TNF-a-induced endothelium-independent vasodilation: a role for phospholipase A2-dependent ceramide signaling

Johns, Douglas G., and R. Clinton Webb. TNF-ainduced endothelium-independent vasodilation: a role for phospholipase A2-dependent ceramide signaling. Am. J. Physiol. 275 (Heart Circ. Physiol. 44): H1592–H1598, 1998.— Ceramide is a novel second messenger generated by hydrolysis of membrane sphingomyelin by a neutral sphingomyelinase (nSMase). Cytokines such as tumor necrosis factor-a (TNF-a) have been shown to increase intracellular ceramide through phospholipase A2 (PLA2)-dependent activation of nSMase. TNF-a has been shown to cause endotheliumindependent relaxation in isolated blood vessels. We have previously shown that exogenously applied sphingomyelinase and ceramide cause endothelium-independent vasodilation in rat thoracic aortas (D. G. Johns, H. Osborn, and R. C. Webb. Biochem. Biophys. Res. Commun. 237: 95–97, 1997). In the present study, we tested the hypothesis that ceramide mediates TNF-a-induced vasodilation. In phenylephrinecontracted rat thoracic aortic rings (no endothelium), TNF-a caused concentration-dependent relaxation in the presence of cyclooxygenase and lipoxygenase inhibitors. The phospholipase A2 antagonist 7,7-dimethyl-(5Z,8Z)-eicosadienoic acid (DEDA; 50 μM) and the nonselective PLA2 antagonist quinacrine (30 μM) inhibited TNF-a-induced relaxation. In cultured rat aortic vascular smooth muscle cells, TNF-a (1027 g/ml) increased intracellular ceramide 1.5-fold over basal level (0.08 nmol/mg protein), which was blocked by the PLA2 antagonist DEDA (50 μM). We conclude that PLA2 activation and increased ceramide generation play a role in mediating TNF-a-induced endothelium-independent vasodilation.