Analysis of wax ester molecular species by high performance liquid chromatography/atmospheric pressure chemical ionisation mass spectrometry

148

146

that are excreted to the skin surface and form sebum. The function of sebum is still a matter of investigation. It is only hypothesized that sebum may play a role in the protection of skin from dehydration, ultraviolet radiation (UVR), wrinkling, and infection ( 1, 2 ). The sebaceous lipid mixture is highly complex and consists of triacylglycerols (TAG), diacylglycerols (DAG), and free fatty acids (FFA), which together account for 50-60% of its composition. Sebum also contains 20-30% wax esters (WE), 10-16% squalene (SQ), and 2-4% cholesterol esters (CE) ( 1, 2 ). Initial analyses of the components of the sebaceous lipid mixture conducted by led to the identifi cation of several different types of acyl chains in esters with glycerol, cholesterol, and waxes. Fatty acids (FA) with an odd number of carbon atoms, branched side chains, and sites of unsaturation at unconventional positions were characterized. However, information on the intact lipids remained to be determined. A detailed characterization of the lipid repertoire in sebum in physiologic and diseased conditions is very limited due to the unavailability of methods for the comprehensive and simultaneous analysis of whole lipids. Prior investigations of the composition of sebum have been mostly concerned with acne, a multifactorial skin disorder that affects the pilosebaceous unit. Currently, only a few parameters are addressed when investigating alterations in sebum, such as SQ levels and the composition of FA obtained from the hydrolysis of TAG, DAG, WE, and CE. The methodology for the targeted analysis of SQ involves gas chromatography (GC) with Abstract Sebum is a complex lipid mixture that is synthesized in sebaceous glands and excreted on the skin surface. The purpose of this study was the comprehensive detection of the intact lipids that compose sebum. These lipids exist as a broad range of chemical structures and concentrations. Sebum was collected with SebuTape TM from the foreheads of healthy donors, and then separated by HPLC on a C8 stationary phase with sub 2 µm particle size. This HPLC method provided high resolution and excellent reproduc- Skin is a metabolically active tissue that contains sebaceous glands, which are specialized organelles equipped for the synthesis of a broad spectrum of lipid compounds

Section: Identifi Cation Of Major Wax Esterssupporting

confidence: 81%

Comprehensive analysis of the major lipid classes in sebum by rapid resolution high-performance liquid chromatography and electrospray mass spectrometry

Camera

Ludovici

Galante

et al. 2010

148

146

“…WE standards were obtained from Nu-Check-Prep, Inc. (Elysian, MN) or synthesized via acid chlorides ( 14 ). The FAs for synthesis were purchased from Sigma-Aldrich (St. Louis, MO), TCI America (Portland, OR), Matreya LLC (Pleasant Gap, PA), and Larodan Fine Chemicals AB (Malmö, Sweden).…”

Section: Standards Of Wesmentioning

confidence: 99%

“…GC coupled with electron ionization mass spectrometry (GC/EI-MS) offers high separation effi ciency, ease of use, and mass spectra allowing structure elucidation. Other analytical methods based on liquid chromatography/mass spectrometry or matrix-assisted laser desorption/ionization mass spectrometry (13)(14)(15) can also be utilized, especially in the case of thermally unstable or insuffi ciently volatile WEs.…”

mentioning

confidence: 99%

Structural characterization of wax esters by electron ionization mass spectrometry

Urbanová

Vrkoslav

Valterová

et al. 2012

Self Cite

This article is available online at http://www.jlr.org Dietary WEs are an important source of very long chain fatty alcohols and acids that exert regulatory roles in the cholesterol metabolism ( 11 ). Naturally occurring WEs usually form complex mixtures composed of many molecular species. These mixtures contain straight-and branchedchain esters of various chain lengths and numbers of double bonds depending on the biochemical synthetic pathways in particular organisms. WEs are also produced industrially and used in large quantities in cosmetics, polishes, lubricants, surface coating, and other applications ( 12 ). Gas chromatography (GC) has frequently been used for analyzing WEs, often after their hydrolysis. The separation of intact WEs has been made possible by the introduction of high-temperature columns. GC coupled with electron ionization mass spectrometry (GC/EI-MS) offers high separation effi ciency, ease of use, and mass spectra allowing structure elucidation. Other analytical methods based on liquid chromatography/mass spectrometry or matrix-assisted laser desorption/ionization mass spectrometry ( 13-15 ) can also be utilized, especially in the case of thermally unstable or insuffi ciently volatile WEs.The research on the mass spectra of FA esters can be traced back to the early days of mass spectrometry. The EI spectra are explained perhaps in all of the textbooks on organic mass spectrometry, but the discussion is mostly limited to methyl or ethyl esters. The EI mass spectra of saturated straight-chain WEs has been studied for more than 40 years using both low-and high-resolution measurements and deuterium-labeling experiments (16)(17)(18)(19)(20)(21)(22). The spectra interpretation is usually straightforward in terms of the determination of the molecular weight and acid/alcohol chain length. However, the structure elucidation becomes much more complicated for branched or unsaturated esters, e.g., in case of samples of animal or human origin. Only a few reports closely dealing with the Abstract The interpretation of the electron ionization mass spectra of straight-chain and methyl-branched saturated and unsaturated wax esters (WEs) is discussed in this study based on the spectra of 154 standards. The most important fragments indicative of the structure of the acid and alcohol chains are identifi ed and summarized for WEs with various number of double bonds in the chains. Briefl y, most WEs provide acylium ions allowing structural characterization of the acid part, whereas the alcohol part gives corresponding alkyl radical cations. The elemental composition of selected important fragments is established from a highresolution accurate mass analysis. The ion abundances are discussed with respect to the length and unsaturation of the aliphatic chains. The interpretation of the spectra of branched or unsaturated WEs requires the recognition of small but important peaks that are diffi cult to discern among the other fragments. We demonstrate that such fragments are easily detected in differential mass spec...

“…In addition, systematic comparisons by guest, on May 7, 2018 www.jlr.org internal standard (Avanti Polar Lipids). Levels of WEs were quantifi ed using three standards; palmitoyl palmitate (C16:0C16:0) was used for WEs with saturated fatty acyl heads, while WEs containing unsaturated fatty acyl heads were quantitated using 13 C18:1C26:0 and 13 C18:1C28:0, which were synthesized in-house using oleic acid-1,2,3,7,8,9,10-13C7 following the procedure described previously ( 25 ). The detailed mass spectrometric procedures for analysis of WEs have been reported elsewhere ( 26 ).…”

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

245

229

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