DNA Aptamers against Taiwan Banded Krait α-Bungarotoxin Recognize Taiwan Cobra Cardiotoxins

Specific Amino Acid Residues in the Three Loops of Snake Cytotoxins Determine Their Membrane Activity and Provide a Rationale for a New Classification of These Toxins

Cytotoxins (CTs) are three-finger membrane-active toxins present mainly in cobra venom. Our analysis of the available CT amino acid sequences, literature data on their membrane activity, and conformational equilibria in aqueous solution and detergent micelles allowed us to identify specific amino acid residues which interfere with CT incorporation into membranes. They include Pro9, Ser28, and Asn/Asp45 within the N-terminal, central, and C-terminal loops, respectively. There is a hierarchy in the effect of these residues on membrane activity: Pro9 > Ser28 > Asn/Asp45. Taking into account all the possible combinations of special residues, we propose to divide CTs into eight groups. Group 1 includes toxins containing all of the above residues. Their representatives demonstrated the lowest membrane activity. Group 8 combines CTs that lack these residues. For the toxins from this group, the greatest membrane activity was observed. We predict that when solely membrane activity determines the cytotoxic effects, the activity of CTs from a group with a higher number should exceed that of CTs from a group with a lower number. This classification is supported by the available data on the cytotoxicity and membranotropic properties of CTs. We hypothesize that the special amino acid residues within the loops of the CT molecule may indicate their involvement in the interaction with non-lipid targets.

Development and optimization of a DNA aptamer to delay β-bungarotoxin-induced lethality in a rodent model

Current treatment of snakebite relies on immunoglobulin-rich antivenoms. However, production of these antivenoms is complicated and costly. Aptamers - single-stranded DNAs or RNAs with specific folding structures that bind to specific target molecules - represent excellent alternatives or complements to antibody-based therapeutics. However, no studies have systematically assessed the feasibility of using aptamers to mitigate venom-induced toxicity in vivo. β-bungarotoxin is the predominant protein responsible for the toxicity of the venom of Bungarus multicinctus, a prominent venomous snake inhabiting Taiwan. In this study, we reported the screening and optimization of a DNA aptamer against β-bungarotoxin and tested its utility in a mouse model. After 14 rounds of directed evolution of ligands by exponential enrichment, an aptamer, called BB3, displaying remarkable binding affinity and specificity for β-bungarotoxin was obtained. Following structural prediction and point-modification experiments, BB3 underwent truncation and was modified with 2'-O-methylation and a 3'-inverted dT. This optimized aptamer showed sustained, high-affinity binding for β-bungarotoxin and exhibited remarkable nuclease resistance in plasma. Importantly, administration of this optimized aptamer extended the survival time of mice treated with a lethal dose of β-bungarotoxin. Collectively, our data provide a compelling illustration of the potential of aptamers as promising candidates for development of recombinant antivenom therapies.

De novo designed proteins neutralize lethal snake venom toxins

Snakebite envenoming remains a devastating and neglected tropical disease, claiming over 100,000 lives annually and causing severe complications and long-lasting disabilities for many more1,2. Three-finger toxins (3FTx) are highly toxic components of elapid snake venoms that can cause diverse pathologies, including severe tissue damage3 and inhibition of nicotinic acetylcholine receptors (nAChRs) resulting in life-threatening neurotoxicity4. Currently, the only available treatments for snakebite consist of polyclonal antibodies derived from the plasma of immunized animals, which have high cost and limited efficacy against 3FTxs5,6,7. Here, we use deep learning methods to de novo design proteins to bind short- and long-chain α-neurotoxins and cytotoxins from the 3FTx family. With limited experimental screening, we obtain protein designs with remarkable thermal stability, high binding affinity, and near-atomic level agreement with the computational models. The designed proteins effectively neutralize all three 3FTx sub-families in vitro and protect mice from a lethal neurotoxin challenge. Such potent, stable, and readily manufacturable toxin-neutralizing proteins could provide the basis for safer, cost-effective, and widely accessible next-generation antivenom therapeutics. Beyond snakebite, our computational design methodology should help democratize therapeutic discovery, particularly in resource-limited settings, by substantially reducing costs and resource requirements for development of therapies to neglected tropical diseases.

