Biliary lipid secretion,bile acid metabolism,and gallstone formation are not impaired in hepatic lipase-deficient mice

Whereas hepatic lipase (HL) has been implicated in lipoprotein metabolism and atherosclerosis, its role in controlling biliary lipid physiology has not been reported. This work characterizes plasma lipoprotein cholesterol, hepatic cholesterol content, bile acid metabolism, biliary cholesterol secretion, and gallstone formation in HL-deficient mice and C57BL/6 controls fed standard chow, a cholesterol-supplemented diet, or a lithogenic diet. Compared with C57BL/6 controls, HL knockout mice exhibited increased basal plasma high-density lipoprotein (HDL) cholesterol as well as reduced cholesterol levels transported in large lipoproteins in response to cholesterol-enriched diets. Hepatic cholesterol content and biliary cholesterol secretion of chow-fed HL knockout and wild-type mice were not different and increased similarly in both strains after feeding dietary cholesterol or a lithogenic diet. There were no differences in biliary bile acid secretion, bile acid pool size and composition, or fecal bile acid excretion between HL-deficient and control mice. HL knockout mice had a similar prevalence of gallstone formation as compared with control mice when both strains were fed with a lithogenic diet. In conclusion, the deficiency of HL has no major impact on the availability of lipoprotein-derived hepatic cholesterol for biliary secretion; HL expression is not essential for diet-induced gallstone formation in mice.     

Deficiency of Niemann‐Pick C1 protein protects against diet‐induced gallstone formation in mice

Background/aims: Receptor‐mediated endocytosis is a critical cellular mechanism for the uptake of lipoprotein cholesterol in the liver. Because Niemann‐Pick C1 (NPC1) protein is a key component for the intracellular distribution of cholesterol originating from lipoprotein endocytosis, it may play an important role in controlling biliary cholesterol secretion and gallstone formation induced by a lithogenic diet. Methods: We studied biliary cholesterol secretion, gallbladder lipid composition and gallstone formation in NPC1‐deficient mice fed a low‐fat lithogenic diet (1.5% cholesterol and 0.5% cholic acid) compared with control animals under the same diet. Results: The lipid secretion response to the lithogenic diet was impaired in NPC1 (?/?) mice, leading to a decreased cholesterol output and an increased hepatic cholesterol concentration compared with the lithogenic diet‐fed wild‐type mice. A decreased cholesterol saturation index was found in the gallbladder bile of NPC1 (+/?) and (?/?) mice after lithogenic diet feeding. Consequently, mice with a partial or a total deficiency of NPC1 had a drastically lower frequency of gallbladder cholesterol crystals and a reduced prevalence of gallstones. Conclusion: Hepatic NPC1 expression is an important factor for regulating the biliary secretion of diet‐derived cholesterol as well as for diet‐induced cholesterol gallstone formation in mice.     

Impaired biliary cholesterol secretion and decreased gallstone formation in apolipoprotein E-deficient mice fed a high-cholesterol diet

BACKGROUND & AIMS: Because apolipoprotein E (apoE) is a key cholesterol transport molecule involved in the hepatic uptake of chylomicron cholesterol, it may play a critical role in controlling bile cholesterol elimination and cholesterol gallstone formation induced by dietary cholesterol. To test this hypothesis, we studied biliary lipid secretion and gallstone formation in apoE-deficient mice fed cholesterol-rich diets. METHODS: Bile lipid outputs and gallstone sequence events were analyzed in apoE-deficient mice fed a high-cholesterol diet or a lithogenic diet compared with control animals. RESULTS: A high-cholesterol diet increased biliary cholesterol secretion and gallbladder bile cholesterol concentration in wild-type mice; the increase in bile cholesterol secretion was significantly attenuated in apoE-deficient mice. ApoE knockout mice fed a high-cholesterol lithogenic diet had a markedly lower frequency of gallbladder bile cholesterol crystal and gallstone formation than wild-type mice, which was most likely a result of the decreased cholesterol saturation index found in gallbladder bile of apoE-deficient mice. CONCLUSIONS: These results show that apoE expression is an important factor for regulating both biliary secretion of diet-derived cholesterol as well as diet-induced cholesterol gallstone formation in mice.     

