Atherosclerosis and the coagulation system

Lipoprotein Lp(a) as predictor of myocardial infarction in comparison to fibrinogen, LDL cholesterol and other risk factors: results from the prospective Göttingen Risk Incidence and Prevalence Study (GRIPS)

Based on pathophysiological findings Lp(a) is considered to be a cardiovascular risk factor. The Göttingen Risk Incidence and Prevalence Study (GRIPS) provides the possibility to evaluate this impact of Lp(a) on the basis of a large prospective cohort study. GRIPS included 6002 men, aged 40-59.9 years at baseline. Data of a 5 year follow-up period is now available for > 95% of the study participants. Multivariate logistic regression models for the estimation of MI risk confirm Lp(a) as an important risk factor, ranking fifth behind LDL cholesterol, family history of MI, plasma fibrinogen and HDL cholesterol (inversely related). The GRIPS data strongly support strategies for the identification and treatment of persons at increased MI risk which focus on LDL cholesterol. However, Lp(a) and fibrinogen have to be seriously considered as additional risk factors and should be included in diagnostic panels for the estimation of MI risk.

Fibrinogen: an important risk factor for atherothrombotic diseases

Epidemiological follow-up studies have suggested that fibrinogen is a major, primary cardiovascular risk factor. Cross-sectional results also show associations between fibrinogen and cardiovascular risk factors or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a secondary risk factor. The determinants of the plasma level of fibrinogen in health and disease are known only incompletely. Our understanding of the mechanisms involved in the atherogenic actions of fibrinogen is similarly fragmentary. These might include blood coagulation, blood rheology, platelet aggregation, direct effects on the vascular wall, and the acute phase response. Thus, many questions are yet to be answered. Nevertheless, the data available at present strongly suggest that fibrinogen represents a major, independent cardiovascular risk factor. Fibrinogen should be considered for screening programmes aimed at identifying individuals at risk.

Fibrinogen: its emerging role as a cardiovascular risk factor

Several epidemiologic studies have produced longitudinal data identifying fibrinogen as a major cardiovascular risk factor. Cross-sectional results show strong associations between fibrinogen and cardiovascular risk factors or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a risk factor for the sequelae of cardiovascular disease. At present, knowledge about the determinants of the plasma level of fibrinogen in health and disease is incomplete. Understanding of the mechanisms that might be involved in the atherogenic action of fibrinogen is also fragmentary. Fibrinogen strongly affects blood coagulation, blood rheology, and platelet aggregation, and in addition it has direct effects on the vascular wall and is a prominent acute-phase reactant. All of these phenomena might provide some insight into the pathophysiologic mechanisms involved in the association between fibrinogen and cardiovascular events. Even though many crucial questions await answers, it is concluded that fibrinogen represents a major, independent risk factor that should be considered for screening programs aimed at identifying individuals at high risk for cardiovascular disease.

Recent observations on the role of hemostatic determinants in the development of the atherothrombotic plaque

Recent evidence suggests that hemostatic determinants play a major role in the evolution of the atherothrombotic plaque. Platelets can serve as cholesterol donors for macrophages, thereby facilitating foam cell formation. Lipoprotein(a) inhibits fibrinolysis and may also contribute to atherogenesis by serving as a ligand for the scavenger receptor. By complexing with fibrin(ogen) in atheromatous lesions, lipoprotein(a) attenuates clearance of this protein, promoting atherogenesis and vascular dysfunction. These observations suggest that thrombotic determinants are critical for the development of the atheromatous plaque, and may guide the appropriate selection of potential therapeutic options in the future.

