Single-bolus injection of recombinant tissue-type plasminogen activator in acute myocardial infarction

Recombinant tissue-type plasminogen activator (rt-PA) has hitherto been administered in acute myocardial infarction as an intravenous infusion with an initial bolus of about 10% of the total dose, both due to its short half-life and to avoid possible early reocclusions. A single-bolus dose would simplify the therapeutic regimen. Therefore, 20 patients with symptom duration of 125 +/- 58 minutes were given a single bolus of 50 mg of rt-PA over 2 minutes. Coronary angiography 60 minutes after the rt-PA bolus revealed a patent infarct-related artery in 15 of 20 patients (patency rate 75%, 95% confidence limits 51 to 91%). In the remaining patients, reperfusion was achieved by coronary angioplasty and intracoronary fibrinolysis; in 2 patients coronary artery bypass grafting was necessary. Control angiograms at 24 hours showed reocclusions in 4 of 18 patients. One woman died due to an intracranial hemorrhage 48 hours after the rt-PA bolus injection. Circulating fibrinogen decreased from 2.7 +/- 0.5 to 1.5 +/- 0.9 g/liter after 2 to 4 hours and reached the initial value within 24 hours. Pharmacokinetic parameters were obtained in 7 patients by measuring rt-PA antigen levels in multiple plasma samples. Mean peak rt-PA concentration was 9.8 +/- 3.6 micrograms/ml, total plasma clearance 476 +/- 148 ml/min and dominant half-life 4.8 +/- 1.0 minutes. Thus, rt-PA administered as a 50-mg single bolus appears to provide similar patency rates and shows similar kinetics in comparison with the conventional infusion regimen. Assessment of the incidence of bleeding complications requires further studies.

Pharmacokinetics and systemic effects of tissue-type plasminogen activator in normal subjects

Pharmacokinetics and systemic effects of recombinant tissue-type plasminogen activator (rt-PA) were studied in 18 healthy male volunteers after 30-minute intravenous infusions of placebo, 0.25 mg/kg rt-PA, and 0.5 mg/kg rt-PA. Highly comparable pharmacokinetic parameters were obtained after analysis of rt-PA as both an antigen and an activity. Mean clearance (antigen) was 620 +/- 70 (SD) ml/min, volume of distribution at steady state was 8.1 +/- 0.8 L, initial volume of distribution was 4.4 +/- 0.6 L, and dominant half-life was 4.4 +/- 0.3 minutes. The pharmacokinetics of rt-PA were linear, showed low interindividual variation, and are compatible with rapid hepatic elimination of the protein. Systemic plasminogen activation was minimal as assessed by hemostatic assays of plasma samples treated with anti-rt-PA Immunoglobulin G (IgG) to inhibit in vitro fibrinogenolysis. Circulating fibrinogen levels, clotting times, and coagulation factors were unchanged; plasminogen and alpha 2-antiplasmin decreased maximally to 85% and 65% of baseline values, respectively. The data are consistent with the fibrin specificity of t-PA, which is derived from its role in physiologic fibrinolysis.

Pharmacokinetic and pharmacodynamic studies in man simulating acute and chronic treatment with oral pirenzepine

Nine healthy, male subjects received controlled-rate i.v. infusions of a new formulation of pirenzepine to produce constant plasma levels of 40 ng/ml and 105 ng/ml. They also received stepped infusions resulting in plasma levels of 20, 40, 80 and 40 ng/ml for defined periods. Peptone-stimulated gastric acid and volume secretion and near point vision decreased dose dependently, whereas gastric acidity was unchanged. There was a significant correlation between inhibition of gastric acid secretion and the pirenzepine concentration in plasma and in gastric juice. During the stepped i.v. infusion, changes in near point vision were closely related to the plasma drug concentration. Antimuscarinic side-effects occurred more frequently when the plasma drug level was high. Overall, there was a close relationship between the plasma concentrations and the effects and side-effects of pirenzepine. Its gastric inhibitory action was characterized only by a reduction in gastric volume secretion. Increasing plasma concentrations during the first days of treatment may be essential for its efficacy as an antiulcer drug.

