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PubMed1988

Fibrin is a determinant of neutrophil sequestration in the lung.

We investigated the role of fibrin in the sequestration of neutrophils in lungs challenged with microembolism. Lungs of chronically prepared awake sheep were imaged after infusion of 111In-neutrophils and 131I-fibrinogen. Thrombin (80 units/kg) was administered to induce fibrin sequestration in the lung. One group received tranexamic acid (4 mg/kg i.v.) to inhibit fibrinolysis, and the control group received a saline infusion. Thrombin infusion increased both 131I-fibrinogen and 111In-neutrophils in the lung, but the increases were greater and more prolonged in the fibrinolysis-inhibited group. We examined the adherence of isolated neutrophils to fibrin matrix to investigate how neutrophil-fibrin interactions could mediate neutrophil sequestration. Unstimulated neutrophils showed a 37.5 +/- 3.1% adherence to fibrin in contrast to a 3.9 +/- 0.4% neutrophil adherence to endothelium and a 6.5 +/- 0.5% adherence to agarose. Neutrophil adherence to fibrin increased to 81.7 +/- 6.2% with activation by phorbol myristate acetate (10(-8) M) and was inhibited by a monoclonal antibody directed against the beta-chain of the CD18 leukocyte adhesion glycoprotein. The findings indicate that retention of pulmonary fibrin microthrombi is associated with increased lung uptake of neutrophils. Fibrin serves as a substrate for neutrophil adherence, and this adherence is mediated by expression of the CD18 glycoprotein complex on neutrophils. Fibrin sequestration in the lung may contribute to lung vascular injury by inducing pulmonary neutrophil uptake.

Animals↗
PubMed1993

Myocardial fibrin deposition in experimental viral myocarditis that progresses to dilated cardiomyopathy.

Myocardial fibrosis is a characteristic late feature in cases of viral myocarditis that progress to dilated cardiomyopathy. However, the pathogenesis of the myocardial fibrosis in such cases is unknown. Prior studies have shown that in healing wounds and tumor stroma generation, interstitial fibrin deposition precedes the development of fibrosis. Therefore, interstitial fibrin deposition in the myocardium was investigated in a murine model of myocarditis in which dilated cardiomyopathy develops. Inbred male C3H/He mice inoculated with coxsackievirus B3 were killed 0, 3, 7, 14, 21, 30, and 60 days after infection. Paraffin sections of hearts were stained with hematoxylin-eosin, Masson's trichrome stain, and antibodies to fibrinogen/fibrin by use of an immunoperoxidase technique. Pretreatment of all mice with anticoagulants and antifibrinolytics 5 minutes before death was used to prevent artifactual fibrin deposition and fibrinolysis during tissue manipulation. Tissue fixation in formalin supplemented with acetic acid served to extract non-cross-linked fibrin, fibrinogen, and fibrinogen and fibrin degradation products, thus ensuring that clotted and cross-linked fibrin was the major immunoreactant. Myocardial fibrin deposition and fibrosis were each quantitated by computer-assisted image analysis. Myocardial fibrin deposition first appeared on day 3, was maximal on day 14, and disappeared by day 30. Conversely, myocardial fibrosis was not detectable until day 14 and was maximal at day 60. Thus, as in healing wounds and developing tumor stroma, fibrin deposition preceded fibrosis in this murine model of myocarditis that progresses to dilated cardiomyopathy.

Animals↗
PubMed1995

Surfactant incorporation markedly alters mechanical properties of a fibrin clot.

