Ischemic stroke is a leading cause of death and disability worldwide. Increasing evidence indicates that
ischemic stroke is a thromboinflammatory disease in which the contact-
kinin pathway has a central role by activating pro-
coagulant and pro-inflammatory processes. The blocking of distinct members of the contact-
kinin pathway is a promising strategy to control
ischemic stroke. Here, a
plasma kallikrein and active FXII (FXIIa) inhibitor (sylvestin, contained 43
amino acids, with a molecular weight of 4790.4 Da) was first identified from forest leeches (Haemadipsa sylvestris). Testing revealed that sylvestin prolonged activated partial thromboplastin time without affecting prothrombin time. Thromboelastography and clot retraction assays further showed that it extended clotting time in whole blood and inhibited clot retraction in platelet-rich plasma. In addition, sylvestin prevented
thrombosis in vivo in FeCl3-induced arterial and
carrageenan-induced tail
thrombosis models. The potential role of sylvestin in
ischemic stroke was evaluated by transient and permanent
middle cerebral artery occlusion models. Sylvestin administration profoundly protected mice from
ischemic stroke by counteracting intracerebral
thrombosis and
inflammation. Importantly, sylvestin showed no signs of
bleeding tendency. The present study identifies sylvestin is a promising contact-
kinin pathway inhibitor that can proffer profound protection from
ischemic stroke without increased risk of
bleeding.