A hydrophilic bile acid effects partial dissolution of cholesterol gallstones in the prairie dog

Hyodeoxycholic acid attenuates cholesterol gallstone formation via modulation of bile acid metabolism and gut microbiota

BACKGROUND & AIMS

Hyodeoxycholic acid (HDCA), a hydrophilic bile acid (BA), may prevent and suppress the formation of cholesterol gallstones (CGs). However, the mechanism by which HDCA prevents CGs formation remains unclear. This study aimed to investigate the underlying mechanism of HDCA in preventing CG formation.

METHODS

C57BL/6J mice were fed either a lithogenic diet (LD), a chow diet, or LD combined with HDCA. The concentration of BAs in the liver and ileum were determined using liquid chromatography-mass spectrometry (LC-MS/MS). Genes involved in cholesterol and BAs metabolism were detected using polymerase chain reaction (PCR). The gut microbiota in the faeces was determined using 16S rRNA.

RESULTS

HDCA supplementation effectively prevented LD-induced CG formation. HDCA increased the gene expression of BA synthesis enzymes, including Cyp7a1, Cyp7b1, and Cyp8b1, and decreased the expression of the cholesterol transporter Abcg5/g8 gene in the liver. HDCA inhibited LD-induced Nuclear farnesoid X receptor (Fxr) activation and reduced the gene expression of Fgf15 and Shp in the ileum. These data indicate that HDCA could prevent CGs formation partly by promoting BA synthesis in the liver and reduced the cholesterol efflux. In addition, HDCA administration reversed the LD-induced decrease in the abundance of norank_f_Muribaculaceae, which was inversely proportional to cholesterol levels.

CONCLUSIONS

HDCA attenuated CG formation by modulating BA synthesis and gut microbiota. This study provides new insights into the mechanism by which HDCA prevents CG formation.

LAY SUMMARY

In this study, we found that HDCA supplementation suppressed LD-induced CGs in mice by inhibiting Fxr in the ileum, enhancing BA synthesis, and increasing the abundance of norank_f_Muribaculaceae in the gut microbiota. HDCA can also downregulate the level of total cholesterol in the serum, liver, and bile.

Hypolipidemic effects of selective liver X receptor alpha agonists

Recently, a number of nuclear receptors have been identified as key regulators of cholesterol homeostasis. Two of these, liver X receptor alpha (LXRalpha) (NR1H3) [1] and ubiquitous receptor (UR) (NR1H2) [1], appear to be involved in cholesterol reverse transport and disposal. LXRalpha null gene mice fail to adapt metabolically to high-cholesterol diets. We have recently shown that some 6alpha-hydroxylated bile acid analogs are selective activators of LXRalpha. In this report, we show that these orally administered LXRalpha agonists have an overall hypolipidemic effect in hypercholesterolemic rats, mice and hamsters, which indicates that in these animal models, endogenous LXRalpha agonist is a limiting factor for induction of cholesterol disposal. Furthermore, in animals, these 6alpha-hydroxylated bile acid analogs exhibit a unique pharmacokinetic profile and do not increase the serum triglyceride level; therefore, they may represent a novel class of therapeutic agents for cholesterol management.

In vivo gallbladder bile diffusion coefficient measurement by diffusion-weighted echo planar imaging in hamster fed normal and lithogenic diets

It is shown that in vivo measurement of bile water apparent diffusion coefficient (ADC) by diffusion-weighted echo-planar imaging (EPI) in hamster gallbladder is possible providing motion artifact-free ADC values. These ADC values are used to estimate bile viscosity variation induced by normal diets, cholesterol gallstone-inducing diets, and an antilithiasic drug, and to determine if a link exists between bile viscosity and cholesterol gallstone formation. Measurements were performed at 4.7 T with respiratory triggering in five groups of hamsters fed a commercial (RC) or a semisynthetic (SSD) diet, a SSD containing 0.2% hyodeoxycholic acid (SSD+HDC) and two lithogenic diets (LD5, LD10). ADC decreased significantly in LD10 (2.15+/-0.07x 10(-3) mm(2)s(-1)) and SSD+HDC (2.03+/-0.04) compared to RC (2.40+/-0.05) but not in the most lithogenic LD5 diet (2.33+/-0.06). No direct relationship was found between bile viscosity and gallstone incidence; however, viscosity seems to be related to lipid contents of diets. Magn Reson Med 43:854-859, 2000.

