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Biomedical subjects

G Nguyen

Publications and source records attributed to G Nguyen.

At least 55 records · Page 3Linked to original sources
PubMed1992

Characterization of the binding of plasminogen activators to plasma membranes from human liver.

The binding of tissue-type plasminogen activator (t-PA) to membranes prepared from human liver was investigated, and a specific, saturable, high-affinity binding site (Kd = 3.4 nM) was identified. The binding of t-PA to liver membranes was not affected by an excess of D-mannose or D-galactose, or by active urokinase (u-PA), whereas binding of t-PA to membranes prepared from human HepG2 hepatoma cells was inhibited by u-PA. HepG2-membrane-bound t-PA was fully complexed to PA inhibitor 1 (PAI-1), whereas liver-membrane-bound t-PA was not complexed. Gel filtration on Sephacryl S300 of membrane proteins solubilized in deoxycholate revealed that high-affinity t-PA binding activity elutes at an apparent molecular mass of 40 kDa. Monoclonal antibodies specific for the growth factor and the kringle 2 domains inhibited the binding of t-PA to liver membranes and the catabolism of t-PA by rat hepatoma cells. Human liver membranes also bound u-PA; binding was inhibited by pro-u-PA, the N-terminal fragment of u-PA, but not by the 33 kDa form of u-PA or by t-PA. Our results show that human liver membranes contain a specific 40 kDa binding protein for t-PA that is different from the PAI-1-dependent receptor described on HepG2 cells and the mannose receptor isolated from human liver.

Animals↗
PubMed1992

Transcriptional activation of the urokinase receptor gene by endothelin-1.

Using an immortalized human glomerular epithelial cell line (E71 A1), we studied the effect of endothelin-1 (ET-1), a potent vasoconstrictor peptide, on the synthesis of urokinase type plasminogen activator (u-PA) and its receptor (u-PAR). The results show that ET-1 had no effect on u-PA synthesis but induced an increase in u-PAR number (2.8 +/- 0.6 x 10(4) vs 1.2 +/- 0.5 x 10(4) sites per cell, p less than 0.001) without change in receptor affinity (280 +/- 80 pM vs 250 +/- 50 pM, NS), maximal effect being observed at 10(-7) M. Time course shows that a plateau was reached after a 24 hour incubation. ET-1 induced-increase in binding capacity was abolished by cycloheximide. ET-1 also induced an increase in u-PAR mRNA level, which was completely blocked by alpha-amanitin (5 micrograms/ml). Cycloheximide (1 microgram/ml) alone induced an increase in u-PAR mRNA level and this effect was enhanced when cycloheximide was combined with ET-1. Our data show that ET-1 can induce an increase in membrane expression of u-PAR through activation of the transcription of the u-PAR gene and de novo protein synthesis.

Amanitins↗
PubMed1992

Demonstration of a specific clearance receptor for tissue-type plasminogen activator on rat Novikoff hepatoma cells.

The binding, internalization, and degradation of tissue-type plasminogen activator (t-PA) were studied in a rat hepatoma (Novikoff) cell line. Binding of t-PA to specific saturable high affinity binding sites (Kd = 12 nM, 54,000 sites/cell) was followed by internalization and degradation and did not require a functional active site. The catabolism of t-PA was not inhibited by an excess of urokinase-type plasminogen activator (u-PA), and t-PA bound to Novikoff membranes was not complexed to PAI-1, suggesting a mechanism independent of PAI-1. Additionally, a mannose receptor is not involved since t-PA binding was not influenced by an excess of mannose, galactose, ovalbumin, or EDTA. Furthermore, the degradation of t-PA was not influenced by 10 mM 6-aminohexanoic acid, a lysine analogue. The t-PA receptor binds to and can be eluted from wheat germ agglutinin-Sepharose. Cross-linking of t-PA with partially purified receptor and ligand blot analysis, suggest that t-PA binds to two proteins, a principal one of 55 kDa and a minor one of 43 kDa. Novikoff cells are able also to bind (Kd = 1.4 nM, 25,000 sites/cell) and degrade u-PA. The binding was inhibited by pro-u-PA and the amino-terminal fragment of u-PA, but not by an excess of t-PA. The u-PA receptor, but not the t-PA receptor, was removed by treatment with phosphatidylinositol-specific phospholipase C. Our results show that the clearance receptor for t-PA on Novikoff cells is different from the mannose receptor and the PAI-1-dependent receptor described in other cells. The rat hepatoma cells are thus a good model to study the PAI-1 independent hepatocyte-specific clearance of t-PA.

