Pathogenesis of arterial vascular disease

Molecular Markers of Hemostatic Activation: Applications in the Diagnosis of Thrombosis and Vascular and Thrombotic Disorders

The recognition of molecular marker events leading to hemostatic and thrombotic disorders and technologic advances in molecular biology and immunology has added a new dimension in the diagnosis of bleeding and thrombotic disorders. Pathophysiologic activation of coagulation, fibrinolysis, kallikrein-kinin system, vascu— lar stress, and intercellular interactions result in the generation of cell/process specific markers of a pathophysiologic event. It has been two decades since the concept of molecular markers was first introduced in the diagnosis of hemostatic and thrombotic disorders. However, due to cost/technologic limitations and lack of understanding of this field at various levels its usage in clinical laboratory diagnosis was rather limited. With the advent of such analytical techniques such as enzyme-linked immunosorbent assays (ELISA) a disease specific molecular profiling can be readily accomplished. Subclinical activation of platelets, endothelial distress, and aberrations of the protease network can be readily diagnosed by utilizing specific assays. The concept of hypercoagulable state is now validated utilizing such markers of hemostatic activation such as platelet factor 4, thromboxane B2, fibrinopeptide A and plasminogen activator inhibitor. Cardiovascular disease risk and blood vascular disorders can be diagnosed utilizing these markers. The monitoring of antithrombotic drugs that do not produce any anticoagulant effects on blood can also be readily accomplished by using some of these lanalytes. Using specific monoclonal antibodies, various diagnostic profiles for such disorders as thrombotic stroke, disseminated intravascular coagulation, primary fibrinolysis, hemodynamic disorders, and diseases of vascular origin can be investigated. Since the introduction of this concept some 50 additional markers have been introduced. The recognition of tissue factor pathway inhibitor (TFPI) has introduced a new concept in the understanding of the plasmatic and vascular interactions. Tissue factor and its inhibitor can now be measured at fmol amounts in plasma and body fluids. Specific antibodies to these markers can also be utilized in immunocytometric and flow cytometric analysis and will provide valuable diagnostic information. High through-put instruments and cost/technologies compliance methodologies are available to provide affordable laboratory approaches in the new era of cost constraint diagnostic medicine. However, a major deficit in the educational programs still exists and warrants the development of these programs in medical and allied health curriculums. Key Words: Molecular markers—Hypercoagulable state—Enzyme-linked immunosorbent assay—Tissue factor pathway inhibitor— Tissue factor.

Oxidative stress and vascular smooth muscle cell growth: a mechanistic linkage by cyclophilin A

Inflammation and oxidative stress contribute to the pathology of many diseases, but specific therapeutic targets remain elusive. Oxidative stress, generated by excessive reactive oxygen species (ROS), promotes cardiovascular disease. However, the precise mechanism of how ROS deteriorate vascular function and promote vascular remodeling in vivo has not been clearly elucidated. Cyclophilin A (CyPA) is a 20 kD chaperone protein that is secreted from vascular smooth muscle cells (VSMC) in response to ROS, and stimulates VSMC proliferation and inflammatory cell migration in vitro and in vivo. CyPA (both intracellular and extracellular) contributes to inflammation and atherosclerosis by promoting endothelial cell (EC) apoptosis and EC expression of leukocyte adhesion molecules, stimulating leukocyte migration, enhancing T helper cell type 1 (Th1) responses, increasing proliferation of macrophages and vascular smooth muscle cells (VSMC), and increasing pro-inflammatory signal transduction in VSMC. We tested the hypothesis that CyPA contributes to cardiovascular diseases by analyzing several genetic interventions that include the CyPA knockout mouse and the CyPA overexpressing transgenic mouse (VSMC-Tg). CyPA plays a crucial role in VSMC proliferation/migration and inflammatory cell recruitment, resulting in cardiovascular diseases in vivo.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Antithrombotic effect of GYKI-14766 in a canine model of arterial and venous rethrombosis: a comparison with heparin

