Mipartoxin-I, a novel three-finger toxin, is the major neurotoxic component in the venom of the redtail coral snake Micrurus mipartitus (Elapidae)

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.

Standard Quality Characteristics and Efficacy of a New Third-Generation Antivenom Developed in Colombia Covering Micrurus spp. Venoms

In Colombia, Micrurus snakebites are classified as severe according to the national clinical care guidelines and must be treated with specific antivenoms. Unfortunately, these types of antivenoms are scarce in certain areas of the country and are currently reported as an unavailable vital medicine. To address this issue, La Universidad de Antioquia, through its spin-off Tech Life Saving, is leading a project to develop third-generation polyvalent freeze-dried antivenom. The goal is to ensure access to this therapy, especially in rural and dispersed areas. This project aims to evaluate the physicochemical and preclinical parameters (standard quality characteristics) of a lab-scale anti-elapid antivenom batch. The antivenom is challenged against the venoms of several Micrurus species, including M. mipartitus, M. dumerilii, M. ancoralis, M. dissoleucus, M. lemniscatus, M. medemi, M. spixii, M. surinamensis, and M. isozonus, following the standard quality characteristics set by the World Health Organization (WHO). The antivenom demonstrates an appearance consistent with standards, 100% solubility within 4 min and 25 s, an extractable volume of 10.39 mL, a pH of 6.04, an albumin concentration of 0.377 mg/mL (equivalent to 1.22% of total protein), and a protein concentration of 30.97 mg/mL. Importantly, it maintains full integrity of its F(ab')2 fragments and exhibits purity over 98.5%. Furthermore, in mice toxicity evaluations, doses up to 15 mg/mouse show no toxic effects. The antivenom also demonstrates a significant recognition pattern against Micrurus venoms rich in phospholipase A2 (PLA2) content, as observed in M. dumerilii, M. dissoleucus, and M. isozonus. The effective dose 50 (ED50) indicates that a single vial (10 mL) can neutralize 2.33 mg of M. mipartitus venom and 3.99 mg of M. dumerilii venom. This new anti-elapid third-generation polyvalent and freeze-dried antivenom meets the physicochemical parameters set by the WHO and the regulators in Colombia. It demonstrates significant efficacy in neutralizing the venom of the most epidemiologically important Micrurus species in Colombia. Additionally, it recognizes seven other species of Micrurus venom with a higher affinity for venoms exhibiting PLA2 toxins. Fulfilling these parameters represents the first step toward proposing a new pharmacological alternative for treating snakebites in Colombia, particularly in dispersed rural areas, given that this antivenom is formulated as a freeze-dried product.

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.

Immunological Cross-Reactivity and Preclinical Assessment of a Colombian Anticoral Antivenom against the Venoms of Three Micrurus Species

Snakebite accident treatment requires the administration of antivenoms that provide efficacy and effectiveness against several snake venoms of the same genus or family. The low number of immunogenic components in venom mixtures that allow the production of antivenoms consequently gives them partial neutralization and a suboptimal pharmacological response. This study evaluates the immunorecognition and neutralizing efficacy of the polyvalent anticoral antivenom from the Instituto Nacional de Salud (INS) of Colombia against the heterologous endemic venoms of Micrurus medemi, and M. sangilensis, and M. helleri by assessing immunoreactivity through affinity chromatography, ELISA, Western blot, and neutralization capability. Immunorecognition towards the venoms of M. medemi and M. sangilensis showed values of 62% and 68% of the protein composition according to the immunoaffinity matrix, respectively. The analysis by Western blot depicted the highest recognition patterns for M. medemi, followed by M. sangilensis, and finally by M. helleri. These findings suggest that the venom compositions are closely related and exhibit similar recognition by the antivenom. According to enzyme immunoassays, M. helleri requires a higher amount of antivenom to achieve recognition than the others. Besides reinforcing the evaluation of INS antivenom capability, this work recommends the use of M. helleri in the production of Colombian antisera.

