Biologically active human anti-crotoxin scFv isolated from a semi-synthetic phage library

Antibodies as Snakebite Antivenoms: Past and Future

Snakebite envenomation is considered a neglected tropical disease, affecting tens of thousands of people each year. The recommended treatment is the use of antivenom, which is composed of immunoglobulins or immunoglobulin fragments obtained from the plasma of animals hyperimmunized with one (monospecific) or several (polyspecific) venoms. In this review, the efforts made in the improvement of the already available antivenoms and the development of new antivenoms, focusing on snakes of medical importance from sub-Saharan Africa and Latin America, are described. Some antivenoms currently used are composed of whole IgGs, whereas others use F(ab’)2 fragments. The classic methods of attaining snake antivenoms are presented, in addition to new strategies to improve their effectiveness. Punctual changes in immunization protocols, in addition to the use of cross-reactivity between venoms from different snakes for the manufacture of more potent and widely used antivenoms, are presented. It is known that venoms are a complex mixture of components; however, advances in the field of antivenoms have shown that there are key toxins that, if effectively blocked, are capable of reversing the condition of in vivo envenomation. These studies provide an opportunity for the use of monoclonal antibodies in the development of new-generation antivenoms. Thus, monoclonal antibodies and their fragments are described as a possible alternative for the production of antivenoms, regardless of the venom. This review also highlights the challenges associated with their development.

Bibliometric Analysis of Literature in Snake Venom-Related Research Worldwide (1933–2022)

Simple Summary

Around the world, snake envenomation poses a serious health risk. Proteins with pharmacological effects are present in snake venom. Recent studies elaborate snake venom and its potential application, including as a cancer drug and antibacterial substances. Our study aimed to analyze the global profile of the literature in snake venom research from documents indexed in the Scopus database between 1933 and 2022. In total, 2999 documents were published with Brazil showing the highest productivity. Antivenom, proteomics, and transcriptomics are emerging as hot topics on a global scale. The present study offers a distinctive overview of snake venom research conducted worldwide.

Abstract

Snake envenomation is a severe economic and health concern affecting countries worldwide. Snake venom carries a wide variety of small peptides and proteins with various immunological and pharmacological properties. A few key research areas related to snake venom, including its applications in treating cancer and eradicating antibiotic-resistant bacteria, have been gaining significant attention in recent years. The goal of the current study was to analyze the global profile of literature in snake venom research. This study presents a bibliometric review of snake venom-related research documents indexed in the Scopus database between 1933 and 2022. The overall number of documents published on a global scale was 2999, with an average annual production of 34 documents. Brazil produced the highest number of documents (n = 729), followed by the United States (n = 548), Australia (n = 240), and Costa Rica (n = 235). Since 1963, the number of publications has been steadily increasing globally. At a worldwide level, antivenom, proteomics, and transcriptomics are growing hot issues for research in this field. The current research provides a unique overview of snake venom research at global level from 1933 through 2022, and it may be beneficial in guiding future research.

Crotalus Durissus Ruruima: Current Knowledge on Natural History, Medical Importance, and Clinical Toxinology

Crotalus durissus ruruima is a rattlesnake subspecies mainly found in Roraima, the northernmost state of Brazil. Envenomings caused by this subspecies lead to severe clinical manifestations (e.g. respiratory muscle paralysis, rhabdomyolysis, and acute renal failure) that can lead to the victim’s death. In this review, we comprehensively describe C. d. ruruima biology and the challenges this subspecies poses for human health, including morphology, distribution, epidemiology, venom cocktail, clinical envenoming, and the current and future specific treatment of envenomings by this snake. Moreover, this review presents maps of the distribution of the snake subspecies and evidence that this species is responsible for some of the most severe envenomings in the country and causes the highest lethality rates. Finally, we also discuss the efficacy of the Brazilian horse-derived antivenoms to treat C. d. ruruima envenomings in Roraima state.

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.