Aminocaproic Acid↗
PubMed1992

[Role of hemostasis in the formation of crescents in extracapillary glomerulonephritis].

Extracapillary glomerulonephritis are associated with fibrin deposition in the urinary space of the glomerulus. Such deposits were correlated with the severity of the disease and with a poor renal outcome. Fibrin formation involves an activation of the coagulation cascade either through the intrinsic pathway, Hageman factor being activated by the altered glomerular basement membrane, either by the extrinsic pathway, infiltrating monocytes and glomerular cells exhibiting a procoagulant activity i.e. thromboplastin or tissue factor. Treatments with heparin or warfarin were shown to decrease the severity of experimental glomerular diseases. A similar beneficial effect was obtained with a monocyte-depleting serum and more recently with a treatment by a tissue type plasminogen activator. Glomerular cells also produce a fibrinolytic activity which could be too low or uneffective on extracapillary fibrin deposits if they contain high amounts of plasminogen activator inhibitors. Thrombin has procoagulant activity, antifibrinolytic activity and has cellular chemotactic and proliferative effects. It could play a major role in the pathogenesis of crescent formation.

Animals↗
PubMed1991

A lifelong bleeding disorder associated with a deficiency of plasminogen activator inhibitor type 1.

A 36-year-old patient was investigated for a lifelong history of epistaxis and delayed bleeding after minor surgeries. Deficiencies or abnormalities of the coagulation system, of platelet function, or of factor XIII and alpha-2-antiplasmin were excluded. Consistently, however, over a period of 7 years, a high basal euglobulin fibrinolytic activity was observed that was characterized by a high tissue-type plasminogen activator (t-PA) activity, normal t-PA antigen, and undetectable plasminogen activator inhibitor type-1 (PAI-1) antigen and activity. The high specific activity of t-PA (640,000 IU/mg) and the minimal amounts of t-PA/PAI-1 complexes detected by fibrin zymography suggest that in this patient all t-PA was active. This is in striking contrast to normal plasma, where the majority of t-PA is complexed to PAI-1. Thus, in this patient, a severe deficiency of PAI-1 is associated with a delayed type bleeding tendency. Our observation underscores the importance of plasma PAI-1 for the stabilization of the hemostatic plug.

Adult↗
PubMed1989

Immunoreactivity of tissue plasminogen activator and of its inhibitor complexes. Biochemical and multicenter validation of a two site immunosorbent assay.

An enzyme linked immunosorbent assay (ELISA) based on goat polyclonal antibodies against human tissue plasminogen activator (tPA) was evaluated. The relative immunoreactivity of tPA in free form and tPA in complex with inhibitors was estimated by ELISA and found to be 100, 74, 94, 92 and 81% for free tPA and tPA in complex with PAI-1, PAI-2, alpha 2-antiplasmin and C1-inhibitor, respectively. Addition of tPA to PAI-1 rich plasma resulted in rapid and total loss of tPA activity without detectable loss of ELISA response, indicating an immunoreactivity of tPA in tPA/PAI-1 complex of about 100%. Three different treatments of citrated plasma samples (acidification/reneutralization, addition of 5 mM EDTA or of 0.5 M lysine) prior to determination by ELISA all resulted in increased tPA levels. The fact that the increase was equally large in all three cases along with good analytical recovery of tPA added to plasma, supported the notion that all tPA antigen present in plasma samples is measured by the ELISA. Analysis by ELISA of fractions obtained by gel filtration of plasma from a patient undergoing tPA treatment identified tPA/inhibitor complexes and free tPA but no low molecular weight degradation products of tPA. Determinations of tPA antigen were made at seven French clinical laboratories on coded and randomized plasma samples with known tPA antigen content. For undiluted samples there was no significant difference between the tPA levels found and those known to be present. The between-assay coefficient of variation was 7 to 10%. In conclusion, the ELISA appeared suited for determination of total tPA antigen in human plasma samples.

Antigen-Antibody Reactions↗
PubMed1989

Long-acting propranolol in migraine prophylaxis: results of a double-blind, placebo-controlled study.

