A fibrinogen-clotting serine proteinase from Cerastes cerastes (horned viper) venom with arginine-esterase and amidase activities. Purification, characterization and kinetic parameter determination

Therapeutic outcome of quercetin nanoparticles on Cerastes cerastes venom-induced hepatorenal toxicity: a preclinical study

Aim: The objective of this study was to investigate the therapeutic potential of quercetin (QT) and QT-loaded poly(lactic-co-glycolic acid) nanoparticles (QT-NPs) on Cerastes cerastes venom-mediated inflammation, redox imbalance, hepatorenal tissue damage and local hemorrhage. Methods: The developed QT-NPs were first submitted to physicochemical characterization and then evaluated in the 'challenge then treat' and 'preincubation' models of envenoming. Results: QT-NPs efficiently alleviated hepatorenal toxicity, inflammation and redox imbalance and significantly attenuated venom-induced local hemorrhage. Interestingly, QT-NPs were significantly more efficient than free QT at 24 h post-envenoming, pointing to the efficacy of this drug-delivery system. Conclusion: These findings highlight the therapeutic potential of QT-NPs on venom-induced toxicity and open up the avenue for their use in the management of snakebite envenoming.

Isolation and Characterization of CD39-like Phosphodiesterase (Cc-PDE) from Cerastes cerastes Venom: Molecular Inhibitory Mechanism of Antiaggregation and Anticoagulation

BACKGROUND

Cerastes cerastes venom contains several bioactive proteins with inhibitory potential of platelet aggregation and blood coagulation.

OBJECTIVE

The current study deals with purification, characterization and determination of structural properties of Cc-PDE, the first phosphodiesterase from Cerastes cerastes venom.

MATERIAL AND METHODS

The purification process consists of three successive chromatographies including G75-Sephadex size exclusion, DEAE exchange chromatography and affinity using Sildenafil as a main PDEs' specific inhibitor. The amino acid sequence of purified Cc-PDE was determined by liquid chromatography coupled off line to MALDI-TOF/TOF. Modeling and structural features were obtained using several bioinformatics tools. In vivo and in vitro antiplatelet aggregation and anticoagulant assays were performed.

RESULTS

Cc-PDE (73 506.42 Da) is a 654-residue single polypeptide with 1-22 signal peptide and it is characterized by the presence of predominant basic amino acids suitable to alkaline pI (8.17). Cc-PDE structure is composed of β-strands (17%) and α-helices (24%) and it shares a high identity with homologous snake venom PDEs. Cc-PDE hydrolyzes both Bis-p-nitrophenyl phosphate (Km = 2.60 ± 0.95 mM, Vmax = 0.017 ± 0.002569 μmol.min-1) and p-nitrophenyl phosphate (Km = 7.13 mM ± 0.04490 mM, Vmax = 0.053 ±0.012 μmol.min-1). Cc-PDE prevents ADP- and ATP-induced platelet aggregation by hydrolyzing ADP and ATP, reducing surface P-selectin expression and attenuating platelet function. In addition, Cc-PDE inhibits coagulation factors involved in the intrinsic pathway demonstrated by a significant prolongation of activated partial thromboplastin time and in vivo long-lasting anticoagulation.

CONCLUSION

The obtained results revealed that Cc-PDE may have a therapeutic potential and could be a remedy for thromboembolic diseases as an alternative of anticoagulant and antiplatelet aggregation chemical origins.

Development and evaluation of polymeric nanoparticles as a delivery system for snake envenoming prevention

Polymer-based nanoparticles have become an appealing carrier for improving vaccine delivery efficiency. In this study, we investigated an interesting approach based on PLGA nanoparticles encapsulating Cerastes cerastes venom as an intranasal vaccine delivery system for snake envenomation prevention. Particles were synthesized by double emulsion solvent evaporation method and characterized for their size, morphology, distribution, and venom-nanoparticles interactions. An immunization trial was performed in mice by the intranasal route to evaluate the immune response, the reactogenicity, and the protective effect of this nanovaccine. The physicochemical and structural characteristics of Cc-loaded PLGA NPs revealed that the particles exhibited a spherical shape with a diameter of 370 nm, and a negatively charged surface with a zeta potential value of 19,9 mV. The immunization with Cc-PLGA NPs can induce a systemic innate and humoral immune response and confers protection against Cerastes cerastes venom (Cc) over than 6 LD50 with a cross-protection against Vipera lebetina venom (Vl) over than 5 LD50. Nano-encapsulation of Cc venom reduced its toxicity and the induced tissue alterations. Our results confirm that the nano-formulation Cc-PLGA NPs is a potent adjuvant system that improve the humoral immune response and provide protection against high lethal doses of viper venoms.

