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)

Approximately 10 in 100,000 persons suffer rupture of a saccular intracranial aneurysm annually, and roughly 60% of these will survive the initial catastrophe in reasonable neurological condition. Of the many ensuing complications of aneurysmal subarachnoid hemorrhage, the most frustrating continues to be a form of delayed-onset cerebral arterial narrowing known as vasospasm. Because it is caused by thick subarachnoid blood clots coating the adventitial surface of cerebral arteries, the distribution and severity of vasospasm correlates closely with location and volume of subarachnoid hematoma as visualized on computed tomography (CT). Critical vasospasm causes cerebral ischemia and infarction: the "second stroke." It is now know that vasospasm represents sustained arterial contraction rather than structural thickening of the vessel wall with lumen encroachment. A large body of evidence points to oxyhemoglobin, released from lysing erythrocytes, as the principal component of blood clot responsible for this contraction. The precise mechanism by which oxyhemoglobin causes prolonged vascular smooth muscle cell constriction has not yet been established, but possibilities include secondary generation of vasoactive free radicals, lipid peroxides, eicosanoids, bilirubin, and endothelin. Vasospasm treatments are directed at preventing or reversing arterial narrowing, or at preventing or reversing cerebral ischemia. Several treatments from the latter category, namely, hypertensive, hypervolemic hemodilutional therapy and the calcium channel blocker nimodipine, have proven moderately effective and are in widespread clinical use. It has also been possible to mechanically dilate vasospastic vessels with transluminal angioplasty improving cerebral blood flow to ischemic brain. However we are still in need of an effective agent to prevent arterial narrowing, and several hopeful candidates in this category of treatment are clot lytic agent tissue plasminogen activator (rt-PA) and an inhibitor of iron-dependent peroxidation, 21-aminosteroid U74006F (tirilazad mesylate).
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PMID:Current concepts of pathophysiology and management of cerebral vasospasm following aneurysmal subarachnoid hemorrhage. 177 40

The study was undertaken to evaluate the effect of antifibrinolytic agents (epsilon-aminocaproic acid, EACA; tranexamic acid, AMCA), anti-inflammatory drugs (indomethacin, IND; ibuprofen, IBU; naproxen, NAP) and root extract of the plant Boerhaavia diffusa (BD) on menstrual cycle length (MCL), duration of menstrual flow (DMF), menstrual iron loss (MIL) and activity of uterine tissue plasminogen activator (tPA) in IUD-fitted monkeys. Premature onset of menstruation was observed in IUD-fitted monkeys (26.0 +/- 0.7 days, mean +/- SE) as compared to controls (28.7 +/- 0.4 days). No noteworthy change was observed in the MCL of drug treated monkeys as compared to IUD-fitted monkeys. An increase of 155%, 123.2%, and 288% was observed in the DMF, MIL and tPA activity after IUD insertion as compared to controls. Antifibrinolytic agents reduced the DMF, MIL and activity of tPA in IUD-fitted monkeys up to 117.4%, 116.4%, and 254%, whereas anti-inflammatory drugs caused a decrease only up to 69%, 95.1%, and 138%, respectively. Conclusively, root extract of B. diffusa treated IUD-fitted monkeys showed noticeable reduction in their DMF (124%), MIL (120.8%) and tPA activity (272%).
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PMID:Management of IUD-associated menorrhagia in female rhesus monkeys (Macaca mulatta). 190 76

