c b1 b2 b3.pdf

II- Water-soluble vitamins This group includes: 1. Vitamin C. 2. Vitamin B Complex Vitamin C or “L-Ascorbic Acid” (Antiscorbutic vitamin) Sources: - Fruits especially citrus fruits (lemon, orange) melon and strawberry. Gawafa is ver...

II- Water-soluble vitamins This group includes: 1. Vitamin C. 2. Vitamin B Complex Vitamin C or “L-Ascorbic Acid” (Antiscorbutic vitamin) Sources: - Fruits especially citrus fruits (lemon, orange) melon and strawberry. Gawafa is very rich in vitamin C. - Vegetables especially green leafy vegetables such as lettuce, tomatoes, raw cabbage, green peppers and germinating seeds are rich source of the vitamin. - Liver and adrenals are animal sources of vitamin C are useless due to destruction of vitamin C by coocking. - Milk is a poor source of vitamin C. Physiological functions: 1. Formation of collagen: - Collagen is essential for the integrity of connective tissue. - Vitamin C is also necessary for bone formation. - vitamin C accelerates the healing of wounds and fractures of bones. - Collagen is a component of the capillary walls, so vitamin C deficiency is associated with capillary fragility. 2. Vitamin C influences the biosynthesis of adrenal cortical hormones and catecholamine (adrenaline and nor adrenaline) as it is present in high concentration in the adrenal gland, especially in periods of stress. 3. Ascorbic acid is required for the formation of carnitine by hydroxylation of procarnitine. Carnitine stimulates fatty acid oxidation in mitochondria. Decreased level of vitamin C may lead to lowered energy levels and muscle weakness. 4. Ascorbic acid is needed for bile acid formation from cholesterol. 3+ 5. It aids in the absorption of iron by reducing it from the ferric (Fe ) to ferrous (Fe2+) state neccessery for absorption. 11 6. Ascorbic acid is necessary for the conversion of folic acid into its physiologically active form tetrahydrofolic acid. 7. Ascorbic acid acts as a general water-soluble antioxidant. It spares vit. A, E and some B vitamins by protecting them from oxidation. 8. 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. The use of vitamin C in large doses ameliorates the symptoms of the common cold and increases the resistance of the body. Deficiency: Causes of deficiency: 1. in chronic disease such as cancer, alcoholism, cigarette smokers and users of contraceptive pills. 2. The classic deficiency disease Scurvy occurs only after chronic deprivation of vitamin C. The clinical manifestations of scurvy include: 1. Easy bruising and haemorrhages under the skin due to increased capillary fragility. 2. Gums become swollen, tender and bleed easily. 3. The teeth become loose and may fall. 4. Delayed wound healing, osteoporosis and anemia. 5. Decreased immunocompetence. Daily requirements: - Adult 75 mg/day and pregnant and lactating female 150 mg/day. - Requirements are increased in diseases and stress conditions. Vitamin B Complex - Vitamin B complex includes the following members: - Thiamin (vit B1). - Riboflavin (Vitamin B2). - Niacin (P.P.F.). - Pyridoxine (Vitamin B6.) - Pantothenic acid. - Biotin (Vitamin H.). - Folic acid. - Vitamin B12. - Lipoic acid - Inositol. - Choline. -P-amino benzoic acid (PABA). 12 General characters of vitamin B complex: - All are soluble in water. - All are present in the same sources (in whole grains, cereals, liver, and yeast). - All members of vitamin B complex serve as coenzymes or cofactors in enzymatic reactions. - All members of vitamin B complex are absorbed in the intestine and transported in the portal circulation. - The tissue stores of most members of vitamin B complex are minimal. - Toxic effects are relatively uncommon. - They are heat stable except vitamin B1. - They destroyed by light except niacin. - They are stable in acid medium but unstable in alkaline medium. Thiamin (Vitamin B1 or Aneurine or Antiberiberi) Sources: - Plants: Seeds as peas, beans, whole cereal grains, bran and yeast. - Animals: liver, eggs and milk. Absorption and Metabolism: - Thiamin is absorbed in the intestine and transported in the portal circulation to the liver and most tissues. - Thiamin pyrophosphokinase present in the liver, erythrocytes and cells of cerebral cortex converts thiamin into thiamin pyrophosphate coenzyme form. Functions: - Its coenzyme, TPP (codecarboxylase) is necessary for decarboxylation of -keto acids which includes: 1. Simple decarboxylation which needs TPP only as a coenzyme. This reaction occurs in yeast, O CO2 O TPP CH3 C COOH CH3 C H Pyruvate decarboxylase Acetaldehyde 13  2. Oxidative decarboxylation which needs TPP and other coenzymes, FAD, NAD, COA-SH and lipoic acid. A similar oxidative decarboxylation of - keto-glutaric acid and -ketocarboxylic acid derivatives of the branched chain amino acids requires TPP. dehydrogenase O CoA-SH O Lipoic acid CH3 C COOH CH3 C~ SCoA Pyruvate FAD Acetyl-CoA TPP + NAD NADH.H CO2 3. Thiamin pyrophosphate is also required for the pentose phosphate pathway. The red blood cell transketolase is the enzyme most commonly used for measuring thiamin status in the body. 4. It is necessary for optimal growth of infants and children. 