Natural inhibitors of snake venom hemorrhagic metalloproteinases

Alpha-1-B glycoprotein (A1BG) inhibits sterol-binding and export by CRISP2

Proteins belonging to the CAP superfamily are present in all kingdoms of life and have been implicated in various processes, including sperm maturation and cancer progression. They are mostly secreted glycoproteins and share a unique conserved CAP domain. The precise mode of action of these proteins, however, has remained elusive. Saccharomyces cerevisiae expresses three members of this protein family, which bind sterols in vitro and promote sterol secretion from cells. This sterol-binding and export function of yeast Pry proteins is conserved in the mammalian CRISP proteins and other CAP superfamily members. CRISP3 is an abundant protein of the human seminal plasma and interacts with alpha-1-B glycoprotein (A1BG), a human plasma glycoprotein that is upregulated in different types of cancers. Here we examined whether the interaction between CRISP proteins and A1BG affects the sterol-binding function of CAP family members. Co-expression of A1BG with CAP proteins abolished their sterol export function in yeast and their interaction inhibits sterol-binding in vitro. We map the interaction between A1BG and CRISP2 to the third of five repeated immunoglobulin-like (Ig) domains within A1BG. Interestingly, the interaction between A1BG and CRISP2 requires magnesium, suggesting that coordination of Mg2+ by the highly conserved tetrad residues within the CAP domain is essential for a stable interaction between the two proteins. The observation that A1BG modulates the sterol-binding function of CRISP2, has potential implications for the role of A1BG and related Ig domain containing proteins in cancer progression and the toxicity of reptile venoms containing CRISP proteins.

Proteotransciptomics of the Most Popular Host Sea Anemone Entacmaea quadricolor Reveals Not All Toxin Genes Expressed by Tentacles Are Recruited into Its Venom Arsenal

While the unique symbiotic relationship between anemonefishes and sea anemones is iconic, it is still not fully understood how anemonefishes can withstand and thrive within the venomous environment of their host sea anemone. In this study, we used a proteotranscriptomics approach to elucidate the proteinaceous toxin repertoire from the most common host sea anemone, Entacmaea quadricolor. Although 1251 different toxin or toxin-like RNA transcripts were expressed in E. quadricolor tentacles (0.05% of gene clusters, 1.8% of expression) and 5375 proteins were detected in milked venom, only 4% of proteins detected in venom were putative toxins (230), and they only represent on average 14% of the normalised protein expression in the milked venom samples. Thus, most proteins in milked venom do not appear to have a toxin function. This work raises the perils of defining a dominant venom phenotype based on transcriptomics data alone in sea anemones, as we found that the dominant venom phenotype differs between the transcriptome and proteome abundance data. E. quadricolor venom contains a mixture of toxin-like proteins of unknown and known function. A newly identified toxin protein family, Z3, rich in conserved cysteines of unknown function, was the most abundant at the RNA transcript and protein levels. The venom was also rich in toxins from the Protease S1, Kunitz-type and PLA2 toxin protein families and contains toxins from eight venom categories. Exploring the intricate venom toxin components in other host sea anemones will be crucial for improving our understanding of how anemonefish adapt to the venomous environment.

The anti-myotoxic effects and mechanisms of Sinonatrix annularis serum and a novel plasma metalloproteinase inhibitor towards Deinagkistrodon acutus envenomation

Non-venomous snakes commonly evolve natural resistance to venom to escape predators. Sinonatrix annularis serum has been shown to inhibit Deinagkistrodon acutus venom-induced hemorrhage and upregulation of serum CK, CK-MB, LDH, AST and ALT levels. Using TMT-labeled proteomics analysis, 168 proteins were found to be altered significantly in the envenomed gastrocnemius muscle and categorized into pathways such as complement and coagulation cascades, leukocyte transendothelial migration, and JAK/STAT signaling. These alterations were mitigated by S. annularis serum. Subsequently, a novel metalloproteinase inhibitor, SaMPI, was isolated from S. annularis serum by two-step chromatography. It showed strong antidotal effects against D. acutus envenomation, including inhibition of subcutaneous bleeding caused by crude venom and DaMP (a metalloproteinase derived from D. acutus) activity in a 1:1 ratio. Histology and immunoblotting analyses demonstrated that SaMPI mitigated myonecrosis, reduced neutrophil infiltration and local inflammatory factor release, and retarded JAK/STAT and MAPK signaling activation. Analysis of the SaMPI gene cloned by 5'-RACE revealed a shared sequence identity of 58-79% with other SVMP inhibitors. These findings demonstrate the protective effects of SaMPI and indicate its potential value as a candidate for viper bite adjuvant therapy.

Neutralization of "Chaco eagle" (Buteogallus coronatus) serum on some activities of Bothrops spp. venoms

