Thiamin (B1) Flashcards
Free Thiamin
- non coenzyme form
- absorbed in the small intestine (into enterocytes) and transported to the liver/tissues
- structure: pyrimidine ring & thiazole
Coenzyme Form of Thiamin
- Thiamine Pyrophosphate (TPP)
- can be made into many cells throughout the body for energy & cell transformation
- other forms: thiamin monophosphate (TMP); thiamin triphosphate (TTP)
Sources of Thiamin
(free and coenzyme forms)
- widely distributed in foods: meats, legumes, enriched grains
- free form = plants
- coenzyme form (TDP/TPP) = animals
thiamin’s reaction to heat
unstable in >100 C temperatures
Anti-thiamin Factors (foods)
- thiaminases (raw fish, bacteria)
- sulfites (food preservation)
- polyhydroxy phenols (caffeic/tannic acids in teas/berries)
- ethanol (alcohol)
food enhancers that help with the absorption of thiamin
vitamin C and citric acid
how is the coenzyme form of thiamin converted to its free form?
TDP and other phosphorylated thiamin are converted to free thiamin via intestinal phosphatases
where is free thiamin absorbed into after being converted from its coenzyme form?
intestinal cells in the small intestine
where is free thiamin transported after being absorbed into the intestinal cells?
transported in blood and taken up by the liver
how is thiamin converted to its coenzyme form TDP?
by thiamin pyrophosphokinase via ATP-dependent reactions
what are the functions of thiamin?
specify if it is a coenzyme or free form role
- energy transformation (coenzyme role)
- synthesis of pentose and NADPH (coenzyme role)
- membrane/nerve conduction to regulate sodium channels (non-coenzyme form)
what is the mechanism of action of coenzyme TDP?
- oxidative decarboxylation
- transferring 2-carbon unit
- energy transformation-TDP-dependent decarboxylation of alpha-keto acids
- coenzyme for transketolase (for synthesis of pentose and NADPH)
importance of pyruvate dehydrogenase complex
important for energy transformation and generation of ATP
what are the 4 vitamins involved in pyruvate dehydrogenase complex?
TDP, coenzyme A (CoA-SH), FAD, and NAD
Thiamin Deficiency(s)
- Berberi “weakness”
- Alcoholism (Wernicke’s encephalopathy)
- elderly population having diseases that impair absorption (late stages of cancer, inflammatory bowel disease)
Berberi
- “weakness”; associated with loss of appetite
- dry berberi: muscle weakness, neurological symptoms
- wet berberi: cardiovascular symptoms
why is alcoholism a thiamin deficiency?
caused by decreased food absorption, liver damage, and decreased thiamine absorbance
what are the biochemical symptoms of thiamin deficiency?
high levels of pyruvate and a-ketoglutarate in the blood
how can thiamin deficiency symptoms be attenuated?
100 mg therapeutic doses of thiamin
what are the therapeutic uses of thiamin?
- maple syrup urine disease (MSUD)
- lactic acidosis
Maple Syrup Urine Disease (MSUD)
- genetic disease, caused by absent or insufficient amounts of branched-chain a-keto acid dehydrogenase (thiamin dependent)
- causes accumulation of branch-chain aa and metabolites (urine smell and color becomes syrup like)
Lactic Acidosis
- a condition caused by the buildup of lactic acid in the body, leading to acidification of the blood
- thiamin-responsive lactic acidosis: high doses of thiamin increase hepatic pyruvate dehydrogenases activity and decrease pyruvate conversion to lactic acid
what physiological process is thiamin involved in?
- TCA cycle
- glycolysis
- amino acid metabolism
- pentose phosphate pathway
