Platelet-endothelial Cell Interactions Research Articles

Platelet-Mediated Inflammation in Cardiovascular Disease. Potential Role of Platelet-Endothelium Interactions

Inflammation of the vascular wall is considered as the principal underlying mechanism in the development of atherosclerosis. Besides their specific functions in haemostasis via thrombus formation after an endothelial injury, a growing body of evidence indicates that platelets play an important role in the inflammatory reactions occurring in the vascular wall as well as in the subsequent tissue repair mechanisms. Platelets interact with activated endothelium as well as with circulating leukocytes and progenitor cells. These interactions, involve direct cell-to-cell interactions as well as autocrine and paracrine pathways, which lead to activation of platelets and their respective cellular counterpart. An increasing body of evidence suggests that antiplatelet therapy may reduce vascular inflammation primarily by inhibiting platelet activation. The aim of the present review is to highlight the molecular basis of platelet-mediated inflammatory response, focusing on the mechanisms underlying the platelet-endothelial cell interaction. The anti-inflammatory effects of current antiplatelet therapies will be also discussed.

Radiation-induced platelet-endothelial cell interactions are mediated by P-selectin and P-selectin glycoprotein ligand-1 in the colonic microcirculation

Antiplatelet reagents have been reported to protect against intestinal damage associated with abdominal radiotherapy, but the mechanisms behind radiation-induced platelet-endothelium interactions are not known. We sought to define the adhesive mechanisms that regulate radiotherapy-induced platelet-endothelial cell interactions in the colon. All mice except the controls were exposed to abdominal radiation with a single dose of 20 Gray. Mice were pretreated with an isotype-matched control antibody or a monoclonal antibody directed against either P-selectin or P-selectin glycoprotein ligand-1 (PSGL-1). Platelet and leukocyte rolling and adhesion in the colon were determined by use of inverted intravital fluorescence microscopy 16 hours after radiation. Radiation-induced intestinal leakage of fluorescein isothiocyanate-conjugated dextran was examined in separate experiments. Immunoneutralization of P-selectin decreased radiation-provoked platelet rolling by 87% and adhesion by 63%. Moreover, inhibition of PSGL-1 decreased platelet rolling and adhesion by 77% and 83%, respectively, in animals exposed to radiation. Similarly, inhibition of P-selectin and PSGL-1 decreased radiation-induced leukocyte rolling and adhesion by more than 84% and 90%, respectively, in the colon. In contrast, inhibition of P-selectin or PSGL-1 had no impact on radiation-induced intestinal leakage. In addition, systemic depletion of platelets and leukocytes did not affect intestinal barrier dysfunction in radiated animals. This study demonstrates that radiation-provoked platelet and leukocyte accumulation are mediated in part by P-selectin and PSGL-1. Radiation-induced gut leakage, however, is independent of accumulation of platelets and leukocytes in the intestinal microvasculature.

Beneficial Effect of Ultra-Low-Dose Aspirin in Platelet Activity Alterations and Haemorrhage Observed in Experimental Portal Hypertension

Ultra-low-dose aspirin has shown a prothrombotic effect in the laser-induced thrombosis model. Several studies of our laboratory have shown a positive effect in rats with two different experimental models of portal hypertension: portal vein ligation, a model with an almost normal liver, and 30 days of bile duct ligation, a model with cirrhosis and presence of ascitis. In both models of portal hypertensive rats, bleeding time was prolonged and thrombi formation, in a laser-induced model of thrombi production, decreased. The hypotheses of the presented studies were that ultra-low-dose aspirin could decrease the bleeding complications in these models and that the mechanism for these effects could act thorough the COX pathway. In different studies, ultra-low dose of aspirin normalized the induced hemorrhage time, thrombi production, and platelet-endothelial cell interaction. The possible beneficial role of these doses of aspirin and mechanism of COX 2 inhibition are discussed.

