Snake venomics and antivenomics: Proteomic tools in the design and control of antivenoms for the treatment of snakebite envenoming

Innovative Immunization Strategies for Antivenom Development

Snakes, scorpions, and spiders are venomous animals that pose a threat to human health, and severe envenomings from the bites or stings of these animals must be treated with antivenom. Current antivenoms are based on plasma-derived immunoglobulins or immunoglobulin fragments from hyper-immunized animals. Although these medicines have been life-saving for more than 120 years, opportunities to improve envenoming therapy exist. In the later decades, new biotechnological tools have been applied with the aim of improving the efficacy, safety, and affordability of antivenoms. Within the avenues explored, novel immunization strategies using synthetic peptide epitopes, recombinant toxins (or toxoids), or DNA strings as immunogens have demonstrated potential for generating antivenoms with high therapeutic antibody titers and broad neutralizing capacity. Furthermore, these approaches circumvent the need for venom in the production process of antivenoms, thereby limiting some of the complications associated with animal captivity and venom collection. Finally, an important benefit of innovative immunization approaches is that they are often compatible with existing antivenom manufacturing setups. In this review, we compile all reported studies examining venom-independent innovative immunization strategies for antivenom development. In addition, a brief description of toxin families of medical relevance found in snake, scorpion, and spider venoms is presented, as well as how biochemical, bioinformatic, and omics tools could aid the development of next-generation antivenoms.

Studying Smaller and Neglected Organisms in Modern Evolutionary Venomics Implementing RNASeq (Transcriptomics)-A Critical Guide

Venoms are evolutionary key adaptations that species employ for defense, predation or competition. However, the processes and forces that drive the evolution of venoms and their toxin components remain in many aspects understudied. In particular, the venoms of many smaller, neglected (mostly invertebrate) organisms are not characterized in detail, especially with modern methods. For the majority of these taxa, even their biology is only vaguely known. Modern evolutionary venomics addresses the question of how venoms evolve by applying a plethora of -omics methods. These recently became so sensitive and enhanced that smaller, neglected organisms are now more easily accessible to comparatively study their venoms. More knowledge about these taxa is essential to better understand venom evolution in general. The methodological core pillars of integrative evolutionary venomics are genomics, transcriptomics and proteomics, which are complemented by functional morphology and the field of protein synthesis and activity tests. This manuscript focuses on transcriptomics (or RNASeq) as one toolbox to describe venom evolution in smaller, neglected taxa. It provides a hands-on guide that discusses a generalized RNASeq workflow, which can be adapted, accordingly, to respective projects. For neglected and small taxa, generalized recommendations are difficult to give and conclusions need to be made individually from case to case. In the context of evolutionary venomics, this overview highlights critical points, but also promises of RNASeq analyses. Methodologically, these concern the impact of read processing, possible improvements by perfoming multiple and merged assemblies, and adequate quantification of expressed transcripts. Readers are guided to reappraise their hypotheses on venom evolution in smaller organisms and how robustly these are testable with the current transcriptomics toolbox. The complementary approach that combines particular proteomics but also genomics with transcriptomics is discussed as well. As recently shown, comparative proteomics is, for example, most important in preventing false positive identifications of possible toxin transcripts. Finally, future directions in transcriptomics, such as applying 3rd generation sequencing strategies to overcome difficulties by short read assemblies, are briefly addressed.

Toxin-resolved antivenomics-guided assessment of the immunorecognition landscape of antivenoms

Snakebite envenoming represents a major issue in rural areas of tropical and subtropical regions across sub-Saharan Africa, South to Southeast Asia, Latin America and Oceania. Antivenoms constitute the only scientifically validated therapy for snakebite envenomings, provided they are safe, effective, affordable, accessible and administered appropriately. However, the lack of financial incentives in a technology that has remained relatively unchanged for more than a century, has contributed to some manufacturers leaving the market and others downscaling production or increasing the prices, leading to a decline in the availability and accessibility for these life-saving antidotes to millions of rural poor most at risk from snakebites in low income countries. The shortage of antivenoms can be significantly alleviated by optimizing the use of current antivenoms (through the assessment of their specific and paraspecific efficacy against the different medically relevant homologous and heterologous snake venoms) and by generating novel polyspecific antivenoms exhibiting broad clinical spectrum and wide geographic distribution range. Research on venoms has been continuously enhanced by advances in technology. Particularly, the last decade has witnessed the development of omics strategies for unravelling the toxin composition of venoms ("venomics") and to assess the immunorecognition profile of antivenoms ("antivenomics"). Here, we review recent developments and reflect on near future innovations that promise to revolutionize the mutually enlightening relationship between evolutionary and translational venomics.

Discovery of human scFvs that cross-neutralize the toxic effects of B. jararacussu and C. d. terrificus venoms

Accidents involving venomous snakes are a public health problem worldwide, causing a large number of deaths per year. In Brazil, the majority of accidents are caused by the Bothrops and Crotalus genera, which are responsible for approximately 80% of severe envenoming cases. The cross-neutralization of snake venoms by antibodies is an important issue for development of more effective treatments. Our group has previously reported the construction of human monoclonal antibody fragments towards Bothrops jararacussu and Crotalus durissus terrificus' venoms. This study aimed to select human single-chain variable fragments (scFvs) that recognize both bothropic and crotalic crude venoms following venoms neutralizing capacity in vitro and in vivo. The cross-reactivity of Cro-Bothrumabs were demonstrated by ELISA and in vitro and in vivo experiments showed that a combination of scFvs neutralizes in vitro toxic activities (e.g. indirect hemolysis and plasma-clotting) of crotalic and bothropic venoms as well as prolonged survival time of envenomed animals. Our results may contribute to the development of the first human polyvalent antivenom against Bothrops jararacussu and Crotalus durissus terrificus venoms, overcoming some undesirable effects caused by conventional serotherapy.

