Invasion and metastasis of hepatocellular carcinoma in relation to urokinase-type plasminogen activator, its receptor and inhibitor

This study was designed to investigate the relationship of urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) to invasion and metastasis of hepatocellular carcinoma (HCC). The expression of uPA, uPAR, and PAI-1 in HCC was determined by immunohistochemistry, Northern blot, and an LCI-D20 nude mouse metastatic model of HCC. The over-expression of uPA, uPAR, and PAI-1 was found in HCC, especially in the patients with portal cancer embolus, tumor invasion, and metastasis. Immunohistochemistry results showed that the rate of positive staining of uPA, uPAR, and PAI-1 were higher in HCC than those in the control groups consisting of cancer-adjacent tissue and normal liver tissue. In the case of HCC invasion, positive uPA and uPAR were seen in 16 and 19 out of 22 patients, respectively (P < 0.01 and P < 0.001, respectively, as compared with the patients without invasion). In those with portal cancer embolus and tumor metastasis, positive uPAR was eight out of eight and six out of six patients. In those with tumor recurrence, positive uPAR was 15 out of 17 patients (P < 0.01 vs no recurrence). In patients who died within 2 years after surgery, positive uPAR was 12 out of 12 patients (P < 0.01 vs survival), and positive PAI-1 was nine out of 12 patients (P < 0.05 vs survival). In those in which uPA, uPAR, and PAI-1 were all positive staining, stronger cancer invasiveness and higher mortality were found (P < 0.05 vs patients with all negative staining). In 30 patients tested with Northern blot analysis, the results were similar to those tested with immunohistochemistry. Higher expression of uPA mRNA and PAI-1 mRNA were detected in tumor tissues and embolus. In the patients with positive signals of uPA mRNA and PAI-1 mRNA, invasive cases were found in seven out of 19 and eight out of 18 patients, respectively, which were significantly higher than those showing negative signals (P < 0.05). In the LCI-D20 nude mouse metastatic model of HCC (MMHCC), PAI-1 activity in plasma and tumor tissue increased with tumor growth, invasion, and metastasis. At an advanced stage of MMHCC, PAI-1 activity rose to 15.4 ± 0.7 Au/ml in plasma and 0.8 ± 0.3 Au/mg in tumor extracts, which was significantly higher than 6.2 ± 1.8 Au/ml in plasma and 0.4 ± 0.1 Au/mg in extracts at an early stage (P < 0.05). PAI-1 activity related to the changes of serum AFP and tumor progress were r=0.9544 and r=0.9648, respectively (P < 0.05). The data suggest that the expression of uPA, uPAR, and PAI-1 is increased in HCC, and related to the invasiveness, metastasis, and prognosis of HCC. Received: 30 September 1999 / Accepted: 10 March 2000     

Expression of urokinase-type plasminogen activator receptor and plasminogen activator inhibitor-1 in gastric cancer

In gastric cancer, the urokinase-type plasminogen activator (uPA) system plays important roles in invasion and metastasis, processes which entail proteolysis and adhesion. Both the urokinasetype plasminogen activator receptor (uPAR) and the plasminogen activator inhibitor-1 (PAI-1) are thought to be important factors in this system. To clarify the relationship between these two factors and gastric cancer invasiveness, we evaluated the expression of uPAR and PAI-1 in 91 cases of gastric cancer by immunohistochemistry and in situ hybridization. Urokinase-type plasminogen activator receptor-mRNA, PAI-1-mRNA, uPAR and PAI-1 protein were diffusely distributed in the cytoplasm of the cancer cells and concentrated at invasive foci. Urokinase-type plasminogen activator receptor protein expression correlated with lymphatic, venous invasion (P<.01) and lymph node metastasis (P<0.05); uPAR-mRNA expression correlated with lymphatic, venous invasion and lymph node metastasis (P<0.05). Plasminogen activator inhibitor-1 protein expression correlated with lymphatic, venous invasion, lymph node metastasis and depth of invasion (P<0.01); PAI-1-mRNA expression was linked to lymphatic, venous invasion (P<0.01), lymph node metastasis and depth of invasion (P<0.05). This suggests that the proteolytic activity of uPAR and the cellular motility of PAI-1 in gastric cancer cells may determine penetration of lymphatic and blood vessels, whereby lymph node metastasis may be promoted and that the promotion of cellular motility by PAI-1 may influence the depth of cancer invasion.     

