Human fibrinogen

Identification of mRNA-miRNA-lncRNA regulatory network associated with the immune response to Aeromonas salmonicides infection in the black rockfish (Sebastes schlegelii)

In aquaculture, Aeromonas salmonicides (A. salmonicida) is a main fish pathogen because of its nearly worldwide distribution, and broad host range. Recently, an increasing number of evidences have uncovered the roles of mRNA-miRNA-lncRNA network in fish diseases. In current study, RNA-seq was conducted in the black rockfish spleen following A. salmonicida infection at 0 h (Sp0 or control) and three different post-infection time-points (2 h: Sp2, 12 h: Sp12 and 24 h: Sp24, respectively) to comprehensively identify differentially expressed (DE) mRNAs, miRNAs and lncRNAs. Enrichment analysis and protein-protein interaction (PPI) analysis of DE mRNAs were performed. Then, expression and correlation analysis for mRNAs and their upstream miRNAs and lncRNAs were conducted. Finally, a total of 1364 mRNAs, 17 miRNAs and 1584 lncRNAs exhibited significantly differential expressions during bacterial infection in the black rockfish spleen. Functional enrichment analysis suggested that they were significantly enriched in several immune-related pathways, including Amino sugar and nucleotide sugar metabolism, Cell adhesion molecules (CAMs), Neuroactive ligand-receptor interaction, Nicotinate and nicotinamide metabolism, Pentose and glucuronate interconversions, Phagosome, Proteasome, etc. Subsequently, 1091 lncRNA-miRNA-mRNA pathways (323 in Sp2, 609 in Sp12 and 207 in Sp24) were constructed including 400 lncRNAs, 69 miRNAs, and 70 mRNAs. Meanwhile, NLRC3/novel-264/LNC_00116154 pathway demonstrated important immune modulating function in the black rockfish against A. salmonicida infection. Finally, the novel mRNA-miRNA-lncRNA sub-networks were established, among which all mRNAs and ncRNAs possessed significant predictive values for further studies for immune responses in the black rockfish.

Albumin-fibrinogen ratio and fibrinogen-prealbumin ratio as promising prognostic markers for cancers: an updated meta-analysis

Objective

Provide an updated and comprehensive evaluation of the prognostic value of the albumin-fibrinogen ratio (AFR) and the fibrinogen-prealbumin ratio (FPR) for patients with cancer.

Materials and methods

Four databases (PubMed, Web of Science, Cochrane Library, and WanFang) were searched. The primary endpoints were overall survival (OS), disease-free survival (DFS), and progression-free survival (PFS). Pooled data were synthesized using StataMP 14 and expressed as hazard ratios (HRs) and 95% confidence intervals (CIs).

Results

This update examined 19 studies (7282 cases) that assessed the correlation of AFR with cancer prognosis. Pooled univariate and multivariate analyses indicated significant correlations of low AFR with poor OS (HR 2.18, 95%CI 1.87–2.55 and HR 1.75, 95%CI 1.54–2.00, respectively), poor DFS (HR 1.89, 95%CI 1.54–2.32 and HR 1.51, 95%CI 1.29–1.76, respectively), and poor PFS (HR 1.68, 95%CI 1.42–1.99 and HR 1.48, 95%CI 1.16–1.88, respectively). Pooled univariate and multivariate analyses of 6 studies (2232 cases) indicated high FPR significantly correlated with poor OS (HR 2.37, 95%CI 2.03–2.77 and HR 1.97, 95%CI 1.41–2.77, respectively). One study reported that high FPR correlated with poor DFS (univariate analysis: HR 2.20, 95%CI 1.35–3.57; multivariate analysis: HR 1.77, 95%CI 1.04–2.99) and one study reported a correlation of high FPR with poor PFS in univariate analysis alone (HR 1.79, 95%CI 1.11–2.88).

Conclusion

A low AFR and a high FPR correlated with increased risk of cancer mortality and recurrence. AFR and FPR may be promising prognostic markers for cancers.