Catch a tiger snake by its tail: Differential toxicity, co-factor dependence and antivenom efficacy in a procoagulant clade of Australian venomous snakes

A paradigm of venom research is adaptive evolution of toxins as part of a predator-prey chemical arms race. This study examined differential co-factor dependence, variations relative to dietary preference, and the impact upon relative neutralisation by antivenom of the procoagulant toxins in the venoms of a clade of Australian snakes. All genera were characterised by venoms rich in factor Xa which act upon endogenous prothrombin. Examination of toxin sequences revealed an extraordinary level of conservation, which indicates that adaptive evolution is not a feature of this toxin type. Consistent with this, the venoms did not display differences on the plasma of different taxa. Examination of the prothrombin target revealed endogenous blood proteins are under extreme negative selection pressure for diversification, this in turn puts a strong negative selection pressure upon the toxins as sequence diversification could result in a drift away from the target. Thus this study reveals that adaptive evolution is not a consistent feature in toxin evolution in cases where the target is under negative selection pressure for diversification. Consistent with this high level of toxin conservation, the antivenom showed extremely high-levels of cross-reactivity. There was however a strong statistical correlation between relative degree of phospholipid-dependence and clotting time, with the least dependent venoms producing faster clotting times than the other venoms even in the presence of phospholipid. The results of this study are not only of interest to evolutionary and ecological disciplines, but also have implications for clinical toxinology.

Cross-reactivity and cross-immunomodulation between venoms of the snakes Bothrops asper, Crotalus simus and Lachesis stenophrys, and its effect in the production of polyspecific antivenom for Central America

A mixture of the venoms of Bothrops asper, Crotalus simus and Lachesis stenophrys is used as immunogen to produce the polyspecific Central American antivenom (PoliVal-ICP). In this work, we studied the ability of each of these venoms to modulate the antibody response induced by the other two venoms included in the immunization mixture. For that, equine monospecific, bispecific and polyspecific antivenoms were prepared and compared regarding their ability to neutralize the phospholipase A₂, coagulant and lethal activities of each venom, and their anti-venom antibodies concentration. Results indicate that there is low cross-reactivity and cross-neutralization between venoms of B. asper, C. simus and L. stenophrys, hence justifying the use of all of them as immunogens for the production of the Central American antivenom. It was also found that the venom of B. asper reduces the anti-crotalic response while the venom of C. simus does not affect the anti-bothropic response. On the other hand, the venoms of B. asper and C. simus increase the anti-lachesic response, and L. stenoprhys venom reduced both the anti-bothropic and anti-crotalic responses. On the basis of these results, the immunization strategy can be adjusted by preventing or taking advantage of cross-immunomodulation between venoms, in order to maximize the antibody response towards all venoms. Immune responses can be improved by injecting horses with several immunogen mixtures, composed by one or two of the three venoms, and administering them at different times during the immunization, eventually generating a high titer against the three venoms. Our results suggest that addressing the issue of immunomodulation by venoms might improve antivenom manufacture worldwide.

Preclinical Evaluation of the Efficacy of Antivenoms for Snakebite Envenoming: State-of-the-Art and Challenges Ahead

Animal-derived antivenoms constitute the mainstay in the therapy of snakebite envenoming. The efficacy of antivenoms to neutralize toxicity of medically-relevant snake venoms has to be demonstrated through meticulous preclinical testing before their introduction into the clinical setting. The gold standard in the preclinical assessment and quality control of antivenoms is the neutralization of venom-induced lethality. In addition, depending on the pathophysiological profile of snake venoms, the neutralization of other toxic activities has to be evaluated, such as hemorrhagic, myotoxic, edema-forming, dermonecrotic, in vitro coagulant, and defibrinogenating effects. There is a need to develop laboratory assays to evaluate neutralization of other relevant venom activities. The concept of the 3Rs (Replacement, Reduction, and Refinement) in Toxinology is of utmost importance, and some advances have been performed in their implementation. A significant leap forward in the study of the immunological reactivity of antivenoms against venoms has been the development of “antivenomics”, which brings the analytical power of mass spectrometry to the evaluation of antivenoms. International partnerships are required to assess the preclinical efficacy of antivenoms against snake venoms in different regions of the world in order to have a detailed knowledge on the neutralizing profile of these immunotherapeutics.

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.

