Lamellar bodies coexist with vesicles and micelles in human gallbladder bile. Ursodeoxycholic acid prevents cholesterol crystal nucleation by increasing biliary lamellae

Abstract

The aggregative forms of lipids in human gallbladder bile and their relation to cholesterol crystallization are controversial. Using combined chemical, gel-chromatographic, optical/electron microscopic and quasielastic light-scatttering methods, we investigated this issue in native gallbladder bile obtained from nine untreated cholesterol gallstone patients and eight cholesterol gallstone patients treated for 1 weeks with 600 mg/day of ursodeoxycholic acid. Bile obtained at cholecystectomy was ultracentrifuged for 2 h at 150 000 g to obtain isotrophic samples. The conventional cholesterol crystal observation time was 3.1 ± 4.1 (SD) days in controls and 19.0±1.9 days in the ursodeoxycholic acid-treated group ( p<0.001). Bile was analyzed by high-resolution gel-chromatography using 7 mM sodium taurocholate in the elution buffer. Biliary lipids eluted in four chromatographic zones: zone #I, corresponding to the column void volume, contained only minimal amounts of lipids; zone #II (apparent m.w. 100–220 kDa) comprised 29.1±12.4% of biliary cholesterol in the untreated group and 8.3 ±4.3% in the ursodeoxycholic acid-group ( p<0.001). At negative staining electron microscopy, this region was composed of roundish vesicles ranging from 7 to 20 nm in diameter. Zone #III (apparent m.w. 50–100kDa) carried 59.1±2.1% of cholesterol in untreated patients and 81.2±9.5% in ursodeoxychlic acid-rich biles, respectively ( p<0.001). At negative staining electron microscopy, this region was composed of lamellar stacks of variable length, usually with 5 nm interspaces and up to 30 nm width. In ursodeoxycholic acid-rich biles, lamellae often appeared in the form of concentric fingerprint-like images. Quasielastic light-scattering measurements in this region were compatible with the size estimates obtained at electron microscopy. Zone #IV (apparent m.w. 6–50 kDa) carried 11.8±9.4% and 11.6±9.0% of cholesterol, respectively (not significant). Since this region comprised a considerable fraction of endogeneous bile salts and had no distinct morphological structures, it was interpreted as mixed micelles. The cholesterol crystal observation time showed a significant inverse correlation (r–0.85, p<0.001) with percent cholesterol carried by vesicles (zone #II) and a direct correlation (R0.86, p <0.001) with percent cholesterol carried by lamellar bodies (zone #III). Vesicles and lamellae identical to those observed in isolated gel-chromatographic fractions were observed also on direct electron microscopic examination of unfractionated isotropic native biles. Similar findings were observed also in matched model biles. In conclusion, this study confirms previous work showing that lamellar bodies represent the predominant cholesterol carrier in gallbladder bile of cholesterol gallstone patients, and indicates that ursodeoxycholic acid feeding prevents cholesterol crystalization by increasing the lamellar carrier.