Antithrombotic effect of a protein-type I class snake venom metalloproteinase, kistomin, is mediated by affecting glycoprotein Ib-von Willebrand factor interaction

Fuentes L, Pimenta A, Nagem RAP, Chávez-Olórtegui C, Schneider FS, Molina F, Sanchez EF, Suárez D, Ferreira RS. Assessing the Interactions between Snake Venom Metalloproteinases and Hydroxamate Inhibitors Using Kinetic and ITC Assays, Molecular Dynamics Simulations and MM/PBSA-Based Scoring Functions

Bothrops species are the main cause of snake bites in rural communities of tropical developing countries of Central and South America. Envenomation by Bothrops snakes is characterized by prominent local inflammation, hemorrhage and necrosis as well as systemic hemostatic disturbances. These pathological effects are mainly caused by the major toxins of the viperidae venoms, the snake venom metalloproteinases (SVMPs). Despite the antivenom therapy efficiency to block the main toxic effects on bite victims, this treatment shows limited efficacy to prevent tissue necrosis. Thus, drug-like inhibitors of these toxins have the potential to aid serum therapy of accidents inflicted by viper snakes. Broad-spectrum metalloprotease inhibitors bearing a hydroxamate zinc-binding group are potential candidates to improve snake bites therapy and could also be used to study toxin-ligand interactions. Therefore, in this work, we used both docking calculations and molecular dynamics simulations to assess the interactions between six hydroxamate inhibitors and two P-I SVMPs selected as models: Atroxlysin-I (hemorrhagic) from Bothrops atrox, and Leucurolysin-a (nonhemorrhagic) from Bothrops leucurus. We also employed a large variety of end-point free energy methods in combination with entropic terms to produce scoring functions of the relative affinities of the inhibitors for the toxins. Then we identified the scoring functions that best correlated with experimental data obtained from kinetic activity assays. In addition, to the characterization of these six molecules as inhibitors of the toxins, this study sheds light on the main enzyme-inhibitor interactions, explaining the broad-spectrum behavior of the inhibitors, and identifies the energetic and entropic terms that improve the performance of the scoring functions.

A Novel P-III Metalloproteinase from Bothrops barnetti Venom Degrades Extracellular Matrix Proteins, Inhibits Platelet Aggregation, and Disrupts Endothelial Cell Adhesion via α5β1 Integrin Receptors to Arginine-Glycine-Aspartic Acid (RGD)-Containing Molecules

Viperid snake venoms are notably abundant in metalloproteinases (proteins) (SVMPs), which are primarily responsible for inducing hemorrhage and disrupting the hemostatic process and tissue integrity in envenomed victims. In this study, barnettlysin-III (Bar-III), a hemorrhagic P-III SVMP, was purified from the venom of the Peruvian snake Bothrops barnetti. Bar-III has a molecular mass of approximately 50 kDa and is a glycosylation-dependent functional metalloproteinase. Some biochemical properties of Bar-III, including the full amino acid sequence deduced from its cDNA, are reported. Its enzymatic activity is increased by Ca2+ ions and inhibited by an excess of Zn2+. Synthetic metalloproteinase inhibitors and EDTA also inhibit its proteolytic action. Bar-III degrades several plasma and ECM proteins, including fibrin(ogen), fibronectin, laminin, and nidogen. Platelets play a key role in hemostasis and thrombosis and in other biological process, such as inflammation and immunity, and platelet activation is driven by the platelet signaling receptors, glycoprotein (GP)Ib-IX-V, which binds vWF, and GPVI, which binds collagen. Moreover, Bar-III inhibits vWF- and convulxin-induced platelet aggregation in human washed platelets by cleaving the recombinant A1 domain of vWF and GPVI into a soluble ectodomain fraction of ~55 kDa (sGPVI). Bar-III does not reduce the viability of cultured endothelial cells; however, it interferes with the adhesion of these cells to fibronectin, vitronectin, and RGD peptides, as well as their migration profile. Bar-III binds specifically to the surface of these cells, and part of this interaction involves α5β1 integrin receptors. These results contribute to a better comprehension of the pathophysiology of snakebite accidents/incidents and could be used as a tool to explore novel and safer anti-venom therapeutics.

