Endothelial cell function and thrombosis

Recent advances in disseminated intravascular coagulation: endothelial cells and fibrinolysis in sepsis-induced DIC

Endothelial cells are highly active, sensing and responding to signals from extracellular environments. They act as gatekeepers, mediating the recruitment and extravasation of proinflammatory leukocytes to the sites of tissue damage or infection. Endothelial cells participate in fibrinolysis by secreting tissue-type plasminogen activator, which converts plasminogen to active enzyme plasmin through constitutive and regulated pathways. Fibrinolysis systems and inflammation are tightly linked, as both responses are major host defense systems against both healing processes of tissue repair as well as pathogenic microorganisms. Endothelial cell dysfunction is one of the early signs of systemic inflammation, and it is a trigger of multiple organ failure in sepsis. The marked increase in plasminogen activator inhibitor-1 level causes fibrinolytic shutdown in endotoxemia or sepsis and is one of the most important predictors of multiple organ dysfunction during sepsis-induced disseminated intravascular coagulation (DIC). Leukocytes exhibit the first-line response to microorganisms. Leukocyte-derived elastase degrades cross-linked fibrin to yield molecular species distinct from those generated by plasmin. The alternative systems for fibrinolysis that interact with the plasminogen activator-plasmin systems may play crucial roles in the lysis of fibrin clots in sepsis-induced DIC.

Engineering an endothelialized vascular graft: a rational approach to study design in a non-human primate model

After many years of research, small diameter, synthetic vascular grafts still lack the necessary biologic integration to perform ideally in clinical settings. Endothelialization of vascular grafts has the potential to improve synthetic graft function, and endothelial outgrowth cells (EOCs) are a promising autologous cell source. Yet no work has established the link between endothelial cell functions and outcomes of implanted endothelialized grafts. This work utilized steady flow, oscillatory flow, and tumor necrosis factor stimulation to alter EOC phenotype and enable the formulation of a model to predict endothelialized graft performance. To accomplish this, EOC in vitro expression of coagulation and inflammatory markers was quantified. In parallel, in non-human primate (baboon) models, the platelet and fibrinogen accumulation on endothelialized grafts were quantified in an ex vivo shunt, or the tissue ingrowth on implanted grafts were characterized after 1mth. Oscillatory flow stimulation of EOCs increased in vitro coagulation markers and ex vivo platelet accumulation. Steady flow preconditioning did not affect platelet accumulation or intimal hyperplasia relative to static samples. To determine whether in vitro markers predict implant performance, a linear regression model of the in vitro data was fit to platelet accumulation data-correlating the markers with the thromboprotective performance of the EOCs. The model was tested against implant intimal hyperplasia data and found to correlate strongly with the parallel in vitro analyses. This research defines the effects of flow preconditioning on EOC regulation of coagulation in clinical vascular grafts through parallel in vitro, ex vivo, and in vivo analyses, and contributes to the translatability of in vitro tests to in vivo clinical graft performance.

2,3,4',5-tetrahydroxystilbene-2-O-β-D-glucoside suppresses expression of adhesion molecules in aortic wall of dietary atherosclerotic rats and promonocytic U937 cells

We sought to investigate whether TSG suppressed the ICAM-1/VCAM-1 expression in dietary atherosclerotic rats and in Ox-LDL-induced U937 cells. For this purpose, 60 male Sprague-Dawley rats were randomly-and-equally divided into six groups. Atherosclerosis was induced by feeding rats a hyperlipidemic diet. TSG (120, 60 or 30 mg/kg/day) was administered by oral gavage. Simvastatin (2 mg/kg/day) was administered as positive control whereas physiological saline (0.9% NaCl) served as untreated control. After 12 weeks, rats were euthanized by ethyl carbonate (1,200 mg/kg) and aortic wall samples were collected. Besides, U937 cells were stimulated for 48 h by Ox-LDL (80 μg/mL) with and without TSG (120, 60, 30 μg/L) or simvastatin (100 μg/L). ICAM-1/VCAM-1 mRNA expression was determined by RT-PCR and protein expression was detected by immunohistochemistry and/or western blotting. The data show that ICAM-1/VCAM-1 mRNA/protein expression was significantly enhanced in atherosclerotic aortas compared with normal diet group. Ox-LDL-induced ICAM-1/VCAM-1 mRNA/protein expression in U937 cells. Importantly, TSG significantly inhibited ICAM-1/VCAM-1 expression in atherosclerotic aortas in a dose-dependent manner. TSG-pretreatment also inhibited ICAM-1/VCAM-1 expression in Ox-LDL-induced U937 cells. Therefore, we concluded that TSG suppressed the expression of adhesion (ICAM-1/VCAM-1) molecules both in vivo (in aortic wall of dietary atherosclerotic rats) and in vitro (U937 cells).

A multiple-channel, multiple-assay platform for characterization of full-range shear stress effects on vascular endothelial cells

Vascular endothelial cells (VECs), which line blood vessels and are key to understanding pathologies and treatments of various diseases, experience highly variable wall shear stress (WSS) in vivo (1-60 dyn cm(-2)), imposing numerous effects on physiological and morphological functions. Previous flow-based systems for studying these effects have been limited in range, and comprehensive information on VEC functions at the full spectrum of WSS has not been available yet. To allow rapid characterization of WSS effects, we developed the first multiple channel microfluidic platform that enables a wide range (~15×) of homogeneous WSS conditions while simultaneously allowing trans-monolayer assays, such as permeability and trans-endothelial electrical resistance (TEER) assays, as well as cell morphometry and protein expression assays. Flow velocity/WSS distributions between channels were predicted with COMSOL simulations and verified by measurement using an integrated microflow sensor array. Biomechanical responses of the brain microvascular endothelial cell line bEnd.3 to the full natural spectrum of WSS were investigated with the platform. Under increasing WSS conditions ranging from 0 to 86 dyn cm(-2), (1) permeabilities of FITC-conjugated dextran and propidium iodide decreased, respectively, at rates of 4.06 × 10(-8) and 6.04 × 10(-8) cm s(-1) per dyn cm(-2); (2) TEER increased at a rate of 0.8 Ω cm(2) per dyn cm(-2); (3) increased alignment of cells along the flow direction under increasing WSS conditions; and finally (4) increased protein expression of both the tight junction component ZO-1 (~5×) and the efflux transporter P-gp (~6×) was observed at 86 dyn cm(-2) compared to static controls via western blot. We conclude that the presented microfluidic platform is a valid approach for comprehensively assaying cell responses to fluidic WSS.

