha-1 nicotinic acetylcholine receptor orthosteric (active) site for amphibian, lizard, snake, bird, and rodent targets. Our results detected prey-selective, intraspecific, and geographical differences of α-neurotoxic binding. The results also suggest that crude venom that shows prey selectivity is likely driven by the proportions of prey-specific α-neurotoxins with differential selectivity within the crude venom. Our results also suggest that since the α-neurotoxic prey targeting does not always account for the full dietary breadth of a species, other toxin classes with a different pathophysiological function likely play an equally important role in prey immobilisation of the crude venom depending on the prey type envenomated. The use of this innovative and taxonomically flexible diverse assay in functional venom testing can be key in attempting to understanding the evolution and ecology of α-neurotoxic snake venoms, as well as opening up biochemical and pharmacological avenues to explore other venom effects.

Toxicological profile of medically relevant Crotalus species from Mexico and their neutralization by a Crotalus basiliscus/Bothrops asper antivenom

Specimens of the Crotalus genus represent a potential snakebite problem in Mexico, and despite the great number of species of Crotalus present in this country, only a few of them are relevant from a medical point of view. Crotalus envenomed patients can present a range of signs and symptoms, depending on the species involved, and their treatment is indistinctly with either of the anti-viperid antivenoms available in the Mexican Public Health System. One of these antivenoms is produced by immunization of horses with a mixture of only two venoms: Crotalus basiliscus and Bothrops asper venoms. In light of the high variability found in Crotalus species venom composition, it is important to demonstrate the cross-neutralization of this antivenom against other Crotalus species. Therefore, in this work the toxic variability of eight medically important Crotalus venoms from Mexico and its neutralization by the Crotalus basiliscus/Bothrops asper antivenom were assessed. The present study evidenced the variability of toxic and enzymatic activities among the following Crotalus venoms: (1) Crotalus atrox, (2) Crotalus basiliscus, (3) Crotalus culminatus, (4) Crotalus simus, (5) Crotalus tzabcan, (6) Crotalus scutulatus salvini, (7) Crotalus scutulatus scutulatus-A, and (8) Crotalus scutulatus scutulatus-B. All venoms studied possess lethal and hemorrhagic activity on a murine model, although there are important variations among the species; in contrast, the PLA₂ activity was similar for all venoms. Interestingly, only C. simus venom exhibited coagulant activity on human plasma under 100 μg. The antivenom neutralized the lethality and all the other assessed activities for all venoms tested. However, the dose required varied depending on the venom and the evaluated activity. Our preclinical data support the recommendation of using this antivenom to clinically manage Crotalus snakebites produced by the species assessed in this study. Nonetheless, only clinical trials could categorically validate these results.

Human neutrophils functionality under effect of an Asp49 phospholipase A2 isolated from Bothrops atrox venom

Bothrops envenomation is associated with a cellular inflammatory response, characterized by pronounced neutrophil infiltration at the site of injury. Neutrophils act as the first line of defence, owing to their ability to migrate to the infected tissue, promoting an acute inflammatory response. At the site of inflammation, neutrophils perform defence functions such as phagocytosis, release of proteolytic enzymes, generation of reactive oxygen species (ROS), and synthesis of inflammatory mediators such as cytokines and lipid mediators. Neutrophils can also form neutrophil extracellular nets (NETs), webs composed of chromatin and granule proteins. This occurs after neutrophil activation and delivers high concentrations of anti-microbial molecules to the site of injury. This study evaluated the impact of BaTX-II, an Asp49 phospholipase A₂ (PLA₂) isolated from Bothrops atrox snake venom on human neutrophils in vitro. At non-toxic concentrations, BaTX-II induced hydrogen peroxide production by neutrophils, and this was reduced by wortmannin, a PI3K inhibitor. BaTX-II stimulated IL-1β, IL-8, LTB₄, myeloperoxidase (MPO), and DNA content release, consistent with NET formation. This is the first study to show the triggering of relevant pro-inflammatory events by PLA₂ Asp49 isolated from secretory venom.

