Folylpolyglutamate synthase is a major determinant of intracellular methotrexate polyglutamates in patients with rheumatoid arthritis

Abstract

We investigated major determinants of the intracellular concentrations of methotrexate polyglutamates (MTXPGs) in patients with rheumatoid arthritis (RA). In 271 RA patients on stable oral low dose weekly pulse MTX therapy, the concentrations of MTXPGs in red blood cells (RBCs) were measured by liquid chromatography-electrospray ionization-tandem mass spectrometry. Polymerase chain reaction-restriction fragment length polymorphism analysis was performed to determine the genotypes of solute carrier family 19 member 1 (SLC19A1), folylpolyglutamate synthase (FPGS), and gamma-glutamyl hydrolase (GGH). The mean total MTXPG concentration and the concentrations of individual MTXPGs increased dose-dependently, but reached a plateau at MTX doses >10 mg weekly. The MTXPG3-5/1-2 ratio was lower in patients with adverse events related to MTX than in patients without adverse events. Three polymorphisms of FPGS significantly influenced the MTXPG3-5/1-2 ratio in RBCs, while polymorphisms of SLC19A1 and GGH had no impact. The minor allele frequencies of 2 FPGS genotypes were significantly increased in our patients compared with a Caucasian population. FPGS may have a major role in regulating intracellular polyglutamation of MTX in RA patients receiving low-dose weekly MTX therapy.

Membrane‐Spanning Protein Genetic Polymorphisms Related to Methotrexate Therapeutic Outcomes in a Chinese Rheumatoid Arthritis Population

“…Our results do not replicate previous findings indicating that RFC‐1 80G>A gene polymorphisms are associated with the response to MTX. Indeed, the same results were found in Yamamoto's study, which showed that there were no relationships between the RFC‐1 80G>A polymorphism and intracellular MTXPG3‐5/1–2 ratios or MTX toxicity. Furthermore, in 327 South Indian Tamil RA patients, the RFC‐1 80G>A gene polymorphism was not found to be associated with the MTX treatment response.…”

“…26 Similarly, a study that included 127 Indian (Asia) RA patients showed that individuals with the RFC1 80 AA/GA genotype had a better response to MTX than was observed in those with the RFC1 80 GG genotype (OR, 2.2; 95%CI, 1.1-4.4; P = .03) but was not associated with ADRs. 27 The disease severity was the same in this study and ours, and the duration 18 study, which showed that there were no relationships between the RFC-1 80G>A polymorphism and intracellular MTXPG3-5/1-2 ratios or MTX toxicity. Furthermore, in 327 South Indian Tamil RA patients, the RFC-1 80G>A gene polymorphism was not found to be associated with the MTX treatment response.…”

“…MTX polyglutamates can persist long term inside the target cell, and these active MTX polyglutamates determine MTX functional status, efficacy, and toxicity. 18 Therefore, it is important for MTX to enter the cell. In the body, MTX is transported intracellularly via RFC-1/SLC19A1.…”

“…The occurrence of MTX‐related toxicity, defined as patients presenting any ADRs related to MTX, was recorded upon each visit . The ADRs mainly included gastrointestinal reactions (abdominal and stomach pain, diarrhea, nausea, hepatic reactions, and indigestion or anorexia), respiratory reactions (interstitial lung disease), and general reactions (pain throughout the body, erythema of the extremities, hair loss, and vertigo reactions), according to other studies . Adverse drug events were observed after 3 months.…”

“…17 The ADRs mainly included gastrointestinal reactions (abdominal and stomach pain, diarrhea, nausea, hepatic reactions, and indigestion or anorexia), respiratory reactions (interstitial lung disease), and general reactions (pain throughout the body, erythema of the extremities, hair loss, and vertigo reactions), according to other studies. [17][18][19] Adverse drug events were observed after 3 months. The response of RA treated with MTX changed >0.6 in DAS28 before and after MTX treatment, in contrast to nonresponse.…”