Initiation of a fibrinolytic system in hepatic resection: the roles of tissue-type plasminogen activator and plasminogen activator inhibitor-1

The factors related to the initiation of fibrinolysis, especially with regard to the tissue-type plasminogen activator (tPA) and the plasminogen activator inhibitor-1 (PAI-1), were investigated in 15 patients who underwent hepatic resection, and the findings were compared between those with normal livers and those with diseased livers. It was found that tPA increased before hepatic division, whereas PAI-1 increased after hepatic division and reached a peak immediately following the operation. Plasminogen decreased during hepatectomy, reaching its lowest point on postoperative day 1, and increasing later. Decreased levels of both plasminogen and the alpha 2-plasmin inhibitor were considered to be partly due to plasmin formation in the blood. Patients with a diseased liver tended to have higher intraoperative values of euglobulin lysis activity and higher postoperative values of plasminogen activator, but significantly lower postoperative values of alpha 2-plasmin inhibitor than those with a normal liver. The results of this study suggest that activation of the fibrinolytic system occurs both during hepatectomy and in the early postoperative period, and that patients with a diseased liver are prone to develop hyperfibrinolysis during hepatectomy. Moreover, the increased levels of both tPA and PAI-1 can serve as one of the most sensitive markers for the vital reaction against surgical stress.     

Coordinated expression of tissue-type plasminogen activator and plasminogen activator inhibitor type 1 during corpus luteum formation and luteolysis in the adult pseudopregnant rat

Proteolytic activity generated by the plasminogen activator (PA) system is associated with many biological processes. Using an adult pseudopregnant rat model, we have studied how two components of the PA system, tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1), are expressed temporally and spatially during different developmental stages of the corpus luteum (CL). Northern blot analysis, in situ hybridization, in situ zymography, and fibrin overlay were used to analyze the expression and distribution of tPA and PAI-1 messenger RNA (mRNA) as well as PA activity in CL of different ages. We demonstrated that during the luteinization period (approximately days 1-2), tPA mRNA was highly and evenly expressed in newly formed CL, whereas PAI-1 mRNA was mainly detected in the central part of the same CL. In accordance with these findings, proteolytic activity generated by tPA was detected in the outer region of newly formed CL by in situ zymography. During the luteotropic period (approximately days 3-10), tPA mRNA expression was very low. PAI-1 mRNA expression was also low, but increased on day 10. As expected, proteolytic activity was very low during this period. During functional luteolysis (days 13-14) and subsequent structural luteolysis, tPA mRNA was elevated. PAI-1 mRNA was also expressed during this period. Moreover, the net PA activity, as determined by fibrin overlay, was relatively high during this period. Our studies indicate that tPA and PAI-1 are coordinately expressed in the CL, resulting in increased proteolytic activities during the luteinization and luteolytic periods. PA-mediated proteolysis may, therefore, play a role in both CL formation and luteolysis in rats.     

In-vitro effect of oncostatin M on the release by endothelial cells of von Willebrand factor, tissue-type plasminogen activator and plasminogen activator inhibitor-1

Epidemiological studies have demonstrated that levels of plasma fibrinogen, von Willebrand factor (vWf), plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (tPA) are associated with the incidence of vascular disease. Since oncostatin M dramatically induces fibrinogen biosynthesis by hepatocytes and could be implicated in vascular injury leading to atherosclerosis, we have analyzed the effect of oncostatin M on PAI-1, vWf and tPA secretion by endothelial cells. A 2-h incubation of human umbilical vein endothelial cells with oncostatin M increases thrombin-induced secretion of vWf to the same extent as tumour necrosis factor-alpha or interleukin-1 (137+/-26% of control for 5 ng/ml oncostatin M, P < 0.001, n=5). The effects on tPA and PAI-1 secretion were different depending on the type of endothelial cells tested. On human umbilical vein endothelial cells, oncostatin M induced an increase in PAI-1 and a decrease in tPA secretion, which could explain the thrombogenicity of oncostatin M on large vessels. On a human microvasculature endothelial cell line, oncostatin M did not modify PAI-1 but induced an increase in tPA secretion. This observation of the effects of oncostatin M on both macro- and microvasculature could explain the increased levels of vWf, PAI-1 and tPA in the plasma of atherosclerotic subjects identified in epidemiological studies, suggesting that oncostatin M could play a key role in the development of atherosclerotic lesions.     

