L1-vitamins. fat soluble vitamins .pptx

L1-vitamins. fat soluble vitamins .pptx

1. V I TA M I N S Dr.Mohammed El Behery

2. DEFINITIONS: A. Vitamins: Are organic compounds most of them are not synthesized in the body and hence they must be supplied in the diet. 1. Essential for many biochemical reactions . 2. Many of them act as coenzymes . 3. They do not enter in the structure of the tissues. 4. They are needed in very small amounts. B. Provitamins: These are precursors of vitamins that converted into vitamins inside the body e.g. carotenes are provitamin A. C. Vitamers: These are different forms of one vitamin e.g. Vitamin D has 2 Vitamers : D 2 and D 3 .

3. Classification of Vitamins Vitamins are divided into two groups. fat soluble vitamins water soluble vitamins. Fat Soluble Vitamins They are vitamins A, D, E and K. They have some common properties. They are: Fat soluble. Require bile salts for absorption. Stored in liver. Stable to normal cooking conditions. Excreted in feces.

4. Water Soluble Vitamins: They are members of vitamin B complex and Vitamin C. Their common properties are Water solubility. Except Vitamin B 12 others are not stored. Unstable to normal cooking conditions. Excreted in urine.

5. FAT SOLUBLE VITAMINS The lipid-soluble vitamins are hydrophobic compounds that can be absorbed efficiently only when there is normal fat absorption. Like other lipids, they are transported in the blood in lipoproteins or attached to specific binding proteins . They have diverse functions—for example, vitamin A, vision, and cell differentiation; vitamin D, calcium and phosphate metabolism, and cell differentiation; vitamin E, antioxidant; and vitamin K, blood clotting.

6. FAT SOLUBLE VITAMINS VITAMIN A (retinoids): Chemistry They are retinol (Vitamin A alcohol), r et i na l ( V it a m i n A), aldehyde) and retinoic acid (Vitamin A acid). They are composed of β−ion o ne ring and side chain containing two isoprene units with four conjugated double bonds. Due to the presence of double bonds in isoprenoid side chain vitamin A exhibits cis-trans (geometric) isomerism and can be oxidized by air or light .

7. VITAMIN A Sources: 1. Animal sources: a) Liver, eggs and milk fat. b) Fish liver oils e.g. shark liver oil. 2. Plant sources: a) Vitamin A is present in plants as carotenes (= provitamin A). b) Carotenes (α, β and γ): 1) Present in carrots, potato, and tomatoes. 2) Carotenes are yellow pigments containing β -ionone ring at one end of the molecule. 3) Carotenes are converted into vitamin A (retinal) in the intestine .

8. Carotenes

9. Beta-Carotenes cleavage in intestinal mucosa

10. Note: Retinol dehydrogenase catalyzes the conversion of Retinol to Retinal (oxidation reaction). Retinoic acid: This is the acid derived from the oxidation of retinal. Retinoic acid cannot be reduced in the body, and, therefore, cannot give rise to either retinal or retinol .

11. Absorption, transport, and storage of vitamin A: Mechanism: I- Transport to the liver: 1. Diet contains retinol esters and β-Carotene . 2. Retinol esters are hydrolyzed into fatty acids and retinol that absorbed into intestinal mucosal cells . 3. β-Carotene is absorbed and converted into retinal (by β-Carotene dioxygenase enzyme). Retinal then converted into retinol. 4. I n the intestinal mucosal cells (contain absorptive cells (enterocytes)), retinol re-esterifies with fatty acid to form retinol ester . 5. Retinol esters are absorbed as a component of chylomicrons into the lymphatic system then, to general circulation (blood). Retinyl esters contained in chylomicron remnants are taken up by, and stored in, the liver .

12. Absorption, transport, and storage of vitamin A: II- Release from the liver: Metabolism: 1. When the body cells need vitamin A, stored retinol esters are hydrolyzed, and free retinol combines with a protein formed by the liver called retinol binding protein (RBP). RBP carries retinol to the retina and target cells . a) In retina , retinol is converted into retinal that essential for visions. b) In other target cells retinol is oxidized into retinoic acid which binds to nuclear receptors. Retinoic acid receptor complexes stimulate genes. This mode of action is similar to that of hormones.

13. Functions of vitamin A: 1. Vision: Retinal is essential for night vision . 2. Reproduction: Retinol is essential for reproduction. It supports sperm formation ( spermatogenesis ) in males and maintains fetus life in females. 3. Growth: Retinol is essential for normal growth and bone & teeth formation. 4. Maintenance of epithelial cells: Retinol and retinoic acid are essential for normal differentiation of epithelial cells. This is important for smoothness of skin and mucus membranes. Retinol is also essential for intact cornea (the outermost layer of your eye).

14. 5. Retinoic acid: is important for a } Glycoprotein synthesis. b) Phospholipids synthesis in the lungs (lung surfactant). c) Cell differentiation. 6. Antioxidant (anticancer) action: Retinoids and carotenoids (carotenes) act as antioxidants and protect tissues from toxic effect of some oxidants that may lead to epithelial tissue cancer .

15. Mechanism of Vision : a) The human retina contains two types of receptor cells for vision; cones and rods : 1) Cone cells are responsible for day vision and color. 2) Rod cells are responsible for vision in poor light e.g. at night. b) Vitamin A is a component of a visual pigment ( rhodopsin ) present in cones and rods. c) Visual ·cycle: 1) Rhodopsin consists of protein called opsin bound to 1 1-cis retinal (double bond at position 11 is in cis-form, while other double bonds are in trans-form). 2) When ·rhodopsin ·is ·exposed to light, 11 cis retinal is converted into all trans retinal (all double ·bonds are in trans-form) .

