Duration of exposure to high fluid shear stress is critical in shear-induced platelet activation-aggregation

Abstract

Platelet functions are increasingly measured under flow conditions to account for blood hydrodynamic effects. Typically, these studies involve exposing platelets to high shear stress for periods significantly longer than would occur in vivo. In the current study, we demonstrate that the platelet response to high shear depends on the duration of shear exposure. In response to a 100 dyn/cm2 shear stress for periods less than 10-20 sec, platelets in PRP or washed platelets were aggregated, but minimally activated as demonstrated by P-selectin expression and binding of the activation-dependent alphaIIbbeta3 antibody PAC-1 to sheared platelets. Furthermore, platelet aggregation under such short pulses of high shear was subjected to rapid disaggregation. The disaggregated platelets could be re-aggregated by ADP in a pattern similar to unsheared platelets. In comparison, platelets that are exposed to high shear for longer than 20 sec are activated and aggregated irreversibly. In contrast, platelet activation and aggregation were significantly greater in whole blood with significantly less disaggregation. The enhancement is likely via increased collision frequency of platelet-platelet interaction and duration of platelet-platelet association due to high cell density. It may also be attributed to the ADP release from other cells such as red blood cells because increased platelet aggregation in whole blood was partially inhibited by ADP blockage. These studies demonstrate that platelets have a higher threshold for shear stress than previously believed. In a pathologically relevant timeframe, high shear alone is likely to be insufficient in inducing platelet activation and aggregation, but acts synergistically with other stimuli.

Platelet Activation Due to Hemodynamic Shear Stresses: Damage Accumulation Model and Comparison to In Vitro Measurements

“…Platelets in platelet-rich plasma (PRP) sheared at 20 dynes/cm 2 for 60 seconds showed approximately 3% activation, as measured by CD62P expression. 40 This value is higher than the 1.65% to 1.67% activation for the 5-minute samples in our T1 = 0 seconds waveform experiments, which shows that constant shear stress yields higher activation values than variable shear stress, where platelets are exposed to a higher value for only a fraction of the total exposure time. Furthermore, platelets in whole blood exposed to a constant shear rate 420 s −1 (corresponding to a shear stress of 14.7 dynes/cm 2 , assuming whole blood viscosity of 3.5 cP) did not express a significant increase in GP IIb/IIIa activation (approximately 1%) at 4.5 minutes, whereas Annexin V binding was detected to be 1.5% to 2%.…”

Atherosclerotic geometries exacerbate pathological thrombus formation poststenosis in a von Willebrand factor-dependent manner

“…A useful measure for the variable wall shear rate to which platelets are exposed is the integral shear history, i.e., the product of shear rate and exposure time (23). A reported threshold of the integral shear history for platelet aggregation in response to constant shear is 50 Pa·s (24).…”

A mechanobiological investigation of platelets

“…The cellular components of blood (-46% of the volume in human blood) consist primarily of red blood cells (RBCs) (or erythrocytes) (-98% in cell number), which may stimulate blood clot formation upon release of an intracellular aggregation agonist (i.e. ADP) (12). The remaining 2% of the cellular phase consists primarily of white blood cells (WBCs) (or leukocytes) and platelets (5, 13), which play major roles in immune and thrombotic processes, respectively.…”

“…This supposition was repeatedly discredited by several studies, namely those using rotational viscometer systems (56,12) that found that platelet activation depends on the presence of vWF and functional platelet glycoprotein complexes GP Ib-IX-V and GP Ilb-IIIa in conjunction with moderate shear stress magnitudes (26,59). This connection between rheologic and vascular factors is supported by the fact that mixing vWF with platelets in a static or stirred suspension will fail to generate a platelet response (26).…”

“…Assuming that the shear stress between laminae is proportional to the shear rate, defined as the change in velocity between two laminae (definition of a Newtonian fluid), then the blood flow through a uniform cylinder takes on a parabolic velocity profile with a maximum shear stress value at the periphery (26) Nevertheless, preliminary testing of thrombosis was predominantly performed in static and stirred mediums (12), which proved insufficient in characterizing thrombotic disease of the coronary and cerebrovascular dynamic circulation (48) since the magnitude of shear stress was low and varied in a complex and uncharacterized way (26). Improvements to mechanical models using circular flow tubes designed to replicate high shear stress in relatively short periods of time (25 - It is important to note that shear stress exposure is different for platelets that circulate through stenotic arteries (26,55), due to different transient exposure times and shear stresses (12). By contrast, platelets that accumulate in a growing thrombus are continuously exposed to shear until the ultimate occlusion of the vessel.…”