Immunological Relationship Between Plasminogen Activator Inhibitors from Different Sources

Retinoids induce the PAI-1 gene expression through tyrosine kinase-dependent pathways in vascular smooth muscle cells

Retinoids exert their pleiotropic effects on several pathophysiologic processes, including neointima formation after experimental vascular injury. Plasminogen activator inhibitor-1 (PAI-1) has been proposed to play an inhibitory role in arterial neointima formation after injury. We examined whether retinoids regulate PAI-1 expression in cultured vascular smooth muscle cells (SMCs). Northern blot analysis showed that all-trans retinoic acid (atRA) and 9-cis retinoic acid (9cRA) increased PAI-1 mRNA levels in a dose-dependent manner. These responses were completely inhibited by tyrosine kinase inhibitors. The half-life of PAI-1 was not affected by atRA, suggesting that induction of PAI-1 mRNA was mainly regulated at the transcriptional levels. Stable and transient transfection assays of the human PAI-1 promoter-luciferase constructs indicate that DNA sequence responsive to either ligand-stimulated or overexpressed retinoic acid receptor-alpha expression vector lies downstream of -363 relative to the transcription start site, where no putative retinoic acid response element is found. These results indicate that atRA and 9cRA increase PAI-1 gene transcription through pathways involving tyrosine kinases in SMCs. Because PAI-1 inhibits the production of fibrinolytic protein plasmin that facilitates SMC migration, induction of the PAI-1 gene expression by atRA may at least partly account for the role of atRA as an important inhibitor of neointima formation.

Hyperglycemia induces PAI-1 gene expression in adipose tissue by activation of the hexosamine biosynthetic pathway

We examined whether acute in vivo increases in either plasma glucose or insulin concentrations stimulate PAI-1 gene expression in fat tissue. We studied chronically catheterized unstressed and awake, lean (approximately 300 g, n=12) and obese (approximately 450 g, n=12) Sprague-Dawley rats. Hyperglycemia (approximately 18mM) was induced for 3 h by glucose infusion during a pancreatic clamp (somatostatin inhibited endogenous insulin secretion). Compared with equivalent saline infusion, hyperglycemia induced a 6-7 fold increase in PAI-1 gene expression in both lean and obese rats (P<0.001). When the rate of cellular glucose uptake was matched during a euglycemic hyperinsulinemic (approximately 60 microU/ml) clamp, PAI-1 gene expression in both obese and lean rats was proportionately and significantly increased (P<0.001). We further examined whether induction of the hexosamine biosynthetic pathway would mimic the effects of hyperglycemia and hyperinsulinemia on PAI-1 gene expression. Indeed, infusion of glucosamine (GlcN, 30 micromol/kg/min), induced a approximately 3-4 fold increase (P<0.01) in PAI-1 gene expression in both lean and obese animals. While obese rats had a four times greater fat mass then the lean rats, PAI-1 gene expression remained significantly higher when expressed as per gram fat. Our results support the hypothesis that increased glucose uptake induces PAI-1 gene expression in adipose tissue, probably through the activation of the hexosamine biosynthetic pathway. These findings may account for some of the fibrinolytic alterations seen in obese type 2 diabetic humans.

The role of fat cell derived peptides in age-related metabolic alterations

Aging in humans is associated with alterations in body fat distribution and a parallel gradual increase in the prevalence of atherosclerotic cardiovascular disease, as well as mortality of all causes. Because of nutrient cost, availability, and the sedentary life-style, half of the western world population has fat mass in excess of 30% of the body weight that weighs 3-4 times more than the fat mass of lean subjects. Recent discoveries of various hormones, cytokines and complement factors secreted by adipose cells opened a new avenue of research, looking at the role of these fat derived peptides in different conditions. We will focus here on the potential role of fat tissue in different physiological and physiopathological conditions associated with age-related metabolism and risk factors for diseases. We will also exemplify how body fat capacity, distribution and function can be directly linked, and may play a central role in energy metabolism and homeostasis, atherosclerosis, and possibly in the defense against cancer. We hypothesize that biological pathways involved in nutrient regulation in fat tissue may be important in inducing longevity in calorie restricted animals.

