Thick Fibrin Fibers Research Articles

The effect of fibrin structure on fibrinolysis.

Fibrin structure contributes to the regulation of the fibrinolytic rate. As the fibrin fiber size is decreased, the fibrinolytic rate also decreases. Fibrin structure was altered by either changing the ratio of thrombin to fibrinogen, i.e. altering the assembly rate or by adding a fibrin assembly inhibitor, iopamidol. Changes in the fibrinolytic rate were followed by measuring the time dependence of the decrease in the fiber mass/length ratio during fibrinolysis. A measure of the overall fibrinolytic rate was determined from the decrease in the mass/length ratio versus time. An 8-fold reduction in the fibrinolytic rate was seen on decreasing the mass/length ratio from 2.7 x 10(12) daltons/cm to 0.5 x 10(12) daltons/cm. It is shown that thin fibrin fibers have a decreased rate of conversion of plasminogen to plasmin by tissue plasminogen activator and that thin fibrin fibers are lysed more slowly than thick fibrin fibers.

Studies on fibrin network structure in human plasma. Part II - Clinical application: Diabetes and antidiabetic drugs

Using measurements of fibrin fibre thickness ( μ T) derived from turbidity and permeability (τ) of clotted plasma, it has been found that glucose in vitro added to plasma decreases permeability of the network despite unaltered fibrinogen conversion. Fibrin fibre thickness ( μ T) in uncontrolled diabetes is found significantly reduced. In diabetic plasma the degree of conversion to fibrin is similar to that in age and sex matched plasma from nondiabetics: the effect on fibrin network and fibre thickness probably arises from glycosylation of fibrinogen. Studies with Gliclazide, Metformin, Glibenclamide and insulin have shown that while all other drugs tested have no effect, Gliclazide increases fibrin fibre thickness ( μ T) significantly, diminishes tensile strength and reduces permeability. In separate experiments lysability of 125I-labelled fibrin networks developed in the presence of all four hypoglycaemic agents by tissue activator was tested. Networks developed in the presence of Metformin were found to lyse more quickly, followed by insulin and Gliclazide. Alterations induced in fibrin networks in diabetes may be nullified by some oral hypoglycaemic agents such as Gliclazide and not by others. Whether nullification of such changes has long-term effects in reducing the incidence of vascular disease in diabetics remains to be established.

Studies on fibrin network structure: The effect of some plasma proteins

Significant differences were found between characteristics of networks developed in plasma and those developed in pure fibrinogen solution. Networks in plasma have thicker fibres, are more permeable and have lower tensile strength. In this investigation determinants of network structure under physiological conditions of clotting have been examined in an attempt to account for the differences in network structure in plasma and fibrinogen solution. Effect of antithrombin III and of physiological concentrations of fibronectin, albumin and gamma-globulin on fibrin network structure was examined using mass-length ratio ( μ T) from turbidity, bulk permeability of networks (τ) and kinetics of network development. At physiological concentrations effect of ATIII was too pronounced to allow this method to quantify changes in network characteristics. Whilst fibronectin and gammaglobulins increased fibrin fibre thickness and network permeability, albumin caused opposite effects. It is concluded that the final network structure is determined by kinetics of fibrin fibre growth and is highly responsive to the presence of plasma proteins.

The effects of in vitro phosphorylation and dephosphorylation on the thrombin-induced gelation and plasmin degradation of fibrinogen

The α-chain of human fibrinogen was found to be phosphorylated in EDTA-anticoagulated whole blood when trace amounts of (γ- 32P)ATP and 7.5 mM Mg 2+ ions were added. Fibrinogen was not phosphorylated if only the ATP was added. The thrombin-induced gelation of fibrinogen phosphorylated by protein kinase A, casein kinase I or II was studied spectrophotomerically. It was found that phosphorylation by protein kinase A caused the formation of thinner fibrin fibres, whereas phosphorylation by casein kinase II resulted in fibres slightly thicker than those of the control fibrinogen (equivalent to a 20% increase in the control fibrinogen concentration). Phosphorylation with casein kinase I did not significantly affect the fibrin fibre thickness. Dephosphorylation by alkaline phosphatase removed 50% of the 32P-labelled phosphate from protein kinase A-phosphorylated fibrinogen and over 90% from the casein kinase I or II-phosphorylated fibrinogens. This dephosphorylation resulted in a general increase in fibre thickness in the gelation assay in all samples, although the fibres of the phosphorylated fibrinogens remained substantially thinner than the dephosphorylated control fibrinogen. Plasmin digestion of the phosphorylated fibrinogens showed that they were more resistant to cleavage, being cleaved at only 30% to 70% of the rate of control fibrinogen and that this resistance was unaltered by dephosphorylation, in contrast to the thrombin gelation experiments.

Effect of homo poly(L-amino acids) on fibrin assembly: role of charge and molecular weight.

