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

In vivo neutralization of coral snake venoms with an oligoclonal nanobody mixture in a murine challenge model

Oligoclonal mixtures of broadly-neutralizing antibodies can neutralize complex compositions of similar and dissimilar antigens, making them versatile tools for the treatment of e.g., infectious diseases and animal envenomations. However, these biotherapeutics are complicated to develop due to their complex nature. In this work, we describe the application of various strategies for the discovery of cross-neutralizing nanobodies against key toxins in coral snake venoms using phage display technology. We prepare two oligoclonal mixtures of nanobodies and demonstrate their ability to neutralize the lethality induced by two North American coral snake venoms in mice, while individual nanobodies fail to do so. We thus show that an oligoclonal mixture of nanobodies can neutralize the lethality of venoms where the clinical syndrome is caused by more than one toxin family in a murine challenge model. The approaches described may find utility for the development of advanced biotherapeutics against snakebite envenomation and other pathologies where multi-epitope targeting is beneficial.

Unveiling Novel Kunitz- and Waprin-Type Toxins in the Micrurus mipartitus Coral Snake Venom Gland: An In Silico Transcriptome Analysis

Kunitz-type peptide expression has been described in the venom of snakes of the Viperidae, Elapidae and Colubridae families. This work aimed to identify these peptides in the venom gland transcriptome of the coral snake Micrurus mipartitus. Transcriptomic analysis revealed a high diversity of venom-associated Kunitz serine protease inhibitor proteins (KSPIs). A total of eight copies of KSPIs were predicted and grouped into four distinctive types, including short KSPI, long KSPI, Kunitz-Waprin (Ku-WAP) proteins, and a multi-domain Kunitz-type protein. From these, one short KSPI showed high identity with Micrurus tener and Austrelaps superbus. The long KSPI group exhibited similarity within the Micrurus genus and showed homology with various elapid snakes and even with the colubrid Pantherophis guttatus. A third group suggested the presence of Kunitz domains in addition to a whey-acidic-protein-type four-disulfide core domain. Finally, the fourth group corresponded to a transcript copy with a putative 511 amino acid protein, formerly annotated as KSPI, which UniProt classified as SPINT1. In conclusion, this study showed the diversity of Kunitz-type proteins expressed in the venom gland transcriptome of M. mipartitus.

The Cloning and Characterization of a Three-Finger Toxin Homolog (NXH8) from the Coralsnake Micrurus corallinus That Interacts with Skeletal Muscle Nicotinic Acetylcholine Receptors

Coralsnakes (Micrurus spp.) are the only elapids found throughout the Americas. They are recognized for their highly neurotoxic venom, which is comprised of a wide variety of toxins, including the stable, low-mass toxins known as three-finger toxins (3FTx). Due to difficulties in venom extraction and availability, research on coralsnake venoms is still very limited when compared to that of other Elapidae snakes like cobras, kraits, and mambas. In this study, two previously described 3FTx from the venom of M. corallinus, NXH1 (3SOC1_MICCO), and NXH8 (3NO48_MICCO) were characterized. Using in silico, in vitro, and ex vivo experiments, the biological activities of these toxins were predicted and evaluated. The results showed that only NXH8 was capable of binding to skeletal muscle cells and modulating the activity of nAChRs in nerve-diaphragm preparations. These effects were antagonized by anti-rNXH8 or antielapidic sera. Sequence analysis revealed that the NXH1 toxin possesses eight cysteine residues and four disulfide bonds, while the NXH8 toxin has a primary structure similar to that of non-conventional 3FTx, with an additional disulfide bond on the first loop. These findings add more information related to the structural diversity present within the 3FTx class, while expanding our understanding of the mechanisms of the toxicity of this coralsnake venom and opening new perspectives for developing more effective therapeutic interventions.

Comparing morphological and secretory aspects of cephalic glands among the New World coral snakes brings novel insights on their biological roles

Oral and other cephalic glands have been surveyed by several studies with distinct purposes. Despite the wide diversity and medical relevance of the New World coral snakes, studies focusing on understanding the biological roles of the glands within this group are still scarce. Specifically, the venom glands of some coral snakes were previously investigated but all other cephalic glands remain uncharacterized. In this sense, performing morphological and molecular analysis of these glands may help better understand their biological role. Here, we studied the morphology of the venom, infralabial, rictal, and harderian glands of thirteen species of Micrurus and Micruroides euryxanthus. We also performed a molecular characterization of these glands from selected species of Micrurus using transcriptomic and proteomic approaches. We described substantial morphological variation in the cephalic glands of New World coral snakes and structural evidence for protein-secreting cells in the inferior rictal glands. Our molecular analysis revealed that the venom glands, as expected, are majorly devoted to toxin production, however, the infralabial and inferior rictal glands also expressed some toxin genes at low to medium levels, despite the marked morphological differences. On the other hand, the harderian glands were dominated by the expression of lipocalins, but do not produce toxins. Our integrative analysis, including the prediction of biological processes and pathways, helped decipher some important traits of cephalic glands and better understand their biology.

Involvement of phospholipase A2 in the neuromuscular blockade caused by coralsnake (Micrurus spp.) venoms in mouse phrenic nerve-diaphragm preparations in vitro

In this work, we examined the neuromuscular blockade caused by venoms from four South-American coralsnakes (Micrurus altirostris - MA, M. corallinus - MC, M. spixii - MS, and M. dumerilii carinicauda - MDC) and the ability of varespladib (VPL), a phospholipase A2 (PLA2) inhibitor, to attenuate this blockade. PLA2 activity was determined using a colorimetric assay and a fixed amount of venom (10 μg). Neurotoxicity was assayed using a single concentration of venom (10 μg/ml) in mouse phrenic nerve-diaphragm (PND) preparations mounted for myographic recordings and then subjected to histological analysis. All venoms showed PLA2 activity, with MS and MA venoms having the highest (15.53 ± 1.9 A425 nm/min) and lowest (0.23 ± 0.14 A425 nm/min) activities, respectively. VPL (292 and 438 μM) inhibited the PLA2 activity of all venoms, although that of MA venom was least affected. All venoms caused neuromuscular blockade, with MS and MDC venoms causing the fastest and slowest 100% blockade [in 40 ± 3 min and 120 ± 6 min (n = 4), respectively]; MA and MC produced complete blockade within 90-100 min. Preincubation of venoms with 292 μM VPL attenuated the blockade to varying degrees: the greatest inhibition was seen with MDC venom and blockade by MS venom was unaffected by this inhibitor. These results indicate that PLA2 has a variable contribution to coralsnake venom-induced neuromuscular blockade in vitro, with the insensitivity of MS venom to VPL suggesting that blockade by this venom is mediated predominantly by post-synaptically-active α-neurotoxins.

