Plasminogen Activator Inhibitor 1: Biosynthesis and mRNA Level Are Increased by Insulin in Cultured Human Hepatocytes

Hypofibrinolysis in type 2 diabetes and its clinical implications: from mechanisms to pharmacological modulation

A prothrombotic state is a typical feature of type 2 diabetes mellitus (T2DM). Apart from increased platelet reactivity, endothelial dysfunction, hyperfibrinogenemia, and hypofibrinolysis are observed in T2DM. A variety of poorly elucidated mechanisms behind impaired fibrinolysis in this disease have been reported, indicating complex associations between platelet activation, fibrin formation and clot structure, and fibrinolysis inhibitors, in particular, elevated plasminogen antigen inhibitor-1 levels which are closely associated with obesity. Abnormal fibrin clot structure is of paramount importance for relative resistance to plasmin-mediated lysis in T2DM. Enhanced thrombin generation, a proinflammatory state, increased release of neutrophil extracellular traps, elevated complement C3, along with posttranslational modifications of fibrinogen and plasminogen have been regarded to contribute to altered clot structure and impaired fibrinolysis in T2DM. Antidiabetic agents such as metformin and insulin, as well as antithrombotic agents, including anticoagulants, have been reported to improve fibrin properties and accelerate fibrinolysis in T2DM. Notably, recent evidence shows that hypofibrinolysis, assessed in plasma-based assays, has a predictive value in terms of cardiovascular events and cardiovascular mortality in T2DM patients. This review presents the current data on the mechanisms underlying arterial and venous thrombotic complications in T2DM patients, with an emphasis on hypofibrinolysis and its impact on clinical outcomes. We also discuss potential modulators of fibrinolysis in the search for optimal therapy in diabetic patients.

Coagulation factors, fibrinogen and plasminogen activator inhibitor-1, are differentially regulated by yellow fever virus infection of hepatocytes

Yellow fever virus (YFV) infection poses a great risk to un-vaccinated individuals living or traveling in the endemic regions of Africa and South America. It is estimated that approximately 30,000 people die each year of this disease. The liver is the main target of YFV, where as many as 80% of the hepatocytes may become involved in the infection. The overwhelming infection of the liver is associated with the observed hemorrhagic disease manifestations such as petechiae, ecchymoses, and hematemesis which are all thought to be linked with the observed coagulation abnormalities that include prolonged clotting times, reduction in clotting factors, fibrin-split products (D-dimers) and elevated prothrombin times. Many factors involved in the coagulation pathway are produced by hepatocytes, such as fibrinogen (FBG) and plasminogen activator inhibitor-1 (PAI-1). Both of these proteins have been indicated in another flavivirus related disease, dengue, as having roles related to the bleeding abnormalities observed and overall outcome of infection. In this study we wanted to determine if FBG and PAI-1 expression levels by human hepatocytes was disrupted or altered by infection with either wild-type Asibi or vaccine strain17-D YFVs. Our findings indicate that YFV infection does affect the transcriptional and translational expression of FBG and PAI-1 in human hepatocytes and that these results are further affected by IL-6 during early stages of infection. These results may lead to further understanding of the molecular mechanism associated with bleeding abnormalities observed during late stage YFV infection.

HDL3, but not HDL2, stimulates plasminogen activator inhibitor-1 release from adipocytes: the role of sphingosine-1-phosphate

Sphingosine-1-phosphate (S1P) is a bioactive lysophospholipid that regulates numerous key cardiovascular functions. High-density lipoproteins (HDLs) are the major plasma lipoprotein carriers of S1P. Fibrinolysis is a physiological process that allows fibrin clot dissolution, and decreased fibrinolytic capacity may result from increased circulating levels of plasminogen activator inhibitor-1 (PAI-1). We examined the effect of S1P associated with HDL subfractions on PAI-1 secretion from 3T3 adipocytes. S1P concentration in HDL3 averaged twice that in HDL2. Incubation of adipocytes with increasing concentrations of S1P in HDL3, but not HDL2, or with S1P complexed to albumin stimulated PAI-I secretion in a concentration-dependent manner. Quantitative RT-PCR revealed that S1P(1-3) are expressed in 3T3 adipocytes, with S1P(2) expressed in the greatest amount. Treatment of adipocytes with the S1P(1) and S1P(3) antagonist VPC23019 did not block PAI-1 secretion. Inhibiting S1P(2) with JTE-013 or reducing the expression of the gene coding for S1P(2) using silencing RNA (siRNA) technology blocked PAI-1 secretion, suggesting that the S1P(2) receptor mediates PAI-1 secretion from adipocytes exposed to HDL3 or S1P. Treatment with the phospholipase C (PLC) inhibitor U73122, the protein kinase C (PKC) inhibitor RO-318425, or the Rho-associated protein kinase (ROCK) inhibitor Y27632 all significantly inhibited HDL3- and S1P-mediated PAI-1 release, suggesting that HDL3- and/or S1P-stimulated PAI-1 secretion from 3T3 cells is mediated by activation of multiple, downstream signaling pathways of S1P(2).

Post-transcriptional regulation of plasminogen activator inhibitor type-1 expression in human pleural mesothelial cells

The plasminogen activator inhibitor type-1 (PAI-1) effectively blocks the activities of free and receptor-bound urokinase-type plasminogen activator. Incubation of cultured human pleural mesothelial (Met5A) cells with TGF-beta increased PAI-1 protein. TGF-beta, phorbol myristate acetate, and the translation inhibitor cycloheximide induced PAI-1 mRNA and slowed its degradation, suggesting that PAI-1 mRNA could be regulated by interaction of a PAI-1 binding protein (PAI-1 mRNABp) with PAI-1 mRNA. We found that an approximately 60 kD cytoplasmic PAI-1 mRNABp is detectable in cytoplasmic extracts of MeT5A human pleural mesothelial and malignant mesothelioma cells. The PAI-1 mRNABp specifically binds to a 33-nt sequence in the 3' untranslated region of PAI-1 mRNA. Insertion of this 33-nt sequence destabilizes otherwise stable beta-globin mRNA, indicating that the binding sequence accelerates decay of endogenous PAI-1 mRNA. Competitive inhibition by overexpression of the 33-nt binding sequence in MeT5A cells reduced PAI-1 mRNA decay and increased PAI-1 protein and mRNA expression, indicating that the PAI-1 mRNABp destabilizes PAI-1 mRNA by its interaction with the endogenous 33-nt binding sequence. Incubation of Met5A cells with TGF-beta attenuated the interaction of the PAI-1 mRNABp with the 33-nt sequence. By conventional and affinity purification, we isolated the PAI-1 mRNABp and confirmed its identity as 6-phospho-d-gluconate-NADP oxidoreductase, which specifically interacts with the full-length and the 33-nt sequence of the PAI-1 mRNA 3' untranslated region. This newly recognized pathway could influence expression of PAI-1 by mesothelial or mesothelioma cells at the level of mRNA stability in the context of pleural inflammation or malignancy.

