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.     

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.     

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.     

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.     

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.     

Phenotypic characterization of Lith genes that determine susceptibility to cholesterol cholelithiasis in inbred mice: soluble pronucleating proteins in gallbladder and hepatic biles.

BACKGROUND/AIMS: Gallstone susceptibility is high in C57L inbred mice (males > females) and low in AKR mice, related to variant lithogenic (Lith) genes. We examined the relationship between biliary crystallization-promoting proteins and gallstone susceptibility. METHODS: Biliary protein and lipid concentrations were determined at 0, 7,14, 21, 28 and 56 days on a lithogenic diet. RESULTS: Protein and soluble mucin concentrations in gallbladder biles increased markedly in males, but remained low in females of both strains and correlated with the cholesterol saturation index (CSI). In all groups, IgA and IgM concentrations decreased initially, but increased at later stages. There were no consistent changes in IgG concentrations, but aminopeptidase-N levels were higher in AKR than in C57L. During the lithogenic diet period, the CSI was > or = 2 in C57L males, approximately 1.5 in AKR males, and 1 in females of both strains. Taurodeoxycholate and taurochenodeoxycholate rose sharply in C57L, but remained low in AKR. CONCLUSIONS: Hydrophobic bile salts, cholesterol supersaturation, and possibly, high mucin concentrations are associated with gallstone formation. In vitro crystallization-promoting immunoglobulins and aminopeptidase-N do not appear to be major factors in murine gallstone pathogenesis, in line with the observation that genes encoding these proteins do not co-localize with any known Lith locus.     

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.     

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.     

Modeling plasma lipoprotein-bile lipid relationships: Differential impact of psyllium and cholestyramine in hamsters fed a lithogenic diet

Hamsters fed a lithogenic diet become hyperlipemic with elevated very-low-density lipoprotein (VLDL) and high-density lipoprotein 2 (HDL₂) cholesterol pools and develop lithogenic bile in which chenodeoxycholate (cheno) typically predominates. The relationship between these distorted lipoprotein and bile lipid profiles and gallstone induction was investigated in male Syrian hamsters fed for 5 weeks a gallstone-inducing purified diet (5% butter, 0.4% cholesterol) or the same diet supplemented with 5% psyllium or 1% cholestyramine, agents known to alter bile acid metabolism. The gallstone diet essentially doubled plasma cholesterol level, whereas psyllium decreased it to near normal, and cholestyramine to a subnormal level, while correcting the distorted distribution of cholesterol among lipoproteins. Both the gallstone diet and psyllium produced cholesterol-laden livers, in contrast to subnormal values produced by cholestyramine. Fecal bile acid excretion was increased eightfold with cholestyramine and fourfold with psyllium relative to the value produced by the gallstone diet and a literature control value. Supersaturated bile developed with the gallstone diet (lithogenic index [LI], 2.3 ± 0.6), whereas the LI was decreased by psyllium (1.2 ± 0.4) and cholestyramine (0.7 ± 0.3). The gallstone diet decreased the concentration of bile acids in gallbladder bile, but greatly increased the percentage of taurochenodeoxycholic acid, whereas psyllium preferentially decreased all taurine-conjugated bile acid levels and expanded glycocholate output. Cholestyramine greatly decreased the secretion of biliary cholesterol and cheno independent of its conjugation. Accordingly, psyllium increased the glycine to taurine ratio of gallbladder bile fivefold, whereas cholestyramine did not affect this ratio, but increased the cholate to cheno ratio dramatically (25-fold) as compared with a threefold increase with psyllium. This combination of biliary lipid and bile acid alterations induced coordinated responses in the LI and the hydrophobicity index (HI) such that cholesterol gallstones developed in 11 of 12 hamsters fed the gallstone diet, whereas only one of 11 of the psyllium-fed and none of 12 cholestyramine-fed hamsters had cholesterol stones. Thus, psyllium and cholestyramine differentially increased bile acid excretion, which improved the lipoprotein profile and inhibited cholesterol gallstone formation. Both agents operated by different means to decrease biliary cholesterol secretion and the percentage of cheno, which decreased the LI and HI, respectively.     

