Human tear film and meibum. Very long chain wax esters and (O-acyl)-omega-hydroxy fatty acids of meibum

Abstract

by various laboratories during the last few decades ( 1-8 ).In TF, meibum is believed to form its outermost layer, which retards evaporation of water from the bulk of TF and from the ocular surface beneath it ( 7 ). Yet another function of meibum is to form a hydrophobic barrier along the margins of the eyelids to contain TF at, and prevent it from leaking out of, the designated ocular surface area ( 2 ). These protective functions imply a very hydrophobic nature of meibum. Indeed, the major meibum components were identifi ed as various wax esters (WEs) and cholesteryl esters (CEs) with long-chain and very longchain FA ( 9-11 ). The information on acylglycerol content of meibum is more limited as no defi nite structural information on the putative meibomian acylglycerols is currently available ( 12, 13 ). Interestingly, lipidomic analyses of human meibum demonstrated that its composition is distinctively different from that of sebum. For example, free cholesterol, squalene, ceramides (Cers), and typical phospholipids were shown to be minor components of meibum ( 9-11, 14, 15 ), although they dominated in the skin ( 16,17 ).Meibum has been analyzed using various experimental techniques, discussion of which goes beyond the scope of this article. Recently, we published preliminary results on the lipid composition of human meibum and tears ( 9-11, 15 ). The major method employed in these studies was normal phase high performance liquid chromatography in combination with atmospheric pressure chemical ionization mass spectrometry (NP HPLC-MS). The main advantage of the NP HPLC is its ability to separate different classes of lipids. For example, mono-, di-, and triacylglycerols (MAGs, DAGs, and TAGs, respectively) elute as three distinctively different groups of HPLC peaks and so do other groups of lipids (free FAs and their amides and Meibum is a lipid-rich secretion that is produced by Meibomian glands located at the ocular lid margins of both upper and lower eyelids of various mammals and humans. Meibum is an intrinsic part of the human tear fi lm (TF), the main role of which is to protect the ocular surface from dehydration. Among other proposed functions of TF are antimicrobial, lubricatory, and nutritional ones. For general information on meibum and TF, the reader is advised to read earlier comprehensive reviews published

Extensive characterization of human tear fluid collected using different techniques unravels the presence of novel lipid amphiphiles

“…1 ; class of amphiphilic compounds fi rst reported in meibum by Butovich, Wojtowicz, and Foulks ( 17 ). The tear (and meibum) lipidomes presented in this study are a signifi cant expansion from a previous report by our group ( 10 ) and those of others ( 2,21,22 ).…”

“…Samples were then centrifuged at 3,000 rpm at 4°C for 5 min and the lower organic phase was extracted. The aqueous resonance spectroscopy, the lipid composition of the human meibomian gland secretions, the predominant source of lipids for the precorneal tear fi lm, has been elucidated with great compositional and structural details (10)(11)(12)(13)(14)(15)(16)(17)(18)(19). A comprehensive lipidomic analysis of the tear fl uid per se, however, has lingered behind.…”

“…NeuAc ␣ 2-3Gal ␤ 1-4Glc ␤ -Cer (GM3) species were quantifi ed using C17-GM3 as an internal standard. O-acyl--hydroxy-fatty acid (OAHFA) species were quantitated using OAHFA 18:1/16:0, which was synthesized as previously described ( 17 ).…”

Epidermal expression of an Elovl4 transgene rescues neonatal lethality of homozygous Stargardt disease-3 mice

“…The obtained m/z data served for reverse phase HPLC/MS and MS collision-induced fragmentation analyses of the lipids of both the band X and total epidermal extracts. The conditions used in HPLC/MS and MS collision-induced fragmentation analysis, and assignment of chemical formulas for analyzed lipids have been described previously ( 22 ).…”

Retinal very long-chain PUFAs: new insights from studies on ELOVL4 protein

“…Very little is therefore known about the metabolism and function of VLC-PUFA and VLC-FA in mammals, except for their increase in disorders of peroxisomal function ( 3,16,20,21 ), as components of the secretions of meibomian glands (22)(23)(24)(25)(26)(27), and their reduction in animal models of autosomal dominant Stargardt-like macular dystrophy (STGD3) ( 28-32 ), a juvenile form of macular degeneration. In contrast, the roles of long-chain PUFA (LC-PUFA) with carbon chains that range from C18 to C24 are fairly well understood, especially in the retina and other neural tissues.…”