Positively charged molecules such as protamine, leukocyte cationic protein, and the carboxyl terminus of platelet factor 4 have been shown to increase fibrin fiber thickness. Synthetic homo poly(L-amino acids) were used to explore the role of charge and molecular weight of cationic molecules on fibrin assembly. The effects of poly(L-lysine) (PLL), poly(L-glutamic acid) (PLG), poly(L-aspartic acid) (PLA), poly(L-histidine) (PLH), and poly(L-arginine) (PLArg) on the assembly and structure of fibrin gels were studied by using light-scattering techniques. At a PLG (Mr 60,000) concentration of 80 micrograms/mL and a PLA (Mr 20,000) concentration of 64 microgram/mL, neither of these negatively charged polymers produced a detectable change in either fibrin assembly kinetics or final structure. Positively charged PLArg (16 micrograms/mL) caused a 30% increase in fibrin fiber mass/length ratio without calcium. In contrast, PLH (16 micrograms/mL), also positively charged, had no effect in the absence of CaCl2 but produced a 40% increase in fiber mass/length ratio with 5 mM CaCl2. At concentrations as low as 1 microgram/mL, positively charged PLL increased the initial fibrin assembly kinetics and led to larger fiber mass/length ratio. The impact on fibrin mass/length ratio was equivalent for three different molecular weight preparations of PLL (Mr 25,000, 90,000, and 240,000). The lack of a molecular weight effect on fiber thickness and the low polymer concentrations required to produce the perturbation argue against an excluded volume effect as the mechanism by which lateral fiber growth is augmented. Mechanisms by which poly(L-amino acids) may perturb fibrin assembly are discussed.

Influence of the subendothelial basement membrane components on fibrin assembly. Evidence for a fibrin binding site on type IV collagen.

Effective repair of a vascular injury depends on establishment of a stable fibrin patch at the injury site. Data presented in this study demonstrate that structural modification of fibrin occurs as a result of fibrin interaction with naturally occurring components of the vascular basement membrane and subendothelial structures. Of the basement membrane components, type IV collagen produces the greatest structural modification, generating thick fibrin fibers; a 3-fold increase in the fiber mass/length ratio occurs when type IV collagen is increased from 0 to 100 ng/ml. Laminin and dermatan sulfate decrease the fibrin fiber mass/length ratio resulting in thinner fibers. However, the overall effect of the basement membrane on fibrin is to increase the fibrin fiber diameter. Electrophoretic light scattering and the binding of type IV collagen by fibrinogen-Sepharose further establish the interaction between type IV collagen and fibrinogen. Incorporation of laminin with type IV collagen onto coated surfaces decreases the ability of type IV collagen to bind fibrinogen. These studies emphasize that the final fibrin structure is influenced by the milieu in which the clot is assembled.

Comparison of fibrin networks in plasma and fibrinogen solution

Mass-Length ratio of fibrin fibres (μ T and μ p) derived independently from turbidity and permeability respectively, in networks made in fibrinogen solution and plasma, have been compared under similar conditions of clotting. Amount of fibrinogen conversion to fibrin was similar in both systems when high thrombin concentrations were used. But networks in plasma had significantly thicker fibres (higherμ T and μ p)than those in fibrinogen solution. This difference arises from differing kinetics of fibrin assembly in the two systems. When lower thrombin concentration is used, fibrin fibre thickness (as indicated by μ p and μ T) is increased in fibrinogen solution but the fibrin content of the network remains unaltered. In plasma, on the other hand, the fibrin content of the network is decreased, μ T remains relatively unchanged while μ p increases. The thrombin concentration dependence of the fibrin content of the network in plasma and the bimodal distribution of fibrin fibre thickness explain the breakdown in correlation between μ p and μ T.

Lateral packing of protofibrils in fibrin fibers and fibrinogen polymers.

AbstractThe distinctive transverse banding pattern of fibrin fibers clearly indicates ordering of molecules in the longitudinal direction. In this study we examined the fibers of fibrin clots, as well as two types of fibrinogen polymers, by thin‐section electron microscopy. The fibrinogen polymers have a transverse banding pattern identical to that of fibrin fibers—clearly indicating a regular longitudinal repeat—but they are larger in diameter, and show little or no branching. We therefore expected their overall ordering to be better than that of fibrin fibers. Several different fixation protocols were used. We readily observed the typical transverse banding seen previously by negative stain and metal replication techniques. However, only very rarely was any regular lateral lattice seen in any of the samples. X‐ray diffraction was used to examine unfixed specimens of the two fibrinogen polymers and, once again, although a longitudinal repeat was evident, only rarely was evidence for lateral crystallinity seen. The electron‐microscope and x‐ray results showed that the needles and pellet fibers of fibrinogen have essentially the same internal architecture as thick fibrin fibers, and that all three types of polymer, although clearly transversely banded, have almost no crystallinity in their lateral protofibril packing.