Standard Quality Characteristics and Efficacy of a New Third-Generation Antivenom Developed in Colombia Covering Micrurus spp. Venoms

In Colombia, Micrurus snakebites are classified as severe according to the national clinical care guidelines and must be treated with specific antivenoms. Unfortunately, these types of antivenoms are scarce in certain areas of the country and are currently reported as an unavailable vital medicine. To address this issue, La Universidad de Antioquia, through its spin-off Tech Life Saving, is leading a project to develop third-generation polyvalent freeze-dried antivenom. The goal is to ensure access to this therapy, especially in rural and dispersed areas. This project aims to evaluate the physicochemical and preclinical parameters (standard quality characteristics) of a lab-scale anti-elapid antivenom batch. The antivenom is challenged against the venoms of several Micrurus species, including M. mipartitus, M. dumerilii, M. ancoralis, M. dissoleucus, M. lemniscatus, M. medemi, M. spixii, M. surinamensis, and M. isozonus, following the standard quality characteristics set by the World Health Organization (WHO). The antivenom demonstrates an appearance consistent with standards, 100% solubility within 4 min and 25 s, an extractable volume of 10.39 mL, a pH of 6.04, an albumin concentration of 0.377 mg/mL (equivalent to 1.22% of total protein), and a protein concentration of 30.97 mg/mL. Importantly, it maintains full integrity of its F(ab')2 fragments and exhibits purity over 98.5%. Furthermore, in mice toxicity evaluations, doses up to 15 mg/mouse show no toxic effects. The antivenom also demonstrates a significant recognition pattern against Micrurus venoms rich in phospholipase A2 (PLA2) content, as observed in M. dumerilii, M. dissoleucus, and M. isozonus. The effective dose 50 (ED50) indicates that a single vial (10 mL) can neutralize 2.33 mg of M. mipartitus venom and 3.99 mg of M. dumerilii venom. This new anti-elapid third-generation polyvalent and freeze-dried antivenom meets the physicochemical parameters set by the WHO and the regulators in Colombia. It demonstrates significant efficacy in neutralizing the venom of the most epidemiologically important Micrurus species in Colombia. Additionally, it recognizes seven other species of Micrurus venom with a higher affinity for venoms exhibiting PLA2 toxins. Fulfilling these parameters represents the first step toward proposing a new pharmacological alternative for treating snakebites in Colombia, particularly in dispersed rural areas, given that this antivenom is formulated as a freeze-dried product.

Development of a Broad-Spectrum Antiserum against Cobra Venoms Using Recombinant Three-Finger Toxins

Three-finger toxins (3FTXs) are the most clinically relevant components in cobra (genus Naja) venoms. Administration of the antivenom is the recommended treatment for the snakebite envenomings, while the efficacy to cross-neutralize the different cobra species is typically limited, which is presumably due to intra-specific variation of the 3FTXs composition in cobra venoms. Targeting the clinically relevant venom components has been considered as an important factor for novel antivenom design. Here, we used the recombinant type of long-chain α-neurotoxins (P01391), short-chain α-neurotoxins (P60770), and cardiotoxin A3 (P60301) to generate a new immunogen formulation and investigated the potency of the resulting antiserum against the venom lethality of three medially important cobras in Asia, including the Thai monocled cobra (Naja kaouthia), the Taiwan cobra (Naja atra), and the Thai spitting cobra (Naja Siamensis) snake species. With the fusion of protein disulfide isomerase and the low-temperature settings, the correct disulfide bonds were built on these recombinant 3FTXs (r3FTXs), which were confirmed by the circular dichroism spectra and tandem mass spectrometry. Immunization with r3FTX was able to induce the specific antibody response to the native 3FTXs in cobra venoms. Furthermore, the horse and rabbit antiserum raised by the r3FTX mixture is able to neutralize the venom lethality of the selected three medically important cobras. Thus, the study demonstrated that the r3FTXs are potential immunogens in the development of novel antivenom with broad neutralization activity for the therapeutic treatment of victims involving cobra snakes in countries.

A Quest for a Universal Plasma-Derived Antivenom Against All Elapid Neurotoxic Snake Venoms

This review describes the research aimed at the development of universal antivenom against elapid neurotoxic snake venoms. The antivenoms produced in Thailand in the 1980s were of low potency, especially against the elapid venoms. This was thought to be due to the low immunogenicity of the α-neurotoxins, which are the most lethal toxins in these venoms. Comparisons of various α-neurotoxin conjugates and polymers, and also different immunological adjuvants, showed that the adjuvant used is the major determinant in the antibody response in horses. The potent Freund's adjuvant was not used due to its severe local side-effect in horses. Therefore, a novel immunization protocol termed 'low dose, low volume multi-site' was developed for use in horses. This immunization protocol has led to the production of highly potent monospecific antivenoms against several elapid and viperid venoms, and two potent polyspecific antivenoms, one against 4 neurotoxic and another against 3 hematotoxic venoms. The immunization protocol has also led to other improvements in antivenom production including: several fold increases in antiserum potency, a reduction in the time required to reach therapeutically useful antibody titers, a 90% reduction in the amount of venom used, and 100% of the horses responding to the immunization program. This development is partly responsible for significant decrease in the Thailand's annual snakebite death toll from a few dozens to mostly nil in recent years. Finally, a simple and novel immunization strategy, using a 'diverse toxin repertoire' composed of numerous elapid toxin fractions as immunogen, was proposed and tested. This immunization procedure has resulted in the successful production of a widely paraspecific antiserum against at least 36 neurotoxic venoms of 28 species encompassing 10 genera and from 20 countries on four continents, and possibly against all elapid venoms with α-neurotoxins as the lethal toxins. These results indicate that, with optimizations of the composition of the 'diverse toxin repertoire', the immunization scheme and antibody fractionation to increase the antivenom neutralizing potency, an effective universal antivenom against the neurotoxic elapid snakes of the world can be produced.

Potency Testing of Venoms and Antivenoms in Embryonated Eggs: An Ethical Alternative to Animal Testing

Venoms are complex mixtures of biologically active molecules that impact multiple physiological systems. Manufacture of antivenoms (AVs) therefore requires potency testing using in vivo models to ensure AV efficacy. As part of ongoing research to replace small animals as the standard model for AV potency testing, we developed an alternate in vivo method using the embryonated egg model (EEM). In this model, the survival of chicken embryos envenomated in ovo is determined prior to 50% gestation, when they are recognized as animals by animal welfare legislation. Embryos were found to be susceptible to a range of snake, spider, and marine venoms. This included funnel-web spider venom for which the only other vertebrate, non-primate animal model is newborn mice. Neutralization of venom with standard AV allowed correlation of AV potency results from the EEM to results from animal assays. Our findings indicate that the EEM provides an alternative, insensate in vivo model for the assessment of AV potency. The EEM may enable reduction or replacement of the use of small animals, as longer-term research that enables the elimination of animal use in potency testing continues.

Wound Infections from Taiwan Cobra (Naja atra) Bites: Determining Bacteriology, Antibiotic Susceptibility, and the Use of Antibiotics-A Cobra BITE Study

Wound necrosis and secondary infection are common complications after Naja atra bites. Clinical tools to evaluate the infection risk after Taiwan cobra bites are lacking. In this Cobra BITE study, we investigated the prevalence of wound infection, bacteriology, and corresponding antibiotic usage in patients presenting with Taiwan cobra snakebites. Patients with wound infection lacking tissue necrosis were included in developing Cobra BITE score utilizing univariate and multiple logistic regression, as patients with wound necrosis require antibiotics for infection treatment. 8,295,497 emergency department visits occurred in the span of this study, with 195 of those patients being diagnosed as having cobra bites. Of these patients, 23 had wound necrosis, and 30 had wound infection, resulting in a wound infection rate of 27.2% (53/195). Enterococcus faecalis and Morganella morganii were the main bacteria identified in the culture report regardless of whether patients’ wounds had necrosis. As per our Cobra BITE score, the three factors predicting secondary wound infection after cobra bites are hospital admission, a white blood cell count (in 103/µL) × by neu-trophil-lymphocyte ratio value of ≥114.23, and the use of antivenin medication. The area under the receiver operating characteristic curve for the Cobra BITE score system was 0.88; ideal sensitivity and specificity were 0.89 and 0.76. This scoring system enables the assessment of wound infections after N. atra bites, and it could be modified and improved in the future for other Naja spp. bites.

De Novo Venom-Gland Transcriptomics of Spine-Bellied Sea Snake (Hydrophis curtus) from Penang, Malaysia-Next-Generation Sequencing, Functional Annotation and Toxinological Correlation

Envenomation resulted from sea snake bite is a highly lethal health hazard in Southeast Asia. Although commonly caused by sea snakes of Hydrophiinae, each species is evolutionarily distinct and thus, unveiling the toxin gene diversity within individual species is important. Applying next-generation sequencing, this study investigated the venom-gland transcriptome of Hydrophis curtus (spine-bellied sea snake) from Penang, West Malaysia. The transcriptome was de novo assembled, followed by gene annotation and sequence analyses. Transcripts with toxin annotation were only 96 in number but highly expressed, constituting 48.18% of total FPKM in the overall transcriptome. Of the 21 toxin families, three-finger toxins (3FTX) were the most abundantly expressed and functionally diverse, followed by phospholipases A₂. Lh_FTX001 (short neurotoxin) and Lh_FTX013 (long neurotoxin) were the most dominant 3FTXs expressed, consistent with the pathophysiology of envenomation. Lh_FTX001 and Lh_FTX013 were variable in amino acid compositions and predicted epitopes, while Lh_FTX001 showed high sequence similarity with the short neurotoxin from Hydrophis schistosus, supporting cross-neutralization effect of Sea Snake Antivenom. Other toxins of low gene expression, for example, snake venom metalloproteinases and L-amino acid oxidases not commonly studied in sea snake venom were also identified, enriching the knowledgebase of sea snake toxins for future study.

