Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.68 (tissue plasminogen activator)
 11,311 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tissue and urokinase-type plasminogen activators are serine proteases with highly restricted specificity, their best characterised role being to release the broad specificity protease plasmin from inactive plasminogen. It has frequently been suggested that these, and similar proteases, are involved in axonal growth and tissue remodelling associated with neural development. To help define what this role might be, we have studied the expression of the plasminogen activators in developing rat nervous tissue. Urokinase-type plasminogen activator mRNA is strongly expressed by many classes of neurons in peripheral and central nervous system. We have analysed its appearance in spinal cord and sensory ganglia, and found the mRNA is detectable by in situ hybridisation very early in neuronal development (by embryonic day 12.5), at a stage compatible with it playing a role in axonal or dendritic growth. Tissue plasminogen activator mRNA, on the other hand, is expressed only by cells of the floor plate in the developing nervous system, from embryonic day 10.5 and thereafter. Immunohistochemical and enzymatic analysis showed that active tissue plasminogen activator is produced by, and retained within, the floor plate. A mechanism is suggested by which high levels of tissue plasminogen activator produced by the stationary cells of the floor plate could influence the direction of growth of commissural axons as they pass through this midline structure.
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PMID:The expression of tissue and urokinase-type plasminogen activators in neural development suggests different modes of proteolytic involvement in neuronal growth. 128 56

Tissue plasminogen activator (t-PA) is an exceptional serine protease, because unlike most other serine protease zymogens single-chain tissue plasminogen activator (sct-PA) possesses a substantial amount of proteolytic activity. The unusual reaction of sct-PA afforded the opportunity to directly compare the active site environment of sct-PA and two-chain tissue plasminogen activator (tct-PA) in solution through the application of a series of nitroxide spin labels and fluorophores. These labels, which have been previously shown to covalently label the catalytic serine of other serine proteases, inactivated both sct-PA and tct-PA. The labels can be divided into two classes: those which form tetrahedral complexes (sulfonates) and those which form trigonal complexes (anthranilates). Those which formed tetrahedral complexes were found to be insensitive to structural differences between sct-PA and tct-PA at the active site. In contrast, those which formed trigonal complexes could differentiate and monitor the sct-PA to tct-PA conversion by fluorescence spectroscopy. Models of the structure of sct-PA and tct-PA were constructed on the basis of the known X-ray structures of other serine protease zymogen and active enzyme forms. One of the nitroxide spin labels was modeled into the sct-PA and tct-PA structures in two possible orientations, both of which could be sensitive to structural differences between sct-PA and tct-PA. These models formed the structural rationale used to explain the results obtained with the "tetrahedral" and "trigonal" probes, as well as to offer a possible explanation for the unique reactivity of sct-PA.
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PMID:Conformational similarities between one-chain and two-chain tissue plasminogen activator (t-PA): implications to the activation mechanism on one-chain t-PA. 131 51

A major adverse effect of recombinant human erythropoietin (r-HuEPO) in hemodialyzed patients are thrombotic events. Several reports on platelet function during r-HuEPO treatment have been published but less is known about fibrinolysis. In the present study, the fibrinolytic capacity was studied in 20 patients on maintenance hemodialysis and treated with r-HuEPO. The patients were randomized into two groups and investigated in a crossover design. r-HuEPO was administered intravenously and subcutaneously in each group and was given for 3 months, respectively. Plasma tissue plasminogen activator (t-PA) and released t-PA remained unaffected by r-HuEPO in both groups throughout the study. Tissue plasminogen activator inhibitor (PAI) increased in a cyclic way reaching peak values 4-6 weeks after the start of investigation and again 4-6 weeks after changing therapy. The increase in PAI was significant in the two groups (0.025 > p > 0.01). Tissue plasminogen antigen was low in the uremic patients. The influence of r-HuEPO on this parameter was not investigated. Compensatory changes in plasma levels of factor XII procoagulant activity, activated protein C and of alpha 2-antiplasmin were not observed. Thrombotic events occurred in 4 patients at peak values of PAI. Six patients required an increase in heparin dose simultaneously with the increase in PAI. Thus, r-HuEPO seemed to affect the fibrinolytic capacity of uremic patients.
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PMID:Fibrinolytic capacity in hemodialysis patients treated with recombinant human erythropoietin. 143 39

