Ex-vivo and in-vivo antithrombotic effect of triflavin, an RGD-containing peptide

Practical applications of snake venom toxins in haemostasis

Snake venom toxins affecting haemostasis have facilitated extensively the routine assays of haemostatic parameters in the coagulation laboratory. Snake venom thrombin-like enzymes (SVTLE) are used for fibrinogen/fibrinogen breakdown product assay and for the detection of fibrinogen dysfunction. SVTLE are not inhibited by heparin and can thus can be used for assaying antithrombin III and other haemostatic variables in heparin-containing samples. Snake venoms are a rich source of prothrombin activators and these are utilised in prothrombin assays, for studying dysprothrombinaemias and for preparing meizothrombin and non-enzymic forms of prothrombin. Russell's viper (Daboia russelli) venom (RVV) contains toxins which have been used to assay blood clotting factors V, VII, X, platelet factor 3 and, importantly, lupus anticoagulants (LA). Other prothrombin activators (from the taipan, Australian brown snake and saw-scaled viper) have now been used to assay LA. Protein C and activated protein C resistance can be measured by means of RVV and Protac, a fast acting inhibitor from Southern copperhead snake venom and von Willebrand factor can be studied with botrocetin from Bothrops jararaca venom. The disintegrins, a large family of Arg-Gly-Asp (RGD)-containing snake venom proteins, show potential for studying platelet glycoprotein receptors, notably, GPIIb/IIIa and Ib. Snake venom toxins affecting haemostasis are also used in the therapeutic setting: Ancrod (from the Malayan pit viper, Calloselasma rhodostoma), in particular, has been used as an anticoagulant to achieve 'therapeutic defibrination'. Other snake venom proteins show promise in the treatment of a range of haemostatic disorders.

Alternagin-C, a Disintegrin-like Protein, Induces Vascular Endothelial Cell Growth Factor (VEGF) Expression and Endothelial Cell Proliferation in Vitro

Alternagin-C (ALT-C), a disintegrin-like protein purified from the venom of the Brazilian snake Bothrops alternatus, interacts with the major collagen I receptor, the alpha(2)beta(1) integrin, inhibiting collagen binding. Here we show that ALT-C also inhibits the adhesion of a mouse fibroblast cell line (NIH-3T3) to collagen I (IC(50) 2.2 microm). In addition, when immobilized on plate wells, ALT-C supports the adhesion of this cell line as well as of human vein endothelial cell (HUVEC). ALT-C (3 microm) does not detach cells that were previously bound to collagen I. ALT-C (5 nm) induces HUVEC proliferation in vitro, and it inhibits the positive effect of vascular endothelial growth factor (VEGF) or FGF-2 on the proliferation of these cells, thus suggesting a common mechanism for these proteins. Gene expression analysis of human fibroblasts growing on ALT-C- or collagen-coated plates showed that ALT-C and collagen I induce a very similar pattern of gene expression. When compared with cells growing on plastic only, ALT-C up-regulates the expression of 45 genes including the VEGF gene and down-regulates the expression of 30 genes. Fibroblast VEGF expression was confirmed by RT-PCR and ELISA assay. Up-regulation of the VEGF gene and other growth factors could explain the positive effect on HUVEC proliferation. ALT-C also strongly activates Akt/PKB phosphorylation, a signaling event involved in endothelial survival and angiogenesis. In conclusion, ALT-C acts as a survival factor, promoting adhesion and endothelial cell proliferation.

