Plinio Cirillo

Monoclonal Antibody Against Tissue Factor Shortens Tissue Plasminogen Activator Lysis Time and Prevents Reocclusion in a Rabbit Model of Carotid Artery Thrombosis

BACKGROUND Tissue factor (TF)-dependent activation of the coagulation is important in the pathophysiology of intravascular thrombus formation. We tested the effects of a monoclonal antibody against TF (AP-1) on lysis time induced by tissue-type plasminogen activator (TPA) and on reocclusion rate in a rabbit model of carotid artery thrombosis. METHODS AND RESULTS Intravascular thrombosis was obtained by placing an external constrictor around carotid arteries with endothelial injury. Carotid blood flow velocity ws measured continuously with a Doppler flow probe. Thirty minutes after thrombus formation, the rabbits received either AP-1 (0.15 mg/kg IV, n=8) or placebo (n=8). All rabbits also received TPA (80 microg/kg bolus plus 8 microg x kg(-1) x min(-1) infusion for up to 90 minutes or until reperfusion was achieved) and heparin (200 U/kg IV as a bolus). At reperfusion, TPA was discontinued, and the rabbits were followed for an additional 90 minutes. AP-1 shortened lysis time from 44+/-8 minutes (mean+/-SEM) in control rabbits to 26+/-7 minutes in AP-1 rabbits (P<.01). Reocclusion occurred in all control rabbits in 10+/-3 minutes, whereas it occurred in only two of eight AP-1 treated rabbits in 72 and 55 minutes (P<.01). No changes in prothrombin time and ex vivo platelet aggregation in response to various agonists were observed after AP-1 administration, indicating the absence of systemic effects by this antibody. CONCLUSIONS TF exposure and activation of the extrinsic coagulation pathway play an important role in prolonging lysis time and mediating reocclusion after thrombolysis in this model. AP-1, a monoclonal antibody against TF, might be suitable as adjunctive therapy to TPA.

Role of β2 Adrenergic Receptors in Human Atherosclerotic Coronary Arteries

Background—Adrenergic regulation of coronary vasomotion is balanced between &agr;1-adrenergic–mediated (&agr;1-AR) constriction and &bgr;2-adrenergic–mediated (&bgr;2-AR) relaxation. This study aimed at assessing the role of &bgr;2-ARs in normal, mildly atherosclerotic, and stenotic human coronary arteries. Methods and Results—During intracoronary (IC) infusion of increasing doses of the &bgr;2-AR agonist salbutamol (0.15, 0.3, and 0.6 &mgr;g/min) and the endothelial vasodilator acetylcholine (1, 3, and 10 &mgr;g/min), we measured (1) changes in lumen diameter (LD) by quantitative coronary angiography in 34 normal, 55 mildly atherosclerotic, and 42 stenotic coronary artery segments and (2) changes in average peak velocity (APV) and coronary blood flow (CBF) with the use of Doppler flow wire in 11 normal, 10 mildly atherosclerotic, and 11 stenotic coronary arteries. In 6 of 11 stenotic coronary arteries, the protocol was repeated after an IC bolus (12 &mgr;g/kg) of the &agr;-adrenergic blocker phentolamine. In 6 of 11 normal coronary arteries, the protocol was repeated after an IC infusion (60 &mgr;mol/min) of NG-monomethyl-l-arginine (L-NMMA), a nitric oxide inhibitor. Neither salbutamol IC infusion nor acetylcholine significantly changed heart rate or blood pressure, whereas L-NMMA slightly increased blood pressure. In normal coronary arteries, salbutamol increased LD (LD max %: 11±2, P<0.05), APV (APV max %: 53±17, P<0.05), and CBF (CBF max %: 57±17, P<0.05), whereas L-NMMA caused a blunted APV (APV max %: 27±6, P<0.05) and CBF (CBF max %: 29±6, P<0.05) response to salbutamol. In mildly atherosclerotic coronary arteries, the salbutamol increase in LD (LD max %: 10±2, P<0.05), APV (APV max %: 33±12, P<0.05), and CBF (CBF max %: 37±12, P<0.05) was preserved. In stenotic coronary arteries, salbutamol induced a paradoxical reduction in LD (LD max %: −6±2, P<0.05), APV (APV max %: −15±9, P<0.05), and CBF (CBF max %: −15±6, P<0.05), which was no longer observed after phentolamine. Acetylcholine increased LD (LD max %: 14±3, P<0.05), APV (APV max %: 61±20, P<0.05), and CBF (CBF max %: 67±19, P<0.05) in normal coronary arteries. In mildly atherosclerotic coronary arteries, acetylcholine induced a significant reduction in LD (LD max %: −15±2, P<0.05) and no changes in APV (APV max %: −6±13, P=NS) and CBF (CBF max %: −10±13, P=NS). In stenotic coronary arteries, acetylcholine significantly reduced LD (LD max %: −15±3, P<0.05), APV (APV max %: −15±9, P<0.05), and CBF (CBF max %: −15±6, P<0.05). Conclusions—In severely atherosclerotic coronary arteries, &bgr;2-adrenergic vasodilatation is impaired, and this might contribute to alter the vasomotor balance, further precipitating myocardial ischemia during sympathetic activation.

