Sex-dependent balance between thrombin and plasmin generation in the presence of thrombomodulin

Thrombomodulin is a stronger indicator of combined oral contraceptives-induced activated protein C pathway resistance in the thrombin generation test than activated protein C

Background

The mechanism by which combined oral contraceptives (COCs) lead to hypercoagulation is not fully understood, although activated protein C (APC) pathway resistance has been implicated. APC and thrombomodulin (TM) tend to be considered as interchangeable reagents, even though their biological action in coagulation is different. However, it remains unclear which reagent is better suited for the detection of APC pathway resistance. We compared the effectiveness of TM and APC in TG to detect COC-induced APC pathway resistance using thrombin generation (TG).

Methods

TG was measured on ST Genesia in 48 healthy women, of whom 24 used COCs. TG was triggered with STG-ThromboScreen (with and without TM), spiked with a low and high concentration of TM or APC (2 or 15 nM TM, or 1.5 or 5.5 nM APC), aimed to achieve 50% and 90% ETP inhibition, respectively.

Results

TG was higher in women using COCs. TM and APC inhibit TG in all women, although their inhibitory effect is more pronounced in women without COC compared to women with COC. The addition of 2 nM TM causes an ETP reduction of 40% (1,289 vs. 768 nM•min) in women without COC and an ETP reduction of 24% (1,704 vs. 1,287 nM•min) in women with COC. The addition of 1.5 nM APC causes an ETP reduction of 41% (1,289 vs. 759 nM•min) in women without COC and an ETP reduction of 23% (1,704 vs. 1,316 nM•min) in women with COC. The difference in effect between women with and without COC is largest when 15 nM TM, aimed at 90% ETP inhibition, is used. 15 nM TM leads to the smallest overlap in ETP inhibition between women with and without COC (27% overlap), compared to 2 nM TM (41% overlap), and 1.5 nM APC (38% overlap) and 5.5 nM APC (41% overlap).

Conclusion

Although TM and APC are often used interchangeably to assess the sensitivity of the APC system in TG, our findings suggest that TM is a better discriminator to detect COC-use induced APC pathway resistance. In addition, we found that the ETP is a better TG test readout for APC pathway resistance testing than the peak height.

Exercise and hypoxia-induced hypercoagulability is counterbalanced in women in part by decreased platelet reactivity

Hypoxia plays an important role in several pathologies, e.g. chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, and is linked to an increased thrombosis risk. Furthermore, oxygen deprivation is associated with hypercoagulability. In this study, we investigated the effect of gender and exercise on the coagulation potential under hypoxic conditions at high altitude by assessing thrombin generation (TG) and platelet activation. Hereto, ten healthy volunteers were included (50 % male, median age of 27.5 years). The measurements were conducted first at sea level and then twice at high altitude (3883 m), first after a passive ascent by cable car and second after an active ascent by a mountain hike. As expected, both the passive and active ascent resulted in a decreased oxygen saturation and an increased heart rate at high altitude. Acute mountain sickness symptoms were observed independently of the ascent method. After the active ascent, platelet, white blood cell and granulocyte count were increased, and lymphocytes were decreased, without a gender-related difference. FVIII and von Willebrand factor were significantly increased after the active ascent for both men and women. Platelet activation was reduced and delayed under hypobaric conditions, especially in women. TG analysis showed a prothrombotic trend at high altitude, especially after the active ascent. Women had a hypercoagulable phenotype, compared to men at all 3 timepoints, indicated by a higher peak height and endogenous thrombin potential (ETP), and shorter lag time and time-to-peak. In addition, ETP and peak inhibition by thrombomodulin was lower in women after the active ascent, compared to men. Interestingly, data normalisation for subject baseline values indicated an opposing effect of altitude-induced hypoxia on α2-macroglobulin levels and TG lag time between men and women, decreasing in men and increasing in women. We conclude that hypoxia increases TG, as well as FVIII and VWF levels in combination with exercise. In contrast, platelets lose their responsiveness at high altitude, which is most pronounced after heavy exercise. Women had a more pronounced prothrombotic phenotype compared to men, which we theorize is counterbalanced under hypobaric conditions by decreased platelet activation.