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Thiamin, Riboflavin, Niacin

Terms in this set (45)

Functions of Thiamin?
-energy transformation
-coenzyme for transketolase in liver & RBCs
-nervous system function (non-coenzyme role here)
Thiamin dietary sources?
-meat, legumes and green veggies, whole (unrefined), enriched or fortified grains, yeast, wheat germ,

-milk & fruit POOR SOURCES
What form of Thiamin is in plants/animals?
-free in plants but mostly TDP in animal products
What form of Thiamin is in supplements?
Thiamin-HCl or thiamin nitrate
How do we lose Thiamin in foods?
-thiaminases
-polyhydroxyphenols
-prolonged exposure to high temps
-exposure to alkaline aqueous solutions
-moves into water during cooking
-lost during processing of grains
-exposure to sulfites
How can we prevent thiamin losses?
...
How is thiamin digested?
-intestinal phosphatases hydrolyze the posphates from TPP prior to absorption
How is thiamin absorbed?
-free thiamin: absorbed in jejunum & duodenum
-phosphorylated in jejunal mucosal cells=TTP
-enters portal system as free thiamin
Active carrier mediated thiamin mediated at what concentration?
-low concentration, Na+ dependent
Thiamin: passive diffusion
higher concentrations
How is thiamin transported?
-most (90%) of thiamin in blood in RBC as TPP
-some free thiamin bound to albumin in blood
How is thiamin taken up by the cells?
-from blood into cells by active transport
-since thiamin activity is in mitochondria, must cross those membranes using a special transporter
How is thiamin stored?
-little real storage, most is used
-most stored in muscle compared to other bc they're functionable
How is thiamin excreted?
-in urine, metabolites
RDA/UL for thiamin?
-men: 1.2 mg/d
-women: 1.1 mg/d
NO UL
Erythrocyte transketolase activity
hydrolyze RBCs and measure transketolase activity (early indicator)
-can also stimulate activity by adding thiamin
why is deficiency possible in thiamin? what's considered deficient?
little stores & rapid turnover
-14 mg/d thiamin=defiecient
Signs and symptoms of thiamin deficiency?
-loss of appetite, cardiac hypertrophy & altered HR, neurologic involvement (irritability, confusion, apathy)
-increased blood levels of pyruvate, aKG, decreased RBC transketolase activity
What is dry Beriberi?
-thiamin deficient disease
-dry: older adults, chronic low thiamin and energy intakes coupled with high CHO diet
-muscle weakness and wasting, peripheral neuropathy
what is wet Beriberi?
-thiamin deficient disease
- higher physical exertion, low thiamin, high CHO intake
-edema, extensive CV involvement, right sided heart failure leads to respiratory involvement and edema
what is acute beriberi?
-thiamin deficient disease
- breast fed infants of thiamin deficient mothers
what is wernicke-korsakoff syndrome?
-brain disorder due to thiamin deficiency
-common in alcoholics bc decreased intake of thiamin due to dec food intake
-inc requirement with liver damage
-dec thiamin absorption
-malabsorption issue, malnutrition also at risk
Functions of riboflavin?
-FMN & FAD are cofactors in oxidation-reduction reactions
what are enzymes called that require FMN & FAD?
flavoproteins
what is FMN useful for?
-vitamin B6 metabolism
-component of complex I in ETC
what is FAD useful for?
-tightly bound cofactor for succinate DH, fatty acyl CoA DH, mitochondrial glycerol phosphate DH
-component of PDH, a-KGDH, BCKADH
-cofactor for glutathione reductase
-cofactor in synthesis of active form of folate
dietary sources of riboflavin?
-wide variety, esp animal origin
-milk/dairy=very good
-legumes, green veggies
-grains;whole and enriched
-light sensitive
what's the bioavailbility of riboflavin?
-well absorbed, 95%
-may occur as free riboflavin (milk, eggs), but mostly as FMN and FAD either loosely or covalently attached to proteins
-alcohol dec. absorption
How is riboflavin digested?
-hydrolyzed from proteins by gastric HCl and absorbed
-FAD ---> FMN ---> riboflavin ultimately absorbed
how is riboflavin absorbed?
-saturable Na+ dependent transport process (facilitated diffusion)
-simple diffusion at high intakes
-inside enterocyte, phosphorylated by flavokinase (traps it in) but then needs to be dephosphorylated before leaving
how is riboflavin transported?
- in blood, bound to albumin or globulins
where is riboflavin stored?
-liver, heart, kidney
-stored as FMN or FAD
how is riboflavin excreted?
-as metabolites in urine
RDA riboflavin?
-Men: 1.3 mg
-Women: 1.1 mg
what does erythrocyte glutathione reductase activity do?
-reduces GSSG using NADPH and FAD is a cofactor in that reaction
riboflavin deficiency?
-no classic deficiency
-rarely occurs in isolation
-symptoms of chronic: cheilosis, angular stomatitis, glossitis, dermatitis, neuropathy, hyperemia and edema of oral cavity
-severe deficiency can result in disturbed vit B6 metabolism
who's at risk for riboflavin deficiency?
-people with congenital heart disease, some cancers, and excess alcohol intake bc of limited dietary intake and excess excretion
-in excretion of riboflavin in ppl with diabetes mellitus, trauma and stress, possibly oral contraceptive users
UL/toxicity of riboflavin?
-no UL
-low risk of toxicity
What are functions of Niacin?
- NAD & NADP as coenzymes
-mostly in oxidation-reduction reactions as they act as a hydrogen donor or electron acceptor
What is the role of NAD+/NADH?
electron transfer for ATP production (catabolic activities)
-glycolysis, TCA cycle, amino acid oxidation
-oxidative and decarboxylation of pyruvate and a-KG
-B-oxidation of FA, oxidation of ethanol
What is the role of NADP+/NADPH?
-more involved in biosynthesis (anabolic) acts as a reducing agent
-synthesis of fatty acids, cholesterol, steroid hormones
-DNA and folate derivative synthesis
What are sources of Niacin?
-meat, fish=best
-cereals, legumes, peanut butter
-enriched grain products
-coffee (produced), tea
-supplements as nicotinamide
what is niacin in animal foods?
-nicotinamide, NAD, NADP
what is niacin in plant foods?
-nicotinic acid
what happens when niacin (corn, wheat) is covalently bound to complex carbs or proteins?
-unavailable unless released
-chemical treatments such as lime water can release it
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