The kinetics of platelet and fibrin deposition on to damaged rabbit carotid arteries in vivo: involvement of platelets in the initial deposition of fibrin

Time-Dependent Thrombus Resolution After Tissue-Type Plasminogen Activator in Patients With Stroke and Mice

BACKGROUND AND PURPOSE

We investigated the relationship between the degree of thrombus resolution and the time from stroke onset or thrombus formation to intravenous tissue-type plasminogen activator (tPA) treatment.

METHODS

In patients with stroke, we measured thrombus volume on thin-section noncontrast brain computed tomographic scans taken at baseline and 1 hour after tPA administration. We determined the association between the time from symptom onset to tPA treatment and the degree of thrombus resolution. In a C57/BL6 mouse model of FeCl3-induced carotid artery thrombosis, we investigated the effect of tPA administered at different time intervals after thrombus formation, using Doppler-based blood flow measurement.

RESULTS

Of 249 patients enrolled, 171 showed thrombus on baseline computed tomography. Thrombus was resolved by ≥50% in 43 patients (25.1%, good volume reduction) and by <50% in 94 patients (55.0%, moderate volume reduction) 1 hour after tPA treatment. In 34 patients (19.9%, nonvolume reduction; either no change or thrombus volume increased), overall thrombus volume increased. The probability of thrombus resolution decreased as the time interval from symptom onset to treatment increased. On multivariate analysis, good volume reduction was independently related with shorter time intervals from symptom onset to tPA treatment (odds ratio, 0.986 per minute saved; 95% confidence interval, 0.974-0.999). In the mouse model, as the interval between thrombus formation and tPA treatment increased, the initiation of recanalization was delayed (P=0.006) and the frequency of final recanalization decreased (P for trends=0.006).

CONCLUSIONS

Early administration of tPA after stroke onset is associated with better thrombus resolution.

Impact of platelet phenotype on myocardial infarction

In acute myocardial infarction patients the injured vascular wall triggers thrombus formation in the damage site. Fibrin fibers and blood cellular elements are the major components of thrombus formed in acute occlusion of coronary arteries. It has been established that the initial thrombus is primarily composed of activated platelets rapidly stabilized by fibrin fibers. This review highlights the role of platelet membrane phenotype in pathophysiology of myocardial infarction. Here, we regard platelet phenotype as quantitative and qualitative parameters of the plasma membrane outer surface, which are crucial for platelet participation in blood coagulation, development of local inflammation and tissue repair.

Composition of coronary thrombus in acute myocardial infarction

OBJECTIVES

We sought to analyze the composition of coronary thrombus in vivo in ST-segment elevation myocardial infarction (STEMI) patients.

BACKGROUND

The dynamic process of intracoronary thrombus formation in STEMI patients is poorly understood.

METHODS

Intracoronary thrombi (n = 45) were obtained by thromboaspiration in 288 consecutive STEMI patients presenting for primary percutaneous intervention, and analyzed using high-definition pictures taken with a scanning electron microscope. Plasma biomarkers (TnI, CRPus, IL-6, PAI-1, sCD40 ligand, and TNF-α) and plasma fibrin clot viscoelastic properties were measured simultaneously on peripheral blood.

RESULTS

Thrombi were mainly composed of fibrin (55.9 ± 18%) with platelets (16.8 ± 18%), erythrocytes (11.5 ± 9%), cholesterol crystals (5.2 ± 8.4%), and leukocytes (1.3 ± 2.0%). The median ischemic time was 175 min (interquartile range: 140 to 297). Ischemic time impacted thrombi composition, resulting in a positive correlation with intracoronary thrombus fibrin content, r = 0.38, p = 0.01, and a negative correlation with platelet content, r = -0.34, p = 0.02. Thus, fibrin content increased with ischemic time, ranging from 48.4 ± 21% (<3 h) up to 66.9 ± 9% (>6 h) (p = 0.02), whereas platelet content decreased from 24.9 ± 23% (<3 h) to 9.1 ± 6% (>6 h) (p = 0.07). Soluble CD40 ligand was positively correlated to platelet content in the thrombus (r = 0.40, p = 0.02) and negatively correlated with fibrin content (r = -0.36; p = 0.04). Multivariate analysis indicated that ischemic time was the only predictor of thrombus composition, with a 2-fold increase of fibrin content per ischemic hour (adjusted odds ratio: 2.00 [95% confidence interval: 1.03 to 3.7]; p = 0.01).

CONCLUSIONS

In acute STEMI, platelet and fibrin contents of the occlusive thrombus are highly dependent on ischemia time, which may have a direct impact on the efficacy of drugs or devices used for coronary reperfusion.

Improved quantitation of delayed-type hypersensitivity responses to sheep erythrocytes in the mouse footpad by estimation of 125I-fibrin deposition

Footpad swelling in response to subcutaneous antigen challenge is widely used to assess delayed-type hypersensitivity responses to xenogeneic erythrocytes in mice. We report here that quantitation of the deposition of 125I-fibrin, compared with that of 125I-human serum albumin, following intravenous isotope administration, provides a less subjective, convenient and antigen specific index of cell-mediated immunity. Moreover, the results obtained correlate well with in vitro assessment of antigen-specific T cell responses.