Folate is a water soluble B vitamin (B9), considered one of the 13 essential vitamins. The primary function of folate is the transfer of methyl and formyl groups, thus, it is essential for cell growth and reproduction, the breakdown and utilization of proteins, the formation of nucleic acids, red blood cell maturation, and a variety of CNS reactions. Dihydrofolate is the dietary form found in orange juice, spinach, asparagus, beans, liver, yeast, whole grain cereals, and eggs. Folic acid is the synthetic form of folate in over-the-counter vitamins and used to fortify the food supply (to help prevent neural tube defects, the FDA mandated folic acid fortification of flour in 1998). Folic acid is also the predominant form used in prescription strength prenatal vitamins. Both folic acid and dihydrofolate are not biologically active forms of folate, but are essentially pro-drugs, and must undergo enzymatic transformation to L-methylfolate in order to be used by cells, and unlike other forms of folate, L-methylfolate readily crosses the blood-brain barrier for use in the CNS.
Almost 85% of dietary folate and nearly all supplemental folic acid is absorbed into the venous system in the proximal small intestine. The enzymatic conversion begins in the intestinal wall—it is a three step process for dihydrofolate, and a four step process for folic acid (Slide 3). Folic acid is converted to dihydrofolate (DHF) by dihydrofolate reductase enzyme (DHFR), and DHF is then converted to tetrahydrofolate (THF). The conversion of THF to 5,10-methyleneTHF follows. Finally, the conversion of 5,10-methyleneTHF to L-methylfolate is achieved by the methyltetrahydrofolate reductase enzyme (MTHFR). This last step completes the four step transformation process by which the bioactive cofactor, L-methylfolate, is made available to the brain to be used in the synthesis of monoamine neurotransmitters associated with mood regulation (serotonin, norepinephrine, and dopamine).
There are five trials that examine folate therapy in depressive disorders. In a study59 with patients who had low or borderline low RBC folate, depressed patients on tricyclic antidepressants or MAOIs were augmented with methylfolate 15 mg (L-methylfolate 7.5 mg) experienced significantly greater clinical improvement and social improvement at 3 months (P<.02) and 6 months (P<.01) compared to patients treated with antidepressants alone. The methylfolate-augmented patients continued to improve for 6 months compared to patients augmented with placebo, and none experienced relapse. In a separate double-blind, controlled trial60 comparing methylfolate 50 mg/day to trazodone 100 mg/day, depressed patients experienced a significant decrease in HAM-D scores at 4 and 8 weeks in both groups, with response rates in the methylfolate group at 45%, and in the trazodone group (not statistically significant) at 29%.
An open label trial61 of methylfolate as monotherapy in elderly depressed subjects demonstrated an 81% response rate (>50% reduction in HAM-D) by 6 weeks of therapy. A second monotherapy study examined a depressed population of 36 chronic alcoholics. After a week of placebo wash-out, subjects received 4 weeks of 90 mg methylfolate therapy. This dosing (30 mg TID) significantly improved depressive symptoms based on the HAM-D scale with the majority reporting improved mood and less fatigue (P<.01).62 Alpert and colleagues63 conducted an open label trial augmenting selective serotonin reuptake inhibitor (SSRIs) with folinic acid in patients who had failed at least 4 weeks of SSRI therapy. The response to folinic acid was not robust (P<.01, n=22), but it was well tolerated overall.
The standard dose of L-methylfolate for the augmentation of antidepressants is one 7.5 mg tablet/day. No titration is necessary, and it is not associated with withdrawal symptoms at discontinuation. The maximum amount of L-methylfolate that can be absorbed in one dose is ~15 mg.67 If more than one 7.5 mg tablet/day is needed, it may be prudent to give in divided doses. All reported adverse events occur at placebo rates or lower, and overall it is an extremely well tolerated agent, allowing patients to continue L-methylfolate therapy as long as necessary to maintain remission. There are no known contraindications and no known drug interactions.
The Role of L-methylfolate in Depressive Disorders
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