Collagen/endogenous thrombin-induced platelet aggregation in whole blood samples

The Antiplatelet Action of S-Nitroso Human Serum Albumin in Whole Blood

Nitric oxide donors (NO-donors) have been shown to have therapeutic potential (e.g., ischemia/reperfusion injury). However, due to their release rate/antiplatelet properties, they may cause bleeding in patients. We therefore studied the antiplatelet effects of the two different NO-donors, i.e., S-NO-Human Serum Albumin (S-NO-HSA) and Diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium-1,2-diolate (DEA-NONOate) in whole blood (WB) samples. WB samples were spiked with S-NO-HSA or DEA-NONOate (100 µmol/L or 200 µmol/L), and the NO release rate (nitrite/nitrate levels via HPLC) and antiplatelet efficacy (impedance aggregometry, platelet function analyzer, Cone-and-platelet analyzer, thrombelastometry) were assessed. S-NO-HSA had a significantly lower NO release compared to equimolar concentrations of DEA-NONOate. Virtually no antiplatelet action of S-NO-HSA was observed in WB samples, whereas DEA-NONOate significantly attenuated platelet function in WB. Impedance aggregometry measurements revealed that Amplitudes (slope: −0.04022 ± 0.01045 ohm/µmol/L, p = 0.008) and Lag times (slope: 0.6389 ± 0.2075 s/µmol/L, p = 0.0051) were dose-dependently decreased and prolonged by DEA-NONOate. Closure times (Cone-and-platelet analyzer) were dose-dependently prolonged (slope: 0.3738 ± 0.1403 s/µmol/L, p = 0.0174 with collagen/ADP coating; slope: −0.5340 ± 0.1473 s/µmol/L, p = 0.0019 with collagen/epinephrine coating) by DEA-NONOate. These results in WB further support the pharmacological potential of S-NO-HSA as an NO-donor due to its ability to presumably prevent bleeding events even at high concentrations up to 200 µmol/L.

Coagulation changes induced by lower-body negative pressure in men and women

We investigated whether lower-body negative pressure (LBNP) application leads to coagulation activation in whole blood (WB) samples in healthy men and women. Twenty-four women and 21 men, all healthy young participants, with no histories of thrombotic disorders and not on medications, were included. LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both men and women using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. LBNP led to coagulation activation determined in both plasma and WB samples. At baseline, women were hypercoagulable compared with men, as evidenced by their shorter “lag times” and higher thrombin peaks and by shorter “coagulation times” and “clot formation times.” Moreover, men were more susceptible to LBNP, as reflected in their elevated factor VIII levels and decreased lag times following LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. Women appear to be relatively hypercoagulable compared with men, but men are more susceptible to coagulation changes during LBNP. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.

NEW & NOTEWORTHY LBNP led to coagulation activation determined in both plasma and whole blood samples. At baseline, women were hypercoagulable compared with men. Men were, however, more susceptible to coagulation changes during LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.

Bed rest does not induce hypercoagulability

BACKGROUND

Although there is no direct evidence, it is generally believed that bed rest shifts the haemostatic system towards hypercoagulability; thus, immobilized patients are commonly treated with anticoagulants. We therefore aimed to investigate whether long-term bed rest actually leads to an elevated risk for thromboembolic events.

MATERIALS AND METHODS

Eleven healthy men were enrolled in our study (bed rest campaign in MEDES Clinique d'Investigation, Toulouse, France). Besides various standard laboratory methods, we used calibrated automated thrombography (CAT) and thrombelastometry (TEM). Activation of samples with minute amounts of relipidated tissue factor allowed sensitive detection of hyper- or hypocoagulable states.

RESULTS

CAT and TEM values were not indicative of bed rest-induced hypercoagulability. On the contrary, several parameters were indicative of a tendency towards a hypocoagulable state. Peak and thrombin formation velocity (VELINDEX) were significantly decreased during bed rest compared to baseline. Coagulation times were significantly increased and alpha angles were significantly decreased, indicating attenuated clot formation. Moreover, F1 + 2 and thrombin/antithrombin complex (TAT) values were significantly decreased during bed rest, indicating suppressed coagulation activation. FVII plasma levels were also significantly decreased during the first week of bed rest.

