Enzymatic characterization, antigenic cross-reactivity and neutralization of dermonecrotic activity of five Loxosceles spider venoms of medical importance in the Americas

Partial characterization of Loxosceles anomala (Mello-Leitão, 1917) venom: A brown spider of potential medical concern

The spider's genus Loxosceles (also known as "brown spiders") is one of the few ones of medical importance in Brazil, being Loxosceles anomala a species of common occurrence in the Southeast region. This species is usually smaller in size than the other members of the Loxosceles group. A single human accident involving L. anomala was reported to date and the clinical picture shared similar characteristics with accidents caused by other Loxosceles species. Despite the potential relevance of L. anomalafor loxocelism in Minas Gerais state, its venom activity has never been characterized. In this work, we provide a preliminary characterization of L. anomala venom, considering its most relevant enzymatic activities and its venom immunorecognition by current therapeutic antivenoms. The results showed that L. anomala venom is immunorecognised by therapeutic antivenoms and by anti-phospholipase D antibodies. Its venom also shows enzymatic activities (sphingomyelinase activity, fibrinogenolytic) described for other Loxosceles venoms. This work contributes to a better knowledge on the venom content and activities of synanthropic Loxosceles species that have the potential of causing relevant human accidents.

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.

Transcriptomic Analysis of the Venom Gland and Enzymatic Characterization of the Venom of Phoneutria depilata (Ctenidae) from Colombia

The transcriptome of the venom glands of the Phoneutria depilata spider was analyzed using RNA-seq with an Illumina protocol, which yielded 86,424 assembled transcripts. A total of 682 transcripts were identified as potentially coding for venom components. Most of the transcripts found were neurotoxins (156) that commonly act on sodium and calcium channels. Nevertheless, transcripts coding for some enzymes (239), growth factors (48), clotting factors (6), and a diuretic hormone (1) were found, which have not been described in this spider genus. Furthermore, an enzymatic characterization of the venom of P. depilata was performed, and the proteomic analysis showed a correlation between active protein bands and protein sequences found in the transcriptome. The transcriptomic analysis of P. depilata venom glands show a deeper description of its protein components, allowing the identification of novel molecules that could lead to the treatment of human diseases, or could be models for developing bioinsecticides.

Evaluation of mesenchymal cells and dapsone for the treatment of dermonecrotic wounds caused by Loxosceles laeta venom in rabbits

Abstract This study aimed to evaluate the efficacy of mesenchymal stem cells (MSC), alone or associated with dapsone (DAP), in treating dermonecrotic wounds caused by Loxosceles laeta venom. Twenty-five male rabbits were distributed into five groups. Negative control received ultrapure water (C-), whilst all other groups were injected with 20 μg of L. laeta venom. After 4 hours, each group received one of the following treatments: PBS (C+), DAP, MSC, and DAP+MSC. Animals were evaluated daily and photographic records made for analysis of wound area. Twelve days after, animals were euthanized and skin samples removed for histological analysis. We observed that DAP showed the best percentage of wound contraction at day 3. In the treatments using MSCs, a negative value of wound contraction was observed for the isolated MSCs, as well as a lower contraction value for the association of the MSC + DAP when compared to PBS, probably, by the increase in initial infammation after the application of stem cells, due to the fact that MSCs secrete a broad spectrum of bioactive molecules such as cytokines and growth factors that favor regeneration. Histologically, it was observed that animals of C+ showed extensive areas of necrosis, ulcers, neutrophilic infiltrate, and mineralization. Collagen deposition showed increase in MSC+DAP treatment, however vascularization remained unchanged. This is the first report using MSC and MSC+DAP as a treatment for cutaneous loxoscelism and more studies are needed to determine its use as an alternative therapy for dermonecrotic lesions caused by Loxosceles spider.

Avaliação de células mesenquimais e dapsona para o tratamento de feridas dermonecróticas causadas pelo veneno de Loxosceles laeta em coelhos

Resumo Este estudo teve como objetivo avaliar a eficácia das células-tronco mesenquimais (CTMs), isoladas ou associadas à dapsona (DAP), no tratamento de feridas dermonecróticas causadas pelo veneno de Loxosceles laeta. Vinte e cinco coelhos machos foram distribuídos em cinco grupos. O controle negativo recebeu água ultrapura (C-), enquanto todos os outros grupos foram injetados com 20 μg de veneno de L. laeta. Após 4 horas, cada grupo recebeu um dos seguintes tratamentos: PBS (C+), DAP, CTMs e DAP + CTMs. Os animais foram avaliados diariamente durante 12 dias, e feitos registros fotográficos para análise da ferida e no 12º dia, foram eutanasiados e, retiradas amostras de pele para análise histológica. Observou-se que a DAP apresentou o melhor percentual de contração da ferida no terceiro dia. Nos tratamentos com CTMs, observou-se uma contração negativa da ferida tanto para as CTMs isoladas, bem como a associação CTMs + DAP em relação ao PBS, possivelmente, pelo aumento da infamação inicial após a aplicação de células-tronco. Isso é devido ao fato de que as CTMs secretam um amplo espectro de moléculas bioativas como citocinas e fatores de crescimento que favorecem a regeneração. Histologicamente, observou-se que os animais de C+ apresentaram extensas áreas de necrose, úlceras, infiltrado neutrofílico, além de mineralização. Houve aumento de deposição de colágeno no tratamento CTMs + DAP, no entanto, a vascularização permaneceu inalterada. Este é o primeiro relato usando CTMs e CTMs + DAP como tratamento para loxoscelismo cutâneo e mais estudos são necessários para determinar seu uso como terapia alternativa para lesões demonecróticas causadas pela aranha Loxosceles.

