Contribution of thrombogenic factors to the pathogenesis of atherosclerosis

Thrombosis Models: An Overview of Common In Vivo and In Vitro Models of Thrombosis

Occlusions in the blood vessels caused by blood clots, referred to as thrombosis, and the subsequent outcomes are leading causes of morbidity and mortality worldwide. In vitro and in vivo models of thrombosis have advanced our understanding of the complex pathways involved in its development and allowed the evaluation of different therapeutic approaches for its management. This review summarizes different commonly used approaches to induce thrombosis in vivo and in vitro, without detailing the protocols for each technique or the mechanism of thrombus development. For ease of flow, a schematic illustration of the models mentioned in the review is shown below. Considering the number of available approaches, we emphasize the importance of standardizing thrombosis models in research per study aim and application, as different pathophysiological mechanisms are involved in each model, and they exert varying responses to the same carried tests. For the time being, the selection of the appropriate model depends on several factors, including the available settings and research facilities, the aim of the research and its application, and the researchers' experience and ability to perform surgical interventions if needed.

Tissue factor-induced thrombin generation in the fasting and postprandial state among elderly survivors of myocardial infarction

INTRODUCTION

Tissue factor (TF)-induced thrombin generation (TG) ex vivo has been suggested to be an important method to assess thrombotic risk. No studies have investigated the impact of postprandial lipemia on TF-induced TG. Since myocardial infarction (MI) is associated with elevated postprandial levels of triglycerides, we hypothesized a differential impact of postprandial lipemia on coagulation activation in MI-patients and healthy controls.

MATERIAL AND METHODS

Elderly survivors of acute MI (n=44) and healthy age-and sex matched controls (n=43) underwent a fat tolerance test (1 gram per kg body weight) to assess coagulation activation during postprandial lipemia.

RESULTS

The incremental area under the curve (AUCi) for serum triglycerides was higher in MI-patients than in healthy age-and sex matched controls (5.64±0.52 mmol/L*h and 3.94±0.39 mmol/L*h, p=0.012) during the postprandial phase. Subsequent endogenous activation of coagulation, assessed by FVIIa and thrombin generation (F1+2), was similar among groups and not related to levels of triglycerides during the postprandial phase. Healthy individuals had a gradual decline in TF-induced thrombin generation ex vivo, assessed by endogenous thrombin potential (ETP) (AUCi=-542.4±71.4 nM*min*h, p<0.001), whereas MI-patients retained their ETP (AUCi=127.4±89.0 nM*min*h, p=0.47) in plasma during the postprandial phase (p for group difference=0.005).

CONCLUSIONS

MI-patients had elevated postprandial lipemia and retained their ability for TF-induced TG in plasma ex vivo in the postprandial phase, whereas the capacity gradually decreased in healthy individuals. Further studies are warranted to reveal underlying mechanism(s) and clinical implications.

Platelet hyperfunction as risk factor for chronic and acute coronary events

Indians have a very high incidence of vascular complications, such as hypertension, atherosclerosis, coronary artery disease (CAD), and stroke, compared to any other ethnic group in the world. They also have a very high incidence of multiple metabolic diseases, including type 2 diabetes. Elevated levels of known risk factors in this population for CAD does not explain adequately the significant increase in the vascular disease burden in this population. There is some speculation that genetic predisposal of this population may account for this increased incidence in vascular diseases. Environmental toxicants may also contribute significantly to the acceleration of these complex risk promoters. Functional and structural changes in the arterial wall precede the development of clinical complications such as endothelial dysfunction, hypertension, atherosclerosis, hyperfunction of platelets, and coagulation cascade. Vascular dysfunction, therefore, is the major contributor for the pathogenesis of hypertension, atherogenesis, thrombosis, and stroke. Alterations in the balance between platelet-associated vasoconstrictors and endothelial-derived vasodilators result in the vascular dysfunction. Blood platelets play a very important role in the pathogenesis of hypertension, atherogenesis, thrombosis, and stroke. These cells interact with a variety of agonists. Such interactions stimulate specific receptors and lead to the activation of intracellular effector enzymes. Ionized calcium is the primary bioregulator and a variety of signaling mechanisms modulate the cellular physiology and functions. Activated platelets promote the formation of thrombin and initiate coagulation cascade. They also interact with other circulating blood cells and facilitate inflammatory response. Little is known about the effect of environmental toxicants on vascular physiology and pathology. This is true also on their effect on the circulating blood cells. There is some evidence that oxidative stress as well as proinflammatory compounds play a role in vascular biology. In this presentation an attempt will be made to briefly review the known risk factors for CAD; the role of toxicants, eicosanoids, and inflammatory mediators on vascular biology specifically; and the role of platelets and platelet-derived biomolecules on hypertension, atherogenesis, thrombosis, and intercellular communications. Alterations in signaling pathways by environmental toxicants may increase the risk for hypertension, atherosclerosis, thrombosis, and stroke.