5. It increases the activity of acetyl choline at nerve endings by inhibiting acetyl choline esterase enzyme. Deficiency: - Beriberi is a nutrition deficiency disease caused by carbohydrate-rich thiamin- low diets, i.e., polished rice or highly refined foods such as sugar and white flour. Certain raw fishes contain a heat labile enzyme thiaminase that destroys thiamin, but this is not considered to be critical in human nutrition. - Deficiency of vitamin B1 and TPP leads to: - Accumulation of pyruvic acid in blood due decreased activity of oxidative decarboxylation, and increase of lactic acid in blood. - Appearance of methyl glyoxal in urine due to decreased activity of glyoxalse enzyme catalyzing the conversion of methyl glyoxal to lactic in the liver. - Accumulation of pentose sugars in red blood cells as a result of decreased transketolase reaction. Manifestations: Beriberi: - There are two forms of beriberi: I. Wet beriberi: Affects mainly the cardiovascular system and it is characterized by extensive edema and high output cardiac failure. 14 II. Dry beriberi: Affects mainly the nervous system and it is associated with: Polyneuritis (Inflammation of peripheral nerves), hyperesthesia, and muscle wasting and loss of weight. Requirements: - Requirement depends on carbohydrates content of the diet. 1.5 mg/day for adults and 0.4 mg/day of children. Riboflavin (Vitamin B2) Sources: - Riboflavin is synthesized by plants and microorganisms but not by mammals. Yeast, whole grain, milk, liver and kidney are good sources of the vitamin. Absorption and Metabolism: - In the intestinal mucosal cells, flavin mononucleotide (FMN) is formed by ATP- dependent phosphorylation of riboflavin catalyzed by flavokinase enzyme. This enzyme is competitively inhibited by chloropromazine drug. Whereas, FAD (the predominant tissue form) is synthesized by a further reaction with ATP in which the AMP moiety of ATP is transferred to FMN. - Both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are active forms of vitamin B2. They are absorbed in the intestine and bind to albumin for their transportation in the blood. Functions: - Riboflavin is converted to FMN and FAD coenzymes which act as hydrogen carriers for certain enzymes called flavoproteins. - Flavoprotein enzymes are wide spread and involved in oxidation-reduction reaction in: 1. Carbohydrate metabolism. 2. Lipid metabolism. 3. Sterol biosynthesis. 4. Intermediary metabolism of amino acids, purine and pyrimidine. Deficiency: 1. In the mouth: Red lips and shiny-Angular stomatitis (inflammation of angles of mouth). Glossitis (inflammation of tongue). 15 2. In the skin: Seborrheic dermatitis (inflammation of sebaceous glands of skin). 3. Occular disturbance: Photophobia and viscularization of cornea. 4. Synthesis of proteins is impaired in severe riboflavin deficiency. Requirements: - Adults, 1.5 – 1.8 mg/day - Children, 0.6 mg/day. - Pregnancy, 2 mg/day - Lactation, 2.5 mg/day. Niacin (Nicotinic acid or Pellagra Preventing Factor, PPF) Sources: - Niacin can be made endogenously from the amino acid tryptophan. Each 60 mg trytpophan can be converted to one mg niacin. This conversion requires vitamin B6, thiamin and riboflavin as coenzymes. - Whole grain cereals, yeast, milk, leafy green vegetables and meat. Meat is rich in tryptophan, so it is important source of niacin. Corn is poor in both niacin and tryptophan. It contains niacin in the form of nicotinyl esters. The body cannot hydrolyze these esters during digestion. Functions: - Nicotinic acid in the form of nicotinamide enters in the formation of: 1. Coenzyme I (NAD): nicotinamide adenine dinucleotide 2. Coenzyme II (NADP): nicotinamide adenine dinucleotide phosphate. - These two coenzymes function as hydrogen carrier and they are essential for many biochemical oxidation-reduction reactions. These reactions are important in carbohydrate, protein and lipid metabolism. - The mechanism of oxidation - reduction involves a reversible addition of a hydride (H-) ion to the pyridine ring plus the generation of free hydrogen ion (H+), NAD + 2H  NADH.H+ - Reduction of NAD+ or NADP+ yields NADH + H+ or NADPH+ H+ which has strong absorption at 340 nm, a feature widely used in assays of pyridine nucleotide dependent enzymes. 16 3. Coenzyme III (NMN): nicotinamide mononucleolide which acts as a coenzyme for synthesis of taurine from cysteine which is used for the synthesis of bile acid (taurocholic acid). - Nicotinic acid and its amide are stimulant to C.N.S. Nicotinic acid is a vasodilator. Nicotinic acid only has been used therapeutically for lowering plasma cholesterol. Deficiency: - Deficiency of niacin interferes with biologic oxidation of carbohydrate, lipids and protein metabolism. It leads to a disease called Pellagra. Causes of deficiency: - Pellagra is usually associated with deficiency of niacin, tryptophan or pyridoxine. - Corn is deficient in both niacin and tryptophan. Thus, people who depend on corn as a major source of protein as some farmers develop pellagra. - In some diseases of tryptophan metabolism as: Hartnup disease and in carcinoid syndrome or after isoniazide therapy for T.B., pellagra can occur. Pellagra is characterized by:- 1. Dermatitis: The exposed skin becomes dry, rough and scaly with brown discoloration, glossitis and stomatitis are seen. 2. Diarrhea. 3. Dementia. Daily requirements: - Adults: 15 mg/day. Pregnant and lactating female: 20 mg/day. Pyridoxine (Vitamin B6 or Pyridoxal) Chemistry: - Vitamin B6 consists of 3 closely related pyridine derivatives: Pyridoxine, pyridoxal and pyridoxamine - Pyridoxal can be phosphorylated by pyridoxal kinase enzyme to pyridoxal phosphate which acts as a coenzyme. 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) 17