The role of platelets in coagulation dysfunction in xenotransplantation, and therapeutic options

Xenotransplantation could resolve the increasing discrepancy between the availability of deceased human donor organs and the demand for transplantation. Most advances in this field have resulted from the introduction of genetically engineered pigs, e.g., α1,3-galactosyltransferase gene-knockout (GTKO) pigs transgenic for one or more human complement-regulatory proteins (e.g., CD55, CD46, CD59). Failure of these grafts has not been associated with the classical features of acute humoral xenograft rejection, but with the development of thrombotic microangiopathy in the graft and/or consumptive coagulopathy in the recipient. Although the precise mechanisms of coagulation dysregulation remain unclear, molecular incompatibilities between primate coagulation factors and pig natural anticoagulants exacerbate the thrombotic state within the xenograft vasculature. Platelets play a crucial role in thrombosis and contribute to the coagulation disorder in xenotransplantation. They are therefore important targets if this barrier is to be overcome. Further genetic manipulation of the organ-source pigs, such as pigs that express one or more coagulation-regulatory genes (e.g., thrombomodulin, endothelial protein C receptor, tissue factor pathway inhibitor, CD39), is anticipated to inhibit platelet activation and the generation of thrombus. In addition, adjunctive pharmacologic anti-platelet therapy may be required. The genetic manipulations that are currently being tested are reviewed, as are the potential pharmacologic agents that may prove beneficial.

Age-related changes in aortic valve hemostatic protein regulation

OBJECTIVE

Although valvular endothelial cells have unique responses compared with vascular endothelial cells, valvular regulation of hemostasis is not well-understood. Heart valves remodel throughout a person's lifetime, resulting in changes in extracellular matrix composition and tissue mechanical properties that may affect valvular endothelial cell hemostatic function. This work assessed valvular endothelial cell regulation of hemostasis in situ and in vitro as a function of specimen age.

APPROACH AND RESULTS

Porcine aortic valves were assigned to 1 of 3 age groups: Young (YNG) (6 weeks); Adult (ADT) (6 months); or Elderly (OLD) (2 years). Histological examination of valves showed that secreted thrombotic/antithrombotic proteins localize at the valve endothelium and tissue interior. Gene expression and immunostains for von Willebrand factor (VWF), tissue factor pathway inhibitor, and tissue plasminogen activator in YNG porcine aortic valve endothelial cells were higher than they were for OLD, whereas plasminogen activator inhibitor 1 levels in OLD were higher than those for YNG and ADT. Histamine-stimulated YNG porcine aortic valve endothelial cells released higher concentrations of VWF proteins than OLD, and the fractions of VWF-140 fragments was not different between age groups. A calcific aortic valve disease in vitro model using valvular interstitial cells confirmed that VWF in culture significantly increased valvular interstitial cell nodule formation and calcification.

CONCLUSIONS

Hemostatic protein regulation in aortic valve tissues and in valvular endothelial cells changes with age. The presence of VWF and other potential hemostatic proteins increase valvular interstitial cell calcification in vitro. Therefore, the increased capacity of elderly valves to sequester the hemostatic proteins, together with age-associated loss of extracellular matrix organization, warrants investigation into potential role of these proteins in the formation of calcific nodules.

Mechanisms of acute brain injury after subarachnoid hemorrhage

Brain injury after subarachnoid hemorrhage (SAH) is a biphasic event with an acute ischemic insult at the time of the initial bleed and secondary events such as cerebral vasospasm 3 to 7 days later. Although much has been learned about the delayed effects of SAH, less is known about the mechanisms of acute SAH-induced injury. Distribution of blood in the subarachnoid space, elevation of intracranial pressure, reduced cerebral perfusion and cerebral blood flow (CBF) initiates the acute injury cascade. Together they lead to direct microvascular injury, plugging of vessels and release of vasoactive substances by platelet aggregates, alterations in the nitric oxide (NO)/nitric oxide synthase (NOS) pathways and lipid peroxidation. This review will summarize some of these mechanisms that contribute to acute cerebral injury after SAH.

Evaluation of hemocompatibility and endothelialization of hybrid poly(vinyl alcohol) (PVA)/gelatin polymer films

Engineered grafts are still needed for small diameter blood vessels reconstruction. Ideal materials would prevent thrombosis and intimal hyperplasia by displaying hemocompatibility and mechanical properties close to those of native vessels. In this study, poly(vinyl alcohol) (PVA)/gelatin blends were investigated as a potential vascular support scaffold. We modified a chemically crosslinked PVA hydrogel by incorporation of gelatin to improve endothelial cell attachment with a single-step method. A series of crosslinked PVA/gelatin films with specific ratios set at 100:0, 99:1, 95:5, and 90:10 (w/w) were prepared and their mechanical properties were examined by uniaxial tensile testing. Tubes, obtained from sutured films, were found highly compliant (3.1-4.6%) and exhibited sufficient mechanical strength to sustain hemodynamic strains. PVA-based hydrogels maintained low level of platelet adhesion and low thrombogenic potential. Endothelial cell adhesion and proliferation were drastically improved on PVA/gelatin films with a feed gelatin content as low as 1% (w/w), leading to the formation of a confluent endothelium. Hydrogels with higher gelatin content did not sustain complete endothelialization because of modifications of the film surface, including phase segregation and formation of microdomains. Thus, PVA/gelatin (99:1, w/w) hydrogels appear as promising materials for the design of endothelialized vascular materials with long-term patency.

Thrombomodulin and the vascular endothelium: insights into functional, regulatory, and therapeutic aspects

Thrombomodulin (TM) is a 557-amino acid protein with a broad cell and tissue distribution consistent with its wide-ranging physiological roles. When expressed on the lumenal surface of vascular endothelial cells in both large vessels and capillaries, its primary function is to mediate endothelial thromboresistance. The complete integral membrane-bound protein form displays five distinct functional domains, although shorter soluble (functional) variants comprising the extracellular domains have also been reported in fluids such as serum and urine. TM-mediated binding of thrombin is known to enhance the specificity of the latter serine protease toward both protein C and thrombin activatable fibrinolysis inhibitor (TAFI), increasing their proteolytic activation rate by almost three orders of magnitude with concomitant anticoagulant, antifibrinolytic, and anti-inflammatory benefits to the vascular wall. Recent years have seen an abundance of research into the cellular mechanisms governing endothelial TM production, processing, and regulation (including flow-mediated mechanoregulation)--from transcriptional and posttranscriptional (miRNA) regulation of TM gene expression, to posttranslational processing and release of the expressed protein--facilitating greater exploitation of its therapeutic potential. The goal of the present paper is to comprehensively review the endothelial/TM system from these regulatory perspectives and draw some fresh conclusions. This paper will conclude with a timely examination of the current status of TM's growing therapeutic appeal, from novel strategies to improve the clinical efficacy of recombinant TM analogs for resolution of vascular disorders such as disseminated intravascular coagulation (DIC), to an examination of the complex pleiotropic relationship between statin treatment and TM expression.

Strategies and techniques to enhance the in situ endothelialization of small-diameter biodegradable polymeric vascular grafts

Due to the lack of success in small-diameter (<6 mm) prosthetic vascular grafts, a variety of strategies have evolved utilizing a tissue-engineering approach. Much of this work has focused on enhancing the endothelialization of these grafts. A healthy, confluent endothelial layer provides dynamic control over homeo-stasis, influencing and preventing thrombosis and smooth muscle cell proliferation that can lead to intimal hyperplasia. Strategies to improve endothelialization of biodegradable polymeric grafts have encompassed both chemical and physical modifications to graft surfaces, many focusing on the recruitment of endothelial and endothelial progenitor cells. This review aims to provide a compilation of current and developing strategies that utilize in situ endothelialization to improve vascular graft outcomes, providing a context for the future directions of vascular tissue-engineering strategies that do not require preprocedural cell seeding.

