Neuromuscular effects of venoms and crotoxin-like proteins from Crotalus durissus ruruima and Crotalus durissus cumanensis

Comparative Analysis of the Enzymatic, Coagulant, and Neuromuscular Activities of Two Variants of Crotalus durissus ruruima Venom and Antivenom Efficacy

Background: We compared the enzymatic, coagulant, and neuromuscular activities of two variants (yellow-CDRy and white-CDRw) of Crotalus durissus ruruima venom with a sample of C. d. terrificus (CDT) venom and examined their neutralization by antivenom against CDT venom. Methods: The venoms were screened for enzymatic and coagulant activities using standard assays, and electrophoretic profiles were compared by SDS-PAGE. Neutralization was assessed by preincubating venoms with crotalic antivenom and assaying the residual activity. Results: SDS-PAGE showed that the venoms had similar electrophoretic profiles, with the main bands being phospholipase A2 (PLA2), serine proteinases, L-amino acid oxidase (LAAO), and phosphodiesterase. CDRy venom had the highest proteolytic and LAAO activities, CDRw venom had greater PLA2 and esterolytic activities at the highest quantity tested, and CDT had greater PLA2 activity than CDRy. CDRw and CDT venoms had similar proteolytic and LAAO activities, and CDRy and CDT venoms had comparable esterolytic activity. None of the venoms altered the prothrombin time (PT), but all of them decreased the activated partial thromboplastin time (aPPT); this activity was neutralized by antivenom. The minimum coagulant dose potency was CDRw >> CDRy > CDT. All venoms had thrombin-like activity that was attenuated by antivenom. CDRy and CDRw venoms showed α-fibrinogenolytic activity. All venoms partially cleaved the β-chain. CDRy and CDT venoms caused neuromuscular facilitation (enhanced muscle contractions) followed by complete blockade, whereas CDRw venom caused only blockade. Antivenom neutralized the neuromuscular activity to varying degrees. Conclusions: These findings indicate that while CDR and CDT venoms share similarities, they also differ in some enzymatic and biological activities and in neutralization by antivenom. Some of these differences could influence the clinical manifestations of envenomation by C. d. ruruima and their neutralization by the currently used therapeutic antivenom.

A Review of Rattlesnake Venoms

Venom components are invaluable in biomedical research owing to their specificity and potency. Many of these components exist in two genera of rattlesnakes, Crotalus and Sistrurus, with high toxicity and proteolytic activity variation. This review focuses on venom components within rattlesnakes, and offers a comparison and itemized list of factors dictating venom composition, as well as presenting their known characteristics, activities, and significant applications in biosciences. There are 64 families and subfamilies of proteins present in Crotalus and Sistrurus venom. Snake venom serine proteases (SVSP), snake venom metalloproteases (SVMP), and phospholipases A2 (PLA2) are the standard components in Crotalus and Sistrurus venom. Through this review, we highlight gaps in the knowledge of rattlesnake venom; there needs to be more information on the venom composition of three Crotalus species and one Sistrurus subspecies. We discuss the activity and importance of both major and minor components in biomedical research and drug development.

Intraspecific Differences in the Venom of Crotalus durissus cumanensis from Colombia

Biochemical and biological differences in the venom of Crotalus durissus cumanensis from three ecoregions of Colombia were evaluated. Rattlesnakes were collected from the geographic areas of Magdalena Medio (MM), Caribe (CA) and Orinoquía (OR). All three regionally distributed venoms contain proteases, PLA₂s and the basic subunit of crotoxin. However, only crotamine was detected in the CA venom. The highest lethality, coagulant, phospholipase A₂ and hyaluronidase activities were found in the MM venom. Also, some differences, observed by western blot and immunoaffinity, were found in all three venoms when using commercial antivenoms. Furthermore, all three eco-regional venoms showed intraspecific variability, considering the differences in the abundance and intensity of their components, in addition to the activity and response to commercial antivenoms.

