Fibrinolysis and atherosclerosis

Pai-1 gene variants and COC use are associated with stroke risk: a case-control study in the Han Chinese women

Genetic variants of plasminogen activator inhibitor type 1 (PAI-1) gene have been suggested to influence the PAI-1 transcription activity and PAI-1 levels as well as might be involved in the pathophysiology of stroke. The aims of this study are to investigate whether the polymorphisms at the PAI-1 gene are associated with the risk of stroke and to explore the combined effects of PAI-1 variants and combined oral contraceptive (COC) use for stroke risk. We conducted a nested case-control study using 453 first-ever female stroke cases and 919 age- and region-matched controls that were recruited from our prospective surveillance cohort. SNP rs1799889 was genotyped by allele-specific polymerase chain reaction (PCR), and SNPs rs7242 and rs2227631 were detected by the TaqMan SNP genotyping assay. We identified that rs1799889 5G allele conferred a protective effect against ischemic stroke while 4G allele conferred an increased risk of ischemic stroke. But we failed to suggest associations of rs7242 and rs2227631. COC users had a 1.31-fold (OR=1.31, 95% CI=1.01-1.71) increased risk of stroke compared with the non-users. Furthermore, COC users with rs1799889 4G5G/5G5G genotype had a decreased risk of ischemic stroke (OR=0.53, 95% CI=0.34-0.83). Moreover, haplotype G-5G-T was associated with an increased risk of overall stroke (OR=1.28, 95% CI=1.01-1.62). In contrast, haplotype A-4G-G and haplotype G-5G-T were slightly associated with the protection from ischemic stroke (OR=0.61, 95% CI=0.46-0.82; OR=0.61, 95% CI=0.44-0.85, respectively). The study assessed the associations of three PAI-1 SNPs and also suggested combined effects of these PAI-1 gene variants and COC use on stroke risk in the Han Chinese women.

Reduced fibrinogen, fibrinolytic biomarkers, and physical parameters after a weight-loss program in obese subjects

Background:

Obese subjects are at risk of multiple comorbidities including stroke and coronary heart disease (CHD), which is partly due to disturbances in the hemostatic system.

Aims:

The aims of the present study were to determine the effects of a weight-loss program on fibrinogen and fibrinolytic markers.

Materials and Methods:

Twenty-eight obese subjects were involved in a weight-loss program consisted of exercise and nutritional education for 12-weeks duration. Physical parameters were documented and blood specimen was tested at pre and post-intervention for fibrinogen, tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), and thrombin activatable fibrinolysis inhibitor (TAFI). Paired t-test was used for statistical analysis.

Results:

There was a significant decline in the levels of t-PA, PAI-I, TAFI and fibrinogen following the weight-loss program (P < 0.01 for each). A significant positive correlation between tPA levels and body weight, body mass index (BMI), waist circumference, and fat-free mass were found. There was also a significant correlation betwen BMI and other blood parameters.

Conclusion:

Reduced fibrinogen, fibrinolytic, and physical parameters were demonstrated in obese subjects following the weight reduction program. These findings suggest the possible beneficial effects of this program on the hemostatic burden particularly on the fibrinolytic biomarkers.

Association of genetic variants of fibrinolytic system with stroke and stroke subtypes

Genetic variants of tPA (PLAT) and PAI-1 genes have been suggested to be the risk factors for stroke. In the present case-control study we investigated the association of -7351C/T polymorphism (rs2020918) and I/D polymorphism of tPA gene and Insertion/deletion polymorphism (4G/5G) of PAI-1 gene with genetic predisposition to ischemic stroke. 516 stroke patients and 513, sex and age matched healthy controls were involved in the study. We did not find a significant association of tPA -7351C/T polymorphism and PAI-1 4G/5G polymorphism with stroke. However, in case of I/D polymorphism significant difference was observed in the genotypic distribution and allelic frequency between the stroke patients and healthy controls. DD genotype and D allele associated significantly with stroke (p=0.002 and <0.001 respectively). We also found significant association of I/D polymorphism with intracranial large artery atherosclerosis and stroke of undetermined etiology. Exploring the association between gene-gene interaction (26 combinations including the three variants) and stroke, we found that individuals with CC+4G4G+DD, CC+5G5G+ID, CT+4G5G+ID, CT+5G5G+II, CT+5G5G+ID and TT+4G5G+II had a significantly higher risk of stroke. The results of this study suggest that -7351C/T polymorphism of tPA and 4G/5G polymorphism of PAI-1 are not associated with stroke, while as DD genotype and D allele of tPA gene are important risk factors for ischemic stroke. Further we found that the subjects with different tPA and PAI genotype combinations displayed a significantly high risk for overall ischemic stroke suggesting that gene-gene interaction involving more variants may change the susceptibility of particular subjects to the disease.