Hydrophilic bile acids: prevention and dissolution experiments in two animal models of cholesterol cholelithiasis

The effects of beta-muricholic acid and hyocholic acid on cholesterol cholelithiasis were examined in two animal models. The following experiments were carried out: A) In a gallstone prevention study, prairie dogs were fed the lithogenic diet with or without 0.1% beta-muricholic or 0.1% hyocholic acid for eight weeks. B) In a second prevention study, hamsters were fed the lithogenic diet with or without 0.1% beta-muricholic acid or 0.1% hyocholic acid for six weeks. C) In a gallstone dissolution study, hamsters were fed the lithogenic diet for six weeks to induce stones; stone dissolution was examined during administration of a cholesterol-free purified diet with or without 0.1% beta-muricholic acid or 0.1% hyocholic acid. In the prevention study in prairie dogs (A), both bile acids failed to prevent stone formation, the cholesterol saturation index of bile was 0.89 in the lithogenic controls, remained unchanged with hyocholic acid and increased to 1.52 in the beta-muricholic acid group. In the prevention study in hamsters (B), beta-muricholic acid completely inhibited the cholesterol cholelithiasis (0% stone incidence); the cholesterol saturation index of bile was 1.78 (compared to lithogenic controls, 1.37). Hyocholic acid reduced stone incidence to 16% with a cholesterol saturation index of 0.98. In the dissolution study in hamsters (C), preexisting cholesterol gallstones were not dissolved by either hydrophilic bile acid after feeding these bile acids for an additional six weeks; at the end of the experiment, the cholesterol saturation indices were below unity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of taurohyodeoxycholic acid, a hydrophilic bile salt, on bile salt and biliary lipid secretion in the rat

Taurohyodeoxycholic acid is a natural 6 alpha-hydroxylated bile acid with an apparent hydrophilicity intermediate between those of tauroursodeoxycholic and taurocholic acids. We investigated in the rat the hepatobiliary metabolism, choleretic properties, and biliary maximum secretory rate (SRmax) of taurohyodeoxycholic in comparison with these two bile salts. Each compound was infused intravenously, at a rate increased in a stepwise manner from 100 to 300 nmol/min/100 g body wt, in bile salt-depleted bile fistula rats. The three bile salts appeared rapidly starting with the infusion and increased to represent more than 95% of the total bile salts. No apparent biliary metabolites were formed. All the bile salts caused a dose-dependent increase in bile flow and biliary lipid output. The absolute increase in bile flow was lower in rats infused with taurohyodeoxycholic acid, yet the volume of bile formed per nanomole of secreted bile salt was 13.8 nl for taurohyodeoxycholic, 6.4 nl for tauroursodeoxycholic acid, and 10.9 nl for taurocholic. The SRmax values were 1080, 3240, and 960 nmol/min/100 g, respectively. At all infusion rates, taurohyodeoxycholic acid caused a greater (P < 0.001) secretion of biliary lecithin compared to the other bile salts. There were no significant differences in the biliary secretion of cholesterol and proteins. Electron microscopy showed the recruitment of vesicles and lamellar bodies around and within bile canaliculi. In conclusion, taurohyodeoxycholic promotes a biliary lecithin secretion greater than expected from physicochemical predictions, representing a novel secretory property with potential pharmacological relevance.

