Thrombin inhibitors of bloodsucking animals

Hematophagous animals have the unique ability to inhibit blood coagulation when sucking blood from a wound. This article concerns thrombin inhibitors from these animals, specifically the one from the insect Rhodnius prolixus. To date, the most-studied inhibitor from these animals is hirudin, which specifically neutralizes thrombin but no other clotting serine proteases. The biochemical properties of hirudin are described. Hirudinlike thrombin inhibitors from the Asian leech Hirudo manillensis, Haemadipsa sylvestris, and Haemadipsidae are also discussed. In addition, a thrombin inhibitor from the insect Rhodnius prolixus, Rhodniin, is extensively reviewed. There is considerable interest in these inhibitors because they may be found useful as treatment modalities for thromboembolic disorders. Hirudin is already extensively investigated, and some of the others may follow. Potentially these new inhibitors could be of greater clinical benefit than the presently used heparins.