16. 3) All trans retinal changes the permeability of cell membrane of eye cells. This allows the -calcium ions to pass out of the cell membrane. This stimulates the nerve impulse in optic nerve. Thus ·the· brain perceives light.   4) For vision, rhodopsin must be regenerated. All· trans retinal are converted back to. 11-cis retinal.

17. Mechanism of Vision:

18. Deficiency of vitamin A: 1. Eye: a) Night blindness: impaired dark adaptation. b) Xero-ophthalmia: dryness and. roughness of cornea. 2. Growth retardation. 3. Skin and mucus membranes: Roughness of skin (goose skin). and mucus. membranes of different body systems e.g. urinary system. This leads to infection. Requirements of vitamin A: 5000 lU /day (1.5 mg) 1 IU =0.3 μg retinol; 1 μg retinol = 3.33 IU. Although, IU is sometimes still used in food labeling. In 2001, The USA/ Canadian Dietary Reference Values report introduced the term retinol activity equivalent (RAE) to take account of the incomplete absorption and metabolism of carotenoids; 1 RAE = 1 μg all-trans-retinol, 12 μg β-carotene, 24 μg α-carotene or β-cryptoxanthin. .

19. Excess vitamin A overdose or hypervitaminosis: Is Vitamin A Toxic in Excess? There is only a limited capacity to metabolize vitamin A, and excessive intakes lead to accumulation beyond the capacity of intracellular binding proteins ( RBP) ; unbound vitamin A causes: membrane lysis and tissue damage . Symptoms of toxicity affect the central nervous (CNS) system (headache, nausea, ataxia (movement impairment), and anorexia (loss of appetite) . I ncreased cerebrospinal fluid pressure ; the liver ( hepatomegaly with histological changes and hyperlipidemia ); calcium homeostasis ( thickening of the long bones , hypercalcemia, and calcification of soft tissues ); and the skin (excessive dryness) .

20. VITAMIN D Chemistry • The D vitamins are a group of sterols that have a hormone-like function It is also called sunshine vitamins. Its active forms are vitamin D2 (ergo calciferol) and vitamin D3 (cholecalciferol). Calcitriol is the most active form of vitamin D 3 that acts as steroid hormone. They are formed from provitamins which are sterols. Absorption, transport and storage • • Dietary vitamin D2 and vitamin D3 are absorbed in the small intestine in presence of bile salts. Absorbed Vit D is incorporated into chylomicrons and enters circulation via lymph. Vitamin D is stored in liver and adipose tissue. .

21. S o u r c e s 1. Sun rays generate the D vitamins from the provitamin ergosterol (in plants) and 7-dehydrocholesterol (in human and animals). 2. Liver, egg, yeast and fish liver oils are rich in vitamin D. Structure and activation of vitamin Dgroup : V itamin D2

22. V itamin D3

23. Functions of vitamin D: 1,25 dihydroxycholecalciferol (calcitriol) acts as a hormone. It has the following functions: 1. Normalization of serum calcium : Calcitriol maintains serum calcium level through its effects on intestine and kidneys. a) On Intestine : It stimulates synthesis of calcium binding protein (calbindin) that responsible for calcium absorption . b) On bones : It stimulates calcium reabsorption from bones. c) On kidneys : It increases renal tubular reabsorption of calcium.

24. 2. Mineralization of bones: a) In small doses : calcitriol helps bone mineralization by providing calcium and phosphate. b) In large doses : The reverse occurs, where calcium and phosphate move from bone to blood. 3. Absorption of phosphate from intestine . It increases also tubular reabsorption of phosphate. 4. Synthesis of osteocalcin: a) It is calcium binding protein present in bones. b) It is important for proper mineralization of bones. c) 1,25( diOH ) D3 stimulates its synthesis in the form of pro-osteocalcin. Note: 24, 25 dihydroxycholecalciferol is biologically inactive. .

25. 1. Hypocalcemia lead to release of parathyroid hormone and ctivation of renal 1 hydroxylase enzyme then, Conversion 25 (OH) D3 into 1,25 ( diOH ) D3 . 2. Hypophosphatemia lead to direct activation of renal 1 hydroxylase enzyme and conversion of 25 D3 into 1,25 ( diOH ) D3 . 3. In the intestinal mucosal cells , 1,25 ( diOH ) D3 is bound to specific cytoplasmic receptors forming a complex. This complex enters the nucleus, stimulating DNA to produce specific mRNA. This mRNA is responsible for synthesis of calcium binding protein ( calbindin ), which helps the absorption of calcium . 4. Absorption of phosphate is similar to the previous mechanism, but it occurs secondary to calcium absorption Mechanism of action of 1,25( diOH ) D3

26. Vit D deficiency symptoms 1. Rickets In children vitamin D deficiency causes rickets, results in soft bones. This leads to deformities in skull, chest, spine, legs and pelvis. 2. Osteomalacia Vitamin D deficiency causes osteomalacia in adults. It is seen in pregnant women and women with inappropriate diet. Skeletal pain is early sign. Deformities of ribs, spine, pelvis and legs are seen. 3. Osteoporosis Vitamin D deficiency causes osteoporosis in old people. Photolysis of provitamins dcreases with age. This and together with decreased sex hormone production may lead to deficiency. • Symptoms are bone pain and porous bones. Bone fractures are common.

27. • 4. Renal rickets: In chronic renal failure there is a deficient formation of active form of the vitamin D3 (decreased 1 hydroxylation of the vitamin) due to renal 1-hydroxylase is diminished or lost . This leads to renal rickets . Excess vitamin D (overdose or hypervitaminosis D): This leads to abnormal calcification of tissues and deposition of calcium and phosphate in different systems e.g. renal stones. Calcification  is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue, causing it to harden