Fat-Soluble Vitamins - 2024-2025 Lecture Notes PDF

Biochemistry of Vitamins Fat- and Water-soluble Vitamins Learning Objectives: List the types and sources of the fat-soluble vitamins and describe their functions and the effect of their deficiencies. List the water-soluble vitamins and mention their sources,...

Biochemistry of Vitamins Fat- and Water-soluble Vitamins Learning Objectives: List the types and sources of the fat-soluble vitamins and describe their functions and the effect of their deficiencies. List the water-soluble vitamins and mention their sources, functions and the effect of their deficiencies Reference: 1. Harper’s Illustrated Biochemistry (31 ed., 2018 McGraw-Hill Education / Medical). 2. Lippincott Illustrated Reviews: Biochemistry, 8th Edition, Wolters Kluwer, 2021. Professor/ Abdel-Raheim M.A. Meki Dr/ Eman Magdy Radwan Sphinx University, Biochemistry Dept. Vitamins Definition: They are organic compounds that have the following characters: They must be supplied in the diet in the required very small amounts and deficiency of any vitamin in the body results in a specific nutrition deficiency disease. They are essential for normal health and growth since they are not synthesized in human body. They do not enter in tissue structure as carbohydrates, fats and proteins. They are not oxidized for energy production as carbohydrates, fats and proteins (Yield no energy, but facilitate energy-yielding chemical reactions) They participate in many chemical reactions in the body as coenzymes.  Classification: Vitamins can be classified according to their solubility into two main groups: I- Fat-soluble vitamins. (ADEK) II- Water-soluble vitamins.  Vitamin A (Vision Vitamin) (retinol, Anti-night blindness, Anti-Xerophthalmia vitamin) Chemistry: The active forms of vitamin A are retinol, retinal (retinaldehyde), and retinoic acid. Retinol Retinal Retinoic Acid  Sources Vitamin A is available to the human either in the form of: 1. Active vitamin A (retinol and retinyl esters) (animal origin). It is present in meat, liver, milk, butter, egg yolk and fish liver oils as retinol esters. 2. Provitamin A (Plant origin) ▪ Vitamin A precursors (provitamin) are called carotenoids or carotenes. ▪ They are called provitamins because they are transformed into vitamin A in the body. ▪ The most important carotenoids are: , , -carotenes. -carotene has the highest activity. ▪ All pigmented (particularly yellow) vegetables, fruits and dark-green leafy vegetables supply carotenes such as carrots, sweet potatoes, tomatoes and spinach.  Functions I- Role of vitamin A (Retinol-Retinal) in vision: The light receptors of the eye are the rod and cone cells in the retina. Rods are responsible for vision in dim light. They contain a photosensitive pigment called rhodopsin which is formed from 11-cis retinal and opsin (a simple protein). Cones are responsible for vision in bright light and contain a photosensitive pigment called iodopsin. II. Role of retinoic acid (hormone A): It works through a receptor-mediated mechanism. 1. It enters in glycoprotein and mucopolysaccharides synthesis. 2. It is required for the synthesis of the iron-transport protein transferrin. 3. It is responsible for the normal structure and normal function of the adrenal gland, which secretes glucocorticoids. 4. It accelerates the normal growth of bones and teeth. 5. It has a role in reproduction in male and female. 6. It is a potent anticancer agent. 7. It is immunostimulant. III. Antioxidant activity: The antioxidant properties of vitamin A partially is also a reason for its anticancer activity  Deficiency 1. In the eye: Night blindness (impaired dark adaptation). Xerophthalmia: cornea becomes dry and rough. 2. Growth retardation 3. Increased liability to cancer and anemia. 4. The skin becomes rough (xeroderma). 5. Roughness of mucous membrane of the urinary, genital, gastrointestinal and the respiratory tracts leading to repeated infections.  Vitamin D (calciferol) Sunshine Vitamin There are two types of vitamin D: Vitamin D2 derived from ergosterol present in plants, and Vitamin D3 derived from cholesterol in animals. Sources: I. Provitamins 1. 7-dehydrocholesterol in animals and man only It is formed in intestinal mucosa from cholesterol then passes to the skin where UV rays of the sun convert it into cholecalciferol (Vitamin D3). This demonstrates the importance of outdoor exposure of infants to sunlight. 