Antivenomics and venom phenotyping: A marriage of convenience to address the performance and range of clinical use of antivenoms

Expanding anti-venom strategies: Camelid polyclonal antibodies with high capacity to recognize snake venom

Camelid immunoglobulins represent a unique facet of antibody biology, challenging conventional understandings of antibody diversification. IgG2 and IgG3 in particular are composed solely of heavy chains and exhibit a reduced molecular weight (90 kDa); their elongated complementarity determining region (CDR) loops play a pivotal role in their functioning, delving deep into enzyme active sites with precision. Serum therapy stands as the primary venom-specific treatment for snakebite envenomation, harnessing purified antibodies available in diverse forms such as whole IgG, monovalent fragment antibody (Fab), or divalent fragment antibody F (ab')2. This investigation looks into the intricacies of IgGs derived from camelid serum previously immunized with crotamine and crotoxin, toxins predominantly in Crotalus durissus venom, exploring their recognition capacity, specificity, and cross-reactivity to snake venoms and its toxins. Initially, IgG purification employed affinity chromatography via protein A and G columns to segregate conventional antibodies (IgG1) from heavy chain antibodies (IgG2 and IgG3) of camelid isotypes sourced from Lama glama serum. Subsequent electrophoretic analysis (SDS-PAGE) revealed distinct bands corresponding to molecular weight profiles of IgG's fractions representing isotypes in Lama glama serum. ELISA cross-reactivity assays demonstrated all three IgG isotypes' ability to recognize the tested venoms. Notably, IgG1 exhibited the lowest interactivity in analyses involving bothropic and crotalic venoms. However, IgG2 and IgG3 displayed notable cross-reactivity, particularly with crotalic venoms and toxins, albeit with exceptions such as PLA2-CB, showing reduced reactivity, and C. atrox, where IgGs exhibited insignificant reactivity. In Western blot assays, IgG2 and IgG3 exhibited recognition of proteins within molecular weight (≈15 kDa) of C. d. collilineatus to C. d. terrificus, with some interaction observed even with bothropic proteins despite lower reactivity. These findings underscore the potential of camelid heavy-chain antibodies, suggesting Lama glama IgGs as prospective candidates for a novel class of serum therapies. However, further investigations are imperative to ascertain their suitability for serum therapy applications.

Venom of the neotropical rattlesnake, Crotalus culminatus: Intraspecific variation, neutralization by antivenoms, and immunogenicity in rabbits

Crotalus culminatus is a medically significant species of rattlesnake in Mexico [1]. While the proteomic composition of its venom has been previously reported for both juvenile and adult specimens, there has been limited research into its functional properties, with only a few studies, including one focusing on coagulotoxicity mechanisms. In this study, we aimed to compare the biochemical and biological activities of the venom of juvenile and adult snakes. Additionally, we assessed antibody production using the venoms of juveniles and adults as immunogens in rabbits. Our findings reveal lethality and proteolytic activity differences between the venoms of juveniles and adults. Notably, juvenile venoms exhibited high proportions of crotamine, while adult venoms displayed a reduction of this component. A commercially available antivenom demonstrated effective neutralization of lethality of both juvenile and adult venoms in mice. However, it failed to neutralize the paralytic activity induced by crotamine, which, in contrast, was successfully inhibited by antibodies obtained from hyperimmunized rabbits. These results suggest the potential inclusion of C. culminatus venom from juveniles in commercial antivenom immunization schemes to generate antibodies targeting this small myotoxin.

High-throughput virtual screening, pharmacophore modelling and antagonist effects of small molecule inhibitors against cytotoxin-induced cytotoxicity

Cobra venom cytotoxins (CTX) cause dermonecrosis in envenomed patients who suffered from limb amputations due to the limitation of serotherapy-based antivenoms. This study aimed to identify small molecule inhibitors against CTX. A structure-based high-throughput virtual screening (HTVS) was conducted based on a conserved CTX, using the Natural Product Activity and Species Source (NPASS) screening library. The hits were valerenic acid, 1-oxo-2H-isoquinoline-4-carboxylic acid, acenaphthene, and 5-bromopyrrole-2-carboxamide, which interacted with contemporary antivenom binding site A and functional loops I-III of CTX, respectively, in molecular docking studies. Furthermore, molecular dynamic simulations were performed along with analysis of ligand fitness through their pharmacophore and pharmacokinetics properties. The antagonist effects of these hits on CTX-induced cytotoxicity were examined in human keratinocytes (HaCaT). Despite having a low binding affinity (KD = 14.45 × 10-4 M), acenaphthene demonstrated a significant increase of cell viability at 6 h and 24 h in experimental envenomed HaCaT. It also demonstrated the highest neutralization potency against CTX with a median effective concentration (EC50) of 0.05 mL/mg. Acenaphthene interacted with the functional loop II, which is the crucial cytotoxic site of CTX. It has an aromatic ring as its primary pharmacophoric feature, commonly used for rational drug design. In conclusion, acenaphthene could be a promising lead compound as a small molecule inhibitor.Communicated by Ramaswamy H. Sarma.

