The vitronectin receptor (alpha v beta 3) is implicated, in cooperation with P-selectin and platelet-activating factor, in the adhesion of monocytes to activated endothelial cells

Targeting Neutrophil β2-Integrins: A Review of Relevant Resources, Tools, and Methods

Neutrophils are important innate immune cells that respond during inflammation and infection. These migratory cells utilize β₂-integrin cell surface receptors to move out of the vasculature into inflamed tissues and to perform various anti-inflammatory responses. Although critical for fighting off infection, neutrophil responses can also become dysregulated and contribute to disease pathophysiology. In order to limit neutrophil-mediated damage, investigators have focused on β₂-integrins as potential therapeutic targets, but so far these strategies have failed in clinical trials. As the field continues to move forward, a better understanding of β₂-integrin function and signaling will aid the design of future therapeutics. Here, we provide a detailed review of resources, tools, experimental methods, and in vivo models that have been and will continue to be utilized to investigate the vitally important cell surface receptors, neutrophil β₂-integrins.

The role of the cell surface glycocalyx in drug delivery to and through the endothelium

Cell membranes are key interfaces where materials engineering meets biology. Traditionally regarded as just the location of receptors regulating the uptake of molecules, we now know that all mammalian cell membranes are 'sugar coated'. These sugars, or glycans, form a matrix bound at the cell membrane via proteins and lipids, referred to as the glycocalyx, which modulate access to cell membrane receptors crucial for interactions with drug delivery systems (DDS). Focusing on the key blood-tissue barrier faced by most DDS to enable transport from the place of administration to target sites via the circulation, we critically assess the design of carriers for interactions at the endothelial cell surface. We also discuss the current challenges for this area and provide opportunities for future research efforts to more fully engineer DDS for controlled, efficient, and targeted interactions with the endothelium for therapeutic application.

Safety of tirofiban for patients with acute ischemic stroke in routine clinical practice

The aim of the present study was to investigate the safety of tirofiban alone and in combination with various treatments in acute ischemic stroke (AIS). A total of 120 patients with AIS were included in the study, and these patients were divided into three treatment groups: Group A (tirofiban alone, n=68), group B (tirofiban plus thrombolytic therapy, n=26), and group C (tirofiban as a 'bridging therapy', n=26). Risk factors, stroke severity, initial imaging, treatment regimens, complications and long-term outcomes were analyzed. In total, eight patients (6.7%) [six patients (23.1%) in group B and two patients (7.7%) in group C] had hemorrhage during or subsequent to treatment. Sixteen patients (six in group A, eight in group B and two in group C) succumbed during the hospital admission period. The mortality rate was 13.3% (8.8% for group A, 30.7% for group B and 7.7% for group C) in the acute phase. A favorable outcome (modified Rankin Scale score, 0-2) in the first three months after stroke was only observed in 43.3% of patients (44.1% in group A, 46.7% in group B and 36.4% in group C). The mean Barthel index was 72.3 in group A, 84.4 in group B and 56.8 in group C (total patient population, 71.0). The results of the present study have shown that stroke treatment with tirofiban is safe in AIS. A large randomized controlled trial in the future is required to decrease the incidence of the minor bleeding complications associated with tirofiban therapy.

Genetic variation is the major determinant of individual differences in leukocyte endothelial adhesion

Objective

To determine the genetic contribution to leukocyte endothelial adhesion.

Methods

Leukocyte endothelial adhesion was assessed through a novel cell-based assay using human lymphoblastoid cell lines. A high-throughput screening method was developed to evaluate the inter-individual variability in leukocyte endothelial adhesion using lymphoblastoid cell lines derived from different donors. To assess heritability, ninety-two lymphoblastoid cell lines derived from twenty-three monozygotic twin pairs and twenty-three sibling pairs were compared. These lymphoblastoid cell lines were plated with the endothelial cell line EA.hy926 and labeled with Calcein AM dye. Fluorescence was assessed to determine endothelial cell adhesion to each lymphoblastoid cell line. Intra-pair similarity was determined for monozygotic twins and siblings using Pearson pairwise correlation coefficients.

Results

A leukocyte endothelial adhesion assay for lymphoblastoid cell lines was developed and optimized (CV = 8.68, Z′-factor = 0.67, SNR = 18.41). A higher adhesion correlation was found between the twins than that between the siblings. Intra-pair similarity for leukocyte endothelial adhesion in monozygotic twins was 0.60 compared to 0.25 in the siblings. The extent to which these differences are attributable to underlying genetic factors was quantified and the heritability of leukocyte endothelial adhesion was calculated to be 69.66% (p-value<0.0001).

Conclusions

There is a heritable component to leukocyte endothelial adhesion. Underlying genetic predisposition plays a significant role in inter-individual variability of leukocyte endothelial adhesion.

Molecular Magnetic Resonance Imaging for the Detection of Vulnerable Plaques: Is It Possible?: Retracted

Recent advances in molecular resonance imaging of atherosclerosis enable to visualize atherosclerotic plaques in vivo using molecular targeted contrast agents. This offers opportunities to study atherosclerosis development and plaque vulnerability noninvasively. In this review, we discuss MRI contrast agents targeted toward atherosclerotic plaques and illustrate how these new imaging platforms could assist in our understanding of atherogenesis and atheroprogression. In particular, we highlight the challenges and limitations of the different contrast agents and hurdles for clinical application. We describe the most promising existing compounds to detect atherosclerosis and plaque vulnerability. Of particular interest are the fibrin-targeted compounds that detect thrombi and, furthermore, the contrast agents targeted to integrins that allow to visualize plaque neovascularization. Moreover, vascular cell adhesion molecule 1-targeted iron oxides seem promising for early detection of atherosclerosis. These targeted MRI contrast agents, however promising and well characterized in (pre)clinical models, lack specificity for plaque vulnerability.

Protein kinase C-θ is required for murine neutrophil recruitment and adhesion strengthening under flow

Protein kinase C (PKC)-θ is involved in T cell activation via regulating the avidity of the β(2) integrin LFA-1 in the immunological synapse. LFA-1 also mediates leukocyte adhesion. To investigate the role of PKC-θ in neutrophil adhesion, we performed intravital microscopy in cremaster venules of mice reconstituted with bone marrow from LysM-GFP(+) (wild-type [WT]) and PKC-θ gene-deficient (Prkcq(-/-)) mice. Following stimulation with CXCL1, both WT and Prkcq(-/-) cells became adherent. Although most WT neutrophils remained adherent for at least 180 s, 50% of Prkcq(-/-) neutrophils were detached after 105 s and most by 180 s. Upon CXCL1 injection, rolling of all WT neutrophils stopped for 90 s, but rolling of Prkcq(-/-) neutrophils started 30 s after CXCL1 stimulation. A similar neutrophil adhesion defect was seen in vitro, and spreading of Prkcq(-/-) neutrophils was delayed. Prkcq(-/-) neutrophil recruitment was impaired in fMLP-induced transmigration into the cremaster muscle, thioglycollate-induced peritonitis, and LPS-induced lung injury. We conclude that PKC-θ mediates integrin-dependent neutrophil functions and is required to sustain neutrophil adhesion in postcapillary venules in vivo. These findings suggest that the role of PKC-θ in outside-in signaling following engagement of neutrophil integrins is relevant for inflammation in vivo.

