Ab0646 Comparison of Methotorexate-Polyglutamate Concentrations in Red Blood Cells and PBMCS in Patients With Ra

Background: Methotrexate (MTX) is a standard treatment drug for rheumatoid arthritis (RA), but the dose and response vary depending on individual patients, making it difficult to determine the optimal dose. Previous studies measured MTX-polyglutamate concentrations in red blood cells and suggested its potential as a biomarker for MTX treatment. However, red blood cells (RBCs) are not immune cells, have a different genetic morphology from other cells, and are thought to have little involvement in the pathological conditions. It may be more meaningful to measure the MTX-PG concentration in peripheral blood monoclear cells (PBMCs), which plays a central role in the patholophysiology of RA. In this study, we measured MTX-PG concentrations in red blood cells and PBMCs of patients with RA and investigated their relationship with disease activity and side effects. Objectives: To investigate differences in MTX-PG concentrations in RBCs and PBMCs in patients diagnosed with RA and initiated on MTX. Methods: We enrolled treatment-naïve patients with rheumatoid arthritis. MTX was started with a dose of 8mg/week with 5mg/week folic acid and increased by 4mg every 4 weeks to 16mg/week unless adverse events occurred. Blood samples were taken at baseline, week 4, 8, 12, 24, 36, 52, 76 weeks. MTX-PG 1-5 concentrations in the RBCs and PBMCs were measured using LC-MS/MS method with stable isotopes of MTX-PG as internal standards. Clinical response and adverse events were collected from their charts, and the correlation between them and MTX-PG levels were analyzed. Results: MTX-PG concentrations in RBCs and PBMCs were measured in 55 patients with treatment-naïve RA. The average MTX doses at weeks 4, 8, 12, 24, 36, 52 and 76 were 7.7mg/w, 10.4mg/w, 12.1mg/w, 11.6mg/w, 11.0mg/w, 10.7mg/w, and 10.6mg/w. Total MTX-PG concentrations were increased in both RBCs and PBMCs in association with an increase of MTX dose but the increase was slower in PBMCs than in RBCs during the first 24 weeks, with a tendency of a rapid increase after 52 weeks. (Figure 1) Total MTX-PG concentrations in RBCs mainly consisted of MTX-PG1,2, and the increase in MTX-PG3 concentrations was gradual different from the trend of MTX-PG concentrations in RBCs. Correlation between each MTX-PG concentrations in RBCs and PBMC was sparce. Total MTX-PG concentrations in RBCs were correlated with DAS and liver dysfunction at week 24, whereas the association between those in PBMCs and disease activity or adverse events was not identified at week 24. Conclusion: The concentrations of MTX-PG in RBCs and PBMC measured up to week 76 showed different pattern and compsisions.. The MTX-PG concentrations in PBMCs were significantly low and exhibited different dynamics from the MTX-PG concentrations in RBCs. Further detailed analyses were needed. REFERENCES: [1] Dervieux T, Ann Rheum Dis 2005;64:1180–5. 10.1136/ard.2004.033399. [2] Chihiro Takahashi, RMD Open 2017 Jan 3;3(1):e000363. doi: 10.1136/rmdopen-2016-000363. eCollection 2017. [3] Renske Cf Hebing, Annals of the Rheumatic Diseases 2023-04-01, DOI:10.1136/ard-2022-223398. Acknowledgements: The authors would like to thank Ms Harumi Kondo for their assistance in the acquisition of clinical information. Disclosure of Interests: None declared.