Bile acids fecal excretion

Key words Cholesterol absorption, phytosterols, cholesterol excretion, reverse cholesterol transport, ACAT, CEL, inhibitors, bile acids, fecal sterols, dual label, obesity, cardiovascular disease. 

In addition to bile and serum bile acids, fecal bile acids can be estimated by the enzymatic method, provided that they are first extracted to remove interfering lipids. Methods for this purpose are continually being simplified and improved (B16, D6, V3). Enzymatic determination of fecal extracts slightly underestimates total bile add excretion, since 3-keto bile acids and bile acids which are sul ted at the 3a position occur in feces and are not... 

The enterohepatic circulation of bile acids is characterized by a large pool of bile acids (2,15,26) which cycles many times (probably six to ten) each day. The size of the pool is determined by the efficiency of intestinal absorption and by the rate of hepatic synthesis of bile acids from cholesterol (94). The efficiency of absorption is high—in health probably greater than 98 %— and the amount of bile acids not absorbed is balanced by hepatic synthesis (Fig. 17). Bile acids are excreted only in feces, and their nucleus is considered invulnerable to bacterial attack therefore, the measurement of fecal bile acids either by chemical estimation or isotope dilution techniques indicates hepatic synthesis (94). The pool size may be estimated directly by isotope dilution, and an indirect estimate of pool size can be obtained by measuring jejunal bile acid concentration during digestion of a test meal. 

Norman (3) demonstrated that the types of bile acids found in normal rat bile were not the same as those which were excreted in the feces. However, when the rats were fed high levels of antibiotics, the fecal bile acids were excreted essentially unchanged from the biliary bile acids (4). The intestinal bacteria were responsible for the hydrolysis of the biliary taurine-conjugated bile acids to the free bile acids found in the feces. Norman also showed that the dehydroxylation of cholic acid to deoxycholic acid could be prevented by Inhibiting the intestinal bacteria. The total amount of fecal bile acid excreted by conventional chicks has been found to be significantly lowered (5) by incorporation of an antibiotic into the diet. 

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., Rieckhoff, D., Kunath-Rau, A., and Erbersdobler, H. F. (1998). Psyllium, not pectin or guar gum, alters lipoprotein and biliary bile acid composition and fecal sterol excretion in the hamster. Lipids 33, 573-582. 

J. H. Cummings, Ft. S. Wiggins, D. J. A. Jenkins, H. Houston, T. Jivraj, B. S. Drasar and M. J. Hill, Influence of diets high and low in animal fat on bowel habit, gastro-intestinal transit time, fecal microflora, bile acid, and fat excretion, J. Clin. Invest., 1978, 61, 953. 

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

Partial summary of lipoprotein metabolism in humans. I to VII are sites of action of hypolipidemic drugs. I, stimulation of bile acid and/or cholesterol fecal excretion II, stimulation of lipoprotein lipase activity III, inhibition of VLDL production and secretion IV, inhibition of cholesterol biosynthesis V, stimulation of cholesterol secretion into bile fluid VI, stimulation of cholesterol conversion to bile acids VII, increased plasma clearance of LDL due either to increased LDL receptor activity or altered lipoprotein composition. CHOL, cholesterol IDL, intermediate-density lipoprotein. 

These drugs are basically anion exchange resins that remain in the gut, bind intestinal bile acids, and greatly increase their fecal excretion (mechanism I in Fig. 23.2). 

Hemagglutinin activity. Saline extract of the dried seed, at a concentration of 10%, was active on the human red blood cells L Hypocholestrolemic activity. Fresh root, taken orally by human adults at a dose of 200 g/person, was active. Daily ingestion at breakfast for 3 weeks decreased cholesterol in serum by 11%, increased fecal bile acid and fat excretion by 50%, and increased stool weight by 25%° . 

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... 

Fecal steroid and lipid excretion. Fiber supplements from sugar cane residue (bagasse), administered to volunteers for 12 weeks, increased stool weights and stool fat excretion. Bagasse increased the daily loss of acid steroids and decreased transit time without alteration in fecal flora. The increased excretion of bile acids and fatty acids failed to lower the plasma cholesterol and TGs after 12 weeks ". 

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

The ring structure of cholesterol cannot be metabolized to C02 and HfeO in humans. Rather, the intact sterol nucleus is eliminated from the body by conversion to bile acids and bile salts, which are excreted in the feces, and by secretion of cholesterol into the bile, which transports it to the intestine for elimination. Some of the cholesterol in the intestine is modified by bacteria before excretion. The primary compounds made are the isomers coprostanol and cholestanol, which are reduced derivatives of cholesterol. Together with cholesterol, these compounds make up the bulk of (neutral fecal sterols. 

Dietary fiber has a pronounced effect on the characteristics of the fecal mass and on the rate of passage of digest through the G1 trad, High fiber diets also play a role in the excretion of bile acids and cholesterol. 

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)... 

There are several ways pectin could reduce serum cholesterol. In studies with human subjects, fecal excretion of bile acids, fatty acids, and total steroids increased when subjects were fed 15-40 g/day of pectin (58, 63, 64). Since pectin usually lowers serum cholesterol only when cholesterol is present in the diet, it seems that pectin might act by reducing cholesterol absorption. Several groups have found that in rats dietary... 

Several other agents have beneficial effects on plasma lipid profiles occurring through various cellular mechanisms.89 Cholestyramine (Questran), for example, attaches to bile acids within the gastrointestinal lumen and increases the fecal excretion of these acids. This action leads to decreased plasma cholesterol concentrations because cholesterol breakdown is accelerated to replace the bile acids that are lost in the feces. 

Saponins appear to lower plasma LDL cholesterol concentration by interfering with cholesterol absorption. Studies in rats and monkeys fed naturally occurring saponins exhibited significant reductions in cholesterol absorption efficiency and an increase in fecal cholesterol excretion (Malinow et al., 1981 Nakamura et al., 1999 Sidhu et al., 1987). Decreased bile acid absorption and increased excretion has also been reported in animals fed saponins (Malinow et al., 1981 Nakamura et al., 1999 Stark and Madar, 1993). One possible mechanism of action for decreased cholesterol absorption is the ability of saponins to form insoluble complexes with cholesterol (Gestetner et al., 1972 Malinow et al., 1977). In an effort to isolate the specific properties of saponins, Malinow (1985) prepared a variety of synthetic saponins in which the complex carbohydrate moieties of native plant saponins were replaced with simplified carbohydrates such as glucose or cellobiose. One of these synthetic saponins, tiqueside (Pfizer, Inc.), can effectively precipitate cholesterol from micelle solutions in vitro and inhibit cholesterol absorption in a variety of animals (Harwood et al., 1993) and in humans (Harris et al., 1997). But despite ample data showing the formation of a saponin/cholesterol complex in vitro, there is essentially no definitive evidence that complexation occurs in the intestinal lumen (Morehouse et al., 1999). 

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. 

The mass of bile acids per 0.5 g feces = mass in 1 ml methanol x dpm 14C-taurocholate added/dpm recovered in 1 ml methanol. As for neutral sterols, the total excreted per 3 days is calculated from the total fecal mass collected and data are reported as mass (or moles) excreted per day per gram body weight. 

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... 

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