Double‐bond patterns of fatty acids and alcohols in steer and human meibomian gland lipids

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Abstract
Ozonolysis studies of the monoenes of the fatty chain types in lipids of steer meibomian gland excreta (meibum) have confirmed earlier structural assignments based on gas liquid chromatography (GLC) retention data and have assisted in assigning complete structures to a group of recently identified ω-hydroxy fatty acids. The ω-hydroxy acids include straight-chain monoenoic acids (85%), saturated anteiso and iso acids (13%), monoenoic acids of the latter group (1%) and, finally, saturates of the normal monoenoic acids (1%). All the fatty chains of meibum can be biosynthesized by a unified process of chain buildup to primary chain lengths of 12∶0–20∶0 for the straight evens, with 16∶0 predominating, 13∶0–21∶0 for the straight odds with 17∶0 predominating, i16∶0 to i28∶0 for the iso and ai17∶0 to ai29∶0 for the anteiso chain types; then Δ9 desaturation of each of these chain types; and finally chain elongation of 1–10 C2 units. Some chain degradation may also occur. The meibum lipid components involved are unsubstituted fatty acids, α-OH fatty acids, ω-OH fatty acids, fatty alcohols and some other lipid components incompletely characterized. The carbon skeletons are straight even, straight odd, iso and anteiso except that the α-OH fatty acids are only straight even and straight odd and these chains are not elongated. All fatty chains are almost entirely saturated and monoenoic, the polyenes occurring in only trace amounts. Biosynthesis of the fatty chains of human meibum evidently occurs similarly, except that considerably more 18∶0 than 16∶0 fatty acids are built up by the fatty acid synthetase, before desaturation and extension.