The nature of the stable blood clot procoagulant activities

The function of tissue factor (Tf)-initiated coagulation is hemorrhage control through the formation and maintenance of an impermeable platelet-fibrin barrier. The catalytic processes involved in the clot maintenance function are not well defined, although the rebleeding problems characteristic of individuals with hemophilias A and B suggest a link between specific defects in the Tf-initiated process and defects in the maintenance function. We have previously demonstrated, using a methodology of "flow replacement" (or resupply) of ongoing Tf-initiated reactions with fresh reactants, that procoagulant complexes are produced during Tf-initiated coagulation, which are capable of reinitiating coagulation without input from extrinsic factor Xase activity (Orfeo, T., Butenas, S., Brummel-Ziedins, K. E., and Mann, K. G. (2005) J. Biol. Chem. 280, 42887-42896). Here we used Tf-initiated reactions in normal and hemophilia blood or in their corresponding proteome mixtures as sources of procoagulant end products and then varied the resupplying material to determine the identity of the catalysts that drive the new cycle of thrombin formation. The central findings are as follows: 1) the prothrombinase complex (fVa-fXa-Ca(2+)-membrane) accumulated during the episode of Tf-initiated coagulation is the primary catalyst responsible for the observed pattern of prothrombin activation after resupply; 2) impairments in intrinsic factor Xase function, i.e. hemophilias A and B, result in an impaired capacity to mount a resupply response; and 3) in normal hemostasis the intrinsic factor Xase function contributes to the durability of the resupply response.

The elasticity of an individual fibrin fiber in a clot

A blood clot needs to have the right degree of stiffness and plasticity to stem the flow of blood and yet be digestable by lytic enzymes so as not to form a thrombus, causing heart attacks, strokes, or pulmonary emboli, but the origin of these mechanical properties is unknown. Clots are made up of a three-dimensional network of fibrin fibers stabilized through ligation with a transglutaminase, factor XIIIa. We developed methods to measure the elastic moduli of individual fibrin fibers in fibrin clots with or without ligation, using optical tweezers for trapping beads attached to the fibers that functioned as handles to flex or stretch a fiber. Here, we report direct measurements of the microscopic mechanical properties of such a polymer. Fibers were much stiffer for stretching than for flexion, as expected from their diameter and length. Elastic moduli for individual fibers in plasma clots were 1.7 +/- 1.3 and 14.5 +/- 3.5 MPa for unligated and ligated fibers, respectively. Similar values were obtained by other independent methods, including analysis of measurements of fluctuations in bead force as a result of Brownian motion. These results provide a basis for understanding the origin of clot elasticity.

Modes and consequences of thrombin's interaction with fibrin

Thrombin mediates the balance between coagulant and fibrinolytic forces and has numerous cellular effects. This intricate balance is maintained by biochemical mechanisms that regulate thrombin activity. Disruption of this balance could lead to bleeding or thrombosis. Once thrombin is generated, two major mechanisms regulate its activity. By binding fibrin, thrombin's activity is localized to the thrombus, a process that limits its systemic procoagulant effects. Thrombin that escapes into the circulation is efficiently inactivated by plasma inhibitors, such as antithrombin, or is sequestered by thrombomodulin on the endothelium. Although thrombin's interaction with fibrin limits its systemic effects, fibrin-bound thrombin resists inactivation and can produce a local procoagulant stimulus that triggers thrombus growth. Direct thrombin inhibitors were developed, at least in part, to target fibrin-bound thrombin. These agents are finding their niche for the prevention and treatment of venous and arterial thrombosis. The mechanisms by which thrombin binds fibrin are reviewed in this paper. As well, the potential pathological consequences of thrombin's interaction with fibrin are discussed.

Fibrinogen and fibrin

Fibrinogen is a large, complex, fibrous glycoprotein with three pairs of polypeptide chains linked together by 29 disulfide bonds. It is 45 nm in length, with globular domains at each end and in the middle connected by alpha-helical coiled-coil rods. Both strongly and weakly bound calcium ions are important for maintenance of fibrinogen's structure and functions. The fibrinopeptides, which are in the central region, are cleaved by thrombin to convert soluble fibrinogen to insoluble fibrin polymer, via intermolecular interactions of the "knobs" exposed by fibrinopeptide removal with "holes" always exposed at the ends of the molecules. Fibrin monomers polymerize via these specific and tightly controlled binding interactions to make half-staggered oligomers that lengthen into protofibrils. The protofibrils aggregate laterally to make fibers, which then branch to yield a three-dimensional network-the fibrin clot-essential for hemostasis. X-ray crystallographic structures of portions of fibrinogen have provided some details on how these interactions occur. Finally, the transglutaminase, Factor XIIIa, covalently binds specific glutamine residues in one fibrin molecule to lysine residues in another via isopeptide bonds, stabilizing the clot against mechanical, chemical, and proteolytic insults. The gene regulation of fibrinogen synthesis and its assembly into multichain complexes proceed via a series of well-defined steps. Alternate splicing of two of the chains yields common variant molecular isoforms. The mechanical properties of clots, which can be quite variable, are essential to fibrin's functions in hemostasis and wound healing. The fibrinolytic system, with the zymogen plasminogen binding to fibrin together with tissue-type plasminogen activator to promote activation to the active enzyme plasmin, results in digestion of fibrin at specific lysine residues. Fibrin(ogen) also specifically binds a variety of other proteins, including fibronectin, albumin, thrombospondin, von Willebrand factor, fibulin, fibroblast growth factor-2, vascular endothelial growth factor, and interleukin-1. Studies of naturally occurring dysfibrinogenemias and variant molecules have increased our understanding of fibrinogen's functions. Fibrinogen binds to activated alphaIIbbeta3 integrin on the platelet surface, forming bridges responsible for platelet aggregation in hemostasis, and also has important adhesive and inflammatory functions through specific interactions with other cells. Fibrinogen-like domains originated early in evolution, and it is likely that their specific and tightly controlled intermolecular interactions are involved in other aspects of cellular function and developmental biology.