Inhibitory mechanism of serpins: loop insertion forces acylation of plasminogen activator by plasminogen activator inhibitor-1

Serpin inhibitors are believed to form an acyl enzyme intermediate with their target proteinases which is stabilized through insertion of the enzyme-linked part of the reactive center loop (RCL) as strand 4 in beta-sheet A of the inhibitor. To test critically the role and timing of these steps in the reaction of the plasminogen activator inhibitor PAI-1, we blocked the vacant position 4 in beta-sheet A of this serpin with an octapeptide. The peptide-blocked PAI-1 was a substrate for both tissue-type plasminogen activator (tPA) and trypsin and was hydrolyzed at the scissile bond. The reactivity of the peptide-blocked substrate PAI-1 was compared to that of the unmodified inhibitor by rapid acid quenching as well as photometric techniques. With trypsin as target, the limiting rate constants for enzyme acylation were essentially the same with inhibitor and substrate PAI-1 (21-23 s-1), as were also the associated apparent second-order rate constants (2.8-2.9 microM-1 s-1). With tPA, inhibitor and substrate PAI-1 reacted identically to form a tightly bound Michaelis complex (Kd approximately Km approximately 20 nM). The limiting rate constant for acylation of tPA, however, was 57 times faster with inhibitor PAI-1 (3.3 s-1) than with the substrate form (0.059 s-1), resulting in a 5-fold difference in the corresponding second-order rate constants (13 vs 2.5 microM-1 s-1). We attribute the ability of tPA to discriminate between the two PAI-1 forms to exosite bonds that cannot occur with trypsin. The exosite bonds retain specifically the distal part of the PAI-1 RCL in the substrate pocket, which favors a reversal of the acylation step. Acylation of tPA becomes effective only by separating the products of the acylation step. With substrate PAI-1, this depends on passive displacement of bonds, whereas with inhibitor PAI-1, separation is accomplished by loop insertion that pulls tPA from its docking site on PAI-1, resulting in faster acylation than with substrate PAI-1.     

Urokinase plasminogen activator is elevated in human astrocytic gliomas relative to normal adjacent brain

We assayed urokinase plasminogen activator (uPA), tissue type plasminogen activator (tPA), and plasminogen activator inhibitor-1 (PAI-1) in 43 human brain tumors (predominantly astrocytic gliomas) and in histologically disease-free brain tissue resected with 21 of the tumors. Levels of uPA, tPA, and PAI-1, measured by enzyme-linked immunosorbent assay, varied widely among individuals in neoplastic and in normal tissue but did not correlate with age or sex. Pairwise comparison of neoplastic and normal tissue from 21 individuals revealed that mean tumor uPA level was elevated 6-fold (P < 0.001). Mean tumor tPA and PAI-1 were 2.5-fold greater than those of normal brain, but these differences were not statistically significant. Tumor uPA was elevated 2- to 30-fold in 16/21 paired samples (76%). In contrast, tumor tPA was elevated 2- to 22-fold in 7/21 (33%) of pairs, whereas tumor PAI-1 was 2- to 13-fold greater in 10/21 (48%) of pairs. Our results demonstrate that elevation of uPA content is frequent in astroglial tumors, as is the case in other major human cancers.     

The mast cell as site of tissue-type plasminogen activator expression and fibrinolysis

Recent data suggest that mast cells (MC) and their products (heparin, proteases) are involved in the regulation of coagulation and fibrino(geno)lysis. The key enzyme of fibrinolysis, plasmin, derives from its inactive progenitor, plasminogen, through catalytic action of plasminogen activators (PAs). In most cell systems, however, PAs are neutralized by plasminogen activator inhibitors (PAIs). We report that human tissue MC as well as the MC line HMC-1 constitutively produce, express, and release tissue-type plasminogen activator (tPA) without producing inhibitory PAIs. As assessed by Northern blotting, highly enriched lung MC (>98% pure) as well as HMC-1 expressed tPA mRNA, but did not express mRNA for PAI-1, PAI-2, or PAI-3. The tPA protein was detectable in MC-conditioned medium by Western blotting and immunoassay, and the MC agonist stem cell factor (c-Kit ligand) was found to promote the release of tPA from MC. In addition, MC-conditioned medium induced fibrin-independent plasmin generation as well as clot lysis in vitro. These observations raise the possibility that MC play an important role in endogenous fibrinolysis.     

