Antithrombotic but not anticoagulant activity of the thrombin-binding RNA aptamer Apta-1

Pharmacological intervention of thrombosis is challenging, requiring a fined tune balance between beneficial antithrombotic effect versus risk of major bleeding complications. In this investigation, we elucidated the antithrombotic capacity of the novel 90-mer RNA aptamer Apta-1 and its underlying mechanism of action.

We utilized three independent in vivo animal models to establish antithrombotic activity and bleeding risk of Apta-1. Several cellular and molecular techniques were utilized to extensively characterize the effects of Apta-1 on primary and secondary haemostasis.

Apta-1 significantly reduced thrombus weight in ferric chloride-induced carotid artery thrombosis. A consistent reduction in thrombus weight was also observed in arteriovenous shunt thrombosis in rats, whereas tail bleeding time was unaffected. Cellular and molecular analyses revealed that Apta-1 interacted with thrombin, resulting in significant inhibition of protease-activated receptor (PAR) signalling in platelets. On the other hand, Apta-1 shortened both thrombin generation and thrombin-induced clotting times.

Apta-1 targets the heparin-binding motif exosite II on thrombin leading to significant suppression of platelet PAR1 and PAR4 signalling. Intriguingly, Apta-1 produces substantial antithrombotic activity without anticoagulant or general antiplatelet properties. In fact, we found that Apta-1 accelerates the formation of blood clots and thus supports haemostasis without exhibiting typical anticoagulant properties. We suggest that Apta-1 may be a promising future drug candidate for treatment of thrombosis in diseases/conditions where there are significant risks of serious bleeding complications.