The increase in plasma PAI-1 associated with insulin resistance may be mediated by the presence of hepatic steatosis

OBJECTIVE

Recent evidence suggests that plasminogen-activator inhibitor-1 (PAI-1) is abundantly produced by the fatty liver, but it is unclear whether hepatic steatosis (HS) can mediate the increase in plasma PAI-1 induced by insulin resistance/compensatory hyperinsulinemia (IR/CH).

METHODS AND RESULTS

To address this issue, we cross-sectionally evaluated IR/CH as area under the curve of plasma insulin (AUC-PI) concentrations during OGTT, metabolic profile, and ultrasound degree of HS in 235 healthy volunteers (132M, age: 60+/-7 years) with normal transaminase concentrations. Circulating PAI-1 was increased in subjects with classical features of IR/CH (overweight, high fasting and post-OGTT insulin and glucose, high triglycerides (TG), and low HDL-cholesterol), and significantly correlated to prevalence and degree of HS, but not to alcohol intake. In a multivariate model, AUC-PI, TG and degree of HS were independent predictors of plasma PAI-1 (R(2)=0.32). However, AUC-PI was significantly correlated to PAI-1 only in subjects with HS, suggesting an interaction between AUC-PI and HS. In addition, in the presence of HS and IR/CH, PAI-1 concentrations were increased to a similar extent both in heavy and moderate drinkers, suggesting that metabolic and alcoholic steatosis have a similar effect on the relationship between IR/CH and PAI-1.

CONCLUSION

These results support the hypothesis that HS has a major impact on the relationship between IR/CH and plasma PAI-1 concentrations, and this effect seems to be unaffected by the etiology of the HS.

Diabetes mellitus as a prothrombotic condition

Diabetes mellitus (DM) is characterized by fasting hyperglycaemia and a high risk of atherothrombotic disorders affecting the coronary, cerebral and peripheral arterial trees. The risk of myocardial infarction (MI) is 3-5 fold higher in Type 2 DM and a DM subject with no history of MI has the same risk as a non-DM subject with a past history of MI. In total around 70% of deaths are vascular with poorer outcomes to both acute events and cardiological interventions. It was proposed that clustering of vascular risk factors (hyperinsulinaemia, dysglycaemia, dyslipidaemia and hypertension) around insulin resistance (IR) accounted for the increase in risk with Type 2 DM. The importance of this became apparent with the recognition that risk clustering occurs in normoglycaemic and impaired glucose tolerance (IGT) subjects with IR, in total around 25% of the population in addition to long-standing Type 1 subjects with renal disease. Evidence indicates that thrombotic risk clustering also occurs in association with IR, suppression of fibrinolysis due to elevated concentrations of the fibrinolytic inhibitor, plasminogen activator inhibitor-1 (PAI-1) is invariable with IR and there is evidence that this is regulated by the effects of triglyceride on the PAI-1 gene promoter. Other studies indicated that prothrombotic risk (coagulation factors VII, XII and fibrinogen) also associates with the IR syndrome. The development of endothelial cell dysfunction with suppression of nitric oxide and prostacyclin synthesis, combined with platelet resistance to the anti-aggregatory effects of these hormones leads to loss of control over platelet activation. In addition, hyperglycaemia and glycation have marked effects on fibrin structure function, generating a clot which has a denser structure, resistant to fibrinolysis. The combination of increased circulating coagulation zymogens, inhibition of fibrinolysis, changes in fibrin structure/function and alterations in platelet reactivity creates a thrombotic risk clustering which underpins the development of cardiovascular disease.

PAI-1 and the Metabolic Syndrome

The link between plasminogen activator inhibitor (PAI)-1 and the metabolic syndrome with obesity was established many years ago. Increased PAI-1 level can be now considered a true component of the syndrome. The metabolic syndrome is associated with an increased risk of developing cardiovascular disease, and PAI-1 overexpression may participate in this process. The mechanisms of PAI-1 overexpression during obesity are complex, and it is conceivable that several inducers are involved at the same time at several sites of synthesis. Interestingly, recent in vitro and in vivo studies showed that besides its role in atherothrombosis, PAI-1 is also implicated in adipose tissue development and in the control of insulin signaling in adipocytes. These findings suggest PAI-1 inhibitors serve in the control of atherothrombosis and insulin resistance.

Familial clustering for features of the metabolic syndrome: the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study

OBJECTIVE

Metabolic syndrome-related traits (obesity, glucose intolerance/insulin resistance, dyslipidemia, and hypertension) have been shown to be genetically correlated. It is less clear, however, if the genetic correlation extends to novel risk factors associated with inflammation, impaired fibrinolytic activity, and hyperuricemia. We present a bivariate genetic analysis of MetS-related traits including both traditional and novel risk factors.

RESEARCH DESIGN AND METHODS

Genetic correlations were estimated using a variance components procedure in 1,940 nondiabetic white individuals from 445 families in the National Heart, Lung, and Blood Institute (NHLBI) Family Heart Study. Twelve MetS-related traits, including BMI, waist circumference, blood pressure, white blood cell count, fasting serum triglycerides, HDL cholesterol, insulin, glucose, plasminogen activator inhibitor-1 antigen, uric acid, and C-reactive protein, were measured and adjusted for covariates, including lifestyle variables.

RESULTS

Significant genetic correlations were detected among BMI, waist circumference, HDL cholesterol, triglycerides, insulin, and plasminogen activator inhibitor-1 antigen and between uric acid and all of the above variables except insulin. C-reactive protein and white blood cell count were genetically correlated with each other, and both showed significant genetic correlations with waist circumference and insulin. Fasting glucose was not significantly genetically correlated with any of the other traits.

CONCLUSIONS

These results suggest that pleiotropic effects of genes or shared family environment contribute to the familial clustering of MetS-related traits.

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.

Is the effect of antihypertensive drugs on platelet aggregability and fibrinolysis clinically relevant?

Hypertension is associated with decreased fibrinolytic potential, mainly expressed as elevated plasma plasminogen activator inhibitor type 1 (PAI-1) levels, and increased platelet aggregability, which may account in part for the increased risk of atherosclerosis and its clinical complications in hypertensive patients. The effects of antihypertensive drugs on this prothrombotic state have been investigated and controversial findings have been reported, possibly because of differences in study designs, patients selected, and methodology used. Scarce and conflicting data exist about the effects of diuretics and beta-adrenoceptor antagonists on the fibrinolytic system, whereas ACE inhibitors have generally been reported to improve the fibrinolytic balance by decreasing plasma PAI-1 levels, calcium channel antagonists have been shown to increase tissue plasminogen activator (tPA) activity, and angiotensin II type 1 (AT(1)) receptor antagonists seem to exert neutral effects. beta-Adrenoceptor antagonists, calcium channel antagonists, and AT(1)-receptor antagonists have been reported to exert anti-aggregatory effects on platelets, while contrasting data exist about the influence of ACE inhibitors. Clinical implications of the changes induced by antihypertensive drugs on the fibrinolytic balance and platelet function are still debated. In particular, the question of whether these changes may translate into different degrees of cardiovascular protection in hypertensive patients remains unanswered. While awaiting more information from clinical trials, the choice of antihypertensive drugs, particularly in high-risk patients, should take into account effects beyond their BP-lowering efficacy. Selected agents should have a favorable, or at least neutral, impact on fibrinolytic function and platelet activity.

