Petter Järemo

Individual variations of platelet inhibition after loading doses of clopidogrel

Abstract. Järemo P, Lindahl TL, Fransson SG, Richter A (Linköping University Hospital, Linköping, Sweden). Individual variations of platelet inhibition after loading doses of clopidogrel. J Intern Med 2002; 252: 233–238.

Elevated inflammatory parameters are associated with lower platelet density in acute myocardial infarctions with ST-elevation

OBJECTIVE Platelets and granulocytes play important roles in coronary disorders. We therefore, investigated platelet and granulocyte alterations in myocardial infarctions (MIs). PATIENTS AND STUDY DESIGN A total of 36 individuals having MI with raised ST-segments who were receiving thrombolytic therapy were studied. Sampling was carried out after thrombolysis within 24 h after hospital admission. After 3 to 6 months of recovery, 25 patients were reinvestigated. At the infarction, peak platelet density was determined using a special designed computerised apparatus. In addition, we did counts on platelets, neutrophils and monocytes. Moreover, plasma levels of soluble P-selectin, myeloperoxidase and interleukin 6 were determined to estimate the degree of platelet, neutrophil and monocyte activation, respectively. Peak platelet density was analysed at the MI. All other parameters were determined at the acute event and at recovery. RESULTS At the MI, compared to the recovery, platelet counts were lower (P<0.001). In addition, increased neutrophil counts (P<0.001), elevated monocyte counts (P<0.001), enhanced myeloperoxidase (P<0.001) and interleukin 6 (P<0.001) levels were demonstrated. We failed to show elevated soluble P-selectin. Compared to individuals with ST-segment elevations and low platelet density (less than or = 1.058 kg/l), patients having peak platelet densities >1.058 kg/l displayed lower neutrophil counts (P<0.01) and decreased interleukin 6 levels (P<0.01). Furthermore, we demonstrate that individuals with higher inflammatory response at the MI had higher neutrophil (r = 0.6; P<0.01) and higher monocyte counts (r = 0.6; P<0.001) at recovery. CONCLUSION W conclude that MI is associated with an inflammatory response. However, a subgroup of patients having MI with ST-elevations and low peak platelet density was identified. Compared to subjects with higher platelet density, they had more severe inflammatory characteristics. The differences persisted during recovery.

P-selectin paradox and dementia of the Alzheimer type: Circulating P-selectin is increased but platelet-bound P-selectin after agonist provocation is compromised

Abstract Objective. Knowledge concerning the neurobiological importance of platelets in Alzheimers disease (AD) is sparse. P-selectin, which is located together with β-amyloid precursor proteins in platelet α-granules, is also found in endothelial cells. Upon activation, P-selectin is relocated to cell surfaces where it acts as a receptor. Subsequently, the protein is cleaved from the membrane, to then be circulated. We investigated P-selectin behavior in AD dementia. Methods. We recruited 23 persons diagnosed moderate AD and 17 healthy elders without obvious memory problems. Circulating P-selectin was analyzed using an ELISA technique and flow cytometry was used to measure surface-bound P-selectin. The latter measure was carried out without provocation (platelet activity) and after in vitro agonist stimulation (platelet reactivity). A thrombin-receptor activating peptide (TRAP-6) (74 μmol/L)) was used as a platelet agonist. Results. Soluble P-selectin was augmented in AD (p = 0.019) but platelet membrane-attached P-selectin did not differ from controls. AD diagnosis was associated with less surface-bound P-selectin after provocation. Significant results were obtained when 74 μmol/L TRAP-6 was used as a platelet agonist (p = 0.0008). Conclusion. 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.

Computerised method for recording platelet density distribution.

Abstract: In the present study a computerized apparatus was employed for scanning light transmission variations along test tubes containing density‐separated platelets. The device consists of a stepping motor, a stationary halogen lamp and a photopotentiometer connected to a personal computer. Anticoagulated whole blood was layered on a preformed continuous Percoll gradient having a density span from 1090 kg/l (bottom) to 1040 kg/l (top). After centrifugation at 3400g for 1.5 hours, high‐density cells (i.e. erythrocytes) pass through to the bottom of the test tube and the lighter platelets remain in the gradient. The test tube is moved by the computer between the halogen lamp and the photopotentiometer. Transmission variations along the gradient were recorded and registered in the computer. Density markers beads were used as an internal standard and platelet peak density was determined. After perforating the test tube the gradient was divided into 45 aliquots. In all fractions determination of platelet counts and mean platelet volume was carried out. In addition, in the aliquots having a platelet count > 20 × 1012/l the ratio β‐thromboglobulin per platelet was also determined. The platelet distribution in the gradient was illustrated graphically. A good agreement was found when comparing platelet distributions in the gradients and light transmission variations along the test tubes.