The effect of anoxia and reoxygenation on the synthesis and secretion of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) was studied in primary cultures of human umbilical vein endothelial cells. Sublethal anoxia, determined by trypan blue dye exclusion and lactate dehydrogenase release, was produced by cell culture under a 95% N2, 5% CO2 atmosphere for 2-24 h and was followed by reoxygenation with 95% air, 5% CO2 for 24 or 48 h. Anoxia did not alter the levels of mRNA for t-PA or PAI-1 in the cells or the secretion of t-PA or PAI-1 into the medium. At 24 h, t-PA secreted into conditioned medium was 7.0 +/- 1.4 ng/2 x 10(6) cells (n = 9) and PAI-1 was 300 +/- 13 IU/2 x 10(6) cells (n = 9), whereas the content of t-PA mRNA was 2.2 pg/micrograms of RNA and PAI-1 mRNA was 180 pg/micrograms of RNA. During reoxygenation, however, t-PA antigen and PAI-1 activity as well as mRNA for PAI-1 decreased proportionally to the duration of anoxia, to reach 27 +/- 1.0, 49 +/- 2.0, and 47 +/- 14% of control values, respectively, within 24 h of anoxia. t-PA mRNA also decreased significantly during reoxygenation following anoxia, but the extent could not be accurately quantitated. Addition, during anoxia, of a 200 micrograms/ml concentration of the superoxide anion radical scavenger superoxide dismutase or of a 5 mM concentration of the iron chelator deferoxamine mesylate prevented the subsequent decrease of t-PA antigen during reoxygenation; addition of these compounds during reoxygenation had no effect. Superoxide dismutase, but not deferoxamine mesylate, when added during anoxia prevented the subsequent decrease in PAI-1 activity. These studies suggest that the marked alteration of endothelial cell fibrinolysis during anoxia followed by reoxygenation is most likely mediated by a mechanism dependent on oxygen radicals. Impaired endothelial cell fibrinolysis may contribute to the pathophysiology of ischemia/reperfusion injury.
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PMID:Oxygen radicals generated during anoxia followed by reoxygenation reduce the synthesis of tissue-type plasminogen activator and plasminogen activator inhibitor-1 in human endothelial cell culture. 212 75

In addition to new knowledge concerning the mechanisms whereby conventional risk factors act, other risk factors have been newly described, such as dietary antioxidants, lack of exercise, insulin resistance, excess iron stores, increased plasma angiotensin-converting enzyme, and left ventricular hypertrophy. An intact endothelium protects both by the formation of nitric oxide, which is a vasodilator and also an inhibitor of platelet aggregation and neutrophil adhesion, and by manufacturing tissue plasminogen activator. The acute thrombotic event occurs with a diurnal variation but may be precipitated by acute exertion, especially in untrained individuals, and reflects a balance between vasoconstrictory and vasodilatory stimuli from the vascular endothelium, as well as procoagulant versus anticoagulant effects of complex balancing systems. Increased risk of sudden cardiac death in the morning is thought to be a reflection of transient risk factors, such as a blood pressure increase, heart rate increase, and changes in coagulation factors, as well as changes in platelet aggregation. There is an apparent paradox between the acute effect of exercise in promoting sudden cardiac death and the chronic effect of exercise training in decreasing the risk of myocardial infarction. The explanation may be that chronic exercise training has an inhibitory effect on adrenergic discharge.
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PMID:New concepts regarding events that lead to myocardial infarction. 856 63

There are a number of therapies available to recanalize occluded arteries. However, even though proven beneficial, these approaches are not without significant shortcomings. Previous research showed that by encapsulating therapeutic thrombolytic enzymes in liposomic formulations, the reperfusion times in vivo were significantly lower than for administration of free thrombolytic. Like liposomes, biodegradable, diblock polymers of poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) have been shown to have therapeutic benefit as delivery vehicles for a variety of drug delivery concepts. We report on new formulations based on tissue plasminogen activator (tPA) encapsulated in magnetic, PLA-PEG microcarriers. We studied the tPA encapsulation efficiency, loading, and release after varying the molecular weight of polymer, carrier size, tPA solution composition, and use of ultrasound to enhance release. We loaded 3.3-9.4wt% tPA and 12-17wt% magnetite into the carriers, depending on the exact formulation. The release of tPA was complete 20min after reconstitution. Ultrasound insonation failed to enhance tPA release rates in smaller carriers but significantly enhanced release in larger carriers. With these formulations, we should be able to achieve lytic concentrations if we can magnetically concentrate 5mg of carrier within about 11ml of blood volume near the clot.
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PMID:Encapsulation and release of plasminogen activator from biodegradable magnetic microcarriers. 1864 39