In-depth immunorecognition and neutralization analyses of Micrurus mipartitus and M. dumerilii venoms and toxins by a commercial antivenom

In Colombia, the Micrurus genus comprises 30 species, including M. mipartitus and M. dumerilii, which are of major clinical relevance due to their wide geographical distribution and the number of snakebites inflicted by them. These neurotoxic envenomations are characterized by neuromuscular paralysis attributed to venom components such as three-finger toxins (3FTx) and phospholipases (PLA2). Additionally, there is limited information available on the neutralizing coverage of commercially available antivenoms, underscoring the need to perform studies to assess the cross-neutralizing ability of these life-saving products. Therefore, we present an in-depth immunorecognition analysis by the anticoral-INS antivenom from Colombia on the M. mipartitus and M. dumerilii venoms. The antivenom cross-recognized the whole venoms and their components with different intensities. For instance, the antivenom showed better recognition on PLA2s than on 3FTxs in both venoms. Moreover, at doses tested, the antivenom totally neutralized the lethal effect of M. dumerilii venom; however, it did not neutralize this effect induced by M. mipartitus venom and its main toxic components from the southwestern region of the department of Antioquia. Furthermore, the anticoral-INS antivenom displayed better cross-immunorecognition of PLA2-predominant Micrurus venoms than of 3FTx-predominant Micrurus venoms. This highlights the need to include venoms from both types of venom patterns in the immunization mixture to produce antivenoms against coral snakes. Finally, our results suggest the need for further research to optimize the composition of immunizing mixtures for antivenom production and improve their efficacy against coral snake envenomation in Colombia and the Americas.

Knowledge about Snake Venoms and Toxins from Colombia: A Systematic Review

Colombia encompasses three mountain ranges that divide the country into five natural regions: Andes, Pacific, Caribbean, Amazon, and Orinoquia. These regions offer an impressive range of climates, altitudes, and landscapes, which lead to a high snake biodiversity. Of the almost 300 snake species reported in Colombia, nearly 50 are categorized as venomous. This high diversity of species contrasts with the small number of studies to characterize their venom compositions and natural history in the different ecoregions. This work reviews the available information about the venom composition, isolated toxins, and potential applications of snake species found in Colombia. Data compilation was conducted according to the PRISMA guidelines, and the systematic literature search was carried out in Pubmed/MEDLINE. Venom proteomes from nine Viperidae and three Elapidae species have been described using quantitative analytical strategies. In addition, venoms of three Colubridae species have been studied. Bioactivities reported for some of the venoms or isolated components-such as antibacterial, cytotoxicity on tumoral cell lines, and antiplasmodial properties-may be of interest to develop potential applications. Overall, this review indicates that, despite recent progress in the characterization of venoms from several Colombian snakes, it is necessary to perform further studies on the many species whose venoms remain essentially unexplored, especially those of the poorly known genus Micrurus.

Unveiling the Venom Composition of the Colombian Coral Snakes Micrurus helleri, M. medemi, and M. sangilensis

Little is known of the biochemical composition and functional features of the venoms of poorly known Colombian coral snakes. Here, we provide a preliminary characterization of the venom of two Colombian endemic coral snake species, Micrurus medemi and M. sangilensis, as well as Colombian populations of M. helleri. Electrophoresis and RP-HPLC techniques were used to identify venom components, and assays were conducted to detect enzyme activities, including phospholipase A2, hyaluronidase, and protease activities. The median lethal dose was determined using murine models. Cytotoxic activities in primary cultures from hippocampal neurons and cancer cell lines were evaluated. The venom profiles revealed similarities in electrophoretic separation among proteins under 20 kDa. The differences in chromatographic profiles were significant, mainly between the fractions containing medium-/large-sized and hydrophobic proteins; this was corroborated by a proteomic analysis which showed the expected composition of neurotoxins from the PLA2 (~38%) and 3FTx (~17%) families; however, a considerable quantity of metalloproteinases (~12%) was detected. PLA2 activity and protease activity were higher in M. helleri venom according to qualitative and quantitative assays. M. medemi venom had the highest lethality. All venoms decreased cell viability when tested on tumoral cell cultures, and M. helleri venom had the highest activity in neuronal primary culture. These preliminary studies shed light on the venoms of understudied coral snakes and broaden the range of sources that could be used for subsequent investigations of components with applications to specific diseases. Our findings also have implications for the clinical manifestations of snake envenoming and improvements in its medical management.

Antibodies against a single fraction of Micrurus dumerilii venom neutralize the lethal effect of whole venom

