Plasminogen Activator Inhibitor-1 Content Research Articles

MicroRNA-30b is involved in the pathological process of diabetes mellitus induced by pancreatic cancer by regulating plasminogen activator inhibitor-1

This study investigated the expression of plasminogen activator inhibitor-1 (PAI-1) and microRNA (miRNA or miR)-30b in tumor tissues, blood and urine from pancreatic cancer (PC) patients with diabetes mellitus. The effect of culture supernatant of PC cells with up-regulated expression of miR-30b on β cells was also investigated. Thirty-one PC patients with diabetes mellitus and 22 PC patients without diabetes mellitus were included. PC tissues and tumor-adjacent tissues, peripheral blood and urine were collected from all PC patients. Quantitative real-time polymerase chain reaction was used to determine the mRNA and miR-30b expression; Western blotting, to determine the expression of PAI-1 protein in tissues; enzyme-linked immunosorbent assay, to determine the PAI-1 content in serum or urine and dual luciferase reporter assay, to identify direct interaction between miR-30b and PAI-1 mRNA. The proliferation of INS-1 cells was determined by MTT assay. The results showed that PAI-1 mRNA and protein expression was elevated in PC patients with diabetes in contrast to that in PC patients without diabetes. By contrast, miR-30b expression was decreased in PC patients with diabetes. miR-30b could bind with the 3′-UTR seed region of PAI-1 mRNA to regulate its expression. Overexpression of miR-30b inhibited the expression of PAI-1, altered the microenvironment surrounding PC cells and promoted the proliferation of islet β-cells. These results suggest that the expression of PAI-1 in PC patients with diabetes is up-regulated, being correlated with the reduced expression of miR-30b. miR-30b is involved in the pathological process of diabetes mellitus induced by PC by regulating PAI-1.

Food deprivation induces adipose plasminogen activator inhibitor-1 (PAI-1) expression without accumulation of plasma PAI-1 in genetically obese and diabetic db/db mice

Relationships between energy intake and fibrinolytic functions have been documented in detail. We evaluated food deprivation (FD) as a means of modulating fibrinolytic activity in genetically obese and diabetic db/db mice and in their lean counterparts. Twelve hours of FD induced considerable gene expression of plasminogen activator inhibitor-1 (PAI-1) in both epididymal (3.8-fold, p < 0.05) and intestinal (2.4-fold, p < 0.05) adipose tissues without affecting plasma PAI-1 levels in db/db mice, whereas the FD did not affect these parameters in wild-type mice. Importantly, 24 hours of FD increased the plasma PAI-1 content in wild-type (1.9-fold, p < 0.01) but not in db/db mice, although adipose PAI-1 mRNA levels were significantly increased in db/db mice. The plasma PAI-1 content significantly correlated with hepatic PAI-1 mRNA levels in wild-type (r = 0.84, p < 0.01) and in db/db (r = 0.63, p < 0.01) mice. However, plasma PAI-1 did not correlate with adipose PAI-1 expression in db/db mice, although adipose tissue in general is thought to be the principal site of PAI-1 production in obesity. Hepatic PAI-1 expression was closely correlated with serum levels of free fatty acids in wild-type (r = 0.72, p < 0.01), but not in db/db mice. Adipose PAI-1 expression significantly correlated with serum corticosterone levels in both genotypes (wild-type, r = 0.52, p < 0.05; db/db, r = 0.51, p < 0.01), suggesting that adipose PAI-1 expression is up-regulated by fasting-induced glucocorticoids. The present findings suggested that fasting differentially affects fibrinolytic activity in obese and lean subjects and that PAI-1 expression in the liver as well as in adipose tissues comprises an important determinant of increased risk for cardiovascular disease in obesity.