Tissue damaging toxins in snake venoms: mechanisms of action, pathophysiology and treatment strategies

Snakebite envenoming is an important public health issue responsible for mortality and severe morbidity. Where mortality is mainly caused by venom toxins that induce cardiovascular disturbances, neurotoxicity, and acute kidney injury, morbidity is caused by toxins that directly or indirectly destroy cells and degrade the extracellular matrix. These are referred to as 'tissue-damaging toxins' and have previously been classified in various ways, most of which are based on the tissues being affected (e.g., cardiotoxins, myotoxins). This categorisation, however, is primarily phenomenological and not mechanistic. In this review, we propose an alternative way of classifying cytotoxins based on their mechanistic effects rather than using a description that is organ- or tissue-based. The mechanisms of toxin-induced tissue damage and their clinical implications are discussed. This review contributes to our understanding of fundamental biological processes associated with snakebite envenoming, which may pave the way for a knowledge-based search for novel therapeutic options.

Towards better antivenoms: navigating the road to new types of snakebite envenoming therapies

Snakebite envenoming is a significant global health challenge, and for over a century, traditional plasma-derived antivenoms from hyperimmunized animals have been the primary treatment against this infliction. However, these antivenoms have several inherent limitations, including the risk of causing adverse reactions when administered to patients, batch-to-batch variation, and high production costs. To address these issues and improve treatment outcomes, the development of new types of antivenoms is crucial. During this development, key aspects such as improved clinical efficacy, enhanced safety profiles, and greater affordability should be in focus. To achieve these goals, modern biotechnological methods can be applied to the discovery and development of therapeutic agents that can neutralize medically important toxins from multiple snake species. This review highlights some of these agents, including monoclonal antibodies, nanobodies, and selected small molecules, that can achieve broad toxin neutralization, have favorable safety profiles, and can be produced on a large scale with standardized manufacturing processes. Considering the inherent strengths and limitations related to the pharmacokinetics of these different agents, a combination of them might be beneficial in the development of new types of antivenom products with improved therapeutic properties. While the implementation of new therapies requires time, it is foreseeable that the application of biotechnological advancements represents a promising trajectory toward the development of improved therapies for snakebite envenoming. As research and development continue to advance, these new products could emerge as the mainstay treatment in the future.

Considerations for the development of a field-based medical device for the administration of adjunctive therapies for snakebite envenoming

The timely administration of antivenom is the most effective method currently available to reduce the burden of snakebite envenoming (SBE), a neglected tropical disease that most often affects rural agricultural global populations. There is increasing interest in the development of adjunctive small molecule and biologic therapeutics that target the most problematic venom components to bridge the time-gap between initial SBE and the administration antivenom. Unique combinations of these therapeutics could provide relief from the toxic effects of regional groupings of medically relevant snake species. The application a PRISMA/PICO literature search methodology demonstrated an increasing interest in the rapid administration of therapies to improve patient symptoms and outcomes after SBE. Advice from expert interviews and considerations regarding the potential routes of therapy administration, anatomical bite location, and species-specific venom delivery have provided a framework to identify ideal metrics and potential hurdles for the development of a field-based medical device that could be used immediately after SBE to deliver adjunctive therapies. The use of subcutaneous (SC) or intramuscular (IM) injection were identified as potential routes of administration of both small molecule and biologic therapies. The development of a field-based medical device for the delivery of adjunctive SBE therapies presents unique challenges that will require a collaborative and transdisciplinary approach to be successful.

The Need for Next-Generation Antivenom for Snakebite Envenomation in India

The limitations posed by currently available antivenoms have emphasized the need for alternative treatments to counteract snakebite envenomation. Even though exact epidemiological data are lacking, reports have indicated that most global snakebite deaths are reported in India. Among the many problems associated with snakebite envenomation, issues related to the availability of safer and more efficient antivenoms are of primary concern. Since India has the highest number of global snakebite deaths, efforts should be made to reduce the burden associated with snakebite envenoming. Alternative methods, including aptamers, camel antivenoms, phage display techniques for generating high-affinity antibodies and antibody fragments, small-molecule inhibitors, and natural products, are currently being investigated for their effectiveness. These alternative methods have shown promise in vitro, but their in vivo effectiveness should also be evaluated. In this review, the issues associated with Indian polyvalent antivenoms in neutralizing venom components from geographically distant species are discussed in detail. In a nutshell, this review gives an overview of the current drawbacks of using animal-derived antivenoms and several alternative strategies that are currently being widely explored.

