Effects of bile acid oxazolines on gallstone formation in prairie dogs

Effects of hyodeoxycholic acid and alpha-hyocholic acid, two 6 alpha-hydroxylated bile acids, on cholesterol and bile acid metabolism in the hamster

The effects of hyodeoxycholic (HDCA) and alpha-hyocholic acids (alpha-HCA), on cholesterol, bile acid and lipoprotein metabolism, were studied in hamsters. The animals were fed a low cholesterol control diet supplemented with 0.1% HDCA or alpha-HCA for 3 weeks. In both treated groups, the LDL-cholesterol concentration was significantly lowered and was associated with a global hypocholesterolemic effect. Moreover, hepatic cholesterol ester storage was reduced and HMGCoA reductase activity was respectively enhanced 13.5-times and 7.7-times in HDCA and alpha-HCA groups compared to controls. In contrast, cholesterol 7 alpha-hydroxylase activity and LDL-receptor activity and mass were not modified. In bile, the cholesterol saturation index was increased 5-fold (HDCA group) and 2-fold (alpha-HCA group) as a consequence of an enlarged proportion of biliary cholesterol. The two 6-hydroxylated bile acids induced an enhanced fecal excretion of neutral sterols (HDCA group: 11.6-times, alpha-HCA group: 3.2-times versus controls) which was consistent with a 59% decrease in intestinal cholesterol absorption in the HDCA group. The major effects due to bile acid treatments were a decrease in LDL-cholesterol concentration, a strong stimulation of hepatic cholesterol biosynthesis and an excessive loss of cholesterol in feces. These perturbations might be the result of the enrichment of bile with hydrophilic bile acids, leading to a limited return of endogenous cholesterol from the intestine to the liver.

Palmitic acid enhances cholesterol gallstone incidence in Sasco hamsters fed cholesterol enriched diets

In an established hamster model of cholesterol cholelithiasis, a semipurified lithogenic diet containing 4% butterfat and 0.3% cholesterol leads to the production of cholesterol gallstones in only 50-60% of animals after a 6-wk feeding period. The purpose of this study was to investigate whether gallstone incidence could be increased while feeding a nutritionally adequate diet of moderate cholesterol content. The semipurified lithogenic diet was modified as follows: (i) substitution of 1.2% palmitic acid for 4% butterfat, and (ii) varying the amount of dietary cholesterol from 0.0 to 0.3% with either butterfat or palmitic acid as the lipid component of the diet. Substitution of palmitic acid for butterfat produced a significantly higher incidence of cholesterol gallstones (94% vs. 53%). Palmitic acid also raised the incidence of gallstones when added to the 0.1% and 0.2% cholesterol diets as compared to butterfat: 0% vs. 44% and 50% vs. 81%, respectively. Gallstone incidence increased from 0% to nearly 100% when the cholesterol content of the palmitic acid diets was raised from 0.0% to 0.3%, indicating a dose response effect with respect to dietary cholesterol. Hamsters fed cholesterol-free diets did not form gallstones. Increased dietary cholesterol led to increased liver weight associated with a significant increase in liver cholesterol concentration. However, the palmitic acid groups had significantly lower liver cholesterol values than the corresponding butterfat groups. Serum and biliary cholesterol concentrations increased with increasing dietary cholesterol intake, but there were no differences between the butterfat and palmitic acid groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of basic cholane derivatives on intestinal cholic acid metabolism: in vitro and in vivo activity

A representative series of hydroxy-5 beta-cholanyl-24-amines were tested both in vitro and in vivo with respect to their activity against the intestinal bacteria responsible for bile acid metabolism. For the in vitro studies, radiolabeled [14C]cholic acid was incubated with human stools both in aerobic and anaerobic conditions in the presence of the title compounds at a dose of 10 micrograms/mL, and the biotransformation of cholic acid into radiolabeled deoxycholic acid and other metabolites was followed by TLC-radiochromatography. Of the compounds studied, 3 alpha, 12 alpha-dihydroxy-5 beta-cholan-24-N-methylamine showed the highest activity. This compound was used for the in vivo studies and was shown to inhibit the formation of endogenous secondary bile acids when chronically administered to rats at a dose of 60 micrograms/day for 15 days. The treated rats showed an increased ratio of taurocholic acid (primary bile acid) to taurodeoxycholic acid (secondary bile acid) in bile, a fact further suggesting a potent antibacterial activity of the compound toward bacteria responsible for bile acid metabolism.