The plasminogen activator system in young and lean women with polycystic ovary syndrome

The purpose of the study was to evaluate the plasminogen activator inhibitor-1 (PAI-1) levels and PAI-1 activity in young and lean women with PCOS and to compare with controls matched for age and weight. Thirty two women with PCOS and 25 weight and age-matched healthy controls participated in this study. Patients were evaluated clinically and by pelvic ultrasound and fasting blood samples were taken for hematological and biochemical tests. Fasting insulin, glucose, lipid profile, FSH, LH, PRL, testosterone, SHBG, 17-hydroxyprogesterone, androstenedione, PAI-1 antigen; PAI-1 activity, insulin sensitivity indices (HOMA and QUICKI) were measured. PAI-1 Ag and activity were significantly higher in PCOS women than healthy control group. PAI-1 levels were directly correlated with BMI, insulin levels and insulin sensitivity indices. PAI-1 activity was also correlated with insulin levels and insulin resistance. As a conclusion PAI-1 Ag levels and activity were increased in lean PCOS women and these were directly correlated with insulin resistance. The finding may contribute to evidence of increase risk of cardiovascular disease and anovulatory infertility in PCOS women.

Antiplatelet agents for the prevention of cardiovascular disease in diabetes mellitus

Patients with diabetes mellitus (DM) have accelerated atherothrombotic disease of coronary, cerebral, leg, and other vessels. The major cause of death is cardiovascular, and the risk for a myocardial infarction (MI) in a patient with DM who has never had a MI is the same as a nondiabetic individual who has already had one. In this paper, we review the major reasons for a prothrombotic state in patients with DM: alterations in the intrinsic coagulation and fibrinolytic systems and many abnormalities of platelet function. Increased platelet thromboxane production as well as activation of platelet receptors for fibrinogen and or adenosine diphosphate (ADP) are often present, and can be treated with aspirin (acetylsalicylic acid) and/or receptor blockers. Review of the major primary prevention trials in DM indicates that a significantly reduced risk for MI or major cardiovascular events may be obtained by enteric-coated aspirin, 81-325 mg/day. There is emerging consensus that this is recommended strategy in adult (aged >30 years) patients with DM who are at high vascular risk. Surveys suggest that this includes virtually every patient with type 2 DM in the US, as well as many patients with complicated type 1 DM. These recommendations are also appropriate for secondary prevention. Data supporting the use of clopidogrel as an alternative drug in the case of aspirin allergy or other contraindications are reviewed. Evidence is presented in support of using aspirin plus clopidogrel in acute coronary syndromes (ACS), and a meta-analysis of six trials of platelet glycoprotein (GP) IIb/IIIa inhibitors and aspirin in diabetic patients with ACS establishes this regimen as an effective choice. Although bleeding episodes are more common with combined antiplatelet therapy for ACS than for aspirin alone, the benefit of a significant reduction in 30-day mortality appears to outweigh the risk of major bleeding. It is concluded that major advances in our understanding of the prothrombotic state in DM have been made. Evidence from controlled clinical trials supports the use of enteric-coated aspirin, 81-325 mg/day, as a primary and a secondary prevention strategy in adults with DM with high vascular risk. In ACS, combination therapy with aspirin plus clopidogrel or alternatively, aspirin plus a platelet GP IIb/IIIa inhibitor is supported by prospective trial data. These approaches should be added to the other multifactorial preventive strategies directed at lowering the risk for major vascular events in patients with DM.

Peroxisome proliferator-activated receptor gamma mediated inhibition of plasminogen activator inhibitor type 1 production and proliferation of human umbilical vein endothelial cells

Insulin resistance and diabetes mellitus promote the atherosclerotic process, where an endothelial dysfunction plays a key role. The diabetic milieu elevates the production of the plasminogen activator inhibitor type 1 (PAI-1) and also increases the proliferation of vascular endothelial cells. Recently the role of peroxisome proliferator-activated receptor gamma (PPARgamma) in atherosclerosis has been extensively studied. However, the direct effect of PPARgamma in vascular endothelial cells is still unclear. Therefore, the effect of PPARgamma was investigated to determine if it plays an important role in PAI-1 production and cellular proliferation in human umbilical vein endothelial cells (HUVEC). A combination of PPARgamma-overexpression and troglitazone treatment (5 ug/ml) significantly decreased both the PAI-1 mRNA and protein expression, while PPARgamma-overexpression or troglitazone alone tended to decrease both the PAI-1 protein and mRNA expression. PPARgamma-overexpression or troglitazone treatment alone reduced the thymidine uptake by the HUVEC with or without TNFalpha treatment. There was a further decrease in the thymidine uptake with troglitazone treatment in the PPARgamma-overexpressed HUVEC. In conclusion, PPARgamma can reduce PAI-1 production in HUVEC directly by transcriptional repression, and may play a beneficial role in preventing cardiovascular events. PPARgamma can also inhibit vascular endothelial cell proliferation, and its clinical relevance in diabetic vascular complications should be elucidated.

Plasma PAI-1 levels are more strongly related to liver steatosis than to adipose tissue accumulation

OBJECTIVE

Because obesity and insulin resistance (IR) are strongly associated with liver steatosis (LS), we investigated the relation between the degree of LS and plasminogen activator inhibitor-1 (PAI-1) in ob/ob mice, in C57/BL6 mice with alcoholic LS, and in severely obese humans.

METHODS AND RESULTS

In both mouse models, plasma PAI-1 levels were associated with PAI-1 expression in the liver and with the degree of LS. Liver PAI-1 antigen was associated with the tumor necrosis factor receptor-II (TNFRII) antigen, whereas association with TNF antigen content was found in ob/ob mice only. No significant correlation between plasma PAI-1 and PAI-1 expression in adipose tissue of ob/ob mice was observed. Furthermore, the relation between plasma PAI-1 levels and body weight was positive in ob/ob mice but negative in C57/BL6 mice (both P<0.001). In humans, PAI-1 levels were correlated with the degree of LS, and 26% of plasma PAI-1 activity was independently explained by LS and serum insulin levels.

CONCLUSIONS

Plasma PAI-1 levels are more closely related to fat accumulation and PAI-1 expression in the liver than in adipose tissue. In steatotic liver, PAI-1 antigen content is associated with those of TNF and TNFRII. Therefore, we suggest that TNF pathway dysregulation in LS could be involved in increased plasma PAI-1 in obesity with IR.