EXPRESSION OF ANGIOSTATIN, INTEGRINαvβ3, AND VITRONECTIN IN HUMAN LUNGS IN SEPSIS

Angiostatin, integrin alphavbeta3, and vitronectin play important roles in inflammation. However, there is very little information on expression of these molecules in the lungs of humans with sepsis. Therefore, as a first step to eventually study the function of these molecules, the authors conducted an immunohistochemical study to evaluate their expression in lungs of normal (N = 8) and sepsis patients (N = 8). In normal lungs, angiostatin expression was minimal in the alveolar septa and alveolar macrophages, and absent in large blood vessels, bronchioles, and interstitium. In sepsis patients, the staining was intense in the septa, neutrophils, alveolar macrophages, and large blood vessels. Integrin alphavbeta3 staining was observed in occasional bronchiolar epithelial cells and a few alveolar macrophages in the normal lungs. The integrin was expressed extensively and intensely in bronchiolar epithelium and alveolar macrophages, and with lesser intensity in large blood vessels in inflamed lungs. Compared to the normal lung, vitronectin expression was increased in alveolar macrophages and in vascular smooth muscles in inflamed lungs. These data show cell-specific increase in the expression of integrin alphavbeta3, angiostatin, and vitronectin in inflamed lungs of sepsis patients. Because all these molecules can have significant influence on inflammation, the data reported in this manuscript create a need for further investigation.

Endothelial cell migration on RGD-peptide-containing PEG hydrogels in the presence of sphingosine 1-phosphate

Sphingosine 1-phosphate (S1P) is a potent chemokinetic agent for endothelial cells that is released by activated platelets. We previously developed Arg-Gly-Asp (RGD)-containing polyethylene glycol biomaterials for the controlled delivery of S1P to promote endothelialization. Here, we studied the effects of cell adhesion strength on S1P-stimulated endothelial cell migration in the presence of arterial levels of fluid shear stress, since an upward shift in optimal cell adhesion strengths may be beneficial for promoting long-term cell adhesion to materials. Two RGD peptides with different integrin-binding specificities were added to the polyethylene glycol hydrogels. A linear RGD bound primarily to beta(3) integrins, whereas a cyclic RGD bound through both beta(1) and beta(3) integrins. We observed increased focal adhesion formation and better long-term adhesion in flow with endothelial cells on linear RGD peptide, versus cyclic RGD, even though initial adhesion strengths were higher for cells on cyclic RGD. Addition of 100 nM S1P increased cell speed and random motility coefficients on both RGD peptides, with the largest increases found on cyclic RGD. For both peptides, much of the increase in cell migration speed was found for smaller cells (<1522 microm(2) projected area), although the large increases on cyclic RGD were also due to medium-sized cells (2288-3519 microm(2)). Overall, a compromise between high cell migration rates and long-term adhesion will be important in the design of materials that endothelialize after implantation.

AlphaV beta3 (?v?3) integrin inhibition reduces leukocyte?endothelium interaction in a pressure-induced reperfusion model

The leukocyte-endothelium interaction is known to contribute to reperfusion injury, which is considered to participate in the pathophysiology of pressure ulcers, and integrin alphaV beta3 (alphavbeta3) has been shown to mediate the processes of cellular adhesion in various types of cells. This study aims to clarify leukocyte behavior in our original microcirculatory pressure-induced reperfusion model, which can visualize the microcirculation in vivo. We also estimated the effect of alphavbeta3 integrin inhibition on the reduction of the leukocyte-endothelium interaction. Mice with dorsal skinfold chambers were divided into three groups: the baseline group (n=6), in which animals received no compression; the compression-reperfusion group (n=6), in which animals underwent 2-hour compression of the dorsal skin, followed by release, and the inhibitor-treated group (n=7), in which an alphavbeta3 inhibitor, CP4715, was administered in addition to the compression-release procedure. Staining with rhodamine 6G quantitatively visualized leukocyte behavior under the intravital fluorescent microscope. Compression-reperfusion induced a significant increase in rolling, sticking, and extravasation of the leukocytes. Treatment with the inhibitor strikingly reduced leukocyte sticking and extravasation. The present experiment has provided evidence that alphavbeta3 inhibition reduces leukocyte-endothelium interaction in our original pressure-induced reperfusion model.

Evaluating the ‘no reflow’ phenomenon with myocardial contrast echocardiography

Based on its ability to measure myocardial blood volume and capillary flow, myocardial contrast echocardiography (MCE) has provided invaluable pathophysiological information regarding the no reflow phenomenon both in humans and in the experimental laboratory. The new area of molecular imaging with MCE allows the identification of molecular events within the microcirculation that have provided further insights into the mechanisms involved in the no-reflow phenomenon. Molecular imaging with MCE has the potential for monitoring molecular events associated with no reflow phenomenon and also to develop strategies to limit the no reflow phenomenon via pharmacological means. This paper will cover these areas briefly.

Low-Density Lipoprotein-Lowering Medication and Platelet Function

Elevated low-density lipoprotein (LDL) cholesterol (LDL-C) levels represent one of the most important risk factors for atherosclerosis and therefore cardiovascular morbidity and mortality. LDL-C operates at different levels and through various classic and non-classic mechanisms. In particular, increased or modified LDL enhances platelet function and increases sensitivity of platelets to several naturally occurring agonists. Agents that lower LDL-C in hypercholesterolemic patients have been shown to interfere with platelet function. Several studies, in fact, suggested that statins exert anti-thrombotic effects largely as a result of an anti-platelet activity. Among the other LDL-C-lowering agents those acting by interfering with cholesterol reabsorption from the gut (cholestyramine, colestipol) do not appear to interfere with platelet function, whereas peroxisome proliferator-activated receptor agonists (such as fibrates) can inhibit platelet function. The full potential of these drugs in vascular protection is only just being realized. Further studies are still needed to elucidate the full therapeutic benefits of these agents in plaque stabilization and thrombosis.

Intraarterial reteplase and intravenous abciximab for treatment of acute ischemic stroke

We performed a preliminary feasibility and safety study using intravenous (IV) administration of a platelet glycoprotein IIb/IIIa inhibitor (abciximab) in conjunction with intraarterial (IA) administration of a thrombolytic agent (reteplase) in a primate model of intracranial thrombosis. We introduced thrombus through superselective catheterization of the intracranial segment of the internal carotid artery in 16 primates. The animals were randomly assigned to receive IA reteplase and IV abciximab ( n =4), IA reteplase and IV placebo ( n =4), IA placebo and IV abciximab ( n =4) or IA and IV placebo ( n =4). Recanalization was assessed by serial angiography during the 6-h period after initiation of treatment. Postmortem magnetic resonance (MR) imaging was performed to determine the presence of cerebral infarction or intracranial hemorrhage. Partial or complete recanalization at 6 h after initiation of treatment (decrease of two or more points in pre-treatment angiographic occlusion grade) was observed in two animals treated with IA reteplase and IV abciximab, three animals treated with IA reteplase alone and one animal treated with IV abciximab alone. No improvement in perfusion was observed in animals that received IV and IA placebo. Cerebral infarction was demonstrated on postmortem MR imaging in three animals that received IA and IV placebo and in one animal each from the groups that received IA reteplase and IV abciximab or IV abciximab alone. One animal that received IV abciximab alone had a small intracerebral hemorrhage on MR imaging. IA reteplase with or without abciximab appeared to be the most effective regimen for achieving recanalization in our model of intracranial thrombosis. Further studies are required in experimental models to determine the optimal dose, method of administration and efficacy of these medications in acute ischemic stroke.

Effects of thrombin on interactions between beta3-integrins and extracellular matrix in platelets and vascular cells

The beta3-integrin family consists of alphaIIbbeta3 (also known as glycoprotein IIb/IIIa) and alpha(v)beta3. alphaIIbbeta3 is found on platelets and megakaryocytes and has an essential role in hemostasis. alpha(v)beta3 has a broader distribution, and it functions in angiogenesis, neointimal formation after vascular injury, and leukocyte trafficking. There are important interactions between thrombin and beta3-integrins relative to both "inside-out" (integrin activation) and "outside-in" (modification of cellular events by ligand binding to integrins) signaling. Thrombin, by binding to G protein-coupled, protease-activated receptors, is a potent activator of alphaIIbbeta3. Conversely, outside-in signaling through alphaIIbbeta3 amplifies events initiated by thrombin and is necessary for full platelet spreading, platelet aggregation, granule secretion, and the formation of a stable platelet thrombus. In smooth muscle cells, alpha(v)beta3-integrins influence various responses to thrombin, including proliferation, c-Jun NH2-terminal kinase-1 activation, and focal adhesion formation. Other interactions between beta3-integrins and thrombin include beta3-integrin promotion of the generation of thrombin by localizing prothrombin to cellular surfaces and/or enhancing the formation of procoagulant microparticles and the requirement of beta3-integrin function for platelet-dependent clot retraction. In summary, there is increasing evidence that interactions between beta3-integrins and thrombin play important roles in the regulation of hemostatic and vascular functions.