Plasminogen activator inhibitor-1 (PAI-1) content in platelets from healthy individuals genotyped for the 4G/5G polymorphism in the PAI-1 gene

We have studied PAI-1 activity and antigen content in platelets and in plasma from 37 healthy individuals who were also genotyped for the 4G/5G polymorphism in the PAI-1 promoter region. The PAI-1 data obtained were compared with the vitronectin and the beta-thromboglobulin contents in platelets from the same individuals. A highly significant correlation between PAI-1 activity and PAI-antigen was obtained, both in the plasma samples (p < 0.0001) and in the platelet lysates (p < 0.001). The specific activity of PAI-1 was higher in plasma than in the platelet lysates, but interindividual variation was more pronounced among platelet lysates (range 159,000-1,190,000 U/mg). The calculated specific activity of PAI-1 in platelets seems to be higher than what could be expected from theoretical considerations regarding half-life of platelets in the circulation and conversion of functional PAI-1 to latent PAI-1. On analysis of the influence of the 4G/5G polymorphism, individuals who were homozygous for the 4G allele seemed to have higher levels of PAI-1 activity and antigen in the platelet lysates, when compared to the other genotypes. In platelet lysates, but not in plasma, a strong correlation was observed between the concentrations of PAI-1 and beta-thromboglobulin (r2 = 0.70, p < 0.001). Vitronectin could be detected in the platelet lysates in low concentrations (497 +/- 334 micrograms/l). However, using a newly developed ELISA method for PAI-1-vitronectin complex we failed to demonstrate such a complex in the platelet lysates. Therefore, the mechanism involved in stabilization of PAI-1 activity in the platelets is at present not understood.

The status of PAI-1 as a risk factor for arterial and thrombotic disease: a review

Plasminogen activator inhibitor-1 (PAI-1) is a rapid inhibitor of tissue plasminogen (tPA) in vivo. Evidence suggests that the level of plasma PAI-1 activity is responsible for the regulation of the whole fibrinolytic process through this tPA/PAI-1 interaction. Levels of PAI-1 have therefore emerged as a candidate for a thrombotic risk factor. Recent epidemiological data supports the view that high plasma levels of PAI-1 may be important in the pathogenesis of arterial and thrombotic disease. These data are reviewed and their significance discussed. PAI-1 expression has been shown to be regulated by many different factors in vitro and the relevance of these data to in vivo physiology is addressed. The current knowledge of the biochemistry, expression and genetics of PAI-1 is also presented and the significance of this to disease pathogenesis is discussed.

Relationship of thrombohemorrhagic complications to endothelial cell function in patients with chronic myeloproliferative disorders

Thrombotic and hemorrhagic disorders are common complications of the myeloproliferative disorders. Endothelial cells release both procoagulant and profibrinolytic factors, which may contribute to these hemorrhagic or thrombotic complications. The pre- and postvenous stasis levels of the procoagulant and profibrinolytic factors produced by endothelial cells were correlated with the occurrence of complications in polycythemia rubra vera (PRV) patients (n = 29) and essential thrombocythemia (ET) patients (n = 17) compared with normal patients (n = 17). Tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor (PAI) activity, von Willebrand's factor (vWF) activity and antigen (vWF:Ag), and factor VIII activity were measured. The resting tPA activity was significantly higher in the two disease groups compared with normal controls, but no difference between the levels of tPA and either complication within the disease groups was observed. Significantly elevated tPA following venous stasis was observed in the patients of both disease groups who had bleeding complications. Significant decreases, compared with the normal group, in both resting and postvenous stasis levels of PAI were observed in the disease groups regardless of complication history. The subjects from both disease groups with thrombotic complications had significantly elevated resting vWF and both resting and postvenous stasis vWF:Ag levels compared with normal controls. The endothelial cell is likely to be responding to abnormal hemostasis rather than being primarily involved in the genesis of a hyper- or hypocoaguable state.

Measurement of plasminogen activator inhibitor 1 (PAI-1) in plasma with various monoclonal antibody-based enzyme-linked immunosorbent assays

