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Membrane transporters expressed by the hepatocyte and enterocyte play critical roles in maintaining the enterohepatic circulation of bile acids, an effective recycling and conservation mechanism that largely restricts these potentially cytotoxic detergents to the intestinal and hepatobiliary compartments. In doing so, the hepatic and enterocyte transport systems ensure a continuous supply of bile acids to be used repeatedly during the digestion of multiple meals throughout the day. Absorption of bile acids from the intestinal lumen and export into the portal circulation is mediated by a series of transporters expressed on the enterocyte apical and basolateral membranes. The ileal apical sodium-dependent bile acid cotransporter (abbreviated ASBT; gene symbol, SLC10A2) is responsible for the initial uptake of bile acids across the enterocyte brush border membrane. The bile acids are then efficiently shuttled across the cell and exported across the basolateral membrane by the heteromeric Organic Solute Transporter, OSTα–OSTβ. This chapter briefly reviews the tissue expression, physiology, genetics, pathophysiology, and transport properties of the ASBT and OSTα–OSTβ. In addition, the chapter discusses the relationship between the intestinal bile acid transporters and drug metabolism, including development of ASBT inhibitors as novel hypocholesterolemic or hepatoprotective agents, prodrug targeting of the ASBT to increase oral bioavailability, and involvement of the intestinal bile acid transporters in drug absorption and drug–drug interactions. [ABSTRACT FROM AUTHOR]

Cereal grains are important stable food worldwide. When used as whole-grain products, they provide a good source, not only of energy and protein, but minerals, vitamins, phytochemicals and dietary fibre. Since 1970s, evidence has been accumulating to suggest that high consumption of whole grains protects against cardiovascular diseases and certain types of cancers, particularly colon cancer. This chapter gives first a brief overview of the epidemiological evidence regarding whole grains and colon cancer and then reviews the substantial number of experimental studies which have investigated the effects of different whole grains and their constituents on colon carcinogenesis in animal models. Lastly, the underlying mechanisms whereby whole grains mediate their effects on colon cancer development will be discussed. [ABSTRACT FROM AUTHOR]

The concentration dependence of the aggregation scheme of two bile anions, i.e., cholate and deoxycholate is investigated in aqueous environment on the basis of molecular dynamics computer simulations. The distribution of the probability that a bile ion belongs to a cluster of a given size is determined. In the analysis we distinguish between hydrogen bonding connections and links of hydrophobic origin. The results show that at low concentrations the systems contain small primary micelles, built up by no more than 10 ions. For cholate, these primary micelles are either kept together by hydrophobic interactions, or by hydrogen bonds, whereas in the case of deoxycholate the number of the hydrogen bonded aggregates is negligibly small. At high concentrations large secondary micelles are formed by the attachment of primary hydrophobic micelles to each other by hydrogen bonds. [ABSTRACT FROM AUTHOR]

A definition of the term "steroids" is presented. Steroids refer to a group of natural substances sharing a common basic structure that is consist of four condensed rings. Important steroids include the D-vitamins and bile acids. Steroid hormones are lipophilic substances that bind to intracellular receptors.

A definition of the term "lithocholic acid" is presented. It refers to a 3α-hydroxy-5βcholanoic acid, a hepatotoxic and cholestatic secondary bile acid, that is formed by bacterial dehydroxylation of primary bile acids in the intestine.