MEIBOMIAN GLAND PHOSPHOLIPIDS

The content of the meibomian gland lipid exprimate is known, but littl e is known about the phospholipids that comprise the glandular cells. The purpose of the present study is to identify and quantitate the pho spholipid complement of the meibomian gland cells that produce the lip id secretion of meibomian oil and which is vital to tear film stabilit y. Eyelids (n = 50) were excised from rabbits, and after surgical remo val of surrounding tissues, the tarsal plates with and without express ing meibomian oil were extracted and phospholipids of the plates quant ified by P-31 nuclear magnetic resonance (NMR). Seventeen phospholipid s were quantified from tarsal plates expressed of oil and tarsal plate s containing meibomian oil: alkylacylphosphatidylcholine (AAPC), dihyd rosphingomyelin (DHSM), dimethylphosphatidylethanolamine, diphosphatid ylglycerol (cardiolipin), ethanolamine plasmalogen (EPLAS), lysoethano lamine plasmalogen, lysophosphatidylcholine, lysophosphatidylethanolam ine, lysophosphatidylserine, phosphatidic acid, phosphatidylcholine (P C), phosphatidylethanolamine (PE), phosphatidylglycerol, phosphatidyli nositol, phosphatidylserine, sphingomyelin (SM), sphingosylphosphorylc holine. The six zwitterionic and neutral phospholipids, DHSM, EPLAS, P E, SM, AAPC, and PC together comprise 79.5% of the total meibomian gla nd phospholipid profile (in meibomian oil this value is 84.2%). The zw itterionic and neutral phospholipids dominate meibomian gland phosphol ipid profiles. Since the meibomian gland cells undergo holocrine secre tion and form the meibomian gland secretion, such a composition is con sistent with the hypothesis that a chemically stable lamellar surfacta nt layer phospholipids bind non-polar meibomian oil to the aqueous lay er of the tear film.