Methotrexate polyglutamate concentrations are not associated with disease control in rheumatoid arthritis patients receiving long-term methotrexate therapy.

University of Otago, Christchurch, New Zealand.
Arthritis & Rheumatology (Impact Factor: 7.48). 02/2010; 62(2):359-68. DOI: 10.1002/art.27201
Source: PubMed

ABSTRACT There are limited data suggesting that methotrexate polyglutamate (MTXGlu) concentrations can guide MTX dosing in patients with rheumatoid arthritis (RA). The aim of this study was to define a therapeutic range of red blood cell (RBC) MTXGlu(n) concentrations (where n refers to the number of glutamate groups), including threshold values for efficacy and adverse effects in patients receiving long-term oral MTX treatment.
A cross-sectional study of 192 patients receiving oral MTX was undertaken. Disease activity was assessed by the swollen and tender joint counts, the C-reactive protein level, and the Disease Activity Score in 28 joints (DAS28). High disease activity was defined as a DAS28 of >3.2. A standardized questionnaire regarding common MTX adverse effects was completed.
The MTX dosage was significantly higher in patients in whom the swollen joint count and DAS28 were higher. The MTXGlu(4), MTXGlu(5), MTXGlu(3-5), and MTXGlu(1-5) concentrations were significantly higher in patients with high disease activity. After correction for age, the estimated glomerular filtration rate, and the MTX dosage, the association remained significant for MTXGlu(5). RBC folate concentrations were significantly higher in the group with high disease activity. There was no association between any MTXGlu(n) concentration and adverse effects.
In contrast to other studies, the results of the present study did not show a relationship between the MTXGlu(n) concentration and reduced disease activity in patients with RA who were receiving long-term MTX therapy. However, disease activity was influenced by the RBC folate level, which may be a more important factor than MTXGlu(n) concentrations for disease control. In accordance with the findings of previous studies, we were unable to show a relationship between MTXGlu(n) concentrations and adverse effects. Prospective studies will be important to determine whether there is a role for measuring MTXGlu(n) concentrations in patients receiving long-term treatment with MTX.

