Platelet Dysfunction and Cellular Microparticles May be Involved in the Hipercoagulable State Observed in Obstructive Sleep Apnea Syndrome

Introduction: Obstructive sleep apnea syndrome (OSA) is a common disorder characterized by repetitive episodes of nocturnal breathing cessation due to upper airway collapse that cause intermittent hypoxia. Because of this, there is an increase in oxidative stress, endothelial damage and mortality associated with the incidence of thrombotic events. The evaluation of platelet function by flow cytometry (FCM) and hemostatic capacity through global hemostasis tests have been successfully used in the study of the prothrombotic state associated to numerous diseases. We anticipate that these techniques may help to clarify the mechanism involved in the prothrombotic state of OSA.

Materials and Methods: We included 16 OSA patients diagnosed in the Pneumology Unit of the University Hospital La Paz and 59 healthy controls recruited in the Donor Unit of the same Hospital.

Platelet surface receptors were analysed by FCM (FACScan, BD Biosciences) with specific monoclonal antibodies (mAbs) against CD41/αIIb and CD61/β3, CD42a and CD42b. Platelet activation was assessed by FCM through PAC1-FITC binding (mAbs that recognizes activated conformation of fibrinogen receptor), P-selectin and CD63 exposure in baseline condition and after stimulation with 100 µM TRAP (agonist of the PAR-1 receptor) and 10 µM ADP. Platelet apoptosis was analysed by FCM through FITC-annexin V (BD Pharmingen) binding to phosphatidylserine (PS) exposed on platelet membrane under basal conditions and by determination of activity of caspases -3/7, -8, and -9 (BD Millipore).

The overall hemostatic capacity was determined by the evaluation of thrombin generation using the Calibrated Automatic Thrombinography (CAT) with fresh platelet-poor plasma (obtained after double centrifugation of whole blood at 2500g, 20 minutes and 24ºC) and by the assessment of kinetics of clot formation using Rotational Thromboelastometry (ROTEM® Gamma, Tem Innovations GmbH, Spain) using whole blood and activation by recalcification (naTEM^® test, Tem Innovations GmbH, Spain).

The statistical analysis was performed using SPSS 9.0 software (SPSS Inc., Chicago, Illinois, USA). Statistical significance was established at p <0.05.

Results: No significant differences in age or sex were found between groups. Patients presented anxiety-depressive disorder (15%), ischemic cardiomyopathy (8%), dyslipidemias (38%), arterial hypertension (69%) and lower minimum oxygen pressures during sleep (mean±SD; patients: 76±8 % vs controls: 89±1 %; p< 0.001) indicating hypoxia. In basal conditions, an increase of CD42a subunit of the von Willebrand factor receptor was observed in patients with OSA but no differences were found in the exposure of fibrinogen receptor either at basal condition or after activation with TRAP or ADP (Table 1 and Figure 1). Platelet PS exposure before and after TRAP stimulation was higher in the patient group (Figure 1) but no differences between groups were observed in caspase activities (Table 2). Clotting time (CT), maximum clot firmness (MCF) and MP-associated thrombin generation were higher in patients with OSA (Figure 2).

Conclusion: Mechanisms related to the mobilization of P-selectin to platelet surface and with the maintenance of phospholipids distribution in platelet membrane might be altered in OSA. The increment of P-selectin exposure may favor the interaction between white cells and platelets through PSGL-1 ligand from lymphocytes which in turn may produce endothelial damage explaining part of OSA's pathophysiology. A lower CT and higher MCF reflected a hypercoagulable state in patients, perhaps related to their higher MP-associated thrombin generation and, at least in part, due to the enhanced platelet-PS exposure. Our results also suggest that both ROTEM and CAT are useful tools for characterizing prothrombotic states in OSA patients.

Work supported by grant from FIS-FEDER PI15/01457. NB holds a Miguel Servet II (FIS-FEDER CP14/00024).

View largeDownload slide

View largeDownload slide

Close modal