P-Selectin expression, platelet aggregates, and platelet-derived microparticle formation are increased in peripheral arterial disease.

Platelet volume has been reported to be increased in vascular disease. Therefore, we studied the relationship of mean platelet volume and platelet count as well as flow cytometrically measured platelet size and platelet function in 50 patients with peripheral arterial disease and 50 healthy volunteers. Platelet activation was measured by P-selectin expression analysis on resting and on stimulated platelets, and the determination of platelet aggregates and platelet-derived microparticles using flow cytometry. P-Selectin expression on platelets was significantly elevated in patients suffering from peripheral arterial disease (all P<0.0001). Platelet aggregates (P<0.0001) and platelet-derived microparticles (P<0.0001) were significantly higher in the patient group compared with controls, whereas mean platelet volume and platelet count showed no significant differences. Platelet count was inversely related to mean platelet volume in patients and controls (r = -0.43, P<0.001). The present study supports the hypothesis of platelet hyperreactivity and circulating activated platelets in peripheral arterial disease. Mean platelet volume, and platelet count cannot be used as predictive markers for platelet activation in peripheral arterial disease patients.     

Thrombopoietin induces rapid resolution of thrombocytopenia after orthotopic liver transplantation through increased platelet production

Thrombopoietin (TPO) deficiency has been proposed as an important etiologic factor for thrombocytopenia in advanced-stage liver disease. To clarify the contributions of platelet production, platelet consumption, coagulation activation, and splenic sequestration to thrombocytopenia in liver disease, we studied TPO serum levels and markers of platelet production, platelet activation, and coagulation activation before and 14 days after orthotopic liver transplantation (OLT) in 18 patients with advanced liver cirrhosis. Thrombocytopenia before transplantation occurred with low-normal serum levels of TPO, normal levels of platelet and coagulation activation markers, and no increase in bone marrow production of platelets. TPO serum levels increased significantly on the first day after OLT, preceding the increase of reticulated platelets by 3 days and peripheral platelets by 5 days. Normalization of the peripheral platelet count occurred in most patients within 14 days of OLT, irrespective of the change in spleen size assessed by computed tomography volumetry. Normalization of platelet counts was not hampered by a certain degree of platelet activation observed during the steepest increase in the peripheral platelet count. Bone marrow production of platelets increased significantly within 2 weeks of transplantation. Low TPO serum levels with low platelet counts and without platelet consumption suggests low TPO production in end-stage liver disease. The rapid increase in TPO serum levels after transplantation induces an increase in the bone marrow production of platelets. Decreased TPO production in the cirrhotic liver is an important etiologic factor for thrombocytopenia in liver disease that is rapidly reversed by transplantation.     

PLATELET THROMBOPLASTIC FUNCTION IN POLYCYTHÆMIA AND THROMBOCYTHÆMIA

The platelet thromboplastic function levels in patients with primary disease of the bone marrow (polycythæmia vera and primary thrombocythæmia) were compared with the findings in patients whose polycythæmia or thrombocytosis was due to a definable underlying disorder. Of the patients with untreated polycythæmia vera, irrespective of the platelet count, 71% showed reduced platelet thromboplastic function, compared with only 12% of patients with secondary polycythæmia which was uncomplicated by either renal or liver disease. Similarly, the platelet thromboplastic function level was reduced in 100% of patients with untreated primary thrombocythæmia, compared with 47% of patients with elevated platelet numbers secondary to other associated diseases. The platelet thromboplastic function test was therefore useful in differentiating between primary and secondary polycythæmia. Normal platelet thromboplastic function virtually excluded a myeloproliferative disease (thrombocythæmia) in patients with raised platelet counts, irrespective of other hæmatological changes. The effect of ³²P in the two conditions due to primary disease of the bone marrow was to produce a rise towards normal platelet thromboplastic function. It is considered that the platelet defect in primary thrombocythæmia is a qualitative one, and not, as has been reported by others, a quantitative anticoagulant effect of high in-vitro platelet numbers.     

