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.