Inhibition of stromelysin-1 by caffeic acid derivatives from a propolis sample from Algeria

Stromelysin-1 (matrix metalloproteinase-3: MMP-3) occupies a central position in collagenolytic and elastolytic cascades, leading to cutaneous intrinsic and extrinsic aging. We screened extracts of a propolis sample from Algeria with the aim to isolate compounds able to selectively inhibit this enzyme. A butanolic extract (B (3)) of the investigated propolis sample was found to potently inhibit MMP-3 activity (IC (50) = 0.15 ± 0.03 µg/mL), with no or only weak activity on other MMPs. This fraction also inhibited plasmin amidolytic activity (IC (50) = 0.05 µg/mL) and impeded plasmin-mediated proMMP-3 activation. B (3) was fractionated by HPLC, and one compound, characterized by NMR and mass spectroscopy and not previously identified in propolis, i.e., (+)-chicoric acid, displayed potent IN VITRO MMP-3 inhibitory activity (IC (50) = 6.3 × 10 (-7) M). In addition, both caffeic acid and (+)-chicoric acid methyl ester present in fraction B (3) significantly inhibited UVA-mediated MMP-3 upregulation by fibroblasts.

Short peptides containing L-lysine and epsilon-aminocaproic acid as potential plasmin inhibitors

Eight short peptides containing L-lysine and epsilon-aminocaproic acid were obtained and their effect on the amidolytic activities of plasmin, thrombin and trypsin was examined. Tripeptide amide Boc-EACA-L-Lys-EACA-NH2 was the most effective and specific plasmin inhibitor.

[Change in levels of plasmin and its inhibitors in blood of patients with dyscirculatory encephalopathy before and after the treatment]

The aim of the investigation was to estimate the serum concentrations of the major proteinase plasmin (PL) and some inhibitors of proteinases, such as alpha 2-macroglobulin (MG), alpha 1-antitrypsin (AT), and the specific complexes plasmin-macroglobulin (PL-MG) in order to study their role in the pathogenesis of dyscirculatory encephalopathy. All the above indices were examined in the sera of 35 patients with dyscirculatory encephalopathy (a study group) and 38 apparently healthy individuals (a control group). The authors determined the levels of PL, MG, and AT by the rocket immunoelectrophoresis technique using monospecific antisera against these proteins and those of specific PL-MG complexes by enzyme immunoassay. During the study, a significant increase in the level of PL and PL-MG complexes was revealed in the study group before and after treatment as compared with the controls. Prior to and following treatment, the serum concentrations of MG and AT in the study group did not differ from those in the control group. The findings may be used for further study of the pathogenesis of dyscirculatory encephalopathy.

Experience with plasmin inhibitors

The involvement and role of the plasminogen activator-plasmin system in normal and pathological wound healing is reviewed. The methods currently available for demonstrating plasmin activity are briefly described. The article also reviews some other serine proteases potentially involved in pathological wound healing processes. The current ophthalmological therapeutic measures used to regulate tissue proteolysis are also described.

Inhibition of p75 neurotrophin receptor attenuates isoflurane-mediated neuronal apoptosis in the neonatal central nervous system

BACKGROUND

Exposure to anesthetics during synaptogenesis results in apoptosis and subsequent cognitive dysfunction in adulthood. Probrain-derived neurotrophic factor (proBDNF) is involved in synaptogenesis and can induce neuronal apoptosis via p75 neurotrophic receptors (p75). proBDNF is cleaved into mature BDNF (mBDNF) by plasmin, a protease converted from plasminogen by tissue plasminogen activator (tPA) that is released with neuronal activity; mBDNF supports survival and stabilizes synapses through tropomyosin receptor kinase B. The authors hypothesized that anesthetics suppress tPA release from neurons, enhance p75 signaling, and reduce synapses, resulting in apoptosis.

METHODS

Primary neurons (DIV5) and postnatal day 5-7 (PND5-7) mice were exposed to isoflurane (1.4%, 4 h) in 5% CO2, 95% air. Apoptosis was assessed by cleaved caspase-3 (Cl-Csp3) immunoblot and immunofluorescence microscopy. Dendritic spine changes were evaluated with the neuronal spine marker, drebrin. Changes in synapses in PND5-7 mouse hippocampi were assessed by electron microscopy. Primary neurons were exposed to tPA, plasmin, or pharmacologic inhibitors of p75 (Fc-p75 or TAT-Pep5) 15 min before isoflurane. TAT-Pep5 was administered by intraperitoneal injection to PND5-7 mice 15 min before isoflurane.

