Platelet-endothelial Interactions Research Articles

Glycine and Taurine Equally Prevent Fatty Livers from Kupffer Cell‐Dependent Injury: An In Vivo Microscopy Study

IRI still is a major problem in liver surgery due to warm ischemia and organ manipulation. Steatosis is not only induced by diabetes, hyperalimentation, alcohol and toxins, but also chemotherapy given before resection. Since steatotic livers are prone to Kupffer cell-dependent IRI, protection of steatotic livers is of special interest. This study was designed to compare the effect of taurine and glycine on IRI in steatotic livers. Steatosis was induced with ethanol (7 g/kg b.w.; p.o.) in female SD rats. Ten minutes after inactivation of Kupffer cells with taurine or glycine (300 mM; i.v.), left liver lobes underwent 60 minutes of warm ischemia. Controls received the same volume of valine (300 mM; i.v.) or normal saline. After reperfusion, white blood cell-endothelial interactions and latex-bead phagocytosis by Kupffer cells were investigated. Liver enzymes were measured to estimate injury. For statistical analysis, ANOVA and Student's t-test were used. Glycine and taurine significantly decreased leukocyte- and platelet-endothelium interactions and latex-bead phagocytosis (p < 0.05). Liver enzymes were significantly lower after glycine and taurine (p < 0.05). This study shows that preconditioning with taurine or glycine is equally effective in preventing injury to fatty livers most likely via Kupffer cell-dependent mechanisms.

Rho kinase signalling mediates radiation-induced inflammation and intestinal barrier dysfunction

Radiotherapy is important in the management of pelvic malignancies, but radiation-induced intestinal damage is a dose-limiting factor. Microvascular injury and epithelial barrier dysfunction are considered to be rate-limiting aspects in radiation-induced enteropathy. This study investigated the role of Rho kinase signalling in radiation-induced inflammation and intestinal barrier dysfunction. The specific Rho kinase inhibitor Y-27632 (1 and 10 mg/kg) was given to C57BL/6J mice before challenge with 20 Gy radiation. Leucocyte- and platelet-endothelium interactions in the colonic microcirculation were assessed by intravital microscopy. Levels of myeloperoxidase (MPO) and CXC chemokines (macrophage inflammatory protein 2 and cytokine-induced neutrophil chemoattractant), and intestinal leakage were quantified after 16 h. Radiation increased leucocyte and platelet recruitment, MPO activity, CXC chemokine production and intestinal leakage. Y-27632 significantly reduced radiation-induced leucocyte rolling and abolished adhesion; it also decreased platelet rolling and adhesion by 55 and 74 per cent respectively (P < 0·050). Inhibition of Rho kinase signalling significantly decreased radiation-provoked formation of CXC chemokines, MPO activity by 52 per cent, and intestinal leakage by 67 per cent (P < 0·050). Rho kinase activity constitutes an important signalling mechanism in radiation-induced inflammation and intestinal barrier dysfunction.

Can we extrapolate the outcomes of in vitro studies on murine endothelium to studies of human platelet-endothelium interactions? A technical note

IntroductionInteractions between vascular endothelium and blood platelets play a crucial role in cardiovascular diseases. Ex vitro models which use endothelial cells and platelets were the essential tools to investigate these interactions and their impact on haemostasis. The impaired interplay between vascular endothelium, blood platelets and leukocytes is believed to contribute to the development of cardiovascular disease. In this study we compared the ability of human (HUVECs) and murine (HECa10) endothelial cells to inhibit human platelet function and reactivity under in vitro conditions.Material and methodsThe aliquots of platelet-rich plasma obtained from 20 healthy donors were incubated with murine endothelial cell line HECa10 or human umbilical vein endothelial cells (HUVECs) (10 min, 37°C) prior to agonizing platelets with 5 µM ADP and monitoring platelet reactivity for 10 min using optical aggregation.ResultsSignificant reduction in ADP-induced platelet aggregation in the presence of endothelial cell cultures remained independent of cell count. HUVECs appeared much more effective in the inhibition of platelet aggregation compared to HECa10 (35.2 ±2.3 AU vs. 43.7 ±2.0 AU, p= 0.025).ConclusionsHECa10 cells have much lower potential to inhibit platelet aggregation than HUVECs. This implies that these two cell lines may not be freely used interchangeably in in vitro experiments. These findings clearly indicate that the outcomes of in vitro studies performed with murine EC lines cannot be unreservedly extrapolated to human platelet-endothelium interactions.

