A protective immune response against lethal, dermonecrotic and hemorrhagic effects of Loxosceles intermedia venom elicited by a 27-residue peptide

Predictive analysis of B-cell antigenic epitopes in phospholipase D toxins from Loxosceles spiders

The Phospholipase D (PLD) toxin family, a major component of the Loxosceles spider venom, is a valuable biotechnological tool for developing antivenom treatment and diagnostic assays to overcome and prevent loxoscelism. However, there is limited knowledge about the antigenic structure of the PLD family or if sequence diversity correlates with antigenic variability. This study aimed to evaluate the possible antigenic diversity of PLDs sequences among different species of spiders of the Loxosceles genus through a predictive analysis of potential continuous and discontinuous antigenic epitopes of two phylogenetic interspecies clusters. Thus, L. laeta had higher amino acid sequence variation than other species, being classified into three phylogenetic clusters at the intra-specie level. Furthermore, multiple alignments of consensus PLD sequences from each Loxosceles species showed two different phylogenetic clusters at interspecies level depending on the amino acid conservation. For each cluster, at least nine continuous antigenic domains were identified, and depending on the phylogenetic cluster belonging to the Loxosceles species, the PLD continuous and discontinuous antigenic structure varies. Also, L. laeta PLDs vary significantly within the Loxosceles species and possess their own antigenic structure compared to other species with common continuous epitopes. Finally, the catalytic loop was identified as a common discontinuous epitope in the PLDs independently of the cluster or the class it belongs to. This antigenic diversity of PLD toxins could have implications for antibody recognition and should be considered in the design strategies for the development of serum treatments and diagnostic assays to detect Loxosceles venom.

Brown Spider Venom Phospholipases D: From Potent Molecules Involved in Pathogenesis of Brown Spider Bites to Molecular Tools for Studying Ectosomes, Ectocytosis, and Its Applications

Accidents caused by Loxosceles spiders, commonly known as brown spiders, are frequent in warm and temperate regions worldwide, with a higher prevalence in South America and the southern United States. In the venoms of species clinically associated with accidents, phospholipases D (PLDs) are the most expressed toxins. This classification is based on the toxins' ability to cleave various phospholipids, with a preference for sphingomyelin. Studies using purified PLDs have demonstrated that these enzymes cleave phospholipids from cells, producing derivatives that can activate leukocytes. A dysregulated inflammatory response is the primary effect following envenomation, leading to dermonecrosis, which is histopathologically characterized by aseptic coagulative necrosis-a key feature of envenomation. Although advances in understanding the structure-function relationship of enzymes have been achieved through molecular biology, heterologous expression, site-directed mutations, crystallography, and bioinformatic analyses-describing PLDs in the venoms of various species and highlighting the conservation of amino acid residues involved in catalysis, substrate binding, and magnesium stabilization-little is known about the cellular biology of these PLDs. Studies have shown that the treatment of various cells with recombinant PLDs stimulates the formation of ectosomes and ectocytosis, events that initiate a cascade of intracellular signaling in PLD-binding cells and lead to the release of extracellular microvesicles. These microvesicles may act as signalosomes for other target cells, thereby triggering an inflammatory response and dermonecrosis. In this review, we will discuss the biochemical properties of PLDs, the target cells that bind to them, and the ectocytosis-dependent pathophysiology of envenoming.

Novel insights into the application of recombinant mutated phospholipases D as antigens for developing new strategies against Loxoscelism

Loxoscelism is the pathological condition triggered by a brown spider bite. The venom of these spiders is rich in phospholipases D (PLDs), which can induce virtually all local and systemic manifestations. Recombinant mutated PLDs from clinically relevant Loxosceles species in South America have been investigated as potential antigens to develop novel therapeutic strategies for loxoscelism. However, certain gaps need to be addressed before a clinical approach can be implemented. In this study, we examined the potential of these recombinant mutated PLDs as antigens by testing some variations in the immunization scheme. Furthermore, we evaluated the efficacy of the produced antibodies in neutralizing the nephrotoxicity and sphingomyelinase activity of brown spider venoms. Our findings indicate that the number of immunizations has a greater impact on the effectiveness of neutralization compared to the amount of antigen. Specifically, two or three doses were equally effective in reducing dermonecrosis and edema. Additionally, three immunizations proved to be more effective in neutralizing mice lethality than one or two. Moreover, immunizations mitigated the signs of kidney injury, a crucial aspect given that acute renal failure is a serious systemic complication. In vitro inhibition of the sphingomyelinase activity of Loxosceles venoms, a key factor in vivo toxicity, was nearly complete after incubation with antibodies raised against these antigens. These findings underscore the importance of implementing an effective immunization scheme with multiple immunizations, without the need for high antigen doses, and enhances the spectrum of neutralization exhibited by antibodies generated with these antigens. In summary, these results highlight the strong potential of these antigens for the development of new therapeutic strategies against cutaneous and systemic manifestations of loxoscelism.

