M. C. Alessi

Plasma plasminogen activator inhibitor-1 in angina pectoris. Influence of plasma insulin and acute-phase response.

Plasminogen activator Inhibitor-1 (PAI-1) is an Important physiological Inhibitor of fibrlnolysls. It circulates in blood both In free active form and In Inactive form comptexed with tissue type plasminogen activator (t-PA). Control mechanisms for Its synthesis and release from hepatocytes and endothellal cells are important In the pathogenesis of thrombosis. Possible risk factors for myocardlal Infarction Include high insulin and PAH levels, which correlate with one another In healthy subjects, and fibrlnogen, which together with PAI-1, Is an acute-phase reactant We therefore studied the Interrelationships between PAI-1, plasma Insulin, and acute-phase proteins In 67 patients with angina pectoris. Plasma Insulin correlated strongly (r=0.59, p<0.001) with PAI activity, free PAI-1 antigen (r=0.60, p<0.001), and total PAI-1 antigen (r=0.58, p<0.001). The acute-phase proteins, fibrlnogen and C-reactive protein, correlated significantly with t-PA antigen, total PAI-1 antigen, and PAH/t-PA complexes but not with PAI activity or free PAI-1. The results suggest that Insulin stimulates synthesis and release of free PAI-1 (probably via hepatocytes as previously shown with cell culture) and that endothellal cell synthesis and release of t-PA, together with PAI-1, reflects a nonspecific acute-phase response to chronic vascular disease. Hyperlnsullnemia found In patients with angina pectoris could play a role In the development of myocardlal Infarction via the Induction of high plasma PAI-1 activity.

Influence of PAI-1 on Adipose Tissue Growth and Metabolic Parameters in a Murine Model of Diet-Induced Obesity

An increased plasma plasminogen activator inhibitor-1 (PAI-1) level is a risk factor for myocardial infarction, particularly when associated with visceral obesity. Although the link between PAI-1 and obesity is well documented, little is known about the physiological relevance of PAI-1 production by adipose tissue. Therefore, we have compared adipose tissue development and insulin resistance plasma parameters in PAI-1-deficient mice (PAI-1(-/-)) and wild-type littermates (PAI-1(+/+)) in a model of nutritionally induced obesity. After 17 weeks of consuming a high-fat diet (HFD), PAI-1(+/+) mice showed marked obesity, with a 52% increase in body weight compared with mice that were kept on a standard fat diet (P<0.0001). This weight gain was accompanied by adipocyte hypertrophy and an increase in the number of stroma cells in the gonadal fat pad, expressed as stroma cells/adipocytes (0.67+/-0.05 versus 0.43+/-0. 02; P<0.001). In plasma, the HFD induced a marked increase in PAI-1 antigen (5.1+/-0.56 versus 2+/-0.22 ng/mL; P<0.001), fasting insulinemia (1.1+/-0.21 versus 0.21+/-0.04 ng/mL; P<0.001), and glycemia (7.4+/-0.5 versus 5+/-0.3 mmol/L; P<0.001), whereas plasma triglyceride levels were not affected. When we compared PAI-1(-/-) and PAI-1(+/+) mice on the HFD, PAI-1(-/-) mice gained weight faster than did PAI-1(+/+) mice, with a significant difference in body weight between 3 and 8 weeks of the diet (32+/-1.7 versus 26+/-1.6 g at 6 weeks; P<0.05). After 17 weeks of the HFD, its effect on weight gain and the number and size of adipocytes was similar in PAI-1(+/+) and PAI-1(-/-) mice. By contrast, the increase in the number of stroma cells presented by PAI-1(+/+) mice was not observed in PAI-1(-/-) mice. In obese PAI-1(-/-) mice, tissue-type PA activity and antigen levels in the gonadal fat pad were significantly higher than in obese PAI-1(+/+) mice (230+/-50 versus 47+/-20 arbitrary units/g, P<0.01; 40+/-13 versus 17+/-13 ng/g, P<0.05, respectively), whereas urokinase-type PA activity and antigen levels were similar in both groups. In plasma, nonobese PAI-1(-/-) mice displayed 62% higher insulin levels (P<0.05) than did PAI-1(+/+) mice. Obese PAI-1(-/-) mice displayed 68% higher triglyceride levels (P<0.01) and 21% lower glucose levels (P<0.05) than did PAI-1(+/+) mice. These data support an effect of PAI-1 on weight gain and adipose tissue cellularity in the induction of obesity in mice. Moreover, PAI-1 influences glucidolipidic metabolism. The elevated expression of PAI-1 observed in human obesity could be involved in mechanisms that control adipose tissue development.

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.