The coralsnake Micrurus dumerilii (Elapidae) is reported to cause envenomings of medical importance. Previous studies characterized the protein composition of its venom, with phospholipase A₂ (PLA₂) proteins the most abundant. However, it is unknown which venom components are responsible for its lethal toxicity. Fractionation of M. dumerilii venom from Colombia was carried out using RP-HPLC and each fraction was screened for lethal effect in mice at a dose of 20 μg by intraperitoneal route. Results showed that only one fraction, F9, was lethal. This fraction displayed PLA₂ activity, induced indirect hemolysis in vitro, as well as edema and myotoxicity in vivo. SDS-PAGE of unreduced F9 evidenced two bands of 8 and 15 kDa, respectively, consistent with the detection of proteins with masses of 13,217.77 Da, 7144.06 Da, and 7665.55 Da. Tryptic digestion of F9 followed by nESI-MS/MS revealed peptide sequences matching proteins of the three-finger toxin (3FTx) and PLA₂ families. Immunization of a rabbit with F9 proteins elicited antibody titers up to 1:10,000 by ELISA. After serum fractionation with caprylic acid, the obtained IgG was able to neutralize the lethal effect of the complete venom of M. dumerilii using a challenge of 2 ×LD₅₀ at the IgG/venom ratio of 50:1 (w/w). In conclusion, present results show that the lethal effect of M. dumerilii venom in mice is mainly driven by one fraction which contains 3FTx and PLA₂ proteins. The antibodies produced against this fraction cross-recognized other PLA₂s and neutralized the lethal effect of whole M. dumerilii venom, pointing out to the potential usefulness of F9 as a relevant antigen for improving current coral snake antivenoms.

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.

Recovery from the Neuroparalysis Caused by the Micrurus nigrocinctus Venom Is Accelerated by an Agonist of the CXCR4 Receptor

Snake envenoming is a major but neglected human disease in tropical and subtropical regions. Among venomous snakes in the Americas, coral snakes of the genus Micrurus are particularly dangerous because they cause a peripheral neuroparalysis that can persist for many days or, in severe cases, progress to death. Ventilatory support and the use of snake species-specific antivenoms may prevent death from respiratory paralysis in most cases. However, there is a general consensus that additional and non-expensive treatments that can be delivered even long after the snake bite are needed. Neurotoxic degeneration of peripheral motor neurons activates pro-regenerative intercellular signaling programs, the greatest of which consist of the chemokine CXCL12α, produced by perisynaptic Schwann cells, which act on the CXCR4 receptor expressed on damaged neuronal axons. We recently found that the CXCR4 agonist NUCC-390 promotes axonal growth. Here, we show that the venom of the highly neurotoxic snake Micrurus nigrocinctus causes a complete degeneration of motor axon terminals of the soleus muscle, followed by functional regeneration whose time course is greatly accelerated by NUCC-390. These results suggest that NUCC-390 is a potential candidate for treating human patients envenomed by Micrurus nigrocinctus as well as other neurotoxic Micrurus spp. in order to improve the recovery of normal neuromuscular physiology, thus reducing the mortality and hospital costs of envenoming.

Anti-Neurotoxins from Micrurus mipartitus in the Development of Coral Snake Antivenoms

In Colombia, the genus Micrurus includes 30 species, of which M. mipartitus and M. dumerilii are the most widely distributed. Micrurus causes less than 3% of the approximately 5000 cases of snakebite per year. The elapid envenomation caused by the snakes from the Micrurus genus, are characterized by the severity of their clinical manifestations, due to the venom neurotoxic components such as three-finger toxins (3FTx) and phospholipases (PLA₂). The treatment for snakebites is the administration of specific antivenoms, however, some of them have limitations in their neutralizing ability. A strategy proposed to improve antivenoms is to produce antibodies against the main components of the venom. The aim of this work was to produce an antivenom, using an immunization protocol including the main 3FTx and PLA₂ responsible for M. mipartitus lethality. The antibody titers were determined by ELISA in rabbits’ serum. The immunized animals elicited a response against toxins and whole venom. The Immunoglobulin G (IgGs) obtained were able to neutralize the lethal effect of their homologous toxins. A combination of antivenom from M. mipartitus with antitoxins improved their neutralizing ability. In the same way, a mixture of anti 3FTx and PLA₂ protected the mice from a 1.5 median lethal dose (LD₅₀) of M. mipartitus venom. The results showed that this might be a way to improve antibody titers specificity against the relevant toxins in M. mipartitus venom and indicated that there is a possibility to develop and use recombinant 3FTx and PLA₂ toxins as immunogens to produce antivenoms. Additionally, this represents an alternative to reduce the amount of venom used in anti-coral antivenom production.

