Dietary vitamin B-6 restriction does not alter rates of homocysteine remethylation or synthesis in healthy young women and men.
BACKGROUND
The effects of vitamin B-6 status on steady-state kinetics of homocysteine metabolism in humans are unclear.


OBJECTIVE
The objective was to determine the effects of dietary vitamin B-6 restriction on the rates of homocysteine remethylation and synthesis in healthy humans.


METHODS
Primed, constant infusions of [(13)C(5)]methionine, [3-(13)C]serine, and [(2)H(3)]leucine were conducted in healthy female (n=5) and male (n=4) volunteers (20-30 y) before and after 4 wk of dietary vitamin B-6 restriction (<0.5 mg vitamin B-6/d) to establish whether vitamin B-6 status affects steady-state kinetics of homocysteine metabolism in the absence of concurrent methionine intake. Effects of dietary vitamin B-6 restriction on vitamin B-6 status, plasma amino acid concentrations, and the rates of reactions of homocysteine metabolism were assessed.


RESULTS
Dietary vitamin B-6 restriction significantly reduced plasma pyridoxal 5-phosphate (PLP) concentrations (55.1 +/- 8.3 compared with 22.6 +/- 1.3 nmol/L; P=0.004), significantly increased plasma glycine concentrations (230 +/- 14 compared with 296 +/- 15; P=0.008), and significantly reduced basal (43%; P < 0.001) and PLP-stimulated (35%; P=0.004) lymphocyte serine hydroxymethyltransferase activities in vitro. However, the in vivo fluxes of leucine, methionine, and serine; the rates of homocysteine synthesis and remethylation (total and vitamin B-6-dependent); and the concentrations of homocysteine, methionine, and serine in plasma were not significantly affected by dietary vitamin B-6 restriction.


CONCLUSIONS
Moderate vitamin B-6 deficiency does not significantly alter the rates of homocysteine remethylation or synthesis in healthy young adults in the absence of dietary methionine intake.
Davis
Steven R
SR
Food Science & Human Nutrition Department, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611-0370, USA.
Scheer
Jennifer B
JB
Quinlivan
Eoin P
EP
Coats
Bonnie S
BS
Stacpoole
Peter W
PW
Gregory
Jesse F
JF
D000328:Adult; D002247:Carbon Isotopes; D003903:Deuterium; D005260:Female; D005998:Glycine / Q000097:blood; D006710:Homocysteine / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D008297:Male; D008715:Methionine / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D008745:Methylation; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics; D011110:Polymorphism, Genetic; D011732:Pyridoxal Phosphate / Q000097:blood*; D012694:Serine / Q000008:administration & dosage / Q000378:metabolism / Q000493:pharmacokinetics; D025101:Vitamin B 6 / Q000008:administration & dosage / Q000494:pharmacology*
D002247:Carbon Isotopes; D006710:Homocysteine; D012694:Serine; D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D008715:Methionine; D003903:Deuterium; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D005998:Glycine