Molecular Imaging of Activated von Willebrand Factor to Detect High-Risk Atherosclerotic Phenotype

We hypothesized that noninvasive molecular imaging of activated von Willebrand factor (vWF) on the vascular endothelium could be used to detect a high-risk atherosclerotic phenotype. Platelet-endothelial interactions have been linked to increased inflammatory activation and prothrombotic state in atherosclerosis. These interactions are mediated, in part, by platelet glycoprotein (GP) Ibα, suggesting that dysregulated endothelial vWF is a marker for high-risk atherosclerotic disease. Microbubbles targeted to activated vWF were prepared by surface conjugation of recombinant GPIbα. Flow-chamber studies were used to evaluate attachment of targeted microbubbles to immobile platelet aggregates bearing activated vWF. Contrast-enhanced ultrasound (CEU) molecular imaging of the aorta from mice was performed: 1) ex vivo after focal crush injury and blood perfusion; and 2) in vivo in mice with advanced atherosclerosis produced by deletion of the low-density lipoprotein receptor and ApoBec-1 editing peptide (LDLR(-/-)/ApoBec-1(-/-)). In flow-chamber studies, tracer attachment to vWF was >10-fold greater for microbubbles bearing GPIbα compared with control microbubbles (p < 0.01). In the ex vivo aortic injury model, CEU signal enhancement for vWF-targeted microbubbles occurred primarily at the injury site and was 4-fold greater than at noninjured sites (p < 0.05). In LDLR(-/-)/ApoBec-1(-/-) mice, inflammatory cell infiltrates and dense vWF expression on the intact endothelium were seen in regions of severe plaque formation. Scanning electron microscopy demonstrated widespread platelet-endothelial interaction and only few sites of endothelial erosion. On CEU, signal enhancement for vWF-targeted microbubbles was approximately 4-fold greater (p < 0.05) in LDLR(-/-)/ApoBec-1(-/-) compared with wild-type mice. En face aortic microscopy demonstrated regions where platelet adhesion and microbubble attachment colocalized. Molecular imaging using GPIbα as a targeting moiety can detect the presence of activated vWF on the vascular endothelium. This strategy may provide a means to noninvasively detect an advanced prothrombotic and inflammatory phenotype in atherosclerotic disease.

P38 Mitogen-activated protein kinase signalling regulates vascular inflammation and epithelial barrier dysfunction in an experimental model of radiation-induced colitis

: Microvascular injury and epithelial barrier dysfunction are rate-limiting aspects in radiation enteropathy. This study examined the role of p38 mitogen-activated protein kinase (p38 MAPK) signalling in radiation-induced colitis in an experimental model. : The p38 MAPK inhibitor SB239063 was administered to mice immediately before exposure to 20 Gy radiation. Leucocyte- and platelet-endothelium interactions in the colonic microcirculation were assessed by intravital microscopy. Levels of myeloperoxidase (MPO) and CXC chemokines (macrophage inflammatory protein (MIP) 2 and cytokine-induced neutrophil chemoattractant (KC)), and albumin leakage were quantified 16 h after irradiation. : Irradiation induced an increase in leucocyte and platelet recruitment, MPO activity, CXC chemokine levels and intestinal leakage. Inhibition of p38 MAPK by SB239063 decreased radiation-induced leucocyte and platelet recruitment (leucocyte rolling and adhesion by 70 and 90 per cent, both P < 0.001; that of platelets by 70 and 74 per cent, both P < 0.001). It also reduced radiation-provoked increases in colonic MPO activity by 88 per cent (P < 0.001), formation of MIP-2 and KC by 72 and 74 per cent respectively (P = 0.003 and P < 0.001), and intestinal leakage by 81 per cent (P < 0.001). : p38 MAPK is an important signalling pathway in radiation-induced colitis.

