Chimerism reveals a role for the streptokinase Beta -domain in nonproteolytic active site formation, substrate, and inhibitor interactions

Streptokinase (SK) and staphylokinase form cofactor-enzyme complexes that promote the degradation of fibrin thrombi by activating human plasminogen. The unique abilities of streptokinase to nonproteolytically activate plasminogen or to alter the interactions of plasmin with substrates and inhibitors may be the result of high affinity binding mediated by the streptokinase beta-domain. To examine this hypothesis, a chimeric streptokinase, SKbetaswap, was created by swapping the SK beta-domain with the homologous beta-domain of Streptococcus uberis Pg activator (SUPA or PauA, SK uberis), a streptokinase that cannot activate human plasminogen. SKbetaswap formed a tight complex with microplasminogen with an affinity comparable with streptokinase. The SKbetaswap-plasmin complex also activated human plasminogen with catalytic efficiencies (k(cat)/K(m) = 16.8 versus 15.2 microm(-1) min(-1)) comparable with streptokinase. However, SKbetaswap was incapable of nonproteolytic active site generation and activated plasminogen by a staphylokinase mechanism. When compared with streptokinase complexes, SKbetaswap-plasmin and SKbetaswap-microplasmin complexes had altered affinities for low molecular weight substrates. The SKbetaswap-plasmin complex also was less resistant than the streptokinase-plasmin complex to inhibition by alpha(2)-antiplasmin and was readily inhibited by soybean trypsin inhibitor. Thus, in addition to mediating high affinity binding to plasmin(ogen), the streptokinase beta-domain is required for nonproteolytic active site generation and specifically modulates the interactions of the complex with substrates and inhibitors.

[Non-allergic angioedema: update]

PURPOSE

Nonallergic isolated angioedema is an uncommon clinical syndrome raising difficult diagnosis and therapeutic problems. Occurrences linked to a C1Inh are the predominant ones and have to be examined as a priority, taking into account the specificity of the associated follow-up.

CURRENT KNOWLEDGE AND KEY POINTS

Diseases with a clinical profile close to hereditary angioneurotic edema, but without C1Inh anomaly, have been described recently. It is in fact family cases, concerning only women, where estrogens seem to play a dominant role. Angioedema's secondary aspects are gathering various pathologies (vasculitis, Gleich's syndrome, angioedema initiated by physical agents). The role played by some drugs must not be forgotten, mainly angiotensin converting enzyme inhibitors, which are at the origin of angiodema in nearly 0.5% of users.

FUTURE PROSPECT AND PROJECTS

Uncontrolled activation of the contact system seems to play a major role in the main part of these angiodemas. The efficiency of the tranexaminic acid (which modulates its activation) is to be taken as evident. The key to the future seems to be the development of plasmin and bradykinin inhibitors.

Enhanced activation of bound plasminogen on Staphylococcus aureus by staphylokinase

Activation of plasminogen (plg) to plasmin by the staphylococcal activator, staphylokinase (SAK), is effectively regulated by the circulating inhibitor, alpha2-antiplasmin (alpha2AP). Here it is demonstrated that intact Staphylococcus aureus cells and solubilized staphylococcal cell wall proteins not only protected SAK-promoted plg activation against the inhibitory effect of alpha2AP but also enhanced the activation. The findings suggest that the surface-associated plg activation by SAK may have an important physiological function in helping staphylococci in tissue dissemination. Amino acid sequencing of tryptic peptides originating from the 59-, 56- and 43-kDa proteins, isolated as putative plg-binding proteins, identified them as staphylococcal inosine 5'-monophosphate dehydrogenase, alpha-enolase, and ribonucleotide reductase subunit 2, respectively.

