Blood clearance and activity of erythrocyte-coupled fibrinolytics

Conjugating tissue-type plasminogen activator (tPA) to red blood cells (RBCs) endows it with features useful for thromboprophylaxis. However, the optimal intensity and duration of thromboprophylaxis vary among clinical settings. To assess how the intrinsic properties of a plasminogen activator (PA) affect functions of the corresponding RBC/PA conjugate, we coupled equal amounts of tPA or Retavase (rPA; a variant with an extended circulation time, lower fibrin affinity, and greater susceptibility to PA inhibitors). Conjugation to RBC markedly prolonged the circulation of each PA in rats and mice, without detrimental effects on carrier RBC. The initial blood clearance of RBC/tPA was faster than RBC/rPA, yet it exerted greater fibrinolytic activity, in part due to greater resistance of tPA and RBC/tPA to plasma inhibitors versus rPA and RBC/rPA observed in vitro. Soluble and RBC-coupled tPA and rPA exerted the same amidolytic activity, yet RBC/tPA lysed fibrin clots more effectively than RBC/rPA, notwithstanding comparable fibrinolytic activity of their soluble counterparts. Conjugation to RBC suppressed rPA's ability to be activated by fibrin, whereas the fibrin activation of RBC-coupled tPA was not hindered. Therefore, the functional profile of RBC/PA is influenced by: pharmacokinetic features provided by carrier RBC (e.g., prolonged circulation), intrinsic PA features (e.g., clearance rate, resistance to inhibitors), and changes imposed by conjugation to RBC (e.g., loss of cofactor stimulation). These factors, different from those guiding the design of soluble PA for lysis of existing clots, can be exploited in the rational design of RBC/PA tailored for specific prophylactic indications.     

The regulation by fibrinogen and fibrin of tissue plasminogen activator kinetics and inhibition by plasminogen activator inhibitor 1

BACKGROUND: Tissue plasminogen activator (tPA) is unusual in the coagulation and fibrinolysis cascades in that it is produced as an active single-chain enzyme (sctPA) rather than a zymogen. Two chain tPA (tctPA) is produced by plasmin but there are conflicting reports in the literature on the behaviour of sc- and tctPA and little work on inhibition by the specific inhibitor plasminogen activator inhibitor-1 (PAI-1) under physiological conditions. OBJECTIVES: To perform a systematic study on the kinetics of sctPA and tctPA as plasminogen activators and targets for PAI-1. METHODS: Detailed kinetic studies were performed in solution and in the presence of template stimulators, fibrinogen and fibrin, including native fibrin and partially digested fibrin. Numerical simulation techniques were utilized to cope with the challenges of investigating kinetics of activation and inhibition in the presence of fibrin(ogen). RESULTS: Enzyme efficiency (k(cat)/K(m)) was higher for tctPA than sctPA in solution with chromogenic substrate (3-fold) and plasminogen (7-fold) but in the presence of templates, such as fibrinogen and native or cleaved fibrin, the difference disappeared. sctPA was more susceptible to PAI-1 in buffer solution and in the presence of fibrinogen; however, in the presence of fibrin, PAI-1 inhibited more slowly and there was no difference between sc and tctPA. CONCLUSIONS: Fibrinogen and fibrin modulate the activity of tPA differently in regard to their activation of plasminogen and inhibition by PAI-1. Fibrinogen and fibrin stimulate tPA activity against plasminogen but fibrin protects tPA from PAI-1 to promote fibrinolysis.     

Fibrin affinity of erythrocyte-coupled tissue-type plasminogen activators endures hemodynamic forces and enhances fibrinolysis in vivo

Plasminogen activators (PAs; e.g., tissue-type, tPA) coupled to red blood cells (RBCs) display in vivo features useful for thromboprophylaxis: prolonged circulation, minimal extravasation, and preferential lysis of nascent versus preexisting clots. Yet, factors controlling the activity of RBC-bound PAs in vivo are not defined and may not mirror the profile of soluble PAs. We tested the role of RBC/PA binding to fibrin in fibrinolysis. RBC/tPA and RBC/tPA variant with low fibrin affinity (rPA) bound to and lysed plasminogen-containing fibrin clots in vitro comparably. In contrast, when coinjected in mice with fibrin emboli lodging in pulmonary vasculature, only RBC/tPA accumulated in lungs, which resulted in a more extensive fibrinolysis versus RBC/rPA (p < 0.01). Reconciling this apparent divergence between in vitro and in vivo behaviors, RBC/tPA, but not RBC/rPA perfused over fibrin in vitro at physiological shear stress bound to fibrin clots and caused greater fibrinolysis versus RBC/rPA (p < 0.001). These results indicate that because of high fibrin affinity, RBC/tPA binding to clots endures hemodynamic stress, which enhances fibrinolysis. Behavior of RBC/PAs under hemodynamic pressure is an important predictor of their performance in vivo.     