Immunoreactivity and neutralization study of Chinese Bungarus multicinctus antivenin and lab-prepared anti-bungarotoxin antisera towards purified bungarotoxins and snake venoms

Bungarus multicinctus is the most venomous snake distributed in China and neighboring countries of Myanmar, Laos, north Vietnam and Thailand. The high mortality rate of B. multicinctus envenomation is attributed to the lethal components of α-, β-, γ- and κ- bungarotoxins contained in the venom. Although anti-B. multicinctus sera were produced in Shanghai, Taiwan and Vietnam, the most widely clinic used product was term as B. multicinctus antivenin and manufactured by Shanghai Serum Bio-technology Co. Ltd. In the present investigation, high purity α-, β- and γ-bungarotoxins were separately isolated from B. multicinctus crude venom. Rabbit anti- α-, β- and γ-bungarotoxin antisera were prepared by common methods, respectively. LD50 values of α-, β- and γ-bungarotoxins were systematically determined via three administration pathways (intraperitoneal, intramuscular and intravenous injections) in Kunming mice. LD50 values of β-bungarotoxin were closely related with injection routines but those of both α- and γ-bungarotoxins were not dependent on the injection routines. Commercial B. multicinctus antivenin showed strong immunoreaction with high molecular weight fractions of the B. multicinctus but weakly recognized low molecular weight fractions like α- and γ-bungarotoxins. Although B. multicinctus antivenin showed immunoreaction with high molecular weight fractions of Bungarus fasciatus, Naja atra, Ophiophagus hannah venoms but the antivenin only demonstrated animal protection efficacy against O. hannah venom. These results indicated that the high molecular weight fractions of the O. hannah played an important role in venom lethality but those of B. fasciatus and N. atra did not have such a role.

A Rapid and International Applicable Diagnostic Device for Cobra (Genus Naja) Snakebites

Cobra snakes (genus Naja) are some of the most dangerous snake species in Asia and Africa, as their bites cause severe life-threatening respiratory failure and local tissue destruction, especially in the case of late diagnosis. The differential diagnosis of snakebite envenomation still mainly relies upon symptomatology, the patient’s description, and the experience of physicians. We have designed a rapid test, immunochromatographic test of cobra (ICT-Cobra), which obtained fair results in improving the diagnosis and treatment of Naja (N.) atra snakebites in Taiwan. In this study, we further investigated the feasibility of applying the kit for the detection of other cobra venoms based on the potential interspecies similarity. We firstly demonstrated the cross-reactivity between eight venoms of medically important cobra species and the rabbit anti-N. atra IgG that was used in ICT-Cobra by Western blotting and sandwich enzyme-linked immunosorbent assay. Then, ICT-Cobra was used to detect various concentrations of the eight venoms to elucidate its performance. Noticeable correlations between the cross-reactivity of venoms from genus Naja snakes and existing geographical characteristics were found. ICT-Cobra could detect venoms from other Asian cobras with variable detection limits comparable to those observed for N. atra, but the kit was less successful in the detection of venom from African cobras. The similar but slightly different venom components and the interaction between venom and rabbit anti-N. atra IgG led to variations in the detection limits. The transcontinental usage of ICT-Cobra might be possible due to the cross-reactivity of antibodies and similarities among the larger-sized proteins. This study showed that the close immunological relationships in the genus Naja could be used to develop a venom detection kit for the diagnosis of cobra envenomation in both Asian and African regions. Additional clinical studies and technical adjustments are still needed to improve the efficacy and broadening the application of ICT-Cobra in the future.

An in vitro α-neurotoxin-nAChR binding assay correlates with lethality and in vivo neutralization of a large number of elapid neurotoxic snake venoms from four continents

The aim of this study was to develop an in vitro assay for use in place of in vivo assays of snake venom lethality and antivenom neutralizing potency. A novel in vitro assay has been developed based on the binding of post-synaptically acting α-neurotoxins to nicotinic acetylcholine receptor (nAChR), and the ability of antivenoms to prevent this binding. The assay gave high correlation in previous studies with the in vivo murine lethality tests (Median Lethal Dose, LD50), and the neutralization of lethality assays (Median Effective Dose, ED50) by antisera against Naja kaouthia, Naja naja and Bungarus candidus venoms. Here we show that, for the neurotoxic venoms of 20 elapid snake species from eight genera and four continents, the in vitro median inhibitory concentrations (IC50s) for α-neurotoxin binding to purified nAChR correlated well with the in vivo LD50s of the venoms (R2 = 0.8526, p < 0.001). Furthermore, using this assay, the in vitro ED50s of a horse pan-specific antiserum against these venoms correlated significantly with the corresponding in vivo murine ED50s, with R2 = 0.6896 (p < 0.01). In the case of four elapid venoms devoid or having a very low concentration of α-neurotoxins, no inhibition of nAChR binding was observed. Within the philosophy of 3Rs (Replacement, Reduction and Refinement) in animal testing, the in vitro α-neurotoxin-nAChR binding assay can effectively substitute the mouse lethality test for toxicity and antivenom potency evaluation for neurotoxic venoms in which α-neurotoxins predominate. This will greatly reduce the number of mice used in toxicological research and antivenom production laboratories. The simpler, faster, cheaper and less variable in vitro assay should also expedite the development of pan-specific antivenoms against various medically important snakes in many parts of the world.

Geographical variations in king cobra (Ophiophagus hannah) venom from Thailand, Malaysia, Indonesia and China: On venom lethality, antivenom immunoreactivity and in vivo neutralization

The wide distribution of king cobra (Ophiophagus hannah), a medically important venomous snake in Asia could be associated with geographical variation in the toxicity and antigenicity of the venom. This study investigated the lethality of king cobra venoms (KCV) from four geographical locales (Malaysia, Thailand, Indonesia, China), and the immunological binding as well as in vivo neutralization activities of three antivenom products (Thai Ophiophagus hannah monovalent antivenom, OHMAV; Indonesian Serum Anti Bisa Ular, SABU; Chinese Naja atra monovalent antivenom, NAMAV) toward the venoms. The Indonesian and Chinese KCV were more lethal (median lethal dose, LD₅₀ ~0.5 μg/g) than those from Malaysia and Thailand (LD₅₀ ~1.0 μg/g). The antivenoms, composed of F(ab)'₂, were variably immunoreactive toward the KCV from all locales, with OHMAV exhibited the highest immunological binding activity. In mice, OHMAV neutralized the neurotoxic lethality of Thai KCV most effectively (normalized potency = 118 mg venom neutralized per g antivenom) followed by Malaysian, Indonesian and Chinese KCV. In comparison, the hetero-specific SABU was remarkably less potent by at least 6 to10 folds, whereas NAMAV appeared to be non-effective. The finding supports that a specific king cobra antivenom is needed for the effective treatment of king cobra envenomation in each region.

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.

Characterization of Chicken-Derived Single Chain Antibody Fragments against Venom of Naja Naja Atra

Traditional, horse-derived antivenin is currently the most efficient treatment against snake bites. However, it is costly and has unpredictable side effects. Thus, alternative, cost-effective strategies for producing antivenin are needed. In this study, we immunized hens with inactivated NNA venom proteins from the cobra Naja naja atra (NNA). Purified yolk IgY antibodies showed specific anti-NNA binding activity comparable to that of the equine-derived antivenin. We used phage display technology to generate two antibody libraries containing 9.0 × 10⁸ and 8.4 × 10⁸ clones with a short or long linker, respectively. The phage ELISA indicated that anti-NNA clones displaying single-chain variable fragments (scFv) were significantly enriched after biopanning. The nucleotide sequences of the light and heavy chain genes of 30 monoclonal scFv antibodies were determined and classified into six groups with the short linker and nine groups with the long linker. These scFv clones specifically bound to NNA proteins but not to venom proteins from other snakes. Their binding affinities were further determined by competitive ELISA. Animal model studies showed that anti-NNA IgY antibodies exhibited complete protective effects, while a combination of scFv antibodies raised the survival rates and times of mice challenged with lethal doses of NNA venom proteins.

