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Biomedical subjects

S Niewiarowski

Publications and source records attributed to S Niewiarowski.

At least 19 recordsLinked to original sources
PubMed1992

Protection of platelets during long-term extracorporeal membrane oxygenation in sheep with a single dose of a disintegrin.

BACKGROUND: Both short- and long-term extracorporeal membrane oxygenation (ECMO) causes platelet loss and dysfunction. Bitistatin is a reversible inhibitor of the platelet glycoprotein IIb/IIIa receptor. This study tests the hypothesis that inhibition of platelets by bitistatin during initial contact with the perfusion circuit preserves platelet number and function during long-term ECMO in sheep. METHODS AND RESULTS: Bitistatin, purified from crude snake venom, was tested for its effect on platelet count, responsiveness to ADP, release of platelet factor 4, and prevention of surface-adsorbed glycoprotein IIIa in vitro and during 24 hours of ECMO in nine splenectomized sheep. During simulated extracorporeal circulation, 0.5-1.0 microgram/ml bitistatin significantly prevented platelet adhesion, attenuated release of sheep platelet factor 4, and preserved platelet responsiveness to ADP. During ECMO at 1.8 l/min for 24 hours, a single dose of bitistatin (200 micrograms/kg) (n = 4) produced higher platelet counts (p = 0.0002) and suppressed release of platelet factor 4 (p = 0.035) for 16 hours compared with five control animals. This dose of bitistatin caused an immediate inhibition of platelet aggregation; however, between 4 and 24 hours of perfusion, platelets of bitistatin-treated animals were more responsive to ADP (p < 0.0001) compared with platelets in control animals. The amount of glycoprotein IIIa antigen extracted by Triton X-100 from the perfusion circuits was reduced in bitistatin-treated sheep. CONCLUSIONS: A single dose of bitistatin given before blood contact with the ECMO circuit briefly inhibits platelet adhesion and aggregation but thereafter preserves platelet numbers and function and suppresses alpha-granule release for 12-16 hours of ECMO.

Adenosine Diphosphate↗
PubMed1979

Thrombocytin, a serine protease from Bothrops atrox venom. 1. Purification and characterization of the enzyme.

Thrombocytin, a platelet-activating enzyme from Bothrops atrox venom, has been purified to homogeneity by precipitation with sodium salicylate and chromatography on heparin--agarose. Thrombocytin is a single-chain glycoprotein with a molecular weight of 36 000 which contains 5.6% carbohydrate. It causes platelet aggregation, release of platelet serotonin, and activation of factor XIII. The most sensitive substrate for the amidolytic activity of thrombocytin was Tos-Gly-Pro-Arg-p-nitroanilide hydrochloride. The activity of thrombocytin on this substrate and on platelets was inhibited by diisopropyl fluorophosphate (DFP), soybean trypsin inhibitor, and several arginine chloromethyl ketones. Active site titration with nitrophenyl guanidinobenzoate demonstrated that approximately 86% of the preparation was in the active form. These experiments demonstrate the presence of serine and histidine in the active site of thrombocytin and suggest that thrombocytin is a classical serine protease with a platelet-activating activity similar to thrombin.

Amidohydrolases↗
PubMed1979

Thrombocytin, a serine protease from Bothrops atrox venom. 2. Interaction with platelets and plasma-clotting factors.

Thrombocytin, a serine protease from Bothrops atrox venom, caused platelet aggregation and release of platelet constituents at a concentration of 10(-7) M and clot retraction at a concentration of 2 x 10(-9) M. Thrombocytin was slightly more active when tested on platelets in plasma than on washed platelets suspended in Tyrode--albumin solution. Thrombin was 5 times more active than thrombocytin when tested on platelets in plasma and 50 times more active when tested on washed platelets. The patterns or release induced by thrombocytin and thrombin were similar. Prostaglandin E1 (10(-5) M) produced complete inhibition of platelet release induced by thrombocytin and thrombin. Indomethacin (10(-4) M) was without any effect. Antithrombin III, in the presence of heparin, inhibited the action of thrombocytin on platelets and on a synthetic peptide substrate (Tos-Gly-Pro-Arg-pNA.HCl). formation of an antithrombin III--thrombocytin complex was demonstrated on NaDodSO4--polyacrylamide gel electrophoresis. Hirudin and alpha 1-antitrypsin did not inactivate thrombocytin. Thrombocytin had a low fibrinogen-clotting activity (less than 0.06% that of thrombin). Thrombocytin also caused progressive degradation of the alpha chain of human fibrinogen, and it cleaved prothrombin, releasing products similar to intermediate 1 and fragment 1 produced by thrombin. Thrombocytin activated factor XIII by limited proteolysis and increased the procoagulant activity of factor VIII in a manner analogous to that of thrombin.

Animals↗
PubMed1977

Function of human platelets during extracorporeal circulation.

The interaction between human platelets and nonbiologic surfaces was studied during in vitro recirculation of 500 ml of fresh, heparinized human blood in four different perfusion circuits. Circuits differed in surface area (0.1 m2 or 0.9 m2) and in surface composition. No important differences were observed between standard silicone-rubber and filler-free, silicone-rubber surfaces. Platelet counts decreased to 85% of control in 0.1- m2 circuits, but retained normal sensitivity to aggregating agents and released only small amounts of platelet factor 4 (PF4). In contrast, platelet counts in 0.9-m2 circuits decreased to 20% of control within 2 min and platelet sensitivity was depressed out of proportion to the fall in platelet count. Plasma PF4 progressively increased and platelet PF4 content progressively decreased during 6 h of recirculation. The results indicate that human platelets may exist in three conditions during extracorporeal circulation. Some platelets are unaltered, some are less sensitive to aggregating agents, and others have undergone extensive release. The ratio of blood volume to surface area appears to be an important determinant of platelet-surface interaction.

Adenosine Diphosphate↗
PubMed1977

Binding of dipyridamole to human platelets and to alpha1 acid glycoprotein and its significance for the inhibition of adenosine uptake.

The interactions of dipyridamole with alpha(1) acid glycoprotein of plasma and with human platelets are related to inhibition of adenosine uptake by platelets. Binding studies by equilibrium gel filtration suggested that 1 mol of dipyridamole binds per mol of alpha(1) acid glycoprotein with a dissociation constant of 1.6 muM. Platelets contain two populations of binding sites, one with high and another with lower affinity for the drug. The binding of dipyridamole to the high-affinity sites follows a Michaelis-Menten binding pattern with a dissociation constant of 0.04 muM. Approximately 2 x 10(4) dipyridamole molecules are bound at the high-affinity sites of each platelet. The lower affinity sites bind the drug with a dissociation constant of 4 muM. In the presence of alpha(1) acid glycoprotein of plasma, the binding of dipyridamole to human platelets is inhibited. Correspondingly, the dipyridamole inhibition of adenosine uptake by platelets is reduced 1,000-fold by purified alpha(1) acid glycoprotein. The binding of dipyridamole to human platelets was found to be essential for its inhibition of adenosine uptake by platelets. Dipyridamole decreases the incorporation of [(14)C]adenosine radioactivity in platelet nucleotides and reduces the [(14)C]-ATP to [(14)C]ADP ratio. Purified alpha(1) acid glycoprotein reverses these effects of dipyridamole on adenosine metabolism of platelets in a concentration-dependent manner. An equilibrium of dipyridamole binding to alpha(1) acid glycoprotein and to platelets is proposed.

Adenine Nucleotides↗