Invertebrate compounds acting on the hemostatic mechanism

Physiological secretions from some invertebrates have toxic effects on mammalian blood coagulation and fibrinolytic systems. Some of these effects occur because the substances contained in the secretions resemble the components of the hemostatic system. Some of the substances have been characterized, and have been found to have similar molecular weights or sequences, which may indicate a common ancestry. The components can be divided into five groups: antithrombic agents (group I); inhibitors and activators of the prothrombinase complex (group II); substances that affect platelet function (group III); substances that affect the fibrinolytic mechanism (group IV); and a group of miscellaneous agents whose activities are difficult to group together (group V). In group I special mention of the antithrombin agents in Hirudo medicinalis should be made. In group II, the agents affecting the prothrombinase complex are antistasin from Haementeria officinalis, ghilanten from Haementeria Ghiliani and the tick anticoagulant protein from Ornithodoros moubata, a factor V activator/inhibitor from Lonomia achelous and factor II and factor X activators from L. achelous and Lonomia obliqua. Examples of factors which affect platelet function (group III) are glossina from the black fly Glossina morsitans, calin from H. medicinalis, decorsin (a desintegrin) from Macrobdella decorsa, and FAGA from Stichopus japonicus selenka. The first three of these are inhibitors of platelet aggregation, and the last is an inducer. The plasminogen activators (group IV) from the L. achelous caterpillar and Eutriatoma maculata trigger the fibrinolytic system, whereas hementin from H. officinalis and hementerin from Haementeria depressa are directly fibrinolytic. The last group of substances (group V) include those with factor-XIIa-like activity from D. farinae, kallikrein-like activity and a factor XIII degrading enzyme from L. achelous, destabilase from H. medicinalis and prolixin S (nitroforin 2, or anti-factor-IXa) from Rhodnius prolixus. Some of these components have been well characterized, cloned and prepared in recombinant form, and seem to be very promising from the therapeutic point of view.