Intra-alveolar clot formation is a common finding in acute and chronic inflammatory lung diseases. Incorporation of lipophilic surfactant components into a growing fibrin clot has recently been reported (Am. J. Respir. Cell Mol. Biol. 1993; 9:213-220). In the present study, we investigated the influence of such surfactant incorporation on the elastic properties and water permeability of the fibrin polymer. Thrombelastography and compaction experiments were employed for assessment of the elastic properties, and the permeability characteristics of the clot material were addressed in fibrin-packed columns. Two calf lung surfactant extracts (CLSE and Alveofact), Curosurf, and a synthetic phospholipid mixture (dipalmitoylphosphatidylcholine, phosphatidylglycerol, and palmitic acid at a ratio of 68.5:22.5:9 [wt/wt]) were used. The presence of surfactant did not affect the cleavage of fibrinopeptide A upon incubation of fibrinogen with thrombin (enzyme-linked immunosorbent assay technique). Similarly, kinetics and extent of factor XIII-induced covalent crosslinkage of the fibrin network remained unchanged in the presence of surfactant (sodium dodecyl sulfate polyacrylamide gel electrophoresis and D-Dimer quantification upon subsequent clot lysis). All surfactants, however, dose-dependently decreased the elastic modulus of the arising fibrin polymer. The maximal amplitude in thrombelastography was reduced, and the recovery of fluid after centrifugation of the fibrin clot increased. Fibrin clots embedding natural surfactant material displayed reduced permeability for saline as compared with control fibrin polymers. Subsequent washout of lipids from these clots with Triton X-100 resulted in increased hydraulic conductivity. This was accompanied by an increase in pore size, suggesting altered architecture of the fibrin matrix generated in the presence of surfactant.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

Significance of cross-linking of alpha 2-plasmin inhibitor to fibrin in inhibition of fibrinolysis and in hemostasis.

When blood is clotted, alpha(2)-plasmin inhibitor (alpha(2)PI) is cross-linked to fibrin by activated fibrin-stabilizing factor (activated coagulation Factor XIII, plasma transglutaminase). The amount of cross-linked alpha(2)-PI is proportional to the amount of alpha(2)PI present at the time of clotting. Plasma from a patient with congenital deficiency of alpha(2)PI was supplemented with various amounts of purified alpha(2)PI. Clots were prepared from these plasmas and were suspended in plasma containing a normal concentration of alpha(2)PI, and spontaneous clot lysis was observed. When the clot was formed in the presence of calcium ions and thereby allowing cross-linking to occur, the rate and extent of fibrinolysis were found to be inversely proportional to the concentrations of alpha(2)PI present in the clot at the time of clotting. When the clot was formed in the absence of calcium ions so that no cross-linking occurred, the clot underwent fibrinolysis at similar rates, regardless of the concentrations of alpha(2)PI in the clot. When the clot formed in the presence of calcium ions was squeezed and washed to remove unbound proteins before being suspended in plasma, the extent of fibrinolysis was also inversely proportional to the amount of alpha(2)PI cross-linked to fibrin. Similar results were obtained when the clot was suspended in buffered saline instead of plasma. These observations suggest that spontaneous fibrinolysis is mainly carried out by plasminogen/plasminogen activator bound to fibrin, and this fibrinolysis caused by fibrin-associated activation of plasminogen was mainly inhibited by alpha(2)PI cross-linked to fibrin. To further support this concept, alpha(2)PI treated with activated fibrin-stabilizing factor and that had lost most of its cross-linking capacity was used in similar experiments. This modified alpha(2)PI had the same inhibitory activity on plasmin as the native inhibitor, but gave significantly less inhibition of fibrinolysis in every experiment, particularly when the clot was compacted by platelet-mediated clot retraction or by squeezing. Thus, it was concluded that alpha(2)PI cross-linked to fibrin plays a significant role in inhibition of physiologically occurring fibrinolysis. It is further suggested that the absence of cross-linked alpha(2)PI contributes to accelerated fibrinolysis and hemorrhagic tendency in patients with congenital deficiency of fibrin-stabilizing factor.

Calcium↗
PubMed1984

Degradation of fibrin and elastin by intact human alveolar macrophages in vitro. Characterization of a plasminogen activator and its role in matrix degradation.