Several species of reptiles and mammals have components in their sera that can neutralize toxic components present in snake venoms. In this manuscript, we studied the neutralizing capacity of Chaco eagle's (Buteogallus coronatus) serum. This South American bird of prey eats snakes as a regular part of its diet and has anatomical features that protect from snakes' bites. The neutralizing potency of the Chaco eagle's serum was tested on lethal, hemorrhagic, procoagulant, and phospholipase activities of the venom of "yarará grande" (Bothrops alternatus) and on phospholipase activity of "yarará ñata" (Bothrops ammodytoides) venom; both snakes are known to be the prey of Chaco eagle. Sera of crested caracara (Caracara plancus-a scavenger, omnivorous pan-American bird of prey), secretary bird (Saggitarius serpentarius-an omnivorous bird of prey from Africa that can include venomous snakes in its diet), common hen (Gallus gallus), rat (Rattus norvegicus), mouse (Mus musculus), horse (Equus caballus), and dog (Canis lupus familiaris) were also tested to compare the inhibitory capacity of neutralization. To test isologous and xenologous neutralization, sera from Bothrops alternatus and white-eared opossum (Didelphis albiventris), respectively, were used due to their known inhibitory activity on Bothrops venoms. As a control for the neutralization activity, antibothropic antivenom was used. Chaco eagle's serum neutralized hemorrhagic and phospholipasic activity and slightly neutralized the coagulation and the lethal activity of Bothrops spp. venom. The neutralizing capacity was present in the non-immunoglobulin fraction of the serum, which showed components of acidic characteristics and lower molecular weight than IgY, in correspondence with the characteristics of PLA₂s and SVMPs inhibitors described in sera from some snakes and mammals. These studies showed that Chaco eagle's serum neutralizes all toxic activities tested at a higher level than sera from animal species in which inhibitors of snake venoms have not been described (p < 0.05), while it is lower or similar in neutralizing capacity to white-eared opossum and B. alternatus sera.

Phenotypic and functional variation in venom and venom resistance of two sympatric rattlesnakes and their prey

Predator-prey interactions often lead to the coevolution of adaptations associated with avoiding predation and, for predators, overcoming those defences. Antagonistic coevolutionary relationships are often not simple interactions between a single predator and prey but rather a complex web of interactions between multiple coexisting species. Coevolution between venomous rattlesnakes and small mammals has led to physiological venom resistance in several mammalian taxa. In general, viperid venoms contain large quantities of snake venom metalloproteinase toxins (SVMPs), which are inactivated by SVMP inhibitors expressed in resistant mammals. We explored variation in venom chemistry, SVMP expression, and SVMP resistance across four co-distributed species (California Ground Squirrels, Bryant's Woodrats, Southern Pacific Rattlesnakes, and Red Diamond Rattlesnakes) collected from four different populations in Southern California. Our aim was to understand phenotypic and functional variation in venom and venom resistance in order to compare coevolutionary dynamics of a system involving two sympatric predator-prey pairs to past studies that have focused on single pairs. Proteomic analysis of venoms indicated that these rattlesnakes express different phenotypes when in sympatry, with Red Diamonds expressing more typical viperid venom (with a diversity of SVMPs) and Southern Pacifics expressing a more atypical venom with a broader range of non-enzymatic toxins. We also found that although blood sera from both mammals were generally able to inhibit SVMPs from both rattlesnake species, inhibition depended strongly on the snake population, with snakes from one geographic site expressing SVMPs to which few mammals were resistant. Additionally, we found that Red Diamond venom, rather than woodrat resistance, was locally adapted. Our findings highlight the complexity of coevolutionary relationships between multiple predators and prey that exhibit similar offensive and defensive strategies in sympatry.

The molecular basis of venom resistance in a rattlesnake-squirrel predator-prey system

Understanding how interspecific interactions mould the molecular basis of adaptations in coevolving species is a long-sought goal of evolutionary biology. Venom in predators and venom resistance proteins in prey are coevolving molecular phenotypes, and while venoms are highly complex mixtures it is unclear if prey respond with equally complex resistance traits. Here, we use a novel molecular methodology based on protein affinity columns to capture and identify candidate blood serum resistance proteins ("venom interactive proteins" [VIPs]) in California Ground Squirrels (Otospermophilus beecheyi) that interact with venom proteins from their main predator, Northern Pacific Rattlesnakes (Crotalus o. oreganus). This assay showed that serum-based resistance is both population- and species-specific, with serum proteins from ground squirrels showing higher binding affinities for venom proteins of local snakes compared to allopatric individuals. Venom protein specificity assays identified numerous and diverse candidate prey resistance VIPs but also potential targets of venom in prey tissues. Many specific VIPs bind to multiple snake venom proteins and, conversely, single venom proteins bind multiple VIPs, demonstrating that a portion of the squirrel blood serum "resistome" involves broad-based inhibition of nonself proteins and suggests that resistance involves a toxin scavenging mechanism. Analyses of rates of evolution of VIP protein homologues in related mammals show that most of these proteins evolve under purifying selection possibly due to molecular constraints that limit the evolutionary responses of prey to rapidly evolving snake venom proteins. Our method represents a general approach to identify specific proteins involved in co-evolutionary interactions between species at the molecular level.

Deimination Protein Profiles in Alligator mississippiensis Reveal Plasma and Extracellular Vesicle-Specific Signatures Relating to Immunity, Metabolic Function, and Gene Regulation

Alligators are crocodilians and among few species that endured the Cretaceous-Paleogene extinction event. With long life spans, low metabolic rates, unusual immunological characteristics, including strong antibacterial and antiviral ability, and cancer resistance, crocodilians may hold information for molecular pathways underlying such physiological traits. Peptidylarginine deiminases (PADs) are a group of calcium-activated enzymes that cause posttranslational protein deimination/citrullination in a range of target proteins contributing to protein moonlighting functions in health and disease. PADs are phylogenetically conserved and are also a key regulator of extracellular vesicle (EV) release, a critical part of cellular communication. As little is known about PAD-mediated mechanisms in reptile immunology, this study was aimed at profiling EVs and protein deimination in Alligator mississippiensis. Alligator plasma EVs were found to be polydispersed in a 50-400-nm size range. Key immune, metabolic, and gene regulatory proteins were identified to be posttranslationally deiminated in plasma and plasma EVs, with some overlapping hits, while some were unique to either plasma or plasma EVs. In whole plasma, 112 target proteins were identified to be deiminated, while 77 proteins were found as deiminated protein hits in plasma EVs, whereof 31 were specific for EVs only, including proteins specific for gene regulatory functions (e.g., histones). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed KEGG pathways specific to deiminated proteins in whole plasma related to adipocytokine signaling, while KEGG pathways of deiminated proteins specific to EVs included ribosome, biosynthesis of amino acids, and glycolysis/gluconeogenesis pathways as well as core histones. This highlights roles for EV-mediated export of deiminated protein cargo with roles in metabolism and gene regulation, also related to cancer. The identification of posttranslational deimination and EV-mediated communication in alligator plasma revealed here contributes to current understanding of protein moonlighting functions and EV-mediated communication in these ancient reptiles, providing novel insight into their unusual immune systems and physiological traits. In addition, our findings may shed light on pathways underlying cancer resistance, antibacterial and antiviral resistance, with translatable value to human pathologies.

