Search PubMed⌕ Search

Biomedical subjects

D Collen

Publications and source records attributed to D Collen.

At least 559 records · Page 31Linked to original sources
PubMed1985

Pharmacokinetics and systemic fibrinogenolytic effects of recombinant human tissue-type plasminogen activator (rt-PA) in humans.

The pharmacokinetics of recombinant human tissue-type plasminogen activator (rt-PA) were studied in 20 subjects during and after its i.v. infusion at three different rates (5.6, 8.3, and 10 micrograms/kg/min). Steady-state plasma concentrations of 0.9 to 1.6 micrograms/ml were reached. The plasma disappearance curves of rt-PA (both antigen and activity) after cessation of infusion were approximated by a sum of two exponential terms and the turnover of rt-PA was represented by a two-compartment mammillary model with peripheral (liver) elimination. The fractional efflux rate constant from the central compartment was 0.10 per min and the fractional catabolic rate constant about 0.02 per min. After cessation of infusion the initial half-life of the drug in plasma was 6 min. Fibrinogen levels were measured by a clotting rate assay and by sodium sulfite precipitation. Infusion of rt-PA at 10 micrograms/kg/min for 30 min did not cause systemic fibrinogen breakdown. Infusion of 5.6 micrograms/kg/min for 90 min was associated with a decrease of fibrinogen to 62% of the preinfusion value (4.5 g/l) as measured with the clotting rate assay, but only 2% was recovered as incoagulable fibrinogen-fibrin degradation products. Infusion of 8.3 micrograms/kg/min for 90 min resulted in a decrease of fibrinogen to 45% of the preinfusion level (2.5 g/l) and generation of 8.5% fibrinogen-fibrin degradation products. Fibrinogen assays with the sodium sulfite method showed a much less extensive decrease of fibrinogen. This extent of systemic fibrinolytic activation and fibrinogen breakdown at high infusion rates and prolonged durations is compatible with that anticipated from the kinetic parameters of the activation of plasminogen by rt-PA.

Fibrin Fibrinogen Degradation Products↗
PubMed1984

In vitro fibrinolytic activity of recombinant tissue-type plasminogen activator in the plasma of various primate species.

The ratio of fibrinolytic to fibrinogenolytic effect of recombinant human tissue-type plasminogen activator was investigated at several concentrations in an in vitro system consisting of 125I-fibrin labeled autologous plasma clots immersed in the plasma of several different primate species. A concentration-dependent fibrinolysis was obtained in each case; however, the degree of fibrinolysis differed markedly from one primate species to the other. At a concentration of 30 IU/ml (300 ng/ml) of recombinant tissue-type plasminogen activator nearly complete thrombolysis was achieved within 4 hr in human plasma, in the chimpanzee, in the cynomolgus macaque, in the bonnet macaque and in the rhesus macaque. The common baboon, the olive baboon and the squirrel monkey were rather resistant to thrombolysis. In all species the thrombolysis achieved was not associated with fibrinogenolysis nor with significant decreases in plasminogen or alpha 2-antiplasmin.

Animals↗
PubMed1984

Influence of cyanogen-bromide-digested fibrinogen on the kinetics of plasminogen activation by urokinase.

The catalytic efficiency (kcat/Km) of high-molecular-mass urokinase for the activation of Glu-plasminogen is increased about 10-fold in the presence of CNBr-digested fibrinogen. This stimulation is similar to that observed with 6-aminohexanoic acid, and yields kinetic parameters comparable to those for the activation of Lys-plasminogen by urokinase. The increase of the activation rate of Glu-plasminogen by urokinase in the presence of CNBr-Fg can thus be explained by a conformational change in the plasminogen molecule similar to that observed upon conversion of Glu-plasminogen to Lys-plasminogen and upon binding of 6-aminohexanoic acid to Glu-plasminogen. Stabilization of the Michaelis complex between urokinase and plasminogen by formation of a cyclic ternary complex with CNBr-Fg, which has been invoked to explain the dramatic stimulatory effect of CNBr-Fg on the activation of plasminogen by tissue-type plasminogen activator, does not appear to play a significant role in the increased activation rate.

