Thiamin Flashcards
What is Thiamin also known as?
Vitamin B1
What are the primary roles of Thiamin in the body?
1) Energy metabolism
2)nervous system function
3) biosynthesis of lipids
what are properties of thiamin?
1) water soluble
2) not stable under UV light, moisture or alkaline solutions
What is the biologically active form of Thiamin? why is this important?
Thiamin Pyrophosphate (TPP)
-Thiamin is not involved in rxn’s on its own, it must be in its active form
what is the active site of thiamin?
Thiazole ring
What is the coenzyme of Thiamin? what other forms can it exist in?
Thiamin Pyrophosphate (TPP)
-Thiamin Monophosphate (TMP)
- Thiamin Triphosphate (TTP)
What is Thiamin’s role in energy production? where is it found?
Coenzyme in oxidative decarboxylation of alpha-keto acids
PDH, αKG-DH, branched chain αKetoacid-DH
what products does TPP form in branched chain αKetoacid-DH?
acetyl coA and succinyl coA
How is Thiamin absorbed in the body? what transporters are used? what types of absorption?
1) passive diffusion when intake is high
2) mediated transport through SLC19A2/3 transoprters when intake is low
How is thiamin absorption regulated?
TPP is dephosphorylated by phosphatases (converted to thiamin) in order to be absorbed and rephosphorylated to “trap” inside the cell for storage (stored as TPP)
What are the main storage sites for Thiamin in the body? how much is stored? what does this mean for nutritional requirements?
1) Skeletal muscle, Liver, Kidneys, Nervous tissues
2) small amount stored (~30mg)
3) thiamin must be eaten on a regular basis to avoid deficiency
-high metabolic rate + low storage
How is thiamin excreted?
1) reabsorbed by renal brush border
2) excreted rapidly if consumed in excess
What are dietary sources of Thiamin?
synthesized by plants + micro organisms * Whole grains
* Legumes
* Nuts
* Organ meats
* milk
* eggs
What are some factors that destroy Thiamin?
- Boiling/blanching
- Baking soda
- UV light exposure
- Thiaminases
*sulfite
*heat stable antagonist
what is the RDA for thiamin? include units. what is the UL?
RDA = no less than 1mg
-no UL set
What are the symptoms of Wet Beriberi?
Cardiovascular symptoms (edema, heart failure)
What is a key method to assess Thiamin status?
1) Transketolase Activity (TPP Effect)
2) urinary excretion
3) pyruvic acid / alpha-KG in blood (not ideal)
what is the TPP Effect in regards to thiamin status?
A way of measuring thiamin status that looks at transketolase activity (best measure)
-TPP added and if activity increases, it is asssumed thiamin is low
what factors increase thiamin deficiency risks?
1) reduced food intake
2) increased metabolic rate (high CHO diet, pregnancy, physical activity)
3) increased depletion (diarrhea)
4) decreased absorption (malnutrition, disease)
What impact does alcoholism have on thiamin status?
excess alcohol intake increases caloric intake:
1) interferes with thiamin absoprtion
2) inhibits TPP activation
what physiological effects do you expect from thiamin deficiency?
1) decreased urinary excretion of thiamin
2) decreased erythrocyte transketolase activity
-symptoms: tired, depressed, weight loss, nausea, vomiting
what causes beriberi? What is the difference between wet and dry beriberi?
Severe thiamin deficiency
Wet (CV): severe physical exertion + high CHO intake
-lactic acidosis
-increased cardiac output
-myocardial exhaustion
Dry (neuritic): inactivity + caloric restriction
-peripheral neuropathy, weakness
-myelin degeneration
What is Wernicke? what causes it?
neurological disorder caused by severe thiamin deficiency (alcoholism / beriberi)
-double vision
-rapid eye movement
-ataxia
what is Korsakoff? what causes it?
phychosis caused by sever thiamin deficiency (alcoholism / beriberi)
- abnormal mental state
-memory loss
-confusion