Platelet activity and cardiovascular risk in apparently healthy individuals: a review of the data

Cardiovascular disease is a major cause of morbidity and mortality. Numerous risk scores exist to identify healthy individuals at increased risk of developing cardiovascular disease. Although platelets are a key mediator in the pathogenesis of cardiovascular disease, the role of platelet activity measurements and the incidence of cardiovascular disease are uncertain. Platelet aggregometry—the most well studied method of platelet function testing—is associated with risk factors for cardiovascular disease. However, data supporting platelet aggregation and incident cardiovascular disease is conflicting. Plasma markers of platelet activation are promising candidates. Soluble CD40L and P-selectin are easily measured with a standardized ELISA, and there is some data to suggest an association with cardiovascular disease, but further studies are required. While mean platelet volume is a promising candidate, platelet count and bleeding time are not specific for platelet activity nor are they associated with cardiovascular disease in a healthy population. For this field to progress, we recommend large-scale, prospective studies that measure a battery of these platelet function tests in individuals without cardiovascular disease to better understand the associations, if any, between platelet activity and cardiovascular disease.     

Mean platelet volume: a useful marker of inflammatory bowel disease activity

OBJECTIVES: We investigated whether the mean platelet volume would be a useful marker in the evaluation of inflammatory bowel disease activity. METHODS: Complete blood count, C-reactive protein, erythrocyte sedimentation rate, serum thrombopoietin and erythropoietin, plasma beta-thromboglobulin, and platelet factor 4 were measured in 93 patients with ulcerative colitis, 66 patients with Crohn's disease, and 38 healthy blood donors. Disease activity was assessed by the Clinical Colitis Activity Index in patients with ulcerative colitis and by the Crohn's Disease Activity Index in patients with Crohn's disease. RESULTS: Mean platelet count was increased in patients with active compared to inactive ulcerative colitis (p < 0.05), and in patients with active compared to inactive Crohn's disease (p = 0.0002) or healthy controls (p < 0.0001). On the other hand, mean platelet volume was significantly decreased in patients with active compared to inactive ulcerative colitis (p = 0.02) or healthy controls (p < 0.0001), and in patients with active compared to inactive Crohn's disease (p = 0.0005) or healthy controls (p < 0.0001). Mean platelet volume was inversely correlated with the white blood cell count (r = -0.17, p = 0.02), C-reactive protein (r = -0.46, p = 0.009) and erythrocyte sedimentation rate (r = -0.28, p = 0.008). No significant correlations were found between mean platelet volume and serum thrombopoietin or erythropoietin levels; however, a strong negative correlation between mean platelet volume and beta-thromboglobulin (r = -0.34, p < 0.0001) and platelet factor 4 (r = -0.30, p = 0.0002) was observed. CONCLUSIONS: Mean platelet volume is significantly reduced in active inflammatory bowel disease and is negatively correlated with the known inflammatory bowel disease activity markers and the platelet activation products. We propose that mean platelet volume provides a useful marker of activity in inflammatory bowel disease.     

Qualitative Platelet Defects with Reduced Life-Span in Acute Leukaemia*

Summary: Qualitative platelet abnormalities, as well as thrombocytopenia, may contribute to the haemorrhagic diathesis in acute leukaemia. The prevalence of impaired platelet function, as reflected by aggregation response to ADP, adrenaline and Ristocetin, and platelet factor III activity, was assessed in 21 patients with acute leukaemia. During the phases of active disease or partial remission, impaired aggregation and/or defective platelet factor lll release occurred in eleven of fifteen patients with active disease and in three of five patients in partial remission. In complete remission, platelet function was normal. In patients with active disease or in partial remission, defective platelet function was associated with reduced autologous platelet life-spans, whilst normal platelet function was coupled with normal platelet survival. Although the mechanisms for the production of thrombocytopenia in acute leukaemia are multifactorial, it is suggested that the acquisition of defective platelets with associated reduced survival may play a contributory role.     

