08 February 2009

Bile, Bacteria and Bears

Enterohepatic circulation is the process of secretion and reabsorption of bile (1;2). When you eat a fatty meal, your gallbladder secretes bile to convert large fat globules to small droplets called micelles to be absorbed (1;2). Ninety percent of the bile is then reabsorbed via active transport or passive transport in the small intestine (1). In the colon, bacteria increase the recycled amount by deconjugating some non-absorbable primary bile acids to secondary acids, which are then absorbed passively (1). Along with bile and its component of cholesterol, other molecules may be circulated.

For this reason, it is important to understand how fiber and bacteria affects enterohepatic circulation. Guar gum, for example, is a soluble fiber that may prevent postprandial increase of conjugated bile acids (3). Other fibers are found to have the same effect (4;5). By absorbing cholesterol and keeping it from re-entering enterohepatic circulation, guar gum and pectin (just as phytostanols and phytosterols) both can be helpful in reducing blood cholesterol (1;6;7). Fiber’s impact also appears to affect enterohepatic circulation of estrogens (8;9).

Prebiotic fiber and probiotics may be useful for drug therapy. One such drug is the secondary bile acid ursodeoxycholic acid (USDA). USDA lowers cholesterol and treats cholestatic liver disease (10-14). But because of how expensive it is to synthesize, the ancient and now illegal practice of “milking” black bears for their bile (which contains USDA) continues in China (15). If prebiotic fiber and probiotics can help recirculate the drug through enterohepatic circulation, it may result in becoming cheaper to use.

On the other hand, the intestinal flora can be detrimental when taken with other drugs. Because of enterohepatic circulation, active promotion of bacteria in recycling drugs can overload the liver and cause damage to the body (16). In such a case, antibiotics may be necessary. Doctors must take this potential toxicity into consideration when helping patients (16).
Lastly, other exogenous or endogenous xenobiotics (toxins) might be recycled by probiotic or pathogenic bacteria through enterohepatic circulation (17). In effect, the liver is performing double duty in such cases by detoxifying and detoxifying again (17). Depending on the situation, antibiotic and probiotic therapy may be needed.

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15. Feng Y, Siu K, Wang N et al. Bear bile: dilemma of traditional medicinal use and animal protection. J Ethnobiol Ethnomed 2009;5:2.
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