Inhibitors of Platelet Adhesion

Platelet aggregation, in fundamental terms, is considered a biological end point that contributes to the occurrence of clinical events among patients with advanced atherosclerotic coronary artery disease. Acute coronary syndrome, including non–ST elevation myocardial infarction (NSTEMI) and ST elevation myocardial infarction (STEMI), accounts for upward of 733 000 hospital admissions yearly in the United States.1 The primary pathophysiological mechanism responsible for the majority of acute coronary syndromes is endothelial plaque disruption with and subsequent platelet adhesion, activation, and thrombus formation.2 The end result is formation of thrombus within a coronary artery, leading to subtotal vessel occlusion with NSTEMI and complete occlusion of the artery with STEMI. In this review, we provide a contemporary view of platelet adhesion as a highly coordinated and teleologically conserved process achieved by surface receptors, protein ligands, and matrix proteins operating at the platelet–subendothelium interface. We also discuss drugs in development, including monoclonal antibodies, inhibitory peptides, and oligonucleotides; preclinical data; and, where available, clinical trial results, highlighting the potential translation of fundamental constructs in platelet biology to patient care. Platelets are derived from a hematopoietic bone marrow stem cell precursor.3 Through a highly conserved program of cellular differentiation, this stem cell precursor becomes a megakaryocyte at a rate of approximately 100 000 000 megakaryocytes produced per day.3 Subsequently, each individual megakaryocyte will give rise to approximately 500 platelets via additional developmental steps within the bone marrow that involve a proplatelet intermediate stage.3 Once released into circulation, a mature platelet has an expected life span of 7 to 10 days.3 Platelet maturation and development involve the expression of receptors on the platelet cell surface. These receptors facilitate platelet adhesion and activation, and they promote thrombus development through receptor–ligand interactions, with several ligands expressed on the surface of endothelial cells, within the …

A sulfaphenazole-sensitive EDHF opposes platelet-endothelium interactions in vitro and in the hamster microcirculation in vivo

A CYP2C9-dependent endothelium-derived hyperpolarizing factor (EDHF) controls blood flow in many microvascular beds of various species by targeting vascular smooth muscle potassium channels. Since platelets express the same channels, we tested whether EDHF hyperpolarizes platelets and exerts an antithrombotic function in vivo. Interaction of injected human platelets with the arteriolar wall (platelet-vessel wall interaction, PVWI) was assessed by intravital microscopy in skin muscle of awake hamsters. To understand the mechanisms of EDHF-induced platelet inhibition, we studied whether cultured human umbilical vein endothelial cells overexpressing CYP2C9-mRNA in vitro released a factor that could hyperpolarize human platelets. Under control conditions, there was no firm adhesion of platelets to the arteriolar wall, but temporary PVWI occurred. Local superfusion of the CYP2C9 inhibitor sulfaphenazole, at doses known to block EDHF-dependent dilations, significantly augmented PVWI, as did inhibition of NO synthase. Inhibition of both factors exerted additive effects on PVWI. Likewise, firm adhesion of a small fraction of platelets was observed. The prothrombotic effects of CYP2C9 inhibition in vivo were reversed by exogenous superfusion with 11,12-epoxyeicosatrienoic acids. Hyperpolarization reduced platelet adhesion to endothelial cells under static conditions in vitro and was dependent on calcium-activated potassium channels. The factor also reduced ADP-induced expression of platelet P-selectin, indicating reduction of platelet activity. The arteriolar endothelium in vivo continuously releases a CYP2C9-derived EDHF. This EDHF exerts its effects by hyperpolarization of platelets through activation of K(Ca) channels and reduction of platelet adhesion molecule expression, indicating that hyperpolarization reduces platelet activation. This demonstrates that EDHF is part of the antithrombotic properties of healthy endothelium in vivo.

Warfarin and Stroke Outcomes in Hemodialysis Patients with Atrial Fibrillation

The prevalence of atrial fibrillation in ESRD is extremely high, reaching 27%,1 and fibrillation, as in the general population, also is associated with increased mortality in hemodialysis patients.2 A large number of trials show the usefulness of oral anticoagulation therapy1 for primary and secondary prevention of stroke in patient populations with atrial fibrillation absent ESRD.3 Recently, a large study demonstrated the superiority of oral anticoagulation therapy compared with the combination of clopidogrel plus aspirin with regard to stroke prevention, with no added risk of bleeding.4 Even trials performed in patients with high hemorrhagic risk who took warfarin, particularly the elderly, show that benefits of treatment exceed the risks when the international normalized ratio (INR) is monitored correctly. The decision to use oral anticoagulation therapy, particularly warfarin, in patients with atrial fibrillation involves weighing the risk of a thromboembolic event without therapy, or with inadequate anticoagulation, against the risk of a hemorrhagic event on therapy, particularly over-anticoagulation. Efficacy and safety of anticoagulation in atrial fibrillation depend on maintaining the INR between 2 and 3,5 as recommended by most practice guidelines.6 Recently an INR of 3.0 to 3.4 has been proposed to achieve optimal anticoagulation intensity in patients with atrial fibrillation.7 However, dialysis populations …

