Thrombin adsorption and possible relations to thrombus formation

Abstract

In the circulation, adherent thrombi are most likely formed by nucleation and growth processes. The adsorption of an anchoring layer must be followed by further constituent interactions; these by crosslinking introduce cooperative effects which affect nucleation and growth rates. Adsorption of thrombin to nonpolar surfaces has been examined using a clotting time assay. Assay discrimination was determined by coefficients of variation: of the assay itself (0.6%), of reproducing diluted thrombin sources (0.37%) and of reproducing sets of dotting tubes containing fibrinogen (1.5%). Adsorptions are 0.54 mg/m² at the solution–air interface, 0.77 mg/m² at the solution–clean wall interface, and 0.04 mg/m² to walls previously treated with thrombin. Average distance between thrombin molecules is 89 Å, the minimum adsorption energy is −11.7 kcal/mole and estimated thrombus adhesive strength 10kg/cm². Thrombin can be the anchoring layer for a thrombus which contains thrombin, fibrin and platelets since all constituents interact with each other. The thrombin–fibrin intersection energy is about −7 kcal/mole. The platelet can, at least on interaction with thrombin, undergo structural changes which increase interaction. A variety of interactions and cooperative effects are possible. A problem is to develop protocols and assays which will permit specification of the anchoring layer and characteristics of subsequent interactions.