A protective vaccine against the toxic activities following Brown spider accidents based on recombinant mutated phospholipases D as antigens

Accidents involving Brown spiders are reported throughout the world. In the venom, the major toxins involved in the deleterious effects are phospholipases D (PLDs). In this work, recombinant mutated phospholipases D from three endemic species medically relevant in South America (Loxosceles intermedia, L. laeta and L. gaucho) were tested as antigens in a vaccination protocol. In such isoforms, key amino acid residues involved in catalysis, magnesium-ion coordination, and binding to substrates were replaced by Alanine (H12A-H47A, E32A-D34A and W230A). These mutations eliminated the phospholipase activity and reduced the generation of skin necrosis and edema to residual levels. Molecular modeling of mutated isoforms indicated that the three-dimensional structures, topologies, and surface charges did not undergo significant changes. Mutated isoforms were recognized by sera against the crude venoms. Vaccination protocols in rabbits using mutated isoforms generated a serum that recognized the native PLDs of crude venoms and neutralized dermonecrosis and edema induced by L. intermedia venom. Vaccination of mice prevented the lethal effects of L. intermedia crude venom. Furthermore, vaccination of rabbits prevented the cutaneous lesion triggered by the three venoms. These results indicate a great potential for mutated recombinant PLDs to be employed as antigens in developing protective vaccines for Loxoscelism.

Immunomic Investigation of Holocyclotoxins to Produce the First Protective Anti-Venom Vaccine Against the Australian Paralysis Tick, Ixodes holocyclus

Venom producing animals are ubiquitously disseminated among vertebrates and invertebrates such as fish, snakes, scorpions, spiders, and ticks. Of the ~890 tick species worldwide, 27 have been confirmed to cause paralysis in mammalian hosts. The Australian paralysis tick (Ixodes holocyclus) is the most potent paralyzing tick species known. It is an indigenous three host tick species that secretes potent neurotoxins known as holocyclotoxins (HTs). Holocyclotoxins cause a severe and harmful toxicosis leading to a rapid flaccid paralysis which can result in death of susceptible hosts such as dogs. Antivenins are generally polyclonal antibody treatments developed in sheep, horses or camels to administer following bites from venomous creatures. Currently, the methods to prevent or treat tick paralysis relies upon chemical acaricide preventative treatments or prompt removal of all ticks attached to the host followed by the administration of a commercial tick-antiserum (TAS) respectively. However, these methods have several drawbacks such as poor efficacies, non-standardized dosages, adverse effects and are expensive to administer. Recently the I. holocyclus tick transcriptome from salivary glands and viscera reported a large family of 19 holocyclotoxins at 38-99% peptide sequence identities. A pilot trial demonstrated that correct folding of holocyclotoxins is needed to induce protection from paralysis. The immunogenicity of the holocyclotoxins were measured using commercial tick antiserum selecting HT2, HT4, HT8 and HT11 for inclusion into the novel cocktail vaccine. A further 4 HTs (HT1, HT12, HT14 and HT17) were added to the cocktail vaccine to ensure that the sequence variation among the HT protein family was encompassed in the formulation. A second trial comparing the cocktail of 8 HTs to a placebo group demonstrated complete protection from tick challenge. Here we report the first successful anti-venom vaccine protecting dogs from tick paralysis.

A prokaryote system optimization for rMEPLox expression: A promising non-toxic antigen for Loxosceles antivenom production

Loxoscelism is the most dangerous araneism form in Brazil and antivenom therapy is the recommended treatment. Antivenom is produced by horse immunization with Loxosceles spider venom, which is toxic for the producer animal. Moreover, due to the high amount of venom required for horse hyperimmunization, new strategies for antigens obtention have been proposed. In this sense, our research group has previously produced a non-toxic recombinant multiepitopic protein derived from Loxosceles toxins (rMEPLox). rMEPLox was a successful immunogen, being able to induce the production of neutralizing antibodies, which could be used in the Loxoscelism treatment. However, rMEPLox obtention procedure requires optimization, as its production needs to be scaled up to suit antivenom manufacture. Therefore, an effective protocol development for rMEPlox production would be advantageous. To achieve this objective, we evaluated the influence of different cultivation conditions for rMEPLox optimum expression. The optimum conditions to obtain large amounts of rMEPlox were defined as the use of C43(DE3)pLysS as a host strain, 2xTY medium, 0.6 mM IPTG, biomass pre induction of OD600nm = 0.4 and incubation at 30 °C for 16 h. Following the optimized protocol, 39.84 mg/L of soluble rMEPLox was obtained and tested as immunogen. The results show that the obtained rMEPLox preserved the previously described immunogenicity, and it was able to generate antibodies that recognize different epitopes of the main Loxosceles venom toxins, which makes it a promising candidate for the antivenom production for loxoscelism treatment.