Thrombopoietin serum levels in patients with inflammatory bowel disease with and without previous thromboembolic events

BACKGROUND/AIMS: Patients affected by inflammatory bowel disease frequently suffer from thromboembolic complications and mesenteric microvascular occlusion could be involved in the pathogenesis of inflammatory bowel disease. Increased platelet counts and abnormal platelet function seem to play a crucial role in determining the hypercoagulable state observed in inflammatory bowel disease. Thrombopoietin is considered the primary regulator of thrombopoiesis and recent studies have investigated the role of thrombopoietin in inflammatory bowel disease. However, the available data are not conclusive. The aim of this study was to assess thrombopoietin serum levels in inflammatory bowel disease patients according to platelet counts, disease activity and previous thrombotic events. METHODOLOGY: Seventy-one patients with inflammatory bowel disease [41 with ulcerative colitis and 30 with Crohn's disease] and 30 healthy controls were investigated. Eight (11%) inflammatory bowel disease patients had suffered previous thromboembolic complications, none had active thrombosis. Thrombopoietin serum levels were measured by ELISA. RESULTS: Mean thrombopoietin levels were significantly increased in inflammatory bowel disease patients with active disease compared to both healthy controls and patients with inactive disease. Platelet counts were significantly higher only in patients with active disease with respect to healthy subjects. No correlation was found between thrombopoietin levels and platelet counts in either controls or inflammatory bowel disease patients. No differences were found either in thrombopoietin levels or in platelet counts comparing inflammatory bowel disease patients with and without thromboembolic complications. CONCLUSIONS: Our data show elevated thrombopoietin levels in active inflammatory bowel disease. However, no correlation was found between platelet counts and thrombopoietin levels, supporting the hypothesis that other circulating factors than thrombopoietin interact in determining reactive thrombocytosis. Furthermore, thrombopoietin levels did not differ in inflammatory bowel disease patients with or without previous thromboembolic events. This finding could be probably explained by the lack of patients with active thrombosis at the moment of inclusion in the study.     

Relation of platelet activation to coronary angiographic severity and collateralization

We investigated whether platelet activation can be correlated with angiographic severity and the degree of collateralization in coronary artery disease (CAD), as well as endothelial damage/dysfunction. No studies have attempted to correlate platelet activation status, as measured by soluble plasma markers (soluble CD40 ligand, soluble P-selectin, soluble glycoprotein V), with the appearance of diseased coronary arteries. We found evidence of increased platelet activation in CAD, but a lack of correlation between the degree of platelet activation and the angiographic disease severity, which may reflect the presence of disease elsewhere or the presence of coronary atheroma not detected by angiography.     

Kinetics and in vivo distribution of 111-In-labelled autologous platelets in chronic hepatic disease: mechanisms of thrombocytopenia

The kinetics and distribution in vivo of autologous 111-In-labelled platelets were studied in 20 patients with chronic hepatic disease. The patients, 16 of whom were thrombocytopenic, exhibited a shortened platelet mean life time, a reduced platelet recovery and a normal platelet turnover, the latter 2 of which were positively correlated to the platelet count. Platelet in vivo recovery was negatively correlated to the spleen volume. In accordance with this, scintigraphic studies revealed that the spleen was the major organ of platelet sequestration and destruction, the role of the liver being almost negligible. Signs of platelet destruction in the bone marrow were also found. Our results indicate that splenic platelet pooling and accelerated platelet destruction, accompanied by inability of the bone marrow to compensate for the thrombocytopenia are the main causes of the thrombocytopenia accompanying chronic hepatic disease.     