Chromosomal localization of the human urokinase plasminogen activator receptor and plasminogen activator inhibitor type-2 genes: Implications in colorectal cancer

Abstract Activation of the proenzyme of urokinase (uPA) on the surface of cancer cells has been implicated in the initiation of focal proteolytic mechanisms that permit invasion and metastasis by colon cancers. The activity of uPA on the cell surface appears to be a function of the number of uPA-specific receptors (uPAR) and the extent of inhibition of uPA by plasminogen activator inhibitors (PAI). The mapping of the genes coding for uPAR, and for PAI-2, was performed to determine whether their chromosomal localization suggested their involvement in the genetic alterations associated with cancer cell DNA.
This study confirms the localization of the human urokinase plasminogen activator receptor gene to chromosome 19q and, using in situ hybridization, provides a precise localization to chromosome 19q13.2. In addition, our results confirm the previous allocation of the human plasminogen activator inhibitor-2 gene to a location 18q21.3 → 18q21.1, a location that corresponds to the commonest (>70%) somatic deletions found in colorectal carcinomas. The mapping of the uPAR and PAI-2 genes enables the elucidation of their possible involvement in the genetic alterations that determine the invasive and metastatic phenotypes in colorectal cancer.     

Increased expression of plasminogen activator and plasminogen activator inhibitor during liver fibrogenesis of rats: role of stellate cells.

BACKGROUND/AIMS: Plasminogen activators and plasminogen activator inhibitors are important regulators of the balance between the proteolytic and antiproteolytic activities that determine extracellular matrix turnover. We examined the expression of plasminogen activator-plasmin system components in experimental liver fibrosis of rats. METHODS: Liver fibrosis was produced in rats by injecting carbon tetrachloride for 6 to 12 weeks. Gene expression for plasminogen activator inhibitor-1 (PAI-1), urokinase and tissue plasminogen activators (uPA and tPA), urokinase plasminogen activator receptor (uPAR), and transforming growth factor-beta1 (TGF-beta1) was examined by Northern analysis. Western analysis was performed to detect protein expression of PAI-1, uPA and uPAR. An immunohistochemical study was performed to detect the localization of PAI-1. Additionally, primary cultured liver cells were examined by Northern and Western analyses for this protein with or without prior incubation with TGF-beta1. RESULTS: At 6 weeks, when fibrosis had occurred, uPA and uPAR mRNAs had increased 2.8-fold and 1.8-fold, respectively; PAI-1 and tPA mRNA levels were unchanged. At the cirrhotic stage (9 to 12 weeks), mRNA levels for PAI-1, uPA, uPAR and tPA were all increased. Western analysis also showed increased uPA and uPAR expressions in fibrotic liver, and increased PAI-1, uPA and uPAR expressions in cirrhotic liver. PAI-1 protein was also demonstrated immunohistochemically along sinusoids, vessels, and bile duct cells of normal and fibrotic liver. In liver cell cultures, Kupffer cells, hepatocytes, and especially stellate cells, expressed PAI-1. Expression was enhanced in stellate cells cultured from fibrotic or cirrhotic liver or stimulated in vitro with TGF-beta1. CONCLUSION: Though increased uPA and uPAR may act on matrix degradation in fibrotic liver, increased PAI-1 together with uPA, uPAR and tPA are associated with overall inhibition of matrix degradation in cirrhotic liver. Hepatic stellate cells are an important source of PAI-1 during liver fibrosis.     

Characteristics of fibrinolytic disorders in acute promyelocytic leukemia

ABSTRACT

Objectives: Catastrophic hemorrhage remains the main cause of acute promyelocytic leukemia (APL) treatment failure. This study was aimed to study the pathogenesis of coagulopathy in patients with APL.

Methods: Multiple procoagulant and profibrinolytic parameters in plasma and peripheral leukocytes from 24 patients with newly diagnosed APL accompanied by coagulopathy before and after arsenic trioxide (ATO) treatment were evaluated.

Results: Prior to the treatment, the patients had elevated D-dimer and decreased fibrinogen levels. Plasma urokinase-type plasminogen activator receptor (uPAR) and plasmin–ɑ₂ antiplasmin complexes (PAP) levels, plasmin (Pn) activity, and cell surface levels of urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA) were significantly higher; plasma plasminogen activator inhibitor-1 (PAI-1) levels and plasminogen (Pg) activity were significantly decreased; plasma plasminogen activator (PA) activity, uPA and tPA levels; and cell surface levels of uPAR and annexin II were not significantly different from levels in the control group. During ATO treatment, both patients’ plasma PA activity and uPAR on leukocytes gradually increased, annexin II on leukocytes increased initially and decreased afterwards, and tPA and uPA on leukocytes remained consistently higher in the patients than in the controls. Other parameters gradually tended toward normal values.

