Gluconeogenesis, glycogen metabolism Amino acid metabolism Neurotransmitter synthesis Nervous system function Immune function Cell-mediated immunity, antibody production Vitamin B6 exists as several forms called vitamers that can be interconverted. It functions as a coenzyme involved in many important metabolic reactions including amino acid metabolism, gluconeogenesis, glycogen metabolism, neurotransmitter synthesis, immune function, and nervous system function. A deficiency can impact these processes and result in impaired immune function or nervous system abnormalities.

1. Vitamin B6
Omar A Obeid
NFSC 315

2. Vitamin B6
• Gyorgy 1934: Antidermatitis (Acrodynia)
factor in rats.
• Crystallized (1938) by 3 groups
• Synthesized (1939) in USA and Germany
• 1945: Three forms of the vitamin

3. VITAMIN B6
O
NH2
HO
HO
OH
PYRIDOXAL
PYRIDOXAMINE
OH
OH
N
OH
N
N
HO
H
PYRIDOXINE

4. Vitamin B6
• Exists as several vitamers
– Interchangeable
– Pyridoxine (PN): alcohol (OH) form
– Pyridoxal (PL): aldehyde form
– Pyridoxamine (PM): amine (NH2) form
• Each has a 5’-phosphate derivative
– PNP, PLP, PMP
– Function as coenzymes

5. Vitamin B6 Structures
O
CH2OH
O P
-
O
CH2OH
OH
H2C
O+
N
H
CH3
Pyridoxine phosphate (PNP)
O P
-
NH2
H
C
O
O
CH3
+
N
H
Pyridoxamine (PM)
CH3
+
N
H
Pyridoxal (PL)
+
N
H
Pyridoxine (PN)
O
OH
HOH2C
OH
HOH2C
CH3
O
CH2
C
OH
HOH2C
NH2
H
OH
H2C
O+
N
H
CH2
O
CH3
Pyridoxal phosphate (PLP)
O P
O
-
O-
OH
H2C
+
N
H
CH3
Pyridoxamine Phosphate (PMP)

6. Chemistry
•
•
•
•
•
Colorless crystalline solid
Soluble in water and alcohol
Stable to heat (-al and -amine less)
Decompose in alkali and light
Pyridoxal 5-phosphate and
pyridoxamine 5-phosphate are the
coenzyme forms.

7. Sources
• All vitamers are found in food
• Pyridoxine
– Most stable
– Found mainly in plants
– Bananas, navy beans, walnuts
• Pyridoxamine and Pyridoxal
– Found in animal products
– Sirloin stead, salmon, and light meat of
chicken.

8. Vitamin B6 Content of Foods
Food
Dairy products
Milk
Yogurt
Cheeses
Meat
Beef
Chicken
Lamb
Pork
Ham
Calf liver
Herring
Haddock
Tuna
Oysters
Shrimp
Vitamin B6(mg/100g)
0.04
0.05
0.04-0.08
0.33
0.33-0.68
0.28
0.35
0.32
0.84
0.37
0.18
0.43
0.05
0.10
Glycosylated(%)
_
_
_
_
_
_
_
_
_
_
_
_
_
_

9. Vitamin B6 Content of Foods
Food
Vitamin B6(mg/100g)
Cereals
Corn meal
Rice
Polished
Unpolished
Wheat, whole
Other
Eggs
Human colostrum
Human milk
Glycosylated(%)
0.20
_
0.17
0.55
0.29
20
23
28
0.19
0.001-0.002
0.010-0.025
_
_
_

10. Vitamin B6 Content of Foods
Food
Vitamin B6(mg/100g)
Glycosylated(%)
Vegetables
Asparagus
Beans
Broccoli
Brussels sprouts
Cabbage
Carrots
Cauliflower
Celery
Corn
Onions
Peas
Potatoes
Spinach
0.15
0.08-0.18
0.17
0.18
0.16
0.15
0.21
0.06
0.20
0.13
0.16
0.25
0.28
_
_
66
_
46
51-86
66
_
_
_
15
32
50

11. Vitamin B6 Content of Foods
Food
Fruits
Apples
Grapefruit
Oranges
Peaches
Strawberries
Tomatoes
NUTS
Peanuts
Pecans
Walnuts
Vitamin B6(mg/100g)
Glycosylated(%)
0.03
0.03
0.06
0.02
0.06
0.10
_
_
_
_
_
46
0.40
0.18
0.73
_
_
7
Sources: USDA data; Leklem, J.E. (1996). In: “Present Understanding in
Nutrition” (E.E. Ziegler and L.J. Filter,Jr.,eds.), 7th Ed., p.175. ISLI Press,
Washington, D.C.