Snake Antivenoms-Toward Better Understanding of the Administration Route

Envenomations induced by animal bites and stings constitute a significant public health burden. Even though a standardized protocol does not exist, parenterally administered polyclonal antivenoms remain the mainstay in snakebite therapy. There is a prevailing opinion that their application by the i.m. route has poor efficacy and that i.v. administration should preferentially be chosen in order to achieve better accomplishment of the antivenom therapeutic activity. Recently, it has been demonstrated that neutralization not only in the systemic circulation but also in the lymphatic system might be of great importance for the clinical outcome since it represents another relevant body compartment through which the absorption of the venom components occurs. In this review, the present-day and summarized knowledge of the laboratory and clinical findings on the i.v. and i.m. routes of antivenom administration is provided, with a special emphasis on the contribution of the lymphatic system to the process of venom elimination. Until now, antivenom-mediated neutralization has not yet been discussed in the context of the synergistic action of both blood and lymph. A current viewpoint might help to improve the comprehension of the venom/antivenom pharmacokinetics and the optimal approach for drug application. There is a great need for additional dependable, practical, well-designed studies, as well as more practice-related experience reports. As a result, opportunities for resolving long-standing disputes over choosing one therapeutic principle over another might be created, improving the safety and effectiveness of snakebite management.

Detection of cytotoxins by sandwich-ELISA for discrimination of cobra envenomation and indication of necrotic severity

Snake envenoming is both a healthcare and socioeconomic problem for developing countries and underserved communities. In Taiwan, clinical management of Naja atra envenomation is a major challenge, since cobra venom-induced symptoms are usually confused with hemorrhagic snakebites and current antivenom treatments do not effectively prevent venom-induced necrosis for which early surgical debridement should be administered. Identification and validation of biomarkers of cobra envenomation is critical for progress in setting a realistic goal for snakebite management in Taiwan. Previously, cytotoxin (CTX) was determined as one of potential biomarker candidates; however, its ability to discriminate cobra envenoming remains to be verified, especially in clinical practice. In this study, we selected a monoclonal single-chain variable fragment (scFv) and a polyclonal antibody to develop a sandwich enzyme-linked immunosorbent assay (ELISA) for CTX detection, which successfully recognized CTX from N. atra venom over that from other snake species. Using this specific assay, the CTX concentration in envenoming mice was shown to remain consistent in about 150 ng/mL during the 2-hour post-injection period. The measured concentration was highly correlated with the size of local necrosis in mouse dorsal skin, which the correlation coefficient is about 0.988. Furthermore, our ELISA method displayed 100 % of specificity and sensitivity in discriminating cobra envenoming among snakebite victims through CTX detection and the level of CTX in victim plasma was ranged from 5.8 to 253.9 ng/mL. Additionally, patients developed tissue necrosis at plasma CTX concentrations higher than 150 ng/mL. Thus, CTX not only serves as a verified biomarker for discrimination of cobra envenoming but also a potential indicator of severity of local necrosis. In this context, detection of CTX may facilitate reliable identification of envenoming species and improve snakebite management in Taiwan.

Exploring the Utility of ssDNA Aptamers Directed against Snake Venom Toxins as New Therapeutics for Snakebite Envenoming

