Effects of chenodeoxycholic and ursodeoxycholic acids on lipid metabolism and gallstone formation in the prairie dog

Increased expression of gallbladder cholecystokinin: a receptor in prairie dogs fed a high-cholesterol diet and its dissociation with decreased contractility in response to cholecystokinin

A series of our studies have shown that formation of cholesterol-supersaturated bile in patients with cholesterol gallstone disease is causatively related to decreased gallbladder contractility and mucin hypersecretion by the gallbladder. Supersaturated bile may modify the composition of gallbladder membranes so that the transduction of smooth muscle regulatory signals is impaired, and it may enhance the inflammation-induced mucin secretion by the gallbladder. To achieve a better understanding of the mechanism by which supersaturated bile impairs the contractility, we studied changes in the expression levels of gallbladder cholecystokinin (CCK-A) receptor messenger ribonucleic acid (mRNA) in prairie dogs fed a high-cholesterol diet. Levels of pathobiological determinants in arachidonate metabolism which are important for mucin secretion were also measured in their bile. Adult male prairie dogs were randomly assigned to receive either a semisynthetic diet (SSD) or an SSD plus 1.2% cholesterol (a high-cholesterol diet) for 2-, 4-, and 6-week periods. The contractile force in response to CCK-octapeptide (CCK-8) was measured by using gallbladder muscle strips. The mRNA levels of the CCK-A receptor were determined by reverse-transcription polymerase chain reaction (RT-PCR). Parallel to the increase in the cholesterol saturation index, the contractile responses to CCK-8 decreased in the animals fed a high-cholesterol diet for 4 weeks and markedly decreased in the animals with gallstone formation. However, in contrast to the decreased contractility, the steady-state mRNA levels of the gallbladder CCK-A receptor were significantly increased in the animals fed a high-cholesterol diet in comparison with the corresponding control animals. In the bile, a high-cholesterol diet caused an increase in the proportion of arachidonyl-phosphatidylcholine species, where phospholipase A(2) activity, prostaglandin E(2), and mucin concentrations were increased parallel to the feeding period. Up-regulation of the CCK-A receptor mRNA in the gallbladder of animals fed a high-cholesterol diet associated with decreased contractility may be due to an impairment of CCK signaling related to increased membrane cholesterol contents and its related reaction of biological compensation in order to increase the receptor concentration. The results of the present study suggest that in prairie dogs fed a high-cholesterol diet both a decrease in gallbladder contractility related to impairment of CCK signaling and phospholipase A(2) (PLA(2))-induced mucosal inflammation in the gallbladder with associated biliary alterations favoring cholesterol crystal formation pathogenetically contribute to the formation of cholesterol gallstones.

Effect of castration and hormonal supplementation on cholesterol cholelithiasis in the male hamster

This study examined the effect of castration and dietary hormonal supplementation on cholesterol cholelithiasis in male hamsters. Animals fed a standard lithogenic diet developed cholesterol gallstones (17%) after 6 wk, while castrated hamsters did not form any stones. Addition of a synthetic androgen, methyltestosterone, to the lithogenic diet induced cholelithiasis in castrated animals (50%). The biles of normal and castrated-hormone supplemented hamsters had cholesterol saturation indices of 1.0 and 1.1, respectively, while the bile of the castrated animals remained unsaturated (0.6). The ratio of cholic acid/chenodeoxycholic acid in bile increased after castration, but returned to normal levels following hormonal supplementation. Biliary cholesterol carriers were separated by ultracentrifugation. Animals in the stone-forming groups (normal and castrated-hormone treated) had a significant proportion of their biliary cholesterol in vesicles (44 and 46%, respectively); castrated hamsters had less cholesterol in vesicle form (9%). The molar ratio of cholesterol/phospholipid in vesicles was reduced after castration (0.93 vs. 0.42) and increased by hormonal supplementation (1.89). In conclusion, when compared to normal male hamsters fed a standard lithogenic diet, castration reduced the cholesterol saturation of bile, lowered the vesicular/micellar ratio in bile, and inhibited cholesterol cholelithiasis. Dietary androgen supplementation increased the lithogenicity of bile, resulting in stone formation in castrated animals.

