Plasma vitamin B-6 forms and their relation to transsulfuration metabolites in a large, population-based study.
BACKGROUND
Vitamin B-6 exists in different forms; one of those forms, pyridoxal 5'-phosphate (PLP), serves a cofactor in many enzyme reactions, including the transsulfuration pathway, in which homocysteine is converted to cystathionine and then to cysteine. Data on the relations between indexes of vitamin B-6 status and transsulfuration metabolites in plasma are sparse and conflicting.


OBJECTIVE
We investigated the distribution and associations of various vitamin B-6 species in plasma and their relation to plasma concentrations of transsulfuration metabolites.


METHODS
Nonfasting blood samples from 10 601 healthy subjects with a mean age of 56.4 y were analyzed for all known vitamin B-6 vitamers, folate, cobalamin, riboflavin, total homocysteine, cystathionine, total cysteine, methionine, and creatinine. All subjects were genotyped for the methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism.


RESULTS
Plasma concentrations of the main vitamin B-6 vitamers--PLP, pyridoxal, and 4-pyridoxic acid--were strongly correlated. Among the vitamin B-6 vitamers, PLP showed the strongest and most consistent inverse relation to total homocysteine and cystathionine, but the dose response was different for the 2 metabolites. The PLP-total homocysteine relation was significant only in the lowest quartile of the vitamin B-6 distribution and was strongest in subjects with the MTHFR 677TT genotype, whereas cystathionine showed a graded response throughout the range of vitamin B-6 vitamer concentrations, and the effect was not modified by the MTHFR 677C-->T genotype.


CONCLUSIONS
This large population-based study provided precise estimates of the relation between plasma concentrations of vitamin B-6 forms and transsulfuration metabolites as modified by the MTHFR 677C-->T genotype.
Midttun
Øivind
Ø
From Bevital A/S, Armauer Hansens Hus, Bergen, Norway. nkjbm@uib.no
Hustad
Steinar
S
Schneede
Jørn
J
Vollset
Stein E
SE
Ueland
Per M
PM
D015331:Cohort Studies; D003540:Cystathionine / Q000097:blood; D005260:Female; D005838:Genotype; D006801:Humans; D006867:Hydrolases / Q000097:blood; D008297:Male; D042965:Methylenetetrahydrofolate Reductase (NADPH2) / Q000235:genetics / Q000378:metabolism; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide; D011730:Pyridoxal / Q000097:blood*; D011732:Pyridoxal Phosphate / Q000097:blood*; D011735:Pyridoxic Acid / Q000097:blood*; D012044:Regression Analysis; D025101:Vitamin B 6 / Q000097:blood*
D003540:Cystathionine; D011730:Pyridoxal; D011735:Pyridoxic Acid; D011732:Pyridoxal Phosphate; D025101:Vitamin B 6; D042965:Methylenetetrahydrofolate Reductase (NADPH2); D006867:Hydrolases; C463961:homocysteinase