RESULTS

Exposure of neurons in vitro (DIV5) to isoflurane decreased tPA in the culture medium, reduced drebrin expression (marker of dendritic filopodial spines), and enhanced Cl-Csp3. tPA, plasmin, or TAT-Pep5 stabilized dendritic filopodial spines and decreased Cl-Csp3 in neurons. TAT-Pep5 blocked isoflurane-mediated increase in Cl-Csp3 and reduced synapses in PND5-7 mouse hippocampi.

CONCLUSION

tPA, plasmin, or p75 inhibition blocked isoflurane-mediated reduction in dendritic filopodial spines and neuronal apoptosis in vitro. Isoflurane reduced synapses and enhanced Cl-Csp3 in the hippocampus of PND5-7 mice, the latter effect being mitigated by p75 inhibition in vivo. These data support the hypothesis that isoflurane neurotoxicity in the developing rodent brain is mediated by reduced synaptic tPA release and enhanced proBDNF/p75-mediated apoptosis.

Proteasome degradation of protein C and plasmin inhibitor mutants

Protein C (PC) deficiency and plasmin inhibitor (PI) deficiency are inherited thrombotic and haemorrhagic disorders. We investigated the intracellular degradation of mutant proteins, using naturally occurring PC and PI mutants that lead to congenital deficiencies. To examine the necessity of N-linked glycosylation for the proteasomal degradation of PC and PI, PC178 and PC331 mutants treated with tunicamycin and N-glycosylation-lacking mutants, PC92Stop and PI-America were pulse chased. The analysis revealed that the speed of degradation of the tunicamycin-treated PC mutants, PC92Stop and PI-America lacking glycosylation, was slower than that of N-glycosylated mutants. Immunoprecipitation and immunoblot analysis showed that PC178 and PC331 mutants were associated with molecular chaperones, Bip, GRP94, and calreticulin. PI-America was associated with only Bip. Although degradation of mutants was mediated by proteasomes, no association with ubiquitin was detected. Cotransfection of endoplasmic reticulum (ER) degradation enhancing alpha-mannosidase-like protein (EDEM) accelerated the degradation of N-glycosylated PC. In the absence of autophagy using Atg5-deficient cell lines, the degradation of the PC331 mutant was mildly accelerated but that of PC178, PI-America and PI-Okinawa mutants was not influenced. While the degradation of the PC and PI mutants was facilitated by N-glycosylation moieties, they were ubiquitin-independently degraded by proteasomes, irrespective of the presence or absence of N-glycosylation. Molecular chaperone binding was influenced by the presence of N-glycosylation moieties. When the misfolded or truncated mutant proteins are functionally active, proteasome inhibitors such as bortezomib may have therapeutic potential for treatment of protein deficiencies.

Biological activity of amide derivatives of lysine

Five substituted amides of lysine with the general formula: X-Lys-NH-Y, where X= acetyl or ethoxycarbonyl, Y= cyclohexyl, benzyl, hexyl or cadaverine residue were synthesised and their effects on fibrinolytic activity of plasmin, clotting activity of thrombin and amidolytic activities of both enzymes were examined.

Effects of netropsin and pentamidine amino analogues on the amidolytic activity of plasmin, trypsin and urokinase

Inhibitory effects of nine carbocyclic DNA minor groove binders on amidolytic activities of plasmin, trypsin and urokinase were examined. Some of the studied compounds affected plasmin or trypsin activity, but not urokinase activity. One of the pentamidine analogues (5) and two bis-netropsin like compounds (6, 8) were potent inhibitors of plasmin (IC50 equals 90 and 100 microM), whereas an analogue of netropsin (2) was trypsin inhibitor (IC50 = 100 microM).