Left ventricular remodelling in patients with moderate systolic dysfunction after myocardial infarction: favourable effects of exercise training and predictive role of N-terminal pro-brain natriuretic peptide.

Aims To investigate the effects of exercise training (ET) on left ventricular (LV) volumes, cardiopulmonary functional capacity and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels in postinfarction patients with moderate LV dysfunction. Methods Sixty-one postinfarction patients were randomized into two groups: group T [n = 30, LV ejection fraction (EF) 41.6 ± 11.3%, mean ± SD] entered a 6-month ET programme, whereas group C (n = 31, EF 42.0 ± 7.6%, P=NS) did not. NT-proBNP assay, Doppler-echocardiography and cardiopulmonary exercise test were performed upon enrolment and at sixth months. Results At sixth months, trained patients showed an improvement in workload (+26%, P<0.001), Vo2peak (+31%, P<0.001), LV end-diastolic volume index (LVEDVI; −9%, P<0.001), a reduction in NT-proBNP (−71%, P<0.001) and a significant correlation between changes in NT-proBNP and in LVEDVI (r=0.858, P<0.001). Baseline NT-proBNP correlated with changes in LVEDVI in both trained (r=0.673, P<0.001) and untrained (r=0.623, P<0.001) patients. Group C showed unfavourable LVEDVI dilation (+8%, P<0.001; T vs. C group, P<0.001) and a smaller reduction in NT-proBNP (−40%, P<0.001; T vs. C group, P<0.001). Conclusions Six month ET induced a favourable LV remodelling and a marked fall in NT-proBNP that could predict LV remodelling in postinfarction patients with moderate LV dysfunction.

Tissue Factor Binding of Activated Factor VII Triggers Smooth Muscle Cell Proliferation via Extracellular Signal–Regulated Kinase Activation

Background—Tissue factor (TF) is the main initiator of coagulation in vivo. Recently, however, a role for TF as a cell receptor involved in signal transduction has been suggested. The aim of the present study was to assess whether activated factor VII (FVIIa) binding to TF could induce smooth muscle cell (SMC) proliferation and to clarify the possible intracellular mechanism(s) responsible for this proliferation. Methods and Results—Cell proliferation was induced by FVIIa in a dose-dependent manner, as assessed by [3H]thymidine incorporation and direct cell counting, whereas no response was observed with active site–inhibited FVIIa (FVIIai), which is identical to FVIIa but is devoid of enzymatic activity. Similarly, no proliferation was observed when binding of FVIIa to TF was prevented by the monoclonal anti-TF antibody AP-1. Activation of the p44/42 mitogen-activated protein (MAP) kinase (extracellular signal–regulated kinases 1 and 2 [ERK 1/2]) pathway on binding of FVIIa to TF was demonstrated by transient ERK phosphorylation in Western blots and by suppression of proliferation with the specific MEK (MAP kinase/ERK kinase) inhibitor UO126. ERK phosphorylation was not observed with FVIIai or when cells were pretreated with AP-1. Conclusions—These data indicate a specific effect by which binding of FVIIa to TF on the surface of SMCs induces proliferation via a coagulation-independent mechanism and possibly indicate a new link between coagulation, inflammation, and atherosclerosis.

