Fibrinogen C-terminal peptidic sequences (Haptides) modulate fibrin polymerization

Abstract

We previously described synthetic peptides of 19-21 amino acid residues, homologous to the C-termini of fibrinogen Fib(340) and Fib(420), from the beta-chain (Cbeta), the extended alphaE chain (CalphaE) and near the end of the gamma-chain (preCgamma) which elicited attachment (haptotactic) responses from mesenchymal cells. We named these haptotactic peptides -Haptides. The effects of Haptides on fibrin clot formation was evaluated and their possible effects on platelet aggregation was examined. The Haptides Cbeta,CalphaE and preCgamma, (2-10 micro M) increased fibrin clot turbidity and also decreased thrombin-induced clotting time. Higher concentrations (>120 micro M of Cbeta or preCgamma) induced fibrinogen precipitation even without thrombin. These precipi-tates exhibited different ultrastructure from thrombin-induced fibrin by scanning and transmission microscopy. C-terminal peptides of the other fibrinogen chains exerted no such effects. Sepharose beads covalently coated with either whole fibrinogen or Haptides (SB-Fib or SB-Haptide) highly adsorbed free (FITC) Haptides. In aqueous solution, Haptides formed nano-par-ticles with average size of approximately 150 nm in diameter. We suggest that such positively charged aggregates could serve to nucleate and accelerate fibrin gel formation. These results also indicate that Cbeta and preCgamma sequences within fibrin(ogen) participate in the docking and condensation of fibrin(ogen) during its assembly into a fibrin clot. By contrast, Haptides up to 100 micro M did not bind to platelets, and had no effect on platelet aggregation. Our findings highlight the roles of the C-terminal sequences of the beta and gamma chains in fibrin(ogen) polymerization as well as in cell attachment.

Heat denaturation of fibrinogen to develop a biomedical matrix

“…In free form, Haptides tended to form multimers and nanoaggregates and significantly modulated the kinetics of fibrin coagulation reactions, resulting in decreased clotting time. [43][44][45] It is possible that the aggregation of heat denatured fibrinogen monomers into globular, multimeric structures (as shown in Figure 3) might be due in part to the binding interactions between heat-exposed Haptide epitopes of partially denatured fibrinogen monomers.…”

“…Immunostaining ( Figure 5) revealed that the heat denatured fibrin presented more exposed Haptide epitopes. In the light of the Haptotactic potency of these epitopes, 45,46 they probably contributed to the high cell binding potency of FMB, though other cell attachment sequences on fibrinogen might also be available. 52,53 However, when heated to 958C, the cell attachment potency of FMB were significantly reduced (Figure 7).…”

Short Homologous Peptides Based on C-Terminal Sequences of Fibrinogen β- and γ-Chains (Haptides) Affect Cardiovascular Function by eNOS Inhibition

“…These peptides were termed ‘Haptides’ because of their haptotactic (cell-binding) properties [12,13]. Haptides were initially studied as cell-binding domains on fibrin(ogen), which are not necessarily mediated by integrins [14,15]. The Haptides are relatively rich in both basic amino acids as well as cyclic hydrophobic groups, and are rapidly internalized into cells and can promote liposome uptake at nonsaturable kinetics, with no apparent cytotoxic effect [12,13].…”