Masako Yamazaki

Measurement of platelet fibrinogen binding and p-selectin expression by flow cytometry in patients with cerebral infarction.

We determined the percentages of fibrinogen-bound and P-selectin-expressed platelets in whole blood using flow cytometry in 254 patients with various cerebral infarction subtypes, as well as in 30 age-matched controls. Patients with atherothrombotic stroke showed significant increases in both fibrinogen-bound and P-selectin-expressed platelets. Patients with lacunar stroke also showed significant increases in both of them, but the percentage of P-selectin expression was significantly lower than that in atherothrombotic stroke. Patients with cardioembolic stroke showed a significant increase in P-selectin-expressed platelets without any increase in fibrinogen-bound platelets. Platelet fibrinogen binding and P-selectin expression were significantly lower in patients treated with ticlopidine but not with aspirin than in those not treated with any antiplatelet agent, and were lowest in those treated with both ticlopidine and aspirin. Our findings suggest that expression of adhesion molecules on platelet membrane surface differs among the patients with subtypes of ischemic stroke and differs among the types of antiplatelet regimens.

Flow cytometric analysis of reticulated platelets in patients with ischemic stroke

Reticulated platelets are newly formed platelets containing a residual amount of RNA, and percentage of reticulated platelets (%RP) has been shown to reflect platelet turnover. Recently, a new flow cytometric approach for analyzing %RP in patients with thrombocytopenic disorders has been reported. We measured %RP by flow cytometry using the fluorescent dye thiazole orange (TO) to evaluate platelet kinetics in patients with different clinical categories of ischemic stroke. Patients with ischemic stroke were categorized into lacunar (n=25), atherothrombotic (n=26) and cardioembolic stroke (n=17). %RP was significantly higher in patients with cardioembolic stroke than in controls (n=140). Stepwise multiple regression analysis also showed cardioembolic stroke (R(2)=0.14) to be significant independent predictors of %RP among stroke patients even after adjustment for other factors. We concluded that %RP is increased in patients with cardioembolic stroke, which may reflect increased platelet turnover as a consequence of platelet consumption during thrombogenesis.

New modalities and aspects of antiplatelet therapy for stroke prevention.

Antiplatelet therapy is indicated for secondary prevention of ischaemic stroke. The first-line antiplatelet agent is aspirin. The effect of aspirin is, however, very limited, and this limited effect of aspirin is argued with termed ‘aspirin resistance’. Strategies against aspirin resistance may include alternative use of other antiplatelet agents, combination of aspirin with other antiplatelet agents and investigation into molecular targets to develop novel antiplatelet agents. Progress in antiplatelet therapy should be directed at further reducing the risk of ischaemic events including ischaemic stroke without increasing the risk of haemorrhagic events including haemorrhagic stroke.

Clinical characteristics of stroke patients with antiphospholipid antibodies

Background: Antiphospholipid syndrome is important as a cause of ischemic stroke, although clinical characteristics of the syndrome are not well documented. Methods: We analyzed differences in clinical characteristics between 40 antiphospholipid-antibody (aPL)-positive and 40 aPL-negative stroke patients. Results: Stroke patients with aPL were significantly younger and were more likely to be women in comparison with stroke patients without aPL. Valvular heart disease, neurological complications and hematological disorders were more frequent in the aPL-positive group. The mean value of thrombin-antithrombin III complex was significantly lower in the aPL-positive group. Cerebral infarctions in the carotid system were less and large-artery lesions more frequent in the aPL-positive patients. Conclusions: Stroke patients with aPL have clinical characteristics distinct from stroke patients without aPL.

Effects of dipyridamole and aspirin on shear-induced platelet aggregation in whole blood and platelet-rich plasma.

Background: Shear-induced platelet aggregation (SIPA) is an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. Methods: We investigated the in vitro effects of dipyridamole (DP) and acetylsalicyclic acid (ASA) on SIPA in whole blood and platelet-rich plasma (PRP). Results: In whole blood, DP 20 µM significantly inhibited SIPA, while DP 5 µM or ASA 5 or 20 µM did not. SIPA in whole blood was, however, significantly inhibited by the combination of 5 or 20 µM of DP and ASA. SIPA in PRP was not inhibited by any concentration of DP or ASA, alone or in combination. Conclusions: These results suggest that DP has an effect on red blood cells and that ASA enhances the inhibitory effect of DP on SIPA in whole blood. These effects may be related to the additive effect of combination therapy with DP and ASA on stroke prevention.