Brown spider venom toxins: what are the functions of astacins, serine proteases, hyaluronidases, allergens, TCTP, serpins and knottins?

Accidents caused by the bites of brown spiders (Loxosceles) generate a clinical condition that often includes a threatening necrotic skin lesion near the bite site along with a remarkable inflammatory response. Systemic disorders such as hemolysis, thrombocytopenia, and acute renal failure may occur, but are much less frequent than the local damage. It is already known that phospholipases D, highly expressed toxins in Loxosceles venom, can induce most of these injuries. However, this spider venom has a great range of toxins that probably act synergistically to enhance toxicity. The other protein classes remain poorly explored due to the difficulty in obtaining sufficient amounts of them for a thorough investigation. They include astacins (metalloproteases), serine proteases, knottins, translationally controlled tumor proteins (TCTP), hyaluronidases, allergens and serpins. It has already been shown that some of them, according to their characteristics, may participate to some extent in the development of loxoscelism. In addition, all of these toxins present potential application in several areas. The present review article summarizes information regarding some functional aspects of the protein classes listed above, discusses the directions that could be taken to materialize a comprehensive investigation on each of these toxins as well as highlights the importance of exploring the full venom repertoire.

Prospective Use of Brown Spider Venom Toxins as Therapeutic and Biotechnological Inputs

Brown spider (genus Loxosceles) venoms are mainly composed of protein toxins used for predation and defense. Bites of these spiders most commonly produce a local dermonecrotic lesion with gravitational spread, edema and hemorrhage, which together are defined as cutaneous loxoscelism. Systemic loxoscelism, such as hematological abnormalities and renal injury, are less frequent but more lethal. Some Loxosceles venom toxins have already been isolated and extensively studied, such as phospholipases D (PLDs), which have been recombinantly expressed and were proven to reproduce toxic activities associated to the whole venom. PLDs have a notable potential to be engineered and converted in non-toxic antigens to produce a new generation of antivenoms or vaccines. PLDs also can serve as tools to discover inhibitors to be used as therapeutic agents. Other Loxosceles toxins have been identified and functionally characterized, such as hyaluronidases, allergen factor, serpin, TCTP and knottins (ICK peptides). All these toxins were produced as recombinant molecules and are biologically active molecules that can be used as tools for the potential development of chemical candidates to tackle many medical and biological threats, acting, for instance, as antitumoral, insecticides, analgesic, antigens for allergy tests and biochemical reagents for cell studies. In addition, these recombinant toxins may be useful to develop a rational therapy for loxoscelism. This review summarizes the main candidates for the development of drugs and biotechnological inputs that have been described in Brown spider venoms.

Production of a novel recombinant brown spider hyaluronidase in baculovirus-infected insect cells

Hyaluronidases are low expressed toxins of brown spider venoms, but, as highly active molecules, they present an important role as spreading factors. By degrading extracellular matrix components, these enzymes favor the diffusion of toxins in the affected tissue and at systemic level. Here, a novel isoform of hyaluronidase of Loxosceles intermedia Mello-Leitão (1934) venom was cloned, expressed in a baculovirus-insect cell expression system and fully active purified. This recombinant enzyme, named LiHyal2 (Loxosceles intermedia Hyaluronidase isoform 2), shares high identity with hyaluronidases of other spiders and scorpions. The catalytic and sugar binding amino acid residues are conserved in LiHyal2, human, and honeybee venom hyaluronidases and the molecular model of LiHyal2 shares major similarities with their crystal structures, including the active site. LiHyal2 was expressed as a 45 kDa protein and degraded hyaluronic acid (HA) and chondroitin sulphate as demonstrated by HA zymography and agarose gel electrophoresis. Lectin blot analysis revealed that LiHyal2 is post-translationally modified by the addition of high mannose N-linked carbohydrates. In vivo experiments showed that LiHyal2 potentialize dermonecrosis and edema induced by a recombinant phospholipase-D (PLD) of L. intermedia venom, as well as enhance the increase in capillary permeability triggered by this PLD, indicating that these toxins act synergistically during envenomation. Altogether, these results introduce a novel approach to express spider recombinant toxins, contribute to the elucidation of brown spider venom mechanisms and add to the development of a more specific treatment of envenomation victims.

Searching for the toxic potential of Loxosceles amazonica and Loxosceles willianilsoni spiders' venoms

The Loxosceles genus belongs to the Sicariidae family and it comprises species whose venom can cause accidents with potentially fatal consequences. We have previously shown that SMase D is the enzyme responsible for the main pathological effects of Loxosceles venom. Despite the severity of accidents with Loxosceles, few species are considered to be of medical importance. Little is known about the venom of non-synanthropic species that live in natural environments. To contribute to a better understanding about the venom's toxicity of Loxosceles genus, the aim of this study was to (i) characterize the toxic properties of Loxosceles amazonica from two different localities and a recent described cave species Loxosceles willianilsoni and (ii) compare these venoms with that from Loxosceles laeta, which is among the most toxic ones. We show here that both L. amazonica venoms (from the two studied locations) and L. willianilsoni presented SMase D activity similar to that exhibited by L. laeta venom. Although L. amazonica and L. willianilsoni venoms were able to induce complement dependent human erythrocytes lysis, they were not able to induce cell death of human keratinocytes, as promoted by L. laeta venom, in the concentrations tested. These results indicate that other species of Loxosceles, in addition to those classified as medically important, have toxic potential to cause accidents in humans, despite interspecific variations that denote possible less toxicity.

