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Vitamins - Water Soluble > Thiamin > Flashcards

Thiamin Flashcards

1
Q

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A

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2
Q

What B vitamin functions as a coenzyme as TPP?

A

thiamin

TPP = thiamin pyrophosphate (also called thiamin diphosphate TDP)

TPP is a required coenzyme for decarboxylation reactions by enzymes

  • pyruvate dehydrogenase
  • alpha-keto-glutarate
  • branched chain amino acid dehydrogenase

also TPP used as cofactor by transketolase in the pentose phosphate pathway

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3
Q

Name the condition that is associated with thiamin deficiency and alcoholism.

A

Wernicke’s encephalopathy or Wernicke-Korsakoff syndrome (also called cerebral beriberi)

a neuro-psychological complication is commonly found in these with alcoholism and AIDS

triad of signs

  • abnormal eye movements
  • stance and gait abnormalities
  • profound memory disorder ter Korsakoff’s amnesia

(Thiamin is vitamin B1 and beriberi starts with a B)

thiamin deficiency can result in beriberi which means weakness

in the US and Western countries thiamin deficiency is often associated with alcoholism

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4
Q

What are the essential roles of thiamin in the body? (3)

A
  1. energy transformation (pyruvate dehydrogenase)
  2. synthesis of pentoses and NADPH (transketolase)
  3. membrane and nerve conduction

Thiamin is involved in energy transformation as TPP a coenzyme required by pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Thiamin again as TPP is involved in the synthesis of pentoses and NAPDH as a cofactor for the enzyme transketolase in the Pentose Phosphate Pathway

Thiamin as TPP in nerve membranes is though to activate ion (specifically chloride) transport

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5
Q

Are flavoproteins involved in the synthesis of NADPH and pentoses?

Quiz ?: Which of the following is not a role of falvoproteins in intermediary metabolism?

A

Synthesis of pentoses and NADPH

thiamin in the form of TPP are required for these

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6
Q

What disease or condition results from an absence or insufficient activity of the branched-chain alpha-keto acid dehydrogenase enzyme complex?

A

Maple syrup urine disease

results from insufficient activity of branched chain alpha-keto acid dehydrogenase. Branched chain amino acids leucine, isoleucine and valine and their keto acids build up in blood and body fluids. This dehydrogenase requires thiamin in the form of TPP

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7
Q

The activity of erythrocyte transketolase is useful for assessing the adequacy of which vitamin?

A

thiamin

adequacy of thiamin nutriture can be assessed by measuring erythrocyte transketolase activity

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8
Q

Which B vitamins are necessary in the pyruvate dehydrogenase complex?

A 
thiamin (TPP)
riboflavin (FAD)
niacin (NAD)
pantothentic acid (CoA-SH)
Lipoic acid

pyruvate dehydrogenase is a multicomplex enzyme that catalyzes the conversion of pyruvate to acetyl CoA so it can enter the TCA cycle

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9
Q

What are the forms of thiamin?

A

Free thiamin - found in plant foods

Thiamin diphosphate (TDP) (also thiamin pyrophosphate (TPP))
found in animal foods (represents about 95% of thiamin in animal foods)
and generated in the body from free thiamin and phosphate

Thiamin monophosphate (TMP)
part of the remaining 5% of thiamin from animal foods
and can be generated in the body

Thiamin triphosphate (TTP)
also part of remaining 5% of thiamin from animal foods
and can be generated in the body

Supplemental forms:
thiamin hydrochloride
thiamin thiamin mononitrite salt

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10
Q

What is the RDA for thiamin?

A

Women 1.1 mg / day
Men 1.2 mg / day
Pregnant women 1.4 mg / day
Lactating women 1.5 mg / day

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11
Q

What is the UL for thiamin?

A

no UL has been established for thiamin.

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12
Q

What are some of the best food sources for thiamin?

A

It is widely distributed in food.

Pork is one of the best sources with 65 mg / 100g

mg/100g
Pork 0.65
Liver 0.26
Beef 0.07
soy beans (green, cooked) 0.26
lima beans 0.14
asparagus 0.16
potato, baked 0.12
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13
Q

What is the source of most of the thiamin in the American diet?