Pharmacokinetics and haemostatic status during consecutive infusions of recombinant tissue-type plasminogen activator in patients with acute myocardial infarction

Pharmacokinetics and systemic effects of recombinant tissue-type plasminogen activator (rt-PA) were determined during coronary thrombolysis in 12 acute myocardial infarction patients using a consecutive intravenous infusion regimen. Ten mg rt-PA were infused in 2 minutes resulting in a peak plasma concentration (mean +/- SD) of 3310 +/- 950 ng/ml, followed by 50 mg in 1 h and 30 mg in 1.5 h yielding steady state plasma levels of 2210 +/- 470 ng/ml and 930 +/- 200 ng/ml, respectively. All patients received intravenous heparin. Total clearance of rt-PA was 380 +/- 74 ml/min, t1/2 alpha was 3.6 +/- 0.9 min and t1/2 beta was 16 +/- 5.4 min. After 90 min, in plasma samples containing anti-rt-PA-IgG to inhibit in vitro effects, fibrinogen was decreased to 54%, plasminogen to 52%, alpha 2-antiplasmin to 25%, alpha 2-macroglobulin to 90% and antithrombin III to 85% of initial values. Coagulation times were prolonged and fibrin D-dimer concentrations increased from 0.40 to 2.7 micrograms/ml. It is concluded that pharmacokinetics of rt-PA show low interpatient variability and that its short mean residence time in plasma allows precise control of therapy. Apart from its moderate effect on the haemostatic system, rt-PA appears to lyse a fibrin pool in addition to the coronary thrombus.

Die molekularbiologischen Eigenschaften des Gewebetyp-Plasminogenaktivators und seiner Varianten

Der Gewebetyp-Plasminogenaktivator (t-PA) ist ein Schlüsselenzym der physiologischen Fibrinolyse und steht heute auch als rekombinantes Protein für therapeutische Zwecke zur Verfügung. Biotechnisch hergestelltes t-PA (Actilyse®) verzeichnet bereits beachtliche klinische Erfolge bei der Behandlung von thromboembolischen Erkrankungen, insbesondere dem akuten Herzinfarkt. t-PA aktiviert Plasminogen zu Plasmin, welches das Fibringerüst eines Thrombus auflösen kann. Diese Aktivierung erfolgt selektiv auf der Thrombusoberfläche und verursacht nur geringe systemische Nebenwirkungen. Die Halbwertszeit von t-PA in vivo ist aufgrund einer raschen hepatischen Elimination sehr kurz (3-5 min).

t-PA ist ein Glykoprotein mit Serinproteaseaktivität, dessen Polypeptidkette aus 527 Aminosäuren besteht und über insgesamt 17 Disulfidbrükken verknüpft ist. Mit dem Ziel, Fibrinspezifität und katalytische Aktivität zu erhöhen oder die Eliminationsrate zu verringern, haben zahlreiche Forschergruppen in jüngster Zeit Modifikationen der molekularen Struktur von t-PA durchgeführt. Durch diese Arbeiten wurden zwar interessante Beziehungen zwischen Struktur und Funktion des t-PA-Moleküls aufgedeckt, jedoch konnte bisher keine klinisch relevante Variante konstruiert werden, die dem natürlich vorkommenden Protein in der Summe seiner Eigenschaften überlegen ist.

Properties of molecular variants of tissue-type plasminogen activator

Tissue-type plasminogen activator (t-PA), an important component of the fibrinolytic system, is now available as a biotechnologically manufactured recombinant protein for therapeutic use. It has proved highly effective in the clinical therapy of acute thromboembolic diseases such as myocardial infarction and pulmonary embolism. t-PA activates plasminogen to plasmin, which subsequently dissolves the fibrin network of a blood clot. This activation by t-PA occurs selectively on the clot surface, with negligible systemic side effects. The half-life of t-PA in vivo is in the order of minutes due to rapid hepatic elimination. t-PA is a glycoprotein with serine protease activity and consists of a polypeptide chain with 527 amino acids. Recently, intensive research efforts have been devoted to modification of the molecular structure of t-PA, with the objective of further increasing fibrin specificity and catalytic activity, or reducing the rate of elimination. As a result, considerable insights into structure-function relationships within the t-PA molecule have been gained, but as yet no clinically utilizable variant has been constructed which is in all respects superior to naturally occurring t-PA.

Steady-state intravenous pharmacokinetics of pirenzepine in patients with differing degrees of renal dysfunction

The steady-state intravenous pharmacokinetics of pirenzepine has been investigated in 57 subjects whose renal function ranged from normal to chronic failure requiring regular haemodialysis. Pirenzepine renal clearance, total clearance and terminal (dominant) half-life were found to be correlated with the creatinine clearance (CLCR), but this was not the case for the volume of distribution and the nonrenal clearance. The therapeutic regimen was well tolerated by all subjects. Haemodialysis did not significantly contribute to the elimination of pirenzepine. Dosage adjustment need only be considered in patients with CLCR less than 25 ml/min in order to reduce the frequency of minor side-effects.