Activated platelets and leucocytes cooperatively stimulate smooth muscle cell proliferation and proto-oncogene expression via release of soluble growth factors

BACKGROUND Previous studies indicate that platelets and leucocytes might contribute to the development of neointimal hyperplasia following arterial injury. The present study was aimed at further investigating the role of platelets and leucocytes, alone or in combination, in promoting vascular smooth muscle cell (SMC) proliferation in vitro, focusing on the relative contribution of different soluble growth factors released by these cells, and on the ability to induce proto-oncogene expression, such as c-fos. METHODS SMCs from rabbit aortas, made quiescent by serum deprivation, were stimulated with either activated platelets, leucocytes, or both, separated from SMCs by a membrane insert. SMC proliferation was evaluated by measuring the incorporation of 3H-thymidine. The relative contribution of different platelet-derived mediators to SMC growth was evaluated by adding either ketanserin, a 5-HT2 receptor antagonist, R68070, a TxA2 receptor antagonist, BN52021, a platelet activating factor (PAF) receptor antagonist, and trapidil, a platelet derived growth factor (PDGF) receptor antagonist. The role of different leucocyte sub-populations (neutrophils and monocytes + lymphocytes) was also determined in additional experiments. RESULTS SMC proliferation was significantly increased by activated platelets to 360 +/- 9% of control values (P < 0.05). This effect was reduced by ketanserin, R68070, BN 52021 or trapidil. Whole leucocytes, neutrophils or lymphocytes + monocytes also increased SMC proliferation with respect to control experiments. Simultaneous stimulation of SMCs by platelets and whole leucocytes was associated with a significant greater increase in SMC proliferation as compared to SMC stimulated with platelets or leucocytes alone. c-fos expression, almost undetectable in unstimulated SMCs, was markedly increased by activated platelets or leucocytes. CONCLUSIONS Activated platelets promote SMC proliferation in vitro via release of soluble mediators, including serotonin, thromboxane A2 PAF and PDGF; activated leucocytes also induce a significant SMC proliferation and exert an additive effect when activated together with platelets; SMCs stimulated with activated platelets and leucocytes show an early expression of the proto-oncogene c-fos.

Reactive Oxygen Species and Antioxidants in the Pathophysiology of Cardiovascular Disease: Does the Actual Knowledge Justify a Clinical Approach?

There is evidence that reactive oxygen species (ROS) are related to the development of cardiovascular disease (CVD). Results from many studies support the hypothesis that ROS released from various sources or dysfunctional mitochondrial respiratory chain play a role in the development of atherosclerosis and its complications. This phenomenon is due to ROS-mediated signalling pathways that are involved in the modulation of several vascular mechanisms. Various animal models have demonstrated that ROS have a causal role in atherothrombosis and other vascular diseases. Oxidative stress is being proposed as the unifying mechanism for many CVD risk factors. In particular, ROS may be responsible for plaque rupture and subsequent thrombosis which lead to myocardial infarction and stroke. Many drugs or agents have been tested to prevent or block oxidation underlying atherothrombotic processes, often with discordant outcomes. We observed that pre-treatment with some antioxidants, such as pyrrolidine dithiocarbamate (PDTC) or N-acetylcysteine, as well as some vitamins with recognized antioxidant properties, namely ascorbic acid (vitamin C), all-trans Retinoic Acid (atRA) and alpha-tocopherol (vitamin E) can suppress oxidative stress (OS)-induced Tissue Factor (TF) expression in human coronary artery endothelial cells. The present review, starting from our experimental observations, focuses on the influence of redox balance on atherothrombotic processes and on the effects of antioxidant treatment. A better understanding of the complex regulation of cellular redox balance could facilitate the development of newer antioxidants aimed at specific cellular targets. Research could also help assess the role of combination pharmacological intervention for the treatment and prevention of vascular disease.

Endogenous Tissue Factor Pathway Inhibitor Modulates Thrombus Formation in an In Vivo Model of Rabbit Carotid Artery Stenosis and Endothelial Injury

BACKGROUND Tissue factor pathway inhibitor (TFPI) is the sole known inhibitor of the extrinsic coagulation pathway of physiological importance; however, its role in modulating thrombosis in vivo is still unclear. METHODS AND RESULTS Intravascular thrombosis was initiated by placing an external constrictor around endothelially injured rabbit carotid arteries (n=10). Carotid blood flow velocity was measured by a Doppler flow probe. After placement of the constrictor, cyclic flow reductions (CFRs), due to recurrent thrombosis, developed at the site of stenosis. Transstenotic TFPI plasma activity was measured in blood samples before induction of CFRs and after 30, 60, and 180 minutes of CFRs. TFPI plasma activity distal to the site of thrombosis was significantly lower than the corresponding proximal values at 30, 60, and 180 minutes of CFRs. In addition, a progressive decrease in TFPI plasma activity was observed in both the proximal and the distal samples, indicating consumption of TFPI during thrombus formation. In 10 additional rabbits, CFRs were abolished by administration of aspirin (10 mg/kg). In the animals in which aspirin abolished CFRs, endogenous TFPI was depleted by a bolus of a polyclonal antibody against rabbit TFPI, and the effects on restoration of CFRs were monitored. In 5 of 6 animals in which aspirin abolished CFRs, depletion of endogenous TFPI activity caused full restoration of CFRs. CONCLUSIONS The data of the present study support the involvement of endogenous TFPI in the process of thrombus formation in vivo and its active role in modulating arterial thrombosis.