Fibrinolysis is amplified by converting alpha-antiplasmin from a plasmin inhibitor to a substrate

alpha(2)-Antiplasmin (alpha(2)-AP) is the fast serpin inhibitor of plasmin and appears to limit the success of treatment for thrombosis. We examined the mechanisms through which monoclonal antibodies (mAbs) against alpha(2)-AP amplify fibrinolysis. The mAbs RWR, 49 and 77 interfered with the ability of alpha(2)-AP to inhibit plasmin, microplasmin and trypsin. In solution, mAbs 49 and 77 bound to alpha(2)-AP with 5-fold to 10-fold higher relative affinity than mAb-RWR, while mAb-RWR bound with greater avidity to immobilized or denatured alpha(2)-AP. Binding studies with chimeric alpha(2)-APs revealed that none of the mAbs bound to sites in alpha(2)-AP that form putative contacts with plasmin, namely the carboxy terminal lysines of alpha(2)-AP, or the reactive center loop in the serpin domain of alpha(2)-AP. Rather, mAb-RWR recognized an epitope in the amino-terminus of alpha(2)-AP (L(13)GNQEPGGQTALKSPPGVCS(32)) near the site at which alpha(2)-AP cross-links to fibrin. mAbs 49 and 77 bound to another conformational epitope in the serpin domain of alpha(2)-AP. mAbs 49 and 77 markedly increased the stoichiometry of plasmin inhibition by alpha(2)-AP (from 1.1 +/- 0.1 to 51 +/- 4 and 67 +/- 7) indicating that they convert alpha(2)-AP from an inhibitor to a substrate of plasmin. This was confirmed by sodium dodecylsulfate polyacrylamide gel electrophoresis analysis showing cleavage of alpha(2)-AP by plasmin in the presence of these mAbs. In summary, these mAbs appear to act at sites distinct from known alpha(2)-AP-plasmin contacts to enhance fibrinolysis by converting alpha(2)-AP from an inhibitor to a plasmin substrate.

Treatment strategy against infection: clinical outcome of continuous regional arterial infusion, enteral nutrition, and surgery in severe acute pancreatitis

BACKGROUND

In severe acute pancreatitis (SAP), infectious complications are the main contributors to high mortality. Since 1995, we have performed continuous regional arterial infusion of protease inhibitor and antibiotics (CRAI) and enteral nutrition (EN) as prevention therapies against infection. When infected pancreatic necrosis was proven, surgical intervention was adapted. The aim of this study was to investigate the clinical outcome of these treatments.

METHODS

We examined the relationship between the historical change of treatment strategy and clinical outcome. We divided 84 patients with acute necrotizing pancreatitis into two groups, CRAI (-) and CRAI (+), and compared the outcome. We divided 145 patients with SAP into two groups, EN (-) and EN (+), and compared the outcome. We also analyzed the outcome of surgical treatment.

RESULTS

In the CRAI (+) group, the incidence of infection, the frequency of surgery, and the mortality rate were lower than those in CRAI (-) group: 34% versus 51%, 27% versus 63% (P < 0.05), and 37% versus 54%, respectively. In the EN (+) group, the frequency of surgery and the mortality rate were lower than those in the EN (-) group: 23% versus 32% and 19% versus 35% (P < 0.05), respectively. These improvement effects were manifest in stage 3 (9 < or = Japanese Severity Score < or = 14). Treatment outcome of necrosectomy for infected pancreatic necrosis was still poor. Bleeding and abscess-gut fistula were postoperative life-threatening complications.

CONCLUSIONS

CRAI and EN may improve the clinical outcome of SAP, reducing infection and averting pancreatic surgery.

Low molecular peptides as potential inhibitors of plasmin

Ten peptides of the general formula A-Phe-Lys-X where A = H, H-D-Val, H-L-Val, H-D-Ala, H-L-Ala and X = OH, NH2 were obtained and tested for their antiplasmin activity with the use of amidolytic test.

Plasmin inhibition increases MMP-9 activity and decreases vein wall stiffness during venous thrombosis resolution

INTRODUCTION

Deep venous thrombosis (DVT) resolution involves the plasmin and the matrix metalloproteinase (MMP) system. This study tested the hypothesis that pharmacological inhibition of the plasmin system would impair DVT resolution and worsen vein wall damage.

METHODS

A rat model of stasis DVT by inferior vena cava (IVC) ligation was performed with intravenous control saline or aprotinin (AP; 2.8 mg/kg at operation), and harvest of thrombosed IVC at 7 days. After laser Doppler imaging, DVT were separated and weighed, and vein wall stiffness was assessed by tensiometry. Thrombus and vein wall tissue analysis included total collagen by colorimetric assay, cytokines, chemokines, and d-dimer by ELISA, urokinase-plasminogen activator (uPA), and plasminogen activator inhibitor-1 (PAI-1) by immuno-blotting, MMP-2 and -9 by zymography, and neutrophil (PMN) and monocyte (ED-1) leukocytes by immunohistochemistry.