Cyclooxygenase Inhibitors: Instrumental Drugs to Understand Cardiovascular Homeostasis and Arterial Thrombosis

Nonsteroidal anti-inflammatory drugs (NSAIDs) and Aspirin target cyclooxygenase (cox) enzymes and inhibit the synthesis of prostanoids. These drugs were originally developed to reduce the cardinal signs of inflammation, primarily pain. Prior to understanding their mechanism of action, investigations of Aspirin response in humans have revealed a protective effect on the cardiovascular system. Daily low-dose Aspirin is a well-established and prevailing treatment for the prevention of arterial thrombosis. Platelet inhibition by Aspirin results from the irreversible inhibition of cyclooxygenase-1 enzyme and prevention of thromboxane A2, a potent aggregatory agent, formation. In an effort to develop drugs with a safer profile for the stomach, a new form of cyclooxygenase was discovered. Subsequently and with the development of cloning strategies, cyclooxygenase-2 was cloned and characterized to have a profile of induction associated with the inflammatory reaction. This provided the rationale to target cox-2 enzyme and development of cox-2 selective drugs such as Vioxx and Celebrex. Coxibs were initially a successful treatment for arthritic patients also providing a reduction in gastric ulceration compared to traditional NSAIDs. Further investigations on the drug response to coxibs revealed a detrimental effect; the increase of myocardial infarctions, and the withdrawal of Vioxx from the market. The current theory to explain the harmful effect of coxib suggests the disruption of the platelet-endothelium interaction and selective inhibition of endothelium cox-2 activity depriving the cardiovascular system of vascular prostacyclin with anti-aggregatory activity. The balancing prostanoid theory to explain coxib cardiovascular complications was recently opposed. Recent investigations of Aspirin drug response have unraveled genetic variations in the cox-1 gene that are associated with the occurrence of Aspirin sensitivity or lack of protections against cardiovascular accidents. Screening for cox-1 gene variants will identify susceptible patients and reduce undesirable side-effects associated with Aspirin. Here we review recent findings in the cyclooxygenase-1 pathway and potential impact for the development of therapeutics that would segregate antithrombotic benefit from bleeding risk. Over 100 years following the initial use of Aspirin, cyclooxygenase inhibitors continue to be instrumental in our understanding of cardiovascular homeostasis and how the cyclooxygenase pathways are disrupted in disease.

Soluble lectin-like oxidized low density lipoprotein receptor-1 in type 2 diabetes mellitus

The lectin-like oxidized low density lipoprotein receptor-1 (LOX-1) can be proteolytically cleaved and released as soluble forms (sLOX-1). We have determined serums LOX-1 in type 2 diabetes and evaluated the effect of glucose and advanced glycation end products (AGEs) on sLOX-1 in vitro and in vivo. Endothelial cells were incubated with glucose or AGEs, and sLOX-1 in cell medium was measured. Serum sLOX-1 was measured in 219 diabetic patients and 187 controls by ELISA. The effect of lowering glucose and AGEs on sLOX-1 was determined in 38 poorly controlled diabetic patients after improvement in glycemic control. Incubation of endothelial cells with AGE-BSA led to a dose-dependent increase in sLOX-1, whereas the effect of glucose on sLOX-1 was less marked. Serum sLOX-1 was 9% higher in diabetic patients compared with controls (P<0.01). In the poorly controlled patients, serum sLOX-1 decreased by 12.5% after improvement in glycemic control (P<0.05). The magnitude of reduction in sLOX-1 correlated with the improvement in hemoglobin A1c and AGEs but not with the reduction in oxidized LDL. sLOX-1 level is increased in type 2 diabetes. Both glucose and AGEs are important determinants of LOX-1 expression, and lowering glucose and AGEs leads to a reduction in sLOX-1.

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.

Platelet-endothelium interaction and thrombus formation in diabetic microcirculation

Platelet-endothelium interaction and thrombus formation in diabetic microcirculation

Reduced Fibrin Deposition and Intravascular Thrombosis in hDAF Transgenic Pig Hearts Perfused With Tirofiban