缺血性脑卒中患者血纤溶活性变化规律的研究

目的 研究脑梗死组和非脑梗死组患者急性期,亚急性期和恢复期组织型纤溶酶原激活物（tPA）,纤溶酶原激活物抑制物-1（PAI-1）的变化规律.方法 135例脑梗死组患者于发病96h内,病后14d、3月、6月、9月分别采血,77例非脑梗死组患者先采血一次,然后分别在第一次采血后14d、3月、6月、9月采血.结果 脑梗死急性期tPA含量明显升高,PAI-1的含量明显升高.恢复期脑梗死即发病后3月,6月,9月tPA的含量比急性期明显降低,且脑梗死后时间越长tPA含量越低,恢复期脑梗死PAI-1的含量比急性期明显降低.结论 在缺血性卒中的患者,高tPA含量提示纤溶活性的降低.高PAI-1代表纤溶抑制增强.     

Characterization and comparative evaluation of a structurally unique PAI-1 inhibitor exhibiting oral in-vivo efficacy.

Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of both tissue-type plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). Elevated levels of PAI-1 are associated with thrombosis and vascular disease, suggesting that high plasma PAI-1 may promote a hypercoagulable state by disrupting the natural balance between fibrinolysis and coagulation. In this study, we identify WAY-140312 as a structurally novel small molecule inactivator of PAI-1, compare its inhibitory activity with other previously identified small molecule inhibitors, and investigate the mechanism of inactivation of PAI-1 in the presence of both tPA and uPA. In an immunofunctional assay, WAY-140312 inhibited PAI-1 with an estimated inhibitory concentration (IC(50)) of 11.7 micro m, which was the lowest value obtained of the four different PAI-1 inactivators tested. Surface activity profiling indicated that the critical micelle concentration for WAY-140312 was 95.8 micro m, and that each inhibitor exhibited unique physical chemical properties. Using a sensitive direct activity assay, the IC(50) for WAY-140312 was similar when either tPA or uPA was used as the target protease. Immunoblot analysis demonstrated that WAY-140312 near the IC(50) inhibited the complex formation between either tPA or uPA and PAI-1. After oral administration, WAY-140312 exhibited 29% bioavailability with a plasma half-life of approximately 1 h. In an in-vivo model of vascular injury, a 10 mg kg(-1) oral dose of WAY-140312 was associated with improvement in arterial blood flow and reduction in venous thrombosis. Thus, WAY-140312 represents a structurally novel small molecule inhibitor of PAI-1, and is the first such molecule to exhibit efficacy in animal models of vascular disease following oral administration.     

纤溶酶原激活物及其抑制剂-1的血浆含量测定在急性肺血栓栓塞症中的意义

目的探讨在急性肺血栓栓塞症(APE)发病中的组织型纤溶酶原激活物(tPA)及其抑制剂-1(PAI-1)的血浆含量、作用及其该病诊断中的意义。方法,对44例APE患者和56例健康正常对照者应用酶联免疫吸附双抗体夹心法(ELISA法)定量测定血浆tPA和PAI-1抗原水平。结果与正常对照组(tPA含量为11．05ng／ml和PAI-1含量为61．31ng／m1)相比,APE组的IPA含量(33．88ng／ml)和PAI-1含量(111．50ng／ml)较高,两组间差异有显著性。在急性肺血栓栓塞症的疾病诊断中,tPA和PAI-1的血浆含量合理诊断截断点分别为21．7ng／ml和79．4ng／ml.结论急性肺血栓栓塞症的发病是由于PAI-1抗原产生和释放增多,而非tPA抗原释放或产生不足所致．tPA和PAI-1抗原血浆含量测定在APE的疾病诊断中具有要意义。     