Diabetes mellitus induces decreased plasma fibrinolytic activity and increased tissue synthesis of plasminogen activator inhibitor-1 (PAI-1) in the rat

In diabetes, plasma fibrinolytic activity is decreased while plasma plasminogen activator inhibitor-1 (PAI-1) is increased. Both liver and adipose tissue can synthesize and release PAI-1, but PAI-1 synthesis in these tissues has not been investigated in diabetes. Furthermore, little is known about PAI-1 localization in arterial wall cells of diabetic animals. The aim of this study was to determine the effect of chronic hyperglycemia on plasma fibrinolysis and plasma PAI-1 levels and on liver, adipose tissue and arterial wall PAI-1 content in the rat.We compared plasma fibrinolytic activity (lysis of fibrin plates) and plasma PAI-1 activity (chromogenic assay) in 10 Sprague Dowley 90% pancreatectomized rats (a model of diabetes characterized by normal fasting insulin and the absence of obesity, therefore closely resembling lean type 2 diabetes) and in 15 sham-operated rats. Furthermore, we measured PAI-1-related fluorescence, by immunofluorescent staining and Laser Scanning Confocal Microscopy, in liver, adipose tissue and aortic wall in diabetic and control animals.In the diabetic animals plasma fibrinolytic activity was reduced (lysis areas = 163 ± 23 vs 308 ± 21 mm2, P< 0.001), while plasma PAI-1 activity was increased (4.61 ± 2.01 AU vs 0.70 ± 0.59 AU, P< 0.02). PAI-1 related fluorescence was increased in the liver (754 ± 25 vs 299 ± 14 AFU, P< 0.0001), in the adipose tissue (721 ± 32 vs 248 ± 14 AFU, P< 0.001) and in the aorta wall (339 ± 18 vs 274 ± 9 AFU,P < 0.005) of the diabetic animals.These data provide evidence that in diabetes mellitus hyperglycemia is associated with increased PAI-1 content in the liver, adipose tissue and in the arterial wall. This suggests that in diabetes the liver and adipose tissue can be important sources for increased plasma PAI-1 and local fibrinolysis can be affected by increased PAI-1 levels in the arterial wall.

The role of cathepsin D and PAI-1 in primary invasive breast cancer as prognosticators and predictors of treatment benefit with adjuvant tamoxifen

In the last few years there has been an increased interest in treatment predictive factors in breast cancer patients. The aim of the study was to analyse the role of cathepsin D and plasminogen activator inhibitor-1 (PAI-1) expression as independent prognosticators and to assess their predictive value with respect to tamoxifen treatment. This study comprises 1851 patients with primary breast cancer diagnosed during 1988–1992. Their median age was 62 years (range: 24–91). The end-point was distant disease recurrence-free interval. Adjuvant treatment with tamoxifen was given to 1136 patients (61%). The median follow-up time was 59 months (range: 39–88). Cathepsin D content was shown to be a significant independent prognosticator in multivariate Cox analysis ( P=0.02). The optimal cut-off level was 10 fmol/mg protein, other cut-off levels did not improve the results. The level of cathepsin D also appeared to predict the benefit of tamoxifen among oestrogen receptor (ER)-positive patients although this result did not reach statistical significance ( P=0.09). In a multivariate Cox analysis including 497 patients PAI-1 content was shown to be a significant independent prognosticator ( P=0.003) but did not appear to predict the benefit of tamoxifen treatment. The optimal cut-off level appeared to be 3 ng/mg protein, which was close to the median value 2.5 ng/mg (range: 0–51). We conclude that cathepsin D is a significant independent prognosticator and may possibly also predict the benefit of tamoxifen amongst ER-positive patients. PAI-1 was also found to be a strong independent prognosticator but no treatment interaction with adjuvant tamoxifen was found.

