Detection of specific forms of plasminogen activator inhibitor type 1-by monoclonal antibodies

Monoclonal antibodies to plasminogen activator inhibitor type-1 (PAI-1) were generated and characterised for their ability to inhibit PAI-1 interaction with tissue plasminogen activator (t-PA) and urokinase (u-PA) and detection of the various forms of PAI-1 (native, complexed, and degraded) by immunoblotting. Mab17 inhibited both complex formation between PAI-1 and t-PA/u-PA and PAI-1 activity in a dose dependent manner by 90%. Mab 25 was much less effective, blocking complex formation less than 30% and PAI-1 activity less than 20%. The Kds of Mab 17 and Mab25 were 2.8×10⁻¹¹ M and 2.6×10⁻¹⁰ M, respectively. Following SDS-PAGE and immunoblotting, Mab 17 detected native PAI-1 only; PAI-1 in complex and the t-PA/u-PA degraded form of PAI-1(M_r=42000) did not react with this antibody. In contrast, Mab25 detected all three forms of PAI-I although the affinity for the native form appeared to be greater than Mab 17 or the PAI-1 polyclonal employed. Despite these differences, both monoclonal antibodies immunoprecipitated native and degraded PAI-1 equally as well. These results suggest that the epitope of Mab 17 is associated with the reactive site of PAI-1 and that this region is either missing or not accessible in the cleaved form or in complex.     

Tissue plasminogen activator, plasminogen activator inhibitors, and activator-inhibitor complex in liver disease.

AIMS--To identify the relative contribution of plasminogen activators, particularly tissue plasminogen activator (t-PA) and specific plasminogen activator inhibitors (PAI-1, PAI-2), to the fibrinolytic changes associated with various types of liver disease or severe chemical and physical damage to the liver. METHODS--Platelet rich (PRP) and platelet poor plasma (PFP) from patients with alcoholic cirrhosis, primary biliary cirrhosis, hepatic malignancy, or paracetamol overdose, or who were undergoing partial hepatectomy or liver transplantation, were assayed for t-PA, PAI-1, t-PA-PAI-1 complex and PAI-2 antigen values using specific enzyme linked immunosorbent assays (ELISAs) developed in this laboratory. RESULTS--Appreciable increases in the plasma concentration of t-PA, PAI-1, and t-PA-PAI-1 were seen in patients with alcoholic cirrhosis, primary biliary cirrhosis, and hepatic malignancy. Liver damage due to paracetamol overdose and partial hepatectomy both resulted in a striking increase in plasma PAI-1 concentration, although concentrations of t-PA and t-PA-PAI-1 complex were less affected. Concentrations of t-PA, PAI-1, and t-PA-PAI-1 complex returned to near normal values after successful liver transplantation in a patient with chronic active hepatitis. PAI-2 was also detected in several patients with chronic liver disorders. CONCLUSIONS--Haemorrhage due to fibrinolytic bleeding is commonly associated with liver disease. The patients studied here all had appreciable increases in circulating t-PA antigen concentrations. This was associated with increased concentrations of PAI-1 antigen and t-PA-PAI-1 complex and the balance between activator and inhibitor did not result in systemic plasmin generation. Reduced PAI-1 activity in cirrhosis or a critical difference in the ratio of t-PA to PAI-1 concentrations may explain the enhanced plasminogen activator activity previously noted in cirrhosis but not metastatic disease. Reduced hepatic clearance of t-PA and t-PA-PAI-1 complex due to impaired liver function may account for increased concentrations of free and complexed t-PA.     

Familial thrombophila associated with high levels of plasminogen activator inhibitor

A family with defective fibrinolytic abnormalities and recurrent thrombotic events is described. Impaired fibrinolysis was associated with high activity and concentration of fast-acting plasminogen activators inhibitor (PAI-1). Acquired conditions associated with PAI-1 increase were excluded. After venous occlusion testing, a different behaviour of fibrinolytic activity inhibition was seen in the family members. In the propositus and in two relatives only tissue (t-PA) plasminogen activity inhibition was found; in two other members, both t-PA and urokinase-type plasminogen activities were completely inhibited by the high PAI-1 levels. This fibrinolytic defect seems to be familial and transmitted as an autosomal trait.     