Strategies for Heterologous Expression, Synthesis, and Purification of Animal Venom Toxins

Animal venoms are complex mixtures containing peptides and proteins known as toxins, which are responsible for the deleterious effect of envenomations. Across the animal Kingdom, toxin diversity is enormous, and the ability to understand the biochemical mechanisms governing toxicity is not only relevant for the development of better envenomation therapies, but also for exploiting toxin bioactivities for therapeutic or biotechnological purposes. Most of toxinology research has relied on obtaining the toxins from crude venoms; however, some toxins are difficult to obtain because the venomous animal is endangered, does not thrive in captivity, produces only a small amount of venom, is difficult to milk, or only produces low amounts of the toxin of interest. Heterologous expression of toxins enables the production of sufficient amounts to unlock the biotechnological potential of these bioactive proteins. Moreover, heterologous expression ensures homogeneity, avoids cross-contamination with other venom components, and circumvents the use of crude venom. Heterologous expression is also not only restricted to natural toxins, but allows for the design of toxins with special properties or can take advantage of the increasing amount of transcriptomics and genomics data, enabling the expression of dormant toxin genes. The main challenge when producing toxins is obtaining properly folded proteins with a correct disulfide pattern that ensures the activity of the toxin of interest. This review presents the strategies that can be used to express toxins in bacteria, yeast, insect cells, or mammalian cells, as well as synthetic approaches that do not involve cells, such as cell-free biosynthesis and peptide synthesis. This is accompanied by an overview of the main advantages and drawbacks of these different systems for producing toxins, as well as a discussion of the biosafety considerations that need to be made when working with highly bioactive proteins.

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.

Assessment of neutralization of Micrurus venoms with a blend of anti-Micrurus tener and anti-ScNtx antibodies

BACKGROUND

Micrurus venoms contain two main groups of toxic protein components: short-chain α-neurotoxins (SNtx) and phospholipases type A₂ (PLA₂). In North America, generally, the Micrurus venoms have low abundance of SNtx compared to that of PLA₂s; however, both are highly toxic to mammals, and consequently both can play a major role in the envenomation processes. Concerning the commercial horse-derived antivenoms against Micrurus from the North America region, they contain a relatively large amount of antibodies against PLA₂s, and a low content of antibodies against short chain α-neurotoxins. This is mainly due to the lower relative abundance of SNtxs, and also to its poor immunogenicity due to their size and nature. Hence, Micrurus antivenoms made in North America usually present low neutralizing capacity towards Micrurus venoms whose lethality depend largely on short chain α-neurotoxins, such as South American Micrurus species.

METHODS

Horses were hyperimmunized with either the venom of M. tener (PLA₂-predominant) or a recombinant short-chain consensus α-neurotoxin (ScNtx). Then, the combination of the two monospecific horse antibodies (anti-M. tener and anti-ScNtx) was used to test their efficacy against eleven Micrurus venoms.

RESULTS

The blend of anti-M. tener and anti-ScNtx antibodies had a better capacity to neutralize the lethality of diverse species from North, Central and South American Micrurus venoms. The antibodies combination neutralized both the ScNtx and ten out of eleven Micrurus venom tested, and particularly, it neutralized the venoms of M. distans and M. laticollaris that were neither neutralized by monospecific anti-M. tener nor anti-ScNtx.

CONCLUSIONS

These results provide a proof-of-principle for using recombinant immunogens to enrich poor or even non-neutralizing antisera against elapid venoms containing short chain α-neurotoxins to develop antivenoms with higher effectiveness and broader neutralizing capacity.

Immunological cross-recognition and neutralization studies of Micrurus mipartitus and Micrurus dumerilii venoms by two therapeutic equine antivenoms

New world Coral snakes comprise 82 species of medical importance distributed from southeastern United States to Argentina. In Colombia, Micrurus mipartitus and M. dumerilii are responsible for most coral snakebite accidents. Although infrequent, the severity of these envenomings, as well as the limited information available on the neutralizing coverage of commercially available antivenoms, underscores the need to perform studies to assess the cross-neutralizing ability of these life-saving immunobiologicals. In the present work, we evaluated the cross-recognition and neutralization ability of two equine therapeutic antivenoms: PROBIOL and SAC-ICP. PROBIOL antivenom showed cross-recognition towards both M. mipartitus and M. dumerilii venoms, with a significantly higher binding to the latter in both whole-venom ELISA and fractionated-venom immunoprofiling. In contrast, SAC-ICP antivenom cross-recognized M. dumerilii venom, but not that of M. mipartitus. Lethality of M. dumerilii venom was neutralized by both antivenoms, with a slightly higher potency for the SAC-ICP antivenom. However, the lethality of M. mipartitus venom was not neutralized by any of the two antivenoms. Results uncover the need to include M. mipartitus venom, or its most relevant toxins, in the production of coral snake antivenoms to be used in Colombia, to assure the neutralizing coverage for this species.