Four monoclonal antibodies, MA-7D4, MA-7F5, MA-12A4 and MA-15H12, were raised against human plasminogen activator inhibitor-1 (PAI-1). MA-7D4 and MA-7F5 had an inhibitory effect on PAI-1 activity, whereas MA-15H12 and MA-12A4 did not affect PAI-1 activity. MA-7D4 was used previously as capture antibody in combination with MA-7F5 conjugated to horseradish peroxidase (7F5-HRP) to construct an ELISA which was 12 times more sensitive towards free PAI-1 as compared to PAI-1 in complex with human tissue-type plasminogen activator (t-PA) (Blood 71: 220-225, 1988). MA-15H12, as capture antibody, in combination with MA-12A4 corjugated to horseradish peroxidase (12A4-HRP) yielded an ELISA which was equally sensitive towards free PAI-1 and PAI-1/t-PA complex. Another ELISA was constructed using MA-15H12 as capture antibody in combination with an anti-t-PA antibody (MA-62E8) conjugated to horseradish peroxidase (62E8-HRP), allowing the specific measurement of t-PA/PAI-1 complexes and the development of an immunofunctional method for the specific quantitation of active PAI-1. These assays were then used to measure PAI-1 levels in plasma and the values obtained were compared with the data obtained by functional methods. It was found that 44% to 60% of free PAI-1 antigen in normal plasma is active and that t-PA occurs mainly as t-PA/PAI-1 complexes. In plasma from 48 patients suffering from angina pectoris no statistical difference in PAI-1 activity, PAI-1 antigen or PAI-1/t-PA complex could be observed as compared to normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification of high and low molecular weight plasminogen activator inhibitor 1 from fibrosarcoma cell-line HT 1080 conditioned medium

Functionally active (high-Mr) and inactive (low-Mr) plasminogen activator inhibitor 1 (PAI) have been purified from fibrosarcoma cell-line HT 1080 conditioned medium, containing 1% fetal calf serum. The two forms were first purified by affinity chromatography on heparin-Sepharose and then separated from each other by gel filtration on Sephadex G-150. The final purification was achieved by affinity chromatography on insolubilized monoclonal antibodies towards human PAI. Alternatively, the low-Mr form was purified by chromatography on carboxymethyl-cellulose. Low-Mr PAI purified in this way, could be almost fully reactivated by treatment with guanidinium chloride. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis followed by immunoblotting revealed that the low-Mr form contained nothing but PAI at an Mr of about 50,000. In addition to PAI, the high-Mr form contained a component, which was not antigenically related to PAI. This compound had a molecular weight of about 75,000 and its NH2-terminal amino acid sequence corresponded to that of human vitronectin. We conclude that the high-Mr form of PAI constitutes a complex between 50,000 Mr PAI and vitronectin from fetal calf serum.

Plasminogen activators and plasminogen activator inhibitor in malignant and non-malignant ascitic fluid

Ascitic fluid from tumour patients (hepatoma, gastric cancer, gallbladder cancer, colorectal cancer, ovarian cancer) and from non-malignant diseases (liver cirrhosis, congestive heart failure) were compared with respect to their content of determinants of the fibrinolytic system, tissue-type plasminogen activator antigen (t-PAag) and activity (t-PAact), urokinase-type plasminogen activator antigen (u-PA) and plasminogen activator inhibitor activity (PAI). Furthermore, SDS-polyacrylamide slab-gel electrophoresis (SDS-PAGE) was performed to evaluate molecular weight distribution of the detectable fibrinolytic parameters. In malignant ascites, PAI activity was three to four times higher, and increased complex formation of PAI with t-PA could be demonstrated, compared with non-malignant ascitic fluid. Tissue-type plasminogen activator antigen and activity showed a similar concentration in ascites of both study groups. Urokinase-type plasminogen activator antigen was detectable neither in ascites of malignant nor in ascites of non-malignant origin. It is concluded that t-PA is the physiological plasminogen activator in ascites and that increased PAI levels followed by increased complex formation between t-PA and PAI might reflect a reaction of the peritoneum.

Angiogenic properties of Kaposi's sarcoma-derived cells after long-term culture in vitro

Cells derived from lung biopsies and pleural effusions from AIDS patients with Kaposi's sarcoma (KS) of the lungs were established in long-term culture with the aid of conditioned medium from HTLV-II-transformed T cells (HTLV-II CM). These AIDS-KS cells were similar to the so-called spindle cells in KS lesions and had some of their features. They produced factors that supported their own growth (autocrine) and the growth of other cells (paracrine), including umbilical vein endothelium and fibroblasts. That the AIDS-KS cells also expressed potent angiogenic activity was demonstrated by the chorioallantoic membrane assay and by subcutaneous inoculation of AIDS-KS cells into nude mice, which resulted in the development of angiogenic lesions composed of mouse cells and showing histological features similar to those of human KS lesions. These data suggest that AIDS-associated KS and possibly other types of KS may be initiated by signals that induce the growth of particular cells (spindle cells of lymphatic or vascular origin) and the expression of autocrine and paracrine activities.

