Platelet P-selectin facilitates atherosclerotic lesion development

P-selectin is an adhesion molecule expressed on activated platelets and endothelium. It is known to play an important role in atherosclerosis. P-selectin also circulates in plasma in a soluble form (sP-selectin), which induces procoagulant microparticle formation. We investigated the role of platelet versus endothelial P-selectin in generating sP-selectin and in the formation of atherosclerotic lesions in the apolipoprotein E (apoE)-deficient mouse model. For this we transplanted apoE(-/-)P-selectin(-/-) and apoE(-/-)P-selectin(+/+) lethally irradiated mice with bone marrow of either genotype. Seven months after transplantation, we determined from the chimeric animals that the majority of circulating sP-selectin was of endothelial origin. Thus, in atherosclerosis, the procoagulant sP-selectin reflects endothelial rather than platelet activation. We found that endothelial P-selectin was crucial for the promotion of atherosclerotic lesion growth because in its absence only relatively small lesions developed. However, platelet P-selectin also contributed to the lesion development because lesions in wild-type recipients receiving transplants with wild-type platelets were 30% larger than those receiving P-selectin-deficient platelets (P <.008) and were more frequently calcified (80% versus 44%). In comparison with P-selectin wild-type animals, absence of either endothelial or platelet P-selectin inhibited migration of smooth muscle cells into the lesion. Thus, in addition to endothelium, platelets and their P-selectin also actively promote advanced atherosclerotic lesion development.     

Effects of sarpogrelate hydrochloride on adenosine diphosphate- or collagen-induced platelet responses in arteriosclerosis obliterans.

To evaluate the effects of the 5-HT2 receptor antagonist sarpogrelate hydrochloride (sarpogrelate) on platelet responses in arteriosclerosis obliterans (ASO), we examined platelet aggregation and its relationships to platelet-derived growth factor (PDGF), soluble P-selectin (sP-selectin), and transforming growth factor-beta 1 (TGF-beta1). Circulating plasma levels of PDGF and sP-selectin in 13 patients with ASO after 1 week of medication with sarpogrelate were significantly lower than those before medication. In contrast, circulating plasma levels of TGF-beta1 after medication were significantly higher than those before medication. When platelet-rich plasma obtained from ASO patients after medication was stimulated with adenosine diphosphate (ADP) or collagen, platelet aggregation was suppressed compared with rates before medication. Significant decreases in levels of PDGF, sP-selectin and TGF-beta1 released from platelets in response to 5 micromol/l ADP and 1 microg/ml collagen after taking of sarpogrelate were found. There were close correlations between platelet aggregation and respective molecules released from platelets. In conclusion, since platelet activation is involved in pathogenesis of thrombotic disease, sarpogrelate may suppress the development of obstructive arteriosclerosis. PDGF and TGF-beta1, as well as sP-selectin, appear to be useful markers for clinical evaluation of anti-platelet drugs.     

Patients with systemic lupus erythematosus show increased platelet activation and endothelial dysfunction induced by acute hyperhomocysteinemia

OBJECTIVE: Hyperhomocysteinemia adversely affects the endothelium, although the exact mechanism is unclear. Systemic lupus erythematosus (SLE) is an inflammatory disease with a high atherothrombotic tendency. We examined whether acute hyperhomocysteinemia exacerbates endothelial and platelet dysfunction in patients with SLE. METHODS: Twelve SLE patients and 15 controls were recruited. Oral methionine was used to achieve acute hyperhomocysteinemia. Endothelial function was assessed by flow-mediated dilatation (FMD) of the brachial artery; also assessed were the levels of von Willebrand factor (vWF) and plasminogen activator inhibitor type 1 (PAI-1). Platelet activation was assessed by the levels of beta-thromboglobulin (beta-TG), fibrinogen binding, and P-selectin expression using flow cytometry. RESULTS: After oral methionine loading, vWF levels increased significantly, whereas FMD remained unchanged in both groups. PAI-1 increased significantly only in controls. Fibrinogen binding to platelets increased significantly only in SLE patients. Beta-TG remained unchanged in SLE patients but increased significantly in controls. Platelet P-selectin expression did not change in either group. CONCLUSION: These results suggest that the prothrombotic tendency after acute hyperhomocysteinemia is mediated by endothelial dysfunction and platelet activation in patients with SLE and healthy controls.     