Biochemical and hemostatic description of a thrombin-like enzyme TLBro from Bothrops roedingeri snake venom

Objective: The current study's objective is to characterize a new throm-bin-like enzyme called TLBro that was obtained from Bothrops roedingeris snake from a biochemical and hemostatic perspective. Methodology: One chromatographic step was used to purify it, producing the serine protease TLBro. Molecular mass was estimated by SDS-PAGE to be between reduced and unreduced by 35 kDa. Tryptic peptide sequencing using Swiss Prot provided the complete amino acid sequence. Expasy.org by conducting a search that is limited to Crotalinae snake serine proteases and displaying a high degree of amino acid sequence. Results: Ser (182) is inhibited by phenylmethylsulfonyl fluoride (PMSF), and TLBro demonstrated the presence of Asp (88) residues. It also deduced the positions of His (43) and Ser (182) in the set of three coordinated amino acids in serine proteases. It was discovered that this substrate had high specificity for BANA, Michaelis-Menten behavior with KM 0 point85 mM and Vmax 1 point89 nmoles -NA/L/min, and high stability between temperatures (15 to 70°C) and pHs (2 point0 to 10 point0). According to doses and incubation times, TLBro degraded fibrin preferentially on the B-chain; additionally, its activities were significantly diminished after preincubation with divalent ions (Zn2 and Cd2). When incubated with PMSF, a particular serine protease inhibitor, enzymatic activities and platelet aggregation were inhibited. Conclusion: The findings revealed distinct structural and functional differences between the serine proteases, adding to the information and assisting in the improvement of the structure-function relationship.

Effects on cell cycle progression and cytoskeleton organization of five Bothrops spp. venoms in cell culture-based assays

Snake envenomation is a neglected tropical disease. In Brazil, the Bothrops genus is responsible for about 86% of snakebite accidents. Despite extensive evidence of the cytotoxicity of snake venoms, the cellular and molecular mechanisms involved are not fully understood, especially regarding the effects on cell cycle progression and cytoskeleton organization. Traditionally, the effectiveness and quality control tests of venoms and antivenoms are assessed by in vivo assays. Despite this, there is a rising effort to develop surrogate in vitro models according to the 3R principle (Replacement, Reduction, and Refinement). In this study, we treated rat liver cells (BRL-3A) with venoms from five Bothrops species (B. jararaca, B. jararacussu, B. moojeni, B. alternatus, and B. neuwiedi) and analyzed cell viability and IC50 by MTT assay, cell cycle phases distribution by flow cytometry, and morphology and cytoskeleton alterations by immunofluorescence. In addition, we evaluated the correlation between IC50 and the enzymatic and biological activities of each venom. Our results indicated that Bothrops spp. venoms decreased the cell viability of rat liver BRL-3A cells. The rank order of potency was B. jararacussu > B. moojeni > B. alternatus > B. jararaca > B. neuwiedi. The mechanisms of cytotoxicity were related to microtubules and actin network disruption, but not to cell cycle arrest. No clear correlation was found between the IC50 and retrieved literature data of in vitro enzymatic and in vivo biological activities. This work contributed to understanding cellular and molecular mechanisms underlying the Bothrops spp. venom cytotoxicity, which can help to improve envenomation treatment, as well as disclose potential therapeutic properties of snake venoms.

The secretory phenotypes of envenomed cells: Insights into venom cytotoxicity

Snake envenomation is listed as Category A Neglected Tropical Diseases (NTD) by World Health Organization, indicates a severe public health problem. The global figures for envenomation cases are estimated to be more than 1.8 million annually. Even if the affected victims survive the envenomation, they might suffer from permanent morbidity due to local envenomation. One of the most prominent local envenomation is dermonecrosis. Dermonecrosis is a pathophysiological outcome of envenomation that often causes disability in the victims due to surgical amputations, deformities, contracture, and chronic ulceration. The key venom toxins associated with this local symptom are mainly attributed to substantial levels of enzymatic and non-enzymatic toxins as well as their possible synergistic actions. Despite so, the severity of the local tissue damage is based on macroscopic observation of the bite areas. Furthermore, limited knowledge is known about the key biomarkers involved in the pathogenesis of dermonecrosis. The current immunotherapy with antivenom is also ineffective against dermonecrosis. These local effects eventually end up as sequelae. There is also a global shortage of toxins-targeted therapeutics attributed to inadequate knowledge of the actual molecular mechanisms of cytotoxicity. This chapter discusses the characterization of secretory phenotypes of dermonecrosis as an advanced tool to indicate its severity and pathogenesis in envenomation. Altogether, the secretory phenotypes of envenomed cells and tissues represent the precise characteristics of dermonecrosis caused by venom toxins.

Bibliometric Analysis of Literature in Snake Venom-Related Research Worldwide (1933-2022)

Snake envenomation is a severe economic and health concern affecting countries worldwide. Snake venom carries a wide variety of small peptides and proteins with various immunological and pharmacological properties. A few key research areas related to snake venom, including its applications in treating cancer and eradicating antibiotic-resistant bacteria, have been gaining significant attention in recent years. The goal of the current study was to analyze the global profile of literature in snake venom research. This study presents a bibliometric review of snake venom-related research documents indexed in the Scopus database between 1933 and 2022. The overall number of documents published on a global scale was 2999, with an average annual production of 34 documents. Brazil produced the highest number of documents (n = 729), followed by the United States (n = 548), Australia (n = 240), and Costa Rica (n = 235). Since 1963, the number of publications has been steadily increasing globally. At a worldwide level, antivenom, proteomics, and transcriptomics are growing hot issues for research in this field. The current research provides a unique overview of snake venom research at global level from 1933 through 2022, and it may be beneficial in guiding future research.