MRI of inducible P‐selectin expression in human activated platelets involved in the early stages of atherosclerosis

The noninvasive imaging of atherosclerotic plaques at an early stage of atherogenesis remains a major challenge for the evaluation of the pathologic state of patients at high risk of acute coronary syndromes. Recent studies have emphasized the importance of platelet-endothelial cell interactions in atherosclerosis-prone arteries at early stages, and the prominent role of P-selectin in the initial loose contact between platelets and diseased vessel walls. A specific MR contrast agent was developed here for the targeting, with high affinity, of P-selectin expressed in large amounts on activated platelets and endothelial cells. For this purpose, PEGylated dextran/iron oxide nanoparticles [PEG, poly(ethylene glycol)], named versatile ultrasmall superparamagnetic iron oxide (VUSPIO) particles, labeled with rhodamine were coupled to an anti-human P-selectin antibody (VH10). Flow cytometry and microscopy experiments on human activated platelets were highly correlated with MRI (performed at 4.7 and 0.2 T), with a 50% signal decrease in T(2) and T(1) values corresponding to the strong labeling of activated vs resting platelets. The number of 1000 VH10-VUSPIO nanoparticles attained per activated platelet appeared to be optimal for the detection of hypo- and hyper-signals in the platelet pellet on T(2) - and T(1) -weighted MRI. Furthermore, in vivo imaging of atherosclerotic plaques in ApoE mice at 4.7 T showed a spatial resolution adapted to the imaging of intimal thickening and a hypo-signal at 4.7 T, as a result of the accumulation of VH10-VUSPIO nanoparticles in the plaque. Our work provides support for the further assessment of the use of VH10-VUSPIO nanoparticles as a promising imaging modality able to identify the early stages of atherosclerosis with regard to the pertinence of both the target and the antibody-conjugated contrast agent used.

Adipose tissue remodeling and chronic inflammation in obesity visualized by in vivo molecular imaging method

Obese visceral adipose tissue remodeling and dysfunction, based on chronic inflammation and local immunological changes, play major roles in the metabolic syndrome. Therefore, an in vivo visualization technique has been developed to assess the dynamic interplay between multiple cell types in obese adipose. In vivo imaging revealed close spatial and temporal interrelationships between angiogenesis and adipogenesis, which were augmented in obese adipose tissue. In addition, increased leukocyte–platelet–endothelial cell interactions were observed in the microcirculation, a hallmark of inflammation. Upregulated expression of adhesion molecules contribute to the local activation of inflammatory processes. We also found that large numbers of CD8+ effector T cells infiltrated into the obese adipose tissue, playing major roles in inflammatory macrophage infiltration into obese adipose tissue, the induction and maintenance of inflammation, and systemic insulin resistance. Our results demonstrate the power of our imaging technique to analyze multi-cellular interactions in inflammation in vivo and to evaluate new therapeutic interventions.

The combined effects of sidestream smoke extracts and glycated serum albumin on endothelial cells and platelets

BackgroundThe purpose of this study was to test the hypothesis that sidestream tobacco smoke extracts would inhibit the culture of endothelial cells and enhance platelet aggregation under diabetic vascular conditions. Sidestream tobacco smoke and advanced glycation end products are known cardiovascular risk factors and we aimed to determine the combined interaction between these two risk factors to promote cardiovascular diseases associated with diabetes.MethodsHuman umbilical vein endothelial cells were cultured in the presence of sidestream tobacco smoke extracts (SHS) or nicotine and glycated albumin (AGE) or non-glycated albumin. After 3 days, endothelial cell viability and density were investigated. Platelets were also incubated with these compounds for up to 6 hours. Platelet aggregation and the surface expression of CD41 and CD62P were examined. In some experiments, platelets were added to the endothelial cell culture to determine if an interaction between platelets and endothelial cells occurs that can alter the responses to SHS or AGE.ResultsIn general, the endothelial cell culture conditions were reduced in the presence of AGE and SHS. Nicotine, did not play a role in this reduction. Platelet aggregation proceeded faster in the presence of AGE and SHS. Interestingly, with the combined culture of endothelial cells and platelets, the endothelial cell culture conditions were improved and the platelet functional changes were diminished in the presence of SHS and AGE, as compared with the individual incubations.ConclusionsOur data suggests that diabetics that are exposed to SHS may have a higher likelihood for cardiovascular disease development through a diminished endothelial cell viability and an increased platelet activity, which are partially mediated by CD41 and not CD62P. This study provides support for an increased cardiovascular risk for diabetic patients that are exposed to SHS. This study also provides a new experimental technique to monitor platelet-endothelial cell interactions.