Acute,short-term hyperglycemia enhances shear stress-induced platelet activation in patients with type II diabetes mellitus

OBJECTIVES: The aim of our study was to assess whether acute, short-term hyperglycemia affects platelet reactivity in patients with Type II diabetes mellitus (T2DM). BACKGROUND: Hyperglycemic spikes are thought to precipitate ischemic events in T2DM. Previous studies have shown in vivo platelet activation in diabetes; however, no studies have assessed whether acute in vivo hyperglycemia induces further activation of platelets. METHODS: In a cross-over, randomized, double-blind study, 12 patients with T2DM underwent 4 h of either acute hyperglycemia (13.9 mmol/l, 250 mg/dl) or euglycemia (5.5 mmol/l, 100 mg/dl). Shear stress-induced platelet activation, P-selectin and lysosomal integral membrane protein (LIMP) expression on platelets in the bleeding-time blood, urinary 11-dehydro-thromboxane B(2) (TxB(2)) excretion, von Willebrand factor:antigen (vWF:Ag), and von Willebrand factor:activity (vWF:activity) were measured before and after hyperglycemia or euglycemia. RESULTS: Shear stress-induced platelet activation, P-selectin and LIMP expression on platelets in the bleeding-time blood, and urinary 11-dehydro-TxB(2) excretion increased significantly after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping. Plasma vWF:Ag and vWF:activity increased strikingly in parallel fashion after hyperglycemic clamping, whereas no changes were observed after euglycemic clamping. CONCLUSIONS: Our data demonstrate that acute, short-term hyperglycemia induces an increased activation of platelets exposed to high shear stress conditions in vitro (filtration method) or in vivo (bleeding time). In vivo platelet activation is reflected by an increased urinary excretion of 11-dehydro-TxB(2). The increased levels of vWF in the circulation correlate with the increase in platelet activation markers and may indicate some degree of causation. Acute, short-term hyperglycemia in T2DM may precipitate vascular occlusions by facilitating platelet activation.     

Studies of biological functions in blood cells from individuals with large platelets

The present study was performed to explore differences in the expression of P-selectin and IL-8 production of blood cells in healthy individuals with large size platelets (MI-families) as compared to people having normal size platelets. A positive correlation between LPS-induced IL-8 production per platelet in whole blood and mean platelet volume (MPV) was found in the large platelet group (R=0.74, P<0.05). When the large and normal groups were combined the correlation was nearly, but not quite significant (R=0.46, P<0.06). There was also a positive correlation between sP-selectin and MPV (R=0.42, P<0.05). Furthermore, IL-8 in serum was positively correlated to sP-selectin in serum (R=0.68, P<0.005). sP-selectin baseline values in citrated plasma correlated significantly with values found in serum (R=0.72, P<0.0005), indicating that sP-selectin in blood originates from the platelets rather than from endothelial cells. Significant correlations were also found in both groups between P-selectin and CD40L (R=0.44, P<0.05) and P-selectin and RANTES (R=0.44, P<0.05). A significant correlation was also found between PDGF and RANTES (R=0.44, P<0.05). Our results suggest that larger platelets enhance the production of IL-8 more than normally sized platelets. This phenomenon is probably mediated through P-selectin exposed on platelets.     

Decrease in P-selectin levels in patients with hypercholesterolaemia and peripheral arterial occlusive disease after lipid-lowering treatment.

At sites of thrombosis and vascular injury, interactions occur among platelets, leucocytes and endothelial cells. Patients with peripheral arterial occlusive disease (PAOD) have been shown to have raised total serum cholesterol and serum triglycerides and increased sP-selectin levels when compared with controls. A total of 31 patients with PAOD and hypercholesterolaemia took part in this three-staged study. Soluble P-selectin (sP-selectin) levels were significantly lowered after 12 weeks of fluvastatin treatment (157.0 ng/ml versus 113.77 ng/ml, p = 0.01), whereas 12 weeks of placebo treatment had no statistically significant effect on sP-selectin levels (150.0 ng/ml versus 139.4 ng/ml). An unpaired t-test almost reached statistical significance (p = 0.051) when the levels by which sP-selectin fell after 12 weeks of active or placebo treatment were compared. The placebo group was then put onto long-term, active treatment and sP-selectin levels were significantly lowered by fluvastatin when compared to pre-treatment levels (150.0 ng/ml versus 110.0 ng/ml, p = 0.03). By lowering the levels of P-selectin, fluvastatin may not only attenuate atherosclerotic progression but may also decrease the platelet activation associated with PAOD.     

