Francis C. Chao

Thrombin inhibition by malignant and normal cells: A cell-bound antithrombin effect

Analysis of fresh surgical specimens of normal tissue and tumor tissue show a cellular antithrombin activity to be present in certain organs. In normal tissues it was noted chiefly in normal colon, testes, breast, and uterus. In malignant tissues it was prominent in adenocarcinomas of the colon, breast, and lung. No epidermoid tumors showed evidence of thrombin binding. The thrombin‐binding activity required the presence of intact cells and was distinct from the soluble antithrombins normally present in plasma and serum. There is growing evidence to suggest an interrelationship between clotting and the growth and dissemination of cancer. The implications of cellular antithrombins are reviewed in this context.

Plateletpheresis by Discontinuous Centrifugation: Effect of Collecting Methods on the in Vitro Function of Platelets

The in vitro function of platelets collected by two different methods during centrifugal plateletpheresis was compared. The RBC method involves collecting platelets with red cells followed by a supplementary spin to remove them, whereas the no‐RBC method requires collecting platelets only from the buffy coat without red cells. Platelet response to adenosine diphosphate (ADP), epinephrine and collagen was slightly reduced in platelet‐rich plasma (PRP) prepared by no‐RBC technique and was markedly decreased in samples obtained by the RBC technique when compared to prepheresis controls. The decrease in platelet response to ADP, epinephrine and collagen was apparent in three testing systems: aggregation, release of serotonin and reptilase clot retraction. Both plasma and platelets appeared to be affected by the pheresis procedure. Platelet preparations obtained by both RBC and no‐RBC techniques showed an increase of platelet factor 3 activity and an enhancement of aggregation, release of serotonin and clot retraction induced by thrombin as compared to prepheresis controls. Postpheresis platelet‐poor plasma contains platelet membrane fragments which exhibit a high platelet factor 3 activity. The results showed that the RBC method, although providing a higher platelet yield, caused more qualitative alterations in platelets than in those obtained by no‐RBC method, and that both methods of collecting platelets activated the procoagulant activity of platelets.

Platelet Antithrombins: Role of Thrombin Binding and the Release of Platelet Fibrinogen

The nature of platelet antithrombin was elucidated by comparison of thrombin binding and antithrombin activities of intact platelets and by purification of antithrombin from platelet lysates using glycerol osmotic lysis, ethanol precipitation and Sephadex gel filtration techniques. The major portion of the antithrombin and thrombin binding activity of intact platelets is lost after brief sonication. The antithrombin activity in destroyed platelets is found to be due to platelet fibrinogen. Treatment of platelets with PGE1 (100 μg/ml) markedly inhibits (>80%) the release of platelet fibrinogen induced by thrombin. However, the PGE1 treatment produced slight (<30%) but significant decrease of antithrombin activity of intact platelets, whereas the binding of thrombin to platelets was not affected by PGE1 treatment. The amounts of thrombin bound to and inactivated by PGE1‐treated platelets at the same cell concentration are identical. The above results suggest that platelets contain at least two antithrombin activities. One, which accounts for the major portion of platelet antithrombin is mediated by thrombin binding to platelets. The other, which attributes to a lesser extent to platelet antithrombin activity, is due to the release of platelet fibrinogen. Also, antithrombin is readily demonstrated in a plasma medium indicating physiological significance of platelet antithrombin.

Kinetic analysis of thrombin-induced aggregation of human platelets: I. Thrombin dependence

Abstract A kinetic equation for thrombin-induced platelet aggregation is established. This equation is used to analyze data obtained from three experiments: (1) a fixed thrombin concentration in the presence of variable platelet numbers, (2) a reverse of (1), and (3) a fixed ratio between thrombin concentration and platelets numbers by simultaneous variation of both.