Neutralization of Bothrops alternatus regional venom pools and individual venoms by antivenom: a systematic comparison

Current situation of snakebites envenomation in the Neotropics: Biotechnology, a versatile tool in the production of antivenoms

Snakebite envenomation is a neglected tropical disease that affects millions of people around the world with a great impact on health and the economy. Unfortunately, public health programs do not include this kind of disease as a priority in their social programs. Cases of snakebite envenomations in the Neotropics are inaccurate due to inadequate disease management from medical records to the choice of treatments. Victims of snakebite envenomation are primarily found in impoverished agricultural areas where remote conditions limit the availability of antivenom. Antivenom serum is the only Food and Drug Administration-approved treatment used up to date. However, it has several disadvantages in terms of safety and effectiveness. This review provides a comprehensive insight dealing with the current epidemiological status of snakebites in the Neotropics and technologies employed in antivenom production. Also, modern biotechnological tools such as transcriptomic, proteomic, immunogenic, high-density peptide microarray and epitope mapping are highlighted for producing new-generation antivenom sera. These results allow us to propose strategic solutions in the Public Health Sector for managing this disease. Keywords: antivenom, biotechnology, neglected tropical disease, omics, recombinant antibody.

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.

Toxicological study of bee venom (Apis mellifera mellifera) from different regions of the province of Buenos Aires, Argentina

Samples of Apis mellifera mellifera venom from different hives in two regions of the Buenos Aires province and its pool were analyzed for their lethal potency, myotoxic, defibrinogenating, hemolytic and inflammatory-edematizing activity and for the histological alterations they produce in the heart, lungs, kidneys, skeletal muscle and liver of mice. In vitro studies focused on the venom's hemolytic activity in different systems and species (horse, man, sheep and rabbit), the cytotoxicity in cellular lines, and on the proteolytic and coagulant activity in plasma and fibrinogen. Hemolytic activity, either observed in vitro or in vivo, showed similar toxicity levels for all samples. Erythrocytes of different species varied in their sensitivity to the venom pool, equines being the most sensitive and sheep the most resistant to direct hemolytic action. Local and systemic myotoxicity was evidenced by either the elevation of serum creatine kinase and/or histopathological lesions, observed in different muscles. All samples caused significant pathological alterations; pulmonary, cardiac, renal and skeletal muscle lesions were substantive and can be related to the pathophysiological mechanisms of envenomation. The venoms from different apiaries and regions of the Buenos Aires province showed very similar toxicological characteristics. These results suggest that severity of envenomation in case of a swarming could therefore be more related to the number of bees than to the differential toxicity of the venom from different regions of the province. This is the first study on the toxicity and toxicological characteristics of Apis mellifera venom in Argentina.

Neutralizing potency and immunochemical evaluation of an anti-Crotalus mictlantecuhtli experimental serum

Snakebite in Mexico is commonly treated with an antivenom which uses Bothrops asper and Crotalus simus venoms as immunogens. Current taxonomic recommendations for the C. simus species complex suggest a novel endemic species from Mexico: Crotalus mictlantecuhtli. The aim of this report was to evaluate the immunogenic properties of C. mictlantecuhtli venom and its potential to generate polyclonal antibodies capable of neutralizing other pitviper venoms. We generated an experimental anti-Crotalus mictlantecuhtli serum, using the rabbit model, to test recognition and neutralizing capacity against the homologous venom as well as venoms from C. atrox, C.basiliscus, C. durissus terrificus, C. scutulatus salvini, C. tzabcan and Ophryacus sphenophrys. Pre-incubation neutralization experiments using our experimental serum showed positive results against venoms containing crotoxin, while venoms from two non-neurotoxic pit-vipers were not neutralized. Rescue experiments in mice showed that, when intravenously injected (i.v.), C. mictlantecuhtli venom is not neutralized by a maximum dose of Antivipmyn® and the experimental serum after 5 min of envenomation, albeit mice envenomated intraperitoneally (i.p.) and rescued i.v. with Antivipmyn® survived even at 50 min after envenomation. Our results highlight the importance of using the highly neurotoxic C. mictlantecuhtli venom to increase antivenom effectiveness against Mexican neurotoxic pitvipers.