The fibrinolytic response after infusion of 1-deamino-8-d-arginine vasopressin (DDAVP) was examined in 4 patients with the severe form and 17 patients with the moderate form of Von Willebrand's disease (VWd) and compared to that of 9 normal subjects. Tissue plasminogen activator (t-PA) antigen (Ag) and activity and tissue plasminogen activator inhibitor (PAI) were measured before and after DDAVP. t-PA Ag was found to be significantly higher before DDAVP in patients than in controls. No release of t-PA Ag was observed in the 4 patients with the severe form of VWd but increased release was observed in patients with moderate forms. However, t-PA released into the circulation in these 17 patients had a lower functional activity as compared to that of normal subjects. PAI was significantly lower in patients before DDAVP than in normal subjects and the decrease in PAI after DDAVP was significantly less in patients than in controls. It is concluded from this study that patients with VWd have an abnormal fibrinolytic response after stimulation regardless of the severity of the disease. Furthermore, the results suggest either that patients with VWd have a double defect in VWF and tissue plasminogen activator or that the primary deficiency of VWF influences the synthesis and/or release of t-PA by endothelial cells.
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PMID:Impaired fibrinolytic response to DDAVP in patients with von Willebrand's disease. 152

We established that plasmin (10(-10) M to 10(-6) M) caused neutrophils (PMN) to aggregate using an in vitro assay. Plasminogen had no PMN aggregatory activity even at a concentration of 2 microM. However, plasminogen caused PMN to aggregate when incubated with plasminogen activators [tissue plasminogen activator (25-200 U/ml) or urokinase (5-500 U/ml)]. Tissue plasminogen activator and urokinase alone had no PMN aggregatory activity. Analysis of these incubation mixtures indicated that plasmin was generated in the process and that the time course of plasmin generation correlated with the aggregation response. Active-site-inhibited plasmin did not induce PMN aggregation, indicating that a functional catalytic site was required for the response. Pretreatment of PMN with either active-site-inhibited plasmin or tranexamic acid prevented PMN aggregation by plasmin, indicating that both binding of plasmin to the cell surface via the lysine binding sites and catalysis were required for the response. The generation of plasmin during activation of fibrinolysis may play a pro-inflammatory role by mediating aggregation of PMN.
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PMID:Plasmin generation induces neutrophil aggregation: dependence on the catalytic and lysine binding sites. 153 99

Fibronectin is a dimeric glycoprotein (Mr 440,000) involved in many adhesive processes. During blood coagulation it is bound and cross-linked to fibrin. Fibrin binding is achieved by structures (type I repeats) which are homologous to the "finger" domain of tissue plasminogen activator. Tissue plasminogen activator also binds to fibrin via the finger domain and additionally via the "kringle 2" domain. Fibrin binding of tissue plasminogen activator results in stimulation of its activity and plays a crucial role in fibrinolysis. Since fibronectin might interfere with this binding, we studied the effect of fibronectin on plasmin formation by tissue plasminogen activator. In the absence of fibrin, fibronectin had no effect on plasminogen activation. In the presence of stimulating fibrinogen fragment FCB-2, fibronectin increased the duration of the initial lag phase (= time period until maximally stimulated plasmin formation occurs) and decreased the rate of maximal plasmin formation which occurs after that lag phase mainly by increasing the Michaelis constant (Km). These effects of fibronectin were dose-dependent and were similar with single- and two-chain tissue plasminogen activator. They were also observed with plasmin-pretreated FCB-2. An apparent Ki of 43 micrograms/ml was calculated for the inhibitory effect of fibronectin when plasminogen activation by recombinant single-chain tissue plasminogen activator was studied in the presence of 91 micrograms/ml FCB-2. When a recombinant tissue plasminogen activator mutant lacking the finger domain was used in a system containing FCB-2, no effect of fibronectin was seen, indicating that the inhibitory effect of fibronectin might in fact be due to competition of fibronectin and tissue plasminogen activator for binding to fibrin(ogen) via the finger domain.
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PMID:Fibronectin decreases the stimulatory effect of fibrin and fibrinogen fragment FCB-2 on plasmin formation by tissue plasminogen activator. 182 40