CONCLUSIONS

Our data indicate that the re-ambulation period is associated with a tendency towards hypercoagulability: ttPeak and StartTail were significantly shorter, Peak and VELINDEX were significantly higher compared to baseline. Moreover, plasma levels of F1 + 2, TAT, FVII and FVIII were significantly higher compared to baseline. The results from our study suggest that bed rest by itself is not associated with hypercoagulable states in healthy subjects.

Effects of a single bout of walking exercise on blood coagulation parameters in obese women

Obesity is associated with increased prevalence of thromboembolic events. We aimed to investigate whether obese women might benefit from vigorous aerobic exercise. Forty-two overweight and obese women performed a 30-min walking exercise test (treadmill ergometer) at an intensity of 70% of individual peak oxygen uptake. Blood samples were collected before and immediately after exercise. Thrombelastometry and platelet function measurements were performed on whole blood. Standard coagulation times, thrombin generation curves, markers of thrombin generation, fibrinolytic parameters, plasma levels of pro- and anticoagulatory factors, and microparticle procoagulant activity were determined in platelet-poor plasma samples. Thrombelastometry revealed a significant prolongation of clot formation time ( P = 0.037) and a significant deceleration of fibrin build up (alpha angle, P = 0.034) after exercise. Calibrated automated thrombography revealed a significant exercise-induced decrease in endogenous thrombin potential ( P = 0.039). Moreover, thrombin formation stopped earlier postexercise, reflected in shortened StartTail ( P = 0.046). Significantly elevated tissue-plasminogen activator levels ( P = 0.001) indicate an exercise-induced activation of the fibrinolytic system. White blood cell count increased significantly from pre- to postexercise ( P = 0.045), indicating a mild exercise-induced leukocytosis. The results of this study demonstrate that vigorous aerobic exercise might be a suitable tool to protect obese women from thrombotic events. We show that a single bout of vigorous aerobic exercise is clearly associated with an activation of the fibrinolytic system and a decreased readiness of the postexercise samples to form a clot and to generate thrombin, the pivotal enzyme of hemostasis.

Coagulation changes during presyncope and recovery

Orthostatic stress activates the coagulation system. The extent of coagulation activation with full orthostatic load leading to presyncope is unknown. We examined in 7 healthy males whether presyncope, using a combination of head up tilt (HUT) and lower body negative pressure (LBNP), leads to coagulation changes as well as in the return to baseline during recovery. Coagulation responses (whole blood thrombelastometry, whole blood platelet aggregation, endogenous thrombin potential, markers of endothelial activation and thrombin generation), blood cell counts and plasma mass density (for volume changes) were measured before, during, and 20 min after the orthostatic stress. Maximum orthostatic load led to a 25% plasma volume loss. Blood cell counts, prothrombin levels, thrombin peak, endogenous thrombin potential, and tissue factor pathway inhibitor levels increased during the protocol, commensurable with hemoconcentration. The markers of endothelial activation (tissue factor, tissue plasminogen activator), and thrombin generation (F1+2, prothrombin fragments 1 and 2, and TAT, thrombin-antithrombin complex) increased to an extent far beyond the hemoconcentration effect. During recovery, the markers of endothelial activation returned to initial supine values, but F1+2 and TAT remained elevated, suggestive of increased coagulability. Our findings of increased coagulability at 20 min of recovery from presyncope may have greater clinical significance than short-term procoagulant changes observed during standing. While our experiments were conducted in healthy subjects, the observed hypercoagulability during graded orthostatic challenge, at presyncope and in recovery may be an important risk factor particularly for patients already at high risk for thromboembolic events (e.g. those with coronary heart disease, atherosclerosis or hypertensives).