Biotechnological Trends in Spider and Scorpion Antivenom Development

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

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

The geographical distribution of scorpions, implication of venom toxins, envenomation, and potential therapeutics in Southern and Northern Africa

Scorpions are predatory arachnids whose venomous sting primarily affects people in tropical and subtropical regions. Most scorpion stings can only cause localized pain without severe envenomation. Less than one-third of the stings cause systemic envenoming and possibly lead to death. About 350,000 scorpion stings in Northern Africa are recorded yearly, resulting in about 810 deaths. In Eastern/Southern Africa, there are about 79,000 stings recorded yearly, resulting in 245 deaths. Farmers and those living in poverty-stricken areas are among the most vulnerable to getting stung by scorpions. However, compared to adults, children are at greater risk of severe envenomation. Scorpion venom is made up of complex mixtures dominated by peptides and proteins that confer its potency and toxicity. These venom toxins have intra- and interspecies variations associated with the scorpion's habitat, sex, diet, and age. These variations alter the activity of antivenoms used to treat scorpion sting envenomation. Thus, the study of the proteome composition of medically important scorpion venoms needs to be scaled up along their geographical distribution and contributions to envenomation in Southern and Northern Africa. This will help the production of safer, more effective, and broad-spectrum antivenoms within these regions. Here, we review the clinical implications of scorpion sting envenomation in Southern and Northern Africa. We further highlight the compositions of scorpion venoms and tools used in scorpion venomics. We discuss current antivenoms used against scorpion sting envenomation and suggestions for future production of better antivenoms or alternatives. Finally, we discuss the therapeutic properties of scorpion venom.

Toxic Peptides from the Mexican Scorpion Centruroides villegasi: Chemical Structure and Evaluation of Recognition by Human Single-Chain Antibodies

Alternative recombinant sources of antivenoms have been successfully generated. The application of such strategies requires the characterization of the venoms for the development of specific neutralizing molecules against the toxic components. Five toxic peptides to mammals from the Mexican scorpion Centruroides villegasi were isolated by chromatographic procedures by means of gel filtration on Sephadex G-50, followed by ion-exchange columns on carboxy-methyl-cellulose (CMC) resins and finally purified by high-performance chromatography (HPLC) columns. Their primary structures were determined by Edman degradation. They contain 66 amino acids and are maintained well packed by four disulfide bridges, with molecular mass from 7511.3 to 7750.1 Da. They are all relatively toxic and deadly to mice and show high sequence identity with known peptides that are specific modifiers of the gating mechanisms of Na+ ion channels of type beta-toxin (β-ScTx). They were named Cv1 to Cv5 and used to test their recognition by single-chain variable fragments (scFv) of antibodies, using surface plasmon resonance. Three different scFvs generated in our laboratory (10FG2, HV, LR) were tested for recognizing the various new peptides described here, paving the way for the development of a novel type of scorpion antivenom.

Pharmacokinetic evaluation of a single chain antibody fragment against scorpion toxins in sheep

A key aspect during the development of antivenoms is the evaluation of the efficiency and security of the therapeutic molecules. In this work, we report the pharmacokinetic analysis of a neutralizing single chain antibody fragment named LR (scFv LR) where three sheep were used as a large animal model. The animals were injected through i.v. route with 2 mg of scFv LR. Blood samples were drawn every minute within the first 15 min, the sampling continues at 20, 25, 30, 45, 60, 90, 120 min, subsequently at 1-h intervals, 3, 4, 5, 6 h, two more samples at 9 and 12 h and, two more samples at 24 and 48 h and finally at one-day intervals during 4 days. scFv LR levels were measured from blood serum and urine samples by an ELISA. The pharmacokinetics of the experimental data was analyzed using the three-exponential kinetics. The value of the fast initial component (τ1=0.409±0.258min) indicated that the scFv is distributed rapidly into the tissues. The mean residence time, MRT, was 45 ± 0.51 min and the clearance (CL), 114.3 ± 14.3 mL/min. From urine samples it was possible to detect significant amounts of scFv LR, which is evidence of renal elimination.

Considerations for Glycoprotein Production

This chapter is intended to provide insights for researchers aiming to choose an appropriate expression system for the production of recombinant glycoproteins. Producing glycoproteins is complex, as glycosylation patterns are determined by the availability and abundance of specific enzymes rather than a direct genetic blueprint. Furthermore, the cell systems often employed for protein production are evolutionarily distinct, leading to significantly different glycosylation when utilized for glycoprotein production. The selection of an appropriate production system depends on the intended applications and desired characteristics of the protein. Whether the goal is to produce glycoproteins mimicking native conditions or to intentionally alter glycan structures for specific purposes, such as enhancing immunogenicity in vaccines, understanding glycosylation present in the different systems and in different growth conditions is essential. This chapter will cover Escherichia coli, baculovirus/insect cell systems, Pichia pastoris, as well as different mammalian cell culture systems including Chinese hamster ovary (CHO) cells, human endothelial kidney (HEK) cell lines, and baby hamster kidney (BHK) cells.

Scorpion venom peptides: Molecular diversity, structural characteristics, and therapeutic use from channelopathies to viral infections and cancers

Animal venom is an important evolutionary innovation in nature. As one of the most representative animal venoms, scorpion venom contains an extremely diverse set of bioactive peptides. Scorpion venom peptides not only are 'poisons' that immobilize, paralyze, kill, or dissolve preys but also become important candidates for drug development and design. Here, the review focuses on the molecular diversity of scorpion venom peptides, their typical structural characteristics, and their multiple therapeutic or pharmaceutical applications in channelopathies, viral infections and cancers. Especially, the group of scorpion toxin TRPTx targeting transient receptor potential (TRP) channels is systematically summarized and worthy of attention because TRP channels play a crucial role in the regulation of homeostasis and the occurrence of diseases in human. We also further establish the potential relationship between the molecular characteristics and functional applications of scorpion venom peptides to provide a research basis for modern drug development and clinical utilization of scorpion venom resources.

