Inflammatory effects of snake venom myotoxic phospholipases A 2

Abstract

Snake venom phospholipases A 2 (PLA 2) show a remarkable functional diversity. Among their toxic activities, some display the ability to cause rapid necrosis of skeletal muscle fibers, thus being myotoxic PLA 2s. Besides myotoxicity, these enzymes evoke conspicuous inflammatory and nociceptive events in experimental models. Local inflammation and pain are important characteristics of snakebite envenomations inflicted by viperid and crotalid species, whose venoms are rich sources of myotoxic PLA 2s. Since the discovery that mammalian PLA 2 is a key enzyme in the release of arachidonic acid, the substrate for the synthesis of several lipid inflammatory mediators, much interest has been focused on this enzyme in the context of inflammation. The mechanisms involved in the proinflammatory action of secretory PLA 2s are being actively investigated, and part of the knowledge on secretory PLA 2 effects has been gained by using snake venom PLA 2s as tools, due to their high structural homology with human secretory PLA 2s. The inflammatory events evoked by PLA 2s are primarily associated with enzymatic activity and to the release of arachidonic acid metabolites. However, catalytically inactive Lys49 PLA 2s trigger inflammatory and nociceptive responses comparable to those of their catalytically active counterparts, thereby evidencing that these proteins promote inflammation and pain by mechanisms not related to phospholipid hydrolysis nor to mobilization of arachidonic acid. These studies have provided a boost to the research in this field and various approaches have been used to identify the amino acid residues and the specific sites of interaction of myotoxic PLA 2s with cell membranes potentially involved in the PLA 2-induced inflammatory and nociceptive effects. This work reviews the proinflammatory and nociceptive effects evoked by myotoxic PLA 2s and their mechanisms of action.