Induction of cyclooxygenase-1 and -2 modulates angiogenic responses to engagement of alphavbeta3

Prostaglandins and cyclooxygenase (COX) have been implicated in the angiogenesis that occurs around tumours, but how they are induced is unclear. Prostaglandin formation is regulated by the availability of arachidonic acid and/or COX activity that in turn are controlled by activation of G-protein-coupled receptors or kinase receptors. Adhesion receptors provide another potential level of control as they transduce a variety of "outside-in" signals implicated in inflammation. We examined whether engagement of the vitronectin receptor (alphavbeta3) modulated prostacyclin (PGI2) formation in human umbilical vein endothelial cells (EC). Engagement of EC alphavbeta3 by vitronectin (versus fibronectin or gelatin) or by monoclonal antibodies (mAbs) LM609 and LIBS6, enhanced PGI2 generation and also induced expression of both COX-1 and -2 isoforms. Alphavbeta3 engagement also led to vascular endothelial cell growth factor (VEGF) generation and EC proliferation that was attenuated by inhibition of both COX-1 and COX-2. COX-1 inhibition also prevented new vessel formation in an in vitro model of angiogenesis that is alphavbeta3 dependent. Inhibition of angiogenesis by the COX-1 inhibitor was partially reversed by removal of the inhibitor or by addition of the stable analogue of PGI2, iloprost. These findings strongly indicate that alphavbeta3-mediated angiogenesis is partly due to induction of both isoforms of COX.

A peptide (P2) derived from the variable heavy chain of an anti-P-selectin monoclonal antibody (LYP20) inhibits leucocyte adhesion to thrombin-activated platelets and endothelial cells

P-selectin, a member of the selectin family of adhesion molecules, is present in endothelial Weibel-Palade bodies and platelet alpha-granules, and is rapidly expressed on their surface upon activation, resulting in leucocyte adhesion. LYP20 is a functional monoclonal antibody previously generated in our laboratory that binds with high affinity and specificity directed against P-selectin. This binding is largely imparted by the specific sequence of amino acids present on the hypervariable portions of the IgG chains. We now show that a peptide derived from the heavy chain of mAb LYP20 dose dependently inhibits the adhesion of poly morphonuclear cells to resting and thrombin-activated endothelial cells (EC) and platelets. The scrambled form of this peptide, identical in amino acid composition to the authentic peptide but with altered sequence, was not inhibitory at corresponding concentrations. Binding studies revealed that this peptide also dose dependently bound to both resting and thrombin-activated EC and platelets. Our results may prove useful for the development of new therapeutic inhibitors to modulate leucocyte interactions in inflammatory disorders.

Stimulation of adhesion molecule expression by Helicobacter pylori and increased neutrophil adhesion to human umbilical vein endothelial cells

Helicobacter pylori upregulates endothelial adhesion molecules but the pattern is unclear. Human umbilical vein endothelial cells (HUVEC) were exposed to control medium or H. pylori 60190. Binding of monoclonal antibodies against P-selectin, E-selectin, vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was determined using enzyme-linked immunosorbent assay. Binding of polymorphonuclear leukocytes to HUVEC was determined on cells exposed as above. After 6 h exposure to H. pylori, there were 30%, 124%, 167% and 100% increases in P-selectin, E-selectin, VCAM-1 and ICAM-1 levels and a 400% increase in polymorphonuclear leukocyte adhesion in HUVEC exposed to H. pylori. Effects of incubation for other intervals between 0 and 18 h are also described. H. pylori exerts some of its effects on gastric mucosa via gastric vasculature. This study gives insight into the pattern of H. pylori-associated endothelial adhesion molecule upregulation.

Impact of different platelet glycoprotein IIb/IIIa receptor inhibitors among diabetic patients undergoing percutaneous coronary intervention: : Do Tirofiban and ReoPro Give Similar Efficacy Outcomes Trial (TARGET) 1-year follow-up

BACKGROUND

The platelet glycoprotein IIb/IIIa receptor inhibitor abciximab, a monoclonal antibody, has been shown to improve early and late outcomes among diabetic patients undergoing percutaneous coronary intervention (PCI). It is unknown whether small-molecule agents confer similar benefits.

METHODS AND RESULTS

In 18 countries, 4809 patients undergoing PCI with stent implantation were randomized to tirofiban or abciximab. At the time of enrollment, patients were stratified according to diabetes status. As compared with non-diabetic patients, patients with diabetes (n=1117) showed similar 30-day ischemic outcomes, an increased incidence of any target vessel revascularization (TVR) at 6 months (10.3% versus 7.8%; P= 0.008), and a trend toward higher 1-year mortality (2.5% versus 1.6%; P=0.056). Among diabetic patients randomized to tirofiban (n=560), the incidence of death, myocardial infarction (MI), or urgent TVR at 30 days was 6.2%, and among those randomized to abciximab (n=557) it was 5.4% (hazard ratio [HR] 1.16; P=0.540). At 6 months, the composite of death, MI, or any TVR occurred in 15.7% and in 16.9% of tirofiban and abciximab patients, respectively (HR 0.93; P=0.610). Any TVR occurred in 9.5% and 11.1%, respectively (HR 0.84; P= 0.366). The 1-year mortality was 2.1% in the tirofiban group and 2.9% in the abciximab group (HR 0.74; P= 0.436).

CONCLUSIONS

Among diabetic patients undergoing PCI, tirofiban and abciximab were associated with comparable event rates, including similar rates of 6-month TVR and 1-year mortality. These findings suggest that the non-glycoprotein IIb/IIIa properties of abciximab do not translate into a discernible long-term clinical benefit among diabetic patients.

ST-Segment resolution as a marker of epicardial and myocardial reperfusion after thrombolysis: insights from the TIMI 14 and in TIME-II trials

Patients with persistent ST segment elevation after fibrinolysis are at high risk for death and congestive heart failure, even if normal epicardial flow has been restored. In the TIMI 14 trial, combination therapy with abciximab plus reduced-dose alteplase enhanced the speed and efficacy of epicardial reperfusion. We also found that combination therapy provided an additional benefit in terms of myocardial reperfusion, as evidenced by greater ST resolution on serial 12-lead electrocardiograms. Specifically, the proportion of patients with complete (> or =70%) ST resolution was higher among patients receiving combination therapy than in those treated with alteplase alone (59% vs 37%; p < 0.0001). Even among patients with normal (TIMI grade 3) epicardial blood flow, combination therapy was associated with a significantly greater likelihood of complete ST resolution than was fibrinolysis alone (69% vs 44%; p = 0.0002). In conclusion, combination reperfusion therapy improved myocardial (microvascular) reperfusion, independent of epicardial flow, suggesting an additional mechanism by which abciximab may improve outcomes in patients with acute MI.

