Low dose aspirin does not prevent fibrinolytic response to venous occlusion

Pharmacological modulation of fibrinolytic response - In vivo and in vitro studies

Fibrinolysis is an action of converting plasminogen by its activators, like tissue- or urokinase-type plasminogen activators (t-PA, u-PA), to plasmin, which in turn cleaves fibrin, thereby causing clot dissolution and restoration of blood flow. Endothelial cells release t-PA, prostacyclin (PGI2) and nitric oxide (NO), the potent factors playing a crucial role in regulation of the fibrinolytic system. Since blood platelets can release not only prothrombotic, but also antifibrinolytic factors, like plasminogen activator inhibitor type-1 (PAI-1), they are involved in fibrynolysis regulation. Therefore agents enhancing fibrinolysis can be preferred pharmacologicals in many cardiovascular diseases. This review describes mechanisms by which major cardiovascular drugs (renin-angiotensin-aldosterone system inhibitors, statins, adrenergic receptors and calcium channel blockers, aspirin and 1-methylnicotinamide) influence fibrinolysis. The presented data indicate, that the influence of these drugs on endothelium-blood platelets interactions via NO/PGI2 pathway is fundamental for its antithrombotic and profibrinolytic action. We also described new approaches for intravital confocal real-time imaging as a tool useful to investigate mechanisms of thrombus formation and the effects of drugs affecting haemostasis and mechanisms of their action in the circulation.

Aspirin and the fibrinolytic response

Apart from the anti-inflammatory action, aspirin (ASA) by inhibiting thromboxane A2 synthesis, decreases platelets activity and possesses the antithrombotic action. However, an ASA effect on fibrinolysis has not been yet finally established. Menon [Lancet 1 (1970) 364] reported increased fibrinolytic response in patients treated with high doses of ASA and this observation started a series of studies to find the relation between aspirin and fibrinolysis. This review comprises the results of those studies, divided into in vitro and in vivo, animal and human experiments. The results of our animal studies are also included. Data survey shows that the ASA effect on fibrinolysis depends on experimental conditions, the dose and the time of drug administration. The results of our study indicate the essential role of plasma components in the fibrinolysis regulation by ASA.

Increased fibrinogen levels and acquired hypofibrinolysis in young adults with ischemic stroke

BACKGROUND AND PURPOSE

Elevated fibrinogen levels and abnormalities in the fibrinolytic system are related to the occurrence of cardiovascular events. However, the role of these factors in the evolution of cerebrovascular disease has received less attention, in particular in young stroke patients. The aim of this study was to evaluate possible abnormalities in plasma fibrinogen levels and the state of the fibrinolytic system in young adults with a first-ever ischemic stroke.

METHODS

This study is based on 102 consecutive patients aged 18 to 44 years admitted between January 1991 and May 1996 as a result of a first ischemic stroke. Forty-one healthy controls were recruited. Evaluations of anthropometric/metabolic variables, plasma fibrinogen levels, and the fibrinolytic system were undertaken >/=3 months (mean, 5.4+/-2.0 months) after admission.

RESULTS

Patients had lower tissue plasminogen activator activity and increased plasminogen activator inhibitor type 1 activity at baseline, as well as increased tissue plasminogen activator mass concentration both at baseline and after a venous occlusion test. Overall, there were no significant differences between the main etiologic subgroups regarding plasma fibrinogen levels and fibrinolytic variables. Baseline fibrinolytic variables were strongly correlated with body mass index, serum triglycerides, and cholesterol levels. After adjustments in multivariate models, fibrinogen levels and tissue plasminogen activator mass concentration both at baseline and after venous occlusion test remained significantly increased in patients. Logistic multiple regression analyses indicated that plasma fibrinogen was a strong predictor of ischemic stroke (odds ratio, 11.25; 95% CI, 3.27 to 38. 69).

CONCLUSIONS

Increased fibrinogen levels and tissue plasminogen activator mass concentration are independently associated with ischemic stroke in young adults. Metabolic perturbations are closely interrelated with aberrations in tissue plasminogen activator and plasminogen activator inhibitor type 1 activity in these patients, findings consistent with an acquired hypofibrinolysis.

