Tetrahydrofolic acid (L-5,6,7,8-Tetrahydrofolic acid)

Tetrahydrofolic acid (L-5,6,7,8-Tetrahydrofolic acid) is a derivative of vitamin B9 (folic acid or pteroyl-L-glutamic acid) which formed during the methyltetrahydrofolic acid-mediated methylation of indoleamines and exerts an inhibitory effect on methyltetrahydrofolic acid-dependent methyltransferase with K_i value of 0.1mM^[1][2]. Tetrahydrofolic acid acts as a suicide substrate of tyrosinase and reduces o-quinones generated by the enzyme in its action on substrates, such as l-tyrosine and l-DOPA (o-dopaquinone), thus inhibiting enzymatic browning^[3].

In vitro, rat pheochromocytoma PC12 cells were incubated with aggregate solutions (10μL/well) for 48h. Preformed aggregates were produced by mixing 50μM αS without and with Tetrahydrofolic acid (αS: Tetrahydrofolic acid molar ratios 1:0.5, 1:1 and 1:2; equivalent to 25, 50 and 100µM) and by mixing Tetrahydrofolic acid with 25μM Aβ40 or Aβ42 in the specified molar ratios (1:1, 1:2 and 1:3; equivalent to 25, 50 and 75µM). Tetrahydrofolic acid could alleviate the cytotoxicity of αS aggregates in a dose-dependent manner and also has a similar inhibitory effect on Aβ induced cytotoxicity^[4]. Adh5^−/−, FancC⁻, FancF^−/− and wild-type DT40 bone marrow cells were exposed to Tetrahydrofolic acid (0-250µM) in vitro for 4h at 37°C in sealed cryovials. The viability of these cells rapidly dropped. Tetrahydrofolic acid is cytotoxic to cells lacking the Fanconi anemia DNA repair pathways or Adh5^[5].

In vivo, Tetrahydrofolic acid was intraperitoneally injected into X-irradiated ICR-JCL mice with the dose of 0.5mg or 1.5mg per animal. In the Tetrahydrofolic acid-treated groups, there observed a singificant delay of time before the first incidence of death of the animals occurred. Furthermore, the treatment with Tetrahydrofolic acid increased the final survival rate from the control level of 50% up to 70% (0.5mg group) or up to 75% (1.5mg group)^[6].

References:
[1] Tjong E, Dimri M, Mohiuddin S S. Biochemistry, Tetrahydrofolate. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan.
[2] Lin R L, Narasimhachari N. Tetrahydrofolic acid: an inhibitor of the methyltetrahydrofolic acid-mediated methylation of indolethylamines. Biochim Biophys Acta. 1975 Apr 7;385(2):268-74.
[3] Molina F G, Muñoz-Muñoz J L, Martínez-Ortiz F, et al. Tetrahydrofolic Acid is a potent suicide substrate of mushroom tyrosinase. J Agric Food Chem. 2011 Feb 23;59(4):1383-91.
[4] Wang W Q, Wu X M, Zhang Q F, et al. Tetrahydrofolic acid accelerates amyloid fibrillization, decreases cytotoxic oligomers and suppresses their toxicity. Int J Biol Macromol. 2025 Feb:290:139041.
[5] García-Calderón C B, Bejarano-García J A, Tinoco-Gago I, et al. Genotoxicity of tetrahydrofolic acid to hematopoietic stem and progenitor cells. Cell Death Differ. 2018 Nov;25(11):1967-1979.
[6] Okazaki M, Sato F, Shikita M, Akaboshi S. Therapeutic effect of tetrahydrofolic acid in midlethally x-irradiated mice. Chem Pharm Bull (Tokyo). 1971 Jun;19(6):1173-7.

Tetrahydrofolic acid (L-5,6,7,8-Tetrahydrofolic acid)是维生素B9（叶酸或蝶酰-L-谷氨酸）的衍生物，在甲基四氢叶酸介导的吲哚胺甲基化过程中形成，并对甲基四氢叶酸依赖性甲基转移酶具有抑制作用，Ki值为0.1mM^[1][2]。Tetrahydrofolic acid作为酪氨酸酶的自毁底物，可减少该酶作用于L-酪氨酸和L-DOPA时生成的邻醌（如多巴醌），从而抑制酶促褐变^[3]。

体外实验，大鼠嗜铬细胞瘤PC12细胞与10μL/孔聚集溶液共孵育48h。聚集物通过将50μM αS与Tetrahydrofolic acid按1:0.5、1:1、1:2摩尔比（对应25、50、100μM）混合，或将25μM Aβ40或Aβ42与Tetrahydrofolic acid按1:1、1:2、1:3摩尔比（对应25、50、75μM）混合制备。Tetrahydrofolic acid可剂量依赖性地减轻αS聚集体的细胞毒性，并对Aβ诱导的细胞毒性具有类似抑制作用^[4]。将Adh5^-/-、FancC⁻、FancF^-/- 及野生型DT40骨髓细胞在密封冻存管中暴露于Tetrahydrofolic acid（0-250μM）4h（37℃），细胞活力快速下降；Tetrahydrofolic acid对缺乏范可尼贫血DNA修复通路或Adh5的细胞具有细胞毒性^[5]。

体内实验，对X射线照射的ICR-JCL小鼠腹腔注射Tetrahydrofolic acid，剂量为0.5mg或1.5mg/只。Tetrahydrofolic acid处理组出现小鼠死亡的时间显著延迟，最终生存率由对照50%提高至70%（0.5mg组）或75%（1.5mg组）^[6]。