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Platelets are very abundant in the blood, where they play a role in hemostasis, inflammation, and immunity. When activated, platelets undergo a conformational change that allows the release of numerous effector molecules as well as the production of extracellular vesicles, which are circulating submicron vesicles (10 to 1,000 nm in diameter) released into the extracellular space. Extracellular vesicles are formed by the budding of platelet and they carry some of its contents, including nucleic acids, surface proteins, and organelles. While platelets cannot cross tissue barriers, platelet-derived extracellular vesicles can enter the lymph, bone marrow, and synovial fluid. This allows the transfer of diverse contents carried by these platelet-derived vesicles to cell recipients and organs inaccessible to platelets where they can perform many functions. This review highlights the importance of these platelet-derived extracellular vesicles under different physiological and pathophysiological conditions.

Purpose: Clinician-investigators have an important role in the development and implantation of new therapies and treatment modalities; however, there have been several reports highlighting a pending shortage in the clinician-investigators’ workforce. In Canada, the Royal College has promoted the development of clinician-investigators programs (CIP) to facilitate the training of these individuals. There is currently a paucity of data regarding the outcomes of such programs. This study aims to identify the strengths and areas of improvement of the Montreal University CIP. Methods: An internet-based 51-question survey was distributed to all the alumni from the University of Montreal CIP. Participation was voluntary and no incentives were provided. The response rate was 64%. Results: Among respondents, 50% (n=16) had completed their clinical residency and all CIP requirements. The majority of these individuals (63%) had become independent investigators and had secured provincial and national funding. Satisfaction of the respondents was high regarding the overall program (85%), the research skills developed during the CIP (84%) and the financial support obtained during the program (72%). The satisfaction rate regarding career planning was lower (63%). Conclusion: This survey demonstrates that, while indicators are favorable, some areas still require improvement. Several steps to improve the CIP have been identified; notably, the transition from the CIP to early independent career has been identified as critical in the development of clinician-investigators and steps have been taken to improve this progression

Platelets play a major role in the processes of primary hemostasis and pathological inflammation-induced thrombosis. In the mid-2000s, several studies expanded the role of these particular cells, placing them in the “immune continuum” and thus changing the understanding of their function in both innate and adaptive immune responses. Among the many receptors they express on their surface, platelets express Toll-Like Receptors (TLRs), key receptors in the inflammatory cell–cell reaction and in the interaction between innate and adaptive immunity. In response to an infectious stimulus, platelets will become differentially activated. Platelet activation is variable depending on whether platelets are activated by a hemostatic or pathogen stimulus. This review highlights the role that platelets play in platelet modulation count and adaptative immune response during viral infection.

Background Antiplatelet therapy with aspirin (acetylsalicylic acid [ASA]) is less efficient in some coronary patients, which increases their risk of developing thrombosis. Elevated blood levels of thromboinflammatory mediators, like soluble CD40L (sCD40L), may explain such variabilities. We hypothesized that in the presence of elevated levels of sCD 40L, the efficacy of ASA may vary and aimed to determine the effects of ASA on CD 40L signaling and aggregation of platelets. Methods and Results The effects of ASA on CD 40L‐treated human platelets, in response to suboptimal concentrations of collagen or thrombin, were assessed at levels of aggregation, thromboxane A 2 secretion, and phosphorylation of p38 mitogen‐activated protein kinase, nuclear factor kappa B, transforming growth factor‐β–activated kinase 1, and myosin light chain. sCD 40L significantly elevated thromboxane A 2 secretion in platelets in response to suboptimal doses of collagen and thrombin, which was reversed by ASA . ASA did not inhibit the phosphorylation of p38 mitogen‐activated protein kinase, nuclear factor kappa B, and transforming growth factor‐β–activated kinase 1, with sCD 40L stimulation alone or with platelet agonists. sCD 40L potentiated platelet aggregation, an effect completely reversed and partially reduced by ASA in response to a suboptimal dose of collagen and thrombin, respectively. The effects of ASA in sCD 40L‐treated platelets with collagen were related to inhibition of platelet shape change and myosin light chain phosphorylation. Conclusions ASA does not affect platelet sCD 40L signaling but prevents its effect on thromboxane A 2 secretion and platelet aggregation in response to collagen, via a mechanism implying inhibition of myosin light chain. Targeting the sCD40L axis in platelets may have a therapeutic potential in patients with elevated levels of sCD 40L and who are nonresponsive or less responsive to ASA.

Platelets are megakaryocyte-derived fragments lacking nuclei and prepped to maintain primary hemostasis by initiating blood clots on injured vascular endothelia. Pathologically, platelets undergo the same physiological processes of activation, secretion, and aggregation yet with such pronouncedness that they orchestrate and make headway the progression of atherothrombotic diseases not only through clot formation but also via forcing a pro-inflammatory state. Indeed, nuclear factor-κB (NF-κB) is largely implicated in atherosclerosis and its pathological complication in atherothrombotic diseases due to its transcriptional role in maintaining pro-survival and pro-inflammatory states in vascular and blood cells. On the other hand, we know little on the functions of platelet NF-κB, which seems to function in other non-genomic ways to modulate atherothrombosis. Therein, this review will resemble a rich portfolio for NF-κB in platelets, specifically showing its implications at the levels of platelet survival and function. We will also share the knowledge thus far on the effects of active ingredients on NF-κB in general, as an extrapolative method to highlight the potential therapeutic targeting of NF-κB in coronary diseases. Finally, we will unzip a new horizon on a possible extra-platelet role of platelet NF-κB, which will better expand our knowledge on the etiology and pathophysiology of atherothrombosis.

Platelets are megakaryocyte-derived acellular fragments prepped to maintain primary hemostasis and thrombosis by preserving vascular integrity. Although they lack nuclei, platelets harbor functional genomic mediators that bolster platelet activity in a signal-specific manner by performing limited de novo protein synthesis. Furthermore, despite their limited protein synthesis, platelets are equipped with multiple protein degradation mechanisms, such as the proteasome. In nucleated cells, the functions of the proteasome are well established and primarily include proteostasis among a myriad of other signaling processes. However, the role of proteasome-mediated protein degradation in platelets remains elusive. In this review article, we recapitulate the developing literature on the functions of the proteasome in platelets, discussing its emerging regulatory role in platelet viability and function and highlighting how its functional coupling with the transcription factor NF-κB constitutes a novel potential therapeutic target in atherothrombotic diseases.