We compared the antithrombotic effects of the thrombin inhibitor, D-methyl-phenylalanyl-prolyl-arginal (GYKI-14766) with those of heparin in a canine model of arterial and venous rethrombosis. Thrombogenesis was induced by electrolytic injury to the endothelial surface of the carotid artery and jugular vein. Either heparin (300 U/kg, n = 7), GYKI-14766 (0.5 mg/kg/h, n = 7), or saline (n = 10) was administered intravenously (i.v.) immediately after the local administration of anisoylated plasminogen streptokinase activator complex (APSAC 0.1 U/kg). Supplemental doses of heparin (100 U/kg) were administered at 1-h intervals. Infusion of GYKI-14766 was maintained for 5 h throughout the experiment. Ex vivo platelet aggregation in response to ADP or arachidonic acid (AA) was not changed in any of the experimental groups. Both GYKI-14766 and heparin increased the activated partial thromboplastin time (aPTT) over their respective baseline values. Heparin, but not GYKI-14766, increased the bleeding time. After successful thrombolysis, arterial and venous rethrombosis occurred in all saline-treated dogs. GYKI-14766 prevented cyclic flow variations and reocclusion in the artery and the vein (p < 0.01). Heparin had only minimal effects on the artery and no effect on the vein. Arterial thrombus weights were reduced by GYKI-14766 [saline control = 24 +/- 4 mg, GYKI-14766 = 9 +/- 3 mg, (p < 0.05); heparin = 14 +/- 2 mg, p = NS]. The venous thrombus weights were reduced slightly by GYKI-14766 and were unchanged by heparin (saline = 25 +/- 5 mg, GYKI-14766 = 13 +/- 4 mg, heparin = 26 +/- 3 mg). The data suggest that GYKI-14766 is effective in preventing occlusive rethrombosis in both the arterial and venous circulation after thrombolysis without augmenting bleeding time. GYKI-14766 may represent an alternative to heparin as an adjunctive agent during thrombolytic therapy.

Characterization of thrombin receptor expression during vascular lesion formation

Blood vessels respond to injury by initiating cell proliferation and migration that result in vascular lesion formation. To determine the roles of thrombin and the thrombin receptor in this process, we characterized thrombin receptor expression in normal and injured arteries, thrombin receptor-mediated smooth muscle cell mitogenesis, and the regulation of thrombin receptor mRNA expression in vitro. Thrombin receptor mRNA was not detected in normal rat or baboon arteries by in situ hybridization. Immunohistochemistry using an antithrombin receptor antibody (TR-R9), directed against the thrombin cleavage site of the rat aortic smooth muscle cell thrombin receptor, revealed low-level staining for thrombin receptor protein in endothelial cells and smooth muscle cells of normal arteries. In contrast, balloon catheter injury increased thrombin mRNA expression in medial smooth muscle cells within 6 hours. This increased thrombin receptor expression continued within the media and in neointimal cells throughout vascular lesion formation, predominantly in areas of active cell proliferation. In vitro, alpha-thrombin stimulates rat aortic smooth muscle cell proliferation in a concentration-dependent manner. That thrombin receptor activation is required for the mitogenic response was confirmed by demonstrating that the polyclonal antibody TR-R9 inhibits thrombin-induced cell proliferation. Thrombin receptor mRNA synthesis was induced by both basic fibroblast growth factor (maximal stimulation of 1.8-fold at 1 hour) and platelet-derived growth factor (maximal stimulation of 2.4-fold at 8 and 24 hours) in quiesced cultured rat aortic smooth muscle cells. In summary, upregulation of smooth muscle cell thrombin receptor expression occurs very early after vascular injury and continues throughout neointimal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelets and atherosclerosis

Despite the broad array of mechanisms designed to protect the endothelial lining of every blood vessel in the body and maintain the fluid state of blood, injury does occur. Chronic and recurrent damage result in development of lesions characteristic of atherosclerosis. The loss of vascular integrity associated with the pathological process of atherogenesis triggers the haemostatic mechanism. As a result, fibrin and platelets become a part of atherosclerotic lesions and play a role in their progression. Growth of the plaques and destruction of normal endothelium triggers further involvement of platelets leading to occlusion of arteries in the heart and brain, resulting in myocardial infarction and stroke. Understanding the role of platelets in atherosclerosis and limiting its contribution may reduce morbidity and mortality of this dread disease.

Platelet hyperaggregability across the coronary bed in response to rapid atrial pacing in patients with stable coronary artery disease

BACKGROUND

Platelet aggregation is believed to contribute to the precipitation of acute ischemic syndromes. Because physical activity has been proposed as one possible trigger in converting a patient with chronic coronary artery disease to one with an acute ischemic syndrome, we examined the hypothesis that platelets become activated when coronary blood flow velocities (and thereby shear stress) increase across an atherosclerotic bed.

METHODS AND RESULTS

During catheterization, 82 patients (36 with left coronary artery disease, 12 with only right coronary artery disease, and 34 with normal coronary arteries) had measurement of whole blood platelet aggregation performed on blood samples obtained simultaneously from the coronary sinus and aorta at rest, 2 minutes after onset of rapid atrial pacing, and 10 minutes after pacing was terminated. There was no arteriovenous difference in platelet aggregation under resting conditions in patients with versus those without coronary artery disease. Atrial pacing in patients with left coronary artery disease (greater than or equal to 50% stenosis in a major epicardial vessel) caused an increase in platelet aggregation in the coronary sinus blood (+64 +/- 9%, p less than 0.01) but not in arterial blood (2 +/- 8% decrease, p = NS). This increase was transient and returned nearly to baseline 10 minutes after termination of pacing. Patients with nonsignificant left coronary artery disease, those with normal coronary arteries, and patients with significant disease only in the right coronary artery (venous drainage not into the coronary sinus) did not show any changes in either the coronary sinus or arterial blood with atrial pacing.