Apolipoprotein A‐I deficiency does not affect biliary lipid secretion and gallstone formation in mice

Background/Aims: Apolipoprotein A‐I (apo A‐I) is the main protein component of plasma high‐density lipoproteins (HDL) and a key determinant of HDL cholesterol levels and metabolism. The relevance of HDL in controlling the traffic of cholesterol from plasma into bile has been partially addressed. The aim of this study was to evaluate the role of apo A‐I expression in controlling the secretion of biliary lipids as well as the risk of gallstone disease in vivo. Methods: We evaluated biliary lipid secretion and bile acid homeostasis in mice deficient for apo A‐I compared with wild‐type animals when fed with low‐ or high‐cholesterol diets. In addition, we assessed the importance of murine apoA‐I expression for gallstone formation after feeding a lithogenic diet. Results: Bile acid pool size and faecal excretion were within the normal range in chow‐ and cholesterol‐fed apo A‐I knockout (KO) mice. Basal biliary cholesterol secretion was comparable and increased similarly in both murine strains after cholesterol feeding. Lithogenic diet‐fed apo A‐I KO mice exhibited an impaired hypercholesterolaemic response owing to a lower increase in cholesterol levels transported in large lipoproteins. However, the lack of apo A‐I expression did not affect biliary cholesterol precipitation or gallstone formation in lithogenic diet‐fed mice. Conclusions: These findings indicate that biliary lipid secretion, bile acid metabolism and gallstone formation are independent of apo A‐I expression and plasma HDL cholesterol levels in mice.     

Insulin injections enhance cholesterol gallstone incidence by changing the biliary cholesterol saturation index and apo A-I concentration in hamsters fed a lithogenic diet.

BACKGROUND/AIMS: A link between insulin and cholesterol gallstone disease has often been suspected but never demonstrated. The aim was to evaluate the direct implication of insulin in the gallbladder cholesterol gallstone formation process. METHODS: Hamsters fed with a soft-inducing lithogenic diet, enriched with sucrose, were injected daily, for 1 week, either with long-acting insulin or saline (controls). RESULTS: Insulin injections doubled the cholesterol gallstone incidence. The cholesterol saturation index (CSI) of bile significantly increased (+19%) and biliary apolipoprotein A-I (apo A-I) decreased, both in concentration (-71%) and the proportion relative to the total biliary proteins (-25%). No modifications in the biliary bile acid composition were noticed. Hepatic HMGCoA reductase activity was higher (+341%), CYP7A1 activity was lower (-52%), whereas CYP27A1 and CYP7B1 were not affected. The hepatic low-density liprotein (LDL)-receptor and SR-BI masses did not vary. The hepatic total cholesterol content increased (+42%). Fasting plasma phospholipid and triglyceride concentrations significantly decreased (-15 and -60%, respectively), but the cholesterol concentration remained constant. CONCLUSIONS: These results suggest that insulin injections enhance cholesterol gallstone incidence by increasing the CSI of bile and decreasing the concentration and proportion of a biliary anti-nucleating protein, apo A-I. Insulin modulates the major enzymes of cholesterol and bile acid metabolisms in vivo.     