Migration of cultured vascular smooth muscle cells into non-crosslinked fibrin gels

We evaluated the migration of vascular smooth muscle cells into fibrin gels, using an in vitro assay system. Vascular smooth muscle cells from bovine fetal aorta migrated into fibrin gels and showed a characteristic elongated spindle-shaped appearance with long cytoplasmic processes. Varying the concentration of thrombin (0.05-1 NIHU/ml) used to form the fibrin gel had little effect on cell migration although higher concentrations of thrombin inhibited the migration. Migration of the cells into fibrin gels was dependent on RNA and protein synthesis but not on DNA synthesis. The addition of antithrombin III, hirudin, and D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone after gel formation had no effect, suggesting that residual thrombin in fibrin gels had no influence on subsequent cell migration. Neither the factor XIII-induced crosslinking of fibrin nor the fibrinopeptides released during gel formation were involved in the present migration assay system. Tranexamic acid, an inhibitor of plasminogen activator, or aprotinin, a plasmin inhibitor, also had no significant effect, suggesting that fibrinolysis induced by plasmin was not involved in this system. These findings showed that fibrin gels themselves induce the migration of vascular smooth muscle cells (haptotaxis) without other chemotactic or chemokinetic substances, suggesting an important role for fibrin in the development and progression of such vascular diseases as atherosclerosis, thrombosis and the development of restenosis following balloon angioplasty.

Plasma fibrinogen levels and their correlates in 6457 coronary heart disease patients. The Bezafibrate Infarction Prevention (BIP) Study

The association between fibrinogen measured in healthy individuals and subsequent development of ischemic heart disease is well established, but studies reporting fibrinogen levels in coronary heart disease patients are scarce. Plasma fibrinogen was determined for 5729 men and 728 women (aged 45 to 74) with established coronary heart disease, screened for participation in the Bezafibrate Infarction Prevention study, with the following lipid profile at the time of the first screening visit: total serum cholesterol < or = 270 mg/dl, high density lipoprotein cholesterol < or = 45 mg/dl and triglyceride < or = 300 mg/dl. Increased age was associated with augmented plasma fibrinogen values. Age-adjusted fibrinogen levels were higher in women than in men. A direct association was found between mean fibrinogen levels and low density lipoprotein cholesterol. On the other hand, the correlation with high density lipoprotein cholesterol was inverse. Fibrinogen was also associated with body mass index, behavioral variables and severity of coronary heart disease. In a multivariable linear regression analysis performed, risk factors considered explained merely 6 and 4% of fibrinogen variation for men and women, respectively. Therefore, most of the fibrinogen level variability in coronary heart disease patients is accounted for by factors that remain to be established by further research.

Fibrin formation and degradation in patients with arteriosclerotic disease

BACKGROUND

The blood coagulation cascade was reported to be activated in patients with arteriosclerotic disease of the lower limbs (peripheral arterial disease, PAD). There is more thrombin and fibrin formation compared with healthy control subjects. In many studies, however, the presence of arteriosclerotic disease had not been thoroughly ruled out in the control group. Therefore, markers of the activation of the blood coagulation cascade were measured in patients with PAD and in a carefully defined control group, both groups being subjected to an exercise test.