Arachidonic acid-induced platelet aggregation and malondialdehyde production in dogs of various ages and in dogs affected with canine ceroid lipofuscinosis

The arachidonate pathway of canine platelets was assessed in dogs of varying ages by examination of platelet aggregation to arachidonic acid and by measurement of arachidonic acid-induced platelet malondialdehyde production. As age increased, arachidonic acid-induced platelet aggregation showed a progressive prolongation in the lag phase before aggregation. The production of malondialdehyde by canine platelets significantly decreased with increasing age. Dogs affected with ceroid lipofuscinosis showed similar declines in platelet aggregation and malondialdehyde production, but at an earlier age. This suggests that changes occur in canine platelet reactivity during natural aging and in a disease of “premature” aging. The lack of change in platelet numbers and volume suggests that the alterations reported were related to the aging process rather than to advancing vascular disease. The findings support the free radical theory of aging.     

Preliminary study showing the relationship between platelet fibronectin, sialic acid, and ADP-induced aggregation levels in coronary heart disease.

Several studies indicate that thrombosis plays an important role in the pathogenesis of coronary heart disease (CHD). Fibronectin is a multifunctional protein in plasma, other body fluids, and cell surface and plays an important role in platelet functions, including mediation of cell-cell and cell-surface interactions. Sialic acid is a regular constituent of glycoproteins and gangliozides in the outer cell membrane of mammalian cells. Therefore, the sialic acid content of platelets, which are characterized by their ability to aggregate with each other, can be important in leading to thrombus formation. In this study, platelet fibronectin, sialic acid-, and adenosine diphosphate (ADP)-induced platelet aggregation levels were determined in patients with CHD. Platelet sialic acid concentrations were determined by Warren's method. Platelet aggregation tests with ADP in platelet-rich plasma (PRP) were analyzed by use of an aggregometer. Platelet homogenate fibronectin levels were determined by ELISA. Total protein levels were determined by Lowry method. Our results indicate that, in patients with no vessel disease (patients with no obstructed vessel but suffering from chest pain, like angina pectoris) platelet fibronectin levels were significantly lower than the total of the other patients (patients with 1, 2, or 3 obstructed coronary vessels) (p<0.05). Sialic acid levels in patients with no vessel disease were significantly lower than the total of the patient group (p<0.05). There was significant (+) correlation between platelet aggregation, platelet fibronectin, platelet sialic acid, and severity of disease (p<0.05). Our preliminary findings suggest that, especially platelet fibronectin levels potentially represent a pathogenic factor for CHD.     

'Spontaneous' platelet aggregation in whole blood in diabetic patients with and without microvascular disease.

Consistent abnormalities of agonist-induced platelet aggregation, in either whole blood or platelet rich plasma, have not been demonstrated in diabetic patients without microvascular disease. In the present study platelet aggregation in the absence of exogenous agonists ('spontaneous' aggregation) was compared between 22 non-diabetic subjects and 23 Type 1 diabetic patients with (n = 12) and without (n = 11) microvascular disease. 'Spontaneous' aggregation was determined by measuring the percentage fall in single platelet number in aliquots of whole blood shaken for 60 min. Diabetic patients without microvascular disease had fewer single platelets remaining (greater aggregation) than non-diabetic subjects at all time-points (69.7 +/- 6.6 vs 82.3 +/- 7.3% at 60 min p less than 0.001), but more platelets remaining than in diabetic patients with microvascular disease at all time-points (69.7 +/- 6.6 vs 61.0 +/- 7.8% at 60 min p less than 0.02). No significant correlations were observed between platelet aggregation and plasma glucose, blood cell counts, or glycated haemoglobin levels. The study suggests that platelet abnormalities antedate the appearance of microvascular disease in diabetic patients.     

Significance of plasma fibrinogen in coronary arterial disease: marker or causative risk factor for arterial thrombosis?

