Open AccessAnalysis of intracellular methotrexate polyglutamates in patients with juvenile idiopathic arthritis: Effect of route of administration on variability in intracellular methotrexate polyglutamate concentrations
Author(s) -
Becker Mara L.,
van Haandel Leon,
Gaedigk Roger,
Lasky Andrew,
Hoeltzel Mark,
Stobaugh John,
Leeder J. Steven
Publication year - 2010
Publication title -
arthritis & rheumatism
Language(s) - English
Resource type - Journals
eISSN - 1529-0131
pISSN - 0004-3591
DOI - 10.1002/art.27434
Subject(s) - medicine , methotrexate , rheumatoid arthritis , interquartile range , arthritis , juvenile rheumatoid arthritis , gastroenterology , intracellular , chemistry , biochemistry
Objective Intracellular methotrexate (MTX) polyglutamates (MTXGlu) have been shown to be potentially useful biomarkers of clinical response in adult patients with rheumatoid arthritis. The present study was undertaken to measure intracellular MTXGlu concentrations in a cohort of patients with juvenile idiopathic arthritis (JIA) to determine the predictors of MTXGlu variability in these patients. Methods Blood samples were obtained from patients with JIA who were being treated with a stable dose of MTX for ≥3 months. Clinical data were collected by chart review. Concentrations of MTXGlu 1–7 in red blood cell lysates were quantitated using an innovative ion‐pairing chromatography procedure, with detection by mass spectrometry. Results Patients with JIA from a single center (n = 99; mean ± SD age 117.8 ± 56.5 months, 69 female) were included in the analysis. The mean ± SD dose of MTX was 0.51 ± 0.25 mg/kg per week, with a median treatment duration of 18 months (interquartile range 3–156 months). MTX was administered subcutaneously in 66 patients (67%). Fifty‐six patients (57%) had active arthritis at the time of the clinic visit. Total intracellular MTXGlu (MTXGlu TOT ) concentrations varied 40‐fold, with a mean ± SD total concentration of 85.8 ± 48.4 nmoles/liter. Concentrations of each MTXGlu subtype (MTXGlu 1–7 ) were measured individually and as a percentage of MTXGlu TOT in each patient. MTXGlu 3 was the most prominent subtype identified, comprising 42% of MTXGlu TOT , and the interindividual variability in the concentration of MTXGlu 3 was the most highly correlated with that of MTXGlu TOT (r = 0.96). The route of MTX administration was significantly associated with MTXGlu 1–5 subtypes; higher concentrations of MTXGlu 1 + 2 were observed in patients receiving oral doses of MTX, whereas higher concentrations of MTXGlu 3–5 were observed in patients receiving subcutaneous doses of MTX ( P < 0.0001). Conclusion In this cohort of patients with JIA, the MTXGlu TOT concentration varied 40‐fold. Individual MTXGlu metabolites (MTXGlu 1–7 ), which have, until now, not been previously reported in patients with JIA, were detected. The route of MTX administration contributed to the variability in concentrations of MTXGlu 1–5 .