Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: pathophysiology of biliary lipid secretion

Abstract

The inbred C57L strain but not the AKR strain of mice carry Lith genes that determine cholesterol gallstone susceptibility. When C57L mice are fed a lithogenic diet containing 15% fat, 1% cholesterol, and 0.5% cholic acid, gallbladder bile displays rapid cholesterol supersaturation, mucin gel accumulation, increases in hydrophobic bile salts, and rapid phase separation of solid and liquid crystals, all of which contribute to the high cholesterol gallstone prevalence rates ( D. Q-H. Wang, B. Paigen, and M. C. Carey. J. Lipid Res. 1997. 38: 1395-1411). We have now determined the hepatic secretion rates of biliary lipids in fasting male and female C57L and AKR mice and the intercross (C57L ؋ AKR)F 1 before and at frequent intervals during feeding the lithogenic diet for 56 days. Bile flow and biliary lipid secretion rates were measured in the first hour of an acute bile fistula and circulating bile salt pool sizes were determined by the "washout" technique after cholecystectomy. Compared with AKR mice, we found that i ) C57L and F 1 mice on chow displayed significantly higher secretion rates of all biliary lipids, and larger bile salt pool sizes, as well as higher bile salt-dependent and bile salt-independent flow rates; ii ) the lithogenic diet further increased biliary cholesterol and lecithin outputs, but bile salt outputs remained constant. Biliary coupling of cholesterol to lecithin increased approximately 30%, setting the biophysical conditions necessary for cholesterol phase separation in the gallbladder; and iii ) no gender differences in lipid secretion rates were noted but male mice exhibited significantly more hydrophobic bile salt pools than females. We conclude that in gallstone-susceptible mice, Lith genes determine increased outputs of all biliary lipids but promote cholesterol hypersecretion disproportionately to lecithin and bile salt outputs thereby inducing lithogenic bile formation. -Wang, D. Q-H., F. Lammert, B. Paigen, and M. C. Carey. Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: pathophysiology of biliary lipid secretion.

Genetic factors at the enterocyte level account for variations inintestinal cholesterol absorption efficiency among inbred strains of mice

“…Strains studied were A/J (A), AKR/J (AKR), BALB/cJ (BALB), C57BL/6J (C57BL), C3H/J (C3H), C57L/J (C57L), DBA/2J (DBA), FVB/J (FVB), SJL/J (SJL), SM/J (SM), SWR/J (SWR), and 129/SvJ (129) mice. We crossed AKR with C57L to breed heterozygous (AKRϫ C57L)F 1 mice (60,61). All animals were maintained in a temperaturecontrolled room (22 Ϯ 1ЊC) with 12-h light cycles (6 am-6 pm).…”

“…We investigated bile flow, biliary lipid secretion, and BS pool size in additional groups of AKR, C3H, BALB, SWR, FVB, and C57L mice (n ϭ 5 per strain) according to our earlier methods (61,62). In brief, the common bile duct was cannulated below the entrance of the cystic duct via a PE-10 polyethylene catheter, with an outer diameter of 0.61 mm (Becton Dickinson, Sparks, MD), and a cholecystectomy was per formed.…”

“…Hepatic bile was collected by gravity every hour for 8 h, with the first-hour samples being used to study biliary lipid outputs and molecular composition of the BS pool, and the 8-h collection for the measurement of pool sizes. After hepatic bile volumes were determined by weighing (61,62), all samples were frozen and stored at Ϫ20ЊC for further lipid analyses (see below). During surger y and bile collection, mouse body temperature was maintained at 37 Ϯ 0.5ЊC with a heating lamp and monitored with a thermometer.…”

“…Laparotomy was performed under sterile conditions through an upper midline incision. After cannulation of the common bile duct, a cholecystectomy was per formed (60) and hepatic bile was drained externally (61,62). After 4-h bile drainage, a PE-10 catheter was inserted into the duodenum 5 mm be- --------------------------------------------------------------------------------------------------------…”

“…Table 3 shows that the circulating BS pool sizes in C57L (3.1 Ϯ 0.4 mol) and FVB mice (2.4 Ϯ 0.2 mol) mice were similar to those in BALB (2.0 Ϯ 0.2 mol) and SWR mice (2.2 Ϯ 0.3 mol), but were significantly larger (P Ͻ 0.05) than those in AKR (1.7 Ϯ 0.3 mol) and C3H mice (1.8 Ϯ 0.3 mol). Furthermore, the total BS pool sizes calculated from the circulating BS pool size plus the BS pool in the gallbladder (61) showed that C57L mice (4.7 mol) had markedly larger total BS pool sizes than SWR mice (3.1 mol) or AKR mice (2.7 mol).…”