Circulating adhesion molecules in patients with stable coronary artery disease

To evaluate platelet and endothelial function in patients with stable coronary artery disease (CAD), we investigated levels of the plasma-soluble (s) adhesion molecules E-selectin (sE-selectin), P-selectin (sP-selectin), and intercellular adhesion molecule-1 (sICAM-1) in 74 patients (mean age, 53 +/- 8 years) with angiographically documented coronary artery disease. Levels were compared to 27 matched healthy control subjects. Patients were excluded if they had recent cardiovascular events or any illness that might influence platelet and endothelial cell function. Concentrations of sP-selectin were significantly higher in patients with stable CAD (276 +/- 61 ng/mL) compared with control subjects (188 +/- 32 ng/mL) (P = .0001), whereas sE-selectin and sICAM-1 levels were similar between the 2 groups. Pooling both groups showed that sICAM-1 correlated weakly with triglycerides (r = 0.240, P = .01) and sP-selectin correlated weakly with low-density lipoprotein cholesterol (r = 0.204, P = .04). Although plasma sICAM-1 concentrations were significantly increased in hypercholesterolemic patients compared with those of normocholesterolemic patients (P = .04), sP-selectin and sE-selectin levels were similar between the 2 groups. In conclusion, significantly increased sP-selectin levels, indicating platelet activation, were found in patients with stable CAD. No other sign of endothelial cell activation in these patients could be detected. Moreover, sP-selectin levels seem to reflect the activation of platelets rather than of endothelial cells.     

Role of von Willebrand factor associated to extracellular matrices in platelet adhesion

The respective role of plasmatic and endothelial extracellular matrix (ECM)-associated von Willebrand factor (vWF) in platelet adhesion was investigated at a high shear rate using a parallel-plate perfusion chamber. Incubation of the endothelial ECM with a monoclonal antibody (MoAb) to vWF, which specifically blocks vWF binding to platelet GP Ib (MoAb 322), inhibited 45% of platelet adhesion. Complete inhibition was achieved by incubating both plasma and endothelial ECM with MoAb 322 at concentrations that blocked only about 50% of adhesion when added separately. The effect of ECM-associated vWF was further demonstrated when a fibroblastic ECM, normally devoid of vWF, was coated with purified plasmatic vWF. Matrix associated-vWF was able to significantly enhance platelet adhesion in both the presence and the absence of plasmatic vWF. In contrast, this effect was not seen on endothelial ECM. Binding of exogenous vWF to the ECM was specific and dose dependent, reached the same value (500 ng/cm2) on both fibroblastic ECM and endothelial ECM, but exhibited a threefold-lower apparent dissociation constant (KD) on fibroblastic than on endothelial ECM. Our studies suggest that vWF deposited by endothelial cells in the ECM may be the most active form in platelet adhesion, whereas plasmatic vWF may only play a secondary role.     

粒细胞-巨噬细胞集落刺激因子与不稳定型心绞痛的关系

目的　观察不稳定型心绞痛 (UAP)患者血清粒细胞 -巨噬细胞集落刺激因子 (GM- CSF)水平的变化 ,并进一步探讨其与血小板激活及内皮损伤之间的关系。方法　采用液相竞争放射免疫法检测 2 0例不稳定型心绞痛患者(U AP组 )、2 0例稳定型心绞痛患者 (SAP组 )及 2 0例正常对照组 (NC组 )血清 GM- CSF浓度 ,用酶联免疫双抗体夹心法测定其血浆血管性血友病因子 (v WF)及 P-选择素含量。结果　 U AP组血清 GM- CSF、血浆 P-选择素、v WF的水平明显高于 SAP组及正常对照组 (P均 <0 .0 1)。SAP组与对照组比较上述指标虽均升高 ,但无统计学意义 (P>0 .0 5 ) ;U AP患者血清 GM- CSF分别与血浆 P-选择素、v WF呈正相关 (r=0 .5 83及 r=0 .5 74 ;P均 <0 .0 1)。结论　不稳定型心绞痛患者血清 GM- CSF浓度升高 ,其可能与不稳定型心绞痛患者血小板激活和内皮损伤有关     