Solid organ xenograft rejection is associated with vascular injury resulting at least in part in platelet activation, and rejected xenografts invariably demonstrate intravascular thrombosis and interstitial hemorrhage. Complement activation plays a prominent role in platelet-endothelial interaction. We tested the effects of platelet GPIIb/IIIa inhibitor tirofiban during perfusion of hDAF pig hearts. Using a working-heart model, nontransgenic and hDAF pig hearts were perfused with tirofiban or human blood only. Myocardial damage was determined by hemodynamic parameters (cardiac output, stroke work index) and creatine phosphokinase. Further monitoring included the assessment of complement factors (C3, C4), platelets, fibrinogen, ATIII, and graft histology. Tirofiban increased cardiac output (CO) and stroke work index (SWI) of nontransgenic pig hearts and improved superior CO and SWI of hDAF pig hearts. Although perfusion time of nontransgenic pig hearts was prolonged by tirofiban (196+/-65 min vs. 162+/-122 min), a similar effect in hDAF pig hearts (218+/-116 min vs. 222+/-30 min) could not be demonstrated. Tirofiban reduced consumption of C3 and C4 independently from hDAF. Depletion of fibrinogen was equally diminished by tirofiban and hDAF; the combination of both agents obtained no further reduction. ATIII consumption was most effectively inhibited by this combination. Intravascular fibrin deposition was reduced by tirofiban and hDAF, but particularly by the combination of the two agents. Improvement of heart performance and reduction of myocardial damage and intravascular thrombosis confirm a role of the GPIIb/IIIa inhibitor tirofiban for the prevention of hDAF pig heart rejection and xenograft function.

Immune Complexes Mediate Rapid Alterations in Microvascular Permeability: Roles for Neutrophils, Complement, and Platelets

Immune complex-induced responses involve multiple cellular and molecular mechanisms. However, how these pathways interact in the initiation of immune complex-induced response is poorly understood. Therefore the aim of this study was to investigate the immediate response of the microvasculature to immune complex formation. The reverse passive Arthus (RPA) model was applied to the mouse cremaster muscle. Intravital microscopy was used to examine alterations in florescein isothiocyanate (FITC)-dextran leakage from microvessels, and endothelial interactions of leukocytes and platelets in postcapillary venules. Immune complex deposition induced rapid increases in microvascular permeability and leukocyte adhesion and emigration. Inhibition of platelet-activating factor (PAF) and leukotrienes inhibited the increase in permeability. Depletion of C3 reduced immune complex-mediated leukocyte recruitment and permeability, and a similar effect on permeability was observed following inhibition of leukocyte adhesion. Mast cell stabilization reduced increases in leukocyte adhesion and emigration but accelerated the increase in microvascular permeability. Platelet-endothelial interactions also increased during the RPA response, and platelet depletion delayed the changes in permeability and inhibited leukocyte recruitment. This study demonstrates that immune complexes induce a rapid induction of complement-dependent leukocyte recruitment, and neutrophil-dependent microvascular dysfunction. Furthermore, this study identifies a role for platelets in promoting immune complex-induced leukocyte recruitment.

P056 Platelet-endothelial interaction in patients with chronic liver diseases

P056 Platelet-endothelial interaction in patients with chronic liver diseases

Platelet Function in Acute Experimental Pancreatitis

Acute pancreatitis (AP) is characterized by disturbances of pancreatic microcirculation. It remains unclear whether platelets contribute to these perfusion disturbances. The aim of our study was to investigate platelet activation and function in experimental AP. Acute pancreatitis was induced in rats: (1) control (n = 18; Ringer’s solution), (2) mild AP (n = 18; cerulein), and (3) severe AP (n = 18; glycodeoxycholic acid (GDOC) + cerulein). After 12 h, intravital microscopy was performed. Rhodamine-stained platelets were used to investigate velocity and endothelial adhesion in capillaries and venules. In addition, erythrocyte velocity and leukocyte adhesion were evaluated. Serum amylase, thromboxane A2, and histology were evaluated after 24 h in additional animals of each group. Results showed that 24 h after cerulein application, histology exhibited a mild AP, whereas GDOC induced severe necrotizing AP. Intravital microscopy showed significantly more platelet–endothelium interaction, reduced erythrocyte velocity, and increased leukocyte adherence in animals with AP compared to control animals. Thromboxane levels were significantly elevated in all AP animals and correlated with the extent of platelet activation and severity of AP. In conclusion, platelet activation plays an important role in acute, especially necrotizing, pancreatitis. Mainly temporary platelet–endothelium interaction is observed during mild AP, whereas severe AP is characterized by firm adhesion with consecutive coagulatory activation and perfusion failure.

