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 Ki 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.