Inverse relationship between platelet density and reactivity alterations at coronary angiography

This work investigates relationships between platelet density and reactivity. 21 individuals subject to coronary angiography were studied. Peak platelet density was analyzed using a newly developed electronic device. The apparatus measures light transmission through test tubes containing density-separated platelets, thus allowing an estimation of the platelet distribution in the gradient. A flow cytometry technique was used for determining platelet reactivity after stimulating with ADP. Platelet counts, mean platelet volumes, peak platelet density and platelet reactivity were determined immediately before (day 1) and 24 h after cardiac catheterization (day 2). For all parameters changes during the day of angiography were compared with platelet density alterations. The subjects were divided into two groups according to density changes at angiography. Group 1 individuals showed density alterations (i.e. day 2 – day 1 value) ≧–8 × 10–5 kg/l. In contrast, group 2 subjects either displayed density changes <–8 × 10–5 kg/l or grossly disturbed platelet density patterns on day 2. Before angiography both groups had similar platelet counts and volumes. Then platelet reactivity when stimulating with ADP did not differ significantly between the two groups. After angiography, the number of fibrinogen-positive cells when stimulating with ADP rose by 6 ± 8% for group 2 patients. The corresponding figure for group 1 was –1 ± 6%. The difference was significant (p = 0.01). No such relationships were found when comparing density alterations and changes of platelet counts and volumes. We conclude that in this study platelet density alterations at coronary angiography are inversely related to variations of platelet reactivity.

Low-density platelet populations demonstrate low in vivo activity in sporadic Alzheimer disease

Platelets contain a substantial quantity of amyloid-precursor protein (APP) and β-amyloid. However, despite the large importance of APP and β-amyloid to dementia, little is known about platelets in sporadic Alzheimer dementia (AD). Furthermore, platelet heterogeneity influences human pathology and has been described to affect the progression of AD. This study investigated AD platelets with respect to density diversity and in vivo activity associated with density sub-fractions. We included 39 AD patients and used, as controls, 22 elderly individuals without apparent memory disorder. A continuous Percoll™ gradient covering the density span 1.04–1.09 kg/l provided the basis to divide platelets of whole blood into density fractions (n = 16). All platelet populations were evaluated accordingly. Platelet counts were determined electronically. A flow-cytometer was put to use to measure surface-bound fibrinogen as a measure of platelet in vivo activity. Samples obtained from patients diagnosed with sporadic AD contained platelets (fractions numbers 4–16) that circulated with significantly less surface-bound fibrinogen, i.e., their platelet activation in vivo was reduced, compared with controls. In particular, highly significant differences (p < 0.001) were obtained for the six less dense platelet populations (fractions numbers 11–16) when comparing sporadic AD with controls. In contrast, the densest AD platelets in fractions numbers 1–3 did not differ significantly from control cells with respect to in vivo platelet-bound fibrinogen. It is concluded that sporadic AD is characterized by lower density platelet populations that, while circulating, exhibited reduced activation. The clinical significance of this finding is unclear but these results suggest the importance of platelet heterogeneity in dementia as a topic for further investigation.

Alzheimer's disease is characterized by more low-density erythrocytes with increased volume and enhanced β-amyloid x-40 content

Alzheimers disease is characterized by more low-density erythrocytes with increased volume and enhanced β-amyloid x-40 content

Alzheimer and platelets: low-density platelet populations reveal increased serotonin content in Alzheimer type dementia.

INTRODUCTION Alzheimers disease (AD) is a progressive form of dementia characterized by an increase in the toxic substance β-amyloid in the brain. Platelets display a substantial heterogeneity with respect to density. They further contain a substantial amount of β-amyloid precursor protein. Platelets take up and store serotonin (5-HT) that plays an important role in the pathogenesis of severe depression. The current study aims to investigate platelet serotonin content in different platelet density populations. MATERIAL AND METHODS The study involved 8 patients (age 70±8 (SD) years) (3 females/5 males) with moderate AD. 6 healthy elderly subjects (age 66±9 (SD) years) (3 females/3 males) served as controls. The platelet population was divided into 17 subpopulations according to density, using a linear Percoll™ gradient. Platelets were counted in all fractions. After cell lysis an ELISA technique was employed to determine the 5-HT content in each platelet subfraction. RESULTS The two study groups did not differ significantly regarding platelet distribution in the gradients, but AD sufferers have a significantly higher 5-HT content (p<0.05) in the lighter platelet populations. DISCUSSION AD-type dementia proved to be associated with lighter platelets containing more 5-HT. It is possible that platelets from AD patients release less 5-HT. It is speculated that AD synapses are affected in a manner comparable to platelets, which could explain why 5-HT reuptake inhibitors are less effective in AD dementia.

Platelet Density Distribution in Essential Thrombocythemia

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.

Alzheimer's disease and granulocyte density diversity

The current study investigates circulating eosinophils and neutrophils in Alzheimer′s (AD) type dementia with respect to density (kg/L). The existence of β‐amyloid plaques in the brain is a feature of AD. Sporadic scientific reports indicate that the disease affects circulating neutrophils. In contrast, numerous publications investigate inflammatory reactions in AD brains. Locally, the plaques evoke a substantial inflammatory response involving activated microglia and astrocytes.