Establishing the role of dietary lipids in meibogenesis

Abstract

Purpose : Meibomian glands (MG) play a vital role in ocular physiology producing meibum – a complex mixture of cholesterol (Chl), Chl esters (CE), triacylglycerols (TAG), and other classes of lipids, in a process termed meibogenesis. The purpose of this study was to establish the role of dietary Chl and TAG in meibogenesis, and determine if dietary lipids can be directly incorporated in meibum without undergoing deep anabolic/catabolic transformations first.

Methods : Wild type C57Bl/6J mice (n=16) were gavaged daily with Chl-2,2,3,4,4,6-d₆ (d₆-Chl) and triolein-1,2,3,7,8-¹³C₅ (¹³C₅-TO) dissolved in a vehicle. At Days 0, 7, 14, and 28 of gavaging, the mice were euthanized (4 mice at each time point) and their tarsal plates, small intestine, liver, plasma, and feces specimens were collected. Then, lipids were extracted from all tissue samples and analyzed using ultra-high-performance liquid chromatography/high-resolution mass spectrometry to determine the fate of the tracers in the tissues.

Results : We established that ¹³C₅-TO and its metabolites could be detected in the small intestine, plasma and liver in diminishing quantities, but not in the feces or meibum even after 4 weeks of gavaging. Our results demonstrate that ¹³C₅-TO underwent deep catabolic transformations and could not be directly incorporated into meibum neither as an intact TAG, nor as its metabolized products (diacylglycerols, monoacylglycerols, free fatty acids, or their esters with other compounds). On the other hand, d₆-Chl was detected in all tested tissues, including meibum. Moreover, in MG d₆-Chl underwent successful esterification into long- and ultra-long-chain CE typical of Meibomian lipids. Importantly, enrichment studies demonstrated that d₆-Chl could be accumulated in meibum in excessive quantities suggesting that increased levels of Chl in blood can increase levels of Chl in MG and meibum.

Conclusions : Our experiments demonstrated that dietary Chl may directly affect Chl and CE homeostasis in MG, while dietary TAG seem to be extensively catabolized in the small intestine, liver, and blood before reaching MG, and, thus, could not directly influence the outcome of meibogenesis.

This is a 2021 ARVO Annual Meeting abstract.