Molecular cloning and functional characterization of recombinant Loxtox from Loxosceles similis venom

Loxoscelism is a recognized public health problem in Brazil, but the venom from Loxosceles similis, which is widespread in Brazil due to its adaptability to the urban environment, remains poorly characterized. Loxtox is a family of phospholipase D enzymes (PLDs), which are the major components of Loxosceles venom and are responsible for the clinical effects of loxoscelism. Loxtox toxins correspond to 15% of L. similis venom gland transcripts, but the Loxtox family of L. similis has yet to be fully described. In this study, we cloned and functionally characterized recLoxtox s1A and recLoxtox s11A. These recombinant toxins exhibited different in vitro activities depending on pH, and recLoxtox s1A had more intense effects on rabbit skin than did recLoxtox s11A in vivo. Both recombinant toxins were used in immunization protocols, and mapping of their epitopes revealed different immunological reactions for the produced immune serums. Additionally, polyclonal antibodies raised against recLoxtox s1A had greater capacity to significantly reduce the in vitro and in vivo effects of L. similis venom. In summary, we obtained and characterized two novel Loxtox isoforms from L. similis venom, which may be valuable biotechnological and immunological tools against loxoscelism.

Synthetic peptides to produce antivenoms against the Cys-rich toxins of arachnids

Scorpion and spider envenomation is treated with the appropriate antivenoms, prepared as described by Césaire Auguste Phisalix and Albert Calmette in 1894. Such treatment requires the acquisition and manipulation of arachnid venoms, both very complicated procedures. Most of the toxins in the venoms of spiders and scorpions are extremely stable cysteine-rich peptide neurotoxins. Many strategies have been developed to obtain synthetic immunogens to facilitate the production of antivenoms against these toxins. For example, whole peptide toxins can be synthesized by solid-phase peptide synthesis (SPPS). Also, epitopes of the toxins can be identified and after the chemical synthesis of these peptide epitopes by SPPS, they can be coupled to protein carriers to develop efficient immunogens. Moreover, multiple antigenic peptides with a polylysine core can be designed and synthesized. This review focuses on the strategies developed to obtain synthetic immunogens for the production of antivenoms against the toxic Cys-rich peptides of scorpions and spiders.

Biotechnological potential of Phospholipase D for Loxosceles antivenom development

Loxoscelism is one of the most important forms of araneism in South America. The Health Authorities from countries with the highest incidence and longer history in registering loxoscelism cases indicate that specific antivenom should be administered during the first hours after the accident, especially in the presence or at risk of the most severe clinical outcome. Current antivenoms are based on immunoglobulins or their fragments, obtained from plasma of hyperimmunized horses. Antivenom has been produced using the same traditional techniques for more than 120 years. Although the whole composition of the spider venom remains unknown, the discovery and biotechnological production of the phospholipase D enzymes represented a milestone for the knowledge of the physiopathology of envenomation and for the introduction of new innovative tools in antivenom production. The fact that this protein is a principal toxin of the venom opens the possibility of replacing the use of whole venom as an immunogen, an attractive alternative considering the laborious techniques and low yields associated with venom extraction. This challenge warrants technological innovation to facilitate production and obtain more effective antidotes. In this review, we compile the reported studies, examining the advances in the expression and application of phospholipase D as a new immunogen and how the new biotechnological tools have introduced some degree of innovation in this field.

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.

Forty Years of the Description of Brown Spider Venom Phospholipases-D

Spiders of the genus Loxosceles, popularly known as Brown spiders, are considered a serious public health issue, especially in regions of hot or temperate climates, such as parts of North and South America. Although the venoms of these arachnids are complex in molecular composition, often containing proteins with distinct biochemical characteristics, the literature has primarily described a family of toxins, the Phospholipases-D (PLDs), which are highly conserved in all Loxosceles species. PLDs trigger most of the major clinical symptoms of loxoscelism i.e., dermonecrosis, thrombocytopenia, hemolysis, and acute renal failure. The key role played by PLDs in the symptomatology of loxoscelism was first described 40 years ago, when researches purified a hemolytic toxin that cleaved sphingomyelin and generated choline, and was referred to as a Sphingomyelinase-D, which was subsequently changed to Phospholipase-D when it was demonstrated that the enzyme also cleaved other cellular phospholipids. In this review, we present the information gleaned over the last 40 years about PLDs from Loxosceles venoms especially with regard to the production and characterization of recombinant isoforms. The history of obtaining these toxins is discussed, as well as their molecular organization and mechanisms of interaction with their substrates. We will address cellular biology aspects of these toxins and how they can be used in the development of drugs to address inflammatory processes and loxoscelism. Present and future aspects of loxoscelism diagnosis will be discussed, as well as their biotechnological applications and actions expected for the future in this field.