Conclusions: In APL, activated coagulation system activated fibrinolytic system, and increased uPAR levels could contribute to the hyperfibrinolysis. Annexin II might not be involved in the coagulopathy.     

Rheumatoid synovial fibroblasts constitutively express the fibrinolytic pattern of invasive tumor-like cells

OBJECTIVE: In rheumatoid arthritis (RA) the synovial membrane proliferates and invades the underlying tissues. The cell-associated fibrinolytic system (urokinase-type plasminogen activator, uPA; uPA receptor, uPAR; plasminogen activator inhibitor-type 1, PAI-1) is pivotal in cell invasion and proliferation. For this reason, the expression and the role of such enzymatic system was investigated in synovial fibroblasts (SF) of normal and RA patients. METHODS: In SF obtained from RA patients and control subjects, uPA, uPAR and PAI-1 were measured by ELISA of cell lysates and culture medium and by RT-PCR of mRNAs. uPA was also studied by zymography. Proliferation was measured by cell counting and cell invasion with the Boyden chamber. RESULTS: RA-SF over-express uPAR and PAI-1 and are more prone than the normal counterpart to spontaneous and uPA-challenged invasion and proliferation, which are counteracted by antagonists of the fibrinolytic system. CONCLUSIONS: RA-SF display the fibrinolytic pattern and behaviour of invasive tumor-like cells. Antagonists of the fibrinolytic system are able to revert growth and invasion of both normal and RA-SF.     

Lack of plasminogen activator inhibitor-1 effect in a transgenic mouse model of metastatic melanoma

Tumor cell invasion and metastasis is a complex, multistep process that is postulated to require degradation of extracellular matrix at several steps. Urokinase-type plasminogen activator (uPA) is expressed on the cell surface of B16 murine melanoma cells and is thought to contribute to the pericellular proteolysis necessary for tumor cell migration. In vitro modification of B16 melanoma cell surface uPA activity has been shown to alter the invasive and metastatic potential of these murine melanoma cells in vivo. Plasminogen activator inhibitor-1 (PAI-1), a rapid inhibitor of both uPA and tissue-type plasminogen activator (tPA) is the major physiologic regulator of plasminogen activator activity. To test the role of host PAI-1 in the invasive and metastatic capacity of B16 melanoma cells we analyzed local tumor growth and pulmonary metastasis in transgenic mice engineered to overexpress murine PAI-1 in multiple tissues including lung, and in mice completely deficient in PAI-1. No significant difference in the number of pulmonary metastases was observed after intravenous inoculation of tumor cells into PAI-1- overexpressing and PAI-1-deficient mice when compared with wild-type controls. Similarly, in a spontaneous metastasis model, PAI-1- overexpressing and PAI-1-deficient mice demonstrated no difference in primary tumor size or overall survival. These data demonstrate that wide variations of host PAI-1 expression, from complete absence to marked overexpression, does not significantly influence the metastatic potential of B16 melanoma cells in a murine model.     