Cyanogen Bromide↗
PubMed1984

Biological and thrombolytic properties of proenzyme and active forms of human urokinase--I. Fibrinolytic and fibrinogenolytic properties in human plasma in vitro of urokinases obtained from human urine or by recombinant DNA technology.

The fibrinolytic and fibrinogenolytic properties of recombinant pro-urokinase (Rec-pro-UK) and recombinant urokinase (Rec-UK) obtained by expression of the human urokinase cDNA in E. coli, were compared with those of natural urokinase (Nat-UK) of urinary origin and of tissue-type plasminogen activator (t-PA) in a system, composed of a radioactive human plasma clot immersed in citrated human plasma. The specific fibrinolytic effects of Nat-UK, Rec-pro-UK and Rec-UK were very similar, causing significant clot lysis at concentrations of 100 IU/ml plasma or more. t-PA caused equivalent degrees of clot lysis at 10-fold lower concentrations. Activation of the fibrinolytic system in the plasma (fibrinogenolysis), was not observed with t-PA in concentrations which induced complete clot lysis within 5 hr (20-30 IU/ml plasma). With Nat-UK and Rec-UK, all concentrations which caused significant clot lysis (100-200 IU/ml plasma) also caused extensive activation of the plasma fibrinolytic system. With Rec-pro-UK an intermediate response was obtained. The highest amounts required for complete clot lysis in 5 hr (200 IU/ml plasma) also caused significant fibrinogenolysis. At intermediate concentrations (50-100 IU/ml), however, significant clot lysis (40-80%) was observed without systemic fibrinolytic activation.

DNA, Recombinant↗
PubMed1984

Biological and thrombolytic properties of proenzyme and active forms of human urokinase--II. Turnover of natural and recombinant urokinase in rabbits and squirrel monkeys.

The turnover of recombinant pro-urokinase (Rec-pro-UK), recombinant urokinase (Rec-UK) and natural urinary urokinase (Nat-UK) was studied in rabbits and in squirrel monkeys (Saimiri sciureus). Following intravenous injection, urokinase activity disappeared rapidly from the blood. The initial disappearance rate could be described by a single exponential term with a t 1/2 of 3 to 6 min for each molecular form of urokinase in both species. Urokinase related antigen, measured with a radioimmunoassay in the plasma of the squirrel monkeys disappeared with a t 1/2 of 3.5 min for Rec-pro-UK, 6.0 min for Rec-UK and 8.0 min for Nat-UK. The clearance and organ distribution of Rec-pro-UK, Rec-UK and Nat-UK was studied with the use of 125I-labeled preparations. In each case the radioactivity initially disappeared rapidly from the plasma, also with a t 1/2 of a few min, but then the disappearance rate slowed down. Labeled Rec-UK in which the active site histidine was irreversibly blocked by alkylation, disappeared equally rapidly from the plasma. Measurement of the organ distribution of 125I at different time intervals revealed that all three types of urokinase were rapidly accumulated in the liver, which was followed by release of degradation products in the blood. Experimental hepatectomy prolonged the t 1/2 of each type of urokinase very markedly (t 1/2 greater than 30 min). These findings indicate that urokinase is rapidly removed from the blood by clearance and degradation in the liver. Recognition by the liver does not require a functional active site and is not mediated via carbohydrate side chains. Inactivation by plasma protease inhibitors does not represent a significant pathway of urokinase inhibition in vivo.

Animals↗
PubMed1984

Biological and thrombolytic properties of proenzyme and active forms of human urokinase--IV. Variability in fibrinolytic response of plasma of several mammalian species.