A Web of Coagulotoxicity: Failure of Antivenom to Neutralize the Destructive (Non-Clotting) Fibrinogenolytic Activity of Loxosceles and Sicarius Spider Venoms

Envenomations are complex medical emergencies that can have a range of symptoms and sequelae. The only specific, scientifically-validated treatment for envenomation is antivenom administration, which is designed to alleviate venom effects. A paucity of efficacy testing exists for numerous antivenoms worldwide, and understanding venom effects and venom potency can help identify antivenom improvement options. Some spider venoms can produce debilitating injuries or even death, yet have been largely neglected in venom and antivenom studies because of the low venom yields. Coagulation disturbances have been particularly under studied due to difficulties in working with blood and the coagulation cascade. These circumstances have resulted in suboptimal spider bite treatment for medically significant spider genera such as Loxosceles and Sicarius. This study identifies and quantifies the anticoagulant effects produced by venoms of three Loxoscles species (L. reclusa, L. boneti, and L. laeta) and that of Sicarius terrosus. We showed that the venoms of all studied species are able to cleave the fibrinogen Aα-chain with varying degrees of potency, with L. reclusa and S. terrosus venom cleaving the Aα-chain most rapidly. Thromboelastography analysis revealed that only L. reclusa venom is able to reduce clot strength, thereby presumably causing anticoagulant effects in the patient. Using the same thromboelastography assays, antivenom efficacy tests revealed that the commonly used Loxoscles-specific SMase D recombinant based antivenom failed to neutralize the anticoagulant effects produced by Loxosceles venom. This study demonstrates the fibrinogenolytic activity of Loxosceles and Sicarius venom and the neutralization failure of Loxosceles antivenom, thus providing impetus for antivenom improvement.

A Combined Strategy to Improve the Development of a Coral Antivenom Against Micrurus spp

Accidents involving Micrurus snakes are not the most common ones but are noteworthy due to their severity. Victims envenomed by Micrurus snakes are at high risk of death and therefore must be treated with coral antivenom. In Brazil, the immunization mixture used to fabricate coral antivenom contains Micrurus frontalis and Micrurus corallinus venoms, which are difficult to be obtained in adequate amounts. Different approaches to solve the venom limitation problem have been attempted, including the use of synthetic and recombinant antigens as substitutes. The present work proposes a combined immunization protocol, using priming doses of M. frontalis venom and booster doses of synthetic B-cell epitopes derived from M. corallinus toxins (four three-finger toxins-3FTX; and one phospholipase A₂-PLA₂) to obtain coral antivenom in a rabbit model. Immunized animals elicited a humoral response against both M. frontalis and M. corallinus venoms, as detected by sera reactivity in ELISA and Western Blot. Relevant cross-reactivity of the obtained sera with other Micrurus species (Micrurus altirostris, Micrurus lemniscatus, Micrurus spixii, Micrurus surinamensis) venoms was also observed. The elicited antibodies were able to neutralize PLA₂ activity of both M. frontalis and M. corallinus venoms. In vivo, immunized rabbit sera completely protected mice from a challenge with 1.5 median lethal dose (LD₅₀) of M. corallinus venom and 50% of mice challenged with 1.5 LD₅₀ of M. frontalis venom. These results show that this combined protocol may be a suitable alternative to reduce the amount of venom used in coral antivenom production in Brazil.

Brown Spider (Loxosceles) Venom Toxins as Potential Biotools for the Development of Novel Therapeutics

Brown spider envenomation results in dermonecrosis with gravitational spreading characterized by a marked inflammatory reaction and with lower prevalence of systemic manifestations such as renal failure and hematological disturbances. Several toxins make up the venom of these species, and they are mainly peptides and proteins ranging from 5–40 kDa. The venoms have three major families of toxins: phospholipases-D, astacin-like metalloproteases, and the inhibitor cystine knot (ICK) peptides. Serine proteases, serpins, hyaluronidases, venom allergens, and a translationally controlled tumor protein (TCTP) are also present. Toxins hold essential biological properties that enable interactions with a range of distinct molecular targets. Therefore, the application of toxins as research tools and clinical products motivates repurposing their uses of interest. This review aims to discuss possibilities for brown spider venom toxins as putative models for designing molecules likely for therapeutics based on the status quo of brown spider venoms. Herein, we explore new possibilities for the venom components in the context of their biochemical and biological features, likewise their cellular targets, three-dimensional structures, and mechanisms of action.