Fibrin deposition is prominent in the histopathology of a number of inflammatory lung diseases. Plasmin, activated locally in the lung, can degrade not only this fibrin but potentially structural proteins important to normal lung architecture. Because alveolar macrophages are prominent in inflammatory processes of the lung, we examined the plasminogen activator (PA) activity of human alveolar macrophages. Intact alveolar macrophages from each of 10 healthy subjects expressed PA activity. There was no difference in activity between smoking and nonsmoking individuals. The activator activity was largely cell-associated, but under certain culture conditions, macrophages released a soluble activator into the culture medium. The membrane-bound activator had an apparent molecular mass of 52-55 kD in nonreduced sodium dodecyl sulfate (SDS) gels, and monospecific antibody to urokinase neutralized the enzyme activity. Immunoprecipitation of [35S]methionine-labeled cells showed that human alveolar macrophages actually synthesize the PA in vitro. SDS-gel analysis of the immunoprecipitated material revealed the predominant species of PA to be structurally similar to reduced, active urokinase. We also examined the role of PA in the degradation of both insoluble fibrin and elastin matrices by live macrophages. Cells degraded an insoluble fibrin matrix in the presence of plasminogen whether or not the macrophages contacted the fibrin as long as proteinase inhibitors were not in the culture medium. In the presence of serum proteinase inhibitors, macrophages still degraded a fibrin matrix, but only if they were in contact with the fibrin. Live macrophages also degraded insoluble elastin only when in contact with the elastin but could do so even in the presence of serum proteinase inhibitors. In matrices containing a mixture of fibrin and elastin, cells did not degrade elastin unless plasminogen was added to the medium. These results indicate that normal alveolar macrophages synthesize and express, probably at the cell surface, a PA. The PA is physically and immunochemically similar to urokinase but is membrane bound. The PA is critical to the degradation of fibrin matrices by normal alveolar macrophages. Under tissue conditions where elastin is embedded within other structural proteins, the activator may be rate-limiting in elastin degradation as well. The findings also suggest that live macrophage proteolytic activity is relatively insensitive to the presence of serum proteinase inhibitors, suggesting a mechanism for proteolytic lung injury even in the presence of proteinase-proteinase inhibitor balance in the soluble phase.

Cell Membrane↗
PubMed1986

Interaction of histidine-rich glycoprotein with fibrinogen and fibrin.

Histidine-rich glycoprotein (HRGP) is a human plasma and platelet protein of apparently diverse biological functions. In this study a new interaction for HRGP is described. HRGP specifically interacts with fibrinogen as demonstrated by two independent systems. Using an enzyme-linked immunosorbent assay it was demonstrated that HRGP bound to adsorbed fibrinogen in a concentration-dependent and saturable manner, with an apparent dissociation constant (Kd) of 6.7 nM. The binding was specific, reversible, and not mediated by a conformationally altered adsorbed fibrinogen molecule. The interaction was divalent cation-dependent and ionic in nature. The HRGP-fibrinogen interaction was also demonstrated using rocket immunoelectrophoresis. The HRGP-fibrinogen interaction had an effect on the kinetics of conversion of fibrinogen to fibrin as demonstrated by a prolongation of the thrombin time. HRGP also became incorporated into fibrin clots in a concentration-dependent and saturable manner, with an apparent Kd of 0.25 microM. The incorporation of HRGP into fibrin clots occurred in a plasma milieu as demonstrated by the direct incorporation of radiolabeled HRGP into plasma clots and by a significant decrease in serum HRGP levels as compared with plasma levels. HRGP prolonged the lag time phase of fibrin gel formation, and decreased the rate of turbidity rise, as well as the final absorbance of fibrin gels. Since the extent of fibrin polymerization was not influenced by the presence of HRGP, these data suggest that fibrin is distributed over more, but thinner, fibrils in the presence of HRGP. In addition to its potential effect on fibrin polymerization, the HRGP-fibrin interaction may play a role in the cell-cell interactions of platelets and macrophages.

Blood Proteins↗
PubMed1996

Fibrin deposition in tissues from endotoxin-treated mice correlates with decreases in the expression of urokinase-type but not tissue-type plasminogen activator.