Enhanced P-selectin expression and increased soluble CD40 Ligand in patients with Type 1 diabetes mellitus and microangiopathy: evidence for platelet hyperactivity and chronic inflammation

Aims/hypothesis Platelet activation, endothelial dysfunction and inflammation may be involved in early stages of diabetic microangiopathy. We therefore investigated patients with Type 1 diabetes mellitus, without (n=19) and with (n=20) microangiopathy, matched for glycaemic control and duration of disease, and matched with healthy control subjects (n=27).Methods Platelet activation was measured as platelet P-selectin expression using whole blood flow cytometry and as soluble P-selectin by immunoassay. Von Willebrand factor antigen in plasma, serum soluble E-selectin, CD40 ligand (sCD40L) and C-reactive protein (CRP) served as markers for endothelial function and inflammation.Results Thrombin-induced platelet P-selectin expression was enhanced, and soluble P-selectin and sCD40L concentrations were increased in patients with microangiopathy compared with the control subjects (p<0.01 for both) and with patients without microangiopathy (p<0.05 for P-selectin expression and sP-selectin), whereas all three parameters were similar in patients without microangiopathy and in the control subjects. CRP and soluble E-selectin were increased in patients with microangiopathy, compared with the control subjects (p<0.01 and p<0.05), whereas von Willebrand factor did not differ between the groups.Conclusions/interpretation Microangiopathy in Type 1 diabetes is associated with platelet hyperactivity, endothelial dysfunction and low-grade inflammation, indicating an increased risk for cardiovascular disease.Abbreviations sP-selectin Soluble P-selectin - sCD40L soluble CD40 Ligand - CRP C-reactive protein     

Effects of stent coating on platelets and endothelial cells after intracoronary stent implantation

BACKGROUND: Adhesion molecules are known to be important in the regulation of endothelial cell and platelet functions. Increased platelets P-selectin expression is a marker of stent thrombosis after uncoated stent placement. HYPOTHESIS: The aim of this study was to compare the effects of intracoronary placement of phosphorylcholine (PC)-coated, versus heparin-coated, versus uncoated stents on platelets and endothelial activity. METHODS: Thirty patients (age 55 +/- 10, 27 men) with significant proximal left anterior descending coronary artery stenoses were randomized to elective implantation of PC-coated, versus heparin-coated, versus uncoated stents. Following stent placement, intravenous heparin and aspirin plus ticlopidine were administered. Venous plasma soluble E-selectin, sP-selectin, and intercellular adhesion molecule-l levels were measured before the procedure and 24 and 48 h thereafter as markers of platelet and endothelial cell activation. Patients were excluded if they had a disease known to influence platelet and endothelial cell function. RESULTS: Plasma sP-selectin levels decreased significantly after implantation of PC- and heparin-coated stents (p = 0.04), but remained unchanged in patients randomized to uncoated stents. Plasma sE-selectin levels increased significantly after uncoated stent placement (p = 0.04) and remained unchanged after coated stent implantation. CONCLUSION: In patients treated with combined antiplatelet therapy, implantation of PC- and heparin-coated stents decreased platelet activity without activating endothelial cells, whereas placement of uncoated stents led to endothelial activation without changing platelet activity. These results suggest that PC-coated and heparin-coated stents may be advantageous in limiting thrombotic complications.     

Immediate and late effects of coronary angiography on soluble endothelial cell markers and P-selectin in patients with and without coronary artery disease.