12. Concentrations (µg per 100g)and proportions of vitamin B6 derivatives
in selected foods.
Total B6
VEGETABLES
Carrots
FRUITS
Apple raw
Apple juice
Orange
Orange juice
%P
206
18
104
87
83
55
33
26
39
42
%Free
29
%PNG
54
52
65
33
36
15
9
28
23
CEREALS
Whole wheat bread
White bread
79
16
39
42
33
51
51
8
NUTS/SEEDS
Almonds
Sunflower seeds
Soyabean
137
605
267
5
14
34
95
34
49
0
52
18
Sources: Reynolds,1998; Bitsh and Schramm, 1992.
%P=%Phosphorylated vitamers; %Free=%non-phosphorylated vitamers; %PNG=

13. Sources
• Loss during refining of cereals (flour)
• Large % Vitamin B6 can bound to proteins
via amino or sulfhydryl groups.
– Less available: resistant to hydrolysis and low
B6 activity.
• Vitamin B6 react with glucose and
become glycosylated.
– Less available
• Storage: loss 10-50%

14. Vitamin B6
• Digestion
– Phosphorylated vitamers must be dephosphorylated
prior to absorption
• Intestinal phosphatases
• Absorption
– PN, PL and PM absorbed primarily by non-saturable
process (passive diffusion)
• Absorption of dietary B6 ranges from 71-82%
• Diffusion linked to phosphorylation: Jejunum and
ileum.
• Dephosphorylation by membrane bound alkaline
phosphatase

15. Absorption of the B6 Vitamins
Pyridoxamine
Pyridoxal
Pyridoxine
PM
PL
PN
PMP
PLP
PNP
ADP
ATP
Mucosal Cell
B6
Pi

16. Vitamin B6
• Within Enterocyte
– PN phosphorylated to PNP
• Pyridoxine kinase (ATP, Zn)
– PL phosphorylated to PLP
• Kinase (ATP, Zn)
– PNP may be converted to PLP
• Pyridoxine phosphate oxidase (FMN)
• Blood
– PLP is main form (~60%) of vitamin in blood
• PL also exists
• Both PL and PLP are bound to albumin
– 0.1% of total B6 in plasma as PLP, bound to
protein

17. Vitamin B6
• Erythrocytes
– PL and PN (rapid simple diffusion)  PLP
– Tight binding to Hb (role in transport!)
• Liver
– Stores about 5 to 10% or vitamin
– Phosphorylation occurs within cytoplasm
– PNP and PMP are converted to PLP
– PL and PLP are released into blood for
transport to extrahepatic tissues

18. Vitamin B6
• Requires removal of P by phosphatase to enter cells
• Muscles (possess majority of PLP)
– PLP must first be hydrolyzed to PL before uptake
– Within cell rephosphorylated
– 80-90% in muscle bound to glycogen
phosphorylase
– Decrease with low energy intake
• B6 in body mainly as PLP
• Human body store is 40-150mg, sufficient for
20-75 days

19. Metabolism
• Interconversion of vatimers
• Metabolism mainly in liver
– PMP and PNP are converted to PLP by:
• Pyridoxal phosphate oxidase require FMN
– Dephosphrylation of PLP to PL to 4-PA
• Intracellular level of PLP
– Controlled by enzymatic hydrolysis
• Excess PLP will be hydrolyzed to PL
– Controlled by product inhibition of
PNP/PMP oxidase

20. Metabolism/Excretion
• Excess PL is converted to Pyridoxic acid (PA)
– PA excreted in urine
– PA excretion reflects recent vitamin intake
• Newly formed PLP is not freely exchangeable with
endogenous PLP
• Major product for excretion is 4-pyridoxic acid
• Urinary 4-pyridoxic acid is inversely related to
protein intake
• Interacts with folate and B12

21. Metabolic functions
•
•
•
•
•
•
•
Amino acid metabolism
Gluconeogenesis/glycogen catabolism
Niacin formation
Nervous system
Immune function
Hormone modulation
Lipid metabolism

