Plasminogen activator inhibitor type-1 synthesis and mRNA expression in HepG2 cells are regulated by VLDL

Hypertriglyceridemia: A Neglected Risk Factor for Ischemic Stroke?

Hypertriglyceridemia is caused by defects in triglyceride metabolism and generally manifests as abnormally high plasma triglyceride levels. Although the role of hypertriglyceridemia may not draw as much attention as that of plasma cholesterol in stroke, plasma triglycerides, especially nonfasting triglycerides, are thought to be correlated with the risk of ischemic stroke. Hypertriglyceridemia may increase the risk of ischemic stroke by promoting atherosclerosis and thrombosis and increasing blood viscosity. Moreover, hypertriglyceridemia may have some protective effects in patients who have already suffered a stroke via unclear mechanisms. Therefore, further studies are needed to elucidate the role of hypertriglyceridemia in the development and prognosis of ischemic stroke.

An investigation into the pleiotropic activity of metformin. A glimpse of haemostasis

The most characteristic features of type 2 diabetes mellitus (T2DM) are hyperglycaemia and insulin resistance, however, patients with T2DM are at higher risk of cardiovascular disease (CVD) and atherosclerosis. Diabetes, frequently related to metabolic and vascular impairments, is also associated with thrombosis, increased blood coagulation and an imbalance between coagulation and fibrinolysis. Metformin is the most often used oral glucose-lowering agent; its beneficial properties include lowering insulin resistance, weight reduction and cardioprotection. Available data suggest that the advantageous properties of metformin stem from its favourable effects on endothelium, and anti-oxidative and anti-inflammatory properties. This paper reviews the favourable impact of metformin on endothelial function, with particular emphasis on the release of endogenous molecules modulating the state of the vascular endothelium and coagulation. It also summarizes the present knowledge on the influence of metformin on platelet activity and plasma haemostasis, including clot formation, stabilization and fibrinolysis. Its findings confirm that metformin should constitute first line therapy of T2DM subjects; however, more comprehensive methodical studies are required to discover the full potential of this drug.

Triglyceride concentration and waist circumference influence alcohol-related plasminogen activator inhibitor-1 activity increase in black South Africans

We investigated the association between alcohol consumption and plasminogen activator inhibitor-1 activity (PAI-1act) and fibrinogen concentration in a black South African population presenting with lower PAI-1act and higher fibrinogen than what is typically observed in white populations. We, furthermore, wanted to investigate the effect of urbanization, sex, central obesity, increased triglycerides, 4G/5G polymorphism (PAI-1 only) and BMI on the association of alcohol with PAI-1act and fibrinogen. Data from 2010 apparently healthy, randomly collected black South African volunteers from the Prospective Urban and Rural Epidemiological (PURE) study were cross-sectionally analyzed. Alcohol consumption was recorded using quantitative food frequency questionnaires and fasting blood samples were collected for biochemical analysis including PAI-1act and fibrinogen. Heavy alcohol consumption is associated with significantly increased PAI-1act, in the total population as well as in the women separately, and tended to be so in men. This alcohol-related PAI-1act increase was observed in volunteers with increased triglycerides and central obesity but not in volunteers with normal levels and waist circumference. Urbanization, the 4G/5G polymorphism and BMI did not affect the association of alcohol with PAI-1act. Moderate alcohol consumption is associated with decreased fibrinogen concentration. Sex and level of urbanization did not affect the association of alcohol with fibrinogen. Fibrinogen decreased in normal and overweight volunteers but not in obese and centrally obese volunteers following moderate alcohol consumption. Triglyceride levels and waist circumference influence alcohol-related PAI-1act increase potentially through modulating adipocyte and triglyceride-induced PAI-1 production. Obesity prevented alcohol-related fibrinogen decrease possibly by counteracting the anti-inflammatory effect of moderate alcohol consumption.

Effects of high glucose and ketosis (acetoacetate, ss-hydroxybutyrate) on PAI-1 secretion in human umbilical vascular endothelial cells

Plasminogen activator inhibitor 1 (PAI-1) is a known contributor of thrombus formation and cardiovascular diseases. Type 1 diabetes is associated with elevated levels of blood PAI-1 and cardiovascular disease (CVD) incidence. However, type 1 diabetic patients have elevated blood levels of ketone bodies acetoacetate (AA) and 3-β-hydroxybutyrate (BHB). This study examined the hypothesis that hyperketonemia (ketosis) contributes to increased secretion of PAI-1 from the cells that form the vascular endothelium. Human umbilical vein endothelial cells (HUVEC) were treated with different concentrations of AA or BHB in the presence or absence of high glucose (HG) and the amount of PAI-1 protein secreted by these cells into conditioned media was determined. Levels of PAI-1 secreted into conditioned media by these treated cells did not change significantly when compared to controls. High glucose induced a significant increase in PAI-1 secretion, but combination with AA or BHB did not cause significant effects on PAI-1 secretion caused by HG. These results indicate that hyperglycemia but not hyperketonemia is a significant contributor to increased blood levels of PAI-1 associated with type 1 diabetes.

Intake of phenol-rich virgin olive oil improves the postprandial prothrombotic profile in hypercholesterolemic patients

BACKGROUND

Oxidative stress associated with postprandial lipemia contributes to endothelial dysfunction, which shifts hemostasis to a more thrombogenic state.

OBJECTIVE

We investigated whether a high concentration of phenols in olive oil can partly reverse this phenomenon.

DESIGN

Twenty-one hypercholesterolemic volunteers received 2 breakfasts rich in olive oils with different phenolic contents (80 or 400 ppm) according to a randomized, sequential crossover design. Plasma concentrations of lipid fractions, factor VII antigen (FVIIag), activated factor VII (FVIIa), and plasminogen activator inhibitor-1 (PAI-1) activity were measured at baseline and postprandially.

