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CNS Exam > W11: Vit B6, biotin > Flashcards

W11: Vit B6, biotin Flashcards

1
Q

The major storage site of vitamin B6 is:

a. skeletal muscle
b. nervous tissue
c. liver
d. kidneys

A

a. skeletal muscle

Also in liver, brain, kidneys, spleen. Adult body has ~40-185 mg of B6

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2
Q

The primary active form of vitamin B6 is:

a. pyridoxal phosphate (PLP)
b. pyridoxine phosphate (PNP)
c. pyridoxamine phosphate (PMP)
d. pyridoxine (PN)

A

a. pyridoxal phosphate (PLP) – aka, pyriodxal 5’-phosphate (P5P)

There are 6 forms (“vitaminers”) of B6, all of comparable activity - however, P5P is the main coenzyme form + considered most important physiologically

  1. pyriodoxal (PL)
  2. pyridoxine (PN)
  3. pyridoxamine (PM)
  4. pyridoxine phosphate (PNP)
  5. pyridoxamine phosphate (PMP)
  6. pyridoxal phosphate (PLP or P5P)
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3
Q

Vitamin B6 is metabolized in:

a. intestine
b. liver
c. circulation
d. muscles

A

b. liver

  • Dephosphorylation via brush border enzyme is required for absorption
  • Not metabolized much in intestine; released directly into portal circulation > liver (taken up by passive diffusion + metabolized here)
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4
Q

The MAIN function of vitamin B6 is acting as a cofactor for:

a. energy production (i.e. CAC, ETC)
b. metabolism of amino acids
c. nucleic acid synthesis
d. metabolism of hormones

A

b. metabolism of amino acids

When you think B6, think amino acids! - Bryan Walsh

B1, B2, B3, B5 = share a lot of the same pathways (i.e. CAC, ETC, fatty acid synthesis & beta oxidation)…B6 has VERY different functions

B6 is involved in 100+ enzymatic rxns…

  • NEUROTRANSMITTERS: rate-limiting cofactor in the synthesis of NTs - serotonin (conversion from tryp), dopamine, GABA, noradrenaline, melatonin
  • RBC FORMATION & FUNCTION: coenzyme in synthesis of heme and can bind hemoglobin; B6 def > defects in heme synthesis + anemia
  • GLUCOSE: catalyzes release of glucose from stored glycogen (glycogenolysis) and generates glucose form AAs (gluconeogenesis)
  • NIACIN FORMATION: coenzyme for synthesis of niacin from tryptophan (adequate B6 = ⬇️ req for niacin)
  • HORMONES: estrogen, progesterone, testosterone act by binding to steroid hormone receptors in cell nuclei, alter gene transcription. PLP bind to receptors, rendering them unavailable for steroid binding -> decreasing effects of hormones, which may have implications for hormone-responsive cancers and other endocrine pathologies)
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5
Q

Which of the following is NOT true of vitamin B6:

a. daily B6 requirements are related to protein intake
b. environmental toxicity may increase B6 requirements
c. B6 increases intracellular uptake of Mg and vice versa
d. B6 supplementation may decrease Zn requirements

A

d. B6 supplementation may decrease Zn requirements - FALSE

  • Reqs related to protein intake (⬆️ intake = ⬆️ B6 req
  • Environmental toxicity may ⬆️ B6 req (can inhibit B6-dept enzymes – i.e. herbicides, PCBs, tobacco smoke, petroleum industry, metal manufacturing)
  • B6 increases intracellular uptake of Mg and vice versa (co-supp advised)
  • B6 supplementation may INCREASE Zn requirements
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6
Q

PLP is mostly found in:

a. plant foods
b. animal foods

A

b. animal foods

All 6 vitamers are found in food:

  • PN, PNP = largely in plant foods (i.e. whole grains, fruits, nuts)
  • PL, PM, PLP, PMP = largely in animal foods (i.e. salmon, chicken, turkey)

Top sources of B6 = chickpeas, beef liver, tuna, salmon, chicken breast, potatoes, turkey meat, bananas, nutritional yeast, avocado

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7
Q

Which of the following leads to the LEAST amount of loss of B6:

a. freezing
b. prolonged heating (sterilizing, canning)
c. processing (milling, refining)
d. storage
e. cooking

A

e. cooking

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8
Q

Co-supplementation with B6 is advised for all of the following EXCEPT:

a. l-tryptophan
b. folate
c. magnesium
d. iodine

A

d. iodine

L-tryptophan – in pts taking l-tryptophan, co-supp may ⬆️ tryptophan uptake in brain (thus ⬆️ anti-depressant effect)

Folate – folate supp ⬆️ B6 reqs; folate + B6 therapy has been seen to result in ⬆️ improvement than supp w/ B6 alone – co-supp is advised

Magnesium – B6 ⬆️ intracellular uptake of Mg + vice versa; co-supp advised

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9
Q

All of the following are NFPE signs of B6 deficiency EXCEPT:

a. angular stomatitis
b. glossitis
c. seborrheic dermatitis
d. aphthous ulcers
e. soft, brittle nails

A

e. soft, brittle nails

Angular stomatitis = red, swollen patches in corners of mouth
Glossitis = swollen and inflamed tongue
Seborrheic dermatitis = scaly patches and red skin, mainly on the scalp; in B6 deficiency, can also happen on face, neck, shoulders, butt
Aphthous ulcers = canker sores