22. Functions
• Amino Acid Metabolism
– PLP via formation of a Schiff base labilizes all the
bonds around the alpha carbon of the amino acid
– Schiff base
• Product formed by an amino group and an aldehyde
– The specific bond that is broken is determined by the
enzyme
• Decarboxylase, Transaminases, Aldolases

23. Transaminations
• PLP and PMP serves as coenzymes
– Aspartic amino transferase (AST)
• Aspartate donates its amino group to an alpha keto
acid forming OAA and a different amino acid
– Alanine aminotransferase (ALT)
• Alanine donates its amine group to an alpha keto
acid forming pyruvate and a different amino acid

24. Transaminations
• Phase I
– The corresponding alpha keto acid (pyruvate)
of the amino acid (alanine) is produced along
with PMP
• Phase II
– New alpha keto acid (alpha keto glutarate)
receives amino group from PMP producing
the new amino acid (glutamate) and PLP

25. Decarboxylations
• GABA Synthesis
– Glutamate decarboxylase
– Conversion of Glutamate to GABA
• Serotonin Production
– 5-Hydroxytryptophan decarboxylase
– Conversion of 5-hydroxytryptophan to
serotonin (5-hydroxytryptamine)

26. Metabolic interconversions of the B6 vitamers
4-PA
PM
PL
PLP
Transaminase
PNPoxidase
(FMN)
Pase
PLkinase
Pase
PLkinase
Pase
PLkinase
PNP
PNPoxidase
(FMN)
Aldehyde
oxidase
(FAD)
Aldehyde
dehydrogenase
(NAD)
PN
PMP

27. Transulfhydrations and
Desulfhydrations
• PLP required for cysteine synthesis from
methionine
– Both cystathionine beta synthase (CBS) and
cystathionase require PLP
• PLP required for desulfhydration followed
by transamination to generate pyruvate.

28. Other reactions
• Cleavage
– PLP required for removal of the methyl group from
serine and transfer to THF
• Glycine produced as well
• Racemization
– PLP required by racemases that catalyze
interconversion of D- and L- amino acids
• Synthesis
– PLP necessary for synthesis of heme, niacin,
histamine from histidine, carnitine, taurine,
dopamine and more.

29. Effect of Protein Intake on Vitamin B6 Status
Treatment
Protein intake (g/Kg/d):
0.5
1.0
2.0
Vitamin B6 intake (mg/g protein):
0.04
0.02
0.01
Parameter (adequate value)
Percentage of subjects with low values
Urinary 4-pyridoxic acid(>3 mmol/day)
11
22
78
Urinary total vitamin B6(>0.5 mmol/day)
56
56
67
Plasma pyridoxal phosphate(>30 mmol/liter)
33
67
78

30. Gluconeogenesis/glycogen
catabolism
• Transamination and glycogen phosphorylase
• Vitamin B6 deficient rats
– Low liver and muscle glycogen phosphorylase
– No effect on B6 conc in Muscle, unlike calorie
restriction
• Rats: IV. B6 (300mg/kg)
– Low liver glycogen and high plasma glucose
• In human:
– No clear relation

31. Nervous system
• Neurotransmitters: serotonin, taurine,
dopamine, norepinephrine, histamine,
GABA
• Rats: mother deficient in B6:
– Offspring: Brain abnormalities
• Infant fed formula low in B6
– Abnormal electroencephalograms (EEGs)
• Adults with B6 deficiency
• Abnormal EEGs with high protein diet

32. B6 and synthesis of neutransmitters
Glutamate
Glutamate
decarboxylase
γ – aminobutyric acid (GABA)
O2
Tryptophan
CO2
5 hydroxy tryp
Hydroxylase
5-OH-Tryptamine
PLP
(Serotonin)

33. CO2
O2
Tyrosine
DOPA
Dopamine
O2
Hydroxylase
Norepinephrine
SAM
CH3
Epinephrine

34. Immune system
• serine transhydroymethylase (PLP) for 1C
metabolism (nucleic acid synthesis)  immune
function
• Vitamin B6 deficient animals:
– Low lymphocyte production, antibody response to
antigens, cell mediated immunity
• Human:
– Elderly with impaired immune system: respond to
50mg PN/d
– Young: Marginal deficiency : no effect
– Health elderly: relation between B6 and immunity (IL2)

