Bile acids excretion

Various mechanisms have been proposed to explain the hypocholesterolemic effect of GA (Annison et al., 1995 Tiss et al., 2001). Some studies have suggested that the viscosity of fermentable dietary fiber contributes substantially to the reduction of lipids in animals and humans (Gallaher et al., 1993 Moundras et al., 1994). However, other studies suggested that this property is not related to plasma lipids (Evans et al., 1992). The mechanism involved is clearly linked to increased bile acid excretion and fecal neutral sterol or a modification of digestion and absorption of lipids (Moundras et al., 1994). 

Moundras, C. Behr, S.R. Demigne, G. Mazur, A. Remesy, G. (1994). Fermentable polysaccharides that enhance fecal bile acid excretion lower plasma cholesterol and apolipoprotein E-rich HDL in rats. Journal of Nutrition, Vol. 124, No.ll, (November 1994), pp. 2179-2188, ISSN 0022-3166. 

Trautwein, E. A., Kunath-Rau, A., and Erbersdobler, H. F. (1999). Increased fecal bile acid excretion and changes in the circulating bile acid pool are involved in the hypocholester-olemic and gallstone-preventive actions of psyllium in hamsters. /. Nutr. 129, 896-902. 

Ezetimibe has a mechanism of action that differs from those of other classes of cholesterol-reducing compounds. Ezetimibe does not inhibit cholesterol synthesis in the liver or increase bile acid excretion. 

Neomycin - Orally administered neomycin increases fecal bile acid excretion and reduces intestinal lactase activity. 

B. Sundberg, P. Aman, and H. Anders- HV083 son. Oat beta-glucan increases bile acid excretion and a fiber-rich barley fraction increases cholesterol excretion in ileostomy subjects. Amer J Clin HV084... 

Cholesterol level decrease. The husks and seeds were administered orally to six normal adult males and five adult males with ileostomy and six normal adult males and four adult males with ileostomy, respectively, at a dose of 10 g/day for 3 weeks. The husk had no effect on cholesterol or triglyceride concentrations in either normal or ileostomy subjects. Total and HDL cholesterol concentrations were reduced on average by 6.4 and 9.3%, respectively, in normal group after seed supplementation. No effect on fecal bile acid excretion in the normal subjects was found after both regimens. Ileostomy bile acids were increased (on average 25%) after seed supplementation, whereas no effect on cholesterol concentrations was found. These results suggest that psyllium seed may be more effective than the husk in... 

Ebihara, K., Shiraishi, R., Okuma, K. (1998). Hydroxypropyl-modifled potato starch increases fecal bile acid excretion in rats. J. Nutri., 128, 848-854. 

Hypocholesterolemic effects of soybean saponins have been dimonstrated. Isolated soybean saponins reduced diet-induced hypercholesterolemia in rats through an increase in bile acid excretion... 

Octreotide 100 pg given subcutaneously to five healthy subjects 30 minutes before meals for 7 days increased fecal fat excretion however, steatorrhea occurred in only two cases fecal bile acid excretion fell to about 25% (35)... 

Another possible mechanism involves the effect of saponins on micelle formation. Saponins are known to alter the size or shape of micelles (Oakenfull, 1986 Oakenfull and Sidhu, 1983), an observation that is consistent with decreased bile acid absorption (Stark and Madar, 1993) and increased fecal bile acid excretion (Malinow et al., 1981 Nakamura et al.,1999). Saponins may also directly bind bile acids (Oakenfull and Sidhu, 1989), which would presumably interfere with micelle formation and decrease cholesterol absorption. Other studies have found that saponins decrease the absorption of fat-soluble vitamins (Jenkins and Atwal, 1994) and triglycerides (Han et al., 2002 Okuda and Han, 2001), indicating decreased micelle formation. However, direct evidence showing impaired micelle formation in vivo is lacking. Moreover, Harwood et al. (1993) reported no change in bile acid absorption or interruption of the enterohepatic circulation of bile acids in hamsters fed tiqueside, despite significant reductions in cholesterol absorption. 

Hassel, C.A., Mensing, E.A., and Gallaher, D.D. 1997. Dietary stearic acid reduces plasma and hepatic cholesterol concentrations without increasing bile acid excretion in cholesterol-fed hamsters. J. Nutr. 127, 1148-1155. 

Levrat, M.A., Favier, M.L., Moundras, C., Remesy, C., Demigne, C., and Morand, C. 1994. Role of dietary propionic acid and bile acid excretion in the hypocholesterolemic effects of oligosaccharides in rats. J. Nutr. 124, 531-538. 

Wright, S.M. and Salter, A.M. 1998. Effects of soy protein on plasma cholesterol and bile acid excretion in hamsters. Comp. Biochem. Physiol. B Biochem. Mol. Biol. 119, 247-254. 

Total neutral sterol excretion by mice (male, C57BL/6) fed a chow diet is typically 80 15 nmol per day per gram body weight and bile acid excretion is 50 10 nmol per day per g body weight. On semi-purified diets, which are low in fiber and reduce gut motility, neutral sterol excretion is reduced as much as 50% and bile acid excretion can be reduced as much as 5-fold or more (unpublished results). Thus, the diet used in a given study must be chosen carefully. Since human diets have a tendency to be low in fiber, a chow diet may partially mask potential treatment benefits because sterol excretion is already quite high. 

If bile acid excretion is different, further experiments should be done to determine if bile acid recovery by the intestine or bile acid pool size is changed. The former can initially be assessed by western blot detection of the transporter ASBT. Pool size is... 

Increased fecal bile acid excretion in transgenic mice with elevated expression of human phospho lipid transfer protein. Arterioscler. Thromb. Vase. Biol. 23, 892-897. 

Dietary Fat and Fiber and Bile Acid Excretion. In order to understand the specifics of the mechanisms whereby dietary fat influences colon cancer, the effect of type and amount of dietary fat on biliary and fecal bile acids was studied in rats (40,47,48). These... 

Haussinger, D., Hallbrucker, C., Saha, N., Lang, F Gerok, W. (1992). Cell volume and bile acid excretion. Biochem. J. 288,681-689. 

The bile acid-dependent fraction (250 ml) is formed chiefly in the periportal acinus, (s. tab 3.2) There is a linear relationship between bile acid excretion and bile flow. Osmotic filtration of water and inorganic ions is proportionally elevated (dependent upon bile salt concentration). Other secretory mechanisms or pump systems may also be activated by bile acids. 

The probable mechanism of the synergetic effect of L-ascorbic acid and substances capable of binding bile acids in the gastrointestinal tract is shown in Scheme 1. An increased intake of L-ascorbic acid accelerates the formation of 7a-hydroxycholesterol and thereby also accelerates the overall rate of cholesterol transformation into bile acids. Bile acids excreted from the liver into the gastrointestinal tract become bound and thus are prevented from affecting 7 -hydroxylation of cholesterol through a feedback mechanism. In this way, a permanent disequilibrium occurs between cholesterol and bile acids with increased cholesterol transformation to bile acids and enhanced irreversible output of the products of this reaction, which results in a decline of cholesterol levels in the blood and tissues. 

Until recently, it was considered that hepatic bile flow was still possible even if no bile acids were excreted. This portion of bile flow was termed bile acid independent and was estimated to account for around one-third of canalicular bile flow in man (B33, P15). More recent evidence suggests that the relationship between bile flow and bile acid excretion is curvilinear, so that bile flow decreases progressively more rapidly as bile acid excretion rates decrease to very low values (B2, B24). Bile-salt-independent bile flow may therefore be much lower than previously thought and represent only a very small fraction of total bile flow (B24). 

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