Blood-derived plasminogen drives brain inflammation and plaque deposition in a mouse model of Alzheimer's disease.

Two of the most predominant features of the Alzheimer's disease (AD) brain are deposition of ß-amyloid (Aß) plaques and inflammation. The mechanism behind these pathologies remains unknown, but there is evidence to suggest that inflammation may predate the deposition of Aß. Furthermore, immune activation is increasingly being recognized as a major contributor to the pathogenesis of the disease, and disorders involving systemic inflammation, such as infection, aging, obesity, atherosclerosis, diabetes, and depression are risk factors for the development of AD. Plasminogen (PLG) is primarily a blood protein synthesized in the liver, which when cleaved into its active form, plasmin (PL), plays roles in fibrinolysis, wound healing, cell signaling, and inflammatory regulation. Here we show that PL in the blood is a regulator of brain inflammatory action and AD pathology. Depletion of PLG in the plasma of an AD mouse model through antisense oligonucleotide technology dramatically improved AD pathology and decreased glial cell activation in the brain, whereas an increase in PL activity through α-2-antiplasmin (A2AP) antisense oligonucleotide treatment exacerbated the brain's immune response and plaque deposition. These studies suggest a crucial role for peripheral PL in mediating neuroimmune cell activation and AD progression and could provide a link to systemic inflammatory risk factors that are known to be associated with AD development.

The Multifaceted Role of Plasminogen in Cancer.

Fibrinolytic factors like plasminogen, tissue-type plasminogen activator (tPA), and urokinase plasminogen activator (uPA) dissolve clots. Though mere extracellular-matrix-degrading enzymes, fibrinolytic factors interfere with many processes during primary cancer growth and metastasis. Their many receptors give them access to cellular functions that tumor cells have widely exploited to promote tumor cell survival, growth, and metastatic abilities. They give cancer cells tools to ensure their own survival by interfering with the signaling pathways involved in senescence, anoikis, and autophagy. They can also directly promote primary tumor growth and metastasis, and endow tumor cells with mechanisms to evade myelosuppression, thus acquiring drug resistance. In this review, recent studies on the role fibrinolytic factors play in metastasis and controlling cell-death-associated processes are presented, along with studies that describe how cancer cells have exploited plasminogen receptors to escape myelosuppression.

Enterococcus faecalis exploits the human fibrinolytic system to drive excess collagenolysis: implications in gut healing and identification of druggable targets.

Perforations, anastomotic leak, and subsequent intra-abdominal sepsis are among the most common and feared complications of invasive interventions in the colon and remaining intestinal tract. During physiological healing, tissue protease activity is finely orchestrated to maintain the strength and integrity of the submucosa collagen layer in the wound. We (Shogan, BD et al. Sci Trans Med 7: 286ra68, 2015.) have previously demonstrated in both mice and humans that the commensal microbe Enterococcus faecalis selectively colonizes wounded colonic tissues and disrupts the healing process by amplifying collagenolytic matrix-metalloprotease activity toward excessive degradation. Here, we demonstrate for the first time, to our knowledge, a novel collagenolytic virulence mechanism by which E. faecalis is able to bind and locally activate the human fibrinolytic protease plasminogen (PLG), a protein present in high concentrations in healing colonic tissue. E. faecalis-mediated PLG activation leads to supraphysiological collagen degradation; in this study, we demonstrate this concept both in vitro and in vivo. This pathoadaptive response can be mitigated with the PLG inhibitor tranexamic acid (TXA) in a fashion that prevents clinically significant complications in validated murine models of both E. faecalis- and Pseudomonas aeruginosa-mediated colonic perforation. TXA has a proven clinical safety record and is Food and Drug Administration approved for topical application in invasive procedures, albeit for the prevention of bleeding rather than infection. As such, the novel pharmacological effect described in this study may be translatable to clinical trials for the prevention of infectious complications in colonic healing.NEW & NOTEWORTHY This paper presents a novel mechanism for virulence in a commensal gut microbe that exploits the human fibrinolytic system and its principle protease, plasminogen. This mechanism is targetable by safe and effective nonantibiotic small molecules for the prevention of infectious complications in the healing gut.