Modulation of Glycoprotein VI and Its Downstream Signaling Pathways as an Antiplatelet Target

Antiplatelet therapy aims to reduce the risk of thrombotic events while maintaining hemostasis. A promising current approach is the inhibition of platelet glycoprotein GPVI-mediated adhesion pathways; pathways that do not involve coagulation. GPVI is a signaling receptor integral for collagen-induced platelet activation and participates in the thrombus consolidation process, being a suitable target for thrombosis prevention. Considering this, the blocking or antibody-mediated depletion of GPVI is a promising antiplatelet therapy for the effective and safe treatment of thrombotic diseases without a significant risk of bleeding and impaired hemostatic plug formation. This review describes the current knowledge concerning pharmaceutical approaches to platelet GPVI modulation and its downstream signaling pathways in this context.

A fibrinolytic snake venom metalloproteinase, mutalysin-II, with antiplatelet activity and targeting capability toward glycoprotein GPIbα and glycoprotein GPVI

Glycoprotein (GP)Ib that binds von Willebrand factor (vWF) and glycoprotein (GP)VI, that binds collagen play a significant role in platelet activation and aggregation, and are potential targets for antithrombotic treatment. They are targeted by snake venom proteinases. The effect of a such proteinase, mutalysin-II, on platelet aggregation was examined using washed human platelets and platelet-rich plasma. Its proteolytic activity on vWF, on its binding partner GPIbα, and on GPVI was analyzed by SDS-PAGE, and immunodetection with the corresponding antibodies after blotting. Dose- and time-dependently, mutalysin-II inhibits aggregation of washed platelets induced by vWF plus ristocetin and by convulxin, but with no significant effect on platelet-rich-plasma. Furthermore, mutalysin-II cleaves vWF into low molecular mass multimers of vWF and a rvWF-A1 domain to realease a ∼27-kDa fragment detectable by SDS-PAGE and blotting with mouse anti-rvWF-A1-domain IgG. Moreover, GPVI was cut by mutalysin-II into a soluble ∼55-kDa ectodomain and a fragment of ∼35-kDa. Thus, mutalysin-II inhibits vWF-induced platelet aggregation via cleavage of bound vWF-A1, and its receptor GPIbα. The additional cleavage of, GPVI, blocks collagen-induced platelets. Our data highlight mutalysin-II as an interesting platelet-directed tool targeting vWF-GPIbα binding and particularly GPVI. Thus, it might be suited for antithrombotic therapy as its combined inactivation of two receptors does not significantly compromise hemostasis, but shows high efficacy and safety. Studies are needed to further develop and demonstrate its potential benefits.

Improved Antithrombotic Activity and Diminished Bleeding Side Effect of a PEGylated αIIbβ3 Antagonist, Disintegrin

Polymer polyethylene glycol (PEG), or PEGylation of polypeptides improves protein drug stability by decreasing degradation and reducing renal clearance. To produce a pharmaceutical disintegrin derivative, the N-terminal PEGylation technique was used to modify the disintegrin derivative [KGDRR]trimucrin for favorable safety, pharmacokinetic profiles, and antithrombotic efficacy. We compared intact [KGDRR]trimucrin (RR) and PEGylated KGDRR (PEG-RR) by in vitro and in vivo systems for their antithrombotic activities. The activity of platelet aggregation inhibition and the bleeding tendency side effect were also investigated. PEG-RR exhibited optimal potency in inhibiting platelet aggregation of human/mouse platelet-rich plasma activated by collagen or ADP with a lower IC₅₀ than the intact derivative RR. In the illumination-induced mesenteric venous thrombosis model, RR and PEG-RR efficaciously prevented occlusive thrombosis in a dose-dependent manner. In rotational thromboelastometry assay, PEG-RR did not induce hypocoagulation in human whole blood even given at a higher concentration (30 μg/mL), while RR slightly prolonged clotting time. However, RR and PEG-RR were not associated with severe thrombocytopenia or bleeding in FcγRIIa-transgenic mice at equally efficacious antithrombotic dosages. We also found the in vivo half-life of PEGylation was longer than RR (RR: 15.65 h vs. PEG-RR: 20.45 h). In conclusion, injectable PEG-RR with prolonged half-life and decreased bleeding risk is a safer anti-thrombotic agent for long-acting treatment of thrombus diseases.

