Snake venom fibrin(ogen)olytic enzymes

Snake venoms contain a number of serine and metalloproteinases and included among these are the fibrin(ogen)olytic proteinases. Some years ago it was postulated that the fibrin(ogen)olytic enzymes may be clinically useful. Over the past 150 years a substantial body of literature has been generated on the identification and characterization of fibrin(ogen)olytic enzymes from a broad spectrum of snake species. In this review we describe the two different classes of fibrin(ogen)olytic enzymes isolated from snake venom and we summarize a number of studies aimed at characterizing the purified enzymes and/or their derivatives. Two distinct classes of venom fibrin(ogen)olytic enzymes have been previously identified, the metalloproteinases and serine proteinases. These two classes of proteinases differ in their mechanism of action and they target different amino acid sequences in fibrin(ogen), but each perform the same role in nature. When a snake envenomates its prey it needs a mechanism to facilitate the spread of the toxic components throughout the circulation. Fibrin(ogen)olytic enzymes break down fibrin rich clots and help to prevent further clot formation by their action on fibrinogen. This characteristic feature has led to development of fibrin(ogen)olytic snake venom enzymes as potential clinical agents to treat occlusive thrombi. Fibrolase, a fibrinolytic metalloproteinase isolated from Agkistrodon contortrix contortrix venom and the serine beta-fibrinogenolytic proteinase from Vipera lebetina have been chosen as representative enzymes from the two classes, and their biochemical and physiochemical properties will be described in detail. Finally, the characterization and development of alfimeprase, a recombinant fibrinolytic enzyme derived from fibrolase, as a clinical agent is described citing the progression from the laboratory bench to its current status as having successfully completed Phase II clinical trials.