Modification of fibrin structure as a possible cause of thrombolytic resistance.

This paper presents a concept according to which free radicals, specifically the most biologically active hydroxyl radicals, induce structural modifications in fibrin(ogen) molecules making them resistant to proteolytic degradation. Such changes are analogous to those in congeneticaly altered fibrinogen that give rise to plasmin resistant fibrin clots and consequently to thrombosis. In view of the fact that hydroxyl radicals are generated in the Fenton reaction in the presence of iron and/or copper ions, the use of chelating agents to facilitate thrombolysis is rationalized. Moreover, the resistance of thrombi older than 3 h to proteolytic degradation may be abrogated by the administration of free radical scavengers, particularly those that can be neutralized by virtue of aromatic hydroxylation, such as salicylates and polyphenolic compounds.