An RGD sequence in the P2Y(2) receptor interacts with alpha(V)beta(3) integrins and is required for G(o)-mediated signal transduction

The P2Y(2) nucleotide receptor (P2Y(2)R) contains the integrin-binding domain arginine-glycine-aspartic acid (RGD) in its first extracellular loop, raising the possibility that this G protein-coupled receptor interacts directly with an integrin. Binding of a peptide corresponding to the first extracellular loop of the P2Y(2)R to K562 erythroleukemia cells was inhibited by antibodies against alpha(V)beta(3)/beta(5) integrins and the integrin-associated thrombospondin receptor, CD47. Immunofluorescence of cells transfected with epitope-tagged P2Y(2)Rs indicated that alpha(V) integrins colocalized 10-fold better with the wild-type P2Y(2)R than with a mutant P2Y(2)R in which the RGD sequence was replaced with RGE. Compared with the wild-type P2Y(2)R, the RGE mutant required 1,000-fold higher agonist concentrations to phosphorylate focal adhesion kinase, activate extracellular signal-regulated kinases, and initiate the PLC-dependent mobilization of intracellular Ca(2+). Furthermore, an anti-alpha(V) integrin antibody partially inhibited these signaling events mediated by the wild-type P2Y(2)R. Pertussis toxin, an inhibitor of G(i/o) proteins, partially inhibited Ca(2+) mobilization mediated by the wild-type P2Y(2)R, but not by the RGE mutant, suggesting that the RGD sequence is required for P2Y(2)R-mediated activation of G(o), but not G(q). Since CD47 has been shown to associate directly with G(i/o) family proteins, these results suggest that interactions between P2Y(2)Rs, integrins, and CD47 may be important for coupling the P2Y(2)R to G(o).

Abciximab and early adjunctive percutaneous coronary intervention are associated with improved ST-segment resolution after thrombolysis: Observations from the TIMI 14 Trial

BACKGROUND

Percutaneous coronary intervention (PCI) improves clinical outcomes in selected patients with failed thrombolysis but has not been proven to benefit patients who achieve a patent infarct-related artery. Even after successful epicardial reperfusion, myocardial perfusion may be inadequate. We sought to evaluate whether a strategy that uses a reperfusion regimen containing abciximab and a reduced-dose thrombolytic agent (combination therapy), followed by early adjunctive PCI, would result in improved myocardial perfusion, as assessed by ST-segment resolution.

METHODS

ST resolution from 90 to 180 minutes after therapy was calculated for all 410 patients from the TIMI 14 trial who had evaluable electrocardiograms at both time points and who were treated with alteplase or reteplase. Patients were grouped according to whether they were treated with combination therapy or full-dose thrombolytic agent alone and whether they underwent PCI between the 90- and 180-minute electrocardiographic measurements.

RESULTS

Among 105 patients who underwent adjunctive PCI between 90 and 180 minutes, mean ST resolution from 90 to 180 minutes was significantly greater in those who had received combination therapy versus those who had received full-dose thrombolytic alone (54% vs 8%; P =.002). Among 241 patients with TIMI grade 3 flow in the infarct-related artery at 90 minutes, adjunctive PCI significantly improved mean ST resolution in patients who had been treated with combination therapy (57% [PCI] vs 24% [no PCI]; P =.006), but PCI did not have this effect in patients who had received thrombolytic therapy alone (1% [PCI] vs 10% [no PCI]; P =.70). In a multivariate model controlling for factors that would be expected to independently influence 90- to 180-minute ST resolution, abciximab treatment remained significantly associated with greater ST resolution (P =.008).

CONCLUSIONS

A strategy that uses a combination reperfusion regimen that includes abciximab, followed by early adjunctive PCI, is associated with greater ST-segment resolution, which may reflect enhanced tissue level and microvascular perfusion. Future studies should evaluate prospectively the clinical efficacy of this strategy.

Platelet glycoprotein IIb/IIIa receptor inhibition in primary angioplasty for acute myocardial infarction: The new paradigm of direct revascularization

Acute myocardial infarction results from thrombotic occlusion superimposed on a ruptured athersoclerotic plaque. Immediate restoration of normal flow in the infarct-related artery can be achieved either with fibrinolytic or with direct mechanical revascularization. Primary PTCA has been shown to be superior to fibrinolytic therapy with respect to mortality, reinfarction, non-fatal stroke and length of hospitalization. Its results can be further improved by the addition of potent platelet inhibitors directed against the final common component of all stimuli for platelet aggregation, the glycoprotein (GP) IIb/IIIa receptor. In randomized clinical trials, primary angioplasty with adjunctive abciximab - a monoclonal antibody against the GP IIb/IIIa - was better than conventional primary angioplasty with heparin only. Abciximab use was associated with a significant reduction in reinfarction, need for urgent target vessel revascularization, microcirculatory dysfunction and regional left ventricular dysfunction as well as with a strong trend towards a reduction in mortality, even in patients receiving coronary stents.

Vascular endothelial growth factor (VEGF) stimulates monocyte migration through endothelial monolayers via increased integrin expression

Monocytes play an important role in collateral vessel formation (arteriogenesis) by attaching to activated endothelium and by invading the walls of innate collateral vessels where they produce growth factors. Previous studies have demonstrated that this process can be promoted by several chemokines and growth factors. In this study we examined the interaction between monocytes and endothelium under stimulation of the angiogenic agent vascular endothelial growth factor (VEGF). We report here the novel finding that VEGF stimulates the expression of the alphaL-, alphaM- and beta2-integrin monomers. In functional assays and by using neutralizing antibodies it was shown that VEGF stimulates adhesion of monocytes to human umbilical vein endothelial cells (HUVEC), and increased transmigration through endothelial monolayers is dependent on interaction of monocyte beta2-integrins with its endothelial counter ligand ICAM-1. Based on these in vitro data we hypothesize that the positive effect of VEGF on arteriogenesis may involve monocyte activation.

Effect of glycoprotein IIb/IIIa receptor blockade with abciximab on clinical and angiographic restenosis rate after the placement of coronary stents following acute myocardial infarction

OBJECTIVES

In the Intracoronary Stenting and Antithrombotic Regimen-2 trial (ISAR-2), we sought to investigate the effect of abciximab on angiographic and clinical restenosis after stenting following acute myocardial infarction (AMI). We also intended to assess the impact of abciximab on clinical outcome in this setting.

BACKGROUND

It is unclear whether abciximab reduces neointima formation after stenting. Such an effect may be particularly prominent in thrombus-containing lesions.

METHODS

Patients undergoing stenting within 48 h after onset of AMI were randomly assigned to receive either standard-dose heparin or abciximab plus reduced-dose heparin. Of 401 patients randomized, 366 without 30-day adverse events were eligible for six-month angiographic follow-up. Scheduled angiography was performed in 80% of these patients.

RESULTS

By 30 days, the composite clinical end point of death, reinfarction, and target lesion revascularization (TLR) was reached in 5.0% of the abciximab group and in 10.5% of the control group (p = 0.038). At one year, absolute reduction in the composite clinical end point by abciximab was still 5.7% but had lost its statistical significance. Our primary end point, late lumen loss, was 1.26+/-0.85 mm with abciximab and 1.21+/-0.74 mm with standard heparin (p = 0.61), and binary angiographic restenosis rates were 31.1% and 30.6%, respectively (p = 0.92).

CONCLUSIONS

In patients undergoing stenting following AMI, abciximab exerted beneficial effects by substantially reducing the 30-day rate of major adverse cardiac events. During one-year follow-up, there was no additional benefit from a reduction in TLR nor did abciximab reduce angiographic restenosis.

Abciximab improves both epicardial flow and myocardial reperfusion in ST-elevation myocardial infarction. Observations from the TIMI 14 trial

BACKGROUND

In the presence of ST-elevation myocardial infarction, patients with successful epicardial reperfusion (TIMI 3 flow) but persistent ST elevation on a 12-lead ECG are at high risk for subsequent death and left ventricular dysfunction. In the TIMI 14 trial, a dose-ranging angiographic study, combined therapy with abciximab plus reduced-dose tPA enhanced the speed and efficacy of epicardial reperfusion. We determined whether the combination of abciximab plus reduced-dose tPA provided additional benefit in terms of myocardial reperfusion, as evidenced by greater resolution of ST elevation.

