Johns D G, Webb R C
Department of Physiology, University of Michigan, Ann Arbor, Michigan 48109, USA.
Am J Physiol. 1998 Nov;275(5):H1592-8. doi: 10.1152/ajpheart.1998.275.5.H1592.
Ceramide is a novel second messenger generated by hydrolysis of membrane sphingomyelin by a neutral sphingomyelinase (nSMase). Cytokines such as tumor necrosis factor-alpha (TNF-alpha) have been shown to increase intracellular ceramide through phospholipase A2 (PLA2)-dependent activation of nSMase. TNF-alpha has been shown to cause endothelium-independent 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-alpha-induced vasodilation. In phenylephrine-contracted rat thoracic aortic rings (no endothelium), TNF-alpha 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 microM) and the nonselective PLA2 antagonist quinacrine (30 microM) inhibited TNF-alpha-induced relaxation. In cultured rat aortic vascular smooth muscle cells, TNF-alpha (10(-7) 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 microM). We conclude that PLA2 activation and increased ceramide generation play a role in mediating TNF-alpha-induced endothelium-independent vasodilation.
神经酰胺是一种由中性鞘磷脂酶（nSMase）水解膜鞘磷脂产生的新型第二信使。肿瘤坏死因子-α（TNF-α）等细胞因子已被证明可通过磷脂酶A2（PLA2）依赖性激活nSMase来增加细胞内神经酰胺。TNF-α已被证明可在离体血管中引起非内皮依赖性舒张。我们之前已经表明，外源性应用鞘磷脂酶和神经酰胺可在大鼠胸主动脉中引起非内皮依赖性血管舒张（D.G.约翰斯、H.奥斯本和R.C.韦伯。生物化学与生物物理学研究通讯。237:95-97，1997）。在本研究中，我们检验了神经酰胺介导TNF-α诱导的血管舒张这一假说。在苯肾上腺素收缩的大鼠胸主动脉环（无内皮）中，TNF-α在环氧化酶和脂氧合酶抑制剂存在的情况下引起浓度依赖性舒张。磷脂酶A2拮抗剂7,7-二甲基-（5Z，8Z）-二十碳二烯酸（DEDA；50微摩尔）和非选择性PLA2拮抗剂奎纳克林（30微摩尔）抑制了TNF-α诱导的舒张。在培养的大鼠主动脉血管平滑肌细胞中，TNF-α（10^-7克/毫升）使细胞内神经酰胺比基础水平（0.08纳摩尔/毫克蛋白质）增加了1.5倍，这被PLA2拮抗剂DEDA（50微摩尔）所阻断。我们得出结论，PLA2激活和神经酰胺生成增加在介导TNF-α诱导的非内皮依赖性血管舒张中起作用。
