LIPID-PEROXIDATION BY ACTIVATED PLATELETS - A POSSIBLE LINK BETWEEN THROMBOSIS AND ATHEROGENESIS

Generation of reactive oxygen species (ROS) by platelets was detected by a cyano-tetrazolium dye (CTC) which forms fluorescent formazan on t he cell surface upon reduction. Fluorescence was quantitated by a dens itometric device. Resting platelets in plasma produced significant flu orescence (P < 0.0001), and addition of thrombin enhanced the fluoresc ence of the coagulated platelet mass even further (by 2 h, a 6- and 8- fold increase over fluorescence of platelet-free plasma was measured, respectively). Blood containing CTC was perfused through a glass capil lary tubing and the action of shear forces resulted in the formation o f an occlusive platelet thrombus. Such thrombi (formed either from who le blood or platelet-rich plasma) were intensely fluorescent, indicati ng formation of ROS in the platelet mass (a 10- and 8-fold increase in fluorescence over coagulated plasma, respectively). Lipid peroxide co ntent of resting platelets in platelet-rich plasma was doubled over 24 h storage, while addition of thrombin caused a 7.4-fold increase (P < 0.0001) of lipid peroxides in the retracted platelet-rich plasma-clot . Transition metal chelator and antioxidant prevented lipid peroxidati on by platelets in response to thrombin. Thrombin activation of (washe d) platelets in plasma-free medium caused only 1.4-fold increase in ox idation of added low density lipoprotein (LDL). In contrast, thrombin activation of platelets suspended in de-lipidated autologous plasma re sulted in a 5.25-fold increase (P < 0.0001) in LDL oxidation. Generati on of ROS and lipid peroxides by platelets can be an important mechani sm through which thrombotic events contribute to atherogenesis.