Lactoferrin is a natural inhibitor of plasminogen activation.

The plasminogen system is essential for dissolution of fibrin clots, and in addition, it is involved in a wide variety of other physiological processes, including proteolytic activation of growth factors, cell migration, and removal of protein aggregates. On the other hand, uncontrolled plasminogen activation contributes to many pathological processes (e.g. tumor cells' invasion in cancer progression). Moreover, some virulent bacterial species (e.g. Streptococci or Borrelia) bind human plasminogen and hijack the host's plasminogen system to penetrate tissue barriers. Thus, the conversion of plasminogen to the active serine protease plasmin must be tightly regulated. Here, we show that human lactoferrin, an iron-binding milk glycoprotein, blocks plasminogen activation on the cell surface by direct binding to human plasminogen. We mapped the mutual binding sites to the N-terminal region of lactoferrin, encompassed also in the bioactive peptide lactoferricin, and kringle 5 of plasminogen. Finally, lactoferrin blocked tumor cell invasion in vitro and also plasminogen activation driven by Borrelia Our results explain many diverse biological properties of lactoferrin and also suggest that lactoferrin may be useful as a potential tool for therapeutic interventions to prevent both invasive malignant cells and virulent bacteria from penetrating host tissues.

Plasminogen mediates communication between the peripheral and central immune systems during systemic immune challenge with lipopolysaccharide.

BACKGROUND: Systemic inflammation has been implicated in the progression of many neurodegenerative diseases and may be an important driver of the disease. Dementia and cognitive decline progress more rapidly following acute systemic infection, and systemic inflammation midlife is predictive of the degree of cognitive decline. Plasmin, the active form of the serine protease plasminogen (PLG), is a blood protein that plays physiological roles in fibrinolysis, wound healing, cell signaling, extracellular matrix degradation, and inflammatory regulation. METHODS: Mice were treated with an antisense oligonucleotide to deplete liver-produced PLG prior to systemic challenge with lipopolysaccharide (LPS), a major component of the outer membrane of gram-negative bacteria, known to induce a strong immune response in animals. Following treatment, the innate immune response in the brains of these animals was examined. RESULTS: Mice that were PLG-deficient had dramatically reduced microgliosis and astrogliosis in their brains after LPS injection. We found that blood PLG regulates the brain's innate immune response to systemic inflammatory signaling, affecting the migration of perivascular macrophages into the brain after challenge with LPS. CONCLUSIONS: Depletion of plasma PLG with an antisense oligonucleotide dramatically reduced glial cell activation and perivascular macrophage migration into the brain following LPS injection. This study suggests a critical role for PLG in mediating communication between systemic inflammatory mediators and the brain.

Epsilon-aminocaproic acid prevents high glucose and insulin induced-invasiveness in MDA-MB-231 breast cancer cells, modulating the plasminogen activator system.

Obesity and type II diabetes mellitus have contributed to the increase of breast cancer incidence worldwide. High glucose concentration promotes the proliferation of metastatic cells, favoring the activation of the plasminogen/plasmin system, thus contributing to tumor progression. The efficient formation of plasmin is dependent on the binding of plasminogen to the cell surface. We studied the effect of ε-aminocaproic acid (EACA), an inhibitor of the binding of plasminogen to cell surface, on proliferation, migration, invasion, epithelial-mesenchymal transition (EMT), and plasminogen activation system, in metastatic MDA-MB-231 breast cancer cells grown in a high glucose microenvironment and treated with insulin. MDA-MB-231 cells were treated with EACA 12.5 mmol/L under high glucose 30 mmol/L (HG) and high glucose and insulin 80 nmol/L (HG-I) conditions, evaluating: cell population growth, % of viability, migratory, and invasive abilities, as well as the expression of uPA, its receptor (uPAR), and its inhibitor (PAI-1), by real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, MMP-2 and MMP-9 mRNAs were evaluated by RT-PCR. Markers of EMT were evaluated by Western blot. Additionally, the presence of active uPA was studied by gel zymography, using casein-plasminogen as substrates. EACA prevented the increase in cell population, migration and invasion induced by HG and insulin, which was associated with the inhibition of EMT and the attenuation of HG- and insulin-dependent expression of uPA, uPAR, PAI-1, MMP-2, MMP-9, α-enolase (ENO A), and HCAM. The interaction of plasminogen to the cell surface and plasmin formation are mediators of the prometastasic action of hyperglycemia and insulin, potentially, EACA can be employed in the prevention and as adjuvant treatment of breast tumorigenesis promoted by hyperglycemia and insulin.

