Meibomian gland phospholipids

Abstract

The content of the meibomian gland lipid exprimate is known, but little is known about the phospholipids that comprise the glandular cells. The purpose of the present study is to identify and quantitate the phospholipid complement of the meibomian gland cells that produce the lipid secretion of meibomian oil and which is vital to tear film stability. Eyelids (n = 50) were excised from rabbits, and after surgical removal of surrounding tissues, the tarsal plates with and without expressing meibomian oil were extracted and phospholipids of the plates quantified by 31P nuclear magnetic resonance (NMR). Seventeen phospholipids were quantified from tarsal plates expressed of oil and tarsal plates containing meibomian oil: alkylacylphosphatidylcholine (AAPC), dihydrosphingomyelin (DHSM), dimethylphosphatidylethanolamine, diphosphatidylglycerol (cardiolipin), ethanolamine plasmalogen (EPLAS), lysoethanolamine plasmalogen, lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine, phosphatidic acid, phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, sphingomyelin (SM), sphingosylphosphorylcholine. The six zwitterionic and neutral phospholipids, DHSM, EPLAS, PE, SM, AAPC, and PC together comprise 79.5% of the total meibomian gland phospholipid profile (in meibomian oil this value is 84.2%). The zwitterionic and neutral phospholipids dominate meibomian gland phospholipid profiles. Since the meibomian gland cells undergo holocrine secretion and form the meibomian glad secretion, such a composition is consistent with the hypothesis that a chemically stable lamellar surfactant layer phospholipids bind non-polar meibomian oil to the aqueous layer of the tear film.

Lipids of human meibum: mass-spectrometric analysis and structural elucidation

“…Thus, BO, Chl-O, and TP are typical representatives of, correspondingly, WE, Chl-E, and TAG, similar to the species previously found in MGS. OA, POPC, and SM were also reported to be present in human meibum (15,25,28). Other lipids mentioned in the text were typical representatives of the corresponding lipid classes.…”

“…No structural evaluations of the intact lipids were performed in any of those studies. A decade ago, 31 P-nuclear magnetic resonance spectroscopy ( 31 P-NMR) was implemented to analyze the PL composition of homogenized tarsal plates of rabbits (14,15). Several PL species were detected, among which phosphatidylcholine (PC) and phosphatidylethanolamine comprised almost 50% of the overall PL pool.…”

Complete Androgen Insensitivity Syndrome

“…Polar lipids, such as phosphatidylethanolamine and phosphatidylcholine, are critical components of the tear film and serve to maintain the oil-aqueous interface and provide functional stability for the neutral lipids. 11,14,27 Therefore, to further test our hypothesis, we endeavored in this study to determine whether androgen receptors affect fatty acid (FA) profiles of neutral and polar lipids in human meibomian gland secretions. To achieve this objective, we compared the lipid patterns in secretion samples from individuals with CAIS with those from agematched female and male controls.…”

Interaction of phospholipid transfer protein with human tear fluid mucins

“…On the basis of analysis of meibomian gland secretions, the lipid layer is suggested to be composed of wax esters, sterol esters, and polar lipids ( 4, 5 ). It has been suggested, based on the hydrophobic effect, that the charged (polar) phospholipids are disposed adjacent to the aqueous-mucin layer and, externally to this, a layer composed of nonpolar lipids, such as cholesteryl esters and triglycerides, face the tear-air interface (6)(7)(8). This type of lipid organization is believed to strongly oppose evaporation.…”