Priority Actions and Progress to Substantially and Sustainably Reduce the Mortality, Morbidity and Socioeconomic Burden of Tropical Snakebite

The deliberations and conclusions of a Hinxton Retreat convened in September 2015, entitled “Mechanisms to reverse the public health neglect of snakebite victims” are reported. The participants recommended that the following priority actions be included in strategies to reduce the global impact of snake envenoming: (a) collection of accurate global snakebite incidence, mortality and morbidity data to underpin advocacy efforts and help design public health campaigns; (b) promotion of (i) public education prevention campaigns; (ii) transport systems to improve access to hospitals and (iii) establishment of regional antivenom-efficacy testing facilities to ensure antivenoms’ effectiveness and safety; (c) exploration of funding models for investment in the production of antivenoms to address deficiencies in some regions; (d) establishment of (i) programs for training in effective first aid, hospital management and post-treatment care of victims; (ii) a clinical network to generate treatment guidelines and (iii) a clinical trials system to improve the clinical management of snakebite; (e) development of (i) novel treatments of the systemic and local tissue-destructive effects of envenoming and (ii) affordable, simple, point-of-care snakebite diagnostic kits to improve the accuracy and rapidity of treatment; (f) devising and implementation of interventions to help the people and communities affected by physical and psychological sequelae of snakebite.

Snakebite Envenoming - A Combined Density Equalizing Mapping and Scientometric Analysis of the Publication History

Estimates suggest that more than 25,000 to 125,000 people die annually from snakebite envenomation worldwide. In contrast to this major disease burden, thorough bibliometric studies do not exist so far that illustrate the overall research activity over a long time span. Therefore, the NewQIS-platform conducted an analysis on snakebite envenoming using the Thomson Reuters database Web of Science. To determine and assess changes regarding the scientific activities and to specifically address the more recent situation we analyzed two time intervals (t). During the first time interval from 1900 to 2007 (t1) 13,015 publications (p) were identified. In the following period (2008-2016 = t2) 4,982 publications were identified by the same search strategy. They originate from 114 (t1) respectively 121 countries (t2), with the USA (p = 3518), Brazil (p = 1100) and Japan (p = 961) being most productive in the first period, and the USA (p = 1087), Brazil (p = 991) and China (p = 378) in the second period, respectively. Setting the publication numbers in relation to GDP/capita, Brazil leads with 92 publications per 10,000 Int$GDP/capita, followed by India with 79 publications per 10000 Int$GDP/capita (t1). Comparing the country's publication activity with the Human Development Index level indicates that the majority of the publications is published by highly developed countries. When calculating the average citation rates (citations per published item = CR) mainly European countries show the highest ranks: From 1900-2007 Sweden ranks first with a CR = 27, followed by the Netherlands (CR = 24.8), Switzerland (CR = 23), Spain, Austria and the USA (CR = 22). From 2008 to 2016 the highest rate achieves Switzerland with a value of 24.6, followed by Belgium (CR = 18.1), Spain (CR = 16.7), Costa Rica (CR = 14.9) and Netherlands (CR = 14). Compared with this, the USA was placed at rank 13 (CR = 9,5). In summary, the present study represents the first density-equalizing map projection and in-depth scientometric analysis of the global research output on snakebites and its venoms. So it draws a sketch of the worldwide publication architecture and indicates that countries with a high incidence of snakebites and a low economical level still need to be empowered in carrying out research in this area.

Proteomic Characterization and Comparison of Malaysian Tropidolaemus wagleri and Cryptelytrops purpureomaculatus Venom Using Shotgun-Proteomics

Tropidolaemus wagleri and Cryptelytrops purpureomaculatus are venomous pit viper species commonly found in Malaysia. Tandem mass spectrometry analysis of the crude venoms has detected different proteins in T. wagleri and C. purpureomaculatus. They were classified into 13 venom protein families consisting of enzymatic and nonenzymatic proteins. Enzymatic families detected in T. wagleri and C. purpureomaculatus venom were snake venom metalloproteinase, phospholipase A₂, l-amino acid oxidase, serine proteases, 5′-nucleotidase, phosphodiesterase, and phospholipase B. In addition, glutaminyl cyclotransferase was detected in C. purpureomaculatus. C-type lectin-like proteins were common nonenzymatic components in both species. Waglerin was present and unique to T. wagleri—it was not in C. purpureomaculatus venom. In contrast, cysteine-rich secretory protein, bradykinin-potentiating peptide, and C-type natriuretic peptide were present in C. purpureomaculatus venom. Composition of the venom proteome of T. wagleri and C. purpureomaculatus provides useful information to guide production of effective antivenom and identification of proteins with potential therapeutic applications.

JA, Zamuner SR. Analgesic Effect of Photobiomodulation on Bothrops Moojeni Venom-Induced Hyperalgesia: A Mechanism Dependent on Neuronal Inhibition, Cytokines and Kinin Receptors Modulation

Background

Envenoming induced by Bothrops snakebites is characterized by drastic local tissue damage that involves an intense inflammatory reaction and local hyperalgesia which are not neutralized by conventional antivenom treatment. Herein, the effectiveness of photobiomodulation to reduce inflammatory hyperalgesia induced by Bothrops moojeni venom (Bmv), as well as the mechanisms involved was investigated.

Methodology/Principal Findings

Bmv (1 μg) was injected through the intraplantar route in the right hind paw of mice. Mechanical hyperalgesia and allodynia were evaluated by von Frey filaments at different time points after venom injection. Low level laser therapy (LLLT) was applied at the site of Bmv injection at wavelength of red 685 nm with energy density of 2.2 J/cm² at 30 min and 3 h after venom inoculation. Neuronal activation in the dorsal horn spinal cord was determined by immunohistochemistry of Fos protein and the mRNA expression of IL-6, TNF-α, IL-10, B1 and B2 kinin receptors were evaluated by Real time-PCR 6 h after venom injection. Photobiomodulation reversed Bmv-induced mechanical hyperalgesia and allodynia and decreased Fos expression, induced by Bmv as well as the mRNA levels of IL-6, TNF-α and B1 and B2 kinin receptors. Finally, an increase on IL-10, was observed following LLLT.