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

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

Identification of a common epitope in knottins and phospholipases D present in Loxosceles sp venom by a monoclonal antibody

In the Americas and specially in Brazil, the Loxosceles intermedia, Loxosceles gaucho and Loxosceles laeta are the three most medically relevant brown spider species, and whose bites can lead to the condition known as loxoscelism. Here, we report the development of a tool capable of identifying a common epitope amongst Loxosceles sp. venom's toxins. A murine monoclonal antibody (LmAb12) and its recombinant fragments (scFv12P and diabody12P) have been produced and characterized. This antibody and its recombinant constructs were able to recognize proteins of Loxosceles spider venoms with specificity. The scFv12P variant was also able to detect low concentrations of Loxosceles venom in a competitive ELISA assay, displaying potential as a venom identification tool. The primary antigenic target of LmAb12 is a knottin, a venom neurotoxin, that has a shared identity of 100 % between the L. intermedia and L. gaucho species and high similarity to L. laeta. Furthermore, we observed LmAb12 was able to partially inhibit in vitro hemolysis, a cellular event typically induced by the Loxosceles sp. venoms. Such behavior might be due to LmAb12 cross-reactivity between the antigenic target of LmAb12 and the venom's dermonecrotic toxins, the PLDs, or even the existence of synergism between these two toxins.

Epidemiology of arthropods envenomation in Brazil: a public health issue

Brazil is located between the Equator and Tropic of Capricorn, which allows diverse climates, reliefs, and habitats for arthropods, which sting represents a risk to human health and a public health issue. This manuscript updates the epidemiological data of cases of human envenoming by spiders, scorpions, and insects with medical relevance in Brazil from 2010 to 2021. Epidemiological data were taken using the Brazilian Notifiable Diseases Information System. Statistics of non-parametric data used the Kruskal-Wallis followed by the Nemenyi test. On average, more than 145,000 envenomation and 145 deaths are recorded annually, and more than 60% of deaths are caused by scorpion bites. When the number of deaths was pondered by the number of cases with each arthropod, bees kill the most. Most stings cause mild symptoms and affect men of working age. The incidence decreases during the colder months, which is better noticeable in regions with well-defined seasons. The distribution is distinct among the regions: Southeast, Northeast, and South have the highest rate of bites. The growing number of cases of envenomation reported annually is a serious public health concern, especially involving scorpions, and highlights the importance of studying arthropod venom and improving the therapies.

Expression in Pichia pastoris of human antibody fragments that neutralize venoms of Mexican scorpions

The methylotrophic yeast Pichia pastoris has been one of the most widely used organisms in recent years as an expression system for a wide variety of recombinant proteins with therapeutic potential. Its popularity as an alternative system to Escherichia coli is mainly due to the easy genetic manipulation and the ability to produce high levels of heterologous proteins, either intracellularly or extracellularly. Being a eukaryotic organism, P. pastoris carries out post-translational modifications that allow it to produce soluble and correctly folded recombinant proteins. This work, evaluated the expression capacity in P. pastoris of two single-chain variable fragments (scFvs) of human origin, 10FG2 and LR. These scFvs were previously obtained by directed evolution against scorpion venom toxins and are able to neutralize different toxins and venoms of Mexican species. The yield obtained in P. pastoris was higher than that obtained in bacterial periplasm (E. coli), and most importantly, biochemical and functional properties were not modified. These results confirm that P. pastoris yeast can be a good expression system for the production of antibody fragments of a new recombinant antivenom.

Current status of structural studies of proteins originating from Arachnida

Arthropods from class Arachnida constitute a large and diverse group with over 100,000 described species, and they are sources of many proteins that have a direct impact on human health. Despite the importance of Arachnida, few proteins originating from these organisms have been characterized in terms of their structure. Here we present a detailed analysis of Arachnida proteins that have their experimental structures determined and deposited to the Protein Data Bank (PDB). Our results indicate that proteins represented in the PDB are derived from a small number of Arachnida families, and two-thirds of Arachnida proteins with experimental structures determined are derived from organisms belonging to Buthidae, Ixodidae, and Theraphosidae families. Moreover, 90% of the deposits come from just a dozen of Arachnida families, and almost half of the deposits represent proteins originating from only fifteen different species. In summary, our analysis shows that the structural analysis of proteins originating from Arachnida is not only limited to a small number of the source species, but also proteins from this group of animals are not extensively studied. However, the interest in Arachnida proteins seems to be increasing, which is reflected by a significant increase in the related PDB deposits during the last ten years.

Bioactive peptides from scorpion venoms: therapeutic scaffolds and pharmacological tools

Evolution and natural selection have endowed animal venoms, including scorpion venoms, with a wide range of pharmacological properties. Consequently, scorpions, their venoms, and/or their body parts have been used since time immemorial in traditional medicines, especially in Africa and Asia. With respect to their pharmacological potential, bioactive peptides from scorpion venoms have become an important source of scientific research. With the rapid increase in the characterization of various components from scorpion venoms, a large number of peptides are identified with an aim of combating a myriad of emerging global health problems. Moreover, some scorpion venom-derived peptides have been established as potential scaffolds helpful for drug development. In this review, we summarize the promising scorpion venoms-derived peptides as drug candidates. Accordingly, we highlight the data and knowledge needed for continuous characterization and development of additional natural peptides from scorpion venoms, as potential drugs that can treat related diseases.