METHODS AND RESULTS

All 346 patients with interpretable baseline and 90-minute ECGs, treated with either tPA alone or abciximab plus reduced-dose tPA (combination therapy), were included. Patients receiving combination therapy (n=221) had a 59% rate of complete (>/=70%) ST resolution at 90 minutes versus 37% in those treated with tPA alone (n=125) (P<0.0001). When the analysis was limited to patients with TIMI 3 flow, patients treated with combination therapy (n=151) remained significantly more likely to achieve complete ST resolution than those receiving tPA alone (n=80) (69% versus 44%; P=0.0002).

CONCLUSIONS

Combination therapy with abciximab and reduced-dose tPA improves myocardial (microvascular) reperfusion, as reflected in greater ST-segment resolution, in addition to epicardial flow. This finding may translate into improved clinical outcomes by enhancing myocardial salvage.

Platelets induce alterations of chemotactic and adhesive properties of endothelial cells mediated through an interleukin-1-dependent mechanism. Implications for atherogenesis

Platelets and alterations of chemotactic and adhesive properties of endothelium play an important role in the pathophysiology of atherosclerosis. We investigated the effect of platelets on secretion of monocyte chemotactic protein-1 (MCP-1) and on surface expression of intercellular adhesion molecule-1 (ICAM-1) of cultured endothelium. Pretreatment of cultured monolayers of endothelial cells with alpha-thrombin-activated platelets significantly enhanced secretion of MCP-1 and ICAM-1 surface expression (P<0.01) that could be inhibited by interleukin-1 (IL-1) antagonists by approximately 40%. Activation of transcription factor nuclear factor-kappaB (NF-kappaB) which regulates transcription of early inflammatory response genes such as MCP-1, was significantly increased in endothelial cells treated with activated platelets via an IL-1 mediated mechanism as determined by electrophoretic mobility shift assay (EMSA) and kappaB-dependent transcriptional activity. In trans-well experiments, alpha-thrombin-activated platelets enhanced IL-1-dependent surface expression of vitronectin receptor (alpha(v)beta(3)) on the luminal aspect of endothelial monolayers and promoted alpha(v)beta(3)-mediated platelet/endothelium adhesion that could be inhibited by the antiadhesive peptides GRGDSP and c(RGDfV). We conclude that activated platelets induce significant changes in chemotactic (secretion of MCP-1) and adhesive (surface expression of ICAM-1 and alpha(v)beta(3)) properties of cultured endothelium. These findings imply a potential pathophysiological mechanism of platelets in an early stage of atherogenesis.

Spatiotemporal changes of fibronectin, tenascin-C, fibulin-1, and fibulin-2 in the skin during the development of chronic contact dermatitis

In order to elucidate how chronic inflammation affects the organization of the extracellular matrix in the skin, a prolonged allergic contact dermatitis was induced in a mouse by repeated application to the ear of 2,4-dinitrofluorobenzene every 3 d for 66 d. Subsequently, the spatiotemporal changes of fibronectin, tenascin-C, fibulin-1, and fibulin-2 in the skin were examined. In the acute phase of inflammation (day 3-day 12), the amount of fibronectin and tenascin-C increased markedly and were degraded, whereas the amount of fibulin-2 changed slightly. Abundant deposition of tenascin-C was observed in the connective tissue. Fibulin-1 and fibulin-2 distributed as fine fibrils. In contrast, the amounts of fibronectin and tenascin-C decreased and their degradation was suppressed in the chronic phase (day 15-day 66), but the amount of fibulin-2 increased. Tenascin-C was observed mainly at and underneath the epidermal basement membrane. In the subepidermal region, many fibulin-2-positive microfibrils were distributed. The amount and distribution of fibulin-1 did not change markedly in either phase. MMP-like enzymes of 62 kDa, probably activated MMP-2, were upregulated in the chronic phase, whereas components of 92, 85, or 67 kDa were highly induced in the acute phase. These results suggest that chronic inflammation in allergic contact dermatitis is associated with temporal changes in the expression, deposition, and degradation of inducible extracellular matrix components.

Evidence that phospholipid oxidation products and/or platelet-activating factor play an important role in early atherogenesis : in vitro and In vivo inhibition by WEB 2086

The goal of the present studies was to determine whether phospholipid oxidation products and/or platelet-activating factor (PAF) are mediators of early atherogenesis in vivo. Monocyte-endothelial cell interactions have been shown to play an important role in early atherogenesis. We and others have demonstrated that PAF and phospholipid oxidation products, present in atherosclerotic lesions, including 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (POVPC), 1-palmitoyl-2-glutaroyl-sn-glycero-3-phosphocholine (PGPC), and 1-palmitoyl-2-epoxyisoprostane E(2)-sn-glycero-3-phosphocholine (PEIPC), mediate the activation of monocytes and/or endothelial cells in vitro. Previous studies have shown that the action of PAF and PAF-like ether-containing phospholipids was inhibited by WEB 2086. We now demonstrate that pretreatment of human aortic endothelial cells with WEB 2086 (10 micromol/L) and several other PAF antagonists before treatment with POVPC and PEIPC but not PGPC prevented the activation of the endothelial cells to bind monocytes. We present evidence to suggest that this inhibition is not mediated by the PAF receptor. The role of bioactive oxidized phospholipids in fatty streak formation was tested using C57BL/6J LDL R-/- mice fed a chow or Western diet for 5 weeks with or without WEB 2086 mixed with drinking water. Quantitative electrospray ionization mass spectrometry showed similar concentrations of WEB 2086 in the plasma of mice on both diets ( approximately 4 to 5 micromol/L); this concentration was inhibitory in vitro. Administration of WEB 2086 did not affect the lipid composition of mouse plasma. However, fatty streak formation was reduced by 62% in animals fed a Western diet, whereas no change was observed in the small lesions of mice on a chow diet. These studies provide evidence that PAF and/or PAF-like phospholipid oxidation products are important mediators of atherosclerotic lesion development in vivo and that specific receptor antagonists for these molecules may represent a novel therapeutic modality.

Quantifying GPIIb/IIIa receptor binding using 2 monoclonal antibodies: discriminating abciximab and small molecular weight antagonists

BACKGROUND

Dosing of glycoprotein (GP) IIb/IIIa receptor antagonists is frequently based on the inhibition of platelet aggregation, which may be influenced by the agonist used or concurrent medications. Here we describe a monoclonal antibody-based technique to quantify total and ligand-occupied GPIIb/IIIa receptors.

METHODS AND RESULTS

In vitro binding of monoclonal antibodies, LYP18 (Mab1) and 4F8 (Mab2), to the GPIIb/IIIa complex, was characterized using purified receptor and to platelets by flow cytometry. Patients undergoing coronary angioplasty received a single 20 mg dose of the oral GPIIb/IIIa antagonist, xemilofiban, or matching placebo, and antibody binding was compared with inhibition of platelet aggregation. Mab1 and Mab2 were bound to purified GPIIb/IIIa and to unoccupied, inactivated receptor on platelets. Mab2 identified the beta3 subunit, whereas Mab1 was complex-specific. Neither antibody interfered with the other's binding, suggesting that they identified distinct sites. Mab1 identified 53 300+/-5423 GPIIb/IIIa sites per platelet, whereas Mab2 identified 50 120+/-5066 sites per platelet. Mab1 binding was inhibited by abciximab in a dose dependent manner (IC50, 0.85+/-0.1 microg/mL), whereas Mab2 binding was unaffected. In contrast, the 2 small molecular weight antagonists, SC-57101A (IC50, 0.22+/-0.06 micromol/L) and eptifibatide (IC50, 0.35+/-0.14 micromol/L) inhibited Mab2 but not Mab1 binding. In patients treated with xemilofiban, Mab1 binding was unaltered but Mab2 binding decreased from 37 930+/-2061 sites per platelet at baseline to 8318+/-870 sites per platelet 6 hours after dosing (P<0.0001). Platelet aggregation to adenosine diphosphate (20 micromol/L) fell to 3+/-3% of baseline in line with the inhibition of Mab2 binding (correlation coefficient 0.8, P<0.0001).