Levothyroxine (LT4) suppression treatment for benign thyroid nodules alters coagulation

OBJECTIVE

Endogenous hyperthyroidism is associated with altered coagulation. The aim of the present study is to investigate the effect of levothyroxine (LT(4)) suppression treatment for benign thyroid nodules on coagulation system.

DESIGN

Prospective case-control study. Patients Thirty consecutive euthyroid pre-menopausal women with nodular goitre disease and 28 healthy controls were included in the study.

MEASUREMENTS

Plasma fibrinogen, d-dimer, von Willebrand factor (vWF), tissue factor (TF), tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI-1) and tissue factor pathway inhibitor (TFPI) levels were measured at baseline and after LT(4) suppression therapy.

RESULTS

Plasma levels of fibrinogen, d-dimer, vWF, TF and PAI-1 increased significantly after treatment with LT(4) for 1 year. Serum FT(4) was a significant predictor of increased fibrinogen, vWF and PAI-1 levels, when the data was controlled for age and BMI.

CONCLUSIONS

Our results suggest that LT(4) suppression therapy for benign thyroid nodules is associated with enhanced coagulation.

Diet and haemostatic processes

Diet plays an important role in the primary and secondary prevention of cardiovascular disease. The growing perception that abnormal haemostatic processes of coagulation, platelet aggregation and fibrinolysis contribute to cardiovascular disease aetiology motivated this review on the relationships of diet, specific foods and nutrients with haemostatic function. Functional endpoints that reflect the function and status of some of these processes and which can be measured in dietary trials are identified. The effects of energy intake and expenditure, alcohol, total fat and specific fatty acids, non-starch polysaccharides (dietary fibre), antioxidant nutrients and some foods on a variety of haemostatic markers are reviewed. The results indicate that the prudent low-fat, high-fibre diet and maintenance of ideal body weight recommended to protect against and treat hyperlipidaemia and coronary heart disease will also benefit haemostatic profiles. It is concluded that more research on specific effects is needed for improved recommendations on a population level for prevention of cardiovascular disease.

Thrombin activatable fibrinolysis inhibitor antigen levels are inversely correlated with plasminogen activator inhibitor-1 antigen levels in hyperthyroid patients

Both increased and decreased fibrinolytic activity have been reported in patients with hyperthyroidism. Elevated levels of plasma plasminogen activator inhibitor-1 (PAI-1) antigen have been found in hyperthyroid patients. Thrombin activatable fibrinolysis inhibitor (TAFI) is a novel plasma protein, which inhibits fibrinolysis through removal of C-terminal lysines from partially degraded fibrin. Previously, we showed that plasma TAFI antigen levels were increased in patients with overt and subclinical hypothyroidism. The aim of this study is to investigate plasma levels of TAFI and PAI-1 antigens in hyperthyroid patients. PAI-1 and TAFI antigen levels were measured in the plasma of 29 patients with hyperthyroidism (14 overt hyperthyroid and 15 subclinical hyperthyroid), and 26 healthy individuals. Although there were increased levels of PAI-1 antigen in hyperthyroid patients, plasma TAFI antigen levels were significantly lower compared to controls (80.79 ng/ml vs. 32.42 ng/ml, p = 0.000 for PAI-1; 10.42 microg/ml vs. 12.24 microg/ml, p = 0.009 for TAFI). Elevated PAI-1 antigen levels were positively correlated with free thyroid hormones, although TAFI antigen levels were in negative correlation with free thyroxine. Furthermore, an inverse correlation between PAI-1 and TAFI antigen levels was found. Our study demonstrated that TAFI antigen levels were decreased in patients with hyperthyroidism. Inverse correlation with PAI-1 suggests that the decrease in TAFI antigen levels may be due to activation of TAFI pathway. Further studies evaluating the underlying mechanisms of low TAFI antigen levels in hyperthyroidism should be undertaken.

