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ARD Online First, published on December 5, 2013 as 10.1136/annrheumdis-2013-203725 Clinical and epidemiological research
EXTENDED REPORT
Methotrexate polyglutamates in erythrocytes are associated with lower disease activity in patients with rheumatoid arthritis Maurits C F J de Rotte,1 Ethan den Boer,1 Pascal H P de Jong,2 Saskia M F Pluijm,3 Maja Bulatović Ćalasan,4 Angelique E Weel,5 A Margriet Huisman,6 Andreas H Gerards,7 Barbara van Schaeybroeck,8 Nico M Wulffraat,4 Jan Lindemans,1 Johanna M W Hazes,2 Robert de Jonge1 Handling editor Tore K Kvien ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/ annrheumdis-2013-203725). For numbered affiliations see end of article. Correspondence to Maurits C F J de Rotte, Department of Clinical Chemistry, Erasmus University Medical Center, ‘s-Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands; [email protected] JMWH and RdJ contributed equally. Received 4 April 2013 Revised 15 September 2013 Accepted 5 November 2013
ABSTRACT Objective To investigate if erythrocyte-methotrexatepolyglutamate (MTX-PG) concentrations in patients with rheumatoid arthritis (RA) are associated with disease activity or adverse events. Methods We used a longitudinal study design with two cohorts. The derivation cohort included 102 and the validation cohort included 285 patients with RA on MTX. We measured erythrocyte-MTX-PG with 1–5 glutamate residues at 3 months, 6 months and 9 months after MTX start with a liquid chromatography (LC)-mass spectrometry (MS)/MS assay. Outcomes were disease activity score in 28 joints (DAS28) and adverse events. Longitudinal associations of MTX-PG concentrations after 3 months, 6 months and 9 months with DAS28 were tested with a linear mixed model adjusted for age, gender, baseline DAS28, MTX dose and comedication. Results In the derivation cohort, mean DAS28 decreased from 4.26 (SE=0.14) at baseline to 2.72 (SE=0.13) after 9 months. Thirty per cent of patients in the derivation cohort experienced more than three adverse events after 3 months, which decreased to 18% after 9 months. In the validation cohort, DAS28 and adverse events were comparable with the derivation cohort. In the derivation cohort, MTX-PG1 (ß=−0.005), MTX-PG2 (ß=−0.022), MTX-PG3 (β=−0.007) and total MTX-PG (ß=−0.004) were associated ( p10 years. Disadvantages of crosssectional analysis are that you cannot distinguish between those treated for weeks or years and that
de Rotte MCFJ, et al. Ann Rheum(or Dis 2013;0:1–7. doi:10.1136/annrheumdis-2013-203725 1 Copyright Article author their employer) 2013. Produced by BMJ Publishing Group Ltd (& EULAR) under licence.
Downloaded from http://ard.bmj.com/ on October 26, 2014 - Published by group.bmj.com
Clinical and epidemiological research you cannot make causal inference.16 Additionally, comparison between patients is complicated because MTX is stopped in obstinate non-responders and because MTX-PG accumulation is a function of time.5 The aim of this prospective, longitudinal study was to investigate if intracellular erythrocyte-MTX-PG concentrations are related to disease activity or adverse events in patients with RA on MTX and thus if MTX-PGs could be a tool for TDM.
