Marcadores genéticos e epigenéticos na mucosite oral em pacientes pediátricos com neoplasias hematológicas

Abstract

Oral mucositis (OM) is an effect of antineoplastic therapy, common in children and adolescents. It manifests as erythematous or ulcerated and painful lesions in the oral cavity, which may cause treatment interruption due to the risk of sepsis. The occurrence of OM is related to the therapy used, sex, age, immunological and nutritional conditions and genetics, being frequent and serious in children with hematological tumors, especially treated with methotrexate (MTX). DNA methylation is the most studied epigenetic mark and, together with genetic polymorphisms, has been related to several inflammatory and tumor diseases. The aim of this study was to investigate the association of genetic and epigenetic markers with OM in pediatric patients with hematological malignancies treated with MTX. Firstly, a review of the literature was carried out on the genetic and epigenetic markers already addressed in the context of chemo-induced OM in pediatric patients with hematological malignancies. Next, an experimental study was carried out in which healthy patients and those with hematological malignancies aged between 5 and 19 years were recruited to collect oral mucosa cells by mouthwash (n=87). DNA was extracted and global DNA methylation analysis (ELISA technique) and specific methylation analysis in the miR-9-1 and miR-9-3 genes (MSP technique) were performed. Furthermore, seven polymorphisms in the MTHFR (rs1801131, rs1801133), DNMT1 (rs2228611), DNMT3A (rs7590760, rs1550117) and DNMT3B (rs6087990, rs2424913) genes were genotyped (PCR-RFLP technique) and an association analysis with global methylation was performed. For the literature review, 22 studies on polymorphisms and 4 studies on DNA methylation were selected. Polymorphisms in the MTHFR, ABCB1, ABCC2, ABCG2, SLCO1B, miR, CAT and VDR genes were associated as risk factors for OM and polymorphisms in the TYMS and miR genes were associated as protective factors. Regarding DNA methylation, a link with OM has not yet been established. However, studies have shown that global methylation is a marker of chemotherapy exposure and changes in the methylation profile in the DNMT1 and TNF-α genes are associated with oral mucosal recovery. In the experimental study, a reduction in global methylation levels was observed in cancer patients recovered from OM compared to healthy cancer patients with or without OM (p<0.05; Kruskal Wallis). The hypomethylated profile of miR-9-1 and hypermethylated miR-9-3 was more frequent in cancer oncological paediatric patients compared to healthy participants (p<0.05; Chi-Square), and with no association with OM. The oncological paediatric patients with the GG genotype of the DNMT1 SNP rs2228611, who had OM, showed higher levels of global methylation compared to carriers of the AA/AG genotypes (p<0.05; Mann Whitney). From the literature review, it is concluded that genetic variants are associated with OM in different biological pathways, such as: folic acid metabolism, transport proteins, epigenetic machinery, oxidative stress and vitamin D metabolism. DNA, which remains poorly understood, is associated as a marker of chemotherapy exposure and mucosal recovery (inflammation and epigenetic machinery pathways). From the experimental study, it is concluded that global methylation is associated with mucosal recovery and the genetic variation of DNMT1 (rs2228611) can influence the level of global methylation in oncological paediatric cancer patients who developed OM.