Two Soluble Isoforms of Receptors for Advanced Glycation End Products (RAGE) in Carotid Atherosclerosis: The Difference of Soluble and Endogenous Secretory RAGE

BACKGROUND Advanced glycation end products (AGEs) promote atherosclerosis through binding to their receptor, RAGE. Since soluble RAGE (sRAGE) and endogenous secretory RAGE (esRAGE) may suppress AGEs-RAGE signaling, we examined the usefulness of sRAGE and esRAGE as biomarkers of early-stage atherosclerosis. METHODS Serum sRAGE and esRAGE levels were measured in 284 subjects with no history of atherothrombotic diseases. The subjects were divided into high-sRAGE and low-sRAGE groups and high-esRAGE and low-esRAGE groups based on respective median values. We investigated the relationships between these parameters and the following factors: number of metabolic components, maximum intima-media thickness of the common carotid artery (IMT Cmax), carotid plaque calcification, and asymptomatic cerebral white matter lesions. RESULTS The low-sRAGE and low-esRAGE groups exhibited significantly more components of metabolic syndrome than the high-sRAGE and high-esRAGE groups, respectively. IMT Cmax was significantly higher in the low-sRAGE and low-esRAGE groups. Low-sRAGE levels were significantly associated with carotid plaque calcification. Multiple linear regression analysis identified body mass index (BMI), age, and high-sensitivity C-reactive protein as determinants of sRAGE, whereas only BMI was identified as a determinant of esRAGE. CONCLUSIONS We demonstrated that sRAGE and esRAGE are associated with atherosclerotic risk factors in early-stage atherosclerosis, suggesting that their levels evolve in correlation with those of metabolic components and inflammation. Interestingly, low-sRAGE and esRAGE levels are associated with high IMT Cmax, but only low-sRAGE levels were associated with carotid plaque calcification. Thus, sRAGE and esRAGE may reflect different aspects of atherosclerosis in its early stage.

Platelet activation and antiplatelet therapy in patients with ischemic stroke

Abstract In patients with ischemic stroke, findings of platelet activation are frequent in platelet function tests. They include increases in plasma levels of beta-thromboglobulin and platelet factor 4, shortening of platelet survival and increasing of platelet lysis, enhancing of shear-induced platelet aggregation (SIPA), and increasing of reticulated platelets as well as platelet fibrinogen binding (PFB) and P-selectin expression (PSE). Aspirin can reduce vascular events including stroke, myocardial infarction and vascular death in high-risk patients with occlusive vascular disease. Aspirins effect on vascular events is J-shaped, which appeared to be related to the effects on platelet aggregation and release reaction as well as prostaglandin synthesis. Thienopyridines can reduce vascular events even more than aspirin. SIPA was inhibited by thienopyridines but not by aspirin. Combination of aspirin and dipyridamole has an additive effect on preventing subsequent stroke. Aspirin enhanced an inhibitory effect of dipyridamole on SIPA in whole blood. PFB and PSE were not inhibited by aspirin but were partially inhibited by ticlopidine, and markedly inhibited by aspirin plus ticlopidine. Glycoprotein (GP) IIb/IIIa inhibitors can block the final common pathway of platelet aggregation. However, PSE and platelet-derived microparticle formation induced by shear stress were never inhibited at lower concentrations and were rather enhanced at higher concentrations of GP IIb/IIIa inhibitors. These results might be related to the fact that many oral GP IIb/IIIa inhibitors fail to show efficacy in patients with acute coronary syndrome.

Measurement of residual platelet thrombogenicity under arterial shear conditions in cerebrovascular disease patients receiving antiplatelet therapy.

Essentials A consensus methodology for assessing the effects of antiplatelet agents has not been established. Measuring platelet thrombus formation (PTF) for evaluating antiplatelet effects was assessed. PTF differentially reflected antiplatelet effects compared to other tests. PTF may be associated with the severity of carotid or intracranial arterial stenosis.

Platelet Activity and Antiplatelet Therapy in Patients with Ischemic Stroke and Transient Ischemic Attack

Ischemic stroke and transient ischemic attack as well as coronary and peripheral artery diseases are platelet-dependent disease states that are categorized as atherothrombosis because they are mainly attributable to the obstruction of brain arteries by platelet-rich thrombi. Indeed, many platelet function tests demonstrate evidence of platelet activation in these patients.