Biliary lipids and cholesterol crystal formation in leptin-deficient obese mice

Background. Obesity is often associated with increased biliary cholesterol secretion resulting in cholesterol gallstone formation. We have previously demonstrated that leptin-deficient C57Bl/6J Lep ob obese mice have abnormal biliary motility and are prone to cholesterol crystal formation. In addition, others have demonstrated that leptin-deficient mice when fed a lithogenic diet for eight weeks are not prone to gallstone formation. However, the biliary lipid and in vivo cholesterol crystal response of homozygous and heterozygous leptin-deficient mice to four weeks on a lithogenic diet has not been studied. Therefore, we tested the hypothesis that lithogenic diets influence gallbladder bile composition, serum lipids and cholesterol crystal formation in homozygous and heterozygous leptin-deficient mice compared to normal lean controls. Methods. 319 female lean control mice, 280 heterozygous lep ob obese mice and 117 homozygous lep ob obese mice were studied. Mice were fed either a lithogenic or control non-lithogenic chow diet for four weeks. Gallbladder volumes were measured, and bile was pooled to calculate cholesterol saturation indices. Serum cholesterol, glucose, and leptin levels were determined. Hepatic fat vacuoles were counted, and bile was observed microscopically for cholesterol crystal formation. Results. The lithogenic diet and mouse strain influenced body and liver weights, gallbladder volume, cholesterol crystal formation, serum cholesterol, glucose and leptin levels and hepatic fat vacuole numbers. However, only diet, not strain, altered biliary cholesterol saturation. Conclusion. The association among obesity, leptin, and gallstone formation may be primarily related to altered gallbladder motility and cholesterol crystal formation and only secondarily to biliary cholesterol saturation.     

Endogenous Hypercholecystokininemia,But Not Aspirin,Reduces the Gallstone Incidence in the Hamster Model

Borch K, Chu M, Kullman E, Carlsson B, Rehfeld JF. Endogenous hypercholecystokininemia, but not aspirin, reduces the gallstone incidence in the hamster model. Scand J Gastroenterol 1994;29:740-743.

Background: Studies in humans and rodents indicate that gallstone development may be prevented by inhibiting gallbladder mucus hypersecretion with non-steroidal anti-inflammatory drugs or by preventing stasis of gallbladder bile with administration of cholecystokinin. Methods: The effect of oral aspirin and pancreaticobiliary diversion with endogenous hypercholecystokininemia on crystal and gallstone formation was studied in Syrian golden hamsters fed a lithogenic diet for 8 weeks. Results: None of the control animals fed a normal diet developed gallstones or crystals in gallbladder bile. Gallstones developed in 67% of the animals fed a lithogenic diet only. The gallstone prevalence did not differ significantly in animals on a lithogenic diet and a daily aspirin dose of 6 mg/kg (gallstone prevalence, 60%) or 100 mg/kg (gallstone prevalence, 70%), whereas it was significantly lower in animals with endogenous hypercholecystokininemia on a lithogenic diet (gallstone prevalence, 29%). The prevalence of crystals in gallbladder bile did not differ significantly between any of the experimental groups. Conclusions: It is concluded that in hamsters on a lithogenic diet, aspirin does not prevent gallstone formation, whereas endogenous hypercholecystokininemia reduces the prevalence of stones without affecting the occurrence of crystals in gallbladder bile.     

Aspirin does not inhibit cholesterol cholelithiasis in two established animal models.

The effect of aspirin on cholesterol cholelithiasis was examined in the hamster and the prairie dog. In the prairie dog, diets were composed of semipurified components of chow, plus cholesterol (1.2%), with and without aspirin. Animals were studied for either 2 weeks or 4 weeks. Cholesterol gallstones were present in all groups at the end of each period; aspirin did not alter the incidence of cholelithiasis. All animals studied had cholesterol crystals in the bile when they were killed. Liver cholesterol levels in prairie dogs with and without aspirin tended to be lower in animals fed chow than in animals fed semipurified diets. There were no significant differences in cholesterol levels in the plasma or bile. The cholesterol saturation index of all biles approached unity when animals were fed chow with aspirin; animals fed the semipurified diets had cholesterol saturation indices of less than 1.0. The prairie dogs fed aspirin plus cholesterol in the semipurified diet showed increased levels of biliary chenodeoxycholic acid amidates and concomitant decreased levels of cholic acid amidates compared with animals fed the same diet without aspirin. Hamsters fed aspirin plus cholesterol in a semipurified diet tended to have a greater incidence of gallstones than animals given no aspirin (80% vs. 55%). Liver and bile cholesterol levels were similar with and without aspirin; plasma cholesterol levels increased significantly with aspirin [14.20 vs. 7.80 mmol/L (549 vs. 301 mg/dL)]. Lithogenic indices in all hamsters were above unity; biliary lipids, total lipid concentration, and biliary bile acid composition were similar. These results show that the addition of aspirin to a lithogenic diet does not reduce the incidence of cholelithiasis.     