Lactobacillus reuteriprevents colitis by reducing P-selectin-associated leukocyte- and platelet-endothelial cell interactions

Recent findings indicate that dextran sodium sulfate (DSS)-induced colitis is associated with a prothrombogenic phenotype, with P-selectin playing a major role in platelet recruitment. It has been suggested that probiotics may ameliorate colonic inflammation. We therefore investigated how treatment with Lactobacillus reuteri influenced P-selectin expression, leukocyte and platelet endothelial cell interactions, and colitis severity in DSS-treated rats. Rats were divided into the following four groups: nontreated, DSS treated (5% in drinking water for 9 days), L. reuteri, and L. reuteri and DSS treated. The rats were anesthetized with Inactin (120 mg/kg ip), and the dual radiolabeled monoclonal antibody technique was used to quantify P-selectin expression. Leukocyte-endothelial and platelet-endothelial cell interactions were studied in colonic venules with intravital microscopy. Colitis severity was assessed using a disease activity index. Disease activity index increased, as did the expression of P-selectin in the entire colon after DSS treatment, but both were reduced to control levels with L. reuteri pretreatment. The increased platelet- and leukocyte-endothelial cell interactions after DSS treatment were abolished by pretreatment with L. reuteri. L. reuteri protects against DSS-induced colitis in rats. The protection is associated with reduced P-selectin expression and a decrease in leukocyte- and platelet-endothelial cell interactions.

Platelets Enhance Endothelial Adhesiveness in High Tidal Volume Ventilation

Although platelets induce lung inflammation, leading to acute lung injury (ALI), the extent of platelet-endothelial cell (EC) interactions remains poorly understood. Here, in a ventilation-stress model of lung inflammation, we show that platelet-EC interactions are important. We obtained freshly isolated lung endothelial cells (FLECs) from isolated, blood-perfused rat lungs exposed to ventilation at low tidal volume (LV) or stress-inducing high tidal volume (HV). Immunofluorescence and immunoprecipitation studies revealed HV-induced increases in cell-surface von Willebrand factor (vWf) expression on FLEC. This increased expression was inhibited by platelet removal from the lung perfusion and by including a P-selectin-blocking antibody in the lung perfusion. The expression was also blocked in lungs from P-selectin knockout (P sel(-/-)) mice perfused with autologous blood, but not with heterologous wild-type blood containing P-selectin-expressing platelets. These findings indicate that in ventilation stress, platelets transfer vWf to the EC surface and that platelet P-selectin plays a critical role in this transfer. Further evidence for such intercellular transfers was the HV-induced FLEC expressions of platelet glycoprotein 1b and of platelet P-selectin. We conclude that in ventilation stress, platelets deposit leukocyte- and platelet-binding proteins on the EC surface, thereby establishing the proinflammatory phenotype of the vascular lining.

Central Role of Rho Kinase in Lipopolysaccharide-Induced Platelet Capture on Venous Endothelium

BackgroundPlatelet-endothelial cell interactions play a key role in hemostasis and pathological coagulation and are dependent on different surface molecules that are expressed upon activation (eg, mediated by lipopolysaccharide [LPS]). Recently,...