METHODS AND RESULTS

Twenty-two patients with angiographically documented PAD of grade II (Fontaine classification) and 13 control subjects in whom the presence of arteriosclerotic lesions was ruled out by noninvasive means in the carotid arteries, abdominal aorta, leg arteries, and coronary arteries took part in the study. Before and immediately after a treadmill stress test, the concentrations of prothrombin fragment F1 + 2 (F1 + 2), thrombin-antithrombin III complexes (TAT), fibrinopeptide A (FPA; this peptide was measured in spot urine also), and D-dimers were measured. Before exercise, the concentrations of F1 + 2 (1.0 +/- 0.6 versus 0.7 +/- 0.3 nmol/L), TAT (2.9 +/- 2.1 versus 1.9 +/- 0.8 micrograms/L), and D-dimers (318.2 +/- 270.1 versus 150.0 +/- 91.4 micrograms/L) were significantly higher in the patients with PAD compared with the healthy control subjects. FPA concentrations in plasma (1.9 +/- 1.0 versus 1.4 +/- 0.6 micrograms/L) and spot urine were not different, however. F1 + 2, FPA, and D-dimer concentrations correlated with the severity of the PAD as assessed by the ankle systolic blood pressure index (ABPI). The symptom-limited stress test did not lead to further activation of the blood coagulation cascade. However, concentrations of F1 + 2 (P < .001) and TAT (P < .01) after exercise correlated with the presence of ischemic changes in the stress-test ECG.

CONCLUSIONS

There is evidence of enhanced thrombin formation in patients with PAD compared with an age- and sex-matched control group without clinical and sonographic evidence of arteriosclerosis. The thrombin formed, however, appears to be almost completely neutralized by antithrombin III. No direct evidence of fibrin formation was obtained, since the FPA concentrations were not different. In the patients with PAD, the higher concentrations of D-dimers are indicative of in vivo fibrinolysis. Thus, some fibrin formation must be postulated to occur in patients with arteriosclerosis.

Lipid composition of platelets in patients with non-insulin-dependent diabetes mellitus: studies before and after treatment of diabetes

The study was designed to investigate whether impaired composition of platelet lipids in untreated diabetic patients improved after diabetic treatment. Fourteen untreated patients with non-insulin-dependent diabetes mellitus (NIDDM) and 15 healthy control subjects were studied. In the diabetic patients, the ratio of free cholesterol to phospholipid (FC/PL) in platelets of 0.33 +/- 0.02 (mean +/- SEM) at pre-treatment, which was statistically (p < 0.05) higher than that of 0.26 +/- 0.02 in control subjects, was significantly decreased to the value of 0.29 +/- 0.02 (p < 0.01) after insulin therapy. Platelet FC level of 9.77 +/- 0.77 micrograms 10(-8) cells pre-treatment was significantly (p < 0.01) reduced to the value of 7.72 +/- 0.38 micrograms 10(-8) cells post-treatment. Platelet PL level showed no significant changes after the treatment. There was a significantly (p < 0.01) positive correlation between the decrease in FC/PL of platelets and that in haemoglobin A1c (HbA1c) after treatment for diabetes (rs = -0.729). These results indicate that the impaired lipid composition in platelets can be improved after an adequate glycaemic control in patients with NIDDM.

Investigations into the haemorheological significance of postprandial and fasting hypertriglyceridaemia

Two study designs were conceived to evaluate the rheological significance of hypertriglyceridaemia. We first investigated the course of serum- (SV) and plasma viscosity (PV) and erythrocyte aggregation in serum (SEA) and plasma (PEA) of healthy normolipidaemic individuals over 4 h after a fatty rich meal, in native material and after removal of triglyceride rich lipoproteins by centrifugation. Secondly, blood from patients with untreated hypertriglyceridaemia was investigated under fasting conditions. PEA and SEA increased in parallel with postprandial triglycerides (+135 mg dl-1), but the effect on PEA was more pronounced (+0.8 abs% increase; 2 h after the meal) as compared to SEA (+0.4 abs% increase). PV and SV increased in parallel to the same extent (+0.05 mPas). In the triglyceride poor infranatant no significant changes occurred. In fasting plasma PEA and PV were significantly lower (1.1 abs% and PV 0.04 mPas respectively) in infranatant than in native plasma, while only small differences in triglyceride (mostly VLDL) were observed. This phenomenon was barely detectable in serum samples. We conclude that triglyceride rich lipoproteins have a profound influence on haemorheological parameters, and that fibrinogen in particular, potentiates the effect of large fasting VLDL on plasma viscosity and erythrocyte aggregation.

