Folic acid supplementation does not reduce intracellular homocysteine, and may disturb intracellular one-carbon metabolism
Folic acid supplementation does not reduce intracellular homocysteine, and may disturb intracellular one-carbon metabolism
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DOI：
10.1515/cclm-2012-0694
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发表时间：
2013-08-01
影响因子：
6.8
通讯作者：
Smulders, Yvo M.
中科院分区：
文献类型：
--
作者：
Smith, Desiree E. C.;Hornstra, Jacqueline M.;Smulders, Yvo M.
背景：在随机试验中，叶酸（FA）降低血浆同型半胱氨酸，但未能降低心血管风险。我们假设这是由于血浆和细胞内的影响FA.Methods之间的差异：在一项双盲试验中，50名志愿者被随机接受500微克FA每天8周，或安慰剂。采用液相色谱-串联质谱法（LC-MS/MS）测定血浆和外周血单个核细胞（PBMC）中同型半胱氨酸、S-腺苷甲硫氨酸（SAM）、S-腺苷同型半胱氨酸、甲硫氨酸、胱硫醚和5-甲基四氢叶酸（生物活性叶酸）的浓度。PBMC被用作细胞模型，因为它们显示一碳（1C）酶和反应的全谱。基线时，血浆浓度不能很好地反映大多数1C代谢物的细胞内浓度，5-甲基四氢叶酸除外（R=0.33，p=0.02）、同型半胱氨酸（Hcy）（R=0.35，p=0.01）和胱硫醚（R=0.45，p=0.001）。FA显著降低血浆同型半胱氨酸（p=0.00），但未能降低细胞内同型半胱氨酸或改变任何其他PBMC 1C代谢物的浓度。在基线时，PBMC同型半胱氨酸浓度与PBMC SAM相关。补充FA后，PBMC同型半胱氨酸不再与PBMC SAM相关，表明SAM的调节功能丧失。在淋巴母细胞的体外实验证实，在较高的叶酸底物浓度，生理浓度的SAM不再有效地抑制关键的调节酶亚甲基四氢叶酸还原酶（MTHFR）。结论：FA补充不降低细胞内浓度的Hcy或任何其密切相关的物质。相反，FA可能通过干扰SAM对MTHFR活性的抑制作用来干扰细胞内1C代谢的生理调节。
Background: In randomized trails, folic acid (FA) lowered plasma homocysteine, but failed to reduce cardiovascular risk. We hypothesize this is due to a discrepancy between plasma and intracellular effects of FA.Methods: In a double-blind trial, 50 volunteers were randomized to received 500 mu g FA daily for 8 weeks, or placebo. Plasma and peripheral blood mononuclear cell (PBMC) concentrations of homocysteine, S-adenosylmethionine (SAM), S-adenosylhomocysteine, methionine, cystathionine and 5-methyltetrahydrofolate (bioactive folate) were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). PBMCs were used as a cellular model since they display the full spectrum of one-carbon (1C) enzymes and reactions.Results: At baseline, plasma concentrations were a poor reflection of intracellular concentrations for most 1C metabolites, except 5-methyltetrahydrofolate (R=0.33, p=0.02), homocysteine (Hcy) (R=0.35, p=0.01), and cystathionine (R=0.45, p=0.001). FA significantly lowered plasma homocysteine (p=0.00), but failed to lower intracellular homocysteine or change the concentrations of any of the other PBMC 1C metabolites. At baseline, PBMC homocysteine concentrations correlated to PBMC SAM. After FA supplementation, PBMC homocysteine no longer correlated with PBMC SAM, suggesting a loss of SAM's regulatory function. In vitro experiments in lymphoblasts confirmed that at higher folate substrate concentrations, physiological concentrations of SAM no longer effectively inhibit the key regulatory enzyme methylenetetrahydrofolate reductase (MTHFR).Conclusions: FA supplementation does not reduce intracellular concentrations of Hcy or any of its closely related substances. Rather, FA may disturb physiological regulation of intracellular 1C metabolism by interfering with SAM's inhibitory effect on MTHFR activity.