A

Fortified grain based foods.

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14
Q

Is thiamin affected by cooking or processing?

A

Yes. Thiamin can be destroyed by

heat
and
alkaline environment

cooking thiamin rich foods in water promotes loss of the vitamin

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15
Q

What are antithiamin factors?

A

Components of the diet that destroy or inactivate thiamin.

Thiaminases

  • found in raw fish
  • destroy thiamin
  • cooking inactivates them

Polyhydroxyphenols

  • found in coffee, tea, blueberries, brussels sprouts and red cabbage
  • inactivate thiamin by oxidation
  • vitamin C or citric acid can prevent oxidation of thiamin by acting as a reducing agent
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16
Q

What is the major form of thiamin in the body?

A

TDP thiamin diphophate

90% of thiamin in the blood is stored in blood cells as TDP

80% of the body’s total thiamin is in the form of TDP

17
Q

What are the major functions of thiamin in the body (3)?

A
  1. Energy generation - act as coenzyme for enzymes that perform
    oxidative decarboxylation reactions

Pyruvated dehydrogenase
Alpha-ketoglutarate dehydrogenase
Branched Chain Keto Acid dehydrogenase

  1. Act as cofactor for transketolase enzymes in the Pentose Phosphate Pathway for the production of pentoses and NADPH
  2. Membrane and nerve conduction
18
Q

What nutrients are required by the dehydrogenase enzyme complexes (pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, Branched chain keto acid dehydrogenase)?

A 
B1 - Thiamin as TDP
B2 - Riboflavin as FAD
B3 - Niacin as NAD
Pantothenic acid as coenzyme A
Lipoic acid
19
Q

What happens if the activity of pyruvate dehydrogenase is insufficient?

A

pyruvate levels increase

acetyl CoA is not produced

ATP can not be produced

20
Q

What happens in alpha-ketoglutarate dehydrogenase activity is deficient?

A

alpha-ketoglutarate levels increase

ATP can not be produced

21
Q

What is the inborn error of metabolism that results in high plasma and urinary levels of valine, leucine, isoleucine and their alpha-keto acids?

What enzyme is involved?

A

Maple Syrup Urine Disease

Caused by insufficient activity of the branched chain keto acid dehydrogenase enzyme.

22
Q

What is the role of thiamin in the pentose phosphate pathway?

A

Thiamin acts as a loosely bound prosthetic group for the transketolase enzyme which is involved in synthesis of pentoses used in nucleic acids and the generation of NADPH.

23
Q

What disease results from deficiency of thiamin?

A

beriberi

beri means “weakness”

Three types
Dry beriberi (adults chronic low intake)
Wet beriberi (adults, more cardiovascular system involvement then dry beriberi)
Acute beriberi (infants)
24
Q

What is the thiamin deficiency disorder associated with alcoholism?

A

Wernicke’s Encephalopathy

Characterized by

  • opthalmoplegia (paralysis of ocular muscles)
  • nystagmus (constant involuntary eyeball movement)
  • ataxia

can turn into brain damage called Wernicke-Korsakoff Syndrome is thiamin deficiency is not treated.

25
Q

What can result from untreated thiamin deficiency associated with alcoholism??

A

Wernicke-Korsakoff syndrome

brain damage associated with untreated thiamin deficiency related to alcoholism and Wernicke’s Encephalopathy.

26
Q

What groups are at risk of thiamin deficiency?

A
  1. people with heart failure
    - low intake of thiamin
    - increase urinary loss due to diuretics
  2. elderly
  3. People with disease that impair absorption
    - some GI tract cancers
    - liver disease
    - inflammatory bowl diseases
  4. People with increased needs
    - some cancers
27
Q

What tests are used to assess thiamin levels?

A
  1. Urinary thiamin levels
    - excretion decreases with decreased thiamin status
  2. erythrocyte transketolase activity
    - sample of RBC inoculated with thiamin
    - change in activity of transketolase enzyme is measured
  3. branched chain keto acids in urine
    - alpha-keto isovalerate (valine)
    - alpha-keto isocaproate (leucine)
    - alpha-keto-beta-methylvalerate (isoleucine)

Vitamins - Water Soluble (8 decks)

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