Production and Functional Evaluation of Anti-Loxosceles Sera Raised by Immunizations of Rabbits with Mutated Recombinant Phospholipases-D

Loxoscelism is the clinical condition triggered after the bite of spiders of the genus Loxosceles. The main species involved in accidents in South America are L. intermedia, L. laeta, and L. gaucho. The only specific treatment is the anti-Loxosceles serum produced with crude venoms. As phospholipases D (PLDs) trigger most of the effects observed in accidents, we developed and evaluated second-generation sera using mutated PLDs as antigens. Three isoforms of PLDs with site-directed mutations without biological activities were used for rabbit immunizations: D32A-E34A (L. gaucho), W230A (L. intermedia), and H12A-H47A (L. laeta). Sera were produced using crude venoms of three species of Loxosceles enriched with mutated recombinant PLDs (MIX) or using only mutated PLDs (REC). Immunizations stimulated the immune system from the second immunization with higher antibody production in the REC group. In vivo neutralization assays demonstrated that both sera reduced edema and dermonecrosis caused by Loxosceles intermedia crude venom. Follow-up of animals during the immunization protocols and in the neutralization assays demonstrated that the mutated proteins and the sera are safe. Results demonstrate the potential of using mutated recombinant PLDs in total or partial replacement of Loxosceles venoms in animal immunizations to produce anti-Loxosceles sera for treatments of Loxoscelism.

Epidemiological and faunistic characterization of scorpionism in the Beni Mellal-Khenifra region, Central Morocco

Scorpionism is a serious public health problem in several parts of the world including Morocco, where is considered as the first cause of intoxication. The Beni Mellal-Khenifra region is one of the most affected regions by this health problem. The aim of this study is to describe the epidemiological and faunistic characteristics of scorpionism in this area. A retrospective epidemiological study was conducted based on the data of 16,388 cases of scorpion stings recorded between 2016 and 2020. In the laboratory, the collected scorpions were determined morphologically based on the valid taxonomic keys. Statistical and descriptive analyses were performed using Excel 2016. Statistical significance was determined by P-value < 0.05. The study comprised 16,388 stung patients. The scorpion stings incidence was 123.58 cases/100,000 population/year and was significantly higher at Azilal province (217.69 cases/100,000 population/year). We found a positive correlation between the scorpion stings incidence and the percentage of the rural population (r = 0.72) and between the scorpion stings incidence and the number of harmful species found in each province (r = 0.69). The general lethality rate was on average of 0.30% with a higher rate in Fquih Ben Salah province (0.63%) followed by Azilal province (0.32%). Children have the highest lethality than adults (p < 0.05). In the study area, eight species were identified, belonging to the families Buthidae and Scorpionidae, including dangerous species. Scorpionism is a real health problem in the Beni Mellal-Khenifra region, which is a rich and diverse area of scorpion fauna. Our findings can be useful for better understanding the problem of scorpionism in this region in order to better control it.

Production of a murine mAb against Bothrops alternatus and B. neuwiedi snake venoms and its use to isolate a thrombin-like serine protease fraction

Accidents with snakes from the genus Bothrops represent ~90 % of all snakebites in Brazil. Monoclonal antibodies (mAbs) targeting venom components can be important assets for treating envenoming syndromes, for developing diagnostic tests and for research purposes. Therefore, in this study, we aimed to generate murine mAbs against the antigenic mixture of Bothropic venoms traditionally used as immunogen to produce Bothropic antivenoms in Brazil. ELISA showed that one of the produced mAbs recognizes B. alternatus and B. neuwiedi venoms (mAb anti-Ba/Bn) specifically and Western Blot revealed that this mAb binds to a single protein band of molecular mass of ≈50 kDa. MAb anti-Ba/Bn inhibited the coagulant activity but was unable to neutralize hemorrhagic and phospholipase A2 activities caused by the B. neuwiedi venom. MAb anti-Ba/Bn was immobilized to Sepharose beads and used for immunoaffinity chromatography of B. neuwiedi venom. Proteolytic activity assays indicated that the immunoaffinity-purified fraction (BnF-Bothrops neuwiedi fraction) has a serine protease thrombin-like profile, which was supported by coagulability assays in mice. Bottom-up proteomic analysis confirmed the prevalence of serine proteases in BnF using label-free quantification. In conclusion, this work characterized a mAb with neutralizing properties against B. neuwiedi coagulant activity and demonstrates that immunoaffinity chromatography using mAbs can be a useful technique for purification of bioactive toxic proteins from Bothrops spp. snake venoms.

Phyto-Phospholipid Conjugated Scorpion Venom Nanovesicles as Promising Carrier That Improves Efficacy of Thymoquinone against Adenocarcinoma Human Alveolar Basal Epithelial Cells

Lung cancer is a dangerous type of cancer in men and the third leading cause of cancer-related death in women, behind breast and colorectal cancers. Thymoquinone (THQ), a main compound in black seed essential oils, has a variety of beneficial effects, including antiproliferative, anti-inflammatory, and antioxidant properties. On the other hand, scorpion venom peptides (SV) induce apoptosis in the cancer cells, making it a promising anticancer agent. THQ, SV, and Phospholipon^® 90H (PL) were incorporated in a nano-based delivery platform to assess THQ’s cellular uptake and antiproliferative efficacy against a lung cancer cell line derived from human alveolar epithelial cells (A549). Several nanovesicles were prepared and optimized using factorial experimental design. The optimized phytosome formulation contained 79.0 mg of PL and 170.0 mg of SV, with vesicle size and zeta potential of 209.9 nm and 21.1 mV, respectively. The IC50 values revealed that A549 cells were significantly more sensitive to the THQ formula than the plain formula and THQ. Cell cycle analysis revealed that THQ formula treatment resulted in significant cell cycle arrest at the S phase, increasing cell population in this phase by 22.1%. Furthermore, the THQ formula greatly increased cell apoptosis (25.17%) when compared to the untreated control (1.76%), plain formula (11.96%), or THQ alone (13.18%). The results also indicated that treatment with THQ formula significantly increased caspase-3, Bax, Bcl-2, and p53 mRNA expression compared to plain formula and THQ. In terms of the inflammatory markers, THQ formula significantly reduced the activity of TNF-α and NF-κB in comparison with the plain formula and THQ only. Overall, the findings from the study proved that a phytosome formulation of THQ could be a promising therapeutic approach for the treatment of lung adenocarcinoma.