Endothelial cells are able to synthesize and release catecholamines both in vitro and in vivo

Recently it has been demonstrated that catecholamines are produced and used by macrophages and mediate immune response. The aim of this study is to verify whether endothelial cells (ECs), which are of myeloid origin, can produce catecholamines. We demonstrated that genes coding for tyrosine hydroxylase, Dopa decarboxylase, dopamine β hydroxylase (DβH), and phenylethanolamine-N-methyl transferase, enzymes involved in the synthesis of catecholamines, are all expressed in basal conditions in bovine aorta ECs, and their expression is enhanced in response to hypoxia. Moreover, hypoxia enhances catecholamine release. To evaluate the signal transduction pathway that regulates catecholamine synthesis in ECs, we overexpressed in bovine aorta ECs either protein kinase A (PKA) or the transcription factor cAMP response element binding, because PKA/cAMP response element binding activation induces tyrosine hydroxylase transcription and activity in response to stress. Both cAMP response element binding and PKA overexpression enhance DβH and phenylethanolamine-N-methyl transferase gene expression and catecholamine release, whereas H89, inhibitor of PKA, exerts the opposite effect, evidencing the role of PKA/cAMP response element binding transduction pathway in the regulation of catecholamine release in bovine aorta ECs. We then evaluated by immunohistochemistry the expression of tyrosine hydroxylase, Dopa decarboxylase, DβH, and phenylethanolamine-N-methyl transferase in femoral arteries from hindlimbs of C57Bl/6 mice 3 days after removal of the common femoral artery to induce chronic ischemia. Ischemia evokes tyrosine hydroxylase, Dopa decarboxylase, DβH, and phenylethanolamine-N-methyl transferase expression in the endothelium. Finally, the pharmacological inhibition of catecholamine release by fusaric acid, an inhibitor of DβH, reduces the ability of ECs to form network-like structures on Matrigel matrix. In conclusion, our study demonstrates for the first time that ECs are able to synthesize and release catecholamines in response to ischemia.

Endothelium--role in regulation of coagulation and inflammation

By its strategic position at the interface between blood and tissues, endothelial cells control blood fluidity and continued tissue perfusion while simultaneously they direct inflammatory cells to areas in need of defense or repair. The endothelial response depends on specific tissue needs and adapts to local stresses. Endothelial cells counteract coagulation by providing tissue factor and thrombin inhibitors and receptors for protein C activation. The receptor PAR-1 is differentially activated by thrombin and the activated protein C/EPCR complex, resulting in antithrombotic and anti-inflammatory effects. Thrombin and vasoactive agents release von Willebrand factor as ultra-large platelet-binding multimers, which are cleaved by ADAMTS13. Platelets can also facilitate leukocyte-endothelium interaction. Platelet activation is prevented by nitric oxide, prostacyclin, and exonucleotidases. Thrombin-cleaved ADAMTS18 induces disintegration of platelet aggregates while tissue-type plasminogen activator initiates fibrinolysis. Fibrin and products of platelets and inflammatory cells modulate the angiogenic response of endothelial cells and contribute to tissue repair.

Antibodies to serine proteases in the antiphospholipid syndrome

It is generally accepted that the major autoantigen for antiphospholipid antibodies (aPL) in the antiphospholipid syndrome (APS) is beta(2)-glycoprotein I (beta(2)GPI). However, a recent study has revealed that some aPL bind to certain conformational epitope(s) on beta(2)GPI shared by the homologous enzymatic domains of several serine proteases involved in hemostasis and fibrinolysis. Importantly, some serine protease-reactive aPL correspondingly hinder anticoagulant regulation and resolution of clots. These results extend several early findings of aPL binding to other coagulation factors and provide a new perspective about some aPL in terms of binding specificities and related functional properties in promoting thrombosis. Moreover, a recent immunological and pathological study of a panel of human IgG monoclonal aPL showed that aPL with strong binding to thrombin promote in vivo venous thrombosis and leukocyte adherence, suggesting that aPL reactivity with thrombin may be a good predictor for pathogenic potentials of aPL.

Biomaterials for vascular tissue engineering

Cardiovascular disease is the leading cause of mortality in the USA. The limited availability of healthy autologous vessels for bypass grafting procedures has led to the fabrication of prosthetic vascular conduits. While synthetic polymers have been extensively studied as substitutes in vascular engineering, they fall short of meeting the biological challenges at the blood-material interface. Various tissue engineering strategies have emerged to address these flaws and increase long-term patency of vascular grafts. Vascular cell seeding of scaffolds and the design of bioactive polymers for in situ arterial regeneration have yielded promising results. This article describes the advances made in biomaterials design to generate suitable materials that not only match the mechanical properties of native vasculature, but also promote cell growth, facilitate extracellular matrix production and inhibit thrombogenicity.

Amelioration of endothelial damage/dysfunction is a possible mechanism for the neuroprotective effects of Rho-kinase inhibitors against ischemic brain damage

We investigated the neuroprotective effects of fasudil's active metabolite, hydroxyfasudil, a Rho-kinase inhibitor, in a rat stroke model in which endothelial damage and subsequent thrombotic occlusion were selectively induced in perforating arteries. By examining the effects on the endothelial damage/dysfunction, we thought to explore the mechanism of Rho-kinase inhibitors. Hydroxyfasudil (10mg/kg, i.p., once daily for 3 days) significantly improved neurological functions and reduced the size of the infarct area produced by internal carotid artery injection of sodium laurate in a rat cerebral microthrombosis model. Treatment with fasudil or hydroxyfasudil concentration-dependently inhibited tumor necrosis factor alpha-induced tissue factor expression on the surface of cultured human umbilical vein endothelial cells. They also inhibited thrombin-induced endothelial hyperpermeability. The present findings suggest that hydroxyfasudil is efficacious in preventing brain damage associated with cerebral ischemia, and is partially responsible for fasudil's cytoprotective potential. The results also suggest that the therapeutic benefits against ischemic injury of Rho-kinase inhibitors are attributed, at least in part, to activity upon endothelial damage/dysfunction.

Flow-Mediated Signaling Modulates Endothelial Cell Phenotype

The focal development of atherosclerosis in the vascular tree may be explained in part by the local nature of blood flow. Bifurcations and branching points, prone to early atherogenesis, experience disturbed and oscillatory flow, whereas straight vascular regions, resistant to atherosclerosis, are exposed to steady laminar flow. A large number of studies suggest that the antiatherosclerotic effects of laminar flow are in part due to the ability of flow to modulate endothelial cell phenotype. Under steady laminar flow, endothelial cells generate molecules that promote a vasoactive, anticoagulant, anti-inflammatory, and growth-inhibitory surface. In contrast, disturbed flow induces a proliferative, prothrombotic, and adhesive phenotype. Endothelial cells are able to sense the variations of flow via mechanosensitive cell surface proteins and to transduce these signals via intracellular pathways to transcription factors in the nucleus leading to phenotypic changes. This review summarizes the "outside-in" signaling events initiated by flow that modulate endothelial cell phenotype.