Intrahepatic cholestasis: a review of biochemical-pathological mechanisms

Intrahepatic cholestasis involves impaired excretion of bile via the hepatobiliary system as a consequence of one or more lesions within the liver. In humans, intrahepatic cholestasis most often results as a side-effect of drug therapy and the clinical manifestation of this condition, jaundice, has been estimated to account for hospitalization in 2 to 5% of the cases for the general population and approaches as much as 20% in the elderly. With the aging of the population and the common occurrence of poly-drug therapy in geriatric patients, it is to be expected that jaundice due to drug-induced intrahepatic cholestasis will become even more prevalent, and accordingly the need to understand the basic mechanisms of this disease condition will become more urgent. The list of culprit agents implicated in the induction of intrahepatic cholestasis in humans is continually expanding. These include various steroid hormones, bile acids, drugs and other chemicals. Experimentally, a wide spectrum of agents has been shown to precipitate intrahepatic cholestasis. Over the years, a number of hypotheses on the biochemical and pathological mechanisms of intrahepatic cholestasis has emerged, including the following: impaired sinusoidal membrane function; interference with the distribution and binding of cytoplasmic endogenous carrier proteins; interference with mitochondrial energy supply; defects in the canalicular membrane including altered Na+/K+ -ATP-ase activity; impairment of microfilament and microtubule functions; interference with bile secretion involving bile acid dependent and independent fractions, and altered bile acid metabolism due to "hypoactive hypertrophic smooth endoplasmic reticulum". In partial agreement with the latter hypothesis, our studies indicated that impairment of the endoplasmic reticulum might represent one of the early stages in the development of intrahepatic cholestasis. Various experimental conditions that induce intrahepatic cholestasis to different degrees resulted in an interference of the synthesis of microsomal phospholipids and altered microsomal function. The conditions included the administration of various hepatotoxic compounds or steroids, pregnancy, delayed development of the endoplasmic reticulum in neonates, and dietary methyl donor or choline deficiency. This review reports the biochemical-pathological mechanisms postulated to be involved in the genesis of intrahepatic cholestasis with specific reference to experimental models of drug-induced intrahepatic cholestasis. The important practical implications of cholestasis are also briefly surveyed.

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.

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.

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.

Alcohol protects against cholesterol gallstone formation

Epidemiologic studies have suggested that alcohol intake may protect against cholelithiasis. Gallstone formation was studied in 20 prairie dogs fed a 0.4% cholesterol-supplemented liquid diet. In ten animals, ethanol provided 35% of total calories. In ten pair-fed controls, ethanol was replaced with isocaloric maltose. After 3 months the gallbladders were inspected for gallstones, and gallbladder bile was analyzed. Cholesterol macroaggregates were present in all controls and pigment concretions were noted in five. No stones were observed in ethanol-fed animals. Bile in the ethanol group contained less cholesterol than the controls (5.60 +/- 0.71 vs. 9.16 +/- 0.61 mmol/L, p less than 0.05) while phospholipids, total bile acids, and bilirubin were unchanged. The resulting cholesterol saturation index was reduced in the ethanol group (0.81 vs. 1.22, p less than 0.05). The ratios of trihydroxy to dihydroxy bile acids were also different (2.07 +/- 0.25 in ETOH vs. 3.29 in controls, p less than 0.05). The bile calcium concentration was higher in control animals presumably secondary to the use of complex sugars (5.36 +/- 0.37 vs. 3.77 +/- 0.32 mmol/L, p less than 0.05). These results confirm that ethanol inhibits cholesterol gallstone formation. They further suggest that this effect is dependent on reductions of biliary cholesterol and selective changes in bile acid concentrations.