Activation of the fibrinolytic system and utilization of the coagulation inhibitors in sepsis: comparison with severe sepsis and septic shock

OBJECTIVES: To determine whether the fibrinolytic system is activated and coagulation inhibitors are utilized in sepsis, to compare the findings detected in sepsis with those found in severe sepsis and septic shock, and to compare the role played by different infectious pathogens on fibrinolysis and coagulation inhibitors. DESIGN AND SETTING: Prospective study comparing patients with sepsis, severe sepsis, and septic shock and healthy volunteers in the general intensive care unit of a tertiary university hospital. PATIENTS: Eighty-two consecutive septic patients (47 with sepsis, 18 with severe sepsis, and 17 with septic shock), and 14 healthy volunteers (controls). MEASUREMENTS AND RESULTS: After blood sampling we measured activation markers of fibrinolysis [plasmin/alpha(2)-antiplasmin complexes (PAP), complexes of tissue plasminogen activator/plasminogen activator inhibitor (tPA/PAI), fibrin(ogen) degradation products (FDPs), D-dimmers fibrin degradation products (D-d)], the utilization marker of antithrombin III (ATIII) thrombin/antithrombin complexes (TAT), several factors of fibrinolysis [plasminogen, tissue plasminogen activator (tPA), plasminogen activator inhibitor 1 (PAI-1), alpha(2)-antiplasmin], and the natural coagulation inhibitors [ATIII, protein C (PrC), protein S (PrS)]. In sepsis, PAP, FDPs, D-d, and TAT were increased to 439.8+/-32.35 microg/l, 57% positive, 49% positive, and 3.46+/-0.27 microg/l, respectively, compared with control subjects (205.57+/-28.58 microg/l, 0% positive, 7% positive, and 1.61+/-0.1 microg/l, respectively). These markers further increased in severe sepsis and septic shock. With the exception of a decrease in ATIII and an increase in tPA and PAI-1, coagulation inhibitors and factors of fibrinolysis were not changed in sepsis. In severe sepsis and mainly in septic shock, coagulation inhibitors (ATIII, PrC) and plasminogen were markedly decreased, whereas tPA and PAI-1 were further increased. All changes were independent of the causative infectious pathogen. CONCLUSIONS: Fibrinolysis is strongly activated and ATIII is utilized in sepsis. These findings are further enhanced in severe sepsis and septic shock. In sepsis only ATIII is decreased. In contrast, in severe sepsis and mainly in septic shock plasminogen and the main coagulation inhibitors (i.e., ATIII, PrC) are depleted, indicating exhaustion of fibrinolysis and coagulation inhibitors. Finally, Gram-positive, Gram-negative and other micro-organisms produce identical impairment.     

Monocyte-macrophage release of IL-1 is inhibited by type-1 plasminogen activator inhibitors

Interleukin-1 (IL-1) release from monocyte-macrophages (Mo) appears dependent on pericellular proteolysis mediated by plasmin. Thus plasminogen activator inhibitors (PAI) which bind the serine proteases responsible for the conversion of plasminogen to plasmin, may inhibit IL-1 release from Mo. We have examined the effect of purified PAI from a hepatoma cell line Hep G2, on IL-1 release from Mo with secondary effects on lymphocyte proliferation in vitro. Fast acting inhibitors of both urokinase (u-PA) and tissue plasminogen activator (two chain t-PA) were noted in harvest fluids of Hep G2 cells. These inhibitors were stable at pH 3 but lost activity at 45 degrees C. They were SDS-stable and migrated with Mr53 and 104 kDa. These properties conformed to characteristics of type-1 plasminogen activator inhibitor (PAI-1). Partially purified PAI-1 added to human Mo cultured on 125I fibrin layer both in the presence and absence of plasminogen inhibited secretion of IL-1 by Mo in response to LPS. This effect, however, did not correlate with the inhibition of plasminogen dependent fibrinolysis. This suggested a degree of sequestration and inaccessibility of membrane bound u-PA of LPS activated Mo to PAI-1. PAI-1, in addition, inhibited mitogen stimulated peripheral blood mononuclear cell (PBMC) proliferation at similar concentration ranges. This effect was abrogated by the addition of specific antisera to PAI-1. PAI-1 may be released as part of an acute phase response. In addition to influencing fibrinolysis, PAI-1 may constitute a negative feedback pathway on Mo IL-1 release and subsequent immune activation in vivo.     

