Background: Thiopurine methyltransferase (TPMT) is a crucial enzyme for azathioprine biotransformation and its activity is higher in very early onset inflammatory bowel disease (VEO-IBD) patients than in adolescents with IBD (aIBD).Aims: The aims of this pharmacoepigenetic study were to evaluate differences in peripheral blood DNA methylation of the TPMT gene and in azathioprine pharmacokinetics in patients with VEO-IBD compared to aIBD.Methods: The association of age with whole genome DNA methylation profile was evaluated in a pilot group of patients and confirmed by a meta-analysis on 3 cohorts of patients available on the public functional genomics data repository. Effects of candidate CpG sites in the TPMT gene were validated in a larger cohort using pyro-sequencing. TPMT activity and azathioprine metabolites (TGN) were measured in patients' erythrocytes by HPLC and associated with patients' age group and TPMT DNA methylation.Results: Whole genome DNA methylation pilot analysis, combined with the meta-analysis revealed cg22736354, located on TPMT downstream neighboring region, as the only statistically significant CpG whose methylation increases with age, resulting lower in VEO-IBD patients compared to aIBD (median 9.6% vs 12%, p = 0.029). Pyrosequencing confirmed lower cg22736354 methylation in VEO-IBD patients (median 4.0% vs 6.0%, p = 4.6 x10- 5). No differences in TPMT promoter methylation were found. Reduced cg22736354 methylation was associated with lower TGN concentrations (rho = 0.31, p = 0.01) in patients with VEO-IBD and aIBD.Conclusion: Methylation of cg22736354 in TPMT gene neighborhood is lower in patients with VEO-IBD and is associated with reduced azathioprine inactivation and increased TGN concentrations.
DNA methylation of the TPMT gene and azathioprine pharmacokinetics in children with very early onset inflammatory bowel disease / Selvestrel, Davide; Stocco, Gabriele; Aloi, Marina; Arrigo, Serena; Cardile, Sabrina; Cecchin, Erika; Congia, Mauro; Curci, Debora; Gatti, Simona; Graziano, Francesco; Langefeld, Carl D; Lucafò, Marianna; Martelossi, Stefano; Martinelli, Massimo; Pagarin, Sofia; Scarallo, Luca; Stacul, Elisabetta Francesca; Strisciuglio, Caterina; Thompson, Susan; Zuin, Giovanna; Decorti, Giuliana; Bramuzzo, Matteo. - In: BIOMÉDECINE & PHARMACOTHÉRAPIE. - ISSN 0753-3322. - 157:(2023), p. 113901. [10.1016/j.biopha.2022.113901]