Effect of a synthetic androgen on biliary lipid secretion in the female hamster

This study was designed to elucidate the effect of the synthetic androgen, methyltestosterone, on bile flow and biliary lipid secretion in female hamsters. Animals were divided into four groups and fed the following diets: group 1, lithogenic diet for three weeks; group 2, lithogenic diet + 0.05% methyltestosterone for three weeks; group 3, lithogenic diet for six weeks; group 4, lithogenic diet + 0.05% methyltestosterone for six weeks. At the end of each experimental period, the hamsters were operated on to establish external biliary fistulas. During the depletion of the endogenous bile acid pool (for two hours), the basal bile flow of group 4 was significantly smaller than that of group 3. Basal bile acid output was significantly lower in the methyltestosterone-fed groups 2 and 4 than in control groups 1 and 3. In contrast, groups 2 and 4 secreted more cholesterol than groups 1 and 3. Group 4 had a higher ratio of cholesterol output to phospholipid output than group 3. Increasing doses of taurocholate were infused after the bile acid depletion period, and it was found that methyltestosterone did not change the bile acid independent bile flow. The increments in cholesterol or phospholipid output induced per increment of bile acid output (linkage coefficients) were analyzed by linear regression. The methyltestosterone-fed groups (groups 2 and 4) had a higher linkage coefficient of cholesterol output to bile acid output than the control groups (groups 1 and 3). The linkage coefficients of phospholipid output to bile acid output of groups 2 and 4 were also higher compared to groups 1 and 3. The linkage coefficient of cholesterol output to phospholipid output of group 2 was higher than that of group 1. These results suggest that methyltestosterone stimulated the cosecretion mechanism of cholesterol and phospholipid in bile associated with an increasing ratio of cholesterol to phospholipid. In conclusion, the synthetic androgen, methyltestosterone, caused a decrease in basal bile flow and bile acid secretion, and an increase in basal cholesterol secretion and the biliary cholesterol-to-phospholipid ratio. These findings explain, in part, how methyltestosterone intensifies the formation of cholesterol gallstones in female hamsters.

Prevention of cholesterol cholelithiasis by dietary unsaturated fats in hormone-treated female hamsters

We examined the effect of diet on gallstone incidence and the composition of biliary phosphatidylcholines in methyltestosterone-treated female hamsters. These hamsters were fed a nutritionally adequate purified lithogenic diet containing 2% corn oil, 4% butterfat, 0.3% cholesterol, and 0.05% methyltestosterone, resulting in a cholesterol gallstone incidence of 86%. This incidence was lowered when mono- and polyunsaturated fats or fatty acids were added to the diet: 2.5% oleic acid resulted in total prevention of cholesterol cholelithiasis, 2.5% linoleic acid, and 4% safflower oil (78% linoleic acid content) reduced gallstone incidence to 26 and 8%, respectively. An additional 4% butterfat (29% oleic acid content) produced gallstones in 50% of the animals. At the end of the 6-wk feeding period, the bile of all hamsters was supersaturated with cholesterol. The major biliary phosphatidylcholine species in all groups were (sn-1-sn-2): 16:0-18:2, 16:0-18:1, 18:0-18:2, 16:0-20:4, and 18:2-18:2. The safflower oil- and linoleic acid-fed hamsters exhibited an enrichment of 16:0-18:2 (16-18%); added butterfat or oleic acid increased the proportion of 16:0-18:1 (9 and 25%, respectively). We conclude that the phosphatidylcholine molecular species in female hamster bile can be altered by dietary fats/fatty acids and that mono- and polyunsaturated fatty acids play a role in suppressing the induced cholelithiasis.

IV chenodeoxycholate prevents calcium bilirubinate gallstones during total parenteral nutrition in the prairie dog

BACKGROUND

The purpose of this study was to determine whether IV chenodeoxycholate (CDC) could prevent total parenteral nutrition (TPN)-associated pigmented gallstones in the prairie dog.

METHODS

Twelve prairie dogs were divided into two equal groups, each receiving an identical TPN regimen. Each animal received 92 kcal/d with 61% of the calories from carbohydrate. The total volume of infusate delivered to each animal was 59 mL/d. Animals in one group, termed the TPN + CDC group, received a daily bolus injection of CDC at a dose of 15 mg/kg. Prairie dogs in the second group, termed the TPN group, received water (vehicle carrier) 1 mL/kg/d. The TPN and TPN + CDC groups received TPN for 40.3 +/- 1.3 and 42.5 +/- 0.6 days, respectively.

