Shear-Induced Platelet Aggregation in Normal Subjects and Stroke Patients

Abstract

SummaryElevated levels of shear stress that occur in stenotic arteries may induce platelet aggregation and initiate thrombosis. Shear-induced platelet aggregation (SIPA) was studied in groups of ischemic stroke patients and normal subjects using a viscometric-flow cytometric technique. Twenty-three patients who sustained an ischemic stroke that was not of cardiac origin were included in this study, and were classified either as atherosclerotic (n = 15) or as lacunar (n = 8) stroke patients. The results show that shear stresses at the levels which occur in arteries partially occluded by atherosclerosis or vascular spasm strongly activate and aggregate platelets, and this response is much more pronounced in non-lacunar stroke patients who had documented atherosclerotic disease of their cerebral vessels. SIPA is not affected by the time of blood drawing after the onset of stroke suggesting that these platelet abnormalities are not transient but chronic. Furthermore, the extent of platelet activation detected by an anti-P-selectin monoclonal antibody and the proportion of neutrophil-platelet aggregates circulating in vivo are significantly higher in the atherosclerotic stroke patients studied at least one month after the onset of stroke. The results indicate that the enhanced platelet responses observed in atherosclerotic stroke patients are not consequences of ischemia, and therefore both platelet activation and elevated SIPA may be considered as important risk factors for stroke. The methodology developed in this work may be useful for characterization of platelet reactivity, and may contribute to our understanding of thrombotic mechanisms.

Comparative Antiplatelet Efficacy of a Novel, Nonpeptide GPIIb/IIIa Antagonist (XV454) and Abciximab (c7E3) in Flow Models of Thrombosis

“…Subsequently, specimens were diluted with 2 mL of 1% formaldehyde and analyzed in a FACScan (Becton-Dickinson) flow cytometer as described elsewhere in detail. 17,23,24 Binding of fluoresceinated CD42b (anti-GPIb), XL086 (an analogue of XV454), 28 or abciximab to platelets was calculated by measuring the mean FITC fluorescence intensity of at least 5000 platelets, which were identified on the basis of their characteristic forward-and side-scatter profiles in citrated blood specimens in the presence or absence of GPIIb/IIIa antagonists. At each experimental state, the FITC fluorescence values were normalized by using as a reference the pre-XV454/preabciximab incubation (control specimen) fluorescence levels.…”

“…A rheometric/flow cytometric method was used to monitor direct shear-induced platelet aggregation in the bulk phase. 17,23,24 In addition, we combined a parallel-plate perfusion chamber with a computerized epifluorescence video microscopy system to visualize in real time and quantify the adhesion and subsequent aggregation of human platelets in whole blood flowing under conditions of abnormally elevated shear stress (1500 s…”

Effects of Abciximab, Ticlopidine, and Combined Abciximab/Ticlopidine Therapy on Platelet and Leukocyte Function in Patients Undergoing Coronary Angioplasty

“…Fixed samples were analyzed using the FACScan flow cytometer. The number of platelet-leukocyte aggregates was determined by identifying the leukocytes by PerCP-fluorescence, gating on each leukocyte subpopulation, 29,30 and measuring the amount of FITC-fluorescence above background in each leukocyte subpopulation (Figure 1). …”

Platelet aggregation in citrated whole blood of the first trimester of pregnancy

“…When citrated whole blood is stirred or mixed in some other way, spontaneous platelet aggregation occurs as a result of platelet activation [1][2][3][4]. A hematology analyzer (CELL-DYN Sapphire Hematology System ® ; Abbott Diagnostics, Abbott Park, IL) [5] with a newly developed software package can specifically count the number of platelet aggregates (PA) in citrated whole blood.…”