Induction of plasminogen activator inhibitor-1 by urokinase in lung epithelial cells

The plasminogen/plasmin system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and its inhibitor (PAI-1), influence extracellular proteolysis and cell migration in lung injury or neoplasia. In this study, we sought to determine whether tcuPA (two chain uPA) alters expression of its major inhibitor PAI-1 in lung epithelial cells. The expression of PAI-1 was evaluated at the protein and mRNA level by Western blot, immunoprecipitation, and Northern blot analyses. We found that tcuPA treatment enhanced PAI-1 protein and mRNA expression in Beas2B lung epithelial cells in a time- and concentration-dependent manner. The tcuPA-mediated induction of PAI-1 involves post-transcriptional control involving stabilization of PAI-1 mRNA. Inactivation of the catalytic activity of tcuPA had little effect on PAI-1 induction and the activity of the isolated amino-terminal fragment was comparable with full-length single- or two-chain uPA. In contrast, deletion of either the uPA receptor binding growth factor domain or kringle domain (kringle) from full-length single chain uPA markedly attenuated the induction of PAI-1. Induction of PAI-1 by exposure of lung epithelial cells to uPA is a newly recognized pathway by which PAI-1 could regulate local fibrinolysis and urokinase-dependent cellular responses in the setting of lung inflammation or neoplasia.

Regulation of plasma PAI-1 concentrations in HAART-associated lipodystrophy during rosiglitazone therapy

OBJECTIVE

Patients with highly active antiretroviral therapy-associated lipodystrophy (HAART+LD+) have high plasminogen activator inhibitor-1 (PAI-1) concentrations for unknown reasons. We determined whether (1). plasma PAI-1 antigen concentrations are related to liver fat content (LFAT) independently of the size of other fat depots and (2) rosiglitazone decreases PAI-1 and LFAT in these patients.

METHODS AND RESULTS

In the cross-sectional study, 3 groups were investigated: 30 HIV-positive patients with HAART+LD+, 13 HIV-positive patients without lipodystrophy (HAART+LD-), and 15 HIV-negative subjects (HIV-). In the treatment study, the HAART+LD+ group received either rosiglitazone (8 mg, n=15) or placebo (n=15) for 24 weeks. Plasma PAI-1 was increased in HAART+LD+ (28+/-2 ng/mL) compared with the HAART+LD- (18+/-3, P<0.02) and HIV- (10+/-3, P<0.001) groups. LFAT was higher in HAART+LD+ (7.6+/-1.7%) than in the HAART+LD- (2.1+/-1.1%, P<0.001) and HIV- (3.6+/-1.2%, P<0.05) groups. Within the HAART+LD+ group, plasma PAI-1 was correlated with LFAT (r=0.49, P<0.01) but not with subcutaneous or intra-abdominal fat or serum insulin or triglycerides. In subcutaneous adipose tissue, PAI-1 mRNA was 2- to 3-fold higher in the HAART+LD+ group than in either the HAART+LD- or HIV- group. Rosiglitazone decreased LFAT, serum insulin, and plasma PAI-1 and increased serum triglycerides but had no effect on intra-abdominal or subcutaneous fat mass or PAI-1 mRNA.

CONCLUSIONS

Plasma PAI-1 concentrations are increased in direct proportion to LFAT in HAART+LD+ patients. Rosiglitazone decreases LFAT, serum insulin, and plasma PAI-1 without changing the size of other fat depots or PAI-1 mRNA in subcutaneous fat. These data suggest that liver fat contributes to plasma PAI-1 concentrations in these patients.

Hypoxia-inducible factor-1 and hypoxia response elements mediate the induction of plasminogen activator inhibitor-1 gene expression by insulin in primary rat hepatocytes

The expression of the plasminogen activator inhibitor-1 (PAI-1) gene is enhanced by insulin both in vivo and in various cell types. Because insulin exerts a number of its biologic activities via the phosphatidylinositol 3-kinase and protein kinase B (PI3K/PKB) signaling pathway, it was the aim of the present study to investigate the role of the PI3K/PKB pathway in the expression of the PAI-1 gene and to identify the insulin responsive promoter sequences. It was shown that the induction of PAI-1 mRNA and protein expression by insulin and mild hypoxia could be repressed by the PI3K inhibitor wortmannin. Overexpression of a constitutively active PKB led to induction of PAI-1 mRNA expression and of luciferase (Luc) activity from a gene construct containing 766 bp of the rat PAI-1 promoter. Mutation of the hypoxia response elements (HRE-1 and HRE-2) in rat PAI-1 promoter, which could bind hypoxia inducible factor-1 (HIF-1), abolished the induction of PAI-1 by insulin and PKB. Insulin and the constitutive active PKB also induced Luc expression in cells transfected with the pGl3EPO-HRE Luc construct, containing 3 copies of the HRE from the erythropoietin gene in front of the SV40 promoter. Furthermore, insulin and the active PKB enhanced all 3 HIF alpha-subunit protein levels and HIF-1 DNA-binding activity, as shown by electrophoretic mobility shift assays (EMSAs). Thus, the insulin-dependent activation of the PAI-1 gene expression can be mediated via the PI3K/PKB pathway and the transcription factor HIF-1 binding to the HREs in the PAI-1 gene promoter.

Insulin resistance but not visceral adipose tissue is associated with plasminogen activator inhibitor type 1 levels in overweight and obese premenopausal African-American women

OBJECTIVE

To compare plasma plasminogen activator inhibitor type 1 (PAI-1) levels and to examine the association of PAI-1 with visceral adiposity and other components of the metabolic syndrome in overweight and obese premenopausal African-American (AA) and Caucasian (CC) women.

DESIGN

Cross-sectional study.

SUBJECTS

33 CC and 23 AA healthy, overweight and obese, premenopausal women (age 19-53 y, body mass index 28.1-48.9 kg/m(2)).

MEASUREMENTS

Body mass index, sagittal diameter, waist circumference, percentage body fat, visceral and subcutaneous adipose tissue (by anthropometry, magnetic resonance imaging (MRI), and bioelectric impedance techniques), PAI-1, leptin, lipids, glucose, insulin, and insulin resistance (by HOMA IR).

RESULTS

AA women had lower triglyceride levels and less visceral adipose tissue (VAT) volume than CC despite similar BMI. PAI-1 levels were not significantly different in the two groups. Insulin resistance was associated with PAI-1 in both groups but only in CC women were VAT, triglyceride, HDL cholesterol and blood pressure related to plasma PAI-1 levels. Multiple regression analysis showed that VAT in CC and insulin resistance in AA were independent predictors of PAI-1.

CONCLUSION

VAT is significantly associated with circulating PAI-1 levels in overweight and obese CC but not AA premenopausal women.