The medical threat of mamba envenoming in sub-Saharan Africa revealed by genus-wide analysis of venom composition, toxicity and antivenomics profiling of available antivenoms

Mambas (genus Dendroaspis) are among the most feared of the medically important elapid snakes found in sub-Saharan Africa, but many facets of their biology, including the diversity of venom composition, remain relatively understudied. Here, we present a reconstruction of mamba phylogeny, alongside genus-wide venom gland transcriptomic and high-resolution top-down venomic analyses. Whereas the green mambas, D. viridis, D. angusticeps, D. j. jamesoni and D. j. kaimosae, express 3FTx-predominant venoms, black mamba (D. polylepis) venom is dominated by dendrotoxins I and K. The divergent terrestrial ecology of D. polylepis compared to the arboreal niche occupied by all other mambas makes it plausible that this major difference in venom composition is due to dietary variation. The pattern of intrageneric venom variability across Dendroaspis represented a valuable opportunity to investigate, in a genus-wide context, the variant toxicity of the venom, and the degree of paraspecific cross-reactivity between antivenoms and mamba venoms. To this end, the immunological profiles of the five mamba venoms were assessed against a panel of commercial antivenoms generated for the sub-Saharan Africa market. This study provides a genus-wide overview of which available antivenoms may be more efficacious in neutralising human envenomings caused by mambas, irrespective of the species responsible. The information gathered in this study lays the foundations for rationalising the notably different potency and pharmacological profiles of Dendroaspis venoms at locus resolution. This understanding will allow selection and design of toxin immunogens with a view to generating a safer and more efficacious pan-specific antivenom against any mamba envenomation.

BIOLOGICAL SIGNIFICANCE

The mambas (genus Dendroaspis) comprise five especially notorious medically important venomous snakes endemic to sub-Saharan Africa. Their highly potent venoms comprise a high diversity of pharmacologically active peptides, including extremely rapid-acting neurotoxins. Previous studies on mamba venoms have focused on the biochemical and pharmacological characterisation of their most relevant toxins to rationalize the common neurological and neuromuscular symptoms of envenomings caused by these species, but there has been little work on overall venom composition or comparisons between them. Only very recently an overview of the composition of the venom of two Dendroaspis species, D. angusticeps and D. polylepis, has been unveiled through venomics approaches. Here we present the first genus-wide transcriptomic-proteomic analysis of mamba venom composition. The transcriptomic analyses described in this paper have contributed 29 (D. polylepis), 23 (D. angusticeps), 40 (D. viridis), 25 (D. j. jamesoni) and 21 (D. j. kaimosae), novel full-length toxin sequences to the non-redundant Dendroaspis sequence database. The mamba genus-wide venomic analysis demonstrated that major D. polylepis venom components are Kunitz-fold family toxins. This feature is unique in relation to the relatively conserved three-finger toxin (3FTx)-dominated venom compositions of the green mambas. Venom variation was interpreted in the context of dietary variation due to the divergent terrestrial ecology of D. polylepis compared to the arboreal niche occupied by all other mambas. Additionally, the degree of cross-reactivity conservation of mamba venoms was assessed by antivenomics against a panel of commercial antivenoms generated for the sub-Saharan Africa market. This study provides a genus-wide overview to infer which available antivenoms may be capable of neutralising human envenomings caused by mambas, irrespective of the species responsible. The information gathered in this study lays the foundations for rationalising the pharmacological profiles of mamba venoms at locus resolution. This understanding will contribute to the generation of a safer and more efficacious pan-Dendroaspis therapeutic antivenom against any mamba envenomation.

Third Generation Antivenomics: Pushing the Limits of the In Vitro Preclinical Assessment of Antivenoms

Second generation antivenomics is a translational venomics approach designed to complement in vivo preclinical neutralization assays. It provides qualitative and quantitative information on the set of homologous and heterologous venom proteins presenting antivenom-recognized epitopes and those exhibiting impaired immunoreactivity. In a situation of worrying antivenom shortage in many tropical and sub-tropical regions with high snakebite mortality and morbidity rates, such knowledge has the potential to facilitate the optimal deployment of currently existing antivenoms and to aid in the rational design of novel broad specificity antidotes. The aim of the present work was to expand the analytical capability of the immunoaffinity second-generation antivenomics platform, endowing it with the ability to determine the maximal binding capacity of an antivenom toward the different toxins present in a venom, and to quantify the fraction of venom-specific antibodies present in a given antivenom. The application of this new platform, termed third generation (3G) antivenomics, in the preclinical evaluation of antivenoms is illustrated in this paper for the case of antivenom EchiTAb-Plus-ICP^® reactivity towards the toxins of homologous (B. arietans) and heterologous (N. melanoleuca) venoms.

A Simple and Novel Strategy for the Production of a Pan-specific Antiserum against Elapid Snakes of Asia

Snakebite envenomation is a serious medical problem in many tropical developing countries and was considered by WHO as a neglected tropical disease. Antivenom (AV), the rational and most effective treatment modality, is either unaffordable and/or unavailable in many affected countries. Moreover, each AV is specific to only one (monospecific) or a few (polyspecific) snake venoms. This demands that each country to prepare AV against its local snake venoms, which is often not feasible. Preparation of a 'pan-specific' AV against many snakes over a wide geographical area in some countries/regions has not been possible. If a 'pan-specific' AV effective against a variety of snakes from many countries could be prepared, it could be produced economically in large volume for use in many countries and save many lives. The aim of this study was to produce a pan-specific antiserum effective against major medically important elapids in Asia. The strategy was to use toxin fractions (TFs) of the venoms in place of crude venoms in order to reduce the number of antigens the horses were exposed to. This enabled inclusion of a greater variety of elapid venoms in the immunogen mix, thus exposing the horse immune system to a diverse repertoire of toxin epitopes, and gave rise to antiserum with wide paraspecificity against elapid venoms. Twelve venom samples from six medically important elapid snakes (4 Naja spp. and 2 Bungarus spp.) were collected from 12 regions/countries in Asia. Nine of these 12 venoms were ultra-filtered to remove high molecular weight, non-toxic and highly immunogenic proteins. The remaining 3 venoms were not ultra-filtered due to limited amounts available. The 9 toxin fractions (TFs) together with the 3 crude venoms were emulsified in complete Freund's adjuvant and used to immunize 3 horses using a low dose, low volume, multisite immunization protocol. The horse antisera were assayed by ELISA and by in vivo lethality neutralization in mice. The findings were: a) The 9 TFs were shown to contain all of the venom toxins but were devoid of high MW proteins. When these TFs, together with the 3 crude venoms, were used as the immunogen, satisfactory ELISA antibody titers against homologous/heterologous venoms were obtained. b) The horse antiserum immunologically reacted with and neutralized the lethal effects of both the homologous and the 16 heterologous Asian/African elapid venoms tested. Thus, the use of TFs in place of crude venoms and the inclusion of a variety of elapid venoms in the immunogen mix resulted in antiserum with wide paraspecificity against elapid venoms from distant geographic areas. The antivenom prepared from this antiserum would be expected to be pan-specific and effective in treating envenomations by most elapids in many Asian countries. Due to economies of scale, the antivenom could be produced inexpensively and save many lives. This simple strategy and procedure could be readily adapted for the production of pan-specific antisera against elapids of other continents.

Immunoreactivity and two-dimensional gel-electrophoresis characterization of Egyptian cobra venom proteome

The first and second (two) dimensional gel electrophoresis has a broad protein resolution power. It was used to separate and identify cobra venom proteome. The importance of characterizing venom proteins contents from the Egyptian elapidae, specifically neurotoxins, is based on the need to produce effective anti-venom. About 30-55distinct protein spots were identified on silver stained two-dimensional gels. Around two-thirds of the venom proteins displayed low a molecular weight and a migration into hydrophobic side. The venoms from Naja haja and Naja nigricollus showed 45-55 spots, while Walternnesia aegyptia had less (31-37) spots. The commercial prepared polyclonal antivenom had a strong signal for anionic and cationic venom protein spots with molecular weight 20-115 kDa. However, it showed weak or non immunoreactivity toward anionic low molecular weight spots (2.5-15 kDa). These results suggest the need to change the immunization schedule to include low molecular weight toxin-proteomes as separate dose or sequester injection.

Preclinical efficacy of Australian antivenoms against the venom of the small-eyed snake, Micropechis ikaheka, from Papua New Guinea: an antivenomics and neutralization study

There is no specific antivenom for the treatment of envenoming by the small-eyed snake, Micropechis ikaheka, a dangerous fossorial species endemic to Papua New Guinea, Irian Jaya (West Papua) and neighbouring islands. This study evaluated one marine (sea snake) and four terrestrial (tiger snake, brown snake, black snake and polyvalent) antivenoms, manufactured in Australia by bioCSL Limited, for their ability to immunoreact ('antivenomic' analysis) and neutralize enzymatic and toxic activities of M. ikaheka venom. All antivenoms neutralized lethality of the venom and attenuated, dose-dependently, myotoxic activity. The polyvalent antivenom also neutralized cardiotoxic activity. In contrast, antivenoms were ineffective in the neutralization of phospholipase A₂ (PLA₂) and anticoagulant activities. Antivenomics outcomes were in concordance with neutralization tests, for chromatographic peaks corresponding to α-neurotoxins of the three finger family, responsible for lethality, were quantitatively retained in the immunoaffinity columns, whereas peaks corresponding to PLA₂s were immunocaptured only to a partial extent. The ability of antivenoms to neutralize lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom, which represent the most relevant clinical manifestations of envenoming, suggests that these antivenoms may provide paraspecific protection in humans, although the poor neutralization of PLA₂ supports the need for well-designed clinical studies to not only determine which antivenoms are most appropriate for treatment of M. ikaheka envenoming, but to also fully describe the syndrome of envenoming caused by this beautiful, but lethal species.