Venoms and Isolated Toxins from Snakes of Medical Impact in the Northeast Argentina: State of the Art. Potential Pharmacological Applications

Among the ophidians that inhabit the Northeast of Argentina, the genus Bothrops such as B. alternatus and B. diporus species (also known as yararás) and Crotalus durisus terrificus (named cascabel), represent the most studied snake venom for more than thirty years. These two genera of venomous snakes account for the majority of poisonous snake envenomations and therefore, constitute a medical emergency in this region. This review presents a broad description of the compiled knowledge about venomous snakebite: its pathophysiological action, protein composition, isolated toxins, toxin synergism, toxin-antitoxin cross-reaction assays. Properties of some isolated toxins support a potential pharmacological application.

Beyond the 'big four': Venom profiling of the medically important yet neglected Indian snakes reveals disturbing antivenom deficiencies

Background

Snakebite in India causes the highest annual rates of death (46,000) and disability (140,000) than any other country. Antivenom is the mainstay treatment of snakebite, whose manufacturing protocols, in essence, have remained unchanged for over a century. In India, a polyvalent antivenom is produced for the treatment of envenomations from the so called ‘big four’ snakes: the spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). In addition to the ‘big four’, India is abode to many other species of venomous snakes that have the potential to inflict severe clinical or, even, lethal envenomations in their human bite victims. Unfortunately, specific antivenoms are not produced against these species and, instead, the ‘big four’ antivenom is routinely used for the treatment.

Methods

We characterized the venom compositions, biochemical and pharmacological activities and toxicity profiles (mouse model) of the major neglected yet medically important Indian snakes (E. c. sochureki, B. sindanus, B. fasciatus, and two populations of N. kaouthia) and their closest ‘big four’ congeners. By performing WHO recommended in vitro and in vivo preclinical assays, we evaluated the efficiencies of the commercially marketed Indian antivenoms in recognizing venoms and neutralizing envenomations by these neglected species.

Findings

As a consequence of dissimilar ecologies and diet, the medically important snakes investigated exhibited dramatic inter- and intraspecific differences in their venom profiles. Currently marketed antivenoms were found to exhibit poor dose efficacy and venom recognition potential against the ‘neglected many’. Premium Serums antivenom failed to neutralise bites from many of the neglected species and one of the ‘big four’ snakes (North Indian population of B. caeruleus).

Conclusions

This study unravels disturbing deficiencies in dose efficacy and neutralisation capabilities of the currently marketed Indian antivenoms, and emphasises the pressing need to develop region-specific snakebite therapy for the ‘neglected many’.

Snakebite is a ‘neglected tropical disease’ that majorly affects the rural populations in developing countries. India bears the brunt of snakebites with over 46,000 deaths and 140,000 disabilities, annually. A significant number of these bites are attributed to the widely distributed ‘big four’ snakes, namely spectacled cobra (Naja naja), common krait (Bungarus caeruleus), Russell’s viper (Daboia russelii), and saw-scaled viper (Echis carinatus). The commercial antivenoms marketed in India are only manufactured against these four species, while neglecting many other medically relevant snakes with restricted geographic distribution. Snakebite pathology is dependent on the venom composition of the population/species, which can, in turn, vary intra- and inter-specifically. Though this variation severely limits the cross-population/species antivenom efficacy, envenomations by the neglected snakes in India are treated with the ‘big four’ antivenom. Therefore, to unravel the underlying venom variability, we investigated venom proteomic, biochemical/pharmacological and toxicity profiles of the major neglected Indian snakes and their ‘big four’ relatives. To assess the effectiveness of the ‘big four’ antivenom in treating bites from these neglected snakes, we performed preclinical experiments, which revealed alarming inadequacies of the commercial antivenoms. Our findings accentuate the compelling necessity for the innovation of highly efficacious next-generation snakebite therapy in India.

