Lipids PPT PDF

Lipids Outline 1. General structure of lipids 2. Types of lipids 3. Metabolism of lipids 4. Types of lipoproteins and apolipoproteins 5. Lipid disorders 6. Methods of determination Lipids Also known as Fats. Contain Carbon, Hydrogen and Oxygen (CHO). Water insoluble hence they are...

Lipids Outline 1. General structure of lipids 2. Types of lipids 3. Metabolism of lipids 4. Types of lipoproteins and apolipoproteins 5. Lipid disorders 6. Methods of determination Lipids Also known as Fats. Contain Carbon, Hydrogen and Oxygen (CHO). Water insoluble hence they are transported in the blood by lipoproteins. Lipids Function 1. Rich source of energy compared to carbohydrates. a. 1 gram of fat= 9 kilocalories. b. 1 gram of Carbohydrates= 4 kilocalories. 2. Forms the structural membrane of the cells (phospholipid bilayer). 3. Precursors of hormone production (steroid hormones). Sources of lipid 1.Dietary sources (majority is triglyceride). 2.Adipose tissue. 3.Synthesized in the liver. Types of lipids 1. Fatty acids 2. Triglycerides 3. Phospholipids 4. Cholesterol Types of lipids Fatty acids The building blocks of lipids. Consist of hydrocarbons with COOH terminal group. Found in triglycerides, cholesterol and phospholipids. In the blood they exist in 2 forms: 1. Fatty acid esters (majority)- bound to triglycerides, cholesterol and phospholipids. 2. Free fatty acids (unesterified)- not bound to any molecule and transported by albumin. Types of lipids Types of fatty acids Saturated fatty acids- fatty acids with NO double bond. Linear hydrocarbon chain. Unsaturated fatty acids- fatty acid with double bond. Bent hydrocarbon chains. Cis form- hydrogen at the same side of C=C bond Saturated – means the maximum number of hydrogen atoms are bonded to each carbon atom in a molecule of fat. Saturated vs unsaturated Saturated fatty acids Unsaturated fatty acids Solid state at room Lower melting point thus temperature. liquid at room temperature. High melting point and higher shelf-life. Low shelf life. Not ideal for Found in animal fat such as long storage. milk, meat and butter others Mostly plant sources like are vegetable oil and coconut oil. vegetable oil, sunflower oil, Synthesized in the body. mustard oil, avocado oil. Examples: stearic acid, palmitic Example: linoleic acid, acid, capric acid and lauric acid. linolenic acid and oleic acid. Types of unsaturated fatty acids 1. Monounsaturated- 1 double bond only in their structure. 2. Polyunsaturated- contains more than 1 double bond in their structure Example: omega 3 and omega 6 fatty acids. Polyunsaturated fatty acids Omega 3 and Omega are not synthesized by the body thus should be supplied from the diet Hydrogenation of fatty acids Hydrogenation- converting of unsaturated fatty acids to saturated fatty acids by addition of hydrogen hence straightening the hydrocarbon chain (partial hydrogenation). The product is trans fats. Trans fat- hydrogen on the opposite side of C=C. more linear compared to cis unsaturated fatty acids. The worst type of fat because it raises the bad cholesterol since no enzyme from the body can metabolized it. Trans fat FATTY ACIDS according to number of carbon a. Short chain(2-4 carbon atoms) b. Medium chain(6-10 carbons) c. Long chain(12-26 carbons)- found in diet. d. Prostaglandins- participate in inflammation and coagulation Types of lipids Triglycerides (triacylglycerol) Consist of 3 fatty acids attached to 1 glycerol by ester bonds. Main storage form of lipids found in adipose tissue. Vegetable source: exist as oils (unsaturated) Animal source: solid at room temperature (saturated) Neutral fats- no charges Functions: source of energy, structural membrane of the cells, insulation and shock absorber. Types of lipids Phospholipids Similar with triglycerides structure except only 2 fatty acids are attached to the glycerol and attached phosphate group serves a head of the molecule. Most abundant lipids in the body. Amphipathic- It forms a hydrophilic head and hydrophobic tail thereby attracting both water and fat. Composed the phospholipid bilayer of the cell membrane. Phospholipid bilayer of the cell membrane Types of phospholipid 1. Lecithin (phosphatidyl choline) important in the transport of fats in the plasma, brain and general cell structure 2. Sphingomyelin found mostly in brain and nerve tissue. Maintain cell membrane structure. 