What Are the Neurotoxins in Hemotoxic Snake Venoms?

Venoms and Extracellular Vesicles: A New Frontier in Venom Biology

Extracellular vesicles (EVs) are nanoparticle-sized vesicles secreted by nearly all cell types under normal physiological conditions. In toxicological research, EVs have emerged as a crucial link between public health and multi-omics approaches, offering insights into cellular responses to disease-causing injury agents such as environmental and biological toxins, contaminants, and drugs. Notably, EVs present a unique opportunity to deepen our understanding of the pathophysiology of envenomation by natural toxins. Recent advancements in isolating and purifying EV cargo, mass spectrometry techniques, and bioinformatics have positioned EVs as potential biomarkers that could elucidate biological signaling pathways and provide valuable information on the relationship between venomous toxins, their mechanisms of action, and the effectiveness of antivenoms. Additionally, EVs hold promise as proxies for various aspects of envenomation, including the toxin dosage, biological characterization, injury progression, and prognosis during therapeutic interventions. These aspects can be explored through multi-omics technology applied to EV contents from the plasma, saliva, or urine samples of envenomated individuals, offering a comprehensive integrative approach to understanding and managing envenomation cases.

Snakebite-induced reversible cerebral vasoconstriction syndrome: Report of three cases

Envenomings from Russell's viper typically result in local tissue damage and bleeding complications, but the bites from common krait and cobra primarily cause neurotoxic effects. While most symptoms can be treated with appropriate antivenom, additional support is necessary for several snakebite victims to tackle a broad range of unusual complications that they develop following bites. Reversible vasoconstriction syndrome (RCVS), characterised by the constriction of cerebral arteries, is a rare but serious issue, presenting with severe headaches and, in extreme cases, haemorrhagic/ischaemic stroke. This report presents three cases of RCVS in snakebite victims following Russell's viper, krait and cobra bites. The patients were admitted to the hospital with neurological and/or haematological complications, and they were treated with polyvalent antivenom. After two days of antivenom treatment, all the patients developed intense headaches that lasted for several hours and failed to respond to commonly used analgesics. While the physical, laboratory and computed tomography examinations were normal, the RCVS was diagnosed with multimodal magnetic resonance angiography. All patients were successfully treated with oral nimodipine, and during their follow-ups, physical and laboratory examinations were unremarkable, and the magnetic resonance imaging confirmed the reversal of RCVS. To achieve positive outcomes in patients, clinicians must swiftly identify such rare complications and make accurate diagnoses to provide prompt treatments. Overall, this report presents an unusual complication of RCVS in snakebite patients and appropriate diagnosis and treatment approaches to tackle this condition.

Breaking muscle: neurotoxic and myotoxic effects of Central American snake venoms and the relative efficacies of antivenom and varespladib

BACKGROUND

The snake genera Atropoides, Cerrophidion, and Metlapilcoatlus form a clade of neotropical pit vipers distributed across Mexico and Central America. This study evaluated the myotoxic and neurotoxic effects of nine species of Atropoides, Cerrophidion, and Metlapilcoatlus, and the neutralising efficacy of the ICP antivenom from Costa Rica against these effects, in the chick biventer cervicis nerve-muscle preparation. Given the prominence of PLA2s within the venom proteomes of these species, we also aimed to determine the neutralising potency of the PLA2 inhibitor, varespladib.

RESULTS

All venoms showed myotoxic and potential neurotoxic effects, with differential intra-genera and inter-genera potency. This variation was also seen in the antivenom ability to neutralise the muscle damaging pathophysiological effects observed. Variation was also seen in the relative response to the PLA2 inhibitor varespladib. While the myotoxic effects of M. mexicanus and M. nummifer venoms were effectively neutralised by varespladib, indicating myotoxicity is PLA2 mediated, those of C. godmani and M. olmec venoms were not, revealing that the myotoxicity is driven by non-PLA2 toxin types.