Plasmin activity is required for myogenesis in vitro and skeletal muscle regeneration in vivo

Plasmin, the primary fibrinolytic enzyme, has a broad substrate spectrum and is implicated in biologic processes dependent upon proteolytic activity, such as tissue remodeling and cell migration. Active plasmin is generated from proteolytic cleavage of the zymogen plasminogen (Plg) by urokinase-type plasminogen activator (uPA) and tissue-type plasminogen activator (tPA). Here, we have investigated the role of plasmin in C2C12 myoblast fusion and differentiation in vitro, as well as in skeletal muscle regeneration in vivo, in wild-type and Plg-deficient mice. Wild-type mice completely repaired experimentally damaged skeletal muscle. In contrast, Plg(-/-) mice presented a severe regeneration defect with decreased recruitment of blood-derived monocytes and lymphocytes to the site of injury and persistent myotube degeneration. In addition, Plg-deficient mice accumulated fibrin in the degenerating muscle fibers; however, fibrinogen depletion of Plg-deficient mice resulted in a correction of the muscular regeneration defect. Because we found that uPA, but not tPA, was induced in skeletal muscle regeneration, and persistent fibrin deposition was also reproducible in uPA-deficient mice following injury, we propose that fibrinolysis by uPA-dependent plasmin activity plays a fundamental role in skeletal muscle regeneration. In summary, we identify plasmin as a critical component of the mammalian skeletal muscle regeneration process, possibly by preventing intramuscular fibrin accumulation and by contributing to the adequate inflammatory response after injury. Finally, we found that inhibition of plasmin activity with alpha2-antiplasmin resulted in decreased myoblast fusion and differentiation in vitro. Altogether, these studies demonstrate the requirement of plasmin during myogenesis in vitro and muscle regeneration in vivo.

Structure-activity relationships of new NAPAP-analogs

Several new analogs of the known thrombin inhibitor NAPAP were synthesized, in which the P2 glycine residue was substituted by natural and unnatural amino acids. The thrombin inhibitory potency was comparable to that of NAPAP. Several of the compounds had inhibition constants lower than 10 nM and a very high selectivity compared to trypsin, factor Xa and plasmin. In addition, analogs were prepared by alkylation of the N(alpha)-atom of the 4-amidinophenylalanine in P1 position, which showed a more than 10-fold lower thrombin inhibition. Furthermore, azaglycine was introduced instead of P2 glycine. For most of the inhibitors similar fast elimination rates were seen in rats after intravenous dosing, as found previously for NAPAP. Only some compounds, which contained a second basic group showed a slightly decreased cumulative biliary clearance.

Immunoglobulin G from patients with antiphospholipid syndrome impairs the fibrin dissolution with plasmin

Immunoglobulin G (IgG) isolated from normal human blood plasma stabilizes the structure of perfused crosslinked fibrin and prolongs the time for its dissolution with plasmin, when the fibrin surface is exposed to 500 s(-1) shear rate flow. The IgG from patients suffering in antiphospholipid syndrome with thrombotic complications exerts even stronger antifibrinolytic effect. A patient, whose IgG does not affect the fibrin dissolution with plasmin, displays a bleeding tendency. The shear stress-induced disassembly of the fibrin clots containing IgGs with antifibrinolytic potency occurs at a much more advanced stage of fibrin digestion, as evidenced by the electrophoretic pattern of the ureatreated samples. The antifibrinolytic effects are also produced under static conditions and these are caused by the variable portion of the IgG molecules (fragment Fab), whereas the constant part (fragment Fc) has no inhibitory effect. The IgGs with antifibrinolytic properties do not affect directly the plasmin activity in amidolytic assay, but the IgGs from APS patients obliterate the competition of the fibrin and the peptidyl-p-nitroanilide for the protease in the same assay system suggesting interference of the IgGs with the plasmin action on the fibrin substrate. Thus, the correlation of the clinical symptoms with the effect of the isolated IgG on the dissolution of perfused fibrin clots supports a physiological and a pathological role of IgG in the fibrinolytic process related to the variability of the cross-reactions of immunoglobulins with fibrin, fibrin degradation products or fibrin-plasmin complexes.

