Half-life of single-chain urokinase-type plasminogen activator (scu-PA) and two-chain urokinase-type plasminogen activator (tcu-PA) in patients with acute myocardial infarction

Can components of the plasminogen activation system predict the outcome of kidney transplants?

Proteolytic and antiproteolytic enzymes play a critical role in the physiology and pathology of different stages of human life. One of the important members of the proteolytic family is the plasminogen activation system (PAS), which includes several elements crucial for this review: the 50 kDa glycoprotein plasminogen activator inhibitor 1 (PAI-1) that inhibits tissue-type (tPA) and urokinase-type plasminogen activator (uPA). These two convert plasminogen into its active form named plasmin that can lyse a broad spectrum of proteins. Urokinase receptor (uPAR) is the binding site of uPA. This glycoprotein on the cell surface facilitates urokinase activation of plasminogen, creating high proteolytic activity close to the cell surface. PAS activities have been reported to predict the outcome of kidney transplants. However, reports on expression of PAS in kidney transplants seem to be controversial. On the one hand there are reports that impaired proteolytic activity leads to induction of chronic allograft nephropathy, while on the other hand treatment with uPA and tPA can restore function of acute renal transplants. In this comprehensive review we describe the complexity of the PAS as well as biological effects of the PAS on renal allografts, and provide a possible explanation of the reported controversy.

A chimeric platelet-targeted urokinase prodrug selectively blocks new thrombus formation

The use of fibrinolytic agents to prevent new thrombus formation is limited by an increased risk of bleeding due to lysis of hemostatic clots that prevent hemorrhage in damaged blood vessels. We sought to develop an agent that provides thromboprophylaxis without carrying a significant risk of causing systemic fibrinolysis or disrupting hemostatic clots. We previously showed that platelet (PLT) α granule-delivered urokinase plasminogen activator (uPA) is highly effective in preventing thrombosis, while being associated with little systemic fibrinolysis or bleeding. Here, we generated a chimeric prodrug composed of a single-chain version of the variable region of an anti-αIIbβ3 mAb fused to a thrombin-activatable, low-molecular-weight pro-uPA (PLT/uPA-T). PLT/uPA-T recognizes human αIIbβ3 on both quiescent and activated platelets and is enzymatically activated specifically by thrombin. We found that this prodrug binds tightly to human platelets even after gel filtration, has a prolonged half-life in mice transgenic for human αIIb compared with that of uPA-T, and prevents clot formation in a microfluidic system. Importantly, in two murine injury models, PLT/uPA-T did not lyse preexisting clots, even when administration was delayed by as little as 10 minutes, while it concurrently prevented the development of nascent thrombi. Thus, PLT/uPA-T represents the prototype of a platelet-targeted thromboprophylactic agent that selectively targets nascent over preexisting thrombi.

Bioactive protein fraction DLBS1033 containing lumbrokinase isolated from Lumbricus rubellus: ex vivo, in vivo, and pharmaceutic studies

DLBS1033 is a bioactive protein fraction isolated from Lumbricus rubellus that tends to be unstable when exposed to the gastrointestinal environment. Accordingly, appropriate pharmaceutical development is needed to maximize absorption of the protein fraction in the gastrointestinal tract. In vitro, ex vivo, and in vivo stability assays were performed to study the stability of the bioactive protein fraction in gastric conditions. The bioactive protein fraction DLBS1033 was found to be unstable at low pH and in gastric fluid. The "enteric coating" formulation showed no leakage in gastric fluid-like medium and possessed a good release profile in simulated intestinal medium. DLBS1033 was absorbed through the small intestine in an intact protein form, confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) analysis. This result confirmed that an enteric coating formula using methacrylic acid copolymer could protect DLBS1033 from the acidic condition of the stomach by preventing the release of DLBS1033 in the stomach, while promoting its release when reaching the intestine. From the blood concentration-versus-time curve, (99m)Tc-DLBS1033 showed a circulation half-life of 70 minutes. This relatively long biological half-life supports its function as a thrombolytic protein. Thus, an enteric delivery system is considered the best approach for DLBS1033 as an oral thrombolytic agent.