Adjunctive low-dose doxycycline therapy effect on clinical parameters and gingival crevicular fluid tissue plasminogen activator levels in chronic periodontitis

Objective and design: The present study examined effectiveness of low-dose doxycycline (LDD) in combination with nonsurgical therapy on gingival crevicular fluid (GCF) tissue plasminogen activator (t-PA) levels and clinical parameters in chronic periodontitis (CP) a over 12-month period. Methods: GCF samples were collected, probing depth (PD), clinical attachment level (CAL), gingival index (GI) and plaque index were recorded at baseline, 3, 6, 9 and 12 months. CP patients (n = 65) were randomized to LDD or placebo groups. LDD group received LDD (20 mg) b.i.d for 3-months plus and root planing (SRP), while placebo group was given placebo capsules b.i.d for 3-months plus SRP. GCF t-PA levels were determined by ELISA. Friedman, Wilcoxon and Mann-Whitney test was used for statistical analysis. Results: Significant improvement was observed in all clinical parameters in both groups over 12-month period (p < 0.01). LDD group had lower PD, CAL and GI scores than placebo group at 6, 9 and 12-months (p < 0.05). GCF t-PA levels reduced in both groups over 12-month period (p < 0.01). LDD group had lower GCF t-PA levels than placebo group at 6 and 9-months (p < 0.05). Conclusions: These results provide additional information about usefulness of LDD therapy as an adjunct to nonsurgical therapy in long-term management of periodontitis. Received 8 May 2006; returned for revision 13 June 2006; accepted by J. Di Battista 12 July 2006     

Complex formation between protein c inhibitor and tissue plasminogen activator during thrombolytic therapy: Evidence of activation of protein C pathway

Protein C inhibitor (PCI) is a heparin-dependent serine protease inhibitor which, in vitro, inhibits activated protein C (APC, urokinase (u-PA) and tissue plasminogen activator (t-PA), plasma kallikrein (KK), thrombin and factors Xa and Ma. We have previously shown in vivo complexes of PCI with APC, u-PA and KK. Here we study the contribution of PCI to the inhibition of t-PA both in vitro and in vivo. PCI complexed to t-PA (t-PA:PCI) was measured by a sandwich ELISA using antibodies directed against each protein in the complex. The formation of t-PA:PCI complexes paralleled the inhibition of t-PA amidolytic activity by PCI in a purified system. In the plasma milieu, after incubation of 8 μg/mL t-PA (final concentration) with human plasma for 2 h at 37°C, in the presence of heparin, the residual t-PA activity was about 38% and plasma contained 0.56 μg/mL t-PA:PCI complexes. To study complex formation in vivo, human plasma samples from patients (n=5) with myocardial infarction were analyzed following infusion of 100 mg recombinant t-PA for 2.5h (10% initial bolus; 40% by a 20min infusion, and 50% by a 2-h infusion). Maximum peak values of t-PA:PCI complexes were measured immediately after the second and third t-PA doses, ranging from 16 to 135 ng/mL. In contrast, during t-PA infusion the level of complexes of t-PA with plasminogen activator inhibitor-1 (t-PA:PAI-1) increased only slightly, from 2.4±1.5 to 7.2±4.6 ng/mL, and reached a maximum mean value of 17.2±20.6 ng/mL 2h post-infusion. PCI antigen decreased during t-PA infusion from 80%±16% to 71%±7%. Protein C antigen levels decreased during t-PA infusion, with the subsequent appearance of complexes between APC and PCI (APC:PCI), and free protein S gradually declined during infusion, reaching levels of 69% of the basal value 2h post-infusion.These data show that in vivo interaction of PCI and t-PA exists, which in turn support the view that PCI may play a role in the regulation of the fibrinolysis pathway. They also show that thrombolytic therapy with t-PA produces activation and a subsequent decrease in protein C antigen levels as well as in free protein S levels.     

The activation of plasminogen by tissue plasminogen activator is not enhanced by different heparin species as assessed in vitro with a solid-phase fibrin method

The aim of this study was to evaluate the effect of several heparin species (standard heparin, heparin of low molecular weight: IC 831422, heparin of high affinity for antithrombin III: IC 831435, and heparin of low affinity for antithrombin III: IC 831436) on the different steps of the fibrinolytic mechanism i.e., interaction of tissue-type plasminogen activator (t-PA) with plasminogen activator inhibitor-1 (PAI-1), binding of t-PA and plasmin(ogen) to fibrin and activation of plasminogen on the fibrin surface, in the presence of plasma proteins and factors that modulate fibrinolysis. Fibrinolytic and plasmin amidolytic activities were measured in the presence and absence of heparin. The spectrophotometric assays were performed in the presence and absence of solid-phase fibrin using selective chromogenic substrates for plasmin and saturating concentrations of plasminogen.The overall fibrinolytic activity, the amidolytic activity of mixtures of t-PA or urokinase with plasminogen in the absence of fibrin, the binding of t-PA and plasmin(ogen) to fibrin and the t-PA/PAI-1 interaction were not modified by heparin. In contrast, the activation of plasminogen by fibrin-bound t-PA decreased as a function of the concentration of heparin. Although this effect was not significant at concentrations usually used in routine heparin therapy (0.1 to 1 iu/ml) it might have some relevance when heparin is injected in bolus doses.In conclusion, by using a solid-phase fibrin method which allows the analysis of t-PA/PAI-1 balance, data were obtained indicating that the heparin species tested here neither competed with fibrin for the binding of t-PA, nor potentiated the activation of plasminogen at the fibrin surface.     