Natural Inhibitors of Snake Venom Metalloproteinases

Snakebites are a hazard in the tropical world. Although antivenom therapy is effective, it is beset with inherent drawbacks. A better understanding of the major components of snake venoms and their neutralisation will help in improving snakebite treatment. Snake venom metalloproteinases (SVMPs) are responsible for severe haemorrhage, the inhibition of coagulation and platelet aggregation, observed in the victims of snakebite envenoming. Inhibitors from various sources including medicinal plants, animal venoms, and sera are sought to block the pharmacological functions of SVMPs. In this review, we describe the interaction of natural inhibitors with SVMPs. To understand their inhibitory mechanisms, we focussed on the complex structures of these inhibitors and SVMPs. There are three distinct classes of inhibitors; namely, chelators, competitive inhibitors, and non-competitive inhibitors. A small number of inhibitors show their anti-hemorrhagic activity in invivo animal models in treatment mode, but most studies evaluate either invitro neutralisation of enzymatic activity or invivo effects in pre-incubation protocols. We propose the distinct strategies and limitations to design either broad-spectrum or highly selective SVMP inhibitors. The goal of designing broad-spectrum inhibitors against SVMPs capable of effective treatment of snakebites without toxicity has been elusive, probably because of the narrow molecular footprint of inhibitors against a large number of SVMPs with distinct molecular surfaces. Our ability to design highly selective inhibitors is limited by the lack of information of interactions between selective inhibitors and SVMPs. Comparisons of structures of hemorrhagic and non-hemorrhagic SVMPs revealed different distributions of electric charge on the surface of SVMPs, which may be exploited to design specific inhibitors. The specific inhibitors may also be useful to identify target molecules of the SVMPs and help to understand their mechanism of action.

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.

Engineered nanoparticles bind elapid snake venom toxins and inhibit venom-induced dermonecrosis

Envenomings by snakebites constitute a serious and challenging global health issue. The mainstay in the therapy of snakebite envenomings is the parenteral administration of animal-derived antivenoms. Significantly, antivenoms are only partially effective in the control of local tissue damage. A novel approach to mitigate the progression of local tissue damage that could complement the antivenom therapy of envenomings is proposed. We describe an abiotic hydrogel nanoparticle engineered to bind to and modulate the activity of a diverse array of PLA2 and 3FTX isoforms found in Elapidae snake venoms. These two families of protein toxins share features that are associated with their common (membrane) targets, allowing for nanoparticle sequestration by a mechanism that differs from immunological (epitope) selection. The nanoparticles are non-toxic in mice and inhibit dose-dependently the dermonecrotic activity of Naja nigricollis venom.

Zoanthid mucus as new source of useful biologically active proteins

Palythoa caribaeorum is a very common colonial zoanthid in the coastal reefs of Brazil. It is known for its massive production of mucus, which is traditionally used in folk medicine by fishermen in northeastern Brazil. This study identified biologically active compounds in P. caribaerum mucus. Crude mucus was collected during low tides by the manual scraping of colonies; samples were maintained in an ice bath, homogenized, and centrifuged at 16,000 g for 1 h at 4 °C; the supernatant (mucus) was kept at -80 °C until use. The enzymatic (proteolytic and phospholipase A₂), inhibitory (metallo, cysteine and serine proteases), and hemagglutinating (human erythrocyte) activities were determined. The results showed high levels of cysteine and metallo proteases, intermediate levels of phosholipase A₂, low levels of trypsin, and no elastase and chymotrypsin like activities. The mucus showed potent inhibitory activity on snake venom metalloproteases and cysteine proteinase papain. In addition, it showed agglutinating activity towards O⁺, B⁺, and A⁺ erythrocyte types. The hemostatic results showed that the mucus prolongs the aPTT and PT, and strongly inhibited platelet aggregation induced by arachidonic acid, collagen, epinephrine, ADP, and thrombin. The antimicrobial activity was tested on 15 strains of bacteria and fungi through the radial diffusion assay in agar, and no activity was observed. Compounds in P. caribaeorum mucus were analyzed for the first time in this study, and our results show potential pharmacological activities in these compounds, which are relevant for use in physiopathological investigations. However, the demonstration of these activities indicates caution in the use of crude mucus in folk medicine. Furthermore, the present or absent activities identified in this mucus suggest that the studied P. caribaeorum colonies were in thermal stress conditions at the time of sample collection; these conditions may precede the bleaching process in zoanthids. Hence, the use of mucus as an indicator of this process should be evaluated in the future.