Snakebite is a neglected tropical disease that causes considerable death and disability in the tropical world. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Antivenoms are the mainstay therapy for treating the toxic effects of snakebite, but despite saving thousands of lives annually, these therapies are associated with limited cross-snake species efficacy due to venom variation, which ultimately restricts their therapeutic utility to particular geographical regions. In this study, we sought to explore the potential of ssDNA aptamers as toxin-specific inhibitory alternatives to antibodies. As a proof of principle model, we selected snake venom serine protease toxins, which are responsible for contributing to venom-induced coagulopathy following snakebite envenoming, as our target. Using SELEX technology, we selected ssDNA aptamers against recombinantly expressed versions of the fibrinogenolytic SVSPs ancrod from the venom of C. rhodostoma and batroxobin from B. atrox. From the resulting pool of specific ssDNA aptamers directed against each target, we identified candidates that exhibited low nanomolar binding affinities to their targets. Downstream aptamer-linked immobilised sorbent assay, fibrinogenolysis, and coagulation profiling experiments demonstrated that the candidate aptamers were able to recognise native and recombinant SVSP toxins and inhibit the toxin- and venom-induced prolongation of plasma clotting times and the consumption of fibrinogen, with inhibitory potencies highly comparable to commercial polyvalent antivenoms. Our findings demonstrate that rationally selected toxin-specific aptamers can exhibit broad in vitro cross-reactivity against toxin isoforms found in different snake venoms and are capable of inhibiting toxins in pathologically relevant in vitro and ex vivo models of venom activity. These data highlight the potential utility of ssDNA aptamers as novel toxin-inhibiting therapeutics of value for tackling snakebite envenoming.

Neutralization of Daboxin P activities by rationally designed aptamers

Inefficacy and associated risks of current antivenom has raised the need for alternative approaches of snakebite management. Aptamers are one such alternative which is being pursued for therapeutic interventions as well as for design of diagnostic kits due to its high specificity. Present study focussed on designing and validating nucleic acid aptamers against snake venom PLA_2, a hydrolytic enzyme present in all venomous snakes. The aptamers were designed by adding nucleic acid chain on the surface of Daboxin P, a major PLA₂ enzyme of Daboia russelii venom. Binding characteristics of the aptamers were confirmed by docking to Daboxin P as well as acidic and basic PLA₂s from different snake species using in silico docking. The aptamers folded into different tertiary structures and bound to the active and Ca²⁺ binding site of PLA₂ enzymes. Molecular dynamics simulation analysis of Daboxin P-aptamer complexes showed that the complexes were stable in an aqueous environment. The electrophoretic mobility shift assay further confirmed the binding of the synthetic aptamers to Daboxin P and other snake venom PLA₂ enzymes. The aptamers inhibited the sPLA₂ activity with an IC₅₀ value ranging between 0.52 μM and 0.77 μM as well as the anticoagulant activity of Daboxin P. The aptamers could also inhibit the PLA₂ activity of Echis carinatus crude venom and anti-coagulant activity of Bungarus caeruleus crude venom, members of big four snakes. However, the aptamers didn't inhibit fibrinogenolytic or proteolytic activity of big four venom as well as the coagulation and hemolytic activities. Thus, aptamers can be rationally designed to inhibit the biochemical and biological activities of snake venom proteins.

Cytotoxin antibody-based colourimetric sensor for field-level differential detection of elapid among big four snake venom

Development of a rapid, on-site detection tool for snakebite is highly sought after, owing to its clinically and forensically relevant medicolegal significance. Polyvalent antivenom therapy in the management of such envenomation cases is finite due to its poor venom neutralization capabilities as well as diagnostic ramifications manifested as untoward immunological reactions. For precise molecular diagnosis of elapid venoms of the big four snakes, we have developed a lateral flow kit using a monoclonal antibody (AB1; IgG1 - κ chain; Kd: 31 nM) generated against recombinant cytotoxin-7 (rCTX-7; 7.7 kDa) protein of the elapid venom. The monoclonal antibody specifically detected the venoms of Naja naja (p < 0.0001) and Bungarus caeruleus (p<0.0001), without showing any immunoreactivity against the viperidae snakes in big four venomous snakes. The kit developed attained the limit of quantitation of 170 pg/μL and 2.1 ng/μL in spiked buffer samples and 28.7 ng/μL and 110 ng/μL in spiked serum samples for detection of N. naja and B. caeruleus venoms, respectively. This kit holds enormous potential in identification of elapid venom of the big four snakes for effective prognosis of an envenomation; as per the existing medical guidelines.