Steady-state intravenous pharmacokinetics of pirenzepine in patients with hepatic insufficiency and combined renal- and hepatic insufficiency

The steady-state intravenous pharmacokinetics of pirenzepine has been investigated in patients with chronic liver disease and others with combined chronic liver disease and renal insufficiency. The plasma clearance (CL) of Pirenzepine, steady-state plasma concentration Cmin(ss) and dominant half life t1/2 gamma were not significantly altered in the chronic liver disease group. In patients with renal and hepatic insufficiency, CL was reduced, t1/2 gamma was prolonged from 11.1 to 19.4 h and Cmin(ss) was elevated from 36 ng/ml to 66 ng/ml compared to healthy controls. Plasma concentrations remained in the therapeutic range and the dosage regimen was well tolerated. Adjustment of the dose of pirenzepine need be considered only in cases of severe impairment of both renal and hepatic elimination.

Pharmacokinetics and biodisposition of recombinant human interferon-alpha 2C in rat and marmoset

Pharmacokinetics and biodiposition of recombinant human interferon-alpha 2C (IFN-alpha 2C) were studied in rats and marmosets (Callitrix jacchus). After intravenous bolus dose, serum concentrations of IFN-alpha 2C antigen declined triexponentially. After administration of 15 MIU/kg IFN-alpha 2C the mean t1/2 alpha was 3 min (rat) and 10 min (marmoset), t1/2 beta was 0.4 h (rat) and 1.2 h (marmoset), the mean terminal half-life t1/2 gamma was 2.8-6.3 h (rat) and 10-14 h (marmoset). The short alpha-phase was dominant, consistent with the high total serum clearance of 5 ml/min/kg (rat) or 2 ml/min/kg (marmoset), respectively. The low volumes of distribution (in both species 0.4-0.8 l/kg) indicated a mainly extracellular distribution of this drug. Absolute bioavailability after intramuscular and subcutaneous dosing ranged from 40-80% and the time of maximum serum level from 0.7-2.7 h (both species). Dose linearity was observed up to 15 MIU/kg for all routes of administration. The results demonstrate similarity of IFN-alpha 2C pharmacokinetics in rat and marmoset. Biodisposition of IFN-alpha 2C in rat was determined both by whole body autoradiography and analysis of antigen concentrations in tissue homogenates. The distribution of IFN-alpha 2C antigen showed a high correlation with capillary permeability and blood content of the different tissues. Thus, high levels were found in serum, kidney, lung, spleen, heart and liver, whereas the concentrations in muscle and brain were extremely low. Taken together, the data indicate that IFN-alpha 2C is predominantly eliminated by glomerular filtration, followed by tubular reabsorption, and finally lysosomal degradation in the kidney.

Pharmacokinetics of antigen and activity of recombinant tissue-type plasminogen activator after infusion in healthy volunteers

Pharmacokinetics of recombinant tissue plasminogen activator (rt-PA, large-scale process) were determined based on antigen and activity after infusion of 0.25 mg/kg in 8 healthy volunteers. Plasma antigen was measured using enzyme-linked immunosorbent assay (ELISA) with and without treatment of blood at collection with D-Phe-Pro-Arg-CH2Cl (P PACK); activity was quantified in acidified plasma both on fibrin plates and in a chromogenic assay. Highest rt-PA concentrations were measured in ELISA with P PACK-treated samples, yielding the following pharmacokinetic parameters (2-compartment model, mean +/- S.D.): Cmax = 973 +/- 133 ng/ml, CL = 687 ml/min, dominant half-life t1/2 alpha = 3.3 +/- 0.4 min, t1/2 beta = 26 +/- 12 min, V1 = 3.9 +/- 0.6 l and Vss = 7.2 +/- 1.0 l. The other assays yielded lower rt-PA concentrations, which affected clearance and volume parameters but not t1/2 beta and t1/2 beta. Linear regressions of the fibrin plate and chromogenic assay results vs. ELISA yielded excellent correlations (R greater than 0.96, n = 55-57) but slopes of 0.76 and 0.64, respectively. This indicates that about 25-35% of rt-PA antigen in thawed plasma samples are not detected in activity assays, due at least partially to in vitro binding of rt-PA by proteinase inhibitors.

