Unusual Cholesterol Esters in the Sebum of Young Children

Cholesterol esters (CE) having fatty acids of more than 18 carbons are a prominent feature of fetal skin surface lipid (vernix caseosa), but are a minor component of adult lipid. The difference may be related to the fact that fetal sebaceous glands generally synthesize little lipid. If so, it would be expected that prepuberal children, who also have very inactive glands, would secrete CE with a large proportion of very-long-chain fatty acids. To test this conjecture, skin surface CE from young children were isolated and analyzed. Sebum was extracted from the hair of 38 children, aged six to nine. To obtain a measure of sebaceous lipogenesis, the class composition of the lipid was determined by quantitative thin-layer chromatography and the ratio of wax esters/ [cholesterol + cholesterol esters] (WE/[CH + CE]) was calculated. CE were then isolated from the lipid and hydrolyzed. The freed fatty acids were converted to fatty acid methyl esters (FAME) and analyzed by capillary gas chromatography to determine the proportion with more than 18 carbons. FAME from five of the subjects were then separated into saturated and monounsaturated fractions and analyzed again by gas chromatography to identify chain types. Ratios of WE/[CH + CE] ranged from 0.08 to 2.8 in the subjects. The proportion of CE FAME with more than 18 carbons ranged from 15 to 72%, with the highest proportion being found in the children with the lowest WE/[CH + CE]. The saturated FAME were mostly iso- or anteisobranched, whereas the monounsaturated FAME were mostly straight-chain extension products of 16: 1Δ9 or 18: 1Δ9