Conclusion/Significance

These data demonstrate that LLLT interferes with mechanisms involved in nociception and hyperalgesia and modulates Bmv-induced nociceptive signal. The use of photobiomodulation in reducing local pain induced by Bothropic venoms should be considered as a novel therapeutic tool for the treatment of local symptoms induced after bothropic snakebites.

Envenoming caused by Bothrops snakes is characterized by drastic local tissue damage involving hemorrhage, blistering, myonecrosis, prominent inflammatory response and intense pain. The most effective treatment for Bothrops snakebites is antivenom therapy, which is very efficient in reversing systemic effects of envenomation but not the severe local effects. Thus, there exists a need to find novel complementary therapies that may further assist in the prevention or even counteract the severe local effects of bothrops snakebite. Several studies have shown the effectiveness of photobiomodulation in reducing local effects induced by Bothropic venoms, however its mechanisms still remain unknown. In this study, we analyzed the effectiveness of photobiomodulation in reducing BmV-induced mechanical allodynia and hyperalgesia as well as part of the mechanisms involved in such effect. Results demonstrate that photobiomodulation reduces venom-induced mechanical allodynia and hyperalgesia and this effect depends on a decrease of nociceptor activation at the spinal cord level and by a modulation of pro- and anti- inflammatory cytokines as well as kinin receptors at mRNA transcriptional levels. These findings make phtobiomodulation a promising candidate to be associated to antivenom therapy for the treatment of the local response induced by Bothrops venoms.

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 Immunoprotection Evaluation of AaHIV from Complex Venom Metalloproteinases of Deinagkistrodon acutus

The aim of this study was to investigate the immunoprotective effects of AaHIV in mice. After purification, a 12% sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed. Bicinchoninic acid was used to determine the molecular weight and concentration of AaHIV. AaHIV, venom complex (VC), and phosphate buffered saline (PBS) were subsequently used to immunize the mice three times, and the blood was sampled 1 week after the third immunization to determine the serum immunoglobulin G (IgG) antibody titer. A skin-bleeding inhibition assay and toxin-eliminating assay were performed on the immunized mice. The purity and concentration of AaHIV were 86.6% and 1.20 mg/mL, respectively. The AaHIV group exhibited higher antibody titers than the VC group. The survival rate of the AaHIV group (7/10) was significantly higher than that of the PBS group (0/10) (P = 0.0031). The high titer of antibodies induced by AaHIV partially neutralized the bleeding activity of the Deinagkistrodon acutus venom complex.

Comparative analysis of local effects caused by Bothrops alternatus and Bothrops moojeni snake venoms: enzymatic contributions and inflammatory modulations

Bothropic envenomation is characterised by severe local damage caused by the toxic action of venom components and aggravated by induced inflammation. In this comparative study, the local inflammatory effects caused by the venoms of Bothrops alternatus and Bothrops moojeni, two snakes of epidemiological importance in Brazil, were investigated. The toxic action of venom components induced by bothropic venom was also characterised. Herein, the oedema, hyperalgesia and myotoxicity induced by bothropic venom were monitored for various lengths of time after venom injection in experimental animals. The intensity of the local effects caused by B. moojeni venom is considerably more potent than B. alternatus venom. Our results also indicate that metalloproteases and phospholipases A2 have a central role in the local damage induced by bothropic venoms, but serine proteases also contribute to the effects of these venoms. Furthermore, we observed that specific anti-inflammatory drugs were able to considerably reduce the oedema, the pain and the muscle damage caused by both venoms. The inflammatory reaction induced by B. moojeni venom is mediated by eicosanoid action, histamine and nitric oxide, with significant participation of bradykinin on the hyperalgesic and myotoxic effects of this venom. These mediators also participate to inflammation caused by B. alternatus venom. However, the inefficient anti-inflammatory effects of some local modulation suggest that histamine, leukotrienes and nitric oxide have little role in the oedema or myotoxicity caused by B. alternatus venom.

Cobra venom proteome and glycome determined from individual snakes of Naja atra reveal medically important dynamic range and systematic geographic variation

Recent progress in snake venomics has shed much light on the intra-species variation among the toxins from different geographical regions and has provided important information for better snakebite management. Most previous reports on snake venomics were based on venoms pooled from different snakes. In this study, we present the proteomic and glycomic profiles of venoms from individual Naja atra snakes. The results reveal wide dynamic range of three-finger toxins. Systematic classification based on cardiotoxin (CTX-) profiles of A2/A4 and A6, respectively, allowed the identification of two putative subspecies of Taiwan cobra from the eastern and western regions. We also identified four major N-glycan moieties on cobra snake venom metalloproteinase on the bi-antennary glycan core. ELISA showed that these glycoproteins (<3%) could elicit much higher antibody response in antiserum when compared to other high-abundance cobra venom toxins such as small molecular weight CTXs (~60%). By removing these high-molecular weight glycoproteins from the immunogen, we demonstrated better protection than that achieved with conventional crude venom immunization in mice challenged by crude venom. We conclude that both intra-species and inter-individual variations of proteomic and glycomic profiles of snake venomics should be considered to provide better antivenomic approach for snakebite management.

