Vitamins Lecture Notes PDF

VITAMINS Prof. Mona Abd El-Hamid El-Baz Prof. of Medical Biochemistry Overview of Vitamins Understand differences between vitamins and coenzymes of water soluble hormones Know pathologies associated with water-soluble vitamins Define vitamins, classify them according to their solubil...

VITAMINS Prof. Mona Abd El-Hamid El-Baz Prof. of Medical Biochemistry Overview of Vitamins Understand differences between vitamins and coenzymes of water soluble hormones Know pathologies associated with water-soluble vitamins Define vitamins, classify them according to their solubility Definition: VITAMINS have historically been classified as water-soluble or lipid-soluble. Water-soluble vitamins are precursors for coenzymes and are reviewed in the context of the reactions for which they are important  Vitamins are organic compounds that characterized by: 1. They are essential for normal health and growth where they are not synthesized in human body. So, they must be supplied in the diet. 2- Their deficiency in the body leading to various diseases. 3. They do not enter in the structure of the tissues or oxidized by them. 4. They are needed in very small amounts. N.B.: Provitamins: These are precursors of vitamins that converted into vitamins inside the body e.g. Carotenes are provitamin A. Vitamers: These are different forms of one vitamin e.g. Vitamin D has 2 vitamers; D2, & D3. Classification: Vitamins can be classified according to their solubility into two main categories: A. Fat soluble vitamins: they include A, D, E and K vitamins. Characters: 1. They are soluble in fat solvents. 2. They need bile salts for absorption. 3. They can be stored in the body. B. Water soluble vitamins: they include vitamin C and B complex group (12 vitamins). Characters: 1. They are soluble in water 2. Most of them are not stored in the body. Water Soluble Vitamins Vitamin C & Vitamin B complex 1. Vitamin C = L-Ascorbic Acid (Antiscorbutic vitamin) Sources: 1- Fruits especially citrus fruits (lemon, orange), melon, strawberry and Guava is very rich in vitamin C. 2- Vegetables especially green leafy vegetables as lettuce, tomatoes, potatoes. 3- Liver and adrenals are animal sources of vitamin C.  Functions A- Formation of collagen protein Ascorbic acid is essential for the conversion of the procollagen (immature collagen) into collagen. Procollagen is a protein containing proline and lysine. Hydroxylation of both amino acids is helped by Vit. C. B- A potent reducing agent Ascorbic acid acts as a specific reducing agent for a of hydroxylase enzyme: Vitamin C may have a role in oxidation-reduction reactions acting as a hydrogen transport agent. C- Anti-Cancer: In large doses, vitamin C may inhibit the formation of carcinogenic N-nitrosocompound during cooking and digestion and lowered the risk for gastric and esophogeal cancers. D- Defense Mechanism: The use of vitamin C in large doses relieve the symptoms of the common cold and required for normal leukocyte function and for histamine release  Deficiency (scurvy) Vitamin C store is sufficient for 3 months. If this store is depleted a disease called scurvy will result. It is characterized by : I- Manifestations due to decrease neurotuanomitters: 1- Behavioral changes 2- Severe emotional disturbances II- Manifestations due to decrease carnitine and fatty acids oxidation: General weakness III- Manifestations due to decrease collagen formation : 1-Bleeding into gum, muscles, joints, kidneys, gastrointestinal tract and pericardium. 2- Bone lesions.3-Necrosis of gums and loss of teeth. 4- Delayed wound healing 5- Easy bruising and haemorrhages under the skin due to increased capillary fragility. B. Vitamin B Complex Definition: These are groups of vitamin B complex that put together in one group of different chemical molecules. They include the following members: 1-Thiamin (vit. B1). 7- Vitamin B12 2-Riboflavin (Vitamin B2). 8- Folic acid. 3-Niacin (P.P.F.). 9- Choline. 4-Pyridoxine (Vitamin B6.) 10- Inositol 5-Pantothenic acid. 11- Lipoic acid 6-Biotin (Vitamin H.). 12- P-amino benzoic acid (PABA)  1- Thiamin = Vitamin B1 (Antiberiberi) Sources Plants: Seeds as peas, beans. Animals: Liver, eggs and milk 1- Thiamin pyrophosphate TPP, the active form of Vitamin B1 2- TPP is essential coenzyme affecting the following enzymes: Pyruvate dehydrogenase , alfa ketoglutarate and transketolase. 3- TPP is necessary for optimal growth of infants and children. 4- TPP essential for the process of nerve conduction and structure of nerve membrane  Deficiency: Beriberi. Biochemical Changes: 1-Accumulation of pyruvic acid in blood and increase of lactic acid in blood. 2- Accumulation of pentose sugars in RBCs as a result of decreased transketolase reaction. Manifestations: There are two forms of beriberi. a- Wet Beriberi: Affects mainly the cardiovascular system and it is characterized by: 1- Extensive edema. 2- Congestive heart failure. 2- Riboflavin = Vitamin B2 Sources: It is abundant in liver, yeast, whole grain and milk. Activation: - Both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are active forms of vitamin B2 affecting only dehydrogenase enzyme. Deficiency 1- Eyes: Occular disturbances including: a- Photophobia b-Vascularization of cornea. 2- Mouth: Red lips and shiny-Angular stomatitis (inflammation of angles of mouth). Glossitis (inflammation of tongue) and cheilosis. 