CONCLUSIONS

Mab1 and Mab2 bind to GPIIb/IIIa and are differentially displaced by abciximab and small molecular weight antagonists. These antibodies may be used to monitor receptor number and occupancy during administration of a GPIIb/IIIa antagonist.

Intracellular mechanisms of hydrogen peroxide-mediated neutrophil adherence to cultured human endothelial cells

We examined which endothelial second messengers are involved in peroxide-mediated endothelial-neutrophil adhesion with respect to endothelial P-selectin expression and platelet-activating factor (PAF). Peroxide (0.5 mM)-mediated adhesion was blocked by a protein kinase C (PKC) inhibitor, Gö6976 (10 nM); an intracellular calcium chelator, TMB-8 (0.1 mM); and a protein kinase G (PKG) inhibitor, KT5823 (0.5 microM); but not by a tyrosine kinase inhibitor, genistein (1 microM), or a protein kinase A inhibitor, H-89 (0.1 microM). These data were consistent with the proadhesive effects of PMA (0.1 microM), a PKC activator; a calcium ionophore, A23187 (1 microM); and dibutyryl cGMP (0.5 and 1 mM); but not phenylarsine oxide (0.1 mM), a tyrosine phosphatase inhibitor, or dibutyryl cAMP (1 mM). Conversely, peroxide-mediated P-selectin expression was blocked by Gö6976 and KT5823, but not by TMB-8. These data are strengthened by the observation that PMA and dibutyryl cGMP, but not A23187, increased P-selectin expression. WEB 2086 (10 microM), a PAF-receptor antagonist, blocked peroxide-, PMA-, and A23187-mediated adhesion, but not peroxide-mediated P-selectin expression. PAF itself (10 nM) stimulated adhesion, but not P-selectin expression. These data indicate that PKC and PKG are involved in peroxide-mediated neutrophil adhesion via P-selectin mobilization and PAF synthesis; however, intracellular calcium appears to mediate adhesion only through PAF synthesis.

Platelet/Polymorphonuclear Leukocyte Interaction: P-Selectin Triggers Protein-Tyrosine Phosphorylation–Dependent CD11b/CD18 Adhesion: Role of PSGL-1 as a Signaling Molecule

Polymorphonuclear leukocyte (PMN) adhesion to activated platelets is important for the recruitment of PMN at sites of vascular damage and thrombus formation. We have recently shown that binding of activated platelets to PMN in mixed cell suspensions under shear involves P-selectin and the activated β2-integrin CD11b/CD18. Integrin activation required signaling mechanisms that were sensitive to tyrosine kinase inhibitors.1 Here we show that mixing activated, paraformaldehyde (PFA)-fixed platelets with PMNs under shear conditions leads to rapid and fully reversible tyrosine phosphorylation of a prominent protein of 110 kD (P∼110). Phosphorylation was both Ca2+ and Mg2+ dependent and was blocked by antibodies against P-selectin or CD11b/CD18, suggesting that both adhesion molecules need to engage with their respective ligands to trigger phosphorylation of P∼110. The inhibition of P∼110 phosphorylation by tyrosine kinase inhibitors correlates with the inhibition of platelet/PMN aggregation. Similar effects were observed when platelets were substituted by P-selectin–transfected Chinese hamster ovary (CHO-P) cells or when PMN were stimulated with P-selectin–IgG fusion protein. CHO-P/PMN mixed-cell aggregation and P-selectin–IgG–triggered PMN/PMN aggregation as well as P∼110 phosphorylation were all blocked by antibodies against P-selectin or CD18. In each case PMN adhesion was sensitive to the tyrosine kinase inhibitor genistein. The antibody PL-1 against P-selectin glycoprotein ligand-1 (PSGL-1) blocked platelet/PMN aggregation, indicating that PSGL-1 was the major tethering ligand for P-selectin in this experimental system. Moreover, engagement of PSGL-1 with a nonadhesion blocking antibody triggered β2-integrin–dependent genistein-sensitive aggregation as well as tyrosine phosphorylation in PMN. This study shows that binding of P-selectin to PSGL-1 triggers tyrosine kinase–dependent mechanisms that lead to CD11b/CD18 activation in PMN. The availability of the β2-integrin to engage with its ligands on the neighboring cells is necessary for the tyrosine phosphorylation of P∼110.

Exogenous nitric oxide increases neutrophil adhesion to cultured human endothelial monolayers through a protein kinase G dependent mechanism

Endothelial-neutrophil adhesion is a critical step in acute inflammatory diseases, which is mediated in part by P-selectin and platelet-activating factor (PAF). Nitric oxide (NO) is well known as an endogenous second messenger derived from endothelial cells, and regulates many important physiological events, however, the direct effects of NO on endothelial-neutrophil adhesion is less well understood. The objective of this study was to examine whether, and how relatively high levels of exogenous NO increases neutrophil adhesion with respect to P-selectin and PAF. Endothelial monolayers were exposed to chemical agents for 30 min, and the adhesion of 51Cr-labeled neutrophils measured in a static adhesion assay. Spermine-NONOate (SNO), an NO donor, significantly increased neutrophil adhesion and expression of P-selectin at a concentration of 1 mM. SNO (1 mM)-mediated neutrophil adhesion was significantly inhibited by a protein kinase G inhibitor, KT5823 (0.5 microM), but not by a classical protein kinase C inhibitor, Gö6976 (10 nM), a tyrosine kinase inhibitor, genistein (1 microM), or a protein kinase A inhibitor, H-89 (0.1 microM). P-selectin surface expression induced by 1 mM SNO was also significantly inhibited by 0.5 microM KT5823. Conversely, a cytoplasm calcium chelator, TMB-8 (0.1 mM), significantly exacerbated both the neutrophil adhesion and P-selectin expression induced by SNO. WEB 2086 (10 microM), a PAF receptor antagonist, blocked neutrophil adhesion, but did not block P-selectin expression induced by SNO. These data suggest that NO increases endothelial-neutrophil adhesion through protein kinase G-mediated P-selectin mobilization to the cell surface and endothelial PAF synthesis.

Platelet/Polymorphonuclear Leukocyte Interaction: P-Selectin Triggers Protein-Tyrosine Phosphorylation–Dependent CD11b/CD18 Adhesion: Role of PSGL-1 as a Signaling Molecule

Polymorphonuclear leukocyte (PMN) adhesion to activated platelets is important for the recruitment of PMN at sites of vascular damage and thrombus formation. We have recently shown that binding of activated platelets to PMN in mixed cell suspensions under shear involves P-selectin and the activated β2-integrin CD11b/CD18. Integrin activation required signaling mechanisms that were sensitive to tyrosine kinase inhibitors.1 Here we show that mixing activated, paraformaldehyde (PFA)-fixed platelets with PMNs under shear conditions leads to rapid and fully reversible tyrosine phosphorylation of a prominent protein of 110 kD (P∼110). Phosphorylation was both Ca2+ and Mg2+ dependent and was blocked by antibodies against P-selectin or CD11b/CD18, suggesting that both adhesion molecules need to engage with their respective ligands to trigger phosphorylation of P∼110. The inhibition of P∼110 phosphorylation by tyrosine kinase inhibitors correlates with the inhibition of platelet/PMN aggregation. Similar effects were observed when platelets were substituted by P-selectin–transfected Chinese hamster ovary (CHO-P) cells or when PMN were stimulated with P-selectin–IgG fusion protein. CHO-P/PMN mixed-cell aggregation and P-selectin–IgG–triggered PMN/PMN aggregation as well as P∼110 phosphorylation were all blocked by antibodies against P-selectin or CD18. In each case PMN adhesion was sensitive to the tyrosine kinase inhibitor genistein. The antibody PL-1 against P-selectin glycoprotein ligand-1 (PSGL-1) blocked platelet/PMN aggregation, indicating that PSGL-1 was the major tethering ligand for P-selectin in this experimental system. Moreover, engagement of PSGL-1 with a nonadhesion blocking antibody triggered β2-integrin–dependent genistein-sensitive aggregation as well as tyrosine phosphorylation in PMN. This study shows that binding of P-selectin to PSGL-1 triggers tyrosine kinase–dependent mechanisms that lead to CD11b/CD18 activation in PMN. The availability of the β2-integrin to engage with its ligands on the neighboring cells is necessary for the tyrosine phosphorylation of P∼110.

