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Biomedical subjects

J W Weisel

Publications and source records attributed to J W Weisel.

At least 19 recordsLinked to original sources
PubMed2006

Altered fibrin architecture is associated with hypofibrinolysis and premature coronary atherothrombosis.

OBJECTIVE: Hypofibrinolysis promotes atherosclerosis progression and recurrent ischemic events in premature coronary artery disease. We investigated the role of fibrin physical properties in this particular setting. METHODS AND RESULTS: Biomarkers of recurrent thrombosis and premature coronary artery disease (CAD) were measured in 33 young post-myocardial infarction patients with angiographic-proven CAD and in 33 healthy volunteers matched for age and sex. Ex vivo plasma fibrin physical properties were assessed by measuring fibrin rigidity and fibrin morphological properties using a torsion pendulum and optical confocal microscopy. The fibrinolysis rate was derived from continuous monitoring of the viscoelastic properties after addition of lytic enzymes. Young CAD patients had a significant increase in plasma concentration of fibrinogen, von Willebrand factor, plasminogen activator inhibitor type 1, and lipoprotein(a) as compared with controls (P<0.05). Fibrin of young CAD patients was stiffer (P=0.002), made of numerous (P=0.002) and shorter fibers (P=0.04), and lysed at a slower rate than that of controls (P=0.03). Fibrin stiffness was an independent predictor for both premature CAD and hypofibrinolysis. CONCLUSIONS: This first detailed study of clot properties in such a group of patients demonstrated that abnormal plasma fibrin architecture is an important feature of both premature CAD and fibrinolysis rate. The determinants of this particular phenotype warrant further investigation.

Adult↗
PubMed2004

The effects of additional carbohydrate in the coiled-coil region of fibrinogen on polymerization and clot structure and properties: characterization of the homozygous and heterozygous forms of fibrinogen Lima (Aalpha Arg141-->Ser with extra glycosylation).

Fibrinogen Lima is an abnormal fibrinogen with an Aalpha Arg141-->Ser substitution resulting in an extra N-glycosylation at Aalpha Asn139, which seems to be responsible for the impairment of fibrin polymerization. We have studied the polymerization and properties of clots made from both plasma and purified fibrinogen of both the homozygous and heterozygous forms. The clot permeation studies with both plasma and purified protein revealed a normal flux through the network for the heterozygous form but very decreased permeation in the homozygous form. Consistent with turbidity results, the clot network of the homozygous form, seen by scanning electron microscopy, was tight and composed of thin fibers, with many branch points, while the appearance of clots from the heterozygous form was similar to that of control clots, but in both cases the fibers were more curved than those of control clots. The rheological properties of clots from the homozygous form were also altered, with rigidity being increased in plasma clots, but decreased in the purified system, a consequence of the balance between numbers of branch points and fiber curvature. From these results it seems that the extra carbohydrate moiety, located in the alpha coiled-coil region close to the betaC domains, impairs the protofibril lateral association process, giving rise to thinner, more curved fibers, with the structural anomalies being most pronounced in the clots from the homozygous plasma. These studies support a model for fibrin polymerization in which the betaC-betaC interactions are involved in lateral aggregation.

Blood Coagulation↗
PubMed2004

Cross-linked gamma-chains in a fibrin fibril are situated transversely between its strands.

There is no evidence for the change from transverse to longitudinal orientation hypothesized to explain X-ray and electron microscope structures. Dissolution of the clot through fibrinolysis to produce soluble products is difficult to reconcile with transverse cross-linking. There are flaws in the interpretation supporting transverse cross-linking of experiments with fibrin as a template and stretching. In summary, the strongest evidence from X-ray crystallography, fibrinolysis, and electron microscopy experiments favors the presence of longitudinal cross-links in fibrin.

Crystallography, X-Ray↗
PubMed2003

Influence of gamma' fibrinogen splice variant on fibrin physical properties and fibrinolysis rate.