Three finger toxins of elapids: structure, function, clinical applications and its inhibitors

The WHO lists snakebite as a "neglected tropical disease". In tropical and subtropical areas, envenoming is an important public health issue. This review article describes the structure, function, chemical composition, natural inhibitors, and clinical applications of Elapids' Three Finger Toxins (3FTX) using scientific research data. The primary venomous substance belonging to Elapidae is 3FTX, that targets nAChR. Three parallel β-sheets combine to create 3FTX, which has four or five disulfide bonds. The three primary types of 3FTX are short-chain, long-chain, and nonconventional 3FTX. The functions of 3FTX depend on the specific toxin subtype and the target receptor or ion channel. The well-known effect of 3FTX is probably neurotoxicity because of the severe consequences of muscular paralysis and respiratory failure in snakebite victims. 3FTX have also been studied for their potential clinical applications. α-bungarotoxin has been used as a molecular probe to study the structure and function of nAChRs (Nicotinic Acetylcholine Receptors). Acid-sensing ion channel (ASIC) isoforms 1a and 1b are inhibited by Mambalgins, derived from Black mamba venom, which hinders their function and provide an analgesic effect. α- Cobra toxin is a neurotoxin purified from Chinese cobra (Naja atra) binds to nAChR at the neuronal junction and causes an analgesic effect for moderate to severe pain. Some of the plants and their compounds have been shown to inhibit the activity of 3FTX, and their mechanisms of action are discussed.

Exploring the antibacterial potential of venoms from Argentinian animals

The resistance to antimicrobials developed by several bacterial species has become one of the main health problems in recent decades. It has been widely reported that natural products are important sources of antimicrobial compounds. Considering that animal venoms are under-explored in this line of research, in this study, we screened the antibacterial activity of venoms of eight snake and five lepidopteran species from northeastern Argentina. Twofold serial dilutions of venoms were tested by the agar well-diffusion method and the minimum inhibitory concentration (MIC) determination against seven bacterial strains. We studied the comparative protein profile of the venoms showing antibacterial activity. Only the viperid and elapid venoms showed remarkable dose-dependent antibacterial activity towards most of the strains tested. Bothrops diporus venom showed the lowest MIC values against all the strains, and S. aureus ATCC 25923 was the most sensitive strain for all the active venoms. Micrurus baliocoryphus venom was unable to inhibit the growth of Enterococcus faecalis. Neither colubrid snake nor lepidopteran venoms exhibited activity on any bacterial strain tested. The snake venoms exhibiting antibacterial activity showed distinctive protein profiles by SDS-PAGE, highlighting that we could reveal for the first time the main protein families which may be thought to contribute to the antibacterial activity of M. baliocoryphus venom. This study paves the way to search for new antibacterial agents from Argentinian snake venoms, which may be a further opportunity to give an added value to the local biodiversity.

Toxic and antigenic characterization of Peruvian Micrurus surinamensis coral snake venom

Micrurus surinamensis is a semi-aquatic coral snake found in primary forest region and can cause relevant human accidents. In this work we investigated the toxic and antigenic activities of the Peruvian Micrurus surinamensis venom (MsV). We found that MsV show hyaluronidase activity but lack LAAO and PLA₂ enzymatic activities. Interestingly, MsV induce edematogenic responses but cannot cause nociceptive effects. Furthermore, MsV can reduce in vitro cell viability in MGSO-3 cell line derived from human breast cancer tissue. To evaluate its antigenic potential, rabbits were immunized with MsV, which proved to be immunogenic. ELISA, immunobloting and in vivo neutralization assays demonstrated that the specific rabbit anti-MsV antivenom is more efficient than the therapeutic Brazilian antivenom in recognizing and neutralizing the lethal activity of MsV. MsV differs in protein profile and biological activities from M. frontalis venom (MfV), used as control, which impairs its recognition and neutralization by Brazilian therapeutic anti-elapidic antivenom. We performed a SPOT immunoassay for the identification of B-cell linear epitopes in the main toxins described for MsV targeted by the elicited neutralizing antibodies previously produced. A membrane containing 15-mer peptides representing the sequences of five 3TFxs and five PLA₂s was produced and probed with anti- MsV antibodies. Results revealed important regions in 3FTx toxins for venom neutralization. Identifying the main MsV components and its biological activities can be helpful in guiding the production of antivenoms and in the optimization of treatment for coral snake envenomation in Brazil.

Cardiac Effects of Micrurus corallinus and Micrurus dumerilii carinicauda (Elapidae) Venoms and Neutralization by Brazilian Coralsnake Antivenom and Varespladib

In this work, we examined the action of two South American coralsnake (Micrurus corallinus and Micrurus dumerilii carinicauda) venoms on rat heart function in the absence and presence of treatment with Brazilian coralsnake antivenom (CAV) and varespladib (VPL), a potent phospholipase A₂ inhibitor. Anesthetized male Wistar rats were injected with saline (control) or a single dose of venom (1.5 mg/kg, i.m.) and monitored for alterations in echocardiographic parameters, serum CK-MB levels and cardiac histomorphology, the latter using a combination of fractal dimension and histopathological methods. Neither of the venoms caused cardiac functional alterations 2 h after venom injection; however, M. corallinus venom caused tachycardia 2 h after venom injection, with CAV (given i.p. at an antivenom:venom ratio of 1:1.5, v/w), VPL (0.5 mg/kg, i.p.) and CAV + VPL preventing this increase. Both venoms increased the cardiac lesional score and serum CK-MB levels compared to saline-treated rats, but only the combination of CAV + VPL prevented these alterations, although VPL alone was able to attenuate the increase in CK-MB caused by M. corallinus venom. Micrurus corallinus venom increased the heart fractal dimension measurement, but none of the treatments prevented this alteration. In conclusion, M. corallinus and M. d. carinicauda venoms caused no major cardiac functional alterations at the dose tested, although M. corallinus venom caused transient tachycardia. Both venoms caused some cardiac morphological damage, as indicated by histomorphological analyses and the increase in circulating CK-MB levels. These alterations were consistently attenuated by a combination of CAV and VPL.

Immunity in Sea Turtles: Review of a Host-Pathogen Arms Race Millions of Years in the Running

The immune system of sea turtles is not completely understood. Sea turtles (as reptiles) bridge a unique evolutionary gap, being ectothermic vertebrates like fish and amphibians and amniotes like birds and mammals. Turtles are ectotherms; thus, their immune system is influenced by environmental conditions like temperature and season. We aim to review the turtle immune system and note what studies have investigated sea turtles and the effect of the environment on the immune response. Turtles rely heavily on the nonspecific innate response rather than the specific adaptive response. Turtles' innate immune effectors include antimicrobial peptides, complement, and nonspecific leukocytes. The antiviral defense is understudied in terms of the diversity of pathogen receptors and interferon function. Turtles also mount adaptive responses to pathogens. Lymphoid structures responsible for lymphocyte activation and maturation are either missing in reptiles or function is affected by season. Turtles are a marker of health for their marine environment, and their immune system is commonly dysregulated because of disease or contaminants. Fibropapillomatosis (FP) is a tumorous disease that afflicts sea turtles and is thought to be caused by a virus and an environmental factor. We aim, by exploring the current understanding of the immune system in turtles, to aid the investigation of environmental factors that contribute to the pathogenesis of this disease and provide options for immunotherapy.