Association of caveolin-3 and cholecystokinin A receptor with cholesterol gallstone disease in mice

AIM: To investigate the role of caveolin-3 (CAV3) and cholecystokinin A receptor (CCKAR) in cholesterol gallstone disease (CGD).METHODS: To establish a mouse model of CGD, male C57BL/6 mice were fed with a lithogenic diet containing 1.0% cholic acid, 1.25% cholesterol and 15% fat; a similar control group was given a normal diet. The fresh liver weights and liver-to-body weight ratio were compared between the two groups after one month. Serum lipid profile and bile composition were determined with an autoanalyzer. The Cav3 and Cckar mRNA and CAV3 and CCKAR protein levels in the liver and gallbladder were determined via real-time polymerase chain reaction and Western blot, respectively.RESULTS: Establishment of the mouse CGD model was verified by the presence of cholesterol gallstones in mice fed the lithogenic diet. Compared with mice maintained on a normal diet, those fed the lithogenic diet had significantly higher mean liver-to-body weight ratio (0.067 ± 0.007 vs 0.039 ± 0.007, P < 0.01), serum total cholesterol (4.22 ± 0.46 mmol/L vs 2.21 ± 0.11 mmol/L, P < 0.001), bile total cholesterol (1.33 ± 0.33 mmol/L vs 0.21 ± 0.11 mmol/L, P < 0.001), and bile phospholipid concentrations (3.55 ± 1.40 mmol/L vs 1.55 ± 0.63 mmol/L, P = 0.04), but lower total bile acid concentrations (726.48 ± 51.83 μmol/L vs 839.83 ± 23.74 μmol/L, P = 0.007). The lithogenic diet was also associated with significantly lower CAV3 in the liver and lower CAV3 and CCKAR in the gallbladder compared with the control mice (all P < 0.05).CONCLUSION: CAV3 and CCKAR may be involved in cholesterol gallstone disease.     

Identification of cholelithogenic enterohepatic helicobacter species and their role in murine cholesterol gallstone formation

BACKGROUND & AIMS: Helicobacter spp are common inhabitants of the hepatobiliary and gastrointestinal tracts of humans and animals and cause a variety of well-described diseases. Recent epidemiologic results suggest a possible association between enterohepatic Helicobacter spp and cholesterol cholelithiasis, chronic cholecystitis, and gallbladder cancer. To test this, we prospectively investigated the effects of Helicobacter spp infection in cholesterol gallstone pathogenesis in the highly susceptible C57L/J mouse model. METHODS: Helicobacter spp-free adult male C57L mice were infected with several different enterohepatic Helicobacter spp or left uninfected and fed either a lithogenic diet or standard mouse chow for 8 and 18 weeks. At the conclusion of the study, bile was examined microscopically and diagnostic culture and polymerase chain reaction were performed. RESULTS: Mice infected with Helicobacter bilis or coinfected with Helicobacter hepaticus and Helicobacter rodentium and fed a lithogenic diet developed cholesterol gallstones at 80% prevalence by 8 weeks compared with approximately 10% in uninfected controls. Monoinfections with H hepaticus , Helicobacter cinaedi , and H rodentium gave a cholesterol gallstone prevalence of 40%, 30%, and 20%, respectively; the latter 2 groups did not differ significantly from uninfected animals. Neither infected nor uninfected mice fed a chow diet developed cholesterol gallstones. CONCLUSIONS: These findings, along with prior epidemiologic studies, suggest that Helicobacter spp play a major role in the pathophysiology of cholesterol gallstone formation in mice and perhaps humans.     

Lith1, a major gene affecting cholesterol gallstone formation among inbred strains of mice.