Cholesterol-lowering action of psyllium mucilloid in the hamster: sites and possible mechanisms of action

These studies were undertaken to examine and compare the metabolic effects of psyllium mucilloid and two other nonabsorbable polymers (cholestyramine and surfomer) on sterol metabolism in the hamster. These three agents all significantly lowered the plasma total cholesterol concentration and the level of cholesterol carried in low-density lipoproteins (LDL). Rates of cholesterol synthesis were markedly increased in the livers of the psyllium-fed animals, but not in other tissues. In contrast, cholestyramine and surfomer feeding increased both hepatic and intestinal sterol synthesis. When cholesterol and saturated triacylglycerols were added to the diet, psyllium feeding essentially completely blocked the increase in the plasma cholesterol concentration and hepatic cholesterol content and the suppression of cholesterol synthesis. The pool of bile acid in the small intestine was increased from the control value (17.9 mumol/animal) by both psyllium (23.0 mumol) and cholestyramine (21.9 mumol) feeding. However, this pool was readily absorbed and secreted into the bile in the psyllium-fed animals (27.9 mumol/4 h), but not in the cholestyramine-treated hamsters (13.0 mumol/4 h). This was consistent with the further observation that there was no binding of bile acid by psyllium under in vitro conditions. Thus, these findings indicate that all three polymers lower plasma cholesterol concentrations by inducing a net negative cholesterol balance across the liver. With psyllium, this effect is presumably articulated through a reduction in cholesterol absorption, as well as an increase in the rate of degradation of cholesterol to bile acids.     

Effects of psyllium on plasma total and lipoprotein cholesterol and hepatic cholesterol in hamsters fed n-3 PUFA or n-6 PUFA with high cholesterol levels

This study was conducted to determine whether psyllium is known to alter cholesterol metabolism modulate the hypercholesterolemic effect of a high cholesterol, n-3 polyunsaturated fatty acids (PUFA) diet in hamsters. Concentrations of plasma, hepatic total cholesterol and lipoprotein cholesterol were measured in male hamsters fed an n-3 PUFA plus psyllium (8%, wt/wt) diet combined with variable levels of cholesterol (0, 0.05, 0.1%, wt/wt) or a cholesterol-enriched (0.2%, wt/wt) n-3 PUFA or n-6 PUFA diet that contained either 8% methyl cellulose or psyllium for 4 weeks. In the n-3 PUFA-fed hamsters, we have found that psyllium was able to reduce plasma total cholesterol and low density lipoprotein (LDL)-cholesterol significantly when 0.1% cholesterol was added to the diet. In contrast, the effects of psyllium were not seen in the n-3 PUFA-fed hamsters without dietary cholesterol or with 0.05% dietary cholesterol. However, no matter in the presence of psyllium or not, the increase of plasma total cholesterol, very-low-density lipoprotein (VLDL)-cholesterol, LDL-cholesterol and high-density lipoprotein (HDL)-cholesterol levels was depend on the content of dietary cholesterol. Although the cholesterol diet increased the liver total cholesterol level, 80 g psyllium/kg diet resulted in a significantly lower concentration of liver total cholesterol in the cholesterol-fed hamsters. In the second experiment, we have also found that psyllium feeding lowered significantly plasma total cholesterol and VLDL-cholesterol concentrations in hamsters fed n-3 PUFA but not in those fed n-6 PUFA. However, the levels of plasma total cholesterol, VLDL-cholesterol and LDL-cholesterol levels of the (n-6) PUFA-fed hamsters were significantly lower than those in the (n-3) PUFA-fed hamsters in the absence or presence of dietary psyllium. Our data also showed that hamsters fed both high-cholesterol n-3 PUFA and n-6 PUFA diets had a significant decrease in hepatic cholesterol with intake of psyllium. Liver total cholesterol concentrations were significantly lower in n-3 PUFA-fed hamsters compared with the n-6 PUFA-fed groups. Therefore, these data may contribute to understanding the interactive effect of psyllium and cholesterol or the type of fat on plasma and liver cholesterol in hamsters.     