Actividad neurotóxica del veneno de serpientes del género Micrurus y métodos para su análisis. Revisión de la literatura

Introducción. Las serpientes del género Micrurus son animales de hábitos fosoriales, de temperamento pasivo y escasa producción de un potente veneno con características neurotóxicas que bloquean la transmisión sináptica en la placa neuromuscular.Objetivo. Presentar un panorama general de la neurotoxicidad del veneno de las serpientes Micrurus y su caracterización funcional mediante métodos de análisis ex vivo.Materiales y métodos. Se realizó una revisión de la literatura en MedLine y ScienceDirect usando términos específicos y sus combinaciones. Estrategia de búsqueda: tipo de estudios: artículos sobre la neurotoxicidad del veneno de serpientes Micrurus y técnicas para determinar su actividad neurotóxica mediante modelos in vitro, in vivo y ex vivo; periodo de publicación: sin limite inicial a junio de 2018; idiomas: inglés y español.Resultados. De los 88 estudios identificados en la búsqueda inicial, se excluyeron 28 por no cumplir los criterios de inclusión (basándose en la lectura de títulos y resúmenes); además, se incluyeron 8 documentos adicionales (libros e informes), que, a criterio de los autores, complementaban la información reportada por las referencias seleccionadas. Los estudios incluidos en la revisión (n=68) correspondieron a las siguientes tipologías: investigaciones originales (n=44), artículos de revisión (n=16) y capítulos de libros, informes, guías y consultas en internet (n=8).Conclusiones. Los estudios que describen el uso de preparaciones ex vivo de músculo y nervio para evaluar el efecto de neurotoxinas ofrecen un buen modelo para la caracterización del efecto presináptico y postsináptico del veneno producido por las serpientes Micrurus.

Fulditoxin, representing a new class of dimeric snake toxins, defines novel pharmacology at nicotinic ACh receptors

BACKGROUND AND PURPOSE

Animal toxins have contributed significantly to our understanding of the neurobiology of receptors and ion channels. We studied the venom of the coral snake Micrurus fulvius fulvius and identified and characterized the structure and pharmacology of a new homodimeric neurotoxin, fulditoxin, that exhibited novel pharmacology at nicotinic ACh receptors (nAChRs).

EXPERIMENTAL APPROACH

Fulditoxin was isolated by chromatography, chemically synthesized, its structure determined by X-ray crystallography, and its pharmacological actions on nAChRs characterized by organ bath assays and two-electrode voltage clamp electrophysiology.

KEY RESULTS

Fulditoxin's distinct 1.95-Å quaternary structure revealed two short-chain three-finger α-neurotoxins (α-3FNTxs) non-covalently bound by hydrophobic interactions and an ability to bind metal and form tetrameric complexes, not reported previously for three-finger proteins. Although fulditoxin lacked all conserved amino acids canonically important for inhibiting nAChRs, it produced postsynaptic neuromuscular blockade of chick muscle at nanomolar concentrations, comparable to the prototypical α-bungarotoxin. This neuromuscular blockade was completely reversible, which is unusual for snake α-3FNTxs. Fulditoxin, therefore, interacts with nAChRs by utilizing a different pharmacophore. Unlike short-chain α-3FNTxs that bind only to muscle nAChRs, fulditoxin utilizes dimerization to expand its pharmacological targets to include human neuronal α4β2, α7, and α3β2 nAChRs which it blocked with IC₅₀ values of 1.8, 7, and 12 μM respectively.

CONCLUSIONS AND IMPLICATIONS

Based on its distinct quaternary structure and unusual pharmacology, we named this new class of dimeric Micrurus neurotoxins represented by fulditoxin as Σ-neurotoxins, which offers greater insight into understanding the interactions between nAChRs and peptide antagonists.