High throughput screening and identification of coagulopathic snake venom proteins and peptides using nanofractionation and proteomics approaches

Snakebite is a neglected tropical disease that results in a variety of systemic and local pathologies in envenomed victims and is responsible for around 138,000 deaths every year. Many snake venoms cause severe coagulopathy that makes victims vulnerable to suffering life-threating haemorrhage. The mechanisms of action of coagulopathic snake venom toxins are diverse and can result in both anticoagulant and procoagulant effects. However, because snake venoms consist of a mixture of numerous protein and peptide components, high throughput characterizations of specific target bioactives is challenging. In this study, we applied a combination of analytical and pharmacological methods to identify snake venom toxins from a wide diversity of snake species that perturb coagulation. To do so, we used a high-throughput screening approach consisting of a miniaturised plasma coagulation assay in combination with a venom nanofractionation approach. Twenty snake venoms were first separated using reversed-phase liquid chromatography, and a post-column split allowed a small fraction to be analyzed with mass spectrometry, while the larger fraction was collected and dispensed onto 384-well plates. After fraction collection, any solvent present in the wells was removed by means of freeze-drying, after which it was possible to perform a plasma coagulation assay in order to detect coagulopathic activity. Our results demonstrate that many snake venoms simultaneously contain both procoagulant and anticoagulant bioactives that contribute to coagulopathy. In-depth identification analysis from seven medically-important venoms, via mass spectrometry and nanoLC-MS/MS, revealed that phospholipase A2 toxins are frequently identified in anticoagulant venom fractions, while serine protease and metalloproteinase toxins are often associated with procoagulant bioactivities. The nanofractionation and proteomics approach applied herein seems likely to be a valuable tool for the rational development of next-generation snakebite treatments by facilitating the rapid identification and fractionation of coagulopathic toxins, thereby enabling specific targeting of these toxins by new therapeutics such as monoclonal antibodies and small molecule inhibitors.

Local and systemic effects of BtaMP-1, a new weakly hemorrhagic Snake Venom Metalloproteinase purified from Bothriopsis taeniata Snake Venom

A new weak hemorrhagic metalloproteinase named BtaMP-1 was purified from Bothriopsis taeniata snake venom by molecular exclusion followed by anion exchange chromatographies. This protein showed a molecular mass of 25,968.16 Da and is composed of 218 amino acid residues. The multiple alignments of its partial amino acid sequence showed high structural identity with other P-I class SVMP. BtaMP-1 showed caseinolytic activity that was enhanced by Ca²⁺ ion, completely inhibited by chelating and reducing agents and can be classified as an α-fibrinogenolytic enzyme. Locally, BtaMP-1 induces hemorrhage and edema, but not myotoxicity. These findings were confirmed by histological analysis of mouse gastrocnemius muscle. "In vitro" studies suggest that BtaMP-1 induce cytotoxicity in myoblast C2C12 but not in the myotubes cell line. BtaMP-1 induced systemic alterations in mice with one MHD and two hours exposure; histological analysis of lungs showed hemorrhagic areas, congestion, and increase the thickness of alveolar septum. Also, this protein induced mild effects on kidney and disruption of coagulation by depletion of fibrinogen plasma levels. This work provides insights into the importance of BtaMP-1 biological effects in envenomation by Bothropsis taeniata snake venom and providing further evidence to understand the role of P-I class SVMP in ophidian envenomation.