Gallstone prevention in prairie dogs: comparison of chow vs. semisynthetic diets

The effects of a standard rodent chow were compared with those of a semisynthetic diet of known composition (with and without added cholesterol) in the prairie dog model of cholesterol cholelithiasis. Gallstone incidence was 40% higher in animals fed a semisynthetic diet plus cholesterol compared to chow plus cholesterol. The semisynthetic diet plus cholesterol caused significant increases in tissue cholesterol levels (serum, liver and bile) and lithogenic index, but significant decreases in the activity of hepatic 3-hydroxy-3-methyl-glutaryl coenzyme A reductase and cholesterol 7 alpha-hydroxylase compared to chow plus cholesterol. Histologic study of liver sections revealed that the semisynthetic diet plus cholesterol resulted in moderate to marked portal tract changes characterized by bile duct proliferation, inflammatory infiltration and fibrosis, whereas the cholesterol-supplemented chow diet caused only slight bile duct proliferation with minimal inflammation and fibrosis in the portal areas. Dietary hyodeoxycholic acid prevented cholesterol gallstones and biliary cholesterol crystals when added to either chow plus cholesterol or semisynthetic plus cholesterol diets. The hyodeoxycholic acid supplements also prevented the development of severe histopathologic alterations along the portal tracts. Biliary cholesterol levels were elevated in prairie dogs fed cholesterol plus hyodeoxycholic acid; these animals had liquid crystals in the bile, and hyodeoxycholic acid and its 6 beta-isomer became the major biliary bile acids. A semisynthetic diet plus cholesterol is superior to a high cholesterol chow diet for gallstone formation and prevention studies, but in prolonged feeding experiments, the potential hepatotoxicity of this diet in the prairie dog must be appreciated.     

Biliary cholesterol hypersecretion in gallstone-susceptible mice is associated with hepatic up-regulation of the high-density lipoprotein receptor SRBI

Enhanced hepatocellular trafficking of cholesterol to the bile canaliculus and cholesterol hypersecretion appears critical for gallstone formation. Therefore, we studied in more detail the hepatic cholesterol transport pathways in a mouse model of cholesterol gallstone disease. Biliary lipid secretion rates, plasma lipoprotein levels, hepatic expression of lipoprotein receptors, lipid regulatory enzymes, and putative cholesterol transporting proteins were analyzed in gallstone-susceptible C57L/J and gallstone-resistant AKR/J mice, which were fed a lithogenic diet. Biliary cholesterol hypersecretion in C57L mice was associated with decreased plasma high-density lipoprotein (HDL) cholesterol levels and significant hepatic induction of the HDL receptor (SRBI) and cholesteryl ester hydrolase. In response to the lithogenic diet, fatty-acid binding protein of liver (FABPL) was markedly induced in both mouse strains. Caveolin 1 was elevated only in plasma membranes of gallstone-susceptible C57L mice, which also failed to down-regulate cholesterol synthesis. These data suggest a role of the reverse cholesterol transport pathway for genetically determined gallstone susceptibility in the mouse.     