The application of laboratory-based analytical tools and techniques for the quality assessment and improvement of commercial antivenoms used in the treatment of snakebite envenomation

Snakebite envenomation is a public health problem of high impact, particularly for the developing world. Antivenom, which contains whole or protease-digested immunoglobulin G, purified from the plasma of hyper-immunized animals (mainly horses), is the mainstay for the treatment of snakebite envenomation. The success of antivenom therapy depends upon its ability to abrogate or reduce the local and systemic toxicity of envenomation. In addition, antivenom administration must be safe for the patients. Therefore, antivenom manufacturers must ensure that these products are effective and safe in the treatment of envenomations. Antivenom efficacy and safety are determined by the physicochemical characteristics of formulations, purity of the immunoglobulin fragments and antibodies, presence of protein aggregates, endotoxin burden, preservative load, and batch to batch variation, as well as on the ability to neutralize the most important toxins of the venoms against which the antivenom is designed. In this context, recent studies have shown that laboratory-based simple analytical techniques, for example, size exclusion chromatography, sodium dodecyl sulphate polyacrylamide gel electrophoresis, mass spectrometry, immunological profiling including immuno-turbidimetry and enzyme-linked immunosorbent assays, Western blotting, immune-chromatographic technique coupled to mass spectrometry analysis, reverse-phase high performance liquid chromatography, spectrofluorometric analysis, in vitro neutralization of venom enzymatic activities, and other methodologies, can be applied for the assessment of antivenom quality, safety, stability, and efficacy. This article reviews the usefulness of different analytical techniques for the quality assessment of commercial antivenoms. It is suggested that these tests should be applied for screening the quality of commercial antivenoms before their preclinical and clinical assessment.

Moringa oleifera Extract Extenuates Echis ocellatus Venom-Induced Toxicities, Histopathological Impairments and Inflammation via Enhancement of Nrf2 Expression in Rats

Echis ocellatus snakebite causes more fatalities than all other African snake species combined. Moringa oleifera reportedly possesses an antivenom property. Therefore, we evaluated the effectiveness of M. oleifera ethanol extract (MOE) against E. ocellatus venom (EOV) toxicities. Thirty male rats were grouped as follows (n = 5): Group 1 (normal control received saline), groups 2 to 6 were administered intraperitoneally, 0.22 mg/kg (LD50) of EOV. Group 2 was left untreated while group 3 to 6 were treated post-envenoming with 0.2 mL of polyvalent antivenom, 200, 400, and 600 mg/kg of MOE respectively. MOE significantly (p < 0.05) normalized the altered haematological indices and blood electrolytes profiles. MOE attenuated venom-induced cellular dysfunctions, characterized by a significant increase in NRF2, and concomitant downregulation of increased antioxidant enzymes (SOD and CAT) activities in the serum and heart of the treated rats. MOE normalized the elevated TNF-α and IL-1β in serum and heart tissues. Furthermore, the IgG titre value was significantly (p < 0.5) higher in the envenomed untreated group compared to the MOE-treated groups. Hemorrhagic, hemolytic and coagulant activities of the venom were strongly inhibited by the MOE dose, dependently. Lesions noticed on tissues of vital organs of untreated rats were abolished by MOE. Our findings substantiate the effectiveness of MOE as a potential remedy against EOV toxicities.

Current research into snake antivenoms, their mechanisms of action and applications

Snakebite is a major public health issue in the rural tropics. Antivenom is the only specific treatment currently available. We review the history, mechanism of action and current developments in snake antivenoms. In the late nineteenth century, snake antivenoms were first developed by raising hyperimmune serum in animals, such as horses, against snake venoms. Hyperimmune serum was then purified to produce whole immunoglobulin G (IgG) antivenoms. IgG was then fractionated to produce F(ab) and F(ab')2 antivenoms to reduce adverse reactions and increase efficacy. Current commercial antivenoms are polyclonal mixtures of antibodies or their fractions raised against all toxin antigens in a venom(s), irrespective of clinical importance. Over the last few decades there have been small incremental improvements in antivenoms, to make them safer and more effective. A number of recent developments in biotechnology and toxinology have contributed to this. Proteomics and transcriptomics have been applied to venom toxin composition (venomics), improving our understanding of medically important toxins. In addition, it has become possible to identify toxins that contain epitopes recognized by antivenom molecules (antivenomics). Integration of the toxinological profile of a venom and its composition to identify medically relevant toxins improved this. Furthermore, camelid, humanized and fully human monoclonal antibodies and their fractions, as well as enzyme inhibitors have been experimentally developed against venom toxins. Translation of such technology into commercial antivenoms requires overcoming the high costs, limited knowledge of venom and antivenom pharmacology, and lack of reliable animal models. Addressing such should be the focus of antivenom research.