Design and Production of a Recombinant Hybrid Toxin to Raise Protective Antibodies Against Loxosceles Spider Venom

Human accidents with spiders of the genus Loxosceles are an important health problem affecting thousands of people worldwide. Patients evolve to severe local injuries and, in many cases, to systemic disturbances as acute renal failure, in which cases antivenoms are considered to be the most effective treatment. However, for antivenom production, the extraction of the venom used in the immunization process is laborious and the yield is very low. Thus, many groups have been exploring the use of recombinant Loxosceles toxins, particularly phospholipases D (PLDs), to produce the antivenom. Nonetheless, some important venom activities are not neutralized by anti-PLD antibodies. Astacin-like metalloproteases (ALMPs) are the second most expressed toxin acting on the extracellular matrix, indicating the importance of its inclusion in the antigen’s formulation to provide a better antivenom. Here we show the construction of a hybrid recombinant immunogen, called LgRec1ALP1, composed of hydrophilic regions of the PLD and the ALMP toxins from Loxosceles gaucho. Although the LgRec1ALP1 was expressed as inclusion bodies, it resulted in good yields and it was effective to produce neutralizing antibodies in mice. The antiserum neutralized fibrinogenolytic, platelet aggregation and dermonecrotic activities elicited by L. gaucho, L. laeta, and L. intermedia venoms, indicating that the hybrid recombinant antigen may be a valuable source for the production of protective antibodies against Loxosceles ssp. venoms. In addition, the hybrid recombinant toxin approach may enrich and expand the alternative antigens for antisera production for other venoms.

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.

Highlights in the knowledge of brown spider toxins

Brown spiders are venomous arthropods that use their venom for predation and defense. In humans, bites of these animals provoke injuries including dermonecrosis with gravitational spread of lesions, hematological abnormalities and impaired renal function. The signs and symptoms observed following a brown spider bite are called loxoscelism. Brown spider venom is a complex mixture of toxins enriched in low molecular mass proteins (4-40 kDa). Characterization of the venom confirmed the presence of three highly expressed protein classes: phospholipases D, metalloproteases (astacins) and insecticidal peptides (knottins). Recently, toxins with low levels of expression have also been found in Loxosceles venom, such as serine proteases, protease inhibitors (serpins), hyaluronidases, allergen-like toxins and histamine-releasing factors. The toxin belonging to the phospholipase-D family (also known as the dermonecrotic toxin) is the most studied class of brown spider toxins. This class of toxins single-handedly can induce inflammatory response, dermonecrosis, hemolysis, thrombocytopenia and renal failure. The functional role of the hyaluronidase toxin as a spreading factor in loxoscelism has also been demonstrated. However, the biological characterization of other toxins remains unclear and the mechanism by which Loxosceles toxins exert their noxious effects is yet to be fully elucidated. The aim of this review is to provide an insight into brown spider venom toxins and toxicology, including a description of historical data already available in the literature. In this review article, the identification processes of novel Loxosceles toxins by molecular biology and proteomic approaches, their biological characterization and structural description based on x-ray crystallography and putative biotechnological uses are described along with the future perspectives in this field.

Protective antibodies against a sphingomyelinase D from Loxosceles intermedia spider venom elicited in mice with different genetic background

In the present investigation we used a recombinant LiD1 toxin, named rLiD1his, from Loxosceles intermedia brown spider to elicit specific antibodies in mice carrying different Human Leukocyte Antigens class II (HLAII) {DRB1.0401 (DR4), DQB1.0601 (DQ6) and DQB1.0302 (DQ8)} as well as in BALB/C and C57BL/6 control mice. All mice strains produced high antibody titers against rLiD1his but DR4 mice antibodies (the lower responder mice) were not able to recognize L. intermedia crude venom. The anti-rLiD1his sera, except from DR4 mice, were able to neutralize dermonecrotic, hemorrhagic and edematogenic effects of rLiD1his in naïve rabbits. Overlapping peptides from the amino acid sequence of LiD1 toxin were prepared by SPOT method and differences in LiD1 epitope recognition were observed using different mice anti-rLiD1his sera. The region (160)DKVGHDFSGNDDISDVGK(177) was recognized by transgenic DQ8 and DQ6 mice sera. Other epitopes were recognized by at least two different animals' sera including (10)MGHMVNAIGQIDEFVNLG(27), (37)FDDNANPEYTYHGIP(51), (70)GLRSATTPGNSKYQEKLV(87) and (259)AAYKKKFRVATYDDN(273). Among these epitopes, the epitopes 37-51 and 160-177 have already been shown in previously studies as good candidates to be used alone or combined with other peptides to induce protective immune response against Loxosceles venoms. The results presented here highlight the importance of HLAII in antibody response and recognition of specific B-cell epitopes of rLiD1his spider toxin according to HLAII type and impact in the epitopic vaccine development against this spider.

