Nutrition Lecture 8: Thiamin Flashcards
What are rich sources of thiamin?
Whole grains, pork, potato skin, fortified wheat-bix and soy milk
What foods cause thiamin losses?
Refining grains (e.g. rice, wheat)
What does a ‘thiamin antagonist’ mean?
Substances that interfere with the absorption of thiamin
What are examples of thiamin antagonists?
- Sulfites (to preserve colour of meat)
- Cyanogenic glycosides (in cassava)
- Tannins (tea, coffee, betel nuts)
What does thiaminases mean?
Enzymes that break down thiamin
What are examples of thiaminases?
- Plants such as bracken fern
- Some kaimoana including carp, mussels
- Insects including african silk worm larvae
What is betel nut chewing?
An important cultural practice in south and south-east Asia, Asia pacific
What are the effects of betel nut chewing?
Stimulant drug, addictive
What are the long term affects of betel nut chewing?
Discolouration of teeth and gums, mouth ulcers and oral cancers
Is thiamin water soluble?
Yes, water soluble, stable in acid solution and when frozen
What is thiamin unstable to?
Heat, UV light and alkali
What type of compound is thiamin?
Colourless organosulfur compound
What is the chemical structure of thiamin?
2 rings and a bridge in-between
What are the names of the two rings that make up thiamin?
Aminopyrimidine ring and Thiazolium ring
What is the name of the bridge that connects the two rings that make up thiamin?
Methylene bridge
How many phosphorylated forms of thiamin are there?
3
What are the three phosphorylated forms of thiamin
TMP, TPP, TTP
What does TMP stand for?
Thiamin monophosphate
What does TPP stand for?
Thiamin diphosphate
What does TTP stand for?
Thiamin triphosphate
What can all three forms of thiamin do?
All can be interconverted in tissues
What percent of total tissue thiamin is TMP, TPP and TTP?
- 80% is TPP
- 5-10% is TTP
- Remainder is TMP
What is the active form of Thiamin?
Thiamin pyrophosphate (TPP)
How is thiamin turned into its active form TPP?
By the enzyme thiamin diphosphotransferase
- This conversion involves the addition of two phosphate groups to thiamin, utilizing ATP in the process
Where does absorption of thiamin happen?
Mainly in the jejunum and ileum
What are the two main mechanisms of absorption of thiamin?
- Active carrier-mediated
- Passive diffusion
When does active-carrier mediated process happen?
When thiamin is at low concentrations
When does passive diffusion occur?
When thiamin is at high concentrations
What is thiamin released by in the upper small intestine?
By phosphatase and pyrophosphatase
What is bioavailability of thiamin affected by?
Little information, alcohol consumption, absorption increases when intakes are low
Where is approximately 90% of thiamin in blood found?
In erthrocytes
Where is majority of thiamin in plasma found?
Mainly bound to proteins, mainly albumin
How much thiamin can humans store?
approx. 25 to 30mg - can be depleted within 2-3 weeks
Where are the highest tissue concentrations of thiamin?
Skeletal muscle, heart, brain, liver and kidneys
What metabolisms are thiamin important for?
Energy metabolism and CHO metabolism (as TPP)
What is thiamin required for the activity of?
- Transketolase
- a-ketoglutarate dehydrogenase
- pyruvate dehydrogenase
- branched chain a-keto acid dehydrogenase
What is Transketolase?
Transketolase is an enzyme that plays a crucial role in the pentose phosphate pathway (PPP)
What is the pentose phosphate pathway (PPP)?
an alternative glucose metabolic pathway parallel to glycolysis, primarily involved in the production of NADPH and ribose-5-phosphate
What is a-ketoglutarate dehydrogenase?
an enzyme complex involved in the citric acid cycle
What is a-ketoglutarate dehydrogenase responsible for?
is responsible for the conversion of α-ketoglutarate to succinyl-CoA
What is pyruvate dehydrogenase?
pyruvate dehydrogenase is a crucial enzyme complex in cellular respiration
What is pyruvate dehydrogenase responsible for?
the conversion of pyruvate to acetyl-CoA to enter the CAC
What is the branched chain a-keto acid dehydrogenase?
complex that helps break down certain types of protein building blocks called branched-chain amino acids (BCAAs)
What is branched chain a-keto acid dehydrogenase responsible for?
forming Acetyl-CoA derivatives to enter the CAC
Consuming what causes risk factors for thiamin deficiency?
Thiamin antagonists, thiaminases
What disease states are risks for thiamin deficiency?
Alcoholism, bariatric surgery
What conditions does thiamin deficiency cause?
Beriberi, wernickes encephalopathy
What is beriberi?
“WET” Oedema and cardiac enlargement due to intense vasodilation from accumulation of pyruvate and lactate in blood and tissues
What is chronic beriberi?
“DRY” Affects peripheral nerves rather than the CV system
What is infantile beriberi?
Infants < 4 months with non-specific signs
What are the symptoms of infantile beriberi?
Irritability, refusal to breastfeed, vomiting, piercing cry, then signs of chronic heart failure
What is the most common form of thiamin deficiency in adults and older children?
Wernickes encephalopathy
What does wernickes encephalopathy affect?
Cerebellum and brain stem
What is the most severe form of wernickes encephalopathy?
Korsakoff’s psychosis
What is Korsakoff’s psychosis?
amnesia, confusion, confabulation, little working memory
What are symptoms of milk thiamin deficiency?
Sleeplessness, depression, weight loss, fatigue and irritability
What are stratagies to improve thiamin status?
Rice and wheat flour fortification with thiamin
What is the EAR for thiamin?
Men = 1.0mg/day
Women = 0.9mg/day
What is the RDI for thiamin?
Men = 1.0mg/day
Women = 1.1mg/day
What is the upper level of intake for thiamin?
No upper level of intake set