The efficacy and safety of long-acting propranolol (LA.P), 160 mg once-daily, in the prophylactic treatment of migraine have been tested against placebo in a multicentric, double-blind, randomized study. The two groups are compared in a parallel manner over a treatment period of 12 weeks, following a 4-week placebo run-in period. Fifty-five of the 74 patients who entered the trial were included at the end of the run-in period. Forty-one patients completed the study. None of the 14 patients who withdrew from the study did so because of side effects. The statistical analysis was done according to the "intention to treat" principle. LA.P was significantly more effective than placebo in reducing the frequency of migraine attacks (p = 0.01 by variance analysis). LA.P reduced the average number of monthly crises by 48% on day 84. There was a slight but significant reduction of the systolic blood pressure and heart rate in the erect position, but there was no significant difference between LA.P and placebo regarding either the number of complaints or the number of side effects elicited out of a 17-item questionnaire. None of the observed side effects led to a withdrawal from treatment.

Adult↗
PubMed1989

[AL amyloidosis and primary fibrinolysis. Study of the mechanism of fibrinolysis].

A 45 years old woman with AL amyloidosis presented with a hypofibrinogenemia (fibrinogen 100 mg/dl) without severe bleeding. There was laboratory evidence of fibrinolysis with shortened euglobulin lysis time, decreased alpha-2 plasmin inhibitor and decreased plasminogen. The mechanism of this primary fibrinolysis remains unclear, since there is no enhancement of the tissue-type plasminogen activator. Analysis of the 8 cases related in the literature of excessive fibrinolysis associated with amyloidosis demonstrated improvement of bleeding manifestations and abnormal fibrinolysis following the administration of antifibrinolytic agents.

Amyloid↗
PubMed1988

Comparison of thrombolytic, fibrinolytic, and fibrinogenolytic properties of tissue plasminogen activator, streptokinase, single-chain urokinase, high molecular weight and low molecular weight urokinase in human plasma in vitro.

Thrombolytic, fibrinolytic, and fibrinogenolytic properties of tissue plasminogen activator (t-PA) from melanoma cells (mt-PA), recombinant t-PA (rt-PA), streptokinase (SK), single-chain urokinase plasminogen activator (scu-PA), and high and low molecular weight urokinase (HMW UK, LMW UK) were compared in vitro by means of systems using human plasma. Thrombolytic activities were tested on standard or labeled hanging clots. When compared on the basis of urokinase international units, t-PA appeared to be slightly more active than scu-PA and streptokinase, and about 10-fold more active than both preparations of UK when they were diluted in plasma. Fibrinolytic activity was evaluated by measuring the lysis time of recalcified plasma containing variable amounts of thrombolytic agents. t-PA was shown to be twice as active as HMW UK, which was itself more active than LMW UK. When scu-PA and both types of UK were compared on bovine fibrin plates, they showed similar fibrinolytic activity, but the t-PA calibration curve was not parallel to those obtained with UK and scu-PA. Relative thrombolytic and fibrinogenolytic properties were studied for each thrombolytic agent. For similar thrombolytic activities, fibrinogenolysis provoked by scu-PA was less marked than with t-PA and with both UK, while SK showed the highest activity. Our results demonstrate that the thrombolytic/fibrinogenolytic ratio is much more favorable to t-PA and scu-PA than to both forms of UK. Another observation clearly shows that fibrinogenolysis can be induced in vitro in human plasma by high doses of t-PA. This consequence may be important since the therapeutic use of t-PA can be associated with high concentrations of t-PA, and thus t-PA infusion could lead in vivo to severe fibrinogen breakdown. In addition, the methodology described could be useful in standardizing comparison between different species of thrombolytic agents.

Fibrinogen↗
PubMed1988

Residual plasminogen activator inhibitor activity after venous stasis as a criterion for hypofibrinolysis: a study in 83 patients with confirmed deep vein thrombosis.

In eighty-three patients with confirmed deep vein thrombosis, the fibrinolytic system was studied before and after a 10-minute venous occlusion. Blood was collected at least 3 months after the last acute episode, and PAI-1 antigen and activity, as well as tissue-type plasminogen activator (t-PA) antigen, urokinase-type plasminogen activator (u-PA) antigen, and fibrinolytic activity were measured in these samples. During venous stasis, plasminogen activator inhibitor (PAI) activity decreased in almost all patients (81 of 83), from a median value of 8.2 to 2.9 U/mL (P less than .001, Wilcoxon signed-rank test). Because PAI-1 antigen augmented from a median value of 16 to 19.2 ng/mL (P less than .001), the decline in PAI activity was attributed to an increase in t-PA antigen from a median value of 10 to 21.7 ng/mL (P less than .001). Neutralization of PAI activity thus reflects the patient's capacity to overcome basal inhibitory potential through t-PA release. Based on residual PAI activity after 10-minute stasis, patients were classified as good or bad responders (PAI activity below detection limit, ie, less than or equal to 1.0 and greater than 1.0 U/ml, respectively). Good responders had a significantly higher fibrinolytic response after stasis than bad responders (median euglobulin clot lysis time 60 v 180 minutes; dilute whole blood clot lysis time 60 v 120 minutes; fibrinolytic activity on fibrin plates 7.7 v 0 U/mL). Furthermore, good responders, as compared with bad responders, had higher t-PA release (median 16.5 v 11.5 ng/mL), lower basal PAI activity (median 4.8 v 11.2 U/mL), and lower basal PAI-1 (median 11 v 21 ng/mL) and u-PA antigen (median 7.9 v 9.0 ng/mL, P less than .02). Hypofibrinolysis, as defined by the inability of released t-PA to overcome PAI-1 basal inhibitory potential, was observed in 45 of 83 patients (54%) and resulted either from an insufficient release of t-PA or from an increased basal PAI activity.