BIOLOGICAL SIGNIFICANCE

Based on the proteomic and glycomic profiles of venoms obtained from individual snakes, we demonstrated a surprisingly wide dynamic range and geographical variation of three-finger toxins in cobra venomics. This provides a reasonable explanation for the variable neutralization effects of antivenom treatment on victims suffering from cobra snakebite and suggests a simple and economic method to produce potent antivenom with better efficacy. Since two major venomic profiles with distinct dynamic ranges were observed for Taiwan cobra venoms isolated from the eastern and western regions, the current venomic profile should be used as a quality control for future production of antivenom in clinical applications.

Older Age and Time to Medical Assistance Are Associated with Severity and Mortality of Snakebites in the Brazilian Amazon: A Case-Control Study

The Amazon region reports the highest incidence of snakebite envenomings in Brazil. We aimed to describe the epidemiology of snakebites in the state of Amazonas and to investigate factors associated with disease severity and lethality. We used a nested case-control study, in order to identify factors associated with snakebite severity and mortality using official Brazilian reporting systems, from 2007 to 2012. Patients evolving to severity or death were considered cases and those with non-severe bites were included in the control group. During the study period, 9,191 snakebites were recorded, resulting in an incidence rate of 52.8 cases per 100,000 person/years. Snakebites mostly occurred in males (79.0%) and in rural areas (70.2%). The most affected age group was between 16 and 45 years old (54.6%). Fifty five percent of the snakebites were related to work activities. Age ≤15 years [OR=1.26 (95% CI=1.03-1.52); (p=0.018)], age ≥65 years [OR=1.53 (95% CI=1.09-2.13); (p=0.012)], work related bites [OR=1.39 (95% CI=1.17-1.63); (p<0.001)] and time to medical assistance >6 hours [OR=1.73 (95% CI=1.45-2.07); (p<0.001)] were independently associated with the risk of severity. Age ≥65 years [OR=3.19 (95% CI=1.40-7.25); (p=0.006)] and time to medical assistance >6 hours [OR=2.01 (95% CI=1.15-3.50); (p=0.013)] were independently associated with the risk of death. Snakebites represent an occupational health problem for rural populations in the Brazilian Amazon with a wide distribution. These results highlight the need for public health strategies aiming to reduce occupational injuries. Most cases of severe disease occurred in the extremes of age, in those with delays in medical attention and those caused by Micrurus bites. These features of victims of snakebite demand adequate management according to well-defined protocols, including prompt referral to tertiary centres when necessary, as well as an effective response from surveillance systems and policy makers for these vulnerable groups.

Effect of diterpenes isolated of the marine alga Canistrocarpus cervicornis against some toxic effects of the venom of the bothrops jararaca snake

Snake venoms are composed of a complex mixture of active proteins and peptides which induce a wide range of toxic effects. Envenomation by Bothrops jararaca venom results in hemorrhage, edema, pain, tissue necrosis and hemolysis. In this work, the effect of a mixture of two secodolastane diterpenes (linearol/isolinearol), previously isolated from the Brazilian marine brown alga, Canistrocarpus cervicornis, was evaluated against some of the toxic effects induced by B. jararaca venom. The mixture of diterpenes was dissolved in dimethylsulfoxide and incubated with venom for 30 min at room temperature, and then several in vivo (hemorrhage, edema and lethality) and in vitro (hemolysis, plasma clotting and proteolysis) assays were performed. The diterpenes inhibited hemolysis, proteolysis and hemorrhage, but failed to inhibit clotting and edema induced by B. jararaca venom. Moreover, diterpenes partially protected mice from lethality caused by B. jararaca venom. The search for natural inhibitors of B. jararaca venom in C. cervicornis algae is a relevant subject, since seaweeds are a rich and powerful source of active molecules which are as yet but poorly explored. Our results suggest that these diterpenes have the potential to be used against Bothropic envenomation accidents or to improve traditional treatments for snake bites.

The red seaweed Plocamium brasiliense shows anti-snake venom toxic effects

BACKGROUND

Snakebite is considered a neglected tropical disease by the World Health Organization. In Brazil, about 70% of the envenomation cases are caused by Bothrops snakes. Its venom may provoke hemorrhage, pain, necrosis, hemolysis, renal or cardiac failure and even death in victims. Since commercial antivenom does not efficiently neutralize the local toxic effects of venoms, natural products have been tested in order to provide alternative or complementary treatment to serum therapy. Therefore, the present study aimed to evaluate the ability of the seaweed Plocamium brasiliense and its active derivatives to neutralize hemorrhagic, edematogenic, hemolytic, coagulant and proteolytic activities of B. jararaca venom.