RESULTS

Concentrations of FVIIa increased less (P = 0.018) and plasma PAI-1 activity decreased more (P = 0.021) 2 h after the high-phenol meal than after the low-phenol meal. FVIIa concentrations 120 min after intake of the olive oil with a high phenol content correlated positively with fasting plasma triacylglycerols (P = 0.001), area under the curve (AUC) of triacylglycerols (P = 0.001), and AUC of nonesterified fatty acids (P = 0.024) and negatively with hydroxytyrosol plasma concentrations at 60 min (P = 0.039) and fasting HDL-cholesterol concentrations (P = 0.005). PAI-1 positively correlated with homeostasis model assessment of insulin resistance (P = 0.005) and fasting triacylglycerols (P = 0.025) and inversely with adiponectin (P = 0.026). In a multivariate analysis, the AUCs of nonesterified fatty acids (R(2) = 0.467; beta: 0.787; SE: 0.02; P < 0.001) and adiponectin (R(2) = 0.232; beta: -1.594; SE: 0.629; P < 0.05) were the strongest predictors of plasma FVIIa and PAI-1, respectively.

CONCLUSIONS

A virgin olive oil with a high content of phenolic compounds changes the postprandial hemostatic profile to a less thrombogenic state.

Hemostatic response to postprandial lipemia before and after exercise training

Chronic hypertriglyceridemia is thought to be atherogenic and is associated with an elevated thrombotic potential, both of which may be improved with aerobic exercise training. Eight subjects were tested for aerobic capacity, body composition, and postprandial lipemia (PPL), followed by 6 mo of exercise training and final testing. Blood samples were obtained for measurement of free fatty acid (FFA), triglycerides (TG), insulin (Ins), and glucose (Glu). Hemostatic variables including factor VII activity (FVIIa), tissue factor pathway inhibitor-factor Xa complex (TFPI/Xa), and plasminogen activator inhibitor-1 (PAI-1) antigen/activity as well as leukocyte tumor necrosis factor-alpha (TNF-alpha) gene expression were determined among four subjects. We found that the exercise training was of sufficient intensity to increase aerobic capacity (P < 0.0001) and improve body composition (P = 0.04). There were no differences between tests among PPL responses of FFA, TG, Ins, or Glu; however, the mean TG response and fat oxidation rate improved. PAI-1 antigen/activity, FVIIa, TFPI/Xa, and TNF-alpha gene expression were all improved after exercise training after adjusting for confounders. We conclude that aerobic exercise training reduces the potential for coagulation, improves fibrinolytic potential, and reduces leukocyte TNF-alpha gene expression after the ingestion of a high-fat meal.

PAI-1 and atherothrombosis

Plasminogen activator inhibitor-1 (PAI-1) is the major physiologic inhibitor of tissue-type plasminogen activator in plasma, and is elevated in a variety of clinical situations that are associated with increased risk of ischemic cardiovascular events. Recent insights into the biology of PAI-1 suggest that it is more than just an innocent bystander in the pathogenesis of ischemic heart disease. Elevated PAI-1 levels appear to increase the risk of atherothrombotic events and may also promote the progression of vascular disease. The development and testing of specific PAI-1 antagonists will enable basic and clinical investigators the opportunity to test the hypothesis that vascular PAI-1 excess promotes the development of intravascular thrombosis and atherosclerosis.

Oxidised-HDL3 induces the expression of PAI-1 in human endothelial cells. Role of p38MAPK activation and mRNA stabilization

Modified lipoproteins have been suggested to modulate endothelial expression of plasminogen activator inhibitor-1 (PAI-1). As oxidized high-density lipoprotein (Ox-HDL) has been found in atheromatous plaques and receptors for modified HDL are present on endothelial cells, we investigated the role of Ox-HDL3 on the expression of PAI-1. Ox-HDL3 but not native HDL3, increased PAI-1 mRNA expression in endothelial cells. Furthermore, PAI-1 antigen expression and activity increased in the supernatant of cells incubated with Ox-HDL3. The intracellular pathways involved in this effect were investigated. Ox-HDL3 activated both extracellular signal-regulated kinases (ERK) 1/2 and p38 mitogen-activated protein kinase (MAPK). Moreover, incubation with specific inhibitors of these kinases showed that p38MAPK was mainly involved in the Ox-HDL3-dependent PAI-1 induction. Transient transfection experiments suggested that none of the response elements in the proximal promoter (-804 to 17) were involved in Ox-HDL3-mediated PAI-1 expression. mRNA stability experiments showed that Ox-HDL3 increased the PAI-1 mRNA half-life. In summary, Ox-HDL3 induced PAI-1 mRNA expression and antigen release through a molecular mechanism involving MAPK activation and mRNA stabilization. Thus, oxidative modification converts HDL to a prothrombotic lipoprotein species.

Association of plasminogen activator inhibitor-1 4G/5G gene polymorphism with variations in the LDL particle size in healthy Japanese men

BACKGROUND

Several studies have supported the association between a predominance of small, dense low-density lipoprotein (LDL) and the risk of coronary artery disease. As another potentially atherogenic factor, impaired fibrinolytic activity due to increased plasminogen activator inhibitor-1 (PAI-1) concentrations has been shown. In addition, the 4G allele of the 4G/5G polymorphism in the promoter region of the PAI-1 gene is reported to be associated with the atherogenic lipid profile. We investigated the relation between the PAI-1 gene polymorphism and LDL particle size.

METHODS

A total of 156 healthy Japanese male subjects were recruited. The diameter of LDL particles was determined at their peak size using polyacrylamide gels using fresh plasma samples.