Inherited Thrombophilia: Impact on Human Reproduction

The development of thrombotic disorders is a major threat for young women during pregnancy. It is one of the main causes of pregnancy-related disorders, which may also result in harm for the conceptus. Successful pregnancies require an even balance of coagulation and fibrinolysis, in order to secure stabilization of the basal plate as well as adequate placental perfusion. Thrombophilia is a laboratory definition for pre-disposing factors of thrombosis, which can be inherited or acquired. Many individuals, who carry a thrombotic defect remain asymptomatic, at least until additional boosting factors arise. The documentation of thrombophilic causes of recurrent miscarriage or pregnancy-related disorders is important, because of availability of effective early treatment. There is a rapidly growing awareness on the relationship of genetic factors influencing hemostasis and pregnancy-related disorders. The aim of our review is to summarize this knowledge, focusing on common genetic variations.

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate. and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR-FTIR. UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 microg/cm2 using PAS solution concentrations of 1mg/ ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic (theta(water) = 43.1 +/- 2.1) relatively to the original SPU films (theta(water) = 70.3 +/- 1.9). The in vitro albumin (BSA) adsorption shows that the PAS-SPU films adsorb more BSA (250/microgmm2) than the original SPU (112 microg mm2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.

Nephrotic proteinuria has No net effect on total body protein synthesis: measurements with (13)C valine

In nephrotic syndrome, significant amounts of plasma proteins, mostly of hepatic origin, are lost in urine. Total hepatic protein synthesis increases, suggesting that other protein pools must be conserved to maintain steady state. This can be accomplished either by decreased amino acid oxidation or decreased protein synthesis in other organs to replace lost liver-derived proteins. To determine the effect of nephrotic syndrome on total-body protein metabolism, we compared whole-body valine use in seven nephrotic patients and five controls using a primed continuous infusion of [1-(13)C]-valine, with additional priming of NaH(13)CO(3). Plasma [(13)C]-valine, (13)C alpha ketoisovaleric acid, and the expired (13)CO(2) enrichments were used to assess whole-body valine flux, valine oxidation, and nonoxidative valine disposal (NOVD). The valine flux into the blood compartment (97.7 +/- 3.0 versus 95.3 +/- 3.3 micromol/kg/h), oxidation of valine (19.4 +/- 1.9 versus 21.2 +/- 2. 8 micromol/kg/h), and NOVD (78.3 +/- 2.5 versus 74.2 +/- 2.7 micromol/kg/h) were not statistically different in patients compared with controls. Valine oxidation correlated positively with urinary urea excretion (r = 0.70; P = 0.01) in all subjects. Compared with control subjects who have similar urinary urea excretion, nephrotic subjects do not compensate for urinary loss of protein by decreased amino acid oxidation or decreased nonoxidative valine disposal. Previous studies have shown that synthesis of several hepatic proteins increases when subjects are fed the same dietary regime, whereas the present study shows that total-body protein synthesis does not increase. This would imply reduced synthesis of nonhepatic protein pools.

Identification of the mechanism responsible for the increased fibrin specificity of TNK-tissue plasminogen activator relative to tissue plasminogen activator

TNK-tissue plasminogen activator (TNK-t-PA), a bioengineered variant of tissue-type plasminogen activator (t-PA), has a longer half-life than t-PA because the glycosylation site at amino acid 117 (N117Q, abbreviated N) has been shifted to amino acid 103 (T103N, abbreviated T) and is resistant to inactivation by plasminogen activator inhibitor 1 because of a tetra-alanine substitution in the protease domain (K296A/H297A/R298A/R299A, abbreviated K). TNK-t-PA is more fibrin-specific than t-PA for reasons that are poorly understood. Previously, we demonstrated that the fibrin specificity of t-PA is compromised because t-PA binds to (DD)E, the major degradation product of cross-linked fibrin, with an affinity similar to that for fibrin. To investigate the enhanced fibrin specificity of TNK-t-PA, we compared the kinetics of plasminogen activation for t-PA, TNK-, T-, K-, TK-, and NK-t-PA in the presence of fibrin, (DD)E or fibrinogen. Although the activators have similar catalytic efficiencies in the presence of fibrin, the catalytic efficiency of TNK-t-PA is 15-fold lower than that for t-PA in the presence of (DD)E or fibrinogen. The T and K mutations combine to produce this reduction via distinct mechanisms because T-containing variants have a higher K(M), whereas K-containing variants have a lower k(cat) than t-PA. These results are supported by data indicating that T-containing variants bind (DD)E and fibrinogen with lower affinities than t-PA, whereas the K and N mutations have no effect on binding. Reduced efficiency of plasminogen activation in the presence of (DD)E and fibrinogen but equivalent efficiency in the presence of fibrin explain why TNK-t-PA is more fibrin-specific than t-PA.