Insulin resistance and thrombosis: a cardiologist’s view

Atherogenesis in the vasculature is accelerated by changes in the dynamic equilibrium between endogenous tissue plasminogen activator and plasminogen activator inhibitor-1 (PAI-1). Increased expression of PAI-1, decreased expression of tissue plasminogen activator, or both can lead to decreased fibrinolytic activity and predispose to thrombosis. Increased concentrations of insulin (and proinsulin) in the plasma increase plasma PAI-1, although the mechanisms of this effect are not known. In addition, it has been observed that basal fibrinolytic activity is decreased in patients with type 2 diabetes; this may accelerate atherosclerosis by exposing vascular luminal wall surfaces to persistent and recurrent thrombi. Abnormalities in the vessel wall appear to contribute to the increased risk. There is also evidence that PAI-1 content is increased in atherosclerotic lesions of patients with type 2 diabetes, suggesting that interventions to reduce insulin resistance and improve glycemic control may improve the fibrinolytic response. Clinical studies in patients with polycystic ovary syndrome (characterized by insulin resistance, hyperinsulinemia, ovarian androgen overproduction, and impaired fibrinolytic capacity) demonstrated that treatment with troglitazone, an insulin-sensitizing agent, can markedly reduce blood levels of PAI-1. There is also clinical evidence that these agents may contribute to regression of intimal medial thickness in patients with type 2 diabetes, providing further indication that antidiabetic interventions may help inhibit the progression of early atherosclerotic lesions.

Plasminogen activator inhibitor-1 is an independent poor prognostic factor for survival in advanced stage epithelial ovarian cancer patients.

High levels of plasminogen activator inhibitor-1 (PAI-1) in tissue extracts have been associated with poor prognosis in many epithelial cancers. Ovarian cancers contain a higher concentration of PAI-1 than benign ovarian tumors or normal ovaries. Reports, however, on the prognostic value of PAI-1 content in ovarian cancers have been conflicting. We used immunohistochemistry to study the primary and metastatic tissues from 131 epithelial ovarian cancer cases. This group has been previously characterized for the expression of urokinase (uPA), uPA receptor, PAI-2 and macrophage colony-stimulating factor (CSF-1). The intensity and extent of staining for PAI-1 in the tumor epithelium was scored. Kaplan-Meier curves of survival were compared using the log-rank test. The Cox regression model was utilized for multivariate analysis. Approximately 50% of the primary tumors and metastases expressed PAI-1. Among invasive stages III and IV patients, those whose primary tumors expressed PAI-1 had a shorter overall survival. The combination of strong expression of PAI-1 and expression of uPA was a highly significant factor for short disease-free and overall survival. Similar results were seen with the combination of high PAI-1 and low PAI-2 expression. Strong PAI-1 expression was significantly associated with expression of uPA receptor or CSF-I in the tumor epithelium, but not with standard clinical parameters, and was an independent prognostic factor for poor survival on multivariate analysis. Our results show that PAI-1 expression in the primary tumor epithelium is an independent poor prognostic factor for survival, underscoring the tumor protective role of PAI-1 in ovarian cancer biology.

Plasminogen activator inhibitor‐1 is an independent poor prognostic factor for survival in advanced stage epithelial ovarian cancer patients

High levels of plasminogen activator inhibitor-1 (PAI-1) in tissue extracts have been associated with poor prognosis in many epithelial cancers. Ovarian cancers contain a higher concentration of PAI-1 than benign ovarian tumors or normal ovaries. Reports, however, on the prognostic value of PAI-1 content in ovarian cancers have been conflicting. We used immunohistochemistry to study the primary and metastatic tissues from 131 epithelial ovarian cancer cases. This group has been previously characterized for the expression of urokinase (uPA), uPA receptor, PAI-2 and macrophage colony-stimulating factor (CSF-1). The intensity and extent of staining for PAI-1 in the tumor epithelium was scored. Kaplan-Meier curves of survival were compared using the log-rank test. The Cox regression model was utilized for multivariate analysis. Approximately 50% of the primary tumors and metastases expressed PAI-1. Among invasive stages III and IV patients, those whose primary tumors expressed PAI-1 had a shorter overall survival. The combination of strong expression of PAI-1 and expression of uPA was a highly significant factor for short disease-free and overall survival. Similar results were seen with the combination of high PAI-1 and low PAI-2 expression. Strong PAI-1 expression was significantly associated with expression of uPA receptor or CSF-1 in the tumor epithelium, but not with standard clinical parameters, and was an independent prognostic factor for poor survival on multivariate analysis. Our results show that PAI-1 expression in the primary tumor epithelium is an independent poor prognostic factor for survival, underscoring the tumor protective role of PAI-1 in ovarian cancer biology. Int. J. Cancer (Pred. Oncol.) 79:449–454, 1998.© 1998 Wiley-Liss, Inc.