Effect of glycoprotein IIb/IIIa receptor blockade on recovery of coronary flow and left ventricular function after the placement of coronary-artery stents in acute myocardial infarction

BACKGROUND

Apart from its established effects on vessel patency after percutaneous coronary revascularization, glycoprotein IIb/IIIa receptor blockade by abciximab may improve myocardial perfusion by inhibition of the interaction of platelets and platelet aggregates with the microvasculature. We investigated the effect of abciximab with stent placement in acute myocardial infarction.

METHODS AND RESULTS

In a prospective randomized trial, patients undergoing stenting in acute myocardial infarction within 48 hours after onset of symptoms were randomly assigned to receive either standard-dose heparin or abciximab plus low-dose heparin. Immediately after the procedure and at 14-day angiographic follow-up, we assessed flow velocity in the recanalized vessel with the Doppler wire and regional wall motion by the centerline method. End points were changes in papaverine-induced peak flow velocities and in wall motion indices. We assigned 98 patients to standard heparin and 102 to abciximab. We obtained 152 paired flow measurements and 151 paired left ventricular function studies. Residual stenoses of the treated lesions did not differ between the 2 groups. Improvement of peak flow velocity (mean [95% CI]: 18.1 cm/s [13.6 to 22.6 cm/s], n=80, versus 10.4 cm/s [5.4 to 15.4 cm/s], n=72, P=0.024) and wall motion index (0.44 SD/chord [0.29 to 0.59 SD/chord], n=79 versus 0. 15 SD/chord [0.00 to 0.30 SD/chord], n=72, P=0.007) was significantly greater in patients assigned to abciximab than in those on heparin alone. At follow-up, the abciximab group had a higher global left ventricular ejection fraction than the heparin group (62% [59% to 65%] versus 56% [53% to 59%], P=0.003).

CONCLUSIONS

Abciximab had important effects beyond the maintenance of large-vessel patency. It improved the recovery of microvascular perfusion and concomitantly enhanced the recovery of contractile function in the area at risk.

Mapping the epitope of a functional P-selectin monoclonal antibody (LYP20) to a short complement-like repeat (SCR 4) domain: use of human-mouse chimaera and homologue-replacement mutagenesis

P-selectin (CD62P), an adhesion molecule localized in platelet alpha-granules and endothelial cell Weibel-Palade bodies, is rapidly expressed on the surface of activated cells. This adhesion molecule, a member of the selectin family, mediates leucocyte interactions with activated platelets or endothelial cells. The aim of this study was to identify and characterize the epitope of a functional blocking P-selectin monoclonal antibody (mAb), LYP20. LYP20 recognizes human or rat, but not mouse, P-selectin. Human/mouse chimaeras and wild-type constructs, modified by homologue replacement mutagenesis, were expressed in COS cells. Blocking anti-(P-selectin) mAbs (G1, G3 or CLB-thromb/6) were observed, by flow cytometry, to bind to the lectin-like domain. In contrast, LYP20 was found to bind to one of the P-selectin short complement-like repeats (SCR domain 4). Homologue replacement mutagenesis of SCR domain 4 (region delineated by amino acid residues 359-457) identified three amino acids (Cys412-->Ser, Cys416-->Ser or Arg415-->Lys) as being implicated in the LYP20 epitope. Deleting the region bearing the LYP20 epitope, from a wild-type CD62P construct, showed a decrease in polymorphonuclear leucocyte (PMNL) binding to transfected COS cells. In addition, mutation of one of the three amino acids, implicated in the LYP20 epitope, markedly affected PMNL binding to transfected COS cells but did not affect the binding of mAbs G1 and CLB-thromb/6. These results are the first to indicate (1) that a functional blocking anti-P-selectin mAb binds to SCR 4, a site other than the lectin-like/epidermal growth factor-like domain, and (2) that SCR domain 4 has a functional role in P-selectin-leucocyte interactions.

Selective alpha v beta 3 integrin blockade potently limits neointimal hyperplasia and lumen stenosis following deep coronary arterial stent injury: evidence for the functional importance of integrin alpha v beta 3 and osteopontin expression during neointima formation

Lumen loss from vascular restenosis remains a leading cause of chronic revascularization failure.

OBJECTIVE

We hypothesized that cell-matrix adhesion, migration, and differentiation events that underlie restenosis are mediated by alpha v beta 3 integrin-ligand interactions.

METHODS

Using immunohistochemistry and in situ hybridization, we examined the spatial and temporal vessel wall expression of alpha v beta 3 and osteopontin following deep coronary arterial injury. Cell migration and adhesion assays were performed to demonstrate the affinity and specificity of XJ 735 for various vessel wall integrins. The effects of XJ 735 (a selective cyclic Arg-Gly-Asp (RGD) peptidomimetic alpha v beta 3 antagonist) on neointimal hyperplasia and lumen stenosis were tested in a porcine coronary injury model. Normolipemic swine underwent oversized stent injury followed by XJ 735 administration (9 animals, 28 lesions; 1 mg/kg bolus + 7 days 4 mg/kg/d infusion + 21 days 2 mg/kg i.v. bolus 12 hourly) or placebo (10 animals, 30 arterial lesions).

RESULTS

Maximal alpha v beta 3 immunoreactivity was observed between 7-14 days following injury in the neointima, media, and adventitia. Maximal osteopontin mRNA signal in the neointima, media, and adventitia was observed at 14, 7 and 28 days respectively. IC50 for XJ 735 alpha v beta 3-mediated inhibition of human and porcine endothelial cell adhesion, and vascular smooth muscle cell migration, ranged from 0.6 to 4.4 microM. In contrast, IC50 for porcine or human alpha IIb/beta 3, alpha 4 beta 1, alpha v beta 5, and alpha 5 beta 1 inhibition exceeded 100 microM. Steady state XJ 735 plasma levels exceeded 5 microM. Despite slightly higher injury scores in XJ 735 treated animals, significant reductions in mean neointima area (43% reduction; p = 0.0009), and mean percent lumen stenosis (approximately 2.9 fold reduction; p = 0.04) were observed in XJ 735 treated animals. XJ 735 treatment did not significantly alter the relative size of the arterial injury and reference sites (geometric remodeling). Comparison of neontima area vs. injury score regression lines revealed significant reductions in slope (p = 0.0001) and intercept (p = 0.0001) for XJ 735.

CONCLUSIONS

Selective alpha v beta 3 blockade is an effective anti-restenosis strategy that potently limits neointimal growth and lumen stenosis following deep arterial injury. The co-ordinate spatial and temporal upregulation of alpha v beta 3 expression following vessel wall injury, and the high affinity and specificity of XJ 735 for alpha v beta 3, confirms the importance of this integrin in adhesive and migratory cell-matrix events underlying coronary restenosis.

Vitronectin receptor (alpha(v)beta3) mediates platelet adhesion to the luminal aspect of endothelial cells: implications for reperfusion in acute myocardial infarction

BACKGROUND

Platelet interaction with endothelium plays an important role in the pathophysiology of coronary microcirculation. We assessed the role of the vitronectin receptor (integrin alpha(v)beta3) in platelet/endothelium adhesion.