METHODS

Specimens of P. brasiliense were collected in Rio de Janeiro state, Brazil, dried and submitted to oil extraction using four solvents of increasing polarities, n-hexane (HEX), dichloromethane (DCM), ethyl acetate (ETA) and hydroalcoholic solution (HYD). The solvents were evaporated, yielding HEX, DCM, ETA and HYD extracts. Further, all extracts were dissolved in dimethylsulfoxide. In addition, two monoterpenes (8-bromo-3,4,7-trichloro-3,7-dimethyl-1E, 5E-octadiene and 1,8-dibromo-3,4,7-trichloro-3,7-dimethyl-1E, 5E-octadiene) and a cholesterol fraction were isolated from the extract of P. brasiliense prepared in hexane. Algal samples were incubated for 30 minutes with B. jararaca venom, and then tested for lethality; hemorrhagic, edematogenic, hemolytic, coagulant and proteolytic effects.

RESULTS

Most of the algal extracts inhibited the toxic effects with different potencies. The DCM extract was the most effective, since it inhibited all types of toxic activity. On the other hand, the HYD extract failed to inhibit any effect. Moreover, the isolated products inhibited proteolysis and protected mice from hemorrhage in 30% of the cases, whereas 8-bromo-3,4,7-trichloro-3,7-dimethyl-1E, 5E-octadiene inhibited 100% and 20% of the hemorrhagic and proteolytic activities, respectively. None of the algal products were toxic to mice.

CONCLUSION

Seaweeds may be a promising source of inhibitors against toxic effects caused by B. jararaca envenomation, which may contribute to antivenom treatment.

Evaluation of cytotoxic activities of snake venoms toward breast (MCF-7) and skin cancer (A-375) cell lines

Snake venoms are mixtures of bioactive proteins and peptides that exhibit diverse biochemical activities. This wide array of pharmacologies associated with snake venoms has made them attractive sources for research into potentially novel therapeutics, and several venom-derived drugs are now in use. In the current study we performed a broad screen of a variety of venoms (61 taxa) from the major venomous snake families (Viperidae, Elapidae and "Colubridae") in order to examine cytotoxic effects toward MCF-7 breast cancer cells and A-375 melanoma cells. MTT cell viability assays of cancer cells incubated with crude venoms revealed that most venoms showed significant cytotoxicity. We further investigated venom from the Red-bellied Blacksnake (Pseudechis porphyriacus); venom was fractionated by ion exchange fast protein liquid chromatography and several cytotoxic components were isolated. SDS-PAGE and MALDI-TOF mass spectrometry were used to identify the compounds in this venom responsible for the cytotoxic effects. In general, viper venoms were potently cytotoxic, with MCF-7 cells showing greater sensitivity, while elapid and colubrid venoms were much less toxic; notable exceptions included the elapid genera Micrurus, Naja and Pseudechis, which were quite cytotoxic to both cell lines. However, venoms with the most potent cytotoxicity were often not those with low mouse LD50s, including some dangerously venomous viperids and Australian elapids. This study confirmed that many venoms contain cytotoxic compounds, including catalytic PLA2s, and several venoms also showed significant differential toxicity toward the two cancer cell lines. Our results indicate that several previously uncharacterized venoms could contain promising lead compounds for drug development.

New immunization protocol to produce crotalic antivenom combining Crotalus durissus terrificus venom and its PLA2

Antivenoms are usually obtained by animal immunization with successive inoculations of increasing sublethal amounts of venom, which may impair the animal health. The high lethality of venom requires prolonged immunization plans with small amounts of venom. Thus, we propose an alternative plan that includes a pre-immunization of the animal with phospholipase A2, the main crotoxin component, which is responsible for the whole venom lethality. For comparison, three different immunization schemes were designed: high dose protocol (HDP; 0.5-27 mg of venom), low dose protocol (LDP; 0.1-7 mg of venom) and Mix protocol (MP; preimmunization 0.1-1.2 mg of crotalic PLA2, and then 4.5-8 mg of venom). Antibody titers were determined by ELISA, in blood plasma obtained from the marginal vein of the ear. The neutralizing ability of the different sera obtained by all protocols (HDS, LDS and MS) was tested against the most important pharmacological activities of whole venom: PLA2 activity, myotoxicity, thrombin like activity and lethality. MS showed the best neutralizing efficacy and at the same time, it was obtained by an immunization protocol that takes account of animal health care, since it requires low quantities of venoms in comparison to traditional protocols.

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.

Epithelium specific ETS transcription factor, ESE-3, of Protobothrops flavoviridis snake venom gland transactivates the promoters of venom phospholipase A2 isozyme genes

Protobothrops flavoviridis (habu) (Crotalinae, Viperidae) is a Japanese venomous snake, and its venom contains the enzymes with a variety of physiological activities. The phospholipases A2 (PLA2s) are the major components and exert various toxic effects. They are expressed abundantly in the venom gland. It is thought that the venom gland-specific transcription factors play a key role for activation of PLA2 genes specifically expressed in the venom gland. Thus, the full-length cDNA library for P. flavoviridis venom gland after milking of the venom was made to explore the transcription factors therein. As a result, three cDNAs encoding epithelium-specific ETS transcription factors (ESE)-1, -2, and -3 were obtained. Among them, ESE-3 was specifically expressed in the venom gland and activated the proximal promoters of venom PLA2 genes, which are possibly regarded as the representatives of the venom gland-specific protein genes in P. flavoviridis. Interestingly, the binding specificity of ESE-3 to the ETS binding motif located near TATA box is well correlated with transcriptional activities for the venom PLA2 genes. This is the first report that venom gland-specific transcription factor could actually activate the promoters of the venom protein genes.