RESULTS

Fasting insulin and triglyceride concentrations were found to be significantly higher, and the LDL particle size was smaller in the homozygotes for the 5G allele than in the carriers of the 4G allele. An analysis of covariance (ANCOVA) adjusting for insulin and triglyceride concentrations showed a consistently significant difference in LDL particle size between the two groups. In the forward stepwise multiple regression analysis, triglycerides, insulin, and the PAI-1 5G/5G genotype remained in the model as independent and significant predictors capable of influencing the LDL particle size.

CONCLUSIONS

Our findings suggest that the 4G/5G polymorphism of the PAI-1 gene might be associated with LDL particle size in healthy Japanese males.

Metabolic syndrome: an appraisal of the pro-inflammatory and procoagulant status

Inflammation and hypercoagulability predispose to atherothrombosis and seem to be important features of the metabolic syndrome. The most convincing evidence is the association with increased levels of C-reactive protein. The hemostatic abnormality that has been most consistently associated with insulin resistance is an elevated plasminogen activator inhibitor-1 level. In contrast, markers of hypercoagulability have been associated inconsistently with hyperinsulinemia and glucose intolerance. Fibrinogen clusters with inflammatory factors, which suggests involvement of adipose tissue-generated inflammatory cytokines. Elevated von Willebrand's factor and factor VIII levels aggregate with indicators of endothelial injury,whereas vitamin K-dependent coagulation proteins correlate with triglyceride levels.

Effect of plasminogen activator inhibitor-1 in diabetes mellitus and cardiovascular disease

Concentrations of plasminogen activator inhibitor-1 (PAI-1) are elevated beginning at the stage of impaired glucose tolerance and continuing through the development of diabetes mellitus and the metabolic syndrome. Evolving evidence of the central role of PAI-1 in mediating fibrosis and thrombosis increasingly supports the theory that it is a significant risk factor for macrovascular complications and cardiovascular disease, particularly in patients with diabetes. Several clinical studies have demonstrated a strong correlation between circulating PAI-1 levels and cardiovascular events and mortality. With the potentially severe effects of elevated PAI-1 levels becoming evident, there is increased interest in developing therapies targeted at reducing PAI-1 expression or circulating concentrations. Thus far, weight loss, inhibitors of the renin-angiotensin system, and insulin sensitization through use of thiazolidinediones (TZDs) appear to be the most promising strategies for managing elevated PAI-1 levels. Of these, TZD therapy is the only one that provides the benefits of both long-term glycemic control and improved cardiovascular risk profile. This article reviews the regulation of PAI-1, its activity in various disease states, and available treatment options.

Beneficial effects of metformin on haemostasis and vascular function in man

Type 2 diabetes is characterised by insulin resistance in association with clustering of atherothrombotic risk factors (dysglycaemia, hyperinsulinaemia, hypertension, raised triglyceride, low HDL cholesterol and increased levels of plasminogen activator inhibitor-1 (PAI-1) and clotting factor VII). There is a 3-5 fold increase in risk of myocardial infarction rising to 10-20 fold in the presence of microalbuminuria and overall around 70-75% of subjects with type 2 diabetes die of cardiovascular disease. However, classical risk factors which associate with insulin resistance do not account for all the increased burden of vascular disease in diabetic subjects. Metformin is a biguanide compound which is antihyperglycaemic, reduces insulin resistance and has cardioprotective effects on lipids, thrombosis and blood flow. Metformin has a weight neutral/weight lowering effect and reduces hypertriglyceridaemia, elevated levels of PAI-1, factor VII and C-reactive protein. In addition recent studies indicate that metformin has direct effects on fibrin structure/function and stabilises platelets, two important components of arterial thrombus. The United Kingdom Prospective Diabetes Study (UKPDS) reported that metformin was associated with a 32% reduction in any diabetes related endpoint (p<0.002), a 39% reduction in myocardial infarction (p<0.01) and a non-significant 29% fall in microvascular complications. The figures for macrovascular complications compare favourably for those described for other cardioprotective agents such as ACE inhibitors and statins. These findings confirm metformin as first line therapy in the management of obese insulin resistant type 2 diabetes and in the prevention of the vascular complications of this common condition.

The genetics of atherothrombotic disorders: a clinician's view

The development of coronary artery disease is dependent on the interaction of multiple biochemical pathways that lead to the development of plaque in the arterial wall and ultimately plaque instability, plaque rupture and thrombosis. The latter stages lead to vascular obstruction, tissue death and the final phenotype of myocardial infarction. Hemostasis gene association studies of atherothrombotic disorders have been unrewarding, with largely underpowered studies reporting inconsistent results. Clinical studies such as the Multiple Risk Factor Intervention Trial clearly indicate that clustering of classical risk increases the likelihood of myocardial infarction, and the addition of diabetes mellitus to the risk profile exponentially increases the risk of a vascular event. The development of insulin resistance is considered to be a pivotal event in vascular risk with associated clustering of dysglycemia, hyperinsulinemia, systolic hypertension, raised triglyceride and low high-density lipoprotein cholesterol. Additionally, elevated levels of plasminogen activator inhibitor-1, factor (F)VII, FXII, fibrinogen and tissue plasminogen activator occur with insulin resistance to create an atherothrombotic risk cluster. Heritability studies of insulin resistance and the vascular risk profile demonstrate genetic pleitropy between diabetes and vascular risk, which indicate that common genes have an important role. Increasingly, it is felt that inflammation underpins both diabetes and cardiovascular disease and that the expression of the final phenotype(s) may depend on complex gene-environment interactions with regulatory genes, including those for nuclear transcription factors and RNA-binding proteins. The complexity of coronary artery disease and the risk factor interactions make it unlikely that genetic epidemiology will identify genes involved in these processes without a better understanding of environmental influences.