The primary hypothesis of this report is that the formation and subsequent removal of fibrin in specific tissues during pathologic processes reflects temporal changes in the local expression of key procoagulant and fibrinolytic genes. To begin to test this hypothesis, we have used quantitative PCR assays and in situ hybridization analysis to examine the effects of endotoxin on the expression of specific genes in murine tissues, and to relate these changes to fibrin deposition/dissolution using immunohistochemical approaches. Endotoxin caused large increases in plasminogen activator inhibitor-1 mRNA and modest increases in tissue factor mRNA in most tissues examined. However, fibrin was only detected in the kidneys and adrenals of endotoxin-treated mice, and it was transient. Unexpectedly, changes in urokinase-type plasminogen activator mRNA but not tissue-type plasminogen activator mRNA correlated with fibrin deposition/dissolution in these tissues. Pretreatment of mice with the fibrinolytic inhibitor epsilon-aminocaproic acid before endotoxin increased both the number of fibrin-positive tissues and the duration of fibrin deposition in the kidneys and adrenals. These results suggest that the absence of fibrin in some tissues reflects ongoing local fibrinolysis, and that increases in plasminogen activator inhibitory and tissue fac- tor gene expression and decreases in urokinase-type plasminogen activator expression are necessary for tissue-specific fibrin deposition. Changes in tissue-type plasminogen activator gene expression do not appear to be essential for fibrin deposition/dissolution in this murine model of sepsis.

Adrenal Glands↗
PubMed1988

Fibrin glue: a review of its preparation, efficacy, and adverse effects as a topical hemostat.

Fibrin glue is composed of two separate solutions of fibrinogen and thrombin. When mixed together, these agents mimic the last stages of the clotting cascade to form a fibrin clot. Fibrin glue is available in Europe but is not commercially available in the U.S.; therefore, investigators have extemporaneously compounded their own fibrin glue. Fibrinogen can be obtained from pooled, single-donor, and autologous blood donors and is usually isolated by the process of cryoprecipitation. The thrombin component is generally derived from commercial bovine sources. Some investigators have added calcium chloride and/or antifibrinolytics (i.e., aminocaproic acid, aprotinin) to their preparations. Fibrin glue can be applied using a double-barrel syringe or by spray application. Although fibrin glue has been used in a variety of surgical procedures, it has been especially useful in heparinized patients undergoing cardiovascular procedures requiring extracorporeal circulation, as it does not require an intact hemostatic system to be effective. Fibrin glue also has been evaluated in presealing woven or knitted Dacron vascular grafts. The major drawback to its use is the risk of transmitted serological disease from pooled and single-donor blood donors. The safest preparations use the patient's own blood to prepare fibrin glue. Overall, fibrin glue is a useful adjunct to other methods to control bleeding in selected surgical patients.

Administration, Topical↗
PubMed2000

Thromboelastograph assay for measuring the mechanical strength of fibrin sealant clots.

In order to provide sustained hemostasis or tissue sealing, fibrin sealants must generate adhesive clots with mechanical properties capable of resisting forces, such as shear, that might break or tear the clot. Commercial preparations of fibrin sealants should generate clots of adequate and consistent mechanical strength. The mechanical strength of fibrin sealants is often measured as bonding strength in in vivo or ex vivo animal wound models. These tests can be useful predictors of clinical efficacy. However, these, as well as many in vitro tensile strength tests for fibrin sealant, tend to be laboratory specific and require extensive reagent preparation time and analyst training. The thromboelastograph has historically been used to screen for plasma protein and platelet disorders that lead to defective clot formation. The authors have developed a simple in vitro test, using a standard thromboelastograph that can provide reliable, reproducible information on the rheology of clots generated by fibrin sealant preparations. Using this method, the shear strength of fibrin sealant clots was measured and shown to correlate with the fibrinogen, but not the thrombin, concentration in the sealant. Shear strength was also shown to correlate with the sealant concentration of the fibrin cross-linking proenzyme, factor XIII. Sealants containing lysine, which can act as an alternate substrate for factor XIII enzyme and prevent efficient fibrin chain cross-linking, were shown by this method to generate clots of substantially reduced shear strength. The method distinguished between thrombin-catalyzed clot formation and other fibrinogen clotting mechanisms as evidenced by the significantly lower shear strength associated with batroxobin-generated fibrin clots.