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.

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.

Diversity of astacin-like metalloproteases identified by transcriptomic analysis in Peruvian Loxosceles laeta spider venom and in vitro activity characterization

Loxosceles spiders are found in almost all countries of South America. In Peru, Loxosceles laeta species is the main responsible for the accidents caused by poisonous animals, being known as "killer spiders", due to the large number of fatal accidents observed. Astacin-like metalloproteases, named LALPs (Loxosceles astacin-like metalloproteases) are highly expressed in Loxosceles spiders venom gland. These proteases may be involved in hemorrhage and venom spreading, being relevant to the envenoming proccess. Thus, the aim of this work was to analyze Peruvian L. laeta venom gland transcripts using bioinformatics tools, focusing on LALPs. A cDNA library from Peruvian L. laeta venom glands was constructed and sequenced by MiSeq (Illumina) sequencer. After assembly, the resulting sequences were annotated, seeking out for similarity with previously described LALPs. Nine possible LALPs isoforms from Peruvian L. laeta venom were identified and the results were validated by in silico and in vitro experiments. This study contributes to a better understanding of the molecular diversity of Loxosceles venom and provide insights about the action of LALPs.

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.

Acanthocytosis and brain damage in area postrema and choroid plexus: Description of novel signs of Loxosceles apachea envenomation in rats

Loxocelism is a neglected medical problem that depends on its severity, can cause a cutaneous or viscero-cutaneous syndrome. This syndrome is characterized by hemostatic effects and necrosis, and the severity of the loxoscelism depends on the amount of venom injected, the zone of inoculation, and the species. In the Chihuahuan desert, the most abundant species is L. apachea. Its venom and biological effects are understudied, including neurological effects. Thus, our aim is to explore the effect of this regional species of medical interest in the United States-Mexico border community, using rat blood and central nervous system (CNS), particularly, two brain structures involved in brain homeostasis, Area postrema (AP) and Choroid plexus (PC). L. apachea specimens were collected and venom was obtained. Different venom concentrations (0, 0.178 and 0.87 μg/g) were inoculated into Sprague-Dawley rats (intraperitoneal injection). Subsequently, blood was extracted and stained with Wright staining; coronal sections of AP were obtained and stained with Hematoxylin-Eosin (HE) staining and laminin γ immunolabelling, the same was done with CP sections. Blood, AP and CP were observed under the microscope and abnormalities in erythrocytes and fluctuation in leukocyte types were described and quantified in blood. Capillaries were also quantified in AP and damage was described in CP. L. apachea venom produced a segmented neutrophil increment (neutrophilia), lymphocyte diminishment (leukopenia) and erythrocytes presented membrane abnormalities (acanthocytosis). Extravasated erythrocytes were observed in HE stained sections from both, AP and CP, which suggest that near to this section a hemorrhage is present; through immunohistofluorescence, a diminishment of laminin γ was observed in AP endothelial cells and in CP ependymal cells when these structures were exposed to L. apachea venom. In conclusion, L. apachea venom produced leukopenia, netrophilia and acanthocytosis in rat peripheral blood, and also generated hemorrhages on AP and CP through degradation of laminin γ.

Loxosceles gaucho Spider Venom: An Untapped Source of Antimicrobial Agents

The remarkable ability of microorganisms to develop resistance to conventional antibiotics is one of the biggest challenges that the pharmaceutical industry currently faces. Recent studies suggest that antimicrobial peptides discovered in spider venoms may be useful resources for the design of structurally new anti-infective agents effective against drug-resistant microorganisms. In this work, we found an anionic antibacterial peptide named U₁-SCRTX-Lg1a in the venom of the spider Loxosceles gaucho. The peptide was purified using high-performance liquid chromatography (HPLC), its antimicrobial activity was tested through liquid growth inhibition assays, and its chemical properties were characterized using mass spectrometry. U₁-SCRTX-Lg1a was found to show a monoisotopic mass of 1695.75 Da, activity against Gram-negative bacteria, a lack of hemolytic effects against human red blood cells, and a lack of cytotoxicity against human cervical carcinoma cells (HeLa). Besides this, the sequence of the peptide exhibited great similarity to specific regions of phospholipases D from different species of Loxosceles spiders, leading to the hypothesis that U₁-SCRTX-Lg1a may have originated from a limited proteolytic cleavage. Our data suggest that U₁-SCRTX-Lg1a is a promising candidate for the development of new antibiotics that could help fight bacterial infections and represents an exciting discovery for Loxosceles spiders.

Morphological and biochemical characterization of the cutaneous poison glands in toads (Rhinella marina group) from different environments

Background

Amphibian defence against predators and microorganisms is directly related to cutaneous glands that produce a huge number of different toxins. These glands are distributed throughout the body but can form accumulations in specific regions. When grouped in low numbers, poison glands form structures similar to warts, quite common in the dorsal skin of bufonids (toads). When accumulated in large numbers, the glands constitute protuberant structures known as macroglands, among which the parotoids are the most common ones. This work aimed at the morphological and biochemical characterization of the poison glands composing different glandular accumulations in four species of toads belonging to group Rhinella marina (R. icterica, R. marina, R. schneideri and R. jimi). These species constitute a good model since they possess other glandular accumulations together with the dorsal warts and the parotoids and inhabit environments with different degrees of water availability.

