Bile acids (also known as bile salts) are steroid acids found predominantly in the bile of mammals. A steroid is a Terpenoid Lipid characterized by a Carbon skeleton with four fused rings generally arranged in a 6-6-6-5 fashion In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are Bile or gall is a bitter yellow or green Alkaline fluid secreted by Hepatocytes from the Liver of most Vertebrates In many species Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands In humans taurocholic acid, and glycocholic acid (derivatives of cholic acid) represent approximately eighty percent of all bile acids. Taurocholic acid, known also as cholaic acid, cholyltaurine, or acidum cholatauricum, is a Deliquescent yellowish crystalline Bile Glycocholic acid, or cholylglycine, is a crystalline Bile acid involved in the Emulsification of Fats It occurs as a sodium Salt Cholic acid is a Bile acid, a white crystalline substance insoluble in water (soluble in alcohol and Acetic acid) with a melting point of 200-201 The two major bile acids are cholic acid, and chenodeoxycholic acid. Cholic acid is a Bile acid, a white crystalline substance insoluble in water (soluble in alcohol and Acetic acid) with a melting point of 200-201 Chenodeoxycholic acid (also known as chenodesoxycholic acid) is a Bile acid. They, their glycine and taurine conjugates, and their 7-alpha-dehydroxylated derivatives (deoxycholic acid and lithocholic acid) are all found in human intestinal bile. Glycine (abbreviated as Gly or G) is the Organic compound with the formula NH2CH2COOH Taurine, or 2-aminoethanesulfonic acid, is an Organic acid. It is also a major constituent of Bile and can be found in the lower intestine and in small Deoxycholic acid, also known as deoxycholate, cholanoic acid, and 3α12α-dihydroxy-5β-cholanate, is a Bile acid.
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Production and distribution
Bile acids are produced in the liver by the oxidation of cholesterol. The liver is a vital organ in the human body and is present in Vertebrates and some other animals Cholesterol is a Lipid found in the Cell membranes and transported in the Blood plasma of all Animals It is an essential component of mammalian They are conjugated with the amino acids taurine or glycine, or with a sulfate or a glucuronide, and are then stored in the gallbladder. The gallbladder (or cholecyst sometimes gall bladder is a small organ whose function in the body is to store Bile and aid in the digestive process Bile acid also serves the purpose of breaking down fats. Upon eating a meal containing fat, the contents of the gallbladder are secreted into the intestine. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists In humans, the rate limiting step is the addition of a hydroxyl group on position 7 of the steroid nucleus by the enzyme cholesterol 7 alpha-hydroxylase. The rate-determining step (RDS is a Chemistry term for the slowest step in a Chemical reaction. Cholesterol 7 alpha-hydroxylase (CYP7A1 the Rate-limiting enzyme in the synthesis of Bile acid from Cholesterol, catalyzing the formation of 7-alpha-hydroxycholesterol Bile acids serve multiple functions, which include: eliminating cholesterol from the body; driving the flow of bile to eliminate catabolites from the liver; emulsifying lipids and fat soluble vitamins in the intestine; and aiding in the reduction of the bacteria flora found in the small intestine and biliary tract.
The term bile acid refers to the conjugated form. In the duodenum's alkaline environment, the bile acids become bile salts as a result of the basic pH and the relative pKa of the acids. Bile salt refers to the ionic form of the secreted bile acid.
Synthesis of bile acids is a major consumer of cholesterol in most species (other than humans). The body produces about 800 mg of cholesterol per day and about half of that is used for bile acid synthesis. In total about 20-30 grams of bile acids are secreted into the intestine daily; about 90% of excreted bile acids are reabsorbed (by active transport in the ileum) and recycled. In Anatomy, the intestine is the segment of the alimentary canal extending from the Stomach to the Anus and in humans and other mammals consists Active transport is the mediated process of moving particles across Biological membrane against the concentration gradient In Anatomy of the Digestive system, the ileum is the final section of the Small intestine. This is referred to as the enterohepatic circulation. Enterohepatic circulation refers to the circulation of Bile from the Liver, where it is produced to the Small intestine, where it aids in Digestion Bile is also used to break down fat goblets into tiny droplets. Bile from slaughtered animals can be mixed to use as soap.
Types
Bile salts constitute a large family of molecules, composed of a steroid structure with four rings, a five or eight carbon side-chain terminating in a carboxylic acid, and the presence and orientation of different numbers of hydroxyl groups. The four rings are labeled from left to right (as commonly drawn) A, B, C, and D, with the D-ring being smaller by one carbon than the other three. The hydroxyl groups have a choice of being in 2 positions, either up (or out) termed beta (often drawn by convention as a solid line), or down, termed alpha (seen as a dashed line in drawings). All bile acids have a hydroxyl group on position 3, which was derived from the parent molecule, cholesterol. In cholesterol, the 4 steroid rings are flat and the position of the 3-hydroxyl is beta.
In many species, the initial step in the formation of a bile acid is the addition of a 7-alpha hydroxyl group. Subsequently, in the conversion from cholesterol to a bile acid, the junction between the first two steroid rings (A and B) is altered, making the molecule bent, and in this process, the 3-hydroxyl is converted to the alpha orientation. Thus, the default simplest bile acid (of 24 carbons) has two hydroxyl groups at positions 3-alpha and 7-alpha. The chemical name for this compound is 3-alpha,7-alpha-dihydroxy-5-beta-cholan-24-oic acid, or as it is commonly known, chenodeoxycholic acid. This bile acid was first isolated from the domestic goose, from which the "cheno" portion of the name was derived.