OBJECTIVE: A splice variant of fibrinogen, gamma', has an altered C-terminal sequence in its gamma chain. This gammaA/gamma' fibrin is more resistant to lysis than gammaA/gammaA fibrin. Whether the physical properties of gamma' and gammaA fibrin may account for the difference in their fibrinolysis rate remains to be established. METHODS AND RESULTS: Mechanical and morphological properties of cross-linked purified fibrin, including permeability (Ks, in cm2) and clot stiffness (G', in dyne/cm2), were measured after clotting gammaA and gamma' fibrinogens (1 mg/mL). gamma'/gamma' fibrin displayed a non-significant decrease in the density of fibrin fibers and slightly thicker fibers than gammaA/gammaA fibrin (12+/-2 fiber/10(-3) nm3 versus 16+/-2 fiber/10(-3) nm3 and 274+/-38 nm versus 257+/-41 nm for gamma'/gamma' and gammaA/gammaA fibrin, respectively; P=NS). This resulted in a 20% increase of the permeability constant (6.9+/-1.7 10(-9) cm2 versus 5.5+/-1.9 10(-9) cm2, respectively; P=NS). Unexpectedly, gamma' fibrin was found to be 3-times stiffer than gammaA fibrin (72.6+/-2.6 dyne/cm2 versus 25.1+/-2.3 dyne/cm2; P<0.001). Finally, there was a 10-fold decrease of the fibrin fiber lysis rate. CONCLUSIONS: Fibrinolysis resistance that arises from the presence of gammaA/gamma' fibrinogen in the clot is related primarily to an increase of fibrin cross-linking with only slight modifications of the clot architecture.

Alternative Splicing↗
PubMed2003

A monoclonal antibody to the fibrinogen gamma-chain alters fibrin clot structure and its properties by producing short, thin fibers arranged in bundles.

BACKGROUND: We previously reported that hamster monoclonal antibody 7E9, which reacts with the C-terminus of the gamma-chain of mouse fibrinogen, inhibits factor (F)XIIIa-mediated cross-linking, platelet adhesion to fibrinogen, and platelet-mediated clot retraction; in addition, it facilitates thrombolysis. OBJECTIVES: To understand the mechanism(s) by which 7E9 acts, we have now studied the effect of 7E9 IgG, 7E9 F(ab')2, and 7E9 Fab on fibrin clot structure using electron microscopy and measurements of clot physical properties. RESULTS: By transmission electron microscopy, 7E9 IgG was found to bind primarily to the ends of the fibrinogen molecule. 7E9 IgG and 7E9 F(ab')2, both of which are bivalent, were capable of binding to two fibrinogen molecules simultaneously. Scanning electron microscopy of clots formed in the presence of equimolar concentrations of fibrinogen and 7E9 IgG demonstrated the presence of very short and thin fibers (63% reduction in fiber diameter) arranged in unusual bundles, surrounding large pores. Clots formed in the presence of 7E9 demonstrated a marked increase in permeation (approximately 25-fold increase in perfusion rate at constant pressure), an approximately 50% reduction in dynamic storage modulus (G'; a reflection of decreased clot stiffness), and an approximately 38% increase in loss tangent (tan delta; a reflection of the clot's ability to undergo irreversible deformation). These clots also showed decreased absorbance at 350 nm, reflecting the clot structure produced by 7E9 IgG. The effects of 7E9 IgG were not observed with control hamster IgG, 7E9 F(ab')2, or 7E9 Fab fragments, indicating requirements for both the binding properties and mass of 7E9 IgG. CONCLUSIONS: These data indicate that 7E9 antibody affects fibrin clot structure in a way that is consistent with the enhanced fibrinolysis we reported previously. Together with our previous observations, we conclude that 7E9 is directed at a strategically important region of fibrinogen with regard to platelet function, FXIIIa-mediated cross-linking, clot retraction, fibrin structure, and fibrinolysis. Thus targeting this region of fibrinogen may have antithrombotic therapeutic potential.

Animals↗
PubMed2002

A structural and dynamic investigation of the facilitating effect of glycoprotein IIb/IIIa inhibitors in dissolving platelet-rich clots.