From Synthetic Fragments of Endogenous Three-Finger Proteins to Potential Drugs

The proteins of the Ly6 family have a three-finger folding as snake venom α-neurotoxins, targeting nicotinic acetylcholine receptors (nAChRs), and some of them, like mammalian secreted Ly6/uPAR protein (SLURP1) and membrane-attached Ly-6/neurotoxin (Lynx1), also interact with distinct nAChR subtypes. We believed that synthetic fragments of these endogenous proteins might open new ways for drug design because nAChRs are well-known targets for developing analgesics and drugs against neurodegenerative diseases. Since interaction with nAChRs was earlier shown for synthetic fragments of the α-neurotoxin central loop II, we synthesized a 15-membered fragment of human Lynx1, its form with two Cys residues added at the N- and C-termini and forming a disulfide, as well as similar forms of human SLURP1, SLURP2, and of Drosophila sleepless protein (SSS). The IC₅₀ values measured in competition with radioiodinated α-bungarotoxin for binding to the membrane-bound Torpedo californica nAChR were 4.9 and 7.4 µM for Lynx1 and SSS fragments, but over 300 µM for SLURP1 or SLURP2 fragments. The affinity of these compounds for the α7 nAChR in the rat pituitary tumor-derived cell line GH4C1 was different: 13.1 and 147 µM for SSS and Lynx1 fragments, respectively. In competition for the ligand-binding domain of the α9 nAChR subunit, SSS and Lynx1 fragments had IC₅₀ values of about 40 µM, which correlates with the value found for the latter with the rat α9α10 nAChR expressed in the Xenopus oocytes. Thus, the activity of these synthetic peptides against muscle-type and α9α10 nAChRs indicates that they may be useful in design of novel myorelaxants and analgesics.

MipLAAO, a new L-amino acid oxidase from the redtail coral snake Micrurus mipartitus

L-amino acid oxidases (LAAOs) are ubiquitous enzymes in nature. Bioactivities described for these enzymes include apoptosis induction, edema formation, induction or inhibition of platelet aggregation, as well as antiviral, antiparasite, and antibacterial actions. With over 80 species, Micrurus snakes are the representatives of the Elapidae family in the New World. Although LAAOs in Micrurus venoms have been predicted by venom gland transcriptomic studies and detected in proteomic studies, no enzymes of this kind have been previously purified from their venoms. Earlier proteomic studies revealed that the venom of M. mipartitus from Colombia contains ∼4% of LAAO. This enzyme, here named MipLAAO, was isolated and biochemically and functionally characterized. The enzyme is found in monomeric form, with an isotope-averaged molecular mass of 59,100.6 Da, as determined by MALDI-TOF. Its oxidase activity shows substrate preference for hydrophobic amino acids, being optimal at pH 8.0. By nucleotide sequencing of venom gland cDNA of mRNA transcripts obtained from a single snake, six isoforms of MipLAAO with minor variations among them were retrieved. The deduced sequences present a mature chain of 483 amino acids, with a predicted pI of 8.9, and theoretical masses between 55,010.9 and 55,121.0 Da. The difference with experimentally observed mass is likely due to glycosylation, in agreement with the finding of three putative N-glycosylation sites in its amino acid sequence. A phylogenetic analysis of MmipLAAO placed this new enzyme within the clade of homologous proteins from elapid snakes, characterized by the conserved Serine at position 223, in contrast to LAAOs from viperids. MmipLAAO showed a potent bactericidal effect on S. aureus (MIC: 2 µg/mL), but not on E. coli. The former activity could be of interest to future studies assessing its potential as antimicrobial agent.

Ancient Diversification of Three-Finger Toxins in Micrurus Coral Snakes

Coral snakes, most notably the genus Micrurus, are the only terrestrial elapid snakes in the Americas. Elapid venoms are generally known for their potent neurotoxicity which is usually caused by Three-Finger Toxin (3FTx) proteins. These toxins can have a wide array of functions that have been characterized from the venom of other elapids. We examined publicly available sequences from Micrurus 3FTx to show that they belong to 8 monophyletic clades that diverged as deep in the 3FTx phylogenetic tree as the other clades with characterized functions. Functional residues from previously characterized clades of 3FTx are not well conserved in most of the Micrurus toxin clades. We also analyzed the patterns of selection on these toxins and find that they have been diversifying at different rates, with some having undergone extreme diversifying selection. This suggests that Micrurus 3FTx may contain a previously underappreciated functional diversity that has implications for the clinical outcomes of bite victims, the evolution and ecology of the genus, as well as the potential for biodiscovery efforts focusing on these toxins.

Envenomation by Micrurus psyches in French Guiana

We report here the first known envenomation by Micrurus psyches, the so-called Carib coral snake, which occurred on April 2016 in the surroundings of Saint-Laurent-du-Maroni, Western French Guiana. Besides local neurological symptoms, it featured unexpected electrocardiogram changes, which were emergence of a first-degree atrioventricular block and biphasic T waves, both transient. NewWorld elapid venoms were not known for being cardiotoxic so far. The possible reasons of this cardiac injury are discussed.

Envenomation by the red-tailed coral snake (Micrurus mipartitus) in Colombia

BACKGROUND

Although the red-tailed coral snake (Micrurus mipartitus) is widely distributed in Colombia and its venom is highly neurotoxic and life threatening, envenomation by this species is rare. Therefore, this report may shed some light on the clinical presentation of M. mipartitus bites.

