Fibrinogen adsorption on a surface results in the modification of its functional characteristics. Our previous studies revealed that fibrinogen adsorbs onto surfaces essentially in 2 different orientations depending on its concentration in the solution: "side-on" at low concentrations and "end-on" at high concentrations. In the present study, we analyzed the thrombin-mediated release of fibrinopeptides A and B (FpA and FpB) from fibrinogen adsorbed in these orientations, as well as from surface-bound fibrinogenfibrin complexes prepared by converting fibrinogen adsorbed in either orientation into fibrin and subsequently adding fibrinogen. The release of fibrinopeptides from surface-adsorbed fibrinogen and from surface-bound fibrinogen-fibrin complexes differed significantly compared with that from fibrinogen in solution. The release of FpB occurred without the delay (lag phase) characteristic of its release from fibrinogen in solution. The amount of FpB released from end-on adsorbed fibrinogen and from adsorbed fibrinogenfibrin complexes was much higher than that of FpA. FpB is known as a potent chemoattractant, so its preferential release suggests a physiological purpose in the attraction of cells to the site of injury. The N-terminal portions of fibrin ␤ chains including residues B␤15-42, which are exposed after cleavage of FpB, have been implicated in many processes, including angiogenesis and inflammation. (Blood. 2011;117(5):1700-1706) IntroductionFibrinogen, one of the most abundant proteins in blood, plays a key role in hemostasis, inflammation, wound healing, and additional physiological and pathological processes. Immediately after blood comes in contact with artificial materials or with an injured vessel wall subendothelium, fibrinogen rapidly adsorbs on the surface and interacts with adhered activated platelets and subendothelial proteins. Numerous studies have demonstrated that fibrinogen in solution and fibrinogen adsorbed on various surfaces exhibit different properties. [1][2][3][4] For example, surface-adsorbed fibrinogen changes its conformation and thus reveals multiple binding sites that interact with the receptors on platelets and leukocytes. 5,6 These reciprocal interactions participate in the process of blood clot formation and in the inflammatory response. Platelet adhesion promoted by the deposition of fibrinogen might contribute to the development of the inflammatory response during ischemia reperfusion. The structural properties of fibrinogen play a key role in its interactions with various biomolecules and cell types.Fibrinogen is a 340-kDa plasma glycoprotein with a complex structure. The fibrinogen molecule consists of 2 identical subunits, each composed of 3 nonidentical polypeptide chains, A␣, B␤, and ␥. These chains are linked together by 29 disulfide bonds and form several structural regions, 2 distal D regions, one central E region, and 2 ␣C regions. 7 Each pair of distal nodules is linked with the central nodule by a triple helical coiled-coil connector composed of the middle po...

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BackgroundPlatelets are small anucleated blood particles that play a key role in the control of bleeding. Platelets need to be activated to perform their functions and participate in hemostasis. The process of activation is accompanied by vast protein reorganization and posttranslational modifications. The goal of this study was to identify changes in proteins in platelets activated by different agonists. Platelets were activated by three different agonists - arachidonic acid, collagen, and thrombin. 2D SDS-PAGE (pI 4-7) was used to separate platelet proteins. Proteomes of activated and resting platelets were compared with each other by Progenesis SameSpots statistical software; and proteins were identified by nanoLC-MS/MS.Results190 spots were found to be significantly different. Of these, 180 spots were successfully identified and correspond to 144 different proteins. Five proteins were found that had not previously been identified in platelets: protein CDV3 homolog, protein ETHE1, protein LZIC, FGFR1 oncogene partner 2, and guanine nucleotide-binding protein subunit beta-5. Using spot expression profile analysis, we found two proteins (WD repeat-containing protein 1 and mitochondrial glycerol-3-phosphate dehydrogenase) that may be part of thrombin specific activation or signal transduction pathway(s).ConclusionsOur results, characterizing the differences within proteins in both activated (by various agonists) and resting platelets, can thus contribute to the basic knowledge of platelets and to the understanding of the function and development of new antiplatelet drugs.

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Fibrinogen is one of the plasma proteins most susceptible to oxidative modification. It has been suggested that modification of fibrinogen may cause thrombotic/bleeding complications associated with many pathophysiological states of organism. We exposed fibrinogen molecules to three different modification reagents—malondialdehyde, sodium hypochlorite, and peroxynitrite—that are presented to various degrees in different stages of oxidative stress. We studied the changes in fibrin network formation and platelet interactions with modified fibrinogens under flow conditions. The fastest modification of fibrinogen was caused by hypochlorite. Fibers from fibrinogen modified with either reagent were thinner in comparison with control fibers. We found that platelet dynamic adhesion was significantly lower on fibrinogen modified with malondialdehyde and significantly higher on fibrinogen modified either with hypochlorite or peroxynitrite reflecting different prothrombotic/antithrombotic properties of oxidatively modified fibrinogens. It seems that, in the complex reactions ongoing in living organisms at conditions of oxidation stress, hypochlorite modifies proteins (e.g., fibrinogen) faster and more preferentially than malondialdehyde. It suggests that the prothrombotic effects of prior fibrinogen modifications may outweigh the antithrombotic effect of malondialdehyde-modified fibrinogen in real living systems.