Platelets and Megakaryocytes in Vascular Disease

Predictors of Symptom Development in Intermediate Carotid Artery Stenosis: Mean Platelet Volume and Platelet Distribution Width

Platelets play an important role in the pathogenesis of atherothrombosis. Platelet activation is associated with increased mean platelet volume (MPV) and platelet distribution width (PDW). In this study, we investigated the relation of MPV and PDW with the risk of stroke in patients with intermediate (50%-70%) carotid artery stenosis. A total of 254 patients (115 symptomatic and 139 asymptomatic) with intermediate carotid artery stenosis were enrolled in this study. Symptomatic and asymptomatic patients were compared in regard to MPV and PDW. Mean platelet volume was significantly greater in the symptomatic group compared with the asymptomatic group (11.1 and 9.4 fL, respectively; P < .001). Platelet distribution width was significantly greater in the symptomatic group compared with the asymptomatic group (15.0% and 11.9%, respectively; P < .001). Multivariate regression analysis showed that an MPV ≥10.2 fL and a PDW ≥14.3% were independent predictors of developing symptomatic carotid artery stenosis. Mean platelet volume and PDW are increased in the presence of symptomatic intermediate carotid artery stenosis. Increased MPV and PDW may be independent predictors of developing symptomatic carotid artery plaque.

Hantavirus infection-induced thrombocytopenia triggers increased production but associates with impaired aggregation of platelets except for collagen

INTRODUCTION

We evaluated the mechanisms of thrombocytopenia encountered in hantavirus disease by studying platelet production together with platelet aggregation and deposition to collagen surface.

PATIENTS AND METHODS

The study group consisted of 31 prospectively recruited, consecutive, hospitalized patients having acute Puumala hantavirus infection. Blood samples were collected acutely and at the control visit and subjected to analysis in Sysmex® XE-5000 to capture mean platelet volume (MPV) and immature platelet fraction (IPF%). Platelet aggregation under low shear rate conditions was assessed with impedance aggregometry Multiplate®, whereas platelet function analyzer (PFA)-100® was applied under blood flow of high shear forces.

RESULTS

IPF% was 3.1-fold higher acutely compared with the control (median 7.4%, range 2.0-23.8% vs. median 2.4%, range 1.4%-5.2%, p<0.001) tightly associating with the low platelet count (r=-0.76, p<0.001). Accordingly, acute MPV was high (median 11.4f l, range 9.4-13.1 fl vs. median 10.5 fl, range 9.0-12.0 fl, p=0.003). Acute platelet aggregation in Multiplate® was decreased to all agonists compared with the later control (p<0.05 for all agonists). Aggregation capacity associated with thrombocytopenia (for all agonists r ≥ 0.81, p<0.001), but impaired aggregation occurred also among patients with a nearly normal platelet count. Triggered by collagen, 20% of values were below reference range, while 73% of responses were low with thrombin receptor activating peptide. Significantly, under high shear platelet deposition to collagen surface was normal despite thrombocytopenia.

CONCLUSIONS

During acute hantavirus disease, platelet aggregation is impaired especially when induced with thrombin. Platelet adhesive mechanisms on collagen are intact despite thrombocytopenia while thrombopoiesis is active.

Original articles: increased platelet volume in patients with adult polycystic kidney disease

Platelet volume is a measure of platelet function. An increased platelet volume is found in acute vascular syndromes and may have a causative role and predict outcome. Patients with autosomal dominant polycystic kidney disease (APKD) are at increased risk of developing, and dying from, premature vascular disease. We hypothesized that platelet volume might be altered in patients with APKD. Platelet volume was measured in 16 normotensive APKD patients with normal renal function and 16 normal volunteers pair-matched for age, gender, race and body mass index. Mean platelet volume was increased by 0.4 fl (95% confidence limits 0.1 to 0.9, 2P=0.017) in patients with APKD as compared with normal subjects: median 8.4 fl (0.7) versus 8.0 fl (0.3) respectively. In contrast, platelet count was lower by 63 × 10(9)/1 (-5 to -108, 2P = 0.031): 225 (40) × 10(9)/1 versus 280 (35) × 10(9)/1 while the platelet mass was not different, -0.36 ml/l (-0.81 to 0.02, 2P=0.070): 1.82 (0.30) ml/l versus 2.28 (0.38) ml/l. Platelet volume and count were inversely correlated across the two groups, r(s)= -0.342 (2P=0.055). Serum levels of erythropoietin, a hormone that contributes to the regulation of thrombopoeisis, were not different between the APKD patients and normal controls, 35 U/1 (-71 to 120, 2P=0.42): 107 U/I (53) versus 84 U/I (57). Although erythropoietin did not correlate with platelet volume, R., = -0.185 (2P =0.36), it was positively associated with platelet count, R., = 0.465 (2P=0.029) and platelet mass, r(s) = 0.466 (2P= 0.028). Since an increased platelet volume is associated with platelet hyperactivity, the increased platelet volume in APKD may be a marker, or even contribute to the development, of premature vascular disease and sudden cardiac death in patients with APKD.

The relationship of mean platelet volume with the risk and prognosis of cardiovascular diseases

BACKGROUND

Mean platelet volume (MPV) is arousing increasing interest as a new independent cardiovascular risk factor.

AIM

To provide a comprehensive review on the biological significance, the main determinants and the prognostic implications of MPV.

METHODS

A literature search was performed using key terms, such as 'MPV' or 'mean platelet volume', together with 'stroke', 'myocardial infarction' and 'diabetes and 'obesity'.