Minireview: adiposity, inflammation, and atherogenesis

Adipose tissue is a dynamic endocrine organ that secretes a number of factors that are increasingly recognized to contribute to systemic and vascular inflammation. Several of these factors, collectively referred to as adipokines, have now been shown regulate, directly or indirectly, a number of the processes that contribute to the development of atherosclerosis, including hypertension, endothelial dysfunction, insulin resistance, and vascular remodeling. Several adipokines are preferentially expressed in visceral adipose tissue, and the secretion of proinflammatory adipokines is elevated with increasing adiposity. Not surprisingly, approaches that reduce adipose tissue depots, including surgical fat removal, exercise, and reduced caloric intake, improve proinflammatory adipokine levels and reduce the severity of their resultant pathologies. Systemic adipokine levels can also be favorably altered by treatment with several of the existing drug classes used to treat insulin resistance, hypertension, and hypercholesterolemia. Greater understanding of adipokine regulation, however, should result in the design of improved treatment strategies to control disease states associated with increase adiposity, an important outcome in view of the growing worldwide epidemic of obesity.

Plasma fibrinolytic capacity in renal transplant recipients: effect of steroid-free immunosuppression therapy

BACKGROUND

Cardiovascular disease is the most common cause of death among renal transplant recipients (RTRs). Impaired fibrinolytic capacity caused by an increase in plasminogen activator inhibitor type 1 (PAI-1) levels is involved in the onset of atherosclerosis and thrombotic complications. Long-term steroid treatment may induce arterial hypertension and metabolic and prothrombotic changes (including up-regulation of PAI-1 synthesis), which increase the cardiovascular risk. We evaluated plasma fibrinolytic behavior in two groups of RTRs treated with different immunosuppressive regimens.

METHODS

Twenty-seven RTRs were randomized to receive long-term (17 patients) or perioperative short-term (10 patients) steroids in addition to immunosuppression with cyclosporine A plus everolimus (Certican; Novartis, Basel, Switzerland) (7 patients) or FK506 plus mycophenolate mofetil (20 patients). In each patient, fibrinolytic capacity was studied with the 20-min venous occlusion test 1 and 6 months after transplantation. The following were assayed: euglobulin lysis time, tissue-type plasminogen activator antigen, and PAI-1 antigen and activity.

RESULTS

One month after transplantation, a severe impairment of fibrinolytic capacity, mainly caused by an increase in PAI-1 antigen and activity levels, was seen in patients with and without steroid treatment. Six months after transplantation, an improvement in fibrinolytic potential as the result of a decrease in PAI-1 levels was observed only in patients without steroid therapy. None of the steroid-treated patients demonstrated PAI-1 values correlating with body mass index, blood pressure, and metabolic parameters, thus confirming the effect of exogenous factors on PAI-1 expression. Moreover, all patients revealed a slight impairment of stimulated endothelial tissue-type plasminogen activator release, regardless of any steroid treatment, which was probably attributable to calcineurin inhibitor-induced endothelial dysfunction.

CONCLUSIONS

Our study suggests that steroid-free immunosuppression is associated with a better fibrinolytic capacity in RTRs. This finding may contribute toward reducing the risk of cardiovascular events.

Hereditary and acquired defects in the fibrinolytic system associated with thrombosis

The fibrinolytic system plays a pivotal role in the regulation of hemostasis and the prevention of thrombosis. There are no drugs that will increase the plasma fibrinolytic activity for a lasting duration to prevent thrombotic events effectively. Despite the ability of vasoactive agents such as nicotinic acid and metformin to release PA from the vessel wall, this therapeutic effect has not been evaluated adequately. The PAs are short-acting and indicated only for thrombolysis and not for prophylaxis. Future directions are directed at finding, agents that can enhance plasminogen activator release or inhibit PAW-1 activity. As there are multiple factors involved in the pathogenesis of thrombosis, there are a number of conditions in which abnormal fibrinolysis is only a contributory factor. Examples are seen in pregnancy, especially during puerperium, when the thromboembolic risk is at its highest. The levels of inhibitors of fibrinolysis. both PAI-1 and PAI-2, are also at their highest. Another example was seen recently in the antiphospholipid syndrome, where antibodies against Annexin II, a receptor for tPA, were found to be higher than in healthy controls. Thus, a thorough investigation into other hereditary and acquired risk factors for thrombosis is recommended.

Valsartan improves fibrinolytic balance in atherosclerotic rabbits

OBJECTIVES

To examine the long-term effects of the angiotensin type I (AT1) receptor antagonist, valsartan, on fibrinolytic balance, coagulation parameters, endothelial function and structural alterations in atherosclerotic rabbits.

METHODS

Animals were submitted to a 1% cholesterol-enriched diet for 10 weeks. Half of the animals were treated with valsartan (3 or 10 mg/kg per day). Systolic arterial pressure was directly measured in awake rabbits. Tissue plasminogen activator (t-PA) and tissue plasminogen activator inhibitor (PAI-1) activities were measured. Plasma concentrations of cholesterol, D-dimer, factor VIII and fibrinogen, as well as thrombin time, were also determined. Responses to acetylcholine, sodium nitroprusside and angiotensin II were evaluated in aortic rings. Morphometric analysis of aortic segments was also performed to calculate atherosclerotic lesion.