The A −844G Polymorphism in the PAI-1 Gene Is Associated With a Higher Risk of Venous Thrombosis in Factor V Leiden Carriers

Identification of combined genetic factors in factor V Leiden carriers is important for a more accurate risk assessment for venous thrombosis (VT). Among these individuals, we evaluated the role of polymorphisms of the plasminogen activator inhibitor-1 (PAI-1) gene in the thrombophilic phenotype. A total of 382 factor V Leiden carriers were included in the study. This population was divided into 3 groups. Group 1 (n=168) included individuals with a personal history of VT; group 2 (n=140) included individuals without personal VT but with a familial history of VT; and group 3 (n=74) included individuals without VT and with a fortuitous discovery of the factor V Leiden mutation. We compared the genotype distribution of 2 polymorphisms, A -844G and -675 4G/5G, located in the promoter region of the PAI-1 gene among these 3 groups of individuals. The A -844G allele frequency differed significantly among the 3 groups (P=0.048), the A allele being more frequent in patients who suffered from VT (61%) than in subjects without VT (52%, P=0.015), whereas no difference was observed between the 2 groups of asymptomatic individuals. The prevalence of genotype AA carriers was higher in patients with VT (38%) than in asymptomatic individuals (21%, P=0. 015), leading to an odds ratio of 1.74 (95% confidence interval, 1.3 to 3.8). Carrying the AA genotype conferred a risk of deep VT of 2. 08 (95% confidence interval, 1.28 to 3.40), whereas it did not seem to significantly influence the risk of pulmonary embolism. Concerning the -675 4G/5G polymorphism, no significant difference was observed among the 3 groups, the 4G allele frequency being 0.54 (in group 1), 0.49 (in group 2), and 0.45 (in group 3). These data suggest a role for the -A844G PAI-1 gene polymorphism in the thrombophilic phenotype of factor V Leiden carriers.

Correlations between t-PA and PAI-1 antigen and activity and t-PA/PAI-1 complexes in plasma of control subjects and of patients with increased t-PA or PAI-1 levels

Tissue-type plasminogen activator (t-PA), a serine protease converting the proenzyme plasminogen to the active enzyme plasmin, plays an important role in the fibrinolytic process (1). It is specifically and rapidly inhibited by plasminogen activator inhibitor 1 (PAI-1) (2). t-PA in plasma may occur in a free form (3) as well as complexed with PAI(4,5), Cl-esterase inhibitor (4), a2 -antiplasmin (6) and a -antitrypsin (6). During thrombolytic therapy with t-PA, t-PA/PAI-1, t-PA a2-antiplasmin f and t-PA/Cl-esterase inhibitor complexes are formed in the circulation (5). In normal subjects, venous occlusion results in an increase of free t-PA while in patients with increased PAIlevels no free t-PA is detected after venous occlusion (3). During venous stasis in normal subjects, both t-PA and t-PA/PAI-1 complex increase (7). Because PAIis the main physiological inhibitor of t-PA in plasma, we quantitated t-PA/PAI-1 complex in addition to t-PA and PAIin plasma, obtained from healthy volunteers and from patients with increased PAIor t-PA levels, before and after venous occlusion.

Molecular forms of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (t-PA) in human plasma

Molecular forms of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (t-PA), identified by gel filtration and specific immunoassays, were studied in plasma from subjects with normal and elevated PAI-1 levels before and after in vitro or in vivo addition of t-PA. In normal plasma, PAI-1 occurs in three molecular forms, a Mr greater than 700 KDa inactive form of heterogeneous composition, an active 450 KDa form containing PAI-1/vitronectin complex and an inactive peak at Mr 50 KDa containing free PAI-1. Stimulation of platelets results in a significant increase of the 50 KDA form and a slight increase of the 450 KDa form. Patients with increased PAI activity levels have an increase of both the 450 KDa and the 50 KDa forms, whereas patients with thrombotic thrombocytopenic purpura have an increased 50 KDa form. In normal plasma, collected in the presence or absence of D-Phe-Pro-Arg-CH2Cl, t-PA occurs primarily as a Mr greater than 700 KDa form containing t-PA/PAI-1 complex. Addition of high concentrations of t-PA (70 ng/ml) to plasma in vitro or t-PA injection in vivo, results in t-PA inhibitor complexes, including t-PA/ alpha 2 antiplasmin. It is concluded that in subjects with increased PAI-1 levels in plasma, PAI-1 may occur as high molecular weight complexes with vitronectin of which 450 KDa was the most important part and as a 50 KDa inactive form; t-PA circulates primarily in complex with inhibitors. Thus, some of the molecular interactions between PAI-1, t-PA and vitronectin, previously demonstrated in purified systems in vitro, also occur in plasma.