Overexpression of the serpin megsin induces progressive mesangial cell proliferation and expansion

Mesangial cells maintain normal glomerular function by mediating ECM remodeling and immune complex disposal. We have recently identified megsin, a novel member of the serine protease inhibitor (serpin) superfamily predominantly expressed in the mesangium. While our previous studies suggested a role for megsin in the pathogenesis of human glomerular diseases, its exact biological significance remained unknown. Here we produced two lines of megsin transgenic mice. Overexpression of megsin led to progressive mesangial matrix expansion and an increase in the number of mesangial cells. These glomerular lesions were accompanied by an augmented immune complex deposition, together with Ig's and complement. Binding and functional assays in vitro identified plasmin as one biological substrate of megsin and confirmed its activity as a proteinase inhibitor. Transgenic animals exhibiting nephritis as a result of treatment with anti--glomerular basement membrane antiserum showed significantly more persistent expansion of the mesangial ECM than was seen in parental mice. Megsin therefore exerts a biologically relevant influence on mesangial function, and on the mesangial microenvironment, such that simple overexpression of this endogenous serpin engenders elementary mesangial lesions.

Inhibitors of plasmin that extend into both the S and S' binding sites: cooperative interactions between S1 and S2

A new procedure for the synthesis of cyclohexanone-based inhibitors of serine proteases is reported. In this procedure the reactive ketone functionality is carried through the synthesis in masked form as a TBDMS-protected alcohol. Deprotection followed by oxidation of the alcohol generates the final form of the inhibitor. Two new inhibitors, which interact with the S1-S3 and S2' subsites of plasmin, are synthesized using this procedure. Inhibitors 1 and 2 have IC50 values against plasmin of 20 and 24 microM, respectively. The inhibition studies show that cooperative binding of inhibitors in the S1 and S2 subsites of plasmin is important for determining inhibitor selectivity.

The fibrinolysis system: regulation of activity and physiologic functions of its main components

This review summarizes basic properties and mechanisms of activation and inhibition of main components of the fibrinolytic system that, acting in accord with the system of blood coagulation, provides temporal formation of fibrin clots at sites of vascular injury for the time required for the regeneration of vascular wall. Impairments in the fibrinolytic system may cause bleedings or thrombotic complications in patients. The predictive value of some components of the fibrinolytic system with respect to the development of complications of atherothrombosis is considered.

Inhibitory effect of JTV-803, a new cyclic guanidine derivative, on factor Xa in vitro and in vivo

JTV-803, 4-[(2-amidino-1,2,3,4-tetrahydroisoquinolin-7-yloxy)methyl]-1-(4-pyridinyl)piperidine-4-carboxylic acid monomethanesulfonate trihydrate showed a competitive inhibitory effect on human factor Xa, with a K(i) value of 0.019 microM. This compound was 100 times more selective in inhibiting human factor Xa as compared to its inhibitory activity against thrombin, plasmin, and trypsin. JTV-803 was also examined for its inhibitory effect on activated factor Xa obtained from plasma of various animal species. JTV-803 exerted a potent inhibitory effect on human factor Xa (IC(50): 0.081 microM). JTV-803 prolonged activated partial thromboplastin time and prothrombin time in a dose-dependent manner. Oral anticoagulant efficacy of JTV-803 was examined ex vivo for its inhibition of human factor Xa in cynomolgus monkeys. JTV-803 produced more than 20% inhibition of human factor Xa for 8 h. Taken together, the results indicate JTV-803 is a long-acting oral anticoagulant which exerts its effect via specific inhibition of human factor Xa.

Design and synthesis of glycolic and mandelic acid derivatives as factor Xa inhibitors

A series of glycolic and mandelic acid derivatives was synthesized and investigated for their factor Xa inhibitory activity. These analogues are highly potent and selective inhibitors against fXa. In a rabbit deep vein thrombosis model, compound 26 showed significant antithrombotic effects (81% inhibition of thrombus formation) at 1.1 microM plasma concentration following intravenous administration.