RESULTS

Cholesterol-fed rabbits presented systolic arterial pressure levels comparable to controls. These animals presented aortic atherosclerotic lesions. Treatment with valsartan did not alter plasma cholesterol levels or arterial pressure in any group. Acetylcholine-induced relaxations and D-dimer and t-PA activity were lower (P < 0.05) in atherosclerotic than in normal rabbits. In contrast, PAI-1 activity was higher (P < 0.05) in atherosclerotic rabbits than in controls. Valsartan increased (P < 0.05) acetylcholine-induced relaxations, D-dimer concentration and t-PA activity, and reduced intimal thickening and PAI-1 activity in cholesterol-fed rabbits. Fibrinogen concentrations and factor VIII concentrations were lower (P < 0.05) and thrombin time was higher (P < 0.05) in atherosclerotic rabbits compared to controls. Valsartan did not affect factor VIII in any group, but reduced fibrinogen levels only in hypercholesterolemic rabbits. Valsartan 10 mg/kg per day reduced (P < 0.05) thrombin time in cholesterol-fed rabbits.

CONCLUSIONS

Impairment of fibrinolytic balance, associated with atherosclerosis in rabbits, appears to be related with angiotensin II via AT1receptors. The beneficial effect of valsartan on fibrinolysis seems to be related to the concomitant amelioration of endothelial dysfunction and reduction of intimal thickening, further supporting the importance of the blockade of angiotensin II actions to prevent thrombotic alterations associated with atherosclerosis.

Plasminogen activator inhibitor-1 in girls with precocious pubarche: a premenarcheal marker for polycystic ovary syndrome?

In both obese and nonobese women, polycystic ovary syndrome (PCOS) is essentially a disorder of hyperinsulinemic insulin resistance, and it may be heralded by precocious pubarche (PP; appearance of pubic hair in girls aged <8 y). The risk of progression from PP to PCOS is related to low birth weight, but there are no early biochemical markers of this risk. As increased plasminogen activator-inhibitor type 1 (PAI-1) activity (act) is an early marker of cardiovascular risk in PCOS, we have sought abnormalities in young girls with PP. In 33 young PP girls (age range 6-11 y), PAI-1-act was increased (mean + SEM: 15.6 +/- 1.5 IU/mL) compared with age-, sex-, and pubertal stage-matched controls (n = 13, 10.7 +/- 1.9, p < 0.05). PAI-1-act levels were inversely related to birth weight SD score (r = -0.33, p < 0.05), and PAI-1-act levels were therefore higher in PP girls with low birth weights (n = 14, 19.5 +/- 2.5 IU/mL) than normal birth weights (n = 19, 12.8 +/- 1.5, p < 0.01). During longitudinal observation in 10 PP girls (mean time interval 2.7 y), PAI-1-act levels in early puberty were positively related to postmenarcheal insulin levels (mean serum insulin SDS postoral glucose, r = 0.65, p < 0.05), and showed a similar relationship to postmenarcheal testosterone levels (r = 0.61, p = 0.06). Together with low birth weight, increased plasma PAI-1-act levels in early pubertal PP girls may indicate those girls with greater risk of developing hyperinsulinemic-hyperandrogenism features of PCOS.

Transcriptional regulation of plasminogen activator inhibitor type 1 gene by insulin: insights into the signaling pathway

Impairment of the fibrinolytic system, caused primarily by increases in the plasma levels of plasminogen activator inhibitor (PAI) type 1, are frequently found in diabetes and the insulin-resistance syndrome. Among the factors responsible for the increases of PAI-1, insulin has recently attracted attention. In this study, we analyzed the effects of insulin on PAI-1 biosynthesis in HepG2 cells, paying particular attention to the signaling network evoked by this hormone. Experiments performed in CHO cells overexpressing the insulin receptor indicate that insulin increases PAI-1 gene transcription through interaction with its receptor. By using inhibitors of the different signaling pathways evoked by insulin-receptor binding, it has been shown that the biosynthesis of PAI-1 is due to phosphatidylinositol (PI) 3-kinase activation, followed by protein kinase C and ultimately by mitogen-activated protein (MAP) kinase activation and extracellular signal-regulated kinase 2 phosphorylation. We also showed that this pathway is Ras-independent. Transfection of HepG2 cells with several truncations of the PAI-1 promoter coupled to a CAT gene allowed us to recognize two major response elements located in the regions between -804 and -708 and between -211 and -54. Electrophoretic mobility shift assay identified three binding sites for insulin-induced factors, all colocalized with putative Sp1 binding sites. Using supershifting antibodies, the binding of Sp1 could only be confirmed at the binding site located just upstream from the transcription start site of the PAI-1 promoter. A construct comprising four tandem repeat copies of the -93/-62 region of the PAI-1 promoter linked to CAT was transcriptionally activated in HepG2 cells by insulin. These results outline the central role of MAP kinase activation in the regulation of PAI-1 induced by insulin.

Increased levels of tPA antigen and tPA/PAI-1 complex in myotonic dystrophy

OBJECTIVE

To assess the fibrinolytic system in myotonic dystrophy (DM1), a disease connected to features of the metabolic syndrome, including a prominent insulin resistance, increased body fat mass, and hypertriglyceridaemia. We hypothesized that abnormalities in the fibrinolytic system are linked to metabolic dysfunction in DM1.

DESIGN

Circulating morning levels of tissue plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) antigens, tPA/PAI-1 complex, lipids and insulin were determined. Genetic analyses, including calculation of allele size, were performed in all patients. Body fat mass was estimated with bioelectrical impedance analysis.

SETTING

Out-patient clinic in collaboration with Umeå University Hospital.

SUBJECTS

A total of 42 otherwise healthy patients with DM1 (22 men, 20 women; median age 41.5 years) and 50 controls (27 men, 23 women; median age 42.0 years).

MAIN OUTCOME MEASURES

The tPA and PAI-1 antigens, tPA/PAI-1 complex, blood lipids and body fat mass.