Tissue plasminogen activator was used to evaluate the clearance of traumatic hyphema in a rabbit model. A neodymium-YAG laser was used to disrupt iris vessels, creating a traumatic hyphema. Tissue plasminogen activator (1800 IU/0.1 mL) was injected into the anterior chamber 24 hours after creation of the hyphema. Two control groups (one receiving balanced salt solution and one receiving no treatment) were used for comparison. A multivariate analysis of covariance indicated that the greatest difference in hyphema clearance between the groups occurred at days 3, 4, and 5. Five days after tissue plasminogen activator treatment, the mean size of the clot remaining in the anterior chamber was 27% of that of the original hyphema. In control eyes, almost 60% of the original clot remained at day 5. Treatment of animals with tissue plasminogen activator doses of 5000 IU and 10,000 IU produced a substantial increase in repeated bleeding episodes in our rabbit model. We concluded that although the use of tissue plasminogen activator in our rabbit model of traumatic hyphema significantly improved clearance of blood from the anterior chamber, the remaining clot was of such size that the clinical benefit was questionable.
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PMID:Intraocular tissue plasminogen activator in a rabbit model of traumatic hyphema. 189 62

Fifty-eight eyes of 31 anesthetized rabbits received one drop of proparacaine hydrochloride, 0.05%, and two drops of tissue plasminogen activator (tPA) separated by 5 minutes. Four eyes of two additional rabbits had epithelial defects created before drug delivery. Tissue plasminogen activator in multiple doses was given to eight eyes of four other rabbits. We used this dosing regimen to investigate the effect of topical tPA on anterior chamber fibrin clots in three rabbits. A two-site enzyme-linked immunosorbent assay test was used to measure tPA levels in the aqueous samples, obtained by paracentesis in each eye. Of 53 eyes treated with the original dosing regimen, 21 (40%) had detectable tPA aqueous levels. Blood and aqueous from eyes of untreated control rabbits, contralateral control eyes of treated rabbits, and eyes with epithelial defects had nondetectable tPA. Multiple tPA drop dosing resulted in 75% of aqueous samples with detectable tPA and a higher average tPA concentration than the original dosing regimen. Eyes treated with tPA showed a significantly faster resolution of anterior chamber fibrin clots than did control eyes.
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PMID:Intraocular penetration of topical tissue plasminogen activator. 190 62

The mechanisms leading to reduction of peritoneal fibrinolytic activity in conditions that are associated with the formation of intra-abdominal adhesions were studied. Tissue plasminogen activator was found, by antibody inhibition techniques, to be the activator of fibrinolysis in homogenates of control peritoneum (n = 6). Homogenates of control (n = 10) and inflamed peritoneum (n = 10) were analysed. Plasminogen activating activity was much lower in inflamed peritoneum (median 0.07 IU/cm2) than in control tissue (median 12.0 IU/cm2) (p less than 0.001). Levels of tissue plasminogen activator and alpha 2-antiplasmin were similar in both control and inflamed tissue. Plasminogen activator inhibitor-1, not detectable in control peritoneum, was present in inflamed tissue and might be the reason for the reduction in functional fibrinolytic activity.
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PMID:Peritoneal fibrinolytic activity and intra-abdominal adhesions. 197 64

We studied the dose-dependent retinal toxicity of the available commercial preparation of human recombinant tissue plasminogen activator in the normal rabbit eye. Tissue plasminogen activator was injected into the midvitreous cavity of albino rabbits in doses (per 100 microL) of 25, 50, 75, and 100 micrograms. Control eyes received 100 microL of balanced salt solution or tissue plasminogen activator vehicle. No evidence of a retinal toxic reaction was seen in eyes receiving 25 micrograms of tissue plasminogen activator. One of four eyes injected with 50 micrograms showed loss of photoreceptor cells by light microscopy. Severe retinal damage was seen by ophthalmoscopy, electroretinography, and light microscopy in three of four eyes receiving 75 micrograms of tissue plasminogen activator and in all eyes treated with 100 micrograms of tissue plasminogen activator or equivalent vehicle. These results suggest that the commercial recombinant tissue plasminogen activator formulation has a narrow margin of safety in nonvitrectomized eyes and that a component of the vehicle is the toxic factor.
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PMID:Retinal toxicity of recombinant tissue plasminogen activator in the rabbit. 210 12


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