RESULTS

There was no statistical difference in the initial and final weights between the two groups. None of the TPN + CDC-treated animals had gallstones or calcium bilirubinate crystals. In contrast, all of the TPN-treated animals had calcium bilirubinate crystals (p = .002), and five of six had macroscopic black pigmented gallstones (p = .015). Cholesterol crystals were not observed in either group of animals. The amount of biliary bilirubin and ionized calcium was significantly greater in the TPN group (both p < .001); however, both groups had a similar total biliary calcium concentration.

CONCLUSION

IV CDC is effective in preventing TPN-associated gallstones in the prairie dog.

Age, sex and source of hamster affect experimental cholesterol cholelithiasis

In the present study, we examined the effect of the following factors on a hamster model of cholesterol cholelithiasis: (i) the source of the golden Syrian hamsters (Sasco, Omaha, NE or Charles River, Wilmington, MA), (ii) the sex of the experimental animals and (iii) their age (4 wk vs. 8 wk of age). All hamsters were fed a semipurified diet which contained cholesterol (0.3%) and palmitic acid (1.2%). No cholesterol gallstones formed in any of the female hamsters regardless of age or source. The 4-week-old male hamsters from Sasco had the greatest incidence of gallstones (93%). The 8-week-old male hamsters tended to have a lower incidence of cholesterol gallstones than the younger ones, regardless of the commercial supplier (67 vs. 93% for Sasco and 27 vs. 40% for Charles River). Female hamsters had higher liver and serum cholesterol levels than the male hamsters; Charles River hamsters had lower serum cholesterol concentrations than the Sasco animals. Total biliary lipid concentrations were highest in Sasco male hamsters, but biliary cholesterol (mol%) was lower in the males than in the females (4.2-4.5% vs. 6.1-7.1%) regardless of age. The cholesterol saturation indices were higher in the Sasco females than the corresponding males; these values were lower in the Sasco hamsters than the Charles River animals, regardless of age or sex. The male Sasco hamsters had a higher total biliary bile acid concentration (98.9 mg/mL) than the Sasco females (58.9 mg/mL) and the Charles River animals (24.6 mg/mL for males and 38.2 mg/mL for females). The percentage of chenodeoxycholic acid in bile was significantly lower, and the percentage of cholic acid was higher in all females as compared to males.(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.

The effect of alfalfa-corn diets on cholesterol metabolism and gallstones in prairie dogs

Cholesterol gallstones were present in prairie dogs fed alfalfa plus corn with and without exogenous cholesterol (0.4%). The diets fed to the animals for eight weeks contained alfalfa plus corn in fixed proportions of 50:50, 85:15 and 15:85 (w/w). At sacrifice, all animals were healthy but had not gained weight; no deaths occurred during the experiment. Cholesterol gallstones were present in all groups. In the absence of exogenous cholesterol, the highest stone incidence was found in the animals which received the lowest fiber (highest corn) diets (alfalfa plus corn, 50:50, 67%; alfalfa plus corn, 15:85, 83%). Cholesterol gallstone incidence was 100% when exogenous cholesterol was added to the alfalfa plus corn diets (50:50 and 15:85). No pigment gallstones were detected in any animal. Liver and plasma cholesterol concentrations were highest in the animals receiving alfalfa plus corn (15:85) plus 0.4% cholesterol (4.29 mg/g, and 356 mg/dl, respectively). These values were lowest in animals receiving 85% alfalfa plus 15% corn without cholesterol (2.19 mg/g and 88 mg/dl, respectively). Lithogenic indices were below 1.00 in all groups. Biliary bile acids were mainly amidates of cholic acid and chenodeoxycholic acid, with the former predominating. Thus, gallstones can be formed in prairie dogs in the absence of exogenous cholesterol; gallstone incidence is reduced by dietary fiber.