RESULTS

DVT weights were 2-fold greater in the AP-treated rats (P < 0.05), but no significant differences in thrombus perfusion, collagen, or d-dimer levels were found. Vein wall stiffness was reduced 50% (P < 0.05), suggesting less biomechanical injury. The total vein wall MMP-9 was increased (P < 0.05) 5-fold in the AP group compared with controls, while MMP-2 was elevated but did not reach significance. No difference was found in vein wall tumor necrosis factor-alpha, tissue growth factor-beta, vein wall or thrombus monocytes, PMN, or uPA/PAI-1 ratio between groups.

DISCUSSION

AP inhibition of the plasmin system was associated with larger thrombi but less vein wall injury, but no difference in other measures of resolution, possibly because of increased vein wall MMP-9 activity. These data suggest an important redundant mechanism for DVT resolution.

Spectroscopic analysis on the effect of temperature on Kunitz domain 1 of human tissue factor pathway inhibitor-2

The conformation of Kunitz domain 1 of human tissue factor pathway inhibitor-2 (hTFPI-2/KD1) has been studied by fourier transform infrared spectroscopy, circular dichroism, and Raman spectroscopy. It was found that hTFPI-2/KD1 contained approximately 17% alpha-helices, 24% beta-strands, 46% random coils, 13% beta-turns, and two kinds of disulfide bonds(ggg and tgt) at 25 degrees C. The detailed conformational changes of the heated protein observed by fourier transform infrared spectroscopy, circular dichroism and Raman spectroscopy revealed that hTFPI-2/KD1 was thermally stable. However, KD1 could form an intermediate form at high temperature, then return to its normal conformation when the temperature was lowered. Activity assays also showed that hTFPI-2/KD1 was able to keep its inhibitory activity on plasmin after being heated to 80 degrees C for 5 min.

Immobilization of Aprotinin to Fibrinogen as a Novel Method for Controlling Degradation of Fibrin Gels

The goal of this work was to demonstrate that aprotinin conjugated to fibrinogen could (1) maintain its function and (2) control fibrin degradation. Using the chick chorioallantoic membrane (CAM) assay, we found that blood vessels did not directly invade fibrin constructs containing immobilized fibroblast growth factor-2. Because the fibrin quickly degraded within approximately 5 days, we hypothesized that controlling fibrinolysis may improve direct blood vessel invasion. Aprotinin, a protease inhibitor typically added to slow fibrinolysis, is a small protein and can diffuse out of the gel resulting in the loss of fibrinolysis protection. Therefore, using a novel synthesis strategy, aprotinin and a fluorescent reporter, Cy3, were chemically conjugated to fibrinogen. In vitro microplate absorbance assays showed that the conjugated aprotinin was able to inhibit plasmin-mediated fibrin degradation and that its activity was comparable to equimolar levels of soluble, nonconjugated aprotinin. Additionally, we found that fibrinolysis rates could be tuned by varying the level of conjugated aprotinin within the gel. The conjugated aprotinin also demonstrated functionality in vivo. In the chick CAM assay, fibrin gels containing conjugated aprotinin were approximately 5 times larger than gels containing soluble aprotinin after 4 days. Also, in support of our hypothesis, we found that immobilized aprotinin within fibrin gels demonstrated substantial blood vessel invasion.

Blood inhibitory capacity toward exogenous plasmin

Stabilized, active plasmin is a novel thrombolytic for direct delivery to clots. Although it is known that protease inhibitors in plasma inhibit plasmin, the amount of plasmin that can be added to plasma/blood before free plasmin is observed is not clear. Determination of free plasmin activity in plasma using chromogenic substrates represents a challenge due to false-positive signals from plasmin entrapped by alpha2-macroglobulin. Size-exclusion chromatography was used to separate the plasmin-alpha2-macroglobulin complex from uninhibited, free plasmin. In this in-vitro study, exogenous plasmin is effectively inhibited up to 2.4 micromol/l after 5-min incubation with plasma at 37 degrees C. Initially, plasmin was consumed predominantly by alpha2-antiplasmin up to 1.2 micromol/l plasmin. Following exhaustion of alpha2-antiplasmin, plasmin was further consumed by alpha2-macroglobulin up to 2.4 micromol/l plasmin added to human plasma. Whole human blood was found to have an increased inhibitory capacity over that of plasma; free plasmin activity could be measured only above 3.8 micromol/l added plasmin. In conclusion, several mechanisms exist that control plasmin activity in human blood; in addition to alpha2-antiplasmin and alpha2-macroglobulin, blood cells contribute to the inhibition of exogenously administered plasmin. These in-vitro results indicate that doses of plasmin up to approximately 12 mg/kg in humans can be completely inactivated by blood.