Monoclonal-Based Antivenomics Reveals Conserved Neutralizing Epitopes in Type I PLA2 Molecules from Coral Snakes

For over a century, polyclonal antibodies have been used to treat snakebite envenoming and are still considered by the WHO as the only scientifically validated treatment for snakebites. Nevertheless, moderate innovations have been introduced to this immunotherapy. New strategies and approaches to understanding how antibodies recognize and neutralize snake toxins represent a challenge for next-generation antivenoms. The neurotoxic activity of Micrurus venom is mainly due to two distinct protein families, three-finger toxins (3FTx) and phospholipases A₂ (PLA₂). Structural conservation among protein family members may represent an opportunity to generate neutralizing monoclonal antibodies (mAbs) against family-conserved epitopes. In this work, we sought to produce a set of monoclonal antibodies against the most toxic components of M. altirostris venom. To this end, the crude venom was fractionated, and its major toxic proteins were identified and used to generate a panel of five mAbs. The specificity of these mAbs was characterized by ELISA and antivenomics approaches. Two of the generated mAbs recognized PLA₂ epitopes. They inhibited PLA₂ catalytic activity and showed paraspecific neutralization against the myotoxicity from the lethal effect of Micrurus and Naja venoms' PLA_2s. Epitope conservation among venom PLA₂ molecules suggests the possibility of generating pan-PLA₂ neutralizing antibodies.

The edematogenic effect of Micrurus lemniscatus venom is dependent on venom phospholipase A2 activity and modulated by non-neurogenic factors

Coral snakes mainly cause neurotoxic symptoms in human envenomation, but experimental studies have already demonstrated several pharmacological activities in addition to these effects. This investigation was carried out with the aim of evaluating (1) non-neurogenic mechanisms involved in the inflammatory response induced by Micrurus lemniscatus venom (MLV) in rat hind paws, (2) participation of PLA₂ in this response, and (3) neutralizing efficiency of commercial anti-elapid antivenom on edema. MLV promoted a rapid, significant increase in vascular permeability, influx of leukocytes, and disorganization of collagen bundles, as demonstrated by histological analysis. Several pretreatments were applied to establish the involvement of inflammatory mediators in MLV-induced edema (5 µg/paw). Treatment of animals with chlorpromazine reduced MLV-induced edema, indicating participation of TNF-α. However, the inefficiency of other pharmacological treatments suggests that eicosanoids, leukotrienes, and nitric oxide have no role in this type of edema formation. In contrast, PAF negatively modulates this venom-induced effect. MLV was recognized by anti-elapid serum, but this antivenom did not neutralize edema formation. Chemical modification of MLV with p-bromophenacyl bromide abrogated the phospholipase activity and markedly reduced edema, demonstrating PLA₂ participation in MLV-induced edema. In conclusion, the non-neurogenic inflammatory profile of MLV is characterized by TNF-α-mediated edema, participation of PLA₂ activity, and down-regulation by PAF. MLV induces an influx of leukocytes and destruction of collagen fibers at the site of its injection.

Pharmacological Screening of Venoms from Five Brazilian Micrurus Species on Different Ion Channels

Coral snake venoms from the Micrurus genus are a natural library of components with multiple targets, yet are poorly explored. In Brazil, 34 Micrurus species are currently described, and just a few have been investigated for their venom activities. Micrurus venoms are composed mainly of phospholipases A₂ and three-finger toxins, which are responsible for neuromuscular blockade—the main envenomation outcome in humans. Beyond these two major toxin families, minor components are also important for the global venom activity, including Kunitz-peptides, serine proteases, 5′ nucleotidases, among others. In the present study, we used the two-microelectrode voltage clamp technique to explore the crude venom activities of five different Micrurus species from the south and southeast of Brazil: M. altirostris, M. corallinus, M. frontalis, M. carvalhoi and M. decoratus. All five venoms induced full inhibition of the muscle-type α1β1δε nAChR with different levels of reversibility. We found M. altirostris and M. frontalis venoms acting as partial inhibitors of the neuronal-type α7 nAChR with an interesting subsequent potentiation after one washout. We discovered that M. altirostris and M. corallinus venoms modulate the α1β2 GABA_AR. Interestingly, the screening on K_V1.3 showed that all five Micrurus venoms act as inhibitors, being totally reversible after the washout. Since this activity seems to be conserved among different species, we hypothesized that the Micrurus venoms may rely on potassium channel inhibitory activity as an important feature of their envenomation strategy. Finally, tests on Na_V1.2 and Na_V1.4 showed that these channels do not seem to be targeted by Micrurus venoms. In summary, the venoms tested are multifunctional, each of them acting on at least two different types of targets.

Partial efficacy of a Brazilian coralsnake antivenom and varespladib in neutralizing distinct toxic effects induced by sublethal Micrurus dumerilii carinicauda envenoming in rats

In this work, we report the efficacy of a combination of Brazilian therapeutic coralsnake antivenom (CAV) and varespladib (phospholipase A₂ inhibitor - VPL) in partially neutralizing selected toxic effects of Micrurus dumerilii carinicauda coralsnake venom in rats. Venom caused local myonecrosis and systemic neurotoxicity, nephrotoxicity, and hepatotoxicity within 2 h of injection. CAV and VPL administered separately failed to prevent most of these alterations. However, a combination of CAV plus VPL offered variable protection against venom-induced coagulation disturbances, leukocytosis, and renal and hepatic morphological alterations.

Snake Venomics: Fundamentals, Recent Updates, and a Look to the Next Decade

Venomic research, powered by techniques adapted from proteomics, transcriptomics, and genomics, seeks to unravel the diversity and complexity of venom through which knowledge can be applied in the treatment of envenoming, biodiscovery, and conservation. Snake venom proteomics is most extensively studied, but the methods varied widely, creating a massive amount of information which complicates data comparison and interpretation. Advancement in mass spectrometry technology, accompanied by growing databases and sophisticated bioinformatic tools, has overcome earlier limitations of protein identification. The progress, however, remains challenged by limited accessibility to samples, non-standardized quantitative methods, and biased interpretation of -omic data. Next-generation sequencing (NGS) technologies enable high-throughput venom-gland transcriptomics and genomics, complementing venom proteomics by providing deeper insights into the structural diversity, differential expression, regulation and functional interaction of the toxin genes. Venomic tissue sampling is, however, difficult due to strict regulations on wildlife use and transfer of biological materials in some countries. Limited resources for techniques and funding are among other pertinent issues that impede the progress of venomics, particularly in less developed regions and for neglected species. Genuine collaboration between international researchers, due recognition of regional experts by global organizations (e.g., WHO), and improved distribution of research support, should be embraced.

Proteomic and toxicological analysis of the venom of Micrurus yatesi and its neutralization by an antivenom

Coralsnakes belong to the family Elapidae and possess venoms which are lethal to humans and can be grouped based on the predominance of either three finger toxins (3FTxs) or phospholipases A₂ (PLA₂s). A proteomic and toxicological analysis of the venom of the coralsnake Micrurus yatesi was performed. This species, distributed in southeastern Costa Rica, was formerly considered a subspecies of M. alleni. Results showed that this venom is PLA₂-rich, in contrast with the previously studied venom of Micrurus alleni. Toxicological evaluation of the venom, in accordance with proteomic data, revealed that it has a markedly higher in vitro PLA₂ activity upon a synthetic substrate than M. alleni. The evaluation of in vivo myotoxicity in CD-1 mice using histological evaluation and plasma creatine kinase release also showed that M. yatesi venom caused muscle damage. A commercial equine antivenom prepared using the venom of Micrurus nigrocinctus displayed a similar recognition of the venoms of M. yatesi and M. nigrocinctus by enzyme immunoassay. This antivenom also immunorecognized the main fractions of the venom of M. yatesi and was able to neutralize its lethal effect in a murine model.