Plasmin-mediated fibroblast growth factor-2 mobilisation supports smooth muscle cell proliferation in human saphenous vein

The focus of this study was identification of the contribution of the plasminogen activator-plasmin system to smooth muscle cell proliferation and migration in human saphenous vein. Segments of human saphenous vein were grown in organ culture for up to 14 days. Smooth muscle cell proliferation and migration were measured by incubating vein segments in bromodeoxyuridine, and smooth muscle cell death was detected by in situ end-labelling. Tissue-type (tPA) and urokinase-type (uPA) plasminogen activator enzymic activities were detectable in cultured saphenous vein segments, and were concentrated in focal zones. Inhibition of plasmin activity with alpha-N-acetyl-L-lysine methyl ester (NALME) or of uPA activity with a neutralising antibody caused significant decreases in smooth muscle cell proliferation in the media and the intima, but no significant changes in smooth muscle cell migration. Intimal thickness was also significantly decreased. Incubation with plasminogen or plasmin caused fibroblast growth factor-2 (FGF2) to be released into the medium. Addition of FGF2 to segments cultured with NALME reversed the inhibition of smooth muscle cell proliferation, and blocking the activity of FGF2 with a neutralising antibody caused a significant decrease in medial smooth muscle cell proliferation. These data suggest that plasmin mobilises FGF2 bound to the extracellular matrix of human saphenous vein, so that it can support smooth muscle cell proliferation and intimal thickening.

Crosslinking of alpha 2-antiplasmin to fibrin

Human alpha 2-antiplasmin (alpha 2AP) is the primary inhibitor of plasmin-mediated fibrinolysis and is an efficient substrate of activated factor XIII (FXIIIa). Among 452 amino acid residues in alpha 2AP, Gln2 is believed to be the sole FXIIIa-reactive site that participates in crosslinking alpha 2AP to fibrin. We studied the effect of mutating Gln2 on the ability of FXIIIa to catalyze crosslinking of alpha 2AP to fibrin. By FXIIIa catalysis, [14C]methylamine was incorporated into a Q2A-alpha 2AP mutant in which Gln2 (Q) was replaced by Ala (A), thereby indicating that wildtype alpha 2AP has more than one FXIIIa-reactive site. To identify the FXIIIa-reactive sites in alpha 2AP, wildtype alpha 2AP and Q2A-alpha 2AP were labeled with 5-(biotinamido)pentylamine by FXIIIa. Each labeled alpha 2AP was digested with trypsin and applied to an avidin affinity column to capture labeled peptides. Edman sequencing and mass analysis of each labeled peptide showed that out of 35 Gln residues in wildtype alpha 2AP, four were labeled with the following order of efficiency: Gln2 > Gln21 > Gln419 > Gln447. Q2A-alpha 2AP was also labeled at the three minor sites, Gln21 > Gln419 > Gln447. Q2A-alpha 2AP became crosslinked to fibirin(ogen) by FXIIIa catalysis at approximately one-tenth the rate of wt-alpha 2AP. These results demonstrate that alpha 2AP has one primary (Gln2) and three minor substrate sites for FXIIIa and that the three minor sites identified in this study can also participate in crosslink formation between alpha 2AP and fibrin, but at a much lower efficiency than the Gln2 site.

Expression of inter-alpha-trypsin inhibitor and tumor necrosis factor-stimulated gene 6 in renal proximal tubular epithelial cells

BACKGROUND

Our previous studies have demonstrated that renal proximal tubular epithelial cells (PTCs) may contribute to renal interstitial fibrosis by the generation of transforming growth factor-beta1 (TGF-beta1). In these in vitro experiments, TGF-beta1 was, however, secreted in its latent form. Plasmin has been implicated as a potential physiological activator of TGF-beta1. The inter-alpha-trypsin inhibitor (IalphaI) family of serum protease inhibitors together with tumor necrosis factor-stimulated gene 6 (TSG-6) recently have been implicated in the regulation of this protease pathway. The aim of the current study was to examine PTC synthesis of these proteins and to relate it to alterations of plasmin-protease activity.