Dietary Flavanols and Platelet Reactivity

Epidemiology studies suggest that the consumption of diets rich in flavonoids is associated with reduced risk of cardiovascular disease. Plant-derived foods and beverages, such as red wine, tea, grape and grape juice, cocoa and chocolate, can be rich in 1 particular class of flavonoid, the flavan-3-ols. There is now an increasing body of research that suggests that consuming flavanol-rich foods can positively affect hemostasis, through mechanisms that either directly affect platelet function or increase certain endothelium-derived factors that maintain platelet acquiescence or increase fibrinolysis. In this paper, we will review a series of in vivo studies on the effects of flavanol-rich cocoa and chocolate on platelet activation and platelet-dependent hemostasis. In addition, we will briefly review the body of literature with regard to other flavanol-rich foods and beverages, and possible mechanisms of action.

Plasminogen Activator Inhibitor-1 4G/5G Polymorphism and Risk of Stroke

Background and Purpose— Impaired fibrinolytic function secondary to elevated plasminogen activator inhibitor-1 (PAI-1) levels has been implicated in ischemic stroke. PAI-1 levels are determined by genetic factors and environmental factors, triglyceride levels in particular. The aim of this study was to investigate the common functional 4/5 guanosine (4G/5G) polymorphism in the promoter region of the PAI-1 gene and the risk of stroke.

Methods— A nested case–control study design was applied, using baseline data for 2 independent cohorts obtained at population-based surveys in northern Sweden. In study A, there were 113, and in study B, there were 275 individuals without major concomitant disease at baseline who later experienced a first-ever stroke. Blood samples obtained at baseline were analyzed for potential risk factors, including the 4G/5G polymorphism of the PAI-1 gene.

Results— The 4G allele of the PAI-1 polymorphism was associated with an increased risk of future ischemic stroke in both studies (odds ratio [OR] of 4G homozygosity, 1.87; 95% CI, 1.12 to 3.15 in study A; OR of 4G homozygosity, 1.56; 95% CI, 1.12 to 2.16 in study B). Individuals with the combination of hypertriglyceridemia and 4G homozygosity were at the greatest risk of developing stroke. Multiple logistic regression analysis identified 4G homozygosity, systolic blood pressure, and diabetes as independent predictors of ischemic stroke.

Conclusions— Identical findings in 2 independent studies strongly suggest a true and clinically important association between PAI-1 4G/5G genotype and risk of future ischemic stroke. The observed modification of the genotype effect by triglycerides may be interpreted as a gene–environment interaction.

Acute hyperglycemia alters von Willebrand factor but not the fibrinolytic system in elderly subjects with normal or impaired glucose tolerance

To assess whether acute hyperglycemia affects fibrinolytic balance in elderly subjects with normal glucose tolerance (NGT) or impaired glucose tolerance (IGT), 40 non-obese elderly subjects (20 NGT, age 68 +/- 8 years; and 20 IGT, age 69 +/- 11 years) were studied. On two experimental days, randomly allocated and spaced 1 week apart, plasma concentrations of glucose, insulin, fibrinogen, tissue plasminogen activator, plasminogen activator inhibitor type 1 and von Willebrand factor (vWF) were measured in each subject at baseline (0) and 30, 60, 90, 120 min after the ingestion of 75 g glucose or a similarly sweet dose of aspartame (250 mg) (control test). In both NGT and IGT elderly subjects, tissue plasminogen activator, plasminogen activator inhibitor type 1 and fibrinogen plasma levels did not significantly change after both oral aspartame and glucose load. In IGT subjects, vWF plasmatic levels decreased after glucose (not aspartame) oral load, reaching the minimum level at 90 min after load (82.7 +/- 7.8 versus 93.7 +/- 10.2, P <0.01). These results demonstrate that acute hyperglycemia does not modify plasma fibrinolysis in elderly subjects. The decrease of plasma concentration of vWF in IGT elderly subjects requires cautious interpretation and further extensive investigations.

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.