Fibrinolytic activity is similar in physically active men with and without a history of myocardial infarction

The purpose of this study was to evaluate fibrinolytic potential at rest and after a fibrinolytic stressor in men with a history of myocardial infarction (MI) compared with an age- and activity-matched group of men without coronary artery disease (CAD). All men were currently enrolled in exercise programs. Tissue-type plasminogen activator (TPA) and plasminogen activator inhibitor 1 (PAI-1) activity and antigen levels were measured at rest and after a maximal exercise test. A 2 x 2 (group x time) ANOVA with repeated measures was used to evaluate fibrinolytic potential. Bivariate regressions were conducted to evaluate relations between fibrinolytic potential and maximal oxygen uptake (VO2max). Age was similar between groups (CAD, 57.5 +/- 6.6; non-CAD, 58.1 +/- 7.3 years); however, VO2max was higher in non-CAD subjects (36.2 +/- 6.2 vs 27.5 +/- 5.9 mL.kg-1.min-1). Mean +/- SEM resting TPA and PAI-1 activities were similar between CAD and non-CAD subjects (TPA, 2.8 +/- 0.2 vs 2.8 +/- 0.2 IU/mL; PAI-1, 15.9 +/- 3.1 vs 13.1 +/- 4.1 AU/mL). Both groups showed similar significant increases in TPA activity with exercise (P < .05), and postexercise TPA activity was also similar (CAD, 9.1 +/- 2.0 IU/mL; non-CAD, 11.7 +/- 2.6 IU/mL). Both groups also showed similar significant decreases in PAI-1 activity with exercise (P < .05) and no differences in postexercise PAI-1 activity (CAD, 13.2 +/- 2.5 AU/mL; non-CAD, 10.4 +/- 3.6 AU/mL). Significantly higher resting TPA antigen levels were seen in CAD (14.8 ng/mL) than non-CAD (10.2 ng/mL) subjects (P < .05), but neither group showed significant changes with exercise (CAD, 12.9 ng/mL; non-CAD, 11.8 ng/mL). Resting PAI-1 antigen was similar in the two groups (CAD, 71.4 ng/mL; non-CAD, 74.2 ng/mL) and did not significantly change with exercise (CAD, 77.9 ng/mL; non-CAD, 72.3 ng/mL). VO2max was positively correlated with postexercise TPA activity (r = .52, P < .05) and negatively correlated with resting TPA antigen (r = -.43, P < .05). Resting TPA antigen was also directly correlated with body mass index (r = .63, P < .05). The finding that functional fibrinolytic activity was not different in physically active men with and without CAD contrasts with previous reports. This suggests that matching subjects on the bases of age and habitual physical activity status and controlling exercise intensity are important factors to consider when evaluating fibrinolytic potential.

Effect of low-dose aspirin during pregnancy on fibrinolytic variables before and after parturition

OBJECTIVE

We assessed the effects of a daily oral dose of 60 to 80 mg of aspirin from 12 weeks' gestation until delivery on fibrinolytic variables before and after parturition.

STUDY DESIGN

In a prospective controlled study labor was electively induced in 24 patients, eight receiving low-dose aspirin and 16 controls. Levels were determined in maternal and cord plasma of tissue-type plasminogen activator antigen and activity, plasminogen activator inhibitor-1 antigen, plasminogen activator inhibitor activity, and plasminogen activator inhibitor-2 antigen. We also determined metabolites of vascular prostacyclin and platelet thromboxane A2.

RESULTS

The only maternal fibrinolytic variable affected by low-dose aspirin was plasminogen activator inhibitor activity, which showed a significant reduction before and after parturition of 40% and 70%, respectively, in low-dose aspirin users compared with controls. Concentrations of thromboxane B2 in women using low-dose aspirin were 7% (maternal serum) and 17% (cord serum) of values in controls, but concentrations of 6-keto-prostaglandin F1 alpha were not affected.

CONCLUSIONS

Low-dose aspirin reduces plasminogen activator inhibitor activity and platelet reactivity, but not prostacyclin synthesis, before and after parturition. The reduction in plasminogen activator inhibitor activity may be caused by inhibition of platelet reactivity.