METHODS

PTCs were grown to confluence and stimulated under serum-free conditions with either interleukin-1beta (IL-1beta) or 25 mmol/L D-glucose. Alterations in IalphaI and TSG-6 generation were detected by Western analysis of both membrane extracts and supernatant samples. Alterations in gene expression were examined by reverse transcription-polymerase chain reaction. The effect of alteration in synthesis of TSG-6 on plasmin activity was determined by quantitating plasmin inhibitory activity of supernatant samples by in vitro calorimetric assay prior to and following TSG-6 immunoprecipitation.

RESULTS

The data demonstrate that human PTCs constitutively express mRNA for bikunin and heavy chain 3 (H3) of IalphaI. Neither IL-1beta (1 ng/mL) nor 25 mmol/L D-glucose influenced their mRNA expression nor protein synthesis. In contrast, the addition of either IL-1beta or 25 mmol/L D-glucose increased TSG-6 mRNA expression. This was accompanied by an early up-regulation of TSG-6 protein expression following IL-1beta stimulation (24 h) and a late up-regulation after the addition of 25 mmol/L D-glucose (96 h) in the cell culture supernatant and associated with the cell membranes. Early induction of TSG-6 mRNA by IL-1beta was unaffected by the addition of the protein synthesis inhibitor cycloheximide. In contrast, the later glucose-stimulated induction of TSG-6 mRNA was abrogated by the addition of cycloheximide. Stimulation of TSG-6 by either IL-1beta or 25 mmol/L D-glucose was associated with an inhibition of total percentage plasmin activity. Immunoprecipitation of TSG-6 in these samples returned plasmin activity to control levels.

CONCLUSIONS

: The data demonstrate that human PTCs constitutively express the bikunin and H3 components of the IalphaI family of serum protease inhibitors. Moreover, the addition of IL-1beta or 25 mmol/L D-glucose up-regulates the expression of TSG-6 in these cells, resulting in an inhibition of plasmin activity.

Prevention of rat hepatic fibrosis by the protease inhibitor, camostat mesilate, via reduced generation of active TGF-beta

BACKGROUND & AIMS

Proteolytic release and activation of latent transforming growth factor beta (TGF-beta) by the hepatic stellate cells (HSCs) are key events for pathogenesis of hepatic fibrosis, and protease inhibitors suppress TGF-beta generation by cultured HSCs, suggesting their potential use as antifibrogenic agents. We explored this idea using camostat mesilate, a serine protease inhibitor, to determine its effects and mechanisms of action in vivo.

METHODS

Camostat mesilate was either added to cultured rat HSCs or administered orally to rats during porcine serum treatment, followed by overexpression of urokinase. We measured cellular and hepatic levels of plasmin, TGF-beta, TGF-beta activity, activated HSC markers (increased cell number, morphologic change, and expression of both alpha-smooth muscle actin and collagen(alpha2)[I]), and fibrosis (Azan-staining and quantification of hydroxyproline content).

RESULTS

Camostat mesilate (500 micromol/L) inhibited generation of TGF-beta by suppressing plasmin activity and reduced the activity of TGF-beta, which blocked in vitro activation of HSCs. In the in vivo model, camostat mesilate (1-2 mg/g of diet) markedly attenuated an increase in hepatic plasmin and TGF-beta levels, HSC activation, and hepatic fibrosis without apparent systemic or local side effects, all of which were reverted by restoration of hepatic plasmin activity.

CONCLUSIONS

Camostat mesilate prevents porcine serum-induced rat hepatic fibrosis via a profound reduction in TGF-beta generation.