Pharmacokinetics and tissue distribution of a novel marine fibrinolytic compound in Wistar rat following intravenous administrations

We investigated a novel marine fibrinolytic compound for use in thrombolytic therapy. Pharmacokinetics and the tissue distribution of this novel marine fibrinolytic compound, FGFC1(2) (fungi fibrinolytic compound 1), were investigated in Wistar rats after intravenous (IV) bolus administration of two concentrations (10 and 20mg/kg). Plasma FGFC1 and tissue extracts were measured using HPLC with UV detection. FGFC1 was detected using a C18 column with a gradient eluted mobile phase of acetonitrile-water (0.1% trifluoroacetic acid), 1.0mL/min. Chromatograms were monitored at 265nm (column temperature: 40°C). Pharmacokinetic data indicate that FGFC1 fitted well to a two-compartment model. Elimination half-lives (t1/2) of FGFC1 were 21.51±2.17 and 23.22±2.11min for 10 and 20mg/kg, respectively. AUC0-t were 412.19±19.09, 899.09±35.86μg/mLmin, systemic clearance (CL) was 0.023±0.002, 0.022±0.002 ((mg/kg)/(μg/mL)/min) and the mean residence time (MRT) was 10.15±0.97, 9.65±1.40min at 10 and 20mg/kg, respectively. No significant differences were observed in the systemic clearance and mean residence time at the tested doses, suggesting linear pharmacokinetics in rats. Tissue distribution data reveal that FGFC1 distributed rapidly in most tissues except the brain and that the highest concentration of the drug was in the liver. In the small intestine, FGFC1 initially increased and then declined, but remained comparatively high 60min after administration, suggesting that enterohepatic circulation may exist.

Plasmin triggers a switch-like decrease in thrombospondin-dependent activation of TGF-β1

Transforming growth factor-β1 (TGF-β1) is a potent regulator of extracellular matrix production, wound healing, differentiation, and immune response, and is implicated in the progression of fibrotic diseases and cancer. Extracellular activation of TGF-β1 from its latent form provides spatiotemporal control over TGF-β1 signaling, but the current understanding of TGF-β1 activation does not emphasize cross talk between activators. Plasmin (PLS) and thrombospondin-1 (TSP1) have been studied individually as activators of TGF-β1, and in this work we used a systems-level approach with mathematical modeling and in vitro experiments to study the interplay between PLS and TSP1 in TGF-β1 activation. Simulations and steady-state analysis predicted a switch-like bistable transition between two levels of active TGF-β1, with an inverse correlation between PLS and TSP1. In particular, the model predicted that increasing PLS breaks a TSP1-TGF-β1 positive feedback loop and causes an unexpected net decrease in TGF-β1 activation. To test these predictions in vitro, we treated rat hepatocytes and hepatic stellate cells with PLS, which caused proteolytic cleavage of TSP1 and decreased activation of TGF-β1. The TGF-β1 activation levels showed a cooperative dose response, and a test of hysteresis in the cocultured cells validated that TGF-β1 activation is bistable. We conclude that switch-like behavior arises from natural competition between two distinct modes of TGF-β1 activation: a TSP1-mediated mode of high activation and a PLS-mediated mode of low activation. This switch suggests an explanation for the unexpected effects of the plasminogen activation system on TGF-β1 in fibrotic diseases in vivo, as well as novel prognostic and therapeutic approaches for diseases with TGF-β dysregulation.

Serine-proteases as plasminogen activators in terms of fibrinolysis

OBJECTIVES

This review should give an overview about the natural human plasminogen activators and their various modified variants as well as similar substances isolated from animals, microorganisms and plants. When a blood clot is formed in a blood vessel, it avoids the oxygen supply of the surrounding tissue. A fast fibrinolytic therapy should redissolve the blood vessel and reduce the degradation of the tissue. All proteases that are part of the human blood coagulation and fibrinolytic system belong to the serine protease family. t-PA (tissue plasminogen activator) and u-PA (urokinase plasminogen activator) are the naturally occurring fibrinolytic agents that are also used in therapy.

KEY FINDINGS

Despite many years of research, t-PA is still the gold standard in fibrinolytic therapy. But it has to be given as an infusion, which needs time. Modified fibrinolytic substances are, were, or perhaps will be in the market. They have different advantages over t-PA, but often the disadvantages predominate.

CONCLUSION

Many substances have been developed but an optimal fibrinolytic agent combined with a simple administration is not in therapeutic use to date.