Involvement of Tissue Factor Pathway Inhibitor in the Coronary Circulation of Patients With Acute Coronary Syndromes

Background—Tissue factor pathway inhibitor (TFPI) is the endogenous inhibitor of the extrinsic coagulation pathway; however, its involvement during thrombus formation in patients with acute coronary syndromes (ACS) is still unknown. Methods and Results—Transcardiac (aorta/coronary sinus) free and total TFPI (free + lipoprotein-bound form) levels, as well as TFPI/factor Xa (FXa) complex levels, were measured in plasma samples obtained from patients with acute myocardial infarction undergoing primary PTCA and patients with unstable angina undergoing urgent PTCA. Patients with stable angina undergoing elective PTCA served as controls. In addition, prothrombin fragment 1+2 and fibrinopeptide A plasma levels were measured. Samples were collected at baseline, after PTCA, and after stent deployment. In patients with ACS, both total and free TFPI plasma levels in the coronary sinus were significantly lower than the corresponding levels measured in the aorta at any time point of the study; conversely, a significant increase in TFPI/FXa complex plasma levels was observed in the coronary sinus as compared with the aorta. In contrast, in patients with stable angina, no differences were observed in TFPI and TFPI/FXa levels at baseline in the coronary sinus as compared with the aorta. Conclusions—TFPI is involved in the process of thrombus formation in vivo in patients with ACS, which suggests a potential role for TFPI in modulating coronary thrombosis.

Neopterin: From Forgotten Biomarker to Leading Actor in Cardiovascular Pathophysiology

Inflammation plays a role at all stages of atherosclerosis. Neopterin, a pteridine mainly synthesized by activated macrophages, is a marker of inflammation, immune system activation and an active participant in cardiovascular disease. Measurement of neopterin levels may help follow the evolution of specific inflammatory conditions (e.g. viral infection, renal transplant rejection, systemic inflammatory diseases, nephritic syndrome and autoimmune diseases). Serum levels of neopterin are elevated also in patients with coronary artery disease (CAD) and peripheral artery disease (PAD). Moreover, plasma levels of this molecule might predict adverse cardiovascular events in patients with CAD, acute coronary syndromes or severe PAD. In addition, neopterin levels are related to the development of heart failure. We provide an updated overview on neopterin and, its links with CAD, left ventricular dysfunction, and PAD. We also describe its potential role in cardiac regenerative strategies with using bone marrow cells.

Expression of exogenous tissue factor pathway inhibitor in vivo suppresses thrombus formation in injured rabbit carotid arteries

OBJECTIVES The aim of the present study was to test the hypothesis that retrovirus-mediated in vivo tissue factor pathway inhibitor (TFPI) gene transfer to the arterial wall would efficiently inhibit thrombosis without causing significant changes in systemic hemostatic variables. BACKGROUND Acute coronary syndromes (unstable angina and acute myocardial infarction) are usually caused by atherosclerotic plaque rupture, with consequent activation of the coagulation cascade and circulating platelets. Tissue factor (TF) exposure represents an early event in this pathophysiologic sequence, leading to activation of the extrinsic coagulation pathway and thrombin formation. Tissue factor pathway inhibitor is a naturally occurring inhibitor of the extrinsic pathway. METHODS In the present study, the gene coding for rabbit TFPI was inserted in a retroviral vector under control of a tetracycline-inducible promoter. Replication-defective, infectious, recombinant retroviruses were used to transfect rabbit carotid arteries with either TFPI or a reporter gene--green fluorescent protein (GFP). RESULTS Retroviral-mediated arterial gene transfer of TFPI resulted in potent inhibition of intravascular thrombus formation in stenotic and injured rabbit carotid arteries, whereas transfection of the contralateral carotid artery with GFP had no effect on thrombosis. No significant changes in systemic hemostatic variables (prothrombin time and partial thromboplastin time) were observed when thrombosis was inhibited. CONCLUSIONS These data suggest that retroviral-mediated transfection of the arterial wall with TFPI might represent an attractive approach for the treatment of thrombotic disorders.