Niacin 3 pp - NIACIN Spring 2011 Reading Assignment 334-338...

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NIACIN Spring 2011 Reading Assignment 334-338 Reading Assignment 334 338 History • When corn was introduced in Europe by explorers from America – many people developed strange “disease” • severe skin lesions • Named pelle agra which in Italian means “rough skin” Niacin Deficiency - Advanced Pellagra
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Niacin: Pellagra • >100,000 people died of pellagra 1900-1940 Pellagra (dermatitis and oral lesions) Niacin Deficiency: Pellagra • Symptoms –Skin •Dark pigmentation •Burned appearance •Much more severe when exposed to light
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Niacin: Deficiency •Symptoms –“Four D’s” Dermatitis • Dermatitis • Diarrhea • Dementia •Death –Goldberger: infectious disease scientist •studied prisoners- used Niacin: Pellagra physicians wife and graduate students as experimental “animals” •proved not caused by infectious agent •associated with diet Animal Model for Pallegra • Dietary deficiency that led to “black tongue” in dogs – responded to nicotinic acid – proved cause and effect – fatal condition cured by niacin
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A) Lesions of hands in pellagra Severe Niacin Deficiency B) Same patient after treatment with nicotinamide Bioavailability of Niacin: Key to Deficiency – Corn Diets • Some corn-based diets associated with pallegra Niacin content not extremely low – Niacin content not extremely low – Exposure to high pH key to release bound niacin – Diets usually low in protein • Tryptophan an inefficient precursor of niacin Niacin: Food Sources • Most concentrated: meat • Poultry, fish, legumes • Tryptophan – Milk – Eggs – Peanut butter • “Enriched” flour and grain
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Niacin: Chemical Structures Niacin: Chemical Properties • Niacin –Nicotinic acid –Nicotinamide –NAD –NADP Niacin Coenzyme Structure
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Conversion Tryptophan to Niacin Niacin: Niacin Equivalents (NE) •P ro te in – 1% tryptophan – 60 gm protein = ~ 600 mg tryptophan (1 gm protein provides ~10 mg tryptophan) • Niacin equivalents – Preformed niacin + niacin from tryptophan •Conve rs ion 60 mg tryptophan 1 mg niacin = 1 NE
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Low Tryptophan Diets • Research data suggest that humans may not utilize tryptophan for niacin when tryptophan levels are low • Protein needs higher priority than conversion to niacin Niacin: Absorption & Metabolism • Absorption –Stomach: passive diffusion –Small intestine: facilitative diffusion; active transport, and passive diffusion •More rapid than in the stomach Inside Enterocyte • Nicotinamide may be converted to NAD or released into portal circulation • Nicotinic acid primarily converted to NAD • Nicotinamide released enzymatically from NAD • Nicotinamide primary circulating form
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•Excretion –methyl nicotinamide Niacin: Absorption & Metabolism methyl nicotinamide •High levels of niacin can stress methyl donor status Niacin: Functions • Electron acceptor/hydrogen donor –Nicotinamide adenine dinucleotide (NAD)
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This note was uploaded on 12/09/2011 for the course HUN 4445 taught by Professor Sitren during the Spring '08 term at University of Florida.

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Niacin 3 pp - NIACIN Spring 2011 Reading Assignment 334-338...

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