Hereditary angioedema: the clinical syndrome and its management in the United States

There have been important breakthroughs in the understanding and treatment of hereditary angioedema (HAE). An associated abnormality of the serum protein C1 inhibitor led to purified protein use to end attacks. Consideration of the endocrine functions led to rediscovery of impeded androgen use in disease prophylaxis. Considerations of pathophysiology led to introduction of epsilon aminocaproic and tranexemic acids in prophylaxis and to a resurgence in trials of new therapeutic agents. We have gone from a situation where it was not uncommon for patients to have a severe attack sometime in their lives that led to airway compromise and possible death to a situation where death from disease is highly unusual. Thus HAE is in many ways a success story of modern medicine.

Structure–activity studies of cyclic ketone inhibitors of the serine protease plasmin: Design, synthesis, and biological activity

Three series of cyclic ketone inhibitors were synthesized and evaluated against the serine protease plasmin. Peptide inhibitors that incorporated 3-oxotetrahydrofuran and 3-oxotetrahydrothiophene 1,1-dioxide groups had the highest activities. Alkylamino substituents, which were designed to bind in the S1 subsite of plasmin, were attached to the inhibitors. Compounds 5c and 5g, which incorporated 6-aminohexyl substituents, were found to be optimal and demonstrated IC(50) values in the low micromolar range. Incorporating conformationally constrained peptide segments into the inhibitors did not improve their activities.

Anti-annexin A2 IgM antibody in preterm infants: its association with chorioamnionitis

Intrauterine infection is associated with chorioamnionitis (CAM), which can lead to preterm delivery. We previously reported that the levels of IgM and the incidence of CAM were elevated in preterm infants with neonatal pulmonary emphysema. The pathogen and target of this IgM remain unclear. By using Western blot and amino acid sequences, we have determined one of the target proteins: annexin A2. Immunohistochemical analysis showed that annexin A2 was expressed at fetal chorion and amnion membranes. Among very low birth weight (VLBW) infants with hyper-IgM (> or = 30 mg/dL), 58.8% showed a high titer against annexin A2 (more than x 16), which accounted for about 20%-40% of the total IgM. Anti-annexin A2 IgM antibody inhibited plasmin generation. Furthermore, the median of anti-annexin A2 IgM titer from preterm infants who were delivered with high-grade (grade III) CAM was significantly higher than those from preterm infants without CAM (p = 0.011) and with low-grade CAM (grade I and II) (p = 0.010). Here, we indicate the fetal autoimmunoreactivity against the fetomaternal interface in preterm infants.

Methylketone inhibitors of plasmin

A series of peptide methylketones with generalformula Y-Phe-Lys-CH3 was prepared as potential inhibitors of plasmin.

Noninhibitory PAI-1 enhances plasmin-mediated matrix degradation both in vitro and in experimental nephritis

Plasminogen activator inhibitor-type 1 (PAI-1) is thought to be profibrotic by inhibiting plasmin generation, thereby decreasing turnover of pathological extracellular matrix (ECM). A mutant, noninhibitory PAI-1 (PAI-1R) was recently shown by us to increase glomerular plasmin generation and reduce disease in anti-thy-1 nephritis. Here, in vitro and in vivo studies were performed to determine whether enhanced plasmin-dependent ECM degradation underlies the therapeutic effect of PAI-1R. 3H-labeled ECM was produced by rat mesangial cells (MCs). The effect of wild-type PAI-1 (wt-PAI-1) and PAI-1R on ECM degradation by newly plated MCs was measured by the release of 3H into medium. In vivo, anti-thy-1 nephritis was assessed in normal, untreated diseased and PAI-1R treated rats with or without the plasmin/plasminogen inhibitor, tranexamic acid (TA). wt-PAI-1 totally inhibited plasmin generation and reduced ECM degradation by 76% when exogenous plasminogen was added. Although PAI-1R alone had no effect, PAI-1R in the presence of wt-PAI-1 reversed the wt-PAI-1 inhibition of ECM degradation in a time- and dose-dependent manner (P<0.001). Plasmin activity and zymography were consistent with ECM degradation. Plasmin inhibitors: alpha2-antiplasmin, aprotinin, and TA completely blocked PAI-1R's ability to normalize ECM degradation (P<0.001). Consistent with the in vitro results, TA reversed PAI-1R-induced reductions in glomerular fibrin and ECM accumulation. Other measures of disease severity were either unaltered or partially reversed. PAI-1R reduces pathological ECM accumulation, in large part through effectively competing with native PAI-1 thereby restoring plasmin generation and increasing plasmin-dependent degradation of matrix components.