The prevalence of cholesterol gallstones differs among inbred strains of mice fed a diet containing 15% (wt/wt) dairy fat, 1% (wt/wt) cholesterol, and 0.5% (wt/wt) cholic acid. Strains C57L, SWR, and A were notable for a high prevalence of cholelithiasis; strains C57BL/6, C3H, and SJL had an intermediate prevalence; and strains SM, AKR, and DBA/2 exhibited no cholelithiasis after consuming the diet for 18 weeks. Genetic analysis of the difference in gallstone prevalence rates between strains AKR and C57L was carried out by using the AKXL recombinant inbred strain set and (AKR x C57L)F1 x AKR backcross mice. Susceptibility to gallstone formation was found to be a dominant trait determined by at least two genes. A major gene, named Lith1, mapped to mouse chromosome 2. When examined after 6 weeks on the lithogenic diet, the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (EC 1.1.1.88) was downregulated as expected in the gallstone-resistant strains, AKR and SJL, but this enzyme failed to downregulate in C57L and SWR, the gallstone-susceptible strains. This suggests that regulation of the rate-limiting enzyme in cholesterol biosynthesis may be pivotal in determining the occurrence and severity of cholesterol hypersecretion and hence lithogenicity of gallbladder bile. These studies indicate that genetic factors are critical in determining gallstone formation and that the genetic resources of the mouse model may permit these factors to be identified.     

Different susceptibilities to the formation of cholesterol gallstones in mice

In the search for an animal model of genetic determinants of cholesterol cholelithiasis, we found strain, gender and individual differences in mice. Male black (C57BL6J) mice had a 50% incidence of cholesterol gallstones after they consumed lithogenic food similar to that used by Tepperman et al. for 2 weeks, whereas similarly treated male agouti (CBA/J) mice and females of both strains were free of gallstones. The male and female mice of both strains were fertile at 8 weeks of age, and the male black mice were first susceptible to induction of gallstones at 24 weeks of age. Male agouti mice of the same age did not form gallstones until they had consumed the lithogenic food for 8 weeks. The gallbladder biles of both strains were supersaturated with cholesterol during the lithogenic regimen. The male agouti mice had much higher fractional turnover rates of [24-14C]cholic acid than did the male black mice. In spite of their small total cholate pools, the agouti mice had higher rates of new cholate synthesis than did the black mice. The rate of disappearance of [1,2-3H]cholesterol from the blood was higher in the male agouti than in the black mice. The gallbladders of the agouti mice contained less bile and weighed less empty than gallbladders of the black mice. They also did not increase in volume in response to the lithogenic diet as much as gallbladders of the black mice. The difference in gallstone induction times between male and female black mice was as great as the difference between the two strains.(ABSTRACT TRUNCATED AT 250 WORDS)     

Activation of liver X receptor sensitizes mice to gallbladder cholesterol crystallization

Gallstone disease is a hepatobiliary disorder due to biochemical imbalances in the gallbladder bile. In this report, we show that activation of nuclear receptor liver X receptor (LXR) sensitized mice to lithogenic diet-induced gallbladder cholesterol crystallization, which was associated with dysregulation of several hepatic transporters that efflux cholesterol, phospholipids, and bile salts. The combined effect of increased biliary concentrations of cholesterol and phospholipids and decreased biliary concentrations of bile salts in LXR-activated mice led to an increased cholesterol saturation index and the formation of cholesterol crystals. Interestingly, the lithogenic effect of LXR was completely abolished in the low-density lipoprotein receptor (Ldlr) null background or when the mice were treated with Ezetimibe, a cholesterol-lowering drug that blocks intestinal dietary cholesterol absorption. These results suggest that LDLR-mediated hepatic cholesterol uptake and intestinal cholesterol absorption play an essential role in LXR-promoted lithogenesis. Conclusion: The current study has revealed a novel lithogenic role of LXR as well as a functional interplay between LXR and LDLR in gallbladder cholesterol crystallization and possibly cholesterol gallstone disease (CGD). We propose that LXR is a lithogenic factor and that the LXR transgenic mice may offer a convenient CGD model to develop therapeutic interventions for this disease.     

