Vitamin A PDF

# Vitamin A ## Dr Kavindya Fernando ## 2 Contents - Vitamin classification - Structure of vitamin A - Sources of vitamin A - Absorption and transport - Mechanism of action - Functions & body requirement ## 3 Vitamin classification **Vitamins** - Water soluble - Non-B complex - Vita...

# Vitamin A ## Dr Kavindya Fernando ## 2 Contents - Vitamin classification - Structure of vitamin A - Sources of vitamin A - Absorption and transport - Mechanism of action - Functions & body requirement ## 3 Vitamin classification **Vitamins** - Water soluble - Non-B complex - Vitamin C - B complex - Thiamin (B1) - Riboflavin (B2) - Niacin (B3) - Biotin - Pantothenic acid - Folic acid - Vitamin B12 - Fat soluble - Vitamin A - Vitamin D - Vitamin E - Vitamin K - Other - Pyridoxine (Vitamin B6) ## 4 Vitamin A ## 5 Structure of Vitamin A - Vitamin A - fat soluble vitamin - Retinoids includes - natural & synthetic forms of vitamin A - that may or may not show vitamin A activity **Structure** - Retinol - Retinal - Retinoic acid - β-Carotene ## 6 Structure of Vitamin A - Retinol - Found in animal tissue, as retinyl ester - Primary alcohol, - containing a β-ionone ring, - with an unsaturated side chain - β-carotene - Found in plant food - Oxidatively cleaved in the intestine to yield two molecules of retinal - In human this conversion is inefficient - Vit A activity of β-carotene is only about 1/12 that of retinol ## 7 Structure of Vitamin A - Retinol - Oxidation - Retinal (Aldehyde) - Retinal - Aldehyde derived from the oxidation of retinol - Retinal and retinol can readily be interconverted - Retinoic acid - Oxidation - Retinoic acid (Acid) - Acid derived from the oxidation of retinal - Cannot be reduced in the body ## 8 Sources of Vitamin A - Preformed vitamin A - Liver, kidney, cream, butter and egg yolk - Beta carotene - precursor of vitamin A - Yellow & dark green vegetables & fruits ## 9 Absorption and transport of vitamin A - Retinyl esters - Hydrolysed - Fatty acids - Retinol - β-Carotene - Retinal - Enterocyte - Fatty acyl CoA - Re-esterification to long chain fatty acid - Retinyl esters - Secreted as a component of chylomicrons lymph - Chylomicron remnants ##10 Absorption and transport of vitamin A ...cnt - Chylomicron remnants - Retinyl palmitate - All-trans-Retinol - Retinol - RBP - Retinol-RBP complex - Retinol - RBP ##11 Mechanism of action of vitamin A - Retinol - Oxidation - Retinoic acid - Control the production of specific proteins - To regulate retinoid-specific RNA synthesis - Specific receptor proteins - Activated retinoic acid-receptor complex - Interact with nuclear chromatin - Eg: retinoids control the expression of the gene of keratin in most epithelial tissues of the body - Epithelial cell ## 12 Mechanism of action of vitamin A - RBP - Plasma retinol-RBP - Retinol - Oxidation - Retinoic acid - Retinoic acid - Inactivate receptor - Activated receptor complex - Cytasol - Epithelial cell - nucleus - gene - mRNA - Cellular differentiation - mRNA - Specific proteins ## 13 Functions of Vitamin A - Retinyl esters - Retinol - Retinal - All-trans retinoic acid (tretinoin) - 13-cis retinoic acid (isotretinoin) - Carotenes - As an therapeutic agent - Psoriasis Tx - Promyelocytic leukemia tx - Severe acne Tx - Vision - Reproduction - Growth - Epithelial tissue differentiation ## 14 Functions of Vitamin A - Retinol- RBP complex - RBP - All-trans-Retinol - esterified - All-trans-retinyl esters - isomerized - 11-cis Retinol - reduced - 11-cis Retinal - oxidized - Opsin - Rhodopsin - Opsin - All-trans-Retinal - When exposed to light - Bleaching - Retinal rod/cone ## 15 Requirement of vitamin A - Measured with - retinol activity equivalents (RAE) - 900 RAE daily → adult male - 700 RAE daily → adult female - 1 RAE equals to - 1 mg of retinol - 12 mg of β carotene - 24mg of other carotinoids ## 16 In Summary - Vitamin A is a fat soluble vitamin - There are 4 forms of vitamin A - Retinol, Retinal, Retinoic acid & β-carotene - They act by controlling the production of specific proteins - It is important in maintaining vision, growth, reproduction & epithelial differentiation - It has a therapeutic importance in the treatment of psoriasis, promyelocytic leukemia and severe acne ## 17 Thank You!