Serum lipids and apolipoprotein concentrations and plasma fibronectin concentrations in renal transplant patients

In those cases where hypertriglyceridaemia was present before renal transplantation, it persisted after transplantation, and hypercholesterolaemia also developed. We studied serum lipid, lipoprotein, and apolipoprotein concentrations and plasma fibronectin concentrations in 57 renal transplantation patients and 29 healthy controls. We concluded that atherosclerosis in renal transplantation patients might be related to alterations in the constitutions of lipoproteins and apolipoproteins, but fibronectin synthesized by vascular endothelial cells seemed not to be associated with the atherosclerotic process.

Substrate-bound fibrinogen, fibrin and other cell attachment-promoting proteins as a scaffold for cultured vascular smooth muscle cells

We have previously reported that fibrinogen/fibrin can induce the migration of vascular smooth muscle cells in vitro. In this study, we examined the effect of substrate-bound fibrinogen/fibrin and other cell attachment-promoting proteins on the adhesion of vascular smooth muscle cells. The amount of fibrinogen/fibrin adsorbed to plastic wells and the adhesion of smooth muscle cells to the wells were found to depend on the concentration of fibrinogen used for coating the wells. The effect of fibrinogen/fibrin was comparable to that of so-called cell attachment-promoting proteins (fibronectin, vitronectin, and type I collagen). Adhesion of smooth muscle cells to fibrinogen/fibrin-coated wells was inhibited by the synthetic peptide GRGDS, but not by a control peptide, GRGES. Vitronectin, fibronectin, type I collagen, denatured type I collagen and commercial gelatin also induced smooth muscle cell adhesion. The adhesion induced by vitronectin, denatured type I collagen, and commercial gelatin was inhibited by GRGDS. However, the adhesion induced by type I collagen was not influenced and that induced by fibronectin was only slightly inhibited. These observations suggest that fibrinogen/fibrin deposited extracellularly in the arterial intima may act as a scaffold in the process of smooth muscle cell migration.

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.

Polyunsaturates, endogenous eicosanoids, and cardiovascular disease

The role of dietary polyunsaturated fats in the prevention of human vascular disease has not been defined, but population and intervention studies have suggested that omega-3 fatty acids (FAs) from marine lipids may have a number of potentially beneficial effects. Eicosanoids are extremely potent autacoids made from polyunsaturated fatty acids and have effects on many vascular parameters, so that the physiological effects of dietary supplementation with polyunsaturated fats are often attributed to alterations in endogenous eicosanoid production. Few studies have attempted to correlate in vivo eicosanoid synthesis and functional effects during such dietary maneuvers, however. This article reviews the relationship between dietary polyunsaturates and endogenous eicosanoid synthesis in man, with particular emphasis on recent studies of the effects of omega-3 FAs. Data on omega-3 FAs and platelet-vascular interactions, blood pressure, and vascular reactivity in human subjects are also summarized, with interpretation of recent work addressing a number of controversial points. A discussion of the significance and future direction of such investigations concludes that further clinical trials in selected patient groups are warranted.

Effects of fibrinogen and fibrin on the migration of vascular smooth muscle cells in vitro

The migration of vascular smooth muscle cells from the media into the intima and their proliferation in the intima play an important role in the pathogenesis of atherosclerosis. We examined the effects of fibrinogen and fibrin on the migration of cultured bovine aortic smooth muscle cells using a modified Boyden chamber assay. The cells migrated to a gradient of soluble fibrinogen. Checkerboard analysis indicated that the effect was largely directional in nature (chemotaxis). The cells also migrated in a dose-dependent manner to a gradient of substrate-bound fibrinogen (haptotaxis). Fibrin, converted from substrate-bound fibrinogen by thrombin, also induced haptotaxis of smooth muscle cells. These observations suggest that, by recruiting smooth muscle cells from the media into the intima, fibrinogen and fibrin may be involved in the pathogenesis of arterial intimal thickening, atherosclerosis, and the organization of a thrombus.