Bovine endothelial cell plasminogen activator inhibitor. Purification and heat activation

A plasminogen activator inhibitor (PAI) was purified from bovine endothelial cell conditioned medium by a simple procedure in the absence of protein denaturant. The yield was 2.2 mg from 1.61 conditioned medium in a typical experiment. The purified inhibitor showed a single band on sodium dodecyl sulfate/polyacrylamide gel electrophoresis and reverse fibrin autography with an apparent molecular mass of 45 kDa. The amino-terminal 40-amino-acid sequence was determined and found to be 70% similar to the reported corresponding sequence of human PAI-1. The amino acid composition also revealed a close relationship between bovine PAI and human PAI-1. The purified PAI was substantially inactive (570 U/mg) but it could be activated by treatment with protein denaturants such as 1% SDS (1.8 X 10(5) U/mg) and 4 M guanidine-HCl (1.5 X 10(5) U/mg). A more effective activation of this latent PAI was achieved by heat treatment at 100 degrees C for 2.5 min, generating the specific activity of 1.0 X 10(6) U/mg. The heat-activated PAI lost its activity during incubation at 56 degrees C for 30 min, but repeated heat at 100 degrees C for 2.5 min could regenerate about 70% of the initial activity. Treatment at 37 degrees C, 56 degrees C and 80 degrees C, however, failed to activate the latent PAI at all. These findings suggest that the buried reactive site of the latent PAI is exposed as a result of a heat-induced, specific conformational change, but tends to be masked again during renaturation under mild conditions, i.e. the PAI protein takes on preferentially a latent form.

Interactions of tissue-type plasminogen activator with plasma inhibitors and their pharmacologic implications

To delineate interactions of infused tissue-type plasminogen activator (t-PA) with inhibitors in plasma and their impact on fibrinolytic activity, serial plasma samples from patients with acute myocardial infarction and from normal rabbits given infusions of t-PA were assayed for t-PA antigen, activity of "fast acting" plasminogen activator inhibitor (PAI-1), and the presence and nature of t-PA-inhibitor complexes. In patients, endogenous t-PA circulated predominantly as a 100 kilodalton (kDa) complex with PAI-1, as verified by immunoprecipitation. During infusions, t-PA circulated not only as free t-PA (55 kDa) but also in complexes with PAI-1 (100 kDa), alpha 2-antiplasmin (110 kDa), and C1-esterase inhibitor (170 kDa). After termination of infusions, levels of free t-PA declined, while inhibitor complexes remained prominent. Free PAI-1 activity, assayed spectrophotometrically, was markedly elevated in the 24 hr interval after infusion of t-PA in 47% of patients with infarction. The specific activity of t-PA during infusions was 0.4 IU/ng or greater. However, during the 3 hr interval after infusions in patients, specific activity declined in association with prominence of t-PA complexes, predominantly with PAI-1. Infusions of t-PA in normal rabbits did not result in reactive increases in PAI-1 activity or in the t-PA-PAI-1 complex. After infusions, t-PA was associated predominantly with alpha 2-antiplasmin and C1-esterase inhibitor rather than PAI-1. t-PA inhibitor complexes were seen despite immediate acidification of whole blood, indicating that they were present in vivo.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of plasminogen activator inhibitor activity and antigen in plasma samples

A double antibody radioimmunoassay for determination of plasminogen activator inhibitor (PA-inhibitor) in plasma samples has been developed. The reliability of the method as assessed by determining the specificity, the accuracy, the detectability and the variability seems sufficient for use in clinical practice. The correlation between PA-inhibitor antigen as measured with this method and PA-inhibitor activity as measured with a spectrophotometric assay in 111 patients with thrombotic diseases was very good (r = 0.89). As calculated from the regression line or from the mean activity and mean antigen values a specific activity of about 800,000-900,000 arb U/mg was obtained for PA-inhibitor in these samples. In 15 healthy individuals a similar figure was obtained. The results suggest that PA-inhibitor in most plasma samples is fully active or close to fully active. PA-inhibitor activity and PA-inhibitor antigen have also been measured after venous occlusion. The data suggest that small amounts of PA-inhibitor is released on venous occlusion, but at the same time an inactivation takes place, most likely due to the formation of enzymatically inactive complex with simultaneously released t-PA.