An integrated study of fibrinogen during blood coagulation

The rate of conversion of fibrinogen (Fg) to the insoluble product fibrin (Fn) is a key factor in hemostasis. We have developed methods to quantitate fibrinopeptides (FPs) and soluble and insoluble Fg/Fn products during the tissue factor induced clotting of whole blood. Significant FPA generation (>50%) occurs prior to visible clotting (4 +/- 0.2 min) coincident with factor XIII activation. At this time Fg is mostly in solution along with high molecular weight cross-linked products. Cross-linking of gamma-chains is virtually complete (5 min) prior to the release of FPB, a process that does not occur until after clot formation. FPB is detected still attached to the beta-chain throughout the time course demonstrating release of only low levels of FPB from the clot. After release of FPB a carboxypeptidase-B-like enzyme removes the carboxyl-terminal arginine resulting exclusively in des-Arg FPB by the 20-min time point. This process is inhibited by epsilon-aminocaproic acid. These results demonstrate that transglutaminase and carboxypeptidase enzymes are activated simultaneously with Fn formation. The initial clot is a composite of Fn I and Fg already displaying gamma-gamma cross-linking prior to the formation of Fn II with Bbeta-chain remaining mostly intact followed by the selective degradation of FPB to des-Arg FPB.

The contribution of activated factor XIII to fibrinolytic resistance in experimental pulmonary embolism

BACKGROUND

The resistance of thrombi to fibrinolysis induced by plasminogen activators remains a major impediment to the successful treatment of thrombotic diseases. This study examines the contribution of activated factor XIII (factor XIIIa) to fibrinolytic resistance in experimental pulmonary embolism.

METHODS AND RESULTS

The fibrinolytic effects of specific inhibitors of factor XIIIa-mediated fibrin-fibrin cross-linking and alpha2-antiplasmin-fibrin cross-linking were measured in anesthetized ferrets with pulmonary emboli. Five experimental groups were treated with heparin (100 U/kg) and/or tissue plasminogen activator (TPA, 1 mg/kg) and the percent (mean+/-SD) lysis of emboli was determined: (1) control, normal factor XIIIa activity (14.1+/-4. 8% lysis); (2) inhibited factor XIIIa activity (42.7+/-7.4%); (3) normal factor XIIIa activity+TPA (32.3+/-7.7%); (4) inhibited factor XIIIa activity+TPA (76.0+/-11.9%); and (5) inhibited alpha2-antiplasmin-fibrin cross-linking+TPA (54.7+/-3.9%). Inhibition of factor XIIIa activity increased endogenous lysis markedly (group 1 versus 2; P<0.0001), to a level comparable to that achieved with TPA (group 2 versus 3; P<0.05). Among groups receiving TPA, selective inhibition of factor XIII-mediated alpha2-antiplasmin-fibrin cross-linking enhanced lysis (group 3 versus 5; P<0.0005). Complete inhibition of factor XIIIa also amplified lysis (group 3 versus 4; P<0.0001) and had greater effects than inhibition of alpha2-antiplasmin cross-linking alone (group 4 versus 5; P<0.0005). No significant fibrinogen degradation occurred in any group.

CONCLUSIONS

Factor XIIIa-mediated fibrin-fibrin and alpha2-antiplasmin-fibrin cross-linking both caused experimental pulmonary emboli to resist endogenous and TPA-induced fibrinolysis. This suggests that factor XIIIa may play a critical role in regulating fibrinolysis in human thrombosis.

