TABLE 2.
Overview of steps involved in delivery of the choline moiety to the liver1
| Choline moiety | Metabolism in SI lumen | Uptake and metabolism in SI enterocytes | Transfer in circulation and delivery to liver |
| Dietary and biliary PC | Conversion to LPC by phospholipase A2 (8) | Uptake from micelles, reacylation of LPC to PC, incorporation into chylomicrons, or further hydrolysis of LPC (4) | Some transfer of chylomicron–PC to HDLs via phospholipid transfer protein (9) |
| Uptake of chylomicron remnants | |||
| Dietary unesterified choline | Uptake of choline | Portal vein | |
| Dietary betaine | Uptake of betaine | Portal vein | |
| HDL PC | Derived from chylomicrons, VLDLs or extrahepatic tissues (reverse PC transport) (10). Uptake by scavenger receptor B1 and other mechanisms (10). Preferentially channeled into bile secretion (11) | ||
| LDL PC | Taken up via LDL receptors and scavenger receptor B1 (9) |
1
LPC, lysophosphatidylcholine; PC, phosphatidylcholine; SI, small intestine.