Glycoprotein IIb/IIIa (GP IIb/IIIa) inhibitors were shown recently to facilitate the rate and the extent of pharmacological thrombolysis. However, their synergistic potential with rtPA in dissolving thrombotic vaso-occlusions is not fully understood. We have therefore developed a dynamic and structural approach for analysis of fibrinolysis to assess the inhibiting effect of platelets and the facilitating effect of GPIIb/IIIa inhibitors in dissolving platelet-rich clots (PRCs). Fluorescent rtPA was used to study the architecture of PRCs, to follow the progression of the rtPA binding front, and to measure the lysis-front velocity using confocal microscopy. Fibrinolysis resistance of PRCs was related to a reduction of both rtPA binding and lysis-front velocities of platelet-rich areas compared with platelet-poor areas (2.4 +/- 0.2 versus 3.5 +/- 0.4 microm/min for rtPA binding velocity, P=0.04, and 1.2 +/- 0.6 versus 2.8 +/- 0.2 microm/min for lysis-front velocity, P=0.008, in platelet-rich and platelet-poor areas, respectively). Fibrinolysis appeared heterogeneous, leaving platelet-rich areas un-lysed. Adding pharmacological concentrations of abciximab (0.068 micromol/L) or eptifibatide (1 micromol/L) before clotting decreased the average surface of platelet-rich areas by 64% (P=0.0005) and 72% (P=0.0007), respectively. The resulting equalization of rtPA binding rate and rtPA binding-front velocity between platelet-rich and platelet-poor areas led to a 3-fold increase of the lysis-front velocity in platelet-rich areas of either abciximab-PRC (P=0.006) or eptifibatide-PRC (P=0.03). The overall lysis rate of treated-PRC was increased by 74% compared with control-PRC (P<0.01). These results demonstrate that fibrinolysis resistance of PRCs is related primarily to the heterogeneity in the clot structure between platelet-rich and platelet-poor areas. GP IIb/IIIa inhibitors facilitate the rate and the extent of fibrinolysis by improving rtPA binding velocity and, subsequently, the lysis rate in platelet-rich areas. These findings provide new insights on the synergistic potential of GP IIb/IIIa inhibitors and fibrinolytic agents.

Abciximab↗
PubMed2001

The structure of lipoprotein(a) and ligand-induced conformational changes.

Lipoprotein(a) is composed of low-density lipoprotein linked both covalently and noncovalently to apolipoprotein(a). The structure of lipoprotein(a) and the interactions between low-density lipoprotein and apolipoprotein(a) were investigated by electron microscopy and correlated with analytical ultracentrifugation. Electron microscopy of rotary-shadowed and unidirectionally shadowed lipoprotein(a) prepared without glycerol revealed that it is a nearly spherical particle with no large projections. After extraction of both lipoprotein(a) and low-density lipoprotein with glycerol prior to rotary shadowing, the protein components were observed to consist of a ring of density made up of nodules of different sizes, with apolipoprotein(a) and apolipoprotein B-100 closely associated with each other. However, when lipoprotein(a) was treated with a lysine analogue, 6-aminohexanoic acid, much of the apolipoprotein(a) separated from the apolipoprotein B-100. In 6-aminohexanoic acid-treated preparations without glycerol extraction, lipoprotein(a) particles had an irregular mass of density around the core. In contrast, lipoprotein(a) particles treated with 6-aminohexanoic acid in the presence of glycerol had a long tail, in which individual kringles could be distinguished, extending from the ring of apolipoprotein B-100. The length of the tail was dependent on the particular isoform of apolipoprotein(a). Dissociation of the noncovalent interactions between apolipoprotein(a) and low-density lipoprotein as a result of shear forces or changes in the microenvironment may contribute to selective retention of lipoprotein(a) in the vasculature.

Cholesterol, LDL↗
PubMed2001

Binding of a fibrinogen mimetic stabilizes integrin alphaIIbbeta3's open conformation.