尿激酶型纤溶酶原激活物对糖尿病大鼠肾脏系膜基质的影响

目的 探讨尿激酶型纤溶酶原激活物（uPA）对糖尿病大鼠肾脏系膜基质表达的影响及机制.方法 8周龄健康雄性SD大鼠（体质量150～200 g）20只尾静脉注射链脲佐菌素,成功建立糖尿病大鼠模型后采用数字表法随机分为糖尿病组（n=10）和uPA组（n=10;尾静脉注射2500 U·kg^-1·d^-1 uPA,共4周）.另以10只正常大鼠为对照组.29d后处死大鼠,心脏取血检测血糖、血肌酐水平.过碘酸六胺银染色测定肾小球平均面积、肾小球平均容积和肾小球系膜区面积.免疫组织化学法检测肾脏尿激酶型纤溶酶原激活物受体（uPAR）、纤溶酶原激活物抑制剂-1（PAI-1）和Ⅳ型胶原表达水平.采用方差分析和q检验进行数据统计.结果 与正常对照组比较,糖尿病组大鼠明显出现尿蛋白[（25.4±4.3）mg/24 h vs（5.5±2.1）mg/24 h,q=4.27,P＜0.01],肾小球体积及系膜基质显著增加,肾小球系膜uPAR、PAI-1、Ⅳ型胶原表达显著增加（q值分别为3.63、3.97、4.21,均P＜0.05）.糖尿病大鼠注射uPA后,尿蛋白明显减少[（12.6±5.4）mg/24 h,q=3.45,P＜0.05],肾小球体积、系膜基质异常有所改善（q值分别为4.34、4.27,均P＜0.01）,肾小球系膜PAI-1、Ⅳ型胶原表达明显减少（q值分别为3.98、4.17,均P＜0.05）.结论注射uPA可明显降低糖尿病大鼠肾小球PAI-1蛋白表达,对uPAR表达的影响不大,提示uPA可能通过与uPAR结合、摄取PAI-1并加速其降解,从而调节肾小球系膜细胞及其基质表达,改善糖尿病系膜基质病变.     

Plasminogen activation in synovial tissues: differences between normal, osteoarthritis, and rheumatoid arthritis joints

OBJECTIVE—To analyse the functional activity of the plasminogen activators urokinase (uPA) and tissue type plasminogen activator (tPA) in human synovial membrane, and to compare the pattern of expression between normal, osteoarthritic, and rheumatoid synovium. The molecular mechanisms underlying differences in PA activities between normal and pathological synovial tissues have been further examined.
METHODS—Synovial membranes from seven normal (N) subjects, 14 osteoarthritis (OA), and 10 rheumatoid arthritis (RA) patients were analysed for plasminogen activator activity by conventional zymography and in situ zymography on tissue sections. The tissue distribution of uPA, tPA, uPA receptor (uPAR), and plasminogen activator inhibitor type-1 (PAI-1) was studied by immunohistochemistry. uPA, tPA, uPAR, and PAI-1 mRNA values and mRNA distribution were assessed by northern blot and in situ hybridisations respectively.
RESULTS—All normal and most OA synovial tissues expressed predominantly tPA catalysed proteolytic activity mainly associated to the synovial vasculature. In some OA, tPA activity was expressed together with variable amounts of uPA mediated activity. By contrast, most RA synovial tissues exhibited considerably increased uPA activity over the proliferative lining areas, while tPA activity was reduced when compared with N and OA synovial tissues. This increase in uPA activity was associated with increased levels of uPA antigen and its corresponding mRNA, which were localised over the synovial proliferative lining areas. In addition, in RA tissues, expression of the specific uPA receptor (uPAR) and of the plasminogen activator inhibitor-type 1 (PAI-1) were also increased.
CONCLUSION—Taken together, these results show an alteration of the PA/plasmin system in RA synovial tissues, resulting in increased uPA catalytic activity that may play a part in tissue destruction in RA.

     

The urokinase plasminogen activator system in cancer: Implications for tumor angiogenesis and metastasis

Substantial evidence exists which implicates the urokinase plasminogen activator system [urokinase plasminogen activator (uPA), urokinase plasminogen activator receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1)] in the neo-vascularization, invasion and metastasis of many solid tumors. Clinical studies have demonstrated an association between high levels of expression of the components of this system in tumors and poor patient prognosis and outcome. Components of the uPA/uPAR system are differentially expressed or activated on motile cells including invading tumor cells and leukocytes, and migrating endothelial cells. In contrast, there is little or no expression on most normal, quiescent cells. Studies performed in vitro have demonstrated the regulation of the expression of uPA and uPAR by growth and differentiation factors as well as by oncogenes. In this review, we summarize recent findings on the role of the components of the uPA/uPAR system in angiogenesis, invasiveness and tumor metastasis. The activities of this system in endothelial and leukocyte cell biology and the relevance of these activities to angiogenesis and tumor metastasis will be considered. Recent experimental evidence obtained using inhibitors of uPA and uPAR has validated this system as a therapeutic target for the development of anti-angiogenic and anti-metastatic therapeutic agents. These studies, as well as additional therapeutic and diagnostic implications for uPAR targeting, will be discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Deflazacort modulates the fibrinolytic pattern and reduces uPA-dependent chemioinvasion and proliferation in rheumatoid arthritis synoviocytes