The influence of lovastatin on thrombomodulin gene expression in vascular endothelial cells--in vitro study

OBJECTIVE

Statins reduce lipids concentration in blood. The latest investigations show they also improved the function of vascular endothelial cells (ECs). Thrombomodulin (TM) is particularly important marker of ECs activity. We investigated the in vitro effect of lovastatin on the expression level of TM gene.

METHODS AND RESULTS

ECs were incubated for 24 h in culture medium including lovastatin in 3 concentrations: 0.1, 1.0, 10.0 mol/l. The mRNA level of TM increased in correlation with rising concentrations of lovastatin to 600 % vs. control group.

CONCLUSIONS

TM is essential antithrombotic factor in endothelial cells. Lovastatin significantly raises thrombomodulin gene expression. It is important characteristics of this medicine, which prevents cardiovascular events.

Polymeric materials for tissue engineering of arterial substitutes

Cardiovascular disease is the leading cause of mortality in the United States. The limited availability of healthy autologous vessels for bypass grafting procedures has led to the fabrication of prosthetic vascular conduits. Synthetic polymeric materials, while providing the appropriate mechanical strength, lack the compliance and biocompatibility that bioresorbable and naturally occurring protein polymers offer. Vascular tissue engineering approaches have emerged in order to meet the challenges of designing a vascular graft with long-term patency. In vitro culture techniques that have been explored with vascular cell seeding of polymeric scaffolds and the use of bioactive polymers for in situ arterial regeneration have yielded promising results. This review describes the development of polymeric materials in various tissue engineering strategies for the improvement in the mechanical and biological performance of an arterial substitute.

Connexin32 is expressed in vascular endothelial cells and participates in gap-junction intercellular communication

Endothelial cells (ECs) play many roles in vascular biology, including control of blood pressure, blood clotting, atherosclerosis, angiogenesis, and inflammation. Gap junctions (GJs) are channel-like assemblies of connexin (Cx) family proteins that connect neighboring cells and modulate and synchronize their intracellular environments by the transfer of intracellular mediators. It has been reported that vascular ECs express Cx37, Cx40, and Cx43, but not Cx32. Here, we showed that Cx32 mRNA and protein are expressed in various cultured human ECs. We confirmed Cx32 expression in blood vessel ECs using wild-type and Cx32 knock-out mice. We observed that dye transfer between cultured ECs through gap junctions is suppressed by an anti-Cx32 monoclonal antibody. These findings suggest that vascular ECs express Cx32, which participates in endothelial gap-junction intercellular communication.

Novel autoantibodies against the activated coagulation factor IX (FIXa) in the antiphospholipid syndrome that interpose the FIXa regulation by antithrombin

We previously reported that some human antiphospholipid Abs (aPL) in patients with the antiphospholipid syndrome (APS) bind to the homologous enzymatic domains of thrombin and the activated coagulation factor X (FXa). Moreover, some of the reactive Abs are prothrombotic and interfere with inactivation of thrombin and FXa by antithrombin (AT). Considering the enzymatic domain of activated coagulation factor IX (FIXa) is homologous to those of thrombin and FXa, we hypothesized that some aPLs in APS bind to FIXa and hinder AT inactivation of FIXa. To test this hypothesis, we searched for IgG anti-FIXa Abs in APS patients. Once the concerned Abs were found, we studied the effects of the Ab on FIXa inactivation by AT. We found that 10 of 12 patient-derived monoclonal IgG aPLs bound to FIXa and that IgG anti-FIXa Abs in APS patients were significantly higher than those in normal controls (p < 0.0001). Using the mean + 3 SD of 30 normal controls as the cutoff, the IgG anti-FIXa Abs were present in 11 of 38 (28.9%) APS patients. Importantly, 4 of 10 FIXa-reactive monoclonal aPLs (including the B2 mAb generated against beta(2)-glycoprotein I significantly hindered AT inactivation of FIXa. More importantly, IgG from two positive plasma samples were found to interfere with AT inactivation of FIXa. In conclusion, IgG anti-FIXa Ab occurred in approximately 30% of APS patients and could interfere with AT inactivation of FIXa. Because FIXa is an upstream procoagulant factor, impaired AT regulation of FIXa might contribute more toward thrombosis than the dysregulation of the downstream FXa and thrombin.

Coagulation dysregulation as a barrier to xenotransplantation in the primate

PURPOSE OF REVIEW

The ability to generate pigs expressing a human complement regulatory protein (hCRP) and/or pigs in which the alpha1,3-galactosyltransferase gene has been knocked out (GT-KO) has largely overcome the barrier of hyperacute rejection of a pig organ transplanted into a primate. However, acute humoral xenograft rejection (AHXR), presenting as microvascular thrombosis and/or consumptive coagulopathy, remains a major hurdle to successful xenotransplantation. This review summarizes recent studies of the coagulation problems associated with xenotransplantation, and discusses potential strategies to overcome them.

RECENT PROGRESS

Organ transplantation into nonhuman primates from GT-KO pigs that express a hCRP are not susceptible to hyperacute rejection. Nevertheless, most recipients of GT-KO and/or hCRP transgenic pig organs develop a consumptive coagulopathy, even when the graft remains functioning. This is associated with platelet aggregation, thrombocytopenia, anemia, and a tendency to bleed. Whilst this may reflect an ongoing immune response against the graft, (as exposure to anti-nonGal antibodies in vitro induces procoagulant changes in porcine ECs, even in the absence of complement), histological examination of the graft often shows only minimal features of immune injury, unlike grafts undergoing typical AHXR. Importantly, recent in vitro studies have indicated that the coincubation of porcine endothelial cells (ECs) with human platelets activates the platelets to express tissue factor, independent of a humoral immune response. These observations suggest that the use of organs from GT-KO pigs that express a hCRP may not be sufficient to prevent the development of a coagulation disorder following xenotransplantation, even if complete immunological tolerance can be achieved.

SUMMARY

Both thrombotic microangiopathy and systemic consumptive coagulopathy are increasingly recognized as barriers to successful xenotransplantation. The breeding of transgenic pigs with one or more human anticoagulant genes, such as CD39 or tissue factor pathway inhibitor, is anticipated to inhibit the procoagulant changes that take place on the graft ECs, and thus may prevent or reduce platelet activation that arises as a result of immune-mediated injury. The identification of the molecular mechanisms that develop between porcine ECs and human platelets may allow pharmacological approaches to be determined that inhibit the development of thrombotic microangiopathy and consumptive coagulopathy. Hopefully, further genetic modification of the organ-source pigs, combined with systemic drug therapy to the recipient, will prolong graft survival further.

The thrombogenicity of human umbilical vein endothelial cell seeded collagen modules

Modular tissue-engineered constructs are assembled from sub-mm sized cylindrical collagen gel modules which are covered with a surface layer of human umbilical vein endothelial cells (HUVEC). The resulting construct is permeated by a network of interconnected endothelial cell lined channels to facilitate blood perfusion and nutrient delivery. This design strategy relies critically on the endothelial cells' layer behaving in a non-thrombogenic manner on the module surface and the objective here was to characterize this thrombogenicity. HUVEC prolonged clotting times in whole blood-module mixtures, and enabled slightly heparinized whole blood perfusion of an assembled modular construct in vitro with no increase in platelet loss compared to background levels. Flow cytometry and scanning electron microscopy indicated that HUVEC seeded modules reduced platelet activation and deposition but not leukocyte activation, compared to collagen only modules. Plasma recalcification times on non-stimulated HUVEC were longer compared to stimulated HUVEC but not different than that on collagen only module films and were not prolonged by incubation with a tissue factor blocking antibody. Together these data suggest that a functional non-thrombogenic layer of EC was generated on the module surface and that this layer should be sufficient to maintain continuous blood flow through an engineered modular tissue. In/ex vivo studies are warranted to confirm this conclusion.

