192. Action of Venom Metalloproteinases on Basement Membranes: Pathogenesis of Hemorrhage and Blistering in Snakebite Envenomings

Abstract

Review: Zinc-dependent metalloproteinases are abundant components of snake venoms, especially in viperid species. Snake venom metalloproteinases (SVMPs) are grouped in three classes (P-I, P-II and P-III), with various subclasses, on the basis of their domain composition. SVMPs play a key role in some of the most relevant pathophysiological manifestations of viperid envenomings, such as hemorrhage, blistering, necrosis and coagulopathy, and also induce prominent inflammation. The pathogenesis of hemorrhage by SVMPs is associated with the ability of these enzymes to degrade proteins of the basement membrane (BM) and surrounding extracellular matrix (ECM) in capillary blood vessels. A combination of in vitro and in vivo experimental approaches has provided novel evidence for understanding this complex phenomenon. Such experimental platforms include electron microscopy, intravital microscopy, immunohistochemistry, electrophoresis, Western blotting, and proteomic analysis of exudate collected in the vicinity of affected tissue. Hemorrhagic and non-hemorrhagic SVMPs of the P-I class have been compared in order to identify differences that might help to understand the basis of this pathological effect. In contrast to a non-hemorrhagic P-I SVMP, a hemorrhagic enzyme is able to hydrolyze perlecan and type IV collagen, as well as types VI and XV collagens, a finding that might have implications for its mechanism of action. On the other hand, P-III SVMPs are, in general terms, more potent hemorrhagic toxins than P-I SVMPs owing to the presence of exosites in their disintegrin-like and cysteine-rich domains, which enable these enzymes to bind to relevant targets in microvessels. Hydrolysis of key structural components in capillary BMs and surrounding ECM, with the consequent mechanical weakening of the microvessel structure, provokes the distention of the capillary wall, due to the action of hemodynamic forces operating in vivo, a process that eventually brings mechanical disruption of the vessel wall and extravasation. Similarly, the action of SVMPs on BM components of the dermal-epidermal interphase provokes the formation of blisters. Further studies are necessary to compare the patterns of BM hydrolysis induced by P-I and P-III SVMPs and to identify the structural determinants of their highly variable toxicological profiles.