[Structure and functions of plasminogen/plasmin system].

The main physiological function of plasmin is a blood clot fibrinolysis and restore normal blood flow. To date, however, it became apparent that in addition to thrombolysis plasminogen/plasmin system plays an important physiological and pathological role in the degradation of extracellular matrix, embryogenesis, cell migration, tissue remodeling, wound healing, angiogenesis, inflammation and tumor cells migration. This review focuses on the structural features of plasminogen, the regulation of its activation by physiological plasminogen activators, inhibitors of plasmin and plasminogen activators, the role of the plasminogen binding to fibrin, cellular receptors and extracellular ligands in performing various functions by formed plasmin.

Activators and inhibitors of the plasminogen system in Alzheimer's disease.

Accumulation and deposition of Aß is one of the main neuropathological hallmarks of Alzheimer's disease (AD) and impaired Aß degradation may be one mechanism of accumulation. Plasmin is the key protease of the plasminogen system and can cleave Aß. Plasmin is activated from plasminogen by tissue plasminogen activator (tPA) and urokinase-type plasminogen activator (uPA). The activators are regulated by inhibitors which include plasminogen activator inhibitor-1 (PAI-1) and neuroserpin. Plasmin is also regulated by inhibitors including α2-antiplasmin and α2-macroglobulin. Here, we investigate the mRNA levels of the activators and inhibitors of the plasminogen system and the protein levels of tPA, neuroserpin and α2-antiplasmin in post-mortem AD and control brain tissue. Distribution of the activators and inhibitors in human brain sections was assessed by immunoperoxidase staining. mRNA measurements were made in 20 AD and 20 control brains by real-time PCR. In an expanded cohort of 38 AD and 38 control brains tPA, neuroserpin and α2-antiplasmin protein levels were measured by ELISA. The activators and inhibitors were present mainly in neurons and α2-antiplasmin was also associated with Aß plaques in AD brain tissue. tPA, uPA, PAI-1 and α2-antiplasmin mRNA were all significantly increased in AD compared to controls, as were tPA and α2-antiplasmin protein, whereas neuroserpin mRNA and protein were significantly reduced. α2-macroglobulin mRNA was not significantly altered in AD. The increases in tPA, uPA, PAI-1 and α2-antiplasmin may counteract each other so that plasmin activity is not significantly altered in AD, but increased tPA may also affect synaptic plasticity, excitotoxic neuronal death and apoptosis.

Tranexamic acid: less bleeding and less thrombosis?

The early administration of tranexamic acid (TXA) to bleeding trauma patients reduces all-cause mortality without increasing the risk of vascular occlusive events. Indeed, the risk of arterial thrombosis appears to be reduced with TXA. In this commentary we hypothesize that TXA has an antithrombotic effect and explore potential mechanisms. These include inhibition of the inflammatory effects of plasmin, effects on platelets and effects on factors V and VIII. If proven, these antithrombotic effects would have major implications for the systemic use of TXA in surgical patients, where TXA has been clearly shown to reduce bleeding.

Inhibition of plasminogen suppresses fibrosis and macrophage foaming in a nonalcoholic steatohepatitis mouse model.