Structure-Based Discovery of Thiosemicarbazone Metalloproteinase Inhibitors for Hemorrhage Treatment in Snakebites

The venoms of snakes are composed by many toxins, which are responsible for various toxic effects including intense pain, bleeding disorders, and local tissue damage caused by hemorrhage and necrosis. The snake venom metalloproteinases (SVMPs) are proteolytic zinc-dependent enzymes acting in different hemostatic mechanisms. In this work, a structure-based molecular modeling strategy was used for the rational design, by means of a homology 3D model of an SVMP isolated from Bothrops pauloensis venom (BpMP-I), followed by synthesis and in vitro evaluation of new thiosemicarbazones as the first inhibitors of the B. pauloensis SVMP. Besides being effective for the SVMP inhibition, two molecules were shown to be effective also in vivo, inhibiting hemorrhage caused by the B. pauloensis whole venom. Docking studies on metalloproteinases from other snake species suggest that the thiosemicarbazones activity is not confined to BpMP-I, but seems to be a common feature of metzincins.

Transcriptome analysis of the response of Burmese python to digestion

Exceptional and extreme feeding behaviour makes the Burmese python (Python bivittatus) an interesting model to study physiological remodelling and metabolic adaptation in response to refeeding after prolonged starvation. In this study, we used transcriptome sequencing of 5 visceral organs during fasting as well as 24 hours and 48 hours after ingestion of a large meal to unravel the postprandial changes in Burmese pythons. We first used the pooled data to perform a de novo assembly of the transcriptome and supplemented this with a proteomic survey of enzymes in the plasma and gastric fluid. We constructed a high-quality transcriptome with 34 423 transcripts, of which 19 713 (57%) were annotated. Among highly expressed genes (fragments per kilo base per million sequenced reads > 100 in 1 tissue), we found that the transition from fasting to digestion was associated with differential expression of 43 genes in the heart, 206 genes in the liver, 114 genes in the stomach, 89 genes in the pancreas, and 158 genes in the intestine. We interrogated the function of these genes to test previous hypotheses on the response to feeding. We also used the transcriptome to identify 314 secreted proteins in the gastric fluid of the python. Digestion was associated with an upregulation of genes related to metabolic processes, and translational changes therefore appear to support the postprandial rise in metabolism. We identify stomach-related proteins from a digesting individual and demonstrate that the sensitivity of modern liquid chromatography/tandem mass spectrometry equipment allows the identification of gastric juice proteins that are present during digestion.

Isolation and characterization of a novel metalloprotease inhibitor from Bothrops alternatus snake serum

Resistance of snakes and some other animals to snake envenomation has been attributed to soluble factors present in their tissues. Here we report the isolation of a novel metalloprotease inhibitor from Bothrops alternatus snake serum (named BaltMPI) with high purity, using a four-step chromatographic method. BaltMPI has molecular weights of 60.5 and 42.4kDa, as determined by SDS-PAGE and mass spectrometry, respectively, and pI=5.27. The first 60 amino acids from the N-terminal region of BaltMPI, determined by Edman's degradation, showed high homology (97%) with the snake venom metalloprotease inhibitor (SVMPI) BJ46a and other SVMPIs (78-82%). The chromatographic fractions and purified BaltMPI exhibited anti-hemorrhagic activity against Batroxase and BjussuMP-I. BaltMPI was stable over wide ranges of pH (1, 5, 8, and 9) and temperature (-80, -20, 4, 60, and 100°C), and suppressed the fibrinogenolytic, fibrinolytic, and azocaseinolytic activities of Batroxase. BaltMPI specifically inhibited the activity of metalloproteases, without affecting the activity of serine proteases. Together, our results suggest that BaltMPI and other SVMPIs are promising molecules for the treatment of snake envenomation, in particular that caused by Bothrops sp.

Natural Inhibitors of Snake Venom Metalloendopeptidases: History and Current Challenges

The research on natural snake venom metalloendopeptidase inhibitors (SVMPIs) began in the 18th century with the pioneering work of Fontana on the resistance that vipers exhibited to their own venom. During the past 40 years, SVMPIs have been isolated mainly from the sera of resistant animals, and characterized to different extents. They are acidic oligomeric glycoproteins that remain biologically active over a wide range of pH and temperature values. Based on primary structure determination, mammalian plasmatic SVMPIs are classified as members of the immunoglobulin (Ig) supergene protein family, while the one isolated from muscle belongs to the ficolin/opsonin P35 family. On the other hand, SVMPIs from snake plasma have been placed in the cystatin superfamily. These natural antitoxins constitute the first line of defense against snake venoms, inhibiting the catalytic activities of snake venom metalloendopeptidases through the establishment of high-affinity, non-covalent interactions. This review presents a historical account of the field of natural resistance, summarizing its main discoveries and current challenges, which are mostly related to the limitations that preclude three-dimensional structural determinations of these inhibitors using “gold-standard” methods; perspectives on how to circumvent such limitations are presented. Potential applications of these SVMPIs in medicine are also highlighted.

Venom Resistance as a Model for Understanding the Molecular Basis of Complex Coevolutionary Adaptations

SynopsisVenom and venom resistance are molecular phenotypes widely considered to have diversified through coevolution between predators and prey. However, while evolutionary and functional studies on venom have been extensive, little is known about the molecular basis, variation, and complexity of venom resistance. We review known mechanisms of venom resistance and relate these mechanisms to their predicted impact on coevolutionary dynamics with venomous enemies. We then describe two conceptual approaches which can be used to examine venom/resistance systems. At the intraspecific level, tests of local adaptation in venom and resistance phenotypes can identify the functional mechanisms governing the outcomes of coevolution. At deeper evolutionary timescales, the combination of phylogenetically informed analyses of protein evolution coupled with studies of protein function promise to elucidate the mode and tempo of evolutionary change on potentially coevolving genes. We highlight case studies that use each approach to extend our knowledge of these systems as well as address larger questions about coevolutionary dynamics. We argue that resistance and venom are phenotypic traits which hold exceptional promise for investigating the mechanisms, dynamics, and outcomes of coevolution at the molecular level. Furthermore, extending the understanding of single gene-for-gene interactions to the whole resistance and venom phenotypes may provide a model system for examining the molecular and evolutionary dynamics of complex multi-gene interactions.