Transport, metabolism, and effect of chronic feeding of cholylsarcosine, a conjugated bile acid resistant to deconjugation and dehydroxylation

To test the effect in rodents of chronic ingestion of a bile acid resistant to deconjugation, cholylsarcosine was synthesized and its transport, metabolism, and effect on biliary bile acid and biliary lipid composition were determined in rabbits, hamsters, and rats. Cholylsarcosine was shown to be well absorbed from the ileum but underwent little absorption from the jejunum or colon. When cholylsarcosine was administered in the diet at 140 mumol/kg.day, it was well absorbed and underwent little biotransformation during enterohepatic cycling; however, both bacterial deconjugation and dehydroxylation (without deconjugation) occurred to a small extent. With chronic feeding, cholylsarcosine accumulated to compose 24%-29% of circulating bile acids in all 3 rodent species. It was rapidly lost from the enterohepatic circulation, with a daily fractional turnover rate of 75%-150%, depending on the species. Cholylsarcosine caused no change in liver tests or hepatic morphology and did not influence biliary lipid secretion. When cholyltaurine was fed, it was also absorbed, but, in contrast to cholylsarcosine, was rapidly deconjugated and dehydroxylated to form deoxycholic acid. The deoxycholic acid accumulated in the enterohepatic circulation, as evidenced by a slow fractional turnover rate of 26%-40% per day, depending on the species. It is concluded that cholylsarcosine is absorbed from the ileum, has an enterohepatic circulation, does not undergo appreciable deconjugation or dehydroxylation in these rodents, and is nontoxic. In the rodent, the circulating bile acids can be somewhat enriched when a bile acid resistant to deconjugation is ingested; but the effect on the steady state biliary bile acid composition is less than that obtained when cholyltaurine is administered because cholyltaurine is biotransformed to deoxycholic acid, which in turn is absorbed and has its own efficient enterohepatic circulation.

7-Methyl bile acids: effects of chenodeoxycholic acid, cholic acid, and their 7 beta-methyl analogues on the formation of cholesterol gallstones in the prairie dog

The purpose of this study was to compare the effects of the naturally occurring bile acids (chenodeoxycholic acid and cholic acid) with their 7-methyl analogues (3 alpha,7 alpha-dihydroxy-7 beta-methyl-5 beta-cholanoic acid and 3 alpha,7 alpha,12 alpha-trihydroxy-7 beta-methyl-5 beta-cholanoic acid) on gallstone formation and prevention and cholesterol metabolism in the prairie dog. Sixty animals were fed a semipurified diet, containing 0.4% cholesterol, with one of the following acids (0.1%): chenodeoxycholic, cholic, 3 alpha,7 alpha-dihydroxy-7 beta-methyl-5 beta-cholanoic, or 3 alpha,7 alpha,12 alpha-trihydroxy-7 beta-methyl-5 beta-cholanoic acid. This concentration of dietary bile acids amounts to a dose of 27-30 mg/kg.day. After 8 wk, 89% of control animals had gallstones and 94% had cholesterol crystals. Chenodeoxycholic and 3 alpha,7 alpha-dihydroxy-7 beta-methyl-5 beta-cholanoic acids decreased the incidence of gallstones to 50%. Cholic acid and 3 alpha,7 alpha,12 alpha-tri-hydroxy-7 beta-methyl-5 beta-cholanoic acid did not prevent gallstone formation. The liver cholesterol level was decreased by chenodeoxycholic acid, whereas cholic and 3 alpha,7 alpha,12 alpha-trihydroxy-7 beta-methyl-5 beta-cholanoic acids increased serum and liver cholesterol. Each administered bile acid became the predominant biliary bile acid and 7-methyl analogues did not increase secondary bile acids. Fecal analysis of radioactive metabolites using 14C-labeled 7-methyl analogues showed that these compounds are resistant to bacterial 7-dehydroxylation. It was concluded that 3 alpha,7 alpha-dihydroxy-7 beta-methyl-5 beta-cholanoic acid inhibited gallstone formation as effectively as chenodeoxycholic acid, whereas both cholic and 3 alpha,7 alpha,12 alpha-trihydroxy-7 beta-methyl-5 beta-cholanoic acids were not effective. The effects of 7-methyl analogues on the parameters of cholesterol metabolism that we studied were similar to those of their parent compounds, chenodeoxycholic and cholic acids. Thus, 3 alpha,7 alpha-dihydroxy-7 beta-methyl-5 beta-cholanoic acid but not 3 alpha,7 alpha,12 alpha-trihydroxy-7 beta-methyl-5 beta-cholanoic acid offers promise in cholelitholytic therapy for the prevention and possibly dissolution of cholesterol gallstones.