Results

We have observed that the toads skin has three types of poison glands that can be differentiated from each other through the morphology and the chemical content of their secretion product. The distribution of these different glands throughout the body is peculiar to each toad species, except for the parotoids and the other macroglands, which are composed of an exclusive gland type that is usually different from that composing the dorsal warts. Each type of poison gland presents histochemical and biochemical peculiarities, mainly regarding protein components.

Conclusions

The distribution, morphology and chemical composition of the different types of poison glands, indicate that they may have different defensive functions in each toad species.

The potential of Loxosceles gaucho spider venom to regulate Pseudomonas aeruginosa mechanisms of virulence

Loxosceles venom is a potential source of bioactive molecules which may be transformed into antimicrobial products against multi-resistant bacteria. Here, it was investigated whether Loxosceles gaucho spider had any influence on the proliferation, enzyme release and biofilm formation of a Pseudomonas aeruginosa strain resistant to two different classes of antibiotic. The results demonstrated that L. gaucho whole venom has no influence on P. aeruginosa proliferation. However, it increases P. aeruginosa production of gelatinase, caseinase and biofilm formation. The same effects were noted when P. aeruginosa was exposed to a L. gaucho venom molecular fraction with mass lower than 1 kDa. Separation of this molecular fraction into different subsets by RP-HPLC demonstrated that, among the molecules with the ability to increase the production of enzymes and biofilm formation, there are some with antimicrobial activities whose effects are not observed in the whole venom. In summary, the results obtained herein indicate that L. gaucho venom has a variety of low molecular mass bioactive components that influence the mechanisms of virulence of P. aeruginosa in different ways.

Recombinant Protein Containing B-Cell Epitopes of Different Loxosceles Spider Toxins Generates Neutralizing Antibodies in Immunized Rabbits

Loxoscelism is the most important form of araneism in South America. The treatment of these accidents uses heterologous antivenoms obtained from immunization of production animals with crude loxoscelic venom. Due to the scarcity of this immunogen, new alternatives for its substitution in antivenom production are of medical interest. In the present work, three linear epitopes for Loxosceles astacin-like protease 1 (LALP-1) (SLGRGCTDFGTILHE, ENNTRTIGPFDYDSIMLYGAY, and KLYKCPPVNPYPGGIRPYVNV) and two for hyaluronidase (LiHYAL) (NGGIPQLGDLKAHLEKSAVDI and ILDKSATGLRIIDWEAWR) from Loxosceles intermedia spider venom were identified by SPOT-synthesis technique. One formerly characterized linear epitope (DFSGPYLPSLPTLDA) of sphingomyelinase D (SMase D) SMase-I from Loxosceles laeta was also chosen to constitute a new recombinant multiepitopic protein. These epitopes were combined with a previously produced chimeric multiepitopic protein (rCpLi) composed by linear and conformational B-cell epitopes from SMase D from L. intermedia venom, generating a new recombinant multiepitopic protein derived from loxoscelic toxins (rMEPLox). We demonstrated that rMEPLox is non-toxic and antibodies elicited in rabbits against this antigen present reactivity in ELISA and immunoblot assays with Brazilian L. intermedia, L. laeta, L. gaucho, and L. similis spider venoms. In vivo and in vitro neutralization assays showed that anti-rMEPLox antibodies can efficiently neutralize the sphingomyelinase, hyaluronidase, and metalloproteinase activity of L. intermedia venom. This study suggests that this multiepitopic protein can be a suitable candidate for experimental vaccination approaches or for antivenom production against Loxosceles spp. venoms.

Recombinant Phospholipase D from Loxosceles gaucho Binds to Platelets and Promotes Phosphatidylserine Exposure

Spider envenomation, from the genus Loxosceles, is frequently reported as a cause of necrotic lesions in humans around the world. Among the many components found in the venom of Loxosceles genus, phospholipases D (PLDs) are the most investigated, since they can cause a massive inflammatory response, dermonecrosis, hemolysis and platelet aggregation, among other effects. Even though the PLDs induce strong platelet aggregation, there are no studies showing how the PLDs interact with platelets to promote this effect. Since many agonists must interact with specific receptors on the platelet membrane to induce aggregation, it is reasonable to expect that the PLDs may, in some way, also interact with platelets, to induce this activity. Therefore, to address this possibility, in this work, a recombinant PLD, called LgRec1, from L. gaucho was fused to enhanced green fluorescent protein (EGFP) and used as a probe to detect the interaction of LgRec1 to platelets, by fluorescence-activated cell sorter (FACS) and confocal microscopy. The preservation of biological activities of this chimera toxin was also analyzed. As a first, the results show that LgRec1 does not require plasma components to bind to platelets, although these components are necessary to LgRec1 to induce platelet aggregation. Also, the attachment of LgRec1 to human platelets’ cell membranes suggests that the exposure of phosphatidylserine (PS) may act as a scaffold for coagulation factors. Therefore, the results add new information about the binding of Loxosceles PLDs to platelets, which may help unravel how these toxins promote platelet aggregation.

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.