Amplification of Snake Venom Toxicity by Endogenous Signaling Pathways

The active components of snake venoms encompass a complex and variable mixture of proteins that produce a diverse, but largely stereotypical, range of pharmacologic effects and toxicities. Venom protein diversity and host susceptibilities determine the relative contributions of five main pathologies: neuromuscular dysfunction, inflammation, coagulopathy, cell/organ injury, and disruption of homeostatic mechanisms of normal physiology. In this review, we describe how snakebite is not only a condition mediated directly by venom, but by the amplification of signals dysregulating inflammation, coagulation, neurotransmission, and cell survival. Although venom proteins are diverse, the majority of important pathologic events following envenoming follow from a small group of enzyme-like activities and the actions of small toxic peptides. This review focuses on two of the most important enzymatic activities: snake venom phospholipases (svPLA2) and snake venom metalloproteases (svMP). These two enzyme classes are adept at enabling venom to recruit homologous endogenous signaling systems with sufficient magnitude and duration to produce and amplify cell injury beyond what would be expected from the direct impact of a whole venom dose. This magnification produces many of the most acutely important consequences of envenoming as well as chronic sequelae. Snake venom PLA2s and MPs enzymes recruit prey analogs of similar activity. The transduction mechanisms that recruit endogenous responses include arachidonic acid, intracellular calcium, cytokines, bioactive peptides, and possibly dimerization of venom and prey protein homologs. Despite years of investigation, the precise mechanism of svPLA2-induced neuromuscular paralysis remains incomplete. Based on recent studies, paralysis results from a self-amplifying cycle of endogenous PLA2 activation, arachidonic acid, increases in intracellular Ca2+ and nicotinic receptor deactivation. When prolonged, synaptic suppression supports the degeneration of the synapse. Interaction between endothelium-damaging MPs, sPLA2s and hyaluronidases enhance venom spread, accentuating venom-induced neurotoxicity, inflammation, coagulopathy and tissue injury. Improving snakebite treatment requires new tools to understand direct and indirect effects of envenoming. Homologous PLA2 and MP activities in both venoms and prey/snakebite victim provide molecular targets for non-antibody, small molecule agents for dissecting mechanisms of venom toxicity. Importantly, these tools enable the separation of venom-specific and prey-specific pathological responses to venom.

Binding of a Naja naja venom acidic phospholipase A2 cognate complex to membrane-bound vimentin of rat L6 cells: Implications in cobra venom-induced cytotoxicity

An acidic phospholipase A₂ enzyme (NnPLA₂-I) interacts with three finger toxins (cytotoxin and neurotoxin) from Naja naja venom to form cognate complexes to enhance its cytotoxicity towards rat L6 myogenic cells. The cytotoxicity was further enhanced in presence of trace quantity of venom nerve growth factor. The purified rat myoblast cell membrane protein showing interaction with NnPLA₂-I was identified as vimentin by LC-MS/MS analysis. The ELISA, immunoblot and spectrofluorometric analyses showed greater binding of NnPLA₂-I cognate complex to vimentin as compared to the binding of individual NnPLA₂-I. The immunofluorescence and confocal microscopy studies evidenced the internalization of NnPLA₂-I to partially differentiated myoblasts post binding with vimentin in a time-dependent manner. Pre-incubation of polyvalent antivenom with NnPLA₂-I cognate complex demonstrated better neutralization of cytotoxicity towards L6 cells as compared to exogenous addition of polyvalent antivenom 60-240 min post treatment of L6 cells with cognate complex suggesting clinical advantage of early antivenom treatment to prevent cobra venom-induced cytotoxicity. The in silico analysis showed that 19-22 residues, inclusive of Asp48 residue, of NnPLA₂-I preferentially binds with the rod domain (99-189 and 261-335 regions) of vimentin with a predicted free binding energy (ΔG) and dissociation constant (K_D) values of -12.86 kcal/mol and 3.67 × 10^-10 M, respectively; however, NnPLA₂-I cognate complex showed greater binding with the same regions of vimentin indicating the pathophysiological significance of cognate complex in cobra venom-induced cytotoxicity.

