Shirley Uitte de Willige

Polyphosphate modifies the fibrin network and down-regulates fibrinolysis by attenuating binding of tPA and plasminogen to fibrin

Activated platelets secrete a negatively charged polymer, polyphosphate (polyP). Here, we explore the interactions of polyP with fibrin(ogen) and its effect on fibrin structure and fibrinolysis. Electrophoretic mobility and binding assays indicate that polyP interacts with fibrinogen and soluble fibrin. Clots formed in the presence of polyP exhibited reduced turbidity and permeability indicative of a tighter fibrin network, but these changes were not related to cross-linking or fibrinopeptide release. Microscopy showed a change in fibrin distribution in clots formed with polyP; with formation of tight aggregates of fibrin fibers interspaced with large pores in contrast to homogenous fiber distribution in control clots. Lysis by tissue plasminogen activator (tPA) and plasminogen or plasmin was delayed in clots formed with polyP and depended on both the activator and polyP concentration. Adding polyP to the clot after fibrin formation or to repolymerizing soluble fibrin did not affect lysis, indicating changes induced by polyP occur at the level of conversion of fibrinogen to fibrin. Surface plasmon resonance showed that the presence of polyP reduced the binding of both plasminogen and tPA to partially lysed fibrin surfaces. These data show that polyP directly influences fibrin architecture and attenuates fibrinolysis through reduced binding of fibrinolytic proteins.

Fibrinogen γ′ in ischemic stroke: A case-control study

Background and Purpose— To determine the contribution of fibrinogen &ggr;′ levels and FGG haplotypes to ischemic stroke. Methods— Associations between fibrinogen &ggr;′ levels, fibrinogen &ggr;′/total fibrinogen ratio, and FGG haplotypes with the risk of ischemic stroke were determined in 124 cases and 125 controls. Results— Fibrinogen &ggr;′/total fibrinogen ratio was higher in patients than in controls during the acute phase of the stroke and lower in the convalescent phase 3 months after the stroke. FGG haplotype 3 (H3) was associated with a reduced risk of ischemic stroke (odds ratio 0.60; 95% CI, 0.38 to 0.94), but not with the fibrinogen &ggr;′/total fibrinogen ratio. In contrast, FGG-H2 was associated with a decreased fibrinogen &ggr;′/total fibrinogen ratio, but not with risk of stroke. Conclusions— Fibrinogen &ggr;′/total fibrinogen ratio is associated with ischemic stroke, especially in the acute phase of the disease. In addition, FGG-H3 haplotype appears to be protective against ischemic stroke.Background and Purpose— To determine the contribution of fibrinogen γ′ levels and FGG haplotypes to ischemic stroke. Methods— Associations between fibrinogen γ′ levels, fibrinogen γ′/total fibrinogen ratio, and FGG haplotypes with the risk of ischemic stroke were determined in 124 cases and 125 controls. Results— Fibrinogen γ′/total fibrinogen ratio was higher in patients than in controls during the acute phase of the stroke and lower in the convalescent phase 3 months after the stroke. FGG haplotype 3 (H3) was associated with a reduced risk of ischemic stroke (odds ratio 0.60; 95% CI, 0.38 to 0.94), but not with the fibrinogen γ′/total fibrinogen ratio. In contrast, FGG-H2 was associated with a decreased fibrinogen γ′/total fibrinogen ratio, but not with risk of stroke. Conclusions— Fibrinogen γ′/total fibrinogen ratio is associated with ischemic stroke, especially in the acute phase of the disease. In addition, FGG-H3 haplotype appears to be protective against ischemic stroke.

Fibrin clot structure remains unaffected in young, healthy individuals after transient exposure to diesel exhaust

Exposure to urban particulate matter has been associated with an increased risk of cardiovascular disease and thrombosis. We studied the effects of transient exposure to diesel particles on fibrin clot structure of 16 healthy individuals (age 21- 44). The subjects were randomly exposed to diesel exhaust and filtered air on two separate occasions. Blood samples were collected before exposure, and 2 and 6 hours after exposure. There were no significant changes on clot permeability, maximum turbidity, lag time, fibre diameter, fibre density and fibrinogen level between samples taken after diesel exhaust exposure and samples taken after filtered air exposure. These data show that there are no prothrombotic changes in fibrin clot structure in young, healthy individuals exposed to diesel exhaust.