BIOLOGICAL SIGNIFICANCE

Snakebite by the small-eyed snake, Micropechis ikaheka, in Papua New Guinea can be life-threatening. The predominant clinical features in this envenoming are neurotoxicity and systemic myotoxicity. Although it accounts for only a small proportion of snakebites on the mainland, 40% of snakebites on Karkar Island are attributed to bites by the Ikaheka snake. However, no specific antivenom is available for the treatment of M. ikaheka envenoming in Papua New Guinea. This study evaluated a panel of Australian bioCSL antivenoms for their paraspecific immunoreaction and neutralization of the toxic activities of M. ikaheka venom. All antivenoms exhibited strong immunorecognition of α-neurotoxins of the 3FTx family and neutralized the lethal, i.e. neurotoxic, and myotoxic activities of M. ikaheka venom. However, these antivenoms exhibited poor neutralization of PLA₂ and anticoagulant activities. This study suggests that the Australian antivenoms may provide paraspecific protection against M. ikaheka venom in humans, a hypothesis that demands studies aimed at assessing whether these antivenoms neutralize neurotoxicity and myotoxicity in the clinical setting.

Neutralization of cobra venom by cocktail antiserum against venom proteins of cobra (Naja naja naja)

Naja naja venom was characterized by its immunochemical properties and electrophoretic pattern which revealed eight protein bands (14 kDa, 24 kDa, 29 kDa, 45 kDa, 48 kDa, 65 kDa, 72 kDa and 99 kDa) by SDS-PAGE in reducing condition after staining with Coomassie Brilliant Blue. The results showed that Naja venom presented high lethal activity. Whole venom antiserum or individual venom protein antiserum (14 kDa, 29 kDa, 65 kDa, 72 kDa and 99 kDa) of venom could recognize N. naja venom by Western blotting and ELISA, and N. naja venom presented antibody titer when assayed by ELISA. The neutralization tests showed that the polyvalent antiserum neutralized lethal activities by both in vivo and in vitro studies using mice and Vero cells. The antiserum could neutralize the lethal activities in in-vivo and antivenom administered after injection of cobra venom through intraperitoneal route in mice. The cocktail antiserum also could neutralize the cytotoxic activities in Vero cell line by MTT and Neutral red assays. The results of the present study suggest that cocktail antiserum neutralizes the lethal activities in both in vitro and in vivo models using the antiserum against cobra venom and its individual venom proteins serum produced in rabbits.

Venom proteomic characterization and relative antivenom neutralization of two medically important Pakistani elapid snakes (Bungarus sindanus and Naja naja)

Intra- and interspecific variation in venom composition has been shown to have a major effect upon the efficacy of antivenoms. Due to the absence of domestically produced antivenoms, Pakistan is wholly reliant upon antivenoms produced in other countries, such as India. However, the efficacy of these antivenoms in neutralising the venoms of Pakistani snakes has not been ascertained. This is symptomatic of the general state of toxicological research in this country, which has a myriad of highly toxic and medically important venomous animals. Thus, there is a dire need for knowledge regarding the fundamental proteomics of these venoms and applied knowledge of the relative efficacy of foreign antivenoms. Here we present the results of our proteomic research on two medically important snakes of Pakistan: Bungarus sindanus and Naja naja. Indian Polyvalent Antivenom (Bharat Serums and Vaccines Ltd), which is currently marketed for use in Pakistan, was completely ineffective against either Pakistani species. In addition to the expected pre- and post-synaptic neurotoxic activity, the venom of the Pakistan population of N. naja was shown to be quite divergent from other populations of this species in being potently myotoxic. These results highlight the importance of studying divergent species and isolated populations, where the same data not only elucidates clinical problems in need of immediate attention, but also uncovers sources for novel toxins with potentially useful activities.

BIOLOGICAL SIGNIFICANCE

Pakistan Bungarus sindanus and Naja naja venoms are differentially complex. Naja naja is potently myotoxic. Neither venom is neutralized by Indian antivenom. These results have direct implications for the treatment of envenomed patients in Pakistan. The unusually myotoxic effects of Naja naja demonstrates the value of studying remote populations for biodiscovery.

Preparation and characterization of immunoglobulin yolk against the venom of Naja naja atra

Chinese Cobra (Naja naja atra) bite is one of the leading causes of snake-bite mortality in China. The traditional anti-cobra venom serum therapy was found to be expensive and with high frequency of side effects. Therefore attempts were made to generate a high titer immunoglobulin from egg yolk (IgY) of crude cobra-venom immunized Leghorn hens, and to standardize an effective method for producing avian antivenom in relatively pure form. The IgY was isolated first by water dilution method to remove the lipid, then extracted by ammonium sulfate precipitation, and purified through anion exchange chromatogram. The different purities of IgY from different isolating stages were submitted to enzyme-linked immunosorbent assay and SDS-PAGE to determine their titers. Immunoblotting showed that the purified IgY (ion exchange chromatography fraction, IECF) recognized several antigenic fractions of cobra venom, and presented with the character of polyclonal antibody. IECF on SDS-PAGE under reducing conditions migrated as a 65 kDa heavy chain and a 35 kDa light chain, respectively. The LD50 of the N. naja atra venom was 0.62 mg/kg body weight in mice. Four times the LD50 dose of venom was selected as challenge dose, and the ED50 of IgY was 3.04 mg IECF/mg venom. The results indicate that the activity of anti-snake venom IgY could be obviously elevated by ion exchange chromatography, thus possessing therapeutic significance for snakebite envenomation.

Development of a sensitive enzyme immunoassay for measuring taipan venom in serum

The detection and measurement of snake venom in blood is important for confirming snake identification, determining when sufficient antivenom has been given, detecting recurrence of envenoming, and in forensic investigation. Venom enzyme immunoassays (EIA) have had persistent problems with poor sensitivity and high background absorbance leading to false positive results. This is particularly problematic with Australasian snakes where small amounts of highly potent venom are injected, resulting in low concentrations being associated with severe clinical effects. We aimed to develop a venom EIA with a limit of detection (LoD) sufficient to accurately distinguish mild envenoming from background absorbance at picogram concentrations of venom in blood. Serum samples were obtained from patients with taipan bites (Oxyuranus spp.) before and after antivenom, and from rats given known venom doses. A sandwich EIA was developed using biotinylated rabbit anti-snake venom antibodies for detection. For low venom concentrations (i.e. <1 ng/mL) the assay was done before and after addition of antivenom to the sample (antivenom difference method). The LoD was 0.15 ng/mL for the standard assay and 0.1 ng/mL for the antivenom difference method. In 11 pre-antivenom samples the median venom concentration was 10 ng/mL (Range: 0.3-3212 ng/mL). In four patients with incomplete venom-induced consumption coagulopathy the median venom concentration was 2.4 ng/mL compared to 30 ng/mL in seven patients with complete venom-induced consumption coagulopathy. No venom was detected in any post-antivenom sample and the median antivenom dose prior to this first post-antivenom sample was 1.5 vials (1-3 vials), including 7 patients administered only 1 vial. In rats the assay distinguished a 3-fold difference in venom dose administered and there was small inter-individual variability. There was small but measurable cross-reactivity with black snake (Pseudechis), tiger snake (Notechis) and rough-scale snake (Tropidechis carinatus) venoms with the assay for low venom concentrations (<1 ng/mL). The use of biotinylation and the antivenom difference method in venom EIA produces a highly sensitive assay that will be useful for determining antivenom dose, forensic and clinical diagnosis.

Transcriptomic basis for an antiserum against Micrurus corallinus (coral snake) venom

BACKGROUND

Micrurus corallinus (coral snake) is a tropical forest snake belonging to the family Elapidae. Its venom shows a high neurotoxicity associated with pre- and post-synaptic toxins, causing diaphragm paralysis, which may result in death. In spite of a relatively small incidence of accidents, serum therapy is crucial for those bitten. However, the adequate production of antiserum is hampered by the difficulty in obtaining sufficient amounts of venom from a small snake with demanding breeding conditions. In order to elucidate the molecular basis of this venom and to uncover possible immunogens for an antiserum, we generated expressed sequences tags (ESTs) from its venom glands and analyzed the transcriptomic profile. In addition, their immunogenicity was tested using DNA immunization.

RESULTS

A total of 1438 ESTs were generated and grouped into 611 clusters. Toxin transcripts represented 46% of the total ESTs. The two main toxin classes consisted of three-finger toxins (3FTx) (24%) and phospholipases A(2) (PLA(2)s) (15%). However, 8 other classes of toxins were present, including C-type lectins, natriuretic peptide precursors and even high-molecular mass components such as metalloproteases and L-amino acid oxidases. Each class included an assortment of isoforms, some showing evidence of alternative splicing and domain deletions. Five antigenic candidates were selected (four 3FTx and one PLA(2)) and used for a preliminary study of DNA immunization. The immunological response showed that the sera from the immunized animals were able to recognize the recombinant antigens.