Nonalcoholic steatohepatitis is a clinically important liver disease. Its symptoms are exacerbated by macrophage foaming, which is promoted by plasminogen in vitro. However, the influence of plasminogen on nonalcoholic steatohepatitis has not been reported. In this study, we evaluated the influence of plasminogen in a mouse model of nonalcoholic steatohepatitis with macrophage foaming. L-/- /A-/- mice, characterized by hypercholesterolemia, were injected with streptozotocin and fed a high-fat diet to develop nonalcoholic steatohepatitis with macrophage foaming. To confirm the influence of plasminogen, we used the well-known plasminogen inhibitor tranexamic acid and L-/- /A-/- /Plg-/- mice, which are deficient in plasminogen and investigated the influence on nonalcoholic steatohepatitis. The influence of plasminogen on the expression levels of proinflammatory cytokines involved in foaming in macrophages was also assessed. The formation of nonalcoholic steatohepatitis lesions with macrophage foaming was confirmed in the L-/- /A-/- mouse model. Tranexamic acid attenuated foaming and fibrosis in the L-/- /A-/- mice. Similarly, foaming and liver fibrosis were also attenuated in the L-/- /A-/- /Plg-/- mice. The mRNA expression levels of TGF-ß1 and IL-1ß in liver and peritoneal macrophages were reduced upon plasminogen inhibition. We show that inhibition of plasminogen suppressed macrophage foaming, cytokine expression, and consequently fibrosis in nonalcoholic steatohepatitis. Our results provide a clue toward various processes leading to fibrosis and may contribute to new therapeutic strategies for nonalcoholic steatohepatitis.

Induction of the fibrinolytic system by cartilage extract mediates its antiangiogenic effect in mouse glioma.

Both the antiangiogenic and antitumoral activity of shark cartilage extracts (SCE) have been demonstrated in animal models and clinical trials. Studies reported that SCE induces the expression of tissue plasminogen activator gene (PLAT) in endothelial cells and increases the activity of the protein (t-PA) in vitro. The aim of this study was to demonstrate the crucial role of t-PA induction in the antiangiogenic and antitumor activity of SCE in experimental glioma. This study showed antiangiogenic and antitumoral effects of SCE in three mice glioma models (C6, HGD and GL26). Histological examination suggested perivascular proteolysis and edema as well as important intratumoral necrosis, which artefactually increased the tumor volume at high doses. Thus, the antiangiogenic effect of SCE correlated with the presence of t-PA and angiostatin in degenerating vessels. Functional in vivo experiments were conducted to modulate the plasminogen pathway. No antiangiogenic effect was observed on tumors overexpressing the plasminogen activator inhibitor-1 (PAI-1). Moreover, therapeutical effects were neutralized in mice that were cotreated with ε-aminocaproic acid (EACA, 120 mg/kg p.o.), an inhibitor that blocks the high-affinity lysine binding sites of both plasminogen and plasmin. In contrast, cotreatment with N-acetylcysteine (NAC, 7,5mg/kg i.p.), a sulfhydril donor that reduces plasmin into angiostatin or other antiangiogenic fragments, increased the benefit of SCE on mice survival. In subcutaneous models, NAC prevented the increase in tumor volume caused by high doses of cartilage extract. In conclusion, this study indicates that induction of t-PA by shark cartilage extract plays an essential role in its antiangiogenic activity, but that control of excessive proteolysis by a plasmin reductor could prevent edema and uncover the full benefit of shark cartilage extract in the treatment of intracranial tumors.

Antiplatelet and antithrombotic activities of timosaponin B-II, an extract of Anemarrhena asphodeloides.

1. Antithrombotic agents are effective in the treatment of ischaemic stroke. Timosaponin B-II (TB-II) is a major active component of Anemarrhena asphodeloides Bunge (Liliaceae; rhizome) that has protective effects against cerebral ischaemic damage. The present study examined the antiplatelet and antithrombotic actions of TB-II. 2. In in vitro experiments, TB-II (20, 40 and 80 mg/mL) potently and dose-dependently inhibited ADP-induced platelet aggregation. Furthermore, 1, 3 and 6 mg/kg TB-II prolonged activated partial thromboplastin time by 9.29, 16.86 and 25.50%, respectively, but had no effect on the prothrombin time. Furthermore, 1, 3 and 6 mg/kg TB-II significantly reduced the wet weight, dry weight and length of the thrombi (%inhibition (based on wet weight): 13.6, 19.8 and 24.7%, respectively). 3. In a rabbit arteriovenous shunt model, 1, 3 and 6 mg/kg, i.v., TB-II had no effect on thrombus formation. Plasma euglobulin lysis time and fibrin degradation product were not affected by 1, 3 and 6 mg/kg TB-II, but plasminogen levels were decreased significantly by 14.4, 18.3 and 29.0%, respectively. 4. The results of the present study demonstrate significant antiplatelet and anticoagulation effects of TB-II and suggest that these actions could contribute to its neuroprotective effect against damage following cerebral ischaemia damage.