Progression of diabetic nephropathy: role of plasma homocysteine and plasminogen activator inhibitor-1

Among patients with diabetic nephropathy, the decline in glomerular filtration rate (GFR) varies substantially, ranging from 2 to 20 mL/min per year. Identification of predictors of progression in diabetic nephropathy is important. Plasma total homocysteine (tHcy) rises with urinary albumin excretion rate in diabetes, and plasminogen activator inhibitor-1 (PAI-1) has been correlated with increased matrix accumulation in various glomerulopathies. In this prospective observational cohort study, we evaluated the importance of baseline tHcy and PAI-1 as predictors of the rate of decline in GFR. Baseline tHcy and PAI-1 were measured in 157 type 1 diabetic patients with diabetic nephropathy (92 men; mean age, 41 +/- 10 years; mean diabetes duration, 27 +/- 8 years; median GFR, 80 mL/min/1.73 m(2) [range, 23 to 143 mL/min/1.73 m(2)]). Hereafter, GFR was measured yearly with a plasma clearance technique for at least 3 years (median, 7 years [range, 3.0 to 8.3 years]). The mean rate of decline in GFR was 3.7 +/- 0.3 mL/min per year. A linear regression analysis revealed a borderline significant relationship between rate of decline in GFR and tHcy (P = 0.069) and PAI-1 (P = 0.087). Analysis of the rate of decline in GFR and tertiles of tHcy and PAI-1 revealed that increasing levels of tHcy were correlated with a significantly faster decline in GFR (P = 0.025), whereas increasing levels of PAI-1 were not. After adjustment for other well-established risk factors for progression of nephropathy in a multiple linear regression analysis, however, neither tHcy levels nor PAI-1 levels were independent predictors of rate of decline in GFR.

Critical role of Rho-kinase and MEK/ERK pathways for angiotensin II-induced plasminogen activator inhibitor type-1 gene expression

Plasminogen activator inhibitor type-1 (PAI-1) plays an integral role not only in the regulation of fibrinolytic activity but also in the pathogenesis of atherosclerosis and hypertension. We investigated the signaling pathways of angiotensin II (Ang II) leading to PAI-1 gene expression. Ang II increased the PAI-1 mRNA and protein levels in a time- and dose-dependent manner through the Ang II type 1 receptor in vascular smooth muscle cells. PAI-1 gene promoter activity measured by luciferase assay was significantly increased by Ang II. PAI-1 mRNA stability was also increased by Ang II. Ang II-induced PAI-1 mRNA upregulation was inhibited by BAPTA-AM, genistein, and AG1478, suggesting that intracellular calcium, tyrosine kinase, and epidermal growth factor receptor transactivation are involved. Furthermore, PD98059, an inhibitor of extracellular signal-regulated kinase (ERK) kinase (MEK), almost completely suppressed Ang II-induced PAI-1 upregulation. Adenovirus-mediated overexpression of the dominant-negative form of Rho-kinase or Y27632, a Rho-kinase inhibitor, also completely prevented PAI-1 induction by Ang II without affecting Ang II-induced ERK activation. These data suggest that activation of MEK/ERK and Rho-kinase pathways plays a pivotal role in PAI-1 gene upregulation by Ang II. The Rho-kinase pathway may be a novel target to inhibit Ang II signaling, and its inhibition may be useful in the treatment of hypertension as well as atherosclerosis.

Plasminogen activator inhibitor-1 and apolipoprotein E gene polymorphisms and diabetic angiopathy

BACKGROUND

A point mutation in the plasminogen activator inhibitor-1 (PAI-1) gene and a three-allelic variation in the apolipoprotein-E (ApoE) gene have been suggested as risk factors for the development of diabetic micro- and macrovascular complications.

METHODS

We studied 198 type 1 diabetic patients with diabetic nephropathy [121 men, age (mean+/-SD) 41+/-10 years, diabetes duration 28+/-8 years] and 192 patients with persistent normoalbuminuria (118 men, age 43+/-10 years, diabetes duration 27+/-9 years).

RESULTS

Male patients with nephropathy had elevated plasma PAI-1 levels [geometric mean (95% CI)], 70 (62-79) ng/ml, compared with normoalbuminuric men, 43 (38-47) ng/ml, P<0.001. Even though nephropathic patients with the 4G4G genotype tended to have higher plasma PAI-1 levels, P=0.06, no difference in allele frequency (4G/5G) was seen between patients with and without nephropathy: 0.538/0.462 vs 0.539/0.461, respectively. Nor did ApoE allele frequencies (epsilon2/epsilon3/epsilon4) differ between nephropathic and normoalbuminuric patients: 0.099/0.749/0. 152 vs 0.081/0.745/0.174, respectively. Genotype distributions were also similar, n.s. Coronary heart disease was more prevalent (36%) among nephropathic patients carrying the atherogenic epsilon4-allele compared with 12% in patients with the epsilon3,epsilon3 genotype, P<0.001. No associations between diabetic retinopathy and PAI-1 or ApoE polymorphisms were observed, n.s.