Comparison of specific antibody, D-Phe-Pro-Arg-CH2Cl and aprotinin for prevention of in vitro effects of recombinant tissue-type plasminogen activator on haemostasis parameters

In vitro, concentration-dependent effects of rt-PA on a range of coagulation and fibrinolytic assays in thawed plasma samples were investigated. In absence of a fibrinolytic inhibitor, 2 micrograms rt-PA/ml blood (3.4 micrograms/ml plasma) caused prolongation of clotting time assays and decreases of plasminogen (to 44% of the control value), fibrinogen (to 27%), alpha 2-antiplasmin (to less than 5%), FV (to 67%), FVIII (to 41%) and FXIII (to 16%). Of three inhibitors tested, a specific polyclonal anti-rt-PA antibody prevented interferences in all fibrinolytic and most clotting assays. D-Phe-Pro-Arg-CH2Cl (PPACK) enabled correct assays of fibrinogen and fibrinolytic parameters but interfered with coagulometric assays dependent on endogenous thrombin generation. Aprotinin was suitable only for a restricted range of both assay types. Most in vitro effects were observed only with rt-PA plasma concentrations in excess of therapeutic values. Nevertheless it is concluded that for clinical application, collection of blood samples on either specific antibody or PPACK is essential for a correct assessment of in vivo effects of rt-PA on the haemostatic system in patients undergoing fibrinolytic therapy.

A selective radioimmunoassay for the determination of pirenzepine in plasma and urine

A radioimmunoassay procedure for the determination of pirenzepine in either plasma or urine was demonstrated to be both sensitive and specific as well as highly reproducible. The assay could detect levels as low as 1.25 ng/ml. The sensitivity was sufficient to allow the analysis of biological samples from both pharmacokinetic and clinical studies. The two metabolites of pirenzepine, LS 75 and LS 822, did not cross-react with the antiserum. The assay was not affected by a change in anticoagulant or by the presence of several over-the-counter or prescription drugs, even at very high levels. Samples could be frozen and stored for at least a year without affecting the analysis. Repeat analysis could be performed on samples that had been refrozen. Several thousand plasma and urine samples, including plasma samples from severely renally impaired patients, have been analyzed for pirenzepine by the RIA with no interferences having been detected.

Automated monoclonal radioimmunoassays for pirenzepine, a selective muscarinic receptor antagonist, in plasma and urine

Sensitive and specific monoclonal radioimmunoassays (RIA) for pirenzepine, a muscarinic receptor (M1) antagonist, were developed and validated for rapid automated routine analysis of plasma and urine samples from clinical studies. Three discrete stable hybridoma clones secreting monoclonal antibodies (MAb) to pirenzepine were produced by fusing the myeloma line X63-Ag8.653 to spleen cells of BALB/c mice immunized with pirenzepine-5-N-propionate-protein conjugates. Of three carrier proteins investigated (HSA, BSA and edestin), optimal humoral immune responses and affinity of hybridoma antibody were attained using HSA. All three MAb displayed high affinity to pirenzepine (Ka = 0.6-1.2 X 10(9) l/mol) but showed differing cross-reactivities with its 4'-N-desmethyl metabolite (less than 1%, 6% and 40% respectively). The MAb with essentially zero metabolite cross-reactivity, 58-7/7, was selected for RIA development. In comparison, eight rabbit polyclonal antisera raised against pirenzepine-5-N-propionate-HSA or pirenzepine-5-N-butyrate-HSA possessed a similar range of affinities to the MAbs, but none approached MAb 58-7/7 in specificity. The bridge length had no significant effect on antisera characteristics. Competitive solid-phase RIAs for pirenzepine in human plasma and urine were established using MAb 58-7/7 and [3H]pirenzepine as tracer. All fluid transfers were automated using a programmable sample processing system (Microlab 2,000). Detection limits were 0.25 ng/ml (plasma) and 4 ng/ml (urine) in 0.1 ml sample. The coefficient of within-assay variation was 4% or better in the range 2-100 ng/ml (plasma) or 30-1,000 ng/ml (urine), the between-assay CV was 5.3% or better in the range 5-90 ng/ml (plasma) or 40-660 ng/ml (urine). Excellent correlation was observed between the plasma monoclonal RIA and the hitherto used polyclonal RIA (n = 106, r = 0.994), and between the urine monoclonal RIA and HPLC (n = 82, r = 0.998). We expect that these assays will prove valuable in pharmacokinetic and pharmacological investigations of pirenzepine.

