|Ph.D Student||Telerman Alona|
|Subject||Platelet Activation in Obstructive Sleep Apnea (OSA)|
and Intermittent Hypoxia In Vitro
|Department||Department of Medicine||Supervisor||Dr. Lena Lavie|
|Full Thesis text - in Hebrew|
Obstructive sleep apnea (OSA) is a major risk factor for atherosclerosis and cardiovascular morbidity, but the underlying mechanisms have not yet been fully elucidated. Oxidative stress, activated inflammatory leukocytes and endothelial cells have been shown to be major contributors that lead to endothelial dysfunction. Although increased platelet activation has been demonstrated in OSA, the effects of OSA related intermittent hypoxia on platelet activity were not investigated thus far. We hypothesized that the apnea-related intermittent hypoxia induces platelet activation which promotes platelet aggregability and platelet interactions with leukocytes and consequently increases the risk of atherosclerosis in OSA patients. Platelets’ activation markers, ROS generation, and platelet/leukocytes interactions were characterized in OSA patients and compared to controls. The effect of OSA treatment on platelet activity was examined. Additionally, platelet activity was studied after exposure to intermittent hypoxia (IH) in vitro and compared to those from normoxia (NOX) and sustained hypoxia (SH). Levels of GPIIb/IIIa (p<0.02), P-selectin (p<0.02), PECAM-1 (p<0.01), and LAMP-3 (p<0.01) on platelets surfaces, fibrinogen (p<0.03) and TF (p<0.01) levels in plasma, and ROS levels in thrombin stimulated platelets (p<0.03) of OSA patients were significantly increased. Platelet/PMNs (p<0.01) and platelet/monocytes (p<0.002) interactions were significantly higher in OSA and correlated with apnea/hypopnea index. These interactions were attenuated by application of dental device (platelet/PMNs- p<0.06; platelet/monocytes -p<0.03). There were significant increases in platelet/PMNs (p<0.01) and platelet/monocytes (p<0.02) interactions and in levels of fibrinogen (p<0.01) and TF (p<0.02) after omitting CPAP for a single night from otherwise treated OSA patients. In vitro treatment with IH and SH also significantly induced the expression of GPIIb/IIIa, P-selectin, and ROS production in thrombin stimulated platelets. NADPH oxidase was highly activated for ROS production under IH, but in SH treatment. Exposure to IH induced platelet/PMNs interactions. Also, inhibition of PMNs’ apoptosis under IH conditions was more pronounced in presence of platelets than in PMNs’ cultures alone. It was established that one of the platelet pathways inhibiting PMNs’ apoptosis under IH conditions is through NFκB activation. Collectively, findings of this research demonstrated hypoxia-related up-regulation of platelet activation in OSA patients. This results in increased platelet/leukocytes interactions, which promotes pro-inflammatory platelet and leukocyte secretion and their possible adhesion to the endothelium, a mechanism that may lead to endothelial cell injury and consequently to the development of cardiovascular diseases. Effective treatment attenuated platelet/leukocytes interactions, thus decreased the risk of atherogenic processes.