Bile salt hydrophobicity influences cholesterol recruitment from rat liver in vivo when cholesterol synthesis and lipoprotein uptake are constant

These studies were undertaken to characterize the role of bile salt hydrophobicity in determining the rate of cholesterol recruitment from the liver. Using an in vivo rat model in which the acquisition of hepatic cholesterol from chylomicron remnants, low-density lipoproteins, and de novo synthesis was measured and kept constant, it was found that the amount of sterol recruited from the liver cell increased progressively as the liver was probed with a constant infusion of progressively more hydrophobic bile salts. The absolute secretion rate of both cholesterol and phospholipid increased nearly 50% as the hydrophobic index of the bile salts traversing the liver increased from 1.7 to 4.5, but the ratio of cholesterol to phospholipid secreted in bile remained nearly constant. Thus, when cholesterol entry into the hepatocyte via lipoproteins and de novo cholesterol synthesis is constant, the mass of cellular cholesterol recruited into the bile is directly proportional to the hydrophobic-hydrophilic balance of the secreted bile salts.

Effect of previous nutritional status on the formation of cholesterol gallstones in the prairie dog

In the prairie dog model of cholesterol cholelithiasis, a high incidence of gallstones is achieved by feeding a semipurified lithogenic diet containing 0.4% cholesterol for 2 mo. On occasion, we noted a decrease in the percentage of animals with gallstones from 90-100% to 50-55%. To explain this phenomenon, we studied the effect of dietary history on gallstone formation. After weaning, animals were fed either rodent chow or alfalfa plus corn (mo 0-3) followed by a cross-over experiment at mo 4-6. Gallstone formation then was studied by feeding the lithogenic diet from mo 7 to 8. At sacrifice, the incidences of gallstones, biliary lipids and tissue cholesterol levels were correlated with dietary history. The incidence of gallstones was 100% only in animals fed the alfalfa-corn diet from weaning to 3 mo. In addition, the feeding of the alfalfa-corn diet at mo 4-6 increased gallstone incidence from 65% to 86%. The lithogenic index of all groups was highest when the animals received only alfalfa-corn prior to the lithogenic stimulus. The activity of hepatic HMG-CoA reductase was elevated in animals fed alfalfa-corn from weaning to 8 mo, suggesting that this diet stimulates hepatic cholesterol synthesis, leading to increased biliary cholesterol secretion. It is concluded that previous nutritional conditioning affects the incidence of gallstones. The prairie dog is a useful model of cholesterol cholelithiasis, but the dietary history of the animals plays an important role in lithogenesis.

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.

Metabolism of the bile acid analogues 7 beta-methyl-cholic acid and 7 alpha-methyl-ursocholic acid

The metabolism of two new bile acid analogues, 7 beta-methyl-cholate and 7 alpha-methyl-ursocholate, was compared with that of cholate in the hamster. After intraduodenal administration of 14C-labeled compounds into bile fistula hamsters, radioactivity was exclusively recovered in bile; the more hydrophobic bile acid was absorbed more rapidly. Hepatic extraction of intravenously infused compounds was efficient and administered analogues became major biliary bile acids. Amidation of cholate was essentially complete, whereas 39% of 7 beta-methyl-cholate and 65% of 7 alpha-methyl-ursocholate were secreted in unconjugated form. After intragastric administration of the compounds, radioactivity was quantitatively recovered in feces. Cholate was 7-dehydroxylated to deoxycholate, whereas 31% of 7 beta-methyl-cholate and 78% of 7 alpha-methyl-ursocholate were recovered unchanged. Fifty percent of 7 beta-methyl-cholate and 15% of 7 alpha-methyl-ursocholate were transformed into ketonic derivatives, without loss of the 7-hydroxyl group. It is concluded that the introduction of the 7-methyl group did not interfere with intestinal absorption, hepatic extraction, and biliary secretion but did affect enzymatic amidation and bacterial 7-dehydroxylation of the analogues.

An animal model of pigment cholelithiasis

Pigment stones of high calcium content were induced in male hamsters of the Harlan Sprague-Dawley strain fed a nutritionally adequate semipurified diet for a period of 14 weeks. The diet contained moderate amounts of cholesterol (0.30 percent) and ethinyl estradiol (15 micrograms/day per animal). At sacrifice, the incidence of pigment stones was 50 percent. When stones were present, they were in the form of numerous black amorphous rods about 0.1 to 0.4 mm in length. Infrared analysis of the dried stones indicated the following composition: calcium phosphate 26.7 percent, calcium bilirubinate 12.8 percent, cholesterol 15.1 percent, and protein 45.4 percent. Pigment stones were associated with an elevated biliary total calcium level (probably induced by the dietary cholesterol) and a paradoxic decrease in the biliary total bilirubin level. The lithogenic diet produced marked elevations in liver and plasma cholesterol levels and cholesterol saturation of bile, but no cholesterol crystals or stones were observed. The accumulation of elevated levels of cholesterol in the livers of the experimental animals produced mild to moderate hepatotoxicity. The precise mechanism of the dietary induction of pigment stones in this hamster model remains to be elucidated.