CONCLUSION

Besides an improvement in our knowledge of the composition of coral snake venoms, which are very poorly known when compared to Old World elapids, the expression profile suggests abundant and diversified components that may be used in future antiserum formulation. As recombinant production of venom antigens frequently fails due to complex disulfide arrangements, DNA immunization may be a viable alternative. In fact, the selected candidates provided an initial evidence of the feasibility of this approach, which is less costly and not dependent on the availability of the venom.

INN-toxin, a highly lethal peptide from the venom of Indian cobra (Naja naja) venom-Isolation, characterization and pharmacological actions

A novel toxic polypeptide, INN-toxin, is purified from the venom of Naja naja using combination of gel-permeation and ion-exchange chromatography. It has a molecular mass of 6951.6Da as determined by MALDI-TOF/MS and the N-terminal sequence of LKXNKLVPLF. It showed both neurotoxic as well as cytotoxic activities. INN-toxin is lethal to mice with a LD(50) of 1.2mg/kg body weight. IgY raised in chicks against basic peptide pool neutralized the toxicity of INN-toxin. INN-toxin did not inhibit cholinesterase activity. It is toxic to Ehrlich ascites tumor (EAT) cells, but it is not toxic to leukocyte culture. The toxin appears to be specific in its mode of action. Interaction of N-bromosuccinamide (NBS) with the peptide resulted in the modification of tryptophan residues and loss of lethal toxicity of INN-toxin.

Proteome and immunome of the venom of the Thai cobra, Naja kaouthia

The proteome of the Thai cobra, Naja kaouthia, venom, revealed by two-dimensional liquid chromatography/tandem mass spectrometry, was found to consist of peptides which could be matched with 61 proteins in the database. These proteins were classified into 12 groups according to the differences in their biological activities: cardiotoxins, cobra venom factors, a cysteine-rich toxin, cytotoxins, kaouthiagin, mocarhagin, muscarinic toxin-like proteins, neurotoxins, an oxoglutarate dehydrogenase, phospholipases, serum albumin, and a weak toxin. Horse derived- anti-N. kaouthia venom hyperimmune serum currently used for the treatment of cobra ophitoxaemia reacted only to the cobra venom factors and phospholipases in the cobra holovenom by two-dimensional gel electrophoresis based-immunoblotting. The venom proteomic insight of this study should pave the way for preparing a therapeutic anti-venom of improved quality, i.e. also containing antibodies to the newly revealed toxic, but poorly immunogenic, minor venom components. It is expected that such a preparation should have a higher effectiveness than the currently used anti-venom in resuscitating cobra-bite victims.

Preparation of a novel antivenom against Atractaspis and Walterinnesia venoms

The two deadly snakes, Walterinnesia aegyptia (black desert cobra) and Atractaspis microlepidota (mole viper) share a common habitat in the central, eastern and western provinces of Saudi Arabia. Bites by either snake were characterized by rapid death, sometimes before reaching any medical facility. Confusing reports of "a black snake bite" are frequently found. The NAVPC had succeeded in preparing a highly effective antivenom against W. aegyptia venom which is now available in the market, but no antivenom against Atractaspis venom is found worldwide. This is probably because of the low molecular weight of sarafotoxins in the venom and hence their poor antigenic properties. At the NAVPC, sarafotoxins were separated by sequential gel filtration of A. microlepidota venom, while toxin T(III) of W. aegyptia venom obtained by cation exchange chromatography and gel filtration. Conjugation of the two toxins was carried out using glutaraldehyde in a two-step procedure followed by exhaustive dialysis. The conjugate was utilized to hyperimmunize 3-years old horses for 10 months, applying a low-dosage protocol and immunostimulants; the crude venoms of both snakes being added during the last 2 months. The F(ab')2 fraction of the antivenom was obtained by pH-guided salt precipitation, enzyme digestion and tangential desalting and filtration. The bivalent antivenom obtained protected mice and rats against the lethal effects of both venoms and rescued the rats challenged with lethal doses of the venoms in recovery experiments. It also neutralized the haemorrhagic, necrotizing and the cardiotoxic effects of A. microlepidota venom and the neuromuscular blocking effect of W. aegyptia venom. The antivenom offers a good rescue potential to those who are bitten by "a black snake" in Saudi Arabia.

Region-specific neutralization of Indian cobra (Naja naja) venom by polyclonal antibody raised against the eastern regional venom: A comparative study of the venoms from three different geographical distributions

Indian cobra (Naja naja) venoms from different geographical locations vary in their composition, biochemical, and pharmacological properties. Venom samples from eastern, western and southern India are compared in this study. The venom from eastern region was found to be the most lethal of the three regional venoms. Monovalent antivenom (NNEV-IgG) prepared against the eastern venom was found to cross-react with the other two regional venoms. NNEV-IgG at an Ag:Ab ratio of 1:25 completely neutralized the lethality of eastern venom. At this ratio, it did not neutralize the other two venoms, but the survival time of experimental mice was extended significantly. Commercially available polyvalent antivenom neutralized the lethality of western venom at an Ag:Ab ratio of 1:60 and increased the survival time of experimental mice injected with eastern and southern venoms marginally. Further, NNEV-IgG neutralized the tested pharmacological and enzymatic activities of all the three venom samples dose dependently, with neutralization potency varying with the geographic origin of the tested venoms. Thus, the present study demonstrates the diversity in the immunological properties of venom from different geographical regions and underscores the importance of developing region-specific antivenoms for therapeutic purpose.

Development of passive haemagglutination (PHA) and haemagglutination inhibition (HAI) technique for potency estimation of Cobra Antisnake Venom Serum (ASVS)

Antibodies against snake venom or antivenom potency are assayed quantitatively by in-vivo neutralization test in mice, which requires large number of laboratory animals. In potency assays of biological substances such as antivenoms, it is highly desirable to avoid suffering and death of animals by substituting in-vivo method with in-vitro methods, provided such methods measure life-saving capability with precision similar to that of in-vivo method. The in-vitro tests determine the neutralizing power of antivenom by permitting the evaluation of a particular biological activity of the venom and its neutralization after mixing the venom with the antivenom [Theakston RDG, Reid HA. Development of simple standard assay procedures for the characterization of snake venom. Bull WHO 1983;61:949-956; Gutierrez JM, Rojas G, Lomonte B, Gene JA, Chaves F, Alvarado J, et al. Standardizing of assays for testing the neutralizing ability of antivenoms. Toxicon 1990;28:1127-1129; Theakston R.D.G. Comments on letter of Gutierrez et al. on standardization of assays for testing the neutralizing ability of antivenoms. Toxicon 1990;28:1131-1132; Harvey AL, Barfaraz A, Thomson E, Faiz A, Preston S, Harris JB. Screening of snake venom for neurotoxic and myotoxic effects using simple in-vitro preparation from rodents and chicks. Toxicon 1994;32:257-265; World Health Organization Progress in characterization of venom and standardization of anti-venoms. Geneva: WHO offset publication; 1981. p. 58.]. Hence, the ideal requirements for an assay in detecting venom and venom antibody include high level of sensitivity, specificity (ability to differentiate between venom and venom antibody produced by closely related species of snakes), reproducibility and simplicity. A new in-vitro procedure for quantitative analysis of potency of ASVS by passive haemagglutination (PHA) and haemagglutination inhibition (HAI) has been explored. The methods described are simple, rapid, economical, reproducible and useful in replacing the more expensive in-vivo neutralization assays. Moreover, it also eliminates the use of laboratory animals.

Quantitation of Indian krait (Bungarus caeruleus) venom in human specimens of forensic origin by indirect competitive inhibition enzyme-linked immunosorbent assay

An indirect competitive inhibition enzyme-linked immunosorbent assay was reported to detect krait venom in human specimens of forensic origin. Polyclonal anti-krait venom antibodies were characterized by indirect antibody capture assay. The calibration plot was constructed based on linear regression analysis (y = 72.85 - 12.29x, r(2) = 0.98) with concentration ranges from 0.013 to 1000 ng/well of krait venom with a limit of detection of 0.2 ng/mL in the assay system. The IC50 (inhibitory concentration at 50% displacement) value of krait venom was observed to be 70 ng. Spiking studies indicated recoveries of 95-100% and 94-100% when various concentrations of krait venom were spiked to rat tissues (skin, liver, and kidneys) and pooled human serum, respectively. Polyclonal anti-krait venom antibodies showed no cross-reactivity with cobra and viper venom when tested in the assay system. The coefficient of variation of various concentrations of working range in intra-assay (n = 6) was <5%, whereas in interassay (n = 6) it was observed to be < or 7%. Further, the method was used to quantitate krait venom in human autopsy and biopsy specimens of forensic origin. Concentration of krait venom was found to be in the range of 4-172 ng/100 mg skin or skin scrapings and 64-378 ng/mL blood or serum. The methodology may find application in forensic laboratories to assess the cause of death in the cases of krait-bite victims.

