Assessment of Erythrocytes Methotrexate Polyglutamate Three Levels in Psoriatic Patients Treated with Methotrexate Monotherapy and Their Association with Disease Response

Methotrexate is used to manage moderate to severe psoriasis and psoriatic arthritis. Methotrexate acts by inhibiting the enzymes involved in nucleotide synthesis. Methotrexate polyglutamates (MTXPGs) have a higher potency to inhibit Dihydrofolate reductase (DHFR), 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (ATIC), and thymidylate synthase (TS), compared to naïve methotrexate. Among all the MTXPGs, methotrexate polyglutamate three (MTXPG-3) is a more potent inhibitor of DHFR, ATIC, and TS enzymes. MTXPG-3 is anticipated to allow therapeutic drug monitoring in immune-mediated inflammatory diseases. We aim to study MTXPG-3 levels as a biomarker for both efficacy and adverse events among psoriatic patients treated with methotrexate monotherapy. We used the LC-MS/MS (Liquid Chromatography Mass Spectrophotometry) system for measuring erythrocyte MTXPG-3. We recruited 106 patients with psoriasis who were treated with methotrexate. Sixty-one of them had psoriatic arthritis (concomitant or in the past). The mean age was 45.08 ± 13.04 years. After twenty-four weeks of methotrexate treatment, 73(69%) were responders, and 33(31%) were non-responders. Thirty-nine (36%) experienced adverse effects, and 67(64%) did not experience any adverse effects. We observed a significant positive correlation between erythrocyte MTXPG-3 and methotrexate dose per week at weeks 12 and 16 but not at week 24. Erythrocyte MTXPG-3 did not correlate with response or adverse effects. It can be used as a marker of compliance.