Background CD40 ligand (CD40L) is a thromboinflammatory molecule that predicts cardiovascular events. CD40L is a strong activator of nuclear factor kappa B (NF‐κB) in platelets that primes and enhances platelet activation in response to thrombotic stimuli. In addition to its classical receptor CD40, CD40L binds αIIbβ3, α5β1, and αMβ2 in various cell types. However, the function of the different CD40L receptors on platelets remains unexplored. The present study aims to identify the receptors of CD40L, involved in platelet NF‐κB activation, their downstream signaling and their implication in platelet aggregation. Methods and Results We showed that platelets express CD40, αIIbβ3, and α5β1 and release CD40L in response to sCD40L stimulation. sCD40L alone dose‐dependently induced platelet NF‐κB activation; this effect was absent in CD40 −/− mouse platelets and inhibited by the CD40 blockade, but was unaffected by the αIIbβ3 or α5β1 blockade in human platelets. sCD40L/CD40 axis activates transforming growth factor‐β‐activated kinase 1 upstream of NF‐κB. In functional studies, sCD40L alone did not affect platelet aggregation but potentiated the aggregation response in the presence of suboptimal doses of thrombin; this effect was abolished by CD40, transforming growth factor‐β‐activated kinase 1, and NF‐κB inhibitors. Conclusions CD40L primes platelets via signaling pathways involving CD40/transforming growth factor‐β‐activated kinase 1/NF‐κB, which predisposes platelets to enhanced activation and aggregation in response to thrombotic stimuli.

Patients with antiphospholipid syndrome (APS) produce antiphospholipid antibodies (aPL) and develop vascular thrombosis that may occur in large or small vessels in the arterial or venous beds. On the other hand, many individuals produce aPL and yet never develop thrombotic events. Toll-like receptor 4 (TLR4) appears to be necessary for aPL-mediated prothrombotic effects in venous and microvascular models of thrombosis, but its role in arterial thrombosis has not been studied. Here, we propose that aPL alone are insufficient to cause thrombotic events in an arterial model of APS, and that a concomitant trigger of innate immunity (e.g. TLR4 activation) is required. We show specifically that anti-β2-glycoprotein I (anti-β2GPI) antibodies, a subset of aPL, accelerated thrombus formation in C57BL/6 wild-type, but not TLR4-deficient, mice in a ferric chloride-induced carotid artery injury model. These aPL bound to arterial and venous endothelial cells, particularly in the presence of β2GPI, and to human TLR4 by enzyme-linked immunoassay. Arterial endothelium from aPL-treated mice had enhanced leukocyte adhesion, compared to control IgG-treated mice. In addition, aPL treatment of mice enhanced expression of tissue factor (TF) in leukocytes induced by the TLR4 ligand lipopolysaccharide (LPS). aPL also enhanced LPS-induced TF expression in human leukocytes in vitro. Our findings support a mechanism in which aPL enhance TF expression by leukocytes, as well as augment adhesion of leukocytes to the arterial endothelium. The activation of TLR4 in aPL-positive individuals may be required to trigger thrombotic events.

The physicochemical properties and potential cytotoxicity of nanoparticles (NPs) are significantly influenced by their inter- action with proteins, which results in corona formation. Here, we have determined whether corona formation, resulting from interactions between superparamagnetic iron oxide nanoparticles (SPIONs) and different cell culture media, may have consequences for driving NP toxic effects. To address this issue, complementary methods were used. The deter- mination of the hydrodynamic size distribution by ζ (zeta) potential measurement indicated that SPIONs were negatively charged under all conditions but that the actual charge was differed with the cell culture medium used. In vitro protein adsorption studies were carried out using the Bradford protein assay and Fourier transform infrared spectroscopy (FTIR). The Bradford assay revealed that the concentration of unadsorbed proteins and other biomolecules decreased when the SPION concentration increased. FTIR showed that the proteins were, indeed, adsorbed onto the NP surface. This was followed by matrix-assisted laser desorption/ionization time-of-flight secondary ion mass spectrometry (MALDI TOF-SIMS), to identify the adsorbed proteins. Ultimately, three different cell viability assays led to the conclusion that the SPIONs were not toxic for all the concentrations used here. In summary, we found that corona formation on the SPIONs depends on the composition of the culture media but has no consequence for nanotoxicity. We have shown that the application of complementary methods has provided novel insights into SPION/protein interactions.

Diabetes mellitus and septic shock increase the incidence of mortality by thrombosis. Although kinin B1 receptor (B1R) is involved in both pathologies, its role in platelet function and thrombosis remains unknown. This study investigates the expression, the inflammatory, and pro-thrombotic effects of B1R in a model of septic shock in diabetic rats. Sprague-Dawley rats were made diabetic with streptozotocin (STZ) (65 mg/kg, i.p.). Four days later, control and STZ-diabetic rats were injected with lipopolysaccharide (LPS) (2 mg/kg, i.p.) or the vehicle. B1R antagonist (SSR240612, 10 mg/kg by gavage) was given either acutely (12 and 24 h prior to endpoint analysis) or daily for up to 7 days. Moreover, a 7-day treatment was given either with cyclooxygenase (COX)-2 inhibitor (niflumic acid, 5 mg/kg, i.p.), non-selective COX-1 and COX-2 inhibitor (indomethacin, 10 mg/kg, i.p.), non-selective nitric oxide synthase (NOS) inhibitor (L-NAME, 50 mg/kg by gavage), iNOS inhibitor (1400W, 5 mg/kg, i.p.), or heparin (100 IU/kg, s.c.). The following endpoints were measured: edema and vascular permeability (Evans blue dye), B1R expression (qRT-PCR, western blot, flow cytometry), aggregation in platelet-rich plasma (optical aggregometry), and organ damage (histology). Rats treated with STZ, LPS, and STZ plus LPS showed significant increases in edema and vascular permeability (heart, kidney, lung, and liver) and increased expression of B1R in heart and kidney (mRNA) and platelets (protein). Lethal septic shock induced by LPS was enhanced in STZ-diabetic rats and was associated with lung and kidney damage, including platelet micro-aggregate formation. SSR240612 prevented all these abnormalities as well as STZ-induced hyperglycemia and LPS-induced hyperthermia. Similarly to SSR240612, blockade of iNOS and COX-2 improved survival. Data provide the first evidence that kinin B1R plays a primary role in lethal thrombosis in a rat model of septic shock in diabetes. Pharmacological rescue was made possible with B1R antagonism or by inhibition of iNOS and COX-2, which may act as downstream mechanisms.

