Midttun Øivind, Hustad Steinar, Schneede Jørn, Vollset Stein E, Ueland Per M
From Bevital A/S, Armauer Hansens Hus, Bergen, Norway.
Am J Clin Nutr. 2007 Jul;86(1):131-8. doi: 10.1093/ajcn/86.1.131.
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.
We investigated the distribution and associations of various vitamin B-6 species in plasma and their relation to plasma concentrations of transsulfuration metabolites.
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.
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.
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.
维生素B-6以不同形式存在；其中一种形式，即磷酸吡哆醛（PLP），在许多酶反应中作为辅助因子，包括转硫途径，在此途径中，同型半胱氨酸转化为胱硫醚，然后再转化为半胱氨酸。关于血浆中维生素B-6状态指标与转硫代谢产物之间关系的数据稀少且相互矛盾。
我们研究了血浆中各种维生素B-6种类的分布及相关性，以及它们与转硫代谢产物血浆浓度之间的关系。
对10601名平均年龄为56.4岁的健康受试者的非空腹血样进行分析，检测所有已知的维生素B-6维生素、叶酸、钴胺素、核黄素、总同型半胱氨酸、胱硫醚、总半胱氨酸、蛋氨酸和肌酐。对所有受试者进行亚甲基四氢叶酸还原酶（MTHFR）677C→T多态性基因分型。
主要维生素B-6维生素（PLP、吡哆醛和4-吡哆酸）的血浆浓度高度相关。在维生素B-6维生素中，PLP与总同型半胱氨酸和胱硫醚的负相关最强且最一致，但两种代谢产物的剂量反应不同。PLP与总同型半胱氨酸的关系仅在维生素B-6分布的最低四分位数中显著，且在MTHFR 677TT基因型受试者中最强，而胱硫醚在维生素B-6维生素浓度范围内呈现分级反应，且该效应不受MTHFR 677C→T基因型的影响。
这项基于大量人群的研究精确估计了维生素B-6形式的血浆浓度与经MTHFR 677C→T基因型修饰的转硫代谢产物之间的关系。