Direct Fibrinolytic Snake Venom Metalloproteinases Affecting Hemostasis: Structural, Biochemical Features and Therapeutic Potential

Snake venom metalloproteinases (SVMPs) are predominant in viperid venoms, which provoke hemorrhage and affect hemostasis and thrombosis. P-I class enzymes consist only of a single metalloproteinase domain. Despite sharing high sequence homology, only some of them induce hemorrhage. They have direct fibrin(ogen)olytic activity. Their main biological substrate is fibrin(ogen), whose Aα-chain is degraded rapidly and independently of activation of plasminogen. It is important to understand their biochemical and physiological mechanisms, as well as their applications, to study the etiology of some human diseases and to identify sites of potential intervention. As compared to all current antiplatelet therapies to treat cardiovascular events, the SVMPs have outstanding biochemical attributes: (a) they are insensitive to plasma serine proteinase inhibitors; (b) they have the potential to avoid bleeding risk; (c) mechanistically, they are inactivated/cleared by α2-macroglobulin that limits their range of action in circulation; and (d) few of them also impair platelet aggregation that represent an important target for therapeutic intervention. This review will briefly highlight the structure–function relationships of these few direct-acting fibrinolytic agents, including, barnettlysin-I, isolated from Bothrops barnetti venom, that could be considered as potential agent to treat major thrombotic disorders. Some of their pharmacological advantages are compared with plasmin.

An αIIb β3 antagonist prevents thrombosis without causing Fc receptor γ-chain IIa-mediated thrombocytopenia

Essentials FcγRIIa-mediated thrombocytopenia is associated with drug-dependent antibodies (DDAbs). We investigated the correlation between αIIb β3 binding epitopes and induction of DDAbs. An FcγRIIa-transgenic mouse model was used to evaluate thrombocytopenia among anti-thrombotics. An antithrombotic with binding motif toward αIIb β-propeller domain has less bleeding tendency.

SUMMARY

Background Thrombocytopenia, a common side effect of Arg-Gly-Asp-mimetic antiplatelet drugs, is associated with drug-dependent antibodies (DDAbs) that recognize conformation-altered integrin αIIb β3 . Objective To explore the correlation between αIIb β3 binding epitopes and induction of DDAb binding to conformation-altered αIIb β3 , we examined whether two purified disintegrins, TMV-2 and TMV-7, with distinct binding motifs have different effects on induction of αIIb β3 conformational change and platelet aggregation in the presence of AP2, an IgG1 inhibitory mAb raised against αIIb β3 . Methods We investigated the possible mechanisms of intrinsic platelet activation of TMV-2 and TMV-7 in the presence of AP2 by examining the signal cascade, tail bleeding time and immune thrombocytopenia in Fc receptor γ-chain IIa (FcγRIIa) transgenic mice. Results TMV-7 has a binding motif that recognizes the αIIb β-propeller domain of αIIb β3 , unlike that of TMV-2. TMV-7 neither primed the platelets to bind ligand, nor caused a conformational change of αIIb β3 as identified with the ligand-induced binding site mAb AP5. In contrast to eptifibatide and TMV-2, cotreatment of TMV-7 with AP2 did not induce FcγRIIa-mediated platelet aggregation and the downstream activation cascade. Both TMV-2 and TMV-7 efficaciously prevented occlusive thrombosis in vivo. Notably, both eptifibatide and TMV-2 caused severe thrombocytopenia mediated by FcγRIIa, prolonged tail bleeding time in vivo, and repressed human whole blood coagulation indexes, whereas TMV-7 did not impair hemostatic capacity. Conclusions TMV-7 shows antiplatelet and antithrombotic activities resulting from a mechanism different from that of all other tested αIIb β3 antagonists, and may offer advantages as a therapeutic agent with a better safety profile.

Proteases of haematophagous arthropod vectors are involved in blood-feeding, yolk formation and immunity - a review

Ticks, triatomines, mosquitoes and sand flies comprise a large number of haematophagous arthropods considered vectors of human infectious diseases. While consuming blood to obtain the nutrients necessary to carry on life functions, these insects can transmit pathogenic microorganisms to the vertebrate host. Among the molecules related to the blood-feeding habit, proteases play an essential role. In this review, we provide a panorama of proteases from arthropod vectors involved in haematophagy, in digestion, in egg development and in immunity. As these molecules act in central biological processes, proteases from haematophagous vectors of infectious diseases may influence vector competence to transmit pathogens to their prey, and thus could be valuable targets for vectorial control.