Terrestrial venomous animals, the envenomings they cause, and treatment perspectives in the Middle East and North Africa

The Middle East and Northern Africa, collectively known as the MENA region, are inhabited by a plethora of venomous animals that cause up to 420,000 bites and stings each year. To understand the resultant health burden and the key variables affecting it, this review describes the epidemiology of snake, scorpion, and spider envenomings primarily based on heterogenous hospital data in the MENA region and the pathologies associated with their venoms. In addition, we discuss the venom composition and the key medically relevant toxins of these venomous animals, and, finally, the antivenoms that are currently in use to counteract them. Unlike Asia and sub-Saharan Africa, scorpion stings are significantly more common (approximately 350,000 cases/year) than snakebites (approximately 70,000 cases/year) and present the most significant contributor to the overall health burden of envenomings, with spider bites being negligible. However, this review also indicates that there is a substantial lack of high-quality envenoming data available for the MENA region, rendering many of these estimates speculative. Our understanding of the venoms and the toxins they contain is also incomplete, but already presents clear trends. For instance, the majority of snake venoms contain snake venom metalloproteinases, while sodium channel-binding toxins and potassium channel-binding toxins are the scorpion toxins that cause most health-related challenges. There also currently exist a plethora of antivenoms, yet only few are clinically validated, and their high cost and limited availability present a substantial health challenge. Yet, some of the insights presented in this review might help direct future research and policy efforts toward the appropriate prioritization of efforts and aid the development of future therapeutic solutions, such as next-generation antivenoms.

A non-lethal method for studying scorpion venom gland transcriptomes, with a review of potentially suitable taxa to which it can be applied

Scorpion venoms are mixtures of proteins, peptides and small molecular compounds with high specificity for ion channels and are therefore considered to be promising candidates in the venoms-to-drugs pipeline. Transcriptomes are important tools for studying the composition and expression of scorpion venom. Unfortunately, studying the venom gland transcriptome traditionally requires sacrificing the animal and therefore is always a single snapshot in time. This paper describes a new way of generating a scorpion venom gland transcriptome without sacrificing the animal, thereby allowing the study of the transcriptome at various time points within a single individual. By comparing these venom-derived transcriptomes to the traditional whole-telson transcriptomes we show that the relative expression levels of the major toxin classes are similar. We further performed a multi-day extraction using our proposed method to show the possibility of doing a multiple time point transcriptome analysis. This allows for the study of patterns of toxin gene activation over time a single individual, and allows assessment of the effects of diet, season and other factors that are known or likely to influence intraindividual venom composition. We discuss the gland characteristics that may allow this method to be successful in scorpions and provide a review of other venomous taxa to which this method may potentially be successfully applied.

The venom of the scorpion Centruroides limpidus, which causes the highest number of stings in Mexico, is neutralized by two recombinant antibody fragments

Phage display and directed evolution have made it possible to generate recombinant antibodies in the format of single chain variable fragments (scFvs) capable of neutralizing different toxins and venoms of Mexican scorpions. Despite having managed to neutralize a significant number of venoms, some others have not yet been completely neutralized, due to the diversity of the toxic components present in them. An example is the venom of the scorpion Centruroides limpidus, which contains three toxins of medical importance, called Cll1, Cll2 and Cl13. The first two are neutralized by scFv 10FG2, while Cl13, due to its sequence divergence, was not even recognized. For this reason, the aim of the present work was the generation of a new scFv capable of neutralizing Cl13 toxin and thereby helping to neutralize the whole venom of this scorpion. By hybridoma technology, a monoclonal antibody (mAb B7) was generated, which was able to recognize and partially neutralize Cl13 toxin. From mAb B7, its scFv format was obtained, named scFv B7 and subjected to three cycles of directed evolution. At the end of these processes, scFv 11F which neutralized Cl13 toxin was obtained. This scFv, administered in conjunction with scFv 10FG2, allowed to fully neutralize the whole venom of Centruroides limpidus scorpion.

Snakebite Envenoming Diagnosis and Diagnostics

Snakebite envenoming is predominantly an occupational disease of the rural tropics, causing death or permanent disability to hundreds of thousands of victims annually. The diagnosis of snakebite envenoming is commonly based on a combination of patient history and a syndromic approach. However, the availability of auxiliary diagnostic tests at the disposal of the clinicians vary from country to country, and the level of experience within snakebite diagnosis and intervention may be quite different for clinicians from different hospitals. As such, achieving timely diagnosis, and thus treatment, is a challenge faced by treating personnel around the globe. For years, much effort has gone into developing novel diagnostics to support diagnosis of snakebite victims, especially in rural areas of the tropics. Gaining access to affordable and rapid diagnostics could potentially facilitate more favorable patient outcomes due to early and appropriate treatment. This review aims to highlight regional differences in epidemiology and clinical snakebite management on a global scale, including an overview of the past and ongoing research efforts within snakebite diagnostics. Finally, the review is rounded off with a discussion on design considerations and potential benefits of novel snakebite diagnostics.

History, challenges and perspectives on Loxosceles (brown spiders) antivenom production in Brazil

Antivenom is the only effective therapy for treating any envenomation. Despite its obvious public health importance, the laborious process of procuring, distributing and controlling the quality of such immunobiologicals is being neglected. Brazil is fully self-sufficient in the production of antivenoms. Since the 1950s, Loxoscelism, a syndrome with an onset after a spider bite from specimens of the Loxosceles genus occurs, is considered a public health issue. The Brazilian history in developing antivenom therapy, its production hindrances, and other challenges are discussed in this paper, as well as some promising novelties that can improve production and processing of Loxosceles antivenom.