CONCLUSIONS

There is no evidence of platelet activation across a normal or an atherosclerotic coronary bed at rest. When coronary blood flow increases in the presence of significant (greater than or equal to 50%) narrowing of epicardial coronary arteries, however, platelets are activated and aggregate more easily. This mechanism may play a role in the precipitation of acute ischemic syndromes in patients with coronary artery disease.

Transcoronary platelet activation and consumption in coronary artery disease: studies at rest

The platelet count(PC), plasma platelet factor 4 (PF4) and plasma beta-thromboglobulin(beta TG) have been measured in blood obtained from a peripheral vein, the aortic root and the coronary sinus in 7 patients with normal coronary arteries, 9 patients with lesser degrees of coronary artery disease(CAD) and in 13 patients with severe CAD under resting conditions. In each patient group values obtained in the peripheral venous blood were similar to those obtained in normal subjects. In each group values obtained in blood from the coronary sinus were similar to those obtained in blood from the coronary aortic root and in most instances these were similar to values obtained in peripheral venous blood. for example, in the 13 subjects with hemodynamically significant 3-vessel or 2-vessel CAD the mean values in blood from a peripheral vein, the aorta and the coronary sinus respectively were: PC-194, 205, and 208 x 10(9)/1; PF4-3.3, 3.7, and 3.5 ng/ml; and beta TG-15.5, 23.0 and 18.6 ng/ml. These findings provide no support for the occurrence of continuous platelet activation or platelet consumption in the coronary vessels or elsewhere in patients with stable CAD, under resting conditions, regardless of its severity.

Studies of hypercholesterolemia in the nonhuman primate. II. Fatty streak conversion to fibrous plaque

This report presents the second portion of the morphologic studies on chronic, diet-induced hypercholesterolemia in nonhuman primates (Macaca nemestrina) examined sequentially between 5 and 13 months. A direct relationship was observed between the rate of cholesterol increase, the level and duration of hypercholesterolemia, and the changes in the artery wall that led to the formation of fatty streaks and their conversion to fibrous plaques. A loss of endothelial continuity was first observed in the iliac arteries between 3 and 4 months of atherogenic diet and appears to be a critical step in the conversion of many fatty streaks to fibrous plaques. With breaks in endothelial junctions and exposure of some of the macrophages in a fatty streak, many of the lipid-filled macrophages appeared to detach and enter the circulation. The number of circulating foam cells increased precipitously between 3 and 4 months, the time when increased sites of endothelial dysjunction and macrophage egress were observed. Exposure of subendothelial macrophages also permitted adherence of platelets to these macrophages and to exposed connective tissue. Fibrous plaques were found at similar anatomic sites where endothelial denudation had been observed at earlier time points but were more prevalent in the abdominal aorta and iliac arteries. These changes subsequently occurred at every level of the aortic tree and appeared to progress in a cephalad fashion with increasing rate, level, and duration of hypercholesterolemia. The results of these studies stress the importance of following cholesterol levels of each animal throughout the entire period of the study and of sampling the entire arterial tree at every level with time. This helped us to understand the complicated interrelationships between the various cells in atherogenesis, provided further support for the "Response to Injury Hypothesis of Atherosclerosis," and helped to explain how hypercholesterolemia may be involved in the different stages of atherogenesis in nonhuman primates and possibly in humans.

Sulfinpyrazone decreases epinephrine-induced platelet aggregation after myocardial infarction

Platelet studies were performed during a controlled double-blind randomized clinical trial of sulfinpyrazone (Anturane Reinfarction Trial) in 41 patients who had recent myocardial infarction. Aggregation of platelet-rich plasma by thrombin (0.185, 0.246 U/ml), collagen, adenosine diphosphate, and adrenaline (0.23, 0.46, and 0.91 microgram/ml) was estimated after a 12 hour fast including abstinence from drugs and cigarette smoking. The tests were carried out 2 weeks after myocardial infarction and 6, 12, and 24 months later. At the last visit, washed platelet suspensions were also tested for aggregation to thrombin (0.03, 0.015 U/ml) +/- epinephrine (0.55 microgram/ml) and their production of malonyldialdehyde was estimated. A significant (p less than 0.02) reduction (50%) of the aggregation response of platelet-rich plasma to epinephrine was found in the group treated with sulfinpyrazone (n = 21) as compared with the placebo group (n = 20). Also, adrenaline evoked a milder (p less than 0.01) potentiation of aggregation by thrombin of the washed platelet suspensions in the sulfinpyrazone versus the placebo group. Other assays including platelet coagulant activity were not useful in discriminating between the 2 groups. It is concluded that sulfinpyrazone (200 mg 4 times daily) normalizes the platelet response to epinephrine; a relation with the drug-reported reduction of sudden death after myocardial infarction is suggested.