Thrombus formation and platelet-vessel wall interaction in the nephrotic syndrome under flow conditions

Increased in vitro platelet aggregability and hypercoagulability are generally held to be main determinants in the prethrombotic state in nephrosis. In vivo, however, thrombotic events depend on the dynamic interaction of flowing blood with the vessel wall. The present study confirms that aggregability of platelets of nephrotic patients is significantly increased by mere stirring or by exogenous stimuli as adenosine diphosphate and arachidonic acid. Moreover, the nephrotic patients have high von Willebrand factor and decreased red blood cell deformability, which normally increase platelet-vessel wall interaction. However, perfusion studies under well-defined flow conditions, in which anticoagulated nephrotic blood was exposed to deendothelialized human umbilical artery segments and sprayed collagen, showed normal platelet adhesion and only a modest increase in the deposition of platelet aggregates. This suggests that some factor counteracts platelet-vessel wall interaction under flow conditions in the nephrotic syndrome. When tissue factor associated with endothelial extracellular matrix (ECM) was allowed to generate thrombin, perfusions with nephrotic blood over this ECM resulted in a strong increase in fibrin generation. The capacity of patient blood to form increased amounts of fibrin appeared strongly correlated with the level of hyperfibrinogenemia. Platelet adhesion as well as aggregation in these experiments was even decreased below control values. This suggests that fibrin coverage may block the direct contact between blood platelets and matrix. We therefore also studied the isolated effect of high fibrinogen on platelet-vessel wall interaction by increasing fibrinogen concentrations in normal blood. Modulation of fibrinogen concentrations in normal blood could mimic all the observations in nephrotic blood: platelet aggregation in suspension increased with increasing concentrations of fibrinogen, while platelet adhesion and aggregate formation under flow conditions decreased. In perfusions over tissue factor-rich matrix, fibrin deposition increased. Therefore, our observations indicate that nephrotic hyperaggregability in suspension is not associated with increased platelet vessel wall-interaction under flow conditions. The latter is probably counteracted by high levels of fibrinogen. Our observations further suggest that hyperfibrinogenemia may be a major thrombotic risk factor in nephrosis by inducing more fibrin depositions.

Involvement of the hemostatic system in the insulin resistance syndrome. A study of 1500 patients with angina pectoris. The ECAT Angina Pectoris Study Group

Hyperinsulinemia, a major indicator of insulin resistance, may exert its influence on the risk of coronary artery disease partially through disturbances of the hemostatic system. The relations of fasting insulin concentrations with the degree of coronary atherosclerosis, other coronary risk factors (including some markers of the insulin resistance syndrome such as body mass index and triglyceride), markers of inflammation, and hemostatic factors were investigated in 1484 patients with angina pectoris. Mean insulin levels were higher in patients with one or more coronary vessel stenoses than in those without (9.9 microU/mL compared with 9.0 microU/mL, P < .0001). However, the association the presence of vessel stenoses was stronger in patients with a previous myocardial infarction than in those without. Insulin increased markedly (P < .0001) and independently of other risk factors with age body mass index, triglyceride concentration, and markers of inflammation, such as white blood cell count and C-reactive protein. The strongest relations between insulin and hemostatic factors were observed with fibrinolytic variables, particularly plasminogen activator inhibitor-1 (PAI-1) levels (r = .44, P < .0001). This relation decreased somewhat (r = .29) after simultaneous adjustment for markers of the insulin resistance syndrome, mainly body mass index and triglycerides, but not after adjustment for markers of inflammation. Therefore, we propose that increased PAI-1 levels, which are essentially related to the classic metabolic aspect of the insulin resistance syndrome, have to be included in this syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Presence of growth-stimulating fibrin degradation products containing fragment E in human atherosclerotic plaques

The key event in the formation of stenosing atherosclerotic lesions is widely thought to be smooth muscle cell proliferation, but the factors primarily responsible for initiating this remain uncertain. Previously we have shown that aqueous extracts of proliferative types of human atherosclerotic plaque stimulate cell proliferation in the chick chorioallantoic membrane (CAM). This has been attributed largely to the fibrin degradation products in the extracts, components removeable by affinity chromatography. We now demonstrate that the fibrinogen content of the extract, removeable by clotting out with thrombin, also makes a contribution to the activity by forming fibrin on the surface of the CAM. Affinity chromatography experiments using anti fragment D and E antisera indicate that activity resides in the E-containing fibrin fragments, consistent with previous work with FDP prepared in vitro.

