Analysis of Abnormal Expression of Sphingomyelin Acylase in Atopic Dermatitis. Resulting in Ceramide Deficiency

以前，我们证明了在特应性皮炎（AD）的病变和非病变前臂角质层中神经酰胺的量显著减少，这表明角质层中神经酰胺的不足是特应性干燥和屏障破坏皮肤的病因。在这项研究中，我们调查，作为一个可能的机制参与神经酰胺缺乏症，是否鞘磷脂（SM）代谢改变AD相比，正常对照组。在AD患者的剥脱角质层和活组织检查的整个表皮中，SM水解在pH4.7下以 * 胆碱-甲基-^<14>C* 鞘磷脂为底物分别显著增加27倍和7倍。反应产物的放射性薄层色谱显示，在年龄匹配的正常对照中，SM水解与鞘磷脂酶（SMase）有关，SMase降解SM产生神经酰胺和磷酸胆碱（PC），而在AD中检测到的大多数SM水解是在 ...更多信息 不是由于SMase而是由于一种迄今未发现的表皮酶。SM酰化酶，释放游离脂肪酸和鞘糖基-PC（Sph-PS）而不是神经酰胺。通过对猪肾酰化酶反应产物的薄层色谱分析和高效液相色谱-质谱分析，证实了该酰化酶通过SM水解生成Sph-PC的潜力。此外，Sph-PC也检测到高性能液相色谱-质谱后，与过敏性角质层样品的SM孵育。另一方面，接触性皮炎或慢性湿疹患者的角质层在放射性薄层色谱分析时既不显示SM水解增加，也不显示Sph-PC的产生。这些发现表明，SM代谢在AD中改变，导致神经酰胺水平降低，这可能是AD中观察到的特应性干燥和屏障破坏皮肤连续生成的病因因素。少

Previously, we demonstrated that there is a marked reduction in the amount of ceramide in the stratum corneum of both lesional and nonlesional forearms in atopic dermatitis(AD), suggesting that an insufficiency of ceramides in the stratum corneum is an etiologic factor in atopic dry and barrier-disrupted skin. In this study, we investigated, as a possible mechanism involved in the ceramide deficiency, whether sphingomyelin (SM) metabolism is altered in AD as compared to normal controls. In stripped stratum corneum and biopsied whole epidermis of patients with AD.SM hydrolysis as measured at pH4.7 using *choline-methyl-^<14>C* sphingomyelin as a substrate were markedly increased by 27-and 7-fold, respectively.Radio-thin-layr chromatography of the reaction products revealed that, whereas the SM hydrolysis in age-matched normal controls were associated with sphingomyelinase (SMase) that degrades SM to yield ceramides and phosphorylcholin (PC), most of the SM hydrolysis detected in AD were … More attributable not to the SMase but to a hitherto undiscovered epidermal enzyme. SM acylase, which releases free fatty acidand sphingosyl-PC (Sph-PS) instead of ceramides. The potential of this acylaselike enzyme to generate Sph-PC through SM hydrolysis was corroborated by thin-layr chromatographic analysis of the reaction products obtained using porcine kidney acylase, followed by high-perfomance liquid chromatography-mass spectrometry. Furthermore, Sph-PC was also detected by high-performance liquid chromatography-massspectrometry after incubation of SM with atopic stratum corneum samples. On the other hand, the stratum corneum of patients with contact dermatitis or chronic eczema exhibited neither increased SM hydrolysis nor the generation of Sph-PC upon radio-thin-layr chromatographic analysis. These findins suggest that SM metabolism is altered in AD,resulting in a decrease in levels of ceramides, which could be an etiologic factor in the continuous generation of atopic dry and barrier disrupted skin observed in AD. Less