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

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

Assessment of snakebite burdens, clinical features of envenomation, and strategies to improve snakebite management in Vietnam

The sheer paucity of scientific documentation of herpetofauna in Vietnam and the rudimentary healthcare response to snakebite have stimulated this review. Over six decades of data culled from public data bases and search engines, have been used to assess snakebite burdens, clinical features of envenomation, and strategies for snakebite management in Vietnam. In addition, biochemical and proteomic analyses to decipher venom composition, rapid analytical techniques to be used for clinical diagnosis of snakebite in Vietnam have been discussed in detail. The assessment of efficacy, safety, and quality of commercial antivenom produced in Vietnam and improvement of antivenom production to meet the national requirement has been critically examined. It is apparent that snake bite incidence in Vietnam is exacerbated by mismatch in demand and supply of antivenom therapy, insufficient medical facilities, preference for traditional healers and poor management of clinical records. The impediments arising from geographical and species-specific variation in venom composition can be overcome by the 'Omics approach', and scientific documentation of pathophysiological manifestations post envenomation. The development of next generation of therapeutics, encouraging clinical research, novel approaches and social awareness against snakebite and its treatments have been suggested to significantly reduce the snakebite mortality and morbidity in this region.

Repurposed drug to the rescue of snakebite victims

Preclinical data suggest the possibility of repurposing a drug for early intervention in envenoming by snake venom rich in metalloproteinases (Albulescu et al., this issue).

Diagnostic and Therapeutic Value of Aptamers in Envenomation Cases

It is now more than a century since Albert Calmette from the Institut Pasteur changed the world of envenomation by demonstrating that antibodies raised against animal venoms have the ability to treat human victims of previously fatal bites or stings. Moreover, the research initiated at that time effectively launched the discipline of toxicology, first leading to the search for toxic venom components, followed by the demonstration of venoms that also contained compounds of therapeutic value. Interest from pharmaceutical companies to treat envenomation is, however, declining, mainly for economic reasons, and hence, the World Health Organization has reclassified this public health issue to be a highest priority concern. While the production, storage, and safety of antivenom sera suffer from major inconveniences, alternative chemical and technological approaches to the problem of envenomation need to be considered that bypass the use of antibodies for toxin neutralization. Herein, we review an emerging strategy that relies on the use of aptamers and discuss how close—or otherwise—we are to finding a viable alternative to the use of antibodies for the therapy of human envenomation.

Varespladib (LY315920) and Methyl Varespladib (LY333013) Abrogate or Delay Lethality Induced by Presynaptically Acting Neurotoxic Snake Venoms

The phospholipase A₂ (PLA₂) inhibitor Varespladib (LY315920) and its orally bioavailable prodrug, methyl-Varespladib (LY333013) inhibit PLA₂ activity of a wide variety of snake venoms. In this study, the ability of these two forms of Varespladib to halt or delay lethality of potent neurotoxic snake venoms was tested in a mouse model. The venoms of Notechis scutatus, Crotalus durissus terrificus, Bungarus multicinctus, and Oxyuranus scutellatus, all of which have potent presynaptically acting neurotoxic PLA₂s of variable quaternary structure, were used to evaluate simple dosing regimens. A supralethal dose of each venom was injected subcutaneously in mice, followed by the bolus intravenous (LY315920) or oral (LY333013) administration of the inhibitors, immediately and at various time intervals after envenoming. Control mice receiving venom alone died within 3 h of envenoming. Mice injected with O. scutellatus venom and treated with LY315920 or LY333013 survived the 24 h observation period, whereas those receiving C. d. terrificus and B. multicinctus venoms survived at 3 h or 6 h with a single dose of either form of Varespladib, but not at 24 h. In contrast, mice receiving N. scutatus venom and then the inhibitors died within 3 h, similarly to the control animals injected with venom alone. LY315920 was able to reverse the severe paralytic manifestations in mice injected with venoms of O. scutellatus, B. multicinctus, and C. d. terrificus. Overall, results suggest that the two forms of Varespladib are effective in abrogating, or delaying, neurotoxic manifestations induced by some venoms whose neurotoxicity is mainly dependent on presynaptically acting PLA₂s. LY315920 is able to reverse paralytic manifestations in severely envenomed mice, but further work is needed to understand the significance of species-specific differences in animal models as they compare to clinical syndromes in human and for potential use in veterinary medicine.