IgE antibodies, FcεRIα, and IgE-mediated local anaphylaxis can limit snake venom toxicity

BACKGROUND

Type 2 cytokine-related immune responses associated with development of antigen-specific IgE antibodies can contribute to pathology in patients with allergic diseases and to fatal anaphylaxis. However, recent findings in mice indicate that IgE also can enhance defense against honeybee venom.

OBJECTIVE

We tested whether IgE antibodies, IgE-dependent effector mechanisms, and a local anaphylactic reaction to an unrelated antigen can enhance defense against Russell viper venom (RVV) and determined whether such responses can be influenced by immunization protocol or mouse strain.

METHODS

We compared the resistance of RVV-immunized wild-type, IgE-deficient, and Fcer1a-deficient mice after injection of a potentially lethal dose of RVV.

RESULTS

A single prior exposure to RVV enhanced the ability of wild-type mice, but not mice lacking IgE or functional FcεRI, to survive challenge with a potentially lethal amount of RVV. Moreover, IgE-dependent local passive cutaneous anaphylaxis in response to challenge with an antigen not naturally present in RVV significantly enhanced resistance to the venom. Finally, we observed different effects on resistance to RVV or honeybee venom in BALB/c versus C57BL/6 mice that had received a second exposure to that venom before challenge with a high dose of that venom.

CONCLUSION

These observations illustrate the potential benefit of IgE-dependent effector mechanisms in acquired host defense against venoms. The extent to which type 2 immune responses against venoms can decrease pathology associated with envenomation seems to be influenced by the type of venom, the frequency of venom exposure, and the genetic background of the host.

Flavorase, a novel non-haemorrhagic metalloproteinase in Protobothrops flavoviridis venom, is a target molecule of small serum protein-3

Some venomous snakes possess anti-toxic proteins in their sera that may play a role in neutralizing the haemorrhagic factors or toxins in their own venom. Five small serum proteins (SSP-1-SSP-5) were isolated from the serum of Japanese viper (Protobothrops flavoviridis), and were found to act as self-defence proteins against the viper's own toxic components. However, the physiological function of SSP-3 has not been completely elucidated. Affinity chromatography of the venom on an SSP-3-immobilized column identified a novel 55-kDa protein as the target molecule of SSP-3. Sequences of internal fragments of this SSP-3-binding protein showed high homology to those of metalloproteinases from the P. flavoviridis venom. The cDNA sequence revealed that this protein, termed flavorase, is a P-III class metalloproteinase consisting of 423 amino acid residues. The purified protein did not show haemorrhagic and cytotoxic activity. Biacore measurements revealed that SSP-3 was bound to flavorase with a dissociation constant of 6.4 × 10(-9) M. SSP-3 non-competitively inhibited the peptidase activity of flavorase with an inhibition constant of 6.6 × 10(-9) M.

Reducing the impact of snakebite envenoming in Latin America and the Caribbean: achievements and challenges ahead

Snakebite envenoming constitutes an important public health problem in Latin America and some countries of the Caribbean. The advances and pending tasks in the study and control of this neglected tropical disease in this region are reviewed in the light of a roadmap proposed in 2006. Significant progress has been achieved in the study of snake venoms, particularly regarding venom proteomics, i.e.'venomics', and the analysis of the mechanism of action of toxins. Likewise, a deeper understanding has been gained in the preclinical efficacy of antivenoms produced in the region. In contrast, despite advances made in the study of clinical manifestations of envenomings and safety and efficacy of antivenoms at the clinical level, much remains to be done in this subject. Improvements have occurred in antivenom manufacturing technologies and availability, although there are still countries where there is insufficient supply of antivenoms, or where manufacture has to be improved. In spite of considerable efforts in some countries in prevention, accessibility to treatment, and training of health staff in the management of envenomings, important challenges remain for the region as a whole, with the long term goal of reducing the impact of this disease in terms of personal and social suffering.

Structural analysis and characterization of new small serum proteins from the serum of a venomous snake (Gloydius blomhoffii)

Some snakes have several anti-toxic proteins in their sera that neutralize their own venom. Five new small serum proteins (SSPs) were isolated from Japanese mamushi (Gloydius blomhoffii) serum by gel-filtration and RP-HPLC, and their N-Terminal sequences were determined. The amino acid sequences of the precursor proteins were deduced from the nucleotide sequences of cDNAs encoding them. Due to the sequence similarity to those of SSPs in habu snake (Protobothrops flavoviridis) serum (>75% identity), these proteins were designated mSSP-1 to mSSP-5 as the homologs of habu proteins. mSSP-1 was stable at 100 °C and in the pH range of 1-10, and inhibited the proteolytic activity of a certain snake venom metalloproteinase. The inhibitory activity was extinguished by modifying the amino groups of mSSP-1. mSSP-1 is the first prostate secretory protein of the 94 amino acid-family protein with a carbohydrate chain in the Asn37 residue.