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The venom proteome of Micrurus yatesi was determined.

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The venom of Micrurus yatesi is a Phospholipase A₂-rich venom.

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When injected in mice, the venom of Micrurus yatesi caused muscle damage.

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An antivenom immunorecognized the main fractions of Micrurus yatesi venom.

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The antivenom was able to neutralize the lethal activity of the venom of Micrurus yatesi.

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

In vivo treatment with varespladib, a phospholipase A2 inhibitor, prevents the peripheral neurotoxicity and systemic disorders induced by Micrurus corallinus (coral snake) venom in rats

In this study, we investigated the action of varespladib (VPL) alone or in combination with a coral snake antivenom (CAV) on the local and systemic effects induced by Micrurus corallinus venom in rats. Adult male Wistar rats were exposed to venom (1.5 mg/kg - i.m.) and immediately treated with CAV (antivenom:venom ratio 1:1.5 'v/w' - i.p.), VPL (0.5 mg/kg - i.p.), or both of these treatments. The animals were monitored for 120 min and then anesthetized to collect blood samples used for haematological and serum biochemical analysis; after euthanasia, skeletal muscle, renal and hepatic tissue samples were collected for histopathological analysis. M. corallinus venom caused local oedema without subcutaneous haemorrhage or apparent necrosis formation, although there was accentuated muscle morphological damage; none of the treatments prevented oedema formation but the combination of CAV and VPL reduced venom-induced myonecrosis. Venom caused neuromuscular paralysis and respiratory impairment in approximately 60 min following envenomation; CAV alone did not prevent the neurotoxic action, whereas VPL alone prevented neurotoxic symptoms developing as did the combination of CAV and VPL. Venom induced significant increase of serum CK and AST release, mostly due to local and systemic myotoxicity, which was partially prevented by the combination of CAV and VPL. The release of hepatotoxic serum biomarkers (LDH and ALP) induced by M. corallinus venom was not prevented by CAV and VPL when individually administered; their combination effectively prevented ALP release. The venom-induced nephrotoxicity (increase in serum creatinine concentration) was prevented by all the treatments. VPL alone or in combination with CAV significantly prevented the venom-induced lymphocytosis. In conclusion, VPL shows to be effective at preventing the neurotoxic, nephrotoxic, and inflammatory activities of M. corallinus venom. In addition, VPL acts synergistically with antivenom to prevent a number of systemic effects caused by M. corallinus venom.

Integration of transcriptomic and proteomic approaches for snake venom profiling

INTRODUCTION

Snake venoms contain many protein and peptide isoforms with high levels of sequence variation, even within a single species.

AREAS COVERED

In this review, we highlight several examples, from both published and unpublished work in our lab, demonstrating how a combined venom gland transcriptome and proteome methodology allows for comprehensive characterization of venoms, including those from understudied rear-fanged snake species, and we provide recommendations for using these approaches.

EXPERT OPINION

When characterizing venoms, peptide mass fingerprinting using databases built predominately from protein sequences originating from model organisms can be disadvantageous, especially when the intention is to document protein diversity. Therefore, the use of species-specific venom gland transcriptomes corrects for the absence of these unique peptide sequences in databases. The integration of transcriptomics and proteomics improves the accuracy of either approach alone for venom profiling.

Cross-reactivity of some Micrurus venoms against experimental and therapeutic anti-Micrurus antivenoms

We developed experimental equine polyvalent and monovalent antivenoms against the venoms of Micrurus (M.) fulvius, M. nigrocinctus and M. surinamensis and studied their immunochemical reactivity on the venoms used as immunogens and on M. pyrrhocryptus, M altirostris and M. balyocoriphus venoms. Assessment of the neutralizing capacity of the polyvalent experimental antivenom was based on inhibition of lethality (preincubation and rescue assay experiments in mice) and indirect hemolytic and phospholipase activities. The immunochemical reactivity and neutralizing capacity were compared with those of two therapeutic antivenoms used for the treatment of coral snake envenomation in North America and in Argentina. In general, the experimental antivenom conferred a comparable level of neutralization against the venoms used as immunogens when compared to the therapeutic antivenoms and a certain level of cross-neutralization against the other venoms. The results suggest the need for additional venoms in the immunogenic mixture used, in order to obtain a broad spectrum anti-Micrurus antivenom with a good neutralizing potency. Paraspecific neutralization of South American coral snake venoms, although present at a higher level than the neutralization conferred by available nonspecific Micrurus therapeutic antivenoms, was rather low in relation to the specific neutralizing capacity.

Venom-gland transcriptomic, venomic, and antivenomic profiles of the spine-bellied sea snake (Hydrophis curtus) from the South China Sea

Background

A comprehensive evaluation of the -omic profiles of venom is important for understanding the potential function and evolution of snake venom. Here, we conducted an integrated multi-omics-analysis to unveil the venom-transcriptomic and venomic profiles in a same group of spine-bellied sea snakes (Hydrophis curtus) from the South China Sea, where the snake is a widespread species and might generate regionally-specific venom potentially harmful to human activities. The capacity of two heterologous antivenoms to immunocapture the H. curtus venom was determined for an in-depth evaluation of their rationality in treatment of H. curtus envenomation. In addition, a phylogenetic analysis by maximum likelihood was used to detect the adaptive molecular evolution of full-length toxin-coding unigenes.

Results

A total of 90,909,384 pairs of clean reads were generated via Illumina sequencing from a pooled cDNA library of six specimens, and yielding 148,121 unigenes through de novo assembly. Sequence similarity searching harvested 63,845 valid annotations, including 63,789 non-toxin-coding and 56 toxin-coding unigenes belonging to 22 protein families. Three protein families, three-finger toxins (3-FTx), phospholipase A₂ (PLA₂), and cysteine-rich secretory protein, were detected in the venom proteome. 3-FTx (27.15% in the transcriptome/41.94% in the proteome) and PLA₂ (59.71%/49.36%) were identified as the most abundant families in the venom-gland transcriptome and venom proteome. In addition, 24 unigenes from 11 protein families were shown to have experienced positive selection in their evolutionary history, whereas four were relatively conserved throughout evolution. Commercial Naja atra antivenom exhibited a stronger capacity than Bungarus multicinctus antivenom to immunocapture H. curtus venom components, especially short neurotoxins, with the capacity of both antivenoms to immunocapture short neurotoxins being weaker than that for PLA₂s.

Conclusions

Our study clarified the venom-gland transcriptomic and venomic profiles along with the within-group divergence of a H. curtus population from the South China Sea. Adaptive evolution of most venom components driven by natural selection appeared to occur rapidly during evolutionary history. Notably, the utility of commercial N. atra and B. multicinctus antivenoms against H. curtus toxins was not comprehensive; thus, the development of species-specific antivenom is urgently needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07824-7.

