Folate Flashcards

1
Q

Dietary sources

A

Beans, nuts, meat (esp. organs), dairy, fruit, grain, cereal

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2
Q

What amino acid does folate catabolize?

A

Histidine - transfers formimino group from formiminoglutamate to THF; results in formimino-THF and glutamate

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3
Q

What compound will be elevated in the urine during folate deficiency?

A

Formiminoglutamate

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4
Q

How does methotrexate work?

A

It is an anti-cancer drug that inhibits DHF reductase (traps DHF in cell), thus preventing THF formation that is needed to form thymidine. Cells can no longer divide quickly.

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5
Q

Role of folate in DNA synthesis

A

Needed to form thymidylate (pyrimidine) and purines (adenine and guanine)

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6
Q

Transmethylation role of folate

A
  • Methylates homocysteine to methionine, which can then be used for various transmethylation reactions
  • Methylaiton inactivates genes, which is important in development
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7
Q

B12 role in methylation

A

Required for MS to work to methylate homocysteine and maintain SAM

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8
Q

How does histone methylation work?

A

Methylation of chromatins turns off DNA, making DNA wrap tightly into histones. Removing methyl groups activates it, making it open. With insufficient SAM, genes will be turned on or off at the wrong time.

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9
Q

What lipid transmethylation reactions is folate involved in?

A

Sterol methylation
- making hormones

Phospholipid methylation
- formation of phosphatidylcholine (PC) requires methylation
- needed to get lipids out of the liver; or else fatty liver occurs because lipids accumulate

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10
Q

What does SAM methylate guanidinoacetate into?

A

Creatine

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11
Q

How much food folate is equivalent to folic acid and what is a DFE?

A

1mcg folic acid = 1.7mcg food folate
DFE = 1mcg food folate or 1.7 X 1mcg folic acid (folic acid is more bioavailable)

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12
Q

Requirements

A

M and F adults: 400mcg
Higher in pregnancy (600mcg DFE) and lactation (500mcg DFE)

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13
Q

UL of folate

A

1mg/day folic acid
- High doses can mask B12 deficiency

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14
Q

Food sources of folate

A

Plant and animal tissues - liver, dark green leafy veg, legumes
- Mostly found in polyglutamate form
- Mostly bound to proteins and storage polysacc
- Folic acid only found in fortified form

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15
Q

What is the bioavailability of food folate?

A

<50% depending on poly- or mono-glu form
- Organic acid inhibit conjugase activity
- Folate is trapped in plant material
- Lost during food processing

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16
Q

Absorption of folate

A
  • Poly-glu folates cleaved to mono-glu folates by folate conjugase
  • Peptidase converts mono-glu folates to THF (folic acid), which can be uptaken into cells by RFC (reduced folate carrier) and FBP (folate binding proteins) – just know that there are transporters and binding partners involved
  • Recycled in bile by liver
  • Circulates as mono-glu
  • Stored as Poly-glu
17
Q

What B vitamins are involved in methylene tetrahydrofolate reductase?

A

Riboflavin and niacin

18
Q

Potential concerns of folic acid fortification of the food supply

A
  • No toxicity has been reported
  • Masking of B12 deficiency
  • Potential increase in risk of colorectal cancer + other cancers
19
Q

How does folate deficiency/supplementation relate to cancer?

A
  • Normal risk: folate deficiency may lead to increased chance of DNA mutations
  • Adenoma (increased risk): folate deficiency may prevent progression to cancer, while supplementation may promote progression
  • Cancer: folate deficiency may prevent cancer progression, while folate supplementation may increase cancer progression