Discovery of a Recombinant Human Monoclonal Immunoglobulin G Antibody Against α-Latrotoxin From the Mediterranean Black Widow Spider (Latrodectus tredecimguttatus)

Widow spiders are among the few spider species worldwide that can cause serious envenoming in humans. The clinical syndrome resulting from Latrodectus spp. envenoming is called latrodectism and characterized by pain (local or regional) associated with diaphoresis and nonspecific systemic effects. The syndrome is caused by α-latrotoxin, a ~130 kDa neurotoxin that induces massive neurotransmitter release. Due to this function, α-latrotoxin has played a fundamental role as a tool in the study of neuroexocytosis. Nevertheless, some questions concerning its mode of action remain unresolved today. The diagnosis of latrodectism is purely clinical, combined with the patient's history of spider bite, as no analytical assays exist to detect widow spider venom. By utilizing antibody phage display technology, we here report the discovery of the first recombinant human monoclonal immunoglobulin G antibody (TPL0020_02_G9) that binds α-latrotoxin from the Mediterranean black widow spider (Latrodectus tredecimguttatus) and show neutralization efficacy ex vivo. Such antibody can be used as an affinity reagent for research and diagnostic purposes, providing researchers with a novel tool for more sophisticated experimentation and analysis. Moreover, it may also find therapeutic application in future.

Recombinant antibodies against Iranian cobra venom as a new emerging therapy by phage display technology

Background:

The production of antivenom from immunized animals is an established treatment for snakebites; however, antibody phage display technology may have the capacity to delivery results more quickly and with a better match to local need. Naja oxiana, the Iranian cobra, is a medically important species, responsible for a significant number of deaths annually. This study was designed as proof of principle to determine whether recombinant antibodies with the capacity to neutralize cobra venom could be isolated by phage display.

Methods:

Toxic fractions from cobra venom were prepared by chromatography and used as targets in phage display to isolate recombinant antibodies from a human scFv library. Candidate antibodies were expressed in E. coli HB2151 and purified by IMAC chromatography. The selected clones were analyzed in in vivo and in vitro experiments.

Results:

Venom toxicity was contained in two fractions. Around a hundred phage clones were isolated against each fraction, those showing the best promise were G12F3 and G1F4. While all chosen clones showed low but detectable neutralizing effect against Naja oxiana venom, clone G12F3 could inhibit PLA₂ activity.

Conclusion:

Therefore, phage display is believed to have a good potential as an approach to the development of snake antivenom.

Diagnostic and Therapeutic Value of Aptamers in Envenomation Cases

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

Scorpion Venom: Detriments and Benefits

Scorpion venom may cause severe medical complications and untimely death if injected into the human body. Neurotoxins are the main components of scorpion venom that are known to be responsible for the pathological manifestations of envenoming. Besides neurotoxins, a wide range of other bioactive molecules can be found in scorpion venoms. Advances in separation, characterization, and biotechnological approaches have enabled not only the development of more effective treatments against scorpion envenomings, but have also led to the discovery of several scorpion venom peptides with interesting therapeutic properties. Thus, scorpion venom may not only be a medical threat to human health, but could prove to be a valuable source of bioactive molecules that may serve as leads for the development of new therapies against current and emerging diseases. This review presents both the detrimental and beneficial properties of scorpion venom toxins and discusses the newest advances within the development of novel therapies against scorpion envenoming and the therapeutic perspectives for scorpion toxins in drug discovery.

Unity Makes Strength: Exploring Intraspecies and Interspecies Toxin Synergism between Phospholipases A2 and Cytotoxins

Toxin synergism is a complex biochemical phenomenon, where different animal venom proteins interact either directly or indirectly to potentiate toxicity to a level that is above the sum of the toxicities of the individual toxins. This provides the animals possessing venoms with synergistically enhanced toxicity with a metabolic advantage, since less venom is needed to inflict potent toxic effects in prey and predators. Among the toxins that are known for interacting synergistically are cytotoxins from snake venoms, phospholipases A₂ from snake and bee venoms, and melittin from bee venom. These toxins may derive a synergistically enhanced toxicity via formation of toxin complexes by hetero-oligomerization. Using a human keratinocyte assay mimicking human epidermis in vitro, we demonstrate and quantify the level of synergistically enhanced toxicity for 12 cytotoxin/melittin-PLA₂ combinations using toxins from elapids, vipers, and bees. Moreover, by utilizing an interaction-based assay and by including a wealth of information obtained via a thorough literature review, we speculate and propose a mechanistic model for how toxin synergism in relation to cytotoxicity may be mediated by cytotoxin/melittin and PLA₂ complex formation.

Loxoscelism: Advances and Challenges in the Design of Antibody Fragments with Therapeutic Potential

Envenoming due to Loxosceles spider bites still remains a neglected disease of particular medical concern in the Americas. To date, there is no consensus for the treatment of envenomed patients, yet horse polyclonal antivenoms are usually infused to patients with identified severe medical conditions. It is widely known that venom proteins in the 30–35 kDa range with sphingomyelinase D (SMasesD) activity, reproduce most of the toxic effects observed in loxoscelism. Hence, we believe that monoclonal antibody fragments targeting such toxins might pose an alternative safe and effective treatment. In the present study, starting from the monoclonal antibody LimAb7, previously shown to target SMasesD from the venom of L. intermedia and neutralize its dermonecrotic activity, we designed humanized antibody V-domains, then produced and purified as recombinant single-chain antibody fragments (scFvs). These molecules were characterized in terms of humanness, structural stability, antigen-binding activity, and venom-neutralizing potential. Throughout this process, we identified some blocking points that can impact the Abs antigen-binding activity and neutralizing capacity. In silico analysis of the antigen/antibody amino acid interactions also contributed to a better understanding of the antibody’s neutralization mechanism and led to reformatting the humanized antibody fragment which, ultimately, recovered the functional characteristics for efficient in vitro venom neutralization.

