Combined Effect of Shear Stress and Secondhand Smoke on Platelet Activation and Aggregation

Abstract

Platelets play important role in hemostasis (physiological), thrombosis and atherosclerosis (pathological). Changes in functional responses of platelets, due to presence of biochemical and biomechanical agonists, can contribute in onset and progression of cardiovascular diseases (CVD). Secondhand smoke (SHS) and altered shear stress in the vasculature are considered as biochemical and biomechanical risk factors for CVD. Though previous studies have investigated the effects of these two factors on change of platelet functions, none of the study have focused on how SHS and altered shear stress together can modulate platelet activation and aggregation. The main objective of this study was to investigate the combined effect of SHS and altered shear stress on platelet functions. Experiments were conducted in vitro on platelets by applying constant (1 and 3 Pa) or physiologically relevant dynamic (normal and elevated) shear stress in a cone-plate shearing device for 60 min, with or without the exposure of SHS (smoke of 1 cigarette/5 L). Platelet activation was quantified by platelet surface P-selection expression using flow cytometry. Following the same procedure, platelet surface GPIbα and GPIIb expressions were also measured. Platelet aggregation parameters were measured from TRAP induced platelet aggregation using Chrono-log aggregometer. Simultaneously, Thromboxane B2 generation was quantified using a sandwich ELISA (enzyme immunoassay) approach. Results from this study indicated that, SHS enhanced shear induced platelet activation represented by enhanced platelet surface P-selectin expression. SHS with elevated constant (3Pa) shear stress significantly increased P-selectin expression. However, platelet surface GPIbα and GPIIb expressions remained unaffected in presence of the combined exposure. In addition, SHS and shear stress combinedly altered platelet aggregation response. Combined exposure of SHS and shear stress had no significant effect on accumulated Thromboxane B2. Thus, the observations of this study indicated that, exposure to environmental SHS can potentially cause detrimental effects on the cardiovascular system by enhancing platelet activation, especially in patients with CVD.