OLIVE OILS AND HEALTH 160 13.1. What is haemostasis? Haemostasis is a complex process whose function is to limit blood loss from an injured vessel in which the cells covering the inner arterial wall play a key role. These cells form the vascular endothelium which is in direct contact with the bloodstream, and the subendothelium, an extracellular protein matrix together with connective tissue. The vascular endothelium hinders platelet activation through prostacyclin and nitrogen monoxide synthesis, both strong vasodilator molecules which widen the vessel thus promoting the passage of blood. The vascular endothelium inhibits clot formation through the synthesis of tissue factor (TF) inhibitors, such as thrombomodulin and heparin. It also regulates clot dissolution through tissue plasminogen activator (t-PA) production which breaks plasminogen starting the fibrinolysis process. The endothelium is thus covered by the subendothelium where platelet adherence occurs and blood coagulation is activated. Under healthy conditions, platelets do not reach the subendothelium. When a blood vessel is damaged, the subendothelium extracellular matrix enters in contact with the bloodstream and platelet activation occurs triggering haemostasis. High risk cardiovascular patients present a procoagulant state due to an increase in LDL cholesterol (cholesterol associated with low density lipoproteins). The loss of blood vessel diameter regulation can promote vascular thrombosis which is a key factor for the onset and development of atherosclerotic plaques. Atherosclerosis is a complex pathological process. Recent studies have highlighted the role of the thrombus phenomena in atheroma plaque formation. The current atherothrombosis concept includes two main processes involved in coronary disease: 1. atherosclerosis which focuses on atheroma plaque formation and development, and 2. thrombosis which focuses on the mechanisms and consequences of an acute failure of blood delivery to organs and tissues. The haemostatic system influences atherosclerosis and atherothrombosis onset and development. Microtears in atherosclerotic plaques, and their repair by the haemostatic system, progressively narrow the blood vessel lumen which can be finally occluded promoting a coronary event. The importance of haemostasis in coronary disease is reflected by the fact that the main pharmacological agents used for its treatment and prevention are platelet aggregation inhibitors such as acetylsalicylic acid and clopidogrel. High risk cardiovascular patients thus present a strong prothrombotic state which includes platelet activation (primary haemostasis), coagulation, (secondary haemostasis), and fibrinolysis. Several experimental studies indicate that these mechanisms can be modulated by extra virgin olive oil (EVOO) (Figure 13.1).
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