The importance of a substantial elastic lamina subjacent to the endothelium in limiting the progression of atherosclerotic changes

This study examines the hypothesis that progressive intimal thickening and atherosclerosis in the larger pulsatile arteries arise from failure to maintain, subjacent to the endothelial cells, a substantial elastin membrane, a component which has been shown to be of special structural significance. The internal thoracic arteries of 293 subjects of all ages up to 60 years were compared histologically with the anterior descending coronary arteries of the same individuals by light- and electronmicroscopy and immunoperoxidase staining for macromolecules. The internal thoracic arteries usually developed a new robust reduplicated internal elastic lamina at an early age, no further intimal thickening, and no significant entry of lipid or cells to the intima. The coronary arteries showed areas of rapid intimal thickening with poor and incomplete reduplicated internal elastic laminae, entry of lipid, macrophages, and other cells to the intima. The reduplicated internal elastic laminae appeared to be formed primarily by the endothelial cells themselves. An elastin membrane subjacent to the endothelial cells appears to be essential. It provides a secure attachment for the cells and a barrier to the entry of macromolecules and cells to the intima. Its absence is associated with progressive intimal thickening and atherosclerosis.

Relation of fibrinogen to presence and severity of coronary artery disease is independent of other coexisting heart disease. The ECAT Angina Pectoris Study Group

Six hundred fifty seven patients with angina pectoris underwent coronary angiography after measurement of plasma fibrinogen levels. Coronary artery disease (CAD) was angiographically confirmed in 75% of the patients. Other cardiac disease, either alone or in combination with CAD, was diagnosed in 8% and 11% of cases, respectively; 17% of the patients had no evidence of overt heart disease. Fibrinogen concentrations showed a graded increase according to the severity of coronary stenosis (p = 0.02) but were not significantly associated with any other cardiac heart disease. However, patients with valvular heart diseases had on average a 5.9% elevation of fibrinogen levels as compared to patients without proven cardiac disease (p = 0.08), similar to the observed 6.9% increase for CAD (p = 0.005). On average, patients with cardiomyopathies or pulmonary hypertension had only a 1.6% or 1.2% increase, respectively. The increase in fibrinogen levels associated with CAD was similar in patients with and without coexisting heart diseases. The results demonstrate a significant positive relation of fibrinogen to the presence and severity of CAD irrespective of a possible confounding influence from other cardiac diseases. The results therefore lend support to the hypothesis of a pathogenetic role for fibrinogen as a cardiovascular risk factor.

The role of fibrinogen as a cardiovascular risk factor

Several epidemiological studies have produced longitudinal data identifying fibrinogen as a major cardiovascular risk factor. Cross-sectional results show strong associations between fibrinogen and a variety of demographic variables, cardiovascular risk factors, or diseases. Clinical cohort studies demonstrate that fibrinogen might also be a risk factor for the sequelae of cardiovascular disease. Knowledge about the determinants of the plasma level of fibrinogen in health and disease is as yet incomplete. Understanding of the mechanisms leading to the atherothrombogenic action of fibrinogen is also fragmentary. Fibrinogen strongly affects blood coagulation, blood rheology and platelet aggregation; in addition fibrinogen and its metabolites have direct effects on the vascular wall. Finally, fibrinogen is a prominent acute phase protein. All of these phenomena might provide some insight into the pathophysiological mechanisms involved. It is concluded that fibrinogen represents a major, independent risk factor that should now be included into the cardiovascular risk profile.

Plasminogen activator inhibitor activity in diabetic and nondiabetic survivors of myocardial infarction