[Mechanism of inhibitory effect of angiostatin on plasminogen activation by its physiologic activators].

The influence of angiostatin K1-4.5--a fragment of the heavy chain of plasmin and a powerful inhibitor of angiogenesis--on kinetic parameters (k(Pg) and K(Pg)) of human Glu-plasminogen activation under the action of urokinase (uPA) not having affinity for fibrin and fibrin-specific tissue plasminogen activator (tPA) was investigated. Angiostatin does not affect the k(Pg) value, but increases the value K(Pg) urokinase plasminogen activation. A decrease in the k(Pg) value and an increase in the K(Pg) value were found for fibrin-stimulated plasminogen activation by tPA with increasing concentrations of angiostatin. The obtained results show that angiostatin is competitive inhibitor of the uPA activator activity, while it inhibits the activator activity of tPA by mixed type. Such an influence ofangiostatin on the kinetic constants ofthe urokinase plasminogen activation suggests that angiostatin dose dependent manner replaces plasminogen in the binary enzyme-substrate complex uPA-Pg. In case of fibrin-stimulated plasminogen activation by tPA, both zymogen and tPA are bound to fibrin with formation of the effective triple tPA-Pg-fibrin complex. Angiostatin replaces plasminogen both from the fibrin surface and from the enzyme-substrate tPA-Pg complex that leads to a decrease in k(Pg) and an increase in K(Pg) of plasminogen activation. Inhibition constants by angioststin (Ki) of plasminogen-activator activities of uPA and tPA determined by Dixon method were found to be 0.59 +/- 0.04 and 0.12 +/- 0.05 microM, respectively.

Inhibition of plasminogen/plasmin system retrieves endogenous nerve growth factor and adaptive spinal synaptic plasticity following peripheral nerve injury.

Dysfunctions of the neuronal-glial crosstalk and/or impaired signaling of neurotrophic factors represent key features of the maladaptive changes in the central nervous system (CNS) in neuroinflammatory as neurodegenerative disorders. Tissue plasminogen activator (tPA)/plasminogen (PA)/plasmin system has been involved in either process of maturation and degradation of nerve growth factor (NGF), highlighting multiple potential targets for new therapeutic strategies. We here investigated the role of intrathecal (i.t.) delivery of neuroserpin (NS), an endogenous inhibitor of plasminogen activators, on neuropathic behavior and maladaptive synaptic plasticity in the rat spinal cord following spared nerve injury (SNI) of the sciatic nerve. We demonstrated that SNI reduced spinal NGF expression, induced spinal reactive gliosis, altering the expression of glial and neuronal glutamate and GABA transporters, reduced glutathione (GSH) levels and is associated to neuropathic behavior. Beside the increase of NGF expression, i.t. NS administration reduced reactive gliosis, restored synaptic homeostasis, GSH levels and reduced neuropathic behavior. Our results hereby highlight the essential role of tPA/PA system in the synaptic homeostasis and mechanisms of maladaptive plasticity, sustaining the beneficial effects of NGF-based approach in neurological disorders.

The fibrinolytic pathway of human plasma. Isolation and characterization of the plasminogen proactivator.

