Incorporation of fibrin molecules containing fibrinopeptide A alters clot ultrastructure and decreases permeability

Previous studies have shown that a heterozygous mutation in the fibrinogen Aalpha chain gene, which results in an Aalpha R16C substitution, causes fibrinolytic resistance in the fibrin clot. This mutation prevents thrombin cleavage of fibrinopeptide A from mutant Aalpha R16C chains, but not from wild-type Aalpha chains. However, the mechanism underlying the fibrinolytic resistance is unclear. Therefore, this study investigated the biophysical properties of the mutant fibrin that contribute to fibrinolytic resistance. Fibrin clots made from the mutant fibrinogen incorporated molecules containing fibrinopeptide A into the polymerised clot, which resulted in a 'spiky' clot ultrastructure with barbed fibrin strands. The clots were less stiff than normal fibrin and were cross-linked slower by activated FXIII, but had an increased average fiber diameter, were more dense, had smaller pores and were less permeable. Protein sequencing showed that unclottable fibrinogen remaining in the supernatant consisted entirely of homodimeric Aalpha R16C fibrinogen, whereas both cleaved wild-type alpha chains and uncleaved Aalpha R16C chains were in the fibrin clot. Therefore, fibrinolytic resistance of the mutant clots is probably a result of altered clot ultrastructure caused by the incorporation of fibrin molecules containing fibrinopeptide A, resulting in larger diameter fibers and decreased permeability to fibrinolytic enzymes.     

Cell proliferation on fibrin: modulation by fibrinopeptide cleavage

Fibrin forms the cohesive network of hemostatic plugs and thrombi, and it also provides the temporary matrix for initial support of healing and revascularization. Because cell proliferation is needed for revascularization after vessel injury, we have characterized structural requirements of fibrin needed to support cell proliferation on fibrin in vitro. Proliferation of cultured human endothelial cells and fibroblasts was measured by 3H-thymidine incorporation on fibrin surfaces varying in structure. Fibrin prepared with thrombin and lacking both fibrinopeptides A and B (desAB fibrin) supported proliferation of both endothelial cells and fibroblasts. In contrast, fibrin prepared with reptilase, which cleaves only fibrinopeptide A, supported significantly less proliferation. Also, fibrin prepared by thrombin treatment of fibrinogen lacking residues beta 1-42 supported only a low level of proliferation. Therefore, fibrinopeptide B cleavage and exposure of beta 15-42 enhanced proliferation of cells on fibrin. Specific proteolytic inhibitors were used to eliminate the potential mitogenic effects of residual fibrin-bound thrombin. Additional controls showed that neither catalytically inactive thrombin nor addition of the thrombin receptor-activating peptide (SFLLRNPNDKYEPF [SFLL]) stimulated proliferation on desA fibrin. The results indicate that cell proliferation on fibrin is enhanced by fibrinopeptide B cleavage and exposure of the amino terminus of the fibrin beta chain. They also show that specific structural features of the temporary fibrin matrix formed at sites of injury may modulate the proliferative response of vascular cells.     

Homophenotypic Aalpha R16H fibrinogen (Kingsport): uniquely altered polymerization associated with slower fibrinopeptide A than fibrinopeptide B release.

We detail for the first time the uniquely altered fibrin polymerization of homophenotypic Aalpha R16H dysfibrinogen. By polymerase chain reaction amplification and DNA sequencing, our new proposita's genotype consisted of a G>A transition encoding for Aalpha R16H, and an 11 kb Aalpha gene deletion. High-performance liquid chromatography disclosed fibrinopeptide A release approximately six times slower than its fibrinopeptide B. Turbidimetric analyses revealed unimpaired fibrin repolymerization, and abnormal thrombin-induced polymerization (1-7 mumol/l fibrinogen, > 96% coagulable), consisting of a prolonged lag time, slow rate, and abnormal clot turbidity maxima, all varying with thrombin concentration. For example, at 0.2-3 U/ml, the resulting turbidity maxima ranged from lower to higher than normal control values. By scanning electron microscopy, clots formed by 0.3 and 3 thrombin U/ml displayed mean fibril diameters 42 and 254% of the respective control values (n = 400). Virtually no such differences from control values were demonstrable, however, when clots formed in the presence of high ionic strength (micro = 0.30) or of monoclonal antibeta(15-42)IgG. The latter also prolonged the thrombin clotting time approximately three-fold. Additionally, thrombin-induced clots displayed decreased elastic moduli, with G' values of clots induced by 0.3, 0.7 and 3 thrombin U/ml corresponding to 11, 34, and 45% of control values. The results are consistent with increased des-BB fibrin monomer generation preceding and during polymerization. This limited the inherent gelation delay, decreased the clot stiffness, and enabled a progressively coarser, rather than finer, network induced by increasing thrombin concentrations. We hypothesize that during normal polymerization these constitutive des-BB fibrin monomer properties attenuate their des-AA fibrin counterparts.     