Significance of serine proteinase and matrix metalloproteinase systems in the destruction of human articular cartilage.

1. During the destruction of articular cartilage, fibrinolytic enzymes and matrix metalloproteinases (MMP) may contribute to the related pathology. The activities, antigens and messenger RNA (mRNA) levels of urokinase-type plasminogen activator (uPA) and plasminogen activator inhibitor-1 (PAI-1) in articular cartilage were measured in patients with no history of joint diseases (control), those with osteoarthritis (OA) classified into osteophyte-formed site (OS) and weight-bearing site (WS), and in patients with rheumatoid arthritis (RA). 2. The uPA content was higher in WS and RA compared to normal. The PAI-1 content was higher in OS and RA compared to normal. Weight-bearing site patients expressed a high uPA mRNA level but a low PAI-1 mRNA level. Osteophyte-formed site patients expressed a low uPA mRNA level but a high PAI-1 mRNA level. 3. The levels of the MMP and mRNA of tissue inhibitors of metalloproteinases (TIMP) were measured in WS, OS, and RA. In WS, the levels of MMP were high and levels of TIMP mRNA expression low. In OS, the levels of TIMP were high and levels of MMP mRNA were low. In RA, the levels of MMP and TIMP mRNA were high. 4. These findings suggest that regulation of fibrinolysis may play an important role in the matrix of articular cartilage with arthropathy.

Prognostic Value of Urokinase Plasminogen Activator and Plasminogen Activator Inhibitor-1 in Renal Cell Cancer

Purpose Urokinase type plasminogen activator and its inhibitor plasminogen activator inhibitor are associated with invasion and formation of metastases in tumors. In a prospective study urokinase and plasminogen activator inhibitor-1 content in renal cell cancer and benign renal tissue was correlated with the traditional prognostic factors of TNM staging and grading as well as ploidy and actual clinical outcome of the patients. Materials and Methods A total of 152 patients, who underwent transperitoneal tumor nephrectomy for renal cell cancer, was followed for a mean of 23.9 months. Urokinase and plasminogen activator inhibitor-1 from the tumor tissue and corresponding benign renal tissue were quantified from detergent extracted tissue samples (1 percent triton-X-100 in TBS) and measured with an enzyme-linked immunosorbent assay. Results Urokinase content correlated with the development of distant metastases (log rank 4.32, p = 0.037). Cutoff value was 0.84 ng./mg. A group of 11 patients were considered to be at high risk for metastases (9 events) based on urokinase greater than 0.84 ng./mg., while 94 patients were considered to be at low risk (5 events) with urokinase less than 0.84 ng./mg. Plasminogen activator inhibitor-1 significantly correlated with the prevalence of distant metastases (log rank 5.17, MO, 10.04 versus M1, 23.79, p = 0.02) and the development of new metastases postoperatively (M0, 10.85 versus M1, 27.36, p = 0.001). Cutoff value was 12 ng./mg. protein. A group of 41 patients were considered at high risk for relapse (6) based on plasminogen activator inhibitor-1 greater than 12 ng./mg. protein compared to 55 patients with plasminogen activator inhibitor-1 less than 12 ng./mg. protein with only 1 relapse during followup. Conclusions Plasminogen activator inhibitor-1, the specific inhibitor of urokinase is a strong and independent prognostic factor in predicting early relapse of renal cell carcinoma. High and low risk groups for disease-free survival can be discriminated by plasminogen activator inhibitor-1 antigen content in the tumor tissue.