We investigated the feasibility and efficacy of target thrombolysis with recombinant tissue plasminogen activator (rtPA) covalently bound to magnetic nanoparticle (MNP) and retained to the target site in vivo by an external magnet. Polyacrylic acid-coated magnetite (PAA-MNP, 246 nm) was synthesized and characterized; rtPA was immobilized to PAA-MNP through carbodiimide-mediated amide bond formation. The enzyme activities of the bound rtPA, as measured by a chromogenic substrate assay and (125)I-fibrinolysis assay, were 87+/-1% and 86+/-3% of that of free rtPA. Under guidance with the magnet moving back and forth along the iliac artery, the thrombolytic activity of PAA-MNP-rtPA with rtPA equivalent to 0.2mg/kg was determined by flowmetry in a rat embolic model. Intra-arterial administration of PAA-MNP-rtPA restored the iliac blood flow within 75 min to 82% of that before the clot lodging, whereas equivalent amount of PAA-MNP or free rtPA exerted no improvement on hemodynamics. At the end of 2-h period, PAA-MNP-rtPA did not alter levels of hemoglobin, hematocrit, or blood cell count. In conclusion, immobilization of rtPA to PAA-MNP with covalent binding resulted in a stable rtPA preparation and predictable amount of rtPA around the target site under magnetic guidance; this approach may achieve reproducible and effective target thrombolysis with <20% of a regular dose of rtPA.
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PMID:Magnetically targeted thrombolysis with recombinant tissue plasminogen activator bound to polyacrylic acid-coated nanoparticles. 1929 10

The effect of different cell culture conditions on N-glycosylation site-occupancy has been elucidated for two different recombinant glycoproteins expressed in Chinese hamster ovary (CHO) cells, recombinant human tissue plasminogen activator (t-PA) and a recombinant enzyme (glycoprotein 2-GP2). Both molecules contain a N-glycosylation site that is variably occupied. Different environmental factors that affect the site-occupancy (the degree of occupied sites) of these molecules were identified. Supplementing the culture medium with additional manganese or iron increased the fraction of fully occupied t-PA (type I t-PA) by approximately 2.5-4%. Decreasing the cultivation temperature from 37 to 33 degrees C or 31 degrees C gradually increased site-occupancy of t-PA up to 4%. The addition of a specific productivity enhancer, butyrate, further increased site-occupancy by an additional 1% under each cultivation temperature tested. In addition, the thyroid hormones triiodothyronine and thyroxine increased site-occupancy of t-PA compared to control conditions by about 2%. In contrast, the addition of relevant nucleoside precursor molecules involved in N-glycan biosynthesis (e.g., uridine, guanosine, mannose) either had no effect or slightly reduced site-occupancy. For the recombinant enzyme (GP2), it was discovered that culture pH and the timing of butyrate addition can be used to control N-glycan site-occupancy within a specific range. An increase in culture pH correlated with a decrease in site-occupancy. Similarly, delaying the timing for butyrate addition also decreased site-occupancy of this molecule. These results highlight the importance of understanding how cell culture conditions and media components can affect the product quality of recombinant glycoproteins expressed in mammalian cell cultures. Furthermore, the identification of relevant factors will enable one to control product quality attributes, specifically N-glycan site-occupancy, within a specific range when applied appropriately.
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PMID:Identification of cell culture conditions to control N-glycosylation site-occupancy of recombinant glycoproteins expressed in CHO cells. 1941 65