Can drugs help patients with lower limb ischaemia?

The prevalence of symptomatic arterial disease of the lower limbs is 2 per cent of the population aged 45-60, but it has a relatively benign course, with 70 per cent of patients requiring no therapy. Of the numerous drugs used in the treatment of the disease, there is no evidence to suggest that antilipaemic drugs, anticoagulants, vasodilators or rheological agents confer any benefit to the patient. The initial use of antiplatelet drugs and prostaglandins has been disappointing despite the undoubted importance of the platelet/endothelial interaction in the aetiology of atherosclerosis. As it is unlikely that we can reverse advanced disease, this is hardly surprising. Long term use of these drugs may prevent deterioration in those patients with progressive disease, and controlled trials on this aspect of treatment are now required. Symptomatic relief in the claudicant may perhaps be obtained with naftidrofuryl and suloctodil and with the former in more severe ischaemia, but their use should not replace the beneficial effects of exercise and cessation of smoking.

Role of hydrogen peroxide in neutrophil-mediated destruction of cultured endothelial cells

Human neutrophils stimulated with phorbol myristate acetate were able to destroy suspensions or monolayers of cultured human endothelial cells. Neutrophil-mediated cytotoxicity was related to phorbol myristate acetate concentration, time of incubation and neutrophil number. Cytolysis was prevented by the addition of catalase, while superoxide dismutase had no effect on cytotoxicity. The addition of the heme-enzyme inhibitors, azide or cyanide, markedly stimulated neutrophil-mediated damage while exogenous myeloperoxidase failed to stimulate cytolysis. Neutrophils isolated from patients with chronic granulomatous disease did not destroy the endothelial cell targets while myeloperoxidase-deficient neutrophils successfully mediated cytotoxicity. Endothelial cell damage mediated by the myeloperoxidase deficient cells was also inhibited by catalase but not superoxide dismutase. The addition of purified myeloperoxidase to the deficient cells did not stimulate cytotoxicity. Glucose-glucose oxidase, an enzyme system capable of generating hydrogen peroxide, could replace the neutrophil as the cytotoxic mediator. The addition of myeloperoxidase at low concentrations of glucose oxidase did not increase cytolysis, but at the higher concentrations of glucose oxidase it stimulated cytotoxicity. The destruction of endothelial cells by the glucose oxidase-myeloperoxidase system was inhibited by the addition of hypochlorous acid scavengers. In contrast, neutrophil-mediated cytolysis was not effectively inhibited by the hypochlorous acid scavengers. Based on these observations, we propose that human neutrophils can destroy cultured human endothelial cells by generating cytotoxic quantities of hydrogen peroxide.

Binding and release of factor VIII/von Willebrand's factor by human endothelial cells

The uptake and release of factor VIII/von Willebrand's protein by cultured human umbilical vein endothelial cells have been examined using highly purified 125I-factor VIII possessing von Willebrand's factor activity. 125I-factor VIII/vWF was taken up by the cells, reaching maximum binding within 4 h with a t1-2 of binding of 15 min. Endothelial cell binding of 125I-factor VIII/vWF reached saturation at a concentration of 1.5 mg/l. Binding was inhibited by coincubation of excess unlabelled factor VIII/vWF. Most of the cell-associated radioactivity was released by treatment of the cells with trypsin. Internalization of bound protein was evidenced by the incorporation into the cells of radioactivity which could not be released by trypsin. Human vascular smooth muscle cells did not bind 125I-factor VIII/vWF. Addition of 0.1 microM epinephrine to the 125I-factor VIII/vWF labelled endothelial cultures induced the release of cell bound, protein-associated radioactivity into the medium. Propranolol inhibited completely epinephrine-induced release, whereas phenylephrine had no effect. Endothelial cells maintained in medium partially depleted of factor VIII/vWF by tricalcium citrate cellulose treatment of plasma did not release factor VIII antigen into the culture medium during subsequent incubation. Although [3H]proline was incorporated into proteins released by endothelial cells under these experimental conditions, specific incorporation of label into factor VIII/vWF antigen was not detectable by a sensitive solid-phase immunoradiometric assay. We conclude that factor VIII/vWF binds to endothelial cells and that this cell-bound protein is mobilized by epinephrine through beta-adrenergic stimulation.