General characterization of Tityus fasciolatus scorpion venom. Molecular identification of toxins and localization of linear B-cell epitopes

This communication describes the general characteristics of the venom from the Brazilian scorpion Tityus fasciolatus, which is an endemic species found in the central Brazil (States of Goiás and Minas Gerais), being responsible for sting accidents in this area. The soluble venom obtained from this scorpion is toxic to mice being the LD50 is 2.984 mg/kg (subcutaneally). SDS-PAGE of the soluble venom resulted in 10 fractions ranged in size from 6 to 10-80 kDa. Sheep were employed for anti-T. fasciolatus venom serum production. Western blotting analysis showed that most of these venom proteins are immunogenic. T. fasciolatus anti-venom revealed consistent cross-reactivity with venom antigens from Tityus serrulatus. Using known primers for T. serrulatus toxins, we have identified three toxins sequences from T. fasciolatus venom. Linear epitopes of these toxins were localized and fifty-five overlapping pentadecapeptides covering complete amino acid sequence of the three toxins were synthesized in cellulose membrane (spot-synthesis technique). The epitopes were located on the 3D structures and some important residues for structure/function were identified.

Synthetic peptides for in vitro evaluation of the neutralizing potency of Loxosceles antivenoms

An important step in the development of therapeutic antivenoms is the pre-clinical testing using in vivo methods to assess their neutralizing potency. For spider antivenoms (Loxosceles species), horse serum potency against the necrotizing activities of Loxosceles intermedia crude venom is currently tested in rabbits. These procedures are time consuming and involve a large number of animals. The aim of this study was to develop an in vitro method to assess the neutralizing potency of anti-Loxosceles sera. We first demonstrated that it was not possible to establish a correlation between the ELISA antibody reactivity of horse anti-Loxosceles serum and their neutralizing potency. We then showed that the antivenoms recognized several peptide epitopes from different regions of SMase-D proteins, which are toxic antigens from Loxosceles venoms. The recognition of some peptides was observed only when high neutralizing potency sera was used. Based on these results, three peptides (peptide 1, DNRRPIWNLAHMVNA and peptide 3, DFSGPYLPSLPTLDA corresponding to residues 2-16 and 164-178, respectively, of SMase-1 protein from Loxosceles laeta, and peptide 2, EFVNLGANSIETDVS corresponding to residues 22-36 of A1H - LoxGa protein from Loxosceles gaucho and LiD1 protein from L. intermedia) were selected. The peptides were synthesized, coupled to bovine serum albumin (BSA), and used as antigens in indirect ELISA to test their reactivity with horse anti-Loxosceles serum of varying neutralizing potencies. We found certain assay conditions that discriminated between the high and low neutralizing potency sera. This study introduced an in vitro and peptide-based neutralization assay for anti-Loxosceles antivenoms.

Generation and characterization of a recombinant chimeric protein (rCpLi) consisting of B-cell epitopes of a dermonecrotic protein from Loxosceles intermedia spider venom

A chimeric protein was constructed expressing three epitopes of LiD1, a dermonecrotic toxin from the venom of Loxosceles intermedia spider. This species is responsible for a large number of accidents involving spiders in Brazil. We demonstrated that the chimeric protein (rCpLi) generated is atoxic and that antibodies previously developed in rabbits against synthetic epitopes reactive with rCpLi in ELISA and immunoblot assays. The antibody response in rabbits against the rCpLi was evaluated by ELISA and we have detected an antibody response in all immunized animals. Overlapping peptides covering the amino acid sequence of the rCpLi were synthesized on a cellulose membrane, and their recognition by rabbit anti-rCpLi serum assessed. Three different antigenic regions were identified. The percentage of inhibition of the dermonecrotic, hemorrhagic and edematogenic activities caused by the recombinant protein LiD1r in naïve rabbits was assessed by pre-incubation with anti-rCpLi antibodies. Anti-rCpLi induced good dermonecrotic and hemorrhagic protection. The levels of protection were similar to the antiboides anti-LiD1r. In summary, we have developed a polyepitope recombinant chimeric protein capable of inducing multiple responses of neutralizing antibodies in a rabbit model. This engineered protein may be a promising candidate for therapeutic serum development or vaccination.