Er:YAG laser ablation of prairie dog gallbladder epithelium for the prevention of gallstones

We hypothesized that laser ablation of gallbladder epithelium would prevent gallstone formation in prairie dogs. An Er:YAG laser (lambda = 2.94 microns) was used to ablate the gallbladder epithelium of 24 prairie dogs; 20 sham-irradiated and 12 non-operated prairie dogs served as controls. Prairie dogs were sacrificed at time periods of 4 days, 2 weeks, and 8-12 weeks and evaluated for the presence of gallstones and cholesterol crystals. Laser-irradiated gallbladders demonstrated a lower rate of gallstone formation at 8-12 weeks than the sham-irradiated gallbladders (39% vs. 79%: P < .02). Crystal formation, however, was not different between laser-irradiated (88%) and sham-irradiated (100%) animals. The laser-irradiated group had less epithelium than the non-operated group at all time periods (P < or = .002) and compared to the sham-irradiated group at 4 days and 8-12 weeks (P < or = .001). These data suggest that laser ablation of gallbladder epithelium can reduce the rate of gallstone formation although this effect may be temporary.

Metabolism and time-course excretion of murideoxycholic acid, a 6 beta-hydroxylated bile acid, in humans

The metabolism and time-courses of urinary and fecal excretions of murideoxycholic acid (MDCA; 3 alpha,6 beta-dihydroxy-5 beta-cholanoic acid), a 6 beta-hydroxylated bile acid, was investigated in man. The study was carried out in two groups of subjects. Six cholecystectomized patients fitted with a cystic duct drain ingested 100 mg of a tracer dose of 3H-MDCA. Time-course of radioactivity in plasma was then followed for an 8-h period. Biliary, urinary and fecal excretions of radioactivity were measured for a 5-day period and excreted MDCA metabolites were identified. Five lithiasic patients with intact enterohepatic circulation ingested 500 mg of the same tracer dose of 3H-MDCA. Radioactivity in plasma was followed for a 49-h period and urinary and fecal excretions of radioactivity were measured daily for 7 days. In the first group, the excretion of the radioactivity by the three routes (bile+urine+feces) reached 97.8 +/- 1.5% of the ingested dose but dropped to 75 +/- 8.3% (urine+feces) in patients in the second group. In cholecystectomized patients, the estimation of intestinal MDCA absorption was dependent on cystic duct drain flow rate and gave values ranging from 20% to 87%. The biological half-life of MDCA in lithiasic patients averaged 3.4 +/- 0.7 days. Radioactivity appeared in the plasma in the first hour and reached a maximum 6 and 3 h after the beginning of the experiment in group I and II respectively. In the second group, another peak of radioactivity in plasma was observed just after breakfast.(ABSTRACT TRUNCATED AT 250 WORDS)

Replacement of cholesterol gallstones by murideoxycholyl taurine gallstones in prairie dogs fed murideoxycholic acid

The effect of two hydrophilic bile acids, murideoxycholic acid (3 alpha,6 beta-dihydroxy-5 beta-cholanoic acid) and ursodeoxycholic acid, on cholesterol and bile acid metabolism and hepatic pathology and gallstone composition was studied in the prairie dog. Cholesterol gallstones were induced by feeding a diet containing 1.2% cholesterol for 75 days. The animals were divided into six groups, and gallstone regression was studied as follows: groups 2 and 5, chow plus 0.2% cholesterol; groups 3 and 6, chow plus 0.2% cholesterol plus 0.15% ursodeoxycholic acid; groups 4 and 7, chow plus 0.2% cholesterol plus 0.15% murideoxycholic acid. Animals in groups 2 to 4 were killed after an additional 6 wk; animals in groups 5 to 7 were killed after an additional 12 wk. Gallstone dissolution did not occur in any group. The gallstones in groups 2, 3, 5 and 6 were typical cholesterol aggregates, as determined by polarized light microscopy and Fourier transform infrared spectrometry. The gallstones of the murideoxycholic acid group were large, solitary, dark stones that appeared radiopaque under 22 kVp x-ray examination. Scanning electron microscopy showed that in these stones the cholesterol crystals had been replaced by an amorphous material, both within the stone and on the stone surface. Chemical analysis indicated that at the end of 12 wk the calcium/sodium salt of the taurine conjugate of murideoxycholic acid (murideoxycholyl taurine) comprised 70% of the stones; protein, cholesterol and small amounts of other bile salts were also present. In vitro studies confirmed the insolubility of the sodium and calcium salts of murideoxycholyl taurine. These studies indicate that the hydrophilic bile acids, murideoxycholic acid and ursodeoxycholic acid, did not achieve gallstone dissolution under the conditions used. In the animals fed murideoxycholic acid, an insoluble calcium salt of murideoxycholyl taurine replaced cholesterol as the major constituent of gallbladder stones. This is the first example of an insoluble dihydroxy taurine-conjugated bile acid; administration of the unconjugated bile acid induced precipitation of a kind of gallstone not previously reported. The final result was transformation of cholesterol stones to bile salt stones.

