Purpose

Sphingolipids (SPL) are a class of lipid molecules that play important functional and structural roles in our body and are a component of meibum. Sphingomyelinases (SMases) are key enzymes in sphingolipid metabolism that hydrolyze sphingomyelin (SM) and generate ceramide (Cer). The purpose of this study was to examine relationships between ocular surface SMases, SPL composition, and parameters of Meibomian gland dysfunction (MGD).

Methods

Individuals were grouped by meibum quality (n = 25 with poor-quality, MGD, and n = 25 with good-quality, control). Meibum and tears were analyzed with LC-MS to quantify SPL classes: Cer, Hexosyl-Ceramide (Hex-Cer), SM, Sphingosine (Sph), and sphingosine 1-phosphate (S1P). SMase activity in tears were quantified using a commercially available ‘SMase assay’. Statistical analysis included multiple linear regression analyses to assess the impact of SMase activity on lipid composition, as well as ocular surface symptoms and signs of MGD.

Results

Demographic characteristics were similar between the two groups. nSMase and aSMase levels were lower in the poor vs good quality group. aSMase activity in tears negatively correlated with SM in meibum and tears and positively with Sph in meibum and S1P in tears. Lower SMase activity were associated with signs of MGD, most notably Meibomian gland dropout.

Conclusion

This study suggests that individuals with MGD have reduced enzymatic activity of SMases in tears. Specifically, individuals with poor vs good meibum quality were noted to have alterations in SMase activity and SPL composition of meibum and tears which may reflect deviations from normal lipid metabolism in individuals with MGD.

中文翻译：

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眼表鞘磷脂酶、睑脂和泪液鞘脂与睑板腺功能障碍的临床参数之间的关系

 目的

鞘脂(SPL) 是一类脂质分子，在我们的身体中发挥着重要的功能和结构作用，并且是睑脂的组成部分。鞘磷脂酶 (SMase) 是鞘脂代谢中的关键酶，可水解鞘磷脂(SM) 并生成神经酰胺(Cer)。本研究的目的是检查眼表SMase、SPL 组成和睑板腺功能障碍 (MGD) 参数之间的关系。

 方法

个体根据睑脂质量进行分组（n = 25 为不良质量，MGD，n = 25 为良好质量，对照）。使用 LC-MS 分析睑脂和泪液以量化 SPL 类别：Cer、己糖基神经酰胺 (Hex-Cer)、SM、鞘氨醇 (Sph) 和 1-磷酸鞘氨醇 (S1P)。使用市售的“SMase 测定”对泪液中的 SMase 活性进行定量。统计分析包括多元线性回归分析，以评估 SMase 活性对脂质成分以及 MGD 眼表症状和体征的影响。

 结果

两组之间的人口统计学特征相似。与优质组相比，劣质组的 nSMase 和 aSMase 水平较低。泪液中的 aSMase 活性与睑脂和泪液中的 SM 呈负相关，与睑脂中的 Sph 和泪液中的 S1P 呈正相关。 SMase 活性较低与 MGD 症状相关，最显着的是睑板腺脱落。

 结论

这项研究表明，患有 MGD 的人泪液中 SMase 的酶活性降低。具体而言，睑脂质量差与好的个体的睑脂和泪液的 SMase 活性和 SPL 组成发生变化，这可能反映了 MGD 个体与正常脂质代谢的偏差。