Biological and proteomic characterization of the venom from Peruvian Andes rattlesnake Crotalus durissus

The Peruvian rattlesnake Crotalus durissus is a venomous species that is restricted to the Peruvian Departments of Puno and Madre de Dios. Although clinically meaningful in this region, Crotalus durissus venom composition remains largely elusive. In this sense, this work aimed to provide a primary description of Peruvian C. durissus venom (PCdV). The enzymatic activities (SVMP, SVSP, LAAO, Hyaluronidase and PLA₂) of PCdV were analyzed and compared to Brazilian Crotalus durissus terrificus venom (BCdtV). PCdV showed higher PLA₂ activity when compared to the Brazilian venom. PCdV also showed cytotoxicity in VERO cells. For proteomic analysis, PCdV proteins were separated by HPLC, followed by SDS-PAGE. Gel bands were excised and tryptic digested for MALDI-TOF/TOF identification. Approximately 21 proteins were identified, belonging to 7 families. Phospholipases A₂ (PLA₂, 66.63%) were the most abundant proteins of the venom, followed by snake venom serine proteinases (SVSPs, 13.37%), C-type lectins (Snaclec, 8.98%) and snake venom metalloproteinases (SVMPs, 7.13%), crotamine (2.98%) and phosphodiesterase (PDE, 0.87%). Moreover, antivenom recognition assays indicated that both Brazilian and Peruvian antivenoms recognize PCdV, indicating the presence of antigenically related proteins in crotalic venoms. The results reported here, may impact in the venom selection for the production of effective Pan-American crotalic antivenom.

Revisiting the potential of South American rattlesnake Crotalus durissus terrificus toxins as therapeutic, theranostic and/or biotechnological agents

The potential biotechnological and biomedical applications of the animal venom components are widely recognized. Indeed, many components have been used either as drugs or as templates/prototypes for the development of innovative pharmaceutical drugs, among which many are still used for the treatment of human diseases. A specific South American rattlesnake, named Crotalus durissus terrificus, shows a venom composition relatively simpler compared to any viper or other snake species belonging to the Crotalus genus, although presenting a set of toxins with high potential for the treatment of several still unmet human therapeutic needs, as reviewed in this work. In addition to the main toxin named crotoxin, which is under clinical trials studies for antitumoral therapy and which has also anti-inflammatory and immunosuppressive activities, other toxins from the C. d. terrificus venom are also being studied, aiming for a wide variety of therapeutic applications, including as antinociceptive, anti-inflammatory, antimicrobial, antifungal, antitumoral or antiparasitic agent, or as modulator of animal metabolism, fibrin sealant (fibrin glue), gene carrier or theranostic agent. Among these rattlesnake toxins, the most relevant, considering the potential clinical applications, are crotamine, crotalphine and gyroxin. In this narrative revision, we propose to organize and present briefly the updates in the accumulated knowledge on potential therapeutic applications of toxins collectively found exclusively in the venom of this specific South American rattlesnake, with the objective of contributing to increase the chances of success in the discovery of drugs based on toxins.

Varespladib (LY315920) prevents neuromuscular blockage and myotoxicity induced by crotoxin on mouse neuromuscular preparations

Varespladib (LY315920) is a synthetic phospholipase A₂ (PLA₂) inhibitor that has been demonstrating antiophidic potential against snake venoms that present PLA₂ neurotoxins. In this study, we evaluate the capacity of Varespladib to inhibit the neuromuscular effects of crotoxin (CTX), the main toxic component of Crotalus durissus terrificus snake venom, and its PLA₂ subunit (CB). We performed a myographic study to compare the neuromuscular effects of CTX or CB and the mixture of these substances plus Varespladib in mice phrenic nerve-diaphragm muscle preparations. CTX (5 μg/mL), CB (20 μg/mL), or toxin-inhibitor mixtures pre-incubated with different concentration ratios of Varespladib (1:0.25; 1:0.5; 1:1; w/w) were added to the preparations and maintained throughout the experimentation period. Myotoxicity was assessed by light microscopic analysis of diaphragm muscle after myographic study. CTX and CB blocked the nerve-evoked twitches, and only CTX induced histological alterations in diaphragm muscle. Pre-incubation with Varespladib abolished the muscle-paralyzing activity of CTX and CB, and also the muscle-damaging activity of CTX. These findings emphasize the clinical potential of Varespladib in mitigating the toxic effects of C. d. terrificus snakebites and as a research tool to advance the knowledge of the mechanism of action of snake toxins.