Snake venom vascular endothelial growth factors (svVEGFs): Unravelling their molecular structure, functions, and research potential

Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis, a physiological process characterized by the formation of new vessels from a preexisting endothelium. VEGF has also been implicated in pathologic states, such as neoplasias, intraocular neovascular disorders, among other conditions. VEGFs are distributed in seven different families: VEGF-A, B, C, D, and PIGF (placental growth factor), which are identified in mammals; VEGF-E, which are encountered in viruses; and VEGF-F or svVEGF (snake venom VEGF) described in snake venoms. This is the pioneer review of svVEGF family, exploring its distribution among the snake venoms, molecular structure, main functions, and potential applications.

Three-Finger Toxins from Brazilian Coral Snakes: From Molecular Framework to Insights in Biological Function

Studies on 3FTxs around the world are showing the amazing diversity in these proteins both in structure and function. In Brazil, we have not realized the broad variety of their amino acid sequences and probable diversified structures and targets. In this context, this work aims to conduct an in silico systematic study on available 3FTxs found in Micrurus species from Brazil. We elaborated a specific guideline for this toxin family. First, we grouped them according to their structural homologue predicted by HHPred server and further curated manually. For each group, we selected one sequence and constructed a representative structural model. By looking at conserved features and comparing with the information available in the literature for this toxin family, we managed to point to potential biological functions. In parallel, the phylogenetic relationship was estimated for our database by maximum likelihood analyses and a phylogenetic tree was constructed including the homologous 3FTx previously characterized. Our results highlighted an astonishing diversity inside this family of toxins, showing some groups with expected functional similarities to known 3FTxs, and pointing out others with potential novel roles and perhaps structures. Moreover, this classification guideline may be useful to aid future studies on these abundant toxins.

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.

Protein composition and biochemical characterization of venom from Sonoran Coral Snakes (Micruroides euryxanthus)

The elapid genus, Micruroides, is considered the sister clade of all New World coral snakes (Genus Micrurus), is monotypic, and is represented by Sonoran Coral Snakes, Micruroides euryxanthus. Coral snakes of the genus Micrurus have been reported to have venoms that are predominantly composed of phospholipases A₂ (PLA₂) or three finger toxins (3FTx), but the venoms of the genus Micruroides are almost completely unstudied. Here, we present the first description of the venom of M. euryxanthus including identification of some proteins as well as transcriptomic, and biological activity assays. The most abundant components within M. euryxanthus venom are 3FTxs (62.3%) and there was relatively low proportion of PLA₂s (14.2%). The venom phenotype supports the hypothesis that the common ancestor of Micrurus and Micruroides had a 3FTx-dominated venom. Within the venom, there were two nearly identical α-neurotoxins (α-Ntx), one of which was designated Eurytoxin, that account for approximately 60% of the venom's lethality to mice. Eurytoxin was cloned, expressed in a soluble and active form, and used to produce rabbit hyperimmune serum. This allowed the analysis of its immunochemical properties, showing them to be different from the recombinant αNTx D.H., present in the venoms of some species of Micrurus. Finally, we observed that the commercial antivenom produced in Mexico for coral snake envenomation is unable to neutralize the lethality from M. euryxanthus venom. This work allowed the classification of Micruroides venom into the 3FTx-predominant group and identified the main components responsible for toxicity to mice.

Advances in venomics: Modern separation techniques and mass spectrometry

Snake venoms are complex chemical mixtures of biologically active proteins and non-protein components. Toxins have a wide range of targets and effects to include ion channels and membrane receptors, and platelet aggregation and platelet plug formation. Toxins target these effectors and effects at high affinity and selectivity. From a pharmacological perspective, snake venom compounds are a valuable resource for drug discovery and development. However, a major challenge to drug discovery using snake venoms is isolating and analyzing the bioactive proteins and peptides in these complex mixtures. Getting molecular information from complex mixtures such as snake venoms requires proteomic analyses, generally combined with transcriptomic analyses of venom glands. The present review summarizes current knowledge and highlights important recent advances in venomics with special emphasis on contemporary separation techniques and bioinformatics that have begun to elaborate the complexity of snake venoms. Several analytical techniques such as two-dimensional gel electrophoresis, RP-HPLC, size exclusion chromatography, ion exchange chromatography, MALDI-TOF-MS, and LC-ESI-QTOF-MS have been employed in this regard. The improvement of separation approaches such as multidimensional-HPLC, 2D-electrophoresis coupled to soft-ionization (MALDI and ESI) mass spectrometry has been critical to obtain an accurate picture of the startling complexity of venoms. In the case of bioinformatics, a variety of software tools such as PEAKS also has been used successfully. Such information gleaned from venomics is important to both predicting and resolving the biological activity of the active components of venoms, which in turn is key for the development of new drugs based on these venom components.

Micrurus surinamensis Peruvian snake venom: Cytotoxic activity and purification of a C-type lectin protein (Ms-CTL) highly toxic to cardiomyoblast-derived H9c2 cells

Micrurus surinamensis (Cuvier, 1817), popularly known as aquatic coral snake, has a broad geographic distribution in the Rainforest of South America. The purpose of this study was to investigate the cytotoxic effect caused by M. surinamensis venom in H9c2 cardiomyoblast cells and to identify protein components involved in cardiotoxic processes. Venom cardiotoxic potential is evidenced by cell viability reduction in a concentration-dependent manner. We have purified one of venom components responsible for this effect after three chromatographic steps: a cytotoxic 23.461 kDa protein, as determined by mass spectrometry. A 19-residue sequence (DCPSGWSSYEGSCYNFFQR) of the purified protein was deduced by MS/MS and exhibited high homology with N-terminal region of C-type lectin from snake venoms. This protein was named Ms-CTL. Morphologically, H9c2 incubation with Ms-CTL led to a significant cellular retraction and formation of cellular aggregates, as observed by microscopy phase-contrast images. Our results indicate that M. surinamensis venom is highly toxic to H9c2 cardiomyoblast cell and less or not cytotoxic to other cell lines, such as HaCat, VERO and U373. Results presented herein will help understanding the mechanisms that underlie cellular damage and tissue destruction, being useful in the development of alternative therapies against these coral snake bites.

Envenomations by coral snakes in an Amazonian metropolis: Ecological, epidemiological and clinical aspects

Envenomation by coral snakes represents a little known burden in Brazilian Amazonia. So far, details on clinical and epidemiological aspects remain obscure in the region. We gathered data from medical charts and from the scientific collection of snakes from Fundação de Medicina Tropical Doutor Heitor Vieira Dourado, finding 26 cases of envenomation by five species of Micrurus in Manaus region, between 1987 and 2018. They represent 0.7% of the snakebites treated in the hospital since the records began, in 1979. Micrurus lemniscatus was responsible for most of the bites (10), followed by M. hemprichii (five), M. spixii (three), M. surinamensis (three) and M. averyi (one). There was no difference between the sexes of the snakes that caused bites. Patients were mostly males, and most of the cases were reported in urban areas. Bites predominated in dry season, and there was a clear geographical segregation among species. We describe seven cases of envenomation, three mild and four severe, all of which evolved to cure. Paresthesia (six), pain (five) and edema (four) were the most common local symptoms. Systemic features such as dyspnea/shallow breath (four), palpebral ptosis (four), blurred vision (three), dysarthria (three) and difficulty to walk (three) were also detected. Two patients bitten by Micrurus sp. and M. hemprichii, showed slight increased serum levels of creatine kinase (reference level <190 U/L), 1184 U/L and 1229 U/L, respectively, indicative of mild systemic myotoxicity. This is the first report of myotoxic manifestation in the envenomation by M. hemprichii. No patient developed respiratory failure, though one bitten by an adult M. spixii required intubation and mechanical ventilation due to decreased level of consciousness during evolution, probably related to induced sedation caused by concurrent alcohol intoxication. All patients were treated with Brazilian Micrurus antivenom (soro antielapídico, median = 10 vials). Six patients were pretreated intravenously with H1 and H2 antagonists and steroids, with two patients developing early adverse reactions. The median length of hospital stay was four days. Envenomations by coral snakes in Manaus region are clinically severe, but rare and sparsely distributed over time, making the detection of epidemiological and clinical patterns a challenge for public health.

