Levomefolic acid (INN) (also known as L-5-MTHF, L-methylfolate and L-5-methyltetrahydrofolate and (6S)-5-methyltetrahydrofolate, and (6S)-5-MTHF) is the primary biologically active form of folate used at the cellular level for DNA reproduction, the cysteine cycle and the regulation of homocysteine. It is also the form found in circulation and transported across membranes into tissues and across the blood-brain barrier.
Treatment and prevention of folate deficiency
Antidote against folic acid antagonists
In the cell, L-methylfolate is used in the methylation of homocysteine to form methionine and tetrahydrofolate (THF). THF is the immediate acceptor of one carbon units for the synthesis of thymidine-DNA, purines (RNA and DNA) and methionine. The un-methylated form, folic acid (vitamin B9), is a synthetic form of folate, and must undergo enzymatic reduction by methylenetetrahydrofolate reductase (MTHFR) to become biologically active.
It is synthesized in the absorptive cells of the small intestine from polyglutamylated dietary folate. It is a methylated derivative of tetrahydrofolate. Levomefolic acid is generated by MTHFR from 5,10-methylenetetrahydrofolate (MTHF) and used to recycle homocysteine back to methionine by methionine synthase (MS).
Mechanism of action
Folates are best known for reducing the incidence of fetal neural tube defects (NTDs). NTDs are congenital malformations produced by failure of the neural tube to form and close properly during embryonic development. During the first four weeks of pregnancy - when many women do not even realize that they have conceived, adequate maternal folate intake is essential to reduce the risk of NTDs. As the postnatal period approaches there is increased demand again for folate regardless of lactation status. Folate is involved in transformylation and methylation metabolism as well as - indirectly, succinylation metabolism (through the "methyl trap" hypothesis). Folate plays a central role in the formation of nucleic acid precursors, such as thymidylic acid and purine nucleotides, which are essential for nucleic acid synthesis and cell division.
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