Secretion of cardiac plasminogen activator during hypoxia-induced right ventricular hypertrophy

In the circulation, fibrinolytic activity is determined to a large degree by the relative levels of tissue plasminogen activator (tPA) and its major inhibitor (PAI-1). Vascular beds in different organs secrete tPA and PAI-1 into the circulation, and the total secretory rate of each protein is balanced by its half-life in the bloodstream. We are testing the hypothesis that in the heart, ventricular hypertrophy will alter the rates of formation of tPA and/or PAI-1 and the rates of their release into the cardiac vasculature. In this study, we have examined the effects of continuous hypoxia on PA activity in extracts of rat heart ventricles, on the activity secreted into the cardiac vasculature of perfused hearts, and on the levels of mRNAs for tPA and PAI-1. Rats were subjected to hypobaric hypoxia at 0.5 atm for 1-21 days. The treatment caused polycythemia within 1-3 days, and right ventricular hypertrophy by 3 days. PA activity in extracts of both right and left ventricles was significantly elevated after 3 days of hypoxia, continued to increase for 4 additional days, and remained elevated for 3 weeks. The actions of inhibitors of urokinase and tPA indicated that the PA activity in heart extracts was exclusively tPA. Fibrin zymography confirmed that result. The mRNAs for tPA and for PAI-1 were elevated after 1 day of hypoxia and then returned to near control levels on days 2 and 3. After 7 days, hearts from hypoxic rats secreted more tPA activity into perfusates than did hearts from controls. The difference in secretory rates was proportional to the differences in the levels of tPA in the corresponding heart extracts.     

Production of urokinase-type plasminogen activator (u-PA) and plasminogen activator inhibitor-1 (PAI-1) in human brain tumours

We investigated the role of plasminogen activators (PAs) and their inhibitor (plasminogen activator inhibitor-1, PAI-1) in human brain tumours. The amounts of urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), and plasminogen activator inhibitor-1 (PAI-1), and the activity of u-PA and t-PA were determined by enzyme-linked immunosorbent assay (ELISA), and u-PA and PAI-1 were immunolocalized using monoclonal antibodies in human brain tumours and normal brain tissues. The tissues were surgically removed from 64 patients; normal brain tissue (5 cases), low-grade glioma (4 cases), high-grade glioma (17 cases), metastatic tumour (9 cases), meningioma (benign 12 cases, malignant 6 cases), acoustic schwannoma (11 cases). u-PA activity and u-PA and PAI-1 antigen levels were significantly elevated in malignant brain tumours (malignant meningiomas, high-grade gliomas, and metastatic tumours) and acoustic schwannomas but very low in benign meningiomas, low-grade gliomas and normal brain. There was no difference in t-PA antigen levels among normal and malignant tissues, however levels of t-PA activity were markedly decreased in metastastic tumours. All malignant brain tumour tissues showed positive immunostaining for u-PA and PAI-1, however, some tumour cells showed negative intensity while others showed strong intensity for these antibodies. This contrasts to the homogeneous staining pattern found in acoustic schwannoma. These findings indicate that malignancy in human brain tumours is associated with elevated levels of u-PA and PAI-1 and that an imbalance between these proteins in a micro-environment contributes (ascribes) to tumour cell invasion.     

Immunohistochemical characterization of the plasminogen activator system in psoriatic epidermis

The relative topographical distribution of urokinase-type plasminogen activator (uPA), tissue-type PA (tPA), PA-inhibitor-1 (PAI-1), PA-inhibitor-2 (PAI-2), plasmin(ogen), alpha 2-antiplasmin, and alpha 2-macroglobulin was studied in lesional epidermis of psoriasis vulgaris, and in normal epidermis, by immunohistochemistry. In psoriatic epidermis, tPA predominated, although uPA was found in some biopsies. PAs were not detected in normal epidermis. PAI-1 was not detected in normal epidermis and was only present in a proportion of biopsies of psoriatic lesions. PAI-2 was found in normal and psoriatic epidermis. Plasmin(ogen) was confined to the basal cell layer of normal epidermis, whereas in lesional psoriatic skin it was scattered throughout the epidermis. Alpha 2-antiplasmin and alpha 2-macroglobulin were not found in the epidermis of normal skin. In psoriatic epidermis alpha 2-antiplasmin was confined to the subcorneal layer, whereas staining for alpha 2-macroglobulin was found only in a proportion of biopsies, in the upper epidermis. Our immunohistological findings indicate that colocalization of tPA and its substrate plasminogen may allow efficient generation of plasmin, and that the focal absence of plasmin inhibitors may then favour the persistence of plasmin activity.     