Contact activation of the plasma coagulation cascade. III. Biophysical aspects of thrombin-binding anticoagulants

A biophysical model linking fibrin polymerization kinetics (following release from a thrombin-fibrinogen complex), coagulation time, and competitive inhibition of thrombin illustrates the utility of thrombin-binding ligands as anticoagulants in blood collection applications. The resulting mathematical relationship connecting fibrinogen, ligand, and thrombin concentrations was tested against experimentally observed anticoagulation of whole, platelet-poor porcine plasma induced by short, single-stranded DNA oligonucleotides originally found to bind thrombin by screening combinatorial libraries. The thrombin-fibrinogen dissociation constant Ks served as the single adjustable parameter in a least-squares fitting of the model to experimental anticoagulation data. Best-fit Ks values corroborated microM values measured in plasma-free systems, and application of the model to a ligand challenge to the intrinsic pathway of plasma coagulation corroborated nM endogenous thrombin concentrations measured in porcine blood activated by endotoxin insult in vivo. The model fit to data suggests that only about 20% conversion of blood fibrinogen to fibrin is required to coagulate (gel) porcine plasma. This prediction is consistent with the common clinical laboratory observation of latent fibrin formation in "serum" separated from blood before fibrinogen is fully converted to fibrin. It was concluded that the thrombin-binding anticoagulation model was a reasonable simulation of the situation in which an initial bolus of either exogenous or endogenous thrombin is rapidly partitioned between fibrinogen-bound and ligand-bound forms with little or no additional free thrombin created over time.

Kinetic pathway for the slow to fast transition of thrombin. Evidence of linked ligand binding at structurally distinct domains

The kinetic pathway for the Na+-induced slow --> fast transition of thrombin was characterized. The slow form was shown to consist of two conformers in a 3:1 ratio (ES2:ES1) at 5 degrees C, pH 7.4, Gamma/2 0.3. ES2 binds Na+ 3 orders of magnitude faster than does ES1. The small molecule active site-directed inhibitor L-371,912, and the exosite I binding ligand hirugen, like Na+, bind selectively to ES2 and induce the slow --> fast conversion of thrombin. The slow --> fast transition is limited by the rate of conversion of ES1 to ES2 (k approximately 28 s-1 at 5 degrees C). Replacement of Arg-221a or Lys-224 at the Na+ binding site with Ala appears to selectively alter the slow form and reduce the apparent affinity of the mutants for Na+ and L-371,912. This replacement, however, has little effect on the affinity for the inhibitor in the presence of saturating concentrations of Na+. The kinetically linked ligand binding at the Na+ binding site, exosite I, and the active site of thrombin characterized in the present study indicates the basis for the plasticity of this important enzyme, and suggests the possibility that the substrate specificity and, therefore, the procoagulant and anticoagulant activities of thrombin may be subject to allosteric regulation by as yet unidentified physiologically important effectors.

The primary fibrin polymerization pocket: three-dimensional structure of a 30-kDa C-terminal gamma chain fragment complexed with the peptide Gly-Pro-Arg-Pro

After vascular injury, a cascade of serine protease activations leads to the conversion of the soluble fibrinogen molecule into fibrin. The fibrin monomers then polymerize spontaneously and noncovalently to form a fibrin gel. The primary interaction of this polymerization reaction is between the newly exposed N-terminal Gly-Pro-Arg sequence of the alpha chain of one fibrin molecule and the C-terminal region of a gamma chain of an adjacent fibrin(ogen) molecule. In this report, the polymerization pocket has been identified by determining the crystal structure of a 30-kDa C-terminal fragment of the fibrin(ogen) gamma chain complexed with the peptide Gly-Pro-Arg-Pro. This peptide mimics the N terminus of the alpha chain of fibrin. The conformational change in the protein upon binding the peptide is subtle, with electrostatic interactions primarily mediating the association. This is consistent with biophysical experiments carried out over the last 50 years on this fundamental polymerization reaction.

Thrombin interaction with fibrin polymerization sites

Thrombin is central to hemostasis, and postclotting fibrinolysis and wound healing. During clotting, thrombin transforms plasma fibrinogen into polymerizing fibrin, which selectively adsorbs the enzyme into the clot. This protects thrombin from heparin-antithrombin inactivation, thus preserving the enzyme for postclotting events. To determine how the fibrin N-terminal polymerization sites of A alpha 17-23 (GPRVVER) and B beta 15-25 (GHRPLDKKREE) and their analogs may interact with thrombin, amidolysis vs. plasma- and fibrinogen-clotting assays were used to differentiate blockade of catalytic site vs. other thrombin domains. Amidolysis studies suggest GPRVVER inhibition of thrombin catalytic site through hydrophobic interaction, and GPRVVER inhibited clotting. Neither GPRP nor VVER nor the B beta 15-25 homologs inhibited amidolysis. Contrary to heparin, acyl-DKKREE promoted plasma-clotting, but inhibited fibrinogen-clotting. In addition, acyl-DKKREE reversed the anticoagulant effect of heparin (0.1 U/ml) in plasma. The results suggest fibrin B beta 15-25 interaction with thrombin, possibly by blocking the heparin-binding site. Together with the reported fibrin A alpha 27-50 binding to thrombin, polymerizing fibrin appears to initially bind to thrombin catalytic site and exosite-1 through A alpha 17-50, and to another thrombin site through B beta 15-25. As these fibrin sites are also involved in polymerization, competition of the polymerization process with thrombin-binding could subsequently dislodge thrombin from fibrin alpha-chain. This may re-expose the catalytic site and exosite-1, thus explaining the thrombogenicity of clot-bound thrombin. The implications of these findings in polymerization mechanism and anticoagulant design are discussed.