Biochemical and immunological characteristics of Peruvian Loxosceles laeta spider venom: neutralization of its toxic effects by anti-loxoscelic antivenoms

This manuscript describes the general biochemical properties and immunological characteristics of Peruvian spider Loxosceles laeta venom (PLlv), which is responsible for the largest number of accidents involving venomous animals in Peru. In this work, we observed that the venom of this spider is more lethal to mice when compared with L. laeta venom from Brazil (BLlv). The LD₅₀ of PLlv was 1.213 mg/kg when the venom was intradermally injected. The venom displayed sphingomyelinase activity and produced dermonecrotic, hemorrhagic and edema effects in rabbits. 2-D SDS-PAGE separation of the soluble venoms resulted in a protein profile ranging from 20 to 205 kDa. Anti-PLlv and anti-BLlv sera produced in rabbits and assayed by ELISA showed that rabbit antibodies cross-reacted with PLlv and BLlv and also with other Brazilian Loxosceles venoms. Western blotting analysis showed that bands corresponding to 25-35 kDa are the proteins best recognized in every Loxosceles spp venoms analyzed. The immunized rabbits displayed protective effect after challenge with PLlv and BLlv. In vitro assays with horse anti-loxoscelic antivenoms produced in Brazil and Peru demonstrated that these commercial antivenoms were efficient to inhibit the sphingomyelinase activity of PLlv and BLlv.

Identification of linear B-cell epitopes on myotoxin II, a Lys49 phospholipase A₂ homologue from Bothrops asper snake venom

Knowledge on toxin immunogenicity at the molecular level can provide valuable information for the improvement of antivenoms, as well as for understanding toxin structure-function relationships. The aims of this study are two-fold: first, to identify the linear B-cell epitopes of myotoxin II from Bothrops asper snake venom, a Lys49 phospholipase A₂ homologue; and second, to use antibodies specifically directed against an epitope having functional relevance in its toxicity, to probe the dimeric assembly mode of this protein in solution. Linear B-cell epitopes were identified using a library of overlapping synthetic peptides spanning its complete sequence. Epitopes recognized by a rabbit antiserum to purified myotoxin II, and by three batches of a polyvalent (Crotalidae) therapeutic antivenom (prepared in horses immunized with a mixture of B. asper, Crotalus simus, and Lachesis stenophrys venoms) were mapped using an enzyme-immunoassay based on the capture of biotinylated peptides by immobilized streptavidin. Some of the epitopes identified were shared between the two species, whereas others were unique. Differences in epitope recognition were observed not only between the two species, but also within the three batches of equine antivenom. Epitope V, located at the C-terminal region of this protein, is known to be relevant for toxicity and neutralization. Affinity-purified rabbit antibodies specific for this site were able to immunoprecipitate myotoxin II, suggesting that the two copies of epitope V are simultaneously available to antibody binding, which would be compatible with the mode of dimerization known as "conventional" dimer.

Cutaneous loxoscelism caused by Loxosceles similis venom and neutralization capacity of its specific antivenom

Members of the spider genus Loxosceles pose a marked health risk to humans because of the seriousness of the necrotic and systemic effects of their bite, known as loxoscelism. The recent confirmation of Loxosceles similis in residences of Belo Horizonte in Minas Gerais Province, Brazil increases the local potential risk of loxoscelism at higher levels. The first characterization of the venom from this species showed that its main biological effects had a similar intensity as other species (e.g. Loxosceles intermedia, Loxosceles laeta, and Loxosceles gaucho). Therefore, we wished to further analyse the biological activity of the L. similis venom as well as the capacity of anti-L. similis-venom serum to reduce dermonecrotic effects to rabbit skin. Histological analysis of rabbit skin 2, 4 and 8h after intradermal injection of L. similis venom demonstrated a dense inflammatory infiltrate, edema, degeneration and necrosis of the skin muscle, dissociation of collagen fibers, and disruption of reticular fibers. Importantly, pre-incubation of the venom with anti-L. similis-venom serum significantly decreased all of these effects. Anti-L. similis antivenom generated antibodies that were strongly reactive to L. similis venom and capable of neutralizing the dermonecrotic effects in rabbits caused by this venom. Moreover, the antivenom significantly reduced the sphingomyelinase activity of L. similis crude venom. Venoms produced by male and female spiders were equally reactive towards anti-L. similis and anti-L. intermedia antivenoms, but female venom induced larger lesions on rabbits. In contrast, female venom acted as an immunization enhancer and protected animals from L. similis envenomation to a greater degree than male venom. In conclusion, the results shown in this study for L. similis antivenom merits a more in depth study of its properties, which may become a valuable tool against loxoscelism.