Assessing the Binding of Venoms from Aquatic Elapids to the Nicotinic Acetylcholine Receptor Orthosteric Site of Different Prey Models

The evolution of an aquatic lifestyle from land dwelling venomous elapids is a radical ecological modification, bringing about many evolutionary changes from morphology to diet. Diet is an important ecological facet which can play a key role in regulating functional traits such as venom composition and prey-specific targeting of venom. In addition to predating upon novel prey (e.g., fish, fish eggs and invertebrates), the venoms of aquatic elapids also face the challenge of increased prey-escape potential in the aquatic environment. Thus, despite the independent radiation into an aquatic niche on four separate occasions, the venoms of aquatic elapids are evolving under convergent selection pressures. Utilising a biolayer interferometry binding assay, this study set out to elucidate whether crude venoms from representative aquatic elapids were target-specific to the orthosteric site of postsynaptic nicotinic acetylcholine receptor mimotopes of fish compared to other terrestrial prey types. Representatives of the four aquatic lineages were: aquatic coral snakes representative was Micrurus surinamensis;, sea kraits representative was Laticauda colubrina; sea snakes representatives were two Aipysurus spp. and eight Hydrophis spp; and water cobras representative was Naja annulata. No prey-specific differences in crude venom binding were observed from any species tested, except for Aipysurus laevis, which showed slight evidence of prey-potency differences. For Hydrophis caerulescens, H. peronii, H. schistosus and M. surinamensis, there was a lack of binding to the orthosteric site of any target lineage. Subsequent testing on the in vitro chick-biventer cervicis muscle preparation suggested that, while the venoms of these species bound postsynaptically, they bound to allosteric sites rather than orthosteric. Allosteric binding is potentially a weaker but faster-acting form of neurotoxicity and we hypothesise that the switch to allosteric binding is likely due to selection pressures related to prey-escape potential. This research has potentially opened up the possibility of a new functional class of toxins which have never been assessed previously while shedding light on the selection pressures shaping venom evolution.

The Sequence and Three-Dimensional Structure Characterization of Snake Venom Phospholipases B

Snake venom phospholipases B (SVPLBs) are the least studied enzymes. They constitute about 1% of Bothrops crude venoms, however, in other snake venoms, it is present in less than 1%. These enzymes are considered the most potent hemolytic agent in the venom. Currently, no structural information is available about these enzymes from snake venom. To better understand its three-dimensional structure and mechanisms of envenomation, the current work describes the first model-based structure report of this enzyme from Bothrops moojeni venom named as B. moojeni phospholipase B (PLB_Bm). The structure model of PLB_Bm was generated using model building software like I-TESSER, MODELLER 9v19, and Swiss-Model. The build PLB_Bm model was validated using validation tools (PROCHECK, ERRAT, and Verif3D). The analysis of the PLB_Bm modeled structure indicates that it contains 491 amino acid residues that form a well-defined four-layer αββα sandwich core and has a typical fold of the N-terminal nucleophile aminohydrolase (Ntn-hydrolase). The overall structure of PLB_Bm contains 18 β-strands and 17 α-helices with many connecting loops. The structure divides into two chains (A and B) after maturation. The A chain is smaller and contains 207 amino acid residues, whereas the B chain is larger and contains 266 amino acid residues. The sequence and structural comparison among homologous snake venom, bacterial, and mammals PLBs indicate that differences in the length and sequence composition may confer variable substrate specificity to these enzymes. Moreover, the surface charge distribution, average volume, and depth of the active site cavity also vary in these enzymes. The present work will provide more information about the structure-function relationship and mechanism of action of these enzymes in snakebite envenomation.

Fangs for the Memories? A Survey of Pain in Snakebite Patients Does Not Support a Strong Role for Defense in the Evolution of Snake Venom Composition

Animals use venoms for multiple purposes, most prominently for prey acquisition and self-defense. In snakes, venom composition often evolves as a result of selection for optimization for local diet. However, whether selection for a defensive function has also played a role in driving the evolution of venom composition has remained largely unstudied. Here, we use an online survey of snakebite victims to test a key prediction of a defensive function, that envenoming should result in the rapid onset of severe pain. From the analysis of 584 snakebite reports, involving 192 species of venomous snake, we find that the vast majority of bites do not result in severe early pain. Phylogenetic comparative analysis shows that where early pain after a bite evolves, it is often lost rapidly. Our results, therefore, do not support the hypothesis that natural selection for antipredator defense played an important role in the origin of venom or front-fanged delivery systems in general, although there may be intriguing exceptions to this rule.

Effects of Mlx-8, a phospholipase A2 from Brazilian coralsnake Micrurus lemniscatus venom, on muscarinic acetylcholine receptors in rat hippocampus

Background:

Here, we described the presence of a neurotoxin with phospholipase A₂ activity isolated from Micrurus lemniscatus venom (Mlx-8) with affinity for muscarinic acetylcholine receptors (mAChRs).

Methods:

The purification, molecular mass determination, partial amino acid sequencing, phospholipase A₂ activity determination, inhibition of the binding of the selective muscarinic ligand [³H]QNB and inhibition of the total [³H]inositol phosphate accumulation in rat hippocampus of the Mlx-8 were determined.

Results:

Thirty-one fractions were collected from HPLC chromatography, and the Mlx-8 toxin was used in this work. The molecular mass of Mlx-8 is 13.628 Da. Edman degradation yielded the following sequence: NLYQFKNMIQCTNTRSWL-DFADYG-CYCGRGGSGT. The Mlx-8 had phospholipase A₂ enzymatic activity. The pK_i values were determined for Mlx-8 toxin and the M₁ selective muscarinic antagonist pirenzepine in hippocampus membranes via [³H]QNB competition binding assays. The pK_i values obtained from the analysis of Mlx-8 and pirenzepine displacement curves were 7.32 ± 0.15, n = 4 and 5.84 ± 0.18, n = 4, respectively. These results indicate that Mlx-8 has affinity for mAChRs. There was no effect on the inhibition ability of the [³H]QNB binding in hippocampus membranes when 1 µM Mlx-8 was incubated with 200 µM DEDA, an inhibitor of phospholipase A₂. This suggests that the inhibition of the phospholipase A₂ activity of the venom did not alter its ability to bind to displace [³H]QNB binding. In addition, the Mlx-8 toxin caused a blockade of 43.31 ± 8.86%, n = 3 and 97.42 ± 2.02%, n = 3 for 0.1 and 1 µM Mlx-8, respectively, on the total [³H]inositol phosphate content induced by 10 µM carbachol. This suggests that Mlx-8 inhibits the intracellular signaling pathway linked to activation of mAChRs in hippocampus.

