Avaliação da associação entre polimorfismos em genes relacionados à metabolização das tiopurinas e a resposta à azatioprina em pacientes com doença de Crohn e retocolite ulcerativa

Abstract

Thiopurines, 6-mercaptopurine (6-MP) and azathioprine (AZA), are used in the treatment of Inflammatory Bowel Diseases (IBD), including ulcerative colitis (UC) and Crohn's disease (CD). Despite the benefits, the efficacy and safety of thiopurines show significant interindividual variability, which is at least partly explained by genetic variations related to pharmacokinetics. Objective: To evaluate the association between polymorphisms in genes related to the metabolism of thiopurines and the response to AZA in patients with IBD. Materials and Methods: Cross-sectional observational study (2016 to 2023), including the collection of blood samples and clinical data from IBD patients, treated with AZA for at least 3 months, attending the IBD Center at the University Hospital (HU) of the Federal University of Juiz de Fora. The intraerythrocytic levels of 6-methylmercaptopurine (6-MMP) and 6-thioguanine (6-TGN) were quantified using High-Performance Liquid Chromatography, coupled with ultraviolet detection. Patients were genotyped for 13 single nucleotide polymorphisms (SNPs) by Quantitative Real-Time Polymerase Chain Reaction in the genes of thiopurine methyltransferase (TPMT) (rs1800462, rs1800460, and rs1142345), inosine triphosphate pyrophosphatase (rs9101, rs8362, rs1127354, and rs7270101), hypoxanthine-guanine-phosphoribosyltransferase (HPRT) (rs1468266), and xanthine oxidase (XO) (rs4407290, rs17323225, rs1884725, rs2295475 and rs17011368). Appropriate statistical tests were applied considering a significance level of 0.05. Results: The study included 151 IBD patients (59.6% women), with 30 having undergone surgical interventions; 59 had complications from IBD or thiopurine treatment, and 112 were in remission. Of these, 33 patients (21.9%) experienced at least one adverse effect related to pharmacotherapy. The metabolites 6-TGN and 6-MMP ranged from 4.5 to 2456.0 pmol/8x108 erythrocytes and 25.8 to 97800.0 pmol/8x108 erythrocytes, respectively. Patients in remission showed higher concentrations of 6-TGN compared to those with active disease, while patients on monotherapy with AZA had higher median levels of 6-MMP compared to those associated with allopurinol. The allele frequencies for the investigated genes ranged from 1.3 to 33%. Heterozygous patients showed higher concentrations of 6-TGN compared to TPMT*1/1 homozygotes. Additionally, patients carrying the A allele for rs1884725 of XO also had higher average concentrations of 6-TGN compared to GG patients. Patients with at least one variant allele of HPRT showed increased liver enzyme values. Leukopenia was more frequently observed in patients with variant alleles for TPMT and XO genes (rs4407290). The latter was associated with neutropenia, being more frequent in heterozygotes. Complaints related to AZA therapy were more frequent in patients with TPMT1/*1 genotype. Conclusion: This is a pioneering study in evaluating the frequency of distribution of polymorphisms in genes associated with the pharmacokinetics of AZA in patients in Minas Gerais. The findings indicate an association between polymorphisms in the TPMT and XO genes with 6-TGN concentration, which is higher in patients carrying the variant allele. Variations in TPMT, HPRT and XO genes were also associated with adverse reactions, including elevated liver enzymes, leukopenia and neutropenia. These findings may impact clinical practice, contributing to personalized therapy.