The conversion of the plasminogen proactivator to plasminogen activator by activated Hageman factor or its fragments has been recognized as an essential step in the conversion of plasminogen to plasmin. The plasminogen proactivator has been completely separated from prekallikrein and pre-PTA, two other proenzyme substrates of activated Hageman factor or its fragments. Plasminogen proactivator, free of any contaminating proteins as assessed by disc gel electrophoresis or isoelectric focusing, revealed a single band with an isoelectric point of 8.9 corresponding in position to the Hageman factor activatable material eluted from replicate unstained gels. After conversion of plasminogen proactivator by Hageman factor fragments to the plasminogen activator, the active site of the plasminogen activator is not inhibited by C1INH and is thus readily distinguished from that of kallikrein or PTA. The plasminogen activator is susceptible to inactivation by DFP while the plasminogen proactivator is not, as has been the case for esterases having a serine in the active site. Its interaction with plasminogen is inhibited by epsilon-aminocaproic acid.

Structural analysis of experimental drugs binding to the SARS-CoV-2 target TMPRSS2.

The emergence of SARS-CoV-2 has prompted a worldwide health emergency. There is an urgent need for therapeutics, both through the repurposing of approved drugs and the development of new treatments. In addition to the viral drug targets, a number of human drug targets have been suggested. In theory, targeting human proteins should provide an advantage over targeting viral proteins in terms of drug resistance, which is commonly a problem in treating RNA viruses. This paper focuses on the human protein TMPRSS2, which supports coronavirus life cycles by cleaving viral spike proteins. The three-dimensional structure of TMPRSS2 is not known and so we have generated models of the TMPRSS2 in the apo state as well as in complex with a peptide substrate and putative inhibitors to aid future work. Importantly, many related human proteases have 80% or higher identity with TMPRSS2 in the S1-S1' subsites, with plasminogen and urokinase-type plasminogen activator (uPA) having 95% identity. We highlight 376 approved, investigational or experimental drugs targeting S1A serine proteases that may also inhibit TMPRSS2. Whilst the presence of a relatively uncommon lysine residue in the S2/S3 subsites means that some serine protease inhibitors will not inhibit TMPRSS2, this residue is likely to provide a handle for selective targeting in a focused drug discovery project. We discuss how experimental drugs targeting related serine proteases might be repurposed as TMPRSS2 inhibitors to treat coronaviruses.

Annexin II incorporated into influenza virus particles supports virus replication by converting plasminogen into plasmin.

For influenza viruses to become infectious, the proteolytic cleavage of hemagglutinin (HA) is essential. This usually is mediated by trypsin-like proteases in the respiratory tract. The binding of plasminogen to influenza virus A/WSN/33 leads to the cleavage of HA, a feature determining its pathogenicity and neurotropism in mice. Here, we demonstrate that plasminogen also promotes the replication of other influenza virus strains. The inhibition of the conversion of plasminogen into plasmin blocked influenza virus replication. Evidence is provided that the activation of plasminogen is mediated by the host cellular protein annexin II, which is incorporated into the virus particles. Indeed, the inhibition of plasminogen binding to annexin II by using a competitive inhibitor inhibits plasminogen activation into plasmin. Collectively, these results indicate that the annexin II-mediated activation of plasminogen supports the replication of influenza viruses, which may contribute to their pathogenicity.

Environmental effects on charge densities of biologically active molecules: do molecule crystal environments indeed approximate protein surroundings?

In the present paper, we investigate whether crystal and enzyme environments influence the electron density (ED) of active compounds in a similar manner. This supposition is essential for high-resolution X-ray studies, which use the EDs obtained from crystals of the pure active compound as approximations for the ED of the active compound in its complex with the target enzyme. The EDs of such complexes determine the molecular recognition process between the targeted enzyme and active compound and are, hence, extremely useful tools for rational drug design. The approximation of such EDs by data obtained from crystals of the pure active compound is needed since high-resolution X-ray experiments of the target-ligand complexes are still extremely demanding. Quantum mechanical/molecular mechanical (QM/MM) and pure QM calculations are employed to determine the EDs of two inhibitors, the reversible trans-4-(aminomethyl)cyclohexane-1-carboxylic acid (AMCHA) and the irreversible E64c in four different environments (the enzyme-inhibitor complex, crystals of the pure compounds, a continuum solvation model, and the gas phase). Our investigation shows that the environment inside of the crystal of the pure active compound generally influences the ED of an active compound in a very similar way as the enzyme surrounding in the complex between the active compound and target enzyme. However, this does not hold any more if the geometrical arrangement of the inhibitor in the enzyme differs significantly from that in the crystal. While EDs computed for gas-phase environments deviate strongly from those in crystal and protein surroundings, polar solvent environments provide rather similar electron distributions. Thus, such continuum solvation models are very well suited to compute density databases which are to be employed for the determination of the ED of macromolecules.