Following treatment with bleomycin- and cisplatin-containing chemotherapy, testicular cancer patients frequently develop vascular complications, which may result from damage to endothelial cells. Understanding bleomycin- and cisplatin-induced endothelial alterations may help to develop strategies to prevent or reduce vascular toxicity. The effects of bleomycin and cisplatin on proliferation and apoptosis of the human dermal microvascular endothelial cell line HMEC-1 were determined. In addition, modulation of drug-induced cytotoxicity by the free radical scavenger amifostine, the low molecular weight heparin dalteparin, the iron-chelator dexrazoxane, the HMG-CoA reductase inhibitor rosuvastatin and the PPAR agonist troglitazone was tested. Furthermore, the effects of bleomycin and cisplatin on endothelial activation measured by the expression of the intercellular adhesion molecule-1 (ICAM-1) and on two main proteins involved in fibrinolysis, tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor type 1 (PAI-1), were measured. Decreased endothelial cell survival induced by bleomycin and cisplatin coincided with the induction of apoptosis. Only troglitazone was able to protect the endothelial cells from both bleomycin- and cisplatin-induced cytotoxicity. At high concentrations, amifostine and dexrazoxane also protected HMEC-1 from drug-induced cytotoxicity. However, due to the required high (toxic) concentrations of both modulators no absolute cell survival benefit could be achieved. Both bleomycin and cisplatin induced up-regulation of ICAM-1, tPA and PAI-1. Summarizing, bleomycin and cisplatin induce alterations in the function of endothelial cells regarding proliferation, inflammation and fibrinolysis in vitro. Strategies aimed at these functions should be developed in order to ameliorate or prevent cytostatic agent-induced vascular damage.
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PMID:Vascular damage in testicular cancer patients: a study on endothelial activation by bleomycin and cisplatin in vitro. 1995 89

Implant-assisted targeting of magnetic particles under the influence of an external magnetic field has previously been verified through mathematical modeling, in vitro studies, and in vivo studies on rat carotid arteries as a feasible method for localized drug delivery. The present study focuses on the development of nanoparticles for the treatment of in-stent thrombosis. Magnetic nanoparticles in the size-range 10-30 nm were synthesized in a one-pot procedure by precipitation of ferrous hydroxide followed by oxidation to magnetite. The nanoparticles were silanized with tetraethyl orthosilicate in the presence of triethylene glycol and/or polyethylene glycol. The surface coated magnetite nanoparticles were activated with either N-hydroxysulfosuccinimide or tresyl chloride for covalent immobilization of tissue plasminogen activator (tPA). Hysteresis loops showed saturation magnetizations of 55.8, 44.1, and 43.0 emu/g for the naked nanoparticles, the surface coated nanoparticles, and the tPA-nanoparticle conjugates, respectively. The hemolytic activity of the nanoparticles in blood was negligible. An initial in vivo biocompatibility test in pig, carried out by intravascular injection of the nanoparticles in a stented brachial artery, showed no short-term adverse effects. In vitro evaluation in a flow-through model proved that the nanoparticles were captured efficiently to the surface of a ferromagnetic coiled wire at the fluid velocities typical for human arteries. A preliminary test of the tPA-nanoparticle conjugates in a pig model suggested that the conjugates may be used for treatment of in-stent thrombosis in coronary arteries.
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PMID:The use of magnetite nanoparticles for implant-assisted magnetic drug targeting in thrombolytic therapy. 2073 12

Venous thrombus is subsequently organized and replaced by fibrous connective tissue. However, the sequential changes in venous thrombi are not reliably detected by current noninvasive diagnostic techniques. The purpose of this study is to reveal whether magnetic resonance (MR) can detect venous thrombus, define thrombus age and predict thrombolytic responses. Thrombus in the rabbit jugular vein was imaged with a 1.5-T MR system at 4 h and at 1, 2 and 4 weeks using three-dimensional (3D) fast asymmetric spin echo T2-weighted (T2W) and 3D-gradient echo T1-weighted (T1W) sequences. The jugular veins were histologically assessed at each time point. Magnetic resonance imaging (MRI) was also performed in vivo before and 30 min after tissue plasminogen activator (t-PA) administration. The thrombi in MRI were comparable in size to histological sections. The signal intensity (SI) of thrombi at 4 h was heterogeneously high or low on T2W or T1W images, respectively. The SI of thrombi on T2W images decreased time-dependently, but increased on T1W images at 1 and 2 weeks. Morphological analysis showed time-dependent decreases in erythrocyte, platelet and fibrin areas and time-dependent increases in smooth muscle cell, macrophage, collagen and iron areas. The t-PA administration significantly decreased thrombus volume at 4 h but not at 1, 2 and 4 weeks. Venous thrombosis can be reliably and noninvasively detected by MRI. Measurement of SI might support assessments of thrombus age and thrombolytic response.
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PMID:MR signal change in venous thrombus relates organizing process and thrombolytic response in rabbit. 2164 43


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