In Vivo Platelet–Endothelial Cell Interactions in Response to Major Histocompatibility Complex Alloantibody

Platelets recruit leukocytes and mediate interactions between leukocytes and endothelial cells. Most studies examining this important platelet immune function have focused on the development of atherosclerosis, but similar mechanisms may contribute to acute and chronic vascular lesions in transplants. Platelets have been described as markers of transplant rejection, but little investigation has critically examined a role for platelets in transplant vasculopathy and, in particular, alloantibody-mediated transplant rejection. We now demonstrate using a skin transplant model that alloantibody indirectly induces platelet activation and rolling in vivo. Repeated IgG2a alloantibody injections result in sustained platelet-endothelial interactions and vascular pathology, including von Willebrand factor release, small platelet thrombi, and complement deposition. Maintenance of continued platelet-endothelial interactions are dependent on complement activation. Furthermore, we demonstrate that platelets recruit leukocytes to sites of alloantibody deposition and sustain leukocyte-endothelial cell interactions in vivo. Taken together, our model demonstrates an important role for platelets in alloantibody induced transplant rejection.

Insulin inhibition of platelet-endothelial interaction is mediated by insulin effects on endothelial cells without direct effects on platelets.

Platelet hyperreactivity contributes to adverse vascular events in diabetes mellitus. It is unclear whether platelet hyperreactivity is due to impaired insulin effects directly on platelets and /or originates from endothelial cells. Here, acute effects of insulin on platelet activation and platelet-endothelial cell interactions were analyzed. Washed human platelets were treated with insulin alone or in combinations with thrombin, collagen and ADP. Insulin signaling was analyzed by intracellular phosphorylation markers of platelet activation (ERK, p38 MAPK, PKB) or inhibition (VASP), platelet aggregation, intracellular Ca(2+) levels, and platelet adhesion to collagen coated surfaces and endothelial cells under flow. Insulin up to 100 nm for 5 min did not change phosphorylation status of VASP, p38, ERK or PKB in platelets. Integrin alpha(IIb)beta(3) activation, P-selectin expression, aggregation, and platelet adhesion to collagen coated surfaces and endothelial cells under flow were not altered by insulin. An insulin receptor was detected on endothelial cells but not on human platelets. Insulin treatment decreased platelet adhesion to endothelial cells through insulin stimulation of endothelial NO production and NOS inhibition interfered with this process. Insulin exerts no direct acute effects on platelet function but inhibits platelet-endothelial interaction by insulin stimulation of endothelial NO production.

Endothelial iNOS versus platelet iNOS: Responsibility for the platelet/leukocyte endothelial cell interaction in murine antigen induced arthritis in vivo

Since an increase of platelet-endothelial cell interactions has been observed in mice with Antigen- induced-Arthritis (AiA) as well as an increase of NO expression, the aim of our study was to investigate in vivo the influence of NO, especially the platelet and endothelial inducible NO Synthase, on the platelet- and leukocyte endothelial cell interaction. C57/Bl6 mice and iNOS deficient mice were disposed in 6 groups (each=7). After induction of AiA, rolling and adherent fluorescence labelled platelets and leukocytes were investigated by intravital microscopy (IVM) on day 8 after AiA. Rank SUM Test and ANOVA on ranks have been performed regarding the data. All arthritic mice presented an increase in platelet and leukocyte interaction with the endothelium compared to control groups. The arthritic iNOS deficient mice showed a more intense interaction of platelets and leukocytes with the endothelium in comparison with the wild-type arthritic mice. The group using arthritic wild-type recipient and iNOS deficient donor mice showed an increase in cell-interactions, leading to an endothelial effect, compared to the group using iNOS deficient arthritic recipient and wild-type donor mice. The IVM data lead to an anti-inflammatory effect of NO, since NO followed an increase in platelet- and leukocyte- endothelial cell interaction in iNOS deficient mice with AiA. In addition, we have shown for the first time in vivo that platelet NO produced by iNOS seems to have a minor influence on the leukocyte induced tissue damage in contrast to endothelial iNOS. Therefore, selective platelet inhibition would not interfere with the protective effect of NO.

