Phospholipids in Meibomian Gland Secretion

Abstract

The bulk of the lipid layer overlying the aqueous portion of the precorneal tear film is composed of polar and nonpolar components. The nonpolar lipids have been the subject of numerous studies; however, the polar lipids have remained relatively uncharacterized. The polar lipids are thought to contain surfactant phospholipids that are critical to the spreading of a lipid film over the aqueous layer, by providing an interface between this layer and the nonpolar lipids. The purpose of the present study is to identify and quantitate the phospholipid complement of meibomian gland secretion which provides the tear film with phospholipids. Meibomian gland secretion was collected from rabbits and phospholipids identified and quan-titated by ³¹P nuclear magnetic resonance spectroscopy. Ten phospholipids were detected from meibomian gland secretion: diphosphatidylglycerol, dihydrosphingomyelin, ethanolamine plasmalogen, phosphatidylethanolamine (PE), phosphatidyl serine, sphingomyelin, lysophosphatidylcholine, phosphate dylinositol, alkylacylphosphatidylcholine, and phosphatidyl-choline (PC). The two major phospholipids were PC and PE, together comprising nearly 60% of the total phospholipid profile. The nature and relative concentrations of the meibomian gland secretion phospholipids are congruous with a surfactant role at the aqueous-lipid interface and, considering the physical chemistry of the tear film, suggest that the phospholipids should be organized in a very flat or planar configuration.

The Combined Effect of Azithromycin and Insulin-Like Growth Factor-1 on Cultured Human Meibomian Gland Epithelial Cells

“…The increase in these neutral and phospholipids, which are major components of meibum, is highly significant, because MGD is characterized by a reduced quantity and quality of meibum. [23][24][25][26][27] For example, CE, FC, and phospholipids are decreased in patients with MGD, 2,21 and we show that AZM increases CE, FC, and phospholipids in meibomian gland epithelial cells in vitro, consistent with the report from a clinical trial that AZM restores the lipid composition and the tear film stability in meibum of MGD patients. 8 The effect of IGF-1 on lipid accumulation is quite distinct from that of AZM.…”

Toward an Animal Model of the Human Tear Film: Biochemical Comparison of the Mouse, Canine, Rabbit, and Human Meibomian Lipidomes

“…The tested species included the steer, the gerbil, the rat, the rabbit, the dog, the hamster, and the mouse. 7,[14][15][16][17][18][19][20][21][22] The approaches used in those studies included various types of chromatography and, in the later studies, mass spectrometry. In most of the studies where structural information on lipids was to be obtained, the lipids were hydrolyzed to make them suitable for subsequent chromatographic analysis.…”

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

“…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.…”