Comparative effects of cholic, chenodeoxycholic, and ursodeoxycholic acids on micellar solubilization and intestinal absorption

Cholesterol absorption was studied in mice receiving cholic, chenodeoxycholic, or ursodeoxycholic acids (0.2% of the diet) for 2 months. Cholesterol absorption was greater with cholic acid (79%) than with chenodeoxycholic acid feeding (60%) and the lowest levels were observed during ursodeoxycholic acid feeding (37%). Under the three diets, bile acid pool and bile acid secretion were not different. Biliary cholesterol secretion was increased by cholic acid. The bile acid fed represents at least 80% of total bile acids. Micellar solubilization of oleic acid and cholesterol in the presence of each tauro-conjugated bile salt (10 mM) was determined in vitro by the coprecipitation method. Whatever the pH conditions, taurochenodeoxycholate solubilized significantly more cholesterol and more oleic acid than taurocholate. Tauroursodeoxycholate had the poorest detergent properties for both lipids. The differences between the three bile salts for cholesterol solubilization were enlarged by lowering pH and by high oleic acid concentration.l Therefore the decrease in cholesterol absorption observed during ursodeoxycholic acid feeding could be explained by the poor detergent properties of this bile salt species. On the other hand, there is no relationship between the detergent properties of taurochenodeoxycholate and taurocholate and their effects on cholesterol absorption in mice. These results suggest that, in this particular case, micellar solubilization is not the rate limiting step in cholesterol absorption,Reynier, M. O., J. C. Montet, A. Gerolami, C. Marteau, C. Crotte, A. M. Montet, and S. Mathieu. Comparative effects of cholic, chenodeoxycholic, and ursodeoxycholic acids on micellar solubilization and intestinal absorption of cho1esterol.J. Lzpul Res. 1981. 22: 467-473. Supplementary key words biliary cholesterol . mixed micelles In spite of conflicting results in man (1 -3), various works have shown that, generally, dihydroxy bile acids are less effective than cholic acid in the promotion of cholesterol absorption (4-6). This difference is often attributed to a specific effect of cholic acid on intestinal cholesterol esterase, an effect not shared by other bile acids (7, 8). However other explanations have not been ruled out. In particular, the role of specific effects of bile acids on intraluminal cholesterol solubilization must be considered. Mixed micelle formation could be modified during bile acid feeding by two mechanisms. First, it has been shown that ursodeoxycholate and its conjugates solubilize much less cholesterol than the other bile salts both in the presence of lecithin (9) and of monoolein-fatty acid mixtures (10). There is no large difference between the solubilizing capacities of cholate and chenodeoxycholate (10, 11) but these results were obtained using total lipid concentrations largely exceeding those observed during fat digestion. Second solubilization depends on the bile acid pool which may be differently modified by each molecular species of bile acid. This work was designed to compare the effects of ursodeoxycholic, chenodeoxycholic, and cholic acids on cholesterol absorption and on biliary secretion in mice and, in vitro, on cholesterol solubilization in bile salt-oleic acid micelles. MATERIALS AND METHODS Treatment of animals Swiss female mice, weighing 22 to 25 g, were divided into four groups and fed one of the following diets: a) chow diet, b) chow diet supplemented with 0.2% cholic acid, c) chow diet plus chenodeoxycholic acid (0.2%), d ) chow diet plus ursodeoxycholic acid (0.2%). The amount of bile acid fed was therefore about 500 mg/kg per day. Two months later, bile secretion or intestinal absorption of cholesterol were studied. Journal of Lipid Research Volume 22, 198 1 467 at P E N N S T A T E U N IV E R S IT Y , on F ebuary 1, 2013 w w w .j.org D ow nladed fom In some animals histological examinations of the small intestine were performed. Intestinal transit time was studied in three mice of each group using carmine red as marker. Cholesterol absorption Intestinal absorption of cholesterol was determined by two methods. The first was the dual isotope ratio method of Zilversmit (12) which measures intestinal absorption of a single dose of cholesterol. After a 15-hr fast, each mouse received by intubation 9.2 pmol of cholesterol containing 0.5 pCi of [l4CC]cholesterol emulsified with albumin and oleate (40 pmol). At the same time they received a colloidal suspension of 1 pCi of [3H]cholesterol intravenously. Feces were collected daily for 3 days to measure the fecal radioactivity in the neutral sterol fraction. The ratio of the specific radioactivities (3H and I4C) of blood cholesterol was calculated 72 hr after intubation. Blood samples were first weighed, then completely oxidized in an Intertechnique Oxymat apparatus J.A. 10 1 before determining the radioactivity content. The second method was the sterol balance method measured isotopically (13). By this method, cholesterol absorption (exogenous cholesterol) is obtained from the determination of the unabsorbed dietary cholesterol = daily fecal total neutral steroids (minus fecal plant sterols) minus endogenous neutral steroids. Cholesterol and plant sterols were determined by gasliquid chromatography. The daily endogenous neutral sterols were estimated isotopically (after injecting [14C]cholesterol) by dividing the radioactivity present in fecal sterols by the specific activity of plasma cholesterol. Mice received [14C]cholesterol (1 pCi intravenously). Three weeks later, stools were collected for four periods of 4 days. The mean plasma cholesterol radioactivity of the 2 first days of each period was used for the calculations.