A protocol for recombinant protein quantification by densitometry

The protein purity is generally checked using SDS‐PAGE, where densitometry could be used to quantify the protein bands. In literature, few studies have been reported using image analysis for the quantification of protein in SDS‐PAGE: that is, imaged with Stain‐Free™ technology. This study presents a protocol of image analysis for electrophoresis gels that allows the quantification of unknown proteins using the molecular weight markers as protein standards. Escherichia coli WK6/pHEN6 encoding the bispecific nanobody CH10‐12 engineered by the Pasteur Institute of Tunisia was cultured in a bioreactor and induced with isopropyl β‐D‐1‐thiogalactopyranoside (IPTG) at 28°C for 12 hr. Periplasmic proteins extracted by osmotic shock were purified by immobilized metal affinity chromatography (IMAC). Images of the SDS‐PAGE gels were analyzed using ImageJ, and the lane profiles were obtained in grayscale and uncalibrated optical density. Protein load and peak area were linearly correlated, and optimal image processing was then performed by background subtraction using the rolling ball algorithm with radius size 250 pixels. No brightness and contrast adjustment was applied. The production of the nanobody CH10‐12 was obtained through a fed‐batch strategy and quantified using the band of 50 kDa in the marker as reference for 750 ng of recombinant protein. The molecular weight marker was used as a sole protein standard for protein quantification in SDS‐PAGE gel images.

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

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

Expression of an scFv antibody fragment in Nicotiana benthamiana and in vitro assessment of its neutralizing potential against the snake venom metalloproteinase BaP1 from Bothrops asper

Human accidents with venomous snakes represent an overwhelming public health problem, mainly in rural populations of underdeveloped countries. Their high incidence and the severity of the accidents result in 81,000 to 138,000 deaths per year. The treatment is based on the administration of purified antibodies, produced by hyper immunization of animals to generate immunoglobulins (Igs), and then obtained by fractionating hyper immune plasma. The use of recombinant antibodies is an alternative to conventional treatment of snakebite envenoming, particularly the Fv fragment, named the single-chain variable fragment (scFv). We have produced recombinant single chain variable fragment scFv against the venom of the pit viper Bothrops asper at high levels expressed transiently and stably in transgenic plants and in vitro cultures that is reactive to BaP1 (a metalloproteinase from B. asper venom). The yield from stably transformed plants was significantly (p > 0.05) higher than the results in from transient expression. In addition, scFvBaP1 yields from systems derived from stable transformation were: transgenic callus 62 μg/g (±2); biomass from cell suspension cultures 83 μg/g (±0.2); culture medium from suspensions 71.75 mg/L (±6.18). The activity of scFvBaP1 was confirmed by binding and neutralization of the fibrin degradation induced by BnP1 toxins from B. neuwiedi and by Atroxlysin Ia from B. atrox venoms. In the present work, we demonstrated the potential use of plant cells to produce scFvBaP1 to be used in the future as a biotechnological alternative to horse immunization protocols to produce anti-venoms to be used in human therapy against snakebites.

Toxin Neutralization Using Alternative Binding Proteins

Animal toxins present a major threat to human health worldwide, predominantly through snakebite envenomings, which are responsible for over 100,000 deaths each year. To date, the only available treatment against snakebite envenoming is plasma-derived antivenom. However, despite being key to limiting morbidity and mortality among snakebite victims, current antivenoms suffer from several drawbacks, such as immunogenicity and high cost of production. Consequently, avenues for improving envenoming therapy, such as the discovery of toxin-sequestering monoclonal antibodies against medically important target toxins through phage display selection, are being explored. However, alternative binding protein scaffolds that exhibit certain advantages compared to the well-known immunoglobulin G scaffold, including high stability under harsh conditions and low cost of production, may pose as possible low-cost alternatives to antibody-based therapeutics. There is now a plethora of alternative binding protein scaffolds, ranging from antibody derivatives (e.g., nanobodies), through rationally designed derivatives of other human proteins (e.g., DARPins), to derivatives of non-human proteins (e.g., affibodies), all exhibiting different biochemical and pharmacokinetic profiles. Undeniably, the high level of engineerability and potentially low cost of production, associated with many alternative protein scaffolds, present an exciting possibility for the future of snakebite therapeutics and merit thorough investigation. In this review, a comprehensive overview of the different types of binding protein scaffolds is provided together with a discussion on their relevance as potential modalities for use as next-generation antivenoms.

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.

Immunoprotection elicited in rabbit by a chimeric protein containing B-cell epitopes of Sphingomyelinases D from Loxosceles spp. spiders

Accidents with venomous animals pose a health issue in Brazil, and those involving brown spiders (Loxosceles sp.) figure between the most frequent ones. The accidental envenomation by brown spiders causes a strong local dermonecrotic effect, which can be followed by systemic manifestations that in some cases lead to death. The production of antivenoms for the treatments of such accidents relies on a variety of animal experiments, from the spider venom extraction to the production of antivenom in horses. In the present work, there is an attempt to reduce and optimize animal experiments with the construction and production of a chimeric protein, named Lil, containing immunodominant epitopes previously mapped from the main proteins of the Loxosceles venom, the Sphingomyelinases D. The Lil protein contains epitopes from Sphinomyelinases D of the three-main species found in Brazil and this chimeric protein was found capable of inducing antibodies with the potential to partially neutralize the toxic effects of Loxosceles intermedia venom in an animal model. Therefore, in order to reduce spider usage and to improve the lifespan of the horses used for immunization we suggest the Lil protein as a potential candidate to replace the venom usage in the antivenom production protocols.

Determination of median effective dose (ED50) of scorpion antivenom against scorpion envenomation using a newly developed formula

BACKGROUND

About 50 species of scorpions cause fatal scorpionism worldwide. Most of these are members of the Buthidae family, and include, among others, Mesobuthus eupeus, Androctonus crassicauda, Leiurus abdullahbayrami, Leiurus quinquestriatus, Tityus pachyurus and Androctonus australis. Because high doses of scorpion venom and antivenom can cause death and hypersensitive reactions, there is a need to develop a formula that can be used to calculate both lethal and effective doses for scorpion venom and antivenom, respectively, thereby obviating the need for laboratory experiments.