Isolation and Functional Identification of an Antiplatelet RGD-Containing Disintegrin from Cerastes cerastes Venom

The current report focuses on purification, structural and functional characterization of Cerastategrin from Cerastes cerastes venom, a novel basic disintegrin (pI 8.36) with 128 amino acid residues and a molecular weight of 13 835.25 Da measured by MALDI-MSMS. The 3D structure of Cerastategrin is organized as α-helix (13%), β-strand (15%) and disordered structure (30%) and presents homologies with several snake venom disintegrins. Structural modeling shows that Cerastategrin presents an RGD motif that connects specifically to integrin receptors. Cerastategrin exhibits the inhibition of ADP induced platelets with an IC₅₀ of 0.88 µg/mL and shows in vivo long stable anticoagulation effect 24 h post-injection of increasing doses ranging from 0.2 to 1 mg/kg, therefore, Cerastategrin maintained irreversibly the blood incoagulable. Moreover, Cerastategrin decreases the amount of bounded αIIbβ3 and reduced significantly the quantity of externalized P-Selectin. Cerastategrin acts as a molecule targeting specifically the receptor α_IIbβ₃; therefore, it behaves as a potent platelet activation inhibitor. As a new peptide with promising pharmacological properties, Cerastategrin could have a potential therapeutical effect in the vascular pathologies and may be a new effective treatment approach.

Myotoxicity induced by Cerastes cerastes venom: Beneficial effect of heparin in skeletal muscle tissue regeneration

Myonecrosis is a relevant tissue damage induced by snakes of Viperidae family often leading to permanent tissue and function loss and even amputation. The aim of this study was to evaluate the effect of heparin on skeletal muscle tissue regeneration after Cerastes cerastes envenomation. Mice received either the venom (1 LD₅₀) by i.m. route, or the venom followed, by heparin administration by i.v. route at 15 min and 4 h. Obtained results showed that Cerastes cerastes venom induced deep tissue structure alterations, characterized mainly by edema, hemorrhage, myonecrosis and inflammation. Myotoxicity was correlated with increased CK levels in sera, concomitant with their decrease in muscle tissue homogenates. Muscle wet weight was restored within 2 weeks after heparin treatment and 28 days in the envenomed group. Heparin treatment significantly decreased MPO activity, suggesting an anti-inflammatory effect. NO, HGF, VEGF and G-CSF levels were increased after heparin administration. These mitogenic factors constitute potent stimuli for satellite and endothelial cells improving, thus, muscle regeneration. This study showed that muscle tissue recovery was significantly enhanced after heparin treatment. Heparin use seems to be a promising therapeutic approach after viper envenomation.

Purification and characterization of a thrombin-like enzyme isolated from Vipera lebetina venom: its interaction with platelet receptor

: Snake venoms contain various molecules that can be used as tools in the diagnosis and in the treatment of hemostatic disorders. This study reports the isolation and functional characterization of a new thrombin-like enzyme and its role in the modulation of platelet aggregation and coagulation. The molecule was purified by gel filtration, anion exchange chromatography and reverse-phase-HPLC on C8 column; its molecular weight was determined. Natural and synthetic substrates were used to evaluate its enzymatic activities. The fibrinogenolytic activity was tested electrophoretically and by reverse-phase-HPLC on C18 column. Otherwise, the effect on blood coagulation and deficient plasma factors were also evaluated. The mechanism by which a thrombin-like enzyme VLCV (thrombin-like enzyme)-induced platelet aggregation was explored in presence of ticlopidin, clopidogrel and aspirin. VLCV (45 kDa) isolated from Vipera lebetina as a thrombin-like enzyme seems to be able to modulate platelet function. This enzyme showed an amidolytic activity by hydrolyzing the chromogenic-specific substrate of thrombin and the α-chain of fibrinogen. It is also able to clot human plasma and the deficient human plasma in factor X, suggesting that it is involved in the intrinsic and common pathways. The aggregating effect of VLCV is more sensitive to ticlopidine than to the clopidogrel suggesting the involvement of ADP/P2Y12/PI3K pathway. VLCV seems to be able to promote human platelet aggregation suggesting an interaction between P2Y12 and PAR1. Due to its ability to replace the missing factor X and its proaggregating activity, VLCV could be used as molecular tool to better understand the hemostasis mechanism.