In vivo interactions of platelets and leucocytes with the endothelium in murine antigen‐induced arthritis: the role of P‐selectin

Objective: Platelets are thought to participate in the pathogenesis of chronic inflammatory diseases such as rheumatoid arthritis (RA). We showed recently an in vivo increase in platelet–endothelial cell interactions in mice with antigen‐induced arthritis (AiA). The underlying mechanisms are not yet clear. The aim of this study was to investigate the impact of P‐selectin in AiA by means of intravital fluorescence microscopy (IVM).Methods: C57/Bl6 mice and P‐selectin‐deficient mice were divided into four groups (n = 7; control/AiA per strain). The extent of AiA was assessed by measuring knee joint swelling and by histological scoring. Rolling and adherent fluorescence‐labelled platelets and leucocytes were investigated by IVM.Results: In arthritic P‐selectin‐deficient mice (rolling: 0.05±0.01; adherent: 130±20 mm−2), compared to arthritic C57/Bl6 mice (rolling: 0.20±0.04; adherent: 1910±200 mm−2), platelet interaction was significantly reduced (p<0.05) and reached the level of both control groups without AiA. In addition, interaction of leucocytes in P‐selectin‐deficient arthritic animals (rolling: 0.12±0.06; adherent: 387±37 mm−2) was significantly decreased in comparison to arthritic C57/Bl6 animals (rolling: 0.21±0.06; adherent: 1492±284 mm−2; p<0.05). Swelling of the knee joint and histological scoring were reduced in arthritic P‐selectin‐deficient mice compared to arthritic C57/Bl6 mice.Conclusion: We have demonstrated for the first time in vivo a significant decrease in the interaction of platelets and leucocytes with the endothelium in P‐selectin‐deficient mice with AiA and a reduction in clinical and histological symptoms of arthritis. These findings suggest that leucocyte–endothelial cell interactions depend at least partially on platelet P‐selectin and therefore platelets may be responsible for the leucocyte tissue damage in AiA.

Role of P-Selectin in Platelet Sequestration in Pulmonary Capillaries during Endotoxemia

Background: There is growing evidence that platelets accumulate in the lung and contribute to the pathogenesis of acute lung injury during endotoxemia. The aims of the present study were to localize platelet sequestration in the pulmonary microcirculation and to investigate the role of P-selectin as a molecular mechanism of platelet endothelial cell interaction. Methods: We used in vivo fluorescence microscopy to quantify the kinetics of fluorescently labeled erythrocytes and platelets in alveolar capillary networks in rabbit lungs. Results: Six hours after onset of endotoxin infusion we observed a massive rolling along and firm adherence of platelets to lung capillary endothelial cells whereas under control conditions no platelet sequestration was detected. P-selectin was expressed on the surface of separated platelets which were incubated with endotoxin and in lung tissue. Pretreatment of platelets with fucoidin, a P-selectin antagonist, significantly attenuated the endotoxin-induced platelet rolling and adherence. In contrast, intravenous infusion of fucoidin in endotoxin-treated rabbits did not inhibit platelet sequestration in pulmonary capillaries. Conclusion: We conclude that platelets accumulate in alveolar capillaries following endotoxemia. P-selectin expressed on the surface of platelets seems to play an important role in mediating this platelet-endothelial cell interaction.

Shigatoxin Triggers Thrombotic Thrombocytopenic Purpura in Genetically Susceptible ADAMTS13-Deficient Mice.