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

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

A Meta-Analysis of the Protein Components in Rattlesnake Venom

The specificity and potency of venom components give them a unique advantage in developing various pharmaceutical drugs. Though venom is a cocktail of proteins, rarely are the synergy and association between various venom components studied. Understanding the relationship between various components of venom is critical in medical research. Using meta-analysis, we observed underlying patterns and associations in the appearance of the toxin families. For Crotalus, Dis has the most associations with the following toxins: PDE; BPP; CRL; CRiSP; LAAO; SVMP P-I and LAAO; SVMP P-III and LAAO. In Sistrurus venom, CTL and NGF have the most associations. These associations can predict the presence of proteins in novel venom and understand synergies between venom components for enhanced bioactivity. Using this approach, the need to revisit the classification of proteins as major components or minor components is highlighted. The revised classification of venom components is based on ubiquity, bioactivity, the number of associations, and synergies. The revised classification can be expected to trigger increased research on venom components, such as NGF, which have high biomedical significance. Using hierarchical clustering, we observed that the genera's venom compositions were similar, based on functional characteristics rather than phylogenetic relationships.

Crotalus Neutralizing Factor (CNF) inhibits the toxic effects of Crotoxin at mouse neuromuscular preparations

Crotalus Neutralizing Factor (CNF) was the first phospholipase A₂ inhibitor isolated from the plasma of the South American rattlesnake (Crotalus durissus terrificus). Previous biochemical and biophysical studies demonstrate an interaction of CNF with Crotoxin (CTX), the main toxic component in the venom of these snakes. CTX promotes the blockade of neuromuscular transmission by a sum of neurotoxic and myotoxic activities. However, the ability of CNF to inhibit these activities has not been shown until the present study. We performed a myographic study to compare the neuromuscular effects of CTX and the mixture CTX plus CNF in mice phrenic nerve-diaphragm muscle preparations. CTX (5 μg/mL) alone, or pre-incubated with CNF (5, 20 or 50 μg/mL) for 15 min was added to the preparations and maintained throughout the experimentation period. Myotoxicity was assessed by light microscopic analysis of diaphragm muscle after myographic study. CTX (5 μg/mL) blocked both indirectly and directly evoked twitches in neuromuscular preparations. In addition, CTX induced histological alterations in diaphragm muscle. Pre-incubation with CNF (50 μg/mL) abolished both the muscle-paralyzing and muscle-damaging activities of CTX. Therefore, the present study confirms, through functional studies, the antiophidic potential of CNF.

Envenoming by the rattlesnake Crotalus durissus ruruima in the state of roraima, Brazil

The aim of this study was to evaluate the clinical-epidemiological factors associated with victims of rattlesnake envenoming in the state of Roraima, Brazil. In this location, rattlesnake accidents are caused by the subspecies Crotalus durissus ruruima. This is a prospective observational study carried out at the General Hospital of Roraima from april 2017 until july 2018. A total of 37 alleged rattlesnake victims had their medical records evaluated. However only one of them proved to be by C. d. ruruima. All individuals were residents from the savannas (lavrados) of Roraima. The town of Bonfim on the border between Brazil and Guyana had the highest occurrence of rattlesnake bites. The most affected group were males aged 13-20 years and farmers. The highest number of incidents occurred during daytime and lower limbs (feet) were the most major affected part of the body. Tourniquets were used as first aid after snake envenoming in 32.4% of victims. Out of 37 patients, 16.2% were classified as severe cases of snakebite envenoming and in 5.4% dry bites seem to have occurred. Among the symptomatic patients, 100% presented local manifestations and 70.3% presented systemic manifestations. The clinical setting showed local effects such as pain and edema while the systemic effects were blurred vision, myalgias, myasthenic facies, palpebral ptosis, muscle weakness and headache. Laboratory results of aspartate aminotransferase (62.2%), creatine phosphokinase (51.3%), lactic dehydrogenase (37.8%), urea level (32.4%) and serum creatinine (29.7%) were increased significantly in relation to the reference standards. In 16.2% of the cases, the victims presented acute kidney injury. Patients were treated with anticrotalic serum in 70.3% of the cases and antibotropic + anticrotalic serum in 24.3%. The victims of C. d. ruruima in Roraima showed a local symptomatology similar to Bothrops envenoming, while systemic symptoms and laboratory analysis proved kidney and muscular injuries, similar to envenoming by Crotalus d. terrificus in Brazil.