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.

Molecular modeling, biochemical characterization, and pharmacological properties of Cc3 -SPase: A platelet-aggregating thrombin-like enzyme purified from Cerastes cerastes venom

Cc3 -SPase (30 kDa-proteinase; pI 5.98) was isolated from Cerastes cerastes venom. Its sequence of 271 residues yielded from LC-MALDI-TOF showed high degrees of homology when aligned with other proteinases. Cc3 -SPase cleaved natural and synthetic proteins such as casein and fibrinogen leaving fibrin clots unaffected. Cc3 -SPase was fully abolished by ion chelators, whereas aprotinin, antithrombin III (Sigma Aldrich, Saint-Louis, Missouri, USA), and heparin were ineffective. Affinity of Cc3 -SPase to benzamidine indicated the presence of an aspartate residue in the catalytic site as confirmed by three-dimensional structure consisting of 14 β-strands and four α-helices. Molecular mechanisms revealed that Cc3 -SPase is capable of promoting dysfunctional platelet aggregation via two signaling pathways mediated by the G-coupled protein receptors and αIIbβ3 integrin. Cc3 -SPase is involved in both extrinsic/intrinsic coagulation pathways in deficient plasmas by replacing defective/lacking factors FII, FVII, and FVIII but not FX. Cc3 -SPase could substitute missing factors in blood diseases related to plasma factor deficiencies.

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.

Purification and characterization of a platelet aggregation inhibitor and anticoagulant Cc 5_NTase, CD 73-like, from Cerastes cerastes venom

The present study is the first attempt to report the characterization of a nucleotidase from Cerastes cerastes venom. A 70 kDa 5'-nucleotidase (Cc-5'NTase) was purified to homogeneity. The amino acid sequence of Cc-5'NTase displayed high homology with many nucleotidases. Its activity was optimal at pH 7 with a specific hydrolytic activity toward mono-, di-, and triphosphate adenylated nucleotides. Cc-5'NTase preferentially hydrolyzed ADP and obeyed Michaelis-Menten kinetics. Among the metals and inhibitors tested, Ni²⁺ and Mg²⁺ completely potentiated enzyme activity, whereas EGTA, PMSF, iodoacetamide, vanillic acid, vanillyl mandelic acid, and 1,10-phenanthroline partially abolished its activity. Cc-5'NTase was not lethal for mice at 5 mg/kg and exhibited in vivo anticoagulant effect. It also dose-dependently inhibited adenosine diphosphate-induced platelet aggregation by converting adenosine diphosphate to adenosine and prohibited arachidonic acid-induced aggregation but was not effective on fibrinogen-induced aggregation. Cc-5'NTase could be a good tool as pharmacological molecule in thrombosis diagnostic and/or therapy.

Isolated biomolecules of pharmacological interest in hemostasis from Cerastes cerastes venom

Biomolecules from Cerastes cerastes venom have been purified and characterized. Two phospholipases isolated from Cerastes cerastes venom share 51% of homology. CC2-PLA2 exhibits antiplatelet activity that blocks coagulation. CCSV-MPase, a non-hemorrhagic Zn²⁺-metalloproteinase, significantly reduced the plasmatic fibrinogen level and hydrolyzes only its Bβ chain. Serine proteinases such as RP34, afaâcytin and CC3-SPase hydrolyze the fibrinogen and are respectively α, αβ and αβ fibrinogenases. In deficient human plasma, afaâcytin replaces the missing factors VIII and IX, and activates purified human factor X into factor Xa. It releases serotonin from platelets and directly aggregates human (but not rabbit) blood platelets. RP34 proteinase also had no effect on both human and rabbit blood platelet aggregation. CC3-SPase revealed a pro-coagulant activity. However, the insolubility of the obtained clot indicates that CC3-SPase does not activate factor XIII. In addition, CC3-SPase clotting activity was carried out with human plasmas from volunteer patients deficient in clotting factors. Results showed that CC3-SPase shortens clotting time of plasma deficient in factors II and VII but with weaker clotting than normal plasma. The clotting time of plasma deficient in factor II is similar to that obtained with normal plasma; suggesting that CC3-SPase is able to replace both factors IIa and VII in the coagulation cascade and thus could be involved in the blood clotting process via an extrinsic pathway. These results imply that CC3-SPase and afaâcytin could repair hemostatic abnormalities and may replace some factors missing in pathological deficiency. Afaâcytin also exhibits α fibrinase property similar to a plasmin-like proteinase. Despite its thrombin-like characteristics, afaâcytin is not inhibited by plasmatic thrombin inhibitors. The procoagulant properties of afaâcytin might have potential clinical applications.