The fibrinolytic and fibrinogenolytic properties of recombinant pro-urokinase (Rec-pro-UK) and recombinant urokinase (Rec-UK) were compared with those of natural urokinase (Nat-UK) and of tissue-type plasminogen activator (t-PA) in an in vitro system consisting of 125I-labeled autologous plasma clots immersed in plasma of humans, five primate species, dogs, rabbits and pigs. With each of the four plasminogen activators, a dose-dependent clot lysis was observed, the degree of which differed, however, very markedly from one species to the other. At a concentration of 100 IU/ml of urokinase extensive plasma clot lysis was obtained in plasma of man, Macaca mulatta, Macaca fascicularis and Macaca radiata, while the plasma clots of Papio cynocephalus, Papio anubis and rabbit, dog and pig were much more resistant to lysis. No significant differences in the extent of lysis were observed between Rec-pro-UK and Rec-UK nor between Rec-UK and Nat-UK. Comparable degrees of lysis were obtained with t-PA at 3- to 5-fold lower concentrations. Lysis with Rec-UK or Nat-UK was always associated with extensive activation of the fibrinolytic system in plasma, evidenced by fibrinogen breakdown and plasminogen activation and alpha 2-antiplasmin consumption. With t-PA, extensive clot lysis was obtained in the absence of fibrinolytic activation in the plasma. With Rec-pro-UK the response was intermediate; at high concentrations (200 IU/ml) extensive lysis in the reactive species was associated with fibrinogen consumption, while at intermediate concentrations (50-100 IU/ml) significant clot lysis was obtained in the reactive species in the absence of marked activation of the fibrinolytic system in the plasma.

Animals↗
PubMed1984

Biological and thrombolytic properties of proenzyme and active forms of human urokinase--III. Thrombolytic properties of natural and recombinant urokinase in rabbits with experimental jugular vein thrombosis.

The thrombolytic properties of recombinant pro-urokinase (Rec-pro-UK), recombinant active urokinase (Rec-UK) and natural urinary urokinase (Nat-UK) were compared with those of tissue-type plasminogen activator (t-PA) in rabbits with a radiolabeled thrombus in the jugular vein. The thrombolytic agents were infused intravenously over a time period of 4 hr and the extent of thrombolysis measured two hours later. In control animals the extent of thrombolysis was 11 +/- 2% (n = 8) after 6 hr. Nat-UK and Rec-UK had very similar thrombolytic properties. Significant thrombolysis was only obtained with infusion of 240,000 IU per kg (41 +/- 2%, n = 4 for Nat-UK and 37 +/- 4%, n = 4 for Rec-UK) and this was associated with a marked systemic activation of the fibrinolytic system, as evidenced by consumption of plasminogen and alpha 2-antiplasmin and fibrinogen breakdown. Infusion of Rec-pro-UK induced thrombolysis at a dose of 60,000 IU per kg (44 +/- 8%, n = 3) but without associated systemic activation of the fibrinolytic system. In this respect the properties of Rec-pro-UK were similar to those of t-PA, which, however, had a 2- to 4-fold higher specific thrombolytic activity (30,000 IU/kg yielding 48 +/- 1% lysis, n = 4). It is concluded that Rec-UK has very similar thrombolytic properties as Nat-UK and that Rec-pro-UK has a better thrombus-selectivity and less systemic side effects than the active enzymes.

Animals↗
PubMed1984

Influence of exogenous and endogenous tissue-type plasminogen activator on the lysability of clots in a plasma milieu in vitro.

The fibrinolytic potential of tissue-type plasminogen activator (t-PA) either incorporated in a clot (endogenous) or added to the surrounding plasma (exogenous), was studied in an in vitro system consisting of 125I-labeled human plasma clots (200 microliters) immersed in human plasma (2 ml). Clot lysis was measured as a function of endogenous t-PA concentration (in the absence of added exogenous t-PA), as a function of exogenous t-PA concentration (without added endogenous t-PA) and as a function of the same concentration of both endogenous and exogenous t-PA. Equivalent clot lysis was obtained with a 2 to 4 times lower concentration of endogenous t-PA as compared to exogenous t-PA, corresponding to a 20 to 40 times smaller total amount of endogenous versus exogenous t-PA. Fifty percent lysis in 5 hrs was obtained with about 5 IU/ml of endogenous t-PA or with 10 IU/ml of exogenous t-PA. The presence of both exogenous (10 IU/ml) and endogenous (5 IU/ml) t-PA resulted in 50 percent lysis in 1.5 hrs, indicating that t-PA incorporated in a thrombus contributes significantly to its lysis by exogenous t-PA. Similar results were obtained with plasma obtained after 10 min of venous occlusion in seven healthy subjects. Spontaneous clot lysis within 5 hrs was only observed with post-occlusion clots in pre- or post- occlusion plasma in two subjects in whom the t-PA level rose to 10-15 IU t-PA/ml. In the five other subjects with post-occlusion t-PA levels below 2 IU/ml, no clot lysis was observed within 24 hrs. The influence of the fast-acting inhibitor of t-PA on clot lysability by endogenous or exogenous t-PA was investigated by immersing clots prepared from normal or inhibitor-rich plasma (endogenous inhibitor) in normal or inhibitor-rich plasma (exogenous inhibitor). Exogenous t-PA inhibitor efficiently neutralizes clot lysis by both exogenous and endogenous t-PA. Endogenous t-PA inhibitor, however, efficiently neutralizes endogenous t-PA but has little influence on clot lysis by exogenous t-PA. These findings indicate that t-PA inhibitor is not concentrated into a clot and that t-PA inhibitor in plasma efficiently neutralizes t-PA incorporated in a clot. alpha 2-Antiplasmin depleted plasma clots were more susceptible to lysis by both endogenous and exogenous t-PA than normal clots.(ABSTRACT TRUNCATED AT 400 WORDS)