2. Ergosterol: it is widely distributed in plants gives ergocalciferol (Vitamin D2). II- Vitamin D: The richest source of vitamin D3 is fish liver oils, e.g. cod and shark liver oil. Egg yolk, liver, butter and milk are poor sources. Storage: Vitamin D is mainly stored in liver  in intestinal mucosa Activation of vitamin D3 (synthesis of calcitriol) Parathyroid hormone (PTH) PTH In the liver, vitamin D3 is UV rays hydroxylated by 25-hydroxylase to 25-(OH)-D3 that passes to the 1 a-Hydroxylase circulation. In kidney, 25-(OH)-D3 is further hydroxylated to 1,25- dihydroxy-D3 (Calcitriol) by 1- hydroxylase enzyme 25-Hydroxylase Parathyroid hormone (PTH) Calcitriol (1,25-dihydroxy- cholecalciferol, 1,25 DHCC)  Regulation of calcitriol synthesis: 1. Parathyroid hormone (PTH): PTH activates 1-hydroxylase enzyme in kidney so increases calcitriol synthesis. 2. Blood calcium level: the decrease in blood calcium level will stimulate parathyroid gland to secrete PTH, which activates 1-hydroxylase and increase calcitriol synthesis. 3. Blood phosphate level: the decrease in blood phosphate level will directly stimulate calcitriol synthesis. 4. Blood calcitriol level: the increase in blood calcitriol level will inhibit 1- hydroxylase enzyme (feedback inhibition).  Functions of active vitamin D (Calcitriol) Active vitamin D functions as a hormone more than as a vitamin. The target tissues include the intestine, bone and kidney. In the intestine: It increases absorption of calcium and phosphate from intestine. In the bone: It increases demineralization of bone In the kidney: It enhances the reabsorption of calcium and phosphate. Deficiency Vitamin D deficiency causes rickets in young children and osteomalacia in adults. The causes of Deficiency include: Decrease intake of vitamin D. Minimal exposure to sunlight. Diseases causing fat malabsorption Severe liver and kidney diseases (failure of activation of vitamin D).  Vitamin D toxicity (Hypervitaminosis) Usually occurs due to self medication. It results in hypercalcemia that leads to abnormal calcification in soft tissues like Kidney leading to kidney stones and Blood vessels leading to hypertension.  Vitamin E (Tocopherols, anti-sterility vitamin) Chemistry: Vitamin E or tocopherols are organic compounds; There are four types of tocopherols: alpha, beta, gamma and delta-Tocopherols. Alpha-Tocopherol is the most potent of the tocopherols. Sources Vegetable oils, e.g., wheat germ, cotton seed, olive and coconut oils. Small amounts are present in liver, egg yolk, milk and colostrum. Functions 1. It is a naturally occurring antioxidant and it prevents hemolytic anemia 2. It has anti-sterility effect, especially in animals. Also, it is essential for continuation of pregnancy in animals.  Vitamin K (Anti-hemorrhagic vitamin) Sources Two types of vitamin K exist: Naturally occurring vitamin K (fat soluble): Vitamin K1 is the major form of vitamin K in plants. Vitamin K1 is present in spinach, cauliflower and cabbage. Vitamin K2 is formed inside the intestine by intestinal bacteria. Functions I- Vitamin K is antihemorrhagic II- Activation of osteocalcin in bones (calcium-binding protein)  Deficiency Causes of Deficiency Deficient intestinal bacteria as in long antibiotic use and in newly born infants. Fat malabsorption syndromes and liver diseases. Long use of dicumarol. This anticoagulant drug antagonizes vitamin K effect. N.B. Deficiency of vitamin K does not occur as a result of deficient intake because it is widely distributed in foods and it is also synthesized by bacteria in large intestine. Effects of Deficiency Hemorrhagic manifestation in skin and mucous membranes. Prolonged clotting time.  Questions Fat-soluble vitamins Write "T" for true or "F" for false for the following: 1. Vitamins are present in normal food in large concentrations ( ). 2. Vitamins do not enter in tissue structure as carbohydrates, fats and proteins( ). 3. Deficiency of any vitamin in the body results in a nutrition deficiency disease ( ). 4. The active forms of vitamin A are retinol, retinal and retinoic acid ( ). 5. -carotene is a provitamin A ( ). 6. Rods are responsible for vision in dim light and they contain a photosensitive pigment called rhodopsin. ( ) 7. Cones are responsible for vision in bright ( ). 8. Rhodopsin is formed from protein called 11-trans retinal and opsin protein ( ). 9. Retinoic acid participates in glycoprotein synthesis ( ) MCQs: 1- Which of the following is anti-night blindness, anti-Xerophthalmia vitamin? a. Vitamin A b. Vitamin E c. Vitamin D d. Vitamin K 2- All of the following regulates calcitriol synthesis EXCEPT: a. Parathyroid hormone c. Blood calcium level; b. Blood phosphate level d. blood glucose level 3- Deficiency of which one of the following causes rickets in young children and osteomalacia in adults? a. Vitamin A b. Vitamin E c. Vitamin D d. Vitamin K 4- Which of the following is anti-sterility vitamin? a. Vitamin A b. Vitamin E c. Vitamin D d. Vitamin K 5- Which one of the following is anti-hemorrhagic vitamin? a. Vitamin A b. Vitamin E c. Vitamin D d. Vitamin K