INCREASED SATURATION OF THE FATTY-ACIDS IN THE SN-2 POSITION OF PHOSPHOLIPIDS REDUCES CHOLESTEROL CRYSTALLIZATION IN MODEL BILES

Changes in the molecular structure of biliary phospholipids were shown to have major effects on cholesterol solubility, carriers and crystal lization in human and model biles. This study investigated systematica lly the effects of varying saturation of the phosphatidylcholine (PC) sn-2 fatty acid on the cholesterol crystallization process in 3 differ ent model biles. Twenty % of the egg PC (EPC) in these biles were repl aced by synthetic PC's with 16:0-18:0, 16:0-18:1, or 16:0-18:2 fatty a cyl chains. With 18:0 in the sn-2 position, the crystal observation ti me (GOT) was prolonged from 2 days in the control EPC solution to 14 d ays (P < 0.05). The crystal growth rate (CGR) was reduced from 0.1 OD/ day to unmeasurable levels, and the total crystal mass on day 14 decre ased by 86%. The introduction of one (18: 1), and two (18:2) double bo nds in the sn-2 fatty acid rapidly reversed these effects. Ultracentri fugal analysis showed precipitable cholesterol as monohydrate crystals . In the 16:0-18:0 test solution, most of the precipitable cholesterol remained in the supersaturated multilamellar vesicles. Saturation of the biliary PC sn-2 fatty acyl chain prolongs the GOT, slows the CGR, reduces the crystal mass, and extends cholesterol solubility in multil amellar vesicles. Desaturation of the sn-2 fatty acid reverses these e ffects. (C) 1998 Elsevier Science B.V.