The platelet integrin alphaIIbbeta3 is representative of a class of heterodimeric receptors that upon activation bind extracellular macromolecular ligands and form signaling clusters. This study examined how occupancy of alphaIIbbeta3's fibrinogen binding site affected the receptor's solution structure and stability. Eptifibatide, an integrin antagonist developed to treat cardiovascular disease, served as a high-affinity, monovalent model ligand with fibrinogen-like selectivity for alphaIIbbeta3. Eptifibatide binding promptly and reversibly perturbed the conformation of the alphaIIbbeta3 complex. Ligand-specific decreases in its diffusion and sedimentation coefficient were observed at near-stoichiometric eptifibatide concentrations, in contrast to the receptor-perturbing effects of RGD ligands that we previously observed only at a 70-fold molar excess. Eptifibatide promoted alphaIIbbeta3 dimerization 10-fold more effectively than less selective RGD ligands, as determined by sedimentation equilibrium. Eptifibatide-bound integrin receptors displayed an ectodomain separation and enhanced assembly of dimers and larger oligomers linked through their stalk regions, as seen by transmission electron microscopy. Ligation with eptifibatide protected alphaIIbbeta3 from SDS-induced subunit dissociation, an effect on electrophoretic mobility not seen with RGD ligands. Despite its distinct cleft, the open conformer resisted guanidine unfolding as effectively as the ligand-free integrin. Thus, we provide the first demonstration that binding a monovalent ligand to alphaIIbbeta3's extracellular fibrinogen-recognition site stabilizes the receptor's open conformation and enhances self-association through its distant transmembrane and/or cytoplasmic domains. By showing how eptifibatide and RGD peptides, ligands with distinct binding sites, each affects alphaIIbbeta3's conformation, our findings provide new mechanistic insights into ligand-linked integrin activation, clustering and signaling.

Binding Sites↗
PubMed2001

The structure and function of the alpha C domains of fibrinogen.

The alpha C domains have been localized on fibrinogen and fibrin. Several model systems have been developed to study their functions. Analysis of the amino acid sequence of the alpha C domains suggested that each is made up of a globular and an extended portion. Microcalorimetry confirmed this result and showed that the two alpha C domains interact intramolecularly. Electron microscopy of fibrinogen with a monoclonal antibody to the alpha C domains demonstrated that these regions normally interact with the central portion of the molecule. In the conversion from fibrinogen to fibrin there is a large scale conformational change, such that the alpha C domains dissociate from the central region and are available for intermolecular interaction. Experiments with highly purified and well characterized fragment X monomer, missing either one or both of the alpha C domains, indicate that intermolecular interactions between alpha C domains are important for the enhancement of lateral aggregation during fibrin polymerization. Isolated alpha C fragments polymerized at neutral pH and interacted with the alpha C domains of fibrin monomer to influence clot formation. Several dysfibrinogenemias in which there are amino acid substitutions in, or truncations of, the alpha C domains revealed that these changes can have dramatic effects on polymerization and clot structure. The polymerization of A alpha 251 recombinant fibrinogen, that contains A alpha chains truncated at residue 251, was altered, as were the mechanical properties and the rate of fibrinolysis of the clots. Altogether, these results help to define the role of the alpha C domains in determining the structure and properties of clots.

Amino Acid Sequence↗
PubMed2001

Clot lysis of variant recombinant fibrinogens confirms that fiber diameter is a major determinant of lysis rate.

Previous studies have suggested that clots with thinner fiber diameter lyse at slower rates than clots with thicker fiber diameter. We examined lysis of fibrin clots formed from three variant fibrinogens, each with substitutions in the N-terminal region of the B beta chain. When we measured lysis as the rate of decrease in turbidity at 350 nm, we found that the rate of lysis was slower than normal for clots with thinner fibers. We noted, however, that the time to complete lysis was the same for all clots. Thus, when the data were considered as the percent of lysis with time, we found that the curves were the same as normal. We suggest that a complete and accurate characterization of clot dissolution requires comparison of normalized lysis rates.

Fibrin↗
PubMed2001

Structure and properties of clots from fibrinogen Bicêtre II (gamma 308 Asn-->Lys). Increased permeability due to larger pores, thicker fibers, and decreased rigidity.

Fibrinogen Bicêtre II is a dysfibrinogenemia in which there is a substitution of Lys for Asn at gamma 308. We have studied the polymerization of this abnormal fibrinogen by measurement of turbidity and have characterized clot structure by scanning electron microscopy, permeation, and viscoelastic measurements. The results of these studies demonstrate that this amino acid substitution has substantial effects on the structure and properties of the clot, resulting in clots made up of thick fibers and large pores with greatly reduced stiffness and increased slippage of protofibrils.

Fibrinogens, Abnormal↗
PubMed2000

End-linked homodimers in fibrinogen Osaka VI with a B beta-chain extension lead to fragile clot structure.