Purification and biochemical characterization of a novel hemorrhagic metalloproteinase from horned viper (Cerastes cerastes) venom

Snake venoms contain metalloproteinases that contribute to the local effects observed after envenoming. In this study, a hemorrhagic metalloproteinase (CcH1) was purified from Cerastes cerastes venom by a combination of gel filtration, ion exchange, affinity and RP-HPLC chromatography. The hemorrhagin was homogeneous on SDS-PAGE, with a molecular mass of 25 kDa. Isoelectric focusing revealed a pI of 5.5. CcH1 displayed hemorrhagic and proteolytic activities, but no esterolytic activity. The hemorrhagic and proteolytic activities of CcH1 were inhibited by EDTA and 1,10-phenanthroline, but not by PMSF, suggesting that this protein is a zinc-metalloproteinase. Furthermore, the hemorrhagic and proteolytic activities of CcH1 were stable in solution at up to 40 degrees C, with a loss of activity at > or =70 degrees C. The molecular mass and the inhibition assays suggest that the metalloproteinase CcH1 belongs to class P-I of SVMPs.

Serine proteases affecting blood coagulation and fibrinolysis from snake venoms

Snake venom proteases, in addition to their contribution to the digestion of the prey, affect various physiological functions. They affect platelet aggregation, blood coagulation, fibrinolysis, complement system, blood pressure and nervous system. This review provides a ready reference for serine proteases that interfere in blood coagulation and fibrinolysis. They exhibit their activity by activation of specific zymogens of coagulation factors. These serine proteases serve as tools to study molecular details in the activation of specific factors involved in coagulation and fibrinolytic cascades and are useful in treating various thrombotic and hemostatic conditions.

Effects of 60Co gamma radiation on toxicity and hemorrhagic, myonecrotic, and edema-forming activities of Cerastes cerastes venom

Antisera are used as effective antidotes against the local effects of snake bites. To improve antisera production and extend the life of surrogates used to produce antibodies, the chronic effects of venom toxicity must be reduced. The present study evaluated the effectiveness of gamma irradiation to reduce the local effects associated with viperid snake bites by evaluating in NMRI mice the toxicity and edematic, hemorrhagic, and myonecrotic activities of native and irradiated Cerastes cerastes venoms. These results indicated that the toxicity of irradiated venoms (1 and 2 kGy) decreased as compared with that of native venom. The edematic and hemorrhagic activities were also reduced in the detoxified samples, particularly with the 2-kGy radiation dose. Futhermore, the creatine phosphokinase (CPK) activity was significantly increased in the serum and decreased in the myocardium after envenomation with native venom, but no significant enzymatic changes were observed in mice envenomated with irradiated venom. Histopathologic evaluation showed that native venom caused severe degenerative changes in the myocardium. In the case of 2-kGy-irradiated venom, no tissue alterations were observed. These results indicate that irradiation of venom with a 2-kGy dose may offer an effective method for reducing the chronic toxic effects of venom in immunized animals.Key words: venom, Cerastes cerastes, gamma radiation, histopathological change.

Cerastes cerastes envenomation in an 18 year old female: a case report

An 18 year old woman was bitten on the second finger of her right hand by a Cerastes cerastes. A literature search revealed very few clinical cases, and most of those were only laboratory and in 'vitro studies'. Local signs included a hemorrhagic wound at the site of the bite with marked swelling of the entire hand. Twelve hours later, the patient developed coagulopathy, which lasted 3 days and required repeated administration of blood products. Treatment was essentially supportive and the patient was discharged from the hospital after 5 days in good condition.