Platelets and Endothelial Cells

The pathogenesis of atherosclerosis, the leading cause of morbidity and mortality in industrial countries, is multifactorial. Atherogenesis, the development of atherosclerotic lesions, is initiated by a mechanical or functional injury of the endothelium. The function of the endothelium is influenced by multiple factors as a consequence of cell-cell interactions. Cell-cell communication between endothelial cells with platelets has only recently begun to receive systematic study. In recent years it has been established that platelet-endothelial interactions are involved at all stages of atherosclerotic disease. This article reviews the interactions between endothelial cells and platelets in the context of their role to initiate and accelerate atherothrombosis, as well as in acute thrombotic occlusion (e.g., at the site of atherosclerotic plaque rupture or subsequent to coronary angioplasty). From a mechanistic standpoint, platelets and endothelial cells communicate on multiple levels. Cross-talk may occur over a distance (paracrine signaling), via transient interactions (so-called give-and-go mechanism), or through receptor-mediated cell-cell adhesion. Platelets may release or transfer substances that influence endothelial cell function, and vice versa. Among many others, adhesion molecules, such as P-selectin (CD62P), are of special interest because of their role in modulating interactions between blood cells and the endothelium, and also because of the possible use of the soluble form as a plasma predictor of adverse cardiovascular events. In addition to dietary, cholesterol and lipid lowering, and other pharmaceutical approaches, antiplatelet therapy plays an important part in the treatment of atherosclerosis and its multifactorial clinical manifestations. Understanding the specific interactions between platelets and the endothelium may lead to the development of novel therapeutic strategies.

Inflammatory Blues Turns Velvet Skin Into Rawhide

The directed homing of leukocytes is crucial during immune surveillance or inflammation and is accomplished by a complex cooperation of signaling and adhesion molecules.1,2 Its pathophysiologic relevance is exemplified by various inflammatory diseases such as atherosclerosis.3 At present, the course of leukocyte trafficking is well established through the classical multistep cascade of initial tethering and rolling of leukocytes over vascular endothelium, followed by firm adhesion and their subsequent spreading and transendothelial migration.1,2 Leukocyte rolling is mediated by a subgroup of C-type lectins; E-, L-, and P-selectin, through shear-resistant binding to particular cell-surface carbohydrates. E- and L-selectin are expressed on activated endothelial cells and most leukocytes, respectively, while P-selectin is stored in the secretory compartments of platelets and endothelial cells to become rapidly upregulated on cell activation. The best characterized ligand for selectins is P-selectin glycoprotein ligand-1 (PSGL-1),4 a heavily posttranslationally modified homodimeric transmembrane glycoprotein. PSGL-1 contains functionally essential sialylated and fucosylated carbohydrate moieties, known as sialyl Lewis X (sLex) groups, and is expressed on blood cells such as neutrophils, monocytes, and platelets.5 The importance of PSGL-1 for cell recruitment is highlighted by studies using transgenic mice deficient in PSGL-1, which revealed a crucial contribution to P-selectin–dependent rolling on inflamed endothelium, indicating a function of PSGL-1 in early inflammatory responses.6 Presented by endothelium-bound leukocytes, PSGL-1 supports the initial L-selectin–dependent tethering of blood-borne leukocytes to the already adherent leukocytes at the inflamed vessel wall followed by E-selectin-mediated rolling on the endothelium.7 Besides supporting leukocyte–endothelium interactions, PSGL-1 promotes the P-selectin–dependent initial tethering of platelets to monocytes8,9 followed by more stable interactions through integrins expressed on both platelets and monocytes. In addition, the interaction between PSGL-1 and P-selectin also plays an essential role in the delivery …

Lung ischemia–reperfusion injury: implications of oxidative stress and platelet–arteriolar wall interactions

Pulmonary ischemia–reperfusion (IR) injury may result from trauma, atherosclerosis, pulmonary embolism, pulmonary thrombosis and surgical procedures such as cardiopulmonary bypass and lung transplantation. IR injury induces oxidative stress characterized by formation of reactive oxygen (ROS) and reactive nitrogen species (RNS). Nitric oxide (NO) overproduction via inducible nitric oxide synthase (iNOS) is an important component in the pathogenesis of IR. Reaction of NO with ROS forms RNS as secondary reactive products, which cause platelet activation and upregulation of adhesion molecules. This mechanism of injury is particularly important during pulmonary IR with increased iNOS activity in the presence of oxidative stress. Platelet–endothelial interactions may play an important role in causing pulmonary arteriolar vasoconstriction and post-ischemic alveolar hypoperfusion. This review discusses the relationship between ROS, RNS, P-selectin, and platelet–arteriolar wall interactions and proposes a hypothesis for their role in microvascular responses during pulmonary IR.