Validity and reliability of telephone administration of the patient-specific functional scale for the assessment of recovery from snakebite envenomation

Objectives

Although more than 1.8 million people survive snakebite envenomation each year, their recovery is understudied. Obtaining long-term follow-up is challenging in both high- and low-resource settings. The Patient-Specific Functional Scale (PSFS) is an easily administered, well-accepted patient-reported outcome that is validated for assessing limb recovery from snakebite envenomation. We studied whether the PSFS is valid and reliable when administered by telephone.

Methods

This is a secondary analysis of data from a randomized clinical trial. We analyzed the results of PSFS collected in-person on days 3, 7, 14, 21, and 28 and by telephone on days 10, 17, and 24. We assessed the following scale psychometric properties: (a) content validity (ceiling and floor effects), (b) internal structure and consistency (Cronbach’s alpha), and (c) temporal and external validity using Intraclass Correlation Coefficient (ICC). Temporal stability was assessed using Spearman’s correlation coefficient and agreement between adjacent in-person and telephonic assessments with Cohen’s kappa. Bland Altman analysis was used to assess differential bias in low and high score results.

Results

Data from 74 patients were available for analysis. Floor effects were seen in the early post-injury time points (median: 3 (IQR: 0, 5) at 3 days post-enrollment) and ceiling effects in the late time points (median: 9 (IQR: 8, 10). Internal consistency was good to excellent with both in-person (Cronbach α: 0.91 (95%CI 0.88, 0.95)) and telephone administration (0.81 (0.73, 0.89). Temporal stability was also good (ICC: 0.83 (0.72, 0.89) in-person, 0.80 (0.68, 0.88) telephone). A strong linear correlation was found between in-person and telephone administration (Spearman’s ρ: 0.83 (CI: 0.78, 0.84), consistency was assessed as excellent (Cohen’s κ 0.81 (CI: 0.78, 0.84), and Bland Altman analysis showed no systematic bias.

Conclusions

Telephone administration of the PSFS provides valid, reliable, and consistent data for the assessment of recovery from snakebite envenomation.

Snakebite envenomation is an important but neglected tropical disease that impacts millions of people worldwide each year. These bites lead to both death and permanent disability. As they occur in tropical and subtropical regions, they primarily impact people from low-income areas of the world. As potential new treatments are being developed, we must understand their potential benefit in humans before they can be widely disseminated. Performing these human studies requires the ability to determine how patients recovered with these treatments. Having people return for evaluation during recovery is difficult in these low-income regions. We evaluated the ability to use a telephone version of an already accepted measurement of recovery in snakebite, the Patient-Specific Functional Scale. This study demonstrates that using this telephone-administered measure is feasible, valid, and reliable. With the results of this study, we now have an important tool to easily measure recovery in areas where snakebite predominates. This tool will help snakebite envenomation researchers evaluate the potential benefit of new treatments and accelerate the process of bringing new effective treatments to those snakebite patients in the most need.

History of Envenoming Therapy and Current Perspectives

Each year, millions of humans fall victim to animal envenomings, which may either be deadly or cause permanent disability to the effected individuals. The Nobel Prize-winning discovery of serum therapy for the treatment of bacterial infections (tetanus and diphtheria) paved the way for the introduction of antivenom therapies for envenomings caused by venomous animals. These antivenoms are based on polyclonal antibodies derived from the plasma of hyperimmunized animals and remain the only specific treatment against animal envenomings. Following the initial development of serum therapy for snakebite envenoming by French scientists in 1894, other countries with high incidences of animal envenomings, including Brazil, Australia, South Africa, Costa Rica, and Mexico, started taking up antivenom production against local venomous animals over the course of the twentieth century. These undertakings revolutionized envenoming therapy and have saved innumerous patients worldwide during the last 100 years. This review describes in detail the above-mentioned historical events surrounding the discovery and the application of serum therapy for envenomings, as well as it provides an overview of important developments and scientific breakthroughs that were of importance for antibody-based therapies in general. This begins with discoveries concerning the characterization of antibodies, including the events leading up to the elucidation of the antibody structure. These discoveries further paved the way for other milestones in antibody-based therapies, such as the introduction of hybridoma technology in 1975. Hybridoma technology enabled the expression and isolation of monoclonal antibodies, which in turn formed the basis for the development of phage display technology and transgenic mice, which can be harnessed to directly obtain fully human monoclonal antibodies. These developments were driven by the ultimate goal of producing potent neutralizing monoclonal antibodies with optimal pharmacokinetic properties and low immunogenicity. This review then provides an outline of the most recent achievements in antivenom research, which include the application of new biotechnologies, the development of the first human monoclonal antibodies that can neutralize animal toxins, and efforts toward creating fully recombinant antivenoms. Lastly, future perspectives in the field of envenoming therapies are discussed, including rational engineering of antibody cross-reactivity and the use of oligoclonal antibody mixtures.

