Grace Coughlan Dawn Dunphy Kaitlyn McDonald Carla van den Berg Vitamin B 6

Overview Introduction to Vitamin B 6 Absorption, Transport, Metabolism, Storage, Excretion Deficiency Static and Functional Tests Gold Standard Setting the EAR Setting the UL Necessary Improvements in Biochemical Assessment & Future Research Recommendations

Functions of Vitamin B 6 Vitamin B 6 plays an important role in the metabolism of amino acids, glycogen and sphingoid bases. Serves as a coenzyme for over 100 enzymes involved in the metabolism of proteins. And because of its role in protein metabolism it plays an important role in the synthesis of heme.

Functions Continued Amino acids involved in the production of the neurotransmitters serotonin, dopamine, norepinephrine, histamine, taurine and Y- aminobutyric acid are dependent on PLP. PLP is the coenzyme for the reaction that converts tryptophan to niacin. Some studies suggest that vitamin B 6 may also play a role in hormonal and cell mediated immune response. (Gibson)

Variations 1.Pyridoxine (PN) and Pyridoxine 5’-phosphate (PNP) 2.Pyridoxamine (PM) and Pyridoxamine 5’-phosphate (PMP) 3.Pyridoxal (PL) and Pyridoxal 5’-phosphate (PLP)

Bioavailability B 6 is about 75% bioavailable in a mixed diet. A mixed diet is typically about 15% PN.

Food Sources Non-Citrus Fruits White Potatoes Fish Poultry Meat Seeds Bran Fortified Ready-To-Eat Cereals

Absorption & Transportation Absorption of Vitamin B 6 occurs in the gut through phosphatase-mediated hydrolysis. Here the nonphosphorylated form into the mucosal cells. The B 6 is then transported through nonsaturable passive diffusion into the blood stream.

Metabolism The absorbed nonphosphorylated B 6 (PN, PL, PM) moves to the liver. Here the phosphate group is added back on to these compounds by reacting with PL kinase. PNP and PMP are then oxidized into PLP. A reverse reaction can occur and transform PLP into PMP.

Metabolism Continued The PLP then becomes bound to proteins within tissues. The binding capacity of these proteins prevent accumulation. When the capacity is reached the liver hydrolyzes PLP and releases it into circulation as its nonphosphorylated form.

Storage The body’s vitamin B 6 stores exist in a two- compartment model.  Muscle Stores and Muscle Pool

Excretion Most of the hydrolyzed vitamin B 6 is released by the liver and excreted in urine.  4-pyridoxic acid (4-PA)

Plasma PLP: The Gold Standard Pyridoxal-5’-phosphate The major transport form of vitamin B6 in the blood Gibson Bound to protein or free IOM The major form of vitamin B6 in tissues IOM The active coenzyme species IOM

Vitamin B 6 Indicators: Direct, indirect & functional Use multiple indicators to evaluate B6 status Many tests are conducted to monitor status

1) Erythrocyte aminotransferase Two enzymes dependent on pyridoxal phosphate as coenzyme : alanine aminotransferase (A1AT) & aspartate aminotransferase (ASAT) Transfer of an amino acid to create L- glutamate In B6 deficiency, enzyme activity falls Measuring of enzyme activity in erythrocytes measures vitamin B6 status

2) Tryptophan catabolites One of the earliest markers of vitamin B6 Measuring the excretion of xanthurenic acid Catabolites follow a pathway which is PLP enzyme dependent When deficient, there is an increase in the excretion of xanthurenic acid It is not known what level of excretion represents vitamin B6 deficiency

3) Methionine Cystathinonine is dependent on B6 to break it down When vitamin B6 is inadequate, there is an increase in cystathinonine excretion because it cannot be broken down in the body The end product of cystathinonine break down is taurine, thus there will also be a decrease in taurine excretion. A level of >350 umol/day of cystathinonine means means vitamin B6 is inadequate

Plasma PLP: The Gold Standard Several studies done from suggested that: IOM ~ ½ of the population have plasma PLP [ ] < 30 nmol/L, but do not show vitamin B 6 deficiency ~ ½ of the population have plasma PLP [ ] < 30 nmol/L, but do not show vitamin B 6 deficiency

Plasma PLP: The Gold Standard Lui et al., 1985 proposed: IOM 20 nmol/L = Plasma PLP cutoff (No health risks) 20 nmol/L = Plasma PLP cutoff (No health risks)