History of Envenoming Therapy and Current Perspectives

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

In vivo neutralization of α-cobratoxin with high-affinity llama single-domain antibodies (VHHs) and a VHH-Fc antibody

Small recombinant antibody fragments (e.g. scFvs and VHHs), which are highly tissue permeable, are being investigated for antivenom production as conventional antivenoms consisting of IgG or F(ab')2 antibody fragments do not effectively neutralize venom toxins located in deep tissues. However, antivenoms composed entirely of small antibody fragments may have poor therapeutic efficacy due to their short serum half-lives. To increase serum persistence and maintain tissue penetration, we prepared low and high molecular mass antivenom antibodies. Four llama VHHs were isolated from an immune VHH-displayed phage library and were shown to have high affinity, in the low nM range, for α-cobratoxin (α-Cbtx), the most lethal component of Naja kaouthia venom. Subsequently, our highest affinity VHH (C2) was fused to a human Fc fragment to create a VHH2-Fc antibody that would offer prolonged serum persistence. After in planta (Nicotiana benthamiana) expression and purification, we show that our VHH2-Fc antibody retained high affinity binding to α-Cbtx. Mouse α-Cbtx challenge studies showed that our highest affinity VHHs (C2 and C20) and the VHH2-Fc antibody effectively neutralized lethality induced by α-Cbtx at an antibody:toxin molar ratio as low as ca. 0.75×:1. Further research towards the development of an antivenom therapeutic involving these anti-α-Cbtx VHHs and VHH2-Fc antibody molecules should involve testing them as a combination, to determine whether they maintain tissue penetration capability and low immunogenicity, and whether they exhibit improved serum persistence and therapeutic efficacy.

Recognition of Vipera ammodytes meridionalis neurotoxin vipoxin and its components using phage-displayed scFv and polyclonal antivenom sera

Vipoxin is a potent postsynaptic heterodimeric neurotoxin isolated from the venom of the Bulgarian snake Vipera ammodytes meridionalis, whose snakebites cause different and strongly manifested pathophysiological effects (neurotoxic, hemolytic, anticoagulant, convulsant, hypotensive, hyperglycemic etc.). The neutralization of snake toxins calls for extensive research through the application of different approaches: antibodies, non-immunologic inhibitors, natural products derived from plants and animals, as well as synthetic drugs. In this study, we applied naive Tomlinson I + J (Cambridge, UK) libraries to obtain recombinant human scFv antibodies against the vipoxin's two subunits--basic and toxic phospholipase A₂ (PLA₂) and acidic, non-toxic component. We found that 33 of more than hundred tested clones were positive and recognized vipoxin and its subunits. Enriched scFv-phage samples (1.2 × 10⁹ pfu/ml) were analyzed for their binding (ELISA) and enzyme-inhibiting abilities. Single chain Fv-phage clones--D₁₂, E₃, F₆, D₁₀ and G₅ exhihest binding affinity for the toxic component. Clones A₁, D₁₂ and C₁₂ recognized preferentially vipoxin's acidic component. Clones E₃, G₅ and H₄ inhibited the enzymatic activity of both vipoxin and its purified and separated toxic subunit to the highest extent. Six of the selected clones (E₃, G₅, H₄, C₁₂, D₁₀ and A₁₁) inhibited direct hemolytic activity of vipoxin and its pure PLA₂ subunit. The obtained specific scFv antibodies will be used for epitope mapping studies required to shed light on the role of the phospholipase A₂ activity for the vipoxin toxicity and its effective neutralization.

Expression of human recombinant antibody fragments capable of partially inhibiting the phospholypase activity of Crotalus durissus terrificus venom

Crotoxin is the main toxic component of the South American rattlesnake Crotalus durissus terrificus venom. It is composed of two different subunits: CA, crotapotin, and CB (basic subunit of cortoxin isolated from C. d. terrificus), a weakly toxic phospholipase A(2) with high enzymatic activity. The phospholipases A(2) are abundant in snake venoms and are responsible for disruption of cell membrane integrity via hydrolysis of its phospholipids. However, in addition to their normal digestive action, a wide range of pharmacological activities, such as neurotoxic, myotoxic, oedema-inducing, hypotensive, platelet-aggregating, cardiotoxic, and anticoagulant effects have been attributed to venom phospholipases A(2). In this study, we used a non-immune human single-chain fragment variable library, Griffin.1 (Medical Research Council, Cambridge, UK) for selection of recombinant antibodies against antigens present in C. d. terrificus venom and identification of specific antibodies able to inhibit the phospholipase activity. Two clones were identified as capable of inhibiting partially this activity in vitro. These clones were able to reduce in vivo the myotoxic and oedema-inducing activity of CB and the lethality of C. d. terrificus venom and crotoxin, but had no effect on the in vitro anticoagulant activity of CB. These results demonstrate the potential of using recombinant single-chain fragment variable libraries in the production of antivenoms.