METHODS

In view of this, a literature search was carried out with the aim of modifying the formula (LD 50 = ED 50 3 × W a × 10 - 4 ) for calculation of the median lethal dose (LD50) of scorpion venom and the ED50 of antivenom. The human equivalent dose (HED) formula was assessed for extrapolation of LD50 and ED50 from animals to human for comparison and relevance with the new formula.

RESULTS

The findings showed that the newly developed formula (LD50 = ED50 1/3 × W a  × 10-4) yielded results that are very close to the reported values. Therefore, the newly developed and HED formulas can be used for calculation of LD50 and ED50 values for scorpion venom and antivenom, respectively.

CONCLUSION

The new formula yielded better results than the HED formula, confirming its predictive validity, precision, and reliability, thereby obviating the need for rigorous experiments and justifying the principles of reduction, refinement, and replacement (3Rs).

Nanobodies as novel therapeutic agents in envenomation

BACKGROUND

An effective therapy against envenoming should be a priority in view of the high number scorpion stings and snakebites. Serum therapy is still widely applied to treat the envenomation victims; however this approach suffers from several shortcomings. The employment of monoclonal antibodies might be an outcome as these molecules are at the core of a variety of applications from protein structure determination to cancer treatment. The progress of activities in the twilight zone between genetic and antibody engineering have led to the development of a unique class of antibody fragments. These molecules possess several benefits and lack many possible disadvantages over classical antibodies. Within recombinant antibody formats, nanobodies or single domain antigen binding fragments derived from heavy chain only antibodies in camelids occupy a privileged position.

SCOPE OF REVIEW

In this paper we will briefly review the common methods of envenomation treatment and focus on details of various in vivo research activities that investigate the performance of recombinant, monoclonal nanobodies in venom neutralization.

MAJOR CONCLUSIONS

Nanobodies bind to their cognate target with high specificity and affinity, they can be produced in large quantities from microbial expression systems and are very robust even when challenged with harsh environmental conditions. Upon administering, they rapidly distribute throughout the body and seem to be well tolerated in humans posing low immunogenicity.

GENERAL SIGNIFICANCE

Scorpion and snake envenomation is a major issue in developing countries and nanobodies as a venom-neutralizing agent can be considered as a valuable and promising candidate in envenomation therapy.

Basics of Antibody Phage Display Technology

Antibody discovery has become increasingly important in almost all areas of modern medicine. Different antibody discovery approaches exist, but one that has gained increasing interest in the field of toxinology and antivenom research is phage display technology. In this review, the lifecycle of the M13 phage and the basics of phage display technology are presented together with important factors influencing the success rates of phage display experiments. Moreover, the pros and cons of different antigen display methods and the use of naïve versus immunized phage display antibody libraries is discussed, and selected examples from the field of antivenom research are highlighted. This review thus provides in-depth knowledge on the principles and use of phage display technology with a special focus on discovery of antibodies that target animal toxins.

Recent Advances in Next Generation Snakebite Antivenoms

With the inclusion of snakebite envenoming on the World Health Organization’s list of Neglected Tropical Diseases, an incentive has been established to promote research and development effort in novel snakebite antivenom therapies. Various technological approaches are being pursued by different research groups, including the use of small molecule inhibitors against enzymatic toxins as well as peptide- and oligonucleotide-based aptamers and antibody-based biotherapeutics against both enzymatic and non-enzymatic toxins. In this article, the most recent advances in these fields are presented, and the advantages, disadvantages, and feasibility of using different toxin-neutralizing molecules are reviewed. Particular focus within small molecules is directed towards the inhibitors varespladib, batimastat, and marimastat, while in the field of antibody-based therapies, novel recombinant polyclonal plantivenom technology is discussed.

Camelid Single-Domain Antibodies (VHHs) against Crotoxin: A Basis for Developing Modular Building Blocks for the Enhancement of Treatment or Diagnosis of Crotalic Envenoming

Toxic effects triggered by crotalic envenoming are mainly related to crotoxin (CTX), composed of a phospholipase A₂ (CB) and a subunit with no toxic activity (CA). Camelids produce immunoglobulins G devoid of light chains, in which the antigen recognition domain is called VHH. Given their unique characteristics, VHHs were selected using Phage Display against CTX from Crotalus durissus terrificus. After three rounds of biopanning, four sequence profiles for CB (KF498602, KF498603, KF498604, and KF498605) and one for CA (KF498606) were revealed. All clones presented the VHH hallmark in FR2 and a long CDR3, with the exception of KF498606. After expressing pET22b-VHHs in E. coli, approximately 2 to 6 mg of protein per liter of culture were obtained. When tested for cross-reactivity, VHHs presented specificity for the Crotalus genus and were capable of recognizing CB through Western blot. KF498602 and KF498604 showed thermostability, and displayed affinity constants for CTX in the micro or nanomolar range. They inhibited in vitro CTX PLA₂ activity, and CB cytotoxicity. Furthermore, KF498604 inhibited the CTX-induced myotoxicity in mice by 78.8%. Molecular docking revealed that KF498604 interacts with the CA–CB interface of CTX, seeming to block substrate access. Selected VHHs may be alternatives for the crotalic envenoming treatment.

Synergistic strategies of predominant toxins in snake venoms

Synergism is a significant phenomenon present in snake venoms that may be an evolving strategy to potentiate toxicities. Synergism exists between different toxins or toxin complexes in various snake venoms, with phospholipaseA₂s (PLA₂s) (toxins or subunits) the main enablers. The predominant toxins, snake venom PLA₂s, metalloproteases (SVMPs), serine proteases (SVSPs) and three-finger toxins (3FTxs), play essential roles in synergistic processes. The hypothetical mechanisms of synergistic effect can be generalized under the effects of amplification and chaperoning. The Toxicity Score is among the few quantitative methods to assess synergism. Selection of toxins involved in synergistically enhanced toxicity as the targets are important for development of novel antivenoms or inhibitors.

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.

