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Cholesterol dynamics in the foetal and neonatal brain as reflected by circulatory levels of 24S‐hydroxycholesterol

Oxysterols, particularly those hydroxylated in the steroid side‐chain, are formed from cholesterol by specific cytochrome P450 enzymes and may facilitate elimination of cholesterol from extrahepatic sources. In humans, the greatest portion of circulating 24S‐hydroxycholesterol (24S‐OH‐Chol) is derived from the brain and the absolute concentration depends on age. In the present study, concentrations of 24S‐OH‐Chol and for comparison 27‐OH‐Chol were determined by a highly sensitive isotope dilution method using gas chromatography‐mass spectrometry in serum samples from normal preterm and term neonates and those with Rhesus haemolytic disease, taken serially for diagnostic purposes. Serum concentrations of cholesterol, 24S‐OH‐Chol and 27‐OH‐Chol were similar in venous versus arterial cord blood of 6 term neonates. Serum concentrations of 24S‐OH‐Chol and 27‐OH‐Chol in 12 small for gestational age (SGA) preterm neonates were significantly lower than those in 12 appropriate for gestational age (AGA) preterm neonates (p < 0.001), and also lower than those in 12 SGA (p < 0.001) and 12 AGA term neonates (p < 0.05). Serum cholesterol was significantly higher in preterm than in term neonates (p < 0.001). 24S‐OH‐Chol serially determined in 8 infants with Rhesus haemolytic disease increased 5‐6‐fold during the first 3 mo after birth (from 42 ± 20 ng ml−1 to 227 ± 71 ng ml−1). 27‐OH‐Chol increased simultaneously from 30 ± 14 ng m ml−1 to 100 ± 39 ng m ml−1.