Fig. 1.
Simplified diagram of the metabolism of orally consumed 2H-labelled methyl-d9-choline and its relationship to CDP–choline and phosphatidylethanolamine N-methyl transferase (PEMT)-derived phosphatidylcholine (PC) and lysophosphatidylcholine (LPC). 2H-labelled methyl groups are represented by black circles; unlabelled methyl groups are represented by white circles. The administered methyl-d9-choline can enter the CDP–choline pathway to produce d9-PC, and undergo further metabolism via phospholipase or lecithin-cholesterol acyl transferase (LCAT) activity to d9-LPC; alternatively, methyl groups from d9-choline can enter one-carbon metabolism and ultimately be donated by S-adenosylmethionine (SAM), the universal methyl donor, for use by the PEMT enzyme to generate d3-PC, and subsequently d3-LPC, via analogous phospholipase/LCAT activity.