Excretion, cholesterol

The cholesterol excreted with the bile is poorly water-soluble. Together with phospholipids and bile acids, it forms micelles (see p. 270), which keep it in solution. If the proportions of phospholipids, bile acids and cholesterol shift, gallstones can arise. These mainly consist of precipitated cholesterol (cholesterol stones), but can also contain Ca " salts of bile acids and bile pigments (pigment stones). 

Disposal in bile either as bile salts or as cholesterol itself is the body s main mechanism for cholesterol excretion. 

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... 

Ezetimibe is a selective inhibitor of intestinal absorption of cholesterol and phytosterols. A transport protein, NPC1L1, appears to be the target of the drug. It is effective even in the absence of dietary cholesterol because it inhibits reabsorption of cholesterol excreted in the bile. 

Ezetimibe Blocks sterol transporter NPC1L1 in intestine brush border Inhibits reabsorption of cholesterol excreted in bile decreases LDL and phytosterols Elevated LDL, phytosterolemia Oral duration 24 h Toxicity Low incidence of hepatic dysfunction, myositis... 

Despite these variables, it appears that the primary attribute of soluble fibers that inhibit cholesterol absorption is the ability to form a viscous matrix when hydrated. Many water-soluble fibers become viscous in the small intestine (Eastwood and Morris, 1992). It is believed that increased viscosity impedes the movement of cholesterol, bile acids, and other lipids and hinders micelle formation, thus reducing cholesterol absorption and promoting cholesterol excretion from the body. Consumption of viscous fibers was shown to increase the thickness of the unstirred water layer in humans (Flourie et al., 1984 Johnson and Gee, 1981) and reduce the amount of cholesterol appearing in the lymph of cannulated rats (Ikeda et al., 1989b Vahouny et al., 1988). Turley et al. (1991, 1994) reported that... 

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). 

Fumagalli, R., Soleri, L., Farina, R., Musanti, R., Mantero, O., Noseda, G., Gatti, E., and Sirtori, C.R. 1982. Fecal cholesterol excretion studies in type II hypercholesterolemic patients treated with the soybean protein diet. Atherosclerosis 43, 341-353. 

Gallaher, D.D., Gallaher, C.M., Mahrt, G.J., Carr, T.P., Hollingshead, C.H., Hesslink, R., Jr., and Wise, J. 2002. A glucomannan and chitosan fiber supplement decreases plasma cholesterol and increases cholesterol excretion in overweight normocholesterolemic humans. J. Am. Coll Nutr. 21, 428-433. 

Schneider, C.L., Cowles, R.L., Stuefer-Powell, C.L., and Carr, T.P. 2000. Dietary stearic acid reduces cholesterol absorption and increases endogenous cholesterol excretion in hamsters fed cereal-based diets. J. Nutr. 130, 1232-1238. 

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

An increased cholesterol excretion, degradation, and decreased synthesis may explain the lower hepatic cholesterol concentration reported in exercised versus sedentary rats. In support of the former, Gollnick and Simmons (73) reported that exercised rats excreted significantly more fecal sterol than sedentary rats. 

Others have reported similar findings (76-78) as well as an increased degradation of cholesterol in exercised mice and an increased duodenal bile flow and biliary cholesterol excretion in subjects following only 30 minutes of cycling. 

Diet or exercise had no effect on carcass cholesterol concentration in Fischer 344 rats fed a hypercholesterolemic diet (71). However, total carcass cholesterol tended to be lower in exercised rats than in sedentary rats. Carcass cholesterol concentration was similar between exercised and sedentary rats, but the body weights of sedentary rats were higher. Both sedentary and exercised rats fed the hypercholesterolemic diet had equivalent food, and hence cholesterol intakes. These data suggest that exercise increases cholesterol excretion and/or degradation, or decreases cholesterol synthesis in the rat. 

Wilson, T.A., DeSimone, A.P., Romano, C.A. and Nicolosi, R.J. (2000) Corn fiber oil lowers plasma cholesterol levels and increases cholesterol excretion greater than corn oil and similar to diets containing soy sterols and soy stands in hamsters. J. Nutr. Biochem., 11, 443 149. 

Probucol (Lorelco) Increases LDL degradation and cholesterol excretion. Hypercholesterolemia, but not other lipid disorders. i Cholesterol, LDL, HDL ... 

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