Effect of thrombin inhibitors on platelet functions: comparative analysis of DuP 714 and hirudin.

Since thrombin plays an important role in platelet-mediated arterial thrombosis, we have examined the antiplatelet activity of a synthetic thrombin inhibitor, DuP 714 (Ac-(D)Phe-Pro-boroArg), in comparison with that of the naturally occurring inhibitor hirudin. Hirudin was slightly more potent than DuP 714 in inhibiting thrombin-induced aggregation in washed human platelets (IC50s of 72 nM and 150 nM, respectively) and in inhibiting the secretion of plasminogen activator inhibitor-I from human platelets (IC50s of 300 nM and 900 nM, respectively). In contrast, DuP 714 was more potent than hirudin in inhibiting thrombin-induced [125I]fibrinogen binding to gel purified platelets, and in inhibiting thrombin-induced intracellular calcium mobilization in washed platelets. These results indicate that the tripeptide DuP 714 has comparable antiplatelet activity to the 65 amino acid hirudin. We conclude that DuP 714 may have clinical utility in the prevention of platelet-dependent, arterial thrombotic processes.

Rapid analysis of fatty acids in plasma lipids.

A rapid and convenient procedure for the quantitative determination of the fatty acid composition of plasma lipids is described. Human plasma was applied directly to the preadsorbent zones of thin-layer silica gel plates with added antioxidant, internal standards and carriers. The thin-layer chromatography (TLC) plates were partially developed with methanol followed by chloroform/methanol (1:1, v/v), and then they were fully developed in hexane/diethyl ether/acetic acid (80:20:1, v/v/v) to separate the major classes of lipids. Silica gel from regions containing the separated lipids was scraped into screw-capped tubes and treated with boron trifluoride-methanol prior to gas chromatography. The method of direct application to TLC plates gave yields and compositions of fatty acids very similar to the method of applying extracted plasma lipids. This relatively simple method is suitable for analyzing the fatty acids in plasma lipids from a 50 microliter finger-tip blood samples from an individual, and it may be useful in wide-scale screening of different individuals to estimate the relative amounts of ingested polyunsaturated fatty acids.

Implementing CQI: measuring levels of service quality at physiotherapy clinics.

The purpose of this study was to provide a profile of patient perceptions of the service quality delivered by a back pain rehabilitation clinic. Data were gathered and analyzed at the clinic level in twelve different locations across Canada. Measurement techniques were based on validated survey methods and developed from a growing stream of social science research. Results provided clinic managers with a profile of perceived service quality in terms of three key aspects: administrative support, quality of therapy received, and satisfaction with the results. The results also provided each clinic with benchmarks so that on-going service quality measurements can be incorporated into a system of continuous quality improvement. This process can assist rehabilitation clinics (and other health care providers) in improving service as well as ultimately reducing the costs of providing treatments involving physiotherapy.

Myocardial anti-ischemic characteristics of a novel class of beta-adrenoceptor blockers.

The effect of different beta-adrenoceptor blockers on free radical-mediated cardiac membrane lipid peroxidation (CMLP) was compared to their beta-blocking potency (pA2). CMLP was determined by the measurement of malondialdehyde (MDA) formation in rat cardiac membrane homogenates exposed to a free radical generating system (FeCL3/ADP/DHF) in the presence or absence of the beta-adrenoceptor blockers (1-1,000 microM). beta-adrenoceptor blocking potency (pA2) was determined using guinea pig right atria stimulated with isoproterenol. The catechol containing beta-blocker (DCC-10255) was shown to be a potent inhibitor of CMLP via an iron-dependent mechanism. On the other hand, the non-catechol beta-adrenoceptor blocker, timolol, was shown to be a weak inhibitor of CMLP. Furthermore, dl- and d-propranolol were active and equipotent though less potent than DCC-10255 in inhibiting CMLP. The myocardial cytoprotective efficacy for catechol and non-catechol beta-adrenoceptor blockers was evaluated in an isolated rat myocyte model. It was demonstrated that catechol-containing agents with either strong or weak beta-adrenoceptor blockade possess a relatively potent in vitro antioxidant and myocardial cytoprotective efficacy against free radical mediated CMLP and myocyte injury, respectively. It is concluded that the inhibition of CMLP by beta-adrenoceptor blockers is independent of their beta-adrenoceptor blockade.

Antiplatelet and antithrombotic efficacy of DMP 728, a novel platelet GPIIb/IIIa receptor antagonist.

BACKGROUND: Currently used antiplatelet drugs, including aspirin, ticlopidine, and others, are effective against certain but not all of the many endogenous platelet activators. Because of their limited efficacy, a significant number of serious thromboembolic complications still occur, highlighting the need for a more effective therapy. Thus, we have identified a systemically active peptide analogue (DMP 728) of the arginine-glycine-aspartic acid (RGD) recognition sequence that mediates the binding of ligands such as fibrinogen to the platelet glycoprotein (GP) IIb/IIIa receptors. The goals of the present study were to determine the antiplatelet and antithrombotic efficacies of DMP 728 in various arterial thrombosis models. METHODS AND RESULTS: DMP 728 demonstrated antiplatelet efficacy in vitro in inhibiting ADP-induced human platelet aggregation (IC50, 46 +/- 2 nmol/L) and fibrinogen binding to human platelets (IC50, 2.3 +/- 0.8 nmol/L) or purified human GPIIb/IIIa receptors (IC50, 0.6 +/- 0.1 nmol/L). DMP 728 demonstrated high affinity and specificity for human platelet GPIIb/IIIa over other adhesion molecules. In anesthetized mongrel dogs, DMP 728 at 0.001 to 1.0 mg/kg IV produced dose-dependent antiplatelet effects in inhibiting ex vivo platelet aggregation induced by ADP and in prolonging template bleeding time. DMP 728 effects on bleeding time prolongation were more rapidly reversible than those on platelet aggregation inhibition. A maximal antiplatelet effect for DMP 728 was demonstrated at 0.01 mg/kg IV bolus. The antithrombotic efficacy of DMP 728 was examined in vitro and in vivo after IV administration at different doses in various models of arterial thrombosis. In the coronary artery Folts model in dogs, DMP 728 demonstrated maximal antithrombotic efficacy at 0.01 mg/kg IV bolus with an ED50 of 0.005 mg/kg IV bolus in inhibiting cyclic flow reductions. Additionally, DMP 728 demonstrated 100% prevention of primary thrombosis and rethrombosis (P < .01) after treatment with different thrombolytics, including tissue plasminogen activator and streptokinase, in an electrolytically induced femoral artery thrombosis model in dogs. CONCLUSIONS: Acute intravenous DMP 728 administration (0.001 to 1.0 mg/kg) has dose-dependent antiplatelet and antithrombotic effects in different arterial thrombosis models. These data suggest that DMP 728, a low-molecular-weight GPIIb/IIIa receptor antagonist, may have therapeutic potential as an effective antithrombotic agent in coronary and peripheral artery thromboembolic disorders.