The relationship between fibrinogen and severity of disease was measured in patients with coronary arterial disease (n = 301) prior to surgical coronary revascularisation. Platelet reactivity (shear-induced haemostasis) was measured from non-anticoagulated blood, in vitro. Coagulation was assessed by the clotting time of flowing native blood (dynamic) and by the conventional (stagnant) tube tests. Significantly enhanced platelet reactivity to shear-stress was observed when patients with one-vessel disease were compared to those with two- or three-vessel disease (P = 0.003). Neither coagulation nor fibrinogen were significantly related to the severity of disease. Furthermore, patients who had myocardial infarction (n = 144) showed enhanced platelet reactivity (P = 0.02) as compared to those who had not (n = 157). Again, neither coagulation nor fibrinogen discriminated between these groups of patients. Relationship between plasma fibrinogen and platelet reactivity was also investigated in vitro. Identical blood samples with normal (220-280 mg/dl) and elevated plasma fibrinogen (approximately 500 mg/dl) were compared by measuring platelet reactivity and coagulation from native blood and platelet aggregation in whole blood. The in vitro studies suggested that plasma fibrinogen and platelet reactivity are inversely associated. Furthermore, increased fibrinogen prolonged dynamic coagulation. These findings do not support the assertion that elevated plasma fibrinogen is a true causative factor for coronary arterial disease and arterial thrombosis.     

Platelet dynamics in chronic liver disease using the 111Indium oxine label

Platelet dynamics in chronic liver disease have been studied using 111Indium-8-hydroxyquinolone (111In-oxine) as a platelet label. In 20 patients, mainly with alcoholic cirrhosis, the platelet mean life span was reduced in 12 and the splenic platelet pool increased, often markedly so, in 15. However, the platelet count was not significantly related to mean bile span, the splenic platelet pool, or spleen size. Whereas splenic platelet pool size is related to spleen size in most of the haematological 'big-spleen' syndromes, this did not apply to those patients with chronic liver disease. Technically, 111In-oxine is a more appropriate platelet label than 51Cr in ill and thrombocytopenic patients with liver disease.     

The effect of different strains of Helicobacter pylori on platelet aggregation.

BACKGROUND AND AIMS: Helicobacter pylori is the major causative agent in peptic ulcer disease and is strongly implicated in the development of gastric cancer. It has also been linked, less strongly, to cardiovascular disease. The mechanisms by which certain strains of H pylori induce platelet aggregation through interactions with platelet glycoprotein Ib have been previously described. METHODS: In the present study, 21 different strains of H pylori, varying in their vacuolating toxin gene, cytotoxic-associated gene A status and other pathogenicity factors, were tested for their ability to induce platelet aggregation. RESULTS: Ten of the 21 strains induced platelet aggregation, a response that appeared to be independent of their vacuolating toxin gene and cytotoxic-associated gene A status. CONCLUSIONS: Platelet aggregation has been suggested to be one of the possible mechanisms involved in the effects on the cardiovascular system induced by H pylori. Our results suggest that any putative role H pylori plays in cardiovascular disease may be strain dependent. Further work to identify the H pylori factors involved in induction of platelet aggregation may allow for identification of 'higher risk' strains for cardiovascular disease.     

Platelet function in chronic liver disease

Abnormalities of platelet aggregation in response to adenosine diphosphate in 56 patients with chronic liver disease correlated with impairment of hepatocellular function but not with the etiology of the liver disease. Platelet-poor plasma from some patients appeared to contain an inhibitor since, in cross-over studies, it reduced the degree of aggregation of control subjects. However, platelet-poor plasma from some other patients enhanced aggregation in controls, and this was thought to be due to the presence of fibrin monomer. In the majority of patients with severe liver disease, platelet function still appeared defective, even after exclusion of the effects of plasma, and was independent of the platelet count in peripheral venous blood. Since patient platelet volumes were smaller than those of controls, these findings might be explained by deficiency of the larger hemostatically active type of platelet as a consequence of either bone marrow failure or splenic sequestration.     