Identification of tissue-type plasminogen activator-specific plasminogen activator inhibitor-1 mutants. Evidence that second sites of interaction contribute to target specificity

Plasminogen activator inhibitor-1 (PAI-1) is the primary inhibitor of the plasminogen activators (PAs), tissue-type plasminogen activator (tPA), and urokinase-type plasminogen activator (uPA). A library of PAI-1 mutants containing substitutions at the P1 and P1' positions was screened for functional activity against tPA and thrombin. Several PAI-1 variants that were inactive against uPA in a previous study (Sherman, P. M., Lawrence, D. A., Yang, A. Y., Vandenberg, E. T., Paielli, D., Olson, S. T., Shore, J. D., and Ginsburg, D. (1992) J. Biol. Chem. 267, 7588-7595) had significant inhibitory activity toward tPA. This set of tPA-specific PAI-1 mutants contained a wide range of amino acid substitutions at P1 including Asn, Gln, His, Ser, Thr, Leu, Met, and all the aromatic amino acids. This group of mutants also demonstrated a spectrum of substitutions at P1'. Kinetic analyses of selected variants identified P1Tyr and P1His as the most efficient tPA-specific inhibitors, with second-order rate constants (ki) of 4.0 x 10(5) M-1s-1 and 3.6 x 10(5) M-1s-1, respectively. Additional PA-specific PAI-1 variants containing substitutions at P3 through P1' were constructed. P3Tyr-P2Ser-P1Lys-P1'Trp and P3Tyr-P2Ser-P1Tyr-P1'Met had ki values of 1.7 x 10(6) M-1s-1 and 2.5 x 10(6) M-1s-1 against tPA, respectively, but both were inactive against uPA. In contrast, P2Arg-P1Lys-P1'Ala inhibited uPA 74-fold more rapidly than tPA. The mutant PAI-1 library was also screened for inhibitory activity toward thrombin in the presence and absence of the cofactor heparin. While wild-type PAI-1 and several P1Arg variants inhibited thrombin in the absence of heparin, a number of variants were thrombin inhibitors only in the presence of heparin. These results demonstrate the importance of the reactive center residues in determining PAI-1 target specificity and suggest that second sites of interaction between inhibitors and proteases can also contribute to target specificity. Finally, the PA-specific mutants described here should provide novel reagents for dissecting the physiological role of PAI-1 both in vitro and in vivo.     

Impact of weight loss on plasminogen activator inhibitor (PAI-1), factor VII, and other hemostatic factors in moderately overweight adults

Based on previous cross-sectional findings, we hypothesized that weight loss could improve several hemostatic factors associated with cardiovascular disease. In a randomized controlled trial, moderately overweight men and women were assigned to one of four weight loss treatment groups or to a control group. Measurements of plasminogen activator inhibitor-1 (PAI-1) antigen, tissue-type plasminogen activator (t-PA) antigen, D-dimer antigen, factor VII activity, fibrinogen, and protein C antigens were made at baseline and after 6 months in 90 men and 88 women. Net treatment weight loss was 9.4 kg in men and 7.4 kg in women. There was no net change (p > 0.05) in D-dimer, fibrinogen, or protein C with weight loss. Significant (p < 0.05) decreases were observed in the combined treatment groups compared with the control group for mean PAI-1 (31% decline), t-PA antigen (24% decline), and factor VII (11% decline). Decreases in these hemostatic variables were correlated with the amount of weight lost and the degree that plasma triglycerides declined; these correlations were stronger in men than women. These findings suggest that weight loss can improve abnormalities in hemostatic factors associated with obesity.     