阻塞性睡眠呼吸暂停低通气综合征患者血管内皮细胞及纤溶系统功能变化

目的：探讨阻塞性睡眠呼吸暂停低通气综合征(OSAHS)患者血管内皮细胞及纤溶系统功能变化。方法：根据多导睡眠呼吸监测仪监测结果，选择年龄、性别、体重指数(BMI)无明显差异的OSAHS患者52例和健康者48例。以Clauss法测定纤维蛋白原(Fg)，以发色底物法测定组织纤溶酶原激活物活性(tPA：A)、纤溶酶原激活物抑制物-1活性(PAI-1：A)，以酶联免疫法测von Willebrand因子含量(vWF)、组织纤溶酶原激活物含量(tPA：Ag)、纤溶酶原含量(PLg：Ag)和纤溶酶原激活物抑制物-1含量(PAI-1：Ag)。结果：与对照组比较，(3SAHS组vWF、Fg、PAI-1：A、PAI-1：Ag水平明显升高，PLg：Ag、tPA：Ag含量明显降低，tPA：A无明显变化。结论：OSAHS患者血管内皮细胞功能受损，纤溶系统功能降低。     

Measurement of different forms of tissue plasminogen activator in plasma

BACKGROUND: We evaluated assays to measure both total tissue plasminogen activator (tPA) and the three principle forms of tPA in plasma: active tPA, tPA complexed with plasminogen activator inhibitor type 1 (PAI-1), and tPA complexed with C1-inhibitor. METHODS: Active tPA was measured by use of an indirect amidolytic assay and immunofunctional assays. tPA/PAI-1, tPA/C1-inhibitor, and total tPA antigen were measured by use of microtiter plates coated with anti-tPA antibodies and, respectively, anti-PAI-1, anti-C1-inhibitor, and anti-tPA antibodies conjugated to peroxidase. RESULTS: The immunofunctional tPA assay detected 1 U/L (0.001 U/mL) tPA and recovered 108% +/- 12% of active tPA added to samples containing high (mean, 60 000 IU/L) PAI-1 activities vs a detection limit of 10 U/L (0.01 U/mL) and 13% +/- 25% recovery for the indirect amidolytic tPA activity assay. For measurement of tPA/PAI-1 complex, polyclonal anti-PAI-1 conjugates recovered 112% +/- 20% of the expected tPA/PAI-1 vs recovery of only 38% +/- 16% when monoclonal anti-PAI-1 conjugates were used. Of three methods tested, two total tPA antigen assays correlated well (r(2) = 0.85) and showed recoveries near 100%, whereas the third method showed lower correlations, higher intercepts, and falsely high recovery. A single anti-tPA capture antibody that performed the best in the individual assay evaluations was used to measure the different forms of tPA in 22 samples with a range of tPA and PAI-1 values. The sum of the molar concentrations of active tPA, tPA/PAI-1, and tPA/C1-inhibitor using the optimized methods was equal to 94% +/- 7% of measured total tPA. CONCLUSION: Optimized assays based on a single anti-tPA capture antibody can be used to accurately measure the major forms of tPA in plasma.     

Development of a new test for the global fibrinolytic capacity in whole blood.

BACKGROUND: The development of global tests for the fibrinolytic capacity in blood is hampered by the low base-line fibrinolytic activity in blood, by the involvement of both plasmatic components and blood cells in the fibrinolytic system and by the loss of fibrinolytic activity as a result of the action of plasminogen activator inhibitor-1 (PAI-1). OBJECTIVE: To develop a new test for the global fibrinolytic capacity (GFC) of whole blood samples. METHODS AND RESULTS: Collection of blood in thrombin increased the subsequent generation of fibrin degradation products. This was ascribed to rapid clot formation and concomitant reduction of in vitro neutralization of tissue-type plasminogen activator (tPA) by PAI-1. On the basis of this observation, the following test was designed: blood samples were collected in thrombin with and without aprotinin and clots were incubated for 3 h at 37 degrees C. The GFC was assessed from the difference between the fibrin degradation products in the two sera. The assay was applied to blood samples from patients and healthy subjects. Other hemostasis parameters were determined in plasma samples taken simultaneously. The GFC varied considerably (normal range 0.13-13.6 microg mL(-1)); physical exercise strongly increased the GFC. Statistically significant correlations were found with tPA activity, PAI-1 activity and fibrinogen level. A mixture of antibodies against tPA and urokinase-type plasminogen activator (uPA) completely inhibited the GFC. An inhibitor of activated thrombin-activatable fibrinolysis inhibitor (TAFI) accelerated fibrinolysis 8-fold. CONCLUSION: The new test represents a global assessment of the main fibrinolytic factors in plasma and potentially those associated with blood cells.     