Batroxobin↗
PubMed1997

Microdialysis assessment of fibrin glue containing sodium alginate for local delivery of doxorubicin in tumor-bearing rats.

This study was designed to assess a local drug delivery system of an anticancer agent, doxorubicin (DOX), using fibrin glue (Beriplast P) as a drug carrier. In vitro release of DOX from the fibrin glue was examined by a dialysis method in the presence and absence of sodium alginate. The in vitro mean dissolution times of DOX with solution, fibrin glue, and fibrin glue containing sodium alginate were 3.7 h, 8.7 h, and 81 h, respectively, indicating a sustained release of DOX from fibrin glue, especially in the presence of sodium alginate. Fibrin glue containing 6 mg of DOX and 2.5 mg of sodium alginate was applied on the surface of an AH60C tumor at the back of rats. DOX concentrations in the tumor extracellular fluid were monitored by a microdialysis method. Local application of DOX using fibrin glue containing sodium alginate to the tumor resulted in extremely higher concentrations in the tumor extracellular fluid than those in plasma (AUC ratio > 800), indicating an advantage of the site-specific delivery of DOX using fibrin glue with sodium alginate. The tumor volumes were inversely correlated with tumor extracellular fluid-to-plasma AUC ratios (r = 0.882), suggesting the relevance of tumor size in the drug efflux from tumor to blood. In conclusion, the site-specific delivery of DOX using fibrin glue with sodium alginate to the tumor was demonstrated to be advantageous with regard to the extent and duration of drug concentrations in the tumor extracellular fluid, as assessed by a microdialysis technique.

Alginates↗
PubMed1995

Fibrin sealant matrix supports outgrowth of peripheral sensory axons.

It has been suggested that fibrin-based matrix has an important role during the early stage of nerve regeneration. A fibrin sealant matrix, which was made by combining diluted human fibrinogen and thrombin, was used as a substrate for in vitro elongation of neurites and in vivo regeneration of axons. In the in vitro experiment, dissociated embryonic chick sensory neurons were cultured on dishes coated with fibrin sealant matrix and compared with the solution of thrombin/calcium chloride, or with poly-D-lysine (PDLctr). After 16 hours, cultures were stained immunohistochemically with a monoclonal antineurofilament antibody. The neurons survived well, and an abundant network of neurites, qualitatively similar to that on PDLctr, developed on the fibrin sealant matrix. The percentage of neurons that had outsprout at 16 hours was the same both in the fibrin sealant matrix and PDLctr groups. By contrast, all the neurons plated on the dishes treated with the solution of thrombin/calcium chloride were dead after 16 hours. Immunohistochemical staining of fibrinogen also showed an even distribution of fibrin matrix over the culture dishes. For the in vivo experiments, 48 rat sciatic nerves were cut and reconnected with two epineurial stitches. Fibrin sealant matrix or phosphate buffer solution was applied to the transsected and repaired region. Pinch reflex test showed that the regeneration of the leading sensory fibre was significantly faster in the fibrin sealant matrix group than in the control group at 3 and 4 days. These results indicate that fibrin sealant matrix accelerates regeneration of axons in vivo during the early phase, and also supports elongation of neurites in vitro.

Animals↗
PubMed2005

Fibrin deimination in synovial tissue is not specific for rheumatoid arthritis but commonly occurs during synovitides.