Endothelial cell injury and platelet activation are considered primary events in the pathogenesis of coronary artery disease (CAD) and are marked by plasma concentrations of von Willebrand factor (vWF) and soluble thrombomodulin, and by soluble P-selectin, respectively. Because both endothelial cells and platelets interact with contrast media, we aimed to detect immediate and 24-h changes in these markers following coronary angiography in patients with and without CAD. Sixteen patients with angiographically proven CAD and 14 patients without significant coronary stenosis were investigated. Blood samples were obtained from an antecubital vein before and 24 h after cardiac catheterization, and from the coronary sinus before and immediately after angiography. Concentrations of the markers were determined using enzyme-linked immunosorbent assays. In the coronary sinus samples, the only significant finding was an increase in levels of soluble P-selectin in the patients with CAD (P < 0.038). In the post-catheterization peripheral blood samples, concentrations of soluble P-selectin (P = 0.004), vWF (P = 0.0007) and soluble thrombomodulin (P = 0.0013) were all increased in patients with CAD. In contrast, patients without CAD demonstrated increased levels of vWF only (P = 0.0015) in peripheral blood samples obtained 24 h after angiography. We conclude that both immediate and 24-h changes take place in endothelial cells and platelet markers in response to cardiac catheterization, and that these changes are different in patients with angiographically proven CAD and in patients free of disease. These differences may reflect alterations in endothelial cell or platelet reactivity in patients with CAD.     

Soluble P-selectin is a marker of plaque destabilization in unstable angina

Unstable coronary syndromes usually involve platelet activation and thrombus formation at the site of atherosclerotic plaque. P-selectin in platelets and endothelial cells mediates adhesive interaction with leucocytes to form thrombi. The aim of this study was to asses the level of soluble P-selectin (CD62P) as a non invasive marker of coronary plaque destabilization in unstable angina (U.A.). Serum samples were collected from 23 male patients with UA, 20 male patients with stable angina (SA) and 13 healthy controls. Soluble P-selectin (sP-selectin) level was measured by ELISA technique. The mean sP-selectin level was significantly higher in patients with UA (87.6+/-30.10 ng/ml) than SA (36.2 +/-13.8 ng/ml) and control subjects (16.7+/-8.6 ng/ml). In conclusion, s-Pslectin level could be used as a marker of plaque destabilization in unstable angina.     

Platelets roll on stimulated endothelium in vivo: an interaction mediated by endothelial P-selectin.

P-selectin, found in storage granules of platelets and endothelial cells, can be rapidly expressed upon stimulation. Mice lacking this membrane receptor exhibit a severe impairment of leukocyte rolling. We observed that, in addition to leukocytes, platelets were rolling in mesenteric venules of wild-type mice. To investigate the role of P-selectin in this process, resting or activated platelets from wild-type or P-selectin-deficient mice were fluorescently labeled and transfused into recipients of either genotype. Platelet-endothelial interactions were monitored by intravital microscopy. We observed rolling of either wild-type or P-selectin-deficient resting platelets on wild-type endothelium. Endothelial stimulation with the calcium ionophore A23187 increased the number of platelets rolling 4-fold. Activated P-selectin-deficient platelets behaved similarly, whereas activated wild-type platelets bound to leukocytes and were seen rolling together. Platelets of either genotype, resting or activated, interacted minimally with mutant endothelium even after A23187 treatment. The velocity of platelet rolling was 6- to 9-fold greater than that of leukocytes. Our results demonstrate that (i) platelets roll on endothelium in vivo, (ii) this interaction requires endothelial but not platelet P-selectin, and (iii) platelet rolling appears to be independent of platelet activation, indicating constitutive expression of a P-selectin ligand(s) on platelets. We have therefore observed an interesting parallel between platelets and leukocytes in that both of these blood cell types roll on stimulated vessel wall and that this process is dependent on the expression of endothelial P-selectin.     

Soluble P-selectin concentration in patients with colorectal cancer

During platelet activation, P-selectin is translocated onto the external platelet membrane. Surface exposure of P-selectin is temporary, and the molecule undergoes endocytosis or shedding to the circulation where it appears in a soluble form as sP-selectin. The aim of the study was to assess platelet activation based on the level of soluble form of P-selectin (sP-selectin) in colorectal cancer patients. The study involved 22 surgically treated patients, divided into two groups depending on histopathological malignancy grade: group I - patients with low malignancy grade (G2), group II - patients with high malignancy grade (G3). The examinations were carried out three times: before surgery (A0) and 3 (A1) and 12 days (A2) after the surgery. Control group (C) consisted of 20 healthy subjects. The sP-selectin level was determined in the plasma using the ELISA Kit (Human sP-selectin, R&D System). In colorectal cancer patients sP-selectin concentration was statistically significantly higher (69.25 ng/ml in group I and 66.50 ng/ml in group II) as compared to healthy subjects (46.01 ng/ml) (p<0.05), irrespective of malignancy grade. The surgical procedure has a significant effect on the dynamics of changes in the level of sP-selectin. Initially, 3 days (A1) after the procedure, there is a decrease in the level of sP-selectin, but after 12 days (A2) a rise is noted again, the level being the highest in group I. It indicates that the surgical procedure does not totally eliminate the factors responsible for platelet activation and did not normalize platelet activation.     