先天性纤溶酶原激活物抑制剂-1缺乏症的诊断研究

目的　诊断 1例先天性纤溶酶原激活物抑制剂 1(PAI 1)缺乏症患者并研究其基因异常。方法　用发色底物法、酶联免疫吸附实验测定组织型纤溶酶原激活物 (tPA)、α2 纤溶酶抑制剂因子(α2 PI )与PAI 1的活性和 (或 )抗原 ,PCR法与DNA测序分析患者的基因异常 ,用限制性内切酶PshAⅠ对患者和 6 0名正常人PCR产物酶切以排除基因多态性。结果　患者优球蛋白溶解时间 (ELT) 70min ,血浆中加入生理浓度的PAI 1(5 0ng ml)后ELT延长至 12 0min ,PAI 1活性 0 .0 4AU ml,PAI 1抗原 5 .6ng ml,α2 PI活性、F活性及tPA抗原和活性均正常。PCR测序证实患者PAI 1基因外显子 2第 4 3位核苷酸G→A杂合性改变 ,导致信号肽第 15位的丙氨酸突变为苏氨酸。酶切鉴定排除了多态性。结论　报道国内首例PAI 1缺乏症患者 ,其基因改变可能为复合杂合子 ,其中之一为Ala15Thr,该突变为一种国际上尚未报道的新的基因突变。     

Thrombin upregulates production of plasminogen activator inhibitor type 1 in human peritoneal mesothelial cells.

OBJECTIVE: To determine the influence of thrombin, which is generated intraperitoneally during peritoneal dialysis, on the synthesis of fibrinolytic system components in human peritoneal mesothelial cells (HMC). METHODS: Confluently grown HMC, isolated from the omental tissue, were used in the experiments. Conditioned media were obtained by incubating cells with serum-free M199 containing the appropriate concentration of the test compound. Tissue type plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1) antigen concentrations were measured by ELISA. Northern blot analysis was conducted for mRNA expression experiments. To test thrombin specificity, we used the thrombin inhibitor hirudin. The protein kinase C (PKC) inhibitor Ro 31-8220 was inserted to examine whether the effect of thrombin depends on PKC activity. RESULTS: Thrombin increased PAI-1 antigen in the conditioned media of HMC in a time- and concentration-dependent manner. After 24 hours incubation, PAI-1 levels increased from 350+/-30 ng/10(5) cells in control conditions to 620+/-30 ng/10(5) cells in HMC exposed to 5 U/mL thrombin (n = 8, p < 0.05). In contrast, there was no effect of thrombin on tPA antigen levels. An increase of PAI-1 mRNA expression was also observed by Northern blot hybridization. Hirudin (10 U/mL) inhibited the thrombin-induced increase in PAI-1 synthesis. In addition, a complete inhibition of the stimulating effect of thrombin on PAI-1 synthesis was obtained by blocking PKC activity with Ro 31-8220 (3 micromol/L). CONCLUSIONS: Thrombin increases PAI-1 synthesis in HMC via a PKC-dependent mechanism.Thereby the synthesis of tPA is not affected. Thus, thrombin may not only promote fibrin formation in the peritoneal cavity, but may also inhibit fibrin degradation by release of free PAI-1 from HMC.     

Interaction between plasminogen activator inhibitor type 1 (PAI-1) bound to fibrin and either tissue-type plasminogen activator (t-PA) or urokinase-type plasminogen activator (u-PA). Binding of t-PA/PAI-1 complexes to fibrin mediated by both the finger and the kringle-2 domain of t-PA.