RESULTS

The tPA antigen and tPA/PAI-1 complex levels were significantly increased in DM1 patients (P < 0.001 and P < 0.05, respectively) whilst levels of PAI-1 did not differ from controls. Triglyceride levels were increased (P < 0.001) whereas HDL cholesterol levels were lower in DM1 patients (P < 0.05). Body fat mass was increased in DM1 patients (P < 0.001).

CONCLUSIONS

The fibrinolytic system is disturbed in DM1 patients, with increased levels of tPA and tPA/PAI-1 complex but paradoxically unaltered levels of PAI-1, in spite of a severely increased body fat mass. This may imply an abnormal function of adipose tissue in DM1, and calls for further studies of the fibrinolytic system in this disease.bstra

Changes in hemostasis during treatment of hypertriglyceridemia with a diet rich in monounsaturated and n-3 polyunsaturated fatty acids in comparison with a low-fat diet

High levels of fibrinogen, factor (F) VIIc, plasminogen activator inhibitor-1 (PAI-1), and plasma viscosity are associated with an increased coronary risk. As positive correlations of these parameters with triglycerides have been shown, the increased coronary risk associated with high levels of triglycerides may be assumed to be due to alterations within the hemostatic system. To reduce the coronary risk to which hypertriglyceridemic patients are exposed, dietary treatment is recommended; the optimal composition of such a diet is, however, a matter of debate. With regard to the effects on hemostasis, we compared in a sequential approach two diets for treatment of 25 nonobese male patients (age, mean+/-S.D., 40.4+/-8.7 years) with fasting triglycerides >2.3 mmol/l. The first diet (high fat) was rich in monounsaturated fatty acids (MUFA) and marine n-3 polyunsaturated fatty acids (PUFA), whereas the second diet (low-fat) was rich in complex carbohydrates and dietary fiber. The high-fat diet induced a significant lowering of FIIc, FIXc, FXc, FVIIc, FVIIa, FXIIa, PAI-1, plasma viscosity, and platelet activity, but led to an increase in fibrinogen, whereas the low-fat diet lowered FXIIc values and induced a nonsignificant decrease in fibrinogen. Probands on this diet had a slightly higher FVIIa and platelet activity than those on the high-fat diet. However, as all changes appeared to be within the normal range of each hemostatic parameter, it remains to be clarified whether the likely beneficial effects of the high-fat diet on most hemostatic factors are outweighed by the small increase in fibrinogen levels.

Subcutaneous and visceral adipose tissue: their relation to the metabolic syndrome

Methods for assessment, e.g., anthropometric indicators and imaging techniques, of several phenotypes of human obesity, with special reference to abdominal fat content, have been evaluated. The correlation of fat distribution with age, gender, total body fat, energy balance, adipose tissue lipoprotein lipase and lipolytic activity, adipose tissue receptors, and genetic characteristics are discussed. Several secreted or expressed factors in the adipocyte are evaluated in the context of fat tissue localization. The body fat distribution and the metabolic profile in nonobese and obese individuals is discussed relative to lipolysis, antilypolysis and lipogenesis, insulin sensitivity, and glucose, lipid, and protein metabolism. Finally, the endocrine regulation of abdominal visceral fat in comparison with the adipose tissue localized in other areas is presented.

Subcutaneous adipose tissue expression of plasminogen activator inhibitor-1 (PAI-1) in nondiabetic and Type 2 diabetic subjects

OBJECTIVE

Increased plasma levels of plasminogen activator inhibitor-1 (PAI-1) have been suggested to be a part of the insulin resistance syndrome, and recent data suggest that adipose tissue participates in the production of PAI-1. We examined the expression and insulin regulation of subcutaneous adipose tissue PAI-1 mRNA and its relationship to insulin sensitivity.

DESIGN

A cross-sectional study involving five lean (60.0+/-3.1 years, BMI 23.5+/-0.5 kg/m(2)) and six obese nondiabetic men (56.0+/-3.1 years, BMI 30.4+/-0.7 kg/m(2)), and six obese Type 2 diabetic men (61.4+/-3.2 years, BMI 31.8+/-1.0 kg/m(2)).

MEASUREMENTS

Subcutaneous adipose tissue PAI-1 mRNA and insulin sensitivity were quantified using RT-competitive PCR and euglycemic hyperinsulinemic clamp technique, respectively.

RESULTS

Subcutaneous adipose tissue PAI-1 mRNA levels were higher in obese nondiabetic and Type 2 diabetic men than in lean nondiabetic men. PAI-1 mRNA levels decreased in the three groups during a 240-min euglycemic hyperinsulinemic clamp (P<0.05 for all groups), and a similar reduction was observed during a 240-min saline control study indicating that adipose tissue PAI-1 gene expression has diurnal variation and is not acutely controlled by hyperinsulinemia. The basal PAI-1 mRNA levels correlated positively with BMI, and waist-to-hip ratio; and negatively with whole-body glucose disposal rate in nondiabetic men.

CONCLUSIONS

Subcutaneous adipose tissue PAI-1 mRNA expression is increased in obese nondiabetic or in Type 2 diabetic men. Subcutaneous adipose tissue PAI-1 mRNA expression is increased in proportion to visceral obesity and to the level of whole-body insulin resistance. Subcutaneous adipose tissue PAI-1 mRNA expression is not acutely regulated by insulin, and it is subject to a diurnal variation.