Use of egg yolk antibody (IgY) as an immunoanalytical tool in the detection of Indian cobra (Naja naja naja) venom in biological samples of forensic origin

An immunoglobulin Y (IgY) based indirect double antibody sandwich enzyme linked immunosorbent assay (ELISA) was developed for the detection of Indian cobra (Naja naja naja) venom in the biological samples of forensic origin. Polyclonal antibodies were raised and purified from chick egg yolk and rabbit serum. The cobra venom was sandwiched between immobilized affinity purified IgY and the rabbit IgG. The detection concentration of cobra venom was in the range of 0.1 to 300ng. The calibration plot was based on linear regression analysis (y=0.2581x+0.4375, r(2)=0.9886). The limit of detection of the assay was found to be 0.1ng. The coefficient of variation (CV) of different concentrations of working range in inter (n=6) and intra-assay (n=6) was observed to be less than 10%. The recovery of venom was found to be in the range of 80-99%, when different concentrations (0.002, 0.1, 0.2, 1, and 2microg) of cobra venom were spiked to pooled normal human serum (ml(-1)). No cross reactivity was observed with krait and viper venom in the immunoassay system in the concentration range of 0.1-1000ng. The method was initially, validated by analyzing specimens (autopsy) of experimental rats injected with cobra venom (1.2mgkg(-1) body mass). Further, human specimens (autopsy and biopsy) of snake bite victims of forensic origin were also analyzed. The methodology developed may find diagnostic application in forensic laboratories.

Toxins not neutralized by brown snake antivenom

The Australian snakes of the genus Pseudonaja (dugite, gwardar and common brown) account for the majority of snake bite related deaths in Australia. Without antivenom treatment, the risk of mortality is significant. There is an accumulating body of evidence to suggest that the efficacy of the antivenom is limited. The current study investigates the protein constituents recognized by the antivenom using 2-DE, immuno-blot techniques and rat tracheal organ bath assays. The 2-DE profiles for all three snake venoms were similar, with major species visualized at 78-132 kDa, 32-45 kDa and 6-15 kDa. Proteins characterized by LC-MS/MS revealed a coagulant toxin ( approximately 42 kDa) and coagulant peptide ( approximately 6 kDa), as well as two PLA(2) ( approximately 14 kDa). Peptides isolated from approximately 78 kDa and 15-32 kDa protein components showed no similarity to known protein sequences. Protein recognition by the antivenom occurred predominantly for the higher molecular weight components with little recognition of 6-32 kDa MW species. The ability of antivenom to neutralize venom activity was also investigated using rat tracheal organ bath assays. The venoms of Pseudonaja affinis affinis and Pseudonaja nuchalis incited a sustained, significant contraction of the trachea. These contractions were attributed to PLA(2) enzymatic activity as pre-treatment with the PLA(2) inhibitor 4-BPB attenuated the venom-induced contractions. The venom of Pseudonaja textilis incited tracheal contractility through a non-PLA(2) enzymatic activity. Neither activity was attenuated by the antivenom treatment. These results represent the first proteomic investigation of the venoms from the snakes of the genus Pseudonaja, revealing a possible limitation of the brown snake antivenom in binding to the low MW protein components.

Pan-African polyspecific antivenom produced by caprylic acid purification of horse IgG: an alternative to the antivenom crisis in Africa

A polyspecific Pan-African antivenom has been produced from the plasma of horses immunized with a mixture of the venoms of Echis ocellatus, Bitis arietans and Naja nigricollis, the three most medically important snakes in sub-Saharan Africa. The antivenom is a whole IgG preparation, obtained by caprylic acid precipitation of non-IgG plasma proteins. The antivenom effectively neutralizes the most important toxic activities of the three venoms used in the immunization in standard assays involving preincubation of venom and antivenom before testing. This antivenom compares favourably with other antivenoms designed for use in Africa with respect to neutralization of the toxins present in the venom of E. ocellatus. Caprylic acid fractionation of horse hyperimmune plasma is a simple, convenient and cheap protocol for the manufacture of high quality whole IgG antivenoms. It constitutes a potentially valuable technology for the alleviation of the critical shortage of antivenom in Africa.

Hypersensitivity to airborne spitting cobra snake venom

BACKGROUND

Although the cytolytic, neurotoxic, and hemolytic actions of snake venoms are well known, the ability of airborne inhaled snake venom of the spitting cobra to induce asthma in snake handlers has not been reported.

OBJECTIVE

To report the allergenicity of inhaled snake venom in a snake handler who developed increasing hypersensitivity to airborne venom, produced by spitting cobras during public demonstrations.

METHODS

Serum samples were obtained from 2 handlers (our study patient and another snake handler who reported developing wheezing when handling spitting cobras), and desiccated venom was obtained from 9 species to which the handlers were exposed. Serum from an asymptomatic and nonatopic snake handler exposed to the same snake species was used as a control. Phosphate-buffered saline extracts were prepared from the desiccated venom, proteins in the venom extracts were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and immunoblotting was performed. Inhibition enzyme-linked immunosorbent assays (ELISAs) were performed to demonstrate cross-reactivity.

RESULTS

The study patient had never been previously bitten by a cobra. Wheezing occurred rapidly on inhalational exposure and was reversed by inhalation of salbutamol. The patient had developed IgE antibodies to 9 different snake venoms on Western immunoblots, with major IgE binding proteins of 59 to 63 kDa and 8 to 15 kDa. The cross-reactive nature of the IgE epitopes in the venoms in the different species was also confirmed by 50% inhibition of IgE binding in an ELISA by preincubation with unrelated species. Life-threatening sensitivity of the patient was sustained after a long period of avoidance.

CONCLUSIONS

We propose that aerosolized snake venom be considered a new potential source of allergens that may result in anaphylaxis on subsequent exposure. Further studies of the development of specific IgE sensitization following snakebites and the risks of such sensitization should be conducted on snake handlers, particularly those who demonstrate the spitting species.

Polyclonal antibodies against native weak toxin Naja kaouthia discriminate native weak toxins and some other three-fingered toxins against their denaturated forms

Polyclonal antibodies obtained by immunization of rabbits with native form of weak toxin (WTX) from cobra Naja kaouthia venom efficiently interacted with WTX and a weak toxin from Naja oxiana venom, but not so with their denaturated forms. These antibodies could also bind with lower affinity other groups of three-fingered toxins: long-chain alpha-neurotoxins, muscarinic toxins and cytotoxins, but practically did not bind short-chain alpha-neurotoxins. The efficiency of toxin-antibody interaction depends on the group (weak toxins, long or short alpha-neurotoxins, cytotoxins etc.) to which the toxin belongs, but not on species of snake from which the toxin originates. There is a correlation between the results obtained and phylogenetic analysis of the three-fingered toxins which revealed that WTX is very close to other weak toxins, relatively close to long alpha-neurotoxins, cytotoxins and muscarinic toxins, but is distant from the short alpha-neurotoxins.

Complement dependency of splenic localization of pneumococcal polysaccharide and conjugate vaccines

The immune response to polysaccharides is initiated when polysaccharides bind complement factor C3d, and these polysaccharide-C3d complexes subsequently localize on splenic marginal zone B cells strongly expressing CD21 (complement receptor 2). Infants and children under the age of 2 years have low or absent expression of CD21 on their marginal zone B cells, and consequently do not adequately respond to polysaccharides. In contrast, polysaccharide-protein conjugate vaccines are able to induce antibodies at this young age. Conjugate vaccines apparently overcome the necessity for CD21-C3d interaction for an antipolysaccharide immune response. We demonstrate in a rat model that localization of pneumococcal polysaccharides on splenic marginal zone B cells indeed is complement dependent. We also show that pneumococcal conjugates do not specifically localize on splenic marginal zone B cells and that splenic localization of polysaccharide conjugates is independent of the presence of complement. Thus, the induction of antipolysaccharide antibodies by conjugate vaccines apparently can occur independently of CD21-C3d interaction. These basic findings may explain the effectiveness of conjugated vaccines in young children and may open the way for their application in other patient groups.

Screening of plants containing Naja naja siamensis cobra venom inhibitory activity using modified ELISA technique

Enzyme-linked immunosorbent assay (ELISA) has been modified for screening plants with antagonistic activity to Naja naja siamensis cobra venom. Aqueous extracts from plants were investigated for their inhibitory effects on the binding of anti-cobra venom antibody to antigen, cobra venom, fixed onto 96-well microtiter plates. Ingredients in extracts were allowed to react with immobilized venom before the subsequent addition of antivenom antibody. Venom components affected by exposure to the extracts, unable to interact with their specific antibody, were predicted to be unable to bind to their native destinations or natural receptors. Curcuma cf. zedoaria, an old Thai medicinal plant, showed clear inhibitory activity in the ELISA test. Neurotoxin and protein degradative enzymes, major components in venom, were identified as targets of this extract in Western immunoblotting analysis. Ingredients in the extract showed high affinity to the toxin in competition assay by immunoprecipitation. The extract attenuated toxin activity by extending contraction time of diaphragm muscle after envenomation and had a potency to protect cellular proteins from venom degradative enzymes. Curcuma parviflora, with less activity in ELISA, exhibited acceptable results in two experiments but negative results in two experiments, whereas Curcuma longa, having low activity in the ELISA test, never showed any favorable results. Screening of 36 samples could classify plants into an inhibition range of 0 to 86%. This modified ELISA is recommended as a preliminary screening method for inhibitors with a large number of samples.

