QUANTITATIVE ASSESSMENT OF COMPARATIVE POTENCIES OF CHOLESTEROL-CRYSTAL-PROMOTING FACTORS - RELATION TO MECHANISTIC CHARACTERIZATION

The crystallization of cholesterol is affected by various factors in b ile. The present study evaluated the relative importance of cholestero l-nucleation-promoting factors and partially characterized the mechani sms of their action. Model biles with an identical relative compositio n of cholesterol, egg-yolk phosphatidylcholine and taurocholate, excep t for replacing phosphatidylcholine (5-20%) with dilinoleoyl-phosphati dylcholine or taurocholate (10-30%) with taurodeoxycholate. Cholestero l crystallization was quantitatively assessed spectrophotometrically a nd morphologically estimated by the laser-scattering diffraction analy ser and video-enhanced microscopy in the absence and presence of conca navalin A-binding glycoprotein isolated from human bile. In a series o f experiments, lipid distribution among particulate species was determ ined after isolation by FPLC. In ah experiments, cholesterol crystalli zation was dose-dependently enhanced with a rank order of: concanavali n A-binding glycoprotein > dilinoleoyl-phosphatidylcholine > taurodeox ycholate. No morphological alteration was evident for vesicles and cry stals, but the cholesterol/phospholipid ratio in vesicles was increase d significantly by replacement with dilinoleoyl-phosphatidylcholine an d excess cholesterol. A high proportion of relatively hydrophilic phos phatidylcholine species such as dilinoleoyl-phosphatidylcholine and ex cess cholesterol in bile cause a redistribution of cholesterol to incr ease a vesicular cholesterol/phospholipid ratio, eventually promoting cholesterol crystallization, whereas concanavalin A-binding glycoprote in acts via differing mechanisms.