35. Effect of Vitamin B6 Status on Mitogenic Responses and
Interleukin 2 Production by Peripheral Blood
Mononucleocytes of Elderly Humans
Parameter
Baseline
B6 deprived
B6 supplemented
Mitogenic response
Concanavalin A
Phytohemagglutinin
Staphylococcus aureas
120
100
115
70
70
60
190
100
200
IL-2 production (Ku/Liter)
105
40
145
Source: Meydani, S.N., Ribaya-Meradi, J.D., Russel, R.M., Sahyoung, N., Morrow,
F.D., and Gershoff, S.N. (1991). Am. J. Clin. Nutr. 53, 1275-1280 .

36. Erythrocyte function
• Binding of PL to α-chain Hb increases O2
binding affinity
• Binding of PLP to β-chain Hb decreases
O2 binding affinity
• PLP cofactor for δ-aminolevulinic acid
synthetase (heme synthesis)
• B6 deficiency:
– Microcytic anemia
– Pyridoxine responsive anemia

37. Hormone modulation/gene expression
• Reversible reaction with receptors for:
– Estrogen, androgen, progesterone, glucocorticoid at
lysine residues.
• Vitamin B6 deficient rats:
–
–
–
–
–
H-estradiol: more incorporation at uterine tissues
Zn and B6 deficiency: more interaction
No of estrogen receptors not affected
mRNA albumin increased (7 times)
mRNA of cytosolic aminotransferase (7 times)
3
• Vitamin B6 may be a modulator of gene
expression

38. Lipid metabolism
• Similarity between EFA and B6
deficiencies
• B6 deficient rats: low body fat
• Conversion of linoleic to arachidonic
• Arachidonic acid and cholesterol
• PLP for carnitine synthesis
– Clarification is needed

39. Cellular processes affected by PLP
Cellular process
Function
1-C metabolism, hormone modulation Immune function
Glycogen phosphorylase,
transamination
Gluconeogenesis
Tryptophan metabolism
Niacin formation
Heme synthesis, transamination, O2
affinity
Red cell metabolism and
formation
Neurotransmitter synthesis, lipid
metabolism
Nervous system
Hormone modulation, binding of PLP
to lysine on hormone receptors
Hormone modulation

40. Nutrient Interactions
• Vitamin B6 is interrelated with Riboflavin
– Riboflavin is coenzyme of PNP/PMP oxidase
which converts PNP/PMP to PLP
• Vitamin B6 is interrelated with Niacin
– Niacin is coenzyme for aldehyde
dehydrogenase which oxidizes PL to PA.
– Conversion of tryptophan to niacin

41. Drug-vitamin B6 interaction
Drug
Examples
Mechanism of interactions
Hydrazines
Iproniazid,
isoniazid,
hydralazine
Reacts with Pl and PLP to forms a
hydrazone
Antibiotic
cycloserine
Reacts with PLP to form an oxime
L-DOPA
L-3,4-(HO)2phenylalanine
Reacts with PLP to form
tetrahydroquinoline derivatives
Chelator
Penicillamine
Reacts with PLP to form thiazolidine
Oral
contraceptives
Alcohol
Increase enzyme level in liver and other
tissues, retention of PLP
Ethanol
Increased catabolism of PLP

42. Vitamin B6 and disease
• Coronary heart disease
– Altered S-AA metabolism
– Hcy elevation
– Cystathionine β-synthase deficiency:
• Arteriosclerosis
– PLP and atherosclerosis: independent of Hcy
and cholesterol
– Relation with cholesterol
– Immunity

43. Vitamin B6 and disease
• HIV/AIDS
–
–
–
–
B6 and progression: inverse
Low status
PLP binds to CD4 receptors
PLP in a noncompetitive inhibitor of HIV-1 reverse
transscriptase
• Premenstrual syndrome
–
–
–
–
PLP status similar between PMS and non-symptoms
B6 suppl: improvement in some symptoms
150-200mg!!
Cell transport competition, receptor

44. Vitamin B6 and disease
• Sickle cell anemia
– Low level
– 100mg PN-HCl (2m): low severity, frequency and
duration of painful crisis
– PL and PLP binding to Hb
• Asthma
– Low PLP status
– 100mg: PN-HCl: low duration, occurrence and
severity
– Theophylline: Low plasma and RBC PLP
• Carpal tunnel syndrome
– Most studies: PN suppl relif symptoms of pain and
numbness in hands