The nanostructure and the oxygen storage capacity against reactive oxygen species (ROS) are essential features to take into account during the design of a new material that will be used as the basis of novel therapeutic technologies. Here we evaluate the incorporation of nano-ceria, which has a demonstrated ability to scavenge free radicals under physiological conditions comparable to those observed for superoxide dismutase and catalase, to TiO2 crystalline assemblies. The material was planned to merge the scavenging properties of CeO2 on a specifically designed structured TiO2 substrate. The presence of Ce atoms has a clear influence in the materials' morphologies, distorting anatase crystal lattice and inducing the formation of fullerene-like structures. The cytotoxicity of the materials against L929 fibroblasts after 24 hours of cell culture was evaluated. Both structural and oxidative properties of the materials have a clear effect on fibroblast viability; in fact it was demonstrated that cellular proliferation can be modulated varying the Ce3+/Ti4+ molar ratio. Fil: Gravina, Noel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Ruso, Juan Manuel. Universidad de Santiago de Compostela; España Fil: Mbeh, Doris Antoinette. École Polytechnique De Montréal; Canadá Fil: Yahia, L'Hocine. École Polytechnique De Montréal; Canadá Fil: Merhi Yahye. University Of Montreal; Canadá Fil: Sartuqui, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina Fil: Messina, Paula Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto de Química del Sur; Argentina. Universidad Nacional del Sur; Argentina

Background Subcutaneously injected lipid‐free apoA‐I (apolipoprotein A‐I) reduces accumulation of lipid and immune cells within the aortic root of hypercholesterolemic mice without increasing high‐density lipoprotein–cholesterol concentrations. Lymphatic vessels are now recognized as prerequisite players in the modulation of cholesterol removal from the artery wall in experimental conditions of plaque regression, and particular attention has been brought to the role of the collecting lymphatic vessels in early atherosclerosis‐related lymphatic dysfunction. In the present study, we address whether and how preservation of collecting lymphatic function contributes to the protective effect of apoA‐I. Methods and Results Atherosclerotic Ldlr −/− mice treated with low‐dose lipid‐free apoA‐I showed enhanced lymphatic transport and abrogated collecting lymphatic vessel permeability in atherosclerotic Ldlr −/− mice when compared with albumin‐control mice. Treatment of human lymphatic endothelial cells with apoA‐I increased the adhesion of human platelets on lymphatic endothelial cells, in a bridge‐like manner, a mechanism that could strengthen endothelial cell–cell junctions and limit atherosclerosis‐associated collecting lymphatic vessel dysfunction. Experiments performed with blood platelets isolated from apoA‐I‐treated Ldlr −/− mice revealed that apoA‐I decreased ex vivo platelet aggregation. This suggests that in vivo apoA‐I treatment limits platelet thrombotic potential in blood while maintaining the platelet activity needed to sustain adequate lymphatic function. Conclusions Altogether, we bring forward a new pleiotropic role for apoA‐I in lymphatic function and unveil new potential therapeutic targets for the prevention and treatment of atherosclerosis.

Rationale: Lymphatic vessels (LVs) are now recognized as prerequisite players in the modulation of cholesterol removal from the artery wall in experimental conditions of plaque regression, and a particular attention has been brought on the role of the collecting LVs in early atherosclerosis-related lymphatic dysfunction. Whereas recent findings revealed that apoA-I restores the neovascularization capacity of the lymphatic system during tumor necrosis factor-induced inflammation, the effect of apoA-I on collecting LV function during atherosclerosis has not been tested. Objective: In the present study, we address whether and how apoA-I can enhance collecting LV function in atherosclerosis-associated lymphatic dysfunction. Methods and Results: A 6-week systemic treatment with lipid-free apoA-I enhanced lymphatic transport and abrogated collecting lymphatic vessel permeability in atherosclerotic Ldlr –/– mice when compared to control. As injection of apoA-I has been shown to protect wild-type mice against flow restriction-induced thrombosis, and that platelets are identified as key elements in the maintenance of lymphatic vessel integrity via their interaction with lymphatic endothelial cells (LECs), we have tested whether the effects of apoA-I could be mediated through a platelet-dependent mechanism. Our in vivo results show that apoA-I kinetics in lymph reflected that of blood. Ex vivo experiments performed with washed platelets isolated from mouse blood reveal that apoA-I decreased thrombin-induced but not podoplanin-induced platelet aggregation. Whereas this result suggests that apoA-I limits platelet thrombotic potential in blood but not in lymph, we demonstrate that treatment of human LECs with apoA-I increases the adhesion of bridge-like platelets on human LECs. Conclusions: Our results suggest that apoA-I can mediate beneficial effects on lymphatic function by promoting platelet adhesion to the lymphatic endothelium and consequently restore collecting LV integrity. Altogether, we bring forward a new pleiotropic role for apoA-I in lymphatic function and unveil new potential therapeutic targets for the prevention and treatment of atherosclerosis.

In addition to its classical receptor, CD40, it is now well established that CD154 also binds αIIbβ3, α5β1, and αMβ2 integrins. Although these integrins are all members of the same family, they bind CD154 differently. The current investigation aims to analyze the interaction of CD154 with α5β1 and αMβ2 and investigate its role in bidirectional signals in various human cell lines. Results obtained herein indicate that the CD154 residues involved in the interaction with α5β1 are N151 and Q166, whereas those involved in αMβ2 binding are common to residues required for CD40, namely Y145 and R203. Soluble CD40/CD154 or αMβ2/CD154 complexes do not interfere with the binding of CD154 to α5β1-positive cells, but inhibit the binding of CD154 to CD40- or αMβ2-positive cells, respectively. Ligation of CD154 on CD154-positive cells with soluble CD40, αIIbβ3, α5β1, or αMβ2 stimulates intracellular signaling, including MAPK phosphorylation. Given that CD154 exists as a trimer, our data strongly suggest that CD154 may bind concomitantly to two receptors of the same or different family, and biologically activate cells expressing both receptors. The characterization of CD154/receptor interactions helps the identification of new therapeutic targets for the prevention and/or treatment of CD154-associated autoimmune and inflammatory diseases.