Adipokines: linking obesity and cardiovascular disease

Obesity is fast becoming one of the most important contributors to cardiovascular disease. Adipose tissue is gaining recognition as a key endocrine organ that secretes a growing number of adipokines, linking adiposity with inflammation, endothelial dysfunction and the initiation of atherosclerosis. In particular, accumulation of visceral adipose tissue is implicated in the development of cardiovascular disease as it is associated with increased macrophage infiltration and oversecretion of proinflammatory and prothrombotic factors, such as TNF-α, IL-6, plasminogen activator inhibitor-1, leptin, resistin and angiotensinogen, and reduced secretion of the antiatherogenic factor adiponectin. As adipokines represent a key molecular link between obesity and the atherogenic state, research directed at understanding the physiology and biochemistry of these factors should open the door for discovery of novel therapeutics.

Changes in tissue factor and the effects of tissue factor pathway inhibitor on transient focal cerebral ischemia in rats

INTRODUCTION

To determine the contribution of tissue factor (TF) to focal cerebral ischemia/reperfusion injury, we investigated the changes in TF in rat brains with transient focal cerebral ischemia and also assessed the effect of TF pathway inhibitor (TFPI).

MATERIALS AND METHODS

Spontaneous hypertensive rats were subjected to 90-min of middle cerebral artery occlusion (MCAO) and then were reperfused for up to 24 h. Immediately after MCAO, recombinant human TFPI (rhTFPI) (50 or 20 microg/kg/min) was administered by means of a continuous intravenous injection for 4.5 h.

RESULTS AND CONCLUSIONS

TF immunoreactivity decreased or scattered in the ischemic area after reperfusion, however, an increased TF expression was observed in the microvasculature with the surrounding brain parenchyma and it peaked at 3 to 6 h, which coincided with the start of fibrin formation. On the other hand, total TF protein in ischemic area continued to exist and did not remarkably change until 24 h after reperfusion. At 24 h after reperfusion, the total infarct volume in the group treated with 50 microg/kg/min rhTFPI was significantly smaller than that in the controls (saline). Western blotting and immunohistochemical studies showed that rhTFPI treatment resulted in a decrease of fibrin in the ischemic brains and microvasculature. TF-mediated microvascular thrombosis is thus considered to contribute to focal cerebral ischemia/reperfusion injury. The continuous infusion of rhTFPI until a peak of TF-mediated microvascular thrombosis therefore attenuates the infarct volume by reducing fibrin deposition in the cerebral microcirculation.

ADAMTS-13, von Willebrand factor and related parameters in severe sepsis and septic shock

BACKGROUND

Insufficient control of von Willebrand factor (VWF) multimer size as a result of severely deficient ADAMTS-13 activity results in thrombotic thrombocytopenic purpura associated with microvascluar thrombosis and platelet consumption, features not seldom seen in severe sepsis and septic shock.

METHODS

ADAMTS-13 activity and VWF parameters of 40 patients with severe sepsis or septic shock were compared with those of 40 healthy controls of the same age and gender and correlated with clinical findings and sepsis outcome.

RESULTS

ADAMTS-13 activity was significantly lower in patients than in healthy controls [median 60% (range 27-160%) vs. 110% (range 63-200%); P < 0.001]. VWF parameters behaved reciprocally and both VWF ristocetin cofactor activity (RCo) and VWF antigen (VWF:Ag) were significantly (P < 0.001) higher in patients compared with controls. Neither ADAMTS-13 activity nor VWF parameters correlated with disease severity, organ dysfunction or outcome. However, a contribution of acute endothelial dysfunction to renal impairment in sepsis is suggested by the significantly higher VWF propeptide and soluble thrombomodulin levels in patients with increased creatinine values as well as by their strong positive correlations (creatinine and VWF propeptide r(s) = 0.484, P < 0.001; creatinine and soluble thrombomodulin r(s) = 0.596, P < 0.001).

CONCLUSIONS

VWF parameters are reciprocally correlated with ADAMTS-13 activity in severe sepsis and septic shock but have no prognostic value regarding outcome.

Significance of endothelial dysfunction in the pathogenesis of early and delayed radiation enteropathy

This review summarizes the current state of knowledge regarding the role of endothelial dysfunction in the pathogenesis of early and delayed intestinal radiation toxicity and discusses various endothelial-oriented interventions aimed at reducing the risk of radiation enteropathy. Studies published in the biomedical literature during the past four decades and cited in PubMed, as well as clinical and laboratory data from our own research program are reviewed. The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. During treatment of abdominal and pelvic tumors, the intestine is frequently a major dose-limiting factor. Microvascular injury is a prominent feature of both early (inflammatory), as well as delayed (fibroproliferative) radiation injuries in the intestine and in many other normal tissues. Evidence from our and other laboratories suggests that endothelial dysfunction, notably a deficiency of endothelial thrombomodulin, plays a key role in the pathogenesis of these radiation responses. Deficient levels of thrombomodulin cause loss of vascular thromboresistance, excessive activation of cellular thrombin receptors by thrombin, and insufficient activation of protein C, a plasma protein with anticoagulant, anti-inflammatory, and cytoprotective properties. These changes are presumed to be critically involved in many aspects of early intestinal radiation toxicity and may sustain the fibroproliferative processes that lead to delayed intestinal dysfunction, fibrosis, and clinical complications. In conclusion, injury of vascular endothelium is important in the pathogenesis of the intestinal radiation response. Endothelial-oriented interventions are appealing strategies to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

Nitric Oxide Modulates Tissue Plasminogen Activator Release in Normotensive Subjects and Hypertensive Patients

We evaluated the possible role of NO in modulating tissue plasminogen activator (t-PA) release in the forearm microcirculation of normotensive subjects and hypertensive patients. Essential hypertensive patients are characterized by endothelial dysfunction because of a reduced NO availability and also show an impaired t-PA release. In healthy volunteers and essential hypertensive patients, we studied local t-PA release and forearm blood flow changes (strain-gauge plethysmography) induced by intrabrachial administration of acetylcholine (0.45 and 1.5 microg/100 mL/min) and of sodium nitroprusside (0.5 and 1.0 microg/100 mL/min), an endothelium-dependent and -independent agonist, respectively. Acetylcholine was also repeated in the presence of intra-arterial infusion of the NO synthase inhibitor N(G)-monomethyl-l-arginine (100 microg/100 mL/min). In normotensive subjects, vasodilation to acetylcholine was blunted by N(G)-monomethyl-l-arginine. In these subjects, acetylcholine infusion induced a significant, dose-dependent increase in net forearm t-PA release. N(G)-monomethyl-l-arginine significantly reduced basal t-PA release, as well as acetylcholine-induced t-PA release. In essential hypertensive patients, vasodilation to acetylcholine was reduced as compared with controls and resistant to N(G)-monomethyl-l-arginine. In contrast to what was observed in healthy control subjects, in hypertensive patients, acetylcholine had no effect on t-PA release. Similarly, N(G)-monomethyl-l-arginine failed to modify either the tonic or the agonist-induced t-PA release. Both tonic and agonist-induced release of NO are directly involved in t-PA release by endothelial cells. Essential hypertension, characterized by a reduction in tonic and stimulated NO availability, is also associated with impaired capacity of t-PA release, suggesting a major role of impaired NO availability in worsening both vasodilation and t-PA release.