Functional venomics of the Big-4 snakes of Pakistan

In South Asia, the "Big-4" venomous snakes Naja naja, Bungarus caeruleus, Daboia russelii, and Echis carinatus are so-called because they are the most medically important snakes in the region. Antivenom is the only effective treatment option for snakebite envenoming but antivenom is not produced domestically in Pakistan making the country reliant on polyvalent products imported from India and Saudi Arabia. The present study investigated the toxin composition and activity of the venoms of Pakistani specimens by means of proteomic and physio/pharmacological experiments. To evaluate the composition of venoms, 1D/2D-PAGE of crude venoms and RP-HPLC followed by SDS-PAGE were performed. Enzymatic, hemolytic, coagulant and platelet aggregating activities of crude venoms were assayed and were concordant with expectations based on the abundance of protein species in each. Neutralization assays were performed using Bharat polyvalent antivenom (BPAV), a product raised against venoms from Big-4 specimens from southern India. BPAV exhibited cross-reactivity against the Pakistani venoms, however, neutralization of clinically relevant activities was variable and rarely complete. Cumulatively, the presented data not only highlight geographical variations present in the venoms of the Big-4 snakes of South Asia, but also demonstrate the neutralization potential of Indian polyvalent against the venom of Pakistani specimens. Given the partial neutralization observed, it is clear that whilst BPAV is a life-saving product in Pakistan, in future it is hoped that a region-specific product might be manufactured domestically, using venoms of local snakes in the immunising mixture.

From molecules to macroevolution: Venom as a model system for evolutionary biology across levels of life

Biological systems are inherently hierarchical. Consequently, any field which aims to understand an aspect of biology holistically requires investigations at each level of the hierarchy of life, and venom research is no exception. This article aims to illustrate the structure of the field in light of a ‘levels of life’ perspective. In doing so, I highlight how traditional fields and approaches fit into this structure as focussing on describing levels or investigating links between levels, and emphasise where implicit assumptions are made due to lack of direct information. Taking a ‘levels of life’ perspective to venom research enables us to understand the complementarity of different research programmes and identify avenues for future research. Moreover, it provides a broader view that, in itself, shows how new questions can be addressed. For instance, understanding how adaptations develop and function from molecular to organismal scales, and what the consequences are of those adaptations at scales from molecular to macroevolutionary, is a general question relevant to a great deal of biology. As a trait which is molecular in nature and has clearer and more direct links between genotype and phenotype than many other traits, venom provides a relatively simple system to address such questions. Furthermore, because venom is also diverse at each level of life, the complexity within the hierarchical structure provides variation that enables powerful analytical approaches to answering questions. As a result, venom provides an excellent model system for understanding big questions in evolutionary biology.

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Venom is a molecular trait used directly in fitness-relevant ecological interaction.

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Venom is consequently an ideal model system for evolutionary biology.

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A ‘levels of life’ perspective is well suited to research in venom biology.

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This structure of the field provides many advantages to guide future studies.

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Clinical implications can arise from studies of venom at all levels of life.

Preliminary Biochemical and Venomic Characterization of the Venom of Phalotris lemniscatus (Serpentes, Colubridae)

BACKGROUND

For many decades, research on snake venom toxinology focused mainly on the venoms of Viperidae and Elapidae species, which were traditionally the only ones considered as venomous. However, much less interest has been given to the venom produced by opisthoglyphous colubrid snakes, since they were typically considered of no clinical relevance.

OBJECTIVE

The aim of this work is to perform a preliminary biochemical and venomic characterization of the venom of the colubrid snake Phalotris lemniscatus, a species that has been responsible for two relevant cases of envenomation in Uruguay.

METHODS

We extracted venom from collected specimens and performed different biochemical and proteomic assays to understand its toxin composition.

RESULTS

We found that the venom of P. lemniscatus is composed of protein families typically present in snake venoms, such as metallo and serine preoteases, L-amino acid oxidases, phospholipases A2s, Ctype lectines-like, Kunitz-type proteins and three-finger toxins. Activity assays demonstrated a highly active gelatinolytic component as well as a potent capability to induce blood coagulation.

CONCLUSION

The results indicate that the venom of P. lemniscatus contains hemotoxic activities and components that resemble those found in Viperidae (Bothrops) snakes and that can induce a clinically relevant accident. Further studies are needed to better understand the venom composition of this colubrid snake and its most active compounds.

Evidence for Snake Venom Plasticity in a Long-Term Study with Individual Captive Bothrops atrox

Variability in snake venom composition has been frequently reported and correlated to the adaptability of snakes to environmental conditions. Previous studies report plasticity for the venom phenotype. However, these observations are not conclusive, as the results were based on pooled venoms, which present high individual variability. Here we tested the hypothesis of plasticity by influence of confinement and single diet type in the venom composition of 13 adult specimens of Bothrops atrox snakes, maintained under captivity for more than three years. Individual variability in venom composition was observed in samples extracted just after the capture of the snakes. However, composition was conserved in venoms periodically extracted from nine specimens, which presented low variability restricted to the less abundant components. In a second group, composed of four snakes, drastic changes were observed in the venom samples extracted at different periods, mostly related to snake venom metalloproteinases (SVMPs), the core function toxins of B. atrox venom, which occurred approximately between 400 and 500 days in captivity. These data show plasticity in the venom phenotype during the lifetime of adult snakes maintained under captive conditions. Causes or functional consequences involved in the phenotype modification require further investigations.

Snake Venomics Display: An online toolbox for visualization of snake venomics data

With the introduction of powerful mass spectrometry equipment into the field of snake venom proteomics, a large body of venomics data is accumulating. To allow for better comparison between venom compositions from different snake species and to provide an online database containing this data, we devised the Snake Venomics Display toolbox for visualization of snake venomics data on linear scales. This toolbox is freely available to be used online at https://tropicalpharmacology.com/tools/snake-venomics-display/ and allows researchers to visualize venomics data in a Relative Abundance (%) visualization mode and in an Absolute Abundance (mg) visualization mode, the latter taking venom yields into account. The curated venomics data for all snake species included in this database is also made available in a downloadable Excel file format. The Snake Venomics Display toolbox represents a simple way of handling snake venomics data, which is better suited for large data sets of venom compositions from multiple snake species.