The life threatening disease TTP is associated with ultra-large von Willebrand Factor multimers (UL-VWF) in the circulation due to inherited or acquired deficiency of the ADAMTS13 metalloprotease. Here we show that ADAMTS13-deficient mice generated by gene targeting are viable and exhibit normal survival through 2 years of age. Despite the absence of VWF-cleaving protease activity (<1% of normal), wild-type and ADAMTS13-deficient plasma exhibit identical VWF multimer distributions, and Adamts13−/− mice develop spontaneous TTP at an extremely low rate (2 cases out of 358 mice). However, intravital microscopy demonstrated that VWF-mediated platelet-endothelial interactions are significantly prolonged in Adamts13−/− mice. These observations suggested that additional environmental triggers and/or genetic modifying factors may be required to bring about TTP in the setting of ADAMTS13 deficiency. To address the effect of VWF level on development of TTP, Adamts13−/− mice were crossed to mice of the CASA/Rk strain which exhibit markedly elevated plasma VWF levels. Resulting CASA/Adamts13−/− mice demonstrated plasma VWF ranging from 150% to 600% of C57BL/6 controls, and we found that 21% of these mice were thrombocytopenic at baseline (vs. 0% of controls). Introduction of the CASA/Rk genetic background also resulted in the appearance of UL-VWF in CASA/Adamts13−/− mice, further prolonged VWF-mediated platelet-endothelial cell interactions, increased the rate of spontaneous TTP, and markedly decreased survival. Challenge of CASA/Adamts13−/− mice with shigatoxin (derived from bacterial pathogens associated with the related human disease hemolytic uremic syndrome) resulted in a striking syndrome closely resembling human TTP, with thrombocytopenia, profound microangiopathic hemolytic anemia, and platelet- and VWF-thrombi seen in multiple organs. Surprisingly, we observed no correlation between plasma VWF level and severity of TTP, implying the existence of TTP-modifying genes distinct from VWF. Our laboratory is pursuing the identification of these genes which may provide insight into the pathogenesis and treatment of TTP in humans. Finally, our data also suggest that microbial-derived toxins, or possibly other sources of endothelial injury, may be among the key factors required to trigger acute TTP in the setting of ADAMTS13 deficiency.

Junctional adhesion molecule-A deficiency increases hepatic ischemia-reperfusion injury despite reduction of neutrophil transendothelial migration

AbstractThe endothelial receptors that control leukocyte transmigration in the postischemic liver are not identified. We investigated the role of junctional adhesion molecule-A (JAM-A), a receptor expressed in endothelial tight junctions, leukocytes, and platelets, for leukocyte transmigration during hepatic ischemia-reperfusion (I/R) in vivo. We show that JAM-A is up-regulated in hepatic venular endothelium during reperfusion. I/R-induced neutrophil transmigration was attenuated in both JAM-A-/- and endothelial JAM-A-/- mice as well as in mice treated with an anti-JAM-A antibody, whereas transmigration of T cells was JAM-A independent. Postischemic leukocyte rolling remained unaffected in JAM-A-/- and endothelial JAM-A-/- mice, whereas intravascular leukocyte adherence was increased. The extent of interactions of JAM-A-/- platelets with the postischemic endothelium was comparable with that of JAM-A+/+ platelets. The I/R-induced increase in the activity of alanine aminotransferase (ALT)/aspartate aminotransferase (AST) and sinusoidal perfusion failure was not reduced in JAM-A-/- mice, while the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL)-positive hepatocytes was significantly higher. Thus, we show for the first time that JAM-A is up-regulated in hepatic venules and serves as an endothelial receptor of neutrophil transmigration, but it does not mediate leukocyte rolling, adhesion, or platelet-endothelial cell interactions. JAM-A deficiency does not reduce I/R-induced microvascular and hepatocellular necrotic injury, but increases hepatocyte apoptosis, despite attenuation of neutrophil infiltration. (Blood. 2005;106:725-733)

Platelet–endothelial cell interactions in murine antigen-induced arthritis

Growing evidence supports the substantial pathophysiological impact of platelets on the development of rheumatoid arthritis. At present there are no methods for studying these cellular mechanisms in vivo. The aim of this study was to visualize and investigate platelet-endothelial cell interaction in the knee joint of mice with antigen-induced arthritis (AiA) by means of intravital microscopy. In 14 mice (Balbc) intravital microscopic assessment was performed on day 8 after AiA induction in two groups (controls, AiA). The severity of AiA was assessed by measuring knee joint swelling and by histological scoring. Ex vivo fluorescently labelled rolling and adherent platelets and leucocyte-endothelium interactions were investigated by intravital fluorescence microscopy. Swelling of the knee joint as well as histological score was significantly enhanced in arthritic animals compared with controls. In control mice intravital microscopy revealed low baseline rolling and sticking of leucocytes and fluorescently labelled platelets. AiA induced a significant increase in the fraction of rolling leucocytes (3 times) and rolling platelets (6 times) compared to the control group. Furthermore, AiA induction resulted in a significantly enhanced number of adherent leucocytes (3-fold) and adherent platelets (12-fold) in comparison with control animals. Platelet kinetics were directly analysed using intravital microscopy in the arthritic microcirculation in vivo for the first time. We provide the first evidence that platelets accumulate in arthritic vessels, indicating platelet activation due to AiA. Platelet recruitment and subsequent activation might play an important role in the pathogenesis of rheumatoid arthritis.