Fate of fibrinogen in human arterial intima

Fibrinogen and fibrinogen/fibrin-related antigen (total FRA) was measured in human normal intima and different types of atherosclerotic lesions and mural thrombi. The amount showed marked variation between groups of tissue samples, but within each group there was a significant correlation between levels of total FRA and low density lipoprotein (LDL), suggesting that some common factor must influence their influx or retention. The total FRA were analyzed by gradient sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting with antisera to whole fibrinogen and fragments D and E, and fibrinopeptide A (FPA). All intimal samples (but not thrombi) contained fragment X, the first product of plasmin digestion of fibrinogen, but fragment Y was present in only half the samples, and no core-fragment E containing FPA was detected in any sample, suggesting that fibrinogenolysis is limited. By contrast, all samples contained fragment E, which was negative for FPA, so presumably derived from fibrin; they also contained fragments D-dimer and DY, which are characteristic degradation products of cross-linked fibrin. There were no differences between samples obtained during reconstructive vascular surgery and samples obtained at autopsy, so the patterns appear to represent the steady state. This implies that within the intima there is continuous formation of cross-linked fibrin and continuous fibrinolysis, both processes generating fragments that may have atherogenic properties.

The arterial supply of the navicular bone in adult horses with navicular disease

A macroscopical, arteriographical and histological study was made of the arterial supply of the navicular bones of horses with clinical and/or radiographic signs of navicular disease. Based on the clinical and radiological findings the navicular bones of 40 Warmblood horses are divided into four different groups. In the pattern of the arteriogram obvious changes are noticed: an imbalance and a distal to proximal shift between the distal and proximal arterial supply occur, indicating a reduction of the distal blood supply with a compensatory reaction of the proximal, medial and lateral supply. The changes in the pattern of the arteriogram are histologically defined by arterio(lo) sclerosis and newly formed arteries. The presence of radiologically visible nutrient foramina is associated with a changed pattern in the arteriogram, increased bone remodelling and fibrosis. Ischaemia and increased pressure (hypertension and/or increased intra-articular pressure) are considered to be responsible for changes in form and number of radiologically visible nutrient foramina.

Fibrinogen is chemotactic for vascular smooth muscle cells

We studied the effect of fibrinogen on the migration of bovine aortic smooth muscle cells in culture, using a Neuro Probe 48-well micro chemotaxis chamber. Fibrinogen stimulated the migration of the cells dose-dependently at concentrations from 30 to 1000 micrograms/ml. A modified checkerboard analysis of the response demonstrated that the effect was largely chemotactic in nature. The present results suggest that fibrinogen may play an important role in the pathogenesis of arterial intimal thickening and atherosclerosis.

Molecular cardiology: new avenues for the diagnosis and treatment of cardiovascular disease

This review summarizes some of the major advances in the investigation of molecular mechanisms underlying both normal and abnormal cardiovascular function. Four major areas are highlighted including cardiac muscle, the blood vessel, atherosclerosis and thrombosis/thrombolysis. The remarkable strides in understanding multifactorial diseases such as atherosclerosis, and the development of innovative new therapies such as the use of thrombolytic agents produced by recombinant deoxyribonucleic acid (DNA) technology, are noted. Moreover, it is concluded that the past decade of basic research has provided a solid framework for improvements in the diagnosis and therapy of other forms of cardiovascular disease as well. An evaluation of current trends in basic cardiovascular research suggests that diagnostic and therapeutic approaches to disease will increasingly target specific molecular processes underlying the pathophysiologic state.