Steady states and dynamics of urokinase-mediated plasmin activation in silico and in vitro

Plasmin (PLS) and urokinase-type plasminogen activator (UPA) are ubiquitous proteases that regulate the extracellular environment. Although they are secreted in inactive forms, they can activate each other through proteolytic cleavage. This mutual interplay creates the potential for complex dynamics, which we investigated using mathematical modeling and in vitro experiments. We constructed ordinary differential equations to model the conversion of precursor plasminogen into active PLS, and precursor urokinase (scUPA) into active urokinase (tcUPA). Although neither PLS nor UPA exhibits allosteric cooperativity, modeling showed that cooperativity occurred at the system level because of substrate competition. Computational simulations and bifurcation analysis predicted that the system would be bistable over a range of parameters for cooperativity and positive feedback. Cell-free experiments with recombinant proteins tested key predictions of the model. PLS activation in response to scUPA stimulus was found to be cooperative in vitro. Finally, bistability was demonstrated in vitro by the presence of two significantly different steady-state levels of PLS activation for the same levels of stimulus. We conclude that ultrasensitive, bistable activation of UPA-PLS is possible in the presence of substrate competition. An ultrasensitive threshold for activation of PLS and UPA would have ramifications for normal and disease processes, including angiogenesis, metastasis, wound healing, and fibrosis.

Evaluation of a pediatric protocol of intrapleural urokinase for pleural empyema: a prospective study

BACKGROUND

Intrapleural urokinase has been shown to be effective in the treatment of pleural effusions in children. However, optimal dosing in children is debated. The aim of this study was to prospectively evaluate a specific pediatric protocol of intrapleural urokinase.

METHODS

All children admitted to a single institution over a 6-year period with a diagnosis of pleural empyema were managed with chest tube and fibrinolytics. Clinical data were collected prospectively. Urokinase (56,000 IU in 56 mL saline/m(2) body surface) was administered twice daily, and was continued until resolution of the effusion. Further operative treatment was considered if urokinase treatment was unsuccessful after >/=3 days. Results are shown as median values (interquartile range).

RESULTS

Forty-one consecutive children aged 4.4 (3.2-6.9) years were included in the study, and received 420,000 (280,000-750,000) IU of urokinase over 7 (4-8) days. Suction through the chest drain was applied for 8 (6-10) days, and IV antibiotics were discontinued after 12 (10-15) days from the start of intrapleural fibrinolytics. Four children (9.8%) required 5 additional operative procedures (3 thoracoscopic debridements and 2 minithoracotomic debridements). Patients were discharged after 13 (11-16) days from the beginning of intrapleural urokinase. No major side effects attributable to urokinase were observed.

CONCLUSION

Intrapleural instillation of urokinase according to a specific pediatric protocol results in a high success rate when applied as a primary treatment in children with pleural empyema. Administration of a size-adjusted dose of urokinase proved to be safe and could optimize drug utilization.

Thrombolysis for intravascular thrombosis in neonates and children

PURPOSE OF REVIEW

Plasminogen activators stimulate the fibrinolytic pathway to accelerate thrombus resolution and can be used to treat serious and life-threatening arterial and venous thrombosis in neonates and children. The main disadvantage of these drugs is the risk of bleeding associated with their use. This article reviews the fibrinolytic pathway and discusses the current agents available for thrombolytic therapy, as well as indications for their use, dosing regimens, safety, and efficacy.

RECENT FINDINGS

There is great variation in the drug dosing regimens used for thrombolysis and in the incidence of bleeding complications that have been reported in pediatric series. Increased experience with these drugs, appropriate patient selection, and careful monitoring appear to have reduced the risk of major bleeding over time. The use of thrombolysis for occlusive deep vein thrombosis, in attempt to reduce the long-term complication of postthrombotic syndrome, is controversial and deserves further investigation.

SUMMARY

The use of thrombolytic therapy in pediatrics has increased over the past two decades. Urokinase and recombinant tissue plasminogen activator are the currently available thrombolytic agents. Catheter-related arterial thrombi that threaten life, organ or limb are the most common indication for their use. There is a tremendous need for well designed clinical studies to improve the safety and efficacy of these drugs in neonates and children.

Thrombolytic therapy in children

Thrombolysis is increasingly considered a treatment option in newborns and children with arterial and venous thromboembolic events, or occluded central venous lines. However, no uniform recommendations are available with regard to indications, drug of choice, route of administration, and dosing regimen. Thus, several protocols are used for the different thrombolytic agents, leading to differing outcome with respect to the effectiveness of therapy and bleeding complications. This article will summarize the available information on the use of thrombolytic agents in newborns and children, focussing on the potential indications, efficacy and safety profiles, and evidence supporting dosing schedules.

Are alterations in plasma protease concentrations during labor associated with poor obstetric outcomes?

OBJECTIVE

The purpose of this study was to assess the association between abnormal connective tissue remodeling during labor as reflected by plasma concentrations of extracellular matrix remodeling proteolytic enzymes and adverse obstetric outcomes.

STUDY DESIGN

A prospective observational study of 176 nulliparous women who attended the antenatal clinics at the Mercy Hospital for Women (Melbourne, Australia) from 1999 to 2000.