Another bile acid, cholic acid (with 3 hydroxyl groups) had already been described, so the discovery of chenodeoxcholic acid (with 2 hydroxyl groups) made the new bile acid a "deoxycholic acid" in that it had one less hydroxyl group than cholic acid. The 5-beta portion of the name denotes the orientation of the junction between rings A and B of the steroid nucleus (in this case, they are bent). The term "cholan" denotes a particular steroid structure of 24 carbons, and the "24-oic acid" indicates that the carboxylic acid is found at position 24, which happens to be at the end of the side-chain. Chenodeoxycholic acid is made by many species, and is quite a functional bile acid. Its chief drawback lies in the ability of intestinal bacteria to remove the 7-alpha hydroxyl group, a process termed dehydroxylation. The resulting bile acid has only a 3-alpha hydroxyl group and is termed lithocholic acid (litho = stone). It is poorly water-soluble and rather toxic to cells. Bile acids formed by synthesis in the liver are termed "primary" bile acids, and those made by bacteria are termed "secondary" bile acids. As a result, chenodeoxycholic acid is a primary bile acid, and lithocholic acid is a secondary bile acid.
To avoid the problems associated with the production of lithocholic acid, most species add a third hydroxyl group to chenodeoxycholic acid. In this manner, the subsequent removal of the 7-alpha hydroxyl group by intestinal bacteria will result in a less toxic, still functional dihydroxy bile acid. Over the course of vertebrate evolution, a number of positions have been chosen for placement of the third hydroxyl group. Initially, the 16-alpha position was favored, particularly in birds. Later, this position was superseded by a large number of species selecting position 12-alpha. Primates (including humans) utilize 12-alpha for their third hydroxyl group position. The resulting primary bile acid in humans is 3-alpha,7-alpha,12-alpha-trihydroxy-5-beta-cholan-24-oic acid, or as it is commonly called, cholic acid.
In the intestine, cholic acid is dehydroxylated to form the dihydroxy bile acid deoxycholic acid. In many vertebrate orders still subject to speciation, new species are discarding 12-alpha hydroxylation in favor of a hydroxy group on position 23 of the side-chain. It should be noted that vertebrate families and species exist that have experimented with and utilize just about every position imaginable on the steroid nucleus and side-chain.
The principal bile acids are:
In humans, the most important bile acids are cholic acid, deoxycholic acid, and chenodeoxycholic acid, Prior to secretion by the liver, they are conjugated with either the amino acid glycine or taurine. Cholic acid is a Bile acid, a white crystalline substance insoluble in water (soluble in alcohol and Acetic acid) with a melting point of 200-201 Chenodeoxycholic acid (also known as chenodesoxycholic acid) is a Bile acid. Glycocholic acid, or cholylglycine, is a crystalline Bile acid involved in the Emulsification of Fats It occurs as a sodium Salt Taurocholic acid, known also as cholaic acid, cholyltaurine, or acidum cholatauricum, is a Deliquescent yellowish crystalline Bile Deoxycholic acid, also known as deoxycholate, cholanoic acid, and 3α12α-dihydroxy-5β-cholanate, is a Bile acid. Cholic acid is a Bile acid, a white crystalline substance insoluble in water (soluble in alcohol and Acetic acid) with a melting point of 200-201 Deoxycholic acid, also known as deoxycholate, cholanoic acid, and 3α12α-dihydroxy-5β-cholanate, is a Bile acid. Chenodeoxycholic acid (also known as chenodesoxycholic acid) is a Bile acid. Conjugation increases their water solubility, preventing passive re-absorption once secreted into the small intestine. As a result, the concentration of bile acids in the small intestine can stay high enough to form micelles and solubilize lipids. The term "critical micellar concentration" refers to both an intrinsic property of the bile acid itself and amount of bile acid necessary to function in the spontaneous and dynamic formation of micelles.
Regulation
As surfactants or detergents, bile acids are potentially toxic to cells and their levels are tightly regulated. Surfactants are wetting agents that lower the Surface tension of a liquid allowing easier spreading and lower the Interfacial tension between two liquids A detergent (as a noun is a material intended to assist Cleaning. They function directly as signaling molecules in the liver and the intestines by activating a nuclear hormone receptor known as FXR also known by its gene name NR1H4. The farnesoid X receptor ( FXR) also known as NR1H4 (nuclear receptor subfamily 1 group H member 4 is a Nuclear hormone receptor with activity similar This results in inhibition of bile acid synthesis in the liver when bile acid levels are too high. Emerging evidence associates FXR activation with alterations in triglyceride metabolism, glucose metabolism and liver growth. (more properly known as, TAG or triacylglyceride) is Glyceride in which the Glycerol is Esterified with three Fatty acids It is the Carbohydrate metabolism denotes the various biochemical processes responsible for the formation, breakdown and interconversion of Carbohydrates
Clinical significance
Since bile acids are made from endogenous cholesterol, the enterohepatic circulation of bile acids may be disrupted as a way to lower cholesterol. This is the mechanism of action behind bile acid sequestrants. The bile acid sequestrants are a group of medications used for binding certain components of Bile in the gastrointestinal tract. Bile acid sequestrants bind bile acids in the gut, preventing their reabsorption. In so doing, more endogenous cholesterol is shunted into the production of bile acids, thereby lowering cholesterol levels. The sequestered bile acids are then excreted in the feces.
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Medical Subject Headings ( MeSH) is a huge Controlled vocabulary (or metadata system for the purpose of indexing journal articles and booksDictionary
bile acid
-noun
- any of the steroid acids produced by the liver, such as cholic acid, that occur in bile as sodium salts and serve to neutralize the contents of the stomach as they enter the duodenum and to aid the emulsification and absorption of fats
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