Periodontitis is associated with platelet activation

There is an epidemiological association between periodontitis and cardiovascular disease (CVD). In periodontitis, low grade systemic inflammation and bacteremia occur regularly. Such events may contribute to platelet activation and subsequent pro-coagulant state. This study aimed to investigate platelet activation in periodontitis patients. The study is composed of two parts. In the first part, plasma levels of soluble(s) P-selectin and sCD40 ligand were measured as general markers of platelet activation in periodontitis patients (n=85) and in healthy controls (n=35). In the second part, surface-exposed P-selectin and the ligand-binding conformation of the glycoprotein IIb-IIIa complex (binding of PAC-1 antibody) were determined on individual platelets in whole blood of periodontitis patients (n=18) and controls (n=16). Patients had significantly elevated plasma levels of sP-selectin (P<0.001) and increased binding of PAC-1 on isolated platelets (P=0.033). Platelet activation was more pronounced in the patients with more severe periodontal disease, showing a severity-dependence. The levels of sCD40 ligand and of platelet-bound P-selectin were not increased. Periodontitis is associated with increased platelet activation. Since platelet activation contributes to a pro-coagulant state and constitutes a risk for atherothrombosis, platelet activation in periodontitis may partly explain the epidemiological association between periodontitis and CVD.     

Indexes of hypercoagulability measured in peripheral blood reflect levels in intracardiac blood in patients with atrial fibrillation secondary to mitral stenosis

Systemic thromboembolism is a major complication in patients with mitral stenosis, especially in those who have atrial fibrillation (AF). It has been suggested that there may be increased regional left atrial coagulation activity in such patients, despite normal systemic coagulation activity on peripheral blood sampling. Our aim was to investigate whether there were significant differences between intracardiac versus peripheral indexes of hypercoagulability in 25 patients (5 men; mean age 60 years) with mitral stenosis who were undergoing percutaneous balloon mitral valvuloplasty and who were all in chronic AF. Two days after halting warfarin therapy, intracardiac (right and left atria) and peripheral (venous and arterial) blood samples from patients were obtained and compared with levels in matched healthy controls in sinus rhythm. Thrombogenicity was assessed by levels of fibrin D-dimer, fibrinogen, indexes of platelet activation (soluble P-selectin and beta thromboglobulin [betaTG]) and indexes of endothelial dysfunction (soluble thrombomodulin [sTM] and von Willebrand factor [vWF]). There were no statistically significant differences in the various markers between the femoral vein and artery, left and right atria, and between the femoral vein and both atria (all p = NS). Plasma fibrinogen, vWf (both p <0.005), and D-dimer (p = 0.011) were significantly higher and levels of sP-selectin and sTM were lower (both p <0.005) in patients when compared with controls. There was no significant difference in plasma betaTG levels. Our results suggest that there is no significant variation in indexes of thrombogenesis, platelet activation, and endothelial dysfunction between left atrium, right atrium, and the peripheral artery or vein. Peripheral samples therefore do reflect atrial coagulation, platelet, and endothelial activities.     

Platelet-dependent primary hemostasis promotes selectin- and integrin- mediated neutrophil adhesion to damaged endothelium under flow conditions