Relationship between lipoprotein(a) phenotypes and plaminogen activator inhibitor type 1 in diabetic patients

It has been demonstrated in vitro that lipoprotein(a) [Lp(a)] increases the endothelial synthesis of plasminogen activator inhibitor 1 (PAI-1). However, this effect in vivo is controversial, and the possible relationship between PAI-1 and Lp(a) phenotypes has not been evaluated. The aim of the study was to determine the influence of Lp(a) and its phenotypes on PAI-1 serum concentrations in diabetic patients. For this purpose we include 75 Caucasian diabetic patients (34 consecutive type I and 41 consecutive type II) without late diabetic complications. Lp(a) and PAI-1 were assessed by ELISA. Lp(a) phenotypes were determined by SDS-PAGE followed by immunoblotting, and grouped according to size in small (F,B,S1,S2), big (S3,S4), and null. A linear correlation between Lp(a) and PAI-1 was not observed either as a whole or when type I and type II diabetic patients were analyzed separately. However, significant differences were detected in PAI-1 levels when Lp(a) phenotypes were considered (small: 42.1+/-31.8 ng/mL; big: 37.2+/-26.1 ng/mL; null: 14.4+/-14.4; p< 0.05). The significant differences were due to the low PAI-1 concentrations observed in patients with null phenotype. Our results suggest that fibrinolytic activity might be preserved in diabetic patients with null Lp(a) phenotype. Furthermore, it could be speculated that diabetic patients with null phenotype should be considered at low risk to develop cardiovascular disease.

Glycation amplifies lipoprotein(a)-induced alterations in the generation of fibrinolytic regulators from human vascular endothelial cells

Increased lipoprotein(a) [Lp(a)] in plasma is an independent risk factor for premature cardiovascular diseases. The levels of glycated Lp(a) are elevated in diabetic patients. The present study demonstrated that glycation enhanced Lp(a)-induced production of plasminogen activator inhibitor-1 (PAI-1), and further decreased the generation of tissue-type plasminogen activator (t-PA) from human umbilical vein endothelial cells (HUVEC) and human coronary artery EC. The levels of PAI-1 mRNA and its antigen in the media of HUVEC were significantly increased following treatments with 5 microgram/ml of glycated Lp(a) compared to equal amounts of native Lp(a). The secretion and de novo synthesis of t-PA, but not its mRNA level, in EC were reduced by glycated Lp(a) compared to native Lp(a). Treatment with aminoguanidine, an inhibitor for the formation of advanced glycation end products (AGEs), during glycation normalized the generation of PAI-1 and t-PA induced by glycated Lp(a). Butylated hydroxytoluene, a potent antioxidant, inhibited native and glycated Lp(a)-induced changes in PAI-1 and t-PA generation in EC. The results indicate that glycation amplifies Lp(a)-induced changes in the generation of PAI-1 and t-PA from venous and arterial EC. This may attenuate fibrinolytic activity in blood circulation and potentially contributes to the increased incidence of cardiovascular complications in diabetic patients with hyperlipoprotein(a). EC-mediated oxidative modification and the formation of AGEs may be implicated in glycated Lp(a)-induced alterations in the generation of fibrinolytic regulators from vascular EC.

Relationship between fibrinolytic and metabolic variables: a study in patients attending a lipid clinic

We investigated the relationship between plasma levels of metabolic and fibrinolytic variables in 163 fasted patients attending a lipid clinic. Of these patients, 118 had hypertriglyceridaemia (HTG) and 45 had normotriglyceridaemia (NTG). In HTG, basal fibrinolytic activity, ie tissue plasminogen activator (t-PA) activity, was impaired as a result of high plasminogen activator inhibitor type 1 (PAI-1) antigen and activity. Multiple stepwise regression analysis identified insulin and triglyceride levels as independent determinants of plasma PAI-1 levels (R2 = 0.18; P = 0.0001). When the patients were stratified into tertiles according to their levels of triglyceride and insulin, PAI-1 antigen levels were found to increase with rising levels of triglyceride in each insulin tertile. In contrast, the increase of PAI-1 with rising insulin levels was evident in the highest triglyceride tertile. In addition, subjects in the lowest tertile of both triglyceride and insulin had the lowest PAI-1 antigen levels, and subjects in the highest tertile of both triglyceride and insulin had the highest levels of PAI-1. Both basal and stimulated levels of t-PA antigen were significantly higher in HTG than in NTG. Multiple stepwise regression analysis identified triglyceride level as the sole major determinant of t-PA antigen levels (R2 = 0.13; P = 0.00003). The observation that both insulin and triglycerides correlate with PAI-1, whereas triglycerides were involved only in the increased secretion of t-PA, suggests that these two proteins are regulated by different mechanisms.

Lipoproteins and the haemostatic system in atherothrombotic disorders

The remarkable extent to which interactions between the plasma lipoproteins, inflammatory factors and the haemostatic system contribute to the response to injury and growth of the plaque in atherosclerosis is being increasingly documented. High plasma concentrations of very-low density (VLDL) and low-density lipoproteins (LDL), together with oxidatively modified LDL and lipoprotein (a), can induce responses in vascular endothelial cells, smooth muscle cells, monocytes/macrophages, platelets, neutrophils and humoral factors that are in a variety of ways both procoagulant and antifibrinolytic. Plasma high-density lipoproteins appear to promote anticoagulant mechanisms. Post-prandial lipaemia is associated with transient changes in factor VII which may be indicative of temporary hypercoagulability. The cellular and humoral effects of LDL and VLDL on the haemostatic system appear to be largely reversible, which may help to explain the prompt improvement in the atherothrombotic state gained by correction of hyperlipidaemia.