Adult↗
PubMed1987

Biological study of intravenous anisoylated plasminogen streptokinase activator complex in acute myocardial infarction.

An anisoylated plasminogen streptokinase activator complex (APSAC) has been administered as a bolus intravenous injection of 30U to 14 patients with acute myocardial infarction. Systemic effects on coagulation and fibrinolysis were studied. In 1 patient, the treatment produced no biological modification, which could be explained by an increased streptokinase resistance in this patient, apparent from the sample collected before treatment. In the other patients, as expected, fibrinogen, plasminogen, alpha 2-antiplasmin and factors V and VIIIc fell dramatically, while there was an increase in serum fibrinogen degradation product concentrations. In addition, plasma fibrin derivatives increased during APSAC therapy, both in patients who had occluded or patent coronary arteries. Discrepancies were found between methods used to measure fibrinogen: with the Ellis and Stransky method, concentrations were higher than with the Clauss method; and for plasminogen, automated methods using different analysers may give higher results in some patients.

Adult↗
PubMed1987

[New thrombolytic agents].

Tissue Plasminogen Activator (t-PA), Single Chain Urokinase Plasminogen Activator or pro-Urokinase (scu-PA or pro-UK) and acyl enzymes are new thrombolytic agents, characterized by a high fibrin affinity, so that they provoke only mild systemic fibrinolytic effect. Their infusion would allie good thrombolytic activity and reduced hemorragic risks, usually related to fibrinogen and others coagulation factors degradation t-PA and scu-PA are natural, physiological substances, obtained by recombinant DNA technology. t-PA infusion in acute myocardial infusion (AMI) has been shown to be at least as efficient than intracoronary Streptokinase (SK) administration, but fibrinogenolysis was much lower as compared to SK. In vitro studies have shown that scu-PA was an efficient thrombolytic agent and has a relative fibrin specificity, at least as similar to t-PA, but much superior to classical Urokinase. The acyl-enzyme APSAC or Eminase is a SK-plasminogen complex in which the proteolytic site has been inactivated with an anisoic-acid. This acyl enzyme has a longer half-life than t-PA and scu-PA, and can be injected as a bolus. Its administration in AMI have shown that APSAC is as effective as SK, but can also provoke severe fibrinogenolysis. These 3 agents seem to have similar thrombolytic activities on coronary thrombi. However, further studies are required to evaluate the bleeding incidence and coronary reocclusion rates associated with their utilisation.

Acylation↗
PubMed1986

[Tissue plasminogen activator (t-PA) in myocardial infarction. Biological aspects].

A group of 37 patients with myocardial infarction less than 6 hours old was given 5,000 IU of heparin and 0.75 mg/kg of tissue plasminogen activator (rt-PA) (Group A, N = 18) or placebo (Group B, N = 19) intravenously over 90 minutes in a double blind study. Blood sampling was performed before, during and after treatment. The plasma rt-PA concentrations (micrograms/ml) of Group A were as follows: (Table: see text) The concentrations of plasminogen and antiplasmin have decreased significantly as did the fibrinogen level: a concentration of 1 g/l was observed in 7 cases during rt-PA therapy, lasting for 4 to 8 hours after the end of the infusion of rt-PA in 3 cases. The increase of FDP during rt-PA (m = 551 and 222 micrograms/ml at the 60th and 90th minutes) was relatively moderate considering the average level of defibrination (61%). No significant biological changes were observed in Group B. These results support those of our in vitro trials: at comparable thrombolytic activities, the reduction of plasma fibrinogen is less with rt-PA than with streptokinase (SK) or urokinase (UK). However, at concentrations 1 microgram/ml, rt-PA causes almost complete defibrination.

Double-Blind Method↗