Crystallization and preliminary X-ray analysis of a Kunitz-type inhibitor, textilinin-1 from Pseudonaja textilis textilis

Textilinin-1 (Txln-1), a Kunitz-type serine protease inhibitor, is a 59-amino-acid polypeptide isolated from the venom of the Australian Common Brown snake Pseudonaja textilis textilis. This molecule has been suggested as an alternative to aprotinin, also a Kunitz-type serine protease inhibitor, for use as an anti-bleeding agent in surgical procedures. Txln-1 shares only 47% amino-acid identity to aprotinin; however, six cysteine residues in the two peptides are in conserved locations. It is therefore expected that the overall fold of these molecules is similar but that they have contrasting surface features. Here, the crystallization of recombinant textilinin-1 (rTxln-1) as the free molecule and in complex with bovine trypsin (229 amino acids) is reported. Two organic solvents, phenol and 1,4-butanediol, were used as additives to facilitate the crystallization of free rTxln-1. Crystals of the rTxln-1-bovine trypsin complex diffracted to 2.0 angstroms resolution, while crystals of free rTxln-1 diffracted to 1.63 angstroms resolution.

Maspin retards cell detachment via a novel interaction with the urokinase-type plasminogen activator/urokinase-type plasminogen activator receptor system

It is well documented that tumor suppressive maspin inhibits tumor cell invasion and extracellular matrix remodeling. Maspin is a cytosolic, cell surface-associated, and secreted protein in the serine protease inhibitor superfamily. Although several molecules have been identified as candidate intracellular maspin targets, the extracellular maspin target(s) remains elusive. Although maspin does not directly inhibit urokinase-type plasminogen activator (uPA) activity, we have shown evidence that maspin may block the pericellular proteolysis mediated by cell surface-associated uPA. In the current study, maspin significantly inhibited the Ca2+ reduction-induced detachment of DU145 cells. This maspin effect was associated with increased and sustained levels of mature focal adhesion contacts (FAC). We noted that maspin (a) colocalized with uPA and uPA receptor (uPAR), (b) enhanced the interaction between uPAR and low-density lipoprotein receptor related protein, and (c) induced rapid internalization of uPA and uPAR. The maspin effects on surface-associated uPA and uPAR required the interaction between uPA and uPAR. Further biochemical and biophysical analyses revealed that maspin specifically bound to pro-uPA with a deduced K(d) of 270 nmol/L and inhibited the plasmin-mediated pro-uPA cleavage. Interestingly, substitution of maspin p1' site Arg340 in the reactive site loop (RSL) with alanine not only abolished the binding to pro-uPA but also diminished the maspin effects on pro-uPA cleavage and cell detachment. These data show an important role of maspin RSL in regulating the uPA/uPAR-dependent cell detachment. Together, our data led to a new hypothesis that maspin may stabilize mature FACs by quenching localized uPA/uPAR complex before uPA activation.

Comparison of Textilinin-1 with Aprotinin as Serine Protease Inhibitors and as Antifibrinolytic Agents

Textilinin-1 (Q8008) was isolated from the venom of the Pseudonaja textilis and has a 47% sequence identity to the antihaemorrhagic therapeutic agent aprotinin. When equimolar concentrations of enzyme and aprotinin were pre-incubated, plasmin was inhibited 100%, plasma kallikrein 58%, and tissue kallikrein 99%. Under the same conditions, textilinin-1 inhibited plasmin 98%, plasma kallikrein 16% and tissue kallikrein 17%. Whole blood clot lysis was inhibited strongly by both aprotinin and textilinin-1, as shown by thrombelastography. At 2 microM inhibitor lysis initiated by t-PA was greater than 99% inhibited by aprotinin (LY60 = 0.4 +/- 0.1) whereas textilinin-1, inhibited lysis by 91% (LY60 = 8.9 +/- 0.7). The same trend was found with the lysis of euglobulin fractions. From these data textilinin-1 appears to be a more specific plasmin inhibitor than aprotinin but aprotinin inhibits clot lysis to a greater extent.