Conclusion:

The results of the present work show, for the first time, that muscarinic receptors are also affected by the Mlx-8 toxin, a muscarinic ligand with phospholipase A₂ characteristics, obtained from the venom of the Elapidae snake Micrurus lemniscatus, since this toxin was able to compete with muscarinic ligand [³H]QNB in hippocampus of rats. In addition, Mlx-8 also blocked the accumulation of total [³H]inositol phosphate induced by muscarinic agonist carbachol. Thus, Mlx-8 may be a new pharmacological tool for examining muscarinic cholinergic function.

Trait differentiation and modular toxin expression in palm-pitvipers

Background

Modularity is the tendency for systems to organize into semi-independent units and can be a key to the evolution and diversification of complex biological systems. Snake venoms are highly variable modular systems that exhibit extreme diversification even across very short time scales. One well-studied venom phenotype dichotomy is a trade-off between neurotoxicity versus hemotoxicity that occurs through the high expression of a heterodimeric neurotoxic phospholipase A₂ (PLA₂) or snake venom metalloproteinases (SVMPs). We tested whether the variation in these venom phenotypes could occur via variation in regulatory sub-modules through comparative venom gland transcriptomics of representative Black-Speckled Palm-Pitvipers (Bothriechis nigroviridis) and Talamancan Palm-Pitvipers (B. nubestris).

Results

We assembled 1517 coding sequences, including 43 toxins for B. nigroviridis and 1787 coding sequences including 42 toxins for B. nubestris. The venom gland transcriptomes were extremely divergent between these two species with one B. nigroviridis exhibiting a primarily neurotoxic pattern of expression, both B. nubestris expressing primarily hemorrhagic toxins, and a second B. nigroviridis exhibiting a mixed expression phenotype. Weighted gene coexpression analyses identified six submodules of transcript expression variation, one of which was highly associated with SVMPs and a second which contained both subunits of the neurotoxic PLA₂ complex. The sub-module association of these toxins suggest common regulatory pathways underlie the variation in their expression and is consistent with known patterns of inheritance of similar haplotypes in other species. We also find evidence that module associated toxin families show fewer gene duplications and transcript losses between species, but module association did not appear to affect sequence diversification.

Conclusion

Sub-modular regulation of expression likely contributes to the diversification of venom phenotypes within and among species and underscores the role of modularity in facilitating rapid evolution of complex traits.

Antimicrobial Activity of Protein Fraction from Naja ashei Venom Against Staphylococcus epidermidis

One of the key problems of modern infectious disease medicine is the growing number of drug-resistant and multi-drug-resistant bacterial strains. For this reason, many studies are devoted to the search for highly active antimicrobial substances that could be used in therapy against bacterial infections. As it turns out, snake venoms are a rich source of proteins that exert a strong antibacterial effect, and therefore they have become an interesting research material. We analyzed Naja ashei venom for such antibacterial properties, and we found that a specific composition of proteins can act to eliminate individual bacterial cells, as well as the entire biofilm of Staphylococcus epidermidis. In general, we used ion exchange chromatography (IEX) to obtain 10 protein fractions with different levels of complexity, which were then tested against certified and clinical strains of S. epidermidis. One of the fractions (F2) showed exceptional antimicrobial effects both alone and in combination with antibiotics. The protein composition of the obtained fractions was determined using mass spectrometry techniques, indicating a high proportion of phospholipases A₂, three-finger toxins, and L-amino acids oxidases in F2 fraction, which are most likely responsible for the unique properties of this fraction. Moreover, we were able to identify a new group of low abundant proteins containing the Ig-like domain that have not been previously described in snake venoms.

The Indian cobra reference genome and transcriptome enables comprehensive identification of venom toxins

Snakebite envenoming is a serious and neglected tropical disease that kills ~100,000 people annually. High-quality, genome-enabled comprehensive characterization of toxin genes will facilitate development of effective humanized recombinant antivenom. We report a de novo near-chromosomal genome assembly of Naja naja, the Indian cobra, a highly venomous, medically important snake. Our assembly has a scaffold N50 of 223.35 Mb, with 19 scaffolds containing 95% of the genome. Of the 23,248 predicted protein-coding genes, 12,346 venom-gland-expressed genes constitute the ‘venom-ome’ and this included 139 genes from 33 toxin families. Among the 139 toxin genes were 19 ‘venom-ome-specific toxins’ (VSTs) that showed venom-gland-specific expression, and these probably encode the minimal core venom effector proteins. Synthetic venom reconstituted through recombinant VST expression will aid in the rapid development of safe and effective synthetic antivenom. Additionally, our genome could serve as a reference for snake genomes, support evolutionary studies and enable venom-driven drug discovery.

Analysis of a near-chromosomal genome assembly and transcriptome profiling of the Indian cobra identifies genes expressed in the venom glands. These data should help develop a new antivenom.

The complete mitochondrial genome of the aquatic coralsnake Micrurus surinamensis (Reptilia, Serpentes, Elapidae)

In this study, we report the first complete mitochondrial genome sequence of the Aquatic Coralsnake Micrurus surinamensis. The mitochondrial genome lengthis 17,375 bp, comprising 13 protein-coding genes, 2 rRNA (12S and 16S) and 22 tRNA, as well as two typical control regions. Phylogenetic analysis based upon 13 protein-coding genes showed clusters based on terrestrial and marine species.

Omics Technologies for Profiling Toxin Diversity and Evolution in Snake Venom: Impacts on the Discovery of Therapeutic and Diagnostic Agents

Snake venoms are primarily composed of proteins and peptides, and these toxins have developed high selectivity to their biological targets. This makes venoms interesting for exploration into protein evolution and structure-function relationships. A single venom protein superfamily can exhibit a variety of pharmacological effects; these variations in activity originate from differences in functional sites, domains, posttranslational modifications, and the formations of toxin complexes. In this review, we discuss examples of how the major venom protein superfamilies have diversified, as well as how newer technologies in the omics fields, such as genomics, transcriptomics, and proteomics, can be used to characterize both known and unknown toxins.Because toxins are bioactive molecules with a rich diversity of activities, they can be useful as therapeutic and diagnostic agents, and successful examples of toxin applications in these areas are also reviewed. With the current rapid pace of technology, snake venom research and its applications will only continue to expand.

A Combined Strategy to Improve the Development of a Coral Antivenom Against Micrurus spp

Accidents involving Micrurus snakes are not the most common ones but are noteworthy due to their severity. Victims envenomed by Micrurus snakes are at high risk of death and therefore must be treated with coral antivenom. In Brazil, the immunization mixture used to fabricate coral antivenom contains Micrurus frontalis and Micrurus corallinus venoms, which are difficult to be obtained in adequate amounts. Different approaches to solve the venom limitation problem have been attempted, including the use of synthetic and recombinant antigens as substitutes. The present work proposes a combined immunization protocol, using priming doses of M. frontalis venom and booster doses of synthetic B-cell epitopes derived from M. corallinus toxins (four three-finger toxins-3FTX; and one phospholipase A₂-PLA₂) to obtain coral antivenom in a rabbit model. Immunized animals elicited a humoral response against both M. frontalis and M. corallinus venoms, as detected by sera reactivity in ELISA and Western Blot. Relevant cross-reactivity of the obtained sera with other Micrurus species (Micrurus altirostris, Micrurus lemniscatus, Micrurus spixii, Micrurus surinamensis) venoms was also observed. The elicited antibodies were able to neutralize PLA₂ activity of both M. frontalis and M. corallinus venoms. In vivo, immunized rabbit sera completely protected mice from a challenge with 1.5 median lethal dose (LD₅₀) of M. corallinus venom and 50% of mice challenged with 1.5 LD₅₀ of M. frontalis venom. These results show that this combined protocol may be a suitable alternative to reduce the amount of venom used in coral antivenom production in Brazil.