Antivenomic characterization of two antivenoms against the venom of the taipan, Oxyuranus scutellatus, from Papua New Guinea and Australia

Antivenoms manufactured by bioCSL Limited (Australia) and Instituto Clodomiro Picado (Costa Rica) against the venom of the taipan snakes (Oxyuranus scutellatus) from Australia and Papua New Guinea (PNG), respectively, were compared using antivenomics, an analytical approach that combines proteomics with immunoaffinity chromatography. Both antivenoms recognized all venom proteins present in venom from PNG O. scutellatus, although a pattern of partial recognition was observed for some components. In the case of the Australian O. scutellatus venom, both antivenoms immunorecognized the majority of the components, but the CSL antivenom showed a stronger pattern of immunoreactivity, which was revealed by the percentage of retained proteins in the immunoaffinity column. Antivenoms interacted with taipoxin in surface plasmon resonance. These observations on antivenomics agree with previous neutralization studies.

Proteomic characterization and comparison of Malaysian Bungarus candidus and Bungarus fasciatus venoms

Kraits (Bungarus spp.) are highly venomous elapids that are only found in Asia. In the current study, 103 and 86 different proteins were identified from Bungarus candidus and Bungarus fasciatus venoms, respectively. These proteins were classified into 18 different venom protein families. Both venoms were found to contain a high percentage of three finger toxins, phospholipase A2 enzymes and Kunitz-type inhibitors. Smaller number of high molecular weight enzymes such as L-amino acid oxidase, hyaluronidases, and acetylcholinesterase were also detected in the venoms. We also detected some unique proteins that were not known to be present in these venoms. The presence of a natriuretic peptide, vespryn, and serine protease families was detected in B. candidus venom. We also detected the presence of subunit A and B of β-bungarotoxin and α-bungarotoxin which had not been previously found in B. fasciatus venom. Understanding the proteome composition of Malaysian krait species will provide useful information on unique toxins and proteins which are present in the venoms. This knowledge will assist in the management of krait envenoming. In addition, these proteins may have potential use as research tools or as drug-design templates.

BIOLOGICAL SIGNIFICANCE

This study has revealed the proteome composition of Malaysian B. candidus and B. fasciatus venoms, two medically important snake species in Asia. Information on the venom proteome of these species will provide useful information for krait bite management and aid in antivenom selection. Venom proteome profiles of these venoms showed that there are significant differences in the venom protein family compositions. Detection of proteins and peptides that have not been documented in these species such as natriuretic peptides, vespryn and serine proteases provides new knowledge on the composition of these venoms. The roles of these new proteins and peptides in krait envenoming are still unknown. Discovery of these proteins and peptides may also be useful for future research tool and therapeutic development.

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

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

An isoflavone from Dipteryx alata Vogel is active against the in vitro neuromuscular paralysis of Bothrops jararacussu snake venom and bothropstoxin I, and prevents venom-induced myonecrosis

Snakebite is a neglected disease and serious health problem in Brazil, with most bites being caused by snakes of the genus Bothrops. Although serum therapy is the primary treatment for systemic envenomation, it is generally ineffective in neutralizing the local effects of these venoms. In this work, we examined the ability of 7,8,3'-trihydroxy-4'-methoxyisoflavone (TM), an isoflavone from Dipteryx alata, to neutralize the neurotoxicity (in mouse phrenic nerve-diaphragm preparations) and myotoxicity (assessed by light microscopy) of Bothrops jararacussu snake venom in vitro. The toxicity of TM was assessed using the Salmonella microsome assay (Ames test). Incubation with TM alone (200 μg/mL) did not alter the muscle twitch tension whereas incubation with venom (40 μg/mL) caused irreversible paralysis. Preincubation of TM (200 μg/mL) with venom attenuated the venom-induced neuromuscular blockade by 84% ± 5% (mean ± SEM; n = 4). The neuromuscular blockade caused by bothropstoxin-I (BthTX-I), the major myotoxic PLA₂ of this venom, was also attenuated by TM. Histological analysis of diaphragm muscle incubated with TM showed that most fibers were preserved (only 9.2% ± 1.7% were damaged; n = 4) compared to venom alone (50.3% ± 5.4% of fibers damaged; n = 3), and preincubation of TM with venom significantly attenuated the venom-induced damage (only 17% ± 3.4% of fibers damaged; n = 3; p < 0.05 compared to venom alone). TM showed no mutagenicity in the Ames test using Salmonella strains TA98 and TA97a with (+S9) and without (−S9) metabolic activation. These findings indicate that TM is a potentially useful compound for antagonizing the neuromuscular effects (neurotoxicity and myotoxicity) of B. jararacussu venom.

Next-generation snake venomics: protein-locus resolution through venom proteome decomplexation

Venom research has been continuously enhanced by technological advances. High-throughput technologies are changing the classical paradigm of hypothesis-driven research to technology-driven approaches. However, the thesis advocated in this paper is that full proteome coverage at locus-specific resolution requires integrating the best of both worlds into a protocol that includes decomplexation of the venom proteome prior to liquid chromatography-tandem mass spectrometry matching against a species-specific transcriptome. This approach offers the possibility of proof-checking the species-specific contig database using proteomics data. Immunoaffinity chromatography constitutes the basis of an antivenomics workflow designed to quantify the extent of cross-reactivity of antivenoms against homologous and heterologous venom toxins. In the author's view, snake venomics and antivenomics form part of a biology-driven conceptual framework to unveil the genesis and natural history of venoms, and their within- and between-species toxicological and immunological divergences and similarities. Understanding evolutionary trends across venoms represents the Rosetta Stone for generating broad-ranging polyspecific antivenoms.