Description of Loxtox protein family and identification of a new group of Phospholipases D from Loxosceles similis venom gland

Envenoming resulting from Loxosceles spider bites (loxoscelism) is a recognized public health problem in Brazil. However, the pathophysiology of loxoscelism caused by L. similis bites, which is widespread in Brazil, remains poorly understood. In the present work, the RNA sequencing (RNA-Seq - Next Generation sequencing - NGS) of the L. similis venom gland was performed to identify and analyze the sequences of the key component phospholipase D. The sequences were aligned based on their classical domains, and a phylogenetic tree was constructed. In the bioinformatics analysis, 23 complete sequences of phospholipase D proteins were found and classified as Loxtox proteins, as they contained the characteristic domains of phospholipase D: the active site, the Mg(2+)-binding domain, and the catalytic loop. Three phospholipase D sequences with non-canonical domains were also found in this work. They were analyzed separately and named PLDs from L. similis (PLD-Ls). This study is the first to characterize phospholipase D sequences from Loxosceles spiders by RNA-Seq. These results contribute new knowledge about the composition of L. similis venom, revealing novel tools that could be used for pharmacological, immunological, and biotechnological applications.

Biochemical and biological characterization of Bothriechis schlegelii snake venoms from Colombia and Costa Rica

Snakebites inflicted by the arboreal viperid snake Bothriechis schlegelii in humans are characterized by pain, edema, and ecchymosis at the site of the bite, rarely with blisters, local necrosis, or defibrination. Herein, a comparative study of Bothriechis schlegelii snake venoms from Colombia (BsCo) and Costa Rica (BsCR) was carried out in order to compare their main activities and to verify the efficacy of Bothrops antivenom produced in Brazil to neutralize them. Biochemical (SDS-PAGE and zymography) and biological parameters (edematogenic, lethal, hemorrhagic, nociceptive, and phospholipase A₂ activities) induced by BsCo and BsCR snake venoms were evaluated. The presence of antibodies in Bothrops antivenom that recognize BsCo and BsCR snake venoms by enzyme-linked immunosorbent assay and Western blotting, as well as the ability of this antivenom to neutralize the toxic activities were also verified. SDS-PAGE showed differences between venoms. Distinctive caseinolytic and hyaluronidase patterns were detected by zymography. BsCo and BsCR showed similar phospholipase A₂ activity. Strong cross-reactivity between BsCo and BsCR was detected using Bothrops antivenom with many components located between 150 and 35 kDa. BsCR was more edematogenic and almost fourfold more hemorrhagic than BsCo, and both venoms induced nociception. BsCR (LD₅₀ 5.60 mg/kg) was more lethal to mice than BsCo (LD₅₀ 9.24 mg/kg). Bothrops antivenom was effective in the neutralization of lethal and hemorrhagic activities of BsCo and BsCR and was partially effective in the neutralization of edematogenic and nociceptive activities. In conclusion, geographic distribution influences the composition and activities of Bothriechis schlegelii venoms. Bothrops antivenom cross-reacted with these venoms and was partially effective in neutralizing some toxic activities of BsCo and BsCR.

Expression and immunological cross-reactivity of LALP3, a novel astacin-like metalloprotease from brown spider (Loxosceles intermedia) venom

Loxosceles spiders' venom comprises a complex mixture of biologically active toxins, mostly consisting of low molecular mass components (2-40 kDa). Amongst, isoforms of astacin-like metalloproteases were identified through transcriptome and proteome analyses. Only LALP1 (Loxosceles Astacin-Like protease 1) has been characterized. Herein, we characterized LALP3 as a novel recombinant astacin-like metalloprotease isoform from Loxosceles intermedia venom. LALP3 cDNA was cloned in pET-SUMO vector, and its soluble heterologous expression was performed using a SUMO tag added to LALP3 to achieve solubility in Escherichia coli SHuffle T7 Express LysY cells, which express the disulfide bond isomerase DsbC. Protein purification was conducted by Ni-NTA Agarose resin and assayed for purity by SDS-PAGE under reducing conditions. Immunoblotting analyses were performed with specific antibodies recognizing LALP1 and whole venom. Western blotting showed linear epitopes from recombinant LALP3 that cross-reacted with LALP1, and dot blotting revealed conformational epitopes with native venom astacins. Mass spectrometry analysis revealed that the recombinant expressed protein is an astacin-like metalloprotease from L. intermedia venom. Furthermore, molecular modeling of LALP3 revealed that this isoform contains the zinc binding and Met-turn motifs, forming the active site, as has been observed in astacins. These data confirmed that LALP3, which was successfully obtained by heterologous expression using a prokaryote system, is a new astacin-like metalloprotease isoform present in L. intermedia venom.

Arthropod venom Hyaluronidases: biochemical properties and potential applications in medicine and biotechnology

Hyaluronidases are enzymes that mainly degrade hyaluronan, the major glycosaminoglycan of the interstitial matrix. They are involved in several pathological and physiological activities including fertilization, wound healing, embryogenesis, angiogenesis, diffusion of toxins and drugs, metastasis, pneumonia, sepsis, bacteremia, meningitis, inflammation and allergy, among others. Hyaluronidases are widely distributed in nature and the enzymes from mammalian spermatozoa, lysosomes and animal venoms belong to the subclass EC 3.2.1.35. To date, only five three-dimensional structures for arthropod venom hyaluronidases (Apis mellifera and Vespula vulgaris) were determined. Additionally, there are four molecular models for hyaluronidases from Mesobuthus martensii, Polybia paulista and Tityus serrulatus venoms. These enzymes are employed as adjuvants to increase the absorption and dispersion of other drugs and have been used in various off-label clinical conditions to reduce tissue edema. Moreover, a PEGylated form of a recombinant human hyaluronidase is currently under clinical trials for the treatment of metastatic pancreatic cancer. This review focuses on the arthropod venom hyaluronidases and provides an overview of their biochemical properties, role in the envenoming, structure/activity relationship, and potential medical and biotechnological applications.