Substitution of the gamma-chain Asn308 disturbs the D:D interface affecting fibrin polymerization, fibrinopeptide B release, and FXIIIa-catalyzed cross-linking

Crystallographic structures indicate that gamma-chain residue Asn308 participates in D:D interactions and indeed substitutions of gammaAsn308 with lysine or isoleucine have been identified in dysfibrinogens with impaired polymerization. To probe the role of Asn308 in polymerization, we synthesized 3 variant fibrinogens: gammaAsn308 changed to lysine (gammaN308K), isoleucine (gammaN308I), and alanine (gammaN308A). We measured thrombin-catalyzed polymerization by turbidity, fibrinopeptide release by high-performance liquid chromatography, and factor XIIIa-catalyzed cross-linking by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the absence of added calcium, polymerization was clearly impaired with all 3 variants. In contrast, at 0.1 mM calcium, only polymerization of gammaN308K remained markedly abnormal. The release of thrombin-catalyzed fibrinopeptide B (FpB) was delayed in the absence of calcium, whereas at 1 mM calcium FpB release was delayed only with gammaN308K. Factor XIIIa-catalyzed gamma-gamma dimer formation was delayed with fibrinogen (in absence of thrombin), whereas with fibrin (in presence of thrombin) gamma-gamma dimer formation of only gammaN308K was delayed. These data corroborate the recognized link between FpB release and polymerization. They show fibrin cross-link formation likely depends on the structure of protofibrils. Together, our results show substitution of Asn308 with a hydrophobic residue altered neither polymer formation nor polymer structure at physiologic calcium concentrations, whereas substitution with lysine altered both.     

Fibrinogen Seattle releases half the normal amount of fibrinopeptide B

Fibrinogen Seattle, a clinically silent, slow-clotting dysfibrinogen, releases 50% of the normal amount of fibrinopeptide B as assessed by amino acid analysis. The reduced dysfibrin exhibited equal quantities of chains with B beta- and beta-charge mobility on polyacrylamide gel electrophoresis in 2 M urea at low pH. By these same techniques, the release of fibrinopeptide A was normal. Clots formed by repolymerizing the thrombin and batroxobin dysfibrin monomers showed a maximal turbidity that was lower than normal. Fibrinogen Seattle was indistinguishable from normal fibrinogen by radial immunodiffusion and immunoelectrophoresis. Degradation by plasmin and transamination by factor XIIIa were normal. The characteristics of fibrinopeptide release by fibrinogen Seattle distinguish it from other reported dysfibrinogens.     

Plasma concentrations of fibrinopeptide A and fibrinopeptide B beta 15-42 in glomerulonephritis and the nephrotic syndrome

Plasma fibrinopeptide A (FPA) and fibrinopeptide B beta 15-42 concentrations were determined by radioimmunoassay in 46 patients with glomerulonephritis and the nephrotic syndrome. An increase in plasma FPA and B beta 15-42 levels was noted in these patients; this increase was marked in the nephrotic patients. There was a positive correlation in these patients between plasma FPA and B beta 15-42 levels. The B beta 15-42/FPA ratio was significantly higher in nonnephrotic patients compared with controls. Intravascular coagulation with subsequent fibrinolysis to regulate fibrin formation may occur in patients. A positive correlation was found between plasma B beta 15-42 level and serum urea nitrogen or serum creatinine concentration, suggesting that plasma B beta 15-42 level is influenced not only by plasmin action, but also by renal dysfunction.     