Studies of cholesterol and bile acid metabolism, and early atherogenesis in hamsters fed GT16-239, a novel bile acid sequestrant (BAS)

The purpose of this study was to compare the efficacy of GT16-239, an alkylated, cross-linked poly(allylamine) bile acid sequestrant with cholestyramine on cholesterol and bile acid metabolism, and early aortic atherosclerosis in hypercholesterolemic male F1B Golden Syrian hamsters. In this controlled study, 42 hamsters were divided into six groups and were fed a chow-based hypercholesterolemic diet supplemented with a 10% oil blend (55% coconut/45% corn), 0.1% cholesterol (w/w) (control) and either 0.9 or 1.2% cholestyramine or 0.2, 0.4 or 0.6% GT16-239 for 13 weeks. Laboratory analyses included evaluating plasma lipoprotein cholesterol and triglyceride concentrations, hepatic HMG-CoA reductase and 7 α-hydroxylase activities, fecal excretion of bile acids and neutral sterols, hepatic cholesterol concentrations, and early atherosclerosis (aortic fatty streak area). Relative to the control diet, the 0.6% GT16-239 versus the 1.2% cholestyramine significantly inhibited the elevation of plasma lipoprotein total cholesterol (TC) (−69% vs −40%), high density lipoprotein-cholesterol (HDL-C) (−49% vs −30%), and non-HDL-C (−81% vs −48%) concentrations; increased the activities of both HMG-CoA reductase (1492% vs 62%) and 7 α-hydroxylase (175% vs 86%); lowered the concentration of hepatic cholesteryl ester (−94% vs −59%); increased fecal cholesterol concentration (+28% vs −10%); and decreased aortic fatty streak area (−100% vs −86%). Unexpected findings of this comparison were increased fecal concentrations of cholic acid (533%) and chenodeoxycholic acid (400%) and the reduction in lithocholic acid (−50%) in the 0.6% GT16-239 compared to the 1.2% cholestyramine group. In summary, GT16-239 had a greater impact on cholesterol metabolism and early atherosclerosis in hypercholesterolemic hamsters than cholestyramine.     

Biliary cholesterol and bile acid excretion do not increase in hamsters fed cereal-based diets containing cholesterol

The major compensatory responses to increased cholesterol consumption are decreased cholesterol synthesis and increased cholesterol excretion through the bile either as free cholesterol or bile acids. The objective of this study was to test the hypothesis that biliary cholesterol excretion is increased in hamsters fed low levels of cholesterol reflecting normal human intake. The hypothesis was based on observations that hamsters generally resist changes in bile acid synthesis when fed large amounts of cholesterol; therefore, increased biliary cholesterol excretion represents a potentially significant pathway for elimination of excess cholesterol in this species. Hamsters were fed modified NIH-07 cereal-based diets containing 0.02%, 0.03%, and 0.05% cholesterol (0.04, 0.06, and 0.10 mg cholesterol/kcal, respectively). The primary response to increasing amounts of dietary cholesterol was downregulation of whole-body cholesterol synthesis, reduced from 3.93+/-0.14 micromol x d(-1) x 100 g(-1) body weight in hamsters fed 0.02% cholesterol to 0.52+/-0.14 micromol x d(-1) x 100 g(-1) in the 0.05% cholesterol group. Biliary cholesterol excretion was also slightly reduced in hamsters fed 0.05% cholesterol, whereas bile acid excretion was not altered by dietary cholesterol. Despite a pronounced downregulation of whole-body cholesterol synthesis, liver and plasma cholesterol concentrations increased in hamsters fed 0.05% cholesterol. The data indicate that increased biliary cholesterol excretion is not a major compensatory route of cholesterol excretion in hamsters consuming cholesterol. Furthermore, cholesterol added to the diet at 0.05% appears to be the approximate threshold at which compensatory mechanisms can prevent increases in liver and plasma cholesterol in male Syrian hamsters. Consequently, this species may be an appropriate animal model for "hyperresponding" individuals in the human population.     