Fibrinolysis↗
PubMed1984

Inhibition of trypsin-like serine proteinases by tripeptide arginyl and lysyl chloromethylketones.

Tripeptide derivatives of lysyl or arginyl chloromethylketone inhibit the trypsin-like serine proteases trypsin, thrombin, plasmin, Factor Xa, urokinase, tissue-type plasminogen activator and protein Ca following the reaction scheme: (formula; see text) Extremely potent tripeptide inhibitors were obtained for thrombin and trypsin (k2/Ki greater than 10(6) M-1s-1), moderate inhibitors for plasmin and Factor Xa (10(6) M-1s-1 greater than k2/Ki greater than 10(4) M-1s-1) and only weak inhibitors for urokinase, tissue-type plasminogen activator and protein Ca (k2/Ki less than 10(4) M-1s-1). Thrombin and Factor Xa as well as urokinase and tissue-type plasminogen activator can be discriminated on the basis of their inhibitory spectrum towards some of these inhibitors.

Amino Acid Chloromethyl Ketones↗
PubMed1984

Involvement of heparin chain length in the heparin-catalyzed inhibition of thrombin by antithrombin III.

The mechanism of the heparin-promoted reaction of thrombin with antithrombin III was investigated by using covalent complexes of antithrombin III with either high-affinity heparin (Mr = 15,000) or heparin fragments having an average of 16 and 12 monosaccharide units (Mr = 4,300 and 3,200). The complexes inhibit thrombin in the manner of active site-directed, irreversible inhibitors: (Formula: see text) That is, the inhibition rate of the enzyme is saturable with respect to concentration of complexes. The values determined for Ki = (k-1 + k2)/k1 are 7 nM, 100 nM, and 6 microM when the Mr of the heparin moieties are 15,000, 4,300, 3,200, respectively, whereas k2 (2 S-1) is independent of the heparin chain length. The bimolecular rate constant k2/Ki for intact heparin is 3 X 10(8) M-1 S-1 and the corresponding second order rate constant k1 is 6.7 X 10(8) M-1 S-1, a value greater than that expected for a diffusion-controlled bimolecular reaction. The bimolecular rate constants for the complexes with heparin of Mr = 4,300 and 3,200 are, respectively, 2 X 10(7) M-1 S-1 and 3 X 10(5) M-1 S-1. Active site-blocked thrombin is an antagonist of covalent antithrombin III-heparin complexes: the effect is monophasic and half-maximum at 4 nM of antagonist against the complex with intact heparin, whereas the effect is weaker against complexes with heparin fragments and not monophasic. We conclude that virtually all of the activity of high affinity, high molecular weight heparin depends on binding both thrombin and antithrombin III to heparin, and that the exceptionally high activity of heparin results in part from the capacity of thrombin bound nonspecifically to heparin to diffuse in the dimension of the heparin chain towards bound antithrombin III. Increasing the chain length of heparin results in an increased reaction rate because of a higher probability of interaction between thrombin and heparin in solution.

Antithrombin III↗
PubMed1984

Histidine-rich glycoprotein modulates the anticoagulant activity of heparin in human plasma.

