Ancrod and Fibrin Formation Perspectives on Mechanisms of Action

Background and Purpose—Ancrod, derived from Malayan pit viper venom, has been tested as ischemic stroke treatment in clinical trials with inconsistent results. We studied the actions of ancrod on fibrinolysis pathways in patient plasma samples and endothelial cell culture systems. Methods—We analyzed fibrinogen levels during the first 6 hours of ancrod infusion in patients entered in the Stroke Treatment with Ancrod Trial. For the in vitro study, human brain microvascular endothelial cells incubated with plasminogen or with human brain microvascular endothelial cell-conditioned medium were co-incubated with ancrod and fibrinogen under normal or oxygen-glucose deprivation conditions over 6 hours. Results—Fibrinogen levels decreased both in vivo and in vitro. Ancrod generated fibrinopeptide A, caused visible clot formation, and reduced levels of tissue-type plasminogen activator antigen in the human brain microvascular endothelial cell system and in a cell-free system with conditioned media. Conclusions—The in vitro results indicate that ancrod causes local fibrin formation and secondary depletion of tissue-type plasminogen activator by binding to fibrin clot. Ancrod-induced fibrin formation could result in cerebral microvascular occlusion and may explain the suboptimal clinical effects of ancrod in human stroke trials. (Stroke. 2011;42:3277-3280.) Key Words: ancrod defibrinogenation fibrinogen fibrinolysis ischemic stroke Ancrod has long been viewed as a potential treatment foracute ischemic stroke.1–6 Derived from the venom of the Malayan pit viper Calloselasma rhodostoma, ancrod pos-sesses a serine protease that cleaves fibrinopeptide A (FPA) from fibrinogen.6–9 This fibrinogenolytic effect underlies ancrod’s potential clinical benefit, which would be based on limited clot propagation, reduced plasma viscosity, improved microcirculatory flow, and activation of endogenous fibrinolysis.6–9 However, results of ancrod in clinical trials of ischemic stroke have not been uniformly successful. Whereas the Stroke Treatment with Ancrod Trial (STAT) showed a favorable benefit–risk profile for patients with ischemic stroke treated within 3 hours of stroke onset,2 the Europea