Release of biologically active TGF-beta from airway smooth muscle cells induces autocrine synthesis of collagen

In severe or chronic asthma, there is an increase in airway smooth muscle cell (ASMC) mass as well as an increase in connective tissue proteins in the smooth muscle layer of airways. Transforming growth factor-beta (TGF-beta) exists in three isoforms in mammals and is a potent regulator of connective tissue protein synthesis. Using immunohistochemistry, we had previously demonstrated that ASMCs contain large quantities of TGF-beta1-3. In this study, we demonstrate that bovine ASMC-derived TGF-beta associates with the TGF-beta latency binding protein-1 (LTBP-1) expressed by the same cells. The TGF-beta associated with LTBP-1 localizes TGF-beta extracellularly. Furthermore, plasmin, a serine protease, regulates the secretion of a biologically active form of TGF-beta by ASMCs as well as the release of extracellular TGF-beta. The biologically active TGF-beta released by plasmin induces ASMCs to synthesize collagen I in an autocrine manner. The autocrine induction of collagen expression by ASMCs may contribute to the irreversible fibrosis and remodeling seen in the airways of some asthmatics.

Purification and characterization of a plasmin-like protease from Tenodera sinensis (Chinese mantis)

A novel type of protease (mantis egg fibrinolytic enzyme, MEF-2) was isolated from the egg cases of Tenodera sinensis. The protease was homogeneous by SDS-PAGE and its apparent molecular mass was 32,900 Da. The amino acids in the N-terminal region were Ile-Val-Gly-Gly-Glu-Glu-Ala-Val-Ala-Gly-Asp-Phe-Pro-Ile-Val-Ser-Leu-Gln-Glu. The enzyme was inhibited by PMSF, TLCK, aprotinin, benzamidine, soybean trypsin inhibitor and also slightly by elastatinal, EDTA, EGTA, cysteine and beta-mercaptoethanol, but TPCK, iodoacetate and E-64 did not affect the activity. MEF-2 was not sensitive to alpha(1)-antitrypsin but antithrombin III and alpha(2)-antiplasmin inhibited the enzyme. MEF-2 preferentially cleaved the oxidized B-chain of insulin between Arg(22) and Gly(23). Among chromogenic protease substrates, the most susceptible to MEF-2 hydrolysis was benzoyl-Phe-Val-Arg-p-nitroanilide with maximal activity at 30 degrees C and pH 5.0. These results indicate that MEF-2 belongs to the trypsin family. Upon incubation of crosslinked fibrin with MEF-2, a steady increase of D-dimer suggests that the enzyme has a strong fibrinolytic activity. In conclusion, MEF-2 is a new type of proteolytic enzyme and has some potential for practical application in fibrinolysis.

In vivo suppression of restenosis in balloon-injured rat carotid artery by adenovirus-mediated gene transfer of the cell surface-directed plasmin inhibitor ATF.BPTI

Injury-induced neointimal development results from migration and proliferation of vascular smooth muscle cells (SMC). Cell migration requires controlled proteolytic degradation of extracellular matrix surrounding the cell. Plasmin is a major contributor to this process by degrading various matrix proteins directly, or indirectly by activating matrix metalloproteinases. This makes it an attractive target for inhibition by gene transfer. An adenoviral vector, Ad.ATF.BPTI, was constructed encoding a hybrid protein, which consists of the aminoterminal fragment (ATF) of urokinase-type plasminogen activator (u-PA) linked to bovine pancreas trypsin inhibitor (BPTI), a potent inhibitor of plasmin. This hybrid protein binds to the u-PA receptor, thereby inhibiting plasmin activity at the cell surface, and was found to be a potent inhibitor of cell migration in vitro. Local infection with Ad.ATF.BPTI of balloon-injured rat carotid artery resulted in detectable expression of ATF.BPTI mRNA and protein in the vessel wall. Morphometric analysis of arterial cross-sections revealed that delivery of Ad.ATF.BPTI to the carotid artery wall at the time of balloon injury inhibited neointima formation by 53% (P < 0.01) at 14 days and 19% (P = NS) at 28 days after injury when compared with control vector-infected arteries. Intima/media ratios were decreased by 60% (P < 0.01) and 35% (P < 0.05) at 14 and 28 days, respectively, when compared with control vector-infected arteries. Furthermore, a small but significant increase in medial area was found in the Ad.ATF.BPTI-treated arteries at 28 days (P < 0.05). These results show that local infection of the vessel wall with Ad.ATF.BPTI reduces neointima formation, presumably by inhibiting SMC migration, thereby offering a novel therapeutic approach to inhibiting neointima development.