Abnormal expression of type 1 plasminogen activator inhibitor and tissue factor in severe preeclampsia

Preeclampsia is a multisystemic obstetric disease of unknown etiology that is commonly associated with fibrin deposition, occlusive lesions in placental vasculature, and intrauterine fetal growth retardation. We previously reported that type 1 plasminogen activator inhibitor (PAI-1) levels are significantly increased in plasma and placenta from pregnant women with preeclampsia compared to normal pregnant women. In the present report we localize the expression of placental PAI-1 in greater detail and compare it with that of tissue factor (TF), a procoagulant molecule, and vitronectin (Vn), a PAI-1 cofactor. We also examine the expression of two cytokines, tumor necrosis factor alpha (TNFalpha) and interleukin-1 (IL-1), in order to begin to define the underlying mechanisms responsible for the elevated levels of PAI-1 and fibrin deposits observed in placenta from preeclampsia. We demonstrate a significant increase in PAI-1, TF and TNFalpha antigen and PAI-1 and TF mRNA in placentas from preeclamptic patients. PAI-1 mRNA was increased not only in syncytiotrophoblast and infarction areas, but also in fibroblasts and in some endothelial cells of fetal vessels in placentas from preeclamptic patients. However, there was no colocalization between PAI-1, TF, Vn and TNFalpha in placental villi. The elevated TNFalpha in the placenta may induce PAI-1 and TF, and thus promote the thrombotic alterations associated with preeclampsia.     

Sex differences in coagulation and fibrinolysis in subjects with coronary artery disease

Women with coronary artery disease (CAD) have a prognosis at least as bad and possibly worse than men. Differences in classical risk factors do not fully account for these findings and there is evidence that circulating levels of haemostatic factors may predict CAD risk. In this study sex differences in haemostatic risk factors were examined in relation to coronary stenosis. 609 (420 men, 69%) subjects admitted for coronary angiography for suspected CAD were recruited. Levels of Factor VII:C (FVII:C), fibrinogen, plasminogen activator inhibitor-1 (PAI-1) and von Willebrand factor (vWF) were estimated in 296 subjects from one centre. Of these, women (n = 107) had higher levels of FVII:C (134% vs 117%, p < 0.0005), and fibrinogen (3.4 g/l vs 3.2 g/l p = 0.01) than men (n = 189) and these differences remained after adjusting for other covariates. In subjects with angiographically significant atheroma these differences in haemostatic factors (n = 50 for women vs n = 147 for men) were exaggerated, (FVII:C 139% vs 117, p < 0.0001, fibrinogen 3.7 g/l vs 3.3 g/l p = 0.003), PAI-1 (26.2 ng/ml vs 19.7 ng/ml, p = 0.02) with a trend towards higher levels of vWF in the women. Women with significant atheroma at angiography (n = 50) had higher levels of PAI-1 (25.0 ng/ml vs 13.4 ng/ml p < 0.0001) and vWF (1.25 IU/ml vs 1.06 IU/ml, p = 0.02) and a trend towards higher levels of both fibrinogen and FVII:C than women with normal or in significant coronary vessel disease (n = 57). Elevated circulating levels of PAI-1, vWF, fibrinogen and FVII:C in women with angiographically proven CAD may contribute to an adverse cardiovascular risk factor profile and the poorer prognosis in females than male patients with proven coronary artery disease.     

Thrombin stimulates expression of tissue-type plasminogen activator and plasminogen activator inhibitor type 1 in cultured human vascular smooth muscle cells

The effect of thrombin on the fibrinolytic potential of human vascular smooth muscle cells (SMC) in culture was studied. SMC of different origin responded to thrombin treatment with a dose and time dependent increase in tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type-1 (PAI-1) levels in both cell lysates and conditioned media with maximum effects achieved at 10-20 IU/ml thrombin. PAI-1 antigen levels also increased in the extracellular matrix of thrombin treated SMC. PAI-2 levels in cell lysates of such SMC were not affected by thrombin. The effect was restricted to active thrombin, since DFP-thrombin and thrombin treated with hirudin showed no increasing effect on t-PA and PAI-1 levels in SMC. Enzymatically active thrombin also caused a four-fold increase in specific PAI-1 mRNA and a three-fold increase in t-PA mRNA. Furthermore we demonstrated the presence of high and low affinity binding sites for thrombin on the surface of SMC with a KD = 4.3 x 10(-10)M and 9.0 x 10(4) sites per cell and a KD = 0.6 x 10(-8) M and 5.8 x 10(5) sites per cell respectively. Thrombin could come in contact with SMC in case of vascular injury or following gap formation between endothelial cells. Our data support the idea that besides its known proliferative effect for SMC, thrombin could also modulate their fibrinolytic system.     

