Smith A R, Visioli F, Frei B, Hagen T M
Department of Biochemistry and Biophysics, Linus Pauling Institute, Oregon State University, Corvallis, OR, USA.
Br J Pharmacol. 2008 Apr;153(8):1615-22. doi: 10.1038/bjp.2008.28. Epub 2008 Feb 25.
The age-related decline in vasorelaxation is largely due to ceramide-induced induction of phosphatase 2A (PP2A), which limits nitric oxide synthase (eNOS) phosphorylation at stimulatory sites. We hypothesized that ceramide accumulation was from an age-related loss of endothelial glutathione (GSH) and subsequent activation of neutral sphingomyelinase (nSMase), an enzyme whose activity increases when GSH is limited.
Old (30-32 mo) F344xBN rats were given (R)-alpha-lipoic acid (LA), an agent known to induce GSH synthesis. Vasorelaxation was measured in aortic rings; GSH and ceramide levels, activity of nSMase and eNOS phosphorylation (by Western blot) was measured in aortic endothelial cells, isolated from the same aortas.
In old animals, endothelium-dependent relaxation in aortic rings was decreased, GSH levels and its redox state in aortic endothelia were over 30% lower and nSMase activity and endothelial ceramide levels were three-fold increased, relative to young (2-4 mo) rats. LA treatment of old animals improved relaxation in aortic rings, reversed the changes in endothelial GSH, in nSMase activities and in ceramide levels. Similar effects on GSH levels and nSMase activity in old rats were also induced by treatment with GSH monoethylester. Activation (by phosphorylation) of eNOS was decreased by about 50% in old rats and this age-related decrease was partially reversed by LA treatment.
Decreased endothelial GSH was partly responsible for the age-related loss of vascular endothelial function and LA might be therapeutically evaluated to treat endothelial dysfunction.
血管舒张功能随年龄增长而下降，这在很大程度上归因于神经酰胺诱导的磷酸酶2A（PP2A）的产生，PP2A会限制一氧化氮合酶（eNOS）在刺激位点的磷酸化。我们推测，神经酰胺的积累源于与年龄相关的内皮谷胱甘肽（GSH）的缺失，以及随后中性鞘磷脂酶（nSMase）的激活，当GSH受限时，该酶的活性会增加。
给30 - 32月龄的老年F344xBN大鼠注射（R）-α-硫辛酸（LA），这是一种已知可诱导GSH合成的药物。测量主动脉环的血管舒张功能；检测从同一主动脉分离出的主动脉内皮细胞中的GSH和神经酰胺水平、nSMase活性以及eNOS磷酸化水平（通过蛋白质印迹法）。
与2 - 4月龄的年轻大鼠相比，老年动物主动脉环的内皮依赖性舒张功能降低，主动脉内皮中的GSH水平及其氧化还原状态降低超过30%，nSMase活性和内皮神经酰胺水平增加了两倍。用LA处理老年动物可改善主动脉环的舒张功能，逆转内皮GSH、nSMase活性和神经酰胺水平的变化。用GSH单乙酯处理老年大鼠也可诱导对GSH水平和nSMase活性产生类似影响。老年大鼠中eNOS的激活（通过磷酸化）降低了约50%，而LA处理可部分逆转这种与年龄相关的降低。
内皮GSH降低部分导致了与年龄相关的血管内皮功能丧失，LA可能值得进行治疗评估以治疗内皮功能障碍。