Recent studies suggest that plasminogen activator inhibitor (PAI-1) may be a risk factor for recurrent myocardial infarction. We measured PAI-1 activity and antigen and tissue-type plasminogen activator (t-PA) antigen in 35 (20 nondiabetic and 15 diabetic) subjects with no clinical or electrocardiographic evidence of ischemic heart disease and in 74 (50 nondiabetic and 24 diabetic subjects) who had survived a myocardial infarction in the preceding 6-24 months. Levels of PAI-1 activity (18.7 +/- 5.6 versus 12.0 +/- 3.8 arbitrary units [AU] per milliliter, p = 0.001) and t-PA antigen (7.0 +/- 1.9 versus 4.6 +/- 2.0 ng/mL, p = 0.001) were significantly higher in diabetic compared with nondiabetic control subjects. Survivors of myocardial infarction had higher levels of PAI-1 activity and antigen and t-PA antigen than control subjects, and the diabetic survivors had higher levels of PAI-1 activity (25.3 +/- 6.7 versus 20.1 +/- 7.1 AU/mL, p = 0.004) and t-PA antigen (10.6 +/- 4.3 versus 8.4 +/- 3.3 ng/mL, p = 0.03) than the nondiabetic survivors. No difference in PAI-1 antigen levels was found between the diabetic subjects and either the nondiabetic control subjects or survivors of myocardial infarction. After venous occlusion in control subjects, there was a significant increase in PAI-1 antigen (mean 26.7%, range 14.1-58.1% in nondiabetics and mean 25.2%, range 6.2-39.7% in diabetics) and t-PA antigen (mean 78.3%, range 13.6-186.2% for nondiabetic and mean 40.7%, range 17.5-76.2% for diabetic subjects), but in the survivors of myocardial infarction, no significant effect of venous occlusion was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

On the role of coagulation and fibrinolysis in atherosclerosis

Atherosclerosis is probably caused by multiple interacting factors such as disturbed lipid metabolism; endothelial cell damage, leading to platelet aggregation and monocyte invasion with the release of mitogenic factors; and disorders of fibrin balance, leading to persisting fibrin deposits. Deficient fibrinolysis may (1) predispose to fibrin deposition and contribute to the pathogenesis of atherosclerosis and (2) contribute to occlusive thrombus formation on fissured plaque, provoking atherothrombosis. Prospective epidemiologic studies have so far not provided definitive evidence that deficient fibrinolysis constitutes a significant risk factor for the development of atherosclerosis. Two recent findings, however, strongly suggest a contribution: (1) Increased lipoprotein(a) levels that reduce tissue-type plasminogen activator (t-PA)-mediated clot lysis are a clear risk factor for atherosclerosis; and (2) increased plasminogen activator inhibitor-1 (PAI-1) levels in patients with disturbed glucose tolerance predispose to an accelerated development of atherosclerotic disease. However, deficient fibrinolysis constitutes a risk factor for the development of thrombotic complications (acute myocardial infarction) in patients with coronary artery disease. The potential role of deficient fibrinolysis in the pathogenesis of atherosclerosis and of atherothrombosis suggests that drugs normalizing deficient endogenous fibrinolysis by either reducing PAI-1 synthesis or by stimulating endogenous t-PA synthesis may be of clinical value. Although regulation of the gene expression of PAI-1 and t-PA is presently under active investigation, no potent specific and safe agents to downregulate PAI-1 or to upregulate t-PA have as yet been identified. Retinoic acid appears to be a specific inducer of t-PA synthesis in human endothelial cells in culture and may constitute a model for the development of drugs that stimulate endogenous t-PA synthesis.

Fibrinogen/fibrin in atherogenesis

Fibrin is a major component of many atherosclerotic plaques. Within the intima there is continuous formation of fibrin, and continuous fibrinolysis. In aortic lesions, a lipoprotein bound to fibrin can be released by incubation with plasmin. Most of this lipoprotein is accounted for by Lp(a). The atherogenicity of Lp(a) may be more associated with lipid deposition than with inhibition of fibrinolysis. Fibrin degradation products may be chemotactic to monocyte-macrophages and stimulate smooth muscle cell proliferation.

Hemobiology, vascular disease, and diabetes with special reference to impaired fibrinolysis

This brief review is intended to emphasize the multiple interactions between diabetes and the pathophysiological processes that lead to ischemic cardiovascular events. The main pathogenetic pathways of atherothrombosis and their relationship with diabetes are largely and frequently analyzed. In this review, we will focus on a particular aspect of this pathological process, namely, the impairment in fibrinolysis, the importance of which has been recently recognized in cardiovascular disease. Fibrinolysis is frequently impaired in diabetic patients.