Inhibition of thromboxane biosynthesis by triflusal in type 2 diabetes mellitus

Triflusal is an antiplatelet drug related to aspirin, with different pharmacological properties and a lower haemorrhagic risk. We aimed at comparing their effects on platelet and endothelial activation in type 2 diabetes mellitus (T2DM). In a randomized, double-blind, parallel group study, we compared the effects of three daily regimens (300, 600, and 900 mg) of triflusal, and aspirin (100 mg/day) on urinary 11-dehydro-thromboxane (TX)B 2, index of in vivo platelet activation, ex vivo platelet function using the analyzer PFA-100, plasma von Willebrand factor (vWF), P-selectin, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and serum nitrite and nitrate (NO 2 − + NO 3 −) in 60 T2DM patients. Triflusal induced a dose-dependent reduction in 11-dehydro-TXB 2 and a prolongation of closure time in the presence of collagen plus epinephrine (Coll/Epi-CT). The effects of the highest triflusal dose were not different from those of aspirin. The closure time in the presence of collagen plus ADP (Coll/ADP-CT), ICAM-1, VCAM-1, and NO 2 − + NO 3 − were not modified either by triflusal or aspirin. Plasma P-selectin and vWF were reduced by triflusal but not by aspirin. In T2DM triflusal causes a profound inhibition of platelet TXA 2 biosynthesis in vivo, acting on different targets involved in the platelet–endothelial cell interactions.

CD40-ligand-dependent induction of COX-2 gene expression in endothelial cells by activated platelets: inhibitory effects of atorvastatin

Increasing evidence shows the importance of platelet-endothelial cell interactions in the progression of atherosclerosis. Platelets contribute to coronary events both as major components of thrombi and as a triggering factor in inflammation that leads to plaque vulnerability. Recent data suggest that statins, besides their lipid-lowering properties, exert pleiotropic effects that may be beneficial in atherosclerosis. Whether activated platelets influence cyclooxygenase-2 (COX-2) expression in human umbilical vein endothelial cells (HUVEC), the effect of atorvastatin, and possible mechanisms were investigated. COX-2 gene expression in HUVEC was studied using real-time polymerase chain reaction. CD40 ligand surface expression of platelets was tested by fluorescence-activated cell sorting analyses. Activated platelets significantly up-regulated COX-2 gene expression in HUVEC. Co-incubation of platelets with atorvastatin was shown to reverse this up-regulation via reduction of CD40 ligand surface expression on platelets. Data suggest that atorvastatin influences CD40-CD40-ligand-dependent platelet-endothelial interaction and that this influence affects platelet-induced COX-2 expression in HUVEC.

Flavanols and Platelet Reactivity

Platelet activity and platelet-endothelial cell interactions are important in the acute development of thrombosis, as well as in the pathogenesis of cardiovascular disease. An increasing number of foods have been reported to have platelet-inhibitory actions, and research with a number of flavanol-rich foods, including, grape juice, cocoa and chocolate, suggests that these foods may provide some protection against thrombosis. In the present report, we review a series of in vivo studies on the effects of flavanol-rich cocoa and chocolate on platelet activation and platelet-dependent primary hemostasis. Consumption of flavanol-rich cocoa inhibited several measures of platelet activity including, epinephrine- and ADP-induced glycoprotein (GP) IIb/IIIa and P-Selectin expression, platelet microparticle formation, and epinephrine-collagen and ADP-collagen induced primary hemostasis. The epinephrine-induced inhibitory effects on GP IIb/IIIa and primary hemostasis were similar to, though less robust than those associated with the use of low dose (81 mg) aspirin. These data, coupled with information from other studies, support the concept that flavanols present in cocoa and chocolate can modulate platelet function through a multitude of pathways.