The rate of fibrinopeptide B release modulates the rate of clot formation: a study with an acquired inhibitor to fibrinopeptide B release

An asymptomatic 50-year-old male with a gamma globulin paraprotein was found to have prolonged prothrombin time, activated partial thromboplastin time, and thrombin time but a normal reptilase time. The prolonged clotting times were not the result of a factor deficiency because they were not corrected by the addition of normal plasma. Instead, this patient had an antibody that delayed thrombin-mediated fibrinopeptide B release thereby producing an apparent dysfibrinogenaemia. His isolated IgG prolonged the thrombin clotting time of both normal plasma and fibrinogen. Precincubation of his IgG with fibrinopeptide B, but not with fibrinopeptide A or thrombin, decreased its ability to prolong the thrombin clotting time. The patient's purified IgG but not control IgG delayed thrombin-mediated fibrinopeptide B release from fibrinogen without affecting the release of fibrinopeptide A. These studies define a novel, clinically silent dysfibrinogenaemia due to an antibody that delays thrombin-mediated fibrinopeptide B release from fibrinogen thereby markedly prolonging the clotting times.     

A descriptive investigation of the ultrastructure of fibrin networks in thrombo-embolic ischemic stroke

Stroke is one of the leading causes of death worldwide. Formation of a fibrin clot is controlled by a group of tightly regulated plasma proteases and cofactors and a change in the fibrin fiber formation causes an alteration in clot morphology. This plays an important role during thrombotic events. In the current study we investigated the ultrastructure of fibrin networks from fifteen ischemic stroke patients by using scanning electron microscopy. Clot morphology was investigated with and without the addition of human thrombin to the platelet rich plasma. Previously it was shown that, when studying the ultrastructure of fibrin networks, the addition of thrombin is necessary to form an expansive, fully coagulated layer of fibers. Results from the addition of thrombin to the plasma showed thick, matted fibrin fibers and a net covering some of the major fibers in stroke patients. Typical control morphology with major thick fibers and minor thin fibers could be seen in some areas in the stroke patients. In stroke patients, without the addition of thrombin, a matted fibrin network still formed, indicating that the factors responsible for the abnormal fibrin morphology are present in the circulating plasma and is the cause of the observed matted, layered morphology. This is not present in healthy individuals. From the results obtained we suggest that this changed morphology might be useful in a screening regime to identify the possibility of a stroke or even to follow the progress of stroke patients after treatment.     

New strategies in the determination of fibrin and fibrin(ogen) derivatives by monoclonal antibodies

Summary Until recently only tests with a limited specificity were available for the assessment of the products of activated coagulation and/or fibrinolysis. Those assays were based on polyclonal antibodies, which crossreact with fibrinogen, and as a consequence they were performed on serum samples i.e. after removal of fibrinogen by clotting. Serum preparation, however, is a notorious source of artefactually high or low levels of fibrin(ogen) degradation products, and is not suitable for the determination of coagulation products. Recently, highly specific monoclonal antibodies (MoAb's) have been developed, the majority of which do not crossreact with fibrinogen. This has enabled new strategies to be developed, i.e. assays using these MoAb's on plasma samples. Furthermore, the new assays can discriminate between (individual) fibrin and fibrinogen degradation products, and coagulation products can be assessed in the same plasma samples.     

脱氧雪腐镰刀菌烯醇对培养软骨细胞影响的超微结构观察

采用体外软骨细胞培养方法，观察脱氧雪腐镰刀菌烯醇（ＤＯＮ）对幼兔关节软骨细胞超微结构的作用，结果表明ＤＯＮ对软骨细胞膜系统和细胞器具有明显的损伤作用，特别是对培养早期的软骨细胞具致命损伤。ＤＯＮ与大骨节病关系待进一步探讨。     

The comparative ultrastructure of fibrin induced by thrombin and by staphylocoagulase.

Fibrin induced by the action of thrombin and by staphylocoagulase was studied by transmission electron microscopy. Periodic striations were consistently observed in the negatively stained preparations of both fibrins. When 4200 major periods in the thrombin fibrin system were measured the mean length was 228 A. For 3666 major periods in the coagulase fibrin system the mean length was 223 A. While the T test analysis of these values gave a value of 10, it is noteworthy that the differences are well within the scatter of periodicity reported in the literature for thrombin-induced fibrin. Gross inspection of the preparations indicated that the coagulase-induced fibrin had a knottier appearance and was accompanied by a greater amount of background debris than the thrombin-induced fibrin.     