CONCLUSIONS

This study characterises the myotoxic and neurotoxic venom activity, as well as neutralisation of venom effects from the Atropoides, Cerrophidion, and Metlapilcoatlus clade of American crotalids. Our findings contribute significant clinical and evolutionary knowledge to a clade of poorly researched snakes. In addition, these results provide a platform for future research into the reciprocal interaction between ecological niche specialisation and venom evolution, as well as highlighting the need to test purified toxins to accurately evaluate the potential effects observed in these venoms.

Neurotoxicity and acute renal injury secondary to Russell's viper bite in an individual: a case report from Nepal

Introduction and importance

Owing to the high number of envenomation and fatalities, the Russell's viper holds greater medicinal significance than any other Asian serpent. South East Asia is one of the most snakebite-prone regions in the world. Dense population, extensive agricultural practices, the abundance of venomous snake species, and an overall lack of knowledge about primary treatment (first aid) are the major culprits associated with snake bite-related morbidity and mortality. The venom of vipers is known to produce vasculotoxicity and contains hemotoxins.

Case presentation

The authors describe a patient who was bitten by a viperine snake and showed signs of both neurotoxicity and acute kidney injury (AKI). The 20 years male was treated in a tertiary care centre in Nepal. The patient developed respiratory failure and needed ventilator support. Further, more haemodialysis was also done to manage AKI. Later, the patient was discharged after a smooth recovery.

Discussion

Numerous clinical manifestations, such as neurotoxicity and vasculotoxicity, can result from a viperine bite. The majority of viperine snakebites are hemotoxic. Dual neurotoxic symptoms are possible after a viperine bite despite their rarity. The prevention of respiratory failure depends critically on the early detection of neurotoxicity.

Conclusion

Unusual neuromuscular paralysis is caused by Russell's vipers (Daboia russelii) in South East Asia. Physicians should know the exceptional presentations of snakebites to diagnose and treat patients.

Fab Antivenom Reversal of Neurotoxicity Caused by a Juvenile Crotalus horridus Lacking Canebrake Toxin

We present a case of neurotoxic effects in a pediatric patient after envenomation by a timber rattlesnake (Crotalus horridus) in the Appalachian upstate of South Carolina. Though some members of this species are capable of primarily neurotoxic envenomation, there is heterogeneity in venom composition, and neurotoxic timber rattlesnakes are not endemic to the Appalachian region. However, neurotoxic effects caused by C horridus species lacking typical neurotoxins have been suspected, though not previously confirmed in the medical literature. This case presents a patient who was envenomated by a genotypically confirmed non-neurotoxic C horridus but who nevertheless presented with symptoms consistent with primary neurotoxicity. Neurotoxic effects can be variable in their response to traditional antivenom, though this patient demonstrated rapid response to treatment, representing a novel case in the literature of neurotoxic effects from a snake lacking typical neurotoxins with documented improvement with traditional antivenom.

Purification, and characterization of a new pro-coagulant protein from Iranian Echis carinatus venom

This work aimed to purify the proteins that cause blood coagulation in the venom of the Iranian Echis carinatus snake species in a comprehensive manner. Gel filtration chromatography (GFC), Ion exchange chromatography (IEC), and Size Exclusion High-Performance Liquid Chromatography (SEC-HPLC) were utilized in the purification of the coagulation factors. The prothrombin clotting time (PRCT) and SDS-PAGE electrophoresis were performed to confirm the coagulative fractions. The fraction with the shortest coagulation time was selected. The components of this designated fraction were identified through matrix-assisted laser desorption/ionization mass spectrometry (MALDI-TOF) following thorough purification. Circular dichroism (CD) was employed to determine the second structure of the coagulation factor. The crude venom (CV) was analyzed and had a total protein concentration of 97%. Furthermore, the PRCT of the crude venom solution at a concentration of 1 mg/ml was determined to be 24.19 ± 1.05 s. The dosage administered was found to be a factor in the venom's capacity to induce hemolysis. According to CD analysis, the protein under investigation had a helical structure of 16.7%, a beta structure of 41%, and a turn structure of 9.8%. CHNS proved that the purified coagulant protein had a Carbon content of 77.82%, 5.66% Hydrogen, 3.19% Nitrogen, and 0.49% Sulphur. In the present investigation, a particular type of snake venom metalloproteinase (SVMP) has undergone the process of purification and characterization and has been designated as EC-124. This purified fraction shows significant efficacy as a procoagulant. Our findings have shown that this compound has a function similar to factor X and most likely it can cause blood coagulation by activating factor II (FII).