Fibrinolysis and angiogenesis in wound healing

The healing wound offers a clear example of the sequence of events in chronic inflammation leading to repair. Although angiogenesis has an obvious and essential role in this process, it has been little studied. For an angiogenic factor to seem relevant, it would have to be shown to precede the peak of increased vascularity. To define this peak, the vessel content of simple, incised mouse wounds was estimated using morphometry of histological sections, and found to rise to a maximum at days 5 and 6. Total angiogenic activity of aqueous extracts was found to reach a peak at day 3. The detection of such activity on the chick chorioallantoic membrane is very dependent on the preparation technique and the choice of proteinase inhibitors. Previous in vitro work by us using purified material has shown fibrin degradation products to be effective in stimulating angiogenesis. Fibrin degradation products are prominent on immunoblotting from day 3, when macrophages are plentiful, with a similar band pattern to human granulation tissue.

The effect of hypercholesterolemia on early atherosclerotic lesions initiated by fibrinopeptide B

Hypercholesterolemia and thrombosis have been implicated as factors in the development of atherosclerosis. Fibrinopeptide B (FPB) is a short chain peptide cleaved from fibrinogen during the production of fibrin. FPB is a known chemoattractant and has been shown to produce experimental atherosclerotic lesions in association with hypercholesterolemia. The present study was designed to examine the role of hypercholesterolemia in this process and to study the time course of the development of these lesions. Twelve New Zealand White rabbits were placed on an atherogenic diet and had suture carrying either FPB, fibrinopeptide A (FPA), or saline (controls) implanted in the adventitia of the femoral arteries and were sacrificed at 14 days. An equal number of animals were left on a standard diet and underwent similar treatment. Eleven animals were treated as the hypercholesterolemic group but were sacrificed at 2, 4, and 7 days. The thickness of the intima was measured adjacent to the suture in the animals sacrificed at 14 days, and the hypercholesterolemic FPB sites were thicker (12.23 mu +/- 6.60) than either hypercholesterolemic FPA (6.06 mu +/- 3.72), saline (4.94 mu +/- 1.42), or the normocholesterolemic FPB (5.99 mu +/- 4.61), FPA (3.89 mu +/- 2.20), or saline (3.97 mu +/- 1.83) (P less than 0.05 for all groups). Transmission electron microscopy of the hypercholesterolemic FPB group showed evidence of macrophages, actively secreting smooth muscle cells with newly deposited elastin, and foam cells by 7 days. We conclude that FPB attracts or stimulates macrophages and smooth muscle cells and that the resultant cellular and extracellular proliferation favors early atherosclerotic lesion formation in the presence of hypercholesterolemia.

Increased plasma plasminogen activator inhibitor 1 levels. A possible link between insulin resistance and atherothrombosis

According to recent prospective studies, hypofibrinolysis due to elevated plasma plasminogen activator inhibitor 1 levels appears to be an independent risk factor for myocardial reinfarction in men, and hyperinsulinaemia, a major indicator of insulin resistance is considered as a risk factor for coronary disease. It has recently been shown that insulin resistance is accompanied by an increased plasma plasminogen activator inhibitor 1 concentration: A significant correlation coefficient was demonstrated between plasminogen activator inhibitor 1 and fasting plasma insulin in the normal population, in obese subjects, in Type 2 (non-insulin-dependent) diabetic patients and in angina pectoris. Attempts to decrease insulin resistance such as fasting, diet, or administration of an oral anti-diabetic drug such as Metformin induced a parallel decrease in plasma insulin and plasminogen activator inhibitor 1 levels. This inhibitor is produced by endothelial cells and by hepatocytes in culture. Plasminogen activator inhibitor 1 synthesis by hepatocytes in culture was stimulated by an increasing insulin concentration, or low density lipoproteins, whereas the endothelial cell synthesis was stimulated by very low density lipoproteins especially when they were obtained from hypertriglyceridaemic patients. Therefore, a direct effect of insulin or lipoprotein changes on the cells which synthesize plasminogen activator inhibitor 1 could be responsible for its increased plasma concentration in insulin resistance states. The increase in plasma plasminogen activator inhibitor 1 levels linked to hyperinsulinaemia is a tempting partial explanation for the association between insulin resistance and coronary disease.

