THE EFFECTS OF PHOSPHOLIPID MOLECULAR-SPECIES ON CHOLESTEROL CRYSTALLIZATION IN MODEL BILES - THE INFLUENCE OF PHOSPHOLIPID HEAD GROUPS

Background/Aims: Variations in the molecular species of biliary phosph olipids have been shown to exert major effects on cholesterol solubili ty and carriers in model and human biles. The aim of this study was to explore systematically the effects of various phospholipid head group s on the cholesterol crystallization process in model biles. Methods: Three different control model biles were prepared using varying propor tions of egg lecithin, cholesterol and Na taurocholate. In the test bi les, 20% of the egg lecithin was replaced with synthetic phosphatidyls erine, phosphatidylethanolamine, phosphatidylglycerol or phosphatidylc holine, keeping the phospholipid acyl chains and other biliary lipids constant in each experiment. Results: Phosphatidylserine and phosphati dylglycerol significantly prolonged the crystal observation time, from 2 days to 10 and 6 days respectively (p<0.02), while phosphatidyletha nolamine had little and phosphatidylcholine no effect. The crystal gro wth rate was significantly slowed down with 20% phospholipid replaceme nt in the following order: phosphatidylglycerol > phosphatidylserine > phosphatidylethanolamine, The total crystal mass after 14 days, as me asured by chemical analysis, was reduced by 59% with phosphatidylserin e (p<0.05), and by 73% with phosphatidylglycerol (p<0,05); while phosp hatidylethanolamine had little effect. The precipitable cholesterol cr ystal fractions after 14 days were significantly reduced with phosphat idylserine (54%) and phosphatidylglycerol (37%), but not with phosphat idylethanolamine or phosphatidylcholine. Conclusions: Variations in th e head groups of biliary phospholipids may markedly slow down the chol esterol crystallization process in model biles.