Plasminogen Activator Inhibitor-1 in Brain Tumors

TUMOR NECROSIS IS a common feature of malignant neoplasms. The pathogenesis of tumor necrosis remains poorly documented. Recent evidence has shown a correlation between the presence of tumor necrosis and low content of tissue plasminogen activator in brain tumors and significantly higher levels of plasminogen activator inhibitor-1 (PAI-1) in human glioblastomas. We subjected fresh brain tumor tissue samples (n = 197) to an enzyme-linked immunosorbent assay to determine PAI-1 content. The results were correlated with the presence of edema and necrosis on imaging studies. The samples studied were from normal brain (n = 10), low-grade gliomas (n = 26), meningiomas (n = 47), acoustic neuromas (n = 18), glioblastomas (n = 45), metastases (n = 45), and areas of tumor necrosis (n = 6). The benign tumor samples (n = 96) had 3.5 times less PAI-1 than did the malignant tumors (n = 101). Tumor necrosis samples contained 3.8 times more PAI-1 than did the nonnecrotic malignant tumor samples (P < 0.000001). The benign meningioma samples showed a similar ratio compared with their malignant counterparts (0.35 versus 1.59 ng/mg, respectively, P = 0.0004). Regression analysis results showed a strong correlation between PAI-1 and necrosis (r = 0.47, P < 0.0000028) and, to a lesser extent, brain edema (r = 0.26, P = 0.001). A negative correlation between PAI-1 and tissue plasminogen activator levels almost reached statistical significance (P = 0.07). There was no correlation between PAI-1 content and the tumor size, duration of symptoms, or the sex or age of the patients. The cellular localization and distribution of PAI-1 messenger ribonucleic acid were related primarily to vascular structures and necrotic foci. The expression of PAI-1 messenger ribonucleic acid was also shown to be associated predominantly with necrotic areas in the tumor tissue. The results of this study indicate that malignant transformation is associated with a significant increase in PAI-1 and that PAI-1 may play an integral role in the pathogenesis of tissue necrosis, perhaps via the inhibition of tissue plasminogen activator and the promotion of microthrombosis.

Plasminogen activator inhibitor-1 in brain tumors: relation to malignancy and necrosis.

Tumor necrosis is a common feature of malignant neoplasms. The pathogenesis of tumor necrosis remains poorly documented. Recent evidence has shown a correlation between the presence of tumor necrosis and low content of tissue plasminogen activator in brain tumors and significantly higher levels of plasminogen activator inhibitor-1 (PAI-1) in human glioblastomas. We subjected fresh brain tumor tissue samples (n = 197) to an enzyme-linked immunosorbent assay to determine PAI-1 content. The results were correlated with the presence of edma and necrosis on imaging studies. The samples studied were from normal brain (n = 10), low-grade gliomas (n = 26), meningiomas (n = 47), acoustic neuromas (n = 18), glioblastomas (n = 45), metastases (n = 45), and areas of tumor necrosis (n = 6). The benign tumor samples (n = 96) had 3.5 times less PAI-1 than did the malignant tumors (n = 101). Tumor necrosis samples contained 3.8 times more PAI-1 than did the nonnecrotic malignant tumor samples (P < 0.000001). The benign meningioma samples showed a similar ratio compared with their malignant counterparts (0.35 versus 1.59 ng/mg, respectively, P = 0.0004). Regression analysis results showed a strong correlation between PAI-1 and necrosis (r = 0.47, P < 0.0000028) and, to a lesser extent, brain edema (r = 0.26, P = 0.001). A negative correlation between PAI-1 and tissue plasminogen activator levels almost reached statistical significance (P = 0.07). There was no correlation between PAI-1 content and the tumor size, duration of symptoms, or the sex or age of the patients. The results of this study indicate that malignant transformation is associated with a significant increase in PAlI1 and that PAI-1 may play an integral role in the pathogenesis of tissue necrosis, perhaps via the inhibition of tissue plasminogen activator and the promotion of microthrombosis.