The influence of biomaterials on endothelial cell thrombogenicity

Driven by tissue engineering and regenerative medicine, endothelial cells are being used in combination with biomaterials in a number of applications for the purpose of improving blood compatibility and host integration. Endothelialized vascular grafts are beginning to be used clinically with some success in some centers, while endothelial seeding is being explored as a means of creating a vasculature within engineered tissues. The underlying assumption of this strategy is that when cultured on artificial biomaterials, a confluent layer of endothelial cells maintain their non-thrombogenic phenotype. In this review the existing knowledge base of endothelial cell thrombogenicity cultured on a number of different biomaterials is summarized. The importance of selecting appropriate endpoint measures that are most reflective of overall surface thrombogenicity is the focus of this review. Endothelial cells inhibit thrombosis through three interconnected regulatory systems (1) the coagulation cascade, (2) the cellular components of the blood such as leukocytes and platelets and (3) the complement cascade, and also through effects on fibrinolysis and vascular tone, the latter which influences blood flow. Thus, in order to demonstrate the thrombogenic benefit of seeding a biomaterial with EC, the conditions under which EC surfaces are more likely to exhibit lower thrombogenicity than unseeded biomaterial surfaces need to be consistent with the experimental context. The endpoints selected should be appropriate for the dominant thrombotic process that occurs under the given experimental conditions.

Antibodies against the activated coagulation factor X (FXa) in the antiphospholipid syndrome that interfere with the FXa inactivation by antithrombin

Antiphospholipid Ab have been shown to promote thrombosis and fetal loss in the antiphospholipid syndrome (APS). Previously, we found IgG anti-thrombin Ab in some APS patients that could interfere with inactivation of thrombin by antithrombin (AT). Considering that activated coagulation factor X (FXa) is homologous to thrombin in the catalytic domains and is also regulated primarily by AT, we hypothesized that some thrombin-reactive Ab may bind to FXa and interfere with AT inactivation of FXa. To test these hypotheses, we studied reactivity of eight patient-derived monoclonal IgG antiphospholipid Ab with FXa and the presence of IgG anti-FXa Ab in APS patients and investigated the effects of FXa-reactive mAb on AT inactivation of FXa. The results revealed that six of six thrombin-reactive IgG mAb bound to FXa and that the levels of plasma IgG anti-FXa Ab in 38 APS patients were significantly higher than those in 30 normal controls (p < 0.001). When the mean plus 3 SDs of the 30 normal controls was used as the cutoff, 5 of 38 APS patients (13.2%) had IgG anti-FXa Ab. Importantly, three of six FXa-reactive mAb significantly inhibited AT inactivation of FXa. Combined, these results indicate that anti-FXa Ab may contribute to thrombosis by interfering with the anticoagulant function of AT on FXa in some APS patients.

Circulating markers of endothelial function in cardiovascular disease

Endothelial dysfunction is a key event in cardiovascular disease. Measurement of endothelial dysfunction in vivo presents a major challenge, but has important implications since it may identify the clinical need for therapeutic intervention, specifically in primary prevention. Several biological markers have been used as indicators of endothelial dysfunction. The soluble adhesion molecules sICAM-1 and sVCAM-1 lack specificity and are increased in inflammatory processes. Both markers are increased in coronary artery disease. sICAM-1 level predicts the risk for cardiovascular disease or diabetes mellitus in healthy individuals. sE-selectin is specific for the endothelium and is increased in coronary artery disease and diabetes mellitus. sE-selectin is also associated with diabetic risk. The endothelium-specific marker, soluble thrombomodulin, is associated with severity of coronary artery disease, stroke or peripheral occlusive arterial disease and is not increased in healthy or asymptomatic subjects. Interestingly, thrombomodulin decreases during treatment of hypercholesterolemia or hyperhomocysteinemia. In contrast, von Willebrand factor is the best endothelial biomarker and predicts risk for ischemic heart disease or stroke.

The prothrombotic paradox of hypertension: role of the renin-angiotensin and kallikrein-kinin systems

Despite increased pulsatile stress, thrombotic rather than hemorrhagic events represent a major complication of hypertension. The pathophysiology of thrombosis in hypertension involves the interaction among vascular endothelium and particularly the renin-angiotensin and kallikrein-kinin systems. Because hypertension is often associated with some degree of inflammation, the combination of chronic inflammation and chronic shear stress may convert the normal anticoagulant endothelium into a procoagulant surface, expressing tissue factor. Activation of the renin-angiotensin system leads to activation of nuclear factor kappaB-dependent proinflammatory genes, also accelerating the expression of tissue factor. Renin-angiotensin and kallikrein-kinin systems interact at several levels to modulate coagulation, fibrinolysis, and vasodilatation in such a way that these 2 systems could have a major influence on the occurrence of thrombotic complications. Treatment with angiotensin-converting enzyme inhibitors and angiotensin II type 1 receptor antagonists may favorably influence the balance between the renin-angiotensin and kallikrein-kinin axis, regulating blood pressure as well as reducing the risk of thrombosis, which may explain part of the clinical efficacy of these drugs.

Endothelial function and its assessment

Endothelial dysfunction is a characteristic aspect of most of the conditions associated with atherosclerosis and is commonly found as an early feature in atherothrombotic vascular disease. An appreciation of the underlying mechanisms of endothelial function, as well as dysfunction, is essential as this has critical influence on the different methods in the assessment of endothelial function and effects of various treatments on its quantification. Furthermore, endothelial dysfunction is recognised as a type of 'target organ damage' in common cardiovascular conditions (e.g., hypertension) and the area is of increasing interest for new drug development, as therapies that modulate the endothelium will have added advantages; thus, for the development of new/experimental drugs, an awareness of ways to assess the endothelium is necessary. In this review, an overview of different methods including biochemical markers, and invasive and non-invasive tools, to determine endothelial function is presented as well as their clinical relevance. Furthermore, the effects of various treatments on endothelial dysfunction and their underlying mechanisms are elucidated.