This study highlights the advantages of chondroitin sulfate (CS) as a sublayer combining selective low-fouling properties, low-platelet adhesion and pro-adhesive properties on endothelial cells, making CS promising for vascular graft applications. These properties were evaluated by comparing CS with well-known low-fouling coatings such as poly(ethylene glycol) (PEG) and carboxymethylated dextran (CMD), which were covalently grafted on primary amine-rich plasma polymerized (LP) films. Protein adsorption studies by quartz crystal microbalance with dissipation monitoring (QCM-D) and fluorescence measurements showed that CS is as effective as PEG in reducing fibrinogen adsorption (~90% reduction). CS also largely reduced adsorption of bovine serum albumin (BSA) as well as fetal bovine serum (FBS) but to a lower extent than PEG and CMD surfaces (72% vs 85% for BSA and 66% vs 89% for FBS). Whole blood perfusion assays indicated that, while LP surfaces were highly reactive with platelets, PEG, CMD, and CS grafted surfaces drastically decreased platelet adhesion and activation to levels significantly lower than polyethylene terephthalate (PET) surfaces. Finally, while human umbilical vein endothelial cell (HUVEC) adhesion and growth were found to be very limited on PEG and CMD, they were significantly increased on CS compared to that on bare PET and reached similar values as those for tissue culture polystyrene positive controls. Interestingly, HUVEC retention during perfusion with blood was found to be excellent on CS but poor on PET. Overall, our results suggest that the CS surface has the advantage of promoting HUVEC growth and resistance to flow-induced shear stress while preventing fibrinogen and platelet attachment. Such a nonthrombogenic but endothelial-cell adhesive surface is thus promising to limit vascular graft occlusion.

Thromboelastography uses cups and pins made of Cyrolite ® plastic to analyze the rate of fibrin clot formation in blood samples. In this study, TEG cups and pins were modified by 4 distinct coating types using plasma-enhanced chemical vapor deposition (PECVD): carboxylated, amine-rich, hydrophobic, SiO 2 , and analyzed for surface chemistry and wettability. We tested the hypothesis that the coagulation kinetics of recalcified citrated blood plasma is controlled by surface chemistry, in the absence of clot activator. Only carboxylated surfaces became negatively charged upon wetting, and accelerated clot formation in a highly reproducible manner, whereas Cyrolite ® and the other coatings had delayed and unpredictable clotting times. These data are consistent with a model whereby carboxylated surfaces selectively adsorb and activate factor XII while repelling other more abundant anionic blood proteins, resulting in reproducible clot kinetics.

SummaryAdult peripheral blood angiogenic early outgrowth cells (EOCs), also known as early endothelial progenitor cells, interact with other blood and vascular cells and may regulate atherothrombosis. We have previously shown that endothelial progenitor cells inhibit platelet function and thrombus formation. The CD40L/CD40 axis is a thrombo-inflammatory mediator that affects platelet and endothelial functions. It has been shown that EOCs express CD40, whereas platelets represent the major source of its soluble ligand (sCD40L), which impairs EOC function. We aimed to test the hypothesis that the sCD40L/CD40 axis affects the anti-platelet function of EOCs. Human peripheral blood mononuclear cell-derived EOCs in culture inhibited platelet aggregation. Pre-treatment of EOCs with sCD40L reduced their in-hibitory effect on platelet aggregation in a CD40-dependent manner. EOCs viability and release of the anti-aggregating agents, prostacyclin and nitric oxide, were not affected by sCD40L. However, production of reactive oxygen species (ROS) was increased in sCD40L–treated EOCs. Blockade of ROS reversed the effects of sCD40L–treated EOCs on platelet aggregation. This study reveals that the sCD40L/CD40 axis impairs the anti-platelet properties of EOCs through increased production of ROS. These data may explain the link between elevated levels of sCD40L, impaired activity of EOCs and enhanced platelet reactivity, and consequently the occurrence of atherothrombotic disease.

Polyethylene glycol (PEG) grafting has a great potential to create nonfouling and nonthrombogenic surfaces, but present techniques lack versatility and stability. The present work aimed to develop a versatile PEG grafting method applicable to most biomaterial surfaces, by taking advantage of novel primary amine-rich plasma-polymerized coatings. Star-shaped PEG covalent binding was studied using static contact angle, X-ray photoelectron spectroscopy (XPS), and quartz crystal microbalance with dissipation monitoring (QCM-D). Fluorescence and QCM-D both confirmed strong reduction of protein adsorption when compared to plasma-polymerized coatings and pristine poly(ethyleneterephthalate) (PET). Moreover, almost no platelet adhesion was observed after 15 min perfusion in whole blood. Altogether, our results suggest that primary amine-rich plasma-polymerized coatings offer a promising stable and versatile method for PEG grafting in order to create nonfouling and nonthrombogenic surfaces and micropatterns.

Biodegradable segmented polyurethanes were prepared with poly(caprolactone) diol as a soft segment, 4,4′-methylene bis(cyclohexyl isocyanate) (HMDI) and either butanediol or dithioerythritol as chain extenders. Platelet adhesion was similar in all segmented polyurethanes studied and not different from Tecoflex® although an early stage of activation was observed on biodegradable segmented polyurethane prepared with dithioerythritol. Relative viability was higher than 80% on human umbilical vein endothelial cells in contact with biodegradable segmented polyurethane extracts after 1, 2 and 7 days. Furthermore, both biodegradable segmented polyurethane materials supported human umbilical vein endothelial cell adhesion, spreading, and viability similar to Tecoflex® medical-grade polyurethane. These biodegradable segmented polyurethanes represent promising materials for cardiovascular applications.

In addition to its classical CD40 receptor, CD154 also binds to αIIbβ3, α5β1, and αMβ2 integrins. Binding of CD154 to these receptors seems to play a key role in the pathogenic processes of chronic inflammation. This investigation was aimed at analyzing the functional interaction of CD154 with CD40, αIIbβ3, and α5β1 receptors. We found that the binding affinity of CD154 for αIIbβ3 is ∼4-fold higher than for α5β1. We also describe the generation of sCD154 mutants that lost their ability to bind CD40 or αIIbβ3 and show that CD154 residues involved in its binding to CD40 or αIIbβ3 are distinct from those implicated in its interaction to α5β1, suggesting that sCD154 may bind simultaneously to different receptors. Indeed, sCD154 can bind simultaneously to CD40 and α5β1 and biologically activate human monocytic U937 cells expressing both receptors. The simultaneous engagement of CD40 and α5β1 activates the mitogen-activated protein kinases, p38, and extracellular signal-related kinases 1/2 and synergizes in the release of inflammatory mediators MMP-2 and -9, suggesting a cross-talk between these receptors.

