Fatty Acids PDF

OSAMAH S. AlROUWAB 1 OSAMAH S. AlROUWAB 2  BIOMEDICAL IMPORTANCE  The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, that are related more by their physical than by their chemical properties.  They have the...

OSAMAH S. AlROUWAB 1 OSAMAH S. AlROUWAB 2  BIOMEDICAL IMPORTANCE  The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, that are related more by their physical than by their chemical properties.  They have the common property of being: (1) relatively insoluble in water (2) soluble in nonpolar solvents such as ether, benzene and chloroform. OSAMAH S. AlROUWAB 3  BIOMEDICAL IMPORTANCE  They are important dietary constituents not only because of the high energy value of fats, but also because essential fatty acids fat-soluble vitamins, and other lipophilic micronutrients are contained in the fat of natural foods.  Dietary supplementation with long chain ω3 fatty acids is believed to have beneficial effects in a number of chronic diseases, including cardiovascular disease, rheumatoid arthritis and dementia. OSAMAH S. AlROUWAB 4  BIOMEDICAL IMPORTANCE  Fat is stored in adipose tissue, where it also serves as a thermal insulator in the subcutaneous tissues and around certain organs.  Nonpolar lipids act as electrical insulators, allowing rapid propagation of depolarization waves along myelinated nerves.  Lipids are transported in the blood combined with proteins in lipoprotein particles  Lipids have an essential roles in nutrition and health and knowledge of lipid biochemistry is necessary for the understanding of many important biomedical conditions, including obesity, diabetes mellitus, and atherosclerosis OSAMAH S. AlROUWAB 5  Structure of Lipids Bloor’s Criteria According to Bloor, lipids are compounds having the following characteristics: They are insoluble in water. Solubility in one or more organic solvents, such as ether, chloroform, benzene, acetone, etc, so called fat solvents. Some relationship to the fatty acids as esters either actual or potential. Possibility of utilization by living organisms. OSAMAH S. AlROUWAB 6 Structure of Lipids carbohydrates proteins Phosphate OSAMAH S. AlROUWAB 7  FATTY ACIDS Fatty acids  Fatty acids are water-insoluble “long chain hydrocarbons”.  Fatty acids may be Essential: cannot be synthesized in the body Nonessential: can be synthesized in the body.  They are mostly monocarboxylic i.e. having one carboxyl group at the end of the chain (-COOH).  They are mostly aliphatic (i.e. not branched). A few branched-chain fatty acids are present in animals and plants  Fatty acids may be Saturated: (no double bonds) or Unsaturated: (containing one or more double bonds). OSAMAH S. AlROUWAB 8  FATTY ACIDS Fatty acids (a) Saturated FA: Examples: Acetic acid CH3COOH Propionic acid C2H5COOH lower fatty acids Butyric acid C3H7COOH Caproic acid C5H11COOH Palmitic acid C15 H31COOH higher fatty acids Stearic acid C17 H35COOH and so on. Saturated fatty acids having 10 carbon or less number of carbon atoms are called lower fatty acids Saturated fatty acids that have more than 10 carbon atoms are called higher fatty acids OSAMAH S. AlROUWAB 9  FATTY ACIDS Fatty acids (b) Unsaturated FA: They are classified further according to the degree of unsaturation: (1) Mono unsaturated (Monoethenoid) fatty acids: They contain one double bond. Example: Oleic acid C17H33 COOH (2) Polyunsaturated (Polyethenoid) fatty acids: There are three polyunsaturated fatty acids of biological importance: A. Linoleic acid: It contains two double bonds between C9 and C10; and between C12 and C13. Dietary sources: Linoleic acid is present in sufficient amounts in peanut oil, corn oil, cottonseed oil, soyabean oil, and egg yolk. OSAMAH S. AlROUWAB 10  FATTY ACIDS Fatty acids B. Linolenic acid: It contains three double bonds between 9 and 10; 12 and 13; and 15 and 16. Dietary Sources: soybean oil, fish viscera, and liver oil. C. Arachidonic acid: It contains four double bonds between 5 and 6; 8 and 9; 11 and 12; and 14 and 15. Dietary source: Found in peanut oil and in animal fats including Liver fats. Note: These three polyunsaturated fatty acids, linoleic acid, linolenic acid, and arachidonic acid are called “Essential fatty acids (EFA)”. They have to be provided in the diet, as they cannot be synthesized in the body. OSAMAH S. AlROUWAB 11 FATTY ACIDS Fatty acids OSAMAH S. AlROUWAB 12  FATTY ACIDS Fatty acids (c) Branched-chain FA: Odd and even carbon branched-chain fatty acids occur in animal and plant lipids, e.g. Sebaceous glands: Sebum contains odd branched-chain FA Even branched-chain FA is present in phytanic acid in butter. OSAMAH S. AlROUWAB 13  FATTY ACIDS Fatty acids CLINICAL ASPECT Virulent strains of Mycobacterium tuberculosis, show a “cord factor” has been isolated from them. It is chemically “trehalose-6-6’-dimycolate” and is present in extremely small quantities on the bacterial surface and appears to be responsible for the virulence of the organism. OSAMAH S. AlROUWAB 14  FATTY ACIDS Fatty acids (d) Cyclic fatty acids: Fatty acids bearing cyclic groups are present in some seeds, e.g.  Chaulmoogric acid  Hydnocarpic acid. Both of them have been used earlier for a long time for treatment of leprosy. OSAMAH S. AlROUWAB 15  FATTY ACIDS Fatty acids (E) Eicosanoids: These are derived from eicosapolyenoic FA. OSAMAH S. AlROUWAB 16  FATTY ACIDS Nomenclature of Fatty Acids (a) The most frequently used systemic nomenclature is based on naming the fatty acids after the hydrocarbon with the same number of carbon atoms, “oic” being substituted for the final “e” in the name of the hydrocarbon. Saturated acids end in “anoic” e.g. octanoic acid (Caprylic acid) Unsaturated acids with double bonds end in enoic, e.g. octadecenoic acid (oleic acid). OSAMAH S. AlROUWAB 17  FATTY ACIDS Nomenclature of Fatty Acids (b) Starting from the carboxyl group: I- 1, 2, 3 system: Give COOH No. 1 then proceed to the terminal CH3. II- α, β, system: the 1st carbon following COOH is α then proceed to the terminal CH3 III- Starting from the terminal methyl group (omega “ω” carbon): - The terminal methyl carbon is given ω1 then proceeds to the COOH group α β OSAMAH S. AlROUWAB 18  FATTY ACIDS Nomenclature of Fatty Acids Position of double bonds: The most commonly used systems for designating the Position of double bonds in unsaturated fatty acids are: (1) The delta (Δ) numbering system e.g. palmitoleic acid C 16:1 Δ9 means that this acid contains 16 carbons (16) and one double bond (1) and the position of the double bond is between carbon number 9 and carbon number 10 starting from carboxyl carbon 1 OSAMAH S. AlROUWAB 19  FATTY ACIDS Nomenclature of Fatty Acids Position of double bonds: The most commonly used systems for designating the Position of double bonds in unsaturated fatty acids are: (2) Omega (ω) system e.g. the palmitoleic acid may be written as C 16:1 ω7 which indicates a double bond on the seventh carbon counting from the ω-carbon atom i.e. last –CH3 carbon. OSAMAH S. AlROUWAB 20  FATTY ACIDS Isomerism (a) Geometric Isomers: They depend on the orientation of the radicals around the axis of the double bonds. If the radicals are on the same side of the bond, it is called as ‘cis’ form. If the radicals are on the opposite side, a ‘trans’ form is produced. ‘Cis’ form is comparatively unstable and is more reactive. Example: Oleic acid and elaidic acid both have same molecular formula – C17H33COOH OSAMAH S. AlROUWAB 21  FATTY ACIDS (b) Positional Isomers: A variation in the location of the double bonds along the