Monoclonal antibodies against a recombinant form of plasminogen activator inhibitor-1: Effects on tissue plasminogen activator neutralizing and vitronectin binding properties

A panel of eight murine monoclonal antibodies was produced against a recombinant form of plasminogen activator inhibitor- 1 (rPAI-1). All the antibodies recognized active and latent forms of rPAI-1, and rPAI-1 complexed with tissue plasminogen activator (t-PA) as determined in enzyme-linked immunosorbent assays (ELISA). Three of the antibodies, FAG9, FAD3 and BBH2, were particularly effective at inhibiting the t-PA neutralizing activity of rPAI-1 as measured in a chromogenic assay. Three different antibodies, DD8E9, FEG7 and FGG7, inhibited the binding of [¹²⁵I]rPAI-1 to vitronectin immobilized on polystyrene wells. The combination of FGG7 and alkaline phosphatase-labeled BBH2 resulted in a sensitive sandwich ELISA for rPAI-I with detection limits in the range of 1–10 ng. Definition of epitopes recognized by these antibodies will be useful for identifying various domains on PAI-1 involved in its interaction with protease substrates and with its protein cofactor, vitronectin.     

Components of the plasminogen activation system in uveal melanoma—a clinico-pathological study

In tumour development, proteases such as plasminogen activators (PAs) play a role in degradation of the extracellular matrix and other tissue barriers. Recently, we demonstrated that plasminogen activators, their inhibitors, and urokinase receptor emerge in late stages of cutaneous melanocytic tumour progression. In this study we investigated the expression and distribution of the various components of the PA system and the presence of PA enzyme activity in 45 freshly frozen primary uveal melanomas with known follow-up (14 spindle and 31 non-spindle type) and in metastases (n=5). Tissue-type PA (t-PA) was found in endothelium of blood vessels and in tumour cells in almost all leisons, and was markedly present at the invasive front (towards the sclera and Bruch's membrane), but no correlation with tumour-related death could be established. Urokinase PA (u-PA) was expressed focally, by only five non-spindle cell melanomas but in all metastases. u-PA expression correlated with occurence of metastasis. u-PA receptor (u-PAR) was present in one-third of all the tumours examined. Plasminogen activator inhibitors (PAI-1 and PAI-2) were found only focally in approximately 10 per cent of the lesions. Staining of t-PA, u-PA, and PAI was observed in all the metastases. We conclude that in uveal melanoma, u-PA expression may be associated with metastatic disease and accordingly with a poor prognosis. Further research on a larger group of tumours with known follow-up is needed to establish whether u-PA positivity is of additional prognostic value in uveal melanoma.     

Quantification of a specific inhibitor (PAI-1) of tissue-type plasminogen activator (t-PA) in the plasma

In human plasma, the activation of plasminogen by tissue plasminogen activator (t-PA) is a fibrin localized process which allows the specific dissolution of thrombi. Most of the t-PA circulates as a complex with its inhibitor, PAI-1, which thereby regulates its activity. In the present work the authors have studied the kinetics of inhibition of t-PA by PAI-1 and have developed an assay for its specific detection. The assay is performed in microtitration plates containing a solid-phase fibrin network, as follows: the source of inhibitor is mixed with solutions containing increasing amounts of t-PA, then the residual t-PA is separated by means of a solid-phase fibrin support and detected with a coupled reaction using a plasmin selective chromogenic substrate. The change in absorbance is measured in a microtiter plate reader and converted to t-PA activity by reference to a standard curve. The residual t-PA activity is inversely proportional to the concentration of PAI-1. The quantitation of PAI-1 is based on the variation of the dissociation constant of the fibrin/t-PA interaction obtained in the presence of the inhibitor. Since other serine-protease inhibitors do not interfere with the assay, the method is specific for PAI-1 and can be safely used in other biological fluids.     