Studies on specific interaction of beta-2-glycoprotein I with HBsAg

AIM: To observe the binding activity of beta-2-glycoprotein I (β2GPI) to hepatitis B surface antigen (HBsAg) and the possible roles of β2GPI in hepatitis B virus (HBV) infection.METHODS: The rationale of ELISA methods and ELISAbased research method and ligand-blotting technique were used to detect the specific interaction of β2GPI with HBsAg.RESULTS: With the increase of rHBsAg, the binding of β2GPI to rHBsAg elevated, and these changes had statistic significance. When we added non- biotinlyated β2GPI, the OD value significantly decreased though they still were positively relevant to rHBsAg, suggesting non- biotinlyated β2GPI competed with biotinlyated β2GPI to saturate the binding sites on rHBsAg. Meanwhile BSA was used as negative control to substitute for rHBsAg coating the plates.The results indicated no interaction between β2GPI and BSA,suggesting the affinity of β2GPI to rHBsAg was specific. The ligand blotling indicated that β2GPI might bind to rHBsAg no matter whether it was under reduced condition or not.CONCLUSION: The binding of β2GPI to HBsAg suggests that β2GPI may be a carrier of HBV and that β2GPI may play important roles in HBV infection.     

Alpha-Chain cross-linking in fibrin(ogen) Marburg

The fibrinogen structural variant, Marburg (A alpha 1-460B beta gamma)2, is comprised of normal B beta and gamma chains but contains severely truncated A alpha chains that are missing approximately one half of their factor XIIIa cross-linking domain. Immunochemical studies of fibrin(ogen) Marburg were conducted to characterize the degree to which deletion of a defined A alpha-chain segment, A alpha 461-610, can affect the process of fibrin stabilization, ie, the factor XIIIa- mediated covalent interaction that occurs between alpha chains of neighboring fibrin molecules and between alpha chains and alpha 2 antiplasmin (alpha 2PI). The ability of Marburg (and control) alpha chains to serve as a substrate for factor XIIIa and undergo cross- linking was examined in an in vitro plasma clotting system. The capacity for alpha-chain cross-linking was evaluated both as the covalent incorporation of the small synthetic peptide, NQEQVSPLTLLK (which represents the first 12 amino acids of alpha 2PI and includes the factor XIIIa-sensitive glutamine residue responsible for the cross- linking of alpha 2PI to fibrin), and as the appearance of native (ie, natural), high-molecular-weight, cross-linked alpha-chain species. Antibodies specific for the (A)alpha and gamma/gamma-gamma chains of fibrin(ogen) and for the peptide and its parent protein, alpha 2PI (68 kD), were used as immunoblotting probes to visualize the various cross- linked products formed during in vitro clotting. Recalcification of Marburg plasma in the presence of increasing concentrations of peptide resulted in the formation of peptide-decorated Marburg alpha-chain monomers. Their size at the highest peptide concentration examined indicated the incorporation of a maximum of 3 to 4 mol of peptide per mole of alpha-chain. In the absence of alpha 2PI 1-12 peptide, the alpha chains of Marburg fibrin cross-linked to form oligomers and polymers, as well as heterodimers that included alpha 2PI. Both the peptide-decorated monomers and the native cross-linked alpha-chain species of Marburg fibrin were smaller than their control plasma counterparts, consistent with the truncated structure of the parent Marburg A alpha chain. Collectively, the findings indicate that, although deletion of the A alpha chain region no. 461-610 in fibrinogen Marburg prevents formation of an extensive alpha polymer network (presumably due to the absence of critical COOH-terminal lysine residues), it does not interfere with initial events in the fibrin stabilization process, namely, factor XIII binding and the ability of alpha chains to undergo limited cross-linking to one another and to alpha 2PI.     