Autoantibodies to deiminated (citrullinated) proteins are the most specific serological markers of rheumatoid arthritis (RA). Deimination is critical in generating the peptidic epitopes they recognize. In the synovial tissue (ST), deiminated forms of the alpha- and beta-chains of fibrin are their major autoantigenic targets (anti-human fibrin(ogen) autoantibodies (AhFibA)). We investigated whether the presence of deiminated fibrin in the ST was specific for RA, because this could explain why AhFibA are RA specific. In 13 patients with RA and 19 patients with various other rheumatological disorders, knee ST biopsies were collected in macroscopically inflamed areas identified under arthroscopy. Synovitis was histopathologically confirmed in all of the biopsies. By immunoblotting, using antisera to fibrin, Abs to citrullyl residues, and AhFibA purified from RA sera, deiminated fibrin was evidenced in ST extracts from all of the patients. Moreover, variations in the degree of fibrin deimination were observed that were not related to the disease. Immunohistochemical analysis, using Abs to citrullyl residues and an antiserum to fibrin on adjacent serial sections of ST, confirmed the results because deiminated proteins colocalized with fibrin in RA as well as in control patients. Therefore, fibrin deimination in the ST is a general phenomenon associated to any synovitis, which does not necessarily induce a B autoimmune response with production of AhFibA.

Adult↗
PubMed1999

Cerebral microvascular obstruction by fibrin is associated with upregulation of PAI-1 acutely after onset of focal embolic ischemia in rats.

The mechanisms underlying cerebral microvascular perfusion deficit resulting from occlusion of the middle cerebral artery (MCA) require elucidation. We, therefore, tested the hypothesis that intravascular fibrin deposition in situ directly obstructs cerebral microcirculation and that local changes in type 1 plasminogen activator inhibitor (PAI-1) gene expression contribute to intravascular fibrin deposition after embolic MCA occlusion. Using laser-scanning confocal microscopy (LSCM) in combination with immunofluorescent staining, we simultaneously measured in three dimensions the distribution of microvascular plasma perfusion deficit and fibrin(ogen) immunoreactivity in a rat model of focal cerebral embolic ischemia (n = 12). In addition, using in situ hybridization and immunostaining, we analyzed expression of PAI-1 in ischemic brain (n = 13). A significant (p < 0.05) reduction of cerebral microvascular plasma perfusion accompanied a significant (p < 0.05) increase of intravascular and extravascular fibrin deposition in the ischemic lesion. Microvascular plasma perfusion deficit and fibrin deposition expanded concomitantly from the subcortex to the cortex during 1 and 4 hr of embolic MCA occlusion. Three-dimensional analysis revealed that intravascular fibrin deposition directly blocks microvascular plasma perfusion. Vascular plugs contained erythrocytes, polymorphonuclear leukocytes, and platelets enmeshed in fibrin. In situ hybridization demonstrated induction of PAI-1 mRNA in vascular endothelial cells in the ischemic region at 1 hr of ischemia. PAI-1 mRNA significantly increased at 4 hr of ischemia. Immunohistochemical staining showed the same pattern of increased PAI-1 antigen in the endothelial cells. These data demonstrate, for the first time, that progressive intravascular fibrin deposition directly blocks cerebral microvascular plasma perfusion in the ischemic region during acute focal cerebral embolic ischemia, and upregulation of the PAI-1 gene in the ischemic lesion may foster fibrin deposition through suppression of fibrinolysis.

Animals↗
PubMed2000

Characterization of the interaction of recombinant apolipoprotein(a) with modified fibrinogen surfaces and fibrin clots.