A non-toxic anticoagulant metalloprotease: purification and characterization from Indian cobra (Naja naja naja) venom

A non-toxic potent anticoagulant metalloprotease NN-PF(3) has been purified to homogeneity from the Indian cobra (Naja naja naja) venom through a combination of column chromatography and electrophoresis. NN-PF(3) is a single chain protein with a molecular weight of 68 kDa by SDS-PAGE. It hydrolysed casein, gelatin, haemoglobin and bovine fibrinogen, but did not hydrolyse bovine serum albumin or synthetic substrates such as TAME, BAEE and BAPNA. EDTA, EGTA and cyanide inhibited the enzymatic activity while 1,10-phenanthroline, PMSF, leupetin and pepstatin did not show any effect. NN-PF(3) is a metalloprotease containing Ca(2+) and Zn(2+) at a molar ratio of 1:1.2 and 1:0.4, respectively, as revealed by atomic absorption spectroscopy. NN-PF(3) was non-lethal up to an i.p. dose of 15 mg/kg body weight of mice and is devoid of myotoxicity, cytotoxicity and haemorrhagic activity. It is weakly oedematic, but strongly anticoagulant in property and the effect observed was both dose and time dependent.

Procoagulant proteins from snake venoms

Several procoagulant proteins from snake venoms have been isolated and characterized. They are either serine proteinases or metalloproteinases, which activate specific zymogens of coagulation factors and initiate the coagulation cascade. These procoagulant proteins are useful in treating various thrombotic and hemostatic conditions and contribute to our understanding of molecular details in the activation of specific coagulation factors. Recent studies have shown that the prothrombin activators with serine proteinase activity are structurally and functionally similar to mammalian coagulation factors. Their structural studies should provide us insight into prothrombinase complex formation. Here, we present an overview of snake venom procoagulant factors.

Cross-reactivities of polyclonal antibodies against factor V activating enzyme, a serine proteinase from Vipera lebetina (snake) venom

Antibodies to the factor V activating enzyme from Vipera lebetina venom were produced by immunizing a rabbit with chromatographically purified factor V activating enzyme probes. The antibodies cross-reacted with different protein fractions in 23 snake venoms (ten viperid, eight crotalid, and five elapid venoms) as demonstrated by western immunoblotting. In the venom of Vipera russelli the antibodies recognized only one protein band which probably belonged to factor V activating enzyme.

Purification and characterization of two fibrinogen-clotting enzymes from five-pace snake (Agkistrodon acutus) venom

From the snake venom of Agkistrodon acutus, two proteases, acuthrombin-A and acuthrombin-C, were isolated and purified to homogeneity. They can cleave the human fibrinogen to release the fibrinopeptide A and fibrinopeptide B with specific activity of 120 and 370 NIH units/mg, respectively; the fibrinogen-clotting activity can be inhibited distinctly by PMSF or DFP or EDTA, but not by heparin. The two proteases show also arginine-esterase activity hydrolyzing some synthetic substrates such as TAME and BAEE. Additionally, they are glycoproteins with an average content of 2.4% (acuthrombin-A) and 2.1% (acuthrombin-C) neutral carbohydrates, respectively. Acuthrombin-A has a MW of 13,900 as estimated by SDS-PAGE under reduced or nonreduced conditions and 28,000 as determined by gel filtration. For acuthrombin-C, there were two protein bands corresponding to MW of 13,900 and 14,800 on SDS-PAGE with different darkness under reduced or nonreduced conditions, while its MW was estimated to be 69,000 by gel filtration. The isoelectric points were 7.5 for acuthrombin-A and 5.0 for acuthrombin-C by isoelectric focusing. Neither acuthrombin-A nor acuthrombin-C has haemorrhagic or lethal activity. Acuthrombin-A has also a small amount of activity to activate the Factor XIII.

Cerastotin, a serine protease from Cerastes cerastes venom, with platelet-aggregating and agglutinating properties