Antivenomics as a tool to improve the neutralizing capacity of the crotalic antivenom: a study with crotamine

Background

Snakebite treatment requires administration of an appropriate antivenom that should contain antibodies capable of neutralizing the venom. To achieve this goal, antivenom production must start from a suitable immunization protocol and proper venom mixtures. In Brazil, antivenom against South American rattlesnake (Crotalus durissus terrificus) bites is produced by public institutions based on the guidelines defined by the regulatory agency of the Brazilian Ministry of Health, ANVISA. However, each institution uses its own mixture of rattlesnake venom antigens. Previous works have shown that crotamine, a toxin found in Crolatus durissus venom, shows marked individual and populational variation. In addition, serum produced from crotamine-negative venoms fails to recognize this molecule.

Methods

In this work, we used an antivenomics approach to assess the cross-reactivity of crotalic antivenom manufactured by IVB towards crotamine-negative venom and a mixture of crotamine-negative/crotamine-positive venoms.

Results

We show that the venom mixture containing 20% crotamine and 57% crotoxin produced a strong immunogenic response in horses. Antivenom raised against this venom mixture reacted with most venom components including crotamine and crotoxin, in contrast to the antivenom raised against crotamine-negative venom.

Conclusions

These results indicate that venomic databases and antivenomics analysis provide a useful approach for choosing the better venom mixture for antibody production and for the subsequent screening of antivenom cross-reactivity with relevant snake venom components.

Proteomic Analyses of Agkistrodon contortrix contortrix Venom Using 2D Electrophoresis and MS Techniques

Snake venom is a complex mixture of proteins and peptides which in the Viperidae is mainly hemotoxic. The diversity of these components causes the venom to be an extremely interesting object of study. Discovered components can be used in search for new pharmaceuticals used primarily in the treatment of diseases of the cardiovascular system. In order to determine the protein composition of the southern copperhead venom, we have used high resolution two dimensional electrophoresis and MALDI ToF/ToF MS-based identification. We have identified 10 groups of proteins present in the venom, of which phospholipase A₂ and metalloprotease and serine proteases constitute the largest groups. For the first time presence of 5′-nucleotidase in venom was found in this group of snakes. Three peptides present in the venom were also identified. Two of them as bradykinin-potentiating agents and one as an inhibitor.

High-throughput immuno-profiling of mamba (Dendroaspis) venom toxin epitopes using high-density peptide microarrays

Snakebite envenoming is a serious condition requiring medical attention and administration of antivenom. Current antivenoms are antibody preparations obtained from the plasma of animals immunised with whole venom(s) and contain antibodies against snake venom toxins, but also against other antigens. In order to better understand the molecular interactions between antivenom antibodies and epitopes on snake venom toxins, a high-throughput immuno-profiling study on all manually curated toxins from Dendroaspis species and selected African Naja species was performed based on custom-made high-density peptide microarrays displaying linear toxin fragments. By detection of binding for three different antivenoms and performing an alanine scan, linear elements of epitopes and the positions important for binding were identified. A strong tendency of antivenom antibodies recognizing and binding to epitopes at the functional sites of toxins was observed. With these results, high-density peptide microarray technology is for the first time introduced in the field of toxinology and molecular details of the evolution of antibody-toxin interactions based on molecular recognition of distinctive toxic motifs are elucidated.

Canopy Venom: Proteomic Comparison among New World Arboreal Pit-Viper Venoms

Central and South American pitvipers, belonging to the genera Bothrops and Bothriechis, have independently evolved arboreal tendencies. Little is known regarding the composition and activity of their venoms. In order to close this knowledge gap, venom proteomics and toxin activity of species of Bothriechis, and Bothrops (including Bothriopsis) were investigated through established analytical methods. A combination of proteomics and bioactivity techniques was used to demonstrate a similar diversification of venom composition between large and small species within Bothriechis and Bothriopsis. Increasing our understanding of the evolution of complex venom cocktails may facilitate future biodiscoveries.

Purification and characterization of five snake venom metalloproteinases from Egyptian Echis pyramidum pyramidum venom

New five P-III snake venom metalloproteinases (SVMPs): EpyB2 (62 kDa), EpyB3 (62+23 kDa), EpyB4 (60 kDa), EpyB5 (67 kDa) and EpyB6 (66 kDa) of the most dangerous viper, Echis pyramidum pyramidum (Epy), were purified and characterized in a set of biochemical assays. The SVMPs were purified by applying a protocol of two successive chromatographic steps. Three purified SVMPs "EpyB2, EpyB4, and EpyB5" have hemorrhagic activity with MHDs, 7 μg, 7.6 μg and 15 μg, respectively; furthermore, they have high preference towards fibronectin, collagen, gelatin, fibrin and hemoglobin substrates compared with non-hemorrhagic SVMPs (EpyB3 and EpyB6). All the purified SVMPs showed remarkable thermal and pH stability, inhibited by metalloproteinase inhibitors and Zn(2+), Mn(2+), Ni(2+), Co(2+), Cu(2+), and Hg(2+). The purified SVMPs act as α-fibrinogenases, prothrombin activators and procoagulants. In conclusion, Epy venom has multiple SVMPs that are responsible for hemorrhagic events and thus represent a significant health hazard for victims of envenomation, however, they may be useful for treating diseases involving abnormal blood clot formation.