Specific Amino Acid Residues in the Three Loops of Snake Cytotoxins Determine Their Membrane Activity and Provide a Rationale for a New Classification of These Toxins

Cytotoxins (CTs) are three-finger membrane-active toxins present mainly in cobra venom. Our analysis of the available CT amino acid sequences, literature data on their membrane activity, and conformational equilibria in aqueous solution and detergent micelles allowed us to identify specific amino acid residues which interfere with CT incorporation into membranes. They include Pro9, Ser28, and Asn/Asp45 within the N-terminal, central, and C-terminal loops, respectively. There is a hierarchy in the effect of these residues on membrane activity: Pro9 > Ser28 > Asn/Asp45. Taking into account all the possible combinations of special residues, we propose to divide CTs into eight groups. Group 1 includes toxins containing all of the above residues. Their representatives demonstrated the lowest membrane activity. Group 8 combines CTs that lack these residues. For the toxins from this group, the greatest membrane activity was observed. We predict that when solely membrane activity determines the cytotoxic effects, the activity of CTs from a group with a higher number should exceed that of CTs from a group with a lower number. This classification is supported by the available data on the cytotoxicity and membranotropic properties of CTs. We hypothesize that the special amino acid residues within the loops of the CT molecule may indicate their involvement in the interaction with non-lipid targets.

Characterization of plant produced VHH antibodies against cobra venom toxins for antivenom therapy

Cobra (Naja kaouthia) venom contains many toxins including α-neurotoxin (αNTX) and phospholipase A2 (PLA2), which can cause neurodegeneration, respiratory failure, and even death. The traditional antivenom derived from animal serum faces many challenges and limitations. Heavy-chain-only antibodies (HCAb), fusing VHH with human IgG Fc region, offer advantages in tissue penetration, antigen binding, and extended half-life. This research involved the construction and transient expression of two types of VHH-FC which are specific to α-Neurotoxin (VHH-αNTX-FC) and Phospholipase A2 (VHH-PLA2-FC) in Nicotiana benthamiana leaves. The recombinant HCAbs were incubated for up to six days to optimize expression levels followed by purification by affinity chromatography and characterization using LC/Q-TOF mass spectrometry (MS). Purified proteins demonstrated over 92 % sequence coverage and an average mass of around 82 kDa with a high-mannose N-glycan profile. An antigen binding assay showed that the VHH-αNTX-Fc has a greater ability to bind to crude venom than VHH-PLA2-Fc.

Pulmonary Thromboembolism following Russell's Viper Bites

Snakebite envenoming and its resulting complications are serious threats to the health of vulnerable people living in rural areas of developing countries. The knowledge of the heterogeneity of symptoms associated with snakebite envenoming and their management strategies is vital to treat such life-threatening complications to save lives. Russell's viper envenomation induces a diverse range of clinical manifestations from commonly recognised haemotoxic and local effects to several rare conditions that are often not reported. The lack of awareness about these unusual manifestations can affect prompt diagnosis, appropriate therapeutic approaches, and positive outcomes for patients. Here, we report pulmonary thromboembolism that developed in three patients following Russell's viper envenomation and demonstrate their common clinical features and diagnostic and therapeutic approaches used. All patients showed clinical signs of local (oedema) and systemic (blood coagulation disturbances) envenomation, which were treated using polyvalent antivenom. They exhibited elevated heart rates, breathlessness, and reduced oxygen saturation, which are non-specific but core parameters in the diagnosis of pulmonary embolism. The recognition of pulmonary embolism was also achieved by an electrocardiogram, which showed sinus tachycardia and computed tomography and echocardiogram scans further confirmed this condition. Anti-coagulant treatment using low-molecular-weight heparin offered clinical benefits in these patients. In summary, this report reinforces the broad spectrum of previously unreported consequences of Russell's viper envenomation. The constant updating of healthcare professionals and the dissemination of major lessons learned in the clinical management of snakebite envenoming through scientific documentation and educational programs are necessary to mitigate the adverse impacts of venomous snakebites in vulnerable communities.