Metalloproteases Affecting Blood Coagulation, Fibrinolysis and Platelet Aggregation from Snake Venoms: Definition and Nomenclature of Interaction Sites

Snake venom metalloproteases, in addition to their contribution to the digestion of the prey, affect various physiological functions by cleaving specific proteins. They exhibit their activities through activation of zymogens of coagulation factors, and precursors of integrins or receptors. Based on their structure–function relationships and mechanism of action, we have defined classification and nomenclature of functional sites of proteases. These metalloproteases are useful as research tools and in diagnosis and treatment of various thrombotic and hemostatic conditions. They also contribute to our understanding of molecular details in the activation of specific factors involved in coagulation, platelet aggregation and matrix biology. This review provides a ready reference for metalloproteases that interfere in blood coagulation, fibrinolysis and platelet aggregation.

Regulation of platelet membrane protein shedding in health and disease

Extracellular proteolysis of platelet plasma membrane proteins is an event that ensues platelet activation. Shedding of surface receptors such as glycoprotein (GP) Ibα, GPV and GPVI as well as externalized proteins P-selectin and CD40L releases soluble ectodomain fragments that are subsequently detectable in plasma. This results in the irreversible functional downregulation of platelet receptor-mediated adhesive interactions and the generation of biologically active fragments. In this review, we describe molecular insights into the regulation of platelet receptor and ligand shedding in health and disease. The scope of this review is specially focused on GPIbα, GPV, GPVI, P-selectin and CD40L where we: (1) describe the basic physiological regulation of expression and shedding of these proteins in hemostasis illustrate alterations in receptor expression during (2) apoptosis and (3) ex vivo storage relevant for blood banking purposes; (4) discuss considerations to be made when analyzing and interpreting shedding of platelet membrane proteins and finally; (5) collate clinical evidence that quantify these platelet proteins during disease.

Venomics of Calloselasma rhodostoma, the Malayan pit viper: A complex toxin arsenal unraveled

The venom of Malayan pit viper (Calloselasma rhodostoma) is highly toxic but also valuable in drug discovery. However, a comprehensive proteome of the venom that details its toxin composition and abundance is lacking. This study aimed to unravel the venom complexity through a multi-step venomic approach. At least 96 distinct proteins (29 basic, 67 acidic) in 11 families were identified from the venom. The venom consists of mainly snake venom metalloproteinases (SVMP, 41.17% of total venom proteins), within which the P-I (kistomin, 20.4%) and P-II (rhodostoxin, 19.8%) classes predominate. This is followed by C-type lectins (snaclec, 26.3%), snake venom serine protease (SVSP, 14.9%), L-amino acid oxidase (7.0%), phospholipase A2 (4.4%), cysteine-rich secretory protein (2.5%), and five minor toxins (nerve growth factor, neurotrophin, phospholipase B, 5' nucleotidase and phosphodiesterase, totaling 2.6%) not reported in the proteome hitherto. Importantly, all principal hemotoxins unveiled correlate with the syndrome: SVSP ancrod causes venom-induced consumptive coagulopathy, aggravated by thrombocytopenia caused by snaclec rhodocytin, a platelet aggregation inducer, while P-II rhodostoxin mediates hemorrhage, exacerbated by P-I kistomin and snaclec rhodocetin that inhibit platelet plug formation. These toxins exist in multiple isoforms and/or complex subunits, deserving further characterization for the development of an effective, polyspecific regional antivenom.