Comparison of the effects of two low fat diets with different alpha-linolenic:linoleic acid ratios on coagulation and fibrinolysis

Fish oils rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to alter coagulation and fibrinolysis variables. This study compared the effects of a traditional cholesterol-lowering diet and a similar diet, which had 50% of the linoleic acid (LA) replaced with the 18 carbon n-3 fatty acid, alpha-linolenic acid (ALA), on selected hemostatic variables. After a 2-week run-in diet with 39.5% total energy (en) from fat, 29 healthy male subjects consumed a 31.5% en fat diet with approximately 7% en from polyunsaturated fat and an ALA:LA ratio of either 1:1.2 (ALA-rich, n=15) or 1:21 (LA-rich, n=14) for 6 weeks. Blood was collected at the beginning, middle and end of test diets for analysis of Factor VIIc and VIIIc, fibrinogen, von Willebrand factor, activated protein C resistance (APC resistance), tissue plasminogen activator and plasminogen activator inhibitor type-1 activities and/or protein concentrations and platelet fatty acids. The ALA-rich diet tripled the percentage of platelet EPA, (P < 0.0005) but had little effect on coagulation and fibrinolysis. The APC ratio demonstrated increased anticoagulant activity on the ALA-rich diet (P < 0.001) only. Studies in patients with vascular pathologies are indicated to corroborate the current findings. Greater ratios of ALA:LA, achievable only with greater amounts of polyunsaturated fat, may be necessary to produce the effects demonstrated after feeding fish oils.

Effects of lipids and lipoproteins on thrombosis and rheology

Atherosclerotic plaque rupture and erosions precipitate thrombus formation and may lead to an acute ischemic syndrome. Lipids and lipoproteins modulate the expression and/or function of thrombotic, fibrinolytic and rheologic factors, and thereby influence hemostasis and potential tissue damage resulting from vascular injury. Triglyceride-enriched lipoproteins are accompanied by elevations in factor VII clotting activity, plasminogen activator inhibitor (PAI-1) and viscosity of blood and plasma. Low density lipoprotein (LDL) promotes platelet activation and tissue factor expression and LDL levels correlate with levels of vitamin K dependent coagulation factors and fibrinogen. Conversely, LDL inhibits tissue factor pathway inhibitor (TFPI) which limits activation of the extrinsic coagulation pathway. High density lipoprotein (HDL) has anti-atherothrombotic properties that result from inhibition of platelet and erythrocyte aggregation, reduced blood viscosity and suppression of tissue factor activity and PAI-1 activity and antigen levels. The effects of lipids and lipoproteins on hemostasis and rheology may have important implications for the clinical sequelae following plaque disruption and erosion.

Polymorphisms of coagulation/fibrinolysis genes: gene environment interactions and vascular risk

Circulating concentrations of plasminogen activator inhibitor-1 (PAI-1), factor VII and fibrinogen have all been related to vascular risk in large prospective studies. Evidence indicates that all three proteins are increased in the presence of insulin resistance and factor VII and PAI-1 correlate strongly with circulating levels of insulin and lipids. Polymorphisms of the genes coding for PAI-1, factor VII and fibrinogen have been investigated in relation to gene environment interactions and vascular risk. Three polymorphisms have been described in the PAI-1 gene, a 3' Hind III RFLP, an intronic CA repeat and a 4G/5G insertion deletion 675 bp 5' of the start site of transcription. The 4G/5G site has been shown to be triglyceride responsive and higher levels of PAI-1 have been reported in subjects homozygous for the 4G allele. Three out of four case control studies have related possession of the 4G/4G genotype to an increased risk of coronary artery disease and our studies in patients undergoing coronary angiography indicate that this is due to increased myocardial infarction rather than atheroma. We have investigated 600 subjects with cerebrovascular disease and found no relationship to the 4G/5G polymorphism. Two major polymorphisms have been identified in the factor VII gene, a promoter decanucleotide repeat and a G-A substitution at codon 353. Evidence indicates that the latter mutation affects factor VII levels by interfering with intracellular processing of the molecule and subjects homozygous for the adenine genotype (M2/M2) have levels of factor VII 20-30% lower than M1/M2 or M1/M1 carriers. Two studies have, however, failed to show a relationship between genotype and cardiovascular disease and we have found no association with cerebrovascular disease. A number of mutations have been described in the genes coding for the alpha, beta and gamma chains of fibrinogen. These polymorphisms are reported to be responsible for from 3% to 50% of circulating levels in various studies and there is evidence that the effect of smoking is genotype specific. In the ECTIM study the beta Bcl I polymorphism has been related to cardiovascular disease and work from our unit has related the Bbeta448 polymorphism to the presence of cerebrovascular disease in women. Further prospective studies are warranted to evaluate the role of these genes in disease.

A new butadiene derivative, T-686, inhibits plasminogen activator inhibitor type-1 production in vitro by cultured human vascular endothelial cells and development of atherosclerotic lesions in vivo in rabbits

Plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of tissue-type plasminogen activator and urokinase, is abundantly expressed in atherosclerotic vascular wall. To determine the role of PAI-1 in vascular wall, we have used a novel inhibitor of PAI-1, (3E, 4E)-3-benzylidene-4-(3,4,5-trimethoxy-benzylidene) -pyrrolidine-2,5-dione (T-686). T-686 was given to human vascular endothelial cells in vitro and to rabbits subjected to high cholesterol diet and mechanical injury in vivo. T-686 attenuated the augmentation of PAI-1 antigen accumulation induced by transforming growth factor beta in conditioned medium from the human umbilical vein endothelial cells. In rabbits with aortic atherosclerosis induced by hypercholesterolemia and implantation of indwelling plastic tubing, oral administration of T-686 (30mg/kg body weight/day) for 8 weeks attenuated the increase in plasma PAI-1 activity induced by vascular injury without decreasing blood triglyceride and cholesterol. This was accompanied by the reduction in aortic PAI-1 mRNA expression and the inhibition of development of atherosclerosis lesions. Thus, T-686 not only decreased PAI-1 synthesis in vascular cells in vitro but also protected against the development of vascular lesions in vivo. This compound may be useful in defining the role of PAI-1 in atherothrombotic states.