3-Skin: Seborrheic dermatitis i.e. inflammation of sebaceous glands of skin. 3. Niacin(Nicotinic acid or Pellagra Preventing Factor, PPF) Sources: 1- Whole grain cereals, yeast, milk, leafy green vegetables and meat. However corn is poor in both niacin and tryptophan 2- Niacin can be made endogenously from the amino acid tryptophan. Each 60 mg tryptophan can be converted to 1 mg niacin. This conversion requires vitamin B6, pyridoxine as a coenzyme. N.B: Meat is rich in tryptophan.  Functions: Niacin is essential for the formation of the coenzymes NAD+ (Also called Coenzyme I ), NADP+ (Also called Coenzyme II) and NMN (Also called Coenzyme III and they are essential for many biochemical oxidation-reduction reaction that require dehydrogenase enzyme Deficiency: It leads to a disease called: Pellagra. Causes of Pellagra: Pellagra is usually associated with deficiency of niacin, tryptophan or pyridoxine. Manifestations of Pellagra: is called a disease of (4 Ds) including: Dermatitis: The exposed skin becomes dry, rough and scaly with brown discoloration, glossitis and stomatitis are seen. Diarrhea. Dementia. Death (if not treated) 4. Pyridoxine “Vitamin B6” Structure: Vitamin B6 consists of 3 closely related pyridine derivatives: Pyridoxine, pyridoxal and pyridoxamine and their corresponding phosphates. All three have equal vitamin activity. Sources: 1. Plants: Yeast, rice polishing, germinal portion of various seeds. 2. Animals: Egg Yolk. 3. Royal Jelly of bees (very rich in vitamin B6) Affecting the following enzymes: 1. Aminotransferase AST, ALT 2. Gama - Aminolevulinc Synthase Deficiency: Pellagra may result, because pyridoxal phosphate is needed for the conversion of tryptophan to niacin. 1-Stomatitis cracking or scaling of lip border and corners of mouth growth retardation. 2-Convulsions &Demyelination of the peripheral nerves and axons. 3-Microcytic, hypochromic anaemia 4-Nausea and vomiting of early pregnancy 5. Pantothenic Acid Sources: Animal: Meat, liver, kidney. but the richest known source of pantothenic acid is the royal jelly of bees. Plant: Legumes , wheat and rice. Affecting enzymes: Fatty acid synthase and fatty acyl CoA synthase Pyruvate dehydrogenase and alfa ketoglutarates dehydrogenases The main function 1- Is in the synthesis of coenzyme A (CoASH) act as acid carrier e.g acetic acid and succicnic acid , fatty acid and other carboxylic acid ) ex :acetic acid to form acetyl COA 2- Act as acyl carrier (ACP )to form acetyl COA protein During the action of extramitchondrial pathway for fatty acid synthesis 6- Biotin(Vitamin H or Coenzyme R) Structure: Biotin is sulpher containing vitamin Sources : -The intestinal bacteria synthesize most of the human requirements of biotin -Egg yolk, animal tissues, tomatoes and yeast are excellent sources of biotin. Activation: Biotin functions as coenzyme of the carboxylase enzyme that catalyze carboxylation reactions. pyruvate carboxylase Acetyl CoA Carboxylase Propionyl CoA Carboxylase. Deficiency: The manifestations of biotin deficiency include: Dermatitis of the extremities, muscle pain and loss of muscular control. Pallor of the skin and Alopecia (loss of hair) Hallucination and depression. Immune deficiency disease (in some cases). 5. Growth retardation.  7. Vitamin B12 = Cyanocobalamin (Anti-pernicious anemia or extrinsic factor) Affecting enzymes Homocyctein methyltransferase & Methylmsaloneyl COA mutase. Sources 1. Meat, egg, milk and milk products. 2. Vitamin B12 is not present in vegetables. Absorption and Transport in Blood: For the absorption of vitamin B12 it combines with a glycoprotein secreted by the gastric parietal cell called intrinsic factor (IF). This IF–B12 complex binds with specific receptor in the ileum.  Deficiency: Causes: 1- Decrease vitamin B12 intake. This may occur among vegetarians. i.e. people who eat vegetables only. 2- Atrophy of gastric mucosa ⎯→ lack of intrinsic factor. This gives rise to a condition known as pernicious anaemia (PA). PA is mostly common in those over 60 years of age. 3- Autoantibodies against gastric parietal cells. And Antibodies against intrinsic factors. 4-Defective absorption as regional enteritis. 5-Drugs induced vitamin B12 deficiency 6-Poor nutrition , aging bacterial overgrowth of terminal ileum secondary to Chrons diseases and chronic pancreatitis Manifestations of deficiency: 1- Megaloblastic anaemia It is a macrocytic hyperchromic anaemia. It is due to abnormal replication of DNA in hematopoietic tissue. 2- Neurological manifestations a- Subacute combined degeneration of the spinal cord of lateral (motor) and posterior (sensory) columns. b- Peripheral neuritis leads to numbness tingling and weakness of extrimities. Laboratory Findings: Increased the excretion of methylmalonyl COA in urine. 8. Folic acid (B9) Sources: 1-The major source is leafy vegatables. 2-Liver, kidney and yeast are also rich in folate. Physiological Functions: Tetrahydrofolic acid (H4 folate) act as a carrier for one– carbon groups. Deficiency: 1- Pancytopenia: i.e. allblood cells are affected a) Megaloblastic anaemia (Marocytic, hyperchromic). It is difficult to differentiate between megaloblastic anaemia resulting from folate deficiency and vitamin B deficiency. But a daily dose of 300–500 ug of folate will improve the blood picture in the first condition. 2- Impaired growth.