Lipidomic platform for structural identification of skin ceramides with α-hydroxyacyl chains

Skin ceramides are sphingolipids consisting of sphingoid bases, which are linked to fatty acids via an amide bond. Typical fatty acid acyl chains are composed of α-hydroxy fatty acid (A), esterified ω-hydroxy fatty acid (EO), non-hydroxy fatty acid (N), and ω-hydroxy fatty acid (O). We recently established a lipidomic platform to identify skin ceramides with non-hydroxyacyl chains using tandem mass spectrometry. We expanded our study to establish a lipidomic platform to identify skin ceramides with α-hydroxyacyl chains. Tandem mass spectrometry analysis of A-type ceramides using chip-based direct infusion nanoelectrospray-mass spectrometry showed the characteristic fragmentation pattern of both acyl and sphingoid units, which can be applied for structural identification of ceramides. Based on the tandem mass spectrometry fragmentation patterns of A-type ceramides, comprehensive fragmentation schemes were proposed. Our results may be useful for identifying A-type ceramides in the stratum corneum of human skin.