Platelet participation in the pathogenesis of dermonecrosis induced by Loxosceles gaucho venom

Loxosceles gaucho spider venom induces in vitro platelet activation and marked thrombocytopenia in rabbits. Herein, we investigated the involvement of platelets in the development of the dermonecrosis induced by L. gaucho venom, using thrombocytopenic rabbits as a model. L. gaucho venom evoked a drop in platelet and neutrophil counts 4 h after venom injection. Ecchymotic areas at the site of venom inoculation were noticed as soon as 4 h in thrombocytopenic animals but not in animals with initial normal platelet counts. After 5 days, areas of scars in thrombocytopenic animals were also larger, evidencing the marked development of lesions in the condition of thrombocytopenia. Histologically, local hemorrhage, collagen fiber disorganization, and edema were more severe in thrombocytopenic animals. Leukocyte infiltration, predominantly due to polymorphonuclears, was observed in the presence or not of thrombocytopenia. Thrombus formation was demonstrated by immunohistochemistry at the microvasculature, and it occurred even under marked thrombocytopenia. Taken together, platelets have an important role in minimizing not only the hemorrhagic phenomena but also the inflammatory and wound-healing processes, suggesting that cutaneous loxoscelism may be aggravated under thrombocytopenic conditions.

Pattern of inflammatory response to Loxosceles intermedia venom in distinct mouse strains: a key element to understand skin lesions and dermonecrosis by poisoning

Envenomation caused by spiders Loxosceles induce intense dermonecrosis at the bite site and systemic disease. In this work we described the hyaluronidase and collagenase activities in vitro of the Loxosceles intermedia venom, but no phospholipase A2 activity. In vivo, we evaluated the effect of L. intermedia venom used different strain of mice, C57BL/6, BALB/c and Swiss. All mice developed paw edema after venom injection, persistent for 24 h in BALB/c and C57BL/6 mice. Histopathological analysis of the skin after venom injection revealed vascular congestion in Swiss mice and an inflammatory reaction in BALB/c and C57BL/6 mice. The mobilization of inflammatory cells from bone marrow, spleen and blood was investigated. Typical innate immune response with mobilization of myeloid cells and cytotoxic CD8 T lymphocytes was observed in C57BL/6 mice. In contrast, typical acquired/humoral immune response was observed in BALB/c mice, with preferential involvement of conventional B lymphocytes and CD4 T helper cells. The skin inflammation associated to mobilization of inflammatory cells indicated that mice models are strongly recommended to investigate specific cell types involved with immune response to the envenomation and mechanisms to inhibit skin lesions.

Helminthes and insects: maladies or therapies

By definition, parasites cause harm to their hosts. But, considerable evidence from ancient traditional medicine has supported the theory of using parasites and their products in treating many diseases. Maggots have been used successfully to treat chronic, long-standing, infected wounds which failed to respond to conventional treatment by many beneficial effects on the wound including debridement, disinfection, and healing enhancement. Maggots are also applied in forensic medicine to estimate time between the death and discovery of a corpse and in entomotoxicology involving the potential use of insects as alternative samples for detecting drugs and toxins in death investigations. Leeches are segmented invertebrates, famous by their blood-feeding habits and used in phlebotomy to treat various ailments since ancient times. Leech therapy is experiencing resurgence nowadays in health care principally in plastic and reconstructive surgery. Earthworms provide a source of medicinally useful products with potential antimicrobial, antiviral, and anticancer properties. Lumbrokinases are a group of fibrinolytic enzymes isolated and purified from earthworms capable of degrading plasminogen-rich and plasminogen-free fibrin and so can be used to treat various conditions associated with thrombotic diseases. Helminth infection has been proved to have therapeutic effects in both animal and human clinical trials with promising evidence in treating many allergic diseases and can block the induction of or reduce the severity of some autoimmune disorders as Crohn's disease or ulcerative colitis. What is more, venomous arthropods such as scorpions, bees, wasps, spiders, ants, centipedes, snail, beetles, and caterpillars. The venoms and toxins from these arthropods provide a promising source of natural bioactive compounds which can be employed in the development of new drugs to treat diseases as cancer. The possibility of using these active molecules in biotechnological processes can make these venoms and toxins a valuable and promising source of natural bioactive compounds. The therapeutic use of helminthes and insects will be of great value in biomedicine and further studies on insect toxins will contribute extensively to the development of Biomedical Sciences.

Not as docile as it looks? Loxosceles venom variation and loxoscelism in the Mediterranean Basin and the Canary Islands

The medical importance of Loxosceles spiders has promoted extensive research on different aspects of their venoms. Most of the reported cases of loxoscelism have occurred in the Americas, and thus, much work has focused on North and South American Loxosceles species. Interestingly, loxoscelism cases are rare in the Mediterranean Basin although Loxosceles rufescens, endemic to the Mediterranean, is an abundant spider even in human-altered areas. Thus, it has been suggested that the venom of L. rufescens could be of less medical relevance than that of its congeners. In this study, we challenge this hypothesis by using multiple approaches to study venom variation in selected species and lineages from the Mediterranean Basin and the Canary Islands. We found that SMase D activity, the key bioactive component of Loxosceles venom, is comparable to American species that are confirmed to have medically relevant bites. The venom protein composition using SDS-PAGE presents some differences among regional Loxosceles taxa in banding pattern and intensity, mostly between the Canarian and L. rufescens lineages. Differences between these species also exist in the expression of different paralogs of the SicTox gene family, with the Canarian species being less diverse. In conclusion, our results do not support the challenged hypothesis, and suggest that venom of these species may indeed be as potent as other Loxosceles species. Pending confirmation of loxoscelism with direct evidence of Loxosceles bites with species identification by professionals, Loxosceles in the Mediterranean region should conservatively be considered medically relevant taxa.

