The unique acyl chain specificity of biliary phosphatidylcholines in mice is independent of their biosynthetic origin in the liver

The liver synthesizes phosphatidylcholine (PC) de novo from choline via the CDP-choline pathway and from phosphatidylethanolamine (PE) via the phospha tidylethanolamine N-methyltransferase (PEMT) pathway. Significant amounts o f PC, which are highly specific in their acyl chain composition, are secret ed into bile by the liver. To determine whether either of the 2 PC biosynth etic routes is sufficient to provide physiological PC concentrations in bil e, or is responsible for the unique acyl chain composition of bile PC, we a nalyzed gallbladder bile composition in mice that synthesized PC either via the PEMT pathway (induced by feeding a choline-deficient diet) or the CDP- choline pathway (based on genetic PEMT-deficiency). The PC concentration in gallbladder bile of mice that synthesize PC mainly via the CDP-choline pat hway was comparable with control mice that synthesize PC via both pathways, whereas it was reduced by approximate to 40% in mice that synthesize PC vi a the PEMT pathway. The acyl chain composition of bile PC was similar irres pective of the active PC biosynthetic pathway in the liver, These data demo nstrate that the CDP-choline pathway alone, but not the PEMT pathway alone, can account for physiological concentrations of PC in gallbladder bile. Mo reover, the specificity of biliary PC fatty acyl composition is determined independently from the synthetic origin of PC.