Plasma PLP: The Gold Standard > 0.05 mg Abnormal encephalogram patterns Plasma PLP [ ] = ~ 9 nmol/L Suboptimal plasma PLP [ ] = 10 nmol/L (Kretsch et al., 1991) IOM

Plasma PLP: The Gold Standard Leklem, 1990: IOM Plasma PLP [ ] of 30 nmol/L = lower end of normal status

Plasma PLP: The Gold Standard The Plasma PLP cutoff is therefore: IOM 20 nmol/L

Protein interferes with vitamin B 6 IOM Tryptophan metabolite excretion Setting the EAR: Men

Baker et al. (1964) IOM =30 g/day = 10 g challenge dose = 1.25 mg EAR < 1.25 mg PN

Setting the Ear: Men Yess et al. (1964) IOM = 100 g/day = 2 g load = 0.16 mg = 0.6 g OR =0.9 g EAR < 0.9 mg PN

Setting the EAR: Men Miller & Linkswiler (1967) IOM = 54 g/day OR = 150 g/day = 0.16 mg = slow excretion over 40 days = 0.6 mg EAR < 0.76 mg PN

Setting the EAR: Men Linkswiler (1978) IOM = 100 g/day = mg PN EAR < mg PN

Setting the EAR: Men Miller et al (1985) IOM = 1.6 mg = 0.5 g/kg OR =1.0 g/kg OR =2.0 g/kg > 30 nmol/L 1.5 mg > EAR

Setting the EAR: Men Selhub et al. (1993) IOM = 1.3 mg Similar homocysteine [ ] EAR < 1.3 mg

Setting the EAR: Men Overall Range: < 0.9 mg  < 1.9 mg EAR for Men = 1.1 mg/day IOM

Setting the EAR: Women Majority used plasma PLP [ ] as indicator IOM

Setting the EAR: Women Brown et al (1975) IOM Depletion Repletion = 78 g/day = 0.16 mg  50  40 nmol/L =1.0 mg OR =2.2 mg  to 24 and 60 nmol/L EAR just under 1.0 mg

Setting the EAR: Women Driskell et al (1989) IOM B6 status of 15 obese women =1.18 mg =60 nmol/L in obese =63 nmol/L in non-obese Obesity does not affect vitamin B 6 status EAR < 1.2 mg

Setting the EAR: Women Kretsch et al. (1995) IOM Baseline values (25 nmol/L) developed from = 1.55 g/kg DepletionRepletion < 0.05 mg =0.5 mg OR =1.0 mg OR =1.5 mg OR =2.0 mg = 2 mg PN Baseline < 10 nmol/L =Restored from mg EAR= 1.0 mg

Setting the EAR: Women Hansen et al. (1996) IOM Looked at effect of protein intake on vitamin B 6 =0.5 g/kg OR =1.0 g/kg OR =2.0 g/kg =1.25 mg PN diet > 30 nmol/L =20-30 nmol/L Assuming PLP [ ] cutoff= 20 nmol/L… EAR considerably < 1.25 mg

Setting the EAR: Women Hansen et al. (1996) IOM Looked at effects on status indicators from diets with low or high glucoside PN = 9% B6 glucoside OR =27% B6 glucoside Indicators suggested lower bioavailability of glucoside > 30 nmol/L EAR < 1.5 mg

Setting the EAR: Women Hansen et al. (1997) IOM = 85 g/day Baseline =1.03 mg OR =0.84 mg Repletion 3-4 different levels for day periods EAR < 0.8 mg

Setting the EAR: Women Huang et al. (1998) IOM = 1.55 g/kg Baseline = 1.6 mg/day Depletion = 0.45 mg/day Repletion =1.26 mg for 21 days =1.66 mg for 21 days =2.06 mg for 14 days Normalized with mg PN EAR between mg; most likely < 1mg

Setting the EAR: Women

UL & Toxicity Vitamin B 6 from food ≠ toxicity IOM Due to supplementation UL = 100 mg  Different for children and adolescents diet.ssuppl.factsheet High pyridoxine levels MK

UL & Toxicity M&K Akinesia Loss of balance and reflexes Altered peripheral sensation Absence of sensory nerve action potentials Convulsions

UL & Toxicity Taking excess vitamin B 6 during pregnancy can cause adverse effects for the infant M&K Large doses during pregnancy should be avoided M&K