Inhibition of angiogenesis in vivo by plasminogen activator inhibitor-1

The process of angiogenesis is important in both normal and pathologic physiology. However, the mechanisms whereby factors such as basic fibroblast growth factor promote the formation of new blood vessels are not known. In the present study, we demonstrate that exogenously added plasminogen activator inhibitor-1 (PAI-1) at therapeutic concentrations is a potent inhibitor of basic fibroblast growth factor-induced angiogenesis in the chicken chorioallantoic membrane. By using specific PAI-1 mutants with either their vitronectin binding or proteinase inhibitor activities ablated, we show that the inhibition of angiogenesis appears to occur via two distinct but apparently overlapping pathways. The first is dependent on PAI-1 inhibition of proteinase activity, most likely chicken plasmin, while the second is independent of PAI-1's anti-proteinase activity and instead appears to act through PAI-1 binding to vitronectin. Together, these data suggest that PAI-1 may be an important factor regulating angiogenesis in vivo.

A truncated plasminogen activator inhibitor-1 protein induces and inhibits angiostatin (kringles 1-3), a plasminogen cleavage product

Plasminogen activator inhibitor-1 (PAI-1) is a serpin protease inhibitor that binds plasminogen activators (uPA and tPA) at a reactive center loop located at the carboxyl-terminal amino acid residues 320-351. The loop is stretched across the top of the active PAI-1 protein maintaining the molecule in a rigid conformation. In the latent PAI-1 conformation, the reactive center loop is inserted into one of the beta sheets, thus making the reactive center loop unavailable for interaction with the plasminogen activators. We truncated porcine PAI-1 at the amino and carboxyl termini to eliminate the reactive center loop, part of a heparin binding site, and a vitronectin binding site. The region we maintained corresponds to amino acids 80-265 of mature human PAI-1 containing binding sites for vitronectin, heparin (partial), uPA, tPA, fibrin, thrombin, and the helix F region. The interaction of "inactive" PAI-1, rPAI-1(23), with plasminogen and uPA induces the formation of a proteolytic protein with angiostatin properties. Increasing amounts of rPAI-1(23) inhibit the proteolytic angiostatin fragment. Endothelial cells exposed to exogenous rPAI-1(23) exhibit reduced proliferation, reduced tube formation, and 47% apoptotic cells within 48 h. Transfected endothelial cells secreting rPAI-1(23) have a 30% reduction in proliferation, vastly reduced tube formation, and a 50% reduction in cell migration in the presence of VEGF. These two studies show that rPAI-1(23) interactions with uPA and plasminogen can inhibit plasmin by two mechanisms. In one mechanism, rPAI-1(23) cleaves plasmin to form a proteolytic angiostatin-like protein. In a second mechanism, rPAI-1(23) can bind uPA and/or plasminogen to reduce the number of uPA and plasminogen interactions, hence reducing the amount of plasmin that is produced.

Like fibrin, (DD)E, the major degradation product of crosslinked fibrin, protects plasmin from inhibition by alpha2-antiplasmin

Plasmin generation is localized to the fibrin surface because tissue-type plasminogen activator (t-PA) and plasminogen bind to fibrin, an interaction that stimulates plasminogen activation over a hundred-fold. To ensure efficient fibrinolysis, plasmin bound to fibrin is protected from inhibition by alpha2-antiplasmin. (DD)E, a major soluble degradation product of cross-linked fibrin that is a potent stimulator of t-PA, compromises the fibrin-specificity of t-PA by promoting systemic activation of plasminogen. In this study we investigated whether (DD)E also protects plasmin from inhibition by alpha2-antiplasmin, facilitating degradation of this soluble t-PA effector. (DD)E and fibrin reduce the rate of plasmin inhibition by alpha2-antiplasmin by 5- and 10-fold, respectively. Kringle-dependent binding of plasmin to (DD)E and fibrin, with Kd values of 52 and 410 nM, respectively, contributes to the protective effect. When (DD)E is extensively degraded by plasmin, yielding uncomplexed fragment E and (DD), protection of plasmin from inhibition by alpha2-antiplasmin is attenuated. These studies indicate that (DD)E-bound plasmin, whose generation reflects the ability of (DD)E to stimulate plasminogen activation by t-PA, has the capacity to degrade (DD)E by virtue of its resistance to inhibition. This provides a mechanism to limit the concentration of (DD)E and maintain the fibrin-specificity of t-PA.