Triclosan inhibits tumor necrosis factor-alpha-stimulated urokinase production in human gingival fibroblasts.

BACKGROUND AND OBJECTIVES: Destruction of the supporting periodontal tissues is mediated by the action of several proteolytic enzymes. Urokinase is a serine protease that plays a key role in connective tissue destruction through conversion of plasminogen into plasmin. The present study was conducted to evaluate the effect of triclosan on the production and activity of urokinase in cultured gingival fibroblasts. MATERIAL AND METHODS: Urokinase production was studied in primary cultures of human gingival fibroblasts stimulated with tumor necrosis factor-alpha. Urokinase activity and production were evaluated using casein zymography and western blotting, respectively. Urokinase mRNA expression was evaluated using the reverse transcription-polymerase chain reaction. Triclosan was used to interfere with this stimulatory effect. The roles of different cell-signaling cascades involved in urokinase production were assessed through western blotting and immunofluorescence using several cell-signaling inhibitors. RESULTS: Tumor necrosis factor-alpha was found to be a strong stimulus for urokinase production and triclosan was able to inhibit this response at the protein and mRNA levels. Triclosan was also able to inhibit conversion of plasminogen into plasmin. Tumor necrosis factor-alpha-stimulated urokinase production was shown to be dependent on the nuclear factor-kappaB and c-Jun N-terminal kinase signaling pathways. Triclosan inhibited c-Jun N-terminal kinase phosphorylation and c-Jun production. CONCLUSIONS: Within the limits of this study, these results show that triclosan may inhibit urokinase production and plasminogen activation in gingival fibroblasts through modulation of the c-Jun N-terminal kinase signaling pathway.

Inhibitory effect of angiostatins on activity of the plasminogen/plasminogen activator system.

Angiostatins, kringle-containing fragments of plasminogen, are potent inhibitors of angiogenesis. Effects of three angiostatin forms, K1-3, K1-4, and K1-4.5 (0-2 microM), on the rate of native Glu-plasminogen activation by its physiological activators in the absence or presence of soluble fibrin were investigated in vitro. Angiostatins did not affect the intrinsic amidolytic activities of plasmin and plasminogen activators of tissue type (tPA) and urokinase type (single-chain scuPA and two-chain tcuPA), but inhibited conversion of plasminogen to plasmin in a dose-dependent manner. All three angiostatins suppressed Glu-plasminogen activation by tcuPA independently of the presence of fibrin, and the inhibitory effect increased in the order: K1-3 < K1-4 < K1-4.5. The inhibitory effects of angiostatins on the scuPA activator activity were lower and further decreased in the presence of fibrin. Angiostatin K1-3 (up to 2 microM) had no effect, while 2 microM angiostatins K1-4 and K1-4.5 inhibited the fibrin-stimulated Glu-plasminogen activation by tPA by 50 and 100%, respectively. The difference in effects of the three angiostatins on the Glu-plasminogen activation by scuPA, tcuPA, and tPA in the absence or presence of fibrin is due to the differences in angiostatin structures, mechanisms of action, and fibrin-specificity of plasminogen activators, as well as due to the influence of fibrin on the Glu-plasminogen conformation. Angiostatins in vivo, which mimic plasminogen-binding activity, can inhibit plasminogen activation stimulated by various proteins (including fibrin) of extracellular matrix, thereby blocking cell migration and angiogenesis. The data of this work indicate that the inhibition of Glu-plasminogen activation under the action of physiological plasminogen activators by angiostatins can be implicated in the complex mechanism of their antiangiogenic and antitumor action.