Neural cell pattern formation on glass and oxidized silicon surfaces modified with poly(N-isopropylacrylamide)

Control over the adsorption of proteins and over the adsorption and spatial orientation of mammalian cells onto surfaces has been achieved by modification of glass and other silicon oxide substrates with poly(N-isopropylacrylamide) (PNIPAM). The functionalization of the substrates was achieved either by a polymer-analogous reaction of aminosilanes with reactive N-(isopropylacrylamide) (NIPAM)-copolymers and by copolymerization of NIPAM with surface-bound methacrylsilane. The obtained coatings were characterized by FT-1R, ellipsometry, and surface plasmon resonance measurements. The adsorption of two proteins-fibrinogen and ribonuclease A-on these surfaces was studied in situ by real time surface plasmon resonance measurements. The PNIPAM-grafted surfaces prepared by either chemical procedure inhibited the adsorption of both proteins. More importantly they prevented the adhesion of neuroblastomaXglioma hybrid cells cultured either in serum-free medium or in a medium containing serum proteins. Deep-UV irradiation was used to perform ablation processes and to create patterns permitting the examination of spatially controlled adhesion and growth of cells. This study showed that patterned ultrathin polymer films on glass are suitable substrates for controlling the interactions of cells with surfaces and are capable of directing the attachment and spreading of cells.

Multiple peaks induced by domain-specific binding of fibrinogen in anion-exchange high-performance liquid chromatography

A domain binding model was developed for explaining the multiple peak chromatograms obtained in the high-performance liquid chromatography of pure fibrinogen on a DEAE polymethacrylate column using different gradients of ammonium chloride. The different peaks for fibrinogen result from the binding of either the D or E domain of fibrinogen to the packing material. This was confirmed by comparing the retention times of the chromatograms for fibrinogen, fragment D1 and fragment E. Native and denatured forms of fibrinogen are proposed to be important to fibrinogen's interaction with the column, hiding or exposing the E domain, respectively. Different gradient speeds resolve a different number of peaks for fibrinogen, with slow gradients yielding essentially one peak and fast gradients 10 or more peaks. Temperature studies were done to confirm the model. Different commercial sources of fibrinogen showed different proportions of native and denatured/degraded forms.

Novel aspects of blood coagulation factor XIII. I. Structure, distribution, activation, and function

Blood coagulation factor XIII (FXIII) is a protransglutaminase that becomes activated by the concerted action of thrombin and Ca2+ in the final stage of the clotting cascade. In addition to plasma, FXIII also occurs in platelets, monocytes, and monocyte-derived macrophages. While the plasma factor is a heterotetramer consisting of paired A and B subunits (A2B2), its cellular counterpart lacks the B subunits and is a homodimer of potentially active A subunits (A2). The gene coding for the A and B subunits has been localized to chromosomes 6p24-25 and 1q31-32.1, respectively. The genomic as well as the primary protein structure of both subunits has been established, and most recently the three-dimensional structure of recombinant cellular FXIII has also been revealed. Monocytes/macrophages synthesize their own FXIII, and very likely FXIII in platelets is synthesized by the megakaryocytes. Cells of bone marrow origin seem to be the primary site for the synthesis of subunit A in plasma FXIII, but hepatocytes might also contribute. The B subunit of plasma FXIII is synthesized in the liver. Plasma FXIII circulates in association with its substrate precursor, fibrinogen. Fibrin(ogen) has an important regulatory role in the activation of plasma FXIII. The most important steps of the activation of plasma FXIII are the proteolytic removal of activation peptide by thrombin, the dissociation of subunits A and B, and the exposure of the originally buried active site on the free A subunits. The end result of this process is the formation of an active transglutaminase, which cross-links peptide chains through epsilon(gamma-glutamyl)lysyl isopeptide bonds. Cellular FXIII in platelets becomes activated through a nonproteolytic process. When intracytoplasmic Ca2+ is raised during platelet activation, the zymogen--in the absence of subunit B--assumes an active configuration. The protein substrates of activated FXIII include components of the clotting-fibrinolytic system, adhesive and contractile proteins. The main physiological function of plasma FXIII is to cross-link fibrin and protect it from the fibrinolytic plasmin. The latter effect is achieved mainly by covalently linking alpha 2 antiplasmin, the most potent physiological inhibitor of plasmin, to fibrin. Plasma FXIII seems to be involved in wound healing and tissue repair, and it is essential to maintaining pregnancy. Cellular FXIII, if exposed to the surface of the cells, might support or perhaps take over the hemostatic functions of plasma FXIII; however, its intracellular role has remained mostly unexplored.