Addition of 0.05 IU of heparin per ml normal plasma prolongs its thrombin time from 20 to 27s , but that of plasma specifically depleted in histidine-rich glycoprotein (by immunoadsorption) from 20 to 180s . Reconstitution of the depleted plasma with normal plasma or with purified histidine-rich glycoprotein normalizes its thrombin time. In 54 plasma samples from hospitalized patients a significant negative correlation was found between the anticoagulant activity of heparin measured by thrombin inhibition and the plasma level of histidine-rich glycoprotein (r = 0.69). It is concluded that the level of histidine-rich glycoprotein modulates the anticoagulant activity of heparin in human plasma to an extent which appears to be pharmacologically and possibly clinically relevant.

Blood Coagulation↗
PubMed1984

Coronary thrombolysis with tissue-type plasminogen activator in patients with evolving myocardial infarction.

Tissue-type plasminogen activator is a naturally occurring, clot-selective activator of fibrinolysis. We recently reported that human tissue-type plasminogen activator isolated from a Bowes-melanoma-tissue-culture supernate lysed coronary thrombi in dogs without depleting circulating fibrinogen or alpha 2-antiplasmin, in contrast to the case with streptokinase and urokinase. In the present study coronary thrombolysis, confirmed angiographically, was induced within 19 to 50 minutes with intravenous or intracoronary tissue-type plasminogen activator in six of seven patients with evolving myocardial infarction. Circulating fibrinogen, plasminogen, and alpha 2-antiplasmin were not depleted by this agent, in contrast to the case in the two patients subsequently given streptokinase. In the one patient in whom lysis was not inducible with tissue-type plasminogen activator, it was also not inducible with streptokinase. These observations indicate that clot-selective coronary thrombolysis can be induced in patients with evolving myocardial infarction by means of tissue-type plasminogen activator, without concomitant induction of a systemic lytic state. Definition of its therapeutic benefit must await greater availability of the agent and the performance of appropriate clinical trials.

Aged↗
PubMed1984

Plasma levels of a specific inhibitor of tissue-type plasminogen activator (and urokinase) in normal and pathological conditions.

Rapid inhibition of tissue-type plasminogen activator (t-PA) in human plasma was measured by addition of 5 IU (50 ng) of purified t-PA per ml plasma and measurement of residual t-PA in the euglobulin precipitate after 5 min incubation at 37 degrees C. The recovery of both t-PA activity and t-PA related antigen in pooled plasma from healthy individuals was approximately 90 percent, indicating that one ml of pooled normal plasma inhibits less than 1 IU or 10 ng of t-PA within 5 min. Of 20 control subjects 13 had less than 1 IU inhibitor activity; 5 subjects inhibited between 1 and 3 IU of t-PA and 2 subjects inhibited around 4.5 IU. The inhibitor titer in the latter two had however decreased to 1.8 and 2.7 IU after two days. Markedly increased rapid inhibition of t-PA (greater than 4 IU per ml) was found in plasma of patients with severe liver disease (3 of 8), pancreatitis (4 of 8), malignancy (5 of 26), but only very occasionally and transiently in that of patients with myocardial infarction (5 of 28) or deep vein thrombosis (2 of 9). Increased inhibition was observed on the first day following coronary bypass (22 of 42) or open heart (16 of 27) surgery but this had disappeared in 15 of 16 patients on the fifth postoperative day. Titration of inhibitor levels revealed maximal amounts of 30 to 50 IU per ml plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Gel↗
PubMed1984

Effect of 24 hours of normoglycaemia on tissue-type plasminogen activator plasma levels in insulin-dependent diabetes.

We have previously demonstrated that a short period of normoglycaemia obtained through an artificial pancreas in uncontrolled insulin-dependent diabetics improves parameters of the functional microangiopathy such as erythrocyte deformability and platelet aggregation. Because recently an immunoradiometric assay for tissue plasminogen activator (t-PA) was developed we measured t-PA levels in 18 uncontrolled insulin-dependent diabetics before and after 24 hr of normoglycaemia induced by insulin to look for a modification of endothelial cells function. After 24 hr of strict control, plasma free insulin levels rose significantly, total t-PA R-Ag, its active fibrin binding fraction and euglobulin fibrinolytic activity were significantly decreased. These results suggest a responsibility for insulin in the decrease in t-PA blood level and could explain at least partially the relation between hyperinsulinism, thrombosis and atherogenesis.

Adolescent↗