Relationship of plasma Dendroaspis natriuretic peptide-like immunoreactivity and echocardiographic parameters in chronic haemodialysis patients

BACKGROUND AND AIMS

The Dendroaspis natriuretic peptide (DNP), which was recently isolated from the venom of the green Mamba snake, Dendroaspis angusticeps, is a 38 amino acid peptide containing a 17 amino acid disulfide ring structure. The purpose of this study was to evaluate the effect of haemodialysis (HD) on the plasma concentration of DNP, and to investigate the relationship between the 2-D echocardiographic parameters and the changes in the plasma DNP levels during HD.

METHODS

Forty-five haemodialysis patients and 22 healthy individuals underwent a measurement of plasma DNP-like immunoreactivity, serum creatinine, haematocrit, blood pressure and bodyweight before and after each HD session. Echocardiography was performed before and after HD. The peak early diastolic transmitral flow velocity (E), peak late diastolic transmitral flow velocity (A), and E/A ratio were measured by using a pulsed Doppler echocardiogram.

RESULTS

The plasma DNP-like immunoreactivity of those in the pre-HD state was significantly higher (235.6 +/- 45.8 pg/mL) than those of the healthy subjects (105.3 +/- 31.1 pg/mL). In addition, the plasma DNP-like immunoreactivity was significantly decreased after HD (204.4 +/- 55.4 pg/mL). The left atrial diameter, left ventricular diameter at end diastole and end systol, E velocity, A velocity, E/A ratio and inferior vena cava diameter were significantly decreased after HD. There were significant correlations between the changes of plasma DNP-like immunoreactivity and the changes in the bodyweight and inferior vena cava diameter, respectively.

CONCLUSION

These results suggest that the plasma DNP-like immunoreactivity might be involved in the regulation of the blood volume in patients undergoing HD.

Immunochemical and biochemical comparisons of equine monovalent and polyvalent snake antivenoms

Although the merit of polyvalent antivenoms is well-recognized, there is still doubt in some medical circles as to the relative efficacy and the propensity to cause adverse reactions of polyvalent (pAV) as compared to monovalent (mAV) antivenoms. Immunochemical and biochemical comparisons of equine polyvalent and monovalent antivenoms prepared under the same immunization protocols were therefore made. These antivenoms were prepared against Naja kaouthia (NK), Ophiophagus hannah (OH) and Bungarus fasciatus (BF) venoms. SDS-PAGE analysis of both types of antivenoms showed similar serum protein profiles. The total amount of immunoglobulin (IgG(T)+IgG) in pAVs was slightly but significantly higher than that of mAVs, while the total serum protein content in mAVs was slightly but significantly higher than that of pAVs. The amounts of total hyperimmune IgG(T), determined by ELISA, were similar in mAVs and pAVs. pAVs contained specific antibodies against the principal NK postsynaptic toxin (NK 3) to the same extent as that observed with the anti-N. kaouthia mAV. The antibodies against OH and BF principal postsynaptic toxins (OH II and BF IX) in pAVs were significantly higher than those of the corresponding anti-O. hannah and anti-B. fasciatus mAVs. These results were in concordance with the comparable in vivo neutralization activities of mAVs and pAV previously reported. The apparent dissociation constant (Kd) of anti-OH II antibody in pAVs was comparable to that of the anti-O. hannah mAVs. The apparent K(d)s of anti-NK 3 and anti-BF IX antibodies in the corresponding mAVs were slightly lower than those in pAVs. The Kd values were all in nM range and were considered to be high affinity binding. It is concluded that pAVs could be prepared with potency and protein contents and thus the propensity to cause adverse reaction that were comparable to those of mAVs.

Biological and enzymatic activities of Micrurus sp. (Coral) snake venoms

The venoms of Micrurus lemniscatus carvalhoi, Micrurus frontalis frontalis, Micrurus surinamensis surinamensis and Micrurus nigrocinctus nigrocinctus were assayed for biological activities. Although showing similar liposome disrupting and myotoxic activities, M. frontalis frontalis and M. nigrocinctus nigrocinctus displayed higher anticoagulant and phospholipase A2 (PLA2) activities. The latter induced a higher edema response within 30 min. Both venoms were the most toxic as well. In the isolated chick biventer cervicis preparation, M. lemniscatus carvalhoi venom blocked the indirectly elicited twitch-tension response (85+/-0.6% inhibition after a 15 min incubation at 5 microg of venom/mL) and the response to acetylcholine (ACh; 55 or 110 microM), without affecting the response to KCl (13.4 mM). In mouse phrenic nerve-diaphragm preparation, the venom (5 microg/mL) produced a complete inhibition of the indirectly elicited contractile response after 50 min incubation and did not affect the contractions elicited by direct stimulation. M. lemniscatus carvalhoi inhibited 3H-L-glutamate uptake in brain synaptosomes in a Ca2+-, but not time, dependent manner. The replacement of Ca2+ by Sr2+ and ethylene glycol-bis(beta-aminoethyl ether) (EGTA), or alkylation of the venom with p-bromophenacyl bromide (BPB), inhibited 3H-L-glutamate uptake. M. lemniscatus carvalhoi venom cross-reacted with postsynaptic alpha-neurotoxins short-chain (antineurotoxin-II) and long-chain (antibungarotoxin) antibodies. It also cross-reacted with antimyotoxic PLA2 antibodies from M. nigrocinctus nigrocinctus (antinigroxin). Our results point to the need of catalytic activity for these venoms to exert their neurotoxic activity efficiently and to their components as attractive tools for the study of molecular targets on cell membranes.

Effectiveness of Two Common Antivenoms for North, Central, and South AmericanMicrurusEnvenomations

Micrurus snakes (coral snakes) may produce severe envenomation that can lead to death by peripheral respiratory paralysis. Only few laboratories produce specific antivenoms, and despite the cross-reactivity found in some Micrurus species venoms, the treatment is not always effective. To test two therapeutic antivenoms against the venom of four species of Micrurus from Southern America, North of South America, Central America, and North America, the determination of the lethal potency of the venoms, the study of some biochemical and immunochemical characteristics, and the determination of the neutralizing activity of both antivenoms were studied. North American and South American antivenoms neutralized well venoms from Micrurus species of the corresponding hemisphere but displayed lower effectiveness against venoms of species from different hemispheres. It was concluded that the neutralization of Micrurus venoms by regional antivenoms could be useful to treat the envenomation by some Micrurus snakes but is necessary to evaluate carefully the antivenoms to be used with the venoms from the snakes of the region. Also, considering the difficulties for coral snake antivenom production, the development of a polyvalent antivenom is useful to treat the envenomation by coral snakes from different regions is necessary.

Statin drugs do not affect serum complement activation in vitro

Statin drugs prevent coronary heart disease through anti-inflammatory mechanisms in addition to the well-known reduction of low-density lipoproteins. The complement system plays an essential role in the inflammatory response and has been postulated to be modified by statins. A direct role for statins in complement activation, however, has not been previously investigated. We therefore studied the effect of statins on in vitro complement activation. Pravastatin, atorvastatin and the active metabolite of the latter, ortho-hydroxy atorvastatin, were added to normal human serum and incubated for 1 h in the absence or presence of aggregated immunoglobulin (classical pathway activation) or cobra venom factor (alternative pathway activation). The degree of complement activation, as detected by specific complement-activation products for the classical pathway (C1rs-C1-inhibitor complexes), the combined classical and lectin pathway (C4bc), the alternative pathway (C3bBbP) and the final common pathway (C3bc and TCC), was not affected by pre-incubation of the serum with any of the statins. Statins do not affect complement activation directly, but indirect effects in vivo may well be operative.

Immunogenicity of venoms from four common snakes in the South of Vietnam and development of ELISA kit for venom detection

The antigenicity and antigenic relationship between venoms of four common snakes in the South of Vietnam-Trimeresurus popeorum, Calloselasma rhodostoma, Naja naja and Ophiophagus hannah-were studied. Most of venom components expressed antigenicity and produced high titre antivenoms. The venoms share common components and antivenoms cross-reacted along them. Furthermore, cross-reactions were observed among non-common antigens, indicating that they share common epitopes. Hence, using single component as immunogen for species diagnosis of snakebites can reduce cross-reaction, perhaps may not be totally specific. A three-step affinity purification protocol was set up for preparation of species-specific antivenom antibodies. The steps involved affinity chromatography of IgG from hyper-immunized rabbit sera with protein A columns, immuno-affinity chromatography of monovalent antivenom antibodies with respective homologous venom columns, and immuno-absorption of cross-species reacting antibody molecules with heterologous venom columns. The antibodies were then used for construction of an enzyme-linked immunosorbent assay (ELISA) test kit. The kit can differentiate among the four common snake venoms in various types of samples with the detection limit of 0.2-1.6 ng/ml, depending on the type of samples and species of the snake. The efficacy of this kit for snake venom detection was successfully demonstrated in experimental envenomation in rats. Preliminary evaluation with 140 samples taken from 88 human snakebite victims in Vietnam showed that the kit could detect venom in human samples and would be a very useful tool for fast identification of snakebites in clinics.