Expression and function of peroxisome proliferator-activated receptor-gamma in mesangial cells

P:eroxisome proliferator-activated receptor-gamma (PPARgamma) is a novel nuclear receptor, which enhances insulin-mediated glucose uptake. Ligands to PPARgamma are currently used as therapy for type II diabetes. Using Western blot analysis, RNase protection assay, and immunostaining, we identified the presence of PPARgamma message and protein in cultured primary rat mesangial cells. Electrophoretic mobility of a labeled PPARgamma response element (PPRE) was retarded in the presence of mesangial cell nuclear extract, suggesting that PPARgamma is functional in these cells. The addition of unlabeled PPRE efficiently competed away the PPARgamma-PPRE protein complex, confirming specificity of binding of the PPARgamma to the PPRE. PPARgamma ligands rosiglitazone (1 to 10 micromol/L) and troglitazone (1 to 10 micromol/L) inhibited platelet-derived growth factor-induced DNA synthesis, measured as bromodeoxyuridine incorporation (P<0.01). This inhibition was dose dependent. When administered in antidiabetic doses to streptozotocin-induced diabetic rats, troglitazone substantially normalized albumin excretion at 3 months (from 687.1 to 137.6 microgram urinary albumin/mg creatinine, P:<0.05) but did not affect hyperglycemia or blood pressure in this model. This treatment also decreased glomerular plasminogen activator inhibitor-1 (PAI-1) expression. These data suggest that PPARgamma activation may directly attenuate diabetic glomerular disease, possibly by inhibiting mesangial growth, which occurs early in the process of diabetic nephropathy, or by inhibiting PAI-1 expression. PAI-1 inhibits the activation of plasmin and matrix metalloproteinase, which degrade extracellular matrix in the glomerulus. Excess glomerular PAI-1 allows the accumulation of extracellular matrix, leading to glomerulosclerosis. These results have therapeutic implications for diabetic nephropathy as well as for proliferative mesangial diseases of the kidney.

Inhibition of human and ovine acrosomal enzymes by tannic acid in vitro

The effect of tannic acid, a common flavonoid, on the acrosin and plasminogen activator activity and plasmin activity of human and ram spermatozoa was evaluated. Acrosin and plasminogen activator activity were determined by spectrophotometry using the chromogenic substrates N-alpha-benzoyl-DL-arginine para-nitroanilide-HCl (BAPNA) and H-D-valyl-L-leucyl-L-lysine-p-nitroanilide-2HCl (S-2251), respectively. In extracts from both human and ovine acrosomes, the activities of acrosin and plasminogen activators were susceptible to tannic acid inhibition. The inhibitory effect of tannic acid was observed at concentrations > 50 micromol l(-1) in a dose-dependent manner. In additional experiments, low concentrations of tannic acid significantly inhibited tissue-type plasminogen activator, urokinase-type plasminogen activator and plasmin activity in a concentration-dependent manner over the range 0.25-200 micromol l(-1). Tannic acid reduced the motility of ram spermatozoa at a concentration of 1000 micromol l(-1) after 2 and 3 h co-incubation with spermatozoa. The motility of human spermatozoa remained unchanged over the range 0.1-1000 micromol tannic acid l(-1) during 3 h co-incubation. These results indicate that tannic acid inhibited the activity of both acrosin and plasminogen activator and indicates a possible mechanism by which flavonoids exert their antifertility effects.