OBJECTIVE: Extracellular fibrinolysis, controlled by the cell-associated fibrinolytic system (urokinase plasminogen activator, uPA; uPA receptor, uPAR; plasminogen activator inhibitor type-1, PAI-1), is involved in cartilage damage generation and in rheumatoid arthritis (RA) synovitis. Since steroids reduce the rate of radiological progression of RA, we planned to evaluate in healthy and RA synoviocytes the effects of the steroid deflazacort on uPA, uPAR and PAI-1 expression, and subsequent phenotypic modifications in terms of uPA/uPAR-dependent invasion and proliferation. METHODS: uPA, uPAR and PAI-1 levels were studied by ELISA, RT-PCR (uPAR) and zymography (uPA) in synoviocytes from four RA patients and four healthy controls. Chemoinvasion was assessed by the Boyden chamber invasion assay, using Matrigel as the invasion substrate. Proliferation was evaluated by cell counting. Both invasion and proliferation were measured upon treatment with deflazacort 5 muM with or without parallel stimulation with uPA 500 ng/ml or in the presence of monoclonal anti-uPA and anti-uPAR antibodies. RESULTS: Invasion and proliferation of RA synoviocytes require a proper functional balance of the fibrinolytic system. Both deflazacort and monoclonal antibodies against uPA and uPAR reduced expression and activity of the system, thus inhibiting invasion and proliferation. In RA synoviocytes, deflazacort induced higher PAI-1 and lower uPA and uPAR levels, as well as a decrease in uPA enzymatic activity. The levels of uPAR mRNA were concomitantly reduced, as was uPA-induced chemoinvasion. All these effects were also shown in controls, though to a lesser extent. CONCLUSIONS: Deflazacort might control RA synovial proliferation and invasion by differential modulation of single members of the fibrinolytic system.     

Progress of tissue injury in appendicitis involves the serine proteases uPA and PAI-1

Objective. Serine proteases and the matrix metalloproteinases (MMPs) are key factors in the proteolytic cascade and participate in extracellular matrix (ECM) degradation. Fibrinolytic activators and inhibitors may have an effect on inflammatory cells, thereby modulating the inflammatory response. It is reasonable to assume that they may be implicated in the tissue injury in acute appendicitis that subsequently leads to appendix perforation. The purpose of this study was to investigate the expression and distribution of urokinase-type plasminogen activator (uPA) and plasminogen-activator inhibitor type 1 (PAI-1) in appendicitis. Material and methods. Expression of uPA and expression of PAI-1 were measured in tissue specimens from patients with appendicitis (n=30) and in control specimens (n=9), using the quantitative ELISA technique. Distribution of enzymes was studied with immunohistochemistry. The uPA and PAI-1 levels in the subgroups of appendicitis and controls were compared. Results. The overall expressions of uPA and PAI-1 were greater in appendicitis than in control specimens (p <0.001 and p<0.0001, respectively). Expressions of uPA and PAI-1 in phlegmonous (n=15), gangrenous (n=6) and perforated appendicitis (n=9) were all higher than those in controls (n=9), (p<0.01). Moreover, the PAI-1 level was elevated in perforated appendicitis compared with phlegmonous appendicitis (p<0.01). uPA staining was observed in connection with vascular endothelial cells and the serosa stained intensely in specimens from perforated appendicitis. Conclusions. The expression of uPA and especially the over-expression of PAI-1 seem to correlate to the progression of local inflammatory response in acute appendicitis.     

Plasminogen activation in human acute leukaemias

Plasminogen activation is implicated in solid tumour growth, invasion and metatastic spread. However, little is known about its role in leukaemia. We investigated the production by leukaemic cells of plasminogen activators [urokinase (uPA) and tissue-type PA (tPA)], cell surface receptor for uPA (uPAR) and PA inhibitors (PAI-1 and PAI-2). Leukaemic cells from 37 patients [26 with acute myeloid leukaemia (AML) and 11 with acute lymphoid leukaemia (ALL)] were analysed for mRNA content and enzymatic activities. High levels of uPA mRNA were found in M1, M2, M3 and M4-M5 AMLs, whereas tPA mRNA was not detected in any of the analysed cases. uPAR mRNA was confined to subtypes M4-M5. PAI-1 mRNA was detected in M3 and M4-M5. PAI-2 mRNA was found predominantly in M2 and M4-M5. SDS-PAGE/zymography analyses of cell extracts and supernatants after 24 and 48 h of culture confirmed the production of active uPA by AML cells (mainly M4-M5). but not by ALL. The finding of uPA, uPAR, PAI-1 and PAI-2 synthesized by leukaemic cells suggests that plasminogen activation may contribute to the invasive behaviour of these cells, the fibrinolytic imbalance observed in leukaemic patients and the differentiation and proliferation of M4-M5 by interaction of uPA with uPAR.     