PATIENTS AND METHODS Study design and patients
Statistical analyses
The derivation cohort was the ‘MTX in Rotterdam’ cohort (MTX-R). The MTX in Rotterdam is a longitudinal prospective cohort of patients who started MTX between January 2006 and March 2011 at the Rheumatology Department, Erasmus University Medical Center, Rotterdam, Netherlands. The validation cohort was the ‘Treatment in Rotterdam Early Arthritis Cohort’. The Treatment in Rotterdam Early Arthritis Cohort is a clinical multicentre, stratified single-blinded trial (ISRCTN26791028), as described earlier.17 18 The medical ethics committee from the Erasmus University Medical Center, Rotterdam approved both studies and patients gave written informed consent before inclusion. Derivation cohort patients were included if diagnosed with RA by the physician. Validation cohort patients were included in if they fulfilled the 2010 American College of Rheumatology/ European League Against Rheumatism (EULAR) criteria for RA.19 Patients on biologicals at baseline were excluded. In the derivation cohort, clinicians chose MTX dosage and comedication for every visit. In the validation cohort, MTX starting dose was set at 25 mg/week (reached after 3 weeks). If patients had disease activity score in 28 joints (DAS28)
ARD Online First, published on December 5, 2013 as 10.1136/annrheumdis-2013-203725 Clinical and epidemiological research
EXTENDED REPORT
Methotrexate polyglutamates in erythrocytes are associated with lower disease activity in patients with rheumatoid arthritis Maurits C F J de Rotte,1 Ethan den Boer,1 Pascal H P de Jong,2 Saskia M F Pluijm,3 Maja Bulatović Ćalasan,4 Angelique E Weel,5 A Margriet Huisman,6 Andreas H Gerards,7 Barbara van Schaeybroeck,8 Nico M Wulffraat,4 Jan Lindemans,1 Johanna M W Hazes,2 Robert de Jonge1 Handling editor Tore K Kvien ▸ Additional material is published online only. To view please visit the journal online (http://dx.doi.org/10.1136/ annrheumdis-2013-203725). For numbered affiliations see end of article. Correspondence to Maurits C F J de Rotte, Department of Clinical Chemistry, Erasmus University Medical Center, ‘s-Gravendijkwal 230, Rotterdam 3015 CE, The Netherlands; [email protected] JMWH and RdJ contributed equally. Received 4 April 2013 Revised 15 September 2013 Accepted 5 November 2013
ABSTRACT Objective To investigate if erythrocyte-methotrexatepolyglutamate (MTX-PG) concentrations in patients with rheumatoid arthritis (RA) are associated with disease activity or adverse events. Methods We used a longitudinal study design with two cohorts. The derivation cohort included 102 and the validation cohort included 285 patients with RA on MTX. We measured erythrocyte-MTX-PG with 1–5 glutamate residues at 3 months, 6 months and 9 months after MTX start with a liquid chromatography (LC)-mass spectrometry (MS)/MS assay. Outcomes were disease activity score in 28 joints (DAS28) and adverse events. Longitudinal associations of MTX-PG concentrations after 3 months, 6 months and 9 months with DAS28 were tested with a linear mixed model adjusted for age, gender, baseline DAS28, MTX dose and comedication. Results In the derivation cohort, mean DAS28 decreased from 4.26 (SE=0.14) at baseline to 2.72 (SE=0.13) after 9 months. Thirty per cent of patients in the derivation cohort experienced more than three adverse events after 3 months, which decreased to 18% after 9 months. In the validation cohort, DAS28 and adverse events were comparable with the derivation cohort. In the derivation cohort, MTX-PG1 (ß=−0.005), MTX-PG2 (ß=−0.022), MTX-PG3 (β=−0.007) and total MTX-PG (ß=−0.004) were associated ( p10 years. Disadvantages of crosssectional analysis are that you cannot distinguish between those treated for weeks or years and that
de Rotte MCFJ, et al. Ann Rheum(or Dis 2013;0:1–7. doi:10.1136/annrheumdis-2013-203725 1 Copyright Article author their employer) 2013. Produced by BMJ Publishing Group Ltd (& EULAR) under licence.
Downloaded from http://ard.bmj.com/ on October 26, 2014 - Published by group.bmj.com
Clinical and epidemiological research you cannot make causal inference.16 Additionally, comparison between patients is complicated because MTX is stopped in obstinate non-responders and because MTX-PG accumulation is a function of time.5 The aim of this prospective, longitudinal study was to investigate if intracellular erythrocyte-MTX-PG concentrations are related to disease activity or adverse events in patients with RA on MTX and thus if MTX-PGs could be a tool for TDM.
PATIENTS AND METHODS Study design and patients
Statistical analyses
The derivation cohort was the ‘MTX in Rotterdam’ cohort (MTX-R). The MTX in Rotterdam is a longitudinal prospective cohort of patients who started MTX between January 2006 and March 2011 at the Rheumatology Department, Erasmus University Medical Center, Rotterdam, Netherlands. The validation cohort was the ‘Treatment in Rotterdam Early Arthritis Cohort’. The Treatment in Rotterdam Early Arthritis Cohort is a clinical multicentre, stratified single-blinded trial (ISRCTN26791028), as described earlier.17 18 The medical ethics committee from the Erasmus University Medical Center, Rotterdam approved both studies and patients gave written informed consent before inclusion. Derivation cohort patients were included if diagnosed with RA by the physician. Validation cohort patients were included in if they fulfilled the 2010 American College of Rheumatology/ European League Against Rheumatism (EULAR) criteria for RA.19 Patients on biologicals at baseline were excluded. In the derivation cohort, clinicians chose MTX dosage and comedication for every visit. In the validation cohort, MTX starting dose was set at 25 mg/week (reached after 3 weeks). If patients had disease activity score in 28 joints (DAS28)