BIOLOGICAL SIGNIFICANCE

Advents in proteomics and bioinformatics have vigorously propelled the scientific discoveries of toxins from various lineages of venomous snakes. The Malayan pit viper, Calloselasma rhodostoma, is a medically important species in Southeast Asia as its bite can cause envenomation, while the venom is also a source of bioactive compounds for drug discovery. Detailed profiling of the venom, however, is inadequate possibly due to the complex nature of the venom and technical limitation in separating the constituents into details. Integrating a multi-step fractionation method, this study successfully revealed a comprehensive and quantitative profile of the composition of the venom of this medically important venomous snake. The relative abundance of the various venom proteins is determined in a global profile, providing useful information for understanding the pathogenic roles of the different toxins in C. rhodostoma envenomation. Notably, the principal hemotoxins were identified in great details, including the variety of toxin subunits and isoforms. The findings indicate that these toxins are the principal targets for effective antivenom neutralization, and should be addressed in the production of a pan-regional polyspecific antivenom. In addition, minor toxin components not reported previously in the venom were also detected in this study, enriching the current toxin database for the venomous snakes.

A Deep Insight into the Sialome of Rhodnius neglectus, a Vector of Chagas Disease

BACKGROUND

Triatomines are hematophagous insects that act as vectors of Chagas disease. Rhodnius neglectus is one of these kissing bugs found, contributing to the transmission of this American trypanosomiasis. The saliva of hematophagous arthropods contains bioactive molecules responsible for counteracting host haemostatic, inflammatory, and immune responses.

METHODS/PRINCIPAL FINDINGS

Next generation sequencing and mass spectrometry-based protein identification were performed to investigate the content of triatomine R. neglectus saliva. We deposited 4,230 coding DNA sequences (CDS) in GenBank. A set of 636 CDS of proteins of putative secretory nature was extracted from the assembled reads, 73 of them confirmed by proteomic analysis. The sialome of R. neglectus was characterized and serine protease transcripts detected. The presence of ubiquitous protein families was revealed, including lipocalins, serine protease inhibitors, and antigen-5. Metalloproteases, disintegrins, and odorant binding protein families were less abundant.

CONCLUSIONS/SIGNIFICANCE

The data presented improve our understanding of hematophagous arthropod sialomes, and aid in understanding hematophagy and the complex interplay among vectors and their vertebrate hosts.

A novel fibrinolytic metalloproteinase, barnettlysin-I from Bothrops barnetti (Barnett´s pitviper) snake venom with anti-platelet properties

BACKGROUND

Viperid snake venoms contain active components that interfere with hemostasis. We report a new P-I class snake venom metalloproteinase (SVMP), barnettlysin-I (Bar-I), isolated from the venom of Bothrops barnetti and evaluated its fibrinolytic and antithrombotic potential.

METHODS

Bar-I was purified using a combination of molecular exclusion and cation-exchange chromatographies. We describe some biochemical features of Bar-I associated with its effects on hemostasis and platelet function.

RESULTS

Bar-I is a 23.386 kDa single-chain polypeptide with pI of 6.7. Its sequence (202 residues) shows high homology to other members of the SVMPs. The enzymatic activity on dimethylcasein (DMC) is inhibited by metalloproteinase inhibitors e.g. EDTA, and by α2-macroglobulin. Bar-I degrades fibrin and fibrinogen dose- and time-dependently by cleaving their α-chains. Furthermore, it hydrolyses plasma fibronectin but not laminin nor collagen type I. In vitro Bar-I dissolves fibrin clots made either from purified fibrinogen or from whole blood. In contrast to many other P-I SVMPs, Bar-I is devoid of hemorrhagic activity. Also, Bar-I dose- and time-dependently inhibits aggregation of washed human platelets induced by vWF plus ristocetin and collagen (IC50=1.3 and 3.2 μM, respectively), presumably Bar-I cleaves both vWF and GPIb. Thus, it effectively inhibits vWF-induced platelet aggregation. Moreover, this proteinase cleaves the collagen-binding α2-A domain (160 kDa) of α2β1-integrin. This explains why it additionally inhibits collagen-induced platelet activation.

CONCLUSION

A non-hemorrhagic but fibrinolytic metalloproteinase dissolves fibrin clots in vitro and impairs platelet function.

GENERAL SIGNIFICANCE

This study provides new opportunities for drug development of a fibrinolytic agent with antithrombotic effect.