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.

Dietary induction of cholesterol gallstones in hamsters from three different sources

Cholesterol gallstones were produced in young male, golden Syrian hamsters, obtained from three different suppliers, by administering a nutritionally adequate, semipurified diet for periods of either 5 or 10 weeks. The major components of the lithogenic diet were casein, cornstarch, butterfat, corn oil and 0.3% cholesterol. The hamsters were obtained from Sesco, Harlan Sprague-Dawley (Engle hamster) and Charles River (Lakeview hamster). There were profound differences among the three groups with respect to gallstone formation and cholesterol metabolism: The highest incidence of gallstones occurred in Sesco hamsters, 44.4% and 63.6% after 5 and 10 weeks on the lithogenic diet, respectively. In the Engle hamster, after a 5-week feeding, cholesterol crystals and gallstones were absent. When the feeding period was extended to 10 weeks, cholesterol gallstones were present in 45.5% of the animals. In the Lakeview hamsters, neither gallstones nor cholesterol crystals were found in the gallbladder after a 5-week period. After 10 weeks, cholesterol gallstones were found in only a single hamster. In all groups, the lithogenic diet produced large increases of liver, serum and biliary cholesterol concentrations and increased liver weights. When the animals were fed for 5 weeks, only the bile of Sesco hamsters became supersaturated. Supersaturated bile was induced in all groups after a 10-week feeding of the lithogenic diet with cholesterol saturation ranging from 1.47 to 1.97. These data indicate that it is possible to induce cholesterol gallstones in hamsters by means of a nutritionally adequate, semipurified diet of moderate cholesterol content.(ABSTRACT TRUNCATED AT 250 WORDS)

Dissolution of cholesterol gallstones by bile acids in the prairie dog

The effect of chenodeoxycholic acid, ursodeoxycholic acid and hyodeoxycholic acid on gallstone dissolution was studied in the prairie dog. Cholesterol gallstones were found in all animals after feeding a semipurified diet plus 1.2% cholesterol for six wk. Gallstone regression was examined by feeding a chow diet containing the bile acids (chenodeoxycholic acid, ursodeoxycholic acid or hyodeoxycholic acid) alone (30 mg/kg/day) or in combination (chenodeoxycholic acid plus ursodeoxycholic acid) for an additional six wk. Chenodeoxycholic acid was effective in dissolving established cholesterol gallstones (two out of 16 animals still had stones) and cholesterol crystals (six out of 16 animals had crystals); the hydrophilic bile acids, ursodeoxycholic acid and hyodeoxycholic acid, were ineffective in the six-wk regression study. The lithogenic indices averaged 1.09 at the end of the induction period; all biles became unsaturated with respect to cholesterol after the six-wk regression period (group 1, 0.82; group 2, 0.66; group 3, 0.81; group 4, 0.84; group 5, 0.66). Cholesterol levels in liver, plasma and bile were elevated after the six-wk induction phase (4.59 mg/g, 610 mg/dl and 0.36 mg/ml, respectively) but returned to near normal levels after the six-wk regression period. Biliary bile acids contained increased levels of the dietary bile acid administered to each group. This experiment shows that relatively hydrophobic bile acids may be more effective than hydrophilic bile acids for gallstone dissolution during the period studied.