Relationship between sex hormones and haemostatic factors in healthy middle-aged men

Associations of plasma testosterone and estradiol with some haemostatic factors (factor VII activity, fibrinogen, antithrombin III and alpha 2-antiplasmin) were cross-sectionally examined in 251 healthy, middle-aged men participating in the Paris Prospective Study II on risk factors for ischaemic heart disease. Testosterone levels were negatively correlated to factor VII activity and alpha 2-antiplasmin, the main inhibitor of fibrinolysis. No association was found either between testosterone levels and both fibrinogen and antithrombin III, or between estradiol levels and the set of haemostatic variables. The associations between testosterone and both factor VIIc and alpha 2-antiplasmin were independent of HDL-cholesterol, LDL-cholesterol, triglycerides, smoking, alcohol, body mass index and blood pressure. These results suggest that low circulating testosterone levels might be associated with a hypercoagulability state and therefore could contribute to an increased risk of IHD.

Atherosclerosis and coronary bypass surgery in hereditary factor VII deficiency

A 66-year-old man with homozygous deficiency of factor VII (less activity than 4 percent of normal) had a minimal hemorrhagic tendency and severe coronary atherosclerosis, and underwent aortocoronary saphenous vein bypass surgery. Although plasma factor VII coagulant activity and cross-reacting material were markedly reduced, comparable amounts of factor VII antigen were detected in peripheral blood mononuclear cells of both the patient and of a normal subject by Western blotting techniques. Accelerated coagulation was observed following brief exposure of the patient's phytohemagglutinin-stimulated peripheral blood mononuclear cells to low concentrations of ambient factor VII in vitro. Evidence indicates that factor VII plays a role in vivo in both hemostasis and atherogenesis and it might be assumed that factor VII deficiency would both predispose to excessive bleeding and forestall atherosclerosis. However, these observations suggest that factor VII-mediated thrombin generation may proceed by partitioning of small amounts of factor VII on tissue factor-expressing cells and that factor VII contained within monocytes may facilitate tissue factor-induced coagulation by these cells. These features may provide efficient coagulation activation despite a deficiency of the plasma coagulant protein. The current results may explain, at least in part, the minimal bleeding tendency, and also the occurrence of thrombosis and atherosclerosis in certain persons with factor VII deficiency.

Dietary supplementation with omega-3 polyunsaturated fatty acids in patients with stable coronary heart disease. Effects on indices of platelet and neutrophil function and exercise performance

It has been suggested that omega-3 polyunsaturated fatty acids (PUFAs) may alter the course of coronary artery disease by influencing platelet and neutrophil function, arachidonic acid metabolism, and circulating lipid concentrations. To examine this hypothesis, placebo or omega-3 PUFAs as Max-EPA (equivalent to 3.2 g of eicosapentaenoic acid and 2.2 g of docosahexaenoic acid daily) was administered to eight patients with stable coronary artery disease and positive exercise stress test results in a randomized, double-blind, crossover fashion over a 12-week period. With Max-EPA administration, platelet aggregation threshold to epinephrine was increased in only two patients, but neutrophil aggregation and chemotaxic functions decreased consistently (both p less than or equal to 0.01 compared with preceding placebo phase) in all eight. Serum and platelet-rich plasma thromboxane B2 concentrations decreased 40 percent and 28 percent, respectively (both p less than or equal to 0.05). Neutrophil leukotriene B4 formation decreased 23 percent (p less than or equal to 0.01) and synthesis of leukotriene B5 became apparent in all subjects. Serum triglyceride concentrations fell 52 percent (p less than or equal to 0.05) without significant change in total cholesterol, high-density lipoprotein-cholesterol, or low-density lipoprotein-cholesterol concentrations. Systolic blood pressure and the double product (heart rate X systolic blood pressure) were lower (p less than or equal to 0.05) at the end of the Max-EPA phase than in the preceding placebo phase. Heart rate, systolic blood pressure, and the double product were also lower (p less than or equal to 0.05) at three as well as at six minutes of an exercise stress test, indicating a significant reduction in myocardial oxygen demand. Despite these alterations in platelet and neutrophil function, arachidonic acid metabolism, serum triglyceride concentrations, and myocardial oxygen demand, there were no significant changes in subjective parameters of coronary artery disease during the Max-EPA phase (angina frequency 3.7 versus 2.8 episodes per week, nitroglycerin consumption 3.0 versus 1.9 tablets per week, both p = NS). Similarly, exercise times to ST-segment depression (6.5 versus 4.1 minutes) and to onset of angina (5.4 versus 5.0 minutes) were not altered by administration of Max-EPA. Thus, short-term dietary supplementation with omega-3 PUFAs to patients with stable coronary artery disease does not appear to alter subjective or objective parameters of myocardial ischemia.