RESULTS

Patients with a prolonged second stage (>120 minutes) had a significantly increased plasma concentration of matrix metalloproteinase 9 after delivery compared with control subjects (P<.001); patients in labor who underwent an emergency caesarean delivery had a significantly lower concentration (P<.001). Patients with a prolonged duration of labor (>11 hours) had a significantly lower urokinase plasminogen activator plasma concentration compared with control subjects (P<.01).

CONCLUSION

Altered plasma concentrations of extracellular matrix remodeling proteolytic enzymes, matrix metalloproteinase 9, and urokinase plasminogen activator were found to be associated with abnormal labor and delivery outcomes. This finding may provide a useful predictor of abnormal obstetric outcomes.

Engineering design of optimal strategies for blood clot dissolution

Blood clots form under hemodynamic conditions and can obstruct flow during angina, acute myocardial infarction, stroke, deep vein thrombosis, pulmonary embolism, peripheral thrombosis, or dialysis access graft thrombosis. Therapies to remove these clots through enzymatic and/or mechanical approaches require consideration of the biochemistry and structure of blood clots in conjunction with local transport phenomena. Because blood clots are porous objects exposed to local hemodynamic forces, pressure-driven interstitial permeation often controls drug penetration and the overall lysis rate of an occlusive thrombus. Reaction engineering and transport phenomena provide a framework to relate dosage of a given agent to potential outcomes. The design and testing of thrombolytic agents and the design of therapies must account for (a) the binding, catalytic, and systemic clearance properties of the therapeutic enzyme; (b) the dose and delivery regimen; (c) the biochemical and structural aspects of the thrombotic occlusion; (d) the prevailing hemodynamics and anatomical location of the thrombus; and (e) therapeutic constraints and risks of side effects. These principles also impact the design and analysis of local delivery devices.

Modulation of plasminogen activation and plasmin activity by methylglyoxal modification of the zymogen

The effect of methylglyoxal on the plasminogen-plasmin system is studied. Treatment of plasminogen with methylglyoxal at a 20-fold molar excess results in covalent modification of the molecule as evidenced by the decreased number of NH(2) side chains, arginine side chain residues and the new band in the non-tryptophan dependent fluorescent spectrum. This structural modification is associated with profound functional alterations: the rate of activation by streptokinase, tissue-type plasminogen activator, urokinase-type plasminogen activator and trypsin decreases and the amidolytic activity of the generated plasmin is impaired. Plasmin treatment with methylglyoxal on the other hand does not alter its steady-state kinetic parameters on a peptidyl-anilide synthetic substrate, indicating that modification susceptible side chains are sensitive to methylglyoxal only in the zymogen. Our data suggest that in vivo fibrinolysis could be impaired under pathological conditions, e.g. increased methylglyoxal formation in diabetes mellitus.

Comparison of double bolus urokinase versus front-loaded alteplase regimen for acute myocardial infarction. Thrombolysis in Myocardial Infarction in Korea (TIMIKO) study group

This study was performed to compare the double bolus urokinase regimen with the front-loaded alteplase regimen for acute myocardial infarction. Double bolus urokinase is an easy, safe, and effective thrombolytic regimen with comparable results to standard front-loaded alteplase in acute myocardial infarction.

Plasmin induces the formation of multicellular spheroids of breast cancer cells

MCF7 and ZR75-1 breast cancer cells grow as adherent monolayers in tissue culture. Treatment with the serum serine protease plasmin causes them to detach and to grow as floating multicellular spheroids. Two plasmin activators, urokinase plasminogen activator and streptokinase, induce the same growth pattern changes in the presence of plasminogen. Serum contains also plasminogen activator inhibitors. Aged serum, deficient in plasminogen activator inhibitors, converts spontaneously monolayer breast cancer cells into multicellular spheroids which readily revert to monolayer growth after addition of fresh serum. Urokinase blocks the reversion. The formation of multicellular spheroids does not affect the proliferative rate of breast tumor cells but endows tumor cells with increased resistance to the chemotherapeutic drugs, doxorubicin and paclitaxel.

Urokinase does not upregulate the vascular endothelial cell-mediated inflammatory response

PURPOSE

Urokinase is used clinically for thrombolysis, but little is known of its direct effect on vascular endothelial cells. The following experiments were preformed to assess the in vitro effects of urokinase on vascular endothelial cell growth, adhesion molecule expression, and interaction with lymphocytes, polymorphonuclear leukocytes, and platelets.

