Pyridoxine (Vitamin B6)

Question 1

What are the forms of vitamin B6?

Answer 1

Pyridoxine
Pyridoxamine
Pyridoxal

Question 2

What is the coenzyme form of vitamin B6?

Answer 2

Pyridoxal Phosphate (PLP)

Question 3

What is the role of vitamin B6 is metabolism?

Answer 3

Transamination
Deamination of hydroxyl amino acids
Decarboxylation of amino acids: Significant in the synthesis of neurotransmitters
Required for synthesis of niacin from tryptophan
Required for methionine and cysteine metabolism (deficiency may lead to hyperhomocystenemia)
Synthesis of heme: Glycine & Succinyl CoA are precursors. ALA synthase is a PLP dependent enzyme (deficiency may lead to hypochromic, microcytic anemia)
Terminating action of steroid hormones: In B6 deficiency, there is increased sensitivity to actions of low concentration of steroid hormones
Required for breakdown of glycogen in muscles
Synthesis of sphinomyelin and phosphatidylcholine

Question 4

RDA of vitamin B6

Answer 4

1.4-2.0 mg/day (for a 65g Protein diet)

Requirement is proportional to protein intake

Question 5

What effects does alcohol have on vitamin B6?

Answer 5

Decreases absorption
Increases degredation and excretion
Inactivates PLP (whcih may cause neuritis)

Question 6

When may requirements of vitamin B6 increase?

Answer 6

Pregnancy
Lactation

Question 7

What are some food sources fo vitamin B6?

Answer 7

Bananas
Whole grain cereals
Legumes
Meats
Green leafy vegetables
Egg yolks
Milk
Yeast

Question 8

What are the symptoms of vitamin B6 deficiency?

Answer 8

Neurological Symptoms: Hyperirritability, convulsions (due to impaired GABA synthesis), depression, nervousness (due to underproduction of neurotransmitters
Anemia: Decreased heme synthesis causes microcytic, hypochromic anemia
Peripheral neuritis: Demyelination of nerves
Pellagra like symptoms: Due to blocked Niacin synthesis from Tryptophan

Question 9

What factors may lead to vitamin B6 deficiency?

Answer 9

Isoniazid, Penicillamine and Cycloserine treatments can induce B6 deficiency by forming an inactive derivative with PLP
Ethanol inactivates PLP making neuritis is common among alcoholics
Oral contraceptives also causes mild deficiency

Question 10

Possible assessments for B6 deficiency?

Answer 10

Assaying erythrocyte transaminases
Tryptophan load test

Question 11

What is the tryptophan load test?

Answer 11

Sensitive indicator of deficiency
Procedure:
2g Tryptophan is given to the patient
Xanthurenic acid is measured in 24 hr. urine sample
Result:
Increased amounts of Xanthurenic acid (>3mg) are found in B6 deficiency states

Question 12

Symptoms of vitamin B6 toxicity

Answer 12

Intake >200mg/day are associated with neurological damage causing imbalance, numbness (particularly in the feet), peripheral neuropathy, muscle weakness and nerve damage.