Analysis of (O-acyl) alpha- and omega-hydroxy fatty acids in vernix caseosa by high-performance liquid chromatography-Orbitrap mass spectrometry
Abstract
Fatty acid esters of long-chain hydroxy fatty acids or (O-acyl)-hydroxy fatty acids (OAHFAs) were identified for the first time in vernix caseosa and characterized using chromatography and mass spectrometry. OAHFAs were isolated from the total lipid extract by a two-step semipreparative TLC.
The general structure of OAHFAs was established using high-resolution and tandem mass spectrometry of intact lipids and their transesterification and derivatization products. Two isomeric lipid classes were identified: O-acyl esters of omega-hydroxy fatty acids (omega OAHFA) and O-acyl esters of alpha-hydroxy fatty acids (alpha OAHFAs).
To the best of our knowledge, alpha OAHFAs have never been detected in any biological sample before. Chromatographic separation and identification of OAHFAs species were achieved using non-aqueous reversed-phase HPLC coupled to electrospray ionization hybrid linear ion trap-Orbitrap mass spectrometry.
The lipid species were detected as deprotonated molecules, and their structures were elucidated using data-dependent fragmentation in the negative ion mode. More than 400 OAHFAs were identified in this way.
The most abundant omega OAHFAs species were 28:0/omega-18:2, 29:0/omega-18:2, 30:0/omega-18:2, 32:0/omega-18:2, and 30:0/omega-18:3, while alpha OAHFAs comprised saturated species 21:0/alpha-24:0, 22:0/alpha-24:0, 23:0/alpha-24:0, 24:0/alpha-24:0, and 26:0/alpha-24:0. OAHFAs were estimated to account for approximately 0.04% of vernix caseosa lipids.