Alterations in hemostatic parameters during hemodialysis with dialyzers of different membrane composition and flow design. Platelet activation and factor VIII-related von Willebrand factor during hemodialysis

The effect of dialyzer membrane and design on hemostatic parameters during hemodialysis were evaluated in a prospective controlled study. This study demonstrated that hemodialysis is associated with significant platelet activation and loss, which are influenced by both dialyzer configuration and membrane composition. In addition, use of the cuprophan membrane is associated with greater perturbations of the vascular endothelium, as reflected in changes in factor VIII-related von Willebrand factor and 6-keto-prostaglandin F1 alpha concentrations not seen with the polyacrylonitrile membrane. Of the dialyzers studied, the polyacrylonitrile membrane in a hollow-fiber configuration appears to minimize platelet loss and activation, and to minimize increases in factor VIII-related von Willebrand factor and 6-keto-prostaglandin F1 alpha.

Thrombosis and atherosclerosis: regulatory role of interactions among blood components and endothelium

Complex interactions among constituents of blood and components of the vessel wall are involved in the pathogenesis of atherosclerosis and its subsequent thrombotic complications. Alterations in the endothelium are central both to the slowly progressive process of atherogenesis and to the acute events leading to thrombotic occlusion. Recent data, obtained by systematic evaluation of chronologic events that occur in diet-induced atherosclerosis, have extended our understanding of interactive processes among endothelium, monocytes, platelets, vascular smooth muscle cells, and humoral hemostatic elements in atherogenesis.

Influence of dietary fats on blood coagulation and prostaglandin production in the common marmoset

Common marmosets were fed a standard marmoset diet (REF) or diets supplemented with 12% (wt/wt) sunflower seed oil (SSO) or sheep fat (SF) for a period of 90 weeks. The values for coagulation indices, clotting time, and Russel viper venom time were consistent with decreased thrombotic tendency of platelets from animals on the SSO diet relative to the low fat, REF diet animals, while an increased tendency to thrombosis was observed with SF-fed marmosets. The SSO- and SF-supplemented marmosets showed a significantly reduced thromboxane (TXB2) generation from platelets aggregating to collagen (ASC) relative to the REF group, while at 50 micrograms/ml ASC this difference was maintained only by the SSO group. The SF diet-fed marmosets showed a reduced prostacyclin (measured as 6-keto-PGF1 alpha) generation from incubated aorta relative to the REF or SSO-fed groups, which were not different from each other. A reduced proportion of platelet phospholipid arachidonic acid (20:4, n-6) and increased alpha-tocopherol concentration was consistent with the decreased aggregability and thromboxane generation of platelets from SSO-fed marmosets relative to the REF and SF groups. The SF diet-fed marmosets, on the other hand, showed minimal change in arachidonic acid, alpha-tocopherol or platelet reactivity from the REF group. These differing responses to dietary fats are discussed in relation to the potential for the development of thrombosis and atherosclerosis.

Eicosanoid effects on cell proliferation in vitro: relevance to atherosclerosis

Several eicosanoids were tested for ability to inhibit proliferation of cells in culture. In rabbit aortic smooth muscle cells and mouse B16BL6 melanoma cells, order of potency was: 12-HETE greater than PGJ2 greater than PGA1 greater than or equal to PGE1 greater than PGE2 greater than or equal to PGD2 greater than or equal to PGA2. PGB1 was active in smooth muscle cells (greater than PGD2) but not in B16 cells. 5-HETE and Leukotriene B4 were weakly active in smooth muscle cells, and PGB2, PGF2 alpha and TXB2 were inactive in both cells types. In Swiss albino mouse 3T3 fibroblasts, PGJ2 and PGE1 showed much lower relative potency than in the other two cell lines, although the profile was otherwise similar. These findings may be relevant to the anti-atherosclerotic (and perhaps anti-tumor activity) of some eicosanoids.