Small serum protein-1 changes the susceptibility of an apoptosis-inducing metalloproteinase HV1 to a metalloproteinase inhibitor in habu snake (Trimeresurus flavoviridis)

Viperidae snakes containing various venomous proteins also have several anti-toxic proteins in their sera. However, the physiological function of serum protein has been elucidated incompletely. Small serum protein (SSP)-1 is a major component of the SSPs isolated from the serum of a Japanese viper, the habu snake (Trimeresurus flavoviridis). It exists in the blood as a binary complex with habu serum factor (HSF), a snake venom metalloproteinase inhibitor. Affinity chromatography of the venom on an SSP-1-immobilized column identified HV1, an apoptosis-inducing metalloproteinase, as the target protein of SSP-1. Biacore measurements revealed that SSP-1 was bound to HV1 with a dissociation constant of 8.2 × 10⁻⁸ M. However, SSP-1 did not inhibit the peptidase activity of HV1. Although HSF alone showed no inhibitory activity or binding affinity to HV1, the SSP-1-HSF binary complex bound to HV1 formed a ternary complex that non-competitively inhibited the peptidase activity of HV1 with a inhibition constant of 5.1 ± 1.3 × 10⁻⁹ M. The SSP-1-HSF complex also effectively suppressed the apoptosis of vascular endothelial cells and caspase 3 activation induced by HV1. Thus, SSP-1 is a unique protein that non-covalently attaches to HV1 and changes its susceptibility to HSF.

Neutralisation of Local Haemorrhage Induced by the Saw-Scaled Viper Echis carinatus sochureki Venom Using Ethanolic Extract of Hibiscus aethiopicus L

The objective of the study is to investigate the anti-snake venom activities of a local plant, Hibiscus aethiopicus L. The H. aethiopicus was dried and extracted with ethanol. Different assays were performed according to standard techniques, to evaluate the plant's acute toxicity and its antivenom activities. The results of evaluating the systemic acute toxicity of the H. aethiopicus extract using “oral and intra-peritoneal” route were normal even at the highest dose (24 g/kg) tested. All guinea pigs (n = 3) when treated with venoms E. c. sochureki (75 μg) alone induced acute skin haemorrhage. In contrast, all guinea pigs (n = 18) treated with both venom and the plant extract at a concentration between 500 and 1000 mg/kg showed no signs of haemorrhage. Moreover, all guinea pigs (n = 18) treated with venom and the plant extract below 400 mg/kg showed acute skin haemorrhage. All guinea pigs treated with venom E. c. sochureki (75 μg) alone induced acute skin haemorrhage after both 24 and 32 hours. In contrast, all guinea pigs treated with both venom and the plant extract (administered independently) at concentrations between 500 and 1000 mg/kg showed no signs of haemorrhage after 32 hours. However, after 24 hours all tested guinea pigs showed less inhibition (<60%) compared to that obtained after 32 hours. The outcome of this study reflects that the extract of H. aethiopicus plant may contain an endogenous inhibitor of venom induced local haemorrhage.

Snake-venom resistance as a mammalian trophic adaptation: lessons from didelphid marsupials

Mammals that prey on venomous snakes include several opossums (Didelphidae), at least two hedgehogs (Erinaceidae), several mongooses (Herpestidae), several mustelids, and some skunks (Mephitidae). As a group, these taxa do not share any distinctive morphological traits. Instead, mammalian adaptations for ophiophagy seem to consist only in the ability to resist the toxic effects of snake venom. Molecular mechanisms of venom resistance (as indicated by biochemical research on opossums, mongooses, and hedgehogs) include toxin-neutralizing serum factors and adaptive changes in venom-targeted molecules. Of these, toxin-neutralizing serum factors have received the most research attention to date. All of the toxin-neutralizing serum proteins discovered so far in both opossums and mongooses are human α1B-glycoprotein homologs that inhibit either snake-venom metalloproteinases or phospholipase A(2) myotoxins. By contrast, adaptive changes in venom-targeted molecules have received far less attention. The best-documented examples include amino-acid substitutions in mongoose nicotinic acetylcholine receptor that inhibit binding by α-neurotoxins, and amino-acid substitutions in opossum von Willebrand factor (vWF) that are hypothesized to weaken the bond between vWF and coagulopathic C-type lectins. Although multiple mechanisms of venom resistance are known from some species, the proteomic complexity of most snake venoms suggests that the evolved biochemical defences of ophiophagous mammals are likely to be far more numerous than currently recognized. Whereas most previous research in this field has been motivated by the potential for medical applications, venom resistance in ophiophagous mammals is a complex adaptation that merits attention from comparative biologists. Unfortunately, evolutionary inference is currently limited by ignorance about many relevant facts that can only be provided by future research.

Adaptive evolution of the venom-targeted vWF protein in opossums that eat pitvipers

The rapid evolution of venom toxin genes is often explained as the result of a biochemical arms race between venomous animals and their prey. However, it is not clear that an arms race analogy is appropriate in this context because there is no published evidence for rapid evolution in genes that might confer toxin resistance among routinely envenomed species. Here we report such evidence from an unusual predator-prey relationship between opossums (Marsupialia: Didelphidae) and pitvipers (Serpentes: Crotalinae). In particular, we found high ratios of replacement to silent substitutions in the gene encoding von Willebrand Factor (vWF), a venom-targeted hemostatic blood protein, in a clade of opossums known to eat pitvipers and to be resistant to their hemorrhagic venom. Observed amino-acid substitutions in venom-resistant opossums include changes in net charge and hydrophobicity that are hypothesized to weaken the bond between vWF and one of its toxic snake-venom ligands, the C-type lectin-like protein botrocetin. Our results provide the first example of rapid adaptive evolution in any venom-targeted molecule, and they support the notion that an evolutionary arms race might be driving the rapid evolution of snake venoms. However, in the arms race implied by our results, venomous snakes are prey, and their venom has a correspondingly defensive function in addition to its usual trophic role.