3. CEPHALINE comprises 10% of phospholipids. phosphatidyl ethanolamine and phosphatidyl serine. Types of lipids Cholesterols Consist of 4 rings (A,B,C and D), unsaturated steroid alcohol. Amphipathic- OH group is hydrophilic, hence cholesterol together with phospholipid forms the cell membrane. Not a source of energy since it is not already catabolized by cells. Majority of cholesterol are synthesized by the liver. Types of cholesterol in the body Unesterifi 1. Cholesterol ed esters/esterified cholesterol- most abundant, consist of a cholesterol ring and fatty acids. 2. Free cholesterol/unesterifi Esterified ed - no fatty acids attached. Functions of cholesterol 1. Integral parts of the cell membrane (present in the lipid bilayer). 2. In the liver it forms into bile acids such as cholic acid and chenodeoxycholic acid that helps in the absorption of fats in the intestine ( fat emulsification). 3. Precursor for steroid hormones such as adrenal hormones, testosterone and progesterone. 4. Precursor of vitamin D which facilitates the absorption of calcium (7-dehydroxycholesterol-Vit D3). Lipid metabolism Lipid metabolism 1. Lipolysis 2. Lipogenesis 3. Ketogenesis Metabolism of lipid Begins at the small intestine through the action of enzymes and hormones. 1.Cholecystokinin(CCK) secreted by the intestine to stimulate lipases and bile. 2.Bile acids- emulsify fats. Secreted from the gall bladder. 3.Pancreatic lipase- breaks down triglycerides to fatty acids then to monoglycerides. Metabolism of lipid 1. Triglycerides, cholesterol molecules and fatty acids are formed micelles of chylomicrons then transported from the small intestine to lymphatic system to circulatory system (blood stream) 2. Once in the circulation they are either go to liver or adipose tissue.  Metabolism of lipid Lipolysis (breakdown of triglycerides into glycerol and fatty acids) 1. Breaking down of triglycerides (fats) to fatty acids and glycerol through hydrolysis. 2. Occurs in adipose cells. 3. Glycerol enters the glycolysis pathway 4. Fatty acids are then undergo Beta oxidation to produce acetyl CoA. 5. Acetyl CoA enters the Krebs cycle to generate energy. Triglycerides yield more than twice the energy compared to carbohydrates and proteins. Metabolism of lipid Lipogenesis (glucose conversion to fatty acids) 1. Excess glucose generates excess Acetyl CoA by the process of glycolysis. 2. Generated fatty acids or triglyceride are then stored at adipose tissues for energy reserves. 3. Occurs in the liver cells, adipose cells and lactating mammary glands. Metabolism of lipid Ketogenesis (production of ketones) 1. Excess products of beta oxidation of fatty acids (lipolysis) are diverted to create ketone bodies. 2. Ketone are: β-hydroxybutyrate, acetoacetate and acetone. 3. The excess product AcetylCoA is converted into hydroxymethylglutaryl CoA (HMG CoA). 4. HMG CoA is then converted into β-hydroxybutyrate, the primary ketone body in the blood. These are water soluble and energy yielding. 5. Ketones serve as alternative source of energy of the brain. 6. Occurs in the liver Ketones Ketones are produced in times of low dietary intake of glucose such prolong fasting and starving (physiological). Brain used ketones efficiently than glucose. Excessive production of ketones are broken down into CO2 and acetone Acetone is removed in exhalation (fruity odor breathe). CO2 accumulation causes acidity in blood pH as seen in diabetic ketoacidosis a type of metabolic acidosis. (pathological) Lipoproteins and apolipoproteins Lipoproteins Lipoproteins are spherical shape which transports lipids such as cholesterol and triglycerides. Composed of lipids and protein (apolipoproteins). Apolipoproteins are found on the surface of the lipoproteins. Functions are maintenance of structural integrity, binds to cell receptor and activators or  Types of lipoproteins Based on centrifugal flotation density 1. ULDL- Chylomicrons 2. VLDL 3. IDL 4. LDL 5. HDL Note: lipoprotein that contains high lipids is larger in size but less denser. Types of lipoproteins CHYLOMICRONS Largest lipoprotein, produced in the intestinal mucosal cells. Composition: 80-90 % triglycerides (majority) Transports exogenous (dietary lipids) to liver and peripheral cells such as adipose tissue. Contain lipase which hydrolysed cholesterol and triglycerides resulting to formation of chylomicron remnants which uptake by the liver. Lowest density and no electrophoretic mobility. Apolipoprotein: apo B-48 Forms a milky or creamy layer at the top of the plasma. (lipemic). Lipemic sample means high amount of chylomicrons and triglycerides. Types of lipoproteins VLDL(Very low density lipoprotein) Pre beta lipoprotein. Composition: 45-65 % triglycerides. Synthesized from chylomicron remnant Apolipoproteins: apo B-100, C-I, C-II, C-III and