The encapsulation of live cells with polymeric coat-ings is a versatile approach to modulate or control the response cells to their environment. The layer-by-layer (LbL) self-assembly of nonimmunogenic polyelectrolytes is employed here to attenuate or suppress the binding of antibodies to live red blood cells (RBCs) and, consequently, decrease their inherent immunogenicity toward foreign RBCs. The optimized shell was composed of four bilayers of alginate (AL) and chitosan-graft-phosphorylcholine (CH-PC) surrounded by two bilayers of AL and poly-l-lysine-graft-polyethylene glycol (PLL-PEG). Experimental parameters, including the polyelectrolytes and RBCs concentrations and the cell handling and purification protocols, were optimized to achieve effective encapsulation of live and functional RBCs in suspension. The viability and functionality of coated RBCs were confirmed by a hemolysis assay and by their ability to take up oxygen. The successful immunocamouflage of RBCs was confirmed by observing that the recognition of the ABO/D (Rh) blood group antigens present on the surface of RBCs by their respective antibodies was muted in the case of coated RBCs. The results of this studies mark an important step toward the production of universal RBCs.

Vascular PET grafts (Dacron) have shown good performance in large vessels (≥ 6 mm) applications. To address the urgent unmet need for small-diameter (2-6 mm) vascular grafts, proprietary high-compliance nonwoven PET fiber structures were modified with various PEG concentrations using PVA as a cross-linking agent, to fabricate non-thrombogenic mechanically compliant vascular grafts. The blood compatibility assays measured through platelet adhesion (SEM and mepacrine dye) and platelet activation (morphological changes, P-selectin secretion, and TXB2 production) demonstrate that functionalization using a 10% PEG solution was sufficient to significantly reduce platelet adhesion/activation close to optimal literature-reported levels observed on carbon-coated ePTFE.

The von Willebrand factor (vWF) aptamer, ARC1779 that blocks the binding of vWF A1-domain to platelet glycoprotein 1b (GPIb) at high shear, may deliver a site-specific antithrombotic effect. We investigated the efficiency of ARC1779 on platelet function in patients with coronary artery disease (CAD) on double antiplatelet therapy. Blood from patients taking aspirin and clopidogrel and from normal volunteers was treated ex vivo with ARC1779 or abciximab, either prior to perfusion (pretherapy) or 10 minutes following the initiation of perfusion (posttherapy) on damaged arteries. Under pre- but not posttherapy, platelet adhesion was significantly reduced by ARC1779 at 83 and 250 nmol/L and by abciximab (100 nmol/L) versus placebo (4.8, 3.8, and 2.9 vs 7.3 platelets × 106/cm2, P < .05). In contrast to abciximab, ARC1779 did not significantly affect platelet aggregation, P-selectin expression, and platelet−leukocyte binding. These proof-of-concept data may constitute the framework for randomized clinical investigations of this novel antiplatelet therapy among patients with CAD.

Recent reports of catheter thrombosis among patients undergoing percutaneous coronary intervention (PCI) have had a significant impact on the development of new antithrombotic therapies. The overall incidence of this complication is unknown, mainly because of underreporting in contemporary clinical trials of coronary intervention. The etiology and pathophysiology of catheter thrombosis is also poorly understood. Introduction of a catheter or guidewire may not provoke the intense thrombotic response that follows angioplasty or stenting, but factors such as catheter materials and device size, equipment surface properties, flow conditions, procedural time and complexity, as well as the antiplatelet and anticoagulant drugs administered during the procedure influence the likelihood, rate and clinical impact of thrombosis. The crucial role of cellular interactions involving tissue-factor bearing cells and platelets in the process of thrombosis also needs to be critically explored when considering blood contact with an exogenous material. Focusing on the inherently prothrombotic environment of percutaneous coronary intervention, we review the physiologic underpinnings of catheter and guidewire thrombosis, and explore the effect of antithrombotic drugs at the interface between blood and material surfaces. We also propose a clinical classification for the diagnosis and investigation of catheter thrombosis in clinical trials of anticoagulant therapy and PCI.

CD154, a member of the tumor necrosis factor-alpha family, has recently been implicated in the pathophysiology of vascular diseases. Indeed, blockade of CD154 by neutralizing antibodies or genetic disruption in mice prevents atherosclerosis and atherothrombosis. CD154 is believed to interact mainly via the CD40 receptor, however, it has also been found to bind with alphaIIbbeta3 integrin and so induces platelet activation. Moreover, we (and others) have recently identified the integrins alpha5beta1 and Mac-1 as novel CD154 receptors expressed on many cell types. Here, we illustrate the various functional features of these molecules, while describing the increasingly important role of CD40 in CD154-associated vascular pathologies such as atherosclerosis and atherothrombosis.

Summary. Background and objectives: Anti-heat shock protein (HSP)60 autoantibodies are associated with atherosclerosis and are known to affect endothelial cells in vitro. However, their role in thrombus formation remains unclear. We hypothesized that anti-HSP60 autoantibodies could potentiate thrombosis, and evaluated the effect of anti-murine HSP60 antibodies in a ferric chloride (FeCl3)-induced murine model of carotid artery injury. Methods: Anti-HSP60, or control, IgG was administered to BALB/c mice 48 h prior to inducing carotid artery injury, and blood flow was monitored using an ultrasound probe. Results: Thrombus formation was more rapid and stable in anti-HSP60 IGG-treated mice than in controls (blood flow = 1.7% ± 0.6% vs. 34% ± 12.6%, P = 0.0157). Occlusion was complete in all anti-HSP60 IgG-treated mice (13/13), with no reperfusion being observed. In contrast, 64% (9/14) of control mice had complete occlusion, with reperfusion occurring in 6/9 mice. Thrombi were significantly larger in anti-HSP60 IgG-treated mice (P = 0.0001), and contained four-fold more inflammatory cells (P = 0.0281) than in controls. Non-injured contralateral arteries of anti-HSP60 IgG-treated mice were also affected, exhibiting abnormal endothelial cell morphology and significantly greater von Willebrand factor (VWF) and P-selectin expression than control mice (P = 0.0024 and P = 0.001, respectively). Conclusions: In summary, the presence of circulating anti-HSP60 autoantibodies resulted in increased P-selectin and VWF expression and altered cell morphology in endothelial cells lining uninjured carotid arteries, and promoted thrombosis and inflammatory cell recruitment in FeCl3-injured carotid arteries. These findings suggest that anti-HSP60 autoantibodies may constitute an important prothrombotic risk factor in cardiovascular disease in human vascular disease.

