Hemorrhagic Toxins from Snake Venoms

Abstract

One of the more dramatic consequences of envenomation by crotalid and viperid snakes is the occurrence of hemorrage. In cases where the envenomation is less severe, the hemorrhagic is generally observed to be localized at the site of the bite. However, hemorrhage can be found disseminated through a substantial area of the involved extremity. In cases where the envenomation is severe, bleeding in organs such as heart, lungs, kidneys and brain may also occur. From the biochemical investigations on these toxins over the past 30 years, the nature of the venom toxins and their mechanism of activity are now becoming clear. Virtually all of the hemorrhagic toxins isolated and characterized thus far have been determined to be metalloproteinases. In this review we discuss the history of the isolation and characterization of these toxins in an attempt to clarify some of the confusion surrounding these toxins and their biochemical activities. We also survey the data available on the natural and synthetic inhibitors against the toxins. Finally, based upon the literature, we propose possible biochemical mechanisms which may give rise to the hemorrhagic pathology associated with crotalid/viperid envenomation.