The Urgent Need to Develop Novel Strategies for the Diagnosis and Treatment of Snakebites

Snakebite envenoming (SBE) is a priority neglected tropical disease, which kills in excess of 100,000 people per year. Additionally, many millions of survivors also suffer through disabilities and long-term health consequences. The only treatment for SBE, antivenom, has a number of major associated problems, not least, adverse reactions and limited availability. This emphasises the necessity for urgent improvements to the management of this disease. Administration of antivenom is too frequently based on symptomatology, which results in wasting crucial time. The majority of SBE-affected regions rely on broad-spectrum polyvalent antivenoms that have a low content of case-specific efficacious immunoglobulins. Research into small molecular therapeutics such as varespladib/methyl-varespladib (PLA2 inhibitors) and batimastat/marimastat (metalloprotease inhibitors) suggest that such adjunctive treatments could be hugely beneficial to victims. Progress into toxin-specific monoclonal antibodies as well as alternative binding scaffolds such as aptamers hold much promise for future treatment strategies. SBE is not implicit during snakebite, due to venom metering. Thus, the delay between bite and symptom presentation is critical and when symptoms appear it may often already be too late to effectively treat SBE. The development of reliable diagnostical tools could therefore initiate a paradigm shift in the treatment of SBE. While the complete eradication of SBE is an impossibility, mitigation is in the pipeline, with new treatments and diagnostics rapidly emerging. Here we critically review the urgent necessity for the development of diagnostic tools and improved therapeutics to mitigate the deaths and disabilities caused by SBE.

The validity, reliability and minimal clinically important difference of the patient specific functional scale in snake envenomation

Objective

Valid, reliable, and clinically relevant outcome measures are necessary in clinical studies of snake envenomation. The aim of this study was to evaluate the psychometric (validity and reliability) and clinimetric (minimal clinically important difference [MCID]) properties of the Patient-Specific Functional Scale (PSFS) in snakebite envenomation.

Methods

We performed a secondary analysis of two existing snakebite trials that measured clinical outcomes using the PSFS as well as other quality of life and functional assessments. Data were collected at 3, 7, 10, and 17 days. Reliability was determined using Cronbach’s alpha for internal consistency and the intraclass correlation coefficient (ICC) for temporal stability at 10 and 17 days. Validity was assessed using concurrent validity correlating with the other assessments. The MCID was evaluated using the following criteria: (1) the distribution of stable patients according to both standard error of measurement (SEM) and responsiveness techniques, and (2) anchor-based methods to compare between individuals and to detect discriminant ability of a positive change with a receiver operator characteristic (ROC) curve and optimal cutoff point.

Results

A total of 86 patients were evaluated in this study. The average PSFS scores were 5.37 (SD 3.23), 7.95 (SD 2.22), and 9.12 (SD 1.37) at 3, 7, and 10 days, respectively. Negligible floor effect was observed (maximum of 8% at 3 days); however, a ceiling effect was observed at 17 days (25%). The PSFS showed good reliability with an internal consistency of 0.91 (Cronbach’s alpha) (95% CI 0.88, 0.95) and a temporal stability of 0.83 (ICC) (95% CI 0.72, 0.89). The PSFS showed a strong positive correlation with quality of life and functional assessments. The MCID was approximately 1.0 for all methods.

Conclusions

With an MCID of approximately 1 point, the PSFS is a valid and reliable tool to assess quality of life and functionality in patients with snake envenomation.