METHODS AND RESULTS

We investigated the effect on platelet/endothelium adhesion of plasma obtained from patients with acute myocardial infarction during reperfusion (before and 8, 24, 48, and 72 hours and 5 to 7 days after direct angioplasty) and with pretreatment with alpha-thrombin (2 U/mL) and recombinant human interleukin-1beta. Platelet/endothelium adhesion was significantly enhanced by approximately 20% after pretreatment of endothelium with patient plasma for 4 hours (P<.05) compared with endothelium treated with pooled control plasma. Plasma-induced platelet/endothelium adhesion was, in part, RGD peptide dependent. Pretreatment of endothelial cells with alpha-thrombin or recombinant human interleukin-1beta enhanced platelet/endothelium adhesion and surface expression of alpha(v)beta3 on the luminal aspect of endothelium (P<.05). The adhesion of platelets, isolated platelet microparticles, and Chinese hamster ovary cells bearing human recombinant alpha(IIb)beta3 (platelet glycoprotein IIb-IIIa) to activated endothelial cells was inhibited by antiadhesive peptides GRGDSP and c(RGDfV) and monoclonal antibodies 4F10, LM609, and 7E3.

CONCLUSIONS

The expression of vitronectin receptor exposed on the luminal aspect of activated endothelium is enhanced and mediates platelet/endothelium adhesion. Vitronectin receptor-mediated platelet attachment to activated endothelium during reperfusion may contribute to reperfusion injury and could be a target for antiadhesive therapy.

Human monocytes activate porcine endothelial cells, resulting in increased E-selectin, interleukin-8, monocyte chemotactic protein-1, and plasminogen activator inhibitor-type-1 expression

Monocytes (Mo) are thought to be important effector cells in early xenograft rejection. Effects of Mo-endothelial cell (EC) interactions on EC activation in vitro were studied by coculturing human Mo or human monocytoid cell lines, U937 and THP-1, with porcine EC. Without preactivation, U937 cells and Mo induced mRNA for the EC-specific adhesion receptor, E-selectin, expressed only on activated cells, after 2 hr. Surface protein was maximal when equal numbers of EC and Mo were cocultured. Increased mRNA expression of the chemokines, interleukin-8 and monocyte chemotactic protein-1, and the antifibrinolytic protein plasminogen activator inhibitor type-1, confirmed EC activation. Like E-selectin, plasminogen activator inhibitor type-1 mRNA was rapidly induced and returned to baseline after 24 hr, whereas chemokine gene expression was slower and more prolonged. Interleukin-1 receptor antagonist failed to modulate induction of E-selectin. Soluble tumor necrosis factor (TNF) alpha receptor inhibited E-selectin induced by TNF alpha, but not by U937 cells, and mRNA and protein on EC in Mo-EC mixtures cocultured at 1:1 ratios were not significantly reduced. The TNF alpha inhibitor did reduce E-selectin expression (30-40%), as well as induced chemokine gene expression (80%), at higher Mo-EC ratios. Despite this, minimal TNF alpha was detectable in supernatants. These results, along with the transwell experiments that confirmed a requirement for Mo-EC contact, suggest that membrane-bound TNF alpha may be involved. Thus, Mo-EC interactions in the porcine to human combination activated several EC functions, suggesting that initial Mo contact with the vessel wall of a xenogeneic graft may promote leukocyte recruitment, inflammation, and maintenance of thrombus, resulting in eventual organ destruction.

Dietary coenzyme Q10 supplementation alters platelet size and inhibits human vitronectin (CD51/CD61) receptor expression

Improved cardiovascular morbidity and mortality have been observed in several clinical studies of dietary supplementation with coenzyme Q10 (CoQ10, ubiquinone). Several mechanisms have been proposed to explain the effects of CoQ10, but a comprehensive explanation of its cardioprotective properties is still lacking. One attractive theory links ubiquinone with the inhibition of platelets. The effect of CoQ10 intake on platelet size and surface antigens was examined in human volunteers. Study participants received 100 mg of CoQ10 twice daily in addition to their usual diet for 20 days. Receptor expression was measured by flow cytometry with monoclonal murine anti-human antibodies CD9 (p24), CD42B (Ib), CD41b (IIb), CD61 (IIIa), CD41a (IIb/IIIa), CD49b (VLA-2), CD62p (P selectin), CD31 (PECAM-1), and CD51/CD61 (vitronectin). An increase of total serum CoQ10 level (from 0.6 +/- 0.1 to 1.8 +/- 0.3 micrograms/ml; p < 0.001) was found at protocol termination. Fluorescence intensity was higher for the large platelets when compared with the whole platelet population. Significant inhibition of vitronectin-receptor expression was observed consistently throughout ubiquinone treatment. Reduction of platelet size was observed at the end of CoQ10 supplementation. Inhibition of the platelet vitronectin receptor and a reduction of the platelet size are direct evidence of a link between dietary CoQ10 intake and platelets. These findings may not be fully explained by the known antioxidant and bioenergetic properties of CoQ10. Diminished vitronectin-receptor expression and reduced platelet size resulting from CoQ10 therapy may contribute to the observed clinical benefits in patients with cardiovascular diseases.

Role of platelets in restenosis after percutaneous coronary revascularization

The role of platelets in the process of restenosis after percutaneous coronary intervention is not fully understood. After vascular injury there is extensive platelet activation, adhesion, aggregation and secretion. Through the liberation of growth factors, such as platelet-derived growth factor, and surface expression of cell adhesion molecules, such as the glycoprotein IIb/IIIa integrin, platelets appear to be a pivotal mediator of the vascular injury response. Experimental models have demonstrated that profound, prolonged thrombocytopenia, or blockade of the IIb/IIIa receptor, may reduce neointimal hyperplasia after arterial balloon injury. However, multiple clinical trials testing conventional or new platelet agents have not yielded any salutary effects. The recent finding that abciximab, a monoclonal antibody fragment directed against IIb/IIIa, reduced clinical restenosis after coronary angioplasty by 26% in patients raises questions about the mechanism of benefit. The alpha v beta 3 vitronectin receptor is responsible for binding endothelial cells to platelets, and it also has a key role in modulating smooth muscle cell migration. It is possible that the antibody fragment exerts its effect on restenosis by means of alpha v beta 3, because abciximab fully cross-reacts to this integrin owing to the shared beta 3 subunit. To date, the other platelet glycoprotein IIb/IIIa inhibitors, including Integrelin, Tirofiban, Lamifiban and Xemilofiban, are specific in binding to this particular integrin. Considerable further study is necessary to unravel the effects of platelets on the restenosis process.

Oxidized low-density lipoprotein induces the expression of P-selectin (GMP140/PADGEM/CD62) on human endothelial cells

It is now well established that monocytes adhere to endothelial cells activated by oxidized low-density lipoproteins (LDL). However, the adhesive receptors on endothelial cells involved in binding monocytes, following an insult by oxidized LDL, remains to be elucidated. In this study we have looked at the effect of native or oxidized LDL on the expression of P-selectin. Native LDL (N-LDL) was oxidized by incubation with either endothelial cells (EC-LDL) or copper (Cu-LDL), or in culture medium as a control (C-LDL). Expression of P-selectin was assayed with an anti-P-selectin (CD62) monoclonal antibody (LYP20). Results show that EC-LDL and Cu-LDL, but not N-LDL or C-LDL, induce the expression of P-selectin by human umbilical-vein endothelial cells (HUVECs). Induction of P-selectin by low concentrations (20 micrograms/ml) of LDL is directly related to the state of oxidation of the LDL particles. In addition, high concentrations (100 micrograms/ml) of N-LDL also activate HUVECs by inducing P-selectin expression. This expression was sustained for a period of over 1 h on LDL-activated endothelial cells, in contrast with thrombin- or histamine-activated endothelial cells, whose P-selectin levels fall within 15-20 min after induction. E-selectin, in contrast with P-selectin, could not be induced by endothelial cells treated with low or high concentrations of oxidized LDL. Results in this study show that P-selectin expressed by oxidized-LDL-treated endothelial cells are involved in mediating the adhesion of a monocytic cell line (U937) or monocytes in peripheral-blood mononuclear cells. An anti-P-selectin monoclonal antibody (LYP20) inhibited the binding of U937 cells and monocytes. These results strongly suggest that P-selectin is involved in the early stages of atherogenesis.