The role of progestationally regulated stromal cell tissue factor and type-1 plasminogen activator inhibitor (PAI-1) in endometrial hemostasis and menstruation.

The physiologic mechanisms whereby the human endometrium maintains hemostasis during endovascular trophoblast invasion, yet permits menstrual hemorrhage, are unknown. This paradoxical relationship was investigated by evaluating endometrial expression of tissue factor (TF), the primary initiator of hemostasis, and plasminogen activator inhibitor-1 (PAI-1), the primary inhibitor of fibrinolysis. We observed increased immunostaining for TF and PAI-1 in sections of decidualized stromal cells from luteal phase and gestational endometrium. To determine whether TF and PAI-1 expression are directly linked to decidualization, both endpoints were monitored in a well described in vitro model of decidualization. Thus, confluent stromal cell cultures were exposed to vehicle control, 10(-8) M estradiol (E2), 10(-8) to 10(-6) M medroxyprogesterone acetate (MPA) or both E2 + MPA for 2-24 days in serum-containing or defined media. The progestin enhanced the content of stromal cell-associated immunoreactive and functionally active TF and PAI-1 released into the medium and elevated levels of stromal cell TF and PAI-1 mRNA. While E2 alone was ineffective, it greatly augmented MPA-enhanced TF and PAI-1 protein and mRNA content. Dose-dependent effects on TF and PAI-1 content were observed between 10(-8) to 10(-6) M MPA +/- E2. Similar results were observed for decidual cells derived from first trimester endometrium and cultured in type 1 collagen gels. Following optimal induction of TF and PAI-1 expression by E2 + MPA in stromal cell cultures, removal of these steroids greatly reduced levels of both TF and PAI-1 protein and mRNA within 4 days. These studies suggest a mechanism whereby endometrial hemostasis is maintained during trophoblast invasion yet reduced at the end of nonfertile cycles to permit menses.

Platelets inhibit fibrinolysis in vitro by both plasminogen activator inhibitor-1-dependent and -independent mechanisms

Platelet-rich thrombi are resistant to lysis by tissue-type plasminogen activator (t-PA). Although platelet alpha-granules contain plasminogen activator inhibitor-1 (PAI-1), a fast-acting inhibitor of t-PA, the contribution of PAI-1 to the antifibrinolytic effect of platelets has remained a subject of controversy. We recently reported a patient with a homozygous mutation within the PAI-1 gene that results in complete loss of PAI-1 expression. Platelets from this individual constitute a unique reagent with which to probe the role of platelet PAI-1 in the regulation of fibrinolysis. The effects of PAI-1-deficient platelets were compared with those of normal platelets in an in vitro clot lysis assay. Although the incorporation of PAI-1-deficient platelets into clots resulted in a moderate inhibition of t-PA-mediated fibrinolysis, normal platelets markedly inhibited clot lysis under the same conditions. However, no difference between PAI-1-deficient platelets and platelets with normal PAI-1 content was observed when streptokinase or a PAI-1-resistant t-PA mutant were used to initiate fibrinolysis. In addition, PAI-1-resistant t-PA was significantly more efficient in lysing clots containing normal platelets than wild-type t-PA. We conclude that platelets inhibit t-PA-mediated fibrinolysis by both PAI-1-dependent and PAI-1-independent mechanisms. These results have important implications for the role of PAI-1 in the resistance of platelet-rich thrombi to lysis in vivo.