Functional characterization of fibrinolytic metalloproteinases (colombienases) isolated from Bothrops colombiensis venom

Researchers trying to improve the safety and efficacy of fibrinolytic therapy have been isolating fibrinolytic enzymes from snake venoms. Two fibrinolytic enzymes, colombienases 1 and 2, with significant activity have been isolated from the venom of Bothrops colombiensis.

METHODS

The colombienases were characterized for various biological activities which include hemorrhagic, fibrinogenolytic, proteolytic, hemolytic, edematogenic and cytotoxic.

RESULTS

Colombienases directly acted on fibrin by degrading fibrinogen Aα and Bβ chains without activating the fibrinolytic system (plasminogen/plasmin), additionally colombienase-2 degraded fibrinogen γ chains as well as the fibronectin molecule. Laminin and type IV collagen were colombienases resistant. Gelatin-zymogram activity was present in B. colombiensis venom (BcV) bands between 64 and 148 kDa. All activities were abolished by metalloproteinases inhibitors. Both enzymes lacked hemorrhagic, hemolytic, cytotoxic, plasminogen activator and coagulant activities.

CONCLUSIONS

Both colombienases had direct fibrino(geno)lytic activity without other toxic side effects including in vivo hemorrhaging, which could be promising in terms of therapeutic potential as thrombolytic agents.

Haemostatically active proteins in snake venoms

Snake venom proteins that affect the haemostatic system can cause (a) lowering of blood coagulability, (b) damage to blood vessels, resulting in bleeding, (c) secondary effects of bleeding, e.g. hypovolaemic shock and organ damage, and (d) thrombosis. These proteins may, or may not, be enzymes. We review the data on the most relevant haemostatically active proteinases, phospholipases A₂, L-amino acid oxidases and 5'-nucleotidases from snake venoms. We also survey the non-enzymatic effectors of haemostasis from snake venoms--disintegrins, C-type lectins and three-finger toxins. Medical applications have already been found for some of these snake venom proteins. We describe those that have already been approved as drugs to treat haemostatic disorders or are being used to diagnose such health problems. No clinical applications, however, currently exist for the majority of snake venom proteins acting on haemostasis. We conclude with the most promising potential uses in this respect.

A snake venom metalloproteinase, kistomin, cleaves platelet glycoprotein VI and impairs platelet functions

BACKGROUND AND OBJECTIVES

Injuries to the vessel wall and subsequent exposure of the matrix of the subendothelial layer resulted in thrombus formation. Platelet glycoprotein (GP) Ib and VI play a crucial role in matrix-induced activation and aggregation of platelets.

METHODS AND RESULTS

In the present study, we reported that the GPIb-cleaving snake venom metalloproteinase (SVMP), kistomin, inhibited collagen-induced platelet aggregation. Moreover, kistomin inhibited platelet aggregation induced by convulxin (CVX, a GPVI agonist) and a GPVI-specific antibody in a concentration and time-dependent manner. Kistomin treatment decreased platelet GPVI but not integrin alpha2beta1 and alphaIIbbeta3, accompanied with the formation of GPVI cleavage fragments, as determined by flow cytometric and Western blot analyses. In addition, intact platelet GPVI and recombinant GPVI were digested by kistomin to release 25- and 35-kDa fragments, suggesting that kistomin cleaved GPVI near the mucin-like region. We designed four synthetic peptides ranging from Leu180 to Asn249 as the substrates for kistomin and found that kistomin cleaved these synthetic peptides at FSE205/A206TA and NKV218/F219TT, as analyzed by MALDI-TOF-MS. In addition, GPVI-specific antibody-induced tyrosine kinase phosphorylation in platelets was reduced after kistomin pretreatment, and platelet adhesion to collagen but not to fibrinogen was attenuated by kistomin.

CONCLUSIONS

We provided here the first evidence that a P-I snake venom metalloproteinase, kistomin, inhibits the interaction between collagen and platelet GPVI through its proteolytic activity on GPVI, thus providing an alternative strategy for developing new anti-thrombotic agents.