CASE PRESENTATIONS

Herein, we describe two cases of patients bitten by red-tailed coral snakes, illustrating the clinical presentation of the victims, the outcomes and treatment provided.

CONCLUSION

Envenomation caused by M. mipartitus provokes predicable neurotoxicity, and its treatment should be based on respiratory support and use of specific antivenom.

Exploration of immunoglobulin transcriptomes from mice immunized with three-finger toxins and phospholipases A2 from the Central American coral snake, Micrurus nigrocinctus

Snakebite envenomings represent a neglected public health issue in many parts of the rural tropical world. Animal-derived antivenoms have existed for more than a hundred years and are effective in neutralizing snake venom toxins when timely administered. However, the low immunogenicity of many small but potent snake venom toxins represents a challenge for obtaining a balanced immune response against the medically relevant components of the venom. Here, we employ high-throughput sequencing of the immunoglobulin (Ig) transcriptome of mice immunized with a three-finger toxin and a phospholipase A₂ from the venom of the Central American coral snake, Micrurus nigrocinctus. Although exploratory in nature, our indicate results showed that only low frequencies of mRNA encoding IgG isotypes, the most relevant isotype for therapeutic purposes, were present in splenocytes of five mice immunized with 6 doses of the two types of toxins over 90 days. Furthermore, analysis of Ig heavy chain transcripts showed that no particular combination of variable (V) and joining (J) gene segments had been selected in the immunization process, as would be expected after a strong humoral immune response to a single antigen. Combined with the titration of toxin-specific antibodies in the sera of immunized mice, these data support the low immunogenicity of three-finger toxins and phospholipases A₂found in M. nigrocinctusvenoms, and highlight the need for future studies analyzing the complexity of antibody responses to toxins at the molecular level.

Maintenance of red-tail coral snake (Micrurus mipartitus) in captivity and evaluation of individual venom variability

La coral “rabo de ají” es una coral bicolor larga y delgada. Esta especie está ampliamente distribuida en Colombia y es la coral que causa el mayor número de accidentes en la región Andina, por esto es importante mantener esta especie en cautiverio con fines de producción de antivenenos e investigación. No obstante, el mantenimiento de esta especie en cautiverio es difícil, debido a que se rehúsan a alimentarse voluntariamente y a que presentan alta mortalidad por el denominado síndrome de mal adaptación. En este estudio se evaluaron varios  sustratos para el mantenimiento, además de una dieta forzada y una técnica de ordeño. Adicionalmente, se evaluó la variabilidad individual del veneno a través de cromatografía liquida de alta eficiencia (HPLC), electroforesis (SDS-PAGE) y las actividades coagulante, anticoagulante y hemolítica indirecta. Los resultados de este estudio demostraron que fue posible incrementar la sobrevivencia de esta especie en cautiverio, así como determinar algunos factores importantes en su mantenimiento. A partir de la evaluación del veneno se encontraron diferencias en el número y en la intensidad de picos en la cromatografía, así como en algunas de sus actividades biológicas.

Venom of the Coral Snake Micrurus clarki: Proteomic Profile, Toxicity, Immunological Cross-Neutralization, and Characterization of a Three-Finger Toxin

Micrurus clarki is an uncommon coral snake distributed from the Southeastern Pacific of Costa Rica to Western Colombia, for which no information on its venom could be found in the literature. Using a ‘venomics’ approach, proteins of at least nine families were identified, with a moderate predominance of three-finger toxins (3FTx; 48.2%) over phospholipase A₂ (PLA₂; 36.5%). Comparison of this venom profile with those of other Micrurus species suggests that it may represent a more balanced, ‘intermediate’ type within the dichotomy between 3FTx- and PLA₂-predominant venoms. M. clarki venom was strongly cross-recognized and, accordingly, efficiently neutralized by an equine therapeutic antivenom against M. nigrocinctus, revealing their high antigenic similarity. Lethal activity for mice could be reproduced by a PLA₂ venom fraction, but, unexpectedly, not by fractions corresponding to 3FTxs. The most abundant venom component, hereby named clarkitoxin-I, was identified as a short-chain (type I) 3FTx, devoid of lethal effect in mice, whose target remains to be defined. Its amino acid sequence of 66 residues shows high similarity with predicted sequences of venom gland transcripts described for M. fulvius, M. browni, and M. diastema.