Platelets Inhibit Fibrinolysis In Vitro by Both Plasminogen Activator Inhibitor-1-Dependent and -Independent Mechanisms

Abstract Platelet-rich thrombi are resistant to lysis by tissue-type plasminogen activator (t-PA). Although platelet alpha-granules contain plasminogen activator inhibitor-1 (PAI-1), a fast-acting inhibitor of t-PA, the contribution of PAI-1 to the antifibrinolytic effect of platelets has remained a subject of controversy. We recently reported a patient with a homozygous mutation within the PAI-1 gene that results in complete loss of PAI-1 expression. Platelets from this individual constitute a unique reagent with which to probe the role of platelet PAI-1 in the regulation of fibrinolysis. The effects of PAI-1-deficient platelets were compared with those of normal platelets in an in vitro clot lysis assay. Although the incorporation of PAI-1-deficient platelets into clots resulted in a moderate inhibition of t-PA-mediated fibrinolysis, normal platelets markedly inhibited clot lysis under the same conditions. However, no difference between PAI-1-deficient platelets and platelets with normal PAI-1 content was observed when streptokinase or a PAI-1-resistant t-PA mutant were used to initiate fibrinolysis. In addition, PAI-1-resistant t-PA was significantly more efficient in lysing clots containing normal platelets than wild-type t-PA. We conclude that platelets inhibit t-PA-mediated fibrinolysis by both PAI- 1-dependent and PAI-1-independent mechanisms. These results have important implications for the role of PAI-1 in the resistance of platelet-rich thrombi to lysis in vivo.

Plasminogen activator inhibitor-1 mRNA is expressed in platelets and megakaryocytes and the megakaryoblastic cell line CHRF-288.

Plasminogen activator inhibitor-1 (PAI-1) is present in the platelet alpha-granule and is released on platelet activation. Platelet PAI-1 could either be synthesized by the megakaryocyte or taken up from the plasma. In this report we confirm the presence of PAI-1 protein in human megakaryocytes by Western blot analysis and show its synthesis in guinea pig megakaryocytes by metabolic labeling. We document the presence of PAI-1 mRNA in human platelets and show a 3-kb mRNA species on Northern blot analysis of guinea pig megakaryocytes. Neither untreated CHRF-288 cells, a megakaryoblastic cell line, nor human erythroleukemia (HEL) cells expressed PAI-1 mRNA. Phorbol ester (phorbol 12-myristate 13-acetate, 160 nM) treatment of CHRF-288 and HEL cells for 4 days induced PAI-1 mRNA expression in CHRF-288 cells but not in HEL cells. These studies show that PAI-1 is synthesized by megakaryocytes. Megakaryocytes most likely determine the PAI-1 content of platelets and thereby establish the antifibrinolytic potential of the platelet.

Stimulating effect of oxidized low density lipoproteins on plasminogen activator inhibitor-1 synthesis by endothelial cells.

Oxidized low density lipoproteins (ox-LDL) are thought to accelerate atherogenesis. It was recently demonstrated that patients with coronary heart disease have defects in plasma fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) levels. Investigation of PAI-1 synthesis by endothelial cells may allow insight into the effect of native LDL (N-LDL) and ox-LDL on endothelial cells. In the present study, secretion of PAI-1 by human umbilical vein endothelial cells (HUVEC) in culture was evaluated after incubation with N-LDL and ox-LDL. Ox-LDL were obtained by peroxidation under ultraviolet radiation, which induced compositional changes in LDL, namely, a decrease in the levels of arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and alpha-tocopherol and an increase in the malondialdehyde content. Ox-LDL induced a dose-dependent increase in PAI-1 secretion by HUVEC as assayed by an enzyme-linked immunosorbent assay. After a 24-hour incubation, a twofold increase in the PAI-1 content was observed with 50 micrograms/ml ox-LDL protein. Studies with inhibitors of protein synthesis and metabolic labeling with [35S]methionine confirmed that PAI-1 synthesis was stimulated by ox-LDL. N-LDL had no detectable effect on PAI-1 secretion. Binding studies with radiolabeled lipoproteins showed that the effect of ox-LDL was independent of the B/E receptor. Our experiments indicate that ox-LDL stimulate PAI-1 secretion from HUVEC and that this effect may involve a scavenger receptor.