Detection and quantification of a β-neurotoxin (crotoxin homologs) in the venom of the rattlesnakes Crotalus simus, C. culminatus and C. tzabcan from Mexico

Snake venom may vary in composition and toxicity across the geographic distribution of a species. In the case of the three species of the Neotropical rattlesnakes Crotalus simus, C. culminatus and C. tzabcan recent research has revealed that their venoms can contain a neurotoxic component (crotoxin homologs), but is not always the case. In the present work, we detected and quantified crotoxin homologs in venom samples from three species distributed across Mexico, to describe variation at the individual and subspecific levels, using slot blot and ELISA immunoassays. We found that all C. simus individuals analyzed had substantial percentages of crotoxin homologs in their venoms (7.6–44.3%). In contrast, C. culminatus lacked them completely and six of ten individuals of the species C. tzabcan had low percentages (3.0–7.7%). We also found a direct relationship between the lethality of a venom and the percentage of crotoxin homologs it contained, indicating that the quantity of this component influences venom lethality in the rattlesnake C. simus.

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Monoclonal antibodies were produced that specifically recognized crotoxin homologs in venoms of Crotalus species.

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Crotoxin homologs were quantified in three species of Crotalus: C. simus, C. culminatus and C. tzabcan.

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All specimens of C. simus contained crotoxin homologs at different levels, while C. culminatus venoms lacked them completely.

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In C. tzabcan, some venoms possess and other lack crotoxin homologs.

Lapachol and synthetic derivatives: in vitro and in vivo activities against Bothrops snake venoms

Background

It is known that local tissue injuries incurred by snakebites are quickly instilled causing extensive, irreversible, tissue destruction that may include loss of limb function or even amputation. Such injuries are not completely neutralized by the available antivenins, which in general are focused on halting systemic effects. Therefore it is prudent to investigate the potential antiophidic effects of natural and synthetic compounds, perhaps combining them with serum therapy, to potentially attenuate or eliminate the adverse local and systemic effects of snake venom. This study assessed a group of quinones that are widely distributed in nature and constitute an important class of natural products that exhibit a range of biological activities. Of these quinones, lapachol is one of the most important compounds, having been first isolated in 1882 from the bark of Tabebuia avellanedae.

Methodology/Principal findings

It was investigated the ability of lapachol and some new potential active analogues based on the 2-hydroxi-naphthoquinone scaffold to antagonize important activities of Bothrops venoms (Bothrops atrox and Bothrops jararaca) under different experimental protocols in vitro and in vivo. The bioassays used to test the compounds were: procoagulant, phospholipase A₂, collagenase and proteolytic activities in vitro, venom-induced hemorrhage, edematogenic, and myotoxic effects in mice. Proteolytic and collagenase activities of Bothrops atrox venom were shown to be inhibited by lapachol and its analogues 3a, 3b, 3c, 3e. The inhibition of these enzymatic activities might help to explain the effects of the analogue 3a in vivo, which decreased skin hemorrhage induced by Bothrops venom. Lapachol and the synthetic analogues 3a and 3b did not inhibit the myotoxic activity induced by Bothrops atrox venom. The negative protective effect of these compounds against the myotoxicity can be partially explained by their lack of ability to effectively inhibit phospholipase A₂ venom activity. Bothrops atrox venom also induced edema, which was significantly reduced by the analogue 3a.

Conclusions

This research using a natural quinone and some related synthetic quinone compounds has shown that they exhibit antivenom activity; especially the compound 3a. The data from 3a showed a decrease in inflammatory venom effects, presumably those that are metalloproteinase-derived. Its ability to counteract such snake venom activities contributes to the search for improving the management of venomous snakebites.

Effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin

In this work, we have studied the effect of Crotalus basiliscus snake venom on the redox reaction of myoglobin (Mb), and by means of electrochemical techniques, we have shown that this reaction is undoubtedly affected following the interaction with the venom. Surface plasmon resonance, electrophoresis, UV-Vis, and circular dichroism showed that the interaction involves the attachment of some constituent of the venom to the protein, although not affecting its first and secondary structures. Mass spectra support this suggestion by showing the appearance of signals assigned to the Mb dimer and to a new species resulting from the interaction between Mb and the venom proteins. In addition, the mass spectra suggest the aromatic amino acids of myoglobin, mainly tryptophan and phenylalanine, are more exposed to the solvent medium upon the exposure to the venom solution. The results altogether indicate that the harmful effects of the venom of Crotalus basiliscus snake are likely connected to the blocking of the redox site of Mb.

Variability in venom composition of European viper subspecies limits the cross-effectiveness of antivenoms

Medically relevant cases of snakebite in Europe are predominately caused by European vipers of the genus Vipera. Systemic envenoming by European vipers can cause severe pathology in humans and different clinical manifestations are associated with different members of this genus. The most representative vipers in Europe are V. aspis and V. berus and neurological symptoms have been reported in humans envenomed by the former but not by the latter species. In this study we determined the toxicological profile of V. aspis and V. berus venoms in vivo in mice and we tested the effectiveness of two antivenoms, commonly used as antidotes, in counteracting the specific activities of the two venoms. We found that V. aspis, but not V. berus, is neurotoxic and that this effect is due to the degeneration of peripheral nerve terminals at the NMJ and is not neutralized by the two tested antisera. Differently, V. berus causes a haemorrhagic effect, which is efficiently contrasted by the same antivenoms. These results indicate that the effectiveness of different antisera is strongly influenced by the variable composition of the venoms and reinforce the arguments supporting the use polyvalent antivenoms.

A novel bactericidal homodimeric PLA2 group-I from Walterinnesia aegyptia venom

A novel non-toxic phospholipase A₂ was purified to homogeneity in a single chromatography step from the venom of Walterinnesia aegyptia, a monotypic elapid snake caught in Saudi Arabia, and its antimicrobial and hemolytic properties were evaluated as well. This enzyme, namely WaPLA₂, is a homodimer with an estimated molecular mass of 30 kDa, and its NH₂-terminal sequence exhibits a significant degree of similarity with PLA₂ group-I. At optimal pH (8.5) and temperature (45 °C), the purified PLA₂ exhibited a specific activity of 2100 U/mg, and it requires bile salts and Ca²⁺ for its activity. However, other cations such as Cd²⁺ and Hg²⁺ diminished the enzyme activity remarkably, thereby suggesting that the catalytic site arrangement has an exclusive structure for Ca²⁺ binding. Furthermore, WaPLA₂ maintained almost 100% and 60% of its full activity in a pH range of 6.0-10 after 24 h incubation or after 60 min treatment at 70 °C, respectively. In the biological activity assays, WaPLA₂ displayed potent indirectly hemolytic and antimicrobial activities that were strongly correlated. These promising findings encourage further in-depth research to understand the molecular mechanism of WaPLA₂'s antimicrobial properties for its possible use as a potential therapeutic lead molecule for treating infections.

Unresolved issues in the understanding of the pathogenesis of local tissue damage induced by snake venoms

Snakebite envenoming by viperid species, and by some elapids, is characterized by a complex pattern of tissue damage at the anatomical site of venom injection. In severe cases, tissue destruction may be so extensive as to lead to permanent sequelae, with serious pathophysiological, social and psychological consequences. Significant advances have been performed in the study of venom-induced tissue damage, including identification and characterization of the toxins involved, insights into the mechanisms of action of venoms and toxins, and study of tissue responses to venom-induced injury. Nevertheless, much remains to be known and understood on the pathogenesis of these alterations. This review focuses on some of the pending issues in the topic of snake venom-induced local tissue damage. The traditional 'reductionist' approach, which has predominated in the study of snake venoms and their actions, needs to be complemented by more integrative and holistic perspectives aimed at capturing the complexity of these pathological alterations. Future advances in the study of these topics will certainly pave the way for innovative therapeutic interventions, with the goal of reducing the impact of this aspect of snakebite envenoming.