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    ABSTRACT: The response to and toxicity of methotrexate (MTX) are unpredictable in patients with juvenile idiopathic arthritis (JIA). Intracellular polyglutamation of MTX, assessed by measuring concentrations of MTX polyglutamates (MTXGlu), has been demonstrated to be a promising predictor of drug response. Therefore, this study was aimed at investigating the genetic predictors of MTXGlu variability and associations between MTXGlu and drug response in JIA. The study was designed as a single-center cross-sectional analysis of patients with JIA who were receiving stable doses of MTX at a tertiary care children's hospital. After informed consent was obtained from the 104 patients with JIA, blood was withdrawn during routine MTX-screening laboratory testing. Clinical data were collected by chart review. Genotyping for 34 single-nucleotide polymorphisms (SNPs) in 18 genes within the MTX metabolic pathway was performed. An ion-pair chromatographic procedure with mass spectrometric detection was used to measure MTXGlu1-7. Analysis and genotyping of MTXGlu was completed in the 104 patients. K-means clustering resulted in 3 distinct patterns of MTX polyglutamation. Cluster 1 had low red blood cell (RBC) MTXGlu concentrations, cluster 2 had moderately high RBC MTXGlu1+2 concentrations, and cluster 3 had high concentrations of MTXGlu, specifically MTXGlu3-5. SNPs in the purine and pyrimidine synthesis pathways, as well as the adenosine pathway, were significantly associated with cluster subtype. The cluster with high concentrations of MTXGlu3-5 was associated with elevated liver enzyme levels on liver function tests (LFTs), and there were higher concentrations of MTXGlu3-5 in children who reported gastrointestinal side effects and had abnormal findings on LFTs. No association was noted between MTXGlu and active arthritis. MTXGlu remains a potentially useful tool for determining outcomes in patients with JIA being treated with MTX. The genetic predictors of MTXGlu variability may also contribute to a better understanding of the intracellular biotransformation of MTX in these patients.
    Arthritis & Rheumatology 10/2010; 63(1):276-85. · 7.48 Impact Factor
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    ABSTRACT: BACKGROUND: Measurement of intracellular concentrations of methotrexate (MTX) and its polyglutamated metabolites (MTXGlu2-5) in red blood cells (RBCs) has been suggested as a potential means of monitoring low-dose MTX treatment of rheumatoid arthritis (RA). However, a possible correlation between RBC MTX and MTXGlu2-5 concentrations and clinical outcomes of MTX treatment in RA is debated. A better understanding of the dose-concentration-time relationship of MTX and MTXGlu2-5 in RBCs by population pharmacokinetic modelling is desirable and will facilitate assessing a potential RBC concentration-effect relationship in the future. AIM: The purpose of this analysis was to describe the pharmacokinetics of MTX and MTXGlu2-5 in RBCs. Secondary objectives included investigation of deglutamation reactions and the loss of MTX and MTXGlu2-5 from the RBC. METHODS: A model was developed using NONMEM® version 7.2 based on RBC data obtained from 48 patients with RA receiving once-weekly low-dose MTX treatment. This model was linked to a fixed two-compartment model that was used to describe the pharmacokinetics of MTX in the plasma. A series of five compartments were used to describe the intracellular pharmacokinetics of MTX and MTXGlu2-5 in RBCs. Biologically plausible covariates were tested for a significant effect on MTX plasma clearance and the intracellular volume of distribution of all MTX species in RBCs ([Formula: see text]). The developed model was used to test hypotheses related to the enzymatic deglutamation of MTXGlu2-5 and potential loss of MTXGlu2-5 from RBCs. RESULTS: The final RBC pharmacokinetic model required the intracellular volumes of distribution for the parent and metabolites to be set to the value estimated for the parent drug MTX alone, and the rate constants describing the polyglutamation steps were fixed at literature values. Significant covariates included effect of body surface area-adjusted estimated glomerular filtration rate on renal plasma clearance and effect of allometrically scaled total body weight with a fixed exponent of 0.75 on non-renal plasma clearance of MTX. The only significant covariate with an effect on [Formula: see text] was mean corpuscular volume (MCV). The model supported single deglutamation steps and a single mechanism of MTX and MTXGlu2-5 loss from RBCs. CONCLUSIONS: The developed model enabled acceptable description of the intracellular kinetics of MTX and MTXGlu2-5 in RBCs. In the future it can form the basis of a full pharmacokinetic-pharmacodynamic model to assess the time-RBC concentration-effect relationship of low-dose MTX treatment in RA.
    Clinical Pharmacokinetics 03/2013; · 5.49 Impact Factor
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    ABSTRACT: Methotrexate (MTX) exerts at least part of its anti-inflammatory effects through adenosine receptors (ADOR). The aims of this study were to determine the expression of all four adenosine receptor genes (ADORA1, ADORA2A, ADORA2B, ADORA3 and ADORA3variant) in rheumatoid synovial tissue and any influence of MTX exposure on this expression. Furthermore, we investigated whether polymorphisms within ADORA3 were associated with response and/or adverse effects associated with MTX. Adenosine receptor gene expression was undertaken using PCR in 20 rheumatoid arthritis (RA) synovial samples. A separate cohort of 225 RA patients receiving MTX was genotyped for SNPs in the ADORA3 receptor gene. Double immunofluorescence was used to identify cells expressing ADOR protein. All ADOR genes were expressed in all synovial samples. ADORA3 and A3variant were the dominant subtypes expressed irrespective of MTX therapy. Expression of ADORA2A and ADORA2B was increased in patients receiving MTX compared to those not receiving MTX. There was no association between the ADORA3 rs1544224 SNP and high and low disease activity or MTX-associated adverse effects. ADORA2B protein expression was most obvious in vascular endothelial cells whereas ADORA3 protein was more abundant and expressed by synovial fibroblasts. We have shown that adenosine receptors are expressed in RA synovium. There is differential expression of receptors such that ADORA3 is expressed at significantly higher levels. This evidence demonstrates the potential for MTX to exert its anti-inflammatory effects at the primary site of pathology within the joints of patients with RA.
    Arthritis research & therapy 06/2012; 14(3):R138. · 4.27 Impact Factor

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