RESULTS

Large platelets are likely more reactive: elevated MPV values are associated with a shortened bleeding time and increased thromboxane B2 plasma levels. Thus, MPV could be considered an indicator of platelet function. Platelet size is mainly determined in the bone marrow during megakaryocytopoiesis, and subsequently does not substantially change. MPV is only partially regulated by thrombopoietin: in fact, growth factors and cytokines may also elicit the production of larger and more reactive platelets in the bone marrow, in the presence of conditions capable of increasing their concentrations, such as obesity, endothelial dysfunction and possibly myocardial and cerebral ischaemia. This phenomenon could play an important role in vascular diseases. In fact MPV is predictive of stroke, acute myocardial infarction (AMI) and restenosis of coronary angioplasty, is increased in the presence of obesity, diabetes mellitus, metabolic syndrome, AMI and stroke and has been shown to have a prognostic significance in patients with stroke and AMI.

CONCLUSION

In assessing whole blood count, MPV should not be undervalued, as its increase should suggest a careful assessment of cardiovascular risk.

Association of mean platelet volume with risk of stroke among 3134 individuals with history of cerebrovascular disease

BACKGROUND AND PURPOSE

Mean platelet volume (MPV) is positively associated with measures of platelet activity and may be a useful indicator of the risk of vascular events in a variety of patient groups.

METHODS

The association of MPV with the risk of stroke was assessed in the Perindopril Protection Against Recurrent Stroke Study (PROGRESS). All participants had a history of cerebrovascular disease at baseline, and analyses were adjusted for the effects of potential confounders.

RESULTS

The study followed 3134 individuals for an average of 3.9 years (mean age, 65 years; 71% male; average MPV, 10.0 fL). Three hundred eighty-three individuals had 402 stroke events, and 160 had major coronary events. MPV was positively associated with the risk of stroke, with an 11% increased relative risk (95% CI, 3% to 19%) of stroke per femtoliter greater MPV. There was no clear association of MPV with the risk of major coronary events (9% decreased relative risk; 95% CI, -23% to 7%). Perindopril did not alter MPV.

CONCLUSIONS

MPV is an independent predictor of the risk of stroke among individuals with a history of stroke or transient ischemic attack. The measurement of MPV may add useful prognostic information for clinicians managing patients with a history of cerebrovascular disease.

Platelets and stroke

Platelets are anucleate cells with little or no capacity for de novo protein synthesis. Their potential haemostatic reactivity is established at or before thrombopoiesis by their precursor cell, the bone marrow megakaryocyte. In some pathologic conditions, the megakaryocyte-platelet-haemostatic axis (MPHA) becomes perturbed, resulting in the formation of hyperfunctional platelets which may contribute to the development of vascular disease or an acute thrombotic event such as ischaemic stroke or myocardial infarction. Laboratory measurements of platelet function have established that platelet reactivity is accentuated in acute ischaemic stroke, particularly following cortical rather than lacunar infarction. Whether accentuated platelet function is a cause or a consequence of stroke is not yet clear, but it is likely that patients with certain risk factor profiles have some degree of platelet activation preceding the stroke. Further work into the MPHA is required to establish whether enhanced post-stroke platelet reactivity can be referred to the megakaryocyte. The antiplatelet agents tested to date are effective in secondary but not primary prevention of stroke. This probably reflects the diverse pathophysiology of stroke: accentuated platelet function is only likely to be a significant factor in cortical stroke.

Reduced platelet serotonin content and release in familial hypercholesterolaemia

Plasma and platelet serotonin (5-HT) concentrations, and resting and collagen-induced 5-HT release in platelet-rich plasma were studied in normal and familial hypercholesterolaemic (FH) subjects. Platelet 5-HT concentrations were significantly reduced (-37%, P < 0.01) in FH patients whilst mean plasma concentrations, although increased, were not significantly different from those in normal subjects. Platelet 5-HT correlated negatively with plasma cholesterol when the data for normal subjects and FH, patients were combined (r = -0.48, P = 0.005). It also correlated negatively with low-density lipoprotein (LDL) (FH data, r = -0.59, P = 0.03; normal and FH data, r = -0.49, P = 0.004) but positively with high-density lipoprotein (HDL) (FH r = 0.79, P = 0.001; normal and FH, r = 0.37, P = 0.03). Collagen (5-160 micrograms/ml) stimulated platelet 5-HT release occurred in a concentration-dependent manner. In FH patients stimulated 5-HT release was reduced (10 micrograms/ml collagen, -40%, P < 0.05) and accompanied by increased collagen EC50 values (P < 0.02). Resting 5-HT release was increased substantially in FH patients but not significantly. Our data provide evidence for a relationship between circulating cholesterol and platelet serotonergic mechanisms. It is proposed that abnormalities relating to platelet-plasma 5-HT dynamics, perhaps due to enhanced platelet activity or decreased platelet uptake, may contribute to the cardiovascular complications in FH.

Platelet size and left ventricular hypertrophy in hypertensive patients over 50 years of age

Both mean platelet volume (MPV) and left ventricular hypertrophy have been described as associated with increased risk for vascular events. Seventy-six hypertensive patients (37 M and 39 F) over 50 years of age were studied. They were divided into subgroups according to the presence of left ventricular hypertrophy (LVH = LV mass index > 125 g m-2, when LV mass was assessed by M-mode echocardiography according to Penn's Convention). MPV was 3% higher in hypertensive patients with LVH compared with those without LVH (P > 0.05) and it was associated with the occurrence of LVH (chi-square = 8.44, P = 0.042). MPV significantly correlated with left ventricular mass index (r = 0.298, P = 0.004) and interventricular septum thickness (r = 0.231, P = 0.022). Both correlations remained significant after adjustment for age, blood pressure and glycaemia. MPV seemed to be associated with increased left ventricular mass and interventricular septum thickness in middle-aged to elderly hypertensive patients.