Application of phage display for the development of a novel inhibitor of PLA2 activity in Western cottonmouth venom

Snakebite envenomation is an important global health concern. The current standard treatment approach for snakebite envenomation relies on antibody-based antisera, which are expensive, not universally available, and can lead to adverse physiological effects. Phage display techniques offer a powerful tool for the selection of phage-expressed peptides, which can bind with high specificity and affinity towards venom components. In this research, the amino acid sequences of Phospholipase A₂ (PLA₂) from multiple cottonmouth species were analyzed, and a consensus peptide synthesized. Three phage display libraries were panned against this consensus peptide, crosslinked to capillary tubes, followed by a modified surface panning procedure. This high throughput selection method identified four phage clones with anti-PLA₂ activity against Western cottonmouth venom, and the amino acid sequences of the displayed peptides were identified. This is the first report identifying short peptide sequences capable of inhibiting PLA₂ activity of Western cottonmouth venom in vitro, using a phage display technique. Additionally, this report utilizes synthetic panning targets, designed using venom proteomic data, to mimic epitope regions. M13 phages displaying circular 7-mer or linear 12-mer peptides with antivenom activity may offer a novel alternative to traditional antibody-based therapy.

Characteristics and Lethality of a Novel Recombinant Dermonecrotic Venom Phospholipase D from Hemiscorpius lepturus

Hemoscorpius lepturus is the most medically important scorpion in Iran. The clinical signs of H. lepturus envenomation are remarkably similar to those reported for brown spiders, including dermonecrosis, hematuria, renal failure and even death. The lethality and toxicity of brown spiders’ venom have been attributed to its phospholipase D activity. This study aims to identify a phospholipase D with possible lethality and dermonecrotic activity in H. lepturus venom. In this study, a cDNA library of the venom glands was generated by Illumina RNA sequencing. Phospholipase D (PLD) from H. lepturus was characterized according to its significant similarity with PLDs from brown spiders. The main chain designated as Hl-RecPLD1 (the first recombinant isoform of H. lepturus PLD) was cloned, expressed and purified. Sphingomyelinase, dermonecrotic and lethal activities were examined. Hl-PLD1 showed remarkable sequence similarity and structural homology with PLDs of brown spiders. The conformation of Hl-PLD1 was predicted as a “TIM beta/alpha-barrel”. The lethal dose 50 (LD₅₀) and dermonecrotic activities of Hl-RecPLD1 were determined as 3.1 µg/mouse and 0.7 cm² at 1 µg respectively. It is the first report indicating that a similar molecular evolutionary mechanism has occurred in both American brown spiders and this Iranian scorpion. In conclusion, Hl-RecPLD1 is a highly active phospholipase D, which would be considered as the lethal dermonecrotic toxin in H. lepturus venom.

Recombinant snakebite antivenoms: A cost-competitive solution to a neglected tropical disease?

Snakebite envenoming is a major public health burden in tropical parts of the developing world. In sub-Saharan Africa, neglect has led to a scarcity of antivenoms threatening the lives and limbs of snakebite victims. Technological advances within antivenom are warranted, but should be evaluated not only on their possible therapeutic impact, but also on their cost-competitiveness. Recombinant antivenoms based on oligoclonal mixtures of human IgG antibodies produced by CHO cell cultivation may be the key to obtaining better snakebite envenoming therapies. Based on industry data, the cost of treatment for a snakebite envenoming with a recombinant antivenom is estimated to be in the range USD 60–250 for the Final Drug Product. One of the effective antivenoms (SAIMR Snake Polyvalent Antivenom from the South African Vaccine Producers) currently on the market has been reported to have a wholesale price of USD 640 per treatment for an average snakebite. Recombinant antivenoms may therefore in the future be a cost-competitive alternative to existing serum-based antivenoms.

Given the medical importance of snakebite envenoming and the current shortage of antivenoms in sub-Saharan Africa, technological advances in antivenom development and production are needed. One of the avenues that could be taken involves the use of recombinant antivenoms based on oligoclonal mixtures of human IgG antibodies, since these may have the benefits of being compatible with the human immune system and their production is independent on animal immune systems and venom procurement. However, an important aspect of introducing recombinant antivenoms to the clinic is their cost of production given that snakebite victims are often poor rural workers living in remote parts of the tropical parts of the developing world. Here, we aim to provide cost estimates of recombinant antivenom manufacture with special focus on snakebite envenoming in sub-Saharan Africa. Our results indicate that recombinant antivenoms in the future will indeed be cost-competitive compared to existing animal-derived serum-based antivenoms. Furthermore, we outline different manufacturing strategies and suggest the use of caprylic acid precipitation as a low cost purification method following cultivation of CHO cells for antibody expression due to its use in current antivenom manufacture.

Exploration of immunoglobulin transcriptomes from mice immunized with three-finger toxins and phospholipases A2 from the Central American coral snake, Micrurus nigrocinctus

Snakebite envenomings represent a neglected public health issue in many parts of the rural tropical world. Animal-derived antivenoms have existed for more than a hundred years and are effective in neutralizing snake venom toxins when timely administered. However, the low immunogenicity of many small but potent snake venom toxins represents a challenge for obtaining a balanced immune response against the medically relevant components of the venom. Here, we employ high-throughput sequencing of the immunoglobulin (Ig) transcriptome of mice immunized with a three-finger toxin and a phospholipase A₂ from the venom of the Central American coral snake, Micrurus nigrocinctus. Although exploratory in nature, our indicate results showed that only low frequencies of mRNA encoding IgG isotypes, the most relevant isotype for therapeutic purposes, were present in splenocytes of five mice immunized with 6 doses of the two types of toxins over 90 days. Furthermore, analysis of Ig heavy chain transcripts showed that no particular combination of variable (V) and joining (J) gene segments had been selected in the immunization process, as would be expected after a strong humoral immune response to a single antigen. Combined with the titration of toxin-specific antibodies in the sera of immunized mice, these data support the low immunogenicity of three-finger toxins and phospholipases A₂found in M. nigrocinctusvenoms, and highlight the need for future studies analyzing the complexity of antibody responses to toxins at the molecular level.