Engineering and functional evaluation of a single-chain antibody against HIV-1 external glycoprotein gp120

The HIV-1 envelope glycoprotein surface subunit gp120 is an attractive target for molecular intervention. This is because anti-HIV-1 gp120 neutralizing antibodies display the potential ability to inhibit HIV-1 infection. The present investigation describes the construction of a genetically engineered single chain antibody (scFv102) against HIV-1 gp120, its expression and functional evaluation. The parental hybridoma cell line (102) produces an immunoglobulin directed against the conserved CD4-binding region of gp120. cDNAs encoding the variable regions of the heavy (V(H)) and light (V(L)) chains were prepared by reverse transcription PCR and linked together with an oligonucleotide encoding a linker peptide (Gly(4)Ser)(3) to produce a single chain antibody gene. The resulting DNA construct was cloned into a prokaryotic expression vector (pET28) and recombinant scFv102 was expressed in Eserichia coli as an insoluble protein. The denatured scFv102 was refolded and purified by immobilized metal ion affinity chromatography. Purified scFv102 had the same specificity as the intact IgG in immuno-blotting assays and immuno-fluorescence (IF) detection, but ELISA analyses demonstrated the affinity of scFv102 to be 5-fold lower than that of the parental monoclonal antibody. In neutralization assays, scFv102 at concentrations lower than 40 microg/ml exhibited efficient interference with viral replication and inhibition of viral infection (90%) across a range of primary isolates of subtype B HIV-1. These results suggest that the constructed anti-HIV-1 gp120 scFv102 has good biological activity and can potentially be used for in vitro diagnostic and in vivo therapeutic applications.

Construction and functional evaluation of a single-chain antibody fragment that neutralizes toxin AahI from the venom of the scorpion Androctonus australis hector

9C2 is a murine monoclonal IgG that participates in the neutralization of Androctonus australis hector scorpion venom. It recognizes AahI and AahIII, two of the three main neurotoxins responsible for almost all the toxicity of the venom when injected into mammals. Using PCR we cloned the antibody variable region coding genes from 9C2 hybridoma cells and constructed a gene encoding a single-chain antibody variable fragment molecule (scFv). This scFv was produced in the periplasm of Escherichia coli in a soluble and functional form and purified in a single step using protein L-agarose beads yielding 1-2 mg.L(-1) of bacterial culture. scFv9C2 was predominantly monomeric but also tended to form dimeric and oligomeric structures, all capable of binding toxin AahI. The affinity of scFv and the parental mAb for toxin AahI and homologous toxin AahIII was of the same magnitude, in the nanomolar range. Similarly, purified forms of scFv9C2 completely inhibited the binding of toxin AahI to rat brain synaptosomes. Finally, scFv9C2 was efficient in protecting mice against the toxic effects of AahI after injection of the toxin and scFv to mice by the intracerebroventricular route in a molar ratio as low as 0.36 : 1. Thus, we produced a recombinant scFv that reproduces the recognition properties of the parent antibody and neutralizes the scorpion neurotoxin AahI, thereby opening new prospects for the treatment of envenomation.

Neutralizing human anti crotoxin scFv isolated from a nonimmunized phage library

Combinatorial phage display technology offers a new possibility for making human antibodies which could be used in immune therapy. We explored the use of this technology to make human scFvs specific for crotoxin, the main toxic component of the venom of the South-American rattlesnake Crotalus durissus terrificus. Crotoxin, a phospholipase A2 neurotoxin constituted by the association of two subunits, exerts its lethal action by blocking neuromuscular transmission. This is the first report of human anticrotoxin scFvs (scFv 1, scFv 6 and scFv 8) isolated from a naive library of more than 1010 scFv clones with in vivo neutralizing activity. Nevertheless, differences are observed at the level of biological and immunological effects. Only scFv 8 is able to reduce the myotoxicity induced by crotoxin and scFv 1 is capable of altering the in vitro enzymatic activity of this toxin. All three scFvs recognize a region of one subunit located at the junction with the other one. Moreover these scFvs share strong amino acid homologies at the level of either the heavy or the light chain. Taken together, our results suggest that the use of human anticrotoxin scFvs may lead to a new and less aggressive passive immune therapy against poisoning by the venom of Crotalus durissus terrificus.

A recombinant single-chain antibody fragment that neutralizes toxin II from the venom of the scorpion Androctonus australis hector

Monoclonal antibody 4C1 specifically binds to and neutralizes the most potent neurotoxin (AahII) of the scorpion Androctonus australis. The cDNAs encoding the variable regions of this antibody were isolated by PCR-mediated cloning. A single-chain Fv gene was engineered and expressed in Escherichia coli. The recombinant protein had neutralizing activity similar to that of the intact antibody in vitro and in vivo. We have thus neutralized the pharmacological and biological properties of a scorpion neurotoxin with a single-chain Fv, which opens new perspectives for the treatment of envenomizations.