Fibrin structures during tissue-type plasminogen activator-mediated fibrinolysis studied by laser light scattering: relation to fibrin enhancement of plasminogen activation

The aim was to relate fibrin structure and the stimulatory effect of fibrin on plasminogen activation during t-PA-mediated fibrinolysis using Lys78-plasminogen as activator substrate. Structural studies were undertaken by static and dynamic laser light scattering, cryo transmission electron microscopy and by the measurement of conversion of fibrin to X-, Y- and D-fragments. The kinetics of plasmin formation were monitored by measurement of the rate of pNA-release from Val-Leu-Lys-pNA. The process of fibrin formation and degradation comprised three phases. In the first phase, protofibrils with an average length of about 10 times that of fibrinogen were formed. The duration of this phase decreased with increasing t-PA concentration. The second phase was characterized by a sudden elongation and lateral aggregation of fibrin fibers, most pronounced at low levels of t-PA, and by formation of fragment X-polymer. The third phase was dominated by fragmentation of fibers and by formation of Y- and D-fragments. Plasmin degraded the fibers from within, resulting in the formation of long loose bundles, which subsequently disintegrated into thin filaments with a length of less than 10 and a mass per length close to one relative to fibrinogen. Plasmin generation at high t-PA concentrations sets in just prior to (and at low t-PA concentrations shortly after) the onset of the rapid second phase of elongation and lateral aggregation of fibrin fibers. The maximal rate of plasmin formation per mol t-PA was the same at all concentrations of activator and was achieved close to the time of the peak level of fragment X-polymer. Plasmin formation ceased after formation of substantial amounts of Y- and D-fragments. At this stage the length was between 300 and 3 and the mass per length close to 1, both relative to fibrinogen. In conclusion our results indicate that (1) formation of short fibrin protofibrils is the minimal requirement for the onset of the stimulatory effect of fibrin on plasminogen activation by t-PA, (2) formation of fragment X protofibrils is sufficient to induce optimal stimulation of plasminogen activation, and (3) plasmin degrades laterally aggregated fibrin fibers from within, resulting in the conversion of the fibers into long loose bundles, which later disintegrate into thin filaments.

Transglutaminase factor XIII uses proteinase-like catalytic triad to crosslink macromolecules

The X-ray crystal structure of human transglutaminase factor XIII has revealed a cysteine proteinase-like active site involved in a crosslinking reaction and not proteolysis. This is among the first observations of similar active sites in 2 different enzyme families catalyzing a similar reaction in opposite directions. Although the size and overall protein fold of factor XIII and the cysteine proteinases are quite different, the active site and the surrounding protein structure share structural features suggesting a common evolutionary lineage. Here we present a description of the residues in the active site and the structural evidence that the catalytic mechanism of the transglutaminases is similar to the reverse mechanism of the cysteine proteinases.

alpha-Thrombin within fibrin clots: inactivation of thrombin by antithrombin-III

To demonstrate that human alpha-thrombin is effectively inactivated by human antithrombin III (AT) during the production of a fibrin clot we measured the amount of alpha-thrombin activity which can be recovered from a clot generated from purified human proteins. We discovered that 0.05-0.07% of the original alpha-thrombin activity is recovered from a fibrin clot produced from a reaction mixture where the initial concentrations of AT and alpha-thrombin were chosen at a ratio (17.5) to allow complete conversion of fibrinogen to fibrin. These results indicated that alpha-thrombin is successfully inactivated by AT during the production of a fibrin clot. Further, when an amount of alpha-thrombin equal to that recovered from a fibrin clot is introduced into a solution of fibrinogen and AT identical to that utilized to produce the clot only 4% of the fibrinogen is converted to fibrin. These results suggest that i) when a fibrin clot is dissolved during fibrinolytic therapy little active alpha-thrombin should be released from the clot and ii) this amount of thrombin is insufficient to catalyze rethrombosis without proposing de novo production of thrombin. The action on factors XI, VIII, and V of the small amount of thrombin released upon thrombolysis, however, may provide the stimulus for de novo production of sufficient thrombin to catalyze rethrombosis.