Variable biological effect of aspirin is suggested to be related to pharmacological resistance. The incidence of this so-called "resistant" state varies with the study population and the assay used. We determined performance features of five assays used to assess aspirin effects in non-smoking healthy volunteers not taking any drug known to interfere with platelet function. Blood and urine samples were obtained immediately before and after 8-10 days of aspirin 80 mg intake. Forty-five participants 19-59 years old were enrolled. The sensitivity (SE), specificity (SP), and optimal cut-off (CO) value to detect the effect of aspirin were: light transmission aggregometry (LTA) with 1.6 mM arachidonic acid (AA) - SE 100%, SP 95.9%, CO 20%; LTA with adenosine diphosphate (ADP) 10 microM - SE 84.4%, SP 77.8%, CO 70%; VerifyNow Aspirin - SE 100%, SP 95.6%, CO 550 ARU; platelet count drop - SE 82.2%, SP 86,7%, CO 55%; TEG((R)) - SE 82,9%, SP 75,8%, CO 90%; and urinary 11-dehydrothromboxane B(2) levels (11-dHTB(2)) - SE 62.2%, SP 82.2%, CO 60 pg/ml. AA-induced LTA and the VerifyNow assay reliably detected aspirin intake in all subjects; there was wide overlap in pre- and post- aspirin results with ADP-induced LTA, platelet count drop, TEG((R)) and urinary 11-dHTB(2) assays. These results suggest that some of the variability in the reported incidence of "aspirin resistance" is unrelated to aspirin intake but related to inherent limitations of some assays to detect aspirin mediated effects or to underlying platelet reactivity variability independent of aspirin-mediated cyclooxygenase-1 inhibition.

Twenty-nine modular stent-grafts deployed transrenally to repair AAAs with short necks in dogs were harvested at autopsy of the animals after scheduled durations of implantations of 10 days, one month, three months, and six months. Analyses of the explanted devices included non-destructive techniques such as gross observations, X-rays CT scan, IVUS and angioscopy. Further to appropriate dissection, histological investigations were carried out by means of scanning electron microscopy (SEM) and light microscopy. All the 29 specimens were extensively encapsulated with fibrous tissues but the fibrous capsule was thin in six of them; four capsules were ulcerated. The X-rays confirmed the stability of the devices that were still straight (12), slightly bent (12) or bent (4). The modules were misaligned in only one case. IVUS and angioscopy confirmed the patency of all the stent-grafts with thin internal capsules both proximally and distally with variable capsulation in the mid-section of the grafts. The left renal artery orifices were found to be patent at dissection with no obstruction to flow. The luminal flow surface of the stent-grafts was smooth and glistening proximally and distally containing endothelial like cells and vasa-vasorum. Poor healing was noted in the aneurysm area. Transrenal deployment of this modular stent-graft is feasible and gave excellent results with regard to biofunctionality and biocompatibility. The device proved to be safe and efficient.

Excessive distension of venous grafts due to arterial pressure enhances the convective water transport (filtration flow) through the vessel wall, and thus might affect the infiltration of macromolecules such as lipoproteins. In this paired experimental study, filtration velocities were measured at 100 mm Hg for canine jugular veins with or without external supports of expanded polytetrafluoroethylene (ePTFE) arterial prostheses. In addition, to assess the effect of filtration velocity on lipid infiltration or uptake, canine jugular veins were wrapped over half of their lengths with ePTFE arterial prostheses and perfused with dog serum containing 3H-cholesterol at a pressure of 100 mm Hg. At 100 mm Hg, the average filtration velocity of the wrapped jugular veins was 7.9 +/- 1.3 x 10(-6) cm/s whereas the average filtration velocity of the unwrapped veins was 27.3 +/- 2.7 x 10(-6) cm/s (p < 0.005). Moreover, the unwrapped veins had a significantly higher uptake rate of labeled cholesterol than the wrapped veins (10.9 +/- 7.3 x 10(-4) cm/h and 5.0 +/- 1.6 x 10(-4) cm/h, respectively, p < 0.005). In conclusion, under arterial pressure, veins experience excessive distention, which leads to significant increases in both filtration flow and cholesterol uptake. An external wrap or support of ePTFE material protects veins from excessive distension and thus may prevent atherosclerosis in venous grafts by reducing cholesterol uptake.

Membrane-covered Express2TM Monorail® stents composed of chitosan (CH) blended with polyethylene oxide (PEO) in 70:30% wt (CH-PEO) were coated with a monolayer of hyaluronic acid (HA). This significantly improved the resistance to platelet adhesion and demonstrated excellent mechanical properties, resisting the harsh conditions during stent crimping and subsequent inflation. CH-PEO/HA membrane was then combined with a paclitaxel (Pac) delivery system via three different approaches for comparison of release profiles of Pac. The activity of Pac in these systems was confirmed since its presence in the membrane significantly decreased cell viability of U937 macrophages. Presented results are promising for applications requiring different release patterns of hydrophobic drugs.

The ability of electrostatically driven layer-by-layer (LbL) assembly to adapt to the morphological features of a template was explored. Subtle cytoskeletal changes in blood platelets became traceable through energy dissipation monitoring in multilayered shells using microgravimetric measurements. This LbL coating was sequentially deposited on protein-modified chips onto which platelets were adhered. In addition to consequently improving the signal sensitivity, the LbL shell acted in synergy with the cell, allowing the determination and quantification of cytoskeletal changes induced by the specific cell adhesion to the protein-modified chip surface used with a quartz crystal microbalance with dissipation. The difference in cell morphology, as a result of the optimization of specific interactions between the protein layer and cell membrane integrins induced viscoelastic changes in the polyelectrolyte shell, thereby providing quantitative data on platelet conformational changes upon their adhesion to protein-modified chip surface.

A patient was fitted with an Anaconda stent graft for which there was a persistent type II endoleak. Two subsequent attempts at embolization were unable to resolve the endoleak. The diameter of the aneurysm varied initially from 5.5 cm in diameter down to 4.8 cm but then later re-dilated to 6.1 cm, with evidence of persistent flow into the aneurysmal sac from the inferior mesenteric artery. Results from serial computed tomography scans demonstrated clear evidence of a type II endoleak that originated from the inferior mesenteric artery with outflow to a distal lumbar artery. The harvested stent graft did not show evidence of a device-related failure. The stent graft and its modular segments were found to have been properly deployed. Only a thin external capsule was evident at explantation. The internal wall of the device showed irregular and thin encapsulation with scattered mural thrombi, which were more prominent at the bifurcation of the main body of the device. Blood deposits and tissue development were sufficient to prevent blood oozing through the wall. The explanted Anaconda stent graft was devoid of any construction flaws or damage (fatigue of the textile or corrosion of the Nitinol wires) after implantation.