Plasminogen activation is catalyzed both by tissue-type-(t-PA) and by urokinase-type plasminogen activator (u-PA). This reaction is controlled by plasminogen activator inhibitor type 1 (PAI-1) that is either present in plasma or bound to fibrin, present in a thrombus. We studied the mechanism of in vitro inhibition of both t-PA and u-PA activity by PAI-1 bound to fibrin. It is shown that activation of latent PAI-1 unmasks a specific fibrin-binding site that is distinct from its reactive site. This reactive site of activated PAI-1 bound to fibrin is fully exposed to form complexes with t-PA and u-PA, that are unable to activate plasminogen. Upon complex formation with either one of the plasminogen activators, PAI-1 apparently undergoes a conformational change and loses its affinity for fibrin. Consequently, complexes of u-PA and PAI-1 dissociate from the fibrin matrix and are encountered in the fluid phase. In contrast, t-PA/PAI-1 complexes remain bound to fibrin. By employing recombinant t-PA deletion-mutant proteins, that precisely lack domains involved in fibrin binding, we demonstrate that binding of t-PA/PAI-1 complexes is mediated by both the "finger" (F) and the "kringle-2" (K2) domain of t-PA. A model is proposed that explains inhibition of the fibrinolytic process, at the level of plasminogen activation by t-PA, directed by PAI-1 bound to fibrin. An implication of the proposed model is that t-PA/PAI-1 complexes and free t-PA compete for the same binding sites on fibrin.     

Pentoxifylline, a methyl xanthine derivative, reduces peritoneal adhesions and increases peritoneal fibrinolysis in rats

Peritoneum has an intrinsic fibrinolytic activity that breaks the peritoneal adhesions. Peritoneal injuries with ischemia interfere this fibrinolytic activity and cause adhesions. Pentoxifylline, a methyl xanthine derivative, improves blood flow by decreasing its viscosity and also increases fibrinolytic activity in plasma. We hypothesized that pentoxifylline would increase peritoneal fibrinolysis and ameliorate adhesions. A rat model of peritoneal adhesion (cecal abrasion with gauze, n = 15 for each group) was used to test this hypothesis and cardinal parameters of peritoneal fibrinolysis were measured in peritoneal samples. No medication was given in control animals, while pentoxifylline was administered intraperitonealy (IP) (25 mg/kg, before abdominal closure to whole abdomen) or intravenously (IV) (25 mg/kg, for 9 days after operation) in the experimental groups. At postoperative day 10, peritoneal biopsies were obtained and adhesions were graded qualitatively. Activities and concentrations of tissue plasminogen activator (tPA), plasminogen activator inhibitor type 1 (PAI-1), tPA/PAI-1 complex and hydroxyproline contents were determined. Total adhesion scores were decreased in both treated groups. Mean levels of tPA concentration and tPA activity were increased in the treated groups compared to controls (p < 0.001 and p = 0.001, respectively). The tPA/PAI-1 complex levels were similar among the three groups. PAI-1 levels were lower in animals receiving IP pentoxifylline compared to control animals and those treated with IV pentoxifylline (p = 0.048, p = 0.015, respectively). Peritoneal hydroxyproline levels were similar among the three groups. Our results suggest that pentoxifylline administration either through IV or IP may reduce peritoneal adhesion formation probably by altering peritoneal fibrinolytic activity.     

Plasminogen and plasmin activity in patients with coronary artery disease

OBJECTIVE: While coronary artery disease (CAD) is associated with disturbances of the plasma fibrinolytic system, the nature of these disturbances is not fully defined. Fibrinolysis is regulated by plasmin, whose production is mediated by plasminogen activator conversion of plasminogen (Plg) to plasmin. The cascade is modulated by feedback loops that include Plg activator inhibitor 1 (PAI-1). Molecular interactions with Plg kringle domains play an important role in regulating plasmin production and its modulation of fibrinolysis. We hypothesized that interactions of tissue plasminogen activator (tPA) with Plg kringle domains regulates plasmin levels in patients with stable CAD. METHODS: Plasma was collected from patients (n = 33) with an angiographically significant CAD and controls (n = 18) with angiographically established normal or minimally diseased arteries. Plasmin activity, tPA activity, and plasma levels of Plg, PAI-1, uPA, and tPA were determined. RESULTS: CAD patients had 1.7-fold greater plasmin activity (P = 0.02) that correlated with 1.5-fold higher tPA activity when compared to controls. Epitope mapping of Plg domains showed Plg differences in epitope exposure between the two groups. Plasma from CAD patients had 50% less (P < 0.001) detectable kringle 4 and 48% less (P = 0.007) detectable kringles 1-3. CONCLUSIONS: Based on detectable differences in Plg, we conclude that in patients with stable CAD, Plg complexed with tPA exists in a conformation that enables increased tPA activity and Plg conversion to plasmin.     