Interaction of tissue-type plasminogen activator with fibronectin and fibronectin fragments

In this paper we present data on the interaction, in solution, of the tissue-type plasminogen activator (t-PA) with fibronectin (FN) and its degradation products (FNdp). A cross radial caseinolytic assay (CRACA) was developed for the evaluation of the effect of the FN and/or FNdp on t-PA and urokinase plasminogen activator (u-PA) activity. A directional caseinolysis was observed when t-PA or u-PA were tested in the proximity of FNdp; no directionality was observed when intact FN or BSA were used. After incubation of t-PA, but not u-PA, with FNdp, PA activity at 170, 150, 100 and 30 kDa was detected by SDS-PAGE followed by zymography. The incubation of intact FN with t-PA gives rise to two forms of 500 and 150 kDa after prolonged incubation of the zymograms; no higher MW forms appear when u-PA substitutes t-PA.The immunoblotting analysis of the mixtures of t-PA and FN or FNdp with anti-t-PA or anti-FN sera showed that intact FN and some of its fragments interact with t-PA, giving rise to complexes recognized by both antisera and resistant to SDS-PAGE. Similar complexes are also evident, in vivo, in biological fluids like human plasma cryoprecipitates (cryos).     

Factors of the plasminogen activator system in human testis, as demonstrated by in-situ hybridization and immunohistochemistry.

A growing body of evidence suggests that the plasminogen activator (PA) system is crucially involved in reproductive physiology in both sexes. Certain factors of the PA system have been found to be present in organs of the male reproductive tract in various species, and the presence of several of the factors was recently demonstrated in monkey testis. The present morphological study was therefore designed to investigate the occurrence and distribution of the tissue and urokinase plasminogen activators (t-PA and u-PA), the u-PA receptor (u-PAR) and the plasminogen activator inhibitors (PAI-1 and PAI-2) in normal human testis. Intraoperative specimens from seven patients undergoing orchidectomy or testicular biopsy were studied using in-situ hybridization (ISH) and immunohistochemistry (IHC). All five factors studied could be detected with both the ISH and IHC procedures. The ISH signals were localized to sites in the testicular tubules in a stage-specific manner. There was good correlation between results obtained with the two methods, though in IHC the tubules were stained more uniformly. The findings provide support for the involvement of the PA system in human male reproductive physiology.     

Neutralization of plasminogen activator inhibitor-1 (PAI-1) by activated protein C is species-dependent

The interaction of bovine and human activated protein C (APC) with type-1 plasminogen activator inhibitor (PAI-1) was studied in a cell-free system. Human plasma and a preparation of PAI-1 obtained from human endothelial cell cultures were used as sources of PAI-1. Bovine APC was able to neutralize PAI-1 inhibitory activity present in both sources in a dose-dependent manner; the concentration of bovine APC required to produce 50% (C₅₀) neutralization of endothelial PAI-1 (0.5nM) was 4 μg/ml (64nM). Moreover, when complexes between tissue plasminogen activator (t-PA, 60ng/ml, 0.84nM) and PAI-1(18.8ng/ml, 0.35nM) were incubated with bovine APC, the amount of such complexes decreased as a function of the concentration of added APC (C₅₀ = 2 μ/ml, 32 nM), and a concomitant increase in the amount of residual t-PA activity was observed. This effect was due to the formation of APC⊎PAI-1 complexes as detected by immunoblotting with monoclonal antibodies directed against PAI-1. By this mechanism bovine APC prevented the initial reaction between PAI-1 and t-PA and interfered with the stability of complexes between t-PA and PAI-1. The latter observation suggests that complexes between t-PA and PAI-1 may dissociate in the presence of bovine APC. In contrast with these findings, when the experiments were performed in an entirely human homologous cell-free system, human APC did not form a complex with PAI-1 and no effect either on PAI-1 or on the stability of preformed t-PA ⊎ PAI-1 complexes was observed. The results indicate that the neutralization of PAI-1 by APC is a phenomenon induced by interspecies molecular interactions.     