CONCLUSIONS

The ApoE polymorphism may accelerate the development of coronary heart disease often seen in Caucasian patients with type 1 diabetes and diabetic nephropathy, a condition characterized by elevated plasma PAI-1 in men. Neither the PAI-1 nor the ApoE gene polymorphism contributes to the genetic susceptibility to diabetic nephropathy or retinopathy.

Novel risk factors for atherosclerosis

In the past several years, evidence has accumulated that factors other than conventional risk factors may contribute to the development of atherosclerosis. Conventional risk factors predict less than one half of future cardiovascular events. Furthermore, conventional risk factors may not have the same causal effect in different ethnic groups in whom novel risk factors may have a role. These newer risk factors for atherosclerosis include homocysteine, fibrinogen, impaired fibrinolysis, increased platelet reactivity, hypercoagulability, lipoprotein(a), small dense low-density lipoprotein cholesterol, and inflammatory-infectious markers. Identification of other markers associated with an increased risk of atherosclerotic vascular disease may allow better insight into the pathobiology of atherosclerosis and facilitate the development of preventive and therapeutic measures. In this review, we discuss the evidence associating these factors in the pathogenesis of atherosclerosis, the mechanism of risk, and the clinical implications of this knowledge.

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.

Effects of gemfibrozil on insulin sensitivity and on haemostatic variables in hypertriglyceridemic patients

In order to assess the efficacy of gemfibrozil on lipid and haemostatic parameters in patients with plurimetabolic syndrome, a multicenter double-blind placebo controlled, parallel study was carried out in 56 patients with primary hypertriglyceridemia and glucose intolerance. These patients had elevated PAI activity and antigen and t-PA antigen levels at rest and after venous occlusion. Gemfibrozil reduced plasma triglyceride levels (P<0.001), whereas it increased free fatty acids (P<0.05) and high density lipoprotein cholesterol levels (P<0.05). In those patients reaching normalization of plasma triglyceride levels (triglyceride reduction > or =50%) (n=15), insulin levels (P<0.05) as well as the insulin resistance index were reduced by gemfibrozil treatment, suggesting an improvement of the insulin resistance index in this patient subgroup. Gemfibrozil treatment did not affect plasma fibrinolysis or fibrinogen levels, despite marked reduction of plasma triglycerides and improvement of the insulin sensitivity associated with triglyceride normalization.

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.

Very low density lipoprotein-mediated signal transduction and plasminogen activator inhibitor type 1 in cultured HepG2 cells

In normal subjects and in patients with cardiovascular disease, plasma triglycerides are positively correlated with plasminogen activator inhibitor type 1 (PAI-1) levels. Moreover, in vitro studies indicate that VLDLs induce PAI-1 synthesis in cultured cells, ie, endothelial and HepG2 cells. However, the signaling pathways involved in the effect of VLDL on PAI-1 synthesis have not yet been investigated. We report that VLDLs induce a signaling cascade that leads to an enhanced secretion of PAI-1 by HepG2 cells. In myo-[(3)H]inositol-labeled HepG2 cells, VLDL (100 microg/mL) caused a time-dependent increase in [(3)H]inositol phosphates, the temporal sequence being tris>bis>monophosphate. VLDL brought about a time-dependent stimulation of membrane-associated protein kinase C (PKC) activity and arachidonate release. Finally, VLDL stimulated mitogen-activated protein (MAP) kinase, and this effect was reduced by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H7), which suggests that PKC plays a pivotal role in MAP kinase phosphorylation. VLDL-induced PAI-1 secretion was completely prevented by U73122, a specific inhibitor of phosphatidylinositol-specific phospholipase C, by H7 or by PKC downregulation, and by mepacrine (all P<0.01 versus VLDL-treated cells). 3,4,5-Trimethoxybenzoic acid 8-(diethylamino)-octyl ester, which prevents Ca2+ release from intracellular stores, inhibited VLDL-induced PAI-1 secretion by 60% (P<0.05), and the MAP kinase/extracellular signal-regulated kinase kinase (MEK) inhibitor PD98059 completely suppressed both basal and VLDL-induced PAI-1 secretion. These data demonstrate that VLDL-induced PAI-1 biosynthesis results from a principal signaling pathway involving PKC-mediated MAP kinase activation.