Plasminogen activator inhibitor-1: physiologic role, regulation, and the influence of common pharmacologic agents

Plasminogen activator inhibitor-1 (PAI-1) is the major inhibitor of endogenous thrombolysis, thereby promoting thrombosis. PAI-1 is also a primary contributor to the development and recurrence of acute myocardial infarction. The renin angiotensin system, hypertriglyceridemia, hyperglycemia and hyperinsulinemia, and estrogen all influence the fibrinolytic system and PAI-1 in particular. Available data strongly suggest that angiotensin-converting enzyme (ACE) inhibitors and hormone replacement therapy with estrogen beneficially reduce PAI-1 production. Metformin, an agent commonly used for non-insulin-dependent diabetes mellitus (NIDDM), appears to favorably decrease PAI-1 production in NIDDM patients but not nondiabetic patients. Among the cholesterol-lowering statins, clinical literature evaluating pravastatin provides the most compelling data to support this agent's favorable effect on PAI-1. Other available statins either have not displayed an effect on PAI-1 or do not have clear data to conclusively define their effects on the fibrinolytic system.

Obesity, haemostasis and the fibrinolytic system

Obese patients are at risk for the development of cardiovascular diseases, which can in part be explained by disturbances in the haemostatic and fibrinolytic systems. Indeed, obese subjects tend to have higher values of fibrinogen, factor VII, factor VIII, von Willebrand factor and plasminogen activator inhibitor compared to non-obese subjects. Abdominal obesity, in particular, has been shown to be associated with disturbances in fibrinogen, factor VIII and von Willebrand factor, while less consistent results have been found for factor VII. Recently it has been demonstrated that the adipocyte itself is able to produce plasminogen activator inhibitor-1, possibly explaining the high levels found in obesity. Different studies have investigated the association between haemostatic and fibrinolytic parameters and the insulin resistance syndrome, often present in obese subjects. Fibrinogen has been found to be related to insulin, but it has been suggested that this relationship is not independent of the accompanying inflammatory reaction. Results from studies on the relationship between insulin resistance and factor VII, factor VIII and von Willebrand factor levels are inconsistent. In contrast, plasminogen activator inhibitor-1 has been found to correlate with all components of the insulin resistance syndrome, and can be considered as a true component of this metabolic syndrome. Weight loss seems to have a beneficial effect on factor VII--probably mediated through a reduction in triglycerides. Data on factor VIII and von Willebrand factor are scarce but weight loss does not seem to have an effect. Fibrinogen does not seem to be reduced by modest weight loss and a more substantial weight loss seems necessary to lower fibrinogen levels. In contrast, both modest and substantial weight loss have been found to significantly reduce plasminogen activator inhibitor-1 levels. In conclusion, the increased cardiovascular risk observed in obesity could in part be explained by the association between insulin resistance and components of the fibrinolytic and haemostatic systems. Whether this relationship is truly causal or indirect needs to be elucidated further.

Sex differences in the association between proinsulin and intact insulin with coronary heart disease in nondiabetic older adults: the Rancho Bernardo Study

BACKGROUND

Insulin or insulin resistance is considered a coronary heart disease (CHD) risk factor, but proinsulin may have a stronger association with CHD than insulin. The role of sex differences in this association is unclear. We examined the cross-sectional association of proinsulin and insulin with CHD in older men and women without diabetes.

METHODS AND RESULTS

A cross-sectional study of community-dwelling men (n=554) and women (n=902), 50 to 97 years of age, without diabetes by history or oral glucose tolerance test, was done between 1992 and 1996; plasma levels of intact insulin, proinsulin, and C-peptide were measured by radioimmunoassay. Based on questionnaire, medical history, or ECG abnormalities, 25% of men (n=136) and 24% of women (n=214) had prevalent CHD. All insulin variables were positively correlated with CHD risk factors. Compared with those without CHD, men and women with CHD had significantly higher levels of proinsulin. Women but not men with CHD also had higher levels of C-peptide and fasting and postchallenge insulin. Only proinsulin was significantly and independently associated with prevalent CHD in both men (OR=2.41, 1.42 to 4.11) and women (OR=1.80, 1.22 to 2.64) (adjusted for age, body mass index, systolic blood pressure, and HDL cholesterol). Similar analyses for fasting and postchallenge intact insulin and for C-peptide showed that among these three variables, only postchallenge insulin was significantly associated with CHD, and only in women.

CONCLUSIONS

In older nondiabetic men and women, proinsulin was more strongly and consistently associated with CHD than was intact insulin.

Treatment for the procoagulant state in type 2 diabetes

A procoagulant state has been found to exist in diabetes mellitus. There may be activation of the intrinsic coagulation system, decreased fibrinolytic activity, or alterations in platelet function. Intensive glycemic control with insulin is effective in reducing the impact of this procoagulant state by favorably affecting all three components of the system. Decreased fibrinolytic activity, as influenced by plasma PAI-1 levels, may be favorably affected by weight loss, exercise, a low-GI diet, or by metformin, thiazolidinediones, gemfibrozil, and ACE inhibitor therapy. Insulin has variable effects on plasma PAI-1 activity. Estrogens will lower the elevated PAI-1 levels seen in the menopausal state. Collaborative trial evidence supports the use of low-dose aspirin as a primary or secondary prevention strategy in diabetic persons who are at high cardiovascular risk. A recent study suggests that this category includes virtually every type 2 diabetic individual in the United States. The American Diabetes Association recommends enteric-coated aspirin, 81 to 325 mg/day, as the first choice. In the case of aspirin allergy, clopidrogel is an alternate choice. Thus, recognition of and therapy for a procoagulant state in diabetes mellitus is likely to result in a decrease in the atherothrombotic events that characterize the later stages of this disease.

Reciprocal regulation of tissue-type and urokinase-type plasminogen activators in the differentiation of murine preadipocyte line 3T3-L1 and the hormonal regulation of fibrinolytic factors in the mature adipocytes

Adipose tissue expresses a variety of genes including tumor necrosis factor alpha and type-1 plasminogen activator inhibitor (PAI-1); and these factors, produced by adipocytes, may be associated with the risk of coronary events in obesity. In this study, we characterized the production of fibrinolytic factors including tissue-type plasminogen activator (tPA), urokinase-type PA (uPA), and PAI-1 in the differentiation of preadipocytes, and examined the hormonal regulation of these fibrinolytic factors in mature adipocytes. Mouse 3T3-L1 preadipocytes were employed as a model of adipocytes. Adipocyte differentiation was induced by insulin, dexamethasone, and 3-isobutyl-1-methyl xanthine (IBMX). alpha-Glycerophosphate dehydrogenase (GPDH) activity and glucose transporter 4 (GLUT4) mRNA, indices for adipocyte maturation, were induced on Day 4, and gradually increased. GPDH activity reached its maximum level on Day 14. The level of tPA, a major PA in preadipocytes, dramatically decreased with differentiation. On the other hand, that of uPA reciprocally increased. PAI-1 production was also dramatically induced concomitant with differentiation. In mature adipocytes, uPA production was dominant (25 microg/ml/24 h vs. 0.8 microg/ml/24 h for tPA). Total PA activity in the mature adipocytes was reduced by insulin or dexamethasone, but not by glucagon. Insulin, IBMX, and dexamethasone significantly decreased both uPA and tPA production, and increased PAI-1 production. Glucagon had no effect on the production of these fibrinolytic factors. Our results reveal that uPA is one of the markers for the differentiation of 3T3-L1 cells and that insulin, IBMX, and dexamethasone are potent regulators of the fibrinolytic activity in differentiated 3T3-L1 cells, reciprocally affecting PA and PAI-1 levels in them.