E. Transports endogenous triglycerides from hepatic to peripheral tissues. VLDL deposits fats to the adipose tissue eventually degraded by lipoprotein lipase resulting decrease in size. Types of lipoproteins IDL(intermediate density lipoprotein) Intermediate between VLDL and LDL. Partly depleted triglyceride. IDL interacts with HDL giving off most of its TAG content in exchange of cholesterol resulting to formation of LDL. Types of lipoproteins LDL(low density lipoprotein) Composition: 45-50 % cholesterol. Apolipoproteins: B-100 “Bad cholesterol” by transporting cholesterol from liver to tissues. Used as a marker for coronary artery disease. Beta lipoprotein, follow the mobility of beta globulin. Types of lipoproteins HDL(high density lipoprotein) Composition: 15-20 % cholesterol and 45-55 % proteins. Produce by liver and intestines. Apolipoprotein: apo A-I ,apo A-II and ApoC “Good cholesterol” because it acts as “scavenger of lipids”, transport cholesterol from tissues to liver for catabolism to form bile acids. (reverse cholesterol transport). Alpha lipoprotein, follow mobility of alpha globulin. Fastest migrating lipoprotein. LDL and HDL action in the blood vessels. a. LDL- transporting cholesterol from liver to peripheral tissues such as adrenal gland, gonads, and blood vessels. b. HDL- transport cholesterol from peripheral tissues to liver for recycling. Abnormal lipoprotein Lp (a) Also known as the “sinking beta lipoprotein”. Same with LDL except in density and mobility. Apolipoprotein: apo (a) Bound to apo B-100 by disulfide bonds. Associated with increase risk of coronary artery disease and cerebrovascular disease. Homologous with plasminogen which interfere with clot lysis.  Abnormal lipoprotein Beta VLDL Floating beta lipoprotein. Contains higher cholesterol than triglycerides. Found in VLDL density range, electropheritically found in LDL. Seen in type III hyperlipoproteinemia. Abnormal lipoprotein LpX Composed mainly by unesterified cholesterol and phospholipids. Found in patient obstructive biliary disease. Migrates towards the cathode in electrophoresis. Separation of lipoproteins 1.Ultracentrifugation 2.Electrophoresis Separation of plasma lipoprotein by ultracentrifugation 1. 4 ml of serum is transferred to a centrifuge tube. 2. Add layering saline of density 1.0061 on top of the serum. 3. Centrifugation for 16 hours at 105 000 g. 4. After centrifugation 3 zones are formed a narrow top layer which is opalescent a clear middle layer a yellow bottom layer Separation of plasma lipoprotein by ultracentrifugation Lipoprotein Density Very low density lipoprotein (VLDL) 240 mg/dl Multiply by 0.026 to convert to mmol/L HDL -cholesterol Method 1. Precipitation method- precipitating reagent is added to precipitate VLDL and LDL, supernatant is for HDL 2. Immunoassays- ELISA and immunonephelometric. HDL-CHOL: Male 28-62 mg/dl Female 37-77 mg/dl < 35 mg/dl – high risk of heart disease LDL-cholesterol FRIEDWALD FORMULA- LDL-C estimation LDL-C mg/dl = TC- HDL- C () TAG/5- estimated VLDL TAG/2.2- used for mmol/L Not Applicable if TG is >400 mg/dl and in Type III hyperlipidemia. The equation assumes a fixed TG to cholesterol ratio for estimating the concentration of the VLDL cholesterol. With high levels of TGs, the relationship may not be valid. If TG is > 400 mg/dl multiply TG by 0.16 Gold standard of LDL quantification is ultracentrifugation. LDL-cholesterol Normal values Desirable 160mg/dl  Phospholipids Chemical method 1. Extraction 2. Oxidation- phospholipid phosphorus is converted to inorganic phosphorus 3. Colorimetry - inorganic phosphorus + molybdate blue = molybdenum blue Total phosphorus X 25= phospholipid mass Phospholipids Enzymatic method 1. Phospholipase D- phospholipid is hydrolyzed to choline 2. Choline oxidase- choline is oxidized to betaine and H2O2 3. Peroxidase –H2O2 is added with phenol and 4- aminoantipyrine = quinonimine dye Color produced is measured at 500 nm Fatty acids 1.Gas-layer chromatography(GLC) 2.Dole titration method NORMAL VALUE: Adult 0.3 – 0.9 mmol/L Children and obese >1.1 mmol/L Chylomicrons Standing plasma test 1. 2 ml of plasma is placed in a 10 X 75 mm test tube. 2. Placed inside the refrigerator overnight. 3. Observe for creamy layer on the top of plasma, this is the chylomicrons. When chylomicrons are observed in a fasting specimen it is considered abnormal. Turbid plasma sample left standing overnight contain high amount of VLDL GUIDELINES TO REDUCE RISK OF CORONARY HEART DISEASE (From the National Cholesterol Education Program) Desirable Borderline High risk Cholesterol(mg/dl)