Tissue plasminogen activator and plasminogen activator inhibitor in patients with liver cirrhosis

The behaviour of tissue plasminogen activator (t-PA) and t-PA inhibitor (PAI) was studied in patients with decompensated liver cirrhosis. t-PA antigen showed a 3-fold significant increase with respect to healthy volunteers. t-PA activity in these patients did not significantly differ from that found in the controls, but the specific activity of t-PA was significantly lowered by 63%. PAI activity was significantly reduced in cirrhosis (−67%), while PAI-1 antigen was increased by 24%. Venous occlusion of the arm for 20min induced similar increases of t-PA antigen both in normal subjects and cirrhotic patients. These findings show that the total amount of t-PA is enhanced in liver cirrhosis, with no increase of t-PA activity due to the capacity of PAI to bind increased circulating t-PA antigen. The increased total amount of t-PA in cirrhotic patients could be explained in terms of a reduced clearance by the hepato-endothelial system.     

Cellular distribution and clinical value of urokinase-type plasminogen activator, its receptor, and plasminogen activator inhibitor-2 in esophageal squamous cell carcinoma

To assess the participation of the plasminogen activation system in the invasiveness of esophageal squamous cell carcinoma, we performed immunohistochemistry and in situ hybridization to study the distribution of a urokinase-type plasminogen activator (u-PA), u-PA receptor (u-PAR), and plasminogen activator inhibitor-2 (PAI-2). u-PA and PAI-2 were expressed heterogeneously in cancer cells, and restricted expression was found in stromal cells, especially fibroblasts, that were located in the immediate proximity of the cancerous cells. u-PAR was found only in cancer cells located at the periphery of tumors. Compared with patients with u-PA-negative cancer cells, patients with u-PA-positive cancer cells more frequently showed a neoplastic invasion beyond the muscularis propria and lymph node metastases. They also showed a significantly shorter 5-year overall survival. Patients with PAI-2-positive fibroblasts showed significantly lower levels of local invasiveness, represented by a neoplastic invasion beyond the muscularis propria, than those who were PAI-2 negative. Our results suggest that the expression of u-PA in esophageal squamous cell carcinoma is predictive of poor survival, whereas the expression of PAI-2 in the fibroblasts surrounding them is protective. An analysis of u-PA and PAI-2 expression in cancer cells and their surrounding fibroblasts may be useful for predicting the prognosis of patients with esophageal squamous cell carcinoma.     

Biological properties of a kringleless tissue plasminogen activator (t-PA) mutant

We have previously described a recombinant t-PA mutant (mt-PA) which lacks the double kringle domains. Purified mt-PA (specific activity comparable to melanoma cell derived t-PA (nt-PA)) exhibits fibrin specificity similar to nt-PA but is inhibited 50 to 80% less than nt-PA by a human platelet PA inhibitor. The biological properties of mt-PA, nt-PA and urokinase (u-PA) were studied in a human plasma circulation system. [¹²⁵I] fibrinogen whole blood Chandler loop thrombi were suspended in a chamber perfused by plasma (50 ml) circulated at 120 ml/min. The plasminogen activators were given as a bolus (20% of the total dose) and followed by a 4 h constant rate infusion. Samples obtained were analysed for [¹²⁵I] fibrin degradation products, plasminogen and fibrinogen. At 5h, thrombolysis (% total thrombus [¹²⁵I]) released was: nt-PA (100u/ml) 51±710 (mean ±s.d.), mt-PA (100u/ml) 79±7%, u-PA (500u/ml) 88±12%. Plasminogen and fibrinogen values (% of control) were: nt-PA 63±90/ plasminogen, 68±19% fibrinogen; mt-PA 69±7% plasminogen, 72±23% fibrinogen; u-PA 34±8% plasminogen, 21±8% fibrinogen. In saline control studies, no thrombolysis and no plasminogen and fibrinogen changes occurred. Thus, mt-PA appears to be a more efficient thrombolysic agent than nt-PA; the two plasminogen activators cause comparable plasminogen and fibrinogen depletion. 100 u mt-PA is comparable to 500u u-PA/ml but as expected, u-PA extensively depletes both plasminogen and fibrinogen.     

Increase of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor type 1 (PAI-1) in plasma after thrombolytic therapy of patients with myocardial infarction. A randomised,placebo-controlled study

Based on recent studies we hypothesised that the marked generation of thrombin in patients who undergo coronary thrombolysis was associated with substantial deviations of endogenous tissue-type plasminogen activator (t-PA) and the plasminogen activator inhibitor type 1 (PAI-1) in plasma.In the present placebo-controlled study we observe in 20 patients treated with recombinant t-PA (rt-PA) a marked increase (p<0.001) of antigen concentrations in plasma of endogenous t-PA and PAI-1 during the first 12h after initiation of treatment. The concentrations of endogenous t-PA and PAI-1 in plasma correlated significantly (p<0.05) with an estimate of generated thrombin in vivo, determined as plasma concentrations of thrombin-antithrombin III complexes. We conclude that the generation of coagulant activity following coronary thrombolysis is associated with an increased synthesis and/or release of endogenous t-PA and PAI-1, which suggests that the procoagulant condition involves an altered functional state of the vascular endothelium.     

