Monitoring of azathioprine metabolite concentrations and cytokine levels in neuromyelitis optica spectrum disorder

BackgroundThe pathogenesis of NMOSD has been linked to the cytokines interleukins (IL) -6, NOD-, LRR-and pyrin domain-containing 3 (NLRP3) and IL-18 that contribute to development of inflammatory reactionsmay. Although azathioprine (AZA) is efficacious in preventing NMOSD recurrence, it may have adverse effects (AEs) maybe related to the plasma concentrations. ObjectiveWe would monitor the blood concentrations of azathioprine in NMOSD, and their relationship with cytokines, severity, efficacy, and safety range of the drug. MethodsA total of 53 NMOSD patients were included in the study, which included 20 patients who had received AZA treatment within one month, and 16 patients who had received AZA treatment within six months, as well as 17 patients who had received AZA treatment over one year. The patients immunotherapy regimen was low-dose hormone combined with AZA. AZA was started at small doses and added every two weeks after no AEs, namely 50 mg qd for two weeks, 50mg bid for two weeks, and maintained at 50mg tid. The following clinical data were collected: gender, age, clinical symptoms, EDSS score, number of recurrences and AEs, etc. Healthy controls (HC) comprised 10 individuals. AZA metabolite concentrations 6-thioguaninenucleotides (6-TGN) and 6-methylmercaptopurine nucleotides (6-MMPN) were measured by High-performance liquid chromatography (HPLC). Levels of IL-6, NLRP3 and IL-18 were measured by Enzyme-linked immunosorbent assay (ELISA). ResultsTreatment with AZA decreased the EDSS score and the ARR. The 6-TGN and 6-MMPN concentrations gradually increased as the medication time increased, and was basically stable by 6 months of medication. EDSS score improvement was positively correlated with 6-TGN concentrations. Patients with AEs had higher concentrations of 6-TGN and 6-MMPN than those without. The serum levels of IL-6, NLRP3, and IL-18 were higher in the patients than in the HC. NLRP3 level was higher in neuropathic pain (NP) patients than in those without NP. ConclusionConsequently, AZA was confirmed to be an effective drug used to treat NMOSD. AEs increased when 6-TGN reached 155.604 pmol/8x108 RBC or 6-MMPN reached 2583.168 pmol/8x108 RBC. In NMOSD remission, IL-6 and NLRP3 levels were significantly higher than in normal subjects, suggesting that they may contribute to the pathogenesis of NMOSD. A high level of NLRP 3 may lead to NP.