Plasminogen activator inhibitor-1 and haemostasis in obesity

The connection between obesity and disordered haemostasis is well established, but incompletely understood. There is a strong link between inhibition of fibrinolysis and obesity, and elevation of the plasma inhibitor, plasminogen activator inhibitor-1 (PAI-1), is regarded as a central factor. Here we explore the increased risk of atherothrombotic disorders in obese subjects, and the evidence for metabolic and genetic causes. There is a clear relationship between plasma PAI-1 and obesity, and adipose tissue synthesises PAI-1, as has been shown in mouse and rat models, and more recently in human material. This tissue also produces several effector molecules that can up regulate PAI-1. These molecules include transforming growth factor beta, tumour necrosis factor alpha, angiotensin II and interleukin 6, all of which up regulate PAI-1 in various cell types. The issue of whether adipose tissue directly contributes to plasma PAI-1, or whether it primarily contributes indirectly, its products stimulating other cells to produce PAI-1 that feeds into the plasma pool, is not yet resolved. Finally, we briefly examine other proteins of haemostasis that are products of adipose tissue. Further studies are needed to define the regulation of these proteins, in adipose tissue itself and in other cells influenced by its products, in order to extend recent insights into the links between obesity and haemostasis.

Overweight/obesity, smoking, and heavy alcohol consumption are important determinants of plasma PAI-1 levels in healthy men

BACKGROUND

Plasma plasminogen activator inhibitor-1 (PAI-1) is thought to contribute to the pathogenesis of atherosclerosis and is a predictor of ischemic heart disease.

METHODS

We investigated the effects of overweight/obesity and lifestyle (smoking and alcohol intake) on plasma PAI-1 levels in 203 healthy men (age 44.5+/-8.1) who visited our department for health check. Information on alcohol intake and smoking habit was obtained by a questionnaire.

RESULTS

Plasma PAI-1 was significantly correlated to plasma leptin, body mass index (BMI), percent body fat, plasma levels of triglyceride, and gamma-glutamyl transpeptidase. Plasma PAI-1 was also increased significantly in smokers and in heavy drinkers. Plasma PAI-1 levels increased in an additive manner by the combination of risk factors (BMI > or =25 kg/m2, smoking, and heavy alcohol consumption). Nonobese, nonsmoking, nondrinkers showed the lowest plasma PAI-1 levels, whereas overweight/obese, smoking, heavy drinkers showed the highest levels (11.2+/-2.2 ng/mL versus. 34.0+/-4.3 ng/mL, P < 0.0001).

CONCLUSIONS

These results suggest that overweight/obesity and unfavorable lifestyle such as smoking and heavy alcohol consumption may increase plasma PAI-1 levels and might be linked to the risk of ischemic heart disease.

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.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

Increased plasma fibrinolysis and tissue-type plasminogen activator/tissue-type plasminogen activator inhibitor ratios after ethanol withdrawal in chronic alcoholics

The effects of alcohol withdrawal on fibrinolysis were studied in 10 middle-aged male chronic alcoholics institutionalized for withdrawal therapy. All patients were sampled on admission [day 1 (D1)] and 21 days after alcohol withdrawal [day 22 (D22)]. The overall plasma fibrinolytic capacity (OFC) was assayed by measuring the ability of patient plasma to generate D-dimers from a standardized fibrin clot, and tissue-type plasminogen activator (t-PA) and t-PA inhibitor (PAI-1) levels were assayed together with serum cholesterol, triglyceride and cholesterol fractions. At D22, the OFC significantly increased in seven patients [D1 = 10 +/- 0.7 microg/h (mean +/- SD), D22 = 17 +/- 7.4 microg/h; P < 0.01], while t-PA and PAI-1 levels decreased in all patients but two (t-PA: D1 = 16.6 +/- 5 ng/ml, D22 = 10.2 +/- 3.8 ng/ml; P < 0.001; and PAI-1: D1 = 46 +/- 39 ng/ml, D22 = 21 +/- 28 ng/ml; P < 0.01). This study clearly demonstrates an increase in overall fibrinolytic activity after alcohol withdrawal, which is mainly due to a decrease in PAI-1 levels. These changes induced by alcohol abstinence might provide clear benefit by reducing the risk of thromboembolic events and particularly of stroke associated with elevated PAI-1 levels described in heavy drinkers.

Release of PAI-1 by human preadipocytes and adipocytes independent of insulin and IGF-1

The effect of insulin and insulin-like growth factor-1 (IGF-1) on plasminogen activator inhibitor-1 (PAI-1) release from primary cultures of human preadipocytes and adipocytes has been investigated. Initial experiments measuring basal PAI-1 release (ng/ml) indicated variability between individual cultures. Using a novel technique for adipocyte quantitation, additional experiments were performed to determine PAI-1 release per cell, indicating a significant reduction with differentiation. Insulin and IGF-1 over a range of concentrations had no effect on PAI-1 release, and RT-PCR of PAI-1 mRNA following treatment with insulin and IGF-1 also indicated similar expression between treatments. The cultures did exhibit insulin-stimulated glyceraldehyde-3-phosphate dehydrogenase (GAPDH) expression and leptin synthesis following differentiation to the adipocyte phenotype. This is the first report of PAI-1 secretion by primary cultures of human preadipocytes and adipocytes, indicating PAI-1 release independent of insulin and IGF-1 and implicating other factors in the elevated plasma PAI-1 observed with insulin resistance.

Occlusive vascular diseases in oral contraceptive users. Epidemiology, pathology and mechanisms

Despite being an unprecedented departure from normal physiology, the combined oral contraceptive is not only highly effective, but it also has a remarkably good safety record. Concerns over safety persist, though, particularly with regard to venous thromboembolism (VTE), stroke and myocardial infarction (MI). Epidemiological studies consistently show an increase in risk of VTE, but the results are more contentious with regard to arterial diseases. Despite 40 years of research, the mechanisms behind these adverse effects are not understood. In this review, we integrate information from published studies of the epidemiology and pathology of the occlusive vascular diseases and their risk factors to identify likely explanations for pathogenesis in oral contraceptive users. Oral contraceptives induce both prothrombotic and fibrinolytic changes in haemostatic factors and an imbalance in haemostasis is likely to be important in oral contraceptive-induced VTE. The complexity of the changes involved and the difficulty of ascribing clinical significance has meant that uncertainty persists. A seriously under-researched area concerns vascular changes in oral contraceptive users. Histologically, endothelial and intimal proliferation have been identified in women exposed to high plasma estrogen concentrations and these lesions are associated with thrombotic occlusion. Other structural changes may result in increased vascular permeability, loss of vascular tone and venous stasis. With regard to arterial disease risk, epidemiological information relating to dose effects and joint effects with other risk factors, and studies of pathology and changes in risk factors, suggests that oral contraceptive use per se does not cause arterial disease. It can, nevertheless, synergise very powerfully with subclinical endothelial damage to promote arterial occlusion. Accordingly, the prothrombotic effects of the oral contraceptive estrogen intervene in a cycle of endothelial damage and repair which would otherwise remain clinically silent or would ultimately progress - in, for example, the presence of cigarette smoking or hypertension - to atherosclerosis. Future work in this area should focus on modification of the effects of established risk factors by oral contraceptive use rather than modification of the supposed risk of oral contraceptive use by established risk factors. Attempts to understand vascular occlusion in oral contraceptive users in terms of the general features of VTE or with reference to atherosclerosis may be limiting, and future work needs to acknowledge that such occlusions may have unique features. Unequivocal identification of the mechanisms involved would contribute considerably to the alleviation of fears over vascular disease and to the development of even safer formulations.

