Human milk plasmalogens: an unrecognized pool of novel lipid enriched in long chain polyunsaturated fatty acids (38.1)

Abstract

Ethanolamine plasmalogens (EPLas) are unique phospholipids (PL) with potential roles in development of the brain and intestine, where they are present in high amounts. PLas, like arachidonic (20:4n‐6) and docosahexaenoic acid (DHA, 22:6n‐3) are found only in animal lipid. They are present in human milk, but not milk substitutes or intravenous lipid. Their characteristics, including fatty acid composition, are poorly understood in part due to challenges of separation and recovery from diacyl PL which differ from PLas by the lack of a carbonyl group on the sn‐1 glycerol carbon. Our objectives were to develop methodology for separation, recovery and analysis of EPLas from human and cow milk, then determine their composition together with that of milk total lipid, diacyl ethanolamine PL (PE) and phosphatidylcholine (PC). Milk PL were separated using solid phase extraction, then diacyl PE, EPLas and PC separated by HPLC, recovered and their fatty acids determined by GLC for mature milk from 25 women. Human milk EPLas were enriched in long chain n‐6 and n‐3 fatty acids, 20:4n‐6 11.2 ±1.4%, eicosapentanoic (20:5 n‐3) 1.2 ± 0.7%, adrenic acid (22:4n‐6) 2.2 ± 0.5%, and DHA 2.9 ± 1.4 % compared to 3.6 ± 0.8; 0.7 ± 0.3; 0.3 ± 0.2; and 1.5 ± 0.9%, respectively, in PE and 0.47 ± 0.07; 0.14 ± 0.09; 0.08 ± 0.02; and 0.39 ± 0.3%, respectively, in milk total lipid. We found a significant correlation between DHA in milk total lipid and PE (r =0.57) and PC (r=0.42), but not EPLas (r=0.13), suggesting little variability in EPLas with maternal diet. Intriguingly, cow milk colostrum and mature milk show similar patterns. In conclusion, our work raises the question of whether EPLas are a distinct pool of bioactive, tightly regulated milk lipids that contribute to n‐6 and n‐3 fatty acids in the breast‐fed infant.