In-vitro neurotoxicity of two Malaysian krait species (Bungarus candidus and Bungarus fasciatus) venoms: neutralization by monovalent and polyvalent antivenoms from Thailand

Bungarus candidus and Bungarus fasciatus are two species of krait found in Southeast Asia. Envenoming by these snakes is often characterized by neurotoxicity and, without treatment, causes considerable morbidity and mortality. In this study, the in vitro neurotoxicity of each species, and the effectiveness of two monovalent antivenoms and a polyvalent antivenom, against the neurotoxic effects of the venoms, were examined in a skeletal muscle preparation. Both venoms caused concentration-dependent inhibition of indirect twitches, and attenuated responses to exogenous nicotinic receptor agonists, in the chick biventer preparation, with B. candidus venom being more potent than B. fasciatus venom. SDS-PAGE and western blot analysis indicated different profiles between the venoms. Despite these differences, most proteins bands were recognized by all three antivenoms. Antivenom, added prior to the venoms, attenuated the neurotoxic effect of the venoms. Interestingly, the respective monovalent antivenoms did not neutralize the effects of the venom from the other Bungarus species indicating a relative absence of cross-neutralization. Addition of a high concentration of polyvalent antivenom, at the t₉₀ time point after addition of venom, partially reversed the neurotoxicity of B. fasciatus venom but not B. candidus venom. The monovalent antivenoms had no significant effect when added at the t₉₀ time point. This study showed that B. candidus and B. fasciatus venoms display marked in vitro neurotoxicity in the chick biventer preparation and administration of antivenoms at high dose is necessary to prevent or reverse neurotoxicity.

Immunological profile of antivenoms: preclinical analysis of the efficacy of a polyspecific antivenom through antivenomics and neutralization assays

Parenteral administration of animal-derived antivenoms constitutes the mainstay in the treatment of snakebite envenomings. Despite the fact that this therapy has been available for over a century, the detailed understanding of the neutralizing and immunoreactivity profiles of the majority of antivenoms is pending. Currently, a combination of preclinical neutralization tests and 'antivenomics', i.e. a proteomic-based assessment of antivenom immunoreactivity, provides a powerful analytical platform to investigate the preclinical efficacy of antivenoms. In this review, the studies performed on the polyvalent antivenom manufactured by Instituto Clodomiro Picado, Costa Rica, are summarized. This antivenom is prepared by immunizing horses with a mixture of the venoms of Bothrops asper, Crotalus simus and Lachesis stenophrys, and is used in Central America for the treatment of envenomings by viperid species. Overall, the antivenom shows a widespread pattern of immunological reactivity against homologous and heterologous venoms, which correlates with its ability to neutralize lethal, hemorrhagic, myotoxic, coagulant, defibrinogenating, phospholipase A2 and proteinase activities of viperid venoms. At the same time, antivenomics detected several venom components against which the antivenom shows only partial or negligible immunorecognition, such as low molecular mass vasoactive peptides, disintegrins, and some phospholipases A2, P-I metalloproteinases and serine proteinases. Such information can be used to design strategies for enhancing the antibody response of horses against poorly immunogenic, toxicologically-relevant venom components in order to further improve the efficacy of this antivenom.

BIOLOGICAL SIGNIFICANCE

The timely parenteral administration of an appropriate antivenom remains, more than a century after the development of the first serum antivenimeux by Calmette and Phisalix and Bertrand, the only currently effective treatment for snakebite envenomings. A key technical issue in the generation of novel antivenoms is the design of optimized immunization venom mixtures that ensure that the resulting antidotes will be effective against the highest number of venoms from snakes of medical concern across the geographical range where they will be used. Antivenomics is a proteomics-based protocol developed to complement in vitro and in vivo standard preclinical tests in the qualitative and quantitative characterization of the immunological profile and the extent of cross-reactivity of antivenoms against homologous and heterologous venoms. Antivenomics is translational venomics. The combination of antivenomics and neutralization assays represents a powerful analytical platform to investigate the efficacy of antivenoms at the molecular and preclinical levels. This article is part of a Special Issue entitled: Proteomics of non-model organisms.

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.

Inhibitory Effect of the Plant Clusia fluminensis against Biological Activities of Bothrops jararaca Snake Venom

The ability of extracts of the plant Clusia fluminensis Planch & Triana (Clusiaceae Lindl.) to neutralize proteolysis, clotting, hemolysis, hemorrhagic and lethality activities of Bothrops jararaca snake venom was studied. Clusianone and lanosterol from the flower and fruit extracts, respectively, were also tested. The extracts of different organs of C. fluminensis inhibited proteolysis and hemolysis induced by B. jararaca venom, but with different potencies. Only the stems prevented blood clotting. Only the acetone extract of the fruit protected mice from hemorrhage while the acetone or methanol extracts prevented mice from death. Clusianone and lanosterol did not inhibit clotting or hemorrhage, but the former inhibited proteolysis and the latter hemolysis.

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.