Snakebite: An Exploratory Cost-Effectiveness Analysis of Adjunct Treatment Strategies

The cost-effectiveness of the standard of care for snakebite treatment, antivenom, and supportive care has been established in various settings. In this study, based on data from South Indian private health-care providers, we address an additional question: "For what cost and effectiveness values would adding adjunct-based treatment strategies to the standard of care for venomous snakebites be cost-effective?" We modeled the cost and performance of potential interventions (e.g., pharmacologic or preventive) used adjunctively with antivenom and supportive care for the treatment of snakebite. Because these potential interventions are theoretical, we used a threshold cost-effectiveness approach to explore this forward-looking concept. We examined economic parameters at which these interventions could be cost-effective or even cost saving. A threshold analysis was used to examine the addition of new interventions to the standard of care. Incremental cost-effectiveness ratios were used to compare treatment strategies. One-way, scenario, and probabilistic sensitivity analyses were conducted to analyze parameter uncertainty and define cost and effectiveness thresholds. Our results suggest that even a 3% reduction in severe cases due to an adjunct strategy is likely to reduce the cost of overall treatment and have the greatest impact on cost-effectiveness. In this model, for example, an investment of $10 of intervention that reduces the incidence of severe cases by 3%, even without changing antivenom usage patterns, creates cost savings of $75 per individual. These findings illustrate the striking degree to which an adjunct intervention could improve patient outcomes and be cost-effective or even cost saving.

A Turn-on Fluorescence Sensor for Heparin Detection Based on a Release of Taiwan Cobra Cardiotoxin from a DNA Aptamer or Adenosine-Based Molecular Beacon

This study presents two sensitive fluorescent assays for sensing heparin on the basis of the electrostatic interaction between heparin and Naja naja atra cardiotoxin 3 (CTX3). Owing to CTX3-induced folded structure of an adenosine-based molecular beacon (MB) or a DNA aptamer against CTX3, a reduction in the fluorescent signal of the aptamer or MB 5'-end labeled with carboxyfluorescein (FAM) and 3'-end labeled with 4-([4-(dimethylamino)phenyl]azo)-benzoic acid (DABCYL) was observed upon the addition of CTX3. The presence of heparin and formation of the CTX3-heparin complex caused CTX3 detachment from the MB or aptamer, and restoration of FAM fluorescence of the 5'-FAM-and-3'-DABCYL-labeled MB and aptamer was subsequently noted. Moreover, the detection of heparin with these CTX3-aptamer and CTX3-MB sensors showed high sensitivity and selectivity toward heparin over chondroitin sulfate and hyaluronic acid regardless of the presence of plasma. The limit of detection for heparin in plasma was determined to be 16 ng/mL and 15 ng/mL, respectively, at a signal-to-noise ratio of 3. This study validates the practical utility of the CTX3-aptamer and CTX3-MB systems for determining the concentration of heparin in a biological matrix.

Detection of Naja atra Cardiotoxin Using Adenosine-Based Molecular Beacon

This study presents an adenosine (A)-based molecular beacon (MB) for selective detection of Naja atra cardiotoxin (CTX) that functions by utilizing the competitive binding between CTX and the poly(A) stem of MB to coralyne. The 5′- and 3′-end of MB were labeled with a reporter fluorophore and a non-fluorescent quencher, respectively. Coralyne induced formation of the stem-loop MB structure through A₂-coralyne-A₂ coordination, causing fluorescence signal turn-off due to fluorescence resonance energy transfer between the fluorophore and quencher. CTX3 could bind to coralyne. Moreover, CTX3 alone induced the folding of MB structure and quenching of MB fluorescence. Unlike that of snake venom α-neurotoxins, the fluorescence signal of coralyne-MB complexes produced a bell-shaped concentration-dependent curve in the presence of CTX3 and CTX isotoxins; a turn-on fluorescence signal was noted when CTX concentration was ≤80 nM, while a turn-off fluorescence signal was noted with a further increase in toxin concentrations. The fluorescence signal of coralyne-MB complexes yielded a bell-shaped curve in response to varying concentrations of N. atra crude venom but not those of Bungarus multicinctus and Protobothrops mucrosquamatus venoms. Moreover, N. nigricollis venom also functioned as N. atra venom to yield a bell-shaped concentration-dependent curve of MB fluorescence signal, again supporting that the hairpin-shaped MB could detect crude venoms containing CTXs. Taken together, our data validate that a platform composed of coralyne-induced stem-loop MB structure selectively detects CTXs.