Thiamin (B1)

Question 1

Free Thiamin

Answer 1

• non coenzyme form
• absorbed in the small intestine (into enterocytes) and transported to the liver/tissues
• structure: pyrimidine ring & thiazole

Question 2

Coenzyme Form of Thiamin

Answer 2

• Thiamine Pyrophosphate (TPP)
• can be made into many cells throughout the body for energy & cell transformation
• other forms: thiamin monophosphate (TMP); thiamin triphosphate (TTP)

Question 3

Sources of Thiamin
(free and coenzyme forms)

Answer 3

• widely distributed in foods: meats, legumes, enriched grains
• free form = plants
• coenzyme form (TDP/TPP) = animals

Question 4

thiamin’s reaction to heat

Answer 4

unstable in >100 C temperatures

Question 5

Anti-thiamin Factors (foods)

Answer 5

• thiaminases (raw fish, bacteria)
• sulfites (food preservation)
• polyhydroxy phenols (caffeic/tannic acids in teas/berries)
• ethanol (alcohol)

Question 6

food enhancers that help with the absorption of thiamin

Answer 6

vitamin C and citric acid

Question 7

how is the coenzyme form of thiamin converted to its free form?

Answer 7

TDP and other phosphorylated thiamin are converted to free thiamin via intestinal phosphatases

Question 8

where is free thiamin absorbed into after being converted from its coenzyme form?

Answer 8

intestinal cells in the small intestine

Question 9

where is free thiamin transported after being absorbed into the intestinal cells?

Answer 9

transported in blood and taken up by the liver

Question 10

how is thiamin converted to its coenzyme form TDP?

Answer 10

by thiamin pyrophosphokinase via ATP-dependent reactions

Question 11

what are the functions of thiamin?

specify if it is a coenzyme or free form role

Answer 11

• energy transformation (coenzyme role)
• synthesis of pentose and NADPH (coenzyme role)
• membrane/nerve conduction to regulate sodium channels (non-coenzyme form)

Question 12

what is the mechanism of action of coenzyme TDP?

Answer 12

• oxidative decarboxylation
• transferring 2-carbon unit
• energy transformation-TDP-dependent decarboxylation of alpha-keto acids
• coenzyme for transketolase (for synthesis of pentose and NADPH)

Question 13

importance of pyruvate dehydrogenase complex

Answer 13

important for energy transformation and generation of ATP

Question 14

what are the 4 vitamins involved in pyruvate dehydrogenase complex?

Answer 14

TDP, coenzyme A (CoA-SH), FAD, and NAD

Question 15

Thiamin Deficiency(s)

Answer 15

• Berberi “weakness”
• Alcoholism (Wernicke’s encephalopathy)
• elderly population having diseases that impair absorption (late stages of cancer, inflammatory bowel disease)

Question 16

Berberi

Answer 16

• “weakness”; associated with loss of appetite
• dry berberi: muscle weakness, neurological symptoms
• wet berberi: cardiovascular symptoms

Question 17

why is alcoholism a thiamin deficiency?

Answer 17

caused by decreased food absorption, liver damage, and decreased thiamine absorbance

Question 18

what are the biochemical symptoms of thiamin deficiency?

Answer 18

high levels of pyruvate and a-ketoglutarate in the blood

Question 19

how can thiamin deficiency symptoms be attenuated?

Answer 19

100 mg therapeutic doses of thiamin

Question 20

what are the therapeutic uses of thiamin?

Answer 20

• maple syrup urine disease (MSUD)
• lactic acidosis

Question 21

Maple Syrup Urine Disease (MSUD)

Answer 21

• 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)

Question 22

Lactic Acidosis

Answer 22

• 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

Question 23

what physiological process is thiamin involved in?

Answer 23

• TCA cycle
• glycolysis
• amino acid metabolism
• pentose phosphate pathway