Co-localization of blood platelets and granulocytes at sites of hemostasis and inflammation has triggered an intense interest in possible interactions between these cellular processes and induction of vessel wall injury. Leukocyte adhesion to endothelial cells decreases with increasing shear and is dependent on an initial rolling phase mediated by selectins. We hypothesized that flow-dependent platelet adhesion at an injured vessel wall will lead to P-selectin expression by platelets, thus mediating leukocyte co-localization. A perfusion chamber was used in which flowing whole blood induced platelet adhesion to a subendothelial matrix (ECM) of cultured human umbilical vein endothelial cells (HUVEC). We compared neutrophil (polymorphonuclear leukocyte [PMN]) interactions with HUVEC and their ECM with and without adhered platelets. PMNs adhered predominantly to ECM-adhered platelets and not to endothelial cells. ECM alone did not support PMN adhesion under flow conditions. PMN adhesion to unstimulated HUVEC was only substantial at low shear (up to 200 cells/mm2 at shear stress 80 mPa). In marked contrast, PMN adhesion to ECM-adhered platelets was dramatically increased, and adhesion was demonstrated at much higher shear stress (up to 640 mPa). Studies with specific antibodies showed that the platelet-dependent neutrophil adhesion was selectin-mediated. Inhibition of P-selectin caused a marked inhibition of adhesion at high shear stress, whereas the role of leukocyte L-selectin was less pronounced. beta2-Integrin-blocking antibodies inhibited static neutrophil adhesion. fMLP induced L-selectin shedding from leukocytes, resulting in decreased leukocyte adhesion. In conclusion, platelet- dependent hemostasis at the ECM appears to be a powerful intermediate in neutrophil-vessel wall interactions at shear stresses that normally do not allow neutrophil adhesion to intact endothelium.     

Studies of biological functions in blood cells from individuals with large platelets

The present study was performed to explore differences in the expression of P-selectin and IL-8 production of blood cells in healthy individuals with large size platelets (MI-families) as compared to people having normal size platelets. A positive correlation between LPS-induced IL-8 production per platelet in whole blood and mean platelet volume (MPV) was found in the large platelet group (R?=?0.74, P?<?0.05). When the large and normal groups were combined the correlation was nearly, but not quite significant (R?=?0.46, P?<?0.06). There was also a positive correlation between sP-selectin and MPV (R?=?0.42, P?<?0.05). Furthermore, IL-8 in serum was positively correlated to sP-selectin in serum (R?=?0.68, P?<?0.005). sP-selectin baseline values in citrated plasma correlated significantly with values found in serum (R?=?0.72, P?<?0.0005), indicating that sP-selectin in blood originates from the platelets rather than from endothelial cells. Significant correlations were also found in both groups between P-selectin and CD40L (R?=?0.44, P?<?0.05) and P-selectin and RANTES (R?=?0.44, P?<?0.05). A significant correlation was also found between PDGF and RANTES (R?=?0.44, P?<?0.05). Our results suggest that larger platelets enhance the production of IL-8 more than normally sized platelets. This phenomenon is probably mediated through P-selectin exposed on platelets.     

Prognostic value of plasma soluble P-selectin and von Willebrand factor as indices of platelet activation and endothelial damage/dysfunction in high-risk patients with hypertension: a sub-study of the Anglo-Scandinavian Cardiac Outcomes Trial

BACKGROUND: Abnormal levels of prothrombotic markers have been described in hypertension, but no such marker has yet been shown to reliably predict cardiovascular outcomes in hypertension. We hypothesized that raised circulating levels of soluble P-selectin (sP-sel, an index of platelet activation) and/or von Willebrand factor (vWF, an index of endothelial damage/dysfunction) would predict vascular events in patients treated for cardiovascular risk. METHODS: We measured vWF and sP-sel levels by an ELISA in 234 hypertensive participants with no prior cardiovascular events who were participating in the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT). Plasma vWF and sP-sel levels were related to the subsequent cardiovascular events over a mean (SD) follow-up period of 59.6 (19) months. RESULTS: Plasma sP-sel was a significant predictor of myocardial infarction (P = 0.03), with the greatest risk amongst those with the highest sP-sel levels. sP-sel did not predict cerebrovascular events (P = 0.53) or composite cardiovascular events (P = 0.06). No significant relationships were found between vWF levels and outcomes. There was no relationship to the presence or absence of diabetes mellitus (DM) at baseline or subsequent development of DM during the follow-up period. CONCLUSIONS: Among 'high-risk' patients with hypertension, raised levels of sP-sel (platelet activation) were predictive of myocardial infarction. Levels of vWF (endothelial damage/dysfunction) were not associated with coronary events and neither marker predicted cerebrovascular or composite cardiovascular endpoints. Platelets (or P-selectin) might represent a target for novel therapies or an adjunctive aid to risk stratification in the setting of hypertension.