Catalytically competent human and bovine zeta-thrombin and chimeras generated from unfolded polypeptide chains

Human and bovine alpha-thrombin cleaved at the B-chain by chymotrypsin generates catalytically competent zeta-thrombins, which are comprised of two noncovalently linked fragments: a 36-(human) or 49-(bovine) residue A-chain linked by a disulfide to B-chain residues B1-148 (zeta 1-thrombin) and B-chain residues B149-259 (zeta 2-thrombin). Human and bovine D-Phe-Pro-Arg-CH2-zeta- and PhMeSO2-zeta-thrombins were prepared by reaction of the active-site histidine (H-B43) and serine (S-B205) with PPACK and PMSF, respectively. Unfolding and dissociation of the noncovalently linked polypeptide chains of either human or bovine D-Phe-Pro-Arg-CH2-zeta- and PhMeSO2-zeta-thrombins in 4.5 M guanidine-HCl and refolding upon 30-fold dilution in 50 mM sodium phosphate buffer pH 6.5, 750 mM NaCl, 0.1% PEG resulted in biphasic generation of catalytic activity. The slow phase was eliminated in the presence of the competitive inhibitor benzamidine-HCl. Unfolding and refolding mixtures of the appropriate inactive precursors generated the active chimeric thrombins bovine zeta 1-thrombin:human zeta 2-thrombin and human zeta 1-thrombin:bovine zeta 2-thrombin. Human zeta 1-thrombin and zeta 2-thrombin were isolated, and, upon recombining, the isolated fragments refolded to generate catalytically competent zeta-thrombin with an active-site content, specific activity toward Chromozym-TH, and a specificity constant (kcat/Km) for FPA release from fibrinogen that were all within 60% of those of native alpha-thrombin.(ABSTRACT TRUNCATED AT 250 WORDS)

New developments in thrombolytic therapy

Pharmacologic lysis of occlusive, ischemia-producing thrombi has become widely accepted during the past decade. New developments in this field have centered around increasing the efficacy of the known plasminogen activators while employing methods to minimize the risk of hemorrhage and decrease the incidence of rethrombosis. Such methods have included the use of thrombus-directed antibodies linked to plasminogen activators, increased plasminogen (substrate) concentration at the thrombus site, anticoagulant and antiplatelet therapy to prevent thrombus propagation and reformation following lysis, and combination plasminogen activator therapy designed to increase efficacy and safety. These new strategies have been extensively tested in vitro and in a variety of animal models. As we have indicated, extrapolation of such results to human patients cannot be done with confidence. However, the strategies are based on sound rationale and the reported findings should serve as the basis for controlled human trials.

The effect of hypercholesterolemia on early atherosclerotic lesions initiated by fibrinopeptide B

Hypercholesterolemia and thrombosis have been implicated as factors in the development of atherosclerosis. Fibrinopeptide B (FPB) is a short chain peptide cleaved from fibrinogen during the production of fibrin. FPB is a known chemoattractant and has been shown to produce experimental atherosclerotic lesions in association with hypercholesterolemia. The present study was designed to examine the role of hypercholesterolemia in this process and to study the time course of the development of these lesions. Twelve New Zealand White rabbits were placed on an atherogenic diet and had suture carrying either FPB, fibrinopeptide A (FPA), or saline (controls) implanted in the adventitia of the femoral arteries and were sacrificed at 14 days. An equal number of animals were left on a standard diet and underwent similar treatment. Eleven animals were treated as the hypercholesterolemic group but were sacrificed at 2, 4, and 7 days. The thickness of the intima was measured adjacent to the suture in the animals sacrificed at 14 days, and the hypercholesterolemic FPB sites were thicker (12.23 mu +/- 6.60) than either hypercholesterolemic FPA (6.06 mu +/- 3.72), saline (4.94 mu +/- 1.42), or the normocholesterolemic FPB (5.99 mu +/- 4.61), FPA (3.89 mu +/- 2.20), or saline (3.97 mu +/- 1.83) (P less than 0.05 for all groups). Transmission electron microscopy of the hypercholesterolemic FPB group showed evidence of macrophages, actively secreting smooth muscle cells with newly deposited elastin, and foam cells by 7 days. We conclude that FPB attracts or stimulates macrophages and smooth muscle cells and that the resultant cellular and extracellular proliferation favors early atherosclerotic lesion formation in the presence of hypercholesterolemia.

Self-assembled organic monolayers: model systems for studying adsorption of proteins at surfaces

Self-assembled monolayers (SAMs) of omega-functionalized long-chain alkanethiolates on gold films are excellent model systems with which to study the interactions of proteins with organic surfaces. Monolayers containing mixtures of hydrophobic (methyl-terminated) and hydrophilic [hydroxyl-, maltose-, and hexa(ethylene glycol)-terminated] alkanethiols can be tailored to select specific degrees of adsorption: the amount of protein adsorbed varies monotonically with the composition of the monolayer. The hexa(ethylene glycol)-terminated SAMs are the most effective in resisting protein adsorption. The ability to create interfaces with similar structures and well-defined compositions should make it possible to test hypotheses concerning protein adsorption.