unsaturated fatty acids chain produces isomers of that compound. Thus, oleic acid could have 15 different positional isomers. OSAMAH S. AlROUWAB 22 FATTY ACIDS OSAMAH S. AlROUWAB 23  FATTY ACIDS ❖ Essential and nonessential fatty acids: A. Nonessential fatty acids: 1. These are fatty acids which can be synthesized in the body. Thus they are not necessary to be obtained from the diet. 2. They include all saturated and monounsaturated fatty acids as palmitoleic and oleic acid. 3. They can be synthesized from acetyl COA (active acetate) derived from glucose oxidation. OSAMAH S. AlROUWAB 24  FATTY ACIDS B. Essential fatty acids: a) These are fatty acids that cannot be synthesized in the body. They must be obtained from the diet. b) They include fatty acids tha t contain more than one double bond (polyunsaturated fatty acids) e.g. lenoleic, lenolenic, arachidonic acids. c) The human body has an enzyme system that can form only one double bond at the ninth carbon atom. OSAMAH S. AlROUWAB 25  Classification of Lipids Sources: a) Vegetable oils e.g. corn oil, soya bean oil, safflower oils, sunflower, linseed oil , and cotton seed oil. b) Fish oils: shark liver oils, which particularly contain the ω3 polyunsaturated fatty acids. Importance: a) Normal growth. b) They enter in the structure of phospholipids and cholesterol esters. c) They enter in the structure of cell membranes and are required for the fluidity of membrane structure. d) They protect against atherosclerosis and fatty liver ( deposition of TAG in liver) OSAMAH S. AlROUWAB 26  FATTY ACIDS Phrynoderma or Toad skin  It is characterized by horny eruptions on the skin (limbs, back, buttocks) Scaly skin, eczema (in children), loss of hair, and poor wound healing.  Causes of Phrynoderma: Although the exact cause of Phrynoderma is not fully understood, it's often associated with nutritional deficiencies, particularly a lack of vitamin A and essential fatty acids.  Usually seen in infants receiving formula diets that have a low-fat content  This can be seen in patients maintained on intravenous nutrition, low in EFA for longer periods OSAMAH S. AlROUWAB 27  FATTY ACIDS Eicosanoids A. Definition: These are cyclic compounds that derived from arachidonic acid (eicosatetraenoic)(20 C) after cyclization of its carbons chain to form a ring. - Hormone-like molecules produced by most mammalian cells - Active within the cell in which they are produced (autocrine) or on adjacent cells (paracrine) - Have many physiological & pathological & Pharmacological actions OSAMAH S. AlROUWAB 28  FATTY ACIDS Eicosanoids B. Components of eicosanoids: 1. Prostanoids: which comprise prostaglandins, prostacycIins and thromboxanes. a) Prostaglandins (PG) 1) PGE2: vasodilatation, relaxation of the uterus and intestine. 2) PGF2 : vasoconstriction, contraction of the uterus and intestine. b) prostacycIins They cause vasodilatation and inhibit platelets aggregation c) Thromboxanes They cause platelets aggregation 2. Leukotriens (LT): a) They are present in leucocytes, platelets and mast cells. b) They cause chemotaxis i.e. Collection of white blood cells at the site of inflammation (↑ vascular permeability). OSAMAH S. AlROUWAB 29  FATTY ACIDS Alcohols I. Introduction: Alcohols associated with lipids include glycerol, cholesterol and higher alcohols (e.g. cetylalcohol, C16H33OH) usually found in the wax. Glycerol: It is polyhydric alcohol containing 3 (-OH) groups: 1. Glycerol is colorless, odorless, and hygroscopic and has a sweet taste. 2. It is soluble in water. 3. It combines with one fatty acid to form monoacylglycerol. Uses of Glycerol: 1. Nitroglycerol is used as a drug for dilatation of coronary arteries. 2. Glycerol enters in manufacturing of creams and lotions for dry skin OSAMAH S. AlROUWAB 30