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

Gallstone formation and dissolution were studied in a prairie dog model of cholesterol (CH) cholelithiasis. Gallstones were induced in 49 prairie dogs by feeding 1.2% CH in a nutritionally adequate semisynthetic diet for 6 wk (period 1). At 6 wk, gallstones had developed in all animals examined. The diets were modified by reducing the amounts of CH to 0.4, 0.2, 0.1 and 0.0% (diets 1-4); hyodeoxycholic acid (HDA; 30 mg/kg/day) was added to these diets (diets 5-8). All animals were fed the modified experimental diets for an additional 8 wk (period 2). At week 14, spontaneous gallstone dissolution had not occurred, even in the groups given no added dietary CH during period 2 (group 4). Addition of HDA to the diet tended to reduce the incidence of biliary CH crystals and the size and number of CH gallstones. Biliary CH remained elevated and the lithogenic indices in all groups were found to be greater than 1.0 at the end of the experiment. Liver and plasma CH levels tended to be lower in the groups fed HDA. In these groups, HDA and 6 beta HDA became the major biliary bile acids. This study demonstrates that HDA achieved partial dissolution of gallstones in bile supersaturated with CH.

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.

Hyodeoxycholic acid: a new approach to gallstone prevention

Hyodeoxycholic acid and its isomer, 6 beta-hyodeoxycholic acid, when added to a lithogenic diet prevented the formation of cholesterol gallstones and crystals in prairie dogs. This beneficial effect occurred in the presence of bile supersaturated with cholesterol. Hyodeoxycholic acid abolished the feedback inhibition of hepatic hydroxymethylglutaryl coenzyme A reductase activity, the rate-limiting enzyme of cholesterol synthesis, and prevented elevations in serum and liver cholesterol observed in animals fed a 0.4 percent cholesterol diet. The gallbladder bile of the animals fed hyodeoxycholic acid and 6 beta-hyodeoxycholic acid contained abundant liquid crystals. This suggests that these bile acids prevented the transition of cholesterol from its liquid crystalline phase to solid crystals and stones.

Effects of bile acid oxazolines on gallstone formation in prairie dogs

The effects of 2 bile acid analogs, chenodeoxy-oxazoline [2-(3 alpha, 7 alpha-dihydroxy-24-nor-5 beta-cholanyl)-4,4-dimethyl-2-oxazoline] and ursodeoxy-oxazoline [2-(3 alpha, 7 beta-dihydroxy-24-nor-5 beta-cholanyl)-4,4-dimethyl-2-oxazoline] were examined in the prairie dog model of cholesterol cholelithiasis. Gallstones and biliary cholesterol crystals were induced in 5 out of 6 male prairie dogs fed a semisynthetic diet containing 0.4% cholesterol for 8 weeks. Six animals maintained on a low cholesterol control diet (0.08% cholesterol) exhibited neither gallstones nor biliary cholesterol crystals. The addition of 0.06% chenodeoxy-oxazoline to the lithogenic diet did not prevent induced cholelithiasis or the appearance of cholesterol crystals in bile. In contrast, 0.06% dietary ursodeoxy-oxazoline prevented gallstones in 5 out of 6 prairie dogs (but cholesterol crystals were present in the bile of 4 of these animals). Histologically, most of the livers from the prairie dogs fed the cholesterol-supplemented semisynthetic diet showed bile duct proliferation, inflammatory infiltration and fibrosis along the portal tracts. These pathologic changes were generally not ameliorated by adding chenodeoxy-oxazoline or chenodeoxy-oxazoline plus chenodeoxycholic acid to the diet. Portal tract pathology was markedly reduced in most animals by adding ursodeoxy-oxazoline to the cholesterol-supplemented diet. The pathologic changes overall could best be correlated with the presence of gallstones, but not with the incidence of biliary cholesterol crystals.