To verify this effect, we chose compounds with distinct effects on the amidolytic activity of thrombin. Fibrinogen is a glycoprotein with a molecular SB202190 nmr weight of 340 kDa, containing in its structure three pairs of different polypeptide chains called, respectively, Aα (610 aa, 67 kDa), Bβ (461 aa, 56 kDa) and γ (411 aa, 48 kDa). These chains are connected by 29 disulfide bonds forming a dimeric MEK inhibitor molecule (Aα Bβ γ)2 (Wolberg, 2007). Thrombin removes the N-terminal peptides from the Aα and Bβ chains which leads to fibrin formation. Thrombin also activates coagulation factor XIII which stabilizes

the fibrin clot by catalysis of covalent bonds between γ chains in the D domains of adjacent fibrin monomers and formation of α-polymers (Bijak et al., 2013a; Muszbek et al., 1999). Preincubation

of thrombin only with three of six tested compounds changed the ability of thrombin to induce fibrinogen polymerization. We observed that only cyanidin, quercetin and silybin in a dose-dependent manner decreased the maximal velocity of thrombin-induced fibrinogen polymerization ICG-001 (Fig. 1a–c). When thrombin was preincubated with cyanin, (+)-catechin or (−)-epicatechin, the velocity of thrombin-induced fibrinogen polymerization was very similar to the velocity of fibrinogen polymerization induced by untreated thrombin (Fig. 1d–f). SDS-PAGE analysis (Fig. 2) confirmed the results obtained by spectrophotometric measurement of fibrinogen polymerization. In this analysis we used the polyphenolic compounds at concentrations equal to IC50 of thrombin amidolytic activity of each of them and ten times higher than these IC50 values, but not more than 1,000 μM. Thrombin exosite I among others is responsible for binding to protease-activated receptors (PAR). Receptors PAR-1 and PAR-4

are present on the human platelet surface. Thrombin cleaves the N-terminal extracellular domain of PAR to expose a new N-terminus, which binds with the central extracellular loop of the same receptor causing its activation and initiating the intracellular signaling events (Hirano and Kanaide, 2003). Our study showed Non-specific serine/threonine protein kinase that exposure of thrombin to cyanidin, quercetin or silybin resulted in a decrease in thrombin ability to induce platelet aggregation (Fig. 3a–c). This experiment also confirmed that cyanin, (+)-catechin and (−)-epicatechin had no inhibitory effect on the proteolytic activity of thrombin (Fig. 3d–f). Both experiments with human fibrinogen and platelets demonstrated that cyanidin, quercetin and silybin inhibited thrombin proteolytic activity. Moreover, the inhibitory effect of silybin on thrombin was significantly weaker than the effect of cyanidin and quercetin. Asmis et al. (2010) suggest that 0.5 % DMSO inhibits platelet response to arachidonate, but aggregation in response to other agonists (ADP, collagen, ristocentin, epinephrine, U46619) was not affected by DMSO. We also checked the effect of 0.