Study of mechanisms involved in prostacyclin biosynthesis induced by a Phospholipase A2, isolated from Crotalus durissus terrificus snake venom: repercussion on anti-inflammatory effects

Abstract

Venom phospholipase A2 (PLA2) enzymes share similarity in structure and catalytic function with mammalian enzymes. PLA2 enzymes hydrolyze membrane phospholipids at the sn-2 position, releasing lysophospholipids and fatty acids. They are important in cellular functions such as signal transduction via biosynthesis of leukotrienes and prostaglandins. The prostanoids are a family of lipid mediators generated by the action of cyclooxygenase on a 20-carbon unsaturated fatty acid, arachidonic acid. Prostanoids are generated widely in response to diverse stimuli and play important roles in normal physiology and disease. Crotalus durissus terrificus snake venom and its major toxin, crotoxin or type II PLA2 (CB) subunit of this toxin, modulates immune and inflammatory responses, interfering with the activity of leukocytes. The CB subunit induce an inhibitory effect on spreading and phagocytosis in macrophages and decreased the number of circulating blood and lymph lymphocytes. Our recent work demonstrated that CB-PLA2 induces prostacyclin (PGI2) release by endothelial cells monolayers (in vitro) through activation of COX-1 and -2 enzyme systems. Moreover, this toxin also up-regulated protein expression of COX-2 isoform, whereas an inhibitor of phospholipases A2 enzyme activity, abrogated this effect. Prostacyclin, a potent vasodilator and inhibitor of platelet aggregation, is the predominant metabolite synthesized by vascular endothelial cells (ECs). These cells are key regulators of the inflammatory response. Lining blood vessels, they provide in the steady state an antiinflammatory surface. However, in the case of injury or infection, ECs control the adhesion and migration of inflammatory cells into the damaged tissue. The role of PGI2 as a immunomodulatory agent is highlighted by its ability to inhibit leukocyte and lymphocyte adhesion to endothelium. In vascular endothelial cells, the activation of peroxisome proliferator-activated receptor (PPAR) by prostanoids inhibits endothelial inflammation by suppressing transcription of pro-inflammatory genes. PPAR is a nuclear receptor and transcription factor that can be activated by several agonists, however, in ECs the most important and abundant is the PGI2. Considering the inhibitory effect of CB-PLA2 on several antiinflamatory parameters, the present study was designed to investigate the effect of this toxin on endothelial cells: I) activation of PPAR (±, ²/´ e ³); II) gene and protein expression of adhesion molecules (ICAM-1, VCAM-1 and E-selectin); III) participation of PPAR and prostacyclin in these effects; IV) involvement of protein kinases (p38MAPK, ERK, MEK, JNK), transcription factor (NF-8B) and prostacyclin synthase (PGIS) in the prostacyclin signaling pathway. In this sense, the present work will promote a better understanding of the antiinflammatory events induced by Crotalus durissus terrificus venom and contribute to the understanding of PLA2 enzymes actions in endothelial cells. Additionally, this study may reveal new therapeutics targets in inflammatory diseases.