Snake venom thrombin-like enzymes

Isolation and Functional Characterization of Erythrofibrase: An Alfa-Fibrinogenase Enzyme from Trimeresurus erythrurus Venom of North-East India

Green pit viper bites induce mild toxicity with painful local swelling, blistering, cellulitis, necrosis, ecchymosis and consumptive coagulopathy. Several bite cases of green pit vipers have been reported in several south-east Asian countries including the north-eastern region of India. The present study describes isolation and characterization of a haemostatically active protein from Trimeresurus erythrurus venom responsible for coagulopathy. Using a two-step chromatographic method, a snake venom serine protease erythrofibrase was purified to homogeneity. SDS-PAGE of erythrofibrase showed a single band of ~30 kDa in both reducing and non-reducing conditions. The primary structure of erythrofibrase was determined by ESI LC-MS/MS, and the partial sequence obtained showed 77% sequence similarity with other snake venom thrombin-like enzymes (SVTLEs). The partial sequence obtained had the typical 12 conserved cysteine residues, as well as the active site residues (His57, Asp102 and Ser195). Functionally, erythrofibrase showed direct fibrinogenolytic activity by degrading the Aα chain of bovine fibrinogen at a slow rate, which might be responsible for causing hypofibrinogenemia and incoagulable blood for several days in envenomated patients. Moreover, the inability of Indian polyvalent antivenom (manufactured by Premium Serum Pvt. Ltd., Maharashtra, India) to neutralize the thrombin-like and plasmin-like activity of erythrofibrase can be correlated with the clinical inefficacy of antivenom therapy. This is the first study reporting an α-fibrinogenase enzyme erythrofibrase from T. erythrurus venom, which is crucial for the pathophysiological manifestations observed in envenomated victims.

"Fanged to Peril": Interesting Snake Bite Case Series

Snakebite is an acute life-threatening medical emergency and is included among the neglected tropical diseases in India. The incidence of snakebite mortality is particularly high in Southeast Asia and India has the highest number of cases of snakebites with a mortality of 35,000 to 50,000 cases per year according to the World Health Organization (WHO) direct estimation. There are three families of venomous snakes in Southeast Asia which mainly include Elapidae, Viperidae, and Colubridae. Snakebite victims show varied clinical presentations ranging from local signs to systemic signs of envenomation. WHO has detailed five syndromes based on various clinical presentations and the most probable family of snakes responsible for that syndrome. There are several cases reported on the initial clinical presentations in the literature; however, case series which include the presentation to ER, the hospital course, and management of complications have not been published in the literature. Following is a case series of five patients of diverse age groups who presented to the Emergency Medicine Department (ED) with a wide spectrum of clinical presentations, diverse clinical courses, and management strategies. These patients not only required the administration of anti-snake venom in the ED but also required additional interventional modalities including renal replacement therapy for acute kidney injury and biopsy-proven acute tubular necrosis, viper-induced consumptive coagulopathy, management of coagulopathy in pediatrics, management of compartment syndrome in pregnancy, mechanical ventilation for respiratory failure and management of neurotoxicity. We hereby emphasize that early recognition of signs of envenomation and early administration of anti-snake venom is imperative in the initial management of snakebites along with the monitoring of a snakebite victim for complications and timely management of the same.

A case report of Ovophis monitcola (Mountain pit-viper) envenoming in northeastern India resulting in prolonged coagulopathy

India is home to a diverse spectrum of medically-significant snakes accounting for the world's largest burden of envenoming, morbidity and mortality. Indian polyspecific antivenom is derived from the venom of four snake species (Daboia russelii, Echis carinatus, Naja naja and Bungarus caeruleus), considered to be responsible for the majority of snakebite morbidity and mortality. The treatment of venomous bites from other less-commonly encountered venomous snake species can be challenging. In this report, we describe the case of a 32-year-old male who presented with features of local cytotoxicity and coagulopathy following a bite from Ovophis monitcola (mountain pit-viper) in Nagaland, northeast India. Local and systemic envenoming, confirmed by bedside and laboratory based clotting assays, failed to respond to polyspecific antivenom and venom-induced consumption coagulopathy persisted for 28 days. Remote consultation with a national Poison Control Centre helped establish the responsible snake species and guide appropriate medical management.