45. Vitamin B6: High doses
• Is toxic in pharmacological amounts
• Chronic ingestion of 2-6 g pyridoxine/d may
cause sensory neuropathy
– Signs similar to deficiency
• Has been used to treat a variety of conditions
– Atherosclerosis, carpal tunnel syndrome,
premenstrual syndrome, depression, muscular
fatigue.
• Rats (500-100mg/kg)
– Decrease in testis epididymis, prostate gland,
mature spermatid counts

46. Dietary Reference Intakes (DRI) For Vitamin B6
Females
Males
RDA (mg/d)
RDA (mg/d)/
U L** (mg/d)
0- 6 months
0.1*
0.1*
ND
7-12 months
0.3*
0.3*
ND
1- 3 yrs.
0.5
0.5
30
4- 8 yrs.
0.6
0.6
40
9-13 yrs.
1.0
1.0
60
14-18 yrs.
1.2
1.3
80
19-50 yrs.
1.3
1.3
100
> 50 yrs.
1.5
1.7
100
1.9
-
80
1.9
-
100
2.0
-
80
2.0
-
100
Life stage group
Infants
Children
Pregnancy
< 18 yrs.
> 18 yrs.
Lactation
< 18 yrs.
> 18 yrs
From Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12,
Pantothenic Acid, Biotin and Choline. Washington, DC: National Academy Press, 1998.

47. Vitamin B6
• 1989 RDA=1.6 - 2.0 mg/d
– Based on protein intake
• 1998 RDA
– Adult = 1.3 mg/d
• UL:
– Adult: 100mg/d

48. Deficiency
• Rare
• Sign of deficiency can be quickly corrected
by administration.
• Deficiency Signs
– Fatigue, cheilosis, glossitis, seizures,
convulsions in infants, hypochromic,
microcytic anemia (impaired heme synthesis)

49. Pyridoxine (Vitamin B6)
Pyridoxine deficiency:
The scaling seborrhea-like
dermatosis in this patient was
induced in volunteers by giving
the
pyridoxine
antagonist
desoxypyridoxine.
Such
lesions have not been proved
to
occur
spontaneously
although it is suspected that
some instances are due to
pyridoxine deficiency.

50. Pyridoxine (Vitamin B6)
Pyridoxine deficiency:
The glossitis in this
patient was induced in
volunteers by giving the
pyridoxine
antagonist
desoxypyridoxine. This is
undistinguishable from
that due to deficiency of
other B group vitamins.

51. Groups at Risk for Deficiency
•Breastfed infants born with low Vitamin B6
•Elderly
•Poor intake and possibly accelerated hydrolysis
of PLP and oxidation of PL to PIC
•Alcoholics
•Conversion of PN and PM to PLP impaired
•Persons on maintenance dialysis
•Variety of Drug Therapies
•Isoniazid, corticosteroids, anticonvulsants

52. Assessment
• Direct:
– Plasma PLP(>30nM)
– Plasma total B6 (>40nM)
– Urinary 4-pyridoxic acid (>3.0µmol/day)
• Indirect:
– Tryptophan loading (2g): xanturenic acid
– Methionine loading (3g): Hcy, cystathionine
– Erythrocyte transaminase stimulation
• Dietary intake
– Intake, B6:protein ratio (>0.02), PN-β-glucosidase
• EEG pattern

53. Assessment of Status
(Tryptophan Load)
TRYPTOPHAN
N-FORMYLKYNURENINE
KYNURENINE
Xanthurenic
Acid
3-OH-KYNURENINE
Kynureninase (PLP)
3-OH ANTHRANILIC ACID
QUINOLINIC ACID
NIACIN
acetyl
CoA
acetoacetyl
CoA

54. Assessment of Status
• Erythrocyte Transaminase Index
– Erythrocyte alanine aminotransferase
– Erythrocyte aspartate aminotransferase
– Look at the activity of the enzyme before
and after addition of Vitamin B6
– A two-fold or more increase in activity of the
enzyme after addition of vitamin B6 is
indicative of deficiency
– Less than a two-fold increase in activity is
indicative of acceptable status