Whole venom of Loxosceles similis activates caspases-3, -6, -7, and -9 in human primary skin fibroblasts

Spiders of the Loxosceles genus represent a risk to human health due to the systemic and necrotic effects of their bites. The main symptoms of these bites vary from dermonecrosis, observed in the majority of cases, to occasional systemic hemolysis and coagulopathy. Although the systemic effects are well characterized, the mechanisms of cell death triggered by the venom of these spiders are poorly characterized. In this study, we investigated the cell death mechanisms induced by the whole venom of the spider Loxosceles similis in human skin fibroblasts. Our results show that the venom initiates an apoptotic process and a caspase cascade involving the initiator caspase-9 and the effector caspases-3, -6, and -7.

Brown spider phospholipase-D containing a conservative mutation (D233E) in the catalytic site: identification and functional characterization

Brown spider (Loxosceles genus) bites have been reported worldwide. The venom contains a complex composition of several toxins, including phospholipases-D. Native or recombinant phospholipase-D toxins induce cutaneous and systemic loxoscelism, particularly necrotic lesions, inflammatory response, renal failure, and hematological disturbances. Herein, we describe the cloning, heterologous expression and purification of a novel phospholipase-D toxin, LiRecDT7 in reference to six other previously described in phospholipase-D toxin family. The complete cDNA sequence of this novel brown spider phospholipase-D isoform was obtained and the calculated molecular mass of the predicted mature protein is 34.4 kDa. Similarity analyses revealed that LiRecDT7 is homologous to the other dermonecrotic toxin family members particularly to LiRecDT6, sharing 71% sequence identity. LiRecDT7 possesses the conserved amino acid residues involved in catalysis except for a conservative mutation (D233E) in the catalytic site. Purified LiRecDT7 was detected as a soluble 36 kDa protein using anti-whole venom and anti-LiRecDT1 sera, indicating immunological cross-reactivity and evidencing sequence-epitopes identities similar to those of other phospholipase-D family members. Also, LiRecDT7 exhibits sphingomyelinase activity in a concentration dependent-manner and induces experimental skin lesions with swelling, erythema and dermonecrosis. In addition, LiRecDT7 induced a massive inflammatory response in rabbit skin dermis, which is a hallmark of brown spider venom phospholipase-D toxins. Moreover, LiRecDT7 induced in vitro hemolysis in human erythrocytes and increased blood vessel permeability. These features suggest that this novel member of the brown spider venom phospholipase-D family, which naturally contains a mutation (D233E) in the catalytic site, could be useful for future structural and functional studies concerning loxoscelism and lipid biochemistry.

HIGHLIGHTS

1- Novel brown spider phospholipase-D recombinant toxin contains a conservative mutation (D233E) on the catalytic site. 2-LiRecDT7 shares high identity level with isoforms of Loxosceles genus. 3-LiRecDT7 is a recombinant protein immunodetected by specific antibodies to native and recombinant phospholipase-D toxins. 4-LiRecDT7 shows sphingomyelinase-D activity in a concentration-dependent manner, but less intense than other isoforms. 5-LiRecDT7 induces dermonecrosis and inflammatory response in rabbit skin. 6-LiRecDT7 increases vascular permeability in mice. 7-LiRecDT7 triggers direct complement-independent hemolysis in erythrocytes.

First report of in vitro selection of RNA aptamers targeted to recombinant Loxosceles laeta spider toxins

BACKGROUND

Loxoscelism is the envenomation caused by the bite of Loxosceles spp. spiders. It entails severe necrotizing skin lesions, sometimes accompanied by systemic reactions and even death. There are no diagnostic means and treatment is mostly palliative. The main toxin, found in several isoforms in the venom, is sphingomyelinase D (SMD), a phospholipase that has been used to generate antibodies intended for medical applications. Nucleic acid aptamers are a promising alternative to antibodies. Aptamers may be isolated from a combinatorial mixture of oligonucleotides by iterative selection of those that bind to the target. In this work, two Loxosceles laeta SMD isoforms, Ll1 and Ll2, were produced in bacteria and used as targets with the aim of identifying RNA aptamers that inhibit sphingomyelinase activity.

RESULTS

Six RNA aptamers capable of eliciting partial but statistically significant inhibitions of the sphingomyelinase activity of recombinant SMD-Ll1 and SMD-Ll2 were obtained: four aptamers exert ~17% inhibition of SMD-Ll1, while two aptamers result in ~25% inhibition of SMD-Ll2 and ~18% cross inhibition of SMD-Ll1.

CONCLUSIONS

This work is the first attempt to obtain aptamers with therapeutic and diagnostic potential for loxoscelism and provides an initial platform to undertake the development of novel anti Loxosceles venom agents.

Purification and characterization of a hyaluronidase from venom of the spider Vitalius dubius (Araneae, Theraphosidae)

BACKGROUND

Venom hyaluronidase (Hyase) contributes to the diffusion of venom from the inoculation site. In this work, we purified and characterized Hyase from the venom of Vitalius dubius (Araneae, Theraphosidae), a large theraphosid found in southeastern Brazil. Venom obtained by electrical stimulation of adult male and female V. dubius was initially fractionated by gel filtration on a Superdex® 75 column. Active fractions were pooled and applied to a heparin-sepharose affinity column. The proteins were eluted with a linear NaCl gradient.