Urokinase-type plasminogen activator receptor regulates leukocyte recruitment during experimental pneumococcal meningitis

Tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA) have been suggested to play an important role in inflammatory diseases. Increased levels of tPA, uPA, uPA receptor (uPAR), and their inhibitor, plasminogen activator inhibitor (PAI)-1, have been found in the cerebrospinal fluid (CSF) of patients with bacterial meningitis. Here, we show that expression of tPA, uPA, uPAR, PAI-1, and PAI-2 is up-regulated during experimental pneumococcal meningitis. In uPAR-deficient mice, CSF pleocytosis was significantly attenuated 24 h after infection, compared with that in infected wild-type (wt) mice. Lack of uPAR did not influence blood-brain barrier permeability, intracranial pressure, expression of chemokines (keratinocyte-derived cytokine and macrophage inflammatory protein-2), bacterial killing, or clinical outcome. No differences in pathophysiological alterations were observed in tPA-deficient mice, compared with those in infected wt mice. These results indicate that uPAR participates in the recruitment of leukocytes to the CSF space during pneumoccal meningitis.     

肝硬化患者血浆中尿激酶型纤溶酶激活物的检测及其意义

目的 探讨肝硬化患者血浆尿激酶型纤溶酶激活物(uPA)、尿激酶型纤溶酶激活物受体(uPAR)、纤溶酶原激活物抑制剂-1(PAI-1)的变化及其意义。 方法 确诊的72例乙型肝炎后肝硬化患者,Child-pugh分级A级23例(A组),B级29例(B组),C级20例(C组)。6例健康志愿献血者为正常对照组。酶联免疫吸附实验测定血浆uPA、uPAR、PAI-1的变化。并同时检测血透明质酸(HA)、Ⅳ型胶原(C Ⅳ)、Ⅲ型前胶原(PC Ⅲ)、血浆白蛋白、胆红素、凝血酶原时间及其活动度改变。 结果 随着肝硬化的进展,血浆uPA、uPAR、PAI-1逐渐增加,HA、PC Ⅲ也明显增加。Child C组患者血浆uPA、uPAR、PAI-1水平(μg/L)分别为1.88±0.64、4.82±2.02和52.60±16.87,A组分别为1.36±0.43、3.03±1.48和24.09±7.14,B组分别为1.79±0.62、4.80±2.22和41.40±17.52,C组与A、B组比较,t值为2.81～7.38,P值均<0.01。A组血浆uPA与PC Ⅲ呈负相关(r=-0.4785,P<0.05);C组PAI-1与HA呈正相关(r=0.5447,P<0.01)。 结论 肝硬化晚期,虽然血浆uPA、PAI-1增加,但总的效应表现为uPA相对不足,肝基质纤维降解受抑制,血浆uPA、PAI-1与肝硬化发展密切相关。     

Hypofibrinolysis in patients with hypercoagulability: The roles of urokinase and of plasminogen activator inhibitor

The prevalence of abnormalities of fibrinolysis in patients with venous thromboembolism is as yet unknown. Defined abnormalities include congenital dysfunction and deficiency of plasminogen, and probably impaired plasminogen activation secondary to elevated levels of plasminogen activator inhibitor type 1 (PAI-1) or to impaired release of tissue plasminogen activator (tPA). In this preliminary study, we analyzed plasma samples from 21 patients for whom an investigation for possible thrombophilia was requested. Twenty of the patients had venous thromboembolism, and one had arterial thrombosis at an early age. Two patients had deficiency of protein C or protein S, but no other recognized biochemical disturbances related to thrombophilia were identified. Patient samples and plasma from 25 normal controls were assayed for tPA activity, PAI-1 activity, and urokinase (uPA) activity and antigen. tPA activity and antigen were not significantly different in patients than in controls. PAI-1 activity was significantly greater in patients (P < 0.0001). uPA activity was not different in the two groups. However, uPA antigen was significantly reduced in patients compared to controls (P = 0.001). These data suggest that hypofibrinolysis leading to a risk of thrombosis may be caused not only by elevated PAI-1 activity but also by reduced total uPA concentration. © 1993 Wiley-Liss, Inc.