METHODS

Commercially available human umbilical vein endothelial cells (HUVEC) were cultured with varying concentrations of urokinase (0 to 10,000 IU/ml) (clinical dosage, < or = 500 IU/ml). HUVEC viability was determined from 1 to 4 days. HUVECs were incubated with urokinase (0 to 2000 IU/ml) from 4 to 72 hours. Adherence of 51-chromium-labeled polymorphonuclear leukocytes, platelets, or lymphocytes was then quantitated. In separate experiments HUVEC adhesion molecule expression (intercellular adhesion molecule-1, vascular cell adhesion molecule-1, or endothelial leukocyte adhesion molecule-1) was determined by flow cytometry.

RESULTS

There was a decrease of HUVEC viability at suprapharmacologic urokinase concentrations of > or = 2000 IU/ml compared with nontreated control samples (0 IU/ml, 73% +/- 2%, 2000 IU/ml, 60.5% +/- 1.9%, p < 0.05) presumably because of drug toxicity. There was no significantly increased polymorphonuclear leukocyte, lymphocyte, or platelet adhesion to urokinase-treated HUVEC monolayes at any time point. This was also true for each adhesion molecule tested.

CONCLUSIONS

Urokinase at clinically relevant concentrations (< or = 500 IU/ml) did not affect endothelial cell viability or growth, nor did it upregulate adhesion molecule expression or cellular adhesion associated with the cell vascular inflammatory response. It is therefore implied that the use of urokinase in vivo similarly would not initiate the vascular inflammatory response.

Computer simulation of systemic circulation and clot lysis dynamics during thrombolytic therapy that accounts for inner clot transport and reaction

BACKGROUND

We developed a computer model to predict lysis rates of thrombi for intravenous thrombolytic regimens based on the convective/diffusive penetration of reacting and adsorbing fibrinolytic species from the circulation into the proximal face of a dissolving clot.

METHODS AND RESULTS

Solution of a one-compartment plasma model provided the dynamic concentrations of fibrinolytic species that served as inlet conditions for stimulation of the one-dimensional spatiodynamics within a dissolving fibrin clot of defined composition. The model predicted the circulating levels of tissue plasminogen activator (TPA) and plasminogen levels found in clinical trials for various intravenous therapies. To test the model predictions under in vitro conditions, plasma clots were perfused with TPA (0.1 mumol/L) and plasminogen (1.0 mumol/L) delivered at constant permeation velocity of 0.1 or 0.2 mm/min. The model provided an accurate prediction of the measured lysis front movement. For TPA administration regimens used clinically, simulations predicted clot dissolution rates that were consistent with observed reperfusion times. For unidirectional permeation, the continual accumulation of adsorbing species at the moving lysis front due to prior rounds of solubilization and rebinding was predicted to provide for a marked concentration of TPA and plasmin and the eventual depletion of antiplasmin and macroglobulin in an advancing (approximately 0.25 mm thick) lysis zone.

CONCLUSIONS

Pressure-driven permeation greatly enhances and is a primary determinant of the overall rate of clot lysis and creates a complex local reaction environment at the plasma/clot interface. With simulation of reaction and transport, it becomes possible to quantitatively link the administration regimen, plasminogena activator properties, and thrombolytic outcome.

Fibrinolytic effects of pro-urokinase combined with low-dose urokinase compared to high-dose urokinase in patients with acute myocardial infarction

20 patients (6 females, 14 males) aged between 47 and and 75 years (mean: 62.6 yrs.) with acute myocardial infarction (onset of symptoms within 6 hours) were treated intravenously with either 200,000 U urokinase (UK) and 4.5 million U pro-urokinase (pro-UK) within 60 min (group I, N = 10), or 2.5 million U UK within 5 min (group II, N = 10). Blood samples for haemostatic and fibrinolytic function tests were taken prior to and repeatedly during the 24 hours following treatment. Peak fibrinolytic activity measured by fibrin plates was equivalent in both regimens. Average decreases, with lowest levels within 60 to 120 min following thrombolytic therapy, were observed of 27% and 70% for plasminogen, of 71% and 91% for alpha-2-antiplasmin, and of 20% and 74% for fibrinogen in group I and II, respectively. The reptilase time reached maximum values of 1.5- and 4.5-fold within 60 to 180 min. Peak levels of D-dimers and thrombin-antithrombin III complexes in group II were 2.6 and 3.2 times those of group I. After 24 hours, in contrast to group I, all these parameters still remained significantly different from pretreatment values in group II. These data indicate that, contrary to high-dose UK, pro-UK in combination with low-dose UK causes minor systemic fibrinolytic effects and is, therefore, assumed to be largely clot-specific, although the fibrinolytic potential is equivalent for both regimens.