Bleeding complications secondary to surgery, trauma or coagulation disorders are important causes of morbidity and mortality. A new paper published in Blood (link is external), from Dr Ramzi Ajjan’s laboratory at the Leeds Institute for Cardiovascular and Metabolic Medicine, describes a fibrinogen-specific Affimer protein that is able to inhibit the breakdown of blood clots and could act as a clinical tool to limit bleeding following trauma or in bleeding disorders.
Dr Ajjan’s team used fibrinogen-specific Affimer proteins with the intention of stabilising fibrin networks and increasing their resistance to lysis. One of these Affimers was able to significantly inhibit fibrinolysis without introducing unwanted changes to fibrin network structure. The effects of this Affimer were consistent using purified proteins, plasma or whole blood samples. Lysis of clots made from factor VIII-deficient plasma were normalised by the Affimer, demonstrating the ability of this conformational protein to work in genetic blood disorders. Interestingly, linear peptides of the same sequence as the Affimer variable regions showed no effect on clot lysis, demonstrating that the interaction is conformational and requires the peptide to be stabilised by the Affimer scaffold.
Probing into mechanisms, the Affimer-based inhibition of clot lysis was shown to be fibrin-dependent by directly inhibiting tissue plasminogen activator-mediated plasmin generation. No effect for this Affimer was observed with the use of non-fibrin-dependent urokinase type plasminogen activator, indicating that the effects are specific to sites of blood clot formation. This has important clinical implications as this highly specific mode of action offers a reversing agent in the form of urokinase, in case of unwanted thrombosis during future clinical use of the Affimer.
Affimer technology offers unique strengths in this application, including low cost production, no risk of patient infection (given this is a recombinant protein) and the inherent ability to control the fibrinolytic system through the fibrin-specific mode of action. This proof-of-concept study may offer a simple and affordable way to limit bleeding following traumatic injury or in pathological conditions with inherited abnormalities in the fibrin network.
Watch our video interview with Dr Ajjan below.