Immunoprotection against lethal effects of Crotalus durissus snake venom elicited by synthetic epitopes trapped in liposomes

Snakebites caused by Crotalus genus are the second most frequent in Brazil. Crotoxin is a beta-neurotoxin responsible for the main envenomation effects of Crotalus biting, while crotamine immobilizes the animal hind limbs, contributing to prey immobilization and to envenoming symptoms. As crotoxin and crotamine represent about 90% of Crotalus venom dry weight, these toxins are of great importance for antivenom therapy. In this sense, knowledge regarding the antigenicity/immunogenicity at the molecular level of these toxins can provide valuable information for the improvement of specific antivenoms. Therefore, the aims of this study are the identification of the B-cell epitopes from crotoxin and crotamine; and the characterization of the neutralizing potency of antibodies directed against the corresponding synthetic epitopes defined in the current study. Linear B-cell epitopes were identified using the Spot Synthesis technique probed with specific anti-C. d. terrificus venom horse IgG. One epitope of crotamine (F¹²PKEKICLPPSSDFGKMDCRW³²) and three of crotoxin (L¹⁰LVGVEGHLLQFNKMIKFETR³⁰; Y⁴³CGWGGRGRPKDATDRCCFVH⁶³ and T¹¹⁸YKYGYMFYPDSRCRGPSETC¹³⁸) were identified. After synthesis in their soluble form, the peptides mixture correspondent to the mapped epitopes was entrapped in liposomes and used as immunogens for antibody production in rabbits. Anti-synthetic peptide antibodies were able to protect mice from the lethal activity of C. d. terrificus venom.

In vitro effects of Crotalus atrox snake venom on chick and mouse neuromuscular preparations

The neuromuscular effect of venoms is not a major clinical manifestation shared between rattlesnakes native to the Americas, which showed two different venom phenotypes. Taking into account this dichotomy, nerve muscle preparations from mice and chicks were used to investigate the ability of Crotalus atrox venom to induce in vitro neurotoxicity and myotoxicity. Unlike crotalic venoms of South America, low concentrations of C. atrox venom did not result in significant effects on mouse neuromuscular preparations. The venom was more active on avian nerve-muscle, showing reduction of twitch heights after 120 min of incubation with 10, 30 and 100 μg/mL of venom with diminished responses to agonists and KCl. Histological analysis highlighted that C. atrox was myotoxic in both species of experimental animals; as evidenced by degenerative events, including edematous cells, delta lesions, hypercontracted fibers and muscle necrosis, which can lead to neurotoxic action. These results provide key insights into the myotoxicity and low neurotoxicity of C. atrox in two animal models, corroborating with previous genomic and proteomic findings and would be useful for a deeper understanding of venom evolution in snakes belonging to the genus Crotalus.

Neuromuscular effect of venoms from adults and juveniles of Crotalus durissus cumanensis (Humboldt, 1811) from Guajira, Colombia

A toxinological study was performed to compare the neuromuscular effect of venom from adult and juvenile specimens from Crotalus durissus cumanensis from Guajira, Colombia. Both venoms exhibited neurotoxic activity in chick biventer cervicis nerve-muscle preparation. In addition, venom from juveniles was faster than adults to produce a neuromuscular blockade. In the contrary to the venom from juvenile's, at high doses, adult's venom affected the ACh and KCl contractures, indicating a myotoxic effect.

Antivenomics as a tool to improve the neutralizing capacity of the crotalic antivenom: a study with crotamine

Background

Snakebite treatment requires administration of an appropriate antivenom that should contain antibodies capable of neutralizing the venom. To achieve this goal, antivenom production must start from a suitable immunization protocol and proper venom mixtures. In Brazil, antivenom against South American rattlesnake (Crotalus durissus terrificus) bites is produced by public institutions based on the guidelines defined by the regulatory agency of the Brazilian Ministry of Health, ANVISA. However, each institution uses its own mixture of rattlesnake venom antigens. Previous works have shown that crotamine, a toxin found in Crolatus durissus venom, shows marked individual and populational variation. In addition, serum produced from crotamine-negative venoms fails to recognize this molecule.

Methods

In this work, we used an antivenomics approach to assess the cross-reactivity of crotalic antivenom manufactured by IVB towards crotamine-negative venom and a mixture of crotamine-negative/crotamine-positive venoms.

Results

We show that the venom mixture containing 20% crotamine and 57% crotoxin produced a strong immunogenic response in horses. Antivenom raised against this venom mixture reacted with most venom components including crotamine and crotoxin, in contrast to the antivenom raised against crotamine-negative venom.

Conclusions

These results indicate that venomic databases and antivenomics analysis provide a useful approach for choosing the better venom mixture for antibody production and for the subsequent screening of antivenom cross-reactivity with relevant snake venom components.