Cerastotin, a thrombin-like enzyme from the venom of the desert viper Cerastes cerastes, has been purified by gel filtration on Sephadex G-75 and two ion-exchange chromatographies on Mono S columns. It is a neutral glycoprotein (pI = 6.6), present as a single polypeptide chain of 40 kDa. Its N-terminal sequence shows strong similarity with those of other thrombin-like enzymes from snake venoms. Cerastotin possesses esterase and amidolytic activities measured with N(alpha)-tosyl-L-arginine methyl ester and the thrombin chromogenic substrate D-phenylalanyl-L-pipecolyl-L-arginine p-nitroanilide, respectively. The amidolytic activity is inhibited by phenylmethylsulfonyl fluoride, N(alpha)-tosyl-L-lysine chloromethane, N(alpha)-tosyl-L-phenylalanyl chloromethane, D-phenylalanyl-L-prolyl-L-arginyl chloromethane and benzamidine, suggesting that cerastotin is a serine protease. Cerastotin efficiently clots human plasma and cleaves preferentially the alpha chain of fibrinogen. Cerastotin did not induce aggregation of washed normal platelets, but did aggregate platelets in the presence of exogenous fibrinogen. A monoclonal antibody directed against glycoprotein (GPIb), which specifically inhibits induced agglutination by ristocetin also completely blocks platelet aggregation induced by cerastotin. However, another anti-GPIb monoclonal antibody, which specifically inhibits alpha-thrombin binding to GPIb, did not prevent this aggregation. Furthermore, platelets which were desensitised by alpha-thrombin still aggregate in the presence of cerastotin, but not alpha-thrombin. Similarly a monoclonal antibody, anti-GPIIb-IIIa, which blocks fibrinogen binding, did not inhibit cerastotin-induced platelet aggregation. This activity is abolished in the presence of 1 mM phenylmethylsulfonyl fluoride and/or 10 mM EDTA. Cerastotin also agglutinates formalin-fixed and washed platelets, only in the simultaneous presence of fibrinogen and of Von Willebrand factor.

Procoagulant and platelet-aggregating properties of cerastocytin from Cerastes cerastes venom

Cerastocytin is a thrombin-like serine protease with potent platelet-proaggregating properties. It is able to activate factor XIII but is less active than thrombin on plasma coagulation. The aggregation induced by cerastocytin resembles that induced by thrombin, since rabbit washed platelets desensitized by a pretreatment with thrombin do not aggregate in the presence of cerastocytin. Furthermore, preincubation of platelets with monoclonal antibodies specific for glycoproteins GPIb or GPIIbIIIa blocks receptor sites for thrombin and fibrinogen, respectively, and prevents their aggregation induced by thrombin or cerastocytin. A monoclonal antibody, inhibitor of von Willebrand factor (VWF)-dependent agglutination, blocks the aggregation induced by cerastocytin. After activation with cerastocytin, washed rabbit platelets degranulate and secrete ATP and phospholipase A2. However, cerastocytin is less potent in inducing the release of phospholipase A2 than in inducing ATP secretion.

Purification and characterization of a fibrinogen-clotting enzyme from the venom of jararacuçu (Bothrops jararacussu)

A clotting enzyme of the venom of Bothrops jararacussu, denoted FC-Bj, was purified by gel chromatography on Sephadex G-100 followed by HPLC on DEAE-5PW-PAK and gel filtration on Sephacryl S-200HR. The enzyme was identified as an acidic glycoprotein which probably consists of a single polypeptide chain with isoelectric point values in the range 3.3-4.4 and containing approx. 19% carbohydrates. On polyacrylamide gel electrophoresis (PAGE) at pH 8.3, the enzyme presented a diffuse protein band. On sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the enzyme showed two protein bands corresponding to mol. wts of 50,600 and 60,000. After treatment of the enzyme with neuraminidase, a strongly stained band and a band weaker in staining intensity were observed on SDS-PAGE, thereby reducing the mol. wts to 44,500 and 56,300, respectively. The clotting factor possessed N-alpha-benzoyl-DL-arginine p-nitroanilide hydrolysing activity and coagulated fibrinogen to fibrin. These activities were 0.548 units/mg and 50.55 NIH thrombin units/mg, respectively. The proteinase was of the serine type, as indicated by sensitivity to phenylmethanesulfonyl fluoride and benzamidine. However, the amidolytic activity of this enzyme was resistant to inhibitors such as heparin, aprotinin, agmatine, EDTA, I-2581 and TLCK. The importance of disulfide bridges for the structural integrity of the purified enzyme was indicated by the loss of amidolytic activity in the presence of beta-mercaptoethanol and dithiothreitol. SDS-PAGE of fibrinogen degraded with this enzyme revealed the disappearance of the A alpha and B beta chains and the appearance of lower mol. wt fragments. The enzyme was able to hydrolyse synthetic chromogenic substrates with arginine as the C-terminal residue, and the kinetic parameters were determined. It hydrolysed the plasma kallikrein substrate H-D-Pro-Phe-Arg-pNA (S-2302) and produced kinin-releasing activity causing ileum contraction. In addition, hypotension and bradycardia were observed in urethane-anesthetized rats upon i.v. injection of the enzyme.