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.

Relationship between plasma plasminogen activator inhibitor 1 and insulin resistance

High plasminogen activator inhibitor 1 (PAI-1) levels are associated with an increased cardiovascular risk of atherothrombosis. Furthermore, increased plasma PAI-1 levels are associated with dyslipidemia, hyperinsulinemia and hypertension. This association between PAI-1 and metabolic components of the Metabolic Syndrome could explain the predisposition of insulin resistant patients to atherothrombosis. Recent studies have suggested that visceral adipose tissue might be the link between elevated plasma PAI-1 and insulin resistance in the Metabolic Syndrome. Indeed, visceral adipose tissue was proposed as a potentially important source of PAI-1 in humans. However, in light of recent studies, visceral adipose tissue appears to be involved in the increase of plasma PAI-1 via the metabolic disorders usually associated with central obesity, rather than directly. High plasma PAI-1 levels are undoubtedly related to insulin resistance, and the mechanisms which could explain such an increase in the Metabolic Syndrome appear to be multi-factorial and remain to be elucidated. These mechanisms may involve several metabolic disorders such as hyperinsulinemia, dyslipidemia, impaired glucose tolerance and hypertension, which would favor PAI-1 synthesis and release from different cell types.

Infantile obesity: a situation of atherothrombotic risk?

Obesity is a major risk factor for cardiovascular disease frequently associated with hypertension, dyslipidemia, and diabetes. In recent years, alterations in the hemostatic system have been added to these dysfunctions. We analyzed some of these alterations in coagulation and fibrinolysis in obese children (6 to 9 years old) of both sexes. We studied 61 obese children (mean body mass index [BMI], 22.35 kg/m2; 95% confidence interval [CI], 21.82 to 22.87) and 70 non-obese children (mean BMI, 16.58 kg/m2; 95% CI, 16.24 to 16.93) as a control group. The obese subjects presented significantly elevated values for insulin (P < .001), tissue-plasminogen activator ([t-PA] P < .001), plasminogen activator inhibitor-1 ([PAI-1] P < .001), and fibrinogen (P < .001) with respect to the control group. We found no significant differences in the concentration of glucose and fragment 1 + 2 of prothrombin (F1 + 2). In the obese subjects, insulin, PAI-1, and F1 + 2 were positively correlated with the BMI. On the other hand, t-PA was correlated with insulin and PAI-1 but not with the BMI. Therefore, in the obese children, there was an increment of the risk factors for cardiovascular disease.

Oral, but not transdermal, administration of estrogens lowers tissue-type plasminogen activator levels in humans without affecting endothelial synthesis

Oral estrogen administration decreases plasma levels of tissue-type plasminogen activator (tPA), which may be explained by a decrease in endothelial tPA synthesis, an increase in its hepatic clearance, or both. In the present study, we determined (1) differences between oral (ie, via the liver) ethinyl estradiol and transdermal (ie, systemic) 17beta-estradiol administration on plasma antigen levels of tPA and plasminogen activator inhibitor type-1 before and after 4 months of hormone administration and (2) effects on endothelial tPA synthesis, by measuring the local increase in plasma tPA during venous occlusion of the upper extremity. Thirty transsexual males (median age 32 years, range 20 to 44 years ) were randomly assigned to either oral ethinyl estradiol (n=15) or transdermal 17beta-estradiol (n=15); both treatments included the antiandrogen cyproterone acetate (CA). Ten males were treated with CA alone. Seventeen transsexual females (median age 27 years, range 18 to 37 years) were treated with intramuscular testosterone esters. Only oral ethinyl estradiol plus CA but neither transdermal 17beta-estradiol plus CA, nor oral CA, nor parenteral testosterone lowered plasma tPA and plasminogen activator inhibitor-1 (P<0.001 for both). tPA release during venous occlusion was not affected by oral ethinyl estradiol plus CA in males (P=0.52) or by parenteral testosterone in females (P=0.89). These data are consistent with a previous observation, in rodents, that the decrease in tPA after oral estrogen administration can be explained by an increase in hepatic tPA clearance, leaving endothelial tPA synthesis unchanged, and suggest that these mechanisms also explain the decrease in tPA in humans.

Plasma plasminogen activator inhibitor 1, insulin resistance and android obesity

Plasma plasminogen activator inhibitor 1 (PAI-1) levels are elevated in insulin-resistant subjects and are associated with increased cardiovascular risk of atherothrombosis. Strong association between PAI-1 and the metabolic components of the insulin resistance syndrome is found in clinical studies, suggesting that insulin resistance may regulate circulating PAI-1. However, the mechanisms underlying increased PAI-1 levels in such conditions are still poorly understood. Several studies have been carried out specifically in patients with central or android obesity, a major characteristic of the insulin resistance syndrome, and have suggested that visceral adipose tissue may be the major component of the relationship between android obesity and PAI-1. Accordingly, adipose tissue PAI-1 production was found to be elevated in obese human subjects, particularly in visceral adipose tissue. The genetic background for having high PAI-1 levels in several populations have been looked for and its role appeared to be weaker than that of the metabolic condition. High plasma PAI-1 levels are then clearly related to android obesity and insulin resistance, but the mechanisms whereby PAI-1 increases in plasma in these diseases remain to be determined.

Local insulin infusion stimulates expression of plasminogen activator inhibitor-1 and tissue-type plasminogen activator in normal subjects

PURPOSE

Plasma levels of plasminogen activator inhibitor-1 are increased in obesity, hypertension, and diabetes. Their correlation with insulin levels supports the hypothesis that hypofibrinolysis may affect the development of atherosclerotic complications in patients with insulin resistance. To investigate the effect of insulin on fibrinolysis, we evaluated levels of plasminogen activator inhibitor-1 (PAI-1) and tissue plasminogen activator (tPA) antigens during insulin infusion in the forearm vascular beds of 8 healthy subjects.