Application of Recombinant Rhodostomin in Studying Cell Adhesion

Rhodostomin from venom of Agkistrodon rhodostoma (also called Calloselasma rhodostoma) contains 68 amino acid residues including 6 pairs of disulfide bonds and an arginine-glycine-aspartic acid (RGD) sequence at positions 49-51. It has been known as one of the strongest antagonists to platelet aggregation among the family termed disintegrin. In this review paper, in addition to introducing the characteristics of disintegrin and its related molecules, the advantages of using recombinant DNA technology to produce rhodostomin are described. The recombinant rhodostomin has been demonstrated to facilitate cell adhesion via interaction between the RGD motif of rhodostomin and integrins on the cell surface. This property allowed us to use the recombinant rhodostomin as an extracellular matrix to study cell adhesion and to distinguish attachment efficiency between two melanoma cell lines B16-F1 and B16-F10, the former is a low metastasis cell while the latter is a high metastasis cell. Furthermore, by using the recombinant rhodostomin as a substrate, osteoprogenitor-like cells are able to be selected and enriched within 3 days from rat bone marrow which contains a heterogeneous cell population. Finally, we show that the recombinant rhodostomin can be immobilized on beads and which serve as an affinity column to dissect cell-surface protein(s) binding to the RGD motif of rhodostomin.

The disintegrin-like domain of the snake venom metalloprotease alternagin inhibits alpha2beta1 integrin-mediated cell adhesion

The alpha2beta1 integrin is a major collagen receptor that plays an essential role in the adhesion of normal and tumor cells to the extracellular matrix. Here we describe the isolation of a novel metalloproteinase/disintegrin, which is a potent inhibitor of the collagen binding to alpha2beta1 integrin. This 55-kDa protein (alternagin) and its disintegrin domain (alternagin-C) were isolated from Bothrops alternatus snake venom. Amino acid sequencing of alternagin-C revealed the disintegrin structure. Alternagin and alternagin-C inhibit collagen I-mediated adhesion of K562-alpha2beta1-transfected cells. The IC50 was 134 and 100 nM for alternagin and alternagin-C, respectively. Neither protein interfered with the adhesion of cells expressing alphaIIbeta3, alpha1beta1, alpha5beta1, alpha4beta1 alphavbeta3, and alpha9beta1 integrins to other ligands such as fibrinogen, fibronectin, and collagen IV. Alternagin and alternagin-C also mediated the adhesion of the K562-alpha2beta1-transfected cells. Our results show that the disintegrin-like domain of alternagin is responsible for its ability to inhibit collagen binding to alpha2beta1 integrin.

Triflavin inhibits platelet-induced vasoconstriction in de-endothelialized aorta

Triflavin, a 7.5-kD cysteine-rich polypeptide purified from Trimeresurus favoviridis snake venom, belongs to a family of Arg-Gly-Asp-(RGD)-containing peptides, termed disintegrins. In this study, aggregating human platelets dose-dependently induced vasoconstriction in de-endothelialized isolated rat thoracic aortas. At 5x10(7) cells per milliliter, platelets induced a peak tension averaging 65 +/- 7.2% of the tension induced by phenylephrine (10 mumol/L). The relative effectiveness of RGD-containing peptides (including venom peptides triflavin and trigramin, small RGD synthetic peptides Gly-Arg-Gly-Asp-Ser [GRGDS], Gly-Arg-Gly-Asp-Phe [GRGDF], and Gly-Arg-Gly-Asp-Ser-Pro-Lys [GRGDSPK]) was examined by testing the inhibitory effect on aggregating platelet-induced vasoconstriction in de-endothelialized aorta. Triflavin (1 mumol/L) significantly inhibited the platelet-induced vasoconstriction, whereas neither trigramin (10 mumol/L) nor small RGD peptides (2 mmol/L) (i.e., GRGDS, GRGDF, and GRGDSPK) showed any significant effect. The release of serotonin and the formation of thromboxane A2 from aggregating platelets were both significantly inhibited by triflavin (2 mumol/L), whereas trigramin and small RGD-containing peptides showed no significant effect. On scanning electron micrographs of de-endothelialized aorta, aggregating platelets adhered to the subendothelium, with loss of their discoid shape, to form irregular spheres with pseudopod extensions. Triflavin (2 mumol/L) markedly reduced the adhesion of platelets to the subendothelium in the same aorta. Furthermore, RGD-containing peptides (including triflavin, trigramin, and small RGD-containing peptides) inhibited the adhesion of 10 micrograms/mL collagen-activated platelets to extracellular matrices (i.e., fibronectin, vitronectin, and von Willebrand factor). It is concluded that the marked ability of triflavin to inhibit aggregating platelet-induced vasoconstriction in de-endothelialized aorta compared with other RGD-containing peptides (including trigramin), may be due at least partly to triflavin's efficiently preventing the activation of platelets subsequent to inhibition of serotonin release and thromboxane A2 formation. However, the different abilities of triflavin compared with other RGD-containing peptides was not related to the ability to inhibit adhesion of platelets to extracellular matrices. Therefore, from the results of this study, it appears that triflavin may be a useful therapeutic agent for the treatment of thromboembolism and its associated angiospasm.