Hydroxyapatite (HA) and HA-alumina (HA/Al2O3) composites, with Al2O3 contents of 5, 10, 20, and 30%, were synthesized using a wet precipitation method and sintered at 900 and 1300°C. We investigated the effect of sintering temperature and relative concentration of HA and Al2O3 on the chemical composition, surface morphology, and cytotoxicity of the composite powders. The XRD results show that in the 1300°C composites, HA partially decomposed into CaO which combined with Al2O3 to form different calcium aluminates. For the 900°C composites the CaO phase was not detected, though a Ca/P ratio larger than 1.67 measured by XPS suggests that CaO was present in trace amounts. SEM-EDX analysis indicated that the HA microstructure was affected by the sintering temperature, and this HA is present on the surface of Al2O3 particles. The cytotoxicity of the composites was assessed indirectly using the MTT assay. The short-term effect of leachables was quantified by exposing a L929 mouse fibroblast cell line to the degradation products released by the composites after immersion in the cell culture medium. Degradation products were less toxic to L-929 at lower extract concentrations (10, 50%) than at 100% concentration. Cell viability was also influenced by leachable size. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007

Biofunctionalization strategies have been developed to improve small-diameter vascular grafts. However, a fully successful coating featuring antithrombogenic properties while allowing for endothelialization has not been achieved yet. In this report, we explored the combination of low-fouling polyethylene glycol (PEG) and adhesion peptides, namely, RGD, YIGSR, and REDV, grafted on top of polyvinylamine (PVAm)-coated polyester. The peptides were grafted over a wide range of density (ca. 20-2000 pmol/cm(2)) on top of a dense PEG underlayer. The coating performances were assessed through HUVEC adhesion, platelet attachment, and protein adsorption, which were all drastically diminished on PEG-coated samples. RGD exhibited the expected high adhesive properties, toward both HUVEC and platelets. REDV had no effect neither on platelet attachment, as expected, nor on HUVEC adhesion, in contrast with previous reports. YIGSR was the most promising sequence even though its combination with other agents should be explored to further decrease thrombogenicity for vascular graft applications.

Interferon gamma (IFN-gamma) was shown to induce CD40 and CD40L expression on endothelial cells (ECs) and consequently to promote neutrophil adhesion. The pro- and anti-inflammatory effects of estrogens are well recognized but their role on the regulation of CD40 and CD40L expression on ECs remains undefined.Treatment of porcine aortic endothelial cells (PAEC) with IFN-gamma for 24 h enhanced CD40 and CD40L expression by 97% and 78%, respectively. Pretreatment of PAEC with 17-beta-estradiol (17betaE) for 24 h prevented the latter expression of CD40/CD40L. Treatment of PAEC with antisense oligomers targeting ERalpha mRNA attenuated the ability of 17betaE to inhibit the IFN-gamma-induced CD40 and CD40L protein expression. The IFN-gamma activation pathway of CD40 is known to involve the phosphorylation of the Janus activated kinase (JAK) and the signal transducer and activator of transcription 1 (Stat1). 17betaE, acting via the estrogen receptor alpha (ERalpha), abrogated IFN-gamma-mediated effects on Stat1 but failed to inhibit Jak1 and Jak2 phosphorylation. Furthermore, 17betaE prevented neutrophil adhesion induced by IFN-gamma.In summary, 17betaE binding to ERalpha blocked IFN-gamma-induced Stat1 phosphorylation, CD40 and CD40L protein expression, and neutrophil adhesion onto ECs.

1 P-selectin is involved, with P-selectin glycoprotein (GP)-ligand-1 (PSGL-1), in platelet/leukocyte interactions during thrombo-inflammatory reactions; it also stabilizes platelet aggregates. Its antagonism accelerates thrombolysis and enhances the anti-aggregatory effects of GPIIb–IIIa inhibitors. This study was designed to investigate the mechanisms of P-selectin-mediated platelet aggregation. 2 In freshly isolated human platelets, P-selectin translocation after thrombin stimulation increased rapidly to 48, 72, and 86% positive platelets after 60, 120, and 300 s, respectively. Platelet aggregation at 60 s post-stimulation averaged 46.7±1.9% and its extent followed closely the kinetics of P-selectin translocation. 3 Pre-treatment of platelets with P-selectin antagonists, a recombinant PSGL-1 (rPSGL-Ig) or a blocking monoclonal antibody, significantly delayed platelet aggregation in a dose-dependent manner. At 100 μg ml−1 of rPSGL-Ig, platelet aggregation was completely inhibited up to 60 s post-stimulation and increased thereafter to reach maximal aggregation at 5 min. The second phase of platelet aggregation, in the presence of rPSGL-Ig, was completely prevented by the addition of a GPIIb–IIIa antagonist (Reopro) at 60 s, whereas its addition in the absence of rPSGL-Ig was without any significant effect. 4 Combination of rPSGL-Ig with Reopro or with an inhibitor of Pi3K (LY294002), which reduces GPIIb–IIIa activation, showed to be more effective in inhibiting platelet aggregation, in comparison to the effects observed individually. 5 rPSGL-Ig blocks P-selectin, whereas Reopro and LY294002 block GPIIb–IIIa and its activation, respectively, without a major effect on the percentage of platelets expressing P-selectin. 6 In summary, platelet P-selectin participates with GPIIb–IIIa in the initiation of platelet aggregation. Its inhibition, with rPSGL-Ig, delays the aggregation process and increases the anti-aggregatory potency of Reopro. Thus, combination of P-selectin and GPIIb–IIIa antagonism may constitute a promising therapeutic option in the management of thrombotic disorders. British Journal of Pharmacology (2006) 148, 299–305. doi:10.1038/sj.bjp.0706734

Membrane-covered devices could help treat disease of the vasculature such as aneurysm, rupture, and fistulas. They are also investigated to reduce embolic complication associated with revascularization of saphenous vein graft. The aim of this study is to design a clinically applicable biodegradable membrane-covered stent based on the natural polysaccharide chitosan, which has been developed. The mechanical properties of the membrane is optimized through blending with polyethylene oxide (70:30% Wt CH:PEO). The membrane was able to sustain the mechanical deformation of the supporting self-expandable metallic stents during its deployment. The membrane was demonstrated to resist physiological transmural pressure (burst pressure resistance >500 mm Hg) and presented a high-water permeation resistance (1 mL/cm(2) min(-1) at 120 mmHg). The CH-PEO membrane showed a good hemocompatibility in an ex vivo assay. Heparin and hyaluronan surface complexation with the membrane further reduced platelet adhesion by 50.1 and 63% (p = 0.05). The ability of the membrane-covered devices to be used as a drug reservoir was investigated using the nitric oxide donor sodium nitroprusside (SNP). SNP-loaded membranes displayed significantly reduced platelet adhesion.