Platelet-derived nitric oxide signaling and regulation

Nitric oxide (NO) exerts important vasodilatory, antiplatelet, antioxidant, antiadhesive, and antiproliferative effects. Although endothelium derived NO has been shown to be of prime importance in cardio- and vasculoprotection, until recently little was known about the role of platelet-derived NO. New evidence suggests that NO synthesized by platelets regulates platelet functions, in particular suppressing platelet activation and intravascular thrombosis. Moreover, platelet NO biosynthesis may be decreased in patients with cardiovascular risk factors or with coronary heart disease, and this may contribute to arterial thrombotic disease in these patients. Here, we review the current state of knowledge as regards the role of platelet-derived NO, both in normal physiology and in cardiovascular disease states, and compare platelet NO signaling and regulation with that in endothelial cells.     

Evidence for an Immunological Pathogenesis of Thrombocytopenia in Chronic Liver Disease

Objectives: To elucidate the roll of platelet-associated IgG (PA-IgG) in the mechanism of thrombocytopenia associated with chronic liver disease. Methods: Platelet count in blood, PA-IgG, and scintigraphic spleen/liver ratio us a marker of splenomegaly was examined in 214 individuals, including 16 controls showing nonspecific reactive change in liver biopsy and 198 patients with chronic liver disease. Results: The mean blood platelet count decreased significantly according to severity of liver disease, from control to liver cirrhosis. PA-IgG levels increased significantly in relation to severity of liver disease, as did spleen/liver ratio. In chronic hepatitis or liver cirrhosis, an inverse correlation was found between platelet counts and PA-IgG levels. An inverse correlation was also observed between platelet count and spleen/liver ratio in liver cirrhosis. The splenic embolization resulted in a significant rise in platelet count and a significant fall in PA-IgG in the 14 cirrhotic patients. Conclusions: These results may give support to evidence for an immunological mechanism mediated by PA-IgG for the thromhocytopenia occurring in chronic liver disease. In the case of liver cirrhosis, this mechanism would act in addition to platelet pooling in the spleen on thrombocytopenia. PA-IgG may also have an important role in thrombocytopenia associated with chronic hepatitis, in which splenic platelet pooling is less marked.     

On the retraction of collagen and fibrin induced by normal, defective and modified platelets

Fibrin clot retraction (FCR) and collagen gel retraction (CGR) were studied in patients with inherited platelet defects, i.e. in Glanzmann's thrombasthenia, Hermansky-Pudlak syndrome, May-Hegglin anomaly, giant platelet syndrome, as well as in patients with von Willebrand disease and factor XIII deficiency. FCR was abnormal only in thrombasthenia, while CGR was found to be reduced in 2 patients with Hermansky-Pudlak syndrome and in 4 out of 5 cases with von Willebrand disease. Both FCR and CGR were normal in May-Hegglin anomaly, giant platelet syndrome and severe factor XIII deficiency. In none of the examined bleeding disorders was a concomitant FCR and CGR reduction detected. Natural polyamines and anti-fibronectin antibodies did not affect platelet potency in FCR or CGR. Peroxidation of platelet membrane components by sodium periodate abolished the platelet-induced FCR and CGR. This effect was reversed by subsequent reduction by sodium borohydride.     

Influence of splenectomy and the functional hyposplenism of coeliac disease on platelet count and volume

Platelet count and volume were measured in 84 splenectomised subjects, 142 patients with coeliac disease and 77 healthy subjects. An inverse, non-linear correlation between platelet count and volume was found in healthy subjects and coeliac patients, but was not present in splenectomised subjects who had higher platelet counts (P = 0.0001) and mean platelet volumes (P = 0.0001) than healthy subjects. Platelet counts correlated with splenic function in patients with coeliac disease and were higher in patients with severe hyposplenism than in normosplenic coeliacs (P = 0.0001). Splenic function did not influence the mean platelet volume (MPV) in coeliac disease but normosplenic coeliacs had higher MPV than normal subjects (P = 0.05). Serum iron and red cell folate were not correlated to MPV in coeliac disease. We conclude that splenic function effects platelet count and volume in non-coeliac subjects and platelet count in coeliac disease. However, other unidentified factor(s) influence the MPV in coeliac disease.