Venom gland transcriptomics for identifying, cataloging, and characterizing venom proteins in snakes

Snake venoms are cocktails of protein toxins that play important roles in capture and digestion of prey. Significant qualitative and quantitative variation in snake venom composition has been observed among and within species. Understanding these variations in protein components is instrumental in interpreting clinical symptoms during human envenomation and in searching for novel venom proteins with potential therapeutic applications. In the last decade, transcriptomic analyses of venom glands have helped in understanding the composition of various snake venoms in great detail. Here we review transcriptomic analysis as a powerful tool for understanding venom profile, variation and evolution.

Functional variability of snake venom metalloproteinases: adaptive advantages in targeting different prey and implications for human envenomation

Snake venom metalloproteinases (SVMPs) are major components in most viperid venoms that induce disturbances in the hemostatic system and tissues of animals envenomated by snakes. These disturbances are involved in human pathology of snake bites and appear to be essential for the capture and digestion of snake's prey and avoidance of predators. SVMPs are a versatile family of venom toxins acting on different hemostatic targets which are present in venoms in distinct structural forms. However, the reason why a large number of different SVMPs are expressed in some venoms is still unclear. In this study, we evaluated the interference of five isolated SVMPs in blood coagulation of humans, birds and small rodents. P-III class SVMPs (fractions Ic, IIb and IIc) possess gelatinolytic and hemorrhagic activities, and, of these, two also show fibrinolytic activity. P-I class SVMPs (fractions IVa and IVb) are only fibrinolytic. P-III class SVMPs reduced clotting time of human plasma. Fraction IIc was characterized as prothrombin activator and fraction Ic as factor X activator. In the absence of Ca²⁺, a firm clot was observed in chicken blood samples with fractions Ic, IIb and partially with fraction IIc. In contrast, without Ca²⁺, only fraction IIc was able to induce a firm clot in rat blood. In conclusion, functionally distinct forms of SVMPs were found in B. neuwiedi venom that affect distinct mechanisms in the coagulation system of humans, birds and small rodents. Distinct SVMPs appear to be more specialized to rat or chicken blood, strengthening the current hypothesis that toxin diversity enhances the possibilities of the snakes for hunting different prey or evading different predators. This functional diversity also impacts the complexity of human envenoming since different hemostatic mechanisms will be targeted by SVMPs accounting for the complexity of the response of humans to venoms.

Intraspecific venom variation in the medically significant Southern Pacific Rattlesnake (Crotalus oreganus helleri): biodiscovery, clinical and evolutionary implications

Due to the extreme variation of venom, which consequently results in drastically variable degrees of neutralization by CroFab antivenom, the management and treatment of envenoming by Crotalus oreganus helleri (the Southern Pacific Rattlesnake), one of the most medically significant snake species in all of North America, has been a clinician's nightmare. This snake has also been the subject of sensational news stories regarding supposed rapid (within the last few decades) evolution of its venom. This research demonstrates for the first time that variable evolutionary selection pressures sculpt the intraspecific molecular diversity of venom components in C. o. helleri. We show that myotoxic β-defensin peptides (aka: crotamines/small basic myotoxic peptides) are secreted in large amounts by all populations. However, the mature toxin-encoding nucleotide regions evolve under the constraints of negative selection, likely as a result of their non-specific mode of action which doesn't enforce them to follow the regime of the classic predator-prey chemical arms race. The hemorrhagic and tissue destroying snake venom metalloproteinases (SVMPs) were secreted in larger amounts by the Catalina Island and Phelan rattlesnake populations, in moderate amounts in the Loma Linda population and in only trace levels by the Idyllwild population. Only the Idyllwild population in the San Jacinto Mountains contained potent presynaptic neurotoxic phospholipase A2 complex characteristic of Mohave Rattlesnake (Crotalus scutulatus) and Neotropical Rattlesnake (Crotalus durissus terrificus). The derived heterodimeric lectin toxins characteristic of viper venoms, which exhibit a diversity of biological activities, including anticoagulation, agonism/antagonism of platelet activation, or procoagulation, appear to have evolved under extremely variable selection pressures. While most lectin α- and β-chains evolved rapidly under the influence of positive Darwinian selection, the β-chain lectin of the Catalina Island population appears to have evolved under the constraint of negative selection. Both lectin chains were conspicuously absent in both the proteomics and transcriptomics of the Idyllwild population. Thus, we not only highlight the tremendous biochemical diversity in C. o. helleri's venom-arsenal, but we also show that they experience remarkably variable strengths of evolutionary selection pressures, within each toxin class among populations and among toxin classes within each population. The mapping of geographical venom variation not only provides additional information regarding venom evolution, but also has direct medical implications by allowing prediction of the clinical effects of rattlesnake bites from different regions. Such information, however, also points to these highly variable venoms as being a rich source of novel toxins which may ultimately prove to be useful in drug design and development.

BIOLOGICAL SIGNIFICANCE

These results have direct implications for the treatment of envenomed patients. The variable venom profile of Crotalus oreganus helleri underscores the biodiscovery potential of novel snake venoms.