SummaryPlatelets and neutrophils constitute a high source of metalloproteinases (MMPs), and their interactions via P-selectin and Pselectin- glycoprotein-ligand-1 (PSGL-1) are involved in thrombosis, vascular remodelling, and restenosis. We investigated the impact of these interactions on platelet MMP-2 secretion and function in platelet and neutrophil aggregation. The secretion of MMP-2 from human platelets was significantly increased threefold after thrombin activation, and enhanced two-fold in the presence of neutrophils. Neutrophil supernatant had no effect on platelet MMP-2 secretion. While no MMP-2 was detected in the supernatant of neutrophils, a high amount of MMP-9 was released by neutrophils, and remained unchanged upon thrombin activation or in the presence of platelets. Platelet P-selectin, which increased significantly after activation, triggered platelet binding to neutrophils that was completely inhibited by P-selectin or PSGL-1 antagonists, and was reduced by 50% with a GPIIb/ IIIa antagonist. P-selectin or PSGL-1 antagonism abolished the enhanced secretion of platelet MMP-2 in the presence of neutrophils and reduced platelet-neutrophil aggregation. Platelet activation and binding to neutrophils enhance the secretion of platelet MMP-2 via an adhesive interaction between P-selectin and PSGL-1, which contribute to increase platelet-neutrophil aggregation.

SummaryThe binding of leukocyte P-selectin glycoprotein ligand-1 (PSGL-1) to platelet P-selectin is central to post-angioplasty restenosis. Although intracoronary stents limit the mechanical component of restenosis, they cause marked thrombo-inflammation and neointimal proliferation leading to greater late luminal loss. We sought to demonstrate that P-selectin antagonism, using recombinant PSGL-1 (rPSGL-Ig), is effective in reducing platelet-leukocyte reactions and in-stent restenosis in doubleinjured porcine coronary arteries. Two weeks after initial injury by angioplasty to the coronary arteries, stents were implanted at the injury-induced lesion site, 15 min after an IV bolus administration of a vehicle or rPSGL-Ig (1 mg/kg). Four weeks later, adhesion of 51Cr-platelets and 111In-neutrophils and histomorphometric analyses were performed. In-stent residual lumen was almost 3 fold larger in rPSGL-Ig-treated arteries (3.1 ± 0.4 mm2) as compared to control (1.1 ± 0.2 mm2), which correspond to 64% vascular stenosis in control with no change in rPSGL-Ig animals. For a similar injury score, in-stent neointima was significantly reduced by 30 to 40% in the rPSGL-Ig group and quantitative coronary angiography showed a significant 35% reduction in late lumen loss. These effects of rPSGL-Ig were associated with a respective 70% and 53% reduction in platelet and neutrophil adhesion. In conclusion, pretreatment with rPSGL-Ig reduces thrombo-inflammatory responses, neointimal proliferation, and in-stent restenosis. P-selectin antagonism offers a promising therapy to improve clinical outcomes of coronary stenting.

Layer-by-layer self-assembly of two polysaccharides, hyaluronan (HA) and chitosan (CH), was employed to engineer bioactive coatings for endovascular stents. A polyethyleneimine (PEI) primer layer was adsorbed on the metallic surface to initiate the sequential adsorption of the weak polyelectrolytes. The multilayer growth was monitored using a radiolabeled HA and shown to be linear as a function of the number of layers. The chemical structure, interfacial properties, and morphology of the self-assembled multilayer were investigated by time-of-flight secondary ions mass spectrometry (ToF-SIMS), contact angle measurements, and atomic force microscopy (AFM), respectively. Multilayer-coated NiTi disks presented enhanced antifouling properties, compared to unmodified NiTi disks, as demonstrated by a decrease of platelet adhesion in an in vitro assay (38% reduction; p = 0.036). An ex vivo assay on a porcine model indicated that the coating did not prevent fouling by neutrophils. To assess whether the multilayers may be exploited as in situ drug delivery systems, the nitric-oxide-donor sodium nitroprusside (SNP) was incorporated within the multilayer. SNP-doped multilayers were shown to further reduce platelet adhesion, compared to standard multilayers (40% reduction). When NiTi wires coated with a multilayer containing a fluorescently labeled HA were placed in intimate contact with the vascular wall, the polysaccharide translocated on the porcine aortic samples, as shown by confocal microscopy observation of a treated artery. The enhanced thromboresistance of the self-assembled multilayer together with the antiinflammatory and wound healing properties of hyaluronan and chitosan are expected to reduce the neointimal hyperplasia associated with stent implantation.

Multiple-indicator-dilution experiments were performed in the lungs of 13 anesthetized dogs by simultaneous bolus injection of 111In-labeled neutrophils, 51Cr-labeled red blood cells, and Evans blue-labeled albumin. Concomitant counts of unlabeled neutrophils were similar in pulmonary artery and aortic blood samples, demonstrating a dynamic balance across the lungs in the physiological state. Outflow profiles of labeled neutrophils were analyzed on the basis of a recirculatory pharmacokinetic model of labeled albumin. The outflow profiles of the recovered neutrophils were composed of a throughput component of circulating neutrophils and a component of reversibly marginated neutrophils. They were interpreted by a model incorporating neutrophil margination (transfer coefficient = 0.195 ± 0.081 s-1), rapid demargination (0.054 ± 0.027 s-1), and transfer to a slow marginated pool (0.023 ± 0.018 s-1). It will be interesting to apply the analysis in future studies aimed at determining whether it could be a useful research tool to investigate the interactions between the pulmonary endothelium and neutrophils in physiological and diseased states.

Background— Coronary artery disease is a significant risk factor for atrial fibrillation (AF), but the basis for this association is incompletely understood. The present study evaluated the hypothesis that atrial ischemia can create a substrate for AF maintenance. Methods and Results— Atrial ischemia was induced by occlusion of an atrial arterial branch that did not provide blood flow to the ventricles. Atrial-arterial occlusion increased the duration of AF induced by burst pacing from 57±32 seconds (control) to 803±214 seconds ( P P 20 minutes) was induced in 0 of 16 dogs (0%) under control conditions, 7 of 16 (44%, P P P P Conclusions— Experimental atrial ischemia creates a substrate for AF maintenance, apparently by causing local conduction slowing that promotes reentry. These results suggest that atrial ischemia may significantly promote AF, and may be relevant to AF mechanisms in association with coronary artery disease.

SummaryP-selectin is translocated from the α-granules to the surface of activated platelets where it participates in thrombosis and inflammation. We investigated the signaling pathways involved in thrombin-induced human platelet P-selectin expression. Assessed by flow cytometry, inhibition of protein kinase C (PKC) with chelerythrine reduced P-selectin expression by 66%, platelet/neutrophil binding, GPIIb/IIIa activation and aggregation (p