Convergent eusocial evolution is based on a shared reproductive groundplan plus lineage-specific plastic genes

Eusociality has convergently evolved multiple times, but the genomic basis of caste-based division of labor and degree to which independent origins of eusociality have utilized common genes remain largely unknown. Here we characterize caste-specific transcriptomic profiles across development and adult body segments from pharaoh ants (Monomorium pharaonis) and honey bees (Apis mellifera), representing two independent origins of eusociality. We identify a substantial shared core of genes upregulated in the abdomens of queen ants and honey bees that also tends to be upregulated in mated female flies, suggesting that these genes are part of a conserved insect reproductive groundplan. Outside of this shared groundplan, few genes are differentially expressed in common. Instead, the majority of the thousands of caste-associated genes are plastically expressed, rapidly evolving, and relatively evolutionarily young. These results emphasize that the recruitment of both highly conserved and lineage-specific genes underlie the convergent evolution of novel traits such as eusociality.

Eusocial caste systems have evolved independently multiple times. Here, Warner et al. investigate the amount of shared vs. lineage-specific genes involved in the evolution of caste in pharaoh ants and honey bees by comparing transcriptomes across tissues, developmental stages, and castes.

Neurotoxicity of Micrurus lemniscatus lemniscatus (South American coralsnake) venom in vertebrate neuromuscular preparations in vitro and neutralization by antivenom

We investigated the effect of South American coralsnake (Micrurus lemniscatus lemniscatus) venom on neurotransmission in vertebrate nerve-muscle preparations in vitro. The venom (0.1-30 µg/ml) showed calcium-dependent PLA₂ activity and caused irreversible neuromuscular blockade in chick biventer cervicis (BC) and mouse phrenic nerve-diaphragm (PND) preparations. In BC preparations, contractures to exogenous acetylcholine and carbachol (CCh), but not KCl, were abolished by venom concentrations ≥ 0.3 µg/ml; in PND preparations, the amplitude of the tetanic response was progressively attenuated, but with little tetanic fade. In low Ca²⁺ physiological solution, venom (10 µg/ml) caused neuromuscular blockade in PND preparations within ~ 10 min that was reversible by washing; the addition of Ca²⁺ immediately after the blockade temporarily restored the twitch responses, but did not prevent the progression to irreversible blockade. Venom (10 µg/ml) did not depolarize diaphragm muscle, prevent depolarization by CCh, or cause muscle contracture or histological damage. Venom (3 µg/ml) had a biphasic effect on the frequency of miniature end-plate potentials, but did not affect their amplitude; there was a progressive decrease in the amplitude of evoked end-plate potentials. The amplitude of compound action potentials in mouse sciatic nerve was unaffected by venom (10 µg/ml). Pre-incubation of venom with coralsnake antivenom (Instituto Butantan) at the recommended antivenom:venom ratio did not neutralize the neuromuscular blockade in PND preparations, but total neutralization was achieved with a tenfold greater volume of antivenom. The addition of antivenom after 50% and 80% blockade restored the twitch responses. These results show that M. lemniscatus lemniscatus venom causes potent, irreversible neuromuscular blockade, without myonecrosis. This blockade is apparently mediated by pre- and postsynaptic neurotoxins and can be reversed by coralsnake antivenom.

Intact protein mass spectrometry reveals intraspecies variations in venom composition of a local population of Vipera kaznakovi in Northeastern Turkey

We report on the variable venom composition of a population of the Caucasus viper (Vipera kaznakovi) in Northeastern Turkey. We applied a combination of venom gland transcriptomics, de-complexing bottom-up and top-down venomics. In contrast to sole bottom-up venomics approaches and gel or chromatography based venom comparison, our combined approach enables a faster and more detailed comparison of venom proteomes from multiple individuals. In total, we identified peptides and proteins from 15 toxin families, including snake venom metalloproteinases (svMP; 37.8%), phospholipases A2 (PLA2; 19.0%), snake venom serine proteinases (svSP; 11.5%), C-type lectins (CTL; 6.9%) and cysteine-rich secretory proteins (CRISP; 5.0%), in addition to several low abundant toxin families. Furthermore, we identified intraspecies variations of the venom composition of V. kaznakovi, and find these were mainly driven by the age of the animals, with lower svSP abundance detected in juveniles. On the proteoform level, several small molecular weight toxins between 5 and 8 kDa in size, as well as PLA2s, drove the differences observed between juvenile and adult individuals. This study provides novel insights into the venom variability of V. kaznakovi and highlights the utility of intact mass profiling for fast and detailed comparison of snake venom. BIOLOGICAL SIGNIFICANCE: Population level and ontogenetic venom variation (e.g. diet, habitat, sex or age) can result in a loss of antivenom efficacy against snakebites from wide ranging snake populations. The current state of the art for the analysis of snake venoms are de-complexing bottom-up proteomics approaches. While useful, these have the significant drawback of being time-consuming and following costly protocols, and consequently are often applied to pooled venom samples. To overcome these shortcomings and to enable rapid and detailed profiling of large numbers of individual venom samples, we integrated an intact protein analysis workflow into a transcriptomics-guided bottom-up approach. The application of this workflow to snake individuals of a local population of V. kaznakovi revealed intraspecies variations in venom composition, which are primarily explained by the age of the animals, and highlighted svSP abundance to be one of the molecular drivers for the compositional differences observed.

Consecutive envenomation of two men bitten by the same coral snake (Micrurus corallinus)

Objective: To report two patients who developed systemic neurotoxicity after consecutive bites by the same coral snake.Case report: Two previously healthy men (32-year-old and 34-year-old) found a coral snake in a woodpile while collecting wood for a barbecue. During the barbecue, both men became drunk and "played" with the snake, believing that they were handling a false coral snake, and were bitten within a few minutes of each other. Both patients were admitted to a referral tertiary care hospital (175 km from where the bites occurred) 16 hours and 19 hours postbite; both showed similar features of envenomation: palpebral ptosis, muscle weakness, dysphagia, and generalized myalgia. No fang marks or local pain were detected in either case. The patients were successfully treated with Brazilian coral snake antivenom (Fab´₂) and discharged one-day postadmission, with improvement of myasthenia, but still showing palpebral ptosis. The offending snake was identified as a 42-cm-long Micrurus corallinus. During follow-up, both patients reported a transitory loss of taste that lasted approximately 3-4 weeks postbite.Conclusion: Consecutive bites by the same coral snake may cause systemic neurotoxicity (acute myasthenia) in more than one person, as well as transitory loss of taste, an underreported complication of snakebites.