Green Pit Viper Envenomations in Bangkok: A Comparison of Follow-Up Compliance and Clinical Outcomes in Older and Younger Adults

We compared older and younger adults envenomated by the green pit viper (GPV) with regard to the following: follow-up compliance, elapsed time between envenomation and emergency department (ED) visit, and clinical/treatment outcomes. This was a two-site retrospective cohort study. We searched hospital electronic medical databases between January 2011 and December 2021. Patients aged 15 and above were eligible if they had a history of snakebite and had at least two VCT and/or platelet count results in their medical records. After the search, 1550 medical records were reviewed and 760 cases were found to be eligible for analysis. In total, 205 cases (27.0%) were ≥60 years old. The median ages in the younger and older groups were 40 (26-51) and 68 (64-75) years, respectively. The median elapsed times from bite to the ED were 47 (30-118) vs. 69 (35-150) min (p-value = 0.001). Overall, 91.3% of all cases were managed as out-patient cases and were eligible for follow-up appointments. The rate of out-patient follow-up at 72 ± 12 h in the older patients was significantly higher (43.2%) than in the younger adult patients (32.4%) (p-value = 0.01). Regarding the clinical/treatment outcomes, the rates of coagulopathy, antivenom administration, and hospital admission were not statistically different between both groups.

Diagnostic Tests for Hypofibrinogenemia Resulting from Green Pit Viper (Trimeresurus albolabris) Envenomation: A Simulated In Vitro Study

INTRODUCTION

The green pit viper (GPV) Trimeresurus albolabris is found in Southeast Asia. Its venom has a thrombin-like activity that can cause hypofibrinogenemia. Fibrinogen measurement is not always available. We aimed to establish a more available diagnostic tool indicating hypofibrinogenemia caused by GPV envenomation.

METHODS

This was an in vitro study, in which healthy subjects aged 20 to 45 y were enrolled. There were 2 experiments. In Experiment 1, blood samples from 1 subject had varying amounts of T albolabris venom added to determine its effect on the fibrinogen level (FL). In Experiment 2, 3 sets of blood samples were obtained from another 25 subjects. The 2 venom doses established in Experiment 1 were used on 2 sets of the samples to simulate severe (FL <1.0 g·L-1) and mild hypofibrinogenemia (FL 1.0-1.7 g·L-1). The third set of samples was venom-free. All samples were used for platelet counts, prothrombin time (PT)/international normalized ratio (INR)/activated partial thromboplastin time (aPTT), and 2 bedside clotting tests. Diagnostic parameters were calculated against the target FL of <1.0 g·L-1 and <1.7 g·L-1.

RESULTS

Twenty-five subjects were enrolled in Experiment 2. On referencing normal cutoff values (platelet count >150,000 cells/mm3, venous clotting time <15 min, normal 20-min whole blood clotting time, INR <1.2, aPTT <30), we found abnormalities of 5, 0, 0, 3, and 22%, respectively. The highest correlation with hypofibrinogenemia was provided by PT/INR. For an FL of <1.0 g·L-1, PT and INR revealed the highest areas under the receiver operating characteristic curve, 0.76 (95% CI, 0.55-0.97) and 0.76 (95% CI, 0.57-0.97), respectively. The highest accuracy and the highest sensitivity were provided by PT/INR.

CONCLUSIONS

PT/INR could be used as a diagnostic test for severe hypofibrinogenemia in GPV envenomation because of its high accuracy and area under the receiver operating characteristic curve.

Uncommon defibrinogenation and coagulopathy caused by Trimeresurus stejnegeri stejnegeri envenomation in a patient with swelling above the ankle

In Taiwan, Trimeresurus stejnegeri stejnegeri (Stejneger's Bamboo pitviper) is responsible for more than half of all venomous snakebites annually. This species often causes local envenoming characterized by tissue swelling and pain, occasional local ecchymosis, bullae and blister formation, and lymphangitis and lymphadenitis. The pathophysiology and treatment of potentially life-threatening coagulopathy and defibrinogenation induced by T. s. stejnegeri systemic envenoming have not been specifically addressed. Here, we describe the case of a man who was bitten by T. s. stejnegeri on his right first toe, which later developed into swelling above the ankle. It was found that there was severe hypofibrinogenemia, prolonged prothrombin time, and reduced activities of factors V and XI, plasminogen, and α2-antiplasmin. Even though a favorable outcome was achieved after repeatedly administering specific antivenom, fresh frozen plasma, and cryoprecipitate, probably low effectiveness of antivenom against the coagulopathy and prodigious amounts of replacement products were observed. To control coagulopathy early and avoid the needless replacement of coagulation factor, which are associated with inherent adverse reactions, more frequent serial blood assessment (e.g., every 6 h) and higher initial antivenom doses may be helpful. Knowledge of the specific coagulation factor deficiencies may improve our understanding of the relationship between hemotoxins and the resulting envenoming syndromes in this snakebite.

