Anticoagulant And Fibrinolytic Properties Of The Salivary Gland Proteins From The Leech Haementeria Ghilianii

Abstract

Blood-sucking animals, such as leeches, mosquitoes, and vampire bats contain in their saliva agents that prevent the host blood from coagulating as it is being withdrawn. The work reported here was carried out to elucidate the nature of the anticoagulant found in the saliva of the giant leech Haementeria ghilianii, native to French Guyana. The two bilateral pairs of salivary glands of H. ghilianii are located at the proboscus base and encapsulated by a thin membrane. The anterior glands are 20 mm long and contain predominantly the cells of large size; the posterior glands are 5 mm long and contain the cells of very small size. Both salivary glands of the leech contain an anticoagulant that not only inhibits the clotting of human and bovine plasma, but also dissolves previously formed fibrin clots. This anticoagulant activity is attributable to an enzyme, for which the name hementin is proposed. Hementin catalyzes the proteolytic degradation of fibrinogen and fibrin, even in the presence of the inhibitors of proteases occurring in human plasma. The enzyme has the same affinity for human fibrinogen and fibrin. It cleaves human fibrinogen to yield characteristic fragments of high molecular weight that are different from Fragments X, Y, D and E resulting from the digestion of fibrinogen by plasmin. Both the anterior and posterior salivary glands contain hementin. Fractionation of salivary gland homogenates by differential ultracentrifugation showed that hementin is found entirely in the cytosol fraction. The salivary extracts do not contain any appreciable amounts of an activator of human plasminogen or an inhibitor of human or bovine thrombin, thus, Haementeria ghilianii prevents coagulation of its host’s blood through a fibrinogenolytic mechanism that is entirely different from that of hirudin, a thrombin inactivating polypeptide present in the saliva of another leech, Hirudo medicinalis.