Interaction of thrombin-activated platelets with extracellular matrices (fibronectin and vitronectin): comparison of the activity of Arg-Gly-Asp-containing venom peptides and monoclonal antibodies against glycoprotein IIb/IIIa complex

Platelets adhere to fibronectin and vitronectin substrates following activation with physiological concentrations of thrombin. Adhesion of activated-platelets to either substrate is dependent upon the amount of fibronectin and vitronectin, and the duration of the adhesion assay. In this study, we showed that the Arg-Gly-Asp-containing peptides (including naturally occurring polypeptides, triflavin, trigramin and rhodostomin, synthetic peptides GRGDS, GRGDSPK, GRGDF, and GRGD and monoclonal antibodies, 7E3, 10E5 and AP2, raised against glycoprotein IIb/IIIa complex, inhibited the adhesion of activated-platelets to fibronectin and vitronectin-coated plates in a dose-dependent manner. In fibronectin-coated plates, GRGDF was shown to be much more efficient than GRGDS, GRGDSPK and GRGD at inhibiting the adhesion of activated-platelets to immobilized fibronectin. On the other hand, there were no marked differences in the abilities of these three peptides (GRGDF, GRGDS and GRGDSPK) to inhibit platelet adhesion to immobilized vitronectin. Furthermore, the RGD-containing venom peptide, triflavin was more effective than rhodostomin and trigramin at inhibiting the adhesion of activated-platelets to either substrates. The monoclonal antibodies raised against glycoprotein IIb/IIIa complex (i.e., 7E3, 10E5 and AP2) inhibited platelet adhesion to fibronectin and vitronectin in a similar dose-dependent manner. Interestingly, we found that 7E3 was more efficient than 10E5 and AP2 in this reaction. These studies suggest that the glycoprotein IIb/IIIa complex, present on activated-platelets, may interact with fibronectin and vitronectin substrates through the Arg-Gly-Asp-dependent mechanism. Since fibronectin and vitronectin are present in the subendothelial matrix, they may be involved in platelet-vessel wall interaction. The Arg-Gly-Asp containing peptide, especially triflavin, is an ideal therapeutic agent for inhibiting thrombus formation by interrupting platelet-platelet and platelet-subendothelium interactions.

Triflavin, an Arg-Gly-Asp-containing peptide, prevents platelet plug formation in in vivo experiments

Triflavin, an Arg-Gly-Asp-containing peptide from Trimeresurus flavoviridis snake venom (M(r) of 7500 Da) inhibits platelet aggregation through the blockade of fibrinogen binding to activated platelets. The present study demonstrated that the intravenous injection of triflavin (0.1 and 0.25 mg/kg) significantly prolonged the bleeding time about 1.8- to 2.4-fold as compared with control (normal saline) of severed mesenteric arteries in rats, whereas the injection of Gly-Arg-Gly-Asp-Ser (GRGDS) (2-8 mg/kg) failed to increase the bleeding time in this model. Continuous infusion of triflavin (0.08 mg/kg/min) significantly increased the bleeding time about 2.6-fold, and the bleeding time returned to normal within 20 min after the cessation of triflavin infusion. Triflavin (10-20 mg/kg) significantly prolonged the occlusion time of platelet plug formation induced by irradiation of mesenteric venules of fluorescein sodium-pretreated mice. In contrast, trigramin (10-20 mg/kg) and GRGDS (500 and 1000 mg/kg) showed no significant effect. These results suggest that triflavin has an effective antiplatelet effect in vivo and this peptide may be a useful therapeutic agent for arterial thrombosis.