Cellular localization of urokinase-type plasminogen activator,its inhibitors,and their mRNAs in breast cancer tissues

The plasminogen activation (PA) system may participate in cancer invasion and metastasis. A series of breast cancer tissue specimens was analysed using in situ hybridization and immunohistochemistry. Urokinase-type plasminogen activator (u-PA) mRNA was detected in cancer cells and fibroblasts adjacent to them and its expression was found to be more intense in invasive than in intraductal regions. In invasive but not in intraductal regions, especially those with abundant stroma, plasminogen activator inhibitor-1 (PAI-1) mRNA was observed in cancer cells, fibroblasts, macrophages, and endothelial cells, and PAI-2 mRNA was present in cancer cells, and fibroblasts, macrophages, and lymphocytes around them. These PAI-1- and PAI-2-positive cancer cells were localized at the periphery of the invasive front. Immunohistochemistry yielded basically similar results. A retrospective study of surgically resected breast cancers from 73 patients revealed significant clinical differences associated with u-PA and PAI-2 expression in cancer cells, associated with a poor and a good prognosis, respectively. These findings indicate that breast cancer cells and fibroblasts express u-PA initially and then its inhibitors, and that this process is related to invasion. Expression of u-PA and PAI-2 in cancer cells themselves may serve to up-regulate and limit PA-mediated invasion and metastasis, respectively. © 1997 John Wiley & Sons, Ltd.     

Levels of tissue-type plasminogen activator and plasminogen activator inhibitor 1 in disseminated intravascular coagulation syndrome

Since disseminated intravascular coagulation (DIC) may directly reflect the abnormal regulation of the fibrinolytic system by endothelial cells, we have measured the levels of tissue-type plasminogen activator (t-PA), type 1 PA inhibitor (PAI-1) and t-PA . PAI-1 complex which is formed as a result of interaction on the two factors, in the plasma of patients with DIC (n = 51) and healthy controls (n = 42). Antigens of t-PA, PAI-1 and t-PA . PAI-1 complex were significantly increased in the DIC plasma (36.4 +/- 25.1, 106.8 +/- 54.7 and 46.6 +/- 34.5 ng/ml, respectively) compared with those in normal plasma (8.5 +/- 4.3, 54.4 +/- 21.2 and 8.6 +/- 3.5 ng/ml, respectively). The molar ratio of t-PA to PAI-1 was much higher in the DIC plasma (1:3) than in normal plasma (1:6), which caused enhancement of the whole fibrinolytic activity in the DIC plasma. These changes resulted in significant consumption of plasminogen, alpha 2-plasmin inhibitor (alpha 2-PI) and a significant increase of plasmin . alpha 2-PI complex (PPI) and D-dimer. These results suggest that t-PA and its specific inhibitor PAI-1 both of which are secreted from endothelial cells into blood, play an important role on the progress of DIC.     

Plasma tissue plasminogen activator and plasminogen activator inhibitor-1 levels in acute myocardial infarction

The cause of the circadian variation in the incidence of acute myocardial infarction (AMI) has not been identified. Tissue plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) have opposing effects on thrombi. Hence, the extent of the clot, the size of the infarct and outcome of patients could depend on t-PA and PAI-1 levels. In an effort to elucidate the pathophysiologic basis of circadian variation of AMI, we investigated the presence of a possible corresponding circadian variation in the levels of endogenous t-PA and PAI-1 in patients diagnosed to have AMI and the effects of hypertension, diabetes and site of the infarct on these levels. We estimated the levels of t-PA and PAI-1 in platelet-poor plasma of 42 patients with AMI on admission, using the enzyme-linked immunosorbant assay. Although not statistically significant, patients having an AMI in the morning hours had the highest t-PA:PAI-1 ratio. The normal circadian variation in PAI-1 levels was lost in patients with AMI, probably due to the disease process. Also, the t-PA levels in hypertensive patients were significantly lower than in nonhypertensives. PAI-1 levels were also significantly lower in patients with anteroseptal than in inferior and anterolateral AMI. This relationship between the fibrinolytic potential and the site of infarction needs further study. Furthermore, t-PA levels on admission were significantly lower in survivors and may have a predictive value in determining the outcome.