Synergistic strategies of predominant toxins in snake venoms

Synergism is a significant phenomenon present in snake venoms that may be an evolving strategy to potentiate toxicities. Synergism exists between different toxins or toxin complexes in various snake venoms, with phospholipaseA₂s (PLA₂s) (toxins or subunits) the main enablers. The predominant toxins, snake venom PLA₂s, metalloproteases (SVMPs), serine proteases (SVSPs) and three-finger toxins (3FTxs), play essential roles in synergistic processes. The hypothetical mechanisms of synergistic effect can be generalized under the effects of amplification and chaperoning. The Toxicity Score is among the few quantitative methods to assess synergism. Selection of toxins involved in synergistically enhanced toxicity as the targets are important for development of novel antivenoms or inhibitors.

Cross-recognition of a pit viper (Crotalinae) polyspecific antivenom explored through high-density peptide microarray epitope mapping

Snakebite antivenom is a 120 years old invention based on polyclonal mixtures of antibodies purified from the blood of hyper-immunized animals. Knowledge on antibody recognition sites (epitopes) on snake venom proteins is limited, but may be used to provide molecular level explanations for antivenom cross-reactivity. In turn, this may help guide antivenom development by elucidating immunological biases in existing antivenoms. In this study, we have identified and characterized linear elements of B-cell epitopes from 870 pit viper venom protein sequences by employing a high-throughput methodology based on custom designed high-density peptide microarrays. By combining data on antibody-peptide interactions with multiple sequence alignments of homologous toxin sequences and protein modelling, we have determined linear elements of antibody binding sites for snake venom metalloproteases (SVMPs), phospholipases A₂s (PLA₂s), and snake venom serine proteases (SVSPs). The studied antivenom antibodies were found to recognize linear elements in each of the three enzymatic toxin families. In contrast to a similar study of elapid (non-enzymatic) neurotoxins, these enzymatic toxins were generally not recognized at the catalytic active site responsible for toxicity, but instead at other sites, of which some are known for allosteric inhibition or for interaction with the tissue target. Antibody recognition was found to be preserved for several minor variations in the protein sequences, although the antibody-toxin interactions could often be eliminated completely by substitution of a single residue. This finding is likely to have large implications for the cross-reactivity of the antivenom and indicate that multiple different antibodies are likely to be needed for targeting an entire group of toxins in these recognized sites.

Although snakebite antivenom is a 120-year-old invention, saving lives and limbs of thousands of snakebite victims every year, little is known about the mechanisms and molecular interactions of how antivenoms neutralize snake toxins. Antivenoms are produced by immunizing large animals with cocktails of snake venoms resulting in antibodies recognizing toxic as well as non-toxic venom proteins to variable degrees. As a result, high doses of antivenom are needed for treating a snakebite victim, causing more severe adverse reactions due to a high burden of heterologous antivenom proteins. For the first time, we have characterized the antibody recognition sites on hundreds of pit viper toxins using high-throughput peptide microarray technology and an antivenom specific for three pit vipers inflicting a high number of bites in Central America. Most pit viper toxins are enzymes known to have a catalytic site important for toxicity. However, our results suggest that the employed antivenom generally does not target such sites, but instead inhibits toxicity by binding to alternative sites, possibly causing conformational shifts in the toxin structures or interference with toxin-target recognition. The identification of these toxin-specific recognition sites may explain why the antivenom is effective against certain snakebites from pit vipers whose venoms are not part of the immunization mixture.