An Emergent Role for Mitochondrial Bioenergetics in the Action of Snake Venom Toxins on Cancer Cells

Beyond the role of mitochondria in apoptosis initiation/execution, some mitochondrial adaptations support the metastasis and chemoresistance of cancer cells. This highlights mitochondria as a promising target for new anticancer strategies. Emergent evidence suggests that some snake venom toxins, both proteins with enzymatic and non-enzymatic activities, act on the mitochondrial metabolism of cancer cells, exhibiting unique and novel mechanisms that are not yet fully understood. Currently, six toxin classes (L-amino acid oxidases, thrombin-like enzymes, secreted phospholipases A2, three-finger toxins, cysteine-rich secreted proteins, and snake C-type lectin) that alter the mitochondrial bioenergetics have been described. These toxins act through Complex IV activity inhibition, OXPHOS uncoupling, ROS-mediated permeabilization of inner mitochondrial membrane (IMM), IMM reorganization by cardiolipin interaction, and mitochondrial fragmentation with selective migrastatic and cytotoxic effects on cancer cells. Notably, selective internalization and direct action of snake venom toxins on tumor mitochondria can be mediated by cell surface proteins overexpressed in cancer cells (e.g. nucleolin and heparan sulfate proteoglycans) or facilitated by the elevated Δψm of cancer cells compared to that non-tumor cells. In this latter case, selective mitochondrial accumulation, in a Δψm-dependent manner, of compounds linked to cationic snake peptides may be explored as a new anti-cancer drug delivery system. This review analyzes the effect of snake venom toxins on mitochondrial bioenergetics of cancer cells, whose mechanisms of action may offer the opportunity to develop new anticancer drugs based on toxin scaffolds.

A comparative cross-reactivity and paraspecific neutralization study on Hypnale hypnale, Echis carinatus, and Daboia russelii monovalent and therapeutic polyvalent anti-venoms

Envenoming by the hump-nosed pit viper (Hypnale hypnale) raises concern as it inflicts significant debilitation and death in the Western Ghats of India and in the adjacent island nation of Sri Lanka. In India, its medical significance was realized only during 2007 due to its misidentification as Echis carinatus and sometimes as Daboia russelii. Of late, several case reports have underlined the ineptness of the existing polyvalent anti-venom therapy against H. hypnale envenoming. Currently, H. hypnale bite has remained dreadful in India due to the lack of neutralizing anti-venom therapy. Hence, this study was undertaken to establish a systematic comparative, biochemical, pathological, and immunological properties of Sri Lankan H. hypnale venom alongside Indian E. carinatus, and D. russelii venoms. All three venoms differed markedly in the extent of biochemical activities including proteolytic, deoxyribonuclease, L-amino acid oxidase, 5'-nucleotidase, hyaluronidase, and indirect hemolytic activities. The venoms also differed markedly in their pathological properties such as edema, hemorrhage, myotoxic, cardiotoxic, and coagulant activities. The venoms showed stark differences in their protein banding pattern. Strikingly, the affinity-purified rabbit monovalent anti-venoms prepared against H. hypnale, E. carinatus, and D. russelii venoms readily reacted and neutralized the biochemical and pathological properties of their respective venoms, but they insignificantly cross-reacted with, and thus failed to show paraspecific neutralization of any of the effects of the other two venoms, demonstrating the large degree of variations between these venoms. Further, the Indian therapeutic polyvalent anti-venoms from VINS Bioproducts, and Bharath Serums and Vaccines failed to protect H. hypnale venom-induced lethal effects in mice.