Cholangiocyte bile salt transporters in cholesterol gallstone-susceptible and resistant inbred mouse strains

Background and Aim: We investigated the dietary and gender influences on the expression and functionality of cholangiocyte bile salt transporters and development of biliary hyperplasia in cholesterol gallstone‐susceptible C57L/J and resistant AKR/J mice. Methods: C57L and AKR mice were fed chow, a lithogenic diet, or a cholic acid‐containing diet for 14 days. Expression of cholangiocyte bile salt transporter proteins ASBT (SLC10A2), ILBP (FABP6), and MRP3 (ABCC3) were studied by Western blot analysis. Taurocholate uptake studies were performed using microperfusion of isolated bile duct units. The pre‐ and post‐perfusion taurocholate concentrations were analyzed by high performance liquid chromatography. Biliary proliferation in liver sections was scored. Results: The lithogenic diet induced ductular proliferation in C57L mice. On chow, SLC10A2 and ABCC3 were overexpressed in male and female C57L compared to AKR mice. A lithogenic diet reduced the expressions of FABP6 in both male and female C57L mice, SLC10A2 in female C57L mice, and ABCC3 in male C57L mice. These alterations in transporter expressions were not associated with changes in taurocholate uptake. The lithogenic diet induced biliary hyperplasia and reduced bile salt transporter expressions in C57L mice. Conclusions: Although bile salt uptake was not increased in the bile duct unit, we speculate that the biliary hyperplasia on the lithogenic diet may lead to an increase in intrahepatic bile salt recycling during cholesterol cholelithogenesis.     

Estrogen enhances dietary cholesterol induction of saturated bile in the hamster.

The influence of ethinyl estradiol (EE) on the effects of dietary cholesterol on the biliary saturation index and on the rate-limiting hepatic enzymes of cholesterol synthesis, hydroxymethylglutaryl-CoA-reductase, and bile acid synthesis, 7 alpha-hydroxylase, were determined. Four groups of 12 male hamsters were treated for 1 month with EE, 15 micrograms per kg per day, or placebo vehicle administered intraperitoneally and fed either a standard diet, 0.8 mg of cholesterol per g of food, or high cholesterol diet, 2.4 mg of cholesterol per g. The high cholesterol diet increased the saturation index to 1.00 +/- 0.03 (P less than 0.01) from 0.65 +/- 0.02 in untreated hamsters on the standard diet. EE treatment on the high cholesterol diet further increased (P less than 0.01) the saturation index to 1.15 +/- 0.02. The high cholesterol diet decreased (P less than 0.01) hydroxymethylglutaryl-CoA-reductase activity from 308 +/- 16 pmoles per mg per min in untreated hamsters on the standard diet. The addition of EE treatment had no effect on hydroxymethylglutaryl-CoA-reductase activity. The high cholesterol diet increased (P less than 0.01) 7 alpha-hydroxylase activity from 23 +/- 1.0 pmoles per mg per min in untreated hamsters on the standard diet. The addition of EE decreased (P less than 0.01) 7 alpha-hydroxylase activity from that in untreated hamsters on the standard diet. The conclusions are as follows: (1) EE prevented dietary cholesterol-induced stimulation of cholesterol 7 alpha-hydroxylase activity; (2) EE enhanced the ability of dietary cholesterol to induce saturated bile; and (3) gallstone formation in estrogen-treated women may result from impaired metabolism of dietary cholesterol.     

Effects of sphingolipid synthesis inhibition on cholesterol gallstone formation in C57BL/6J mice