The role of venom proteomics and single-domain antibodies for antivenoms: Progress in snake envenoming treatment

Single-domain antibodies (sdAbs) hold promise for developing new biopharmaceuticals to treat neglected tropical diseases (NTDs), including snakebites, which are severe and occur frequently. In addition, limitations of conventional snakebite treatments, especially in terms of local action, and the global antivenom crisis incentivize the use of this biotechnological tool to design next-generation snakebite antivenoms. Conventional antivenoms for snakebite treatment are usually composed of immunoglobulin G or F(ab')2 fragments derived from the plasma of immunized animals. sdAbs, the smallest antigen-binding fragments, are derived from the variable domains of camelid heavy-chain antibodies. sdAbs may have some advantages over conventional antivenoms for local toxicity, such as better penetration into tissues due to their small size, and high solubility and affinity for venom antigens due to their unique antigen-binding loops and ability to access cryptic epitopes. We present an overview of current antivenom therapy in the context of sdAb development for toxin neutralization. Furthermore, strategies are presented for identifying snake venom's major toxins as well as for developing antisnake toxin sdAbs by employing proteomic tools for toxin neutralization.

Clinical Laboratory Investigations and Antivenom Administration after Malayan Pit Viper (Calloselasma rhodostoma) Envenoming: A Retrospective Study from Southernmost Thailand

The Malayan pit viper (MPV: Calloselasma rhodostoma) is a medically important venomous snake causing numerous envenomations in Thailand. Administration of specific snake antivenom is the only effective treatment for MPV-envenomed patients. However, inappropriate administration or misuse of snake antivenom is problematic in some remote areas of tropical countries where the snakebite envenoming rate is notable. Currently, the indications for administration of MPV antivenom are focused mainly on hematological factors. These include 1) venous clotting time > 20 min, 2) unclotted 20-minute whole-blood clotting time, 3) international normalized ratio > 1.2, 4) platelet count < 50 × 103/μL, 5) systemic bleeding, and 6) impending compartment syndrome. We aimed to determine the association between laboratory data and antivenom administration in MPV-envenomed patients. A retrospective study of data from 2016 to 2021 in Narathiwat Province, the southernmost province in Thailand, was conducted. A total of 838 MPV-bitten patients were included in this study. Local effects and systemic effects were observed in 58.8% and 27.7% of patients, respectively. Coagulopathies, which range from abnormal blood clotting to systemic bleeding, represented the majority of systemic effects. Acute kidney injury developed in 2.5% of patients. In this study, 57.3% of patients were considered appropriate antivenom recipients. Interestingly, the present study revealed that local bleeding and mild to moderate thrombocytopenia became the independent factors for inappropriate use of MPV antivenom. Reeducation and supervision regarding the rational use of snake antivenom are needed to minimize the misuse of antivenom.

Changes in attachment and metabolic activity of rat neonatal cardiomyocytes and nonmyocytes caused by Macrovipera lebetina obtusa venom

The Caucasian viper Macrovipera lebetina obtusa (MLO) is one of the most prevalent and venomous snakes in the Caucasus and the surrounding regions, yet the effects of MLO venom on cardiac function remain largely unknown. We examined the influence of MLO venom (crude and with inhibited metalloproteinases and phospholipase A2) on attachment and metabolic activity of rat neonatal cardiomyocytes (CM) and nonmyocytes (nCM), assessed at 1 and 24 h. After exposing both CM and nCM to varying concentrations of MLO venom, we observed immediate cytotoxic effects at a concentration of 100 μg/ml, causing detachment from the culture substrate. At lower MLO venom concentrations both cell types detached in a dose-dependent manner. Inhibition of MLO venom metalloproteinases significantly improved CM and nCM attachment after 1-hour exposure. At 24-hour exposure to metalloproteinases inhibited venom statistically significant enhancement was observed only in nCM attachment. However, metabolic activity of CM and nCM did not decrease upon exposure to the lower dose of the venom. Moreover, we demonstrated that metalloproteinases and phospholipases A2 are not the components of the MLO venom that change metabolic activity of both CM and nCM. These results provide a valuable platform to study the impact of MLO venom on prey cardiac function. They also call for further exploration of individual venom components for pharmaceutical purposes.