Ending the drought: new strategies for improving the flow of affordable, effective antivenoms in Asia and Africa

The development of snake antivenoms more than a century ago should have heralded effective treatment of the scourge of snakebite envenoming in impoverished, mostly rural populations around the world. That snakebite still exists today, as a widely untreated illness that maims, kills and terrifies men, women and children in vulnerable communities, is a cruel anachronism. Antivenom can be an effective, safe and affordable treatment for snakebites, but apathy, inaction and the politicisation of public health have marginalised both the problem (making snakebite arguably the most neglected of all neglected tropical diseases) and its solution. For lack of any coordinated approach, provision of antivenoms has been pushed off the public health agenda, leading to an incongruous decline in demand for these crucial antidotes, excused and fed by new priorities, an absence of epidemiological data, and a poor regulatory framework. These factors facilitated the infiltration of poor quality products that degrade user confidence and undermine legitimate producers. The result is that tens of thousands are denied an essential life-saving medicine, allowing a toll of human suffering that is a summation of many individual catastrophes. No strategy has been developed to address this problem and to overcome the intransigence and inaction responsible for the global tragedy of snakebite. Attempts to engage with the broader public health community through the World Health Organisation (WHO), GAVI, and other agencies have failed. Consequently, the toxinology community has taken on a leadership role in a new approach, the Global Snakebite Initiative, which seeks to mobilise the resources, skills and experience of scientists and clinicians for whom venoms, toxins, antivenoms, snakes and snakebites are already fields of interest. Proteomics is one such discipline, which has embraced the potential of using venoms in bio-discovery and systems biology. The fields of venomics and antivenomics have recently evolved from this discipline, offering fresh hope for the victims of snakebites by providing an exciting insight into the complexities, nature, fundamental properties and significance of venom constituents. Such a rational approach brings with it the potential to design new immunising mixtures from which to raise potent antivenoms with wider therapeutic ranges. This addresses a major practical limitation in antivenom use recognised since the beginning of the 20th century: the restriction of therapeutic effectiveness to the specific venom immunogen used in production. Antivenomic techniques enable the interactions between venoms and antivenoms to be examined in detail, and if combined with functional assays of specific activity and followed up by clinical trials of effectiveness and safety, can be powerful tools with which to evaluate the suitability of current and new antivenoms for meeting urgent regional needs. We propose two mechanisms through which the Global Snakebite Initiative might seek to end the antivenom drought in Africa and Asia: first by establishing a multidisciplinary, multicentre, international collaboration to evaluate currently available antivenoms against the venoms of medically important snakes from specific nations in Africa and Asia using a combination of proteomic, antivenomic and WHO-endorsed preclinical assessment protocols, to provide a validated evidence base for either recommending or rejecting individual products; and secondly by bringing the power of proteomics to bear on the design of new immunising mixtures to raise Pan-African and Pan-Asian polyvalent antivenoms of improved potency and quality. These products will be subject to rigorous clinical assessment. We propose radically to change the basis upon which antivenoms are produced and supplied for the developing world. Donor funding and strategic public health alliances will be sought to make it possible not only to sustain the financial viability of antivenom production partnerships, but also to ensure that patients are relieved of the costs of antivenom so that poverty is no longer a barrier to the treatment of this important, but grossly neglected public health emergency.

Antisnake Venom Activity of Hibiscus aethiopicus L. against Echis ocellatus and Naja n. nigricollis

The objective of the study is to investigate whether the Hibiscus aethiopicus L. plant has neutralization activity against venoms of two clinically important snakes. The H. aethiopicus was dried and extracted with water. Different assays were performed to evaluate the plant's acute toxicity and its anti-snake venom activities. The results showed that H. aethiopicus extract alone had no effect on the viability of C₂C₁₂ muscle cells, but significantly (P < .05) protected muscle cells against the toxic effects of E. ocellatus venom at 55, 150, and 300 μg/mL. The maximum protective effect of the extract was exhibited at 75 μg/mL. The extract significantly (P < .001) inhibited the cytotoxic effects of E. ocellatus venom at 300 μg/mL. All rabbits (n = 10) and guinea pigs (n = 10) were alive after the two weeks of given the lethal dosage 16 g/Kg of the H. aethiopicus extract herbal solution. No abnormal behaviour was observed of both groups of animals. All guinea pigs (n = 3) treated with venoms alone (5 mg/kg) died. However, all guinea pigs (n = 21) treated with venom (5 mg/kg) and the extract (400 to 1000 mg/kg) survived. Guinea pigs (n = 3) treated with Naja n. nigricollis venom alone (2.5 mg/kg) and guinea pigs (n = 21) venom with the extract (400 to 1000 mg/kg) died. The H. aethiopicus completely (100%) blocked the haemorrhagic activity of E. ocellatus in the egg embryo at 3.3 mg/mL of extract. These findings suggest that H. aethiopicus may contain an endogenous inhibitor of venom-induced haemorrhage.

Neutralization of lethality and proteolytic activities of Malayan pit viper (Calloselasma rhodostoma) venom with North American Virginia opossum (Didelphis virginiana) serum

Malayan pit viper (Calloselasma rhodostoma) envenomation is a major health problem in South East Asia. During envenomation, venom components mainly affect the hemostatic system. The sera from the North American Virginia opossums (Didelphis virginiana) were able to neutralize the venom of the Malayan pit viper. These natural inhibitors could be explored as potential therapeutics against envenomations of a variety of venomous snake species in different geographical habitats.