The Potential Relevance of the Multiple Lipid-Independent (Pleiotropic) Effects of Statins in the Management of Acute Coronary Syndromes

Emerging data suggest that acute presentations of coronary artery disease may involve a complex interplay between the vessel wall, inflammatory cells, and the coagulation cascade. Although a culprit thrombotic lesion may be treated effectively by antithrombotic therapy and revascularization, this will have little effect on the global processes that determine recurrent events at non-culprit sites. Thus, additional systemic treatment is required to modulate the adverse biological features that are the hallmark of acute coronary syndromes (ACS). Statins possess multiple beneficial effects that are independent of low-density-lipoprotein cholesterol (LDL-C) lowering and that have favorable effects on inflammation, the endothelium, and the coagulation cascade. In the Pravastatin or Atorvastatin Evaluation and Infection Therapy-Thrombolysis In Myocardial Infarction 22 (PROVE IT-TIMI 22) trial, differences were seen based on achieved LDL-C that could be further discriminated by the achieved C-reactive protein level. Studies of non-vascular disease such as multiple sclerosis have shown that statins reduce inflammation, supporting the presence of lipid-independent effects of statins. This review focuses on the potential importance of these effects in the management of ACS.

Targeted deletion of Fgl-2/fibroleukin in the donor modulates immunologic response and acute vascular rejection in cardiac xenografts

BACKGROUND

Xenografts ultimately fail as a result of acute vascular rejection (AVR), a process characterized by intravascular thrombosis, fibrin deposition, and endothelial cell activation.

METHODS AND RESULTS

We studied whether targeted deletion of Fgl-2, an inducible endothelial cell procoagulant, (Fgl-2-/-) in the donor prevents AVR in a mouse-to-rat cardiac xenotransplantation model. By 3 days after transplant, Fgl-2+/+ grafts developed typical features of AVR associated with increased levels of donor Fgl-2 mRNA. Grafts from Fgl-2-/- mice had reduced fibrin deposition but developed cellular rejection. Treatment with a short course of cobra venom factor and maintenance cyclosporine resulted in long-term acceptance of both Fgl-2+/+ and Fgl-2-/- grafts. On withdrawal of cyclosporine, Fgl-2+/+ grafts developed features of AVR; in contrast, Fgl-2-/- grafts again developed acute cellular rejection. Rejecting Fgl-2+/+ hearts stained positively for IgG, IgM, C3, and C5b-9, whereas rejecting Fgl-2-/- hearts had minimal Ig and complement deposition despite xenoantibodies in the serum. Furthermore, serum containing xenoantibodies failed to stain Fgl-2-/- long-term treated hearts but did stain wild-type heart tissues. Treatment of Fgl-2-/- xenografts with mycophenolate mofetil and tacrolimus, a clinically relevant immune suppression protocol, led to long-term graft acceptance.

CONCLUSIONS

Deletion of Fgl-2 ameliorates AVR by downregulation of xenoantigens and may facilitate successful clinical heart xenotransplantation.

Biocompatibility screening in cardiovascular implants

BACKGROUND

Interest in information on biocompatibility of implants is increasing. The purpose of this paper is to discuss methods and results of pathological biocompatibility screening of explanted cardiovascular implants.

METHODS

Use of standard histology after embedding in paraffin is limited since metallic implants have to be removed during workup with disruption of the specimen. Alternatively, tissue blocks containing an implant can be embedded in methylmethacrylate or hydroxyethylmethacrylate and processed by sectioning with a diamond cutter and grinding, thus leaving the implant in situ and saving the tissue/implant interface for detection of local inflammatory reactions. Another important aspect of evaluation is the progress of thrombus organisation after initial fibrin clotting on the metal surface or in the inner part of occlusion devices. New methacrylate resins and embedding techniques allow for specific immunohistochemical staining of the specimen thus enabling characterisation of tissues surrounding the implant. Information on endothelialisation of the vascular surface of the implant can be obtained by means of immunohistochemistry or by scanning electron microscopy.

RESULTS

Illustrating the use of these technologies, we demonstrate findings in tissue specimens from animal studies with different types of devices (i.e. stents, occlusion devices). We present corresponding findings in human specimens with implants that were removed during corrective surgery for congenital heart defects. Early endothelialisation of the vascular surface was seen after implantation in all types of devices. Cells within occlusion devices could be characterised histologically and immunohistochemically as fibromuscular cells as seen in intimal hyperplasia after stent implantation. Inflammatory implant-host reactions ranged from mild to moderate (medical grade stainless steel, nitinol) to severe (polytetrafluoroethylene [PTFE]).

CONCLUSIONS

With an optimal work-up of cardiovascular implants, ingrowth and endothelialisation as well as inflammatory reactions in the surrounding tissue can be assessed. This information allows evaluation of individual tissue reactions to the implant and may serve as valuable basis for optimisation of biocompatibility by implant modification.

Platelet nitrate responsiveness in fasting and postprandial type 2 diabetes

Vascular responsiveness to exogenous nitrates in type 2 diabetes (T2DM) is attenuated in brachial and coronary vessels. We determined platelet responsiveness to nitric oxide (NO) in T2DM and control subjects. We examined whether the postprandial (PP) state affected platelet sensitivity to NO donors in T2DM patients and the extent of correlation between this and measures of oxidative stress, compared to changes in endothelial function. Twelve T2DM subjects were studied fasting and four hours after a test meal and compared with 15 healthy controls. We assessed the inhibitory effects of NO donors on adenosine 5'-diphosphate (ADP)-induced platelet aggregation. Oxidative stress was assessed by lipid-derived free radicals, ex vivo by electron paramagnetic resonance spectroscopy and markers of lipid peroxidation. Endothelial function was assessed by flow-mediated vasodilatation (FMD) of the brachial artery. Results are expressed as (mean +/- SEM). Fasting platelet aggregation was increased in diabetics versus controls (14.86 +/- 1.1 Ohms vs. 10.76 +/- 1.1 Ohms, p < 0.05). Sodium nitroprusside (SNP) and glyceryl trinitrate (GTN) inhibited ADP-induced aggregation by 73.1 +/- 5.9% and 50.3 +/- 7.7% in healthy controls compared to 15.4 +/- 7% and 19.5 +/- 8.2% in T2DM (p < 0.05). Fasting and postprandial inhibition of platelet aggregation with NO donors in T2DM was similar. T2DM patients had higher levels of oxidative stress in the fasting state and postprandially. There were no PP correlations with platelet NO resistance. In conclusion, there is platelet hyporesponsiveness to NO donors (SNP/GTN) in T2DM compared to controls, with increased ADP-induced platelet aggregation. Platelet abnormalities were associated with increased oxidative stress.

Thrombo-ischaemic pinnal necrosis associated with fenbendazole treatment in a dog

An 11-week-old, female West Highland white terrier was presented with necrosis of the distal third of both pinnae. Haematology, biochemistry and urinalysis, Coombs test, antinuclear antibody and cold autoagglutinin antibody tests were normal. A drug reaction to fenbendazole was diagnosed. The necrotic ear tips were surgically removed. Histopathology revealed extensive coagulative necrosis of the epidermis and superficial to mid-dermis, a moderate interstitial neutrophilic infiltrate and complete thrombotic occlusion and necrosis of blood vessels. There was also endothelial cell activation and proliferation with endothelial cell cushions protruding into the vascular lumen. Immunohistochemistry for factor VIII-related antigen confirmed endothelial cell involvement. This case represents an unusual, drug-induced, thrombo-ischaemic necrosis of the pinnae. It is also, to the authors' knowledge, the first report of fenbendazole sensitivity in a dog. The histopathology is similar to previous cases of proliferative thrombovascular pinnal necrosis, suggesting that drug reactions should be considered in this condition.

