Anti-platelet activity of the peptides composing the Lebetin 1 family, a new class of inhibitors of platelet aggregation

We have purified from Vipera lebetina venom a family of inhibitors of platelet aggregation, named Lebetins. They are composed of two peptide groups of short (Lebetin 1: L1 alpha: GDNKPPKKGPPNG; L1 beta: DNKPPKKGPPNG) and long (Lebetin 2: L2 alpha: GDNKPPKKGPPNGCFGHKIDRIGSHSGLGCNKVDDNKG; L2 beta: DNKPPKKGPPNGCFGHKIDRIGSHSGLGCNKVDDNKG) size. The sequence presenting anti-platelet activity is mainly present within the Lebetin sequence [Barbouche, R. Marrakchi, N., Mansuelle, P., Krifi, M., Fenouillet, E., Rochat, H. and El Ayeb, M. (1996) Novel anti-platelet aggregation polypeptides from Vipera lebetina venom: isolation and characterization. FEBS Lett. 392, 6 10]. Here, the peptides that compose the Lebetin 1 family were synthesized. Their respective activity was determined. Synthetic L1 alpha and L1 beta inhibited collagen-induced platelet aggregation in the nanomolar range. A peptide corresponding to L1 beta deleted by D at its N terminus (L1 gamma) also inhibited platelet aggregation potently; further truncation of L1 gamma impaired its activity. Because L1 peptides efficiently inhibited fibrinogen-induced alpha-chymotrypsin treated-platelet aggregation, we tested whether they act mainly through the inhibition of platelet binding to fibrinogen and showed that they failed to inhibit platelet binding to fibrinogen-coated wells. The activity of L1 peptides was also tested in vivo: their intravenous administration strongly inhibited collagen-induced thrombocytopenia in rats. (C) 1998 Elsevier Science Ltd. All rights reserved.