Polyglutamation of methotrexate with common polymorphisms in reduced folate carrier, aminoimidazole carboxamide ribonucleotide transformylase, and thymidylate synthase are associated with methotrexate effects in rheumatoid arthritis

Abstract

Objective. Methotrexate (MTX) enters cells through the reduced folate carrier (RFC-1) and exerts part of its effects through polyglutamation to MTX polyglutamates (MTXPGs) and inhibition of 5-aminoimidazole-4-carboxamide ribonucleotide transformylase (ATIC) and thymidylate synthase (TS). We investigated the contribution of common genetic polymorphisms in RFC-1 (G80A), ATIC (C347G), and TS (28-bp tandem repeats located in the TS enhancer region [TSER*2/*3]) and of MTXPGs to the effect of MTX in patients with rheumatoid arthritis.Methods. The study was cross-sectional. All patients received MTX for at least 3 months. The numbers of tender and swollen joints, the Visual Analog Scale (VAS) scores for the physician's global assessment of disease activity, and the modified Health Assessment Questionnaire scores were collected. Using the VAS score for the physician's assessment of patient's response to MTX, the population of patients was dichotomized into responders to MTX (VAS score <2 cm) and nonresponders to MTX (VAS score >2 cm). A pharmacogenetic index was calculated as the sum of homozygous variant genotypes (RFC-1 AA ؉ ATIC 347GG ؉ TSER *2/*2) carried by the patients. MTXPG concentrations were measured in red blood cells (RBCs) by high-performance liquid chromatography.Results. The dose of MTX was not associated with the effects of MTX (P > 0.05). In contrast, increased RBC long-chain MTXPG concentrations (median 40 nmoles/liter; range <5-131 nmoles/liter) and an increased pharmacogenetic index were associated with a lower number of tender and swollen joints (P < 0.05) and a lower score for the physician's global assessment of disease activity (P < 0.001). Patients with RBC MTXPG levels of >60 nmoles/liter and carriers of a homozygous variant genotype were 14.0-fold (95% confidence interval [95% CI] 3.6-53.8) and 3.7-fold (95% CI 1.7-9.1), respectively, more likely to have a good response to MTX (P < 0.01).Conclusion. These data suggest that measuring RBC MTXPG levels and/or the common polymorphisms in the folate-purine-pyrimidine pathway may help in monitoring MTX therapy.The folate antagonist methotrexate (MTX) is currently one of the most widely prescribed drugs for the treatment of rheumatoid arthritis (RA) (1,2). Although MTX is among the best-tolerated disease-modifying antirheumatic drugs, a major drawback of MTX therapy is great interpatient variability in the clinical response and the unpredictable appearance of a large spectrum of side effects that include gastrointestinal disturbances, alopecia, elevation of liver enzyme levels, and bone marrow suppression (3,4). Several well-controlled clinical trials have demonstrated that MTX decreases functional disability, with a maximum effect observable after 6 months of therapy (2,3). However, recent findings

Investigation of inter-individual variability of the one-carbon folate pathway: a bioinformatic and genetic review

“…Earlier studies have described an association between individuals possessing the GG genotype of a common c.347C4G; p.T112S polymorphism (rs2372536) and a decreased response to methotrexate in the treatment of rheumatoid arthritis. 68 A case has also been reported of AICA-ribosiduria, a disease characterized by deficiency in purine biosynthesis, where an infant possessed a K426R amino-acid substitution in ATIC on one allele and a frameshift mutation on the other. 69 This individual presented with dysmorphic features, severe neurological defects and congenital blindness.…”

“…An amino-acid substitution polymorphism encoding a histidine to arginine change at residue 27 of SLC19A1 (rs1051266) has been associated with decreased methotrexate therapeutic response in individuals with rheumatoid arthritis 68 and childhood acute lymphoblastic leukemia. 76 This same p.H27R polymorphism has also been identified as a risk factor for NTDs.…”

Reduced folate carrier-1 80G>A polymorphism affects methotrexate treatment outcome in rheumatoid arthritis

“…The RFC-1 80G4A polymorphism (resulting in a histidine-to-arginine substitution at codon 27 of RFC-1) was detected using a polymerase chain reaction-restriction fragment length polymorphism method, as described previously. 6 Reduced folate carrier-1…”

“…[6][7][8] In the present study, we examined the association between RFC-1 G80A polymorphism and treatment outcome in patients with RA administered MTX.…”

Analysis of intracellular methotrexate polyglutamates in patients with juvenile idiopathic arthritis: Effect of route of administration on variability in intracellular methotrexate polyglutamate concentrations

“…Recent literature suggests that intracellular MTX polyglutamation may be correlated with the efficacy of MTX in adult patients with rheumatoid arthritis (RA) (16)(17)(18). One may also speculate that increased intracellular concentrations of MTX contribute to the risk of toxicity, but this has not been rigorously evaluated to date.…”