Biochemical assessment of cardiac function and damage in animal species. A review of the current approach of the academic, governmental and industrial institutions represented by the Animal Clinical Chemistry Association

Species differences in metabolism, tissue localization, specificity and sensitivity for cardiac damage influence the choice of biochemical investigation used in the assessment of cardiotoxicity. The tests currently used in toxicological studies are broadly categorized herein as enzymes and other proteins, lipids and electrolytes; some limitations of these tests are also discussed.

Fibrinogen as a major risk factor in cardiovascular disease

Evidence has accumulated over the past ten years to implicate elevated plasma fibrinogen levels in cardiovascular disorders such as ischaemic heart disease, stroke and peripheral vascular disease. At a cellular level, insight has been gained into the molecular regulation of fibrinogen biosynthesis and the mechanisms through which fibrinogen may be involved in these disease processes. Here, Nigel Cook and David Ubben summarize this evidence and consider the possibilities for novel therapies targeted at fibrinogen. A variety of structurally diverse pharmacological agents, many of which were developed for their effects on plasma lipids, have serendipitously been found to lower plasma fibrinogen levels.

Factors influencing the accumulation in fibrous plaques of lipid derived from low density lipoprotein. I. Relation between fibrin and immobilization of apo B-containing lipoprotein

The lipid that accumulates in some fibrous atherosclerotic lesions appears to be derived from plasma low density lipoprotein (LDL). An early stage in lipid accumulation may be immobilization of a fraction of the LDL, and this is released by incubation with proteolytic enzymes, of which the most effective is the fibrinolytic enzyme, plasmin. We have examined the relationship between release of fibrin degradation products (FDP) and LDL in controlled plasmin incubations of 42 samples of normal intima and atherosclerotic lesions from aortas of 10 patients. In three patients (group 1) no LDL was released from any of the 11 tissue samples although they comprised lesions as well as normal intima. In 2 more patients (group 2) LDL was consistently low. However, in 5 patients (group 3) substantial amounts of LDL were released from all 21 tissue samples, and there was a significant correlation between the amounts of FDP and LDL (P less than 0.001). In spite of this correlation there were marked differences in the ratio FDP/LDL, but analysis by SDS-polyacrylamide gel electrophoresis and immuno blotting of the FDP released showed no consistent pattern related to LDL binding. Although the ratio FDP/LDL showed a 4-fold range, in 6 lesions subjected to successive 2-h incubations with plasmin the ratio within each lesion remained constant, supporting the concept that fibrin and LDL are linked.

Factors influencing the accumulation in fibrous plaques of lipid derived from low density lipoprotein. II. Preferential immobilization of lipoprotein (a) (Lp(a))

The extracellular lipid that accumulates in fibrous atherosclerotic lesions appears to be derived directly from plasma low density lipoprotein (LDL). One factor that may influence the lipid deposition is immobilization of part of the LDL in lesions, and an immobilized fraction can be released by incubation with the fibrinolytic enzyme, plasmin, suggesting that it is associated with fibrin. The lipoprotein variant Lp(a) is associated with increased risk of arterial disease, and its characteristic apoprotein, apo(a), is structurally related to plasminogen, suggesting that it might bind to the plasminogen binding sites on fibrin. In this study we have compared blood Lp(a) and the soluble and plasmin-releasable Lp(a) in 45 samples of normal intima and different types of lesion. Levels of soluble and plasmin-releasable Lp(a) were dependent on both blood level and type of tissue sample. Although the amount of soluble LDL was 5-20 times higher than Lp(a) in intima, the amounts released by plasmin were similar, and Lp(a) appears to account for most of the apo B-containing lipoprotein that is immobilized in lesions.