Pharmacokinetics and effects on fibrinolytic and coagulation parameters of two doses of recombinant tissue-type plasminogen activator in healthy volunteers

Pharmacokinetics and pharmacological effects of two intravenous doses of recombinant tissue-type plasminogen activator (rt-PA) (40 and 60 mg over 90 min) were determined in healthy volunteers. Mean maximum plasma concentrations were 1080 and 1560 ng/ml respectively. The steady state level during subsequent maintenance infusion of 30 mg over 6 h was 250 ng/ml. The pharmacokinetics of rt-PA showed a bi-exponential disappearance from plasma consistent with a 2-compartment model of t1/2 alpha = 5.7 min, a t1/2 beta = 1.3 h and a total clearance of 380 ml/min. Mean fibrinogen levels at the end of the infusions of 40 mg or 60 mg rt-PA over 90 min, measured in thawed plasma samples collected on citrate/aprotinin, decreased to 74% and 57% of the preinfusion values respectively. Plasminogen fell to 55% and 48%, and alpha 2-antiplasmin to 28% and 18% of initial values. No further decrease of these parameters was observed during the infusion of 30 mg rt-PA over 6 h. Only 2% of the preinfusion fibrinogen levels could be recovered as fibrinogen-fibrin degradation products. This moderate extent of systemic fibrinogenolysis is much less than that reported for therapeutic i.v. infusions of streptokinase.

Immunochemical studies on fibrinogen

The immunochemistry of fibrinogen has been subject of concise studies during the last years. Fibrinogen is a strong immunogen, based on a large variety of antigenic determinants located at different sites in the molecule. By using purified antibodies several of the surface and masked antigenic determinants on the individual chains and the large disulfide bonded CNBr-peptides were identified. According to these investigations the γ-chain is partially buried in the native molecule, whereas the antigenic determinants of a CNBr-peptide covering the C-terminal half of the α-chain are located on the surface of the protein. The structure of the antigenic determinants of this peptide which exhibits an extreme species variability has been more precisely defined in both bovine and human fibrinogen. A distinct structural variability was also observed for different antigenic determinants located m fibrinopeptides A and B.

Supported by the Deutsche Forschungsgemeinschaft, SFB 51.

Immunochemical Studies on Fibrinogen

The immunochemistry of fibrinogen has been subject of concise studies during the last years. Fibrinogen is a strong immunogen, based on a large variety of antigenic determinants located at different sites in the molecule. By using purified antibodies several of the surface and masked antigenic determinants on the individual chains and the large disulfide bonded CNBr-peptides were identified. According to these investigations the γ-chain is partially buried in the native molecule, whereas the antigenic determinants of a CNBr-peptide covering the C-terminal half of the α-chain are located on the surface of the protein. The structure of the antigenic determinants of this peptide which exhibits an extreme species variability has been more precisely defined in both bovine and human fibrinogen. A distinct structural variability was also observed for different antigenic determinants located in fi-brinopeptides A and B.

Supported by the Deutsche Forschungsgemeinschaft, SFB 51.

Nuclear-magnetic-resonance study of the active-site structure of yeast phosphoglycerate kinase

The enzyme 3-phosphoglycerate kinase from yeast has been studied by observation of the proton nuclear magnetic resonance spectrum at 270 MHz using Fourier transform techniques. Difference spectroscopy was used to enhance the resolution and to identify specific ligand binding effects and conformational changes. Perturbations involving single protons of amino-acid residues could thus be detected despite the relatively high molecular weight of the protein (47000), particularly in the aromatic (6-9 ppm) and methylene (2-3 ppm) regions of the spectrum.

Quantitative determination of the conformation of ATP in aqueous solution using the lanthanide cations as nuclear-magnetic-resonance probes

Chemical shift perturbations of the eight 1H resonances and of the three 31P resonances in the nuclear magnetic resonance spectra of ATP in 2H2O, pH 6.0, have been induced by specifically bound lanthanide cations Ln3+ (Ln = Pr, Nd, Eu, Yb). After separation of contact (through bond) perturbations the resultant through-space shifts, which are found to have axial symmetry, are used in an analysis of the conformation of the Ln3+ -ATP complex. A computer program was used to search for the conformations of the molecule which fit the nuclear magnetic resonance data. The "best" solutions obtained represent a small closely interrelated family of conformations. Effects of the cation Gd3+ on the longitudinal relaxation rates of five of the protons of ATP were also measured and used to confirm the conformational family. One of these conformations corresponds closely to one of the crystal structure forms, with an anti arrangement of the base-ribose unit and and a right-hand helical phosphate chain folded towards the adenine part of the molecule. The lanthanide ion binds predominantly to the beta and gamma phosphates and does not interact with the purine ring, these two centres being separated by at least one water molecule.