Unsaturated fatty acids increase plasminogen activator inhibitor-1 expression in endothelial cells

In vivo studies have demonstrated a strong positive correlation between plasma very low density lipoprotein (VLDL) triglyceride and plasma plasminogen activator inhibitor-1 (PAI-1) activity levels. Furthermore, VLDL has been shown to induce PAI-1 secretion from cultured endothelial cells. In contrast, no or variable effects on PAI-1 secretion have been reported for native low density lipoprotein. It could be speculated that fatty acids derived from VLDL triglycerides are the actual mediators, resulting in an enhanced secretion of PAI-1. In the present study, we have analyzed the effects of both saturated and unsaturated fatty acids on PAI-1 expression and secretion by endothelial cells. Addition of 0 to 50 micromol/L of either palmitic acid or stearic acid had no effect on PAI-1 secretion from human umbilical vein endothelial cells or EA. hy926 cells. In contrast, addition of oleic acid, linoleic acid, linolenic acid, and eicosapentaenoic acid resulted in a significant increase in PAI-1 secretion from both cell types. Northern blot analysis of PAI-1 mRNA levels was in agreement with these findings. Transfection experiments demonstrated that addition of linolenic acid and eicosapentaenoic acid significantly increased PAI-1 transcription. The fatty acid response region was localized to a previously described VLDL-inducible region of the PAI-1 promoter. Electromobility shift assays demonstrated that unsaturated fatty acids induced the same complex as did VLDL, whereas saturated fatty acids had no effect. Furthermore, it was demonstrated that the activation procedure did not involve fatty acid oxidation to any significant extent. In conclusion, the present study demonstrates that unsaturated fatty acids increase PAI-1 transcription and secretion by endothelial cells in vitro. The effect appears to be mediated by a previously described VLDL-inducible transcription factor.

The relationships between insulin and plasminogen activator inhibitor 1 levels: assessment in groups of subjects with dyslipidaemia and hypertension

Elevated plasminogen activator inhibitor-1 (PAI-1) levels have been described in some populations to associate with hyperinsulinaemia in the metabolic syndrome which predisposes to coronary heart disease (CHD). This association, if consistently present, could provide more evidence for a synergistic role for insulin resistance and altered fibrinolysis in the pathogenesis of CHD. To test the hypothesis further therefore, we explored the relationships between the fasting levels of insulin and PAI-1 and lipids in groups of non-diabetic Arab subjects classified as: A: normolipidaemic (n = 148); B: hyperlipidaemic: (n = 99), subdivided into - C: normotensive (n = 71) and D: hypertensive (n = 28); and E: patients with CHD (n = 12). In Group A, fasting insulin (FI) was 7.2+/-(SD) 3.4 mU/l, PAI-1 30.6+/-9.7 ng/ml, both levels significantly lower (P < 0.05) than in Group B as a whole (FI 9.7+/-5.2, PAI-1 36.9+/-10.6), or as normotensive Group C (FI 9.4+/-5.4, PAI-1 36.7+/-10.3) or hypertensive Group D (FI 10.9+/-4.8, PAI-1 37.2+/-11.5). These values were highest in the hyperlipidaemic hypertensive Group D. There were no significant differences relative to the hyperlipidaemic phenotype of predominant hypercholesterolaemia, hypertriglyceridaemia or mixed hyperlipidaemia. PAI-1 (34.7+/-13.8) and FI (7.0+/-2.4) levels in Group E with CHD were similar to those of Group A but lower than values seen in Groups B, C and D. Consistent positive correlations (r = 0.32-0.41, P <0.01) were demonstrable in all the groups between PAI-1 and triglycerides levels. There were also significant correlations between insulin and PAI-1 (r = 0.20, P<0.1) in all the subjects (grouped as a whole, n = 259) and in normolipidaemic Group A (r = 0.29, P < 0.01) but not in any of the hyperlipidaemic groups or in patients with CHD. This study therefore suggests that levels of insulin and PAI-1 are increased in hyperlipidaemic subjects, particularly when also hypertensive. The further observation of significant correlations between insulin and PAI-1 levels only in normolipidaemic subjects and not those who were hyperlipidaemic or with CHD is at variance with observations in Caucasians in whom strong positive correlations between insulin and PAI-1 had suggested that elevated PAI-1 levels should constitute one more component of the metabolic syndrome which strongly predisposes to CHD. Whether this is a racial variation or an artifact of the insulin/PAI-1 assay methodology is unclear and deserves further study.