Studies on the basis for the properties of fibrin produced from fibrinogen-containing gamma' chains

Human fibrinogen 1 is homodimeric with respect to its gamma chains (gammaA-gammaA'), whereas fibrinogen 2 molecules each contain one gammaA (gammaA1-411V) and one gamma' chain, which differ by containing a unique C-terminal sequence from gamma'408 to 427L that binds thrombin and factor XIII. We investigated the structural and functional features of these fibrins and made several observations. First, thrombin-treated fibrinogen 2 produced finer, more branched clot networks than did fibrin 1. These known differences in network structure were attributable to delayed release of fibrinopeptide (FP) A from fibrinogen 2 by thrombin, which in turn was likely caused by allosteric changes at the thrombin catalytic site induced by thrombin exosite 2 binding to the gamma' chains. Second, cross-linking of fibrin gamma chains was virtually the same for both types of fibrin. Third, the acceleratory effect of fibrin on thrombin-mediated XIII activation was more prominent with fibrin 1 than with fibrin 2, and this was also attributable to allosteric changes at the catalytic site induced by thrombin binding to gamma' chains. Fourth, fibrinolysis of fibrin 2 was delayed compared with fibrin 1. Altogether, differences between the structure and function of fibrins 1 and 2 are attributable to the effects of thrombin binding to gamma' chains.     

The changed ultrastructure of fibrin networks during use of oral contraception and hormone replacement

Contraceptives and hormone replacement have been extensively used since the late 1950s. However, adverse effects are common and include an increased risk of cardiovascular diseases, including thrombo-embolic diseases. Previous research has shown that ultrastructure of fibrin networks may provide great insight regarding the thrombotic potential of patients. The current study investigates the scanning electron microscopy (SEM) ultrastructure of fibrin networks of individuals using oral contraceptive therapy as well as individuals using hormone replacement. We compare micrographs of these two groups with micrographs of young, healthy individuals not using oral contraception. Platelet rich plasma and thrombin was used to prepare the fibrin clots. Here we show that during contraceptive and hormone replacement use, a netted fibrin layer forms. We suggest that oestradiol use causes fibrin network changes and these changes can be seen using SEM technology. These changes may provide further evidence regarding the increased occurrence of thrombotic events during contraceptive and hormone replacement therapy.     

Serum crosslinked fibrin (XDP) and fibrinogen/fibrin degradation products (FDP) in disorders associated with activation of the coagulation or fibrinolytic systems

Soluble crosslinked fibrin derivatives (XDP) in serum were determined by enzyme immunoassay utilizing monoclonal antibodies and compared with serum fibrinogen/fibrin degradation products (FDP) assayed by conventional techniques. In healthy subjects and patients with miscellaneous disorders not usually associated with activation of the haemostasis mechanism, mean XDP levels were 45 and 70 ng/ml respectively. However, elevated levels of XDP occurred in conditions commonly associated with intravascular and possibly extravascular activation of the coagulation system. Markedly raised mean XDP values (677-6900 ng/ml) occurred in treated pulmonary embolism, disseminated neoplasia, severe inflammatory disorders and complicated postoperative states, and lesser but significant elevation (mean 150-400 ng/ml) in treated venous thrombosis, uneventful postsurgical states, localized neoplasia, liver disease and symptomatic arterial disease. Levels during initial streptokinase therapy (mean 24 000 ng/ml) fell tenfold as treatment was continued. The degree of XDP elevation over normal values was significantly higher than that of FDP in conditions with a propensity for venous thrombosis (post-operative states, disseminated neoplasia and inflammatory diseases) than in liver disease, localized neoplasia or patients receiving heparin therapy for venous thromboembolism.     

Hydration of fibrinogen, fibrin, and fibrin degradation product (FDP) as estimated by nuclear magnetic resonance (NMR) spectroscopy

The relaxation times (T1 and T2) of water proton in nuclear magnetic resonance (NMR) were measured with solutions containing bovine fibrinogen (Fbg), fibrin degradation products (FDP) and with fibrin-gel (Gel), at varying protein concentrations (0.7-70 mg/ml). Both T1 and T2 declined exponentially with increasing protein concentration. At a protein concentration of 35 mg/ml, the T1 of Fbg, Gel and FDP were 2.32, 2.12 and 2.82 s and the T2 values were 0.35, 0.17 and 0.70, respectively. The relaxation times for the control samples (0.2 M borate buffer) were 3.41 (T1) and 2.28 (T2). When the relaxation rates (the inverse of T1 and T2), R1 and R2 were plotted against the protein concentration, there were positive linear correlations between them. Using the slopes of the plots, the hydration value of each protein was calculated. The hydration value (g of H2O/g of protein) was 0.24 for Fbg, 0.34 for Gel and 0.14 for FDP.