Background: Sphingolipids play a very important role in cell membrane formation, signal transduction and plasma lipoprotein metabolism. The first rate‐limiting step in the sphingolipid biosynthetic pathway is catalyzed by serine palmitoyltransferase (SPT), and myriocin is a potent and specific inhibitor of SPT. We investigated the impact of SPT inhibition on cholesterol gallstone formation in C57BL/6J mice. Methods: Three groups of eight‐week‐old C57BL/6J mice were utilized. Each group consisted of 20 mice; group A, B, and C were fed normal chow, lithogenic diet with phosphate buffered saline, and lithogenic diet with myriocin (0.3 mg/kg), respectively, for 6 weeks. The ceramide levels in both serum and bile were assessed by high performance liquid chromatography analysis. Protein expression of ERK, JNK and p38 in the extracted gallbladder were determined by Western‐blot analysis. Results: Myriocin treatment caused a significant decrease in the rate of cholesterol gallstone formation. The lithogenic diet mice (group B) showed the highest ceramide activities in both the serum and bile among all the tested groups and there was significant suppression of the ceramide levels in both the serum and bile of the myriocin‐treated mice (group C, p < 0.05). Phosphorylation of p38 in the gallbladder was increased in the lithogenic‐diet mice and the expression of phosphorylated p38 was significantly suppressed in the myriocin treated mice. Conclusions: SPT inhibition by myriocin suppressed gallstone formation and the levels of ceramide in both the serum and bile. p38 in the cellular signaling pathways might be associated with cholesterol gallstone formation.     

Bile acids substituted in the 6 position prevent cholesterol gallstone formation in the hamster

The aim of the present study is to examine the efficacy of 6-hydroxy substituted bile acids on the prevention of cholesterol gallstones in a new hamster model of cholesterol cholelithiasis. Male golden Syrian hamsters were fed a nutritionally adequate semipurified lithogenic diet consisting of casein, cornstarch, soluble starch, butterfat, corn oil, and cellulose plus 0.3% cholesterol. Six different bile acids were added to this diet at the 0.05% level: chenodeoxycholic acid, ursodeoxycholic acid, hyodeoxycholic acid, murideoxycholic acid, 6 beta-methyl-hyodeoxycholic acid, and 6 alpha-methyl-murideoxycholic acid. At the end of the 6-wk feeding period, the control group receiving the lithogenic diet had a 55% incidence of gallstones. It was found that all bile acids had inhibited the formation of cholesterol gallstones; complete prevention of gallstones was observed with all 4 3,6-dihydroxy bile acids, whereas chenodeoxycholic acid and ursodeoxycholic acid were somewhat less effective (80% and 75% prevention, respectively). The accumulation of cholesterol in serum and liver induced by the lithogenic diet was inhibited to some extent by all of the bile acids; hyodeoxycholic acid, murideoxycholic acid, and 6 beta-methyl hyodeoxycholic acid were most effective in this respect. The administered bile acids tended to predominate in bile in the case of chenodeoxycholic acid, hyodeoxycholic acid, and 6 beta-methyl-hyodeoxycholic acid. In contrast, ursodeoxycholic acid seemed to be converted to chenodeoxycholic acid and murideoxycholic acid to hyodeoxycholic acid. Only 4% of the 6-methyl analogue of murideoxycholic acid, 6 alpha-methyl-murideoxycholic acid, was recovered in gallbladder bile. These experiments show that the new hamster model of cholesterol cholelithiasis is suitable for gallstone-prevention studies. It was not possible to draw definite conclusions concerning the mechanism of action of the administered bile acids on the basis of cholesterol saturation or the presence of liquid crystals. The detailed mechanism of gallstone prevention by hydrophilic bile acids in this model remains to be elucidated.     

Biliary lipid outputs in young women with cholesterol gallstones

Hepatic secretions of biliary lipids were determined in eight young women with cholesterol gallstones and 14 white women without gallstones. All of the gallstone patients were non-Indian; seven were white and one was black. Hourly outputs of biliary cholesterol were significantly greater in gallstone patients than in white controls. This increased cholesterol output was a major factor in the production of lithogenic bile. The greater cholesterol output in gallstone patients was apparently related to obesity. Despite an increased hepatic secretion of cholesterol, secretion rates of bile acids were relatively low in gallstone patients. However, there was considerable overlap between secretion rates of bile acids in subjects with and without stones, and it was not demonstrated that an absolute deficiency of bile acids existed in gallstone patients. Nevertheless, the contribution of an increased output of biliary cholesterol to the formation of lithogenic bile was clearly evident in our patients.