Hemostatic Analysis of Simulated Gloydius ussuriensis Envenomation Using Canine Blood: A Comparison of Thromboelastography and Classical Coagulation Tests

Snake envenomation may lead to venom-induced consumptive coagulopathy (VICC), usually diagnosed by classical coagulation tests (CCTs), such as prothrombin time (PT) and activated partial thromboplastin time (aPTT). However, the results of CCTs are frequently normal in the initial stages, which may delay anti-venom treatments. Thromboelastography (TEG) is a point-of-care and real-time diagnostic tool that enables a comprehensive assessment of the coagulation process. This in vitro study aimed to determine concentration-dependent changes in canine blood caused by Gloydius ussuriensis (G. ussuriensis) envenomation using TEG and CCTs. Lyophilized G. ussuriensis venom was reconstructed using mouse intravenous lethal dose 50 (LD50iv) and serially diluted to 25% LD50iv, 50% LD50iv, and 75% LD50iv to reproduce VICC at different concentrations. Normal saline was used for the control. We compared TEG values of the reaction time (R), kinetic time (K), rate of clot formation (α-angle), maximum amplitude (MA), fibrinolysis at 30 min (LY30), and global strength of the clot (G) with those of PT, aPTT, fibrinogen, and platelet counts (PLTs). Most TEG parameters, except R and LY30, demonstrated statistically significant changes compared with the control at all concentrations. CCTs, except PLTs, revealed significant changes at ≥50% LD50iv. Thus, TEG could be a useful diagnostic strategy for early VICC and preventing treatment delay.

Functional and biological insights of rCollinein-1, a recombinant serine protease from Crotalus durissus collilineatus

BACKGROUND

The prevalent class of snake venom serine proteases (SVSP) in Viperidae venoms is the thrombin-like enzymes, which, similarly to human thrombin, convert fibrinogen into insoluble fibrin monomers. However, thrombin-like serine proteases differ from thrombin by being unable to activate factor XIII, thus leading to the formation of loose clots and fibrinogen consumption. We report the functional and biological characterization of a recombinant thrombin-like serine protease from Crotalus durissus collilineatus, named rCollinein-1.

METHODS

Heterologous expression of rCollinein-1 was performed in Pichia pastoris system according to a previously standardized protocol, with some modifications. rCollinein-1 was purified from the culture medium by a combination of three chromatographic steps. The recombinant toxin was tested in vitro for its thrombolytic activity and in mice for its edematogenicity, blood incoagulability and effect on plasma proteins.

RESULTS

When tested for the ability to induce mouse paw edema, rCollinein-1 demonstrated low edematogenic effect, indicating little involvement of this enzyme in the inflammatory processes resulting from ophidian accidents. The rCollinein-1 did not degrade blood clots in vitro, which suggests that this toxin lacks fibrinolytic activity and is not able to directly or indirectly activate the fibrinolytic system. The minimal dose of rCollinein-1 that turns the blood incoagulable in experimental mice is 7.5 mg/kg. The toxin also led to a significant increase in activated partial thromboplastin time at the dose of 1 mg/kg in the animals. Other parameters such as plasma fibrinogen concentration and prothrombin time were not significantly affected by treatment with rCollinein-1 at this dose. The toxin was also able to alter plasma proteins in mouse after 3 h of injection at a dose of 1 mg/kg, leading to a decrease in the intensity of beta zone and an increase in gamma zone in agarose gel electrophoresis.

CONCLUSION

These results suggest that the recombinant enzyme has no potential as a thrombolytic agent but can be applied in the prevention of thrombus formation in some pathological processes and as molecular tools in studies related to hemostasis.

Thrombin-like enzymes from snake venom: Structural characterization and mechanism of action

Snake venom thrombin-like enzymes (SVTLEs) constitute the major portion (10-24%) of snake venom and these are the second most abundant enzymes present in the crude venom. During envenomation, these enzymes had shown prominently the various pathological effects, such as disturbance in hemostatic system, fibrinogenolysis, fibrinolysis, platelet aggregation, thrombosis, neurologic disorders, activation of coagulation factors, coagulant, procoagulant etc. These enzymes also been used as a therapeutic agent for the treatment of various diseases such as congestive heart failure, ischemic stroke, thrombotic disorders etc. Although the crystal structures of five SVTLEs are available in the Protein Data Bank (PDB), there is no single article present in the literature that has described all of them. The current work describes the structural aspects, structure-based mechanism of action, processing and inhibition of these enzymes. The sequence analysis indicates that these enzymes show a high sequence identity (57-85%) with each other and low sequence identity with trypsin (36-43%), human alpha-thrombin (29-36%) and other snake venom serine proteinases (57-85%). Three-dimensional structural analysis indicates that the loops surrounding the active site are variable both in amino acids composition and length that may convey variable substrate specificity to these enzymes. The surface charge distributions also vary in these enzymes. Docking analysis with suramin shows that this inhibitor preferably binds to the C-terminal region of these enzymes and causes the destabilization of their three-dimensional structure.