A fluorescent probe study of plasminogen activator inhibitor-1. Evidence for reactive center loop insertion and its role in the inhibitory mechanism

A mutant recombinant plasminogen activator inhibitor 1 (PAI-1) was created (Ser-338-->Cys) in which cysteine was placed at the P9 position of the reactive center loop. Labeling this mutant with N,N'-dimethyl-N-(acetyl)-N'-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) ethylene diamine (NBD) provided a molecule with a fluorescent probe at that position. The NBD-labeled mutant was almost as reactive as wild type but was considerably more stable. Complex formation with tissue or urokinase type plasminogen activator (tPA or uPA), and cleavage between P3 and P4 with a catalytic concentration of elastase, all resulted in identical 13-nm blue shifts of the peak fluorescence emission wavelength and 6.2-fold fluorescence enhancements. Formation of latent PAI showed the same 13-nm spectral shift with a 6.7-fold fluorescence emission increase, indicating that the NBD probe is in a slightly more hydrophobic milieu. These changes can be attributed to insertion of the reactive center loop into the beta sheet A of the inhibitor in a manner that exposes the NBD probe to a more hydrophobic milieu. The rate of loop insertion due to tPA complexation was followed using stopped flow fluorimetry. This rate showed a hyperbolic dependence on tPA concentration, with a half-saturation concentration of 0.96 microM and a maximum rate constant of 3.4 s-1. These results demonstrate experimentally that complexation with proteases is presumably associated with loop insertion. The identical fluorescence changes obtained with tPa.PAI-1 and uPA.PAI-1 complexes and elastase-cleaved PAI-1 strongly suggest that in the stable protease-PAI-1 complex the reactive center loop is cleaved and inserted into beta sheet A and that this process is central to the inhibition mechanism.     

Urokinase-type plasminogen activator receptor in gastric cancer: tissue expression and prognostic role

The urokinase-type plasminogen activator (UPA) and its inhibitor PAI-1 are thought to play an important part in gastric cancer (GC) invasion and metastasis. Little is known about the behavior and prognostic impact of the receptor for UPA (UPAR). The aims of the present study were: (1) to measure UPAR, UPA and PAI-1 levels in GC and in non-malignant tissue distant from the tumor (NORM); (2) to evaluate their relationship with histomorphological parameters; and (3) to determine their prognostic value. UPAR, UPA and PAI-1 levels were determined by ELISA in GC and NORM samples from 20 patients with GC undergoing surgery. The GC was also examined in terms of the presence (n = 10) or absence (n = 10) of metastasis, differentiation (five differentiated, 15 undifferentiated) and histotype. Survival was analysed using life table analysis. UPAR, UPA and PAI-1 were significantly higher in GC vs NORM, in the presence of metastasis (UPAR, UPA) and in undifferentiated GC (UPAR, PAI-1). UPAR significantly correlated with UPA and PAI-1. Low levels of UPAR (P = 0.04), UPA (P = 0.007) and PAI-1 (P = 0.02) were associated with a better survival. Our results demonstrate a sharp increase in UPAR in GC and suggest a prognostic role for it. The concomitant activation of UPAR, UPA and PAI-1 in GC confirm the important role of the plasminogen activator system in the process of invasion and metastasis.     

Binding of tissue plasminogen activator to endothelial cells. The effect on functional properties. Localization of a ligand in the B-chain of tPA

The binding of 125I-labelled tissue plasminogen activator (tPA), the tPA A- or B-chain to endothelial cells (EC) were studied in suspensions of cultured human umbilical vein EC (HUVEC) or immortalized microvascular EC (HMEC). By determinations of the concentration-dependent binding it was shown that both the A-chain and the B-chain, which were isolated after partial reduction of two-chain tPA, contain ligands for binding to EC. The affinity for the B-chain was much higher than for the A-chain according to Scatchard analysis (Kd 24 and 515 nM, respectively), whereas the number of binding sites was higher for the A-chain than for the B-chain (Bmax 8 x 10(5) and 1.2 x 10(5), respectively). There were no cross interactions between the A- and B-chains and their binding sites. The binding of tPA to EC induced an almost 100-fold increase of the activation rate when compared to the same amount of enzyme in free solution, which in contrast to the fibrin-induced stimulation was not inhibited by antibodies against fibrin. The enzymatic activity of the B-chain was much less affected by the association to the cells. Both tPA and the tPA B-chain were largely protected against inhibition by an excess plasminogen activator type-1 (PAI-1) when bound to EC, whereas the same amount of free tPA was totally inactivated. The competition studies strongly indicated that an N-terminal segment in the B-chain, AKHRRSPGER, may be the ligand part of the B-chain. It is interesting to note that this polypeptide segment also participates in a binding site for PAI-1, necessary for effective inhibition. This implies a possible competition between PAI-1 and a tPA-receptor for binding of tPA. High molecular weight urokinase had no quenching effect on the binding of the B-chain to EC.     

