Sphingolipids (SPL) composition in meibum and tears in patients with poor vs good meibum quality differs considerably, according to a study published in The Ocular Surface. Researchers suggest this data might be useful to determine therapeutic targets for disease.
This class of lipids have a role in cell signaling, inflammation, and apoptosis, researchers report. The investigators designed their study to examine meibum and tear SPL composition in patients with good and poor meibum quality. They looked at patients grouped by meibum quality (n=25 with poor quality, case group and n=25 with good quality, control group). They analyzed meibum and tears using liquid chromatography-mass spectrometry (LC-MS) to quantify SPL classes. They compared semiquantitative and relative composition (mole percent) of SPL and major classes, ceramide (Cer), hexosyl-ceramide (Hex-Cer), sphingomyelin (SM), sphingosine (Sph), and sphingosine 1-phosphate (S1P) between groups.
They determined that demographic characteristics were similar between the 2 groups. However, “overall, individuals with poor meibum quality had more SPL pmole in meibum and tears than controls,” the study explains. “Relative composition analysis revealed that individuals with poor meibum quality had SPL composed of less Cer, Hex-Cer, and Sph and more SM compared to individuals with good quality meibum. This pattern was not reproduced in tears as individuals with poor meibum quality had SPL composed of a similar amount of Cer, but more Hex-Cer, Sph and SM compared to controls.”
“In meibum, SPL pmole and relative composition most strongly correlated with MG metrics while in tears, SPL pmole and relative composition most strongly correlated with tear production. SPL in both compartments, specifically Cer pmole in meibum and S1P% in tears, correlated with DE symptoms,” according to the report.
Their study’s limitations include their MGD definitions and collection and analysis methodology. Meibum quality had been graded on a 0 to 2 scale (clear, cloudy, and yellow) with increasing quantities of unsaturated free fatty acid (FFA) “noted” with increasing meibum grade in previous research. In this current study, researchers looked at various classes of SPL but not FFA, grading meibum quality with a clinically standard scale (range 0–4: clear, cloudy, granular, toothpaste, no meibum extracted). They also subclassified meibum by “poor” vs “good” categories based on their own clinical interpretation of the grading.
Galor A, Sanchez V, Jensen A, et al. Meibum sphingolipid composition is altered in individuals with meibomian gland dysfunction-a side by side comparison of meibum and tear sphingolipids. Ocul Surf. 2021;23:87-95. doi:10.1016/j.jtos.2021.11.011