Mode of action of ancrod as a defibrinating agent

Abstract

ANCROD is a thrombin-like enzyme obtained from the venom of Agkistrodron rhodostroma. When added to plasma, ancrod initiates fibrin polymerisation by the cleavage of fibrinopeptide A from fibrinogen¹ but activates factor XIII (plasma transglutaminase) very slowly². Factor XIII, when activated, catalyses the formation of crosslinks between the α chains and between the γ chains of fibrin³. The absence of these cross-linked chains, especially the α chain polymers, allows fibrin to be easily degraded by plasmin^4,5. Thus it is believed that ancrod acts as a defibrinating agent in vivo by producing non-cross-linked easily lysable fibrin deposits. We wish to present some preliminary evidence to show that commercial preparations of ancrod activate factor XIII in plasma in vitro and may also mediate the conversion of prothrombin to thrombin. In addition a hypothesis is presented to explain the defibrinating effect of ancrod in vivo.