DEGREE OF FATTY ACYL-CHAIN UNSATURATION IN BILIARY LECITHIN DICTATES CHOLESTEROL NUCLEATION AND CRYSTAL-GROWTH

To clarify factors involved in the formation of cholesterol gallstones , we studied the relationship between the degree of fatty acyl chain u nsaturation of biliary lecithin and bile metastability. We used supers aturated model bile solutions (molar taurocholate/lecithin/cholesterol ratio (73:19.5:7.5), total lipid concentration 9 g/dl) that contained equimolar egg yolk or soybean lecithins or a sn-1 palmitoyl, sn-2 lin oleoyl phosphatidylcholine. Gel permeation chromatographic studies sho wed that the vesicular cholesterol distribution and dimension were inv ersely related to the degree of unsaturation of the lecithin species, estimated by reverse phase, high-performance liquid chromatography. Di fferential interference contrast microscopy and assay of cholesterol c rystal growth showed that a higher degree of fatty acyl chain unsatura tion of the lecithin species was associated with a faster nucleation t ime and rate of crystal growth. Our results suggest that vesicular lec ithins containing more unsaturated fatty acyl chains bind less tightly to cholesterol than lecithins containing predominantly saturated fatt y acids, and that the biliary lecithin species dictates, in part, the nucleation and growth of cholesterol crystals in bile.