Biochemical and immunochemical characterization of venoms from snakes of the genus Agkistrodon

In the present work, venoms from five species of the genus Agkistrodon were evaluated in terms of their enzymatic (Phospholipase A2 and caseinolytic) and biological (edema forming, hemorrhagic, procoagulant and lethal) effects. Horses were used to produce monovalent hyperimmune sera against each of three venoms (A. bilineatus, A. contortrix and A. piscivorus) and their neutralizing potency, expressed as Median Effective Dose (ED50), was determined against the venoms of all five species. In terms of PLA2 and caseinolytic activities, all venoms are extremely homogeneous. PLA2 activity is high, while caseinolytic activity is low when in contrast with that of the rattlesnake Crotalus simus. On the other hand, biological activities showed marked interspecific differences, particularly between the species from Mexico and those from the United States. Mexican species displayed higher edema-forming, hemorrhagic and lethal effects than US species, while none of the species studied presented procoagulant activity. All three monovalent hyperimmune sera showed good neutralizing potency against the analyzed venoms. Nonetheless, we observed relevant immunochemical differences among the venoms using ELISA and Western Blot assays. We conclude that the venoms of A. piscivorus (USA) and A. bilineatus would be ideal to use as immunogens for the production of a polyvalent antivenom with good neutralizing potency against the venoms of all the species of the genus.

Horse immunization with short-chain consensus α-neurotoxin generates antibodies against broad spectrum of elapid venomous species

Antivenoms are fundamental in the therapy for snakebites. In elapid venoms, there are toxins, e.g. short-chain α-neurotoxins, which are quite abundant, highly toxic, and consequently play a major role in envenomation processes. The core problem is that such α-neurotoxins are weakly immunogenic, and many current elapid antivenoms show low reactivity towards them. We have previously developed a recombinant consensus short-chain α-neurotoxin (ScNtx) based on sequences from the most lethal elapid venoms from America, Africa, Asia, and Oceania. Here we report that an antivenom generated by immunizing horses with ScNtx can successfully neutralize the lethality of pure recombinant and native short-chain α-neurotoxins, as well as whole neurotoxic elapid venoms from diverse genera such as Micrurus, Dendroaspis, Naja, Walterinnesia, Ophiophagus and Hydrophis. These results provide a proof-of-principle for using recombinant proteins with rationally designed consensus sequences as universal immunogens for developing next-generation antivenoms with higher effectiveness and broader neutralizing capacity.

Snakebite: When the Human Touch Becomes a Bad Touch

Many issues and complications in treating snakebite are a result of poor human social, economic and clinical intervention and management. As such, there is scope for significant improvements for reducing incidence and increasing patient outcomes. Snakes do not target humans as prey, but as our dwellings and farms expand ever farther and climate change increases snake activity periods, accidental encounters with snakes seeking water and prey increase drastically. Despite its long history, the snakebite crisis is neglected, ignored, underestimated and fundamentally misunderstood. Tens of thousands of lives are lost to snakebites each year and hundreds of thousands of people will survive with some form of permanent damage and reduced work capacity. These numbers are well recognized as being gross underestimations due to poor to non-existent record keeping in some of the most affected areas. These underestimations complicate achieving the proper recognition of snakebite’s socioeconomic impact and thus securing foreign aid to help alleviate this global crisis. Antivenoms are expensive and hospitals are few and far between, leaving people to seek help from traditional healers or use other forms of ineffective treatment. In some cases, cheaper, inappropriately manufactured antivenom from other regions is used despite no evidence for their efficacy, with often robust data demonstrating they are woefully ineffective in neutralizing many venoms for which they are marketed for. Inappropriate first-aid and treatments include cutting the wound, tourniquets, electrical shock, immersion in ice water, and use of ineffective herbal remedies by traditional healers. Even in the developed world, there are fundamental controversies including fasciotomy, pressure bandages, antivenom dosage, premedication such as adrenalin, and lack of antivenom for exotic snakebites in the pet trade. This review explores the myriad of human-origin factors that influence the trajectory of global snakebite causes and treatment failures and illustrate that snakebite is as much a sociological and economic problem as it is a medical one. Reducing the incidence and frequency of such controllable factors are therefore realistic targets to help alleviate the global snakebite burden as incremental improvements across several areas will have a strong cumulative effect.