Elevated levels of lipoprotein(a) [Lp(a)] in plasma are a significant risk factor for the development of atherosclerotic disease, a property which may arise from the ability of this lipoprotein to inhibit fibrinolysis. In the present study we have quantitated the binding of recombinant forms of apolipoprotein(a) [17K and 12K r-apo(a); containing 8 and 3 copies, respectively, of the major repeat kringle sequence (kringle IV type 2)] to modified fibrinogen surfaces. Iodinated 17K and 12K r-apo(a) bound to immobilized thrombin-modified fibrinogen (i.e., fibrin) surfaces with similar affinities (Kd approximately 1.2-1.6 microM). The total concentration of binding sites (Bmax) present on the fibrin surface was approximately 4-fold greater for the 12K than for the 17K (Bmax values of 0.81 +/- 0.09 nM, and 0.20 +/- 0.01 nM respectively), suggesting that the total binding capacity on fibrin surfaces is reduced for larger apolipoprotein(a) (apo(a)) species. Interestingly, binding of apo(a) to intact fibrin was not detected as assessed by measurement of intrinsic fluorescence of free apo(a) present in the supernatants of sedimented fibrin clots. In other experiments, the total concentration apo(a) binding sites available on plasmin-modified fibrinogen surfaces was shown to be 13.5-fold higher than the number of sites available on unmodified fibrin surfaces (Bmax values of 2.7 +/- 0.3 nM and 0.20 +/- 0.01 nM respectively) while the affinity of apo(a) for these surfaces was similar. The increase in Bmax was correlated with plasmin-mediated exposure of C-terminal lysines since treatment of plasmin-modified fibrinogen surfaces with carboxypeptidase B produced a significant decrease in total binding signal as detected by ELISA (enzyme linked immunosorbent assay). Taken together, these data suggest that apo(a) binds to fibrin with poor affinity (low microM) and that the total concentration of apo(a) binding sites available on modified-fibrinogen surfaces is affected by both apo(a) isoform size and by the increased availability of C-terminal lysines on plasmin-degraded fibrinogen surfaces. However, the low affinity of apo(a) for fibrin indicates that Lp(a) may inhibit fibrinolysis through a mechanism distinct from binding to fibrin, such as binding to plasminogen.

Apolipoproteins A↗
PubMed2002

Stability of fibrin sealant in cerebrospinal fluid: an in vitro study.

OBJECTIVE: The in vitro stability of fibrin sealant in cerebrospinal fluid (CSF) was investigated to verify the efficacy of intracranial application of fibrin sealant. METHODS: Human CSF was collected from 11 patients. Fibrin glue spheres (diameter, 5 mm) were incubated in CSF specimens at 37 degrees C. At 2, 4, 8, 24, and 48 hours, the diameter of the spheres was measured and the ultrastructure was evaluated by transmission electron microscopy. A control group consisted of sealant spheres in physiological saline (n = 2). RESULTS: In all CSF samples, the fibrin sealant did not degrade with time. The size, consistency, color, and shape of the sealant remained unchanged, even 48 hours after placement in the CSF. Transmission electron microscopic analysis of the fibrin sealant revealed an amorphous, fibrinous meshwork. No morphological differences existed between fibrin sealant complex placed in the CSF for different time periods and sealant placed in physiological saline. CONCLUSION: Within the limitations of this in vitro study, human CSF has no adverse effects on fibrin sealant in terms of alteration of structure and morphology. Fibrin sealant is stable in a CSF environment and can be effectively used in the cisternal or subarachnoidal space.

Adult↗
PubMed2003

Molecular mechanisms of initiation of fibrinolysis by fibrin.

Fibrinogen is rather inert in the circulation, however, after conversion into fibrin it participates in various physiological processes including fibrinolysis. Initiation of fibrinolysis occurs through a number of orchestrated interactions between fibrin, plasminogen and its activator tPA which result in generation of plasmin. Numerous studies localized a set of specific low affinity tPA- and plasminogen-binding sites in each D region of fibrin(ogen). The tPA-binding site includes residues gamma312-324 and the plasminogen-binding site includes residues Aalpha148-160; they bind tPA and plasminogen with a K(d) of about 1 micro M. Another set of high affinity tPA- and plasminogen-binding sites (K(d)s = 16-33 nM) was identified in the compact portion of each fibrin(ogen) alphaC-domain within residues Aalpha392-610. All these sites are cryptic in fibrinogen and become exposed in fibrin. Recent studies with recombinant and proteolytic fibrin(ogen) fragments clarified the molecular mechanisms by which these sites become exposed. Namely, upon fibrin assembly, the interaction between the D and E regions causes conformational changes in the former that expose the low affinity binding sites. The exposure of the high affinity binding sites in the alphaC-domains is connected most probably with their switch from an intramolecular interaction in fibrinogen to an intermolecular one in fibrin. These mechanisms serve to minimize degradation of circulating fibrinogen and confine fibrinolysis to places of fibrin deposition.