Relation between dietary fiber consumption and fibrinogen and plasminogen activator inhibitor type 1: The National Heart, Lung, and Blood Institute Family Heart Study

Considerable evidence suggests that high plasma concentrations of plasminogen activator inhibitor type 1 (PAI-1) and fibrinogen increase the risk of cardiovascular disease. Recent studies report beneficial effects of dietary fiber on coronary artery disease, although the mechanisms by which high fiber intake reduces the risk of heart disease are not well understood. This study examined the relation of dietary fiber intake to PAI-1 and fibrinogen concentrations in 883 men and 1116 women aged 50.4 +/- 13.8 and 52.1 +/- 13.7 y, respectively, in the National Heart, Lung, and Blood Institute Family Heart Study. Diet was assessed with a semiquantitative food-frequency questionnaire. The natural logarithm was used to transform PAI-1 because of a skewed distribution. In the first through fifth age- and energy-specific quintiles of fiber intake, mean (ln)PAI-1 was 6.09, 5.91, 5.88, 5.82, and 5.67 pmol/L, respectively, for men and 5.50, 5.37, 5.39, 5.23, and 5.18 pmol/L, respectively, for women. Multiple regression showed that when the lowest was compared with the second, third, fourth, and fifth age- and energy-specific quintiles of fiber intake, (ln)PAI-1 was 0.21, 0.25, 0.22, and 0.32 pmol/L lower in men (P for trend = 0.009) and 0.08, 0.06, 0.14, and 0.20 pmol/L lower in women (P for trend = 0.037), respectively, with anthropometric, lifestyle, and metabolic factors adjusted for. No significant association was found between fiber intake and fibrinogen. Waist-hip ratio did not modify the relation of fiber intake to PAI-1 (P for interaction = 0.39 for men and 0.36 for women). These data suggest that higher fiber intake is inversely associated with PAI-1, but not with fibrinogen concentration.     

Gene polymorphisms for plasminogen activator inhibitor-1/tissue plasminogen activator and development of allograft coronary artery disease

BACKGROUND: Impaired fibrinolytic activity has been linked to the presence and severity of allograft vasculopathy (Tx CAD). This impairment may be associated with the presence of certain fibrinolytic protein gene polymorphisms. METHODS AND RESULTS: To investigate the relation between donor-specific fibrinolytic protein genotypes and Tx CAD, we identified donor plasminogen activator inhibitor-1 (PAI-1) HindIII and tissue plasminogen activator (TPA) EcoRI restriction fragment length polymorphisms-based genotypes by Southern blot analysis in 48 recipients of cardiac allografts and correlated these genotypes with the development of CAD. No association was found between donor TPA genotypes and the presence of Tx CAD. Among the 48 patients, 17% were homozygous for the 1/1 PAI-1 genotype, 51% for the 2/2 PAI-1 genotype, and 32% for the 1/2 PAI-1 genotype. The actuarial freedom from any CAD for the recipients with each respective donor PAI-1 genotype at 12 and 24 months was 100% and 100% for the 1/1 PAI-1 genotype, 92% and 92% for the 1/2 PAI-1 genotype, and 75% and 45% for the 2/2 PAI-1 genotype (P=0.03). Recipients with a diseased 2/2 PAI-1 genotyped allograft had longer ischemic times (P=0.02) than those recipients with a Tx CAD-free allograft. CONCLUSIONS: These data suggest that recipients with a 2/2 PAI-1 genotype are at a significant risk of developing Tx CAD. This genotype may serve as a useful screening tool for predicting the future development of Tx CAD.