Introduction

Bile acids, a group of steroidal acids with a carboxyl group in the side chain, are the major end products of cholesterol catabolism, formed in the liver, conjugated with amino acids, glycine and taurine, and secreted into the bile. In most animal species, bile acids contain 24 carbons, with the terminal side chain carbon in the form of a carboxyl group; however, certain reptiles have 27-carbon bile acids as the major biliary bile acids. Primary bile acids are formed via the 5ft-saturation of cholesterol double bond by hepatic enzymes, epimerization of 3ft-hydroxyl group to a-configuration and further insertion of 7a- and/or 12a-hydroxyl group, shortening of the side chain by three carbons and oxidation of the terminal carbon to a carboxyl group. Structures of some of the bile acids found in animal species are shown in Figure 1. Bile acids facilitate the absorption of dietary lipids, including fat-soluble vitamins and cholesterol, via their detergent action. The detergent properties of bile acids result from their unique structure with a nonpolar steroid skeleton and a polar carboxyl group and a-oriented hydroxyl groups, further increased by hepatic conjugation with glycine and taurine (Figure 1).

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Bile acid conjugates form micelles with phospholipids that solubilize cholesterol in the bile. The primary bile acids, cholic acid and chenodeoxycholic acid, are effectively reabsorbed from ileum during their en-terohepatic circulation, but approximately 5% that escape reabsorption seep into the colon, and are subjected to modification to secondary bile acids by intestinal bacteria. These modified bile acids, in particular the 7a-dehydroxylated bile acids, lithocholic acid and deoxycholic acid, are the major faecal bile acids and are also significantly absorbed from the colon and circulate in the enterohepatic circulation, with deoxycholic acid as one of the major plasma and biliary bile acids in humans. Whereas only small amounts of bile acids are excreted into the urine, approximately 500 mg per day is excreted in faeces and forms a major catabolic pathway for the elimination of body cholesterol.

In hepatobiliary and intestinal diseases, the hepatic synthesis and clearance of bile acids and their intestinal absorption are abnormal, which disturbs both cholesterol synthesis and its metabolism, causing increased plasma, urinary and faecal concentrations of bile acids. This results in accumulation of precursors of cholesterol or bile acids and clinical malformations ensue. Early diagnosis of such conditions is often possible from bile acid analysis in bile, serum, urine and faeces. On the other hand, bile acids have therapeutic applications in conditions of abnormal cholesterol biosynthesis and metabolism, and che-nodeoxycholic acid, and its 7ft-hydroxy epimer, ursodeoxycholic acid, are used for medical treatment of gallstones while ursodeoxycholic acid is also being

Gas Chromatography

R-i = aOH; R2=i50H; R3=H; Ursodeoxycholic acid

R1; R3=aOH; R2=i50H; Ursocholic acid

R-i = aOH; R2=i50H; R3=H; Ursodeoxycholic acid

R1; R3=aOH; R2=i50H; Ursocholic acid

Glycocholic acid Taurocholic acid

Figure 1 Structures of bile acids and their derivatives.

Glycocholic acid Taurocholic acid

Figure 1 Structures of bile acids and their derivatives.

used in clinical trials for a variety of hepatobiliary diseases, including primary biliary cirrhosis, primary sclerosing cholangitis and hepatitis C, and is suggested to suppress colon polyp formation in experimental animals. Thus, bile acid analysis is an important diagnostic tool for diseases of the liver and intestine, and for monitoring bile acid therapy in such diseases. Of the several methods employed for bile acid analysis in biological fluids, gas chromatography (GC) has proven to be the most versatile and is sensitive enough to quantitate nanomole to picomole amounts present in biological specimens.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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