Heritability of Clot Formation

The development of occlusive arterial and venous disease is contingent on the formation of a fibrin mesh that occurs following tissue damage and activation of the coagulation system. Clinical evidence indicates that fibrin structure and function are important determinants of cardiovascular risk, and the difference between clots formed from plasma and from purified fibrinogen highlights the importance of plasma factors in determining final clot structure. Twin, family, and case-control studies indicate there is a significant genetic contribution to variance in coagulation and fibrinolytic factors that may influence clot structure. Additionally, studies indicate a smaller but significant genetic contribution to fibrin structure, with a larger component provided by the environmental contribution. Future studies of the influence of post-translational modifications to fibrin(ogen) and other factors involved in clot formation may provide important insights into thrombotic disease mechanisms.

Proteolytic and genetic variation of the alpha-2-antiplasmin C-terminus in myocardial infarction

Alpha-2-antiplasmin (α2AP) undergoes both N- and C-terminal cleavages, which significantly modify its activities. Compared with other Ser protease inhibitors (serpins), α2AP contains an ~50-residue-extended C-terminus, which binds plasmin(ogen). We developed 2 new ELISAs to measure the antigen levels of free total α2AP and free C-terminally intact α2AP to investigate whether α2AP antigen levels or α2AP C-terminal cleavage were associated with myocardial infarction (MI) in 320 male MI survivors and 169 age-matched controls. Patients had 15.2% reduced total α2AP antigen levels compared with controls (93.8 vs 110.6 U/dL, P < .001), with a 10.1-fold (95% confidence interval [CI]: 5.5-18.9) increased MI risk for levels in the 1st quartile compared with the 4th quartile. The percentage of C-terminal cleavage did not differ between patients and controls (38.7% and 38.1%, respectively, P = .44). In addition, all individuals were genotyped for the polymorphism Arg407Lys, which is located near the start of the extended C-terminus. Arg407Lys was not associated with α2AP C-terminal cleavage, total α2AP antigen levels, or MI risk (odds ratios compared with Arg/Arg: Arg/Lys 0.74, 95% CI: 0.50-1.10; Lys/Lys 0.77, 95% CI: 0.31-1.92). Our data show that levels of free full-length α2AP were decreased in MI, that the percentage of C-terminally cleaved α2AP was unaltered, and that Arg407Lys did not influence α2AP levels or MI risk.

Fibrinogen γ′ in Ischemic Stroke

Background and Purpose— To determine the contribution of fibrinogen &ggr;′ levels and FGG haplotypes to ischemic stroke. Methods— Associations between fibrinogen &ggr;′ levels, fibrinogen &ggr;′/total fibrinogen ratio, and FGG haplotypes with the risk of ischemic stroke were determined in 124 cases and 125 controls. Results— Fibrinogen &ggr;′/total fibrinogen ratio was higher in patients than in controls during the acute phase of the stroke and lower in the convalescent phase 3 months after the stroke. FGG haplotype 3 (H3) was associated with a reduced risk of ischemic stroke (odds ratio 0.60; 95% CI, 0.38 to 0.94), but not with the fibrinogen &ggr;′/total fibrinogen ratio. In contrast, FGG-H2 was associated with a decreased fibrinogen &ggr;′/total fibrinogen ratio, but not with risk of stroke. Conclusions— Fibrinogen &ggr;′/total fibrinogen ratio is associated with ischemic stroke, especially in the acute phase of the disease. In addition, FGG-H3 haplotype appears to be protective against ischemic stroke.Background and Purpose— To determine the contribution of fibrinogen γ′ levels and FGG haplotypes to ischemic stroke. Methods— Associations between fibrinogen γ′ levels, fibrinogen γ′/total fibrinogen ratio, and FGG haplotypes with the risk of ischemic stroke were determined in 124 cases and 125 controls. Results— Fibrinogen γ′/total fibrinogen ratio was higher in patients than in controls during the acute phase of the stroke and lower in the convalescent phase 3 months after the stroke. FGG haplotype 3 (H3) was associated with a reduced risk of ischemic stroke (odds ratio 0.60; 95% CI, 0.38 to 0.94), but not with the fibrinogen γ′/total fibrinogen ratio. In contrast, FGG-H2 was associated with a decreased fibrinogen γ′/total fibrinogen ratio, but not with risk of stroke. Conclusions— Fibrinogen γ′/total fibrinogen ratio is associated with ischemic stroke, especially in the acute phase of the disease. In addition, FGG-H3 haplotype appears to be protective against ischemic stroke.