Paraspecificity of Vipera a. ammodytes-specific antivenom towards Montivipera raddei and Macrovipera lebetina obtusa venoms

Antivenom raised against the venom of nose-horned viper, Vipera ammodytes (V. a.) ammodytes (European viper venom antiserum, Zagreb antivenom), contains neutralising equine F(ab')₂ fragments that are clinically successful against homologous venom, but also against the venoms of several others medically important European snakes due to its paraspecific action. In this work we demonstrated that Zagreb antivenom is preclinically effective in neutralising lethal toxicity and hemorrhagicity of venoms of Armenian mountain snakes--Montivipera raddei and Macrovipera lebetina obtusa as well. In order to better understand the biochemical basis of the observed paraspecificity, the ability of anti-V. a. ammodytes serum to recognise and neutralise proteinases of the two venoms was also investigated. Anti-V. a. ammodytes serum showed surprisingly low capacity to inhibit metalloproteinases of both venoms included in the study, probably due to weak immunorecognition of their P-I representatives. Also, it completely failed to abolish enzymatic action of serine proteinases from Macrovipera lebetina obtusa venom. Relevance of such finding is yet to be established.

Comparison of phylogeny, venom composition and neutralization by antivenom in diverse species of bothrops complex

In Latin America, Bothrops snakes account for most snake bites in humans, and the recommended treatment is administration of multispecific Bothrops antivenom (SAB – soro antibotrópico). However, Bothrops snakes are very diverse with regard to their venom composition, which raises the issue of which venoms should be used as immunizing antigens for the production of pan-specific Bothrops antivenoms. In this study, we simultaneously compared the composition and reactivity with SAB of venoms collected from six species of snakes, distributed in pairs from three distinct phylogenetic clades: Bothrops, Bothropoides and Rhinocerophis. We also evaluated the neutralization of Bothrops atrox venom, which is the species responsible for most snake bites in the Amazon region, but not included in the immunization antigen mixture used to produce SAB. Using mass spectrometric and chromatographic approaches, we observed a lack of similarity in protein composition between the venoms from closely related snakes and a high similarity between the venoms of phylogenetically more distant snakes, suggesting little connection between taxonomic position and venom composition. P-III snake venom metalloproteinases (SVMPs) are the most antigenic toxins in the venoms of snakes from the Bothrops complex, whereas class P-I SVMPs, snake venom serine proteinases and phospholipases A₂ reacted with antibodies in lower levels. Low molecular size toxins, such as disintegrins and bradykinin-potentiating peptides, were poorly antigenic. Toxins from the same protein family showed antigenic cross-reactivity among venoms from different species; SAB was efficient in neutralizing the B. atrox venom major toxins. Thus, we suggest that it is possible to obtain pan-specific effective antivenoms for Bothrops envenomations through immunization with venoms from only a few species of snakes, if these venoms contain protein classes that are representative of all species to which the antivenom is targeted.

Snakebite envenomation is a serious health issue in Latin America, particularly in the Amazon, where antivenom administration may be delayed due to logistic constraints. Bothrops snakes are involved in most of the snakebite-related accidents in Brazil. This work reports a comparative study of the toxin composition and antigenicity of the Bothrops venoms used to prepare the commercial antivenom and its effectiveness against the venom from Bothrops atrox, a prevalent Amazon species that is not included in the pool. Our data show a lack of connection between Bothrops taxonomic identity and venom composition. We also show that different toxins display distinct reactivity with the tested antivenom. However, the antivenom reacted similarly with each class of toxin present in the venoms of the different snakes studied. Important evidence was the neutralization of the major toxic effects of B. atrox venom, not included in the mixture of antigens used to produce the antivenom. Based on the observed antigenicity of the distinct protein classes of toxins, we suggest that it is possible to obtain pan-specific and efficient Bothrops antivenoms via immunization with venoms from a few species of snakes that are representative of the protein composition of a large number of targeted species.

Molecular basis for prey relocation in viperid snakes

BACKGROUND

Vertebrate predators use a broad arsenal of behaviors and weaponry for overcoming fractious and potentially dangerous prey. A unique array of predatory strategies occur among snakes, ranging from mechanical modes of constriction and jaw-holding in non-venomous snakes, to a chemical means, venom, for quickly dispatching prey. However, even among venomous snakes, different prey handling strategies are utilized, varying from the strike-and-hold behaviors exhibited by highly toxic elapid snakes to the rapid strike-and-release envenomation seen in viperid snakes. For vipers, this mode of envenomation represents a minimal risk predatory strategy by permitting little contact with or retaliation from prey, but it adds the additional task of relocating envenomated prey which has wandered from the attack site. This task is further confounded by trails of other unstruck conspecific or heterospecific prey. Despite decades of behavioral study, researchers still do not know the molecular mechanism which allows for prey relocation.

RESULTS

During behavioral discrimination trials (vomeronasal responsiveness) to euthanized mice injected with size-fractionated venom, Crotalus atrox responded significantly to only one protein peak. Assays for enzymes common in rattlesnake venoms, such as exonuclease, L-amino acid oxidase, metalloproteinase, thrombin-like and kallikrein-like serine proteases and phospholipase A(2), showed that vomeronasal responsiveness was not dependent on enzymatic activity. Using mass spectrometry and N-terminal sequencing, we identified the proteins responsible for envenomated prey discrimination as the non-enzymatic disintegrins crotatroxin 1 and 2. Our results demonstrate a novel and critical biological role for venom disintegrins far beyond their well-established role in disruption of cell-cell and cell-extracellular matrix interactions.