Cardiovascular, haematological and neurological effects of the venom of the Papua New Guinean small-eyed snake (Micropechis ikaheka) and their neutralisation with CSL polyvalent and black snake antivenoms

Cardiovascular and haematological effects of venom of the small-eyed Snake (Micropechis ikaheka) were examined in ventilated anaesthetised piglets. Neurotoxic effects were examined in chick biventer cervicis nerve-muscle preparations. Immunoreactivity of venom was tested against the monovalent antivenom components in a CSL Ltd Venom Detection Kit. Neutralisation was tested in vivo and in vitro with CSL Ltd polyvalent snake and Black Snake (Pseudechis australis) antivenoms. Venom in 0.1% bovine serum albumin in saline was infused into piglets in doses 1-2000 microg/kg. Pulmonary hypertension (P= 0.0007) and depression of cardiac output (P= 0.002) were observed up to 3 h after 150-160 microg/kg. The concentration of plasma free-haemoglobin increased more than 50-fold, indicating haemolysis. Neither coagulopathy nor thrombocytopenia occurred. Creatine phosphokinase and serum potassium levels did not increase suggesting absence of acute rhabdomyolysis. The venom caused post-synaptic neurotoxicty. Immunoreactivity of venom with Black Snake antivenom was observed at very high venom concentrations. Cardiovascular effects were absent and haemolysis was less after venom was pre-incubated at 37 degrees C for 30 min with polyvalent antivenom. Neutralisation by Black Snake antivenom was less effective. The neurotoxicity was neutralised by polyvalent or Black Snake antivenoms. Human envenomation may be treated with CSL Ltd polyvalent snake antivenom.

Species-dependent variations in the in vitro myotoxicity of death adder (Acanthophis) venoms

Based on early studies on Acanthophis antarcticus (common death adder) venom, it has long been thought that death adder snake venoms are devoid of myotoxicity. However, a recent clinical study reported rhabdomyolysis in patients following death adder envenomations, in Papua New Guinea, by a species thought to be different to A. antarcticus. Subsequently, a myotoxic phospholipase A2 component was isolated from A. rugosus (Irian Jayan death adder) venom. The present study examined the venoms of A. praelongus (northern), A. pyrrhus (desert), A. hawkei (Barkly Tableland), A. wellsi (black head), A. rugosus, A. sp. Seram and the regional variants of A. antarcticus for in vitro myotoxicity. Venoms (10-50 microg/ml) were examined for myotoxicity using the chick directly (0.1 Hz, 2 ms, supramaximal V) stimulated biventer cervicis nerve-muscle preparation. A significant contracture of skeletal muscle and/or inhibition of direct twitches were considered signs of myotoxicity. This was confirmed by histological examination. All venoms displayed high phospholipase A2 activity. The venoms (10-50 microg/ml) of A. sp. Seram, A. praelongus, A. rugosus,and A. wellsi caused a significant inhibition of direct twitches and an increase in baseline tension compared to the vehicle (n=4-6; two-way ANOVA, p<0.05). Furthermore, these venoms caused dose-dependent morphological changes in skeletal muscle. In contrast, the venoms (10-50 microg/ml; n=3-6) of A. hawkei, A. pyrrhus, and regional variants of A. antarcticus were devoid of myotoxicity. Prior incubation (10 min) of CSL death adder antivenom (5 U/ml) prevented the myotoxicity caused by A. sp. Seram, A. praelongus, A. rugosus, and A. wellsi venoms (50 microg/ml; n=4-7). In conclusion, clinicians may need to be mindful of possible myotoxicity following envenomations by A. praelongus, A. rugosus, A. sp. Seram, and A. wellsi species.

Role of leukocyte immunoglobuin G receptors in vaccine-induced immunity to Streptococcus pneumoniae

Members of the leukocyte immunoglobulin (Ig) G receptor (FcgammaR) family play a key role in antibody-mediated phagocytosis and can either enhance antigen presentation or down-modulate immune responses. We studied immune responses to a pneumococcal conjugate (pneumococcal polysaccharide serotype 1 [PPS1]-tetanus toxoid) and antibody-mediated protection in mice deficient for individual FcgammaRs and complement receptor 3 (CR3). FcR gamma chain-deficient (FcR gamma chain(-/-)) mice, which lack expression of both FcgammaRI and III, had significantly lower anti-PPS1 IgG2b and IgG3 responses than did wild-type mice, whereas FcgammaRII-deficient (FcgammaRII(-/-)) mice had significantly higher IgG2a and IgG3 titers. Wild-type and FcgammaRII(-/-) mice were protected against infection with pneumococcal serotype 1, whereas immunized FcR gamma chain(-/-) and FcgammaRIII-deficient mice were not. Immunized CR3-deficient mice were protected against disease, and complement depletion had little effect on protection. These data indicate that activatory leukocyte FcgammaR, but not FcgammaRII (a murine homologue of human FcgammaRIIb), contributes to IgG-mediated protection against pneumococcal disease.

Biological and immunochemical characterization of Micrurus altirostris venom and serum neutralization of its toxic activities

Micrurus altirostris venom from Rio Grande do Sul State, Brazil, was characterized by its biological activities, immunochemical properties and electrophoretic pattern. The results showed a high edematogenic activity, whose peak was observed after 30min of venom injection, as well as a high indirect hemolytic activity. This venom was myotoxic, as shown by a peak of CK release at 6h after injection, and also by the appearance of muscular lesions characterized by necrosis, loss of striated muscle fibers, and the presence of vacuolization, edema and inflammatory infiltrate. This venom showed minimum proteolytic activity and no hemorrhagic, dermonecrotic or coagulant activities. Nonetheless, M. altirostris venom presented high lethal activity. Electrophoretic patterns of Micrurus frontalis and M. altirostris venoms showed different protein bands. Anti-elapidic serum could recognize M. frontalis (homologous) and M. altirostris (heterologous) venoms by Western blotting, and both venoms presented similar titers when assayed by ELISA. The results observed on neutralization tests showed that the anti-elapidic serum produced by Instituto Butantan neutralized myotoxic and hemolytic activities. However, this antivenom could not neutralize the lethal activity of M. altirostris venom. Thus, these data suggest that M. altirostris venom presents different biological, enzymatic and immunological characteristics from other Micrurus venoms, and some activities are not neutralized by the commercial anti-elapidic serum produced in Brazil.

A pilot experiment for production of Malayan krait antivenom: immunization of rabbits with Bungarus candidus venom

Immunization with Bungarus candidus venom was performed in four rabbits at high dose (initial dose, 75 microg/kg) and low dose (initial dose, 50 microg/kg). Each dose group consisted of two rabbits; one rabbit received the venom subcutaneously (s.c.) and the other intradermally (i.d.). The venom was injected as emulsified solutions with the same volume of Freund's complete adjuvant until the 4th immunization, thereafter as plain solutions. By stepwise increments of the immunizing dose, the higher dose group received a dose of 200 microg/kg and the lower dose group 150 microg/kg after the 5th immunization, respectively. Thereafter, seven additional immunizations were performed within six months. All rabbits were sacrificed two weeks after the last immunization (12th). Antilethal activity of the immunized antisera thus obtained was determined not only with the homologous venom but also with two heterologous venoms from Bungarus fasciatus and Bungarus flaviceps. Immunodiffusion analysis was also performed with these venoms. The results obtained in this pilot trial provided useful information for production of Malayan krait antivenom at Queen Saovabha Memorial Institute.

Assay of specific antibodies produced in organs of mice immunized with nerve growth factor

Immunization of mice with nerve growth factor (NGF) leads to the production of antibodies, which can be assayed, from the serum. Currently, it is considered that the spleen of an immunized animal is predominantly involved in the production of antibodies. Therefore, spleen cells of the immunized animal are used to fuse with the respective species of myeloma cells to create in vitro immortalized antibodies secreting hybridomas. This investigation reports that besides spleen, other organs are involved in the production of antibodies. Adult Balb/c female mice were immunized with cobra venom derived NGF, 10 microg/mouse, three times, ten days apart. A set of immunized mice was sacrificed after each injection for organs. The serum and organ homogenates were assayed for antibodies specific to NGF. It was revealed that the liver and the ovaries showed the highest level of antibodies, higher than serum of the immunized mice. Spleen showed a higher level of antibodies than kidney, lung, and salivary glands. The homogenates of bone, brain, muscle, pancreas, and skin did not show detectable antibodies. This is a first-hand investigation reporting the involvement of organs other than spleen in the production of antibodies.

Sandwich enzyme-linked immunosorbent assay for Taiwan cobra venom

Poisonous snake bite victims usually have difficulty identifying the species, and clinical manifestations alone are not reliable because of overlapping symptoms. Thus, it is important to develop a quick and reliable mean of identifying the snake responsible. We describe the development of a sandwich-ELISA method for detection of venom in biological samples and apply it to a case of snakebite to confirm the clinical diagnosis. The sandwich-ELISA takes 6 h to complete. Cobra venom antigen gave positive absorbance at about 500 pg/ml. Good linearity with R2 values over 0.99 were observed in dilution series of 1:100 ng/mL of cobra venom in calf serum and human urine. A snakebite initially thought to be Trimeresurus mucrosquamatus was proven cobra with a serum venom level up to 288 ngmL 3 h after envenoming. Sandwich-ELISA provides a rapid and accurate method for clinical identification and evaluation of toxic antigens circulating in individuals bitten by the Taiwan cobra snake.