Afaâcytin, an alpha beta-fibrinogenase from Cerastes cerastes (horned viper) venom, activates purified factor X and induces serotonin release from human blood platelets

Afaâcytin, a proteinase with caseinolytic, arginine-esterase and amidase activities, was purified from the venom of Cerastes cerastes (horned viper) in two steps by gel filtration through Sephadex G75, then HPLC on carboxymethyl-cellulose. Afaâcytin has an isoelectric point of 6.25, and consists of two subunits, alpha and beta, which have the same apparent molecular mass (40,000) and are indistinguishable in the absence of reduction or/and deglycosylation. Subunit beta is constituted of two disulfide-linked polypeptidic chains, beta and beta'. The respective apparent molecular mass of the chains are 43,000 (alpha), 35,500 (beta) and 10,200 (beta') as determined by SDS/PAGE under reducing conditions. Both chains alpha and beta are N-glycosylated. The two chains have the same N-terminal sequence (20 residues) which is similar to those of other proteinases from snake venom. Susceptibility of afaâcytin to diisopropyl fluorophosphate and benzamidine indicates the presence of a serine and an aspartic (or glutamic) acid residues in the catalytic site. Ca2+ appears to be required for structural cohesion of the afaâcytin molecule. Afaâcytin exhibits alpha beta-fibrinogenase and alpha-fibrinase properties. It replaces missing factors VIII and IX in deficient plasmas, and activates purified human factor X into factor Xa. It releases serotonin from platelets and directly aggregates human (but not rabbit) blood platelets. Despite its thrombin-like characteristics, however, afaâcytin is not inhibited by plasmatic thrombin inhibitors. The procoagulant properties of afaâcytin therefore have potential clinical applications.

Characterization of a potent platelet aggregation inducer from Cerastes cerastes (Egyptian sand viper) venom

A potent, proteinaceous inducer of platelet aggregation designated as IVa, has been purified to homogeneity from Cerastes cerastes venom by molecular sieve and ion exchange chromatography. It is composed of 2 subunits with total M(r) of 62,000 as shown by native gel chromatography and chemical cross-linking with disuccinimidyl suberate. It is not clear at the present time whether both subunits are identical gene products, however, both have identical N-terminal sequences for the first 15 amino acids. The protein has a pI above 9.6. IVa (0.1 micrograms/ml) could aggregate platelets up to 80% and was inhibited by p-APMSF, leupeptin, iodoacetamide, protein kinase C inhibitor, phosphatase inhibitor, ATP and PGE1, while it was insensitive to acetylsalicylic acid, ADP scavenger system, protein kinase A inhibitor and hirudin. Protein IVa is a serine proteinase with thrombin-like activity as it hydrolysed thrombin chromogenic substrate CBS 34.47, its aggregatory activity was partially inhibited by monoclonal antibodies against GPIb and the thrombin receptor, as was the thrombin, and its ability to induce intracellular Ca2+ release was blocked by pretreating platelets with thrombin. Unlike thrombin, the IVa protein showed very weak coagulant activity as indicated by plasma recalcification time and fibrinogen clotting time although it could hydrolyse fibrinogen alpha-chains.

Cerastocytin, a new thrombin-like platelet activator from the venom of the Tunisian viper Cerastes cerastes

Cerastocytin, a thrombin-like enzyme from the venom of the desert viper, Cerastes cerastes, has been purified to homogeneity by fast performance liquid chromatography (FPLC) on Mono-Q and Mono-S columns. It is a basic protein (isoelectric point higher than 9) made of a single polypeptide chain of 38 kDa. Its N-terminal polypeptide sequence shows strong similarities with other thrombin-like enzymes from snake venoms. Nanomolar concentrations of cerastocytin induce aggregation of blood platelets. This activity is inhibited by chlorpromazine, theophylline and mepacrine, as in the case of platelet aggregation stimulated by low doses of thrombin. Cerastocytin also possesses an amidolytic activity measured with the thrombin chromogenic substrate S-2238. The platelet aggregating activity and the amidolytic activity of cerastocytin were inhibited by PMSF, TPCK, TLCK and soybean trypsin inhibitors, suggesting that cerastocytin is a serine proteinase. On the other hand, both amidolytic activity and platelet aggregating activity of cerastocytin were unaffected by hirudin or by antithrombin III in the presence of heparin. High concentrations of cerastocytin (1-10 microM) also cleaved prothrombin and Factor X.