Low‐Dose Methotrexate Alters Cellular Folate Mediated One Carbon Metabolism

Impairments in folate‐dependent metabolism are associated with several human pathologies including neural tube defects, cancers, and vascular diseases. Folate mediated one carbon metabolism is an important target for cell proliferation diseases in human including rheumatic diseases. Low‐dose methotrexate (MTX) is one of the most common immunosuppressants used in rheumatic and other inflammatory conditions. MTX is a potent inhibitor of dihydrofolate reductase and thymidylate synthase, which can deplete folates and inhibit DNA synthesis. MTX also interferes with the enzymes methylenetetrahydrofolate reductase and methionine synthase, resulting in reduced cellular 5‐methylTHF levels and decreased homocysteine remethylation. Methionine S ‐adenosyltransferase (MAT) catalyzes the only reaction that produces the major methyl donor in mammals. We reported that low‐dose MTX inhibits MAT in vitro and in vivo . The present study was conducted to further investigate how low‐dose MTX alter 1‐carbon metabolic fluxes in vitro and in vivo . Hepatoma and human liver derived cell lines were cultured under folate restriction or in low‐dose MTX with or without folate or methionine supplementation. Male C57BL/6J mice received regimens that reflected low‐dose clinical use of MTX in humans. Metabolic fluxes in 1‐carbon metabolism were investigated using stable isotopic tracers and GCMS. Concurrent folinate supplementation ameliorated MAT2A reduction and restored S ‐adenosylmethionine in HepG2 cells. However, posttreatment folinate rescue failed to restore MAT2A reduction or S ‐adenosylmethionine level in cells preexposed to MTX. Furthermore, the enrichments from isotopic tracers indicated that MTX inhibits endogenous formate production and alter the partitioning of 1‐carbon flow in our cell models. The impacts of low dose MTX on one carbon metbolic kinetics are under investigation. This study may provide new insights on the regulatory mechanisms by which DMARDs alter cellular one carbon metabolism and thus give potential therapeutic strategies in treating human rheumatic diseases. Support or Funding Information supported by NSC102‐2320‐B‐005‐006‐MY3;MOST104‐2320‐B‐005‐010‐MY3;and MOST104‐2911‐I005‐ 301