THE EFFECTS OF DIETARY PHOSPHOLIPIDS ENRICHED WITH PHOSPHATIDYLETHANOLAMINE ON BILE AND RED-CELL MEMBRANE-LIPIDS IN HUMANS

The role of phospholipids in biliary cholesterol solubilization and cr ystallization has only recently begun to be appreciated, Phospholipid vesicles are believed to be the metastable carrier from which choleste rol nucleates. Cholesterol crystallization is influenced by the phosph olipid species in bile. Feeding rats and hamsters with diets enriched in phospholipids or their precursors, especially ethanolamine, resulte d in reduced cholesterol saturation of bile. Although whole phospholip ids are normal dietary constituents, the effects and safety of phospho lipid components have not been tested in humans. In the present study, we have evaluated the effects of a dietary phospholipid mixture, enri ched with phosphatidylethanolamine, on human bile and red blood cell m embrane lipid composition. Five ambulatory volunteers having a chronic indwelling T-tube, with an intact enterohepatic circulation, were inv estigated. Thirty-six grams of phospholipids (54% phosphatidylethanola mine, 54% linoleyl acyl chains) were added to their daily diet for fou rteen days. Biliary nucleation time, cholesterol carriers, as well as plasma, red blood cell membrane, and bile lipid compositions, were mon itored. Following phospholipid supplementation, the proportion of lino leyl chains (18:2) in biliary phospholipids increased significantly fr om 31.1 +/- 1.2 to 37.7 +/- 5.3%, while that of oleyl chains (18:1) de creased from 11.4 +/- 1.6 to 9.6 +/- 1.1%. These changes were accompan ied by an increase of linoleate and its metabolite, arachidonate, in r ed cell membranes. Phospholipid feeding did not cause any side effects , and no significant changes in biliary nucleation time, cholesterol, phospholipid, or bile salt concentrations, or in the distribution of c holesterol within micelles or vesicles. We conclude that phospholipid feeding is safe, and can be effective as a vehicle for lecithin fatty acyl chain modulation of bile and lipid membranes. These findings may provide a basis for a controlled modulation of biliary phospholipids t o increase cholesterol solubility in bile.