Cholesteryl esters as a depot for very long chain fatty acids in human meibum

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of the ocular surface. Tears hydrate and lubricate the mucous membranes constituting the ocular surface, supply nourishment to the avascular corneal epithelium, and provide a smooth optical surface essential for visual acuity. The drainage of tears via the lacrimal puncta fl ushes contaminants and irritants out of the eye, thereby functioning as a fi rst line of defense for the anterior eye against invading pathogens ( 1, 2 ). The typical volume of tears in normal eyes ranges from 3.4 to 10.7 l per eye ( 3 ). Despite its small volume, tears represent a biological fl uid of immense complexities with a wide array of proteins/peptides, electrolytes, lipids, and small molecule metabolites contributed by distinct sources ( 1 ). The precise balance of these various metabolites is crucial in ensuring proper physiological function and maintaining biophysical integrity of the precorneal tear fi lm. Perturbations in this delicate equilibrium may be manifested in various ocular conditions such as dry eye syndrome (DES) and blepharitis ( 1,4,5 ).Recent decades have witnessed tremendous progress in the systematic profi ling of proteins as well as small molecule metabolites present in tears ( 1, 6-9 ). Furthermore, with technological advancements in MS and nuclear magnetic Abstract The tear fi lm covers the anterior eye and the precise balance of its various constituting components is critical for maintaining ocular health. The composition of the tear fi lm amphiphilic lipid sublayer, in particular, has largely remained a matter of contention due to the limiting concentrations of these lipid amphiphiles in tears that render their detection and accurate quantitation tedious. Using systematic and sensitive lipidomic approaches, we validated dif ferent tear collection techniques and report the most comprehensive human tear lipidome to date; comprising more than 600 lipid species from 17 major lipid classes. The tear fl uid covers the anterior surface of the cornea and serves critical functions in maintaining the homeostasis

Section: Lipid Extractionmentioning

confidence: 99%

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

Lam

Tong

Duan

et al. 2014

243

229

“…For both saturated CEs, the ESI technique proved to have a better signal intensity than APCI mode ( ‫ف‬ 7-to 13-fold better). Having said that, other researchers, including Butovich et al ( 26,27 ), have shown the application of APCI to measure in one analytical run free cholesterol and cholesterol esters coupled to a reversed phase column. But in their research, they were not measuring metabolic fl ux of free cholesterol and cholesterol esters in plasma.…”

Section: Gc/ms Of Total Plasma Palmitate and Cholesterolmentioning

confidence: 99%

In vivo D2O labeling to quantify static and dynamic changes in cholesterol and cholesterol esters by high resolution LC/MS

Castro-Perez

Previs

McLaren

et al. 2011

high level of cholesterol in the body circulation is strongly associated with atherosclerosis ( 6-10 ). The source of cholesterol comes from different areas: dietary, de novo synthesis, and synthesis in extrahepatic tissues. The liver acts as a cross-junction at which cholesterol is incorporated into HDL/LDL, and then secreted as free cholesterol in the bile or in the form of bile salts/acids.Studies of cholesterol metabolism typically require measurements of static concentrations of cholesterol to identify differences between models or to determine the presence or absence of a disease phenotype. The simultaneous use of stable or radio isotope fl ux analysis can aid in understanding the nature of a metabolic abnormality and yield information regarding the dynamics that contribute to altered or perturbed homeostasis.Questions surrounding cholesterol dynamics have been addressed using isotopic-labeled water for nearly 70 years, beginning with the pioneering studies of Schoenheimer The liver plays a vital role in cholesterol metabolism ( 1-5 ) and homeostasis. In addition to this, production of bile acids from cholesterol also plays an important role in the secretion and degradation of plasma lipoproteins. A 25 September 2010. Published, JLR Papers in Press, September 30, 2010 DOI 10.1194 In vivo D2O labeling to quantify static and dynamic changes in cholesterol and cholesterol esters by high resolution LC/MS Manuscript received 27 July 2010 and in revised form

“…The samples of normal human meibum were collected from both lower and upper eyelids of seven volunteers (three males and four females) using a platinum spatula, dried, and stored exactly as described earlier (9)(10)(11)15 ). The samples were used for structural analyses of meibomian lipids only; no conclusions about the effects of gender, age, type of diet, etc .…”

Section: Sample Collectionmentioning

confidence: 99%

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

Butovich

Wojtowicz

Molai

2009

Self Cite

158

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