Coralsnake Venomics: Analyses of Venom Gland Transcriptomes and Proteomes of Six Brazilian Taxa

Venom gland transcriptomes and proteomes of six Micrurus taxa (M. corallinus, M. lemniscatus carvalhoi, M. lemniscatus lemniscatus, M. paraensis, M. spixii spixii, and M. surinamensis) were investigated, providing the most comprehensive, quantitative data on Micrurus venom composition to date, and more than tripling the number of Micrurus venom protein sequences previously available. The six venomes differ dramatically. All are dominated by 2-6 toxin classes that account for 91-99% of the toxin transcripts. The M. s. spixii venome is compositionally the simplest. In it, three-finger toxins (3FTxs) and phospholipases A₂ (PLA₂s) comprise >99% of the toxin transcripts, which include only four additional toxin families at levels ≥0.1%. Micrurus l. lemniscatus venom is the most complex, with at least 17 toxin families. However, in each venome, multiple structural subclasses of 3FTXs and PLA₂s are present. These almost certainly differ in pharmacology as well. All venoms also contain phospholipase B and vascular endothelial growth factors. Minor components (0.1-2.0%) are found in all venoms except that of M. s. spixii. Other toxin families are present in all six venoms at trace levels (<0.005%). Minor and trace venom components differ in each venom. Numerous novel toxin chemistries include 3FTxs with previously unknown 8- and 10-cysteine arrangements, resulting in new 3D structures and target specificities. 9-cysteine toxins raise the possibility of covalent, homodimeric 3FTxs or heterodimeric toxins with unknown pharmacologies. Probable muscarinic sequences may be reptile-specific homologs that promote hypotension via vascular mAChRs. The first complete sequences are presented for 3FTxs putatively responsible for liberating glutamate from rat brain synaptosomes. Micrurus C-type lectin-like proteins may have 6-9 cysteine residues and may be monomers, or homo- or heterodimers of unknown pharmacology. Novel KSPIs, 3× longer than any seen previously, appear to have arisen in three species by gene duplication and fusion. Four species have transcripts homologous to the nociceptive toxin, (MitTx) α-subunit, but all six species had homologs to the β-subunit. The first non-neurotoxic, non-catalytic elapid phospholipase A₂s are reported. All are probably myonecrotic. Phylogenetic analysis indicates that the six taxa diverged 15-35 million years ago and that they split from their last common ancestor with Old World elapines nearly 55 million years ago. Given their early diversification, many cryptic micrurine taxa are anticipated.

rBaltMIP, a recombinant alpha-type myotoxin inhibitor from Bothrops alternatus (Rhinocerophis alternatus) snake, as a potential candidate to complement the antivenom therapy

Phospholipase A₂ inhibitors (PLIs) are important targets in the search and development of new drugs. This study aimed at evaluating the potential of an alpha-type phospholipase A₂ inhibitor from Bothrops alternatus (Rhinocerophis alternatus) snake in its recombinant form (rBaltMIP) to complement the conventional antivenom therapy. Biochemical experiments showed that rBaltMIP presented pI 5.8 and molecular masses of ∼21 kDa by SDS-PAGE and 19.57 kDa by MALDI/TOF MS. After tryptic peptides sequencing, the results were compared with other PLIs available in databases, showing 100% identity between rBaltMIP and its native inhibitor BaltMIP and from 92% to 96% identity with other inhibitors. Myotoxic activities of BthTX-I and BthTX-II toxins were measured via plasma CK levels, showing myotoxic effective concentrations (EC50) of 0.1256 μg/μL and 0.6183 μg/μL, respectively. rBaltMIP neutralized the myotoxicity caused by these two toxins up to 65%, without promoting primary antibody response against itself. Nevertheless, this recombinant PLI was immunogenic when standard immunization protocol with Freud's adjuvant was used. In paw edema assays, EC50 of 0.02581 μg/μL and 0.02810 μg/μL, respectively, were observed with edema reductions of up to 40% by rBaltMIP, suggesting its use as an additional antivenom. In addition, myotoxicity neutralization experiments with the myotoxin BthTX-I showed that rBaltMIP was more effective in inhibiting muscle damage than the conventional antivenom. Thus, considering the severity of envenomations due to Bothrops alternatus (Rhinocerophis alternatus) and the low neutralization of their local effects (such as myotoxicity) by the current antivenoms, rBaltMIP is a promising molecule for the development of novel therapeutic strategies for clinical applications.