Integrative characterization of the venom of the coral snake Micrurus dumerilii (Elapidae) from Colombia: Proteome, toxicity, and cross-neutralization by antivenom

In Colombia, nearly 2.8% of the 4200 snakebite accidents recorded annually are inflicted by coral snakes (genus Micrurus). Micrurus dumerilii has a broad distribution in this country, especially in densely populated areas. The proteomic profile of its venom was here studied by a bottom-up approach combining RP-HPLC, SDS-PAGE and MALDI-TOF/TOF. Venom proteins were assigned to eleven families, the most abundant being phospholipases A2 (PLA2; 52.0%) and three-finger toxins (3FTx; 28.1%). This compositional profile shows that M. dumerilii venom belongs to the 'PLA2-rich' phenotype, in the recently proposed dichotomy for Micrurus venoms. Enzymatic and toxic venom activities correlated with protein family abundances. Whole venom induced a conspicuous myotoxic, cytotoxic and anticoagulant effect, and was mildly edematogenic and proteolytic, whereas it lacked hemorrhagic activity. Some 3FTxs and PLA2s reproduced the lethal effect of venom. A coral snake antivenom to Micrurus nigrocinctus demonstrated significant cross-recognition of M. dumerilii venom proteins, and accordingly, ability to neutralize its lethal effect. The combined compositional, functional, and immunological data here reported for M. dumerilii venom may contribute to a better understanding of these envenomings, and support the possible use of anti-M. nigrocinctus coral snake antivenom in their treatment.

BIOLOGICAL SIGNIFICANCE

Coral snakes represent a highly diversified group of elapids in the New World, with nearly 70 species within the genus Micrurus. Owing to their scarce yields, the biochemical composition and toxic activities of coral snake venoms have been less well characterized than those of viperid species. In this work, an integrative view of the venom of M. dumerilii, a medically relevant coral snake from Colombia, was obtained by a combined proteomic, functional, and immunological approach. The venom contains proteins from at least eleven families, with a predominance of phospholipases A2 (PLA2), followed by three-finger toxins (3FTx). According to its compositional profile, M. dumerilii venom can be grouped with those of several Micrurus species from North and Central America that present a PLA2-predominant phenotype, to date it is the most southerly coral snake species to do so. Other coral snake species that a 'PLA2-rich' venom, M. dumerilii venom contains both components that form MitTx, a pain-inducing heterodimeric complex recently characterized from the venom of Micrurus tener, also present in Micrurus mosquitensis and M. nigrocinctus venoms. In addition to a lethal three-finger toxin, PLA2s participate in the toxicity of M. dumerilii venom, some of them displaying ability to induce cytolysis, muscle necrosis, and lethality to mice. An antivenom to M. nigrocinctus demonstrated significant cross-recognition of M. dumerilii venom proteins, and accordingly, ability to neutralize its lethal effect, being of potential therapeutic usefulness in these envenomings.

Neuromuscular activity of Micrurus laticollaris (Squamata: Elapidae) venom in vitro

In this work, we have examined the neuromuscular activity of Micrurus laticollaris (Mexican coral snake) venom (MLV) in vertebrate isolated nerve-muscle preparations. In chick biventer cervicis preparations, the MLV induced an irreversible concentration- and time-dependent (1–30 µg/mL) neuromuscular blockade, with 50% blockade occurring between 8 and 30 min. Muscle contractures evoked by exogenous acetylcholine were completely abolished by MLV, whereas those of KCl were also significantly altered (86% ± 11%, 53% ± 11%, 89% ± 5% and 89% ± 7% for one, three, 10 and 30 µg of venom/mL, respectively; n = 4; p < 0.05). In mouse phrenic nerve-diaphragm preparations, MLV (1–10 µg/mL) promoted a slight increase in the amplitude of twitch-tension (3 µg/mL), followed by neuromuscular blockade (n = 4); the highest concentration caused complete inhibition of the twitches (time for 50% blockade = 26 ± 3 min), without exhibiting a previous neuromuscular facilitation. The venom (3 µg/mL) induced a biphasic modulation in the frequency of miniature end-plate potentials (MEPPs)/min, causing a significant increase after 15 min, followed by a decrease after 60 min (from 17 ± 1.4 (basal) to 28 ± 2.5 (t₁₅) and 12 ± 2 (t₆₀)). The membrane resting potential of mouse diaphragm preparations pre-exposed or not to d-tubocurarine (5 µg/mL) was also significantly less negative with MLV (10 µg/mL). Together, these results indicate that M. laticollaris venom induces neuromuscular blockade by a combination of pre- and post-synaptic activities.