The authors have identified a 12-residue carboxyl-terminal extension of Lys-Ser-Pro-Met-Arg-Arg-Phe-Leu-Leu-Phe-Cys-Met in a dysfibrinogen derived from a woman heterozygotic for this abnormality and associated with severe bleeding. This extension is due to a T-to-A mutation that creates AAG encoding Lys at the stop (TAG) codon, thus translating 36 base pairs in the noncoding region of the Bbeta gene. The extra Cys residues appear to be involved in 1 or 2 disulfide bonds between 2 adjacent abnormal fibrinogen molecules, forming a fibrinogen homodimer as indicated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Indeed, about half of the fibrinogen molecules exist as end-linked dimers oriented in parallel or with an angle, as observed by transmission electron microscopy. These end-linked dimers may well alter the conformations of D and DD regions on fibrin assembly, leading to increased fiber branching at their sites in the growing protofibrils. By scanning electron microscopy, the Osaka VI fibrin network appears to have a lacelike structure composed of highly branched, thinner fibers than the normal fibrin architecture. Such fibrin networks may be easily damaged to form large pores when fluids are allowed to pass through the gels. The fragility of Osaka VI fibrin clots, further confirmed by permeation and compaction studies, may account for the massive bleeding observed in this patient. (Blood. 2000;96:3779-3785)

Adult↗
PubMed2000

Novel interactions between urokinase and its receptor.

Urokinase-type plasminogen activator (uPA) binds to its receptor (uPAR) with a K(d) of about 1 nm. The catalytic activity of the complex is apparent at uPA concentrations close to K(d). Other functions of the complex, such as signal transduction, are apparent at much higher concentrations (35-60 nm). In the present study, we show that uPA and recombinant soluble uPAR (suPAR), at concentrations that exceed the K(d) and the theoretical saturation levels (10-80 nm), establish novel interactions that lead to a further increase in the activity of the single-chain uPA (scuPA)/suPAR and two-chain uPA (tcuPA)/suPAR complexes. Experiments performed using dynamic light scattering, gel filtration, and electron microscopy techniques indicate that suPAR forms dimers and oligomers. The three techniques provide evidence that the addition of an equimolar concentration of scuPA leads to the dissociation of these dimers and oligomers. Biacore data show that suPAR dimers and oligomers bind scuPA with decreased affinity when compared with monomers. We postulate that uPAR is present in equilibrium between oligomer/dimer/monomer forms. The binding of uPA to suPAR dimers and oligomers occurs with lower affinity than the binding to monomer. These novel interactions regulate the activity of the resultant complexes and may be involved in uPA/uPAR mediated signal transduction.

Fibrinolysis↗
PubMed2000

The factor XIII V34L polymorphism accelerates thrombin activation of factor XIII and affects cross-linked fibrin structure.

Factor XIII on activation by thrombin cross-links fibrin. A common polymorphism Val to Leu at position 34 in the FXIII A subunit is under investigation as a risk determinant of thrombosis. Because Val34Leu is close to the thrombin cleavage site, the hypothesis that it would alter the function of FXIII was tested. Analysis of FXIII subunit proteolysis by thrombin using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-performance liquid chromatography showed that FXIII 34Leu was cleaved by thrombin more rapidly and by lower doses than 34Val. Mass spectrometry of isolated activation peptides confirmed the predicted single methyl group difference and demonstrated that the thrombin cleavage site is unaltered by Val34Leu. Kinetic analysis of activation peptide release demonstrated that the catalytic efficiency (k(cat)/K(m)) of thrombin was 0.5 for FXIII 34Leu and 0.2 (micromol/L)(-1) x sec(-1) for 34Val. Presence of fibrin increased the catalytic efficiency to 4.8 and 2.2 (micromol/L)(-1) x sec(-1), respectively. Although the 34Leu peptide was released at a similar rate as fibrinopeptide A, the 34Val peptide was released more slowly than fibrinopeptide A but more quickly than fibrinopeptide B generation. Cross-linking of gamma- and alpha-chains appeared earlier when fibrin was incubated with FXIII 34Leu than with 34Val. Fully activated 34Leu and 34Val FXIII showed similar cross-linking activity. Analysis of fibrin clots prepared using plasma from FXIII 34Leu subjects by turbidity and permeability measurements showed reduced fiber mass/length ratio and porosity compared to 34Val. The structural differences were confirmed by electron microscopy. These results demonstrate that Val34Leu accelerates activation of FXIII by thrombin and consequently affects the structure of the cross-linked fibrin clot.

Blood Coagulation↗