Protection against the toxic effects of Loxosceles intermedia spider venom elicited by mimotope peptides

The venom of Loxosceles intermedia (Li) spiders is responsible for cutaneous lesions and other clinical manifestations. We previously reported that the monoclonal antibody LimAb7 can neutralize the dermonecrotic activity of crude Li venom. In this study, we observed that this antibody recognizes several proteins from the venom dermonecrotic fraction (DNF), including LiD1. Identifying the epitope of such a neutralizing antibody could help designing immunogens for producing therapeutic sera or vaccination approaches. To this aim, two sets of 25- and 15-mer overlapping peptides that cover the complete amino acid sequence of LiD1 were synthesized using the SPOT technique. None of them was recognized by LimAb7, suggesting that the epitope is discontinuous. Then, the screening of four peptide phage-display libraries yielded four possible epitope mimics that, however, did not show any obvious similarity with the LiD1 sequence. These mimotopes, together with a 3D model of LiD1, were used to predict with the MIMOP bioinformatic tool the putative epitope region (residues C197, Y224, W225, T226, D228, K229, R230, T232 and Y248 of LiD1) recognized by LimAb7. This analysis and the results of alanine-scanning experiments highlighted a few residues (such as W225 and D228) that are found in the active site of different SMases D and that may be important for LiD1 enzymatic activity. Finally, the only mimotope NCNKNDHLFACW that interacts with LimAb7 by SPOT and its analog NSNKNDHLFASW were used as immunogens in rabbits. The resulting antibodies could neutralize some of the biological effects induced by crude Li venom, demonstrating a mimotope-induced protection against L. intermedia venom.

Mimotopes of mutalysin-II from Lachesis muta snake venom induce hemorrhage inhibitory antibodies upon vaccination of rabbits

Mutalysin-II (mut-II) from Lachesis muta snake venom is an endopeptidase with hemorrhagic activity. A mAb against mutalysin-II that neutralized the hemorrhagic effect was produced previously. To identify the mAb epitopes, sets of 15-mer overlapping peptides covering the mut-II amino acid sequence were synthesized using the SPOT method and tested but failed to react with the mAb. Using a phage-display approach seventeen clones reactive with mAb were identified. Additional immunoassays with the peptides and mAb identified the QCTMDQGRLRCR, TCATDQGRLRCT, HCFHDQGRVRCA, HCTMDQGRLRCR and SCMLDQGRSRCR sequences as possible epitopes. Immunization of rabbits with these peptides induced antibodies that recognize mut-II and protected against the hemorrhagic effects of Lachesis venom.

Brown spider (Loxosceles genus) venom toxins: tools for biological purposes

Venomous animals use their venoms as tools for defense or predation. These venoms are complex mixtures, mainly enriched of proteic toxins or peptides with several, and different, biological activities. In general, spider venom is rich in biologically active molecules that are useful in experimental protocols for pharmacology, biochemistry, cell biology and immunology, as well as putative tools for biotechnology and industries. Spider venoms have recently garnered much attention from several research groups worldwide. Brown spider (Loxosceles genus) venom is enriched in low molecular mass proteins (5–40 kDa). Although their venom is produced in minute volumes (a few microliters), and contain only tens of micrograms of protein, the use of techniques based on molecular biology and proteomic analysis has afforded rational projects in the area and permitted the discovery and identification of a great number of novel toxins. The brown spider phospholipase-D family is undoubtedly the most investigated and characterized, although other important toxins, such as low molecular mass insecticidal peptides, metalloproteases and hyaluronidases have also been identified and featured in literature. The molecular pathways of the action of these toxins have been reported and brought new insights in the field of biotechnology. Herein, we shall see how recent reports describing discoveries in the area of brown spider venom have expanded biotechnological uses of molecules identified in these venoms, with special emphasis on the construction of a cDNA library for venom glands, transcriptome analysis, proteomic projects, recombinant expression of different proteic toxins, and finally structural descriptions based on crystallography of toxins.

Cardiotoxic effects of Loxosceles intermedia spider venom and the recombinant venom toxin rLiD1

Loxosceles spider bites cause many human injuries worldwide. Injections in mice of whole Loxosceles (L.) intermedia venom or a recombinant toxin (rLiD1) produce systemic symptoms similar to those detected in envenomed humans. This animal model was used to characterize the effects of Loxosceles intermedia venom in cardiac tissues. L. intermedia antigens were detected by ELISA in kidney, heart, lung and liver of experimentally envenomed mice. In addition, rLiD1 binding to cardiomyocytes was demonstrated by immunofluorescence and confocal microscopy. Furthermore, isolated perfused heart preparations and ventricular cardiomyocytes from envenomed mice showed heart function impairment, and a significant increase of I(Ca,L) density and intracellular Ca(2+) transients, respectively. Thus, L. intermedia spider venom, as shown through the use of the recombinant toxin rLiD1, causes cardiotoxic effects and a protein from the sphingomyelinase D family plays a key role in heart dysfunction. Thus, L. intermedia spider venom and the Loxtox rLiD1 play a key role in heart dysfunction.