No abstract

This study describes apparently paradoxical P-selectin reactions in moderate AD. While soluble P-selectin was higher in the disease group, membrane-attached P-selectin without agonist stimulation was no different between the disease and control groups. In contrast, AD was linked to lower platelet reactivity. The current findings encourage further research into this P-selectin paradox and its relevance for AD and, perhaps, other types of dementia as well.

No abstract

Stroke is worldwide a leading cause of death and disability. Its etiology is regarded as heterogeneous. Platelets are implicated in its pathophysiology, but our understanding of their specific role is incomplete. Only sparse and conflicting information exists about platelet reactivity and activity in acute stroke. Some scientists take the view that platelets activate in conjunction with acute cerebral infarctions. Others put forward evidence corroborating the contrary notion. Increased soluble P-selectin as a sign of platelet and/or endothelial activity seems to be a feature of the disease. The latter point of view is opposed by other researchers. Due to these conflicting opinions, this study is devoted to platelet characteristics in acute cerebral infarctions. We studied subjects (n ¼ 72; age 74 AE 10(SD) years; 31 females) having acute stroke. As controls served atrial fibrillation (AF) patients (n ¼ 58; age 69 AE 7(SD) years; 12 females) subject to electrical cardioversion, a flow cytometer was put to use for measuring platelet reactivity and activity. After agonist provocation, both platelet bound P-selectin and fibrinogen were employed as estimates of platelet reactivity. Dilutions of a thrombin-receptor-activating peptide (TRAP-6) (74 and 57 mmol/l) (P-selectin and fibrinogen) and ADP (8.5 and 1.7 mmol/l) (fibrinogen only) were put to use as platelet agonists. Membrane-bound P-selectin without agonist stimulation served as a measure of in vivo platelet activation. Soluble P-selectin, as determined from a commercial ELISA, was used to assess platelet and/or endothelial activity. In acute stroke neither platelet-bound P-selectin nor fibrinogen after stimulation, i.e. reactivity, differed from AF controls. In contrast, lower platelet activity as judged from surface attached and circulating P-selectin without agonist stimulation proved to be a feature of cerebral infarctions. The p-values were p < 0.001 and p < 0.01, respectively. It is concluded that acute stroke is not associated with platelet reactivity platelets circulate less activated during the disease. It is evident that the mechanisms reflecting platelet reactivity and activity being investigated in this study play minor roles in stroke pathophysiology. New powerful platelet inhibitory drugs are currently introduced. To avoid major bleeding studies on platelet, behavior in acute stroke are necessary before including these medications in stroke treatment protocols.

Essential thrombocythemia (ET) is characterized by high platelet counts and a slightly increased bleeding risk. Why severe hemorrhage does not occur more frequently is not known. Variations of platelet density (kg/l) depend mainly on cell organelle content in that high-density platelets contain more α and dense granules. This study compares ET patients (n = 2) and healthy volunteers (n = 2) with respect to platelet density subpopulations. A linear Percoll™ gradient containing prostaglandin E₁ was employed to separate platelets according to density. The platelet population was subsequently divided by density into 16 or 17 subpopulations. Determination of platelet counts was carried out. In each density fraction, platelet in vivo activity, i.e. platelet-bound fibrinogen, was measured using a flow cytometer. To further characterize platelet subpopulations, we determined intracellular concentrations of CD40 ligand (CD40L) and P-selectin in all fractions. Patients and controls demonstrated similar density distributions, i.e. 1 density peak. High-density platelets had more surface-bound fibrinogen in conjunction with signs of platelet release reactions, i.e. with few exceptions they contained less CD40L and P-selectin. Peak density platelets showed less surface-bound fibrinogen. These platelets contained less CD40L and P-selectin than nearby denser populations. The light platelets had more surface-bound fibrinogen than peak platelets together with elevated concentrations of CD40L. In ET, the malignant platelet production could exist together with platelets originating from normal megakaryocytes. It is also possible that clonal megakaryocytes produce platelets covering the entire density span. The ‘normal’ density distribution offers a tenable explanation as to why serious bleedings do not occur more frequently.