Properties and cDNA cloning of antihemorrhagic factors in sera of Chinese and Japanese mamushi (Gloydius blomhoffi)

An antihemorrhagic protein has been isolated from the serum of Chinese mamushi (Gloydius blomhoffi brevicaudus) by using a combination of ethanol precipitation and a reverse-phase high-performance liquid chromatography (HPLC) on a C8 column. This protein-designated Chinese mamushi serum factor (cMSF)-suppressed mamushi venom-induced hemorrhage in a dose-dependent manner. It had no effect on trypsin, chymotrypsin, thermolysin, and papain but inhibited the proteinase activities of several snake venom metalloproteinases (SVMPs) including hemorrhagic enzymes isolated from the venoms of mamushi and habu (Trimeresurus flavoviridis). A similar protein (Japanese MSF, jMSF) with antihemorrhagic activity has also been purified from the sera of Japanese mamushi (G. blomhoffi). The N-terminal 70 and 51 residues of the intact cMSF and jMSF were directly analyzed; a similarity between the sequences of two MSFs to that of antihemorrhagic protein (HSF) from habu serum was noticed. To obtain the complete amino acid sequences of MSFs, cDNAs encoding these proteins were cloned from the liver mRNA of Chinese and Japanese vipers based on their N-terminal amino acid sequences. The mature forms of both MSFs consisted of 305 amino acids with a 19-residue signal sequence, and a unique 17-residue deletion was detected in their His-rich domains.

Microvesicles in the venom of Crotalus durissus terrificus (Serpentes, Viperidae)

Microvesicles with electron-dense content are consistently observed by transmission electron microscopy on the luminal face of secretory cells of venom glands of viperid snakes. In this work, we evaluated their presence in Crotalus durissus terrificus venom glands and also in freshly collected venom. Microvesicles were found in the venom glands mainly in regions of exocytosis. They ranged from 40 to 80 nm in diameter. Freeze-fracture replicas of the glands revealed particles on the cytoplasmic leaflet (P-face) of these vesicles, suggesting that they carry transmembrane proteins. Vesicles separated by ultracentrifugation from cell-free venom were similar in size and structure to the microvesicles observed in the glands. A fine fuzzy coat surrounded each microvesicle. The function of these venom vesicles is still unknown, but they may contribute to inactivation of stored venom components, or their activation after the venom is released.

Active fragments of the antihemorrhagic protein HSF from serum of habu (Trimeresurus flavoviridis)

Certain snakes have antihemorrhagic proteins in their sera. Habu serum factor (HSF), an antihemorrhagic protein isolated from the serum of the Japanese habu snake (Trimeresurus flavoviridis) is composed of two cystatin-like domains (D1 and D2) and a His-rich domain, and it inhibits several snake venom metalloproteinases (SVMPs). The activity of HSF can be abolished by trinitrophenylation of Lys residues with 2,4,6-trinitrobenzene sulphonic acid. Upon complex formation of HSF with SVMP, however, the loss of its inhibitory activity by the chemical modification was suppressed, and Lys(15), Lys(41), and Lys(103) residues in HSF were not trinitrophenylated. In order to identify the domain that is critical to the inhibitory activity on SVMPs, native HSF was digested with papain followed by cleavage with cyanogen bromide, yielding a low-molecular mass fragment that was composed of two peptide chains (residues 5-89 and 312-317) linked by a disulfide bond. This fragment inhibited several SVMPs and showed significant antihemorrhagic activity. This indicates that the N-terminal half of D1 is indispensable for the antihemorrhagic activity of HSF. Furthermore, a three-dimensional model of two cystatin-like domains constructed by the homology modeling has indicated that three Lys residues (15, 41, and 103) are exposed to the same surface of HSF molecule.

Bothrops jararaca venom gland transcriptome: analysis of the gene expression pattern

Bothrops jararaca is a pit viper responsible for the majority of snake envenoming accidents in Brazil. As an attempt to describe the transcriptional activity of the venom gland, ESTs of a cDNA library constructed from B. jararaca venom gland were generated and submitted to bioinformatics analysis. The results showed a clear predominance of transcripts coding for toxins instead of transcripts coding for proteins involved in cellular functions. Among toxins, the most frequent transcripts were from metalloproteinases (52.6%), followed by serine-proteinases (28.5%), C-type lectins (8.3%) and bradykinin-potentiating peptides (BPPs) (6.2%). Results were similar to that obtained from the transcriptome analysis of B. insularis, a phylogenetically close sister of B. jararaca, though some differences were observed and are pointed out, such as a higher amount of the hypotensive BPPs in B. insularis transcriptome (19.7%). Another striking difference observed is that PIII and PII-classes of metalloproteinases are similarly represented in B. jararaca in contrast to B. insularis, in which a predominance of PIII-class metalloproteinase, which present a more intense hemorrhagic action, is observed. These features may, in part, explain the higher potency of B. insularis venom. The results obtained can help in proteome studies, and the clones can be used to directly probe the genetic material from other snake species or to investigate differences in gene expression pattern in response to factors such as diet, aging and geographic localization.

Neutralisation of venom-induced haemorrhage by IgG from camels and llamas immunised with viper venom and also by endogenous, non-IgG components in camelid sera

Envenoming by snakes results in severe systemic and local pathology. Intravenous administration of antivenom, prepared from IgG of venom immunised horses or sheep, is the only effective treatment of systemic envenoming. Conventional antivenoms, formulated as intact IgG, papain-cleaved (Fab) or pepsin-cleaved F(ab')2 fragments, are however ineffective against the local venom effects because of their inability to penetrate the blood/tissue barrier. We have embarked on a new research program to examine (i) whether the unusually small (15 kDa) antigen-binding fragment of camelid heavy chain IgG (V(H)H) can be exploited to neutralise the local effects of envenoming and (ii) whether a novel antivenom to treat both the systemic and local effects of envenoming can be formulated by combining anti-snake venom V(H)H and conventional F(ab')2. In this preliminary study, we demonstrate that camels and llamas respond to immunisation with Echis ocellatus venom with high antibody titres and broad antigen specificity. These encouraging immunological results were matched by the successful elimination of venom-induced haemorrhage by IgG from the venom-immunised camels and llamas. Unexpectedly, we report for the first time that camelid serum contains a non-IgG, highly potent inhibitor of venom-induced haemorrhage.