The addition of endothelial cell growth factor and heparin to human umbilical vein endothelial cell cultures decreases plasminogen activator inhibitor-1 expression.

Plasminogen activator inhibitor-1 (PAI-1) is a specific and rapid inhibitor of tissue plasminogen activator (tPA) and urokinase. Clinical studies suggest that PAI-1 may play a crucial role in the regulation of fibrinolysis. A number of factors modulate PAI-1 activity in endothelial cell culture, and the isolation of PAI-1 cDNA now allows study of PAI-1 regulation at the mRNA level. We examined the effect of endothelial cell growth factor (ECGF) and heparin on PAI-1 expression in human umbilical vein endothelial cell (HUVEC) culture. The addition of ECGF and heparin to HUVEC cultures results in a 3-10-fold decrease in the PAI-1 activity secreted into the conditioned media. This effect is mediated at the mRNA level. A decrease in PAI-1 is also seen with higher concentrations of ECGF alone, but is greatly enhanced by the addition of heparin. No significant change in tPA antigen or mRNA levels was observed.     

气腹及腹腔镜手术对腹膜影响的临床研究

目的探讨腹腔镜与开腹手术中腹膜纤维蛋白溶酶的变化。方法在腹腔镜与开腹手术前、手术后立即、分别测量腹膜组织中组织型纤溶酶原激活物(t-PA)、纤溶酶原激活物抑制物-1(PAI-1)浓度及t-PA活性。结果腹膜组织中t-PA浓度在腹腔镜手术和传统腹部手术2组术中均下降,但在传统腹部手术组下降更显著(P<0.05)。而腹膜组织中PAI-1水平在腹腔镜手术组术前较高(P<0.05),PAI-1浓度在传统腹部手术组术中明显升高,但在手术后,2组PAI-1浓度无显著差异。t-PA活性在2组术前、术后均无明显差异,但术中2组均显著下降(P<0.05)。结论本次临床研究结果表明:腹腔镜手术和传统腹部手术对腹膜的影响是相似的,腹腔镜手术中最初的腹膜组织中PAI-1浓度的升高由CO2气腹造成并影响腹膜组织的修复。     

Bleomycin-induced pulmonary fibrosis in fibrinogen-null mice

Mice deleted for the plasminogen activator inhibitor-1 (PAI-1) gene are relatively protected from developing pulmonary fibrosis induced by bleomycin. We hypothesized that PAI-1 deficiency reduces fibrosis by promoting plasminogen activation and accelerating the clearance of fibrin matrices that accumulate within the damaged lung. In support of this hypothesis, we found that the lungs of PAI-1(-/-) mice accumulated less fibrin after injury than wild-type mice, due in part to enhanced fibrinolytic activity. To further substantiate the importance of fibrin removal as the mechanism by which PAI-1 deficiency limited bleomycin-induced fibrosis, bleomycin was administered to mice deficient in the gene for the Aalpha-chain of fibrinogen (fib). Contrary to our expectation, fib(-/-) mice developed pulmonary fibrosis to a degree similar to fib(+/-) littermate controls, which have a plasma fibrinogen level that is 70% of that of wild-type mice. Although elimination of fibrin from the lung was not in itself protective, the beneficial effect of PAI-1 deficiency was still associated with proteolytic activity of the plasminogen activation system. In particular, inhibition of plasmin activation and/or activity by tranexamic acid reversed both the accelerated fibrin clearance and the protective effect of PAI-1 deficiency. We conclude that protection from fibrosis by PAI-1 deficiency is dependent upon increased proteolytic activity of the plasminogen activation system; however, complete removal of fibrin is not sufficient to protect the lung.