Other signs of deficiency: irritable, depression, confusion, anxiety, headaches, insomnia, ab pain, muscle twitching, peripheral neuropathy, B6-responsive anemia, neuro signs (severe def)

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10
Q

All of the following increase risk of deficiency of B6 except:

a. alcohol abuse
b. being elderly
c. strict vegetarians
d. being anemic

A

d. being anemic

Severe deficiency is uncommon, but marginal deficiency is very common (from increased consumption of canned, frozen, refined foods)

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11
Q

It is generally recommended not to exceed ____ mg of B6 in supplementation:

a. 200 mg
b. 300 mg
c. 400 mg
d. 500 mg

A

a. 200 mg - lowest dose that has shown to be neurotoxic is 500mg

Clinical notes:

  • In some, exceeding 50mg/d may lead to nervousness and insomnia (feeling “wired”), which can be prevented by taking magnesium (200-400mg/d)
  • High doses of B6 long term can lead to neuro symptoms - i.e. sensory neuropathy, ataxia, degeneration of neurons + sensory fibers of peripheral nerves
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12
Q

Which of the following does NOT interfere with B6 metabolism?

a. Anti-tuberculosis medications
b. Penicillamines
c. Levodopa
d. Vasodilators
e. Oral contraceptives

A

e. Oral contraceptives

Penicillamines (immunosuppressive / heavy metal binder - used for Wilson’s disease (excess Cu) and RA) and Levodopa form a complex w/ B6, lessening/preventing absorption.

Other drugs that can lead to lowered B6 status: Chemotherapy, Gentamicin, neuroleptic meds, Phenelzine, Tranylcypromine, Thenophylline

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13
Q

True or false: Signs attributed to riboflavin deficiency may be due to low PLP.

A

True: Riboflavin is required for pyridoxine > PLP conversion, so signs attributed to riboflavin deficiency may be due to low PLP

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14
Q

The RDA of B6 for adults aged 14-50 years old is:

a. 1.3 mg for males, 1.2 mg for females
b. 2.3 mg for males, 2.2 mg for females
c. 4.5 mg for males, 4.4 mg for females
d. 5.5 mg for males, 5.4 mg for females

A

a. 1.3 mg for males, 1.2 mg for females

Age 51+ = increases to 1.7 mg for males, 1.5 mg for females

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15
Q

Biotin deficiency is rare because some biotin ___________
A. is stored in the jejunum
B. can be synthesized by bacteria in the large intestine
C. is fat soluble
D. none of the above

A

B. can be synthesized by bacteria in the large intestine

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16
Q

Biotin deficiency (although rare) can occur:
A. in those who consume large quantities of raw eggs
B. in individuals with GI disorders with malabsorption
C. with chronic use of antibiotics
D. in those who consume excess alcohol
E. all of the above

A

E. all of the above
Excessive alcohol inhibits absorption, and chronic use of antibiotics (reduces or eliminates the synthesis of biotin from bacteria)

17
Q 
Biotin is mainly absorbed in the:
A.  esophagus
B. rectum
C. jejunum
D. colon and brush border of SI
A

D. colon and brush border of SI

18
Q

Anticonvulsants can ________the absorption of biotin in the small intestine
A. increase
B. decrease
C. inhibit

A

C. inhibit

19
Q 
The RDA for Biotin for adults 19+ is
A. 12mg
B. 20mg
C. 30mg
D. 150mg
A

C. 30mg

20
Q

Signs of biotin deficiency include
A. hives, pica, irritability
B. skin rashes, hair loss, and brittle nails
C. Itchy feet, blood shot eyes, hair loss
D. muscle atrophy, constipation, bad breath

A

B. skin rashes, hair loss, and brittle nails
Therefore, biotin supplements are often promoted for hair, skin, and nail health. However, these claims are supported, at best, by only a few case reports and small studies.

21
Q 
The TUL of Biotin is:
A. 100mg
B. 200mg
C. Anything over 50mg
D. There is no TUL
E. None of the above
A

D. there is no TUL

22
Q

TESTING: FUN FACT
Very high intakes of biotin may interfere with diagnostic assays that use biotin-streptavidin technology and are commonly used to measure levels of hormones (such as thyroid hormone) and other analytes such as 25-hydroxyvitamin D, producing falsely normal or abnormal results.

A

As a result, a few recent case reports have described findings falsely indicating Graves disease and severe hyperthyroidism in patients taking 10–300 mg biotin per day, including six children receiving high doses of biotin (2–15 mg/kg body weight per day) to treat inherited metabolic diseases [33-37].

Even a single 10 mg dose of biotin has interfered with thyroid function tests administered within 24 hours of taking the supplement

https://ods.od.nih.gov/factsheets/Biotin-HealthProfessional/

23
Q

T/F

Biotinidase deficiency is a rare autosomal recessive disorder that prevents the body from releasing free biotin

A

True
Without treatment, biotinidase deficiency produces neurological and cutaneous symptoms, and profound biotinidase deficiency can lead to coma or death

24
Q

Testing:
Plasma biotin is assessed, however low plasma levels do not correlate with intake/status.

Urinary biotin is preferred: deficiency <6 mcg/d or <200 pg/mL

A

Increased excretion of organic acids in the urine, particularly 3-hydroxyisovaleric acid (3-HIA), can indicate a biotin deficiency.

CNS Exam (45 decks)

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