Snake Venom: A Promising Source of Neurotoxins Targeting Voltage-Gated Potassium Channels

The venom derived from various sources of snakes represents a vast collection of predominantly protein-based toxins that exhibit a wide range of biological actions, including but not limited to inflammation, pain, cytotoxicity, cardiotoxicity, and neurotoxicity. The venom of a particular snake species is composed of several toxins, while the venoms of around 600 venomous snake species collectively encompass a substantial reservoir of pharmacologically intriguing compounds. Despite extensive research efforts, a significant portion of snake venoms remains uncharacterized. Recent findings have demonstrated the potential application of neurotoxins derived from snake venom in selectively targeting voltage-gated potassium channels (Kv). These neurotoxins include BPTI-Kunitz polypeptides, PLA2 neurotoxins, CRISPs, SVSPs, and various others. This study provides a comprehensive analysis of the existing literature on the significance of Kv channels in various tissues, highlighting their crucial role as proteins susceptible to modulation by diverse snake venoms. These toxins have demonstrated potential as valuable pharmacological resources and research tools for investigating the structural and functional characteristics of Kv channels.

Novel Toxicodynamic Model of Subcutaneous Envenomation to Characterize Snake Venom Coagulopathies and Assess the Efficacy of Site-Directed Inorganic Antivenoms

Venomous snake bite adversely affects millions of people yearly, but few animal models allow for the determination of toxicodynamic timelines with hemotoxic venoms to characterize the onset and severity of coagulopathy or assess novel, site-directed antivenom strategies. Thus, the goals of this investigation were to create a rabbit model of subcutaneous envenomation to assess venom toxicodynamics and efficacy of ruthenium-based antivenom administration. New Zealand White rabbits were sedated with midazolam via the ear vein and had viscoelastic measurements of whole blood and/or plasmatic coagulation kinetics obtained from ear artery samples. Venoms derived from Crotalus scutulatus scutulatus, Bothrops moojeni, or Calloselasma rhodostoma were injected subcutaneously, and changes in coagulation were determined over three hours and compared to samples obtained prior to envenomation. Other rabbits had ruthenium-based antivenoms injected five minutes after venom injection. Viscoelastic analyses demonstrated diverse toxicodynamic patterns of coagulopathy consistent with the molecular composition of the proteomes of the venoms tested. The antivenoms tested attenuated venom-mediated coagulopathy. A novel rabbit model can be used to characterize the onset and severity of envenomation by diverse proteomes and to assess site-directed antivenoms. Future investigation is planned involving other medically important venoms and antivenom development.

Snake Antivenoms-Toward Better Understanding of the Administration Route

Envenomations induced by animal bites and stings constitute a significant public health burden. Even though a standardized protocol does not exist, parenterally administered polyclonal antivenoms remain the mainstay in snakebite therapy. There is a prevailing opinion that their application by the i.m. route has poor efficacy and that i.v. administration should preferentially be chosen in order to achieve better accomplishment of the antivenom therapeutic activity. Recently, it has been demonstrated that neutralization not only in the systemic circulation but also in the lymphatic system might be of great importance for the clinical outcome since it represents another relevant body compartment through which the absorption of the venom components occurs. In this review, the present-day and summarized knowledge of the laboratory and clinical findings on the i.v. and i.m. routes of antivenom administration is provided, with a special emphasis on the contribution of the lymphatic system to the process of venom elimination. Until now, antivenom-mediated neutralization has not yet been discussed in the context of the synergistic action of both blood and lymph. A current viewpoint might help to improve the comprehension of the venom/antivenom pharmacokinetics and the optimal approach for drug application. There is a great need for additional dependable, practical, well-designed studies, as well as more practice-related experience reports. As a result, opportunities for resolving long-standing disputes over choosing one therapeutic principle over another might be created, improving the safety and effectiveness of snakebite management.