MATERIALS AND METHODS

Insulin was infused in the brachial artery of each subject to raise local venous concentrations to approximately 100 microU/mL. Blood samples were obtained from the brachial artery and vein at baseline, after 30, 60, 90, and 120 minutes of infusion, and 30 minutes after the end of the infusion.

RESULTS

Following intra-arterial infusion of insulin, forearm blood flow (mean +/- SD) increased progressively from 2.7 +/- 0.6 to 4.0 +/- 0.6 mL/dL/min (P <0.01) and did not return to baseline after the end of the infusion. Plasminogen activator inhibitor-1 balance increased (345 +/- 160 versus 8 +/- 152 fmol/dL/min, P <0.02) at 60 minutes, reaching baseline levels after the end of the infusion. After 90 minutes, tPA balance increased (40 +/- 26 versus 7 +/- 29 fmol/dL/min, P <0.01) with a profile similar to forearm blood flow.

CONCLUSIONS

Local hyperinsulinemia induces regional vasodilation and expression of PAI-1 and tPA antigens. An alteration of this physiological process could be involved in the development of hypofibrinolysis and atherosclerosis in states of insulin resistance.

PAI-1 produced ex vivo by human adipose tissue is relevant to PAI-1 blood level

Human adipose tissue has been shown to produce plasminogen activator inhibitor type 1 (PAI-1). However, the importance of adipose tissue in the regulation of the PAI-1 plasma level is not known. The aim of this study was to investigate the relation between the production of PAI-1 by adipose tissue, plasma PAI-1 level, and variables related to the insulin resistance state. The link between the production of PAI-1 inducers such as tumor necrosis factor-alpha and transforming growth factor-beta and the production of PAI-1 by adipose tissue was also evaluated. Blood samples were obtained as soon as possible to the induction of anesthesia from 30 patients undergoing elective abdominoplasty. PAI-1 antigen levels measured in conditioned media after a 19-hour incubation period of adipose tissue explants were significantly correlated with plasma PAI-1 antigen levels (r=0.54, P=0.004) and with systemic lipid parameters such as triglycerides and high density lipoprotein cholesterol (r=0. 46, P=0.014; r=-0.50, P=0.01, respectively) but not with insulinemia and body mass index. PAI-1 production by adipose tissue was correlated with those of TNF-alpha (r=0.5, P=0.01) and TGF-beta (r=0. 53, P=0.007). These results emphasize the role of adipose tissue in determining plasma levels of PAI-1, with a local contribution of TNF-alpha and TGF-beta in PAI-1 production by adipose tissue.

Insulin-like growth factor binding protein-1 in NIDDM: relationship with the insulin resistance syndrome

OBJECTIVE

In order to examine the role of insulin-like growth factors in the pathogenesis of accelerated macrovascular disease in noninsulin-dependent diabetes mellitus (NIDDM), we investigated the relationship between the insulin resistance syndrome and the IGF axis.

DESIGN

Cross-sectional analysis of the relationship between insulin resistance syndrome variables and concentrations of IGF-1, IGF-2, IGFBP-1 and IGFBP-3 in 80 subjects with NIDDM.

RESULTS

After correcting for age, sex and body mass index, concentrations of IGFBP-1, correlated with those of HDL-cholesterol (r = 0.40; P < 0.001), triglycerides (r = -0.24; P = 0.04), insulin (r = -0.39; P < 0.001), intact proinsulin (r = -0.32; P = 0.006), des 31,32 proinsulin (r = -0.40; P = 0.001), and with insulin sensitivity (r = 0.38; P = 0.001) and PAI-1 activity (r = -0.24; P = 0.05); IGF-1 levels only correlated with those of HDL-cholesterol (r = -0.33; P = 0.005), and this was not explained by IGFBP-1 or insulin sensitivity. With additional correction for insulin, concentrations of IGFBP-1 still correlated with HDL-cholesterol (r = 0.40; P < 0.001), but not those of triglycerides or PAI-1 activity. There were no significant relationships between levels of IGF-2 and any of the variables investigated, and IGFBP-3 levels only correlated with those of total cholesterol (r = 0.24, P = 0.04).

CONCLUSIONS

In NIDDM, concentrations of IGFBP-1 are related to those of insulin, insulin sensitivity, serum lipoproteins and PAI-1 activity. The relationship between concentrations of IGFBP-1 and HDL-cholesterol is not explained by insulin. Concentrations of IGF-1 are linked to HDL-cholesterol, and this is not explained by levels of IGFBP-1. IGFBP-1 concentrations were related to PAI-1 activity, and this may be explained by insulin, which regulates the production of IGFBP-1 and PAI-1.

On the role of c-Jun in the induction of PAI-1 gene expression by phorbol ester, serum, and IL-1alpha in HepG2 cells

We have characterized the regulation of plasminogen activator inhibitor-1 (PAI-1) gene expression by phorbol 12-myristate 13-acetate (PMA), serum, and interleukin-1alpha (IL-1alpha) in the human hepatoma cell line HepG2. PMA, serum, and IL-1alpha induced a rapid and transient 28-fold (PMA), 9-fold (serum), and 23-fold (IL-1alpha) increase in PAI-1 mRNA, peaking after approximately 4 hours. These inductions of PAI-1 mRNA accumulation were reduced by pretreatment of the HepG2 cells with the protein tyrosine kinase inhibitor genistein. Conversely, stimulation of tyrosine phosphorylation by sodium orthovanadate, an inhibitor of protein tyrosine phosphatases, caused an increase in PAI-1 mRNA levels. The effects of PMA, serum, and IL-1alpha on PAI-1 mRNA expression have been compared with their ability to modulate the expression of a chloramphenicol acetyltransferase (CAT) reporter plasmid, which was under control of the -489 to +75 region of the PAI-1 promoter, and stably transfected into HepG2 cells. This region of the PAI-1 promoter was previously found to contain a tetradecanoyl phorbol acetate-response element (TRE; between -58 and -50) necessary for PMA responsiveness and with a high affinity for c-Jun homodimers. Whereas incubation of these transfected HepG2 cells with PMA and serum showed an induction profile of CAT mRNA similar to that of PAI-1 mRNA, hardly any induction of CAT mRNA was found with IL-1alpha. In line with these findings, IL-1alpha poorly induced c-Jun homodimer binding to the PAI-1 TRE in gel mobility-shift assays. Pretreatment of HepG2 cells with the protein kinase C inhibitor Ro 31-8220 or the mitogen-activated protein kinase kinase (MAPKK)1,2 activity blocker PD98059 selectively suppressed the induction of PAI-1 (and CAT) expression by PMA, but not that by IL-1alpha. In contrast, the protein tyrosine kinase inhibitor herbimycin A blocked PAI-1 mRNA induction by IL-1 alpha only. We propose 2 separate PAI-1 inductory pathways for PMA and IL-1alpha in HepG2, both involving protein tyrosine kinase activation; the serum-induced signaling pathway may (partially) overlap with the PMA-activated protein kinase C/mitogen-activated protein kinase kinase pathway, leading to c-Jun homodimer binding to the PAI-1 TRE.