Cardiac and vascular imaging with labeled platelets and leukocytes

The contribution of platelets in atherosclerosis and thrombosis in animal models and in clinical studies has been quantified with 111In-platelet scintigraphy. New in vitro quantitative techniques have been developed using 111In-labeled platelets to determine the number of adherent platelets on deendothelialized surfaces of damaged vessel walls and synthetic vascular grafts. In vivo imaging techniques are semi-quantitative in nature; in these studies 111In radioactivity on thrombotic vessels or graft surfaces of iliac, femoral, or popliteal arteries is compared with contralateral vessels. Background 111In radioactivity in the circulating blood pool of venous and capillary networks and radioactivity in marrow decreases the sensitivity of these techniques. Despite these limitations, the dynamic process of platelet deposition in most of the denuded, atherosclerotic vessels and prostheses in the circulatory system can be recorded. This ongoing thrombosis and embolization has been observed in 5-10-year-old vascular grafts of Teflon and Dacron biomaterials. Currently used platelet function inhibitor drugs, eg, aspirin, Persantine, sulfinpyrazone, and Motrin, have a demonstrable effect on platelet deposition. Slight changes in reduction of platelet deposition on these surfaces due to medical intervention have been observed by noninvasive imaging with 111In-platelets. Subtraction of blood pool radioactivity with 99mTc-labeled autologous red cells and calculation of 111In radioactivity associated with platelet thrombus on vessel walls also have been performed for coronary, carotid, and femoral arteries. Although platelet concentrates are used frequently after open heart surgery (one to six per patient), consumption of platelets in the artificial lung or oxygenator, lysis of platelets during pumping, and suction of blood only recently have been quantified with the use of 111In-labeled platelets. These studies also demonstrated far less trauma to platelets with the use of a membrane rather than a bubble oxygenator. Further reduction in platelet consumption and trauma was observed with the use of prostacyclin, a short-acting drug with significant beneficial effect on platelet thrombus reduction and disaggregation of aggregated platelets. The role of polymorphonuclear leukocytes in inflammation, infection and myocardial infarction, and in vivo evaluation with 111In-leukocyte scintigraphy in animals and humans has been described.(ABSTRACT TRUNCATED AT 400 WORDS)

Role of plasma, platelets, and endothelial cells in tumor metastasis

This review studies interactions of tumor cells with a particular host system which is normally responsible for hemostasis and the physiological integrity of the blood vessel luminal surface. With malignancy components of this system are frequently activated, producing abnormalities of blood coagulation, increased platelet responses, and conditions favoring tumor growth and metastasis. Activation of the clotting cascade is mediated by tumor and macrophage procoagulants, acting via Factor X or VII. Thrombin and fibrin are formed. Thrombin also interacts with platelets and the endothelium, potentiating or decreasing coagulation. Generation of thrombin or other tumor mechanisms activate platelets, leading to direct aggregation or secretion of ADP, serotonin, and/or intermediates of the arachidonate metabolism. Vascular lesions caused by tumor attack, platelet secretion, or exogenous agents promoting metastasis may also activate the hemostatic system. It is not yet fully understood how activation of the clotting system, including platelets, contributes to metastasis. Secretion of platelet products appears, however, to be heavily involved. Based on putative mechanisms of action, anticoagulants, platelet inhibitors, thrombocytopenic or vascular repairing agents have been used to control tumor spread. Results depended on the agent and experimental model of metastasis used. Except for coumarin, which was beneficial even against spontaneous metastases, other anticoagulants and platelet inhibitors, excluding perhaps Nafazatrom, gave equivocal results. Thrombocytopenic agents, however, were effective in every tumor system and with any experimental model of metastasis, indicating that platelets play a role in this process. Also consistent were the inhibitory effects of leech salivary gland extract (probably a vascular repairing agent) against lung tumor colonization promoted by ionizing radiation, cyclophosphamide, and cortisone.