Lethality and histopathological alterations caused by Phoneutria nigriventer spider venom from Argentina: Neutralization of lethality by experimental and therapeutic antivenoms

Although the spiders of the genus Phoneutria cause envenomation and their presence has been described in several provinces of the north of Argentina, they are not as common as other spiders of sanitary importance. In the present work, we studied the toxicity of samples of venom of Phoneutria spiders from the provinces of Misiones (where severe envenomation and deaths by Phoneutria have been recorded) and Jujuy (where no deaths have been recorded and severe envenomations are not frequent). To this end, we assessed the lethal potency in mice and guinea pigs and the histopathological alterations caused by both venoms, as well as the neutralization by the commonly used therapeutic antivenom produced by the Butantan Institute in Brazil and by an experimental antivenom developed with venom of P. nigriventer from Misiones. There were no differences in the lethality of the venoms of spiders from both regions. Post mortem examination showed that the heart and lungs were the most affected organs, while important pulmonary edema was seen macroscopically. Histological analysis showed edema, atelectasis, emphysema and cardiac lesion in both experimental models. The antivenoms assayed showed good neutralization of the venoms in the two experimental models. Despite the different geographic origins, the venoms showed similar toxicity and both the experimental antivenom and therapeutic antivenmos were able to neutralize the venoms of Argentinean P. nigriventer.

Biochemical characterization of the venom of the coral snake Micrurus tener and comparative biological activities in the mouse and a reptile model

The objective of this study was to identify the venom components that could play a relevant role during envenomation caused by the coral snake Micrurus tener, through its biochemical characterization as well as the analysis of its effects on a murine model. Furthermore, it aimed to evaluate crude venom, in addition to its components, for possible specificity of action on a natural prey model (Conopsis lineata). The toxicity of the crude venom (delivered subcutaneously) showed a significant difference between the Median Lethal Dose (LD₅₀) in mice (4.4 μg/g) and in Conopsis lineata (12.1 μg/g) that was not observed when comparing the Median Paralyzing Dose (PD₅₀) values (mice = 4.7 μg/g; snakes = 4.1 μg/g). These results are evidence that the choice of study model strongly influences the apparent effects of crude venom. Moreover, based on the observed physical signs in the animal models, it was concluded that the most important physical effect caused by the venom is flaccid paralysis, which facilitates capture and subduing of prey regardless of whether it is alive; death is a logical consequence of the lack of oxygenation. Venom fractionation using a C18 reverse phase column yielded 35 fractions from which 16.6% caused paralysis and/or death to both animal models, 21.9% caused paralysis and/or death only to C. lineata and 1.6% were murine specific. Surprisingly, the diversity of snake-specific fractions did not reflect a difference between the PD₅₀s of the crude venom in mice and snakes, making it impossible to assume some type of specificity for either of the study models. Finally, the great diversity and abundance of fractions with no observable effect in snakes or mice (42.7%) suggested that the observed lethal fractions are not the only relevant toxic fractions within the venom and emphasized the possible relevance of interaction between components to generate the syndrome caused by the venom as a whole.

Intraspecific variation of biological activities in venoms from wild and captive Bothrops jararaca

The venom of Bothrops jararaca is composed of complex mixture of molecules, mainly lectins, metalloproteinases, serinoproteinases, desintegrins, phospholipases, and peptides. This composition may vary according to the snake's age, gender, and region of origin. The aim of the was to determine individual variation in Bothrops jararaca venom in the Botucatu region, Sao Paulo State, Brazil, by means of enzymatic, biochemical, and pharmacological characterization, utilizing in vitro tests and biological assays. The activities were compared with those of Brazilian Reference Venom (BRV). Protein concentration varied between adult and juvenile groups. The electrophoretic profiles were similar, with molecular masses ranging between 25 and 50 kD, but with intraspecific variations. Reverse-phase high-performance liquid chromatography (RP-HPLC) revealed protein concentration differences. Coagulant activity did not differ significantly among adult groups, but there was a large variation between juvenile venom and BRV, which coagulated more extensively. Venoms from adults displayed greater hemorrhagic activity, especially in males recently obtained from the wild. In contrast, juveniles kept in captivity and adult males showed higher values. Edematogenic activity displayed an increase in edema in all groups. At the mean lethal dose (LD₅₀), toxicity varied significantly between groups, with venom from captive females being threefold more toxic than juvenile venom. Data illustrate the intra- and interspecific complexity that occurs in snake venoms, which may be attributed to ontogenetic, sexual, and environmental factors that affect variability in Bothrops jararaca venom. Further, it is proposed that Brazilian public health authorities document the constitution of pooled venom employed in the immunization of serum-producing animals due to this variability in venom properties. Given the large Brazilian territory, this variability requires regional monitoring and evaluation of the efficacy of bothropic antivenom in treatment of snakebite and consequent permanent sequelae observed.