Negative regulation of platelet function by a secreted cell repulsive protein, semaphorin 3A

Semaphorin 3A (Sema3A) is a secreted disulfide-bound homodimeric molecule that induces growth cone collapse and repulsion of axon growth in the nervous system. Recently, it has been demonstrated that Sema3A is produced by endothelial cells and inhibits integrin function in an autocrine fashion. In this study, we investigated the effects of Sema3A on platelet function by using 2 distinct human Sema3A chimera proteins. We detected expression of functional Sema3A receptors in platelets and dose-dependent and saturable binding of Sema3A to platelets. Sema3A dose-dependently inhibited activation of integrin alphaIIbbeta3 by all agonists examined including adenosine diphosphate (ADP), thrombin, convulxin, phorbol 12-myristate 13-acetate, and A23187. Sema3A inhibited not only platelet aggregation induced by thrombin or collagen but also platelet adhesion and spreading on immobilized fibrinogen. Moreover, Sema3A impaired alphaIIbbeta3-independent spreading on glass coverslips and aggregation-independent granular secretion. Sema3A inhibited agonist-induced elevation of filamentous action (F-actin) contents, phosphorylation of cofilin, and Rac1 activation. In contrast, Sema3A did not affect the levels of cyclic nucleotides or agonist-induced increase of intracellular Ca2+ concentrations. Thus, the extensive inhibition of platelet function by Sema3A appears to be mediated, at least in part, through impairment of agonist-induced Rac1-dependent actin rearrangement.

Predictors of the rise in vWF after ST elevation myocardial infarction: implications for treatment strategies and clinical outcome

AIMS

Prior studies suggest that acute coronary syndromes (ACSs) are associated with endothelial activation and that this is of prognostic significance. We hypothesized that endothelial activation, as measured by a rise in von Willebrand Factor (DeltavWF), was influenced by the thrombolysis in myocardial infarction flow grade (TFG), the corrected TIMI frame count (CTFC) and the choice of anticoagulant therapy after fibrinolysis in ST elevation myocardial infarction (STEMI).

METHODS AND RESULTS

Data were drawn from the enoxaparin and tenecteplase tissue plasminogen activator (TNK-tpa) with or without GPIIb/IIIa inhibitor as the reperfusion strategy in the STEMI trial (ENTIRE-TIMI 23). Three hundred and fourteen patients had serial measurements of vWF (baseline and 48-72 h) and angiographic data available. TFG<3 (P=0.0042) or CTFC>/=40 at 60 min (P=0.0035) were associated with a higher DeltavWF. DeltavWF >/=75th percentile was associated with a higher incidence of death or myocardial infarction (MI) at 30 days, compared with <75th percentile (11.2 vs. 4.1%, P=0.027). Enoxaparin independently reduced the DeltavWF (P=0.019) and also the composite of death or MI (OR 0.33, 95% CI 0.12-0.91, P=0.03) compared with unfractionated heparin.

CONCLUSION

In STEMI treated by fibrinolysis, coronary flow at 60 min and choice of adjunctive anticoagulant appear to be independent determinants of DeltavWF. Enoxaparin is independently associated with a reduction in DeltavWF and a reduction in death or MI. The clinical benefits of enoxaparin as an adjunctive treatment in STEMI may be mediated in part by a reduction in vWF release.

Upregulation of neutrophil surface adhesion molecules in infants of pre-eclamptic women

OBJECTIVE

To evaluate evidence of neutrophil activation in infants born to pre-eclamptic women and examine any association between degree of neutrophil activation and severity of pre-eclampsia.

DESIGN

This study utilized quantitative flow cytometry to determine whether the expression of surface adhesion molecules: CD18, CD11a, CD11b, and CD11c on cord blood neutrophils using mean channel fluorescence values (MCF). A total of 20 infants of pre-eclamptic women were compared with a control group of 19 infants of normotensive women.

RESULTS

MCF values were significantly higher in infants born to pre-eclamptic women vs controls: CD18 (432.0+/-236.3 vs 230.5+/-97.9; p=0.002), CD11a (552.9+/-272.4 vs 326.9+/-268.6; p=0.003), CD11b (937.2+/-521.9 vs 576.6+/-352.9; p=0.025), and CD11c (228.5+/-130.3 vs 133.0+/-77.1; p=0.006), respectively. The mean MCF values appeared higher in severe vs mild pre-eclampsia.

CONCLUSIONS

This study revealed neutrophil activation in infants born to pre-eclamptic women. The relationship between neutrophil activation and severity of pre-eclampsia warrants further study.

Age-related endothelial dysfunction : potential implications for pharmacotherapy

Aging per se is associated with abnormalities of the vascular wall linked to both structural and functional changes that can take place at the level of the extracellular matrix, the vascular smooth muscle and the endothelium of blood vessels. Endothelial dysfunction is generally defined as a decrease in the capacity of the endothelium to dilate blood vessels in response to physical and chemical stimuli. It is one of the characteristic changes that occur with age, independently of other known cardiovascular risk factors. This may account in part for the increased incidence of cardiovascular events in elderly people that can be reversed by restoring endothelial function. A better understanding of the mechanisms involved and the aetiopathogenesis of this process will help in the search for new therapeutic agents.Age-dependent alteration of endothelium-dependent relaxation seems to be a widespread phenomenon both in conductance and resistance arteries from several species. In the course of aging, there is an alteration in the equilibrium between relaxing and contracting factors released by the endothelium. Hence, there is a progressive reduction in the participation of nitric oxide and endothelium-derived hyperpolarising factor associated with increased participation of oxygen-derived free radicals and cyclo-oxygenase-derived prostanoids. Also, the endothelin-1 and angiotensin II pathways may play a role in age-related endothelial dysfunction. The use of drugs acting at different levels of these signalling cascades, including antioxidant therapy, lipid-lowering drugs and estrogens, seems to be promising.

Endothelial cell functions

Endothelial cells play a wide variety of critical roles in the control of vascular function. Indeed, since the early 1980s, the accumulating knowledge of the endothelial cell structure as well as of the functional properties of the endothelial cells shifted their role from a passive membrane or barrier to a complex tissue with complex functions adaptable to needs specific in time and location. Hence, it participates to all aspects of the vascular homeostasis but also to physiological or pathological processes like thrombosis, inflammation, or vascular wall remodeling. Some of the most important endothelial functions will be described in the following review and more specifically, their role in blood vessel formation, in coagulation and fibribolysis, in the regulation of vascular tone as well as their participation in inflammatory reactions and in tumor neoangiogenesis.

Relationship between circulating E-selectin, DD genotype of angiotensin-converting-enzyme, and cardiovascular damage in central obese subjects

Fifty-six young central obese patients were investigated to evaluate relationships between soluble E-selectin (sE-S), angiotensin-converting enzyme (ACE) gene polymorphism, left ventricular function and structure, and carotid morphology by determination of sE-S and ACE genotypes. Our results indicated that central obese subjects with concomitant higher levels of sE-S and ACE DD genotype may be characterized by early cardiovascular alterations and then considered a particular subset of subjects at higher risk of cardiovascular disease.