Osteopontin plays an anti‐nucleation role in cholesterol gallstone formation

Aim: To investigate the role of osteopontin in cholesterol gallstone formation. Methods: Nucleation time was determined in model and human gallbladder bile in vitro. Effect of osteopontin on vesicles of bile was investigated via transmission electron microscopy. The mRNA and protein expression of osteopontin were detected in human calculus and normal gallbladder tissues, and then lipid compositions of human bile were determined via commercial kits. Results: Osteopontin could prolong the nucleation time in a dose‐dependent manner, and inhibit the pro‐nucleation effect induced by calcium ion. Cholesterol crystal growth was inhibited by osteopontin in a dose‐dependent manner in model and human gallbladder bile, but not affected by calcium. Furthermore, the formation, aggregation and fusion of vesicles were suppressed by osteopontin in model and human bile as demonstrated by transmission electron microscopy. The mRNA and protein expression of osteopontin in calculus gallbladder tissues were lower than those in normal tissues. The concentrations of cholesterol, phospholipid and bile acids, and cholesterol saturated index were higher and the contents of osteopontin and calcium, nevertheless, were found to be lower in lithogenic bile than those in normal controls. Conclusion: These findings indicated that osteopontin could inhibit the cholesterol gallstone formation as an anti‐nucleation factor, which may be involved in the pathogenesis of cholesterol gallstone formation.     

Gallbladder mucosal blood flow increases during early cholesterol gallstone formation.

Gallbladder absorption increases during early cholesterol gallstone formation and is influenced by the intraluminal presence of lithogenic bile. The effect of lithogenic bile on gallbladder mucosal blood flow is unknown. The current study tested the hypothesis that the presence of lithogenic gallbladder and hepatic bile enhances gallbladder mucosal blood flow in cholesterol-fed (0.4%) prairie dogs, as determined by hydrogen gas clearance. Gallbladder mucosal blood flow in control animals was 35.57 +/- 3.9 mL.min-1.100 g-1. In contrast, basal gallbladder mucosal blood flow in cholesterol-fed animals was significantly (P less than 0.01) increased to 64.94 +/- 8.7 mL.min-1.100 g-1. In crossover studies, the addition of lithogenic gallbladder bile to control animals (n = 6) resulted in a significant (P less than 0.025) 26% increase in gallbladder mucosal blood flow, whereas the addition of nonlithogenic gallbladder bile into gallbladders of cholesterol-fed prairie dogs resulted in a significant (P less than 0.025) 58% decrease in gallbladder mucosal blood flow. Similarly, hepatic bile crossover studies showed that the addition of lithogenic hepatic bile to control gallbladders significantly increased (P less than 0.025) gallbladder blood flow by 30%, whereas instillation of nonlithogenic hepatic bile in gallbladders of cholesterol-fed animals significantly (P less than 0.025) decreased gallbladder mucosal blood flow by 29%. These results suggest that alterations in gallbladder mucosal blood flow, influenced by the presence and absence of lithogenic bile, may play a role in cholesterol gallstone formation.     

Effect of Beta-sitosterol on Cholesterol-cholic Acid-induced Gallstone Formation in Mice

Beta-sitosterol has been shown to prevent gallstone formation in mice fed 1.2% cholesterol and 0.5% cholic acid (lithogenic diet). The incidence of gallstone formation in the mouse by the addition of 2.5% sitosterol in the lithogenic diet is about 35.5% in male and 25% in female. The condition of the liver, whether fatty or normal, did not correlate with the presence or absence of cholelithiasis. The serum and liver cholesterol levels of mice fed either sitosterol and cholesterol or sitosterol and cholic acid is lower than those of mice fed cholesterol or cholic acid alone. Elevation, of liver phospholipid concentration was noticed in mice fed sitosterol or a combination of sitosterol with cholesterol or cholic acid or both cholesterol and cholic acid.