CONCLUSIONS

These findings reveal the evolutionary significance of free disintegrins in venoms as the molecular mechanism in vipers allowing for effective relocation of envenomated prey. The presence of free disintegrins in turn has led to evolution of a major behavioral adaptation (strike-and-release), characteristic of only rattlesnakes and other vipers, which exploits and refines the efficiency of a pre-existing chemical means of predation and a highly sensitive olfaction system. This system of a predator chemically tagging prey represents a novel trend in the coevolution of predator-prey relationships.

Snake venom metalloproteinases

Recent proteomic analyses of snake venoms show that metalloproteinases represent major components in most of the Crotalid and Viperid venoms. In this chapter we discuss the multiple activities of the SVMPs. In addition to hemorrhagic activity, members of the SVMP family also have fibrin(ogen)olytic activity, act as prothrombin activators, activate blood coagulation factor X, possess apoptotic activity, inhibit platelet aggregation, are pro-inflammatory and inactivate blood serine proteinase inhibitors. Clearly the SVMPs have multiple functions in addition to their well-known hemorrhagic activity. The realization that there are structural variations in the SVMPs and the early studies that led to their classification represents an important event in our understanding of the structural forms of the SVMPs. The SVMPs were subdivided into the P-I, P-II and P-III protein classes. The noticeable characteristic that distinguished the different classes was their size (molecular weight) differences and domain structure: Class I (P-I), the small SVMPs, have molecular masses of 20-30 kDa, contain only a pro domain and the proteinase domain; Class II (P-II), the medium size SVMPs, molecular masses of 30-60 kDa, contain the pro domain, proteinase domain and disintegrin domain; Class III (P-III), the large SVMPs, have molecular masses of 60-100 kDa, contain pro, proteinase, disintegrin-like and cysteine-rich domain structure. Another significant advance in the SVMP field was the characterization of the crystal structure of the first P-I class SVMP. The structures of other P-I SVMPs soon followed and the structures of P-III SVMPs have also been determined. The active site of the metalloproteinase domain has a consensus HEXXHXXGXXHD sequence and a Met-turn. The "Met-turn" structure contains a conserved Met residue that forms a hydrophobic basement for the three zinc-binding histidines in the consensus sequence.

Identification of linear B-cell epitopes on myotoxin II, a Lys49 phospholipase A₂ homologue from Bothrops asper snake venom

Knowledge on toxin immunogenicity at the molecular level can provide valuable information for the improvement of antivenoms, as well as for understanding toxin structure-function relationships. The aims of this study are two-fold: first, to identify the linear B-cell epitopes of myotoxin II from Bothrops asper snake venom, a Lys49 phospholipase A₂ homologue; and second, to use antibodies specifically directed against an epitope having functional relevance in its toxicity, to probe the dimeric assembly mode of this protein in solution. Linear B-cell epitopes were identified using a library of overlapping synthetic peptides spanning its complete sequence. Epitopes recognized by a rabbit antiserum to purified myotoxin II, and by three batches of a polyvalent (Crotalidae) therapeutic antivenom (prepared in horses immunized with a mixture of B. asper, Crotalus simus, and Lachesis stenophrys venoms) were mapped using an enzyme-immunoassay based on the capture of biotinylated peptides by immobilized streptavidin. Some of the epitopes identified were shared between the two species, whereas others were unique. Differences in epitope recognition were observed not only between the two species, but also within the three batches of equine antivenom. Epitope V, located at the C-terminal region of this protein, is known to be relevant for toxicity and neutralization. Affinity-purified rabbit antibodies specific for this site were able to immunoprecipitate myotoxin II, suggesting that the two copies of epitope V are simultaneously available to antibody binding, which would be compatible with the mode of dimerization known as "conventional" dimer.

Snake venomics of Crotalus tigris: the minimalist toxin arsenal of the deadliest Nearctic rattlesnake venom. Evolutionary Clues for generating a pan-specific antivenom against crotalid type II venoms [corrected]

We report the proteomic and antivenomic characterization of Crotalus tigris venom. This venom exhibits the highest lethality for mice among rattlesnakes and the simplest toxin proteome reported to date. The venom proteome of C. tigris comprises 7-8 gene products from 6 toxin families; the presynaptic β-neurotoxic heterodimeric PLA(2), Mojave toxin, and two serine proteinases comprise, respectively, 66 and 27% of the C. tigris toxin arsenal, whereas a VEGF-like protein, a CRISP molecule, a medium-sized disintegrin, and 1-2 PIII-SVMPs each represent 0.1-5% of the total venom proteome. This toxin profile really explains the systemic neuro- and myotoxic effects observed in envenomated animals. In addition, we found that venom lethality of C. tigris and other North American rattlesnake type II venoms correlates with the concentration of Mojave toxin A-subunit, supporting the view that the neurotoxic venom phenotype of crotalid type II venoms may be described as a single-allele adaptation. Our data suggest that the evolutionary trend toward neurotoxicity, which has been also reported for the South American rattlesnakes, may have resulted by pedomorphism. The ability of an experimental antivenom to effectively immunodeplete proteins from the type II venoms of C. tigris, Crotalus horridus , Crotalus oreganus helleri, Crotalus scutulatus scutulatus, and Sistrurus catenatus catenatus indicated the feasibility of generating a pan-American anti-Crotalus type II antivenom, suggested by the identification of shared evolutionary trends among South and North American Crotalus species.

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.