Amino Acid Sequence↗
PubMed1992

A unique factor XIII inhibitor to a fibrin-binding site on factor XIIIA.

An 81-year-old woman, who presented with sudden episodes of spontaneous bleeding, was found to have a specific inhibitor of factor XIII. Her fibrin clots had approximately 70% gamma-gamma and no alpha polymer formation, under conditions where normal fibrin was fully cross-linked; the patient's clots were soluble in urea or monochloroacetic acid. Factor XIII activity in her plasma was 24%, measured by the dansylcadaverine incorporation assay. When mixed with normal plasma, the patient's plasma inhibited fibrin cross-linking; however, in mixtures of patient and normal plasma, there was no inhibition of factor XIII activity when assayed by the incorporation of dansylcadaverine into casein. Thus, this inhibitor was active against fibrin cross-linking but not against ligation of small molecules to casein. Consequently, gel electrophoresis of reduced, sodium dodecyl sulfate-solubilized fibrin clots was a simple, quantitative method that was used to measure inhibitor activity. This inhibitor is unique and has been designated inhibitor New Haven. It was neutralized by anti-IgG and anti-kappa. It did not inhibit the activation of factor XIII but did inhibit fibrin cross-linking. There was complex formation between the inhibitor and activated factor XIII (A', A*) but not between A2 or fibrinogen. Only A', A* and the 56-Kd fragment bound to affinity columns made with this IgG. The inhibitor significantly decreased the binding of A', A* to fibrin clots. These data indicate that the epitope for this inhibitor is in a fibrin binding site. It is hidden in the zymogen and expressed on A' and A*, indicating that the conformational change occurring with the cleavage of the activation peptide is sufficient to expose the fibrin binding site.

Aged↗
PubMed1992

Vampire bat salivary plasminogen activator exhibits a strict and fastidious requirement for polymeric fibrin as its cofactor, unlike human tissue-type plasminogen activator. A kinetic analysis.

The vampire bat salivary plasminogen activator (BatPA) is virtually inactive toward Glu-plasminogen in the absence of a fibrin-like cofactor, unlike human tissue-type plasminogen activator (tPA) (the kcat/Km values were 4 and 470 M-1 s-1, respectively). In the presence of fibrin II, tPA and BatPA activated Glu-plasminogen with comparable catalytic efficiencies (158,000 and 174,000 M-1 s-1, respectively). BatPA's cofactor requirement was partially satisfied by polymeric fibrin I (54,000 M-1 s-1), but monomeric fibrin I was virtually ineffective (970 M-1 s-1). By comparison, a variety of monomeric and polymeric fibrin-like species markedly enhanced tPA-mediated activation of Glu-plasminogen. Fragment X polymer was 2-fold better but 9-fold worse as cofactor for tPA and BatPA, respectively, relative to fibrin II. Fibrinogen, devoid of plasminogen, was a 10-fold better cofactor for tPA than fibrinogen rigorously depleted of plasminogen, Factor XIII, and fibronectin; the enhanced stimulatory effect of the less-purified fibrinogen was apparently due to the presence of Factor XIII. By contrast, the two fibrinogen preparations were equally poor cofactors of BatPA-mediated activation of Glu-plasminogen. BatPA possessed only 23 and 4% of the catalytic efficiencies of tPA and two-chain tPA, respectively, in hydrolyzing the chromogenic substrate Spectrozyme tPA. However in the presence of fibrin II, BatPA and tPA exhibited similar kcat/Km values for the hydrolysis of Spectrozyme tPA. Our data revealed that BatPA, unlike tPA, displayed a strict and fastidious requirement for polymeric fibrin I or II. Consequently, BatPA may preferentially promote plasmin generation during a narrow temporal window of fibrin formation and dissolution.

Animals↗