RESULTS

Active fractions were pooled and assessed for purity by SDS-PAGE and RP-HPLC. The physicochemical tests included optimum pH, heat stability, presence of isoforms, neutralization by flavonoids and assessment of commercial antivenoms. Hyase was purified and presented a specific activity of 148 turbidity-reducing units (TRU)/mg (venom: 36 TRU/mg; purification factor of ~4). Hyase displayed a molecular mass of 43 kDa by SDS-PAGE. Zymography in hyaluronic-acid-containing gels indicated an absence of enzyme isoforms. The optimum pH was 4-5, with highest activity at 37°C. Hyase was stable up to 60°C; but its activity was lost at higher temperatures and maintained after several freeze-thaw cycles. The NaCl concentration (up to 1 M) did not influence activity. Hyase had greater action towards hyaluronic acid compared to chondroitin sulfate, and was completely neutralized by polyvalent antiarachnid sera, but not by caterpillar, scorpion or snakes antivenoms.

CONCLUSION

The neutralization by arachnid but not scorpion antivenom indicates that this enzyme shares antigenic epitopes with similar enzymes in other spider venoms. The biochemical properties of this Hyase are comparable to others described.

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.

A novel hyaluronidase from brown spider (Loxosceles intermedia) venom (Dietrich's Hyaluronidase): from cloning to functional characterization

Loxoscelism is the designation given to clinical symptoms evoked by Loxosceles spider's bites. Clinical manifestations include skin necrosis with gravitational spreading and systemic disturbs. The venom contains several enzymatic toxins. Herein, we describe the cloning, expression, refolding and biological evaluation of a novel brown spider protein characterized as a hyaluronidase. Employing a venom gland cDNA library, we cloned a hyaluronidase (1200 bp cDNA) that encodes for a signal peptide and a mature protein. Amino acid alignment revealed a structural relationship with members of hyaluronidase family, such as scorpion and snake species. Recombinant hyaluronidase was expressed as N-terminal His-tag fusion protein (∼45 kDa) in inclusion bodies and activity was achieved using refolding. Immunoblot analysis showed that antibodies that recognize the recombinant protein cross-reacted with hyaluronidase from whole venom as well as an anti-venom serum reacted with recombinant protein. Recombinant hyaluronidase was able to degrade purified hyaluronic acid (HA) and chondroitin sulfate (CS), while dermatan sulfate (DS) and heparan sulfate (HS) were not affected. Zymograph experiments resulted in ∼45 kDa lytic zones in hyaluronic acid (HA) and chondroitin sulfate (CS) substrates. Through in vivo experiments of dermonecrosis using rabbit skin, the recombinant hyaluronidase was shown to increase the dermonecrotic effect produced by recombinant dermonecrotic toxin from L. intermedia venom (LiRecDT1). These data support the hypothesis that hyaluronidase is a “spreading factor”. Recombinant hyaluronidase provides a useful tool for biotechnological ends. We propose the name Dietrich's Hyaluronidase for this enzyme, in honor of Professor Carl Peter von Dietrich, who dedicated his life to studying proteoglycans and glycosaminoglycans.

Accidents involving brown spiders (Loxosceles genus) are reported throughout the world. South and Southeast of Brazil are endemic areas for this spider. Loxosceles bites commonly trigger local signs as swelling, erythema, hemorrhage and the hallmark symptom: a dermonecrotic lesion with gravitational spreading. Systemic effects are less common; however, are implicated in more severe cases. Hyaluronidases are referred in several venoms as “spreading factors” due to their enzymatic activity upon extracellular components. This activity facilitates the permeation of other toxins through the victim's body. In fact, a previous study identified the activity of L. intermedia venom upon glycosaminoglycans which are abundant components in the extracellular matrix of many tissues. Disclosing a little more about the role of hyaluronidases within this venom, we investigated the activities of a recombinant hyaluronidase from L. intermedia venom. Dietrich's hyaluronidase, as it was designated, was produced as a recombinant protein. By performing a rabbit skin dermonecrosis assay using Dietrich's Hyaluronidase and a dermonecrotic toxin, we showed that Dietrich's Hyaluronidase increased the dermonecrotic area induced by the dermonecrotic toxin. Our results confirm that hyaluronidases are a “spreading factor” of L. intermedia venom.

Sphingomyelinase D in sicariid spider venom is a potent insecticidal toxin

Spider venoms have evolved over hundreds of millions of years with a primary role of immobilizing prey. Sphingomyelinase D (SMase D) and homologs in the SicTox gene family are the most abundantly expressed toxic protein in venoms of Loxosceles and Sicarius spiders (Sicariidae). While SMase D is well known to cause dermonecrotic lesions in mammals, little work has investigated the bioactivity of this enzyme in its presumed natural role of immobilizing insect prey. We expressed and purified recombinant SMase D from Loxosceles arizonica (Laz-SMase D) and compared its enzymatic and insecticidal activity to that of crude venom. SMase D enzymatic activities of purified protein and crude venom from the same species were indistinguishable. In addition, SMase D and crude venom have comparable and high potency in immobilization assays on crickets. These data indicate that SMase D is a potent insecticidal toxin, the role for which it presumably evolved.