Effect of aspirin on the fibrinolytic response in perfused rat hindquarters

The role of aspirin on tissue plasminogen activator (t-PA) release was studied in rats after experimental venous occlusion. For this purpose, we developed a new experimental model which combines a vascular perfusion system (isolated rat hindquarters) with vascular stimulation, namely the application of venous stasis. Application of venous stasis for 30 min induced the release of t-PA from the vascular endothelium into the perfusate (from 0.19 +/- 0.05 to 0.39 +/- 0.05 UI/ml), reaching a peak 90 s after reperfusion. Aspirin administered to rats 60 min before the experiments (100 mg/kg i.v.), or dissolved in Tyrode solution (100 microM), suppressed 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) synthesis (0.38 +/- 0.09 in control and < 0.01 and 0.15 +/- 0.09 ng/ml, respectively, in aspirin-treated groups) but did not prevent the increase in fibrinolytic activity after venous occlusion (from 0.20 +/- 0.04 to 0.38 +/- 0.06 and from 0.07 +/- 0.03 to 0.27 +/- 0.03 IU/ml, respectively, in the aspirin-treated group). Our results suggest that the increase in fibrinolytic activity after experimental venous occlusion in isolated rat hindlegs is modulated by mechanism(s) other than the cyclooxygenase pathway in the vascular wall.

Baseline fibrinolytic state and the risk of future venous thrombosis. A prospective study of endogenous tissue-type plasminogen activator and plasminogen activator inhibitor

BACKGROUND

Although isolated abnormalities of plasminogen activation and inhibition have been reported among selected patients with venous thrombosis, it is unclear whether these deficiencies of fibrinolysis are important risk factors for thromboembolic disease.

METHODS AND RESULTS

To evaluate whether baseline levels of endogenous tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) predict the future occurrence of venous thrombosis, levels of these proteins were measured in prospectively collected plasma samples from 55 participants in the Physicians' Health Study who later developed deep venous thrombosis or pulmonary embolism and from an equal number of age- and smoking-matched control subjects who remained free of vascular disease during a mean follow-up period of 60.2 months. Overall, there were no statistically significant differences between case patients and control subjects in baseline levels of PAI-1 (50.5 versus 59.5 ng/ml, p = 0.26), t-PA (13.4 versus 13.3 ng/ml, p = 0.94), or PAI-1:t-PA ratio (6.84 versus 6.58, p = 0.82). No evidence of a threshold effect or trend was seen when these data were analyzed by increasing quartiles of PAI-1 (p = 0.73), t-PA (p = 0.62), or PAI-1:t-PA ratio (p = 0.93). These results were unchanged after multivariate analysis that simultaneously controlled for other baseline cardiovascular risk factors.

CONCLUSIONS

In contrast to previous uncontrolled case series and smaller retrospective studies, these prospective data provide strong evidence that baseline fibrinolytic state, as measured by t-PA and PAI-1, does not predict the occurrence of future venous thrombosis.

Decreased fibrinolytic activity in juvenile chronic arthritis

The basal fibrinolytic activity in 17 children with active juvenile chronic arthritis (JCA) was investigated. It was found that patients with JCA, and particularly those with the systemic form, show decreased plasma fibrinolytic activity and a marked increase in plasminogen activator inhibitor. Additionally, it was found that patients with systemic JCA, but not those with the polyarticular or pauciarticular form, have increased circulating levels of tissue-type plasminogen activator, and endothelial cell protein, suggesting possible endothelial cell participation in systemic JCA.

Depressed fibrinolysis in patients with acute leukaemia

The fibrinolytic system was studied in 46 patients with acute leukaemia at diagnosis. Untreated patients (with the sole exception of the M3 subgroup) showed an inhibition of fibrinolytic activity, measured by the euglobulin lysis time and area. This inhibition was accompanied by reduced t-PA antigen and t-PA inhibitor activity. No correlation was found between the above-mentioned fibrinolytic parameters and the biochemical haematological values considered, nor with clinical and/or laboratory features of DIC, fever, liver failure. The decrease in immunological plasminogen and functional alpha 2-antiplasmin, showed a significant correlation with the presence of clinical and/or laboratory signs of DIC, as diagnosed on the basis of concomitant increase in fibrin monomers, plasmatic fibrinopeptide A and serum FDP.